Determination of the Sb/Si(111) interfacial structure by back-reflection x-ray standing waves and surface extended x-ray-absorption fine structure

Based on the surface extended x-ray-absorption fine-structure (SEXAFS) {ital absolute} surface coordination numbers, Woicik {ital et} {ital al}. (Phys. Rev. B 43, 4331 (1991)) argued that Sb trimers adsorb on the Si(111) surface in a modified bridge'' configuration rotated by 60{degree} relative to the atop milk stool'' geometry proposed by Abukawa {ital et} {ital al}. (Surf. Sci. Lett. 201, 513 (1988)). Using the accurate near-neighbor bond lengths as determined from SEXAFS, these models predict perpendicular distances of 1.76 and 2.60 A between the top Si atoms and the Sb layer, respectively. New back-reflection x-ray standing wave data find the Sb atoms to reside 2.53{plus minus}0.1 A above the Si surface, in clear support of the milk stool geometry. Polarization-dependent SEXAFS {ital relative} coordination numbers support the milk stool model as well.