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A Study Of Ion Implanted Silicon Using Rutherford Backscattering Spectroscopy With Ion Channeling, Thomas J. Pollock

Masters Theses

Rutherford Backscattering Spectroscopy with channeling is the only nondestructive method for analyzing crystals which have been ion implanted. An RBS with channeling procedure has been established at the Accelerator Lab of Western Michigan University. It utilizes a tandem Van de Graaff accelerator for an incident helium beam, a goniometer for crystal alignment, and a computer for experimental control and data aquisition. State of the art measurements can be made with accuracies comparable to other labs. Specifically, ion implanted silicon was studied wherein crystal damage due to implanting was found to vary directly with implanting energy and fluence and was also …

Effects Of A Magnetic Field On The Thermodynamics Of Dilute Classical Spin Chains, Guoqing Hu

Masters Theses

The thermodynamics of a diluted chain of ferromagnetic classical spin in the presence of an external magnetic field is determined in the limit of the continuum model. The magnetization, susceptibility, specific heat are determined for both the isotropic Heisenberg and the classical XY models as functions of temperature, magnetic field and magnetic concentration. Scaling law for the behavior of the thermodynamic quantities in field, temperature, and magnetic concentration are obtained.

The calculations will be based on the continuum model of classical spin which was solved for the infinite chain system by McGurn and Scalapino.

University Of Missouri-Rolla Cloud Simulation Facility: Proto Ii Chamber, Daniel R. White, James L. Kassner, John C. Carstens, Donald E. Hagen, John L. Schmitt, Darryl J. Alofs, Alfred R. Hopkins, Max B. Trueblood, Max W. Alcorn, William L. Walker

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The Graduate Center for Cloud Physics Research at UMR Has Developed a Cloud Simulation Facility to Study Phenomena Occurring in Terrestrial Clouds and Fogs. the Facility Consists of a Pair of Precision Cooled-Wall Expansion Chambers Along with Extensive Supporting Equipment. the Smaller of These Chambers, Described in This Article, is Fully Operational, and is Capable of Simulating a Broad Range of In-Cloud Thermodynamic Conditions. It is Currently Being Used to Study Water Drop Growth and Evaporation for Drops Nucleated (Activated) on Well-Characterized Aerosol Particles. Measurements Have Been Made Not Only for Continuous Expansions (Simulated Updraft) But Also for Cyclic Conditions, …

Dynamics Of Multiply Charged Ion-Atom Collisions: U³²⁺+Ne, Ronald E. Olson, J. Ullrich, H. Schmidt-Bocking

Physics Faculty Research & Creative Works

Measurements and calculations are presented for the mean recoil-ion energies of Nei+ produced in 1.4 MeV u^-1 (0.33 GeV) collisions of U³²⁺ with Ne. Recoil-ion charge states i=1-8 have been observed; the mean recoil energies are low and do not exceed 1 eV until i>6. Calculations employing a newly developed n-body classical trajectory Monte Carlo method are found to yield results in qualitative agreement with the recoil-ion experiment. Calculations also are presented for the ionisation and charge exchange cross sections, the projectile energy loss and the ejected-electron energy and angular spectra. The importance of fast ejected electrons …

Observation Of Substitutional Site Preference In A Quasicrystal And Implication On Local Structure, M. Eibschütz, M. E. Lines, H. S. Chen, J. V. Waszczak, G. C. Papaefthymiou, Richard B. Frankel

Physics

A combination of magnetic susceptibility and Mössbauer measurements on quasicrystalline i-Al₇₄Mn_20-xFe_xSi₆ (0.02≤x≤7.5) establishes that Mn atoms in i-Al₇₄Mn₂₀Si₆ occupy two distinct classes of sites, and that Fe substitutes for only one of them. The two classes are distinguished by the possession or otherwise of a localized magnetic moment. The data are consistent with a structure of interconnecting Mackay icosahedra (MI) in which localized moments are possessed only by Mn atoms adjacent to "broken" MI connections. The implied connectivity of the resulting MI network is close to …

Anaerobes Pumping Iron, Richard B. Frankel

Physics

No abstract provided.

Defect Production In Electron-Irradiated, N-Type Gaas, David C. Look, J. R. Sizelove

Physics Faculty Publications

Temperature-dependent Hall-effect measurements have been performed on pure, n-type, vapor-phase epitaxial GaAs, irradiated by 1-MeV electrons at room temperature. The energies and production rates of two dominant defect centers, C₂ and C₃, are as follows: E₂ = E_C - 0.148, E₃ = E_C2 = 2.0 and τ₃ = 0.5 +/1 0.2 cm^-1, in good agreement with deep level transient spectroscopy (DLTS) data. However, the most important result of this study is a very high production rate, τ_AS ≅ +/- 1 cm^-1, for "shallow" acceptors (C …

Equivalence Of Donor And Acceptor Fits To Temperature-Dependent Hall Data: General Case, David C. Look

Physics Faculty Publications

Recently, it was shown that the usual statistical-mechanical formulation used to fit carrier concentration versus temperature data cannot distinguish between the donor or acceptor nature of one single-charge-state center. Here we generalize that result to include any number of donor and acceptor centers, of arbitrary charge multiplicity, and also show how that by fitting one particular case (e.g., every center assumed to be a donor), all of the other possible cases can be immediately solved by inspection.

Photoresistivity And Photo-Hall-Effect Topography On Semi-Insulating Gaas Wafers, David C. Look, E. Pimentel

Physics Faculty Publications

By placing a semi-insulating GaAs wafer on a fiat, rare-earth magnet, and irradiating the surface with two perpendicular slits of light to form a Greek cross configuration, it is possible to perform photoresistivity and photo-Hall-effect topography on the wafer. The technique is nondestructive in that the contacts are tiny, removable In dots which are placed only on the periphery. By varying the wavelength of the light, selective centers, such as EL2, can be mapped. We compare a 1.1-μ, photoexcited electron concentration map with a quantitative EL2 map on a 3-in. undoped, liquid-encapsulated Czochralski wafer.

Numerical Methods For Free-Free Radiative Transition Matrix Elements, Bo Gao, Anthony F. Starace

Anthony F. Starace Publications

Increasing interest in multiphoton absorption processes above the ionization threshold has led theorists to reexamine numerical techniques for calculating radiative transition matrix elements between states of a continuum electron moving at large radial distances in the field of an atom or an ion. Here it is shown that accurate free-free radial matrix elements may be obtained using the usual dipole length formula by means of a rotation at finite distance in the complex coordinate plane together with solution of the free-electron wave function's phase and amplitude at finite distance in the complex coordinate plane. The procedure is designed for use …

Normal-Metal Aharonov-Bohm Effect In The Presence Of A Transverse Electric Field, S. Washburn, H. Schmid, D. Kern, Richard A. Webb

Faculty Publications

The effects of transverse electric fields on the conductance fluctuations in an Sb loop have been studied. We show that the electric field can be used to tune the position (or phase) of Aharonov-Bohm oscillations as well as to alter the aperiodic conductance fluctuation patterns. We disucss two mechanisms which might cause the observed dependence of the fluctuation pattern on transverse electric field. The first is the electrostatic Aharonov-Bohm effect, and the second is the spatial shifting of the electron trajectories by the electric field.

Photoluminescence In Electrically Reversible (Semiconducting To Semiinsulating) Bulk Gaas, Phil W. Yu, David C. Look, W. Ford

Physics Faculty Publications

A photoluminescence study has been made of electrically reversible, bulk, liquid-encapsulated Czochralski GaAs at temperatures 2-300 K. The reversibility from the semiconducting to the semi-insulating state is made by slow or fast cooling, respectively, following a 5-h, 950°C heat treatment in an evacuated quartz ampoule. A donor level at E_c - 0.13 eV and two acceptor levels at Ev + 0.069 eV and Ev + 0.174 eV are produced after the heat treatment. Only the acceptor levels were detected by photoluminescence. A tentative model assigning the acceptor to the intrinsic defect pair V_Ga-Ga_As is discussed.

Site-Diagonal T-Matrix Expansion For Anisotropic Transport And Percolation On Bond-Disordered Lattices, Paul Ernest Parris

Physics Faculty Research & Creative Works

A study is made of the dynamical behavior of an electron or exciton undergoing anisotropic hopping on a d-dimensional bond-disordered lattice. Starting with a master equation for the site probabilities, an exact equation of motion is obtained for the probability currents that flow along the bonds connecting nearest-neighbor sites. Unlike the original master equation, the equation of motion which couples the microscopic currents contains the randomly distributed hopping rates in a form which is strictly site diagonal. The simplification that results leads to a new and exact expansion for the diffusion tensor in powers of an appropriately defined single-bond t …

Angular-Differential Studies Of Excitation In Quasi-One-Electron Collisions At "High" Energy, E. Redd, Timothy Gay, D. M. Blankenship, John T. Park, Jerry Peacher, Denver G. Seely

Physics Faculty Research & Creative Works

Qualitative differences have been observed between two types of "quasi-one-electron" collision systems. We have studied valence-electron excitation at "high" energy (relative collision velocities up to 0.5 a.u.) in the Mg⁺+He and Na⁺+H collision systems, and find that while Mg⁺+He collisions are dominated by "direct" excitation, the Na⁺+H collisions exhibit significant "molecular" excitation, even at the highest velocities. This behavior can be understood in terms of the molecular structure of the respective collision complexes, and the energy separation between the ground and first excited states of the valence electron.

Angular-Differential Studies Of Excitation In Quasi-Oneelectron Collisions At "High" Energy, E. Redd, Timothy J. Gay, D. M. Blakenship, J. T. Park, J. L. Peacher, D. G. Seely

Timothy J. Gay Publications

Qualitative differences have been observed between two types of "quasi-one-electron" collision systems. We have studied valence-electron excitation at "high" energy (relative collision velocities up to 0.5 a.u.) in the Mg⁺+He and Na⁺+H collision systems, and find that while Mg⁺+He collisions are dominated by "direct" excitation, the Na⁺+H collisions exhibit significant "molecular" excitation, even at the highest velocities. This behavior can be understood in terms of the molecular structure of the respective collision complexes, and the energy separation between the ground and first excited states of the valence electron.

Raman Detection Of The Superconducting Gap In Ba-Y-Cu-O Superconductors, K.B. Lyons, Sy_Hwang Liou, M. Hong, H.S. Chen, J. Kwo, T.J. Negran

Sy-Hwang Liou Publications

We have utilized an iodine absorption cell to enable detailed Raman studies at low frequency (down to 15 cm^-1) in a thin film of the high-temperature superconductor Ba₂YCu₃O₇. Subtraction of spectra just above and well into the superconducting phase reveals a weak broad feature (maximum near 400 cm^-1, half width at half maximum approximately 250 cm^-1), which we tentatively interpret as due to scattering near the superconducting gap. The large width of the feature may be partially related to smearing of the transition, or to gap anisotropy. Its …

A Study Of Flow Separation In Transonic Flow Using Inviscid And Viscous Cfd Schemes, James Andrew Rhodes

Mechanical & Aerospace Engineering Theses & Dissertations

A comparison of flow separation in transonic flows is made using various computational schemes which solve the Euler and the Navier-Stokes equations of fluid mechanics. The flows examined are computed using several simple two-dimensional configurations including a backward facing step and a bump in a channel. Comparison of the results obtained using shock fitting and flux vector splitting methods are presented and the results obtained using the Euler codes are compared to results on the same configurations using a code which solves the Navier-Stokes equations.

Square-Lattice Ising Model In A Weak Uniform Magnetic Field: Renormalization Group Analysis, Miron Kaufman

Physics Faculty Publications

For the two-dimensional ferromagnetic Ising critical point, I show that the known values of the critical exponents imply the absence of logarithms of the reduced temperature in the leading contributions to any field derivative of the free energy at zero magnetic field. For the square-lattice Ising antiferromagnet in a weak magnetic field, I compute the critical line T_c(H)=T_c⁰(1-0.038 023 259H²) and the leading contribution to the susceptibility χ=0.014 718 006 6H²ln(1/ǁtǁ), where t is the reduced temperature.

The Effects Of A Mandatory Early Shutdown Of Maine Yankee, Maine State Planning Office

Maine Collection

The Effects of a Mandatory Early Shutdown of Maine Yankee

Maine State Planning Office - Richard Silkman, Director (September 1987).

Contents: Introduction / Legal Issues / Economic Issues / Health and Environmental Issues / Conclusions / Appendices

High Acceptor Production Rate In Electron-Irradiated N-Type Gaas - Impact On Defect Models, David C. Look

Physics Faculty Publications

Defect production rates have been studied in electron-irradiated GaAs by temperature-dependent Hall-effect (TDR) measurements. The TDH results agree well with deep level transient spectroscopy (DLTS) results for the wen-known electron traps E1, E2, and E3, but conclusively demonstrate a much higher production rate (4 ± 1 cm^-1) of acceptors below E3 than the total of all other DLTS traps. These findings strongly affect current defect models, and, e.g., are consistent with the existence of Ga sublattice damage, not seen before.

Energy-Transfer Theory For The Classical Decay Rates Of Molecules At Rough Metallic Surfaces, P.T. Leung, Thomas F. George

Physics Faculty Publications and Presentations

The problem of the decay rates for molecules at rough metallic surfaces is considered, where the classical electromagnetic energy-transfer theory of Chance, Prock, and Silbey for a flat surface is generalized to the case of a rough boundary. A dynamical theory is constructed through the combination of the Sommerfeld antenna theory and the integral equation formalism of Maxwell's equations at rough boundaries established mainly by Maradudin, Mills, and Agarwal. Perturbative solutions are obtained and numerical results are given with reference to a shallow sinusoidal grating surface. The results, when compared with those obtained previously from the application of the image …

Structural And Superconducting Properties Of Orientation-Ordered Y1Ba2Cu3O7-X Films Prepared By Molecular-Beam Epitaxy , J. Kwo, T.C. Hsieh, R.M. Fleming, M. Hong, Sy_Hwang Liou, B.A. Davidson, L.C. Feldman

Sy-Hwang Liou Publications

Superconducting Y₁Ba₂Cu₃O_7-x films were produced by metal molecular-beam epitaxy with one electron beam and two thermal cells and a molecular oxygen-gas source. The films were epitaxially grown on SrTiO₃ (100) with an a-axis orientation perpendicular to the plane, and b and c axes ordered in the plane. A sharp resistive superconducting transition with T_c (R=0) at 82 K was obtained. A lower limit of the average J_c in the plane is 10³ A/cm² at 77 K, 5×10⁴ A/cm² at 70 K, and 10 …

Superconducting Y-Ba-Cu-O Oxide Films By Sputtering, M. Hong, Sy_Hwang Liou, J. Kwo, B.A. Davidson

Sy-Hwang Liou Publications

We have prepared superconducting thin films of Y-Ba-Cu-O with T_c onsets above 95 K by both diode and magnetron sputtering. Films with full superconductivity (R=0) at 85 K have been produced by dc magnetron sputtering. The compositions of the films are fairly uniform across an area 50 mm in diameter and through the film thickness. Structural properties of the films were studied by x-ray diffraction. Critical current densities in the range of 3000 to 10⁴ A/cm² have been measured at 4.2 K. Applied Physics Letters is copyrighted by The American Institute of Physics.

N-Level Quantum Systems With Su(2) Dynamic Symmetry, Foek T. Hioe

Physics Faculty/Staff Publications

We present an analytic solution of the coherent evolution of a laser-driven N-level quantum system that possesses an SU(2) dynamic symmetry.

Interaction Of Hg Overlayers With An Ag(100) Surface, Peter A. Dowben, Y.J. Kime, Shikha Varma, M. Onellion, J.L. Erskine

Peter Dowben Publications

The electronic band structure of one, two, and five monolayers of Hg on Ag(100) has been investigated by angle-resolved photoemission. Hg overlayers on Ag(100) form metastable structures that develop via Frank–van der Merwe growth modes. Hg-Hg hybridization results in the formation of a two-dimensional band structure while hybridization of Hg with the underlying Ag(100) substrate results in the adoption of bulklike characteristics for some Hg-induced bands. The Hg-Hg as well as Hg-Ag interactions are discussed.

Transition-Matrix Theory For Two–Photon Ionization Of Rare–Gas Atoms And Isoelectronic Ions With Application To Argon, Anthony F. Starace, Tsin-Fu Jiang

Anthony F. Starace Publications

A transition-matrix theory for two-photon ionization processes in rare-gas atoms or isoelectronic ions is presented. Uncoupled ordinary differential equations are obtained for the radial functions needed to calculate the two-photon transition amplitude. The implications of these equations are discussed in detail. In particular, the role of correlations involving virtually excited electron pairs, which are known to be essential to the description of single-photon processes, is examined for multiphoton ionization processes. Additionally, electron scattering interactions between two electron-hole pairs are introduced into our transition amplitude in the boson approximation since these have been found important in two-photon ionization of xenon by …

29th Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Program and abstracts from the 29th annual meeting of the Rocky Mountain Conference, co-sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy and the Rocky Mountain Chromatography Discussion Group. Held in Denver, Colorado, August 2-6, 1987.

Simple Model For The Resonant Vibrational Excitation Of Molecules And Its Application To Li2 And N2, J M. Wadehra, P J. Drallos

Physics and Astronomy Faculty Research Publications

A simple model for the resonant vibrational excitation of a molecule by electron impact is proposed in which the potential curves of the electronic states of the molecule and its resonant anion are replaced by those of linear harmonic oscillators of arbitrary frequencies and equilibrium internuclear separations. A closed-form expression for the excitation amplitude is derived. Useful recursion relations among amplitudes are obtained which allow convenient evaluation of cross sections for any inelastic or superelastic vibrational transition. The model is used to generate the cross sections for vibrational excitation of Li_2 and N_2 by the impact of low-energy electrons.

Contributions Of Higher Partial Waves To The Elastic Scattering Amplitude For Various Long Range Interactions, J M. Wadehra, Sultana N. Nahar

Physics and Astronomy Faculty Research Publications

The contributions of higher partial waves to the elastic scattering amplitude are dominated by long-range interactions which fall off as r^(−n) as r→∞. Closed-form expressions for the contributions of higher partial waves (2l>n-3) to the scattering amplitude for various long-range interactions (n ranging from 3 to 8) are presented.

Static Magnetic Field Models Consistent With Nearly Isotropic Plasma Pressure, Harlan E. Spence, Margaret G. Kivelson, Raymond J. Walker

Physics & Astronomy

Using the empirical magnetospheric magnetic field models of Tsyganenko and Usmanov (TU), we have determined the self-consistent plasma pressure gradients and anisotropies along the midnight meridian in the near-Earth magnetosphere. By “inverting” the magnetic field, we determine what distributions of an anisotropic plasma, confined within the specified magnetic field configuration, are consistent with the magnetohydrostatic equilibrium condition, J × B = ∇ · P. The TU model, parameterized for different levels of geomagnetic activity by the Kp index, provided the magnetic field values from which J × B was numerically evaluated. A best fit solution was found that minimized the …