Figure 1. Scheme and characterization of the electronic sorted SWCNTs.

(A) Scheme for the preparation of electronic sorted SWCNTs. P2 SWCNTs were sorted into metallic and semiconducting species using density gradient ultracentrifugation (DGU) methods. Briefly, a P2 SWCNTs stock solution was prepared by dispersing the tubes in an aqueous solution containing 1% w/v sodium cholate (SC) followed by 1 h ultrasonication. The stock suspension was then centrifuged at 7500 rpm for 10 min in the presence of sodium dodecyl sulfate (SDS) and SC (SDS:SC ratios of 3:2 vs. 1:4 were used for metallic and semiconducting sorting, respectively) to remove large aggregates. The remaining supernatant was for DGU sorting, using iodixanol to make the gradients. After the dispersion was centrifuged at 32,000 rpm for 18 h, 0.25 mm fractions of the supernatant was collected as either metallic or semiconducting tubes. The detailed methodology appear in the Supporting Information. (B) Characterization of the sorted SWCNTs. Photograph of the DGU separation tube (a) and corresponding optical absorption spectra (b). The purity of the final dispersions were >98.8% for M-SWCNT and >98.5% for S-SWCNT as determined by optical absorbance spectroscopy. (C and D) Characterization of semiconducting (C) and metallic (D) SWCNTs by AFM and optical absorption spectroscopy. Panels (c) and (g) show the AFM images, panels (d) and (h) show the optical absorption spectra, panels (e) and (i) show length distributions, while panels (f) and (j) show the diameter distributions.