Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 92-93).

Thesis (Ph. D.)--Washington State University, May 2006. / Includes bibliographical references.

Thesis (Ph.D.)--George Mason University, 2007. / Title from PDF t.p. (viewed Oct. 29, 2007). Thesis director: Mulpuri V. Rao. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Vita: p. 170. Includes bibliographical references (p. 160-169). Also available in print.

This dissertation focuses on the characterization of hydrogen implanted 3C-SiC and helium implanted 6H-SiC and the interaction of silver and palladium with the SiC. The main technique used for the analysis of the implanted SiC was transmission electron microscopy (TEM), although scanning electron microscopy (SEM) and nanoindentation hardness testing were also used. Both H and He implantations were done at an ion energy of 100 keV and the total dose for both species was 1017 ions/cm2. Specimens were annealed at 1000 °C for 20 min in an inert atmosphere. The observed depth of ion damage agreed closely with that predicted by TRIM 2008. The damaged region in the He implanted specimens had a high density of small bubbles but no cracks were observed. Severe cracking was observed along the damaged region in the H implanted specimens. A second phase hexagonal (4H-SiC) was detected in two grains in the 3C-SiC and some grown in voids were also observed. The wettability of SiC by a 2:1 by volume mixture of Ag and Pd is extremely low but is significantly increased through the addition of Si to the mixture. The Si containing metal mixture was found to migrate along the grain boundaries of polycrystalline 3CSiC while sealing the point of entry. Pd attacks SiC and severe etching was observed on the surface of 6H-SiC. An epitaxially orientated Pd2Si inclusion was observed in the 6H-SiC. No effect of implantation damage on the interaction of Pd and Ag with SiC was observed. Pd etched the surface of the He implanted 6H-SiC down through the damaged region with no evidence of implantation damage left after 67 hours of annealing and thus no conclusions could be drawn. The metal mixture interacted with the non implanted surface of the H implanted 3C-SiC after dissolving the Si substrate and therefore the effect of the ion damage on the interaction could not be investigated. Nanoindentation hardness measurements showed a marked increase in hardness of He implanted 6H-SiC annealed for 20 min at 1000 °C over that of as implanted and virgin material. There was also a large decrease in hardness corresponding to the depth of the ion damage.

This dissertation focuses on an electron microscopy investigation of the microstructure of SiC layers in TRISO coated particles deposited by chemical vapour deposition under different experimental conditions, which include temperature, concentration of gases and deposition time. The polycrystalline β-SiC was deposited from the decomposition of methyl trichlorosilane MTS in the presence of hydrogen (H2) as carrier gas. Scanning electron microscopy (SEM), using the backscattered electron (BSE) mode, was used to image the microstructure of and defects in the SiC layers of TRISO particles. Electron backscatter diffraction (EBSD) in the SEM was used to determine the SiC grain sizes and distribution thereof in TRISO particles deposited under different conditions. For samples with a poor EBSD indexing rate, transmission Kikuchi diffraction and transmission electron microscopy (TEM) investigations were also carried out. From the results, the effects of growth temperature on the SiC microstructure, specifically on the grain size and shape and the porosity were determined. The effects of cooling or non-cooling of the gas inlet nozzle on the SiC microstructure were also investigated. TEM and scanning TEM (STEM) analyses of the SiC layers in TRISO particles were performed to image the defects and reveal the crystallinity of SiC layers. The microstructure and composition of SiC tubes fabricated by reaction bonding (RB) was also investigated by using electron microscopy and Raman spectroscopy. SEM-BSE imaging of RBSiC samples allowed the identification of impurities and free silicon in the RBSiC. Finally, the penetration of the metallic fission product, palladium, in reaction bonded SiC at a temperature of a 1000ºC is determined. A brief comment on the suitability of RBSiC as candidate for fuel cladding in a PWR is made. A short discussion of the suitability of the characterisation techniques used is included at the end.

Graphene has attracted significant research attention for next generation of semiconductor devices due to its high electron mobility and compatibility with planar semiconductor processing. In this dissertation, the influences of Ohmic metals and high dielectric (high-k) constant aluminum oxide (Al2O3) deposition on the structural and electrical properties of multi-layer epitaxial graphene (MLG) grown by graphitization of silicon carbide (SiC) substrates have been investigated. Uniform MLG was successfully grown by sublimation of silicon from epitaxy-ready, Si and C terminated, 6H-SiC wafers in high-vacuum and argon atmosphere. The graphene formation was accompanied by a significant enhancement of Ohmic behavior, and, was found to be sensitive to the temperature ramp-up rate and annealing time. High-resolution transmission electron microscopy (HRTEM) showed that the interface between the metal and SiC remained sharp and free of macroscopic defects even after 30 min, 1430 °C anneals. The impact of high dielectric constant Al2O3 and its deposition by radio frequency (RF) magnetron sputtering on the structural and electrical properties of MLG is discussed. HRTEM analysis confirms that the Al2O3/MLG interface is relatively sharp and that thickness approximation of the MLG using angle resolved X-ray photoelectron spectroscopy (ARXPS) as well as variable-angle spectroscopic ellipsometry (VASE) is accurate. The totality of results indicate that ARXPS can be used as a nondestructive tool to measure the thickness of MLG, and that RF sputtered Al2O3 can be used as a (high-k) constant gate oxide in multilayer grapheme based transistor applications.

Bibliography: pages 51-54. / The microstructure of different types of industrially produced heating elements was examined and an x-ray diffraction method was devised to determine the relative amounts of α- and β-silicon carbide present in these materials. It was confirmed that the α- to β-silicon carbide transformation occurs during heat treatment, because of the influence of the nitrogen atmosphere in the furnace. The fabrication parameters important in the manufacture of heating elements were investigated. Porous sintered silicon carbide samples were made using different proportions of grit sizes and various firing schedules. Both resistivity and crushing strength were determined. It was found that the resistivity is dependent upon degree of sintering (indicated by crushing strength) as well as the packing density of the porous body.

This work demonstrates design of analog circuit blocks using radiation-hardened and temperature tolerant silicon carbide enhancement and depletion JFET. Most of the work to date in silicon carbide is focused on CMOS like circuits, which are less temperature tolerant, compared to JFETs. In this work, efforts have been made to accurately model silicon carbide depletion and enhancement mode n-JFETs. I-V characteristics of the models were simulated for different values of channel thickness and doping concentration. Analog circuit building blocks such as current mirrors and sources are presented for both enhancement mode and depletion mode JFETs at different temperatures. A source coupled differential amplifier was designed using depletion mode silicon carbide n-JFETs. Various differential amplifier specifications such as Voltage swing, input common mode range (ICMR), differential gain, common mode gain and Common mode rejection ratio (CMRR) are simulated at room temperature and at 673K.

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references (p.139-151).

The reflectivity of crystalline and radiation-damaged silicon carbide and silicon has been measured in the 2-12 eV spectral region. Measurements were made using a standard Seya-Namioka Monochrometer which was modified to compensate for the fluctuations of the light source and interfaced to a micro-computer to facilitate data collection. The reflectivities of crystalline silicon carbide polytypes 6H, 15R, and 4H were found to be similar and the reflectivity of 3C-SiC showed agreement with the predictions of published band structure calculations. The observed reflectivity of radiation damage SiC agreed with the prediction of a simple model which takes into account the breakdown of k(→) -conservation and uses a realistic Bethe-lattice Hamiltonian to calculate the amorphous valence density of electron states.