Self-organized two-dimensional lattice of magic clusters

Under certain deposition conditions, gallium induces almost exclusive formation of a type of especially stable clusters—magic clusters, on the 7×7-reconstructed silicon(111) surface. The cluster has a triangular closed-shell structure and resides on the center of a 7×7 half unit-cell. As the gallium coverage is increased, the cluster density increases proportionally, leading essentially to the complete filling of the 7×7 half unit-cells and the creation of an unprecedented two-dimensional lattice of magic clusters. A structure model employing three silicon atoms to link six gallium atoms into a configuration with satisfied bonding is proposed to qualitatively account for the cluster’s stability.