CuO-doped WO3 thin film H2S sensors

Abstract

WO3 and CuO-doped WO3 (0.03CuO-0.97WO3) thin films were prepared by electron beam evaporation on fused silica and alumina substrates and their optical and H2S sensing properties were studied. As-deposited films were amorphous and crystallized into the monoclinic WO3 phase after annealing at 400 °C for 2 h in air. The thicknesses of the WO3 and CuO-doped WO3 films were 830 ± 10 nm and 642 ± 10 nm, respectively. The refractive indices were in the range: 2.33−1.80 in UV–vis-NIR region. The surface electrical conductivity of WO3 decreased drastically by ∼103 times on doping with 3 mol% of CuO. The H2S response of films was measured as a function of operating temperatures in the range of 200 °C–300 °C and it is found that CuO doping produces a large enhancement in H2S response. The sample 0.03CuO-0.97WO3 shows peak response of 11,700 for 600 ppm H2S at 275 °C. The response and recovery transients improve significantly with CuO doping in WO3 and with an increase in the sensor operating temperature from 200 °C–300 °C.