Charging and interaction of individual impurities in a monolayer organic crystal

We use a scanning tunneling microscope to study the charging of Ag-doping centers in a monolayer of C-60 molecules supported on a thin Al2O3 film grown on the NiAl(110) surface. Differential conductance spectroscopy shows that charging affects the conduction through C-60 molecules located around the doping centers. This effect is used to observe the electrostatic interaction of a pair of centers. Charging of one doping center affects the energy levels of the other, an analogue of the field-effect action.