CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / O presente trabalho explora a fabricaÃÃo, montagem e testes de micro-reatores e de sensores de gÃs baseados em nanotubos de carbono. A configuraÃÃo dos sensores de gases foi planejada de modo a permitir o uso de nanotubos de carbono de muitas paredes â como adquiridos comercialmente, oxidados ou decorados com nanopartÃculas - como elementos sensores de comportamento semelhante a um elemento sensor formado por nanotubos de carbono de uma Ãnica parede e com grandes diÃmetros (~20 nm). Nesta configuraÃÃo, os nanotubos foram depositados utilizando a tÃcnica dieletroforese com as pontas apoiadas sobre as bordas dos eletrodos e com a parte central suspensa (em ponte) sobre um gap de ~1 m de largura por ~5 m de profundidade, de modo a ligar as extremidades de eletrodos metÃlicos padronizados prÃ-produzidos. Uma nova abordagem para melhorar o contato elÃtrico e tÃrmico entre nanotubos de carbono de mÃltiplas paredes depositados por dieletroforese e eletrodos de metal foi desenvolvida, usando aquecimento espacialmente localizado, atravÃs do uso de laser. Subsequentemente à deposiÃÃo, os nanotubos foram diretamente aquecidos, em atmosfera ambiente, por um feixe de laser focado. O sinal Raman dos nanotubos foi usado para determinar a temperatura atingida no processo e este mÃtodo foi utilizado para melhorar o contato elÃtrico com diferentes eletrodos (W, Ti e Au). A reduÃÃo na resistÃncia elÃtrica foi de atà trÃs ordens de magnitude, resultando em resistividade de contato tÃo baixa quanto ~ 0,1-1 kΩ.μm2, com os menores valores obtidos para Au. Um novo mÃtodo de deposiÃÃo de nanotubos com simultÃnea decoraÃÃo por nanopartÃculas de ouro crescidas pelo mÃtodo eletroquÃmico tambÃm à apresentado. O mÃtodo possibilita obtenÃÃo de estruturas hÃbridas com alto potencial de aplicaÃÃo em dispositivos opto-eletrÃnicos, tais como sensores de gases, biossensores ou fotodetectores. A caracterizaÃÃo estrutural e morfolÃgica de cada elemento sensor usado neste trabalho foi feita principalmente por microscopia eletrÃnica de varredura, microscopia eletrÃnica de transmissÃo, espectroscopia de energia dispersiva, espectroscopia Raman e medidas elÃtricas. Foram usados elementos sensores com diferentes combinaÃÃes de materiais nanoestruturados (MWCNTs como adquiridos comencialmente, oxidados, ou decorados com nanopartÃculas metÃlicas), testados em atmosferas inertes (N2 ou Ar) e oxidante (O2). ParÃmetros determinantes para um bom funcionamento dos sensores de gÃs (tempos especÃficos de resposta/recuperaÃÃo, sensibilidade, estabilidade, reprodutibilidade, etc) foram investigados com base nos dados experimentais obtidos. / This work exploits the fabrication, setup and tests of the micro-reactors and gas sensors based on carbon nanotubes. The configuration of the gas sensors was designed to allow the use of multi-walled carbon nanotubes - as commercially acquired, oxidized or decorated with nanoparticles â as sensor elements which have similar behavior to a sensor element formed of a single-walled carbon nanotube with large diameter (~ 20 nm). In this configuration, the nanotubes were deposited using dielectrophoresis technique with their ends supported on the edges of the electrodes and the central part suspended (bridged) over a gap ~ 1 m wide and ~5 m deep, in order to connect the ends of pre-produced standard metal electrodes. A new approach to improve the electrical and thermal contact between multi-walled carbon nanotubes deposited by dielectrophoresis and metal electrodes was developed by using heating spatially localized, through the use of laser radiation in the microRaman setup. Subsequent to deposition, the nanotubes were directly heated in the ambient atmosphere by a focused laser beam. The Raman signal of the nanotubes was used to determine the temperature reached in the process and this method has been used to improve the electrical contact with different electrodes (W, Ti and Au). The reduction in electrical resistance was up to three orders of magnitude, resulting in contact resistivity as low as ~ 0,1-1 kΩ.μm2, with the lowest values obtained for Au. A new method of simultaneous deposition of nanotubes and decoration with gold nanoparticles grown by electrochemical method is also presented. The method enables the production of hybrid structures with high potential for application in opto-electronic devices such as gas sensors, biosensors or photodetectors. The structural and morphological characterization of each sensor element used in this work was mainly made by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, Raman spectroscopy and electrical measurements. Sensing elements with different combinations of nanostructured materials (MWCNTs as commercially acquired, oxidized, or decorated with metal nanoparticles) were tested in inert (Ar or N2) and oxidant (O2) atmosphere. Crucial parameters for the proper functioning of gas sensors (specific response time/recovery, sensitivity, stability, reproducibility, etc.) were investigated based on the obtained experimental data.

No description available.

L’analyse des gaz d’échappement des moteurs à combustion interne a été traditionnellement réalisée en laboratoires en utilisant des analyseurs de gaz en vrac avec des équipements coûteux. Afin de créer un système capable de réaliser le travail de ces analyseurs, un capteur pouvant détecter plusieurs gaz simultanément est indispensable pour en mesurer la concentration. En effet, utiliser un capteur pour chaque gaz est couteux et peut amener à des procédures complexes d’analyse en raison des différentes technologies utilisées. De plus, l’utilisation de multiples capteurs donne lieu à une perte de ressources financières et humaines. Pour pallier ce problème, une approche alternative proposée dans cette thèse consiste à utiliser un seul capteur pour l’analyse simultanée des différents gaz. Cette approche contribue à réduire la complexité des analyses, la taille et la collecte de données des mesures de gaz mentionnés précédemment. Elle permet également la baisse du coût de l’ensemble du système des mesures.Cette thèse présente la conception, la méthodologie et le développement d’une nouvelle approche pour la mesure de la concentration de gaz utilisant le traitement d’images numériques à travers la modélisation du mélange des couleurs d’émission de lumière dans le tube de décharge de gaz. L’application du modèle inverse permet d’obtenir le pourcentage de chaque gaz dans un mélange contenant jusqu'à quatre gaz connaissant la couleur d’émission du mélange et la couleur d’émission de chaque gaz. Nous discutons aussi le potentiel de certaines méthodes quant à leurs propriétés de miniaturisation et leurs limites. Une comparaison entre les différents capteurs miniaturisés est réalisée en termes suivant la sensibilité, la sélectivité, le coût et d’autres conditions. Pour atteindre les objectifs de recherche, les problèmes techniques rencontrés tels que la modélisation de mélange des couleurs, l’étalonnage de capteurs pour l’acquisition d’images, et le traitement des erreurs de mesures ont été identifiés et des solutions ont été proposées. / Gases represent one of the most important key measurands in many industrial and domestic activities. The need to detect single gas or a group of gases at the same time varies from one application to another. One of the most important applications of gas sensing is in the concentration measurement of exhaust emissions in internal combustion engines. The variety of gases emitted by these engines and the necessity for a precise measurement of their concentrations are the major incentives for researchers to develop gas sensors that are not only limited to a certain type of gases but to a variety of gases. The most interest gases include CO, NO, NO2, NH4, SO2, CO2, CH4 and other hydrocarbons. These gases can be harmful to human health if present beyond a certain concentration. The analysis of exhaust emissions of internal combustion engines has traditionally been achieved in laboratories using bulk gas analyzers and costly equipments. In order to create a system which can do the work of these analyzers, a sensor that can measure the concentration of multiple gases at the same time is needed. Instead of using a sensor for each gas which is costly and introduce another complexity to the analysis procedure due to the different technologies that are used in the detection of different types of gases. This directly translates into loss of financial and human resources that could otherwise be productively used. In an effort to remedy this situation, this dissertation proposes an alternate approach that uses one sensor to analyze multiple gases simultaneously. This has a significant potential in reducing the aforementioned complexity, size and data collection tasks, and at the same time can lower the cost of the overall system.This dissertation presents the design, methodology, and development of a new method for gas concentration measurement using digital image processing through modeling the color mixing of light emissions in gas discharge tube. The application of the inverse model allows us to get the percentages of each gas in a mixture of up to four gases knowing already the color of emission of the whole mixture and the color of emission of each gas alone. It also discusses the miniaturization potential of some of the methods that are promising in the ability of their miniaturization but suffer from different problems. A comparison is also done among the miniaturized sensors in terms of different parameters like sensitivity, selectivity, cost and other terms. In achieving the research objectives, major technical challenges such as color mixing modeling, imaging sensor calibration, and measurements’ error handling have been successfully identified and addressed.

L’objectif principal de ce travail de thèse est de contribuer au développement d’un outil de diagnostic miniaturisé permettant d’identifier et de quantifier une combinaison de composés organiques volatils (COVs) présents dans l’haleine et qui sont considérés comme des marqueurs chimiques du cancer du poumon. Les principaux verrous scientifiques de ce projet sont liés aux très faibles concentrations de ces composés cibles (de l’ordre de quelques ppb) et également à la présence de nombreux autres composés chimiques qui sont naturellement présents dans l’haleine. La voie de développement proposée dans ce projet est d’utiliser un micro-capteur résistif à base de SnO2 associé à un micro-préconcentrateur et une micro-colonne chromatographique afin d’aboutir à un dispositif sélectif et présentant des limites de détection très basses. Dans un premier temps, plusieurs adsorbants ont été caractérisés en vue d’être utilisés dans le micro-préconcentrateur afin de concentrer les marqueurs du cancer du poumon. Les résultats ont permis de sélectionner deux types de zéolites (DaY et NaY) ainsi que des microsphères de carbone W5. Par la suite, les unités de préconcentration et de séparation des COVs ont été développées en s’appuyant sur la technologie silicium/verre disponible en salle blanche. La dernière étape de cette étude a concerné l’évaluation des performances du système d’analyse alors assimilable à un micro-chromatographe en phase gazeuse. Après avoir déterminé les conditions optimales d’élution et de préconcentration des COVs, le système miniaturisé a permis d’analyser une haleine artificielle constituée de trois COVs présents à des concentrations proches des celles mesurées dans l’haleine (toluène (24 ppb), propanol (21 ppb) et o-xylène (5 ppb)) même en présence des interférents majeurs de l’haleine (vapeur d’eau et dioxyde de carbone). / The main goal of this research is to develop a miniaturized diagnostic equipment in order to identify some volatile organic compounds present in exhaled breath and referred as lung cancer biomarkers. The main scientific and technical obstacles of this project are linked to the very low concentrations of these chemical compounds and the presence of high concentrations of H2O and CO2 naturally present in exhaled breath. To address these issues, we suggest to use a SnO2-based gas sensor combined with a micro-preconcentrator and a chromatographic micro-column in order to engineer a low detection limit system. First, some specific adsorbents have been characterized with a view to concentrate chemical biomarkers trough the micro-preconcentrator. In accordance with research findings, two types of zeolites (DaY and NaY) and one type carbonaceous microspheres (W5) have been selected. Then micro-preconcentrators and chromatographic micro-columns have been developed on silicon wafers by using clean room facilities. The last step of this study was to evaluate the performances of the analytical device. After determining optimal elution and pre-concentration conditions of each VOCs, the miniaturized system achieved the analysis of an artificial breath constituted of toluene (24 ppb), 1-propanol (21 ppb) and o-xylene in presence of high concentrations of water vapors and carbon dioxide.

Orientador: César Renato Foschini / Resumo: O óxido de zinco (ZnO) apresenta uma grande versatilidade física, elétrica, mecânica e propriedades químicas que podem ser exploradas em uma variedade de aplicações, tais como fotocatálise, nanoadsorventes e sensoriamento de gases. Os materiais nanoestruturados têm atraído a atenção da ciência e tecnologia nos últimos anos porque podem melhorar suas propriedades em nanoescala. A prata em escala nanométrica tem gerado interesse de pesquisadores de diferentes áreas, pois a prata é moldável e maleável, possui elevada condutividade térmica e elétrica, além de ser um forte oxidante. Neste trabalho, foram desenvolvidos filmes de óxido de zinco puro e dopados com nanopartículas de prata, visando aplicação em sensores de gás. Os filmes de óxido de zinco foram fabricados pelo método dos precursores poliméricos e utilizados como matriz devido a sua interatividade com os gases. As nanopartículas de prata foram produzidas por meio de reação em emulsão, explorando sua alta condutividade elétrica. Dessa forma, por meio das propriedades de ambos os materiais, desenvolveu-se um sensor de gás composto de óxido de zinco na forma de filmes em substratos de Al2O3, com diferentes camadas dopadas e não dopadas com nanopartículas de prata. Notou-se que o desenvolvimento de um material compósito do tipo filme de ZnO dopado com as nanopartículas de prata, apresentou propriedades melhoradas, como por exemplo, a resposta elétrica do material quando comparada com o filme contendo apenas o filme de ZnO p... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Zinc oxide (ZnO) presents a great physical, electrical, mechanical and chemical versatility that can be exploited in a variety of applications, such as photocatalysis, nanoadsorbents and gas sensing. Nanostructured materials have attracted the attention of science and technology in recent years because they can improve their nanoscale properties. The silver in nanoscale has generated interest of researchers of different areas, because the silver is moldable and malleable, has high thermal and electrical conductivity, besides being a strong oxidant. And this project was developed based on the production of silver nanoparticles and zinc oxide films for the application in gas sensors. The zinc oxide films were manufactured by the method of the polymeric precursors and used as matrix due to its interactivity with the gases. The silver nanoparticles were produced by means of emulsion reaction, exploring their high electrical conductivity. Thus, through the properties of both materials, a gas sensor composed of zinc oxide in the form of films on substrates of Al2O3, with different layers doped and not doped with silver nanoparticles was developed. It was noted that the development of a ZnO film-like composite material doped with the silver nanoparticles exhibited improved properties, such as the electrical response of the material as compared to the film containing only the pure ZnO film. / Mestre

In this work, a chemiresistor-type sensing platform based on aligned arrays of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) was developed. Our N-MWCNT based sensors can be made on both rigid and flexible substrates; they are small, have low power consumption and are suitable for highly efficient and reliable detection of different biomolecules and gases, at room temperature. The performance of these sensors was demonstrated for avian influenza virus (AIV) subtype H5N1 DNA sequences and toxic gases NO and NH3 at low concentrations. In our study, chemical vapor deposition (CVD) method was applied to synthesize vertically aligned nitrogen doped carbon nanotube arrays on a large area (> 1 cm2) on Si/SiO2 substrate using Fe/Al2O3 layer as a catalyst and a mixture of ethanol and acetonitrile as a C/N source. Especially, the diameter, length, nitrogen-doping concentration and morphology of the nanotubes were controllably tailored by adjusting the thickness of catalyst film, reaction duration and temperature as well as the amount of nitrogen-containing precursor. For integrating N-MWCNTs into chemiresistor devices, we developed a direct contact printing method for a dry, controllable and uniform transferring and positioning of the CVD-grown vertical nanotubes onto well-defined areas of various rigid and flexible substrates. After horizontally aligned N-MWCNT arrays were formed on a target substrate, interdigitated metallic microelectrodes with an interspacing of 3 µm were deposited perpendicular to the nanotube alignment direction to fabricate chemiresistor devices for biomolecule and gas sensing. This way, well-aligned nanotubes were laid across the Au/Cr interdigitated electrode fingers, had a strong adhesion with the electrodes and served as conducting channels bridging the electrodes. The N-MWCNT based chemiresistor device was applied as a label-free DNA sensor for a highly sensitive and fast detection of AIV subtype H5N1 DNA sequences. For this, the nanotubes were functionalized with probe DNA, which was non-covalently attached to sidewalls of the N-MWCNTs via π-π interaction. Such functionalized sensors were applied to quantitatively detect complementary DNA target with concentration ranging from 20 pM to 2 nM after 15 min incubation at room temperature. The sensors showed no response to non-complementary DNA target for concentrations up to 2 µM showing an excellent selectivity. Investigations on the efficient gas sensing of N-MWCNT-based chemiresistor of reducing/ oxidizing gases NH3 and NO were also reported in this work. The aim was to assess the possibility for N-MWCNTs to be applied as innovative sensing materials for room temperature gas sensing. N-MWCNTs with varying doping levels (N/C ratio of 5.6 to 9.3at%) were used as sensing materials and exposed to NH3 (1.5-1000 ppm) and NO (50-1000 ppm) for exploring and comparing their sensing performance. This study offered an effective route for further modification of CNTs according to various sensing application. Finally, our investigations showed a high potential of the developed N-MWCNT-based sensing platform for various applications ranging from environmental monitoring to point-of-care medical diagnostics.

The semiconductor industry was benefited by the advances in technology in the last decades. This fact has an impact on the sensors field, where the simple transducer was evolved into smart miniaturized multi-functional microsystems. However, commercially available gas and biological sensors are mostly bulky, expensive, and power-hungry, which act as obstacles to mass use. The aim of this work is gas and biological sensing using capacitive structures. Capacitive sensors were selected due to its design simplicity, low fabrication cost, and no DC power consumption. In the first part, the dominant structure among interdigitated electrodes (IDEs), fractal curves (Peano and Hilbert) and Archimedean spiral was investigated from capacitance density perspective. The investigation consists of geometrical formula calculations, COMSOL Multiphysics simulations and cleanroom fabrication of the capacitors on a silicon substrate. Moreover, low-cost fabrication on flexible plastic PET substrate was conducted outside cleanroom with rapid prototyping using a maskless laser etching. The second part contains the humidity, Volatile Organic compounds (VOCs) and Ammonia sensing of polymers, Polyimide and Nafion, and metal-organic framework (MOF), Cu(bdc)2.xH2O using IDEs and tested in an automated gas setup for experiment control and data extraction. The last part includes the biological sensing of C - reactive protein (CRP) quantification, which is considered as a biomarker of being prone to cardiac diseases and Bovine serum albumin (BSA) protein quantification, which is used as a reference for quantifying unknown proteins.

No description available.

Nous proposons dans ce travail une méthode robuste et bas-coût afin de fabriquer des détecteurs de gaz à base de Nanotubes de Carbone bi-parois (DWCNTs) chimiquement fonctionnalisés. Ces nano-objets (DWCNTs) sont synthétisés par dépôt catalytique en phase vapeur (CCVD), puis purifiés avant d'être oxydés ou bien fonctionnalisés par des terminaisons fluorées ou aminées. Les dispositifs de détection électriques ont été fabriqués par lithographie douce en utilisant un pochoir de PDMS (Poly-DiMethyl Siloxane) et un dépôt en phase liquide à la pipette d'une suspension aqueuse contenant les nanotubes fonctionnalisés, rinçage puis séchage à l'azote sec. Chaque dispositif (1 cm X 2 cm) est équipé d'un jeu de 7 résistors à base de DWCNTs. Chaque résistor peut accueillir des nanotubes fonctionnalisés par une entité chimique différente afin de cibler un gaz spécifique, permettant ainsi une détection multiplexée. En raison de leur faible encombrement et la possibilité de les fabriquer sur tout type de substrat y compris des substrats souples, ces détecteurs pourraient être utilisés pour une large gamme d'applications et notamment les détecteurs de gaz portatifs et intégrés. La résistance électrique des résistors s'avère décroître avec la température suggérant une conduction électrique gouvernée par l'effet tunnel et les fluctuations au sein du tapis désordonné de nanotubes de carbone. Nous avons cependant montré dans ce travail que pour des applications réelles de détection de gaz, une régulation thermique des dispositifs n'est pas nécessaire car les variations de résistance engendrées par l'adsorption de molécules de gaz sont significativement plus grandes que les variations causées par de possibles fluctuations de température. Les dispositifs produits présentent un caractère métallique à température ambiante et pour des applications de détection de gaz nous avons sélectionné des dispositifs présentant des résistances inférieures à 100 kO. Le principe de base de la détection de gaz étant basé sur la mesure directe de la résistance électrique du dispositif, la consommation électrique de ces dispositifs reste faible (<1 µW). La réponse des dispositifs à base de nanotubes de carbone non fonctionnalisés aux analytes testés (éthanol, acétone, ammoniac et vapeur d'eau) est faible. Les nanotubes de carbone fonctionnalisés présentent quant à eux, une réponse modérée à la vapeur d'eau, à l'éthanol et à l'acétone mais montrent une sensibilité excellente à l'ammoniac. En particulier, les nanotubes de carbone oxydés se sont avérés capables de détecter des concentrations sub-ppm d'ammoniac en présence de vapeur d'eau en excès et à température ambiante et ont montré une grande stabilité dans le temps même pour des expositions de gaz répétées. Nous pensons que les groupes chimiques fonctionnels ancrés à la surface des nanotubes de carbone modifient les interactions entre les molécules de gaz et les nanotubes et que le transfert de charges induit provoque les modifications de la conductance électrique du système. / We have successfully fabricated gas sensors based on chemically functionalized double-wall carbon nanotubes (DWCNTs) using a robust and low cost process. The DWCNTs were synthesized by catalytic chemical vapor deposition (CCVD) method. They were then purified before functionalization (oxidation, amination, and fluorination). The sensor devices were fabricated by soft lithography using PDMS (Poly-DiMethylSiloxane) stencils and liquid phase pipetting of a suspension of chemically functionalized DWCNTs in deionized water, rinsing and finally drying in a nitrogen flow. Each device (1 cm x 2 cm) is equipped with a set of 7 DWCNT based resistors. Each resistor can accommodate a precise chemical functionalization for targeting a specific gas species, allowing a multiplexed (up to 7) detection. Due to their small size and the possibility to fabricate them on soft substrates, they could be used for many kinds of applications including wearable devices. The electrical resistance of the produced resistors turned out to decrease with temperature, suggesting fluctuations induced tunneling conduction through the disordered network of metallic nanotubes. However, we have shown in our work that for realistic applications, gas sensing can be achieved without any temperature regulation of our devices, because the variations of electrical conductance caused by gas molecules adsorption are significantly larger than those caused by possible temperature fluctuations. The as fabricated devices exhibit at room temperature a metallic conducting behavior. Devices with a resistance less than 100 kO were selected for gas detection. Because the sensing principle is based on the direct measurement of the resistance, our scheme ensures low power consumption (<1 µW). Raw (not functionalized) DWCNTs-based gas sensors exhibited a low sensitivity to the tested analytes, including ethanol, acetone, ammonia and water vapor. Functionalized DWCNTs-based gas sensors exhibited a moderate sensitivity to ethanol, acetone and water vapor but the response to ammonia, even in the presence of additional water vapor, was excellent. In particular, oxidized DWCNTs based gas sensors exhibited a high stability in the case of prolonged and repeated gas exposures. The oxidized DWCNTs gas sensors were also able to detect ammonia vapor at sub-ppm concentration in the presence of water vapor at high concentration.

No description available.