DISSOCIATIVE ADSORPTION OF O-2 AND H2O ON SI(113) - CHEMICAL-SHIFTS OF THE SI 2P LEVEL

Using high-resolution Si 2p surface core-level spectroscopy, dissociat ive adsorption of O-2 and H2O was studied on the Si(113)-(3 x 2) surfa ce. Dissociation of O-2 gives rise to the known chemically shifted Si 2p components of Si1+ (-930 meV, shifted the larger binding energy), S i2+ (-1760 meV), Si3+ (-2510 meV), and Si4+ (-3500 meV). The relative abundance of the Si2+ component lies between those for the Si(001) and Si(111) surfaces. Following dissociative adsorption of H2O, H-derived (at -220meV) and OH-derived (at -900 meV) surface core-level shifts w ere observed. The dissociative adsorption is found to be similar td th at on Si(001), lending support to the recent structure model of the Si (113) surface which assumes Si dimers as constituents at the surface. Anneaing to higher temperatures leads to a decomposition of the OH gro up into H and O which desorb sequentially at higher temperatures. 5-10 % of the H2O saturation dose leads to quenching of the Si(113)-(3 x 2) surface states and to a pinning of the Fermi level at 730 meV above t he valence-band maximum.