Photoemission and inverse photoemission study of the electronic structure of C60 fullerenes encapsulated in single-walled carbon nanotubes

We have measured the valence-band photoemission and inverse photoemission spectra of single-walled carbon nanotubes (SWNTs) with mean radii of 0.7 and 0.64 nm encapsulating C60 fullerenes (peas), so-called "peapods." The photoemission spectrum of the C60 peas in the SWNTs is obtained by subtracting the spectrum of empty SWNTs from the spectrum of the peapod. The structures in the C60 pea spectra correspond well to those in the spectrum of a C60 face-centered-cubic solid. No structure is observed at binding energies ranging from the Fermi level (EF) to the onset of the highest occupied molecular orbital (HOMO) peak; the t1u level of the C60 peas inside the SWNT stays above EF