Élaboration et caractérisation de capteurs de gaz à base de nanofils de ZnO

Metal oxides based gas sensors are widely used in industrial, military and environmental applications. But the main fault of these sensors remains on their lack of selectivity and requiring high working temperature to obtain a good sensitivity. Nanostructuration of the materials presents an efficient way to enhance the reaction surface between gas and the host material, thus improving the sensor performance. ZnO is an n-type semiconductor with large bandgap energy of 3.37 eV at room temperature owning many interesting physical and chemical properties, and is also very sensitive for reducing gases. In recent years, many studies develop and improve the ZnO related nanostructures for various applications. The goal of this thesis consists in the synthesis of the ZnO nanowire arrays via hydrothermal method and the study of their sensing properties. The first part of this work shows a systematic study of the various influencing parameters during the ZnO nanowire synthesis. The results show that the growth temperature, the solution pH value and the growth time influence the nanowire morphology. Nanowires with an aspect ratio about 30 have been obtained under optimized growth conditions. The second part of this work consists of the study of the ZnO nanowire sensing properties, using both electrical and optical methods. The electrical measurements show a resistivity variation of the nanowires, while the UV absorption spectra reveal a bandgap shift under injected gas. A resistivity reduction and a blue-shift of a bandgap of the ZnO nanowires were observed under injected reducing gas such as ethanolLes capteurs de gaz à base d'oxydes métalliques connaissent un engouement croissant pour des applications industrielles, militaires et environnementales. Néanmoins, ces capteurs se montrent peu sélectifs et nécessitent des températures de travail élevées pour obtenir une bonne sensibilité. La nanostructuration des matériaux permet d'augmenter la surface de réaction entre le gaz et le matériau hôte, améliorant ainsi la performance du capteur. ZnO est un semi-conducteur à large gap direct (3,37 eV) possédant de nombreuses propriétés physico-chimiques intéressantes, et aussi un matériau très prometteur pour les capteurs de gaz de type oxyde métallique. L'Elaboration de nanostructures de ZnO a conduit à un grand nombre d'études pour divers domaines d'applications. Dans ce contexte, cette thèse a pour objectif la synthèse des réseaux de nanofils de ZnO par voie hydrothermale et l'étude de leurs propriétés de détection. La première partie de ce travail porte sur l'étude systématique des différents paramètres influençant la synthèse des nanofils de ZnO. Les résultats montrent que la température de croissance, le pH de la solution et le temps de croissance influent sur la morphologie des nanofils de ZnO. Des nanofils avec un facteur d'aspect proche de 30 ont été obtenus sous conditions d'élaboration optimisées. La seconde partie de ce travail consiste en l'étude des propriétés de détection de nanofils de ZnO, par des méthodes électrique et optique. Les mesures électriques montrent une variation de résistance des nanofils, tandis que l'absorption UV révèle un déplacement du bandgap en présence du gaz. Une diminution de la résistance et un blue-shift de bandgap ont été observés lors de la présence d'un gaz réducteur tel que l'éthano

Elaboration et characterization of ZnO nanowires for gases sensor application

Les capteurs de gaz à base d'oxydes métalliques connaissent un engouement croissant pour des applications industrielles, militaires et environnementales. Néanmoins, ces capteurs se montrent peu sélectifs et nécessitent des températures de travail élevées pour obtenir une bonne sensibilité. La nanostructuration des matériaux permet d'augmenter la surface de réaction entre le gaz et le matériau hôte, améliorant ainsi la performance du capteur. ZnO est un semi-conducteur à large gap direct (3,37 eV) possédant de nombreuses propriétés physico-chimiques intéressantes, et aussi un matériau très prometteur pour les capteurs de gaz de type oxyde métallique. L'Elaboration de nanostructures de ZnO a conduit à un grand nombre d'études pour divers domaines d'applications. Dans ce contexte, cette thèse a pour objectif la synthèse des réseaux de nanofils de ZnO par voie hydrothermale et l'étude de leurs propriétés de détection. La première partie de ce travail porte sur l'étude systématique des différents paramètres influençant la synthèse des nanofils de ZnO. Les résultats montrent que la température de croissance, le pH de la solution et le temps de croissance influent sur la morphologie des nanofils de ZnO. Des nanofils avec un facteur d'aspect proche de 30 ont été obtenus sous conditions d'élaboration optimisées. La seconde partie de ce travail consiste en l'étude des propriétés de détection de nanofils de ZnO, par des méthodes électrique et optique. Les mesures électriques montrent une variation de résistance des nanofils, tandis que l'absorption UV révèle un déplacement du bandgap en présence du gaz. Une diminution de la résistance et un blue-shift de bandgap ont été observés lors de la présence d'un gaz réducteur tel que l'éthanolMetal oxides based gas sensors are widely used in industrial, military and environmental applications. But the main fault of these sensors remains on their lack of selectivity and requiring high working temperature to obtain a good sensitivity. Nanostructuration of the materials presents an efficient way to enhance the reaction surface between gas and the host material, thus improving the sensor performance. ZnO is an n-type semiconductor with large bandgap energy of 3.37 eV at room temperature owning many interesting physical and chemical properties, and is also very sensitive for reducing gases. In recent years, many studies develop and improve the ZnO related nanostructures for various applications. The goal of this thesis consists in the synthesis of the ZnO nanowire arrays via hydrothermal method and the study of their sensing properties. The first part of this work shows a systematic study of the various influencing parameters during the ZnO nanowire synthesis. The results show that the growth temperature, the solution pH value and the growth time influence the nanowire morphology. Nanowires with an aspect ratio about 30 have been obtained under optimized growth conditions. The second part of this work consists of the study of the ZnO nanowire sensing properties, using both electrical and optical methods. The electrical measurements show a resistivity variation of the nanowires, while the UV absorption spectra reveal a bandgap shift under injected gas. A resistivity reduction and a blue-shift of a bandgap of the ZnO nanowires were observed under injected reducing gas such as ethano

Growth mechanism studies of ZnO nanowire arrays via hydrothermal method

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Direct Structuring of multifunctional Zinc Oxide using holography

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Direct Holographic Patterning of ZnO

International audienceZinc oxide thin films are holographically patterned on submicronic scale by direct photodissolution method. The photodissolution process in solution is highly sensitive in the UV range (355 nm). 1D and 2D nanostructures are successfully obtained by this photoresist‐free process. The kinetic of the reaction is studied by recording the transmitted intensity through the evolution of the ZnO film thickness along the reaction time. Application of an electrical potential strongly increases the dissolution rate (1.5 μm min−1) and decreases the pattern formation time. As a first demonstration of the potential of all‐in liquid direct ZnO heterostructuring, selective growth of ZnO nanorods is performed by chemical bath deposition using holographically patterned ZnO films as a substrate

Simple and Versatile High Aspect Ratio Nanostructuring via Zinc Oxide Masking

International audienceThis article reports a new universal masking technique based on ZnO. This technique combines two main properties of the material. ZnO has an extremely low pulverization rate making the material well adapted for dry etching, and second, it can be easily chemically dissolved in solution making the material well suited for masking. Using ZnO as a mask on silicon, one can achieve selectivity as high as 60. This allows one to etch holes through a 30 μm thick wafer. Sub‐100 nm features are obtained using interferential lithography as a masking technique. There is no intrinsic limitation in this technique excepting the texture of the initial ZnO thin film. To demonstrate the versatility of this technique, it has been successively applied to other materials such as Si3N4, TiO2, and an organic resist (SU‐8) with a selectivity of up to 15:1, 5:1, and 35:1, respectively. The technique reported in this article opens the way to universal masking which is extremely important for the development of multifunctional nanostructured surfaces in any kind of materials with direct applications in antireflection coating, hydrophobicity, and hydrophilicity to only name a few

ZnO top-down structuring for UV photonic applications (Conference Presentation)

International audienceZnO is a promising II-VI semiconductor for UV applications although p-type ZnO is not yet available. Nevertheless it remains an alternative material for GaN and its alloy InGaN. For example, the exciton binding energy of ZnO (60 meV) is higher than that of GaN (21 meV). This allows ZnO to emit light at ambient temperature and interestingly, it increases the device brightness. Besides promising intrinsic properties, light-matter control and especially in the UV relies on the ability of material nanostructuring. We present here two different kinds of top-down process in order to nanostructure ZnO. The first one relies on Electron Beam Lithography (EBL) combined with a lift-off process and inductively coupled plasma (ICP) reactive ion etching (RIE). Nickel (Ni) has been used as a mask in order to have a high selectivity in the presence of C2F6 and O2 ionized gases. The etching rate used was 26nm/s in order to avoid roughness. The second process is called Direct Holographic Patterning (DHP). ZnO thin films have been holographicaly patterned for the first time by direct photodissolution in NaCl solution using laser interference lithography. Application of an electrical potential strongly increases the dissolution rate and decreases the pattern formation time. Both processes will be discussed in terms of their respective potential for light confinement in the UV

Effect of growth time and annealing on the structural defect concentration of hydrothermally grown ZnO nanowires

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ZnO as a multifunctional photonic material: emphasis on enhanced optical properties and controllable nanostructuring

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