We have measured the valence-band photoemission and inverse photoemission spectra of single-walled carbon nanotubes (SWNTs) with mean radii of 0.7 and $0.64\mathrm{nm}$ 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 $\left(E_{\mathrm{F}}\right)$ 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 $E_{\mathrm{F}}$.

• Received 11 September 2005

DOI:https://doi.org/10.1103/PhysRevB.73.075406