STM-mediated atom motion: a Co atom and mixed CoCu_n chains on a Cu(111) surface

摘要

Performing atomic scale simulations, we study the effect of the scanning tunneling microscopy tip on atom motion on a metal surface at zero bias voltage. We concentrate on a Co atom and mixed CoCun (n ≤ 8) chains on a Cu(111) surface. It is revealed that the atom motion can be tuned by adjusting the tip-substrate distance. The change in the potential landscape induced by the tip is found to depend on the tip height. In the presence of the tip, the Co atom can freely jump from the fcc site to the hcp site or vice versa when putting the tip above the adatom at a certain height. For the mixed CoCu_n chains on the Cu(111) surface, the diffusion barrier of the end Co atom from the fcc site to the nearby hcp site increases with the increasing chain length and reaches the limit when the chain length is beyond CoCu_7 without the tip. Especially, the short chains can perform a collective motion with the help of the tip. The importance of the relaxation induced by the tip-adatom interaction is demonstrated.