Adatom migrations and nucleations on reconstructed (001) surfaces I. Si

Single Si adatom migration and the initial stage of epitaxial growth on (2 × 1) reconstructed Si(001) surfaces were investigated by an ab initio method using density functional theory. The obtained results are as follows: (a) the most stable binding site of a single Si adatom is different from the position that is required by epitaxial growth; (b) two Si adatoms interacting in order to produce a dimer take just the positions required for epitaxial growth. We conclude that the extreme stability of the Si dimer compared to other structures generated from two Si adatoms interacting on Si(001) surfaces is the origin of the formation of the perpendicular dimer rows alternately layer by layer on the reconstructed Si(001) surface in the process of epitaxial growth.