Multiwalled nanotube faceting unravelled

TL;DR

This paper explains the formation and characteristics of circumferential faceting in multiwalled nanotubes, linking it to interlayer registry patterns and chiral angle matching, with implications for their mechanical and electronic properties.

Contribution

It provides a comprehensive rationalization of nanotube faceting phenomena based on interlayer registry, chiral angles, and diameter effects, advancing understanding of nanotube morphology.

Findings

Faceting requires matching of chiral angles between layers.

Achiral nanotubes show evenly spaced axial facets above a critical diameter.

Faceting is suppressed with uncorrelated wall chiralities, leading to outer layer corrugation.

Abstract

Nanotubes show great promise for miniaturizing advanced technologies. Their exceptional physical properties are intimately related to their morphological and crystal structure. Circumferential faceting of multiwalled nanotubes reinforces their mechanical strength and alters their tribological and electronic properties. Here, the nature of this important phenomenon is fully rationalized in terms of interlayer registry patterns. Regardless of the nanotube identity (that is, diameter, chirality, chemical composition), faceting requires the matching of the chiral angles of adjacent layers. Above a critical diameter that corresponds well with experimental results, achiral multiwalled nanotubes display evenly spaced extended axial facets whose number equals the interlayer difference in circumferential unit cells. Elongated helical facets, commonly observed in experiment, appear in nanotubes that exhibit small interlayer chiral angle mismatch. When the wall chiralities are uncorrelated, faceting is suppressed and outer layer corrugation, which is induced by the moir\'e superlattice, is obtained in agreement with experiments. Finally, we offer an explanation for the higher incidence of faceting in multiwalled boron nitride nanotubes with respect to their carbon-based counterparts.