Surface photoemission from ultrathin potassium films adsorbed on tungsten

The initial stage of formation of ultrathin potassium films on W(100) is studied by threshold photoemission spectroscopy using p-and s-polarized light in a photon energy range of 1.6–3.5 eV. It is found that the photoemission current spectrum depends on the surface coverage by the alkaline atoms. Mathematically, this shows up as the dependence of the matrix elements responsible for photoemission excitation on surface coverage. The matrix elements vary because the photoelectron escape depth is small; hence, the emission comes from the surface layer under irradiation by both p-and s-polarized light.