Direct EELS observation of the oxidation states of Sm atoms in Sm@C_wn metallofullerenes (74( =)2n( =)84)

摘要

The oxidation states of Sm atoms in various fullerene cages are directly investigated by electron energy-loss spectroscopy. The observed peak positions of the M_(45) edges of the Sm atom in Sm@C_2n [2n=74,78,80,82 (isomers I, III), 84 (isomers I,II,III)] are apparemtly shifted to the lower binding energy region in comparison with those of a trivalent Sm~(3+) in Sm_2O_3. The results indicate that the Sm atoms take +2 valence states irrespective of the fullerene cages. This observation is discussed based on a simple thermochemical cycle model. We also report that the Sm metallofullerenes have been converted to Sm carbide materials under a prolonged electron beam irradiation.