Crystallization behavior of the amorphous carbon nanotubes prepared by the CVD method

We report the crystallization behavior of the amorphous carbon nanotubes at high temperature in this paper. Transmission electron microscopy and X-ray diffraction were performed to characterize the structures of the carbon nanotubes. The results reveal that the microstructure of the as-grown carbon nanotubes, prepared by the floating catalyst method, is roughly amorphous. The as-grown carbon nanotubes were annealed at high temperatures, and the crystallization behavior of the amorphous carbon nanotubes was investigated systematically. Because the carbon nanotubes have finite dimensions and tube-like shape, their crystallization behavior is completely different from the bulk amorphous carbons. The results reveal that the graphene layers in the annealed carbon nanotubes will form into a uniform two-dimensional turbostratic stack, a configuration of carbon nanotubes with the lower Gibbs free energy. A thermodynamic model is presented to explain the crystallization behavior of the amorphous carbon nanotube. (C) 2001 Elsevier Science B.V. All rights reserved.