Dynamics and energetics of Si ad-dimers and Si ad-dimer clusters on Ge(001)

The early stages of silicon heteroepitaxial growth on Ge(100) have been studied with scanning tunneling microscopy. Four different Si ad-dimer configurations as well as metastable strings of ad-dimers on Ge(100) have been experimentally identified using dual bias imaging. The metastable strings are aligned along 〈130〉 directions and play an important role in binding of Si atoms and nucleation of Si islands. Various dynamic events, such as the collapse of metastable strings into islands and diffusion events of ad-dimers both along and across substrate dimer rows, have been observed.