Structural, optical and methanol sensing properties of sprayed In2O3 nanoparticle thin films

Indium oxide (In2O3) nanoparticle thin films were grown on cleaned glass substrates by the chemical spray pyrolysis technique using the precursor solution of indium nitrate (In (NO3)3). The XRD studies confirm that the films are polycrystalline In2O3, possessing cubic structure with lattice parameters, a = b = c = 10.17 Å. The optical studies show a direct optical band gap of 3.32 eV and an indirect band gap of 2.6 eV in the prepared films. The films exhibit high optical transparency >80% in the visible region, reaching a maximum of 85% at 684 nm wavelength. Further, the gas sensing properties of the films have been investigated for various concentrations of methanol in air at different operating temperatures. At 300 °C the film exhibits a very high response 99% to methanol vapor at a concentration of 40 ppm in air, which is ideal to be used as a methanol sensor. The film shows fast response and recovery to methanol vapor at higher operating temperatures. A possible methanol sensing mechanism has been proposed.