<%BANNER%>

Optical Studies of High Temperature Superconductors and Electronic Dielectric Materials


PAGE 1

OPTICAL STUDIES OF HIGH TEMPE RATURE SUPERCONDUCTORS AND ELECTRONIC DIELECTRIC MATERIALS By MINGHAN CHEN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2005

PAGE 2

Copyright 2005 by Minghan Chen

PAGE 3

iii ACKNOWLEDGMENTS Many people have contributed to this work and have been constant sources of encouragement and support. First and foremo st, it is my great pleasure to thank my dissertation advisor, Professo r David B. Tanner, for giving me the opportunity to study the most exciting area of solid state physic s and for his valuable guidance, advice, constant support, patience and encouragemen t all throughout my graduate work at the University of Florida. My work could not possibly have been completed without his guidance and support. The many things I have learned from him will be my treasures. During the course of my Ph.D. study, I also received great help from Professor Juan. C. Nino. I have had many interesting discussions with him and the terahertz measurements were done with his help. In part icular, I am very grat eful to him for his help, suggestion and collaboration. Hi s kindness and knowledge are admired. I would like equally to thank Professor Arthur F. Hebard, Peter J. Hirschfeld, David H. Reitze, and John R. Reynolds for reading th is dissertation and fo r their interest in serving on my supervisory committee. Another special thank you goes to professo r David B. Tanner for his great help in using the analyzing software, which made it possible for me to present data for this dissertation. I also want to thank the staff member in the Physics Department Machine Shop and the engineers in the Physics De partment for their technical support. I would like to acknowledge Professor J. Mannhart at Augsburg University for providing good quality high Tc film samples.

PAGE 4

iv All the magnetic field measurements were done in the National High Magnetic Field Laboratory with help from Dr. Yong-Ji e Wang. I am very grateful to him for his help. Thanks also go to all my past and pres ent colleagues in Professor Tanner’s group for their friendship, useful conversation a nd cooperation through my graduate work.

PAGE 5

v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES...........................................................................................................viii LIST OF FIGURES.............................................................................................................x ABSTRACT.....................................................................................................................xi ii CHAPTER 1 OPTICAL THEORY....................................................................................................1 1.1 Light Phenomena...............................................................................................1 1.2 Determination of Optical Constants...................................................................7 1.2.1 Fresenel’s Equation...................................................................................7 1.2.2 Kramers-Kronig Analysis.........................................................................9 1.2.3 Reflectance and Transmittance at a Thin Film on a Thick Substrate.....10 1.2.4 Microscopic Models...............................................................................14 2 INSTRUMENTATION AND TECHNIQUES..........................................................22 2.1 Far Infrared Techniques...................................................................................22 2.1.1 General Principles...................................................................................22 2.1.2 Apodization.............................................................................................25 2.1.3 Phase Correction.....................................................................................26 2.1.4 Sampling.................................................................................................27 2.2 Terahertz Technique........................................................................................28 2.2.1 General Principles...................................................................................28 2.2.2 Some Important Issues with THZ-TDS Technique................................31 2.3 Grating Spectrometer.......................................................................................34 2.4 Instrumentation................................................................................................35 2.4.1 Bruker 113v FT-IR Spectrometer...........................................................35 2.4.2 TPI 1000 Terahertz Spectrometer...........................................................37 2.4.3 Perkin-Elmer Grating Spectrometer.......................................................38 2.4.4 Low Temperature Apparatus..................................................................40 3 OPTICAL PROPERTIES OF SUOPE RCONDUCTING YBCO FILM IN THE OPTIMALLY DOPED AND OVERDOPED REGION............................................48

PAGE 6

vi 3.1 Introduction......................................................................................................49 3.1.1 Fermi Liquid (FL) and Marginal Fermi Liquid model...........................49 3.1.2 Optical Measurement of Hi gh Temperature Superconductor.................51 3.1.3 The Crystal Structure of YBCO.............................................................56 3.1.4 Phase Diagram........................................................................................57 3.1.5 Pseudogap Phase.....................................................................................57 3.1.6 d-wave Character of High Temperature Superconductor.......................58 3.1.7 Two-Component Mode for the Dielectric Function...............................59 3.2 Experiments and Results..................................................................................61 3.2.1 Sample Preparation.................................................................................61 3.2.2 Optical Measurement of the Substrate — SrTiO3..................................62 3.2.3 Optical Measurement of the YBCO Thin Films.....................................63 3.3 Discussion........................................................................................................65 3.3.1 Dielectric Function Analysis..................................................................65 3.3.2 Charge Transfer Band a nd Interband Transition....................................68 3.3.3 Temperature Dependent Optical Conductivity.......................................69 3.3.4 Quasi-Particle Scattering Rate................................................................70 3.3.5 Frequency-dependent Scattering Rate (MFL)........................................72 3.3.6 Superfluid Density..................................................................................73 3.4 Summary..........................................................................................................76 4 FAR-INFRARED PROPERTIES OF SUPERCONDUCTING YBCO FILMS IN ZERO AND HIGH MA GNETIC FIELDS.................................................................94 4.1 Introduction......................................................................................................94 4.1.1 Background.............................................................................................94 4.1.2 Type I and Type II Superconductors......................................................98 4.1.3 Superconducting Response in High Magnetic Field...............................99 4.2 Experiment and Results.................................................................................101 4.2.1 Sample Preparation...............................................................................101 4.2.2 Sample zero field properties.................................................................102 4.2.3 Optical Measurement in the High Magnetic Field................................103 4.3 Discussion......................................................................................................104 4.4 Summary........................................................................................................106 5 TERAHERTZ AND OPTICAL STUDY OF ELECTRONIC DIELECTRIC MATERIALS...........................................................................................................112 5.1 Introduction....................................................................................................112 5.1.1 Background...........................................................................................112 5.1.2 Crystal Structure...................................................................................113 5.2 Experiment and Result...................................................................................115 5.2.1 Sample Preparation...............................................................................115 5.2.2 Experimental Procedure........................................................................116 5.2.3 Optical Measurement............................................................................117 5.3 Discussion......................................................................................................122 5.3.1 Infrared-active modes...........................................................................122

PAGE 7

vii 5.3.2 Mode at 850 cm-1.................................................................................123 5.3.3 Mode Splitting......................................................................................124 5.3.4 Low-frequency Behavior......................................................................127 5.3.5 Temperature Effects..............................................................................128 5.4 Summary........................................................................................................129 6 SUMMARY AND CONCLUSION.........................................................................141 6.1 High Temperature Superconductor................................................................141 6.1.1 Doping Dependent Measurement.........................................................141 6.1.2 Field Dependent Measurement.............................................................142 6.2 Dielectric Materials........................................................................................143 APPENDIX: TERAHERTZ MEASUR EMENT OF YBCO FILMS..............................144 LIST OF REFERENCES.................................................................................................146 BIOGRAPHICAL SKETCH...........................................................................................153

PAGE 8

viii LIST OF TABLES Table page 2-1 Bolometer 113V measurement setup parameters: Bolom. Stands for the bolometer detector; Bm.Spt is the beam splitter; Scn.Sp. stands for the scanner speed; Sp.Rn stands for the spectral ra nge; Phs.Crc.Md stands for the phase correction mode; Opt. Filter stands for the optical filter; BLK.Ply. Stands for black polyethylene; Apd. Fctn. Stands for the apodization function; Bk-Hrs 3 stands for the Balckman-Harris 3 term ; and Hp-Gng stands for Happ-Gengel.......37 2-2 Perkin-Elmer grating monochromat or parameters. GB stands for globar. W stands for tungsten. D2 stands for deuterium arc lamp. TC stands for thermo couple. Pbs stands for lead slifide. 576 standsfor Si photoconducting detector (Hamamatsu 576).....................................................................................................39 3-1 The charge transfer band fitting parameters* (obtained from Lorentz model) for the SrTiO3, optimally doped YBa2Cu3O7and overdoped Y0.7Ca0.3Ba2Cu3O7.....66 3-2 Parameters (obtained from Drude Lorentz model) giving the best fit to the reflectance (between 25 cm-1 and 4000 cm-1) of SrTiO3 at different temperatures.............................................................................................................67 3-3 Parameters (obtained from Drude Lorentz model) giving the best fit to the reflectance (between 25 cm-1 and 4000 cm-1)of YBa2Cu3O7(optimally doped).......................................................................................................................67 3-4 Parameters (obtained from Drude Lorentz model) giving the best fit to the reflectance (between 25 cm-1 and 4000 cm-1)of Y0.7Ca0.3Ba2Cu3O7(overdoped) at differe nt temperatures......................................................................68 3-5 The scattering rate (obtained from Drude Lorentz model) of optimally doped and overdoped YBCO films in different temperature.....................................................71 3-6 The Drude part and superflu id part plasma frequency below Tc in the optimally doped and overdoped samples..................................................................................73 4-1 Oscillator parameters of both the MgO substrate and YBa2Cu3O7at 4.2 K........103 5-1 Lattice parameters and atomic positions at 298 K and 12 K for the cubic BZN pyrochlore. (The upper and lower entries in each site correspond to the position at 298 K and 12 K respectively.)............................................................................114

PAGE 9

ix 5-2 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BZT pyrochlore at 300K a nd 50K. indicates mode splitting..............119 5-3 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BMN pyrochlore at 300K a nd 50K. indicates mode splitting............119 5-4 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BMT pyrochlore at 300K a nd 50K. indicates mode splitting.............120 5-5 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BZN pyrochlore at 300K a nd 50K. indicates mode splitting. ** indicates split A-O mode described in the present work......................................121 5-6 The mass ratio of the B site ions in different pyrochlores......................................125

PAGE 10

x LIST OF FIGURES Figure page 1-1 Light incidents upon smooth surface.......................................................................20 1-2 Light incidents onto a th in film with thickness d.....................................................21 2-1 A simplified Michelson interferomet er diagram. Light travels distance S from source to the beam-splitter. Partially re flected travels to the fixed mirror (M1) and partially transmitted beam travels a variable distance toward the movable mirror (M2). The beam is recombined at the beam splitter and half of the beams returns to the source, and the other proceeds to a detector.......................................41 2-2 Schematic diagram of a THz-TDS spectrometer using a femtosecond laser source and photoconductive THz transmitters and receivers. Partially reflected laser light was used as the gate signal for the THz detector. Partially transmitted light reaches THz transmitter to excite th e THz pulse. Sample is placed in the beam focus point......................................................................................................42 2-3 Curve shows the THz transient after propagation through a BaTeO3 pellet. The main pulse is followed by a series of pulse of decreasing amplitude that originate from multiple reflections within the pellet................................................43 2-4 Diagram of grating spectrometer show ing the incident and diffracted rays and the operation of grating............................................................................................44 2-5 Schematic diagram of Bruker 113 V FTIR spectrometer. The lower channel has the specially designed reflectance optical stage for reflectance measurement in the sample chamber..................................................................................................45 2-6 Schematic diagram of Perkin-Elm er monochromator spectrometer........................46 2-7 High-Tran system flow diagram..............................................................................47 3-1 The unit cell of YBa2Cu3O7(Ca substitute for Y in the overdoped sample).........77 3-2 Schematic phase diagram of the holedoped cuprates (x is the doping level).........78 3-3 Room temperature reflectance of SrTiO3 and the fitting spectrum..........................79 3-4 Temperature dependent re flectance spectra of SrTiO3 substrate.............................80

PAGE 11

xi 3-5 Room temperature reflectance spectra of the optimally doped and the overdoped samples.....................................................................................................................81 3-6 Temperature dependent reflectance spectra of the optimally doped YBa2Cu3O7film........................................................................................................................... 82 3-7 Temperature dependent reflect ance spectra of the overdoped Y0.7Ca0.3Ba2Cu3O7film.........................................................................................................................8 3 3-8 The measured and fitted room temper ature reflectance of both optimally doped and overdoped films.................................................................................................84 3-9 Measured and fitted reflectance of optimally doped YBa2Cu3O7at room temperature and 50 K...............................................................................................85 3-10 Measured and fitted reflectance of overdoped Y0.7Ca0.3Ba2Cu3O7at room temperature and 50 K...............................................................................................86 3-11 Optical conductivity (obt ained from Drude Lorentz model) of the optimally doped and overdoped samples at room temperature................................................87 3-12 Number of carrier participating in optical transition per Cu atom, Neff, as a function of frequency...............................................................................................88 3-13 Temperature dependent optical condu ctivity obtained from Drude Lorentz model of optimally doped and overdoped samples..................................................89 3-14 Temperature dependent scattering rate (obtained from Drude Lorentz model) of the optimally doped and overdoped samples...........................................................90 3-15 Imaginary part of quasi-particle self energy (obtained from Marginal Fermi liquid model) of both optimally doped and overdoped samples..............................91 3-16 Superfluid density calculated from sum rule and imaginary part of the optical conductivity in both optimally doped and overdoped samples................................92 3-17 Temperature dependent imaginary part (obtained from Drude Lorentz model) of the optical conductivity in the optim ally doped and overdoped samples................93 4-1 Transmittance of different YBCO film samples. YBCO/sapphire (a), YBCO/MgO (b), YBCO/silicon (c) samp les in different magnetic fields.............108 4-2 Measured and fitted spectra of YBa2Cu3O7/MgO sample...................................109 4-3 Real and imaginary part of optical conductivity of optimally doped YBCO.........110 4-4 Magneto resistance of different YBCO film samples. YBCO/sapphire (a), YBCO/MgO (b), YBCO/silicon (c) samp les in different magnetic fields.............111

PAGE 12

xii 5-1 Low temperature cofired ceramics (L TCC) multilayer manufacturing process....131 5-2 The crystal structure of the bismuth pyrochlore.....................................................132 5-3 The displacement of A site cation and O’ anion....................................................133 5-4 The reflectance of different bismuth sa mples. (a) BZT, (b) BMN, (c) BMT, and (d) BZN..................................................................................................................134 5-5 The real part of the dielectric function ( ) of different bismuth samples. (a) BZT, (b) BMN, (c) BMT, and (d) BZN.................................................................135 5-6 The imaginary part of the dielectric function ( ) of different bismuth samples. (a) BZT, (b) BMN, (c) BMT, and (d) BZN............................................................136 5-7 The absorption coefficient and conductiv ity of BZN at room temperature and at cryogenic temperature. (a) absorptio n coefficient, (b) conductivity......................137 5-8 Measured and calculated reflectivity of BMN at different temperatures. (a) 300 K and (b) 50 K........................................................................................................138 5-9 The splitting of the B-O stretching mode in BMT.................................................139 5-10 Temperature dependence of the phonon m ode frequencies in BZT, BMN, BMT, and BZN.................................................................................................................140 A-1 The temperature dependent transmittance of the YBa2Cu3O6/sapphire (a), YBa2Cu3O7/sapphire (b), and sapphire (c)...........................................................145

PAGE 13

xiii Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy OPTICAL STUDIES OF HIGH TEMPE RATURE SUPERCONDUCTORS AND ELECTRONIC DIELECTRIC MATERIALS By Minghan Chen December 2005 Chair: David B. Tanner Major Department: Physics Infrared and optical spectroscopy has been applied to study both the normal state and superconducting state electronic prope rties of cuprate superconductors. Two important parameters used in our experiments are the applied field and substitutional doping. The ab -plane optical responses of Ca-doped YBa2Cu3O7films were studied from optimally doped region to overdoped regimes. The temperature dependent reflectance spectra were measured from far infrared (20 cm-1) to ultraviolet (43,000 cm-1). The spectra were analyzed by a two component model and marginal Fermi liquid model. The result indicates a further increase of plasma frequency which is consistent with the study of BSCO samples by other groups Another interesti ng result is the decreased superfluid density in the overdoped region. This result is consistent with decreased superconducting transition temperature with increasing th e doping level within the overdoped region.

PAGE 14

xiv Magnetic field dependent, low temperatur e infrared transmittance was used to study the vortex dynamics in high temp erature superconductors. Optimally doped YBa2Cu3O7and YBa2Cu3O6 samples were used for the measurements. We saw no significant field-sensitive features in the far infrared transmittance spectra at low temperature. The temperature dependence of the refl ectance of cubic bismuth pyrochlores Bi3/2ZnTa3/2O7 (BZT), Bi3/2MgNb3/2O7 (BMN), Bi3/2MgTa3/2O7 (BMT) and Bi3/2Zn0.92Nb1.5O6.92 (BZN) has been investigated by in frared spectroscopy. Spectra were collected from 30 to 3300 cm-1 between 50 and 300 K, and the optical constants were estimated by Kramers-Kronig analysis and cl assical dispersion th eory. In addition, BZN was studied by terahertz techniqu e at lower frequencies (3 cm-1 to 60 cm-1) between 300 K and 50 K. Infrared-active phonon modes have been assigned to specific bending and stretching vibrational modes. A previously unassigned infrared mode at about 850 cm-1 is discussed. A splitting of the B-O stretchi ng phonon modes and O-B-O bending modes is assigned to mixed cation occupancy. The temperature dependence of the phonon frequencies and the damping coefficients are cons istent with a decrease of lattice constant and with orientational disorder at low temperatures.

PAGE 15

1 CHAPTER 1 OPTICAL THEORY The optical properties of materials arise from the characteristic of their interactions with electromagnetic waves. Different classes of materials will, in general, differ in their response to optical radiation. In this chapte r, we will provide a ge neral background of the theory of the optical properties of materials. The first part is a review of the principle of optics and some phenomena that occur when light propagates through a medium. Then, we will introduce the famous Maxwell’s equations which describe the behavior of electromagnetic fields. Following this part, several techniques and equations will be introduced to explain how to get quantitative optical parame ters from the experimental spectrum. Finally, we will give the microsco pic models to describe the interaction between light and the atoms of the materials. De tails of the subject of this chapter can be found in most books on optics and electromagnetism [1-7]. 1.1 Light Phenomena Light propagates as elect romagnetic waves. Theref ore, there are certain characteristics of waves, and in particular electrom agnetic waves, that must be reviewed in order to understand the behavior of light and its interaction with matter. Traveling waves can be either longitudinal or transverse. The electromagnetic field wave is transverse. If light incident on th e source is absorbed and the only light emitted by the source is the light generated by the oscillators of the sour ce material, then the source is named a black-body. Planck’s equation for spectral intens ity as a function of wavelength R( ) (in J/cm3 etc .) for the black-body ra diation spectrum is

PAGE 16

2 1 1 2 ) (5 2 T k hcBe h c R (1-1) where T defines the temperature in degree Kelvin (K), h is Planck’s constant (6.63x10-34 J.s) and kB is Boltzman’s constant The wavelength corresponding to the peak emission intensity for each temperature can be derivied from equation 1.1. K m 10 28978 0o 2 Tm (1-2) Equation 1.2 is Wein displacement law. When light is shining onto a medium, some of it will be reflected and the rest of the light is going to transmit and propagate in th e material. As the light propagates in the medium, part of the light will be reduced by the absorption or scattering by the material. If we assume the optical properties such as refractive index, absorption coefficient, and reflectivity are independent of light intensity, this is called linear optics. All the discussion of this thesis will be restricted to the linear optics. Within linear optics, the refractive index of a material is defined by the ratio of the velocity of light in free space to the velocity of light as it passes through the materials. v c n (1-3) The group velocity of light traveling through a material is less than the velocity in free space. It is also true th at light with different wavele ngth travels at different speed through the same material. This leads to the fact that the refractive index of any matter

PAGE 17

3 has the same wavelength dispersion or a variat ion in value as a func tion of wavelength or frequency ) ( n n (1-4) The absorption of light in the matter can be quantified by absorption coefficient defined as the fraction of the power abso rbed in a unit length of the material. xe I I x I dx dI 0 and ) ( (1-5) The response of a material to the external electric field E can be characterized by a few macroscopic vect ors: polarization P electric displacement and current densityJ For weak electromagnetic field and in local lim it, the response of the medium is linear and can be written by the constitutive relations (all the equations are written in c.g.s unit). ~ ~ and ~ 4 1 ~ ~ 4 ~ ~ 4 1 ~ ~ 4 ~ 2 1 2 1 e i E t P J H M H B H M i E P E D E Pm m e (1-6) The parameter ~ is a complex dielectric constant and ~ is the complex conductivity of the medium The real parts of ~ and ~ are the frequency-dependent dielectric function and conductiv ity, respectively, of the medi um. For simplicity, we take = 1; this is the case for most of nonmagnetic materials. Thus, we can set H B The propagation of the electromagnetic wave can be described by a set of four differential equations known as Ma xwell’s macroscopic equations.

PAGE 18

4 f fJ c t D c H t B c E B D 4 1 1 0 4 (1-7) where E and H are the electric and magnetic fields, D and B are the displacement field and magnetic induction, f andfJ are the free charge and free current density respectively. If the medium is isotropic and homogenous, ~ and ~ are scalar quantities rather than tensors and have no space variation. In the absence of external charges and free current density, Maxwell equations are given by t D c H t H c E H D 1 1 0 0 (1-8) assume the fields have the plane-wave form ) ( exp0 0t x q i H E H E (1-9)

PAGE 19

5 where the vector0E 0H and q are in general complex a nd independent of space and time, then t and can be replaced by i and q i respectively. Then, Maxwell’s equations can be changed into E c D c H q H c E q H q E q D q ~ 0 0 ~ 0 (1-10) Equation (1-10) indicates q E H are mutually perpendicula r with each other, if we assume ~ is a scalar, the case for isotropic materials. The solution for the above Maxwell’s equations is ~2 2 c q (1-11) The conclusion provides that light is a transverse electromagnetic wave. One can define a complex refractive index yielding the very useful dispersion relationship ) ( ~ik n c N c q (1-12) Comparing equation (1-11) and (1-12), we find ~ ~ N (1-13) or nk k n22 2 2 1 (1-14) and

PAGE 20

6 2 1 1 2 1 2 2 2 1 2 1 1 2 1 2 2 2 1) ( 2 1 ) ( 2 1 k n (1-15) Considering the case of normal incidence and q parallel to x, then equation (1-9) has the form t nx c i kx c t Nx c ie e H E e H E H E 0 0 0 0 (1-16) This solution is an attenuated wave with a skin depth = (c/ )k or a power absorption coefficient = 2/ = (2 k)/c, the phase velocity is vp = c/n. The optical response of a material can be described by various quantities (called optical “constants”) which are not inde pendent and can be interrelated by ~ 4 1 ~ ~ ~ 12 2i N Z (1-17) where the complex surface impendence Z = R + iY with R and Y being the impendence and reactance, has been introduced. Note all the optical “constants” introduced are (in general) frequency dependent. For our experiment, the most interesting thing is the real part of the optical conductivity, 1, because it is directly proportional to the power dissipation of the electromagnetic field unit volume by the medium. 2 12 1 *] ) Re[( 2 1 *) Re( 2 1E E E E J dV dPdissip (1-18) E J J JP f ~ is the total charge current induced by the electric field E The result indicates that only the in -plane conduction current E Jf 1 dissipates power. While the

PAGE 21

7 displacement current E c i Jd ) / ( and the polarization current E i JP 2do not, because they are /2 out of phase with E ; thus time average of energy flow is zero. 1.2 Determination of Optical Constants The purpose of our experiment is to find the optical conductivity. But, unfortunately, in most situations, optical conductivity cannot be measured directly. Information about the materials is often obtained by studying the electromagnetic waves reflected from and/or transmitted across interfaces between materials with different optical properties. In the experiment, the transmittance T( ) and reflectance R( ) are usually measured in a special frequency range. And the optical constant, such as 1( ) and 2( ), will be deduced from R and T. 1.2.1 Fresenel’s Equation In Figure 1-1, light incident upon the smooth surface will be reflected and refracted. The incident, reflected and refracted rays lie in the same plane of incidence. The reflected beam from a flat, polishe d surface will propagate at an angle (r = i) that which equals the angle of incidence. The re fracted or transmitted beam will propagate at an angle t that obeys t t i in n sin sin (1-19) At the interface, the reflected and refract ed beam intensities must satisfy the requirement that the parallel to the inte rface components of the total electric and magnetic fields be continuous across the boundaries. This relationship leads to the Fresnel formulae. For normal incidence (i = t = 0) the boundary condition can be written as the following equations

PAGE 22

8 t r i t r iH H H E E E (1-20) where the subscripts i, r and t denote the incident, reflected and transmitted light respectively at the interface. The relation between E and H can be simplified asE N H ~ Thus, a plane wave is propagating across the interface between medi um a and medium b, and it satisfies t b t r a r i a iE N H E N H E N H~ ~ ~ (1-21) where a and b are the complex refractive indices in medium a and medium b. The complex amplitude coefficients of the reflected r and transmitted t electric field are b a b a i rN N N N E E r ~ ~ ~ ~ (1-22) b a a i tN N N r E E t 2 1 (1-23) If we assume medium a is vacuum, then we can take Na = 1 and Nb = N = n + ik. The reflectance of medium b is simply given by 2 2 2 2 *) 1 ( ) 1 ( ~ ~k n k n r r R (1-24) The reflectance R and phase change of the reflected electric field wave are related to n and k by 2 21 2 tan and ) 1 ( ) 1 ( k n k ik n ik n r e Ri (1-25)

PAGE 23

9 In the single-beam optical measurement, only the reflectance R can be measured. Thus, n and k cannot be determined alone. Therefore, we need another equation to relate n and k. The Kramers-Kronig relation offers a practical solution to the problem. 1.2.2 Kramers-Kronig Analysis The Kramers-Kronig technique makes use of the optical functions, such as reflectance, transmittance or other linear respons e functions. This analysis is based on the causality requirement on the response function, i.e., that the response of the system cannot occur until an external dr iving force is applied. These equations relate a dispersive process to an absorptive process due to the requirement of causality for linear response function. The Kramers-Kronig relation for th e complex refraction index and the complex dielectric function may be stated as follows, 0 2 2 0 2 2' 1 ) ( 2 ) ( ' ) ( 2 1 ) ( d n P k d k P n (1-26) 0 2 2 1 2 0 2 2 2 1' 1 ) ( 2 ) ( ' 1 ) ( 2 1 ) ( d P d P (1-27) where P is the Principal value of the integral. Fo r the reflectance at a plane interface, the amplitude reflection coefficient given in e quation (1-24) is a co mplex quantity. One commonly used technique is to measure the re flectance over a wide frequency range, and we get

PAGE 24

10 ' ) ( ln ' ln 2 1 ' ) ( ln ) ( ln ) (0 0 2 2 d d R d d R R (1-28) An obvious drawback of the Kramers-Kronig technique is the requirement of large frequency range measurement. Extrapolati ons to zero and infinite frequencies are required. One typical extrapolation [3] is that above the highest frequency (37,000 cm-1) measured, the reflectance is usually expressed as -s with 0 < s < 4. The reflectance is due to interband transition in th is region and can be expressed as s f fR R ) ( (1-29) At low frequency, the reflectance is assumed to be constant if the sample is an insulator. In the case of a meta l, the reflectance is expressed in term of the Hagen-Rubens law [3] and is written as A R 1 ) ( (1-30) 1.2.3 Reflectance and Transmittance at a Thin Film on a Thick Substrate A thin film has a thickness d << and d << and is the penetration depth. If light incident onto this system, some part of it will be reflected and some will be transmitted. In the film, we can expect multiple reflections. This can be clearly described by the following model. As shown in Figure 1-2, medi um 1, medium 2, and medium 3 constitute this two interface system. The first and third media are assumed to be non-absorbing and to span semi-infinite space with their complex refractive index N1 and N3 respectively. The second medium has its thickness d with refractive index 2. For simplicity, only

PAGE 25

11 normal incidence will be considered. The ge neral transmission a nd reflection can be expressed as ~ 2 21 23 ~ 23 12 2 ~ 2 21 23 ~ 2 21 23 ~ 23 12~ ~ 1 ~ ~ ] ) ( ) ( 1 [ ~ ~ ~ i i i i ie r r e t t e r r e r r e t t t (1-31) and ~ 2 23 21 ~ 21 23 12 12 2 ~ 2 23 21 ~ 2 23 21 ~ 21 23 12 12~ ~ 1 ~ ~ ~ ~ ) ( ) ~ ~ ( 1 ~ ~ ~ i i i i ie r r e t r t r e r r e r r e t r t r r (1-32) where rij and tij are the amplitude reflection and transmission coefficients between medium i and j ~ is the complex phase depth of th e second medium which is defined by d i d n c d N c 2 ~ ~2 2 (1-33) where is the absorption coefficient. The resultant transmission and reflection are obtained cos ~ ~ 2 ~ ~ 1 ~ 21 23 2 2 21 2 23 2 23 2 12 1 3 2 1 3 d d de r r e r r e t t n n t n n T (1-34) cos ~ ~ 2 ~ ~ 1 cos ~ ~ 2 ~ ~21 23 2 2 21 2 23 12 23 2 2 23 2 12 2 d d d de r r e r r e r r e r r r R (1-35) 21 23 22 d n c (1-36) where ij is the phase shift upon reflection at th e interface. The cosine term leads to interference fringes in the spectrum which is due to multiple internal reflections in the second medium.

PAGE 26

12 When the second medium is thick ( d >> ) or wedged, there is no coherence among multiple reflections. For a thick sample of thickness d with complex refractive index being measured in a vacuum, it is straightforward to find the average transmittance and reflectance d s d s avee R e n k R T 2 2 2 2 21 ) / 1 ( ) 1 ( (1-37) and ) 1 (d ave s avee T R R (1-38) where Rs is the single bounce reflectan ce given by equation (1-24). Let us consider the structure of a thin film with thickness d deposited on a thick substrate, as shown in Figure 1-2. Take N1 = 1; then from equation (1-31) and (1-32) with the following approximations, y d c iN i e n n N N N Ni 4 2 1 12 2 3 3 2 1 2 (1-39) Here, we have applied the long wavelength lim it and assumed that film is thin enough such that <<1. It can be shown that the transmittance across the film into substrate and the reflectance from the film are given by Glover-Tinkham equations [8, 9]. 2 2 2 1 2) 1 ( 4 1 ~ 1 1 y n y n n y Tf (1-40) and

PAGE 27

13 2 2 2 1 2 2 2 1) 1 ( ) 1 ( y n y y n y Rf (1-41) where n is the refractive index of the substrate, y1 and y2 are real and imaginary part of the complex admittance of film y ~ respectively. y ~ is related to th e complex conductivity 2 1~ i of the film by d Z y ~ ~ 0 where Z0 is the impendence of free space. In reality, the substance has a finite thic kness and it is a four medium problem with medium 4 being vacuum. For a nearly opaque metal film, the overall reflectance of film plus substance in this 4-medium system is x f s x s f fe R R e R T R R 2 21 (1-42) Equation (1-40) gives the transmittance across the film into substrate. The measured transmittance T is given by f x f s x sT e R R e R T 2 '1 ) 1 ( (1-43) where x is the thickness and the absorption coefficient of the substrate. The other terms of equation (1-42) and (1-43) are substrateincident (backside) re flection of the film. 2 2 2 1 2 2 2 1 ') 1 ( ) 1 ( y n y y n y Rf (1-44) and for a weakly absorption substrate such that k = ( c )/( 2 )<< n The single boundary reflection of the substrate may be approximated as 21 1 n n Rs (1-45) From the measurement of the transmittance and reflectance of the substrate, we can get the index of refraction n and the absorption coefficient of the substrate using

PAGE 28

14 equation (1-37), and (1-38). The term k2/n2 in equation (1-37) can be neglected for a weak absorbing substrate. With the knowledge of substrate’s optical properties, 1, 2 and all other response functions can be expected by inverting equation (1-40) (1-44), after measuring both transmittance and reflectance of the film-on-substrate system. For a structure with more layers, the analysis becomes progressively more complicated. 1.2.4 Microscopic Models Up to this point, we have not describe d the optical phenomena from a microscopic point of view. There are various microscopic models which explain the optical behavior observed experimentally. The classical theory of absorption and dispersion is due mainly to Lorentz and Drude. The Lorentz model is applicable to insulator; its quantum mechanical analog includes all direct interband transitions, i.e. all transitions from which the final state of an electron lies in a different band, but with no change in K -vector in the reduced zone scheme. The Drude model is appl icable to free-electron metals; its quantum mechanical analog includes intraband transiti on, where intraband transition is taken to mean all transitions not involving a reciprocal lattice vector. Both the Lorentz and Drude model are useful as starting points and for developing a feeling fo r optical properties. Many features of these classical models have quantum mechanical counterparts which are easily understood as generalizations of their classical analogs. 1.2.4.1 Lorentz model The Lorentz model is a simple, yet very us eful classical model dielectric function that can be derived for a set of damped ha rmonic oscillators. The motion of an electron bound to the nucleus is described by

PAGE 29

15 ) (2 0 2 2t E e r m dt r d mr dt r d m (1-46) The field E(t) is the local electrical field acting on the electron as a driving force. The term dt r d mr represents viscous damping and provides for an energy loss mechanism. The actual loss mechanism is radiation damping for a free atom, but it arises from various scatting mechanisms. The term r m 2 0 is a Hooke’s law restoring force. In the classical model, there are two approximations in equation (1-46). The nucleus has been assumed to have infinite mass; otherwise the reduced mass should have been used. We also have neglected the small forcec B V e / arising from interaction between the electron and the magnetic field of th e light wave. It is negligible because the velocity of the electron is small compared w ith c (c is the speed of light in vacuum). Inserting a solution of the form t ie r r0 into equation (1-46), yields E i m e r 2 2 01 (1-47) and the induced macroscopic polarization is E i m Ne Ner P 2 2 0 21 (1-48) Assuming there are N oscillators per unit volume, th e resonant contribution to the macroscopic polarization is E i m Ne Ner P 2 2 0 21 (1-49) For isotropic matter, the susceptibilit y arising from the oscillator is i m Ne 2 2 0 21 ~ (1-50)

PAGE 30

16 the total polarization is E E Pe) ~ ( ~ total (1-51) where is the background susceptibility that ar ises from the polarization due to all the other oscillators at higher frequencies. The dielectric function can be determined ip 2 2 0 2) ( ~ (1-52) plasma frequency can be defined by m Nep2 24 (1-53) where N q and m are the number density, effective charge and effective mass of the type j oscillator respectively. If the sy stem has several oscillators and Nj is number density of jth oscillator, Nj should satisfy the following equation. j jN N (1-54) A corresponding quantum mechanical version of equation (1-52) can be written as j j j j pi f 2 2) ( ~ (1-55) fj is introduced as the notion of oscilla tor strength. The os cillator strength fj is related to the probability of a quantum mechanical transition which can be calculated using Fermi’s golden rule. It satisfies a sum rule. j jf 1 (1-56) The oscillator strength allows us an explanation for diffe rent absorption strength of different transitions.

PAGE 31

17 1.2.4.2 Drude model The Drude model describes the optical res ponse of free carrier in good metals. It is just a particular case of Lorentz oscillator with 0 in equation (1-46) being zero. ipD D 2 21 ~ (1-57) where pD is the Drude plasma frequency defined by 42 2m NepD (1-58) The real and imaginary parts are ) 1 ( 1 12 2 2 2 2 2 2 2 1 pD D pD D (1-59) The conductivity based on the Drude mode is i 1 ) ( ~0 (1-60) where 0 is the DC conductivity defined as *2 0m Ne (1-61) The real and imaginary parts are 2 2 0 2 2 2 0 11 1 D D (1-62) The relation between ~and ~is ) ( ~ 4 ) ( ~ i (1-63)

PAGE 32

18 in the limit of low frequency where << -1 is satisfied, we can obtain the following relations 2 1 0 2 1 2 1 0 2 2 2 2 1) / 2 ( 1 / 2 1 ) 2 / ( / 4 / n R k nD pD D pD D (1-64) From the above equations, we can find the absorption coefficient c c k 08 2 (1-65) or the skin depth 02 2 c (1-66) So, the skin depth is inversel y proportional to the square ro ot of the DC conductivity and frequency. This implies that a material w ith higher DC conductiv ity allows shorter penetration of AC fields. Considering the special case with Drude width -1= 0, the dielectric functions are given by ) 0 ( 01 2 2 2 1 D D pD D (1-67) For superconductor, the super-fluid part of dielectric contributi on is satisfied with the above equation. This equation tells us that D < 0 for frequencies below the plasma edge pD(). Then, the complex refractive index is purely imaginary and thus the reflectance R is 1 in this frequency range and system suddenly becomes transparent above plasma edge.

PAGE 33

19 1.2.4.3 Drude-Lorentz model When both the Drude and Lorentz types of dielectric response are observed in a spectrum, we can model the dielectric function by a sum of these terms. j p j j pji i 2 2 2 2 2) ( ~ (1-68) This relation is called the Drude-Lorentz mode. In the optical spectrum of the high Tc superconductors, the Lorentz pa rt of contribution is used to describe the mid-infrared contribution. The Drude part is used to describe the free carri er or quasi-particle contribution. All these terms plus the superf luid term will be used to describe the dielectric function of the op tical properties of the high Tc superconductor. Unlike Kramers-Kronig relation, fitting data with model function can be employed in a finite frequency range as long as we have a well-defined background contribution beyond the measured frequency range. 1.2.4.4 f -Sum rule For f -sum rule. It states that the area under the conductivity 1( ) is conserved. 0 2 2 12 8 ) ( m Ne dp (1-69) where m and e are the bare mass and electric charge of a free electron. This sum rule means that area, or oscillator strength, is independent of factors such as the sample temperature, the scatting rate, phase transition, etc The sum rule has an important impact on a superconductor, in which an energy gap develops between the transition temperature Tc. The spectral weight at < 2 shifts into the origin ( function), causing an infinite DC conductivity.

PAGE 34

20 Figure 1-1 Light incidents upon smooth surface.

PAGE 35

21 Figure 1-2 Light incidents onto a thin film with thickness d.

PAGE 36

22 CHAPTER 2 INSTRUMENTATION AND TECHNIQUES This chapter describes the experimental eq uipment and technique used to perform our near-normal incidence reflectance and transmittance measurement, as well as the various techniques used to char acterize our samples. The first section is a description of Fourier spectroscopy. We then discuss the terahertz measurements and the diffraction grating spectrometer. Then, we will introdu ce the instruments used in my experiments which are Bruker 113V FT-IR spectrometer, TPI Spectra 1000 spectrometer, and the Perkin-Elmer Mid 16U monochromator. In the final part, we will discuss the cryogenic system used to take the temperature depe ndent measurement for the YBCO films and electronic dielectric samples. 2.1 Far Infrared Techniques 2.1.1 General Principles Let us consider the basic experiment s hown in Figure 2-1, which is a simplified Michelson interferometer. All the theories are general and will hold for any type of interferometer. Without losing generality, we can consider that a monochromatic plane wave of the forum ) . ( 0) (t r q ie E t r E (2-1) is incident on the beamsplitter from the source. Here q is the wave vector, r is a position vector, is the angular frequency, t is the time and 0E is the amplitude of the electric

PAGE 37

23 field. The light travels a distance S to the beamsplitter which has a reflection coefficient rb (light will be reflected to mirror M1) and a transmittance coefficient tb at a given frequency. The reflected beam goes a distance x1 to a fixed mirror with a reflection coefficient ry and a phase y and transmitted beam goes a variable distance x2=( x1+ x ) to a moving mirror with a reflection coefficient rx and phase x in term of frequency. The two beams return to the beam splitter and are ag ain transmitted and reflected with coefficient tb and rb. Some proportions of the beam go back to the source and the rest of the beam travels a distance D to the detector. At the det ector, the electric field is a superposition of the fields of the two beams. Both q and r are parallel to each other. For our discussion, we will assume the end mirrors are near perfect reflectors such that rx ry -1. And we define the angular frequency by the relation, v c v q 2 2 2 (2-2) The resulting field from the interf erometer toward the detector is ] [) 2 ( ) 2 ( 02 1t x i t x i b b De e E t r E (2-3) Thus, the light intensity at the detector is ) 2 cos( 1 )[ ( 2 10 *x I E E SD D D (2-4) where x is the optical path difference, x = x2x1, is the beam splitter efficiency 24 rt and the source intensity is I0( ) (equals to 2 02 E ). SD(x) is the intensity of light at the detector for a single given frequency. In ge neral, the following equation holds for the practical beam splitter. 1 t r a (2-5)

PAGE 38

24 where a is the absorption of the beam splitter. For an ideal beam splitter, it has a =0, and t = r This expression can be simplified to )] 2 cos( 1 )[ ( ) ( x v v f x S (2-6) ) ( v f (equals to ) ( 8 10I ) is spectral input that depends only on v. S(x, ) is the detector signal for a monochromatic source. The cosine term gives the modulation on the detector signal as a function of x However, in FT-IR spectrometer, we measure the intensity of light, ID(x) for all frequencies v x S x SD D, as a function of the optical path difference x 0 0)] 2 cos( 1 )[ ( ) ( ) ( v d x v v f v d v x S x ID (2-7) At x =0, the detector signal reaches its maximum value, 0) ( 2 ) 0 (v d v f S (2-8) This position corresponds to zero optical path difference where all frequency components interfere constructively. As x on the other hand, the coherence of the modulated light is completely lost. The de tector signal is around an average value. 02 ) 0 ( ) ( ) (S v d v f S (2-9) The interferogram is the difference between the intensity of each point and the average value. 0) 2 cos( ) ( ) ( ) ( ) (v d x v v f S x S x F (2-10)

PAGE 39

25 ) ( v f is the cosine Fourier transform of F(x) The ) ( v f can be written as 0) 2 cos( ) ( 4 ) (dx x v x F v f (2-11) 2.1.2 Apodization In practice, the interferogram cannot be measured to infinite optical path (retardation), and it must be within finite ra nge or truncated. This type of truncation can be obtained by multiplying the complete in terferogram with a truncation function G(x) which vanishes outside the range of the data acquisition. The act ual function which is transformed is the product of the inte rferogram and the truncation function. To explain the effect of the truncation function, consider the truncation function described by a boxcar function G(x) L L x x G x if 0 if 1 ) ( (2-12) where L is the maximum retardation. The Fourier transform (FT) of F(x) is the spectrum ) ( v f The FT of G(x) is the sinc function ) 2 ( sin 2 2 ) 2 sin( 2 )] ( [ L v c L L v L v L x G FT (2-13) This Sinc function has a center maximum at 0 and several oscillat ions. The width of the function is 1/L If a single wave of frequency 1v is convolved with a boxcar truncation with maximum length L the resultant spectrum would be a sinc( x ) function centered at 1v with width 1/L Thus, the resolution is limited to L v 1 The side-lobes (oscillations) may be reduced by using an a podization function different from boxcar but

PAGE 40

26 this will come at the cost of a further reduction of resolution. Some of other popular apodization functions are HappGenzel [10], Norton-Beer (w eak, medium, strong) [11], and Blackman-Harris (3-term, 4-term) [12] A nice discussion about the apodization function can be found in Griffiths [13]. 2.1.3 Phase Correction Up to this point in our discussion, the interferogram, F ( x ), is perfectly symmetric about the zero point ( F ( x ) = F (x )). In a real experiment, because of the existence of a phase error, that must be included to desc ribe the actual measured interferogram. The phase error mainly stems from optical path difference. Phase error could lead to a negative spectrum or to a slight shift of sh arp frequencies. When the system has a phase error, the interferogram given by equation 2.10 is modified to 0 2 0 ) 2 (] ) ( [ ) ( ) (v d e e v f v d e v f x Fx v i i v i 2.14 where is the phase error. This error leads to an asymmetric interferogram. In order to correct the phase error, we firs t take an interferogram between –L
PAGE 41

27 There are several phase correction modes avai lable. In my experiments, Mertz phase correction [12] is used. More detailed disc ussion of phase correction methods can be found in other papers [14, 15]. 2.1.4 Sampling Another error occurs in the practical measurement or sampling the interferogram. The analog signal must be converted to digitized data sets before a ny sort of manipulation can take place. For this reason, the interferogram is sampled at small, equally spaced discrete retardations. This discrete nature can be handled mathema tically by using the one dimensional Dirac Delta Comb nn x x ) ( ) ( (2-17) where n is an integer. In a real expe riment, there is always an error x between the measured point and zero point. The real sampled interferogram is given by F’(x) nx n x x n F x x F x x x F ) ( ) ( ) ( ) ( (2-18) Then, the spectrum derived from FT of F’(x) will be nv n v f v f v v v v f ) ( ) ( 1 ) ( (2-19) when x v 1 and ) ( ) ( x F FT v f This sampling of the interferogram cause s two effects. Firs t, it introduces an additional phase term v ie( is the frequency of the light wave) into the spectrum. This term can be used as another kind of phase er ror, to be handled in part of the phase

PAGE 42

28 correction. The second effect is that it makes the spectrum periodic. This effect leads to the possibility of aliasing or “folding”. Th is effect can be prevented by insuring that, 2 or 2min max x v v (2-20) These conditions state that the highest fre quency needs to be sampled at least twice per-wavelength. This is called the Nyquist sampling criterion. It is experimentally important either to ensure di gitizing an interferogram at a high enough sampling rate or to limit the range of frequency input to the det ector using optical and/ or electronic filters. Following the above arguments, it is quite obvious that the measurement of a narrow frequency range requires a smaller numbe r of data points. But if the number of points is too small, the spectral may not be de fined. In such case, we can add extra zerovalued data points at the end of the interfer ogram keeping the same sample spacing. This technique known as zero filling effectively produces a larger number of spectrum points per resolution element. Since the points adde d are zero, the actual spectral resolution will not increase. It merely provides a smoother sp ectral line shape. More detailed information about infrared spectroscopy can also be found in other papers [16]. 2.2 Terahertz Technique 2.2.1 General Principles The Terahertz technique is the marriage of microwave and optical techniques. By its very nature, terahertz ra diation bridges the gap between the microwave and optical regimes. Much of the research in the terahe rtz has been based on the melding of the ideas in both areas. Terahertz Time-Domain Spectroscopy (THz-TDS) is a new spectroscopic technique. It is based on elec tromagnetic transients generate d opto-electronically with the

PAGE 43

29 help of femtosecond (1 fs=10-15 s) duration laser pulses. These terahertz transients are single-cycle bursts of electroma gnetic radiation of typically le ss than 1 ps [17] duration. Their spectral density spans the range from below 100 GHz to more than 5 THz [18]. Optically gated detection allows a direct meas urement of the terahertz electric field with a time resolution of a fraction of a picosecond. From this measurement, both the real and imaginary part of the dielectric function of a medium may be extracted. Furthermore, the brightness of the terahertz transients exceeds that of conventional thermal source and the gated detection is order of magnitude mo re sensitive than bolometric detection. Figure 2-2 is a schematic diagram of a TH Z-TDS spectrometer. It consists of a femtosecond laser source (1). A beam splitte r divides the laser beam into two. An optically-gated THz transmitter (2), focusing a nd collimating optics (3), the sample (4), an optically-gated THz detector (5), a variable delay line (6) that va ries the optical delay between the pulses gating the THz transmitter an d detector, a current amplifier (7) and a Lock-in amplifier (8). A computer (9) controls the variable delay li ne and displays the detector photo current versus path length. In the following sections, we will describe each of these components. 2.2.1.1 Laser A solid-state laser, Ti-sa pphire laser delivering pulses with a wavelength near 800 nm, is used in the instrument. The typical repetition rate of thes e lasers is about 100 MHz. 2.2.1.2 Terahertz transmitter and detector Both the source and the detector consist of the same building blocks [19, 20] which are based on a photo conductive (Auston) switch. It consists of a semiconductor bridging the gap in an antenna line structure. The current through the switch rises very rapidly

PAGE 44

30 after injection of photo carrier s by the optical pulse, and then decays with a time constant given by the carrier life time of semi conductor. The transient photocurrent J(t) radiates into free space according to Maxwell’s equation, ) ( ) ( ) ( t t J t E Because of the time derivative, the radiated field is dominated by the rising edge of phot ocurrent transient, which is invariably much faster than the delay. Long tails of the photocurrent decay are largely irrelevant to the radiat ed field. While the structure of the receiver is close to the structure of the detector, more efficient transmitter structures have since been devised [21, 22, 23]. To convert the Auston switch for use as a detector of short electrical pulses, an ammeter (or current-to-voltage amplifier) is connected across the photoconductor, replacing the voltage bias. The electric field of an incident terahe rtz pulse now provides the driving field for the photocarriers. Current flows throug h the switch only when both the terahertz field and photo-ca rrier are present. Since elect ronics is not fast enough to measure the THz transients directly, repeti tive photoconductive sampling is used. If the photo-carrier life time is much shorter than the te rahertz pulse, the photoconductive switch acts as a sampling gate which samples the terahertz field for a time Because the laser pulses which trigger the transmitter and gate the detector originate from the same source, the photoconductive gate can be move d across the terahertz wave form with an optical delay line. Using this technique, the entire terahertz transient is mapped without the need for fast electronics. There are a number of ways in which this measurement can be performed. In the most common, the optical beam exciting the transmitter is mechanically chopped and the voltage from the current amplifier is synchr onously detected using a lock-in amplifier.

PAGE 45

31 The optical delay is slowly scanned and the photocurrent acquired into a computer. Another technique is “rapid scan”, in which th e time-delay is scanned at a rate of tens to hundreds of Hz using a shaker with an optical retro-reflector. To enhance the signal-tonoise ratio, each scan is co-adde d using an averaging digital oscilloscope. Rapid-scan can significantly reduce the noise due to 1/f laser power fluctua tions. In many applications, the photocurrent signal is so la rge (nA level), that the output from the current amplifier can be directly digitized for further proce ssing without using a lock-in amplifier [24]. 2.2.2 Some Important Issues with THZ-TDS Technique 2.2.2.1 Frequency Limit of Terahertz Detector The beam width of the detection proce ss is determined by two factors, the photocurrent response and the frequency dependen ce of the antenna structure. In general, the low-frequency cut-off of the detectors re sults from the collection efficiency of the dipole, while the upper frequency limit is de termined by the photo carrier response. We focus first on the photocurrent response which is the convoluti on of the transient photoconductivity (t) and the electric field E(t) across the photoconductor ' ') ( ) ( ) ( dt t E t t t J (2-21) where J(t) is the photocurrent transient. E(t) is faithfully reproduced by J(t) when the photocurrent transient becomes much shorter than the THz waveform. The photocurrent decay time in the Auston switch must be less than roughly 0.5 ps in order to resolve transients in the THz regime. Recombination in a semiconductor with low defect density tends to be far slower; therefore the carrier lifetime has to be reduced below its intrinsic value. This reduction is commonly accomplished by introducing defect states that have a fast carrier capture rate. An example of the first case is low-temperature

PAGE 46

32 grown GaAs (LT-GaAs), which has been shown to have carrier lifetime as short as 280fs when properly annealed. An example of th e latter is radiation-damaged silicon-onsapphire (RD-SOS), in which di slocations are formed by impl anting argon, silicon, or oxygen ions [25, 26]. The electric field across the photoconducto r can differ from the THz pulse in free space due to the frequency-response of the antenna structure. Using the reciprocity principle, the collection efficiency of the detector is identical to the radiation efficiency of the transmitter. For a Hertzian dipole, where the antenna dimension is much less than the wavelength, the radiation effici ency (and thus the collection efficiency) is proportional to (corresponding to the first derivative of the current). For “real” dipoles, the frequency response will be more complicated [27]. 2.2.2.2 Signal to Noise Ratio and Dynamic Range The estimated average power of the THz b eam is about 10nW. The peak power is much higher, by a factor 104, because the energy appears in 1ps bursts every 10ns. The energy per burst is about 0.1fJ, corres ponding to roughly 50,000THz photons. The reason for the large S/N ratios is the use of gated det ection. The detector is off for most of the time between pulses. Hence the average resist ance of the switch is high and the Johnson noise is negligible. In addition, gated detec tion discriminates effectively against thermal background noise. In fact, van Exter [20] ha s shown that the thermal background noise usually exceeds the average power of the THz radiation by a f actor of ten, and that the minimum detectable THz signal (amplitude) can be 160 times smaller than the incoherent thermal background radiation. Because THz-TDS measures electric field ra ther than intensity, the measurements typically have a greater dynamic range than more conventional technique.

PAGE 47

33 2.2.2.3 Phase sensitivity In many applications, the most importa nt advantage of THz-TDS is direct measurement of the electric field E(t) Fourier transformation of E(t) yields both amplitude and phase of both the propagation or transmission coefficient. Measurement of both amplitude and phase in THz-TDS yields re al and imaginary parts of the dielectric function over the frequency range spanned by th e THz pulse. This is a crucial difference in comparison with conven tional FT-IR spectroscopy. 2.2.2.4 Resolution and Time-Window of Data In THz-TDS, the spectral resolution is the inverse of the optical delay time provided by the moving mirror. Because the measurement is performed in the timedomain, substrate reflection can be windowed out of the raw data without much loss in spectral resolution and little infl uence on the accuracy of the data. 2.2.2.5 Time-Domain Data Analysis Linear spectroscopy requires that the radiation intera cts with the medium under study by either reflection or transmission. As with most spectroscopic technique, THzTDS requires two measurements: one reference waveform Eref(t) measured without the sample or with a sample of known dielec tric properties, and a second measurement Esample(t) in which the radiation interacts with the sample. For spectral analysis, E(t) can directly be Fourier-transformed to yield the complex amplitude spectrum E( ) in both amplitude and phase. In my experiment, I m easured thick pellet samples. Figure 2-3 shows a typical measurement. The curve shows the THz transi ent after propagation through a 0.2mm thick BaTeO3 pellet. In addition to the main transmitted pulse, there is a secondary, time-delayed pulse. This second tran sient is the first of the infinite series which appears due to multiple reflections. Th e detail information about data analyzing

PAGE 48

34 has been talked in chapter one. More detaile d description of THz-TD S technique can also be found elsewhere [27,28]. 2.3 Grating Spectrometer The grating spectrometer cons ists of several parts incl uding the source, chopper, high pass and low pass filters, grating for pr ism monochromator, sample or reference stage, and detector. All parts are very importa nt. But the core of the grating system is monochromator. In the grating monochromator, as shown in Figure 2-4, the reflecting grating diffraction equation is satisfied ...) 2 1 0 ( ) sin (sin n n a (2-22) where is the grating constant (cm/line), and are angle of the in cident and diffracted light respectively, and n is the order of diffraction. When equation (2-33) is satisfied, the interference is constructive. One can then rewrite equation (2-33) as sin cos 2 a n (2-23) where =( )/2 and =( + )/2. In practice, is fixed (2 = 4o) regardless of the grating position because the incident and diffracted lig ht paths are predetermined by the physical geometry, where changes as the grating (or its surface normal) is rotated. It can be seen from equation (2-34) that at = 0, it will give a zero-order diffraction (white light) for all frequencies. Therefore, is the rotation angle of the grating surface normal, N ( ), with respect to the zero-order position, N (0). The first order is the desire d one and the high orders (n 2) are removed by the proper optical filters. Taking n = 1, one gets ) csc( / 1 C v (2-24)

PAGE 49

35 with C =1/2 a cos being a constant. Equation (2-35) indi cates that the frequency is linearly related to csc( ). As the grating is rotated, a single component at frequency satisfying equation (2-35) is selected and emerges thr ough the exit slit into the sample chamber. The monochromator is mechanically designed su ch that the grating, driven by a stepping motor, is moved linearly with csc thus the scanning is linear in wavenumber. The rotation angle has been designed in the range 15o 60o, the optimum quasi-linear range in the cosecant function. To find the resolution of the monochromator, one simply needs to take the derivative of e quation (2-35) in its logarithm form (2.26) cot (2.25) sin ln ln ln d v dv C v where d is the angle subtended by the slit (with a width s ) at the collimator with a focal length f = 26.7 cm, i e ., d = s / f Equation (2-37) implies that a larger will give a better resolution. Dispersion which is a measure of the separation between diffracted light of different wavelength is given by the followi ng equation. Angular dispersion, D, is cos sin sin cos d n d d D (2-27) Linear dispersion is dependent of the effective focal length of the system, i e ., F D where F is the effective focal length of the system. 2.4 Instrumentation 2.4.1 Bruker 113v FT-IR Spectrometer The Bruker 113V, as shown in figure 2-5, is a Fourier transform interferometer with rapid scan (one of the working state of the scan mirror). With proper choice of source, beam splitter and detector, it can cover the full spectral range from the very far infrared ( 20 cm-1) up to the mid-infrared. The fricti on-free air bearing scanner makes it

PAGE 50

36 possible to achieve very stable rapid scan. Digital signal processi ng electronics provide precise scanner control and instrument auto mation for source, aper ture and detector selections. The beam-splitter is changed automatically during measurement. Combing the fast scan rate capability with superior precision spectroscopy, a high signal to noise ratio (S/N) is possible even in the far infrared (20 cm-1). The instrument operates under vacuum (<3 mbar) to record spectra free from absorption from H2O and CO2 vapor in the far and mid infrared. A He-Ne laser (633nm, normal 17 mw) is used to control the position of the moving mirror (the scanne r) and to control the data acquisition process. The monochromatic beam produced by this He-Ne la ser is modulated by the interferometer to produce a sinusoidal signal. A photodiode de tector is placed at outputs of the interferometer. Signals from these detectors are monitored with an oscilloscope and the amplitudes of signals are used to optimize th e alignment of the beam-splitter. When the beam splitter is not aligned properly, the amp litude can become too small to control the scanner and then data acquisiti on will be interrupted. The sample chamber contains two channels. One of the channels is designed for reflectance and the other for transmittance measurements. For the reflectance sample ch amber in figure 2-5, a mercury (Hg) arc lamp is used as the source for far infrared (20~700 cm-1) and a globar source is used for mid infrared (400 ~ 5000 cm-1 ). The detector used for far infrared regi on is a liquid Helium (He) cooled 4.2K silicon (Si) bolometer and that for mid infr ared is a room temperature pyroelectric deuterated triglycine sulfate (DTGS) detect or. The liquid He cooled detector has much

PAGE 51

37 better S/N ratio as compared with the DTGS The bolometer system consists of three main parts: detector, liquid He dewar with li quid nitrogen dewar jacket, and preamplifier. In Table 2-1, we show measurement para meters for the Bruker 113V. In the table, the scanner speed is in unit of kHz. This is the frequency at which lig ht of He-Ne laser is modulated ) cm ( Hz) ( cm/s) (1 laserf v (2-28) where laser is the wavenumber of the He -Ne laser, which is 15,798 cm-1. For example, f (Hz) = 25 kHz is converted into (cm/s) = 25,000 Hz/15,798 (cm-1) = 1.58 cm/s. Table 2-1 Bolometer 113V measurement setup parameters: Bolom. Stands for the bolometer detector; Bm.Spt is the beam splitter; Scn.Sp. stands for the scanner speed; Sp.Rn stands for the spectral ra nge; Phs.Crc.Md stands for the phase correction mode; Opt. Filter stands for the optical filter; BLK.Ply. Stands for black polyethylene; Apd. Fctn. Stands for the apodization function; Bk-Hrs 3 stands for the Balckman-Harris 3 term ; and Hp-Gng stands for Happ-Gengel. Setup FIR1 FIR2 FIR3 FIR4 MIR Source Hg Lamp Hg Lamp Hg Lamp Hg Lamp Globar Detector Bolom. Bolom. Bolom. Bolom. DTGS/KBr Bm.Spt( m ) Metal Mesh Mylar 3.5 Mylar 12 Mylar 23 Ge/KBr Scn.Sp.(KHz) 29.73 25 29.73 29.73 12.5 Sp.Rn.(cm-1) 0-72 9-146 9-584 10-695 21-7,899 Phs.Crc.Md Mertz Mertz Mertz Mertz Mertz Opt.Filter Blk.Ply Blk.Ply Blk.Ply Blk.Ply Open Apd.Fctn Bk-Hrs 3 Bk-Hrs 3 Bk-Hrs 3 Bk-Hrs 3 BK-Hr 3 2.4.2 TPI 1000 Terahertz Spectrometer TPI spectra 1000 spectrometer is the tr ansmittance spectrometer produced by Bruker and Teraview companie s. It covers from 1.3 cm-1 to 133.32 cm-1 (40GHz ~ 4THz) with spectral resolution about 0.1 cm-1. Laser-gated photo c onductive semiconductor emitter is used as the THz source. The spectrome ter can be operated in both step scan and

PAGE 52

38 rapid scan mode. The whole system can be used in both the nitrogen purged state and vacuum state. 2.4.3 Perkin-Elmer Grating Spectrometer Spectra spanning the midinfrared through the UV region (800-40,000 cm-1) were measured using a Perkin-Elmer 16U grating spectrometer. A schematic diagram of the instrument is shown in Figure 2-6. The spectrometer is enclosed in a vacuum tank, which is evacuated to pressures of about 100 milli torr. This reduces the absorption by water vapor and carbon dioxide. The three light sources that are used ar e glowbar source for midinfrared, a quartz tungsten lamp for near infrared and a deuter ium arc lamp for visible and UV region. The system contains three detectors: thermoc ouple for midinfrared (0.12 ~ 0.9 eV), lead sulfide (PbS) detector for near infrared (0.5 ~ 2.5 eV), and Si photoconducting detector (Hamamatsu 576) for visible and UV (2-2 ~ 5.5 eV). For getting less noisy data we use a phase sentative amplifer. The light from the source passed through a chopper and a series of filters: high frequency filters in a big wheel and low frequency filters installed inside the grating monochromator. Th e chopper generates a square wave signal for lock-in detection. The filter diminishes the unwanted higher order diffraction from the grating, which occurs at the same angle as the desired first-order component. The light beam passing through the entrance slit of the monochromator is collimated into a grating in the littrow conf iguration where the different wavelengths are diffracted. The angle of incidence is changed at predetermi ned intervals consistent with the necessary spectral resolution by rotating the grating; it is driven by a lead screw that is turned by a stepping motor. This allows access to differe nt wavelength sequentially. The steps in angle of rotation together with the exit slit width determine resolution of the

PAGE 53

39 monochromator. Increasing the slit widths increases the intensity of the emerging radiation [higher signal to noise (S/N) ratio] at cost of lower resolution. The electrical signal from the detector is sent to a lo ck-in amplifier (Itha do model 393). The output signal from the lock-in system is then averag ed over a given time interval and converted into digital data by an integrating digital voltmeter (Flike 8520A). The data are finally transmitted through the IEEE-488 Bus and a ge neral purpose interface box to a PDP 1123 computer and recorded on the hard disk fo r subsequent analysis. The table 2-2 shows the Perkin-Elmer grating monochromator parameters. Table 2-2 Perkin-Elmer grating monochromator parameters. GB stands for globar. W stands for tungsten. D2 stands for deuterium arc lamp. TC stands for thermo couple. Pbs stands for lead slifide. 576 standsfor Si photoconducting detector (Hamamatsu 576). Frequency (cm-1) Grating (line/mm) Slit width (micron) Source Detetor 801-965 101 2000 GB TC 905-1458 101 1200 GB TC 1403-1752 101 1200 GB TC 1644-2612 240 1200 GB TC 2467-4191 240 1200 GB TC 4015-5105 590 1200 GB TC 4793-7977 590 1200 W TC 3829-5105 590 225 W Pbs 4793-7822 590 75 W Pbs 7511-10234 590 75 W Pbs 9191-13545 1200 225 W Pbs 12904-20144 1200 225 W Pbs 17033-24924 2400 225 W 576 22066-28059 2400 700 D2 576 25706-37964 2400 700 D2 576 36386-45333 2400 700 D2 576 For reflectance, single beam spectra are obtained for both the sample and a reference aluminum mirror pla ced at the same position. The mirror and sample mounted on the same sample holder are rotated into th e beam to allow each single beam spectrum

PAGE 54

40 to be recorded. The reflectance spectrum is then calculated by taking the ratio of the single beam spectrum of the sample to th at of the mirror and correcting with the reflectance of aluminum. 2.4.4 Low Temperature Apparatus The cryogenic system consists of three majo r parts: Hansen HighTran refrigerator (cryostat), transfer line, a nd helium supply dewar [29]. The sample temperature can be varied from 4 K to 450 K by a controlled ope ration of liquid helium transfer. Figure 2-7 illustrates the flow diagram of he experimental set-up. The sample holder is attached to the cryo-tip end of the refrig erator. An optical spectroscopy vacuum shroud is used to isolate the cold tip from the outside environm ent. Optical windows can be installed on the vacuum shroud to allow the reflection and transmission measurements. The sample temperature is sensed by a cal ibrated silicon diode thermome ter (Si-410A) buried into the cold finger. The accuracy of the diode is 1K. The sample can be warmed by adding electrical heat to the tip heater and the temperature is controlled automatically and monitored by a temperature controller (Han sen & Associates 8000). A thermal radiation shield is attached to the s econd cold stage to project the sample and to absorb the 300K black body radiation from the vacuum shroud; he nce the heat load near the cold tip can be reduced. All these steps are necessary in order to minimize the systematic error in temperature recording. Before the helium flow is started, the cryostat is evacuated to a pressure of 10-4 torr or less in the vacuum shroud. By pressuring the He dewar, the liquid helium is transferred from the dewar through th e transfer line to the cryostat. The flow rate can be regulated by two flow meters with hoses and shut off values which control the tip flow and shield gas flow.

PAGE 55

41 Figure 2-1 A simplified Michelson interfer ometer diagram. Light travels distance S from source to the beam-splitter. Partially re flected travels to the fixed mirror (M1) and partially transmitted beam travels a variable distance toward the movable mirror (M2). The beam is recombined at the beam splitter and half of the beams returns to the source, and th e other proceeds to a detector.

PAGE 56

42 Figure 2-2 Schematic diagram of a THz-TDS spectrometer using a femtosecond laser source and photoconductive THz transmitters and receivers. Partially reflected laser light was used as the gate signal for the THz detector. Partially transmitted light reaches THz transmitter to excite the THz pulse. Sample is placed in the beam focus point.

PAGE 57

43 Figure 2-3 Curve shows the THz transi ent after propagation through a BaTeO3 pellet. The main pulse is followed by a series of pulse of decreasing amplitude that originate from multiple reflections within the pellet.

PAGE 58

44 Figure 2-4 Diagram of grating spectrometer sh owing the incident a nd diffracted rays and the operation of grating.

PAGE 59

45 Figure 2-5 Schematic diagram of Bruker 113 V FTIR spectrometer. The lower channel has the specially designed reflectan ce optical stage for reflectance measurement in the sample chamber.

PAGE 60

46 Figure 2-6 Schematic diagram of Perkin-Elmer monochromator spectrometer.

PAGE 61

47 Figure 2-7 High-Tran sy stem flow diagram.

PAGE 62

48 CHAPTER 3 OPTICAL PROPERTIES OF SUOPE RCONDUCTING YBCO FILM IN THE OPTIMALLY DOPED AND OVERDOPED REGION After the discovery in 1911 of superconduc tivity in mercury at 4 K by Kamerlingh Onnes [30] the search for new superconducting materials led to a slow increase in the highest known transition temperature Tc over the decades. Alloys and compound [31] such as Nb3Ge held the record for the highest tr ansition temperatures from 1954 to 1986. After 13 more years, the path to radically higher transition temp eratures was opened by the discovery in 1986 of superconductivity at ~ 35 K in “LBCO” (a mixed oxide of lanthanum, barium, and copper) by Bednorz and Muller [32], for which they were awarded the Nobel prize in 1987. The discovery was surprising and exciting, not simply because of the large increase in Tc, but also because it revealed that the ox ides formed an unsuspected new class of superconducting materials with great potential. Another big jump to Tc ~ 90 K followed quickly with the discovery made of “123” class of materials, exemplified by YBa2Cu3O7(“YBCO”) [33]. In this structure, the Y (y ttrium) can be replaced by many other rare earth elements, e.g. Yb, Nd, Sm, Eu, Gd, Ho, Er, and Lu, with similarly high Tc [34,35]. Shortly after, still high Tc values were found in the “BSCO” [36] system (mixed oxides of bismuth, strontium, calcium, and copper) and the “TBCO” [37] system (mixed oxides of thallium, barium, calcium, and copper). In this chapter, we are going to disc uss the general background of the high Tc superconductor materials, such as the struct ure and the phase diagram. Then we will

PAGE 63

49 describe the sample preparation, and fina lly focus on the optical properties of the optimally doped and overdoped YBa2Cu3O7films. The basic theory of superconductivity can also be found elsewhere [38-41]. 3.1 Introduction 3.1.1 Fermi Liquid (FL) and Marginal Fermi Liquid model Conduction electrons obey Fermi-Dir ac statistics. The corresponding F-D distribution function (3-x1) can be written in term of the energy E as. 1 1 ) (] / ) [( T k Ebe E f (3-1) where is the chemical potential which corresponds to the Fermi temperature (Tf) by equation, F B FT k E (3-2) TF is typically about 105 K. This means that the distribution function f (E) is one for EEF and assumes intermediate values only in a narrow energy range kBT wide near EF. The electron kinetic energy can be written as ) ( 22 2 2z y x Kk k k m E (3-3) In the reciprocal space, each Cartesian component of K can assume discrete values, x xL n / 2 in x direction of length Lx, and likewise for y and z direction of length Ly and LZ, respectively. For simplicity, we will assume Lx=Ly=Lz=L Hence the total number of electrons N is 3 3) / 2 ( 3 / 4 2 L k NF (3-4)

PAGE 64

50 The electron density3/ / L N V N n at Fermi energy is, 2 3 2 22 3 1 FmE n (3-5) and the density of states (DOS) D(E) per unit volume can be get 2 3 2 22 2 1 ) ( ) ( m E n dE d E D (3-6) Despite the success of Fermi liquid theory in describing the conventional metals, high temperature superconductor materials canno t be totally described by the FL theory. Varma et al. [42] proposed a phenomenological mode l for the oxide superconductors to explain many of the anomalous behavior in cuprates. This idea was that the electron interacts with a spectrum of bosoni c excitation that is flat over T< < c, where c is a high energy scale that cut off the spectrum. According to this theory, the real and imaginary part of the quasi-particle selfenergy goes as T i i Tc 2log 2 (3-7) T T T 2~ ) ( Im (3-8) 2 Re 2 1 ) (* bm m (3-9) where is the quasi-particle self energy, m* is the frequency de pendent renormalized mass and mb is the band mass which appears in the frequency p=4 ne2/mb.

PAGE 65

51 3.1.2 Optical Measurement of High Temperature Superconductor In all of the high Tc superconductor systems, copper oxide planes form a common structural element, which is thought to dominate the superconducting properties. Depending on the choice of stoichiometry, th e crystallographic unit cell contains varying number of CuO2 planes. In addition, the 123 com pounds contain CuO “chains”, which are thought to serve largely as reservoir to c ontrol the electron density in the planes. The exact Tc depends on these particulars but roughly speaking, the highest Tc achieved in the YBCO [43], BSCCO [44], and TBCCO [45] systems are 93, 110, and 130 K, respectively. These very high transition temperatures ar e of obvious technical interest because they opens the way to applica tions which require only liquid N2 cooling (77 K) rather than liquid helium. They also pose intri guing fundamental questions: what is the mechanism responsible for the high Tc? Whatever the mechanism is the nature of the superconducting state basically th e same Cooper-paired state as in BCS [46], or is it fundamentally different? Spectroscopic studies of el ectrodynamics are emerging as the premier experimental tools of high Tc superconductivity. In combination, THz and infrared (IR)/optical methods enable experimental access to the optical constants in the frequency range critical for the understanding of physics underlying strongly correlated phenomena in solids. Optical spectroscopy of metals or semiconductors has provided invaluable insights into the electronic band structure and elementa ry excitations. The validity of theoretical descriptions of electronic bands in solids as well as of electron dynamics is routinely verified against optical data. Moreover, in situations where the theoretical guidance for data interpretation is insufficient, quantitativ e information still can be extracted from the

PAGE 66

52 spectroscopic measurements th rough model-independent anal ysis of optical constants based on a variety of sum rules. This latt er forte of the IR/optical approach is indispensable for high Tc research, since properties of th ese novel superconductors signal a breakdown of standard theories of meta ls. Therefore, knowledge of the optical constants establishes an experimental foundati on for the crucial tests of proposed models and also motivates the development of novel th eoretical constants. TH z-IR/optical results generated by many research team s worldwide facilitate inferen ce of universal patterns in the electromagnetic response of high Tc cuprates that are not specific to a particular family of materials but instead, are along w ith genuine features of the interplane conductivity. The parent, undoped, compounds of high Tc cuprates are Mott-Hubbard (MH) insulators [40]. When a moderate density of charge carriers is introduced in a MH system, all of its physical properties are radi cally modified. This le ads to complex phase diagrams that have been methodically studi ed in many materials using THz/IR optics. This work [47] has uncovered common attributes of the cuprates and other classes of MH insulators. As of today, there is no ge nerally accepted picture of the electromagnetic response of the CuO2 planes in superconducting phase of th e cuprates. Significant progress in the understanding of the carrier dyn amics, particularly in the overdoped region, has been achieved. The normal state of high Tc cuprates is anomalous and is not compatible with the standard treatment of excitations in term of Landau quasi-partic les. This property challenges the applicability of the Bardeen, Cooper and Schrieffer (BCS) [46] scheme

PAGE 67

53 describing superconductivity in terms of paring instability of an ensemble of quasiparticles. Spectroscopic experiments indicate that the origin of high Tc superconductivity may be related to lowering of the electronic kinetic energy and not of the potential energy as in the conventional BCS scheme. This conclusion is inferred from subjecting the optical constants of several classes of high Tc materials to the scrutiny of sum rules. Numerous advances in both the spect roscopy of micro-samples and in the preparation of high quality single crystals ha ve facilitated studies of the interlayer electrodynamics in many families of c uprates. These measurements provide straightforward experimental access to prope rties directly relate d to the quasi twodimensional nature of the electronic transport. Many groups have presented measurements of ab-plane infrared spectra of YBa2Cu3O7[48, 49, 50]. The first complete (i n terms of wavelength and temperature coverage) study of the a-b plan e infrared properties of YBa2Cu3O7was reported by Schutzmann et al. [51, 52]. Romero et al [53] and later Gao et al. [54] measured both transmittance and the reflectance of the ab -plane oriented YBa2Cu3O7films. Their data showed that the quasi-particle relation rate 1/ had a fast decrease below Tc and then saturated well below Tc. Above Tc, 1/ exhibited a linear temperature dependence, in accord with the linear DC resistivity in the normal state. The fast decrease of 1/ was unique and intrinsic to the high Tc cuprates; it did not o ccur in conventional BCS superconductors, where the scattering from impurity or phonons. The low frequency conductivity 1 inferred from the far infrared tran smittance and reflectance measurements exhibited a peak just below Tc. The peak in 1 was attributed to the rapid drop in 1/ combined with a decreasing of normal fluid density. Kamaras et al. [55] studied the

PAGE 68

54 frequency dependent conductivity of laser deposited YBa2Cu3O7thin films. Their experiment showed an onset of th e mid-infrared absorption at ~ 140 cm-1 and structure in 400 ~ 500 cm-1 region. This low energy absorpti on occurred both above and below Tc, making them unlikely to be the super c onducting gap in the usual BCS sense. The absorption across the gap was weak because the high Tc materials were in the clean limit; this weak absorption is masked by the mid-infrared absorption. Thomas et al. [48], Cooper et al. [56] and Orenstein et al. [57] have studied a series of high-quality of YBa2Cu3O7crystals which have different vales of The measured reflectance drops steadily throughout the infr ared, with a sort of plasmon minimum around 10,000 cm-1. As oxygen is removed, reducing th e carrier concentration on both CuO2 plane and b-axis Cu-O chain, the reflec tance in the midinfrared is substantially reduced. At low frequencies, the reflectance is high, being above 90% for all four samples, as expected for a c onducting materials. The reduced Tc samples show a break or shoulder in the normal state reflectance at 500 cm-1. The reflectance of a “fullyoxygenated” YBa2Cu3O7with Tc= 93 K has been reported by Collins et al. [50]. Their data show a noticeable dip or minimu m in the 45 K reflectance around 800 cm-1. They interpret it as a result of the collapse below Tc of the free carrier component ( ) to a delta function. To study the intrinsic properties of CuO2 plane, several investigations have been done for the Br2Sr2CaCu2O8 (Bi-2212) crystals. Compari ng with Y-123 material, Bi-2212 provides a better opportunity to study the issu e of the electronic structure of the CuO2 planes because there are no chains in these Bi-based compounds. Quijada et al [58] did the polarized reflectance measurement. Th eir room temperatur e optical conductivity

PAGE 69

55 suggested a scattering rate for the free carriers that showed ab anisotropy in both magnitude and temperature dependence. In th e superconductivity state, the penetration depth D was also found larger along b-axis than a-axis :( D b > D a). Liu et al [59] studied the Pb doped Bi-2212 si ngle crystals over a wide fr equency range. His result indicated the a-axis reflectance was higher than the b-axis reflectance in the far infrared region. However, in the visible to ultraviole t region, the b-axis reflectance was higher. After analyzing their data by Kramers-Kroni ng method, they found the anisotropy in the normal state conductivity was about 10%, with th e far infrared conductivity higher in the a-polarization while higher frequenc y conductivity is hi gher along b-axis. In the overdoped region, only a few measur ements have been done in the c-axis. Katz et al [60] reported the infrared study of c-axis electrodynamics of Tl2Ba2CuO6+ crystals. A sum rule analysis revealed spectral weight shifts. Their calculated the ratio of the spectral weight difference (between nor mal state and superconductor state) to the superfluid density. Their result showed the di fference of these two values is about 40% in the overdoped Tl2Ba2CuO6+ and 10% in the optimally doped Tl2Ba2CuO6+ They interpreted the result as a kinetic energy ch ange at the superconducting transition. In optimally doped crystals, the kinetic energy was lowered at T < Tc, but no significant change was found in the overdoped samples. Basov et al [61] also expressed the similar idea. Their analyses of the interlayer infrared conductivity of the cuprates in high transition temperature superconductors resu lted an anomalously large energy scale extending up to mid infrared frequencies that could be attributed to formation of the superconducting condense. They indicated one possible interp retation of these experiments was in terms of a kinetic ener gy change associated with the superconducting

PAGE 70

56 transition. Other groups, such as Deutscher et al ., [62] investigated the c-axis of Bi-2212 system. The experiment showed the change of kinetic energy from a fully compatible conventional BCS behavior to an unconventi onal behavior as the free carrier density decreases. Unlike the result of Katz et al ., they found the kinetic energy almost had no changing in the optimally doped cuprate system and an increasing of kinetic energy in the overdoped region. They also suggested if a single mechanism was responsible for super conductivity across the whol e phase diagram of hi gh critical temperature superconductors, this mechanism should allow for a smooth transition between such two regimes around optimally doping. Hwang et al. [63] studied the overdoped Bi-2212 system. They found the evidence of increa sing the spectral weight in the overdoped region. 3.1.3 The Crystal Structure of YBCO The YBa2Cu3O7compound comes in tetragonal and or thorhombic varieties. It is the latter phase which is or dinarily superconducting. In the tetragonal phase the oxygen sites in the chain layer are in a random or disordered manner, and in the orthorhombic phase are ordered into –Cu-Ochains along the b direction. The oxygen vacancy along a direction causes the unit cell to compress slightly so that a < b and the resulting distortion is of th e rectangular type. Hauck et al. [64] proposed a classification of superconducting oxide structures in term of the sequence (1) superconducting layers (2) insulating layers, (3) hole donating layers. The high-temperature superconducto r compounds have a horizontal reflection plane called h at the center of the unit. Every plane of atoms in the lower half of the cell at the height z is duplicated in the uppe r half at the height 1z Such atoms, of course, appear twice in the unit cell, while atoms right on the symmetry planes only occur once

PAGE 71

57 since they cannot be reflected. Figure 3-1 shows a Cu-O pl ane at the height z reflected to the height 1z A particular interesting feature in the figure is that the puckering (Cu-O plane) preserves the reflection symmetry ope ration. Superconductors that have this reflection plane, but lack end-centering and body centering op erations are called aligned because all of their copper atoms are of one type; either all on the edge in E position or all centered at C sites. 3.1.4 Phase Diagram High Tc superconductivity is achieved when a m oderate density of charge carrier is introduced into the parent an tiferromagnetic phases of the cuprates. This “doping” is realized either by chemical substitution or significant deviations from stoichiometry. The hole-doped sides of the phase diagram displayed in Figure 3-2 shows a number of common elements. One finds: 1) antif erromagnetism of the undoped parent compound is transformed by doping into a fairly good c onducing system in the carrier density range of n = 1020-1021; 2) a critical doping leve l that is needed to tr igger superconductivity; 3) a transition temperature that fi rst increases with doping (the underdoped region) reaches a maximum value for a given series (the optim ally doping) but is suppressed with further increase in doping level (the overdoped regi me); 4) a superconducting state is preceded by the formation of the enigmatic pseudogap w ith an onset temperat ure that decreases with doping. 3.1.5 Pseudogap Phase As shown in the phase diagram of Figure 31, the high temperature cuprates have a pseudogap phase at the low doping level. One ge neral class of theories proposed that the pseudogap phase represents pre-formed pairs [65]. Transport measurements revealed hat resistivity was dead linear in te mperature over a large range. Lobo et al [66] measured

PAGE 72

58 the ab-plane resistivity of Y1-xPrxBa2Cu3O7. Their experiment indicated below ~ 195 K, the resistivity no longer showed a linear th ermo dependence in the x=0.4 sample. The result suggest that non-cohe rent cooper pairs are the origin of the pseudogap. As we know, undoped cuprates should be t hought of as Mott insu lators. In the low doping level, the number of carriers is small and the phase fluctuation could play an important role in the underdoped side of the phase diagram. Anderson et al [67] proposed that the doped holes would only be phase coherent below a temperature which scaled linearly with doping. The main debate of the origin of pseudogap is whether pseudogap represents a state with true long ra nge order or simply some precursor phase [65]. 3.1.6 d-wave Character of High Temperature Superconductor A BCS superconductor has an isotropic s uperconducting gap which leads to an exponential temperature dependen ce of the penetration-depth (T). However, ab-plane penetration depth measurements of hi gh temperature superconductor do not find exponential behavior. The linear variation of penetration dept h with temperature was first observed by Gao et al. [68]. In their experi ment, the surface impedance of superconductor YBa2Cu3O7 films as a function of temperature at 10 GHz was measured. The penetration depth (T) was also determined. Their result ex hibited a linear dependence down to 6 K. the following theory by Hirschfeld et al. [ 69] indicated that a pe netration depth which varies linearly with temperat ure is expected for superconductor with d-wave symmetry. Other experiments, such as angle-re solved photoemission spectroscopy (ARPES), have been done. Shen et al [70] did an ARPES measur ement in the ab-plane of Bi2Sr2CaCu2O8+ samples and found that the superc onducting gap anisotro py is at least

PAGE 73

59 an order of magnitude larger than that of conventional supe rconductors. All these experiments indicate a d-wave nature of the high temperature superconductors. 3.1.7 Two-Component Mode for the Dielectric Function Common to all high Tc superconductors is the presence of a non-Drude midinfrared absorption that shows very little temperature dependence. In contrast, the farinfrared reflectance exhibits a definite te mperature dependence, with the far-infrared conductivity above Tc in good agreement with the DC conductivity. There are several ways to explain this difference between far-i nfrared and mid-infrared behavior. In our experiment, both two component model and Marginal Fermi liquid model are used. In this approach, the infrared conductivit y results from the combination of two types of carriers: free carr iers which give rise to a Drude-like component at = 0, with a strongly temperature depende nt scatting rate, and bound carriers with a nearly temperature independent broad midinfrared ba nd. In this approach, the free carriers condense into the superfluid below Tc, while the midinfrared carriers remain unaffected by the superconducting transition. Th e total dielectric function is MIR D) ( (3-10) A model dielectric function which is in accord with this picture is N j j j pj pDi i1 2 2 2 2 2) ( (3-11) where the first term describes Drude carriers with a plasma frequency pD and a relaxation rate 1/ The second term describes the br oad mid-infrared component and interband components as a sum of oscillators where j, pj, and j are the center frequency, strength, and width of the j th oscillator, respectively. Finally, represents the

PAGE 74

60 high frequency limit of ( ) which includes interband tran sition at frequencies higher than measured frequency. 3.1.8 Marginal Fermi Liquid Model for the Dielectric Function Another very commonly used method is the marginal Fermi liquid model due to Varma et al. [42, 71]. The model assumes that the ch arge carriers intera ct with a fairly flat spectrum of excitation over the interval T < < c where c is high frequency cutoff. The dielectric response for this model can be written as 2 / 2 ~2 p (3-12) where is the quasiparticle self energy, given by T i i Tc 2log 2 (3-13) here T is the temperature is a coupling constant and c is the cutoff frequency. The limiting forms of this expression go as T T T 2~ ) ( (3-14) Since the imaginary part of th e self energy is effectively th e scattering rate, Equation (314) predicts the linear variati on of the DC resistivity, which is observed in most transport studies of the cuprates. In a similar way the real part of the self energy gives the mass enhancement carrier 2 2 1 ) (* bm m (3-15) where m* is the frequency depende nt renormalized mass and mb is the band mass which appears in the plasma frequency p=4 ne2/mb.

PAGE 75

61 3.1.9 Motivation of Experiments for Overdoped Cuprates Despite extensive experiment effort, th ere is not many experiments done for the overdoped high temperature superconductors. As yet, there is no report about the ab plane property in the overdoped region for YBCO superconductor. In order to get the complete information of high temperatur e cuprates, experiments for the overdoped samples are necessary. We explored the opt ical spectra of the optimally doped and overdoped Y-123 thin film from the far infrar ed to the ultraviolet region. Our result indicates although the carrier de nsity increase with increasi ng the doping, the superfluid density will decrease in the overdoped region. 3.2 Experiments and Results 3.2.1 Sample Preparation Various high Tc superconducting samples have been us ed in this experiment. In this chapter, we will only focus on the optimally doped YBCO/SrTiO3 thin films and the over-doped YBCO/SrTiO3 thin films. Other samples, such as the YBCO/sapphire etc. will be introduced in the following chapters. Two YBCO thin films are prepared at the Center for Electronic Correlation and Magnetism, institute of physics, Augsburg Univ ersity, Germany [72, 73]. Both of these samples are deposited on the SrTiO3 substrate with dimens ion 5 mm 5 mm. The substrate has a perovskite st ructure which makes a good latti ce match with the films. The optical study of the substrate is needed in order to get the parameters of the YBCO thin films. And this part of the work w ill be introduced in the next section.

PAGE 76

62 The optimally doped YBa2Cu3O7thin film is deposited on the 1mm thick SrTiO3 substrate by pulse-laser ablati on from a stoichiometry YBa2Cu3O7target. After deposition at 760 oC the sample is cooled within one hour to 400 oC in an oxygen atmosphere of 0.4 bar and, after holding this temperature for 20 minutes, further to room temperature. The over-doped sample is prepar ed by the similar way described before. The only difference is the ta rget. Instead of YBa2Cu3O7, Y0.7Ca0.3Ba2Cu3O7is used as the target for sample deposition. The film thic kness for both samples is 1500 . In order to measure the critical temperature, the resist ivity measurement is done in the Center for Electronic Correlations and Magnetism. The critical temperature ( Tc) for the optimally doped samples is 90 K; it is 79 K for the overdoped samples. 3.2.2 Optical Measurement of the Substrate — SrTiO3 SrTiO3 was the subject of several studies in the early 60’s. At T = 110K, it is known to undergo a phase transition of sec ond order. The cubic high-temperature structure undergoes a tetragona l distortion at the transition characterized by an unstable or soft phonon at the R corner of the Brillouin zone. The phonon mode has a frequency that decreases substantially as the transiti on temperature is approached from above or below. This structural phase transi tion corresponds to a rotation of BO6 octahedra around the cubic axis. SrTiO3 crystallizes in the simple cubic perovskite structure (Oh) at room temperature and tetragonal (D4h 18) at low temperature. Its lattice constant 3.91 , nearly matches the basal plane lattice constant of YBa2Cu3O7. Superconducting films grown on SrTiO3 exhibit high current densities and sharp resistive transitions. Unfortunately, the high frequency properties of SrTiO3 limit its use in technological applications. The static dielectric constant is orders of magnitude higher than the typical values for dielectric

PAGE 77

63 material. At microwave frequencies, the loss is extremely high and w ould result in a poor performance for any microwave devices fabricated from a high temperature superconductor film on SrTiO3. Figure 3-3 shows the room temperature re flectance (normal incidence) and the fitting result (by the Lorentz model) of SrTiO3 crystal in the spectral range between 25 cm-1 and 40000 cm-1. The temperature-dependent reflectance between 25 cm-1 and 4000 cm-1 is shown in Figure 3-4. With decreasing temperature, the reflectance of the SrTiO3 increase a little. Prominent phonon f eatures occur at 90, 170 and 540 cm-1. Perry et al. [74] assigned the lowest mode at 90 cm-1 to a Sr-TiO3 lattice mode, the mode at 170 cm-1 to a Ti-O-Ti bending mode, and the mode at 540 cm-1 to Ti-O stretch mode. Just above the plasma edge, which is about 800 cm -1, the reflectance becomes flat without any significant features. In the visible and ultraviolet region, two inter-band absorptions are shown clearly in the reflectance spectrum. Th e details of these high frequency bands have been studied by Cardona et al [75]. 3.2.3 Optical Measurement of the YBCO Thin Films Figure 3-5 shows the room temperature ab -plane reflectance of the optimally doped and overdoped YBCO thin films on SrTiO3 substrates over the spectra range (25 cm-1 ~ 40,000 cm-1). The reflectance of each samples drops steadily (but not quite linearly) throughout the infrared, with a sort of plasma minimum around 15,000 cm-1 in all cases. Both films show high values of reflec tance (over 85%) at low frequencies, 300 cm-1, as expected for conducting materials. Th e optimally doped sample shows a higher reflectance in the visible to ultraviolet fre quency range than the overdoped sample. After the plasma minimum (which is about 15,000 cm-1), the optimally doped sample shows a clear charged transfer band (around 20,500 cm-1) and inter-band transition (around

PAGE 78

64 33,600 cm-1). The overdoped sample spectrum does not show these feat ures as strongly as the Ca2+ replaces the Y3+ ions. The concentration of car rier, holes in YBCO, increases in the Cu2O-plane. However, as in other doping studi es [48, 56], this increasing in the carrier concentration has littl e effect on the frequency minimum. Both spectra show a plasma minimum around 15,000 cm-1. Figure 3-6 shows the temperature dependent reflectance spectra for the optimally doped YBCO film between 25 cm-1 and 4000 cm-1. At 30 K, only far infrared data was measured from 25 cm-1 to 600 cm-1. In the low frequency region, there is a kink in the reflectance spectra of each temperature, whic h is especially significant in the higher temperatures. This effect is due to the soft mode in the SrTiO3 crystal substrate, which was discussed above. The reflectance spectra show a systematic in crease with decreasing temperature. There is a noticeable dip around 800 cm-1 in the 50 K and 70 K reflectance, which is similar to the data from other gr oups [48, 51, 56]. As discussed in the next section, this structure can be qualitatively understood as a resu lt of the collapse of the free carrier component of ( ) to a delta function below Tc. Below 100 K, the spectrum shows a “shoulder” or “knee” around 500 cm-1. This phenomenon is also s een in other data [55]. Plausible arguments had been made for superconducting gaps in YBCO at 500 cm-1. However, Kramaras et al. [55] measured YBCO films. They fitted the reflectance by the two component model. After subtracting the Drude component, the conductivity spectra in all temperatures show a clearly decrease around 500 cm-1. Their conclusion indicates that the “shoulder” at 500 cm-1 in the reflectance of YBCO samples is the sign of the condensation of the Drude part contribution to the conductivi ty instead of the appearance of the superconducting gap.

PAGE 79

65 The temperature dependent reflectance of the overdoped YBCO sample is shown in Figure 3-7. The spectra show similar featur es as the optimally doped samples. Around 800 cm-1, the dip or minimum which is shown obvi ously in the optimally doped samples, is not significant comparing with the optima lly doped samples. This probably indicates that comparing with the optimally doped Y BCO, the superfluid condensation in the overdoped samples is not as strong as in the optimally doped samples. 3.3 Discussion 3.3.1 Dielectric Function Analysis Because of the effect of the substrate, the Kramers-Kronig method cannot be used directly to the measured reflecti on data. In order to analyze the ab -plane optical spectra of the YBCO film, two component analyses is used. According to this picture, the cuprates are viewed as consis ting of two types of carriers: free carriers which track the DC conductivity above Tc and bound carriers which are re sponsible for the broad midinfrared excitation (The detail inform ation has been talked in chapter 1). Below Tc, two fluid model was used. The diel ectric function is made up to four parts MIR Dsup) ( (3-16) ) ( 22 2 2 sup p pi (3-17) where sup is the superfluid part contribution, D is the free carrier or normal Drude intraband contribution; MIR is the bound-carrier contribution, and is the high frequency contribution. After getting all the oscillator information, optical conductivity and other parameters can be calculated.

PAGE 80

66 Figure 3-8, shows the measured spectra and the fitting result for the optimally doped and overdoped samples at room temperature between 25 cm-1 and 40,000 cm-1. Figure 3-9 and 3-10 show measured and fitting spectra at room temperature and 50 K for optimally doped sample and overdoped sample respectively. Table 3-1 shows the high frequency oscillator parameters of the SrTiO3, YBa2Cu3O7(optimally doped) and Y0.7Ca0.3Ba2Cu3O7(overdoped). Table 3-2, 3-3 and 34 show the far infrared and mid infrared oscillator parameters of the SrTiO3, YBa2Cu3O7(optimally doped) and Y0.7Ca0.3Ba2Cu3O7(overdoped) samples at differe nt temperatures respectively. Table 3-1 The charge transfer band fitting parameters* (obtained from Lorentz model) for the SrTiO3, optimally doped YBa2Cu3O7and overdoped Y0.7Ca0.3Ba2Cu3O7ST** OP** OD** p1(cm-1) 9418 9750 1(cm-1) 11503 12205 1/ 1(cm-1) 9985 7746 p2(cm-1) 18792 20568 19028 2(cm-1) 32990 20997 21959 1/ 2(cm-1) 2950 14211 17015 p3(cm-1) 45450 33353 33127 3(cm-1) 38313 38173 43046 1/ 3(cm-1) 10976 18376 26522 2.9 2.2 2.8 All the parameters are used to fit reflectance and then to calculate conductivity. ** ST means SrTiO3 substrate ** OP means optimally doped YBCO ** OD means overdoped YBCO

PAGE 81

67 Table 3-2 Parameters (obtained from Drude Lorentz model) giving the best fit to the reflectance (between 25 cm-1 and 4000 cm-1) of SrTiO3 at different temperatures. 300 K 200 K 100 K 70 K 50 K 30 K p1 1419 1501 1508 1510 1494 1506 1 87 71 47 33 22 3 1/ 1 15.3 12.5 10.5 10.4 10.4 8.6 p2 341 268 222 200 179 172 2 176 174 172 171 171 171 1/ 2 5.7 2.5 1.7 1.5 1.4 1.3 p3 571 615 616 600 597 605 3 544 546 547 546 547 547 1/ 3 22.7 16.7 10.9 12.5 8.9 7.7 4.6 4.8 4.8 4.8 4.8 4.8 Table 3-3 Parameters (obtained from Drude Lorentz model) giving the best fit to the reflectance (between 25 cm-1 and 4000 cm-1)of YBa2Cu3O7(optimally doped) 300 K 200 K 100 K 70 K 50 K 30 K pS 7452 7957 10903 pD 10420 11453 11748 8933 8753 1756 1/ D 405 296 187 123 84 77 p1 3785 2042 3733 3587 3812 3747 1 281 301 301 303 295 295 1/ 1 835 868 663 660 730 239 p2 11548 10878 11369 13810 14664 2 720 726 712 787 865 1/ 2 1813 1621 1684 1760 1718 p3 13645 14640 14414 13551 17036 3 3412 3219 3461 3286 3075 1/ 3 9310 9083 9288 6241 7594 4.1 3.3 4.0 3.2 3.0

PAGE 82

68 Table 3-4 Parameters (obtained from Drude Lorentz model) giving the best fit to the reflectance (between 25 cm-1 and 4000 cm-1)of Y0.7Ca0.3Ba2Cu3O7(overdoped) at diffe rent temperatures. OD 300 K 200 K 100 K 70 K 50 K 30 K pS 1215 3581 4854 pD 12580 13206 12705 13060 12039 11682 1/ D 436 282 126 120 95 93 p1 5157 5957 7311 6794 6444 8842 1 302 310 308 272 273 273 1/ 1 878 652 844 771 767 1223 p2 12427 10287 15919 14042 15439 2 748 760 806 778 781 1/ 2 2177 2323 2770 2366 2343 p3 13674 14058 17430 19444 11418 3 3284 3303 3281 3285 3258 1/ 3 9052 8717 9302 10898 11064 3.4 3.5 3.3 3.1 2.8 3.3.2 Charge Transfer Band and Interband Transition The room temperature optical conductiv ities of both optimally and overdoped YBCO films are shown in Figure 3-11. At hi gher frequencies, we observed the onset of the charge transfer absorption at about 20,000 cm-1, which corresponds to the optical transitions between the occupied O-2p ba nd and the empty Cu-3d upper Hubbard band. Other interband transitions also appear around 35,000 cm-1. In the overdoped samples, as suggested by the data in Figure 3-11, there is a spectral weight lost in the infrared region. The number of carrier participating in optical transition per Cu is plotted in Figure 3-12. The weight lost below the charge transfer absorption band is roughly equal to the increase of the spectral weight at the lower frequencie s. The spectral weight is proportional to the square of the plasma frequency. We can cal culate the difference of the square of the plasma frequency to know the spectral weight changing. According to table 3-1 and table 3-2, the spectral weight lost is about (7x107 cm-2). While in the mid infrared spectral

PAGE 83

69 weight increase in the ov erdoped sample is about (8x107 cm-2). The ratio of the decrease of spectral weight in the char ge transfer band to the increas e of spectral weight in the midinfrared absorption band is about 0.9. Th is is not an unreasonable value; these two values are close to each other. The differe nce of the two values may be due to the contribution of higher frequency band whic h is beyond our measured high frequency range. 3.3.3 Temperature Dependent Optical Conductivity The real part of the conductivity 1( ) is shown in Figure 3-13 (a) and (b). The ab plane optical conductivity spectra of the optimally doped and overdoped samples have a lot of common features. There is a peak around =0 and a long tail extending to higher frequencies in the infrared region where 1( ) falls as -1, slower than -2 decay of a Drude spectrum. In the far infrared regi on, both optimally doped and overdoped sample spectra are very sensitive with the temper ature. For the optimally doped sample, above Tc, the conductivity increase with decreasing the temperature. While, just below Tc, the conductivity drops significantly co mparing with the value above Tc. This is due to part of the spectra weight transfer to the function. There is an obviously minimum at 430 cm-1. Some papers indicate this is probably the sign of the superconductor gap. Kamaras et al. [55] measured a series of YBCO films. After analyz ing the reflectivities by two component model, their data in dicate the minimum appeared in the optical conductivity is the result of the superf luid condensation instead of the “gap” effect. In comparison with the conduc tivity of optimally doped sa mple, the conductivity of the overdoped sample does not show the minimum. Just like the optimally doped samples, above Tc, in the far-infrared re gion the conductivity incr eases with decreasing the temperature. But just below Tc, instead of a big “drop” as in the optimally doped

PAGE 84

70 sample, the conductivity just decrease a litt le. This is because the overdoped sample shows only a small fraction of the Drude comp onent oscillator strength condensed into the ( ) super fluid condensate. The Drude and superfluid fitting parameters are shown in table 3-1, are agreed with this point. At 50 K, in optimally doped sample, about 45% Drude oscillator strength transfer to the function. But in the overdoped sample, only 8% of the oscillator strength transfers to the superfluid part ( function). Same result can be gotten in the 30 K. In the optimally doped sa mple, about 97% of Drude part oscillator strength goes into function. While, in overdoped sample, this value is only 21%. It should be noted below Tc, there remains a pronounced c onductivity at low frequencies suggesting no sign of a superconducting gap. Comparing with far infrared, the conductiv ity in the mid-infrared region does not show much temperature dependence. As shown in figure 3-13, the temperature dependence at frequencies above 1000 cm-1 is relatively modest. It is in fact mostly due to a narrowing of the Drude like peak at ze ro frequency. We used three Lorentzian oscillators to model the mid-infrared contri bution to the dielectric function. As being expected, in the mid-infrared, the conductivity d ecreases steadily as it reaches the plasma minimum [48]. Finally, weak phonon modes, which are comp letely screened by the free carriers, cannot be seen in the ab -plane conductivity spectra. 3.3.4 Quasi-Particle Scattering Rate Figure 3-14 (a) and (b) show the temperat ure dependent scattering rate of the optimally and overdoped samples. When T > Tc, 1/ D varies linearly with temperature for all the doping level studied. Such a temperature linear behavior in 1/ D above Tc has also been observed in other cuprates. We write / D = 2 DkBT + / 0 where D is the

PAGE 85

71 dimensionless coupling constant that couples the charge carriers to the temperaturedependent excitations responsible for the sc attering. Table 3-5 shows the width of the Drude part oscillator (1/ D). Both samples show a normal state 1/ D linear with T with all about the same slope, giving D ~ 0.2 0.3. In our measurement, the optimally doped YBCO has D = 0.25 while in the overdoped YBCO sample this value is 0.31. Taking vF = 2107 cm/sec and using our relaxation rate of 1/ = 183 cm-1 (optimally doped YBCO), 160 cm-1 (overdoped sample at 100 K). We can estimate the mean free path l = vF = 58 and 66 . Because the ab -plane coherence length is less than 20 , the values of the mean free path also prove that the high Tc superconductor is in the clean limit. Table 3-5 The scattering rate (obtained from Drude Lorent z model) of optimally doped and overdoped YBCO films in different temperature. OP* OD* Temperature (K) 1/ D (cm-1) 1/ D (cm-1) 300 405 436 200 296 282 100 187 126 70 123 120 50 84 95 30 77 93 OP means optimally doped YBCO OD means overdoped YBCO Below Tc, in the optimally doped sample, the scattering rate 1/ exhibits a sudden drop with saturation at T 50 K. This result suggests a strong suppression of the scattering channel at the superconducting tran sition. Presumably, the carrier-scattering process that is responsible for the temperatur e linear resistivity in the normal state is suppressed when the free carrier condense. Other experiments that found a similar fast

PAGE 86

72 drop in 1/ include infrared measurements of Br2Sr2CaCu2O7[77, 78] and time resolved transition-absorption measurements of YBa2Cu3O7[79]. This striking feature seems to be a unique property of the copper-oxide superconductors because ordinary phonon or impunity scattering, which dominate conven tional superconductors, does not change dramatically at Tc. It is evidence that the quasi-particl es interact with some spectra of excitation which is affected by the onset of the superconductor. While scattering rate of the overdoped sample also shows drop below Tc, but comparing with the optimally doped sample, the drop is not that dramatic. 3.3.5 Frequency-dependent Scattering Rate (MFL) Another approach, based on the marginal Fermi Liquid (MFL) theory [42, 71], can be used. The dielectric f unction can be written as )] 2 / ( 2 [ ) (2 p (3-18) where p is the plasma frequency, is the quasi particle self energy of the charge carrier; and the imaginary part of the is given by T T T 2~ ) ( Im (3-19) The room temperature spectra of bot h optimally doped and overdoped samples were fitted MFL theory. The plasma frequencies p is 24,900 cm-1 and 28,100 cm-1 for optimally doped and overdoped sample resp ectively. The imaginary part of the quasiparticle self energy is s hown in Figure 3-15. Clearly, th ere is a region of negative slope below100 cm-1 in both films. This behavior s uggests that at low frequency the carrier mobility is strongly suppressed at low frequency. A negative slope has been theoretically pred icted for disordered two dimens ional conductors [76]. Above 100 cm-1,

PAGE 87

73 the linear behavior of the scattering rate ex ists. According to the MFL prescription, we calculate the slope of –Im ( ) above 100 cm-1 at 300 K, which yields a coupling constant ~ 0.5. Later we will discuss that the coupling constant obtained from the Drude contribution is about 0.3, which is smaller than the value of MFL theory. This may indicate that besides the free carrier band other absorption may also contribute to the absorption. 3.3.6 Superfluid Density A superconductor has a low frequency 1( ) that is a function at = 0; in turn this function gives a contribution to 1( ) = ps 2/ 2. Table 3-6 shows the Drude part of plasma frequency and the superfluid part plasma frequency for all the samples below Tc. Table 3-6 The Drude part and superflu id part plasma frequency below Tc in the optimally doped and overdoped samples. 50 K pD (cm-1) ps (cm-1) fs OP* 8753 7957 0.45 pD (cm-1) ps (cm-1) fs OD* 12039 3581 0.08 OP means optimally doped YBCO OD means overdoped YBCO The superfluid fraction fs increases with decreasing the temperature. It is interesting to note at the same temperature the ov erdoped sample shows higher total plasma frequency which indicates the overdoped samp le has more charge carrier than the optimally doped sample. This is agreed with Hwang et al .’s [63] BSCO-2212 measurement result. However, the overdoped sample shows lower superfluid plasma

PAGE 88

74 frequency and lower su per fluid fraction ( fs), which directly related to the superfluid density. The BCS theory predicates a lower Tc with lower superfluid density. And the overdoped sample does show lower Tc (79 K) comparing with the value of the optimally doped sample (90 K). The SR measurement of overdoped Tl2Ba2CuO6 (Tl2201) [80] system also found both Tc and ns decrease with increasing doping level. Farber et al. [81] measured the penetration dept h of the optimally doped YBa2Cu3O7, and overdoped Y0.9Ca0.1Ba2Cu3O7samples. Comparing with the optimally doped sample, overdoped sample does show longer penetration depth. Fukuzumi et al. [82] measured in plane resistivity of the Zn dope single crystals of YBa2Cu3O7and La2-xSrxCuO4 with various hole densities. They indicated a radical change of the electronic state for in highly doped regime. And they also suggested that these might be due to some inherent inhomogeneity such as phase separation. Using the partial sum rule, the effective carrier density ( eff) can be gotten from the effective carrier ( Neff) by the following equations 0 ' 1 2 *) ( 2 ) ( d e mV m m NCu eff (3-20) ) / )( ( ) (*m m Neff eff (3-21) where m is the mass of the electron and m* is the mass of the coopers. 0 ' 1 1 2) ( ) ( 2 ) ( d e mVs n Cu s (3-22) At the low temperatures, if we assume that the superfluid dominates the low frequency part of the imagin ary part of the conductivity, the superfluid density is proportional to 2( ) Then in the low wavenumber we have

PAGE 89

75 ) ( ) (2 2 s Cu se mV (3-23) In the ideal situation (London condi tion), at low temperature, both s( ) and s ’( ) will be a constant in the low frequency region. By comparing s( ) and s ’( ) the kinetic energy changing discussed by Katz et al .’s [60] paper can be explored. Figure 3-16 shows both s and s ’ in optimally doped and overdoped samples respectively. For the optimally doped sample, both s and s ’ show the value close to each other. This result is agreed with Deutscher et al .’s [62] result and ot her previous work. However for the overdoped sample, the s ’, which is calculated from the sum rule, is significantly smaller than the optimally dope d sample. There is no “flat part” in the spectrum of s ’. This make it is impossible to compare with the spectrum of s. Thus, we cannot tell if there is any kinetic energy change for the sample above and below Tc. The absence of the “flat part” can be easily explai ned in the spectrum of the imaginary part of conductivity ( 2). Figure 3-17 shows the imaginary part of the conductivity for both optimally doped and overdoped sample. At 50 K, the imaginary part of conductivity ( 2) shows a relation linear in 1/ But in the overdoped sample, this relation is not significant. As indicated in tabl e 3-4, at 50 K, the superfluid fraction is about 41% in the optimally doped sample but only 8% in the ove rdoped sample. At lower temperature, the superfluid will dominate the system in the optimally doped sample. While in the overdoped sample, Drude part may still be im portant in the conductiv ity. Equation (3-23) is not valid for the overdoped system. This may explain why there are so much paradox conclusions in the previous work. Due to the substrate effect, our data cannot be analyzed model independent. Further single crystal e xperiments and model i ndependent analyzing in different doping levels are ne eded to confirm the result.

PAGE 90

76 3.4 Summary In this chapter, we present the temp erature and frequency-dependent optical functions of Ca doped YBa2Cu3O7from the far infrared thro ugh the ultraviolet region. The data are analyzed by the two component model and marginal Fermi liquid model. With an increasing of the carri er concentration in the CuO2 planes, spectral weight lost in the high frequency charge transfer band is obs erved. The weight lost below the charge transfer absorption band is transferred to lower frequencie s. With increased the doping level into the overdoped region, the plasma frequency increases correspondingly because of the charge density increase. However, the superfluid density decreases in this regime and the Drude part still dominant the low fr equency part of the op tical conductivity. This property makes it difficult to calculate th e changing of the kinetic energy in the overdoped YBCO system above and below Tc. The quasi-particle scattering rate is derived from the two component model. Above Tc, the scattering rate is linear with the temperature. Below Tc, the scattering rate drops and becomes saturate at the lower temperatur e. More measurements with different doping level samples are needed in order to get completed picture in this area.

PAGE 91

77 Figure 3-1 The unit cell of YBa2Cu3O7(Ca substitute for Y in the overdoped sample) [83].

PAGE 92

78 Figure 3-2 Schematic phase diagram of the hol e-doped cuprates (x is the doping level).

PAGE 93

79 Figure 3-3 Room temperature reflectance of SrTiO3 and the fitting spectrum.

PAGE 94

80 Figure 3-4 Temperature dependent reflectance spectra of SrTiO3 substrate.

PAGE 95

81 Figure 3-5 Room temperature reflectance spectra of the optimally doped and the overdoped samples.

PAGE 96

82 Figure 3-6 Temperature depe ndent reflectance spectra of the optimally doped YBa2Cu3O7film.

PAGE 97

83 Figure 3-7 Temperature dependent re flectance spectra of the overdoped Y0.7Ca0.3Ba2Cu3O7film.

PAGE 98

84 Figure 3-8 The measured and fitted room te mperature reflectance of both optimally doped and overdoped films.

PAGE 99

85 Figure 3-9 Measured and fitted re flectance of optimally doped YBa2Cu3O7at room temperature and 50 K.

PAGE 100

86 Figure 3-10 Measured and fitte d reflectance of overdoped Y0.7Ca0.3Ba2Cu3O7at room temperature and 50 K.

PAGE 101

87 Figure 3-11 Optical conductivity (obtained from Drude Lorent z model) of the optimally doped and overdoped samples at room temperature.

PAGE 102

88 Figure 3-12 Number of carrier participating in optical transition per Cu atom, Neff, as a function of frequency.

PAGE 103

89 Figure 3-13 Temperature dependent optical conductivity obtained from Drude Lorentz model of optimally doped and overdoped samples.

PAGE 104

90 Figure 3-14 Temperature dependent scattering rate (obtained from Drude Lorentz model) of the optimally doped and overdoped samples.

PAGE 105

91 Figure 3-15 Imaginary part of quasi-particle self energy (obtained from Marginal Fermi liquid model) of both optimally doped and overdoped samples.

PAGE 106

92 Figure 3-16 Superfluid density cal culated from sum rule and imaginary part of the optical conductivity in both optimally doped and overdoped samples.

PAGE 107

93 Figure 3-17 Temperature dependent imaginary part (obtained from Drude Lorentz model) of the optical conductivity in the optimally doped and overdoped samples.

PAGE 108

94 CHAPTER 4 FAR-INFRARED PROPERTIES OF SU PERCONDUCTING YBCO FILMS IN ZERO AND HIGH MAGNETIC FIELDS 4.1 Introduction 4.1.1 Background A superconductor is a material that exhibits two characteristic properties, namely zero electrical resistance and perfect diama gnetism [83], when it is cooled below the critical temperature Tc. At high temperatures it is a norma l metal, and ordinarily is not a very good conductor. In the normal state some superconducting metals are weakly diamagnetic and some are paramagnetic. Perfect diamagnetism, the second char acteristic property, means that a superconducting material does not permit an externally applied magnetic field to penetrate into its inte rior. Those superconductors that to tally exclude an applied magnetic flux are known as type I superconductor. Other superconducto rs, called type II superconductors, are also perfect conductors of electricity, but th eir magnetic properties are more complex. They totally exclude magnetic flux when the applied field is low (H
PAGE 109

95 There is no B field inside a perfect diam agnet because the magnetism M is directed opposite to the H field and thereby cancels it H M 4 (4-2) When a superconductor is placed betw een the pole pieces of a magnet, the B field lines from the magnet go around it instead of en tering, and its own internal field remains zero. This field distribution is the result of the superposition of th e uniform applied field and a dipole field from the oppositel y magnetized superconducting sphere. There are two aspects to pe rfect diamagnetism in in both type I and type II superconductors. The first is flux exclusion: If a material in the normal state is zero field cooled (ZFC), that is, cooled below Tc to the superconducting state without any magnetic field present, and is then placed in an extern al magnetic field, the field will be excluded from the superconductor. The second aspect is fl ux expulsion: If the same material in its normal state is placed in a magnetic field, the field will penetrate and have almost the same value inside and out side because the permeability is so close to the free-space value 0. If this material is then field cooled (FC), that is, cooled below Tc in the presence of this field, the field will be expelled from the material, a phenomenon called the Meissner effect. Although ZFC and FC lead to the same result (absence of magnetic flux inside the sample below Tc), nevertheless the two process are not equivalent. Thompson [84] found that for a “defect-fre e” high-purity niobium sphere the ZFC and FC susceptibilities were almost identi cal. A second high-purit y sphere of similar composition that exhibited strong pinning was also examined and the same ZFC results were obtained. However, no Meissner flux expulsion following field cooling (FC) was observed. To further clarify the magnetic fi eld configurations in side a superconductor,

PAGE 110

96 consider a long cylindrical sample placed in a uniform applied magnetic field with its axis in the field direction. Since there ar e no applied currents, the boundary condition at the cylindrical surface is // //H H (4-3) The above equation shows that the H field is uniform inside with the same value as the applied field in appH H (4-4) The B field has only a z component with value Bapp = 0Happ outside and zero inside, Bin = 0. There is, however, a transition layer of thickness called the penetration depth, at the surface of the superconductor where the B field drops exponentially from its value Bapp on the outside to zero inside, in accordance with the expression ] / ) ( exp[ ) (0 r R B r B (4-5) Thus the B field exits only in the surface layer, and not in the bulk. Since )] ( 4 [ ) ( r M H r Bin in (4-6) with Hin = Happ, we have for M(r) ) ( exp 1 4 1 ) ( r R H r Mapp (4-7) again subject to the assumption that << R This exponential decay process arises naturally in the Ginzburg-Landau and London theories, and that these th eories provide an explicit fo rmula for what is called the London Penetration depth L, namely 2 1 2 24 ne mcL (4-8)

PAGE 111

97 where n is the carrier number, e is the electron charge, m is the electron mass and 0 is the permeability. In the absence of any applied transport current we set J = 0 (also D / t = 0 ) in Maxwell’s equation, to obtain sh inJ c B 4 (4-9) whereshJis called the shielding or magnetization current density M J csh 1 (4-10) Since Bin has only a z or axial component, the curl, e xpressed in terms of cylindrical coordinates, gives the following shielding cu rrent density which flows along the cylinder in the negative direction ) ( exp ) ( exp 10r R J r R B dr B d Japp sh (4-11) where 0J Bapp (4-12) The vectors B and shJ do not exist in the bulk of th e superconductor but only in the surface layer where they are perp endicular to each other, with B oriented vertically and shJ flowing around the cylinder in horizontal circles. It may be looked upon as a

PAGE 112

98 circulating demagnetizing current that shields or screens the interior of the superconductor by producing a negative B field that cancels appB so that 0 inB inside. Thus we see that the superconducting medium reacts to the presence of the applied field by generating shielding currents that cancel the B field. The reaction of the medium may also be looked upon as generating a magnetization M that cancels the interior B field, as was explained above. These are tw o views of the same phenomenon, since the shielding current density Jsh and the compensating magnetization M are directly related through equation (4-10). The negative B field that cancels Bapp is really a magnetization in the negative z direction. 4.1.2 Type I and Type II Superconductors Type I superconductors are superconductors that exhibit zero resi stance and perfect diamagnetism. They are also perfect diama gnets for applied magnetic fields below the critical field Bc, and become normal in higher applied fields. Their coherence length exceeds their penetration depth so it is not energetically favorable for boundaries to form between their normal and superconductor pha ses [83]. Superconducting elements, with the exception of niobium are all type I. When the penetration depth is larger than the coherence length it becomes energetically favorable for domain walls to form between the superconducting and normal regions. When such a superconductor, ca lled type II, is in a magnetic field, the free energy can be lowed by causing domains of normal materials containing trapped flux to form with low energy boundaries created between the normal core and the surrounding superconducting field which exceed s a value referred to as the lower critical field, Bc1. The magnetic field inside a type II superconduc tor is strong in the normal cores of the

PAGE 113

99 vortices, and becomes very small far away from the cores. For much higher applied fields the vortices overlap and the field inside the superconductor becomes strong everywhere. Eventually, when the applied field reaches a value called the upper critical field Bc2, the material becomes normal. Alloys and com pounds exhibit type II s uperconductivity, with mixed-type magnetic behavior a nd partial flux penetration above Bc1. Type II superconductors also have zero resistance, but their perfect diamagnetism occurs only below the lower critical field Bc1. The superconductors used in practical applications, which have relatively high transition temp eratures, carrying large currents and often being operated in large magnetic fields, are all of type II. The typical optimal doped YBa2Cu3O7materials with Tc about 92.4 K have lower critical field Bc1 (in ab -plane) smaller than 5mT. The higher critical field Bc2 (in ab -plane) is much larger. It is about 240 Tesla. 4.1.3 Superconducting Response in High Magnetic Field The electronic properties of high Tc superconductors are aff ected by the application of magnetic fields. The simp le picture of the high Tc materials, in the mixed state, is the sample penetrated by an array of magnetic vortices each of which contained a quantized magnetic flux. In the applied current densityextJ and the average magnetic flux density B there will be a Lorentz force densityB J fext on the vortices. If the vortices are at rest, the resistance will be effectively zero. If the vortices are moving with a mean velocity v an electric fieldB v E appears. However, the behaviors of the complex dynamics of vortex motions in the presence of viscous, pinning forces and the function either of thermal origin or due to the influence of de fects in the sample becomes complicated and are not yet well understood.

PAGE 114

100 Far-infrared spectrosc opy has been widely applie d to investigate the vortex dynamics in the high Tc superconductors. Historically, mi crowave experiments have been widely used to study the vortex dynamics in type II superconductor. Microwave measurements can sense the fluctuations a bout the pinning site. Measuring the complex surface impedance provides information related to the pinning force constant and vortex viscosity. At higher frequencies, far-infrared spectroscopy has been applied to investigate the vortex dynamics in the high Tc superconductors. Shimamoto et al. [85] observed a large (20%) and field-dependent change in farinfrared transmission in both YBCO and Ba2Sr2Ca2Cu3Ox films at field up to 100T; the behavior was explained by a flux-flow model. Terahert z measurements [86] over frequencies from 100 to 1000 GHz (3-3-33.3 cm-1) found a non-linear dependence of the complex conductivity on the magnetic field strength. Karrai et al. [87, 88] measured the transmittance of the YB2C3O7thin films. Their data showed an increase in transmittance below ~ 125 cm-1 with increasing field. This effect was attributed to dipole transitions associate with bound states in the vortex co res. Evidence from magneto-optical activity was also found, interpreted as cyclotron resi stance in the mixed state. These effects occurred at a temperature as low as 2.2 K a nd in magnetic fields between 2 and 15 T. The experiments prompted several theoretical ca lculations of the optical response of the vortex core states. Measurements of the far-infrared reflectivity R of a superconducting YBa2Cu3O7thin film by Eldridge et al. [89] found a strong dependence on magnetic field, suggesting that the incr ease in transmission at low wa venumber in the experiment of Karrai et al. [87] was mainly due to a decrease in reflectivity. In their experiment they also observed the far-infrared phonon mode in the high magnetic field, which was usually

PAGE 115

101 not expected in the ab -plane films at zero field. The Kramers-Kronig analysis then, gave the field dependent conductivity, which showed a broad resonance between 50 cm-1 and 250 cm-1 whose shape, but not magnitude, could be fitted by a theory involving vortex motion with pinning. In contrast, Brunel et al. [90] reported th e reflectance of Bi2Sr2CaCu2O8 (BSCCO) at several far-infrared fre quencies as a function of temperature and field (up to 17T). They found a fiel d-induced drop in the reflectance, which correspond to the onset of a resistive state a nd thus only occurred at higher temperatures. Gerrits et al. [91] reported practic ally no influence of the magnetic field up to 15.5 T in the far-infrared reflectance of a YBCO thin film at 1.2 K. Liu et al. [92] measured the YBCO film in the different temperatures in the magnetic field up to 30 T. Their data clearly indicated that in the low temperatur e (below 50 K) there was no significant field dependence in both the reflectance and transmitt ance. But at higher temperatures, such as 72 K and 95 K, their data showed that with increasing the magnetic fields, there was a clearly increasing of the transmittance in far infrared region spectrum (below ~120 cm-1). In this chapter, we will report the far-in frared transmittance measurement of YBCO films at 4.2 K in magnetic field up to 18 Te sla. However, as the magnetic field (with H perpendicular to the ab – plane and with unpolarized li ght) varying, at constant temperature (4-2 K), the transmittance spect rum shows no discernible field dependence up to 18 T. This result is the same as Liu’s et al. [92] result. 4.2 Experiment and Results 4.2.1 Sample Preparation We have studied three types of optimally doped films on three different substrates. The substrates used are MgO, sapphires and silicon. The samples were made by the PLD method. The detailed sample preparation pro cesses were already described in Dr. Wint’s

PAGE 116

102 Ph.D. thesis [93]. The substrate thickne ss was about 0.2 mm and films are about 400 thick with Tc around 92 K. Our experiment was done in the Nationa l High Magnetic Field Lab, Tallahassee FL. The experiments used a Bruker 113V spect rometer and light pipe sample probe in conjunction with the 18-Tesla superconducting magnet and a 4.2 K bolometer detector. The sample probe allows alternate sample and reference measurement [94]. Compared with the resistive magnets, the superconducting magnet has le ss vibrational noise, which is important especially to the far infrared measurement. Because of these advantages for the superconducting magnet, the final result showed a high signal to noise ratio. 4.2.2 Sample zero field properties Figure 4-1 (a), (b) and (c) show th e transmittance of the YBCO/silicon, YBCO/sapphire and YBCO/MgO film respect ively taken at 4.2 K and at several magnetic fields. Note that for the two superc onducting samples (Figure 4-1, panels a and b) the low frequency transmittance tends to zero, as expected for a sample where the far infrared properties are domina ted by the inductive response ( 2). Were the loss ( 1) significant, there would be finite transmittan ce at low frequencies. The YBCO/MgO film transmittance spectra was fitted by the two-fl uid model. Figure 4-2 shows the fitting result. Due to the multiple internal reflection, the reflectance show strong fringes. Table 4-1 shows the fitting parameters for both the substrate and YBa2Cu3O7films. Figure 4-3 shows the real and imaginary part of conductiv ity of the sample film. As dicussed before, imaginary part of conductivity ( 2) dominates the far infrared optical properties. The sample show high reflectance and low transmittance [95]. It is necessary to point out that the temperature dependent transmittance and reflectance measurement of all these films in the zero magnetic field had already been

PAGE 117

103 finished by Dr. Wint [93] and Dr. Boychev [96]. The spectra were already fitted by different models and all the parameters were already published. The detailed information can be read Dr. Wint’s (2004, University of Florida) and Dr. Boychev’s (2002, University of Florida) Ph.D. thesis. Table 4-1 Oscillator parameters of both the MgO substrate and YBa2Cu3O7at 4.2 K. YBCO MgO pS(cm-1) 8900 pD(cm-1) 1000 1/ D(cm-1) 87 p1(cm-1) 3672 7.206 1(cm-1) 290 66.950 1/ 1(cm-1) 100 86.935 p2(cm-1) 9800 1.764 2(cm-1) 740 146.518 1/ 2(cm-1) 1550 23.671 p3(cm-1) 0.306 3(cm-1) 121.868 1/ 3(cm-1) 2.273 p4(cm-1) 0.002 4(cm-1) 183.998 1/ 4(cm-1) 171.081 p5(cm-1) 0.002 5(cm-1) 243.173 1/ 5(cm-1) 194.192 p6(cm-1) 9.670 6(cm-1) 292.180 1/ 6(cm-1) 19.942 25 3.01 d 400 0.3 mm 4.2.3 Optical Measurement in the High Magnetic Field As shown in Figure 4-1, for different samples taken at 4.2 K and at several magnetic fields, we observe practically no infl uence of magnetic field on the far infrared transmittance spectra of the film. To inve stigate further, the magneto-transmittance measurements taken at several magnetic fi elds for YBCO/silicon, YBCO/sapphire and

PAGE 118

104 YBCO/MgO is showed in figure 4-4 (a), (b) and (c) respectively. Similarly, we do not find any evidence for changes in the transmission ratio for all samples in this temperature and field range. Here it is necessary to poi nt out that typical no ise variations of our measurements in the magnetic field are on th e order of 8%. On the other hand, we are unable to pursue our studies at lower frequency ( < 25 cm-1) on these films due to the low transmitted intensity in the superconducting states. And because of the technique limitation at this point, we cannot measure the sample in higher temperatures. Thus, we can conclude that with the external fiel d perpendicular to th e superconducting YBCO film, no far infrared magneto resistance is detected at 4.2 K and in the high field regime. We observe practically no influence of the magnetic field on the far infrared transmittance spectra of any of the films. The noise around 140 and 230 cm-1 is due to poor beam-splitter efficiency at these fre quencies. Outside of these two regions, the variation in transmission with field is T/T < 8%, set by the signal to noise ratio in the data. We can conclude that with the extern al field perpendicular to the superconducting YBa2Cu3O7film, no far-infrared magneto resistance is detected at 4.2 K and in the high field regime. The non-superconducting sample (F igure 4-1, panel c) also shows no fielddependent absorption. (The oscillations in this sample are due to multiple internal reflections in the Si substrate.) 4.3 Discussion In the presence of magnetic field the electrodynamic response of Type-II superconductor is affected by vortex dynamics We are going to discuss the magnetooptics data at 4.2 K show in Figure 4-4. Ou r spectra do not show any significant changes within the applied field range, which is agree with Liu et al. [92] and other group’s result but in contrast to several other groups’ reports. To acquire a better understanding, we

PAGE 119

105 consider the simple picture at T << Tc: The vortex can be driven either by an ac electric field or by super-flow. Because our high fr equency field oriented perpendicular to ab plane, the vortices oscillate within their pi nning potential. The area of the vortex cores is in the normal state and the outside of them is the superconducting st ate. The fraction area of the cores is H/Hc2(T) and Hc2 is the upper critical field. The dielectric function of this system at low temperature may be written as ir e e pe D pn c s ps c psi i H H i H H i 2 2 2 2 2 2 2 2) / ( ) / ( 1 ) 0 ( ) ( (4-14) Here, 1/ s is the damping constant inside the vort ex. The entire change in the dielectric response will be attributed to pair-breaking e ffect and to quasipartic le excitations inside the vortex cores. In order to explain the abse nce of changes in our optical spectrum, consider the change of optical conductivity as the vortex density is increased: s( )= ps 2[1H/Hc 2] /4 i ; n( )= ps 2[ H/Hc 2] S( )/4 Here, S( ) is the frequency dependence of the vortex conductivity and is initially dominated by 1/( i – 1/ s) The change in ( ) due to a conversion of super to normal fluid is given by ( ) = ps 2 (H/Hc2)[S( ) – i/ ]/4 Specifically, ( ) is maximum at zero frequency and decreases rapidly with frequency for > 1/ s. In our experiment, the measurements are limited to > 25 cm-1 and the quasi-particle scattering rates 1/ s of our film are smaller than 50 cm-1 for T <50 K at zero field. Moreover, the change in ( ) is expected to be not big for fields up to our maximum field of 18 T when Hc2 is about 240 T. Thus, it is possible that any change in the spectra should be relatively small in our far-infrared freque ncy and magnetic field range.

PAGE 120

106 Many studies [97, 98] have focused on the quasi-particle local density of states inside a vortex core. The physics of the vortex core for a type II supe rconductor is usually described by Bardeen-Stephen model [99]. Howe ver this model is based on the dirty limit description ( l << ), in which the motion of the qua si-particle gets well randomized within the core. The first calculation of the electronic vortex structur e in the clean limit ( l >> ) and for H<> 1 and the energy of the lowest bound state (minigap) 2/EF ~ 1/ 2 is very small. This picture is well established in the classical superc onductor. But, for the high Tc superconductors the situatio n is quite different, since is large and EF is smaller than in the classical superconductors. Hence, only a few bound states in the vortex core are expected for the high Tc superconductors. Recent spectr oscopic experiments appear to have confirmed this expectation. A characte ristic resonance has been observed by Karrai et al. [87] in the mixed state of YBCO thin film at ~65 cm-1. They interpret their spectra as the vortex core resonance frequency. Based on the microscopic theory of vortex dynamics, this feature corres ponding core levels spacing 0 = E1/2 – E-1/2 is about 40 cm-1 Evidence for a large core spacing has al so found in scanning tunneling spectroscopy (STS) on YBCO single crystals. In contrast such dipole transiti on between the quasiparticle levels in the vortex core is no t present in our high field measurements. 4.4 Summary In summary, we present the magnetic fiel d dependence of the far infrared optical data of YBCO films on different substrate where the transmittance spectra have been measured at the liquid helium temperature 4.2 K. Varying the magnetic field at constant

PAGE 121

107 temperature (4-2 K) allow us to study the vortex dynamics in the high temperature superconductors. In our current work, we do not see any field dependent features in far infrared transmittance spectra of YBCO films at 4.2 K. This observation suggests that the pair-breaking effects could be too small to be seen in our frequency and field range. And the anisotropic pairing effects in the high te mperature superconductors might lead to the complexity of excitations insi de a vortex core. We hope that this work will stimulate more completely experimental and th eoretical work for understanding the electrodynamics of cuprates in a high magnetic field. Future work can be done in higher temperatures and higher fields and, if possible, in the lower frequency range.

PAGE 122

108 Figure 4-1 Transmittance of different YBCO film samples. YBCO/sapphire (a), YBCO/MgO (b), YBCO/silicon (c) samples in different magnetic fields.

PAGE 123

109 Figure 4-2 Measured and fitted spectra of YBa2Cu3O7/MgO sample.

PAGE 124

110 Figure 4-3 Real and imaginary part of op tical conductivity of optimally doped YBCO.

PAGE 125

111 Figure 4-4 Magneto resistance of different YBCO film samples. YBCO/sapphire (a), YBCO/MgO (b), YBCO/silicon (c) samples in different magnetic fields.

PAGE 126

112 CHAPTER 5 TERAHERTZ AND OPTICAL STUDY OF ELECTRONIC DIELECTRIC MATERIALS 5.1 Introduction 5.1.1 Background The telecommunication technology industr y today requires high-volume and lowcost circuit fabrication, while at the same time demanding excellent electrical performance, reliability, circuit miniatur ization and surface mounting techniques. Lowtemperature co-fired ceramics (LTCC) provi de a module technology capable of dramatic volume saving over individual integrated ci rcuit (IC) mounting, by stacking several ceramic substrates each only several m thick, and building-in passive components (resistors, capacitors, insulators, etc .) and other ICs. The f ilters and other components used in a radio frequency (RF) circuit come to about dozen in all, and LTCC makes it possible to pack all components into a package only a few mm square. Compared to a conventional multi-layer la minated structure, LTCC offers a number of advantages: low dielectric loss (low tan ), better controlled dielectric properties, well suited to producing modules in low-cost pack ages. Although some of these features are also available from some conventional thick f ilm ceramic processes, a multi-layer format is not so readily available. The multiple layer structure of LTCC allows the realization of innovation printed structures, such as filters a nd baluns, and facilitate s miniaturization. In addition to this, the fact that the layers are produced in parallel results in shorter fabrication time, reduced cost, and increased yields. Figure 5-1 shows the basic

PAGE 127

113 multilayer LTCC process. A distinguishing feature is that LTCC technology allows parallel processing of the individual layers. One of the important areas for LTCC technology is the development of novel dielectric materials for LTCC system. The el ectrical and thermo mechanical demands are obvious for enabling the production and usage of reliable components. The dielectric properties such as low dissipation factor, appropriate permittiv ity, and near zero temperature coefficient of the resonance frequency (Tf) are important. These values enable the construction of RF devices with convenient size, low insertion loss, and stable operation at ambient temperatures. Bismuth-containing compositi ons have recently been reported with sintering temperatures around 920oC. Since the firing temper ature is below the melting temperature of silver, pure silver electrode materials can potentially be used. The general objective of this chapter is to investigate Bi -based pyrochlore materi als. More detailed description of the applic ation of LTCC materials can be found elsewhere [100]. 5.1.2 Crystal Structure Pyrochlores typically have a nominal composition A2B2O7 and adopt a cubic structure with space group F d3m The crystal structure can be described as consisting of interpenetrating networks of BO6 octahedra and A2O chains [101]. Py rochlores allow for a broad range of atomic substi tutions at the A, B and O site s; therefore, compounds with the pyrochlore structure exhibit a wide variet y of very interesting physical properties. Figure 5-2 shows the structure of cubic bi smuth pyrochlores. Recently, bismuth-based pyrochlore compounds have demonstrated excel lent properties for use in capacitor and high-frequency filter applications: low-lo ss, high-permittivity, and good temperature stability [102]. Golovschikova et al. [103] and Jeanne et al. [104] first investigated

PAGE 128

114 bismuth-based pyrochlore materials for dielectri c applications in the early 70’s. Detailed studies by Levin et al. [105] determined the stoichiome try of single-phase cubic bismuth zinc niobium to be Bi3/2Zn0.92Nb1.5O6.92 (BZN) in the pyrochlore structure (A2B2O6O) with partial Zn occupancy of both A and B s ites. Table 5-1 shows the lattice parameters of cubic BZN in different temperatures. In addition, displacements from the ideal crystallographic positions were identified fo r both A and O ions. Figure 5-2 shows the ideal crystal structure without consider ing the displacement of the ions. The displacements of the ions are shown in Figur e 5-3. The A-site cations were found to be randomly displaced from the ideal eightfold-c oordinated positions along the six <112> directions, perpendicular to the O-A-O li nks. The O ions were found to be randomly displaced along the <110> directions. It will be shown that this displacement disorder is required to explain the infrar ed vibrational spectroscopy. Ba sed on the crystal chemical considerations, Withers et al. [106] found the bond length of A-O is different. Their data indicated the length of the longer A-O bond is 2.351 while the shorter A-O bond length is 1.961. The experiment and subs equent Monte Carlo simulation results did provide a good representation of the local s hort range order and a ssociated structural relaxation in the A2O sub-structure. Table 5-1 Lattice parameters and atomic positions at 298 K and 12 K for the cubic BZN pyrochlore [105]. (The upper and lower en tries in each site correspond to the position at 298 K and 12 K respectively.) Unit T=298 K T=12 K Cell a= 10.56156(7) 10.55668(6) Fd3m Vol= 1178.11(1) 3 1176.47(1) 3 227 Atom Site x y z Occupancy Ux100 0.34403(27)0.34403(27)0.3776(5) 2.05(21) O’ 96g 0.34361(23)0.34361(23)0.3761(4) 0.0767 1.19(18)

PAGE 129

115 Table 5-1 Continued 0.31984(7) 1/8 1/8 2.28 O 48f 0.31965(6) 1/8 1/8 1.000 1.79 0.46731(34)0.51499(35)0.51499(35)1.62(5) Bi/Zn 96g 0.46800(31)0.51671(31)0.51671(31) 0.125/0.035 1.20(5) 0 0 0 1.37(2) Nb/Zn 16c 0 0 0 0.75/0.25 1.02(2) Vibrational spectroscopy can provide unique information about materials, including phonon modes, the presence of impurities or de fects, ordering, and the orientation of dipoles. Infrared spectra of pyrochlores were reported by Brisse and Knop [107]. The vibrational modes of stannate pyrochlores were identified, si te occupancy was discussed, and trends were analyzed. Later McCauley [ 108] studied the general characteristic of infrared absorption in the pyr ochlore structure. Factor group analysis was employed, vibrational modes were classi fied, and infrared-active lattice modes were assigned to either a bending or stretching modes. More recently, Kamba et al. [109] measured the reflectance of BZN material and Nino et al. [110] assigned each infrared-active mode to a bending or a stretching mode. However, until now only the spectra of BZN have been reported. There have been neither stud ies of the phonon mode s in other bismuth pyrochlores nor detailed invest igations of the temperatur e-dependent trends of the infrared absorption in pyrochlores. Here, we report temperature-dependent reflectivity measurement for four cubic pyrochlore ceramics Bi3/2ZnTa3/2O7 (BZT), Bi3/2MgNb3/2O7 (BMN), Bi3/2MgTa3/2O7 (BMT) and Bi3/2Zn0.92Nb1.5O6.92 (BZN). 5.2 Experiment and Result 5.2.1 Sample Preparation All the samples were made by Dr. Nino at the Pennsylvania State University [100]. The starting materials were reag ent grade oxide powders of Bi2O3, ZnO and Nb2O5

PAGE 130

116 (Aldrich Chemical Company Lt d). A stoichiometric mixtur e of powders of the cubic pyrochlore phase with nominal composition (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 was added to deionized water and dispersant to form a 60 vol% solids slurry and milled for 24 h in zirconia media. The powder was then dried at 120C and calcined at 800C for 4 h in closed alumina crucibles. The initia l calcination step between ZnO and Nb2O5 to form the columbite ZnNb2O6 was performed at 1000C for 4h. Columbite formation was confirmed through XRD. After the final calcination, powders were remilled for 24 h in water and dispersant, forming a 60 vol% slurry. The powder was then dried at 120C for 16 h. Approximately 2wt% Acryloid binder was added to assist in forming. Pellets were uniaxially pressed, at approximately 120 MPa, into discs 6 mm in diameter and 2 mm thick. Binder burnout and sintering were performed in a single heating run under flowing air (500 cm3/min) and 950C for 4 h. The detail information of sample prepar ation has been descri bed elsewhere [111]. 5.2.2 Experimental Procedure Temperature-dependent reflectivity wa s obtained using a Fourier Transform Spectrometer (Bruker IFS 113v) in conjunction with a liquid Helium-cooled Si bolometer (over 30-700 cm-1) and a room temperature DTGS detector (over 650-3300 cm-1). The reflection stage provided an a ngle of incidence of about 15o for the light. Temperatures between 50 and 300 K were obtained in a Hans on flow cryostat with polyethylene (far infrared) or KBr windows (mid-infrared). Te mperature-dependent terahertz transmission spectra of BZN were measured with a TP I Spectra 1000 spectrometer and a Hanson flow cryostat with polyethylene windows.

PAGE 131

117 5.2.3 Optical Measurement 5.2.3.1 Reflectance spectra The temperature dependent reflectance of BZT, BMN, BMT, and BZN between 30 and 1500 cm-1 is shown in Figure 5-4. The re flectance is not shown above 1500 cm-1 because it is flat at these frequencies, a pproaching the value given by the high frequency permittivity Strong structure due to the vibrati onal modes is seen over much of the range. The low frequency reflectance is very large, consistent with the large static dielectric constant observed in these materials. The refl ectivity spectra do not change significantly with temperature, which implies there is no phase transition within the temperature range investigated. This is in ag reement with earlier infrared measurements in BZN [100]. There is a slight increase in th e maxima of the vibrati onal features at lower temperatures. 5.2.3.2 Kramers-Kronig analysis The real and imaginary parts of the dielectr ic constant in the infrared range can be estimated from the reflectance R( ) via Kramers-Kronig analysis [3]. In calculating the Kramers-Kronig integral, we extrapolated the re flectance as constant at low frequencies, appropriate for an insulator. At high freque ncies we also took the reflectance to be constant up to very hi gh frequencies (10,000,000 cm-1; 12,000 eV) and then used freecarrier behavior, R ~ -4, above that. Figures 5-5 a nd 5-6 show respectively the temperature dependence of the real and imag inary parts of the dielectric function for BZT, BMN, BMT, and BZN. The imaginary part shows a number of peaks due to phonon modes and becomes very small above ~800 cm-1. The real part is quite large (5060) at low frequencies, shows derivative-like features in the vibrational region, and falls to a high frequencies value of about 5.

PAGE 132

118 5.2.3.3 Terahertz spectra Terahertz transmission spectra of BZN and BMN were measured at both room temperature and cryogenic temperature between 3 cm-1 and 60 cm-1. The absorption coefficient was estimated from the transm ittance, and combined with the infrared Kramers-Kronig results to give the absorption coefficient sp ectra shown in Figure 5-7 (a) over 3-1500 cm-1. Figure 5-7 (b) shows another optical function, the opt ical conductivity 1( ). At low frequencies, the optical conductivity de creases, consistent with the small dielectric loss in these materials. 5.2.3.4 Oscillator-model fits The complex dielectric function ) ( ~ in the infrared range can also be obtained by fitting the reflectance R( ) using a model dielectric functio n that consists of the sum of several damped oscillators plus a high frequency permittivity originating from the electronic polarization n i i i i i phj1 2 2 2~ ) ( ~ (5-1) where i, i, and i denote respectively the eige nfrequencies, the damping coefficient, and the contribution to dielectric permittivity from the ith polar phonon mode and ph ~ is the phonon contribution to the comple x dielectric function. The infrared reflectivity spectra and the oscillator fit fo r BMN measured at room temperature and cryogenic temperature are shown in Figure 5-8. The oscillator fits for the other samples are of similar quality. Tables 5-2, 5-3, 5-4 and 5-5 show the fitting parameters for the reflectance spectra.

PAGE 133

119 Table 5-2 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BZT pyrochlore at 300K a nd 50K. indicates mode splitting. 300K BZT 50K Mode Resonant frequency (cm-1) Oscillator strength Damping coefficient (cm-1) Mode assignment Resonant frequency n (cm-1) Oscillator strength n Damping coefficient (cm-1) Mode 7 52 15.1 47 (O-A-O) Bend* 50 16.1 43 7 7 86 2.1 29 (O-A-O) Bend 90 2.9 29 7 6 145 13.3 32 (O-A-O) Bend 144 14.8 24 6 5 192 6.0 68 (A-BO6) Stretch 191 9.2 73 5 4 268 3.6 62 (O-B-O) Bend 268 3.8 46 4 3 303 4.7 47 (A-O) Stretch 303 5.1 38 3 2 499 1.2 81 (A-O) Stretch 496 1.3 72 2 1 570 0.78 64 (B-O) Stretch* 571 0.86 53 1 1 639 0.12 40 (B-O) Stretch 640 0.12 30 1 5.24 5.67 (sum) 47.0 54.2 Table 5-3 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BMN pyrochlore at 300K and 50K. indicates mode splitting. ** indicates split A-O mode described in the present work. 300K BMN 50K Mode Resonant frequency (cm-1) Oscillator strength Damping coefficient (cm-1) Mode assignment Resonant frequency n (cm-1) Oscillator strength n Damping coefficient (cm-1) Mode 7 41 12.4 31 (O-A-O) Bend* 42 21.6 40 7 7 83 19.1 94 (O-A-O) Bend 108 18.5 126 7 6 178 15.2 84 (O-A-O) Bend 173 16.0 73 6 5 211 3.7 79 (A-BO6) Stretch 208 4.6 75 5

PAGE 134

120 Table 5-3 Continued 300K BMN 50K Mode Resonant frequency (cm-1) Oscillator strength Damping coefficient (cm-1) Mode assignment Resonant frequency n (cm-1) Oscillator strength n Damping coefficient (cm-1) Mode 4 291 2.0 95 (O-B-O) Bend 292 2.3 90 4 3 367 3.6 79 (A-O) Stretch 368 3.9 73 3 2 483 0.82 68 (A-O) Stretch 477 0.69 48 2 1 556 0.89 108 (B-O) Stretch* 548 0.84 99 1 1 599 0.35 97 (B-O) Stretch 595 0.40 91 1 n ** 850 0.01 34 (A-O) Stretch 851 0.01 33 n ** 5.44 5.52 (sum) 58.0 68.9 Table 5-4 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BMT pyrochlore at 300K a nd 50K. indicates mode splitting. 300K BMT 50K Mode Resonant frequency (cm-1) Oscillator strength Damping coefficient (cm-1) Mode assignment Resonant frequency n (cm-1) Oscillator strength n Dampi ng coeffici ent (cm-1) Mode 7 56 18.8 60 (O-A-O) Bend* 54 18.0 53 7 7 108 4.7 62 (O-A-O) Bend 110 6.4 54 7 6 149 3.2 35 (O-A-O) Bend 145 3.6 27 6 5 178 10.8 71 (A-BO6) Stretch 177 12.1 64 5 4 259 3.9 81 (O-B-O) Bend 262 5.0 80 4 4 295 1.5 50 (O-B-O) Bend 299 1.4 42 4 3 336 3.0 79 (A-O) Stretch 337 3.1 74 3 2 495 0.73 64 (A-O) Stretch 492 0.77 55 2 1 536 0.36 54 (B-O) Stretch* 534 0.37 47 1

PAGE 135

121 Table 5-4 Continued 300K BMT 50K Mode Resonant frequency (cm-1) Oscillator strength Damping coefficient (cm-1) Mode assignment Resonant frequency n (cm-1) Oscillator strength n Dampi ng coeffici ent (cm-1) Mode 1 578 0.60 65 (B-O) Stretch* 577 0.64 55 1 1 642 0.11 47 (B-O) Stretch 644 0.11 36 1 4.98 5.18 (sum) 47.8 51.5 Table 5-5 Parameters from the dispersion an alysis of the phonon modes in the infrared spectra of BZN pyrochlore at 300K and 50K. indicates mode splitting. ** indicates split A-O mode de scribed in the present work. 300K BZN 50K Mode Resonant frequency (cm-1) Oscillator strength Damping coefficient (cm-1) Mode assignmen t Resonant frequency n (cm-1) Oscillator strength n Damping coefficien t (cm-1) Mode 7 45 30.8 46 (O-A-O) Bend* 42 48.8 50 7 7 81 10.0 48 (O-A-O) Bend 88 12.8 57 7 6 142 16.3 41 (O-A-O) Bend 142 18.9 34 6 5 178 10.9 84 (A-BO6) Stretch 181 10.2 76 5 4 259 2.3 86 (O-B-O) Bend 263 2.8 82 4 3 340 4.9 96 (A-O) Stretch 341 5.3 88 3 2 482 0.84 73 (A-O) Stretch 480 0.87 62 2 1 551 0.88 90 (B-O) Stretch* 550 0.84 74 1 1 624 0.08 64 (B-O) Stretch 615 0.13 59 1 n ** 850 0.01 38 (A-O) Stretch 849 0.02 38 n ** 5.24 5.50 (sum) 77.0 100.7

PAGE 136

122 5.3 Discussion 5.3.1 Infrared-active modes We now turn to assignments of the vibrationa l features. If the ions in A site and O site are ordered in their ideal positions, the factor group analysis yields [108]. g u u g g g u uF F IR F R F R E R A E A1 2 1 2 1 22 4 ) ( 8 ) ( 4 ) ( ) ( 3 3 (5-2) Only seven F1u infrared-active modes are infrared allowed. (One F1u mode is an acoustic mode.) However, since in BZN th e atoms in the A sites occupy one of six possible positions and each O atom is disordered among 12 possible positions [105], the factor group analysis of BZN yields the following phonon modes at the center of the Brillouin zone [109] (assuming some occupancy of all the sites simultaneously, which gives the largest estimate of the expected mode numbers), g u u g g g u g u uF F IR F R F R E R A E A A A1 2 1 2 1 2 2 110 11 ) ( 15 ) ( 13 ) ( 7 ) ( 5 8 2 6 2 (5-3) The modified irreducible representation is the result of pe rforming factor group analysis of the pyrochlore structure with th e refined atomic positions (from Levin et al. [105]) for BZN. The overall symmetry of the BZN pyrochlore remains as Fd3m. However, as the neutron diffraction experime nts show, the A and O sites are displaced from their ideal pyrochlore positions (16d a nd 8b, respectively) to off-center ones (96g and 96g respectively). While th ese displacements affect the local symmetry of the atoms and lead to mode splitting due to cation and anion partitioning, the overall unit cell symmetry is kept i.e. the structure remain s a pyrochlore Fd3m. Further details are provided in Levin et al [105]. In modified irredu cible representation, 14 F1u modes are infrared active (one F1u is an acoustic mode). Ten oscill ators are required to fit the infrared reflectivity spectra for BMN and BZN (in agreement with previous work on

PAGE 137

123 BZN [109]) and nine modes are needed for BZT and for BMT. Furthermore, similarities in the spectra also suggest possible analogous A-site cation and O anion displacements to those observed in BZN [105, 106 and 109] Assignments of the phonon (lattice) modes are presented in Tables 5-2, 5-3, 5-4 and 5-5 following the classification of McCauley [108] and Nino et al. [110]. Modes identified wi th an asterisk (*) s how a splitting that is inconsistent with the ideal pyrochlore struct ure, as discussed in more detail below. 5.3.2 Mode at 850 cm-1 Both BMN and BZN exhib it a phonon mode around 850 cm-1, identified as n ** in Tables 5-3 and 5-5. This featur e is seen as a weak structure near the reflectance minimum in Figure 5-4 (b) and (d). In contrast, th e spectra of BMT and BZT do not show this feature. The room temperature fits, repor ted in Table 5-3 and Table 5-4, put the n ** mode in BMN and BZN at very similar frequencies (850 cm-1). This n ** mode shows no significant difference in resonant frequency, oscillator strength ( ), or damping coefficient ( ) as temperature changes between room temperature and cryogenic temperature. The oscillator strength of this mode ( n **) is the smallest among all the lattice modes of both BZN and BMN. McCauley [108] measured the infrared absorption spectra of several pyrochlore-structure mate rials. The data showed a number of very weak absorption bands in the 800-1100 cm-1 region, leading to th e suggestion that this lattice mode is an indication of an additional structural complexity. Wither et al. [106] indicated the bond-length differe nce for the A-O bond in the A2O sub-structure. Their data show the longer bond length is 2.351 and the shorter bond length is 1.961, about a 20% difference. Hector and Wiggin [112] show ed that the displacements of both the O anion and the A site cation must be cooperative within domains and this may lead to one

PAGE 138

124 A-O bond being shortened and the other being le ngthened. According to this picture, the vibration of the shorter A-O bond ma y correspond to the phonon mode around 850 cm-1 and the vibration of the longer bond may lead to a phonon mode around 483 cm-1. It has been recently proposed that the diso rder of A and O ions is due to static displacements in all py rochlores in which the A cation ha s active lone pairs [113]. And, it has been noted [114, 115] that in some pyr ochlores the lone pair character of Bi3+ is reduced by mixing of the Bi 6s electron pairs and the d orbitals (of B-site cations). In BMT and BZT, because of the low electronegativity of Ta5+ ions, it can be expected that the Bi3+ 6s electron and d orbital mixing is stro nger in BZT and BMT than that in BZN and BMN. This suggests that in BMT and B ZT, the displacement from the symmetrical position of the A site cation and the O anions is not as large as in BZN and BMN. In this way, in BMT and BZT, the distinction betw een the long and short A-O bonds disappears or it is greatly reduced and as a consequence, the n ** mode is no longer clearly observed. Furthermore, the phonon mode 2 (483 cm-1 in BMN and 482 cm-1 in BZN), which corresponds to the vibration of the longer A-O bond, shifts to higher frequencies (495 cm-1 in BMT and 499 cm-1 in BZT). At the same time, the n ** mode would shift to lower frequencies in both BMT and BZT; however, due to its low oscillator strength, the n ** mode cannot be detected in the infrar ed spectrum when it is close to the 1 mode. 5.3.3 Mode Splitting Not counting the n ** mode, BZT, BMN and BZN ha ve in total nine observed infrared modes whereas BMT shows eleven os cillator modes. This difference suggests some additional effects in BMT. The splitting in principle could be due to force constant

PAGE 139

125 or mass effects. Table 5-6 shows the mass ratio (the ratio of the mass of the heavier B site ions divided by the mass of the lighter B s ite ions) of the B site ions for all the compounds investigated. Table 5-6 The mass ratio of the B site ions in different pyrochlores. Materials BMT BMN BZT BZN Mass ratio 7.444 3.823 2.767 1.421 Ta5+ has the largest mass of all the B site ions whereas Mg2+ is the lightest of all the B site ions. The significant mass difference in BMT leads to a splitting of the B-O stretching mode and O-B-O bendi ng mode that is large enoug h to separate the single normal mode into two distinct modes. If we assume that 4 (259cm-1) and 4 (295cm-1) are the O-B-O bending modes in BMT, corre spond to the vibration frequency of Ta5+ and Mg2+ respectively, the mass difference induced phonon mode splitting can be explained as follows. We write 2 2 0) ( 4 Ze NP p (5-4) where p is the plasma frequency, is the oscillator strength, is the reduced mass of the ions and (Ze) is the charge of the ions. From the above equations, 2 0 2) ( Ze (5-5) so that the reduced mass ratio becomes 18 3 ) ( 2 ) ( 52 2 2 2 Mg Mg Ta Ta Mg Ta (5-6)

PAGE 140

126 In the octahedral structure, the re duced mass can be calculated directly. o Mg o Mg Mg o TA o Ta Tam m m m m m m m 6 ) 6 ( 6 ) 6 ( (5-7) where mTa, mMg, and mo are the mass of Ta5+, Mg2+, and O2respectively, making the reduced mass ratio be 23 3 Mg Ta (5-8) This result is in agreement with the reduced mass ratio estimated from the oscillator strength. Using this simple spring model, th e ratio of the bond strength between different B site ions can be calculated. 2K (5-9) 49 24 2 2 4 Mg Ta Mg TaK K (5-10) This result is reasonable. Comparing the radius of the B site ions (sixfold coordinated), one sees that Mg2+ and Zn2+ have similar radii (0.72 and 0.74 respectively) whereas Ta5+ is smaller (0.64) [114]. The smaller radius of Ta5+ will result in a shorter bond distance a nd higher bond strength. Thus, KTa is larger than KMg. In BMN, the material which has the second larg est mass ratio, the width of B-O stretching mode and O-B-O bending mode is rather broad. The large values may indicate the contribution by several phonon modes, modes whic h are too close to a ppear as individual features in the infrared spectra. In both BZT and BZN, the mass difference at the B site is

PAGE 141

127 smaller than that of the BM N; correspondingly, the width of O-B-O and B-O modes is smaller than that of BMN. The analysis of the B-O stretching mode in BMT requires additional considerations. BMT shows only three B-O st retching modes instead of the four modes that are expected from the mass-differenceinduced mode splitting. Figure 5-9 shows this situation. One begins with a single B-O stre tching mode. The first splitting is due to partial occupancy as well as to the local distortion of the [BO6] octahedra. The second splitting is due to the mass difference. The two phonon modes which have the central frequencies (midway between 536 cm-1 and 642 cm-1) are very close to each other and are not separated in the spectrum Thus, the spectrum of BMT only shows a single mode at 578 cm-1 with a slightly larger damping coefficient (65 cm-1) than the damping of the other two modes (54 and 47 cm-1, respectively). 5.3.4 Low-frequency Behavior The reflectance rises slowly below 100 cm-1 (Figure 5-4). As made clear by the result of our terahertz transmission measurements (Figure 5-7), as well as from the fits to the reflectance, there is a br oad vibrational absorption in the range between ~10 and ~100 cm-1. This has been studied in some detail for BZN by Kamba et al. [109]. At lower frequencies, the optical conduc tivity decreases to a very sm all value. These samples are insulators; there is no free car rier contribution to the conductivity in the measured frequency range. Our estimates of the phonon contri bution to the static dielectric constant are in Tables 5-2—5-5. Incl uding the high-frequency electr onic contribution of around 5, the low-frequency dielectric constants of our samples are between 52 and 106.

PAGE 142

128 5.3.5 Temperature Effects In BZT, the 7 mode shifts to higher frequencie s at low temperature. In BMN, frequency of 7 increases significantly at low temperatures. In BZN, 7 and 4 shift significantly to higher frequencies. In BM T, there is also an increase of the phonon frequency for the 4 mode at low temperatures. Figure 5-10 show these processes. These phenomena are due to the decrease of the lat tice constant on cooli ng and are consistent with X-ray and neutron diffracti on measurements of BZN [105]. The 1 *, 1, 2, and 6 modes in BMN and the 1 mode in BZN behave differently, shifting to lower frequencies with decreasing temperature. The same is observed in BMT for the 6 phonon mode. This behavior probably indicates a more complicated situation cont rolling these phonon modes. Other phonon modes in these samples do not show significant changes in frequencies at low temperatures. The widths of phonon modes 1, 1 *, 2, 3, 4, 4 and 6, decrease with decreasing temperature for all of the sample s. The broadening of the phonon mode can be accounted for by structural diso rder, orientational disorder, and anharmoncicity. Because the widths of these modes are temperature de pendent, orientational disorder may play a very important role. Orientational disorder wa s also found in titanate pyrochlore materials [116] and in bismuth oxide and its deriva tives [117] using Raman spectroscopy. The widths of the O-B-O ( 4) and the B-O modes ( 1 and 1) may be due to orientational disorder in the BO6 octahedra. The width of the A-O the A-O stretching modes may be due to the randomization of the orientati on of the nonbonding lone pair orbital of Bi3+ on the A site. This conclusion is in agreement with other experiments [117].

PAGE 143

129 The variation of the widt hs for O-A-O modes ( 7 and 7) is not easy to understand. For BMN and BZN, the widths of the 7 and 7 modes increase as temperature is reduced. In BMT, the widths of 7, and 7 decrease as the temperature is reduced. In BZT, the widths of 7 decrease while the width of the 7 mode does not change at cryogenic temperatures. The be nding of O-A-O bonds, which leads to the separation of the positive and negative char ge center, creates the dipoles in these materials. The displacement of A-site ca tions and O anions might increase the orientation disorder of thes e dipoles. The displacement -induced dipole orientational disorder does not decrease at low temperat ures. With the present data, there are no discernable trends in the widths of the 7, and 7 modes; consequently additional spectroscopy in the THz region is needed. This part of work is beyond the range of this paper. Finally, the width of the A-BO6 ( 5) stretching mode depends on both the orientation of the non-bonding lone pair of A-site Bi3+ and the orientation of the BO6 octahedra, and therefore its analysis is not trivial. While, the width of 5 increases in BZT as the temperature decreases, in BMN, BMT and BZN it decreases. 5.4 Summary Dispersion analyses of the infrared re flectance of BZT, BMN, BMT, and BZN show behavior of the phonon modes which c onfirms the A site cation and O anion displacement. The assignment of the n ** mode indicates the existence of a complex structure induced by the displacement wh ich is influenced by the mixing of Bi3+ 6 s electron with d orbital in the B site ions. The splitting of phonon modes due to cation mass difference is also found in our data. The temperature dependence of resonant frequencies and damping coeffici ents confirms the decreasing of both the lattice constant

PAGE 144

130 and provides further confirmation of the orie ntational dipolar diso rder in the bismuth pyrochlores.

PAGE 145

131 Figure 5-1 Low temperature cofired cerami cs (LTCC) multilayer manufacturing process [100].

PAGE 146

132 Figure 5-2 The crystal structure of the bismuth pyrochlore [100]. A B vacancy O’ O

PAGE 147

133 Figure 5-3 The displacement of A site cation and O’ anion [100].

PAGE 148

134 Figure 5-4 The reflectance of different bism uth samples. (a) BZT, (b) BMN, (c) BMT, and (d) BZN.

PAGE 149

135 Figure 5-5 The real part of the dielectric function ( ) of different bismuth samples. (a) BZT, (b) BMN, (c) BMT, and (d) BZN.

PAGE 150

136 Figure 5-6 The imaginary part of the dielectric function ( ) of different bismuth samples. (a) BZT, (b) BMN, (c) BMT, and (d) BZN.

PAGE 151

137 Figure 5-7 The absorption coefficient and c onductivity of BZN at room temperature and at cryogenic temperature. (a) absorption coefficient, (b) conductivity.

PAGE 152

138 Figure 5-8 Measured and calculated reflectivity of BMN at different temperatures. (a) 300 K and (b) 50 K.

PAGE 153

139 Figure 5-9 The splitting of the B-O stretching mode in BMT.

PAGE 154

140 Figure 5-10 Temperature dependence of th e phonon mode frequencies in BZT, BMN, BMT, and BZN.

PAGE 155

141 CHAPTER 6 SUMMARY AND CONCLUSION 6.1 High Temperature Superconductor 6.1.1 Doping Dependent Measurement The temperature and frequency depe ndent optical properties of YBa2Cu3O7and Y0.7Ca0.3Ba2Cu3O7have been studied from the far infrared through the ultraviolet region. The data are analyzed by a two com ponent model. With an increasing of the carrier concentration in the CuO2 planes, there is spectral weight lost in the high frequency charge transfer band. The weight lost below the charge-transfer absorption band is transferred to lower frequencies regi me. With increasing doping, in the overdoped region, the plasma frequency increases co rrespondingly because of the higher charge carrier density. However, superfluid density decreases in this regime and the Drude part may still be important at the low frequency region of the optical conductivity. This property makes it difficult to calculate the changing of the kinetic energy in the over doped YBCO system above and below Tc. The quasi-particle scattering rate is derived from the two component model. Above Tc, the scattering rate is linear with the temperature. Below Tc, the scattering rate becomes saturate at the lower temperature. The data were also analyzed by marg inal Fermi liquid (MFL) model. The frequency dependent imaginary part of quasi-particle self energy shows negative slope in the low frequency region (below 100 cm-1) because the carrier mobility is strongly

PAGE 156

142 suppressed at low frequency. Above 100 cm-1, the linear behavior of the scattering rate exists, which yields a coupling constant ~ 0.5. More measurements with different dopi ng level samples and model independent analyzes are needed in order to ge t completed picture in this area. 6.1.2 Field Dependent Measurement The far infrared transmittance spectr a of different samples (YBCO/MgO, YBCO/Sapphire and YBCO/Si) were studied at 4.2 K at high magnetic field in the National High Magnetic Field Laboratory. One sample spectrum (YBCO/MgO) was analyzed by the two fluid model. All the superconductor samples (YBCO/MgO sample and YBCO/Sapphire) show very low transmittan ce in the far infrared region. This is because, at 4.2 K, imaginary part of conductivity ( 2) dominates the far infrared optical properties. The spectra also show fringes which is due to the multilayer reflection. Varying the magnetic field at constant temper ature (4-2 K) allows us to study the vortex dynamics in the high temperature superconduc tors. Currently, we do not see any field dependent features in transmittance spectra of YBCO films at 4.2 K within our measured spectrum range. This observati on suggests that the pair-br eaking effects could be too small to be seen in our frequency and field range. And the anisotropi c pairing effects in the high temperature superconductors might lead to the complexity of excitations inside a vortex core. We hope that this work will st imulate more completely experimental and theoretical work for understand ing the electrodynamics of cuprates in a high magnetic field. Future work can be done in higher temp eratures and higher fiel ds and, if possible, in the lower frequency range.

PAGE 157

143 6.2 Dielectric Materials The temperature dependence of the reflectance of cubic bismuth pyrochlores Bi3/2ZnTa3/2O7 (BZT), Bi3/2MgNb3/2O7 (BMN), Bi3/2MgTa3/2O7 (BMT) and Bi3/2Zn0.92Nb1.5O6.92 (BZN) has been investigated by in frared spectroscopy. Spectra were collected from 30 to 3300 cm-1 between 50 and 300 K and the optical constants were estimated by Kramers-Kronig analysis and clas sical dispersion theory. In addition, BZN was studied by terahertz techniques to lo wer frequencies. Infrared-active phonon modes have been assigned to specific bending and stretching vibrational modes. A previously unassigned infrared mode at ~850 cm-1 is discussed. A splitting of the B-O stretching phonon modes and O-B-O bending modes is assi gned to mixed cation occupancy. The temperature dependence of the phonon frequenc ies and the damping coefficients are consistent with a decrease of lattice consta nt and with orientati onal disorder at low temperatures. In the future, more temperature dependent terahertz measurement can be done to explore the properties of A site cation related phonon modes.

PAGE 158

144 APPENDIX TERAHERTZ MEASUREMENT OF YBCO FILMS The temperature dependent terahertz transmittance spectra of optimally doped YBa2Cu3O7, YBa2Cu3O6 and sapphire substrate are measured by the terahertz spectrometer TPT1000. Temperatures between 10 and 300 K are obtained in a Hanson flow cryostat with polyethylene windows. The samples are grown by the PLD method with thickness of the films about 600 . The dimension of the sample is 5mm by 5mm. The whole spectro meter is purged with the dry nitrogen gas in order to ge t rid of the water vapor influence. Figure A-1 (a), (b) and (c) shows the te mperature dependent transmittance spectra of YBa2Cu3O6/sapphire, YBa2Cu3O7/sapphire and sapphire subs trate respectively within the frequency range from 3 cm-1 to 80 cm-1. All the spectra show strong interference fringes due to multiple internal reflections. The transmittance of the YBa2Cu3O6/sapphire sample does not show significant change with in the measured temperature range. While, the transmittance of YBa2Cu3O7/sapphire shows significant decrease when the temperature drops from room temperature to 10 K. The sapphire substrate transmittance does not have significant change when the temperature was lowered from 300 K to 10 K.

PAGE 159

145 Figure A-1 The temperature depe ndent transmittance of the YBa2Cu3O6/sapphire (a), YBa2Cu3O7/sapphire (b), and sapphire (c).

PAGE 160

146 LIST OF REFERENCES 1. M. Fox Optical Properties of Solids, Oxford University Press Inc., New York, NY (2001). 2. E. Hecht Optics, Addison-Wesley Inc., 3rd edition, Boston, MA (1988). 3. F. Wooten Properties of Solids, A cademic Press, New York, NY (1972). 4. D. Jackson Classical Electrodynamics, 2nd edition, John W iley & Sons Inc., New York, NY (1975). 5. G. R. Fowles, Introduction to Modern Optics, Second Edition, Holt, Rinehart and Winston, Inc. New York, NY (1975). 6. M. Born and E. Wolf, Principle of Optics, 7th expanded edition, Cambridge University Press, New York, NY (1999). 7. M. Dressel and G. Gruner, Optical Properties of Electrons in Matter, Cambridge University Press, New York, NY (2002). 8. M. Tinkham, Physical Review 104, 845 (1956). 9. S. S. Mitra and S. Nudelman, editors, Farinfrared Properties of Solids. Plenum Press, New York, NY, (1970). 10. H. Happ and L. Genzel, Infrared Phys. 1, 39 (1961). 11. R. H. Norton and R. Beer, J. Opt. Soc. Am. 66, 259 (1976). 12. L. Mertz, Infrared Phys 7, 17 (1967). 13. P. Griffiths and J. Haseth, Fourier Transform Infrared Spectroscopy, John Wiley & Sons Inc., New York, NY, (1986). 14. C. D. Porter and D. B. Tanner, Int. J. Infrared and Millimeter wave 4, 273 (1983). 15. B. Bowie, P. Griffiths, Applied Spectroscopy 54, 1192 (2000). 16. D. B. Tanner, R. McCall, Appl. Opt. 23, 2363 (1984). 17. W. H. Knox, Optical Photon, News 3, 10 (1992).

PAGE 161

147 18. G. Gruner, Millimeter and Submilli meter Wave Spectroscopy of Solids 74, Springer, New York, NY (1998). 19. P. R. Smith, D. H. Auston, M. C. Nuss, Subpicosecond photoconducting dipole antennas, IEEE QE-24, 255 (1988). 20. M. Van Exter, D. R. Grischkowsky, Characterization of Optoelectronc Terahertz Beam System, IEEE Trans. MIT-38, 1684 (1990). 21. N. Katzenellenbogen, D. Grischkowsky, Appl. Phys. Lett. 58, 222 (1991). 22. B. B. Hu, J. T. Darrow, X. C. Zhang, D. H. Auston, Appl. Phys. Lett. 56, 886(1990). 23. D. You, R. R. Jones, P. H. Bucksb aum, D. R. Dylcaar, Optics Letter 18, 290 (1993). 24. B. B. Hu, E. A. de Souza, W. H. Knox, J. E. Cunningham, M. C. Nuss, A. V. Kuzenetsov, S. L. Chuang, Phys. Rev. Lett. 74, 1689 (1995). 25. P. R. Smith, D. H. Auston, M. C. Nuss, IEEE J. QE-24, 255 (1988). 26. F. E. Dpany, D. Grischkowsky, C. C. Chi, Appl. Phys. Lett. 50, 460 (1987). 27. G. Grruner, Millimeter and submillim eter Wave Spectroscopy of Solids, Springer Inc., New York (1998). 28. A. Pashkin, E. Buixaderas, P. Kuzel, M. Liang, C. Hu, I. Lin, Ferroelectrics 254, 113 (2001). 29. Technical Manual of High-Tran Cooling System, R. G.Hansen & Assciates, Santa Barbara California (1986). 30. H. Kamerlingh Onnes, Leiden Comm. 120b (1911). 31. K. Maki, Phys. Rev. Lett. 23, 1223 (1969). 32. G. Bednorz and K. A. Muller, Z. Physik 189, 1364 (1986). 33. W. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang, and C. W. Chu, Phys. Rev. Lett. 58, 908 (1987). 34. R. Beyers and T. M. Shaw, Sol. State Phys. 42, 135 (1989). 35. J. T. Market, Y. alichaouch, and M. B. Maple in Physical Properties of High Temperature Superconductors I, D. M. Ginsberg, editor, World Scientific, Farrer Road, Singapore (1989).

PAGE 162

148 36. M. Maeda, Y. Tanaka, M. Fukutomi, and A. Asano, Jpn. J. Appl. Phys. 27, L209 (1988). 37. Z. Z. Sheng, and A. M. Hermann, Nature 332, 55 (1988). 38. F. London and H. London, Z. Physik 96, 359 (1935). 39. V. L. Ginzburg and L. D. Landau, Soviet Phys. JETP USSR 20, 1064 (1950). 40. M. Tinkham Introduction to Superco nductivity, Krieger Publishing Co. Malabar, FL (1980). 41. G. Rickayzen Theory of Superconductiv ity, Inter. Science Publishers, New York, NY (1965). 42. C. M. Varma, P. B. Littlewood, S. Schmitt-Rink, E. Abrahams, and A. E. Ruckenstein, Phys. Rev. Lett. 63, 1996 (1989). 43. C. W. Chu, P. H. Hor, R. L. Me ng, L. Gao, Z. J. Huang, Science 235, 567 (1987). 44. C. W. Chu, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang and Y. Q. Wang, Phys. Rev. Lett. 58, 405 (1987). 45. R. M. Hazen, L. W. Finger, R. J. Angel, C. T. Prewitt, N. L. Ross, H. K. Mao, C. G. Hadidacos, P. H. Hor, A. C. Meng and C. W. Chu, Phys. Rev. B 35, 7238 (1987). 46. J. Bardeen, L. N. Cooper and J. R. Schrieffer, Phys. Rev. 108, 1175 (1957). 47. F. Gao, G. L. Carrr, C. Porter, D. B. Tanner, G. Willims, C. Hirschmug, B. Dutta, X. Wu, S. Etemad, Phys. Rev. B 54, 700 (1996). 48. G. A. Thomas, J. Orenstein, D. H. Ra pkine, M. Capizzi, A. J. Millis, R. N. Bhatt, L. F. Schneemeyer and J. V. Wasczczak, Phys. Rev. Lett. 61, 1313 (1988). 49. T. Timusk, S. L. Herr, K. Kamaras, C. D. Porter, D. B. Tanner, D. A. Bonn, J. D. Ganet, C. V. Stager, J. E. Greedan and M. Reedyk, Phys. Rev. B 38, 6683 (1988). 50. R. T. Collins, Z. Schlesinger, F. Holtzb erg, P. Chaudhari and C. Field, Phys. Rev. B 39, 6571 (1989). 51. J. Schutzmann, W. Ose, J. Keller, K. F. Renk, B. Roas, L. Schultz and G. Saemann-Ischenko, Europhys. Lett. 8, 679 (1989). 52. U. Holffmann Solid State Communication 70, 325 (1989).

PAGE 163

149 53. D. B. Romero, C. D. Porter, D. B. Ta nner, L. Forro, D. Mandrus, L. Mihaly, G. L. Carr, G. P. Williams, Phys. Rev. Lett. 68, 1590 (1992). 54. F. Gao, Temperature Dependence of Infr ared and Optical Properties of High Temperature Superconductors, Ph.D. Disse rtation, University of Florida, Gainesville, FL, (1999). 55. K. Kamaras, S. L. Herr, C. D. Porter, N. Tache, D. B. Tanner, S. Etemad, T. Venkatesan, E. Chase, A. Inam, X. D. Wu, M. S. Hegde and B. Dutta, Phys. Rev. Lett. 64, 84 (1990). 56. S. L. Cooper, G. A. Thomas, J. Oenstein, D. H. Rapkine, M. Capizzi, T. Timusk, A. J. Millis, L. F. Schneemey er and J. V. Waszczak, Phys. Rev. B 40, 11358 (1989). 57. J. Orenstein, G. A. Thomas, A. J. Millis, S. L. Cooper, D. H. Rapkine, T. Timusk, L. F. Schneemeyer and J. V. Waszczak, Phys. Rev. B 42, 6342 (1990). 58. M. A. Quijada, D. B. Tanner, R. J. Kelley, M. Onelion, H. Berger and G. Margaritondo, Phys. Rev. B 60, 14917 (1999). 59. H. Liu, G. Blumberg, M. Klein, P. Guptasarma, D. Hinks, Phys. Rev. Lett. 82, 3524 (1999). 60. A. Katz, S. Woods, E. Singly, T. Li, M. Xu, D. Hinks, R. Dynes, D. Basov, Phys. Rev. B 61, 5930 (2000). 61. D. Basov, S. Woods, A. Katz, E. Sing ley, R. Dynes, M. Xu, D. Hinks, C. Homes, M. Strongin, Science 283, 49 (1999). 62. G. Deutscher, A. F. Santander-Syro, N. Bontemps, Condensed Matter, (in press) 63. J. Hwang, T. Timusk, A. V. Puchkov, N. L. Wang, G. D. Gu, C. C. Homes, J. J. Tu, and H. Eisaki, Phys. Rev. B (in press). 64. J. Hauck, S. Denker, H. Hindriks, S. Ipta, and K. Mika, Z. Phys. B 84, 31 (1991) 65. M. R. Norman, C. Pepin, Rep. Prog. Phys. 66, 1547 (2003). 66. R. P. S. M. Lobo, N. Bontemps, D. Racah, Y. Dagan, G. Deutscher, Europhys. Lett. 55, 854 (2001). 67. P. W. Anderson, G. Baskaran, Z. Zou, T. Hsu, Phys. Rev. Lett. 58, 2790 (1987).

PAGE 164

150 68. F. Gao, J. W. Kruse, C. E. Platt, M. Feng, M. V. Klein, Appl. Phys. Lett. 63, 2274 (1993). 69. P. J. Hirschfeld, W. O. Putikka, D. J. Scalapino, Phys. Rev. B 50, 10250 (1994). 70. Z. X. Shen, D. S. Dessau, B. O. wells, D. M. King, W. E. Spicer, A. J. Arko, D. Marshall, L. W. Lombardo, A. Kap itulnik, P. Dickinson, S. Doniach, J. DiCarlo, A. G. Loeser, C. H. Park, Phys. Rev. Lett.70, 1553 (1993). 71. P. B. Littlewood and C. M. Varma, J. Appl. Phys. 69, 4979 (1991). 72. G. Hammerl, A. Schmehl, R. R. Schulz, B. Goetz, H. Bilefeldt, C. W. Schnelder, H. Hilgenkamp, and J. Mannhart, Nature 407, 162 (2000). 73. S. Leitenmeier, H. Bielefeldt, G. Ha mmerl, A. Schmehl, C. W. Schneider, and J. Mannhart, Ann. Phys. 11, 497 (2002). 74. C. H. Perry, B. N. Khanna and G. Rupprecht, Phys. Rev. 135, A408 (1964). 75. M. Cardona, Phys. Rev. 140, A651 (1965). 76. P. B. Allen, Phys. Rev. B 3, 305 (1971). 77. D. B. Tanner, D. B. Romero, K. Kamara s, G. L. Carr, L. Forro, D. Mandrus, L. Mihaly and G. P. Williams, in Electronic Structure and Mechanism for High Temperature Superconducting, edited by G. C. Vezolli et al. Plenum Press, New York (1991). 78. D. B. Tanner, T. Timusk, Optical Properties of High-Temperature Superconductors III, World Scientif ic, Farrer Road, Singapore (1992). 79. J. M. Chwalek, C. Uher, J. F. Whitaker, G. A. Mourou, J. Agostinelli and Lelental, Appl. Phys. Lett. 57, 1696 (1990). 80. Y. J. Uemura, A. Keren, L. P. Le, G. M. Luke, W. D. Wu, Y. Kubo, T. Manako, Y. Shimakawa, M. Subramanlan, J. L. Cobb, and J. T. Markert, Nature 364, 605 (1993). 81. E. Farber, G. Deutscher, B. Gorshunov, and M. Dressel, Europhysics Letters 67, 835 (2004) 82. Y. Fukuzumi, K. Mizuhashi, K. Takenaka, and S. Uchida, Phys. Rev. Lett. 76, 684 (1996). 83. C. P. Poole, H. A. Farach, R. J. Creswick, Superconductivity Academic Press Inc. San Diego, California (1995). 84. R. S. Thompson, Phys. Rev. B 1, 327 (1970).

PAGE 165

151 85. Y. Shimamoto, T. Takamasu, N. Miura, M. Natio, N. Kubota, and Y. Shiohara, Physica B 201, 266 (1994). 86. B. Parks, S. Spielman, J. Orenstein, D. T. Nemeth, F. Ludwig, J. Clarke, P.Merchant, and D. J. Lew, Phys. Rev. Lett. 74, 3265 (1995). 87. K.Karrai, E. Choi, F. Dunmore, S. Liu, H. Drew, Phys. Rev. Lett. 69, 152 (1992). 88. K. Karrai, E. Choi, S. Liu, X. Ying, Q. Li, T. Venkatasan, H. Dew, D. Fenner, Phys. Rev. Lett. 69, 355 (1992). 89. J. Eldridge, M. Dressel, D. Matz, B. Gross, and W. Hardy, Phys. Rev. B 52, 4462 (1995). 90. L. C. Brunel, S. G. Louie, G. Martin ez, S. Labdi, and H. Raffy, Phys. Rev. Lett. 66, 1346 (1991). 91. A. M. Gerrits, T. J. B. M. Janssen, A. Wittlin, N. Y. Chen, and P. J. M. Van Bentum, Physical C 235-240, 1114 (1994). 92. H. Liu, A. Zibold, D. B. Tanner, Y. Wang, M. Burns, K. Delin, M. Li, M. Wu, Solid State Communication 109, 7 (1999). 93. A. C. Wint, Search for an Infrared Electro-Optic Effect in Thin High Temperature Superconductor Films, Ph.D. Dissertation, University of Florida (2004). 94. H. K. Ng, Y. J. Wang, in: Z. Fisk et al. (Eds.) Proceedings of Physical Phenomena at High Magnetic Fields-II, World Scientific Press, Farrer Road, Singapore, 729 (1996). 95. C. Caroli, P. G. de Gennes, and J. Matricon, Phys. Rev. Lett. 9, 307 (1964). 96. V. Boychev, Far-Infrared Studies of Superconducting Thin Films and FabryPerot Resonators Made of Such Films, Ph.D. Dissertation, University of Florida (2002). 97. L. Kramer and W. Pesch, Z. Phys. 269, 59 (1974). 98. W. Pesch and L. Kramer, J. Low Temp. Phys. 15, 367 (1973). 99. J. Bardeen and M. J. Stephen, Phys. Rev. 140, A1197 (1965). 100. J. C. Nino, Ph. D. Thesis, The Pennsylvania State University, 2002. 101. A. W. Sleight, Inorg. Chem. 7, 1704 (1969).

PAGE 166

152 102. M. Lanagan, D. Anderson, A. Baker, J. Nino, S. Perini, C. A. Randall, T. R. Strout, T. Sogabe, and H. Youn, Proceedings of the International Symposium on Microelectronics 155 (2001). 103. G. I. Golovshchikova, V. A. Isupov, A. G. Tutov, I. E. Mylnikova, P. A. Nikitnia and O. I. Tulinova, Sov. Phys. Solid State 14, 2539 (1973). 104. G. Jeanne, G. Desgardin, and B. Raveau, Matt. Res. Bull. 9, 1321 (1974). 105. I. Levin, T. G. Amos, J. C. Nino, T. A. Vanderah, C. A. Randall, and M. T. Lanagan, J. Solid State Chem. 168, 69 (2002). 106. R. L. Withers, T. R. Welberry, A.-K. La rsson, Y. Liu, L. Noren, H. Rundlof, and F. J. Brink, J. Solid State Chem. 177, 231 (2004). 107. F. Brisse and O. Knop, Can. J. Chem. 48, 859 (1968). 108. R. A. McCauley, Journal of th e Optical Society of America 63, 721 (1973). 109. S. Kamba, V. Porokhonskyy, A. Pashkin, V. Bovtun, J. Petzelt, J. C. Nino, S. Trolier-McKinstry, M. T. Lanagan, and C. A. Randall, Phys. Rev. B 66, 054106 (2002). 110. J. C. Nino, M. T. Lanaguan and C. A. Randall, Appl. Phys. Lett. 81, 4404 (2002). 111. J. C. Nino, M. T. Lanagan, and C. A. Randall, J. Mater. Res. 16, 1460 (2001). 112. A. L. Hector and S. B. Wi ggin, J. Solid State Chem. 177, 139 (2004). 113. M. Avdeev, M. K. Hass, J. D. Jorgensen, R. J. Cava, J. Solid State Chem. 169, 24 (2002). 114. R. D. Shannon, Acta Crystallogr. Sect. A 32, 751 (1976). 115. B. J. Kennedy, Mater. Res. Bull. 32, 479 (1997). 116. B. E. Scheetz, W. B. White, Optical Engineering 22, 302 (1983). 117. R. J. Betsch and W. B. White, Spectrochim. Acta. 34A, 505 (1978).

PAGE 167

153 BIOGRAPHICAL SKETCH I was born in the southwest part of China. After completing my high school education, I went to the s outheast part of China and started my undergraduate study in Nanjing University. In 1997, I got my Bachel or of Science degree. I enter Professor An Hu’s group and studied the metal multilayer, magnetic junction device and colossal magnetic materials (CMR) for my graduate de gree. In 2000, I got my Master of Science at Nanjing University. Then I decided to study aboard. I came to the University of Florida in August 2000. I joined Professor Tanner’s research group as a research assistant. My research included the optical properties of high temperature su perconductor, electronic dielectric materials, energetic materials and polymer material s and devices. I focused on studying the terahertz and optical properties.


xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID E20110330_AAAAMX INGEST_TIME 2011-03-30T22:01:35Z PACKAGE UFE0012986_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC
FILES
FILE SIZE 64282 DFID F20110330_AACHWS ORIGIN DEPOSITOR PATH chen_m_Page_063.jpg GLOBAL false PRESERVATION BIT MESSAGE_DIGEST ALGORITHM MD5
8e3a13ca03026572d3fed623ef3717e0
SHA-1
b3a2574a88652e2fc36f99db92d775332b06b98a
1053954 F20110330_AACGTQ chen_m_Page_069.tif
ea8c3e47afcc6a0d1b70d360b1ae1762
9ef92d6718b9a33653217e8d9bd322a3709bc4d1
34932 F20110330_AACGUE chen_m_Page_053.QC.jpg
f5ed0b8678bf6ffbc070fdd9210ce6aa
9d0b5f1545ffe02316c9fa2132460284aa69cc7a
33566 F20110330_AACHWT chen_m_Page_065.QC.jpg
0ac89bb7786a511ea7a4b7c5fbb4c3e0
64f5b64512fb47472eb617a1363336c0102f473c
26296 F20110330_AACGTR chen_m_Page_039.QC.jpg
9a95cc0618378516d0d4898e1d9580af
53e1889fd4e2ee515bb36b0f47bae426f5c9dbb4
F20110330_AACGUF chen_m_Page_030.tif
6a1ba076f5abc2fa71c2fecb464ff9eb
cf9ad31e18e3e7bf9973f36bdf6af83a30ce3cde
94843 F20110330_AACHWU chen_m_Page_066.jpg
de53264fce779e7b7cfacb8485cf4f98
5d5e4b1c8744015291371d4bf4e2989015bee117
25271604 F20110330_AACGTS chen_m_Page_092.tif
0187bba4fac3961cb5adda55fb5739b1
0a161b111e822d1d2727c6b93802d7a370759b5a
1426 F20110330_AACHAA chen_m_Page_007.txt
04d71dda9c7016fff71578989448c5fb
f8a04e57cd3474dfc6dd15d6856843e10ac6756a
109982 F20110330_AACGUG chen_m_Page_128.jp2
0e5cae766f5849d2a459ace9f7e55c18
b65670a6e73944965343f4735bc47a2fb65ed582
100728 F20110330_AACHWV chen_m_Page_068.jpg
b8fcc793ff16b81c4dc2c01e37ad70c5
9f46cf4b28a69392c6db2feac67305111e9d1b55
54466 F20110330_AACGTT chen_m_Page_096.jpg
cca92c342260db7c73c10fe55b9c0eaf
e465f596161c152617ee38e34796a5a4d3a46938
48613 F20110330_AACHAB chen_m_Page_054.pro
9caa80591f68c590c9aa17479cef076a
54b023408a3c38146ad5870e9dbc07d8d9da791b
30566 F20110330_AACGUH chen_m_Page_049.QC.jpg
a190e08c2ecc1caf2baba6b345ba74b6
654649fe6abb0716d6f54d59687940c2106c9d7b
98395 F20110330_AACHAC chen_m_Page_162.jpg
4f1c9a1c1af5c9b30cb3603998f7e0cb
795eb6a812587d02abb7c3bf96fd96e3c723027c
F20110330_AACGUI chen_m_Page_040.tif
55233dc773d2ea3b36d680dae53dfddc
4b03e7ab73ff20a91d93a13ba7d37e8fc7e7a2a2
101718 F20110330_AACHWW chen_m_Page_072.jpg
798ddf24235df155b4647b909b375af6
08851ba22553689a72a6892e2f1e158add15a9a8
11540 F20110330_AACGTU chen_m_Page_145.pro
0c80e3a6e90f0f18921c23de8b57e529
508d52ae161cd38721157df92033c97c42672dd6
F20110330_AACHAD chen_m_Page_060.tif
3616ab98464555a859f0fe82610b6c8e
30eca7cc574af5e10d47d3f86b96ff8786d2bb73
23613 F20110330_AACGUJ chen_m_Page_019.pro
a14e8c21ed541f064c9e4ac1ab3ac238
52b7db3b3a1af45f6aa3ce6273785c6d39a7d4b3
33157 F20110330_AACHWX chen_m_Page_072.QC.jpg
9e5fc6158ac64b71338455ef31e007a5
aaa239c176cc45198f746ab4ee37860aa3ed05cb
6037 F20110330_AACGTV chen_m_Page_013thm.jpg
529a24d95930c2c5426d2a33a4ebfe6f
68904ee828fdba2946e0c6addfc14636194b5be2
103681 F20110330_AACHAE chen_m_Page_164.jp2
452e5b52d03091756baf54a7538a2e17
17dcccbe708f3eba59ce291afc228aed32477a3f
3887 F20110330_AACGUK chen_m_Page_057thm.jpg
ba789678efaff5347ba6638fb99cec42
3efd26ed15c09d4b5d2dd524547c8f4970a9c524
92491 F20110330_AACHWY chen_m_Page_073.jpg
9749615f687c226e07f18415d903b714
0f8e3b6b4c2eb49e8063c8a4066f2f2c4b7d0e5b
17819 F20110330_AACGTW chen_m_Page_122.pro
802fe1fcfe96fe764a9127fb1c9bc063
1fd2a42164c0a9b64af04184611fbcd0a1c25296
5200 F20110330_AACHAF chen_m_Page_096thm.jpg
4ec80d21827eb6c138a15533e307c22d
f0578f540ca2745220b28d6c6802e254c2cbcb0f
359739 F20110330_AACGUL chen_m_Page_106.jp2
f3c3bda1733ab87a70c1bb8fbda2c18e
56bef4f31d1acfd9311e50c8d49e5179272fc34c
69869 F20110330_AACHWZ chen_m_Page_074.jpg
7bc33a40497bfe2bc3608413a4eba892
d62da08e6d4d1ce3316003d73dbfb0e65bc1783a
7712 F20110330_AACGTX chen_m_Page_050thm.jpg
5c4e10efdef9728d780ca95d6e53f9f1
cfeaa02d0015468d94629e51c70db1311565a846
6861 F20110330_AACHAG chen_m_Page_087thm.jpg
25b0877e67b2b56c0b51c665a770d3de
2aca76543ec1429551e5c5d360fed24972a2dfe2
604 F20110330_AACGVA chen_m_Page_002thm.jpg
a3ab4fb03ba602f4b473673891a3a7f3
018767bcde3e4ece6c248919025759d2216eb631
9759 F20110330_AACGUM chen_m_Page_096.pro
4c24084e451cf9c9191f55279a991677
61c1d36d42fad2aa7d68de85403669b849071bb3
41285 F20110330_AACGTY chen_m_Page_048.pro
1c01ee8f890cd4abd7b21d14bd6b8c79
89359e0a4b061135217b36304ae0a27af0c47b91
50821 F20110330_AACHAH chen_m_Page_067.pro
5b8209148d379d3801fcf6662c3ac5cc
24b3d1ed03740489570239eb9e69c00183cd4467
63869 F20110330_AACGVB chen_m_Page_010.pro
46f657f60410c38ab1f4077baf1a729b
4d780783a4fd4490b07f7b4f1b95a93c568ea164
552 F20110330_AACGUN chen_m_Page_101.txt
239d9e8a7897e7a4f81c7bd9091080fe
262426c5096ddadfeff83e6075e70c2517b9041c
8307 F20110330_AACGTZ chen_m_Page_084thm.jpg
1e372d1e83f023e411e7e9bf839b7de1
db74693bdc1c39018d0fb3cb1e1482d6346fa497
8356 F20110330_AACHAI chen_m_Page_065thm.jpg
89a11a5116672fe0ebaccf293deff1f8
6b096601ff47469c0190986cc3fe981f7b846d83
44506 F20110330_AACGVC chen_m_Page_098.jpg
c61e33425177be1132834fa85c9ca301
730534510f6df9f8b13061154b3af8eaca7c07bd
2984 F20110330_AACGUO chen_m_Page_144.pro
c9c60bbd0b2d8b56af3a6345a89093cd
447e36bdc114f8f393021a1faf4f33b0b38dd3d1
1149 F20110330_AACHAJ chen_m_Page_103.txt
0916acea072614c5ad427b89e514208d
23c7a75dcc1cb1701c972c77be89e041c3a10cea
12450 F20110330_AACGVD chen_m_Page_107.pro
db97f373506e1bcf13090776e8e13e04
e28ee9c3291f79c0873a95a64194f606de29344b
8816 F20110330_AACGUP chen_m_Page_057.pro
361a852d05f6b0e3a59dd95ff86ee488
d584702564f3f32de3896948848124882a0b7e4b
16438 F20110330_AACHAK chen_m_Page_167.QC.jpg
3b8192cfb43b062e4aa48a82a07e1b6c
afb78ecbb6e01bf2b17ec261ed1aca79e92e9ec3
375158 F20110330_AACGVE chen_m_Page_151.jp2
0c07e865d7013a1858d4801692090be8
8c30d11035d497ddd1b469f9bd94eb3c6b1b6023
2878 F20110330_AACGUQ chen_m_Page_058thm.jpg
f0efb3764f5789b8983ada4bba9285aa
de96ed63d4eaa0836b57bac1dc14ec0ca725bd1e
F20110330_AACHAL chen_m_Page_051.tif
bc2dcfb0e76a9087ceebf1877aced23b
501ecc03e63d438b80a49170ea97cffa5d120828
27109 F20110330_AACGVF chen_m_Page_125.QC.jpg
042225597969590ca550e454e0d52483
4f8e9f2ef4669e82eb1eeae0fd8aebae2fdef1d0
1715 F20110330_AACGUR chen_m_Page_024.txt
7b5a9f1cd872be3971009869e091be76
40cdc4a3aa9868c86048b9bd5476a6aa2c9282c1
49753 F20110330_AACHBA chen_m_Page_167.jpg
9e9058c95e5156bc2b9fed3150d5eaf4
a2a85eb197345a94443af4f67297366b7783acde
3324 F20110330_AACHAM chen_m_Page_135.txt
3b14fa7a7e5375fd148518cadbbb383e
243ab58f822eea92bbaac942c2ba97f450902af0
7647 F20110330_AACGVG chen_m_Page_049thm.jpg
dad4482f505a15e65b43c530de4d2e1b
66372ac1d8f4c9eba4bcbee0653203f046aa9b40
66603 F20110330_AACGUS chen_m_Page_059.jpg
ce927a6dc2f5d620e9b1039d1e54966c
b8bb583896d34859f9671558ad5b5c0dedfc0f30
101354 F20110330_AACHAN chen_m_Page_163.jpg
27cdb02c3ab8751674d7ae84493cfe8c
695c2238335ceab943e6a20bdc964385e25637e0
706 F20110330_AACGVH chen_m_Page_145.txt
bee9359963c0f5c541afaa5e3c484949
4e2e78e10cc07739876d69fe3a204de531d7cfbc
1931 F20110330_AACGUT chen_m_Page_047.txt
2b1dc2951825d14fe7f1b1102c41a565
f638ebc14f235001dda08e88b370bd7c33adc0f2
3247 F20110330_AACHBB chen_m_Page_134.txt
66dc27dcc2b560a849333ddd7f9aed67
28e98787b369ef39dc247c6eafd0d2f6518d2dcd
92598 F20110330_AACHAO chen_m_Page_062.jpg
dd569dea7141c8781d439908897c78e5
04995d12554cbb4d22acd26f73046492e64b0bde
75097 F20110330_AACGVI chen_m_Page_074.jp2
66da4499d7e72b4d68a75644dcd88b8c
009ca60fbc8aef9dae2121cdbaac294803e58c25
24199 F20110330_AACGUU chen_m_Page_139.QC.jpg
78935d701a55f207df953f407e95b61a
bd7b5fb6bc2d05fe25f7a194b43e5b56021ceb24
F20110330_AACHBC chen_m_Page_091.tif
eefef66e51cda6024b063ef06c676ceb
97debca6843f78d39f4db5371f69cd91e51271f7
40858 F20110330_AACHAP chen_m_Page_037.pro
276e49b16bf744149a9aa73c5cab1783
4e551ec02d9d5af9b7562b5259255f9f5c93b5f4
550 F20110330_AACGVJ chen_m_Page_097.txt
756cff55fd6d825682debdada9a6de07
2313d83d8e4596dd8cd07133feb27adfb69b9a2e
F20110330_AACHBD chen_m_Page_129.tif
8e0389ea53fc34c592af254cb39e748a
e360a6310b3c3d3050fe6e0663bf7a83e6cb3cf5
12668 F20110330_AACHAQ chen_m_Page_151.QC.jpg
bec948629d94f2f6a0cc1cff7e2242fb
b114f09c4062f205c130c6690e9a07da5917590f
50443 F20110330_AACGVK chen_m_Page_070.pro
e9fe3aad46eccb1267e60bf29814f10f
445f717cb8b3919b5138733e4fee034d92fdd3a7
104240 F20110330_AACGUV chen_m_Page_047.jp2
bc6d5a0c75bcf55eaf973ebbff0e26b4
fea86a391d1dbc95f670931aeca4c1779f733d6f
97816 F20110330_AACHBE chen_m_Page_073.jp2
e183abe1fae4293e701c9bc75d9a3173
550c5c0a482c310abe4a19bf25902351155d8f44
5829 F20110330_AACHAR chen_m_Page_080thm.jpg
bae23915f67252d132b69e459e1a750b
29e2f4e5cc03b4666e2202674a8372e714001102
1543 F20110330_AACGVL chen_m_Page_080.txt
7a28aecd82f0d625adf789e7d73bd591
60dd80d692c19252453b23507cc7144d32e1d788
47083 F20110330_AACGUW chen_m_Page_042.pro
d7772858ffa889062154b999b70654d6
21db25e1c1c43f17a342c2fa925e8b2760bbf3ed
F20110330_AACHBF chen_m_Page_152.tif
6a59b9e7bec935abccb0acf87bb9dfa0
13af1b27a1e7ec5cb4f27dd79fc02e8118180f20
35023 F20110330_AACGWA chen_m_Page_023.pro
5631dce7cad54e26497e0c9484a07844
35186fe909cb84686daf037fd2d1ec70011319aa
37587 F20110330_AACHAS chen_m_Page_104.jpg
3c3b73e210ffd96b9f764986ed356ff4
e3f18a4fd41d936c7ef2a375d00b416a62026dfc
35704 F20110330_AACGVM chen_m_Page_134.QC.jpg
a662313f5772a74dc9b083c6cf260b83
5364420568e87d3e85cdbc7c7491945f19701a31
111368 F20110330_AACGUX chen_m_Page_082.jpg
896ce2184e743fd8c5e72c57c0c9019b
c33181fb8caed9c99a49ad39b35c3094be70dc66
F20110330_AACHBG chen_m_Page_105.tif
d70114f49faa54a2ae674acfd5c84327
d689ff889d4b6012dd807a0f552db76e1e9346af
96709 F20110330_AACGWB chen_m_Page_162.jp2
085c4ce3eada938334c81945bda478f5
79221ff67bc8a97db6641c6a1f0906849b820dec
F20110330_AACHAT chen_m_Page_039.tif
0dcc871ecf2f862bc6e6b0efbd40d0b5
0cb5b140588f8f18483059f4672f6289af515e32
100520 F20110330_AACGVN chen_m_Page_156.jp2
69b0193f2b1eb192d19fa5e40b009755
65aeb985e44b74e9104f148cd8bc7f669bc68ad8
3332 F20110330_AACGUY chen_m_Page_055thm.jpg
af4f07861bcad02e3318370772f7c9c4
052d38272a69abd46d0833c207e9c78498d8c61b
2056 F20110330_AACHBH chen_m_Page_049.txt
5cd3ac3656024d03aafcb3d7a3f7f493
bd3459debc425fb9181d974f17c281b7fb0f9137
93997 F20110330_AACGWC chen_m_Page_130.jpg
f1895dec092bd76f1c6d18b3981642c4
30a051771d8ce54bdf02517b0499b7ae44b236bd
34490 F20110330_AACHAU chen_m_Page_076.QC.jpg
461cac508affea1b42b31edbc4ab95f1
b27560b337138cca13a1805daa6c5957cc3f6f1f
F20110330_AACGVO chen_m_Page_162.tif
111fbd5301a6e9b74091af7dfe47a1b5
65103bed88d9dbc126e1e9b5ca63b28770b01558
27388 F20110330_AACGUZ chen_m_Page_081.QC.jpg
b15f48d0aa9c41c7954c51dd958bbdb2
f6dcb56f1388593de0ce924f40309ab7e1253eaf
28597 F20110330_AACHBI chen_m_Page_003.QC.jpg
710f8c7d64482627fb2881ea1b4845dc
96280450122a5a38949375116d918b8cdfd2baee
33326 F20110330_AACGWD chen_m_Page_152.jpg
ff8719bc60e17c318dbf8fd3ae9a31c8
173dce35284a6b3dd76b88abd2aa7aba49612249
248 F20110330_AACHAV chen_m_Page_123.txt
c234f1f3b094b0996ef9fcc5cd046460
568e31e9cd6090c23e1ec05649ea6e0db70afacc
24152 F20110330_AACGVP chen_m_Page_014.QC.jpg
8bfbdb4d9a1b2496ca3e77b66b3d5047
0521f542419be5d175bfa7d67449f1c76a3109db
100910 F20110330_AACHBJ chen_m_Page_109.jpg
2a5023fb0f7e0cf79941cf9f3a2dd0c1
351e734e2f0ab28253a0b5e5be57d0a7cce46524
487297 F20110330_AACGWE chen_m_Page_150.jp2
d9a93baa8597b427a0e771b75a34fcf4
e7d2fd9044d3b1d7d2c5447aec9674d6acb976cd
52504 F20110330_AACHAW chen_m_Page_082.pro
2f7d17583bd5102407c01f0c8e284b8d
e3024d2145ed804d55d9633911d78474674503c7
23863 F20110330_AACGVQ chen_m_Page_122.QC.jpg
c9227d15df37a4dc7c6d98cdd014fc4d
a2f730089c85b207fe6fb64afa926f92703da5c5
103208 F20110330_AACHBK chen_m_Page_078.jpg
539d6738a30f823640832c43a3b17d95
bc0b472c42a97fc1069ddca6b249d712c6629cc2
36290 F20110330_AACGWF chen_m_Page_120.QC.jpg
c9db6252df5daa1be91c28bb29ad97b2
0dd3dd25460e758cde8fa22cad6add15277bd85e
485611 F20110330_AACHAX chen_m_Page_148.jp2
80b3630ca5a5ae120812f84e2174d105
658d8c3a1dbd33ccb1c4731dfd6ce685b8376a52
48922 F20110330_AACGVR chen_m_Page_145.jpg
3e2bbda084d2b15d7032524c189064ff
bb4e5b654c72ef02413d90e512924c791f11d673
F20110330_AACHCA chen_m_Page_115.tif
57a7d7499086dece333207e7eff00725
1ea05d0ef91c4b72dddddfb1efe3e1b7ea611374
308 F20110330_AACHBL chen_m_Page_100.txt
e2c69fe1b6b0ae67fb2aa8aa1071fbd8
b77dc6182ab6dd96568e3d99cde370c862ec6415
106867 F20110330_AACGWG chen_m_Page_051.jp2
38117aaaaa92cd9676c34f91756adcdf
478c899c9cb96f46fbb2b82ba162b772642f5b8e
16849 F20110330_AACHAY chen_m_Page_111.QC.jpg
926212b314acc30bab8b26d6b0ed061b
ad1c29b225b6809a715628793cc6658b2a4727a3
4472 F20110330_AACGVS chen_m_Page_006.txt
69439c2ebcb56118058b17928aa0c051
b3be0b6fcbdfe79270f72f8f2abdf03bb17fb90c
82138 F20110330_AACHCB chen_m_Page_108.jp2
747ad18e25ec3b62ab4d601a72cdbb67
3ab08bb064375777e9b3fad3ccde0e54b43baf4c
47857 F20110330_AACHBM chen_m_Page_129.pro
4c2e0640f22e79cc0e54bce320743772
e398ea3fbff7220514932d3f8524d45b4bffc3f2
26366 F20110330_AACGWH chen_m_Page_024.QC.jpg
4bab2e746fbde4bda966434a5261526d
b53a66f58b6ffd905d807842f2810ebfe9db9cb1
568 F20110330_AACHAZ chen_m_Page_055.txt
10d38ac4f8833704338db30d105d8051
3afba506f8bce23059bf2729d078e2693f358863
8131 F20110330_AACGVT chen_m_Page_138thm.jpg
2f506e6d41ec445516a92d92b8ae9c74
f84ace4b0ef09eb1b058fd34156374a59162d205
108033 F20110330_AACHBN chen_m_Page_053.jpg
1a476befb8bb29dc2de26073c9d87b3b
5ed8cbf224be5bcc446bdd3f8f51d8ce5b6e666f
98235 F20110330_AACGWI chen_m_Page_071.jpg
c37c85666643707c766735ada8545526
4d41fdd473e470ff24a608d83b998b9f29643a19
102039 F20110330_AACGVU chen_m_Page_066.jp2
5d26f2107f8fbe0316b7ea44fb249f95
a0dd6abc7710d9713c72896f4dc79a14676fb490
75317 F20110330_AACHCC chen_m_Page_158.jp2
1b4a85ee3b45b05e8faf35a4acfbfed9
e3b00f7a81b06e9f7ddbd8a960e1d94f09588f36
F20110330_AACHBO chen_m_Page_023.tif
c1b643dc6fc6670e4e854d12e76214c5
9b20a031fc13218a9cb0b3355f5fb408ca744a28
F20110330_AACGWJ chen_m_Page_065.tif
5d32fa7634386efe9b6538ecc73fceb9
3784cf8e27bb2d851849b014c2f4c64c468a99c6
F20110330_AACGVV chen_m_Page_076.tif
89c781243bd5356090e2b850cb8aea8b
42bb8831d4111465e56b69c2bdd98db8f4643017
44226 F20110330_AACHCD chen_m_Page_094.jpg
423a5b58c2ba19a87ade7c8eb3d1d813
9fd60b29276c31d7ca7a733bf7e8e5443232dbff
7737 F20110330_AACHBP chen_m_Page_071thm.jpg
5d3d49c278dad54dd1c9bb85fef8a268
c5630a51c8e06d61dd01bdca89d343aa113530ce
34943 F20110330_AACHCE chen_m_Page_115.QC.jpg
9287a991ef9b56a7cfa5c8458e3d5d8e
04bea4e5dd27febb8ce4f42f76cd66505b59cd2d
38388 F20110330_AACHBQ chen_m_Page_160.pro
512798e699d0b9cbf36a92aee5ca31f9
be298e21fbf1d038b80edd5026523f87c9f0b4ba
107980 F20110330_AACGWK chen_m_Page_046.jp2
b46352cc09fb0128dd7b6cfcbe4dc98d
878b1967b725aa680072fb2ddef5672b254029a8
108671 F20110330_AACGVW chen_m_Page_052.jp2
897b5ed743a7117780b2d34742cbde83
5bd856e24ca3ba38239bb182be7cf9e81b0c1fbf
27988 F20110330_AACHCF chen_m_Page_126.QC.jpg
4203620d3c0eefeb42c8f576f2483608
41fdcc997cc5f8f7b8e4295d09d12852a7594ee0
683481 F20110330_AACHBR chen_m_Page_096.jp2
2286eeaa11931e30b1d1be75398277ff
e65b4c392fc413058aeb94bd4c25f59ceeb92b23
46388 F20110330_AACGWL chen_m_Page_073.pro
e046731316bb9ccc0ca21d371f051677
8eb4e99a76100bd98d011004c4496a48612cf9ea
99274 F20110330_AACGVX chen_m_Page_138.jpg
666898ec7a27170e5521192c7bcd9531
23738774df5c5626fd28cc952e333bfb4b983bd9
36687 F20110330_AACHCG chen_m_Page_101.jpg
fbc88def4b295c25a91c69b097b1e145
df3a6216804d13d602be9bb41b434a77b533dfcd
27301 F20110330_AACGXA chen_m_Page_092.jpg
fc6b4c585025b75105508915fd30b325
2ca6e56c89534061ddfa98551ddd1dc63477f044
7955 F20110330_AACHBS chen_m_Page_042thm.jpg
4943b1201f3311cb4381fc93e5302904
7b3710d7d06039589e4b4ba435437628415a89db
43481 F20110330_AACGWM chen_m_Page_085.pro
e0d626ab973dd47a31c7bbe10fdd1830
ea108483af12057405731fd14d4734734113cf17
69947 F20110330_AACGVY chen_m_Page_029.jpg
414ff8ceec829434665bb633f34539d9
190c5518a234637cb7d2aa586fea8b8e52460ab5
F20110330_AACHCH chen_m_Page_067.tif
3407778b1387db26c799ebdd8f37ac48
f1bb8cdc2ce6cd0af6d2e85bc4d7efb54027ac98
2130 F20110330_AACGXB chen_m_Page_164.txt
7cd46fffb33c9bd6b306fae3fc7d7ce5
42db4eda117d7a0f8540bf0e8076144510efdce9
102087 F20110330_AACHBT chen_m_Page_131.jp2
0a69be9d95ef0b3dfd2992bf46d6b71c
7ca59c8c27c1b92e9b3d4f9940d3ba9d7271b58a
F20110330_AACGWN chen_m_Page_001.tif
c5876eff6e7bb9e06b94ad106ffe45b4
7b4047aa2e066bf049e5395da2906c65936a4ba3
611 F20110330_AACGVZ chen_m_Page_098.txt
dd07e2505188fe0da05a23c21176b7c0
969b78d828a82973703cf48020df141704a93e22
8279 F20110330_AACHCI chen_m_Page_067thm.jpg
e5f6d0c96405a3ae35f957a386e5354c
a399b140c84bd2d99e8b9bc2c050463d9dd783bc
120553 F20110330_AACGXC chen_m_Page_010.jpg
90c9d8893588b5b4ae2dc50fe6c127be
9b6e39ce245d4792683df4980750676842a3ebeb
84842 F20110330_AACHBU chen_m_Page_037.jp2
87a88f4c2706f67f56cd2984cd33af1d
ca552f5c6ff4b785ca9d05b0dc456b3e25569ce0
14571 F20110330_AACGWO chen_m_Page_019.QC.jpg
81c17977ac0b2b88f744cf11f2d95291
fed4fbd2010a024bac6412d0e2b678fc894b2c80
3665 F20110330_AACHCJ chen_m_Page_009thm.jpg
21115e675ab735a762b5eebded1cc5e8
8727211b5c340cd33b60db9fb840a4db568f0be1
32482 F20110330_AACGXD chen_m_Page_071.QC.jpg
001b8c6f38b9af958667bb4eea61f4c4
0188ff4cfe06c16681fe51cc43fb6b650b216a6f
21695 F20110330_AACHBV chen_m_Page_035.jpg
98dfc7c330d4dc2c13cc3376d9f85f97
b3026d9224d0031594ea09c440dc51fdc0106991
101221 F20110330_AACGWP chen_m_Page_052.jpg
b8d5388ab8b47d64439bbab20b0258b9
810db1e54cc27cc59096edc92b0a5f4b695d2195
2000 F20110330_AACHCK chen_m_Page_067.txt
1d2dbd968d2541354d0dcf99ed5aa4cb
5050bb2d2cbb67329ee7598025eb76917a7c0b4d
107327 F20110330_AACGXE chen_m_Page_128.jpg
5de29aae2ace578778f78fed137896d0
59183f795824c05ab7a35a4d651e7c5526de7dc1
18399 F20110330_AACHBW chen_m_Page_064.QC.jpg
06d1ea202007115dab6b8e0b4ccae848
4b75b72b94af55f6eda1287eb78cafa131f03169
F20110330_AACGWQ chen_m_Page_108.tif
6684a3709fb1cc27b06870b5e7241a90
c90dbd4d4e14e3c73d3d09dce8377cf47864c3cd
30831 F20110330_AACHDA chen_m_Page_163.QC.jpg
66f730f2ea00c08b773d32bbdd9e9362
c4956f47ab26a34f7a5479abe1fbb10f0a8ec126
F20110330_AACHCL chen_m_Page_143thm.jpg
15c9010f71ffb79e7462dcf8979cbf6b
f98159f6343a9bea5ce69bc1aa341a7d42e30eb7
9263 F20110330_AACGXF chen_m_Page_058.QC.jpg
28ec03a018fb49bf69f8db3c7944e5b2
8987c8c0b0ea7c72493fb7c35c86094287bb807a
30680 F20110330_AACHBX chen_m_Page_030.pro
7fcd293dab5b5a5548807c1f36e2653c
54e689c1cbc7909dbeb7249df4415384105f68c6
4917 F20110330_AACGWR chen_m_Page_145thm.jpg
e2a594eb0a0a50b6703db89f255ce2ac
9b193e87a18ff23c08233fbce397416bf755de5d
4507 F20110330_AACHDB chen_m_Page_154thm.jpg
65741d8b63abce06db41c95234db20cd
514d18d59afcf8189dec5cbe4dd54a661a44c933
24722 F20110330_AACHCM chen_m_Page_041.QC.jpg
23f2a53b4f19dd1da34750f2fdeb625c
8e4453292b8ba1f574cf216ff9820660cffbb408
50184 F20110330_AACGXG chen_m_Page_127.pro
53efe3ebf0faeaed5b0c54c849d77514
16f4c199f4758230466392ad271a9a41499eced9
F20110330_AACHBY chen_m_Page_055.tif
8973efe383a4bf04e6f00b2a9339892d
7c1c08113355865f491ce96a86ee80a272182fcc
137825 F20110330_AACGWS chen_m_Page_153.jp2
24547ceb98c6e71cf10fa09e7b5cd672
931eeb26abb0fbd2e7cbbd1a12669357035240f8
51921 F20110330_AACHDC chen_m_Page_128.pro
9e247c528ab0812bc99c0c7fae47f52e
a2b7065c5af3b8b4f5a1a1d0138624f2f14d1ba8
103708 F20110330_AACHCN chen_m_Page_065.jpg
25e8dcc73e8f230999eb9d43ba05aea7
1ff77d38e16e2b33abeb90af8dbb45b012890b9f
11138 F20110330_AACGXH chen_m_Page_056.pro
18799cbd3585627ff440588f429d8eb0
f2b3304d57797c7d11e6a88a6e9dcf2eb1b8934c
64716 F20110330_AACHBZ chen_m_Page_030.jp2
48296d2acc95dc07dd8ac14dd6b97c3d
2493e7588d1eaf52308df6a90e9d182dc65bcace
2502 F20110330_AACGWT chen_m_Page_146.pro
5a2f38e7de941b0983914158e21ff61c
173a4383d4a600ed0f87b0654c84e13a053b395c
86767 F20110330_AACHCO chen_m_Page_166.jpg
490d24ae413f0361ada021ffe77633b7
08f2e1fb807824fede49787d2ab0828688910d5a
74664 F20110330_AACGXI chen_m_Page_011.pro
7c3a3181ece859f081c1a5488aecc600
5bda41cf6e85689f7e278f70d767ab354c8992d7
74239 F20110330_AACGWU chen_m_Page_013.jpg
d107a7ff5bff430a2497a68d5228def1
46ce78360a76ef1e0970a4668c1a7505c6ff4e32
6239 F20110330_AACHDD chen_m_Page_014thm.jpg
1ef1e02d8421515abd2e883889828dcc
b6dce382735ccff9fc17797dc47d1fe30a5c404a
5504 F20110330_AACHCP chen_m_Page_032thm.jpg
91a9d09e36754f2464bec4f1bcbcabfb
ca8fb0df30129e1189b8c5e3b09ec4673192162f
109456 F20110330_AACGXJ chen_m_Page_116.jp2
66fc10272e6bc268fba31ecf239f63ed
95dd170feac3a5432a7acbc1ea0525e05556b6e0
47459 F20110330_AACGWV chen_m_Page_134.pro
d8005a15b78f2c5777f69aaae9c05694
988eb78a84f78fbe551241b6fe2889686f9aafbe
7511 F20110330_AACHDE chen_m_Page_086thm.jpg
cdbb8b825d2b948fb55da6b75f02bf32
3c7beef8a7943989e5634743df368361fa6c6d95
20942 F20110330_AACHCQ chen_m_Page_063.QC.jpg
119755edb5b337ad4dde6f189269b270
c58462ade697f144a36d12136e42b71006946459
8008 F20110330_AACGXK chen_m_Page_119thm.jpg
0f1b9c381e54d928394cf22fe1d6ee18
e53698ef2d1c6aadb93d994ba267f41291ee419f
290127 F20110330_AACGWW chen_m_Page_104.jp2
d536e1cbce046a6ab00cab4f40f147e2
0d5ddc18aa17fb2966d4f079d2eefc09241d0111
47975 F20110330_AACHDF chen_m_Page_162.pro
1ffbd4b037bcb2f4887559e33ad65384
c9f0aaa76b01ee852837d4a45bc1c5f6f410c35c
75145 F20110330_AACHCR chen_m_Page_039.jpg
b2f8f1f89965263ecd396f00bc29a307
b84a81d52583b4c7b566e74bd0061ab8be3a4325
1762 F20110330_AACGXL chen_m_Page_126.txt
0490e8a5e0b44bef2d8385781f82a3d5
11dfe70508a243cbf06b6370efcf148394802051
960 F20110330_AACHDG chen_m_Page_102.txt
34b6482a92216323b29e1c64f046e09b
1a70c76e9ef77858183fe78431d51673bb6317a1
80813 F20110330_AACGYA chen_m_Page_080.jp2
af2b03da3a0e32f4d63538520272cd0e
e5bc43181d71ee611dc70ec59484df69b9e72c2d
37912 F20110330_AACHCS chen_m_Page_087.pro
6368f4e86820e9cd394255645ade8e1e
05a733c8f5f5c3ff17f2ac436598978f79f7dd76
450822 F20110330_AACGXM chen_m_Page_146.jp2
264fce4db9e19aff169010f108006d39
4ec86609f90f85ea570f91b877a63dba75894152
63889 F20110330_AACGWX chen_m_Page_032.jp2
77918894e5bb81151f7a0533e1dfa300
7c2b7cf9f55d7506ce43b56ff1ed59652b02456a
105234 F20110330_AACGYB chen_m_Page_069.jpg
5e063c88c63ea91bff8d790521dcbdc2
51ee5bd1abc51cd556abf05091373aa3f1610af5
45883 F20110330_AACHCT chen_m_Page_141.pro
aa8536f0f2b9943a32c5fa3160523f50
726e3639ba797a5be5b710bfea55f4332926b3c3
8197 F20110330_AACGXN chen_m_Page_127thm.jpg
4681b886255d057190b6e298a6b94497
2987322f18d7b193027d2aaf9c2e517c78b59410
9111 F20110330_AACGWY chen_m_Page_134thm.jpg
77d9509302b71de29005a09564b49a38
014d0f778d049dfe08193a43ab094692e31764c5
8020 F20110330_AACHDH chen_m_Page_001.QC.jpg
9fd4cab0d220cbeeab87fc755cef4cc7
ee76506939fc8a8d96fc4657c3eb720fed539a49
33009 F20110330_AACGYC chen_m_Page_068.QC.jpg
50f0e98369255d08a7d8e9b6fe31329b
0fd3bb4d221d0decebd92db5a0ca486620bd8311
F20110330_AACHCU chen_m_Page_010.tif
6cc77c195399e49f236af4ad0a4d247c
d6204cc4781dace4ce94b9e5253d42d378dce1d0
F20110330_AACGXO chen_m_Page_127.tif
46c323309b003a7cb7eeb3d534d8fe2b
5c1175f1a12cdba5d7b69b5fabf977c236e9eb56
F20110330_AACGWZ chen_m_Page_107.tif
bcf23504d4bf698832ae3bfa669899aa
d7cad90472df4a9726679fdd04ea90b98b3fc7d8
70870 F20110330_AACHDI chen_m_Page_139.jpg
c5757dd6e43a61fb186c498b9552c6b5
bb6951209f1b4c9d66fad02f24a29c4f61f97bdf
31685 F20110330_AACIAA chen_m_Page_164.QC.jpg
c658a6d8b495d3afdc3eba607d37900b
3c59d9309ddafb07afae3281a5cd4a9e4f401cd6
1981 F20110330_AACGYD chen_m_Page_070.txt
7ff3e8a6dd66be5df2ffb29cb3d6d351
fc7daa1cdf9aed3bc4bff168d3f10336f6848bf0
6625 F20110330_AACHCV chen_m_Page_122thm.jpg
6b23202944b0e656ccf79ce5df3587e8
906866c58149b6464f99d9e07c4fb1be36c18e5e
487874 F20110330_AACGXP chen_m_Page_056.jp2
9181114a1300d4a1570260e16510447c
5cb57a2533c47937a96a18bdf008c137eea68f32
7489 F20110330_AACHDJ chen_m_Page_028thm.jpg
ffa2cc5b6644f91c62b1cc7c2a698ca9
976a0105a2aa6e597a201747a29ba01080d788bd
27919 F20110330_AACIAB chen_m_Page_166.QC.jpg
f0440566ecbace97db74ac5245e3833e
06da7004fc38feac9aa60fd010bb9fd4e00a6f7b
F20110330_AACGYE chen_m_Page_036.tif
c98c80bf63a19844dc9163de146adb5b
4f173b50c300e08c839690461d52bcc5ab800aba
34608 F20110330_AACHCW chen_m_Page_128.QC.jpg
9d3486e55726b328a8dddda86fb62028
243059ee0c424d6647d67090796acebb6d2d069d
7083 F20110330_AACGXQ chen_m_Page_126thm.jpg
97851ab3a41c2be5e07bbb872ab331b3
0a27e29d0fd2875d602ff79ff1112f17ab4b5689
24585 F20110330_AACHDK chen_m_Page_040.QC.jpg
d790f5933e0b5e4582ed1e0d0b7a3828
30b07f759edd298dc808ba82ecfebd0ae547e75f
24265 F20110330_AACIAC chen_m_Page_001.jp2
bc9f5f071ad40fcf8ce29c2c123964e0
959a850eacaa8c1f1aafb8f7cf9eb5078b4eae13
234 F20110330_AACGYF chen_m_Page_152.txt
00aa3e3e36eb0cf69a91c6e79eaaac8a
437035154a11d62c232ce1a18b52ce13f271b316
163 F20110330_AACHCX chen_m_Page_144.txt
fe89e6dfa8eb6e93b7b402ede38645b3
bee7ed4dbdf79900eb331a57d64f2f72d0a80868
402451 F20110330_AACGXR chen_m_Page_099.jp2
7cd7c1b0b22a4a56b06adb42c2f01238
84a544a9b0e6939230de39cf5cb08037f0c9568e
34273 F20110330_AACHEA chen_m_Page_046.QC.jpg
a0b9bb175080c34fcc17b43ab796a5db
6d8a7ca4e168e9f049f96dd1041a0d724d7417a1
F20110330_AACHDL chen_m_Page_061.tif
d01d46535ffadd56c2cdc516d886c860
d9350fe983444db2ae748a03da8c74dd3fc63c0f
1051962 F20110330_AACIAD chen_m_Page_005.jp2
8b7594db1413a4f1fd37b2e5e4c019e9
f2c23149fc5a4dbbce2e183cdf45f5f949b4768e
332768 F20110330_AACGYG chen_m_Page_102.jp2
c711ac7437fa2fbe94fd51cda16fb22f
ce210cb92b4a44983a11876098ed3f6393ab7903
82858 F20110330_AACHCY chen_m_Page_079.jpg
c301c2797fba4b44a0fc6d7de3d40fdf
211840d34939f2104ad196c77e98c3d4892e81da
35550 F20110330_AACGXS chen_m_Page_080.pro
6a5819d8f49e1aaf43920a46b641bfd9
3d48e298771d3c8f6b6f5bdde4d10790ad04ea52
34581 F20110330_AACHEB chen_m_Page_017.pro
eac6e2a5f4fa9562600797a3aba98827
3efa1b41f911b34a1cba58e409679582bf0f874b
30122 F20110330_AACHDM chen_m_Page_064.pro
e9a2826404d6497c4fefb3f9f29e99ec
0fc927cbf707d21237509442a3022bfa03285804
1051975 F20110330_AACIAE chen_m_Page_006.jp2
a1fea8ebd9e902d9878c749e64dbdeee
eb96d9bde7003d0339168452b62fc64a59a39cbb
534500 F20110330_AACGYH chen_m_Page_094.jp2
f791bce5345870825569c403f407672e
bb89c97154a624aa72718148f906ac4108424242
2157 F20110330_AACHCZ chen_m_Page_120.txt
53d120e1e6913603b49559a351a218d1
9b42315bd6b612b97b3b570407f5600636ef078b
7987 F20110330_AACGXT chen_m_Page_043thm.jpg
b109063f1168c70a8ce8d3957da41326
d042b6cb1f99e9b6d67a43ec224f923b5a7c03a9
2041 F20110330_AACHEC chen_m_Page_114.txt
eacfde46a58e8384d48d7de9a727e828
91cf6a78904ef17cdaaceefc3154652834cdd0bb
84884 F20110330_AACHDN chen_m_Page_033.jp2
0db111d145a0f7d52bd8a79f86482a89
d9c770bf0449e6ac54273bdf053d674d2fec3e2a
1051946 F20110330_AACIAF chen_m_Page_011.jp2
42522dbbf09cf17bf8eb8904cabaa2d8
a15abd6d3ed7a791f86181a92802da7f3b00f549
99290 F20110330_AACGYI chen_m_Page_113.jpg
90a065c944881deb4198910d7489941b
7ad8779f5eb6f07453a9f1b4abe2b2bbd538e4cb
5124 F20110330_AACGXU chen_m_Page_098thm.jpg
73c9c33ea783af838cee30b28e14fefa
463fab05ead5fbf5e73d1c28a8512b51a0c99585
720 F20110330_AACHED chen_m_Page_125.txt
a2056212b5b07cd6266306a3ea951347
8d947ac0678992f8b4dc551a50a039ee66998813
1980 F20110330_AACHDO chen_m_Page_127.txt
b19ad1e802a51653b0780c78a9892048
c28c76a678ae77379a83ba807e271f16ff6b3b64
1051967 F20110330_AACIAG chen_m_Page_012.jp2
5e67c3cfee0e1f8a45d024e103e343f6
625fbc8627bf668cda519f7094091af9bb1543f1
F20110330_AACGYJ chen_m_Page_094.tif
a4afd573c3c8a166bdb0d70afbe33571
18f6c9708aa8f41b92bc2b726afecf8697fd4647
F20110330_AACGXV chen_m_Page_014.tif
89eb986bde577a33beb98fa1af5387d7
12c4d97bcbf9acac596c2964a33be22bf3a732cc
109604 F20110330_AACHDP chen_m_Page_065.jp2
b18c55b50b2c73c3da75043be502b475
de9b9865bc3eedd66a99d0868154b107ee15659a
77930 F20110330_AACIAH chen_m_Page_013.jp2
d98b4ccef5312c22a439d49486cb989b
26c157979c8a624e5a259d4f1c3ad14d40472d6f
13356 F20110330_AACGYK chen_m_Page_060.QC.jpg
a743c90452a76af88b2aed2e66f70abb
02f478489f3a5830edc54d496c79048ba51a0185
7999 F20110330_AACGXW chen_m_Page_149.pro
a1e607ac4e605f699a7fc4b1577c1b5d
10720d5acbdebe4cf7e9ae2ecbaafa71eccaa0bb
36692 F20110330_AACHEE chen_m_Page_039.pro
7b2c3cfdfe8e5db4ed52e7be45f75c11
60f537d97baa4886e52eea838bd2f84397ad356a
14904 F20110330_AACHDQ chen_m_Page_099.QC.jpg
21912e5e00b89eee7dc710157773ef62
55efb9db1e73e17973a8cb11193605a1ab6f4c8b
80457 F20110330_AACIAI chen_m_Page_014.jp2
dc191871d34ba78b9c95cffc9dd8a61a
88fe41bf1359a1d14de17ead4c4a13d333bd3263
F20110330_AACGYL chen_m_Page_141.tif
07bc6e9efb4ee5a4ddfe0f32ff9e758b
cef97d5dd1bbe15576e280b79ec5814eddf84a39
27512 F20110330_AACGXX chen_m_Page_079.QC.jpg
57ed3919219e02b55e7dff17f9fb3a28
cae2d3971cc4f56d460c8d01e8a66da23a0c777a
14122 F20110330_AACHEF chen_m_Page_121.QC.jpg
864cf46c9f04fcf2b2db133a420e329d
3c6007a9fd4915bdcadbbad836862b40b4f6611b
55691 F20110330_AACHDR chen_m_Page_022.jp2
ba2f0665f171bb58a25a2dc66d99f322
c7b44c4b4cdabdb0bc08fabd2f03fe6e89501f7d
94001 F20110330_AACIAJ chen_m_Page_015.jp2
fe9c608b0b5de8ed34b6e973f2dc45cb
4b8ca9af6b9c3e84e99982bc656eae25eb548e51
2091 F20110330_AACGYM chen_m_Page_118.txt
ede7864b397a72696892b6937a4d4780
0bd96a4df675e42a8ebbfe18de13842ff6d933d2
51524 F20110330_AACHEG chen_m_Page_115.pro
42f9da6d219f53923208135787c956e9
81202e69ac7b3bc1f63deec9d850a9385f4fcb6f
44380 F20110330_AACGZA chen_m_Page_121.jpg
19a807314caea5ebc9d73213bc78dffa
d12b029d4c0d3d7ee10cd293b481dc1a93ff5baf
68908 F20110330_AACHDS chen_m_Page_063.jp2
7af230aa7b35f4f5274d6bf2cd25f7d9
952918b6dfb8ce3be5f9dcf24447a6ce3117cf53
74033 F20110330_AACIAK chen_m_Page_017.jp2
a7b0633f36acf633b52bcac15184f6bb
b0f6162ce0ee0beb34a41c873510751ad1cc9304
49161 F20110330_AACGYN chen_m_Page_133.pro
0b902909cb38514b56d4aaec3202bc16
a753202c73b7692465cc573941c9e15da13f0af7
F20110330_AACGXY chen_m_Page_060.pro
3597ac9c615c9b7341f6834e8c2ca9c6
de60dbc53675e528de228d69ac5e2100124c2c95
70004 F20110330_AACHEH chen_m_Page_110.jp2
fe7b2056725682cf0b18aff78e386b96
cfc3f23ee0a140c73b3c2de36cff9cd6d07da3b3
5879 F20110330_AACGZB chen_m_Page_038thm.jpg
8bf625b171cb868c4bdb4c9500cbd98e
993cead6c492203dd0a1515230fbe5e31d0ce471
69406 F20110330_AACHDT chen_m_Page_020.jpg
e010512dc9ec72c1700420d0ee9e3d4e
8cf023bba25d23e3209d1c5a4025c56e5c288ac6
40491 F20110330_AACIAL chen_m_Page_018.jp2
ba76ebcaf44ea2badc27bfbeb0f4505d
6efaabbb2200f9e52e450af9b18ec882294088f0
34457 F20110330_AACGYO chen_m_Page_143.QC.jpg
3670a16c68dbfe7a281a1eccd1f9bb52
f1a583baee25526ba07300afd28a54e16a562d59
1919 F20110330_AACGXZ chen_m_Page_033.txt
0387a7ff73e4ed8a7de40c09721b65e0
81f86e83626e6e7ade05b61a5ce0308a7726ba84
86035 F20110330_AACHEI chen_m_Page_075.jpg
0423ab7b7a1b7f09fc530f060905159a
4683fd4bd77e86f3f7491c755c2d0894133800e5
95552 F20110330_AACGZC chen_m_Page_119.jpg
ac1a58b07454d857ab11a619a5d918af
89f25b384793dddcee8ba69edcc961c1ac51f3bd
2417 F20110330_AACHDU chen_m_Page_082.txt
d63f9ad1aca285bce89255aa7f9174a7
ecec8d98067549e79e19c6235b9ade9ccb81cd93
325233 F20110330_AACIBA chen_m_Page_055.jp2
ac2a77597934208d0de30034979d67cd
c00258a78f026c4ad0726568f7b6bd22f20d4ace
49992 F20110330_AACIAM chen_m_Page_019.jp2
43aeb21d40b150f2fc988f61a80e9f23
0285bdf55b68476bce0644c6a9bd6898ced44ef5
34515 F20110330_AACGYP chen_m_Page_077.QC.jpg
f5dee1f82fb7bfc0a9d4e83a98013cfe
0a67fbc62c8c44ce56bb97b49fb966e6af274e8c
2958 F20110330_AACHEJ chen_m_Page_011.txt
4999679296cf4c211f5fa2d163ee868c
7e4c092c2f1bd05e92777351472fb84f9db8ffeb
1795 F20110330_AACGZD chen_m_Page_039.txt
606918b7750eb9c6e5ea9af2ad2dbe16
a6612ff070633efb3622ba07ebd55333f0d8b75b
F20110330_AACHDV chen_m_Page_078.tif
ec9ee201875244fde1927641a115d377
2a3ad8285cb2d75d91eda438a339ac7c8db9c1c8
265959 F20110330_AACIBB chen_m_Page_057.jp2
043638bea080e89d851981926fb665ab
aba2aa2ec3568042800e76788e49eb0149bff797
88203 F20110330_AACIAN chen_m_Page_021.jp2
eeea7205f5a0f2e904ff28509f74b41d
19fa0bd2b1f2bd5fc86919216bbb9ee1433a53c0
448 F20110330_AACGYQ chen_m_Page_149.txt
650a9399efa3424814be52709d3220b8
6c1a19c86fb66e7aba02fe8ea63a549b67a5e256
204 F20110330_AACHEK chen_m_Page_060.txt
92603bbdaa769637d92e9e3da42a0d6a
77b16054b55f035d59653e07881df65450f95e3f
F20110330_AACGZE chen_m_Page_148.tif
7db1cf07d0fc1b77ce9b875a5066cf79
d709c762308e6d6a38d9d1b24308ca677d6c0cf9
96334 F20110330_AACHDW chen_m_Page_086.jp2
7dbb52e96298010f1073a3814b26bd79
9ed2e5403a7fea884b8423527dee7c01b4743ff6
656702 F20110330_AACIBC chen_m_Page_059.jp2
e174c37d14d44be8332519d297e0ffb6
b9694d77be9ba79e198c684a82f8c7638d4a370e
59543 F20110330_AACIAO chen_m_Page_025.jp2
d140119241e4e3bb643be029af3b23c8
897e9083ce8e87b52ff063b5d93d4f8fe3fe6e6b
1882 F20110330_AACGYR chen_m_Page_140.txt
3ac5d2070a24b1d7b30c29055abcc4d6
7500ca6b3d0990cb79396c947b16be68fd5a8d86
28690 F20110330_AACHFA chen_m_Page_015.QC.jpg
61061a9ab68f615029a105a79561a9f7
b0b20b9be5161af26f0b0f2205ac8894ed1939d9
5202 F20110330_AACHEL chen_m_Page_100thm.jpg
dbdc4ab1b0fc14b0e5c188fcee6edad6
3b26974e86b978f147f225211111147633282cd3
33035 F20110330_AACGZF chen_m_Page_109.QC.jpg
5b39f9d15e9558cf91c04407f0d6eefc
4ac0c33cb2a0c049bd3f71b26c8494d98786ad02
F20110330_AACHDX chen_m_Page_057.tif
b9b6af5a36aa266b7e94cc0e59c68f9d
6b9824fe72d31fe5f1155c67176576e2f6c3f034
309377 F20110330_AACIBD chen_m_Page_060.jp2
3cad1623ca34ab38b2a86ce5d24b470a
247fedae3d43538dd50bdb9d5313da2ac1f654df
60247 F20110330_AACIAP chen_m_Page_026.jp2
696fa9f0791375fddf57aacdea4789c8
d2ed3d5bc7fb169f4fb9b6f34d02a729ec7745e6
6340 F20110330_AACGYS chen_m_Page_040thm.jpg
6559c203f9f4c668f11a6c6db37c4dbf
eee94659cd941c023e87a4abd64fbb3a79e085cb
91613 F20110330_AACHFB chen_m_Page_159.jpg
91c95d3d91aa45348a7f7f46ed51d6b3
64d29a032201717025c3bd15cdcb44b475bc5cf1
100139 F20110330_AACHEM chen_m_Page_143.jpg
ab691159d74cff0c807400733f07d02f
d9cae00e2e12ccd421dfbd4d33eff2a16ca58cf0
F20110330_AACGZG chen_m_Page_166.tif
3b42952286a1f88a45a714a2c8e51a36
4c1af35374eb3baaf4bb9e0dc52a1019b2e4d94d
258765 F20110330_AACHDY chen_m_Page_091.jp2
743dd2cab658c0dbbac2901ad767fe01
421e832b956479aad470cd411d549818954353eb
507237 F20110330_AACIBE chen_m_Page_061.jp2
5e4d3779161925a86038199f5dac33e5
1668c237a65b06ab3925b1428ae43056604afa30
74545 F20110330_AACIAQ chen_m_Page_029.jp2
11e50927cc55903b77d871e6e1c14d09
e4a5132eb473876e4c5d94ec249165c5055cd1ab
10295 F20110330_AACGYT chen_m_Page_159.pro
d96b7783a16929d065a1658d2350c07c
4317665aabc998650c81606bfd78d9680e4ed0dc
1627 F20110330_AACHFC chen_m_Page_074.txt
117312f72e0cee01103cd68d9a6497d8
085e6743f1653bd46c9dd132834aede58c0c0c83
80354 F20110330_AACHEN chen_m_Page_033.jpg
9e7b3718365cafb8e79c42de6f9ac8ab
5bc935322b699c744e6584f83c91bf669347c3db
33473 F20110330_AACGZH chen_m_Page_070.QC.jpg
b846b0eb9cf7f657aa91be67b92baf3a
670f3ad4cadb3350518f4f65206ba46d712fd0fc
107882 F20110330_AACHDZ chen_m_Page_006.pro
a450887b3e674bce85d59f542f545161
58b341aa9c47550954d14ce5db8849f592798122
95284 F20110330_AACIBF chen_m_Page_062.jp2
ad04541240775d44b29d2c2d8bd3dad0
dfa8ad538cd2b503be8599edf5d95cdf8905aa9c
165630 F20110330_AACIAR chen_m_Page_035.jp2
014910d7cff927d364b3cc8d520067cc
d87e101fe23d060795cb4b217daf0bb5c2e54649
15323 F20110330_AACGYU chen_m_Page_150.QC.jpg
feb9179b8b04e53cfc7c412f93c04316
d2fcd81cbd05e883ff5e6194b722fa5240d2f745
76767 F20110330_AACHFD chen_m_Page_117.jp2
5768cbec47235b6a1522dd8dff7888b9
c6ae19020d2e262ae574fb20e441683c63460ad0
30154 F20110330_AACHEO chen_m_Page_156.QC.jpg
322e980713a2f19f68014aa947ad881c
4242f1b59e315913d64974084b0d7f8a501407bb
1910 F20110330_AACGZI chen_m_Page_138.txt
cb9d3a0aafdfe158ff794a8f701fb168
b3a7073e38430579584f8e4d5254b2cbc9211082
65329 F20110330_AACIBG chen_m_Page_064.jp2
2a4ed99bbc010dbae59e094e46527242
5f65b5631fd21aad0fc8a5bfd8775408349e2a3e
67151 F20110330_AACIAS chen_m_Page_038.jp2
184d59a4ab50cd51f140e0cb5d48b717
4d690e2da44841aaa4f3166c29a18112cb84efd6
5950 F20110330_AACGYV chen_m_Page_158thm.jpg
dab6815314ba20063a38df8213a8448c
a5cb0af1b974cab073fa073b1fdd59ef0f6a89ec
2078 F20110330_AACHFE chen_m_Page_027.txt
906b1a769a83afed06c6645ef3b204ac
08f9163450937546ec32c7062168951387ee4914
3771 F20110330_AACHEP chen_m_Page_018thm.jpg
bc643f5c20a63d89bb32c4ccdea42d83
15df9be6a1e483275381023545deecc943289ad4
5315 F20110330_AACGZJ chen_m_Page_026thm.jpg
805ad97b2bfdeb857abe83ab631db108
46fbf9c052b03a0af94286aa1c39f992dfa14572
109028 F20110330_AACIBH chen_m_Page_067.jp2
dcac7832dd96d21cf7068f7146c1778b
030e25101ce23336667727ba6d6fcab8fd77901c
77400 F20110330_AACIAT chen_m_Page_039.jp2
dc87a22df9068e92e8ac8b32efcf8fbf
9f0324bbed306f1355e67c9e0f094ff65319d6a3
1611 F20110330_AACGYW chen_m_Page_160.txt
6dc51a0a56eb5acd8dd0de9b94183422
9e4b4399b6c8f77f0f769fdff7de6ecfafe89369
F20110330_AACHEQ chen_m_Page_138.tif
2756ec52e50fd1885111a7ae1ab1cb6b
c75310ae3e4eefa3bc8c05eb69a9f1038fc8bcfd
46768 F20110330_AACGZK chen_m_Page_142.pro
f6b13d1c52f20a07c72aa30ad33b1e86
6d6124ea9bdc36e13f6035924c1ec279f004f2cf
107768 F20110330_AACIBI chen_m_Page_068.jp2
45cc3ff87b60b040398b28f21b64d2c8
6c4a9b78bcf778b368cac4c6152dcae6212ef567
75742 F20110330_AACIAU chen_m_Page_040.jp2
0957d89bbe85a3b613d2502882ff36f0
43ba8c3e6e328f4e9419d7872855b79958e70285
4802 F20110330_AACGYX chen_m_Page_103thm.jpg
7619d3a858e9ce98ef6fa362a96c32f0
93d4b89e1faa1824e7432abbebb12bce460975dc
32532 F20110330_AACHFF chen_m_Page_158.pro
97e816ed761b72489fd508e15fcf752b
d6022414ebe4c80c763cd893da88e040ca59e4b5
8106 F20110330_AACHER chen_m_Page_066thm.jpg
7dc99fe1fe6a22c386599f114a049a99
61d9c8b637ee70ff62f06c496598c7bf172b44d4
7149 F20110330_AACGZL chen_m_Page_147.QC.jpg
8e3e5cfb409b63d5120808c3d2bc37a3
9491a60fad9691ff03118fcbfe8d5ce42d6995e2
113135 F20110330_AACIBJ chen_m_Page_069.jp2
071f839bf24384bcbde16d522c0063bb
6ed8bad13a074a2dffdc3aca4508dbc3954e6b65
75371 F20110330_AACIAV chen_m_Page_041.jp2
c2e3130967972b4a1feeb5586beef4ad
7d3d685c132ad707ab6f6b4b9b6dafaac38fc9fb
F20110330_AACGYY chen_m_Page_011.tif
065d416b7ff9397bbf56d3a64378e01e
f22eb9effd6f022b4f5eb9b0f5c12d41a8855501
52432 F20110330_AACHFG chen_m_Page_069.pro
313e44a57a51aae2ec6532787e57a42f
2164a1b2fcdb80d1c5811bea6ce9f4aae1e867cc
106686 F20110330_AACHES chen_m_Page_084.jp2
b70920bf446b436a6b9da70ba587e797
b6d0fabd146ff55595b7a91146f84de1b1346761
40779 F20110330_AACGZM chen_m_Page_079.pro
e6009a9c7d962d62d90ef73e631480cf
186fe65fb2301e47685a8cc6296ef1b72c6ee453
108689 F20110330_AACIBK chen_m_Page_070.jp2
1942c0e28c6b6228fe297bdc2cc8821c
949bebdfb1ba09b3ecb43fef7a457448bbd00cc7
104357 F20110330_AACIAW chen_m_Page_043.jp2
535a8b5ffc4c49e3d210a7611bfc331b
d15fdf9f6de60bcd29dc53eaa38c6ec8d5520f73
8481 F20110330_AACHFH chen_m_Page_137thm.jpg
9e7acbb6417ee12e3d37f588acbe6228
bfacf6d4b03d17e9e3eeeacb6d993ed8e0906a03
5852 F20110330_AACHET chen_m_Page_012thm.jpg
9841a8c6a66bdd1a94c9d88104784dd9
a6bedda0df4dbb9306cd15321b948a4849f99f56
2015 F20110330_AACGZN chen_m_Page_042.txt
37f6655ff1b0166c0c8f43708ca38398
21fde803365ebd34be5b229ec8a43eec886a581d
110356 F20110330_AACICA chen_m_Page_118.jp2
b425143361874ef6d705aba1245e165d
7fb48be43232fa55cdd2ae3424887e2e63c52d6a
106338 F20110330_AACIBL chen_m_Page_071.jp2
564cf243450260ef7532bebbbdf3a517
bdf762d77af456fac09acfe641be0ceb354bea56
101333 F20110330_AACIAX chen_m_Page_050.jp2
7fec77ff0eeae800d5b923c5e554f6b5
4c2fc48ac282c83e20f6b10d28de10e49b90c63b
32888 F20110330_AACGYZ chen_m_Page_146.jpg
a3011ab9eb6c6d3c51d5fe817cde765b
0237dc57809ba21d7b566060d87e9e2b7422347e
4528 F20110330_AACHFI chen_m_Page_123.pro
6d1bb3b2691d56199a861dedebddbb6a
36201aa88a4cbc0e46985e5f109b889b8ddab644
1806 F20110330_AACHEU chen_m_Page_048.txt
1af81f8267b2f54771558d4988497540
908791782d1ea711da51f035690be9a594a316f2
4973 F20110330_AACGZO chen_m_Page_107thm.jpg
9d3e1f5384a465a9e902842eee77676c
b9299ba985423f3ef1276db7a5c15abe221bfdb1
90183 F20110330_AACIBM chen_m_Page_075.jp2
08bfe0ca37b738b71adb3a5e50a46504
5620aa15e6116bd2f6642cb3e22bc798ee8306bd
104105 F20110330_AACIAY chen_m_Page_053.jp2
f86caf0be6a2ae92e12fcd927187036a
d40a99b5aa446788c345d62775392d23a2287143
85409 F20110330_AACHFJ chen_m_Page_087.jp2
ad9386cf87da7f06af5d4084547e4241
5ea5ee8e6e5e30548ffc81d54936d400e80a4c73
15709 F20110330_AACHEV chen_m_Page_061.QC.jpg
d8b9e48acc3194633965c1a741f1c33e
7084ecffcd3633e1e6629ddf870b1a3c7a3722ca
32863 F20110330_AACGZP chen_m_Page_067.QC.jpg
29e2818cfa6595b7f45d147bfc224c3e
67df9725461999d98e5f8033abb88c349ff15e43
113734 F20110330_AACICB chen_m_Page_120.jp2
05385876f8033700a168d279715aec16
f73a9f3c8c0ad4a763a12fdbf88fff2c84d428d8
109942 F20110330_AACIBN chen_m_Page_077.jp2
c62b738173b4ab51a3abbdfb34154771
8c250eb02a0c952a0ad1e150b473ac2952fe3d94
103941 F20110330_AACIAZ chen_m_Page_054.jp2
7e0d132f3e5765e523804cc6d941e9cf
60d4faec16a04c4d23f86ef0698b1bdcc380ebb5
33031 F20110330_AACHFK chen_m_Page_078.QC.jpg
6ea695e5efea02b0973748157e785ff7
8fc0328759c705d4a298005a887a873f5c43331a
2039 F20110330_AACHEW chen_m_Page_083.txt
6fd3e4a4ce9a5c387a2ffcd1ec3af5f4
ebd632509efab16a546e6b2ebc299bc4e6764a3b
F20110330_AACGZQ chen_m_Page_098.tif
2f997e7505c1216a4181f63329097968
b8ed4ee26da35292440c85d9b27bc3967336da73
392121 F20110330_AACICC chen_m_Page_123.jp2
348cff3c25012d9896da1d3be11952be
7d15a9a350d8428ff1fbd49d856f6b10efebf102
87630 F20110330_AACIBO chen_m_Page_079.jp2
c49b0289987f8c641181b9f0bdd90d2d
c4224726697549f0361d808336a24d9aa011ddc2
32454 F20110330_AACHFL chen_m_Page_136.QC.jpg
d6a29aad3cd8c396e0fe9f30b1c8b22b
0dd734ac9de56af1432b9b242712606d3b2ac465
47498 F20110330_AACHEX chen_m_Page_165.pro
a7828284925737d47e558f1662866c04
70aedf3fd9e0652981d2a7f5d03b347a14de93c2
34751 F20110330_AACGZR chen_m_Page_040.pro
2454f00f9cb43dc2bf72e81d25d87489
8ec55fc4bfb5ad704c8a4cde83e2745a4dd0e0e4
1767 F20110330_AACHGA chen_m_Page_023.txt
9914601e723920940bfa94bba51a0014
49e9236d656eca42aa7ad1ae5f43a580021095b9
89786 F20110330_AACICD chen_m_Page_126.jp2
7bb517f273bcda6ca3f840122df71c05
8af31238630efc5e14a94667b7262335126a41f2
108215 F20110330_AACIBP chen_m_Page_082.jp2
df5662f09989bfbd3e2aa6ae0584d404
3858008961b596f5833456d1ebe91c20599e9670
48827 F20110330_AACHFM chen_m_Page_112.pro
ef4585de8a8eb4d5dd71a4cfec7abddf
f9431db18e61dabd06aad7ea59f452be531540cd
1593 F20110330_AACHEY chen_m_Page_026.txt
103cf667735050c53ef3f3b2a65fafb3
cd1db1fab4c61cef9423815fa372b5c8b828d6e0
6968 F20110330_AACGZS chen_m_Page_033thm.jpg
f7895bbee979287a3ef28acbbeab8d3f
18be9c4d4e473941092071cd9a09a2395a985e09
46602 F20110330_AACHGB chen_m_Page_121.jp2
bbdfb3cc8eab08af5a5354cf6c144b32
80b6f67a053ab2db9e68c377d3c569a654c4b058
108468 F20110330_AACICE chen_m_Page_127.jp2
1f02ebec23eee51e389b695964be94e3
49231e5b55ed44edc14e8b3d51dfacfc5270f39c
90447 F20110330_AACIBQ chen_m_Page_085.jp2
1e8b3c9c077f863fdea29ab88baa5017
80ee3e9422c7efb1f2b0b4085caafd2e6180c76f
84726 F20110330_AACHFN chen_m_Page_166.jp2
895c61dd3d13615199c140ff29eaa80d
e8b4f7b359b3a9a6fffa45a450b074a862afb01a
F20110330_AACHEZ chen_m_Page_113.tif
4fdfba360134f343e75b19e200103e82
da980ce4b4757a14bb93f3614085b6b80cba3463
23934 F20110330_AACGZT chen_m_Page_012.QC.jpg
bfd6c79fd10dee58abf353a080e689c1
e17da4c31f9883379bd81a40dbf3d750c9a1c299
76719 F20110330_AACHGC chen_m_Page_081.jp2
923085246680759da56f9d462d6392b4
424f4bc8621a88882acbdd6c5339031f702c9f08
100789 F20110330_AACICF chen_m_Page_130.jp2
af17d4514af7d79338c2db79a7270075
1ea19369c2a39da98949df82831ff4f0739e60dc
108061 F20110330_AACIBR chen_m_Page_089.jp2
6d2c1dcd153ffd979f972b55806c069c
2bd5d3ac8189e6727cebd20de031c3b1999c3576
47769 F20110330_AACHFO chen_m_Page_136.pro
9eeaccaa00979a77842bd7ae5284014d
d916ce0dc534940e44615834ff83ce9cc845d3fb
4462 F20110330_AACGZU chen_m_Page_104thm.jpg
1679507e1490740eb307763bc0713227
bf5a52a478d342b99ca41324e014729f46c4bca0
30317 F20110330_AACHGD chen_m_Page_073.QC.jpg
407c4f99c00b3c66a9ea3ad8aac15385
420378e7bfd5d2d70f100f65f6f043490e74c1f2
86550 F20110330_AACICG chen_m_Page_132.jp2
bb154f6211d33cc870120739f8e59eb4
e33cbef89aa075e9b7c32753d47d38c1ae78b6d0
228261 F20110330_AACIBS chen_m_Page_092.jp2
481adde4a0ce44fa298644f57ef65f6c
962b257be49cc248300b8e41022724f597bfe9c5
28099 F20110330_AACHXA chen_m_Page_075.QC.jpg
1ab4325d7e14f681dd052b92cf137e2c
3094d5edc8af22644228ee8369e9c3701009c930
3081 F20110330_AACHFP chen_m_Page_133.txt
c449c88332da4382e7b7a4461b35268e
b4e8acd59de9de1b53cc9b8ca71e94854b8371d2
1835 F20110330_AACGZV chen_m_Page_066.txt
0cd22cdffb52018095d64c929a70a6de
93492c62bb2ff3f518df7fbf22d56346ed23f96c
6444 F20110330_AACHGE chen_m_Page_016thm.jpg
8abd2002a54dd9b37feb8b73efcbee4d
c8b2731a14a4ba83f2b08a5534531ac31594076b
101555 F20110330_AACICH chen_m_Page_136.jp2
021b5c61a38b40d8ce3b57490d5af827
4e391a91501499cbbddab6a0e17257ee11d3520e
346945 F20110330_AACIBT chen_m_Page_093.jp2
f89074043da3fb7aae81874189cf1cb8
4053d7a46d98f6c7eddf92038d856a03f2f39f56
105534 F20110330_AACHXB chen_m_Page_077.jpg
791c7aaa525d0b1a478436c83a6e8cc7
fb8dcb602c9a0651bbbc16117407f6abbf1f42d0
1997 F20110330_AACHFQ chen_m_Page_044.txt
20a2e6d2c3ba3207c6dec91ad46f7dcd
2637bbec6e56af4d3f5def00ce48b8c782e79553
339967 F20110330_AACGZW chen_m_Page_154.jp2
3b6c018748fa3e26eb97fbad3e4369da
90c831f5b494704061481a56af432f754ea9de75
97469 F20110330_AACHGF chen_m_Page_165.jpg
4175c20ee1353af4ce156741cf94ebd6
f31f5fa17a00d98f1e27503881e872b4123c2221
98888 F20110330_AACICI chen_m_Page_141.jp2
1a67238bae342fdbe276028d204196ae
934a3716436588ce95aa9c2834556f7dd7a6134e
344909 F20110330_AACIBU chen_m_Page_095.jp2
897bda20e160b32fe82cd8d7d6720e55
10cfe2b4d8ea1475242679b2062caaa5a20a7113
24466 F20110330_AACHXC chen_m_Page_080.QC.jpg
4ba936b1252456b18abe92308632b07a
c2eb8be4d9d33ea93d92fb1644a6a722b1a8fff1
27151 F20110330_AACHFR chen_m_Page_048.QC.jpg
a3fb914b69b40625c4f0cbbb617aea75
29ff7d8d854b3f18258d99d310054b461aa64aea
58826 F20110330_AACGZX chen_m_Page_032.jpg
445de4e99d9e739b17794d4f5e0ed821
04e3d2665428b69731323be985f9bb38517f4d47
101043 F20110330_AACICJ chen_m_Page_142.jp2
ac1b5d85564b3cad677cfd9a8ef1756e
866dcfdfe38786de31cc2e6d72e4deed0f73960e
410502 F20110330_AACIBV chen_m_Page_100.jp2
f261f6f23bb9d76b9031bab74b770058
4d859c6d98c6ae8658f22489c39736b2c6ab7139
90118 F20110330_AACHXD chen_m_Page_081.jpg
d93e530e60a0bb17ad5e3023914af68e
354a9adeaee4019ff03c8322f9161725fdee3e32
F20110330_AACHFS chen_m_Page_075.tif
6e39d2202e990d33d2c676a3ee7bc0ba
e4687c3b388ea420c498852142b5d5f35ddca784
440 F20110330_AACGZY chen_m_Page_154.txt
fc696a4ce7b31aba3e31aae5e8ac1c7b
f1d880f45efef04f0c84a8e7cd2e9c721890453a
7810 F20110330_AACHGG chen_m_Page_010thm.jpg
c9371fae5459b043e1d2c0919dd16db2
282e1c33f95008b77796f3d1ea268f617b160bdb
518869 F20110330_AACICK chen_m_Page_145.jp2
a1f41dfe645e9bca8e9eabf50f5de5cb
c801766a4f5d8293c0b498935087cfab6572b562
519131 F20110330_AACIBW chen_m_Page_107.jp2
7db9cfdbaa30eb57f4569fe39a0fcbb2
e40dc93a2baa4e1092bdbcdfee1b261ab76824c9
34720 F20110330_AACHXE chen_m_Page_082.QC.jpg
1c95c70c0a9e56453265173caf2442d6
e3ca2cd0b815d7db3f6a8e6caa7954063c0898cd
72160 F20110330_AACHFT chen_m_Page_020.jp2
92de420b8fbf53d80c93ae2e9cadfe11
68a31a250c492316a0e87780c06b0003c3a6f818
8395 F20110330_AACGZZ chen_m_Page_076thm.jpg
30467a152cd482799b83ef9b7a5ba8c2
dfbc6a415496e1103bc29c7084de388d6d485884
16991 F20110330_AACHGH chen_m_Page_103.QC.jpg
13bf07bb20a2f5420955a42b403e58c0
609eb8fac9206937d17097269369ac1e03039466
6160 F20110330_AACIDA chen_m_Page_023thm.jpg
baf964ed8cbe34ae1876454fb8d879b1
667a79e1eb61c2065861717f2a0f1f94e15d8090
299812 F20110330_AACICL chen_m_Page_152.jp2
65e8c923831c4c172b520a0e9f83f372
dada801bb6118069f3a96e5a1f75fee780d2cff0
106699 F20110330_AACIBX chen_m_Page_109.jp2
c6926aa4218fc82b53b4fa18f296d6d2
760672c9ad969570e74c0e1f553c948a972f699a
34484 F20110330_AACHXF chen_m_Page_083.QC.jpg
827cbd39e7a92af44ddb0e3b484cc448
d3a21e7da6c76c32ee84e41a911fb8dae9e9f099
F20110330_AACHFU chen_m_Page_066.tif
059b58d0e014c801ffa82ca6d987f98c
49e4642111cd23bfe7730711d497385d5745b5d1
8174 F20110330_AACHGI chen_m_Page_136thm.jpg
08b84dd7a7f26af03eb6b3c4b3bd170c
387b37eb940183e452d0ffd817e2f50df5fb2606
6681 F20110330_AACIDB chen_m_Page_024thm.jpg
63fa44ad1a7a993a062dadfa1682c12f
7c54f8ca6d690bd3676641a1db66a9606df79803
67168 F20110330_AACICM chen_m_Page_157.jp2
8a5330527a0fc1fd83ade154efaafb7b
e947c4c30df41a857966fdd44fface12257632a2
106340 F20110330_AACIBY chen_m_Page_112.jp2
8de7745dd785ca23c152547e54c8f5f3
58be5d7487cb4e38f3d673be454cb9a99068f59d
100248 F20110330_AACHXG chen_m_Page_084.jpg
34d1b686ac5dfd60137863d3bc707c18
d069817f26dfd8ad6eed9fd1fe5a911da1e90d97
17733 F20110330_AACHFV chen_m_Page_145.QC.jpg
55a9e058dd054ff2494b22f3ef1ed3b4
e96448deafb9fb4cb8f215ff6e72540dea99a70e
F20110330_AACHGJ chen_m_Page_155.tif
973dabb7db7bb772a7d2b98e8b17109c
74c18af91303b976863f4d8dce786a17523845df
F20110330_AACICN chen_m_Page_159.jp2
60132dacc587b000ba2a9e9bc0c1a68a
2f70c88b53a03d9f62a25d87191f16621bbd7522
109122 F20110330_AACIBZ chen_m_Page_115.jp2
fb8e9a8ce5366e31e39d9aba909f0a73
20d032fa4dc3d70cc250430041fdbf3c7df19d55
F20110330_AACHXH chen_m_Page_085.jpg
0a9c123a977a137b39e34d1fbdbe0680
7f5fe70e678691e76e437a255e65be37ae677fee
4028 F20110330_AACHFW chen_m_Page_060thm.jpg
07f3649bfd9c22a5e9dc880a63333684
70812300343c5fa908d7c0cb3092c1fe15db22cc
18624 F20110330_AACHGK chen_m_Page_147.jpg
dd091ef6d202d204302c91a2e6ae4462
f46b456ecafc2548c059de8e5e165be913828bb8
5234 F20110330_AACIDC chen_m_Page_025thm.jpg
d5f2a2ab402e1e5faef2a94005b1055e
413b8426ed0788e81cd442045af15eca70ff5d8c
97973 F20110330_AACICO chen_m_Page_161.jp2
c24cc6f08908e234828b2a5fafbade9c
0a0f08b6655fcd82562873c2ce1b97f5a5109bde
29206 F20110330_AACHXI chen_m_Page_085.QC.jpg
8313b3611cbf69220770a11f1a5799dd
1534aa48b160d8b80226f222507678542004ce85
1851 F20110330_AACHFX chen_m_Page_015.txt
6367f79ecd7ee61e85972ba1d0743830
b8b63000e2e119b7eab3cc67cc335bdb5fed1083
F20110330_AACHHA chen_m_Page_142.tif
728782b845ea35f8435288c15ffc36dc
f5e9d4aa86592a17fa4da69f595baa55cac29ad0
50381 F20110330_AACHGL chen_m_Page_052.pro
e75df13c3b5472b3c834b4c3fd1b3837
f6006fa54147dd7e79e6488296901aed200ec2be
6430 F20110330_AACIDD chen_m_Page_027thm.jpg
412cb37eccba4157b2ebb85a4ca8160a
fba091fda88c59c10c78e3fea0ab91a815f52f58
97220 F20110330_AACICP chen_m_Page_163.jp2
be45c317563ad01025ed1a9cb42f3990
7390382464ba9c3dff7b51b840427b6b7f5ab0e0
90905 F20110330_AACHXJ chen_m_Page_086.jpg
130da41482fd485d5ec657592b3efce0
aa9bd10ac94c1f681300bee60aafaabeca3c0b6f
941 F20110330_AACHFY chen_m_Page_167.txt
95ca35f487fd20b0f2e2b04798352d41
feb0efc35ac4ffab6b32003b6bc64e333c9f5e87
105020 F20110330_AACHHB chen_m_Page_083.jpg
056fa0098ea41d3bcfa0d3a8e993b0ce
5abe80017c65eb4bb31da1ad82a27283144413e4
42431 F20110330_AACHGM chen_m_Page_003.pro
e00553a5d19cf9a87a1c5313bdcdfa38
26201f9d3075417d64f80dcd39a57a852f78a9bc
5751 F20110330_AACIDE chen_m_Page_030thm.jpg
50a3acee8ad379af5440bbced93f892f
17e7782353edc8169956f39327d92eb473a40d5f
96100 F20110330_AACICQ chen_m_Page_165.jp2
9d6232210cfb0fedb142d6379b8cc11d
d9ed3e00af2ddd17420b99234ab5c477d4fa5457
31417 F20110330_AACHXK chen_m_Page_086.QC.jpg
d6014cc9b22835dc8d543b4f706b7ce9
c6c13ade71802f3ddbae9118fabd81b37f36345a
25989 F20110330_AACHFZ chen_m_Page_108.QC.jpg
b5cf70bf8321207781d5e747a66c949f
e41c55df36f53f508d4e50692ea5a8beda5b502b
10149 F20110330_AACHHC chen_m_Page_125.pro
f0b4598e1bf2b823fb9b7527a9201fd1
b530dd1a7be2af0e33182abeacfb6cb6eab4b2f7
8160 F20110330_AACHGN chen_m_Page_035.QC.jpg
8dae412b00be65c49f66ee6bf3128a83
08dffbbee6bc6decd82a25ac0281b39b8344f449
1895 F20110330_AACIDF chen_m_Page_034thm.jpg
beaf08c96789bc6f2042ccc1dd9d52d6
ed71149008c39b483f0e648e7c01da70a7cf7158
51699 F20110330_AACICR chen_m_Page_167.jp2
b8b778b8f7f3b97202aa988a4d205f35
e165523ae0169c376f806cf73d8c34362264f386
82681 F20110330_AACHXL chen_m_Page_087.jpg
ef8cbc633cb944af5ed99412456d6ffb
0d46220f38e20d3fba6315db58beaa8b6e167df9
102684 F20110330_AACHHD chen_m_Page_046.jpg
1233453ab5fb8943be9cc1f1fa35802c
b658f3a318a9424f66c487da436f1ad194720a2f
24229 F20110330_AACHGO chen_m_Page_016.QC.jpg
765ce8bb5a54764dbff02c7cdcbba3a7
696aa7a0cf9bb2d25c3fabf403d957428e13805b
2815 F20110330_AACIDG chen_m_Page_035thm.jpg
49b7c7c4fef9c72c5f0ba371388be416
ecf9f5b5d74af36dc0fce52d8b9bed4882e85cec
7088 F20110330_AACICS chen_m_Page_003thm.jpg
7ea8b09ae151520dbda3d5669736d981
b16dee45f5b32f59b429ffce9cec88cee17a7f83
13577 F20110330_AACHYA chen_m_Page_104.QC.jpg
4a1645fe446335de2f864c546494589b
9aabe50a41866b88c86d3a7c97b68d2ac1dd541b
86322 F20110330_AACHXM chen_m_Page_088.jpg
7e8b7f614606e10cf2daa49bf2166703
83093953a60e139be4bacd107d6631b9c838ff77
3101716 F20110330_AACHHE chen_m.pdf
7d97a47a21434cd7828df354ff4f47eb
65e8b1264d00020187e90730ce0938a3098a35ad
55829 F20110330_AACHGP chen_m_Page_025.jpg
927eebb0e77c21fa4fa1251ef6709900
07656ad3492804d16b6b287e9dc444d2974a5fd3
6715 F20110330_AACIDH chen_m_Page_039thm.jpg
8ca38e7ab2371c28e9d4927926d7eddf
e6076aba49e6d7dc510eb1f1fe71a60f16aac030
2136 F20110330_AACICT chen_m_Page_004thm.jpg
027b3a0da6e0a6f1208197933d3d1ec6
b1fb8b105f78d14be87ef43a51faba0ca876e26d
38965 F20110330_AACHYB chen_m_Page_105.jpg
4eba0bf327fecf1081dec72ca5635957
885c7d7f9de424cb0832ba16fcf6b6818c47a3a0
33815 F20110330_AACHXN chen_m_Page_089.QC.jpg
77cb6d32e524a154cecaacdaf609da0e
d6741683b9b188bfbc4ecdcccec347973385de4a
8412 F20110330_AACHHF chen_m_Page_045thm.jpg
5cf6a84398225f0877d80df1541cf09c
b01ddc60ed7017298f3ccf1437ba5a4ca3c2f2b8
7399 F20110330_AACHGQ chen_m_Page_085thm.jpg
f23d5b13ff15334722cb1d01ec618c8d
59cc86b04a9d5abc029b92ea2724388db9cd0a53
6566 F20110330_AACIDI chen_m_Page_041thm.jpg
b72d36471a77b8c62e69387ad3757b58
238901d12bdec12615470bc41461ad243ff8ba2b
5701 F20110330_AACICU chen_m_Page_005thm.jpg
d3bc0a7cb7cb3bfebba43eafe21c140f
7af94b583fdda4e1fdc3b5aab6785d9372cb5abe
13466 F20110330_AACHYC chen_m_Page_105.QC.jpg
a820b15324e0786870a29c2baebf2a36
9290f770dcd4778688c8c3231e249443b3e9319f
69607 F20110330_AACHXO chen_m_Page_090.jpg
d19a589be05bd233db48c079c239db75
ab8a5892dd656ad87f548f00d5c98b1c3fcd2bd3
70790 F20110330_AACHHG chen_m_Page_027.jpg
d42f5aeab983630c559221a519578802
4551573b79d8872c2d1ab836e83fb3f89600e4cf
11926 F20110330_AACHGR chen_m_Page_093.QC.jpg
58539845844b4592e20ec5c93ec5da23
5d71562973cb145180b9ffe43614de24c7d75def
8407 F20110330_AACIDJ chen_m_Page_044thm.jpg
be64ca2c20ea23f5f5b8828eee38193f
2890d6afc28c3b84450350458e229a94a553f3aa
7678 F20110330_AACICV chen_m_Page_006thm.jpg
ce11f81d08c1b839dab682ab96d7c313
0fc015d2751fcc9d524b204e31e11cac22fc139f
42730 F20110330_AACHYD chen_m_Page_106.jpg
a1b5009cfe70551ffce187b11261f8d8
00a6752115cb3bec1cf0c7ca85b07a135491f05f
22931 F20110330_AACHXP chen_m_Page_090.QC.jpg
6e91c5144b6d969ba79ae0ada5e66479
b9012b859ccb209c342d0b3550f490279628689a
40090 F20110330_AACHGS chen_m_Page_081.pro
dccda6708d603fa9a9764c314399c6ba
efe19552a00b0a67eaf2375814f9b19c819fab6d
7123 F20110330_AACIDK chen_m_Page_048thm.jpg
d6d52abba9860c81e5946ee78083e3ca
0663628ecda21562ed9028a68ea854d2fd7b90ac
8280 F20110330_AACICW chen_m_Page_008thm.jpg
c86e63a9cb6f46e5bae3cba12ff61996
b1c02abbd9111cc215a443cb826a999266f6d4c9
52992 F20110330_AACHYE chen_m_Page_107.jpg
136ff12deac17000a11d81bd44bceeb5
38c077fd1f9080f3927303ae0c81670f03ffc47f
12162 F20110330_AACHXQ chen_m_Page_091.QC.jpg
5a2f067dd7c3c522577b9936a7f46e56
9d9ff44826a67d8275e65fd3d80d24ebdd8ef992
2667 F20110330_AACHHH chen_m_Page_147thm.jpg
be6b1cfccc9fa7c563e2db4509859adf
72f9a8c5623149edc8e62104ef48dc946c11afc5
F20110330_AACHGT chen_m_Page_121.tif
29a6ee9839ef1f89a1103da005080816
ec8967a68e62b54e1b8a64492feea5f874353236
4386 F20110330_AACIEA chen_m_Page_093thm.jpg
9daa755ff967eb182012bf259e827915
ae8c8584a5ca492dc81f3f1495a1079ea7ab45f5
8166 F20110330_AACIDL chen_m_Page_051thm.jpg
59025605f9982c3b46b5fdb7ddfdae86
89f77e5e145dc802f8a2f4a88020f22c3c7da830
7263 F20110330_AACICX chen_m_Page_015thm.jpg
d7b4bf54a27a36babbcf8f1e7efb3bfd
cd8819ad7cb02c3f060b8a3c913fa817d19414c0
80144 F20110330_AACHYF chen_m_Page_108.jpg
3439d6f8149b2c779ca1994d501d0c48
80bac5751e6caeaa78d9aee76138a057f460777e
10238 F20110330_AACHXR chen_m_Page_092.QC.jpg
0ccf1736316ff9384f5a6c0094b315e5
de76bbd3a5fd9ecc366a860189b749edf934a189
110519 F20110330_AACHHI chen_m_Page_076.jp2
b7afb3ff745e57b3cbbcb15fb9f35f24
88742a6e6f7532abe5a3197dade3971508354d94
34229 F20110330_AACHGU chen_m_Page_102.jpg
fb212dfabaadce4fa5036b194ae96440
3170cbf6cbfe6d93f6ed0662d6e2fe5ed425cecc
4448 F20110330_AACIEB chen_m_Page_094thm.jpg
f07cec28ef63c5bc283b363bb7e732ba
d6fb92cf59998dd5c025f34498cc8c6f0e5c70f4
8155 F20110330_AACIDM chen_m_Page_054thm.jpg
a8ad32a31741c2803472bfe89ac7d1fa
d3d6c42da0292d4fc395e6a461c43e5ff7aaea52
6425 F20110330_AACICY chen_m_Page_017thm.jpg
e789b70471b924bbb64974cb34ab7f1c
08eeb3dd30173c01a2c3b61b49a2123a8cfaddf9
66791 F20110330_AACHYG chen_m_Page_110.jpg
0b28ca3a7c345ef84ee1a69490455a86
1f121b0f8b8a33c0d81dd6ace6aab688b8daec5d
34155 F20110330_AACHXS chen_m_Page_093.jpg
3e0dc8d654ef62a7bb02ae10a5b99071
802d127b01a8015ac0f0bd3552fa7d158cffa789
2233 F20110330_AACHHJ chen_m_Page_081.txt
69cbf1b6dfb50619163bdfa96d916537
192bf54f99edaf60c1e69495373a27fa0f286bf9
F20110330_AACHGV chen_m_Page_037.tif
b075c99af0ae69e85ead8c12a0b0cd7a
270c250fb523763b845544410e11c29ce6c92870
3958 F20110330_AACIEC chen_m_Page_095thm.jpg
e5f6a1498fdcb631401aa29150babfed
f295ccddd008abf15bed5612a4ef94863311c861
6046 F20110330_AACIDN chen_m_Page_056thm.jpg
ea95452aa1e78790e368d945eee240ac
9595647a7649c5abd5457c82607707c2d93f5b9c
7086 F20110330_AACICZ chen_m_Page_021thm.jpg
878fdbab1298292db0ad0d9b5d707693
c80806c303ba87c25d257b2d25c4635efe56932a
98193 F20110330_AACHYH chen_m_Page_112.jpg
9d15bc3af0b84e50d55913acaed79021
fb26f50e02cc64adb8c45ba05def2abb81f37f42
17388 F20110330_AACHXT chen_m_Page_096.QC.jpg
9b5d16a576abd6a9fa27ae9629518560
84f27c434581c0abe580bf56bacb29b90ab7b966
F20110330_AACHHK chen_m_Page_101.tif
dfade3b09f15e021507a9fc853573eb7
ceb8820a3ca57ec302b0025fb2bcb5e1360cbf29
30264 F20110330_AACHGW chen_m_Page_050.QC.jpg
cbdb9e78ef0b3adb37d46fbd1108555a
bdb50a4ce0730c853b79f0a30eb818d5381af4c1
7576 F20110330_AACIDO chen_m_Page_062thm.jpg
c8d6c53fab33bee4758c3ddca0d8a87a
a02bcb70bc51123c68d3ff92d2889190bea05ad2
32711 F20110330_AACHYI chen_m_Page_112.QC.jpg
6fc8f58d8549f798d083759628aaa94a
086032958a1e9a76ce449875184b045050b8a06b
43542 F20110330_AACHXU chen_m_Page_097.jpg
7dd4ca60d1a044adabb995912127db3f
88ad25ea67258bbbe8add679eaa6120c7867e7c0
35434 F20110330_AACHIA chen_m_Page_117.pro
220f1a303beafc4d690d5854ee743748
9d3e5a4b79129a674825de3fc88e509654010a42
78846 F20110330_AACHHL chen_m_Page_037.jpg
90545a95c2ec4a3ca4baef4d3e7bf058
44d8bd8aee829fddc85cfd235b82b394fcad50db
3837 F20110330_AACHGX chen_m_Page_151thm.jpg
5febf1ea5a800f825a7c092e1dbfaf0c
e58045a5c866df9b4b25e52773dfd059c41eb9a2
5075 F20110330_AACIED chen_m_Page_099thm.jpg
20bd04fc7dad3d7b3ba2b8688d00b285
e5f58f46c95f38182be9dcdce7f8857faa1e9645
5527 F20110330_AACIDP chen_m_Page_064thm.jpg
ce8d0d245eb29d7fa4eb5b2a5d2d11d4
7db110dec96cd27fcc978c7270e29239e7c830dd
32762 F20110330_AACHYJ chen_m_Page_113.QC.jpg
4298b1e2da4f3731be42af8d8a5e79ab
53ee93b9ccfe35961055cc6c1fe30d5394ee81f6
15798 F20110330_AACHXV chen_m_Page_097.QC.jpg
9464cbb8a99d89a39a6c92875801d145
a84873806fec84674741eb05a9944c329a930678
2165 F20110330_AACHIB chen_m_Page_119.txt
10d22b5f40739536f35d066f83baf613
63d54a6c15e1640459ebce40fd1b542f02115911
F20110330_AACHHM chen_m_Page_154.tif
6b537c9f8e3bc6cd7196a7a8ab40f72a
44d50d5bc886ff890f672cfdf8bf678fcee48e2b
86527 F20110330_AACHGY chen_m_Page_155.jp2
72ffdd5538ee5e34bb0c3acedf676fc1
4d4b648e4ec66e9edb70e5d378541e65a2851b2d
3921 F20110330_AACIEE chen_m_Page_102thm.jpg
94a9fa5cefb735f1a620af605c075da4
446739929190ce8aafea110afbf33ef273902b83
8324 F20110330_AACIDQ chen_m_Page_068thm.jpg
ecddc8884705f4a4fff6b8a11ba2b7cb
549e6a8350a7af1524a013de9a34a94cf7967471
105491 F20110330_AACHYK chen_m_Page_114.jpg
2dc4a6b6262e13581d138caaa0ea0c25
455877b24b327b4904988979f23fcdfacab5a4f2
15392 F20110330_AACHXW chen_m_Page_098.QC.jpg
24306f6fe13a3558fbb8061a81fa923a
2ecdee57d59cad9c1d8d5323b41d82ecfe5f959b
F20110330_AACHIC chen_m_Page_163.tif
20ccfa29d03a4d7649bb717a92eb423f
c61e7e0d4e36b35397de42ff132d10fcf77bff28
93963 F20110330_AACHHN chen_m_Page_042.jpg
1e0f165494da1f71ecc7dd24f82f6a85
85b49072a261e025d89973931802a693a5e6ea2e
106211 F20110330_AACHGZ chen_m_Page_076.jpg
45e35da7c4f31c838315f18fda20fe2f
1276e15cde364b97117a7db1c44092b69b30fda7
4307 F20110330_AACIEF chen_m_Page_105thm.jpg
1ae56a5c5d594349e1dae65bbadb91f7
c987611c441d5d27126547dfe039eb237d6a25bd
7924 F20110330_AACIDR chen_m_Page_073thm.jpg
bbac0285a0ed479fcc3c06c943424e5d
fda6076528eb7be21bf1d2abdd0c32629f3da6ce
34040 F20110330_AACHYL chen_m_Page_114.QC.jpg
568cec5b3079e0d11fab7a4b68f4a6d0
d95f8f9736bd8f343bbf9db7760128af968126bd
83175 F20110330_AACHID chen_m_Page_021.jpg
c53aaf15dca9795f763f4576969582b4
474b34e65128ea102b49e347532ccb13408d1e3c
7898 F20110330_AACHHO chen_m_Page_047thm.jpg
7f93f6d8315ee8e01ab81f7ff38c113d
3a4604304d4ae6d8de203dd5957dc31946d69b24
8233 F20110330_AACIEG chen_m_Page_109thm.jpg
05cbff961728391628c50bc1921b7652
283eae48673c89dbaa4d59e9296de20b81a9c8d8
6485 F20110330_AACIDS chen_m_Page_074thm.jpg
ad393f29105693e3fd16753d20ae122a
1692d98d62069271ef0ee37558e4cd7bb29668fa
102076 F20110330_AACHZA chen_m_Page_134.jpg
7c4f7eb8b1def904634ccdc3eba4878f
7d19c292c0670c3759532ef80a9ddeab6805d305
33562 F20110330_AACHYM chen_m_Page_116.QC.jpg
894c2c81bbecbc559dcb2b862b4699bd
f8582727a41645434225c49f57280fbb3847032d
40595 F20110330_AACHXX chen_m_Page_099.jpg
d6c4683d7e3a4abcdc949da1d2224fce
2fa0a26c6bda34f7c680381387e2e230dcd5be49
94070 F20110330_AACHIE chen_m_Page_141.jpg
8b529e88fc7fe6e04ed95e9e94d181f8
392d4cc53aab4a2ee667a605b4a39826669156ba
F20110330_AACHHP chen_m_Page_059.tif
d2925e4a158774a16fa0758a7e821f2e
54a0871c8a6d1fefad96216f70c4e302a3a9075c
6767 F20110330_AACIEH chen_m_Page_110thm.jpg
ead49df9cc372ed20a42a34d988effbe
b5377ef264dcaf0be184f688f23f20bb3670427e
7200 F20110330_AACIDT chen_m_Page_075thm.jpg
87ec8c104f2ac7513cf2f23378a75227
364170303f2d2d3b6e2ec0a3c341f2a8244ced61
32693 F20110330_AACHZB chen_m_Page_135.QC.jpg
13fb68d390732872ff8697c9369dfbe8
ca23cd6662a24f6d2e952271b76d09b966f6f90c
25623 F20110330_AACHYN chen_m_Page_117.QC.jpg
3d6fc80fa97b15cd0c610d66fd2981a4
707cd0322ad94cd33989ffdb1318babfcffe4b54
15071 F20110330_AACHXY chen_m_Page_100.QC.jpg
cd51b60f32c013d7c47826465af3cdd0
6a54e928270d3b64190516918146200259e0eacb
48698 F20110330_AACHHQ chen_m_Page_072.pro
494316308b783e9ba6871ba2e9c5261b
f541c2e455f25d0ea50244f75f7888f6db0f5f54
1776 F20110330_AACHIF chen_m_Page_062.txt
7bd45d1e8f6b9667378ae6a7450b0354
c6eae919d012872636340c713886fd60d0e7b6c3
8341 F20110330_AACIEI chen_m_Page_115thm.jpg
6fea1b2cb78a8b22616c5f778a65cce3
934b5a85dcfecaef48275495e14d069b6ad7c497
7076 F20110330_AACIDU chen_m_Page_079thm.jpg
9cc4a9510c09fb397401d5c095811d81
367599b4d93eccc1dcf6e811e3bf725402dbdab6
104674 F20110330_AACHZC chen_m_Page_137.jpg
4a45fc106f59e920e11f5f4a9c33c807
1f3ce1c66c49b6c0cdaf3fbeab1657025a162735
103787 F20110330_AACHYO chen_m_Page_118.jpg
213666d1e5eb7497ce9ae05f15aae733
becdbe9cac29e5945d37a3a076544b44e68c1734
48583 F20110330_AACHXZ chen_m_Page_103.jpg
f6e318154b34afcc0e4f8700b245159b
0adfaeecb1dd08b7026de51aa7d702a8d96ed2fe
103150 F20110330_AACHHR chen_m_Page_070.jpg
17ffbe89ace683bebc69b6edc0bbd53a
82f3dacc8ef2e799fdf0f05acedff9cae5e6eb9a
1295 F20110330_AACHIG chen_m_Page_018.txt
8b9a4859ffc9fe94c187e5bb1fb84b1f
cb8671a82ded052b0ecf6aad987f9b01515ae36a
6017 F20110330_AACIEJ chen_m_Page_117thm.jpg
d2a4dba6490564d896c0136f3b1dd3ad
3ee0d39923ce6f27cbbb30ca0c34df7388db3692
6679 F20110330_AACIDV chen_m_Page_081thm.jpg
c476212d765b55fa5d4d5f1192452b88
8b08d6a22a12ed0cdf9e9de79fcd47b6058552b7
34821 F20110330_AACHZD chen_m_Page_137.QC.jpg
316690472ab46a70c5341d553c46ff10
4af0afe1ca8cf4219426abe00f366cbb4d4e4882
34516 F20110330_AACHYP chen_m_Page_118.QC.jpg
58f117a58b32c2a7ca0f2aa0f09b9f1f
6b8af8ea51b201724de86cbdabc6c8dc510f5bfb
7228 F20110330_AACHHS chen_m_Page_093.pro
d0005f549118b3b9cb2eb3c7d945db6f
f7a55ea45c5bc5ad4a355cbe14dc4abba03db29d
7705 F20110330_AACHIH chen_m_Page_161thm.jpg
ddb305aabfb4406d7c1f40fb46e27ae7
27faacc39f101243c42b80cd3996f5b47cb7e7a3
8529 F20110330_AACIEK chen_m_Page_120thm.jpg
263ee2646714391e57ff9c4773d39e71
ae21fcc2cdeef0f04b316688cd2aad7dc66ff41c
8376 F20110330_AACIDW chen_m_Page_083thm.jpg
1311dd39813a4fdd8957d17a5891b1aa
0d8818f2c45222d407b36ebbba61150d0ef0f29c
34233 F20110330_AACHZE chen_m_Page_138.QC.jpg
3584e7bcc4eea7f5489fdac9d16463b5
20ca87f5bf5b16d40013115241f813c1e8ece54f
70379 F20110330_AACHYQ chen_m_Page_122.jpg
d8ccad73518b953ed9dd40bc8e02ad72
9774c81738e0a66d97bf01c44e0a1964ce44d686
75856 F20110330_AACHHT chen_m_Page_016.jp2
fe999d0221d820fea37b1c4496a6a3e0
fe4382e17ccecb579c7b7bf784423095ed4ecf00
8087 F20110330_AACIFA chen_m_Page_162thm.jpg
74caaa05b61f80ed322d6d3dfb3df1fd
4c82b1724f047d6082c26c0c2d0a93941144edc4
3670 F20110330_AACIEL chen_m_Page_121thm.jpg
152b224b9ec29f62836a45566308a808
3d0fb92b536c1be7fdb5bb66529d7833bfc3223f
7389 F20110330_AACIDX chen_m_Page_088thm.jpg
c2e852f6df34384407e6782f8da95632
8857275f4cc6f861c8835d4f9acfc0d98ad634a6
22311 F20110330_AACHZF chen_m_Page_140.QC.jpg
54c5a4776c4fd9ade56d3ca0673cd376
a876f19c02fae6ec3fa369056b1ae7e9662032a3
36867 F20110330_AACHYR chen_m_Page_123.jpg
57339d0c2ac1c1246e928e20c3aa8d15
994f225bc6b6138df121b7ff36b5c173a44c0c93
F20110330_AACHHU chen_m_Page_102.tif
54ade5fef2e47b2d3ff29d92deedef2a
6f664962da1caeb281248e1c14b9a82df21a3ba0
41458 F20110330_AACHII chen_m_Page_021.pro
7fd2b0d16fc227508b981043fa3f532f
15429ca1c7992659588fdd06f2b47b35d47e5707
7938 F20110330_AACIFB chen_m_Page_163thm.jpg
9ee88cc04d1a7df2555fe572cec2409a
203c0659fc0c889c89a785f2197c4e9730c318b2
3850 F20110330_AACIEM chen_m_Page_123thm.jpg
5546929a2b8631296d1d34d7622e68be
e2feca535a71c314f9a0ec5a8480be7bda04250b
5675 F20110330_AACIDY chen_m_Page_090thm.jpg
d039f8e204158b94e1ad45863a45435c
f893ef76765558d04b83dd010ab6155a37c5f181
30580 F20110330_AACHZG chen_m_Page_141.QC.jpg
60b3704154e5e3a25271b5dcc8ea2c20
ca8a6e9d28daf4449c8276f6101f685c36cf585e
F20110330_AACHYS chen_m_Page_124.jpg
6df67bee27a6c1ee6826fce503fc3d8b
0e86a2338b366df92d849be11b96d2d17058f3c8
F20110330_AACHHV chen_m_Page_146.tif
c45ddccbf0b37f8cf00b6f7790209aaf
785090d53176a71e4b993a89f4480b5c491212cc
71053 F20110330_AACHIJ chen_m_Page_040.jpg
bfd04896a798964e29c39f00ff564a7d
a5b1ab779b39e4a7e206b2f10c55b0ac023cb25c
7993 F20110330_AACIFC chen_m_Page_165thm.jpg
bbba00320cd8946bf0e461436486f2c6
90551d7478c333cd316ec6a14d4b5765fae94c3f
8619 F20110330_AACIEN chen_m_Page_128thm.jpg
bea642592008ad9c398d813841d7a70f
c2f10eb03e1c1b791e850c8ab537a78b19e338bc
3344 F20110330_AACIDZ chen_m_Page_092thm.jpg
1367afa8f6dc837348354594f8058516
e4c20d18744cd37fd1836daf29df707acdca209b
97219 F20110330_AACHZH chen_m_Page_142.jpg
00bdfeb87a2ca0f9cc21a89ef1a56e55
f7b830d4688bd5fca095baa9e304dd66e517f1d9
84868 F20110330_AACHYT chen_m_Page_125.jpg
2179e1472691b40f067e4e19a38145f7
6bb3cf037834631fce8a9dfbf5ba863d03846c58
F20110330_AACHHW chen_m_Page_003.tif
bc11ab6bf782a9b987050628e31a9131
9ea5a1df4a27e99fc4742dde7af1837522ea5094
45236 F20110330_AACHIK chen_m_Page_130.pro
c92c7ca194611c71416ca8499275c3e2
ec153cd8e842d06d5c092ed2e4c6f173de6094dd
4471 F20110330_AACIFD chen_m_Page_167thm.jpg
39ce4182fdd81d4b50da892f06806b3e
aa0efd6935a7dc5a574e9de4137e98097a1b67fd
6872 F20110330_AACIEO chen_m_Page_132thm.jpg
3aa8fa1328a6238590ef3874fe6da7bd
ee1385eb4f84554ca5539a10b4e54f8bb2934e86
30615 F20110330_AACHZI chen_m_Page_142.QC.jpg
c965b19b1977db1b5fc3d6d540ca0d93
784da4107999fa2c45d28626b718681e402ce479
101177 F20110330_AACHYU chen_m_Page_129.jpg
94a4d6516d4e675677bff66ad6876a84
0ff02ab694562247e58cf6034dedcc712852cf67
31237 F20110330_AACHHX chen_m_Page_162.QC.jpg
06bc2a2fdeb192afcffc8d1542db6596
c09ab47f531491ff07e87ba71cfd3af083b9ba8b
96424 F20110330_AACHJA chen_m_Page_136.jpg
7497c062e8b093f9a94a7d93fcd93ff0
347f07fcf76a204dcb0301afb2848aa9766c2fda
F20110330_AACHIL chen_m_Page_131.tif
df808273ee87109ab8394ca41cae2979
d9758f5b31c6f265de5bc97b90638d81e3dd86ca
8758 F20110330_AACIEP chen_m_Page_133thm.jpg
2776a86ac2a93b2097eb569ef3b90376
d25f067c6c617d061ded31bda3f2cf6347ac9c2f
8234 F20110330_AACHZJ chen_m_Page_144.jpg
6f9d8c38ab9300a4a828abbe7fbad8f0
dd0e07c8b4dba62a7806309649c64b27422a7b7d
33010 F20110330_AACHYV chen_m_Page_129.QC.jpg
00a58dd32ea105b0e4e8d2f08daf1792
f011aac577457d9362741e7835221704678e7fb5
28951 F20110330_AACHHY chen_m_Page_157.pro
5fc5fb36ef7c53c35666bc0aa89896d3
b3941f79d13f1a4f5574c51901180bd435f90d37
F20110330_AACHJB chen_m_Page_087.tif
b036224ca90cb5a5a2b3431fbc74afa2
6b33506be26f4a0ce15c80ba866e98c43c5a8822
F20110330_AACHIM chen_m_Page_021.tif
3526d9abccbac2db3ca22ffc1830843f
bbbcd2884478fd6021f1188caa167725dc91fc37
193728 F20110330_AACIFE UFE0012986_00001.mets FULL
3bc13b7648bff4895f6ddd2ce53b3682
a69c6f57a794baaa30948a9922adbd475d749586
6421 F20110330_AACIEQ chen_m_Page_140thm.jpg
b10e41f61313d1cf72e12a9fc49d78cf
20f98403fb9da64b6712b32f3c2b77ce4530d3c3
3112 F20110330_AACHZK chen_m_Page_144.QC.jpg
53eadecd87f1bc1bb6022e7341cf33e5
8e1ebb8d2485c2d81bee7eb5c13982f55cd53eb5
30788 F20110330_AACHYW chen_m_Page_130.QC.jpg
707ded5bfa2c75757931914ae4030b4f
49bd49e68622a958e0919b5729d00baae36ed107
92172 F20110330_AACHHZ chen_m_Page_088.jp2
3544acfff1e7771a1142576ce75865a9
37e88d437baabaeb1fbfc1b1de3d7441355f529c
73453 F20110330_AACHJC chen_m_Page_139.jp2
554e39f899d814eb22c178621aef9567
6eb79d4466a28b6a3499afdcc52cbab94542578a
7569 F20110330_AACHIN chen_m_Page_150.pro
0bc6953cf0b589c450977c3b383f0367
9afc8870d5f7d7af0ec762424e0c968a511bac78
7689 F20110330_AACIER chen_m_Page_141thm.jpg
e66b75e78626e039a6f225df05a4c95a
0c08538eb40b9965e199690dc34797dc74ae5da8
45219 F20110330_AACHZL chen_m_Page_148.jpg
c6c3725f248c5a9eb4f94106b04a8460
495685d5203c73179e9dbf3d2ffa8b79b04739ab
32621 F20110330_AACHYX chen_m_Page_131.QC.jpg
7be06ef0ae15cbf71a36753b23c7d65c
14dc60da33dcd664f353b60a574fc77e3c847ff3
101332 F20110330_AACHJD chen_m_Page_164.jpg
735a2cf8e498fbfb4f22113c964fbee9
8898a0ddd479005a6ea9bcbe65d4a2e9384b1228
4317 F20110330_AACHIO chen_m_Page_091.pro
e7fba5ecd3af4b6e46bca2169aac1fae
c7e43ecee57f3360f1dc39c75038ad3e18d00d47
7768 F20110330_AACIES chen_m_Page_142thm.jpg
82a7d787857de50121d4b2a6e94c5fd4
4294e59ae218835368503d5217c7dbbe3e9acfe5
46863 F20110330_AACHZM chen_m_Page_149.jpg
5538c46deed0ca2e2039c4d6f7f7bd0e
cec167f5f572f1528e46852664787f1c86c3d71a
104675 F20110330_AACHJE chen_m_Page_129.jp2
e330c90ae517c53e23c1129bfc36873c
94c628f1758d79b538cd2980c57f319ee4d85f55
97731 F20110330_AACHIP chen_m_Page_135.jpg
91d9b9324b94f03f7ff69e82aef7533d
294f68e26a38fcf17524c42db9b09ae4170abefd
885 F20110330_AACIET chen_m_Page_144thm.jpg
ec54f9753510694c9edd27591a58e50e
bfd7ad28babfc4072df05a1ba507befd40d99ee5
15651 F20110330_AACHZN chen_m_Page_149.QC.jpg
f513b67dc0d442eaae7749f4391e073d
238ff8ef2bbb3cc2e06570da5f6ca9723a8cedcb
101088 F20110330_AACHYY chen_m_Page_133.jpg
f59dd446d53c2f07c531b6ca5b29fad8
5af5031b4270ea8db81ed9f36eb840a96fa3f463
42955 F20110330_AACHJF chen_m_Page_012.pro
6b059139b16f7b713c24bd6103167b0e
11f03ea4f53a4d11b257119418005f3ecb3ab9fa
214 F20110330_AACHIQ chen_m_Page_058.txt
e6d4dbfce615bae04f0dd17d0cb45582
9a8d965b793be546184c9325a06e11977c79219a
4766 F20110330_AACIEU chen_m_Page_146thm.jpg
850f884b11b7ca76c79710ee7dfeb1b5
dee5d8e3840349c079b5e9ba20bec0bf1a377e78
37519 F20110330_AACHZO chen_m_Page_151.jpg
b5ade45e0fbaf5038cdd73c698fe7058
23583b0231b56d67d4a366dddbb92734220de51d
33352 F20110330_AACHYZ chen_m_Page_133.QC.jpg
43b8532247d425eae8c88b849bec9553
d1ac2f48c67c6ed7fa4e40c69de84fb1918bc168
F20110330_AACHJG chen_m_Page_056.tif
f50338873836743f1edf77cb97b021fb
5e0f6e6b7d3d174e5a86ace262ac70a7070d322e
F20110330_AACHIR chen_m_Page_008.tif
b8fea3f07f68048cc4548a310e3668f1
ba104ef381537372dbeebfbfd75f6153b937a291
4503 F20110330_AACIEV chen_m_Page_150thm.jpg
55c27a5764251713f2376c5c28e492c4
d1f91e3deae8df93dd0a083a3f6fcb06cda4bab6
11746 F20110330_AACHZP chen_m_Page_152.QC.jpg
0034096529b1437f0fade3fabaa616fb
ce6767bbc346d6a8d45e972005e00e8254718d9b
26218 F20110330_AACHJH chen_m_Page_132.QC.jpg
f7af85cd2243f32e8be0fcb6df05233e
12b4954cd73fc6d8ff93b0e63bc1aa7539e5ea24
51184 F20110330_AACHIS chen_m_Page_077.pro
bce7a8dc72b1beff60e7cb38e016fa72
097a133523fc129695ee596f3ef528efe7791e48
2487 F20110330_AACIEW chen_m_Page_153thm.jpg
6fee0faea5ab97c973fb99274324c955
59a1420626251a71223945d1df73896f1fe99628
16382 F20110330_AACHZQ chen_m_Page_153.jpg
bf6a51437ff26521c53a4e163d0ffacb
f2363e8c0fa094150775362f764fa81df529e740
6995 F20110330_AACHJI chen_m_Page_154.pro
02cd9f8e2a391e497acac4a142eefb2c
0291a3ab7e1688b7b96f89f6a72b88095e4d8c91
5739 F20110330_AACHIT chen_m_Page_059thm.jpg
12ea9f8ea2f12fb07a3d93e74e94e920
d41b80e102db7235311d3b7f0f7c9e486b5c8003
6646 F20110330_AACIEX chen_m_Page_155thm.jpg
4920de0eed3bc6744cfa1b5bb0f8b744
1c598fde748fe2e9a644ea7e38ff664c6a4a4f4c
6127 F20110330_AACHZR chen_m_Page_153.QC.jpg
0b816c0fd6d86d1780d04af10ccce3b4
f29f658a5586f907d7dd3fff10f2523181fb82df
26718 F20110330_AACHIU chen_m_Page_021.QC.jpg
08c7ce63dff1c9e1234ff10bb64ccb74
6f2e3b8e65c61c2ee730452bfa4496c212d75381
5029 F20110330_AACIEY chen_m_Page_157thm.jpg
f35ae5bad614a2a4d96b0c55d271633b
c295858128ff4759b9427137d23f20343f0fed98
13927 F20110330_AACHZS chen_m_Page_154.QC.jpg
3acc783f40aa12392641a606a851b4f9
e3d6301dcd4708b1511433a5121ad7069296fadb
F20110330_AACHJJ chen_m_Page_153.tif
03b073b51faee4e4926061a5d897daf4
f46a8a0b1f9e83936b237dda900c32d4a13fd02d
235553 F20110330_AACHIV chen_m_Page_124.jp2
4f697020061706e1c4a95394e9e766da
c91964bbca03e38fb2d9738f306c47ae014fbb3a
6535 F20110330_AACIEZ chen_m_Page_160thm.jpg
7c66a75246f4e876849eb8eaccc5eddb
cb853d71a9ff9b43475e4ebf209dd97a8a55d6b4
26747 F20110330_AACHZT chen_m_Page_155.QC.jpg
91b34b1cd4cf7ad8cd39f5f9c244dbc1
fbf8fe36920834b34d9d112af8ef2d38ecb0d6ae
641 F20110330_AACHJK chen_m_Page_059.txt
039ea49e0e37275068729ddd95ecbdc7
db3b91bfb07860783f45c9a748bfd2b97721172b
10753 F20110330_AACHIW chen_m_Page_057.QC.jpg
e15ac6f80ff0ac303a25f1149879c1e6
c8ec0d8801a43ed16bd55ea86914a180e444d5c3
93405 F20110330_AACHZU chen_m_Page_156.jpg
bac147dad2c49dd939307b6cd97e5f32
faa089b674e49d6e730d91a8365e435a96696852
1041908 F20110330_AACHKA chen_m_Page_009.jp2
1df1f36b5742c314ab67c10a2f252487
95f7f66a685b15fc8ac319cc626153b877a27054
2085 F20110330_AACHJL chen_m_Page_129.txt
351524b4ed65ae7fbe15d4444abd0807
a67ff10bbb6884bb1855caf61155b272db7d0820
1694 F20110330_AACHIX chen_m_Page_064.txt
5bed17d34cde0a16446149da9b657e0d
766762947295be295ca79c272daf4c4dbc27922f
62884 F20110330_AACHZV chen_m_Page_157.jpg
ee9da586db52c5fe6c335429bfbf09b2
d3518c3035de75773162fc453791fe7d6d958c0f
52258 F20110330_AACHKB chen_m_Page_009.jpg
3c0a21cd2946484c176f10afa6a1aa35
cb74868e6640f1f91a494345adabec98b8aa2612
1915 F20110330_AACHJM chen_m_Page_086.txt
a5ec9b27f213e46f30c7d2e897a6891f
04866085c1a8072f86f3224631e3b6c0cae47276
911313 F20110330_AACHIY chen_m_Page_007.jp2
361765fb996f6285d934fe3a0df4f855
59e3ab8eeed27ebb9a45a23163303baa3f20691b
23156 F20110330_AACHZW chen_m_Page_158.QC.jpg
51730806071f7f846b3bd747d89d1ed8
47af0ee62386b6e7578373c1c7f3d1d883a2b2d4
494519 F20110330_AACHKC chen_m_Page_098.jp2
dc8371f892e85ce75c6f90cbf9487054
a55aca2599e92c0d334fe16c3cd9f6ddb7809a58
72083 F20110330_AACHJN chen_m_Page_016.jpg
8b8433ef03a68cc0465ea783bd52a3ab
e208f3b73d90616aa179939de5311810462c00bc
50573 F20110330_AACHIZ chen_m_Page_044.pro
26374f1c8559861b17ebfb34d966c022
d027a5132117804b96c059630113b6cce57c7556
28675 F20110330_AACHZX chen_m_Page_159.QC.jpg
417fc1870f85f00d46d2e4577cdcdacb
d212a97906c6bf33a0add4a1df445cfad30744c9
37212 F20110330_AACHKD chen_m_Page_108.pro
a5482b9e0459e17cc717c530eff10ab6
b089f00fa43e44b469d84952adfe12936f006277
27525 F20110330_AACHJO chen_m_Page_037.QC.jpg
948e85da264c4596882cf5038e09c5e6
e9fde960aaa33d9242354ad8038565ca1fd6ff6e
26114 F20110330_AACHZY chen_m_Page_160.QC.jpg
e03b44a9a9048c04d2a3d2313558a175
c0f348c9d960806b972fed5ff6703a99fe4d0f4a
7078 F20110330_AACHKE chen_m_Page_166thm.jpg
160ff8effd154c9c0d49e6bb6862b86d
2bc16937b758b3143d13e9d2d727cd1cf162515c
1724 F20110330_AACHJP chen_m_Page_012.txt
1843295b8bfc7df1f81632cdcc98d2d9
9088714db066ce5ba7f93972d8c5faf53aadf58d
8237 F20110330_AACHKF chen_m_Page_129thm.jpg
ddf87c0e66bbdbc16cb694b67d928c84
133d933aeed25d874fd827b2eef5a59d1ace9741
3852 F20110330_AACHJQ chen_m_Page_091thm.jpg
e74c30205fe3e6589e519dfc9dd50c4b
cbf70e1482d897e64d006d6702984f3de631fa38
31264 F20110330_AACHZZ chen_m_Page_161.QC.jpg
c25f04e76b7677070736ecb80904b981
e0ffda904c07cfc059415ec485619e53e2994533
78593 F20110330_AACHKG chen_m_Page_080.jpg
37d5cfda565e60de1cf9de084da98721
4f0dd731a0f11ef27514c066b21eadbcc3d69359
91839 F20110330_AACHJR chen_m_Page_028.jpg
00a810aa58e2f0c6603af971d0b79a9b
fbf20a849b95239b9b2b74c775b3848b39999947
F20110330_AACHKH chen_m_Page_117.tif
fcda3a8933ba26edcb4c7f9376d91c77
0d2ae55b7bd96e51500c4ef3496919b4beae64ab
F20110330_AACHJS chen_m_Page_004.tif
55799271c196a4549d20253644ce2b46
94b1a5f16c76374cb2113bfc916054966dcaa88c
76655 F20110330_AACHKI chen_m_Page_023.jp2
cfc6576f50deb4e05316cfdd53c4e8b0
6acab04dcfb5c33e2aebd9a9a876b0ba7d4dc1b7
36685 F20110330_AACHJT chen_m_Page_018.jpg
1542232d39a1ea250aa1fd3ed6e77232
8b4d9eedaeec5cdac78dc7c9f4c05c5042029003
4544 F20110330_AACHKJ chen_m_Page_149thm.jpg
ccfd33fb49329d8abb694c25b72ff7f6
8edca4f6054f2b3ca4cf88130b0473e7832e46e4
309 F20110330_AACHJU chen_m_Page_148.txt
be08c6517698cad5bfb7cffca060763c
d87c024b81c0ba97b16cd43871b202bf2c98ea27
F20110330_AACHJV chen_m_Page_110.tif
27081de6747ca708ba674b96e51b5175
ed09d513b2d15be4c38a980b1cb56ada1317c524
F20110330_AACHKK chen_m_Page_112.tif
63102f15469274c1225a951942f35bf6
49da5fa8d54fe3f4ea2cda62b90d4703e84a455c
6728 F20110330_AACHJW chen_m_Page_108thm.jpg
ee54e3a8350ace28dda9ff7a4c0dad46
7fbd4ee18eb636115ba3d3ae3abd5582f158b528
51892 F20110330_AACHKL chen_m_Page_114.pro
8a6a96c4963c40e3c12470f4169d37e1
029675cc9241a0b663cdf4d3e698891ddc6615e7
F20110330_AACHJX chen_m_Page_167.tif
59281f0b62398589f9fa12ce8ad64d59
8828a994068de87ba8f47f6c03c5a64455886d33
26594 F20110330_AACHLA chen_m_Page_087.QC.jpg
c0fdda3fb4ff612a9ed8b6381619e11f
1ff6f53b09e362a69cb50ab6de0b18ef3c236cd5
34222 F20110330_AACHKM chen_m_Page_069.QC.jpg
87f18c3b456cdeda598b26bdc5f08f61
8ff23d777efbc04e52f0f8b945a3663d0823b0fb
F20110330_AACHJY chen_m_Page_119.tif
6389d857d1ea2ab5fc0b6ab0cdca77da
0e3533a158600d3f455bfe073f3f393eaf55b119
8489 F20110330_AACHLB chen_m_Page_114thm.jpg
0e829a175137f213df6f1f2565ceefc7
0d44d5759c63ef08e63663b01dfd0b3db28c4e73
99502 F20110330_AACHKN chen_m_Page_119.jp2
ebb0fb3642e0ae439c8d2071de64c57b
0ed8bd829d193af0683a04687081778d70163818
107004 F20110330_AACHJZ chen_m_Page_044.jp2
60083a9400cf44c20a516c256fc77f2e
7814687bf53842ca5879e2e8993c49c648c76b98
22973 F20110330_AACHLC chen_m_Page_004.jp2
7d44a813e9a7bd05e0e9272708a69be4
ea8351bd73f42dbfabbe14b72233990d7ccc1abb
33370 F20110330_AACHKO chen_m_Page_127.QC.jpg
2b701766501c187a35c8d1d1bf66117b
b839a03b149bb761db31275d3d74b0c7c85c7c74
510170 F20110330_AACHLD chen_m_Page_103.jp2
3d0952d9bea1fa2f4ce00bf9ac4781ec
5c344748c0fcd57317bed6cef0d55bde884c8ca8
74230 F20110330_AACHKP chen_m_Page_090.jp2
cd33406db7951be9f84e2d2a311a5898
76b5c3d6c9a074b7f1ef0cd2449bf0f558fac398
5472 F20110330_AACHLE chen_m_Page_022thm.jpg
9b632e6ab634e3d1f432949f01ac4950
1e9c8a4ec61677b679e1f976018c922a8075bb5f
1926 F20110330_AACHKQ chen_m_Page_072.txt
f25d7b5914adbac3626912f4a6c54ad2
2e1db4e49ed1cad7027b284f8c0390dab0ddaac9
F20110330_AACHLF chen_m_Page_052.tif
adac97a844f6aa9705cf54def224aed2
6bb6387e0aa214c04827c0a003f28cf2965b4675
F20110330_AACHKR chen_m_Page_100.tif
2799b3010f748626a953b7a2c881142e
d9347f0991b981ed2af199a9aafb878b5290c9a6
33364 F20110330_AACHLG chen_m_Page_139.pro
3c437c950039d2cd5f8c2c8794b611e7
63255daf5925c5a4b65894b6850d77c4efda4b0d
307 F20110330_AACHKS chen_m_Page_099.txt
7081b3af05d2dccce64cd391948946f6
e479e1c510d937c4c500b244d5d022aa309ff290
211395 F20110330_AACHLH chen_m_Page_058.jp2
e40382a377e609300ef75807ed5265c8
7018b21ed5a2193d898dcd74b67e4912c9c2bb9d
F20110330_AACHKT chen_m_Page_074.tif
e3966195b18c2eb8b97bd5a79a20eaa5
804f59f7eadb093372c483cc4a45298a9d88fce8
F20110330_AACHLI chen_m_Page_041.tif
3868c0068411757317e592d3d2db3ce9
db4b7812b7dc754f85e7dba50168504e2cc38d33
1513 F20110330_AACHKU chen_m_Page_036.txt
da9c770e84e1465ed37fb2b92f4df380
f6534e52dde472dda912276f8bee413ec727cc92
F20110330_AACHLJ chen_m_Page_086.tif
b08b414ecaaf3f07e33b33625615ee46
1cd6e9b7eabe670b5e8f9a0fc889ce04a340e282
219746 F20110330_AACHKV chen_m_Page_147.jp2
f41e908e05e5c15c8ec8ab19414ea4f7
fd6bfdbb37f054b94d72dda2cafb4dcd84ddd6c6
F20110330_AACHLK chen_m_Page_131.jpg
a8ca906f14de52ef77d48133500ff057
612d45f7969597ecb0982b4b3865e0511617f5c5
2691 F20110330_AACHKW chen_m_Page_008.txt
e928c4bdd1bbae6babefa95e70f0a3de
b77cc250942a0b30ae9a227d95df2bca4badcc78
18591 F20110330_AACHKX chen_m_Page_030.QC.jpg
542ebf57d9a8da0777c5ca30d037a78c
b3a2fe0de5aba33fb4b13a47e8bd7f9ce169f0fb
5157 F20110330_AACHMA chen_m_Page_111thm.jpg
999036d0bc9afb3c7c3cad9088a3e5fb
63277afe0d0c2988e9e968903b8f186a0847e028
140 F20110330_AACHLL chen_m_Page_035.txt
ca8b997bcbdad4eb4d02867249fc48e7
2b6f5edfbb4ac3783b329a4e0b5592a3d57d0161
372854 F20110330_AACHKY chen_m_Page_101.jp2
bedfdd3a2d7b992dd83d7569e0fcc639
ac4503b998c35b3e991ffdcef44838bed5aad7a8
99362 F20110330_AACHMB chen_m_Page_042.jp2
065354c5dd5671d360e70ad1aaf1292d
b30ef55430725c9033808634ca318094db5fe841
33819 F20110330_AACHLM chen_m_Page_091.jpg
bbd276f52cb1c33d3a82c98bb7baea81
475ee63a68fe5f6dbb130467c05383ed112431c5
17507 F20110330_AACHKZ chen_m_Page_018.pro
b0813c784d7e03ab33be0748baa6affa
ea20fa1a6d8e5638a029cb99df75826b9a1e8e38
2060 F20110330_AACHMC chen_m_Page_115.txt
a1827b6cc54485e7867d24a93e97747f
57acf692a4faa1df26c0cec7127e044ef490962f
4527 F20110330_AACHLN chen_m_Page_106thm.jpg
af12726f2d649faa8d4b95bd50a9c571
12af52b1fb3b2f3562b58b2983c931daa4072006
F20110330_AACHMD chen_m_Page_165.tif
e71701d98ca185ae9896e60e3f14bbd5
1a1861c3bcf88bcadfc3643cc26dd4e279e4cf31
1706 F20110330_AACHLO chen_m_Page_016.txt
95a80dc41dbe12aa0f9a588464a46a55
9a6d84bcdbf88b76deae79e3f053d51e07b2ff5d
F20110330_AACHME chen_m_Page_062.tif
8e2664e8d5e42d94b336468b65128f33
32522d7a27ea17225acbf3c55a0b5eedc4da317f
107575 F20110330_AACHLP chen_m_Page_120.jpg
6e89d60add724ced5b3772b51ac547ec
d0c7e3351e0f920b34c9765e1f40d4f4ffd7ab83
7299 F20110330_AACHMF chen_m_Page_125thm.jpg
7a646fca11393280c8fb966de93e113b
83eaf0ee2a5de9b7a276360f9babf3b045c8c8af
3013 F20110330_AACHLQ chen_m_Page_005.txt
9e28e85f86393e6afae524c301900216
cfe1488c185b971042d171dd5a295b4fce2840d0
F20110330_AACHMG chen_m_Page_044.tif
b658407bed669aab4268a3ef70ea04f1
8940050d496a0bc79c23f0b936ee694f29d67507
F20110330_AACHLR chen_m_Page_145.tif
cf8e677073e00f8155e055ab29daafce
9a5fd43b266781fc19f62963933989865743ae23
139143 F20110330_AACHMH chen_m_Page_008.jpg
07d76a61d0d143833456d02d6a4184ca
d760819be419cc53dff7e4cc54299889f3332e95
104309 F20110330_AACHLS chen_m_Page_116.jpg
69275d8e31af0e3c62418d0eb3cad2bd
97c54a9af2062abca23ef9f9d480c3d1f6d6e2a3
340 F20110330_AACHMI chen_m_Page_061.txt
7686349dcbf0fa28920a3e12bad5d9ad
34f38c8039df8495d5027087a01b99e7bbee68dd
1544 F20110330_AACHLT chen_m_Page_013.txt
4198e9048a87de99f6bd38873785fc6e
df0210114c8ee90c2760aa59b593a0ab19ff37c5
266685 F20110330_AACHMJ UFE0012986_00001.xml
bf3dfb14d5946bbba4e9c0bd97a8c6dd
4a2e53215f601910f30d3274fc09144b731a5385
8443 F20110330_AACHLU chen_m_Page_116thm.jpg
0e6c92976af2c1eb3b92aa99e8c8f150
2a28bcad04eb6025ed4e1fbc63c2897cad6bf698
6497 F20110330_AACHLV chen_m_Page_139thm.jpg
436a6f37a2d7e010344b5155c30be6ba
f9ac72cf28dc2778b81f5b73ac3a55910d053888
1051 F20110330_AACHLW chen_m_Page_122.txt
7d6ccf9de8001da55ef0663c9d65efa6
3a06399833a816b9489e8bba2b9c24b55f3359fb
F20110330_AACHNA chen_m_Page_027.tif
80bbd1200642d728f009d5ba000a9508
563c37e74596fc1d85fb7f2631aee4ba3143156e
47343 F20110330_AACHLX chen_m_Page_135.pro
891f13508c8daa9448ceb0b06bb4de7d
e8b28796e9100a76a69f8aa23465c8e34e6f7314
F20110330_AACHNB chen_m_Page_028.tif
5f7cf973e71bda72f78de96139eedf91
4c30e854f2a2a26d2871c79c257af37234790013
F20110330_AACHMM chen_m_Page_002.tif
a5a2ce7074e290056d21ba9b4c8a4343
dbdba7963aff6629782a7fc844e9f6bfa85659ef
51895 F20110330_AACHLY chen_m_Page_111.jpg
70c33b9a79f0124d59c646ed8a8170d0
434e669c660bb33264850d32ce212cf3e6e1609f
F20110330_AACHMN chen_m_Page_005.tif
85bc11ff0923079e5f5e91bda6326499
d49ef0f0ba00e46b06a9500f0c6c45459080f4f6
F20110330_AACHLZ chen_m_Page_058.tif
5fa1c5e010233d8568d7ebce5a74c022
067251117b1a2f23d936da270d9256b1f194b7b4
F20110330_AACHNC chen_m_Page_029.tif
57d7910a95be1c36719bf70e84ead929
67d512eddc8674c701905b8bc859a953ac5e80bc
F20110330_AACHMO chen_m_Page_006.tif
c5b904dbc6215c9734c77b1eb9c7e0f5
3e8e3a467c985ee1eb159611ffb112d7d14c5f92
F20110330_AACHND chen_m_Page_031.tif
fe3fd34c0e7313e4b06ae78b76e89823
27caf8554fbdda6eaeb36340c14ff86eb0e9ddac
F20110330_AACHMP chen_m_Page_007.tif
f76fb3ab3700ad17bb2925441d01d2bf
70e7b683e8aa739b9d30544ece038e02d8e41fb2
F20110330_AACHNE chen_m_Page_032.tif
be66f0c4ea0d2fa9c37e7df104784f6c
6f207fefd6e22928bd687862da1aa88a5c6468fc
F20110330_AACHMQ chen_m_Page_009.tif
ff126f77693ccd9f66e8f17c80d30221
39cbb0a3e9ca73a2c00d7a35a53cedbff3d60f09
F20110330_AACHNF chen_m_Page_034.tif
28de7f5796246d9dd2aeb34c520a1f86
8bb5538244d39b2811612af35dd6c3f69ebc7897
F20110330_AACHMR chen_m_Page_012.tif
e5deffc6a2122fe60882f4e37a311027
22357cd5d68f8fa44d0fe4770df4d05435406166
F20110330_AACHNG chen_m_Page_035.tif
9044ffec5373fdad854aaafc596d4a24
2d58248b68cc903f789bf232d7d58440789fbf16
F20110330_AACHMS chen_m_Page_015.tif
259741d143abd65aa7f7da8c07369095
07b1014d30553246a945dc04a04a84521c5b4896
F20110330_AACHNH chen_m_Page_038.tif
4c481861c92fcfa3cc8c0b7fa0082cf0
0c3b46b77f35cb2c532eb6292a93132db499b7f0
F20110330_AACHMT chen_m_Page_016.tif
cc0343e8a06fe47b68df2cb25ef8fe55
11505abab930c70911b3810c5709793e70231d98
F20110330_AACHNI chen_m_Page_043.tif
1375c6cbb2206c7473a2f14dc302497e
36e35c312c07d2ddc4cfddc34ee639303bbe7fb5
F20110330_AACHMU chen_m_Page_018.tif
7f2de19ab879d32b1b504413551fb85f
4d7e5b743db65fae0f0a9e0c39cffa4c98b0be3c
F20110330_AACHNJ chen_m_Page_046.tif
269de357e636daeed98ebcb590f7b241
2ba3498ca46d6e687aa84b88cbc0df0e8ffb014d
F20110330_AACHMV chen_m_Page_019.tif
5303e6830a0d845152e9cff2dad0beb8
d8a4c6ec5f25a4bdfb84272086befad6f1387e40
F20110330_AACHNK chen_m_Page_048.tif
f785e695d0c778824cdd9692282bbb2d
aeb27bee3e0fc9cacdb688da9ab9fd565dca0eec
F20110330_AACHMW chen_m_Page_020.tif
a6b9da2a8a60be6f62b506f9e1b3c7b3
97129f10a6fe895ddc81edd9526b7c809ac28d65
F20110330_AACHNL chen_m_Page_049.tif
20fb88c4ecc7cf5c26220fd7034661db
a01ab147b563175baa58947eb7a5e7c89b77b4df
F20110330_AACHMX chen_m_Page_022.tif
7d4fdfc06e9f08d65e8220e11fb921ef
f65007342b3cdbd58b5eabc2976028e13a5fbc5f
F20110330_AACHOA chen_m_Page_089.tif
f3d73ab6ccc39cdba65c8874da469c13
0aec95e25901bfd3cb2608f4c63ebbf1fabe391d
F20110330_AACHNM chen_m_Page_050.tif
8d29e27d64ba1881265660d28af9b20b
fb46159f162a529e4d65d801409fe9f301201b57
F20110330_AACHMY chen_m_Page_024.tif
1860efd8df9f3297adebe52c2faea3b2
e216dc48a431151b567831363b72cfae0cfc527d
F20110330_AACHOB chen_m_Page_090.tif
8eb0fff7f30b67d94d4510b15e3f0dc7
e12cdd3f2a9c5b2b4b114e3cbc50339f1424fb64
F20110330_AACHMZ chen_m_Page_026.tif
5c19d70f39c84902b20db552815bd3a2
f760b5eec33363352babdf5e89fa6d4a94967d12
F20110330_AACHOC chen_m_Page_093.tif
67c2626e59d07aa87bf951a7ca22fc8f
d6f142c3b1d370be086d14bbf4fddd015e6f1752
F20110330_AACHNN chen_m_Page_063.tif
a97b7d575bbdc7206ab8c7ba758e1960
0e75f5191a33319ff5d6b2f39547d80daddeb6db
F20110330_AACHOD chen_m_Page_095.tif
2580470d1eec8ed3771168aab96a4a88
78f9632a187fce782503896b6081d7a0ab0351d7
F20110330_AACHNO chen_m_Page_064.tif
dff45a1379bf426ac23f42473a487f94
684cd7e6bb9958b4635f15b1d24f3f2babf18363
F20110330_AACHOE chen_m_Page_096.tif
bfa4e2e961acd5d8deb2852083fbbc56
e33c886ec419e0e42a5f7e86c3504537ee0c19e6
F20110330_AACHNP chen_m_Page_070.tif
5325cb0d55ce7e46f7a2e3518b3ca451
f5c2f66b54361530582d82b0b3e82c1447ee9b11
F20110330_AACHOF chen_m_Page_097.tif
e9d696588923971620f2b351dbfc5858
334eea2ee41b432b7e627e2afd7db8c4e8bc337d
F20110330_AACHNQ chen_m_Page_071.tif
85b4ebfc715ccd6e586030b4dc34fdca
a6f0127ff8270625fd5f1ee9dae940543e0055d9
F20110330_AACHOG chen_m_Page_099.tif
48aef7742661edd3836ed63ef27f7378
ecfda1f155b5ddeb04d916f10ad81f9bb65a07de
F20110330_AACHNR chen_m_Page_072.tif
e2ea7d147f6dcce3fa155996781369cd
3d503958a010d63a754bb7c519a500ebb73e82ae
F20110330_AACHOH chen_m_Page_103.tif
671c7226dcdd9904d7b43dbbe8f7ecf6
3f0fef31415fe03c04f6a3635112032729715565
F20110330_AACHNS chen_m_Page_073.tif
a410acb029f2900230f0e6b0e0909002
07a6a495242e3476bdba38738291e00fbfe9d3c7
F20110330_AACHOI chen_m_Page_104.tif
8a14105fbbfb2576c76636c313d6cc74
43661726648ee4b95226ced3f090d456c861ada9
F20110330_AACHNT chen_m_Page_079.tif
21e518d6cb7e9f76f1f7daadecbc43fe
10d78b040894c8a904243cbc2500b6037f087d99
F20110330_AACHOJ chen_m_Page_106.tif
2e8c19d0fd60beded6b6c9ce5c541c18
0c3c85705034ea776ea7221a2c48d77dcb1839a5
F20110330_AACHNU chen_m_Page_080.tif
6818d0c1909d0dd85769691a4479cdaf
1ac7210db3d5710ca750778d0fa8d54c3f2e605c
F20110330_AACHOK chen_m_Page_111.tif
70c1a1d0b90a338c164997aece94b4ef
4e56543745a4b75c6038a83eae797f3ff381b0aa
F20110330_AACHNV chen_m_Page_081.tif
a28f4aecd181e620b3d5250da7c86659
22547e540cd856c44baac4537d960b8cb26a1427
F20110330_AACHOL chen_m_Page_114.tif
e943f97a1de7144eb5fc5df4a19d9c3d
a5fc362597edc21ebcf4143d27c94cf37f1cfd8e
F20110330_AACHNW chen_m_Page_083.tif
c2dae811cbb8aa45ed2e55f6d1bca2c6
5656980eab4a4affaf83c687b7d4ef46cd565f6a
F20110330_AACHPA chen_m_Page_143.tif
e695af75c1dc670c620f966293ab85b6
d2d06b7a8950d523a27c02cba3280bef6ecd7fdb
F20110330_AACHOM chen_m_Page_116.tif
c27716186c1bf198ed800ab09f729bf8
43f0811163eb3cf477f320b4e7f93652832cc524
F20110330_AACHNX chen_m_Page_084.tif
144fe2a672b108b6b2c0b7f3d796ca9d
6fa32b04c50642357ef837409cbc2ac068eb4481
F20110330_AACHPB chen_m_Page_144.tif
4e4f36723064c340ce1a03184d0a51b7
f4b82f15fd24a15b860d68a5b39a13a9ba498215
F20110330_AACHON chen_m_Page_118.tif
61d9b041cec4c9afab74824481731721
bf5ba14f4704b16cec74adc649ac20154a3b257f
F20110330_AACHNY chen_m_Page_085.tif
bc592fcfdd9063502d2eb360d57dee33
33627cfec2c5d51fbabdb8dfb46864ce16a3b338
F20110330_AACHPC chen_m_Page_150.tif
b70abd0f37a8a79ca08c64d2bf952f14
185936971b02f972d5ff68304af025e7118b950b
F20110330_AACHNZ chen_m_Page_088.tif
b8e631f5db91c008a73204257eb784e4
f454a0b4a299fd5b93f4b0ce4ad3c6624fb4664e
1847 F20110330_AACGMB chen_m_Page_022.txt
c851b2a35268ce0e0ab06b43faf216df
dc4c004be959d1e36619539235e513c91fbbaeed
F20110330_AACHPD chen_m_Page_151.tif
d10b817e87271f069abb2dcc7afe5eef
e148b72cdec09fe700eeb4726d54b6e7638a4d48
F20110330_AACHOO chen_m_Page_120.tif
e11aed910366828a0bd2652f0feaa3e8
145d699d62f199db8bd0def3f3027451d217c1a4
87752 F20110330_AACGMC chen_m_Page_003.jpg
998c281b45458c9170444d25ef273ee3
5c09d5b7400d63510f8fb92dbae93fc0a9f33e1f
F20110330_AACHPE chen_m_Page_157.tif
290cc364caefdc859b70582f1912eb17
2e0b05aaf42c4a6387316b88f9c10c99a83b1bbc
F20110330_AACHOP chen_m_Page_122.tif
e22a89ea764cf41adf912729ca17cc12
bbb4457aac68fe6acbb9fe12d4a1a11d01d0b6de
3197 F20110330_AACGMD chen_m_Page_007thm.jpg
fa654b816d081b3d7af9ac6ec6ebda13
73a6e30ecb1019c52e1b828724a259b6e6c298e1
F20110330_AACHPF chen_m_Page_159.tif
46357135b537e8f0061d684bcd47ebe9
b926c6db012f42f6ad4a2d85add9a57c2c466cda
F20110330_AACHOQ chen_m_Page_123.tif
ac360e4100a68dcf0c8c5b1388278033
0aca9b15c1fe4610dea2c30e01d619db1ea8ed24
F20110330_AACGME chen_m_Page_033.tif
c4c697acf0eee100b38f9ed33fb812a4
5ac8a4d816dda6831c25c5a171c3a8bc6195c455
F20110330_AACHPG chen_m_Page_160.tif
ae533dc12a6f6b99f1f4a0731608f2c5
48efab5ca84b3de8bc6ac203c91d06f230ae0006
F20110330_AACHOR chen_m_Page_125.tif
d2ad324a31be97fa44ec5775f9e07d7b
d48c74a04dd002695e4faa7fbe829e9f5fe30881
89707 F20110330_AACGMF chen_m_Page_134.jp2
90a5d0b1855b8dc47d62853fb5ccef63
e091ae50a27ec60453a1db59929f9c7259643d5b
F20110330_AACHPH chen_m_Page_161.tif
03f15e061ed22a2ebdf1b4b14960d177
bdf37eb4368d19b93876cb845ea11f54c9024cce
F20110330_AACHOS chen_m_Page_126.tif
b2eba05dd509dc344c126d83dc115bf7
3294d5394cdc8146df2f34ee2b8a003fcf8866eb
8218 F20110330_AACGMG chen_m_Page_053thm.jpg
f82d6b18db8c2c0348a32c1ec36b0517
47a812ce173c68cbfb66fbd8f281bcb6de3ce5ec
460 F20110330_AACHPI chen_m_Page_001.txt
efed2ebf630402e8c706fa96b97f5da9
bb867d4d149bfece00bfa2d3d3d2bf92e7cea152
F20110330_AACHOT chen_m_Page_128.tif
bcb1af420b5011602ccc54a90f42a2f4
58ccd74ba2d4af865960c077986102a6ccf75d1f
45601 F20110330_AACGMH chen_m_Page_150.jpg
2f75988c0f5a0382bd00d932e8763ffc
d64af30299ffdea9de49aeebeb8b04e1d8245485
106 F20110330_AACHPJ chen_m_Page_002.txt
ea2f9859da841a9fe43b2c37dd173652
80374e521b052b61e1fb4d34de3a2c4049ada1b5
F20110330_AACHOU chen_m_Page_134.tif
3bfc27d41139dc08beb483544c4277e9
85ae2772c555878ffddf5e42c77b3a7f159a22e7
6061 F20110330_AACGMI chen_m_Page_063thm.jpg
5c1d54fed163e03fa4d9296b3c529135
11a6052019a16362d7c35738fea6656bb473bd6f
372 F20110330_AACHPK chen_m_Page_004.txt
1f3fbc9f3d6854b1b8ee85b042f5c2c6
113541759d864f441aac1881df2a9d239f7c9d39
F20110330_AACHOV chen_m_Page_135.tif
2844e3f3ab05e42f13e98eb80be1f4d6
fc40c7bde628cf48ab9a9075babbba0d4e535e28
101316 F20110330_AACGMJ chen_m_Page_127.jpg
e503e46598efb4de63977bbf54612a71
463483bcc3d11595372898745b2a05974a375fa4
2601 F20110330_AACHPL chen_m_Page_010.txt
cb9b75d23582782eeda7a40f2dbd51ff
40ad9d3a174eb740f5019b699188d62d6ca76fb2
F20110330_AACHOW chen_m_Page_136.tif
d6902697ea825dc8b56d3871959da723
49eb16b347b49fbe8e54d702b5cb34f83842fa76
6419 F20110330_AACGMK chen_m_Page_036thm.jpg
24fd15d8c4097a6a8842eb54959e93c1
31a0f92cf67fa29c0ece02d8a6b9cd18446beb21
1383 F20110330_AACHPM chen_m_Page_014.txt
b3374a7d041313a86d1700ec1dd75fc8
e925569555bad87ad02f18a045a3fcbdf15caf05
F20110330_AACHOX chen_m_Page_137.tif
0181699f1f93b158b33e19a966dce245
1f32e3125971862724c399b4ec7f1787be1e2855
1850 F20110330_AACHQA chen_m_Page_050.txt
588c9f71fe9938d65e43dc7cd02aa6b2
880d939dc8b95e59e8134d0def2ac3f851e64a17
8108 F20110330_AACGML chen_m_Page_113thm.jpg
7a4ca8dc6f75876be5e12414f62b51df
9e855f904440ee84cb422f9a47b8452c98c670d7
1587 F20110330_AACHPN chen_m_Page_017.txt
eb2d1ed3695242210512717b93cec5c8
8f18c450f8e8ac35a62fb08756b4b4392d27338c
F20110330_AACHOY chen_m_Page_139.tif
7cd54c4b41484609484edb6dd75d6c60
7eced09c999b8a6d3a07c985c46e36f55e16b4ec
1913 F20110330_AACHQB chen_m_Page_054.txt
8a5086ac73ea74462da089780f490cd3
beff94cd6700a2ada50676be611a2b0152b7ed84
1878 F20110330_AACGMM chen_m_Page_085.txt
42774ab18952d18def84455f6cdc50ba
2db8bc45dd5d23058938307693802dd2725542ed
1814 F20110330_AACHPO chen_m_Page_020.txt
be4bc8079ff2edffee2381f27ee0d14b
10564569b5e332289d184834250835b38721162f
F20110330_AACHOZ chen_m_Page_140.tif
d100d4ff335d7e3eb36900732b728976
b7d8391b66c1e3cb1b895432fd7a4025e1380f27
8308 F20110330_AACGNA chen_m_Page_070thm.jpg
448d4fb2dbe4f1986b3865bcc6f22055
fbd7a837d027e64b5a15e5b931583ccf20915639
1636 F20110330_AACHQC chen_m_Page_063.txt
84ed8101b3f439c3c4bab8bce2215039
024fb96d01f94000b92429a52cef547bef27a680
8023 F20110330_AACGNB chen_m_Page_164thm.jpg
e045c66bd49c6dd265461eedd16338c5
d4a90c915b50a6a367e56de3ee8954bc1bbd6f5b
1995 F20110330_AACHQD chen_m_Page_065.txt
db11a0e89979835dc1c3094f4a6e2f0e
73f1cde8636c1d544b9caebd436a058fe7755cf0
11549 F20110330_AACGMN chen_m_Page_124.QC.jpg
639ba92d169b1fa2b7cf901ab460a016
53b55ceb2ea37ca362d8f6980a9ab2ff4702d9d1
1723 F20110330_AACHPP chen_m_Page_021.txt
6ad47b1a3f55ad987dfee0aff5dee908
bf6d5a9ee6705b2ddc4dc00b1d738d6b8cb428bb
8081 F20110330_AACGNC chen_m_Page_112thm.jpg
9e8500a02f0ec4b34d135225285032d0
972a90e4d0e2a8291a6df262322fd0773e631013
2057 F20110330_AACHQE chen_m_Page_069.txt
ca0a55ce5eecc3e04edbaddd36998baa
deb5d073a5af706128cffa29e35d1a4e2d3fdadb
8951 F20110330_AACGMO chen_m_Page_004.pro
a2e2a80a1901b693ceda4220d84b8366
1e3a70b2a50afa6148d277258937a50c84282413
1685 F20110330_AACHPQ chen_m_Page_025.txt
edf0da8c74669b83a344a3d454046bae
34fe85f0c0dad0d48b7f0450bf3275cb4506bc7a
7114 F20110330_AACGND chen_m_Page_037thm.jpg
e8c7e9dcd824c7d9db2fa0f7bef02bc7
63438f3a7d940f7e004ecfbe7de7fd08f245516c
1659 F20110330_AACHQF chen_m_Page_075.txt
9f29a2925c0f39a3a69e0a12e086892e
0439a3800833eda5614e00516835d6315c5b6def
1822 F20110330_AACHPR chen_m_Page_028.txt
156259e18d1458dcc0856871045e4305
96345b29242a9133a383f5ec4d3bafb7418efa22
81258 F20110330_AACGNE chen_m_Page_132.jpg
3b1ffd381853d2fcb1d3a3f75a40c8cd
b5b3869d7cf2dda7543cc8d79197336298c46941
2049 F20110330_AACHQG chen_m_Page_076.txt
5937faa1ae5a7f9e8bea0f2bb5427437
8c7e0c4222cdf9e060bc1a1421a863cee670d6d4
2301 F20110330_AACGMP chen_m_Page_001thm.jpg
b76c77c7af666868ccd4cd60561c7fbe
3eef4772bf06c5876c3b17ac049b9fb3d3d673fb
1977 F20110330_AACHQH chen_m_Page_078.txt
228c03f6ba4fdd0ae7f3d37b6fafdac4
2dda4f00ce3eff192fe0f74d91f9739f5b9ab7a2
2006 F20110330_AACHPS chen_m_Page_029.txt
558d4f734888bc534c471d8c53a59fa9
b9d6b7651a8d08d69783e318c49a8c50b64410de
7688 F20110330_AACGNF chen_m_Page_156thm.jpg
c6bf3f24ccfa4b1cddcc6a014fd865a1
c2e82da6d6c69f2c9280039e835e3c8b2564fcd4
8511 F20110330_AACGMQ chen_m_Page_069thm.jpg
9403c252f4f49abbeb6f6ab2caa151ea
b6af7d6622074bcfff4950a83bc0def75f836bc4
1965 F20110330_AACHQI chen_m_Page_084.txt
1e24fd3c9cdfc8e30424c301bfb23d29
7fe6216b5ff93067b3b34f0bed161b9ef75455bd
1837 F20110330_AACHPT chen_m_Page_031.txt
0b4941629a96935eb01b094966918805
230041c1606b529aea07059c7c3a30889d9495ee
99980 F20110330_AACGNG chen_m_Page_047.jpg
523952871d049d1d5f202389a1f0a672
3a04dd562d95722d7d36e4740e248f1382ff490e
36222 F20110330_AACGMR chen_m_Page_029.pro
a5e34a4e13176823b0b8d131086d10a3
20d54343b6cfeb5c296604631757963eda47d26e
1692 F20110330_AACHQJ chen_m_Page_087.txt
d5681178b8a14e0a0730386254151c2a
0ad5dddd587989a09401358667de40757f53383f
1812 F20110330_AACHPU chen_m_Page_032.txt
ba50611a4c747bca2d46e022c143671d
92e8e2ec609b3e33fc9e96010345e563284b07d9
89695 F20110330_AACGNH chen_m_Page_015.jpg
c1afce86870e5e252c51c30ae00f0e79
317977352fba4970802ed5c98ce2ac20ade73164
1966 F20110330_AACGMS chen_m_Page_068.txt
83646d6ebe1b1426cbb52bbce7706b6d
28f38e131a1741b21c3825a5a394f589e48e05f7
1357 F20110330_AACHQK chen_m_Page_090.txt
54f6d89e29b45b01d8475e9576ac9965
8708dedf0765b5a6e635e505acdf7274fa9cfb4f
85 F20110330_AACHPV chen_m_Page_034.txt
430b6dfe991536c6f90aa1052af799f1
080c2530deee7f45f50e36bacf09a834cbfb0124
35444 F20110330_AACGNI chen_m_Page_154.jpg
948993e05559bdccbf11592033253a3d
c915512e3279e7fe8206d74b716f557626c08f1e
1717 F20110330_AACGMT chen_m_Page_110.txt
07129926dcb4cffda6feac7262a36da6
1262158f8a97f810df6bcfc9cb2d7b6d70f090d0
283 F20110330_AACHQL chen_m_Page_092.txt
3a933f74b1c507e985a92028cb3b479d
4c4c24aeaea4ca250941659d1fab52912edfb211
1763 F20110330_AACHPW chen_m_Page_038.txt
173020d4791fcb1ba114bfec67e723e4
1ae870e871b182ac408fce992a86f85d01bf6b3a
12612 F20110330_AACGNJ chen_m_Page_102.QC.jpg
659f49b4e2e4064bccbf4c1f2a6ff8c4
97278538f8d9c6b2f3177a384c57d72d028d3b0b
1973 F20110330_AACGMU chen_m_Page_046.txt
d54fc2ac87409221d844216bc3576a0c
6a7744733a35f005705c639a2f7bfd5756a08245
2205 F20110330_AACHRA chen_m_Page_128.txt
b0547c319e928c151728f0be0fd2e60d
86e4598fa99eaf0764553262a13188478f4ba022
426 F20110330_AACHQM chen_m_Page_093.txt
cfbf660f6d580f38dcf7f9f7a7053a11
e0eb57773fcb2fbce7ee9dd00fe78e07317aabf1
1574 F20110330_AACHPX chen_m_Page_040.txt
52115d14c3bfc796c802c2d083c913b2
607a83f39533dcb2a3b7f1d2627befa7eada7b55
8195 F20110330_AACGNK chen_m_Page_052thm.jpg
f00ea2ca96a9d0dfcc59a9a3f8feecc0
1a75653f4331afbce5067b0a820f02bb90c2121f
F20110330_AACGMV chen_m_Page_025.tif
1758328113fd54b1b2c959cb103289d8
b6374d97f8822c26e404b813f849067c24d123c6
1802 F20110330_AACHRB chen_m_Page_130.txt
beecebde2281620424b6373ddc1a7d9c
5c20e9845a8c2288ab66c2fa7d8668faa7101c21
667 F20110330_AACHQN chen_m_Page_096.txt
93804b6d92d849b56ad38558e6512747
417601685d183ecf14a4d849257e1185ad47c698
1937 F20110330_AACHPY chen_m_Page_043.txt
23b588a224a4c475b7d902c250eac8ab
3b515a75679e69b99b342733c5887eced5073e1b
3671 F20110330_AACGNL chen_m_Page_152thm.jpg
96b300c3509b1a1a2c8f6a7e40f625a6
97eeba3774f408df34151c6bdfcbd2ad74a9b6e3
4586 F20110330_AACGMW chen_m_Page_002.jpg
1530802fac0d8bcaa401895cc442e22d
ff9d31fec6be142f0d41c6e89e558df32b1515a7
1934 F20110330_AACHRC chen_m_Page_136.txt
6f65cd9e9e50562f134c0ecc0738a9a2
07b8a7a59ac2dca8252ced3f9dafa627bfe8c948
781 F20110330_AACHQO chen_m_Page_104.txt
ada102b47badaf1f4f45352a6841c1e8
d4f087ca67fdcb0d3b0cbb7b04a8490e3108fb62
2001 F20110330_AACHPZ chen_m_Page_045.txt
c5ee473cb7dc4c84038b0959656bfab8
cc46105453fa840d0be233223fefb03d884afe8a
1979 F20110330_AACGOA chen_m_Page_162.txt
9e4510cb92a5eac45c60749f357900f3
216a3a1f0c87e078212d52a0d9491f9fe753d4b7
107127 F20110330_AACGNM chen_m_Page_072.jp2
f308ed00325e2c67cbace6c719935181
b9268590a6ce57d02fafe1a78612dd9a942168af
4540 F20110330_AACGMX chen_m_Page_019thm.jpg
e3318669fbe71ba1433a0c91c09866e5
872f7a2c3b073fb5862a2580dbfda25f680339f2
1996 F20110330_AACHRD chen_m_Page_137.txt
f0a8285bab1929accaf210569daa1842
9d629b915a4ebb0efd494039a59c7076cf20031b
586 F20110330_AACHQP chen_m_Page_105.txt
c8c140dae6ccceeb0e7b0cd86ea9bb0e
dfbbfa98d82ffbe72ad686b8fe459ea67477ec5f
2009 F20110330_AACGOB chen_m_Page_163.txt
3b57db5be1949ec2904b75d8a8084514
305ec8f1338de2e3ba34546fd0ba77ae39da35e1
61195 F20110330_AACGNN chen_m_Page_038.jpg
dd51f99d78c334276725497c6f0e0b76
1e73fc1311ecb37dccd0799a3167b03ddeaab995
19621 F20110330_AACGMY chen_m_Page_026.QC.jpg
724f014a786a363b66cccc26bf54774e
d0cd34fcfb0358df8451a3c9e798fc39f3809a50
1690 F20110330_AACHRE chen_m_Page_139.txt
98025df2ba487c71b06ef06c6a907f51
5b7245833a1e63be0256ba33acafb05d80bb109c
1823 F20110330_AACGOC chen_m_Page_088.txt
44ec020f5459daffdb18f39719a5c680
d4664a0131c0102faece66f6e432f6992dea6b7f
37057 F20110330_AACGMZ chen_m_Page_027.pro
6a1b58683da04e7743ab0b185807148a
902a5120073aabc397a20b2c0dd23da772129905
1816 F20110330_AACHRF chen_m_Page_141.txt
6a405d3f3c02322a022df7892f5f119f
7aa3fe1df9819998f94215e89de468f758e025e5
861 F20110330_AACHQQ chen_m_Page_106.txt
ad190d43a1faadd308a63478406f3549
6268d94e1b26ea4376680cf5b749d834b8924bf5
51872 F20110330_AACGOD chen_m_Page_083.pro
e0d7c30032ceef869bf31876d695cfa0
8dda9e0b67f11f69feaf308db0dffa18239d2efb
915 F20110330_AACGNO chen_m_Page_009.txt
55731a7a9260f4f62f899ec656dd6dd2
e05bcfe205a014718d308bfede5365a88f46cf7c
1856 F20110330_AACHRG chen_m_Page_142.txt
6850cf8b068a24cbf3d2c76ded086a60
10fb04d50a2f13ba7993887f58cc3602c21e9e16
763 F20110330_AACHQR chen_m_Page_107.txt
4b7af87e0015c682101297310ed5b06e
067dcbce22a73290942928d5ba790171b9ce2c0d
F20110330_AACGOE chen_m_Page_017.tif
23ad45e4c176b153086c63e17cf8f6e2
51daf3adf1d94676731a1a57de17f181a4eb4eff
87614 F20110330_AACGNP chen_m_Page_126.jpg
c377fb7fb084c581d7223174271b7094
5eaef67130715292022e5779a038329e52fa0335
1962 F20110330_AACHRH chen_m_Page_143.txt
c05c1f9e6afae560dd9e36d6e5f6af69
8a390013cefeb7d0cce16ee0ff4147c683d82f9c
1679 F20110330_AACHQS chen_m_Page_108.txt
1f3a48d7f18074e9f7296cd6b3d11c5b
76095533c8dde1e968c945a4ecc55312e4f3f8a0
15878 F20110330_AACGOF chen_m_Page_103.pro
df1099414f4d4c68ad8636703a3feb93
e95f531269e8188631536f36924970473e93ce7d
14072 F20110330_AACGNQ chen_m_Page_059.pro
56f80e0749c70159355307d77677c684
829fe753e925ea94cbc052e676e400ca614c1c51
191 F20110330_AACHRI chen_m_Page_146.txt
d42241b445ea9dd6928a19cdef20d47e
46a8c5284b25d5de7f123d886addfc9e636c6db0
2047 F20110330_AACHQT chen_m_Page_109.txt
76414c4f3399e28c9ed3d4d3bd674522
62209f764d3123c71a6c2ec16660d0a78962434d
8375 F20110330_AACGOG chen_m_Page_118thm.jpg
a26e806c917fc44013f5ec662206e8c3
f0cbc3fe4f22af120abf89fcc7efb1f45bb3dd24
F20110330_AACGNR chen_m_Page_125.jp2
a1e19818b5746f51c82d2aa408be6ad9
793ebc460222485d51221805d2f2dc326ff52733
435 F20110330_AACHRJ chen_m_Page_150.txt
1cf65f38e33422eeeb267376b38f2819
56b15c22e428fd7e508727e6dae7e88cb643c5bf
1604 F20110330_AACHQU chen_m_Page_111.txt
71b6c3e63b58d0d8775ed1b987289a60
6ea98f5ba28f0b94f8b20605a948e15e0f638444
51078 F20110330_AACGOH chen_m_Page_007.jpg
ea262f459cef2de09797198b55d0c7e1
e9f113b8fc348bca610ccd52d7eb26f1d52a71c4
9596 F20110330_AACGNS chen_m_Page_011thm.jpg
1182b621e21e09b0dd48cc833221e681
6de67465e6cd6cdee6abc696d374a895356d6a45
353 F20110330_AACHRK chen_m_Page_151.txt
6c6117144656d3e45d5750273b6c0b5f
8346d255904f193cb88a89bda188ef065e56c357
1930 F20110330_AACHQV chen_m_Page_112.txt
b89faad0bf9d9eaafe8cfac83ae8d9cc
82fbb469fe69d8e26caa9d40e2db6f8f58d87dfe
108422 F20110330_AACGOI chen_m_Page_078.jp2
9bbf2951ebe943323023ad2b1bcd5bbb
effbc5a38d06625b02ff5b6248251ab2015a67bc
104682 F20110330_AACGNT chen_m_Page_143.jp2
770003c160061b7b1ec25f1f2e785211
7735c0277a88a2e1b914948fa91d8e2463518e98
211 F20110330_AACHRL chen_m_Page_153.txt
8066ae23d05c5bf58467bd4b07a9e407
30574e892b87d2cecfcfbdb466da3aa439c49b62
2004 F20110330_AACHQW chen_m_Page_116.txt
03b1f31dedbc6db37ed6674148752238
46b431a43c78b15aeb219e1db37546f0de7a1879
474 F20110330_AACGOJ chen_m_Page_056.txt
695638516680f2f010576a40cf8c4177
7d4500f7a7ebddd862802062b35bc8e1510122c9
11626 F20110330_AACGNU chen_m_Page_055.QC.jpg
67eccf4801b91b1c9ad3f97add8da884
a5c30a841855c8866eb7505ac3b4d7efc71bdbbf
44068 F20110330_AACHSA chen_m_Page_015.pro
784b6783cfa979ee3d44fdb3939d34e7
ba61fa0afff063e43bc5fc841b069500a562e0af
1789 F20110330_AACHRM chen_m_Page_156.txt
ab6f8defac7f5cf32ff039825eaff7b9
a0bc4e0ecf21280325bdf9c31a872e871d82b4d0
1551 F20110330_AACHQX chen_m_Page_117.txt
f81dce35c2456abf6318c958987b8945
0508ada15ac422ad94a831de66d553ff267307aa
317002 F20110330_AACGOK chen_m_Page_105.jp2
cf3170e598c6cf2ffd2af26febee5829
ae6af5e88ce0de6d7fecc80c08238ba8c8ae188e
F20110330_AACGNV chen_m_Page_082.tif
4f3f77456a0eee901367eb41ebc5a901
6145c6d7e864ddd6b45b94849951ec580aac4622
36254 F20110330_AACHSB chen_m_Page_016.pro
f7754589a2e826f7207bb2585e32a87e
0448bae746bde03f6f722a3bfac63c3813b1e202
1187 F20110330_AACHRN chen_m_Page_157.txt
c2731f74713fed58fa882956801cee70
1efb97a1ef97490964fb21b490a994549d6fa52b
805 F20110330_AACHQY chen_m_Page_121.txt
860c13f1c5d5385957e8be54704217a7
a4ec1c81cbd78ae206c098a9608277af52b9a23f
942390 F20110330_AACGOL chen_m_Page_122.jp2
f71af41be0276ce5f376c60af176d857
405ac720c65da341b0393f43d2e4203d3a3e3e14
98399 F20110330_AACGNW chen_m_Page_028.jp2
a2b5d6f5cdeeddc97bc5f5e4de5398bc
c950a72f41ea4b859da22e60bc7fac5c95ffccc4
35333 F20110330_AACHSC chen_m_Page_020.pro
b11267bd499d7cfd25ac1ba405ef29be
83ad859da3915075fde734982a39a668098497c8
1370 F20110330_AACHRO chen_m_Page_158.txt
e87b04590869d0fe21f2121d734dea91
151bb85c0a0af06460217d574faf9c0ee4543b51
420 F20110330_AACHQZ chen_m_Page_124.txt
4cf0edc3662e104b89c0bfe023e93c85
202f92cf1cad655c14faa53be090917d46046dcb
111193 F20110330_AACGOM chen_m_Page_083.jp2
0c0fdf5494cfcc068c0592fe60f49db4
e63cdbd3a680470739d67e2d4ed836672bce61ec
2586 F20110330_AACGNX chen_m_Page_053.txt
b9396e9c201495be7ea423bd558298bd
924c726835aeb2deb48b14597636d666245c210e
104334 F20110330_AACGPA chen_m_Page_138.jp2
383b06c746a12acbd7ed45682c7ca49c
f73aa4995b5829017f588033407bc0dbac31e995
27784 F20110330_AACHSD chen_m_Page_022.pro
de45500c4a74dfe3924702ed5c1ec4e8
509bccdbdd4a8a16a7200a7c77d8c95a71060d68
679 F20110330_AACHRP chen_m_Page_159.txt
ddbd228ba5d1ce094f10c313064d0ab2
b42a1bbd0e78ff8dc260b443c441a307151f6181
88248 F20110330_AACGON chen_m_Page_048.jp2
a46bf387fcc79a2731e5bed389efb272
d49f439c96e7f8e2f33e6507d139eb1a3ad183b4
14401 F20110330_AACGNY chen_m_Page_094.QC.jpg
4d6c886a8521e0b8e1cb0e51fa487be4
f883314e63b3988653b77417725e0c77d1d9c0dc
9839 F20110330_AACGPB chen_m_Page_098.pro
1fa05d351ae060cf51c524072445d43f
95934b17d45c74db2da65b6d2bd2987c68132871
37995 F20110330_AACHSE chen_m_Page_024.pro
e3244702eeeb24d874e9ce78ba58eb4d
97f86cfad5433403d2fab2a3a9a6f73906023cc9
1939 F20110330_AACHRQ chen_m_Page_161.txt
b30d81741a8975b129f96066b936b00c
1474c0b9acacc1d45b472644c9553df421519107
4215 F20110330_AACGOO chen_m_Page_031thm.jpg
c803788207c640748a9ce08b8fb307e9
daef4b0b5e7e6564502535426927b53f8a8dbe66
23775 F20110330_AACGNZ chen_m_Page_005.QC.jpg
ee6ebd5a1a7905f5ec69aec2464a4f31
286314cd4baef62e49bf34c1a0d175168c444a49
12562 F20110330_AACGPC chen_m_Page_146.QC.jpg
43b7d28bf48950758ccaf53a50445640
23b3b8d16b49bbc8b1dc95e3aab877553a9e7adf
28898 F20110330_AACHSF chen_m_Page_025.pro
ab8d11c3dd47caecadc65f758d1395a2
1b008c01c70e8d3b77b0319d76bb903ebe0274ae
83285 F20110330_AACGPD chen_m_Page_024.jp2
0ad63977e4886e60fa2dba658eaae736
b887de9b80e427f5e8316e7bcfa78f5fc69de8b3
28386 F20110330_AACHSG chen_m_Page_026.pro
97eb4ac5a51b11056c646c3e1177d7cf
d483470ffa096176874901fdd98daf07e3202bb3
1987 F20110330_AACHRR chen_m_Page_165.txt
0c823df7e1cae7232f3727a19675e160
a9fa1c2af222a718f79a3b233d082cc9d892198b
29937 F20110330_AACGOP chen_m_Page_066.QC.jpg
3e7f7d9bdfc6aaf9cd3b4b13ca8352c5
f97be350dc0891fe6959d807e0915ced13962a1b
1588 F20110330_AACGPE chen_m_Page_041.txt
9a2faba0dd43ae53eb0eba406b8676c8
293f7f4cc799a871b60c0b3e645d89e85e5232e4
21446 F20110330_AACHSH chen_m_Page_031.pro
105efcb9f6909adda591021e89eb6948
46b05e12cfaaa6895d8cdba588174e20224fcd41
1736 F20110330_AACHRS chen_m_Page_166.txt
4c51ea33b3b210032ff100aa3cddddd8
d67e7fa3dd01b25a7cd3c19b89c62209b90489a9
109991 F20110330_AACGOQ chen_m_Page_137.jp2
8194784d3812178d68f1b5b16e1aec52
8cce5d639dc1c590dfa5b144035d1e2562f97f5e
22268 F20110330_AACGPF chen_m_Page_110.QC.jpg
adc447651e4ca4dd217b0e8fb60ebc54
f6bb2b1b7d6afbd7f8a01a05f3a8def7c8762ccc
29442 F20110330_AACHSI chen_m_Page_032.pro
7a7018f91f9af3510e97e7f014c88c51
a92f317e1f60b5349cdbf80765af4961c8dee2f8
8198 F20110330_AACHRT chen_m_Page_001.pro
51d4719ff16946acd2776589477640c5
a6a0a58790b3483a806f9c57c4417d63b1dcfbb8
F20110330_AACGOR chen_m_Page_068.tif
b6540e5705633474f964873c342c1e8e
f5658af45627cbdf91619aae5ccb2f2830dfdf5d
F20110330_AACGPG chen_m_Page_149.tif
46ed68e463386b425fe86e6f0b6b1099
83a928a85041bfe49c12186f5e9bd857cfec7ba7
40848 F20110330_AACHSJ chen_m_Page_033.pro
3549efff372a8e49115c804db80ba817
f3c948591877aff514248a5cc63efc4f41235614
1095 F20110330_AACHRU chen_m_Page_002.pro
cc4f916613f6f970a980b292bf0acc93
9437f2cf57fdde1c694ab41bb67183c3974b991c
1867 F20110330_AACGOS chen_m_Page_131.txt
2569967767799ce82d87e831c24c520b
f1edc9fcc2bf49d1146a84b38a8d875bf8e83e8d
194 F20110330_AACGPH chen_m_Page_091.txt
8e7428341c1980841b06ba2192620236
687ce3ca83fe2cc5142aceedb283c8f509b71633
1801 F20110330_AACHSK chen_m_Page_034.pro
8e1c5774b972645d42c33e3664c47ba4
99b555063295c078c7f7ced15be0b2eb74130953
74002 F20110330_AACHRV chen_m_Page_005.pro
a184af51d6fa6551fa8973deaf8da8de
1e9af05616341c5040811fa3ce1960ed68566c21
F20110330_AACGOT chen_m_Page_052.txt
d00e7e2d2cc4e056914b34e0b87198b4
7080b74279f98b3c18034c847bc4bc150a673f1c
43191 F20110330_AACGPI chen_m_Page_031.jp2
04d7a9bf53befade77d717113a6de713
95107aa39a25e45f24260b0726aaf4e9796a61a0
3470 F20110330_AACHSL chen_m_Page_035.pro
dd6fc08dcdc7ee1565b3fc324e850ae1
59f8be2933c4b9a67b6677ce788ad278d3147f32
34808 F20110330_AACHRW chen_m_Page_007.pro
60147861017feb528a905df8ff87cca5
ac785f026659b28d8549bdbc0878277893c44772
2355 F20110330_AACGOU chen_m_Page_051.txt
a9ccd56949a69ff39ff4af3dd259abab
4cf930dc0a36aeab7f8b963f04216c1504c0b2ad
7786 F20110330_AACGPJ chen_m_Page_130thm.jpg
83277015f0bf88819027c9c11e1171a5
ca04ace19dc531dc1d950ea92d135bbb7f1fdf36
46216 F20110330_AACHTA chen_m_Page_066.pro
000ce1088127d7ecbcbf3ba4ca3ff4b2
9c91c8fc0ec94fd04b3a3873264807059334c12d
34425 F20110330_AACHSM chen_m_Page_036.pro
d071cd3b0468cf86031edcd24c7b7b28
32437f9ed65803bd1b073147b5c5808562992c74
66123 F20110330_AACHRX chen_m_Page_008.pro
13ffb8954f78cbbb9f640f4ad75a56be
554323f75efc7be9db55a889a70f73a23a8aaefd
530133 F20110330_AACGOV chen_m_Page_097.jp2
6ec7b3112c40059a16d09102bb757f5a
76947603a03bf56b061ad78e4fc3cc0b5ba547b1
181 F20110330_AACGPK chen_m_Page_147.txt
5985568171bcf930a36c16487e9f6bbb
a2ffa6aae84a3c57df3aebbabdde30d8f573cf44
49917 F20110330_AACHTB chen_m_Page_068.pro
f8360763978163075fa1a137cb689723
2f51e892e2b090d1c1a380f6d55c1ba9f29e4d84
31189 F20110330_AACHSN chen_m_Page_038.pro
5ee88004d510cd1d175048a68080bb7d
5f707b1de1fff7587376a21b453f3db0db4b13b8
22501 F20110330_AACHRY chen_m_Page_009.pro
6b17a19920d36f264df9d2825296b1f5
2899cb8ac20fa19be0e009c31f96b309cd479ef6
3948 F20110330_AACGOW chen_m_Page_101thm.jpg
3d01040d22796f934e90bb3cde9beb32
847a0079041b2df42bd61289c5ff60c1533cdf30
8402 F20110330_AACGPL chen_m_Page_078thm.jpg
76fa27eb51794c3bc58caa6397e5eee2
38eb4aaa18d853d39c54160a7a8feec75b34e1df
48860 F20110330_AACHTC chen_m_Page_071.pro
1f496e8c2366108106170cb8049375b1
9dbeb68c9d392dce4f7dd7d32e4df731303c3dd0
34432 F20110330_AACHSO chen_m_Page_041.pro
19c663c18b79eb9c79bc7a8754036d5e
8513a9c3d347f607505c67605a54796fd0a55e7a
34486 F20110330_AACHRZ chen_m_Page_014.pro
4f1c69c5be7e842ea14812db7ef81e46
f1ce1d4b141870b9af41259a9da9dfa9d2135a64
491453 F20110330_AACGOX chen_m_Page_149.jp2
d1b31db5bc63784cbc81264bc50ec443
d23dbc69f1062a60ca25eec73110909553eb2597
F20110330_AACGQA chen_m_Page_132.tif
3a62ca8d3565791052e04e27b7103088
56770d4fb8ad44b4b65acb552940d9ad15cd7cb4
34277 F20110330_AACGPM chen_m_Page_013.pro
a54dfb0225ee3b844643d7c2d5f233bf
34cffd43ba6d884f081570355f6d3ab6945534ae
33674 F20110330_AACHTD chen_m_Page_074.pro
ab85ca8a52630a960c21618b982c0021
207b2cd8ca04816c5a8621b641b231fb143760d4
49819 F20110330_AACHSP chen_m_Page_045.pro
df845d37387dbc486d826830be13beb0
3f270ea413fc040d37cc1bb3f130728c04e2a8d3
72981 F20110330_AACGOY chen_m_Page_140.jp2
c431116dcacc21f290af8ac4ab64418d
80d34ca698dc3ccc061de39c9ead9c0d7a6438ed
F20110330_AACGQB chen_m_Page_053.tif
cc04f631d81ded9ab57410eb6df1902e
07a6c384e9acd608d547340e07504828f17a668e
6702 F20110330_AACGPN chen_m_Page_029thm.jpg
d21e00e6eef733cf08981e295295298c
78ba3041fad9cd34054fe51bc1382539124578fe
40954 F20110330_AACHTE chen_m_Page_075.pro
0faeb6f44bd572d055098bd98deae45a
ec33ba7f065e13de388bd7de89aebdd444850b47
48913 F20110330_AACHSQ chen_m_Page_047.pro
fd2631f9e2f148321399ff58a0d90d39
281266ae42c1d83fa3b09a4a94c0267a075bb785
12728 F20110330_AACGOZ chen_m_Page_095.QC.jpg
620d5dd09f2714c5f69ebacd97770c29
62caff56ac7b42f834d75c365c72a7a701324914
45787 F20110330_AACGQC chen_m_Page_028.pro
e98b68a2cf54ac4e052ca1e1981b10e2
a4f88ad823db3a11ac79e50fc58e0b673b4b1ddb
68712 F20110330_AACGPO chen_m_Page_140.jpg
3d1d533b00f303ce21b6afec8e9ec086
91e4fabe92ba60813021968358c2627a5cd1aa05
51949 F20110330_AACHTF chen_m_Page_076.pro
c8b6d996ec6348547f8d107ea8a83ec9
2692f6a813febde6453b9f3a8f8d045dba253f25
45557 F20110330_AACHSR chen_m_Page_049.pro
e742beb47ced0d1ac690f31e85f9f41b
f302b1096fd8d3f55e81f3b3f27582491435bc85
7195 F20110330_AACGQD chen_m_Page_151.pro
81159a12fe9f01a6bcefbf0c8926377a
2a7190742343a450399f1c95c060aba2de1e710b
54959 F20110330_AACGPP chen_m_Page_111.jp2
a6d86b287c429922eacdaa2c91a36cae
d464cee2464db9affeb23e38c713abf53204c31a
50265 F20110330_AACHTG chen_m_Page_078.pro
2d89999f21ed9bd56ce0c01eb85a2e59
73ee08fec7ab2ef4128d30a1c7740bfc5d884779
7168 F20110330_AACGQE chen_m_Page_148.pro
b745855687709d6b8732ba8c91bacf48
41d51e597db73644294acf31ff88baf22910bd9e
40563 F20110330_AACHTH chen_m_Page_088.pro
3e580c756a7fd5b5e83c3cdda13700fb
b0cea839fc1dd487b5c061a99a8fae0f0339d37f
46774 F20110330_AACHSS chen_m_Page_050.pro
81f28c167a56eecc0d2864cb133e7721
5d9f8e40798eb0edbf3eec5c6cb7a08db39d331d
4997 F20110330_AACGQF chen_m_Page_097thm.jpg
5a05e31fd2e4015b02947c6cd2874ed5
b10ba9219e20f7980e001a73922aad11d045a8f9
F20110330_AACGPQ chen_m_Page_156.tif
02206cb1c60a8596cbd02b55bdcfd2d2
2b0b0b08ad05ad3f81c9c4466b89a48e417f1815
50869 F20110330_AACHTI chen_m_Page_089.pro
c993def72d46ef5f652b83a2546f6790
5a5a1ec71de2cfbfa726d5ad6aa91960cbfe8d3c
52147 F20110330_AACHST chen_m_Page_051.pro
b3ff8a170b9b5a709918cee510cbcc6d
0bca76a6c4cd0965e6f191ffbce9db5a017d8474
15910 F20110330_AACGQG chen_m_Page_148.QC.jpg
6220d7d8001da42b27691c452d724087
1d7a70e82de90ed501dc95fe3e08cf9ff4511367
486 F20110330_AACGPR chen_m_Page_094.txt
634aa37c6f73f42450dea0db2bf0cd0b
964c8d32dddb2b6caa608de16adfc8c8956e78e2
32985 F20110330_AACHTJ chen_m_Page_090.pro
edb5dfdd902ba6b3051791c8815cbc4b
c0f4e3fe3cf9bccb23ea0ab830563be72f598dee
54087 F20110330_AACHSU chen_m_Page_053.pro
f83227f6eeb366535dea5210d32a851c
8334641ce5a0faa79c77c98a5333a6c7a65c857e
F20110330_AACGQH chen_m_Page_158.tif
43d22d705ee3e728872ae17ef2820f3f
a0665e131f49e6ea1a0e9651819e946f81f59c31
27376 F20110330_AACGPS chen_m_Page_088.QC.jpg
83f5bcdd8d81c584556de916f3d7ad34
fb2ceb3e5eb039fbcb5c4c773f5b83a2b7978973
4953 F20110330_AACHTK chen_m_Page_092.pro
eb0b4992e9166eb3f8ca217bdf0c0fd7
fec05bda92d55789164a2009f476828abc1c51a9
11728 F20110330_AACHSV chen_m_Page_055.pro
5ca72d27bbd38b7be8a969ed62fd8153
ab310a51ddd1af96962182b44c1a23dca4820563
105062 F20110330_AACGQI chen_m_Page_045.jp2
93c88d5b0533b5acae1c6c8f7234fce9
7769f064985bb0dfcec706f194ae602224ef2bfd
79507 F20110330_AACGPT chen_m_Page_160.jpg
3384ad93e03cc88cc294ff53f900516b
577a071fa1ca994018dbd3d89ab70d68941802b2
8150 F20110330_AACHTL chen_m_Page_094.pro
369274483c4c306f002e3bf400e0fdcb
6111c5de204a3e23d1f3ca6ceaf14260d69d2ff9
4769 F20110330_AACHSW chen_m_Page_058.pro
1efe6b1105a6cd248e97cd4c117f2fba
9f532d6cf09c2f5618bf1d3ec895ea5b1a56e248
71284 F20110330_AACGQJ chen_m_Page_158.jpg
4f8b950d15b7dc264ad6a6fa9f49239b
b83af284907b2b9bc17ebc2b0e460062f101c659
7838 F20110330_AACGPU chen_m_Page_131thm.jpg
d3a71821d58bfb4546f8698bb8cb464c
e6f05f72d367f9be1f3571040d9de107a5c83931
6309 F20110330_AACHUA chen_m_Page_124.pro
1b453279a6ffbca632dbe5c5acb216a9
ddc1c472949cc033afd9c53c4d2c5ff9abc263ca
7322 F20110330_AACHTM chen_m_Page_097.pro
c4cdfdf7c4a69bc2d4e26c091bed0620
62ce33b1d84ab5e2887a0e89f90c76d72e85d7d2
43296 F20110330_AACHSX chen_m_Page_062.pro
94ca4379736ccc64c435a7e4e8428abe
5012a5bcb498ffa0587d74bc8793f7a66b00550e
13601 F20110330_AACGQK chen_m_Page_123.QC.jpg
07d1e27fb64d01455d65b52385f01dd1
e25617ec39a8406ca8363acd45ee7c40ad0bfccb
F20110330_AACGPV chen_m_Page_047.tif
3a6361fe50db7699ce859bbd790ceb34
7cb8403e1e4ef288eae665613263e6bcfc7ac2d1
41692 F20110330_AACHUB chen_m_Page_126.pro
692e384b6353cf2623d8ab3960709bd5
6210bb45c6ee0effa1bf7ab2d49f94b4613fda43
5913 F20110330_AACHTN chen_m_Page_099.pro
54d47ba252b7e79b067808da44008301
eacaddf7c6e934d3d630066f6871710f4637abf3
31754 F20110330_AACHSY chen_m_Page_063.pro
2420737c57083e86493ec367dec05cf6
56b68445bae39589874c2ee5ea9e75ca9493621c
24040 F20110330_AACGQL chen_m_Page_017.QC.jpg
32fe18ebbea8638d749df0cbefede5b2
9e90d8a63b2435d49fe91e3f9a368d4f26b382dc
1603 F20110330_AACGPW chen_m_Page_132.txt
14102925e73a3c13e81a582418be3aaa
51ab0c4a0f5b460ef239ee60eeb51e39989d17a3
39111 F20110330_AACHUC chen_m_Page_132.pro
dc1b3a2543011058c1c36f2601186fe3
f39eaf3e81a89ba403ea810d2a23cfd5a88446c0
5773 F20110330_AACHTO chen_m_Page_100.pro
c5e8a51c9ee7202c47ae915d079b6118
a7d9736c1e1c0b6ea59c942502593d530f2aec38
50671 F20110330_AACHSZ chen_m_Page_065.pro
a11c410a954f229888ffca8473b04f9c
4fcc2cd9f60e92ce2a94f35f58a9e5ad83cefd28
F20110330_AACGRA chen_m_Page_071.txt
cf8a5d35b5fe22ae13967555a52cc789
5e5ef682d7745d6a7b129e48267f51680e60edb7
49908 F20110330_AACGQM chen_m_Page_046.pro
298c45197aa78acc0a3326ef0db04abe
50a95e5a414caaf5318914f2f39ca42aa27473ba
35500 F20110330_AACGPX chen_m_Page_008.QC.jpg
4e42dab116a661c7e11afc1ef4fe4873
a615747c15b3677fb417a11bc79c2523315cb10e
50895 F20110330_AACHUD chen_m_Page_137.pro
21400a81045b6e79e868644324fcdd8f
36dfeb18543843274e7f02615e2016ef68fd6ce9
8659 F20110330_AACHTP chen_m_Page_101.pro
1a00c5acb5be0ff9831f33adf6fb97af
9f1e800fad9f70353ab175d4c6b4a5273475cf06
1581 F20110330_AACGRB chen_m_Page_019.txt
10409725c6d968397cf69285e2d9818c
753683d20f0a224ca6f4332ada42f9710fe92eab
48906 F20110330_AACGQN chen_m_Page_043.pro
ab7375eec20289c1b4264f52320a77ce
19dbe4a77bf63fb5153ebe50c9f74d16ebebcca5
9535 F20110330_AACGPY chen_m_Page_144.jp2
b59cc52cfd4c6c6aeb19b1b08a57223a
7b076d79086bd860d35f817b85cadc6b4c251143
48236 F20110330_AACHUE chen_m_Page_138.pro
84b7c20abf1c005f846421217d038108
5191a73df2a599980574b23a4db1acb2f04b450b
11058 F20110330_AACHTQ chen_m_Page_102.pro
75d52ad0223753d2e28fb562ddfaffce
ccd3398db9e0cbd13d7bae958d9b82b1b4682af7
F20110330_AACGRC chen_m_Page_109.tif
c3c329f71d71bd03418cd9acbd0c73ec
5ed368a54aa35cc84c4447f6ee63b031503d40dd
F20110330_AACGQO chen_m_Page_042.tif
437d47353f198a95051fb284fbead5e4
70e42887fcc4d2bf94a9ae3863d95bbf6c6f7f4f
331 F20110330_AACGPZ chen_m_Page_095.txt
348afae7c299a297d3c81f54b9257470
d6fa6a63d2e09fd460de232daf7ba4424ba9b03e
34226 F20110330_AACHUF chen_m_Page_140.pro
630464a2d4855d3f37db8f3cb4ab9072
e001d8c1f23926bbe7983422d1866296d4d8cc75
12525 F20110330_AACHTR chen_m_Page_106.pro
d840f124220102abd43d401269ee7abb
f8c7ee13aa501426565306e89823d8e4344152e5
1771 F20110330_AACGRD chen_m_Page_030.txt
7c31973761f4bbd83d83dffc437f1656
403ad6504983a523b49746cd7867938aee102292
59052 F20110330_AACGQP chen_m_Page_064.jpg
abb01faaf6234866bbe65db66ec6680f
6e4869f4af633f8629fc3645cde3a20af910d07e
3372 F20110330_AACHUG chen_m_Page_147.pro
53cdfc0f910894e21eb77cc88f8b073c
3fe44e178588f7cff3a53e1addedc9a9e522ba66
50343 F20110330_AACHTS chen_m_Page_109.pro
dbc9a3ccad4e3e92deb36f68eadba151
29643ca7f6481467ca9739f13d69b69b024ac799
36695 F20110330_AACGRE chen_m_Page_060.jpg
fdbee529e8dea4583448302064e22006
f0f77b08ba79de64b2ee1712d440811644e65088
25703 F20110330_AACGQQ chen_m_Page_111.pro
fbeb809da1ef9825fc22351baab60ce9
cbf7ea155257b7e1293ea8ad9e9ccbd9880af943
4993 F20110330_AACHUH chen_m_Page_152.pro
8020128077cc83d6f7ab397c75d5ea00
f2692adb4320130ec2099a116c5449b28f8d5df0
1730 F20110330_AACGRF chen_m_Page_003.txt
2809d8d87cc2921f6a4d0e223d81e1c7
a831ff209a164f561315b8d0c8d7bc923cf11365
4284 F20110330_AACHUI chen_m_Page_153.pro
489b5a7e28a820915373f78c12ce7cc8
6e0fe65469ef12f04bd462d5358554e170939fd0
33259 F20110330_AACHTT chen_m_Page_110.pro
f6a66abcaef085fa15034d30f1b7a460
5eda37e6e6ea79ec2edb7ff29d4ae286c919b91a
92356 F20110330_AACGRG chen_m_Page_049.jpg
ef37f4d3169503c3dd8e3e95a917b5a2
c7dc654a33d2fd91a85b2e997cb61977c7876366
8482 F20110330_AACGQR chen_m_Page_077thm.jpg
d6e62e535e2a203aa7e2cce6e2b18309
5c51c174850b73864447b0d5c638738bbe3ed9d3
45101 F20110330_AACHUJ chen_m_Page_156.pro
305ecd582e0c45bfa66ff480f66c2c54
abc57b33ace54ebfbf9e4f5e489d763fca2ddd3a
49309 F20110330_AACHTU chen_m_Page_113.pro
e33de441dad081d165641d612157ba7e
599a897d272d6e55b1ad121c883ac631b434924f
F20110330_AACGRH chen_m_Page_164.tif
c414d60051e275b171cd7a298ae1d6e3
e23e650cf5d77679d6cfd74ff62e24140cd03db5
77731 F20110330_AACGQS chen_m_Page_117.jpg
2ecfec23ddfc90d041882f8b48efac8f
fa69d7a11e4833209e2386e64eaa43e276df0e07
47345 F20110330_AACHUK chen_m_Page_161.pro
99d789ec0cb2eae8ed74516d1a8c57f7
5a89fb47c4af9fcc1b6a2f2c32654feb6e57abeb
50791 F20110330_AACHTV chen_m_Page_116.pro
9abbd91186d48b94080a9cbb079b9cad
aa67f24314eb3e6cfb200c5906d2b7bfc4ab03ec
81330 F20110330_AACGRI chen_m_Page_155.jpg
084df782bbfbfe22149cf299e82a07ee
3f896c497ae85364cc334cd1522c34bcb5e7b2b0
8904 F20110330_AACGQT chen_m_Page_135thm.jpg
deaa97fbbdcd27564606adc5450a39d2
2b9ac740db527404c97f39f1ccea6bec5191c769
48323 F20110330_AACHUL chen_m_Page_163.pro
061fb2bdd3d29b09c3d3480a2c53827e
38946d8c42fd9e63e1ce372e2809075aa4383efa
52347 F20110330_AACHTW chen_m_Page_118.pro
cdd3ac162da78b5fd53d72bd56a0c27e
36a4cb4d50042e59d0df630ddea52abf0970d673
99829 F20110330_AACGRJ chen_m_Page_161.jpg
4ee51f2893954863e42156f3883b5fee
56304639678a95941f53688fa4639736913d0a77
4966 F20110330_AACGQU chen_m_Page_061thm.jpg
f1a5c346cfc8d86024ff0ac10e386542
2a5ada6f8efb9606387bd316b9ef6f923f04296c
85577 F20110330_AACHVA chen_m_Page_012.jpg
f07fa730565d8ac7f69a96c5222b0645
891273564c358083399900582912ea7a0ef5c83a
51696 F20110330_AACHUM chen_m_Page_164.pro
0220bec478b7c372397f6685e0d15030
e30afc9055acf3287e20f8697e1be4e04bf52a7d
49808 F20110330_AACHTX chen_m_Page_119.pro
c9145d4a19146c3965c9c0a9ba25a16b
6241e6887496da7b4417d66e3cae581150a3b674
15310 F20110330_AACGRK chen_m_Page_106.QC.jpg
37c0b2d897ae54dfff36d713e06329a2
a8b57bf27a307b1da9f43f6895b57c7238d1e831
6684 F20110330_AACGQV chen_m_Page_020thm.jpg
d6afe612b693614aa2618b7392596be7
700182f036dba30e40f7f4c2c715070543a4d348
22371 F20110330_AACHVB chen_m_Page_013.QC.jpg
2cab49ac0af598959baf52a431520199
2c0061c7dd1f37e47b0d169adbfe52273e062e77
41704 F20110330_AACHUN chen_m_Page_166.pro
7ee8f55ce3359c88c76a56cdc0302ab1
cb822a733c736afd0516fba0025c8af1a8f435d8
53868 F20110330_AACHTY chen_m_Page_120.pro
eb1e5408ecea1588393909703e302bab
6c0cfb256de233527436b603b8f2b6d4c9cfc29b
5520 F20110330_AACGRL chen_m_Page_002.jp2
4fec48cc9e71dc273a62b6b3f7572653
250efff56fe9adadbb1f996815167f0afee1bead
7520 F20110330_AACGQW chen_m_Page_159thm.jpg
0406a3b27d60f95aefcd6f368de39a86
df2fdbef167f1f1ece51bafe32a555bfcf12b7e3
73805 F20110330_AACHVC chen_m_Page_014.jpg
53b0989d3ab2e57c63fcf18e0baa0350
9c3598ea5e1bb2e033e4ee58db329daab71f48e8
22265 F20110330_AACHUO chen_m_Page_167.pro
c7063f5cafc791a4a0962f17039a2c27
61b8b3e7637e22a5cf9abf4fd68482c74b22e780
20269 F20110330_AACHTZ chen_m_Page_121.pro
40128c8d2dc17b0d0cafb5f75ac57e80
cd3c37ff49e4ca7108508024ae79227d16824b18
F20110330_AACGRM chen_m_Page_077.tif
6944480eebcd5025d7b1211786f53950
e46278eeb99eaf57b2049a18f51d3b516323a8b5
F20110330_AACGQX chen_m_Page_013.tif
8ff8c828939399f7aa8036b5ef7f1c97
7e03dd7db0df342be298765d2994af1a72a10f06
1897 F20110330_AACGSA chen_m_Page_037.txt
adb3b8eb25f623fb31011747b106dd06
dcb7f912f663708dcd0fb41bf6f4c9051dae8af2
69835 F20110330_AACHVD chen_m_Page_017.jpg
749361e50c1c14ae55e0146d58bf83c2
d9b6c97f4c9fa827bad1bf13d7c1c33484e166e5
26266 F20110330_AACHUP chen_m_Page_001.jpg
7da66ae4937d735de5167a2d7e720cb7
78c4f7e3767ac71b0d6cf1d6e6788c78727e223a
102497 F20110330_AACGQY chen_m_Page_089.jpg
6e9f0dbda52040864954e930c9bfc3f5
86b8f9e601810ef4559b6697c8fabdb0b298a4eb
8309 F20110330_AACGSB chen_m_Page_089thm.jpg
47cfe48a862cef3ad06e94f8280062fb
4abc2408ad30db0bf7552ae2516b85e1f982afe4
1051984 F20110330_AACGRN chen_m_Page_010.jp2
ed1e35537202e484689717b29d4beee5
8d19e020e17f26381cf7b674853e739aab02f734
13009 F20110330_AACHVE chen_m_Page_018.QC.jpg
c6a441bff9ea5ca4f246e968c4150b31
32e900b168c7c77fe8140cff26eacceeeb4d3683
1582 F20110330_AACHUQ chen_m_Page_002.QC.jpg
1c617ac2f89b6d7bb18275a023c89bba
f4508bfdd7d3204d648fefed4486c08ffc6d6e87
1628 F20110330_AACGQZ chen_m_Page_155.txt
fa56041be19e4d1ffa1900bf818d281a
5336eb6459345dc501eeb9e52f3d08398db70d84
2133 F20110330_AACGSC chen_m_Page_089.txt
a4de1e632c4a4df3d75e9c0ca2f735ee
da8d0ef24d0659fed861f252a98e4b782ccac4af
4085 F20110330_AACGRO chen_m_Page_124thm.jpg
c9d5ced2e3b27d16db7b3cbd8a87b73b
b05c6233c91f765b497d1ff9418599e83ac68359
47314 F20110330_AACHVF chen_m_Page_019.jpg
b3c6e493ef0ac7cd25c252ed97df11ed
41c8a6a4f0c072557ef6cb0e4381357ab3b8d542
21395 F20110330_AACHUR chen_m_Page_004.jpg
9db37911c82eb04ce8dea2bf0d16c3c2
ae5c8815ce4986d7d26930e2417776ff035bf2cf
12262 F20110330_AACGSD chen_m_Page_101.QC.jpg
671332d1e741aa142837275fac24267d
a8ddf2b8997055d198bbd756c2b16af1ff588249
112687 F20110330_AACGRP chen_m_Page_114.jp2
4a604801343feb17862f3fd43a2dcda8
495974914e65dd8f7a26c4fa5cac88823afa5b0b
24171 F20110330_AACHVG chen_m_Page_020.QC.jpg
456bb5c3604390c87d91f1a3054bfcf4
1a78a9c294e8a68b978b992bd9cfe5cdea11ca28
7385 F20110330_AACHUS chen_m_Page_004.QC.jpg
ef48ab039653cb9893b239e743a3b2d4
095a5b2379f1d6ce68bd2243cfd1cb9b2d3cc834
24124 F20110330_AACGSE chen_m_Page_074.QC.jpg
f23a27eb980f4f7049fd819241d64d9e
b799a076d8efe2caa6f559586984897958eb37e9
41184 F20110330_AACGRQ chen_m_Page_100.jpg
55f63860b7bd8d110033d64552ee5027
622036c11f58457e10d7d16099cd66105a4df23c
54291 F20110330_AACHVH chen_m_Page_022.jpg
3c659486b435ce76ed8b1f121504ae32
fd706f9dde24189dc196e6aa2dd716532f3a9c1f
103495 F20110330_AACHUT chen_m_Page_005.jpg
88536dc1476065c9fcef7fcc1e1ce64b
6079a2c6ac4f1c7d5e8b2ff87255798248b24221
8512 F20110330_AACGSF chen_m_Page_046thm.jpg
10996ced10fae86a6a4fafef3df56548
c6bc4958a8273ef2b8dea751ab9468ac4b241e0b
2003 F20110330_AACGRR chen_m_Page_073.txt
3fd34c9d016ee64c3e9bcf6ea5498fa8
069e5ffd831412411de9dbc7808844303559790e
71068 F20110330_AACHVI chen_m_Page_023.jpg
8972318026e105f283372ffbe928a0e4
f8ad3bcc9fbed1dc906f041a8971f1df183d3cd4
30553 F20110330_AACGSG chen_m_Page_165.QC.jpg
a350b763d6074e18f09fcafaeb28e9af
fa811b133739d2b3612cb8a62f0485ce25042045
24464 F20110330_AACHVJ chen_m_Page_023.QC.jpg
4a3e742dc172869030b1ad1c632837d2
ea78ce5348abb17f86c0d67f610a3064414b5fcf
151428 F20110330_AACHUU chen_m_Page_006.jpg
c1078ea7a8a343b8dd3127fdd85519f7
85a36ef2f5557b0a9c2a7e06ac6a690c69a5b469
547 F20110330_AACGSH chen_m_Page_057.txt
32a8ff52b66fbe3e078f6c9683c8fafc
221abc6737c64fd15511e590ef81b76bd83decf3
86218 F20110330_AACGRS chen_m_Page_135.jp2
43ff3244e0144ffd4c90f131f6446c31
9259eadec211835a0a58b86229b833ef24241aa1
78472 F20110330_AACHVK chen_m_Page_024.jpg
a1854d1f93d9d7509f00e7a91f2a7093
94289d54a679cb3f487d193612b599ac69edac4f
33840 F20110330_AACHUV chen_m_Page_006.QC.jpg
91f25a45196cb80033efedde096238b3
98c01a3389eed5d14c2371f3835d6b0c826cd63a
38592 F20110330_AACGSI chen_m_Page_155.pro
82b9256fce191772f7ae0bb40050a04a
0401db90035e4690c2db735c4f58d61099918b00
103821 F20110330_AACGRT chen_m_Page_115.jpg
5cd8ecd3ef98266263e93d8e9db248b2
a217524f17ad8f64440662594ddc5cd89bbf0039
18693 F20110330_AACHVL chen_m_Page_025.QC.jpg
bcd5e853d7d44e51a2a5ce7e154a71e8
5a384fb3454a88f037e6dae1bcc0ae64dc5771d4
12130 F20110330_AACHUW chen_m_Page_007.QC.jpg
eb14682ebd27273f94a4a7631bc77b2e
97552c5ac5fedac81ea468a940c3d1faf64634aa
5197 F20110330_AACGSJ chen_m_Page_034.QC.jpg
a32b7de7cc026241271db1abb39eaa32
bbb48e00659bbfbba3f295b9113005a22eaec669
74275 F20110330_AACGRU chen_m_Page_027.jp2
b928c4303df9cab57131340685a28921
ddbf736fe78514269f2589b17cf0b47d1882ebb3
100997 F20110330_AACHWA chen_m_Page_044.jpg
0e533d097e489da691c397c1402e9941
020ebb3d5bd1395e4d205712d0d372db924291c3
57560 F20110330_AACHVM chen_m_Page_026.jpg
ef1d7b1a6816affb32c3411b895a0c4b
c017586f7c4783a7fd47038584c09bb3aa4b6b47
32991 F20110330_AACHUX chen_m_Page_010.QC.jpg
ffc76699d614df603d9174c64ba071cf
a9ca8520c24a3eb8308f1a0a3f52cbf083306c8c
91650 F20110330_AACGSK chen_m_Page_003.jp2
44ab6705e5a653eb273105d36dc544b7
5109cd62544e2118d4dff01288e065c990021cd2
35595 F20110330_AACGRV chen_m_Page_095.jpg
9db9b6e71d496c55966afe34df5e46f4
7e7a15607985da24ec61c420684fff3e6dcfbeb7
33269 F20110330_AACHWB chen_m_Page_044.QC.jpg
cdc51722461b01ed8e79b47c48f060a0
c355c144e6754188f93abdacb57f396e3f4595d5
23286 F20110330_AACHVN chen_m_Page_027.QC.jpg
b0b3acfa411a0a9cff39a66ccaa1ede7
aa1788096497107dec02729cce2b572762ad96fa
146959 F20110330_AACHUY chen_m_Page_011.jpg
e1bbd97ef4c4fde68b7e03cb9cfeeb69
eb8245faa08e8a8671ed7b1f9df5b9f1e80ba236
91484 F20110330_AACGSL chen_m_Page_133.jp2
a6b5068035563e89a14b47006ef8bb42
fac429f195b721a589f0ed20427edbfcb6b1fdf6
8573 F20110330_AACGRW chen_m_Page_082thm.jpg
3498184e1fa9268b59723d28e7faa077
38771770bd9318fbb5dec6a0bf4ed888f039dcb6
99242 F20110330_AACHWC chen_m_Page_045.jpg
c38d660196fa3e8dece12bbf138dae77
174e613a6578c84d439c90fff29d662d6a5d46e5
29776 F20110330_AACHVO chen_m_Page_028.QC.jpg
283e2dbfb7f153099d3fd2d8295d0d90
93765f6a65938da8214b568cadd099592d4e4f5b
39996 F20110330_AACHUZ chen_m_Page_011.QC.jpg
d1fc32c5678f894591f7b04a619c48f9
e345e51cdff0b596b099016eb4ea93a04ba4c60e
33221 F20110330_AACGTA chen_m_Page_084.QC.jpg
aa0cff3a4b6f0cc34271d458d63fb3ea
66303d91c9544b6b59188264a584c231009b590f
1051979 F20110330_AACGSM chen_m_Page_008.jp2
2649485660135458a0bbdbf370c41970
5bbee5d6110d18b48123da1360888c3af0d36828
5861 F20110330_AACGRX chen_m_Page_095.pro
ac8b974e542f634517c478c3fd7a1f50
c7d8fbf0689081802cae6f86de6276c69d5c8286
32904 F20110330_AACHWD chen_m_Page_045.QC.jpg
fe8416cf8eeaf1bdbd0a7ef656da00d4
81cf613f1853154e1d6aabb104b0258faaa464d5
23297 F20110330_AACHVP chen_m_Page_029.QC.jpg
acbda9e72abce3984610657a0fadb2b7
9e8a0312719ec31afa8ca4e66e68660351637581
1940 F20110330_AACGTB chen_m_Page_113.txt
a673426134c9eee4475defc7c02265b4
ef6189ffcb2fef30d1780498a687fea3e72a1848
44092 F20110330_AACGSN chen_m_Page_086.pro
e7ee07aee3e317b93f40bf87ee3482e0
1c88397a239d83be4741780a5ac654aed992a81c
12521 F20110330_AACGRY chen_m_Page_104.pro
0a1f9740b6aa209aa85a62c40dd7ba1d
0a726ba219f1523d199fa4f22fc733213068afec
32595 F20110330_AACHWE chen_m_Page_047.QC.jpg
932698f8e285546e5d28201a8430f683
e184619ebcdc691595db97741165f61900af22d3
59871 F20110330_AACHVQ chen_m_Page_030.jpg
7d43811bb61a5088afd6e40e4c975230
2decf689d590597aa357045c6f9dfc78dac14db5
F20110330_AACGTC chen_m_Page_045.tif
be20b75e43f708192459b27114f76c09
28dfe881e64a03cd3837c5dd7187f9970127691f
95238 F20110330_AACGSO chen_m_Page_034.jp2
bb339e2cf8cce06fdabf5fada1d97866
85afc4fd8f686daa9164329b6033cc0ed177fd7e
F20110330_AACGRZ chen_m_Page_124.tif
bf92788775a8907642a8c08f71b36013
e55612eb5af909a5b0f6589d00b6741d35223a3a
95418 F20110330_AACHWF chen_m_Page_050.jpg
8788ac1d6ea18b8723cf52acdbf2a756
38241ba37d72b07f63f454471b6f0348fa0d6700
13250 F20110330_AACHVR chen_m_Page_031.QC.jpg
3b4ae87ea5b9636cf2b702387d735fd3
708e10d012d61ac26300ac39393dc07ca50203f9
31658 F20110330_AACGTD chen_m_Page_119.QC.jpg
176eeafe53cb716d1c8ebe6ddc51658f
7590fa32c1db6f09041126a35fb9f799db324798
9871 F20110330_AACGSP chen_m_Page_105.pro
f3f97090d11874e388b0c77e919fdedc
44667a97fb590ddbcb0777675bc5bf8253367bc9
107223 F20110330_AACHWG chen_m_Page_051.jpg
ba06eb0d301887c63bd1b064122d37f9
7c3d47b90f490d064cd2a531a504edbafb787f5a
20114 F20110330_AACHVS chen_m_Page_032.QC.jpg
4e527f92cd318ab580e0ab39f63753ca
b2f8e67b79eae609622db95f198edd408bd8b78d
49750 F20110330_AACGTE chen_m_Page_084.pro
f7ec41e78cf45dac494c810d9406b930
6803bc58988a2050bca3e671ffa37a4b35e84799
102501 F20110330_AACGSQ chen_m_Page_067.jpg
934a29ae43bb4d510d80953489d899bd
ef7267d1a6b5436ee0c861a3f48c2e0e7fa6a712
33372 F20110330_AACHWH chen_m_Page_051.QC.jpg
c7726a46f5456338c7bedf728c4ce17f
2aaa38767a58a06e4123be9bcc90bd130b177e49
25922 F20110330_AACHVT chen_m_Page_033.QC.jpg
cde7bc3fe5db25b0089ea3363504d027
1ae79bc72f8cc79cc3c06c9a5ddd1c85361ecdb6
F20110330_AACGTF chen_m_Page_054.tif
fb0070477366f2b117442f9b1542240d
48a2502c98d7d8c0e32de720c31ab97c25e8a556
8427 F20110330_AACGSR chen_m_Page_072thm.jpg
14d3c8cf6de3c841ef1a4d7fa8aca182
5d871da47bc9b424856e965b32f592b08337a6ed
33443 F20110330_AACHWI chen_m_Page_052.QC.jpg
5c6acf7f229c2e4ca1cd773548ade673
426a93c35e46c12edfefd66e0789d4d5c3ce9076
13054 F20110330_AACHVU chen_m_Page_034.jpg
a33e6f935cc9bae60678891f285175f0
c86b601d6c119cae3d5995b7cc5baa66cce33304
47301 F20110330_AACGTG chen_m_Page_131.pro
8f1ed998e08945876d51674e94942f37
42847f9e40b344311b54aa6dad49773662dd182d
15113 F20110330_AACGSS chen_m_Page_009.QC.jpg
879ecc8a46aed13317f59174a8f028bb
4fb564b0d4bb538a852b4725459bc64c6acedda3
98168 F20110330_AACHWJ chen_m_Page_054.jpg
b1e1b4bbb81768b7f21e55ff3c3cc727
da8008b6af5f7af3a1bb5baa438985ff341342a1
18786 F20110330_AACGTH chen_m_Page_022.QC.jpg
34ee801b485c5b4f5f09cd053ef86f1e
f08b18a3a9a33a6e10fbac3ff0ddeadfa68e8ae5
32098 F20110330_AACHWK chen_m_Page_054.QC.jpg
69af3e604cb75aa05e9bd2127627f4cd
da20015bfc56a6c825bb3ff33609b09637b4ba68
72729 F20110330_AACHVV chen_m_Page_036.jpg
67e2ae4b8f60c1bd592ceedf44b5327a
3be1746dc90b1db54bb0f2ae019ffd2f3674a1c1
F20110330_AACGTI chen_m_Page_133.tif
f0b3c2a3135629358458b10f9f6922ff
a8cc74d05a7c626e233a99d349ed98955005c586
F20110330_AACGST chen_m_Page_130.tif
8cdbdf0ee08dc10a8adde792e13ee8bb
413f583e3a7b79901db54a754690552eea7c3922
F20110330_AACHWL chen_m_Page_055.jpg
e6c94fde249a2fa99074607ba02e567b
1d334156d06108d59d2c25bd4263db0e374eddd7
22743 F20110330_AACHVW chen_m_Page_036.QC.jpg
1e6aa9eb70f6000825afe52c189005a1
baddbf0a4c3386cd00cc88eddd2cf9bf7b56f4ac
81698 F20110330_AACGTJ chen_m_Page_160.jp2
4ca85e14b89e6e7a698dc2eaa440d25b
d4d10c65f325b41371fae73e74e98e8c3fa4c061
105853 F20110330_AACGSU chen_m_Page_113.jp2
e1824ba7bb38299aca6c2b0813014a17
e7cbfe3c855084b81cae12cb007f8ed306ee3d1e
56137 F20110330_AACHWM chen_m_Page_056.jpg
c033790b2eb58941810e79654b296886
f5ab917b5f9842052d803df0d44442bb655ce747
21126 F20110330_AACHVX chen_m_Page_038.QC.jpg
73ebda7ae8207dd90e68de5c99d49c4f
cdd889beb8ddef07c346527aa001c51cebd11d36
2011 F20110330_AACGTK chen_m_Page_077.txt
1c275812529be2bf9fd747a72fe29f2c
9fc059196df0a0ec4382850a83a41d5a9f8a41fe
20472 F20110330_AACGSV chen_m_Page_157.QC.jpg
8426a35ff8fbf3df34bae1f2b02d2828
197b552d4df65ffde8fe54a44b1783fc9bbce593
19442 F20110330_AACHWN chen_m_Page_056.QC.jpg
5847ff02fbae6dea585230ab3bdb9374
8623a3451f010ec9854222bc2de8eb7c4251cbb5
69378 F20110330_AACHVY chen_m_Page_041.jpg
e88038638e3d13bc5a60edff6ec4b1c9
47ef07f58a3b1300f5f87f37ef5461c74b66927c
4482 F20110330_AACGTL chen_m_Page_148thm.jpg
8a6e6d3036ed0b24f639919f55390dc3
7aced22d7c66e18aea28ac7da4c480e62df2a83b
17938 F20110330_AACGSW chen_m_Page_107.QC.jpg
9dbfb8eaa44da440a3dfa1c916f90578
9d492ba82e980bab1160e1692b3742adaadbeccb
31743 F20110330_AACHWO chen_m_Page_057.jpg
a072a2d0dabc355f86a91e6ecaa70bf6
354128aab3f84490af74871d5e23006ed0318662
97793 F20110330_AACHVZ chen_m_Page_043.jpg
2ae27ad7d72c11aa8092e44cf264eafb
b4ae2e16d5497783149f12f27662958bfc6f0190
96627 F20110330_AACGTM chen_m_Page_049.jp2
a5611d929ce6e0c742aced12a20c0d0a
33d1033a54dbd575cdb5aa9474f3af2f63b404e6
33639 F20110330_AACGSX chen_m_Page_043.QC.jpg
a536d003bf35bdf0c0d93939b4676553
e2e7e55ef260ea611cbe6881b854a0fe7bdd4a76
39818 F20110330_AACGUA chen_m_Page_031.jpg
c42f4d713cb677e7b0d0154caf3912cf
28388e2945c18b60ff9af8f9577c2e81356be74b
25091 F20110330_AACHWP chen_m_Page_058.jpg
515ef97d2e10b9a58b5d7612fc01ce5f
2cb3661577513311da134f5f43653b6b4aca05e5
48852 F20110330_AACGTN chen_m_Page_061.jpg
18bb477799a14db9cc0a221d890ad6c4
1172395362ead4c05f949c9b6c00c8e5211d1471
F20110330_AACGSY chen_m_Page_147.tif
f59d8b72af37a45e2d15612a2e8baed3
ff3995cc67ba98e2c7924d5d359a82bf797fffed
76235 F20110330_AACGUB chen_m_Page_036.jp2
8c8155d0c598291fb7862bdee4fd4f81
dfbba7e28825dba8b10993776a676e0e962bb8ff
20310 F20110330_AACHWQ chen_m_Page_059.QC.jpg
34db97b0211997535fc3f3718d1bcb52
6f3b1fa28bf0f199f154d197bb0cd0ce2d550671
48953 F20110330_AACGTO chen_m_Page_143.pro
03ddbdc45359cba8ed083c9e66602eb0
33ed0bf2b268babceaaa7cb4033f6d380df33275
6653 F20110330_AACGSZ chen_m_Page_061.pro
aadeb6810f6080326fe12fb1f7f6bc6c
a844071df418ce4e30508ae062f6cf0e2aa4eb2b
30501 F20110330_AACGUC chen_m_Page_042.QC.jpg
40878b1542ae98d6592e8d13c8fd0222
cd8b76d4078d7baa4b3241678e4492eba8d40f3b
29407 F20110330_AACHWR chen_m_Page_062.QC.jpg
0a53f1e7ca748b07c6efe950cd8ae2b7
3481a1610d7e24b619ef2c83449cbdfdfc913655
82137 F20110330_AACGTP chen_m_Page_048.jpg
89e118fcb2d94179f92559c21531c589
ba3db37c879b650aa5b892123f1d22885c14bebb
1831 F20110330_AACGUD chen_m_Page_079.txt
6eccb87a283f35527855e4dea91a4b5b
1d028b4b2c8861db3c399475dfdd917dea2700dd


Permanent Link: http://ufdc.ufl.edu/UFE0012986/00001

Material Information

Title: Optical Studies of High Temperature Superconductors and Electronic Dielectric Materials
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0012986:00001

Permanent Link: http://ufdc.ufl.edu/UFE0012986/00001

Material Information

Title: Optical Studies of High Temperature Superconductors and Electronic Dielectric Materials
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0012986:00001


This item has the following downloads:


Full Text












OPTICAL STUDIES OF HIGH TEMPERATURE SUPERCONDUCTORS AND
ELECTRONIC DIELECTRIC MATERIALS















By

MINGHAN CHEN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2005

































Copyright 2005

by

Minghan Chen















ACKNOWLEDGMENTS

Many people have contributed to this work and have been constant sources of

encouragement and support. First and foremost, it is my great pleasure to thank my

dissertation advisor, Professor David B. Tanner, for giving me the opportunity to study

the most exciting area of solid state physics and for his valuable guidance, advice,

constant support, patience and encouragement all throughout my graduate work at the

University of Florida. My work could not possibly have been completed without his

guidance and support. The many things I have learned from him will be my treasures.

During the course of my Ph.D. study, I also received great help from Professor

Juan. C. Nino. I have had many interesting discussions with him and the terahertz

measurements were done with his help. In particular, I am very grateful to him for his

help, suggestion and collaboration. His kindness and knowledge are admired.

I would like equally to thank Professor Arthur F. Hebard, Peter J. Hirschfeld, David

H. Reitze, and John R. Reynolds for reading this dissertation and for their interest in

serving on my supervisory committee.

Another special thank you goes to professor David B. Tanner for his great help in

using the analyzing software, which made it possible for me to present data for this

dissertation. I also want to thank the staff member in the Physics Department Machine

Shop and the engineers in the Physics Department for their technical support.

I would like to acknowledge Professor J. Mannhart at Augsburg University for

providing good quality high Tc film samples.









All the magnetic field measurements were done in the National High Magnetic

Field Laboratory with help from Dr. Yong-Jie Wang. I am very grateful to him for his

help.

Thanks also go to all my past and present colleagues in Professor Tanner's group

for their friendship, useful conversation and cooperation through my graduate work.
















TABLE OF CONTENTS



A C K N O W L E D G M E N T S .................................................................... ......... .............. iii

LIST OF TABLES ......... ..... .. ................................ ................ .... viii

LIST OF FIGURES ............................... ... ...... ... ................. .x

A B S T R A C T .......................................... ..................................................x iii

CHAPTER

1 OPTICA L TH EORY ........................................................... .... ............... 1

1.1 L eight P henom ena .............................................................................. .
1.2 Determination of Optical Constants........ ..................................7
1.2.1 Fresenel's Equation.............. ...... ..................................
1.2.2 Kramers-Kronig Analysis ......................... ................................9
1.2.3 Reflectance and Transmittance at a Thin Film on a Thick Substrate.....10
1.2.4 M icroscopic M odels ........................................ .......... ............... 14

2 INSTRUMENTATION AND TECHNIQUES .................................. ...............22

2.1 Far Infrared Techniques........................................................ ............... 22
2.1.1 G general P rinciples........................................................ ............... 22
2.1.2 A podization.......... ...................................................... .. .... .... .....25
2.1.3 P hase C orrection ......................................... ......... ....... ........ ...... .... 26
2.1.4 Sam pling ..................................................................... ......... 27
2.2 T erahertz Technique ............................................... ............................. 28
2.2.1 G general Principles............................ .. .. ..... ................... 28
2.2.2 Some Important Issues with THZ-TDS Technique ............................31
2 .3 G rating Spectrom eter ......... ................. .......................................................34
2 .4 In strum entation .............. .. .. ................................................ ............. ..35
2.4.1 Bruker 113v FT-IR Spectrometer ................. ................................. 35
2.4.2 TPI 1000 Terahertz Spectrometer........................ .................... 37
2.4.3 Perkin-Elm er Grating Spectrometer ....................................... .......... 38
2.4.4 Low Tem perature Apparatus ...................................... ............... 40

3 OPTICAL PROPERTIES OF SUOPERCONDUCTING YBCO FILM IN THE
OPTIMALLY DOPED AND OVERDOPED REGION ............. ....................48









3.1 Introduction ......... ............... ............ .. ... ... ........ ...............49
3.1.1 Fermi Liquid (FL) and Marginal Fermi Liquid model .........................49
3.1.2 Optical Measurement of High Temperature Superconductor ............... 51
3.1.3 The Crystal Structure of YBCO .................................. ............... 56
3 .1.4 P h ase D iag ram ...................................................................... .............. .. 5 7
3.1.5 Pseudogap Phase...................... .................. ................... 57
3.1.6 d-wave Character of High Temperature Superconductor....................58
3.1.7 Two-Component Mode for the Dielectric Function ............................59
3.2 Experim ents and Results.......................... .................... ....... ......... 61
3.2.1 Sam ple Preparation ................................. ................ .. .............. 61
3.2.2 Optical Measurement of the Substrate SrTiO3 .............................62
3.2.3 Optical Measurement of the YBCO Thin Films..................................63
3 .3 D iscu ssio n ................. ................... ......... ............... ................ 6 5
3.3.1 Dielectric Function Analysis ...................................... ............... 65
3.3.2 Charge Transfer Band and Interband Transition ..................................68
3.3.3 Temperature Dependent Optical Conductivity .................. ............69
3.3.4 Quasi-Particle Scattering Rate............................................................. 70
3.3.5 Frequency-dependent Scattering Rate (MFL) .....................................72
3.3.6 Superfluid D ensity ............................................................................ 73
3.4 Summary ................... ................................................ 76

4 FAR-INFRARED PROPERTIES OF SUPERCONDUCTING YBCO FILMS IN
ZERO AND HIGH MAGNETIC FIELDS...................................... ...............94

4 .1 In tro d u ctio n ................................................................................................ 9 4
4.1.1 B background ..................... .............. ......... ... ....... .. ............ 94
4.1.2 Type I and Type II Superconductors ...................................................98
4.1.3 Superconducting Response in High Magnetic Field............................99
4.2 Experim ent and R results ...........................................................................101
4.2.1 Sam ple Preparation ..................................... ......................... .. ......... 101
4.2.2 Sample zero field properties ............................ ....... ............... 102
4.2.3 Optical Measurement in the High Magnetic Field.............................103
4 .3 D isc u ssio n ................................................................................................ 1 0 4
4.4 Sum m ary .......................................... ................... .... ........ 106

5 TERAHERTZ AND OPTICAL STUDY OF ELECTRONIC DIELECTRIC
M ATERIALS .............. .... .. ................................... 112

5.1 Introduction ............................ ..................112
5.1.1 B background ....... ........................... ........ ...... .. .. ........ .. 112
5.1.2 Crystal Structure ....................................... .......... .... .............. 113
5.2 Experim ent and R esult ........................................................ ............. ..115
5.2.1 Sam ple Preparation ..................................... ......................... .......... 115
5.2.2 Experim ental Procedure............................................... .................. 116
5.2.3 Optical M easurem ent.......................... ............... ........ ........117
5.3 D discussion ..................................... ......... .................... 122
5.3.1 Infrared-active m odes ........................................ ........ ............... 122









5.3.2 M ode at 850 cm ...........................................................................123
5.3.3 M ode Splitting ............................ .. ............ .................. ........ 124
5.3.4 Low-frequency Behavior ......................................... ............ 127
5.3.5 Tem perature Effects......................................... .......... ............... 128
5.4 Sum m ary .......................................... ................... .... ........ 129

6 SUM M ARY AND CONCLU SION .................................. .................................... 141

6.1 High Temperature Superconductor ............. .......................... .................141
6.1.1 D oping D dependent M easurem ent ....................................................... 141
6.1.2 Field Dependent Measurement ................................................142
6.2 D electric M aterials............. .......................................... ........ ............. 143

APPENDIX: TERAHERTZ MEASUREMENT OF YBCO FILMS..............................144

L IST O F R E F E R E N C E S ...................................................................... ..................... 146

BIOGRAPHICAL SKETCH ............................................................. ............... 153















LIST OF TABLES


Table page

2-1 Bolometer 113V measurement setup parameters: Bolom. Stands for the
bolometer detector; Bm.Spt is the beam splitter; Scn. Sp. stands for the scanner
speed; Sp.Rn stands for the spectral range; Phs.Crc.Md stands for the phase
correction mode; Opt. Filter stands for the optical filter; BLK.Ply. Stands for
black polyethylene; Apd. Fctn. Stands for the apodization function; Bk-Hrs 3
stands for the Balckman-Harris 3 term; and Hp-Gng stands for Happ-Gengel. ......37

2-2 Perkin-Elmer grating monochromator parameters. GB stands for globar. W
stands for tungsten. D2 stands for deuterium arc lamp. TC stands for thermo
couple. Pbs stands for lead slifide. 576 standsfor Si photoconducting detector
(H am am atsu 576). ........................ .......................... ... ........... .......... ... .. 39

3-1 The charge transfer band fitting parameters* (obtained from Lorentz model) for
the SrTiO3, optimally doped YBa2Cu307- and overdoped Yo.7Cao.3Ba2Cu307 ......66

3-2 Parameters (obtained from Drude Lorentz model) giving the best fit to the
reflectance (between 25 cm-1 and 4000 cm-1) of SrTiO3 at different
tem peratures. .........................................................................67

3-3 Parameters (obtained from Drude Lorentz model) giving the best fit to the
reflectance (between 25 cm-1 and 4000 cm-1)ofYBa2Cu307-6 (optimally
doped) ................................. .......................... ...... ..... ......... 67

3-4 Parameters (obtained from Drude Lorentz model) giving the best fit to the
reflectance (between 25 cm-1 and 4000 cm-1)of Y0.7Ca0.3Ba2Cu307-6
(overdoped) at different temperatures. .............. ................... .......................68

3-5 The scattering rate (obtained from Drude Lorentz model) of optimally doped and
overdoped YBCO films in different temperature............................................... 71

3-6 The Drude part and superfluid part plasma frequency below To in the optimally
doped and overdoped sam ples.......................................... ............................ 73

4-1 Oscillator parameters of both the MgO substrate and YBa2Cu307-O at 4.2 K........103

5-1 Lattice parameters and atomic positions at 298 K and 12 K for the cubic BZN
pyrochlore. (The upper and lower entries in each site correspond to the position
at 298 K and 12 K respectively.)........ .. ........... .... .......................... .. 114









5-2 Parameters from the dispersion analysis of the phonon modes in the infrared
spectra of BZT pyrochlore at 300K and 50K. indicates mode splitting ............ 119

5-3 Parameters from the dispersion analysis of the phonon modes in the infrared
spectra of BMN pyrochlore at 300K and 50K. indicates mode splitting ..........19

5-4 Parameters from the dispersion analysis of the phonon modes in the infrared
spectra of BMT pyrochlore at 300K and 50K. indicates mode splitting..........120

5-5 Parameters from the dispersion analysis of the phonon modes in the infrared
spectra ofBZN pyrochlore at 300K and 50K. indicates mode splitting. **
indicates split A-O' mode described in the present work. .....................................121

5-6 The mass ratio of the B site ions in different pyrochlores.................................... 125















LIST OF FIGURES


Figure p

1-1 Light incidents upon smooth surface. ........................................... ............... 20

1-2 Light incidents onto a thin film with thickness d. .................................................21

2-1 A simplified Michelson interferometer diagram. Light travels distance S from
source to the beam-splitter. Partially reflected travels to the fixed mirror (Mi)
and partially transmitted beam travels a variable distance toward the movable
mirror (M2). The beam is recombined at the beam splitter and half of the beams
returns to the source, and the other proceeds to a detector................. .......... 41

2-2 Schematic diagram of a THz-TDS spectrometer using a femtosecond laser
source and photoconductive THz transmitters and receivers. Partially reflected
laser light was used as the gate signal for the THz detector. Partially transmitted
light reaches THz transmitter to excite the THz pulse. Sample is placed in the
beam focus point. ......................... ......................................... .. ..... 42

2-3 Curve shows the THz transient after propagation through a BaTeO3 pellet. The
main pulse is followed by a series of pulse of decreasing amplitude that
originate from multiple reflections within the pellet ............................................43

2-4 Diagram of grating spectrometer showing the incident and diffracted rays and
the operation of grating. .............................. .................................. ......... ...... 44

2-5 Schematic diagram of Bruker 113 V FTIR spectrometer. The lower channel has
the specially designed reflectance optical stage for reflectance measurement in
the sam ple cham ber. ...................... .................... .................... .. ..... 45

2-6 Schematic diagram of Perkin-Elmer monochromator spectrometer.....................46

2-7 High-Tran system flow diagram ........................................ ......................... 47

3-1 The unit cell of YBa2Cu307. (Ca substitute for Y in the overdoped sample). .......77

3-2 Schematic phase diagram of the hole-doped cuprates (x is the doping level). ........78

3-3 Room temperature reflectance of SrTiO3 and the fitting spectrum..........................79

3-4 Temperature dependent reflectance spectra of SrTiO3 substrate ...........................80









3-5 Room temperature reflectance spectra of the optimally doped and the overdoped
sam ples. ............................................................................ 8 1

3-6 Temperature dependent reflectance spectra of the optimally doped YBa2Cu307-O
fi lm ................................................................................. 82

3-7 Temperature dependent reflectance spectra of the overdoped Yo.7Ca0.3Ba2Cu307-
S fi lm ................................................................................ 83

3-8 The measured and fitted room temperature reflectance of both optimally doped
and overdoped film s. ..................... .................. ................... ...........84

3-9 Measured and fitted reflectance of optimally doped YBa2Cu307-O at room
tem perature and 50 K .......................... ........................ .. .. ....... ............ 85

3-10 Measured and fitted reflectance of overdoped Yo.7Ca0.3Ba2Cu307- at room
tem perature and 50 K ................................... ... .. ....... ............ 86

3-11 Optical conductivity (obtained from Drude Lorentz model) of the optimally
doped and overdoped samples at room temperature. .............................................87

3-12 Number of carrier participating in optical transition per Cu atom, Neff, as a
function of frequency. .................................................................. .. .... ............... ..88

3-13 Temperature dependent optical conductivity obtained from Drude Lorentz
model of optimally doped and overdoped samples ............................................89

3-14 Temperature dependent scattering rate (obtained from Drude Lorentz model) of
the optimally doped and overdoped samples. .................................. .................90

3-15 Imaginary part of quasi-particle self energy (obtained from Marginal Fermi
liquid model) of both optimally doped and overdoped samples. ..........................91

3-16 Superfluid density calculated from sum rule and imaginary part of the optical
conductivity in both optimally doped and overdoped samples...............................92

3-17 Temperature dependent imaginary part (obtained from Drude Lorentz model) of
the optical conductivity in the optimally doped and overdoped samples. ...............93

4-1 Transmittance of different YBCO film samples. YBCO/sapphire (a),
YBCO/MgO (b), YBCO/silicon (c) samples in different magnetic fields ...........108

4-2 Measured and fitted spectra of YBa2Cu307-5/MgO sample. .................................. 109

4-3 Real and imaginary part of optical conductivity of optimally doped YBCO.........110

4-4 Magneto resistance of different YBCO film samples. YBCO/sapphire (a),
YBCO/MgO (b), YBCO/silicon (c) samples in different magnetic fields.............111









5-1 Low temperature cofired ceramics (LTCC) multilayer manufacturing process. ...131

5-2 The crystal structure of the bismuth pyrochlore ...................................................132

5-3 The displacement of A site cation and 0' anion. ......................... 133

5-4 The reflectance of different bismuth samples. (a) BZT, (b) BMN, (c) BMT, and
(d) B Z N ........................................................................... 134

5-5 The real part of the dielectric function (e') of different bismuth samples. (a)
BZT, (b) BMN, (c) BM T, and (d) BZN. ...................................... ............... 135

5-6 The imaginary part of the dielectric function (s") of different bismuth samples.
(a) BZT, (b) BM N (c) BM T, and (d) BZN ...........................................................136

5-7 The absorption coefficient and conductivity of BZN at room temperature and at
cryogenic temperature. (a) absorption coefficient, (b) conductivity......................137

5-8 Measured and calculated reflectivity of BMN at different temperatures. (a) 300
K and (b) 50 K ................................................... .................................. 138

5-9 The splitting of the B-O stretching mode in BMT........ ........... .................139

5-10 Temperature dependence of the phonon mode frequencies in BZT, BMN, BMT,
an d B Z N ......................................................................... 14 0

A-1 The temperature dependent transmittance of the YBa2Cu306/sapphire (a),
YBa2Cu307 -/sapphire (b), and sapphire (c) ........... .... ............... ................... 145















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

OPTICAL STUDIES OF HIGH TEMPERATURE SUPERCONDUCTORS AND
ELECTRONIC DIELECTRIC MATERIALS

By

Minghan Chen

December 2005

Chair: David B. Tanner
Major Department: Physics

Infrared and optical spectroscopy has been applied to study both the normal state

and superconducting state electronic properties of cuprate superconductors. Two

important parameters used in our experiments are the applied field and substitutional

doping.

The ab-plane optical responses of Ca-doped YBa2Cu307-O films were studied from

optimally doped region to overdoped regimes. The temperature dependent reflectance

spectra were measured from far infrared (20 cm-1) to ultraviolet (43,000 cm-1). The

spectra were analyzed by a two component model and marginal Fermi liquid model. The

result indicates a further increase of plasma frequency which is consistent with the study

of BSCO samples by other groups. Another interesting result is the decreased superfluid

density in the overdoped region. This result is consistent with decreased superconducting

transition temperature with increasing the doping level within the overdoped region.









Magnetic field dependent, low temperature infrared transmittance was used to

study the vortex dynamics in high temperature superconductors. Optimally doped

YBa2Cu307-O and YBa2Cu306 samples were used for the measurements. We saw no

significant field-sensitive features in the far infrared transmittance spectra at low

temperature.

The temperature dependence of the reflectance of cubic bismuth pyrochlores

Bi3/2ZnTa3/207 (BZT), Bi :MlNb :07 (BMN), Bi-, :MuTa3/207 (BMT) and

Bi, :Zn,,.92Nb1.506.92 (BZN) has been investigated by infrared spectroscopy. Spectra were

collected from 30 to 3300 cm-1 between 50 and 300 K, and the optical constants were

estimated by Kramers-Kronig analysis and classical dispersion theory. In addition, BZN

was studied by terahertz technique at lower frequencies (3 cm-1 to 60 cm-1) between 300

K and 50 K. Infrared-active phonon modes have been assigned to specific bending and

stretching vibrational modes. A previously unassigned infrared mode at about 850 cm-1 is

discussed. A splitting of the B-O stretching phonon modes and O-B-O bending modes is

assigned to mixed cation occupancy. The temperature dependence of the phonon

frequencies and the damping coefficients are consistent with a decrease of lattice constant

and with orientational disorder at low temperatures.














CHAPTER 1
OPTICAL THEORY

The optical properties of materials arise from the characteristic of their interactions

with electromagnetic waves. Different classes of materials will, in general, differ in their

response to optical radiation. In this chapter, we will provide a general background of the

theory of the optical properties of materials. The first part is a review of the principle of

optics and some phenomena that occur when light propagates through a medium. Then,

we will introduce the famous Maxwell's equations which describe the behavior of

electromagnetic fields. Following this part, several techniques and equations will be

introduced to explain how to get quantitative optical parameters from the experimental

spectrum. Finally, we will give the microscopic models to describe the interaction

between light and the atoms of the materials. Details of the subject of this chapter can be

found in most books on optics and electromagnetism [1-7].

1.1 Light Phenomena

Light propagates as electromagnetic waves. Therefore, there are certain

characteristics of waves, and in particular electromagnetic waves, that must be reviewed

in order to understand the behavior of light and its interaction with matter.

Traveling waves can be either longitudinal or transverse. The electromagnetic field

wave is transverse. If light incident on the source is absorbed and the only light emitted

by the source is the light generated by the oscillators of the source material, then the

source is named a black-body. Planck's equation for spectral intensity as a function of

wavelength R(2) (in J/cm3 etc.) for the black-body radiation spectrum is













R(A) =- (1-1)
e"B -1


where Tdefines the temperature in degree Kelvin (K), h is Planck's constant (6.63x10-34

J.s) and kB is Boltzman's constant

The wavelength corresponding to the peak emission intensity for each temperature

can be derived from equation 1.1.

AmT = 0.28978 x102 mK (1-2)

Equation 1.2 is Wein displacement law.

When light is shining onto a medium, some of it will be reflected and the rest of the

light is going to transmit and propagate in the material. As the light propagates in the

medium, part of the light will be reduced by the absorption or scattering by the material.

If we assume the optical properties such as refractive index, absorption coefficient,

and reflectivity are independent of light intensity, this is called linear optics. All the

discussion of this thesis will be restricted to the linear optics.

Within linear optics, the refractive index of a material is defined by the ratio of the

velocity of light in free space to the velocity of light as it passes through the materials.

c
n (1-3)


The group velocity of light traveling through a material is less than the velocity in

free space. It is also true that light with different wavelength travels at different speed

through the same material. This leads to the fact that the refractive index of any matter









has the same wavelength dispersion or a variation in value as a function of wavelength or

frequency

n = n(co) (1-4)

The absorption of light in the matter can be quantified by absorption coefficient a

defined as the fraction of the power absorbed in a unit length of the material.

dl= -aodx I(x) and I= Ie" (1-5)

The response of a material to the external electric field E can be characterized by a

few macroscopic vectors: polarizationP, electric displacement and current density J. For

weak electromagnetic field and in local limit, the response of the medium is linear and

can be written by the constitutive relations (all the equations are written in c.g.s unit).

P = ,E D E+ 4 = EE E = 1 + 42ie8 = l + i'2
M = H B + 4;dM = fiU, / = 1+ 4Z,,m (1-6)

and J = E = oa + i2,,
at

The parameter W is a complex dielectric constant and & is the complex

conductivity of the medium. The real parts of W and a are the frequency-dependent

dielectric function and conductivity, respectively, of the medium. For simplicity, we take

u = 1; this is the case for most of non-magnetic materials. Thus, we can setB = H.

The propagation of the electromagnetic wave can be described by a set of four

differential equations known as Maxwell's macroscopic equations.









V D = 4;rp,
V-B=0

VxE- 1B (1-7)
c at
Vxi 1 OD 4;r -
V xH + -J
c 9t c J



where E andH are the electric and magnetic fields, D and B are the displacement field

and magnetic induction, pf and Jf are the free charge and free current density

respectively.

If the medium is isotropic and homogenous, W and & are scalar quantities rather

than tensors and have no space variation. In the absence of external charges and free

current density, Maxwell equations are given by

V-D=0
V-H =

VxE = -1 H (1-8)
c 9t

VxH =1L
c 9t

assume the fields have the plane-wave form


S= oep[i(. ot)] (1-9)
H HOi










where the vector E,, H, and q are in general complex and independent of space and


time, then yt and V can be replaced by -ico and i respectively. Then, Maxwell's


equations can be changed into

qjD 0O::::: > E = 0
q-H =0

c

qx H = D =--sE
C C

Equation (1-10) indicates q, H are mutually perpendicular with each other, if

we assume W is a scalar, the case for isotropic materials. The solution for the above

Maxwell s equations is


-2 (<' 1 n
S= (1-11)
c

The conclusion provides that light is a transverse electromagnetic wave. One can

define a complex refractive index N, yielding the very useful dispersion relationship


q = -N -(n+ik) (1-12)
c c

Comparing equation (1-11) and (1-12), we find

N=j- (1-13)

or

El = n2 k2
S 2 (1-14)
2 = 2nk










[ = (,1 + E=2 +( 1
k (1-15)
_2L [(E1 J )YJ ]Y
k= (e 2 + 1


Considering the case of normal incidence and q parallel to x, then equation (1-9)

has the form


= e = e c ec (1-16)


This solution is an attenuated wave with a skin depth 6 = (c/o)k or a power

absorption coefficient a = 2/ 6 = (2 wk)/c, the phase velocity is v = c/n.

The optical response of a material can be described by various quantities (called

optical "constants") which are not independent and can be interrelated by

1 4~ 47-
N2 = 1+1i- (1-17)
Z2 o)

where the complex surface impendence Z = R + iY, with R and Y being the impendence

and reactance, has been introduced. Note all the optical "constants" introduced are (in

general) frequency dependent.

For our experiment, the most interesting thing is the real part of the optical

conductivity, Io, because it is directly proportional to the power dissipation of the

electromagnetic field unit volume by the medium.

dP 1 1 1 -- 2
dp =Re( E*)= -Re[(o)- E*.]= -cl, (1-18)
dV 2 2 2

J = Jf + Jp = a-E is the total charge current induced by the electric field E. The result

indicates that only the in-plane conduction current Jf = aCE dissipates power. While the









displacement current Jd = -i(ca / c)E and the polarization current Jp = ic2E do not,

because they are 7t/2 out of phase with E; thus time average of energy flow is zero.

1.2 Determination of Optical Constants

The purpose of our experiment is to find the optical conductivity. But,

unfortunately, in most situations, optical conductivity cannot be measured directly.

Information about the materials is often obtained by studying the electromagnetic waves

reflected from and/or transmitted across interfaces between materials with different

optical properties. In the experiment, the transmittance T(co) and reflectance R(co) are

usually measured in a special frequency range. And the optical constant, such as al(co)

and a2(c), will be deduced from R and T.

1.2.1 Fresenel's Equation

In Figure 1-1, light incident upon the smooth surface will be reflected and

refracted. The incident, reflected and refracted rays lie in the same plane of incidence.

The reflected beam from a flat, polished surface will propagate at an angle (O = O,) that

which equals the angle of incidence. The refracted or transmitted beam will propagate at

an angle Ot that obeys

n, sin 8, = n, sin (1-19)

At the interface, the reflected and refracted beam intensities must satisfy the

requirement that the parallel to the interface components of the total electric and

magnetic fields be continuous across the boundaries. This relationship leads to the

Fresnel formulae. For normal incidence (, = Ot = 0) the boundary condition can be

written as the following equations









+ E(1-20)
H ,- =iH,

where the subscripts i, r and t denote the incident, reflected and transmitted light

respectively at the interface.

The relation betweenE andH can be simplified asH NE. Thus, a plane wave is

propagating across the interface between medium a and medium b, and it satisfies

H, = NE,
H, = NE (1-21)
H, = NbE,

where Na and Nb are the complex refractive indices in medium a and medium b. The

complex amplitude coefficients of the reflected r and transmitted t electric field are

E N N,
r =E N (1-22)
E, N N + Nb

E 2N0
t = -r-= 2, (1-23)
E, N, +Nb

If we assume medium a is vacuum, then we can take N = 1 and Nb = N = n + ik. The

reflectance of medium b is simply given by

R_, (1- n)2 +k2 (
R=rr = -- (1-24)
(1 + n)2 +k2

The reflectance R and phase change p of the reflected electric field wave are related to n

and k by


Re r (1 n) ik
(1 + n) + ik (1-25)
2k
and tan p = 2
1-n2 -k2









In the single-beam optical measurement, only the reflectance R can be measured.

Thus, n and k cannot be determined alone. Therefore, we need another equation to relate

n and k. The Kramers-Kronig relation offers a practical solution to the problem.

1.2.2 Kramers-Kronig Analysis

The Kramers-Kronig technique makes use of the optical functions, such as

reflectance, transmittance or other linear response functions. This analysis is based on the

causality requirement on the response function, i.e., that the response of the system

cannot occur until an external driving force is applied. These equations relate a dispersive

process to an absorptive process due to the requirement of causality for linear response

function. The Kramers-Kronig relation for the complex refraction index and the complex

dielectric function may be stated as follows,


n(co) -1 = -P 2 d9 '
0 C(1-26)

k(co) = P jn(o do'
0 (2o -o


2 0j'2(')- 1 2
E, (0)-1 = 2-P --' ----2 do'
0 (1-27)
E2 -2o 3 El, -'(0')- do)
2(co)= 2P 2 2d1'
Z 0 -C9

where P is the Principal value of the integral. For the reflectance at a plane interface, the

amplitude reflection coefficient given in equation (1-24) is a complex quantity. One

commonly used technique is to measure the reflectance over a wide frequency range, and

we get












1 r '+o d lnR(o3') d
l In "d
2) 0 I3'-(3 do'

An obvious drawback of the Kramers-Kronig technique is the requirement of large

frequency range measurement. Extrapolations to zero and infinite frequencies are

required. One typical extrapolation [3] is that above the highest frequency (37,000 cm-1)

measured, the reflectance is usually expressed as co- with 0 < s < 4. The reflectance is

due to interband transition in this region and can be expressed as


R(o) R= R (1-29)


At low frequency, the reflectance is assumed to be constant if the sample is an

insulator. In the case of a metal, the reflectance is expressed in term of the Hagen-Rubens

law [3] and is written as

R(o) = Ao (1-30)

1.2.3 Reflectance and Transmittance at a Thin Film on a Thick Substrate

A thin film has a thickness d<
incident onto this system, some part of it will be reflected and some will be transmitted.

In the film, we can expect multiple reflections. This can be clearly described by the

following model. As shown in Figure 1-2, medium 1, medium 2, and medium 3 constitute

this two interface system. The first and third media are assumed to be non-absorbing and

to span semi-infinite space with their complex refractive index N1 and N3 respectively.

The second medium has its thickness d with refractive index N2. For simplicity, only









normal incidence will be considered. The general transmission and reflection can be

expressed as

t 12 t23e' [+ (r23r2e'2 )+ (r23r21e'2 )2 +_.]
12 T23e'g (1-31)
1- 23r21e2



and

r =12 +t12r23 t21e'8[i +(r213e'2e)+(r2 r23e' 2)2 +...j
12r23 t2 e'1 (1-32)
=r1 + r
1 21 e23 2

where r, and t, are the amplitude reflection and transmission coefficients between

medium i andj. 3 is the complex phase depth of the second medium which is defined by

S= Nd =-n 2d+i-d (1-33)
c c 2

where a is the absorption coefficient. The resultant transmission and reflection are

obtained


T =3 t2 = 12 23 e- (1-34)
n1 1 1+ 1+23 212 e2d 2 23 1121 e- cos


2 12 + r23 e 2 + 223 l2e e cos (1-35)
R1 =j1 2 (1-35)
1 + 3 2 l 22212e 2e- 223j e cosO


0 = 2- nd + 23 + 2 (1-36)
c

where oij is the phase shift upon reflection at the interface. The cosine term leads to

interference fringes in the spectrum which is due to multiple internal reflections in the

second medium.









When the second medium is thick (d>>A) or wedged, there is no coherence among

multiple reflections. For a thick sample of thickness d with complex refractive index i

being measured in a vacuum, it is straightforward to find the average transmittance and

reflectance

(1-R,)2(1+k2/n )e -d
ve = (1-37)
e 1 R~ e -2ad

and

Re = Rs(1+ Te- a) (1-38)

where Rs is the single bounce reflectance given by equation (1-24).

Let us consider the structure of a thin film with thickness d deposited on a thick

substrate, as shown in Figure 1-2. Take N = 1; then from equation (1-31) and (1-32) with

the following approximations,

N2 > N = 1
N2 >> IN 3 =n n
e'2 & 1+i23 (1-39)

iN2 3 -od = y
c

Here, we have applied the long wavelength limit and assumed that film is thin enough

such that 6<<1.

It can be shown that the transmittance across the film into substrate and the

reflectance from the film are given by Glover-Tinkham equations [8, 9].

1 4n
Tf = 2 =2 (1-40)
+ (y, +n +l +Y2









(y, +n-1)2 +y'
R = 2 (1-41)
(y + n + 1)2 + y


where n is the refractive index of the substrate, ys and y2 are real and imaginary part of

the complex admittance of film y respectively. y is related to the complex conductivity

C = a1 + io2 of the film by y = Zo&d where Zo is the impendence of free space.

In reality, the substance has a finite thickness and it is a four medium problem with

medium 4 being vacuum. For a nearly opaque metal film, the overall reflectance of film

plus substance in this 4-medium system is

TfR e-2
R = Rf + (1-42)
s R fRe 2

Equation (1-40) gives the transmittance across the film into substrate. The

measured transmittance T is given by

(1 R )e o
T= T Rse- T (1-43)
1-RRe-2- f

where x is the thickness and a the absorption coefficient of the substrate. The other terms

of equation (1-42) and (1-43) are substrate-incident (backside) reflection of the film.

(y, -n+ 1)2 + 2
R' (y-n ) 22 (1-44)
(Y +n+l+)2 +Y2
f (y, + n + 1)2 + y2

and for a weakly absorption substrate such that k = (ca)/(2o)<
reflection of the substrate may be approximated as


Rs= -n 2 (1-45)
1+n

From the measurement of the transmittance and reflectance of the substrate, we can

get the index of refraction n and the absorption coefficient a of the substrate using









equation (1-37), and (1-38). The term k2/n2 in equation (1-37) can be neglected for a

weak absorbing substrate.

With the knowledge of substrate's optical properties, o-, oa and all other response

functions can be expected by inverting equation (1-40) (1-44), after measuring both

transmittance and reflectance of the film-on-substrate system. For a structure with more

layers, the analysis becomes progressively more complicated.

1.2.4 Microscopic Models

Up to this point, we have not described the optical phenomena from a microscopic

point of view. There are various microscopic models which explain the optical behavior

observed experimentally. The classical theory of absorption and dispersion is due mainly

to Lorentz and Drude. The Lorentz model is applicable to insulator; its quantum

mechanical analog includes all direct interband transitions, i.e., all transitions from which

the final state of an electron lies in a different band, but with no change in K-vector in the

reduced zone scheme. The Drude model is applicable to free-electron metals; its quantum

mechanical analog includes intraband transition, where intraband transition is taken to

mean all transitions not involving a reciprocal lattice vector. Both the Lorentz and Drude

model are useful as starting points and for developing a feeling for optical properties.

Many features of these classical models have quantum mechanical counterparts which are

easily understood as generalizations of their classical analogs.

1.2.4.1 Lorentz model

The Lorentz model is a simple, yet very useful classical model dielectric function

that can be derived for a set of damped harmonic oscillators. The motion of an electron

bound to the nucleus is described by










d2r dFr 2
md + mr d- + m0= -eE(t) (1-46)
dt2 dt

The field E(t) is the local electrical field acting on the electron as a driving force.


The term mr- represents viscous damping and provides for an energy loss mechanism.
dt

The actual loss mechanism is radiation damping for a free atom, but it arises from various

scatting mechanisms. The term m( 2F is a Hooke's law restoring force.

In the classical model, there are two approximations in equation (1-46). The

nucleus has been assumed to have infinite mass; otherwise the reduced mass should have

been used. We also have neglected the small force- eV x B / c arising from interaction

between the electron and the magnetic field of the light wave. It is negligible because the

velocity of the electron is small compared with c (c is the speed of light in vacuum).

Inserting a solution of the form r = roe into equation (1-46), yields


r = -- E (1-47)
m 09 0)

and the induced macroscopic polarization is

Ne2 1
P = Ner = N1 E (1-48)
m (0-)0 -iy()

Assuming there are N oscillators per unit volume, the resonant contribution to the

macroscopic polarization is

Ne2 1
P = Ner = N1 E (1-49)
m 0 0 110)

For isotropic matter, the susceptibility arising from the oscillator is

Ne2 1
S= 2 (1-50)
m (y00









the total polarization is

total = ZeE = ( Z)E (1-51)

where X is the background susceptibility that arises from the polarization due to all the

other oscillators at higher frequencies.

The dielectric function can be determined

2
(C=s) = o + cp (1-52)
2 -0D) 2 ;,0


plasma frequency can be defined by

4_Ne 2
=2 (1-53)
m

where N, q and m are the number density, effective charge and effective mass of the type

j oscillator respectively. If the system has several oscillators and N, is number density of

jth oscillator, N, should satisfy the following equation.

NJ =N (1-54)


A corresponding quantum mechanical version of equation (1-52) can be written as


s(o) = +L 0 2 (1-55)
SCO2 ) 2 iyj co

j is introduced as the notion of oscillator strength. The oscillator strength is related to

the probability of a quantum mechanical transition which can be calculated using Fermi's

golden rule. It satisfies a sum rule.

Z =1 (1-56)


The oscillator strength allows us an explanation for different absorption strength of

different transitions.







17


1.2.4.2 Drude model

The Drude model describes the optical response of free carrier in good metals. It is

just a particular case of Lorentz oscillator with o, in equation (1-46) being zero.

2
0) pD
ED = 1 D (1-57)


where COpD is the Drude plasma frequency defined by

2 4Ne2
po m- (1-58)
pD


The real and imaginary parts are


D 1 2 2
ED1 1 2
+2 (1-59)
2 0) pD Z
S(1 + o2r 2)

The conductivity based on the Drude mode is


( C) = O- (1-60)
1 i or

where ao is the DC conductivity defined as

Ne2r
-o = (1-61)
m*

The real and imaginary parts are


Oi
D1 I
1 Z2 (1-62)
CO C9Z
D2 1 + )o2Z2


The relation between W and c is


W(go) = E + 4'-i r(go) (1-63)
CO









in the limit of low frequency where co << T is satisfied, we can obtain the following

relations

E I 2 2
8D1 -CpD
ED2 o 2r/m = 4cr, / 0) >> ED1
(1-64)
n k (c2 /2)2

R 1-2/n1 (2a /I o-) )2

From the above equations, we can find the absorption coefficient


a = k 8 (1-65)
c c

or the skin depth

2 c
3 = C (1-66)
a 2770=0)

So, the skin depth is inversely proportional to the square root of the DC conductivity and

frequency. This implies that a material with higher DC conductivity allows shorter

penetration of AC fields.

Considering the special case with Drude width r'= 0, the dielectric functions are

given by

2
COpD
D1 2= (1-67)

ED2 = D1I = 0 () A 0)

For superconductor, the super-fluid part of dielectric contribution is satisfied with

the above equation. This equation tells us that eD < 0 for frequencies below the plasma

edge (o < a pD -< ). Then, the complex refractive index R is purely imaginary and

thus the reflectance R is 1 in this frequency range and system suddenly becomes

transparent above plasma edge.









1.2.4.3 Drude-Lorentz model

When both the Drude and Lorentz types of dielectric response are observed in a

spectrum, we can model the dielectric function by a sum of these terms.

2 2
W()- P (1-68)
+ 2 2 2 i
ic j -o) -iy Jo) +iaoyr

This relation is called the Drude-Lorentz mode. In the optical spectrum of the high

Tc superconductors, the Lorentz part of contribution is used to describe the mid-infrared

contribution. The Drude part is used to describe the free carrier or quasi-particle

contribution. All these terms plus the superfluid term will be used to describe the

dielectric function of the optical properties of the high Tc superconductor.

Unlike Kramers-Kronig relation, fitting data with model function can be employed

in a finite frequency range as long as we have a well-defined background contribution E.

beyond the measured frequency range.

1.2.4.4 f-Sum rule

Forf-sum rule. It states that the area under the conductivity oa(co) is conserved.

O 2 Ne 2
cr (o)do) = 2 (1-69)
f 8 2 m

where m and e are the bare mass and electric charge of a free electron. This sum rule

means that area, or oscillator strength, is independent of factors such as the sample

temperature, the scatting rate, phase transition, etc. The sum rule has an important impact

on a superconductor, in which an energy gap develops between the transition temperature

Tc. The spectral weight at wc < 2A shifts into the origin (6 function), causing an infinite

DC conductivity.













0i Or


Figure 1-1 Light incidents upon smooth surface.






Medium 1, A1
Medium 2, N2
Medium 3, N3


K/AY


Figure 1-2 Light incidents onto a thin film with thickness d.


\*\














CHAPTER 2
INSTRUMENTATION AND TECHNIQUES

This chapter describes the experimental equipment and technique used to perform

our near-normal incidence reflectance and transmittance measurement, as well as the

various techniques used to characterize our samples. The first section is a description of

Fourier spectroscopy. We then discuss the terahertz measurements and the diffraction

grating spectrometer. Then, we will introduce the instruments used in my experiments

which are Bruker 113V FT-IR spectrometer, TPI Spectra 1000 spectrometer, and the

Perkin-Elmer Mid 16U monochromator. In the final part, we will discuss the cryogenic

system used to take the temperature dependent measurement for the YBCO films and

electronic dielectric samples.

2.1 Far Infrared Techniques

2.1.1 General Principles

Let us consider the basic experiment shown in Figure 2-1, which is a simplified

Michelson interferometer. All the theories are general and will hold for any type of

interferometer.

Without losing generality, we can consider that a monochromatic plane wave of the

forum

E(r, t) = Eoe (qr t) (2-1)

is incident on the beamsplitter from the source. Here q is the wave vector, F is a position

vector, co is the angular frequency, t is the time and E, is the amplitude of the electric









field. The light travels a distance S to the beamsplitter which has a reflection coefficient

rb (light will be reflected to mirror Ml) and a transmittance coefficient tb at a given

frequency. The reflected beam goes a distance xl to a fixed mirror with a reflection

coefficient r, and a phase py and transmitted beam goes a variable distance x2=(xi+x) to a

moving mirror with a reflection coefficient rx and phase px in term of frequency. The two

beams return to the beam splitter and are again transmitted and reflected with coefficient

tb and rb. Some proportions of the beam go back to the source and the rest of the beam

travels a distance D to the detector. At the detector, the electric field is a superposition of

the fields of the two beams. Both c and F are parallel to each other. For our discussion,

we will assume the end mirrors are near perfect reflectors such that r ry -l. And we

define the angular frequency V by the relation,

2izv 2r -
q-
q = -=- 2IV
c A (2-2)

The resulting field from the interferometer toward the detector is

ED = rbtbE [e' (2wxl -ot) + e(2-2 ot)] (2-3)

Thus, the light intensity at the detector is


SD EDED = I (i)[1 + cos(2;Vrx) (2-4)
2

where x is the optical path difference, x=x2-xl, e is the beam splitter efficiency E = 4rt ,


and the source intensity is Io(V) (equals to 2E, 12). SD(x) is the intensity of light at the

detector for a single given frequency. In general, the following equation holds for the

practical beam splitter.


a+r+t=l


(2-5)









where a is the absorption of the beam splitter. For an ideal beam splitter, it has a=O, and

t=r. This expression can be simplified to

S(x, v) = f(v)[1 + cos(2;rvx)] (2-6)

1
f(v) (equals to -I0 (i)) is spectral input that depends only on v. S(x, v) is the detector
8

signal for a monochromatic source. The cosine term gives the modulation on the detector

signal as a function ofx.

However, in FT-IR spectrometer, we measure the intensity of light, ID(x) for all

frequencies [SD (x) -> SD (, vjl as a function of the optical path difference x.


ID (x) S(x, v)dv
0 (2-7)

= f(v)[1 + cos(27rvx)]dv
0

At x=0, the detector signal reaches its maximum value,


S(0)= 2jf(v)dv (2-8)
0

This position corresponds to zero optical path difference where all frequency

components interfere constructively. As x---o, on the other hand, the coherence of the

modulated light is completely lost. The detector signal is around an average value.

S(0)
S( =) = f (v)dv = (2-9)
0

The interferogram is the difference between the intensity of each point and the average

value.


F(x) = S(x) S(c) = f(v)cos(2'rvx)dv (2-10)
0









f(v) is the cosine Fourier transform of F(x). The f(v) can be written as


f(v) = 4 F(x) cos(2;rvx)dx (2-11)
0

2.1.2 Apodization

In practice, the interferogram cannot be measured to infinite optical path

(retardation), and it must be within finite range or truncated. This type of truncation can

be obtained by multiplying the complete interferogram with a truncation function G(x),

which vanishes outside the range of the data acquisition. The actual function which is

transformed is the product of the interferogram and the truncation function.

To explain the effect of the truncation function, consider the truncation function

described by a boxcar function G(x).

r ifx <; L
G(x)= if L (2-12)
0 if x > L

where L is the maximum retardation. The Fourier transform (FT) ofF(x) is the

spectrum f(v). The FT of G(x) is the since function

sin(2fivL)
FT[G(x)] = 2L s L = 2L sin c(2ivL) (2-13)
2;rvL

This Sinc function has a center maximum at V = 0 and several oscillations. The width of

the function is 1/L. If a single wave of frequency v, is convolved with a boxcar

truncation with maximum length L, the resultant spectrum would be a sinc(x) function

centered at v, with width 1/L. Thus, the resolution is limited to Av I The side-lobes

(oscillations) may be reduced by using an apodization function different from boxcar but









this will come at the cost of a further reduction of resolution. Some of other popular

apodization functions are Happ-Genzel [10], Norton-Beer (weak, medium, strong) [11],

and Blackman-Harris (3-term, 4-term) [12]. A nice discussion about the apodization

function can be found in Griffiths [13].

2.1.3 Phase Correction

Up to this point in our discussion, the interferogram, F(x), is perfectly symmetric

about the zero point (F(x) = F(-x)). In a real experiment, because of the existence of a

phase error, that must be included to describe the actual measured interferogram. The

phase error mainly stems from optical path difference. Phase error could lead to a

negative spectrum or to a slight shift of sharp frequencies. When the system has a phase

error, the interferogram given by equation 2.10 is modified to


F(x) =jf (v)e'(2 ; )dv [f ()e'"o l2 2 vxdv 2.14
0 0

where 0 is the phase error. This error leads to an asymmetric interferogram. In order to

correct the phase error, we first take an interferogram between L
corresponding to zero point). The phase spectrum can be found from

-Im [f (v)]
0(v)= arctan m ) 2.15
Re[f (v)])

After calculating 0, the complex spectrum f(v)may be corrected by multiplying it by

e1 so


f()crrected = f (v)e" e = f (v)


(2-16)









There are several phase correction modes available. In my experiments, Mertz phase

correction [12] is used. More detailed discussion of phase correction methods can be

found in other papers [14, 15].

2.1.4 Sampling

Another error occurs in the practical measurement or sampling the interferogram.

The analog signal must be converted to digitized data sets before any sort of manipulation

can take place. For this reason, the interferogram is sampled at small, equally spaced

discrete retardations. This discrete nature can be handled mathematically by using the one

dimensional Dirac Delta Comb


'(x) = Z (x- n) (2-17)
.= co

where n is an integer. In a real experiment, there is always an error Ax between the

measured point and zero point.

The real sampled interferogram is given by F'(x)


F'(x) = F(x) = Ax F(nAx)3(x -nAx) (2-18)


Then, the spectrum derived from FT of F'(x) will be

1 v +
f' (v) = *f(v) = -f(v-nAv) (2-19)
Av wAvh n 1 a

when Av =1 j and f(v) = FT[F(x)]

This sampling of the interferogram causes two effects. First, it introduces an

additional phase term e -^A (co is the frequency of the light wave) into the spectrum. This

term can be used as another kind of phase error, to be handled in part of the phase









correction. The second effect is that it makes the spectrum periodic. This effect leads to

the possibility of aliasing or "folding". This effect can be prevented by insuring that,

Av Am
Vmax
2 2

These conditions state that the highest frequency needs to be sampled at least twice

per-wavelength. This is called the Nyquist sampling criterion. It is experimentally

important either to ensure digitizing an interferogram at a high enough sampling rate or to

limit the range of frequency input to the detector using optical and/or electronic filters.

Following the above arguments, it is quite obvious that the measurement of a

narrow frequency range requires a smaller number of data points. But if the number of

points is too small, the spectral may not be defined. In such case, we can add extra zero-

valued data points at the end of the interferogram keeping the same sample spacing. This

technique known as zero filling effectively produces a larger number of spectrum points

per resolution element. Since the points added are zero, the actual spectral resolution will

not increase. It merely provides a smoother spectral line shape. More detailed information

about infrared spectroscopy can also be found in other papers [16].

2.2 Terahertz Technique

2.2.1 General Principles

The Terahertz technique is the marriage of microwave and optical techniques. By

its very nature, terahertz radiation bridges the gap between the microwave and optical

regimes. Much of the research in the terahertz has been based on the melding of the ideas

in both areas.

Terahertz Time-Domain Spectroscopy (THz-TDS) is a new spectroscopic

technique. It is based on electromagnetic transients generated opto-electronically with the









help of femtosecond (1 fs=10 15 s) duration laser pulses. These terahertz transients are

single-cycle bursts of electromagnetic radiation of typically less than 1 ps [17] duration.

Their spectral density spans the range from below 100 GHz to more than 5 THz [18].

Optically gated detection allows a direct measurement of the terahertz electric field with

a time resolution of a fraction of a picosecond. From this measurement, both the real and

imaginary part of the dielectric function of a medium may be extracted. Furthermore, the

brightness of the terahertz transients exceeds that of conventional thermal source and the

gated detection is order of magnitude more sensitive than bolometric detection.

Figure 2-2 is a schematic diagram of a THZ-TDS spectrometer. It consists of a

femtosecond laser source (1). A beam splitter divides the laser beam into two. An

optically-gated THz transmitter (2), focusing and collimating optics (3), the sample (4),

an optically-gated THz detector (5), a variable delay line (6) that varies the optical delay

between the pulses gating the THz transmitter and detector, a current amplifier (7) and a

Lock-in amplifier (8). A computer (9) controls the variable delay line and displays the

detector photo current versus path length. In the following sections, we will describe each

of these components.

2.2.1.1 Laser

A solid-state laser, Ti-sapphire laser delivering pulses with a wavelength near 800

nm, is used in the instrument. The typical repetition rate of these lasers is about 100

MHz.

2.2.1.2 Terahertz transmitter and detector

Both the source and the detector consist of the same building blocks [19, 20] which

are based on a photo conductive (Auston) switch. It consists of a semiconductor bridging

the gap in an antenna line structure. The current through the switch rises very rapidly









after injection of photo carriers by the optical pulse, and then decays with a time constant

given by the carrier life time of semiconductor. The transient photocurrent J(t) radiates

into free space according to Maxwell's equation, E(t) oc aJ(t(t)f Because of the time


derivative, the radiated field is dominated by the rising edge of photocurrent transient,

which is invariably much faster than the delay. Long tails of the photocurrent decay are

largely irrelevant to the radiated field. While the structure of the receiver is close to the

structure of the detector, more efficient transmitter structures have since been devised

[21, 22, 23].

To convert the Auston switch for use as a detector of short electrical pulses, an

ammeter (or current-to-voltage amplifier) is connected across the photoconductor,

replacing the voltage bias. The electric field of an incident terahertz pulse now provides

the driving field for the photo-carriers. Current flows through the switch only when both

the terahertz field and photo-carrier are present. Since electronics is not fast enough to

measure the THz transients directly, repetitive photoconductive sampling is used. If the

photo-carrier life time r is much shorter than the terahertz pulse, the photoconductive

switch acts as a sampling gate which samples the terahertz field for a time r. Because the

laser pulses which trigger the transmitter and gate the detector originate from the same

source, the photoconductive gate can be moved across the terahertz wave form with an

optical delay line. Using this technique, the entire terahertz transient is mapped without

the need for fast electronics.

There are a number of ways in which this measurement can be performed. In the

most common, the optical beam exciting the transmitter is mechanically chopped and the

voltage from the current amplifier is synchronously detected using a lock-in amplifier.









The optical delay is slowly scanned and the photocurrent acquired into a computer.

Another technique is "rapid scan", in which the time-delay is scanned at a rate of tens to

hundreds of Hz using a shaker with an optical retro-reflector. To enhance the signal-to-

noise ratio, each scan is co-added using an averaging digital oscilloscope. Rapid-scan can

significantly reduce the noise due to 1/f laser power fluctuations. In many applications,

the photocurrent signal is so large (nA level), that the output from the current amplifier

can be directly digitized for further processing without using a lock-in amplifier [24].

2.2.2 Some Important Issues with THZ-TDS Technique

2.2.2.1 Frequency Limit of Terahertz Detector

The beam width of the detection process is determined by two factors, the

photocurrent response and the frequency dependence of the antenna structure. In general,

the low-frequency cut-off of the detectors results from the collection efficiency of the

dipole, while the upper frequency limit is determined by the photo carrier response. We

focus first on the photocurrent response which is the convolution of the transient

photoconductivity a(t) and the electric field E(t) across the photoconductor

J(t) = c(t- t')E(t')dt' (2-21)

where J(t) is the photocurrent transient. E(t) is faithfully reproduced by J(t) when the

photocurrent transient becomes much shorter than the THz waveform.

The photocurrent decay time in the Auston switch must be less than roughly 0.5 ps

in order to resolve transients in the THz regime. Recombination in a semiconductor with

low defect density tends to be far slower; therefore the carrier lifetime has to be reduced

below its intrinsic value. This reduction is commonly accomplished by introducing defect

states that have a fast carrier capture rate. An example of the first case is low-temperature









grown GaAs (LT-GaAs), which has been shown to have carrier lifetime as short as 280fs

when properly annealed. An example of the latter is radiation-damaged silicon-on-

sapphire (RD-SOS), in which dislocations are formed by implanting argon, silicon, or

oxygen ions [25, 26].

The electric field across the photoconductor can differ from the THz pulse in free

space due to the frequency-response of the antenna structure. Using the reciprocity

principle, the collection efficiency of the detector is identical to the radiation efficiency of

the transmitter. For a Hertzian dipole, where the antenna dimension is much less than the

wavelength, the radiation efficiency (and thus the collection efficiency) is proportional to

co (corresponding to the first derivative of the current). For "real" dipoles, the frequency

response will be more complicated [27].

2.2.2.2 Signal to Noise Ratio and Dynamic Range

The estimated average power of the THz beam is about 10nW. The peak power is

much higher, by a factor 104, because the energy appears in Ips bursts every 10ns. The

energy per burst is about 0. fJ, corresponding to roughly 50,000THz photons. The reason

for the large S/N ratios is the use of gated detection. The detector is off for most of the

time between pulses. Hence the average resistance of the switch is high and the Johnson

noise is negligible. In addition, gated detection discriminates effectively against thermal

background noise. In fact, van Exter [20] has shown that the thermal background noise

usually exceeds the average power of the THz radiation by a factor often, and that the

minimum detectable THz signal (amplitude) can be 160 times smaller than the incoherent

thermal background radiation.

Because THz-TDS measures electric field rather than intensity, the measurements

typically have a greater dynamic range than more conventional technique.









2.2.2.3 Phase sensitivity

In many applications, the most important advantage of THz-TDS is direct

measurement of the electric field E(t). Fourier transformation of E(t) yields both

amplitude and phase of both the propagation or transmission coefficient. Measurement of

both amplitude and phase in THz-TDS yields real and imaginary parts of the dielectric

function over the frequency range spanned by the THz pulse. This is a crucial difference

in comparison with conventional FT-IR spectroscopy.

2.2.2.4 Resolution and Time-Window of Data

In THz-TDS, the spectral resolution is the inverse of the optical delay time

provided by the moving mirror. Because the measurement is performed in the time-

domain, substrate reflection can be windowed out of the raw data without much loss in

spectral resolution and little influence on the accuracy of the data.

2.2.2.5 Time-Domain Data Analysis

Linear spectroscopy requires that the radiation interacts with the medium under

study by either reflection or transmission. As with most spectroscopic technique, THz-

TDS requires two measurements: one reference waveform Ereft) measured without the

sample or with a sample of known dielectric properties, and a second measurement

Esample(t), in which the radiation interacts with the sample. For spectral analysis, E(t) can

directly be Fourier-transformed to yield the complex amplitude spectrum E(co) in both

amplitude and phase. In my experiment, I measured thick pellet samples. Figure 2-3

shows a typical measurement. The curve shows the THz transient after propagation

through a 0.2mm thick BaTeO3 pellet. In addition to the main transmitted pulse, there is a

secondary, time-delayed pulse. This second transient is the first of the infinite series

which appears due to multiple reflections. The detail information about data analyzing









has been talked in chapter one. More detailed description of THz-TDS technique can also

be found elsewhere [27,28].

2.3 Grating Spectrometer

The grating spectrometer consists of several parts including the source, chopper,

high pass and low pass filters, grating for prism monochromator, sample or reference

stage, and detector. All parts are very important. But the core of the grating system is

monochromator.

In the grating monochromator, as shown in Figure 2-4, the reflecting grating

diffraction equation is satisfied

a(sin a + sin /) = nA (n = 0, 1, 2...) (2-22)

where a is the grating constant (cm/line), a and / are angle of the incident and diffracted

light respectively, and n is the order of diffraction. When equation (2-33) is satisfied, the

interference is constructive. One can then rewrite equation (2-33) as

nA = 2a cos 8 sin 0 (2-23)

where 6=(a-f/)/2 and 0=(a+,/)/2. In practice, 6 is fixed (26 = 4) regardless of the grating

position because the incident and diffracted light paths are predetermined by the physical

geometry, where 0 changes as the grating (or its surface normal) is rotated. It can be seen

from equation (2-34) that at 0 = 0, it will give a zero-order diffraction (white light) for all

frequencies. Therefore, 0 is the rotation angle of the grating surface normal, N(O), with

respect to the zero-order position, N(0).

The first order is the desired one and the high orders (n > 2) are removed by the

proper optical filters. Taking n = 1, one gets

v = 1/ =C csc(O) (2-24)









with C=1/2acos6 being a constant. Equation (2-35) indicates that the frequency is linearly

related to csc(O). As the grating is rotated, a single component at frequency v satisfying

equation (2-35) is selected and emerges through the exit slit into the sample chamber.

The monochromator is mechanically designed such that the grating, driven by a stepping

motor, is moved linearly with cscO, thus the scanning is linear in wavenumber. The

rotation angle has been designed in the range 15< < 600, the optimum quasi-linear

range in the cosecant function. To find the resolution of the monochromator, one simply

needs to take the derivative of equation (2-35) in its logarithm form

Inv = InC In sin 8, (2.25)
dv
= cot 8d0, (2.26)
v

where dO is the angle subtended by the slit (with a width s) at the collimator with a focal

length= 26.7 cm, i.e., dO = s/f Equation (2-37) implies that a larger 0 will give a better

resolution. Dispersion which is a measure of the separation between diffracted light of

different wavelength is given by the following equation. Angular dispersion, D, is

D df n sin a+ sin/
dA dcos A cos/

Linear dispersion is dependent of the effective focal length of the system, i.e., F D,

where F is the effective focal length of the system.

2.4 Instrumentation

2.4.1 Bruker 113v FT-IR Spectrometer

The Bruker 113V, as shown in figure 2-5, is a Fourier transform interferometer

with rapid scan (one of the working state of the scan mirror). With proper choice of

source, beam splitter and detector, it can cover the full spectral range from the very far

infrared (> 20 cm-) up to the mid-infrared. The friction-free air bearing scanner makes it









possible to achieve very stable rapid scan. Digital signal processing electronics provide

precise scanner control and instrument automation for source, aperture and detector

selections. The beam-splitter is changed automatically during measurement. Combing the

fast scan rate capability with superior precision spectroscopy, a high signal to noise ratio

(S/N) is possible even in the far infrared (20 cm-1). The instrument operates under

vacuum (<3 mbar) to record spectra free from absorption from H20 and CO2 vapor in the

far and mid infrared.

A He-Ne laser (633nm, normal 17 mw) is used to control the position of the

moving mirror (the scanner) and to control the data acquisition process. The

monochromatic beam produced by this He-Ne laser is modulated by the interferometer to

produce a sinusoidal signal. A photodiode detector is placed at outputs of the

interferometer. Signals from these detectors are monitored with an oscilloscope and the

amplitudes of signals are used to optimize the alignment of the beam-splitter. When the

beam splitter is not aligned properly, the amplitude can become too small to control the

scanner and then data acquisition will be interrupted. The sample chamber contains two

channels. One of the channels is designed for reflectance and the other for transmittance

measurements. For the reflectance sample chamber in figure 2-5, a mercury (Hg) arc

lamp is used as the source for far infrared (20-700 cm-1) and a globar source is used for

mid infrared (400 5000 cm-1 ).

The detector used for far infrared region is a liquid Helium (He) cooled 4.2K

silicon (Si) bolometer and that for mid infrared is a room temperature pyroelectric

deuterated triglycine sulfate (DTGS) detector. The liquid He cooled detector has much









better S/N ratio as compared with the DTGS. The bolometer system consists of three

main parts: detector, liquid He dewar with liquid nitrogen dewar jacket, and preamplifier.

In Table 2-1, we show measurement parameters for the Bruker 113V. In the table,

the scanner speed is in unit of kHz. This is the frequency at which light of He-Ne laser is

modulated

f(Hz)
v(cm/s) = (2-28)
Vlaser (cm )

where vlaser is the wavenumber of the He-Ne laser, which is 15,798 cm-1. For example,

f(Hz) = 25 kHz is converted into v(cm/s) = 25,000 Hz/15,798 (cm1) = 1.58 cm/s.

Table 2-1 Bolometer 113V measurement setup parameters: Bolom. Stands for the
bolometer detector; Bm.Spt is the beam splitter; Scn.Sp. stands for the scanner
speed; Sp.Rn stands for the spectral range; Phs.Crc.Md stands for the phase
correction mode; Opt. Filter stands for the optical filter; BLK.Ply. Stands for
black polyethylene; Apd. Fctn. Stands for the apodization function; Bk-Hrs 3
stands for the Balckman-Harris 3 term; and Hp-Gng stands for Happ-Gengel.


Setup FIR1 FIR2 FIR3 FIR4 MIR
Source Hg Lamp Hg Lamp Hg Lamp Hg Lamp Globar
Detector Bolom. Bolom. Bolom. Bolom. DTGS/KBr
Bm.Spt(um) Metal Mesh Mylar 3.5 Mylar 12 Mylar 23 Ge/KBr
Scn.Sp.(KHz) 29.73 25 29.73 29.73 12.5
Sp.Rn.(cm1) 0-72 9-146 9-584 10-695 21-7,899
Phs.Crc.Md Mertz Mertz Mertz Mertz Mertz
Opt.Filter Blk.Ply Blk.Ply Blk.Ply Blk.Ply Open
Apd.Fctn Bk-Hrs 3 Bk-Hrs 3 Bk-Hrs 3 Bk-Hrs 3 BK-Hr 3


2.4.2 TPI 1000 Terahertz Spectrometer

TPI spectra 1000 spectrometer is the transmittance spectrometer produced by

Bruker and Teraview companies. It covers from 1.3 cm-1 to 133.32 cm-1 (40GHz 4THz)

with spectral resolution about 0.1 cm-1. Laser-gated photo conductive semiconductor

emitter is used as the THz source. The spectrometer can be operated in both step scan and









rapid scan mode. The whole system can be used in both the nitrogen purged state and

vacuum state.

2.4.3 Perkin-Elmer Grating Spectrometer

Spectra spanning the midinfrared through the UV region (800-40,000 cm-1) were

measured using a Perkin-Elmer 16U grating spectrometer. A schematic diagram of the

instrument is shown in Figure 2-6. The spectrometer is enclosed in a vacuum tank, which

is evacuated to pressures of about 100 millitorr. This reduces the absorption by water

vapor and carbon dioxide.

The three light sources that are used are glowbar source for midinfrared, a quartz

tungsten lamp for near infrared and a deuterium arc lamp for visible and UV region. The

system contains three detectors: thermocouple for midinfrared (0.12 0.9 eV), lead

sulfide (PbS) detector for near infrared (0.5 2.5 eV), and Si photoconducting detector

(Hamamatsu 576) for visible and UV (2-2 ~ 5.5 eV). For getting less noisy data we use a

phase sentative amplifer. The light from the source passed through a chopper and a series

of filters: high frequency filters in a big wheel and low frequency filters installed inside

the grating monochromator. The chopper generates a square wave signal for lock-in

detection. The filter diminishes the unwanted higher order diffraction from the grating,

which occurs at the same angle as the desired first-order component.

The light beam passing through the entrance slit of the monochromator is collimated into

a grating in the littrow configuration where the different wavelengths are diffracted. The

angle of incidence is changed at predetermined intervals consistent with the necessary

spectral resolution by rotating the grating; it is driven by a lead screw that is turned by a

stepping motor. This allows access to different wavelength sequentially. The steps in

angle of rotation together with the exit slit width determine resolution of the









monochromator. Increasing the slit widths increases the intensity of the emerging

radiation [higher signal to noise (S/N) ratio] at cost of lower resolution. The electrical

signal from the detector is sent to a lock-in amplifier (Ithado model 393). The output

signal from the lock-in system is then averaged over a given time interval and converted

into digital data by an integrating digital voltmeter (Flike 8520A). The data are finally

transmitted through the IEEE-488 Bus and a general purpose interface box to a PDP 11-

23 computer and recorded on the hard disk for subsequent analysis. The table 2-2 shows

the Perkin-Elmer grating monochromator parameters.

Table 2-2 Perkin-Elmer grating monochromator parameters. GB stands for globar. W
stands for tungsten. D2 stands for deuterium arc lamp. TC stands for thermo
couple. Pbs stands for lead slifide. 576 standsfor Si photoconducting detector
(Hamamatsu 576).
Frequency Grating Slit width Source Detetor
(cm1) (line/mm) (micron)
801-965 101 2000 GB TC
905-1458 101 1200 GB TC
1403-1752 101 1200 GB TC
1644-2612 240 1200 GB TC
2467-4191 240 1200 GB TC
4015-5105 590 1200 GB TC
4793-7977 590 1200 W TC
3829-5105 590 225 W Pbs
4793-7822 590 75 W Pbs
7511-10234 590 75 W Pbs
9191-13545 1200 225 W Pbs
12904-20144 1200 225 W Pbs
17033-24924 2400 225 W 576
22066-28059 2400 700 D2 576
25706-37964 2400 700 D2 576
36386-45333 2400 700 D2 576


For reflectance, single beam spectra are obtained for both the sample and a

reference aluminum mirror placed at the same position. The mirror and sample mounted

on the same sample holder are rotated into the beam to allow each single beam spectrum









to be recorded. The reflectance spectrum is then calculated by taking the ratio of the

single beam spectrum of the sample to that of the mirror and correcting with the

reflectance of aluminum.

2.4.4 Low Temperature Apparatus

The cryogenic system consists of three major parts: Hansen High-Tran refrigerator

cryostatt), transfer line, and helium supply dewar [29]. The sample temperature can be

varied from 4 K to 450 K by a controlled operation of liquid helium transfer. Figure 2-7

illustrates the flow diagram of he experimental set-up. The sample holder is attached to

the cryo-tip end of the refrigerator. An optical spectroscopy vacuum shroud is used to

isolate the cold tip from the outside environment. Optical windows can be installed on the

vacuum shroud to allow the reflection and transmission measurements. The sample

temperature is sensed by a calibrated silicon diode thermometer (Si-410A) buried into the

cold finger. The accuracy of the diode is 1K. The sample can be warmed by adding

electrical heat to the tip heater and the temperature is controlled automatically and

monitored by a temperature controller (Hansen & Associates 8000). A thermal radiation

shield is attached to the second cold stage to project the sample and to absorb the 300K

black body radiation from the vacuum shroud; hence the heat load near the cold tip can

be reduced. All these steps are necessary in order to minimize the systematic error in

temperature recording. Before the helium flow is started, the cryostat is evacuated to a

pressure of 10-4 torr or less in the vacuum shroud. By pressuring the He dewar, the liquid

helium is transferred from the dewar through the transfer line to the cryostat. The flow

rate can be regulated by two flow meters with hoses and shut off values which control the

tip flow and shield gas flow.












Source


Beam-Splitter
i'


0
Detector

Figure 2-1 A simplified Michelson interferometer diagram. Light travels distance S from
source to the beam-splitter. Partially reflected travels to the fixed mirror (Mi)
and partially transmitted beam travels a variable distance toward the movable
mirror (M2). The beam is recombined at the beam splitter and half of the
beams returns to the source, and the other proceeds to a detector.


X/









Collimating
/ optics (3)


THz
Transmitter (2)


THz (5)


Figure 2-2 Schematic diagram of a THz-TDS spectrometer using a femtosecond laser
source and photoconductive THz transmitters and receivers. Partially reflected
laser light was used as the gate signal for the THz detector. Partially
transmitted light reaches THz transmitter to excite the THz pulse. Sample is
placed in the beam focus point.











20000



16000



12000


c0

0


4000



0-



-4000



-8000

28 29 30 31 32 33

Time delay (ps)




Figure 2-3 Curve shows the THz transient after propagation through a BaTeO3 pellet. The
main pulse is followed by a series of pulse of decreasing amplitude that
originate from multiple reflections within the pellet.











Rotable grating



incident ray


\, / diffracted ray


Figure 2-4 Diagram of grating spectrometer showing the incident and diffracted rays and
the operation of grating.








































I Source Chamber
a Near-, mid- or far- IR sources
b Automated Aperture


II Interferometer Chamber IV Detector Chamber
c Optical filter k Near-, mid-, or far-IR
d Automatic beamsplitter changer detectors
e Two-side movable mirror
f Control Interferometer
g Reference laser
h Remote control alignment mirror


Figure 2-5 Schematic diagram of Bruker 113 V FTIR spectrometer. The lower channel
has the specially designed reflectance optical stage for reflectance
measurement in the sample chamber.
















































~1 -
=
0
C

0
C


2
0


Figure 2-6 Schematic diagram of Perkin-Elmer monochromator spectrometer.








47













-4+"-- DEWAR PRESSURIZATION FLOW
-- PRODUCT FLOW
--- HEUUM EXHAUST
---.- SHROUD VACUUM


TRANSFER
LINE





ADJUSTMENT
KNOB -


HELIUM EXHAUST
PORT


RADIATION
SHIELD


SAMPLE
HOLDER


Figure 2-7 High-Tran system flow diagram.














CHAPTER 3
OPTICAL PROPERTIES OF SUOPERCONDUCTING YBCO FILM IN THE
OPTIMALLY DOPED AND OVERDOPED REGION

After the discovery in 1911 of superconductivity in mercury at 4 K by Kamerlingh

Onnes [30] the search for new superconducting materials led to a slow increase in the

highest known transition temperature Tc over the decades. Alloys and compound [31]

such as Nb3Ge held the record for the highest transition temperatures from 1954 to 1986.

After 13 more years, the path to radically higher transition temperatures was opened by

the discovery in 1986 of superconductivity at 35 K in "LBCO" (a mixed oxide of

lanthanum, barium, and copper) by Bednorz and Muller [32], for which they were

awarded the Nobel prize in 1987.

The discovery was surprising and exciting, not simply because of the large increase

in Tc, but also because it revealed that the oxides formed an unsuspected new class of

superconducting materials with great potential. Another big jump to T, 90 K followed

quickly with the discovery made of "123" class of materials, exemplified by YBa2Cu307Oa

("YBCO") [33]. In this structure, the Y yttriumm) can be replaced by many other rare

earth elements, e.g. Yb, Nd, Sm, Eu, Gd, Ho, Er, and Lu, with similarly high T, [34,35].

Shortly after, still high T, values were found in the "BSCO" [36] system (mixed oxides of

bismuth, strontium, calcium, and copper) and the "TBCO" [37] system (mixed oxides of

thallium, barium, calcium, and copper).

In this chapter, we are going to discuss the general background of the high T,

superconductor materials, such as the structure and the phase diagram. Then we will









describe the sample preparation, and finally focus on the optical properties of the

optimally doped and overdoped YBa2Cu307-5 films. The basic theory of

superconductivity can also be found elsewhere [38-41].

3.1 Introduction

3.1.1 Fermi Liquid (FL) and Marginal Fermi Liquid model

Conduction electrons obey Fermi-Dirac statistics. The corresponding F-D

distribution function (3-xl) can be written in term of the energy E as.


f(E)= e[(Eb1 (3-1)

where / is the chemical potential which corresponds to the Fermi temperature (Tf) by

equation,

= EF = kBTF (3-2)

TFis typically about 105 K. This means that the distribution functionj(E) is one for E
and zero for E>EF and assumes intermediate values only in a narrow energy range ksT

wide near EF.

The electron kinetic energy can be written as


EK = (k +k2 + k2) (3-3)
2m

In the reciprocal space, each Cartesian component of K can assume discrete values,

2mnx / Lx in x direction of length Lx, and likewise for y and z direction of length Ly and Lz,

respectively. For simplicity, we will assume L=Ly,=L =L. Hence the total number of

electrons Nis

S4,k& / 3
AN=2 3 (3-4)
(2r/L)3









The electron density n = N/V = NIL3 at Fermi energy is,

1 (2mEF .
n =I( 2mEF2 (3-5)
3T2 h2 )

and the density of states (DOS) D(E) per unit volume can be get

d 1 (2m2
D(E) = n(E) = 2 ) (3-6)
dE 2 h 2

Despite the success of Fermi liquid theory in describing the conventional metals,

high temperature superconductor materials cannot be totally described by the FL theory.

Varma et al. [42] proposed a phenomenological model for the oxide superconductors to

explain many of the anomalous behavior in cuprates. This idea was that the electron

interacts with a spectrum ofbosonic excitation that is flat over T
high energy scale that cut off the spectrum.

According to this theory, the real and imaginary part of the quasi-particle self-

energy goes as


S= 2A0)log T-i0) i22AT (3-7)



-Im E(0) < T (3-8)
z[o7TA) CD > T

m-(0)) 2
m*( 1 Re )l (3-9)


where I is the quasi-particle self energy, m* is the frequency dependent renormalized

mass and mb is the band mass which appears in the frequency cop=4rne2/mb.









3.1.2 Optical Measurement of High Temperature Superconductor

In all of the high Tc superconductor systems, copper oxide planes form a common

structural element, which is thought to dominate the superconducting properties.

Depending on the choice of stoichiometry, the crystallographic unit cell contains varying

number of CuO2 planes. In addition, the 123 compounds contain CuO "chains", which

are thought to serve largely as reservoir to control the electron density in the planes. The

exact Tc depends on these particulars but, roughly speaking, the highest T, achieved in the

YBCO [43], BSCCO [44], and TBCCO [45] systems are 93, 110, and 130 K,

respectively.

These very high transition temperatures are of obvious technical interest because

they opens the way to applications which require only liquid N2 cooling (77 K) rather

than liquid helium. They also pose intriguing fundamental questions: what is the

mechanism responsible for the high T,? Whatever the mechanism is the nature of the

superconducting state basically the same Cooper-paired state as in BCS [46], or is it

fundamentally different?

Spectroscopic studies of electrodynamics are emerging as the premier experimental

tools of high T, superconductivity. In combination, THz and infrared (IR)/optical

methods enable experimental access to the optical constants in the frequency range

critical for the understanding of physics underlying strongly correlated phenomena in

solids. Optical spectroscopy of metals or semiconductors has provided invaluable insights

into the electronic band structure and elementary excitations. The validity of theoretical

descriptions of electronic bands in solids as well as of electron dynamics is routinely

verified against optical data. Moreover, in situations where the theoretical guidance for

data interpretation is insufficient, quantitative information still can be extracted from the









spectroscopic measurements through model-independent analysis of optical constants

based on a variety of sum rules. This latter forte of the IR/optical approach is

indispensable for high Tc research, since properties of these novel superconductors signal

a breakdown of standard theories of metals. Therefore, knowledge of the optical

constants establishes an experimental foundation for the crucial tests of proposed models

and also motivates the development of novel theoretical constants. THz-IR/optical results

generated by many research teams worldwide facilitate inference of universal patterns in

the electromagnetic response of high Tc cuprates that are not specific to a particular

family of materials but instead, are along with genuine features of the interplane

conductivity.

The parent, undoped, compounds of high T, cuprates are Mott-Hubbard (MH)

insulators [40]. When a moderate density of charge carriers is introduced in a MH

system, all of its physical properties are radically modified. This leads to complex phase

diagrams that have been methodically studied in many materials using THz/IR optics.

This work [47] has uncovered common attributes of the cuprates and other classes of MH

insulators.

As of today, there is no generally accepted picture of the electromagnetic response

of the CuO2 planes in superconducting phase of the cuprates. Significant progress in the

understanding of the carrier dynamics, particularly in the overdoped region, has been

achieved.

The normal state of high T, cuprates is anomalous and is not compatible with the

standard treatment of excitations in term of Landau quasi-particles. This property

challenges the applicability of the Bardeen, Cooper and Schrieffer (BCS) [46] scheme









describing superconductivity in terms of paring instability of an ensemble of quasi-

particles. Spectroscopic experiments indicate that the origin of high Tc superconductivity

may be related to lowering of the electronic kinetic energy and not of the potential energy

as in the conventional BCS scheme. This conclusion is inferred from subjecting the

optical constants of several classes of high Tc materials to the scrutiny of sum rules.

Numerous advances in both the spectroscopy of micro-samples and in the

preparation of high quality single crystals have facilitated studies of the interlayer

electrodynamics in many families of cuprates. These measurements provide

straightforward experimental access to properties directly related to the quasi two-

dimensional nature of the electronic transport.

Many groups have presented measurements of ab-plane infrared spectra of

YBa2Cu307-O [48, 49, 50]. The first complete (in terms of wavelength and temperature

coverage) study of the a-b plane infrared properties of YBa2Cu307-O was reported by

Schutzmann et al. [51, 52]. Romero et al. [53] and later Gao et al. [54] measured both

transmittance and the reflectance of the ab-plane oriented YBa2Cu307-O films. Their data

showed that the quasi-particle relation rate 1/T had a fast decrease below T, and then

saturated well below Tc. Above Tc, 1/r exhibited a linear temperature dependence, in

accord with the linear DC resistivity in the normal state. The fast decrease of 1/T was

unique and intrinsic to the high T, cuprates; it did not occur in conventional BCS

superconductors, where the scattering from impurity or phonons. The low frequency

conductivity Io inferred from the far infrared transmittance and reflectance measurements

exhibited a peak just below Tc. The peak in Io was attributed to the rapid drop in 1/i

combined with a decreasing of normal fluid density. Kamaras et al. [55] studied the









frequency dependent conductivity of laser deposited YBa2Cu307_- thin films. Their

experiment showed an onset of the mid-infrared absorption at 140 cm- and structure in

400 500 cm-1 region. This low energy absorption occurred both above and below Tc,

making them unlikely to be the super conducting gap in the usual BCS sense. The

absorption across the gap was weak because the high Tc materials were in the clean limit;

this weak absorption is masked by the mid-infrared absorption.

Thomas et al. [48], Cooper et al. [56] and Orenstein et al. [57] have studied a series

of high-quality of YBa2Cu307_- crystals which have different vales of 6. The measured

reflectance drops steadily throughout the infrared, with a sort of plasmon minimum

around 10,000 cm-1. As oxygen is removed, reducing the carrier concentration on both

CuO2 plane and b-axis Cu-O chain, the reflectance in the midinfrared is substantially

reduced. At low frequencies, the reflectance is high, being above 90% for all four

samples, as expected for a conducting materials. The reduced T, samples show a break or

shoulder in the normal state reflectance at 500 cm-1. The reflectance of a "fully-

oxygenated" YBa2Cu307_- with Tc= 93 K has been reported by Collins et al. [50]. Their

data show a noticeable dip or minimum in the 45 K reflectance around 800 cm-1. They

interpret it as a result of the collapse below T, of the free carrier component E(co) to a

delta function.

To study the intrinsic properties of CuO2 plane, several investigations have been

done for the Br2Sr2CaCu20 (Bi-2212) crystals. Comparing with Y-123 material, Bi-2212

provides a better opportunity to study the issue of the electronic structure of the CuO2

planes because there are no chains in these Bi-based compounds. Quijada et al. [58] did

the polarized reflectance measurement. Their room temperature optical conductivity









suggested a scattering rate for the free carriers that showed ab anisotropy in both

magnitude and temperature dependence. In the superconductivity state, the penetration

depth XD was also found larger along b-axis than a-axis :( Db > XDa). Liu et al. [59]

studied the Pb doped Bi-2212 single crystals over a wide frequency range. His result

indicated the a-axis reflectance was higher than the b-axis reflectance in the far infrared

region. However, in the visible to ultraviolet region, the b-axis reflectance was higher.

After analyzing their data by Kramers-Kroning method, they found the anisotropy in the

normal state conductivity was about 10%, with the far infrared conductivity higher in the

a-polarization while higher frequency conductivity is higher along b-axis.

In the overdoped region, only a few measurements have been done in the c-axis.

Katz et al. [60] reported the infrared study of c-axis electrodynamics of T12Ba2CuO6+6

crystals. A sum rule analysis revealed spectral weight shifts. Their calculated the ratio of

the spectral weight difference (between normal state and superconductor state) to the

superfluid density. Their result showed the difference of these two values is about 40% in

the overdoped Tl2Ba2CuO6+6 and 10% in the optimally doped Tl2Ba2CuO6+6. They

interpreted the result as a kinetic energy change at the superconducting transition. In

optimally doped crystals, the kinetic energy was lowered at T< Tc, but no significant

change was found in the overdoped samples. Basov et al. [61] also expressed the similar

idea. Their analyses of the interlayer infrared conductivity of the cuprates in high

transition temperature superconductors resulted an anomalously large energy scale

extending up to mid infrared frequencies that could be attributed to formation of the

superconducting condense. They indicated one possible interpretation of these

experiments was in terms of a kinetic energy change associated with the superconducting









transition. Other groups, such as Deutscher et al., [62] investigated the c-axis of Bi-2212

system. The experiment showed the change of kinetic energy from a fully compatible

conventional BCS behavior to an unconventional behavior as the free carrier density

decreases. Unlike the result of Katz et al., they found the kinetic energy almost had no

changing in the optimally doped cuprate system and an increasing of kinetic energy in the

overdoped region. They also suggested if a single mechanism was responsible for super

conductivity across the whole phase diagram of high critical temperature

superconductors, this mechanism should allow for a smooth transition between such two

regimes around optimally doping. Hwang et al. [63] studied the overdoped Bi-2212

system. They found the evidence of increasing the spectral weight in the overdoped

region.

3.1.3 The Crystal Structure of YBCO

The YBa2Cu307- compound comes in tetragonal and orthorhombic varieties. It is

the latter phase which is ordinarily superconducting. In the tetragonal phase the oxygen

sites in the chain layer are in a random or disordered manner, and in the orthorhombic

phase are ordered into -Cu-O- chains along the b direction. The oxygen vacancy along a

direction causes the unit cell to compress slightly so that a < b, and the resulting

distortion is of the rectangular type.

Hauck et al. [64] proposed a classification of superconducting oxide structures in

term of the sequence (1) superconducting layers, (2) insulating layers, (3) hole donating

layers. The high-temperature superconductor compounds have a horizontal reflection

plane called oh at the center of the unit. Every plane of atoms in the lower half of the cell

at the height z is duplicated in the upper half at the height 1-z. Such atoms, of course,

appear twice in the unit cell, while atoms right on the symmetry planes only occur once









since they cannot be reflected. Figure 3-1 shows a Cu-O plane at the height z reflected to

the height 1-z. A particular interesting feature in the figure is that the puckering (Cu-O

plane) preserves the reflection symmetry operation. Superconductors that have this

reflection plane, but lack end-centering and body centering operations are called aligned

because all of their copper atoms are of one type; either all on the edge in E position or

all centered at C sites.

3.1.4 Phase Diagram

High Tc superconductivity is achieved when a moderate density of charge carrier is

introduced into the parent antiferromagnetic phases of the cuprates. This "doping" is

realized either by chemical substitution or significant deviations from stoichiometry.

The hole-doped sides of the phase diagram displayed in Figure 3-2 shows a number

of common elements. One finds: 1) antiferromagnetism of the undoped parent compound

is transformed by doping into a fairly good conducing system in the carrier density range

of n = 1020-1021; 2) a critical doping level that is needed to trigger superconductivity; 3) a

transition temperature that first increases with doping (the underdoped region) reaches a

maximum value for a given series (the optimally doping) but is suppressed with further

increase in doping level (the overdoped regime); 4) a superconducting state is preceded

by the formation of the enigmatic pseudogap with an onset temperature that decreases

with doping.

3.1.5 Pseudogap Phase

As shown in the phase diagram of Figure 3-1, the high temperature cuprates have a

pseudogap phase at the low doping level. One general class of theories proposed that the

pseudogap phase represents pre-formed pairs [65]. Transport measurements revealed hat

resistivity was dead linear in temperature over a large range. Lobo et al. [66] measured









the ab-plane resistivity of Yl-xPrxBa2Cu307. Their experiment indicated below 195 K,

the resistivity no longer showed a linear thermo dependence in the x=0.4 sample. The

result suggest that non-coherent cooper pairs are the origin of the pseudogap.

As we know, undoped cuprates should be thought of as Mott insulators. In the low

doping level, the number of carriers is small and the phase fluctuation could play an

important role in the underdoped side of the phase diagram. Anderson et al. [67]

proposed that the doped holes would only be phase coherent below a temperature which

scaled linearly with doping. The main debate of the origin of pseudogap is whether

pseudogap represents a state with true long range order or simply some precursor phase

[65].

3.1.6 d-wave Character of High Temperature Superconductor

A BCS superconductor has an isotropic superconducting gap which leads to an

exponential temperature dependence of the penetration-depth X(T). However, ab-plane

penetration depth measurements of high temperature superconductor do not find

exponential behavior. The linear variation of penetration depth with temperature was first

observed by Gao et al. [68]. In their experiment, the surface impedance of superconductor

YBa2Cu307 films as a function of temperature at 10 GHz was measured. The penetration

depth X (T) was also determined. Their result exhibited a linear dependence down to 6 K.

the following theory by Hirschfeld et al. [69] indicated that a penetration depth which

varies linearly with temperature is expected for superconductor with d-wave symmetry.

Other experiments, such as angle-resolved photoemission spectroscopy (ARPES),

have been done. Shen et al. [70] did an ARPES measurement in the ab-plane of

Bi2Sr2CaCu20s+5 samples and found that the superconducting gap anisotropy is at least









an order of magnitude larger than that of conventional superconductors. All these

experiments indicate a d-wave nature of the high temperature superconductors.

3.1.7 Two-Component Mode for the Dielectric Function

Common to all high Tc superconductors is the presence of a non-Drude mid-

infrared absorption that shows very little temperature dependence. In contrast, the far-

infrared reflectance exhibits a definite temperature dependence, with the far-infrared

conductivity above Tc in good agreement with the DC conductivity. There are several

ways to explain this difference between far-infrared and mid-infrared behavior. In our

experiment, both two component model and Marginal Fermi liquid model are used.

In this approach, the infrared conductivity results from the combination of two

types of carriers: free carriers which give rise to a Drude-like component at wc = 0, with a

strongly temperature dependent scatting rate, and bound carriers with a nearly

temperature independent broad midinfrared band. In this approach, the free carriers

condense into the superfluid below Tc, while the midinfrared carriers remain unaffected

by the superconducting transition. The total dielectric function is

E(o)) = ,D + R + (3-10)

A model dielectric function which is in accord with this picture is

2 N 2
E(W)=- pD 2 Y ^ (3-11)
)2 +io) j= j2 ) 2C --io)Y

where the first term describes Drude carriers with a plasma frequency wpD and a

relaxation rate 1/r. The second term describes the broad mid-infrared component and

interband components as a sum of oscillators where wo, opj, and y, are the center

frequency, strength, and width of thejth oscillator, respectively. Finally, e, represents the









high frequency limit of (co) which includes interband transition at frequencies higher

than measured frequency.

3.1.8 Marginal Fermi Liquid Model for the Dielectric Function

Another very commonly used method is the marginal Fermi liquid model due to

Varma et al. [42, 71]. The model assumes that the charge carriers interact with a fairly

flat spectrum of excitation over the interval T
The dielectric response for this model can be written as

0) 2

E- 4 2(/)j (3-12)

where I is the quasiparticle self energy, given by


I = 2A log

here Tis the temperature 2 is a coupling constant and wc is the cutoff frequency. The

limiting forms of this expression go as


g2-() T {) SrAco o) > T

Since the imaginary part of the self energy is effectively the scattering rate, Equation (3-

14) predicts the linear variation of the DC resistivity, which is observed in most transport

studies of the cuprates. In a similar way the real part of the self energy gives the mass

enhancement carrier


m*(o)=1 (3-15)


where m* is the frequency dependent renormalized mass and mb is the band mass which

appears in the plasma frequency c)=47rne2/mb.













3.1.9 Motivation of Experiments for Overdoped Cuprates

Despite extensive experiment effort, there is not many experiments done for the

overdoped high temperature superconductors. As yet, there is no report about the ab-

plane property in the overdoped region for YBCO superconductor. In order to get the

complete information of high temperature cuprates, experiments for the overdoped

samples are necessary. We explored the optical spectra of the optimally doped and

overdoped Y-123 thin film from the far infrared to the ultraviolet region. Our result

indicates although the carrier density increase with increasing the doping, the superfluid

density will decrease in the overdoped region.

3.2 Experiments and Results

3.2.1 Sample Preparation

Various high To superconducting samples have been used in this experiment. In this

chapter, we will only focus on the optimally doped YBCO/SrTiO3 thin films and the

over-doped YBCO/SrTiO3 thin films. Other samples, such as the YBCO/sapphire etc.,

will be introduced in the following chapters.

Two YBCO thin films are prepared at the Center for Electronic Correlation and

Magnetism, institute of physics, Augsburg University, Germany [72, 73]. Both of these

samples are deposited on the SrTiO3 substrate with dimension 5 mm x 5 mm. The

substrate has a perovskite structure which makes a good lattice match with the films. The

optical study of the substrate is needed in order to get the parameters of the YBCO thin

films. And this part of the work will be introduced in the next section.









The optimally doped YBa2Cu307-O thin film is deposited on the Imm thick SrTiO3

substrate by pulse-laser ablation from a stoichiometry YBa2Cu307-O target. After

deposition at z 760 C the sample is cooled within one hour to 400 C in an oxygen

atmosphere of 0.4 bar and, after holding this temperature for 20 minutes, further to room

temperature. The over-doped sample is prepared by the similar way described before. The

only difference is the target. Instead of YBa2Cu307-5, Yo.7Ca0.3Ba2Cu307-5 is used as the

target for sample deposition. The film thickness for both samples is 1500 A. In order to

measure the critical temperature, the resistivity measurement is done in the Center for

Electronic Correlations and Magnetism. The critical temperature (Tc) for the optimally

doped samples is 90 K; it is 79 K for the overdoped samples.

3.2.2 Optical Measurement of the Substrate SrTiO3

SrTiO3 was the subject of several studies in the early 60's. At T = 110K, it is

known to undergo a phase transition of second order. The cubic high-temperature

structure undergoes a tetragonal distortion at the transition characterized by an unstable

or soft phonon at the R corer of the Brillouin zone. The phonon mode has a frequency

that decreases substantially as the transition temperature is approached from above or

below. This structural phase transition corresponds to a rotation of BO6 octahedra around

the cubic axis.

SrTiO3 crystallizes in the simple cubic perovskite structure (Oh) at room

temperature and tetragonal (D4h18) at low temperature. Its lattice constant 3.91 A, nearly

matches the basal plane lattice constant ofYBa2Cu307-O Superconducting films grown on

SrTiO3 exhibit high current densities and sharp resistive transitions. Unfortunately, the

high frequency properties of SrTiO3 limit its use in technological applications. The static

dielectric constant is orders of magnitude higher than the typical values for dielectric









material. At microwave frequencies, the loss is extremely high and would result in a poor

performance for any microwave devices fabricated from a high temperature

superconductor film on SrTiO3.

Figure 3-3 shows the room temperature reflectance (normal incidence) and the

fitting result (by the Lorentz model) of SrTiO3 crystal in the spectral range between 25

cm-1 and 40000 cm-1. The temperature-dependent reflectance between 25 cm-1 and 4000

cm-1 is shown in Figure 3-4. With decreasing temperature, the reflectance of the SrTiO3

increase a little. Prominent phonon features occur at 90, 170 and 540 cm-1. Perry et al.

[74] assigned the lowest mode at 90 cm-1 to a Sr-TiO3 lattice mode, the mode at 170 cm-1

to a Ti-O-Ti bending mode, and the mode at 540 cm-1 to Ti-O stretch mode. Just above

the plasma edge, which is about 800 cm -1, the reflectance becomes flat without any

significant features. In the visible and ultra-violet region, two inter-band absorptions are

shown clearly in the reflectance spectrum. The details of these high frequency bands have

been studied by Cardona et al. [75].

3.2.3 Optical Measurement of the YBCO Thin Films

Figure 3-5 shows the room temperature ab-plane reflectance of the optimally doped

and overdoped YBCO thin films on SrTiO3 substrates over the spectra range (25 cm-1

40,000 cm-1). The reflectance of each samples drops steadily (but not quite linearly)

throughout the infrared, with a sort of plasma minimum around 15,000 cm-1 in all cases.

Both films show high values of reflectance (over 85%) at low frequencies, wc < 300 cm-1,

as expected for conducting materials. The optimally doped sample shows a higher

reflectance in the visible to ultraviolet frequency range than the overdoped sample. After

the plasma minimum (which is about 15,000 cm-1), the optimally doped sample shows a

clear charged transfer band (around 20,500 cm-1) and inter-band transition (around









33,600 cm-1). The overdoped sample spectrum does not show these features as strongly

as the Ca2+ replaces the Y3+ ions. The concentration of carrier, holes in YBCO, increases

in the Cu20-plane. However, as in other doping studies [48, 56], this increasing in the

carrier concentration has little effect on the frequency minimum. Both spectra show a

plasma minimum around 15,000 cm1.

Figure 3-6 shows the temperature dependent reflectance spectra for the optimally

doped YBCO film between 25 cm-1 and 4000 cm-1. At 30 K, only far infrared data was

measured from 25 cm-1 to 600 cm-1. In the low frequency region, there is a kink in the

reflectance spectra of each temperature, which is especially significant in the higher

temperatures. This effect is due to the soft mode in the SrTiO3 crystal substrate, which

was discussed above. The reflectance spectra show a systematic increase with decreasing

temperature. There is a noticeable dip around 800 cm-1 in the 50 K and 70 K reflectance,

which is similar to the data from other groups [48, 51, 56]. As discussed in the next

section, this structure can be qualitatively understood as a result of the collapse of the free

carrier component of E(co) to a delta function below T,. Below 100 K, the spectrum shows

a "shoulder" or "knee" around 500 cm-1. This phenomenon is also seen in other data [55].

Plausible arguments had been made for superconducting gaps in YBCO at 500 cm1.

However, Kramaras et al. [55] measured YBCO films. They fitted the reflectance by the

two component model. After subtracting the Drude component, the conductivity spectra

in all temperatures show a clearly decrease around 500 cm-1. Their conclusion indicates

that the "shoulder" at 500 cm-1 in the reflectance of YBCO samples is the sign of the

condensation of the Drude part contribution to the conductivity instead of the appearance

of the superconducting gap.









The temperature dependent reflectance of the overdoped YBCO sample is shown in

Figure 3-7. The spectra show similar features as the optimally doped samples. Around

800 cm-1, the dip or minimum which is shown obviously in the optimally doped samples,

is not significant comparing with the optimally doped samples. This probably indicates

that comparing with the optimally doped YBCO, the superfluid condensation in the

overdoped samples is not as strong as in the optimally doped samples.

3.3 Discussion

3.3.1 Dielectric Function Analysis

Because of the effect of the substrate, the Kramers-Kronig method cannot be used

directly to the measured reflection data. In order to analyze the ab-plane optical spectra

of the YBCO film, two component analyses is used. According to this picture, the

cuprates are viewed as consisting of two types of carriers: free carriers which track the

DC conductivity above To and bound carriers which are responsible for the broad mid-

infrared excitation (The detail information has been talked in chapter 1).

Below Tc, two fluid model was used. The dielectric function is made up to four

parts

E(o) = Esup + D + E R + E (3-16)

02 ~2o
Esup = -- + P (w)) (3-17)
02 2ao

where e,,p is the superfluid part contribution, eD is the free carrier or normal Drude

intraband contribution; eMIR is the bound-carrier contribution, and e. is the high frequency

contribution. After getting all the oscillator information, optical conductivity and other

parameters can be calculated.









Figure 3-8, shows the measured spectra and the fitting result for the optimally

doped and overdoped samples at room temperature between 25 cm-1 and 40,000 cm1.

Figure 3-9 and 3-10 show measured and fitting spectra at room temperature and 50 K for

optimally doped sample and overdoped sample respectively. Table 3-1 shows the high

frequency oscillator parameters of the SrTiO3, YBa2Cu307-O (optimally doped) and

Yo.7Ca0.3Ba2Cu307-6 (overdoped). Table 3-2, 3-3 and 3-4 show the far infrared and mid

infrared oscillator parameters of the SrTiO3, YBa2Cu307-O (optimally doped) and

Yo.7Cao.3Ba2Cu307-6 (overdoped) samples at different temperatures respectively.

Table 3-1 The charge transfer band fitting parameters* (obtained from Lorentz model) for
the SrTiO3, optimally doped YBa2Cu307-5 and overdoped Yo.7Cao.3Ba2Cu307-5


ST OP** OD"

Cw (cm- 9418 9750
wc(cm ) 11503 12205
1/rl(cm1) 9985 7746
co2(cm1) 18792 20568 19028
(2(cm1) 32990 20997 21959
1/r2(cm1) 2950 14211 17015
c,3(cm1) 45450 33353 33127
(03(cm1) 38313 38173 43046
1/rs(cm-1) 10976 18376 26522
e_ 2.9 2.2 2.8


* All the parameters are used to fit reflectance and then to
** ST means SrTiO3 substrate
** OP means optimally doped YBCO
** OD means overdoped YBCO


calculate conductivity.









Table 3-2 Parameters (obtained from Drude Lorentz model) giving the best fit to the
reflectance (between 25 cm-1 and 4000 cm-) of SrTiO3 at different
temperatures.


300 K 200 K 100 K 70 K 50K 30K
co] 1419 1501 1508 1510 1494 1506
(1 87 71 47 33 22 3
1/r1 15.3 12.5 10.5 10.4 10.4 8.6
Cp2 341 268 222 200 179 172
02 176 174 172 171 171 171
1/T2 5.7 2.5 1.7 1.5 1.4 1.3
Cp3 571 615 616 600 597 605
(3 544 546 547 546 547 547
1/T3 22.7 16.7 10.9 12.5 8.9 7.7
E 4.6 4.8 4.8 4.8 4.8 4.8

Table 3-3 Parameters (obtained from Drude Lorentz model) giving the best fit to the
reflectance (between 25 cm1 and 4000 cm')of YBa2Cu307-O (optimally
doped)


300 K 200 K 100 K 70 K 50K 30K
CoPs 7452 7957 10903
copD 10420 11453 11748 8933 8753 1756
1/TD 405 296 187 123 84 77
co1 3785 2042 3733 3587 3812 3747
O1 281 301 301 303 295 295
1/r1 835 868 663 660 730 239
COp2 11548 10878 11369 13810 14664
c02 720 726 712 787 865
1/r2 1813 1621 1684 1760 1718
Cop3 13645 14640 14414 13551 17036
co3 3412 3219 3461 3286 3075
1/h3 9310 9083 9288 6241 7594
Em 4.1 3.3 4.0 3.2 3.0









Table 3-4 Parameters (obtained from Drude Lorentz model) giving the best fit to the
reflectance (between 25 cm-1 and 4000 cm1)of Yo.7Cao.3Ba2Cu307-
(overdoped) at different temperatures.


OD 300 K 200 K 100 K 70 K 50 K 30 K
cws 1215 3581 4854
wpD 12580 13206 12705 13060 12039 11682
1/TD 436 282 126 120 95 93
cp1 5157 5957 7311 6794 6444 8842
(o1 302 310 308 272 273 273
1/r1 878 652 844 771 767 1223
wo) 12427 10287 15919 14042 15439
(o0 748 760 806 778 781
1/r2 2177 2323 2770 2366 2343
co 13674 14058 17430 19444 11418
cs3 3284 3303 3281 3285 3258
1/r3 9052 8717 9302 10898 11064
geo 3.4 3.5 3.3 3.1 2.8


3.3.2 Charge Transfer Band and Interband Transition

The room temperature optical conductivities of both optimally and overdoped

YBCO films are shown in Figure 3-11. At higher frequencies, we observed the onset of

the charge transfer absorption at about 20,000 cm-1, which corresponds to the optical

transitions between the occupied O-2p band and the empty Cu-3d upper Hubbard band.

Other interband transitions also appear around 35,000 cm-1. In the overdoped samples, as

suggested by the data in Figure 3-11, there is a spectral weight lost in the infrared region.

The number of carrier participating in optical transition per Cu is plotted in Figure 3-12.

The weight lost below the charge transfer absorption band is roughly equal to the increase

of the spectral weight at the lower frequencies. The spectral weight is proportional to the

square of the plasma frequency. We can calculate the difference of the square of the

plasma frequency to know the spectral weight changing. According to table 3-1 and table

3-2, the spectral weight lost is about (7x107 cm-2). While in the mid infrared spectral









weight increase in the overdoped sample is about (8x107 cm-2). The ratio of the decrease

of spectral weight in the charge transfer band to the increase of spectral weight in the

midinfrared absorption band is about 0.9. This is not an unreasonable value; these two

values are close to each other. The difference of the two values may be due to the

contribution of higher frequency band which is beyond our measured high frequency

range.

3.3.3 Temperature Dependent Optical Conductivity

The real part of the conductivity oi(co) is shown in Figure 3-13 (a) and (b). The ab-

plane optical conductivity spectra of the optimally doped and overdoped samples have a

lot of common features. There is a peak around co0 and a long tail extending to higher

frequencies in the infrared region where ci(co) falls as ow slower than w-2 decay of a

Drude spectrum. In the far infrared region, both optimally doped and overdoped sample

spectra are very sensitive with the temperature. For the optimally doped sample, above

Tc, the conductivity increase with decreasing the temperature. While, just below Tc, the

conductivity drops significantly comparing with the value above Tc. This is due to part of

the spectra weight transfer to the 6 function. There is an obviously minimum at 430 cm1.

Some papers indicate this is probably the sign of the superconductor gap. Kamaras et al.

[55] measured a series of YBCO films. After analyzing the reflectivities by two

component model, their data indicate the minimum appeared in the optical conductivity is

the result of the superfluid condensation instead of the "gap" effect.

In comparison with the conductivity of optimally doped sample, the conductivity of

the overdoped sample does not show the minimum. Just like the optimally doped

samples, above Tc, in the far-infrared region the conductivity increases with decreasing

the temperature. But just below Tc, instead of a big "drop" as in the optimally doped









sample, the conductivity just decrease a little. This is because the overdoped sample

shows only a small fraction of the Drude component oscillator strength condensed into

the 6(co) super fluid condensate. The Drude and superfluid fitting parameters are shown

in table 3-1, are agreed with this point. At 50 K, in optimally doped sample, about 45%

Drude oscillator strength transfer to the 6 function. But in the overdoped sample, only 8%

of the oscillator strength transfers to the superfluid part (6 function). Same result can be

gotten in the 30 K. In the optimally doped sample, about 97% of Drude part oscillator

strength goes into 6 function. While, in overdoped sample, this value is only 21%. It

should be noted below Tc, there remains a pronounced conductivity at low frequencies

suggesting no sign of a superconducting gap.

Comparing with far infrared, the conductivity in the mid-infrared region does not

show much temperature dependence. As shown in figure 3-13, the temperature

dependence at frequencies above 1000 cm-1 is relatively modest. It is in fact mostly due

to a narrowing of the Drude like peak at zero frequency. We used three Lorentzian

oscillators to model the mid-infrared contribution to the dielectric function. As being

expected, in the mid-infrared, the conductivity decreases steadily as it reaches the plasma

minimum [48].

Finally, weak phonon modes, which are completely screened by the free carriers,

cannot be seen in the ab-plane conductivity spectra.

3.3.4 Quasi-Particle Scattering Rate

Figure 3-14 (a) and (b) show the temperature dependent scattering rate of the

optimally and overdoped samples. When T> Tc, I/TD varies linearly with temperature for

all the doping level studied. Such a temperature linear behavior in I/TD above T, has also

been observed in other cuprates. We write h/D = 27 XDkBT + h/To where XD is the









dimensionless coupling constant that couples the charge carriers to the temperature-

dependent excitations responsible for the scattering. Table 3-5 shows the width of the

Drude part oscillator (I/TD). Both samples show a normal state I/TD linear with T, with all

about the same slope, giving XD- 0.2 0.3. In our measurement, the optimally doped

YBCO has XD = 0.25 while in the overdoped YBCO sample this value is 0.31. Taking vF

= 2x107 cm/sec and using our relaxation rate of /T = 183 cm-1 (optimally doped YBCO),

160 cm-1 (overdoped sample at 100 K). We can estimate the mean free path 1 = vFT = 58

A and 66 A. Because the ab-plane coherence length is less than 20 A, the values of the

mean free path also prove that the high Tc superconductor is in the clean limit.

Table 3-5 The scattering rate (obtained from Drude Lorentz model) of optimally doped
and overdoped YBCO films in different temperature.


OP* OD*
Temperature I/TD I/TD
(K) (cm-) (cm-1
300 405 436
200 296 282
100 187 126
70 123 120
50 84 95
30 77 93


* OP means optimally doped YBCO
* OD means overdoped YBCO


Below Tc, in the optimally doped sample, the scattering rate 1/T exhibits a sudden

drop with saturation at T < 50 K. This result suggests a strong suppression of the

scattering channel at the superconducting transition. Presumably, the carrier-scattering

process that is responsible for the temperature linear resistivity in the normal state is

suppressed when the free carrier condense. Other experiments that found a similar fast









drop in 1/T include infrared measurements of Br2Sr2CaCu207-5 [77, 78] and time resolved

transition-absorption measurements of YBa2Cu307-O [79]. This striking feature seems to

be a unique property of the copper-oxide superconductors because ordinary phonon or

impunity scattering, which dominate conventional superconductors, does not change

dramatically at T,. It is evidence that the quasi-particles interact with some spectra of

excitation which is affected by the onset of the superconductor. While scattering rate of

the overdoped sample also shows drop below Tc, but comparing with the optimally doped

sample, the drop is not that dramatic.

3.3.5 Frequency-dependent Scattering Rate (MFL)

Another approach, based on the marginal Fermi Liquid (MFL) theory [42, 71], can

be used. The dielectric function can be written as

2
E(c) = E, (3-18)
o[o 21(o /2)]

where co) is the plasma frequency, I is the quasi particle self energy of the charge carrier;

and the imaginary part of the I is given by


Im ()) T (3-19)


The room temperature spectra of both optimally doped and overdoped samples

were fitted MFL theory. The plasma frequencies cp is 24,900 cm-1 and 28,100 cm-1 for

optimally doped and overdoped sample respectively. The imaginary part of the

quasiparticle self energy is shown in Figure 3-15. Clearly, there is a region of negative

slope belowl00 cm-1 in both films. This behavior suggests that at low frequency the

carrier mobility is strongly suppressed at low frequency. A negative slope has been

theoretically predicted for disordered two dimensional conductors [76]. Above 100 cm-1,









the linear behavior of the scattering rate exists. According to the MFL prescription, we

calculate the slope of -Im X(w) above 100 cm-1 at 300 K, which yields a coupling

constant X 0.5. Later we will discuss that the coupling constant obtained from the Drude

contribution is about 0.3, which is smaller than the value of MFL theory. This may

indicate that besides the free carrier band other absorption may also contribute to the

absorption.

3.3.6 Superfluid Density

A superconductor has a low frequency ci(co) that is a 6 function at co = 0; in turn

this 6 function gives a contribution to el(co) = e ops2/2. Table 3-6 shows the Drude

part of plasma frequency and the superfluid part plasma frequency for all the samples

below Tc.

Table 3-6 The Drude part and superfluid part plasma frequency below To in the optimally
doped and overdoped samples.


50K
OP COpD (cm-) Cps (cm-1
8753 7957 0.45
OD* Op (cm-1) Ops (cm)
12039 3581 0.08


* OP means optimally doped YBCO
* OD means overdoped YBCO


The superfluid fraction, increases with decreasing the temperature. It is interesting

to note at the same temperature the overdoped sample shows higher total plasma

frequency which indicates the overdoped sample has more charge carrier than the

optimally doped sample. This is agreed with Hwang et al.'s [63] BSCO-2212

measurement result. However, the overdoped sample shows lower superfluid plasma









frequency and lower super fluid fraction (f), which directly related to the superfluid

density. The BCS theory predicates a lower To with lower superfluid density. And the

overdoped sample does show lower To (79 K) comparing with the value of the optimally

doped sample (90 K). The atSR measurement of overdoped Tl2Ba2CuO6 (T12201) [80]

system also found both Tc and n decrease with increasing doping level. Farber et al. [81]

measured the penetration depth of the optimally doped YBa2Cu307-O and overdoped

Yo.9Cao.1Ba2Cu307-6 samples. Comparing with the optimally doped sample, overdoped

sample does show longer penetration depth. Fukuzumi et al. [82] measured in plane

resistivity of the Zn dope single crystals of YBa2Cu307-O and La2-xSrxCuO4 with various

hole densities. They indicated a radical change of the electronic state for in highly doped

regime. And they also suggested that these might be due to some inherent inhomogeneity

such as phase separation.

Using the partial sum rule, the effective carrier density (pef) can be gotten from the

effective carrier (Neff) by the following equations

m 2mV j o-, (w')dw' (3-20)
m


Pf (o) Nf ()(m /m ) (3-21)

where m is the mass of the electron and m* is the mass of the coopers.

p 2m) V, J 1 oC(01)')O)l (3-22)
0

At the low temperatures, if we assume that the superfluid dominates the low

frequency part of the imaginary part of the conductivity, the superfluid density is

proportional to co'a2(c). Then in the low wavenumber we have









mV
p, = () n,2COU ()) (3-23)
e

In the ideal situation (London condition), at low temperature, both ps(w) and ps (c)

will be a constant in the low frequency region. By comparing ps(w) and ps (c), the kinetic

energy changing discussed by Katz et al.'s [60] paper can be explored.

Figure 3-16 shows both p, and p, in optimally doped and overdoped samples

respectively. For the optimally doped sample, both p, and ps show the value close to each

other. This result is agreed with Deutscher et al.'s [62] result and other previous work.

However for the overdoped sample, the ps, which is calculated from the sum rule, is

significantly smaller than the optimally doped sample. There is no "flat part" in the

spectrum ofps. This make it is impossible to compare with the spectrum ofps. Thus, we

cannot tell if there is any kinetic energy change for the sample above and below T,. The

absence of the "flat part" can be easily explained in the spectrum of the imaginary part of

conductivity (a2). Figure 3-17 shows the imaginary part of the conductivity for both

optimally doped and overdoped sample. At 50 K, the imaginary part of conductivity (a2)

shows a relation linear in 1/o. But in the overdoped sample, this relation is not

significant. As indicated in table 3-4, at 50 K, the superfluid fraction is about 41% in the

optimally doped sample but only 8% in the overdoped sample. At lower temperature, the

superfluid will dominate the system in the optimally doped sample. While in the

overdoped sample, Drude part may still be important in the conductivity. Equation (3-23)

is not valid for the overdoped system. This may explain why there are so much paradox

conclusions in the previous work. Due to the substrate effect, our data cannot be analyzed

model independent. Further single crystal experiments and model independent analyzing

in different doping levels are needed to confirm the result.









3.4 Summary

In this chapter, we present the temperature and frequency-dependent optical

functions of Ca doped YBa2Cu307- from the far infrared through the ultraviolet region.

The data are analyzed by the two component model and marginal Fermi liquid model.

With an increasing of the carrier concentration in the CuO2 planes, spectral weight lost in

the high frequency charge transfer band is observed. The weight lost below the charge

transfer absorption band is transferred to lower frequencies. With increased the doping

level into the overdoped region, the plasma frequency increases correspondingly because

of the charge density increase. However, the superfluid density decreases in this regime

and the Drude part still dominant the low frequency part of the optical conductivity. This

property makes it difficult to calculate the changing of the kinetic energy in the

overdoped YBCO system above and below Tc.

The quasi-particle scattering rate is derived from the two component model. Above

Tc, the scattering rate is linear with the temperature. Below Tc, the scattering rate drops

and becomes saturate at the lower temperature. More measurements with different doping

level samples are needed in order to get completed picture in this area.










tpuo i -]


[ Ba]


[.-.VI


i


[IoBa] I
[Cuo- ]i


Figure 3-1 The unit cell of YBa2Cu307-6 (Ca substitute for Y in the overdoped sample)
[83].









350



300



250



200


I-
150



100



50



0
0.00


0.05 0.10 0.15 0.20 0.25


0.30


Figure 3-2 Schematic phase diagram of the hole-doped cuprates (x is the doping level).










1.0 1 1 1 1 1.. I





0.8 SrTiO3





S0.6
4--


(D
0.4





0.2 -
Experiment
Fitting



0.0 *
25 100 1000 10000 40000
Frequency (cm-)


Figure 3-3 Room temperature reflectance of SrTiO3 and the fitting spectrum.


















0.8 I '





0.6
CU
6-
0

4-) 300 K
S0.4 -200 K

100 K
.--.-70 K
0. 50 K

0.2 -------- 30 k





0.0 .. I .. .. .
25 100 1 1000
Frequency (cm )


Figure 3-4 Temperature dependent reflectance spectra of SrTiO3 substrate.


4000









1.0





0.8





0 0.6
C6
C.



0.4





0.2





0.0 -
25


10000 20000 30000
Frequency (cm
Frquency (cm )


40000


Figure 3-5 Room temperature reflectance spectra of the optimally doped and the
overdoped samples.








'1. .,-,-., ', ,
i 4V.




0.9 I ,.



C)
21-2
0.8 -optially doped YBCO
n,

300 K
---- 200 K
0.7 100 K
70 K
-------- 50 K

1 30 K

0 .6 '
25 100 1 1000 4000
Frequency (cm )




Figure 3-6 Temperature dependent reflectance spectra of the optimally doped
YBa2Cu307-5 film.









1.0





0.9



c-)
U Overdoped YBCO
"5
S0.8 -



300 K
--200 K
0.7 100 K
--70 K
--50 K
------- 30 K



25 100 1000 4000
Frequency (cm )





Figure 3-7 Temperature dependent reflectance spectra of the overdoped
Yo.7Ca0.3Ba2Cu307-s film.









1.0


0.8 I- Experiment data
-- -Fitting data

0.6 -


0.4 Optimally doped YBa2CuO 3


0.2


1.0 -


0.8 -

0.6
Overdoped Y07 ,Ca03Ba2 307-
0.4

0.2 -

0.0-

0 10000 20000 30000 40000
Frequency (cm')





Figure 3-8 The measured and fitted room temperature reflectance of both optimally
doped and overdoped films.









1.0


0.9


0.8


0.7

Co

CD-


0.9


0.8


0.7



0.6 -
25


1000 2000
Frequency (cm')


3000


4000


Figure 3-9 Measured and fitted reflectance of optimally doped YBa2Cu307-O at room
temperature and 50 K.









1.0




0.9




0.8




S0.7




0.9




0.8


500 1000 1500 2000

Frequency


2500 3000 3500 4000
(cm-1)


Figure 3-10 Measured and fitted reflectance of overdoped Yo.7Cao.3Ba2Cu307- at room
temperature and 50 K.