The influence of a static scanning tunneling microscope tip on the diffusion of xenon atoms adsorbed on a Cu(110) stepped surface was studied. Semi-empirical potentials for the Xe–surface interaction and a N-body energy based method for the Xe–tip contribution were used to calculate the adsorption energy of adsorbates in the scanning tunnelling microscope junction. Firstly, the variation of this energy was analyzed when the adatom was placed near to a step edge and for different tip positions. When the tip was situated in the neighbourhood of the step edge, the Ehrlich–Schwoebel barrier experienced by the adatom was lowered. This opens a specific diffusion channel, allowing a possible crossing of the step edge. Second, through a kinetic Monte Carlo approach coupled to the elastic scattering quantum chemistry method, the noisy tunneling current created by the random motion of diffusing atoms in the vicinity of the tip could be analyzed. It was shown that, by counting the number of diffusion events, it was possible to determine effective barriers that were related to the most dominant processes contributing to the diffusion at a particular temperature. It was also demonstrated that the interaction mode of the tip (attractive or imaging) greatly modified the diffusion processes.

Atomic Diffusion inside a STM Junction - Simulations by Kinetic Monte Carlo Coupled to Tunnelling Current Calculations. S.Baud, X.Bouju, C.Ramseyer, H.Tang: Surface Science, 2003, 523[3], 267-78