Photoemission from H adsorbed on Ni(111) and Pd(111) surfaces

The electronic states of H chemisorbed onto the Ni(111) and Pd(111) surfaces are investigated as a function of H concentration using angle-resolved photoelectron spectroscopy and synchrotron radiation as the light source. Exposure of either crystal surface to molecular H₂ results at low temperature in adsorption of approximately one monolayer of atomic H. This saturation coverage of H is characterized by a H-induced band split off from the bulk bands with 1×{}1 dispersion and by dramatic changes in the d-band surface states. As the H concentration is decreased, the split-off state moves upwards towards the bulk bands at all k? until it disappears at a H concentration of {~}0.5 [0.3] of the saturation coverage for Ni(111) [for Pd(111)]. In contrast to the behavior of the split-off state the substrate surface states shift continuously with H concentration. We propose that the split-off state results from the attractive H potential but its dispersion is dictated by the substrate symmetry.