The electronic properties of nickel phosphide surfaces: Angle-resolved and resonant photoemission studies

The electronic structures of (1 × 1) Ni2P(0 0 0 1) and image have been investigated by photoemission spectroscopy (PES). For both surfaces, the valence PES spectra consisted of a Ni 3d–P 3p hybrid band (main band) and a satellite; the main band is observed at 0–4 eV and the satellite is observed at 8 eV. Resonant PES study showed that the satellite is associated with the photoemission process leading to a two-hole bound final state. On image, a P 3p-induced surface state is formed around 0.6 eV along the boundary of the surface Brillouin zone of the c(2 × 4) lattice. The surface core-level shifts were observed in P 2p spectra for both surfaces; the surface components were shifted to the lower binding energy side by 0.9 eV for (0 0 0 1) and by 0.6 eV for image. These results suggest that the coordination number of surface P atoms is much reduced from that in the bulk. The segregation behavior of P atoms in Ni2P was investigated by Auger electron spectroscopy and PES. It was found that the segregation of P atoms proceeds by annealing at 260–330 °C. The valence PES study showed that the 3d levels of the surface Ni atoms are stabilized through the bonding with segregated P atoms.