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Articles 1 - 24 of 24
Full-Text Articles in Physics
Far-Field Scattering Of A Non-Gaussian Off-Axis Axisymmetric Laser Beam By A Spherical Particle, James A. Lock, Joseph T. Hodges
Far-Field Scattering Of A Non-Gaussian Off-Axis Axisymmetric Laser Beam By A Spherical Particle, James A. Lock, Joseph T. Hodges
Physics Faculty Publications
Experimental laser beam profiles often deviate somewhat from the ideal Gaussian shape of the axisymmetric TEM(00) laser mode. To take these deviations into account when calculating light scattering of an off-axis beam by a spherical particle, we use our phase-modeling method to approximate the beam-shape coefficients in the partial wave expansion of an experimental laser beam. We then use these beam-shape coefficients to compute the near-forward direction scattering of the off-axis beam by the particle. Our results are compared with laboratory data, and we give a physical interpretation of the various features observed in the angular scattering patterns. (C) 1996 …
Effect Of Multistep Wafer-Annealing On Main Traps In Czochralski-Grown Semi-Insulating Gaas, Z-Q. Fang, David C. Look, H. Yamamoto, H. Shimakura
Effect Of Multistep Wafer-Annealing On Main Traps In Czochralski-Grown Semi-Insulating Gaas, Z-Q. Fang, David C. Look, H. Yamamoto, H. Shimakura
Physics Faculty Publications
Both multistep wafer‐annealed (MWA) and ingot‐annealed semi‐insulating (SI) GaAs wafers, grown by the Czochralski technique, are characterized by using normalized thermally stimulated current (NTSC) spectroscopy. Two main NTSC traps, T3 at 200 K and T5 at 140 K, which are thought to be related to arsenic vacancy defects, are found to be largely suppressed by MWA processes, especially by a new MWA process. Concomitant with a decrease of these traps, a significant increase of the threshold electrical field for both the thermal quenching of T5 and the low‐temperature photocurrent saturation has been observed
An Exactly Soluble Fresnel Diffraction Model Of Two-Slit Interference, James A. Lock
An Exactly Soluble Fresnel Diffraction Model Of Two-Slit Interference, James A. Lock
Physics Faculty Publications
Using the formalism of Fresnel diffraction, we examine the diffraction and interference of two initially widely separated parallel Gaussian light beams. This two-beam configuration is a version of Young's two-slit interference problem that is free of the mathematical complexity that occurs in most Fresnel diffraction calculations. As a result, it clearly and simply illustrates the transition from ray optics to wave interference. (C) 1996 American Association of Physics Teachers.
Simple Measurement Of 300 K Electron Capture Cross Section For El2 In Gaas, David C. Look, Z-Q. Fang
Simple Measurement Of 300 K Electron Capture Cross Section For El2 In Gaas, David C. Look, Z-Q. Fang
Physics Faculty Publications
A simple experiment involving only the measurement of dark current Idark and 1.1 μm photocurrent IPC in semi‐insulating (SI) GaAs allows an accurate determination of the electron capture cross section σn for the important defect EL2 in GaAs. For 45 SI GaAs samples, from 12 different boules, grown by three different techniques, we find that IPC/Idark=1.96±0.05 at 300 K. This relationship gives σn=1.4±0.4×10−16 cm2, which is compared to previously estimated values.
Deep-Center Hopping Conduction In Gan, David C. Look, D. C. Reynolds, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç
Deep-Center Hopping Conduction In Gan, David C. Look, D. C. Reynolds, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç
Physics Faculty Publications
Molecular‐beam‐epitaxial GaN layers change from strongly conductive (ρ≂10−2 Ω cm at 300 K) to semi‐insulating (ρ≂106 Ω cm) as the N flux is increased. Layers grown at low fluxes show strong n‐type conduction, with transport in the conduction band at high temperatures and in a shallow donor band at low temperatures. For layers grown at high N fluxes, the Hall coefficients become too small to measure, suggesting hopping conduction among deep centers. The temperature‐dependent resistivity data are most consistent with multiphonon, rather than single‐phonon, hopping.
On Hall Scattering Factors For Holes In Gaas, David C. Look, C. E. Stutz, J. R. Sizelove, K. R. Evans
On Hall Scattering Factors For Holes In Gaas, David C. Look, C. E. Stutz, J. R. Sizelove, K. R. Evans
Physics Faculty Publications
Hall scattering factors for electrons and holes in molecular beam epitaxial GaAs layers have been determined by comparing carrier concentrations measured by the Hall effect with those measured by the electrochemical capacitance–voltage technique. The conclusion is that both the electron and hole scattering factors are near unity for n ranging from 2×1016 to 7×1017 cm−3, and p ranging from 5×1016 to 4×1019 cm−3. This conclusion is consistent with the present theory for electrons, but not with that for holes.
Far-Field Scattering Of An Axisymmetric Laser Beam Of Arbitrary Profile By An On-Axis Spherical Particle, James A. Lock, Joseph T. Hodges
Far-Field Scattering Of An Axisymmetric Laser Beam Of Arbitrary Profile By An On-Axis Spherical Particle, James A. Lock, Joseph T. Hodges
Physics Faculty Publications
Experimental laser beam profiles often deviate somewhat from the ideal Gaussian shape of the TEM(00) laser mode. In order to take these deviations into account when calculating light scattering, we propose a method for approximating the beam shape coefficients in the partial wave expansion of an experimental laser beam. We then compute scattering by a single dielectric spherical particle placed on the beam's axis using this method and compare our results to laboratory data. Our model calculations fit the laboratory data well. (C) 1996 Optical Society of America
Ground And Excited State Exciton Spectra From Gan Grown By Molecular-Beam Epitaxy, D. C. Reynolds, David C. Look, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç, D. N. Talwar
Ground And Excited State Exciton Spectra From Gan Grown By Molecular-Beam Epitaxy, D. C. Reynolds, David C. Look, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç, D. N. Talwar
Physics Faculty Publications
The emission and reflection spectra of GaN have been investigated in the intrinsic region and the data have been interpreted in terms of the wurtzite crystal band structure. Three intrinsic exciton transitions have been observed, one associated with each of the valence bands. Exciton excited states associated with the two top valence bands were also observed. The exciton binding energies, the band-gap energies, and the exciton Bohr radii are all reported along with the dielectric constant and the spin-orbit and crystal-field parameters for GaN.
Thermally Stimulated Current Trap In Gan, David C. Look, Z-Q. Fang, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç
Thermally Stimulated Current Trap In Gan, David C. Look, Z-Q. Fang, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, H. Morkoç
Physics Faculty Publications
A thermally stimulated current peak, occurring at 100 K for a heating rate of 0.4 K/s, has been found in semi‐insulating GaN grown by molecular beam epitaxy. This peak has contributions from two traps, with the main trap described by the following parameters: emission thermal activation energy E≂90±2 meV, effective capture cross‐section σ≂3±1×10−22 cm−2, and Nμτ≂3±1 × 1014 cm−1 V −1, where N is the trap concentration, μ the mobility, and τ the free‐carrier lifetime. This trap is much deeper than the typical shallow donors in conducting GaN, but shallower than any …
Stability Analysis Of A Model For The Defect Structure Of Yba2cu3ox, Gregory Kozlowski, Tom Svobodny
Stability Analysis Of A Model For The Defect Structure Of Yba2cu3ox, Gregory Kozlowski, Tom Svobodny
Physics Faculty Publications
Unusual microstructures of YBa2Cu3Ox (123) crystals have been observed. These structures have been shown to pass very high transport currents. A model of the solidification of 123 from a melt with Y2BaCuO5 (211) inclusions indicates that the stability of the 123 interface can depend on the sizes of the 211 inclusions. The observed formations are interpreted in the light of this instability.
Electron Impact Vibrational Excitation Cross Sections Of Sif4, R. Nagpal, A. Garscadden, Jerry D. Clark
Electron Impact Vibrational Excitation Cross Sections Of Sif4, R. Nagpal, A. Garscadden, Jerry D. Clark
Physics Faculty Publications
Electron drift velocities in mixtures of SiF4 and Ar have been measured using a pulsed‐Townsend type drift tube. A set of vibrational excitation cross sections of electron scattering in SiF4 has been subsequently determined by the swarm analyses of measured transport data in highly dilute SiF4−Ar mixtures. The derived cross sections are consistent with the electron transport properties over an order of magnitude in SiF4 concentration in gas mixtures, thus providing evidence that the main features of their near threshold behavior, and of their absolute magnitude have been captured.
Ionization Of Rydberg Wave Packets By Subpicosecond, Half-Cycle Electromagnetic Pulses, C. Raman, C. W. S. Conover, C. I. Sukenik, P. H. Bucksbaum
Ionization Of Rydberg Wave Packets By Subpicosecond, Half-Cycle Electromagnetic Pulses, C. Raman, C. W. S. Conover, C. I. Sukenik, P. H. Bucksbaum
Physics Faculty Publications
We have studied the ionization of Rydberg wave packets by subpicosecond, nearly unipolar electromagnetic field pulses, in the regime where the duration of the electric field is less than the classical Kepler orbit time 2n3 for the wave packet. In contrast to the subpicosecond optical pulses, subpicosecond field pulses can ionize wave packets when the probability density near the inner turning point of the Kepler orbit is low. The transfer of energy from the electromagnetic field to essentially free electrons demonstrates that the pulses are substantially shorter than one field cycle. Such half-cycle pulses can track the wave packet throughout …
Spectroscopy Of Atoms Confined To The Single Node Of A Standing Wave In A Parallel-Plate Cavity, V. Sandoghar, C. I. Sukenik, S. Haroche, E. A. Hinds
Spectroscopy Of Atoms Confined To The Single Node Of A Standing Wave In A Parallel-Plate Cavity, V. Sandoghar, C. I. Sukenik, S. Haroche, E. A. Hinds
Physics Faculty Publications
We have performed spectroscopy on sodium atoms that are optically channeled in the single node of a laser standing wave set up across a parallel-plate cavity. Using this technique we have extended our previous measurement of the Lennard-Jones van der Waals energy-level shift [Sandoghdar et al., Phys. Rev. Lett. 68, 3432 (1992)] down to a cavity width of ~500 nm. We discuss the applications of this technique to the precise measurement of atom-surface distances.
Ray Scattering By An Arbitrarily Oriented Spheroid .Ii. Transmission And Cross-Polarization Effects, James A. Lock
Ray Scattering By An Arbitrarily Oriented Spheroid .Ii. Transmission And Cross-Polarization Effects, James A. Lock
Physics Faculty Publications
Transmission of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit is considered in the context of ray theory. The transmitted electric field is added to the diffracted plus reflected ray-theory electric field that was previously derived to obtain an approximation to the far-zone scattered intensity in the forward hemisphere. Two different types of cross-polarization effects are found. These are (a) a rotation of the polarization state of the transmitted rays from when they are referenced with respect to their entrance into the spheroid to when they are referenced with respect to their exit from …
Ray Scattering By An Arbitrarily Oriented Spheroid .I. Diffraction And Specular Reflection, James A. Lock
Ray Scattering By An Arbitrarily Oriented Spheroid .I. Diffraction And Specular Reflection, James A. Lock
Physics Faculty Publications
Diffraction and reflection of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit are considered in the context of ray theory. A closed-form solution for both diffraction and reflection is obtained, and the polarization character of the diffracted plus reflected electric field is obtained. It is found that the magnitude of the reflected electric field is multivalued for forward scattering. This is interpreted in terms of the variation of the spheroid's Gaussian curvature at the points where grazing ray incidence occurs.
Tribological Properties Of Fullerenes C60 And C70 Microparticles, Wei Zao, Jinke Tang, Ashok Puri, Ray L. Sweany, Yuxin Li, Liquan Chen
Tribological Properties Of Fullerenes C60 And C70 Microparticles, Wei Zao, Jinke Tang, Ashok Puri, Ray L. Sweany, Yuxin Li, Liquan Chen
Physics Faculty Publications
The frictional behaviors of fullerenes C60 and C70 were studied because they were speculated to be solid lubricants. For the sublimated pure C60 films on Si(001), a high friction coefficient (0.55–0.8) was observed under different loads and pin materials. For the C70 film, the friction coefficient showed a pin dependence, which changed from 0.5 with an Al2O3 pin to about 0.9 with a 440 stainless steel pin. The relatively high friction coefficients of C60 and C70 films were due to the tendency of the C60 and C70 particles to …
Residential Radon-222 Exposure And Lung Cancer: Exposure Assessment Methodology, R. William Field, Daniel J. Steck, Charles F. Lynch, Christine P. Brus, John S. Neuberger, Burton C. Kross
Residential Radon-222 Exposure And Lung Cancer: Exposure Assessment Methodology, R. William Field, Daniel J. Steck, Charles F. Lynch, Christine P. Brus, John S. Neuberger, Burton C. Kross
Physics Faculty Publications
Although occupational epidemiological studies and animal experimentation provide strong evidence that radon-222 (222Rn) progeny exposure causes lung cancer, residential epidemiological studies have not confirmed this association. Past residential epidemiological studies have yielded contradictory findings. Exposure misclassification has seriously compromised the ability of these studies to detect whether an association exists between 222Rn exposure and lung cancer. Misclassification of 222Rn exposure has arisen primarily from: 1) detector measurement error; 2) failure to consider temporal and spatial 222Rn variations within a home; 3) missing data from previously occupied homes that currently are inaccessible; 4) failure to link …
Effects Of In Profile On Material And Device Properties Of Algaas/Ingaas/Gaas High Electron Mobility Transistors, David C. Look, B. Jogai, R. Kaspi, J. L. Ebel, K. R. Evans, R. L. Jones, K. Nakano, R. E. Sherriff, C. E. Stutz, G. C. Desalvo, C. Ito
Effects Of In Profile On Material And Device Properties Of Algaas/Ingaas/Gaas High Electron Mobility Transistors, David C. Look, B. Jogai, R. Kaspi, J. L. Ebel, K. R. Evans, R. L. Jones, K. Nakano, R. E. Sherriff, C. E. Stutz, G. C. Desalvo, C. Ito
Physics Faculty Publications
The molecular‐beam‐epitaxial growth of InxGa1−xAs on GaAs or AlyGa1−yAs leads to a variation of In content with depth, due to In segregation. However, by predepositing In at the beginning of InxGa1−xAs growth, and also thermally removing the excess In at the end, we can produce a layer with the ideal ‘‘square’’ In profile. We find that the performance of AlyGa1−yAs/InxGa1−xAs/GaAs high electron mobility transistors is most enhanced by the predeposition step alone.
Wet Chemical Digital Etching Of Gaas At Room Temperature, Gregory C. Desalvo, Christopher A. Bozada, John L. Ebel, David C. Look, John P. Barrette, Charles L. A. Cerny, Ross W. Dettmer, James K. Gillespie, Charles K. Havasy, Thomas J. Jenkins, Kenichi Nakano, Carl I. Pettiford, Tony K. Quach, James S. Sewell, G. David Via
Wet Chemical Digital Etching Of Gaas At Room Temperature, Gregory C. Desalvo, Christopher A. Bozada, John L. Ebel, David C. Look, John P. Barrette, Charles L. A. Cerny, Ross W. Dettmer, James K. Gillespie, Charles K. Havasy, Thomas J. Jenkins, Kenichi Nakano, Carl I. Pettiford, Tony K. Quach, James S. Sewell, G. David Via
Physics Faculty Publications
A new room temperature wet chemical digital etching technique for GaAs is presented which uses hydrogen peroxide and an acid in a two‐step etching process to remove GaAs in approximately 15 Å increments. In the first step, GaAs is oxidized by 30% hydrogen peroxide to form an oxide layer that is diffusion limited to a thickness of 14 to 17 Å for time periods from 15 to 120 s. The second step removes this oxide layer with an acid that does not attack unoxidized GaAs. These steps are repeated in succession until the desired etch depth is obtained. Experimental results …
Magnetophotoluminescence Study Of Excited States Associated With Donor Bound Excitons In High-Purity Gaas, D. C. Reynolds, David C. Look, B. Jogai, G. L. Mccoy, K. K. Bajaj
Magnetophotoluminescence Study Of Excited States Associated With Donor Bound Excitons In High-Purity Gaas, D. C. Reynolds, David C. Look, B. Jogai, G. L. Mccoy, K. K. Bajaj
Physics Faculty Publications
Detailed magnetic-field splitting of the two rotator states designated as (Γ6+Γ8, J=5/2) and (Γ7, J=1/2) associated with donor bound excitons in high-purity epitaxial GaAs is observed in magnetophotoluminescence spectra. These two states are associated with the light-hole mass and are split by the spin-orbit interaction. The ordering in energy of these two states agrees with that predicted by theory. Also observed are the rotator states in which, after the radiative collapse of the exciton, the donor is left in the excited states. A good agreement between the energies of the excited states of the …
Deep Inelastic Scattering Of Polarized Electrons By Polarized ³He And The Study Of The Neutron Spin Structure, P. L. Anthony, R. G. Arnold, H. R. Band, H. Borel, P. E. Bosted, V. Breton, G. D. Cates, T. E. Chupp, F. S. Dietrich, J. Dunne, R. Erbacher, J. Felbauum, H. Fonvielle, R. Gearhart, R. Holmes, E. W. Hughes, J. R. Johnson, D. Kawall, C. Keppel, S. E. Kuhn, R. M. Lombard-Nelsen, J. Marroncle, T. Maruyama, W. Meyer, Z.- E. Meziani, H. Middleton, J. Morgenstern, N. R. Newbury, G. G. Petratos, R Pitthan, R. Prepost, Y. Robin, S. E. Rock, S. H. Rokni, G. Shapiro, T. Smith, P. A. Souder, M. Spengos, F. Staley, L. M. Stuart, Z. M. Szlata, Y. Terrien, A. K. Thompson, J. L. White, M. Woods, J. Xu, C. C. Young, G. Zaplac, E142 Collaboration
Deep Inelastic Scattering Of Polarized Electrons By Polarized ³He And The Study Of The Neutron Spin Structure, P. L. Anthony, R. G. Arnold, H. R. Band, H. Borel, P. E. Bosted, V. Breton, G. D. Cates, T. E. Chupp, F. S. Dietrich, J. Dunne, R. Erbacher, J. Felbauum, H. Fonvielle, R. Gearhart, R. Holmes, E. W. Hughes, J. R. Johnson, D. Kawall, C. Keppel, S. E. Kuhn, R. M. Lombard-Nelsen, J. Marroncle, T. Maruyama, W. Meyer, Z.- E. Meziani, H. Middleton, J. Morgenstern, N. R. Newbury, G. G. Petratos, R Pitthan, R. Prepost, Y. Robin, S. E. Rock, S. H. Rokni, G. Shapiro, T. Smith, P. A. Souder, M. Spengos, F. Staley, L. M. Stuart, Z. M. Szlata, Y. Terrien, A. K. Thompson, J. L. White, M. Woods, J. Xu, C. C. Young, G. Zaplac, E142 Collaboration
Physics Faculty Publications
The neutron longitudinal and transverse asymmetries A1n and A2n have been extracted from deep inelastic scattering of polarized electrons by a polarized 3He target at incident energies of 19.42, 22.66, and 25.51 GeV. The measurement allows for the determination of the neutron spin structure functions g1n (x,Q2) and g2n(x,Q2) over the range 0.032 of 2 (GeV/c)2. The data are used for the evaluation of the Ellis-Jaffe and Bjorken sum rules. The neutron spin structure function g1n(x,Q2) is small and …
Inclusive Electron Scattering From Nuclei At X≃1, J. Arrington, P. Anthony, R. G. Arnold, 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, W. Lorenzon, A. Lung, N.C.R. Malkins, 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, K. Van Bibber, J.F.J. Van Den Brand, J. L. White, D. Winter, B. Zeidman
Inclusive Electron Scattering From Nuclei At X≃1, J. Arrington, P. Anthony, R. G. Arnold, 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, W. Lorenzon, A. Lung, N.C.R. Malkins, 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, K. Van Bibber, J.F.J. Van Den Brand, J. L. White, D. Winter, B. Zeidman
Physics Faculty Publications
The inclusive A(e,e') cross section for x≃1 was measured on 2H, C, Fe, and Au for momentum transfers Q2 from 1 to 6.8 (GeV/c)2. The scaling behavior of the data was examined in the region of transition from y scaling to x scaling. Throughout this transitional region, the data exhibit ξ scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.
Operator Expansion For High-Energy Scattering, Ian Balitsky
Operator Expansion For High-Energy Scattering, Ian Balitsky
Physics Faculty Publications
I demonstrate that the leading logarithms for high-energy scattering can be obtained as a result of evolution of the non-local operators—straight-line ordered gauge factors—with respect to the slope of the straight line.
Q² Evolution Of Chiral-Odd Twist-3 Distributions HL(𝓍, Q²) And E(𝓍, Q²) In Large- NC Qcd, I.I. Balitsky, V. M. Braun, K. Koike, K. Tanaka
Q² Evolution Of Chiral-Odd Twist-3 Distributions HL(𝓍, Q²) And E(𝓍, Q²) In Large- NC Qcd, I.I. Balitsky, V. M. Braun, K. Koike, K. Tanaka
Physics Faculty Publications
We prove that the twist-3 chiral-odd parton distributions obey simple Gribov-Lipatov-Altarelli-Parisi evolution equations in the limit Nc → ∞ and give analytic results for the corresponding anomalous dimensions. To this end we introduce an evolution equation for the corresponding three-particle twist-3 parton correlation functions and find an exact analytic solution. For large values of n (operator dimension) we are further able to collect all corrections subleading in Nc, so our final results are valid to O((1/N2c)ln(n)/n) accuracy