Chirality-Dependent Kinetics of Single-Walled Carbon Nanotubes from Machine-Learning Force Fields

TL;DR

This study uses machine-learning force fields in molecular dynamics simulations to explore how the chirality of single-walled carbon nanotubes is influenced by defect kinetics and diameter control mechanisms during growth.

Contribution

It develops a cobalt-carbon MLFF and a microkinetic modeling workflow to reveal the chirality-dependent growth kinetics of SWCNTs under VLS conditions.

Findings

Chirality preference is linked to initial cap configurations.

Pentagon defects form and resolve immediately after nucleation.

Diameter control mechanisms significantly influence chirality distribution.

Abstract

The origin of the chirality of single-walled carbon nanotubes (SWCNTs) has been a long-standing dispute. Molecular dynamics (MD) simulations driven by machine-learning force fields (MLFF), which can study the interface dynamics under near ab-initio accuracy, provides a powerful technique to reveal the formation mechanism of SWCNTs. Here, we develop a cobalt-carbon MLFF and perform growth simulations on a cobalt catalyst to investigate the chirality preference of the growth of SWCNTs under the vapor-liquid-solid (VLS) regime. Through microkinetic modeling, we reproduce the observed growth and defect kinetics, demonstrating their dependence on the chirality. It is observed that while the initial chirality assignment is likely related to the configurational degeneracy of the nanotube caps, pentagon defects immediately form and resolve after nucleation. Such processes, which we name as diameter control mechanisms, not only control the diameter toward an optimum but also shift the chirality distribution drastically. Our work therefore offers a microkinetic modeling workflow for the chirality-dependent kinetics of the SWCNTs, highlighting the important contribution of the defect kinetics to the chirality origination.