SURFACE-CHEMISTRY OF H2S-SENSITIVE TUNGSTEN-OXIDE FILMS

We have applied X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) to characterize thin tungsten oxide films and to investigate their interaction with hydrogen sulfide in vi ew of their use as very sensitive hydrogen sulfide gas sensors, W 4f c ore-level spectra indicate a partial reduction of W6+ after the reacti on. No evidence for band bending after H2S dosing could be found in th e valence-band spectra. The results suggest that the primary sensing m echanism involves the formation of oxygen vacancies on the surface in the presence of hydrogen sulfide, Alternative mechanisms, such as the formation of a tungsten sulfide or a hydrogen tungsten bronze on the s urface, are judged to be unlikely.