Electron Energy-Loss Spectra of Carbon Nanotubes

Carbon nanotubes were investigated by means of electron energy-loss spectroscopy. Two peaks due to the π plasmon and the π+σ plasmon were observed. The energy of the π+σ plasmon peaks varied from 22.0 eV to 24.5 eV, which roughly agrees with the average plasmon energy of graphite. A shoulder due to single electron excitations was observed at 13 eV, which was not observed in graphite. There were two kinds of nanotubes which exhibited their respective π plasmon peaks at 5.2 eV and 6.4 eV. The peaks in the dielectric function obtained by Kramers-Kronig analysis of the spectra were broader than those of graphite probably due to the curving of the graphitic sheets.