InP quantum dot (QDs) lasers grown on GaAs substrates have potential applications in photodynamic therapies, as multi-wavelength sources and for biophotonic sensing. However, to make these devices practical, further improvements are required in threshold current at elevated temperature. The main reason for this study is to identify the factors in the improved performance of lasers with respect to lowering the threshold current density and lowering the temperature dependence of threshold current density for samples with different Ga composition in the upper confining layer (UCL). A new way of determining the mode loss per unit length (αi) was introduced by extracting the peak net modal gain (G - αi) value of 6 cm-1 for a 2-mm-long laser from the averaged value of the modal gain (G), which is more accurate and significant than determining αi just at the value which loss (at net modal absorption or A + αi) and gain (at net modal gain or G - αi) spectra tend to at low photon energy. The highest αi value is 2.30 cm-1 for Ga = 0.54, 1.10 cm- 1 for Ga = 0.52, and Ga = 0.56 and 0.58 have almost zero αi values. I show that to maintain the same peak modal gain at 300 K at a higher temperature, for instance 360 K, one will need to compensate for two situations. First, increasing the current density to achieve 300 K inversion level (or the difference between the quasi-Fermi level separation and the absorption edge) to compensate for the increased nonradiative recombination processes and secondly adding more current density on top of that to compensate for the carrier spreading to higher energy states, in order to reach the peak net modal gain required at 360 K. Spontaneous emission rate spectra measured at J6 cm -1 show more filled QW states for Ga = 0.54 compared to Ga = 0.58 and compared with data taken at constant inversion level indicates that more carriers are supplied to the Ga = 0.54 to compensate for its high optical mode loss (αi), when compared to Ga = 0.58. As the temperature increases, some of the energetic carriers from the QW escape to the lower confining layer (LCL) and spontaneous emission measurements show this happens more in the Ga = 0.58 than in the Ga = 0.54. Absorption measurements indicate this is because QD and QW states move closer to the LCL states as the Ga composition in the well increases. Three series of samples grown at different times but with similar designs were compared in the study. Lowering the Al composition in the cladding layer, tends to lower the optical confinement factor (Γ), which causes the threshold current density to be increased in Series 1. The results show that αi plays the dominant role, not only in lowering the Jth but also lowering the threshold current temperature-dependence of these series.

Nuclear magnetic resonance has been used to look at a number of colourful ceramic pigment systems, most of which are sold commercially in large quantities. Doped zircon (ZrSi04) pigments were examined using 19F, 23Na, 29Si, 51 Y and 91Zr NMR. In these systems, paramagnetic species are incorporated into the sample in small quantities creating the colourful pigment. The impurity dopants in the systems studied either dope directly into lattice sites in the zircon, or form an extra chemical phase. NMR was able to distinguish between these two doping mechanisms in a number of doped zircon pigments. Most spectra showed effects which were due to the magnetic influence of paramagnetic colouring species, and the strength of the interaction depended on the magnetic moment of the ion containing the unpaired electron. In the case of vanadium doped zircon, the moment was small enough that it allowed extra contact shifted peaks to be resolved in the spectra which indicated that the y4+ colouring ion probably substitutes into both the tetrahedral Si04 site, and at the dodecahedral ZrOg site. This is of current interest, and many other spectroscopic and computational experiments have also been performed to elucidate which of the two sites y4+ is located at. A 17 O-enriched zircon sample was also synthesised through a sol-gel route, and the local environment at the oxygen sites was followed through zircon formation from the TEOS and Zr-isopropoxide precursors. A multinuclear approach looking at the llB, 23N a, 27 Al and 29Si isotopes within silver containing glasses was able to provide information about the coordination of the isotopes within the glasses. 109 Ag NMR was evaluated as an experimental technique for examining silver containing compounds. 119Sn NMR was used to quantify the amount of Sn(II) and Sn(IY) in orange coloured SnO-ZnO-Ti02 (TZT) produced pigments, and the colour of the sample was found to correlate with the width of the Sn(IV) peak. The level of Na2C03-loading in yellow coloured TZT pigments also influenced the Sn(IV) linewidth, indicating that Sn(IV) is likely to be responsible for the perceived colour of the pigment. 170-enriched Sn02 was also synthesised, and the 170 and 119Sn spectra allowed a measure of the crystallinity of the sample to be determined as it was successively heated to higher temperatures.

Several methods of strengthening, including surface precipitation of low solubility particles, vapour treatment, ion-exchange, chemical vapour deposition (CVD) and combination treatments, have been investigated to improve the pristine strength of commercially available container and related glass compositions; their relative applicability in container manufacture has also been evaluated and discussed. As a part of this, a wide range of soda lime silica compositions, that includes typical container glass specifications, have been investigated to study their crystallisation behaviour in terms of the effect of nucleating agent, viscosity, time and temperature. Significant flexural strength enhancement of 16 to 163 % has been achieved for the processes studied, with a maximum of ~ 500 MPa and ~ 400 MPa for glasses using lithium ion exchange and exposure to LiBr and/or AlBr3 vapour respectively. Treatment times are short, compared to those currently used in industry. The mechanism of strengthening relies on surface compression by production of a glass skin or surface crystallised phase(s) having a low thermal expansion coefficient than the bulk of the glass. The physical properties of the glasses have been characterised by differential thermal analysis (DTA) and X-ray diffraction (XRD) as well as other methods such as high temperature viscometry and dynamic secondary ion mass spectroscopy (SIMS).

Measurements of the branching fractions of B0d,s→K*±h∓ (h = π,K) decays are performed, using pp collision data at the LHCb experiment. The data sample corresponds to an integrated luminosity of 1:0 fb-1, collected at a centre-of-mass energy of 7TeV. First observation of the B0s→K*±K∓ and evidence for the B0s→K*-π+ decay modes are reported. The following branching fraction measurements and limits of the B0d,s→K*±h∓ (h = π,K) decay modes, relative to the well measured B0→K*+π- decay, are obtained B (B0s→K*±K∓) / B (B0→K*+π-) = 1.49 ± 0.22 (stat.) ± 0.18 (syst.) B (B0→K*±K∓) / B (B0→K*+π-) < 0.06 at 95% CL. B (B0s→K*-π+) / B (B0→K*+π-) = 0.39 ± 0.13 (stat.) ± 0.05 (syst.)

X-ray excited optical luminescence (XEOL) refers to the trans-visible emission produced as a consequence of X-ray bombardment and provides an alternative detection method for X-ray absorption spectroscopy (XAS). Whereas XAS measured by conventional means (absorption, X-ray fluorescence) generally yields spectra characteristic of the bulk, the shallow escape depth of visible photons provides surface specificity of ~ 200 nm. Combining this with the relative ease of manipulating the emission using conventional optics gives us the basis for a method of mapping surface chemical states on the micron scale — XEOL microscopy (XEOM). As part of an ongoing project looking into the use of XEOL to study the chemical systems relevant to the corrosion of heritage artefacts, a portable XEOM instrument, XEOM1, has been constructed. Here, a detailed account of the development process is given, including descriptions of the microscope itself (optics, detectors, auxiliary hardware) and of its support system (control electronics and software). Data processing challenges are also discussed. Testing of XEOM1 has involved deployment on multiple synchrotron beamlines and data acquired from samples comprising of corroded copper surfaces (coupons, meshes) are presented in order to demonstrate how XEOM1 can be used for surface chemical analysis. XEOL spectra have been obtained by acquiring image 'stacks' — each stack is sequence of images resolved in energy across an absorption edge — and extracting data from regions of interest (ROIs) in each image. Chemical identification is achieved through analysis of the nearedge structure (XANES). Subtraction of pre- and post-edge images also gives a method for fast elemental mapping. Several options for future development of the XEOM1 hardware and related investigations are also proposed.

Modulation doped heterostructures consisting of a strained Ge (sGe) quantum well on a Si0.2Ge0.8 virtual substrate have been used to study enhancement of the transport properties of holes in the sGe channel due to the effective reduction of impurity scattering by placing the doping layer away from the channel. Electrical and structural analysis was performed for sGe heterostructures produced with a range of growth parameters. The highest hole mobility was 1.34×106 cm2 /Vs at 0.5 K for a sGe quantum well in a 'normal' structure (i.e. doped above the channel) at a sheet density of 2.9×1011 cm-2, which is the largest hole mobility reported in Ge to date. 'Inverted' structures (doping layer under the channel) were also studied for different sample parameters such as channel thickness, spacer thickness, doping and different temperature growth, with a hole mobility as high as 5.08×105 cm2 /Vs at a sheet density of 5.14×1011 cm-2 at 90 mK. Simulations of the scattering limited mobility for inverted and normal structures were performed and showed that at low sheet density background impurity scattering limits the low temperature hole mobility. However, as the sheet density increases interface roughness scattering becomes the mobility limiting process, especially in the case of inverted structures where the resistivity and mobility anisotropy is more pronounced. Magnetotransport measurements revealed the lowest reported effective mass for holes in Ge of 0.063±0.001 m0 for the normal structure and 0.07±0.002 m0 & 0.063±0.003 m0 for two inverted structures, and highest Dingle factors of α=78 and 33 for the normal and inverted structures, respectively. The low level of background impurities, high structural quality, and pure Ge channel revealed by structure characterisation are believed to be responsible for these exceptionally high values of mobility.

This thesis presents a world-first measurement of the CP parameters of B0s -> Dsπ with the aim of testing the flavour-specific nature of the decay. The measurement is made using ∫L = 1.0 fb−1 of pp collisions recorded at a centre-of-mass energy of √s = 7TeV collected during 2011. The measured values of the CP parameters are S = 0.197 ± 0.150 ± 0.025, D = −0.888 ± 0.098 ± 0.541, ΔS = 0.066 ± 0.083 ± 0.004, ΔD = −0.062 ± 0.050 ± 0.169, where the first uncertainties are statistical and the second are systematic. These results are consistent with the Standard Model prediction. A measurement of the CP parameters of B0s -> DsK is also presented, producing C = 1.01 ± 0.50 ± 0.23, Sf = −1.25 ± 0.56 ± 0.24, Sf = 0.08 ± 0.68 ± 0.28, Df = −1.33 ± 0.60 ± 0.26, Df = −0.81 ± 0.56 ± 0.26, where the first uncertainties are statistical and the second are systematic.

Existing codes for directly solving for the particle distribution function in laser plasma interaction studies either assume a collisionless plasma or solve for the full Fokker-Planck collision term. The former approach is the basis of an existing code at Warwick (VALIS). The latter approach is computationally expensive and often relies on a spherical harmonic expansion of the distribution function, making the implementation of a laser driver difficult. Here the existing collisionless code is extended by including reduced collision operators based on both the Krook and Fokker-Planck operator. The formulation of a fully conservative velocity-dependent Krook operator that shows agreement classical transport co-efficients in the regimes they are valid. The accuracy of the operator is shown to be improved using a normalisation method to ensure the Krook model yields the same heat flux as the Fokker-Planck model. The Krook model is also shown to be in agreement with full Vlasov-Fokker-Planck simulations of non-local transport. Two forms of a model Fokker-Planck operator are also included as a comparison to other reduced models of collisions.

Non-centrosymmetric superconductors (NCS) and related compounds have been studied using magnetic, specific heat and transport measurements as well as by neutron scattering and muon spin relaxation/rotation (μSR). The crystal structures of NCS lack inversion symmetry and in the presence of a finite antisymmetric spin orbit coupling, the Cooper pairs are a mixture of spin-singlet and spin-triplet states. In particular, the cerium based NCS have been reported to display unconventional superconductivity. Two different approaches for studying NCS are used. Firstly, the ground states of materials in the CeTX3 (T = transition metal, X = Si or Ge) family have been studied. CeCoGe3 is an antiferromagnet at ambient pressures and becomes superconducting at p > 4.3 GPa and was studied using inelastic neutron scattering (INS), muon spin relaxation/rotation (μSR), neutron diffraction and magnetic susceptibility measurements. The crystal electric fields (CEF) were studied using INS and magnetic susceptibility and the CEF scheme was evaluated. From this a ground state magnetic moment of 1.01 μB/Ce along the c axis was predicted. However, a magnetic moment of 0.405 μB/Ce along the c axis was observed in single crystal neutron diffraction measurements, indicating a reduced magnetic moment due to hybridization between the cerium f-electrons and the conduction band. The INS response was compared to the isostructural CePdSi3, CePtSi3 and CeRuSi3. The former two order antiferromagnetically and the Kondo temperatures were evaluated from the quasielastic scattering. CeRuSi3 is non-magnetic and there is a broad peak in the magnetic scattering at 59 meV. Another approach is to study weakly correlated NCS to look for evidence of unconventional behaviour. In particular, systems where the spin-orbit coupling can be varied by the substitution of heavier atoms into non-centrosymmetric positions were considered. LaPdSi3 and LaPtSi3 are superconductors with Tc = 2.65 and 1.52 K respectively and crystallize in the same crystal structure as the CeTX3 compounds. Magnetization, specific heat and μSR measurements reveal that both compounds are weakly coupled, fully gapped s-wave superconductors but LaPdSi3 is a type-I material while LaPtSi3 is type-II with a Ginzburg-Landau parameter of 2.49. The superconducting properties of single crystals of Nb0.18Re0.82 have been investigated and are discussed.

In this thesis a variety of photoelectron spectroscopy techniques have been applied to study CdO, in order to gain a more detailed knowledge of both the bulk and surface electronic properties of this material. Hard x-ray photoelectron spectroscopy (HAXPES) has been used, relaxing the surface preparation requirements of conventional photoemission techniques. This allows CdO to be measured in an as-grown condition with the associated higher carrier concentrations. The effects of conduction band filling and final state screening have been observed, and a discussion of the bulk-like sensitivity of HAXPES is given. The use of synchrotron radiation allows variation of the photon energy used to excite photoelectrons, and this is combined with the associated changes in photoionisation cross-sections to study the orbital character of the CdO valence band (VB). These measurements have been compared to density functional theory (DFT) calculations, using three functionals. It was found that using LDA+U and employing a theoretically calculated value of U = 2.34 eV can adequately reproduce the experimentally measured Cd 4d shallow core level position. The photon energy dependence of the shape of the VB, however, was not reproduced by the DFT calculations, indicating that additional Cd 5p character may be present within the VB, and that the O 2p photoionisation cross-sections may by underestimated at higher photon energies. The electron accumulation layer known to exist at the CdO surface has been tuned by the addition of Rb, which allowed the 2D electron density to be almost doubled. The effects of the increased 2D electron density on the surface band gap narrowing have been investigated by simulating the subband dispersion using the Poisson-Schrödinger model. The effective mass of the subband states has been extracted, and was found to be significantly lower than the reported bulk mass, which is discussed in the context of other recent results.