Stone-Wales--type transformations in carbon nanostructures driven by electron irradiation

TL;DR

This paper demonstrates that electron irradiation can induce Stone-Wales-type defects in carbon nanostructures at energies below displacement thresholds, revealing new mechanisms of defect formation and amorphization.

Contribution

It combines experiments and simulations to show defect formation by single electron impacts at sub-threshold energies and explains irradiation effects in curved graphene structures.

Findings

Defects form via single electron impacts below displacement energy.

Moderate energy irradiation tends to amorphize graphene.

Stone-Wales defects can form in curved structures due to incomplete defect recombination.

Abstract

Observations of topological defects associated with Stone-Wales-type transformations (i.e., bond rotations) in high resolution transmission electron microscopy (HRTEM) images of carbon nanostructures are at odds with the equilibrium thermodynamics of these systems. Here, by combining aberration-corrected HRTEM experiments and atomistic simulations, we show that such defects can be formed by single electron impacts, and remarkably, at electron energies below the threshold for atomic displacements. We further study the mechanisms of irradiation-driven bond rotations, and explain why electron irradiation at moderate electron energies (\sim100 keV) tends to amorphize rather than perforate graphene. We also show via simulations that Stone-Wales defects can appear in curved graphitic structures due to incomplete recombination of irradiation-induced Frenkel defects, similar to formation of Wigner-type defects in silicon.