Tight-binding model calculations in the theory of photoemission from quantum-well states in ultra-thin metallic films: Application to the Ag/V(1 0 0) overlayer system

A modification is proposed to the simple tight-binding (TB) model in a slab formulation for calculating the photoemission from valence band quantum-well states (QWS) in ultra-thin metallic films. In our approach the on-cite and hopping parameters of the model are treated as a function of film thickness in order to yield the correct binding energies of QWS in comparison with experiment. In the calculations of the photoemission intensities from the QWS the final-state electron effective mass normal to the film surface is regarded as the parameter adjusted so as to fit the experimental data. In the model adopted this effective mass turns out to be thickness-dependent and its values for the films considered are found to be anomalously large (by a factor of more than 2) relative to the free-electron mass, thus producing intriguing variations with film thickness of the final-state band dispersion along the direction perpendicular to the surface. It is shown that such unexpected behaviour is capable of explaining the basic features of intensity oscillations with photon energy observed in normal-photoemission spectra of different thickness Ag films on a V(1 0 0) substrate over the photon energy range 15–45 eV. Although some discrepancies exist between experiment and theory, the model developed provides a very good first-order description of the data, and its applicability to photoemission studies of other substrate/film systems is suggested.