  In-situ high pressure Raman spectroscopy is used to study monolayer, bilayer
and few-layer graphene samples supported on silicon in a diamond anvil cell to
3.5 GPa. The results show that monolayer graphene adheres to the silicon
substrate under compressive stress. A clear trend in this behaviour as a
function of graphene sample thickness is observed. We also study unsupported
graphene samples in a diamond anvil cell to 8 GPa, and show that the properties
of graphene under compression are intrinsically similar to graphite. Our
results demonstrate the differing effects of uniaxial and biaxial strain on the
electronic bandstructure.
