One-dimensional ordering of Ge nanoclusters along atomically straight steps of Si(111)

Ge nanostructures grown by molecular beam epitaxy on a vicinal Si(111) surface with atomically well-defined steps are studied by means of scanning tunneling microscopy and spectroscopy. When the substrate temperature during deposition is around 250 °C, Ge nanoclusters of diameters less than 2.0 nm form a one-dimensional array of the periodicity 2.7 nm along each step. This self-organization is due to preferential nucleation of Ge on the unfaulted 7×7 half-unit cells at the upper step edges. Scanning tunneling spectroscopy reveals localized electronic states of the nanoclusters.