Structure of flattened carbon nanotubes

A large number of flattened multi-walled carbon nanotubes have been synthesized using chemical vapor deposition. They are often capped with elongated crystalline cobalt catalyst nanoparticles. Sample rotation studies inside the transmission electron microscope show that the catalyst nanoparticles have a cylindrical rather than a rectangular shape, indicating that the flattened structure of the nanotubes is not templated by the shape of the catalyst particles. Observations reveal the existence of nanotube flattening parallel to the long axis and a spiraling of fully flattened nanotube around the long axis of the nanotube. The flattening of the nanotubes is attributed to the pressure difference between the inside and outside of the nanotubes which are sealed by the catalyst nanoparticles during their growth. The flattening and the spiraling are ascribed to axial compression and torsion, respectively.