Deactivation mechanisms of gas sensors based on semiconducting oxides

The present paper summarizes an approach based on surface science for the study and the characterization of the properties of solid state gas sensors using semiconducting oxides for hydrocarbon detection. In these sensors the detection mechanism relies on the conductivity changes induced by the catalytic reaction of gaseous species on the oxide surface. Devices based on these oxides can be sensitive to better than one ppm of hydrocarbons in the atmosphere. Surface science techniques based, for instance, on electron or ion spectroscopy can be used to determine surface parameters suck as the degree of oxidation, the stoichiometry of the topmost layers in the sensing element, the presence of impurities and/or dopants, and the mechanisms of reaction and deactivation on the surface. These data can be of fundamental importance in the design of new, more selective and more sensitive sensors. Some examples are reported in the present paper for a study on SnO2 based sensors for hydrocarbon detection.