Quantitative Analysis of the Effect of Reabsorption on the Raman Spectroscopy of Distinct (n, m) Carbon Nanotubes

We quantitatively analyze the effect of reabsorption on the Raman spectroscopy of (10, 3) and (8, 3) single-chirality single-wall carbon nanotube (SWCNT) solutions by varying the detection depth in confocal micro-Raman measurement and SWCNT concentration in sample solution. The increase of detection depth and concentration of SWCNTs enhance the reabsorption effect and decrease the intensities of the Raman features. More importantly, reabsorption exhibits different effects on different Raman features such as the radial breathing mode (RBM) and G+ band, strongly depending on the resonance degree of the scattered light energy and the interband transition of SWCNTs. When (10, 3) SWCNTs are excited with 633 nm, the scattered light from RBM has stronger resonance with the interband transition of the SWCNTs than that from G+ band, leading to a faster reduction in RBM intensity and a lower intensity ratio of RBM to G+ band. In contrast, when (8, 3) SWCNTs are excited with 633 nm, reabsorption has same effect on the RBM and G+ band intensities and thus maintains a constant intensity ratio of RBM to G+ band. Furthermore, we precisely establish a quantitative relationship of the intensities for the Raman features such as RBM, G+ band and their intensity ratio as a function of the focal depth and SWCNT concentration by theoretical calculation and numerical simulation, which reproduce the experimental results well. These results are very useful in the precise analysis of the Raman spectroscopy of SWCNTs and thus their applications in molecular detection and imaging.