Carbon nanotube bundles self-assembled in double helix microstructures

Double helix microstructures consisting of two parallel strands, each composed of hundreds of multiwalled carbon nanotubes (MWCNTs) are synthesised by chemical vapour deposition (CVD) of ferrocene/toluene vapours on thermochemically treated metal substrates, such as steel, Cu, Al and W. The thermochemical treatment produces a thin and brittle layer of SiOx. During the CVD process, carbon nanotubes (CNT) grow adhered to this layer, and as growth progresses, small SiOx microparticles detach from the substrate, directing the helical development of the growing MWCNTs double strands. This growth model for the helical microstructures is compared in the manuscript with models previously reported for coiled carbon fibres grown in the gas phase. A unique aspect of these double helices when they are composed of carbon nanotubes is that they grow on top of a forest of aligned CNTs.