ADSORBATES AND THEIR EFFECTS ON GAS-SENSING PROPERTIES OF SPUTTERED SNO2 FILMS

The surfaces of SnO2 films and their adsorbates under ambient air cond itions are crucial for their gas sensing properties. We present result s of angle resolved X-ray induced photo-electron spectroscopy (ARXPS) investigations carried out under 'real' sensing conditions. We found p olymerized hydrocarbon clusters as residues from the sputtering proces s that may reduce the effective sensor surface by up to 50%, but do no t, most probably, disturb the gas sensor action. More important are OH or H2O adsorbates. ARXPS measurements revealed strongly chemisorbed H 2O-OH, even during heat treatment at 400 degrees C inside high vacuum (HV). We conclude from these measurements that under 'real' sensing co nditions, 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. (C) 1998 Elsevier Sci ence B.V.