This thesis presents results on the applications and limitations of plasma enhanced chemical vapour deposition for silicon-based photonics, with an emphasis on optical microcavities for the control of light emission from silicon nanocrystals. ¶ Silicon nanocrystals were formed by precipitation and growth within Si-rich oxide layers (SiOx) deposited by plasma enhanced chemical vapour deposition. The films were found to exhibit strong room temperature photoluminescence, with the optimum emission depending on the composition and processing of the films. The strongest emission was achieved for films with a silicon content of ~40%, following hydrogen passivation. Hydrogen was introduced into the samples by two different methods: by annealing in forming gas (95% N2: 5% H2) or by annealing with a hydrogenated silicon nitride capping layer. Both methods caused an increase in photoluminescence intensity due to the passivation of defects. In contrast, the presence of low levels of iron and gold were shown to reduce the concentration of luminescent nanocrystals due to the creation of non-radiative centres. ¶ Optical microcavity structures containing silicon nanocrystals were also fabricated by Plasma enhanced chemical vapour deposition, using silicon dioxide, silicon nitride and silicon-rich oxide layers. The microcavities consisted of a silicon-rich oxide layer between two distributed Bragg reflectors formed of alternating silicon dioxide/nitride layers. The optical emission from these and related structures were examined and compared with that from individual layers in the structure. This revealed a complex interplay between defect and nanocrystal luminescence, hydrogen passivation and materials structure. The resulting microcavity structures were shown to be suitable for producing a stop-band over the wavelength range of interest for nanocrystal emission, 500-1000nm, and to produce significant intensity enhancement and spectral narrowing. Quality factors of 50-200 were demonstrated. ¶ The application of plasma deposited films was shown to be limited by stress-induced failure that resulted in cracking and delamination of the films during annealing. The SiOx films thicker than about 600nm failed predominantly by cracking. This was shown to be caused by tensile stress in the film caused by hydrogen desorption during high temperature annealing. The resulting cracks showed preferred alignment depending on the crystallographic orientation of the silicon substrate. For films deposited on (100) silicon, two modes of crack propagation were observed, straight cracks aligned along < 100> directions, and wavy cracks aligned along < 110> directions. For films deposited on (110) silicon, straight cracks were observed along [-1 10] directions, with a lesser number aligned along [001] directions. Cracks were also observed for films on (111) silicon. These showed 3-fold symmetry consistent with crack propagation along < 211> directions due to plastic deformation. Details of these crack geometries and their dependencies are discussed.

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Glass-fibre reinforced plastic pipes are widely used to convey fluids for various purposes. They offer a number of distinct advantages over conventional metals, such as high specific strengths, high specific moduli, superior corrosion resistance and low coefficient of thermal expansion. However, their behaviour under lateral quasi-static and impact loading are still not well known. The research programme described in this thesis was designed to characterise the performance of 55&deg; winding angle GRP pipes, subjected to lateral quasi-static and impact loading. Two approaches: experimental tests and finite element analysis, were used to investigate the behaviour of the GRP pipes. The experimental investigation was started with diametral compression of short GRP pipes to examine the structural behaviour and failure mechanisms. Subsequently, lateral indentation tests were conducted on rigid-foundation supported or simply supported specimens using two different indenter geometries: line-ended and flat-ended. Furthermore, low-velocity impact tests were performed under similar conditions as those for indentation tests in order to characterise the response of the GRP pipes and to identify the correlation between the two forms of loading. The pipes exhibited multi-mode failure mechanisms, resin cracks, delaminations and fibre breakage. It is found that delamination, which resulted in significant loss in stiffness and strength, was the most significant mode of failure for the GRP pipes. A good correlation in behaviour was identified between quasi-static indentation and its energy equivalent low-velocity impact when the global bending stiffness of the GRP specimens were high. Specimens with span S 10.5D i, where Di is the internal diameter of the pipe, are considered to have high bending stiffness, while simply supported specimens with S10.5D i have low bending stiffness. Irrespective of the support conditions and loading type, specimens with high bending stiffness followed a failure mechanism sequence: local resin failure, delamination and the fibre breakage. However, the large global bending experienced by low bending stiffness specimens resulted in a change of failure mechanism, only local damage and surface tensile cracks were observed.

In the design of cryogenic fuel tanks for the next generation Reusable Launch Vehicles (RLVs), the permeability of liquid hydrogen (LH2) across the thickness of the tank is a critical issue. The rate of permeation of LH2 is largely dependent on the internal damage state of the composite tank wall. Damage in the form of matrix cracks in the composite material of the tank is responsible for the through-the-thickness permeation of LH2. In this context, the detection of matrix cracks takes on an unprecedented significance. In this work, an ultrasonic technique for the ply-by-ply detection of matrix cracks in laminated composites is developed. Experimental results are presented for graphite/epoxy laminates with different lay-ups and laminate thicknesses. Matrix cracks in each of the plies of the laminated composites were detected even when there was a rather high density of cracks in all of the plies. The ultrasonic data were calibrated by comparing them with the corresponding results obtained by using the traditional methods of optical microscopy and penetrant enhanced X-radiography. Excellent quantitative correlation was observed between the results obtained with ultrasonics and the traditional methods.