Physics Commons^™

Growth And Characterization Of Carbon Nanomaterials, Jay Patel

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In this thesis, single and multi-layered graphene films were epitaxially grown on either Si-face or C-face of SiC single crystal substrates. The film growth conditions, such as decomposition temperatures and pressures, and their surface morphologies were optimized. These films were then characterized by using surface analysis tools including SEM, TEM, AFM evanescent wave microscopy and electron educed spectroscopy. In addition to studying graphene decomposed from SiC crystals, carbon nanotube material was fabricated using a floating catalyst technique. These carbon nanotube material was then studied for potential cathode applications in this thesis. Field emission properties of these cathodes was measured and …

Determining Metastable Densities In An Argon Discharge Through Optical Emission Spectroscopy, Jared A. Miles

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A plasma diagnostic technique has been experimentally demonstrated where optical emission measurements of relative intensities of spectral lines in the violet range were combined with available electron-impact cross sections to yield absolute Ar metastable species concentration. An enabling factor of this analysis was that the electron excitation pattern was quite different between the Ar ground state and the metastable state. The result of this pattern was that the optical spectrum was unique depending on whether the emission was generated by direct excitation from the ground state, or by stepwise excitation from one of the metastable states. This study has shown …

Experimental Comparison Of Acr And Icamrl Magnetic Resonance Imaging Accreditation Protocols, Brock Andrew Prater

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Two primary accrediting bodies exist for magnetic resonance imaging systems: the American College of Radiology (ACR) and the Intersocietal Commission for the Accreditation of Magnetic Resonance Laboratories (ICAMRL), each of which defines specific standards for specific image quality criteria at which MRI images must be produced. An MRI clinic that wishes to show a commitment to image quality may do so by becoming accredited by one of these organizations of their choosing. The limits of these image criteria were compared to demonstrate the standards of each accrediting body. Images were produced that fell well within the standards of both accrediting …

Ostwald Ripening Of Iron (Fe) Catalyst Nanoparticles On Aluminum Oxide Surfaces (Al2O3) For The Growth Of Carbon Nanotubes, Roberto I. Acosta

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Theoretical models have proposed that the nucleation and growth mechanism of carbon nanotubes (CNTs) has been affected by the catalytic activity of transition metals. The catalyst behavior during growth has been mainly associated as the responsible mechanism for the termination of CNT growth. Although several hypotheses have been developed to explain this mechanism, is still today an unresolved phenomenon. It was recently shown that the Ostwald ripening of iron (Fe) nanoparticles played a dominant role in the termination of CNT growth. The Ostwald ripening mechanism was further investigated as a function of thermal annealing in Hydrogen (H₂) for …

Atmospheric Effects On The Propagation Of Mmw And Sub-Mmw Radiation, John S. Cetnar

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This thesis is a study of the propagation of millimeter wavelength (MMW) and submillimeter wavelength (sub-MMW) electromagnetic radiation (a.k.a. THz radiation) through the Earth's atmosphere. THz radiation is electromagnetic radiation that exists between the microwave and far infrared regions of the electromagnetic spectrum. It is nonionizing radiation but can penetrate through materials that are opaque to visible light so therefore has many new and useful applications. Unfortunately, THz radiation is heavily attenuated by the Earth's atmosphere as it propagates through it. This therefore represents a challenge to communications and sensing applications at millimeter and sub-millimeter wavelengths. In this work, the …

Proximity And Thickness Estimation Of Aluminum 3003 Alloy Metal Sheets Using Multi-Frequency Eddy Current Sensor, Sunil S. Kamanalu

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The research work is focused on conducting a feasibility study on a new "non-contact" single probe dual coil inductive sensor for sensing the proximity and thickness of Aluminum (Al) 3003 alloy metal sheets, which is a non-magnetic metal. A bulk of the research and development work has already been done in the area of non-destructive testing (NDT) using eddy current technology targeted to various applications like corrosion detection, material thickness, material conductivity, etc. The research work presented in this thesis uses the prior research and development work completed in NDT as a platform for conducting this study to estimate proximity …

Respiratory-Gated Imrt Quality Assurance With Motion In Two Dimensions, Michael Todd Massie

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Intensity modulated radiation therapy (IMRT) plans can be further customized to each patient with the use of a four-dimensional (4D) respiratorygated computed tomography (CT), with time being the fourth dimension. The 4D respiratory-gated CT allows for the internal margin (IM), the expansion of the tumor volume that accounts for physiologic motions, to be addressed in the treatment planning process and no longer assumes that the treatments will be delivered to a fixed or rigid patient anatomy. Delivering the IMRT plan with a gated technique limits the treatment to a duty cycle when the target motion is at a minimum.

The …

The Derivation And Testing Of Three-Dimensional Line Equations That Predict The Location Of Brachytherapy Sources, Rhett Ellis Lindsey

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In High Dose Rate brachytherapy, a catheter is placed inside the body and a radioactive source is allowed to dwell at specific positions to treat a tumor. In normal usage, anatomical images acquired before the treatment are used to plan dwell positions, and then the plan is executed without further verifying source locations during treatment. However, slight errors in catheter positioning and shifts in internal anatomy cause variations in source position. In this study, a general method for determining dwell positions during treatment is evaluated. For this method, the treatment source exposes the tumor to radiation and creates an image …

Dosimetric Effects Near Implanted Vascular Access Ports Under External Electron Beam Radiation, David Coll Segarra

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Previous studies on dosimetry show important effects for metal vascular access ports for x-rays and electron beams and moderate to no effects for plastic ports for x-ray beams when ports are in the path of the beam. No previous studies exist regarding the effects of electron beams on vascular access ports other than for those made of metal although it has been suggested that electron beam attenuation through non-metal ports may be possible.

Measurements of relative ionization through the device and adjacent to the device anteriorly and laterally were taken. A clinical particle accelerator delivered typical clinical electron beams of …

Temperature And Frequency Dependent Conduction Mechanisms Within Bulk Carbon Nanotube Materials, John Simmons Bulmer

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The resistance of three types of bulk carbon nanotube (CNT) materials (floating catalyst CNT yarn, forest grown CNT yarn, and super acid spun CNT fiber) was measured from room temperature to 900 C. Fitting the curves to established conduction equations for disordered materials, competing conduction mechanisms pertaining to the material could be determined. Floating catalyst CNT yarn displayed both semiconductive and metallic isotropic behavior with a resistance minimum, similar to the behavior of crystalline graphite. It was found that, at room temperature, the semiconducting contribution-most likely junctions between CNTs-accounted for 99.99% of the overall resistance. The resistance of forest grown …

Sub-Mm Wave Imaging And Waveguiding Techniques For Non-Destructive Materials Evaluation, Izaak Vincent Kemp

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Sub-mm wave technology (also known as Terahertz/THz) is a rapidly developing field of electro-optics which has great potential in a variety of applications. Generally defined as the band of the electro-magnetic spectrum with frequencies spanning from 300 GHz to 30 THz, sub-mm waves are non-ionizing and are capable of passing through a wide range of dielectric substances making them well suited for imaging purposes such as non-destructive materials evaluation (NDE). Because of their high sensitivity to metals and ability to penetrate surface obscurants such as paint, oil, and epoxy sub-mm waves are capable of imaging corrosion damage on metallic surfaces …

Characterization Of Inert Gas Rf Plasma-Treated Indium Tin Oxide Thin Films Deposited Via Pulsed Dc Magnetron Sputtering, Amber Nicole Reed

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In this work, the effects of a post-deposition RF plasma treatment on indium tin oxide (ITO) thin films prepared with pulsed DC magnetron sputtering in argon were investigated. The parameters of the post-deposition were studied to determine what RF power and gas pressure resulted in the greatest reduction in resistivity in the films while producing the smallest increase in substrate temperature for treatments with both argon and oxygen plasmas. The as-deposited (untreated) films and the treated films were characterized using Raman spectroscopy and X-ray diffraction to determine the effects of the post-deposition treatment on the degree of film crystallization. XPS …

Evanescent Microwave Microscopy Of Porcine Skin Tissue, Richard A. Kleismit

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This thesis describes the application of a custom designed λ/4 resonant coaxial probe to measurements of the complex permittivity of in vitro freshly excised porcine skin tissue. The dielectric properties of the organic material within the near field of the tip of the probe frustrates the electric field and measurably changes the resonant frequency and quality factor Q of the coaxial sensor, where the change in resonant frequency and quality factor of a tuned resonance is measured as a function of tip-sample separation. The design of the probe enables better spatial resolution than previously developed probes. The following studies were …

Comparison Of Two Methods Of External Scatter Dose Contributions To The Contralateral Breast, James Cutlip

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The treatment outcomes of many forms of breast cancer have become very favorable. The usual standard of successful treatment of five years without a recurrence is not adequate any longer for breast cancer. Many patients live well beyond this time interval only to have a second malignancy develop in the contralateral breast ten or twenty years later. Boice et al (1992) found that there was a correlation between the amount of dose to the contralateral breast and the likelihood of a secondary malignancy forming.

The normal practice today is to use multi-leaf collimators (MLC) to modulate the photon beam in …

Investigation Of The Reflective Properties Of A Left-Handed Metamaterial, Amanda Durham

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The purpose of this project is to investigate the reflective properties of a left-handed metamaterial (LHM) through the use of a finite element analysis software called FEMLAB. In the 1960's, V. Veselago theorized that a material with negative permeability and negative permittivity has a negative index of refraction. In 2000, such a metamaterial was built and demonstrated at microwave frequencies. Previous work had focused on the transmission properties of the metamaterial. In our work, the reflected wave was examined for a LHM subject to an incident transverse electric wave. The different generalizations, first proposed by Veselago, of the Fresnel and …

Fabrication And Study Of Zno Micro- And Nanostructures, Monica Morales-Masis

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ZnO micro-structures and nano-structures have been grown on two types of substrate by reacting condensed Zn vapor with oxygen. The source material was either pure zinc powder or zinc acetate which was either evaporated or decomposed. This was done in the temperature range 500 C to 650 C, in a flowing Ar plus oxygen ambient at atmospheric pressure. Variations in the carrier gas composition, gas flow rate and the position of the substrate in the furnace were found to control the formation and the morphology of the nanostructures. Scanning electron microscopy images of samples grown from a Zn powder source …

Evanescent Microwave Characterization Of Carbon Nanotube Films Grown On Silicon Carbide Substrate, Kineshma Munbodh

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The electromagnetic characterization of carbon nanotube films (CNT) grown by the surface decomposition of silicon carbide (SiC) has been performed. The CNT films formed on the carbon and silicon terminated face of the SiC substrate were uncapped by an annealing process at a temperature of 4000 C with dwelling time up to 60 minutes in oxygen or carbon dioxide atmosphere. X-Y scans of the quality factor were used to deduce the local conductive properties of the films measured by evanescent microwave microscopy. Real and imaginary permittivity values, as determined by these electromagnetic measurements, provided valuable information for future field emission …

Comparative Investigation Of Dosimetric Tools In Imrt, Aaron Nicholas Garcia

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Verification of the isodose distribution delivered to the planned tumor volume is required for quality assurance in the clinic. Verification in this context means ensuring that the actual dose delivered to a volume matches the dose that a computerized planning system intended that volume to receive. The computerized planning is performed by a Computerized Medical Systems (CMS) Intensity Modulated Radiation Therapy (IMRT) plan. Two methods of measuring the delivered dose are film dosimetry and diode dosimetry. This project will compare the relative isodose distribution profiles of film dosimetry and MapCheck (Sun Nuclear Corporation, a diode-based dosimetry system) to the relative …

Fabrication Of Silver Nanoparticles By Solution Phase Method And Physical Characterization Of Their Arrays, Jaesung Oh

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Synthesis of silver nanostructures has been an active research area for many decades because of their importance in biological sensing, imaging, electronics, optoelectronics and catalysis. In particular, much effort has been devoted to the controlled synthesis of silver nanowires because of their potential use as interconnects or active components in fabricating nanoscale devices. The solution phase method is used here to form Ag nanoparticles by reducing silver nitrate with ethylene glycol heated to 160°C. The additional presence of polyvinyl pyrrolidone plays a role of stabilizer to prevent an agglomeration and/or a capping agent to produce highly anisotropic nanowires. Silver nanoparticles …

Polarization Reversal In Potassium Titanyl Phosphate, William D. Mitchell

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Polarization reversal in both hydrothermal and flux grown potassium titanyl phosphate was studied using square pulses at room temperature from 1600 V/mm to 5000 V/mm. Maximum switching current and inverse switching time data is compared to the ferroelectric polarization reversal model developed by Fatuzzo and Merz in the last century. Room temperature calculation of spontaneous polarization is reported and compared to that of potassium titanyl phosphate in the literature.

Development Of A Fourier Transform Far Infrared (Ftfir) Spectrometer To Characterize Broadband Transmission Properties Of Common Materials In The Terahertz Region, William Paul Ford

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With sub-millimeter wave or terahertz devices becoming more readily available, there is interest in developing sensors in this region of the spectra. To support this interest, we have developed a Fourier Transform Far InfraRed (FTFIR) spectrometer to characterize broadband transmission and reflectance coefficients of materials. The spectrometer utilizes a broadband blackbody source, a Michelson interferometer, and silicon bolometer. The path difference in the Michelson is obtained using a linear stage and data acquisition and stage control were both implemented in a Labview programming environment. The details of the experimental setup and experimental results are presented in this thesis. The instrument …

Models Of Disordered Media And Predictions Of Associated Hydraulic Conductivity, L. Aaron Blank Jr.

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In the late 20th century there was a spill of Technetium in eastern Washington State at the US Department of Energy Hanford site. Resulting contamination of water supplies would raise serious health issues for local residents. Therefore, the ability to predict how these contaminants move through the soil is of great interest. The main contribution to contaminant transport arises from being carried along by flowing water. An important control on the movement of the water through the medium is the hydraulic conductivity, K, which defines the ease of water flow for a given pressure difference (analogous to the electrical conductivity). …

Electronic Properties Of Silicon-Based Nanostructures, Gian Giacomo Guzman-Verri

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We have developed a new unifying tight-binding theory that can account for the electronic properties of recently proposed Si-based nanostructures, namely, Si graphene-like sheets and Si nanotubes. We considered the sp²s* and sp³ models up to first- and second-nearest neighbors, respectively. Our results show that the corresponding Si nanotubes follow the so-called Hamada's rule. Comparison to a recent ab initio calculation is made.