The diffusion of Si dimers on the (001) surface, at temperatures of between ambient and 128C, was measured by using a novel atom-tracking technique that could resolve individual diffusion events by using lateral positioning feedback to lock the scanning tunnelling microscope probe into position above selected atoms to within a small fraction of a nanometre. When locked, the scanning tunnelling microscope tracked the atoms as they migrated over the crystal surface. By tracking individual atoms directly, the ability to measure dynamic events was increased by a factor of about 1000 with respect to conventional scanning tunnelling microscopic imaging techniques. The results could be described by an attempt frequency of about 1013/s and an activation energy of 0.94eV.

B.S.Swartzentruber: Physical Review Letters, 1996, 76[3], 459-62