Effect of phosphorus concentration on the electronic structure of Ni-P nanocrystalline electrodeposited alloys: an XPS and XAES study

A surface analysis has been conducted on a series of electrodeposited nickel-phosphorus (Ni–P) alloys containing from 6 to 29 at.% phosphorus, using X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES). No changes in core-level binding energies, Ni2p3/2 and Ni2p1/2, P2p, P2s, or X-ray excited NiLMM and PKLL Auger lines were observed regardless of phosphorus concentration. The only systematic differences observed concerned: (i) the binding energy of the Ni2p satellite peak, (ii) the fine structure of the NiLMM Auger lines, (iii) the percentage of the satellite in the total Ni2p3/2 spectrum and (iv) the valence band density of states in the Ni3d electrons region, all related to the electronic structure of the Ni–P alloys. For the first time, it has been possible to describe and rationalise the influence of (phosphorus) ligand concentration on the electronic structure of nickel-based alloys, using a screening model proposed in the literature for clarifying the role of substituents on the electronic structure of conductor compounds of nickel. As the phosphorus content increases, the number of non-bonding Ni3d electrons decreases. Thus the d-type core-hole screening is less pronounced and the binding energy of the satellite for the final state with a filled Ni4s shell increases.