Physical Sciences and Mathematics Commons^™

Temperature And Supersaturation Dependent Nucleation Rates Of Heterogeneous Water By Molecular Cluster Model Calculation, Chen K. Lutrus, Donald E. Hagen, Sung-Ho Suck Salk

Physics Faculty Research & Creative Works

A statistical mechanical method to evaluate the energy of formation of water clusters attached to a foreign particle surface is described, with the binding energy being evaluated on a molecular level, using semiempirical modified neglect of diatomic overlap (MNDO) theory. The model is applied to water nucleation on a silicon oxide surface. The binding energy contribution, which represents the energy of formation at T=0 K, is found to slightly (but not negligibly in the thermal sense) increase with the number of hydrogen bonds between the water cluster and the condensation nucleus whose surface is made of silicon oxide. An analytic …

Size Imperfections In One-Dimensional Periodic Optical Arrays, Yan Zhong

Masters Theses

The concepts of band theory for electrons can also be employed to describe the behavior of electromagnetic waves propagating in periodic dielectric structures. These periodic structures can produce photonic band gaps in which the propagation of electromagnetic waves is strictly prohibited. The introduction of impurities in such system gives rise to donor and acceptor gap modes in electron system and to energy gap modes in photonic system.

In my thesis, the impurity modes in one-dimensional, periodic, dielectric system will be studied. These modes are introduced in the 1-d dielectric structure by altering the thickness of one slab in an otherwise …

Semi-Insulating Nature Of Gas Source Molecular Beam Epitaxial Ingap Grown At Very Low Temperatures, David C. Look, Y. He, J. Ramdani, N. Elmasry, S. M. Bedair

Physics Faculty Publications

In_xGa_1−xP lattice matched to GaAs (x≂0.51) has proven to be useful in many device applications. Here we show that undoped, semi‐insulating InGaP is possible by growing with gas source molecular beam epitaxy at very low temperatures, 150–250 °C. The material grown at about 200 °C is n‐type with a 296‐K resistivity of 9×10⁵ Ω cm, a mobility of 120 cm²/V s, and a donor activity energy of 0.48 eV. When annealed at 600 °C for 1 h, the resistivity increases to greater than 10⁹ Ω cm and the …

Electron-Beam Modification Of Gaas Surface-Potential - Measurement Of Richardson Constant, S. M. Lindsay, Joseph W. Hemsky, David C. Look

Physics Faculty Publications

The surface potential of GaAs is strongly modified in the presence of a high‐energy electron beam due to the creation of electron‐hole pairs in the depletion region and the subsequent drift of the holes to the surface where they neutralize surface states. This effect is modeled in terms of a parameter K=A∗T²/I_b(dE/dz)η, where I_b is the beam current density, A∗ is the effective Richardson constant, dE/dz is the beam energy loss per unit length, and η⁻¹ is the average energy required to …

Electron-Drift Velocities In Argon-Boron Trichloride Gas-Mixtures, Donald L. Mosteller Jr., Merrill L. Andrews, Jerry D. Clark, A. Garscadden

Physics Faculty Publications

Electron drift velocities were measured for argon gas mixtures containing 25 ppm to 0.5% boron trichloride additive using a pulsed-Townsend drift tube. These results show a marked sensitivity to mixture ratio and the gas mixtures also show negative differential conductivity and strong attachment at low electric field/gas number density.

Orientational Phase Transition In Na_{X}C_{60} (1, T. Yildirim, J. E. Fischer, A. B. Harris, Peter W. Stephens, Dengfa Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

X-ray diffraction and calorimetry data on cubic Na_xC₆₀(1<x60, e.g., T_m(x=1.3)=325 K. The ordered phases are the same as in pure C₆₀: simple cubic, space group Pa3¯, but the orientations in the disordered phase are more restricted. We explain how Na stabilizes the ordered phase to rather high T, while K and Rb do not, in terms of Coulomb interactions between C₆₀ molecules and and Na ions which we calculate from the local charge density of C₆₀.

Observation Of Non-Isotropic Auger Angular Distribution In The C(1s) Shape Resonance Of Co, Oliver Hemmers, Franz Heiser, J. Eiben, R. Wehlitz, U. Becker

Environmental Studies Faculty Publications

Angle-resolved high-resolution C(KVV) Auger spectra of CO were taken in the vicinity of the C(1s) σ^* shape resonance. These spectra show clear evidence for the theoretically predicted anisotropic K-shell Auger emission in molecules. Complementary results from angle-resolved photoion spectroscopy show that the small size of the observed effect is, besides the varying intrinsic anisotropy of the Auger decay, also due to a smaller anisotropy in the primary absorption process than originally predicted but in good agreement with more recent calculations. Contrary to this, satellite Auger transitions show unexpectedly large anisotropies.

Diffraction Of A Gaussian Beam By A Spherical Obstacle, James A. Lock, Edward A. Hovenac

Physics Faculty Publications

The Kirchhoff integral for diffraction in the near-forward direction is derived from the exact solution of the electromagnetic boundary value problem of a focused Gaussian laser beam incident on a spherical particle. The diffracted intensity in the vicinity of the particle is computed and the way in which the features of the diffraction pattern depend on the width of the Gaussian beam is commented on.

Comparison Of Ion Adsorption To Phophatidylcholine/Phosphatidylserine And Sarcoplasmic Reticulum Membranes, Martin Mense

Dissertations and Theses

Artificial lipid membranes have been used in biophysical studies as well defined models of biological membranes. In the present work we studied adsorption of ions to artificial lipid membranes, composed of phosphatidylcholine (PC) and phosphatidylserine (PS), and to biological membrane from sarcoplasmic reticulum (SR). The studies of ion adsorption and electrokinetic characterization of membranes were done by means of microelectrophoresis of PC/PS liposomes and SR vesicles. The ions of interest were positively charged potassium (K), calcium (Ca), tetraphenylarsonium (TPAs), tetraphenylphosphonium (TPP) and negatively charged pentachlorophenol (PCP).

Electrophoretic mobility of PC/PS liposomes and SR vesicles has been measured as a function …

Diminishing Sign Anomaly And Scaling Behavior Of The Mixed-State Hall Resistivity In Tl2Ba2Ca2Cu3O10 Films Containing Columnar Defects, R.C. Budhani, Sy_Hwang Liou, Z.X. Cai

Sy-Hwang Liou Publications

The issues of sign reversal of the Hall voltage and scaling between longitudinal (ρ_χχ) and Hall (ρ_χy) resistivities are studied in Tl₂Ba₂Ca₂Cu₃O₁₀ films in which the vortex dynamics is drastically changed by flux pinning at heavy-ion-irradiation–induced linear defects. While the sign anomaly diminishes with increasing defect concentration, the power law ρ_χy∼ρ_{χχ ^β} , β=1.85±0.1, holds even after irradiation. This result shows that the scaling is a universal feature of the mixed state in this system. The sign anomaly, on the other hand, is not …

Driven Diffusion, Kawasaki Dynamics, Mixing, And Spatial Ordering In An Interacting Lattice-Gas, Yan He, Ras B. Pandey

Faculty Publications

Kawasaki dynamics is used to study the transport properties of a nonequilibrium steady state system of interacting lattice gas of oppositely charged particles in a linear gradient field in two dimensions. The rms displacements show unusual nondiffusive transport. The effective conductivity varies with the temperature which deviates from the Arrhenius law and depends on the range of interaction. Density of a fully mixed state decays with temperature with a power law. Onset of spatial ordering occurs in a certain temperature range at a fixed range of interaction.

35th Rocky Mountain Conference On Analytical Chemistry

Rocky Mountain Conference on Magnetic Resonance

Program, abstracts, and information about the 35th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, 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, July 25-29, 1993.

A Retarding-Potential Analyzer For Measuring Energy Distributions In Electron Beams, Li Zhou

Dissertations and Theses

An energy analyzer for electron beams, based on a retarding-potential method, has been studied both experimentally and theoretically. In this method a potential energy barrier at right-angles to the beam acts as a high-pass energy filter allowing electrons having energies greater than the barrier height to pass through while turning back electrons of lower energy. The potential barrier in the present study was created by applying a negative potential to an electrode consisting of a 600/inch hexagonal copper mesh or an electrode having a pair of single apertures in series (compound aperture). Two different compound apertures, of diameters 0.4 mm …

Symmetry Selection Rules For Vibrational Excitation By Resonant Electron Impact And A Unified Treatment Of Vibronic Coupling Between Resonances And To The Continuum: A Complete Symmetry Analysis Of Vibrational Excitation In Benzene, Gordon A. Gallup

Gordon Gallup Publications

A symmetry analysis of the contributions to the transition operator from vibronic coupling provides symmetry selection rules for vibrational excitation by resonant electron impact in polyatomic molecules. In the context of electron scattering vibronic coupling operates in two modes. These are named internal and external vibronic coupling. Internal vibronic coupling operates within and among the quasibound states giving rise to the resonances. External vibronic coupling operates between the quasibound states and the continuum. We discuss the differences, particularly with respect to the angular distribution of electron scattering. A complete symmetry analysis of vibrational excitation is given using benzene as an …

New Singularity In Anisotropic, Time-Dependent Solutions To Maximally Gauss-Bonnet Extended Gravity, T. Kitaura, James Thomas Wheeler

All Physics Faculty Publications

Among the solutions for anisotropic, time-dependent, maximally Gauss-Bonnet extended gravity, we find a class of curvature singularities for which the metric components remain finite. These new singularities therefore differ in type from the standard Kasner-like divergences expected for this class of theories. We study perturbative solutions near the singularity and show that there exist solutions with timelike paths that reach the singularity in finite proper time. Solving the equation of geodesic deviation in the same approximation, we show that the comoving coordinate system does not break down at the singularity. A brief classification of the corresponding singularity types in Robertson-Walker …

Interpretation Of Electron Correlation In Local-Density Approximation For Exchange, Viraht Sahni, Marlina Slamet

Physics Faculty Publications

We provide a new interpretation of how electron correlations are represented within the local-density approximation for exchange by deducing via Harbola-Sahni theory the corresponding pair-correlation density. The expression differs from that in the literature and contains, in addition to the uniform electron-gas result, a term proportional to the gradient of the density. Thus, the nonuniformity of the electron density is explicitly incorporated in the approximation, and constitutes thereby the reason underlying its success.

Design And Construction Of A Lithium Vapor Oven, Corey A. Leon

Honors Theses

A lithium vapor oven to be used as a source of lithium target atoms in atomic collision experiments was designed and constructed. The oven was installed in the beamline of the Van de Graaff accelerator at Western Michigan University. Test results indicated the oven produced a diffuse cloud of evaporated lithium instead of the intended concentrated jet spray. Recommendations concerning the design are made for future efforts.

Low‐Cost Technique For Preparing N‐Sb2S3/P‐Si Heterojunction Solar Cells, O. Savadogo, K. C. Mandal

Faculty Publications

No abstract provided.

Upper Limits To The Nightside Ionosphere Of Mars, Jane L. Fox

Physics Faculty Publications

The nightside ionosphere of Mars could be produced by electron precipitation or by plasma transport from the dayside, by analogy to the Venus, but few measurements are available. We report here model calculations of upper limits to the nightside ion densities on Mars that would be produced by both mechanisms. For the auroral model, we have adopted the downward traveling portions of the electron spectra measured by the HARP instrument on the Soviet Phobos spacecraft in the Martian plasma sheet and in the magnetotail lobes. For the plasma transport case, we have imposed on a model of the nightside thermosphere, …

Ionicity Of Alkali Metal Adsorbates, Reply, D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

A Comment on the Letter by D. M. Riffe et al. Phys. Rev. Lett. 64, 571 (1990).

Apparent And True Feature Heights In Force Microscopy, Nancy Burnham

Nancy A. Burnham

In a force microscope, the stiffness of the cantilever beam convolutes with the tip‐sample interaction stiffness to influence the data in a systematic way. The analysis presented here relates the measured feature height to the true feature height in the variable force, constant force, and constant force gradient modes of operation. In this way, one can understand previously published data: the enhanced measured atomic corrugation observed in high resolution force microscopy images, its increase with load, and the improved resolution of lateral force images. The correct interaction stiffness can be obtained for use in surface force and mechanical properties studies. …

Copper Association With Iron Sulfide Magnetosomes In A Magnetotactic Bacterium, Dennis A. Bazylinski, Anthony J. Garratt-Reed, Afshin Abedi, Richard B. Frankel

Physics

Greigite (Fe₃S₄) and pyrite (FeS₂) particles in the magnetosomes of a many-celled, magnetotactic prokaryote (MMP), common in brackish-to-marine, sulfidic, aquatic habitats, contained relatively high concentrations of copper which ranged from about 0.1 to 10 atomic per cent relative to iron. In contrast, the greigite particles in the magnetosomes of a curved magnetotactic bacterium collected from the same sampling site did not contain significant levels of copper. The ability of the MMP to biomineralize copper within its magnetosomes appeared to be limited to that organism and dependent upon the site from which it was collected. …

High-Voltage Mosfet Bipolar Square-Wave Generator, T. D. Usher, Grant A. Mcauley

Physics Faculty Publications

he construction of a high‐voltage (up to 1000 V) bipolar metal‐oxide‐semiconductor field‐effect transistor square‐wave generator is described. This generator is capable of producing both positive and negative going square waves with variable amplitude, repetition rate, and width. The circuit was designed for ferroelectrics research, however other applications are possible. The rise time of the prototype was 200 ns which was quite satisfactory for the present ferroelectric research project however the rise time can be decreased to 50 ns if necessary. The reader with a modest knowledge of electronics should be able to construct the circuit. Possible pitfalls and critical points …

Prominent Thermally Stimulated Current Trap In Low-Temperature-Grown Molecular-Beam Epitaxial Gaas, Z-Q. Fang, David C. Look

Physics Faculty Publications

By far, the largest thermally stimulated current trap in molecular beam epitaxial GaAs grown at 200–250 °C is T₅, with an activation energy of 0.27 eV and most likely related to V_Ga. After an anneal at 300–350 °C, another trap T₆^☒ appears, with an activation energy of 0.14 eV and closely identified with V_As or the complex, V_As‐As_Ga. Proposed defect reactions in this As‐rich material include V_Ga+As_As→V_As‐As_Ga, and V_Ga+As_Ga→V_Ga‐As_Ga.

Annealing Dynamics Of Molecular-Beam Epitaxial Gaas Grown At 200°C, David C. Look, D. C. Walters, G. D. Robinson, J. R. Sizelove, M. G. Mier, C. E. Stutz

Physics Faculty Publications

By separating a 2‐μm‐thick molecular‐beam‐epitaxial GaAs layer grown at 200 °C from its 650‐μm‐thick substrate, we have been able to obtain accurate Hall‐effect and conductivity data as functions of annealing temperature from 300 to 600 °C. At a measurement temperature of 300 K, analysis confirms that hopping conduction is much stronger than band conduction for all annealing temperatures. However, at higher measurement temperatures (up to 500 K), the band conduction becomes comparable, and a detailed analysis yields the donor and acceptor concentrations and the donor activation energy. Also, an independent absorption study yields the total and charged As_Ga concentrations. …

Analytical Two-Layer Hall Analysis - Application To Modulation-Doped Field-Effect Transistors, David C. Look, C. E. Stutz, Christopher A. Bozada

Physics Faculty Publications

The classical magnetic‐field‐dependent Hall coefficient and conductivity equations are inverted to give the mobilities μ₁ and μ₂ and carrier concentrations n₁ (or p₁) and n₂ (or p₂) in two degenerate bands. The two‐band solution holds for arbitrary magnetic‐field strength as long as quantum effects can be ignored (i.e., kT≳ℏeB/m∗), and it is argued that the analysis can also be applied to two separate layers up to reasonable field strengths. The results are used to determine the two‐dimensional electron gas mobility and carrier concentration in a modulation‐doped field‐effect …

Connection Between Superelastic And Inelastic Electron-Atom Collisions Involving Polarized Collision Partners, Klaus Bartschat, Don H. Madison

Physics Faculty Research & Creative Works

It is shown how the results of a recent experiment by Jiang, Zuo, Vuković, and Bederson [Phys. Rev. Lett. 68, 915 (1992)], who investigated low-energy electron scattering from laser-excited polarized sodium atoms in the initial (3p) ²P°_3/2 (F=3, M_F=3) state, can be related to the inelastic 3S→3P transition involving initially unpolarized electron and atom beams. Hence, this method can provide an independent check of the traditional electron-scattering experiment with unpolarized beams.

A Neutron Diffraction And Mössbauer Effect Study Of The Magnetic Properties Of Pr₂Fe₁₇ And Pr₂Fe₁₇N₂.₆, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, William B. Yelon, K. H. Buschow

Chemistry Faculty Research & Creative Works

The neutron diffraction powder patterns of Pr₂Fe₁₇ and Pr₂Fe₁₇N_2.6 have been measured at 295 K and refined within the Th₂Zn₁₇ structure type to give the structural changes which occur upon nitrogenation; changes which include a 6.4% expansion of the unit cell volume. The Mössbauer spectra of Pr ₂Fe₁₇ and Pr₂Fe₁₇N_2.6 have been measured between 85 and 295 K and analyzed with a model which is based on the Wigner-Seitz cell environment of each iron site, the basal orientation of the magnetization, and …

Long-Range Random Walks On Energetically Disordered Lattices, B. D. Bookout, Paul Ernest Parris

Physics Faculty Research & Creative Works

Although the master equation describing long-range random walks on an energetically disordered lattice is governed by a nonsymmetric transition matrix W, it may be mapped through a similarity transform onto an imaginary-time Schrödinger equation governed by a Hermitian (Hamiltonian) operator H₀ having a nondegenerate ground state. Under this mapping the diffusion constant D can be expressed in terms of the exact ground state energy of operators that are infinitesimally perturbed from H₀.

Three-Body Distorted-Wave Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison, Achim Franz, P. L. Altick

Physics Faculty Research & Creative Works

We report a theoretical calculation for electron-impact ionization of atoms that includes short-range electron-atom effects for wave functions that satisfy the exact asymptotic boundary conditions. Results of this theory, which we label as the three-body distorted-wave Born approximation, are compared with experiment and other theories for ionization of hydrogen and helium for incident-electron energies from 4 to 18 times the ionization energy.