Quantum-well states in Ag/W(1 0 0) and their symmetric evolution in the atomic limit of thickness

The behavior of quantum-well states (QWS) in ultrathin Ag-films grown on W(1 0 0) with thickness from 1 to 12 monolayers (ML) is probed by angle-resolved photoemission for the first time. Unlike the related and established systems Ag/Fe(1 0 0) and Ag/V(1 0 0), the QWS energies are with increasing thickness seen to evolve symmetrically about the QWS of 1 ML Ag (-2.5 eV). The QWSs are well described by the phase accumulation model down to lowest thicknesses only if the nearly-free-electron description of the parent Ag band established for Ag/Fe(1 0 0) is replaced by the simplest tight-binding approximation (linear chain approximation) with the band centered around the energy of the QWS of 1 ML Ag. The total phase shift across the bulk band gap is found to be of the order of 2 π, i.e., larger than reported for Ag/Fe(1 0 0).