Softening to hardening of stretched diamondene nanotubes

Abstract

Diamondene, a carbon nanomaterial containing both sp² and sp³ carbon atoms, is obtained by compressing two or more layers of graphene. By curving rectangular diamondene and matching the unsaturated C–C bonds on the two unbent edges, a nanotube is built. We build two diamondene nanotubes (DNTs) with different radii and test their strengths under uniaxial tension. From the stress–strain curves, we discover that DNTs exhibit softening followed by hardening. The mechanism is as follows: the bond lengths and bond angles impart different stiffnesses to the tube at different axial strains. Molecular dynamics simulations demonstrate that the feature of the softening–hardening process is independent of either the tube radii or the system temperature. The critical strain for the tensile strength of a DNT becomes lower at a higher temperature. This is caused by thermal vibration of the atoms in the tubes. At the same temperature, for a DNT with a larger radius, the value of critical strain is higher. These properties will be beneficial for the potential applications of DNTs in nanodevices.