X-ray Photoelectron and Absorption Spectroscopy of Metal-Rich Phosphides M2P and M3P (M = Cr-Ni)

The electronic structures of metal-rich binary phosphides M2P and M3P (M = Cr-Ni) have been examined by means of X-ray photoelectron and absorption spectroscopy and compared with those of the monophosphides MP. The P 2p(3/2) binding and P K-edge absorption energies decrease with greater ionic character of the M-P bonding and indicate the presence of anionic phosphorus, contrary to previous theoretical assertions but consistent with our previous results. Interatomic effects play a more important role in affecting the energy shifts in these metal-rich phosphides than in the monophosphides, becomng more pronounced with higher metal concentration. Although the M 2p(3/2) XPS spectra show no discernible shifts in binding energies, they reveal satellite features whose intensity can be related to metal charge in the Co- and Ni-containing phosphides. In these cases, the metal charge becomes less positive with higher metal concentration. For Ni2P and Ni3P, this trend was confirmed from an analysis of the Ni L-edge and M-edge XANES spectra.