Alcohol-sensing characteristics of spray deposited ZnO nano-particle thin films

ZnO nano-particle thin films were deposited on cleaned glass substrates by spray pyrolysis technique using the precursor solution of zinc acetate dihydrate [Zn(CH3COO)2·2H2O]. Structural analyses and surface morphology of the resulting films were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analyses confirm that the films are polycrystalline zinc oxide, possessing hexagonal wurtzite structure with crystallite size ∼25 nm. The SEM micrograph of the film shows a good uniformity and a dense surface having spherical-shaped grains. Alcohol sensing characteristics of the deposited films have been investigated for various concentrations of methanol, ethanol and propan-2-ol in air at different operating temperatures. At 150 ppm concentration, the film shows maximum response (85.2%) to propan-2-ol at the operating temperature of 250 °C; whereas at the same concentration 150 ppm, the maximum responses to methanol and ethanol at 300 °C are observed to be 75.8% and 52.4%, respectively. Also, the film exhibits selective high response to propan-2-ol, followed by ethanol and methanol, respectively at each operating temperature up to 275 °C. This selectivity is more pronounced in the region of lower operating temperatures and concentrations. A possible reaction mechanism of alcohol sensing has been proposed.