Particular attention will be focused on efficient self-assembly pyrolytic routes to large arrays (<2.5 cm2) of aligned C, CNx and BxCyNz nanotubes (15-80 nm od and < 100 microns length). In general, these 'hollow' fibres do not easily break upon bending and may behave as shock absorbing fillers in the fabrication of robust composites. The electronic and field emission properties, as well as the density of states (DOS) of CNx and BCx nanotubes using scanning tunneling spectroscopy (STS) will be presented. We further demonstrate that the presence of N and B are responsible for introducing donor and acceptor states near the Fermi Level. Novel applications of these doped materials will also be discussed. Finally, it will be shown that high electron irradiation during annealing at 700 - 800 °C, is capable of coalescing and joining single-walled nanotubes (SWNTs). Vacancies induce the merge via a zipper-like mechanism, imposing a continuous reorganization of atoms on individual tube lattices within the adjacent tubes. Other topological defects induce the polymerization of tubes and creation of 'Y', 'T' and 'X' nanotube junctions. The latter results pave the way to the fabrication of nanotube contacts, nanocircuits and strong 3D composites using irradiation doses under annealing conditions.
In situ experiments, based on electron irradiation at high temperature in a transmission electron microscope, are used
to investigate isolated, packed and crossing single-wall nanotubes. During continuous, uniform atom removal, surfaces of isolated single-wall nanotubes heavily reconstruct leading to drastic dimensional changes. In bundles, coalescence of single-wall nanotubes is observed and induced by vacancies via a zipper-like mechanism. 'X', 'Y',
and 'T' carbon nano-structures are also fabricated by covalently connecting crossed single-wall nanotubes in order to pave the way towards controlled fabrication of nanotube based molecular junctions and network architectures exhibiting exciting electronic and mechanical behavior. Each experiment is followed by quantum modeling in order to investigate the effect of the irradiation process at the atomic level.