Possible mechanisms of atom transfer in scanning tunneling microscopy

Various mechanisms for the sudden transfer of an atom from or to the tip of a scanning tunneling microscope are considered. It is concluded that thermal desorption could be responsible and also that quasi-contact in which the adsorbed atom is in effect “touching” both surfaces, which would still be separated from each other by 2–4 Å, can lead to unactivated transfer via tunneling. For barrier widths as small as 0.5 Å, however, tunneling becomes negligible.