  The electronic structure of graphene on Cu(111) and Cu(100) single crystals
is investigated using low energy electron microscopy, low energy electron
diffraction and angle resolved photoemission spectroscopy. On both substrates
the graphene is rotationally disordered and interactions between the graphene
and substrate lead to a shift in the Dirac crossing of $\sim$ -0.3 eV and the
opening of a $\sim$ 250 meV gap. Exposure of the samples to air resulted in
intercalation of oxygen under the graphene on Cu(100), which formed a
($\sqrt{2} \times 2\sqrt{2}$)R45$^{\rm o}$ superstructure. The effect of this
intercalation on the graphene $\pi$ bands is to increase the offset of the
Dirac crossing ($\sim$ -0.6 eV) and enlarge the gap ($\sim$ 350 meV). No such
effect is observed for the graphene on Cu(111) sample, with the surface state
at $\Gamma$ not showing the gap associated with a surface superstructure. The
graphene film is found to protect the surface state from air exposure, with no
change in the effective mass observed.
