The interpretation of work-function variation in alkali chemisorption from the atomic viewpoint

The changes in work function with surface coverage of adsorbed alkali atoms on a transition metal substrate are studied. An analysis valid at low coverages incorporating the experimental results available in this region, is used to estimate values for the widths of the s and p levels (assumed equal), and their mean energy for different assumed values of the substrate-adatom distance d. A self-consistent numerical treatment is developed over a wide range of coverages. From this treatment a more complete determination of the parameters from comparison with experimental work function against coverage curves is achieved. The level width Delta for Cs on Re(0001) is estimated to lie in the range 0.7 eV<or= Delta <or=2 eV, with the Cs 6s valence level at about 1.8 eV above the Fermi level. An implication is that the absorbate levels are strongly hybridized. A much smaller value of Delta is estimated for Cs on a monolayer of oxygen on tungsten.