CPM Seminar

In this talk, I will describe the fabrication methods and the response to various reducing gases of gas sensors based on thick and porous SnO₂ films. The main part of the presentation deals with a phenomenological model for the gas-sensing processes occurring at the semiconductor-gas interface. The model accepts the conduction mechanism as being governed by the Schottky potential barriers at the junctions between adjoining grains which are modulated by the surface coverage of the SnO₂ grains with negatively charged chemisorbed oxygen species.

To describe the interaction of reducing gas molecules with the chemisorbed oxygen, I used adsorption isotherms. The central idea was to write the grand-partition function describing the "conditioned adsorption" of the reducing species on the pre-adsorbed oxygen which has as an effect the reduction of the oxygen and an increase in the overall conductivity. The theoretical response curve for a thick-film gas sensor was compared with the experimental variation in the conductance with changes in concentration of ethanol (C₂H₅OH) and Carbon Monoxide (CO) vapors in air for several types of SnO₂-based gas sensor. The predictions made in the frame of the theoretical model are in good (or maybe only "decent") agreement with the experimental data.

Monday, April 12th 1999, 12:30
Ernest Rutherford Physics Building, Board room