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

Abstract

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