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 measurements and SWCNT concentration the in sample solution. The increase of the detection depth and concentration of SWCNTs enhances the reabsorption effect and decreases 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 a 633 nm laser, the scattered light from RBM has stronger resonance with the interband transition of the SWCNTs than that from the G(+) band, leading to a faster reduction in the RBM intensity and a lower intensity ratio of RBM to the G(+) band. In contrast, when (8, 3) SWCNTs are excited with a 633 nm laser, reabsorption has the same effect on the RBM and G(+) band intensities and thus maintains a constant intensity ratio of RBM to the G(+) band. Furthermore, we precisely establish a quantitative relationship of the intensities of the Raman features such as RBM, the G(+) band and their intensity ratio as a function of the focal depth and SWCNT concentration by theoretical calculations and numerical simulation, which reproduces 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.