QUANTUM ATOM SWITCH - TUNNELING OF XE ATOMS

Recently Eigler, Lutz, and Rudge [Nature 352, 600 (1991)] have reported a bistable switch that derives its function from the motion of a single Xe atom. It has been shown that this atom can be transferred, in a reversible way, from a scanning-tunneling-microscope tip to a sample by means of a voltage pulse. In this paper we show that the atom transfer process can be understood in terms of a single-atom-tunneling process, while a mechanism similar to the heating-assisted electromigration cannot account for the experimental observations. We find that there is a nonzero probability of atom transfer even at zero applied voltage, i.e., the transfer rate cannot follow a power-law dependence with the applied pulse at small voltages. We present a tunneling model, based on the charge transfer from the metal to the 6s resonance of the Xe atoms, which is consistent with the available experimental data.