Morphological stabilization, destabilization, and open-end closure during carbon nanotube growth mediated by surface diffusion

Abstract

In this paper, the growth stability of open-ended carbon nanotubes mediated by surface diffusion on the lateral surface of the nanotube is considered in detail. Nanotube growth and destabilization is viewed as a competition of two processes at the open growth edge: (i) hexagon formation sustaining the continuous growth of the regular hexagonal network, and (ii) thermally activated pentagon formation, which causes inward bending of the nanotube wall resulting in end closure, i.e., growth termination. The edge of the open-ended nanotube, if it is fed by a sufficiently large surface diffusion flux, may remain stable even without extrinsic stabilizing effects. The closure of the open end of the growing nanotube is shown to happen whenever a change in the growth conditions (temperature, carbon vapor pressure, or surface area from which the open end is fed) decreases the surface diffusion flux, and the characteristic time for new atom arrival on the edge becomes larger than the characteristic time for pentagon defect formation. These kinetic effects are also shown to define the transition from single wall to multiwall nanotube growth. Additionally, the effect of surface diffusion feeding nanotube growth from behind the growth interface is shown to stabilize open edge morphology, effectively smoothing the growth perturbations which may be caused by diffusion-limited aggregation at the edge.

Formation Mechanism of Pentagonal Defects and Bamboo-Like Structures in Carbon Nanotube Growth Mediated by Surface Diffusion

“…covered with large protuberances, transforming into cap-like edge structures and destabilizing the NT growth. This destabilization can not be smoothed out by C diffusion over the edge [18,19]. In effect, linear perturbation analysis shows, that in the far from equilibrium case, the increment of edge perturbation w is given by [19] w ffi 2pWl À1 D s ern ,…”

“…These studies show, that NT growth proceeds via the stages of adsorption and surface diffusion (SD) of carbon atoms on the NT surface, which underlie a set of effects crucial for the NT formation [14][15][16][17][18][19][20][21]. In this paper a short review of carbon NT growth kinetics is given outlining the major role of SD in the formation of pentagon defects, NT open end closure and bamboo-like structures during synthesis by physical and chemical vapor deposition.…”

Adsorption and migration of carbon adatoms on carbon nanotubes: Density-functionalab initioand tight-binding studies

“…However, it seems to be more plausible that the atoms first absorb onto the SWNT surface and then they migrate to the SWNT growing end. 1,2 The adsorbed atoms ͑adatoms͒ can also aggregate and form clusters ͑amorphous carbon͒ and detach from the nanotube surface. Thus, knowing the adatom migration mechanism and such key quantities like adsorption and migration energies is indispensable for the comprehensive theory of SWNT synthesis.…”

“…Many microscopic SWNT growth models have been developed [1][2][3][4][5][6] with growth taking place either at the nanotube edge 1-3 ͑capped or open͒ or its root. 4 -6 However, whatever the mechanism is, the quantitative understanding of the synthesis process is not possible without knowing how the ''building blocks''-carbon atoms and clusters-are supplied to the place where the SWNT growth occurs.…”

Diffusive growth of fullerenes and carbon nanotubes

“…[4][5][6][7][8] Our purpose here is to formulate the simplest possible diffusion model which might exhibit all the major observed features of the process. Unlike previous models of the diffusive growth of fullerenes, we are concerned with the carbon vapor concentration in the entire environment, rather than just on the surface of the fullerene.…”