Electronic structure of K doped C60 monolayers on Ag(001)

The doping of a C60/Ag(100) interface with K is studied by high resolution valence band photoemission spectroscopy. With increasing potassium exposure the progressive filling of the C60 lowest unoccupied molecular orbital (LUMO) derived band is observed. The charge transfer onto the C60 molecules is quantified from the observed binding energies of the LUMO derived band. Up to a half filled LUMO no rigid band shift is found. Furthermore the intensity of the highest occupied molecular orbital is not constant but shows in normal emission a pronounced dip between half and complete LUMO filling.