Strain-Mediated Friction Tuning of Atomic Step Edges by Carbon Chain Grafting

Two-dimensional (2D) layered materials are well known for superlubricity on their basal plane, but friction and stress can be more than an order of magnitude larger at step edges, preventing the 2D materials from achieving superlubricity in macroscale applications. Here, taking graphene as an example, we show a strategy to achieve friction reduction by introducing carbon chains at step edges via hydrogen plasma treatment. After grafting dodecyl chains, friction at single-layer graphene step edges is reduced by up to 67%. A series of molecular dynamics simulations are performed to unravel the tuning effect, showing that the grafted carbon chains alleviate interfacial strain concentration, which plays a dominant role in friction reduction. This work proposes a selective functionalization strategy for atomic step edges to reduce friction and provides deeper insight into the origin of high friction at step edges.