Gas-chromism in ultrasonic spray pyrolyzed tungsten oxide thin films

摘要

A simple and inexpensive ultrasonic spray pyrolysis (USP) technique has been employed to deposit tungsten oxide (WO_3) thin films by spraying 2.0 mM aqueous ammonium metatungstate solution onto the amorphous glass substrates kept at 250 deg C. The films were further annealed at 400 deg C for 4 h in air. X-ray diffraction (XRD) technique was used to determine the crystallinity and to identify the WO_3 phases. It was found that the films were sub-stoichiometric, WO_(3-z). To study gas-induced properties, a catalyzing layer of platinum (Pt) was sputtered onto it. The gas-induced electrical and optical properties of Pt/WO_3/glass samples were studied and results reported. It was found that electrical resistivity decreased by a factor of 10 within 2 min and stabilized after 15 min, after H_2 gas exposure. Similarly the optical transmittance of the samples attenuated from 55 percent to 10 percent within 15-20 min. The reversible changes in electrical resistivity and optical transmittance were observed when the samples were exposed to oxygen. The response times and sensitivity of the samples were estimated.