Interplay between thin silver films and epitaxial graphene

Abstract

Thin Ag films, with nominal thickness in the range 2 to 30 nm, are deposited using direct current magnetron sputtering and film morphology is studied by means of plan-view scanning electron microscopy. We find that for 2 nm nominal thickness the film surface consists of isolated circular nanoscale islands, which become interconnected as further material is deposited, leading to a continuous film at a nominal thickness of 30 nm. Our experimental findings are discussed in the context of the density functional theory results, which show that van der Waals forces dominate the interaction between Ag and epitaxial graphene. We also performed micro-Raman analysis and we find that the G and 2D modes of epitaxial graphene exhibit a red-shift upon Ag-layer deposition; which is interpreted as a result of charge transfer at the Ag/graphene interface. Moreover, we observed a pronounced enhancement of the G peak amplitude and area irrespective of the film nominal thickness and morphology, which we attribute to a combination of the charge transfer and plasmonic resonance effects. Our observations provide a critical information on the interaction between Ag and epitaxial graphene, which can be useful to design electronic and sensing devices based on Ag-epitaxial graphene hybrids.