The migration of Si adatoms over the flat reconstructed (001) surface was studied by using molecular dynamics techniques and the empirical Stillinger-Weber potential. The potential-energy surface which was seen by a single adatom over the surface was mapped out. The binding of an adatom to the (001) surface was found to be quite strong. Its value of 3.0eV made up a sizable fraction of the energy of a bulk Si atom (4.33eV). In agreement with previous studies, it was found that the diffusion of single adatoms over the surface was anisotropic; with the fast diffusion direction lying along the dimer rows. Direct measurement of a diffusion coefficient was carried out by studying the motion of individual adatoms over periods of 300ps. The motion of individual adatoms conformed quite well to the underlying energy surface. However, frequent exchange events between adatoms and atoms near to the surface were observed. These furnished an additional contribution to the rate of diffusion. In addition, the potential energy surfaces which were seen by a Si adatom over (001) surfaces that were under compressive and tensile strains were mapped out. Here, the binding was found to increase or decrease depending upon whether the surface was compressed or expanded. Little change was observed in the anisotropy of the diffusion constant. A study was also made of diffusion over a (001) surface in which the compression was either along, or perpendicular to, the dimer axis. Compression of the surface perpendicular to the dimer axis decreased the diffusional anisotropy, while compression of the surface parallel to the dimer axis increased the diffusional anisotropy.

C.Roland, G.H.Gilmer: Physical Review B, 1992, 46[20], 13428-36