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Physics Faculty Publications

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Articles 1921 - 1950 of 2178

Full-Text Articles in Physical Sciences and Mathematics

Summary Of The Workshop On The Applications Of X-Ray Standing Waves In Studies Of Surfaces, Fiims, And Buik Materiais, David R. Heskett, L. Berman Feb 1995

Summary Of The Workshop On The Applications Of X-Ray Standing Waves In Studies Of Surfaces, Fiims, And Buik Materiais, David R. Heskett, L. Berman

Physics Faculty Publications

Highlights of the satellite workshop on the technique of x-ray standing waves which preceded the 5th International Conference on Synchrotron Radiation Instrumentation held at the State University of New York at Stony Brook, USA are presented. At the workshop, many applications of the x-ray standing-wave technique were described in both invited and contributed talks. While the predominant use of the XSW technique was to analyze the structure of adsorbates on surfaces, applications in the characterization of thin films, interfaces, clean surfaces, and bulk materials were also presented. Most of the talks concentrated on experimental results, but some theory was also …

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Convenient Determination Of Concentration And Energy In Deep-Level Transient Spectroscopy, David C. Look, Z-Q. Fang, J. R. Sizelove Feb 1995

Convenient Determination Of Concentration And Energy In Deep-Level Transient Spectroscopy, David C. Look, Z-Q. Fang, J. R. Sizelove

Physics Faculty Publications

For defects or impurities with deep energy levels, such as the commonly observed EL2, EL3, and EL6 in GaAs, it is very important to take account of the so‐called λ effect in order to deduce the correct concentrations of these centers when using capacitance techniques. By measuring capacitance at several forward bias voltages for a given reverse bias voltage it is possible to determine concentration NT and energy ET without requiring the usual emission rate analysis. Convenient formulas for NT and ET are given, although only NT can be determined with a high degree of …

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Improved Gaussian Beam-Scattering Algorithm, James A. Lock Jan 1995

Improved Gaussian Beam-Scattering Algorithm, James A. Lock

Physics Faculty Publications

The localized model of the beam-shape coefficients for Gaussian beam-scattering theory by a spherical particle provides a great simplification in the numerical implementation of the theory. We derive an alternative form for the localized coefficients that is more convenient for computer computations and that provides physical insight into the details of the scattering process. We construct a FORTRAN program for Gaussian beam scattering with the localized model and compare its computer run time on a personal computer with that of a traditional Mie scattering program and with three other published methods for computing Gaussian beam scattering. We show that the …

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Demonstrating Hysteresis In Ferroelectric Materials, Deborah Schurr, Timothy Usher Jan 1995

Demonstrating Hysteresis In Ferroelectric Materials, Deborah Schurr, Timothy Usher

Physics Faculty Publications

No abstract provided.

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Monte-Carlo Simulation Of Bulk Hole Transport In Alxga1-Xas, In1-Xalxas, And Gaasxsb1-X, M. J. Martinez, David C. Look, J. R. Sizelove, F. L. Schuermeyer Jan 1995

Monte-Carlo Simulation Of Bulk Hole Transport In Alxga1-Xas, In1-Xalxas, And Gaasxsb1-X, M. J. Martinez, David C. Look, J. R. Sizelove, F. L. Schuermeyer

Physics Faculty Publications

We report a Monte Carlo study of hole transport in AlxGa1−xAs, In1−xAlxAs, and GaAsxSb1−x. The effects of alloy scattering are significant in all three cases, but mobilities are still high enough to be advantageous in particular device applications. We separately calculate the Hall r factors by a Boltzmann transport method and show that these factors are vitally important when attempting to compare Monte Carlo drift mobilities with experimental Hall data.

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A Theoretical Study Concerning The Solar Cycle Dependence Of The Nightside Ionosphere Of Venus, Zoltan Dobe, Andrew F. Nagy, Jane L. Fox Jan 1995

A Theoretical Study Concerning The Solar Cycle Dependence Of The Nightside Ionosphere Of Venus, Zoltan Dobe, Andrew F. Nagy, Jane L. Fox

Physics Faculty Publications

We modeled the chemical and physical processes taking place in the nightside ionosphere of Venus by solving the one dimensional coupled continuity and momentum equations for 12 ion species [CO2+, O2+, O+, H+, NO+, CO+, N2+, N+, He+, C+, O+ (²D) and O+ (²P)]. We investigated the relative importance of the two major processes responsible for maintaining the nightside plasma densities: atomic ion transport from the dayside and impact ionization due to energetic electron precipitation. …

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Demonstration Of Semiconductor Characterization By Phonon Side-Band In Photoluminescence, D. C. Reynolds, David C. Look, D. N. Talwar, G. L. Mccoy, K. R. Evans Jan 1995

Demonstration Of Semiconductor Characterization By Phonon Side-Band In Photoluminescence, D. C. Reynolds, David C. Look, D. N. Talwar, G. L. Mccoy, K. R. Evans

Physics Faculty Publications

In this paper two GaAs samples were investigated; one was a very pure sample grown by chemical-vapor deposition, the other was grown by molecular-beam epitaxy. The dominant optical transition in the high-purity sample was the donor-bound-exciton transition. Phonon sidebands associated with both the free exciton and the donor-bound exciton were observed. The active phonons were the longitudinal-optical (LO) and the transverse-optical (TO) modes associated with both the free exciton and the donor-bound exciton at the Γ point in k space; the TO mode from the donor-bound exciton at the X point, the LO from the free exciton at the L …

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Two-Body Photodisintegration Of The Deuteron Up To 2.8 Gev, J. E. Belz, D. H. Potterveld, S. E. Kuhn, J.F. J. Van Den Brand, J. L. White, B. Zeidman, Et Al. Jan 1995

Two-Body Photodisintegration Of The Deuteron Up To 2.8 Gev, J. E. Belz, D. H. Potterveld, S. E. Kuhn, J.F. J. Van Den Brand, J. L. White, B. Zeidman, Et Al.

Physics Faculty Publications

Measurements were performed for the photodisintegration cross section of the deuteron for photon energies from 1.6 to 2.8 GeV and center-of-mass angles from 37° to 90°. The measured energy dependence of the cross section at θc.m. = 90° is in agreement with the constituent counting rules.

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A-Dependence Of Nuclear Transparency In Quasielastic A (E, E'P) At High Q², T. G. O'Neill, W. Lorenzon, P. Anthony, R. G. Arnold, J. Arrington, E. J. Beise, J. E. Belz, P. E. Bosted, H.- J. Bulten, M. S. Chapman, K. P. Coulter, F. Dietrich, R. Ent, M. Epstein, B. W. Filippone, H. Gao, R. A. Gearhart, D. F. Geesaman, J.- O. Hansen, R. J. Holt, H. E. Jackson, C. E. Jones, C. E. Keppel, E. R. Kinney, S. Kuhn, K. Lee, A. Lung, N.C.R. Makins, D.J. Margaziotis, R. D. Mckeown, R. G. Milner, B. Mueller, J. Napolitano, J. Nelson, V. Papavassiliou, G. G. Petratos, D. H. Potterveld, S. E. Rock, M. Spengos, Z. M. Szalata, L. H. Tao, K. Van Bibber, J.F.J. Van Den Brand, J. L. White, B. Zeidman Jan 1995

A-Dependence Of Nuclear Transparency In Quasielastic A (E, E'P) At High Q², T. G. O'Neill, W. Lorenzon, P. Anthony, R. G. Arnold, J. Arrington, E. J. Beise, J. E. Belz, P. E. Bosted, H.- J. Bulten, M. S. Chapman, K. P. Coulter, F. Dietrich, R. Ent, M. Epstein, B. W. Filippone, H. Gao, R. A. Gearhart, D. F. Geesaman, J.- O. Hansen, R. J. Holt, H. E. Jackson, C. E. Jones, C. E. Keppel, E. R. Kinney, S. Kuhn, K. Lee, A. Lung, N.C.R. Makins, D.J. Margaziotis, R. D. Mckeown, R. G. Milner, B. Mueller, J. Napolitano, J. Nelson, V. Papavassiliou, G. G. Petratos, D. H. Potterveld, S. E. Rock, M. Spengos, Z. M. Szalata, L. H. Tao, K. Van Bibber, J.F.J. Van Den Brand, J. L. White, B. Zeidman

Physics Faculty Publications

The A-dependence of the quasielastic A(e, ef'p) reaction has been studied at SLAC with 2H, C, Fe, and Au nuclei at momentum transfers Q2 = 1, 3, 5, and 6.8 (GeV/c)2. We extract the nuclear transparency T(A, Q2), a measure of the average probability that the struck proton escapes from the nucleus A without interaction. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as Color Transparency. Within the measurement uncertainty, no increase is seen for any of the nuclei studied.

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Evidence For Virtual Compton Scattering From Proton, J.F.J. Van Den Brand, R. Ent, P. L. Anthony, R. G. Arnold, J. Arrington, E. J. Beise, J. E. Belz, P. E. Bosted, H. J. Bulten, M. S. Chapman, K. P. Coulter, F. S. Dietrich, M. Epstein, B. W. Filippone, H. Gao, R. A. Gearhart, D. F. Geesaman, J.-O. Hansen, R. J. Holt, H. E. Jackson, C. E. Jones, C. E. Keppel, E. R. Kinney, S. Kuhn, K. Lee, W. Lorenzon, A. Lung, N.C.R. Makins, D.J. Margaziotis, R.D. Mckeown, R.G. Milner, B. Mueller, J. Napolitano, J. Nelson, T. G. O'Neill, V. Pavavassiliou, G. G. Petratos, D. H. Potterveld, S. E. Rock, M. Spengos, Z. M. Szalata, L. H. Tao, K Van Bibber, D. A. Wasson, J.L. White, B. Zeidman Jan 1995

Evidence For Virtual Compton Scattering From Proton, J.F.J. Van Den Brand, R. Ent, P. L. Anthony, R. G. Arnold, J. Arrington, E. J. Beise, J. E. Belz, P. E. Bosted, H. J. Bulten, M. S. Chapman, K. P. Coulter, F. S. Dietrich, M. Epstein, B. W. Filippone, H. Gao, R. A. Gearhart, D. F. Geesaman, J.-O. Hansen, R. J. Holt, H. E. Jackson, C. E. Jones, C. E. Keppel, E. R. Kinney, S. Kuhn, K. Lee, W. Lorenzon, A. Lung, N.C.R. Makins, D.J. Margaziotis, R.D. Mckeown, R.G. Milner, B. Mueller, J. Napolitano, J. Nelson, T. G. O'Neill, V. Pavavassiliou, G. G. Petratos, D. H. Potterveld, S. E. Rock, M. Spengos, Z. M. Szalata, L. H. Tao, K Van Bibber, D. A. Wasson, J.L. White, B. Zeidman

Physics Faculty Publications

In virtual Compton scattering an electron is scattered off a nucleon such that the nucleon emits a photon. We show that these events can be selected experimentally, and present the first evidence for virtual Compton scattering from the proton in data obtained at the Stanford Linear Accelerator Center. The angular and energy dependence of the data is well described by a calculation that includes the coherent sum of electron and proton radiation.

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Exclusive Electron Scattering From Deuterium At High Momentum Transfer, H. J. Bulten, P. L. Anthony, R. G. Arnold, J. Arrington, E. J. Beise, E. Belz, K. Van Bibber, P. E. Bosted, J.F.J. Van Den Brand, M. S. Chapman, K. P. Coulter, F. S. Dietrich, R. Ent, M. Epstein, B. W. Filippone, H. Gao, R.A. Gearhart, D. F. Geesaman, J.-O. Hansen, R. J. Holt, H. E. Jackson, C. E. Jones, C. E. Keppel, E. Kinney, S. E. Kuhn, K. Lee, W. Lorenzon, A. Lung, N.C.R. Makins, D. J. Margaziotis, R.D. Mckeown, R. G. Milner, B. Mueller, J. Napolitano, J. Nelson, T.G. O'Neill, V. Papavassiliou, G. G. Petratos, D. H. Potterveld, S. E. Rock, M. Spengos, Z. M. Szalata, L. H. Tao, J. L. White, B. Zeidman Jan 1995

Exclusive Electron Scattering From Deuterium At High Momentum Transfer, H. J. Bulten, P. L. Anthony, R. G. Arnold, J. Arrington, E. J. Beise, E. Belz, K. Van Bibber, P. E. Bosted, J.F.J. Van Den Brand, M. S. Chapman, K. P. Coulter, F. S. Dietrich, R. Ent, M. Epstein, B. W. Filippone, H. Gao, R.A. Gearhart, D. F. Geesaman, J.-O. Hansen, R. J. Holt, H. E. Jackson, C. E. Jones, C. E. Keppel, E. Kinney, S. E. Kuhn, K. Lee, W. Lorenzon, A. Lung, N.C.R. Makins, D. J. Margaziotis, R.D. Mckeown, R. G. Milner, B. Mueller, J. Napolitano, J. Nelson, T.G. O'Neill, V. Papavassiliou, G. G. Petratos, D. H. Potterveld, S. E. Rock, M. Spengos, Z. M. Szalata, L. H. Tao, J. L. White, B. Zeidman

Physics Faculty Publications

Cross sections are presented for the reaction 2H(e,e′p)n for momentum transfers in the range 1.2 ≤Q2≤ 6.8 (GeV/c)2 and for missing momenta from 0 to 250 MeV/c. The longitudinal-transverse interference structure function has been separated at Q2=1.2(GeV/c)2. The observables are compared to calculations performed in nonrelativistic and relativistic frameworks. The data are best described by a fully relativistic calculation.

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Diffuse Band Profiles In The Rho Ophiuchi Cloud, C Gregory Seab, Theodore P. Snow Jan 1995

Diffuse Band Profiles In The Rho Ophiuchi Cloud, C Gregory Seab, Theodore P. Snow

Physics Faculty Publications

High-resolution, high signal-to-noise ratio line profiles are presented for the 5780 and 5797 A diffuse interstellar bands toward six stars in the Rho Oph dark cloud. Target stars were chosen to exhibit a wide range of interstellar grain properties, as measured by grain polarization and far-UV extinction. The extreme case of the heavily reddened star HD 147889 is included; this star has one of the highest known lambdamax values, indicative of unusually large grains. Despite the differences in the grain properties, the line profiles and central wavelengths for the 5780 A band were found to be essentially identical for …

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The Weakness Of Diffuse Bands In Nebular Environments. Possible Impact On Thepah+ Hypothesis, T P. Snow, E L. Bakes, R H. Buss Jr., C G. Seab Jan 1995

The Weakness Of Diffuse Bands In Nebular Environments. Possible Impact On Thepah+ Hypothesis, T P. Snow, E L. Bakes, R H. Buss Jr., C G. Seab

Physics Faculty Publications

It has been widely suggested that PAH cations (PAH+) may be the carriers of the diffuse interstellar bands, so it is of interest to probe diffuse behavior in regions suspected of having high abundances of PAHs. Here we examine the strengths of several of the visible-wavelength diffuse interstellar bands in two nebular environments where infrared emission and ultraviolet indicators show that PAHs are abundant. One might expect the PAHs to be predominantly positively ionized in these regions, yet the diffuse bands are systematically weak. This led us to examine the ionization balance for see whether the weakness of the diffuse …

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Prediction Of Signal‐To‐Noise Ratio Gain For Passive Higher‐Order Correlation Detection Of Energy Transients, Lisa A. Pflug, George E. Ioup, Juliette W. Ioup, Robert L. Field Jan 1995

Prediction Of Signal‐To‐Noise Ratio Gain For Passive Higher‐Order Correlation Detection Of Energy Transients, Lisa A. Pflug, George E. Ioup, Juliette W. Ioup, Robert L. Field

Physics Faculty Publications

In general, higher‐order correlation detectors perform well in passive detection for signals of high third‐ and fourth‐order moments. Previous studies by the authors have shown that the normalized third‐ and fourth‐order signal moments are reliable indicators of higher‐order correlation detector performance [Pflug et al. (1992b)]. For a deterministic energy transient of known moments through fourth order, it is possible to predict theoretically the amount of gain over an ordinary cross‐correlation detector for a bicorrelation or tricorrelation detector applied in a noise environment of known variance. In this paper, formulas that predict detector performance for passive detection at the minimum …

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Accurate Nucleon-Nucleon Potential With Charge-Independence Breaking, R. B. Wiringa, V. G. J. Stoks, R. Schiavilla Jan 1995

Accurate Nucleon-Nucleon Potential With Charge-Independence Breaking, R. B. Wiringa, V. G. J. Stoks, R. Schiavilla

Physics Faculty Publications

We present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which we designate Argonne 𝑣18. The model has a charge-independent part with 14 operator components that is an updated version of the Argonne 𝑣14 potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen pp and np scattering database, low-energy nn scattering parameters, and deuteron binding energy. With 40 adjustable parameters it gives a χ2 per datum of 1.09 for 4301 pp and np data in the range 0–350 …

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Further Thoughts On Newton's Zero-Order Rainbow, James A. Lock, Timothy A. Mccollum Dec 1994

Further Thoughts On Newton's Zero-Order Rainbow, James A. Lock, Timothy A. Mccollum

Physics Faculty Publications

A zero-order rainbow angle may be defined as the relative minimum angle of deviation of geometrical light rays transmitted without internal reflections through a transparent particle. If the incident rays are parallel and the particle is a sphere, such a minimum does not exist. But if the incident rays ale not parallel or if the particle has an elliptical rather than circular cross section, an angle of minimum deviation, hence a zero-order rainbow, can occur. For a spherical water droplet, the zero-order rainbow will occur when a point source is placed less than a droplet radius away from its surface. …

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Interaction Of A Group Of Dislocations Within The Framework Of The Continuum Frenkel-Kontorova Model, Naum I. Gershenzon Nov 1994

Interaction Of A Group Of Dislocations Within The Framework Of The Continuum Frenkel-Kontorova Model, Naum I. Gershenzon

Physics Faculty Publications

The Frenkel-Kontorova (FK) model of edge dislocation is analyzed. Solutions of the continuum limit of the FK model [the sine-Gordon (SG) equation] are obtained in a form convenient for investigation of dynamics of a large number of interacting dislocations. We consider, based on these solutions, some nonstationary processes: dislocation generation, diffusion of dislocations, and crack-dislocation interaction. Simple relations connecting the velocity of plastic deformation, density and velocity of dislocations, and the force of interaction between dislocations are obtained. The nucleation of dislocations at a moving crack tip is described.

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Nondestructive Mapping Of Carrier Concentration And Dislocation Density In N(+)-Type Gaas, David C. Look, D. C. Walters, M. G. Mier, J. R. Sizelove Oct 1994

Nondestructive Mapping Of Carrier Concentration And Dislocation Density In N(+)-Type Gaas, David C. Look, D. C. Walters, M. G. Mier, J. R. Sizelove

Physics Faculty Publications

Transmission mappings (500 μm×500 μm resolution) at wavelengths of 0.9–1.5 μm on 3 in., n+‐GaAs wafers (n≂1–2×1018 cm-3) correlate well with carrier concentration n, measured by the Hall effect, and dislocation density, as confirmed by KOH etch‐pit patterns. The absorption for λ≳1.0 μm (below band edge) varies directly with n via free‐carrier interconduction‐band transitions, while the absorption for λ≲0.95 μm (near band edge) varies inversely with n because of band‐filling effects. Both phenomena are highly useful for n+‐GaAs wafer characterization.

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Diamagnetic Shifts Of Excitons Associated With Symmetrical And Antisymmetric Wave Functions In Coupled Inxga1-Xas-Gaas Quantum Wells, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz Oct 1994

Diamagnetic Shifts Of Excitons Associated With Symmetrical And Antisymmetric Wave Functions In Coupled Inxga1-Xas-Gaas Quantum Wells, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz

Physics Faculty Publications

Magneto‐optical data obtained from photoluminescence and photoluminescence excitation measurements performed in the presence of applied magnetic fields were used to determine the diamagnetic shifts of free excitons. The samples studied were coupled InxGa1−xAs–GaAs quantum wells. In all cases the excitons associated with antisymmetric wave functions were found to have larger diamagnetic shifts than the excitons associated with symmetric wave functions. This suggests that the excitons associated with antisymmetric wave functions have a smaller binding energy than excitons associated with symmetric wave functions. These properties are consistent with the fact that excitons associated with antisymmetric wave …

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Magnetoluminescence Studies In Gaas-Alxga1-Xas Single Heterojunctions - Observation Of Parity-Forbidden Landau-Level Transitions, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz, R. Jones, K. K. Bajaj Oct 1994

Magnetoluminescence Studies In Gaas-Alxga1-Xas Single Heterojunctions - Observation Of Parity-Forbidden Landau-Level Transitions, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz, R. Jones, K. K. Bajaj

Physics Faculty Publications

We have observed a number of allowed and parity-forbidden Landau-level transitions in a modulation-doped GaAs-AlxGa1-xAs single heterojunction structure using photoluminescence-excitation spectroscopy at 2 K. The GaAs layer in this structure is 5000 Å thick. From the allowed Landau-level transitions we determine the reduced mass of the electron-hole pair to be 0.07me. Using a heavy-hole mass of 0.45me, we determine the average value of the electron effective mass to be 0.084me. From the parity-forbidden transitions where the hole Landau level is the same but the electron Landau levels are different, we …

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Rigorous Justification Of The Localized Approximation To The Beam Shape Coefficients In Generalized Lorenz-Mie Theory .1. On-Axis Beams, James A. Lock, Gérard Gouesbet Sep 1994

Rigorous Justification Of The Localized Approximation To The Beam Shape Coefficients In Generalized Lorenz-Mie Theory .1. On-Axis Beams, James A. Lock, Gérard Gouesbet

Physics Faculty Publications

Generalized Lorenz-Mie theory describes electromagnetic scattering of an arbitrary light beam by a spherical particle. The computationally most expensive feature of the theory is the evaluation of the beam-shape coefficients, which give the decomposition of the incident light beam into partial waves. The so-called localized approximation to these coefficients for a focused Gaussian beam is an analytical function whose use greatly simplifies Gaussian-beam scattering calculations. A mathematical justification and physical interpretation of the localized approximation is presented for on-axis beams.

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Radiative Recombination At The Alxga1-Xas-Gaas Heterostructure Interface By 2-Dimensional Excitons, D. C. Reynolds, David C. Look, B. Jogai, Phil W. Yu, K. Evans, C. E. Stutz, L. Radomsky Sep 1994

Radiative Recombination At The Alxga1-Xas-Gaas Heterostructure Interface By 2-Dimensional Excitons, D. C. Reynolds, David C. Look, B. Jogai, Phil W. Yu, K. Evans, C. E. Stutz, L. Radomsky

Physics Faculty Publications

Radiative recombination from the AlxGa1-xAs-GaAs heterostructure interface was investigated using photoluminescence and photoluminescence-excitation spectroscopy in modulation-doped and undoped samples. This emission is identified as H-band A, resulting from an indirect excitonlike transition in real space. The exciton is made up of a two-dimensional electron in the interface notch and a valence-band hole in the neutral region, having a binding energy of 1.8 meV. The H-band A exciton is directly excited by a free exciton making a vertical transition in real space. H-band A may be a distortion of the vertical direct free exciton in real space …

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Light And Color In The Open Air: Introduction By The Feature Editors, James A. Lock Jul 1994

Light And Color In The Open Air: Introduction By The Feature Editors, James A. Lock

Physics Faculty Publications

The natural environment is still rich in new observable phenomena despite centuries of scientific observation. Reflecting this fact, the papers in this feature issue of Applied Optics report the observation and analysis of both new and well-known naked-eye optical phenomena.

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Rainbow Scattering By A Coated Sphere, James A. Lock, J. Michael Jamison, Chih-Yang Lin Jul 1994

Rainbow Scattering By A Coated Sphere, James A. Lock, J. Michael Jamison, Chih-Yang Lin

Physics Faculty Publications

We examine the behavior of the first-order rainbow for a coated sphere by using both ray theory and Aden-Kerker wave theory as the radius of the core alpha12 and the thickness of the coating delta are varied. As the ratio delta/alpha12 increases from 10(-4) to 0.33, we find three classes of rainbow phenomena that cannot occur for a homogeneous-sphere rainbow. For delta/alpha12 less than or similar to 10(-3), the rainbow intensity is an oscillatory function of the coating thickness, for delta/alpha12 almost-equal-to 10(-2), the first-order rainbow breaks into a pair of twin rainbows, and for delta/alpha12 almost-equal-to 0.33, various rainbow-extinction …

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Correlated Light Scattering By A Dense Distribution Of Condensation Droplets On A Window Pane, James A. Lock, Chin-Lien Chiu Jul 1994

Correlated Light Scattering By A Dense Distribution Of Condensation Droplets On A Window Pane, James A. Lock, Chin-Lien Chiu

Physics Faculty Publications

An analytical model of the scattering structure factor for an assembly of noninteracting hard disks has recently appeared in the literature [Phys. Rev. A 42, 5978-5989 (1990)]. We employ this model to calculate correlated light scattering by monodispersions and binary mixtures of condensation droplets on a window pane. We find that an area fraction of f greater-than-or-equal-to 0.6 is required for producing the near-forward direction scattering suppression and that a moderately wide polydispersion of droplet sizes is capable of producing the experimentally observed bright ring of colored light.

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Deep Traps In Molecular-Beam-Epitaxial Gaas Grown At Low Temperatures, David C. Look, Z-Q. Fang, H. Yamamoto, J. R. Sizelove, M. G. Mier, C. E. Stutz Jul 1994

Deep Traps In Molecular-Beam-Epitaxial Gaas Grown At Low Temperatures, David C. Look, Z-Q. Fang, H. Yamamoto, J. R. Sizelove, M. G. Mier, C. E. Stutz

Physics Faculty Publications

Deep‐level transient spectroscopy has been performed on Si‐doped GaAs layers grown by molecular‐beam epitaxy at substrate temperatures of 400–450 °C. The λ effect is taken into account and overlapping peaks are analyzed numerically. An 0.65 eV electron trap of concentration 2×1016 cm−3 is believed to be related to the AsGa‐associated 0.65 eV Hall‐effect center, and also to the trap EB4 found in electron‐irradiated GaAs.

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Magneto-Hall Characterization Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Structures, David C. Look, B. Jogai, C. E. Stutz, R. E. Sherriff, G. C. Desalvo, T. J. Rogers, J. M. Ballingall Jul 1994

Magneto-Hall Characterization Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Structures, David C. Look, B. Jogai, C. E. Stutz, R. E. Sherriff, G. C. Desalvo, T. J. Rogers, J. M. Ballingall

Physics Faculty Publications

Conventional Hall‐effect determination of the two‐dimensional electron gas (2DEG) concentration n2D in pseudomorphic high electron mobility transistor structures is invalid because of interference from the highly doped GaAs cap. Furthermore, the usual methods of dealing with this cap‐interference problem, namely, (1) etching off the cap totally, (2) etching the cap until the mobility reaches a maximum, or (3) growing a separate structure with a thin, depleted cap, in general, give n2D values that are too low. However, we show here that magnetic‐field‐dependent Hall (M‐Hall) measurements can separately determine the carrier concentrations and mobilities in the cap and 2DEG …

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Observation Of A Metastable Defect Transition In Gaas, David C. Look, Z-Q. Fang, J. R. Sizelove Jun 1994

Observation Of A Metastable Defect Transition In Gaas, David C. Look, Z-Q. Fang, J. R. Sizelove

Physics Faculty Publications

We show that the well-known 0.15-eV donor in bulk GaAs quenches under IR-light illumination and that the quenched (metastable) state has an electronic transition energy about 0.14 eV deeper than the ground state and can be observed by temperature-dependent-resistivity and Hall-effect measurements. The quenched state thermally recovers by an Auger-like process at a rate of r=2.3×10-12 nvn exp(-0.18/kT). Many of the properties exhibited by this donor are similar to those predicted theoretically for the complex defect AsGa-VAs.

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Scaling Behavior Of Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher May 1994

Scaling Behavior Of Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher

Physics Faculty Publications

In nematic liquid crystals, director fluctuations correpond to the dynamical mode that is critical for all temperatures in zero external fields. The Hurst exponent characterizes the temporal behavior of the mean square displacement of director fluctuations, 〈[δn(r,t)-δn(r,0)]2〉∼t2H. We find H=1/2 in finite fields and H=3/4 in zero field. This result differs from that of Zhang et al. [Phys. Rev. Lett. 70, 1834 (1993)] who find a Hurst exponent that varies continuously from H≃1 in zero field to H≃1/2 in moderate fields.

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Low-Temperature Growth Of High Resistivity Gaas By Photoassisted Metalorganic Chemical Vapor Deposition, J. C. Roberts, K. S. Boutros, S. M. Bedair, David C. Look May 1994

Low-Temperature Growth Of High Resistivity Gaas By Photoassisted Metalorganic Chemical Vapor Deposition, J. C. Roberts, K. S. Boutros, S. M. Bedair, David C. Look

Physics Faculty Publications

We report the photoassisted low‐temperature (LT) metalorganic chemical vapor deposition (MOCVD) of high resistivity GaAs. The undoped as‐grown GaAs exhibits a resistivity of ∼106 Ω cm, which is the highest reported for undoped material grown in the MOCVD environment. Photoassisted growth of doped and undoped device quality GaAs has been achieved at a substrate temperature of 400 °C in a modified atmospheric pressure MOCVD reactor. By using silane as a dopant gas, the LT photoassisted doped films have high levels of doping and electron mobilities comparable to those achieved by MOCVD for growth temperatures, Tg≳600 °C.

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