Single-walled carbon nanotubes (SWNTs) present unique structure-dependent properties and the controlled preparation of chemically and structurally pristine SWNTs is a crucial issue for their advanced applications (e.g. nanoelectronics) and has been a great challenge.Epitaxial growth of SWNTs from well-defined seeds has shown to be a promising strategy to control the structure of SWNTs. Inspired by the specificity of enzyme-catalyzed reactions, we realized that only catalysts with unique crystal structure and desired atomic arrangements can act as the structural templates for chirality specific growth of SWNTs, relying on the high selectivity in geometry match between catalysts and SWNTs. We developed a new family of catalysts, tungsten-based intermetallic compounds, which have high melting point and very special crystal structure, to synthesize SWNTs with designed chirality. Using W₆Co₇ catalysts, (12, 6) SWNTs was directly grown with the purity higher than 92%. The selective growth of (12, 6) tubes is due to a good structural match between the carbon atom arrangement around the nanotube circumference and the metal atom arrangement of (0 0 12) planes in the catalyst. Similarly, (16, 0) SWNT exhibits good structural match to (1 1 6) plane of Co₇W₆ catalyst. By manipulating the chemical vapor deposition (CVD) conditions, zigzag (16, 0) SWNTs, which are generally known as a kinetically unfavorable species in CVD growth, were obtained at the purity of ~80%. The chirality-specific growth of SWNTs is realized by the cooperation of two factors: the structural match between SWNTs and the catalysts makes the growth of SWNTs with specific chirality thermodynamically favorable; and further manipulation of CVD conditions obtains optimized growth kinetics for SWNTs with this designed chirality. This idea has also been proved to be valid for SWNTs with other chiralities and intermetallic catalysts.

References

1.  Yang, F.; Wang, X.; Zhang, D.; Yang, J.; Da, L.; Xu, Z.; Wei, J.; Wang, J.-Q.; Xu, Z.; Peng, F.; Li, X.; Li, R.; Li, Y.; Li, M.; Bai, X.; Ding, F.; Li, Y., Nature 2014, 510, 522-524.

2.  Yang, F.; Wang, X.; Zhang, D.; Qi, K.; Yang, J.; Xu, Z.; Li, M.; Zhao, X.; Bai, X.; Li, Y.,  J. Am. Chem. Soc. 2015, 137, 8688-8691.