Adsorbates and their effects on gas sensing properties of sputtered SnO films

The surfaces of SnO2 films and their adsorbates under ambient air conditions are crucial for their gas sensing properties. We present results of angle resolved X-ray induced photo-electron spectroscopy ARXPS.investigations carried out under ‘real’ sensing conditions. We found polymerized hydrocarbon clusters as residues from the sputtering process that may reduce the effective sensor surface by up to 50%, but do not, most probably, disturb the gas sensor action. More important are OH or H2O adsorbates. ARXPS measurements revealed strongly chemisorbed H2O–OH, even during heat treatment at 4008C inside high vacuum HV.. We conclude from these measurements that under ‘real’ sensing conditions, i.e. when using SnO2 gas sensors in environmental atmosphere, a mono- or bilayer of water molecules is always present on SnOx OH.y, supposed to influence gas sensing reactions. q1998 Elsevier Science B.V.