Electronic properties of the leaky quantum-well system Ag(111)/Au/Ag

Angle-resolved photoemission has been employed to examine the electronic properties of a lattice-matched, epitaxial system prepared by depositing first a thin Au(111) layer on a Ag(111) substrate, and then a Ag(111) overlayer. The Au layer acts as a potential barrier for electron motion in the system. The Ag overlayer can be regarded as a quantum well, but in our experiment, the Au barrier is rather thin, and there is substantial coupling between the valence electrons in the Ag overlayer and the continuum states in the substrate. Nevertheless, well-defined quantum-well resonances are observed for Au barriers as thin as two atomic layers. These resonances can be understood as a result of partial trapping of valence electrons in the Ag overlayer. A calculation which takes into account the band structure and surface properties is carried out, and the results are in good agreement with the experiment. Initial- and final-state features in the spectra are identified by comparison with theoretical models. The effects of lattice match or mismatch at the interface will be discussed.