The formation of pentagonal defects and bamboo-like structures in C nanotube growth was viewed within the framework of the surface diffusion growth model. Nanotube open edge stability was considered to be a competition between hexagon formation which depended upon the rate at which C units were fed by surface diffusion to the edge, and on thermally activated pentagon formation, which caused inward bending of the edge; resulting in end closure and growth termination. The closure of the growing nanotube was shown to occur when a change in the conditions (temperature, C vapor pressure or surface area from which the open end was fed) decreased the surface diffusion flux, and the time for the hexagon formation on the edge became larger than that for pentagon formation. An analysis of C nanotube forest growth by chemical vapor deposition on prefabricated metal nanoparticle arrays suggested that C species were unable to penetrate to the forest bottom whenever the mean-free-path in the gas was much larger than the distance between nanotubes. They instead collided with nanotube walls, chemisorbed within the top few microns, diffused along the nanotube surface and fed the growth at the nanotube tip. When a metal nanoparticle was present at the substrate or on the nanotube tip, in the post-nucleation stage, its role in feeding nanotube growth by C dissolution and bulk diffusion was negligibly small in comparison with the surface diffusion of C species on the nanotube surface. The bulk diffusion of C through the nanoparticle governed the characteristic times of C penetration to the nanoparticle base and surface saturation with C. It played a major role in the selection of the initial mode of nanotube nucleation and growth, and led to the formation of straight wall nanotubes or bamboo-like nanotube structures.

Formation Mechanism of Pentagonal Defects and Bamboo-Like Structures in Carbon Nanotube Growth Mediated by Surface Diffusion. O.A.Louchev: Physica Status Solidi A, 2002, 193[3], 585-96