It was recalled that, in field ion microscopic experiments, the electric field gradient drove the diffusion of atoms at the surface. The same idea had been proved to apply to scanning tunnelling microscopic experiments (as when Cs atoms had been caused to move on a GaAs (110) surface by applying an electric field and taking advantage of the high Cs static dipole moment). It was demonstrated here that this effect was more general, and could even be used in systems that had a small dipole moment; such as surface Au adatoms on Au(111). Experiments were performed under ultra-high vacuum, using a clean surface and tip. By applying a voltage increase, and maintaining a constant tunnelling current, it was possible to produce protrusions (under the tip) that were several atoms in height; as well as smaller clusters which occupied large areas. A study was also made of the effect of the duration of the pulse, and of the voltage amplitude. It was noted that surface modifications were produced by an electric field of 2V/nm. It was suggested that the clusters were produced by an increase in the density of free adatoms in the high electric field region.

J.Méndez, J.Gómez-Herrero, J.I.Pascual, J.J.Sáenz, J.M.Soler, A.M.Baró: Journal of Vacuum Science and Technology A, 1996, 14[2], 1145-8