The adsorption and diffusion of a Si adatom on H-terminated Si(100) surfaces was analyzed by means of first-principles total-energy calculations. It was found that the adatom spontaneously substituted for a H atom upon adsorption. The resultant diffusing species on the surface was no longer a single atom, and the usual approach which was based upon a single potential energy surface was therefore invalid. The diffusion pathways of the adatom-H unit were instead traced here, while simultaneously examining the effect of H release and capture by the adatom. Extensive investigations of the 2 x 1 phase showed that the adatom released the H atom which was bonded to it, and captured another H atom as it migrated on the surface. In addition, the adatom penetrated into the surface; breaking a surface back-bond. This resulted in exchange of the adatom and a surface Si atom. These mechanisms of H release and capture, and of adatom exchange, were also expected to occur on other phases of H-terminated Si(100) surfaces.

Diffusion Mechanisms of a Si Adatom on H-Terminated Si(100) Surfaces S.Jeong, A.Oshiyama: Physical Review B, 1998, 58[19], 12958-63