STRUCTURE OF THE SI(111) SQUARE-ROOT-OF-3 X SQUARE-ROOT-OF-3-SB INTERFACE BY SURFACE X-RAY ABSORPTION FINE-STRUCTURE AND PHOTOEMISSION

The combined techniques of surface extended x-ray absorption fine structure (SEXAFS) and high resolution core level photoelectron spectroscopy have been used to investigate the local bonding structure of the Sb/Si(111) interface. We find that the adsorption of 1 monolayer (ML) of Sb completely eliminates the surface components of the Si 2p core level spectrum. The Sb induced Si 2p interfacial core level has been found to be shifted 0.20 +/- 0.02 eV toward higher binding energy with an intensity that corresponds to the top 1 ML 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. Together, these results indicate that Sb trimers occupy the three fold atop sites of the Si(111) surface where each Sb atom is bonded to two Si atoms in a modified bridge configuration.