Two-dimensional character of the interface-π plasmon in epitaxial graphene on Ni(1 1 1)

The graphene/Ni(1 1 1) system has been studied by angle-resolved electron-energy-loss spectroscopy. The interface-π plasmon, related to interband transitions involving hybridized states at the K point of the hexagonal Brillouin zone, has been measured at different scattering geometries. The resulting dispersion curve exhibits a square root behavior, indicating the Two-dimensional (2D) character of the interface collective excitation.