Abstract
Free-standing graphene is inherently crumpled in the out-of-plane direction due to dynamic
flexural phonons and static wrinkling. We explore the consequences of this crumpling on the
effective mechanical constants of graphene.We develop a sensitive experimental approach to
probe stretching of graphene membranes under low applied stress at cryogenic to room
temperatures. We find that the in-plane stiffness of graphene is 20–100Nm1 at room
temperature, much smaller than 340Nm1 (the value expected for flat graphene).
Moreover, while the in-plane stiffness only increases moderately when the devices are cooled
down to 10 K, it approaches 300Nm1 when the aspect ratio of graphene membranes is
increased. These results indicate that softening of graphene at temperatures o400 K is
caused by static wrinkling, with only a small contribution due to flexural phonons. Together,
these results explain the large variation in reported mechanical constants of graphene devices
and pave the way towards controlling their mechanical properties.
