The migration of anion and cation vacancies on the (110) surface was studied by means of scanning tunnelling microscopy. Marked asymmetries were found in the direction and bias-polarity dependence of the migration probability. This indicated the importance of the bonding topology at the surface. The asymmetry showed that vacancy motion was driven by the recombination of carriers, injected by the scanning tunnelling microscope tip, with carriers from the bulk. The impact-parameter dependence of the reaction cross-section showed that this injection occurred via resonant tunnelling into dangling-bond defect states.

G.Lengel, J.Harper, M.Weimer: Physical Review Letters, 1996, 76[25], 4725-8