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 nit ride under low nitrogen pressure, inducing a stiff radial temperature gradi ent, rising locally over the dissociation temperature. Boron nitride nanotu bes and faceted boron nitride onions were found on the heated surface, segr egated in specific zones. Nanotubes were grown in macroscopic quantity, sto ichiometric, 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 o ccupied by a boron nanocrystal. The recombination of boron and nitrogen bot h in plasma and on surface is suggested for the nucleation process. (C) 200 0 American Institute of Physics. [S0003-6951(00)05122-6].