Multiwall carbon nanotubes as substrates for the growth of unique pyrolytic carbon morphologies

Multiwall carbon nanotubes were first prepared by thermocatalytic decomposition of methane in the presence of hydrogen over iron nanoparticles. Then pyrolytic carbon deposition was achieved onto the MWNTs by thermal cracking of a mixture CH4/H-2. Peculiar MWNTs-based morphologies were obtained, which basically associate sequences of beads and cones inside which the graphene display is always concentric to the MWNTs, with a variable nanotexture. Temperature and gas phase composition may vary so that a whole range of morphologies can be obtained, characterised by the variable development of the beads from absent to more or less elongated grains and that of the cones from fully developed to truncated. The formation of each morphology is quite controllable. Growth mechanisms are assumed to be related to the energetics of a liquid polycondensed phase issued from the cracking of CH4 deposited onto a nano-sized wire. Various interesting applications are expected, such as AFM tips or composite reinforcement.