Long ropes of boron nitride nanotubes grown by a continuous laser heating

A continuous CO2 laser beam was focused on a surface of hexagonal boron nitride under low nitrogen pressure, inducing a stiff radial temperature gradient, rising locally over the dissociation temperature. Boron nitride nanotubes and faceted boron nitride onions were found on the heated surface, segregated in specific zones. Nanotubes were grown in macroscopic quantity, stoichiometric, well crystallized, mostly with few layers, and self-assembled in ropes as long as 40 mu m. The cavity of boron nitride onions was often occupied by a boron nanocrystal. The recombination of boron and nitrogen both in plasma and on surface is suggested for the nucleation process. (C) 2000 American Institute of Physics. [S0003-6951(00)05122-6].