Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

1990

Iowa State University

Discipline
Keyword
Publication
Publication Type

Articles 1 - 30 of 32

Full-Text Articles in Physics

Photoemission Study Of Au On A-Si:H, Tun-Wen Pi, A.-B. Yang, C. G. Olson, David W. Lynch Nov 1990

Photoemission Study Of Au On A-Si:H, Tun-Wen Pi, A.-B. Yang, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

We report a high-resolution photoemission study of Au evaporated on rf-sputtered a-Si:H at room temperature. Three regions of coverage can be classified according to the behavior of the valence-band and core-level spectra: an unreacted region with an equivalent thickness of 2 Å, followed by an intermixed Au/a-Si overlayer (∼9 Å), and a dual-phase region at higher coverage. Au adatoms are dispersed in the unreacted region. They subsequently cluster in the intermixed region, where they attach to Si atoms that are not hydrogen bonded, suggesting that the intermixed Si is mainly from those that have dangling bonds ...


Photoemission Study Of Cr On A-Si:H, Tun-Wen Pi, C. G. Olson, David W. Lynch Nov 1990

Photoemission Study Of Cr On A-Si:H, Tun-Wen Pi, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

We report a synchrotron-radiation photoemission study of Cr evaporated on rf-sputtered a-Si:H at room temperature. The evolution of the interface qualitatively follows that on c-Si, despite differences in the valence-band emission. The interface begins with an inactive layer (≤1 Å) of Cr, followed by an intermixed Cr/a-Si:H layer (≤12 Å). With further Cr deposition, bulklike Cr metal begins to develop on top of these. Some features exhibited by the Cr/a-Si:H interface are specific to a-Si:H surfaces. For instance, Cr adatoms are found around the dangling-bond neighborhood at coverages below ...


Optical Properties And Electronic Structures Of The Intermetallic Compounds Auga2 And Ptga2, Kwang-Joo Kim, Bruce N. Harmon, Liang-Yao Chen, David W. Lynch Nov 1990

Optical Properties And Electronic Structures Of The Intermetallic Compounds Auga2 And Ptga2, Kwang-Joo Kim, Bruce N. Harmon, Liang-Yao Chen, David W. Lynch

Physics and Astronomy Publications

The electronic structures of AuGa2 and PtGa2 have been studied with use of spectroscopic ellipsometry and the dielectric functions have been determined in the 1.2–5.5-eV region. Both compounds show interband absorption at low photon energies (<1.3 eV). The interband absorption for AuGa2 is strong at about 2 eV while that for PtGa2 shows a broad structure in the range 2.5–4.5 eV, with a shoulder at 3.3 eV. The observed interband features in ε2 can be interpreted in terms of self-consistent relativistic band-structure calculations using the linear augmented-plane-wave method. The interband contribution to the imaginary part of the dielectric function εb2 has been calculated including the effect of the electric dipole matrix elements. The overall agreement is good between the band calculations and the ellipsometry results in the 1.2–5.5-eV region for both the magnitude and the positions of the structures. Below 1.2 eV the calculational results for both compounds show interband absorption, which is also qualitatively suggested by the ellipsometry results.


Theory Of Compositional And Magnetic Correlations In Alloys: Interpretation Of A Diffuse Neutron-Scattering Experiment On An Iron-Vanadium Single Crystal, J. B. Staunton, Duane D. Johnson, F. J. Pinski Sep 1990

Theory Of Compositional And Magnetic Correlations In Alloys: Interpretation Of A Diffuse Neutron-Scattering Experiment On An Iron-Vanadium Single Crystal, J. B. Staunton, Duane D. Johnson, F. J. Pinski

Duane D. Johnson

We describe a first-principles theory for compositional and magnetic correlations in alloys and compare the results of the theory with recent diffuse, unpolarized, neutron-scattering measurements on a single crystal of ferromagnetic Fe0.865V0.135. The nuclear cross section is described very well by the theory and we are able to connect the q-dependent structure to the underlying electronic structure of the alloy. The magnetocompositional and magnetic correlations also may be obtained for comparison to polarized measurements.


Ce-Catalyzed Oxidation Of Ta(110), C. Gu, David W. Lynch, A. B. Yang, C. G. Olson Jul 1990

Ce-Catalyzed Oxidation Of Ta(110), C. Gu, David W. Lynch, A. B. Yang, C. G. Olson

Physics and Astronomy Publications

Photoemission spectroscopy was used to investigate the initial oxidation of the Ce/Ta(110) interface at room temperature. The oxidation of Ta(110) is dramatically enhanced by a thin Ce overlayer. A Ta suboxide TaOχ (0.5≤χ≤1) is formed first in the interface, followed by the rapid formation of Ta2O5 upon further oxygen exposure. A weak interface reaction exists in Ce/Ta(110), but is excluded as the main cause of the catalytic oxidation. An earlier suggestion is reconfirmed that the Ce layer converts O2 to oxygen ions and thus promotes the oxidation of the substrate.


High-Resolution Angle-Resolved Photoemission Study Of The Fermi Surface And The Normal-State Electronic Structure Of Bi2sr2cacu2o8, C. G. Olson, R. Liu, David W. Lynch, R. S. List, A. J. Arko, B. W. Veal, Y. C. Chang, P. Z. Jiang, A. P. Paulikas Jul 1990

High-Resolution Angle-Resolved Photoemission Study Of The Fermi Surface And The Normal-State Electronic Structure Of Bi2sr2cacu2o8, C. G. Olson, R. Liu, David W. Lynch, R. S. List, A. J. Arko, B. W. Veal, Y. C. Chang, P. Z. Jiang, A. P. Paulikas

Physics and Astronomy Publications

High-resolution angle-resolved photoelectron spectroscopic measurements were made of the Fermi edge of a single crystal of Bi2Sr2CaCu2O8 at 90 K along several directions in the Brillouin zone. The resultant Fermi-level crossings are consistent with local-density band calculations, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250 K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level the spectra show correlation effects in the form of an increased effective mass, but the essence ...


Inverse-Photoemission Measurement Of Iron Oxides On Polycrystalline Fe, Bong-Soo Kim, Sayong Hong, David W. Lynch Jun 1990

Inverse-Photoemission Measurement Of Iron Oxides On Polycrystalline Fe, Bong-Soo Kim, Sayong Hong, David W. Lynch

Physics and Astronomy Publications

We measured the inverse-photoemission spectra (IPES) of iron oxides grown on an Fe substrate and calculated the band structure of paramagnetic FeO to analyze the IPES. The band-structure calculation showed some overlap between Fe 3d states and O 2p states in the region of occupied states, and s,p-like states of Fe in the unoccupied region. Isochromatic IPES showed two structures at ∼2.5 and ∼7.5 eV above the Fermi energy. We estimated from the IPES data a full band gap of 2.5 eV for FeO.


Total-Energy And Pressure Calculations For Random Substitutional Alloys, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Györffy, G. M. Stocks May 1990

Total-Energy And Pressure Calculations For Random Substitutional Alloys, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Györffy, G. M. Stocks

Duane D. Johnson

We present the details and the derivation of density-functional-based expressions for the total energy and pressure for random substitutional alloys (RSA) using the Korringa-Kohn-Rostoker Green’s-function approach in combination with the coherent-potential approximation (CPA) to treat the configurational averaging. This includes algebraic cancellation of various electronic core contributions to the total energy and pressure, as in ordered-solid muffin-tin-potential calculations. Thus, within the CPA, total-energy and pressure calculations for RSA have the same foundation and have been found to have the same accuracy as those obtained in similar calculations for ordered solids. Results of our calculations for the impurity formation energy ...


Interpretation Of The Magnetization Mechanism In Terfenol‐D Using Barkhausen Pulse‐Height Analysis And Irreversible Magnetostriction, David C. Jiles, S. Hariharan May 1990

Interpretation Of The Magnetization Mechanism In Terfenol‐D Using Barkhausen Pulse‐Height Analysis And Irreversible Magnetostriction, David C. Jiles, S. Hariharan

Electrical and Computer Engineering Publications

The ternary alloy Dy0.7Tb0.3Fe1.9, known as Terfenol‐D, is a highly magnetostrictive alloy with magnetostriction coefficients along the principal crystallographic directions of λ1 1 1=1640×10−6and λ1 0 0≤100(±30)×10−6. The bulk magnetostriction λ is dependent on the state of magnetization M, on the original domain configuration, and on the texture of the material. This paper reports on Barkhausen measurements and magnetostriction. The pulse‐height distribution of Barkhausen emissions revealed events occurring at a specific amplitude which were stress dependent. The magnetostriction results gave ...


Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo Mar 1990

Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo

Chemistry Publications

We present a different mechanism to explain the occurrence of long-lived oscillations in diffraction spot intensities during epitaxial growth of metal films on fcc (100) substrates at low temperature. Rather than rely on the common picture of cyclical nucleation and growth to produce the oscillations, the model invokes ‘‘downward funneling’’ deposition dynamics to fourfold-hollow adsorption sites.


Seeing With Light, Sound, Microwaves, X-Rays, Gamma Rays, Etc., Glen Wade Jan 1990

Seeing With Light, Sound, Microwaves, X-Rays, Gamma Rays, Etc., Glen Wade

Review of Progress in Quantitative Nondestructive Evaluation

It is common to regard humans as being able to see only with light, but about a hundred years ago at the beginning of the modern era, along came x-rays and sonograms. By now technology has made it possible for us to see in a great many different ways. Important views such as underground pools of oil, tumors in the brain, fine structure in the rings of Saturn, ship wreckage on the bottom of the ocean, cracks in the ice packs of the Arctic, all these views and many more, completely unperceivable one hundred years ago, are available to us ...


Coincidence Orientations Of Crystals In Tetragonal Systems, With Applications To Yba2cu3o7, Abha Singh, N. Chandrasekhar, Alexander H. King Jan 1990

Coincidence Orientations Of Crystals In Tetragonal Systems, With Applications To Yba2cu3o7, Abha Singh, N. Chandrasekhar, Alexander H. King

Alexander H. King

We have developed a method for the characterization of coincidence-site lattices (CSL's) in tetragonal or near-tetragonal orthorhombic structures, by suitable modifications to the method of Grimmer & Warrington [Acta Cryst. (1987), A43, 232-243]. We have applied our method to determine coincidence rotations and the associated information appropriate for forming constrained CSL's in the high-To superconductor YBazCu307-n. The unit cell is orthorhombic with lattice parameters a = 3.82, b = 3"89 and c = 11.67 A for the nominal composition. We present tables of coincidence rotation angles, .Z, CSL, DSCL and associated step vectors up to ,~ = 50. We find our ...


High Resolution Electron Energy Loss Studies Of O2, H, N, No, And N2o Adsorption On Germanium Surfaces , Anthony G. Entringer Jan 1990

High Resolution Electron Energy Loss Studies Of O2, H, N, No, And N2o Adsorption On Germanium Surfaces , Anthony G. Entringer

Retrospective Theses and Dissertations

The first high resolution electron energy loss spectroscopy (HREELS) studies of the oxidation and nitridation of germanium surfaces are reported. Both single crystal Ge(111) and disordered surfaces were studied. Surfaces were exposed to H, O[subscript]2, NO, N[subscript]2O, and N, after cleaning in ultra-high vacuum. The Ge surfaces were found to be non-reactive to molecular hydrogen (H[subscript]2) at room temperature. Exposure to atomic hydrogen (H) resulted hydrogen adsorption as demonstrated by the presence of Ge-H vibrational modes. The HREEL spectrum of the native oxide of Ge characteristic of [nu]-GeO[subscript]2 was obtained ...


Qcd Corrections To Properties Of Technipions In Technicolor Theories , David H. Slaven Jan 1990

Qcd Corrections To Properties Of Technipions In Technicolor Theories , David H. Slaven

Retrospective Theses and Dissertations

In this work we calculate QCD corrections to technipion processes in a one family technicolor model. Our approach is to use an effective technipion Lagrangian analogous to the effective Lagrangian of QCD. The effective Lagrangian includes the Wess-Zumino-Witten Lagrangian (adapted to technicolor), and we gauge the QCD subgroup of the chiral symmetry to obtain couplings between the technipions and gluons. Here we examine processes involving the P[superscript]0[superscript]', a colorless, neutral, electroweak singlet, and the lightest technipion in a one family technicolor model. In addition to the Wess-Zumino-Witten Lagrangian, we assume couplings between technipions and ordinary fermions, due ...


Localization And Electron-Phonon Interaction In Disordered Systems , Yi Wan Jan 1990

Localization And Electron-Phonon Interaction In Disordered Systems , Yi Wan

Retrospective Theses and Dissertations

The problem of localization of electrons in the presence of electron-phonon interaction in disordered one-dimensional system is studied. In the mean-field approximation, the electron-phonon interaction results in a distorted lattice, the Peierls instability. At the same time, a gap opens at the Fermi level in the electron band. It is known that the scattering of the electrons by the disorder will destroy the lattice distortion and close the gap. However, there is disagreement on the way this happens and on the nature of the resulting electronic states. Recent progress in the experimental and theoretical studies of the one-dimensional organic polymer ...


Synchrotron Radiation Photoemission Study Of Metal Overlayers On Hydrogenated Amorphous Silicon At Room Temperature , Tun-Wen Pi Jan 1990

Synchrotron Radiation Photoemission Study Of Metal Overlayers On Hydrogenated Amorphous Silicon At Room Temperature , Tun-Wen Pi

Retrospective Theses and Dissertations

We study Au, Cr, and Ag metals evaporated on rf-sputtered a-Si:H at room temperature using high-resolution photoemission techniques. For Au/a-Si:H, three regions of coverage can be classified: an unreacted region with an equivalent thickness of 2 A, followed by an intermixed Au/a-Si overlayer (~9 A), and a dual-phase region at higher coverage. Au adatoms are dispersely distributed in the unreacted region. They subsequently cluster in the intermixed region, where they attach to Si atoms that are not hydrogen-bonded, suggesting that the intermixed Si were mainly those that had dangling bonds. In the dual-phase region, two sets ...


Neutral Technicolor Pseudo Goldstone Bosons Production And Qcd Background At The Ssc , Wang-Chuang Kuo Jan 1990

Neutral Technicolor Pseudo Goldstone Bosons Production And Qcd Background At The Ssc , Wang-Chuang Kuo

Retrospective Theses and Dissertations

The production of the neutral technicolor pseudo Goldstone bosons, P[superscript]0[superscript]' and Psp80[superscript]', at large transverse momentum in pp collisions, pp → g(q)P[superscript]0[superscript]' (Psp80[superscript]')X has been investigated in reactions at a high energy collider such as the SSC. The major two-body and three-body decay modes in tree diagrams are investigated in detail. The t[macron] t decay channel would dominate both the decays of P[superscript]0[superscript]' and Psp80[superscript]' if it is allowed. Otherwise, gg and 3g will be the dominant decay modes unless the mass of the P ...


Inverse-Photoemission Spectroscopy Of Fexo, Ag , Bongsoo Kim Jan 1990

Inverse-Photoemission Spectroscopy Of Fexo, Ag , Bongsoo Kim

Retrospective Theses and Dissertations

I measured the inverse-photoemission spectra (IPES) of iron oxides grown on an Fe substrate, and calculated the band structure of paramagnetic FeO to analyze the IPES. The band calculation showed some overlap between Fe3 d states and O2 p states in the region of occupied states, and s,p-like states of Fe in the unoccupied region. Isochromatic IPES showed structures at ~2.5 eV and ~7.5 eV above the Fermi energy. I estimate the full band gap of FeO as 2.5 eV from the IPES data;Angle-resolved inverse-photoemission spectra (ARIPES) have been measured on single-crystal Ag. The results ...


An Angular Momentum Approach To Three-Dimensional Supersymmetric Quantum Mechanics With Applications To N-N Scattering , Cindy Neyer Jan 1990

An Angular Momentum Approach To Three-Dimensional Supersymmetric Quantum Mechanics With Applications To N-N Scattering , Cindy Neyer

Retrospective Theses and Dissertations

Angular momentum theory is applied to a fully three-dimensional model of supersymmetric quantum mechanics. The unique solution of the algebra is demonstrated and the matrix elements of the supersymmetric transformation operator are calculated so that the effect of such transformations on scattered states may be extracted. Comparison of the transformed and original states yields a relation between the phase shifts and mixing parameter for coupled states. This relation is tested against experimental N-N scattering data, but no evidence of supersymmetry is found. It is shown that the extra repulsive core in the supersymmetric potential is too soft;Angular momentum theory ...


First-Principles Study Of The Contractive Reconstruction Of Gold And Silver Monolayers On Gold, Silver, And Aluminum , Noboru Takeuchi Jan 1990

First-Principles Study Of The Contractive Reconstruction Of Gold And Silver Monolayers On Gold, Silver, And Aluminum , Noboru Takeuchi

Retrospective Theses and Dissertations

We investigated the structures of Au and Ag monolayers on a number of metal surfaces. It is energetically favorable for both Au and Ag to transform from a square to hexagonal arrangement and to contract to a higher surface density, but Au gains substantially more energy than Ag. This is true both for a monolayer in isolation as well as on top of a jellium surface. We calculated the "mismatch" energy (energy loss when the top layer loses registry with the substrate) for Au and Ag, and found that Ag has a slightly higher mismatch energy. The results offer a ...


Topics In Theoretical Surface Science: I Structures Of Clean And Adsorbate Covered Surfaces Ii Epitaxy Of Metals On Metal Surfaces , Todd Joseph Raeker Jan 1990

Topics In Theoretical Surface Science: I Structures Of Clean And Adsorbate Covered Surfaces Ii Epitaxy Of Metals On Metal Surfaces , Todd Joseph Raeker

Retrospective Theses and Dissertations

The energetics and structures of clean and adsorbate covered surfaces are investigated in this dissertation. First, the formalism, within the Corrected Effective Medium (CEM) method, for calculating the surface energy of a clean surface is derived. The surface energies for many different metals and their low index surfaces are presented. The minimization of the surface energy is then used to predict the multilayer relaxation of the Al(111), (100), (110), Ni(100), (110) and Fe(100) surfaces. The driving forces behind surface relaxation is then examined within the CEM method;Extensions of the surface CEM formalism to calculate the binding ...


High-Resolution Angle-Resolved Photoemission Studies Of High Tc Superconductor Bi2sr2cacu2o8 , Rong Liu Jan 1990

High-Resolution Angle-Resolved Photoemission Studies Of High Tc Superconductor Bi2sr2cacu2o8 , Rong Liu

Retrospective Theses and Dissertations

An angle-resolved photoemission study of the normal and superconducting states in Bi[subscript]2Sr[subscript]2CaCu[subscript]2O[subscript]8 was performed. Measurements in the normal state show bands dispersing through the Fermi level from at least 350 meV below E[subscript]F. The Fermi level crossings are consistent with local-density band calculation, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level, the ...


Scanning Tunnel Microscopy Studies Of Tetrahedrally Bonded Materials , Patricia E. Allen Jan 1990

Scanning Tunnel Microscopy Studies Of Tetrahedrally Bonded Materials , Patricia E. Allen

Retrospective Theses and Dissertations

The Scanning Tunnel Microscope (STM) is a surface analysis tool that has been used to study the geometric and electronic properties of metals, semimetals and semiconductors. Evaporated gold deposited on glass was examined as a preliminary test of the McAllister/RHK STM. Calibration of the STM system was accomplished by imaging annealed pyrolytic graphite (APG), but with surprising results. The peak spacing agreed with the accepted value for STM graphite images of 2.46 A, but the shape of the peaks were often distorted. These distortions can be understood in view of the theoretical work of Kobayashi and Tsukada on ...


Photoemission And Inverse Photoemission Studies Of Cesn3 And Lasn3 , Sayong Hong Jan 1990

Photoemission And Inverse Photoemission Studies Of Cesn3 And Lasn3 , Sayong Hong

Retrospective Theses and Dissertations

Angle-resolved photoemission spectra (ARPES) and angle-resolved inverse photoemission spectra from single crystals of CeSn[subscript]3 (111) and LaSn[subscript]3 (111) were measured and discussed. The results were compared with the calculated band structures and fitted by the Gunnarsson-Schonhammer (G-S) model. The two-peak structure from the resonance photoemission of CeSn[subscript]3 was fitted by G-S model well by placing the single f-level at 2.0 eV below the Fermi energy before hybridization. ARPES from both CeSn[subscript]3 and LaSn[subscript]3 showed a peak near the Fermi energy without noticeable dispersion. In LaSn[subscript]3, the experimental ...


Optical Properties And Electronic Structures Of D- And F-Electron Metals And Alloys, Ag-In, Ni-Cu, Auga2, Ptga2, [Beta]'-Nial, [Beta]'-Coal, Cesn3, And Lasn3 , Kwang Joo Kim Jan 1990

Optical Properties And Electronic Structures Of D- And F-Electron Metals And Alloys, Ag-In, Ni-Cu, Auga2, Ptga2, [Beta]'-Nial, [Beta]'-Coal, Cesn3, And Lasn3 , Kwang Joo Kim

Retrospective Theses and Dissertations

Optical properties and electronic structures of disordered Ag[subscript]1-xIn[subscript]x (x = 0.0, 0.04, 0.08, 0.12) and Ni[subscript]1-xCu[subscript]x(x = 0.0, 0.1, 0.3, 0.4) alloys and ordered AuGa[subscript]2, PtGa[subscript]2, [beta][superscript]'-NiAl, [beta][superscript]'-CoAl, CeSn[subscript]3, and LaSn[subscript]3 have been studied. The complex dielectric functions have been determined for Ag[subscript]1-xIn[subscript]x,Ni[subscript]1-xCu[subscript]x,AuGa[subscript]2, and PtGa[subscript]2 in the 1.2-5.5 eV region and for CeSn[subscript]3 and LaSn ...


Measurement Of [Alpha Subscript S]From Energy-Energy Correlations In E+E- Annihilation At 29 Gev , Hsiao-Ying Chao Jan 1990

Measurement Of [Alpha Subscript S]From Energy-Energy Correlations In E+E- Annihilation At 29 Gev , Hsiao-Ying Chao

Retrospective Theses and Dissertations

We have studied the energy-energy correlation in e[superscript]+e[superscript]- annihilation into hadrons at √s = 29 GeV using the TPC/2[gamma] Detector Facility at PEP. We found that [alpha][subscript]s = 0.161 ±.004 ±.011 for the average hadronic event sample using GKS matrix elements and LUND symmetric string fragmentation.


Modeling Of Ultrasonic Scattering Experiments With Applications To System And Transducer Characterization , David Duane Bennink Jan 1990

Modeling Of Ultrasonic Scattering Experiments With Applications To System And Transducer Characterization , David Duane Bennink

Retrospective Theses and Dissertations

The voltage signal output by the receiver electronics, which represents the observable quantity in an ultrasonic scattering experiment, is written as a product, in the frequency domain, of two factors: the system efficiency and the scattering coefficient. The system efficiency represents the combined electrical properties of both the generator and receiver electronics and is a function of frequency only. The scattering coefficient represents the acoustic nature of the experiment (the radiation, propagation, scattering and reception of ultrasonic waves) and depends on the distributed field properties of the transducers involved and their locations and orientations, on the number and type of ...


Application Of Ultrasonic Guided Waves To The Characterization Of Texture In Metal Sheets Of Cubic And Hexagonal Crystallites , Yan Li Jan 1990

Application Of Ultrasonic Guided Waves To The Characterization Of Texture In Metal Sheets Of Cubic And Hexagonal Crystallites , Yan Li

Retrospective Theses and Dissertations

Texture (preferred grain orientation) of polycrystalline metal sheets is an important material property which influences the process of making products such as aluminum cans and automobile and aircraft components. Traditionally, the texture is determined by X-ray or neutron diffraction techniques which are often destructive and time-consuming in nature. Over the last decade, ultrasonics has been found to provide an alternative way to characterize texture nondestructively and quickly. This dissertation makes an in-depth study of the fundamental physical principles of ultrasonic characterization of texture in metal sheets of cubic and hexagonal crystallites. The foundation is laid by investigations of wave propagation ...


Magnetic And Thermal Properties Of High Tc Superconductors , Wonchoon Lee Jan 1990

Magnetic And Thermal Properties Of High Tc Superconductors , Wonchoon Lee

Retrospective Theses and Dissertations

Measurements of the normal state magnetic susceptibility [chi](T) of YBa2Cu3O7, Bi1.8Pb0.2Sr2CaCu2O8+[delta], and Bi2- xPb xSr2Ca2Cu3O10+[delta] (x = 0.2 and 0.25) were carried out. All [chi](T) data show negative curvature below ~ 2T c. The data for YBa2Cu3O7 are in excellent agreement with a new calculation of the superconducting fluctuation and diamagnetism. From the analysis, we infer s-wave pairing and microscopic parameters are obtained. For [chi](T) of YBa2Cu3O7, part of the negative curvature is inferred to arise from the normal state background. We find a strong temperature dependent anisotropy [delta][chi] ≡ [chi] c - [chi ...


Cluster Diffusivity: Structure, Correlation, And Scaling, H. C. Kang, P. A. Thiel, James W. Evans Jan 1990

Cluster Diffusivity: Structure, Correlation, And Scaling, H. C. Kang, P. A. Thiel, James W. Evans

Physics and Astronomy Publications

We have investigated the diffusion of clusters on a triangular lattice using Monte Carlo simulations. A cluster is defined as a two‐dimensional collection of particles which are connected to each other, either directly or indirectly through other particles in the cluster, by nearest‐neighbor bonds. Each particle is allowed to hop, with probability αδb/2/(α−δb/2+αδb/2), to a vacant nearest‐neighbor site with the constraint that the hop does not break the cluster. The change in the number of bonds is given by δb. The equilibrium clusters are correlated animals with ...