Catalyst-free synthesis of boron nitride single-wall nanotubes with a preferred zig-zag configuration

Boron nitride nanotubes (BNNTs) were synthesized in gram quantities using a continuous ${\mathrm{CO}}_2$ laser ablation reactor without the benefit of a metal catalyst. High-resolution transmission electron microscopy analyses have shown the samples to be composed of single-wall nanotubes organized in long and well-crystallized bundles containing about ten tubes. The samples also contain a small amount of double-wall BNNTs and multiwall boron nitride fullerenelike “cages.” The majority of the BNNTs were identified as having the zig-zag configuration, as attested by the 0.2 nm period array of spots observed along tube walls; the other tubes are either armchair or chiral. The BNNTs seem to be attached at one end to nanoparticles which were shown in electron spectroscopy imaging mode to be composed of pure boron, thus supporting a root-based growth mechanism.