Phase accumulation model analysis of quantum well resonances formed in ultra-thin Ag, Au films on W(110)

Series of quantum well states (QWS's) have been observed in photoemission s pectra for the Ag/W(110) and Ag/Au/W(110) systems in a binding energy regio n lying outside of the substrate energy gap that is needed for full confine ment of electronic waves in the adlayer. It is shown that the observed feat ures can be described as the quantum well resonance states. An extended pha se accumulation model has been applied for analysis of these states and the ir energy positions. It has been shown that a good correlation with experim ental results can be reached. when a phase shift is introduced into the mod el which is related to partial scattering of confined waves on the electron ic states in region of QWS formation outside of the substrate energy gap. T he resulting total phase shift obtained on the base of this approach correl ates nicely with the experimental one for both investigated systems. (C) 20 01 Elsevier Science B.V. All rights reserved.