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 degreesC. The diameter of nanotubes is in the range of 40-100 nm. The nanotubes grown below 1100 degreesC possess exclusively a bamboo-like structure. As the temperature increases to 1200 degreesC, almost all nanotubes show a cylindrical structure in which the boron nitride sheets are tilted to the tube axis by an angle of about 25degrees. Electron energy-loss spectroscopy identities that the ratio of boron and nitrogen is almost one. The Raman scattering peak associated with the E-2g mode shifts to the I higher frequency and narrows as the growth temperature increases. The results indicate that the growth temperature can be a crucial growth pararneter in controlling the structure and crystallinity of boron nitride nanotubes. Oil the basis of the structural features, we suggest a base-growth mechanism for both bamboo-like and cylindrical boron nitride nanotubes. (C) 2003 Elsevier Science B.V. All rights reserved.