A scalable spray processing technique was used to fabricate carbon nanotube (CNT)-based film electrodes and solid-state supercapacitors. The sprayed CNT-based electrodes comprised a randomly interconnected meso-porous network with a high electrical conductivity. Layer-by-layer (LbL) deposition of functionalised and oppositely charged single-wall carbon nanotubes (SWNTs) increased the electrode density and improved charging and discharging kinetics when compared with carboxylic functionalised only SWNT electrodes. The capacitance was further increased to 151 F g-1 at 2 mV s-1 and 120 F g-1 at 100 mV s-1 after vacuum and H2 heat treatments that removed the functional groups, and resulted in a hybrid microstructure of SWNTs and multi-layer graphene sheets from unzipped SWNTs. Flexible solid-state supercapacitors were fabricated by directly spraying multi-wall carbon nanotube (MWNT)-based aqueous suspensions onto both sides of a Nafion membrane and dried. A single cell with MWNT-only electrodes had a capacitance of 57 F g-1 per electrode at 2 mV s-1 and 44 F g-1 at 150 mV s-1. Cells with MWNT/ionomer electrodes showed a higher H+ mobility and a lower charge transfer resistance, and the capacitance increased to 145 F g-1 at 2 mV s-1 and 91 F g-1 at 150 mV s-1. Finally, MWNT/TiO2 nanoparticle/ionomer hybrid electrodes were used in the same solid-state supercapacitor configuration and provided a capacitance of 484 F g-1 per electrode at 5 mV s-1 and 322 F g-1 at 100 mV s-1. A qualitative model of the charge storage mechanism was developed, where TiO2 promoted H+ ions via redox reactions that fed protons into the proton-conducting ionomer coating over the MWNTs (in which the TiO2 was embedded), while electrons were readily conducted through the MWNT scaffold. This solid-state supercapacitor provided both attractive energy (31.8 Wh kg-1) and power (14.9 kW kg-1) densities, where such high energy density is difficult to achieve for MWNTs alone and such high power density is difficult for metal oxides alone, especially in the solid state.

This thesis presents work relating to the fabrication of novel thin film electrodes for energy storage applications, with a focus on low cost, nanostructured transition metal oxides, and electrode manufacture by atomised spray deposition. Iron oxide (FeO_x) nanowires were synthesised hydrothermally and combined with multi-walled carbon nanotubes (MWNT) in sprayed electrodes, which provided the necessary conductivity enhancement for effective energy storage. The spray processing technique allowed for facile control over the relative fraction of MWNTs in the sprayed electrodes. Optimised electrodes were investigated in a range of aqueous electrolytes, and the best energy storage behaviour occurred in Na₂SO₃ with a maximum capacitance from cyclic voltammetry of 312 Fg^-1 at a scan rate of 2 mVs^-1. The FeO_x/MWNT electrodes were investigated for their suitability as lithium-ion battery anodes and showed reasonable energy storage behaviour. Nickel oxide (NiO) electrodes were manufactured by hydrothermal synthesis and annealing followed atomised spray deposition. The performance of the NiO electrodes was enhanced though combination with aqueous graphene suspensions, produced in-house by ultrasonic exfoliation of graphite. The processing route used to combine the nanomaterials was considered and a co-synthesis route resulted in the best performing electrodes. Different substrates were investigated, as the most commonly used Ni-foam substrate reacted with the basic electrolytes necessary for electrochemical activity of NiO. NiO/graphene electrodes showed charge/discharge capacitances of up to 571 Fg^-1 at a current density of 10 Ag^-1, which was maintained at over 300 F/g at a very high current density of 100 Ag^-1. Asymmetric supercapacitor devices were constructed using various combinations of FeO_x, NiO, and commercial carbon black electrodes to extend the operating potential window beyond the ~1.23 V limit of symmetric aqueous-electrolyte devices. Power densities of over 20 kWkg^-1 were achieved for an FeO_x/MWNT-carbon device, which was comparable with current commercial carbon-only supercapacitors.

Silks are biomaterials made by spiders and silkworms, evolved for natural functions ranging from protection to predation. The research presented in this Thesis combines principles and methods from engineering, physics and biology to study the material properties of single silk fibres from a biological perspective. In particular, the factors that contribute to the variation in properties of single silk fibres are investigated. The first part of the Thesis focuses on silks made by silkworms. Whether naturally spun or forced reeled, the mechanical properties of these silks are sensitive to a range of environmental and processing conditions, such as humidity, stretching and reeling speed. The research presented in this section contributes to the understanding of how these applied conditions affect silk mechanical properties, which can be understood in terms of silk’s protein structure and biological context. The second section compares both silkworm and spider silk single fibres to other materials in terms of their sonic properties – how the materials propagate sound waves, whether following impact, or propagating vibrations. The results are discussed in the context of the silk’s natural function for impact resistance (silkworm cocoon or spider web) and vibrational signalling (spider silks). The Thesis ends with a discussion of how the presented techniques can be applied to help further our understanding of orb web function through studying spider silks. Overall, this interdisciplinary Thesis contributes to our understanding of the structure-property-function links of these fascinating biomaterials.

This work investigated the protection of mechanism of organic coatings on steel exposed to 3% sodium chloride solution at 50°C, coupled with the use of electrochemical impedance spectroscopy (EIS) to monitor progress of corrosion and degradation of coating. Unlike Walter, EIS measurement was conducted at 50°C as well as after cooling, and measurements at intermediate temperatures have been used to characterize the dependence of the process involved. The proposition that corrosion rate is controlled by the ionic resistance of an organic coating has been tested. EIS results were fitted to a model circuit and changes in the film resistance and charge-transfer resistance with temperature were analyzed to deduce activation energies for the processes involved. Surprisingly, the calculated activation energy for coating resistance is significantly lower than the activation energy for the charge transfer resistance. This suggests that ion conduction in the coating, as apparent in an AC measurement, cannot be controlling the corrosion rate. Potentiostatic pulse tests on coated metal enable iR-corrected polarization curves to be plotted at different temperatures. From this, the activation energy determined from the corrosion currents also higher matches the higher activation energy value calculated from the charge transfer resistance. However, measurements of coating resistance on free films of the same coating also generate higher activation energy values, leaving two possible models that can account for the results.

Well-logging and aerospace applications require electronics capable of withstanding elevated temperature operation. A key element of high temperature packaging technology is the Si die attach material, and a comparative study of two die attach systems for use in harsh environment has been performed. Die bond sample packages, using commercial adhesives and an Au-Si eutectic solder, have been manufactured and were subsequently thermally exposed for various times at 250 and 300°C respectively. The adhesive die bond packages comprised a high temperature co-fired ceramic (HTCC) substrate with W, Ni and Au metallisations whereas the Au-Si die bond packages used thick film Au metallised on a Al₂O₃ substrate. Optimisation of the eutectic die bonding parameters was successfully performed for the Au-Si system by an experimental design method, which improved mean and spread of maximum bonded areas and consequently, the shear load to failure. Bonded area was systematically assessed by scanning acoustic microscopy (SAM) followed by digital image analysis (DIA). Accelerated testing comprised thermal cycling and thermal shock and although showing some degradation, Au-2wt%Si die bonds were surprisingly robust, showing excellent subsequent stability during industrial device testing investigations.

This thesis provides a research into properties of nickel-based single crystal superalloys. The underlying quantitative relationship between alloy chemistry and the important properties have been studied. To design new grade of single crystal superalloys, computational modelling methods have been proposed which build on the findings of composition-microstructure-property relationships. A physical model for the creep deformation of single crystal superalloys is presented, in which the dependence of the kinetics of creep deformation on alloy chemistry is rationalised. The rate-controlling step is considered to be climb of dislocations at the matrix/particle interfaces and their rate of escape from trapped configurations. The effects of microstructural scale precipitate size, geometry and spacing are also studied. A first order estimate for the rate of creep deformation emerges from the model, which is useful for the purposes of alloy design. Three new single crystal superalloys have been isolated using theory-based computational modelling approaches, termed Alloys-By-Design methods. They are (i) an oxidation-resistant low Re-containing alloy with balanced properties, intended for general-purpose gas turbine applications; (ii) an alloy containing 5.6 wt.% Re and 2.6 wt.% Ru suitable for high performance jet engine applications, and (iii) a cheap, corrosion-resistant alloy for power generation applications. The new alloys have been manufactured using investment casting techniques, and their creep and oxidation behaviour evaluated. The multicomponent composition space pertinent to the single crystal nickel-based superalloys has been mapped and searched, by using newly developed numerical algorithms. This allowed compositions of alloys conferring the microstructures needed for optimal properties to be identified, at a resolution of 0.1 wt.%. Databases have been constructed which contain all appropriate compositions available in these systems. When coupled with composition- and microstructure-dependent property models, the databases can be searched to identify new alloys predicted to exhibit the very best properties or combinations of them.

This thesis concerns the experimental application of the technique of optical sectioning in the aberration-corrected scanning transmission electron microscope (STEM). Another aim was to perform optical sectioning experiments on the still relatively new scanning confocal electron microscope (SCEM). To test the feasibility of this technique, experiments were performed on a variety of samples to measure the achievable depth response. Deconvolution methods were explored in an attempt to further improve the depth response. Finally, some of the first optical sectioning experiments were performed in the SCEM using both elastic and inelastically scattered electrons. The results showed a clear need to investigate confocal electron microscopy due to the missing cone problem for incoherent imaging in the STEM. This is particularly evident when imaging objects of greater width than the STEM probe. Confocal electron microscopy using inelastic electrons appeared to be a promising imaging mode for the future with this thesis consisting of early work in the field.

Understanding the plastic deformation mechanisms in polycrystals is a long-standing fundamental problem and its improvement has significant potential impact on the increase in materials resistance to typical failure modes such as fatigue cracking and stress corrosion cracking and hence the increase in the materials strength. However many deformation models are yet to be validated as quantitative experimental results at mesoscale to correlate dislocations and microstructure features are limited. This thesis furthers the High Resolution EBSD (HR-EBSD) technique in Geometrically Necessary Dislocation (GND) density measurement from qualitative analysis with a typical map size of 100 μm x100 μm to quantitative analysis with a map of 500 μm x500 μm by determining the optimised scanning step size (0.5 μm) and detector binning level (4x4 binning). This allows a statistically large number of grains to be sampled. Combining with obtained crystallographical information from a conventional EBSD system, systematic studies on GNDs behaviours with respect to a range of microstructure features such as grain boundaries and triple junctions were conducted on monotonically deformed polycrystal copper samples under tension. Relatively high GND density points were found near triple junctions and some grain boundaries whereas the low GND density points tend to appear near the grains’ interiors. These tendencies are particularly profound in low and moderately deformed samples. Hence more detailed analyses were performed to investigate the relations of GND density and the properties of grain boundaries and triple junctions. These quantitative analyses were complemented with direct visual assessment. The visual inspection provides interesting findings such as the strong GND structure dependence on grain orientations and GND structure development through increasing deformation; grain-grain interaction influences on GND structure development and GND structures near triple junctions. These GND density studies provide experimental results to validate some of the existing plastic deformation models for instance Ashby’s model of hardening and Hall-Petch relation. However, some of the new observations on GND structures at mesoscale cannot be fully rationalised by existing proposed mechanisms. Hence new models have been proposed that these GND structures might be generated from the intersections of different slip systems which occurred in various parts of a grain, or by the dislocation piling-up at some microstructural features e.g. triple junctions and twin boundaries.

This thesis studies the application of silver nanowire transparent conductors in PbS quantum dot photovoltaics. Silver nanowires were synthesized using a colloidal method and characterized using scanning electron microscopy. Nanowires were deposited on glass substrates by a stamp transfer process to generate a low density continuous network of conductive nanowires. This resulted in a highly conductive and transparent film appropriate for optoelectronic applications. Nanowire synthesis, deposition, and processing were optimised to produce transparent conductors suitable for thin film photovoltaics. These nanowire films were used to fabricate lead sulphide (PbS) colloidal quantum dot solar cells. In this structure, p-type PbS quantum dots form a junction with a n-type ZnO nanoparticle layer. A variety of fabrication and processing treatments were developed in order to reduce short-circuiting of devices and to enhance cell performance. Moderate nanowire density, improved ZnO adherence, slight device aging, and increased PbS film thickness proved to result in the highest quality devices. The champion device developed in this thesis achieved a power conversion efficiency of 2.2%.

Despite over 100 years of scientific research, a full understanding of superconductivity remains elusive. While it is known that the electron-phonon interaction is responsible for the formation of Cooper pairs in conventional superconductors, many superconductors exhibit behaviour suggestive of more exotic pairing mechanisms. In this thesis, two novel superconducting materials are considered, monolayer transition metal dichalcogenide, MoS₂, and iron-based superconductor, LaFeAsO_1−xF_x. The former is ideal for the study of the electron-phonon interaction, as it not only has potential applications as an atomically thin transistor, but also displays a dome-shaped superconductive state as a function of electron doping. In the latter, the superconductive state emerges from a magnetic parent compound upon flourine doping. Its high critical temperature is thought to be enhanced by magnetic fluctuation rather than being purely phonon-mediated. By using novel first-principles techniques, the electron-phonon interaction in electron doped single-layer MoS₂ is investigated. The superconducting gap is calculated using the Migdal-Eliashberg theory, and by considering the electronic structure and lattice dynamics in this material, an explanation is provided for the experimentally observed doping-dependent critical temperature in this material. The origin of the doping-induced transition from a magnetic phase to a nonmagnetic phase in LaFeAsO_1−xF_x is determined. A new model to capture the effects of the fluorine dopants is developed, which has implications for the electron-phonon interaction in this material.