Coaxial carbon nanotubes: from springs to ratchet wheels and nanobearings

Abstract

Quantum mechanical calculations are performed for double-walled and triple-walled carbon nanotubes (DWCNTs, TWCNTs). We show how the DWCNTs may be modelled by mechanical analogues with interactions mediated by spring forces with weakening elastic constants in addition to a weak van der Waals -like interaction. This enables us to predict the natural frequency of longitudinal oscillations of the DWCNTs, their elastic spring constant and the corresponding interaction between the CNTs. Results of the interaction energy ΔE for the DWCNT system obtained from the mechanical model are in remarkable agreement with those obtained from our quantum mechanical calculations, and we obtain functional dependencies of ΔE on axial elongation and inter-wall separation of the DWCNTs. Our density functional theory calculations reveal that the armchair-armchair systems are significantly more stable than both the corresponding armchair-chiral configurations, as well as the corresponding stacked graphene sheets. The results obtained for translational and rotational motion (slide / roll) of the CNTs indicate a potential use of DWCNTs as springs, ratchet wheels, nanogears and bearings in miniaturized devices. Our work enables us to predict the behavior of DWCNTs of different dimensions and would be of practical importance in the actual construction of nanoscale mechanical parts.