Frankfurt (Main), Univ., Diss., 2008

Universiẗat, Diss., 2003--Stuttgart.

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.

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-07-10Bitstream added on 2014-06-13T19:16:39Z : No. of bitstreams: 1 bueno_je_me_guara.pdf: 4834367 bytes, checksum: aaf1ac72afcdf02ebd179c37cd676523 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Sendo um importante e emergente ramo dentro da área dos novos materiais, a deposição de filmes de diamante CVD tem despertado cada vez mais interesse na comunidade científica internacional. O propósito principal dessa dissertação é contribuir com os trabalhos de pesquisa sobre deposição de filmes de diamante CVD, assistidos por filamento quente. O desenvolvimento dos experimentos ocorreu utilizando-se amostras com substratos de Si, sobre as quais foram depositados diamante CVD, com adição de baixa concentração de N2 à mistura gasosa precursora. Optou-se pela baixa concentração, sendo esta uma condição desafiadora, com poucas informações disponíveis. As amostras resultantes dos experimentos foram caracterizadas através do MEV, DRX e EDX revelando, respectivamente uma morfologia com mesmo tamanho e formato dos cristais, confirmando ainda a presença de filme de diamante CVD, cujos cristais apresentaram dimensões uniformes e o filme formado teve cobertura de toda amostra. Assim verificou-se que com a adição de 0,75% em volume de N2 houve a deposição de diamante CVD de alta pureza cristalina, ou seja, de alta qualidade. / As an important and emergent material the CVD diamond has got the attention of the international scientific communities. This study is aimed at continuing the research about CVD diamond using a hot-filament reactor, analyzing its potential and possibilities of its technological applications. The development of the experiments were done on Si substrate samples and the growth process was studied with the introduction of small concentration of N2 in the feed gas mixture, during the diamond growth, in the hot-filament reactor by the chemical vapor deposition technique. The decision to choose a small concentration of N2 was taken because there are few papers and published results. The diamond samples were characterized by scanning electron microscopy and X-ray to verify the properties of the sample and also its morphology. The diamond growth in the nitrogen atmosphere resulted in crystals and thin films with similar morphology and dimensions. Therefore, by the characterization techniques it was verified that the addition of 0,75% in volume of N2 has resulted in a high crystalline purity CVD diamond deposition.

abstract: The thesis studies new methods to fabricate optoelectronic Ge1-ySny/Si(100) alloys and investigate their photoluminescence (PL) properties for possible applications in Si-based photonics including IR lasers. The work initially investigated the origin of the difference between the PL spectrum of bulk Ge, dominated by indirect gap emission, and the PL spectrum of Ge-on-Si films, dominated by direct gap emission. It was found that the difference is due to the supression of self-absorption effects in Ge films, combined with a deviation from quasi-equilibrium conditions in the conduction band of undoped films. The latter is confirmed by a model suggesting that the deviation is caused by the shorter recombination lifetime in the films relative to bulk Ge. The knowledge acquired from this work was then utilized to study the PL properties of n-type Ge1-ySny/Si (y=0.004-0.04) samples grown via chemical vapor deposition of Ge2H6/SnD4/P(GeH3)3. It was found that the emission intensity (I) of these samples is at least 10x stronger than observed in un-doped counterparts and that the Idir/Iind ratio of direct over indirect gap emission increases for high-Sn contents due to the reduced gamma-L valley separation, as expected. Next the PL investigation was expanded to samples with y=0.05-0.09 grown via a new method using the more reactive Ge3H8 in place of Ge2H6. Optical quality, 1-um thick Ge1-ySny/Si(100) layers were produced using Ge3H10/SnD4 and found to exhibit strong, tunable PL near the threshold of the direct-indirect bandgap crossover. A byproduct of this study was the development of an enhanced process to produce Ge3H8, Ge4H10, and Ge5H12 analogs for application in ultra-low temperature deposition of Group-IV semiconductors. The thesis also studies synthesis routes of an entirely new class of semiconductor compounds and alloys described by Si5-2y(III-V)y (III=Al, V= As, P) comprising of specifically designed diamond-like structures based on a Si parent lattice incorporating isolated III-V units. The common theme of the two thesis topics is the development of new mono-crystalline materials on ubiquitous silicon platforms with the objective of enhancing the optoelectronic performance of Si and Ge semiconductors, potentially leading to the design of next generation optical devices including lasers, detectors and solar cells. / Dissertation/Thesis / Ph.D. Chemistry 2013

O Grafeno tem sido estudado há 60 anos, mas só foi desde sua primeira obtenção mediante esfoliação de grafite em 2004 por Novoselov, que obteve grande interesse por parte de pesquisadores, pois tem uma série de notáveis propriedades físicas e químicas que dificilmente são encontradas num mesmo material, o que o torna uma ferramenta de primeira ordem em muitas aplicações de diversos campos. Além disso, sua produção se limita a pequenas folhas, com defeitos e empilhadas formando multicamadas, o qual não permite seu uso em nível industrial. Isso demanda não só que o grafeno seja produzido em grande escala, mas também conservando suas propriedades. O presente trabalho reporta o estudo e estabelecimento de condições para o crescimento de folhas de grafeno, utilizando técnicas de deposição química na fase de vapor a pressão ambiente (APCVD) catalítica, e deposição química na fase vapor assistida por plasma (PECVD), também catalítica, com filmes finos de Níquel e Cobre como metais catalisadores, visto que são as técnicas e metais que tem reportado melhores resultados. Desta forma, esta pesquisa foi encaminhada a um ajuste das variáveis que intervém nas duas técnicas, tais como os gases, seus fluxos e relação entre eles, a temperatura, o tempo de deposição e as espessuras do catalisador. No caso do PECVD, a potência de RF para a geração do plasma e a pressão. Os filmes foram caracterizados por microscopia Raman, que permite ter uma avaliação aproximada do número de camadas e os defeitos presentes no material, e por microscopia eletrônica de varredura (MEV), que permite observar a morfologia das amostras e a possível presença de grafeno, e assim ter certeza da qualidade do grafeno enquanto a continuidade e tamanho das folhas. Além disso, mediante Espectroscopia de raios X por dispersão de energia (EDS), instrumento associado ao MEV, é possível identificar os elementos presentes na amostra em pontos específicos e sua porcentagem. Estes análises revelaram que o grafeno obtido foi de grande área (1 cm2) com alta cristalinidade e poucos defeitos pontuais. / Graphene has been studied for 60 years, but was only since its first achievement by graphite exfoliation in 2004 by Novoselov that got great interest by researches, because it has remarkable physical and chemical properties which are hardly found in a single material, which makes it a first-order tool for many applications in several fields. Besides that, its production is limited to small sheets with defects and stacked in multilayers, which does not allow its use at industrial level, that requires not only a large scale production of graphene but also conservation of its properties. This work reports the study and find suitable conditions for the growth of graphene sheets, using catalytic atmospheric pressure chemical vapor deposition (APCVD) and plasma enhanced chemical vapor deposition (PECVD) techniques and thin nickel and copper films as catalysts. This choice is based on the fact that both, these techniques and the metals had lead to better reported results. Thus, this research is focused on the adjustment of the parameters that intervene in the two techniques, such as precursor gases, their flows and the relationship among them, temperature, deposition time and the catalyst thickness. In the case of the PECVD, the RF power to generate the plasma and the deposition pressure. The films were characterized by Raman spectroscopy, which allows an approximate evaluation of the number of layers and the defects in the material, and by Scanning Electron Microscopy (SEM), which allows to observe the morphology of the deposited layers, and thus to ensure the quality of the graphene as far as the continuity and size of the sheets are concerned. In addition, energy dispersive X-ray spectroscopy (EDS) associated to the SEM instrument was utilized to identify the elements present in particular locations of the sample as well as their percentage. These group of analyses revealed that the obtained graphene achieved areas about 1 cm2 with high crystallinity and low punctual defects.

This thesis addresses the health economic evaluation of community-based interventions against cardiovascular disease (CVD), with special emphasis on the Västerbotten Intervention Project (VIP), run since 1985. The framework is a simple evaluation model consisting of two parts; the selection and measurement of empirical consequences caused by the project under evaluation (e.g. changes in mortality, well-being, use of resources) and a set of values (e.g. efficiency, equity) aimed at assessing the goodness of these consequences. The project’s effects on CVD were predicted by means of risk factors measured in Norsjö between 1985-1990, applied to an epidemiological model based on a logistic risk equation derived from the Framingham population. Cost per life-years saved ranged from £14 900 to net savings, depending on the assumptions. The favourable cost-effectiveness in this kind of intervention has earlier been predicted from theoretical models, but this is the first study based on real experiences from contemporary community-based interventions against CVD. Furthermore, all social classes have benefited from the intervention. Also potential adverse effects in the form of excess mortality due to low cholesterol levels were investigated, and they were negligible in comparison with the health gains. The value of an intervention from a citizen’s perspective was investigated through an interview study (n≈100) in accordance with the contingent valuation method. Great expectations concerning mortality effects on the community level and future savings in health care were good predictors for assigning the intervention a high value. On the contrary, personal benefits in the form of a decreasing risk for CVD had no positive association with the value of the intervention. Hence, the consequences that the cost-effectiveness analysis accounts for - mortality and savings - coincide with the most valuable consequences from the citizen's perspective. In a democracy, the set of values used to determine the success or failure of a programme like a prevention project must agree with values held by the majority of the citizens. Therefore, the attitudes to ethical values among Swedish politicians (n≈450) responsible for health care have been mapped. The support for the health maximization principle was weak, and a trade-off between efficiency and equity was preferred. About 70% of the respondents were prepared to sacrifice health gains to achieve increased equity. / digitalisering@umu

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17161号 / 工博第3651号 / 新制||工||1554(附属図書館) / 29900 / 京都大学大学院工学研究科電子工学専攻 / (主査）教授 藤田 静雄, 教授 髙岡 義寛, 教授 川上 養一 / 学位規則第4条第1項該当

Philosophiae Doctor - PhD / In this century most major medical advances have resulted in part from research on animals and non-human primates such as the African green monkey and therefore often serve as a critical link between basic research and human clinical application. Due to its close evolutionary relationship to humans, the African green monkey is known to be an excellent and most sought after models for studies of human cardiovascular disease (CVD). While the human genome project and some others related to model organisms are very well advanced or even complete, little sequence information has been acquired for the African green monkey. Given the importance of this species in biomedical research generally and CVD specifically, and the fundamental significance of sequence data, it is critical that this paucity of genome information concerning this specific animal model be addressed in order to better define the molecular basis and to further understand the mechanism of cholesterol metabolism in this species which will also contribute immensely to primatology. There is a growing interest in the role of genetic polymorphisms in predicting susceptibility to disease and responsiveness to drug interventions. Since plasma lipid abnormalities are risk factors for coronary atherosclerosis, determination of these plasma lipid concentrations, especially for genes involved in lipid transport and metabolism may be influenced by genetic variations. In this study, the African green monkey was used as a model to evaluate the effect of niacin on plasma lipids and reverse cholesterol transport by examine gene expression and the influence of several polymorphisms found in genes that are involved in cholesterol metabolism in humans. A survey of genetic variation spanning ten prioritised “candidate” genes was conducted, all of which are known to produce proteins that play key roles in the reverse cholesterol pathway (RCT), and in the homeostatic regulation of blood lipid profiles related to cardiovascular health and disease. everse transcription polymerase chain reaction (RT-PCR) was used to evaluate mRNA expression of those “candidate” genes. Twenty two coincident singlenucleotide polymorphisms (cSNPs), reported to play a vital role in RCT, were genotyped within these genes. This study’s findings implicate a subset of six of the twenty two genetic variants, spanning five “candidate” genes. To assess possible involvement of these prioritised “candidate” genes and their polymorphisms, biochemical analyses of known risk factors of coronary artery disease such as HDL-C and LDL-C were conducted. Eight healthy African green monkeys were entered in this study of which four were treated with niacin at an escalating dosage. Their mean lipid-lowering response following drug therapy was analysed, compared to those with the same genotype in a control group. Niacin treatment was associated with a considerable reduction in LDL-Cholesterol, up-regulation of HDL synthesis, and increase of apo A-1 levels. Gene expression had minimal effect on niacin treatment, except CYP7A1 which was down-regulated at the same time when considerable change in HDL-C, LDL-C and apoA-1 levels was observed. The presence of CYP7A1:Asn233Ser polymorphism may have played a critical role in metabolising niacin and influencing the up-regulation of HDL-C synthesis in the African green monkey. Although cholesterol lowering alone may explain the anti-atherosclerotic effect of niacin on HDL-C, in this study, gene expression data also shed some light in supporting the hypothesis that genetic variants may influence the expression of genes involved in RCT, which may also have played a role in the anti-atherosclerotic effect of the drug.

There is much interest in the electronic potential of ‘nano’-semiconductors. The avenue of research pursued in this project was in inorganic analogues of graphene, namely metal chalcogenides MxEy (M = metal, E = S, Se, Te, x ≠ y = integer value). Thin films of these materials have been used in solar cells, ambient thermoelectric generators and IR detectors, due to their interesting properties, such as: optoelectronics, magnetooptic, piezoelectric, thermoelectric and photovoltaic, as well as electrical conductivity. The key issues with the use of these materials are the formation of controlled films, especially in terms of stoichiometry, crystallinity and uniformity, and also the precursor system used. The aim of this research was to synthesise and isolate novel precursor compounds for use in the deposition of metal sulfide thin films (for use with molybdenum and tungsten). The potential viability of the compounds as single source precursors (ssp) was judged following ThermoGravimetric Analysis (TGA). The compounds were also subjected to analysis using NMR (1H, 13C and 31P where applicable), infrared and UV-Vis spectroscopy, as well as elemental analysis. Cadmium sulfide (CdS) is one of the key direct band gap II-VI semiconductors, having vital optoelectronic applications for laser light-emitting diodes, and optical devices based on non-linear properties. The ratio of these films should ideally be 1:1, however, during the formation of cadmium sulfide films, particularly at elevated temperatures, a common problem encountered is the production of sulfur deficient films. These films have a formula consistent with 〖Cd〗_x S_y, where x is an integer value greater than y, but the sulfur deficiency is generally no greater than 10 %. In order to correct this sulfur deficiency, it was decided to investigate deposition making use of both a ssp and an additional sulfur source, with the aim of producing uniform films with 1:1 Cd:S.Molybdenum disulfide films have been deposited previously from multi source precursors and more recently using ssp. In this project MoS2 was deposited using novel ssps in both LP and AACVD on a variety of substrates with the aim of producing uniform thin films and assessing any differences in the morphology of the deposition. This work was continued with the deposition of WS2 and MoxW1-xS2 from ssps which had not been reported previously. The films deposited were analysed using XRD, SEM, EDX (when available) and Raman spectroscopy.