Hydrogen chemisorption on Si(111)7×7 studied with surface-sensitive core-level spectroscopy and angle-resolved photoemission

Photoelectron spectroscopy of the Si 2p core level has been performed in order to determine surface core-level shifts for the Si(111)``7×{}1'':H and Si(111)7×{}7 surfaces, as well as to determine the Fermi-level position in the bulk band gap for the ``7×{}1'':H surface. Angle-resolved ultraviolet photoelectron spectroscopy has been used to determine the initial energy versus k-parallel dispersion for the surface state on the hydrogen-exposed surface. The results of these measurements imply that the monohydride phase is formed within the 7×{}7 unit cell after the hydrogen exposure. The core-level spectroscopy results obtained for the 7×{}7 surface are in good qualitative agreement with earlier results, but we suggest, in contradiction to a previous interpretation, that the surface component which shifted to lower binding energy corresponds to the rest atoms and not to the adatoms.