Manipulating quantum-well states by surface alloying: Pb on ultrathin Ag films

The electronic structure of ultrathin Ag films with 1/3 monolayer (ML) of Pb alloyed at the surface was investigated by angle-resolved photoemission spectroscopy. Compared to clean ultrathin Ag films, the energy positions of the quantum-well states (QWSs) moved closer to the Fermi level due to the change of the potential barrier at the film/vacuum interface. We found that the parabolic band dispersion of the QWSs become disturbed where they cross the surface-state bands, and furthermore, they were shown to follow the periodicity that is only present at the surface. Our results suggest that it is possible to tune the properties of the QWSs whose thickness is more than 10 ML just by submonolayer deposition of heteroelements at the surface.