Ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction and flash-desorption studies of the chemisorption and decomposition of H2S and H2O on W(100)

Abstract

The chemisorption of H2X (X = S, O) on a W(100) surface at 300 K has been studied by ultraviolet photoelectron spectroscopy (u.p.s.), Auger electron spectroscopy (A.e.s.) low-energy electron diffraction (LEED) and flash-desorption measurements. The results suggest that H2X decomposes on a W(100) surface at 300 K to give initially an adsorbed layer of the constituent atoms. Increasing exposure to H2X subsequently results in the displacement of the adsorbed H and a simultaneous increase in the amount of adsorbed X. At this stage a small amount of a molecular fragment is also formed on the surface. On the basis of the photoelectron spectra the fragment is identified as —XH. Saturating the W(100) surface with H2S at 300 K gives rise to a p(2 × 1)+p(1 × 2) LEED pattern. On heating the surface to successively increasing temperatures a series of sharp ordered structures: C(4 × 2), [graphic omitted] C(2 × 2), and p(2 × 2) are observed at 83, 66, 44 and 8% of the saturation sulphur coverage, respectively. The overlayers, having different structures, all give rise to peaks at approximately the same positions but of varying intensities in their photoelectron spectra. Saturating the W(100) surface with H2O at 300 K results in blurring of the (1 × 1) LEED pattern of the clean surface. Further heating to increasing temperatures causes a gradual reduction of oxygen coverage and a corresponding set of LEED patterns and photoelectron spectra expected of adsorbed O atoms are obtained.