We report on the formation of equilateral triangular clusters hollow inside with 5–6 atoms per side, self-assembled on Ni adislands grown on Rh(111). The observation of standing wave patterns on the Ni adislands and the Rh(111) indicates that the self-assembly is mediated by Friedel oscillations. In this context, we propose a model based on the energy of interaction between adsorbates, which explains the formation of the clusters as a result of the assembly of rows of 5–6 adatoms.

• Received 30 May 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.165701