Arrayed Arrangement of 13C Isotopes During the Growth of Inner Single-Walled Carbon Nanotubes

Abstract

The growth of single-walled carbon nanotubes (SWCNT) inside host SWCNTs remains a compelling alternative to the conventional catalyst-induced growth processes. It not only provides a catalyst free process but also the ability to control the constituents of the inner tube if appropriate starting molecules are used. We report herein the growth of inner SWCNTs from 13C-enriched benzene or toluene and C60 fullerene with a natural isotopic distribution. The latter molecule is essentially a stopper which acts to retain the smaller toluene inside the tubes. The Raman spectrum of the inner nanotubes is anomalous as it contains a highly isotope shifted “tail,” which cannot be explained by assuming a homogeneous distribution of the isotopes. Semi-empirical calculations of the Raman modes indicate that this unusual effect is explicable if small arrays of 13C are assumed. This indicates the absence of carbon diffusion during the inner tube growth.