There is a considerable interest in the use of tungsten oxide in the research and development of new materials and devices, such as gas sensors and as photocatalysts. In order to improve the photocatalytic properties of WO3, its combination with metals which allows the preparation of WMxOy materials are believed to be promising photocatalysts under visible light. The present work deals with the synthesis of homo- and hetero-metallic tungsten alkoxide and amide compounds using the single source precursor approach for potential chemical vapour deposition precursors of mixed-metal oxide films.

There are a number of “smart” coatings that can be applied to glass. These include self-cleaning coatings based on titanium dioxide, and low-E coatings based on fluorine-doped tin oxide. Products are often more desirable with colour options such as Pilkington Activ BlueTM. There are currently no alternatives to body tinting glass to achieve colour, which is a time-consuming and expensive procedure. The work in this project details a number of coloured coatings via the AACVD or combustion processing of metal nitrate/urea precursors.

Two-dimensional (2D) materials have attracted extensive research interest in recent years. Among them, graphene and the semiconducting transition metal dichalcogenides (TMDs) are considered as promising candidates for future device applications due to their unique atomic thickness and outstanding properties. The study on graphene and TMDs has demonstrated great potential to further push the scaling of devices into the sub-10 nanometer regime and enable endless opportunities of novel device architectures for the next generation. In this thesis, crucial challenges facing 2D materials are investigated from material synthesis to electronic applications. A comprehensive review of the direct synthesis of graphene on arbitrary substrates with an emphasis on the metal-catalyst-free synthesis is given, followed by a detailed study of the contact engineering in TMDs with a focus on the strategies to lower the contact resistance. Effective approaches have been demonstrated to solve these issues. These include: (1) metal-catalyst-free synthesis of graphene on various insulating substrates; (2) Fermi level pinning observed in TMDs and integration of graphene contact to lower the contact resistance; and (3) application of metal-insulator-semiconductor (MIS) contact in TMD field-effect transistors (FETs). First, a direct low-temperature synthesis of graphene on insulators without any metal catalysts has been realized. The effects of carbon sources, NH3/H2 concentrations, and insulating substrates on the material synthesis have been systematically investigated. Graphene transistors based on the as-grown material have been fabricated to study the electronic properties, which can further confirm the nitrogen-doped graphene has been synthesized from the electrical characterizations. Then electronic devices focusing on the semiconducting TMDs has been studied. The Fermi level pinning has been observed and studied in WS2 FETs with four metal materials. A novel method of using graphene as an insertion layer between the metal and TMDs has been proven to effectively reduce the contact resistance. Owing to the benefit of tuning the graphene work function via the electric field, the contact resistance can further be reduced. Finally, the effectiveness of MIS contacts in WS2 FETs has been demonstrated. A thickness dependence research has been conducted to find the optimal thickness of the inserted insulator. Moreover, the possible physical mechanism of how this MIS contact reduces the contact resistance in 2D materials has been discussed.

Background: The prevalence of overweight, obesity and obesity-related disease, mainly cardiovascular disease (CVD), is increasing in both developed and developing countries. Ethnic differences have been reported in the prevalence of overweight, obesity and CVD. However, measures used to define overweight and obesity, and identify increased risk of CVD were developed and validated in predominately Caucasian populations in developed countries. Consequently, these measures may not accurately define disease risk in all population groups. Therefore the specific aims of this programme of study were: 1. To establish the relationship between adiposity and cardiovascular risk factors in different ethnic groups. 2. To identify field measures of adiposity, relating to cardiovascular risk in different ethnic groups. 3. To compare the relationship of adiposity and cardiovascular risk factors in a single ethnic group, that of a rural and an urban population in Zimbabwe. 4. To identify risk factors for CVD related to adiposity in a population of African origin. Study design: Three empirical studies were undertaken. In study one, 312 adult subjects from three ethnic groups (Afro-Caribbean (n=106), Caucasian (n=165) and South Asian (n=41)) were recruited from a University. Twenty-six (26) of each group were individually matched for age (±3 years) gender and BMI (±2 kg/m2) to allow for comparability. Measures of body composition included height, weight, waist and hip circumferences, skinfold thickness measures, body density and percentagebody fat. In study two, 81 subjects from two ethnic groups (Afro-Caribbean (n=39) and Caucasian (n=42)) were recruited and tested. They were matched for age, gender and BMI using the same criteria as study one. In addition to the body composition measures taken in study one, random non-fasting blood glucose, total cholesterol, triglycerides and blood pressure were taken. In study three, 55 men and 108 women from rural Zimbabwe, 8 men and 17 women from an urban low-density suburb in Harare Zimbabwe, and 28 male and 16 female students from the University of Zimbabwe were recruited and tested. In addition to all measures of body composition in studies one and metabolic analysis in study two, participants’ dietary intake was assessed by food frequency questionnaire and 24hour recall and physical activity was assessed by a physical activity questionnaire. Main findings: • The relationship between BMI and %BF was not the same in all ethnic groups. (aim 1) • There were ethnic differences in the cardiovascular risk predictors between Afro-Caribbean and Caucasian men and women. (aim 1) • It is not recommended that BIA is used as a substitute for TBW estimation in multi-compartment models. (aim 2) • In three groups of Zimbabweans from urban, rural and university locations, a pattern emerged. Amongst women, urban women were at greatest risk, reporting highest values for all variables, followed by rural then university women. Amongst men, urban men were at highest risk, however there were few differences between rural and university men. (aim 3). • Finally, increased WC and dyslipidemia are associated with increasing BMI in populations of African origin. (aim 4) Conclusions: The relationships between overweight, obesity and risk of obesity-related disease differ between different ethnic groups. Moreover, in the groups from Zimbabwe, differences in obesity-related risk were associated with being female and living in urban areas. Therefore, application of universal measures for defining obesity and related diseases may not be applicable to all ethnic groups.

<p>Dosimetric characteristics of a CVD single crystal diamond detector have been evaluated. Detector stability, linearity, optimal bias, temperature dependence, directional dependence, priming and pre-irradiation behaviour, depth dose curves and dose profiles were investigated.</p><p>The optimal bias was determined to be 50 V. The detector stability measurement showed a too large variation for absolute dosimetry in a day to day measurement, but acceptable variation during one and the same day. The linearity constant, , in the relation between signal and dose rate, (Fowler 1966), was determined to 0.978 and 0.953 for two detectors. The sub-linearity was also observed in the depth dose curves and could be eliminated with a correction method. The diamond detector showed smaller temperature dependence than the EFD silicon diode. The directional dependency was, <1 %, up to at least ± 15˚ and therefore no angular correction is needed. A priming dose of 0.6 Gy was determined, which is considerably smaller than for existing detectors on the market. After pre-irradiation with electrons (8 and 18 MeV) a large and permanent desensitization of up to 31 % / 500 Gy was detected. This is in contradiction to what previous published articles claim. 15 MV photons also reduced the sensitivity of the detector, but no evidence that 5 MV photons do has been found. A 50 Gy dose of 180 MeV protons did not reduce the sensitivity either. The detector dose rate linearity was improved by electron pre-irradiation. The dose profile penumbras of the diamond detector were, for the most part, smaller than the RK ionization chamber, indicating a better spatial resolution.</p>

L'objectif de ce travail est d'étudier l'usinabilité des CMMp comme matériau de structure en substitution aux alliages réfractaires et de comprendre les mécanismes générateurs de poussière inhérents à leur usinage à sec. Les différents niveaux de chargement en céramique du CMM (5, 15, 25, 35 % de SiCp) ainsi que la variété d'outils PCD et des revêtements diamants nanostructurés étudiés, a permis d'évaluer dans un premier temps le choix structurel d'outillages en liaison avec la faisabilité industrielle de leur usage en usinage grande vitesse à sec d'un CMM Al/SiC. L'étude de faisabilité et la préconisation d'outillages ont été effectuées en prenant en compte des critères énergétiques et de qualité structurelle et environnementale. Les modes d'endommagement ainsi que les performances d'outils coupants ont été observés et analysés lors d'essais d'usure accélérée et de durabilité. La présence d'une usure adhésive suivie d'un mode abrasif de consommation d'interface accroit l'importance de la structure de l'outil (homogénéité, multiplicité des interfaces

En raison de leur compatibilité avec la technologie conventionnelle du silicium, les nanofils de silicium semblent très prometteurs pour être utilisés comme briques de base de composants électroniques à l'échelle. Ce travail de thèse se focalise sur la croissance épitaxiale et la caractérisation de tels nanofil. Les nanofils de silicium sont fabriqués par la méthode Vapeur-Liquide-Solide (VLS) à partir de catalyseurs d'or, en utilisant deux techniques: dépôt chimique en phase vapeur (CVD) et épitaxie par jets moléculaire (MBE). Dans la première partie de cette étude, les catalyseurs d'or sont déposés sur le substrat Si(111) en ultravide pour bénéficier d'interface or-silicium de grande qualité. A partir de ces ilôts d'or, des nanofils orientés <111> sont obtenus par MBE et CVD, lorsque la pression partielle de silane est faible. En profitant de l'orientation contrôlée des fils qui favorise leur intégration dans les composants, plusieurs structures basées sur les nanofils ont donc été développées. Dans la deuxième partie de cette étude, les structures atomiques des surfaces facettées de nanofils orientés <111> ont été étudiées par microscopie à l'effet tunnel (STM) à basse température. En combinant ces observations avec des images de fils identiques en microscopie électronique, nous avons révélé la diffusion d'atomes d'or depuis le catalyseur le long des fils. Cette diffusion a plusieurs conséquences : elle conduit en partie à la forme conique des nanofils et est certainement à l'origine de l'alternance de la taille des parois des nanofils. Une troisième partie a porté sur le dopage des nanofils. Des gaz tels que la phosphine ou le diborane peuvent être utilisés pour incorporer des dopants de type n ou type p dans les nanofils pendant la croissance. La tomographie par sonde atomique (TAP) a été utilisée pour caractériser la distribution des impuretés dans le volume de nanofils de silicium dopés au bore et orientés <111>. Une distribution uniforme de bore à été observée au centre de nanofils et la concentration des impuretés mesurée correspond bien à la valeur estimée par le rapport entre le flux de silane et de diborane. Enfin, ces observations ont été comparés avec des mesures de conductivité dans des nanofils individuels.

Current research in materials science and engineering continues to drive it's attention to systems on the nanoscale. Thin films, nano-particles, quantum dots, nano-wires, etc are just a few of the areas that are becoming important in projects ranging from biomedical transport to nano-gears. Thus, understanding, producing, and creating these system is also becoming an important challenge for scientists and engineers to overcome. Physically manipulating objects on the atomic scale requires more than just "micro tweezers" to arrange them in a particular system. Another concern is that forces and interactions that could be ignored or approximated at larger scales no longer hold in this regime. It is the goal of this project to use computational models to simulate nano-particles interacting with customized, highly tailored surfaces in order to confine and pattern them to desired specifications. The interactions to be considered include electrostatic attraction and repulsion, hamaker forces, steric effects, dielectric effects of the medium, statistical variability, mechanical induced surface vibrations, etc. The goal is to be able to manufacture such systems for experimentation in order to compare results to the models. If the models do not hold, we hope to understand the origin of these discrepancies in order to create more robust models for this length scale. Lithography, CVD, and chemical etching will be the primary methods used to create these surfaces on glass substrates. TEM analysis will be compared to modeling through various MD program packages. / Singapore-MIT Alliance (SMA)

The present thesis focuses on characterisation of microstructure and the resulting mechanical and tribological properties of CVD and PVD coatings used in metal cutting applications. These thin and hard coatings are designed to improve the tribological performance of cutting tools which in metal cutting operations may result in improved cutting performance, lower energy consumption, lower production costs and lower impact on the environment.  In order to increase the understanding of the tribological behaviour of the coating systems a number of friction and wear tests have been performed and evaluated by post-test microscopy and surface analysis. Much of the work has focused on coating cohesive and adhesive strength, surface fatigue resistance, abrasive wear resistance and friction and wear behaviour under sliding contact and metal cutting conditions. The results show that the CVD deposition of accurate crystallographic phases, e.g. α-Al2O3 rather than κ-Al2O3, textures and multilayer structures can increase the wear resistance of Al2O3. However, the characteristics of the interfaces, e.g. topography as well as interfacial porosity, have a strong impact on coating adhesion and consequently on the resulting properties.  Through the deposition of well designed bonding and template layer structures the above problems may be eliminated. Also, the presence of macro-particles in PVD coatings may have a significant impact on the interfacial adhesive strength, increasing the tendency to coating spalling and lowering the surface fatigue resistance, as well as increasing the friction in sliding contacts. Finally, the CVD-Al2O3 coating topography influences the contact conditions in sliding as well as in metal cutting. In summary, the work illuminates the importance of understanding the relationships between deposition process parameters, composition and microstructure, resulting properties and tribological performance of CVD and PVD coatings and how this knowledge can be used to develop the coating materials of tomorrow.

Dosimetric characteristics of a CVD single crystal diamond detector have been evaluated. Detector stability, linearity, optimal bias, temperature dependence, directional dependence, priming and pre-irradiation behaviour, depth dose curves and dose profiles were investigated. The optimal bias was determined to be 50 V. The detector stability measurement showed a too large variation for absolute dosimetry in a day to day measurement, but acceptable variation during one and the same day. The linearity constant, , in the relation between signal and dose rate, (Fowler 1966), was determined to 0.978 and 0.953 for two detectors. The sub-linearity was also observed in the depth dose curves and could be eliminated with a correction method. The diamond detector showed smaller temperature dependence than the EFD silicon diode. The directional dependency was, &lt;1 %, up to at least ± 15˚ and therefore no angular correction is needed. A priming dose of 0.6 Gy was determined, which is considerably smaller than for existing detectors on the market. After pre-irradiation with electrons (8 and 18 MeV) a large and permanent desensitization of up to 31 % / 500 Gy was detected. This is in contradiction to what previous published articles claim. 15 MV photons also reduced the sensitivity of the detector, but no evidence that 5 MV photons do has been found. A 50 Gy dose of 180 MeV protons did not reduce the sensitivity either. The detector dose rate linearity was improved by electron pre-irradiation. The dose profile penumbras of the diamond detector were, for the most part, smaller than the RK ionization chamber, indicating a better spatial resolution.