Thermal physics in carbon nanotube growth kinetics

Abstract

The growth of single wall carbon nanotubes (SWNTs) mediated by metal nanoparticles is considered within (i) the surface diffusion growth kinetics model coupled with (ii) a thermal model taking into account heat release of carbon adsorption-desorption on nanotube surface and carbon incorporation into the nanotube wall and (iii) carbon nanotube-inert gas collisional heat exchange. Numerical simulations performed together with analytical estimates reveal various temperature regimes occurring during SWNT growth. During the initial stage, which is characterized by SWNT lengths that are shorter than the surface diffusion length of carbon atoms adsorbed on the SWNT wall, the SWNT temperature remains constant and is significantly higher than that of the ambient gas. After this stage the SWNT temperature decreases towards that of gas and becomes nonuniformly distributed over the length of the SWNT. The rate of SWNT cooling depends on the SWNT-gas collisional energy transfer that, from molecular dynamics simulations, is seen to be efficient only in the SWNT radial direction. The decreasing SWNT temperature may lead to solidification of the catalytic metal nanoparticle terminating SWNT growth or triggering nucleation of a new carbon layer and growth of multiwall carbon nanotubes.

Boundary layer chemical vapour synthesis of self-organised ferromagnetically filled radial-carbon-nanotube structures

“…Previous reports of this synthesis using conventional solid-and liquid-source CVD do not comment on the absence of Ni3C and Fe3C in the final product nor attempt to describe the growth mechanism [31][32][33][34][35][36][37][38] . The absence of Fe3C and Ni3C diffraction peaks in Fig.5 suggests that 45 there is direct formation of FeNi alloys without the intermediate metal carbide formation, or MWCNT growth is driven by the carbon supply from an unstable carbide that decomposes that high rate.…”

“…Ultimately, this poor control is a manifestation of the heterogeneous nucleation (metal/substrate interaction) and natural fluctuation in steady-state diffusion gradients. 45 Here we demonstrate the principle of production of alloyed nanowire in radial structures by boundary layer chemical vapour synthesis. Radial -FeNi alloy-filled-MWCNTs were synthesised in vapour produced by the thermal decomposition of ferrocene and nickelocene.…”

“…The subsequent growth of the MWCNT and the filling of its central capillary by elemental iron or an iron-carbide is driven by supply of species from the vapour either to the base of the structure or to the open tip, or both. This is an entirely self- 45 organised production process. It is important to note that the nucleation of the MWCNT growth is heterogeneous, i.e.…”

Progress in Understanding Controlled Single-Walled Carbon Nanotube Growth from Computer Simulations

“…Theoretical studies of SWNT growth are primarily based on stationary point calculations using density functional theory (DFT), 21-32 semi-empirical methods, 33-40 molecular dynamics (MD) and direct dynamics methods, [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] Monte Carlo (MC) methods, 36-38 kinetic 58 and thermodynamic 59 models. Similarly to the experimental studies, an exhaustive review is not possible here and we limit the discussion to a few key results.…”

Simulation of Carbon Arc Discharge for the Synthesis of Nanotubes

“…1(d) shows the schematic of nanotube growth in plasma. Because of high temperature in the arc region and low species fluxes far away from the arc, it is presumed that nanotubes grow in the region just outside the arc where temperatures vary from 2000 to 1000 K. In fact, it was shown analytically that the growth rate of nanotubes is high in this temperature range which is limited on the upper and lower ends by the formation and condensation of catalyst clusters [6]. In these simulations, this region extends from 8 to 16 mm in the radial direction, and the average number density of C, Ni, and Y is 10 22 , 5 × 10 20 , and 1.25 × 10 20 m −3 , respectively.…”