Photoemission study of electronic structures of fullerene and metallofullerene peapods

We have investigated the electronic structures of single-wall carbon nanotubes (SWCNTs) encapsulating C₇₀ fullerene and metallofullerenes M@C₈₂ (M = La, Gd, Dy), C₇₀ peapods (C₇₀@SWCNT) and metallofullerene peapods (M@C₈₂@SWCNT), using photoemission spectroscopy. The photoemission spectra of C₇₀ and M@C₈₂ peas are obtained by subtracting the spectrum of pristine SWCNTs from those of the corresponding peapods. The electronic structure of the C₇₀ peas is similar to that of the C₇₀ film. For the M@C₈₂ peapods, on the other hand, the electronic structures of the M@C₈₂ peas are different. For the La@C₈₂ peapods, the singly occupied molecular orbital (SOMO) for the La@C₈₂ peas is located nearer to the Fermi level when compared with that in the La@C₈₂ film. For the Dy@C ₈₂ peapods, the effective Dy valence is estimated to be +2.9. This result demonstrates that effective charges move back from the C₈₂ cage to Dy following encapsulation of Dy@C₈₂ peas in the SWCNTs because of the strong hybridization interaction between Dy 4f and C 2p electrons, taking into account the Dy valence of +3 in the Dy@C₈₂ film.