▎ 摘　　要

The excitation spectrum in the region of the intraband (Dirac plasmon) and interband (pi plasmon) plasmons in graphene/Pt-skin terminated Pt3Ni(111) is reproduced by using an ab-initio method and an empirical model. The results of both methods are compared with experimental data. We discover that metallic screening by the Pt layer converts the square-root dispersion of the Dirac plasmon into a linear acoustic-like plasmon dispersion. In the long-wavelength limit, the Pt d electron excitations completely quench the pi plasmon in graphene at about 4.1 eV, that is replaced by a broad peak at about 6 eV. Owing to a rather large graphene/Pt-skin separation (approximate to 3.3 angstrom), the graphene/Pt-skin hybridization becomes weak at larger wave vectors, so that the pi plasmon is recovered with a dispersion as in a free-standing graphene.