Condensation of disilane or germane on a metallic surface: a photoemission study

Abstract

To shed some light on the problem of hydride adsorption on semiconducting surfaces, we have performed a photoemission study to compare gases like disilane (Si2H6) and germane (GeH4) in the condensed (or physisorbed) state (−150°C) with disilane and germane in the chemisorbed state (at room temperature). These molecules were condensed on a metallic substrate to minimize the charging effect resulting from the formation of insulating films. X-ray photoemission experiments revealed a shift of about 1.2 eV towards lower binding energies of the Si2s and Ge3d core-level peaks between the condensed state and the adsorbed state. In the chemisorbed state, the energy location of those peaks is the same as in the bulk material. We conclude that Si2H6 and GeH4 molecules are already chemisorbed on the surface at room temperature. We also found that such a “physisorbed state → chemisorbed state” transition could be induced at low temperature (−150°C) by a 2 keV Ar+ ion bombardment of the condensed film. These results are discussed in relation to our previously published conclusions on hydride adsorption on semiconducting surfaces.