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Characterization of Metal Nanocatalyst State and Morphology during Simulated Single-Walled Carbon Nanotube Growth

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posted on 13.06.2013, 00:00 by Diego A. Gómez-Gualdrón, Jenni M. Beetge, Perla B. Balbuena
The catalyst nanoparticle structure has been proposed as a potential template to guide nanotube growth toward desired chiralities during chemical vapor deposition synthesis of single-walled carbon nanotubes. However, exploitation of such an effect depends on understanding the state of the nanocatalyst throughout the various stages of nanotube growth for different reaction conditions. Here we show that during nucleation there is a high carbon transport activity through the nanoparticle, but eventually a nickel–carbon core is stabilized. The nickel–carbon stoichiometry of the nanoparticle at such a state is found to correspond to known carbide compositions, with such composition varying with nanoparticle size. The Ni–C core adopts layered structures that resemble those found along the [100] and [001] directions in Ni2C (Pbcn or Pnnm) and Ni3C (P6322). The calculated self-diffusion coefficients of nickel atoms are consistent with viscous-solid nanoparticles, where atomic mobility changes are observed during growth according to variations in the nanoparticle carbon content.