ATOMIC GEOMETRY OF THE PBS(100) SURFACE

The surface structure of PbS(100), in the form of the mineral galena, was studied with the X-ray standing wave technique using surface-sensi tive Auger electron yield detection and normal incidence geometry. We find that neither S nor Pb surface atoms are displaced from their resp ective bulk site positions. This lack of surface relaxation differs fr om the recent suggestion based on theory that a sizable contraction is needed to explain the experimentally observed lack of a surface core- level shift in Pb 5d photoemission data. To shed more light on this is sue, we have also measured high-resolution Pb 4f, Pb 5d, and S 2p phot oemission spectra for PbS(100) and confirmed that the surface core-lev el shifts are absent for cations as well as for anions. (C) 1998 Elsev ier Science B.V.