Tight binding molecular dynamics studies of boron assisted nanotube growth

In this paper we report a theoretical study of the effects of the presence of boron in growing carbon nanotubes. We employ a well established tight bi nding model to describe the interactions responsible for the energetics of these systems, combined with the molecular dynamics simulation technique an d structural relaxation calculations. We find, in agreement with the previo us theoretical/experimental work of Blase [Phys. Rev. Lett. 83, 5078 (1999) ], that boron favors (n,0) (zig-zag) tubular structures over (n,n) (arm-cha ir) ones by stabilizing the zig-zag edge. Furthermore, it is shown that bor on has the effect of delaying the tube closure process, a fact which could explain the improved aspect ratio experimentally observed in nanotubes synt hesized in the presence of boron. Our dynamical simulations lead us to prop ose a mechanism through which this extension of the closure time can be exp lained. (C) 2000 American Institute of Physics. [S0021-9606(00)71533-9].