Physics Commons^™

Impurity Photomagnetoelectric Effect: Application To Semi-Insulating Gaas, David C. Look

Physics Faculty Publications

The theories of the photomagnetoelectric (PME) and photoconductivity (PC) effects in semiconductors are extended to include unequal excitation rates of holes and electrons, as might be expected from impurity photo-excitation. The results are applied to two semi-insulating Cr-doped GaAs crystals, which exhibit mixed conductivity. It is seen that the PC and PME effects give complementary information on the holes and electrons. In the impurity excitation region the PME current responds strongly to changes in the absorption coefficient, and provides a convenient way to study this quantity.

The Electrical Characterization Of Semi‐Insulating Gaas: A Correlation With Mass‐Spectrographic Analysis, David C. Look

Physics Faculty Publications

The room‐temperature electrical properties of 28 semi‐insulating GaAs crystals have been determined by using a mixed‐conductivity analysis. It is shown that for most of these samples, such an analysis gives good accuracy for the electron mobility μ_n and electron concentration n, but poorer accuracy for the hole mobility μ_p, hole concentration p, and intrinsic concentration n_i. The intrinsic concentration is determined at 296 °K to be n_i ≈ (1.7±0.4) ×10⁶ cm⁻³, which compares favorably with the theoretical value deduced from the band gap and the effective masses. From a …

Intense Flowing Hollow Cathode Lamp, F. H.K. Rambow, Laird D. Schearer

Physics Faculty Research & Creative Works

An inexpensive, simple, and versatile hollow cathode lamp has been developed which produces intense ion resonance radiation of about 1 mW into 4π/25 sr. The lamp employs flowing helium gas to sustain the discharge. The construction permits a variety of cathode seed materials to be easily interchanged. The same lamp has been used as a source of ion resonance radiation for Ca, Ba, Zn, Mg, Sr, Yb, and Eu.

Alignment Of Helium Excited By Thin Carbon Foils, R. D. Hight, R. M. Schectman, H. G. Berry, G. Gabrielse, Timothy J. Gay

Timothy J. Gay Publications

We have measured the linear polarization of the 5016-Å, 2s ¹S-3p ¹P transition of Hei excited by a thin carbon foil perpendicular to the incident He⁺ beam at ion energies 50-500 keV. We find that the alignment of the 3p ¹P term depends upon the beam current density within the range (2- 150 μA cm^-2) measured. Oscillations in the dependence of both M / I (the linear polarization fraction) upon energy and the current density variation of M / I with energy are observed. We discuss possible origins of these …

Alignment Of Helium Excited By Thin Carbon Foils, R. D. Hight, R. M. Schectman, H. G. Berry, G. Gabrielse, Timothy J. Gay

Timothy J. Gay Publications

We have measured the linear polarization of the 5016-Å, 2s 1S-3p 1P transition of Hei excited by a thin carbon foil perpendicular to the incident He+ beam at ion energies 50-500 keV. We find that the alignment of the 3p 1P term depends upon the beam current density within the range (2- 150 μA cm-2) measured. Oscillations in the dependence of both M / I (the linear polarization fraction) upon energy and the current density variation of M / I with energy are observed. We discuss possible origins of these variations.

Ferromagneticlike Resonance Behavior In Superfluid 3he-B, Richard A. Webb

Faculty Publications

Nonlinear cw NMR behavior, similar to that observed on ferromagnets at high rf powers, has been observed in superfluid ³He-B using a superconducting quantum interference device (SQUID) magnetometer in fields of 31, 102, 180, and 308 Oe and at a pressure of 21 bar. It is observed that beyond some threshold value of the transverse H₁ field the z component of magnetization anomalously decreases and is followed by a rapid increase back to the normal resonance curve as the frequency of the H₁ field is swept through resonance.

The Water Monomer On The Basal Plane Of Ice Iₕ: An Effective Pair, Central Force Potential Model Of The Static Interaction, Jerry Kiefer, Barbara N. Hale

Physics Faculty Research & Creative Works

The H₂O-H₂O intermolecular central force potential of Lemberg and Stillinger is used to obtain optimal binding energy surfaces, vibrational frequencies, and bonding configurations of an adsorbed water monomer on a model basal plane of ice I_h. The monomer interacts (pairwise) with 50 molecules arranged in two layers of the unrelaxed bulk ice lattice. The results of calculations for three model surface sites of differing proton arrangement indicate the existence of diffusion barriers of the order of 2.5 kcal/mole and optimal monomer bonding sites at about 9 kcal/mole with nonepitaxial characteristics. Perspective computer-drawn plots of …

Single-Element Rotating-Polarizer Ellipsometer For Film-Substrate Systems, A.-R. M. Zaghloul, R. M.A. Azzam

Electrical Engineering Faculty Publications

A novel and very simple ellipsometer for the characterization of film-substrate systems that employs one rotating optical element (a polarizer) is proposed. The ellipsometer is based on detecting the angles of incidence at which a film-substrate system has equal amplitude attenuations for light polarized parallel (p) and perpendicular (s) to the plane of incidence. At a certain wavelength, the film thickness of the filmsubstrate system has to lie within permissible-thickness bands (PTB) for the technique to apply.

The Use Of Nuclear Reactions And Sims For Quantitative Depth Profiling Of Hydrogen In Amorphous Silicon, David D. Allred, G. J. Clark, C. W. White, B. R. Appleton, C. W. Magee, D. E. Carlson

Faculty Publications

Depth profiles for hydrogen in amorphous silicon have been determined by the use of resonant nuclear reactions [1H(15N,αγ)12C and 1H(19F,αγ)16O] and by secondary ion mass spectroscopy (SIMS). Independent calibration procedures were used for the two techniques. Measurements were made on the same amorphous silicon film to provide a direct comparison of the two hydrogen analysis techniques. The hydrogen concentration in the bulk of the film was determined to be about 9 at % H. The SIMS results agree with the resonant nuclear reaction results to within 10%, which demonstrates that quantitative hydrogen depth profiles can be obtained by SIMS analysis …

Erratum: Excitation Of The N=2 State Of Atomic Hydrogen By Electron Impact In The Distorted-Wave Approximation (Physical Review A (1977) 16, 2), Ralph V. Calhoun, Don H. Madison, W. Neil Shelton

Physics Faculty Research & Creative Works

No abstract provided.

X-Ray Investigation Of The Critical Exponent Η In Argon, Harold D. Bale, J. S. Lin, Duane A. Dolejsi, James L. Casteel, Oran Allan Pringle, Paul W. Schmidt

Physics Faculty Research & Creative Works

Measurements were made of the small-angle x-ray scattering intensity from argon near the critical point. After the scattering curves are corrected for all known effects except those resulting from irrelevant variables, a value of the critical exponent η=0.09±0.02 is obtained, while if a correction for the estimated effect of irrelevant variables is also made, η=0.03±0.03. The scattering data for argon therefore show that if irrelevant variables can be neglected, the critical exponent η for argon is in good agreement with the value obtained by Warkulwiz, Mozer, and Green from small-angle neutron scattering data for neon. These values of η, however, …

³⁴Cl Via The ³²S(³He,P) Reaction, Oleksa-Myron Bilaniuk, D. J. Crozier, H. T. Fortune, R. Middleton

Physics & Astronomy Faculty Works

The structure of ³⁴Cl has been investigated with the reaction ³²S(³He,p). Angular distributions were obtained for 29 levels below 5 MeV excitation. Extracted L values, combined with previous information, allow J^π assignments of 3⁺ for states at 2181 and 2611 keV, negative parity for the J=4 state at 3600 keV, 2⁻ for the level at 4514 keV, and 3⁻ (2⁻) for states at 4416 and 4461 keV. Two new states are observed at excitation energies of 4693 and 4825 keV. [NUCLEAR REACTIONS ³²S(³He,p),E(³He)=18 MeV; measured σ(Ep,θ); gas H2S target. ³⁴Cl deduced levels, L, J, π.]

Behavior Of Partial Cross Sections And Branching Ratios In The Neighborhood Of A Resonance, Anthony F. Starace

Anthony F. Starace Publications

Starting from the treatment of Fano for the behavior of the total cross section in a photoionization (or electron-ion scattering) experiment in the vicinity of a resonance, we present a theoretical formula for the behavior of an individual final-state channel in the neighborhood of a resonance. This result is then used to derive another theoretical formula for the behavior of the ratio of two partial cross sections (i.e., the branching ratio) in the vicinity of a resonance. This branching-ratio formula depends on the profile parameters q, Γ, and ρ2 for the resonance, on the branching ratio outside the resonance, …

Photoelectron Angular Distributions Of S Electrons In Open-Shell Atoms, Anthony F. Starace, Robert H. Rast, Steven T. Manson

Anthony F. Starace Publications

It is shown that the photoelectron angular distribution of s electrons in an open-shell atom, having outer configuration ns²np^q, is not described by the asymmetry parameter β=2, as predicted by more approximate theories, but has dramatic variations with energy even within LS coupling. Calculations for the 3s subshell in Cl are presented as an example.

Sio2-Si Film-Substrate Reflection Polarizers For Different Mercury Spectral Lines, A.-R. M. Zaghloul, R. M.A. Azzam

Electrical Engineering Faculty Publications

No abstract provided.

Light Scattering Studies Of Transverse Sound Wave And Molecular Motion In Benzonitrile, Scott L. Whittenburg, C. H. Wang

Chemistry and Biochemistry Faculty Publications

The zero‐frequency shear wave dip appearing in the depolarized Rayleigh spectrum in benzonitrile has been studied as a function of concentration and temperature. The solution study was carried out at constant viscosity equal to the viscosity of liquid benzonitrile at each temperature. The result indicates that the presence of shear wave fine structure does not depend on the collective orientational fluctuations. The orientational and vibrational relaxation times of benzonitrile were measured at various concentrations and temperatures. The orientational relaxation times show no concentration dependence at any temperature, suggesting that the pair correlation is negligible at all concentrations. The orientational relaxation …

Measurement Of The Difference Between The Dynamic Nmr And Static Susceptibilites Of Superfluid 3he-B Using An Rf-Biased Superconducting Quantum-Interference Device, Richard A. Webb

Faculty Publications

The temperature-dependent susceptiblity of superfluid ³He-B has been measured both statically and via a pulse technique in a field of 309 G using an rf-biased superconducting quantum-interference device (SQUID). In the pressure range 26.5 to 18 bar, the dynamic NMR susceptiblity agrees qualitatively with the theoretical weak-coupling predictions for the Balian-Werthamer state. However, the static susceptiblity, measured using the same rf-biased SQUID and detection system, is significantly smaller thatn the dynamic susceptibility.

Light Scattering Studies Of Rotational And Vibrational Relaxations Of Acetonitrile In Carbon Tetrachloride, Scott L. Whittenburg, C. H. Wang

Chemistry and Biochemistry Faculty Publications

The rotational and vibrational relaxation times of acetonitrile–carbon tetrachloride solutions were investigated as a function of concentration, viscosity, and temperature using depolarized Rayleigh and Raman scattering. Using a Fabry‐Perot interferometer and single frequency laser source, we have shown that reliable results for the single particle orientational correlation times (τ_s) for CH₃CN can be obtained by carrying out a concentration dependent depolarized Rayleigh scattering study. Raman scattering was shown to yield inconsistent results for τ_s in CH₃CN. At constant viscosity, it was found that the Rayleigh scatteringrelaxation time (τ_Ray) of CH_{3 …}

A Study Of He+ + Ar Collisions At Energies Between 600 Ev & 1500 Ev, Alton Dull Jr.

Masters Theses & Specialist Projects

This investigation was undertaken in order to confirm and to extend earlier studies of processes whereby energy and angular momentum are transferred from external to internal degrees of freedom in low velocity collisions between ions and atoms. Specifically, this investigation sought to verify the proper functioning of a device designed to study low velocity atomic and molecular collisions, to confirm results obtained in an earlier study of spectra produced by collisions of He⁺ions with argon atoms, and to extend the energy and wavelength ranges of this study to 1500 eV and 6200 Å, respectively.

The data was in …

Measurement Of The Xenon Σ3/2:Σ1/2 Branching Ratio Within The Xe 5s5p66p(1P1) Resonance, Peter C. Kemeny, James A. R. Samson, Anthony F. Starace

Anthony F. Starace Publications

Photoionization of the 5p6 shell in xenon leaves the ion in either the 5p⁵(²P_3/2) or np⁵(²P_1/2) state. Measurements of the ²P_3/2 : ²P_1/2 branching ratio are reported within the Xe 5s5p⁶6p(¹P₁) resonance and fitted to a new theoretical expression. The maximum value of the ratio as determined by a two-parameter fit of theory to experiment is 8.8 ± 0.5 within the resonance, almost six times the nearly constant value of 1.55 found outside any resonance.

Theory And Applications Of An Atoms In Molecules Approach To The Xα -Scf Method, J. Tylicki, R.J. Hood, Gordon A. Gallup, C.J. Eckhardt

Gordon Gallup Publications

We have studied the Xα -SCF problem with an atoms in molecules approach. LCAO-molecular orbitals are used and the molecular charge and exchange densities are built up from atomic contributions. We have applied our method to CH₃F with subsequent comparison to ab initio calculations. The Xα -SCF dipole moment of CH₃F is 1.76 D compared with an experimental value of 1.79 D. We also give calculations of TCNQ and TTF with comparisons to recent Xα calculations using the overlapping sphere modification of a muffin-tin potential. Quadrupole moments for TCNQ and TTF have also been determined. The …

Mössbauer Study Of Spin Alignment In Substituted Lithium Ferrites, C. R. Abeledo, Richard B. Frankel

Physics

To explain the decrease of magnetic moment in zinc substituted lithium ferrites Dionne has proposed a model which includes canting of the B sublattice moments as zinc is substituted in the A sublattice. Mössbauer spectroscopy in external magnetic fields is applied to investigate the existence of canting in (Li₀,₅Fe₀, ₅)_1-xZn_xFe₂O₄ with x = 0 and x = 0.3. The samples used were either polycrystalline powders or circular disks cut from pressed blocks and lapped down to a thickness of 0.1 mm. In the x = 0 …

Electron Tunneling, Charge Transfer, And The Intermolecular Forces Between Two H2 Molecules, Gordon A. Gallup

Gordon Gallup Publications

The spherically averaged van der Waals potential for the system H₂–H₂ has been calculated using a nonorthogonal CI method based on SCF orbitals for the individual molecules. With suitable restrictions on the CI calculation we have isolated various contributions to the van der Waals potential, and have found that charge transfer and dispersion effects are comparable to distances corresponding to the potential minimum. The charge transfer contribution is further discussed in terms of a mechanism involving electron tunneling through the intervening space between the molecules. Our calculation gives a spherically averaged van der Waals well depth of …

Fermi-Surface Topology Of 2h-Tase2 At 4.2k, Paul D. Hambourger

Physics Faculty Publications

The magnetoresistance of single-crystal 2H-TaSe₂ in the commensurate charge-density-wave state has been measured at 4.2 K in magnetic fields up to 48 kG. The results indicate that the Fermi surface supports open orbits parallel to the [0001] direction for all orientations of magnetic field in the (0001) plane. No evidence of open orbits in other directions was observed.

Differential Energy-Loss Cross Sections For Ionization Of Atomic Hydrogen By 25-200-Kev Protons, John T. Park, Judith E. Aldag, Jacob M. George, Jerry Peacher, Jim H. Mcguire

Physics Faculty Research & Creative Works

Ionization continuum cross sections, differential in energy loss, have been determined from the energy-loss spectra of 25-, 50-, 75-, 145-, and 200-keV protons scattered from atomic hydrogen. The theoretical differential cross sections in the Glauber and Born approximations that are presented show that the theory and the experimental results for 200-keV proton impact agree very well, but below 200 keV there are differences. These differences, which are more pronounced at the lower projectile energies, may be explained in terms of charge transfer to the continuum, which is not treated in our Born and Glauber calculations of direct Coulomb ionization. The …

Can Physics Develop Reasoning?, Robert Fuller, Robert Karplus, Anton E. Lawson

Robert G. Fuller Publications

The life of every physicist is punctuated by events that lead him to discover that the way physicists see natural phenomena is different from the way non-physicists see them. Certain patterns of reasoning appear to be more common among physicists than in other groups. These include:
• focusing on the important variables (such as the force that accelerates the apple, rather than the lump it makes on your head);
• propositional logic ("if heat were a liquid it would occupy space and a cannon barrel could only contain a limited amount of heat, but this is contrary to my observations, …

Generalization Of The Rosen-Zener Model Of Noncrossing Interactions. I. Total Cross Sections, T. R. Dinterman, John B. Delos

Arts & Sciences Articles

The formalism developed previously to study electronic transitions by the curve-crossing mechanism is used to obtain a general model for transitions which take place due to the strong coupling of curves which do not cross. This exactly solvable model is a generalization of a model developed by Rosen and Zener. The model is shown to give respectable agreement with exact calculations at low velocities, and to go to the correct resonant-charge-exchange limit at high velocities. Predictions of the model are shown to give good agreement with the measured total cross sections for charge exchange in the sytem Li+ + Na⇄Li+Na+.

Generalization Of The Rosen-Zener Model Of Noncrossing Interactions. Ii. Differential Cross Sections., T. R. Dinterman, John B. Delos

Arts & Sciences Articles

The generalized Rosen-Zener model developed in the accompanying paper is used to calculate differential cross sections for a model noncrossing system, and the structure of the cross sections is explained in terms of the deflection functions. It is found that the angular threshold effects that are typical of potential-curve crossings do not appear in this noncrossing system.

Influence Of Fringing Fields On The Field-Induced Quantum Beats Of Atomic Hydrogen, Gordon W. F. Drake

Physics Publications

Calculations are presented which include exactly the effects of fringing fields on the electric-field-induced quantum beats of atomic hydrogen. The results explain some recently observed phaseshifts of the quantum beats relative to the predictions of the 'sudden approximation'. The general features produced by finite rise-time and overshoot are discussed.

Vector-Coupling Approach To Orbital And Spin-Dependent Tableau Matrix Elements In The Theory Of Complex Spectra, Gordon W. F. Drake, M. Schlesinger

Physics Publications

The power of the Young tableau scheme for labeling a complete spin-adapted basis set in the theory of complex spectra lies in one's ability to evaluate matrix elements of irreducible tensor operators directly in terms of the tableau labels and shapes. We show that the matrix-element rules stated by Harter for one-body operators can be easily derived from simple vector-coupling considerations. The graphical method of angular momentum analysis is used to derive closed-form expressions for the matrix elements of two-body operators. This study yields several interesting new relationships between spin-dependent operators and purely orbital operators. © 1977 The American Physical …