(Invited) In Situ Study on Cleation and Growth of Single-Walled Carbon Nanotubes on Catalysts

Abstract

Understanding the growth mechanism is prerequisite to design the methodology for controlled growth of single-walled carbon nanotubes (SWNTs). By using an environmental aberration-corrected transmission electron microscope in combination with in situ synchrotron X-ray absorption spectroscopy, we directly present the structural and composition evolution of cobalt and cobalt-tungsten intermetallic catalysts during the nucleation and growth of SWCNTs under carbon feeding. The co-existence of cobalt and cobalt carbide was generally observed among the pure cobalt catalysts which are active in nucleating tubes. The nucleation and growth behaviors of tubes on solid state cobalt nanoparticles and molten ones have been compared. It was found that the tubes grown from solid state catalysts always present smaller diameter than the catalysts. No structure-correlation between catalyst and nanotube was found. Distinct different from cobalt, no carbides or carbon diffusion induced structural change was observed from the in situ characterization. The atomic structure of Co7W6 was stable when CNTs nucleating. These observations reveal that cobalt-tungsten intermetallic catalysts act as the stable structure template for the chirality controlled growth of SWNTs.