Charge Transfer between Metal Clusters and Growing Carbon Structures in Chirality-Controlled Single-Walled Carbon Nanotube Growth

Synthesis of single-walled carbon nanotubes (SWCNTs) with specific chirality has been a great challenge. The detailed role of catalyst clusters in chirality-selective growth of SWCNTs is still unclear. We studied armchair (5,5), chiral (6,5), and zigzag (9,0) nanotube growths on a relaxed Ni-55 cluster. Although adhesion energies and chemical potentials of growing carbon structures only show small differences, charges are evidently transferred (or redistributed) from Ni atoms to the growing end edges of nanotubes, which enhance the reactivity of carbon edges. Different chiral nanotubes exhibit distinct reaction active sites. (5,5) has five identical double-carbon active sites, while (9,0) has nine single-carbon active sites. (6,5) has a kink site with the highest reaction activity. These findings imply that the structures of metal clusters strongly correlate with nanotube growth sites through charge transfer (or redistribution). Potential opportunities exist in enabling (n,m) selective growth by engineering charge transfer between metal dusters and growing carbon structures.