Electromigration at atomic-scale metal nanojunctions driven by "lucky electrons"

We have performed electrical break junction experiments on gold nanocontacts. When the nanocontacts are in the diffusive transport regime, we find that the number of atoms removed by Joule heating is rather small (less than 15%) and that the majority of atoms are removed at voltages determined by the surface self-diffusion potentials of gold. We propose a model in which a small fraction of electrons ("lucky electrons") traverse the constricted region ballistically and transfer their kinetic energy to metal atoms and remove them. Electromigration experiments on other metal species of high melting temperatures (Ni, Pd) strongly support this interpretation.