Clustering of Au on the faulted half of the Si(111)-7 X 7 unit cell

We present a structure for Au deposited on the Si(111)-7 X 7 surface at very low coverage obtained by x-ray diffraction. We have found Au adsorbed exclusively on the faulted side of the Si(111)-7 X 7 unit cell. The Au atoms are found to reside in sites which lie above the Si and do not cause significant rearrangement of the covalent bonding network of the substrate, suggesting they are weakly bound. The sites have considerable disorder and can be modeled by a strongly anisotropic Debye-Waller factor. From this we extract the potential for interaction of Au with Si(111) 7 X 7, which is in reasonable agreement with theoretical predictions for Si and other species on Si(111) 7 X 7.