A scanning tunnelling microscopy method for studying surface diffusion was based upon measurements of the displacement distribution of adsorbates via so-called image-anneal-image cycles. This permitted direct observation of the diffusion process, while avoiding potential scanning tunnelling microscope tip effects. The method was used to study the anisotropic diffusion of Sb dimers on Si(001). The energy barrier (1.2eV) and the prefactor (0.0001cm2/s) for the faster diffusion across the substrate dimer rows were measured. It was noted that the diffusion which was observed by using the so-called image-while-hot method appeared to be almost isotropic, and much faster. It was shown that this discrepancy was due to an influence of the tip, which interfered in the latter method.

Direct Determination of Surface Diffusion by Displacement Distribution Measurement with Scanning Tunneling Microscopy. Y.W.Mo: Physical Review Letters, 1993, 71[18], 2923-6