Microstructure and microscopic deposition mechanism of twist-shaped carbon nanocoils based on the observation of helical nanoparticles on the growth tips

Carbon nanocoils possessing a twisting form were prepared from an Fe-based alloy (SUS410) catalyst, the crystallographic properties of the catalyst surface, which was present on the growth tip, were examined, and a novel growth mechanism of the nanocoils is presented. Single-helix twisted carbon nanocoils with a coil diameter of 300-400 nm were obtained at 700-800 °C with a yield of 60% and a purity of nearly 100%. The catalyst structure observed on the growth tip was a Fe5C2 (monoclinic) or Fe7C3 (orthorhombic) single crystal, in which some of the Fe atoms were substituted by Cr. Carbon nanoparticles with a helical structure were observed on the surface of catalyst particle. It is considered that the carbon nanoparticles are a helical carbon supply source. That is, the catalyst particle supplies microscopic carbon nanoparticles by helical deposition patterns on the catalyst surface to form macroscopic helical patterns of carbon nanocoils.