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��-SiC is a semiconductor for high temperature devices, which exhibits several outstanding properties such as high thermal stability, good chemical stability and wide band gap. There is a possibility of fabricating a crack-free ultrathin SiC film on silicon wafers by pyrolysis of polymethylsilane (PMS) film. This study looks into the possibility, as the first phase, to modify the surface of silicon and graft PMS onto the surface. A new technique reported in this thesis consists of a surface modification with trimethoxysilylpropene (TSP) followed by the surface attachment of dichloromethylsilane (DMS) in the presence of a platinum catalyst, which acts as the first unit for grafting PMS molecules by the sodium polycondensation of additional DMS monomers. The grafted PMS polymers would serve as the pyrolytic precursor to be converted into thin layers of SiC. Surface analysis of these films on silicon wafers by X-ray photoelectron spectroscopy (XPS) indicated that the silicon surface was successfully modified with TSP, attached with DMS, and finally grafted with PMS. It was also confirmed by powder X-ray diffraction (XRD) that PMS formed simultaneously in the bulk solution was converted into SiC by pyrolysis at temperatures above 1100��C under Ar atmosphere. Extended studies showed that the PMS-derived coatings, formed in an Ar stream containing 1% H��� at 400��C, were significantly oxidized, and further heating to 700��C yielded a Si0��� layer with graphitic carbon. The intensity of the graphite peak decreased with an increase in the pyrolysis temperature. Based on these preliminary studies towards the second phase, i.e. the pyrolysis of PMS to SiC, the need for further research to eliminate the oxidation source(s) is strongly suggested. / Graduation date: 2001

Part I discusses the development of an aluminum-magnesium-silicon alloy that may combine strength, extrudability, favorable corrosion resistance with low cost and scrap compatibility. The first part of the study determined the effects of small composition, heat treatment and mechanical processing changes on the ambient temperature tensile properties of the alloy. A combination of magnesium and silicon of about 2%, 1% copper, 0.2% chromium and 0.1% vanadium can produce a T6 alloy with significant higher strength, fatigue and corrosion fatigue properties for both ingot and extrusion than those of 6061 but with only a modest increase in cost. The new alloy has been designated as AA6069. The second part of the study determined the T6 properties of 6069 alloy. The tensile test results of cold and hot extrusions of hollow, solid bars, and high pressure cylinders indicate that the T6 properties ranged from 55-70 ksi (380-490 MPa) UTS, 50-65 ksi (345-450 MPa) yield strength, and 10-18% elongation. It also appears that the fracture toughness and general corrosion resistance in saline environment are comparable or better than those of 6061 T6. Part II attempted to evaluate the formation, formability, thermal and mechanical properties of semi-solid A356, A357 and modified aluminum silicon semi-solid alloys. The semi-solid alloy microstructure was produced in this study by purely thermal treatment rather than conventional and expensive electromagnetic or mechanical stirring. Three heat-up stages in semi-solid treatment were evaluated. Stage I is related to the heating of the alloy in the solid state. Stage II is related to the eutectic reaction. Stage III is related to the heating of the semi-solid slurry. Stage II requires the longest time of the three heat-up stages due to the endothermic reaction on heating. An increase of furnace temperature can greatly reduce the time of stage II. The atmosphere (vacuum, air, argon) of the semi-solid treatment does not appear to greatly affect the T6 properties of semi-solid alloys. The microstructure and T6 properties of semi-solid A356 do not appear sensitive to the homogenization treatments before semi-solid treatment. The porosity of semi-solid ingots and pressed parts increases as the cooling rate decreases in unformed and subsequent-to-moderate pressure forming. The T6 properties basically appear sensitive to voids, with a degradation of properties as the void concentration increases. The formability of A357 may be improved as the spheroidal particle size decreases. Hence, formability may improve with decreasing ingot grain size. The mechanism of coarsening of the solid phase at isothermal temperatures is related to Ostwald ripening and/or "merging" of particles. The mechanical properties of die-casting parts show that the method of thermal treatment to produce a spheroidal microstructure is an effective method for industrial production of semi-solid aluminum-silicon alloys. / Graduation date: 1997

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

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--Dept. of Physics and School of Computing and Engineering. University of Missouri--Kansas City, 2005. / "A dissertation in physics and computer networking." Advisor: Wai-Yim Ching. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed March 12, 2007. Includes bibliographical references (leaves 256-267). Online version of the print edition.

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.

The performance of negative electrodes based on Si nanoparticles for Li-ion batteries has been investigated. Electrodes consisted of Si nanoparticles, carbon black and Na-CMC. The investigation covered electrode production parameters such as pre-treatment of the Si-powder, different emulsifiers and cycling with two different electrolytes. Testing of the electrodes’ performance was done electrochemically with two different galvanostatic approaches: constant charge rate and stepped-up charge rate. Electrodes’ morphology, stability and surface chemistry were also evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thickness measurements and X-ray photoelectron spectroscopy (XPS).   High electrode capacities were achieved though strong variation depending on electrode thickness has been found. For the best performing electrodes the capacity exceeded 1600 mAh/g with slight fading after 10-15 cycles. The difference in performance could not be assigned to the different production parameters, but had a clear correlation to the thickness of the electrode and the different electrolytes used. Propylene carbonate based electrolyte gives a lower coulombic efficiency and lower capacity retention than an ethylene carbonate-diethyl carbonate based electrolyte. The electrodes could not store any capacity at cycling rates higher than 2C, but were not damaged by cycling rates up to 50C. SEM micrographs revealed that a solid electrolyte interface (SEI) was formed on the electrodes during cycling and their surface analysis by XPS suggested that the SEI was formed by decomposition of electrolyte components.

The interaction and orbital energy levels of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules on a Pb/Si(111) 1x1 substrate have been investigated. A Si(111) sample was annealed to form the 7x7 configuration. 1.5 monolayer of Pb was evaporated onto the surface, which was then annealed. 0.5 monolayer of PTCDA was applied to the substrate through molecular beam epitaxy (MBE). The surface configuration of the substrate was monitored step by step by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Scanning tunneling spectroscopy (STS) was used to pinpoint the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules. It was found that the PTCDA molecules formed a herringbone pattern on the substrate. The PTCDA electronic energy levels corresponding to the HOMO and the LUMO were obtained. From these values the energy gap between these orbitals, the molecular bandgap of PTCDA on Pb/Si(111) 1x1, was determined.

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