SYNCHROTRON-RADIATION PHOTOEMISSION-STUDY OF BA ON W(110)

Synchrotron-radiation photoemission study of the Ba adsorption on W(11 0) is presented:The adsorbate 4d core-level spectra show sequentially the interface, surface, and bulk components with thicknesses, as in th e alkali-metals (AM) adsorption. However, in contrast to the AM adsorp tion, the Ba-coordinated tungsten atoms have increased the surface cor e-level shift to -400 meV, which is due to a strong interaction betwee n the Ba d and W d surface-states in the final state. The Ba adsorptio n 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 in teract with the charge underneath the W surface layer. As a-result, a bulk valence state originated from that region shifts toward higher bi nding energy, and a component, shifted + 107 meV, appears in the W 4f core-level spectra.