Electromigration of single metal atoms observed by scanning tunneling microscopy

The authors show in this letter that single metal atoms on a Ni(111) surface can be pushed by electromigration forces from a scanning tunneling microscope tip. This repulsive interaction is observed over a length scale of 6 nm. While for voltages above -300 mV the atoms are pulled by the microscope tip, the atoms are pushed away below this threshold. This migration is explained by a resonant scattering of strongly correlated electrons. At small voltages chemical forces are pulling the atom, while for larger voltages the atomic manipulation is assisted by the tunneling current. (c) 2007 American Institute of Physics.