Controlled Growth-Reversal of Catalytic Carbon Nanotubes under Electron-Beam Irradiation

The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni₃C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni₃C (2−13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes.