Formation and evolution of a self-organized hierarchy of Ge nanostructures on Si(111)-(7 × 7):STM observations and first-principles calculations

摘要

We report scanning-tunneling-microscopy observations and first-principles calculations for the formation and evolution of self-organized Ge nanostructures on Si(111)-(7 × 7) surfaces for Ge coverages up to 0.5 ML. We show that individual Ge atoms initially form a triangular lattice. At higher coverages, Ge nanoparticles 1 nm in diameter gradually form in both the faulted and unfaulted half unit cells with an initial preference in the faulted halves, ultimately driving ordered hexagonal arrays. The underlying 7 × 7 surface periodicity, the triangular single-Ge lattice, and the nanoparticle hexagonal superstructures coexist. Charge transfer from Si adatoms to Ge nanoparticles is shown to play a key role in the self-organization.