Physical Sciences and Mathematics Commons^™

The Effects Of Fast Secondary Electrons On Low Voltage Electron Beam Lithography, Mehdi Bolorizadeh

Doctoral Dissertations

In 1981 Prof. Sir Alec Broers suggested that the spatial limit of direct writing electron beam lithography (DWEBL) would be limited to ~10 nm by the laterally scattered fast secondary electrons (FSE) even in atomically thin resist. Experiments and simulations have been carried out to quantify the contribution of FSE to the energy deposition that results in exposure of the resist over high beam energies. One possible solution to this restriction would be to use low energy electrons.

To examine Broers' hypothesis in low voltage electron beam lithography (EBL), studies in the low energy range on the effects of FSE …

Linear And Nonlinear Chiroptical Effects, Watheq Ahmad Al-Basheer

Doctoral Dissertations

Chiroptical effects of linear and nonlinear nature are investigated by employing a variety of spectroscopic methods, such as linear and nonlinear circular dichroism, optical rotation, vibrational Raman scattering, infrared absorption and Vibrational Circular Dichroism. (2+1) Resonance Enhanced Multiphoton Ionization Circular Dichroism (REMPICD) is a direct demonstration of the nonlinear chiroptical effects of a sample of R-(+)-3-methylcyclopentanone. Solvent effects on circular dichroism is studied for 35 common solvents, which is significantly attributed to the solute- solvent electrostatic and Van der waals interactions for CD and ORD of R3MCP. Hartree-Fock and Density Function Theoretical calculations of R3MCP CD and …

Combined Study Of Reactor And Terrestrial Antineutrinos With Kamland, Mikhail Batygov

Doctoral Dissertations

This dissertation presents a combined study of antineutrinos of terrestrial and reactor origin detected by Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND). Of special physical interest are neutrino oscillation parameters and the terrestrial antineutrino flux, the former being of a profound importance for new physics beyond the Standard Model, and the latter having significant implications for geophysics. The analysis described here uses a comprehensive likelihood model to naturally combine terrestrial and reactor antineutrino studies within a single framework. The use of this likelihood model and better event reconstruction tools allowed to obtain narrower limits for the oscillation parameters and the terrestrial …

Interference Effects Among J = 3/2+ Resonances In 19Ne System & Searching For Resonances In The Unbound 6Be Nucleus, Kyung Yuk Chae

Doctoral Dissertations

The ¹⁸F(p,α)¹⁵O reaction plays a crucial role in understanding γ-ray emission from novae. Because of the importance of understanding the ¹⁸F + p reactions, a number of studies of the A=19 isobars have been made using stable and exotic beams. The interference effects among J ^π = 3/2⁺ resonances in the ¹⁸F + p system, however, have never been measured, but they can change the S-factor by a factor of 20 at nova energies. R-matrix calculations indicate that the cross sections above the Ec.m. = 665 keV resonance are sensitive …

Single-Molecule Detection With Active Transport, David Allan Ball

Doctoral Dissertations

A glass capillary is used near the focal region of a custom-built confocal microscope to investigate the use of active transport for single-molecule detection in solution, with both one and two-photon laser excitation. The capillary tip has a diameter of several microns and is carefully aligned nearby to the sub-micron laser beam waist, collinear to the optical axis, so that a negative pressure-difference causes molecules to be drawn into the capillary, along the laser beam axis. The flow of solution, which is characterized by fluorescence correlation spectroscopy (FCS), can increase the single-molecule detection rate for slowly diffusing proteins by over …

Regularization Of The Particle-Particle Interaction In The Nuclear Density Functional Theory, Piotr Jerzy Borycki

Doctoral Dissertations

In this work we show how to regularize the ultraviolet divergences appearing in the local pairing term of the energy density functional. Our approach, entirely rooted in the framework of the Density Functional Theory, is based on the regularization of local densities and currents and can be applied to various classes of energy density functionals. We demonstrated, that for the particular choice of the pairing term of energy density functional, our procedure gives the same regularization scheme to the one obtained earlier by the means of the pairing gap regularization.

We also investigated the non-unitarity of the Bogoliubov tranformation due …

Measurement Of The 32S(P,D)31S Reaction And Its Astrophysical Implications, Zhanwen Ma

Doctoral Dissertations

The ³⁰P(p,γ)³¹S reaction plays a crucial role in the synthesis of heavier nuclear species, from Si to Ca, in nova outbursts on ONe White Dwarfs [26, 28, 35]. However, its rate is very uncertain as a result of the lack of spectroscopic information on the levels above proton threshold in ³¹S. The currently adopted rate of this reaction, based on statistical Hauser-Feshbach calculations [36], could have an uncertainty as much as a factor of 100 higher or lower under nova conditions [26].

To reduce these uncertainties, we have measured differential cross sections for the ³²S(p,d) …

Photochemical Route To The Production Of Fullerene Allotropes, Olga Ovchinnikova

Masters Theses

A photochemical route to the formation of two C₆₀ molecules which are bridged by one and up to eighteen carbon atoms to form bucky-dumbbell shaped molecules, i.e., C₆₀ > C < C₆₀ to C₆₀ > C = C = C = C = C = C = C = C = C = C < C₆₀, etc. is described. Irradiation of C60 in solutions of chloroform and iodine (magenta color) with pulsed laser light from the frequency tripled (355 nm) Nd:YAG laser produced a dark crimson color. Matrix assisted laser desorption ionization (MALDI) negative ion mass spectroscopy was used to …

Neutron Diffraction Study Of Heavy Water Intercalation In Superconducting Deuterated Sodium Cobaltate Na0.35Coo21.4d2O, Cinzia Metallo

Masters Theses

When Na-deficient Na_xCoO₂ is intercalated with water¹ or heavy water², it becomes a superconductor. The maximum critical temperature of 4.5 K is found for the composition Na_xCoO₂yD₂O (x= 0.3 and y=1.4). In spite of its low transition temperature, several similarities with high temperature superconducting cuprates have raised interest in this compound. Nevertheless, up to now, a clear understanding of the role of water has not been achieved.

Since superconductivity appears only when water is inserted in the parent compound, the goal of this research work was to understand …

Four-Dimensional Mvct Imaging And Spatial Translation Of Helical Tomotherapy Dose Distributions Using Sinogram Modification, Samuel Scott Outten

Masters Theses

Helical tomotherapy systems have the unique attribute of using sinograms as a machine input and a machine output. These sinograms have well understood properties that may allow for operational changes that simplify and/or improve radiation treatment.

In the first part of this work, the detector array output sinogram of an MVCT imaging study is used to produce images of an object at different locations along a pattern of motion and the multi-leaf collimator (MLC) control sinogram is used to translate dose distributions in space. A temporal re-binning algorithm was written that divided the MVCT sinogram projections into positional bins that …

Cross Sections Fall 2006, Department Of Physics And Astronomy

Cross Sections

No abstract provided.

Growth And Superconductivity Of Pb And Pb-Bi Alloys In The Quantum Regime, Mustafa Murat Ozer

Doctoral Dissertations

Superconductivity is a collective quantum phenomenon that is inevitably suppressed in reduced dimensionality. Questions of how thin superconducting wires or films can be before they lose their superconducting properties have important technological ramifications and go to the heart of understanding formation, coherence, and robustness of the superconducting state in quantum confined geometries. Suppression of superconductivity in low dimensions is usually attributed to thermal or quantum fluctuations, or to pair-breaking Coulomb interactions in the presence of strong disorder. Control and quantification of a film’s disorder length scale remained a critical experimental obstacle, however. Here, we exploit quantum confinement of itinerant electrons …

Ab-Initio Calculations Of The Charge-Density Response In Complex Materials, Oscar Dario Restrepo Tovar

Doctoral Dissertations

Our main goal is to have a realistic description of the charge excitations in complex materials in the range of energies such as the coulomb energy U, which is in the eV range. Spectra of these charge excitations, for a large range of wave vector transfers, may provide signatures of the underlying electronic structures. The charge-density response function calculated within Time-dependent Density functional (TDDFT) is an ideal theoretical framework for the calculation of these excitations, since comparison with experimental data (in particular with non-resonant inelastic x-ray scattering experiments) can be done in absolute units (without the need of any adjustable …

Neutron Scat- Tering In The Novel Quantum Magnets: Livo2 And Dmacucl3, Wei Tian

Doctoral Dissertations

The behavior of magnetic systems in the extreme quantum limit is one of the most interesting forefront areas in condensed matter physics. This dissertation investigates two particularly interesting quantum magnets: LiVO₂ and DMACuCl₃. Systematic studies were performed on single crystal samples using different experimental techniques, especially inelastic neutron scattering. Detailed experimental results and corresponding model calculations are presented and discussed in this dissertation.

LiVO₂ is a good candidate to study the interplay between “magnetic frustration” and orbital ordering. V³⁺ ions in LiVO₂ form a triangular lattice involving threefold degenerate t_2g orbitals. LiVO2 undergoes …

Manifestations Of Broken Symmetry: The Surfaces Phases Of Ca2−XSrXRuo4, Robert G. Moore Ii

Doctoral Dissertations

The discovery of superconductivity in Sr₂RuO₄ has renewed vigor in the study of correlated electron systems. The evolution of a p-wave superconducting state from a para- magnetic 2-dimensional Fermi liquid shows the ruthenate superconductivity is anything but conventional. Sr₂RuO₄ is isostructural with La₂CuO₄, the parent compound for the high temperature superconducting family La2_−xSr_xRuO₄. The substitution of Ca²⁺ for Sr²⁺ generates a different structure involving a static rotation and tilt of the RuO₆ octahedral, however, the antiferromagnetic insulating ground state of Ca …

Surface Studies Of Selective Hydrogen Desorption From Silicon, Jason Kenneth Smith

Masters Theses

This thesis examines quantum confined quasi-one-dimensional structures on silicon surfaces. An in situ prepared and hydrogenated Si(100)-(2x1) is investigated, on which a quasi-dimensional nanostructure is fabricated via scanning tunneling microscopy. Also, the feasibility of STM-based nanolithography on an ex situ hydrogenated Si(111)-(1x1) surface is explored. Using methods such as those discussed herein it is possible to create quasi one-dimensional semiconducting metallic nanowires as well as contact pads, useful for four point probe measurements at the nanoscale. Using a STM, dimer wide strips of hydrogen are removed from the passivated layer to reveal bare silicon surface bonds forming a nanowire approximately …

Ultraviolet Image Analysis Of Spacecraft Exhaust Plumes, Karen L. Norton

Masters Theses

Data obtained during the April 26, 2000 MirEx experiment is used to infer the chemical mechanisms responsible for ultraviolet radiation observed to emanate from Russian spacecraft exhaust plumes in low Earth orbit. The principle objective of this experiment was to use the Mir Space Station instruments to study the plume collisional processes occurring in the rarified atmosphere of the far-field; at distances greater than one kilometer away from the spacecraft. This was accomplished by observing the automated Progress cargo ship as the auxiliary engines were being retrofired in a ram-burn configuration at 330 kilometers in altitude above Earth. The primary …

Superdeformation And High Spin Spectroscopy Studies On 174Hf, Martin Krassimirov Djongolov

Doctoral Dissertations

High-spin states of the nucleus ¹⁷⁴Hf were populated using the heavy-ion reactions at the Atlas accelerator facility at the Argonne National Laboratory and the 88" cyclotron facility at the Lawrence Berkeley National Laboratory. The de-exciting [gamma] rays are detected with the GAMMASPHERE spectrometer. In this nucleus, eight superdeformed bands are observed for the first time. Studies on these bands as well as eight bands with normal deformation are performed. The hypothesis for presence of a triaxial shape at high deformation in ¹⁷⁴Hf is tested via lifetime measurements of the states of the superdeformed structures. The deduced quadrupole moments …

Magnetism And Transport Properties Of Transition Metal Oxides And Nanoparticles, Dane Thomas Gillaspie

Doctoral Dissertations

This dissertation is devoted to the study of the properties of transition metal oxides in both thin film and nanocrystalline forms.

The first section is devoted to the transport properties of manganese oxide thin film samples. The colossal magnetoresistance in these materials is usually explained using double-exchange, but this explanation is only partially correct. Recent theoretical and experimental work has shown that these compounds have a strong tendency towards phase-separation. The impact of strain on phase separation has been investigated by growing films of La_5/8-0.3Pr_0.3Ca_3/8MnO₃ on a variety of substrates. Very small changes …

The Role Of Novel Magnetic Interactions In Surface-Supported Magnetic Nanodot Assemblies, Maria Asuncion Torija Juana

Doctoral Dissertations

The manipulation of matter at the atomic scales facilitates understanding of the fundamental properties of magnetism and opens the possibility of designing systems with novel magnetic properties with limitless industrial applications. This thesis seeks to identify nano-scale magnetic coupling mechanisms in nanostructures assemblies and to better understand different magnetic phases and the associated transitions. This was accomplished through the study of three prototype systems: Fe nanodots of controlled size and density on single crystal substrates of nonmagnetic metals, fractal – dimensional Fe on Cu(111), and FeGe nanowires on Ge(111). The first system shows the presence of a novel magnetic coupling …

Applications Of Modern Statistical Methods To Analysis Of Data In Physical Science, James Eric Wicker

Doctoral Dissertations

Modern methods of statistical and computational analysis offer solutions to dilemmas confronting researchers in physical science. Although the ideas behind modern statistical and computational analysis methods were originally introduced in the 1970’s, most scientists still rely on methods written during the early era of computing. These researchers, who analyze increasingly voluminous and multivariate data sets, need modern analysis methods to extract the best results from their studies.

The first section of this work showcases applications of modern linear regression. Since the 1960’s, many researchers in spectroscopy have used classical stepwise regression techniques to derive molecular constants. However, problems with thresholds …

Cross Sections Spring 2006, Department Of Physics And Astronomy

Cross Sections

No abstract provided.

Population Size Bias In Descendant-Weighted Diffusion Quantum Monte Carlo Simulations, G. Lee Warren, Robert J. Hinde

Chemistry Publications and Other Works

We consider the influence of population size on the accuracy of diffusion quantum Monte Carlo simulations that employ descendant weighting or forward walking techniques to compute expectation values of observables that do not commute with the Hamiltonian. We show that for a simple model system, the d-dimensional isotropic harmonic oscillator, the population size must increase rapidly with d in order to ensure that the simulations produce accurate results. When the population size is too small, expectation values computed using descendant-weighted diffusion quantum Monte Carlo simulations exhibit significant systematic biases.

Interaction-Induced Dipole Moment Of The Ar–H2 Dimer: Dependence On The H2 Bond Length, Robert J. Hinde

Chemistry Publications and Other Works

We present ab initio calculations of the interaction-induced dipole moment of the Ar–H₂ van der Waals dimer. The primary focus of our calculations is on the H₂ bond length dependence of the dipole moment, which determines the intensities of both the collision-induced H₂ = 1 ← 0 fundamental band in gaseous Ar–H₂ mixtures and the dopant-induced H₂ = 1 ← 0 absorption feature in Ar-doped solid H₂ matrices. Our calculations employ large atom-centered basis sets, diffuse bond functions positioned between the two monomers, and a coupled cluster treatment of valence electron correlation; core-valence correlation …