Insights on the Excitation Spectrum of Graphene Contacted with a Pt Skin

The excitation spectrum in the region of the intraband (Dirac plasmon) and interband ([Formula: see text] plasmon) plasmons in graphene/Pt-skin terminated Pt [Formula: see text] Ni(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 [Formula: see text] plasmon in graphene at about [Formula: see text] eV, that is replaced by a broad peak at about 6 eV. Owing to a rather large graphene/Pt-skin separation (≈3.3 Å), the graphene/Pt-skin hybridization becomes weak at larger wave vectors, so that the [Formula: see text] plasmon is recovered with a dispersion as in a free-standing graphene.