Dynamics of the radial deformation recovery process of single-wall carbon nanotubes

Carbon nanotubes, and more specifically single walled carbon nanotubes (SWNTs), possess unusual properties which are valuable for nanotechnology and other fields of materials science and technology, owing to their extraordinary thermal, electrical, and in particular mechanical properties. Most of the desirable mechanical properties, including a high tensile strength, result from the covalent sp(2)-bonds formed between individual carbon atoms. However, SWNTs are much softer in their radial compared to their axial direction, which results in a reversible elastic deformation of the cross section when applying sufficiently strong hydrostatic pressures. This article provides further evidence, via time dependent Raman spectroscopy, that a stable deformed state exists as a result of van-der-Waals-interactions within individual tubes and specifically that these tubes can fully recover from this deformed state on surprisingly long time scales on the order of tens of minutes. In order to distinguish inter-tube from intra-tube effects, all experiments have been performed with densely packed, vertically aligned, free-standing SWNT arrays in comparison to individual, de-bundled SWNTs. These insights lead to far reaching conclusions regarding the mechanical properties and binding energies of the found stable state and, via a detailed analysis of the D-mode, enable the distinction of fully reversible deformations from defect induced states. (c) 2018 Elsevier Ltd. All rights reserved.