Shear Modulus of Monolayer Graphene Prepared by Chemical Vapor Deposition

We report shear modulus (G) and internal
friction
(Q–1) measurements of large-area
monolayer graphene films grown by chemical vapor deposition on copper
foil and transferred onto high-Q silicon mechanical
oscillators. The shear modulus, extracted from a resonance frequency
shift at 0.4 K where the apparatus is most sensitive, averages 280
GPa. This is five times larger than those of the multilayered graphene-based
films measured previously. The internal friction is unmeasurable within
the sensitivity of our experiment and thus bounded above by Q–1 ≤ 3 × 10–5, which is orders-of-magnitude smaller than that of multilayered
graphene-based films. Neither annealing nor interface modification
has a measurable effect on G or Q–1. Our results on G are consistent
with recent theoretical evaluations and simulations carried out in
this work, showing that the shear restoring force transitions from
interlayer to intralayer interactions as the film thickness approaches
one monolayer.