The columnar microstructure of most thermally evaporated thin films detrimentally affects many of their properties through a reduction in packing density. In this work, we have investigated ion-assisted deposition as a means of disrupting this columnar growth for a number of coating materials. A Kaufman hot-cathode ion source bombarded thermally evaporated films with low-energy (< 1000 eV) positive ions during deposition in a cryopumped box coater. We have investigated MgF₂, Na₃AIF₆, AIF₃, LaF₃, CeF₃, NdF₃, Al₂O₃, and AIN. Argon ion bombardment of the fluoride coatings increased their packing densities dramatically. We achieved packing densities near unity without significant absorption for MgF₂, LaF₃, and NdF₃, while Na₃AIF₆, AIF₃, and CeF₃ began to absorb before unity packing density could be achieved. Fluorine was preferentially sputtered by the ion bombardment, creating anion vacancies. The films adsorbed water vapor and hydroxyl radicals from the residual chamber atmosphere. These filled the vacancy sites, eliminating absorption in the visible, but the oxygen complexes caused increased absorption in the ultraviolet. For LaF₃ and NdF₃, a sufficient amount of oxygen caused a phase transformation from the fluoride phase to an oxyfluoride phase. The refractive indices of Al₂O₃ films increased with ion bombardment. Values as high as 1.70 at 350 nm were achieved with bombardment by 500 eV oxygen ions. Since all of the Al₂O₃ films had packing densities near unity and were amorphous, we postulate that the increase in refractive index was due to a change in amorphous networking. Aluminum nitride was deposited by bombarding thermally evaporated aluminum with nitrogen ions. Films with N:Al ratios of 0.5-1.5 could be deposited by varying the deposition conditions. Films with low absorption for wavelengths longer than 1 μm could be deposited. Annealing the films at 500°C eliminated absorption at wavelengths longer than 500 nm.

One of the most critical processes in CdTe device production is the activation process induced by cadmium chloride (CdCl2). In this thesis, the CdCl2 treatment has been optimized using both wet and thermal evaporation methods for close-spaced sublimated (CSS) devices. Maximum cell efficiencies of η=7.24% and η=9.37% respectively have been measured without the use of copper in the back contact. A clear link has been established between treatment conditions, electrical measurements and microstructure, where parameters such as the dwell annealing temperature for evaporated CdCl2 and the concentration of the solution for the wet treatment are varied. It has been shown that a certain concentration of chlorine is necessary to remove high densities of planar defects present in the as-deposited material. The CSS CdTe is deposited in a dual layer structure with smaller grains at the CdS interface and with larger grains developing towards the surface. The defects are initially removed in the smaller grains at the CdS interface. When the temperature and concentration increase, more grains recrystallize with the total removal of stacking faults. At a critical temperature and Cl concentration, the entire CdTe film recrystallizes into large grains with no stacking faults. The CdS grains and the interface with the CdTe also changes with sulphur migration into the CdTe. The results indicate that the recrystallization actually initiates at the CdS/CdTe junction. This has been observed clearly for both sputtered and electrodeposited CdTe. The recrystallization process gradually propagates towards the surface as the concentration of the CdCl2 solution in methanol is increased. This observation is not intuitive because the solution is initially in contact with the outer surface of the CdTe. Finally, the use of different chlorine containing compounds has been used as an alternative to CdCl2 and to further understand the role of chlorine in the process. All the samples treated with Cl containing compounds have shown the elimination of the dual layer structure and the recrystallization of the small grains at the interface. Tellurium tetrachloride (TeCl4) and zinc chloride (ZnCl2) have shown the most promising increase in conversion efficiency. The maximum efficiencies measured using these two solutions were 4.58% and 5.05% respectively. TeCl4 has shown an encouraging open circuit voltage of 594 mV, while the open circuit voltage using ZnCl2 was 494 mV. However, TeCl4 has shunting issues and low current density (17.9 mA/cm2), whereas ZnCl2 has the promising current density of 20.8 mA/cm2. This work has shown that alternatives to CdCl2 treatment exist, however further work is required to optimize the performance of these treatments to enable them to be competitive. Advanced materials characterization techniques are essential to understand and then enhance photovoltaic cell and module performance. New and improved tools are being developed to deliver fast, accurate and non-destructive characterization. One of these tools is coherence correlation interferometry (CCI) which has been developed by Taylor Hobson Ltd. This is a particular variant of scanning white light interferometry used for surface metrology with a high vertical resolution. In this thesis, it has been shown that the capability of the CCI can be extended to perform accurate thin film thickness measurements using the Helix Complex Field (HFC) function. The main attraction of this technique for thin film PV applications is that it allows surface metrology and thin film thickness measurements to be obtained simultaneously from the same area of the sample in the same system. The results obtained from CCI on a variety of materials, used in thin film PV, correlate very well the results obtained from other techniques such as ellipsometry, electron microscopy and atomic force microscopy. The CCI has also been used in the optimization of a new one-step interconnect process (OSI) for thin film PV module interconnects.

A Thulium Germanate thin disk laser prototype is developed and its potential applications are discussed. Unfortunately, the thin disk gain material for the CW prototype was unable to lase due to thermal limitations within the disk. However, a CW output power model and a physical pump chamber module have been developed, along with the supporting Zemax models and alignment procedures so other gain materials and future improvements can be tested.

The semiconducting sulphosalt Wittichenite has been identified as a possible absorber material for thin film photovoltaic devices. It has the chemical formula Cu3BiS3 and its component elements are those of low toxicity and high abundance making it a very attractive prospect for photovoltaic devices. The copper bismuth sulphur material system is not very well understood and information on it limited to a few small regions. To aid understanding of this system a pseudo-binary phase diagram along the CuS-Bi join of the Cu-Bi-S ternary phase diagram was constructed by making bulk samples of various compositions along the join and analysing them using X-ray diffraction and differential scanning calorimetry. This join was chosen because is crosses the point at which Cu3BiS3 would be expected to occur due to its stoichiometry. The CuS-Bi phase diagram shows Cu3BiS3 forms across a wide compositional range but is mixed with either bismuth metal or copper sulphides depending on composition. Films of Cu3BiS3 were made using sputtered copper and bismuth films annealed in a sulphur atmosphere and thermal co- evaporation of copper sulphide and bismuth.

This small exploratory study was designed to test the hypothesis that thin melanoma lesions contain nuclei of two similar phenotypes, in different proportions. In lesions likely to progress to metastatic disease, one of these phenotypes predominates. Histopathological sections from 18 cases of thin melanomas which did not progress to metastasis, and from 10 cases which did progress were imaged and digitized at high resolution, with a total of 2084 and 1148 nuclei, respectively, recorded. Five karyometric features were used to discriminate between nuclei from indolent and from potentially metastatic lesions. For each case, the percentage of nuclei classified by the discriminant function as having come from a potentially metastatic lesion was determined and termed as case classification criterion. Standard histopathological criteria, such as ulceration and high mitotic index, indicated in this material the need for intensive therapy for only one of the 10 participants, as compared with 7/10 identified correctly by the karyometric measure. Using a case classification criterion threshold of 40%, the overall accuracy was 86% in the test set. The proportion of nuclei of an aggressive phenotype may lend itself as an effective prognostic clue for thin melanoma lesions. The algorithm developed in this training set appears to identify those patients at high risk for metastatic disease, and demonstrates a basis for a further study to assess the utility of prognostic clues for thin melanomas.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

Linear oligosacchardies of 1,4 linked β-D-glucopyranose are commonly referred to as cellodextrins (CD) or cellooligosaccharides (CO). They are of interest to those working in disciplines involving cellulose chemistry because they are often used as model substrates for cellulose itself. They are of interest to food scientists and nutritionists because they are easily incorporated into foods as non-digestible oligosaccharides, a category of food ingredients that is thought to be beneficial lo human health. The intent of the research presented in this thesis was to evaluate the potential of using cellulose supports for the chromatographic separation of soluble CDs differing in their degree of polymerization (DP; a numerical value indicating the number of glucose substituents per molecule). Soluble CDs range in DP from 2 to 8. Thin layer chromatography (TLC), using cellulose-coated TLC plates, was used as a model chromatographic system. Mixed CD preparations, containing CDs ranging in DP from 2 to 8 were prepared by incomplete acid-catalyzed hydrolysis of cellulose. The DP profiles of the different CD preparations were qualitatively demonstrated by TLC using silica-coated plates, an organic solvent-based mobile phase, and a standard carbohydrate visualizing reagent (p-anisaldehye in sulfuric acid). CD-preparations were then chromatographed on cellulose-coated TLC plates. Visualization of the chromatographed CDs was accomplished using a silver nitrate-sodium hydroxide reagent system, a reducing-sugar visualizing reagent. The silver nitrate-sodium hydroxide system was found to be the most appropriate, based on detection limits, simplicity and safety, of the several visualization reagents tested. Eight different mobile phases, all aqueous-based, were tested as potential solvents for the resolution of CDs, differing in DP, on cellulose-coated tlc plates at room temperature. The optimum solvent was found to be 60% ethanol/40% water. This solvent clearly resolved CDs of DP 3, 4 and 5. CD preparations chromatographed with the same mobile phase, but with silica-coated TLC plates, were not resolved. These combined results suggest that the TLC system with the cellulose stationary phase behaves similar to an affinity system, since silica and cellulose are both relatively hydrophilic stationary phases (i.e. both systems are typically considered examples of normal phase adsorption chromatography). The results further illustrate that cellulose supports have potential for use in the preparation of CDs of defined DP. / Graduation date: 2002

The work presented in this thesis may be considered in two main parts; firstly a description of the design and operation of a display type photoelectron spectrometer. Secondly a series of experiments investigating the electronic properties of thin epitaxial films (1-5 atomic layers) of cobalt grown on a clean single crystal copper (001) substrate. Conventional angle resolved photoelectron spectrometers of the deflection type are only capable of observing one point in the (E,θ,φ) space at a time. This is often perfectly acceptable if one is concerned with optimal resolution in order to perform accurate band mapping experiments. However certain experiments are essentially impossible, for instance the observation of the emitted photocurrent over all θ,φ at the fermi energy. This is partly because of the time limitations imposed by the necessity to keep the sample atomically clean in the U.H.V. environment. Several previous workers have tackled this problem by designing spectrometers that observe large sections of θ,φ space simultaneously, for a given energy. The first part of this work concerns the design and implementation of a display type spectrometer which embodies some new and quite novel features. Thin epitaxial films of ferromagnetic materials grown on non-magnetic substrates have long been of interest. Partly as a prototypical surface for the investigation of surface magnetism, and partly for the investigation of the changes induced in the magnetic properties as the dimensionality is reduced or as the lattice size is changed. The second part of this thesis concerns experiments using three different spectroscopies on a system of this type, specifically Co on Cu(001). Firstly, a photoemission study using the display spectrometer is presented, observations of the spin-split bands as a function of wavevector parallel to the surface are shown. Secondly an Auger electron study of the growth mode of the epitaxial film, together with a LEED I/V study of the changing lattice strain as a function of film thickness are presented. Although none of these measurements directly probe the magnetism of the films, they provide very necessary information in order to understand their behaviour.