Quantum chemical simulations reveal acetylene-based growth mechanisms in the chemical vapor deposition synthesis of carbon nanotubes

Abstract

Nonequilibrium quantum chemical molecular dynamics (QM/MD) simulation of early stages in the nucleation process of carbon nanotubes from acetylene feedstock on an Fe 38 cluster was performed based on the density-functional tight-binding (DFTB) potential.Representative chemical reactions were studied by complimentary static DFTB and density functional theory (DFT) calculations. Oligomerization and cross-linking reactions between carbon chains were found as the main reaction pathways similar to that suggested in previous experimental work. The calculations highlight the inhibiting effect of hydrogen for the condensation of carbon ring networks, and a propensity for hydrogen disproportionation, thus enriching the hydrogen content in already hydrogen-rich species and abstracting hydrogen content in already hydrogen-deficient clusters. The ethynyl radical C 2 H was found as a reactive, yet continually regenerated species, facilitating hydrogen transfer reactions across the hydrocarbon clusters. The nonequilibrium QM/MD simulations show the prevalence of a pentagon-first nucleation mechanism where hydrogen may take the role of one "arm" of an sp 2 carbon Y-junction. The results challenge the importance of the metal carbide formation for SWCNT cap nucleation in the VLS model and suggest possible alternative routes following hydrogen-abstraction acetylene addition (HACA)-like mechanisms commonly discussed in combustion synthesis.

Quantum Chemical Simulation of Carbon Nanotube Nucleation on Al2O3 Catalysts via CH4 Chemical Vapor Deposition

“…The formation and adsorption of CH groups on the Al 2 O 3 surface is also thermochemically favourable. Since C-C bond formation is a highly exothermic process, 67 both CH and CH 2 groups will rapidly aggregate on the surface due to their carbon dangling bonds. Ultimately this will result in polyyne chain formation, consistent with our QM/MD simulations.…”

Small binary iron‐carbon clusters with persistent high magnetic moments. A theoretical characterization

“…All of the above denotes how the investigation on iron clusters interacting with carbon atoms and derivatives is relevant . Whereas the characterization of TMCs by means of experimental techniques is quite complicated; theoretical and computational studies emerge as a natural alternative to get results and conclusions about these systems with enough accuracy.…”

Ab initio molecular dynamics simulation of ethanol decomposition on platinum cluster at initial stage of carbon nanotube growth

“…Especially, Khalilov et al [25] have recently succeeded to simulate the carbon cap formation on the nickel cluster starting from hydrocarbon molecules. Moreover, quantum chemical molecular dynamics simulation based on the density-functional tight-binding (DFTB) potential revealed the early stages in the nucleation process of CTNs from acetylene feedstock on an iron cluster [28]. Although simulations including reaction processes have contributed the understanding of some aspects of the dissociation process, it is still hard to attain the quantitative discussion on the charge transfer in associated with the chemical reaction by a classical MD simulation.…”