Formation of multi-walled carbon nanotubes with a metal-free chemical vapor deposition and their stepwise evolution

Multi-walled carbon nanotubes and one-dimensional wire-like nanostructures have been synthesized using acetylene as carbon sources with a metal-free mild chemical vapor deposition process. It shows that anisotropic carbon nanostructures can interact to form nanotubes by self-function. Furthermore, the detailed microscopic observation of the obtained nanostructures indicates that the development of fully hollow carbon nanotubes should undergo a quite complex physical and chemical transformation process, and their formation abides by the “particle–wire–tube” stepwise evolution mechanism. In this process, the one-dimensional wire-like nanostructures can be viewed as the intermediate stages of carbon nanotube formation, which record traces about nanotube evolution.