First-principles total-energy calculations were made of H adatom diffusion on a (100) 2 x 1 surface. The transition states for H diffusion pathways were established by mapping the potential energy for a H atom which was migrating between the dangling bonds of a (100) 2 x 1 surface, The latter was modelled by using embedded finite Si clusters. It was found that the diffusion barriers were high (2 to 3eV) and wide (0.3 to 0.4nm); thus suggesting that H diffusion on (100) occurred mainly via a classical hopping mechanism, rather than tunnelling. Moreover, the diffusion of H was predicted to be anisotropic, being preferentially directed parallel to Si-dimer rows; with an activation energy of 2.0eV. Higher activation energies (2.5 and 2.7eV) were predicted (for diffusion perpendicular to dimer rows) for the cases of hopping from one dangling bond to a neighboring dangling bond which was on the same dimer or on an adjacent dimer, respectively. The mechanism for H-atom diffusion along dimer rows was markedly different to that which had been proposed for Si adatom diffusion on (100). That is, H atoms were predicted to diffuse along the edges of the dimer rows, rather than down the middle.

C.J.Wu, E.A.Carter: Physical Review B, 1992, 46[8], 4651-8