Density-functional tight-binding molecular dynamics simulations of SWCNT growth by surface carbon diffusion on an iron cluster

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