First Principles Studies of the Effect of Nickel Carbide Catalyst Composition on Carbon Nanotube Growth

Abstract

Density functional theory calculations were used to investigate the stability of single walled carbon nanotubes (CNTs) attached to nanoparticles. The total energies and the adhesion energies between the CNTs and the nanoparticles were calculated for systems where the nanoparticles were either pure Ni or Ni carbide. It was found that the adhesion between the CNT and a pure Ni cluster is stronger than between the same CNT and a Ni-carbide cluster although the energy difference was small compared to the total adhesion energies. This adhesion strength implies that CNTs are likely to remain attached to both pure Ni and Ni-carbide clusters and that either pure Ni or Ni-carbide clusters may be docked onto the open CNT ends to achieve continued growth or electronic contacts between CNTs and electrode materials. The system with a CNT attached to a pure Ni cluster was found to be energetically favoured compared to a system containing the same CNT attached to a Ni carbide. The difference in total energy implies that a CNT should act as a sink for C atoms dissolved in the Ni-carbide cluster which means that the dissolved C atoms will be drained from the cluster, yielding a pure metal in the zero Kelvin thermodynamic limit. It is argued that this draining procedure is likely to occur even if carbon is added to the cluster at a proper rate, e.g. during CNT growth.

Carbon nanotube growth: First-principles-based kinetic Monte Carlo model

“…These calculations include DFT geometry optimization [13][14][15][16], molecular dynamics (MD) [17][18][19][20][21][22][23][24][25], and tight binding Monte Carlo (TBMC) simulations [26][27][28], in which different aspects of the CNT growth process were studied, e.g. role of carbon/catalyst/support interaction [16,19], catalyst nanoparticle state [17,18], or CNT growth with chiralities [29][30][31][32].…”

Simulation and modeling of carbon nanotube synthesis: current trends and investigations

“…Borjesson and Boltan [42] also used density functional theory calculations to study the effect of nickel carbide catalyst composition on CNT growth. Total energies and adhesion energies between CNTs and nanoparticles were calculated for systems where nanoparticles were either pure Ni or nickel carbide, as shown in Figure 6D.…”

“…Borjesson and Bolton [42] used first-principles based DFT calculations to study the effect of nickel carbide catalyst composition on nanotube growth. The salient feature of this approach is that it directly gives the total energy and local adhesion energy of the system.…”

Computational studies of catalyst-free single walled carbon nanotube growth

“…The supercell was 14.8 Å × 30 Å × 10 Å for the graphene sheet with the zigzag edge (72 atoms) and 17.1 Å × 30 Å × 10 Å for the graphene sheet with the armchair edge (88 atoms). Previous studies 31,42 have shown that these systems are sufficiently large to obtain valid energies and structures when atoms, molecules, or clusters are added to the edge.…”

“…The probability for catalyst encapsulation depended on the adhesion strength for temperatures larger than 600 K, and the slow carbon diffusion at lower temperatures appeared to hinder the cap formation and lift-off. Börjesson et al 31 and Page et al 32 used first principles and semi-empirical methods to show that growth may be possible from both metallic and carbide particles. Amara and co-workers studied nucleation of SWNTs on nickel nanoclusters using a tight binding (TB) Monte Carlo (MC) model, focusing on the effect of the chemical potential on the growth mechanisms.…”