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Applications of zinc oxide (ZnO) for optoelectronic devices, including light emitting diodes, semiconductor lasers, and solar cells have not yet been realized due to the lack of high-quality p-type ZnO. In the research presented herein, pulsed laser deposition is employed to grow Ag-doped ZnO thin films, which are characterized in an attempt to understand the ability of Ag to act as a p-type dopant. By correlating the effects of the substrate temperature, oxygen pressure, and laser energy on the electrical and microstructural properties of Ag-doped ZnO films grown on c-cut sapphire substrates, p-type conductivity is achieved under elevated substrate temperatures. Characteristic stacking fault features have been continuously observed by transmission electron microscopy in all of the p-type films. Photoluminescence studies on n-type and p-type Ag-doped ZnO thin films demonstrate the role of stacking faults in determining the conductivity of the films. Exciton emission attributed to basal plane stacking faults suggests that the acceptor impurities are localized nearby the stacking faults in the n-type films. The photoluminescence investigation provides a correlation between microstructural characteristics and electrical properties of Ag- doped ZnO thin films; a link that enables further understanding of the doping nature of Ag impurities in ZnO. Under optimized deposition conditions, various substrates are investigated as potential candidates for ZnO thin film growth, including r -cut sapphire, quartz, and amorphous glass. Electrical results indicated that despite narrow conditions for obtaining p-type conductivity at a given substrate temperature, flexibility in substrate choice enables improved electrical properties. In parallel, N+-ion implantation at elevated temperatures is explored as an alternative approach to achieve p-type ZnO. The ion implantation fluence and temperature have been optimized to achieve p-type conductivity. Transmission electron microscopy reveals that characteristic stacking fault features are present throughout the p-type films, however in n-type N-doped films high-density defect clusters are observed. These results suggest that the temperature under which ion implantation is performed plays a critical role in determining the amount of dynamic defect re- combination that can take place, as well as defect cluster formation processes. Ion implantation at elevated temperatures is shown to be an effective method to introduce increased concentrations of p-type N dopants while reducing the amount of stable post-implantation disorder. Finally, the fabrication and properties of p-type Ag-doped ZnO/n-type ZnO and p-type N-doped ZnO/n-type ZnO thin film junctions were reported. For the N-doped sample, a rectifying behavior was observed in the I-V curve, consistent with N-doped ZnO being p-type and forming a p-n junction. The turn-on voltage of the device was ∼2.3 V under forward bias. The Ag-doped samples did not result in rectifying behavior as a result of conversion of the p-type layer to n-type behavior under the n- type layer deposition conditions. The systematic studies in this dissertation provide possible routes to grow p-type Ag-doped ZnO films and in-situ thermal activation of N-implanted dopant ions, to overcome the growth temperature limits, and to push one step closer to the future integration of ZnO-based devices.

The objective of this thesis is to present the fabrication of a multiphoton microscope and the underlying theory responsible for its proper functioning. A basic introduction to nonlinear optics will give the necessary knowledge to the reader to understand the optical effects involved. Femtosecond laser pulses will be presented and characterized. Each part of the microscope, their integration and the design of the microscope will be discussed. The basic concepts of laser scanning microscopy are also required to explain the design of the scanning optics. Fast scanning problems and their solutions are also briefly viewed. As a working proof, the first images taken with the microscope will be presented. Fluorescent beads, rat tail tendon, gold nanoparticles and pollen grain images using various nonlinear effects will be shown and discussed.

The main focus of this thesis is the characterization of defects and microstructure in high-energy ball milled magnesium hydride powder and magnesium-based multilayered composites. Enhancement in kinetics of hydrogen cycling in magnesium can be achieved by applying severe plastic deformation. A literature survey reveals that, due to extreme instability of -MgH2 in transmission electron microscope (TEM), the physical parameters that researchers have studied are limited to particle size and grain size. By utilizing a cryogenic TEM sample holder, we extended the stability time of the hydride phase during TEM characterization. Milling for only 30 minutes resulted in a significant enhancement in desorption kinetics. A subsequent annealing cycle under pressurized hydrogen reverted the kinetics to its initial sluggish state. Cryo-TEM analysis of the milled hydride revealed that mechanical milling induces deformation twinning in the hydride microstructure. Milling did not alter the thermodynamics of desorption. Twins can enhance the kinetics by acting as preferential locations for the heterogeneous nucleation of metallic magnesium. We also looked at the phase transformation characteristics of desorption in MgH2. By using energy-filtered TEM, we investigated the morphology of the phases in a partially desorbed state. Our observations prove that desorption phase transformation in MgH2 is of nucleation and growth type, with a substantial energy barrier for nucleation. This is contrary to the generally assumed core-shell structure in most of the simulation models for this system. We also tested the hydrogen storage cycling behavior of bulk centimeter-scale Mg-Ti and Mg-SS multilayer composites synthesized by accumulative roll-bonding. Addition of either phase (Ti or SS) allows the reversible hydrogen sorption at 350C, whereas identically roll-bonded pure magnesium cannot be absorbed. In the composites the first cycle of absorption (also called activation) kinetics improve with increased number of fold and roll (FR) operations. With increasing FR operations the distribution of the Ti phase is progressively refined, and the shape of the absorption curve no longer remains sigmoidal. Up to a point, increasing the loading amount of the second phase also accelerates the kinetics. Microscopy analysis performed on 1-2 wt.% hydrogen absorbed composites demonstrates that MgH2 formed exclusively on various heterogeneous nucleation sites. During activation, MgH2 nucleation occurred at the Mg-hard phase interfaces. On the subsequent absorption cycles, heterogeneous nucleation primarily occurred in the vicinity of internal free surfaces such as cracks. / Materials Engineering

Human bone is considered one of the most direct and insightful sources of information on peoples of the past. As a result, curation protocols have been developed to ensure that the integrity of human skeletal collections is maintained. Although collections are generally considered safe when these protocols are followed, the results of this investigation show that the Tell Leilan skeletal collection from Syria (circa 2900 – 1900 BCE) was contaminated by microbial growth (also known as biodeterioration) during curation. This biodeterioration was evaluated by light microscopy (LM), by the application of a histological preservation index (HPI), and by scanning electron microscopy (SEM). All samples (n=192) were found to be biodeteriorated by LM and the HPI. SEM confirmed that the Tell Leilan skeletal material had been contaminated by a complex microbial aggregate known as a biofilm. Amycolatopsis sp. and Penicillium chrysogenum, along with species of Aspergillus, Chaetomium, and Cladosporium were isolated and cultured from several contaminated bones and were identified based on morphology and DNA sequences. The results of this research suggest that we must focus on new techniques to examine bone as well as on new conservation protocols designed to limit the growth of biofilms in human skeletal collections in the future.

We have designed and engineered bi-catalyst magnesium hydride composites with superior sorption performance to that of ball milled magnesium hydride catalyzed with the individual baseline catalysts. We have examined the effect of single-walled carbon nanotube (SWCNT)-metallic nanoparticle additions on the hydrogen desorption behavior of MgH2 after high-energy co-milling. We showed the synergy between SWCNT's and metallic nanoparticles in catalyzing the sorption of magnesium hydride. The optimum microstructure for sorption, obtained after 1 h of co-milling, consists of highly defective SWCNTs in intimate contact with metallic nanoparticles and with the hydride. This microstructure is optimum, presumably because of the dense and uniform coverage of the defective SWCNTs on the MgH2 surface. Cryo-stage transmission electron microscopy (TEM) analysis of the hydride powders revealed that they are nanocrystalline and in some cases multiply twinned. Since defects are an integral component of hydride-to-metal phase transformations, such analysis sheds new insight regarding the fundamental microstructural origins of the sorption enhancement due to mechanical milling. The nanocomposite shows markedly improved cycling as well. Activation energy analysis demonstrates that any catalytic effect due to the metallic nanoparticles is lost during cycling. Improved cycling performance is instead achieved as a result of the carbon allotropes preventing MgH2 particle agglomeration and sintering. The nanocomposite received over 100 sorption cycles with fairly minor kinetic degradation. We investigated the catalytic effect of Fe + Ti bi-metallic catalyst on the desorption kinetics of magnesium hydride. Sub-micron dimensions for MgH2 particles and excellent nanoscale catalyst dispersion was achieved by high-energy milling. The composites containing Fe shows DSC desorption temperature of 170 °C lower than as-received MgH2 powder, which makes it suitable to be cycled at relatively low temperature of 250 °C. The low cycling temperature also prevents the formation of Mg2FeH6. The ternary Mg-Fe-Ti composite shows best performance when compared to baseline ball milled magnesium hydride with only one catalytic addition. With a very high BET surface area it also shows much less degradation during cycling. The synergy between Fe and Ti is demonstrated through use of TEM and by carefully measuring the activation energies of the baseline and the ternary composites. / Materials Engineering

Bone response is one of the key determining factors in the overall success of biomaterials intended for bone regeneration and osseointegration. Understanding the formation of bone at an implant surface may lead to the improved design of biomaterials for the future. However, due to the inhomogeneity of bone tissue at an interface, two-dimensional images often lack detail on the interfacial complexity. Furthermore, the increasing use of nanotechnology in the design and production of biomaterials demands characterization techniques on a similar nano length scale. While current analysis methods, such as X-ray tomography, transmission electron microscopy, focused ion beam microscopy and scanning electron microscopy, provide a basis for analysing biomaterials and biointerfaces, they are incapable of doing so with both nanometre resolution and three-dimensional clarity. In contrast, electron tomography may be used to characterize the three-dimensional structure of biomaterials and their interfaces to bone with nanometre resolution. In this work, hydroxyapatite scaffolds, and laser-modified titanium and Ti6Al4V implants were studied in contact with human or rabbit bone. Z-contrast electron tomography revealed that the orientation of collagen in bone apposing hydroxyapatite, titanium and Ti6Al4V implants is consistently parallel to the implant surface, where the bioactive layer that precipitates on HA is oriented perpendicular to the implant surface. With this method, complete three-dimensional nanoscale osseointegration of titanium-based implants was also established. The extension of this technique from interfacial analyses to the design of biomaterials provided an understanding of the pore structure of mesoporous titania. In further investigations, the open three-dimensional pore network, as revealed by electron tomography, showed promise as a coating that improves implant osseointegration and enables site-specific drug-delivery from an implant surface. In summary, it was demonstrated that two-dimensional characterization techniques were insufficient for the investigation of nanostructured biomaterials, as well as their interfaces to bone. Visualizing biointerfaces and biomaterials with nanometre precision in three-dimensions can expose new fundamental information on materials properties and bone response, enabling better design of biomaterials for the future.

Coronary artery disease is a leading cause of morbidity and mortality in developed countries. Percutaneous transluminal coronary angioplasty (PTCA) is an important treatment option when intervention is required; namely for patients with relatively severe occlusions. However, adverse events including recurrence of angina pectoris and restenosis of the treated artery limit patient prognosis, with subsequent re-vascularisation often necessary. Platelet activation accompanies PTCA, with platelet adhesion and aggregation involved in thrombus formation during restenosis. During platelet activation, highly coagulant platelet-derived microparticles (PMPs) are formed, and it is likely that these PMPs will also be produced during PTCA. While platelet aggregation inhibitors used during PTCA limit platelet aggregation and decrease the incidence of restenosis, they do not prevent PMPs being formed. PMPs are capable of adhesion and aggregation, and adhere to PTCA treated arteries in an animal model. Therefore, in order to understand the phenomenon of restenosis and its improved limitation, it is necessary to investigate PMP formation during PTCA. The field of PMP study is in its infancy, with conflicting results from the substantial inequities in methods of PMP measurement, which may be exacerbated by PMP heterogeneity. The current literature on this topic is reviewed in Chapter 2, where the PMP surface and possible functions are considered, and the PMP size and morphology examined. To conclude, the relationship between PMPs and PTCA is explored, with a focus on the potential role of PMPs in restenosis. The knowledge deficiencies in this field are highlighted at the conclusion of this chapter. Very little is known regarding the production of PMPs with PTCA. The level of PMPs during PTCA was monitored in paired arterial blood samples obtained from seventy-five patients undergoing the procedure (Chapter 3). A significant increase in PMPs from baseline to completion of PTCA was clearly demonstrated for the first time. This indicated that procoagulant PMPs are produced during PTCA and may contribute to subsequent restenosis. Furthermore, administration of the platelet aggregation inhibitor abciximab to a group of thirty-eight high risk patients limited PMP formation; given that abciximab patients required more rigorous PTCA, the protective benefit of this medication for PMP production is underlined. Although few patients in this study experienced restenosis, it is interesting to note that of those treated with abciximab, all patients suffering subsequent restenosis were revascularised using PTCA. This demonstrates that their occlusions were comparatively mild as the need for coronary artery bypass grafting was avoided, and suggests that minimisation of PMP levels may assist in limiting the progression of severe restenosis. The increased peripheral level of PMPs predicated investigation of the coronary circulation to determine local events. Although the level of PMPs increased significantly within the coronary arteries of PTCA patients, there was no corresponding increase in the coronary sinus (Chapter 4). This important finding indicated that significant levels of PMPs remained within the coronary circulation, where their ability to adhere, aggregate and accelerate haemostasis may allow them to contribute directly to restenosis. During the time when increased levels of PMPs were being formed, there was no evidence of platelet lysis, which refuted the hypothesis that PMPs are merely membrane fragments of lysed platelets. A wide variation in reported PMP sizes has contributed to the hypothesis that PMPs are heterogeneous. As morphological information can assist in understanding physiology, the final study was designed to investigate platelet morphology from PTCA patients (Chapter 5). Most platelets were activated prior to and following PTCA, with a slight decrease in body size occurring due to PTCA, presumably due to loss of cytoplasm in PMPs being shed as reported in the previous chapter. Importantly, platelet distal pseudopod buds were observed, and these did not alter significantly with PTCA. These buds were probably unformed PMPs, although the exact mechanism of PMP formation remains undetermined. The platelet pseudopods were longer and significantly thinner distally with PTCA, which may be due to movement of cytoplasm into these terminal swellings. In addition, buds or swellings directly on the platelet body were smaller following PTCA, and it is likely these may also be PMPs prior to detachment from the parent platelet. This work has contributed substantially to knowledge of PMPs produced during PTCA. The level of PMPs increased significantly in peripheral arterial samples, with the platelet aggregation inhibitor abciximab preventing this occurrence. This may indicate that functional aggregation receptors are an essential requirement for PMP formation under these conditions. However, it is possible for PMPs to be formed when aggregation is inhibited, and therefore the molecular mechanisms of PMP formation remain unconfirmed. The examination of PMPs from the coronary circulation provided valuable data indicating that PMPs are produced during PTCA but remain within the coronary circulation. As PMPs are capable of adhesion and aggregation, this strongly suggests that PMPs within the coronary circulation would contribute directly to pathogenesis of restenosis, although further investigation on PMPs with PTCA is necessary to confirm this association. The examination of platelet morphology during PTCA indicated that platelets possessed terminal pseudopod swellings, and cell surface swellings. Importantly, the terminal swellings, which are likely to be unformed PMPs, were observed for the first time during PTCA.