Observations of the D-band feature in the Raman spectra of carbon nanotubes

We examine the behavior of the D-band feature in the Raman spectra of single-walled carbon nanotube (SWNT) bundles, observed between 1250 and 1450 cm{sup -1}, as a function of the laser excitation energy. We used three SWNT samples with different diameters, and show that the D-band behavior of SWNTs differs from sp{sup 2} carbons, depending on whether the SWNTs are metallic or semiconducting, and shows a frequency {omega}{sub D} that is dependent on nanotube diameter.