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Theses and Dissertations

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Articles 421 - 436 of 436

Full-Text Articles in Materials Science and Engineering

Phase Conjugation In Optical Fiber Via Stimulated Brillouin Scattering With Feedback From A Barium Titanate Crystal, Patrick R. Emmert Dec 1992

Phase Conjugation In Optical Fiber Via Stimulated Brillouin Scattering With Feedback From A Barium Titanate Crystal, Patrick R. Emmert

Theses and Dissertations

The goal of this thesis was to obtain phase conjugation in multi-mode optical fiber via stimulated Brillouin scattering (SBS) with the aid of a barium titanate crystal which formed a phase conjugate cavity for the Stokes beam. SBS was demonstrated but the SBS threshold was unaffected by the presence of the barium titanate crystal and no evidence for the presence of phase conjugation in the optical fiber was obtained.

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Processability Of Polythiophene Thin Films By Ultraviolet Photo Bleaching, Derek D. Fletcher Dec 1992

Processability Of Polythiophene Thin Films By Ultraviolet Photo Bleaching, Derek D. Fletcher

Theses and Dissertations

Materials possessing strong ��(3) optical properties such as Polythiophene are sought for the production of optical switches. Polythiophene thin films produced by plasma enhanced CVD show a surface rms roughness of 10-15 angstroms over single square micron areas which is acceptable for wave guiding in the near IR. This research investigates permanently changing the optical properties of such a thin film by exposure to UV radiation (254 nm, 35 mW/cm2), known as photo bleaching, in hope of creating a refractive index boundary for use in total internal reflection. After 60 minutes exposure the refractive index shows …

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Cathodoluminescence Spectroscopy Of Zinc Germanium Phosphide Zngep2, Michael R. Gregg Dec 1992

Cathodoluminescence Spectroscopy Of Zinc Germanium Phosphide Zngep2, Michael R. Gregg

Theses and Dissertations

Zinc Germanium Phosphide (ZnGeP2) is a nonlinear semiconductor suitable for use as a laser tuning element over the two to six micron wavelength range. Although this crystal has been studied in the past, its luminescent properties are not yet well understood. In this present study, ZnGeP2 has been examined using cathodoluminescence spectroscopy (CL). Specifically, the spectral dependence of the CL was obtained as a function of electron beam energy, beam current and temperature. The resulting CL was found to be polarized with a peak structure that was dependent on the polarization. This peak structure observed by CL …

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The Effect Of Oxide Layers And Boron Doping On The Breakdown Of High Purity Silicon, Brian A. Hibbeln Dec 1992

The Effect Of Oxide Layers And Boron Doping On The Breakdown Of High Purity Silicon, Brian A. Hibbeln

Theses and Dissertations

For many applications such as lasers and radar drive circuits, there exists a need for solid state high voltage, high current switches. Current gaseous discharge switches fail to satisfy the ruggedness, reliability, and lifetime requirements of today's systems. A promising alternative is the Photoconductive Semiconductor Switch (PCSS). The limiting factor in the operation of these switches is the occurrence of breakdown through channels formed slightly below the surface. A theory on the formation of these channels is presented based upon band bending at the metal-semiconductor interface, a nonhomogeneous space charge due to irregular trap distributions, and thermal runaway in localized …

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A Response Surface Methodology Study Of Ferroelectric Memory Devices, Kevin C. Smith Mar 1992

A Response Surface Methodology Study Of Ferroelectric Memory Devices, Kevin C. Smith

Theses and Dissertations

Fatigue in ferroelectric memory devices was studied. The application of fatigue pulses to a ferroelectric sample was controlled by the RT-66 Ferroelectric Tester, a variation of the Sawyer-Tower circuit. The RT-66 also controlled data collection following the fatiguing process. Seven variables were evaluated for their potential- affect on fatigue. A sequence of fatigue tests, which varied the settings of these variables, was developed using Response Surface Methodology (RSM) experimental designs. Least-squares regression models were developed once a particular RSM set of design experiments was completed. These models were evaluated using RSM tools, and the analysis of these models allowed the …

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Characterizing The Sensitivity, Selectivity, And Reversibility Of The Metal-Doped Phthalocyanine Thin-Films Used With The Interdigitated Gate Electrode Field-Effect Transistor (Igefet) To Detect Organophosphorous Compounds And Nitrogen Dioxide, Clayton P. Howe Dec 1991

Characterizing The Sensitivity, Selectivity, And Reversibility Of The Metal-Doped Phthalocyanine Thin-Films Used With The Interdigitated Gate Electrode Field-Effect Transistor (Igefet) To Detect Organophosphorous Compounds And Nitrogen Dioxide, Clayton P. Howe

Theses and Dissertations

This study investigated the sensitivity, reversibility, and selectivity of the thin film coatings used on the interdigitated gate electrode field effect transistor (IGEFET) gas microsensor. These responses were quantified based on the dc resistance changes and frequency domain responses of the microsensor. The thin-film materials included: copper phthalocyanine (CuPc), nickel phthalocyanine (NiPc), and cobalt phthalocyanine (CoPc). The challenge gases included: diisopropyl methylphosphonate (DIMP), dimethyl methylphosphonate (DMMP), nitrogen dioxide, ammonia, and boron trifluoride. Tests of the CuPc thin-films and nitrogen dioxide challenges established the primary set of test parameters expected to maximize the selectivity, sensitivity, and reversibility of the thin-film coatings. …

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Failure Characterization Of A Fiber Reinforced Ceramic Matrix Composite With Circular Holes, Daniel E. Bullock Dec 1991

Failure Characterization Of A Fiber Reinforced Ceramic Matrix Composite With Circular Holes, Daniel E. Bullock

Theses and Dissertations

The purpose of this study was to investigate the performance of a fiber reinforced ceramic matrix composite with circular holes. The specific objectives were to (1) determine the relationship between tensile failure stress and the ratio of hole diameter to specimen width, and (2) to examine the initiation and progression of damage. The ceramic matrix composite used was SiC/ 1723, composed of continuous silicon titanium carbide fibers in an aluminosilicate glass ceramic matrix. Uniaxial tensile tests were performed at room temperature on two different layups; unidirectional [0]8, and [0/90]2s symmetric. Each layup was tested at three diameter-to-width …

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Crack Growth Rate Modeling Of A Titanium-Aluminide Alloy Under Thermal-Mechanical Cycling, John J. Pernot Dec 1991

Crack Growth Rate Modeling Of A Titanium-Aluminide Alloy Under Thermal-Mechanical Cycling, John J. Pernot

Theses and Dissertations

In this study, a model is developed to predict crack growth rates in a titanium-aluminide alloy under thermal-mechanical fatigue (TMF). This TMF crack growth rate prediction model, which requires only isothermal data to define its parameters, is distinguished from earlier models in two ways. First, it accounts for mechanical-fatigue and environmental crack growth rate contributions while it also considers a retardation mechanism thought to be caused by creep blunting of the crack tip. This is the first study to account for such a retardation mechanism during TMF. The second uniqueness of the model is that its general form can account …

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Thermomechanical Fatigue Of Scs-6/Β21-S [0/90]2s Composite, Dana G. Hanson Dec 1991

Thermomechanical Fatigue Of Scs-6/Β21-S [0/90]2s Composite, Dana G. Hanson

Theses and Dissertations

The objective of this study was to investigate the material behavior of SCS-6/β21-S [0/90]2s in a thermomechanical fatigue environment. Samples of the SCS-6/β21-S composite were subjected to in-phase and out-of-phase cyclic loading; four samples were tested under in-phase conditions and eight samples were tested under out-of-phase conditions. Stress, temperature, and total strain values were acquired during the test sequence and analyzed for indication of possible trends. Experimental results indicated in-phase specimen possessed shorter fatigue lives then their out-of-phase counterparts above the static first ply failure of the matrix. The out-of-phase specimen showed a shorter fatigue life below the first …

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Calculated Point Defect Properties Of The Intermetallic Compounds Nickel Titanium (Niti) And Iron Titanium (Feti), Russell T. Lutton Mar 1991

Calculated Point Defect Properties Of The Intermetallic Compounds Nickel Titanium (Niti) And Iron Titanium (Feti), Russell T. Lutton

Theses and Dissertations

Atomistic simulation with a modified version of the DYNAMO code was used to calculate the point defect properties of the intermetallic compounds nickel titanium and iron titanium. The calculated energies are believed to be experimentally accurate to within ± 0.1 eV. Vacant Ni or Fe lattice sites were preferred and had energies of 6.356 eV for NiTi and 5.899 eV for FeTi. Removing a Ti atom resulted in a neighboring antisite defect caused by migration of a Ni or Fe atom into the vacant Ti site. These configurations had energies of 7.024 eV for NiTi and 6.336 eV for FeTi. …

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Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas Dec 1990

Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas

Theses and Dissertations

The optical sensors of United States Air Force reconnaissance vehicles, such as satellites, are subject to temporary or permanent blinding from hostile (or threat) laser radiation. By detecting and determining the angle of arrival (AOA) of the hostile radiation, the reconnaissance vehicle may be able to protect its optical sensors by taking evasive maneuvers or by shutting down the optical sensor (such as closing a shutter) until the threat has passed. In addition, the vehicle can relay information to its ground terminal allowing the intelligence community to determine the source of the hostile laser radiation. This thesis demonstrated that an …

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Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski Dec 1990

Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski

Theses and Dissertations

Low temperature photoluminescence studies were performed on holmium implanted into InP, GaAs, and Si; and thulium implanted into AlGaAs, GaAs, and Si. Samples were annealed by the conventional furnace and rapid thermal techniques. None of the characteristic 4f emissions of holmium were found in the spectral region of .73 to 1.55 eV. AlGaAs:Tm showed strong thulium emissions in the .93 to 1.03 eV region. These emissions were studied and compared to those in GaAs:Tm. Low and high temperature annealed samples showed evidence of trivalent Tm centers. Temperature dependence studies showed that thulium 4f emissions were present above 200 K but …

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Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp Dec 1990

Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp

Theses and Dissertations

Lifetime measurements of the excited states of three GaAs semiconductors doped with the rare earth elements Erbium (ER), Praseodymium (Pr) , and Thulium (Tm) has been studied using a pulsed nitrogen laser and germanium detector. The measurements were made with an experimental set up with a system response time of 0.34 micro seconds. A 330 milliwatt nitrogen laser with a wavelength of 3370 angstrums was used to excite transitions of the rare earth elements.

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Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel Dec 1990

Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel

Theses and Dissertations

The introduction of two-beam coupling in photorefractive materials has resulted in an extensive amount of research into their use as optical processing/computing elements. This dissertation develops the theoretical equations for two-beam coupling in barium titanate as an optical amplifier. One of the factors which limits the optical gain in photorefractive crystals is the loss of pump beam power to the amplification of parasitic light (beam fanning). This parasitic light is produced by light scattered from the pump beam by imperfections on both the crystal face and within the crystal. Through the analysis of signal and noise amplification as functions of …

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Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe Dec 1990

Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe

Theses and Dissertations

Metal matrix composites (MMCs) are rapidly becoming strong candidates for high temperature and high stiffness structural applications such as the Advanced Tactical Fighter (ATF). This study systematically investigated the failure modes and associated damage in a cross-ply, [0/90]2s SCS6/Ti-15-3 metal matrix composite under in-phase and out-of-phase thermomechanic fatigue. Initiation and progression of fatigue damage were recorded and correlated to changes in Young's Modulus of the composite material. Experimental results show an internal stabilization of reaction zone size but degradation and separation from constituent materials under extended cyclic thermal loading. Critical to damage were transverse cracks initiating in the 90° …

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Investigation Of The Platinum-Rich Portion Of The Platinum-Tantalum Phase Diagram, Bob Dean Browning Aug 1961

Investigation Of The Platinum-Rich Portion Of The Platinum-Tantalum Phase Diagram, Bob Dean Browning

Theses and Dissertations

The Pt-Ta binary system was investigated at two isotherms;1000°C and 1500°C, and at eleven alloy compositions in the range of 50 to 100 atomic percent platinum. The alloys were examined by x-ray diffraction and metallography. Three intermetallic compounds, Pt2Ta, Pt3Ta, and Pt4Ta were found to exist in this composition range. The Pt4Ta intermetallic appeared only at the 1500°C isotherm. Platinum dissolved tantalum substitutionally to 90 atomic percent at 1500 °C and to approximately 80 atomic percent at 1000 °C.

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