Amorphous ZnO modified anatase TiO2 thin films templated by tripropylamine and their electrical properties

Abstract

In the present study we report on a low cost synthesis of amorphous ZnO modified anatase TiO2 (40 and 20 mol% ZnO) thin films deposited via sol-gel spin coating technique on glass substrate. The effects of the composition on the structural, morphological and surface chemistry properties were discussed and correlated with the electrical behavior. Thus, by X-ray diffraction and Raman spectroscopy only TiO2 indexed in the anatase crystalline structure was identified without any ZnO characteristic crystalline phase. The surface chemistry assessed by X-ray Photoelectron spectroscopy highlighted the presence of Ti4+ in TiO2 as well as the presence of Zn2+ coordinated in the amorphous ZnO proved by the Auger ZnLMM transition shifted toward lower binding energies. The films are continuous, homogeneous with grain size below 20 nm and exhibit an intergranular porosity, as it was displayed by Scanning Electron Microscopy.The sensor signal towards CO exposure is strongly related to the amount of the ZnO amorphous phase formation. Thus, we found that a higher content of the ZnO amorphous phase leads to a lower sensitivity. The electrical and sensing measurements were performed in the temperature range (room temperature 400 °C), over the range of CO concentrations (0-2000 ppm). The sensor containing 20 mol.% amorphous ZnO exhibits a good sensitivity at ~300 °C for a low CO concentration .