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Full-Text Articles in Physics

Interface Motion In Random Media At Finite Temperature, Lee-Wen Chen, M. Cristina Marchetti Aug 1994

Interface Motion In Random Media At Finite Temperature, Lee-Wen Chen, M. Cristina Marchetti

Physics

We have studied numerically the dynamics of a driven elastic interface in a random medium, focusing on the thermal rounding of the depinning transition and on the behavior in the

T = 0 pinned phase. Thermal effects are quantitatively more important than expected from simple dimensional estimates. For sufficient low temperature the creep velocity at a driving force equal to the T = 0 depinning force exhibits a power-law dependence on T, in agreement with earlier theoretical and numerical predictions for CDW’s. We have also examined the dynamics in the T = 0 pinned phase resulting from slowly increasing the driving force ...


Low-Temperatures Vortex Dynamics In Twinned Superconductors, M. Cristina Marchetti, Valerii M. Vinokur May 1994

Low-Temperatures Vortex Dynamics In Twinned Superconductors, M. Cristina Marchetti, Valerii M. Vinokur

Physics

We discuss the low-temperature dynamics of magnetic flux lines in samples with a family of parallel twin planes. A current applied along the twin planes drives flux motion in the direction transverse to the planes and acts like an electric field applied to {\it one-dimensional} carriers in disordered semiconductors. As in flux arrays with columnar pins, there is a regime where the dynamics is dominated by superkink excitations that correspond to Mott variable range hopping (VRH) of carriers. In one dimension, however, rare events, such as large regions void of twin planes, can impede VRH and dominate transport in samples ...


Ac Response Of The Flux-Line Liquid In High-Tc Superconductors, Lee-Wen Chen, M. Cristina Marchetti May 1994

Ac Response Of The Flux-Line Liquid In High-Tc Superconductors, Lee-Wen Chen, M. Cristina Marchetti

Physics

We use a hydrodynamics theory to discuss the response of a viscous flux-line liquid to an ac perturbation applied at the surface of the sample. The theory incorporates viscoelastic effects and describes the crossover between liquid-like and solid-like response of the vortex array as the frequency of the perturbation increases. A large viscosity from flux-line interactions and entanglement leads to viscous screening of surface fields. As a result, two frequency-dependent length scales are needed to describe the penetration of an ac field. For large viscosities the imaginary part of the ac permeability can exihibit, in addition to the well-know peak ...


Connection Between Nmr And Electrical Conductivity In Glassy Chalcogenide Fast Ionic Conductors , Kyung-Han Kim Jan 1994

Connection Between Nmr And Electrical Conductivity In Glassy Chalcogenide Fast Ionic Conductors , Kyung-Han Kim

Retrospective Theses and Dissertations

Pulsed Nuclear Magnetic Resonance measurements and electric conductivity measurements have been performed in glassy fast ionic conductors, lithium thiogermanates ( xLi2S+(1-x)GeS2) and lithium thioborates ( xLi2S+(1-x)B2S3) in order to investigate the microscopic mechanism of ion dynamics. Both 7Li nuclear spin lattice relaxation rate (NSLR) versus temperature at several resonance frequencies (4 MHz to 135 MHz) and conductivity, [sigma]([omega]) versus temperature, in the frequency range from 1 Hz to 4 MHz have been measured. The 7Li NSLR show BPP-type behavior with strong asymmetry of the bell shaped curve on the two sides of the maximum. A sizable dependence ...


Optical And Magnetic Resonance Studies Of Novel Pristine And Photo-Oxidized Conjugated Polymers , Andrew Vernon Smith Jan 1994

Optical And Magnetic Resonance Studies Of Novel Pristine And Photo-Oxidized Conjugated Polymers , Andrew Vernon Smith

Retrospective Theses and Dissertations

Optical and magnetic resonance properties of several [pi]-conjugated polymers were studied and the results consolidated in this thesis. Photoluminescence (PL), electron spin resonance (ESR), and the novel Ultraviolet Optically Detected Magnetic Resonance (UV-ODMR) results on poly(p-phenyleneethynyleneaniline) (PPEA) derivatives are shown. The source wavelength, [lambda][subscript]ex, dependence of the ODMR is investigated on several [pi]-conjugated polymers including poly(p-phenylenevinylene) (PPV), poly(p-phenyleneacetylene) (PPA), and poly(3-alkylthiophene) (P3AT) derivative films. The effects of photo-oxidation on the UV- and laser-excited ODMR of dioctoxy substituted PPV (DOOPPV) films is shown. The ODMR results on unsubstituted PPV and CN-PPV films are ...


Fabrication And Characterization Of Hydrogenated Amorphous Silicon Films, Cvd Diamond Films, And Their Devices , Hao Jia Jan 1994

Fabrication And Characterization Of Hydrogenated Amorphous Silicon Films, Cvd Diamond Films, And Their Devices , Hao Jia

Retrospective Theses and Dissertations

Hydrogenated amorphous silicon (a-Si:H) films have been prepared by radio frequency (rf) sputtering technique, and studied by infrared (IR) absorption, small angle x-ray scattering (SAXS), electron spin resonance (ESR), and secondary ion mass spectrometry (SIMS). The optoelectronic properties of a-Si:H films were improved dramatically by annealing at 250-330°C; strong correlation between hydrogen content and SAXS determined microvoid was found in a-Si:H film; and contradictory evidences to the widely invoked "multiple trapping" model for hydrogen diffusion in a-Si:H were also found for the first time and discussed in this work;As the second part of this ...


Theory Of Magneto-Optics And Circular Magnetic X-Ray Dichroism , Xindong Wang Jan 1994

Theory Of Magneto-Optics And Circular Magnetic X-Ray Dichroism , Xindong Wang

Retrospective Theses and Dissertations

This thesis contains three parts. In the first part, before getting into the discussion of magneto-optical properties for the systems under study, the author reviews some background subjects, such as the energy-band theory within the framework of density functional theory, the multiple scattering approach to the solution of band problem and its relation with the LMTO method, an account of the tight-binding LMTO method which we use exclusively in our calculations, the linear response theory and its application to the quantum theory of dielectric constants. In the second part, circular magnetic x-ray dichroism, as a powerful and newly developed experimental ...


Classical Wave Propagation In Periodic And Random Media , Sreela Datta Jan 1994

Classical Wave Propagation In Periodic And Random Media , Sreela Datta

Retrospective Theses and Dissertations

This thesis presents the results of numerical studies of scalar and electromagnetic wave propagation in periodic and random dielectric media. The photonic energy band structure of periodic composite materials, consisting of regular spherical arrays or scaffoldings of one kind of dielectric material in a different background material, are studied using the plane wave expansion method in order to determine, among other things, the optimum conditions (crystal structure, dielectric constant ratio, filling ratio etc.) for the existence of photonic band gaps. The significance of these numerical studies lies in the potential for important applications of photonic band gap materials and also ...


Photoemission Study Of Some Novel Materials: Rare Earth/Transition Metal Interface, Ba06k04bio3 And Alpdmn , Xilin Wu Jan 1994

Photoemission Study Of Some Novel Materials: Rare Earth/Transition Metal Interface, Ba06k04bio3 And Alpdmn , Xilin Wu

Retrospective Theses and Dissertations

Synchrotron radiation photoemission spectroscopy and low energy electron diffraction (LEED) are applied to explore several novel materials: (a) Ce epitaxial growth on W (110) surfaces; (b) Eu epitaxial growth on Ta (110) surfaces; (c) Sm epitaxial growth on Ta (110) surfaces; (d) quasicrystalline AlPdMn; (e) superconducting Ba[subscript]1-xK[subscript] xBiO[subscript]3. In the case of rare earth overlayers on transition metal surface, resonance photoemission spectroscopy is used to enhance the 4f features. The metal surface phase transition is investigated on an atomic-scale. In the case of quasicrystalline AlPdMn and superconducting Ba[subscript]1-xK[subscript] xBiO[subscript]3 the ...


Magnetization Studies Of Oxides Related To The High Temperature Cuprate Superconductors , Zhaorong Wang Jan 1994

Magnetization Studies Of Oxides Related To The High Temperature Cuprate Superconductors , Zhaorong Wang

Retrospective Theses and Dissertations

An Oxford Instruments Faraday magnetometer, capable of operating in the temperature range between 1.5 K and 1000 K, and magnetic field range between 0 T to 8 T, with a sensitivity of 3x10[superscript]-8 cm[superscript]3G, was assembled and calibrated. The pumping station which supported this magnetometer was designed and built. Software for reducing the raw data and generating calibration files was written. The magnetic properties of several oxides related to the high temperature cuprate superconductors BaCuO[subscript]2+x, La[subscript]2CuO[subscript]4, Sr[subscript]2IrO[subscript]4, Sr[subscript]2RhO[subscript]4, Sr[subscript ...


Optical Anisotropy Of (110) Surfaces Of Ag And Cu , Zai Chen Jan 1994

Optical Anisotropy Of (110) Surfaces Of Ag And Cu , Zai Chen

Retrospective Theses and Dissertations

A reflectance-difference spectroscopy (RD) system was designed and built. Automatically controlled by a computer (PC), the system was used to study the anisotropic optical response of the (110) surfaces of Ag and Cu. Four Ag(110) surfaces were prepared, one epitaxially-grown single-crystalline thin film surface and three chemically etched single crystal surfaces. The RD spectra show all surfaces have very similar anisotropic peaks around 3.8 eV and 3.9 eV. This anisotropy is produced by the surface layer of atoms and is sensitive to the details of the electronic band structure. The peak structures can be attributed to transitions ...


Magnetic Resonance Spectroscopy Of Fullerenes And [Pi]-Conjugated Polymers , Paul Andrew Lane Jan 1994

Magnetic Resonance Spectroscopy Of Fullerenes And [Pi]-Conjugated Polymers , Paul Andrew Lane

Retrospective Theses and Dissertations

The photophysics of two novel [pi]-conjugated systems, buckminsterfullerene and [pi]-conjugated polymers, are studied by the technique of Photoluminescence-Detected Magnetic Resonance (PLDMR);The PLDMR of C60 and C70 dissolved in toluene/polystyrene glasses and of fullerene films is described. The PLDMR of the glasses is due to a triplet exciton delocalized over the entire molecule. That of 3C70 strikingly differs from 3C60 in both lineshape and dynamics, due to the much longer triplet lifetime of 3C70. The PLDMR of films indicates that the delocalized triplet is distorted by intermolecular interactions and reveals a half-field resonance due to triplet-triplet fusion ...


Sub-Micron Scale Conduction Processes On Clean Surfaces , Kevin R. Kimberlin Jan 1994

Sub-Micron Scale Conduction Processes On Clean Surfaces , Kevin R. Kimberlin

Retrospective Theses and Dissertations

Fundamental electrical conductance measurement has been studied in-situ in two dimensions in the Ag/Si(111) system as a function of the incident adatom flux rate with a four probe technique. A conductance study in a three dimensional conical structure was also carried out with field emission techniques. Field emission is now well established and has been used in this case to characterize a novel geometry for use in flat panel displays to replace cathode ray tube monitors. For the two dimensional study on Ag/Si(111), the origin of conduction is still unclear, as both transport by means of ...