Bundling up carbon nanotubes through Wigner defects

TL;DR

This study demonstrates that Wigner defects, interstitial carbon atoms near vacancies, can form in carbon nanotube bundles, significantly impacting their mechanical properties by increasing shear modulus.

Contribution

It reveals that Wigner defects can exist in nanotube bundles and act as strong inter-tube links, a novel insight into defect formation and mechanical enhancement.

Findings

Wigner defects have lower formation energy in nanotubes than vacancies.

Defects increase the shear modulus of nanotube bundles.

Wigner defects are likely prevalent after irradiation.

Abstract

We show, using ab initio total energy density functional theory, that the so-called Wigner defects, an interstitial carbon atom right besides a vacancy, which are present in irradiated graphite can also exist in bundles of carbon nanotubes. Due to the geometrical structure of a nanotube, however, this defect has a rather low formation energy, lower than the vacancy itself, suggesting that it may be one of the most important defects that are created after electron or ion irradiation. Moreover, they form a strong link between the nanotubes in bundles, increasing their shear modulus by a sizeable amount, clearly indicating its importance for the mechanical properties of nanotube bundles.