Roles of STM tip and external electric field in the single atom manipulation on Si(111)-7x7 surface

The roles of STM tungsten tip and external static electric field in single corner silicon adatom extracting from Si(111)-7 x 7 surface are studied usi ng discrete variational-local density functional (DV-LDF) method with duste r models. The binding energy and the different charge density distribution of the system are calculated under various conditions. The results show tha t, the activation barrier decreasing is a chemical effect due to the proxim ity of th eletrodes. The effect of external electric field depends on its p olarity. A monotonous decrease in the activation barrier is seen for positi ve bias case, while a small increasing is seen for negative bias case. The single corner silicon adatom cannot transfer from the sample surface if onl y considering the role of the static interaction among the tip, external el ectric field and sample surface. The mechanisms of atomic population on sem iconductor surfaces are discussed.