Resonance photoemission from clean and oxygen-covered ni₃al

A marked resonance photoemission peak has been found about 7 eV below the Fermi level on Ni₃Al surfaces for photon energies in the vicinity of the Ni 3p threshold. In Ni₃Al the Ni 3d band is lowered well below the Fermi level, thus raising the possibility that the 3d band is either full (resembling Cu) or has considerably fewer d holes than in Ni metal (resembling Pd). Consideration of the intensity of the resonant peak may favor the latter possibility. When oxygen is adsorbed on either Ni₃Al(001) or Ni₃Al(lll) a peak appears about 6 eV below the Fermi level (originating from the O 2p level) which also exhibits a strong resonance enhancement at the Ni 3p threshold. The explanation of this phenomenon leads to the conclusion that the adsorbed oxygen is close to Ni, not Al, atoms. This result constitutes the first determination of adsorption sites on surfaces by means of resonance photoemission.