Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In this research the possible utilization of carbon nanomaterials in gas sensing applications are investigated. These materials include the 2-dimensional honeycomb-lattice carbon structure called graphene, and the 1-dimensional structures referred to as carbon nanotubes (CNTs). The extraordinary properties and unique morphology of these nanomaterials, make them excellent candidates for sensory applications. This research thus entails the investigation and development of gas sensors with these carbon nanomaterials. This includes the synthesis of CNTs via a chemical vapour deposition (CVD) technique and the fabrication of resistive thin film sensors with the various materials. The functionalization of carbon nanomaterials is also explored, which delivers promising results for sensing gases at room temperature, especially acetylene (C2H2). Furthermore, a unique method is developed to fabricate ultra thin aluminium microstructures. These metallic electrodes are found to be ideal for nanomaterial integration. An experiment is performed to manufacture an integrated sensor with MWCNTs and following the results, a refinement of the procedure and the investigation of FET-based devices are recommended. The results obtained during this work, indicate that engineered carbon nanostructures, such as CNTs and graphene, can potentially be applied in future sensing technologies. / AFRIKAANSE OPSOMMING: Hierdie navorsing ondersoek die moontlike toepassing van koolstof nano-materiale as gas-sensor tegnologie. Hierdie materiale sluit die 2-dimensionele koolstof struktuur, grafeen, asook die sogenaamde 1-dimensionele koolstof nano-buise in. Die buitengewone eienskappe en unieke morfologie van hierdie nano-materiale, maak hul uitstekende kandidate vir sensor toepassings. Hierdie navorsing ondersoek dus die ontwikkeling van gas-sensors met koolstof nano-materiale, insluitend die sintese van koolstof nano-buise deur middel van ’n chemiese damp-neerslag proses, asook die fabrikasie van resistiewe dun film sensors. Die funksionalisering van koolstof nano-materiale is ook ondersoek en belowende resultate is opgelewer met betrekking tot die deteksie van gasse by kamertemperatuur, veral vir asetileen (C2H2) gas. Verder is ’n unieke metode ontwikkel om ultra dun aluminium mikrostrukture te vervaardig en hierdie metaal elektrodes word as ideaal beskou vir die integrasie van nano-materiale. ’n Eksperiment is uitgevoer om ’n geïntegreerde sensor te vervaardig met multi-wand koolstof nano-buise, waarvan die resultate aandui dat die proses verfyn moet word en dat die moontlike toepassing van veld-effek-transistor toestelle ondersoek moet word. Die resultate wat opgelewer is gedurende hierdie navorsing dui daarop dat ontwikkelde nanostrukture, soos koolstof nano-buise en grafeen, as toekomstige sensor tegnologie geïmplementeer kan word.

Les équipes micro-capteurs (IM2NP) et capteurs de gaz (LMMA) développent des capteurs à base de couches minces de CuxO et étudient leurs réponses électriques sous O3. Les travaux de cette thèse ont pour but de mieux comprendre l’interaction solide-gaz à l’échelle atomique en simulant l’adsorption de l’O3 sur les surfaces (111) du CuO et du Cu2O. Pour cela nous avons utilisé la DF T (Density Functional Theory) dans le cadre de deux approximations de la fonctionnelle : la LDA (Local Density Approximation) et la GGA (Generalized Gradient Approximation).Pour le CuO, la correction de Hubbard (DF T + U) a été également prise en compte pour reproduire correctement les comportements semiconducteuret antiferromagnétique du matériau. Tous les calculs ont été menés avec le code SIESTA et montrent que pour les deux matériaux, l'ozone s’adsorbe sur la surface sans défauts, sans se dissocier, induisant un dopage p du matériau. Ceci est en accord avec la diminution de la résistance électrique mesurée expérimentalement sous ozone. Ensuite, l’ozone se dissocie en formant une molécule de O2 et un atome d’oxygène qui restent adsorbés. Cette étape ne semble pas modifier le dopage. Par contre lorsque le capteur n’est plus en présence d'O3, la molécule d’O2 désorbe et le dopage est annihilé. Dans ce mécanisme les énergies mises en jeu sont du même ordre de grandeur pour CuO ou pour Cu2O (allant de −3 eV à −1 eV). Dans l’objectif de développer un capteur de gaz, le CuO, plus facile à obtenir par les techniques de dépôt courantes en microélectronique, semble donc être plus pertinent que le Cu2O, qui a une réponse similaire (voire moindre) mais dont il est difficile d’obtenir une phase pure. / Micro-sensors (IM2NP) and gas sensors (LMMA) team develop sensors based on CuO and Cu2O thin layers and study their electrical responses to O3. The aim of this thesis is a better understanding of the solid-gas interactions at the atomic scale by simulating the adsorption of O3 molecule on the (111) surfaces of CuO and Cu2O. Simulations were performed using the DF T (Density Functional Theory) within two functional approximations : the LDA (Local Density Appriximation) and GGA (Generalized Gradient Approximation). In the case of CuO, the Hubbard correction (DF T + U) was taken into account to properly reproduce the semiconductor and antiferromagnetic behaviors of the material. All calculations were performed with the SIESTA code and show that for the CuO as for Cu2O, O3 is adsorbed on the defect-free surface, without dissociating inducing a p-doping of the material. This observation is consistent with the decrease in electrical resistance measured experimentally under ozone. In a second stage ozone dissociates into a molecule of O2 and an oxygen atom which remains adsorbed. This step does not appear to change the doping. However, when the sensor is no longer in the presence of ozone, O2 molecule is desorbed and doping disappears. In this mechanism, the energies involved during the adsorption or the dissociation of ozone are of the same order of magnitude for CuO or Cu2O (ranging from −1 eV to −3 eV). Aiming to develop a gas sensor, and since the CuO material is easier to obtain by standard deposition techniques (RF sputtering), it seems to be more appropriate than the Cu2O, which has a similar response (even lower) but is more difficult to synthesize in a pure phase.

Os materiais de estrutura perovskita compreendem um vasto grupo de compostos cuja estrutura na sua forma mais simples pode ser representada pela fórmula química ABO3. Uma das principais vantagens que a estrutura perovskita apresenta é o alto grau de flexibilidade em acomodar uma grande variedade de átomos nos sítios A e B, permitindo um maior controle de suas propriedades físicas e químicas bem como a manutenção de sua estrutura básica, mesmo para altas concentrações de átomos substituintes. Devido estas propriedades, estes materiais têm sido aplicados com sucesso como capacitores, varistores, fotoeletrodos, memóriasferroelétricas e sensores de gases. Nas últimas décadas, tem sido reportada a utilização do titanato de estrôncio (SrTiO3, ST) na forma de filmes finos e espessos como sensor de gás oxigênio em altas temperaturas (>500 °C). Recentemente, foi mostrado que o titanato de estrôncio dopado com Fe apresentava uma excelente sensibilidade ao gás ozônio. Entretanto, neste trabalho, somente uma composição foi caracterizada e nem todas as propriedades importantes em relação a esta aplicação foram completamente exploradas. Neste contexto, esta tese de doutorado teve como objetivo verificar o efeito da substituição do átomo de estrôncio pelo lantânio e do titânio pelo Ferro no composto SrTiO3 na forma de pó e filmes finos nanoestruturados com a finalidade de verificar o efeito destas substituições nas propriedades sensoras do material. Inicialmente, com o objetivo de avaliar a influência da adição de La na estrutura do composto ST, amostras na forma de pó do sistema Sr1-xLaxTiO3.(SLT) foram preparadas através do método dos precursores poliméricos. Posteriormente, pelo mesmo método, foram sintetizadas amostras do sistema SrTi1-xFexO3 (STF) e Sr1-XLaxTi1-yFeyO3 (SLTF). A partir das amostras na forma de pó e na forma de solução, filmes finos e espessos foram respectivamente obtidos através das técnicas de deposição por feixe de elétrons (EBD) e spin-coating (SC). As amostras nanoestruturadas na forma de pó e na forma de filmes foram caracterizadas por difração de raios X, espectroscopia de absorção de raios X (XANES) na borda K do Ti e do Fe e espectroscopia de fotoelétrons excitados por raios X (XPS). A análise morfológica foi realizada através das técnicas de microscopia eletrônica de varredura (MEV) e microscopia de força atômica (MFA). As amostras do sistema STF e SLTF na forma de filmes finos foram avaliadas em relação à sensibilidade aos gases O3, NO2, NH3 e CO. Os resultados indicaram que os filmes do sistema SLTF depositados pela técnica de deposição por feixe de elétrons apresentam uma maior sensibilidade ao gás ozônio, enquanto o filme de mesma composição depositado pelo método de spin-coating apresentou uma melhor estabilidade e tempo de recuperação em relação a este mesmo gás. / The perovskite structure materials comprise a large group of compounds with the structure in simple form can be represented by the ABO3. chemical formula. The main advantage that the perovskite structure presents is the high degree of flexibility to accommodate a wide variety of atoms in sites A and B, allowing a greater control of physical and chemical properties of the material, maintaining its structure even for a high concentrations of substituent\'s. Due to these properties, these materials have been successfully applied as capacitors, varistors, photoelectrodes, ferroelectric memories and gas sensors. In the last decade, strontium titanate (SrTiO3, ST) in the form of thin and thick films have been reported as oxygen gas sensor at higher temperatures (> 500 °C). Recently, strontium titanate doped with Fe was used as the first ozone sensor. However, the work was carried out only with a certain composition and some important properties for this application have not been fully exploited. In this context, this PhD thesis aimed to the synthesis of strontium titanate system in powder form and nanostructured thin films with the substitution of Sr for La and Ti for Fe. In order to verify the effect of these substitutions in material properties initially Sr1-xLaxTiO3 (SLT) samples were prepared in powder form by the polymeric precursor method in order to evaluate the influence of the addition of La in the structure of the compound ST. Subsequently, samples were synthesized from SrTi1-x Fex O3 (STF) and Sr1-XLaxTi1-yFeyO3 (SLTF) systems through the polymeric precursors, which were used for the deposition of thin and thick films, which were respectively obtained through electron beam deposition techniques (EBD) and spin-coating (SC). Samples in the form of nanostructured powder and thin films were characterized by X-ray diffraction, X-ray absorption spectroscopy (XANES) at Ti and Fe K-edges and by X-ray photoelectron spectroscopy (XPS). Morphological analysis was performed using the scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The STF and SLTF samples in a thin film form were evaluated towards their sensitivity to O3, NO2, NH3 and CO gases. The results indicated that SLTF films deposited by electron beam deposition technique exhibit higher sensitivity to ozone gas. However the same composition deposited by spin-coating showed a better stability and recovery time relative to the same gas.

Os polímeros conjugados, principalmente da classe dos politiofenos, despontaram como materiais alternativos para a obtenção de camadas quimicamente seletivas em sensores de gases. Dentre as principais vantagens desses materiais estão a possibilidade de obtenção de dispositivos sensores que operem à temperatura ambiente e a diversidade de materiais. Assim, por exemplo, com uma simples modificação da cadeia lateral do politiofeno pode-se obter materiais com diferentes afinidades químicas, o que pode contribuir para a melhora da seletividade desses dispositivos. A seletividade e a sensibilidade são as maiores limitações práticas dos sensores de gases que utilizam os polímeros conjugados como camadas sensoras. Neste trabalho, diferentes derivados do politiofeno foram sintetizados via polimerização oxidativa com cloreto férrico e caracterizados químico-estruturalmente por FTIR, RMN 1H, HPSEC e análise térmica (TG). Filmes desses polímeros foram obtidos pelas técnicas spin-coating e casting, sendo que a escolha da técnica de preparo foi baseada na solubilidade desses polímeros em clorofórmio. Foi demonstrado que as características superficiais e as propriedades de absorção no Uv-vis e de emissão dos filmes desses politiofenos são influenciadas pelos tipos de cadeias laterais presentes nesses polímeros. Esses filmes foram também utilizados no estudo das suas propriedades sensoras óticas e elétricas para a detecção de VOCs e umidade, sendo demonstrado que os sensores óticos são menos sensíveis aos analitos propostos do que os sensores elétricos, apresentando valores de sensibilidades no intervalo de 10-7 a 10-5 ppm-1, respectivamente, com algumas exceções. As respostas de ambos os tipos de sensores contendo PHT foram qualitativamente e quantitativamente reprodutíveis, entretanto, as características de reprodutibilidade dos sensores elétricos de PHT apresentaram grande influência das condições elétricas iniciais de seus filmes. Diferentes padrões de detecção foram apresentados para as detecções óticas e elétricas de um determinado polímero, demonstrando que estes polímeros são bons candidatos para serem utilizados como camadas ativas em dispositivos de detecção de VOCs (compostos orgânicos voláteis). / The conjugated polymers, especially polythiophenes, have emerged as alternative materials to obtain chemically selective layers in gas sensors. The main advantages of these materials are the possibility of obtaining sensing devices that operate at room temperature and the diversity of materials. For example, a simple modification of the side chain of polythiophene can provide materials with different chemical affinities, which can contribute to the improvement of the selectivity of these devices. The selectivity and sensitivity are the main practical limitations of the gas sensors containing conjugated polymers as sensing layers. In this study, different polythiophene derivatives have been synthesized by oxidative polymerization with ferric chloride and characterized by FTIR, 1H NMR, HPSEC and thermal analysis (TG). Films of these polymers have been obtained by spin-coating techniques and casting, depending on their solubility in chloroform. It has been shown that the surface characteristics and the properties of absorption in the UV-vis and the emission of the films of these polythiophene derivatives are dependent on the type of side chain attached to the thiophene ring. These films have been used in the study of their optical and electrical sensing properties of VOCs and humidity, and it has been demonstrated that optical sensors are less sensitive to these analytes than the electrical ones. Their fractional sensitivities are 10-7 and 10-5 ppm-1, respectively, with some exceptions. The responses of such sensors have been qualitatively and quantitatively reproducible, however, the responses of electrical sensors showed influence of the initial electrical characteristics of the films. Different detections patterns were showed for optical and electrical detections of a particular polymer, showing that these polymers are good candidates to be used as active layers in sensing devices to detect VOCs.

Orientador: Alexandre Zirpoli Simões / Resumo: Devido à problemática das intoxicações com monóxido de carbono ser responsável pelo maior tipo de envenenamento do século 21, objetivou-se a produção de materiais nanoestruturados a base de céria, pura e dopada com lantânio (La 3+ ), através do método hidrotermal assistido por micro-ondas com posterior deposição na forma de filmes, para caracterização como dispositivos sensores na detecção de atmosfera de CO, por meio da técnica de sonda de duas pontas. O método de síntese empregado foi eficaz na produção de nanopartículas, com dimensões inferiores a 10 nm, apresentando elevada cristalinidade, caracterizada por um ordenamento periódico a curta e longas distâncias, além da ausência de fases secundárias, comprovadas pelas caracterizações realizadas por difratometria de raios-X (DRX), bem como pelas técnicas de espectroscopias Raman, Infravermelho, Ultravioleta- Visível ou ainda por Ressonância Paramagnética de Elétrons. Os filmes depositados apresentaram uma resposta frente ao gás CO extremamente rápida e seletiva, com tempos de resposta em 54, 12, 5.5 e 2 s para as amostras pura e dopadas com lantânio em 4, 8 e 12%, respectivamente. Além da resposta elétrica, os filmes apresentaram ainda uma resposta óptica, com destaque para a amostra com 8%, a qual muda de cor em menos de 1s, a 380 °C sob pressão de 5 mmHg de CO, tornando-se promissores sensores de gás com resposta dupla (óptica e elétrica). / Doutor

Nos últimos anos, vem crescendo o interesse em investigar o fenômeno da magnetorresistência em diversos materiais (inorgânicos ou orgânicos), uma vez que esse fenômeno se encontra diretamente ligado à fabricação de discos rígidos com elevada capacidade de armazenamento de dados. Estudos anteriores mostraram que o polímero PDO14FV apresenta magnetorresistência de intensidade superior as apresentadas por materiais inorgânicos. Sendo assim, o presente trabalho pretendeu desenvolver a síntese e caracterização de dois oligômeros, o dímero (DO14FV-dim) e o trímero (DO14FV-trim), e investigar o fenômeno da magnetorresistência nesses materiais. Surpreendentemente, esses oligômeros apresentaram magnetorresistência superior àquela obtida com o polímero correspondente. Esses resultados poderão contribuir, em trabalhos futuros, na elucidação do mecanismo desse fenômeno em materiais orgânicos. A síntese dos oligômeros foi feita por reação de Wittig, obtendo-se moléculas de estrutura bem definida e com configuração trans, sendo caracterizadas por métodos espectroscópicos. Visando outras aplicações, os oligômeros e o polímero foram estudados em sensores de gases, na diferenciação entre tipos e marcas de chá. Foi observado que quanto maior é a molécula, maior é seletividade, e, portanto, o polímero foi quem apresentou os melhores resultados. / There is a growing interest in investigating the phenomenon of magnetoresistance in various materials (both organic and inorganic), since it is directly linked to the manufacture of high capacity hard disk drives. Previous studies showed that the polymer PDO14FV presents magnetoresistance with higher intensity than inorganic materials. Therefore, this work consisted in the synthesis and characterization of two oligomers, the dimer (DO14FV-dim) and trimer (DO14FV-trim), of this polymer and the investigation of magnetoresistance in these materials. Surprisingly, these oligomers presented higher magnetoresistance than that exhibited by the polymer. These results may contribute in future works aiming the elucidation of the mechanism of this phenomenon in organic materials. The synthesis of the oligomers was performed by Wittig reaction. Molecules of well defined structure and trans configuration were obtained and characterized by spectroscopic methods. Aiming other applications, the oligomers and polymer were tested in gas sensors, for the discrimination between different types and brands of tea. It was observed that the greater the molecule, the greater the selectivity, and therefore, the polymer gave the best results.

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-11-16Bitstream added on 2014-06-13T19:01:19Z : No. of bitstreams: 1 savu_r_dr_bauru.pdf: 10688901 bytes, checksum: 4c1846c73d88b2e598b43e7a14ea1b7c (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A presente pesquisa teve como principal objetivo a obtenção de estruturas nanométricas de óxido de índio, óxido de estanho e óxido de zinco por evaporação térmica e síntese hidrotérmica e a construção e teste de sensores de gases e de fotodetectores de ultravioleta baseados nessas nanoestruturas. Foram realizados estudos da influência dos parâmetros experimentais das duas rotas de síntese usadas sobre as morfologias e as propriedades das estruturas. Para a obtenção das camadas nanoestruturadas por evaporação térmica foi especialmente construído um forno tubular que permitiu o controle da temperatura de deposição independente da temperatura de evaporação e da distância entre a fonte de evaporação e o substrato. Esses parâmetros, pouco explorados nas pesquisas reportadas na literatura, exerceram uma grande influência sobre a morfologia e as propriedades dos nanofios obtidos. O equipamento permitiu ainda um controle preciso da composição da atmosfera e da pressão de síntese. Na síntese química em solução, a construção de um reator hidrotérmico permitiu o estudo da influência da taxa de resfriamento sobre as dimensões, cristalinidade, morfologia e propriedades das nanoestruturas. Esse estudo, o primeiro do gênero na literatura, ressaltou a importância no controle deste parâmetro para sintetizar estruturas com propriedades melhoradas. As demais variáveis estudadas foram: a concentração das soluções, as camadas catalisadoras, a temperatura e o tempo de síntese. Foram testadas duas estratégias para a obtenção dos filmes nanoestruturados: spin-coating de suspensões de nanoestruturas sobre substratos de silício oxidado ou o crescimento das mesmas, durante a síntese, sobre substratos com camadas catalisadoras de zinco. Os nanofios e as camadas funcionais foram caracterizados por Difração de Raios-X (DRX), Microscopia Eletrônica de Varredura... / The subject of this thesis covers the synthesis and growth of indium, tin and zinc oxide nanostructures by thermal evaporation and hydrothermal synthesis and the fabrication and testing of gas sensors and ultraviolet photodetectors based on these nanosized structures. For both chemical and physical routes, the influence of processing conditions over the morphology, dimensions and electrical properties of the nanowires was investigated. In order to obtain nanostructured layers by thermal evaporation a tubular furnace was specifically builti, allowed the control of the source-substrate distance and the deposition temperature independently of the evaporation one. These parameters, slightly explored in the literature, granted a big influence over the nanowires morphology and properties. Moreover, the equipment permitted the control of deposition atmosphere and pressure. The design and assembly of a hydrothermal reactor allowed studying the influence of the cooling rate over the dimension, morphology, cristallinity and, consequently, the properties of the nanostructures. This study highlighted the importance of controlling this particular parameter in the hydrothermal process, yielding nanostructured materials with enhanced properties. Variables such as solution concentration, synthesis temperature and time, surfanctants and precursors were also explored in the hydrothermal process. In order to obtain nanostructured thin films using the chemical bath deposition, two processing techniques were employed: spin-coating of powder suspensions over oxidized silicon substrates and nanostructured anisotropic growth directly from solution using zinc coated substrates. The nanowires and the functional nanostructured layers were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE - SEM), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS)... (Complete abstract click electronic access below)

Porté par les préoccupations actuelles en matière de sécurité et de qualité environnementale ainsi que par les efforts de recherche entrepris dans ce domaine, le marché mondial des capteurs de gaz est en pleine expansion. Dans le contexte de la commercialisation d'un capteur de gaz, une phase d'amélioration de ses performances, et notamment de sa sensibilité et de sa stabilité, est naturellement nécessaire. Cependant, il s'avère également pertinent d'envisager d'en diminuer le coût de fabrication. Pour cela, il convient de développer une technologie utilisant d'une part des matériaux bas coût et d'autre part permettant de réduire la consommation électrique du dispositif. Dans cette optique, ce travail de thèse a porté sur la réalisation et la caractérisation d'un capteur de gaz oxyde semi-conducteur entièrement basé sur le tungstène et le trioxyde de tungstène pour la détection d'hydrogène sulfuré en milieu industriel. Le principal onjectif était de fabriquer un capteur faible coût en utilisant des techniques d'élaboration simples et des matériaux peu onéreux. Pour cela, notre travail a consisté, dans un premier temps, à développer un élément chauffant en tungstène pouvant fonctionner jusqu'à 500°C. Les procédés mis au point pour la conception de l'élément chauffant ont été utilisés dans l'élaboration des électrodes permettant de mesurer la résistance électrique du film de trioxyde de tungstène. Ensuite, nous avons travaillé sur l'optimisation du procédé de pulvérisation cathodique radio fréquence pour l'élaboration de l'élément sensible en trioxyde de tungstène. Des essais sous gaz ont montré des résultats prometteurs pour la détection d'hydrogène, de dioxyde d'azote et d'ammoniac. / Driven by current safety and environmental quality concerns and research efforts in this area, the global market for gas sensors is expanding rapidly. In the context of the marketing of a gas sensor, a phase of improvement in its performance, and in particular its sensitivity and stability, is naturally necessary. However, it is also relevant to consider reducing the cost of manufacturing. To achieve this, it is necessary to develop a technology that uses low-cost materials and reduces the device's power consumption. In this perspective, this thesis work focused on the realization and characterization of a semiconductor oxide gas sensor entirely based on tungsten and tungsten trioxide for the detection of hydrogen sulfide in an industrial environment. The main objective was to manufacturate a low-cost sensor using simple processing techniques and low-cost materials. To achieve this, our work initially consisted in developing a tungsten heating element that can operate up to 500°C. The processes developed for the conception of the heating element were used in the development of the electrodes for measuring the electrical resistance of the tungsten trioxide film. Then, we worked on the optimization of the radio frequency sputtering process for the development of the tungsten trioxide sensing element. Gas measurements have shown promising results for the detection of hydrogen sulfide, nitrogen dioxide and ammonia.

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.

Effects of urban air pollution on health and environment have lead researchers to find economic air quality monitoring regulations. Since tin dioxide (SnO2) was demonstrated as a gas sensing device in 1962, tin oxide based thin film sensors have been widely studied due to their high sensitivity and fast response. The main advantages of using tin oxide sensors are their low cost, small size and low power consumption for mobile system applications. But, in order SnO2 based sensors to meet low concentration of gases they should be highly upgraded in sensitivity, selectivity and stability. This study was focused on the capacity of dopants in the SnO2 layer to increase the sensitivity of the sensor in detecting carbon monoxide. 1 wt. % Pd promoted and 0.1 wt. % Na-1 % Pd promoted SnO2 multilayer thin films were produced by sol-gel technique followed by spin coating route on soda-lime glass substrates. The EDX and SEM studies showed the surface composition and the surface structure is homogeneous throughout the films. The film thickness was determined app. 450 nm from the SEM image of the cross-section, after coating 8 layers. The experiments conducted at several temperatures namely 150, 175 and 200oC, in oxygen free and 1% oxygen containing atmospheres showed that the responses at higher temperatures in the presence of oxygen were much sharper with respect to others. Besides, Na promoted test sensors showed larger responses with shorter response time in oxygen free atmospheres at relatively lower temperatures. The results showed that the sensor signal is not directly correlated with the carbon dioxide production in oxygen free atmospheres.