Dynamics of local chirality during SWCNT growth: Armchair versus zigzag nanotubes

We present an analysis of the dynamics of single-walled carbon nanotube (SWCNT) chirality during growth, using the recently developed local chirality index (LOCI) method [ Kim et al. Phys. Rev. Lett. 2011, 107, 175505 ] in conjunction with quantum chemical molecular dynamics (QM/MD) simulations. Using (5,5) and (8,0) SWCNT fragments attached to an Fe ₃₈ catalyst nanoparticle, growth was induced by periodically placing carbon atoms at the edge of the SWCNT. For both armchair and zigzag SWCNTs, QM/MD simulations indicate that defect healing-the process of defect removal during growth-is a necessary, but not sufficient, condition for chirality-controlled SWCNT growth. Time-evolution LOCI analysis shows that healing, while restoring the pristine hexagon structure of the growing SWCNT, also leads to changes in the local chirality of the SWCNT edge region and thus of the entire SWCNT itself. In this respect, we show that zigzag SWCNTs are significantly inferior in maintaining their chirality during growth compared to armchair SWCNTs.