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 Department: Department of Physics
Electron Density and Collision Frequency Studies Using a Resonant Microwave Cavity as a Probe

Electron Density and Collision Frequency Studies Using a Resonant Microwave Cavity as a Probe

Date: May 1973
Creator: Freeman, Ronald Harold
Description: Electron densities and collision frequencies were obtained on a number of gases in a dc discharge at low pressures (0.70-2mm of Hg). These measurements were performed by microwave probing of a filament of the dc discharge placed coaxially in a resonant cavity operating in a TM₀₁₀ mode. The equipment and techniques for making the microwave measurements employing the resonant cavity are described. One of the main features of this investigation is the technique of differentiating the resonance signal of the loaded cavity in order to make accurate measurements of the resonant frequency and half-power point frequencies.
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Carbon nanotube/microwave interactions and applications to hydrogen fuel cells.

Carbon nanotube/microwave interactions and applications to hydrogen fuel cells.

Access: Use of this item is restricted to the UNT Community.
Date: May 2004
Creator: Imholt, Timothy James
Description: One of the leading problems that will be carried into the 21st century is that of alternative fuels to get our planet away from the consumption of fossil fuels. There has been a growing interest in the use of nanotechnology to somehow aid in this progression. There are several unanswered questions in how to do this. It is known that carbon nanotubes will store hydrogen but it is unclear how to increase that storage capacity and how to remove this hydrogen fuel once stored. This document offers some answers to these questions. It is possible to implant more hydrogen in a nanotube sample using a technique of ion implantation at energy levels ~50keV and below. This, accompanied with the rapid removal of that stored hydrogen through the application of a microwave field, proves to be one promising avenue to solve these two unanswered questions.
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A New Approach for Transition Metal Free Magnetic Sic: Defect Induced Magnetism After Self-ion Implantation

A New Approach for Transition Metal Free Magnetic Sic: Defect Induced Magnetism After Self-ion Implantation

Date: May 2013
Creator: Kummari, Venkata Chandra Sekhar
Description: SiC has become an attractive wide bandgap semiconductor due to its unique physical and electronic properties and is widely used in high temperature, high frequency, high power and radiation resistant applications. SiC has been used as an alternative to Si in harsh environments such as in the oil industry, nuclear power systems, aeronautical, and space applications. SiC is also known for its polytypism and among them 3C-SiC, 4H-SiC and 6H-SiC are the most common polytypes used for research purposes. Among these polytypes 4H-SiC is gaining importance due to its easy commercial availability with a large bandgap of 3.26 eV at room temperature. Controlled creation of defects in materials is an approach to modify the electronic properties in a way that new functionality may result. SiC is a promising candidate for defect-induced magnetism on which spintronic devices could be developed. The defects considered are of room temperature stable vacancy types, eliminating the need for magnetic impurities, which easily diffuse at room temperature. Impurity free vacancy type defects can be created by implanting the host atoms of silicon or carbon. The implantation fluence determines the defect density, which is a critical parameter for defect induced magnetism. Therefore, we have studied the influence ...
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Theoretical Study of Second Harmonic Generation of a Blue Laser at 486 nm Using a BBO Crystal in a Standing Wave Buildup Cavity

Theoretical Study of Second Harmonic Generation of a Blue Laser at 486 nm Using a BBO Crystal in a Standing Wave Buildup Cavity

Date: May 2002
Creator: Khademian, Ali
Description: For a spectroscopy purpose, we are interested in producing continuous wave (CW) UV laser light at 243 nm with at least 2 mW power. The theory of nonlinear optics suggests that we should be able to produce a desired 2.9 mW of 243 nm light by second harmonic generation (SHG) from a 50 mW blue laser at 486 nm using a BBO crystal in a build up cavity. The most important physical parameters are calculated. A 10 mm Brewster cut BBO crystal can provide phase matching conditions for coupling two ordinary photons at 486 nm and make a secondary beam at 243 nm. The single pass conversion efficiency is calculated not to be enough to generate 2.9 mW of SH light. My investigation shows that a standing wave build up cavity can provide a buildup factor of 94 and an overall conversion efficiency of 5.9% if one use an input coupler mirror with 1.1% transmission at 486 nm.
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Photoelectric Emission Measurements for CVD Grown Polycrystalline Diamond Films

Photoelectric Emission Measurements for CVD Grown Polycrystalline Diamond Films

Date: August 1999
Creator: Hassan, Tarek
Description: We examined CVD grown polycrystalline diamond films having different methane concentrations to detect defects and study the possible correlation between the methane concentration used during the growth process and the defect density. SEM and Raman results show that the amorphous and sp2 carbon content of the films increases with methane concentration. Furthermore, photoelectric emission from diamond is confirmed to be a two-photon process, hence the electrons are emitted from normally unoccupied states. We found that the photoelectric yield, for our samples, decreases with the increase in methane concentration. This trend can be accounted for in two different ways: either the types of defects observed in this experiment decrease in density as the methane concentration increases; or, the defect density stays the same or increases, but the increase in methane concentration leads to an increase in the electron affinity, which reduces the overall photoelectric yield.
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Transport Phenomena in Indium Arsenide at Low Temperatures

Transport Phenomena in Indium Arsenide at Low Temperatures

Date: August 1968
Creator: Luke, Paul Jacob
Description: This thesis looks at the transport phenomena in indium arsenide at low temperatures.
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Solutions of the Equations of Radiative Transfer by an Invariant Imbedding Approach

Solutions of the Equations of Radiative Transfer by an Invariant Imbedding Approach

Date: January 1969
Creator: Adams, Charles N.
Description: This thesis is a study of the solutions of the equations of radiative transfer by an invariant imbedding approach.
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Monte Carlo Calculations of Reflected Intensities for Real Spherical Atmospheres

Monte Carlo Calculations of Reflected Intensities for Real Spherical Atmospheres

Date: January 1969
Creator: Montgomery, John A.
Description: To calculate the emergent radiation field, a realistic atmospheric model and algorithm must be developed. The radiation field may be characterized by the emergent intensities of scattered light. This is possible only if the algorithm determines these intensities as dependent upon atmospheric and angular parameters.
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Boundary Scattering of Electrons in Thin Cadmium Single Crystals

Boundary Scattering of Electrons in Thin Cadmium Single Crystals

Date: August 1968
Creator: Fortmayer, Gary William
Description: In the present investigation, zinc was plated onto a cadmium crystal to determine the effect on the scattering parameter.
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Size Effect in the Electrical Conductivity of Bismuth

Size Effect in the Electrical Conductivity of Bismuth

Date: August 1967
Creator: Vaughn, Bobby J.
Description: If a physical dimension of a metallic specimen is comparable with, or smaller than, the mean free path of the conduction electrons, then the observed electrical conductivity will be less than that of a conventional bulk sample. This phenomenon is called a size effect, and is the result of electron scattering from the specimen surfaces. In the present investigation, measurements were made on electropolished monocrystalline specimens ranging from matchbox geometry to thick-film geometry in order to obtain further information on the size effect in bismuth at liquid helium temperatures.
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