Chiral-Angle Distribution for Separated Single-Walled Carbon Nanotubes

Chiral indices (n,m) of metallic and semiconducting single-walled carbon nanotubes (SWNTs) selectively separated via the density-gradient ultracentrifugation process were individually assigned by using an aberration-corrected transmission electron microscope (TEM) operated at 80 W. Our statistical analysis revealed that armchair (n,n) and chiral (n,n-3) SWNTs with large chiral angles (> 20 degrees) are dominant metallic nanotubes in the separated samples, whereas such a noticeable preference of particular indices was not observed for semiconducting nanotubes. Some significant discrepancies were found between the TEM and spectroscopic results on the major chiral indices and the metal/semiconductor ratios in these SWNTs.