Formation and decay of metastable Ge clusters on Ge(001)

The initial stages of room temperature homoepitaxial growth of Ge(001) have been studied with scanning tunneling microscopy. The smallest entities obs erved after deposition are dimers. Several different adsorption sites for t he dimers have been identified. We have observed three different diffusion pathways for these adsorbed dimers at room temperature: two along and one a cross the substrate dimer rows. As well as the isolated dimers. metastable dimer clusters and epitaxial islands are observed. The metastable dimer clu sters always consist of chains of trough dimers oriented along a [130] dire ction and have a profound influence on the buckling registry of the Ge(001) substrate. At room temperature the metastable dimer clusters show limited mobility. By stz itching a terminating (tail) or middle (body) dimer betwee n equivalent positions the cluster can change its shape. The metastable dim er clusters eventually convert to epitaxial islands. Based on the experimen tal observations, a pathway for this conversion process is proposed.