First-principles study of Na atom transfer induced by the tip of a STM

We have explored the mechanism of atom manipulation by STM on the basis of a first-principles calculation. The systems in which a single Na atom is transferred between a tip and a surface are considered and the behavior of an interstitial atom subjected to strong field and current is examined, The electron density around the Na atom decreases near the positive electrode and shows an ionization tendency, which is consistent with the traditional view of field evaporation, On the other hand, the Na atom near the negative electrode shows polarized behavior. The effect of the bias voltage on the force acting on the Na atom reveals quite different features near the positively biased and the negatively biased surfaces.