A number of experimental techniques have been brought together to create a powerful investigative tool. This laser vaporisation, supersonic expansion, laser ionisation mass spectrometry amalgam has allowed the study of two distinct types of molecular species. Many heteronuclear diatomic species have been prepared and investigated for the first time. These novel molecules are of interest due to their utility as bulk phase alloys. Mass spectra are presented for many such combinations. Homonuclear diatomic species have been analysed using these techniques for some time. In particular, this work has focused on transition metal species as this is one of the few methods which permits such study. Spectroscopic investigations of the A, B and C states of the silver dimer (Ag<SUB>2</SUB>) molecule are presented here. The analysis of this work has provided the following rotational constants for these states; X state B<SUB>e</SUB> = 0.04878 cm<SUP>-1</SUP> A state B<SUB>e</SUB> = 0.04432 cm<SUP>-1</SUP> B state B<SUB>e</SUB> = 0.04544 cm<SUP>-1</SUP> and C state B<SUB>0</SUB> = 0.04851 cm<SUP>-1</SUP>. All values are for the <SUP>107,109</SUP>Ag<SUB>2</SUB> isotopomer. The first ionisation potential (I.P.) of any molecular system is an important parameter in the understanding of that species. The value of the I.P. has been evaluated for the silver dimer molecule under differing experimental conditions. It is reported here both under the influence of a potential field (I.P. = 61658.4 cm<SUP>-1</SUP>) and under field free conditions (I.P. = 61740.0 cm<SUP>-1</SUP>).

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Surface-active agents play an important role in lubrication technology and are often used as additives in liquid lubricants films to reduce the friction and wear. Under high loads, in asperity contacts or when there is no relative motion between two surfaces, fluid lubrication breaks down and boundary lubricants are essential to prevent wear and seizure. In other applications where the use of ‘thick’ films of liquid lubricants is not possible or desirable (i.e. micromotors, hard disk drives), lubrication between contacting surfaces is exclusively in the boundary regime. Despite the use of boundary lubricants in engineering applications for centuries, our understanding of how boundary lubricants work at the molecular level remains unclear. My thesis describes the use of total internal reflection (TIR) Raman scattering to characterise model boundary lubricants both ex situ and in situ, under realistic conditions of pressure and shear. The model systems comprise either Langmuir-Blodgett (LB) monolayers of long chain fatty acids (e.g. Zn arachidate) and phospholipids (e.g. DPPC) deposited on silica and SF10 glass, or phospholipid bilayers (e.g. DMPC) fused to silica and SF10 glass surfaces in water. TIR Raman scattering is a form of vibrational spectroscopy with sub-nanometer sensitivity and spatial resolution of a few microns. Control of the polarisation of the incoming and scattered light allows us to probe the orientation of adsorbed molecules and how that orientation changes under pressure and shear. The resonant frequency and intensity of different molecular vibrations is also sensitive to the packing and conformational order in the lubricant film. LB monolayers of Zn arachidate and DPPC are first characterised ex situ and then subjected to increasing load (upto ~750 MPa) in a contact between a fused silica ball and the flat surface of an SF10 hemisphere. A better packing or a higher orderliness of the molecules are observed at higher pressure without the monolayers being squeezed out. In contrast, application of load to the DMPC bilayer appears to squeeze some of the lipid materials out of contact. The designs of two Raman tribometers are described that allow Raman measurements in a sheared contact with simultaneous measurements of friction and load. Elasto-hydrodynamic and boundary lubrication regimes are studied with the tribometers overcoming the engineering difficulties up to a significant extent.

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Presented in this thesis is a detailed investigation of the optical properties of sets of InGaN/GaN and InGaN/AIGaN quantum well structures, supported by the results of microstructural experiments from the University of Cambridge. The effect of the depth of a single InGaN/GaN quantum well below the sample surface on its optical properties was investigated. Oscillations in the photoluminescence excitation spectra of the samples were observed at temperatures below 50 K and at photon energies above the GaN band gap. These features were attributed to the excitation of electrons at multiples of the LO-phonon energy above the GaN conduction band minimum. The rapid relaxation of the electrons and their capture into the quantum well led to a shift in the photoluminescence peak energy, and therefore the oscillations in the excitation spectra. The shifts in the photoluminescence spectra were attributed to a modification to the carrier distribution amongst localised states in the quantum well. A comparison of the optical properties of a set of semi-polar InGaN/GaN quantum well structures with those of nominally identical polar control samples was made. Evidence for a reduction in the electric field strength across the quantum wells was observed in the form of blue-shifts of the photoluminescence peak energy, increased rates of radiative recombination and sharpening of the quantum well excitation spectra, with respect to the controls. However, the reduction in the electric field strength across the wells does not result in an improvement in the room temperature internal quantum efficiency; an observation which was attributed to an increased density of non-radiative recombination centres due to an order of magnitude increase in the threading dislocation density in the semi-polar samples. The optical properties of a set of InGaN/AIGaN multiple quantum well samples with no capping layer, a GaN capping layer and a magnesium doped capping layer were also compared. It was found that the intensity of the quantum well luminescence in the capped samples was reduced at T = 6 K compared to that of the uncapped quantum wells, due to carriers generated in the cap layer not being captured into the wells. At room temperature the difference in quantum well luminescence intensity between the capped and uncapped samples increased due to the lower carrier density in the wells in the capped samples. In the case of the uncapped sample the higher carrier density resulted in the saturation of the impurity luminescence bands meaning that more carriers could contribute to the quantum well luminescence. However, in the capped samples the impurity luminescence was not saturated and so it is possible that carriers could be thermalised out of the wells and be captured at impurity sites, hence not contributing to the quantum well luminescence. Finally, the optical properties of InGaN/GaN multiple quantum well structures grown on 2 and 6 inch silicon substrates were studied. It was discovered that the reflectivity of silicon varies at low temperatures, which inevitably affects the outcome of measurements of internal quantum efficiency. After taking into account the effects of the changes to the reflectivity of the substrate, the room temperature photoluminescence internal quantum efficiencies of the samples were estimated to be 33 %,57 % (2 inch substrates) and 38 % (6 inch substrate).

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