EELS study of the epitaxial graphene/Ni(1 1 1) and graphene/Au/Ni(1 1 1) systems

We have performed electron energy-loss spectroscopy (EELS) studies of Ni(1 1 1), graphene/Ni(1 1 1), and the graphene/Au/Ni(1 1 1) intercalation-like system at different primary electron energies. A reduced parabolic dispersion of the π plasmon excitation for the graphene/Ni(1 1 1) system is observed compared to that for bulk pristine and intercalated graphite and to linear for free graphene, reflecting the strong changes in the electronic structure of graphene on Ni(1 1 1) relative to free-standing graphene. We have also found that intercalation of gold underneath a graphene layer on Ni(1 1 1) leads to the disappearance of the EELS spectral features which are characteristic of the graphene/Ni(1 1 1) interface. At the same time the shift of the π plasmon to the lower loss-energies is observed, indicating the transition of initial system of strongly bonded graphene on Ni(1 1 1) to a quasi free-standing-like graphene state.