  Two-dimensional (2D) materials such as graphene offer a variety of
outstanding properties for a wide range of applications. Their transport
properties in particular present a rich field of study. However, the studies of
transport properties of graphene under pressure are mostly limited to $\sim$1
GPa, largely due to the technical challenges and difficulties of placing
graphene inside a diamond anvil cell (DAC) and maintaining good electrical
contacts under pressure. We developed a novel technique allowing for direct
measurements of the transport properties of high quality chemical vapor
deposition (CVD) monolayer graphene under pressures. Combined Raman
spectroscopic and direct resistivity measurements on pure monolayer graphene up
to 40 GPa shows an effective out of plane stiffness of
$c_{33}$=0.26$\pm_{.09}^{.11}$ GPa, and observe relatively constant resistances
with pressure, suggesting high pressure as a useful technique for producing
large biaxial strains within graphene.
