Figure 3 - Tuning the structure–density relationship for optimal separation by diameter and bandgap or electronic type (metal–semiconductor).

a–c, Optimization of separation by diameter and bandgap. The concentration of the (6,5), (7,5) and (9,5)/(8,7) chiralities of CoMoCAT-grown SWNTs (coloured red, green and blue; diameters (ref. 5) of 7.6, 8.3 and 9.8/10.3 Å, respectively) are plotted against . Concentrations were determined from absorbance spectra (Fig. 1c and Supplementary Fig. S1). The encapsulation agents and conditions were SC, no buffer, pH 7.4 (a), SC, 20 mM Tris buffer, pH 8.5, enhanced isolation of the larger diameter SWNTs, (9,5)/(8,7) (b), SC with the addition of SDS as a co-surfactant (1:4 ratio by weight, SDS/SC), enhanced isolation of the smaller diameter SWNTs, (6,5), pH 7.4 (c). for the fractions with the highest (6,5) chirality relative concentration in a–c are all 1.08  0.02 g cm^-3. Arrows mark shifts with respect to a. d,e, Optimization of separation by electronic type. d, Photograph of laser-ablation-grown SWNTs separated in a co-surfactant solution (1:4 SDS/SC). The top band (orange) corresponds to predominantly semiconducting SWNTs (absorbance spectra plotted in red in e) and the band just below it (green) is highly enriched in metallic SWNTs, although some semiconducting SWNTs remain (absorbance spectra plotted in Supplementary Fig. S6). between the two bands and for the top band are 0.006 g cm^-3 and 1.12  0.02 g cm^-3, respectively. Further tuning of the structure–density relationship (3:2 ratio by weight SDS/SC) results in the isolation of predominantly metallic SWNTs (absorbance spectra plotted in blue in e; heterogeneous mixture before sorting plotted with a dashed grey line). (S33, M11, S22 highlighted as in Fig. 1g.)