Electronic transitions and excitations in solid C70 studied by EELS and XPS C1s satellite structures

The electronic transition and excitation properties of highly ordered C70 films have been studied by reflection electron-energy-loss spectroscopy (EELS) and x-ray photoemission spectroscopy (XPS) C 1s satellite structures. The EELS study revealed a total of 11 features in the energy-loss range 1–40 eV. These include two tight-binding Frenkel excitonic levels in C70 fullerite, at 1.53 and 1.88 eV; the feature at 2.20 eV correlated with the onset of the electron transitions between the highest occupied molecular-orbital- and lowest occupied molecular-orbital-derived bands; a doublet at around 6 eV showing evidence of the π-plasmon splitting of fullerite C70. A broad hump at ∼28 eV corresponds to the excitation of the (σ+π) plasmon. The XPS C 1s satellite structures were found to be in overall agreement with the EELS results in the corresponding energy-loss range. By comparing the EELS data with the direct and inverse photoemission data, the on-site Coulomb correlation energy has been determined to be 1.2±0.2 eV for C70 fullerite.