Torsional stick-slip behavior in WS2 nanotubes.

We experimentally observed atomic-scale torsional stick-slip behavior in individual nanotubes of tungsten disulfide (WS2). When an external torque is applied to a WS2 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. We present a theoretical model based on density-functional-based tight-binding calculations, which explains the torsional stick-slip behavior in terms of a competition between the effects of the in-plane shear stiffness of the WS2 walls and the interwall friction arising from the atomic corrugation of the interaction between adjacent WS2 walls.