<p>This work examined the systematic approach to protein crystallization, exploring some of the techniques that have been developed to enhance the success rate of crystallization. The work was centered on two proteins / namely Vaccinia virus complement control protein (VCP) and glutamate dehydrogenase (GDH) from Bacteriodes fragilis. The crystal structures of the full lengthe native VCP and VCP bound to heparin had already been determined. In the same way, the structure of GDH from Bacteriodes fragilis is not known, even though structures of other GDHs from different organisms have been determined.</p>

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The work described in this thesis is a study of imperfections in high purity, low dislocation content synthetic quartz single crystals which are grown on a commercial scale by the General Electric Company. Hydrogen and metal ion impurities in quartz were studied using low temperature transmission Fourier Transform Infrared Spectroscopy, (FTIR). Incorporation of impurities in quartz was investigated using crystals which were doped with Al, Fe, Cr, Co, Ti, P, Cu and K. Orientation of hydroxyl impurities was determined using polarised infrared spectroscopy. Deuterated quartz crystals were grown and studied as analogues to high purity crystals. X-ray diffraction topography was used to evaluate crystal quality and to perform a study of quartz which had been treated by electrodiffusion, or sweeping. Crystal lattice strain and sweeping damage was studied using double crystal topography at the Synchrotron Radiation Source, (SRS), at the Daresbury Laboratory. Metal ion impurities were sh own to incorporate interstitially into quartz crystals. The only exceptions were aluminium and iron, which incorporated substitutionally. All the impurities studied introduced hydrogen impurities such as hydroxyl ions and water molecules into quartz. A relationship between impurity concentration and hydrogen content was clearly indicated. The 3200 cm-1 broad absorption band characteristic of impure and fast grown synthetic quartz was strongly implicated as being due to interstitially incorporated water molecules. The major hydrogen impurities in quartz were sodium hydroxide molecules which were preferentially aligned along the X, Y and Z growth axes. Hydroxyl ions were not incorporated directly from the growth solution. Sweeping was shown to induce the formation of a negative space charge in treated quartz which gave rise to inhomogeneous lattice strain. The strain was gradually relieved upon prolonged exposure to x-rays. A mechanism for the production and relief of lattice strain has been proposed. Sweeping produced surface damage on mechanically polished crystals but not on those treated by chemical polishing using hydrofluoric acid. No further detrimental effects of sweeping were observed. Double crystal topographic studies revealed two possible bulk defects in Quartz. The first of these was a previously unreported planar defect parallel to the X-Y plane of quartz. The second was possibly a planar defect associated with the cellular growth cells in the (00.1) growth sector of quartz. The validity of these observations was put in doubt by the possibility of defect projection from the silicon monochromator which had been used in double crystal studies.

Si,Ge,-, alloy is an emerging semiconductor material with many important potential applications in the electronic industry due to its adjustable physical, electronic and optical properties. It has been scrutinized for the fabrication of high-speed micro electronics (e.g., SiGe heterojunction bipolar transistors (HBT) and high electron mobility field effect transistors) and thermo-photovoltaics (e.g., photodetectors, solar cells, thermoelectric power generators and temperature sensor). Other applications of Si,Ge,-, include tuneable neutron and x-ray monochromators and y-ray detectors. In these applications, SixGel-, alloy is generally used in the form of epilayers that have to be deposited on a lattice-matched substrate (wafer). Therefore, SixGel-, bulk single crystals with a specific composition (x) are needed for the extraction of such wafers. LPEE (Liquid Phase Electroepitaxy) was considered as a technique of choice for the growth of single crystals. However, LPEE growth process needs a single crystal seed with the same composition as the crystal to be grown. Yet, such a seed substrate with particularly higher composition is not commercially available. In order to address this important issue in LPEE, a crystal growth technique, which is named "Liquid Phase Diffusion" (LPD), was developed and used to produce the needed seed substrate materials. This was the main motivation of the present research. This thesis presents a combined experimental and modelling study for LPD growth of compositionally graded, germanium-rich single crystals of 25 rnrn in diameter for use as lattice-matched seed substrates. The experimental part focuses on the design and development of a complete LPD grow system. The experimental set-up was tested by growing ten Si,Ge,-, single crystals. Grown crystals were characterized by macroscopic and microscopic examinations after chemical etching for delineation of the degree of . . . Abstract 111 single crystallinity and growth striations. Compositional mapping of selected crystals were performed by using Electron Probe Micro Analysis (EPMA) as well as Energy Dispersive X-ray analysis (EDX). It was shown that the LPD technique can be successfully utilized to obtain Si,Ge,-, single crystals up to 6-8 % at.Si with uniform radial composition distribution. The modeling part presents a rational continuum mixture model developed to study transport phenomena (heat and mass transfer, fluid flow) occurring during the LPD growth of Si,Ge,-, . Based on the continuum model developed, two and three-dimensional transient numerical simulations were carried out. The numerical simulation models presented account for some important physical features of the LPD growth process ofSi,Ge,-, , namely (1) a growth zone design on the thermal field, (2) the structure of the buoyancy induced convective flow and its effect on the growth and transport mechanisms, (3) the shape and evolution of the initial and progressing growth interfaces, and (4) the spatial and time variation of the crystal growth velocity. It was numerically shown that, as the name LPD implies, the growth of Si,Ge,-, by LPD is mainly a diffusion driven process except the initial stages of the growth process during which the natural convection in the solution zone is prominent and has significant effects on the composition of the grown crystal. The simulated evolution of the growth interface agrees with experimental observations. In addition, the numerical growth velocities are in good agreement with those of experiments. The numerical model developed can be used to study other crystal growth processes such as LPEE, Traveling Heater Method THM, and vertical Bridgman with slight modifications.

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