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34th Rocky Mountain Conference On Applied Spectroscopy

Rocky Mountain Conference on Magnetic Resonance

Program and registration information for the 34th annual meeting of the Rocky Mountain Conference on Applied Spectroscopy, co-sponsored by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, August 2-6, 1992.

Ultrahigh Vacuum Chamber For Synchrotron X-Ray Diffraction From Films Adsorbed On Single-Crystal Surfaces, John R. Dennison, S. K. Wang, P. Dai, T. Angot, H. Taub, S. N. Ehrlich

All Physics Faculty Publications

An ultrahigh vacuum chamber has been developed for structural analysis of adsorbed films and single‐crystal surfaces using synchrotron x‐ray diffraction. It is particularly well suited for investigations of physisorbed and other weakly bound films. The chamber is small enough to transport and mount directly on a standard four‐axis diffractometer and can also be used independently of the x‐ray diffractometer. A low‐current, pulse‐counting, low‐energy electron diffraction/Auger spectroscopy system with a position‐sensitive detector enables in situ characterization of the film and substrate while the sample is located at the x‐ray scattering position. A closed‐cycle He refrigerator and electron bombardment heater provide controlled …

Traps In Semi-Insulating Inp Studied By Thermally Stimulated Current Spectroscopy, Z. Q. Fang, David C. Look, J. H. Zhao

Physics Faculty Publications

Traps in Fe‐doped semi‐insulating InP samples have been studied by thermally stimulated current spectroscopy with IR (hν≤1.12 eV) excitation at 81 K. The possible involvement of native defects in determining the compensation mechanisms is suggested based on the observation of other than the usual 0.64 eV Fe‐related activation energy for the dark current in one of the four samples supplied from different sources. A metastable behavior of traps in another sample was found and explained by a charge‐controlled defect reaction model. Three out of the six traps observed are suggested to be electron traps and one among the …

Development Of Membrane Film Fiber Optic Based Sensors For The Remote Monitoring Of The Quality Of Surface And Groundwater, Leonidas G. Bachas

KWRRI Research Reports

The objective of this study was the development of chromo- and fluoroionophores and their subsequent use in sensors capable of surface and groundwater monitoring. Several reagents (modified crown ethers and porphyrins) were synthesized based on principles of chemical recognition and used for metal and pH sensing. The modified crown ether reagents include a chromogenic or fluorogenic group. The selectivity of these reagents is controlled by the size of the crown ether ring and the type of the chromogenic or fluorogenic side-arm. In addition, a fluorogenic crown ether was synthesized that incorporates a fluorogenic side-arm and a perfluorinated carbon chain. The …

Construction Of A Lithium Vapor Oven For Electron Capture And Multiple Ionization Experiments, Oliver Woitke

Masters Theses

A Li vapor oven, to be used as a source of Li target atoms in electron capture and multiple ionization experiments, was designed and installed in the beamline of the Van de Graaff accelerator at Western Michigan University. The oven was tested using two different projectile beams, protons and He+. The test results indicate that Li evaporated from the oven in the form of a cloud rather than as a jet spray. For He+ colliding with Li it was found that the projectile single-electron loss yield is about three orders of magnitude larger than the single-electron capture yield, as expected …

Review: 'Theory Of Dielectric Optical Waveguides,' 2nd Edition, By Dietrich Marcuse, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

I suppose I ought to say up front that while preparing this review I often found myself feeling very much like a student evaluating his teacher. After all, it was, in part, the first edition of Dietrich Marcuse's Theory of Dielectric Optical Waveguides (among a handful of other similar texts) from which I first studied the principles of optical waveguide theory under the demanding, yet patient and graceful guidance of Dr. Ahmad Safaai-Jazi. Thus with the utmost respect for a teacher whom I have never met, I shall try to faithfully share my thoughts and feelings regarding the second edition …

Charge Conservation In The Incommensurate-Commensurate Transition Of Charge Density Waves, Jörg Kastrup

Masters Theses

W ith the complex continuation method, introduced by Gupta and Sutherland (1976), the grand partition function for the sine-Gordon model of charge density waves may be calculated without violation of charge conservation. Contrary to previous works by Okwamoto, Takayama and Shiba (1979) and Turkevich and Doniach (1982) the chemical potential becomes temperature dependent. By direct comparison of numerical results with those of the above mentioned authors it is shown that the incommensurate-commensurate transition does not occur in the previously predicted temperature range.

A Study Of The Transfer Matrix Method For The Classical Statistical Mechanics Of One Dimensional Systems, Dietmar R.A. Johlen

Masters Theses

Two formalisms using the transfer matrix technique, the first one by Gupta and Sutherland (1976) and the second one by Guyer and Miller (1979), are investigated and a proof is given for their equivalence.

Furthermore, it is pointed out that previous studies neglected the difficulties that arise from nonhermitian pseudo Hamiltonian. This work proves that the same results are obtained by taking into account the nonhermiticity of the pseudo Hamiltonian.

Thus, the transfer integral technique is extended to nonhermitian pseudo Hamiltonians.

Localization Of Light In One Dimensional Randomly Disordered Dielectric Medium, K. Balaji

Masters Theses

The concept of localization of electrons in semiconductors has been known ever since the 1960's when P. W. Anderson and N. F. Mott made detail investigations on the transport properties of alloys. At the end of the last decade, however, physicist started looking for localization in other systems. Specifically, they looked at the localization of light and acoustic waves in disordered systems. Localization is a property which arises for all wavelike excitations in disordered media.

In this study we analyze the localization of light in one dimensional randomly disordered dielectric medium using computer simulation (numerical integration method) technique. The results …

Adiabatic Cooling Of Atoms By An Intense Standing Wave, Jian Chen, J. Greg Story, Jeffrey J. Tollett, Randall G. Hulet

Physics Faculty Research & Creative Works

Lithium atoms channeled in the nodes of an intense standing-wave radiation field are cooled to near the recoil limit by adibatically reducing the radiation intensity. The final momentum distribution has a narrow component with a root-mean-squared momentum of 2ħk in one dimension, where ħk is the momentum of a radiation-field photon. The data are compared with the results of a Monte Carlo simulation using a two-level atom model. This process may be useful for cooling and increasing the phase-space density of atoms confined in a magnetic trap.

Critical Behavior Of Charge Density Waves Below Threshold: Numerical And Scaling Analysis, Alan Middleton, Daniel S. Fisher

Physics - All Scholarship

The critical behavior of pinned charge density waves (CDW's) is studied as the threshold for sliding is approached. Using the Fukuyama-Lee-Rice Hamiltonian with relaxational dynamics, the polarization and linear response are calculated numerically. ... On the irreversible approach to threshold, the response due to avalanches triggered by local instabilities dominates the polarizability, which diverges in one and two dimensions. Characteristic diverging length scales are studied using finite-size scaling of the sample-to-sample variations of the threshold field in finite systems and finite-size effects in the linear polarizability and the irreversible polarization. A dominant diverging correlation length is found which controls the …

Measurement Of The Λ→N+Γ Branching Ratio, William J. Fickinger, D. K. Robinson

Faculty Scholarship

The branching ratio for the Λ weak radiative decay has been measured to be B(Λ→n+γ)/(Λ→anything) =[1.78±0.24(stat)±0.160.14(syst)]×10-3. A low-energy kaon beam was used to produce the Λ hyperons via the reaction K-+p→Λ+π0 at rest. Photons from the signal channel and π0 decay were detected with a NaI(Tl) array. The final spectrum contains 287 events after background subtraction, an order of magnitude more events than from the only previous measurement.

Planar H2O Masers In Star-Forming Regions, Moshe Elitzur, David J. Hollenbach, Christopher F. Mckee

Physics and Astronomy Faculty Publications

The planar geometry of shocked material is the key property in enabling the high brightness temperatures of H20 masars in star-forming regions. We solve for the brightness temperature, the beaming angle, and the maser spot size for thin, saturated planar masers under the assumption that the velocity change across the maser due to ordered motions is small compared with the thermal or microturbulent line width. For a given set of physical parameters, the brightness temperature is essentially fully determined by the length of the velocity-coherent region in the shocked plane along the line of sight. The geometry in the transverse …

Electron Mean-Free Paths In The Alkali Metals, G. K. Wertheim, D. Mark Riffe, N. V. Smith, P. H. Citrin

All Physics Faculty Publications

Photoemission data in which the signal from the first atomic layer is well resolved from that of the bulk are used to determine accurately the kinetic-energy dependence of the inelastic-electron mean free path in the alkali metals. At the higher kinetic energies, the data are in very good agreement with the theory of Penn. Below about 10 eV, the mean free path in the heavier alkali metals drops markedly below the theoretical values. This is attributed to electron decay processes involving the unoccupied d bands.

Flux Trapping In Superconducting Pellets, Andreas Straub

Dissertations and Theses

This research concerns the effects on samples of nominal composition Bi_1.8Pb_0.2Sr₂Ca₂Cu₃O_y which were exposed to hot, dense argon in a ballistic compressor.

The investigations were concentrated on two specimens which were exposed to hot, dense argon at about 1800 K (peak pressure 330 atm) and 1500 K (peak pressure 230 atm), respectively. Sample Bi #1 showed a completely melted surface structure after triple exposure in the ballistic compressor at 1800 K while the surface of sample Bi #7 was just partly melted after double exposure at 1500 K.

Changes …

Modification Of The Magnetic Flux-Line Interaction At A Superconductor's Surface, M. Cristina Marchetti

Physics - All Scholarship

The pair interaction between magnetic flux lines in a semi-infinite slab of an anisotropic type-II superconductor in an external field is derived in the London limit. The case where the applied field is normal to the superconductor/vacuum interface is considered. The presence of stray fields near the surface leads to an additional contribution to the repulsive interaction between flux lines that vanishes exponentially with the distance from the interface. The pair interaction is used to obtain the continuum elastic energy of a distorted semi-infinite flux-line array. The presence of the superconductor/vacuum interface yields surface contributions to the compressional and tilt …

Structures Of Selected Boranes And Carboranes, Sunwoo Lee, Peter A. Dowben, A.T. Wen, A.P. Hitchcock, John A. Glass Jr., James T. Spencer

Peter Dowben Publications

Nido-pentaborane(9) (B₅H₉), 1, nido-2,3-diethyl-2,3-dicarbahexaborane(8)[( C₂H₅)₂C₂B₄H₆], 2, nido-decaborane (14) (B₁₀H₁₄), 3, closo- 1,2-dicarbadodecaborane(12) (H₂C₂B₁₀H₁₀), 4, can be used as possible source compounds for boron and boron carbide thin film deposition. Inner shell electron energy-loss spectroscopy (ISEELS) studies of the boron Is and carbon Is core excitations of gas phase species have been undertaken so as to characterize these molecular precursors at solid surfaces. The near edge structure of ISEELS provides a good "fingerprint" …

Convective Instability Of Autocatalytic Reaction Fronts In Vertical Cylinders, D. A. Vasquez, J. W. Wilder, Boyd F. Edwards

All Physics Faculty Publications

Linear stability analysis predicts that the onset of convection for an ascending autocatalytic reaction front in a vertical cylinder corresponds to a nonaxisymmetric mode. This mode consists of a single convective roll confined to the region near the reaction front, with fluid rising in half of the cylinder and falling in the other half. Experiments show a flat front below the onset of convection and an axisymmetric front well above the onset of convection. New experiments are called for to closely examine the onset of convection in order to test this prediction.

Defect Models In Electron-Irradiated N-Type Gaas, B. Ziebro, Joseph W. Hemsky, David C. Look

Physics Faculty Publications

1 MeV electron irradiation has been performed in degenerate, n‐type (n≂2×10¹⁷ cm^-3), molecular beam epitaxial GaAs layers, and Hall effect measurements have been carried out during the irradiation in order to get accurate defect production data. The results have been fitted with statistical models, and are most consistent with the usual E1 (E_C-0.045 eV) and E2 (E_C-0.15 eV) levels being the (-/0) and (0/+) transitions of the As vacancy, respectively. Also, an acceptor well below EC-0.15 eV is produced at a much higher rate than that of E1 and E2.

Analysis Of Multifrequency Dispersive Optical Bistability And Switching In Nonlinear Ring Cavities With Large Medium-Response Times, Pawel Pliszka, Partha P. Banerjee

Electrical and Computer Engineering Faculty Publications

Using a simple model of a ring cavity comprising a cubically nonlinear medium, we analyze dispersive optical bistability in the presence of more than one spectral component. We show the phenomenon of so-called competition for resonance. In addition to presenting cavity characteristics for the cases of two and three different frequencies, we also discuss the general method for finding steady-state solutions and checking their stability. A simple and efficient algorithm, based on a relaxation method, is devised to find steady-state solutions satisfying appropriate boundary conditions. The relaxation dynamics is physically related to a finite response time of the medium.

Recoil Effects And Cp Violation In Neutron Scattering, Vladimir Gudkov

Faculty Publications

The problem of the imitation of CP violation in neutron scattering is discussed. The thermal motion of nuclei cannot contribute to symmetry-violating effects. The influence of the nuclear depolarization due to neutron scattering is estimated.

Electronic Structure Of Borane Cage Molecules Adsorbed On Si(111), Sunwoo Lee, Dongqi Li, Sophie M. Cendrowski-Guillaume, Peter A. Dowben, F. Keith Perkins, S.P. Frigo, R.A. Rosenberg

Peter Dowben Publications

We compare the valence band photoemission resulting from molecular adsorption of nido-decaborane(14) (B₁₀H₁₄) and nido-2,3-diethyl-2,3-dicarbahexaborane on Si(111) at 100 K. The relative shift of the apparent valence band edge with increasing molecular coverage is consistent with the relative energy difference in the highest occupied molecular orbital for these two molecules as inferred from modified neglect of differential overlap calculations. The results suggest that the screening is very similar, despite the very different molecular structures of these two nido cage molecules.

Photoluminescence Study Of Si1-XGeX/Si And Si/Ge Strained Layer Superlattices, Todd D. Steiner

Theses and Dissertations

In recent years, there has been interest in obtaining efficient photoluminescence (PL) and electroluminescence from Si_1-xGe_x/Si or Si/Ge superlattices. In this dissertation, longperiod c/Si superlattices grown by molecular beam epitaxy at 500°C and annealed post-growth using rapid thermal annealing were investigated using photoluminescence (PL). The as-grown samples have broad PL bands from isoelectronic centers related to Ge complexes as well as sharp near-edge bound exciton lines. The broad PL band was found to be 120 meV below the band gap, after accounting for the effects of confinement of holes. Post-growth annealing resulted in a reduction in …

Multi-Ion Ambipolar Diffusion, Thomas E. Gist

Theses and Dissertations

The continuity and momentum equations for electrons and multiple ion species are solved analytically and numerically using a new model for ambipolar diffusion. The general form of the model is valid for any quasi-neutral plasma for which the diffusion approximation is appropriate, including positive or negative ions, arbitrary geometries, and time dependence. The model provides criteria for determining when single ion diffusion theory is appropriate for describing multi-ion discharges, when a multi-ion proportional model is appropriate, and when a multi-ion nonproportional model is necessary. An expression is developed which provides a necessary condition for proportionality and provides the proportionality constant …

Experimental Investigation Of Crossflow Instability Waves In Rotating Disk Flow, Alan E. Blanchard

Mechanical & Aerospace Engineering Theses & Dissertations

For the past 40 years, the crossflow (or inflectional) instability associated with rotating disk flow has been generally assumed to be a pure vortex that is fixed with respect to the disk; however, the terms "wave" and "vortex" have also been used interchangeably throughout the computational and experimental literature to describe this instability. Through the use of both hot-wire surveys and smoke-wire flow visualizations in the present investigation, the existence of crossflow instability waves prior to vortex formation has been shown. The results of the hot-wire surveys and smoke-wire flow visualizations for both a "clean" disk case and a disk …

Investigation Of Alignment Dynamics In Mg-Ne And Mg-Ar Two-Photon Fractional Collisions, David Allen Olsgaard

Physics Theses & Dissertations

A new technique is used to observe the dynamics of electronic alignment in a dissociating collision complex. The technique requires the absorption of two optical photons during a single binary collision. Two exciting light fields are tuned into the wings of the 3s¹s₀-3p₁ and 3p¹p₁-5s¹s₀ resonances of Mg where strong collisions with rare gas atoms induce transitions between corresponding molecular states. The alignment produced in the intermediate state by the first excitation is probed by the second laser as a function of relative linear laser polarization and laser …

Quasi-Discretization Of The Electron Continuum Emitted In Collisions Of 0.6 Mev U−¹ Au11+ With Noble Gases, S. Hagmann, W. Wolff, J. L. Shinpaugh, H. E. Wolf, Ronald E. Olson, C. P. Bhalla, R. Shingal, C. Kelbch, R. Herrmann, O. Jagutzki, R. Dörner, R. Koch, J. Euler, U. Ramm

Physics Faculty Research & Creative Works

We have measured relative doubly differential cross sections for electron emission in collisions of 0.6 MeV u⁻¹ Au¹¹⁺ projectile ions with He, Ne and Ar targets for laboratory electron-detection angles between 17' and 80' and electron energies from 100 eV to well above the classical binary encounter region. The authors observe that, independent of the target Zt, the electron spectra display three characteristic peak-line structures whose energies are nearly invariant with observation angle. These structures are attributed to the diffraction of quasi-free target electrons in the potential of the projectile. © 1992 IOP Publishing Ltd.

Electron Emission From Foils Induced By Energetic Heavy-Ion Impact, R. A. Sparrow, Ronald E. Olson, D. Schneider

Physics Faculty Research & Creative Works

Doubly differential cross sections have been measured and calculated for the electron emission produced by collisions of 3.5 MeV u⁻¹ U³⁸⁺ on thin carbon foils. The electron emission is observed in both forward and backward directions. Calculations are in reasonable agreement with the experimental results in both shape and absolute magnitude. At intermediate foil thicknesses, a double binary peak structure is observed that is due to 0° binary electrons being elastically scattered to angle θ along with those that are produced at θ and suffer no large-angle scattering events in the foil. Absolute electron yields show that several …

Numerical Study Of C>1 Matter Coupled To Quantum Gravity, Simon Catterall, John B. Kogut, Ray L. Renken

Physics - All Scholarship

We present the results of a numerical simulation aimed at understanding the nature of the `c = 1 barrier' in two dimensional quantum gravity. We study multiple Ising models living on dynamical \phi^3 graphs and analyse the behaviour of moments of the graph loop distribution. We notice a universality at work as the average properties of typical graphs from the ensemble are determined only by the central charge. We further argue that the qualitative nature of these results can be understood from considering the effect of fluctuations about a mean field solution in the Ising sector.

Coherent Population Transfer Via The Continuum, C. E. Carroll, Foek T. Hioe

Physics Faculty/Staff Publications

We present a remarkable analytic result which suggests that a continuum can be used as an intermediary for a significant transfer of population from one discrete state to another discrete state in a stimulated Raman transition. the population transfer is accomplished by employing two laser pulses that overlap in time, arranged in the so-called counterintuitive order. That a continuum can be used for population transfer is shown here for the first time. It promises to open up more channels for selective coherent excitation of atoms or molecules.