paper

Switchable friction enabled by nanoscale self-assembly on graphene

arXiv:1504.05253 · doi:10.1038/ncomms10745

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.

This version contains new data which show that the stripes observed in AFM are adsorbates rather than structural ripples. We also clarify that the stripe axis is parallel to the axis of high friction, rather than perpendicular, as we previously claimed following others' studies; our revised conclusion is based on a more careful imaging sequence which avoided reorienting frictional domains

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