To further increase the sensitivity of the aLIGO detectors, upgrading the monolithic fused silica suspension is considered for an upgrade option: a higher stress in the fibre and a longer final stage. One of the challenges for this upgrade will be producing thinner and longer fibres that can hold the test mass safely. Since laser power fluctuations during the fibre fabrication process can produce potentially weak fibres, we present a laser intensity stabilisation technology for fused silica fibre fabrication that was investigated to allow further improvements on fibre production consistency which could be applied to aLIGO upgrades. Fibres fabricated with this new technique showed 30% decreased standard deviation of breaking stress, which indicates that the application of intensity stabilisation technology can improve the statistical strength of fused silica fibres. Combined with a longer polishing duration, the average breaking stress also improved by 9%. As higher stress in the fibre and the longer final stage can improve the detector's sensitivity, these enhanced technologies will enable us to fabricate thin and robust fibres that can achieve future suspension upgrade requirements.

In this thesis, the lattice Boltzmann (LB) method for transport phenomena is combined with the simulated annealing (SA) algorithm for digitized porous media reconstruction to study fluid flow and heat transfer in random porous media. It is noted that in contrast to previous studies which simplify porous media as arrays of regularly shaped objects or effective pore networks, the LB+SA method in this thesis can model statistically meaningful random porous structures in irregular morphology, and simulate pore-scale transport processes inside them. To be specific, this thesis applies the SA algorithm to construct digitized random porous structures based on limited but meaningful statistical morphological information, which is defined either by analytical formulas or experimental samples. Then the LB models are applied to simulate isothermal fluid flow, heat conduction and heat convection in these digitized representations. The results of simulations in this thesis demonstrate that the LB+SA numerical strategy can well resolve pore-scale fluid transport details in random geometries, which is far beyond the common simplifications of real porous media as arrays of regular-shape objects. More significantly, the upscaling averages over the computational volumes and the related effective transport properties were also computed based on these pore-scale numerical results. Good agreement between the numerical results and theoretical predictions or experimental data at REV-scale was found. Moreover, this multiscale approach reveals the intrinsic links between porous structure characteristics to pore-scale and REV-scale fluid transport features. It evidences how the irregular geometries impact the flow and heat transfer processes, and presents unusual phenomenon of occlusion in percolation which cannot be manifested in simplification of porous media as arrays of regular-shape objects. The numerical simulations in this thesis demonstrate a combination of the LB method with the SA algorithm is a viable and powerful numerical strategy for simulating transport phenomena in random porous media with complex geometries at pore-scale.

The major objective of this thesis is the analysis of novel AlInSb/InSb QW Schottky diodes which may play an important role in future low-power high-speed electronic devices such as FETs, as well as showing promise for high frequency rectification. Although InSb has the highest electron mobility among the III-V semiconductors, due to lattice mismatch with common binary substrates, its 2DEG systems have far less mobility than anticipated values. The large lattice mismatch between AlInSb alloy and the substrate GaAs in AlInSb/InSb system results in a high density of structural defects which results in a high leakage current. Both large leakage current and low barrier height introduce difficulties in forming good Schottky diodes. Schottky diodes in this material system are largely unexplored. Two different planar structure designs (elementary, and surface channel) were used in this thesis to form AlInSb/InSb QW Schottky diodes. Various surface treatments were trialled to suppress diode leakage current. The fabricated AlInSb/InSb QW Schottky diodes were evaluated based on I-V measurements over a wide range of temperatures 3-290 K. Various models are evaluated and successfully used to describe the I-V characteristics of these AlInSb/InSb QW Schottky diodes. Depending on the applied surface treatment, two barrier heights (Φ).

This thesis describes an experimental study of the heat transport between the tip of a Scanning Thermal Microscope –Atomic Force Microscope (SThM-AFM) and nanofabricated sample. SThM is one of the most flexible tools available for measuring thermal transport at the nanoscale. However, heat transfer between the probe and sample has a complicated nature as it depends on different parameters such as the nature of the surrounding gas (pressure, temperature, degree of humidity), and that of the mechanical contact between probe tip and sample (surface roughness and topography, mechanical properties of the tip surface and sample surface and the force applied). So understanding the heat flow between tip and sample requires careful study of all of these parameters. Thus quantification of tip and sample thermal contact is a key problem in the interpretation of SThM measurements. In this work the fabrication of devices to quantify SThM tip and sample surface thermal resistance in one single contact are presented. The fabrication was performed using lithographic nanofabrication and MEMS technology. Thermally grown silicon dioxide was chosen as a membrane material for all devices due to its low thermal and electrical conductivity and ease of fabrication.

This thesis presents my work that I have done together with my supervisor, Dr Egor Muljarov. It is based on the resonant state expansion (RSE), a rigorous perturbation theory, recently developed in electrodynamics. Here, the RSE is applied to non-relativistic quantum mechanical systems in one dimension. To facilitate the analytics, the model of Dirac delta functions for describing quantum potentials was employed. The resonant states (RSs) of a symmetric double quantum well structure modeled by delta functions was first calculated. The full set of these RSs is investigated. This includes bound, anti-bound and normal resonant states which are all eigenstates solutions of Schrodingers equation with boundary conditions of outgoing waves. These RSs are then taken as an unperturbed basis state, for the quantum mechanical (QM) analogue of the RSE (QM-RSE). The transformation of the RSs and their transitions between different subgroups as well as the role of each subgroup in observables, such as the quantum transmission, is also analysed. The resonant state expansion is first verifed for a triple viii quantum well systems, showing convergence to the available analytic solution as the number of resonant states in the basis increases. The method is then applied to multiple quantum well and barrier structures, including finite periodic systems. Results are compared with the eigenstates in triple quantum wells and in- finite periodic potentials described by the famous Kronig-Penney model, revealing the nature of the resonant states in the studied systems.

This thesis is focused on the production and characterization of diamond films and diamond nanoparticles containing custom colour centres. These defects intentionally created into the diamond lattice are promising candidates for single photon sources, and are becoming more important for quantum information technologies as photons can carry quantum information over long distances. With outstanding properties such as up to 80% of the photons emitted into the zero phonon line (ZPL), single photon count rates up to several Mcps under continuous excitation and a narrow ZPL at room temperature, the SiV centre has recently attracted more attention. Although different approaches for the creation of colour centres have been reported, this thesis details the creation of SiV centres by chemical vapour deposition. Colour centres are created through the incorporation of impurities during diamond growth. While Si doping can easily be achieved due to plasma etching of Si substrates or the incorporation of a Si solid source inside the reactor vacuum chamber, controlling the exact amount of Si present in the gas phase or effectively incorporated is still a handicap. Chapters five and six show comprehensive studies performed towards the creation of diamond nanoparticles with single emitters. Control over the Si content within the gas phase is achieved using silane as gas source. The subsequent milling of the diamond films hosting the SiV centres and their inclusion into a stable solution, will facilitate SiV coupling and incorporation into cavities or emission-enhancer devices.

The generation of dark solitons in Bose-Einstein condensates has been an area of interest since the first experimental condensates were produced. The ubiquity of solitons in the natural world makes them an important phenomenon to understand. Despite excellent theoretical work in two dimensional dark solitons, few experiments have had the opportunity to investigate this regime. The work presented investigates the generation of dark solitons in a Rb-87 Bose-Einstein condensate. The evolution and decay of these topological excitations are investigated. The decay of the dark solitons is found to vary with the phase-step used to generate them. Dark solitons created with a phase-step width of 0.60 ±0.15 μm are found to decay into vortices after 10 ms. Dark solitons generated with larger phase-steps are found not to exhibit this vortex decay, instead dissipating over 10-15 ms back into the condensate. The first experimental generation of two dimensional Jones-Roberts solitons is reported in this work. These dark solitons differ from the standard planar dark soliton in that they are finite in extent and are found to be more dynamically stable. The Jones-Roberts solitons are observed for 40 ms with no observed change in energy.

A search is performed for the decay \(\lambda\frac{0}{b}\)→pKη' using pp collision data collected with the LHCb detector at centre-of-mass energies of \(\sqrt{s}\) = 7TeV and \(\sqrt{s}\) = 8TeV, corresponding to an integrated luminosity of 3 fb\(^-\)\(^1\). The search is performed in two decay channels; the η' is reconstructed through the decays η'→\(\pi^+\pi^-\gamma\) and η'→\(\pi^+\pi^-\eta\). In the η'→\(\pi^+\pi^-\gamma\) decay channel 117 ± 15(stat.) ± 10(sys.) signal events are observed and 45 ± 8(stat.) ± 2(sys.) signal events are observed in the η'→\(\pi^+\pi^-\eta\) decay channel. The combined statistical significance of these signals is 12.0σ, therefore this is the first observation of the decay \(\lambda\frac{0}{b}\)→pKη' . The branching fraction of the decay \(\lambda\frac{0}{b}\)→pKη' is measured relative to the decay B\(^+\)→K\(^+\)η'. The ratio of branching fractions is measured to be \(\frac{\beta(\lambda\frac{0}{b}→pKη')}{\beta(B^+→K^+η'}\)= 0.120 ± 0.013(stat.) ± 0.013(sys.). Using the world average value for the branching fraction of the decay B\(^+\)→K\(^+\)η', the branching fraction of \(\lambda\frac{0}{b}\)→pKη' is measured to be, \(\beta\)\((\lambda\frac{0}{b}→pKη')\) = 8.48 ± 0.88(stat.) ± 0.97(sys.) x 10\(^-\)\(^6\) . This is the first observation of a b-baryon decaying to an η.

Chapter I describes an experiment to study proton-proton interactions at 970 MeV. A high pressure diffusion cloud chamber was filled with hydrogen at 25 atmospheres and operated in the proton beam from the Birmingham synchrotron. A pulsed magnetic field of 13,000 oersted, applied to the chamber, enabled momenta of primary and secondary particles to be measured. 1029 events were observed due to the interaction of protons with protons. Of these, 565 events were attributed to elastic collisions and are discussed in terms of the optical model of the nucleus, giving a radius of interaction of 0.9 ± 0.1 × 10⁻¹³cms. Information from 458 inelastic events is compared with the statistical theory of pion production due to Fermi, and the isobar theory due to Peaslee. The results for positive pion production support Peaslee's theory but there are certain anomalies in the neutral pion production. Chapter II contains a description of a 9" diameter liquid hydrogen bubble chamber for use with the Birmingham synchrotron. Details are given of the chamber and expansion system along with the cryogenic, vacuum, high pressure and optical systems and the method for obtaining a pulsed magnetic field. The operation of the apparatus is discussed and an enclosed system for filling the chamber with deuterium is described. Finally, possible experiments that may be performed are mentioned.

In this thesis aberration corrected scanning transmission electron microscopy is employed to study the atomic structure of size-selected nanoclusters. The nanoclusters are produced using a magnetron sputtering gas aggregation cluster source with lateral time of flight mass filter, which enables the deposition of high precision samples. For Au nanoclusters, the combination of these techniques is used to determine atomic structure as a function of size, elucidate cluster growth mechanisms, determine the lowest energy structural isomers and investigate control of atomic structure through growth conditions. To further investigate the atomic structure of Au nanoclusters, an in-situ heating holder for the ac-STEM is used to extract a quantitative value for the energy difference between competing structural isomers. A study of surface melting of Au clusters on amorphous-carbon is also presented and the results are discussed with reference to several models for nanoscale melting. Finally, ac-STEM and STEM EELS are used to study the atomic structure and ageing in air of size-selected Ag nanoclusters. It is shown that exposure to air induces a change in both atomic structure and chemical composition.