Electron Confinement Effects in Silver Films Embedded between Graphene and Metallic Substrates

We examine the electronic structure of Ag deposits intercalated between graphene and Co(0001). Angle-resolved photoemission spectroscopy measurements reveal the formation of Ag sp-derived quantum well states due to finite electron reflectivity across the buried metal/metal interface. This observation provides evidence of flat Ag(111) film growth underneath graphene, in analogy with the layer-by-layer growth of Ag on the corresponding graphene-free surfaces. Band dispersion and spectral properties of the quantum well states reflect primarily the interaction with the supporting substrate. Signatures of the coupling between graphene and the underlying films are the shift of the Ag(111) surface state, the hybridization gap opening of the pi state crossing the Ag 4d states, the downward shift of the Dirac point (n-type doping), and the gap between pi and pi* Dirac cones. Similar observations are reported for Ag(111) films intercalated between Gr and Pt(111). These systems can be considered as prototypes of graphene-protected thin metal films displaying electron confinement effects.