Tuning the charge state of a C60 single layer on Ag(1 0 0) by Na deposition

Core level and valence band photoemission spectroscopies show that for an ordered single layer of C60 chemisorbed on a clean Ag(1 0 0) surface metallic phases are formed at any Na doping level, following a rigid band filling behaviour, until the conduction band is completely filled with 6 electrons/molecule. These observations, that contrast with the bulk phases behaviour, can be explained with an efficient screening of the Hubbard energy U in the C60 bands due to the close proximity to a metallic surface and highlight the important role of electron correlation in the electronic properties of these systems.