Research towards understanding continuous thin film flows and droplet spreading is as relevant today as it ever was. Theoretically, lubrication theory has played a pivotal role with the equations involved requiring numerical solution. The most commonly employed solvers are based upon either a time-splitting or multigrid strategy; no consensus has been reached as to which is the most accurate and efficient. With modern engineering applications demanding solutions at smaller and smaller scales, in turn requiring the use of finer grids to ensure mesh independent solutions, efficiency is a necessary consideration. The work of this thesis divides into two strands. First, a three-dimensional continuous film problem is modelled and formulated in two equivalent ways: as two coupled second-order equations, or as a single fourth-order equation. These are solved numerically by multigrid and time-splitting solvers, finding that, due to the larger time-steps which are possible, the multigrid scheme, when solving the coupled equations, offers the fastest route to converged solutions; the accuracy of solution for each solver is comparable. Following the use of static mesh adaptivity, the conclusions drawn for uniform meshes concerning the solvers are found to be equally valid on non-uniform meshes. Following that, a new model is proposed to investigate unpinned droplets evaporating from a thick, heated substrate into the surrounding atmosphere. A study of accuracy and efficiency is also conducted for a droplet spreading problem; it isfound that the multigrid scheme, when solving the coupled system of equations, is again the most efficient solver. This scheme is adapted for the evaporation model, leading to excellent qualitative and some quantitative agreement with previous studies of both the pinned and unpinned stages of evaporation. To the' author's knowledge, this is the first model to successfully capture the behaviour in both stages of evaporation and also the change in this behaviour depending upon the properties of the substrate and liquid considered.

The work in this thesis concentrates on the production and characterisation of microbubbles that are suitable for use' as ultrasound contrast agents. Initially microbubbles were produced using a mechanical agitation technique that forced a gas supernatant into a suspension of shell material. This technique has been demonstrated to be quick and versatile, facilitating the production of high concentrations of microbubbles (-1010 bubbles/nil) with varying shell compositions. However, the majority of microbubbles studied within this thesis have been produced by microfluidic flow focussing as this technique is shown to produce less disperse samples and offer greater control and reproduction of the mean bubble diameter. Microbubbles with lipid, PEG, streptavidin and PEG+streptavidin shell compositions have been produced and were characterised for size, concentration and stability using white light microscopy. A modified Epstein-Plesset model has been fitted to the stability data and used to determine the resistance to gas permeation of each of the shell compositions. AFM Force spectroscopy has been employed to measure the mechanical properties of the microbubbles, providing a measure of the stiffness of the bubble encapsulation. The stiffness values obtained have shown to decrease monotonically with micro bubble radius and have been used in combination with the modified Rayleigh-Plesset to predict the resonance frequency of the microbubbles for each of the shell compositions. The displacement creep and the effect of temperature on the mechanical properties of lipid coated microbubbles have also been investigated. An increase in temperature of 27 QC has been shown to result in a reduction (-3x) of microbubble stiffness. Finally, the standard linear model has been applied to the displacement creep data of a lipid bubble in order to access the visco-elastic properties of the microbubble shell.

Since the theoretical prediction of room temperature intrinsic ferromagnetism in doped ZnO, there has been a huge amount of research in the area. Such a property would make ZnO an excellent candidate for spintronic materials, which would potentially have many advantages over the technologies currently available. Whilst some see room temperature intrinsic ferromagnetism upon doping ZnO with small amounts of transition metals, others present evidence of ferromagnetism from extrinsic transition metal clusters or have failed to see ferromagnetism at all. This thesis investigates the properties of doped ZnO thin films in an attempt to increase the understanding of this material.

It is believed that the interfacial structure can significantly affect the magnetic properties of magnetic multilayer thin films. X-ray scattering techniques provide a powerful method with which to study the bulk and interface morphology in these systems, and are therefore crucial in developing an understanding of the dominant factors influencing the magnitude of the perpendicular magnetic anisotropy (PMA).The inter-relation between magnetic and structural properties of a series of magnetic multilayer thin films is investigated. Magnetometry measurements on a series of Fe/Au multilayers showed that some samples exhibited in-plane magnetization. X-ray data and simulations showed that the interface roughness was high in these samples. However, the formation and propagation of uncorrelated roughness followed a systematic trend for surface growth. On the other hand, x-ray data and simulations for a single 100-bilayer sample showed that the interfaces are much better defined with significantly lower roughness. This was the only sample to show perpendicular anisotropy supposing the suggestion that the absence of PMA in all other samples is associated with high interface roughness. Magnetometry measurements of the PMA in Co/Pt multilayers show an increase in effective anisotropy at about 15 bilayers. X-ray data showed that the roughness of the interfaces was correlated in all samples and that the interfaces were sharp with no detectable interdiffusion. No systematic trend in roughness or crystallographic texture is detected with increasing bilayer repeat X-ray measurements on four series of Co/Pd multilayers show interface roughness independent of bilayer repeat number. For Co/Pt, the in-plane correlation length was independent of bilayer number while for Co/Pd and Fe/Au it increased. A saturation of the in-plane correlation length for the Au/Fe system where island growth of the Au occurs was observed. The out-of-plane correlation length increased with bilayer repeat for Co/Pt and Co/Pd. The interfaces in samples with higher PMA had a fractal parameter close to unity.

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The fundamental understanding of the interfacial charge on gas bubbles and the consequences of such charge are essential in understanding the behaviour of physicochemical systems involving liquid/gas and solid/liquid/gas interfaces. Such interfaces are involved in many industrial processes such as electrolytic gas evolution, particle flotation and bubble coalescence. The knowledge of such interfaces will aid mass transfer calculations. This thesis describes the application of a laser Doppler anemometer (LDA) system to the measurement of bubble electrophoretic mobilities, giving a measure of adsorbed charge. Single bubbles were electrogenerated in surfactant-free electrolytes, characterised by bubble rise rates, and their behaviour investigated in an electric field applied parallel to the direction of rise, so that, depending on the field direction, an increase or a decrease in the rise velocities was obtained. This field orientation served to decouple the hydrodynamic and field-induced charge polarisation. The velocity measurements using LDA showed a large degree of scatter despite numerous modifications to the optics and the signal processing. This culminated in the belief that a double LDA system was necessary to optimise the reliability and accuracy of the technique. Measurements using a Kodak high speed camera and recording system showed that the bubbles were negatively charged over the pH range studied (3-11), as indicated by their migration towards the anode under the influence of an applied electric field, with mobilities showing a radius and field dependence, implying that the adsorbed charge at the gas/electrolyte interface was mobile and polarisable. Large mobilities (10-60 x 10"® m2 s"^ V"^) were observed in comparison with results from previous bubble electrophoresis experiments with lateral fields. This was explained in terms of the enhanced charge polarisation occurring in the parallel electric field to the rise vector. A qualitative explanation for the decoupling of the hydrodynamic and field-induced charge polarisation has also been provided. In a separate series of experiments, under sufficient field conditions to overcome buoyancy forces, rising bubbles were stopped and held stationary. It was shown by extrapolation that bubbles possessed an iso electric point between pH 2 and 3, being positively charged below pH 2 and negatively charged above pH 3, supporting the hypothesis that the preferential adsorption of OH /H+ ions gives rise to the net charge. A laser reflection technique was investigated to measure the thickness of a liquid film formed between a bubble and the planar gas/electrolyte interface when they are in close proximity of each other. Preliminary investigations on macroscopic soap films showed the technique to be suitable for studying film thinning rates, though further refinement is necessary to study microscopic transient films. Electrophoresis measurements using a high speed camera have shown that bubbles preferentially adsorbed OH-/H+ ions from the solution in the absence of surfactants. This charge resided on a highly mobile interface and could be polarised by the actions of the hydrodynamics and the electric field. The laser Doppler anemometer system requires further development to achieve more accurate bubble velocity profiles in order to detect the small changes that occur.

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The investigation of ternary compounds for the fabrication of thin film solar cells is well documented but the production of thin films by electrostatic spray deposition (ESD) is still limited. This thesis represents the first attempt to deposit photovoltaic thin films using this novel method. The lack of information regarding the deposition of CuInS2 by ESD required a statistical investigation of the effects of different deposition variables. To achieve this, a new image analysis method was developed to calculate the variation of the thickness of the as-deposited films using their optical density. The thickness variation across the sample was then used to define its uniformity. Once the conditions for the best uniformity were defined, different needle and substrate materials were investigated to try and improve the performance of the ESD method for potential large scale production. A formation of precipitates was observed during the preparation of the chloride precursor solutions (prepared from CuCl2, InCl3 and thiourea salts). A possible reaction mechanism was proposed and the chemical composition of precipitates analysed. An explanation of the absence of the precipitate during the preparation of a nitrate starting solution (from Cu(NO3)2, In(NO3)3 and thiourea salts) was reported. The behaviour of the aerosol cone for the two different starting solutions (nitrate and chloride) was established using the laser-based particle image velocimetry (PIV) measurement technique. The properties of as-deposited films sprayed by the two precursor solutions were thoroughly investigated using a number of techniques including X-ray diffraction (XRD), Rutherford backscattering (RBS), optoelectronic characterisation and miniSIMS. The effect of different precursor molar ratios on the properties of as-deposited films was studied for both the nitrate and chloride based solutions using the above techniques. ZnS films were also deposited using ESD for the first time. Using the information acquired during the deposition of the CuInS2, a fully comprehensive analysis of the effect of different deposition conditions and starting solution properties was performed. Finally, CdS/CuInS2 and ZnS/CuInS2 junctions were prepared and tested using EQE measurements in solution. Substrate and superstrate device configurations were used to prepare complete solar cells which were analysed using IV measurements.