Influence of In doping on the structural, optical and acetone sensing properties of ZnO nanoparticulate thin films

Indium-doped zinc oxide (ZnO) nanoparticle thin films were deposited on cleaned glass substrates by spray pyrolysis technique using zinc acetate dihydrate [Zn(CH3COO)(2) 2H(2)O] as a host precursor and indium chloride (InCl3) as a dopant precursor. X-ray diffraction results show that all films are polycrystalline zinc oxide having hexagonal wurtzite structure. Upon In doping, the films exhibit reduced crystallinity as compared with the undoped film. The optical studies reveal that the samples have an optical band gap in the range 3.23-3.27 eV. Unlike the undoped film, the In-doped films have been found to have the normal dispersion for the wavelength range 450-550 nm. Among all the films investigated, the 1 at% In-doped film shows the maximum response 96.8% to 100 ppm of acetone in air at the operating temperature of 300 degrees C. Even at a lower concentration of 25 ppm, the response to acetone in this film has been found to be more than 90% at 300 degrees C, which is attributed to the smaller crystallite size of the film, leading to sufficient adsorption of the atmospheric oxygen on the film surface at the operating temperature of 300 degrees C. Furthermore, In-doped films show the faster response and recovery at higher operating temperatures. A possible reaction mechanism of acetone sensing has been explained. (C) 2012 Elsevier Ltd. All rights reserved.