An improved quenching technique is described. This technique allows samples to be quenched at slow quenching rates without introducing unwanted dislocations during quench. High quality platinum single crystals 1 mm in diameter have been quenched from temperatures between 900°C and 1550°C using this technique. The data have been analysed and discussed using a sink model for vacancy loss proposed by Emrick. The formation energy was found to be (1.30 ± 0.03) eV. The entropy of formation and the concentration of vacancies at the melting point have been determined to be respectively (0.42 ± 0.11)k and (9.4 ± 0.7)10⁻⁴. High purity palladium single crystals have also been quenched using the same technique. Due to the need for a temperature scale, measurements of the electrical resistance of an ultra pure palladium single crystal have been made to a temperature within 100°C of the melting point. These, along with measurements of the liquid palladium resistivity, are reported. The results are discussed and compared to previously reported values.

published_or_final_version / Physics / Master / Master of Philosophy

No description available.

published_or_final_version / Physics / Master / Master of Philosophy

In this investigation, controlled thermal annealing and oxidation treatments were carried out on wafers obtained from seed-end and tang-end regions of (100)-oriented, 75 mm-diameter, Czochralski-grown, "typical" silicon single crystals. The radial variation of resistivity was characterized with four-point probe and spreading resistance probe measurements. The defects were studied by preferential etching and optical microscopy, using Wright etch for characterizing the individual etch figures, whereas the overall distribution of defects was obtained by using a modified form of Sirtl etch. The preferential etching was carried out in a Teflon barrel under controlled conditions. Transmission electron microscopy (TEM) was carried out on selected samples to study the defect structure in the as-grown crystal as well as after specific thermal treatments. In the p-type as well as n-type crystals studied in this work, the relative radial gradient as well as the magnitude of resistivity are greater at the seed-end than at the tang-end. An annealing treatment at 650°C for 100 min on seed-end wafers stabilized the resisitivity by destroying oxygen-donor complexes. Such an annealing treatment on tang-end wafers has a minor effect on the resistivity of the sample, which was uniform initially. The "swirl" patterns, as revealed by preferential etching, showed that they are more pronounced in seed-end wafers and are almost absent in tang-end wafers. A pre-annealing treatment at 650°C in argon for 100 min followed by a high-temperature (≥800°C) treatment precipitates the swirl pattern much more intensely, in comparison to just the high temperature treatment without any preanneal at 650°C. For comparable oxide thicknesses (0.5 μm) for thermal oxidation in steam at three different temperatures (900°C, 1050°C, 1200°C), it was found that the swirl pattern was most severe at 900°C and the dissolution of the defect structure progressively increased with increasing temperature. It was found in this investigation that bulk-type stacking faults are generated after argon annealing at 1050°C. This is in contrast to the generally prevailing confusion that thermal oxidation is essential for generation of stacking faults in silicon. It must be distinguished here that the formation of surface-type stacking faults requires thermal oxidation, whereas bulk-type stacking faults nucleate at individual swirl defects due to precipitation of dissolved oxygen. TEM work done in this investigation showed that as-grown CZ silicon defect structure consists of an assortment of precipitates, small dislocation lines, and a helical type of long (∼24 μm) dislocation line, and another long linear defect with periodically spaced nodes. The annealing treatment at 650°C as well as thermal oxidation at 900°C produce a spectrum of precipitates and small dislocations.

No description available.

This thesis uses multiscale computational modelling to find the fundamental principles that govern defects forming during the operation of new electro-optical devices and the processing of spider silk fibers. The generalized approach developed in this thesis bridges engineering devices and biological processes based on liquid crystalline materials. / Three types of defects are encountered: inversion walls, lines and points. Inversion wall defects are found in the electro-optical device when a nematic thin film undergoes a temperature-induced surface anchoring transition. Point defects naturally occur in the tubular extrusion duct of spiders, while line defects present close topological connections with point defects and are widespread in many high-performance industrial fibers. Three models are used in this thesis and their usage is dependent on the characteristics of the defects studied. / In the case of inversion wall defects, computational modelling is used to verify, complement and analyze experimental measurements made with fluorescence confocal polarizing microscopy by our collaborator at the Georgia Institute of Technology. The various simulation results agree and explain very well experimental observations and provide a thorough understanding of the wall defects behavior. A computational technique is developed to enable the precise determination of the interaction between the liquid crystal and the device substrate. Understanding the behavior of wall defects and estimating interfacial properties are indispensable to the development and optimization of the electro-optical device as they affect properties like temperature of operation, switching voltages and response time. / Computational modelling is also used to investigate the behavior of nematic point defects confined in cylindrical cavities as observed along spiders' spinning apparatus, and to examined textural connections with other well know structures seen in industrial fibers. The various scenarios investigated include: interactions between point defects, topological transformations between point, line and ring defects as well as interactions between ring defects. The simulation results agree and complement previous investigations but also offer a new fundamental understanding on the nature and stability of defects in cylindrical cavities. Understanding the behavior of nematic point and line defects in cylindrical geometries is important as they play a fundamental role in the processing of natural and industrial high-performance fibers.

No description available.

published_or_final_version / Physics / Master / Master of Philosophy

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.