The dispersion strengthening is a process that strengthens the material's matrix with use of the smallest precipitates. The most power comes from the character of the nanostructures, their chemical compositions, crystallographic structures, sizes, shapes and interfaces between matrix and precipitates. Through analytical methods it is possible to study and achieve the optimal mechanical properties of elements produced from high-manganese steels with dispersive nanoparticles such as carbides or carbo-nitrides. So far the most effective research methods are transmission electron microscopy and spectroscopy with use of multiple detectors such as Dual Electron Energy Loss Spectrometer (DualEELS), Energy Dispersion X-ray detector, (EDX) or Gatan Imaging Filter (GIF). The DualEELS, which is mostly developed during this thesis, is a technique which results in spectrum imaging of all elements presented in the analyzed area. The material studied during this Ph.D. is a high-manganese steel with vanadium and niobium carbides or carbo-nitrides with various sizes from few to dozen of nanometers, but the average is less than 20nm. The main goal of this Ph.D. is to advance the current available methods of nano-analysis using DualEELS of the smallest precipitates embedded in the matrix supported by improved and optimized sample preparation method with Focused ion Beam (FIB) lamella. The advancement is made in several fields including development of acquisition conditions, development of sample preparation technique using low voltages at FIB, and development and adaptation of the novel post-processing routines of the acquired data using Gatan DualEELS QuantumER post-column detector. The post-processing routine involved quantitative and qualitative analysis of precipitates, which required new values of partial cross-sections and mean free paths of inelastic scattering events estimated and calculated based on experimental (standards) approach. The results consist of fully quantified precipitates (V,Ti)(N,C) and ((Nb,Ti)C) supported by chemical profiles, comparison discussion between specimen, with a pseudo-3D reconstruction of spectrum imaging of these precipitates, which means that all elements have individually calculated thicknesses. The results gave a glimpse into the nucleation of the smallest precipitates, unexpectedly different than in most literature, showing that in this case there is no core-shell structure in mixed transition metal carbides. The Ti, which is not an intentional part of the alloy, acts as a nucleation sites, but is not built over core for the V or Nb mixed precipitates. These results are shown by four examples of V-steel and three of Nb-steel. They are presented as spectrum imaging signals, separated from matrix, with pseudo 3D representation and quantified in absolute manner with the accuracy down to a few atoms.

Solid state nuclear magnetic resonance (NMR) is a powerful probe of inorganic materials systems. Through carefully changing materials compositions and synthesis methods, the impact on the local structure can be investigated. These have been applied to three main materials sectors: Paramagnetic materials in NMR have traditionally suffered from poor resolution due to broadening experienced at the nuclei from localised unpaired electrons. In this work, a fast magic angle spinning (MAS) and low field approach has been applied to these paramagnetic cathode materials to improve this resolution, and elucidate structural information from the investigated materials. The resolution gained from these techniques has been used to highlight differences observed in the 7Li shifts of lithium iron phosphate (LFP) produced by different synthesis techniques. This was found to be related to the cell volume of the LiFePO4 phase. Furthermore, the investigation of V doped LFP by 7Li and 31P MAS NMR has resulted in the observation of many common impurities resulting from synthesis. Additionally, 31Presonances could be identified that were related to V near the phosphorus site, indicating successfully doping in some of the higher Li containing samples. Through 29Si and 17O MAS NMR, changes in the local structure between Ca and Zn doped Stöber nanoparticles are observed. Similarly to other Ca containing materials, incorporation of Ca into the Stöber network has been shown to disrupt Sibridging bonds promoting the formation of non-bridging bonds in the silica network. However, addition of Zn tells a different story. This is first observed in the static measurements, where incorporation of high amounts of Zn leads to no evidence of hydroxyls observed in the Stöber network. Whereas, high resolution transmission electron microscopy (HRTEM) and density functional theory (DFT) calculations confirm the presence of crystalline Zn2SiO4 -II in the nanoparticles. Finally, activation of two series of synthetic sodium- and aluminium substituted calcium silicate hydrate (C-(N)-(A)-S-H) geopolymers are investigated. Increasing the CaO has been shown to increase the disorder of the silica network, and also to promote the increase of crystallinity of the systems through observation of calcium aluminate phases. Additionally, increasing the amount of aluminium relative to the silicon in the system, promotes more of these crystalline phases to form.

Today, CMOS-compatible Flash memory technology dominates the non-volatile memory storage market due to high density and low fabrication costs. However, with CMOS approaching fundamental scaling limits, research into novel emerging non-volatile memory storage technologies that exploit materials properties including resistance, spin and polarisation, has significantly progressed. The ideal non-volatile memory technology would compete with Flash, offering high-density memory storage at low costs, however it would outperform Flash due to its faster operating speeds, lower energy requirements, greater endurance and greater potential for scaling. Of all the emerging technologies, resistive RAM (RRAM) elements, in which reproducible (switchable) and distinct high and low resistance states are the basis of memory storage, are considered most advantageous due to their superior potential for scaling, fastest exhibited operating speeds and extremely low energy requirements. Despite progress in the field of RRAM research, the underlying mechanisms that allow a device to switch between high and low resistance states remains unclear in many materials systems and is the key motivation behind this work. Here, Pulsed Laser Deposited (PLD) RRAM devices that incorporate resistive switching transition metal oxide thin films were studied using Electron Energy Loss Spectroscopy (EELS). Basic metal/oxide/metal RRAM heterostructures that incorporated strongly oxidising titanium electrodes and polycrystalline ZnO and manganese-doped ZnO were investigated in Chapter 3. These devices were designed for direct comparison to a device in presented the literature which displayed the simultaneous co-switching of resistance and magnetisation states. In the devices fabricated here, EELS analysis revealed Mn-phase segregation both at grain boundaries both above and below the top and bottom electrodes, which supported the proposed co-switching mechanism. In Chapter 4, epitaxial single crystal perovskite oxide Pr0.48Ca0.52MnO3 was incorporated into a novel metal/oxide/tunnel-oxide/metal RRAM structure, where the thickness of the interfacial Yttria-stabilised Zirconia tunnel oxide varied the output current density. In both the ZnO and Pr0.48Ca0.52MnO3 devices, EELS analysis revealed that the observed resistive switching was mediated by the field-induced exchange of oxygen vacancies between the bulk oxide and an interfacial oxide. Despite this similarity, the overall device resistance was governed by different effects: for the polycrystalline ZnO-based devices, this was the oxygen-vacancy induced formation and dissolution of a highly resistive TiO2 interfacial layer; in contrast, for the epitaxial Pr0.48Ca0.52MnO3 device, this was the oxygen-vacancy induced charge accumulation and dissipation in the tunnel oxide, which modulated the tunnel barrier height.

The radiofrequency (rf) pulses used in NMR are subject to a number of imperfections, such as those resulting from the inhomogeneity of the rf field or an offset of the transmitter frequency from exact resonance. In spin-echo experiments, these imperfections yield spectra with reduced signal intensity and distorted phase. Composite pulses, which have tailored bandwidth properties with respect to experimental frequency parameters such as the rf field strength or resonance offset, offer a route to improving the amplitude of the spin-echo signal. However, the symmetry of the pulse sequence must be carefully considered to prevent the introduction of phase errors into the spin-echo signal. Here, composite pulses will be studied as a means to improving one of the most common techniques for 1H background suppression in MAS NMR, the ”Depth” sequence. Novel composite 180° pulses will be presented for this application and verified experimentally. The composite pulse Depth experiment yields spectra with improved amplitude of the 1H signals of interest, while successfully maintaining good suppression of background signals. Novel families of dual-compensated 180° composite pulses for I = 1/2 will also be designed for use in NMR spin-echo experiments. These pulses are capable of simultaneously compensating for resonance offset and rf inhomogeneity problems. Crucially, unlike many composite pulses that have been presented before, these new pulses have the correct symmetry properties to form a spin echo without phase distortion. Composite pulses have found wide usage in solution-state NMR, and although in principle the same pulses can be applied in solid-state NMR experiments, complications can arise under magic angle spinning (MAS). The effects of MAS on composite pulse performance will be explored both through computer simulations and 31P experiments. Finally, on a different theme, we will investigate spin-locking of half-integer quadrupolar nuclei in solids. Spin-locking is an important feature of many NMR experiments, yet the complex behaviour observed for quadrupolar nuclei is not fully understood. Using the theoretical model introduced by Ashbrook and Wimperis, we will investigate the far off-resonance case of spinlocking for I = 3/2 and I = 5/2 nuclei.

The idea is now well established that light possesses angular momentum and that this comes in two distinct forms, namely spin and orbital angular momentum which are associated with circular polarisation and helical phase fronts respectively. In this thesis, we explain that this is, in fact, a mere glimpse of a much larger picture: light possesses an infinite number of distinct angular momenta, the conservation of which in the strict absence of charge reflects the myriad rotational symmetries then inherent to Maxwell's equations. We recognise, moreover, that many of these angular momenta can be identified explicitly in light-matter interactions, which leads us in particular to identify new possibilities for the use of light to probe and manipulate chiral molecules.

a-tricalcium phosphate (a-TCP, Ca3(PO4)2) demonstrates both bioactive and resorbable characteristics. Substitution of SiO4 4- for PO4 3- in a-TCP (Si-a-TCP) is found to stabilize the structure at lower temperatures and improve mechanical (and possibly bioactive) properties. The mechanism of electroneutrality in the Si-a-TCP structure is not fully understood, though is thought to take place through the creation of O2- vacancies or through excess Ca2+. This study addresses some structural properties of a-TCP using 31P MAS NMR at intermediate B0 fields (11.7 T) and 43Ca DOR NMR at multiple fields (20.0 T, 14.1 T, 11.7 T), and via correlation of the measured 31P and 43Ca isotropic chemical shifts (Oiso) against calculated values obtained with GIPAW DFT methods using the CASTEP code. These results show that the structure has high short range order and clearly support the monoclinic P21/a (12 P site/18 Ca site) model. In contrast, solid state 31P MAS and 43Ca DOR NMR studies of Si-a-TCP demonstrate that significant disorder broadening is characteristic of these data, however the corresponding 29Si MAS NMR data affords reasonably resolved resonances, a low intensity Q2 resonance at 0iso {84.5 ppm, and multiple resonances in the range 0iso - {70 -{75 ppm, despite this shift range normally associated with Q0 speciation, 29Si refocused-INADEQUATE data shows that Q1 resonances can also exist in this region. 31P-29Si HETCOR data from these systems suggests that, despite the intrinsic disorder, explicit PO43- framework species can be associated with the different Q0/Q1 Si species, and while there is some dispersion of the silicon throughout the structure it is predominantly associated with a small number of P sites. DFT calculations for the Si-a-TCP system suggest that the more favourable mechanism for charge balance is Ca2+ excess, despite this, the 29Si NMR data is in greater agreement with the DFT calculations for the O2- mechanism, whereby two adjoining cation-anion-columns in the structure are bridged together by a Q1 unit , 29Si NMR data also suggests the existence of Ca2SiO4 and Ca3Si3O9 existing as solid solutions within the a-TCP structure.

We have developed simplified microfluidic droplet generators and employed them to fabricate anisotropic polymer particles and capsules in the size range of 100–500 μm. We used cheap and generally available materials and equipment to design and assemble microfluidic devices. All our devices were made of standard wall borosilicate capillaries (OD 1.0mm, ID 0.58mm), steel dispensing needles without bevel (30 G, 32 G), microscopy glass slides, fast-curing epoxy glue (Araldite-80805) and diamond scribe to process the glass. We designed four different geometries for each device, which can be separated for two groups: single and double droplet generators. The performance of the devices was validated using computational fluid dynamics and laboratory experiments. First of all, we tried to fabricate intricate single emulsion droplets and then moved on to double emulsion droplets. The range of the fabricated particles and capsules includes anisotropically-shaped amphiphilic polymer “microbuckets”, biphasic particles, capsules with various fillers and stimuli responsive polymer vesicles. To produce such objects we employed different functional monomers, for instance “clickable” glycidyl methacrylate or hydrophilic 2-hydroxyethyl methacrylate. We also utilized several chemical and physical phenomena such as internal phase separation, wettability or polymer chain cross-linking to tune the properties of the synthesized particles. We investigated properties of the above mentioned particles and capsules. For example, “microbuckets” which are hydrophilic at the exterior surface, but hydrophobic inside the cavity, were able to withdraw oil droplets from an aqueous phase and “arrest” them inside the cavity.

The photoconductivity of cadmium iodide is described in this dissertation. Measurements have been made at temperatures between 300oK and 1OoK on high quality single crystals grown from solution. A sensitive electrometer, with a noise level of less than 10-16 amps enabled low currents to be measured and low illumination intensities to be used; the photocurrent was then proportional to the intensity. The photoresponse has been determined at energies up to ~6.5eV; at high energies, near 5.6eV, where exciton effects become important, the photoconductivity is comparable to that in the adjacent band to band transition regions. Reflectivity measurements have been made in the same apparatus, many of the reflectivity features appeared in the photoconductivity spectrum in particular the high energy exciton reflectivity peaks appeared as photoresponse dips. The reflectivity spectra enabled the photoresponse to be corrected for photons lost by reflection. When the photoresponse for absorbed photons was plotted against absorption coefficient .a smooth curve was obtained. The points corresponding ,to the exciton lines at 5.7eV and 6.2eV did not fall on the curve, however, the exciton photoresponse was some 100% greater than that predicted on the basis of absorption coefficient. The smooth curve may be interpreted in terms of the De Vore model and the increased photoresponse at the exciton lines in terms of an exciton diffusion process. A semi-empirical electron energy level scheme has been given, this is based upon the correspondence between the optical spectra obtained from many metallic iodides. The scheme is consistent with the available optical information,and agrees with the photoconductivity results. The measurements of photoconductivity, particularly those made at low temperatures, were involved with the polarisation of the sample caused by the trapping of charge carriers. This polarisation was found to be both intensity and energy dependent, so that it could influence the shape of the photoresponse spectrum. An explanation has been given. for these effects, in particular the energy dependence was explained in terms of the variation of the absorption coefficient. The thermally stimulated current curve method has been used in an investigation of trapping levels. Illumination took place at 10oK, subsequent warming indicated that many different trapping levels were active. The trapping level energies were.determined and glow peaks compared in two different electrode geometries. Some peaks were enhanced when a volume sensitive electrode geometry was used; it was therefore possible to distinguish volume and surface distributed traps. These conclusions were substantiated when a thin film was used, since only surface traps would then be important. Spectrographic analysis of typical crystals showed that the impurity content was low, the chief impurity was iron with 3 ppm. A discussion of the effects of intense ultra-violet illumination, i.e. photodecomposition, on cadmium iodide is given in Chapter Seven. These experiments indicated that decomposition occurred most readily at crystal imperfections. After visible decomposition the surface resistance of typical crystals fell by many orders of magnitude to a value of ~106[omega]. This resistance was not strongly temperature dependent, the current was thought to be carried along filaments of decomposition products. Part of the photodecomposition investigation lead to the discovery of the diffusion of silver in CdI2 at temperatures near 250 degrees C. This result indicated that silver electrodes were not suitable for photoconductivity or ionic conductivity measurements at high temperature and explained why previous high temperature measurements were unreliable. Evaporated gold has been shown to give ohmic contacts and to be stable at high temperatures even after prolonged use. The electronic and optical properties of CdI2 were summarized in Chapter Eight. Proposals have been made for future experiments to investigate these properties. Amongst these a new technique for the measurement of photoconductivity and simultaneous correction for reflectivity loss was described.

The structures of a variety of disordered materials were determined using the technique of total neutron scattering. The synthesis of various polymorphs of Ga2O3 and related materials was investigated and the structures of the hitherto uncharacterised polymorphs were examined in detail. The structure of y-Ga2O3 was found to be a cubic defect spinel with four partially occupied Ga sites, however, the octahedral Ga coordination environments were found to be distorted from the average cubic structure. The cation distribution in y-Ga2O3 was found to depend on particle size and synthesis method. Examination of the structure of E-Ga2O3 revealed that it is analogous to a disordered, hexagonal form of E-Fe2O3. The poorly crystalline product of the thermal decomposition of Ga(NO3)3.9H2O was found to be a nanocrystalline modification of E-Ga2O3, rather than a distinct phase with the bixbyite structure, as had been previously reported. The structure of a novel gallium oxyhydroxide, Ga5O7(OH), was determined to be analogous to tohdite, Al5O7(OH), and in its thermal decomposition pathway was revealed a new Ga2O3 polymorph: orthorhombic K-Ga2O3. A solvothermal synthetic route to spinel structured ternary gallium oxides, of general formula MxGa3-xO4-y, was developed. The structures of the materials where M = Zn or Ni were found to be consistent with those previously published. The materials where M = Co or Fe possess novel, oxygen-deficient compositions and exhibit interesting magnetic behaviour. A series of cerium bismuth oxides of formula Ce1-xBixO2-1/2x were found to adopt the cubic fluorite structure with significant local distortion due to the preference of Bi3+ for an asymmetric coordination environment. A sodium cerium titanate pyrochlore was also structurally characterised and it was determined that, due to the presence of three different cations on the A site, the local structure required a model with reduced symmetry. In situ neutron scattering experiments were carried out on amorphous zeolite precursor gels in the presence of the reaction liquid. These experiments revealed structural features unique to the gel, and proved that the gel undergoes irreversible structural changes on drying. Preliminary analysis of the gel structure indicated that the Na+ cations play an important role in the development of the ordered zeolitic framework, and revealed no strong evidence for the existence of discrete structural building units in the gel.

The aim of this project was to investigate EELS from two-layer systems and relate the results to the existing theory. Two systems were investigated, magnesium silicide platelets within an aluminium matrix and silicon precipitates within an aluminium matrix. Both systems were prepared through thermal treatment of a 6061 A1 alloy. The majority of the data presented in this thesis was acquired using EELS. However, energy dispersive x-ray spectroscopy (EDX) and electron microscopy were also used. EELS was performed on two different electron microscopes, the VG HB5 STEM and the FEI Tecnai TF20 (S)TEM. The bulk of the results were acquired on the HB5. To facilitate the comparison of theoretical and experimental results, the data was separated into bulk and interface components. The component amounts were then plotted against distance from the interface. Bessel functions were then fitted to this plot to give characteristic values. These values represented how well the optimal interface position had been chosen, the comparative decay of the interface plasmon on each side of the interface and the relative thickness of the bulk material. The experimental data from most of the interfaces examined indicated significant variations in the thickness of the sample. Despite this, the experimental results were found to follow the trend suggested by the theoretical equations. Analysis of the characteristic values indicated that the data from the HB5 and Tecnai for an interface showed a strong correlation. However, comparison of the experimental values with the theoretical reference showed a deviation of ~20%. Though the source of this deviation was not clear, a number of possible causes were investigated. Theoretical models were generated of systems with a variety of thickness profiles. In addition, systems containing steps, wide and narrow bulk plasmons and a thin interfacial layer of a third material were all considered. The deviation between the results from experiment and the simple theoretical model was believed to be consistent with the factors affecting EELS from a real interface. In particular, thickness variations and imperfections at the interface were found to be the most likely cause of the discrepancy between theory and experiment.