Switchable friction enabled by nanoscale self-assembly on graphene

TL;DR

This study reveals that atmospheric adsorbates form superlattice stripes on graphene, causing switchable anisotropic friction, and demonstrates precise reversible manipulation of these frictional domains.

Contribution

It uncovers that frictional anisotropy in graphene is due to self-assembled atmospheric adsorbates, not structural ripples, and shows how to control these domains with a scanning probe.

Findings

Frictional domains are caused by self-assembled atmospheric adsorbates, not structural ripples.

Superlattice stripes can be reversibly manipulated with submicron precision.

Frictional anisotropy exceeds 200 percent and is tunable via adsorbate patterning.

Abstract

Graphene monolayers are known to display domains of anisotropic friction with twofold symmetry and anisotropy exceeding 200 percent. This anisotropy has been thought to originate from periodic nanoscale ripples in the graphene sheet, which enhance puckering around a sliding asperity to a degree determined by the sliding direction. Here we demonstrate that these frictional domains derive not from structural features in the graphene, but from self-assembly of atmospheric adsorbates into a highly regular superlattice of stripes with period 4 to 6 nm. The stripes and resulting frictional domains appear on monolayer and multilayer graphene on a variety of substrates, as well as on exfoliated flakes of hexagonal boron nitride. We show that the stripe-superlattices can be reproducibly and reversibly manipulated with submicron precision using a scanning probe microscope, allowing us to create arbitrary arrangements of frictional domains within a single flake. Our results suggest a revised understanding of the anisotropic friction observed in graphene and bulk graphite in terms of atmospheric adsorbates.