Large-scale synthesis and HRTEM analysis of single-walled B- and N-doped carbon nanotube bundles

Bundles of B- and N-doped single-walled carbon nanotubes (SWNTs) containing up to similar to 10 at% B and up to similar to 2 at% N were synthesized at high yields under thermo-chemical treatment of pure C SWNT bundles and B2O 3 in a flowing nitrogen atmosphere. The bundles were characterized by means of high-resolution transmission electron microscopy and electron energy lo ss spectroscopy. The effects of synthesis temperature (1503-1773 K) and tim e (30-240 min) on the B and N contents and yield of the SWNT bundles were d etermined. The maximum yield of the B- and N-doped SWNT bundles was obtaine d under synthesis at 1553 K over 30 min. Atomic structure and morphology of individual SWNTs in the bundles, in particular, packing of doped SWNTs, he licity distribution, encapsulation of fullerene-like clusters, diameter and shell number variations were studied. The synthesized SWNTs in the bundles were stacked in a honeycomb array with the uniform inter-tube spacing of s imilar to 0.3 nm. No preferable orientation for the graphene-like tubular s hells was found, i.e. both zigzag and armchair edges were observed with app roximately equal proportions. Frequently, diameter increase took place for the outer tubes in a bundle and for isolated SWNTs. C-based or BN-based ful lerene-like encapsulates were observed in individual SWNTs. Carbon oxidatio n by the B2O3 vapor and B and N substitution for C is thought to underlie t he doping of C SWNTs. The substitution reaction temperature-time limits wit h respect to the morphological stability of B- and N-doped SWNT bundles are finally elucidated (C) 2000 Elsevier Science Ltd. All rights reserved.