Photoemission and inverse photoemission study of the electronic structure ofC60fullerenes encapsulated in single-walled carbon nanotubes

Abstract

We have measured the valence-band photoemission and inverse photoemission spectra of single-walled carbon nanotubes (SWNTs) with mean radii of 0.7 and $0.64\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ encapsulating ${\mathrm{C}}_{60}$ fullerenes (peas), so-called ``peapods.'' The photoemission spectrum of the ${\mathrm{C}}_{60}$ peas in the SWNTs is obtained by subtracting the spectrum of empty SWNTs from the spectrum of the peapod. The structures in the ${\mathrm{C}}_{60}$ pea spectra correspond well to those in the spectrum of a ${\mathrm{C}}_{60}$ face-centered-cubic solid. No structure is observed at binding energies ranging from the Fermi level $({E}_{\mathrm{F}})$ to the onset of the highest occupied molecular orbital (HOMO) peak; the ${t}_{1\mathrm{u}}$ level of the ${\mathrm{C}}_{60}$ peas inside the SWNT stays above ${E}_{\mathrm{F}}$.