L’objectif de cette étude est de concevoir et caractériser une plate-forme micro-fluidique permettant la concentration et la séparation d’un produit de dégradation du trinitrotoluène :l’ortho-nitrotoluène (ONT) considéré comme un traceur de composés explosifs. Les capteurs àbase de dioxyde d’étain (SnO2) utilisés ici comme détecteurs présentent un réel manque desélectivité et leur sensibilité peut s’avérer insuffisante pour la détection de traces de polluantsdans l’atmosphère. L’approche originale envisagée dans cette étude consiste à travailler en amontdu capteur chimique (SnO2), en particulier, en développant d’une part un micro-préconcentrateurde gaz afin d’améliorer l’aspect sensibilité et d’autre part une micro-colonne chromatographiquepour s’affranchir du manque de sélectivité.Dans un premier temps, une série d’adsorbants ont été étudiés et caractérisés pour laconcentration de l’ONT. Les résultats obtenus ont permis de sélectionner trois types de charbonsactifs (N, KL2 et KL3) et une zéolithe hydrophobe DAY.Ensuite, les micro-systèmes fluidiques ont été réalisés sur un substrat de silicium et élaborés enutilisant la technologie silicium/verre.La dernière partie de ce travail est consacrée à l’évaluation des performances d’analyse de cetteplate-forme en termes de concentration et de séparation de l’ONT. En particulier, après avoirévalué les conditions optimales de concentration et d’élution de l’ortho-nitrotoluène, le couplageentre la plate-forme micro-fluidique et le capteur à base de dioxyde d’étain a permis d’une part demontrer que la limite de détection de l’ortho-nitrotoluène est inférieure à 365 ppb. Dans ce cas,une désorption totale de la molécule cible et un facteur de concentration constant ont été obtenusavec la zéolithe DAY. D’autre part, l’utilisation de ce type de plate-forme a permis d’obtenir unebonne performance de détection et de séparation de l’ONT en présence d’un interférent (toluène)et d’un taux d’hygrométrie élevé. / The objective of this study is to develop and characterize a micro-fluidic platform allowing theconcentration and the separation of a degradation compound of trinitrotoluene: the orthonitrotoluenerecognized as an explosive taggants. Tin dioxide gas sensors (SnO2) used here asdetectors suffer from a luck of selectivity and have an insufficient sensitivity toward most ofpollutants. For that, our original approach consists to work in front of a chemical gas sensor(SnO2), in particular, by developing on the one hand a gas micro-preconcentrator to improve thesensitivity and on the other hand, a chromatographic micro-column in order to overcome the luckof selectivity.First, various adsorbents have been studied and characterized for the ONT concentration. Theobtained results allowed to select three types of activated carbons (N, KL2 and KL3) and ahydrophobic zeolite DAY. Then, the micro-system devices have been realized on a siliconsubstrate and manufactured using the silicon/glass technology.The last part of this work is devoted to the evaluation of the platform performances in terms ofconcentration and separation of ONT. In particular, after the optimization of the experimentalconditions concerning the concentration and the elution of ortho-nitrotoluene, the couplingbetween the micro-fluidic platform and a tin dioxide gas sensor allowed on the one hand to showthat the detection limit of the ONT pollutant is lower than 365 ppb. In this case, a total desorptionof the analyte and a constant concentration factor were obtained with the zeolite DAY. On theother hand, the use of this type of platform allowed to obtain a good separation and detectionperformance of ONT in presence of interferent (toluene) and at high humidity rate

<p>In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).</p>

<p>In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).</p>

Made available in DSpace on 2014-12-17T14:07:02Z (GMT). No. of bitstreams: 1 MichelineRA_DISSERT.pdf: 3734590 bytes, checksum: b9c518dbcf57b2b63cf9d386db2a5df1 (MD5) Previous issue date: 2012-02-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Continuous Synthesis by Solution Combustion was employed in this work aiming to obtain tin dioxide nanostructured. Basically, a precursor solution is prepared and then be atomized and sprayed into the flame, where its combustion occurs, leading to the formation of particles. This is a recent technique that shows an enormous potential in oxides deposition, mainly by the low cost of equipment and precursors employed. The tin dioxide (SnO2) nanostructured has been widely used in various applications, especially as gas sensors and varistors. In the case of sensors based on semiconducting ceramics, where surface reactions are responsible for the detection of gases, the importance of surface area and particle size is even greater. The preference for a nanostructured material is based on its significant increase in surface area compared to conventional microcrystalline powders and small particle size, which may benefit certain properties such as high electrical conductivity, high thermal stability, mechanical and chemical. In this work, were employed as precursor solution tin chloride dehydrate diluted in anhydrous ethyl alcohol. Were utilized molar ratio chloride/solvent of 0,75 with the purpose of investigate its influence in the microstructure of produced powder. The solution precursor flux was 3 mL/min. Analysis with X-ray diffraction appointed that a solution precursor with molar ratio chloride/solvent of 0,75 leads to crystalline powder with single phase and all peaks are attributed to phase SnO2. Parameters as distance from the flame with atomizer distance from the capture system with the pilot, molar ratio and solution flux doesn t affect the presence of tin dioxide in the produced powder. In the characterization of the obtained powder techniques were used as thermogravimetric (TGA) and thermodiferential analysis (DTA), particle size by laser diffraction (GDL), crystallographic analysis by X-ray diffraction (XRD), morphology by scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) and electrical conductivity analysis. The techniques used revealed that the SnO2 exhibits behavior of a semiconductor material, and a potentially promising material for application as varistor and sensor systems for gas / A S?ntese Cont?nua por Combust?o em Solu??o (SCCS) foi empregada na obten??o de p?s de di?xido de estanho nanoestruturados. Basicamente, uma solu??o precursora ? preparada, sendo posteriormente atomizada e aspergida na chama, onde ocorre a combust?o, levando ? forma??o das part?culas. A t?cnica apresenta um grande potencial na produ??o de nanopart?culas, principalmente pelo baixo custo de insumos e equipamentos. O di?xido de estanho (SnO2) nanoestruturado tem sido amplamente utilizado em diversas aplica??es, principalmente como sensores de g?s e varistores. No caso dos sensores ? base de cer?micas semicondutoras, em que as rea??es de superf?cies s?o respons?veis pela detec??o dos gases, a import?ncia da ?rea superficial e do tamanho de part?culas ? ainda maior. A prefer?ncia por um material nanoestruturado deve-se ao fato de que essas entidades apresentam alguns pontos fundamentais tais como, o aumento significativo da ?rea superficial comparados aos p?s microcristalinos convencionais e o reduzido tamanho de part?cula, que pode beneficiar certas propriedades como alta condutividade el?trica, alta estabilidade t?rmica, mec?nica e qu?mica. Neste trabalho, foram empregados como solu??o precursora cloreto de estanho dihidratado dilu?dos em ?lcool et?lico anidro. Foi utilizada a raz?o molar cloreto/solvente de 0,75 no intuito de investigar sua influ?ncia na microestrutura do material obtido. O fluxo da solu??o precursora foi de 3 mL/min. A an?lise por difra??o de raios X da solu??o precursora com raz?o molar cloreto/solvente de 0,75 indicou a obten??o de um p? cristalino e monof?sico e todos os picos s?o atribu?dos a fase SnO2. Par?metros de s?ntese como dist?ncia da chama com o atomizador, dist?ncia do sistema de capta??o com a chama piloto, raz?o molar e fluxo da solu??o precursora n?o afetaram a fase di?xido de estanho no material obtido. Na caracteriza??o do p? obtido, foram utilizadas t?cnicas como an?lises termogravim?tricas (ATG) e termodiferenciais (ATD), granulometria por difra??o de laser (GDL), an?lise cristalogr?fica por difra??o de raios X (DRX), morfologia por microscopia eletr?nica de varredura (MEV), microscopia eletr?nica de transmiss?o (MET), medida de ?rea superficial espec?fica (BET) e ensaio de condutividade el?trica. O conjunto de t?cnicas revelaram que o SnO2 apresenta comportamento de um material semicondutor, sendo um material potencialmente promissor ? aplica??o como varistor e em sistemas de sensores ? gases

Magister Scientiae - MSc / In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE). / South Africa

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O diÃxido de estanho (SnO2) em forma de filme fino pode ser produzido com grande transparÃncia à luz visÃvel e boa condutividade elÃtrica. Os filmes finos de SnO2 possuem muitas aplicaÃÃes tecnolÃgicas na indÃstria, principalmente em aparelhos eletrÃnicos que utilizam display de visualizaÃÃo, como em dispositivos em laboratÃrios de pesquisa. Uma das aplicaÃÃes mais promissoras à a sua utilizaÃÃo como Ãxido condutor transparente em cÃlulas solares fotovoltaicas. Devido as suas caracterÃsticas de transparÃncia Ãtica no espectro visÃvel e baixa resistividade, os filmes finos de diÃxidos de estanho sÃo empregados como componente constituinte de cÃlulas solares fotovoltaicas. A proposta deste trabalho à a utilizaÃÃo de um forno, que utiliza a tecnologia de CombustÃo em Meios Porosos para fabricaÃÃo de filmes finos de diÃxido de estanho sobre substratos de vidro, utilizando a tÃcnica de spray pirÃlise. O forno utilizado nesse projeto possui uma cÃmara, onde os filmes de SnO2 sÃo sinterizados, e uma antecÃmara, onde a soluÃÃo precursora dos filmes à aplicada sobre substratos de vidro. Uma pistola spray foi adaptada ao forno, acoplada a antecÃmara, para a aspersÃo da soluÃÃo de estanho sobre substratos de vidro. Foi utilizada a tÃcnica de dopagem dos filmes finos com flÃor com o intuito de reduzir a resistÃncia à corrente elÃtrica. Os filmes finos de SnO2 foram caracterizados em relaÃÃo a transmitÃncia Ãtica ao espectro visÃvel e em relaÃÃo a resistÃncia elÃtrica. TambÃm foram realizadas medidas de difraÃÃo de raios-X e microscopia de forÃa atÃmica para a revelaÃÃo e estudo da estrutura dos filmes de Ãxido de estanho. / The tin dioxide (SnO2) as thin film can be produce with high transparency to visible light and good electrical conductivity. The SnO2 thin films have many technological applications in industry, mainly in electronic devices that use preview display, such as devices in research laboratories. One of the most promising applications is its use as a transparent conductive oxide in photovoltaic solar cells. Due to its transparency in the visible spectrum and low resistivity, the films of tin dioxide are used as a constituent component of photovoltaic solar cells. The present work aims to use a heat furnace, which uses combustion in porous media technology for the production of thin films of tin dioxide (SnO2) on glass substrates, using the technique of spray pyrolysis. The furnace used has a chamber where the films of SnO2 are sintered and a pre-chamber, where the precursor solution is applied films on glass substrates. Spray gun was adapted to furnace and coupled to the antechamber for the spraying of the solution of tin on glass substrates. The technique of doping thin films of Fluoride was used in order to reduce the resistance to electrical current. The thin films of SnO2 was characterized by their optical transmittance spectrum and electrical resistance. The structure of films of tin oxide was study by x-ray diffraction and atomic force microscopy.

L’objectif de cette étude est le développement d’un capteur de gaz à base de couche hybrideSnO2/SWNTs dans le but d’améliorer les performances des capteurs chimiques « classiques »uniquement constitués de dioxyde d’étain. En premier lieu, afin de maîtriser la synthèse dumatériau sensible, nous avons validé l’élaboration d’une couche sensible à base de dioxyded’étain préparée par procédé sol-gel. Le matériau synthétisé a été déposé par la technique ‘microgoutte’sur une micro-plateforme permettant simultanément le chauffage de la couche sensible etla mesure de sa conductance. L’étude des réponses électriques du capteur de gaz en présence dubenzène a permis de valider la possibilité d’utilisation du sol d’étain préparé pour la réalisation decouches sensibles aux gaz. En effet, des traces de benzène (500 ppb) ont été détectées à latempérature optimale de couche sensible de 420°C.Le second volet de cette étude repose sur la fabrication du matériau hybride obtenu par dispersiondes nanotubes de carbone dans un sol d’étain. Les couches sensibles élaborées par dip-coating àpartir du sol d’étain modifié par les nanotubes de carbone ont clairement montré la possibilité dedétection de divers gaz (ozone et ammoniac) à température ambiante. Ce résultat constitue l’undes points importants de ce travail de thèse dans la mesure où jusqu’à présent les capteurschimiques à base de dioxyde d’étain ne présentaient une forte sensibilité aux gaz que pour destempératures de fonctionnement de l’ordre de 350-400°C. Pour les deux gaz cibles étudiés dans lecadre de ce travail, la limite de détection à température ambiante a été évaluée à 1 ppm enprésence de NH3 et est inférieure à 20 ppb en présence d’ozone.La dernière partie de ce travail a porté sur l’optimisation des performances de détection descouches hybrides. Dans ce cadre, les expérimentations ont porté sur l’étude de l’influence dedivers paramètres tels que la quantité de nanotubes dans le matériau hybride, la température decalcination de la couche sensible, la température de fonctionnement ou encore les propriétésphysico-chimiques des nanotubes de carbone (mode de synthèse, diamètre,…) sur l’efficacité dedétection des couches sensibles. Les résultats ainsi obtenus en termes de performance de détectionont été discutés en relation avec les paramètres expérimentaux utilisés. / The objective of this study is to develop a gas sensor based on a hybrid layer of SnO2/SWNTs inorder to improve the performance of “Conventional” chemical sensors basically made from tinoxide. First, in order to control the synthesis of the sensitive material, we validated the elaborationof a sensitive layer based on tin dioxide prepared using the sol-gel process. The synthesizedmaterial was deposited by the 'microdrop' technique on a micro-platform which simultaneouslyallows the heating of the sensitive layer whilst also measuring its conductance. The study of theelectrical responses of the gas sensor in the presence of benzene has allowed us to validate thepossibility of using our prepared tin sol for the realization of gas sensitive layers. In fact, it waspossible to detect benzene at traces with an optimal temperature of the sensing layer found to be420ºC.The second part of this study describes the synthesis of the hybrid sensor obtained by dispersingSWNTs in the tin-oxide based sol. The sensitive layers made by dip-coating from the carbonnanotubes modified tin sol have clearly shown the possibility of detecting various gases (ozoneand ammonia) at room temperature. This result is one the most important points of this work tothe extent that until now the chemical sensors based on tin dioxide only showed a high sensitivityto gases when they were operated at temperatures in the range of 350 - 400ºC. Concerning the twotarget gases tested in this work, the detection limit at room temperature was evaluated at 1 ppm inthe presence of NH3 and was lower than 20 ppb in the presence of ozone.The last part of this work has focused the optimization of the detection performance of thesensitive layers. In this case, the experimental study was oriented towards examination of theeffect of various parameters such as the amount of nanotubes in the hybrid material, thecalcination temperature of the sensitive layer, the sensor working temperature and also thephysico-chemical properties of the carbon nanotubes (synthesis method, diameter...) on thedetection efficiency of the sensing layers. The results obtained in terms of detection performancewere discussed in relation to the experimental parameters used.

[pt] Catalisadores Mo-SnO2 foram obtidos a partir da precipitação, em solução aquosa, do SnO2.xH2O na presença de (NH4)2Mo7O24 em dois teores de Mo: 5,5 e 14,5 por cento em massa, os quais foram, posteriormente, impregnados com 1 por cento em massa de cátion sódio. Os sólidos obtidos foram caracterizados por espectroscopia de reflectância difusa na região do UV- visível, difração de raios-X, adsorção de nitrogênio, redução à temperatura programada, e espectroscopia de absorção na região do infravermelho de metanol e de piridina adsorvidos. Verificou-se que a presença de sódio resulta na diminuição da área específica, na eliminação dos microporos e dos poros de diâmetro elevado, sendo os últimos referentes aos polimolibdatos. Verificou-se, também, que a presença de sódio propicia o consumo das espécies dispersas de molibdênio, resultando na sua aglomeração, com formação de polimolibdatos. Com relação à acidez dos sólidos, verificou-se que a ação do Na é função da concentração superficial de Mo. No caso de baixa concentração de Mo, observou-se que o sódio promove a eliminação dos sítios de Brönsted e a formação de sítios fracos de Lewis; já para a concentração elevada, observouse, além da formação de sítios fracos de Lewis, um aumento da concentração dos sítios de Brönsted. Assim, o Na altera de forma significativa a textura, a acidez e as espécies de Mo presentes nos catalisadores Mo- SnO2. / [en] Mo-SnO2 catalysts were prepared by SnO2.xH2O precipitation with ammonium heptamolybdate solution. Two Mo amounts were used: 5,5 and 14,5 percent (wt); Afterwards, these samples were impregnated with 1 percent Na (wt). These solids were characterized by nitrogen adsorption, UV-visible diffuse reflectance spectroscopy, temperature programmed reduction, X-ray diffraction, infrared spectroscopy of adsorbed pyridine and methanol. It was observed that the Na addition decreases the surface area of the Mo-SnO2 solids, caused by elimination of the micropores and the large pores of polymolybdates. It was also verified that Na promotes the agglomeration of Mo species, i.e. the amount of Mo dispersed species decreases and the polymolybdate one increases. Sodium also changes the solid acid properties: for the low Mo amount it was observed that Na promoted the formation of weak Lewis acid sites and the elimination of Brönsted sites; on the other hand for the high Mo amount, both Brönsted and weak Lewis acid sites content increased when Na was added. These results showed that sodium changed the texture, the Mo species and the acid properties of Mo-SnO2 catalysts.

Orientador: Luis Vicente de Andrade Scalvi / Resumo: Este trabalho visa apresentar o desenvolvimento e as principais conclusões referentes à combinação de heterojunções a base de GaAs com óxidos semicondutores, para aplicações em dispositivos optoeletrônicos. O texto foi dividido em duas partes principais, sendo a primeira parte voltada para a síntese e produção do SnO2, relacionada com a formação da heteroestrutura GaAs/SnO2; e a segunda parte é focada na produção dos ressonadores de onda acústicas de bulk,na ordem de GHz, a base de GaAs/ZnO. Na primeira parte, priorizou-se filmes de SnO2, que foram depositados por duas técnicas: sol-gel dip-coating e evaporação resistiva. Os filmes foram depositados sobre substratos de vidro soda-lime, e sobre substratos de GaAs, de quartzo e de a-SiO2. SnO2 foi também depositado sobre filme de GaAs depositado por sputtering. No caso da evaporação resistiva, a rota sol-gel é utilizada também para a preparação do pó que é utilizado como precursor para a evaporação resistiva de filmes de SnO2, combinando essas duas técnicas. Foram investigadas as propriedades ópticas e elétricas de filmes finos de SnO2 dopado com 1% de Er3+ e estruturas hibridas de GaAs/SnO2: Er3+. Entre os principais resultados, verificou-se: 1) espectros de luminescência diferentes do íon Er3+ ao se depositar SnO2 sobre substrato de vidro ou GaAs; 2) Microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva de raios-x (EDX) para filmes de SnO2, depositados por evaporação resistiva, atestaram uma relação... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work aims to present the development and the main conclusions obtained so far regarding the combination of GaAs-based heterojunctions with semiconductor oxides, for applications in optoelectronic devices. The text has been divided in two main parts, where the first one is related to the synthesis and production of SnO2, associated with the formation of the heterostructure GaAs/SnO2; and the second one if focused on the production of bulk acoustic wave resonators, with frequencies in GHz range, based on GaAs/ZnO. In the first part, attention was given to SnO2 films, deposited by two techniques: sol-gel dipcoating and resistive evaporation, on soda-lime glass substrates, and on GaAs, quartz and a-SiO2 substrates. SnO2 was also deposited on GaAs film deposited by sputtering. In the case of resistive evaporation, the sol-gel route is also used to prepare the powder which is used as a precursor for resistive evaporation of SnO2 films, then, by combining these two techniques. Optical and electrical properties of Er3+ -doped SnO2 thin films were investigated as well as the hybrid structure GaAs/SnO2 .Among the main results were: 1) different luminescence spectra of Er3+ ion when depositing SnO2 on glass or GaAs substrate; 2) scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) for SnO2 films deposited by resistive evaporation show a relationship of the thermal annealing temperature with the concentration of Er ions in the surface layers; 3) this con... (Complete abstract click electronic access below) / Doutor

This project is aimed at semiconductive gas sensors based on tin dioxide. In the first part, gas sensors are divided depending on their principal of functionality. Next part is about functionality of tin dioxide gas sensors and the possibilities of active layer modification. Experimental describes gas sensor from its drawing until construction, testing and characterization. Several microelectronic technologies such as thin-film, thick-film, LTCC, spray-coating or wire-bonding were used for constructing the sensor. In the last part properties of gas sensors and differences in functionality between modified and unmodified gas sensor are summarized.