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The development of next generation devices for high speed switching, high efficiency energy conversion, spintronic devices require the development of advanced material systems. While conventional group IV, group II-VI and group III-V based materials systems have served as a base material in many modern device structures, they posses fundamental materials properties that limit their suitability in next generation device structures. The group III-N material system is very promising for the development of advanced device structures. GaN is currently widely used in high efficiency lighting applications. However, the development of this material system has been limited to material systems with limited indium. The growth of high indium concentration materials such as InN and GaxIn1-xN has proven difficulty due to the high thermal decomposition pressure of InN. In response to this difficulty, a high pressure chemical vapor deposition reactor system has been developed for the growth of InN which enables elevated processing temperatures as compared to conventional low-pressure growth techniques. The design criteria and implementation of this unique design is presented here. In addition, the results of in-situ real time optical characterization capabilities of this reactor system are presented as applied to thermal characterization, flow dynamics, gas phase kinetics and surface reactions. Ex-situ InN thin films grown on sapphire substrates and GaN epilayers have been analyzed by x-ray diffraction, transmission spectroscopy and raman spectroscopy. These results indicated single crystal indium nitride films with an optical absorption edge which varies between 0.7 and 1.9 eV as a function of precursor flow stoichiometry.

In the industry of metal cutting tools the conditions are extreme; the temperature can vary thousand degrees rapidly and the pressure can be tremendously high. To survive this kind of stress the cutting tool must be both hard and tough. In order to obtain these properties different coatings are used on a base of cemented carbide, WC-Co. Common coatings are hard ceramics like titanium nitride and titanium carbon-nitride with an outer layer of aluminium oxide. In this thesis the possibility of using titanium dioxide as an interlayer between titanium carbon-nitride and aluminium oxide to control the morphology and phase of aluminium oxide is investigated. Of the different aluminium oxide phases only the alpha-Al2O3 is stable. The titanium carbon-nitride coatings are made by CVD (chemical vapour deposition); also the alumina is deposited by CVD. The titanium dioxide was deposited by atomic layer deposition (ALD) which is a sequential CVD technique that allows a lower deposition temperature and better control of the film growth than CVD. The obtained thin films were analyzed using XRD, Raman spectroscopy, ESCA and SEM. To test the adhesion of the coatings the samples were sand blasted. A thin interlayer of titanium dioxide causes the aluminium oxide to grow as alpha-Al2O3, thinner TiO2 gave better adhesion.

<p>Silicon ceramics are popular in both commercial applications and material research. The purpose of this thesis is to present measurements and analysis of four different silicon ceramics: á, â and ã phases of silicon nitride and silicon oxynitride using soft x-ray spectroscopy, which analyses the electronic structure of materials by measuring the absorption and emission of x-ray radiation. Absorption and emission spectra of these materials are presented, many of which have not be previously documented. The results are compared to model spectra and together they provide information about the electronic structure of the material.</p><p>Assignments of emission features to element, orbital, and site symmetry are performed for each material. Combinations of silicon and nitrogen emission spectra provide insight into the strained bonding structure of nitrogen. It is concluded that p-dð interaction plays a role in the bonding arrangement of nitrogen and oxygen sites within these structures. The emission features of non-equivalent silicon sites within ã-Si3N4 are identified, which represents some of the first analysis of same element, non-equivalent sites in a material.</p><p>Silicon absorption and emission spectra were plotted on the same energy scale to facilitate measurement of the band gap. Since previously measured band gaps are not well represented in literature, the measured band gaps were compared to values predicted using DFT calculations. The band gap values are in reasonable agreement to calculated values, but do not vary as widely as predicted.</p>

Six ã-Al2O3 supported metallic nitride and carbide catalysts were chosen for a scouting test for the production of a diesel fuel cetane enhancer from canola oil. The six catalysts chosen for study were ã-Al2O3 supported molybdenum (Mo) carbide and nitride, tungsten (W) carbide and nitride, and vanadium (V) nitride and carbide. All six catalysts were prepared by the impregnation method and characterized using various techniques. The six catalysts were screened for their affinity for oxygen removal, fatty acid conversion, alkane/olefin selectivity, hydrogen consumption, and gas-by product production from oleic acid. The scouting test was carried out at a reaction temperature of 390°C, a LHSV of 0.46 hr-1, and elevated hydrogen partial pressures of greater than 7000 kPa, in a laboratory microreactor in an upflow configuration. The scouting test revealed that the two molybdenum catalysts performed the best with oxygen removal near 100% and alkane/olefin content of greater than 30%. <p>Next, the supported molybdenum carbide and nitride catalysts were compared against one another over a wider range of operating conditions. A temperature range of 380 390°C, a LHSV range of 0.64 1.28 hr-1, and a hydrogen partial pressure of 7100 kPa were used. Both catalysts had the same metal loading of 7.4 wt% molybdenum. The two catalysts were compared on the basis of oxygen removal, alkane/olefin selectivity, diesel fuel selectivity, and hydrogen consumption, while using both triolein and canola oil as the feed. It was found that the supported molybdenum nitride was the superior choice for this process, specifically when using the more complex canola oil feed. The supported molybdenum nitride catalyst delivered oxygen removal of greater than 85%, alkane/olefin selectivity of greater than 20%, and diesel fuel selectivity of greater than 40%, for all conditions studied. <p>Finally, a preliminary catalyst and process optimization was carried out on the chosen ã-Al2O3 supported molybdenum nitride catalyst. The catalyst optimization consisted of varying the metal loading of the catalyst from 7.4 wt% to 22.7 wt%. The catalysts were examined over a temperature range of 390 410°C, a LHSV range of 0.9 1.2 hr-1, and a hydrogen partial pressure of 8300 kPa, with canola oil as the chosen feed. It was found that the increase in molybdenum loading on the catalyst delivered an average increase in the alkane/olefin selectivity of 43.2% and an average increase in the diesel fuel selectivity of 5.3 %. The process optimization studied a temperature range of 390 410°C, a LHSV range of 0.6 1.2 hr-1, and a hydrogen partial pressure range of 7800 - 8900 kPa, with canola oil as the chosen feed. Within the limits of the design, it was found that the optimum operating conditions were 395°C, 1.05 hr-1, and 8270 kPa. At these conditions the predicted yields of alkane/olefin products and diesel fuel are 47.3 and 50.5 g/100g liquid fed, respectively.

Photovoltaics offers a unique solution to energy and environmental problems simultaneously. However, widespread application of photovoltaics will not be realized until costs are reduced by about a factor of four without sacrificing performance. Silicon crystallization and wafering account for about 55% of the photovoltaic module manufacturing cost, but can be reduced significantly if a ribbon silicon material, such as String Ribbon Si, is used as an alternative to cast Si. However, the growth of String Ribbon leads to a high density of electrically active bulk defects that limit the minority carrier lifetime and solar cell performance. The research tasks of this thesis focus on the understanding, development, and implementation of defect passivation techniques to increase the bulk carrier lifetime in String Ribbon Si in order to enhance solar cell efficiency. Hydrogen passivation of defects in Si can be performed during solar cell processing by utilizing the hydrogen available during plasma-enhanced chemical vapor deposition (PECVD) of SiNx:H films. It is shown in this thesis that hydrogen passivation of defects during the simultaneous anneal of a screen-printed Al layer on the back and a PECVD SiNx:H film increases the bulk lifetime in String Ribbon by more than 30 ?A three step physical model is proposed to explain the hydrogen defect passivation. Appropriate implementation of the Al-enhanced defect passivation treatment leads to String Ribbon solar cell efficiencies as high as 14.7%. Further enhancement of bulk lifetime up to 92 ?s achieved through in-situ NH3 plasma pretreatment and low-frequency (LF) plasma excitation during SiNx:H deposition followed by a rapid thermal anneal (RTA). Development of an optimized two-step RTA firing cycle for hydrogen passivation, the formation of an Al-doped back surface field, and screen-printed contact firing results in solar cell efficiencies as high as 15.6%. In the final task of this thesis, a rapid thermal treatment performed in a conveyer belt furnace is developed to achieve a peak efficiency of 15.9% with a bulk lifetime of 140 ?Simulations of further solar cell efficiency enhancement up to 17-18% are presented to provide guidance for future research.

In this study, we used the Density functional theory (DFT) to obtain the relationship between mechanical property and electronic property of Boron nitride nanotubes (BNNTs) under the uni-axial strain. Moreover, we also investigated one CO molecule adsorbed on the BNNTs under the uni-axial strain. We also use the molecular dynamics to introduce the mechanical property and dynamic behavior of (8,8)BNNT under the uni-axial strain. There were three parts in this study: The first part: The effect of uni-axial strain on the electronic properties of (5,5) and (8,0)boron nitride nanotubes were obtained by DFT calculation. We used the HOMO-LUMO Gap¡Bbond angle¡Bbond length and radial buckling to analyze the electronic properties and mechanical properties. The stress-strain profiles indicated that different BNNTs types displayed very similar mechanical properties, but there were variations in HOMO-LUMO gaps at different strains, indicating that the electronic properties of BNNTs not only depend on uni-axial strain, but on BNNT type. In addition, the variations in nanotube geometries, partial density of states (PDOS) and charges of boron and nitride atoms were also discussed for (8,0) and (5,5) BNNTs at different strains. The second part: The DFT was used to investigate electronic properties of CO molecule adsorbed on BNNT under the uni-axial strain. The stress-strain profiles indicated that the CO molecule adsorption on BNNT leaded only to a local mechanical deformation. The strength of BNNT could not be affected when the CO molecule adsorbed on that. Moreover, we obtained that the charge of CO will slightly transfer to the adsorbed atom of BNNT when strain increased. Hence, the adsorption energy increased slightly under the uni-axial strain. The third part: The molecular dynamics simulations were performed to investigate deformation behaviors of (8,8)BN nanotubes under axial tensile strains at 300k. Variations with the tensile strain in the axial stress, bond lengths, bond angles, radial buckling, and slip vectors were all examined. The axial, radial, and tangential components of the slip vector were also employed to monitor, respectively, the local elongation, necking, and twisting deformation near the failure of the nanotube. The components of the slip vector grew rapidly and abruptly after the failure strain, especially for the axial component. This implies that the local elongation dominates the failure of the loaded BN nanotube and finally results in a chain-like tensile failure mode.

In this study, we used the Density functional theory (DFT) and Molecular dynamics (MD) to obtain the suitable hydrogen storage structure of Rh nanoclusters on the boron nitride sheet and Li atoms on the graphene. The reason of studying two type of nanoparticles is that there are two adsorption method in hydrogen storage, such as the adsorption of hydrogen molecules and hydrogen atoms. Using Rh nanoclusters on the boron nitride sheet to store hydrogen belong to the adsorption of hydrogen atoms. Using Li atoms on the graphene to store hydrogen belong to the adsorption of hydrogen molecules. We use these two models to simulate the hydrogen storage in this study. There were four parts in this study: The first part: The Density functional theory is utilized to obtain the configuration and corresponding energy of Rh nanoclusters, boron nitride sheet, Rh nanoclusters adsorbed on the boron nitride sheet, Li atoms adsorbed on the graphene, hydrogen adsorbed on the graphene and hydrogen adsorbed on the Li atoms. Then, we use the Force-matching method (FMM) to modify the parameters of potential function by the reference data which are obtained by Density functional theory. Finally, we use the modified parameters of potential function to perform Molecular dynamics in this study. The second part: In this part, the dynamical behavior of Rh nanoclusters with different sizes on the boron nitride sheet are investigated in temperature-rise period. The migration trajectory, square displacement and mean square displacement of the mass center of the Rh nanoclusters are used to analyze the dynamics behavior of Rh nanoclusters on the boron nitride sheet. The third part: In this part, the pristine graphene and graphen with Li atoms are investigated the efficiency of hydrogen storage at different temperature and pressure. In order to obtain the temperature (77K and 300K) and pressure effect of hydrogen storage, the densimetric distribution and gravimetric capacity (wt%) are analyzed. The fourth part: The Molecular dynamics is utilized to study the hydrogen storage and delivery when the distance between two graphene is different. Then, the temperature effect (77K and 300K) of hydrogen storage, the gravimetric capacity (wt%) are analyzed. In addition, the gravimetric capacity (wt%) of hydrogen delivery are also analyzed in the larger system space at 300K.

The group III nitride semiconductor grown on c-plane sapphire by radio frequency plasma assisted molecular beam epitaxy has been studied. To archive good quality GaN film, nitridation and low temperature buffer layer were applied to overcome the issue of lattice mismatch. Low temperature and long period nitridation process shows better improved of optical properties and crystal quality of GaN film. Buffer layer grown with slightly Ga-rich, substrate temperature at 522¢J, for 2 minutes leads to better GaN film. High substrate temperature and sufficient nitrogen to gallium ratio are two important factors to control the growth of the good quality GaN epilayer. Chemical etching and observation of surface reconstructions were used to characterize the polarity of group III nitrides. The Ga-polarity GaN film shows 2x surface reconstruction with high chemical resistance while the N-polarity is sensitive to chemical and displays the 3x reconstruction pattern. The process of indium incorporated with GaN is very sensitive to growth temperature. The indium content decreased with increasing the substrate temperature and also decreased along the growth direction. The N-polar GaN with an indium-facilitated growth technique was also studied. Upon the incorporation of indium during growth, the photoluminescence intensity and electron mobility of GaN has been enhanced by a factor of 15 and 6 respectively. The electron concentration drastically increases by several orders of magnitude. The biaxial strain of GaN film estimated with Micro-Raman technique reduces from 0.6729 to 0.5044GPa. The full-widths at half maximum of asymmetric (10-12) x-ray reflection which related to the density of overall threading dislocations increases from 593 to744 arcsec. In contrast, the symmetric (0002) reflection related only to threading dislocations having a non-zero c-component Burgers vectors reduces from 528 to 276 arcsec. The enhancement of GaN optical property is generally attributed to the reduction of non-zero c-component dislocations. The reduction in density is confirmed by cross-sectional transmission electron microscopy.

The temperature coefficient of frequency (TCF), electromechanical coupling coefficient (K2) and surface acoustic wave (SAW) velocity are the major factors when choosing the substrates for surface acoustic wave devices. There exist a wide range for the designer to controll the above factors. This thesis adopted several methods to change the properties of SAW devices. First, the SAW velocity is increased using aluminum nitride (AlN) thin films deposited on z-cut LiNbO3 substrates. Besides, the ST-quartz is adopted as substrate for comparison to clarify the temperature characteristic of AlN itself. The well-known positive TCF material, silicon dioxide (SiO2), is also deposited on z-cut LiNbO3 substrates for the purpose of improving the TCF of SAW devices. Finally, the optimal piezoelectric bilayer structures will be conducted for the improvement of the properties of SAW devices on LiNbO3 substrate. AlN and SiO2 thin films are selected to be deposited on z-cut LiNbO3 and ST-cut quartz substrates using the reactive RF magnetron sputtering. The characteristics of AlN thin films are evaluated using the analyses of XRD, SEM and AFM. The optimized growth parameters of highly c-axis oriented AlN films deposited on LiNbO3 substrate are sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. On the other hand, the optimal parameters for highly c-axis oriented AlN films deposited on quartz substrate are sputtering pressure of 15 mTorr, nitrogen concentration of 30%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. In addition, the interdigital transducers (IDTs) are fabricated on LiNbO3, AlN/LiNbO3, SiO2/LiNbO3, quartz and AlN/quartz substrates, respectively. The characteristic parameters of SAW devices are measured by Hewlett-Packard (HP) 8720 network analyzer. For SiO2/LiNbO3 SAW devices, the SiO2 thin films reveal the compensation of TCF, but the surface wave velocity remain almost unchanged. For AlN/quartz SAW devices, the positive temperature coefficient of AlN is clarfied by taking ST-quartz substrates as comparison. For AlN/LiNbO3 SAW devices, the characteristic improvements of frequency increase and TCF compensation of LiNbO3 SAW devices are achieved at the same time.