by Poon Ming-Cheong. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves [163-175]

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We have developed a new coarsening theory that more completely describes grain growth of a system of anisotropic particles such as completely faceted crystals by Ostwald ripening. Our model takes the anisotropy of surface energies on dissimilar facets into account, and the particle sizes are described by a distribution function. The theory is applied to study the coarsening of ,B-silicon nitride in a liquid medium due to the anisotropic growth of grains in different crystallographic directions. A model of the growth of silicon nitride grains is obtained based on the numerical solution of the equations of the new theory. Computer experiments are performed to determine how the distribution function evolves, to investigate the influence of various parameters such as diffusion and interfacial reaction constants on grain growth and to extract grain growth exponents from this model in order to determine the growth mechanisms that are responsible for the anisotropic growth behaviour. Only preliminary numerical results are available thus far due to 1/r instabilities that occur in the theory as r → 0. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.

2 ��m average sized silicon powder was nitrided with 90% N���/10% H��� in a fluidized-bed reactor, operated at 1200��C, 1250��C and 1300��C. To fluidize silicon powder, alumina particles with an average size of 300 ��m were used as an inert fluidizing conditioner. The feasibility and operating conditions of the fluidization were studied at room temperature. The effects of silicon content and operating temperature on the nitridation of silicon as well as on the formation of ��- and ��-silicon nitride were investigated in batch and semi-continuous operations. The effects of the average residence time of silicon/alumina mixtures in the fluidized-bed reactor on the nitridation process were studied in semi-continuous operations. In batch operations, a maximum mass fraction of 15 wt% silicon powder could be added to alumina particles at temperatures in the range of 1200 to 1300��C without changing the fluidization quality. When the silicon fraction was increased to 20 wt%, fluidization failed immediately. With a mass fraction of 5% silicon powder, almost 100% ��-silicon nitride, which was preferred in applications, was found in the product. ��-silicon nitride was facilitated with an increase in silicon fractions in silicon/alumina mixtures. The nitridation process was strongly affected by the reaction temperature. The overall conversion of silicon increased with an increase in reaction temperature. Higher temperature also promoted the formation of ��-silicon nitride. The overall conversion of silicon into silicon nitride was also enhanced by hydrogen concentrations. An increase in hydrogen concentration facilitated the formation of ��-form silicon nitride. In the semi-continuous operation, the nitridation of 30 wt% silicon/70 wt% alumina mixtures could be achieved without changing the fluidizing quality. Almost 100% ��-silicon nitride was found in the product when a 20 wt% silicon/80 wt% alumina mixture was nitrided at 1250��C for an average residence time of up to 4 hours. However, ��-silicon nitride was formed when the mixture was nitrided at 1300��C for an average residence time of 3 hours. A mathematical model incorporating kinetic data and carryover of silicon powder was developed to described the total conversion of silicon in batch operation. A semi-continuous model was also proposed, which successfully predicted the overall conversion of silicon powder. / Graduation date: 1997

Flash memory is one sort of non-volatile memory, focus on the dates holding and capacity. Conventional non-volatile memory applies poly-crystalline for floating gate material, because the poly-crystalline (like poly-silicon) itself is the semiconductor material, will cause leakage problem, recently, Oxide-nitride-oxide multi-layer structure is under development for the place of conventional floating gate. Because it is the insulator material, can suppress leakage current, and it contains a deeper trapping energy level, and has a partial trapped carriers phenomenon to give a multi-bits memory solution. My effort is to propose a pair of ONO three layers stack, which is located close to the beneath of D/S region and a column like. Such structure can overcome miniaturization limitation of channel length, and a somewhat depth oxide can promise good isolation and separation between the trapping layer and other area, and a reliable distance of the two trapped unit can prevent interference issue. My proposal can suppose a higher devices density and a feasible and flexible solution to develop memory devices, a cost down to be more competitive, certainly bring much favor for the future improvement.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

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Thesis (M.S.) in Physics--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 82-87).