The first part of this dissertation is an introduction describing a brief historical background of carbon nanotubes (CNTs) and their pseudo 1D structure responsible for many exotic electronic properties. The second part describes our experimental setup. The third part is about the growing of Multi-Walled Carbon Nanotubes (MWCNTs) by the chemical vapor deposition (CVD) method. Then the fourth part demonstrates a simple but reliable method to make firm contact junctions between MWCNTs and metals such as tungsten (W). The novel point of our method consists, after making a mechanical preliminary contact at a selected MWCNT, in applying a series of voltage pulses across the contact. Thin oxide layers that may form between the MWCNT and the W wire, are removed in steps by the resistive heating and electron impact during the application of each voltage pulse. Furthermore, this simple process of contact welding in steps does not bring about any permanent change in the electronic transport properties of the MWCNTs. The fifth part discusses our bending experiments. We apply a uniform and continuous bending to a selected MWCNT at room and liquid nitrogen temperatures to study the strain effect on the electrical transport in the MWCNT. There are a few published experimental works related to the bending deformation; however, this is the first study of electronic transport properties in continuous bending and releasing deformations. We observed a saturation behavior with the MWCNT and also found the bending deformation causing an anomalous change in the saturation behavior. In the sixth part we depict some interesting phenomena due to the stretching deformation of MWCNT, where we were able to propose a simple model for electron localization induced by the deformation. The last part deals with the formation of the "X-junction" between two MWCNTs. A strong X-junction can be formed simply by means of the e-beam inside the Scanning Electron Microscope (SEM). The X-junctions may form the basic elements of nano-electronic circuits such as various metal-insulator junctions, quantum dots, and similar devices. / text

Unikaliomis savybėmis pasižyminčios anglinės nanostruktūros panaudojamos dangų ir plėvelių gamyboje, kurios pritaikomos nanoelektronikoje, biotechnologijoje ir kitose srityse. Šio darbo tikslas buvo susintetinti daugiasienius anglinius nanovamzdelius ir grafito oksidą, pagaminti ir ištirti jų dangas. Mūsų laboratorijoje daugiasieniai angliniai nanovamzdeliai buvo susintetinti cheminio nusodinimo iš garų fazės metodu. Susintetinto produkto valymui nuo katalizatoriaus priemaišų pirmą kartą buvo panaudoti CCl4 garai. Ištyrus CCl4 garais paveiktą medžiagą buvo pagrįstas šio valymo metodo efektyvumas. Grafito oksidas buvo gautas oksiduojant grafitą Hummers'o metodu. Anglinių nanovamzdelių dangos ant skirtingų pagrindų buvo pagamintos cheminio nusodinimo iš garų fazės metodu bei suformuotos panaudojant medžiagos vandenines suspensijas. Grafito oksido su Kongo raudonojo dažo priedu dangos ir plėvelės buvo pagamintos laboratorijoje sukurtu filtravimo į tirpalą metodu. Anglinių nanovamzdelių ir jų dangų tyrimo rezultatai parodė, kad dangų morfologija priklauso nuo sintezės sąlygų, o paviršiaus savybes nulemia prisijungusių funkcinių grupių pobūdis ir kiekis. Ištyrus grafito oksido plėveles ir dangas buvo nustatyta, kad Kongo raudonojo dažo priedas skatina kompaktiškesnių nanokompozitų susidarymą ir stiprina dangų bei plėvelių patvarumą. / Films and coatings of carbonaceous nanostructures are employed in nanoelectronics, biotechnology and other fields. The aim of the research was to synthesize multi-walled carbon nanotubes and graphite oxide and fabricate coatings thereof. Consequently, multi-walled carbon nanotubes and their coatings were synthesized by the catalytic chemical vapour deposition method. As-grown carbon nanotubes inevitably contain remains of metal catalyst particles. A method developed in the laboratory using CCl4 was successfully applied to remove the residual catalyst from the batch of synthesized carbon nanotubes. Simultaneously, graphite oxide was synthesized from graphite powder by Hummer's method. Coatings and films of carbonaceous nanostructures were fabricated from carbon nanotubes and graphite oxide aqueous suspensions. The analysis of carbon nanotubes coatings revealed that their morphology depends on synthesis parameters. The surface properties of these coatings depend on the amount and nature of functional groups attached to carbon nanotube walls. The analysis of graphite oxide films indicated that Congo red dye addition leads to more compact structure of the nanocomposites due the interaction between functional groups of these particles.

<p>This study reports on the changes in the structural properties of a tungsten-filament when exposed to a methane / hydrogen ambient for different durations at various filament-temperatures.</p>

Films and coatings of carbonaceous nanostructures are employed in nanoelectronics, biotechnology and other fields. The aim of the research was to synthesize multi-walled carbon nanotubes and graphite oxide and fabricate coatings thereof. Consequently, multi-walled carbon nanotubes and their coatings were synthesized by the catalytic chemical vapour deposition method. As-grown carbon nanotubes inevitably contain remains of metal catalyst particles. A method developed in the laboratory using CCl4 was successfully applied to remove the residual catalyst from the batch of synthesized carbon nanotubes. Simultaneously, graphite oxide was synthesized from graphite powder by Hummer's method. Coatings and films of carbonaceous nanostructures were fabricated from carbon nanotubes and graphite oxide aqueous suspensions. The analysis of carbon nanotubes coatings revealed that their morphology depends on synthesis parameters. The surface properties of these coatings depend on the amount and nature of functional groups attached to carbon nanotube walls. The analysis of graphite oxide films indicated that Congo red dye addition leads to more compact structure of the nanocomposites due the interaction between functional groups of these particles. / Unikaliomis savybėmis pasižyminčios anglinės nanostruktūros panaudojamos dangų ir plėvelių gamyboje, kurios pritaikomos nanoelektronikoje, biotechnologijoje ir kitose srityse. Šio darbo tikslas buvo susintetinti daugiasienius anglinius nanovamzdelius ir grafito oksidą, pagaminti ir ištirti jų dangas. Mūsų laboratorijoje daugiasieniai angliniai nanovamzdeliai buvo susintetinti cheminio nusodinimo iš garų fazės metodu. Susintetinto produkto valymui nuo katalizatoriaus priemaišų pirmą kartą buvo panaudoti CCl4 garai. Ištyrus CCl4 garais paveiktą medžiagą buvo pagrįstas šio valymo metodo efektyvumas. Grafito oksidas buvo gautas oksiduojant grafitą Hummers'o metodu. Anglinių nanovamzdelių dangos ant skirtingų pagrindų buvo pagamintos cheminio nusodinimo iš garų fazės metodu bei suformuotos panaudojant medžiagos vandenines suspensijas. Grafito oksido su Kongo raudonojo dažo priedu dangos ir plėvelės buvo pagamintos laboratorijoje sukurtu filtravimo į tirpalą metodu. Anglinių nanovamzdelių ir jų dangų tyrimo rezultatai parodė, kad dangų morfologija priklauso nuo sintezės sąlygų, o paviršiaus savybes nulemia prisijungusių funkcinių grupių pobūdis ir kiekis. Ištyrus grafito oksido plėveles ir dangas buvo nustatyta, kad Kongo raudonojo dažo priedas skatina kompaktiškesnių nanokompozitų susidarymą ir stiprina dangų bei plėvelių patvarumą.

Vertically aligned multi walled carbon nanotube (MWCNT) arrays fabricated by xylene pyrolysis in anodized aluminum oxide (AAO) templates without the use of a catalyst, were integrated into a resistive sensor design. The steady state sensitivities as high as 5% and 10% for 100 ppm of NH3 and NO2 respectively at a flow rate of 750 sccm were observed. A study was undertaken to elucidate (i) the dependence of sensitivity on the thickness of amorphous carbon layers, (ii) the effect of UV light on gas desorption characteristics and (iii) the dependence of room temperature sensitivity on different NH3 and NO2 flow rates. An equivalent circuit model was developed to understand the operation and propose design changes for increased sensitivity. Multi Walled Carbon NanoTubes (MWCNTs) – Polymer composite based hybrid sensors were fabricated and integrated into a resistive sensor design for gas sensing applications. Thin films of MWCNTs were grown onto Si/SiO2 substrates via xylene pyrolysis using chemical vapor deposition technique. Polymers like PEDOT:PSS and Polyaniline (PANI) mixed with various solvents like DMSO, DMF, 2-Propanol and Ethylene Glycol were used to synthesize the composite films. These sensors exhibited excellent response and selectivity at room temperature when exposed to low concentrations (100ppm) of gases like NH3 and NO2. Effect of various solvents on the sensor response imparting selectivity to CNT – Polymer nanocomposites was investigated extensively. Sensitivities as high as 28% was observed for a MWCNT – PEDOT:PSS composite sensor when exposed to 100ppm of NH3 and -29.8% sensitivity for a MWCNT-PANI composite sensor to 100ppm of NO2. A novel nanostructured electrode design for Li based batteries and electrochemical capacitor applications was developed and tested. High density and highly aligned metal oxide nanowire arrays were fabricated via template assisted electrochemical deposition. Nickel and Molybdenum nanowires fabricated via cathodic deposition process were converted into respective oxides via thermal treatments and were evaluated as electrodes for batteries and capacitor applications via Cyclic Voltammetery (CV). Several chemical baths were formulated for the deposition of pristine molybdenum nanowires. Superior electrochemical performance of metal (Ni and Mo) oxide nanowires was observed in comparison to the previously reported nano-particle based electrodes.

abstract: Low temperature fuel cells are very attractive energy conversion technology for automotive applications due to their qualities of being clean, quiet, efficient and good peak power densities. However, due to high cost and limited durability and reliability, commercialization of this technology has not been possible as yet. The high fuel cell cost is mostly due to the expensive noble catalyst Pt. Alkaline fuel cell (AFC) systems, have potential to make use of non-noble catalysts and thus, provides with a solution of overall lower cost. Therefore, this issue has been addressed in this thesis work. Hydrogen-oxygen fuel cells using an alkaline anion exchange membrane were prepared and evaluated. Various non-platinum catalyst materials were investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201) and compared with commercial noble metal catalysts. Co and Fe phthalocyanine catalyst materials were synthesized using multi-walled carbon nanotubes (MWCNTs) as support materials. X-ray photoelectron spectroscopic study was conducted in order to examine the surface composition. The electroreduction of oxygen has been investigated on Fe phthalocyanine/MWCNT, Co phthalocyanine/MWCNT and commercial Pt/C catalysts. The oxygen reduction reaction kinetics on these catalyst materials were evaluated using rotating disk electrodes in 0.1 M KOH solution and the current density values were consistently higher for Co phthalocyanine based electrodes compared to Fe phthalocyanine. The fuel cell performance of the MEAs with Co and Fe phthalocyanines and Tanaka Kikinzoku Kogyo Pt/C cathode catalysts were 100, 60 and 120 mW cm-2 using H22 and O2 gases. This thesis also includes work on synthesizing nitrogen doped MWCNTs using post-doping and In-Situ methods. Post-doped N-MWNCTs were prepared through heat treatment with NH4OH as nitrogen source. Characterization was done through fuel cell testing, which gave peak power density ~40mW.cm-2. For In-Situ N-MWCT, pyridine was used as nitrogen source. The sample characterization was done using Raman spectroscopy and RBS, which showed the presence ~3 at.% of nitrogen on the carbon surface. / Dissertation/Thesis / M.S.Tech Technology 2012

Este trabalho traz a aplicação de alta pressão e alta pressão/temperatura (4.0 GPa e 400º C), em amostras de nanotubos de carbono de paredes múltiplas (NTCPM) comerciais para a obtenção de amostras compactas. Os NTCPM foram funcionalizados com ácido nítrico e ácido nítrico/ácido sulfúrico e, também foram usados nanotubos de carbono dopados com nitrogênio. Foram também processadas amostras contendo nanotubos de carbono de paredes múltiplas incorporados em matriz de zircônia obtida pelo método sol-gel. Para aplicação da alta pressão foi usado um sistema com câmaras do tipo toroidal, utilizando grafite como meio transmissor de pressão. Foram obtidas amostras macroscópicas autossuportadas e com resistência ao manuseio principalmente nas amostras de nanotubos de carbono funcionalizados com ácido nítrico/ácido sulfúrico incorporados em zircônia. Para a caracterização das amostras foram utilizadas as técnicas de Microscopia Eletrônica de Transmissão, Espectroscopia Raman, Difração de Raios X e isotermas de adsorção/dessorção de nitrogênio com as quais foi possível determinar que mesmo após a aplicação de alta pressão/temperatura os nanotubos de carbono não sofrem significativas modificações na sua estrutura e nas suas propriedades morfológicas e texturais, confirmando então que os NTCPM mantém suas características originais, apresentando condições para aplicações em dispositivos. As amostras macroscópicas contendo nanotubos de carbono de paredes múltiplas incorporados em zircônia apresentaram ainda resistência à carga de milhares de vezes o seu peso e comportamento de materiais semi-condutores. / This work presents the application of high pressure and/or high pressure/temperature (4.0 GPa and 400 ° C), on different samples of commercial multi-walled carbon nanotube (MWCNT) to obtain compacted samples. MWCNT were functionalized with nitric acid and nitric acid/sulfuric acid, and also carbon nanotubes doped with nitrogen. MWCNT incorporated in a zirconia matrix obtained by sol-gel method were also processed. For high pressure application it was used a system with the toroidal-type chamber, using graphite as a pressure transmitting medium. Self-supported macroscopic samples were obtained, easy to handle, especially in samples of functionalized carbon nanotubes with nitric and sulfuric acid and also incorporated in zirconia. To characterize the samples it was used Transmission Electron Microscopy, Raman Spectroscopy, X-ray diffraction and nitrogen adsoption/desorption isotherms and it was determined that even after application of high pressure/temperature carbon nanotubes do not suffer significant changes in their structure and in their morphological and textural properties, confirming that the CNT keeps its original characteristics and providing conditions for device applications. The macroscopic samples containing MWCNT incorporated in zirconia also exhibited resistance to load of thousands times its own weight and behavior like semiconductor materials.

Este trabalho traz a aplicação de alta pressão e alta pressão/temperatura (4.0 GPa e 400º C), em amostras de nanotubos de carbono de paredes múltiplas (NTCPM) comerciais para a obtenção de amostras compactas. Os NTCPM foram funcionalizados com ácido nítrico e ácido nítrico/ácido sulfúrico e, também foram usados nanotubos de carbono dopados com nitrogênio. Foram também processadas amostras contendo nanotubos de carbono de paredes múltiplas incorporados em matriz de zircônia obtida pelo método sol-gel. Para aplicação da alta pressão foi usado um sistema com câmaras do tipo toroidal, utilizando grafite como meio transmissor de pressão. Foram obtidas amostras macroscópicas autossuportadas e com resistência ao manuseio principalmente nas amostras de nanotubos de carbono funcionalizados com ácido nítrico/ácido sulfúrico incorporados em zircônia. Para a caracterização das amostras foram utilizadas as técnicas de Microscopia Eletrônica de Transmissão, Espectroscopia Raman, Difração de Raios X e isotermas de adsorção/dessorção de nitrogênio com as quais foi possível determinar que mesmo após a aplicação de alta pressão/temperatura os nanotubos de carbono não sofrem significativas modificações na sua estrutura e nas suas propriedades morfológicas e texturais, confirmando então que os NTCPM mantém suas características originais, apresentando condições para aplicações em dispositivos. As amostras macroscópicas contendo nanotubos de carbono de paredes múltiplas incorporados em zircônia apresentaram ainda resistência à carga de milhares de vezes o seu peso e comportamento de materiais semi-condutores. / This work presents the application of high pressure and/or high pressure/temperature (4.0 GPa and 400 ° C), on different samples of commercial multi-walled carbon nanotube (MWCNT) to obtain compacted samples. MWCNT were functionalized with nitric acid and nitric acid/sulfuric acid, and also carbon nanotubes doped with nitrogen. MWCNT incorporated in a zirconia matrix obtained by sol-gel method were also processed. For high pressure application it was used a system with the toroidal-type chamber, using graphite as a pressure transmitting medium. Self-supported macroscopic samples were obtained, easy to handle, especially in samples of functionalized carbon nanotubes with nitric and sulfuric acid and also incorporated in zirconia. To characterize the samples it was used Transmission Electron Microscopy, Raman Spectroscopy, X-ray diffraction and nitrogen adsoption/desorption isotherms and it was determined that even after application of high pressure/temperature carbon nanotubes do not suffer significant changes in their structure and in their morphological and textural properties, confirming that the CNT keeps its original characteristics and providing conditions for device applications. The macroscopic samples containing MWCNT incorporated in zirconia also exhibited resistance to load of thousands times its own weight and behavior like semiconductor materials.

Made available in DSpace on 2018-06-27T18:56:01Z (GMT). No. of bitstreams: 2 Pamela Andrea Mantey dos Santos.pdf: 2526880 bytes, checksum: 65765d7ccb4a7545ed4eba0ac7107949 (MD5) Pamela Andrea Mantey dos Santos.pdf.jpg: 3186 bytes, checksum: 0f9641eb6b0cc6bd929c9c7c3f165b1b (MD5) Previous issue date: 2011-03-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / It is well known in the scientific community the importance of carbon nanotubes viewed first by Iijima in 90 s. Carbon nanotubes show great potential in many applications in different fields of knowledge, especially in the development of new materials. Several studies introduce applications of carbon nanotubes as reinforcement in many types of matrices such as ceramics and polymers, which are subjected to high pressure, in order to improve the mechanical properties of these materials. These studies are intended to use these compacts as electronic devices, mechanical applications, waveguides, and others. However, there are no studies in literature about application of high pressure on carbon nanotubes self-sustaining, that is, only carbon nanotubes, in order to obtain dense compacts, for possible applications of these materials. Thus, this work brings innovative ways of application of high pressure on multi- walled carbon nanotubes using two different pressure transmitting media, to evaluate their behavior. These evaluations were performed by characterizations such as Raman spectroscopy. It was estimated the defect level in the samples and also the dependence of the G band with pressure and with the pressure transmitting media used. It s possible to associate this relationship to the level of tension and/or compression that carbon nanotubes were submitted. X-ray diffraction allowed determination of impurities trapped in carbon nanotubes in its manufacturing process, suggesting that these impurities may possibly act as binding in compression. By surface area measurements using the BET method, it was possible to compare the surface areas of the samples in different pressure transmitting media and its influence on compression. Finally, transmission electron microscopy was used to get images of the samples, which enabled an assessment of the morphology of carbon nanotubes after different processes. / Já é de conhecimento da comunidade científica a grande importância dos nanotubos de carbono referenciados pela primeira vez por Iijima, nos anos 90. Os nanotubos de carbono demonstraram ter um grande potencial em diversas aplicações, nas mais variadas áreas do conhecimento, especialmente no desenvolvimento de novos materiais. Vários trabalhos na literatura trazem a aplicação de NTC como reforço em matrizes poliméricas, também trabalhos envolvendo matrizes cerâmicas são encontrados. Entre esses, alguns materiais são submetidos à alta pressão, com a finalidade de aprimorar as suas propriedades mecânicas. Porém, não há trabalhos na literatura que tratam da aplicação de alta pressão em NTC de forma auto-sustentada, isto é, somente NTC, para obtenção de compactos densos, para uma possível aplicação destes materiais. Assim sendo, este trabalho traz de forma inovadora a aplicação de alta pressão (até 7,7 GPa) em nanotubos de carbono de paredes múltiplas, em dois distintos meios transmissores de pressão, para avaliação e compreensão de seu comportamento. Estas amostras foram caracterizadas através de espectroscopia Raman, onde é possível verificar o nível de defeito nas amostras e também a dependência da banda G com a pressão e o meio transmissor utilizado, sendo possível avaliar através desta relação o nível de tração e/ou compressão a que foram submetidos os nanotubos de carbono. Através da técnica de difração de raios X foi possível determinar as impurezas retidas nos nanotubos de carbono, no seu processo de fabricação, sugerindo-se que estas impurezas podem eventualmente atuar como ligantes na compactação. Através de medidas de área superficial utilizando o método de BET, foi possível a comparação das áreas superficiais das amostras nos diferentes meios transmissores de pressão e a influência do meio transmissor na compactação. Por fim, foram obtidas imagens das amostras, através da técnica de microscopia eletrônica de transmissão, a qual possibilitou uma avaliação da morfologia dos nanotubos de carbono após os diferentes processamentos.

Magister Scientiae - MSc / This study reports on the changes in the structural properties of a tungsten-filament when exposed to a methane / hydrogen ambient for different durations at various filament-temperatures. / South Africa