ABSTRACTIt has been shown experimentally that the growth of carbon nanotubes in an arc discharge is open-ended. This is surprising, because dangling bonds at the end of open tubes make the closed tube geometry more favorable energetically. Recently, it has been proposed that the large electric fields present at the tip of tube is the critical factor that keeps the tube open. We have studied the effects of the electric field on the growth of the nanotubes via ab initio molecular dynamics simulations. Surprisingly, it is found that the electric field cannot play a significant role in keeping the tubes open, implying that some other mechanism must be important. Extensive studies of the energetics and simulations of the growth of tubes were performed using a threebody Tersoff-Brenner potential. Our results show that there exists a critical diameter of ∼ 3 nm above which a defect-free growth of a straight tubule is possible. Narrower tubes stabilize configurations with adjacent pentagons that lead to tube-closure and termination of the growth. This explains the absence of tube narrower than 2.2 nm in arc discharge experiments.
Numerical simulation of the plasma parameters of a low-pressure arc discharge in helium
