Atomic structure and formation mechanism of identically sized Au clusters grown on Si ( 111 ) - ( 7 × 7 ) surface

Identically sized Au clusters are grown on the Si ( 111 ) - ( 7 × 7 ) surface by room temperature deposition of Au atoms and subsequent annealing at low-temperature. The topographical images investigated by in situ scanning tunneling microscopy show a bias-dependent feature. The current-voltage properties measured by scanning tunneling spectroscopy indicate some semiconducting characteristics of the Au adsorbed surface, which is attributable to the saturation of Si dangling bonds. These experimental results, combined with the simulated scanning tunneling microscopy images and the first-principles adsorption energy calculations, show that the Au cluster is most likely to have a Au 6 Si 3 structure. In the Au 6 Si 3 cluster, three adsorbed Au atoms replace the three Si center adatoms, forming a hollow triangle, while the replaced Si atoms and other three Au atoms connect into a hexagon locating within the triangle. The formation mechanism of this atomic configuration is intimately associated with the complicated chemical valences of Au and the specific annealing conditions.