Superlubric to stick-slip sliding of incommensurate graphene flakes on graphite

TL;DR

This study investigates the frictional behavior of incommensurate graphene flakes on graphite, revealing a load-induced transition from superlubricity to stick-slip due to edge atom distortions, applicable to layered materials.

Contribution

It uncovers a reversible friction increase mechanism in incommensurate graphene on graphite caused by vertical edge distortions, not rotations or dislocations.

Findings

Friction increases suddenly with load for incommensurate graphene flakes.

The transition is due to vertical edge atom distortions, not rotations or dislocations.

Behavior is relevant to all layered materials with strong in-plane bonds.

Abstract

We calculate the friction of fully mobile graphene flakes sliding on graphite. For incommensurately stacked flakes, we find a sudden and reversible increase in friction with load, in agreement with experimental observations. The transition from smooth sliding to stick-slip and the corresponding increase in friction is neither due to rotations to commensurate contact nor to dislocations but to a pinning caused by vertical distortions of edge atoms also when they are saturated by Hydrogen. This behavior should apply to all layered materials with strong in-plane bonding.