Using scanning tunneling microscopy and first principles calculations, the adsorption sites of single Cu, Ag, and Au atoms on the $\mathrm{Si}(111)\mathrm{\text{−}}(7\times 7)$ surface have been systematically investigated and identified. Despite their monovalence, these atoms were found to adsorb at high coordination sites, seeking to saturate the maximum number of dangling bonds. The stable adsorption sites were further observed to be distinctly different in the faulted and unfaulted half unit cells, showing an asymmetry that has never been observed for many other adsorbates.

• Received 8 September 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.176104