Diffusion of atoms on Au(111) by the electric field gradient in scanning tunneling microscopy

Abstract

It has been shown in field ion microscopy experiments that the electric field gradient drives the diffusion of atoms on a surface. The same idea has been proved to work in a scanning tunneling microscopy experiment, as was first demonstrated when Cs atoms were induced to move on GaAs(110) by the electric field, taking advantage of the high Cs static dipole moment. In this work we demonstrate that this effect is more general and can be used even in systems that have a small dipole moment, such as the surface Au adatoms of Au(111). The experiment is performed in ultrahigh vacuum with a clean surface and tip. By applying a voltage increase and maintaining constant the tunneling current we are able to produce protrusions under the tip of several atom-heights and smaller clusters occupying large areas. We study the influence of the time duration of the pulse and the voltage amplitude. Surface modifications are already produced at 0.2 V/Å electric field value. We suggest that the clusters are produced by an increase of the density of free adatoms in the high electric field region.