The early stages of Si hetero-epitaxial growth on Ge(100) were studied by means of scanning tunnelling microscopy. Four different Si ad-dimer configurations, as well as metastable strings of ad-dimers, on Ge(100) were experimentally identified by using dual bias imaging. The metastable strings were aligned along <130> directions, and played an important role in binding Si atoms and in the nucleation of Si islands. Various dynamic events, such as the collapse of metastable strings into islands and the migration of ad-dimers both along and across substrate dimer rows, were observed.

W.Wulfhekel, B.J.Hattink, H.J.W.Zandvliet, G.Rosenfeld, B.Poelsema: Physical Review Letters, 1997, 79[13], 2494-7