An ab initio study was made of the diffusion of Ge adatoms, and of the disordering of Ge(111) c(2 x 8), at about 300 C. In the absence of adatom vacancies, it was found that the most likely diffusion mechanism was an anisotropic correlated process in which several adatoms of a [1¯10] row hopped concertedly along the same row. When surface vacancies were present, adatoms could instead hop one-by-one along [1¯10] in an uncorrelated manner. The anisotropy arose from the special bonding topology of the c(2 x 8) structure. Calculated scanning tunnelling microscopic images of the diffusion process showed that adatom jumps were accompanied by a large electron back-flow.

N.Takeuchi, A.Selloni, E.Tosatti: Physical Review B, 1994, 49[15], 10757-60