Atomic-scale imaging of carbon nanofibre growth

The synthesis of carbon nanotubes with predefined structure and functionality plays a central role in the field of nanotechnology(1,2), whereas the inhibition of carbon growth is needed to prevent a breakdown of industrial catalysts for hydrogen and synthesis gas production(3). The growth of carbon nanotubes and nanofibres has therefore been widely studied(4-10). Recent advances in in situ techniques now open up the possibility of studying gas - solid interactions at the atomic level(11-12). Here we present time-resolved, high-resolution in situ transmission electron microscope observations of the formation of carbon nanofibres from methane decomposition over supported nickel nanocrystals. Carbon nanofibres are observed to develop through a reaction-induced reshaping of the nickel nanocrystals. Specifically, the nucleation and growth of graphene layers are found to be assisted by a dynamic formation and restructuring of mono-atomic step edges at the nickel surface. Density-functional theory calculations indicate that the observations are consistent with a growth mechanism involving surface diffusion of carbon and nickel atoms. The finding that metallic step edges act as spatio-temporal dynamic growth sites may be important for understanding other types of catalytic reactions and nanomaterial syntheses.