Experimental and theoretical studies of indium oxide gas sensors fabricated by spray pyrolysis

Surface structures of In2O3 films have been studied by employing experimental methods for surface characterization together with theoretical modeling for geometries, electronic structures and surface energetics. Polycrystalline In2O3 films deposited by spray pyrolysis were analyzed by using XRD, HRTEM and XPS methods. It is found that the most abundant (4 0 0) surface face reconstructs considerably leading to formation of surface mono-oxygen and di-oxygen forms. This uppermost surface layer exhibit high ability to reduction/oxidation processes during the thermal treatment. The unsaturated indium ions appearing at the reconstructed surface serve as the active sites for the chemisorbed oxygen species. Therefore, the mechanisms of In2O3 sensitivity to reducing gases include both “redox” and catalytic effects in a very thin surface layer. On the other hand, response of In2O3-based gas sensors to oxidizing gases is limited by diffusion type processes.