The experimental work discussed in this thesis explores the effects of metal modification on the electroanalytical ability of boron doped diamond electrodes. Boron doped diamond (BDD) electrodes have found increased application to electroanalysis in the past two decades, yet relatively little of the literature is focused on metal, nano and microparticle modification of the substrate. In this thesis three metals have been used to modify the BDD electrode; bismuth, antimony and nickel. Bismuth and antimony nanoparticle modified BDD electrodes were directly compared to unmodified BDD and a bulk bismuth electrodes in the determination of trace levels of cadmium and lead using anodic stripping voltammetry. In both instances, the modified electrode allowed for the simultaneous determination of each analyte that was otherwise unattainable at the unmodified BDD electrode. The nickel modified BDD (Ni-BDD) electrode was used in the determination of organic analytes, namely glucose, methanol, ethanol and glycerol. The nickel nano and microparticle electrodes gave the characteristic Ni(OH)₂/NiOOH redox couple in alkali pH, the oxidised form of which (NiOOH) catalysed the oxidation of the organic analytes. The chapter on glucose sensing with the Ni-BDD electrode is preceded by an extensive literature review on the advances of non-enzymatic glucose sensing, and the application of catalytic metals and nanomaterials in this field. Throughout the course of this DPhil, there has been a collaborative project between Asylum Research and myself within the Compton group to develop a commercial electrochemical atomic force microscope (EC-AFM) cell. The aim was to produce an adaptable EC-AFM cell capable of dynamic electrochemical experiments whilst simultaneously or instantaneously acquiring an AFM image of the modified surface, in-situ. This project was successful, and the EC-AFM cell has contributed to a number of chapters in this thesis, and has now been commercialised.

Silicon based semiconductor devices are rapidly approaching the theoretical limit of operation and are becoming unsuitable for future military requirements. The scope of semiconductor devices has been expanded by wide bandgap devices such as gallium nitride (GaN) to include the possibility for high power and high frequency operation. A new generation of high speed â high frequency devices is required to meet current and future military needs. The Gallium Nitride High Electron Mobility Transistor (HEMT) is showing great promise as the enabling technology in the development of military radar systems, electronic surveillance systems, communications systems and high voltage power systems. Typically, sapphire or silicon carbide is utilized as the substrate material in most HEMT designs. This thesis explores the possibility of utilizing a diamond substrate to increase the power handling capability of the AlGaN/GaN HEMT. Diamond offers increased thermal property parameters that can be simulated in the commercially available Silvaco software package. A complete electrical and thermal analysis of the model was conducted and compared to actual device characteristics. The results of the software simulation and measurements on the test devices indicate diamond substrates will enable the HEMT to be operated at a higher power than traditional sapphire substrate HEMTS.

Fiber amplifiers with high power and high pulse energy are strongly in demand for both scientific research and industrial applications. Ytterbium-doped fiber has been an outstanding choice for its broad-gain bandwidth and excellent power conversion efficiencies. In this dissertation, we introduced a compact high power high pulsed energy laser system with chirally coupled core (3C) Yb-doped fibers as the gain media. Traditional standard fibers and photonic crystal fibers are not suitable for compact high power high pulse energy laser systems because of poor higher order modes (HOMs) management and complicated air-hole structure. Newly invented 3C silica fibers solve these problems. A helical side-core around the Yb-doped central core extracts the HOMs from the central core. By adjusting this chirally structure, the core of the 3C fiber can be enlarged and the transverse mode of the fiber can be single mode at certain wavelengths. To simulate the amplification process with high power high pulse energy better, a new modeling method based on a combination of the rate equations and the nonlinear Schrödinger equations is invented. The gain was calculated from rate equations and the pulse evolution was analyzed using nonlinear Schrödinger equation. The simulation provided a good guidance for building compact high power high pulse energy laser systems. To achieve high power and high pulse energy, the system is designed as a two-stage structure. The laser

The major objective of the research described in this dissertation is the development of new laser vaporization methods for the synthesis of metal and semiconductor nanoparticles, graphene, B- and N-doped graphene, and metal and semiconductor nanoparticles supported on graphene. These methods include the Laser Vaporization Controlled Condensation (LVCC) approach, which has been used in this work for the synthesis of: (1) gold nanoparticles supported on ceria and zirconia nanoparticles for the low temperature oxidation of carbon monoxide, and (2) graphene, boron- and nitrogen-doped graphene, hydrogen-terminated graphene (HTG), metal nanoparticles supported on graphene, and graphene quantum dots. The gold nanoparticles supported on ceria prepared by the LVCC method exhibit high activity for CO oxidation with a 100% conversion of CO to CO2 at about 60 °C. The first application of the LVCC method for the synthesis of these graphene and graphene-based nanomaterials is reported in this dissertation. Complete characterizations of the graphene-based nanomaterials using a variety of techniques including spectroscopic, X-ray diffraction, mass spectrometric and microscopic methods such as Raman, FTIR, UV-Vis, PL, XRD, XPS, TOF-MS, and TEM. The application of B- and N-doped graphene as catalysts for the oxygen reduction reaction in fuel cell applications is reported. The application of Pd nanoparticles supported on graphene for the Suzuki carbon-carbon cross-coupling reaction is reported. A new method is described for the synthesis of graphene quantum dots based on the combination of the LVCC method with oxidation/reduction sequences in solution. The N-doped graphene quantum dots emit strong blue luminescence, which can be tuned to produce different emission colors that could be used in biomedical imagining and other optoelectronic applications. The second method used in the research described in this dissertation is based on the Laser Vaporization Solvent Capturing (LVSC) approach, which has been introduced and developed, for the first time, for the synthesis of solvent-capped semiconductor and metal oxide nanoparticles. The method has been demonstrated for the synthesis of V, Mo, and W oxide nanoparticles capped by different solvent molecules such as acetonitrile and methanol. The LVSC method has also been applied for the synthesis of Si nanocrystals capped by acetonitrile clusters. The acetonitrile-capped Si nanocrystals exhibit strong emissions, which depend on the excitation wavelength and indicate the presence of Si quantum dots with different sizes. The Si and the metal oxide nanoparticles prepared by the LVSC method have been incorporated into graphene in order to synthesize graphene nanosheets with tunable properties depending on graphene-nanoparticle interactions.

The aim to this work was to develop methods for the determination of 2 aminobiphenyl (2-AB), 3 aminobiphenyl (3-AB), and 4-aminobiphenyl (4-AB) in model mixtures. Concretely, the direct determination of the mixture of studied analytes has been tested using spectrophotometry and differential pulse voltammetry (DPV). Furthermore, separation and detection of 2-AB, 3-AB, and 4-AB have been performed using high performance liquid chromatography with electrochemical detection (HPLC-ED) with boron-doped diamond film thin electrode (BDDFE) in ,,wall-jet" configuration and using high performance liquid chromatography with UV detection (HPLC-UVD). It was found out that the spectrophotometric determination of 2-AB, 3-AB, and 4-AB is impossible in their mixture because of nearby values of local absorption maxima wavelengths of all three analytes studied. Upon the determination of 2-AB, 3-AB, and 4-AB in their mixture using DPV in BR buffer pH 2.0, the difference in peak potentials of 2-AB and 3-AB is too low for their determination in mixture. Upon the determination of mixture containing 2-AB and 4-AB in BR buffer pH 12.0, the limits of determination (LDs) were obtained in the concentration order of 10-6 mol.l-1 for 2-AB and 10-7 mol.l-1 for 4-AB. LDs for the mixture containing 3-AB and 4-AB were obtained in the...

Master of Science / Department of Chemistry / Emily McLaurin / Cu-doped ZnSe/CdSe core/shell nanocrystals were synthesized using the growth doping method. Upon shell growth, the nanocrystals exhibit dual emission. The green luminescence peak is assigned as band edge emission and the broad, lower energy red peak is due to Cu dopant. Although, the oxidation state of Cu in the nanocrystals is debated, the emission is explained as recombination of a hole related to Cu²⁺ with an electron from the conduction band. The emission changed in the presence of dodecanethiol. Generally, the band edge emission intensity decreases and the Cu emission intensity increases. One explanation is the thiol acts as a hole trap, preventing hole transfer to the conduction band. Samples were obtained with varying amounts of Cd²⁺. In the presence of larger amounts of Cd²⁺, the nanocrystals had “thicker shells”, and both the band edge and Cu emission were less sensitive to thiol. The sensitivity likely decreased because the shelled, larger nanocrystals have fewer surface defects resulting in more available electrons.

Master of Science / Department of Chemistry / Kenneth Klabunde / Remediation of the indoor environment led to the development of novel catalysts which can absorb light in the visible range. These catalysts were prepared using the wet chemistry method known as sol-gel chemistry because preparation via sol-gel provides a homogeneous gel formation, which can be treated via supercritical drying to produce an aerogel. These aerogels have been found to have high surface areas when a combination of titania/silica is used. The increase in surface area has been shown to enhance the activity of the catalysts. Mixed metal oxide systems were prepared using titanium isopropoxide and tetraethyl orthosilicate to yield a 1:1 system of titania/silica (TiO2/SiO2). These systems were doped during the initial synthesis with transition metals (Mn or Co) to create mixed metal oxide systems which absorb light in the visible light range. These materials were assessed for potential as heterogeneous catalysts via gas-solid phase reactions with acetaldehyde. Degradation of acetaldehyde as well as the formation of CO2 was monitored via gas chromatography-mass spectrometery. To increase the activity, visible light was introduced to the system. Experiments have shown that a 10 mol % manganese doped titania/silica system, in the presence of light, can degrade acetaldehyde. The cobalt doped counterpart showed dark activity in the presence of acetaldehyde resulting in the formation of CO2 without the addition of visible light. In the hope of increasing surface area a mixed solvent (toluene/methanol) synthesis procedure was applied to the manganese doped catalyst. The resulting materials were of a low surface area but showed a significant increase in degradation of acetaldehyde. Examination of the interactions between mixed metal oxide systems and semivolatile organic compounds (SVOCs) was studied. The pollutant, triphenyl phosphate, was dissolved in n-pentane and exposed to 10 mg of a given catalyst. These reactions were monitored using UVVis. All systems but the manganese doped titania/silica system resulted in the observation of no activity with triphenyl phosphate. The manganese doped catalyst shown a peculiar activity, the increase in absorbance of the triphenyl phosphate peaks as well as the formation of a new peak.

Neste trabalho investigamos as duas contribuições mais importantes ao índice de refração não-linear, n2, em sólidos dopados: o efeito de Lente Térmica (LT) e o efeito de Lente de População (LP). Nós estudamos cristais fluoretos dopados com Cr+3 e vidros fluoretos dopados com Nd+3. As medidas de n2 foram feitas com a técnica de Z-scan resolvida no tempo, que é uma técnica simples mas muito sensível. Também realizamos medidas usando a técnica de Lente Térmica de modo descasado onde usou-se dois feixes de laser (um de excitação e outro de prova). Nós mostramos que pode-se separar temporalmente as contribuições a n2 devido a LT e LP, através da variação da freqüência do chopper / In this work we investigated the two more important contributions to the index of no-lineal refraction, n2, in ion doped solid: the effects of Thermal Lens (LT) and Population Lens (LP). We studied Cr+3 doped fluoride crystals and Nd+3 doped fluoride glasses. The n2 measurements were made with the time-resolved Z-scan technique that is a simple but very sensitive technique. We also performed time¬ resolved Mode-mismatched Thermal Lens measurements, where two laser beams were used (one excitation beam and another probe beam). We showed that it is possible to temporally separate the contributions of LT and LP for n2, through the variation of the chopper frequency

Através do processo de evaporação térmica é possível produzir filmes de KCl e KBr altamente dopados com íons Cu+. Investigamos o efeito de altas concentrações de Cu+ (1020 - 1021 cm -3) nestes filmes policristalinos, onde, associado com o efeito fora de centro do Cu+, origina uma forte banda de absorção propícia para aplicação ótica destes filmes como filtros passa banda na região do UV. Os filmes estudados, de 1 UM, foram preparados por coevaporação resistiva de KCl (Br), como hospedeiro, com 1 a 10% de CuCl(Br), como dopante, sobre diferentes substratos. Diversas técnicas foram usadas para obter as propriedades estrutural e ótica, tais como: microscopia eletrônica de varredura (MEV), difração de raios-X, elipsometria, absorção ótica e transmitância. Do estudo da morfologia é observado um aumento na densidade dos grãos com a concentração nominal de Cu+ de até 1021 átomos/cm-3. Este comportamento também resulta em um aumento na transmitância na região do visível. A banda de absorção em 266 nm (278 nm) para KCl ()KBr): Cu+ é atribuída à transição eletrônica parcialmente permitida de 3d10 3d94s e sua área integrada em função da temperatura mostra o comportamento da força do oscilador com a temperatura, que é propriedade do efeito fora de centro. A este efeito fora de centro está associado um dipolo elétrico devido ao deslocamento da carga da posição substitucional. Para verificar a existência de um sistema de relaxação dipolar elétrica, usamos o método de Corrente de Despolarização Termicamente Estimulada (CDTE). As medidas de CDTE mostram uma fraca e alargada banda em 49K, com energia de ativação média de 147 meV e um fator pré-exponencial de 2x10-14 seg, para amostras de KCl + 1% CuCl, com 3 UM de espessura. Nossos resultados são discutidos e comparados com outros observados em monocristais do mesmo material / Through the thermal evaporation procedure it is possible to obtain highly Cu+ doped KCl and KBr films. We have investigated the effect of 1020 - 1021 cm-3 Cu<sup+ concentration in these polycristalline films, where beside the Cu+ off-center effect it is detected a strong absorption band suitable for UV band pass optical filter application. The studied films are APROXIMADAMENTE 1 UM thick and are prepared from coevaporated KCl (KBr), as host, jointly with 1 to 10% of CuCl (CuBr) nominal doping value. Several techniques were used to obtain the optical and structural properties, such as optical absorption and transmittance, scanning electronic microscopy (SEM), X-ray diffraction and ellipsometry. From the morphology study it is observed that the grain density increases as the Cu+ concentration increase. This behavior results in an increasing transmittance in the visible region tôo. The absorption banda t 266 nm (276 nm) for KCl (KBr):Cu+ is attributed to the Cu+ partially allowed electronic transition 3d10 3d94s and its integrated área shows a temperature independent oscillator strenght behavior which is a property of the off-center effect. To this off-center effect it is associated a electric dipole due to the íon charge displaced from the substitutional position. To verify the existence of a relaxing electric dipole system, we use the thermally stimulated depolarization current (TSDC) method to find out for the Cu+ off-center electric dipole system. The TSDC measurements show a very weak result for our KCl + 1% CuCl samples, resulting in a meanactivation energy of 147 meVwith a peak position at 49K and a pré-exponential Arrhenius time of 2x10-14 sec. We compare and discuss the present results with others found in the same single crystal materials

A solução sólida céria-samária é uma das principais candidatas para aplicação como eletrólito sólido em células a combustível de óxido sólido, devido sua alta condutividade iônica em temperaturas intermediárias (500-750 ºC) de operação. Um dos problemas ainda não solucionados com relação a este material é sua relativamente baixa sinterabilidade. Nesse trabalho foi utilizado o método de sinterização em duas etapas visando melhorar a densificação com reduzido tamanho médio de grãos. Soluções sólidas comercial e obtida por mistura de óxidos de composição Ce0,8Sm0,2O1,9 foram utilizadas. Para fins comparativos também foi utilizado o método denominado sinterização em duas etapas tradicional que visa a obtenção de amostras densas independentemente do tamanho médio de grãos. Resultados de densidade aparente e retração linear revelaram que ambos os tipos de amostras têm comportamento distinto. Para a solução sólida comercial, a retração total até 1400 ºC foi de ~18%. Só foram obtidos resultados de densidade significativos ao utilizar temperaturas elevadas (igual ou superior a 1300 ºC). Para o material obtido por mistura de óxidos não foi possível atingir densidades maiores que 90% da densidade teórica. A sinterização em duas etapas tradicional produziu amostras densas, da mesma forma, que a não-tradicional, mas com tamanhos de grãos consideravelmente maiores. Amostras sinterizadas por ambos os processos foram analisadas por espectroscopia de impedância para a determinação da condutividade elétrica em função da temperatura, e não apresentaram variação significativa nas condutividades intra e intergranular. A sinterização em duas etapas não resultou em melhorias na densificação e nem na condutividade elétrica das amostras. Entretanto, a redução obtida no tamanho médio de grãos pode melhorar as propriedades mecânicas. / Samaria-doped ceria solid solution has been proposed to be used as solid electrolyte in Solid Oxide Fuel Cells due to its high ionic conductivity at intermediate temperatures (500-750 ºC). One of the main problems related to this solid solution is the relatively low sinterability. In this work, sintering of powder compacts was carried out by the two-step sintering method to improve the densification with simultaneous reduction of the mean grain size. Samaria-doped ceria, both commercial and prepared by solid state reactions, with composition Ce0.8Sm0.2O1.9 were investigated. For comparison purposes, the traditional two-step sintering method, by which dense specimens are produced, was also utilized. Apparent density and linear shrinkage results showed distinct features depending on the type of specimen. Total linear shrinkage for commercial solid solution up to ~ 1400 ºC was 18%, but high density values were obtained only for sintering experiments conducted at high temperatures ( 1300 ºC). Specimens prepared by solid state reactions did not attain density values higher than 90% of the theoretical one. The traditional method produced dense specimens as well as the two-step sintering, although the grain size was considerably higher in the former. Specimens sintered by the two methods were used for electrical conductivity measurements. No significant variation in both the grain and the grain boundary conductivities was obtained. The two-step sintering did not allow any improvement in the densification and in the electrical conductivity of samaria-doped ceria. However, the decrease in the mean grain size may contribute to improve the mechanical properties of this solid solution.