Adatom diffusion and disordering at the Ge(111)-c(2×8)-(1×1) surface transition

We present an ab initio study of the diffusion of Ge adatoms and the disordering of Ge(111)-c(2×8) at ∼300°C. In the absence of adatom vacancies, we find that the most likely diffusion mechanism is an anisotropic correlated process in which several adatoms of a [11̄0] row hop concertedly along the same row. When surface vacancies are present, adatoms can instead hop one by one along [11̄0] in an uncorrelated way. Anisotropy arises from the special bonding topology of the c(2×8) structure. Calculated scanning tunneling microscopy images of the diffusion process show that adatom jumps are accompanied by an important electron backflow.