Bw. Reed et M. Sarikaya, Electronic properties of carbon nanotubes by transmission electron energy-loss spectroscopy - art. no. 195404, PHYS REV B, 6419(19), 2001, pp. 5404
We present electron energy-loss spectroscopy measurements on isolated singl
e-walled carbon nanotubes and their bundles performed in a scanning transmi
ssion-electron microscope, Spectra are obtained over a range of impact para
meters, from the centers of the samples to several nanometers outside the m
aterial. Curve-fitting techniques reveal five peaks in the range similar to
2-30 eV. These include surface and bulk plasmons and direct pi to pi* inter
band transitions. The energies, heights, and widths of these peaks are trac
ked throughout the data sets in order to determine their dependence on bund
le diameter and impact parameter. The heights of the externally excited sur
face mode peaks are compared to a model that varies exponentially with impa
ct parameter and by a power law with bundle diameter. The power-law exponen
t varies from similar to0.4 for the pi to pi* mode to similar to1.3 for the
pi+sigma bulk plasmon, with the surface plasmons close to 1. The peak heig
ht data suggest a sensitivity to density inhomogeneities in one of the bund
les and possibly to random variations in the chiral vectors among the singl
e tubes and small bundles. These patterns are further elucidated in the pea
k energy and width data.