Density functional methods were used to study a recent non-contact atomic force microscopic experiment on the lateral manipulation of Sn and Ge adatoms on a Ge(111)-c(2x8) surface, with the aim of elucidating the atomistic details of the manipulation process. Two different processes were considered: a tip-assisted surface diffusion, and active tip participation in pair exchange via adatom pick-up/deposition processes. Unlike previous results, the calculated adatom diffusion profiles indicated that the diffusion was almost isotropic in both the [110] and [11¯2] directions; with fairly modest energy barriers of between 0.6 and 0.8eV. These barriers could be reduced by the action of the tip. Compression of a rest atom by the tip could completely delocalise the adatoms on the surface so that they moved in a barrier-less way. However, a diffusion-mediated exchange mechanism appeared to be precluded by a large barrier to (Sn, Ge) pair exchange which, in all cases, was larger than 1eV. This left open the possibility of another mechanism, in which tip-induced adatom pick-up/deposition entered into the exchange process.

Simulation of Lateral Manipulation with Dynamic AFM - Interchange of Sn and Ge Adatoms on Ge(111)-c(2x8) Surface. P.Dieska, I.Stich: Nanotechnology, 2007, 18[8], 084016 (6pp)