Abstract
The atomic structure of ultra-long carbon nanotubes grown by catalytic chemical vapor deposition has been studied along the nanotube length via electron diffraction and high-resolution transmission electron microscopy. Contrary to other techniques, electron diffraction studies provide a direct determination of the chiral structure of nanotubes. These studies demonstrate that the chirality of the nanotubes remained constant all along their length. A tendency to double-walled nanotubes has been observed, as well as, a preferential distribution to armchair configuration. Furthermore, the studies yield a metallic:semiconducting ratio close to the one expected from a natural distribution of nanotubes (1:2).