The semiconductor alloy indium gallium nitride (InxGa1-xN) offers substantial potential in the development of high-efficiency multi-junction photovoltaic devices due to its wide range of direct band gaps, strong absorption and other optoelectronic properties. This work uses a variety of characterization techniques to examine the properties of InxGa1-xN thin films deposited in a range of compositions by a novel plasma-enhanced evaporation deposition system. Due to the high vapour pressure and low dissociation temperature of indium, the indium incorporation and, ultimately, control of the InxGa1-xN composition was found to be influenced to a greater degree by deposition temperature than variations in the In:Ga source rates in the investigated region of deposition condition space. Under specific deposition conditions, crystalline films were grown in an advantageous nano-columnar microstructure with deposition temperature influencing column size and density. The InxGa1-xN films were determined to have very strong absorption coefficients with band gaps indirectly related to indium content. However, the films also suffer from compositional inhomogeneity and In-related defect complexes with strong phonon coupling that dominates the emission mechanism. This, in addition to the presence of metal impurities, harms the alloy’s electronic properties as no significant photoresponse was observed. This research has demonstrated the material properties that make the InxGa1-xN alloy attractive for multi-junction solar cells and the benefits/drawbacks of the plasma-enhanced evaporation deposition system. Future work is needed to overcome significant challenges relating to crystalline quality, compositional homogeneity and the optoelectronic properties of In-rich InxGa1-xN films in order to develop high-performance photovoltaic devices. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-09-29 21:28:58.898

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This thesis aims to evaluate the compositional changes that occur when raw clays are transformed into finished vessels, and how these compositional changes impact provenance research. Petrographic and chemical techniques are used to analyse clays at each stage in the production sequence used by Zulu potters in KwaZulu-Natal, South Africa. The results of this research demonstrate that tempering behaviour, particularly the mixing of clays, can significantly alter the composition of ceramic vessels, depending on the ratio of clay types. The provenance of mixed clays and vessels can be determined when the range of variation between clay sources is known. Different ratios of constituent clays significantly affect the composition of finished vessels.

Hyperthermophiles are microorganisms that can grow at temperatures close to the boiling point of water or above. They are potential resources of thermostable enzymes including alcohol dehydrogenases (ADHs). Both Thermococcus guaymasensis and Thermotoga hypogea produce ethanol as an end product using glucose as substrate. However, the metabolic pathway and enzymes involved in alcohol production by these hyperthermophiles were not clear. ADH is a key enzyme responsible for alcohol metabolism, and the enzyme has been purified and characterized. T. hypogea is an extremely thermophilic anaerobic bacterium capable of growing at 90??C. The NADP+-dependent ADH from T. hypogea was purified to homogeneity and a homodimeric protein with a subunit size of 40 ?? 1 kDa. A part of its encoding gene was cloned and sequenced, from which a major part of the amino acid sequence of the enzyme was deduced and found to have high similarities to iron-containing ADHs from other Thermotoga species and harbored typical iron and NADP+-binding motifs. The conserved domain search showed that T. hypogea ADH was a member of the family of uncharacterized iron-containing ADHs. The iron content of the enzyme was determined to be 1.02 ?? 0.06 g-atoms per subunit. It is the first characterized iron-containing ADH from hyperthermophilic bacteria. Similar to known iron-containing ADHs, T. hypogea ADH was oxygen sensitive; however, the loss of enzyme activity upon exposure to oxygen could be recovered by incubation with dithiothreitol and Fe2+. The enzyme was thermostable with a half-life of about 10 h at 70??C, and its catalytic activity increased along with the rise of temperatures up to 95??C. Optimal pH values for the production and oxidation of alcohol were determined to be 8.0 and 11.0, respectively. The enzyme had a broad specificity in utilizing primary alcohols and aldehydes as substrates. Apparent Km values for ethanol and 1-butanol were much higher than that for acetaldehyde and butyraldehyde and thus the enzyme was likely to catalyze the reduction of aldehydes to alcohols in vivo. T. guaymasensis is a hyperthermophilic anaerobic archaeon capable of catalyzing the starch degradation and producing ethanol and acetoin as end-products. The purified T. guaymasensis ADH was an NADP+-dependent homotetramer with a subunit of 40 ?? 1 kDa. The enzyme was a primary-secondary ADH, but it exhibited substrate preference on secondary alcohols and corresponding ketones. In particular, it catalyzed the reduction of diacetyl to 2, 3-butanediol via acetoin in which the reduction from diacetyl to acetoin was irreversible. For the oxidation of 2, 3-butanediol, the enzyme exhibited higher activities on (2R, 3R)-(-)-2, 3-butanediol and meso-2, 3-butanediol than (2S, 3S)-(+)-2, 3-butanediol while the stereoselective reduction of racemic (R/S)-acetoin produced (2R, 3R)-(-)-2, 3-butanediol and meso-butanediol but not (2S, 3S)-(+)-2, 3-butanediol. The optimal pHs for the oxidation and formation of alcohols were determined to be 10.5 and 7.5, respectively. The enzyme activity increased along with the rise of temperatures up to 95??C, and it was highly stable with a half-life of 24 hours at 95??C. The enzyme was resistant to 30% (v/v) methanol (retaining 40% of its full activity). NADPH for the ketone reduction was efficiently regenerated using isopropanol as a substrate. The apparent Km value for NADPH was 40 times lower than that of NADP+, and the specificity constant with NADPH were 5 times higher than that of NADP+. Therefore, the physiological role of the enzyme was likely to be responsible for the reactions involving the NADPH oxidation???coupled formation of ethanol and/or acetoin. The fully active T. guaymasensis ADH contained 0.9 ?? 0.03 g atom zinc per subunit determined by inductively coupled plasma mass spectrometry (ICP-MS) and was the first characterized zinc-containing ADH from Thermococcus species. The gene encoding this enzyme was cloned and sequenced, and the deduced amino acid sequence contained 364 amino acids showing high similarities (85%) to those ADHs from Thermoanaerobacter species which have only the catalytic zinc atom. The motif analyses also indicated the enzyme lacked of the structural zinc-binding motif; thus, zinc might play a catalytic role in the enzyme. Further analyses showed the presence of the conserved domains of L-threonine dehydrogenases; however, the enzyme could not oxidize L-threonine or L-serine. Distinct from most of zinc-containing ADHs, the enzyme activity was almost fully inhibited by 100 ??M Zn2+ in the assay mixture. Moreover, it was sensitive to oxygen. An NADP+-dependent ADH was purified from the hyperthermophilic anaerobic archaeon Thermococcus strain ES1, an ethanol producer. The recombinant enzyme over-expressed in Escherichia coli was purified using a two-step procedure including heat treatment, and characterized in comparison with the native enzyme. The purified recombinant enzyme exhibited a specific activity of 52.8 U mg-1, close to that of the native enzyme (57 U mg-1). Both native and recombinant enzymes were homotetramers with a subunit size of 45 ?? 1 kDa. Their optimal pHs for the ethanol oxidation and acetaldehyde reduction were determined to be 10.5 and 7.0, respectively. Both enzymes were able to oxidize a series of primary alcohols and diols. Metal contents of the fully active recombinant enzyme were determined by ICP-MS to be 1.0 ?? 0.04 g atom iron per subunit, and both iron-containing enzymes were oxygen sensitive. Their kinetic parameters showed lower Km-values of acetaldehyde and NADPH than those of ethanol and NADP+, suggesting the native enzyme could be involved in ethanol formation in vivo. The recombinant and native enzymes had almost identical characteristics and thus its encoding gene was successfully over-expressed in E. coli. The deduced amino acid sequence of the ADH from Thermococcus strain ES1 was a 406 amino acid polypeptide. Its amino acid sequence showed high identities (80%) to iron-containing ADHs from the related archaea Thermococcus zilligii and Thermococcus hydrothermalis. The conserved domain search revealed it belonged to the family of iron-containing ADHs. Moreover, the sequence of the enzyme had catalytic metal and dinucleotide-binding motifs typical for iron-containing ADHs. In conclusion, the results indicate that iron- and zinc-containing ADHs from hyperthermophiles have significant differences in terms of biophysical, biochemical and molecular properties. The hyperthermophilic bacterial and archaeal iron-containing ADHs are divergent while the zinc-containing ADH from T. guaymasensis has significant similarity to thermophilic bacterial ones.

There is an ever-increasing desire to develop novel materials that could control the release of active compounds and increase their stability. Replacing petroleum-based synthetic polymers with sustainable materials has many advantages, such as reducing the dependence on fossil fuels, and diminishing environmental pollution. Recently, cellulose nanocrystal (CNC) obtained by acid hydrolysis of cellulose fibres has gained a lot of interest. The high mechanical strength, large and negatively charged surface area, and the presence of several hydroxyl groups that allow for modification with different functionalities make CNC an excellent candidate for various applications in the biomedical field. This thesis explores (i) the surface modification and characterization of modified CNC and (ii) the biomedical applications of these novel sustainable nanomaterials. In the first part, amine functionalized CNC was prepared. Ammonium hydroxide was reacted with epichlorohydrin (EPH) to produce 2-hydroxy-3-chloro propylamine (HCPA), which was then grafted to CNC using an etherification reaction. A series of reactions were carried out to determine the optimal conditions. The final product (CNC-NH2(T)) was dialyzed for one week. Further purification via centrifugation yielded the sediment (CNC-NH2(P)) and supernatant (POLY-NH2). The presence of amine groups was confirmed by FT-IR and the amine content was determined by potentiometric titration and elemental analysis. A high amine content of 2.2 and 0.6 mmol amine/g was achieved for CNC-NH2(T) and CNC-NH2(P), respectively. Zeta potential measurements confirmed the charge reversal of amine CNC from negative to positive when the pH was decreased from 10 to 3. TEM images showed similar structural properties of the nanocrystals along with some minor aggregation. This simple, yet effective synthesis method can be used for further conjugation as required for various biomedical applications. Moreover, the surface of CNC was modified with chitosan oligosaccharide (CSos). First, the primary alcohol groups of CNC were selectively oxidized to carboxyl groups using the catalyst, 2,2,6,6- tetramethylpiperidine-1-oxyl radical (TEMPO), and were then reacted with the amino groups of CSos via the carbodiimide reaction using N-hydroxysuccinimide (NHS) and 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC). The appearance of C=O peak in FT-IR spectrum of oxidized CNC (CNC-OX), accompanied by calculations based on potentiometric titration revealed that CNC was successfully oxidized with a degree of oxidation of 0.28. The grafting of CSos on oxidized CNC was confirmed by the following observations: (i) the reduction of the C=O peak in FT-IR of CNC-CSos and the appearance of new amide peaks; (ii) the significant reduction of the carbonyl peak at 175 ppm in the 13C NMR spectrum for CNC-CSos; (iii) a higher decomposition temperature in TGA of CNC-CSos; (iv) a positive zeta potential of CNC-CSos at acidic pH; and (v) a degree of substitution of 0.26, which is close to the DO (0.28), indicating that 90% of COOH groups on CNC-OX were involved in the formation of amide bonds with CSos. TEM and AFM studies also revealed a completely diff erent morphology for CNC-CSos. In the second part, the potential of exploiting CNCs as delivery carriers for two cationic model drugs, procaine hydrochloride (PrHy) and imipramine hydrochloride (IMI), were investigated. IMI displayed a higher binding to CNC derivatives compared to PrHy. Isothermal titration calorimetry (ITC), transmittance and zeta potential measurements were used to elucidate the complexation between model drugs and CNC samples. It was observed that the more dominant exothermic peak observed in the ITC isotherms leading to the formation of larger particle-drug complexes could explain the increased binding of IMI to CNC samples. Drug selective membranes were prepared for each model drug that displayed adequate stability and rapid responses. Different in vitro release profiles at varying pH conditions were observed due to the pH responsive properties of the systems. Both drugs were released rapidly from CNC samples due to the ion-exchange e ffect, and CNC-CSos displayed a more sustained release profile. Furthermore, the antioxidant properties of CNC samples and the potential of CNC-CSos as a carrier for the delivery of vitamin C was investigated. CNC-CSos/vitamin C complexes (CNCS/VC) were formed between CNC-CSos and vitamin C via ionic complexation using sodium tripolyphosphate (TPP). The complexation was confirmed via DSC and UV-Vis absorbance measurements. TEM images showed complexes with a size of approximately 1 micron. The encapsulation efficiency of vitamin C was higher (91%) at pH 5 compared to pH 3 (72%). The in vitro release of vitamin C from CNCS/VC complexes exhibited a sustained release of up to 3 weeks, with the released vitamin C displaying higher stability compared to a control vitamin C solution. Antioxidant activity and kinetics of various CNC samples were studied using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. CNC-CSos possessed a higher scavenging activity and faster antioxidant activity compared to its precursors, CNC-OX and CSos, and their physical mixture. Therefore, by loading vitamin C into CNC-CSos particles, a dynamic antioxidant system was produced. Vitamin C can be released over a prolonged time period displaying enhanced and sustained antioxidant properties since the carrier CNC-CSos also possesses antioxidant properties. As a result of this doctoral study, knowledge on the surface modification of CNC with amine groups and CSos have been advanced. The in vitro drug release and antioxidant studies suggest that systems comprising of CNC could be further explored as potential carriers in biomedical applications.

This thesis aims to evaluate the compositional changes that occur when raw clays are transformed into finished vessels, and how these compositional changes impact provenance research. Petrographic and chemical techniques are used to analyse clays at each stage in the production sequence used by Zulu potters in KwaZulu-Natal, South Africa. The results of this research demonstrate that tempering behaviour, particularly the mixing of clays, can significantly alter the composition of ceramic vessels, depending on the ratio of clay types. The provenance of mixed clays and vessels can be determined when the range of variation between clay sources is known. Different ratios of constituent clays significantly affect the composition of finished vessels.

An apparatus intended to measure the pressure oscillations generated by nanoparticle suspensions in response to an AC electric field was designed and made operational. Electroacoustic measurements were performed on nanoparticle systems covering a range of particle sizes and zeta-potentials, determined using typical particle characterization techniques. The results of the electroacoustic experiments were mapped to the hydrodynamic size and zeta-potentials of the various nanoparticle systems. It was determined that while the electroacoustic technique can be used successfully to measure the motion of nanoparticles in response to an AC electric field, additional improvements to the electroacoustic apparatus are required to allow for a more rigorous mapping of electroacoustic measurements to particle hydrodynamic size and zeta-potential.

The objective of this thesis is to explore the synthesis and characterization of high quality binary ZnTe nanowires with great potential for development of optoelectronic devices including high efficiency photovoltaic cells for energy conversion and high sensitivity photodetectors for green fluorescent protein bioimaging at single molecule level. To systematically explore the fabrication process for high quality nanowires, a chemical vapour deposition system was built for nanowire growth. Computational fluid dynamics simulations were used to optimize the reactor and growth parameters. The simulations were validated by experimental measurements. Room temperature photoluminescence measurements showed that high crystal quality with very low defects by single step growth was achieved. This single step growth technique makes a great improvement compared to the reported growth followed by annealing, which achieved equivalent crystal quality. This simplification could be of use in large scale synthesis of nanowires. The simulation results also showed that reactant species concentration is a key factor influencing the growth. A metal-organic chemical vapour deposition system was thus built to independently control reactant concentrations for ZnTe nanowire growth. Temperature-dependent photoluminescence measurements of as-grown ZnTe nanowires showed a strong near band-edge emission. In addition, a deep level oxygen-related band was observed for the first time. From the detailed analysis of thermal quenching of the photoluminescence, it was shown that the deep level emission was partially from the intermediate band of the material. This is of great importance due to the theoretical absorption efficiency that is as high as 63% for intermediate band materials, which is more than two times of that of current single junction concentrators, and few materials possessing this property. Individual ZnTe nanowires, grown after optimization, were patterned and contacted, and their conductivity and photoconductivity were measured at room temperature. A single ZnTe nanowire serving as a photodetector was shown to have the highest reported visible responsivity of 360 A/W (at 530 nm), and a gain of 8,640 (at 3 V bias). The responsivity is roughly 18 times higher than that of silicon avalanche photodiodes. This demonstrates that ZnTe nanowires are strong candidates for single photon detection.

Polyolefins are the most important commodity polymers today. Their end use properties polymers depend primarily on their molecular weight (MWD) and chemical composition (CCD) distributions. Several characterization techniques are used to analyze the microstructures of the polyolefins. High-temperature gel permeation chromatography (GPC) is the most widely used technique for MWD determination. Temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) are routinely used for CCD measurement. There have been significant improvements over the last few years on CCD characterization techniques for polyolefins with the introduction of crystallization elution fractionation (CEF) and high-temperature thermal gradient interaction chromatography (HT-TGIC). The main objective of this thesis was to conduct systematic studies on HT-TGIC and CEF to provide a better understanding on the separation mechanism of these new techniques and to find out operational conditions that enhance the resolution of the measured CCDs. The effects of cooling rate, adsorption/desorption temperature range, heating rate and sample size on HT-TGIC fractionation were investigated using polyethylene and ethylene/1-octene copolymers made with metallocene catalyst. It was found out that HT-TGIC was relatively insensitive to the cooling rate within the range investigated in this study. However, the obtained profiles depended strongly on the heating rate applied during the desorption cycle. Chromatograms measured under faster heating rates were broader and had lower resolutions, supposedly due to co-desorption effects. Analysis of polyolefin blends by HT-TGIC showed that sample volume was a very important parameter affecting peak separation of the blend components; reducing the volume of the injected sample can be used to minimize the degree of co-adsorption and co-desorption effects. The effect of solvent type on HT-TGIC analysis was investigated using o-dichlorobenzene (ODCB), 1,2,4-trichlorobenzene (TCB), and chloronaphthalene (CN). Polyolefin blends were analyzed using these solvents and the best resolution was obtained iv when ODCB was used as the mobile phase. The profiles obtained using TCB and CN were similar and both were strongly affected by the co-adsorption and co-desorption phenomena. HT-TGIC profiles of ethylene homopolymers and ethylene/1-octene copolymers were also compared with the equivalent CEF profiles. Interestingly, it was found out that the differences between the profiles measured by these techniques decreased as the comonomer content increased, with CEF systematically measuring sharper profiles for samples with low 1-olefin comonomer content. A new method was also developed to quantify the degree of co-crystallization of polyolefin blends analyzed by CEF and was used to quantify operating conditions that influenced co-crystallization. The results showed that co-crystallization can be minimized using slower cooling rates, but heating rates play a less important role. A detailed study on the effect of CEF operating conditions on CCD resolution was also conducted using industrial LLDPE resins that have broad MWDs and CCDs. Cooling rate and solvent flow rate during the cooling cycle significantly affect the degree of co-crystallization of CEF profiles. However, varying the heating rate does not have a marked impact on these separations. The CEF profiles of these resins were compared with the equivalent HT-TGIC profiles, showing that CEF provided better peak separation than HT-TGIC. Finally, a new mathematical model was developed to simultaneously deconvolute the MWD and CCD of polyolefins made with multiple site-type catalysts such as Ziegler-Natta catalysts. The model was applied to several industrial linear low-density polyethylene (LLDPE) resins to estimate the minimum number of active site types, the number average molecular weight, the average comonomer mole fraction, and the mass fraction of soluble and non-soluble polymer made on each site type.

Characterization of connectivity in compartmentalized deepwater Gulf of Mexico (GoM) reservoirs is an outstanding challenge of the industry that can significantly impact the development planning and recovery from these assets. In these deep formations, temperature gradient can be quite significant and temperature data can provide valuable information about field connectivity, vertical fluid displacement, and permeability distribution in the vertical direction. In this paper, we examine the importance of temperature data by integrating production and temperature data jointly and individually and conclude that including the temperature data in history matching of deep GoM reservoirs can increase the resolution of reservoir permeability distribution map in the vertical direction. To illustrate the importance of temperature measurements, we use a coupled heat and fluid flow transport model to predict the heat and fluid transport in the reservoir. Using this model we ran a series of data integration studies including: 1) integration of production data alone, 2) integration of temperature data alone, and 3) joint integration of production and temperature data. For data integration, we applied four algorithms: Maximum A-Posteriori (MAP), Randomized Maximum Likelihood (RML), Sparsity Regularized Reconstruction and Sparsity Regularized RML methods. The RML and Sparsity Regularized RML approaches were used because they allow for uncertainty quantification and estimation of reservoir heterogeneity at a higher resolution. We also investigated the sensitivity of temperature and production data to the distribution of permeability, which showed that while production data primarily resolved the distribution of permeability in the horizontal direction, the temperature data did not display much sensitivity to permeability in the horizontal extent of the reservoir. The results of these experiments were compelling in that they clearly illuminated the role of temperature data in enhancing the resolution of reservoir permeability maps with depth. We present several experiments that clearly illustrate and support the conclusions of this study.