Metal-Metal Oxide Sandwich: A New Gas Sensitive Structure for Smart Sensors

In our report we are discussing the novel sandwich structure based on semiconducting metal oxide top-layer and thin metal bottom-films. The model structure consists of several thin films: the metallic Pt-film covered by ultrathin Ni and the semiconducting cap of the structure produced by deposition of the SnO2-film. The resistance of the sandwich is nearly equal to the resistance of the bottom layer at the room temperature in the clean air. The temperature dependence of the resistance of the sandwich is unique when compared with the well known resistive gas sensors. The resistance of the sandwich is selective to NOx gas. The sandwich without the Ni inter-layer is insensitive to NOx. We think that the effects obtained are related to (1) the field effect controlled electron transport through the narrowest parts of the bottom-layer, (2) the dependence of the interface potential on the density of the extra surface charge induced by gas chemosorption on the top-film and (3) the influence of the work function of the metal on both the Fermi energy position in the band gap of the SnO2-film and the chemosorption of gas species on the surface of the top-film.