The formation of pentagonal defects and bamboo-like structures in carbon nanotube growth was studied within the framework of the surface diffusion growth model. Carbon nanotube open edge stability was considered as a competition between hexagon formation, which depended upon the rate at which C units were fed by surface diffusion to the edge, and thermally activated pentagon formation, which caused inward bending of the edge; resulting in end closure and growth termination. Closure of the growing carbon nanotube was shown to occur whenever 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 hexagon formation on the edge became larger than that for pentagon formation. An analysis of carbon 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 carbon nanotubes. They instead collided with carbon nanotube walls, chemisorbing within the top few microns, diffused along the carbon nanotube surface and fed the growth at carbon nanotube tips. Wherever a metal nanoparticle was present at the substrate or on the carbon nanotube tip, in the post-nucleation stage, its role in feeding carbon nanotube growth by C dissolution and bulk diffusion was negligibly small in comparison with the surface diffusion of C species on the carbon nanotube surface. Bulk diffusion of C through the nanoparticle defined the characteristic times of C penetration to the nanoparticle base and surface saturation with C, and played a major role in the selection of the initial mode of carbon nanotube nucleation and growth, leading to the formation of straight-wall carbon nanotube or bamboo-like carbon 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