Digital Commons Network^™

Scanning Tunneling Microscopy Study Of Intermediates In The Dissociative Adsorption Of Closo-1,2-Dicarbadodecaborane On Si(111), J.M. Carpinelli, E. Ward Plummer, Dongjin Byun, Peter A. Dowben

Peter Dowben Publications

Closo-1,2-dicarbadodecaborane (C₂B₁₀H₁₂) is a source compound found to be suitable for the deposition of a high resistivity form of boron-carbide (B₅C), and the fabrication of boron-rich semiconductor devices. A scanning tunneling microscope (STM) was used to image these molecular icosahedra on Si(111)-(7x7). Molecular decomposition (tip induced and otherwise! produced a boron-carbide/silicon interface with pronounced heterojunction electronic characteristics. In STM, this interface is characterized by a disordering of the Si(111)-(7x7) reconstruction. We suggest, based on Auger electron spectroscopy data and low-energy electron diffraction observations, that boron atoms from the dissociated source molecules …

On The Mechanism Of Giant Electromotility In Polyelectrolyte Gels, Kimberly Ann Branshaw '95

Honors Projects

Electromotility, i.e. bending in response to an electric field, of polyelectrolyte gels in ionic solutions has recently been investigated at a few leading academic and industrial labs as a potential chemomechanical engine. We have discovered that the underlying physics in these systems is more complex than previously believed. We have found that the bending, which seems to obey a {t power law, is inconsistent with the simple idea of a bending speed, but is consistent with a diffusion mechanism. Evidence of diffusion was independently provided by experiments on gels grown or bent in the presence of dyes. We have explored …

Novel Swelling Structures And Electromotility Response In Polyelectrolyte Gels, Dana Deardorff

Honors Projects

Electromotility, the bending in response to an electric field, of polyelectrolyte gels in ionic solutions has been identified as a candidate for a potential chemomechanical engines such as muscles. We discovered that the underlying physics of these systems is more complex than previously believed. We found that the bending as a function of time obeys a square root power law. This points strongly towards a diffusion mechanism for the bending. Kinetic evidence for diffusion was independently corroborated by experiments on gels grown or bent in the presence of dyes. We explored the effects of varying poly-ion concentration in the backbone …

Partial-Wave Representations Of Laser Beams For Use In Light-Scattering Calculations, Gérard Gouesbet, James A. Lock, Gérard Gréhan

Physics Faculty Publications

In the framework of generalized Lorenz-Mie theory, laser beams are described by sets of beam-shape coefficients. The modified localized approximation to evaluate these coefficients for a focused Gaussian beam is presented. A new description of Gaussian beams, called standard beams, is introduced. A comparison is made between the values of the beam-shape coefficients in the framework of the localized approximation and the beam-shape coefficients of standard beams. This comparison leads to new insights concerning the electromagnetic description of laser beams. The relevance of our discussion is enhanced by a demonstration that the localized approximation provides a very satisfactory description of …

Conduction-Electron Screening In The Bulk And At Low-Index Surfaces Of Ta Metal, D. Mark Riffe, W. Hale, B. Kim, J. L. Erskine

All Physics Faculty Publications

High-resolution core-level photoemission spectra from Ta(100) have been measured. The well-resolved peak from the first atomic layer allows a separate assessment of bulk and surface-layer screening responses: singularity indices α_B=0.10±0.01 and α₁₀₀=0.205±0.025, respectively, are obtained. The measured surface-atom lifetime broadening of 70±20 meV (compared to 37±5 meV in the bulk) is consistent with published Auger–photoemission coincidence measurements. The result for the bulk singularity index has been applied in the analysis of previous data in order to extract the screening response in the first atomic layer of Ta(111) (α₁₁₁=0.16±0.01) and Ta(110) (α₁₁₀=0.150±0.015). The …

Microstructure Of The Cr Underlayer And Its Effect On Sm-Co//Cr Thin Films, Yi Liu, B. W. Robertson, Z.S. Shan, Sy_Hwang Liou, David J. Sellmyer

Sy-Hwang Liou Publications

Sm-Co film is a potential candidate for the future high density recording media of 10 Gb/in² which requires bit sizes of the order of 300 nm and grain sizes of about 10 nm. This article investigates the microstructure of the Cr underlayer in Sm-Co thin films and its effect on Sm-Co thin films prepared by the dc magnetron sputtering technique. The grain size of the Cr underlayer is found to be about 25 nm. Grains with small angle misorientation usually form local agglomerates. Studies by transmission electron microscopy (TEM) bright field images at different defocus settings and by high …

Scaling And The Fractal Geometry Of Two-Dimensional Quantum Gravity, Simon Catterall, G. Thorleifsson, Mark Bowick, V. John

Physics - All Scholarship

We examine the scaling of geodesic correlation functions in two-dimensional gravity and in spin systems coupled to gravity. The numerical data support the scaling hypothesis and indicate that the quantum geometry develops a non-perturbative length scale. The existence of this length scale allows us to extract a Hausdorff dimension. In the case of pure gravity we find d_H approx. 3.8, in support of recent theoretical calculations that d_H = 4. We also discuss the back-reaction of matter on the geometry.

Target Dependence Of Binary Encounter Electron Peak Anomalies In Collisions Of Partially Stripped Heavy Ions With Molecular Hydrogen And Noble Gases, W. Wolff, J. Wang, H. E. Wolft, J. L. Shinpaugh, Ronald E. Olson, D. H. Jakubassa-Amundsen, S. Lencinas, U. Bechthold, R. Herrmann, H. Schmidt-Bocking

Physics Faculty Research & Creative Works

A systematic search was performed for the manifestation of quantum interference effects in the shape and angular distribution of the binary-encounter electron peak in collisions of partially stripped, or structured, heavy ions with noble gases and molecular hydrogen. The ionic species investigated were Cu5+,19+, I7+,23+, Au11+,29+ and U13+, all at the same nominal velocity equivalent to 0.6 MeV amu-1. Experimental double-differential cross sections for secondary electron emission in the binary encounter energy region are compared with a simple model based on the elastic scattering of quasi-free target electrons in the projectile field as well as with results of impulse approximation …

On Science Schooling, Seminar Style, E. H. Weinberg, I. Semeniuk, Peter J. Collings, G. Greenstein

Physics & Astronomy Faculty Works

No abstract provided.

Review: 'Integrated Optics: Design And Modeling,' By Reinhard Marz, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

My overall impression is that Integrated Optics: Design and Modeling will make a fine addition to almost anyone's collection of books on integrated optics. It will, however, serve its readers better as a reference book than as a text from which to first learn the basic concepts of integrated optics. I say this because the book is written at a fairly sophisticated technical level, though the author often moves rather quickly to the "bottom line" without providing material much beyond what is first necessary to introduce a problem or concept, and then a statement of the results and/or implications. It …

Dynamics Of Optical-Field-Ionized Plasmas For X-Ray Lasers, Thomas D. Donnelly, R. W. Lee, R. W. Falcone

All HMC Faculty Publications and Research

The success of recombination-pumped x-ray laser schemes is determined by the kinetics of ions in plasmas with relatively dense, cold-electron distributions. We examine how laser gain in such systems is affected by a multipeaked electron distribution generated by sequential ionization of atoms using high-intensity, ultrashort-pulse lasers. We also investigate the role of heating processes that modify electron energy distributions during the recombination and the accompanying collisional cascade. We find that conditions for the success of these schemes are critically modified by the inclusion of these effects.

Effects Of Imperfect Unipolarity On The Ionization Of Rydberg Atoms By Subpicosecond Half-Cycle Pulses, N. E. Tielking, Thomas J. Bensky, Robert R. Jones

Physics

Rydberg atoms are ionized by nearly unipolar, subpicosecond electromagnetic pulses. Deviations from a perfectly unidirectional pulse are found to alter substantially the ionization probability as a function of peak field. Quantitative agreement between classical theory and experiment is achieved if the pulse imperfections are significantly attenuated.

Collisional Effects In He I: An Observational Analysis, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosynthesis. Unfortunately, there is some question whether current theory can account for collisional contributions to He I. We present new observations of two planetary nebulae (PNs) in the range λ850-λ9650, which we use to assess the importance of collisonal effects in the He I spectrum. The first object, NGC 7027, is expected to show relatively strong collisional enhancement, while the second, NGC 7026, should display only small effects. We derive new collision-to-recombination correction factors, based on new collision strengths from the 29-state quantal calculation …

Monitoring Nuclear Test Ban Treaties, David W. Hafemeister

Physics

With the end of the Cold War, the emphasis on monitoring nuclear weapons tests has shifted from the 1976 Threshold Test Ban Treaty (TTBT), which confined the US and USSR to a limit of 150 kilotons (kt), to the Comprehensive Test Ban (CTB) Treaty, which would ban all nuclear tests by the signatories. 1995 will be a watershed year to control the proliferation of nuclear weapons, as the Nuclear Non-Proliferation Treaty (NPT) must be considered for renewal. The fate of the NPT is dependent on a successful CTB negotiation, because the two treaties are politically linked. This paper will cover …

Computer-Simulation Study Of The Permeability Of A Porous Sediment Model, Ras B. Pandey, Jeffrey L. Becklehimer

Faculty Publications

A computer simulation model is used to study the permeability of fluid flow through porous media generated by the random distribution of the sediments in a two-dimensional lattice. Fluid particles are confined to pore space with the sediments forming the rigid barriers at the pore boundaries. An interaction between the fluid particles and the pore substrate is introduced to incorporate the additional drag in the pore space. The pressure gradient causes a bias to drive the fluid and the Metropolis algorithm is used to hop the fluid particles. The permeability of this system is studied as a function of the …

Resonantly Laser-Driven Plasma Waves For Electron Acceleration, Donald P. Umstadter, J. Kim, Eric Esarey, E. Dodd, T. Neubert

Donald Umstadter Publications

A method for generating large-amplitude nonlinear plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is analyzed in one dimension both theoretically and numerically (using both Maxwell-fluid and particle-in-cell codes). Optimal pulse widths and interpulse spacings are computed for pulses with either square or finite-rise-time sine shapes. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The width of this region, and thus the optimal finite-rise-time laser pulse width, was found to decrease with increasing background plasma density and plasma wave amplitude, …

An Experimental Apparatus For Studying Differential Scattering Of Multiply-Charged Ions From Neutral Targets Following Capture, John Edward Edens

Masters Theses

An experimental apparatus has been designed, enabling measurement of angular differential cross sections for single-electron capture (SEC). The design consists of a microchannel plate detector with a one-dimensional position sensitive anode. A bow-time shaped aperture was employed to convert a radially scattered distribution into an approximate linear one. An electrostatic retarding grid was used to separate SEC contributions from the reaction products. Measurements were made of the angular differential cross sections for SEC of Ar^q+ (q=4-6,8) ions scattering from He and Ar at impact energies of 600 to 3000 eV and angles between 0 and 23 mrad. The experimental …

Coulomb Holes And Correlation Potentials In The Helium Atom, Marlina Slamet, Viraht Sahni

Physics Faculty Publications

In this paper we investigate Coulomb correlation effects in the He atom by studying the structure of the static and dynamic Coulomb hole charge distributions as determined by the analytical 39-parameter correlated wave function of Kinoshita. The static Coulomb hole, which is defined in terms of the radial electron-electron distribution function, shows that as a result of Coulomb repulsion there is a reduction in probability of electron approach within a distance of one atomic unit and an increase in this probability for greater separations. The dynamic Coulomb hole defined directly in terms of the pair-correlation density describes the probability of …

Wing-Section Optimization For Supersonic Viscous Flow, Cem Cihan Item

Mechanical & Aerospace Engineering Theses & Dissertations

The recent interest in the High Speed Civil Transport (HSCT) has resulted in renewed research studies of optimized supersonic cruise transport configurations. Incorporation of flow viscosity effects in the design process of such a supersonic wing is currently under investigation. This may lead to more accurate problem formulations and, in tum, greater aerodynamic efficiency than can be obtained by the traditional, inviscid, linear theories. In this context, for a design code to be a candidate for a complex optimization problem, such as three-dimensional viscous supersonic wing design, it should be validated using simpler building-block shapes.

To optimize the shape of …

Measurement Of Hyperfine Coupling Constants Of The 5d²D₃/₂ And 5d²D₅/₂ Levels In Atomic Cesium Using Polarization Quantum Beat Spectroscopy, Wo Yei

Physics Theses & Dissertations

Accurate measurements of hyperfine constants have revealed effects that can not be explained by a simple hydrogenic picture of the alkali atoms such as cesium [1-3]. More precise experimental results and theoretical treatments are in demand for the alkali elements, especially for atomic cesium because of its wide range of applications. Therefore, it is essential to understand its atomic and nuclear structure. Precision measurement of its excited-states properties such as hyperfine structure provides global information on nuclear charge and current distributions and also serves as a check to the theory and a calibration of calculated excited state wave functions. Accurate …

Thermal Effects On Y2O3:Eu3+ For Fiber Optic Temperature Sensing, Arnel C. Lavarias

Electrical & Computer Engineering Theses & Dissertations

Fiber optic methods have gained acceptance in the past several years as non­ intrusive optical techniques of measuring environmental variables, particularly under hostile conditions. Fiber optic temperature sensors are required for many applications which have a large operating range. One way to implement this sensor is to introduce rare earth-doped materials into a fiber showing temperature-dependent optical emission characteristics. The thermal effects on optical emission characteristics of Y₂O₃:Eu³⁺ were studied. The thermal broadening and temperature dependence of the lifetime (τ) of the 611.4 nm emission due to the ⁵D₀ ➔ 7F …

Excited-State Magnesium-Rare Gas Optical Collisions, Rosemary A. Lasell

Physics Theses & Dissertations

Polarization and intensity spectra have been obtained for excited-state magnesium (3s3p ¹P₁) - rare gas optical collisions. The magnesium was excited by a linearly polarized laser tuned to the 3s²1s₀ → 3s3p ¹P₁ atomic transition at 285 nm. A second linearly polarized laser was tuned near the 3s3p ¹P₁ → 3s5s ¹S₀ transition at 571 nm (experiment A) and near the 3s3p ¹P₁ → 3s4d ¹D₂ transition at 553 nm (experiment B). The polarization vector of the second laser was oriented either parallel or …

Identification And Characterization Of The Iron-Zinc Intermetallics Formed In Galvanneal Steel, Richard Frederick George Grant

Physics Theses & Dissertations

The demand to improve the corrosion resistance of steel sheet, particularly for use within the automotive industry, has led to a dramatic increase in the use of coated steels in place of cold-rolled sheet steel. Galvanneal steel results from the post annealing of the zinc-coated steel sheet, in which iron and zinc are interdiffused to form an iron-zinc alloy coating. Within this alloy coating, four main iron-zinc phases, Zeta, Delta, Gamma-1, and Gamma may be present. Manufacture of the most suitable coating requires identifying which phases form during the galvannealing process, an understanding of the properties of each phase and …

Measure Of Fine Tuning, Greg W. Anderson, Diego Castano

Chemistry and Physics Faculty Articles

Fine-tuning criteria are frequently used to place upper limits on the masses of superpartners in supersymmetric extensions of the standard model. However, commonly used prescriptions for quantifying naturalness have some important shortcomings. Motivated by this, we propose new criteria for quantifying fine tuning that can be used to place upper limits on superpartner masses with greater fidelity. In addition, our analysis attempts to make explicit the assumptions implicit in quantifications of naturalness. We apply our criteria to the minimal supersymmetric extension of the standard model, and we find that the scale of supersymmetry breaking can be larger than previous methods …

Heavy Quark Solitons: Towards Realistic Masses, Joseph Schechter, A. Subbaraman, S. Vaidya, H. Weigel

Physics - All Scholarship

A generalization of the effective meson Lagrangian possessing the heavy quark symmetry to finite meson masses is employed to study the meson mass dependence of the spectrum of S-- and P wave baryons containing one heavy quark or anti-quark. These baryons are described as respectively heavy mesons or anti-mesons bound in the background of a soliton, which is constructed from light mesons. No further approximation is made to solve the bound state equation. For special cases it is shown that the boundary conditions, which have to be satisfied by the bound state wave--functions and stem from the interaction with the …

Resolving Ordering Ambiguities In The Collective Quantization By Particle Conjugation Constraints, Joseph Schechter, H. Weigel

Physics - All Scholarship

We formulate the particle conjugation operation and its convenient realization as G--parity in the framework of several chiral soliton models. The Skyrme model, the Skyrme model with vector mesons and the chiral quark model are specifically treated. The vector and axial vector currents are classified according to their behavior under G--parity. In the soliton sector particle conjugation constrains {\it a priori} ambiguous orderings of operators in the space of the collective coordinates. In the Skyrme model with vector mesons and in a local chiral model with an explicit valence quark this classification scheme provides consistency conditions for the ordering of …

Optically Thin Broad-Line Clouds In Active Galactic Nuclei, Joseph C. Shields, Gary J. Ferland, Bradley M. Peterson

Physics and Astronomy Faculty Publications

The broad-line region (BLR) in Seyfert galaxy nuclei exhibits correlated variations in continuum and emission-line luminosity that are qualitatively consistent with photoionization of ionization-bounded (optically thick) clouds. However, evidence is growing that a nonnegligible fraction of the BLR cloud population is optically thin to the Lyman continuum and fully ionized in hydrogen. We consider the implications of this nebular component for observed line emission and find that inclusion of thin clouds in photoionization calculations can resolve several outstanding puzzles of Seyfert variability, notably the behavior of the C IV λ1549/Lyα ratio as a function of continuum luminosity.

A …

Energy And Angular Distributions Of Electrons From Ion Impact On Atomic And Molecular Hydrogen. I. 20- 114-Kev H+ + H2, M. W. Gealy, G. W. Kerby, Iii, Y.-Y. Hsu, M. Eugene Rudd

M. Eugene Rudd Publications

Apparatus and procedures are described for the measurement of absolute cross sections, differential in ejected electron energy and angle, for ionization of atomic and molecular hydrogen by ion impact. A hemispherical electrostatic energy analyzer, rotatable from 15° to 165° with respect to the direction of the incident ion beam, was used to measure energy spectra of secondary electrons from 1.5 to 300 eV. Cross sections at ten angles (nine at some energies) and five incident-ion energies from 20 to 114 keV for H⁺ +H₂ collisions are given. The doubly differential cross sections were integrated over angle and electron …

Challenging Weak-Scale Supersymmetry At Colliders, Greg W. Anderson, Diego Castano

Chemistry and Physics Faculty Articles

Experimental searches for supersymmetry are entering a new era. As future experiments explore the mass range above the current lower bounds on superpartner masses, a failure to observe signals of superpartner production will begin to erode the central motivation for supersymmetry at the weak scale. In this article we present a detailed examination of which regions of supersymmetric parameter space are most natural and the extent to which weak-scale supersymmetry becomes unnatural if no superpartners are observed at CERN LEP II, the Fermilab Tevatron, possible upgrades of these machines, and the CERN LHC.

Ion‐Implanted Charge Collection Contacts For High Purity Silicon Detectors Operated At 20 Mk, Betty A. Young, K. M. Yu

Physics

We have developed a technique for fabricating high resolution, ohmic contacts for cryogenic silicon detectors operated at temperatures well below 1 K. In this paper, we give a detailed description of the techniques used to fabricate these boron‐implanted contacts, and present characterization data obtained on 24 test samples studied during the design phase of our program. We then describe the fabrication and operation of a 23 g prototype silicon hybrid detector which simultaneously senses both the phonons and ionization produced by a single event, and which incorporates these new contacts into its design. Finally, we present data obtained using a …