Characterisation of the catalyst-semiconductor interaction mechanism in metal-oxide gas sensors

Catalysts may affect the iutergranular contact regions in polycrystalline metal-oxide films with two mechanisms: spillover and Fermi energy control. In this work, a simple experimental method is proposed consisting of monitoring sensor resistance as a function of oxygen partial pressure, in order to distinguish which of these mechanisms is dominant in certain catalyst-metal oxide interfaces. Interpretation of experimental results, using the theoretical background for these two mechanisms in the case of InOx sensors with palladium and platinum catalysts, indicates that the electronic interaction of Fermi energy control dominates in the case of palladium, while the chemical interaction of spillover dominates in the case of platinum. These results are also confirmed by Monte Carlo simulation of the spillover process. (C) 1997 Elsevier Science S.A.