Photoautotrophic organisms have been highlighted as carbon capture and conversion platforms for sustainable production of agricultural and chemicals in KSA. Previously two cyanobacterial strains, Geitlerinema spp. CT7801 and CT7802, were isolated from an industrial brine outfall site in the Eastern Province of the Kingdom of Saudi Arabia. Initial characterization of their growth characteristics showed growth at high temperature (38 ºC) and high salinity ( > 60 PSU), making them potentially good candidates for industrial applications. In this study, quantitative growth assays were performed using standardized methods developed for the analysis of Red Sea photosynthetic microorganisms supported by microscopic observations, optimal growth media preference assays, CO2 concentration effect, photoperiod effect, mixotrophic and heterotrophic growth tests. Data was recorded for absorbance (600 and 750 nm wave lenght), dry cell weight (DCW), colorimetric observations, and chlorophyll a content. Both CT7801 and CT7802 exhibited a clear preference for Walne's Red Sea medium. An analysis on media composition highlights B and Fe as growth enhancers, as well as a base requirement of seawater. Tests on the effect of supplied concentration of CO2 showed that air enhanced with 1 % v/v CO2 allows approximately 2-fold increase in DCW for Geitlerinema spp. CT7802. Photoperiod tests showed that continuous light is disadvantageous for phototrophic growth of Geitlerinema spp. CT7801 and CT7802. Results for mixotrophic and heterotrophic growth of Geitlerinema spp. CT7801 and CT7802 revealed their ability to metabolize glycerol. Analysis on the complete genome of CT7802 identified three key enzymes, glycerol kinase, glycerol-3-phosphate dehydrogenase and triosephosphate isomerase, which may catalyze the glycerol metabolic pathway in the strain. Utilization of glycerol, a residue of the biodiesel industry, might provide a sustainable alternative for growth of Geitlerinema sp. CT7802.

The growth optimization and fabrication of 980nm quantum well (QW) lasers is presented. Photoluminescence (PL) spectroscopy is used to determine the optimized growth conditions for the QWs. The results are presented for optimization of both growth temperature and group V overpressure. Broad area lasers, with active regions grown at and around optimized QW growth conditions, are fabricated and characterized under pulsed conditions. These results are used to determine the optimum growth conditions for a ridge waveguide (RWG) laser structure. Once grown, RWG lasers are fabricated and characterized under continuous wave (CW) conditions. External quantum efficiencies as high as 71 % and cavity losses as low as 5.2 cm-1 are achieved. / Thesis / Master of Engineering (ME)

Metallic glasses possess attractive properties, such as high strength, good corrosion resistance, and superior soft magnetic performance. They also serve as precursors for synthesizing nanocrystalline materials. In addition, a new class of composites having crystalline phases embedded in amorphous matrix is evolving based on selective crystallization of metallic glasses. Therefore, crystallization of metallic glasses and its effects on properties has been a subject of interest. Previous investigations from our research group related to laser assisted crystallization of Fe-Si-B metallic glass (an excellent soft magnetic material by itself) showed a further improvement in soft magnetic performance. However, a fundamental understanding of crystallization and mechanical performance of laser treated metallic glass was essential from application point of view. In light of this, the current work employed an integrated experimental and computational approach to understand crystallization and its effects on tensile behavior of laser treated Fe-Si-B metallic glass. The time temperature cycles during laser treatments were predicted using a finite element thermal model. Structural changes in laser treated Fe-Si-B metallic glass including crystallization and phase evolution were investigated with the aid of X-ray diffraction, differential scanning calorimetry, resistivity measurements, and transmission electron microscopy. The mechanical behavior was evaluated by uniaxial tensile tests with an InstronTM universal testing machine. Fracture surfaces of the metallic glass were observed using scanning electron microscopy and site specific transmission electron microscopy. Fe-Si-B metallic glass samples treated with lower laser fluence (<0.49 J/mm2) underwent structural relaxation while higher laser flounces led to partial crystallization. The crystallization temperature experienced an upward shift due to rapid heating rates of the order of 104 K/s during laser treatments. The heating cycle was followed by termination of laser upon treatment attainment of peak temperature and rapid cooling of the similar order. Such dynamic effects resulted in premature arrest of the crystallite growth leading to formation of fine crystallites/grain (~32 nm) of α-(Fe,Si) as the major component and Fe2B as the minor component. The structural relaxation, crystallization fractions of 5.6–8.6 Vol% with α-(Fe,Si) as the main component, and crystallite/grain size of the order of 12 nm obtained in laser fluence range of 0.39-0.49 J/mm2 had minimal/no influence on tensile behavior of the laser treated Fe-Si-B metallic glass foils. An increase in laser fluence led to progressive increase in crystallization fractions with considerable amounts of Fe2B (2-6 Vol%) and increase in grain size to ~30 nm. Such a microstructural evolution severely reduced the strength of Fe-Si-B metallic glass. Moreover, there was a transition in fracture surface morphology of laser treated Fe-Si-B metallic glass from vein pattern to chevron pattern. Tensile loading lacked any marked influence on the crystallization behavior of as-cast and structurally relaxed laser-treated metallic glass foils. However, a significant crystallite/grain growth/coarsening of the order of two and half times was observed in the fractured region compared to the region around it for the laser-treated partially crystallized metallic glass foils. The simultaneous effects of stress generation and temperature rise during tensile loading were considered to play a key role in crystallite/grain growth/coarsening.