Catalyst- and Etchant-Dependent Mechanisms of Single-Walled Carbon Nanotube Nucleation during Chemical Vapor Deposition

Abstract

Recent experiments have shown that single-walled carbon nanotube (SWCNT) chirality and diameter can be modulated by adjusting the carbon/hydrogen chemical potentials at the catalyst surface and also by adding chemical etchants, such as ammonia, to the chemical vapor deposition (CVD) feedstock. Here, we present nonequilibrium quantum chemical molecular dynamics simulations showing how these factors control the SWCNT nucleation mechanism in different ways on Fe and Ni catalyst nanoparticles. Polygonal carbon rings form on Ni catalysts via the collapse of extended, partially saturated carbon chains that are adsorbed weakly to the catalyst surface, while SWCNT nucleation on Fe is strongly mediated by the catalyst surface. The weaker Ni–C interaction here means that the carbon desorption rate, and hence carbon chemical potential, on Ni is consistently lower than it is on Fe. Ni also activates adsorbed C–H and N–H bonds more effectively than Fe. Nevertheless, the hydrogen chemical potential is consistently lowe...