Structural and electrical properties of In2O3–SeO2 mixed oxide thin films for gas sensing applications

In 2 O 3 – SeO 2 mixed oxide thin films have been obtained by thermal evaporation of a stoichiometric In–Se starting charge and subsequent thermal annealing in an oxygen flow. High-resolution transmission electron microscopy, small area electron diffraction, and digital image processing have been employed in order to investigate the structure and the morphology of the films obtained. Hall effect and resistivity measurements in a vacuum and in a controlled atmosphere have been performed to obtain information about physical properties of these films. The experimental data show evidence that the electrical conductivity of these films undergoes a remarkable variation due to exposure to small concentrations of NO in dry synthetic air or argon. To interpret the behavior of such films, an adsorption kinetic model has been developed and the conductivity variation as a function of gas concentrations, time, and temperature has been derived. The fitting of the theoretical and experimental behavior allows us to determine the adsorption kinetic parameters.