Theory of Sensitivity of Nanoscale-Structured Layers of Metal Oxides to Reducing Gases

Abstract

A theory of sensor response on reducing gases of nanoscale-structured semiconducting oxides with the high concentration of conduction-band electrons has been developed (modeled on In2O3). The distribution of charges in nanoparticles is determined by the functional relationship of the density of negative and positive charges in nanoparticles and electrons on their surface. The capture of conduction electrons by adsorbed oxygen atoms causes electron redistribution in nanoparticles, such that the near-surface density of electrons and the conductivity of the system decrease. In this case, the conditions of the association and dissociation of oxygen molecules on the surface also change. During the adsorption of reducing gases (H2, CO), atomic oxygen ions react with them and electrons are released that enter bulk nanoparticles. The conductivity of the system increases, which corresponds to the sensor effect. A kinetic scheme of chemical reactions, which corresponds to the that described above, has been plotted and corresponding equations were solved. As a result, theoretical dependences of the sensitivity of sensor on the temperature and pressure of hydrogen were found, which agree well with experimental curves at qualitative and quantitative level.