Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 62-67). Also available in electronic version.

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Submitted by MARCIA ROVADOSCHI (marciar@unifra.br) on 2018-08-14T17:19:59Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_LucianoSchonsTrevisan.pdf: 2258349 bytes, checksum: f8fa9fb772187e33211210fbbb5722df (MD5) / Made available in DSpace on 2018-08-14T17:19:59Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_LucianoSchonsTrevisan.pdf: 2258349 bytes, checksum: f8fa9fb772187e33211210fbbb5722df (MD5) Previous issue date: 2009-03-30 / This paper explain about the design and construction of an electric arc discharge reactor to synthesis of carbon nanotubes, using graphite rods as precursors. Unlike the conventional method, it uses the water into open vessel to isolate the reaction of external environment, without needing a sealed and pressurized chamber immersed in inert gas. The project is divided into three parts: mechanical, electronics and software. Preliminary tests provided initial values for the electric current applied to the graphite electrodes during the cycles of synthesis. It was performed in order to ensure the operation of electromechanical system. The samples formed in the reactor were characterized by Raman spectroscopy and Thermal Gravimetric Analysis techniques. Different types of nanostructures were observed in colected samples. The results indicated the presence of low percentage of amorphous carbon in the material formed, as well as the presence of multiple wall carbon nanotubes. The apparatus allows the easy manipulation of the parameters involved in synthesis therefore is able to promot the growth of nanostructured materials so selective and controlled. / Este trabalho aborda o projeto e a construção de um reator de arco elétrico para síntese de nanotubos de carbono, empregando como precursores bastões de grafite. Diferente do método convencional, o proposto reator utiliza água, em uma cuba aberta para garantir o isolamento da reação do meio externo dispensando com isso uma câmara selada, pressurizada e imersa em um gás inerte. O projeto divide-se em três partes: mecânica, eletrônica e o software. Testes preliminares forneceram os valores iniciais para a corrente elétrica aplicada aos eletrodos de grafite durante os ciclos de síntese que foram executados no intuito de certificar o funcionamento do conjunto eletromecânico. As amostras formadas no reator foram caracterizadas por técnicas de espectroscopia Raman e análise termo gravimétrica. Nas amostras coletadas diferentes tipos de nanoestruturas foram observadas. Os resultados indicaram a presença de baixa porcentagem de carbono amorfo junto ao material formado, assim como a presença de nanotubos de carbono de múltiplas paredes. O aparato permite a fácil manipulação dos parâmetros envolvidos na síntese, sendo assim capaz de promover o crescimento de materiais nanoestruturados de forma seletiva controlada.

This thesis deals with the detection of gases. Based on the research, the theoretical part is devoted to the principles and construction of chemical gas sensors, especially the chemoresistive gas sensors, mainly with the active layer consisting of metal oxides and carbon nanotubes. In the second half of the theoretical part the carbon nanostructures, their properties and the methodology of preparation are reviewed. The experimental part deals with the type of support structure, preparation of the active layer and the method of its deposition and he principle of detection. In the results and discussion, the thesis focuses on the detailed processing of the results and the evaluation of the response ammonia, the impact of the modifications and procedures. In the end, the results obtained are compared, both with each other and with the relevant literature.

The electronic structure of the zero-gap two-dimensional graphene has a charge neutrality point exactly at the Fermi level that limits the practical application of this material. There are several ways to modify the Fermi-level-region of graphene, e.g. adsorption of graphene on different substrates or different molecules on its surface. In all cases the so-called dispersion or van der Waals interactions can play a crucial role in the mechanism, which describes the modification of electronic structure of graphene. The adsorption of water on graphene is not very accurately reproduced in the standard density functional theory (DFT) calculations and highly-accurate quantum-chemical treatments are required. A possibility to apply wavefunction-based methods to extended systems is the use of local correlation schemes. The adsorption energies obtained in the present work by means of CCSD(T) are much higher in magnitude than the values calculated with standard DFT functional although they agree that physisorption is observed. The obtained results are compared with the values available in the literature for binding of water on the graphene-like substrates. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.