Modeling of sensor properties for reducing gases and charge distribution in nanostructured oxides: A comparison of theory with experimental data

Abstract

The theory is developed of sensory response to reducing gases of nanostructured semiconductor oxides such as In2O3 with large concentration of electrons in the conduction band. The charge distribution in nanoparticles is determined by the functional relationship between the density of negative and positive charges inside the nanoparticles and electrons on the surface. The capture of conduction electrons by adsorbed oxygen atoms causes redistribution of electrons in the nanoparticles, thereby decreasing the near-surface electron density and the conductivity of the system. Thus, there is a functional relationship between negative charge on the surface and charge structure inside the nanoparticle, which has to be considered. The conditions for the association-dissociation reactions of oxygen molecules on the surface also change. On adsorption of a reducing gas, the O− ions react with the gas molecules and the electrons are released into the volume of the nanoparticles. The conductivity of the system thereby increases, which constitutes the sensory effect. The radial distributions of the conduction electrons and electrostatic potential in a nanoparticle are here calculated as a function of the hydrogen concentration in the ambient air. A kinetic scheme is developed of chemical reactions corresponding to the above sensory mechanism, and the associated equations are solved. As a result, the theoretical functional relationships of sensitivity to temperature and hydrogen concentration are established. The theoretical results are in good agreement with the experimental data.