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Reduced activation oxide dispersion strengthened (ODS) steels are candidate alloys for use in fusion reactor systems and are fabricated by mechanically alloying yttrium oxide to a reduced activation ferritic steel powder. The product is consolidated at high temperature by hot isostatic pressing (HIP), producing a dispersion of nanometre sized oxide particles throughout the ferritic microstructure. These particles have been shown to both improve the high temperature mechanical properties of the alloy and provide trapping sites for helium gas. The use of these particles to sequester helium is of particular significance in the development of a structural ODS steel for fusion reactor systems. A fusion power reactor, based on the ITER design, is expected to produce over 2000 appm transmutant helium in any steel components exposed to the core neutron flux. At these gas concentrations, conventional steels undergo severe swelling and embrittlement, motivating the development of materials capable of managing helium accumulation. This thesis investigates the use of the oxide particle dispersion in sequestering helium introduced by ion implantation. An initial characterisation of a model Fe-14Cr-0.25Y2O3 (wt%) system was completed using high resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). This demonstrated the efficacy of the production methods and the gas trapping capabilities of the oxide particles via argon gas, introduced during the mechanical alloying process. The subsequent consolidation of a full set of Fe-14Cr-3W-0.2Ti-0.25Y2O3 (wt%) ODS alloys at 1150°C, 1050 °C and 950 °C produced a systematic variation in the density of the particle dispersion. The characterisation of these materials using APT provided an insight into the consistent Y2Ti3O5 particle chemistry found in each consolidation, and identified a stoichiometric shift from Y2Ti3O5 to YTiO2 following short term annealing periods at 1000°C. Though further work is required, this shift is thought to be consistent with a thermodynamically mediated transition of the metastable clusters to stable oxide particles. Following implantation with 2000 appm helium and examination under TEM, the helium bubble and particle densities were found to be closely correlated thus providing evidence for an association between the particles and the gas bubbles. Controlling the helium bubble density via the particle dispersion demonstrates the potential use of processing temperature in controlling how helium accumulates in an implanted ODS microstructure. The effects of both bubble and particle densities on mechanical properties were investigated further using nanoindentation methods. Significant local variation in the hardness of the ODS steels was found to result from the bimodal grain size distribution of the material. By using only those measurements taken from large grained regions of the ODS, the grain refinement and particle hardening effects could be deconvolved and used to quantify particle hardening using a dispersed barrier model. The significant hardening effects with helium addition observed in the reference alloys were found to be almost entirely absent from the ODS systems, though anomalous softening in the 950°C consolidation indicated a potentially unexpected interaction between the bubble and particle populations. A possible explanation for this anomaly and a proposal for further work to establish its origin is discussed.

Platinum-based catalysts for hydrogen fuel-cell applications have progressed greatly with the addition of a second element in either a mixed-alloy or core-shell structure. Not only do they contain a reduced amount of the more expensive platinum metal but they have been shown to demonstrate a significant improvement in catalytic activity. Further improvement of these systems can only be made by careful investigation of such catalyst panoparticles on an atomic scale. These nanoparticles provide a significant characterisation challenge due to their minute size and beam sensitivity. A new method of quantifying the annular dark-field (ADF) scanning transmission electron microscope (STEM) signal on an absolute scale has been developed to address this problem. Experimental images are scaled to a fraction of the incident beam intensity from a detector map. The integrated intensity of each individual atomic column is multiplied by the pixel area to yield a more robust imaging parameter: a scattering cross section, σ. Using this cross section approach and simulated reference data, I show it is possible to count the number of atoms in individual columns. With some prior knowledge of the sample, this makes it possible to reconstruct the 3-dimensional structures of pure platinum nanoparticles. Such an approach has subsequently been extended to bimetallic particles here the elements are close in atomic number, using the platinum-iridium system as an example. In the same way that the cross section can be calculated from ADF image intensity, it is possible to calculate an energy dispersive x-ray (EDX) partial scattering cross section, beneficial especially because of the simplicity of its implementation. In sufficiently thin samples such that the number of x-ray counts is linearly proportional to sample thickness, we can determine element-specific atom counts. Finally, it is possible to combine EDX and ADF cross sections to provide us with quantitative structural and compositional information.

Electron beam induced current (EBIC) and atom probe tomography (APT) were used in this study to determine electrical activities and impurity compositions at extended defects in multicrystalline silicon (mc-Si) samples. The results provide, for the first time, information regarding the chemical species present at defects whose electrical activity has previously been measured. A new APT specimen fabrication process was developed with the ability to select a specific defect for APT analysis. Development of the APT specimen fabrication process proceeded by first selecting and optimising the preferential etching for nano-scale defect delineation. Three etchants were evaluated, namely Secco, Sirtl and Dash, from which the Secco etch was selected. Three parameters were optimised to produce etch pits with geometries that meet the requirements imposed by APT specimen fabrication methods. The optimum parameters were 0.05M potassium dichromate concentration, 20°C etch temperature, and 30sec etch time. In the second stage, marking techniques were developed in order for the defects to be located throughout the APT specimen fabrication process. However, it became apparent that the conventional APT specimen fabrication method could not be used to fabricate APT specimens containing selected defects in a mc-Si sample. This led to the development of a novel APT specimen fabrication approach which allowed APT specimens to be fabricated, reproducibly, containing grain boundaries and isolated dislocations. In order to evaluate accurately iron contamination in mc-Si, four atom probe parameters were optimised to maximise detection sensitivity: the evaporation rate, the laser beam energy, the pulse repetition rate and the specimen temperature. The optimisation process can be divided in to two parts. In the first part, a matrix of pre-sharpened single-crystal silicon specimens was subjected to a variety of experimental parameters. The optimised parameters were determined to be 0.3% evaporation rate, 0.5nJ beam energy, 160kHz repetition rate and 55K specimen temperature. The second part was to determine the iron detection efficiency –the percentage of detected Fe ions that can be correctly identified as Fe– and sensitivity using these parameters to analyse a specially prepared iron calibration specimen. The values were determined to be a detection efficiency of about 35% and sensitivity of 54ppm or 2.70x1018 atom/cm3. The APT specimen fabrication process and the optimised APT analysis parameters were used to analyse four extended defects in mc-Si samples subjected to three different processing conditions, namely gold-contaminated, as-grown and phosphorus diffusion gettering (PDG). The important aspects of the analysis are listed below: • Gold was not detected at the grain boundary and its associated dislocations in the gold-contaminated specimen. The binding enthalpy of gold to such defects is thus less than 0.63eV. • Iron was not detected in any specimen. • Copper was observed at the grain boundary in the as-grown specimen in the form of individual atoms as well as clusters with diameters ranging between 4nm and 9nm. The electrical activity of the grain boundary was about 58%. • Nickel and carbon were detected at the grain boundary in the post-PDG specimen with the former having platelet structures with diameters and thicknesses ranging between 4nm-7nm and 2nm-4nm, respectively. The recombination strength of the defect was about 22%. • Two nickel clusters were found at the isolated dislocation in the post-PDG specimen. The clusters were spherical with an average diameter of 10nm. The distance between the two clusters was 35nm. The recombination strength of the defect was about 4%.

Particulate reinforced Al alloy composites (AlMCs) are recognized as important structural materials due to their lightweight, high modulus and strength and high wear resistance. In order to understand the effect of matrix, reinforcement and secondary processing techniques on the microstructure development and mechanical properties of AlMCs produced by powder metallurgy routes, Al alloy composites reinforced with three types of reinforcements by different secondary processing techniques have been produced and examined. Fabrication of Al or 6061Al alloy based composites reinforced with nano-sized SiC particles (~500nm), micro-sized (<25µm) quasicrystalline alloy particles (hereinafter referred to as “NQX”) and micro-sized Nb particles (~130µm) has been carried out by powder metallurgy routes followed by extrusion or cold rolling. After extrusion, a homogeneous distribution of secondary particles has been obtained with rare interfacial reaction products. The 6061Al/SiC composites exhibit superior mechanical properties than either monolithic alloys or composites reinforced with micro-sized particles with retained ductility while the 6061Al/NQX and 6061Al/Nb composites show limited improvement in tensile strength mainly due to their reinforcement size and poor interfacial bonding. After cold rolling, the evolution in microstructure, texture and strength has been analysed. A typical near β fibre texture with highest intensities near Copper and Brass orientations has been developed for 6061Al/NQX and 6061Al/Nb composites. For 6061Al/SiC composites, a randomized texture with very small grains has achieved due to the presence of the non-deformable SiC particles. Mechanical property tests including microhardness, three-point bending tests and tensile tests have been carried out on cold rolled samples and the results exhibit some level of improvement when compared with as-extruded samples due to work hardening. Finally, the work moves on to the general discussion based on the previous result chapters. The microstructural development related to reinforcement, matrix and interfacial areas during extrusion and cold rolling has been summarised and the correlation between microstructure and mechanical properties has been discussed. The thesis provides a thorough understanding of AlMCs produced by powder metallurgy routes in terms of matrix, reinforcement and processing techniques. It can provide reference to the future development of AlMCs for high strength applications.

Novel semiconductor nanostructures possess a range of notable properties that have the potential to be harnessed in the next generation of optical devices. Electron microscopy is uniquely suited to characterising the complex microstructure, the results of which may be related to the growth conditions and optical properties. This thesis investigates three such novel materials: (1) GaN/InGaN core/shell nanowires, (2) n-GaN/InGaN/p-GaN core/multi-shell microrods and (3) Zn3N2 nanoparticles, all of which were grown at Sharp Laboratories of Europe. GaN nanowires were grown by a Ni-catalysed VLS process and were characterised by various techniques before and after InGaN shells were deposited by MOCVD. The majority of the core wires were found to have the expected wurtzite structure and completely defect free – reflected in the strong strain-free photoluminescence peak –with a- and m- axis orientations identified with shadow imaging. A small component, <5%, were found to have the cubic zinc-blende phase and a high density of planar faults running the length of the wires. The deposited shells were highly polycrystalline, partially attributed to a layer of silicon at the core shell interface identified through FIB lift-out of cross section samples, and accordingly the PL was very broad likely due to recombination at defects and grain boundaries. A high throughput method of identifying the core size indirectly via the catalyst particle EDX signal is described which may be used to link the shell microstructure to core size in further studies. An n-GaN/InGaN/p-GaN shell structure was deposited by MOCVD on the side walls of microrods etched from c-axis GaN film on sapphire, which offers the possibility of achieving non-polar junctions without the issues due to non-uniformity found in nanowires. Threading dislocations within the core related to the initial growth on sapphire were shown to be confined to this region, therefore avoiding any harmful effect on the junction microstructure. The shell defect density showed a surprising relationship to core size with the smaller diameter rods having a high density of unusual 'flag' defects in the junction region whereas the larger diameter sample shells appeared largely defect free, suggesting the geometry of the etched core has an impact on the strain in the shell layers. The structure of unusual 'flag' defects in the m-plane junctions was characterised via diffraction contrast TEM, weak beam and atomic resolution ADF STEM and were shown to consist of a basal plane stacking faults meeting a perfect or partial dislocation loop on a pyramidal plane, the latter likely gliding in to resolve residual strain due to the fault formed during growth. Zn3N2 has the required bandgap energy to be utilised as a phosphor with the additional advantage over conventional materials of its constituent elements not being toxic or scarce. The first successful synthesis of Zn3N2 nanoparticles appropriate to this application was confirmed via SAD, EDX and HRTEM, with software developed to fit experimental polycrystalline diffraction patterns to simulated components suggesting a maximum Zn3N2 composition of ~30%. There was an apparent decrease in crystallinity with decreasing particle size evidenced in radial distribution function studies with the smallest particles appearing completely amorphous in 80kV HRTEM images. A rapid change in the particles under the electron beam was observed, characterised by growth of large grains of Zn3N2 and ZnO which increased with increasing acceleration voltage suggesting knock-on effects driving the change. PL data was consistent with the bandgap of Zn3N2 blue shifted from 1.1eV to around 1.8eV, confirming the potential of the material for application as a phosphor.

Experimental investigations of the optical properties of GaN nanostructured light emitting diode (LED) arrays are presented. Microphotoluminescence spectroscopy with pulsed and continuous wave lasers was used to probe the carrier dynamics and emission mechanisms of nanorod LED arrays fabricated by a top down etching method. Results show a possible reduction in internal electric field as nanorod diameter decreases. Localisation effects were also observed, affecting the spectral shape of the nanorod emission. Under two-photon excitation, quantum dot-like sharp spectral peaks in the PL spectra are found to exist in abundance amongst all the nanorod samples. The optical properties of these localised states, which are shown to be associated with the nanorod free-surfaces, are characterised using non-linear and time resolved spectroscopy. An investigation into spatially resolved single nanorods was also carried out. Single nanorods were isolated, and characterised using pulsed lasers. The etching is shown to increase the carrier decay life-time at extended intervals over several hundred ns. The temporal evolution and excitation power density dependence of the quantum dot-like states are also presented for the first time. The long lived localised states are thought to arise from surface effects, in particular Fermi-surface pinning, causing localisation and spatial separation of carriers. Additional work on nano-pyramid array LEDs, with quantum wells on semi-polar surfaces is also presented. Optical properties using micro-photoluminescence are compared to cathodoluminescence studies. An uneven distribution of emission wavelengths across the pyramid facet is thought to lead to an emission mechanism involving carriers transferring between multiple spatially localised states. Finally, experimental techniques and fabrication methods for future work are documented in detail.

The displacement damage induced by primary recoils of fusion neutrons in tungsten and alloys has been studied with self-ion irradiations, followed by damage characterization with electron microscopy. Tungsten and alloys (≤ 5 wt.% Re, Ta, V) were implanted with 2 MeV W+ ions over a dose range of 3.3×1017 - 2.5×1019 W+m-2 at temperatures ranging from 300 to 750°C. Dislocation loops of b = ½<111> (> 60%) and b = <100> were identified, and that ½<111> loops were found more thermally stable. Among loops that were large enough for nature determination, at least 50% were found to be of interstitial type, with larger fractions in high-temperature and high-dose conditions. The diameter of loops did not exceed 20 nm, with the majority being ≤ 5 nm. The loop number density varied between 1022 and 1023 m-3. The effects of ion dose, irradiation temperature, composition and grain orientation on damage microstructure were investigated. In-situ irradiations (150 keV W+ ions) were carried out as a complement to the bulk implantations. Qualitative trends in loop size, geometry and nature with irradiation dose and temperature were similar to bulk irradiated specimens. Also, the dynamics of defects and their effects on the damage evolution were explored. In-situ annealing of irradiated thin foils was performed to investigate the thermal stability of radiation damage in tungsten. The majority of microstructure transformations were completed within 15 min of annealing. However, extended durations did favour the increase of loop size and the fraction of ½<111> loops.

Ferritic ODS steels show improved high temperature strength and irradiation tolerance compared with conventional ferritic steels, and are one of the key potential materials for fusion blanket structural applications. The processing of ODS steels is critical to their subsequent performance; however knowledge of the optimum processing approaches for these alloys is not complete. The microstructural evolution of ODS steels containing Y2O3 and other additions during manufacture has been investigated and the processing conditions optimised based on microstructural and mechanical investigations. Ferritic powders with Y2O3 and other additions were investigated, primarily using analysis on the micro- and nano-scale, with an emphasis on identifying the requirements for homogenization of the Y within the steel matrix. The Y2O3 dispersion and subsequent development of the nano-precipitates during thermal treatment was investigated using in-situ neutron diffraction. The nano-precipitates were resolved at approximately 900◦C after 1hr, with coarsening and/or re-precipitation progressively increasing at higher temperatures. A significantly increased number density of nano-precipitates (∼2x1023m−3 to ∼7x1023m−3) was established by hot isostatically pressing an Fe-14Cr-3W-0.2Ti0.25Y2O3 alloy at 950◦C compared with more traditional temperatures at 1150◦C, attributed to the increased coarsening and/or re-precipitation of the nano-precipitates at the higher temperatures. The influence of the mechanical alloy (MA)ing conditions on bulk mechanical properties was investigated using four point bend. The highest fracture toughness of ∼55MN/m3/2 and ultimate strength of ∼1450MPa was achieved under conditions that minimised the mechanical alloying time and increased the average final size of the powders. An Fe-14Cr-3W-0.2Ti-0.25Y2O3 (wt%) ODS alloy manufactured under optimised conditions showed a bi-modal grain structure size distribution and had a comparatively high yield strength of >1200MPa at 20◦C and >330MPa at 700◦C. The grain structure and high yield strength were attributed to the random distribution of 25nm radius of gyration (Rg) Y, Ti and O rich nano-precipitates randomly dispersed throughout the alloy. Long term thermal ageing (750hr at 1000◦C) reduced the room temperature yield strength and increased the proportion of larger grains in the bi-modal distribution, but high temperature yield strength was remarkably stable.

This thesis describes an investigation into silk spinning, with the objective of producing high performance silk fibres in the laboratory using a novel spinning device based upon observations on natural spinning glands and processes. After an in-depth literature review the work is reported in two sections: natural and artificial spinning. The literature provides fragmented data on different aspects of natural silk production, and artificial spinning has not yet reproduced fibres with the properties of native silk fibres, despite unfounded claims of biomimetic spinning. The first half of the thesis looks at natural silk spinning. The work started with a general study of the morphology of spider and silkworm spinning ducts: First, how the silk fibre develops as the dope flows through the gland; and second the relationship between silk fibre properties and both gland morphology and spinning speed. More detailed studies using histochemical and spectroscopic investigations showed that the silk ducts of the spider Nephila edulis and the silkworm Bombyx mori both contain β-chitin, despite an evolutionarily distant common ancestor. Finally, observations showed that the duct of N. edulis consists of alternating nanoporous discs, and FEA modelling indicated that the duct is optimised for mechanical integrity and permeability. The second half of the thesis describes the development of a spinning device that uses natural silk dope mainly taken from B. mori as feedstock. It begins with a description of the gradual development of the engineering aspects of the spinning device, to meet challenges raised during the spinning investigation. The development of a centrifugal capillary rheometer, for practical quantitative insights into rheological processes is then presented. Finally the spinning investigation is reported: first, the screening of spinning in glass capillaries based upon natural gland dimensions and flow rates, which have been shown to induce fibrillation in silk dope in a rheometer, and also included initiation of instability through heat applied along the capillary; second, the final spinning evaluation, using lessons learned from all the screening trials throughout the project, but also including a key development of a hydrophobic coating on the capillary tip to inhibit droplet formation and massively increase the process stability and ease of fibre production. The main conclusions from this work are that good silk fibre cannot be spun by flow shear stress alone; and, that heat instability induces indiscriminate gelation of the silk, whose disordered molecular structure gives poor silk fibre properties. The body of work behind these conclusions provides fundamental background information and new insights that will contribute to the next stages of development of artificial silk spinning, from obtaining a better understanding of the biology of natural spinning glands to the engineering difficulties of implementing the bioinspired principles.

The combination of X-ray imaging and diffraction techniques provides a unique tool for structural and mechanical analysis of engineering components. A variety of modes can be employed in terms of the spatial resolution (length-scale), time resolution (frequency), and the nature of the physical quantity being interrogated. This thesis describes my contributions towards the development of novel X-ray “rich” imaging experimental techniques and data interpretation. The experimental findings have been validated via comparison with other experimental methods and numerical modelling. The combination of fast acquisition rate and high penetration properties of X-ray beams allows the collection of high-resolution 3-D tomographic data sets at submicron resolution during in situ deformation experiments. Digital Volume Correlation analysis tools developed in this study help understand crack propagation mechanisms in quasi-brittle materials and elasto-plastic deformation in co-sprayed composites. For the cases of crystalline specimens where the knowledge of “live” or residual elastic strain distributions is required, diffraction techniques have been advanced. Diffraction Strain Tomography (DST) allows non-destructive reconstruction of the 2-D (in-plane) variation of the out-of-plane strain component. Another diffraction modality dubbed Laue Orientation Tomography (LOT), a grain mapping approach has been proposed and developed based on the translate-rotate tomographic acquisition strategy. It allows the reconstruction of grain shape and orientation within polycrystalline samples, and provides information about intragranular lattice strain and distortion. The implications of this method have been thoroughly investigated. State-of-the-art engineering characterisation techniques evolve towards scrutinising submicron scale structural features and strain variation using the complementarity of X-ray imaging and diffraction. The first successful feasibility study is reported of in operando stress analysis in an internal combustion engine. Finally, further advancement of ‘rich’ imaging techniques is illustrated via the first successful application of Time-of-Flight Neutron Diffraction Strain (TOF-NDST) tomography for non-destructive reconstruction of the complete strain tensor using an inverse eigenstrain formulation.

Graphene has unrivalled properties and is heralded as a revolutionary material for the 21st century. Chemical vapour deposition (CVD) on metals is a promising method to produce large-area graphene. Controlling the properties of CVD graphene is vital for its integration in a wide-range of future applications. Many factors can influence the CVD growth of graphene and its properties, therefore further investigations will be beneficial to fully understand and control this technique. In this thesis I expand the knowledge about the growth of pure and heteroatom-doped graphene by low pressure chemical vapour deposition (LPCVD) and atmospheric pressure chemical vapour deposition (APCVD) on commercially available Cu and Pt foils. Using a range of characterisation techniques, I investigate the influence of the substrate’s properties and the synthesis conditions on the growth of graphene, in pursuit of improved, controlled or optimised production, which can promote high quality, large-area, single-layer graphene, or other as desired. By characterising the topography, surface roughness, crystallographic orientations, and chemical composition of six Cu foils, I find that their properties vary greatly and this influences the growth of CVD graphene. I elucidate that the commonly used 99.8 % Alfa Aesar Cu foil has a surface coating composed of calcium, chromium, and phosphorus, which detrimentally influences graphene growth. Cleaning Cu foils with CH3COOH is shown to reduce the concentration of surface contaminants, consequently reducing the nucleation density and increasing the growth rate of CVD graphene. I also demonstrate that the shape, orientation, edge-geometry and thickness of CVD graphene domains can be controlled by the Cu crystallographic orientations. Single layer LPCVD graphene domains align with zigzag edges parallel to a single <101> direction on Cu{111} and Cu{101}, while bilayer domains align to two directions on Cu{001}. Hexagonal APCVD domains also preferentially align with edges parallel to the <101> direction(s). This discovery resolves a key challenge of controlling the orientation of individual graphene domains and opens a new avenue for tailored production of large-area CVD graphene with improved properties. By controlling the synthesis conditions of APCVD graphene on Pt foils I optimise production of ~0.5 mm single layer graphene domains with reduced nucleation density and increased growth rate of ~100 μm/min by synthesis at 1150°C, a higher temperature than previously reported. The absence of large, hexagonal, single-crystal domains on pristine Pt foil, and observation of a reaction between quartz and Pt that promotes hexagonal domains, suggests that a silicon or platinum silicide surface layer may be advantageous for improved growth of graphene. Finally, I demonstrate that the dopant concentration of nitrogen-doped graphene is increased at lower synthesis temperatures and higher NH3 concentration, up to 1.3 %, but with an associated decrease in the growth rate. Direct visualisation, elemental confirmation, and electronic characterisation of individual nitrogen atoms is shown for the first time using aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy. Boron-doped graphene is also synthesised. The implications of these findings, and many additional minor contributions, are wide-ranging and of considerable importance for the future understanding of CVD growth of graphene on metals, and more generally for the advancement of scientific knowledge for manufacturing large-area graphene. Collectively, these discoveries represent a significant body of work that can improve the efficiency of production and assist with controlling the properties of large-area CVD graphene.

The pursuit of high quality, large area graphene has been a major research focus of contemporary materials science research, in the wake of the discovery of the multitude of exceptional properties exhibited by the material. The DPhil project was undertaken with the objective of developing an understanding of the growth of large graphene sheets by chemical vapour deposition (CVD), and also in the subsequent characterisation of their material properties. By conducting atmospheric pressure CVD growth at high methane flow rates, it was found that few-layered graphene (FLG) could be deposited on a copper catalyst. It is demonstrated that the self-limiting property of a copper catalyst is not universal to all deposition conditions, and shown that FLG grows in a terrace-like configuration. In depth transmission electron microscopy (TEM) studies were carried out on FLG. By selective image reconstruction from the inverse power spectrum of the TEM images, it was possible to elucidate the inter-grain connectivity of few-layer graphenes. It was determined that there were two possible inter-grain configurations possible; specifically an overlap of graphene layers or a discrete atomic bonding edge. The perturbation of the few-layer structure when subject to an out of plane distortion was found to incur a shift in the conventional AB-Bernal stacking of FLG. By utilising the aberration corrected TEM (AC-TEM) at Oxford it was possible to resolve atomic detail in CVD synthesised monolayer films, including atomic bond rotations and vacancies. The use of a high current density at low accelerating voltage (80 kV) was demonstrated to allow for the controlled defect creation in graphene sheets. This permitted the creation of monovacancies and iron doped vacancy complexes suitable for further study. The behaviour of these two defect types under electron beam irradiation was subsequently studied.

This thesis aims to measure the mechanical properties of ceramics on the microscale using microcantilever beams. Focussed Ion Beam milled triangular cross-sectional beams (approximately 3 x 5 x 20µm) were fractured using a nanoindenter to measure the Young’s modulus, fracture strength, and fracture toughness. By developing the technique with a sapphire bicrystal, it was found that the mechanical properties could be successfully ascertained if correction factors were used. Experiments and theoretical work showed that sapphire and polycrystalline alumina beams undergo moisture assisted sub-critical crack growth when tested in air. Whilst corrections for the Young’s modulus have been previously reported, this is the first reported attempt to correct for the notch tip residual stress and the first to consider sub-critical crack growth. Once these factors were characterised using the sapphire bicrystal, the technique was applied to a range of different ceramics, such as polycrystalline α-alumina and silicon nitride. These are the first reported direct measurements the grain boundary toughness of these ceramics using microcantilever beams. The grain boundary toughness was correlated with the macroscopic fracture properties and the characteristics of the ceramic (grain boundary composition, impurities, and fracture mode). Two grades of α-alumina were used and the macro- and micro-scale properties extensively compared. The damage evolution during uniaxial compression of alumina was investigated in depth, and compared to a previous reported microcrack evolution model using the measured grain boundary toughness. Investigation of whether deformation twins formed during loading was undertaken and the phenomenon was shown to not occur.

This project considers the co-rotating twin screw extrusion of a confectionery paste comprising powdered proteins, sugars, water and fats. As is the case with many food industry products, this process has been developed experimentally with little quantitative understanding of how variations in processing conditions influence the formation of the extrudate. A variety of techniques have therefore been developed to characterise and quantify the dispersive mixing, distributive mixing and rheological flow properties of this complex, multiphase, viscoelastic, unstable material. These techniques have then been utilised in a pilot plant extruder study of the mechanics of mixing and paste formation during extrusion, considering the influence of both processing conditions and screw profile. The internal evolution of paste microstructure has been successfully tracked along the length of screw profile using dead-stop extractions of the screws. A rigorous off-line assessment of shear yield strength behaviour using cone penetrometry has shown the use of conventional off-line rheometers to be unviable due to rapid post extrusion hardening. This highlighted the need for an in-line rheological measurement technique for continuous extrusion analysis where the extruded material is severely time dependent and not extractable. In pursuit of this, a novel arrangement of bender elements is proposed and trialled, to rapidly characterise material parameters of viscoelastic pastes. A second technique looking to extend the application of shear wave interface reflection to multiphase pastes is also trialled. A novel analysis of thermogravimetric data (TGA) has generated a viable index of distributive mixing, suitable for use on complex multi-component materials where thermal decomposition temperatures of the components are not well defined. Quantitative image analysis of pastes using scanning electron microscopy (SEM), optical microscopy protein staining and a novel application of multiphoton microscopy (MPM) have been used to visualise paste microstructure and quantify dispersive mixing. From the pilot plant extruder study, the application of these techniques was successful in mapping the evolution of paste mixing and the resulting microstructure, as well as identifying key differences between pastes mixed by twin screw extrusion and batch mixing.

This thesis presents an investigation of the dynamic properties of wide range of interfacial systems, from colloidal particles in solution, through the realm of aerosols and onto studies of molecular adsorption at an interface. The primary experimental technique utilized is optical tweezers. An exploration of the history of the use of radiation pressure to manipulate matter is presented, followed by an introduction to how optical tweezers work. Some of the more advanced methods of tweezing are discussed, with an emphasis on the use of spatial light modulators (SLMs) to realise dynamic holographic optical tweezers (DHOTs), an example of which has been constructed within our laboratory using off-the-shelf optical components, and combined with a spectrometer to facilitate high resolution spectroscopic studies of microscopic systems. The spectroscopic analysis of microparticles is greatly enhanced by optical feedback generated when the wavelength of light utilized is an integer number of wavelengths around the circumference of the microsphere. Enhanced signal occurs at these wavelengths, termed whispering gallery modes (WGMs). The absolute position of these resonances depends strongly upon the shape, size and refractive index of the particle, and is predicted by Mie theory. A discussion of the concepts behind Mie theory, as well as how to use an experimental WGM spectrum to deduce the size and composition of a microparticle, is provided. This technique is then put to use in a detailed study on the properties of single aerosols, comprised of sodium chloride solution, and generated using a handheld medical nebulizer. Studies have been carried out on both evaporating and growing droplets trapped with a Gaussian beam; in the latter case, periods of size stability are observed, owing to resonant absorption of radiation at the trapping laser wavelength. The SLM can be used to change the trapping laser to a Laguerre-Gaussian (LG) mode, and an investigation of how this affects the dynamics of the droplet is presented. It is found that the use of LG modes with $ellgeq10$ produced Raman spectra with significantly more intense WGMs, and also suppressed droplet evaporation. Through observations made with fluorescent polystyrene microspheres, it is argued that the LG modes are more efficient at coupling into WGMs of the droplets. Leading on from these experiments on salt water droplets, experiments have been conducted using ionic liquids (ILs). These fluids have many fascinating properties and potential applications. The optical trapping of droplets comprised of aqueous solutions of the ionic liquid ethylammonium nitrate (EAN) and water has been demonstrated for the first time. These droplets are analysed spectroscopically by illuminating them with the output from a broadband LED; WGMs that are observed in the backscattered light are used to determine their size and composition. The response of the droplets to conditions of varying relative humidity has also been investigated. In order to characterise the relative humidity experienced by both the salt water and IL droplets, the concentration of water vapour within the trapping cells has been measured using diode laser absorption spectroscopy. The spatially modulated laser beam is then utilized in a different fashion; instead of optically tweezing a sample, a low numerical aperture objective lens is utilized to focus the laser onto the surface of a gold coated microscope slide. When a colloidal sample is placed on this surface, the thermal gradients cause the particles to form two dimensional crystals. The SLM is utilized to form multiple nucleation sites, and the dynamics of the crystals are directly observed in real time using video microscopy. It is found that grain rotation-induced grain coalescence (GRIGC) occurs, with the rotation of both crystals before coalescence. Control over the grain size is achieved by altering the separation of the laser spots, and shows that the time scale for grain boundary annealing in our system is in good agreement with theoretical expressions formulated for nanocrystal growth. Finally, as a complimentary technique to the microparticle spectroscopy previously discussed, a bulk interface is probed by using evanescent wave broadband cavity enhanced absorption spectroscopy (EW-BBCEAS) specifically to study the adsorption of cytochrome c (cyt c) to a fused silica surface. Visible radiation from a supercontinuum source is coupled into an optical cavity consisting of a pair of broadband high reflectivity mirrors, and a total internal reflection (TIR) event at the prism/water interface. Aqueous solutions of cyt c are placed onto the TIR footprint on the prism surface and the subsequent protein adsorption is probed by the resulting evanescent wave. The time integrated cavity output is directed into a spectrometer, where it is dispersed and analysed. The broadband nature of the source allows observation of a wide spectral range (ca 250 nm in the visible). The system is calibrated by measuring the absorption spectra of dyes of a known absorbance. Absorption spectra of cyt c are obtained for both S and P polarized radiation, allowing information about the orientation of the adsorbed protein to be extracted.

Reduced-activation ferritic steels are considered as the primary candidate materials for structural applications within nuclear fusion power plants. It is known that by mechanically alloying ferritic steel powder with Y (usually in the form of Y₂O₃) then consolidating the material by hot isostatic pressing, a nanoscale dispersion of oxygen rich nanoclusters as small as ~2nm is introduced into the microstructure. This vastly improves high temperature strength and creep resistance, and the nanoclusters also act as trapping sites for helium and point defects produced under irradiation. In this thesis, the evolution of the oxide nanoclusters in a Fe-14Cr-2W-0.3Ti & 0.3Y₂O₃ ODS alloy was investigated primarily using atom probe tomography. The microstructure was characterised at various points during processing to give an insight into the factors influencing the formation of the nanoclusters. It was found that the nanoclusters nucleated during the mechanical alloying stage, then followed near classical nucleation and growth mechanisms keeping the same composition of ~8%Y, ~12%Ti,~25%O and ~45%Cr throughout. The formation and evolution of 5-15nm grain boundary oxides was also observed, and these were shown to form first as Cr₂O₃ particles that subsequently transform into a Y-Ti-O based oxide on further processing. The influence of mechanical alloying with 0.5wt.%Fe₂Y rather than 0.3wt.%Y₂O₃ was also investigated, and this showed that there was no difference in the final microstructure produced provided the level of Ti in the starting powder was tightly controlled. Without sufficient Ti, the nanoclusters were Y-O based and ~6nm diameter. Both the Y-O and Y-Ti-O nanoclusters were moderately stable on annealing at 1200°C for up to 100 hours, with only minimal coarsening observed. Ti was found not to influence the coarsening rate of the nanoclusters significantly. The stability of the oxide nanoclusters under irradiation was investigated by using Fe²⁺ ion irradiation to simulate displacement cascade damage in the ODS-Eurofer material (the official European candidate material for testing in the ITER fusion test reactor). Doses up to ~6 dpa at 400°C were used, and there was no significant change to the nanocluster distribution. However segregation of Mn to dislocations was observed after irradiation. These results indicate that ODS steels are good candidate structural materials, as the microstructure is stable at high temperature and under irradiation. The starting powders, and processing parameters need to be tightly controlled in order to produce the optimal material for use in service.

Degenerative disorders of the rotator cuff tendons account for nearly 75% of all shoulder pain, causing considerable pain and morbidity. Given the strong correlation between age and tendinopathy, and unprecedented population aging, these disorders will become increasingly prevalent. Improved understanding of tendon degeneration will guide the development of future diagnostic and treatments, and is therefore urgently needed. However, the aetiology and pathology of rotator cuff tendinopathy remain unclear. The complicated mechanical environment of the rotator cuff is hypothesised to influence the susceptibility of the tendons to degeneration and tearing. Studies have reported biological adaptations in torn cuff tendons indicative of increased compressive loading within the tendon. The material adaptations of healthy and degenerative cuff tendons are largely unreported but will provide further insight into the role of the mechanical environment in rotator cuff aetiology and pathology. This thesis examined the material adaptations of healthy and diseased tendons to explore the role of mechanical loading in rotator cuff pathology. The material adaptations of healthy animal tendons, and healthy and delaminated human cadaveric rotator cuff tendons, in response to different loading environments were characterised. The effects of age, tears, steroid injection and subacromial decompression surgery on the structural adaptations of human cuff tendons were also studied, as was the effect of tendon cell proliferation on the mechanical properties and degradation behaviour of collagen scaffolds. Loading environment significantly affected the structural adaptations of healthy tendons. Regions exposed to compressive and shear strains exhibited thinner fibres, shorter crimp lengths and thinner, less aligned fibrils compared with regions exposed to tensile strains alone. In healthy rotator cuff tendons, the inhomogeneous loading environment produced topographically inhomogeneous structural adaptations. The tendons of a delaminated rotator cuff exhibited less topographical variation in properties and thinner, less aligned fibrils compared with healthy cuff tendons. Torn cuff tendons exhibited thinner fibrils and shorter crimp lengths compared with control samples. These adaptations were identifiable early in the disease progression, and neither steroid injection nor subacromial decompression surgery significantly influenced these adaptations at seven weeks post‐treatment. Significant correlations between decreasing dimensions and increasing tear size were found when age was included as a confounding factor, reflecting the importance of age and tear size in determining the material properties of tendons. Tendon cell proliferation influenced the mechanical properties and degradation behaviour of the collagen scaffolds, emphasising the integral role of cells in the functional adaptation of biological materials. These results demonstrate the effect of mechanical environment on the material adaptations of tendons. They also indicate the importance of the complicated mechanical environment experienced by the rotator cuff tendons in predisposing the tendons to degeneration and tearing. The observed material adaptations of degenerative and torn tendons suggest that rotator cuff pathology is associated with increased levels of compressive and/or shear strains within the tendon. These changes begin early in the disease progression and neither steroid injection nor sub‐acromial decompression surgery are capable of reversing the changes in the timeframe investigated. These findings highlight the urgent clinical need for pre‐rupture diagnostic techniques for the detection of early pathological changes in the rotator cuff. They also emphasize the requirement for new intervention strategies that restore the healthy mechanical environment and reverse early pathological adaptations in order to prevent catastrophic failure of the tendons.

Previous attempts to produce carbon nanotube (CNT) ceramic composites have resulted in poorly dispersed, unaligned and non-continuous CNTs in the composites with modest improvements in properties. The research presented in this thesis pertains to the production of dense aluminoborosilicate (ABS) glass matrix composites containing aligned and continuous multi-walled carbon nanotubes (MWCNT) of millimetre lengths. This was achieved by infiltrating CVD grown MWCNT preforms using a precursor sol and sintering which achieved 80 ± 2&percnt; dense composites. Focused ion beam milling together with image analysis showed that the composites contained 20 ± 2 vol.&percnt; MWCNTs, which are aligned and continuous within the glass matrix. Indentation studies showed greater damage tolerance in the composite compared to unreinforced ABS glass. Under compression, there is no significant change in the compressive strength between the composite and the unreinforced glass. The bend strength of microcantilever beams were 1.4 to 1.3 GPa for the composite and glass respectively. Elastic modulus of 84 GPa and fracture toughness (KIC) of up to 2.4 MPa √m were obtained for the composite. The elastic modulus and fracture toughness results are an improvement of 30 &percnt; and 240 &percnt; over that of unreinforced ABS glass. Fracture surfaces showed apparent MWCNT pullout lengths of up to &Tilde; 1 μm. Analysis indicates that crack bridging by intact MWCNTs provides the majority of the improvement in fracture toughness. Interlayer sliding of the MWCNTs and "sword in sheath" failure mechanism of the MWCNTs prevented the maximum potential performance, with respect to elastic modulus and fracture toughness, from being achieved. Electrical conductivity in the alignment direction of the CNTs showed improvements by a factor of 10E6 compared to unreinforced ABS glass. Furthermore, improvement of a factor of &Tilde; 10 in the thermal conductivity was obtained for the composite over that of ABS glass.

Austenitic stainless steels are frequently used in the cooling circuits of nuclear reactors. It has been found that cold-worked 304 stainless steels can be particularly susceptible to stress corrosion cracking at the operating conditions of such reactors. Despite more than 130 years of research underlying mechanisms are still not properly understood. For this reason, the effects of cold-work and applied stress on the oxidation behaviour of 304SS have been studied in this thesis. A set of samples with/without prior cold-work, and with/without stress applied during oxidation, were oxidized in autoclaves under simulated pressurised water reactor primary circuit conditions. Atom-probe tomography and analytical transmission electron microscopy were used to investigate the local chemistry and microstructure in the different samples tested. Regions containing grain boundaries, deformation bands, and matrix material in contact with the environment, were extracted from the coupon specimens with a focused ion beam machine. Cross-sections of crack tips were studied with secondary ion mass spectrometry and electron backscatter diffraction. The compositions of oxides grown along the surface and the different microstructural features were analysed. Fe-rich spinels were found at the surface and Cr-rich spinels were observed along fast diffusion paths. Ni-enrichment was found at the metal/oxide interfaces and a Ni-rich phase was detected in precipitates ahead of grain boundary oxides. Li was observed in all oxidised regions and B segregation, originating from impurities in the alloy, was observed in grain boundaries and crack tip oxides. Cavities and hydrogen associated with Ni-rich regions were found ahead of the bulk Cr-rich oxide in some of the samples. The implications of these findings for the understanding of SCC mechanisms are discussed. It is suggested that Ni precipitation as well as the presence of deformation bands may play an important role in controlling SCC susceptibility in 304 stainless steel. A modification of the film-rupture model including internal oxidation and fast diffusion along H-stabilised vacancies in strain fields at the crack front is proposed.

Nanomaterials have attracted great interest due to the unique physical properties and great potential in the applications of nanoscale devices. Two dimensional atomic crystals, which are atomic thickness, especially graphene, have triggered the gold rush recently due to the fascinating high mobility at room temperature for future electronics. The crystal structure of nanomaterials will have great influence on their physical properties. Thus, this thesis is focused on developing the methods to control the crystal structure of nanomaterials, namely quantum dots as semiconductor, boron nitride (BN) as insulator, graphene as semimetal, with low cost for their applications in photonics, structural support and electronics. In this thesis, firstly, Mn doped ZnSe quantum dots have been synthesized using colloidal synthesis. The shape control of Mn doped ZnSe quantum dots has been achieved from branched to spherical by switching the injection temperature from kinetics to thermodynamics region. Injection rates have been found to have effect on controlling the crystal phase from zinc blende to wurtzite. The structural-property relationship has been investigated. It is found that the spherical wurtzite Mn doped ZnSe quantum dots have the highest quantum yield comparing with other shape or crystal phase of the dots. Then, the Mn doped ZnSe quantum dots were deposited onto the BN sheets, which were micron-sized and fabricated by chemical exfoliation, for high resolution imaging. It is the first demonstration of utilizing ultrathin carbon free 2D atomic crystal as support for high resolution imaging. Phase contrast images reveal moiré interference patterns between nanocrystals and BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes using a newly developed equation method. Double diffraction is observed and has been analyzed using a vector method. As only a few microns sized 2D atomic crystal, like BN, can be fabricated by the chemical exfoliation. Chemical vapour deposition (CVD) is as used as an alternative to fabricate large area graphene. The mechanism and growth dynamics of graphene domains have been investigated using Cu catalyzed atmospheric pressure CVD. Rectangular few layer graphene domains were synthesized for the first time. It only grows on the Cu grains with (111) orientation due to the interplay between atomic structure of Cu lattice and graphene domains. Hexagonal graphene domains can form on nearly all non-(111) Cu surfaces. The few layer hexagonal single crystal graphene domains were aligned in their crystallographic orientation over millimetre scale. In order to improve the alignment and reduce the layer of graphene domains, a novel method is invented to perform the CVD reaction above the melting point of copper (1090 ºC) and using molybdenum or tungsten to prevent the balling of the copper from dewetting. By controlling the amount of hydrogen during the growth, individual single crystal domains of monolayer over 200 µm are produced determined by electron diffraction mapping. Raman mapping shows the monolayer nature of graphene grown by this method. This graphene exhibits a linear dispersion relationship and no sign of doping. The large scale alignment of monolayer hexagonal graphene domains with epitaxial relationship on Cu is the key to get wafer-sized single crystal monolayer graphene films. This paves the way for industry scale production of 2D single crystal graphene.

The ability of RNA bases to self-assemble into larger structures is an important research area relevant to the origins of life. In the RNA helix the bases are arranged on a sugar-phosphate carcass but it has been suggested that the initial ordering could form on a flat surface. This thesis is an attempt to establish experimentally whether the complementary RNA bases, adenine and uracil, have the ability to self-assemble into large ordered structures when adsorbed on metal and mineral surfaces. The Au (111) surface was chosen as a preferred substrate as it is flat, relatively free of defects, chemically inert and reconstructs in a characteristic pattern of corrugation lines, which provide a reference for crystallographic directions. Six of the molecular phases shown were observed for the first time with molecular resolution and the possible two-dimensional arrangements of adenine and uracil molecules for these phases are proposed. The pure adenine and pure uracil structures have chiral unit cells and in the case of pure uracil alternating monochiral domains within the polychiral islands are created. Well-ordered intricate uracil-adenine bimolecular networks were also observed. The self-assembly of both uracil and adenine appears to be weakly influenced by the surface crystallography. The (100) surface of the mineral pyrite (FeS₂) was chosen as the alternative substrate as it is the most common face that occurs naturally in pyrite crystals. The experiments show the formation of small adenine and uracil crystals at the terrace edges. Neither uracil nor adenine were observed to form a monolayer on the surface of the terraces. The results of the experiments described in this thesis are very interesting in terms of establishing the possible mechanisms for creating regular chiral molecular networks and provide a useful insight into the role of surfaces in the processes of self-assembly of RNA bases.

This thesis presents information on the subcellular localisation of two important trace elements, selenium and arsenic, in wheat, rice and rice roots for what is believed to be the first time. The general aim of this work was to illustrate the potential of using physical science techniques to solve biological problems. High resolution secondary ion mass spectrometry was undertaken using the CAMECA NanoSIMS50 with a sensitivity down to ppm concentrations and a lateral resolution of less than 100 nm. Selenium in wheat grain was found to be distributed across both the bran layer and the endosperm region with Se-rich hotspots found in the aleurone cells and a higher intensity of Se in the subaleurone region. Arsenic in rice grain was found in two key regions. In grains with high As and high dimethylarsinic acid (DMA) content, As was predominantly localised to the subaleurone region yet in lower concentration, hydroponically grown As(III)-treated grains the As was only localised to the aleurone layer near the ovular vascular trace (OVT). A combined NanoSIMS and S-XRF experiment revealed As hotspots near the OVT. A combination of high pressure freezing, high resolution secondary ion mass spectrometry and TEM was used to localise As in the roots of rice plants revealing a contrasting subcellular distribution of As and Si in the roots even though arsenite and silicic acid are transported across the plasma membranes by the same transporters. Fe plaque forms only on the root epidermis and was shown to be a strong sink for As. Colocalisation of S with As in the vacuoles of the endodermis, pericycle and xylem parenchyma supports the notion that As is stored as arsenite-phytochelatin complexes in the roots while Si is localised in the endodermis cell walls and is not strongly affected by the Lsi2 mutation.

Semiconductor nanostructures have attracted great interest owing to their unique physical properties and potential applications in nanoscale functional devices. The enhancement of the physical properties of semiconductor nanostructures and their performance in devices requires a deeper understanding of their fundamental microstructural properties. Thus this thesis is focused on the experimental and theoretical studies of the microstructural properties of two important semiconductor nanostructures: axial heterostructured silicon nanowires with varying doping and indium nitride colloidal nanoparticles. In this thesis, axial heterostructured silicon nanowires with varying doping were synthesized on an oxide-removed Si{111} substrate using a vapour-liquid-solid approach. Their fundamental microstructural properties, including the crystalline structure, wire growth direction and morphologies, were studied using various characterization techniques. It is found that a very small fraction of the silicon nanowires crystallize in a hexagonal (wurtzite) phase, which is thermodynamically unstable in bulk silicon under ambient conditions, while a large majority of the synthesized silicon nanowires exhibit the expected diamond cubic crystalline structure. About 75% of the diamond cubic silicon nanowires synthesized grow in a single <111> direction, while the rest contain growth-related kinks, where the nanowire switches to another direction during the growth. The ~109° silicon nanowire kinks are the most commonly observed, and the growth direction before and after such ~109° kink are both <111>. The sidewalls of silicon nanowires do not change abruptly at the ~109° kink, but exhibit an elbow-shaped structure. It is also found that the nanowire sidewalls exhibit periodic nanofaceting, which is strongly doping-dependent. The nanofaceting is found to occur during the enhanced sidewall growth that arises when the diborane dopant gas is introduced. A thermodynamic model predicting the dependence of nanofacet period on the wire diameter is developed. Another semiconductor nanostructure studied in this thesis is indium nitride colloidal nanoparticles, which were grown using a solution-phase chemical method. The formation of such indium nitride colloidal nanoparticles is confirmed by studying their compositions, crystalline structures and shape using various electron microscopy techniques. The size of the indium nitride colloidal nanoparticles was controlled by varying the time of solution-phase reactions. The most probable size of the colloidal nanoparticles increases and the size distribution broadens with the increase of reaction time. The crystalline structures of the indium nitride colloidal nanoparticles are found to be particle size dependent. The observed dependence of the band gap blueshift of the indium nitride colloidal nanoparticles on the reaction time (hence the particle size) is explained by the quantum-size effect.

Solid state chemical storage of hydrogen in metals offers promising advantages over compressed hydrogen gas and condensed liquid hydrogen, especially for mobile applications with respect to safety and energy efficiency. However, no single metal hydride simultaneously satisfies the essential performance criteria for onboard hydrogen storage namely, high gravimetric and/or volumetric energy density, fast kinetics and favorable thermodynamics. Recently, a breakthrough achievement was made by the development of reactive hydride composites in which two metal hydride systems (e.g. NaBH4 and MgH2) are mixed together resulting in better sorption properties than the individual pure systems. In this approach, the formation of MgB2 by exothermic reaction destabilizes the composite and consequently reduces the overall enthalpy and sorption temperature of the endothermic desorption reaction. In this work the thermodynamic and kinetic properties of reactions in 2NaH + MgB2 + 4H2 ↔ 2NaBH4 + MgH2 and 3NaH + MgB2 + 4H2 ↔ 2NaBH4 + NaMgH3 were established using multiple experimental techniques like volumetric measurements, ex-situ and in-situ X-ray diffraction, calorimetry, and especially electron microscopy. Under the applied experimental conditions of 50 bar hydrogen and 400 °C during the hydrogenation of 2NaH + MgB2 and 0.1 bar hydrogen and 450 °C during the dehydrogenation of 2NaBH4 + MgH2, both reactions were kinetically limited and proceeded in multisteps. The absorption reaction was partial, being restricted by the unexpected formation of NaMgH3 which limits the formation of NaBH4 while the desorption reaction was complete and limited by the growth of MgB2 through some intermediate complexes at the Mg/NaBH4 interface where the intermediate phase forms a barrier to diffusion. Conversely, in the 3NaH + MgB2 system, absorption in 100 bar hydrogen and 300 °C was complete but slow, while in the 2NaBH4 + NaMgH3 system, complete desorption was achieved in multisteps under 0.1 bar hydrogen and 450 °C. The formation of intermediate and stable complexes during these reactions poses a significant restraint to hydrogen sorption reactions. However, lower onset sorption temperatures have been established in these systems than in the pure compounds due to their simultaneous destabilization in the composite state. This study have demonstrated the complexity of desorption and absorption mechanisms in these composite systems and the difficulty of obtaining such reactions at low temperatures required for mobile applications. This understanding of the rate limiting reaction steps in reactive hydride composites provides the basis for further optimization of these materials for efficient hydrogen storage applications.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful technique for the analysis of organic surfaces and interfaces for many innovative technologies. However, despite recent developments, there are still many issues and challenges hindering the robust, validated use of ToF-SIMS for quantitative measurement. These include: the lack of metrology and fundamental understanding for the use of novel cluster primary ion beams such as C60n+ and Ar2000+; the need for validated and robust measurement protocols for difficult samples, such as those with significant micron scale surface topography; the lack of guidance on novel data analysis methods including multivariate analysis which have the potential to simplify many time-consuming and intensive analyses in industry; and the need to establish best practice to improve the accuracy of measurements. This thesis describes research undertaken to address the above challenges. Sample topography and field effects were evaluated experimentally using model conducting and insulating fibres and compared with computer simulations to provide recommendation to diagnose and reduce the effects. Two popular multivariate methods, principal component analysis (PCA) and multivariate curve resolution (MCR), were explored using mixed organic systems consisting of a simple polymer blend and complex hair fibres treated with a multi-component formulation to evaluate different multivariate and data preprocessing methods for the optimal identification, localisation and quantification of the chemical components. Finally, cluster ion beams C60n+ and Ar500-2500+ were evaluated on an inorganic surface and an organic delta layer reference material respectively to elucidate the fundamental metrology of cluster ion sputtering and pave the way for their use in organic depth profiling. These studies provide the essential metrological foundation to address frontier issues in surface and nanoanalysis and extend the measurement capabilities of ToF-SIMS.

Microscopic beams of penetrating synchrotron radiation provide a unique tool for the analysis of material structure and deformation. This thesis describes my contributions to the development of new synchrotron X-ray micro-beam diffraction experimental techniques and data interpretation, and the use of experimental results for the validation of material deformation models. To study deeply buried material volumes in thick samples, the micro-beam Laue technique was extended to higher photon energies. Through-thickness resolution was achieved either by a wire scanning approach similar to Differential Aperture X-ray Microscopy (DAXM), or by applying tomographic reconstruction principles to grain-specific Laue pattern intensity. Both techniques gave promising first results. For reliable micro-beam Laue diffraction measurements of elastic strains in individual grains of a polycrystal, understanding of the error sources is vital. A novel simulation-based error analysis framework allowed the assessment of individual contributions to the total measurement error. This provides a rational basis for the further improvement of experimental setups. For direct comparison of experimental measurements and dislocation dynamics simulations, diffraction post-processing of dislocation models in two and three dimensions was developed. Simulated diffraction patterns of two-dimensional dislocation cell/wall type structures captured correctly some of the features observed experimentally in reciprocal space maps of a large-grained, lightly deformed aluminium alloy sample. Crystal lattice rotations computed from three-dimensional dislocation dynamics simulations of a Frank-Read source showed anisotropic orientation spread similar to that observed in micro-beam Laue experiments. For the experimental study of crystal lattice distortion, a novel technique was proposed that combines micro-beam Laue diffraction with scanning white-beam topography. Diffraction topography allows the study of lattice rotation at scales smaller than the scanning beam size. The new technique makes it possible to apply classical topography methods to deformed samples.

The factors controlling the reliability of Pb-free solders when subject to thermomechanical regimes relevant to the harsh aerospace environment have been studied. Ball grid array (BGAs) typical of microelectronic devices have been manufactured in-house and subjected to isothermal ageing and thermal cycling. The BGAs comprised both Cu and Ni-Au metallizations, Pb-free Sn-Ag-Cu 400 and 600μm solder balls, FR4 and Al2O3 boards, and included circuits to measure resistance changes due to damage in the joints during thermal cycling. Microstructural evolution within the solders balls and complex interfacial reactions were studied in all configurations using various types of electron microscopy. The mechanical properties of the different phases formed within solder joints were studied using nanoindentation at room and elevated temperatures up to 175°C for the first time. Intermetallic compounds (IMCs) were stiff, hard and brittle with very low creep rates, while the softer primary Sn, eutectic regions and Cu metallization readily underwent creep. Two-dimensional finite element analysis (FEA) of nanoindentation was used to understand better the physical meaning of nanoindentation creep data. Reliability experiments comprised both thermal cycling and FEA of BGAs. The difference in coefficient of thermal expansion (CTE) in the BGA materials caused interfacial fatigue damage in the solder joints, which was detected primarily at the solder/metallization interface of the outermost, most strained solder joint. Accumulated creep strain per cycle at this interface was evaluated using 3D FEA of the stress-strain state of the BGA and results calibrated against experimental BGA mean lifetimes using the Coffin-Mason relationship. Nanoindentation combined with FEA has been shown to be a viable route for the rapid assessment of creep performance and lifetime in lead-free solders under aerospace thermal cycles.

The initiation and high resolution control of surface confined chemical reactions would be both beneficial for nanofabrication and fundamentally interesting. In this work, spatially controlled scanning probe directed organometallic coupling, patterned functional protein immobilisation and highly localised reversible redox reactions on SAMs were investigated. Catalytically active palladium nanoparticles were mounted on a scanning probe and an appropriate reagent SAM was scanned in a reagent solution. This instigated a spatially resolved organometallic coupling reaction between the solution and SAM-phase reagents. Within this catalytic nanolithography a spatial resolution of ~10nm is possible, equating to zeptomole-scale reaction. The methodology was applied to reactions such as Sonogashira coupling and local oligo(phenylene vinylene) synthesis. By altering the experimental protocols, relating probe scan velocity to reaction yield and characterising the nanopattern, a PVP matrix model describing a proposed mechanism of catalytic nanolithography, was presented. Though ultimately limited by probe deactivation, calculations indicated that activity per immobilised nanoparticle is very high in this configuration. For biopatterning, surface nanopatterns defined by carboxylic functionality were generated from methyl-terminated SAMs by local anodic oxidation (LAO) initiated by a conductive AFM probe. By employing suitable linker compounds, avidin and Stefin-A quadruple Mutant (SQM) receptive peptide aptamers were patterned at sub-100nm resolution. The multiplexed sensing capability of an SQM array was demonstrated by reacting generated patterns with single or a mixture of multiple antibodies. The reversible redox conversion and switching of reactivity of hydroquinone-terminated SAMs was electrochemically demonstrated prior to an application in redox nanolithography. In this methodology, spatially controlled probe-induced in situ "writing" and "erasing" based on reversible redox conversion were conducted on hydroquinone terminated SAM. In combination with dip-pen nanolithography, a novel method of redox electro-pen nanolithography was designed and the method’s application for lithography was examined.

This thesis describes the design, manufacture and characterisation of thick vacuum plasma sprayed tungsten (W) coatings on steel substrates. Fusion is a potentially clean, sustainable, energy source in which nuclear energy is generated via the release of internal energy from nuclei. In order to fuse nuclei the Coulomb barrier must be breached - requiring extreme temperatures or pressures – akin to creating a ‘star in a box’. Tungsten is a promising candidate material for future fusion reactors due to a high sputtering threshold and melting temperature. However, the large coefficient of thermal expansion mismatch with reactor structural steels such as the low activation steel Eurofer’97 is a major manufacturing and in-service problem. A vacuum plasma spraying approach for the manufacture of tungsten and tungsten/steel graded coatings has been developed successfully. The use of graded coatings and highly textured 3D interface surfi-sculpt substrates has been investigated to allow the deposition of thick plasma sprayed tungsten coatings on steel substrates. Finite element models have been developed to understand the residual stresses that develop in W/steel systems and made use of experimental measurements of coating thermal history during manufacture and elastic moduli measured by nano-indentation. For both the graded and surfi-sculpt coating, the models have been used to understand the mechanism of residual stress redistribution and relief in comparison with simple W on steel coatings, particularly by consideration of stored strain energy. In the case of surfi-sculpt W coatings, the patterned substrate gave rise to regular stress concentrating features, and allowed 2mm thick W coatings to be produced reproducibly without delamination. Preliminary through thickness residual stress measurements were compared to model predictions and provided tentative evidence of significant W coating stress relief by regulated coating segmentation.

Hardness measurements and Three-Dimensional Atom Probe (3DAP) were used to characterize the early stages of precipitation in three different Al-Mg-Si alloys (Al-0.50 wt%Mg-1.00 wt%Si) with different Cu contents (0.03 wt%, 0.15 wt%, or 0.80 wt% Cu). Heat treatments were chosen to simulate an industrial production line for car body-sheet material and included natural ageing (NA), pre-ageing at 80 °C (PA), paint-bake ageing at 180 °C (PB) and 10 second ageing at 180 °C (spike). The Cu content and the chosen heat treatments were found to influence the microstructural evolution of the alloy considerably. Based on the determined microstructures and matrix solute concentrations, mechanisms for the effect of NA, PA and Cu additions were proposed. NA had a deleterious effect on the PB hardening response, which was delayed dramatically after 20 minutes NA or longer. When the NA time was 1 minute, β" precipitates were formed within 30 minutes PB resulting in high hardness of the alloy. The delay with NA time was caused by a decrease in the nucleation rate of elongated precipitates during the subsequent PB. This decrease was thought to be due to a combination of a decrease in the matrix solute concentrations and clusters acting as vacancy sinks. PA before NA improved the PB response due to the formation of a high density of short elongated precipitates. Small Mg-Si clusters were detected after both NA and PA. Clusters formed during PA were found to be, on average, Mg-richer and larger than those formed during NA. Larger clusters were found to be more stable during PB and, upon PB, to grow into nucleation sites for elongated precipitates. Application of a spike before PA resulted in faster growth of clusters during PA. Growth of clusters and nucleation of short elongated precipitates during PB was found to be enhanced with increasing Cu content when no PA was given. Cu was found to be present in all precipitates and clusters in the alloy with the highest Cu content. These precipitates were thought to be precursors to the Q' phase.

This thesis is comprised of two closely related studies of fullerenes. The first part is an investigation of C60 and C70 nanocrystals using both experimental and simulated electron energy loss (EEL) spectra. Through a detailed comparison of particular features in EEL spectra collected from these materials in a transmission electron microscope, with simulated spectra, it is established that differences in spectra from different materials can be linked to particular aspects of the structural models. For example, in the case of C60 differences in experimental spectra from different samples can be linked to differences in the bond lengths within the molecules of different samples. In the case of C70, it is found that features within the spectrum which have previously been attributed to the ten equatorial atoms do not have this origin in a crystal. The second part is an experimental investigation of endohedral fullerenes Nd@C82 and Sc3N@C80. The effect of temperature on the EEL spectrum is investigated and, in the case of Nd@C82, the effect of the presence of different isomers is also investigated. Spectra are successfully obtained from the encapsulated atoms, and the importance of careful experiments in terms of avoiding contamination is highlighted.