Synchrotron-radiation photoemission study of the Ba adsorption on W(110) is presented. The adsorbate $4d$ core-level spectra show sequentially the interface, surface, and the bulk components with thicknesses, as in the alkali-metals (AM) adsorption. However, in contrast to the AM adsorption, the Ba-coordinated tungsten atoms have increased the surface core-level shift to -400 meV, which is due to a strong interaction between the Ba d and W d surface states in the final state. The Ba adsorption has lowered the system work function to a minimum value of 2.02 eV, corresponding to one-third of a monolayer. Above that, Ba starts to interact with the charge underneath the W surface layer. As a result, a bulk valence state originated from that region shifts toward higher binding energy, and a component, shifted +107 meV, appears in the W $4f$ core-level spectra.

• Received 9 January 1998

DOI:https://doi.org/10.1103/PhysRevB.58.4149