Torsional Stick-Slip Behavior in WS$_{2}$ Nanotubes

We experimentally observed atomic-scale torsional stick-slip behavior in individual nanotubes of tungsten disulfide (WS$_{2})$. When an external torque is applied to a WS$_{2}$ nanotube, all its walls initially stick and twist together, until a critical torsion angle, at which the outer wall slips and twists around the inner walls, further undergoing a series of stick-slip torque oscillations. This is contrary to what happens in a multi-wall carbon nanotube, where an external torque causes the outer wall to slip and twist smoothly around the inner walls. We present a theoretical model based on DFTB calculations, which explains the torsional stick-slip behavior of WS$_{2}$ nanotubes in terms of a competition between the effects of the in-plane shear stiffness of the WS$_{2}$ walls and the inter-wall friction arising from the atomic corrugation of the interaction between adjacent WS$_{2}$ walls. K. S. Nagapriya, Ohad Goldbart, Ifat Kaplan-Ashiri, Gotthard Seifert, Reshef Tenne, and Ernesto Joselevich, Phys. Rev. Lett. \textbf{101}, 195501 (2008).