In this thesis, investigations into fabricating tin oxide hydrogen gas sensors from films assembled by the deposition of tin clusters are reported. The tin clusters were formed in a UHV compatible cluster apparatus by DC magnetron sputtering and inert gas aggregation. Through SEM imaging, it was found that the morphology of tin cluster assembled films deposited onto silicon nitride substrates was highly coalesced. The coalescence between the clusters was significantly reduced by reacting the clusters with nitrogen before they were deposited. This resulted in granular films with a grain size close to that of the deposited clusters. The coalesced and granular tin films were used to fabricate tin oxide conducti-metric gas sensors. This was done by depositing the tin films onto gold contacts and then oxidising them by baking them at 250°C for 24 hours. The sensors were tested using a purpose built gas test rig. It was found that the sensors with the granular film morphology were much more sensitive to 500 ppm, 1000 ppm, and 5000 ppm of hydrogen at 200°C in ambient air with zero humidity. This was attributed to the smaller grain size and the larger surface area of the granular films.

The widespread use of Liquid Petroleum Gas (LPG) for cooking and as fuel for automobile vehicles requires fast and selective detection of LPG to precisely measure the leakage of gas for preventing the occurrence of accidental explosions. The adoption of Micro-Electro-Mechanical-System (MEMS) technology for fabricating the gas sensor provides other potential advantages for sensing applications, which includes low power consumption, low fabrication cost, high quality, small size and reliability. MEMS based gas sensor requires a sensitive layer of oxide material like ZnO, SnO2, TiO2, Fe2O3, etc. The tin oxide material used in the present work changes its electrical properties, as it interacts with the reducing gas like LPG. The sensor material becomes active only at high temperature such as 400ºC, thereby realizing the need of a micro heater to reach the desired temperature. To control the temperature of micro heater and to determine the change in electrical properties of the sensor due to its interaction with LPG an Application Specific Integrated Circuit (ASIC) forms an essential constituent of the MEMS based gas sensor. In the present work, an attempt has been made to improve the sensitivity of LPG gas sensor and it is correlated with other properties by different characterization techniques. The work also includes the design as well as testing of ASIC for gas sensor system. Process parameters particularly deposition time and substrate temperature have a profound influence on the microstructure of the tin oxide film, which in turn affects the gas sensing properties. To study the effects of these parameters, RF magnetron sputtering system is used for depositing tin oxide films onto the silicon substrate, which is compatible with CMOS technology. The effects of structural properties, optical properties and the porosity of the films are also studied and correlated with the gas sensing properties. In this direction the deposited films are characterized using X-Ray Diffraction (XRD) to determine the structure orientation. The morphology of the sensor films are analyzed by Scanning Electron Microscope (SEM) while the refractive index, thickness and porosity of the films are determined using ellipsometry studies. The thickness of the deposited films is also confirmed by the surface profilometer. The change in composition of the deposited film along its depth is determined using Secondary Ion Mass Spectrometer (SIMS). Maximum sensitivity 5.5 is obtained for 470 nm thick films, which corresponds to a grain size of 38nm at the operating temperature of 4000C. Following these studies, an ASIC has been designed using Tanner EDA Tools on AMIS 0.7 µm CMOS process, fabricated through Euro practice’s ASIC prototyping service, Belgium and tested successfully after fabrication. The temperature control module of ASIC has been designed using relaxation oscillator technique to control the temperature of the in house developed heater. The resistance to period conversion technique is explored for the design of the sensor read out module of ASIC. The heater is integrated successfully with the sensor film, ASIC and microcontroller based LCD module. The test results show good agreement with the simulation results.

No description available.

Neste trabalho foram investigados o efeito da adição de diferentes quantidades de IrO2 (entre 1 e 30% em mol) em eletrodos de SnO2 e suas atividades eletrocatalíticas para a reação de oxidação de etanol. A inovação deste trabalho está na composição do eletrodo onde a concentração de IrO2 varia de níveis da ordem de dopante até concentrações típicas de ADE. O método de preparação utilizado permitiu a obtenção de filmes homogêneos e com estequiometria controlada, comprovados pela técnica de Energia Dispersiva de Raios-X (EDX). A análise de Microscopia Eletrônica de Varredura (MEV) mostrou que os filmes possuem morfologia com trincas. Na análise por Difração de Raios-X (DRX) ficou evidente a formação de solução sólida. A caracterização por Voltametria Cíclica mostrou que a carga voltamétrica e a corrente relacionada a reação de desprendimento de oxigênio (RDO) aumentam com a concentração de IrO2 na composição do eletrodo. Adicionalmente, a ordem da estabilidade eletroquímica encontrada é a seguinte: 30 >> 1 @ 10 > 5% em mol de IrO2. Para avaliar a atividade eletrocatalítica destes eletrodos para a reação de oxidação de etanol foram utilizadas as técnicas de voltametria cíclica, eletrólise a corrente constante e Infravermelho com Transformada de Fourier (FTIR) in situ. Foram identificados como produtos acetaldeído, acido acético e CO2. Comprovouse que o ácido acético não é oxidado nas condições experimentais empregadas. Observou-se que os eletrodos contendo 5 e 10% em mol de IrO2 apresentaram as maiores velocidades de oxidação do etanol formando preferencialmente ácido acético. Os eletrodos contendo 1 e 30% em mol de IrO2 apresentaram maior seletividade para CO2 em relação as outras composições. A adição de 1% em mol de IrO2 no SnO2 foi suficiente para promover uma estabilidade satisfatória para a aplicação deste eletrodo. Outra observação importante foi que este eletrodo apresentou a menor seletividade para a formação de ácido acético permitindo uma maior formação de CO2. / In this work was investigated the effect of the IrO2 addition (1 30 mol% contents) on SnO2 electrodes and its electrocatalytic activities towards ethanol oxidation. The new approach of this work is related to the IrO2 contents on the electrodes compositions shifts between the dopant levels until Dimensionally Stable Anodes (DSA®) concentrations. The preparation method used allowed to obtain homogeneous films with controlled stoichiometry, that was confirmed by Energy Dispersive X-ray (EDX) analysis. The Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) analysis showed a cracked morphology and the formation of solid solution, respectively. The voltammetric experiments showed an increase in the Oxygen Evolution Reaction (OER) currents and the voltammetric charges for the higher IrO2 contents. In addition, the stability order found is 30 >> 1 @ 10 > 5 mol% IrO2. In order to investigate the electrodes activities towards ethanol oxidation, the cyclic voltammetry, electrolysis and Fourier Transform Infrared (FTIR) in situ techniques were used. The presence of products as acetaldehyde, acetic acid and CO2 was detected. Acetic acid was not oxided in the experimental conditions employed. The 5 and 10 mol% IrO2 electrodes showed higher ethanol oxidation rates with the preferential acetic acid formation. The electrodes containing 1 and 30 mol% IrO2 are more selective to CO2 production than the others compositions. The addition of 1 mol% IrO2 was enough to enhance the electrode stability, that make it applicable. Another interesting observation is that the IrO2 1 mol% electrode presented the smaller selectivity for the acid acetic formation allowing the complete oxidation of ethanol possible.

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2015 / Nanocrystalline materials of defect free anatase and rutile SnO2 together with Ti and Y in anatase SnO2 have been modelled successfully using classical molecular dynamics simulations together with Buckingham potential. The structural properties of these SnO2 phases were analysed using radial distribution functions (RDFs). The effect of increasing temperature in pure SnO2 and doped SnO2 were studied. In both pure and doped materials, RDFs suggest phase transition at higher temperature, where anatase SnO2 transforms to rutile SnO2. Rutile SnO2 was found to be more stable than anatase SnO2. The results showed that the dopants have different effects on the SnO2 material. Ti defect is found to lower the transformation temperature of anatase to rutile SnO2. Y defect is found not to have any effect on the anatase to rutile SnO2 transformation. Thermodynamic properties such as volume thermal expansion coefficient and specific heat capacity were also calculated from above Debye temperature. Volume thermal expansion coefficient was obtained from volume versus temperature curves. Volume thermal expansion coefficient for rutile and Ti-anatase SnO2 were found to be not of the same order with the calculated results. Specific heat capacity calculated from energy versus temperature curves was found to be in agreement with the Dulong and Petit law of solids. Nanocrystalline Al/Y co-doped SnO2 powders were successfully synthesized using the sol-gel method. The samples were subjected to different temperatures 100 (as prepared) 200, 400, 600, 800 and 1000 oC. The effects of co-doping and temperature on the structural and optical properties of Al/Y co-doped SnO2 nanoparticles as well as morphology were investigated. The characterization techniques used were X-ray powder diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) and UV-visible spectroscopy (UV-vis). The average particle sizes were found to be in the range between 2.5–8 nm and the strains were calculated to be 2.76–0.53 with increasing temperature for as prepared and the sample sintered at different tempe-ratures. The Raman bands were found to correspond with the literature. At a higher temperature of about 800 oC the materials were found to contain the second phase which is yttrium stannate. However no information about aluminium was found. The optical band gap were found to be between 3.3–3.99 eV in the temperature range 200–1000 oC.

Indium-tin oxide (ITO) is commonly used as the transparent electrode in organic photovoltaic (OPV) devices. ITO's transparent properties come at the expense of less than ideal electrode characteristics arising from insulating over-oxidized surface species. OPVs fabricated on the native ITO surface tend to exhibit poor performance with a high degree of variability from device to device. Aggressive acid etching of the ITO surface removes the majority of the insulating surface species leading to improvements in OPV efficiency with greater reproducibility and increased device to device consistency.Organic light emitting diodes (OLEDs) are planar electroluminescent light sources that naturally couple a portion of their emission into internally reflected modes within the device substrate. Although this coupling property is well known, few attempts have been made to integrate OLEDs as light sources for internal reflection elements. Furthermore, OPVs share the optical coupling properties of OLEDs and therefore can be used as integrated internal reflection detectors. Integrating both an OLED light source and an OPV detector onto the same substrate results in an internal reflection sensing platform that requires no free-space optics, has low power consumption requirements, and can be easily fabricated on substrates occupying an area less than one square inch. In this work we establish a functional prototype design, characterize the fundamental coupling properties, and demonstrate several surface sensing responses of this fully integrated optical sensing platform.The net solar power production from OPVs arises from the interactions between multiple currents through the device. The photocurrent is the only power producing current in the device and understanding the voltage dependent nature of this current is essential in OPV research. Analysis methods of conventional, inorganic photovoltaics do not adequately describe the photocurrent behavior commonly observed in OPVs. OPV analysis is therefore somewhat limited by the methods commonly employed. To improve upon the convention methods we develop a simplified method of OPV photocurrent analysis based on electrochemical methods that accurately describes the voltage dependence of the photocurrent and leads to greater insight into the key parameters involved in solar power production from OPVs.

Neste trabalho foram investigados o efeito da adição de diferentes quantidades de IrO2 (entre 1 e 30% em mol) em eletrodos de SnO2 e suas atividades eletrocatalíticas para a reação de oxidação de etanol. A inovação deste trabalho está na composição do eletrodo onde a concentração de IrO2 varia de níveis da ordem de dopante até concentrações típicas de ADE. O método de preparação utilizado permitiu a obtenção de filmes homogêneos e com estequiometria controlada, comprovados pela técnica de Energia Dispersiva de Raios-X (EDX). A análise de Microscopia Eletrônica de Varredura (MEV) mostrou que os filmes possuem morfologia com trincas. Na análise por Difração de Raios-X (DRX) ficou evidente a formação de solução sólida. A caracterização por Voltametria Cíclica mostrou que a carga voltamétrica e a corrente relacionada a reação de desprendimento de oxigênio (RDO) aumentam com a concentração de IrO2 na composição do eletrodo. Adicionalmente, a ordem da estabilidade eletroquímica encontrada é a seguinte: 30 >> 1 @ 10 > 5% em mol de IrO2. Para avaliar a atividade eletrocatalítica destes eletrodos para a reação de oxidação de etanol foram utilizadas as técnicas de voltametria cíclica, eletrólise a corrente constante e Infravermelho com Transformada de Fourier (FTIR) in situ. Foram identificados como produtos acetaldeído, acido acético e CO2. Comprovouse que o ácido acético não é oxidado nas condições experimentais empregadas. Observou-se que os eletrodos contendo 5 e 10% em mol de IrO2 apresentaram as maiores velocidades de oxidação do etanol formando preferencialmente ácido acético. Os eletrodos contendo 1 e 30% em mol de IrO2 apresentaram maior seletividade para CO2 em relação as outras composições. A adição de 1% em mol de IrO2 no SnO2 foi suficiente para promover uma estabilidade satisfatória para a aplicação deste eletrodo. Outra observação importante foi que este eletrodo apresentou a menor seletividade para a formação de ácido acético permitindo uma maior formação de CO2. / In this work was investigated the effect of the IrO2 addition (1 30 mol% contents) on SnO2 electrodes and its electrocatalytic activities towards ethanol oxidation. The new approach of this work is related to the IrO2 contents on the electrodes compositions shifts between the dopant levels until Dimensionally Stable Anodes (DSA®) concentrations. The preparation method used allowed to obtain homogeneous films with controlled stoichiometry, that was confirmed by Energy Dispersive X-ray (EDX) analysis. The Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) analysis showed a cracked morphology and the formation of solid solution, respectively. The voltammetric experiments showed an increase in the Oxygen Evolution Reaction (OER) currents and the voltammetric charges for the higher IrO2 contents. In addition, the stability order found is 30 >> 1 @ 10 > 5 mol% IrO2. In order to investigate the electrodes activities towards ethanol oxidation, the cyclic voltammetry, electrolysis and Fourier Transform Infrared (FTIR) in situ techniques were used. The presence of products as acetaldehyde, acetic acid and CO2 was detected. Acetic acid was not oxided in the experimental conditions employed. The 5 and 10 mol% IrO2 electrodes showed higher ethanol oxidation rates with the preferential acetic acid formation. The electrodes containing 1 and 30 mol% IrO2 are more selective to CO2 production than the others compositions. The addition of 1 mol% IrO2 was enough to enhance the electrode stability, that make it applicable. Another interesting observation is that the IrO2 1 mol% electrode presented the smaller selectivity for the acid acetic formation allowing the complete oxidation of ethanol possible.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15389号 / 工博第3268号 / 新制||工||1492(附属図書館) / 27867 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 井上 正志, 教授 垣内 隆 / 学位規則第4条第1項該当

Recent advances in the electric & hybrid electric vehicles and rapid developments in the electronic devices have increased the demand for high power and high energy density lithium ion batteries. Graphite (theoretical specific capacity: 372 mAh/g) used in commercial anodes cannot meet these demands. Amorphous SnO2 anodes (theoretical specific capacity: 781 mAh/g) have been proposed as alternative anode materials. But these materials have poor conductivity, undergo a large volume change during charging and discharging, large irreversible capacity loss leading to poor cycle performances. To solve the issues related to SnO2 anodes, we propose to synthesize porous SnO2 composites using electrostatic spray deposition technique. First, porous SnO2/CNT composites were fabricated and the effects of the deposition temperature (200,250, 300 oC) & CNT content (10, 20, 30, 40 wt %) on the electrochemical performance of the anodes were studied. Compared to pure SnO2 and pure CNT, the composite materials as anodes showed better discharge capacity and cyclability. 30 wt% CNT content and 250 oC deposition temperature were found to be the optimal conditions with regard to energy capacity whereas the sample with 20% CNT deposited at 250 oC exhibited good capacity retention. This can be ascribed to the porous nature of the anodes and the improvement in the conductivity by the addition of CNT. Electrochemical impedance spectroscopy studies were carried out to study in detail the change in the surface film resistance with cycling. By fitting EIS data to an equivalent circuit model, the values of the circuit components, which represent surface film resistance, were obtained. The higher the CNT content in the composite, lower the change in surface film resistance at certain voltage upon cycling. The surface resistance increased with the depth of discharge and decreased slightly at fully lithiated state. Graphene was also added to improve the performance of pure SnO2 anodes. The composites heated at 280 oC showed better energy capacity and energy density. The specific capacities of as deposited and post heat-treated samples were 534 and 737 mAh/g after 70 cycles. At the 70th cycle, the energy density of the composites at 195 °C and 280 °C were 1240 and 1760 Wh/kg, respectively, which are much higher than the commercially used graphite electrodes (37.2-74.4 Wh/kg). Both SnO2/CNTand SnO2/grapheme based composites with improved energy densities and capacities than pure SnO2 can make a significant impact on the development of new batteries for electric vehicles and portable electronics applications.

We have built an imaging mass spectrometer adapted for ultrashort laser pulses as its ionization technique, as an alternative to other imaging techniques. Before my arrival, the mass spectrometer has only been subject to preliminary tests on noble gases. Since then, we’ve made some modifications to the system in order to properly analyze solids. This thesis shows how we obtain our ultrashort laser pulses, the inner workings of our homemade imaging mass spectrometer, and the results that we’ve obtained with it so far. We tested two modes of operation concerning the extraction of the ions from the system into the mass analyzer: continuous and pulsed. We discuss the advantages and disadvantages of each configuration. We also display preliminary imaging results with our imaging technique of a simple WO3 and ITO structure. We conclude by comparing the resolution of this image to the different techniques in imaging mass spectrometry, how we can further improve our mass spectrometer, and the future use of this machine. Nous avons construit un spectromètre de masse adapté pour les pulses de laser très courts comme technique d’ionisation, pour acquisition des images d’un échantillon. Avant je suis arrivé, le spectromètre de masse avait seulement été utilisé pour des tests préliminaires de gaz nobles. Depuis ce moment, nous avons modifié le système pour analyser les solides. Cette thèse démontre comment on obtient nos pulses de laser très courts, comment notre spectromètre fait maison fonctionne et les résultats nous avons obtenus jusqu’à présent. Nous avons testé deux configurations différentes au sujet de l’extraction des ions du système : constant et pulsé. Nous discutons aussi les avantages et désavantages de chaque mode d’opération. Nous démontrons aussi des images préliminaires d’un substrat mixte de WO3 et ITO. Nous concluons par comparer la résolution des images aux autres techniques de collection d’images, comment nous pouvons améliorer notre spectromètre de masse et les plans pour la machine dans le futur.