Iron-catalyzed SWCNT growth by carbon diffusion starting from a carbon cap was demonstrated in density-functional tight-binding molecular dynamics simulations. A C40(5,5) SWCNT cap attached to an Fe38 cluster was used as an initial model system. After 40 carbon atoms were supplied to the iron surface for 20ps, dynamics were continued for 160ps without supply of further carbon feedstock. Growth of the SWCNT sidewall was mainly due to surface-diffusion of short carbon chains, and to a lesser degree due to sub-surface diffusion. Newly created rings consisted only of pentagons and hexagons, while heptagons were infrequent and short-lived, which seemed to be caused by the slower, more ordered sidewall growth due to the diffusion process.

Density-Functional Tight-Binding Molecular Dynamics Simulations of SWCNT Growth by Surface Carbon Diffusion on an Iron Cluster. Ohta, Y., Okamoto, Y., Irle, S., Morokuma, K.: Carbon, 2009, 47[5], 1270-5