Diameter dependence of the Raman D-band in isolated single-wall carbon nanotubes

Raman D-band spectra are reported for several different SWNTs using two different laser energies ( Elaser 51.58 and 2.41 eV!. At a fixedElaser , individual isolated SWNTs exhibit different diameter-dependent D-band frequencies v D around an average value. For both semiconducting and metallic tubes, v D decreases with decreasing nanotube diameter, though v D for isolated metallic SWNTs is higher than for isolated semiconducting SWNTs. The average D-band frequency depends linearly on Elaser , as previously observed for SWNT bundles, suggesting that the D-band in SWNTs is activated by defects or by the finite size of the SWNTs.