Observation of Exposed and Hidden Au Quantum Well States in Au/Ag Heterostructures*

In this work, atomically uniform Au films are grown on a Ag(111) thin film. The Au quantum well states (QWS) are clearly observed by using Angle-resolved photoemission spectroscopy (ARPES). The Au QWSs hybridize with the Ag states and thus, show an energy dependence on the thickness of the supporting Ag film. Furthermore, a sandwich structure of Ag/Au/Ag is fabricated with various thicknesses of each constituent layer. The Au QWSs, though buried under the Ag overlayer, are still observable through hybridization with the Ag states. Interestingly, the hybrid quantum well states with Au d orbitals states possess a large effective mass as a result of hybridization with partially localized d states. Detailed first-principles simulations are performed to illustrate the orbital components of hybrid QWSs and provide an insight into the band dispersion of hybrid states.