Subsurface core-level shifts for an Au monolayer buried in Ag(111)

The Au 4$f_{7/2}$ core-level energy has been measured using photoemission for an Au(111) monolayer buried in Ag(111). The measured core-level energy as a function of the distance between the Au monolayer and the sample surface shows that the effective spatial range of surface effects is about three atomic layers. This range is significantly larger than what is expected from a simple model for the screening of potential changes in jellium. The result implies that significant subsurface core-level shifts can occur for close-packed metal surfaces.