Stiffness and Atomic-Scale Friction in Superlubricant MoS2 Bilayers

Molecular dynamics simulations, performed with chemicallyaccurate ab initio machine-learning force fields,are used to demonstratethat layer stiffness has profound effects on the superlubricant stateof two-dimensional van der Waals heterostructures. We engineer bilayersof different rigidity but identical interlayer sliding energy surfaceand show that a 2-fold increase in the intralayer stiffness reducesthe friction by a factor of & SIM;6. Two sliding regimes as a functionof the sliding velocity are found. At a low velocity, the heat generatedby the motion is efficiently exchanged between the layers and thefriction is independent of the layer order. In contrast, at a highvelocity, the friction heat flux cannot be exchanged fast enough anda buildup of significant temperature gradients between the layersis observed. In this situation, the temperature profile depends onwhether the slider is softer than the substrate.