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No description available.

An investigation into the fabrication of thin film silicon solar cells constructed onto polyester textile substrates is presented. The absence of a photovoltaic effect was found to be due to oxygen contamination in the silicon layers of the cell stack. This was concluded from FTIR absorption lines, as the Si-H2 peak had been blue-shifted from its original location, through the inductive effect of oxygen atoms being incorporated into the molecule. From the current-voltage analysis of the cells, the oxygen contamination was reconfirmed, as an electric field ample enough to create a depletion region across the i-layer to result in a PV effect, could not be established. Through the use of fibre melding techniques, amorphous/nanocrystalline silicon semiconductor junctions were successfully deposited on thermally bonded nonwoven spunlace. (hydroentanglement) PET. This new technique reduoed the density of electrical breaks within the textile, thus rectifying junctions possessing characteristics analogous to those deposited on solid glass sheets \vere produced.

The thesis investigates the wavelength dependent laser ablp..~ion in dielectric materials used for the fabrication ofhigh density Printed Circuit Boards (PCBs) in the electronics industry. Here the market for consumer and industrial products of ever-rising complexity has led to a demand for increased miniaturisation and low costs of multilevel printed circuit boards (PCBs) interconnected by microvias, which electrically connect the various circuit layers. Laser machining offers a potential solution to this need. The main objective of the research is to investigate the wavelength-dependence of the laser machining/drilling efficiency of two important sets of PCB materials, categorised as Organics and Ceramics using a carbon dioxide laser which can be tuned across its emission spectrum in the 9flm - 11 flm spectral region.. The organics include commercially available electronic materials with trade names such as Kapton, ArIon, FR4 and RCC and the ceramics materials studied are alumina and low temperature cofired ceramic (LTCC). The aim is to determine the optimum laser wavelength for maximum processing efficiency Le. to find the wavelength where the laser parameters are best matched to the optical, thermal and mechanical properties of each of the materials. A CO2 laser machining system was constructed which incorporated a novel laser source developed in the research programmes. The laser source was a MOPA system with a line-tuneable cw oscillator and a five pass power planar waveguide rf discharge-excited power operating in the so-called enhanced power regime to produce maximum peak power. An Acousto-optic modulator between the master oscillator and the amplifier allowed convenient control of pulse amplitude and duration. The system enabled the wavelength dependent studies on the wavelength and pulse energy dependence of the laser ablation properties (e.g. ablation threshold fluence and ablation rates) - to derive the so-called 'ablation spectrum' of the selected materials A comparison is made of the wavelength dependence of ablation with the room temperature absorption spectrum measured for each material using ellipsometry. It was observed that the 'ablation spectrum' information does not always appear to match the simple expectations derived from the room temperature 'absorption spectrum' of the material. This disparity in results is likely due to the change of absorption properties of • material because of rise in temperature, chemical decomposition or melting of material during ablation. However, the room temperature absorption spectrum (while not adequate alone), did provide a useful guide to the selection of a sub-set of the 40+ lines that would otherwise have to be studied. The results may be of direct application in the electronics industry to increase the efficiency oflaser machining.

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Magnetocaloric and magnetoelastic materials can be utilised in various device applications and have a potential to increase their efficiency by a considerable amount. In this thesis, Gd5(SixGei_x)4 is extensively researched on its magnetic properties such as magnetic phase transition temperature, magnetostriction, magnetoresistance and anisotropy. Field induced phase transition in Gd5(SixGei_x)4 was observed in several compositions and the rate of change of the first order phase transition temperature was determined to be approximately 5 K/Tesla. Various methods of transition temperature measurements were compared and the Arrott plot technique was determined to be accurate method for magnetocaloric materials. An advanced technique based on Arrott plots was developed to estimate the second order phase transition temperature when it is suppressed by the first order phase transition. This technique was also extended to estimate the transition temperature of mixed phase alloys. Field induced phase transition at high temperature using high magnetic field measurements up to 9 Tesla were carried out on two compositions of Gd5(SixGei-x)4 for x=0.5 and x=0.475 to validate the Arrott plot technique. Magnetostriction measurements were carried out on Gd5(SixGei_x)4 for various compositions. Fine structure was observed in the magnetostriction measurement in single crystal and polycrystalline Gd5Si1.95Ge2.05 samples but not on other compositions, which might be due to the presence of a secondary phase. It was demonstrated that a giant magnetostriction of the order of 1813 ppm could be obtained by varying the temperature using a Peltier cell and removing the requirement of bulky equipment such as Physical Properties Measurement System (PPMS). Magnetoresistance was measured for various compositions and an irreversible increase in resistivity was observed which depended linearly on the number of thermal cycles passing through the first order phase transition temperature. The irreversibly increased resistivity was recovered by holding the samples at high temperature for a long period of time of up to 3 days. A theoretical model was developed to explain the recovery in the resistance and was experimentally verified. First order magnetocrystalline anisotropy constant Kj, easy and hard axes of the single crystal Gd5Si2.7Gei j sample were determined using magnetic moment as a function of angle of rotation of the sample at room temperature. Dependence of the first order phase transition temperature on the angle of rotation of the single crystal Gd5Si2Ge2 sample was determined to be negligible. Additionally polycrystalline samples of Gd5Sii.8Ge2.2 and Gd5Sii.9Ge2.i were prepared by arc- melting and heat treatment was carried out on these samples in accordance with the literature to remove residual secondary phases in the sample at the Materials and Metallurgy Department of the Birmingham University. XRD measurements were carried out on these samples to confirm the crystal structure.

In this work, the largely theoretical existing research on class F has been extended to include a measured waveform based analysis. The results demonstrate how optimum class F performance can be achieved using real devices and highlights a number of interesting issues that a designer of a class F amplifier should consider.

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No description available.