Dynamics of Topological Defects in Single-Walled Carbon Nanotubes during Catalytic Growth

Nucleation and healing of structural defects in single-walled carbon nanotubes (SWCNTs) studied through reactive molecular dynamics simulations (RMD) and RMD trajectories reveal formation and healing mechanisms of various topological defects on the catalyst surface. A quality percentage of nanotubes is measured by calculating the amount of hexagons per carbon atom relative to the same quantity for a perfect nanotube of the same length. Following this approach, the concentration of defects is estimated for nanotubes grown on catalysts with different sizes and morphologies and for various temperatures and gas-phase densities. From this analysis, we identify specific catalyst morphologies that favor the growth of SWCNTs with low defect concentration. Vacancies, 5–7, and Stone–Wales defects are observed to nucleate distinctly in the tubes depending on the catalyst morphology. We find that a strong interaction between the catalyst surface and the graphitic lattice of the nanotube is absolutely necessary for healing and formation of defects. Our study suggests that defects can be healed independently of the degree of embedment of the defective structure into the tube structure. Diffusion and catalytic events at the catalyst/tube interface are the main sources of nanotube structural recovery on the catalyst surface. Finally, optimal growth conditions are identified that allow significant structural healing in nanotubes.