Preparation, morphology, and microstructure of diameter-controllable vapor-grown carbon nanofibers

Pure vapor-grown carbon nanofibers (VGCNF's) with controllable diameters of 10-200 nm were prepared by an improved floating catalyst method. Through transmission electron microscopy (TEM) observation, it was found that VGCNF's have a duplex structure, a hollow and high-crystallinity graphite filament called primary carbon fiber surrounded by a pyrocarbon layer with low graphite crystallinity. It was observed using high-resolution TEM that VGCNF's have excellent graphitic crystallinity with graphite layers stacked neatly parallel to fiber axis. Moreover, x-ray diffraction results showed that the graphitic crystallinity of carbon fibers became higher with decreasing diameter of carbon fibers.