Protonation and sonication effects on aggregation sensitive Raman features of single wall carbon nanotubes

The G-band and the G'-band (similar to 2600-2700 cm (1)) Raman spectra of single walled carbon nanotubes (SWCNTs) in a sodium dodecyl sulphate aqueous solution were investigated as a function of sonication energy density (rho). The relative intensity of the G-band feature around similar to 1520-1560 cm(-1) (G(-)) and the linewidth (Gamma) of the G'-band decrease monotonically with rho where the former dependence is probably due to charge transfer (promoted by sonication induced pH decrease/solubilisation) and consequently not an unambiguous indication of solubilisation. In contrast Gamma is shown to be independent of pH, which suggests that the linewidth of the G'-band may be an important indicator of the aggregation state of SWCNTs. (C) 2008 Elsevier Ltd. All rights reserved.