Formation of carbon nanotubes catalyzed by rare earth oxides

Multi-wall carbon nanotubes (MWCNTs) were synthesized by detonation-assisted chemical vapor deposition using a series of rare earth (RE) oxides as catalysts. Energy dispersive X-ray spectroscopy, selected area electron diffraction and powder X-ray diffraction show that the catalysts, usually located outside the MWCNTs, have not been reduced, in sharp contrast to conventional catalysts in the form of metals or carbides. With the help of intermediate objects found in TEM images, it is proposed that the formation of MWCNTs follows a particle-wire-tube step-wise evolution mechanism. The RE oxides may play a major role in promoting the self-assembly of anisotropic carbon nanoparticles into a 1-D structure, and the cavities in the tubes evolve through structure self-reorganization and crystallization of the particles.