Diffusion of chlorine atoms on Si(111)-(7x7) surface enhanced by electron injection from scanning tunneling microscope tips

We found that electron injection from the probe tips of scanning tunneling microscopes enhances the diffusion and desorption of Cl atoms on a Si(111)-(7 x 7) surface, featured by a significant peak at a sample bias of similar to +4 V for the diffusion, the linear dependence on the injected current, the spatial spread of the effect laterally over a range of similar to 10 nm from the tip position without extending beyond the step edges. The local density of states spectrum in the chlorinated Si surface experimentally measured by scanning tunneling spectroscopy exhibits a peak of Cl origin at +4.1 eV which coincides with the peak in the bias dependence. These facts are well interpreted by the model that electrons primarily injected to empty surface bands propagate until they are resonantly localized at Si-Cl anti-bonding states, which then leads to destabilization or weakening of the bonds resulting in Cl atom diffusion. (C) 2001 Elsevier Science B.V. All rights reserved.