UNT Theses and Dissertations - 261 Matching Results

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K-Shell Ionization Cross Sections of Selected Elements from Fe to As for Proton Bombardment from 0.5 to 2.0 MeV

Description: The problem with which this investigation is concerned is that of making experimental measurements of proton-induced K-shell x-ray production cross sections and to study the dependence of these cross sections upon the energy of the incident proton. The measurements were made by detection of the characteristic x-rays emitted as a consequence of the ionization of the K-shell of the atom. The method for relating this characteristic x-ray emission to the x-ray production cross section is discussed … more
Date: December 1973
Creator: Lear, Richard Dean
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The Shubnikov-de Haas Effect in N-Type Indium Antimonide

Description: The Shubnikov-de Haas effect is an oscillation in the electrical resistivity or conductivity of a metal, semimetal, or semiconductor as a function of changing magnetic field which occurs at low temperatures. The effect is caused by the quantization of the momentum and energy of the charge carriers by the magnetic field. Since the nature of the oscillation depends strongly on the energy band structure of the material in which it is measured, the effect could be quite useful as an investigative t… more
Date: August 1975
Creator: Stephens, Anthony Earl
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Density Profile of a Quantized Vortex Line in Superfluid Helium-4

Description: The density amplitude of an isolated quantum vortex line in superfluid 4He is calculated using a generalized Gross-Pitaevskii (G-P) equation. The generalized G-P equation for the order parameter extends the usual mean-field approach by replacing the interatomic potential in the ordinary G-P equation by a local, static T matrix, which takes correlations between the particles into account. The T matrix is a sum of ladder diagrams appearing in a diagrammatic expansion of the mean field term in an … more
Date: May 1975
Creator: Harper, John Howard
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K-Shell Ionization Cross Sections For Elements Se To Pd: 0.4 To 2.0 MeV

Description: K-Shell ionization cross section for protons over the energy range of 0.4 to 2.0 MeV have been measured on thin targets of the elements Se, Br, Rb, Sr, Y, Mo and Pd. Total x-ray and ionization cross sections for the K-shell are reported. The experimental values of the ionization cross sections are compared to the non-relativistic plane-wave Born approximation, the binary-encounter approximation, the constrained binary-encounter approximation, and the plane-wave Born approximation with correctio… more
Date: December 1974
Creator: Criswell, Tommy L.
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The Role of Defects in the Quantum Size Effect

Description: This investigation is a theoretical study of the influence of defects of finite volume on the electrical conductivity in the quantum size effect regime. Correction terms to existing equations are derived, and a physical explanation of the results is given. Many macroscopic properties of films exhibit an oscillatory dependence on thickness when the thickness is comparable to the de Broglie wavelength of an electron at the Fermi surface. This behavior is called the quantum size effect. In very th… more
Date: December 1974
Creator: Malone, Farris D.
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Collision Broadening of Microwave Spectral Lines of Monomeric Formaldehyde and Formic Acid

Description: Line width parameters for a number of spectral lines in the pure rotational spectrum of formaldehyde (CH20) and formic acid (HCOOH) have been measured using a sourcemodulated microwave spectrograph. All transitions studied in this investigation were of the type ΔJ=O (i.e. Q-branch transitions), with ΔK-1=0 and ΔK+1 =+l. The center frequencies of the measured lines varied from 8662.0 MHz to 48612.70 MHz. The experimentally determined collision diameters for self broadening interactions involving… more
Date: August 1975
Creator: Venkatachar, Arun C.
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A Classical Theory of the Dielectric Susceptibility of Anharmonic Crystals

Description: An expression for the dielectric susceptibility tensor of a cubic ionic crystal has been derived using the classical Liouville operator. The effect of cubic anharmonic forces is included as a perturbation on the harmonic crystal solution, and a series expansion for the dielectric susceptibility is developed. The most important terms in the series are identified and summed, yielding an expression for the complex susceptibility with an anharmonic contribution which is linearly dependent on temper… more
Date: May 1976
Creator: Kennedy, Howard V.
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L X-Ray Production in the Rare Earths by 0.33-2.66-MeV/amu Carbon- and 0.50-2.25-MeV/amu Oxygen-Ion Bombardment

Description: Experimentally measured L-shell x-ray production cross sections are presented for 8-36-MeV oxygen-ion bombardment of Ce, Pr, Sm, Eu, Dy, and Ho; for 4-32-MeV carbon-ion bombardment of La and Yb; for 6-32-MeV carbon-ion bombardment of Pr, Nd, Sm, and Dy; and for ll-29-MeV carbon-ion bombardment of Ce, Eu, Gd, and Ho. Theoretical predictions via the plane wave Born approximation (PWBA) with corrections for increased binding of target electrons and Coulomb deflection of the incident projectile ten… more
Date: August 1975
Creator: Pepper, George H.
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Collision Broadening in the Microwave Rotational Spectrum of Gaseous Monomeric Formaldehyde

Description: A source-modulation microwave spectrograph was utilized to measure line width parameters for several spectral lines in the pure rotational spectrum of formaldehyde (H₂CO). The spectrograph featured high-gain ac amplification and phase-sensitive detection, and was capable of measuring microwave lines having absorption coefficients as small as 10⁻⁷ cm⁻¹ with a frequency resolution on the order of 30 kHz. Center frequencies of the measured lines varied from 4,830 MHz to 72,838 MHz; hence, most of … more
Date: December 1973
Creator: Rogers, David Valmore
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Proton-Induced L-shell X-Rays of Pr, Sm, Eu, Gd, and Dy

Description: Characteristic L-shell x rays of the five rare earths Pr, Sm, Eu, Gd, and Dy were studied in this work. The x rays were produced by ionization from 0.3 to 2.0 MeV protons from the 2.0 MV Van de Graaff at North Texas State University. Total L-shell ionization and x-ray production cross sections were measured for Sm and compared to the BEA, CBEA and PWBA theories. Total L-shell ionization cross sections were measured for Pr, Eu, Gd, and Dy and compared to the BEA, CBEA, and PWBA. The CBEA and PW… more
Date: August 1974
Creator: Abrath, Frederick G.
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Effects of Quantum Coherence and Interference

Description: Quantum coherence and interference (QCI) is a phenomenon that takes place in all multi-level atomic systems interacting with multiple lasers. In this work QCI is used to create several interesting effects like lasing without inversion (LWI), controlling group velocity of light to extreme values, controlling the direction of propagation through non-linear phase matching condition and for controlling the correlations in field fluctuations. Controlling group velocity of light is very interesting b… more
Date: August 2013
Creator: Davuluri, Subrahmanya Bhima Sankar
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An Electro- Magneto-static Field for Confinement of Charged Particle Beams and Plasmas

Description: A system is presented that is capable of confining an ion beam or plasma within a region that is essentially free of applied fields. An Artificially Structured Boundary (ASB) produces a spatially periodic set of magnetic field cusps that provides charged particle confinement. Electrostatic plugging of the magnetic field cusps enhances confinement. An ASB that has a small spatial period, compared to the dimensions of a confined plasma, generates electro- magneto-static fields with a short range.… more
Date: May 2014
Creator: Pacheco, Josè L.
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The Effects of Residual Gases on the Field Emission Properties of ZnO, GaN, ZnS Nanostructures, and the Effects of Light on the Resistivity of Graphene

Description: In this dissertation, I present that at a vacuum of 3×10-7 Torr, residual O2, CO2, H2 and Ar exposure do not significantly degrade the field emission (FE) properties of ZnO nanorods, but N2 exposure significantly does. I propose that this could be due to the dissociation of N2 into atomic nitrogen species and the reaction of such species with ZnO. I also present the effects of O2, CO2, H2O, N2, H2, and Ar residual gas exposure on the FE properties of GaN and ZnS nanostructure. A brief review of… more
Date: May 2014
Creator: Mo, Yudong
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Synthesis, Characterization, Structural, and Optical Properties of Zinc Oxide Nanostructures Embedded in Silicon Based Substrates

Description: Structural and optical properties of ZnO nanostructures synthesized by low energy ion implantation technique were examined. ZnO molecular ions were implanted into Si/SiO2 substrates at room temperature and then furnace annealed under different temperatures and environments. In all as-implanted samples only Zn nanostructures with varying diameters distributed into the Si/SiO2 matrices were observed. No trace of ZnO was found. The distributions of Zn nanostructures in Si/SiO2 closely matched resu… more
Date: May 2014
Creator: Pandey, Bimal
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Synthesis Strategies and a Study of Properties of Narrow and Wide Band Gap Nanowires

Description: Various techniques to synthesize nanowires and nanotubes as a function of growth temperature and time were investigated. These include growth of nanowires by a chemical vapor deposition (CVD) system using vapor-liquid-solid (VLS) growth mechanism and electro-chemical synthesis of nanowires and nanotubes. Narrow band gap InSb Eg = 0.17 eV at room temp) nanowires were successively synthesized. Using a phase diagram, the transition of the nanowire from metallic- semiconducting- semi-metallic phase… more
Date: May 2014
Creator: Sapkota, Gopal
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How Cooperative Systems Respond to External Forces

Description: Cooperative interactions permeate through nature, bringing about emergent behavior and complexity. Using a simple cooperative model, I illustrate the mean field dynamics that occur at the critical point of a second order phase transition in the framework of Langevin equations. Through this formalism I discuss the response, both linear and nonlinear, to external forces. Emphasis is placed on how information is transferred from one individual to another in order to facilitate the collective resp… more
Date: May 2014
Creator: Svenkeson, Adam
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Novel Semi-Conductor Material Systems: Molecular Beam Epitaxial Growth and Characterization

Description: Semi-conductor industry relies heavily on silicon (Si). However, Si is not a direct-band gap semi-conductor. Consequently, Si does not possess great versatility for multi-functional applications in comparison with the direct band-gap III-V semi-conductors such as GaAs. To bridge this gap, what is ideally required is a semi-conductor material system that is based on silicon, but has significantly greater versatility. While sparsely studied, the semi-conducting silicides material systems offer gr… more
Date: December 2013
Creator: Elmarhoumi, Nader M.
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Nonlinear Optical Properties of GaAs at 1.06 micron, picosecond Pulse Investigation and Applications

Description: The author explores absorptive and refractive optical nonlinearities at 1.06 [mu]m in bulk, semi-insulating, undoped GaAs with a particular emphasis on the influence of the native deep-level defect known as EL2. Picosecond pump-probe experimental technique is used to study the speed, magnitude, and origin of the absorptive and refractive optical nonlinearities and to characterize the dynamics of the optical excitation of EL2 in three distinctly different undoped, semi-insulating GaAs samples. I… more
Date: August 1992
Creator: Cui, A.G. (Aiguo G.)
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Development and Application of a Nonlinear Optical Characterization Technique

Description: This dissertation reports a sensitive single beam experimental technique for measuring nonlinear refraction and nonlinear absorption in a wide variety of materials. The experimental setup is described and a comprehensive theoretical analysis including cases where nonlinear refraction and nonlinear absorption are also presented.
Date: August 1991
Creator: Said, Ali A. (Ali Ahmad)
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Computer Simulations of Mechanical Behavior of Polymer Liquid Crystals

Description: In this dissertation molecular dynamics simulations of behavior of polymer liquid crystals (PLC's) under tensile deformation have been performed. PLC's composed of random or block copolymers of rigid and flexible segments have been studies. Systems of fully flexible chains have been simulated for comparison. Stress-strain relations and fracture mechanics have been investigated.
Date: December 1991
Creator: Blonski, Slawomir
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Fluorine K-Shell X-Ray Cross Section Measurements for ⁷Li, ¹⁰B, ¹²C, ¹⁴N, and ¹⁶O Ions on Ultra-Clean, Ultra-Thin Yf₃ Solid Target Foils

Description: In this study, procedures were developed to produce ultra-clean, ultra-thin target foils and to remove x-ray interference from electron bremsstrahlung and low energy K-shell x-rays from contaminant elements.
Date: August 1991
Creator: Marble, Daniel Keith
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A New Method for Measuring the Nuclear Hexadecapole Interaction in Some Solids

Description: A new method for measuring the nuclear hexadecapole interaction (HDI) in solids based on NMR quadrupole echoes is described. Theoretical values of the shifts of the quadrupole echo times caused by the HDI are given for two pulse and three pulse echoes in a nuclear spin 5/2 system. The method is applied to 1271 in an almost strain free crystal of KI and a hexadecapole coupling frequency (e2M16m16/h) of 630 Hz was found. Here e is the electronic charge, em16 is the fourth gradient of the external… more
Date: August 1991
Creator: Ni, QingWen
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Coherent Resonant Interaction and Harmonic Generation in Atomic Vapors

Description: This work examines the use of higher order multiphoton resonances in higher harmonic generation together with judicious exploitation of coherent interaction properties to achieve efficient harmonic generation. A detailed experimental study on third harmonic generation in two photon resonant coherent interaction and a theoretical study on four photon resonant coherent interaction have been conducted. Two photon resonant coheren propagation in lithium vapor (2S-4S and 2S-3D interaction) has been … more
Date: August 1987
Creator: Mukherjee, Nandini
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Picosecond Measurement of Interband Saturation, Intervalence Band Absorption, and Surface Recombination in Germanium

Description: The picosecond optical response of five thin germanium samples was measured following intense optical excitation using two variations of the excitation and probe technique. Seven-picosecond laser pulses of wavelength 1.054 um were used to measure the optical transmission of the samples for a variety of probe delays, excitation fluences, and sample temperatures. These parametric experiments were performed in an effort to determine if carrier cooling, carrier diffusion, or carrier recombination d… more
Date: August 1984
Creator: Perryman, Gary Paul
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