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Ryan, Benjamin Thomas. "Polymeric gas sensors." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531149.
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Archer, P. B. M. "Organometallic gas sensors." Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379015.
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Udina, Oliva Sergi. "Smart Chemical Sensors: Concepts and Application." Doctoral thesis, Universitat de Barcelona, 2012. http://hdl.handle.net/10803/84079.
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This PhD thesis introduces basic concepts of smart chemical sensors design, which are afterwards applied to a particular application: the analysis of natural gas.
The thesis addresses thus two sets of objective, a first set of objectives related to the conceptual design of a smart chemical sensor using smart sensor standards:
- The design of an optimal smart chemical sensor architecture
- The novel combination in a working prototype of the highly complementary smart sensor standards IEEE-1451 and BS-7986
A second set of objectives is directly related to the selected application. Natural gas quality control. Natural gas is an energy source of major importance in the world energy supply, its quality control is increasingly important due to its origin-dependent properties and the progressive liberalization of the energy market. The objectives related to this application are:
- To solve the natural gas quality analysis problem by using a lower cost approach taking advantage of MEMS technology, smart sensor features, and embedded intelligent signal processing.
- To select suitable sensing technologies and associated signal processing.
An overall goal addressed by the PhD Thesis is in the end the reporting of a working smart sensor prototype implementing all the smart sensor features, MEMS based natural gas analysis and advanced signal processing as a demonstration of a novel low-cost and high speed natural gas analyzer.
The thesis covers this research along 7 chapters, introducing the concepts and application in chapters 1 and 2, the objectives in chapter 3, the simulation of a proposed MEMS sensor approach in chapter 4, the description of the advanced signal processing approach adopted in chapter 5, the description of the electronics and engineering of the smart natural gas analyzer prototype in chapter 6, and finally the conclusions of the work in chapter 7.La tesis introduce conceptos básicos sobre el diseño de sensores químicos inteligentes, en particular presenta los estándares propuestos IEEE-1451 y BS-7986, y elabora una propuesta para el diseño óptimo de dichos sensores químicos inteligentes. Se implementa la propuesta de diseño para una aplicación concreta, el análisis de gas natural. Además de la aplicación de los conceptos sobre sensores químicos inteligentes se pretende además diseñar un analizador compacto, rápido y de bajo coste, para ello se estudia el uso de un microsensor termoeéctrico como sensor principal del analizador. Una vez probada su viabilidad se implementan ambos conceptos (sensores inteligentes y microsensor termoeléctrico) en un prototipo funcional validado en laboratorio. Como resultado se obtiene una propuesta para el diseño de sensores químicos inteligentes basada en estándares, y por otro lado se presenta un nuevo analizador de gas natural, más rápido y compacto que los existentes. Los resultados obtenidos originan diversas publicaciones en revistas así como dos patentes de método y sistema.
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Wallgrén, Kirsi. "Novel amperometric gas sensors." Thesis, University of Nottingham, 2005. http://eprints.nottingham.ac.uk/49484/.
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The electrochemistry of oxygen and methanol at solid polymer electrolyte (SPE)-based amperometric sensors, fabricated according to an all-planar design concept, has been investigated. The solid protonic conductors used were Nafion®-117 membranes and Polybenzimidazole (PBI) films. The working and counter electrodes were non-porous gold and/or platinum layers (300-1500 nm thick), sputtered on the same face of the solid electrolyte, separated by a gap of the ionic conductor (10-1 mm wide) and in contact with the gas sample. Such all-planar solid-state devices could offer potential advantages over sandwich-type gas sensors namely, reduction in precious metal electrode area and simplified fabrication. Sensors based on both materials exhibited near-linear response to oxygen concentration changes (in the 0.1-21% v/v range) and response times comparable to those of commercially available sensors, irrespective to sample relative humidity, but the magnitude of the signal did depend on the latter even after ohmic correction or at low currents. A systematic study of the effect of humidity on oxygen reduction and gold surface electrochemistry reveals, that the fall in the oxygen signal with decreasing humidity cannot be explained simply in terms of decreasing membrane conductivity and increased ohmic losses, but is related to the effect of water on the number of electro active sites, their catalytic activity and oxygen reduction mechanism in general. The latter is further supported by the unusually high Tafel slopes obtained both on gold and platinum electrodes with decreasing levels of test gas humidification. The shape of the oxygen reduction current-potential curves observed at open all-planar gold-based devices and the magnitude of current at both gold-and platinum-based ones, when compared to those of sandwich-and capillary-type arrangements, point to high mass transport rates and a thin or porous mass transport barrier. Current distribution considerations supported by surface electrochemistry estimates suggest that parts of the deposit closer to the reference and counter electrodes contribute more to the observed currents. Further experimentation by varying the deposit thickness and progressive masking of working electrode areas, revealed that the test gas reacted both at the line formed by the gas/solid electrolyte/metal layer interface (diffusion from the gas phase) and underneath the deposit (diffusion from the back of the sensor and through the Nafion® membrane), but not through the metal layer. For monitoring of dissolved methanol (0.5-3 M) in acidic solutions using bare platinum micro disc electrodes and of methanol vapours (in eqUilibrium with 2-10% w/w or ca. 0.6-3 M aqueous solutions of methanol) using Nafion®-based all-planar platinum sensors, a simple amperometric method was developed. For both types of sensors a clear voltarnmetric picture was obtained with a good separation of methanol oxidation and oxygen reduction curves. The amperometric response could be correlated to the variations in methanol concentration, demonstrating the suitability of the method for crude monitoring of dissolved methanol levels in a range applicable to the feed of direct methanol fuel cells.
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Belghachi, Abderrahmane. "Metal phthalocyanine gas sensors." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293280.
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Rigby, Geraldine Patricia. "NOâ†x gas sensors." Thesis, University of Kent, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333520.
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Martínez, Hurtado Juan Leonardo. "Gas-sensitive holographic sensors." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244643.
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Holographic sensors are photonic layered structures contained in analyte sensitive lms that upon illumination produce monochromatic reflections (λ). The present work reports the fabrication of oxygen and ammonia sensors in Nafi on membranes and hydrocarbon and volatile organic compound sensors in poly(dimethylsiloxane) (PDMS) films. A holographic recording technique was developed to suit these materials consisting of the in situ formation of nanoparticles of 18nm average diameter and their subsequent ordered ablation with a 300mJ laser. The wavelength of the monochromatic reflections depends principally on the refractive index of the resulting layers (n) and the separation between them (Λ). Changes in these parameters are generated by the analyte-sensor interactions and their magnitude can be correlated to the analyte concentration. The strength of these interactions is determined by the thermodynamic properties of the analytes, such as the cohesive energy density (δ^2), and this, was coupled with a photonic model for the prediction of the holographic response. After exposure to different concentrations of the analytes, the kinetics of the responses were determined and the lowest detection limits (LDL) established as follows: Hydrocarbons in PDMS holograms 1% (v/v) in 3s for a range of concentrations from 0-100%; ammonia in Nafi on holograms 0.16% in 100s in the 0-12.5% range; the LDL for oxygen sensing could not be determined although the response was recorded down to 12.5% and up to 100% in 100s. Holographic sensors show competitive responses comparable to commercially available gas sensors for biomedical diagnostics and industrial process monitoring because of their facile fabrication and their shared sensing platform allowing multiplexing.
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Haque, M. S. "Gas sensors using carbon nanotubes." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603677.
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A novel approach has been adopted for in-situ growth of CNTs on CMOS Silicon on Insulator (SOI) devices. The growth and deposition of CNTs on SOI CMOS has been successfully implemented at high temperature (>700°C) using tungsten as an interconnect. A detailed study of the nanotubes growth dependence on a number of parameters has been carried out on fully processed SOI CMOS substrates. A novel growth process of depositing CNTs using the very low power CMOS microhotplate acting as the thermal source has also been carried out. One of the key advantages of this process is the confinement of high temperature to the heater region only during the CNT growth, thereby, keeping the electronic circuitry unaffected. The results of the growth were highly repeatable with no degradation of the CMOS devices. High quality multi walled CNTs were locally grown, self-aligned onto the pre-formed sensing metal interdigitated electrodes. A low temperature process (<450°C) for single walled and multi walled CNTs was also developed using a hot filament stage. This process is suitable for devices with aluminium interconnect and is CMOS compatible. The locally growth CNTs on the sensor devices were tested with NO2 extensively and showed response at room temperature which was an improvement on the present gas sensing technologies. The sensor was found to offer reasonable sensitivity to 100 ppb of NO2 and faster chemical response time at elevated temperatures (tens of seconds). The smart CNT micro-sensor also showed responses to ammonia, methanol and ethanol. The ultra-low power consumption of the hotplates on ultra-thin CMOS compatible membranes and the growth of CNTs on multi-chips at the same time, in parallel, show great potential for high volume manufacturability and is a potential way forward for the next generation nanostructured material sensors.
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Watt, Esther Jane. "Poly(pyrrole) based gas sensors." Thesis, Birkbeck (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338770.
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Khunou, Ramotseng. "Gas sensing properties of Ceo2 nanostructures." University of the Western Cape, 2020. http://hdl.handle.net/11394/7909.
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>Magister Scientiae - MScThe industrial safety requirements and environmental pollution have created a high demand to develop gas sensors to monitor combustible and toxic gases. As per specifications of World Health Organization (WHO) and Occupational Safety and Health Administration (OSHA), lengthy exposure to these gases lead to death which can be avoided with early detection. Semiconductor metal oxide (SMO) has been utilized as sensor for several decades. In recent years, there have been extensive investigations of nanoscale semiconductor gas sensor.
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Ash, Peter William. "Studies of tin oxide gas sensors for gas chromatographic detection." Thesis, University of Plymouth, 1990. http://hdl.handle.net/10026.1/2066.
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Gas sensitive semiconductors have been known for many years and applied in static gas alarm systems for the monitoring of hazardous gases, however, their application has been limited by a lack of selectivity. In this work a semiconducting gas sensor has been configured for use as a gas chromatographic detector thus combining the sensitivity of semiconductor sensors with the selectivity of gas chromatography. The study has been confined to tin oxide devices, more specifically the Taguchi gas sensor (TGS) . The majority of this work has concentrated on the TGS 813 although the use of other TGS is described. The development of suitable instrumentation is described and rigorous optimisation of the operating parameters e.g. heater voltage and column temperature has been performed using the variable step size simplex technique. Attention was concentrated on the response of the TGS 813 to hydrogen which was used as a test gas. A novel figure of merit, response multiplied by retention time and divided by skew factor was designed so that optimum response was obtained whilst maintaining adequate chromatographic separation. Optimum conditions were verified by univariate searches and the response was observed to be most dependant upon heater voltage. A limit of detection of 20 ppb v/v of hydrogen in a 1 ml sample was obtained at optimal conditions. Illustrative analyses of hydrogen were performed in human breath and laboratory air with results found to be in close agreement with literature values. Calibration was found to be linear over at least three orders of magnitude. The response of the TGS 813 to low molecular weight alkanes has also been investigated. It was observed that different heater voltage optima existed for each of the C1-C5 alkanes and that the sensor was relatively more sensitive to the higher molecular weight compounds. As with hydrogen linear response was obtained over at least three orders of magnitude and an illustrative analysis of natural gas showed excellent agreement with known levels. A compromise optimum heater voltage was used to study the response of the TGS 813 to alcohols, aldehydes, ketones and some Cs hydrocarbons. Capillary columns were used in this investigation and it was noted that they had potentially wider application than packed columns due to the use of an inert carrier with an air make-up flow to the detector. This replaced the air carrier gas used previously which might degrade certain stationary phases. Three different types of TGS: the 813; 822 and 831 were used in a study of the response and skew factor for the detection of halogen-containing compounds. Very high skew factors were often observed, although, for some compounds it appeared that symmetrical peaks could be obtained within narrow heater voltage ranges. Skewed response was observed to be dependant upon sensor type, heater voltage and halogen proportion and type. Analysis of the three sensor types was performed and differences in potential surface area and tin oxide additives observed. The presence of additives was observed to adversely affect sensor recovery.
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Besnard, Isabelle. "Improvement of conducting polymer gas sensors." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341716.
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Gautam, Madhav. "Development of Graphene Based Gas Sensors." University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1365030920.
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Weisser, Karl. "Gas monitoring system using ultrasound sensors." Thesis, KTH, Mikrosystemteknik (Bytt namn 20121201), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91814.
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This thesis reports a collaboration between KTH Microsystem Technology Labs and Maquet critical care. Maquet is a company that produces medical ventilators and anesthesia machines. In an anesthesia machine it is important to monitor the anesthesia concentration that is delivered so that the delivered anesthesia concentration does not deviate from the desired concentration. Furthermore, in case of fail function there is a need to stop the delivery of anesthesia to the patient and flush the system. The anesthetic agent concentration is presently monitored with an infrared spectrometer. By using ultrasound technology it is possible to determine the volume concentration of a gas mixture by knowing the sound speed in the gases. Maquet has an ultrasound sensor that is developed to measure the oxygen concentration in air. This sensor was modified in order to measure nitrous oxide and anesthesia. The anesthesia concentration was measured by placing sensors upstream and downstream from the vaporizer. Using this ultrasound sensor system one can observe that the average discrepancy of the entire concentration range is ±0.84 % for Desflurane and 0.17 % for Isoflurane in relation to the infraredspectrometer sensor that is presently used in the anesthesia machine to monitor the anesthetic agent. Measurements show that the rise time of the ultrasound sensor varies when placing the sensor in different orientations with respect to the airway flow. It also show that by placing a flow restrictor that is used to force the airway flow in to the sensors measurement chamber reduces the rise time to a tenth of its previous value.
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Pearce, Ruth Elizabeth. "Carbon nanotubes as fire gas sensors." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/5551.
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Multi walled carbon nanotubes (MWCNTs) possess properties that make them particularly relevant for sensing applications in both the gas and liquid phase. This study presents an evaluation of cheap readily available CVD grown MWCNTs for use as fire gas sensors. Current fire detectors exploit heat and smoke detectors and it is hoped that the inclusion of gas detectors will increase the speed and reliability of detection. In order to prepare a variety of different MWCNTs a range of CVD synthesis were employed including an injected catalyst method where MWCNTs grew in dense mats from quartz substrates, MWCNTs were also synthesised using a sputtered Fe catalyst layer with acetylene as the carbon source which enabled control over the positioning of the growth. In each case, the growth parameters were varied until aligned growth was achieved. Doping of MWCNTs was also carried out as this may enhance and enable some control over the electrical properties of the CNTs; nitrogen was also added as a dopant by including 1,4-diazine as a precursor, and the effects on morphology of the MWCNTs produced were studied. The chemistry of the surface is also known to affect the sensing properties of CNTs. A batch of MWCNTs produced via the injected catalyst method were purifed by acid reflux, base washing and high temperature vacuum annealing, then modified with platinum or palladium metal nanoparticles via a reduction of the metal salts under hydrogen. MWCNTs were also coated with the polymer polyethyleneimine and with copperphthalocyanine. Prototype sensor devices were fabricated by electrophoretic deposition of these modified MWCNTs, and gas testing was carried out with the gases NO2, NH3, CO, H2 and C3H6. The mechanisms of sensing were investigated by repeating the tests at different temperatures, which revealed which sensing mechanisms were dominant and responses were compared between the differently modified MWCNTs. Sensor response was also investigated with a series of vapours to probe the dispersive and polar interactions on the MWCNT walls.
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ZONTA, GIULIA. "Chemoresistive gas sensors for cancer prevention." Doctoral thesis, Università degli studi di Ferrara, 2017. http://hdl.handle.net/11392/2488301.
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Zhang, Chen. "Piezoelectric-Based Gas Sensors for Harsh Environment Gas Component Monitoring." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538769/.
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In this study, gas sensing systems that are based on piezoelectric smart material and structures are proposed, designed, developed, and tested, which are mainly aimed to address the temperature dependent CO2 gas sensing in a real environment. The state-of-the-art of gas sensing technologies are firstly reviewed and discussed for their pros and cons. The adsorption mechanisms including physisorption and chemisorption are subsequently investigated to characterize and provide solutions to various gas sensors. Particularly, a QCM based gas sensor and a C-axis inclined zigzag ZnO FBAR gas sensor are designed and analyzed for their performance on room temperature CO2 gas sensing, which fall into the scope of physisorption. In contrast, a Langasite (LGS) surface acoustic wave (SAW) based acetone vapor sensor is designed, developed, and tested, which is based on the chemisorption analysis of the LGS substrate. Moreover, solid state gas sensors are characterized and analyzed for chemisorption-based sensitive sensing thin film development, which can be further applied to piezoelectric-based gas sensors (i.e. Ca doped ZnO LGS SAW gas sensors) for performance enhanced CO2 gas sensing. Additionally, an innovative MEMS micro cantilever beam is proposed based on the LGS nanofabrication, which can be potentially applied for gas sensing, when combined with ZnO nanorods deposition. Principal component analysis (PCA) is employed for cross-sensitivity analysis, by which high temperature gas sensing in a real environment can be achieved. The proposed gas sensing systems are designated to work in a high temperature environment by taking advantage of the high temperature stability of the piezoelectric substrates.
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Dungey, S. J. "Modelling of gas transport in porous zeolite-modified discriminating gas sensors." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1310248/.
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The ability to distinguish effectively between a range of gases in a reliable, repeatable manner is of major interest with both scientific and commercial relevance. Semiconducting metal oxide gas sensors have a long life-span, are inexpensive and are highly sensitive; however, they are generally found to lack a desired level of selectivity. One highly viable approach for enhancing the selective power of such devices is the addition of a transformation layer. This will typically be a micro- or meso-porous, solid which will act to transform the analyte gas stream by some means. Here the use of zeolite compounds for this purpose is investigated. Different theoretical models are used to probe the dependency of the response of a porous metal oxide sensor on the transport properties of gas through the device, including through an additional zeolite layer. Through the use of a force-field based method, shape and size selective adsorption is predicted and used to justify experimental results of zeolite modified sensors, for example, the reduction of response to linear hydrocarbons as the chain-length is increased. However, the limit of such calculations is also realised such that this approach is unlikely to provide an adequate predictive tool for selecting a suitable zeolite for a particular gas sensing task. Following this, a model based on the method of diffusion eigenstates has been developed to calculate bulk effective diffusivities and rate constants for porous systems representing both the sensor and zeolite porous layers. The effective properties are found to depend strongly on the microstructure, the partitioning between phases and diffusion coefficients of the different phases. The effective parameters are then interpreted in terms of sensor response by solving the one-dimensional diffusionreaction equation for a simple two-layered macroscopic geometry. The method of finite differences is used to find the concentration profile which generates a response on interaction with an electric field established between two electrodes. The concentration profile and hence the response depends on the balance of diffusion and reaction of the analyte gas within both the sensor and zeolite layers. It is shown how the response can be explored to expose such differences by firstly looking at both the steady state response and response time and also by varying the positioning of the electrodes used to measure the response. Good correlation with experimental response data is demonstrated, supporting the importance of the diffusion-reaction properties modelled to the sensing mechanism, and the potential of developing a predictive tool based on the models presented is discussed.
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Díaz, Delgado Raül. "Tin Oxide Gas Sensors: An Electrochemical Approach." Doctoral thesis, Universitat de Barcelona, 2002. http://hdl.handle.net/10803/2743.
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En la actualidad existe una preocupación creciente en lo concerniente a los problemas medioambientales provocados por la actividad humana y en cómo estos problemas pueden afectar a nuestra salud. Uno de los problemas medioambientales más acuciantes es la creciente presencia de gases contaminantes en la atmósfera, y la investigación en este campo trata de determinar tanto las especies que son perjudiciales como las concentraciones a partir de las cuales son nocivas. Por lo que a este último punto se refiere, las legislaciones medioambientales son cada vez más restrictivas respecto a las concentraciones máximas permitidas, por lo que se necesitan materiales capaces de detectar concentraciones de gases contaminantes cada vez más pequeñas. Y no tan sólo eso sino que, además, sean de coste moderado para permitir un uso particular de ellos. Es en este contexto en el que se enmarca esta tesis, que trata del estudio de nuevos materiales que permitan la detección de gases nocivos como el monóxido de carbono o el metano a bajas concentraciones y a un coste menor que los actuales materiales, permitiendo la comercialización de estos detectores a escala masiva.Uno de los materiales más estudiado por lo que a este tipo de materiales se refiere es el SnO2. Para optimizar la detección de este tipo de gases por parte de este material, uno de los procesos cruciales consiste en la adición de pequeñas cantidades de metales. Esta adición y, por tanto, las características de estos materiales como detectores de gases depende del método usado. En este trabajo se estudia un nuevo método de adición de metales sobre SnO2 basado en una reacción electroquímica espontánea que añade estos metales en forma de partículas nanométricas sobre este material, lo que constituye una característica fundamental para optimizar la detección de gases. El método constituye, por tanto, una interesante alternativa a otros métodos usados en la actualidad, con el importante añadido de ser un método de bajo coste y fácilmente implementable a escala industrial.
Por otro lado, en este trabajo también se ha empezado el estudio electroquímico de las reacciones de oxidación y reducción del estaño. El objetivo final de este estudio es la formación electroquímica de una capa de SnO2 de propiedades perfectamente controlables de manera que, al poner esta capa en contacto con un cierto gas, se pueda medir la influencia del gas en estas propiedades y, por tanto, desarrollar sensores electroquímicos de gases. Más aún, lo que se pretende es estudiar en condiciones realistas los mecanismos de intercambio electrónico implicados en la detección de gases para entender estos procesos. Es por ello que se ha empezado el estudio electroquímico del monocristal de Sn (100) y, como primer paso de este estudio, se ha desarrollado un proceso químico de preparación de la superficie de este monocristal que también se puede aplicar al policristal de estaño. Este proceso mejora sensiblemente los procesos usados hasta la fecha ya que disminuye considerablemente la contaminación en la superficie y, además, es capaz, en el caso del monocristal, de preparar superfies atómicamente planas siendo, por su sencillez y resultados, un método ideal para preparar estas superficies y efectuar estudios mecanísticos en este sistema.
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DeBoer, John Raymond. "Evaluation Methods for Porous Silicon Gas Sensors." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4971.
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This study investigated the behavior of porous silicon gas sensors under exposure to CO, NO, and NH3 gas at the part per million level. Parameters of interest in this study included the electrical, environmental, and chemi-resistive performance associated with various porous silicon morphologies. Based upon the variability of preliminary results, a gas pulsing method was combined with signal processing in order to analyze small impedance changes in an environment of substantial noise. With this technique, sensors could be effectively screened and characterized. Finally this method was combined with various post-treatments in order to improve the sensitivity and selectivity of individual sensors.
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Kukkola, J. (Jarmo). "Gas sensors based on nanostructured tungsten oxides." Doctoral thesis, Oulun yliopisto, 2013. http://urn.fi/urn:isbn:9789526202082.
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Abstract The aim of this thesis is to study whether nanostructured particles of WO3 could be competitive counterparts of traditional, more bulky materials in resistive gas sensor applications. Pristine and various surface decorated derivatives of three different types of WO3 nanoparticles applied on the surface of lithographically defined Si chips were used in the work to analyse the electrical behaviour of thin films when exposed to different gas atmospheres. Nanosized particles of WO3, obtained by capillary force-induced collapse of porous anodic tungsten oxide in water, were demonstrated as a sensing medium for the detection of H2 and NO analytes. Commercially available nanoparticles of WO3 were also studied. After decorating their surface with metal/metal oxide nanoparticles (Ag, PdOx and PtOx), stable aqueous dispersions were made and used for the inkjet printing of conductive patterns on test chips. Surface decoration was found to affect substantially the gas response behaviour of the materials with the largest differences in response to H2 and NO. The third type of tungsten oxide applied consisted of hydrothermally synthesized nanowires that were also surface decorated with PdO as well as with PtOx. The nanowires were suspended in water and drop cast on test chips for gas sensing measurements. The nanowire based devices allowed ultrasensitive detection of H2 even at room temperature. The results summarized in this thesis indicate that resistive gas sensors based on nanostructured tungsten oxides are excellent alternatives to existing devices utilizing porous thick films or bulky thin films. Their high sensitivity, low operating temperature and low electrical power consumption may enable the construction of portable sensors, for example by inkjet printing, thus having great potential for fast prototyping but also for large scale production at low costTiivistelmä Väitöstyön tavoitteena on tutkia nanorakenteisten WO3 hiukkasten kilpailukykyä suhteessa perinteisiin suuremman kidekoon materiaaleihin resistiivisissä kaasusensorisovelluksissa. Työssä tutkittiin kolmella eri tekniikalla valmistettujen WO3 nanopartikkeleiden alkuperäisistä ja pintakäsitellyistä versioista muodostettujen ohutkalvojen sähköisiä ominaisuuksia erilaisten kaasukehien funktiona. Veden kapillaarivoimien aikaan saaman huokoisen anodisen volframioksidirakenteen romahduksen kautta saatujen WO3 nanopartikkeleiden osoitettiin toimivan havaintoväliaineena H2 ja NO kaasuille. Myös kaupallisia WO3 nanopartikkeleita tutkittiin. Partikkelien pinta päällystettiin metalli- ja metallioksidinanopartikkeleilla (Ag, PdOx and PtOx), jonka jälkeen niistä muodostettiin vakaita vesipohjaisia seoksia johtavien kuvioiden mustesuihkutulostukseen testisubstraateille. Pintakäsittelyn havaittiin vaikuttavan merkittävästi materiaalien kaasuvasteisiin erityisesti H2:n ja NO:n tapauksessa. Kolmannen tyyppinen väitöskirjassa tutkittu volframioksidimateriaali koostuu hydrotermisesti syntetisoiduista nanojohdoista, jotka ovat pintakäsitelty PdO tai PtOx nanopartikkeleilla. Nanojohdot sekoitettiin veteen ja pipetoitiin testisubstraateille kaasumittauksia varten. Tämän tyyppiset kaasusensorit olivat erityisen herkkiä H2 kaasulle jopa huoneenlämmössä. Väistökirjan tulosten mukaan nanorakenteiset volframioksidimateriaalit ovat erinomainen vaihtoehto perinteisille huokoisille paksukalvoille ja suhteellisen paksuille ohutkalvoille kaasusensorisovelluksissa. Niiden suuri herkkyys, alhainen toimintalämpötila ja matala sähkönkulutus voivat mahdollistaa kannettavien kaasusensorien valmistuksen, esimerkiksi mustesuihkuteknologilla, nopeaan testaukseen ja suuren mittakaavan tuotantoon alhaisin kustannuksin
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Weglicki, Peter Stanislaw. "MOCVD of tin oxide for gas sensors." Thesis, University of Salford, 1990. http://usir.salford.ac.uk/26961/.
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Thin films of a wide variety of materials can be produced using an assortment of physical and chemical techniques. Such techniques are reviewed and compared, with particular reference to the deposition of tin oxide films. In the present study, MOCVD (Metal organic chemical vapour deposition) was used to grow thin films of tin oxide from dibutyltin diacetate precursor on a variety of substrates. A series of reactor prototypes were developed in accordance with specific requirements of reproducibility and process control. The evolution of the designs leading to the final working system is detailed. The theory of MOCVD is given with particular reference to the reactor used in this project. The effects of various deposition parameters on tin oxide film growth rates were investigated, and the results are discussed with reference to the deposition kinetics in the system. Films were characterised by optical interferometry, optical and electron microscopy, X-ray diffraction, Rutherford backscattering and electrical measurements. The films were generally uniform, conducting and polycrystalline, and were comprised of very small grains, resulting in a high density. A specific application of metal oxide materials is in solid state gas sensors, which are available in various forms and operate according to different mechanisms. These are compared and a detailed account is given on the theory of operation of surface conductivity modulated devices. The application of such devices based on tin oxide in thin film form was investigated in the present work. The prepared sensor samples were comprised of very small grains, resulting in a high density. The observation that preferred (310) orientation occurred in thicker films, can be attributed to dendritic growth. The sensors generally showed response to numerous reducing gas ambients, although there was evidence of a degree of selectivity against methane. Sensor response times due to changes in gas ambients between hydrogen and dried air were related to sensor thickness in terms of a grain surface defect diffusion process. This is driven by the equilibrium requirement between the exposed, gas modulated film surface states and inter-grain surface defects which are not subject to direct interaction with the gas ambient, owing to low structural porosity.
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Cavanaugh, Curtis. "AN ADAPTIVE ELECTRONIC INTERFACE FOR GAS SENSORS." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-20020108-121219.
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CAVANAUGH, CURTIS C. An Adaptive Electronic Interface for Gas Sensors (Under the direction of H. Troy Nagle).This thesis focuses on the development of an adaptive electronic interface for gas sensors that are used in the NC State electronic nose. We present an adaptive electronic interface that allows for the accurate mapping of the sensor?s voltage output to sensor resistance profiles. The adaptive interface uses a linearized Wheatstone bridge in a constant current configuration. The balancing of the bridge and the adjustment of the subsequent gain stage is performed using programmable variable resistors. The programmable resistors are controlled by a LabVIEW® program. The same control program also determines and records all the resistor values in the interface circuit. The resistance of each sensor is accurately computed by LabVIEW® using the interface-circuit, resistor values, and the voltage output of the circuit. Compensating for sensor drift can be done in LabVIEW® by adjusting the programmable resistor values so that a zero-voltage output is produced during the reference cycle. By doing this zero adjustment between each ?sniff? of an odorant, the baseline drift can be minimized.A single channel of the adaptive electronic interface has been designed and tested. The interface can be calibrated so that it is 99% accurate when performing sensor resistance measurements.A new conducting polymer sensor chamber has also been designed and tested. The new radial flow sensor chamber was minimizes the dead volume in the chamber and also deliver the odorant to each sensor at the same time. Two operating modes were compared: continuous-flow and sniff-and-hold. Both modes gave good classification performance while testing four different coffee samples. Experimental testing indicates that sensor response is highly correlated with the sample flow rate. Future work to more fully characterize this correlation is recommended.
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Khawaja, Jaleed Ejaz. "Asic gas sensors based on ratiometric principles." Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/2230/.
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The wide-scale usage of VOCs in industrial processes requires monitoring the concentrations of these vapours to keep a safe operating environment. Most combustible hydrocarbons can be ignited as a gas-air mixture in the range of 0.5% to 15% by volume. This has led to the development of several portable air quality monitoring instruments. However, the high costs and lack of durability of these instruments has remained an issue to be addressed. This PhD thesis reports on the development and characterization of a novel low cost smart gas sensor technology adaptable for use in a portable instrument. The smart gas sensor devices have been developed to target four different VOCs in air. The smart gas sensor device combines a smart ASIC (SRL 194 designed at SRL, Warwick University) fabricated in standard 0.7 μm CMOS technology and two alkyl-dithiol based self-assembled gold nanoparticle chemoresistive sensors (fabricated at Sony Deutschland GmbH) in a ratiometric array to offer a robust system which can address the common mode variations found in polymer based gas sensor systems. The ratiometric ASIC sensor array architecture allows for the reduction of the baseline value’s dependence on environmental variations and the elimination of baseline drift due to long term application of DC voltage. Three ratiometric array arrangements - mono-type uni-variate with only one chemosensor per device, mono-type bi-variate with two chemosensors of the same film material per device and duo-type with a polar and a non-polar chemosensor per device and their variations were characterized in an automated FIA test station against exposure to methanol, ethanol, propan-1-ol, and toluene at 30°C and 0-5% rh. It was determined that the devices’ response output to VOC analytes was entirely dependent on the variation of the resistance ratio of the chemoresistive sensors in the ratiometric sensor array. The effects of variations of the temperature and rh on the smart sensor output were calibrated. The mono-type devices gave a high magnitude response to the vapours whereas the duo-type arrangement offered a high degree of discrimination between the test analytes with little post-processing steps. Three different alkyl-dithiol chemoresistive sensor films on gold electrodes were successfully used as the VOC vapour sensitive elements in each arrangement. The effects of using a silicone sealant gel as a partitioning layer were characterized and it was observed that at vapour concentrations less than 3000 ppm the silicone encapsulated chemosensor devices reported a larger response to the VOC analytes as compared to those without the silicone. The test devices reported promising response repeatability and reproducibility with excellent return to baseline properties, a negligible hysteresis and an error margin of under 10%. Ideal operating temperature was determined to be 40°C at which rh variations were found to be minimal. The test devices were found to be robust with little variation in the quality of the device output over the course of 18 months. The novel research demonstrated that it is possible to get high level of diversification between analytes from a low cost and robust gas sensor system for monitoring VOCs. The work carried out here has opened the opportunity to develop highly integrated programmable hand-held gas sensor and e-nose systems for environmental monitoring use in health and safety applications.
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Chan-Henry, Robert Yatshein. "Design and development of electrochemical gas sensors." Thesis, City University London, 1992. http://openaccess.city.ac.uk/7730/.
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Historically, electrochemical gas sensors had suffered from several drawbacks such as poor temperature coefficient, leakage, susceptibility to shock and vibration and orientation sensitivity, which led to poor field reliability. In the present work these problems have largely been overcome by superior design, drawing on field experience in fuel cell and battery technology. The culmination of a sensor design embodying a number of unique concepts has revolutionised electrochemical gas sensor analysis and has pioneered the way for many new and hitherto difficult applications. The main features are: (a) A capillary diffusion-limiting barrier, based on gas-through-gas diffusion, with a theoretical temperature coefficient of 0.17% of signal per °C (at 20°C). (b) Very active fuel cell-type Pt black electrodes with large activity reserves giving rise to low span temperature coefficients, wide dynamic measurement ranges and enhanced long-term stability. (c) A close-wick sandwich arrangement of the electrodes conferring very good stability, to the extent that the sensors are substantially immune to shock and orientation problems. The sandwich design also enables the sensors to be very compact. (d) Use of strong sulphuric acid electrolyte in balance with ambient relative humidity (RH) - about 65% on average in temperate climates - in conjunction with a wick dipping into an expansion reservoir, giving maintenance-free, continuous dynamic range of operation between 20% and 90% RH and very long residence times outside these limits -several weeks in zero RH and several months in 100% RH at 20°C. (e) Extensive use of porous polytetrafluoroethylene (PTFE) membrane sealing techniques, which have dramatically improved cell integrity to the extent that leakage is virtually eliminated.(f) Matched sensing and reference electrodes in conjunction with zero bias cell operation, which allows the sensing and reference electrodes to be shorted out when the instrument is switched off; this gives almost instant warm-up when the instrument is switched on and the cell has excellent (NULL) stability under all conditions. (g) Since the sensor does not need to be powered-up when the instrument is switched off, there is a considerable saving on battery power in portable, hand-held instruments. (h) Inclusion of a second sensing (auxiliary) electrode, which enables the cancellation of partially reacting cross-interfering gases such as hydrogen. The auxiliary electrode can also substantially offset baselines; this is especially beneficial in biased sensors which generate large baselines. (i) Use of inboard chemical filters, which can remove cross interfering gases such as NO, N02, SO2, C12, NH3 and C2H4 by chemical reaction/adsorption.
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Darby, John Edward. "Semiconducting Langmuir-Blodgett films as gas sensors." Thesis, University of Kent, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293551.
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Steele, J. M. "Metal oxide single crystals as gas sensors." Thesis, University of Kent, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233273.
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Morris, Ljuibov. "Surface modification of solid state gas sensors." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392366.
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Wales, Dominic. "Planar integrated optical Bragg grating gas sensors." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/366987/.
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This thesis reports the development and modification of direct ultraviolet (UV) written planar integrated optical Bragg grating refractometers for detection of gases and vapours. The technique of direct UV writing utilises the localised refractive index increase within a UV-photosensitive silica layer, when the layer is exposed to a tightly focussed UV beam, to fabricate a wide range of optical waveguides and optical components. One such component, the Bragg grating, is used as an optical sensor for changes in refractive index. This thesis reports on the development of practical planar integrated optical Bragg grating gas sensors. This has been achieved through the use of two approaches. The first approach was to increase the number of gas molecules that can interact with the evanescent wave through the use of films of material that extended normally to the surface of the sensor device. Upon functionalisation of a planar Bragg grating sensor device with sol-gel thin films, a response between relative humidity and Bragg wavelength shift was revealed. Functionalisation of the Bragg grating sensor device with a polysiloxane polymer imparted sensitivity to solvent vapours. A quantitative structure-activity relationship (QSAR) approach was used to develop a linear regression model, between Bragg wavelength shift and solvent properties, which had good predicting power. The second approach was to utilise the associated change in refractive index of a material, when the material changed colour upon exposure to a gas, to create a measurable Bragg wavelength shift. This method was successfully achieved upon interrogation of a Bragg grating sensor device, which had been modified with an encapsulated pH sensitive organic dye upon exposure to hydrogen chloride fumes.
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Cittadini, Michela. "Nanostructured materials for plasmonic based gas sensors." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423667.
Full textAbstract:
My research work during the PhD was devoted to the development of optical gas sensors based on plasmonics. Sensors based both on Localized Surface Plasmon Resonance (LSPR) and Propagating Surface Plasmon Resonance (PSPR), also known as surface plasmon polaritons (SPP) have been studied. The thesis has been divided in two main chapters.
In the first one LSPR based gas sensor has been developed using gold nanoparticels (NPs) of different shapes like nanorods (NRs) with medium and high aspect ratio, 3 and 6 respectively, nanodumbbells (NDs) and nanostars (NSs). The LSPR is sensitive to changes in the local dielectric environment, and this allows the monitoring of the gases interacting with the matrices, and the output is a shift of the plasmon peak in terms of wavelength. The use of different shapes of NPs is oriented to the increase of sensitivity towards the changes in the local dielectric environment. This higher sensitivity is due to the local field enhancement effect linked to the elongated shapes or with the spikes, in the case of nanostars. The main difficulty about using these NPs is their tendency towards reshaping at the temperature’s increase. This constraint enforces the gas sensing tests to be performed at low temperature, therefore, to catalyze the red-ox reaction between the target gases and the sensitive material, platinum NPs are needed.
The gold NRs were also investigated with Dark Field Microscopy (DFM), a technique which enables the monitoring of the single particles behavior in hydrogen flow. Their sensitivity has been tested in both a TiO2 and ZnO matrix.
The ZnO sensitive material has been tested also directly as plasmonic material, because of its plasmon in the IR region triggered by the doping with Ga3+ or Al3+ ions, towards hydrogen and nitrogen oxide.
TiO2 based materials have been also used, in comparison with phenyl-functionalized SiO2 based materials, coupled with Au NPs as Aromatic Volatile Organic Compound A-VOC (xylene, toluene and benzene) sensors.
All the studied materials showed good sensitivity towards the tested gases, and the most important thing is that almost all these really good performances are at low temperature, thanks to the heterogeneous catalysis promoted by the Pt NPs.
These sensitive oxide materials have been tested also, in the second chapter, using SPP, excited illuminating a gold sinusoidal nanometric layer constituting a plasmonic crystals with a sensitive film on the top, interacting with the analyte.
TiO2 and phenyl-functionalized SiO2 have been used as sensitive materials in plasmonic crystals to monitor A-VOC and VOC at room temperature and hydrogen at 300 °C, obtaining good performances, comparable to the one of the system based on LSPR.
Moreover the comparison of the same sensitive material in the two configurations, with localized and propagating plasmons, allowed a better understanding of the transducing mechanism.Il presente lavoro di tesi è focalizzato sullo sviluppo di sensori ottici di gas basati sulla plasmonica. In particolare saranno studiati sensori basati sia su Risonanza Plasmonica Superficiale Localizzata (LSPR) che su Risonanza Plasmonica Superficiale Propagante (PSPR) noti anche come Plolaritoni Superficiali Propaganti (SPP). Tale tesi è divisa in due capitol principali. Il primo capitolo è dedicato ai sensori basati sulla LSPR, questi sensori sono stati sviluppati usando nanoparticelle di oro (NPs) con forme diverse (quali nanorod (NRs) con aspect ratio media e alta, 3 e 6 rispettivamente, nanodumbell e nanostelle). La LSPR è sensibile ai cambiamenti della costante dielettrica nell’intorno delle particelle, ciò permette di monitorare i gas che interagiscono con la matrice e ciò risulta in uno spostamento in lunghezza d’onda del picco plasmonico. L’utilizzo di diverse forme di NPs è legato al all’obiettivo di migliorare la sensibilità del plasmone ai cambiamenti nell’ambiente circostante. Tale aumento della sensibilità è legato ad un fenomeno di local field enhancement relativo alle forme allungate o con punte, come nel caso delle nanostelle. La maggiore difficoltà relativa all’uso di tali NPs sta nella loro tendenza al cambiare forma e sferoidizzare con la temperatura. Ciò permette di attuare i test di gas sensing solo a basse temperature, quindi per catalizzare le reazioni di ossido-riduzione dovute all’interazione tra i gas e il materiale sensibile vengono utilizzate NPs di platino. I NRs di oro sono stati utilizzati nella microscopia Dark Field (DFM) con applicazioni sensoristiche; tale tecnica permette di monitorare il comportamento ottico dei singoli NRs durante l’interazione con l’idrogeno. La sensibilità dei NRs è stata testata sia in matrice di ossido di titanio (TiO2) che di ossido di zinco (ZnO). Lo ZnO, in quanto material sensibile, è stato utilizzato anche direttamente come materiale plasmonico, grazie al plasmone nell’IR che viene innescato mediante drogaggio con ioni Ga3+ e Al3+, per il sensing di idrogeno e ossido di azoto. E’ stato inoltre utilizzato il TiO2 come materiale sensibile e le sue performances sono state confrontate con quelle dell’SiO2 sol-gel funzionalizzato con gruppi fenile per il sensing dei VOC (Volatile Organic Compound) Aromatici, quali benzene, toluene e xylene. Tutti i materiali studiati in tale capitolo mostrano una buona sensibilità ai gas testati, la cosa più importante è che gran parte delle misure sono state fatte a basse temperature, grazie alla catalisi eterogenea. Tali materiali sono stati anche testati, nel secondo capitolo, utilizzando i SPP, accesi illuminando uno strato nanometrico sinusoidale di oro, facente parte di un cristallo plasmonico, insieme ad uno strato sensibile che quello che entrerà in contatto con l’analita. TiO2 e SiO2 funzionalizzato con gruppi fenile sono stati usati come materiali sensibili nei cristalli plasmonici per monitorare VOC Aromatici e VOC a temperatura ambiente e idrogeno a 300 °C. Le prestazioni sono piuttosto buone, confrontabili con quelle dei sistemi basati su LSPR. Inoltre, il confronto degli stessi materiali sensibili nelle due configurazioni, con plasmoni localizzati e propaganti, permette di capire più a fondo i meccanismi coinvolti.
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Abhijith, N. "Semi Conducting Metal Oxide Gas Sensors: Development And Related Instrumentation." Thesis, Indian Institute of Science, 2006. https://etd.iisc.ac.in/handle/2005/281.
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A sensor is a technological device or biological organ that detects, or senses, a signal or physical condition and chemical compounds. Technological developments in the recent decades have brought along with it several environmental problems and human safety issues to the fore. In today's world, therefore, sensors, which detect toxic and inflammable chemicals quickly, are necessary. Gas sensors which form a subclass of chemical sensors have found extensive applications in process control industries and environmental monitoring.
The present thesis reports the attempt made in development of Zinc oxide thin film based gas sensors. ZnO is sensitive to many gases of interest like hydrocarbons, hydrogen, volatile organic compounds etc. They exhibit high sensitivity, satisfactory stability and rapid response. In the present work the developed sensors have been tested for their sensitivity for a typical volatile organic compound, acetone. An objective analysis of the various substrates namely borosilicate glass, sintered alumina and hard anodized alumina, has been performed as a part of this work. The substrates were evaluated for their electrical insulation and thermal diffusivity. The microstructure of the gas sensitive film on the above mentioned substrates was studied by SEM technique. The gas sensitive Zinc oxide film is deposited by D.C reactive magnetron sputtering technique with substrate bias arrangement. The characterization of the as-deposited film was performed by XRD, SEM and EDAX techniques to determine the variation of microstructure, crystallite size, orientation and chemical composition with substrate bias voltage. The thesis also describes the development of the gas sensor test setup, which has been used to measure the sensing characteristics of the sensor. It was observed that the ZnO sensors developed with higher bias voltages exhibited improved sensitivity to test gas of interest.
Gas sensors essentially measure the concentration of gas in its vicinity. In order to determine the distribution of gas concentration in a region, it is necessary to network sensors at remote locations to a host. The host acts as a gateway to the end user to determine the distribution of gas concentration in a region. However, wireless gas sensor networks have not found widespread use because of two inherent limitations:
Metal oxide gas sensors suffer from output drift over time; frequent recalibration of a
number of sensors is a laborious task.
The gas sensors have to be maintained at a high temperature to perform the task of gas
sensing. This is power intensive operation and is not well suited for wireless sensor
network.
This thesis reports an exploratory study carried out on the applicability of gas sensors in wireless gas sensor network. A simple prototype sensing node has been developed using discrete electronic components. A methodology to overcome the problem of frequent calibration of the sensing nodes, to tackle the sensor drift with ageing, is presented. Finally, a preliminary attempt to develop a strategy for using gas sensor network to localize the point of gas leak is given.
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Abhijith, N. "Semi Conducting Metal Oxide Gas Sensors: Development And Related Instrumentation." Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/281.
Full textAbstract:
A sensor is a technological device or biological organ that detects, or senses, a signal or physical condition and chemical compounds. Technological developments in the recent decades have brought along with it several environmental problems and human safety issues to the fore. In today's world, therefore, sensors, which detect toxic and inflammable chemicals quickly, are necessary. Gas sensors which form a subclass of chemical sensors have found extensive applications in process control industries and environmental monitoring.
The present thesis reports the attempt made in development of Zinc oxide thin film based gas sensors. ZnO is sensitive to many gases of interest like hydrocarbons, hydrogen, volatile organic compounds etc. They exhibit high sensitivity, satisfactory stability and rapid response. In the present work the developed sensors have been tested for their sensitivity for a typical volatile organic compound, acetone. An objective analysis of the various substrates namely borosilicate glass, sintered alumina and hard anodized alumina, has been performed as a part of this work. The substrates were evaluated for their electrical insulation and thermal diffusivity. The microstructure of the gas sensitive film on the above mentioned substrates was studied by SEM technique. The gas sensitive Zinc oxide film is deposited by D.C reactive magnetron sputtering technique with substrate bias arrangement. The characterization of the as-deposited film was performed by XRD, SEM and EDAX techniques to determine the variation of microstructure, crystallite size, orientation and chemical composition with substrate bias voltage. The thesis also describes the development of the gas sensor test setup, which has been used to measure the sensing characteristics of the sensor. It was observed that the ZnO sensors developed with higher bias voltages exhibited improved sensitivity to test gas of interest.
Gas sensors essentially measure the concentration of gas in its vicinity. In order to determine the distribution of gas concentration in a region, it is necessary to network sensors at remote locations to a host. The host acts as a gateway to the end user to determine the distribution of gas concentration in a region. However, wireless gas sensor networks have not found widespread use because of two inherent limitations:
Metal oxide gas sensors suffer from output drift over time; frequent recalibration of a
number of sensors is a laborious task.
The gas sensors have to be maintained at a high temperature to perform the task of gas
sensing. This is power intensive operation and is not well suited for wireless sensor
network.
This thesis reports an exploratory study carried out on the applicability of gas sensors in wireless gas sensor network. A simple prototype sensing node has been developed using discrete electronic components. A methodology to overcome the problem of frequent calibration of the sensing nodes, to tackle the sensor drift with ageing, is presented. Finally, a preliminary attempt to develop a strategy for using gas sensor network to localize the point of gas leak is given.
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Gad, Alaaeldin [Verfasser]. "Solar Diodes: Novel Heterostructured Materials for Self-Powered Gas Sensors / Alaaeldin Gad." München : Verlag Dr. Hut, 2013. http://d-nb.info/1045987670/34.
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Sasaki, Isao. "Higher-order Sensors for Fast Detection of Gases." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7591.
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The research is divided into two main parts: the sensing part and the gas delivery part.
The reliable chemical information from the chemical sensor requires that the sensitive layer of the sensor exhibits long-term stability. To improve the stability of the sensing layer, camphorsulfonic acid was added to the formic acid. The introduction of photo-irradiation at 254 nm as an additional treatment to the sensing layer was proved to be effective.
For gas selectivity of PANI matrix, metal or metal oxide clusters have been incorporated into the matrix. The composite materials of PANI with silver, copper, iron, nickel, palladium and mercury were also prepared and exposed to different gases.
The second part of the thesis discusses the gas delivery system to the sensors using the synthetic jet technology. The sniffing functionality was demonstrated using the designed jet cell for operation in the open system. The gas sniffing experiments showed that in the presence of the jet, the response time of the sensor is faster by about two orders of magnitude (20 compared to 1800 seconds).
The jet sampling system was applied to continuous monitoring of ammonia gas filter performance using the chemFET array. The jet system collected the gas before and after filtering, and the difference between the two responses was compared to observe the break-through of the filter. It was concluded that the gas sensing system integrated with the gas sampling functionality can be applied to monitor a gas filter performance.
The cell was designed so that the impinging jet covers the sensing active area of the array of eight chemFETs. The two-dimensional distribution of the ammonia gas concentrations showed that the jet covers the active sensing area in an effective way so that the sampling volume for sensing is significantly reduced compared with the conventional gas flow cell system.
Based on these initial studies shown in this thesis, the proposed gas sniffing system was shown to be effective in realizing fast detections of gases for critical applications of a gas sensor system.
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Hills, M. "Solid state sensors for gas monitoring and control." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604069.
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A probe for the continuous on-line measurement of hydrogen dissolved in liquid aluminium has been developed using the perovskite proton conductor CaZrO3-In, in conjunction with a Zr,ZrH2 solid state reference. The probe has been designed to an industrial prototype standard, and measurements were in good agreement with established (but cumbersome) hydrogen measurement methods such as the AISCAN analyser, LECO analysis, and the Straube-Pfeiffer technique. The electrolytic domain of CaZrO3-In has been investigated using a novel double-cell arrangement to simultaneously fix the chemical potential of both hydrogen and oxygen at the electrodes of a pellet of the electrolyte. As predicted from the defect equilibria, the electrolyte makes the transition from the hydrogen ion conduction domain to the oxygen ion domain under conditions of low oxygen partial pressure and high hydrogen partial pressure. The pO2 corresponding to the Zr,ZrO2 equilibrium is low enough to locate CaZrO3-In in the oxygen ion conduction domain. Sodium b-alumina was employed to measure the pO2 developed under operating conditions at the sensor reference electrode by a sample zirconium containing dissolved oxygen. This was found to be many orders of magnitude higher than the pO2 corresponding to the Zr,ZrO2 equilibrium, and was five magnitude higher than the pO2 marking the H+/O2- conduction domain boundary for CaZrO3-In, suggesting that Zr, ZrH2 may be suitable as a reference material. Hydrogen sensors manufactured using CaZrO3-In as the solid electrolyte and a Zr,ZrH2 solid state reference were found to provide stable, reproducible emfs at constant temperature and pH2, and showed full Nernstian response following a change in pH2 at the measuring electrode. The recently developed Current Reversal Mode can accurately determine the emf of a solid electrolyte sensor, and also provides additional information in the form of the sensor resistance. A detailed study has identified how the CRM parameters should be selected in order to make accurate measurements. The sensor resistance measurement was used to improve measurement accuracy and stability of an internally heated yttria stabilised zirconia oxygen sensor. When applied to a commercially available probe for measuring hydrogen dissolved in liquid aluminium it was found that erroneous emf readings, measured after prolonged use in the melt, were accompanied by a corresponding increase in the sensor resistance, opening up the possibility of using CRM as an on-line diagnostic tool.
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Patra, Nandini. "Atomic Scale Design of Graphene based Gas Sensors." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-224193.
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In this project work, we have performed Density Functional Theory (DFT) calculations to study the gas (CO, NO and CO2) sensing mechanism of pure and doped (B, N and B-N) graphenesurfaces. Generalized gradient approximation (GGA-PBE) within projector-augmented wave (PAW) methodology were adopted to investigate the electronic properties of such materials. The adsorption energies of the various toxic gases (CO, NO, and CO2) on the pure and doped graphene surfaces have been calculated to check their thermodynamic stability and selectivity.The B, N mono-doping has been done to verify whether p- and n-type of doping could improve the graphene's gas sensing properties. Moreover, B-N co-doping is being done to check whether p-n doping could even further improve their gas sensing mechanism. Here we report p-n doping on graphene surface significantly improves their gas sensing properties.
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Covington, James A. "CMOS and SOI CMOS FET-based gas sensors." Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/3589/.
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In recent years, there has been considerable interest in the use of gas/vapour monitors and electronic nose instruments by the environmental, automotive and medical industries. These applications require low cost and low power sensors with high yield and high reproducibility, with an annual prospective market of 1 million pounds. Present device and sensor technologies suffer a major limitation, their incompatibility with a standard silicon CMOS process. These technologies have either operating/annealing temperatures unsuited for MOSFET operation or an inappropriate sensing mechanism. The aim of this research is the development of CMOS compatible gas/vapour sensors, with a low cost of fabrication, high device repeatability and, in the future, transducer sensor amalgamation. Two novel approaches have been applied, utilising bulk CMOS and SOI BiCMOS. The bulk CMOS designs use a MOSFET sensing structure, with an active polymeric gate material, operating at low temperatures (<100°C), based on an array device of four elements, with channel lengths of 10 μm or 5 μm. The SOI designs exploit a MOSFET heater with a chemoresistive or chemFET sensing structure, on a thin membrane formed by the epi-taxial layer. By applying SOI technology, the first use in gas sensor applications, operating temperatures of up to 300 °C can be achieved at a power cost of only 35 mW (simulated). Full characterisation of the bulk CMOS chemFET sensors has been performed using electrochemically deposited (e.g. poly(pyrrole)/BSA)) and composite polymers (e.g. poly(9-vinylcarbazole)) to ethanol and toluene vapour in air. In addition, environmental factors (humidity and temperature) on the response and baseline were investigated. This was carried out using a newly developed flow injection analysis test station, which conditions the test vapour to precise analyte (<15 PPM of toluene) and water concentrations at a fixed temperature (RT to 105°C +- 0.1), with the sensor characterised by either I-V or constant current instrumentation. N-channel chemFET sensors operated at constant current (10 μA) with electrochemically deposited and composite polymers showed sensitivities of up to 1.1 μV/PPM and 4.0 μV/PPM to toluene vapour and to 1.1 μV/PPM and 0.4 μV/PPM for ethanol vapour, respectively, with detection limits of <20 PPM and <100 PPM to toluene and <20 PPM and 10+ PPM to ethanol vapour (limited by baseline noise), respectively. These responses followed either a power law (composite polymers) or a modified Langmuir isotherm model (electrochemically deposited polymers) with analyte concentration. It is proposed that this reaction-rate limited response is due to an alteration in polymers work function by either a partial charge transfer from the analyte or a swelling effect (polymer expansion). Increasing humidity caused, in nearly all cases a reduction in relative baseline, possible by dipole formation at the gate oxide surface. For the response, increasing humidity had no effect on sensors with composite polymers and an increase for sensors with electrochemically-deposited polymers. Higher temperatures caused a reduction in baseline signal, by a thermal expansion of the polymer, and a reduction in response explained by the analyte boiling point model describing a reduction in the bulk solubility of the polymer. Electrical and thermal characterisation of the SOI heaters, fabricated by the MATRA process, has been performed. I-V measurements show a reduction in drain current for a MOSFET after back-etching, by a degradation of the carrier mobility. Dynamic measurement showed a two stage thermal response (dual exponential), as the membrane reaching equilibrium (100-200 ms) followed by the bulk (1-2 s). A temperature coefficient of 8 mW/°C was measured, this was significantly higher than expected from simulations, explained by the membrane being only partially formed. Diode and resistive temperature sensors showed detection limits under 0.1°C and shown to measure a modulated heater output of less than 1°C at frequencies higher than 10Hz. The principal research objectives have been achieved, although further work on the SOI device is required. The results and theories presented in this study should provide a useful contribution to this research area.
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Woodward, S. F. "Mechanistic and potentiostatic studies of electrochemical gas sensors." Thesis, Bucks New University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371233.
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Chwieroth, Brian. "Design and modeling of metal oxide gas sensors /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486397841222182.
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Aygun, Seymen Murat. "Gas Sensors Based on Ceramic p-n Heterocontacts." Ames, Iowa : Oak Ridge, Tenn. : Ames Laboratory ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/837264-2ckydm/webviewable/.
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Thesis (M.S.); Submitted to Iowa State Univ., Ames, IA (US); 19 Dec 2004.Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2498" Seymen Murat Aygun. US Department of Energy 12/19/2004. Report is also available in paper and microfiche from NTIS.
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Blanchard, Jeffrey Allen 1974. "Specific gas sensing using zirconia amperometric oxygen sensors." Thesis, The University of Arizona, 1998. http://hdl.handle.net/10150/278662.
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An analytical model for the specific gas detection of oxygen, carbon dioxide, and water vapor using zirconia amperometric oxygen sensors has been developed. Sensors of this type have been designed, fabricated, and tested using planar ceramic technology. Furthermore, an experimental setup has been designed and constructed for sensor characterization. This testbed can accurately control gas partial pressures as well as the total system pressure over a wide range of flow rates. Extensive effort has been put into design and construction of this testbed to ensure accurate scientific measurements. Special attention has been paid to ensuring that the apparatus is leak-tight from air to ensure accurate measurements at low oxygen partial pressures. Results of the experimentation for oxygen detection as well as the detection of carbon dioxide and water vapor are presented. The effects of electronic conduction in the zirconia electrolyte at low oxygen partial pressures are examined. Possible applications of the sensor, as well as suggestions for further research are discussed.
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Robins, Ian. "Gas sensitive field effect transistors." Thesis, King's College London (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318466.
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Ben, Aziza Zeineb. "Graphene based gas sensors : Fabrication, characterization, and study of gas molecules detection mechanism." Thesis, Limoges, 2015. http://www.theses.fr/2015LIMO0102.
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Ce travail nous a permis de réaliser une étude de capteurs de gaz et d’humidité à base de graphène. Cette étude pourrait être utile non seulement pour améliorer les performances des capteurs à base de graphène mais aussi pour mieux comprendre l’interaction entre le graphène et les molécules de gaz. Ceci semble indispensable pour faire avancer les applications du graphène comme un matériau prometteur pour la détection des gaz. Des avancées significatives ont été présentées au niveau de la fabrication de ces capteurs, leurs différentes caractérisations électriques ainsi que d’autres techniques employées pour analyser le mécanisme contrôlant la détection des molécules de gaz/vapeur. Ces outils ont été mis en place pour concevoir et fabriquer plusieurs structures de capteur en utilisant différents substrats support du graphène d’une part et en modifiant les propriétés du graphène par utilisation des produits chimiques d’autres part. La caractérisation de ces capteurs sous différents environnements a permis de comparer les différentes réponses des capteurs et d’en tirer plusieurs conclusions sur le fonctionnement de ces dispositifs. En effet, le Mica, un substrat lisse et transparent, a été utilisé comme substrat pour le graphène. Le dopage induit par le mica a été étudié ainsi que son impact sur la sensibilité du graphène au gaz d’ammoniac. Ceci a permis de mettre en évidence le fait que le substrat joue un rôle important pour la détection de l’ammoniac. De plus, ces capteurs fabriques sur mica et SiO2 ont été testés sous différentes conditions de températures et d’oxygène. Dans une autre approche, un polymère a été utilisé pour doper le graphène. Une étude détaillée a été menée pour analyser le comportement de ce graphène fonctionnalisé par rapport aux molécules d’eau. Ces nouveaux résultats expérimentaux obtenus pendant cette thèse constituent un bon support à plusieurs résultats théoriques établis et permettent d’optimiser la conception des capteurs de gaz à base de graphène pour des meilleures performancesIn this research, we report on a study of graphene based gas and humidity sensors. This study could be useful not only to improve the performance of graphene based sensors but also to better understand the interaction between graphene and gas molecules. This seems necessary to promote the applications of graphene as a promising material for gas sensing. Significant advances have been made to design and fabricate these sensors: the different electrical characterizations as well as other techniques used to analyze the mechanism controlling the detection of gas/vapor molecules. These tools have been set up to design and manufacture various sensor structures using different underlying substrates for graphene on one hand and chemical modification of graphene properties on the other hand. The characterization of these sensors under different environments was used to compare the different responses of the sensors and draw several conclusions about gas sensing mechanism. Indeed, Mica, a smooth and transparent substrate, was used as a supporting substrate for graphene. Doping induced to graphene by mica and its impact on graphene sensitivity to ammonia gas were studied. This has made it possible to highlight the fact that the substrate plays an important role for the detection of ammonia. In addition, these sensors made on mica and SiO2 were tested under a variety of temperatures and oxygen. In another approach, a polymer was used to dope graphene. A detailed study was realized about the behavior of water molecules on functionalized graphene. The obtained experimental results, reported for the first time, represent a good support for several theoretical studies already made and could be used to optimize the design of graphene based gas sensors
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Fawcett, Timothy J. "Investigation into the hydrogen gas sensing mechanism of 3C-SiC resistive gas sensors." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001537.
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Vukusic, Peter. "Sensing thin layers using surface plasmon resonance." Thesis, University of Exeter, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358142.
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Szabo, Nicholas F. "DEVELOPMENT OF HARSH ENVIRONMENT NITROGEN OXIDES SOLID-STATE GAS SENSORS." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1046980412.
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Page, Julian. "Factors affecting low temperature performance of zirconia gas sensors." Thesis, Middlesex University, 2001. http://eprints.mdx.ac.uk/8007/.
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A reduction in the operation temperature of zirconia ceramic gas sensors is highly desirable for a number of practical reasons. This work seeks to investigate the factors that prevent a reduction in operation temperature and propose methods by which these may be resolved. A novel approach to sensor fabrication has been developed and employed with the advantage of reduced device complexity that should lead to subsequent cost and reliability benefits. Leakage rates in these devices have been shown to be small and electrochemical in origin. Leakage was greater than reported for gold seal devices, partly due to increased electrode activity. The flexibility of device configuration allows a variety of sensor geometries and functions to be realised. This flexibility led to the characterisation of sensors at the upper and lower ends of measurement range and the identification of deviations from theoretical performance. These deviations have been reconciled with theory extended to cover these limits. Such sensors are known to be sensitive to reducible gas species such as CO2 and H2O with a second limiting plateau allowing quantification of these gases. Such analysis capabilities have been found to be extended by incorporating a second pair of electrodes. These effects have not previously been reported. Sensors have been shown to be more sensitive to H2O than to CO2. To investigate the low temperature response of sensors, a variety of techniques and analyses have been developed and are employed with varying success. Impedance spectroscopy was by far the most useful and revealing tool but this is a function of the highly developed hardware and sophisticated control and analysis software bought as a complete system. Gas step changes and current / voltage sweeps were also useful as comparative techniques but could not separate out component mechanisms. Scanning electron microscopy proved to be a vital tool as it allowed vital information to be obtained concerning electrode and electrolyte microstructure. Again this is a function of a highly developed and sophisticated instrument. The techniques of pressure and concentration modulation were limited in terms of ease of use, measurement range and results interpretation. The main drawbacks were limited frequency ranges and laborious data collection and analysis. They do both however show large potential for improvement. Both amperometric and potentiometric sensors response rates were analysed with a variety of noble metal electrodes using each technique. Electrode material proved to have a marked effect on sensor performance with the best results obtained with silver and electro-deposited platinum. Scanning electron microscopy of silver showed that a finely divided and openly porous electrode was not required for high performance contrary to expectations. This is thought to be due to the solubility of oxygen in this metal. With platinum however, the improved microstructure is thought to be a signifîcant factor in electro-deposited and cermet electrode performance. Response rates in amperometric sensors did not show any significant temperature dependence although a restriction in measurement range was observed. Response rates were suspected to be mainly influenced by sensor geometry whilst measurement range was a function of sensor geometry, electrolyte conductivity and electrode activity. Improved electrolytes will provide improvements and may come in the form of attention to the YSZ system or by employing an alternative ion conductor such as ceria. Close attention to sensor dimensions provides possibility for enhancements. In amperometric devices for instance a long, thin diffusion barrier is required leading to a small internal cavity with a large electrode surface area and a thin electrolyte membrane.
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Shao, Feng. "New strategies in metal oxide nanowire based gas sensors." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/145058.
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This thesis presents the results of applying new strategies to understand the mechanism and explore the sensing performance of metal oxide (MOX) nanowire based gas sensors by testing individual nanowire gas sensors, running density functional theory (DFT) calculations, using new materials, applying ex-situ analysis and temperature-pulsed operation mode. These MOX nanowires include SnO2, CuO decorated SnO2, CuO and ZnO, electrically contacted either individually or in bundles.
With SnO2-NH3 as a model system, DFT calculations were made to draw the pictures of surface-gas interactions, which were combined with empirical modeling of individual nanowire sensors to determine the sensing mechanism of this system. The surface reaction routine that involves non lattice oxygen was found to responsible for the sensing effect. As an interfering substance to NH3 sensing, H2O was also studied in this approach. At the new material front, CuO decorated SnO2 nanowire showed significantly increased sensitivity toward H2S while keeping other gases, e.g., CO and NH3 low, offering good selectivity to this gas. Ex-situ analysis has shown that sulfurization and desulfurization reactions happened on CuO, confirming the charge transport channel depletion model proposed for this material. The less common p-type CuO was obtained with the facile thermal oxidation method. NH3, H2S and NO2 sensing have all indicated the key role of surface adsorbed oxygen species in its gas sensing. Due to its intrinsic property, the ZnO nanowires assembled onto micro hot plate (μHP) substrates by dielectrophoretic (DEP) alignment showed relative NH3 selectivity from CO. When operated in temperature-pulsed mode, sensitivity enhancement was seen at the low temperature end. Such effect was ascribed to the fast regulation of surface oxygen, H2O and NO2 in the pulsed mode.
The current dissertation is organized as follows: Chapter 1 introduces the general background of the MOX gas sensors and the basic idea of computational chemistry. Chapter 2 gives a brief introduction to density functional theory, which is the major theoretical tool in this work. Chapter 3 describes the experimental and theoretical techniques that have been applied. Chapter 4 deals with the NH3/H2O sensing of SnO2 nanowire, DFT calculations and empirical modeling. The sensing mechanism of NH3 by SnO2 and the interfering principle of H2O were unveiled. Chapter 5 reports the H2S sensing of SnO2 and CuO decorated SnO2 nanowires and the study of the corresponding mechanisms. Chapter 6 explores the NH3, H2S and NO2 sensing properties of the individual CuO nanowire. The importance of surface oxygen species in gas sensing was demonstrated. Chapter 7 is about the DEP deposition of ZnO nanowires onto the μHP sensing substrate and the NH3 sensing in isothermal and temperature-pulsed mode. Chapter 8 reviews the present work, highlighting the main achievements and proposes future directions.Aquesta tesi se centra en l’estudi dels mecanismes de detecció de gasos amb sensors basats en nanofils d’òxids metàl•lics. Amb aquest objectiu, s’han estudiat les respostes de sensors formats per un únic nanofil, s’ha modelitzat la seva resposta mitjançant càlculs DFT (Density Functional Theory) i s’han analitzat nous materials i explorat modes de funcionament no estàndards com és el polsat de temperatura. Als tres primers capítols de la dissertació se’n fa una introducció als dispositius basats amb òxids metàl•lics, es revisen els fonaments teòrics que hi ha darrera de les simulacions DFT i es presenten els mètodes experimentals que s’han fet servir per completar aquest treball doctoral. El quart capítol se n’ocupa de les interaccions del sistema SnO2-NH3 mitjançant la combinació de càlculs teòrics amb DFT i dades experimentals. Es presenta i valida el mecanisme de detecció de l’amoníac amb l’òxid d’estany així com es discuteix les interferències d’aquest contaminant amb la humitat. Al cinquè capítol es presenta la detecció de H2S amb heteroestructures formades per nanofils de SnO2 decorats amb nanopartícules de CuO. La gran sensitivitat a aquest gas que es troba experimentalment, especialment si es compara amb les respostes típiques obtingudes amb nanofils no decorats, s’ha analitzat i modelitzat. El capítol sisè explora la utilització d’òxid de coure, un semiconductor tipus p, com a sensor de gas; i les seves respostes a diferents contaminants es comparen amb les obtingudes amb l’òxid d’estany, el semiconductor tipus n de referència. Ja al capítol setè, es presenta el dipòsit controlat de nanofils de ZnO sobre hotplates mitjançant dielectroforesi (DEP) així com la millora de la sensitivitat quan els dispositius obtinguts són operats en mode de temperatura polsada. Finalment, el capítol vuitè i últim resumeix tots els capítols anteriors destacant els resultats més significatius aconseguits, i s’exploren noves línies de treball per a futures tesis.
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Tsolov, Peter. "Design, fabrication and characterization of thick-film gas sensors." Doctoral thesis, Universitat Rovira i Virgili, 2004. http://hdl.handle.net/10803/8450.
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DE LA TESIS DOCTORALTítulo: Diseño, fabricación y caracterización de sensores de capa gruesa
Doctorando: Peter Tsolov Ivanov
Director: Xavier Correig Blanchar
Los sensores de gases de estado sólido han demostrado ser muy prometedores para
supervisar la emisión de los agentes contaminadores en el aire, porque son una opción
de bajo coste para la construcción de analizadores de gases. Algunos problemas se
relacionados con este tipo de dispositivos, especialmente su baja selectividad y el alto
consumo de energía, siguen sin resolver. El objetivo de esta tesis doctoral es el
desarrollo de nuevos sensores y matrices de sensores con mejorada selectividad y
reducido consumo de energía.
La metodología usada en esta tesis consiste en fabricar matrices de sensores hechas de
sensores con distintas selectividades. Como la respuesta del sensor es diferente en
distintas temperaturas de trabajo y como los distintos dopantes o los filtros catalíticos
aceleran o reducen la respuesta del sensor, los diferentes sensores dan diferentes
reacciones. Combinando estas reacciones y con la ayuda de técnicas del reconocimiento
de patrones, se pueden crear grupos de sensores capaces de distinguir entre distintos
agentes contaminantes.
La tesis comienza repasando los métodos usados para la fabricación de los sensores de
gases y discutiendo los problemas relacionados con la baja selectividad de los óxidos
metálicos. Se especifican también los diferentes métodos para aumentar la selectividad.
Se introduce y se describe detalladamente la técnica de screen-printing. Los
experimentos se realizaron con cuatro tipos de substratos de sensores (cerámica, silicio,
microhotplate y silicon-on-insulator) y con más de 15 capas activas basadas en dióxido
de estaño y trióxido de tungsteno (puras y dopadas con oro, platino, plata, titanio y
paladio). Una amplia variedad de compuestos volátiles (amoníaco, etanol, acetona y
benceno), de gases (monóxido de carbono, dióxido de nitrógeno, metano y sulfuro de
PhD thesis of Peter Tsolov Ivanov Resumen de la tesis doctoral
hidrógeno) y de algunas mezclas binarias ha sido medida. Los resultados obtenidos por
los análisis cuantitativos y cualitativos de los gases estudiados con una matriz de
sensores basada en cuatro sensores simples nos han llevado a descubrir el óptimo
sensor/matriz para los distintos gases/mezclas binarias.
Los resultados demostraron que, con la ayuda de redes neuronales Fuzzy ARTMAP, es
posible identificar y cuantificar simultáneamente los gases analizados usando solamente
una matriz de microhotplates (cuatro sensores) con la misma capa activa. Los sensores
de SnO2 y de WO3 dopados demostraron diversa respuesta a los agentes contaminantes
probados. Componiendo cuidadosamente la matriz de sensores y definiendo bien la
temperatura de trabajo podemos discriminar, con un alto grado de éxito, los diversos
gases probados sin la necesidad de técnicas de reconocimiento de patrones.
La conclusión principal que se puede sacar de esta tesis es que las matrices de sensores,
junto con las técnicas de reconocimiento de patrones, se pueden utilizar para aumentar
perceptiblemente la selectividad de los sensores de óxidos metálicos. La simplicidad de
los métodos propuestos permite su uso en el desarrollo de analizadores de gases más
baratos y narices electrónicas portátiles.
A partir de la investigación realizada durante esta tesis doctoral se han elaborado 15
artículos publicados en revistas internacionales, 10 comunicaciones en las conferencias
internacionales y 3 comunicaciones en conferencias españolas.
PhD thesis of Peter Tsolov Ivanov Resume of the doctoral thesis
OF THE DOCTORAL THESIS
Title: Design, Fabrication and Characterization of Thick-Film Gas Sensors
Doctorate: Peter Tsolov Ivanov
Director: Xavier Correig Blanchar
Solid-state gas sensors have proved to be very promising for monitoring the emission of
air pollutants because they are a low cost option for constructing gas analysers. Some
problems associated to this approach, especially their deficient selectivity and high
power consumption, remain unsolved. The aim of this doctoral thesis is to develop new
sensors and sensor matrices that can improve the selectivity of metal oxide gas sensors
and decrease their power consumption.
The methodology used here consists of creating sensor matrices made from sensors with
different selectivities. As the sensor response is different at different working
temperatures and as the different dopants or catalytic filters accelerate or reduce the
sensor response, the different sensors give different reactions. If these reactions are
combined, sensor groups capable of discriminating between different pollutants can be
obtained with the help of pattern recognition techniques.
The thesis begins by reviewing the methods used for fabricating gas sensors and
discussing the problems caused by the poor selectivity of metal oxide gas sensors and
the methods for increasing their selectivity. Then, the screen-printing technique is
introduced and described. The experiments were performed with four different types of
gas sensor substrates (ceramic, silicon, microhotplate and silicon-on-insulator) and more
than 15 active layers (undoped and doped with gold, platinum, silver, titanium and
paladium tin dioxide and tungsten trioxide sensitive layers). A wide variety of volatile
compounds (ammonia, ethanol, acetone and benzene), gases (carbon monoxide,
nitrogen dioxide, methane and hydrogen sulphide) and some binary mixtures were
measured. The results obtained from quantitative and qualitative gas analysis using the
PhD thesis of Peter Tsolov Ivanov Resume of the doctoral thesis
sensor response from a simple 4 sensor based matrix led to the optimal sensor/sensor
matrix for gas/binary mixtures.
The results showed that, with the help of fuzzy ARTMAP neural networks, it is possible
to identify and simultaneously quantify the gases analysed by using only one MHP-chip
(four sensors) with the same active layer. The doped SnO2 and WO3 sensors showed
different response to the tested pollutants. Composing carefully the sensor matrix and
defining well the working temperature we were able to discriminate, with a high success
rate, between the different test gases with no need for pattern recognition techniques.
The main conclusion that can be drawn from this thesis is that sensor matrices can be
used, coupled to dynamic pattern recognition techniques, to significantly increase the
selectivity of metal oxide sensors. The simplicity of the methods implemented makes
them suitable for developing low-cost gas analysers and hand-held e-noses.
The research carried out during this doctoral thesis resulted in 15 articles being
published in international journals, 10 communications at international conferences and
3 communications at a Spanish national conference.
PhD thesis of Peter Tsolov Ivanov Resumen de la tesis doctoral
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Reyes, Hernández Luis Fernando. "Tungsten trioxide nanocrystalline films for applications in gas sensors." Universidad Nacional de Ingeniería. Programa Cybertesis PERÚ, 2008. http://cybertesis.uni.edu.pe/uni/2008/reyes_hl/html/index-frames.html.
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