Selectivity improvement of SnO2 films by superficial metallic films

The purpose of this paper is to demonstrate the possibility of modifying th e sensitivity of tin dioxide (SnO2) films by depositing metallic catalysts on the surface of SnO2 layer. The aim is to reduce the effect of ethanol wh ich is considered as an interfering gas in many domestic or industrial appl ications. Two catalysts have been so studied (platinum and palladium), depo sited on two types of SnO2 layers which present different textures. Both ca talysts reduce the sensitivities to ethanol, carbon monoxide and methane. B ut the decrease of the alcohol sensitivity is more significant and conseque ntly, the relative sensitivities to CO and CH4 are increased. This effect i s more important with the SnO2 layers which have a high porosity. An other application where tin dioxide sensors can be used is the automotive applica tion. In this case, nitrogen oxides are considered as interfering gases for the carbon monoxide detection. Several catalysts are studied in order to d ecrease the influence of nitrogen oxides and especially the conductance dec rease under NO2. One of the catalysts which can be used to reduce the nitro gen oxide effect is rhodium. The results obtained with such rhodium films d eposited on SnO2 sensors allow us to consider future applications in the au tomotive field. (C) 1999 Elsevier Science S.A. AU rights reserved.