Quantifying carbon-nanotube species with resonance Raman scattering

The method for quantifying the amount of each carbon nanotube specie, as defined by its diameter and chiral angle, as well as the semiconducting-to-metallic ratio in any type of carbon nanotube sample is discussed. Single-wall carbon nanotubes grown by the cobalt-molybdenum catalyst based (CoMoCAT) process are characterized. The semiconducting-to-metallic ratio is found to be 11:1. A single semiconducting specie, named the (6,5) nanotube represents $2∕5$ of the sample, while the most abundant metallic nanotube is the (7,4), which exhibits a diameter similar to the (6,5).

Figure 1

(Color online) RBM spectra vs $E_{\text{laser}}$ for CoMoCAT SWNT samples. A, B, and C stand for the as-grown purified sample, the $\mathrm{SWNT}+\mathrm{SDS}$ solution sample, and the $\mathrm{SWNT}+\mathrm{SDS}$ precipitate sample, respectively. The Raman intensity is given by different colors, as shown in the intensity bars on the right (arb. units). The horizontal traces on the right-hand side of the 2D maps give the excitation laser energies that have been used to produce these maps. The union of spectral profiles is made within the MatLab interpolation process.

Figure 2

(Color online) (A) $E_{ii}$ vs ${\omega }_{\mathrm{RBM}}$ plot based on an extended tight binding model (Ref. 9) and corrections to account for many-body effects (Ref. 7). Solid, open, and crossed symbols stand for $(n,m)$ SWNTs with $(2n+m)\mathrm{mod}3=0$ (metallic), 1 or 2 (semiconducting) SWNTs, respectively. The gray lines connect SWNTs within the same $(2n+m)$ family. The $(2n+m)$ numbers are displayed close to each family. (B) A plot similar to Fig. 1B, but now with a color pattern that follows a log scale (see change in the intensity bar) to clearly show the low intensity RBM peaks. The white ellipses define the ranges where $E_{22}^S$, $E_{11}^M$, and $E_{33}^S$ optical transitions are observed.

Figure 3

The $(n,m)$ dependent populations $\left(P\right)$ vs diameter (left) and chiral angle (right) for various CoMoCAT SWNTs. Filled and open circles stand for metallic and semiconducting SWNTs, respectively. The $P$ values for metallic SWNTs are multiplied by 10 to more clearly relate their $d_t$ and $\theta$ behavior to that for semiconducting SWNTs. The $(n,m)$ for the most intense $P$ values are given.