Electronic excitation spectrum of calcium-doped picene: Electron energy-loss spectroscopy study

摘要

The electronic excitations of Ca-doped picene films have been investigated using electron energy-loss spectroscopy in transmission. We demonstrate that a composition of Ca_3picene can be achieved by evaporation of Ca onto pristine picene films under ultrahigh vacuum conditions. The core level excitations indicate a charge transfer of one electron per added Ca to the picene molecules and a hybridization of Ca and picene derived electronic states. Upon doping a new spectral feature is observed at about 2 eV in the electronic excitation spectrum. This new feature does not disperse which signals its localized character. The data analysis using a Kramers-Kronig transformation suggests that Ca_3picene has a nonmetallic ground state.