  Single-walled carbon nanotubes (SWNTs) with varying degrees of disorder were
investigated using multiple-excitation Raman spectroscopy. The lattice disorder
was imparted into the nanotubes by the addition of varying amounts of sulfur to
the iron catalyst in a thermal chemical vapor deposition process. Changes in
the intensities of peaks occurring due to a double resonance Raman process were
studied. The intensity of the disorder-induced D band increased with a decrease
in the sulfur content. Upon post-synthesis heat treatment, the double resonance
process got quenched due to defect healing. The second order G' band and iTOLA
bands exhibited a two-peak structure, of which one of the peaks is relatively
more sensitive to defects and decreased in intensity with heat treatment.
