title: Quantum chemical molecular dynamics simulation of single-walled carbon nanotube cap nucleation on an iron particle.
abstract: The atomic scale details of single-walled carbon nanotube (SWNT) nucleation on metal catalyst particles are elusive to experimental observations. Computer simulation of metal-catalyzed SWNT nucleation is a challenging topic but potentially of great importance to understand the factors affecting SWNT diameters, chirality, and growth efficiency. In this work, we use nonequilibrium density functional tight-binding molecular dynamics simulations and report nucleation of sp(2)-carbon cap structures on an iron particle consisting of 38 atoms. One C(2) molecule was placed every 1.0 ps around an Fe(38) cluster for 30 ps, after which a further 410 ps of annealing simulation without carbon supply was performed. We find that sp(2)-carbon network nucleation and annealing processes occur in three sequential and repetitive stages: (A) polyyne chains on the metal surface react with each other to evolve into a Y-shaped polyyne junction, which preferentially form a five-membered ring as a nucleus; (B) polyyne chains on the first five-membered ring form an additional fused five- or six-membered ring; and (C) pentagon-to-hexagon self-healing rearrangement takes place with the help of short-lived polyyne chains, stabilized by the mobile metal atoms. The observed nucleation process resembles the formation of a fullerene cage. However, the metal particle plays a key role in differentiating the nucleation process from fullerene cage formation, most importantly by keeping the growing cap structure from closing into a fullerene cage and by keeping the carbon edge "alive" for the addition of new carbon material.
authors.affiliation: Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto, Japan.
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Ohta
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Alister J
authors.initials: AJ
authors.lastname: Page
authors.forename: Stephan
authors.initials: S
authors.lastname: Irle
authors.forename: Keiji
authors.initials: K
authors.lastname: Morokuma