Narrow and intense resonances in the low-frequency region of surface-enhanced Raman spectra of single-wall carbon nanotubes

摘要

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 from undecorated arrays. The linewidths of the resonances (down to 0.3 cm"1) are ten 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.