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

Abstract

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.

Electroless deposited Ni–P alloys: corrosion resistance mechanism

“…The binding energy of the Ni2p3/2 signal is found at 853.0 ± 0.1 eV in good agreement with the literature [11,33]. The distance of the satellite is found here to be 7.2 eV, thus clearly higher than the 6 eV reported for pure nickel but in keeping with the concept of the influence of phosphorus content on the electronic properties of Ni-P alloys [33]. A very small amount of nickel phosphate (856.4 ± 0.1 eV) is also found.…”

“…5) is very similar to the typical Ni2p3/2 plus satellite structure as known from pure metallic nickel [33]. The binding energy of the Ni2p3/2 signal is found at 853.0 ± 0.1 eV in good agreement with the literature [11,33].…”

“…On the other hand, the authors' work on amorphous Fe70Cr10P13C7 alloys has shown that phosphorus in the bulk of this alloy has a partial negative charge [23,24] in agreement with the literature data for Ni-P alloys [27,28] and on a series of binary nickel-phosphides [29]. Thus phosphorus in the bulk of the Ni-P alloy undergoes partial covalent bonding with the metal atoms, influencing both the structural order [29,30,31] and the electronic state of nickel in Ni-P compounds and alloys [29,32,33].…”

“…5) is very similar to the typical Ni2p3/2 plus satellite structure as known from pure metallic nickel [33]. The binding energy of the Ni2p3/2 signal is found at 853.0 ± 0.1 eV in good agreement with the literature [11,33]. The distance of the satellite is found here to be 7.2 eV, thus clearly higher than the 6 eV reported for pure nickel but in keeping with the concept of the influence of phosphorus content on the electronic properties of Ni-P alloys [33].…”

“…4.5 Electronic structure of Ni-P alloys XPS/XAES measurements have provided evidence of the metallic character of crystalline Ni-phosphides [29]. The high corrosion resistance of Ni-P alloys might be influenced by the electronic structure of these alloys [32] that in turn is affected by phosphorus content [33]. As also shown by the negatively charged (-0.4 eV) phosphorus in the bulk alloy (see above), nickel and phosphorus undergo partial covalent bonding between Ni 3d and P 3p bands [29,33,34].…”