Hexagonal arrangement of Ge clusters self-organized on a template of half unit cells of Si(1 1 1)-7 × 7 observed by scanning tunneling microscopy

We observe initial nucleation of Ge clusters and their arrangement on Si(1 1 1)-7 × 7 by ultrahigh-vacuum scanning tunneling microscopy on an atomic scale; germanium amounts of sub-monolayer are slowly deposited at room temperature at a rate of 0.005 ML/min, and post-annealed. The clusters are arranged uncovering the corner holes and dimer rows of 7 × 7 structure, resulting in a regular hexagonal arrangement of Ge clusters with a periodicity of half unit cell of 7 × 7. This presents direct evidence of the self-organized hexagonal arrangement formed on a template of the 7 × 7 periodicity, which has been under debate between Yan et al. [Surf. Sci. 506 (2002) L255] and Ratto and Rosei [Discussion: Surf. Sci. 530 (2003) 221].