LOCAL BONDING STRUCTURE OF SB ON SI(111) BY SURFACE EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE AND PHOTOEMISSION

The combined techniques of surface extended x-ray-absorption fine structure (SEXAFS) and high-resolution core and valence photoelectron spectroscopy have been used to study the local bonding structure of the Sb/Si(111) interface. From photoemission, we find that the Sb atoms adsorb in a unique environment that completely saturates the dangling bonds of the Si(111) surface and that completely eliminates the surface components of the Si 2p core-level spectrum. The Sb-induced Si 2p interfacial core level is found to be shifted 0.20 +/- 0.02 eV towards higher binding energy with an intensity that corresponds to the top monolayer of surface atoms. The SEXAFS determination of the absolute surface coordination numbers and bond lengths within the first Sb shell is 2.1 +/- 0.3 Sb atoms at 2.86 +/- 0.02 angstrom and 2.0 +/- 0.4 Si atoms at 2.66 +/- 0.03 angstrom. Combined, these results indicate that Sb trimers occupy the threefold atop sites of the Si(111) surface, where each Sb atom is bonded to two Si atoms in a modified bridge configuration.