Mysterious Role of Cap Configuration in Single-Walled Carbon Nanotube Catalytic Growth

TL;DR

This study introduces a new algorithm to analyze cap structures in SWCNT growth, revealing how cap topology and catalyst curvature influence chirality selection and stability, advancing understanding of nanotube synthesis.

Contribution

The paper presents a novel algorithm for determining cap chirality and explores how cap and catalyst interactions affect SWCNT growth, providing insights into chirality control.

Findings

Cap topology and catalyst curvature significantly influence formation energies.

AC and near-AC caps show superior stability and flexibility.

A shape factor correlates deformation with formation energy.

Abstract

Understanding the role of cap structure during the nucleation and growth of single-walled carbon nanotubes (SWCNTs) is essential for achieving chirality-controlled synthesis. In this work, we propose a novel and intuitive algorithm to determine the chirality of nascent carbon caps by tracking the relative shifts of six pentagons within a topological coordinate system. Based on this algorithm, we propose three routes of pentagon shifts for the chirality mutations from armchair (AC) to near-AC caps, namely the transverse shift (n,n) to (n+1,n-1), inward shift (n,n) to (n-1), and outward shift (n,n) to (n+1,n), can occur according to the energy profiles calculated based on the density function theory (DFT), providing a new perspective to explain the experimental abundance of near-AC SWCNTs. After that, we construct 24 representative short caps and long SWCNTs with different chiralities and symmetries, and perform DFT calculations to evaluate their thermodynamic stability and deformation behaviors on flat Ni(111) surfaces and curved Ni55 particle, respectively. The results reveal that cap topology and catalyst curvature together induce dual deformations that significantly influence the formation and interface energies. Notably, AC and near-AC caps exhibit superior flexibility and robust energetic advantages, especially the (6,6) cap with C6v symmetry. A linear correlation between cap-induced deformation and formation energy is established through a defined shape factor, highlighting the interaction between cap structure and catalyst interface as a key driver of chirality selection. This study theoretically reveals the cap evolution mechanism and lays the foundation for the rational design of SWCNT growth strategies.