Vapor-solid-solid growth of single-walled carbon nanotubes

TL;DR

This study reveals that vapor-solid-solid (VSS) growth of single-walled carbon nanotubes is diffusion-limited, facet-dependent, and requires precise control of temperature and carbon supply to optimize growth quality and chirality.

Contribution

It provides the first atomistic insight into VSS SWCNT growth mechanisms, highlighting facet-dependent surface diffusion and the importance of controlling growth conditions.

Findings

VSS growth is diffusion-limited and facet-dependent.

Surface diffusion is significantly slower than in liquid catalysts.

Optimal growth requires strict temperature and carbon supply control.

Abstract

Single-walled carbon nanotubes (SWCNTs) are promising for nanoscale electronics and photonics, but practical deployment requires chirality control. Most catalytic chemical vapor deposition (CCVD) growth of SWCNTs proceeds on liquid metal nanoparticles via a vapor-liquid-solid (VLS) mechanism and yields broad chirality distributions, whereas improved selectivity has been reported for high-melting-point crystalline catalysts, suggesting vapor-solid-solid (VSS) growth. However, the atomistic mechanism and kinetic of VSS SWCNT growth remain unclear. Here it is shown, using machine-learning interatomic potential-driven molecular dynamics on rhenium nanoparticles, that VSS growth is diffusion-limited and governed by facet-dependent surface carbon transport coupled to carbon-driven facet reconfiguration without catalyst melting. Surface diffusion is up to $\sim 50\times$ slower than carbon diffusion in liquid iron, imposing a strict upper bound on sustainable carbon supply and producing a narrow growth window: insufficient transport drives carbon accumulation and multiple nucleation, whereas higher temperatures favor graphitic encapsulation. In contrast to defect-free VLS growth, defects persist, indicating slow defect healing, and equilibrium simulations reveal suppressed edge configurational entropy with stabilization of zigzag-rich, Klein-decorated edges. Together, these results establish facet evolution and surface diffusion as joint regulators of diffusion-limited VSS growth and motivate stringent control of temperature and carbon supply.