Boron nitride nanotubes synthesized in the temperature range 1000–1200 °C

Boron nitride nanotubes were synthesized on the iron-deposited alumina substrates by a catalytic reaction of the ball-milled boron and boron nitride powder mixture with ammonia in the temperature range 1000–1200 °C. The diameter of nanotubes is in the range of 40–100 nm. The nanotubes grown below 1100 °C possess exclusively a bamboo-like structure. As the temperature increases to 1200 °C, almost all nanotubes show a cylindrical structure in which the boron nitride sheets are tilted to the tube axis by an angle of about 25°. Electron energy-loss spectroscopy identifies that the ratio of boron and nitrogen is almost one. The Raman scattering peak associated with the E2g mode shifts to the higher frequency and narrows as the growth temperature increases. The results indicate that the growth temperature can be a crucial growth parameter in controlling the structure and crystallinity of boron nitride nanotubes. On the basis of the structural features, we suggest a base-growth mechanism for both bamboo-like and cylindrical boron nitride nanotubes.