Rozprawy doktorskie na temat „Oxygen Gas Sensors”

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.

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.

Aspects relating to and including the development of thick film amperometric zirconia oxygen sensors were investigated. These devices, which were operated in the range 550-950°C, had a laminated structure in which a cathode, an electrolyte and an anode were printed, in that order, onto a planar alumina substrate. The anode and electrolyte were porous and during sensor Operation also acted as a diffusion barrier, restricting the rate of oxygen diffusion to the cathode. A thick film platinum heater was also developed to maintain the sensor at its operating temperature while acting simultaneously as a résistance thermometer; it was screen-printed onto the substrate on the reverse side to the sensor. The individual components were characterised and optimised prior to assembly of complete sensors. Zirconia films were deposited by screen-printing onto alumina substrates. Careful attention was paid to formulation of zirconia inks, drying and firing procedures. Temperatures above 1350°C were necessary to sinter the zirconia to a low (<0.1%) though not zero porosity. The high sintering temperatures were found to result in the diffusion of impurities from the 96% alumina Substrate into the zirconia film which accelerated grain growth. X-ray diffraction showed that the grain growth resulted in transformation of the metastable tetragonal zirconia to the monoclinic form: where this occurred frequency response analysis of the films showed the expected decrease in ionic conductivity. These effects were absent on high purity (99.6%) alumina substrates. Platinum-zirconia cermets were investigated as possible electrodes. When screen-printed and fired at 1000°C for 1 hour and operated in the range 500-700°C, electrode activity was orders of magnitude greater than for pure porous platinum electrodes and increased substantially with increasing zirconia fractions provided electronic continuity was maintained within the film. High firing temperatures (> 1000°C), which were necessary for preparing a sensor with co-fired electrolyte and electrodes, decreased electrode activities although cermets remained greatly superior to pure platinum. Planar amperometric zirconia oxygen sensors were prepared using thick-film technology exclusively. When a voltage (0.5-1.4 V) was applied between the electrodes, a current flowed which was directly proportional to the oxygen concentration in the range up to 21%; this has not previously been achieved with such sensors. Characteristics were shown to be dependent upon firing temperature and substrate purity. Interestingly, temperature coefficients of the output were positive and negative for sensors fired at temperatures up to 1400 and above 1450°C respectively. Operation in the combustion products of a gas-burning flue demonstrated linear dependence upon calculated oxygen concentration. Heaters, printed using either fritted or unfritted platinum inks, were given extended treatments in a furnace at elevated temperatures (1000-1300°C) to accelerate ageing effects. Measurements were made of résistance (at 20°C), platinum evaporation rate and film cross-sectional area and these were correlated with the microstructure. The variation of résistance (at 20°C) of the films was analysed using effective medium theory invoked in order to quantify the blocking effect of the non-metallic fractions. During the initial phase (résistance decreasing) the governing factor was probably the high resistance of necks between contacting platinum particles. During the subsequent phase (resistance increasing) the resistance was controlled principally by the formation and growth of voids.

Crystalline indium oxide nanowires were synthesized following optimization of growth parameters. Oxygen vacancies were found to impact the optical and electronic properties of the as-grown nanowires. Photoluminescence measurements showed a strong U.V emission peak at 3.18 eV and defect peaks in the visible region at 2.85 eV, 2.66 eV and 2.5 eV. The defect peaks are attributed to neutral and charged states of oxygen vacancies. Post-growth annealing in oxygen environment and passivation with sulphur are shown to be effective in reducing the intensity of the defect induced emission. The as-grown nanowires connected in an FET type of configuration shows n-type conductivity. A single indium oxide nanowire with ohmic contacts was found to be sensitive to gas molecules adsorbed on its surface.

Despite advantages highlighted by Metal OXides (MOX) based gas sensors, these devices still present drawbacks in their performances (e.g. selectivity, stability and high operating temperature), so further investigations are necessary. Researchers tried to address these problems in several ways, which includes new synthesis methods for innovative materials based on MOX, such as solid solutions, addition of catalysts and doping of MOX by using external atoms or oxygen vacancies. Concerning this last issue, literature presents a lack of studies on how the arrangement and number of oxygen vacancies affect the sensing performance and only a few preliminary works highlighted interesting results. Another way to overcome MOX sensor drawbacks is to investigate novel class of materials, such as metal organic framework or 2D materials. Among these, phosphorene is one of the best candidates for such technological application, since it shows a chemoresistive activity at room temperature. The goal of this work is to decrease the operating temperature of SnO2 based gas sensors by exploiting the oxygen vacancies. First, a theoretical investigation was done in the framework of Density Functional Theory (DFT) to investigate, on the atomic scale, how oxygen vacancies influence the physical and chemical properties of the material. The effect of oxygen vacancies on the structural, electronic and electrical properties of bulk SnO2 at two different concentrations was studied, then the formation of surface oxygen vacancies was investigated in order to study the adsorption of oxygen molecules from the surrounding atmosphere on the stoichiometric and reduced SnO2 surface. Then, reduced SnO2-x was synthesized and devices based on the produced material were fabricated and tested. The results showed a high response of the sensors towards low concentrations of nitrogen dioxide NO2 (500 ppb) at 130°C instead of the typical operating temperature of 450°C for SnO2-based gas sensors. This decrease in the operating temperature results in a decrease of the power consumption of the device, opening up to its possible employment on portable devices like mobile phones. The results were interpreted characterizing the material by mean of X-ray Powder Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM) and Ultraviolet–visible spectroscopy (UV-visible) analysis. In the end, the experimental results were compared to the DFT outputs obtained. As mentioned before, phosphorene is one of the promising 2D materials for gas sensing applications, but it still presents some drawbacks, mainly due to the material degradation over the time when exposed to ambient conditions. Many investigations were done on decorating phosphorene with metal atoms in order to enhance its performance for different technological applications. Nickel is one of metals proposed for such purpose, but few studies were done on nickel decorated phosphorene for gas sensing applications, especially for gas sensing application. In the innovative work here proposed, DFT calculations were carried out to explain how nickel influences the electronic properties of phosphorene since the decoration with nickel showed better stability of the sensor and high response towards NO2 at room temperature. The theoretical results explained this behavior by studying the adsorption of oxygen molecules on pristine and nickel loaded phosphorene. The DFT calculations showed that oxygen molecules dissociate on the layer of pristine phosphorene and react with phosphorus atoms (oxidation of the material), while in the presence of the nickel atoms the later play the role of acceptors and interact with the oxygen molecules. Finally, the sensing mechanism towards NO2 was investigated theoretically by studying the charge transfer occurring at the surface of the material during the adsorption process.
I sensori di gas basati sugli ossidi metallici semiconduttori (MOX) si sono rivelati negli ultimi anni una tecnologia estremamente vantaggiosa. Nonostante i progressi fatti in questo campo, questi dispositivi presentano ancora alcuni punti deboliche spingono la ricerca ad effettuare ulteriori indagini per perfezionare il loro funzionamento. I ricercatori hanno cercato di risolvere questi svantaggi in diversi modi, focalizzandosi sullo sviluppo di MOX innovativi, tra cui il drogaggio tramite l’utilizzo di additivi o l’introduzione nel materiale di vacanze di ossigeno a concentrazione controllata. Questa’alternativa sta attirando l’attenzione di molti gruppi di ricerca, anche se, ad oggi, la letteratura scientifica presenta una mancanza di studi su come la disposizione e concentrazione di vacanze di ossigeno influenzano le performance di sensing e solo alcuni lavori preliminari hanno portato a risultati interessanti. Per cercare di ovviare ai limiti dei sensori MOX, una seconda via è stata lo sviluppo e di materiali 2D basati su solfuri metallici, grafene o similari. Il fosforene è uno dei migliori candidati per tale applicazione tecnologica, poiché mostra un'attività elettrica anche a temperatura ambiente, anche se studi preliminari hanno evidenziato un alto tasso di degradazione nel tempo del materiale durante il suo utilizzo. L'obiettivo di questo lavoro è quello di diminuire la temperatura di funzionamento di sensori di gas basati su SnO2 sfruttando il controllo delle vacanze di ossigeno. A tale scopo, è stato fatto inizialmente uno studio della letteratura e un’analisi analitica nell’ambito della DFT per indagare come le vacanze di ossigeno influenzano le proprietà fisico-chimiche del materiale. È stato studiato l'effetto di due diverse concentrazioni di vacanze di ossigeno sulle proprietà chimico-fisiche dello SnO2 bulk. Successivamente è stata studiata la formazione della vacanze in superficie per investigare l'adsorbimento di molecole di ossigeno dall'atmosfera circostante sulla superficie dello SnO2 è stato sintetizzato tramite sintesi sol-gel e la riduzione è stata ottenuta tramite trattamento termico in presenza di H2 a diverse temperature. I risultati hanno mostrato un'alta risposta dei sensori basati su SnO2-x in presenza di basse concentrazioni di NO2 spostando a 130 °C la temperatura ottimale di funzionamento del dispositivo. Questa diminuzione della temperatura operativa implica una diminuzione del consumo energetico del dispositivo Come menzionato precedentemente, il fosforene è uno dei materiali 2D più promettenti per lo sviluppo di sensori di gas chemoresistivi, ma presenta ancora alcuni svantaggi. Molti studi sono stati sviluppati sulla decorazione del fosforene con atomi metallici al fine di migliorare le sue prestazioni per diverse applicazioni tecnologiche, ma non sono stati ancora condotti studi specifici su questa particolare forma di fosforene decorato per applicazioni di sensoristica gassosa. Nello studio qui proposto, sono stati eseguiti calcoli DFT per spiegare come il nichel influenzi le proprietà elettroniche del fosforene, poiché la decorazione con nichel ha mostrato una migliore stabilità del sensore e un’alta sensibilità all’NO2. Tramite simulazione DFT è stato possibile investigare l'adsorbimento delle molecole di ossigeno sul Fosforene tal quale e decorato con nichel. I risultati hanno evidenziato che le molecole di ossigeno si dissociano sullo strato di fosforene tal quale e reagiscono con gli atomi di fosforo, ossidandolo, mentre in presenza dei cluster di nichel è quest’ultimo a svolgere il ruolo di catalizzatore, interagendo con le molecole di ossigeno. Infine, il meccanismo di interazione tra NO2 e la superficie del fosforene tal quale e funzionalizzato è stato caratterizzato teoricamente studiando il trasferimento di carica che avviene sulla superficie del materiale in esame.

Electronic instrumentation was developed for the measurement of the oxygen partial pressure, P1, in a sample gas using fully-sealed zirconia pump-gauge oxygen sensors operated in an AC mode. These sensors, operated typically at 700°C, consisted of two discs of zirconia with porous platinum electrodes on each face separated by a gold seal and enclosing a small internal volume. One disc was operated as a pump enabling oxygen to be electrochemically transferred into and out of the enclosed volume; the other disc operated as a gauge, the Nernst EMF across the electrodes providing a measure of the ratio of the internal to the external oxygen partial pressure. By careful design of the circuitry it was possible to measure the oxygen partial pressure, P, without the need for a separate reference gas supply. Subsequently, a novel "tracking" mode of operation was proposed and implemented in which leakage effects generally associated with sealed pump-gauge devices were minimised: the sensor was operated in a feedback control-loop in order to adjust automatically the mean internal reference oxygen partial pressure, P0, so as to maintain the ratio (Px/P0) close to unity. The signal-to-noise ratio was markedly improved by using gauge EMFs with high amplitudes which inevitably display a distorted sinusoid due to the logarithmic term in the Nernst equation. Surprisingly, mathematical analysis predicted that the linearity of the output of the instrument using phase-sensitive detection should not be affected by the deviation from a sinusoid and this was confirmed experimentally: signal processing was practically implemented using simple analogue electronics. As anticipated there was a strong influence of sensor temperature on the output of the instrument: consequently, methods for temperature compensation were proposed and shown to be feasible with minimum hardware. The theory of Operation of leaky pump-gauge was also developed which indicated that a physical leak in the sensor should cause a phase shift and amplitude change in the sensor output. Experimental results were, in general, in agreement with the theory demonstrating the influences of the geometry and dimensions of the leak and of the operating frequency. Importantly, the theory predicted that, when operated in the AC mode, devices with major leakage may still be used for oxygen partial pressure measurement: again this was confirmed by experiment and the additional benefit of a concomitant substantial simplification of the electronic circuitry also realised. Interestingly an unexpected but small influence of oxygen concentration on the phase shift was observed: this requires additional study.

Amperometric gas sensors are widely used for environmental and industrial monitoring. They are sensitive and cheap but suffer from some significant limitations. The aim of the work undertaken in this thesis is the development of ‘intelligent’ gas sensors to overcome some of these limitations. Overall the thesis shows the value of ionic liquids as potential solvents for gas sensors, overcoming issues of solvent volatility and providing a wide potential range for electrochemical measurements. Methods have been developed for sensitive amperometry, the tuning of potentials and especially proof-of-concept (patents Publication numbers: WO2013140140 A3 and WO2014020347 A1) in respect of the intelligent self-monitoring of temperature and humidity by RTIL based sensors. Designs for practical electrodes are also proposed. The specific content is as follows. Chapter 1 outlines the fundamental principles of electrochemistry which are of importance for the reading of this thesis. Chapter 2 reviews the history and modern amperometric gas sensors. Limitations of present electrochemical approaches are critically established. Micro-electrodes and Room Temperature Ionic Liquids (RTILs) are also introduced in this chapter. Chapter 4 is focused on the study of analysing chronoamperometry using the Shoup and Szabo equation to simultaneously determine the values of concentration and diffusion coefficient of dissolved analytes in both non-aqueous and RTIL media. A method to optimise the chronoamperometric conditions is demonstrated. This provides an essential experimental basis for IL based gas sensor. Chapter 5 demonstrates how the oxidation potential of ferrocene can be tuned by changing the anionic component of room temperature ionic liquids. This ability to tune redox potentials has genetic value in gas sensing. Chapters 6 and 7 describe two novel patented approaches to monitor the local environment for amperometric gas detection. In Chapter 6, an in-situ voltammetric ‘thermometer’ is incorporated into an amperometric oxygen sensing system. The local temperature is measured by the formal potential difference of two redox couples. A simultaneous temperature and humidity sensor is reported in Chapter 7. This sensor shows advantageous features where the temperature sensor is humidity independent and vice versa. The Shoup and Szabo analysis (Chapter 4) requires ‘simple’ electron transfer and as such the reduction of oxygen in wet RTILs can be complicated by dissolved water. Chapter 8 proposes a method to stop oxygen reduction at the one electron transfer stage under humid conditions by using phosphonium based RTILs to ‘trap’ the intermediate superoxide ions. Chapters 9 and 10 report the fabrication of low cost disposable electrodes of various geometries and of different materials. The suitability of these electrode for use as working electrodes for electrochemical experiments in aqueous, non-aqueous and RTIL media is demonstrated. Their capability to be used as working probes for amperometric gas sensing systems is discussed.

El control dels nivells d'oxigen és una etapa crítica en molts processos industrials.
En alguns d'aquests, els nivells d'oxigen han de ser detectats i controlats fins i tot en el rang de les ppm. Encara que ja es coneguin molts mètodes, ja provats per a la detecció d'oxigen, la majoria d'ells són costosos i complexes. Altres mètodes més accessibles com els sensors Lambda i les cel·les electroquímiques també presenten alguns problemes. Els primers requereixen d'elevades concentracions d'oxigen o bé de controls de temperatura força precisos amb la finalitat de treballar sense interferència d'altres gasos. Els segons es poden veure afectats per temps d'exposició massa perllongats a gasos "àcids" com el diòxid de carboni i no es recomana el seu ús en atmosferes amb un contingut de més del 25% d'aquests gas.
Són moltes les avantatges dels sensors de gasos: baix cost, mida reduïda i solidesa entre d'altres. Això fa que aquests dispositius despuntin com a solució per a la detecció d'oxigen. Molts autors han fet esment a la detecció d'oxigen a nivells de ppm emprant aquests tipus de sensors. De totes formes, la majoria s'han desenvolupat mitjançant tecnologia de capa fina. En aplicacions industrials, la tecnologia més usada és la de capa gruixuda, ja que aquests sensors són més fàcils de fabricar i de dopar que els de capa fina. En el cas dels sensors de capa gruixuda la detecció de traces d'oxigen és una tasca encara difícil i es necessita treballar a elevades temperatures (> 700 ºC).
El mecanisme de detecció d'oxigen en els sensors basats en òxids semiconductors es basa en la interdependència de la conductivitat elèctrica d'aquests òxids i la pressió parcial d'oxigen en l'ambient. El diòxid de titani és l'òxid semiconductor que més s'usa en la detecció d'oxigen. Els sensors basats en òxid de titani (en fase cristal·lina rutil) necessiten d'elevades temperatures per a un correcte funcionament (700 ºC-1000 ºC), ja que la detecció d'oxigen en la fase rutil es deu principalment a la difusió dels ion d'aquests gas en el volum del material. Per a que es produeixi la reacció en el volum o propi cos del material es necessiten elevades temperatures. Això comporta un consum també elevat de potència, que a la llarga serà un problema en determinades aplicacions industrials.
Al tenir l'òxid de titani en fase anatasa més electrons lliures, la reacció de l'oxigen amb aquests material es pot associar a una reacció superficial. Aquesta reacció es pot donar a temperatures més baixes, al voltant dels 400 ºC-500 ºC i per tant, mantenir la fase anatasa en l'òxid permet disminuir la temperatura de treball, la qual cosa és desitjable per al disseny del sensor.
Tal i com es reflecteix en algunes referències bibliogràfiques, en dopar l'òxid de titani amb ions pentavalents com el Nb5+, aquests ions s'introdueixen en l'estructura cristallina de l'òxid de titani en fase anatasa, creant certa tensió interna que provoca una resistència al canvi de fase anatasa a rutil, inhibint el creixement del gra.
Per altra banda, també s'ha posat de manifest en moltes fonts que el dopatge d'òxid de titani amb niobi augmenta la sensibilitat d'aquests material vers l'oxigen. Aquests dopatge fa que l'òxid presenti una impedància menor, per la qual cosa es facilita el disseny de l'electrònica associada al sensor.
Tenint en compte aquestes dues premisses, un dels objectius d'aquesta tesi ha estat la síntesi, mitjançant la tècnica del sol-gel, de diferents tipus d'òxid de titani per a la fabricació d'un sensor d'oxigen que operi en una marge de temperatura relativament moderat (300 ºC-600 ºC). Es treballà amb òxids sense dopar i amb òxids dopats amb un 3 % de niobi.
Cadascun es calcinà a diferents temperatures: 600 ºC, 700 ºC, 800 ºC i 900 ºC.
Amb l'objectiu de correlacionar l'estructura i la sensibilitat i selectivitat dels òxids sintetitzats, aquests es van sotmetre a diferents tècniques de caracterització. En primer lloc l'espectrometria de plasma acoblada inductivament (ICP) s'utilitzà amb el fi de determinarne la composició química i quantificar la proporció de cada component. En segon lloc també es va fer servir la difracció de raigs X (XRD) per a determinar les fases cristallines de l'òxid i la mida dels cristalls. També es va analitzar la porositat i es van fer mesures de l'àrea superficial (BET) dels nanopols . En darrer lloc, la microscopia d'escàner d'electrons (SEM) fou aplicada amb la finalitat d'obtenir detalls de l'estructura de la capa activa i de la grandària dels grans. Per a l'anàlisi quantitatiu i també qualitatiu de les capes s'utilitzà l'espectroscopia de dispersió d'energia per raig X (EDS).
Com a substrat, es va desenvolupar un substrat d'alúmina que pot albergar quatre capes actives treballant a una mateixa temperatura, conformant així una matriu de sensors.
Treballant amb aquests substrat aparegueren certs inconvenients (relacionats amb l'encapsulat del sensor) operant a temperatures superiors als 450 ºC. Això comportà un retard en l'obtenció de resultats amb aquests substrat i es decidí introduir-ne un de nou, resistent a altes temperatures i adquirit en l'Institut Kurchatov (Moscou, Rússia). Tots els resultats presentats en aquesta tesi es van obtenir amb l'ús d'aquests últim substrat. En l'actualitat s'està treballant amb el primer d'ells.
Un cop fabricat els sensors, es provà la sensibilitat d'aquests en un sistema de flux continu. Es provaren tres diferents concentracions: 20 ppm d'O2 amb balanç de N2, 30 ppm d' O2 amb balanç CO2 i 15 ppm d'O2 amb balanç CO2. També es testaren les respostes dels sensors cap a altres gasos interferents (SO2, CH4, H2S i C2H4) per a determinar la selectivitat d'aquests sensor vers l'O2 en presència d'interferents.
La millor resposta vers l'oxigen s'aconseguí amb els sensors dopats i calcinats a 700 ºC. Aquesta millora es pot atribuir al dopatge amb niobi. Aquets metall inhibeix el creixement del gra i per tant s'aconsegueixen òxids amb major àrea superficial. Un altre motiu pot ser el retard del pas de la fase rutil a la fase anatasa induït també pel dopatge de Niobi.
La sensibilitat denotada pels òxids dopats amb niobi i calcinats a 600 ºC fou molt baixa tot i que en principi aquests òxids presentaven característiques físiques potencialment millors que els calcinats a 700 ºC. Aquests fet es pot explicar degut a la presència d' alguns depòsits de carboni que no es pogueren eliminar durant la calcinació. La presència d'aquests dipòsits fou confirmada per l'anàlisi Raman d'aquests materials. Les estructures de carboni presents en aquests residus cobreixen gran part de la superfície de l'òxid i contribueixen a la desactivació del procés catalític que té lloc en aquesta superfície.
Concernint a les mesures realitzades sota atmosfera de CO2, els òxids dopats amb niobi i calcinats a 700 ºC també respongueren a l'oxigen. La resposta en el cas de 15 ppm d'O2 s'invertí del tipus oxidant a tipus reductor. A baixes concentracions d'oxigen els ion CO- provinents de la dissociació del CO2 s'adsorbeixen a la superfície del material actiu.
L'oxígen, enlloc de deplexionar-se, interactua amb aquests ions per a formar CO2, alliberant electrons a la capa activa i això fa que la natura de la resposta sigui reductora. Les respostes vers altres gasos contaminants com SO2, CH4, H2S foren tipus reductor com era esperat, la qual cosa indicava que el canvi de resposta no era atribuïble al canvi de l'òxid conductor de tipus n a tipus p, si no més aviat en un canvi en la naturalesa de la reacció.
Amb l'objectiu de millorar la sensibilitat de l'òxid dopat es provà d'incrementar la seva àrea superficial i porositat utilitzant un surfactant com a motlle durant el procés de síntesi. El surfactant usat fou la dodecilamina, que forma una estructura miscel·lar que fa de motlle en el procés de nucleació de l'òxid, generant així grans menors amb major àrea superficial i major porositat. De tres diferents temptatives, els millors resultats es varen obtenir quan s'addicionaven 8 ml de dodecilamina a la solució del sol-gel immediatament desprès de la hidròlisi dels alcòxids. Les proves XRD mostraren que l'addició del surfactant retarda encara més la transició de les fases rutil a anatasa i també inhibeix el creixement dels cristalls. Aquests resultats es recolzen sobre les micrografies del SEM i l'anàlisi BET, que revelaren un creixement en la porositat del material i un gra menor. Malgrat aquests resultats prometedors en la determinació estructural, les mesures de l'oxigen amb aquests sensors revelaren una poca sensibilitat dels sensors modificats amb el surfactant. Els espectres RAMAN mostraren alguns pics corresponents a diferents morfologies de carboni.
Els dipòsits d'aquests material en la superfície, tal i que com s'ha mencionat anteriorment, inhibeixen la resposta de la capa activa vers l'oxigen.
El control de los niveles de oxígeno es una etapa crítica en muchos procesos industriales. En algunos de estos procesos, los niveles de oxígeno deben ser detectados y controlados incluso en el rango de las ppm. Aunque existen varios métodos ya probados para la detección de oxígeno en estos sistemas de control, la mayoría de ellos son costosos y complejos. Otros métodos de detección más accesible como los sensores Lambda o las celdas electoquímicas también presentan problemas: los primeros requieren de altas concentraciones de oxígeno, o de controles de temperatura bastante precisos para poder trabajar sin interferencias de otros gases Los segundos pueden verse afectados por una prolongada exposición a gases "ácidos" como el dióxido de carbono y no se recomienda para uso continuo en atmósferas con un contenido de mas del 25 % de dicho gas.
Debido a muchas ventajas tales como su bajo costo, tamaño reducido y solidez, los sensores basados en semiconductores aparecen como una solución para la detección de oxígeno. Algunos autores han reportado la detección de oxígeno a niveles ppm empleando este tipo de sensores. Sin embargo, la mayoría de ellos han sido desarrollados mediante tecnología de capa fina. En aplicaciones industriales, la tecnología más usada es la de capa gruesa, ya que estos sensores son más fáciles de fabricar y de dopar que los sensores de capa fina. En los sensores de capa gruesa, la detección de trazas de oxígeno es aun una tarea difícil de alcanzar, siendo normalmente necesarias altas temperaturas (> 700 ºC) para lograrlo.
El mecanismo de detección de oxígeno en los sensores basados en óxidos semiconductores esta basado en la fuerte dependencia de la conductividad eléctrica de estos materiales a la presión parcial de oxígeno en el ambiente. El dióxido de titanio es el óxido semiconductor más ampliamente usado en la detección de oxígeno. Los sensores basados en TiO2 (usualmente en la fase cristalina rutilo) necesitan trabajar a elevadas temperaturas (700 ºC - 1000 ºC), ya que la detección de oxígeno en la fase rutile se debe principalmente a la difusión de los iones de oxígeno en el volumen del material. Para que se produzca la reacción en el volumen hacen falta altas temperaturas, lo que conlleva un alto consumo de potencia que puede ser un handicap en determinadas aplicaciones industriales.
Por otro lado, el dióxido de titanio en fase anatase posee más electrones libres, así que la detección de oxígeno en este material puede asociarse a una reacción de superficie, la cual tiene lugar a no tan altas temperaturas (400 ºC - 500 ºC).Por lo tanto, puede concluirse que mantener la fase anatase permitiría la detección de oxígeno a temperaturas moderadas, lo cual es deseable para el diseño del sensor.
Se ha reportado que cuando el TiO2 es dopado con iones pentavalentes, i.e. Nb5+, tales iones se introducen en la estructura cristalina de dicho óxido en estado anatase, obstruyendo la transformación de dicha fase a rutile, inhibiendo el crecimiento del grano.
También se ha reportado que el dopado con niobio aumenta la sensibilidad del dióxido de titanio hacia el oxígeno. El óxido dopado también presenta una impedancia más baja a temperaturas de trabajo menores, por lo que se facilita el diseño de la electrónica asociada al sensor.
Basándonos en estos puntos, uno de los objetivos de esta tesis fue la síntesis, mediante un proceso de sol-gel, de diferentes tipos de dióxido de titanio para la fabricación de un sensor de oxígeno que opere en un margen de temperaturas moderado (300 ºC - 600 ºC). Para ello se desarrollaron óxidos dopados con un 3 % de niobio y óxidos sin dopar.
Cada uno de ellos fue calcinado a diferentes temperaturas: 600 ºC, 700 ºC, 800 ºC y 900 ºC.
Con el objetivo de correlacionar la estructura y la sensibilidad y selectividad de los óxidos sintetizados, estos se sometieron a diferentes técnicas de caracterización. La espectroscopia de Plasma Acoplado Inductivamente (ICP) fue empleada para determinar la composición química de las muestras y cuantificar la porción de cada componente. La Difracción de Rayos-X (XRD) fue usada para establecer las fases presentes en la estructura cristalina del material y para determinar el tamaño el tamaño de los cristales en cada material. Se realizaron medidas de área BET con los nanopolvos para conocer el área superficial y la porosidad de cada material. La Microscopia de Escáner de Electrones (SEM) fue aplicado para obtener detalles de la estructura de la capa y del tamaño de las partículas.
Para hacer un análisis cuantitativo y cualitativo de las capas se utilizó la Espectroscopia de Dispersión de Energía por Rayos -X (EDS).
Para realizar las medidas, se desarrolló un substrato de alúmina para ser usado en el sensor de oxígeno. Este substrato puede soportar cuatro capas activas trabajando a la misma temperatura formando una matriz de sensores. Sin embargo, debido a algunos problemas relacionados con el encapsulado del substrato cuando las temperaturas de trabajo sobrepasaban los 450 ºC, su empleo para el sensor de oxígeno se retrasó y los resultados obtenidos con el mismo no estaban lo suficientemente completos para ser presentados en este trabajo. Para solventar la necesidad de un substrato que pudiese resistir altas temperaturas para aplicaciones de detección de oxígeno, se introdujo un nuevo substrato adquirido en el Instituto Kurchatov (Moscú - Rusia). Los resultados expuestos en este trabajo se obtuvieron con este último substrato.
Una vez fabricados los sensores, las capacidades de sensado de los materiales fueron probadas. La sensibilidad hacia el oxígeno fue medida en tres situaciones diferentes: 20 ppm de O2 en balance de N2, 30 ppm y 15 ppm de O2 en balance de CO2. Las respuestas de los sensores hacia otros gases contaminantes (SO2, CH4, H2S y C2H4) también fueron probadas para observar la influencia de dichos gases en el proceso de detección de oxígeno.
La mejor respuesta hacia el oxígeno se consiguió con los sensores basados en materiales dopados calcinados a 700 ºC. Esto puede atribuirse a los iones de niobio que inhiben el crecimiento del grano y por lo tanto producen un aumento del área superficial de dichos materiales, que beneficia al mecanismo de detección, y a su fase cristalina, mayoritariamente anatase, la cual permite la detección a las temperaturas deseadas (300 ºC - 600 ºC). Las especies de niobio también contribuyen al proceso de catálisis.
Otro motivo puede ser la fase cristalina, mayoritariamente anatase, la cual permite la detección a las temperaturas deseadas (300 ºC - 600 ºC).
Por otro lado, los materiales dopados calcinados a 600 ºC tuvieron una pobre respuesta, a pesar de que estos tienen mejores características físicas que los calcinados a 700 ºC. Este hecho puede explicarse por la presencia de algunos depósitos de carbono, residuales del proceso de síntesis, que no pudieron ser eliminados durante la calcinación. La presencia de estos depósitos fue confirmada mediante los análisis Raman de estos materiales.
Ya que estas estructuras de carbono cubren gran parte de la superficie del material, y que además son poco catalíticas, el resultado es una desactivación de la catálisis.
Concerniente a las medidas realizadas en atmósfera de CO2, los óxidos dopados con niobio y calcinados a 700 ºC también respondieron al oxígeno. Sin embargo, la respuesta hacia 15 ppm de oxígeno presentó una inversión de tipo oxidante a tipo reductora. A bajas concentraciones de oxígeno, los iones de CO-, provenientes de la disociación del CO2, se adsorben en la superficie del material activo. El oxígeno, en lugar de deplexionarse, interactúa con estos iones para formar CO2, liberando electrones a la capa activa, dando lugar así a una respuesta reductora. Por otra parte, las respuestas hacia otros gases contaminantes tales como H2S, SO2 y CH4 fueron de tipo reductora, como era esperado, lo cual indica que el cambio de respuesta no puede atribuirse al cambio del óxido conductor de tipo n a tipo p, sino más bien a un cambio en la naturaleza de la reacción.
Para mejorar la sensibilidad de los óxidos dopados, se intentó incrementar su área superficial y porosidad usando un surfactante como plantilla o molde durante el proceso de síntesis. El surfactante empleado fue dodecylamina, la cual forma una estructura micelar que hace de molde durante el proceso de nucleación del óxido, generando así granos menores con mayor área superficial y mayor porosidad. Entre tres diferentes intentos, los mejores resultados se obtuvieron cuando 8ml de dodecylamina fueron agregados a la solución del sol-gel inmediatamente después de la hidrólisis de los alkóxidos. Los análisis de XRD de este material mostraron que la adición de surfactante retarda aun más la transición de fase de anatase a rutile y también evita el crecimiento de los cristalitos. Estos resultados son soportados por las microfotografías de SEM y los análisis BET, los cuales mostraron un retardo en el crecimiento del grano y un incremento del área superficial. El área BET también evidenció un incremento de la porosidad del óxido. Sin embargo, los resultados de las medidas de oxígeno revelaron una pobre respuesta de los sensores basados en el óxido en cuestión. Los espectros Raman de este material mostraron algunos picos correspondientes a carbono con diferentes morfologías. Como fue explicado previamente, estos depósitos de carbono retardan la respuesta de este óxido al oxígeno.
Control of oxygen levels is a critical step in many industrial processes. In some of these processes, levels of oxygen must be detected and controlled even in ppm range.
Although there are several probed methods for oxygen detection in these control systems, most of them are expensive and complex. More accessible methods as Lambda sensors or electrochemical cells present also problems: first ones need high concentration of oxygen, or an extremely accurate temperature control, to work without interference from other gases.
Second ones may be affected by prolonged exposure to "acid" gases such as carbon dioxide and it is not recommended for continuous use in atmospheres which contain more than 25% of CO2.
Due to many advantages as low cost, small size and robustness, semiconductor sensors appear as a good solution for oxygen detection. Some authors had reported detection of oxygen at ppm levels employing this kind of sensors. However, most of them were made through thin film technology. For industrial applications, the most usual technology is thick film, because it is easier to fabricate and to dope than thin film sensors. For thick film sensors, detection of traces of oxygen is still a very difficult goal to reach and usually high temperatures (>700 ºC) are needed.
The basic oxygen sensitivity mechanism of oxygen sensors based on semiconductor oxides is their strong dependencies of electrical conductivity on oxygen partial pressures.
Titanium dioxide is the semiconductor material most widely used for oxygen detection.
Titania (usually rutile crystalline phase) based sensors need to work at high temperatures (700 ºC - 1000 ºC), since oxygen detection in rutile state is mainly due to diffusion of oxygen ions in the bulk of the material. For bulk reaction it is necessary to work at these high temperatures, leading to high power consumption, which is not desirable for electronic applications.
On the other hand, anatase state Titania has more free electrons. So, oxygen detection can be associated to surface reactions, which take place at not so high temperatures (400 ºC - 500 ºC). Then, it can be derived that maintaining an anatase structure would allow the detection of oxygen at medium temperatures, which is desirable for sensor design.
It had been reported that when Titania is doped with pentavalent impurity ions, i.e. Nb5+, such ions get into the anatase Titania crystalline structure, giving rise to a hindering in the phase transformation to rutile and an inhibition in grain growth. It has been also reported that Nb-doped Titania shows higher sensitivity towards oxygen than pure TiO2. The doped material also shows lower impedance at low operating temperatures and hence, it is easier to design associated electronic circuitry.
In this work pure Titania and Niobium doped Titania nanopowders were synthesized by a simplified sol-gel route. Based on the literature, the doping concentration in doped materials was set to Nb/Ti = 3 at%. In order to set the crystalline structure of the active materials, they were calcined at four different temperatures: 600 ºC, 700 ºC, 800 ºC and 900 ºC.
The obtained materials were characterized by different techniques. The objective of these characterizations was to obtain information about the material structure that could be related to its detection properties. Inductively Coupled Plasma (ICP) spectroscopy was employed to determine the chemical composition of the samples and quantify the amount of each component. X-ray Diffraction (XRD) was used to establish the phases present in the crystalline structure of the material and to determine the size of the crystallites in each material. Area BET measurements were done to nanopowders to know the surface area and the porosity of each material. Scanning Electron Microscopy (SEM) was used to obtain details on the film structure and the grain size. To make quantitative and qualitative analysis, Energy-Dispersive X-ray Spectroscopy (EDS) was also applied.
For the measurements, an alumina substrate was developed to be used in the oxygen sensor. This substrate can support four active layers working at the same temperature forming a sensor array. However, due some problems related with the substrate package at working temperatures above 450 ºC, the use of this substrate for oxygen sensor application was delayed and the results obtained whit it were not complete enough to be presented in this work. In order to resolve the necessity of a substrate that can resist high working temperatures for oxygen sensing applications, it was introduced a new substrate acquired from the Kurchatov Institute (Moscow-Russia). The results exposed in this work were obtained by using this last substrate.
Using these substrates, the sensing capabilities of the materials were also tested. The sensitivity toward oxygen was measured under three different conditions: 20 ppm of O2 in N2 balance, 30 ppm and 15 pmm of O2 in CO2 balance. The sensors responses toward other pollutant gases (SO2, CH4, H2S and C2H4) were also tested in order to see the influence of such gases in the oxygen detection process.
The best response toward oxygen was achieved in those sensors based on Nb-doped materials calcined at 700 ºC. This may be attributed to the niobium ions which hinder the grain growth and hence give rise to a high surface area that benefits the detection mechanism. The good response may be also attributed to the crystalline phase, mostly anatase, which allows the detection at desire temperatures (300 ºC - 600 ºC).
On the other hand, the doped materials calcined at 600 ºC had a poor response, in spite of they have better physical characteristics than doped materials calcined at 700 ºC.
This problem was mainly related to some carbon deposits detected in these materials trough Raman analyses. Such carbon deposits may be residual of the synthesis process, which could not be eliminated during the calcination. Since these carbon structures cover a great part of the material surface, and they are also poorly catalytic, the result is a deactivation of the catalysis.
Concerning to the measurements carried out under CO2 atmosphere, Nb-doped Titania calcined at 700 ºC also responded to oxygen. However, the response toward 15 ppm of oxygen presented an inversion from oxidative type to reductive type. At low oxygen concentrations, the CO- ions from CO2 disassociation are adsorbed on the active material surface. The oxygen, instead deplexing, interacts with these ions forming CO2, liberating electrons to the active layer giving rise to a reductive type response. On the other hand, the responses toward other pollutant gases such H2S, SO2, C2H4 and CH4 were of reduction type, as they were expected, which support the idea that the change in the response type is not due to the change in the physics of the semiconductor oxide from n type to p type, but to a change in the reaction nature.
In order to improve the sensing capabilities of doped materials, it was attempted to increase their surface area and porosity by using a surfactant as a template during the synthesis process. The surfactant employed was dodecylamine, which forms a micellar structure that works as template in the nucleation process of the oxide, generating small grains with higher surface area and porosity. Among three different attempts, the best results were obtained when 8 ml of surfactant were added to the sol-gel solution just after the hydrolysis of the metal alkoxides. XRD analyses of this material showed that the addition of surfactant retards even more the phase transition from anatase to rutile and also hinder the crystallites growth. These results were supported by SEM micrographs and BET analysis, which show a hinder in grain growth and an increase of the surface area. Area BET also evidences an increment of the material porosity. However, the results of the oxygen measurement reveal a poor response of the considered material. The Raman spectroscopy of this oxide shows some peaks that correspond to carbon with different morphologies. As it was explained before, these deposits of carbon retard the response of this material toward oxygen.

Cette thèse est dédiée à l’élaboration de couches minces d'oxydes de tungstène par pulvérisation cathodique réactive. Afin de jouer sur la composition des films, le procédé de pulsation du gaz réactif (RGPP) est mis en œuvre pour changer les concentrations en oxygène et en tungstène. En parallèle, la technique de dépôt sous incidence oblique (GLAD) est développée pour produire différentes architectures, à savoir des colonnes inclinées, des zigzags ou encore des spirales, et augmenter le rapport surface-volume dans les films. La co-pulvérisation GLAD est également étudiée en utilisant deux cibles inclinées et séparées de W et WO3. Les relations entre la microstructure, la composition, les propriétés électroniques et optiques des films d'oxydes de tungstène sont systématiquement étudiées. Ils sont finalement appliqués comme couches actives pour des capteurs résistifs afin d'améliorer la détection de vapeur de dodécane et d'ozone gazeux. La microstructure poreuse élevée des colonnes inclinées produite par GLAD combinée à une composition ajustée par RGPP conduit à définir une gamme de films d'oxydes de tungstène attractifs pour améliorer les performances capteurs
This thesis is focused on the reactive sputter deposition of W-O thin films. In order to play with their composition, the Reactive Gas Pulsing Process (RGPP) is implemented and allows tunable oxygen and tungsten concentrations. Similarly, the GLancing Angle Deposition (GLAD) technique is developed to produce various architectures, namely inclined columns, zigzags and spirals, and increases the surface-to-volume ratio of the films. The GLAD co-sputtering approach is also investigated by means of two inclined and separated W and WO3 targets. Relationships between microstructure, composition, electronic and optical properties of W-O films are systematically studied. They are finally applied as active layers for resistive sensors in order to improve detection of dodecane vapor and ozone gas. The high porous microstructure of inclined columns produced by GLAD combined to the suitable composition adjusted by RGPP leads to define a range of W-O films attractive for sensing performances

In this master´s thesis various types of gas sensors, their characteristics, principle, active layer and structure are described. This work is focused on semiconductor gas sensors. In the experimental part gas test station is used to measure the main characteristic of commercial sensor Figaro TGS 822 and own SnO2 gas sensors and reaction to oxygen. Both sensors and measurement results are compared with each other.

L'émergence des nouvelles applications dans le domaine de la micro et nanotechnologie requière de faibles coûts de fabrication et la caractérisation de dispositifs électroniques ayant des propriétés telles que la flexibilité, la portabilité, la légèreté, et des matériaux de faibles coûts. Les méthodes traditionnelles de fabrication impliquent de longues étapes de production, et des procédés de fabrication impliquant des étapes avec des produits chimiques. Le but de cette thèse est d'étudier la conception et la caractérisation de capteurs d'ammoniac et d'ozone sur support souple fabriqués par des processus de photolithographie et de gravure laser. Le support flexible est composé de Kapton avec des électrodes interdigitées de Ti/Pt pour la détection de gaz et un microchauffage. Les motifs du circuit ont été réalisés par photolithographie et gravure laser. L'utilisation de gravure laser sur support souple permet de réduire les coûts liés au temps de fabrication, aussi représente une excellente alternative aux processus chimiques. Des nanoparticles de ZnO déposées par gouttes ont été utilisées comme matériaux sensibles en raison de leurs excellentes propriétés dans la détection de gaz. Les conditions de détection de gaz ont été étudiées pour différentes concentrations d'ozone et d'ammoniac. Afin de tester une méthode de dépôt utilisée dans la production industrielle à grande échelle, un dépôt par spray ultrasonique a été effectué. Les capteurs réalisés montrent une large gamme de détection de 5 ppb à 500 ppb à 200 °C pour l'ozone et de 5 ppm à 100 ppm à 300 °C pour l'ammoniac avec une bonne reproductibilité, stabilité et de rapides temps de réponse et de retourn
Nowadays the emerging of new applications in the micro and nanotechnology field required to reduce fabrication costand to improve electronic devices with properties such as flexibility, portability, lightweight, and low cost. Traditional methods involve expensive and long production steps, and chemical vapor deposition. The purpose of this work is to present the conception and characterization of flexible ammonia and ozone sensors fabricated by photolithography and laser ablation processes. The flexible platform is composed of Kapton substrate with interdigitated Ti/Pt electrodes for gas detection and a micro-heater device. The circuit patterns were realized by photolithography and laser ablation. Photolithography is a well-known and reliable patterning process used on rigid substrate. The application of laser ablation process not only reduces fabrication time, but also represents an excellent viable alternative instead of chemical processes. ZnO thin films deposited by drop coating have been used as sensitive materials due to their excellent properties in the gas detection. The gas sensing condition and the performances of the devices are investigated for ozone and ammonia at different gas concentrations and different thin film thicknesses. In order to test a deposit methodology used in large scale industrial production, an ultrasonic spray deposition was done. The sensor provides a wide range of detection from 5 ppb to 500 ppb for ozone and from 5 ppm to 100 ppm for ammonia. Their best sensibilities were obtained at 200°C for ozone and 300 °C for ammoniac with good repeatability, stability and fast response/recovery time

Les préoccupations actuelles de protection de l’environnement et de la santé publique se focalisent sur la qualité de l’air dans l’industrie, les villes et foyers domestiques. De nos jours, les capteurs de gaz sur papier présentent un intérêt croissant au vu de leur faible coût, leur biodégradabilité, leur flexibilité, et leurs applications dans les textiles, les pansements et les emballages intelligents.L’oxyde de graphène (GO) est un dérivé du graphène qui présente des propriétés électriques, mécaniques et thermiques exceptionnelles. Ce matériau est très prometteur pour le développement de capteurs de gaz peu chers et fonctionnant à température ambiante.Dans ce contexte, cette thèse a pour objectif d’intégrer une couche sensible d’oxyde de graphène dans un papier poreux pour la détection de gaz. La première partie de ce travail est consacrée à la mise au point et à l’optimisation d’un processus de fabrication et de fonctionnalisation de capteurs capacitifs poreux sur papier. Un nouveau processus de réduction locale d’oxyde de graphène sur papier en électrodes est également introduit. Il s’agit de la thermocompression, économique et compatible avec la fabrication grande échelle.La seconde partie du travail porte sur l’étude des propriétés de détection d’humidité et d’ammoniac des capteurs. L’oxyde de graphène sur papier, présente une sensibilité élevée à l’ammoniac, l’humidité étant un gaz interférent. La réduction locale du GO en électrodes, et sa fonctionnalisation par de l’oxyde de zinc augmentent la sensibilité et la sélectivité des capteurs à l’humidité. Les capteurs fabriqués sont répétables, stables, reproductibles et flexibles
Current concerns for environmental protection and public health focus on air quality in industries, cities and households. Nowadays, paper-based gas sensors are of increasing interest due to their low cost, biodegradability, flexibility and applications in e-textiles, e-dressings and e-packaging.Graphene oxide is a derivative of graphene with exceptional electrical, mechanical and thermal properties. Graphène oxide is a promising material for the development of low-cost room temperature gas sensors.In this context, this thesis aims to integrate a graphene oxide sensing layer inside a porous paper substrate for humidity and ammonia detection. The first part of this work focuses on the fabrication, functionalization and optimization of capacitive porous gas sensors on paper. A new local reduction process of graphene oxide into electrodes is introduced. The process is hot-plating, a low cost technique compatible with large scale productionThe second part of this work studies the humidity and ammonia sensing capabilities of the sensors. Graphene oxide on paper exhibits a high sensitivity towards ammonia, with humidity as an interfering gas. The local reduction of graphène oxide into electrodes, and its functionalization with zinc oxide increased the sensitivity and selectivity of the device towards humidity. The fabricated sensors exhibit a good repeatability, reproducibility and flexibility

L'objectif de cette recherche est d’explorer de nouvelles voies dans le domaine de la détection de gaz en ajustant finement la nature chimique, la texture et la morphologie de la couche active pour concevoir de nouveaux capteurs de gaz sélectifs. Ainsi, l’obtention de matériau présentant une haute sélectivité vis-à-vis des gaz constitue un enjeu majeur dans le domaine des capteurs de gaz. Notre approche est basée sur la conception de précurseurs moléculaires uniques - les alcynylorganoétains - qui contiennent toutes les fonctionnalités requises pour obtenir des matériaux hybrides stables par le procédé sol-gel, ces matériaux permettant une détection sélective des gaz nocifs / toxiques. Puis, les propriétés de détection de gaz de ces matériaux ont été comparées à celles de nanoparticules de dioxyde d'étain (SnO2) synthétisées à pression autogène. Une série de matériaux fonctionnels à base d'organooxoétains a été déposé sous forme de films minces films par le procédé d’enduction centrifuge puis ces films ont été caractérisés par des mesures de XRD, FT-IR, RAMAN, AFM, SEM, TEM, sorption d’azote et TGA-DTA. Les études de détection de gaz montrent que l'un des oxydes d'organoétain hybride présente une réponse sélective de détection de gaz tels que le CO, H2, l'éthanol, l'acétone et le NO2, tandis que les nanoparticules SnO2 conduisent à une détection non sélective des m^mes gaz dans les mêmes conditions. Ainsi, la meilleure sélectivité vis-à-vis du CO (à 100 et 200 ppm), de H2 (à 100, 200 et 400 ppm) et de NO2 (à 1, 2, 4 et 8 ppm) a été obtenue à 100 ° C pour le matériau hybride organostannique tandis que ce matériau ne conduisait à aucune réponse avec l’éthanol et l’acétone. Par ailleurs, les films de SnO2 nanoparticulaire sont sensibles à tous les gaz testés à de faibles concentrations (CO: 10 ~ 100 ppm, NO2: 0,5 à 4 ppm, H2: 100 à 800 ppm, acétone: 25 à 200 ppm, éthanol : 10 ~ 100 ppm) sur une plage de température comprise entre 200 et 400 °C. En outre, la sélectivité des matériaux SnO2 vis-à-vis de NO2 (entre 0,5 à 4 ppm) peut être optimisée en contrôlent bien la température de détection. Enfin, les matériaux à base d’organoétains et de dioxyde d’étain présentent une capacité de détection de gaz très élevée à de faibles concentrations en gaz. Ces résultats ont permis de développer une classe de matériaux entièrement nouvelle pour la détection sélective de gaz ainsi offrent la possibilité d'intégrer une fonctionnalité organique dans les oxydes métalliques capables de détecter les gaz
The ultimate objective of this research is to draw new prospects in the gas sensing field by finely tuning the chemical nature, the texture and the morphology of the active layer to develop new type selective gas sensors. High gas selectivity has been a challenging issue during the past decades in the gas sensing area. Our approach is based on the design of molecular single precursors – alkynylorganotins which contain suitable functionalities required to obtain stable hybrid materials by the sol-gel method exhibiting selective gas detection towards harmful/toxic gases. Their gas sensing properties have been compared with those of tin dioxide (SnO2) nanoparticles synthesized by the hydrothermal route. A series of functional organooxotin-based materials have been processed as films by the spin or drop coating method and characterized by XRD, FT-IR, RAMAN, AFM, SEM, TEM, N2 sorption and TGA-DTA measurements. Gas sensing studies show that one of the hybrid organotin oxides exhibits an outstanding selective gas sensing response towards various gases, such as CO, H2, ethanol, acetone and NO2 whereas SnO2 nanoparticles present non-selective gas sensing ability under the same experimental condition. Thus, the best gas selectivity toward CO (at 100 and 200 ppm), H2 (at 100, 200 and 400 ppm) and NO2 (at 1, 2, 4 and 8 ppm) was achieved at 100 °C for the hybrid organooxotin-based film, however, it showed no response to ethanol/acetone at the same working temperature. On the other hand, the nanoparticulate SnO2 films prepared are sensitive to all the gases tested at low concentrations (CO: 10~100 ppm; NO2: 0.5~4 ppm; H2: 100~800 ppm; acetone: 25~200 ppm; ethanol: 10~100 ppm) in an operating temperature range from 200 to 400 °C. Moreover, the selectivity of SnO2 materials towards NO2 (between 0.5 ~ 4 ppm) can be optimized by well-manipulating the sensing temperatures. Finally, both organooxotin-based and tin oxide-based materials display superior gas sensing ability at low gas concentrations which opens a fully new class of gas sensing materials as well as a new possibility to integrate organic functionality in gas sensing metal oxides

Cette thèse est consacrée à l'étude de la physico-chimie des structures électroniques et microélectroniques à base de phosphure d'indium (InP). Le contexte scientifique de cette étude est d'abord abordé dans une description de la pollution atmosphérique ainsi que de sa métrologie. Les propriétés physico-chimiques et électroniques de InP sont particulièrement détaillées. Les structures des capteurs de gaz en cours de développement pour cette application sont ensuite répertoriées. Les méthodes de caractérisation chimique (spectroscopie de surface XPS et Auger, microscopie à force atomique AFM) et électronique (Van der Pauw) ainsi que l'analyse théorique des propriétés électroniques des couches minces sont également présentées. Enfin, des mesures en laboratoire à température et concentration variables de NO2 proches de celles rencontrées dans une atmosphère urbaine sont présentées. Les résultats obtenus suite à l'analyse théorique et aux différentes expériences ont montré le rôle prédominant des oxydes natifs présents à la surface de InP sur les réponses des capteurs. Ces derniers interviennent également sur la stabilité de la réponse aux gaz, tout comme leurs propriétés physico-chimiques. Les résultats des caractérisations électroniques et chimiques corroborent les résultats des essais des capteurs et permettent une modélisation de l'action du gaz sur InP

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

L’objectif principal de cette thèse est de proposer une analyse des spécificités de la transduction microonde dans le cadre d’une application capteur d’ammoniac. Les deux spécificités principales sont la caractérisation large bande (1 et 8 GHz) et les matériaux sensibles (diélectriques). Cette méthode de transduction repose sur l’interaction entre un gaz polluant et un matériau sensible déposé à la surface d’une structure propagative spécifique aux microondes. La réponse du capteur n’est pas directement induite par les propriétés diélectriques de la molécule gazeuse, mais plutôt par celles de l’espèce cible adsorbée à la surface du matériau sensible. Cette adsorption provoque une modification des paramètres du capteur mesurés par un analyseur de réseau vectoriel. Contrairement à des transductions conventionnelles comme la conductimétrie, ce principe fonctionne à température ambiante avec tout type de matériau, y compris les isolants électriques.Les premiers travaux réalisés durant cette thèse ont conduit au développement d’un nouveau banc expérimental. Il est spécifiquement adapté à l’étude de capteurs microondes par mesures des coefficients de réflexion et de transmission. Ce développement comprend la conception de deux nouvelles générations de capteurs, recouverts d’oxydes métalliques (fer ou titane) commerciaux ou synthétisés dans le cadre de l’étude. Le premier capteur comporte des circuits interdigités tandis que le second est un résonateur trapézoïdal. Ce dernier est caractérisé par une série de fréquences d’intérêt distribuées régulièrement entre 1 et 8 GHz. L’association d’un spectromètre de masse au banc de mesure a permis de suivre les adsorptions/désorptions de l’espèce cible qui est l’ammoniac (10-100 ppm), mais également le comportement du gaz vecteur utilisé, l’argon, et de l’eau adsorbée initialement sur le matériau sensible ou volontairement ajoutée en cours de l’expérience. L’objectif est d’étudier le rôle de l’eau comme interférent vis-à-vis de la détection de l’ammoniac. Une troisième molécule d’intérêt, l’éthanol, a été également été utilisée durant les expériences afin d’estimer de potentielles différences de comportement entre les molécules détectées. Les résultats expérimentaux ont été exploités au moyen de protocoles de traitement de données spécifiquement établis durant cette thèse. Des traitements temporels ont été conduits afin d’étudier le comportement cinétique du capteur, tandis que des traitements spectraux ont permis d’appréhender l’aspect large bande de la réponse du capteur en présence de polluants.Le premier résultat majeur est l’augmentation significative de la sensibilité à l’ammoniac, qui a permis d’abaisser le seuil de détection à des concentrations d’ammoniac de l’ordre de 10 ppm. Le dioxyde de titane a été identifié comme un bon candidat pour la détection d’ammoniac, avec des variations de coefficient de réflexion allant jusqu’à 6 dB pour 300 ppm d’ammoniac. Le rôle de l’eau initialement adsorbée sur le matériau sensible a été élucidé, montrant que son influence n’est significative que lors des premières minutes des expérimentations. Ainsi, il est possible de détecter l’ammoniac en présence d’humidité. Les processus liés aux expositions aux flux gazeux et particulièrement au gaz vecteur ont été identifiés et ont confirmé que la réponse du capteur était uniquement due à son interaction avec les molécules cibles. Un autre résultat majeur est la définition des conditions opératoires nécessaires à l’établissement de la sélectivité. Notre analyse théorique a clairement démontré l’intérêt des mesures large bande en termes de discrimination de molécules cibles. Cette analyse a été testée dans le cadre d’expériences multicibles utilisant l’ammoniac, l’eau et l’éthanol. Ces observations ont permis d’établir un cahier des charges d’une nouvelle génération de capteurs microondes, garantissant une discrimination systématique entre ces trois molécules
The main objective of this thesis is to propose an analysis of the microwave transduction specificities in the framework of ammonia sensing applications. The two main features of this transduction are its broadband characterization (1 to 8 GHz) as well as its sensitive materials (dielectrics). This transduction method is based on the interaction between a polluting gas and a sensitive material deposited on the surface of a microwave-specific propagating structure. The response of the sensor is not directly induced by the dielectric properties of the gaseous target molecule, but rather by those of the target species adsorbed on the surface of the sensitive material. This adsorption causes a modification of the sensor parameters measured by a vector network analyzer. Unlike more conventional transducers such as conductimetry, this principle works at room temperature with any type of material, including electrical insulators.The first work carried out during this thesis led to the development of a new experimental bench adapted specifically for the study of microwave gas sensors by measuring the S-parameters in reflection and transmission modes. This development includes the design of two new generations of sensors, coated with metal oxides (iron or titanium oxides) commercially available or synthesized during the study. The first sensor comprises interdigital circuits while the second sensor is a trapezoidal resonator. The latter is characterized by a series of frequencies of interest regularly distributed between 1 and 8 GHz. The association of a mass spectrometer with the measurement bench allowed to follow the adsorption and desorption behavior of the target species which is ammonia (10-100 ppm), but also the behavior of the vector gas conventionally used, argon, and water initially adsorbed on the sensitive material or intentionally added during the experiment. The objective is to study the role of water as interfering with the detection of ammonia, the main target species. A third molecule of interest, ethanol, was also used during the experiments in order to estimate the possible differences in the detected molecules behaviors. The experimental results were exploited using specific data processing protocols established during this thesis. Temporal treatments were carried out to study the kinetic behavior of the sensor, while spectral treatments allowed to apprehend the broadband aspect of the sensor response in the presence of pollutants.The first major result is the significant increase in sensitivity to ammonia, which significantly lowered the detection threshold to ammonia concentrations in the 10 ppm range. Titanium dioxide has been identified as a good candidate for ammonia detection, with reflection coefficient variations up to 6 dB for 300 ppm. The role of the water initially adsorbed on the sensitive material has been elucidated, showing that its influence is significant only during the first few minutes of the experiments. Thus, it is possible to detect ammonia in the presence of residual moisture. The processes induced by the gaseous exposures and particularly by the carrier gas were identified, and confirmed that the sensor response was solely due to its interaction with the target molecules. Another major result is the definition of the operating conditions that are necessary for the establishment of the selectivity. Our theoretical analysis clearly demonstrated the interest of broadband measurements in terms of discrimination of target molecules. This analysis has been tested in multitarget experiments using ammonia, water and ethanol. These observations allowed to establish the specifications of a new generation of microwave sensors, guaranteeing systematic discrimination between these three molecules

Ce sujet de thèse porte sur l’élaboration et l’étude de l’effet de la substitution du fer par le cobalt sur les propriétés physiques (structurales, morphologiques et magnétiques) et particulièrement la détection des deux gaz réducteurs NH3 et CO des composés La0,8Ca0,1Pb0,1Fe1-xCoxO3 (x = 0,00 ; 0,05 ; 0,10 ; 0,15 et 0,20). La diminution du volume a été, par la suite, confirmée par l’approximation SGGA+U en utilisant la théorie fonctionnelle de la densité (DFT). De même l’étude morphologique a révélé des micrographies poreuses présentant des particules agrégées et agglomérées de taille nanométrique et de forme irrégulière. Les analyses structurales et morphologiques nous ont permis de prédire que le composé avec x = 0,05 peut être considéré comme un bon candidat pour l’application dans le domaine de la détection des gaz. Les résultats des mesures électriques ont montré que la résistance diminue pour des taux de Co inférieurs à 0,10 puis augmente avec des taux supérieurs. De même les réponses électriques sous gaz ont montré que nos composés sont capables de détecter des gaz, avec une variation de la résistance électrique aisément mesurable suite à l’exposition sous différentes concentrations des deux gaz (NH3 et CO) et de déduire que le composé La0,8Ca0,1Pb0,1Fe0,95Co0,05O3 (x = 0,05) présente la meilleure réponse envers les deux gaz testés
This thesis deals with the elaboration and study of the effect of iron substitution by cobalt on the physical properties (structural, morphological and magnetic) and particularly the detection of the two reducing gases NH3 and CO of the compounds La0.8Ca0.1Pb0.1Fe1-xCoxO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20). The decrease of valume was subsequently confirmed by the SGGA + U approximation using the Density Functional Theory (DFT). Similarly, the morphological study reveals porous micrographs presenting aggregated and agglomerated particles of nanometric size and irregular shape. Structural and morphological analyzes predicted that the compound with x = 0.05 could be considered as a good candidate for application in the field of gas detection. The results of the electrical measurements have shown that the resistance decreases for Co rate below 0.10 and then increases with higher rate. Similarly, electrical responses under gas have shown that our compounds are able to detect gases, with a variation of the electrical resistance easily measurable following exposure under different concentrations of both gases (NH3 and CO) and to deduce that the compound La0.8Ca0.1Pb0.1Fe0.95Co0.05O3 (x = 0.05) presents the best response towards the two tested gases

La qualité de l’air extérieur (QAE) a fait l’objet d’une législation dès 1996 avec la loi LAURE. Depuis 2008, la directive européenne 2008/50/CE a instauré des obligations de mesure et de seuils à ne pas dépasser pour certains polluants à l’échelle européenne. Selon de nombreuses données toxicologiques et épidémiologiques, la pollution de l’air est à l’origine d’insuffisances respiratoires, d’asthme, de maladies cardiovasculaires et de cancers.Les composés organiques volatils (COV) et notamment le benzène, le toluène, l’ethylbenzène et les xylènes (les composés BTEX) sont des polluants avérés et participent grandement à la dégradation de la qualité de l’air intérieur et extérieur. Ce travail de thèse a concerné la réalisation d’un multicapteur de gaz à base d’oxyde métallique pour la détection de traces de BTEX dans le cadre du projet SMARTY (SMart AiR qualiTY). Un système de caractérisation électrique complet a été conçu et mise au point pour la détection de très faibles concentrations de BTEX (le ppb). Après une étude bibliographique, plusieurs matériaux ont été sélectionnés (WO3, ZnO, SnO2). Les caractérisations électriques des couches sensibles sélectionnées ont été effectuées sous air sec et sous différents taux d’humidité en présence de BTEX et de gaz interférents (NO2, CO2). Le WO3 a montré les meilleures performances en présence d’humidité et a été choisi pour le transfert de technologie qui accompagne les nouveaux transducteurs brevetés AMU. Le multicapteur à base de WO3 a montré une détection limite de 1 ppb sous 50% d’humidité relative et a permis de détecter et de quantifier de manière efficace les BTEX
Outdoor air quality is subjected to the law LAURE since 1996. In 2008, the european directive 2008/50/EC introduced measurement requirements and thresholds that should not be exceeded for certain pollutants on a european scale. According to several toxicological and epidemiological studies, air pollution causes respiratory failure, asthma, cardiovascular diseases and cancers. In Europe, air pollution is responsible for more than 300 000 early deaths a year.Volatile organic compounds (VOCs), particularly benzene, toluene, ethylbenzene and xylenes (BTEX compounds) are proven pollutants and play a major role in the degradation of indoor and outdoor air quality. This thesis is dedicated to the development of a metal oxide based multi-gas sensor for the detection of traces of BTEX within the framework of the SMARTY project (SMart AiR qualiTY). A complete electrical characterization system was designed and implemented for the detection of sub-ppm concentrations of BTEX.Based on the state-of-art, several materials were selected (WO3, ZnO, SnO2). The electrical characterizations of the selected sensitive layers were carried out under dry air and under different humidity levels in the presence of BTEX and interfering gases (NO2, CO2). Tungsten oxide (WO3) exhibits the best performance in the presence of moisture and is chosen for the technology transfer that accompanies the new patented AMU transducers. The WO3-based multi-sensor has a lower limit of detection (LOD) of 1 ppb at 50% relative humidity and effectively detects and quantifies BTEX

La mesure de la qualité de l'air intérieur est un besoin relativement récent. Les êtres humains passent plus de 90 % de leurs temps dans un environnement fermé (pièce intérieure) qui contient plusieurs polluants gazeux. L'existence de tels contaminants gazeux dans l'air intérieur d'une pièce fermée ainsi que l'exposition à court ou à long terme à ces polluants peuvent provoquer des problèmes respiratoires et plusieurs maladies chroniques. Des études montrent que la qualité de l'air intérieur a un impact direct sur le bien-être et la productivité d'une part et sur la santé à plus long terme, d'autre part. Les COVs (composés organiques volatils) sont une classe importante de ces polluants, comme l'acétaldéhyde et le formaldéhyde provenant de matériaux utilisés dans l'aménagement intérieur (équipements informatiques, mobilier, peintures, tissu! s, sols...). Nous trouvons aussi des contaminants comme le CO2 provenant de l'utilisation intensive et d'une mauvaise aération des locaux, ainsi que le CO, et le NO2 issus de la pollution urbaine. Les bureaux, les salles de réunions, les salles de classes et les salles de travaux pratiques dans les milieux universitaires ou/et scolaires sont donc potentiellement pollués. Dans une pièce densément occupée et mal aérée la mesure du taux de COV/CO2 peut dépasser les seuils règlementaires. Ces polluants gazeux dans l'air à des concentrations importantes, faute d'une ventilation suffisante et d'un contrôle de la qualité de l'air, peut provoquer des somnolences et diminution de la productivité. La mesure et la surveillance de la qualité de l'air intérieur est donc indispensable pour assurer une meilleure qualité de vie dans les espaces de travail. Cette thèse est réalisée dans le cadre du GIS (groupement d'intérêt scientifique) neOCampus, porté par l'université Paul Sabatier et dédié au développement d'un campus innovant, connecté et durable pour une meilleure qualité de vie des usagers. Nous nous sommes intéressés au développement de micro-capteurs de gaz MOS (capteurs à oxydes métalliques) et à leur pilotage pour la surveillance de la qualité de l'air intérieur dans les bureaux, les salles de classes et les salles de réunions. L'objectif de cette étude est de suivre ces niveaux de pollution pour les corriger par des mesures d'aération des locaux. La prise de décision concernant l'action de correction de qualité de l'air est une étape essentielle du processus. Citons par exemple : la régulation de la ventilation dans une pièce en cas de dépassement du seuil autorisé pour les polluants identifiés. Dans le cadre de ces travaux, nous avons réalisé des prototypes de multi-capteurs de gaz miniaturisés et intégrés avec leur carte électronique dans une pièce témoin et capables de détecter des niveaux de pollution de l'air intérieur. [...]
Measuring indoor air quality is a relatively recent need. Humans spend more than 90% of their time in a closed environment that contains several gaseous pollutants. The existence of such gaseous contaminants in the indoor air as well as short or long term exposure to these pollutants can causes many respiratory problems and several chronic diseases. Studies show that the indoor air quality has an impact on well-being and productivity. VOCs (volatile organic compounds) such as acetaldehyde and formaldehyde are strongly presented in indoor air. This type of pollutants come from materials used in interior design (computer equipment, furniture, paints, fabrics, floors, etc.). We can also found in close envirements many others contaminants such as CO2, CO, and NO2 which come from urban pollution, intensive use of location and poor ventilation. Offices, meeting rooms, classrooms and practical work rooms in universities and / or schools are therefore potentially polluted. In a densely occupied and poorly ventilated room, the measurement of the VOC/CO2 rate may exceed the regulatory thresholds. These gaseous pollutants in the air in high concentrations, due to lack of sufficient ventilation and air quality control, can cause drowsiness and decreased productivity. Measuring and monitoring indoor air quality is therefore essential to ensure a better quality life in workspaces. This thesis is being carried out within the framework of the neOCampus GIS (scientific interest group), led by Paul Sabatier University and dedicated to the development of an innovative, connected and sustainable campus for a better quality life for users. We are interested by the development of micro-gas sensors MOS (metal oxide sensors) and the indoor air quality monitoring in offices, classrooms and meeting rooms. The objective of this study is to control these pollution levels in order to correct them through measures to ventilate the premises. Making a decision about how to correct air quality is an essential step in the process. For example: regulating ventilation in a room if the authorized threshold is exceeded for the identified pollutants. As part of this work, we produced prototypes of miniaturized multi-gas sensors integrated with their electronic card in a witness room and capable of detecting levels of indoor air pollution. These prototypes include a multi-sensor cell (with 4 independent cells), proximity electronics allowing the control and recovery of data from these cells, an IOT (internet of things) type communication module based on the LoRA protocol allowing send to the "Cloud NeoCampus", remotely and wirelessly, an indoor air quality status signal. This multi-sensor is based on semiconductor sensors based on nanostructured metal oxides synthesized at the LCC (coordination chemistry laboratory). [...]

De nombreuses études récentes ont montré la présence de quantités élevées de polluants à l'intérieur de l'habitacle automobile. La solution proposée pour pallier ce problème est l'élaboration d'un capteur de gaz capable de détecter les polluants pénétrant à l'intérieur du véhicule, engendrant la fermeture des volets d'aération lors de l'observation d'un pic de pollution. Les micro-capteurs chimiques à oxydes métalliques sont les meilleurs candidats pour résoudre cette problématique : ils présentent une grande sensibilité à de nombreux gaz, des temps de réponse rapides, et leur coût de production est faible. Leur principal défaut est un manque de sélectivité. Les travaux de recherches effectués ont consisté à mettre au point un micro-dispositif intégrant un réseau multicapteur de gaz à détection conductimétrique : sur une même puce micro-usinée en silicium sont intégrées plusieurs couches sensibles différentes, visant à détecter sélectivement plusieurs gaz : le monoxyde de carbone (CO), le dioxyde d'azote (NO2), l'ammoniac (NH3), l'acétaldéhyde (C2H4O) et le sulfure d'hydrogène (H2S). Pour se faire, trois axes d'études principaux se sont dégagés. La première partie de cette étude s'est portée sur la conception des micro-plateformes chauffantes à l'aide d'un outil de simulations numériques multiphysiques, pour optimiser, d'une part leur structure et leur géométrie afin d'atteindre les performances thermiques escomptées (optimisation du rendement thermoélectrique et minimisation d'interaction d'une cellule à l'autre), et d'autre part les performances thermomécaniques compte tenu de la possibilité d'utiliser un mode de fonctionnement des capteurs en transitoires thermiques rapides. Le modèle obtenu a été validé par comparaison à des mesures physiques. Celui-ci nous a permis d'améliorer le comportement thermique à la surface de la membrane et de réduire les coûts de fabrication en simplifiant le design. La fabrication en centrale technologique de la plateforme multicapteurs a ensuite été réalisée en tenant compte des améliorations proposées par la modélisation. Une étude spécifique sur l'intégration dans le procédé d'une technique industrielle des dépôts des matériaux sensibles par jet d'encre a été menée. Nous avons ainsi mis au point une méthode permettant de déposer rapidement et à bas coûts plusieurs couches sensibles (ZnO, CuO et SnO2) sur une même structure de détection. Enfin, nous avons procédé à l'élaboration d'un système décisionnel, comprenant deux éléments : la mise au point d'un profil optimisé de contrôle des résistances chauffantes et sensibles permettant d'améliorer la sensibilité, la sélectivité et la stabilité, et une analyse multivariée des données. Il a de ce fait été possible de détecter sélectivement la plupart des gaz ciblés (seuls et mélangés) à de faibles concentrations (0,2 ppm de NO2, 2 ppm de C2H4O, 5 ppm de NH3 et 100 ppm de CO).

La mesure du taux de CO2 est un besoin relativement récent. Les travaux sur l'utilisation de nouveaux matériaux pour la réalisation de capteurs de gaz, efficaces et peu chers, suscitent des intérêts scientifique et technologique croissants. L'objectif de ces travaux de thèse est l'élaboration et la caractérisation de nouvelles couches sensibles obtenues par pulvérisation cathodique radiofréquence pour la réalisation de capteurs de CO2. Les films minces ont été déposés à partir d'une cible céramique de CuO, dans diverses conditions de dépôt, en variant la pression d'argon dans l'enceinte et la puissance RF appliquée. Dans un premier temps, nous avons caractérisé la structure et la microstructure des films bruts et recuits sous air par DRX, MEB, AFM et spectroscopie Raman. Nous avons également étudié les propriétés physiques des films minces ainsi que leur surface accessible par adsorption de gaz krypton (méthode de Brunauer, Emmett et Teller). Le traitement thermique à 450°C n'affecte pas la structure cristalline des couches, en revanche il tend à faire chuter fortement la surface accessible entre les colonnes. Après l'optimisation des paramètres de fonctionnement de la cellule de mesure, nous avons caractérisé les performances des films de CuO pour la détection du CO2. La meilleure réponse (?R/R=51 %) a été obtenue pour une couche élaborée à 2 Pa avec une puissance RF de 30W. De plus, la température optimale de mesure est relativement basse (T= 250°C). Le contrôle de la microstructure et plus particulièrement de la taille des grains s'est avéré être le paramètre principal qui impacte la réponse sous CO2. Les meilleurs résultats ont été obtenus avec des tailles de grains proches d'une vingtaine de nanomètres de diamètre. Une bonne modélisation de la réponse électrique en fonction de la taille des grains a pu être réalisée en prenant en compte un circuit électrique équivalent comportant une zone enrichie en porteur de type trous à la surface des grains et dont l'épaisseur est de l'ordre de la longueur de Debye
The measure of the rate of CO2 is a recent need. The works on the use of new materials for the conception of gas sensors based semiconductor oxides, effective and not expensive; arouse a huge interest in our society. The objective of this thesis is the elaboration and the characterization of new sensitive layers obtained by RF sputtering for the realization of the sensors of CO2. Thin films were deposited using two targets: CuFeO2 and CuO, under three conditions by varying argon pressure and RF power. First of all, the structure and the microstructure were studied for the as-deposited samples. Surface investigations carried out by Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Raman spectroscopy, BET measurements and MEB-FEG images have shown a strong influence of deposition technique parameters on film surface topography and morphology. In a second step, the thin films were annealed in air in order to oxidize the phase. For the composite CuO/CuFe2O4, Glow discharge optical emission spectrometry technique showed a structure in two layers stacked on top of each other for the thinner films. For the cupric films, no changes on both structure and microstructure have been revealed. Our films have then been evaluated for CO2 detection. The sensitive layers with different thicknesses were sensitive to 5000 ppm of CO2. The deposition parameters are optimized to obtain microstructure features which can enhance the sensitivity of the thin films as gas sensors. Best response was obtained for a cupric sample deposited in P2 30W conditions and was close to 50% at T = 250°C. We have demonstrates that cupric oxide alone can detect the CO2 gas and that the growth conditions determine the film surface characteristics. The gas sensing characteristics of these films are strongly influenced by both surface morphology and microstructure

Afin de contrôler l'émission totale des NOx dans l'échappement automobile, un capteur potentiométrique à base de zircone stabilisée à l'yttrium a été développé par la technique de sérigraphie. Il est montré que l'utilisation d'un filtre catalytique, déposé directement sur l'élément sensible, permet d'éliminer les interférences venant d'autres gaz réducteurs dans l'échappement, en particulier monoxyde de carbone (CO), hydrogène (H2), hydrocarbures (CxHy) et ammoniac (NH3). En plus, il est possible de fixer avec le filtre catalytique le rapport NO/NO2 correspondant à l'équilibre thermodynamique. Par conséquent la réponse du capteur n'est plus dépendante du rapport NO/NO2, mais seulement de la température. De plus, la sensibilité et la sélectivité du capteur à NO2 peut considérablement être améliorée en appliquant un courant de polarisation.

L'équipe micro-capteurs de l'IM2NP développe des capteursde gaz dont le principe de détection est basé sur la mesure de la variationde la conductance en présence de gaz. Le matériau utilisé comme élémentsensible est l'oxyde de tungstène (WO3) en couches minces. L'objet de cettethèse est donc d'étudier la surface de WO3 dans sa reconstruction c(2x2),obtenue par clivage selon la direction [001]. Cette étude a été également suivied'une étude des lacunes par des calculs ab initio basés sur la DFT, dans lesdeux approximations LDA et GGA. Ensuite, l'dsorption de molécules de gazsimples (O3, COx, NOx) sur des surfaces plus ou moins riches en oxygènea été effectuée. Pour simuler ces systèmes, nous avons fait le choix du codeSIESTA basé sur la DFT et qui présente l'avantage de pouvoir travailler
The team of micro sensors at IM2NP mainly focuses onthe development of gas sensors based on measurement in conductancevariation in presence of gas. The material used as sensitive element istungsten oxide (WO3) thin film. The objective of present thesis is to studythe surface properties of WO3 in its reconstruction c(2x2), obtained bycleavage along the [001] direction. This study is also followed by a gapanalysis using ab initio calculations based on DFT in both LDA andGGA approximations. Then, the adsorption of molecules of simple gases((O3, COx NOx) for these surfaces (more or less rich in oxygen), is performed.To simulate these systems, we have chosen the SIESTA code based onDFT which is used for the larger number of atoms as compared to other codes

Nous présentons dans ce manuscrit l'élaboration par électrofilage (ES) de nanofibres hybrides métal/oxyde métallique (HMMOC) et leurs caractérisations physico-chimiques. Leurs utilisations dans le cadre d’applications de type « énergie » et « environnement » ont été évaluées. En particulier, la photocatalyse de nanofibres TiO2-Au pour la dégradation en solution aqueuse du bleu de méthylène et l’utilisation de nanofibres WO3-Au comme capteurs de gaz (VOCs) ont été examinées. En lien étroit avec les résultats obtenus sur l'évaluation des performances comme photocatalyseurs ou capteurs à gaz de ces nouvelles structures HMMOC, l'influence de nombreux paramètres a été étudiée : la concentration en ions aurique, la méthode utilisée pour introduire ces derniers à l’intérieur ou les déposer à la surface des nanofibres d’oxydes et finalement le traitement thermique. En effet, on peut soit mélanger directement, avant la procédure d’électrofilage, la solution contenant les ions aurique à la solution polymérique (composée de PVP, PAN, ou PVA contenant le précurseur d'oxyde métallique), soit déposer sous forme de goutte cette solution d’ions Au à la surface des nanofibres d’oxyde métallique une fois la procédure d’électrofilage effectuée. Quant au traitement thermique, il joue un rôle multiple puisqu’il permet à la fois, d’éliminer les composés organiques des solutions polymériques, participant ainsi à la structuration de la partie oxyde du HMMOC, mais aussi de réduire les ions Au sous forme de nanoparticules.Des résultats prometteurs en photocatalyse ont été obtenus sur des fibres optimisées de TiO2 contenant des nanoparticules d’Au de 10 nm (concentration en Au : 4 wt%). En effet, pour cet échantillon, on montre une dégradation 3 fois plus rapide du bleu de méthylène en solution aqueuse que celle obtenue sur les nanofibres de TiO2 de références et sur le catalyseur commercial P25. De la même manière, des nanofibres de WO3 décorées de nanoparticules d’Au de 10 nm, utilisées comme capteurs de gaz, permettent d’obtenir une réponse 60 fois plus importante que dans le cas de nanofibres de WO3 pure et en améliorant grandement la sélectivité par rapport au n-butanol
We present in this manuscript the elaboration by Electrospinning (ES) process of hybrid metal-metallic oxide composite (HMMOC) nanofibers (NFs), and their physical-chemical characterizations. Their applications, especially the photocatalysis of TiO2-Au composite NFs for photocatalytic degradation for methylene blue (MB) in an aqueous solution and WO3-Au composite NFs for gas sensing of the volatile organic compounds (VOCs) have been investigated. According to the performance evaluation results as photocatalyst or gas sensors, the influence of many parameters have been studied: gold ions concentration, the way to introduce them into or at the NFs surface, typically by mixing them into the polymeric solution (composed of PVP, PAN, or PVA with the metallic oxide precursor) before the ES process or by simple droplet deposition onto the NFs after ES process, and finally the annealing treatment. This latter plays an important role since it both removes the organic components of the polymeric solution, thus forming the metal oxide and in-situ participates to the Au reduction.Concerning the photocatalytic properties, an optimized HMMOC material based on TiO2 NFs including 10 nm Au nanoparticles (NPs) has been obtained and shows 3 times significantly improvement of MB degradation compared to pure TiO2 NFs and the commercial catalyst P25. For gas sensing elaboration, we have shown that a HMMOC material based on WO3 NFs decorated at their surface with 10 nm Au NPs can exhibit 60 times higher response and significantly improved selectivity toward n-butanol compared with pure WO3 NFs

Des couches minces de dioxyde d'etain (sno#2) pures et dopees (cu, ni) ont ete elaborees par le procede pyrosol sur des substrats de silicium oxyde en utilisant la pyrolyse d'un aerosol genere par ultrasons. Une etude systematique a permis de determiner l'influence des conditions d'elaboration sur la composition et la microstructure des couches. L'influence du cu et du ni sur les proprietes electriques de sno#2 a ete etudiee dans la gamme de temperature 77-773 k. Une concentration de cu de 1. 2-1. 5 at% et une concentration de ni de 0. 4-0. 6 at% conduisent a une augmentation de la resistance de h#2s d'un facteur 10#3. Les proprietes electriques des couches obtenues ont ete etudiees en regime stationnaire et en regime dynamique en fonction de la concentration des dopants et de la temperature en presence des melanges gazeux: 100-1200 ppm de h#2s dans l'azote, 300 ppm de co dans l'air et 80 ppm de c#2h#5oh dans l'air. Le dopage par le cu et par le ni augmente la sensibilite de sno#2 a h#2s d'un facteur 10#-#2-10#-#3. Contrairement au cas du cuivre, le nickel augmente la sensibilite de sno#2 en presence de co et de c#2h#5oh. Un modele d'interaction des couches sno#2(cu) et sno#2(ni) avec h#2s et l'oxygene de l'atmosphere est propose. Ce modele est base sur les reactions chimiques qui modifient l'etat des dopants dans sno#2 en fonction de la composition de la phase gazeuse

碩士
國立成功大學
工程科學系碩博士班
91
The objective of the study is to design and develop a semiconductor-type oxygen gas sensor for a microscopic energy consumption measurement system, which will be used for monitoring of health condition of premature babies. The sensors are fabricated on silicon substrates using MEMS technologies and compatible with IC process. The device consists of five major components, including a micro-heater, an isolator, conducting electrodes, a sensing film and an etching-stop layer. Doped polysilicon resistor is used as a heater to make the sensor operate at an appropriate temperature, resulting in a better sensitivity to the oxygen gas. Then a layer of silicon oxide is sputtered as an electrical isolator between the heater and the sensing layer. Lastly, the sensing film, tin-dioxide doped with 2wt% Li, is deposited. In order to minimize power consumption, a suspended membrane is formed by backside-etching of Si using KOH. Experimental data show that the micro-heater can heat the membrane up to 150℃ by applying 220 mW. The oxygen sensor can successfully detect oxygen gas with the concentration ranging from 21% to 50%. It is found that the relative change of resistance is linearly proportional to the oxygen concentration while measuring time is 10 minutes. The developed sensor is suitable for clinical applications in the hospital.

碩士
國立成功大學
電機工程學系碩博士班
93
In this study, two fabrication methods were used to deposit the tin dioxide thin film to investigate the influence of the fabrication parameters on the lattice orientation and oxygen gas sensitivity of the tin dioxide thin films. 　The tin dioxide layer with the 2 wt% doped Li, which served as the sensing materials, was deposited by sputtering with Ar/O2 (3:1) gas mixtures and annealed in an oxygen gas at 600℃ for 2 hours. By the static measurement, the experimental data showed that the maximum sensitivity was 25.1, and it achieved when the tin dioxide film was grown at 300℃. 　With the spin coating process, the porous films with high surface areas can be generated, and the sensitivity for O2 gas can reach 111. By the static measurement, experimental data also indicated that the pours film will generate the maximum sensitivity when the tin oxide films are grown at 250℃. 　Thus, the sensitivity of the tin dioxide thin film used the spin coating process deposition is higher than that of sputtering method. In addition, the temperature of the former is also at lower than that of the latter.

碩士
國立臺灣科技大學
材料科學與工程系
101
Ceria-based materials have been extensively investigated as oxygen gas sensor in automotive exhaust systems due to their excellent properties of fast response time and superior sensitivity. Since the response time and sensitivity are influenced by the ceria parameters of surface area, crystalline size and cerium valence ratio (Ce(III)/(Ce(IV)), these parameters correlate with their particle morphologies.Therefore, manipulation of particle morphology is urgent and important for application in oxygen gas sensors. However, so far, the studies of varying morphologies to investigate response time and sensitivity for the oxygen gas sensors are scarce. So, the morphologies of mesoporous, porous, core-shell and solid spherical ceria powders were prepared by spray pyrolysis, and screen printed on the alumina substrates with platinum wires. The formation of thick films with 5-11μm thickness undergoes the gel decomposition at 500oC for 5h and sintering at 1200oC for 2h, and measured the properties of response time and sensitivity. The morphology, surface area, crystalline size, and cerium valence ratio were characterized by transmission electron microscopy, BET (Brunauer–Emmer–Teller) method, X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The experimental results suggest that higher surface area and smaller crystalline size shorten response time, and higher Ce(III) concentration enhances the sensitivity of oxygen gas sensor. Mesoporous Zr-doped ceria powders were prepared by spray pyrolysis(10ZDC、20ZDC、30ZDC、50ZDC, 10、20、30、50 mole% Zr doped ceria). And, the resistive oxygen gas sensors based on thick film made from this powder were fabricated. The response time of the thick film were investigated. The experimental results suggest that the lattice constant decrease with increasing ZrO2 concentration. Therefore, the electron hopping distance decrease, and the resistance of thick film decrease. The 30ZDC thick film had a lower latiice constant and crystallite size. Hence, it had lower resistance and a shorter response time. The results showed that 30ZDC thick film exhibited superior oxygen sensing properties.

碩士
逢甲大學
材料科學所
99
In this study, nanocrystalline zirconia-added ceria powder was prepared from cerium nitrate hydrate (CeNH) and zirconium nitrate hydrate (ZrNH) by precipitation method. Zirconia with various additions, 0, 5, 10, and 15 at.%, was added into ceria as CeO2, 5ZDC, 10ZDC and 5ZDC. The modification of the oxygen sensing characteristics of ceria powder was investigated. The influence of different amounts of zirconium ion additions on the electric conductivity, oxygen sensing behavior, and activation energy of electric resistance of ceria coating as a function of temperature was discussed. The experimental results were then applied to a temperature-independent oxygen sensor device in the final part of the study. The experimental results indicated that the ceria powder obtained from precipitation showed an irregular shape with a good crytallinity. The crystallite size was ca. 6 to 7 nm. After heat-treating the powder at 900C and 1200C, zirconia could inhibit the growth of CeO2 crystals significantly and reduce the lattice constant of ceria, shortening the hopping distance of ions. In the mean time, the amount of Ce4+ reacted to Ce3+ was enhanced to cause the increase of electric conductivity of the composite. Ceria powders were then prepared as a resistive oxygen sensor by screen printing technique where the 10ZDC exhibited better electric resistance reduction and oxygen sensing kinetics in this system. The experimental result showed that the connection and porosity influence significantly the electric conduction and gas sensing behavior of the powder coatings. According to the calculation of the activation energy from the temperature vs. electric resistance plots, respective the 5ZDC and the 10ZDC were used as temperature compensating material (TCM) and oxygen partial pressure measurement material (OMM) for the fabrication of resistive oxygen sensor which would not be affected by temperature change. The results showed that the device exhibited excellent temperature-independence and oxygen sensing behaviors.

碩士
義守大學
電子工程學系碩士班
94
In this thesis, we study on fine field emission characteristic of CNTs and make gas sensor with CNTs film. Various kinds of gas have unique breakdown voltage; we do a discussion to CNTs field emission characteristic in oxygen. Because CNTs has pipe diameter of nanometre-scale, great aspect ratio, steady chemical property and tough mechanical nature, so, it has been a new developing material extremely with potentiality all the time. While measurement of field emission, it’s found CNTs has very excellent characteristic of discharging. We synthesize CNTs film on Si-substrate by CVD, and use this CNTs film for examining to the discharging carried on of the proportion of oxygen to gas specifically under the atmosphere pressure. We design a CNTs gas sensor measurement, differentiate and enter pure nitrogen and pure oxygen, the quantity of carrying on voltage-current is examined. And then regard nitrogen as background gas, examine oxygen which enters the different proportions in chamber in quantity, and analyze I-V Curve; because make use of field emission of CNTs to detect the gas, there is extremely good sensitivity. And detect the proportions of gas with the I-V Curve change of discharging, there are not the questions of adsorption and desorption of gas, and it is not limited by consideration of reversibility, and operate it in the extremely low electric field. So CNTs is quite suitable for regarding as gas sensor.

碩士
國立高雄海洋科技大學
微電子工程研究所
100
Recently, there are many researches about amorphous oxide semiconductors in optical-electrical applications, such as ZnO and amorphous InGaZnO (a-IGZO). a-IGZO has lots of advantages including high uniformity, high mobility and low fabrication temperature. Therefore, it is suitable to be adopted in the active layers of thin-film transistor sensor (TFTS). In this research, when positive gate-bias stress is imposed on the device in oxygen environment at 80℃, the device exhibits a significant change of electrical characteristics, which can be utilized in oxygen-sensing. The drain current of TFTS is decreased as high as 95.38%, and the maximum value of ΔVt about 16.98 V can be achieved. The sensitivity of oxygen gas sensor is -0.4 mA/mole. The properties of threshold voltage in recovery phenomenon under light illumination demonstrate that de-trapping effect of charge was enhanced under light illumination which is compared to that under dark environment. Furthermore, the adsorbed oxygen on the back channel of IGZO active layer can be desorbed under light illumination, and this feature can be employed for the quick recovery characteristic of IGZO TFTS device.

The design of a photonics-based multi-gas sensor is presented. Absorption spectroscopy theory has been analyzed to derive key requirements for effective gas concentration measurements. HITRAN spectral analyses have determined appropriate ranges for single and multi-gas sensing. A discussion of two setups (large-scale setup and portable prototype) outlines relevant results for the development of innovative data processing algorithms (floating-point technique (FPT)). Eight absorption lines were experimentally detected (761 nm range), facilitating the recognition of oxygen spectra with surety. The FPT was used to measure oxygen concentration with an approx. 2.5% error when scanning one absorption line. Strategies to reduce the error to below 0.1% and to improve the prototype are presented. The sensor is expected to operate in an inhomogeneous network. The network utilizes different sensors capable of cross-using information to achieve high reliability and accuracy, in order to predict, prevent, and recognize man-made and natural threats.

碩士
國立臺灣大學
電子工程學研究所
104
A novel volatile organic compound (VOC) sensor with the MoS2 atomic-layers was developed in this research. Such sensor was made by transferring the MoS2 atomic-layers grown with the chemical vapor deposition (CVD) method onto the interdigitated electrode manufactured by microelectromechanical systems for indicating the sensing ability by the impedance change. The density of defects on the MoS2 film surface was controlled by the ratio of precursors and surface treatment. The sensing mechanism related to surface defects created was illustrated using the photoluminescence spectrometer. The surface defects were found to be increased with the increasing oxygen plasma treatment (OPT) cycles due to the increase of surface defects. An optimized number of OPT cycles was found to get the excellent gas detection performance. The treated MoS2 gas sensor exhibited the good performance, sensing range, and repeatability. The chemical compounds operated at different temperatures and intensity of light power were also observed. Traditional gas sensors utilizing metal oxide as the sensing material were typically equipped with a heater. Although the gas adsorption and desorption were increased by incorporating a heater, one more photo-masking and additional processing were required to define the heater. With the high temperature heating, it’s not desirable to integrate with CMOS-based circuits and use in explosive environment. In this work, we developed a MoS2-based gas senor which can detect methanol with high sensitivity at room temperature without the extra light-activation and react with many kinds of VOCs. Based on the structure of gas, the gas sensor has the different response that shows a great potential to the environment detection.

碩士
國立臺灣大學
材料科學與工程學研究所
100
In this thesis, Stille coupling were employed to synthesize low band conjugated copolymers consisting of electron-donating units (3-hexylthiophene,3HT) and electron-accepting units units, 2,3-bis(2-ethylhexyl)thieno-[3,4-b]pyrazine (TP) in different ratios with varied coplanarity in order to adjust the electronic band structure of the copolymers. Each unit was decorates with long alkyl side chains to enchance the solubility. The compositions of the random copolymers were very different from the feed ratios of the comonomers, which could possibly result from the very distinctive reactivities of the comonomers. Alternating copolymers containing 3HT and TP in 1:1 and 1:2 molar ratios were successfully obstained via Stille coupling, and these copolymers showed reasonable solubility in THF . Thermal decomposition temperatures ranged from 282 oC to 357oC and the thermal stability was enchanced with increasing 3HT content. The wavelengths of the maximum of optical absorption of these copolymers in THF solution were extended to longer wavelengths (557~688nm) comparing to P3HT due to strong intramolecular donor-acceptor interaction, and the optical band gaps were 1.2~1.28 eV. The thin filmsexhibited red shifts in optical absorptions in comparison with the absorptions in solution, and better coplanarity benefited the red shift. HOMO levels (-4.69~-5.39 eV) and LUMO levels (-3.5~3.91eV), obtained from cyclic voltametry, were elevated and lowered respectivity with increasing TP ratio in the copolymer. The copolymers with strong coplanarity would elevated the HOMO. By tuning the composition, the arrangement and the coplanaity of these TP containing low band gap copolymers, they could be potential candicates for oxygen sensors with enhancing sensitivity.

碩士
國立交通大學
電子研究所
107
In this study, a novel material ethanol gas sensor was developed, which uses tin dioxide as a sensing layer to make a resistive gas sensor, and uses lithography process technology to transfer to the interdigitated electrode in the mask, by measuring the current signal as an indicator of the gas response of the sensor, a gas sensor capable of detecting ethanol gas in a general environment is successfully produced with Dual E-Gun Evaporation System and used to realize the process of growing tin dioxide by physical vapor deposition (PVD) and the process of oxygen plasma treatment by atomic layer chemical vapor deposition system, due to the technology of thin film deposition or the technology of the end plasma treatment, etc., causes the surface roughness of the material and to be different from the hydrophilicity of the gas molecules. By changing the time of the oxygen plasma treatment, it is inferred from the literature that the oxygen plasma is treated with the gas of tin dioxide. Sensing mechanisms play an important role and are supported by the relationship between material analysis and electrical measurements. In this study, the optimal processing time was found by oxygen plasma treatment. The tin dioxide gas sensor by oxygen plasma treatment has good sensing performance and has a wide range of applications in life.

碩士
輔仁大學
電機工程學系碩士在職專班
104
In this paper we use both a smartphone and a portable oxygen sensor module to detect and monitor the amount of oxygen, CO and gas concentration by means of Bluetooth communication. When the oxygen, CO and gas concentration exceeds the normal range, our portable oxygen, CO and gas concentration detection and monitor system will notify the user immediately. We use an oxygen, CO and gas sensor both to detect ambient air and to generate the relative voltage value with respect to the oxygen level. This voltage value is amplified first through an instrumentation amplifier and the input to a MCU (Micro Controller Unit). The MCU calculates and transfers the oxygen value to a percentage of data. This design is easy both to read and to ascertain how much oxygen, CO and gas concentration is present in the air. When the time interval of low oxygen or high CO and gas concentration in the environment is longer than the value setting, the smartphone will set off an alarm to remind the user in order to prevent harm to human health.

A novel technique for measuring gas temperature and spectral particle emissivity in high-temperature gas-particle streams is presented. The main application of this optical sensor is to improve the process control of batch unit operations, such as steelmaking furnaces. The spectral emission profile of CO and CO2 and the continuous particle emission in the 3.5 to 5 μm wavelength region was recorded and analyzed in real time with a low-resolution passive sensor. The sensor consisted of light collecting optics, a dispersion element (grating spectrometer) and a 64-pixel pyroelectric array. Wavelength and radiance calibrations were performed. The temperature of the gas-particle medium (Tg+p) followed from the least-squares minimization of the difference between the measured radiance in the 4.56-4.7 μm region –which saturates due to the large CO2 concentrations and path lengths in industrial furnaces– and the corresponding blackbody radiance. Particle emissivity (εp) was calculated at 3.95 μm from an asymptotic approximation of the Radiative Transfer Equation that yields the emerging radiance from a semi-infinite particle cloud. The major source of error in the magnitude of Tg+p and εp could come from particle scattering. Through the method of embedded invariance an expression was developed to estimate the lowering effect of particle size and volume fraction on the saturation of the 4.56-4.7 μm CO2 emission region. An iterative procedure for correcting the values of the gas-particle temperature and particle emissivity was applied to the datasets from the two industrial tests. Results from the measurement campaigns with the infrared sensor prototype at two full-scale furnaces are presented. A proof-of-concept test at a coal-fired boiler for electricity production was followed by more extensive measurements at a Basic Oxygen Furnace (BOF) for steelmaking. The second test provided temperature and particle emissivity profiles for eight heats, which highlighted the simplicity of the technique in obtaining in-situ measurements for modeling studies. Through the analysis of the particle emissivity profile in the BOF and the definition of a new variable –the minimum carbon time– a novel end-point strategy to stop the injection of high-purity oxygen during low-carbon heats in BOF converters was proposed.

Vital components are more or less prone to fail in a diving apparatus. This thesis examines the performance of oxygen sensors, carbon dioxide scrubber monitoring and composite gas cylinders. A partial pressure of oxygen sensor authentication is suggested in a published patent and poster, weaknesses in carbon dioxide scrubber monitoring systems near surface are revealed in a published paper and potential harmful gas permeability properties of a composite gas cylinder, altering the gas composition and decreases the oxygen fraction, is measured and determined in a submitted paper.The importance of adequately and thoroughly performed safety tests that are standardized becomes even more relevant when managing personal protective equipment. The European Committee for Standardization have ratified relevant standard for the work in this thesis;EN-14143 Respiratory equipment – Self-contained re-breathing diving apparatus,EN-12245:2009+A1:2011 Transportable gas cylinders – Fully wrapped composite cylinders, andISO 11119-3:2013 Gas cylinders – Refillable composite gas cylinders and tubes – Design, construction and testing.These tests form a base-line for the methods, tests and result evaluations performed here and are considered safe; however improvements to the tests and standards can be made and are here suggested.