  Recent theoretical considerations have demonstrated that freestanding
graphene doped with alkali metals (AC x ) supports strong Dirac and weak
acoustic plasmons. Here we show that when AC x is deposited on a metallic
surface, the intense Coulomb screening completely washes out these collective
modes. However, even small increase of separation between AC x and metallic
surface causes recovery of AC x plasmonic properties and especially the
enhancement of acoustic plasmons intensities not present in the freestanding
case. We further provide the physical background of these intriguing phenomena.
The studied systems consist of lithium- and cesium-doped graphene deposited on
Ir(111) surface.
