Physical Sciences and Mathematics Commons^™

Incorporation Of Si And Al In Low Temperature Mbe Gaas, M. O. Manasreh, K. R. Evans, C. E. Stutz, David C. Look

Physics Faculty Publications

The localized vibrational modes (LVMs) of silicon donor (Si_Ga) and aluminum isovalent (Al_Ga) impurities in molecular beam epitaxial GaAs layers grown at various temperatures are studied using the infrared absorption technique. It is found that the total integrated absorption of these impurities LVMs is decreased as the growth temperature decreases. This finding suggests a nonsubstitutional incorporation of Si and Al in GaAs layers grown at 200 °C. On the other hand, a subtitutional incorporation is obtained in GaAs layers grown at temperatures higher than 350 °C. A recovery of the Si_Ga LVMs in GaAs layers …

Incorporation Of Silicon And Aluminum In Low-Temperature Molecular-Beam Epitaxial Gaas, M. O. Manasreh, K. R. Evans, C. E. Stutz, David C. Look, Joseph Hemsky

Physics Faculty Publications

The localized vibrational modes (LVMs) of silicon donor (Si_Ga) and aluminum isovalent (Al_Ga) impurities in molecular beam epitaxial GaAs layers grown at various temperatures are studied using the infrared absorption technique. It is found that the total integrated absorption of these impurities LVMs is decreased as the growth temperature decreases. This finding suggests a nonsubstitutional incorporation of Si and Al in GaAs layers grown at 200 °C. On the other hand, a subtitutional incorporation is obtained in GaAs layers grown at temperatures higher than 350 °C. A recovery of the Si_Ga LVMs in GaAs layers …

Multiplet Fine Structure Of The Gd And Tb 5p Levels, Dongqi Li, Peter A. Dowben, M. Onellion

Peter Dowben Publications

Fine structure is observed in the photoemission of Gd and Tb 5p levels as a result of multiplet splitting. These splittings are the consequence of different J final states that occur as a result of interactions with partly filled 4f and/or 5d levels.

Demonstrating The Utility Of Boron Based Precursor Molecules For Selective Area Deposition In A Scanning Tunneling Microscope, F. Keith Perkins, M. Onellion, Sunwoo Lee, Peter A. Dowben

Peter Dowben Publications

The scanning tunneling microscope (STM) can be used to selectively deposit material from a gaseous precursor compound. Ultra-small (less than a 100 nm across) spatial dimensions for selective area deposition may be achieved by this means. In this paper we outline a scheme for selecting and designing main group cluster compounds and organometallics for this type of selective area deposition using nido-decaborane(l4) as an example.

An Embedded Ring Approach To The Vibrational Dynamics Of Disordered Two-Dimensional Materials, Timothy Edwin Doyle

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A theoretical approach was developed to model the vibrational dynamics of amorphous, two-dimensional materials. The materials were modeled as continuous random networks (CRN's) comprising an assemblage of planar rings of diverse size. In-plane vibrational modes for symmetric 4-, 5-, 6-, 7-, and 8-membered rings were examined. Vibrational states of isolated rings were modified by coupling the rings to a continuous network to represent rings embedded in a CRN. An effective force constant was used to couple the ring vibrations to the network's collective motions. Potentials were approximated with the use of a central force model (bond-stretching force constant) and a …

Thermal Conductivity Of Thermoelectric Si0.8‐Ge0.2 Alloys, D. P. White, P. G. Clemens

Physics Faculty Publications

The thermal conductivity of heavily doped, n-type Si-Ge alloys has been studied from 300 to 1200 K. The scattering rate of several phonon scattering mechanisms has been calculated, including intrinsic scattering, mass defect and distortion scattering, phonon-electron scattering, and scattering by inclusions. These rates were then used to calculate the lattice thermal conductivity. The electronic component of the thermal conductivity was calculated from the calculated Lorenz ratio and measured values of the electrical conductivity. The total thermal conductivity was then compared to measured values for a specimen studied by Vining et al.

Transmission Studies Of Explosive Vaporization Of A Transparent Liquid Film On An Opaque Solid Surface Induced By Excimer-Laser-Pulsed Irradiation, P.T. Leung, Nhan Do, Leander Klees, Wing P. Leung, Frank Tong

Physics Faculty Publications and Presentations

Examines the dynamics of the explosion of a liquid film by an ultraviolet excimer pulsed laser studied experimentally on top of an amorphous silicon film deposited on fused quartz. Background on thermal physics of superheated pure or mixed liquids; Techniques for surface temperature measurement; Experimental of probe laser and pulsed excimer laser.

Dephasing Processes In Glasses With Strong Strain Interactions, Ulrich Zürcher, R. Silbey

Physics Faculty Publications

Spectral diffusion decay is calculated for a glass modeled by two level systems which are strongly coupled to phonons. The spin-phonon interaction induces an effective spin-spin interaction which dominates the energy scale. We show that spectral diffusion is a property of macroscopic local fields which fluctuate on time scales that are much longer than the spin-phonon relaxation time T1. We assume for the spectral diffusion a Gaussian distribution and derive a self-consistent equation for its variance which is nonlocal in time. At high temperatures, the variance grows linearly with time while at low temperatures, we find strong deviations from simple …

Senior Theses: Department Of Physical Sciences, Patrick M. Higgins, Timothy Howard, Leah Carol Ross

Morehead State Theses and Dissertations

1992 Senior Theses from the Department of Physical Science at Morehead State University.

The Abundance, Diversity, and Stratigraphy of the Upper Crab Orchard Formation, Lewis County, Kentucky by Patrick M. Higgins.

The Modification of Flemion for Use in a Solid Electrolyte Battery by Timothy Howard.

Simple Analog Computers by Leah Carol Ross.

The Three-Line Magnetic Hyperfine Spectrum Of 57Fe, Norman A. Blum, Richard B. Frankel

Physics

Longitudinal magnetization of a ⁵⁷Co in iron metal foil source and an iron metal foil absorber in a uniform external magnetic field results in a simple three-line magnetic hyperfine absorption spectrum. Measurement of the spectral splitting as a function of applied magnetic field yields the ⁵⁷Fe excited-and ground-state g-factors.

Review: 'Optical Fiber Communications' (2nd Edition), By Gerd Keiser, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

If first impressions are worth anything (and they usually are), I would have to admit that my first impression of the second edition of Gerd Keiser's now popular text Optical Fiber Communications was quite good. My compliments are hereby extended to the publisher for choosing a rather handsome cover and dust jacket. It stands in strong contrast to the text's first edition, which still ranks as probably the ugliest book I own, with color choices ranging from dull cream and "baby" blue to pale pink! I am now happy to say that this older version has been discretely·retired to the …

Assessing The Contributions Of Surface Waves And Complex Rays To Far-Field Mie Scattering By Use Of The Debye Series, Edward A. Hovenac, James A. Lock

Physics Faculty Publications

The contributions of complex rays and the secondary radiation shed by surface waves to scattering by a dielectric sphere are calculated in the context of the Debye-series expansion of the Mie scattering amplitudes. Also, the contributions of geometrical rays are reviewed and compared with those of the Debye series. Interference effects among surface waves, complex rays, and geometrical rays are calculated, and the possibility of observing these interference effects is discussed. Experimental data supporting the observation of a surface-wave-geometrical-ray-interference pattern are presented.

Optical Caustics In Natural Phenomena, James A. Lock, James H. Andrews

Physics Faculty Publications

When observing a distant point source of light through a water droplet adhering to a pane of glass near one's eye or the scattering of light from raindrops, one often sees optical caustics. In this paper, diffraction integrals are used to investigate these caustics. The caustic shapes are related to divergences in the stationary phase method for approximating the diffraction integrals. These divergences correspond to the coalescing of two or more geometrical light rays in ray optics or the coalescing of two or more regions of stationary phase in wave optics. The number of coalescing light rays is related to …

Design And Development Of A Superconducting Induction Motor, Terry Bowness

Opportunities for Undergraduate Research Experience Program (OURE)

The discovery of high-T_c superconductors has led to the development of a number of experimental superconducting motors. This report documents the design, construction, and methods of evaluating the performance of an induction motor with a high-T_c superconducting rotor. While others have utilized the Meissner effect, our superconducting motor works due to Lenz’s law. In theory such a device will act as an induction motor only during start-up, after which its behavior is more like that of a synchronous machine. With a one-pole copper squirrel cage providing start-up torque two high-T_c discs encased in the rotor core act …

Automated Seebeck Measurements Applied To Conducting Ceramics, J. S. Shapiro

Opportunities for Undergraduate Research Experience Program (OURE)

The Seebeck coefficient (also known as thermopower) is important in the characterization of conducting ceramics because it is very sensitive to the electronic structure. An apparatus was built during the Fall of 1990 and Spring of 1991 which was designed to measure the Seebeck coefficient in small high-resistivity samples in the temperature range from 80 K to 450 K. A reproducible thermocouple-to-sample electrical and thermal contact technique was found to be important to data accuracy but difficult to achieve. The goals of this project were to improve the thermocouple block design to give better thermal and electrical contact with the …

Spatial Variation Of A Short-Lived Intermediate Chemical Species In A Couette Reactor, R. Dennis Vigil, Q. Ouyang, Harry L. Swinney

R. Dennis Vigil

We have conducted experiments and simulations of the spatial variation of a short-lived intermediate species (triiodide) in the autocatalytic oxidation of arsenite by iodate in a reactor that is essentially one dimensional-the Couette reactor. (This reactor consists of two concentric cylinders with the inner one rotating and the outer one at rest; reagents are continuously fed and removed at each end in such a way that there is no net axial flux and there are opposing arsenite and iodate gradients.) The predictions ?f a one-dim~ns~onal . reaction-diffusion model which has no adjustable parameters, are In good qualItative (and, In some …

Bulk And Surface Singularity Indices In The Alkali Metals, G. K. Wertheim, D. Mark Riffe, P. H. Citrin

All Physics Faculty Publications

Photoemission data from (110) films of Li, Na, and Rb, in which the signal from the first atomic layer is well resolved, show that the core-hole-screening singularity index is ∼40% larger at the surface than in the bulk for all three metals. This result, which is indicative of the more atomiclike character of metal surface atoms, in general, is particularly large for the alkali metals because their conduction-electron screening is mainly s-like. In addition to quantifying the difference in screening at the surface, the data provide bulk singularity indices of 0.22, 0.16, and 0.14 for Li, Na, and Rb, respectively. …

Quark-Antiquark Condensates In Strong Magnetic Fields, Alec Schramm, Berndt Muller, Stefan Schramm

Alec J Schramm

We discuss the effect of large external magnetic fields on the QCD vacuum structure. We show that the deformed vacuum leads to substantial changes in the hadronic spectrum.

Ion Composition Of The Topside Equatorial Ionosphere During Solar Minimum, S. A. Gonzales, Bela G. Fejer, R. A. Heelis, W. B. Hanson

Bela G. Fejer

We have used observations from both the Bennett ion mass spectrometer and the retarding potential analyzer on board the Atmosphere Explorer E satellite to study the longitudinally averaged O+, H+, and He+ concentrations from 150 to 1100 km in the equatorial ionosphere during the 1975–1976 solar minimum. Our results suggest that the ion mass spectrometer measurements need to be increased by a factor of 2.15 to agree with the densities from the retarding potential analyzer and with ground-based measurements. The peak H+ concentrations are about 2.5×104 cm−3 during the day and 104 cm−3 at night and vary little with season. …

Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Y.-K. Kim, D. H. Madison, Timothy J. Gay

Timothy J. Gay Publications

All known data on the energy distribution of secondary electrons from collisions of protons with atoms and molecules have been reviewed and differential cross sections have been collected. The two experimental methods used to obtain the data are discussed and possible sources of error pointed out. Theoretical treatments are reviewed and several methods of checking the consistency of the data are discussed. Two semiempirical models have been chosen to represent the differential cross sections, and parameters for these models are given which fit the average of the experimental data, subject to known constraints. Recommended values of differential cross sections are …

Temperature-Dependent Electronic Structure In A Localized-Magnetic-Moment System: Gadolinium, Dongqi Li, Jiandi Zhang, Peter A. Dowben, M. Onellion

Peter Dowben Publications

At normal emission, the bulklike band in gadolinium overlayers on W(110) shifts toward EF from 1.64 eV at 310 K to 1.43 eV at 230 K in photoemission. This is accompanied by an increase of the feature width from 0.8 eV at 320 K to 1.1 eV at 230 K. The surface-state binding energy remains unchanged, though the width increases significantly with increasing temperature. The different effects of temperature upon the photoemission results obtained for the bulklike and surface states are interpreted as magnetic-order-induced band movement and spin mixing, respectively, and are discussed in the light of a quasiparticle theory. …

Scaling Dynamics Of Aerosol Coagulation, B. J. Olivier, C. M. Sorensen, Thomas W. Taylor

Physics Faculty Publications

A combination of static and quasielastic light scattering and the theory of scaling solutions to Smoluchowski's equation was used to determine the absolute coagulation rate K'0 and kernel homogeneity lambda of a coagulating liquid-drop aerosol. Droplet sizes ranged from 0.23 to 0.42-mu-m, implying Knudsen numbers in the range 0.26 and 0.14. The temporal evolution of the number concentration M0 and the modal radius r(M) of an assumed zeroth-order log-normal distribution showed near-power-law behavior similar to that predicted by the scaling theory. From the temporal scaling behavior of M0(t) and r(M)(t), the absolute coagulation rate was calculated. The coagulation rates from …

Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Yongki Kim, Don H. Madison, Timothy Gay

Physics Faculty Research & Creative Works

All known data on the energy distribution of secondary electrons from collisions of protons with atoms and molecules have been reviewed and differential cross sections have been collected. The two experimental methods used to obtain the data are discussed and possible sources of error pointed out. Theoretical treatments are reviewed and several methods of checking the consistency of the data are discussed. Two semiempirical models have been chosen to represent the differential cross sections, and parameters for these models are given which fit the average of the experimental data, subject to known constraints. Recommended values of differential cross sections are …

Angular Distributions For Near-Threshold (E,2E) Processes For H, He, And Other Rare-Gas Targets, Cheng Pan, Anthony F. Starace

Anthony F. Starace Publications

Distorted-wave calculations of the triply differential cross sections for electron-impact ionization of H, He, Ne, Ar, Kr, and Xe are presented for final-state electrons sharing ≤4 eV excess energy and for the coplanar, θ₁₂=π geometry. Results for H and He targets, presented briefly elsewhere [C. Pan and A. F. Starace, Phys. Rev. Lett. 67, 185 (1991)], are analyzed in greater detail and compared with available experimental and other theoretical results. In particular, for He targets the effects of exchange and of second-order capture processes are exhibited. These are shown to be of lesser importance than other short-range effects …

Single And Double Ionization Of Helium By Highly Charged Sulfur Ions, Karen M. Lifrieri

Masters Theses

Single and double ionization of helium by highly charged sulfur projectiles is investigated over an energy range of 0.16 to 1.6 MeV/u. Absolute cross sections for the processes of pure ionization, ionization associated with single capture, and ionization associated with single loss by S^6,13+ projectiles were experimentally determined and compared with previous results and theories. Ratios of double-tosingle ionization for each outgoing projectile charge state were also determined and compared with theory. The pure ionization ratios for S⁶⁺ at the highest energies investigated show the q²/E dependence predicted by Knudsen et al. (1984). For S^{13+ …}

Search For The Mössbauer Effect In 109ag, Shokrollah Rezaie-Serej

Physics Theses & Dissertations

The 88-keV first-excited nuclear state in ¹⁰⁹Ag has a mean lifetime of 57.1 sec and a corresponding natural linewidth of 1.15 x 10^-17 eV which is nearly six orders of magnitude narrower than the width for the 93-keV 13.2-μsec state in ⁶⁷Zn. The 93-keV transition in ⁶⁷Zn has the narrowest linewidth for which the Mossbauer effect has been observed. The 88-keV transition in ¹⁰⁹Ag is obviously a very difficult case for the observation of the Mossbauer effect and provides a stringent test for exploring the practical limits of inhomogeneous line broadening in real single …

Hyperspherical Coordinate Description Of Single- And Multiphoton Processes In Two-Electron Systems, Anthony F. Starace

Anthony F. Starace Publications

The purpose of this chapter is to review the use of the adiabatic hyperspherical approximation for the quantitative calculation of single- and multiphoton cross sections of two-electron systems. In Section 2 we provide a brief general orientation to the hyperspherical coordinate representation, the adiabatic approximation, and a diabatic approximation for treating strongly avoided crossings between adiabatic potential curves. In Section 3 we review applications to photoionization and photodetachment processes in He, Be, H^–, and Ps^–. In Section 4 we review applications to multiphoton processes in H^–. Finally, in Section 5 we assess the adiabatic …

Pinski Et Al. Reply, F. J. Pinski, B. Ginatempo, Duane D. Johnson, J. B. Staunton, G. M. Stocks, B. L. Gyorffy

Duane D. Johnson

With our calculations [I], we uncovered the electronic mechanism responsible for inducing atomic short-range order (SRO) in the disordered solid solution of NiPt as it is cooled. Usually, but not always, SRO, whether derived theoretically or measured experimentally, indicates the nature of the long-rangeordered (LRO) state that will stabilize at low temperature. Our calculation of the atomic SRO, while agreeing with experiments [2], neglected the relativistic effects in the electronic structure. Lu, Wei, and Zunger (LWZ) [3,4], on the other hand, have calculated the L lo-ordered alloy formation energy and find that only when relativistic effects are included is the …

Thermal And Surface Core-Electron Binding-Energy Shifts In Metals, D. Mark Riffe, G. K. Wertheim, D. N. E. Buchanan, P. H. Citrin

All Physics Faculty Publications

High-resolution photoemission spectra from the shallow core levels of alkali metals and of In have been obtained between 78 K and room temperature. The data yield values for the alkali-metal surface-atom core-level shift and show thermal shifts of comparable size for bulk and surface. The positive surface shifts are due to the spill-out of conduction-electron charge, which is responsible for the surface dipole layer. The surface shifts are in good agreement with values obtained from a Born-Haber cycle expressed in terms of surface energies. The thermal shifts are proportional to the lattice expansion, and arise from both initial-state and final-state …

Pressure Dependence Of The Thermal Conductivity Of Pyrophyllite To 40 Kbar, Wei Chen, Daniel L. Decker

Faculty Publications

A mathematical model for calculating the temperature distribution as a function of power delivered to a line source and the thermal conductivity of the surrounding medium in the pressure cell of a cubic-anvil press was derived. The model will handle anisotropic thermal conductivities. A simple sample assembly consisting of a line source and two or three thermocouple junctions is described. A comparison of measured to calculated temperatures yields the thermal conductivity. Thermal conductivity measurements were made on natural pyrophyllite and baked pyrophyllite to 40 kbar. For the natural pyrophyllite the thermal conductivity parallel to the bedding plane at room temperature …