Nanostructured TiO 2 and W:TiO 2 Thin Films by a Novel Sol-Gel Processing for Alcohol Sensing Devices
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Nanostructured TiO2 and W:TiO2 Thin Films by a Novel Sol-Gel Processing for Alcohol Sensing Devices Carlotta Garzella, Elisabetta Comini, Elza Bontempi1, Laura E. Depero1, Cesare Frigeri2 and Giorgio Sberveglieri INFM and Department of Chemistry and Physics for Engineering and Materials, Brescia University, via Valotti 9, 25133 Brescia, Italy 1 INFM and Structural Chemistry Laboratory, Department of Mechanical Engineering, Brescia University, via Branze 38, Brescia, Italy 2 CNR-MASPEC Institut, Parco Area della Scienze, Parma, Italy ABSTRACT TiO2 and W:TiO2 thin films have been prepared by a chemically modified sol-gel technique, that implies hydrolysis and condensation of tetraethylortotitanate in the presence of a polymer dissolved in ethanol. Oxide-polymer films were deposited by dip-coating. Annealing at 500°C results in nanosized structurally stable oxides films. For doping tungsten(V)ethoxide was used in concentration that led to a final W/Ti atomic ratio of 1/33, 5/33, 10/33. The morphological and structural characteristics of thin films were studied through microraman, GIXRD, SEM and TEM. A microstructural comparison between pure and doped TiO2 layers is reported. Ethanol and methanol sensing properties are tested. INTRODUCTION In a previous work we reported the first application of the chemically modified sol-gel technique in the gas sensor field [1]. This technique results an effective method for performing nanosized structurally stable titanium dioxide thin films. The role of polymer as “steric stabilizer” during the film structural evolution has been described. TiO2 thin films presented interesting alcohol sensing performances. In this work we undertake an experimental study to investigate the doping effects on structural features and sensing response of TiO2. Tungsten doped TiO2 thin films were obtained by Depero et al. by R.F. sputtering [2]. A particularly high gas sensing capability was observed. Indeed, the addition of tungsten prevented formation of coarse-grained structure, allowing to obtain a high surface area layer. We have deposited tungsten doped TiO2 thin films using the chemically modified sol-gel technique. To our knowledge this dopant has never been studied for sol-gel titanium dioxide in the gas sensor field. The relationships between the morphology, crystalline structure and chemical composition of these films and the gas sensing properties will be discussed. EXPERIMENTAL DETAILS Synthesis of TiO2 and W:TiO2 solutions TiO2 sol preparation was made using the chemically modified sol-gel procedure proposed by Nagpal et al. [3] which implies hydrolysis and condensation of tetraethylortotitanate (TEOT) in F5.39.1
the presence of hydroxypropylcellulose (HPC) dissolved in ethanol. Concentration of TEOT and water were respectively 0.02 M and 2.3 M; the addition of HPC led to a final TiO2-HPC ratio of 48/52 wt.%. Under these conditions a full conversion of TEOT is obtained. Equal volumes of TEOT in anhydrous ethanol were mixed with solutions of HPC in ethanol and water. The TEOT solution was p
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