Manipulation/Extraction of an Adatom from a Mound

We present results of manipulation/extraction of Ag/Cu atoms from small Ag/Cu mounds on Ag(111)/Cu(111), rescpectively. Molecular dynamics (MD) and molecular static (MS) simulations were carried out using interaction potentials from the embedded atom method. Evaluation of the energy landscape in the absence of tip shows that for a Ag atom, lateral (sliding downwards) and vertical (climbing upwards) diffusion,the activation barrier is about 0.3 eV. We show that the presence of a Ag tip lowers the energy barrier for both lateral and vertical diffusion. We find that the optimum position of the tip to achieve extraction is when the tip is at the edge of the mound in front of the adatom, and at a height of 2.43 {\AA} from the Ag adatom, for which the barriers for diffusion drop to 0.032 eV for lateral and 0.182 eV for vertical diffusion. In this case, the adatom is manipulated in the pulling mode. In the case of Cu, we found that the adatom manipulation/extraction is performed in the sliding/dragging mode.