Abstract
Previously unexplored low-frequency Raman modes of single wall carbon nanotubes (SWNTs) are reported. Gold deposited onto a randomly oriented top layer of vertically aligned carbon nanotube arrays was used to induce surface enhanced Raman scattering (SERS) 'hot spots' on large-diameter SWNTs with SERS intensities up to 1900 times greater than normal Raman intensities. The linewidths of the resonances (down to 0.3 cm-1) are 10 times narrower than previously measured for individual SWNTs. Pairs of intense sharp resonances with identical excitation profiles were found and tentatively interpreted as the low-energy longitudinal optical and radial breathing modes of the same nanotube. SERS lines in the region of 14-30 cm-1 were tentatively assigned to the ring modes of SWNTs in agreement with existing theories
