Interaction of vapours of mercury with PbS(0 0 1): a study by X-ray photoelectron spectroscopy, RHEED and X-ray absorption spectroscopy

Abstract The interactions of mercury on cleaved and polished galena PbS(0 0 1) were studied at room temperature. The surface of the samples was characterised by X-ray photoelectron spectroscopy (XPS), RHEED and X-ray absorption spectroscopy (EXAFS) before and after interaction with a pressure of 2.5×10 −3 mbar of mercury vapours. Sorbed mercury was oxidised to Hg(II), as revealed by the chemical shift observed on the Hg 4f 7/2 levels. Since the adsorption of mercury is completely inhibited when the oxidation products of galena cover the surface, the formation of Hg–S bonding is most likely to occur. The amount of adsorbed mercury at saturation was estimated to be about one monolayer, i.e. one atom of mercury per surface atom of sulphur. A (1×1) structure was observed by RHEED for the longest exposures. The analysis of the EXAFS oscillations at the L III edge of mercury allowed an estimate of the Hg–S bond length of 2.62 A and a co-ordination number of 3. A model is proposed for the structure of the chemisorbed layer of mercury.