Graphene on Pt3Ni(111): a suitable platform for tunable charge doping, electron-phonon coupling and plasmonic excitations

Despite intensive investigations, the comprehension of the mechanisms ruling the interplay of charge doping, electron-phonon coupling and dynamic screening in supported graphene remains elusive yet. Using a combination of surface-science spectroscopies, we have studied these phenomena for graphene on both Pt-skin-terminated and nickel-oxide-skin-terminated Pt3Ni(111). Graphene epitaxially grown on the (111)-oriented Pt skin behaves as a charge-neutral graphene/metal contact, exhibiting a reduced coupling of the out-of-plane optical phonon with Dirac-cone electrons. Conversely, p-doped graphene/Pt(111) exhibits giant Kohn anomalies arising from the electron-phonon coupling. Upon oxidation, the Pt skin of Pt3Ni(111) evolves into a nickel-oxide skin, which results into a p-type doped graphene sheet. The plasmonic spectrum shows dramatic changes when going from a graphene/Pt-skin/Pt3Ni to a graphene/nickel-oxide/Pt3Ni configuration. Finally, we show that the presence of Ni atoms in the metal alloy does not affect the temperature at which the graphene phase is formed, contrarily to the interpretation of previous experiments.