Molecular\nDynamics of Chirality Definable Growth of Single-Walled Carbon Nanotubes

Abstract

In\norder to achieve the chirality-specific growth of single-walled carbon\nnanotubes (SWCNTs), it is crucial to understand the growth mechanism.\nEven though many molecular dynamics (MD) simulations have been employed\nto analyze the SWCNT growth mechanism, it has been difficult to discuss\nthe chirality determining kinetics because of the defects remaining\non the SWCNTs grown in simulations. In this study, we demonstrate\nMD simulations of defect-free SWCNTs, that is, chirality definable\nSWCNTs, under the optimized carbon supply rate and temperature. The\nchiralities of the SWCNTs were assigned as (14,1), (15,2), and (9,0),\nindicating the preference of near-zigzag and pure-zigzag SWCNTs. The\nSWCNTs contained at least one complete row of defect-free walls consisting\nof only hexagons. The near-zigzag SWCNTs grew <i>via</i> a kink-running process, in which bond formation between a carbon\natom at a kink and a neighboring carbon chain led to formation of\na hexagon with a new kink at the SWCNT edge. Defects including pentagons\nand heptagons were sometimes formed but effectively healed into hexagons\non metal surfaces. The pure-zigzag SWCNTs grew by the kink-running\nand the hexagon nucleation processes. In addition, chirality change\nevents along SWCNTs with incorporation of pentagon–heptagon\npair defects were observed in the MD simulations. Here, pentagons\nand heptagons were frequently observed as adjacent pairs, resulting\nin (<i>n</i>,<i>m</i>) chirality changes by (±1,0),\n(0,±1), (1,–1), or (−1,1).