Interaction of reducing gases with tin oxide films prepared by reactive evaporation techniques

SnO2−x films were prepared by reactive thermal and e-beam evaporation of Sn on alumina substrates and by post deposition thermal treatment. X-ray diffraction measurements found that films are tin dioxide (SnO2) phase with small amounts of SnO phase. The surface conductivity of films was measured in air and in presence of H2S, H2 and C2H5OH vapors at four sensor operating temperatures of 433–493 K. The resistance of SnO2−x films decreases on exposure to H2S but shows no change with hydrogen and ethanol. H2S response decreases with rise in sensor temperature while both response and recovery times improve. H2S signal enhances with increase in resistivity of SnO2−x coatings. Our experiments conclude that increase in film conductance is due to chemical reaction between H2S and SnO2−x surface and there is little or no role of interaction of gas molecules with surface adsorbed charged oxygen species.

► Gas sensing properties of SnO2−x films measured for H2S, H2 and C2H5OH.
► No interaction between surface adsorbed charged oxygen species and reducing gases.
► Rise in electrical conductivity of SnO2−x films with H2S due to chemical reaction.
► H2S sensitivity increases with decrease in oxygen vacancy concentration in SnO2−x.