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 view of their use as very sensitive hydrogen sulfide gas sensors. W 4f core-level spectra indicate a partial reduction of W6+ after the reaction. No evidence for band bending after H2S dosing could be found in the valence-band spectra. The results suggest that the primary sensing mechanism 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 surface, are judged to be unlikely

The formation and stability of sulfhydryl groups on the Au(110) surface

The resistivity change of thin films of gold upon exposure to H2S has been employed to develop gas sensors that detect H2S. The exact mechanism by which H2S alters the conductivity of these films is not known. However, the adsorption and bonding of H2S on gold surfaces is clearly a critical step in the overall mechanism. In this study, we have explored the interaction of H2S with the clean Au(l 10) single-crystal surface. A variety of ultrahigh vacuum surface science techniques were used including X-ray photoelectron spectroscopy (XPS), low electron energy diffraction (LEED), temperature-programmed desorption (TPD), and high-resolution electron energy loss spectroscopy (HREELS). H2S was found to adsorb with a sticking probability of close to unity on the clean surface at 120 K. This adsorption produced a molecularly adsorbed H2S species on the surface that exhibits an SH stretching vibration at 2450 cm-1 and an H2S scissor mode at 1150 cm-1 in the HREEL spectra. TPD results suggest that the H2S desorbs directly as a molecule without decomposition at temperatures above 200 K. When defects are present in the Au surface or when the adsorbed H2S layer is irradiated with electrons, H2S will dissociate into adsorbed hydrogen and sulfhydryl (SH)