Vapor-liquid-solid-solid growth mechanism of carbon micro-coils

Carbon micro-coils, which have double helix structure, are generally prepared by catalytic chemical vapor deposition of acetylene, using Ni as the catalyst. It is well known that the coils are formed because of the catalytic anisotropy, however the growth process of carbon micro-coils is still unclear. In this paper, it is reported that the fiber constructing the carbon micro-coil is composed of three sub-fibers. Referring to this experimental finding and known facts from the phase diagrams, a vapor-liquid-solid-solid growth mechanism of carbon micro-coils is proposed. In this mechanism every catalyst particle can be divided into two parts, one is liquid while the other is solid. The schematic growth process of the carbon micro-coil is shown. Carbon atoms firstly permeate into the liquid portion from gas, then disperse into the solid portion, and finally deposit from six crystallographic facets of the catalyst to form the carbon micro-coil.