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The measurement of the absolute concentration of sputtered neutrals from a metal Li surface and polycrystalline NaC1 target has been achieved using the technique of concentration modulated absorption spectroscopy. The dependence of the amount sputtered on the target temperature, ion energy and target density has been investigated. The atomic density of the plume has been mapped in two dimensions under varying sputtering conditions. Utilising a previous theory describing a radial sputter distribution function the experiments have yielded values for the sputter yield of lithium and sodium. The profiling of sputtered neutrals across a planar glow discharge under varying cell conditions and discharge gases has been achieved using the laser spectroscopic technique. These experiments show that the sticking coefficient, α, of Li atoms on Li metal is non-unity. The experiments have been fitted using a Monte-Carlo model to generate values of α. An analytical model has also been developed to fit the experimental data. The model yields useful physical parameters concerning the plasma. This includes sticking coefficient data. The model has been compared with the computer-based method. High-energy collision induced decomposition mass spectrometry has been to investigate the possible effect of the internal energy of the precursor ion on the appearance of the spectra. Deuterated ethanol and the protonated deuterium counterpart were specifically produced in the ion source isomerically pure and to eliminate the presence of isotope scrambling. The experiments show that the spectra do vary significantly depending on the reaction conditions of temperature and pressure under which the protonated ethanol or the deuterated equivalent is produced.

Excess electron and hole drift mobilities in hydrogenated amorphous silicon-carbon alloy thin films have been investigated using the time-of-flight technique. A detailed study of the temperature and electric field dependence of these parameters has been carried out. This has permitted the computation of the energy distributions of conduction and valence band tail localised states as a function of carbon concentration in the films. It is apparent from these data that increased carbon incorporation is associated with an increase in the total number of both the conduction and valence band tail states. This is supported by the experimental behaviour of the pre-transit currents. The present range of materials were produced by conventional low power radio frequency glow discharge of silane and methane. Typical carbon contents are below 10at.% and optical measurements show that the samples have optical energy gaps <I>E</I><SUB>g</SUB> up to ˜2.0eV. Time-of-flight charge collection experiments have been performed to investigate the free carrier mobility-lifetime products as a function of carbon concentration in the films. Results show a considerable decrease in this parameter with increasing carbon content. This is likely to be primarily associated with an increase in density of recombination centres in the films. The density of localised states in the materials have also been computed using a Fourier transformation of transient photo-current data. This reveals the increase in density of the conduction band tail states, as detected using the drift mobility analysis, but also reveals an increase in density and energetic broadening of the deep state distribution as carbon content is increased. This is consistent with the reduced carrier lifetimes inferred by the charge collection experiments. Combining the present data with localised state energy distributions measured using other techniques, we are able to illustrate the effect of carbon alloying on the entire localised state population. Preliminary transient photoconductivity results for glow discharge deposited diamond films are also reported.

This thesis describes an experimental and theoretical study of the kinetics of myoglobin adsorption on recently introduced rigid, porous particles, Bakerbond Wide-Pore cation-exchange and Wide-Pore hydrophobic interaction adsorbents. Theoretical models have been developed and validated which described the adsorption kinetics of smaller protein molecules on polydisperse particles. The influence of various process parameters on the adsorption rate has also been investigated. Two modes of process operation have been studied, a stirred cell and a packed bed. A three-step model of the adsorption process involving extra-particle film mass transfer, intra-particle pore diffusion and surface reaction, has been formulated for monodisperse systems in a stirred cell. A two-step model, neglecting the surface reaction, has been developed for polydisperse particles in both stirred cell and packed-bed modes of operation. The main feature of the improved two-step model, compared with previous models, is the introduction of particle size distribution. Also considered in the two-step model is the mixing chamber effect in the stirred cell sampling loop and the packed bed inlet concentration profile. The validity of the models has been verified by applying the values of the pore diffusivity obtained from the stirred cell to predict the breakthrough curves in the packed bed operations. The introduction of particle size distribution has improved the fit between the experimental data and the simulation results. Adsorption isotherms of different systems have been obtained in the experiments. Also studied was the influence of various parameters on the adsorption isotherms, including solution pH, buffer type, salt concentration and particle size. The effects of particle size distribution, effective pore diffusivity and film mass transfer coefficient on adsorption rate have been examined by simulation and curve-fitting. The validated models and the data obtained on the adsorption systems studied provide a basis for predicting the performance of protein adsorption processes.

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This thesis investigates the use of thin resistive metal electrodes in the formation of Schottky barrier structures where the resistance measured along the electrode exhibits a characteristic change as a function of temperature dictated by the Schottky barrier properties. A combination of optical and resistance measurements (15-300K) on thin Al films were undertaken. Deviations of the real and imaginary parts of the . dielectric function from bulk valuek were significant for films thinner than ~15nm. The observed trend was confirmed by evaluating the resistivity data. The estimated thickness threshold for which the resistivity ratio (pjilm/pbulk) -- -I} became significantly greater than unity is ~8 nm for Al films. Thinner Al film showed poor inter-grain connectivity and a deteriorating interface quality. Resistance measurements on macro-scale Al and Pt electrodes and micro-scale Pt electrodes on p-type Si revealed a marked resistance increase by a factor of up to six over a temperature interval of 40-60K when decreasing temperature. The characteristic change of resistance is due to thermal confinement of charge carriers in the metal electrode, preventing any conduction channel through the substrate. This behaviour was modelled by considering the electrode and the substrate as two resistors in parallel with the Schottky barrier (barrier height determined by applying theory of thermionic emission) acting as the connecting component. The electrical and structural properties of Focused Ion Beam deposited Pt nanowires were analysed. EDX analysis revealed metal rich grains (atomic composition 31%Pt) in a large non-metallic matrix. Resistivity measurements (15-300K) indicated insulating behaviour with the room-temperature resistivity varying from 80 to 300 times higher than that of bulk Pt. Temperature dependent current-voltage measurements exhibited non-linear behaviour with the non-linearity increasing with decreasing temperature. The conduction mechanism can be explained in terms of a disordered solid with inter-grain tunnelling.

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No description available.

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No description available.