Microscopic Theory of Plasmons in Substrate-supported Borophene

Two-dimensional boron, or borophene, is a metallic monolayer material that hosts low-loss, high-confinement, and visible light plasmons. In contrast with graphene, borophene cannot be exfoliated and has been synthesized on a variety of metallic substrates. Here, we present first-principles density functional theory calculations of the dielectric and plasmonic properties of borophene grown on Ag(111). We systematically investigate the linear response and the momentum-dependent polarizability of borophene as a function of its proximity to the metallic substrate. Our calculations indicate that the plasmons in borophene are quenched by the substrate, which we explain via a simple electrodynamic model of coupled polarizabilities between the monolayer and substrate. Using this model, we predict that the substrate plasmon frequency can be tuned to minimize the quenching of the monolayer plasmons.