Published online by Cambridge University Press: 01 February 2011
Three dimensional helical coiled carbon nanostructures including coiled nanowires and nanotubes were synthesized at ambient pressure using a thermal chemical vaporization deposition (CVD) process in which xylene and acetylene were used as the primary carbon source. A bi-metal catalyst formed from a mixture of ferrocene and indium isopropoxide served as the seed to initiate the growth of these helical coiled nanostructures. The as-synthesized coiled nanowires and nanotubes are pure without the presence of amorphous carbon nanoparticles. By precisely controlling the atomic ratio of In / (Fe+In), coiled nanowires or nanotubes can be synthesized exclusively. The diameters of the as-grown coiled nanowires vary from several tens to several hundreds nanometers, whereas the diameters of the coiled nanotubes are around 20 nm. The structure of coiled nanowires and nanotubes were determined using scanning electron microscopy and transmission electron microscopy. The key novel aspects of this research are: (i) to synthesize helical coiled nanotubes or nanowires exclusively by controlling the bi-catalyst concentration of Fe and In, and (ii) no preformed substrates are required which implies that our process is amenable for scaled-up synthesis of these nanostructures.