Controlled synthesis of pointed carbon nanotubes

To fully realize the potential for the many applications of carbon nanotubes, it is necessary to control their morphology at will. Here we describe the controlled synthesis, on the fibers of a carbon paper, of multi-walled carbon nanotubes having either a regular cylindrical morphology or a novel morphology consisting of nanometric cylindrical tubes terminated by pointed tips about 0.5–1 μm long. Reshaping of the Ni–Co catalyst particle during the growth process has been directly observed for both regular and pointed nanotubes. However, total liquefaction of the catalyst particle is only observed during the growth of pointed tubes. Regular tubes result from the spiral scrolling of a graphene sheet resulting in a herringbone texture, while the tip of the pointed tubes displays a concentric textural character. The change in growth mechanism seems to occur upon total liquefaction of the catalyst.