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The thesis describes the research carried out into fabrication of multilayer microwave capacitance structure with ferroelectric films in paraelectric state; and confirmation of the possibility to develop on their base an electronically switchable bulk acoustic wave (BAW) resonator. Different eigenmodes of acoustic resonances can be excited and switched electronically through the application to ferroelectric layers of the resonator unidirectional or oppositely directed dc biased electric fields. The resonator was fabricated out of a SrRuO3/SrTiO3/SrRuO3/YSZ multilayer structure deposited on top of Si substrate. Pulsed Laser Deposition, Magnetron Sputtering, Photolithography, Argon Ion Beam Milling, and Reactive Ion Etching were the fabrication methods used to make this resonator. This novel device is a demonstrator that will contribute to the telecommunications industry's demand for flexibility in both microwave frequency switching and tuning. The Si MEMS concept of this resonator allows easy circuit board integration into many electronics products.

Photovoltaic modules are under active consideration as a major contributor to future energy requirements. Coupled with an electrolyzer, this energy system converts energy harvested from the sun into chemical power. As the demand for a sustainable yet efficient and cost effective approach of producing hydrogen increases, researchers are seeking ways to improve the technology of forming solar fuel. Mimicking the idea of how nature collects and stores solar energy in chemicals bonds through photosynthesis, economically viable water splitting cells capable of splitting water directly at the semiconductor surface are being developed. The catalytic semiconductor is designed to be both a light absorber and an energy converter to store solar energy in the simplest chemical bond, H2, thereby eradicating significant fabrication and system costs involved with the use of separate electrolyzers wired to photovoltaic cells. In this work, water-splitting materials have been designed to consist of multi-component nanorods of titanium dioxide and platinum with well-defined nanostructures to function as photocatalytic cell for hydrogen production. As the TiO2-Pt nanorods are irradiated with light in the presence of a water source, oxygen and hydrogen are evolved at the anode TiO2 and cathode Pt segments of the nanorods respectively. The alternating segments of TiO2 semiconductor and Pt metal enable the control of the direction of charge movement and light absorption pathways in the material, thereby presenting a solution to improving the overall efficiency of photocatalytic hydrogen production. By employing templated electrodeposition, homogeneous multi-segmented TiO2/Pt nanorods have been successfully fabricated in anodic aluminium oxide membrane (AAM). This simple method of synthesis permits an easier control of the position and composition of TiO2 and Pt along the length of the nanorods, which allows for a customizable and highly reproducible method of obtaining segmented rods with uniformly distributed active sites for efficient catalytic activity. The morphology and material composition of the as-prepared Pt-TiO2 multi-segmented nanorods were characterized using the scanning electron microscope (SEM), transmission electron microscope (TEM) and the x-ray diffraction (XRD); and the photocatalytic properties of these multi-segmented TiO2/Pt nanorods are then examined by carrying out absorption studies using Rhodamine B (RhB). Two different Ti precursors, TiOSO4 and TiCl3 were employed in the successful fabrication of TiO2 nanorod segments. High potentiostatic conditions of -1.2 V (vs. 3 M Ag/AgCl) using TiOSO4 precursor resulted in TiO2 nanorods, but at the same time had promoted hydrogen evolution, which made it challenging for TiO2 nanorods to be deposited onto noble metal surfaces such as Pt; while lowering the potentiostatic voltages resulted in the growth of TiO2 nanotubes. Cyclic voltammetry and chemical tests were carried out to determine the detailed mechanisms of their respective growth, and the difference in the formation of TiO2 nanorods and nanotubes was attributed to be the regeneration of high amounts of NO3- species occurring at more negative deposition voltages. Using TiCl3, a protocol has been developed for the electrodeposition of TiO2 nanorods, which involved a low deposition voltage of -0.1 V (vs. 1 M Ag/AgCl) that would facilitate the deposition of TiO2 on noble metals such as Pt. This protocol allows both the flexibility of preparing TiCl3 precursor solution and the electrodeposition of TiO2 nanorods to be carried out at ambient conditions. In the presence of TiO2/Pt nanorods, RhB degradation studies reveal several pertinent characteristics of the photoactivities of the TiO2/Pt nanostructures, where nanostructural morphology, addition of Pt metal and TiO2/Pt interfaces were found to enhance TiO2 photoactivity. The effects of varying TiO2 length segments of Pt-TiO2 nanorods on the photoactivities of TiO2/Pt nanorods reveal an interesting trend, demonstrating an interplay between light absorption and the amount of light reaching the TiO2/Pt interface. Lastly, differences in the orientation of bi-segmented TiO2/Pt nanorods to the light source are presented, which may be useful in any future work on the investigation of the photoactivities of nanostructure arrays.

This investigation originated from work by Dr. A.H. McIlraith of the National Physical Laboratory who, in 1966, described a new type of charged particle oscillator. This makes use of two equal cylindrical electrodes to constrain the particles in such a way that they follow extremely long oscillatory paths between the electrodes under the influence of an electrostatic field alone. The object of this work has been to study the principle of the oscillator in detail and to investigate its properties and applications. Any device which is capable of creating long electron trajectories has potential application in the field of ultra high vacuum technology. It was therefore considered that a critical review of the problems associated with the production and measurement of ultra high vacuum was relevant in the initial stages of the work. The oscillator has been applied with a considerable degree of success as a high energy electrostatic ion source. This offers several advantages over existing ion sources. It can be operated at much lower pressures without the need of a magnetic field. The oscillator principle has also been applied as a thermionic ionization gauge and has been compared with other ionization gauges to pressures as low as 5 x 10- 11 torr. This new gauge exhibited a number of advantages over most of the existing gauges. Finally the oscillator has been used in an evaporation ion pump and has exhibited fairly high pumping speeds for argon gas relative to those for nitrogen. This investigation supports the original work of Dr. A.H. McIlraith and shows that his proposed oscillator has considerable potential in the fields of vacuum technology and electron physics.

The suitability of silicon for micro and sub-micro electronic devices is being challenged by the aggressive and continuous downscaling of device feature size. New materials with superior qualities are continually sought-after. In this thesis, defects are examined in two sets of silicon alternate materials; germanium (Ge) and III-V semiconductors. Point defects are of crucial importance in understanding and controlling the properties of these electronic materials. Point defects usually introduce energy levels into the band gap, which influence the electronic performance of the material. They are also key in assisting mass transport. Here, atomistic scale computational methods are employed to investigate the formation and migration of defects in Ge and III-V semiconductors. The behaviour of n-type dopants coupled to a vacancy in Ge (known as E-centres) is reported from thermodynamic and kinetic points of view, revealing that these species are highly mobile, consequently, a strategy is proposed to retard one of the n-dopants. Further, the electronic structure of Ge is examined and the changes induced in it due to the application of different types of strain along different planes and directions. The results obtained agree with established experimental values regarding the bands transition from indirect to direct under biaxial strain. This is used to support further predictions, which indicate that a moderate strain parallel to the [111] direction can efficiently transform Ge into a direct band gap material, with a band gap energy useful for technological applications. Vacancies and antisites in III-V semiconductors have been studied under various growth and doping conditions. Results presented in this thesis help predict and explain the stability of some defects over a range of growth conditions. This, together with knowledge of the kinetics of migration of Ga and As/Sb vacancies is used to explain the disparities in self-diffusion between GaAs and GaSb.

Recently, great interest has been shown in the fabrication of periodic micro- and nanostructures over large area due to their increasing applications in diverse research fields including optics and electronics, cell biology, bioengineering and medical science. Diamond turning using multi-tip single crystal diamond tools fabricated by focused ion beam (FIB), as a new machining technique, shows powerful capacity in the fabrication of micro- and nanostructures. However, lack of support from systematic theoretical research has seriously hindered the advance and industrialization of this technique. As such, molecular dynamics (MD) simulations and experimental trials have been undertaken in this research work to systematically investigate this new technique from the FIB-induced damage during the tool fabrication process to the nanometric cutting mechanism using nanoscale multi-tip diamond tools. The transmission electron microscope (TEM) measurements were carried out to characterize the FIB-induced damaged layers in single crystal diamond under different ion beam processing voltages. A novel multi-particle collision MD model was developed to simulate the FIB-induced dynamic damage process in diamond. The results indicated that the fabrication of diamond tool by FIB can create an impulse-dependent damaged layer at the tool surface. The nature of FIB-induced damaged layer in the diamond tool is a mixture phase of sp² and sp³ hybridization and accommodates a significant proportion of the implanted gallium. The nanometric cutting process of using nanoscale multi-tip diamond tools was studied by MD simulations. The results provide in-depth understandings of the nanostructure generation process, the cutting force, the thermal effect, and the tool geometry-dependent shape transferability. The investigation shows that the formation mechanism of nanostructures when using multi-tip tools is quite different from that of using single tip tools. Since the nanostructures are synchronously formed by a single cutting pass, the effect of feed rate and the alignment issues associated with the use of single tip tools to achieve the same nanostructure can be completely eliminated when using nanoscale multi-tip tools. The unique tool geometrical parameters of a nanoscale multi-tip tool including the tool tip distance, tip angle, and tip configuration play important roles in the form accuracy of the machined nanostructures. A hypothesis of a minimum ratio of tip distance to tip base width (L/Wf) of the nanoscale multi-tip tool has been proposed and qualitatively validated by nanometric cutting experiments. A series of nanometric cutting experiments and associated MD simulations were further carried out to study the influence of processing parameters on the integrity of the machined nanostructures and tool wear. Under the studied cutting conditions, the burr and structure damage are the two major types of machining defects. With the increase of the depth of cut and the cutting speed, the increasing overlap effect between the tool tips is responsible for the formation of side burrs and structural damage. The tool wear was initially found at the sides of each tool tip after a cutting distance of 2.5 km. The FIB-induced damaged layer, the friction produced at each side of the tool tip, and the high cutting temperature distributed at the tool cutting edges are responsible for the initiation of tool wear. Based on the research objectives achieved, generic suggestions are proposed for the further development of diamond turning using nanoscale multi-tip tools in terms of selective parameters used in tool fabrication, optimal design of tool geometry, and optimization of processing parameters in nanometric cutting practice.

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