New tetramer structures in the initial process of Si homoepitaxial growth on Si (0Â 0Â 1)

We have studied the interaction between Si ad-dimers in the initial process of Si homoepitaxial growth on Si (0 0 1) surface by molecular dynamics simulations using the Stillinger-Weber potential. The interactions determine the formation of larger clusters from diffusing dimers. We show different pathways for the formation of multiple-dimer clusters and propose two new tetramer structures (TBB and TCC) formation by two diffusing dimers interacting. These tetramer structures have been found to be energetically stable with respect to isolated ad-dimers. Moreover, their local bonding configuration is very similar to the B-type step edge which is known to be the favored adsorption site for epitaxial growth. The proposed tetramers may play a crucial role as the nucleus of the new epitaxial layer on Si (0 0 1).