SPILLOVER EFFECTS IN THE DETECTION OF H-2 AND CH4 BY SPUTTERED SNO2 FILMS WITH PD AND PDO DEPOSITS

The deposition of up to 10 monolayers of Pd on SnO2 (110) crystal faces in ultrahigh vacuum (UHV) is observed by Auger spectroscopy (AES). After initial layer-by-layer growth, cluster formation occurs. Oxygen from the substrate is transferred to the clusters and the existence of metallic tin is derived from AES lineshape analysis. After annealing above 650°C in UHV, the AES lineshape of tin oxide reappears. The observed behavior is typical for strong metal-support interaction (SMSI). Sputtered SnO2 films with a deposit of 8 ML Pd show an open substrate surface besides Pd clusters in X-ray photoelectron spectroscopy (XPS). The conductance of films without Pd clusters, with Pd clusters and with oxidized Pd clusters (PdO) was recorded in air containing hydrogen or methane in the range 100 to 1000 ppm. Spillover effects are discussed to explain the conductance increase in the presence of Pd clusters.