▎ 摘　　要

We propose a composite layered structure for tunable, low-loss plasmon resonances, which consists of a noble metal thin film coated in graphene and supported on a hexagonal boron nitride (hBN) substrate. We calculate electron energy loss spectra (EELS) for these structures, and numerically demonstrate that bulk plasmon losses in noble metal films can be significantly reduced, and surface coupling enhanced, through the addition of a graphene coating and the wide-band-gap hBN substrate. Silver films with a trilayer graphene coating and hBN substrate demonstrated surface plasmon-dominant spectral profiles for metallic layers as thick as 34 nm. A continued-fraction expression for the effective dielectric function, based on a specular reflection model which includes boundary interactions, is used to systematically demonstrate plasmon peak tunability for a variety of configurations. Variations include substrate, plasmonic metal, and individual layer thickness for each material. Mesoscale calculation of EELS is performed with individual layer dielectric functions as input to the effective dielectric function calculation, from which the loss spectra are directly determined. DOI: 10.1103/PhysRevB.87.045428