Charging single atoms

Individual gold atoms on an ultrathin insulating sodium chloride film supported by a copper surface exhibit two different charge states, which are stabilized by the large ionic polarizability of the film. The charge state and associated physical and chemical properties such as diffusion and electron scattering can be controlled by adding or removing a single electron to or from the adatom with a scanning tunneling microscope tip.
The simple physical mechanism behind the charge bistability in this case suggests that this is a common phenomenon for adsorbates on polar insulating films.

The STM image shows a charged and an uncharged Au-atom on a NaCl-covered Cu(111).

J. Repp, G. Meyer, F. E. Olsson, M. Persson, Controlling the Charge State of Individual Gold Adatoms, Science 305 (2004), 493.