The role of carbon precursor on carbon nanotube chirality in floating catalyst chemical vapour deposition

We have studied the influence of different carbon precursors (methane, ethanol and toluene) on the type, diameter and chiral angle distributions of carbon nanotubes (CNTs) grown with the floating catalyst technique in a horizontal gas-flow reactor. Using electron diffraction to study their atomic structures, we found that ethanol and toluene precursors gave high single-wall CNT yields (92% and 89% respectively), with narrow diameter distributions: 1.1 nm to 1.7 nm (ethanol); 1.3 nm to 2.1 nm (toluene), with a propensity for armchair-type chiral angles. In contrast, methane-grown CNTs gave high double-wall CNT yields (75%) with broader diameter populations: 1.2 to 4.6 nm (inner CNT) and 2.2 to 5.3 nm (outer CNT) with a more uniform spread of chiral angles, but weakly peaked around 15 to 20 degrees. These observations agree with known growth models. However, double-wall CNTs grown with toluene showed an unusually narrow interlayer spacing of 0.286 +/- 0.003 nm with suggestions of large, 20 degrees to 25 degrees, differences between inner and outer CNT chiral angles. Methane gave a large interlayer spacing (0.385 +/- 0.002 nm) with suggestions of small 5 degrees to 10 degrees inter-tube chirality correlations.