Doping dependence of C$_{60}$ monolayers studied by scanning tunneling microscopy

The electronic properties of C$_{60}$ compounds can be tuned by charge-doping them with alkali impurities. This results in an interplay between molecular charge transfer, Coulomb repulsion, phonon coupling, and nearest neighbor interactions. Here we present a scanning tunneling microscopy/spectroscopy study of K doped C$_{60}$ monolayers on Au(111). We find that the morphology and electronic structure of C$_{60}$ monolayers change significantly with doping level. In addition to LUMO/LUMO+1 shifts, we observe strong variations in the low-energy local density of states.