Les températures classiques de fonctionnement de la plupart des capteurs chimiques de gaz sont généralement supérieures à 300°C, ce qui ne représente pas les conditions favorables de leur fonctionnement en termes de stabilité, répétabilité et consommation énergétique. Pour ce, dans ce travail, nous avons développé une nouvelle méthode d’élaboration par voie sol-gel des couches minces à base de dioxyde d’étain(SnO2) sensibles à la détection de l’ozone et de l’ammoniac à température ambiante et à l’état de traces. L’ajustement des paramètres expérimentaux relatifs à ce procédé (solvant, concentration du dispersant, température et temps de recuit,…) a permis d’optimiser les conditions de préparation des couches minces et par la suite de contrôler les caractéristiques chimiques et texturales des couches sensibles développées. Dans cette étude les précurseurs du SnO2 ont été préparés selon deux approches.[...]Les résultats de détection de gaz ont montré qu’à l’inverse des couches élaborées par voie aqueuse qui sont quasiment insensibles à l’ozone, le procédé sol-gel en milieu alcoolique a permis de développer des couches très sensibles à ce gaz à des teneurs de l’ordre de 60 ppb, inférieures au seuil limite autorisé qui est de 75 ppb. L’originalité de ce travail porte sur le fait que les couches développées permettent la détection de O3 à température ambiante, ce dont aucune étude antérieure ne faisait état à l’origine de ce travail. Pour l’ammoniac, les deux voies de synthèse ont permis d’élaborer avec succès des capteurs sensibles à ce gaz, à température ambiante. La concentration minimale détectée de l’ordre de 5 ppm est inférieure aux 16,7 ppm correspondant au niveau maximum autorisé pour la détection olfactive par l’humain. Les performances de détection des deux gaz cibles, à température ambiante, ont été améliorées par addition dans les sols d’étain de surfactant (TX-100). En effet, les réponses des couches déposées en présence de surfactant ont été multipliées par un facteur 1,5 pour l’ozone et de 2 pour l’ammoniac, comparées avec celles des capteurs SnO2 sans additif.[...] / The conventional operating temperatures of most chemical gas sensors are generally above 300°C, which are not favorable to their functioning in terms of stability, repeatability and energy consumption. For this reason, in this study, we have developed a new method of thin film synthesis via sol-gel process, based on tin dioxide (SnO2) sensitive detection of very low ozone and ammonia concentrations at room temperature (RT). The adjustment of the experimental parameters (solvent, concentration of dispersant, temperature and annealing time,...) has been optimized for the preparation of SnO2 thin films highly sensitive to these target gases at RT. The precursors of SnO2 were prepared using two approaches. The first one is a synthesis pathway in which an aqueous solution of tin tetrachloride (SnCl4) is neutralized with an aqueous solution of ammonia (NH3, H2O). The second one consists of a synthesis of tin(IV) tetraethoxide by organic way via an alcoholysis reaction of anhydrous SnCl4 in absolute ethanol in the presence of triethylamine. To better control the texture of SnO2 layers obtained by this last route, small amounts of surfactant TX-100 were added to the alcoholic sol. The results particularly highlighted the importance of the nature of the solvent, annealing conditions and the concentration TX-100 on the composition and morphology of sensitive layers. This study showed that the materials synthesized by alcoholic way (SnO2(al)) have crystallites size more important than those prepared by aqueous method (SnO2(aq)), but most especially, the SnO2(al) surface is weakly hydrated, compared to that of SnO2(aq). Moreover, the microscopic analysis revealed evident differences between the two layer morphologies. In fact, the SnO2(al) films exhibit porous nanostructures whereas the SnO2(aq) layer rather appeared as a continuous film with a low porosity. The electrical responses showed that both kinds of sensitive layers enabled the detection of ozone but the sensitivity was higher for the SnO2(al) layers compared to that of SnO2(aq) thin films. The alcoholic sol–gel process enabled the development of very sensitive layers to ozone, working at ambient temperature since concentrations lower than 60 ppb were detected. This value is lower than the limit ozone detection threshold which is 75 ppb. As regards the sensitivity to the ammonia, both synthesis ways enabled its detection at room temperature. The minimum concentration detected was 5 ppm, which is less than 16.7 ppm, corresponding to the maximum level allowed for olfactive detection. In addition, it was demonstrated that the performance of ozone and ammonia detection at room temperature, was improved by the addition of surfactant (TX-100) in the organic sol. Indeed, the sensitivities of SnO2(al) layers prepared in the presence of TX-100 were multiplied by 1.5 and 2 for ozone and ammoniac respectively compared to those of SnO2(al) sensors without additive. The results of the physico-chemical characterization and the electrical responses using both layers led to the proposition of ozone and ammonia detection mechanisms using tin dioxidebased gas sensors.Finally, the development, by a simple and inexpensive sol–gel method, of novel tin dioxidesensors able to monitor ozone and ammonia gases at room temperature, was successfullyachieved. This original and multidisciplinary study, presents new and original results concerning the detection of ozone and ammonia whose detection was up to now reported to be possible at trace levels only by using metal oxide-based sensors working at high temperatures. This approach shed new light on fabricating toxic gas sensors based on metal oxides operating at room temperature.

Three-dimensional (3D) TiO₂–SnO₂–graphene aerogels (TTGs)were built up from the graphene oxide nanosheets supported with both TiO₂ and SnO₂ nanoparticles (NPs) via a facile hydrothermal assembly process. The resulting TTGs exhibit a 3D hierarchical porous architecture with uniform distribution of SnO₂ and TiO₂ NPs on the graphene surface, which not only effectively prevents the agglomeration of SnO₂ NPs, but also facilitates the fast ion/electron transport in 3D pathways. As the anode materials in lithium ion batteries (LIBs), TTGs manifest a high reversible capacity of 750 mA h g⁻¹ at 0.1 A g⁻¹ for 100 cycles. Even at a high current density of 1 A g⁻¹, a reversible capacity of 470mA h g⁻¹ can still be achieved from the TTG based LIB anode over 150 cycles.

Diluted magnetic semiconductor oxides (DMSOs) have received great attention recently due to their outstanding applications in optoelectronic and spintronic devices. Ever since the initial observation of ferromagnetism at room temperature in cobalt-doped titania, extensive effort is concentrated on preparation of transition metal doped wide band gap semiconductors, especially Mn- doped ZnO. Compared to Mn-doped ZnO, magnetic interactions in SnO! and In!O! semiconductors have been underexplored. SnO! and In!O! semiconductors have many applications, owing to their high charge carrier density and mobility as well as high optical transparency. Investigation on electronic structure changes induced by dopants during the synthesis procedure can effectively influence magnetic interactions between charge carriers. In this work, a combination of structural and spectroscopic methods was used to probe as-synthesized SnO! and In!O! nanocrystals doped with Mn!! and Mn!! as precursors. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy are powerful techniques to explore formal oxidation state of manganese dopant, electronic environment, number of nearest neighbors around the absorbent, and bond lengths to the neighboring atoms. Analysis reveals the presence of multiple oxidation states in the doped nanocrystals, and establishes a relation between !"!! ratio and expansion or contraction of lattice parameters. !"!! Although doping semiconductors are crucial for manipulating the functional properties, the influence of dopants on nanocrystals structure is not well understood. Nanocrystalline films prepared from colloidal Mn-doped SnO! and In!O! nanocrystals through spin coating process exhibit ferromagnetic behavior in temperatures ranging from 5 K to 300 K. Magnetic transformation from paramagnetic in free-standing Mn-doped nanocrystals to strong ferromagnetic ordering in nanocrystalline films is attributed to the formation of extended structural defects, e.g., oxygen vacancies at the nanocrystals interface. Magnetic circular dichroism (MCD) studies clearly show that Mn!! occupies different symmetry sites in indium oxide, when bixbyite and rhombohedral In!O! nanocrystals (NCs) are compared.

My dissertation research focuses on the investigation of the transport and magnetic properties of transition metal and rare earth doped oxides, particularly SnO2 and HfO2 thin films. Cr- and Fe-doped SnO2 films were deposited on Al2O3 substrates by pulsed-laser deposition. Xray- diffraction patterns (XRD) show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction peaks of Cr-doped samples exhibit a systematic shift toward higher angles with increasing Cr concentration. This indicates that Cr dissolves in SnO2. On the other hand, there is no obvious shift of the diffraction peaks of the Fe-doped samples. The magnetization curves indicate that the Cr-doped SnO2 films are paramagnetic at 300 and 5 K. The Fe-doped SnO2 samples exhibit ferromagnetic behaviour at 300 and 5 K. Zero-field-cooled and field-cooled curves indicate super paramagnetic behavior above the blocking temperature of 100 K, suggesting that it is possible that there are ferromagnetic particles in the Fe-doped films. It was found that a Sn0.98Cr0.02O2 film became ferromagnetic at room temperature after annealing in H2. We have calculated the activation energy and found it decreasing with the annealing, which is explained by the increased oxygen vacancies/defects due to the H2 treatment of the films. The ferromagnetism may be associated with the presence of oxygen vacancies although AMR was not observed in the samples. Pure HfO2 and Gd-doped HfO2 thin films have been grown on different single crystal substrates by pulsed laser deposition. XRD patterns show that the pure HfO2 thin films are of single monoclinic phase. Gd-doped HfO2 films have the same XRD patterns except that their diffraction peaks have a shift toward lower angles, which indicates that Gd dissolves in HfO2. Transmission electron microscopy images show a columnar growth of the films. Very weak ferromagnetism is observed in pure and Gd-doped HfO2 films on different substrates at 300 and 5 K, which is attributed to either impure target materials or signals from the substrates. The magnetic properties do not change significantly with post deposition annealing of the HfO2 films.

Este trabalho consiste na utilização de técnicas de caracterização elétrica e óptica para filmes de SnO2 puro e dopado com Sb+3 ou Nb+5, preparados através da técnica de molhamento -\'dip coating\'- a partir de suspensões coloidais. Em contraste com a extensa aplicação deste filmes e ao sucesso empírico dos dispositivos em comercialização, a compreensão dos passos elementares dos mecanismos de transporte elétricos, dos processos de espalhamento, do papel dos dopantes, dos possíveis estados de carga das armadilhas presentes, das barreiras devido aos contornos de grãos e da microestrutura ainda é pequena. Utilizando-se técnicas de caracterização tais como: corrente-voltagem em função da temperatura,corrente-voltagem com incidência de luz, absorção óptica e fotocondutividade objetivou-se o conhecimento dos mecanismo de transporte dos portadores de carga e a presença de defeitos-armadilha nestes filmes visando a melhoria das propriedades de transporte dos filmes de SnO2 produzidos pela técnica de molhamento. Esta técnica de deposição influencia nas propriedades elétricas e óticas. Filmes recém-depositados apresentam alta resistividade. Posterior tratamento térmico em vácuo e incidência de luz ultravioleta melhoram a condutividade das amostras. Este fenômeno está ligado a adsorção química e a fotodesorção de oxigênio na superfície do filme / This work is a contribution to optical and electrical characterization of pure and Sb+3 or Nb+5 doped SnO2 thin films prepared by sol-gel dip coating technique. In contrast to widespread applications of these films, and in contrast to the success of device commercialization, the elementary steps of the electrical transport mechanisms, electron scattering, influence of dopants, possible charge state of traps, potential barrier due grain boundary and microstructure are not fully understood yet. We have used characterization techniques such as current-voltage as function of temperature, current-voltage under steady monochromatic light, optical absorption and photoconductivity, which have yield knowledge of carrier transport and electron trapping in these films, giving an improvement of SnO2 films deposited by dip-coating. This deposition technique has influence on electrical and optical properties. Freshly deposited films exhibit high resistivity. Heat-treatment under vacuum and ultra-violet photo-excitation improve the conductivity of the samples. Chemisorptions and photo-desorption of oxygen are suggested to be the principal cause

Les "Oxydes Transparents et Conducteurs" (TCOs) possèdent une conductivité de type métallique tout en conservant, à l'état de films minces, une absorption négligeable dans tout le domaine visible. Malgré les recherches intensives menées durant ces 35 dernières années, il est nécessaire d'obtenir des TCOs avec de meilleures performances afin de répondre aux exigences des nouveaux dispositifs opto-électroniques. C'est dans cette optique que nous avons étudié des TCOs suivants sous forme de céramiques et de couches minces : (i) ATO et AZTO (symbolisant respectivement l'oxyde d'étain dopé à l'antimoine et l'oxyde d'étain co-dopé à l'antimoine et au zinc) ; (ii) IO (symbolisant l'oxyde d'indium) dopé avec des éléments spécifiques (résultats confidentiels) qui confèrent une conductivité électronique remarquable même lorsque le dépôt est réalisé sur substrat plastique. Dans le cas de AZTO, le co-dopage nous a permis d'obtenir des céramiques très denses et conductrices, sans perte d'antimoine lors du frittage. Par ailleurs, la conductivité électronique des films minces AZTO peut être modulée grâce au co-dopage. Ainsi nous pouvons proposer de nouveaux TCOs présentant des performances adaptées aux besoins d'applications spécifiques.

The Lithium-ion (Li-ion) battery is one of the major topics currently studied as a potential way to help in reducing greenhouse gas emissions. Major car manufacturers are interested in adapting the Li-ion battery in the power trains of Plug-in Hybrid Electric Vehicles (PHEV) to improve fuel efficiency. Materials currently used for Li-ion batteries are LiCoO2 (LCO) and graphite—the first materials successfully integrated by Sony into Li-ion batteries. However, due to the high cost and polluting effect of cobalt (Co), and the low volumetric capacity of graphite, new materials are being sought out. LiFePO4 (LFP) and SnO2 are both good alternatives for the cathode and anode materials in Li-ion batteries. But, to create high-performance batteries, nano-sized carbon-coated particles of LFP and SnO2 are required. The present work attempts to develop a new synthesis method for these materials: organic template-assisted synthesis for three-dimensionally ordered macroporous (3DOM) LFP and porous SnO2. With the newly developed synthesis, highly pure materials were successfully synthesized and tested in Li-ion batteries. The obtained capacity for LFP was 158m Ah/g, which is equivalent to 93% of the theoretical capacity. The obtained capacity for SnO2 was 700 mAh/g, which is equivalent to 90% of the theoretical capacity. Moreover, Hybrid Pulse Power Characterization (HPPC) was used to test LFP and LCO for comparison and feasibility in PHEVs. HPPC is generally used to test the feasibility and capacity fade for PHEVs. It simulates battery use in various driving conditions of PHEVs to study pulse energy consumption and regeneration. In this case, HPPC was conducted on a half-cell battery for the first time to study the phenomena on a single active material, LFP or LCO. Based on the HPPC results, LFP proved to be more practical for use in PHEVs.

The Lithium-ion (Li-ion) battery is one of the major topics currently studied as a potential way to help in reducing greenhouse gas emissions. Major car manufacturers are interested in adapting the Li-ion battery in the power trains of Plug-in Hybrid Electric Vehicles (PHEV) to improve fuel efficiency. Materials currently used for Li-ion batteries are LiCoO2 (LCO) and graphite—the first materials successfully integrated by Sony into Li-ion batteries. However, due to the high cost and polluting effect of cobalt (Co), and the low volumetric capacity of graphite, new materials are being sought out. LiFePO4 (LFP) and SnO2 are both good alternatives for the cathode and anode materials in Li-ion batteries. But, to create high-performance batteries, nano-sized carbon-coated particles of LFP and SnO2 are required. The present work attempts to develop a new synthesis method for these materials: organic template-assisted synthesis for three-dimensionally ordered macroporous (3DOM) LFP and porous SnO2. With the newly developed synthesis, highly pure materials were successfully synthesized and tested in Li-ion batteries. The obtained capacity for LFP was 158m Ah/g, which is equivalent to 93% of the theoretical capacity. The obtained capacity for SnO2 was 700 mAh/g, which is equivalent to 90% of the theoretical capacity. Moreover, Hybrid Pulse Power Characterization (HPPC) was used to test LFP and LCO for comparison and feasibility in PHEVs. HPPC is generally used to test the feasibility and capacity fade for PHEVs. It simulates battery use in various driving conditions of PHEVs to study pulse energy consumption and regeneration. In this case, HPPC was conducted on a half-cell battery for the first time to study the phenomena on a single active material, LFP or LCO. Based on the HPPC results, LFP proved to be more practical for use in PHEVs.

Abstract Aqueous solution containing tin chloride as precusor was traditionally added with NH3(aq) to promote hydrolysis and hence condensation. This results in a particulate sol which possesses little viscosity and the aggregation of precusor particles makes the subsequcently spin-coated thin film very rough in the surface and poorly-adhered with the substrate. One objective of this work is to improve the film quality by refluxing the sol to reduce precursor aggregation, enhance hydrolysis and promote HCl(g) evaporation. Experimtntal results show that, after refluxing the sol with DI-water or methanol as solvent, one obtains better films when basic sol (NH3(aq) added) and SnCl2 precursor is used instead of acidic sol (HCl(aq)added) and SnCl4 precursor. Moreover, to further reduce the effect of Cl¡Ð ion in aggregation and increase viscosity, ethylene glycol was used as solvent and two-stage heating-stirring of the sol in 80 oC and 130 oC ~150 oC was carried out to promote generation of H2O(g) and HCl(g). The evaporation of H2O(g) and HCl(g) enhances the polymerization of precursor and increase the viscosity of the sol. The aggregation caused by Cl¡Ð ions is thus reduced due to the steric effect present in the polymerical sol. XRD, SEM, FT-IR , TGA and DSC were used to examine the evolution from sol to films. FT-IR results show that absorbtion peaks of the xerogel appear at 636 cm-1(O-Sn-O) and 500 cm-1 (Sn-O). XRD results of the calcined (4 hr) powders show that rutile (SnO2) crystallization starts at 200 oC for that derived from the SnCl2-containing sol while powder derived from the SnCl4-containing sol starts crystallization at 250 oC. However, grain growth is faster in powder derived from SnCl4-containing sol as their XRD peaks become sharper than that corresponding to SnCl2 precursor as calcination temperature is raised. Based on the examination of the evolution process, it is concluded that SnCl2 polymerizes in ethylene glycol as a one dimensional chain while SnCl4 forming a 3-D network after polymerizing in ethylene glycol.

In this work the influence of solid electrolyte additives on the gas sensing properties of tin oxide layers was investigated systematically for the first time. NASICON (NAtrium, Super Ionic CONductor, Na(1+x)Zr2SixP(3-x)O12; 0 <= x <= 3) was used as a model for solid electrolyte additives. The structure of that material is ideally suitable for studies of the correlation between material parameters and the gas sensitivity of the layers. In the NASICON structure the content of mobile Na+-ions can be varied by a factor of four resulting in a simultaneous change of the ionic conductivity sigma(Na+) by approximately three orders of magnitude without considerable structural alterations. Powders of SnO2 and NASICON (x = 0; 2.2; 3) were prepared separately by means of sol-gel routes and mixed in a volume ratio of 80/20. Pastes were prepared from these powders with different compositions and screen printed on alumina substrates with a fourfold structure of thin film gold electrode combs. Four different compositions were characterised simultaneously at elevated temperatures in various gas atmospheres. The conductivity of the layers, when measured in air, decreases considerably with increasing Na+-content in the NASICON additive. This is correlated with enhanced activation energy of the electronic conductivity. The sensitivity of the layers to polar organic molecules like R-OH (alcohols), R-HO (aldehydes) and ROOH (carboxylic acids) is highly enhanced by the NASICON additive. This is observed especially on the admixtures with NASICON of high Na+-content (x = 2.2 and x = 3). On the other hand, the sensitivity to substances with mid-standing functional groups like 2-propanol or propanone can not be enhanced by NASICON additives. Furthermore the sensitivity of these composite layers to CO, H2, NH3, methane, propane, propene and toluene (all exposed as admixtures with air) is lower than the sensitivity of pure SnO2-layers. These observations are well correlated with the results of gas consumption measurements on SnO2/NASICON powders by means of FTIR spectroscopy. In spite of the lack of surface analytical data, a model of surface chemical gas reactions based on a triple phase boundary (SnO2/NASICON/gas atmosphere) was developed, which explains the experimental observations qualitatively. It is assumed that the decrease of the electronic conductivity as observed in the presence of NASICON additives with increasing Na+-content is due to an enhanced electron depletion layer. This is formed in the SnO2 grains by Na+/e- interactions across the SnO2/NASICON-interface. The enormous enhancement of the sensitivity to polar organic molecules may be due to specific nucleophilic interactions with the Na+-ions and coupled Na+/e--interactions at the triple phase reaction sites.