FACETING IN MULTI-WALLED NANOTUBES

Nanotubes hold great promise for the miniaturization of advanced technologies. Their exceptional physical properties are intimately related to their detailed morphological and crystal structure. Importantly, circumferential faceting of multi-walled nanotubes serves to reinforce their mechanical strength and alter their tribological and electronic properties. Here, nanotube faceting is fully rationalized in terms of interlayer registry patterns. We find that, regardless of the nanotube identity, faceting requires chiral angle matching between adjacent layers. Above a critical diameter that corresponds well with experimental findings, achiral multi-walled nanotubes display evenly spaced extended axial facets, the number of which is determined by the interlayer difference in circumferential unit cells. Elongated helical facets, most commonly observed in experiment, appear in nanotubes exhibiting a small interlayer chiral angle mismatch. In the case of uncorrelated wall chiralities faceting is suppressed and surface corrugation induced by the Moiré superlattice is obtained in excellent agreement with experiment. It is therefore evident that gaining control over their interlayer registry matching provides a route for the mechanical enforcement as well as tribological and electronic properties tuning of MWNTs.