Length-dependent Raman spectroscopy of single-walled carbon nanotubes:   the effect of dispersant on defects
  We compare Raman spectra from aqueous suspensions of length-separated single-walled carbon nanotubes (SWCNTs) dispersed using either polymer adsorption of single-stranded DNA or miscelle encapsulation with sodium deoxycholate surfactant. The Raman spectral features, other than the D-band, increase monotonically with nanotube length in both dispersion schemes. The intensity ratio of the disorder-induced D to G' Raman bands decays as a function of SWCNT length, proportional to 1/L, as expected for endcap defects. While the UV-vis absorption and fluorescence also increase with length for both dispersants, the fluorescence intensity is dramatically lower for DNA-wrapped SWCNTs of equal length. The similarities in the length-dependent D/G' ratios exclude defects as an explanation for the fluorescence decrease in DNA versus deoxycholate dispersions. 
J. R. Simpson, J. A. Fagan, M. L. Becker, E. K. Hobbie, and A. R.   Hight Walker