Probing potassium on Ni(100) with adsorbed rare gas atoms.

Changes in the Ni(100) surface due to controlled coverages of K are studied through the photoemission spectra of rare gas adsorbates. Valence band photoemission spectra indicate Xe and Ar states on the K/Ni surface which are related to local interactions with the partially ionized K adatoms. In addition, all photoemission spectra are shifted linearly to higher binding energy due to a reduction in the surface work function caused by the K. An investigation of the Xe Auger parameter reveals that the increase in binding energy is accompanied by an increase in the extra-atomic screening of the core holes by the metal electrons. The work function change which results from Xe adsorption indicates that as K is added the polarization of the Xe electrons shifts away from the Ni substrate toward the K overlayer. A third, very weakly bound Xe state is observed at higher K coverages. This state is linked to Xe atoms which have lost contact with the Ni substrate.