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Processamento de sinais e reconhecimento de padrões de resposta de sensores de gases através da geometria fractal.; Signal processing and pattern recognition of gas sensors response by fractal geometry.

Gonschorowski, Juliano dos Santos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/03/2007 PT
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O objetivo do presente trabalho foi propor métodos de processamento de sinais e reconhecimento de padrões dos sinais de respostas de sensores de gás, utilizando técnicas e modelos da geometria fractal. Foram analisados e estudados os sinais de resposta de dois tipos de sensores. O primeiro sensor foi um dispositivo de óxido de estanho, cujo princípio de funcionamento baseia-se na mudança da resistividade do filme. Este forneceu sinais de respostas com características ruidosas como resposta à interação com as moléculas de gás. O segundo sensor foi um dispositivo Metal-Óxido-Semicondutor (MOS) com princípio de funcionamento baseado na geração de foto corrente, fornecendo respostas imagens bidimensionais. Para as análises dos sinais ruidosos do sensor de óxido de estanho, foi proposto um método de processamento baseado no modelo do movimento Browniano fracionário. Com este método foi possível a discriminação de gases combustíveis com uma taxa de acerto igual a 100%. Para as análises das respostas do tipo imagem do sensor MOS, foram propostos dois diferentes métodos. O primeiro foi embasado no princípio de compressão fractal de imagens e o segundo método proposto, foi baseado na análise e determinação da dimensão fractal multiescala. Ambos os métodos propostos mostram-se eficazes para a determinação da assinatura...

Síntese de poli(p-fenilenovinileno)s alcoxilados e sua aplicação em diodos emissores de luz e em sensores de gases; Synthesis of alkoxylated poly(p-phenylenevinylene)s and their application in light emitting diodes and in gas sensors

Yamauchi, Elaine Yuka
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/12/2006 PT
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57.30162%
O presente trabalho envolveu a eletrossíntese de três polímeros da família dos poli(p-fenilenovinileno)s, PPVs, apresentando como substituintes grupos alcóxi de cadeia longa. Esses polímeros foram caracterizados espectroscopicamente (RMN de 1H, IV e UV/VIS), termicamente (TG), por cromatografia por exclusão de tamanho (SEC), eletronicamente por voltametria cíclica e eletricamente por meio de curvas I x V em dispositivos do tipo sanduíche (metal/polímero/metal). Os polímeros foram utilizados na construção de sensores de gases para avaliação da capacidade sensitiva a vapores orgânicos, mostrando-se promissores para utilização em narizes eletrônicos. Construíram-se, também, dispositivos emissores de luz orgânicos (OLEDs) com utilização desses polímeros como camada ativa, no intuito de se conhecer sua aplicabilidade em dispositivos optoeletrônicos. Para tal, foram feitas determinações de luminância e de eficiência quântica de luminância dos OLEDs construídos. Os dispositivos do tipo sanduíche, os OLEDs e as medidas correspondentes foram realizados em Curitiba, em colaboração com o Prof. Dr. Ivo Alexandre Hümmelgen, líder do Grupo de Dispositivos Optoeletrônicos Orgânicos do Departamento de Física da Universidade Federal do Paraná.; The present work describes the electrosynthesis of three polymers of the poly(p-phenylenevinylene) (PPV) family...

Síntese e aplicação de polímeros condutores em sensores olfativos; Synthesis and application of conductive polymers in olfactory sensors

Cordeiro, Juliana Ribeiro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/02/2010 PT
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Os objetivos do trabalho consistem em síntese e caracterização de três polímeros: poli(2,1,3-benzotiadiazol-4,7-ilenovinileno) (PBTDV), poli(2,1,3-benzotiadiazol-4,7-ilenovinileno-co-2-bromo-5-hexilóxi-p-fenilenovinileno (PBTDV-co-BHPPV) e poli(2-bromo-5-hexilóxi-p-fenilenovinileno) (BHPPV), sendo os dois primeiros inéditos; aplicação de polímeros condutores no desenvolvimento de um nariz eletrônico capaz de identificar madeiras; e aplicação de polímeros condutores em um sensor de pressão. Os polímeros foram preparados de maneira satisfatória via redução catódica de seus precursores tetra-halogenados, que forneceu produtos com rendimentos apreciáveis. Para o projeto do nariz eletrônico que pretende identificar madeiras, dois conjuntos de espécies de madeira foram estudadas: (a) mogno e cedro e (b) imbuia e canela-preta. O nariz eletrônico desenvolvido apresenta um conjunto de quatro sensores de gás, que foram construídos por meio da deposição de finos filmes de polímeros dopados sobre a superfície de eletrodos interdigitados. Esse conjunto de sensores foi desenvolvido com sucesso, sendo capaz de diferenciar as espécies de madeira com taxa de acerto de 100%. Por fim, foi desenvolvido também com sucesso um sensor de gás capaz de atuar como sensor de pressão. Esse dispositivo mostrou-se sensível à variação de pressão...

Simulações de sensores de gás nanoscópicos baseados em nanotubos de carbono: estrutura eletrônica e transporte de elétrons; Computational simulations of nanoscopic gas sensors based on carbon nanotubes: electronic structure and electronic transport

Souza, Amaury de Melo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 10/02/2011 PT
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67.59425%
Desde sua descoberta por S. Iijima em 1991, os nanotubos de carbono têm sido considerados um dos materiais nanoestruturados mais promissores para o desenvolvimento de novos dispositivos eletrônicos em escala nanoscópica. Devido _a sua alta razão entre a área superficial e o volume, esse material se destaca para aplicações como sensores de gás. No presente trabalho, estudamos através de simulações computacionais, a possibilidade de nanotubos de carbono com defeitos de nitrogênio (os chamados nanotubos CNx), poderem ser usados como sensores de moléculas gasosas. Na primeira parte do trabalho foram realizados cálculos de estrutura eletrônica baseados na Teoria do Funcional da Densidade (DFT) para diferentes sistemas formados pelo nanotubo e pela molécula. Através de cálculos de energia de ligação, foi possível identificar quais gases poderiam ou não serem adsorvidos à superfície do nanotubo. Dentre as moléculas investigadas, o monóxido de carbono e a amônia mostraram ser as mais facilmente adsorvidas ao nanotubo. Na segunda parte, foram realizados cálculos das propriedades de transporte utilizando o formalismo das funções de Green fora do equilíbrio (NEGF) recursivo. Foi possível concluir que os nanotubos estudados poderiam ser usados para detectar o monóxido de carbono e a amônia. Todavia...

Síntese e caracterização do sistema nanoestruturado Sr1-XLaxTi1-yFeyO3: Aplicação como sensor de gás; Synthesis and characterization of nanostructured system Sr1-XLaxTi1-yFeyO3: application as gas sensor

Escanhoela Júnior, Carlos Augusto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/05/2015 PT
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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...

The role of hierarchical morphologies in the superior gas sensing performance of CuO-based chemiresistors

Volanti, Diogo P.; Felix, Anderson A.; Orlandi, Marcelo O.; Whitfield, George; Yang, Dae-Jin; Longo, Elson; Tuller, Harry L.; Varela, José Arana
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1759-1766
ENG
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The development of gas sensors with innovative designs and advanced functional materials has attracted considerable scientific interest given their potential for addressing important technological challenges. This work presents new insight towards the development of high-performance p-type semiconductor gas sensors. Gas sensor test devices, based on copper (II) oxide (CuO) with innovative and unique designs (urchin-like, fiber-like, and nanorods), are prepared by a microwave-assisted synthesis method. The crystalline composition, surface area, porosity, and morphological characteristics are studied by X-ray powder diffraction, nitrogen adsorption isotherms, field-emission scanning electron microscopy and high-resolution transmission electron microscopy. Gas sensor measurements, performed simultaneously on multiple samples, show that morphology can have a substantial influence on gas sensor performance. An assembly of urchin-like structures is found to be most effective for hydrogen detection in the range of parts-per-million at 200 °C with 300-fold larger response than the previously best reported values for semiconducting CuO hydrogen gas sensors. These results show that morphology plays an important role in the gas sensing performance of CuO and can be effectively applied in the further development of gas sensors based on p-type semiconductors. High-performance gas sensors based on CuO hierarchical morphologies with in situ gas sensor comparison are reported. Urchin-like morphologies with high hydrogen sensitivity and selectivity that show chemical and thermal stability and low temperature operation are analyzed. The role of morphological influences in p-type gas sensor materials is discussed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA...

Exploitation of Unique Properties of Zeolites in the Development of Gas Sensors

Zheng, Yangong; Li, Xiaogan; Dutta, Prabir K.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 20/04/2012 EN
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The unique properties of microporous zeolites, including ion-exchange properties, adsorption, molecular sieving, catalysis, conductivity have been exploited in improving the performance of gas sensors. Zeolites have been employed as physical and chemical filters to improve the sensitivity and selectivity of gas sensors. In addition, direct interaction of gas molecules with the extraframework cations in the nanoconfined space of zeolites has been explored as a basis for developing new impedance-type gas/vapor sensors. In this review, we summarize how these properties of zeolites have been used to develop new sensing paradigms. There is a considerable breadth of transduction processes that have been used for zeolite incorporated sensors, including frequency measurements, optical and the entire gamut of electrochemical measurements. It is clear from the published literature that zeolites provide a route to enhance sensor performance, and it is expected that commercial manifestation of some of the approaches discussed here will take place. The future of zeolite-based sensors will continue to exploit its unique properties and use of other microporous frameworks, including metal organic frameworks. Zeolite composites with electronic materials...

TREFEX: Trend Estimation and Change Detection in the Response of MOX Gas Sensors

Pashami, Sepideh; Lilienthal, Achim J.; Schaffernicht, Erik; Trincavelli, Marco
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 04/06/2013 EN
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Many applications of metal oxide gas sensors can benefit from reliable algorithms to detect significant changes in the sensor response. Significant changes indicate a change in the emission modality of a distant gas source and occur due to a sudden change of concentration or exposure to a different compound. As a consequence of turbulent gas transport and the relatively slow response and recovery times of metal oxide sensors, their response in open sampling configuration exhibits strong fluctuations that interfere with the changes of interest. In this paper we introduce TREFEX, a novel change point detection algorithm, especially designed for metal oxide gas sensors in an open sampling system. TREFEX models the response of MOX sensors as a piecewise exponential signal and considers the junctions between consecutive exponentials as change points. We formulate non-linear trend filtering and change point detection as a parameter-free convex optimization problem for single sensors and sensor arrays. We evaluate the performance of the TREFEX algorithm experimentally for different metal oxide sensors and several gas emission profiles. A comparison with the previously proposed GLR method shows a clearly superior performance of the TREFEX algorithm both in detection performance and in estimating the change time.

Gas Sensors Based on Semiconducting Nanowire Field-Effect Transistors

Feng, Ping; Shao, Feng; Shi, Yi; Wan, Qing
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 17/09/2014 EN
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One-dimensional semiconductor nanostructures are unique sensing materials for the fabrication of gas sensors. In this article, gas sensors based on semiconducting nanowire field-effect transistors (FETs) are comprehensively reviewed. Individual nanowires or nanowire network films are usually used as the active detecting channels. In these sensors, a third electrode, which serves as the gate, is used to tune the carrier concentration of the nanowires to realize better sensing performance, including sensitivity, selectivity and response time, etc. The FET parameters can be modulated by the presence of the target gases and their change relate closely to the type and concentration of the gas molecules. In addition, extra controls such as metal decoration, local heating and light irradiation can be combined with the gate electrode to tune the nanowire channel and realize more effective gas sensing. With the help of micro-fabrication techniques, these sensors can be integrated into smart systems. Finally, some challenges for the future investigation and application of nanowire field-effect gas sensors are discussed.

Development of Fabric-Based Chemical Gas Sensors for Use as Wearable Electronic Noses

Seesaard, Thara; Lorwongtragool, Panida; Kerdcharoen, Teerakiat
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 16/01/2015 EN
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Novel gas sensors embroidered into fabric substrates based on polymers/ SWNT-COOH nanocomposites were proposed in this paper, aiming for their use as a wearable electronic nose (e-nose). The fabric-based chemical gas sensors were fabricated by two main processes: drop coating and embroidery. Four potential polymers (PVC, cumene-PSMA, PSE and PVP)/functionalized-SWCNT sensing materials were deposited onto interdigitated electrodes previously prepared by embroidering conductive thread on a fabric substrate to make an optimal set of sensors. After preliminary trials of the obtained sensors, it was found that the sensors yielded a electrical resistance in the region of a few kilo-Ohms. The sensors were tested with various volatile compounds such as ammonium hydroxide, ethanol, pyridine, triethylamine, methanol and acetone, which are commonly found in the wastes released from the human body. These sensors were used to detect and discriminate between the body odors of different regions and exist in various forms such as the urine, armpit and exhaled breath odor. Based on a simple pattern recognition technique, we have shown that the proposed fabric-based chemical gas sensors can discriminate the human body odor from two persons.

Residual oil monitoring in pressurised air with SnO2-based gas sensors; Restölüberwachung in Druckluft mit SnO2-basierten Gassensoren

Papamichail, Nikos
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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The doctoral thesis at hand describes the investigations undertaken in order to develop a newly invented procedure for the monitoring of residual oil in pressurised air. The problem of this application lies on the one hand in the state of aggregation of the oil, most of it is liquid and forms aerosols, and on the other hand in the general challenge to measure a small concentration in a changing matrix by means of unspecific sensors. The oil origins from the compressors, which typically use oil as a lubricant and as a cooling medium. Usually the oil is removed by a filtering cascade, adapted to the respective application, but up to now there is no possibility to easily monitor their effectiveness online. The first filter in this line is the oil separator, mounted inside the compressor. Its filtering performance was observed in this work. A patent pending process for the detection of liquid components in aerosol stream was developed and used to enable the quantification of the oil with highly sensitive gas sensors. The process takes advantage from the Kelvin-effect and the fact that the pressurised air has to be expanded anyway in order to operate the sensors at ambient pressure, which is the most common case. Preliminary tests at a gas mixing system equipped with oil filled vaporisers proved the sensitivity of the sensors towards the headspace of the oil. Most of the measurements were performed with a real life set-up including a typical screw-type compressor taking in ambient air. Samples were taken inside the compressor...

Characterisation and functionality of SnO2 gas sensors using vibrational spectroscopy; Schwingungspektroskopische Charakterisierung der Funktionsweise von SnO2-Sensoren; Schwingungspektroskopische Charakterisierung der Funktionsweise von SnO2-Sensoren

Harbeck, Serpil
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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In the last years the interest in heterogeneous catalysis of semiconducting materials has substantially increased and the relevancy of the catalysis for the understanding of metal oxide chemical gas sensors has been realized. Up to now several investigations on different metal oxides have been carried out, especially on tin oxide (SnO2), which is one of the most attractive materials for metal oxide gas sensors. In spite of the huge number of investigations the CO reaction mechanism on the surface as well as the interfering effect of the present water on the CO sensing mechanisms are not well understood. The aim of the work was the characterisation of various thick film tin oxide gas sensors (un-doped and Pd-doped sensors) and CO adsorption studies at working conditions of the sensors (elevated temperatures, presence of humidity) using DRIFT (Diffuse Reflectance Infrared Fourier Transformation) spectroscopy. This special technique proved to provide complementary information to the phenomenological measurements. During this work a special set-up was developed and optimised and this made it possible for the first time to conduct an in-situ characterisation of thick film sensors during gas exposure. Parallel to the DRIFT spectra, the resistance of the sensors was recorded in order to find the correlations between spectroscopic and electrical measurements. Additionally...

Impedanzspektroskopie an SnO2-Dickschicht-Sensoren; impedance spectroscopy on SnO2 thick film sensors

Sachlara, Ourania
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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47.894546%
Im Allgemeinen sind Sensoren miniaturisierte Messeinrichtungen, die für bestimmte Messgrößen optimiert werden und in großer Stückzahl möglichst preiswert produziert werden können. Das Anwendungsgebiet ist sehr breit und umfaßt Problemstellungen im physikalischen, biologischen und chemischen Bereich. Bei letzteren sind die Messaufgaben sehr komplex und Störungen bzw. Querempfindlichkeiten nicht zu vernachlässigen. Chemische Gassensoren mit SnO2 als sensitive Schicht sind in der Detektion von toxischen und entzündlichen Gasen, wie CO, sehr weit verbreitet. Die mangelnde Selektivität und der störende Effekt der Luftfeuchtigkeit, der je nach Gas die Empfindlichkeit erhöht oder erniedrigt, behindern die Anwendung als Detektoren in analytischen Geräten. Durch gezielte Dotierung wurden die Sensoreigenschaften verbessert. Die Pulverdotierung ist die herkömmliche Dotiermethode. Da aber die neue Methode der Geldotierung zu besseren Sensorreaktionen und einer effektiveren Fixierung des Dotiermittels an der Oxidoberfläche geführt hat, wurden Pd- und Pt- geldotierte Dickschicht-Sensoren Gegenstand dieser Arbeit. Die Untersuchungen wurden mittels Impedanzspektroskopie durchgeführt, da diese eine zerstörungsfreie Methode mit vergleichbar geringem instrumentellem Aufwand ist und sich schnell feststellen lässt...

Nanostructured Metal Oxide Gas Sensors for Air Quality Monitoring

RICKERBY David; SERVENTI Alessandra
Fonte: Elsevier Publicador: Elsevier
Tipo: Articles in books Formato: Printed
ENG
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Tin dioxide was the first material used to fabricate gas sensors, though many other metal oxides have been employed since. Doping the gas sensitive layer with a noble metal and the application of thin film technology allows a significant improvement in performance of these devices due to the catalytic effect of the metal on reactions between the oxide and adsorbed gas molecules and the formation of a Schottky barrier. The microstructure of the metal oxide also plays a fundamental role and systematic studies of the relationship between deposition conditions and film structure are therefore essential to understand the sensor response. A low deposition temperature leads to a porous granular structure, while for a higher temperature the greater atomic mobility results in more ordered columnar structures. This latter type of structure increases the efficiency of gas detection because the intercolumnar interfaces facilitate diffusion of gas molecules. The sensitivity is also increased by reducing the grain size of the metal oxide films to ~10nm, so that the depth of the depleted region becomes comparable with the grain diameter. Two commonly used techniques for the production of metal oxide thin films, reactive r.f. sputtering and pulsed laser deposition...

Portable mid-infrared gas sensors: Development and applications

Richter, Dirk
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
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Several novel compact architectures of diode laser based absorption gas sensors have been developed, characterized and applied to real world applications. The motivation for this research has been the need to develop highly sensitive, selective and rapid response gas sensors that operate reliably in a non-laboratory environment. The gas sensors utilize rare earth doped fiber amplified near infrared diode lasers and are difference frequency mixed in periodically poled LiNbO3 to generate narrow linewidth muW to mW-level mid infrared light in the molecular fingerprint region from 3 to 5 mum. In particular, the spectroscopic performance of an automated widely tunable (3.3--4.4 mum) multi-species and a high-power single species (3.5 mum) gas detection sensor are discussed. Sensitive, selective and real-time detection of over 10 gas species including CH4, H2CO, CO2, CH 3OH, NO2, N2O; SO2, HCl, C6H 6, and H2O using extractive gas sampling in a multi-pass cell was demonstrated. The gas sensors were used for an evaluation of a trace contaminant catalyst system at TDA Research, Wheat Ridge, Colorado, and successfully applied to the detection of volcanic gases at Masaya volcano, Nicaragua.

Ab-initio calculations for a realistic sensor: A study of CO sensors based on nitrogen-rich carbon nanotubes

Rocha, Alexandre Reily; Fazzio, Adalberto; Souza, Amaury de Melo; Silva, Antonio Jose Roque da
Fonte: AMER INST PHYSICS; MELVILLE Publicador: AMER INST PHYSICS; MELVILLE
Tipo: Artigo de Revista Científica
ENG
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The use of nanoscale low-dimensional systems could boost the sensitivity of gas sensors. In this work we simulate a nanoscopic sensor based on carbon nanotubes with a large number of binding sites using ab initio density functional electronic structure calculations coupled to the Non-Equilibrium Green's Function formalism. We present a recipe where the adsorption process is studied followed by conductance calculations of a single defect system and of more realistic disordered system considering different coverages of molecules as one would expect experimentally. We found that the sensitivity of the disordered system is enhanced by a factor of 5 when compared to the single defect one. Finally, our results from the atomistic electronic transport are used as input to a simple model that connects them to experimental parameters such as temperature and partial gas pressure, providing a procedure for simulating a realistic nanoscopic gas sensor. Using this methodology we show that nitrogen-rich carbon nanotubes could work at room temperature with extremely high sensitivity. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4739280]; FAPESP; FAPESP; CNPq; CNPq

Estudio de puertas catalíticas en sensores de gas en tecnología de SiC; Catalitic gates for gas sensors based on SiC technology

Godignon, Philippe; Casals, O.; Haffar, M.; Barcones, B.; Romano, A.; Serre, C.; Pérez, A.; Morante, J. R.; Montserrat, J.; Millán, José
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 331335 bytes; application/pdf
SPA
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[ES] En este trabajo se presenta un estudio químico y estructural de las capas metálicas de Pt y TaSix utilizadas como puerta catalítica en sensores de gas de alta temperatura basados en dispositivos MOS de SiC. Para ello se han depositado capas de diferentes espesores sobre substratos de Si. Los resultados muestran que con la reducción del espesor de Pt y con un recocido se consigue aumentar la rugosidad de las capas de puerta, lo que debería aumentar la sensibilidad y la velocidad de respuesta de los dispositivos que las incorporasen. Otro efecto del recocido es la transformación química del material de la puerta que, para capas delgadas de Pt con TaSix, produce la transformación total Pt en Pt2Ta, lo que podría afectar a las características catalíticas de la puerta. Los primeros resultados eléctricos indican que, a pesar de que las capas de Pt empleadas son gruesas y compactas, los diodos MOS túnel de SiC son sensibles a los gases CO y NO2, aunque presentan una velocidad de respuesta bastante lenta.; [EN] In this work the chemical and structural characterisation of metallic layers of Pt and TaSix, employed as catalytic gates in high temperature gas sensors based on MOS devices on SiC substrates, is presented. For the study layers of different thickness have been deposited on Si substrates. The results show that the roughness of the layers increases with the reduction of the thickness of Pt and with annealing...

Enhanced spectroscopic gas sensors using in-situ grown carbon nanotubes

De Luca, A.; Cole, M. T.; Hopper, R. H.; Boual, S.; Warner, J. H.; Robertson, A. R.; Ali, S. Z.; Udrea, F.; Gardner, J. W.; Milne, W. I.
Fonte: AIP Publicador: AIP
Tipo: Article; accepted version
EN
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This is the author accepted manuscript. The final version is available from AIP at http://scitation.aip.org/content/aip/journal/apl/106/19/10.1063/1.4921170.; In this letter, we present a fully complementary-metal-oxide-semiconductor (CMOS) compatible microelectromechanical system thermopile infrared (IR) detector employing vertically aligned multi-walled carbon nanotubes (CNT) as an advanced nano-engineered radiation absorbing material. The detector was fabricated using a commercial silicon-on-insulator (SOI) process with tungsten metallization, comprising a silicon thermopile and a tungsten resistive micro-heater, both embedded within a dielectric membrane formed by a deep-reactive ion etch following CMOS processing. In-situ CNT growth on the device was achieved by direct thermal chemical vapour deposition using the integrated micro-heater as a micro-reactor. The growth of the CNT absorption layer was verified through scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The functional effects of the nanostructured ad-layer were assessed by comparing CNT-coated thermopiles to uncoated thermopiles. Fourier transform IR spectroscopy showed that the radiation absorbing properties of the CNT adlayer significantly enhanced the absorptivity...

A Parametric study of gas sensing response of ZnO nanostructures and carbon nanotubes

Saluja, Amandeep S.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
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Solid state chemical sensors are gaining popularity and finding extensive use in process control, environmental monitoring and residential safety. ZnO, a semiconducting metal oxide, and carbon nanotubes (CNTs) have attracted great interest over the years for their sensitivity to a variety of gases. Nanostructured sensing materials, such as nanowires, nanotubes and quantum dots offer an inherently high surface area, thus reducing operating temperatures and increasing sensitivity to low concentrations of analytes. In this work, ZnO nano-structures and CNTs have been tested as chemical sensors and a detailed study on the effect of different process parameters such as temperature, carrier gas flow, inter-electrode spacing, gas concentration and material properties on gas sensitivity is presented. Initial ZnO nanoparticles were prepared by a simple solution chemical process and characterized by Secondary Electron Microscopy (SEM) and Brunauer, Emmet and Teller (BET) Sorptometer to demonstrate the morphology and surface area respectively. The gas sensor platforms consisted of Pt inter-digitated fingers with a spacing of 10 μm. The sensor platform was dip-coated with ZnO nano-platelets suspended in terpineol to form a uniform film. Sensing was performed in a closed quartz chamber where...

SnO2 thick film gas sensors additivated with noble metal nanoparticles obtained by chemical synthesis

Fraigi,L.B; Weinstock,A; Moina,C.A
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2006 EN
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In this work, Pt nanoparticles obtained by different synthetic routes were incorporated into nanostructured SnO2 powders by contact transference. The presence of the nanoparticles was confirmed by XRD and TEM. When used as sensitive material in the fabrication of gas sensors, the SnO2/Pt nanoparticle composites obtained showed a high sensitivity towards the detection of reductive gases such as CO.