Length-dependent Raman spectroscopy of single-walled carbon nanotubes: the effect of dispersant on defects

TL;DR

This study compares Raman spectra of length-separated single-walled carbon nanotubes dispersed by DNA or surfactant, revealing length-dependent defect signatures and fluorescence differences unrelated to defects.

Contribution

It demonstrates that the dispersant type influences fluorescence without affecting defect-related Raman features, clarifying the role of dispersants in nanotube spectroscopy.

Findings

Raman D/G' ratio scales as 1/L, indicating endcap defects.

Fluorescence is lower in DNA-dispersed SWCNTs of equal length.

Defect levels are similar across dispersants, suggesting other factors affect fluorescence.

Abstract

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.