Made available in DSpace on 2014-06-11T19:27:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-12-19Bitstream added on 2014-06-13T20:56:56Z : No. of bitstreams: 1 lima_lm_me_arafo.pdf: 817104 bytes, checksum: 137c4b299daadfdf7ba4a2a6bd1a030b (MD5) / A tecnologia CVD (Chemical Vapor Deposition) aplicada à confecção de pontas odontológicas diamantadas possibilitou aderência do diamante à haste metálica suficiente para suportar o efeito do ultra-som, surgindo então uma técnica alternativa para corte de tecido dentário. O objetivo deste estudo in vitro foi avaliar a efetividade dos corte realizados com as pontas CVD cilíndrica e esférica para ultra-som (pontas CVDentUSÒ), em esmalte e dentina de dentes permanentes, variando-se o sentido de movimento (frontal e lateral). Foram utilizados 40 terceiros molares, num total de 80 preparos cavitários confeccionados por meio de um dispositivo padronizador. Os cortes foram realizados com 30 movimentos consecutivos da ponta sobre a superfície dentária, correspondendo a 27 segundos de utilização das pontas CVDentUSÒ. A profundidade e largura dos preparos cavitários foram analisadas em microscopia eletrônica de varredura e medidas por meio de uma análise cefalométrica modificada no programa Radiocef 4.0 (Radiocef Memory Ltda). A análise estatística pelo teste não paramétrico de Kruskal-Wallis ao nível de significância de 5% mostrou que as maiores médias de largura e profundidade foram observadas nos preparos de dentina, sendo a ponta esférica responsável por cavidades mais profundas e a cilíndrica por cavidades mais largas, não havendo influência dos sentidos de movimento da ponta. / The CVD (Chemical Vapor Deposition) technology applied in dental diamond burs manufacture allowed to the diamond to have enough adherence to the metallic stem supporting the ultrasound effect. This technique is bringing back an alternative method to cut dental tissue. The aim of this in vitro study was to evaluate the cutting effectiveness of cylindrical and round CVD-coated diamond burs for ultrasound (CVDentUSÒ system), in enamel and dentine of permanent teeth, changing the movement sense (frontal and lateral). Forty third molars were used, in a total of 80 cavity preparations made using a standard device. The cuts were made with 30 consecutive movements of the bur on the dental surface, corresponding to 27 seconds of CVDentUSÒ tips use. The depth and width of the cavity preparations were analyzed by scanning electronic microscopy and the measures were made using a modified cefalometric analysis in a Radiocef 4.0 program (Radiocef Memory Ltda). The statistical analysis applying Kruskal-Wallis non-parametric test, at 5% significance level, showed that the largest width and depth averages were observed in dentine cavities, being the round bur responsible for deeper cavities and the cylindrical for wider cavities. The movement senses had no influence on cavity size.

O presente trabalho estuda a produção e modificações físico-químicas do grafeno frente a tratamentos térmicos. Em uma primeira etapa, foi investigada a síntese de grafeno pela técnica de Deposição Química a partir da fase Vapor (CVD) sobre fitas de cobre. Nós variamos quatro parâmetros que influenciam no crescimento de grafeno: fluxo de metano (CH4), fluxo de hidrogênio (H2), tempo de crescimento e grau de pureza do cobre. Usando as técnicas de caracterização de espectroscopia Raman e microscopia óptica, observamos que fluxo menor de H2 e fluxo intermediários de CH4 favorecem o crescimento de grafeno de alta qualidade. Além disso, vimos que 15 minutos de crescimento de grafeno é suficiente para cobertura do substrato de cobre com grafeno. Por fim, foi visto que o maior grau de pureza do cobre permite a produção de monocamadas de grafeno mais homogêneas. Numa segunda etapa, foi realizado um estudo com objetivo de entender a interação de hidrogênio com monocamadas de grafeno. Nós usamos amostras de grafeno depositadas em filmes de SiO2 (285 nm)/Si e tratadas termicamente em atmosfera controlada de deutério (99,8%) em temperaturas entre 200 e 800 °C. Nós também investigamos a dessorção de hidrogênio do grafeno usando amostras previamente tratadas em deutério a 600 °C e depois tratadas em atmosfera controlada de nitrogênio em temperaturas entre 200 e 800 °C. Após os tratamentos, análise por reação nuclear (NRA) foi realizada para quantificar o deutério, onde nós observamos uma grande incorporação de deutério no grafeno acima de 400 °C, tendo um aumento moderado até 800 °C. Nós também observamos que a dessorção do deutério do grafeno ocorre apenas em 800 °C, embora a dessorção de deutério do óxido de silício ocorra a partir de 600°C. Espectroscopia Raman também foi realizada após cada tratamento térmico. Os resultados mostram que os defeitos na estrutura do grafeno têm um grande aumento para as etapas de maior temperatura na incorporação de deutério. Análises realizadas com Espectroscopia de Fotoelétrons Induzidos por Raios X (XPS) mostraram que a incorporação de deutério para maiores temperaturas causa o "etching" do grafeno. Por fim, caracterizações usando Espectroscopia de Absorção de Raios X (NEXAFS) mostraram que o deutério liga-se ao grafeno sem orientação preferencial. / The present work studies the production and physical-chemical modifications of the graphene under thermal annealings. In a first study, the graphene synthesis by Chemical Vapor Deposition (CVD) on copper foils was investigated. We varied four parameters that influence the growth of graphene: methane flow (CH4), hydrogen flow (H2), growth time and copper purity. Using Raman spectroscopy and optical microscopy, we observed that lower flux of H2 and intermediate flux of CH4 leads to the growth of high quality graphene. In addition, we observed that 15 minutes growth of graphene is sufficient to cover the copper substrate. A higher copper purity allows the production of homogeneous graphene monolayers. In a second step, a study was carried out to understand the interaction of hydrogen with graphene monolayers. We used graphene samples deposited on SiO2 (285 nm)/Si films and annealed in a controlled atmosphere of deuterium (99.8%) at temperatures between 200 and 800 °C. We also investigated the hydrogen desorption of graphene using samples previously treated in deuterium at 600 °C and then annealed in a controlled atmosphere of nitrogen at temperatures between 200 and 800 °C. After the annealings, nuclear reaction analysis (NRA) was performed to quantify the deuterium, where we observed a large incorporation of deuterium in graphene above 400 °C, with a moderate increase up to 800 °C. We also observed that desorption of deuterium occurs only at 800 °C, although deuterium desorption from silicon oxide occurs at 600 °C. Raman spectroscopy was also performed after each annealing. The results show that defects in the structure of graphene have a large increase for deuterium incorporation. Analyzes carried out with X-ray Photoelectron Spectroscopy (XPS) showed that the deuterium incorporation at higher temperatures leads to graphene etching. Finally, characterizations using X-ray Absorption Spectroscopy (NEXAFS) showed that deuterium binds to graphene without preferential orientation.

Dans le vaste domaine des nanosciences et nanotechnologies, les nanotubes de carbone (NTC) suscitent un intérêt particulier en raison de leur structure originale qui leur confère des propriétés exceptionnelles. Alors que le nombre d'applications ainsi que la quantité de NTC produite ne cessent d'augmenter chaque année, il est essentiel de comprendre les mécanismes régissant la formation de ces nanomatériaux afin de contrôler leur structure et leur organisation, optimiser les rendements, diminuer les risques sanitaires et environnementaux et améliorer les performances des matériaux et composants sous-jacents. Parmi les techniques de synthèse répertoriées, la CVD d'aérosol (Chemical Vapor Deposition) développée au laboratoire MSSMat, permet la croissance continue de NTC multi-feuillets de haute qualité sur divers substrats par l’injection simultanée de sources carbonées liquide (xylène) et gazeuse (acétylène) et de précurseur catalytique (ferrocène) dans un réacteur porté à une température comprise entre 400 et 1000°C. L'objectif de cette étude a consisté à examiner les différentes étapes de la formation des NTC dès l'injection des précurseurs jusqu'à la fin de la croissance. Grâce une nouvelle approche expérimentale faisant intervenir plusieurs diagnostics in situ couplés à des modèles numériques, nous avons pu suivre l'évolution des différents réactifs et produits lors de synthèses dans des conditions thermodynamiques (flux de gaz et températures) et chimiques (concentrations des différents précurseurs) variées. De fait, après avoir examiné l'évolution spatiale des gouttelettes formées lors de l'injection, la germination des nanoparticules en phase gazeuse a été étudiée par incandescence induite par laser (L2I) et spectroscopie de plasma induit par laser (LIPS). Une relation entre la taille de ces particules et celle des NTC a ainsi pu être mise en évidence. Les réactions chimiques pendant la synthèse ont ensuite été analysées par spectrométrie de masse et chromatographie en phase gazeuse. Différents mécanismes réactionnels ont ainsi pu être identifiés en fonction des sources de carbone utilisées, alors que l'effet de l'hydrogène sur la croissance, soit accélérateur ou soit inhibiteur selon les conditions, a été étudié. Les rôles du substrat ont par ailleurs été examinés en comparant la croissance et la morphologie des NTC obtenus sur différentes surfaces telles que des plaques de quartz, des fibres de carbone ou des micro-particules d'alumine, de carbure de silicium, de carbure de titane et de graphène de formes variées. L'effet catalytique de certains substrats ou mélanges de substrats sur la croissance des NTC a d'ailleurs été mis en évidence, de même que l'importance du rapport surface/volume des substrats sur les rendements massiques des NTC. La cinétique de croissance des NTC a finalement été étudiée et différents mécanismes à l'origine de la désactivation des catalyseurs ont été identifiés. Enfin, les différentes nanostructures hybrides issues de la croissance de NTC sur différents substrats ont servi à concevoir des matériaux composites multi-fonctionnels à hautes-performances dont les propriétés électriques, thermiques et mécaniques ont été analysées. / In the vast field of nanoscience and nanotechnology, carbon nanotubes (CNTs) are of particular interest because of their unique structure which provides them outstanding properties. While the number of CNT-based applications as well as the amount of CNTs produced are increasing year by year, it is essential to understand the mechanisms governing the formation of these nanomaterials to control their structure and organization, maximize the yields, reduce the health and environmental risks and improve the performance of the underlying materials and components. Among the listed synthesis techniques, the aerosol-assisted chemical vapor deposition (CVD) process developed in the laboratory MSSMat allows continuous growth of multi-walled CNTs (MWNTs) on various substrates by the simultaneous injection of carbon feedstock(s) (xylene and/or acetylene) and catalytic precursor (ferrocene) in a reactor heated up to a temperature ranging between 400 and 1000°C. The aim of this study was to analyse the different stages of the CNT formation from the first precursor injection until the growth termination. By the mean of a new experimental approach involving several in situ diagnostics coupled with numerical models, we were able to follow the evolution of the different products and reagents during the synthesis under various thermodynamic and chemical conditions. Hence, after investigating the spatial evolution of the droplets formed in the injection, the nanoparticle germination and nucleation in the gas phase has been studied by time resolved laser-induced incandescence (TRL2I) and laser-induced breakdown spectroscopy (LIBS). A relationship between the size of the particles and the CNTs has been highlighted. Moreover, the chemical reactions during the synthesis were analyzed by mass spectrometry (MS) and gas phase chromatography (GPC). Different reaction pathways have thus been identified depending on the carbon source(s) used, while the effect of hydrogen on the CNT growth, either accelerating or inhibiting based on the CVD conditions, was studied. The substrates' roles were then examined by comparing the growth and morphology of the CNTs obtained on various surfaces such as quartz plates, carbon fibers or micro-particles of alumina, silicon carbide, titanium carbide and graphene. The catalytic effect of some substrates or mixtures of substrates on the CNT growth has also been highlighted, as well as the importance of the substrate's surface/volume ratio on the CNT mass yields. Furthermore, the CNT growth kinetics have been studied and different mechanisms inducing catalyst deactivation and subsequently growth termination were identified. Finally, the different as-synthesized nanostructures originated from the hybridization of CNTs with other materials were used to prepare high-performance multi-functional composites. The electrical, thermal and mechanical properties of these materials have been examined.

Orientador: Ioshiaki Doi / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-07T10:45:55Z (GMT). No. of bitstreams: 1 Teixeira_RicardoCotrin_D.pdf: 2331304 bytes, checksum: 01dc54b878be8180e9b3c17033a3feb1 (MD5) Previous issue date: 2006 / Resumo: Conforme os dispositivos eletrônicos atingem dimensões nanométricas, surgem limitações que não podem ser solucionadas com os materiais empregados atualmente, como efeito de canal curto, depleção de porta, corrente de fuga e variação do Vt devido à variação estatística da dopagem. Dessa forma, novos materiais devem ser introduzidos no processo de fabricação para solucionar estes problemas. Um dos materiais cotados é a liga de silício germânio policristalino (SiGe-poli) em substituição ao Silício poli cristalino (Si-poli), utilizado atualmente como material de porta em MOSFET's. Nesta tese, estudamos a deposição de filmes de SiGe-poli utilizando um reator LPCVD vertical visando a fabricação de dispositivos MOS. Tanto o processo de deposição como características morfológicas e físicas dos filmes obtidos foram analisadas. Também foram realizadas medidas elétricas nas amostras e em dispositivos. Verificamos que os filmes obtidos apresentam uma excelente uniformidade e suas características elétricas permitem o seu uso em eletrodos de porta de dispositivos MOS / Abstract: As electron devices shrinks to nanometric scale, new concerns emerge that can not be solved using the materials employed nowadays such as short channel effect, gate depletion, high leakage current and Vt spreading due to statistical variation of the doping process. Thus, new materials must be included in the manufacturing process in order to solve these problems. One of these materials is the polycrystalline silicon germanium alloy (poly-SiGe) as substitution for the polycrystalline silicon (poly-Si) in MOSFET gate applications. In this thesis, we study the deposition of poly-SiGe thin films using a vertical LPCVD reactor aiming for MOS devices fabrication. 80th the deposition process and morphological and physical characteristics of the deposited samples were evaluated. Electrical measurements were also performed on the samples and on devices. We found that the obtained samples have an excellent uniformity and that the electrical characteristics allow its usage as gate electrodes in MOS devices / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica

O dióxido de titânio possui diversas aplicações tecnológicas, desde pigmento em tintas, até revestimentos funcionais. É um material resistente à degradação eletroquímica e fotoquímica. Com o aumento da produção industrial de corantes, há um aumento significativo da produção de rejeitos, sendo necessário o desenvolvimento de novas técnicas de degradação, a fim de reduzir a formação de efluentes. Dentre essas técnicas encontram-se os processos oxidativos avançados (POAs), que se baseiam na formação de radicais hidroxila para a degradação dos compostos liberados nos efluentes. A fotocatálise heterogênea utiliza um material semicondutor ativado por radiação ultra-violeta a fim de produzir os radicais hidroxila. Apesar de existirem estudos relacionados à utilização do TiO2 como fotocatalisador, há poucos dados com relação à sua aplicação na forma de filme suportado. Este trabalho teve por objetivos crescer filmes de TiO2 sobre borossilicato, por meio da técnica de deposição química de organometálicos em fase vapor, nas temperaturas de 400 e 500ºC por até 60 minutos, bem como proceder à caracterização microestrutural, morfológica e fotocatalítica desses filmes. Anatase foi a fase identificada em todos os filmes. Os filmes crescidos a 400°C apresentaram estrutura densificada, enquanto que os filmes crescidos a 500°C apresentaram estrutura colunar bem definida. A fotodegradação foi avaliada por meio da degradação do corante alaranjado de metila nos valores de pH 2,00; 7,00 e 10,00. Os resultados de degradação do corante mostraram que a maior eficiência do processo de degradação ocorre em pH = 2. Nessa condição, os melhores resultados ocorrem com o filme crescido por 30 minutos a 400°C, que apresentou 65,3% de degradação. / Titanium dioxide has many technological applications, as pigment in paints, and functional coatings. It is resistant to electrochemical and photochemical degradation. The increase of the industrial production of dyes results in a significant increase in production of wastes, which requires the development of new degradation techniques to reduce the release of effluents. Among these techniques there is the advanced oxidation process (AOP), which is based on the formation of hydroxyl radicals to the degradation of the compounds in the effluent released. The heterogeneous photocatalysis uses a semiconductor material activated by UV radiation to yield hydroxyl radicals. Although there are studies regarding the use of TiO2 as photocatalyst, there are few data related to its application in the form of supported film. The aim of this study was to grow TiO2 films on borosilicate substrate at 400 and 500°C for up to 60 minutes by using metallorganic chemical vapor deposition technique and proceed to the microstructural, morphology and photocatalytic characterization of the films. Anatase phase was identified in all films. The films grown at 400°C presented a densified structure, while the films grown at 500°C showed well defined columnar structure. The photodegradation was assessed by degradation of methyl orange dye in pH 2.00; 7.00 and 10.00. The results of dye degradation showed that the highest efficiency occurred at pH 2. In this condition, the best results occurred for the film grown for 30 minutes at 400°C and presented a degradation of 65.3%.

Orientador: Vitor Baranauskas / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-12T10:05:32Z (GMT). No. of bitstreams: 1 Zanin_HudsonGiovani_M.pdf: 3301666 bytes, checksum: 22536873a4dfcbe671296b78145e6dda (MD5) Previous issue date: 2008 / Resumo: Foi projetado e construído um reator para sintetização de filmes diamantíferos tubulares, por processo de deposição química a partir da fase vapor assistido por filamentos quentes (também conhecido como processo HFCVD - "Hot Filament assisted Chemical Vapor Deposition"). Obtiveram-se filmes de alta homogeneidade com a manutenção do substrato em rotação durante o crescimento. O torque para a rotação ocorre por acoplamento magnético de ímãs posicionados no suporte do substrato e ímãs montados em sistema externo ao reator, mantidos em rotação por um pequeno motor elétrico. Os materiais usados como substratos poderão ter secção de corte transversal circular, quadrada, triangular ou outra qualquer. No caso dos substratos serem ocos (caso mais comum) a temperatura é medida no interior do substrato durante o crescimento, sendo útil para determinar o tipo de material diamantífero que se pretende sintetizar: diamante, DLC (Diamond Like Carbon), carbono amorfo, diamante micro e nanocristalino, etc. São apresentados resultados de crescimento de filmes sobre tubos cilíndricos de quartzo e análise dos mesmos por microscopia eletrônica de varredura e espectroscopia Raman. / Abstract: A hot-filament chemical vapor deposition system was designed and built to grow diamond thin films. This system fed with ethanol highly diluted in hydrogen was employed to deposited diamond layers onto quartz tubes with diameters of 6 mm and length of 10 cm. High uniformity microcrystalline diamond films were obtained thanks the maintenance of the substrate in rotation during growth process. The rotation of the substrate was carried out by magnetic coupling of magnets positioned into support of the substrate and magnets mounted in the system held in rotation by a small electric motor outside of the reactor. The temperature of the substrates was measured inside of them during the growth process. The control of the temperature is useful to determine the type of material that is intended to synthesize: micro and nanodiamond, Diamond Like Carbon (DLC), amorphous carbon and so on. This work presents the results of these growths and their characterization by scanning electron microscopy and Raman spectroscopy. / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / The effects of process conditions on the material’s properties were investigated for the sublimation growth of aluminum nitride and the epitaxial growth of silicon carbide. Since the mid 1990’s, these semiconductors have made new types of high power electronics and short wavelength optoelectronics that were never before feasible. The sublimation growth of AlN crystals on SiC seeds was carried out to produce high quality AlN bulk crystals. Si-face, 3.5 º off-axis 6H-SiC (0001) and 8 º off-axis 4H-SiC (0001) wafers were used as the substrates. An investigation of the initial growth demonstrated 1800 – 1850ºC was the optimum temperature for AlN growth. By optimizing the temperature gradient, large area AlN layer was deposited. Consecutive growths and continuous growth were performed to enlarge the crystal thickness. Single-crystalline AlN layers, each with a thickness of 2 mm and a diameter of 20 mm, were produced. X-ray diffraction confirmed the grown AlN had good crystal quality. Approximately 3 – 6 at% of Si and 5 – 8 at% of C were detected in the crystals by x-ray photoelectron spectroscopy, which came from the decomposition of SiC seeds and the degradation of the graphite components in the furnace. Molten KOH/NaOH etching revealed the dislocation density decreased from 108 cm-2 to 106 cm-2 as the AlN layer thickness increased from 30 μm to 2 mm. Epitaxial growth of SiC was carried out in a chemical vapor deposition system. High-quality 6H-SiC and 4H-SiC homoepitaxial films were produced at growth rates up to 80 μm/hr by using a novel single precursor, methyltrichlorosilane (MTS). Inclusions of 3C-SiC were circumvented by employing 8º mis-orientated substrates. Adjusting the H2/Ar flow ratio in the carrier gas effectively changed the C/Si ratio in the gas phase due to the reaction between H2 and the graphite heater; thereby, influencing surface roughness and dislocation density. Low H2/Ar ratios of 0.1 and 0.125 produced smooth surfaces without step-bunching. Higher H2/Ar ratios of 0.2 and 0.33 enhanced the conversion of basal plane dislocations into threading edge dislocations, and reduced the density of basal plane dislocations to approximately 600 cm-2.

Doctor of Philosophy / Department of Physics / Hongxing Jiang / The correlation between polarity and material quality of un-doped Al[0.81subscript]Ga[0.19subscript]N was studied. The overall material quality is significantly influenced by the growth polarity. The epilayers with aluminum-polarity have a much higher crystalline quality and better surface morphology than those of nitrogen-polarity. Nitrogen-polar growth more readily incorporates unintentional impurities. A-plane AlN epilayers have been grown on r-plane sapphire substrates. The orientation and high crystalline quality were confirmed by x-ray diffraction (XRD) [Theta]-2[Theta] scan exhibiting a reflection peak at 2[Theta] = 59.4[0superscript] and rocking curve of the (110) reflection having a line width of 940 arcsec. Room temperature photoluminescence (PL) spectroscopy showed that the surface emission intensity of a-plane AlN epilayers is comparable to that of c-plane AlN. PL spectra of Mg-doped a- and c-plane AlN revealed that the Mg level in both a- and c-plane AlN is identical and is about ~ 0.5 eV. Identically designed a-plane and c-plane AlN/A1[0.65subscript]Ga[0.35subscript]N QWs have been grown on a-and c-plane AlN/Al[2subscript]O[3subscript] templates respectively, and their PL emission properties were studied. Low temperature PL characteristics of a-plane QWs are primarily governed by the quantum size effect, whereas those of c-plane QWs are significantly affected by the polarization fields. The growth of AlN epilayers on SiC substrates was investigated. A smooth, crack free AlN epilayer with high optical and crystalline quality was achieved. Because of its high quality, AlN was used as active layer in a hybrid Schottky photodetector. Highly conductive Si-doped Al[subscript0.75]Ga[0.25subscript]N alloys were grown on AlN/SiC templates. The effects of using Indium as a surfactant during the growth of Si-doped Al[0.75subscript]Ga[0.25subscript]N epilayers at relatively high temperature 1050 [degrees]C were studied. Indium significantly increases the doping efficiency as shown by RT Hall measurements. RT PL measurements show a clear correlation between emission intensity of the defect related transition and indium flow rate. P-type conductivity has been obtained in beryllium doped GaN by MOCVD. The activation energy of the beryllium acceptor was estimated to be 118 [plus or minus] 4 meV, which is about 40 meV less than the activation energy of the Mg acceptor in GaN.

Master of Science / Department of Chemical Engineering / James H. Edgar / 4H-silicon carbide (4H-SiC) is a wide band gap semiconductor with outstanding capabilities for high temperature, high power, and high frequency electronic device applications. Advances in its processing technology have resulted in large micropipe-free single crystals and high speed epitaxial growth on off-axis silicon face substrates. Extraordinarily high growth rates of high quality epitaxial films (>100 [Mu]m per hour) have been achieved, but only on off-axis substrates (misoriented 4° to 8° from the (0001) crystallographic plane). There is a strong incentive to procure an on-axis growth procedure, due to the excessive waste of high quality single crystal associated with wafering off-axis substrates. The purpose of this research was to develop a reliable process for homoepitaxial growth of 4H-SiC on on-axis 4H-SiC. Typically the use of on-axis SiC for epitaxial growth is undesired due to the increased probability of 3C-SiC inclusions and polycrystalline growth. However, it is believed that the presence of chlorine during reaction may reduce the presence of 3C-SiC and improve the quality of the epitaxial film. Therefore homoepitaxial SiC was deposited using methyltrichlorosilane (MTS) and ethane sources with carrier gases consisting of argon-hydrogen mixtures. Ethane was used to increase the C/Si ratio, to aid in the prevention of 3C-SiC, and to help eliminate silicon droplets deposited during epitaxial growth. Deposition occurred in a homemade, quartz, cold wall chemical vapor deposition reactor. Epitaxial films on on-axis 4H-SiC were deposited without the presence of 3C-SiC inclusions or polycrystalline SiC, as observed by defect selective etching, scanning electron microscopy and optical microscopy. Large defect free areas, [similar to]5 mm[superscript]2, with epitaxial film thicknesses of [similar to]6 [Mu]m were grown on on-axis 4H-SiC. Epitaxial films had approximately an 80%, [similar to]20 cm[superscript]-2, decrease in defect density as compared to the substrates. The growth rate was independent of face polarity and orientation of the substrate. The optimal temperature for hydrogen etching, to promote the smoothest epitaxial films for on-axis substrates (both C- and Si-polarities), is [similar to]1550 °C for 10 minutes in the presence of 2 slm hydrogen. The optimum C/Si ratio for epitaxial growth on on-axis 4H-SiC is 1; excess carbon resulted in the codeposition of graphite and cone-shaped silicon carbide defects.

The goal of this thesis work is to investigate the possibility to grow graphene by Chemical Vapor Deposition (CVD) on copper foil with acetylene as a precursor and varigon (5\% H$_2$ in Ar) as a carrier gas. The possibility of nitrogen doping by ammonia treatment during the growth process is also investigated. The possibility of graphene transfer, with the use of Poly(Methyl Metacrylate) (PMMA), from the copper onto another target substrate, Flourine doped Tin Oxide (FTO), is also explored. The main technique of characterization of the grown and transfered graphene is Raman spectroscopy, a great tool for investigating the number of graphene layers and amount of defects. Other characterization methods used are Scanning Electron Microscopy (SEM) X-ray Photoelectron Spectroscopy (XPS) to investigate morphology and elemental composition, respectively. The result of this thesis study is that graphene growth is entirely possible with acetylene as a precursor, as shown by the Raman spectroscopy, XPS and SEM. The grown graphene has a high quality with few layers and a low number of defects. The ammonia treatment, however, doesn't seem to have an immediate effect on the graphene growth. The XPS data indicates that there are no nitrogen doping in the graphene, though there might be a correlation between the ammonia and the number of layers, but further investigations has to be made. Transfer is also proven possible with the method developed. However, improvements to the transfer method can be done since there are both larger tares, caused by the transfer onto the FTO, as well as microscopic tares, possibly caused by thermal expansion of the PMMA.