Doping of C60 (sub)monolayers by Fermi-level pinning induced electron transfer

Fermi-level pinning of C-60 (sub)-monolayers on a sexithiophene (6T) bilayer grown on Ag(111) is shown to induce electron transfer from the metal to a fraction of the C-60 molecules. The electrostatic potential resulting from the charge transfer process is responsible for a potential drop within the 6T interlayer and, more remarkably, for dipole-dipole repulsion, leading to a disproportionation into coexisting neutral and charged C-60 molecules. We suggest that charge ordering phenomena may occur for such systems.