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

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Abstract
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 [11¯0] row hop concertedly along the same row. When surface vacancies are present, adatoms can instead hop one by one along [11¯0] 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.