How Graphene Slides: Measurement and Theory of Strain-Dependent Frictional Forces between Graphene and SiO2

<http://pubs.acs.org/doi/abs/10.1021/nl4007112>

Strain, bending rigidity, and adhesion are interwoven in determining how
graphene responds when pulled across a substrate. Using Raman
spectroscopy of circular, graphene-sealed microchambers under variable
external pressure, we demonstrate that graphene is not firmly anchored
to the substrate when pulled. Instead, as the suspended graphene is
pushed into the chamber under pressure, the supported graphene outside
the microchamber is stretched and slides, pulling in an annulus.
Analyzing Raman G band line scans with a continuum model extended to
include sliding, we extract the pressure dependent sliding friction
between the SiO2 substrate and mono-, bi-, and trilayer
graphene. The sliding friction for trilayer graphene is directly
proportional to the applied load, but the friction for monolayer and
bilayer graphene is inversely proportional to the strain in the
graphene, which is in violation of Amontons’ law. We attribute this
behavior to the high surface conformation enabled by the low bending
rigidity and strong adhesion of few layer graphene.