Relative intensities of resonant Raman spectral features, specifically the radial breathing mode (RBM) and G modes, of eleven, chirality-enriched, single-wall carbon nanotube (SWCNT) species were established under second-order optical transition excitation. The results demonstrate an under-recognized complexity in the evaluation of Raman spectra for the assignment of (n,m) population distributions in agreement with theory predicted by a symmetry-adapted nonorthogonal tight-binding model.[1] Strong chiral angle and mod dependencies affect the intensity ratio of the RBM to G modes.  Furthermore, we report five additional values for chirality dependent G⁺ and G^- Raman peak positions and intensity ratios extending the available data to cover more of the smaller diameter regime by including the first (5,4) second-order, resonance Raman spectra.[2] Together, the Raman spectral library is demonstrated to be sufficient for decoupling multiple species viaa spectral fitting process, and enables fundamental characterization even in mixed chiral population samples.  

References:

[1] Popov, V. N.; Henrard, L.; Lambin, P. Resonant Raman Intensity of the Radial Breathing Mode of Single-Walled Carbon Nanotubes within a Nonorthogonal Tight-Binding Model. Nano Lett. 2004, 4, 1795–1799.

[2] Telg, H.; Duque, J. G.; Staiger, M.; Tu, X.; Hennrich, F.; Kappes, M. M.; Zheng, M.; Maultzsch, J.; Thomsen, C.; Doorn, S. K. Chiral Index Dependence of the G+ and G– Raman Modes in Semiconducting Carbon Nanotubes. ACS Nano 2012, 6, 904–911.