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The dissertation focuses on the analysis of the extended defects present in as-grown and proton bombarded β-SiC (annealed and unannealed) grown by chemical vapour deposition (CVD) on (001) Si. The proton irradiation was done to a dose of 2.8 × 1016 protons/cm2 and the annealing took place at 1300°C and 1600°C for 1hr. The main techniques used for the analysis were transmission electron microscopy (TEM) and high resolution TEM (HRTEM). From the diffraction study of the material the phase of the SiC was confirmed to be the cubic beta phase with the zinc-blende structure. The main defects found in the β- SiC were stacking faults (SFs) with their associated partial dislocations and microtwins. The SFs were uniformly distributed throughout the foil. The SFs were identified as having a fault vector of the type 1/3 <111> with bonding partial dislocations of the type 1/6 <121> by using image simulation. The SFs were also found to be predominantly extrinsic in nature by using HRTEM analysis of SFs viewed edge-on. Also both bright and dar-field images of SFs on inclined planes exhibited symmetrical and complementary fringe contrast images. This is a result of the anomalous absorption ratio of SiC lying between that of Si and diamond. The analysis of the annealed and unannealed irradiated β-SiC yielded no evidence of radiation damage or change in the crystal structure of the β-SiC. This confirmed that β-SiC is a radiation resistant material. The critical proton dose for the creation of small dislocation loops seems to be higher than for other compound semiconductors with the zinc-blende structure.

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A study has been undertaken to investigate the loss of ductility and modified work hardening characteristics of zinc single crystals coated with mercury. Important results of tensile tests performed under fixed experimental conditions are summarized to be: (1) increase in critical resolved shear stress, and increase of work hardening slope in stage A and stage B (2) decrease in transition strain from stage A to stage B (3) decrease in fracture stress and fracture strain. The results have been interpreted in the context of the present understanding of deformation theory of C.P.Hex. metals. In addition, relevant mechanisms for crack initiation have been studied with the aid- of microscopic observations of deformed crystals. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

An investigation as to the characteristics of flow and fracture for alpha-uranium were carried out over the temperature range -196°C to 270°C. The parameters relevant to grain size and strain rate were investigated. It was established that the flow stress and the fracture stress in the semi-brittle region vary linearly with the grain size parameter (1/D½). Evidence suggests that the sensitivity of flow stress to grain size is directly related to the importance of glide dislocation action as the deformation mode. Strain rate change irreversibility was found to exist at low strains for all temperatures investigated. This evidence, correlated with the effect of grain size, indicates that massive structural changes occur in the early stages of flow. This agrees with electron transmission microscopy results as established by other workers. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The theory of ferroelectricity, and in particular the ferroelectric behavior of barium titanate, are discussed and qualitative agreement is obtained with experimental results. Limitations of the theory are pointed out. Experimental procedure used to manufacture samples of polycrystaline barium titanate ceramic, and to investigate their ferroelectric properties is outlined. The phenomena of permanent polarization and hysteresis are investigated in the ferroelectric temperature range, and are discussed. An electric equivalent of the Barkhausen effect is observed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The etching of silicon by atomic and molecular chlorine and bromine was studied as a function of etchant pressure and reaction temperature. Various types of silicon were employed in the etching experiments including intrinsic and n-type polycrystalline silicon as well as the (100) face of intrinsic single crystal silicon. The pressures of Cl₂ and Br₂ varied from 0.1 to 30 Torr and the partial pressure of Cl and Br atoms was between 0.08 and 0.2 Torr. Temperatures of between 365 and 600°C were required for CI₂ and Br₂ etching, while lower temperatures of 25 to 470°C were sufficient for the more reactive Cl and Br atoms. The reaction between silicon and Br atoms was shown to be first order with respect to the partial pressure of atoms and a first order dependence was assumed for Cl atom etching. The rate constants were determined for the Cl and Br atom etching of intrinsic and n-type polycrystalline silicon, with a dopant concentration of 5x10¹⁸ atoms cm⁻³. The reactivity of Cl atoms with n-type silicon was approximately 90 times greater than with intrinsic silicon. This enhancement in reaction rate is primarily due to an increase in the preexponential factor in k₁, with the activation enthalpy for the process remaining unchanged at approximately 28 kJ mol⁻¹. For Br atom etching, the reaction rate for the n-type silicon was over 300 times greater than for intrinsic silicon and was characterized by activation enthalpies of 55 and 63 kJ mol⁻¹ respectively. The enhancement in reactivity can also be attributed principally to an increase in the preexponential factor. The preexponential factors for the rate constants are larger than those expected, based on the collision frequencies of Cl and Br atoms. This is interpreted as evidence for a preadsorption step in these reactions. The reactions of silicon with CI₂ and Br₂ were found to display a complex pressure dependence. The etch rates varied linearly with (etchant pressure)¹′² and the intercepts from a linear regression of the data were slightly negative. To account for the half order pressure dependencies observed in these etching reactions, a reversible dissociative adsorption mechanism is proposed whereby Br₂ (or CI₂) is dissociatively adsorbed, in a reversible reaction, onto the silicon surface yielding two atoms bound to the surface. This step is then followed by a first order reaction leading to the formation of a species which is either gaseous product or some precursor which forms that product in a subsequent non rate-determining step. From the slopes of etch rate versus (pressure)¹′² plots, composite half order rate constants were calculated and from the intercepts it was possible to evaluate the rate constant for dissociative adsorption of the halogen molecules. At high etchant pressures, where the reaction was half order with respect to Br₂ (or CI₂), a half order "composite" rate constant characterized the etching reaction. Values for the half order rate constant were determined for a number of wafers at various temperatures. From the temperature dependencies of these rate constants, activation enthalpies of 131±8 and 116±7 kJ mol⁻¹ were calculated for Br₂ and CI₂ etching of intrinsic polycrystalline silicon respectively. A value of 121±7 kJ mol⁻¹ was deterrnined for the Br₂ etching of silicon (100). Higher reaction rates were observed for the etching of n-type polycrystalline silicon, with greater enhancements observed for Br₂ relative to Cl₂ etching. The enhancements in etch rates were found to be principally due to a lower activation enthalpy for the half order rate constant. An activation enthalpy for the composite rate constant of 82±3 kJ mol⁻¹ was determined for Cl₂ etching of n-type silicon with a dopant atom concentration of 5x10¹⁸ atoms cm⁻³. Br₂ etching of the same wafer yielded an activation enthalpy of 86±3 kJ mol⁻¹. At low pressures, the reaction becomes first order and the temperature dependence of the corresponding first order rate constant yielded activation enthalpies of 109 and 83 kJ mol⁻¹ for intrinsic and n-type polycrystalline silicon. / Science, Faculty of / Chemistry, Department of / Graduate

Two types of devices employing ferroelectric modulation of a semiconductor thin-film have been realized and studied. The first consists of a cadmium selenide film with electrodes deposited on a barium titanate substrate together with a switching electrode on the other side of the substrate. This gives a two-valued resistor; in effect, a nondestructive readout of the state of the ferroelectric crystal which is regarded as a storage element. The second device is a thin-film transistor (TFT) deposited on a barium titanate crystal. A fourth counterelectrode - on the other side of the crystal allows changing between two opposite polarization directions in the crystal, thus giving a TFT with two sets of characteristics, roughly equivalent to a two-valued built-in gate bias. The read-in, or switching time, of the device is substantially determined by the barium titanate crystal and can be in the microsecond range for high switching fields. Readout of the devices can be continuous or not, as desired. Characteristics of the TFT, which is considered equivalent to a two-gate device, are analyzed in terms of the gradual channel approximation. Experimental results of the two devices are presented and discussed in relation to the predicted behaviour. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate