Excimer laser treatment of TiO2/WO3 thin films for self-cleaning gasochromic applications: Preparation and characterization

Abstract

Surface poisoning of gasochromic tungsten oxide layers is one of the most challenging effects, which needs to be resolved. In this paper, first amorphous TiO2/WO3/glass thin films have been prepared by reactive pulsed laser deposition (PLD) method. Then they were irradiated by a single-pulse of excimer laser (λ=248nm) with different incident energies (110, 140, 170 and 200mJ) in order to obtain a thin top layer of anatase TiO2 (a-TiO2) with high photocatalytic activity. By means of X-ray diffraction (XRD), it was observed that by excimer laser treatment (ELT) at 110mJ, a-TiO2 phase is forming while a mixture of a-TiO2 and monoclinic WO3 (m-WO3) is forming at higher energies. X-ray photoelectron spectroscopy (XPS) revealed that laser treatment removes surface contaminants and hydroxyl groups, increases the W/Ti ratio, shifts surface tungsten oxidation states to lower binding energies and leads to the formation of TiC compound on the surface. The surface morphology of samples was investigated by atomic force microscope (AFM) and field emission scanning electron microscope (FESEM). It was revealed that the surface roughness increases with the laser energy, which is due to an increase in the height of surface granular particles. The films hydrophilicity, measured by water contact angle, was found to increase with the incident laser energy. The photocatalytic activity was investigated by methylene orange (MO) degradation test. It was observed that the sample irradiated at 110mJ has the most increased photocatalytic activity. The variation of optical transmittance was investigated by UV–vis spectrophotometer. The gasochromic properties of samples with and without laser treatment were compared in the presence of diluted hydrogen (10%H2/90%Ar) gas.