Electronic transitions and excitations in solid C70 studied by reflection electron energy loss spectroscopy

摘要

The electronic transition and excitation properties of highly ordered C70 films have been studied by reflection electron energy loss spectroscopy (EELS). The EELS study revealed a total of eleven features in the energy loss range 1–40 eV. These include a prominent peak at 2.55 eV revealing the first dipole allowed transition across the band gap in C70 fullerite; a feature at 2.20 eV correlated with the electron transition between the highest-occupied-molecular-orbital- and lowest-unoccupied-molecular-orbital-derived bands; two excitonic levels corresponding to a tight-binding Frenkel exciton in C70 fullerite at 1.53 and 1.88 eV; and a doublet at 5.2 and 5.9 eV showing evidence of the π-plasmon splitting in fullerite C70. A broad hump at ~28 eV corresponds to the excitation of the (σ+π) plasmon.