The perimeter of oxide-supported metal particles is suggested to be of pivotal importance for various catalytic processes. To elucidate the underlying effects, the electronic properties of edge and corner atoms of planar Au clusters on MgO/Ag(001) thin films have been analyzed with scanning tunneling microscopy and electronic structure calculations. The low-coordinated perimeter atoms are characterized by a high density of $s$-derived states at the Fermi level. Those states accommodate transfer electrons from the MgO/Ag substrate, which render the perimeter atoms negatively charged. In contrast, the inner atoms of the island are not affected by the charge transfer and remain neutral. This combination of charge accumulation and high state-density explains the specific relevance of the cluster perimeter in adsorption and reaction processes.

• Received 16 February 2010

DOI:https://doi.org/10.1103/PhysRevB.81.153406