Temperature Dependence of Catalyst-Free Chirality-Controlled\nSingle-Walled Carbon Nanotube Growth from Organic Templates

Abstract

The\ntemperature dependence of catalyst-free single-walled carbon\nnanotube (SWCNT) growth from organic molecular precursors is investigated\nusing DFTB quantum chemical molecular dynamics simulations and DFT\ncalculations. Growth of (6,6)-SWCNTs from [6]­cycloparaphenylene ([6]­CPP)\ntemplate molecules was simulated at 300, 500, and 800 K using acetylene\n(C₂H₂) and ethynyl radicals (C₂H)\nas growth agents. The highest growth rates were observed with C₂H at 500 K. Higher temperatures lead to increased defect formation\nin the SWCNT structure during growth. Such defects, which cause the\nloss of SWCNT chirality control, were driven by radical addition reactions\nwith inherently low kinetic barriers. We therefore propose that lower\ntemperature is optimal for the C₂H radical mechanism of\nSWCNT growth, and predict the existence of an optimum SWCNT growth\ntemperature that balances the rates of growth and defect formation\nat a given C₂H/C₂H₂ ratio.