Physical Sciences and Mathematics Commons^™

Degradation And Breakdown In Ultra-Thin Silicon Oxides, Christopher Franck

Theses

Emerging trends in the semiconductor device industry call for detailed knowledge of the properties of devices whose dimensions are small enough to exploit Quantum Mechanical effects. This thesis presents a complete picture of oxide degradation in MOS direct tunnel diodes (t0 <3.4 nm). It is demonstrated that for structures fabricated at different facilities and stressed with either gate or substrate injection, a universal degradation mode is revealed which is manifested as the build up of positive charge in the oxide. The data gathered demonstrates that the positive charging phenomena in sub-3.5 nm oxides is independent of oxide thickness, and is characterized by a voltage threshold and two-regime temperature dependence. Further, the catastrophic failure, or breakdown, of these oxides was studied and the strongest evidence to date is presented which links the positive charging phenomena to the oxide breakdown. This thesis concludes with the presentation of a novel device design which can exploit the properties of degradation and breakdown, in thin oxides, to achieve an EEPROM memory cell of superior endurance.

Supermassive Binaries And Extragalactic Jets, C. Martin Gaskell

Department of Physics and Astronomy: Faculty Publications

Some quasars show Doppler shifted broad emission line peaks. I give new statistics of the occurrence of these peaks and show that, while the most spectacular cases are in quasars with strong jets inclined to the line of sight, they are also almost as common in radio-quiet quasars. Theories of the origin of the peaks are reviewed and it is argued that the displaced peaks are most likely produced by supermassive binaries. 3C 390.3 shows precisely the change in radial velocity predicted by the supermassive binary model. The separations of the peaks in 3C 390.3-type objects are consistent with orientation-dependent …

The Flat Phase Of Crystalline Membranes, Simon Catterall, Mark Bowick, Konstantinos N. Anagnostopoulos

Physics - All Scholarship

We present the results of a high-statistics Monte Carlo simulation of a phantom crystalline (fixed-connectivity) membrane with free boundary. We verify the existence of a flat phase by examining lattices of size up to 128^2. The Hamiltonian of the model is the sum of a simple spring pair potential, with no hard-core repulsion, and bending energy. The only free parameter is the the bending rigidity \kappa. In-plane elastic constants are not explicitly introduced. We obtain the remarkable result that this simple model dynamically generates the elastic constants required to stabilise the flat phase. We present measurements of the size (Flory) …

The Flat Phase Of Crystalline Membranes, Mark Bowick, Simon Catterall, Marco Falcioni, Gudmar Thorleifsson, Konstantinos N. Anagnostopoulos

Physics - All Scholarship

We present the results of a high-statistics Monte Carlo simulation of a phantom crystalline (fixed-connectivity) membrane with free boundary. We verify the existence of a flat phase by examining lattices of size up to $128^2$. The Hamiltonian of the model is the sum of a simple spring pair potential, with no hard-core repulsion, and bending energy. The only free parameter is the the bending rigidity $\kappa$. In-plane elastic constants are not explicitly introduced. We obtain the remarkable result that this simple model dynamically generates the elastic constants required to stabilise the flat phase. We present measurements of the size (Flory) …

The Structure Of Alkali Halide Dimers: A Critical Test Of Ionic Models And New Ab Initio Results, T. Törring, S. Biermann, J. Hoeft, Richard J. Mawhorter, Robert J. Cave, C. Szemenyei

All HMC Faculty Publications and Research

In semiempirical ionic models a number of adjustable parameters have to be fitted to experimental data of either monomer molecules or crystals. This leads to strong correlations between these constants and prevents a unique test and a clear physical interpretation of the fit parameters. Moreover, it is not clear whether these constants remain unchanged when the model is applied to dimers or larger clusters. It is shown that these correlations can be substantially reduced when reliable information about dimers is available from experiments or ab initio calculations. Starting with Dunham coefficients of the monomer potential determined from microwave measurements, we …

A Classical Analysis Of Proton Collisions With Ground-State And Excited, Aligned Sodium Targets, C. J. Lundy, Ronald E. Olson

Physics Faculty Research & Creative Works

The dependence of electron capture and ionization processes on the pre-collision electronic distribution is examined for the systems H+ + Na(3s, 3pΣ, 3pΠ) primarily in the energy range 1-15 keV. Populations of the capture and ionization channels as well as the coherence of the post-collision electronic distribution of the capture product are formulated using the classical trajectory Monte Carlo (CTMC) method. Total capture and ionization cross sections arising from initially aligned Na(3p) targets exhibit transient behaviour near the velocity-matching energy of 5.7 keV. This observation is described in terms of anisotropy parameters; anisotropy effects are also analysed for the capture …

State-Selective Electron Capture In Low Velocity Multiply Charged Ion, Helium Collisions, A. Cassimi, S. Duponchel, X. Flechard, P. Jardin, P. Sortais, D. Hennecart, Ronald E. Olson

Physics Faculty Research & Creative Works

Recoil ion momentum spectroscopy has been applied to study low energy, state-selective single electron capture by highly charged projectiles. The specific systems investigated are fully stripped 6.82 keV/u Ne10+ 6.82 keV/u Ar18+ on He. Measurements of the He+ recoil ion longitudinal momenta are used to determine the final n-state dependence of the captured electron. Simultaneous measurement of the transverse momenta of the recoil ion yields information about the impact parameter dependence of the reaction and the reaction window for electron capture. © 1996 The American Physical Society.

Vortex Dynamics And Defects In Simulated Flux Flow, Alan Middleton, Michael Chance Faleski, M. C. Marchetti

Physics - All Scholarship

We present the results of molecular dynamic simulations of a two-dimensional vortex array driven by a uniform current through random pinning centers at zero temperature. We identify two types of flow of the driven array near the depinning threshold. For weak disorder the flux array contains few dislocation and moves via correlated displacements of patches of vortices in a {\it crinkle} motion. As the disorder strength increases, we observe a crossover to a spatially inhomogeneous regime of {\it plastic} flow, with a very defective vortex array and a channel-like structure of the flowing regions. The two regimes are characterized by …

Distribution Of Ionized And Neutral Halogenated Phenols In An Octanol-Water Membrane Model System, Robert Word

Dissertations and Theses

The accumulation of xenobiotics, such as halogenated phenols, in soils, sediments, and living organisms is primarily a partitioning process between an aquatic and organic phase. It is traditional to use a bulk octanol-water system to model the partitioning of a compound between complex biological lipid membranes and aqueous media. The octanol-water partition coefficient K_OW successfully approximates the lipid membrane-water partition coefficient K_LipW of neutral compounds. However, the ionized species of substituted phenols were shown to have a higher affinity for lipid membranes than predicted from octanol-water results.

Data on the octanol-water partition coefficients of molecular ions is limited. …

Scaling Behavior In Soliton Models, Joseph Schechter, Masayasu Harada, F. Sannino, H. Weigel

Physics - All Scholarship

In the framework of chiral soliton models we study the behavior of static nucleon properties under rescaling of the parameters describing the effective meson theory. In particular we investigate the question of whether the Brown--Rho scaling laws are general features of such models. When going beyond the simple Skyrme model we find that restrictive constraints need to be imposed on the mesonic parameters in order to maintain these scaling laws. Furthermore, in the case when vector mesons are included in the model it turns out that the isoscalar form factor no longer scales according to these laws. Finally we note …

Reconnecting The Sciences, John Eggebrecht, Raymond Dagenais, Don Dosch, Norman J. Merczak, Margaret N. Park, Susan C. Styer, David Workman

Faculty Publications & Research

During the last three years at the Illinois Mathematics and Science Academy, we have been working on a partial reconstruction of Whitehead's "one subject matter," a course reconnecting biology, chemistry, earth and space sciences, and physics into an Integrated Science program.

The Interaction Of Intense Laser Pulses With Atomic Clusters, T. Ditmire, Thomas D. Donnelly, A. M. Rubenchik, R. W. Falcone, M. D. Perry

All HMC Faculty Publications and Research

We examine the interaction of intense, femtosecond laser radiation with the large (50–200 Å) clusters produced in pulsed gas jets. Both experiment and simulation show that the plasmas produced during these interactions exhibit electron temperatures far in excess of that predicted by above-threshold ionization theory for a low-density gas. Efficient heating of the clusters by the laser is followed by rapid expansion of the clusters and long-lived x-ray emission from hot, decaying, underdense plasma.

Relativistic Momentum, Paul Finkler

Paul Finkler Papers

Introductory treatments of relativistic dynamics rely on the invariance of momentum conservation (i.e., on the assumption that momentum is conserved in all inertial frames if it is conserved in one) to establish the relationship for the momentum of a particle in terms of its mass and velocity. By contrast, more advanced treatments rely on the transformation properties of the four-velocity and/or proper time to obtain the same result and then show that momentum conservation is invariant. Here, we will outline a derivation of that relationship that, in the spirit of the more advanced treatments, relies on an elemental feature of …

Auger Electron Spectroscopy Of Free Argon Clusters, A. Knop, D.N. Mcilroy, Peter A. Dowben, E. Ruhl

Peter Dowben Publications

Auger electron spectra and Auger yields of free argon clusters in the Ar(2p) excitation regime are reported. The Auger yield spectra show characteristic changes as a function of cluster size. The results indicate that the Auger yield signal originates primarily from the surface of the clusters. The results are compared to bulk-sensitive experimental techniques, such as total electron yields (TEY), zero kinetic energy electron (ZEKE) spectra for variable size clusters, as well as Auger yield spectra of condensed argon multilayers.

The Observatory That Never Was, M. Eugene Rudd

M. Eugene Rudd Publications

Astronomy has been taught at the University of Nebraska since it first opened its doors in 1871, but for almost half of this time the university had no telescope larger than a Cinch Brashear refractor. Goodwin DeLoss Swezey, the astronomy professor at the turn of the century, had a small observatory built on campus to house this and other astronomical instruments.
Despite Swezey's ambitions for a larger telescope, the university's resources were limited. So he proposed to build a 12-inch refractor himself with the help of Charles S. Minnich, a nearby country doctor and amateur astronomer. Not only could Minnich …

Far-Ultraviolet Stellar Photometry: Fields Centered On Ρ Ophiuchi And The Galactic Center, Edward G. Schmidt, George R. Carruthers

Edward Schmidt Publications

Far-ultraviolet photometry is presented for 121 objects in a 20" diameter field centered on ρ Oph and for 649 objects in a field covering the Galactic center. Broadband magnitudes with effective wavelengths of 1375 Å and 1781 Å are given. The Galactic center field overlaps two fields which were discussed in an earlier paper. Eighty-eight percent of the ultraviolet objects in the ρ Oph field were identified with visible stars using the SIMBAD database, while only 9% of the objects are blends of early-type stars too close together to separate with our resolution. The photometric calibration was studied in detail, …

Surface-Enhanced Raman Scattering At Elevated Temperatures, P.T. Leung, M. H. Hider, Erik J. Sánchez

Physics Faculty Publications and Presentations

The effect on surface-enhanced Raman scattering due to the increase in temperature of the metallic substrate is studied via a simple model for physisorbed molecules. Surface roughness is represented by a spherical or spheroidal island, and the temperature effects on the surface plasmon are accounted for via a slightly modified Ujihara model. It is found that the enhancement ratio in general decreases as substrate temperature increases. For noble metals like silver, this temperature effect is particularly pronounced at scattering frequencies close to that of the surface-plasmon resonance; and for frequencies well below the surface plasmon frequency, the enhancement ratio is …

Critical Point For The Blue-Phase-Iii-Isotropic Phase Transition In Chiral Liquid Crystals, Z. Kutnjak, C. W. Garland, Colin G. Schatz , '97, Peter J. Collings, C. J. Booth, J. W. Goodby

Physics & Astronomy Faculty Works

The highly chiral compound S,S-4 ''-(methylbutyl)phenyl-4'-(methylbutyl) biphenyl carboxylate (S,S-MBBPC) undergoes a continuous supercritical evolution from the isotropic (I) phase to the third blue phase (BPI III). Mixtures of S,S-MBBPC and its racemate have been studied with high-resolution calorimetry capable of quantitative latent heat determinations and with optical activity measurements. Both experiments indicate that the first-order BP III-I transition line ends at a critical point when the chiral mole fraction X(c) similar or equal to 0.45. Analysis of C-p and optical activity data for the near-critical mixture with X = 0.45 indicates mean-field behavior instead of the theoretically predicted Ising fluctuation …

A Study Of The Gradient Drift Instability In The High-Latitude Ionosphere Using The Utah State University Time Dependent Ionospheric Model, Mahesh Subramanium

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Research over the years has established that the Gradient Drift Instability process causes small-scale irregularities, mostly along the edges of the high-latitude polar cap patches. Studying these irregularities will help in the development of a Global Scale Ionospheric model, which is a central part of a global space weather forecast system. Much theoretical work has been done with varying degrees of complexity to study this instability in the high latitude patches.

In this work we have used the Utah State University Time Dependent Ionospheric Model to model the high-latitude patches, calculate the growth rate of the instability, and perform a …

Characterization Of Spatial And Temporal Anisotropy In Turbulent Mixing Layers Using Optical Techniques, Patrick J. Gardner

Theses and Dissertations

The optical aberrations induced by mixing layers of dissimilar gases are recorded and analyzed in order to characterize the spatial and temporal properties of the flow. Laser light was propagated through a mixing layer of Helium and Nitrogen gas, having velocities of 8.5 m/sec and 1.5 m/sec, respectively. The light was propagated in a direction perpendicular to the plane of the mixing layer. The mixing layer was evaluated in two experimental regimes: free turbulent mixing, where the mixing layer spreads into the surrounding air; and channel flow, where the mixing layer is confined to a rectangular channel. The optical perturbations …

Polarization Stability And Dynamics In A Model For A Polarization-Isotropic Laser That Goes Beyond Third-Order Lamb Theory, N. B. Abraham, Mark Matlin, R. S. Gioggia

Physics Faculty Research and Scholarship

Instabilities and dynamical pulsations are common features of solutions of a model that includes the material variable dynamics for a laser with a polarization isotropic resonator and with a homogeneously broadened j=1 --> j=0 transition. These resemble in some respects features found in third-order Lamb theories under anisotropic conditions, such as splitting of the optical field into two relatively independent orthogonally polarized modes with different optical frequencies. At higher intensities the amplitudes and frequencies of these modes exhibit such strong coupling that a ''two-mode'' description loses its usefulness or effectiveness. Various periodic attractors with strong intensity and polarization pulsations are …

Simulations Of Electrostatic Modes Of Non-Neutral Plasmas With Small Aspect Ratio In A Penning Trap, Grant W. Mason, Ross L. Spencer, Jonathan A. Bennett

Faculty Publications

The dependence on induced charge, experimental geometry, and temperature of electrostatic modes in very low aspect ratio non-neutral plasmas in a Penning trap is considered. The modes are of interest as non-destructive diagnostics of the shape of the plasmas. These investigations include equilibrium calculations of plasma shapes and profiles at finite temperature and particle-in-cell simulations of axisymmetric modes. The results of the simulations are compared to the zero-temperature theory by Dubin [Phys. Rev. Lett. 66, 2076 (1991)] taken to first-order in the aspect ratio and to experimental measurements by Weimer et al. [Phys. Rev. A 49, 3842 (1994)]. In general, …

An Instrument For Experimental Secondary Electron Emission Investigations, With Application To The Spacecraft Charging Problem, Robert Davies

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Secondary electron emission (SEE) and incident-particle backscattering are important processes accompanying the impact of energetic electrons and ions on surfaces. The phenomena play a key role in the buildup of electrical charge on spacecraft surfaces. and are therefore of particular interest to scientists attempting to model spacecraft charging. In response to a demonstrated need for data, techniques for determining total secondary electron (SE) and backscatter (BS) yields S and n, and associated scattering-angle-resolved, scattering-energy-resolved, and simultaneous angle-energy-resolved yields have been developed. Further, an apparatus capable of making the necessary measurements for experimental determination of these quantities-for conducting materials in …

Fabrication Of Large Arrays Of Micron-Scale Magnetic Features By Selective Area Organometallic Chemical Vapor Deposition, D. Welipitiya, Y.L. He, Jiandi Zhang, P.I. Oden, T. Thundat, R.J. Warmack, Ismail Gobulukoglu, Z.S. Shan, David J. Sellmyer, Peter A. Dowben

Peter Dowben Publications

We demonstrate that it is possible to deposit a wide range of magnetic features, using photoassisted selective area organometallic chemical vapor deposition. Large arrays of identical micron-scale Ni features were deposited on a Si(111) wafer by this method. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features. This method can be adapted to the fabrication of smaller-scale magnetic and electronic devices. ©1996 American Institute of Physics.

Very High Density Clumps And Outflowing Winds In Qso Broad-Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, R. F. Carswell, F. Hamann, M. M. Phillips, D. A. Verner, Belinda J. Wilkes, R. E. Williams

Physics and Astronomy Faculty Publications

Intercomparison of the spectra of seven high-luminosity quasi-stellar objects (QSOs) shows that there is a gradation of properties in their broad emission-line regions (BELRs) that can be understood as differing mixtures of different gas components. Six of these seven objects have unusually narrow BELR profiles, which greatly facilitates the disentangling of blends and measuring of weak lines. In the QSO 0207 - 398, the BELR is made up of at least three kinematically distinct components; its spectrum is in fact a composite of the spectra of the more homogeneous BELRs in the QSOs at either end of our sequence of …

High Metal Enrichments In Luminous Quasars, Gary J. Ferland, Jack A. Baldwin, Kirk T. Korista, Fred Hamann, R. F. Carswell, Mark Phillips, Belinda J. Wilkes, Robert E. Williams

Physics and Astronomy Faculty Publications

We discuss observations of the broad emission line in luminous intermediate redshift quasars, with emphasis on Q0207 -398. This object has relatively sharp lines, allowing us to deconvolve the profiles into distinct components. In this paper we examine the high ionization region, which we show must be matter-bounded, partially transparent to ionizing radiation. We measure a large N V λ1240/He II λ1640 ratio in Q0207-398, but detailed calculations predict this ratio to be ~1 for standard cloud properties. We show that no choice of incident continuum, ionizing photon flux, density, or even the appeal to nonradiative energy sources, can reproduce …

The Chemical Enrichment Of Gas In Broad Absorption Line Qsos: Rapid Star Formation In The Early History Of Galaxies, Kirk Korista, Fred Hamann, Jason W. Ferguson, Gary J. Ferland

Physics and Astronomy Faculty Publications

Utilizing spectra from ground-based and Hubble Space Telescope observations, Korista et al. identified at least 12 broad absorption lines in the broad absorption line (BAL) QSO 0226-1024 (z_em = 2.256), many for the first time. In the present paper we use seven of their measured column densities to investigate the BAL gas ionization equilibrium and metallicity. We assume that the metal abundances follow the rapid star formation (RSF) models of Hamann & Ferland or are simply scaled from solar ratios to (1) limit the free parameters in constraining the overall metallicity and (2) test the applicability of such a …

Magnetic Hardening Of Melt-Spun Nanocomposite Nd2Fe14B/Fe Magnets, I. Panagiotopoulos, L. Withanawasam, A.S. Murthy, George C. Hadjipanayis, E.W. Singleton, David J. Sellmyer

David Sellmyer Publications

Coercivity optimization studies were done on melt-spun nanocomposite Nd₄R₂Fe_87-xNbT_xB₆ (R=Nd,Y,Dy; T=Ag,Cu) isotropic ribbon samples. The maximum attainable coercivities, after adjusting the annealing time, were found to be very sensitive to the annealing temperatures. The optimum magnetic properties [H_c=3.9 kOe, (BH) _max=10 MGOe] were obtained by annealing at 750–775 °C for a few minutes. Optimization by flash annealing gave similar results. Microstructural studies show that the grain size is greater than the theoretically predicted grain size for optimum coupling between the hard and the soft phase. With the …

Electronic Origins Of Ordering In Multicomponent Metallic Alloys: Application To The Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski, J. B. Staunton

Duane D. Johnson

We investigate the ordering tendencies of the fcc Cu-Ni-Zn system using a recently developed first-principles, density-functional-based theory of atomic short-range order (ASRO) in disordered substitutional alloys of an arbitrary number of components. We find for the binary alloys a variety of effects which should lead to competition in the ternaries: commensurate ordering (Ni-Zn), long-period ordering (Cu-rich Cu-Zn), and clustering (Cu-Ni), in agreement with experiment. We calculate the ASRO of various disordered ternary alloys (as described by the Warren-Cowley pair-correlation function) and discuss its relationship to the electronic structure of the binary and ternary disordered alloys. We find [100]-type ASRO over …

Magnetic Properties And Magnetization Reversal In Co/Au Multilayers (Abstract), Z. S. Shan, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We report studies of magnetic properties in CoX Å/Au60 Å multilayers (X = 5,6,7,8,12,20 Å), which were prepared by sputtering on Si(111) substrates, with emphasis on the magnetization reversal. Magnetization reversal was investigated by measurements of initial magnetization curves, minor loops, coercivity as a function of the maximum field of minor loops, temperature dependence of magnetic properties using Kronmüller’s model, time decay of Kerr rotation angle UK, and the field-sweep speed dependence of coercivity H_c(dH_a/dt) at room and/or low temperature. It is found that (1) the thermal activation volumes determined by H_{c …}