Hidden surface states on pristine and H-passivated Ni(111): Angle-resolved photoemission and density-functional calculations

By means of angle-resolved photoemission, we have uncovered surface related states on the pristine and hydrogen saturated Ni(111) surfaces. Near normal emission spectra were recorded at room temperature as a function of photon energy. A hidden Tamm surface state is found on the clean Ni(111) surface at a binding energy of similar to 1.19 eV, completely masked by the Lambda(1) bulk d band. The existence of this surface state is in agreement with the density-functional theory calculations presented here. On the other hand, a surface state related to hydrogen adsorbed on the surface has been identified at a binding energy of similar to 0.22 eV. Under hydrogen exposure, it grows at the same rate as the three other surface states of the clean Ni(111) vanish.