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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.

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We have developed a high energy resolution electron energy-loss spectroscopy (EELS) microscope, which can take spectra from specified small specimen areas and specified small reciprocal space areas to investigate detailed electronic structures. The EELS microscope is equipped with retarding Wien filters as the monochromator and the analyser. The filters are designed to achieve a stigmatic focus. The energy resolutions are 12 meV and 25 meV for cases without and with a specimen, respectively. Spatial and momentum resolutions are 30-110 nm in diameter and 1.1 nm-1 in angular diameter, respectively. EELS spectra are presented to show the performance of this instrument.

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