Quantum size effects in Pb/Si(111) investigated by laser-induced photoemission

We use laser-induced photoemission spectroscopy at 6 eV photon energy to investigate quantum well states of epitaxial Pb films on Si(111) as function of film thickness. The binding energies of the quantum well states were found in good agreement with density-functional calculations for a freestanding Pb slab. An oscillation of the work function with a period of 2 ML was observed as a function of film thickness, which correlates well with the oscillatory electron density at the Fermi level determined from the photoemission spectra.