Atmospheric pressure plasma, APP, jets, are now attracting great interest because of their potential uses in many applications; for example surface modification and plasma medicine. These applications require an insight into their plasma chemistry, which is strongly influenced by the electron energy distribution function. In this work the dynamic behaviour of a 20 kHz-driven APP jet operating with helium as the main gas and oxygen as an additive is investigated. The jet has a commonly used configuration, a cylindrical quartz tube with two electrodes used to form a dielectric barrier discharge. This atmospheric pressure plasma jet was used to generate non thermal plasma bullets away from the production region. The characteristics of the plasma plume and streamer were diagnosed using, current-voltage measurements, ICCD imaging, and optical emission spectroscopy. Here, the use of Thomson scattering to measure the electron properties in the plasma plume created by 20 kHz was reported. The investigation reveals a "ring-like" radial distribution of both the electron density and temperature. A 532nm Nd:YAG laser beam was focused into the plasma plume. The temporally and spatially resolved spectra of light at 900 to the laser direction were detected. The spectra contain light from Thomson Scattering from electrons, along with Rayleigh and Raman scattering from atoms and molecules. The use of a atmospheric pressure helium non-thermal plasma jet to assist a SCR deNOx reaction over a silver-based catalyst at low temperature using simulated diesel fuels was explored. A coupled IR-plasma reactor was developed allowing direct interaction of the plasma with the catalyst bed whilst accommodating a FTIR spectrometer and NOx analyzer. Two KHz, quartz tube jet designs were developed to operate at low gas flows, one with a circular copper electrode but with a grounded electrode in the reaction area, and the other with a central powered electrode with the vessel as a ground. The catalyst was prepared by the impregnation of ?-AI203 with a silver nitrate solution. NOx and hydrocarbon conversions were studied with toluene and octane on an Ag-catalyst at two different temperatures.

In this thesis, a body of work is presented which contributes towards the improved understanding of plasma mirror operation and in 'particular, the switch-on dynamics and picosecond timescale reflectivity. Degradation in the performance of the baseline anti-reflective properties of the plasma mirrors is observed 1.5 picoseconds prior to the main pulse peak. This is believed to be the first observation of this effect. The rise time of these plasma optics is measured in a simple numerical model constructed to elucidate the underlying physics. The ultimate aim is to reveal the underlying dynamics so as to be able to ascertain how to best operate these optics to achieve ultra-high contrast. This would benefit high-intensity interactions, potentially enhancing laser-driven ion acceleration and high harmonic production. This thesis also explores the use of these enhanced-contrast pulses in laser-driven ion acceleration studies, at the cutting edge of both on-target intensity and ultra-thin foil thickness. Continuous wave laser heating of skin depth foils is investigated for the purpose of contaminant removal and target thinning. In addition, ultra-high intensity interactions were explored, where it was hoped the dynamics might indicate a transition to a new and more efficient acceleration regime, namely radiation pressure acceleration. Both of these ion studies have a key signature of higher peak ion energies, and although the energy range of ions was not increased as far as had been hoped, the thesis endeavors to shed light on the current observations and highlight limitations encountered, such as to inform the ongoing research moving forward.

Simulating heterogeneous catalytic processes occurring at solid-liquid interfaces requires the use of quantum mechanical methods to allow for a description of bond breaking and bond forming. These methods must also allow a sufficiently sized statistical sampling of the liquid to be gathered. Current approaches based on density functional theory (DFT) are too expensive to satisfy these requirements so it is therefore desirable to develop alternative, faster methods. Self consistent tight binding (TB) methods, which are derived from a second-order expansion of the Kohn-Sham energy functional and use a parametrised Hamiltonian matrix, can be significantly faster than DFT making them ideal for the above task. In this thesis we describe the development of a TB model for organic molecules containing carbon, hydrogen and oxygen. This model has been fitted using a combination of intuition, analytical fitting and genetic optimisation. We have also developed a framework for the description of inter-molecular Van der Waals interactions using long-ranged empirical potentials. We have shown that this model is capable of describing the gas-phase structural and dynamic properties of a range of organic molecules, as well as the structure and dynamics of liquid-phase alcohols and solvated organic molecules. We have also shown how the the model can be used to describe chemical reactions in solution. The model forms part of a larger collection which also includes models for water and titania. All models within this collection share a single transferable oxygen species. When combined with a parametrisation of a metal such as platinum this collection could be used for the study of catalytic processes.

The work presented in this thesis is an experimental investigation into the sputtering of oxygen and water ice by 4 ke V ions under conditions existing in the Interstellar Medium (ISM). This work is divided into two main parts : 1) sputtering of oxygen ice by singly and doubly charged ions He+, Ar+, C+, N+ ,0, C2+, N2+ and 0 2+ and 2) sputtering of water ice by C+, N+, 0+, C2+, N2+ and 0 2+. The experimental sputter yield obtained for both oxygen and water ice is compared with those from a theoretical obtained model and found to be in reasonable agreement within the experimental errors. For oxygen and water ice, deposited at 10 K, the refractive index was experimentally determined and found to have values of 1.285 and 1.282 respectively that are in good agreement with previous results. In the case of oxygen ice the sputtering yields are at least nine times larger compared to that of water ice. For water ice the doubly charged ions have, the same sputtering yield ,as the singly charged ions within the experimental errors. In the case of oxygen ice the doubly charged ions have the same sputtering yield as the singly charged ions, except 0+ and 0 2+, where 0 2+ has a significantly lower sputtering yield.

No description available.

This thesis looks at plasmas produced in vapour layers in electrically conducting solutions, with a particular focus placed on adapting existing diagnostic techniques to the novel environment. An asymmetrical geometry with a 0.5 or 1 mm wire electrode surrounded by a dielectric tube with 0.5 or 1 mm extruded, and a larger area collar or plate electrode is used to generate the plasmas. The discharge is operated with negative voltages on the order of several hundred volts applied to the wire electrode for several hundred microseconds with the larger electrode grounded and both electrodes submerged in solutions with room temperature conductivities ranging between 10 and 40 mS/cm. Due to area asymmetry between the electrodes, vapour layer formation occurs around the wire electrode via Joule heating so that the vapour layer/liquid boundary acts as the effective ground electrode with the resistance of the conductive solution limiting current flow within the plasma. Fast camera imaging, voltage, current and PMT measurements as well as multiphysics modelling are used across a range of pressures to establish that geometric field enhancement is present to the extent that streamer breakdown is the most likely initiation mechanism for the plasma. After this the plasma quickly transitions to an atmospheric pressure glow mode. Diagnostics used to further characterise this mode of the plasma include time resolved Stark broadening measurements of the hydrogen beta line to determine electron density and time averaged measurements of the relative intensities of barium II lines to determine electron temperature. Chemical measurements also performed on the conducting solution surrounding a separate plasma system in a similar operating regime but with a bipolar voltage waveform at kHz frequency to determine the production rate for hydrogen peroxide along with electrical measurements to allow a production efficiency to be calculated.

The focus of the work presented in this thesis is to understand the influence of the condensed phase environment on the synthesis of organic molecules in conditions typical of the interstellar medium and our Solar System. First principles molecular dynamics (FPMD) has been used to study the interaction of neutral and positively charged carbon (C+) with amorphous solid water clusters at 3D K. Reactions involving the carbon species at an initial energy of 11 eV and 1.7 eV with 3D-molecule clusters have been investigated. In each case the dominant products and formation mechanisms were identified. Subsequently, the isomerization of hydroxymethylene to formaldehyde was considered. Using constrained molecular dynamics simulations, the mechanism of this reaction was elucidated while the catalytic properties of water in the process were also confirmed. Path integral methods were utilized to study isotopic effects and the impact of temperature here. Finally, using a methodology similar to that employed for the carbon reactions, the formation of methanol via successive hydrogenation of formaldehyde was studied.

This thesis investigates the growth of Heusler alloys via pulsed laser deposition (PLO), and their use in tunnel magnetoresistance (TMR) devices. In doing so it investigates the capabilities of a novel beam scanning system with good potential uniformity characteristics over large areas. This thesis has presented a novel PLO system whose beam scanning system allows large diameter samples. Initially, the characteristics of this beam scanning system are analysed and shown to offer exceptional uniformity beyond typical PLO, such that variations of 2% thickness of films across a 3-inch wafer were realised. Thicknesses of deposited films were equally as reliable, with x-ray diffraction (XRD) analysis showing these results across both CF AS and MgO, used as a tunnel barrier material for TMR devices. Magnetic tunnel junctions were fabricated using a novel combination of photolithography phases, yielding a 4-point probe capable device. Data obtained from transmission electron microscopy of the deposited CFAS layers showed semi-qualitative results indicating levels of iron were lower than expected however broadly in line with that expected of a stoichiometric sample. The quality of the barrier interface was shown to be poor in large areas, with defects and poor crystal growth. Many devices were analysed to discover the TMR ratios and thus the spin polarisation of the CFAS junctions, and whilst the theoretical 100% spin polarisation was not observed, values as high as P=0.89 or 783% TMR ratios were observed at room temperature. The low iron levels combined with these structural problems may suggest why the observed TMR was lower than that predicted by theory. Despite this, the repeated observation of high spin polarisations of P=0.83 to 0.89 make these results amongst the highest such ratios to date for CFAS/MgO junctions

Cu is one of the most detrimental impurities to the Si devices. A theoretical investigation into diffusing interstitial Cu (Cuj) in Si and the interactions of Cu with other impurities and defects of the host lattice is strongly desired in order to understand and control the reaction paths of this impurity. We have performed ab initio modelling of the interactions of isolated Cu with bulk Si and the Si(OOl) surface, presenting explanations to a previously unsolved phenomena for the interactions of Cu with Si: according to our studies, Cu is a shallow donor with a closed 3d shell, strongly affected by inherent distortions of the Si environment The attraction of Cu to Si(OOl) is explained by surface reconstruction induced distortions of the Si environment with Cu-Si bond formation (leading to trapping of the impurity) only occurring within three layers of the surface. Our results provide promising results for gettering of Cu and Cu nanowire formation on the Si(OOl) surface. Rare earth (RE) disilicide nanowires on the Si(OOl) surface have been intensely studied by experiment as a candidate for next generation interconnects in devices. Our investigations of these systems represent the first theoretical studies of the interacting wire and substrate. We have focussed on the importance of treating the wire growth as a ID phenomenon, presenting a new candidate structure for the epitaxially grown wire on the basis of these considerations. Our studies, involving Y (not a RE metal but displaying the same behaviour with regards to wire growth) for simplicity, have verified the stability of the wire relative to the RE metal and Si atom reservoirs on the substrate. Finally, initial studies of atomic strings observed in very recent experiments upon deposition of Y on Si(OOl) have been carried out.

The aim of the present study is to explore the motivational factors of Hong Kong vocational students in learning English. A qualitative case study approach was employed with a combination of surveys with self-completion questionnaire, semi-structured interviews and diary notes. The research, which was carried out in two phases from September to June 2005-6 in one academic year, had the objective of examining whether there was any change of motivation for learning English. Ten students from a vocational institute were selected for the interviews, each were interviewed twice. They were also invited to write diaries, and to record their daily English activities. The data collected were used to triangulate with the interview findings when analyzing the results. The study was initiated by students’ differences in learning attitudes and the variations in their standard of English. Research on motivation for, and attitudes towards learning English reveal that instrumental and intrinsic motivations often apply to secondary school and tertiary-level learners, but prior to this study the research did not extend to vocational students in Hong Kong. The findings show that vocational students not only have strong instrumental motivation for learning English but also have intrinsic motivation. It was apparent that in the process of their learning English, participants regarded English as a functional language which was tied up with their career. This finding is the same as that of previous research on attitudes towards learning English of Hong Kong students. In addition, vocational students’ motivation for learning English was found to be influenced and encouraged by many factors, particularly significant others, such as parents. The present study will enable English teachers to have a greater understanding of vocational students’ motives for learning English. This could help to improve teaching strategies, teaching materials and language policies; and, thus, enhance more effective learning of English in the vocational setting of Hong Kong