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An automated ellipsometer was used to study three topics associated with the anodic oxide films of tantalum and niobium. The electro-optic effect was measured on tantalum and niobium oxides and was found to be quadratic. The change in refractive index upon application of a field occurred in two phases: an instantaneous change followed by a slower change. The effects on Nb₂O₅ were greater than on Ta₂O₅. The effect of ultra violet light on the two oxides was found to cause a change in the refractive index before appreciable photo-induced growth occurred. The results indicated that it was unlikely that the u.v.-induced change in refractive index occurred uniformly throughout the film. The effects of annealing and temperature are discussed in relation to the constant field current transient. The change in the refractive index during the transient was monitored with the ellipsometer. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A flash evaporation system is constructed in order to deposit thin films of Gallium Antimonide. The system includes a substrate heater-holder, a film thickness monitoring device and a powdered evaporant feeder. Thin films of GaSb, 2 to 4 microns thick are deposited on glass, sapphire and silicon substrates maintained at temperatures up to 365°C. The deposited films are observed to have many structural defects. The films exhibit semiconductor-like properties. Optical studies of the fundamental absorption edge at liquid-nitrogen temperature show that the films deposited on heated sapphire substrates have a polycrystalline structure and a band gap of 0.78 eV. The nature of the films is dependent on the type and temperature of the substrate. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Investigations are made into the properties of 20 - 600 A gold films deposited onto freshly cleaved mica substrates by high vacuum evaporation. An accurate method of determining the equivalent thickness of a film is developed by combining a radio frequency technique employing quartz crystals with direct weighing. It is found that thicknesses as low as 0.5 A can be monitored to within ± 5%. An attempt is made to improve the structure of the gold films by using rapid deposition rates (15 to 20 A per second) and by depositing the gold films on nucleating silver layers of molecular thicknesses. The effect of increasing nucleating layer thicknesses (up to 25 A) is studied by electron microscopy and d.c. resistance measurements. A critical nucleating layer thickness for silver is found to exist between 5 to 7 A. On these critical layers, gold films down to 25 A are found conducting. All the films tested show an irreversible change in conductivity with heating. Without a silver layer, continuous decrease in the conductivity of gold films is observed, the film being destroyed at 450° C. On the other hand, increasingly better conductivities are observed by heating the gold-on-silver films, and an optimum annealing temperature of about 350° C is indicated. Above this temperature the conductivity decreases; however, films are still conducting and continuous at 600° C. These films are, therefore, suitable as heat reflecting windows. D.C, and high frequency measurements (at 9.7 Gc) on gold films are given. In both cases, almost identical values of surface resistance are obtained in the range 10 to 1,000 ohms per square. A method for preparing gold film bolometer elements using interrupted deposition of gold on a nucleating silver layer is discussed. As very thin gold on silver films with high d.c. conductivities are found to have low microwave transmission coefficients, the possible application of visual protection from microwave radiation is discussed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The present thesis is concerned mainly with space charge and high field effects on the electrical properties of thin amorphous films. A theory of space charge contribution to the polarization current in thin dielectric films is proposed. The transient current on short-circuiting a thin dielectric film is believed to consist of two components, one due to the dielectric polarization and the other due to trapped space charge. The space charge contribution is investigated using a model for a film containing distributed traps. Computed results seem to be consistent with experimental results on Ta/Ta₂O₅/Au diodes, so that space charge effects are more important at low preapplied fields. The applicability of step response techniques to determine low frequency dielectric losses is discussed and the effect of space charge on the dielectric losses is analysed. The theory of thermoluminescence and thermally stimulated currents is extended to the case of traps with distributed binding energies to investigate the possibility of distinguishing between distributed and discrete trap levels. It seems possible to distinguish experimentally between distributed and discrete traps by using different doses of optical radiation to obtain initially different amounts of trapped charges, and by varying the frequency of optical excitation over a suitable frequency range to allow only certain energy levels to be occupied by excited electrons. High field electronic conduction through very thin films sandwiched between two metal electrodes is analysed. In view of the fast tunneling time of electrons through very thin films, MIM structures can be used for microwave detection. It is shown that the maximum responsivity-bandwidth product of such detectors is obtained when they are biased at a voltage equal to the anode work function (in volts), and that the presence of invariant positive space charge increases the magnitude of this maximum. In considering high field switching in thin films of semiconducting glasses, it is suggested that Joule heating, which could account for the delay times observed experimentally, serves only to initiate an electronic switching mechanism. A model for current-controlled negative resistance due to space charge formation is proposed and its dc characteristics are computed. Carrier injection from the electrodes is taken to occur either by Schottky thermionic emission or a Fowler-Nordheim tunneling mechanism. The injected carriers develop space charge regions near the electrodes by impact ionization. The position dependent generation-recombination rate is discussed. The small ac signal equivalent circuit of the model is given. The formation of current filaments is analysed. Memory devices are discussed in terms of filament formation and phase change mechanisms due to excessive heating. Filamentary breakdown has been observed in anodic films grown on Ta, Al, Nb and Ti. A detailed experimental study of film growth and the effects of growth conditions, film thickness, counterelectrodes and temperature on breakdown strength has been carried out. A possible mode of breakdown, in which breakdown can result from thermal effects following a non-destructive electron avalanche, is proposed and its limitations are pointed out. It is concluded that breakdown in thin anodic films would occur due to disruption of the chemical bonds as the applied field approaches the formation field. The product of the molecular dissociation and the presence of energetic electrons could start an accumulative process which might end with the formation of a highly conducting channel. The injected electrons, field distortion and thermal runaway could assist in the channel development. Once the channel is developed, the sample's stored energy starts to dissipate through the channel. The voltage collapse has been found experimentally to occur in a time of less than 200 nanoseconds. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The Y₁Ba₂Cu₃0x superconducting thin films were made by both sequential electron-beam evaporation and co-evaporation of Cu, BaF₂ and Y, followed with high temperature post-deposition annealing. The possibility of making Y₁Ba₂Cu₃0x superconducting film in situ with BaF₂ as the Ba source was investigated by studying the conditions of in situ conversion of BaF₂ to BaO. The BaO concentration in the film as function of the substrate temperature was estimated with an equilibrium thermodynamic model and found to agree with the experimental results. A brief experimental and theoretical exploration of BaCl₂ also showed that BaCl₂ does not have any advantage over BaF2 as the Ba source for in situ growth of Y-Ba-Cu-0 films from the growth temperature point of view. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The classical theory of rectilinear vortex motion has been generalized to include vortices in thin fluids of varying depth on curved surfaces. The equations of motion are examined to lowest order in a perturbation expansion in which the depth of fluid is considered small in comparison with the principal radii of curvature of the surface. Existence of a generalized vortex streamfunction is proved and used to generate conservation laws. A number of simple vortex systems are described. In particular, criteria for the stability of rings of vortices on surfaces of revolution are found. In contradistinction to the result of von Karman, double rings (vortex streets) in both staggered and symmetric configurations may be stable. The effects of finite core size are examined. Departures from radial symmetry in core vorticity distributions are shown to introduce small wobbles in the vortex motion. The case of an elliptical core is treated in detail. Applications of the theory to atmospheric cyclones and superfluid vortices are discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The first study investigated the deposition and characterization of the CoO and Co3O4 phases of cobalt oxide. It was determined that both phases can be easily distinguishable by XPS, LEED and EELS and grown by only altering the oxygen partial pressure during MBE deposition. This fundamental knowledge gives a foundation for further experiments involving graphene growth on cobalt oxides. The second study focused on the layer-by-layer growth of graphene on another metal oxide, MgO. Past research gives promise of favorable interfacial interactions at the graphene/MgO interface though the exact growth mechanism is unknown. Layer by layer growth by MBE resulted in the characterization of a complex graphene oxide/buckled graphene/ graphene heterostructure confirmed by XPS, AES, LEED and EELS and supported by DFT calculations performed by the project's collaborators at the California Institute of Technology. This detailed look into graphene growth give valuable information that can be allied to graphene growth on similar oxide surfaces. The last project deviates from graphene-based studies and instead focused on interfacial interactions between two metal oxides, chrome oxide and titanium oxide. A corundum phase TiO2-x film was grown on Al2O3 via MBE and characterized using XPS, AES, LEED, and EELS. Data taken gives evidence of the presence of a two-dimensional election gas at the TiO2-x surface because of oxygen vacancies present after deposition. Deposition of chrome in UHV results in the formation of an oxidized chrome overlayer by abstraction of oxygen from the TiO2-x underlayer increasing the number of vacancies present. MOKE measurements taken by the project's collaborators at the University of Nebraska-Lincoln indicate that there is an interfacial exchange bias at the interface of the two oxides, a favorable property for magnetic device applications.

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