A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d94s2 (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd9L and the unscreened cd8 final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)2, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni2+ and Ni3+ simulate the main line and satellite structures for Ni(OH)2 and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed.

Ni2p3/2 X-ray photoelectron spectral peak binding energies of Ni metal, NiS, and NiAs (all conductors) span a range of about 0.5 eV and are, consequently, insensitive to formal Ni oxidation state and to the nature of the ligand to which Ni is bonded, relative to other metals (e.g., Fe). Ni2p3/2 peak structures and binding energies reflect two energetic contributions. The major contribution is that associated with the electrostatic field produced by ejection of the Ni(2p) photoelectron, the minor contribution is the relaxation energy associated with filling unoccupied, conduction band 3d9 and 4s Ni metal orbitals. These conduction band orbitals become localized on the Ni photoion (and sometimes filled) in response to the field created by the photoemission event. Because only the core Ni2p electron and nonbonding orbitals of predominantly metallic character are affected, the main peak of all three conductors are affected similarly, leading to similar Ni2p3/2 main peak binding energies. NiO, Ni(OH)2, and NiSO4 are insulators in which Ni is divalent and is bonded to oxygen. Although Ni is bonded to oxide in these phases, Ni2p binding energies differ substantially, and reflect primarily the nature of the ligand (O2−, OH−, SO4 2−) to which Ni is bonded. The influence of the ligand is the result of charge (electron) transfer from valence band bonding orbitals of dominantly ligand character, to unoccupied conduction band orbitals localized on Ni photoions. Relaxation energy resulting from charge transfer is acquired by the emitted photoelectron, thus Ni2p3/2 photopeak binding energies of these insulators reflect the nature of the ligand to which Ni is bonded. The Ni2p main peak binding energy of these conductors and insulators is a poor guide to Ni oxidation states. The Ni2p3/2 binding energies of insulators reflect, however, the nature of the ligand in the first coordination sphere of Ni. The intensity of the Doniach–Sunjic contribution to Ni2p XPS spectra of NiS and NiAs is dependent on the nature of the ligand. The Doniach–Sunjic contribution to ligand XPS core-level photopeaks (e.g., S2p of NiS and As3d of NiAs) has not been explained and is poorly understood.

Ni2p3/2 X-ray photoelectron spectral peak binding energies of Ni metal, NiS, and NiAs (all conductors) span a range of about 0.5 eV and are, consequently, insensitive to formal Ni oxidation state and to the nature of the ligand to which Ni is bonded, relative to other metals (e.g., Fe). Ni2p3/2 peak structures and binding energies reflect two energetic contributions. The major contribution is that associated with the electrostatic field produced by ejection of the Ni(2p) photoelectron, the minor contribution is the relaxation energy associated with filling unoccupied, conduction band 3d9 and 4s Ni metal orbitals. These conduction band orbitals become localized on the Ni photoion (and sometimes filled) in response to the field created by the photoemission event. Because only the core Ni2p electron and nonbonding orbitals of predominantly metallic character are affected, the main peak of all three conductors are affected similarly, leading to similar Ni2p3/2 main peak binding energies. NiO, Ni(OH)2, and NiSO4 are insulators in which Ni is divalent and is bonded to oxygen. Although Ni is bonded to oxide in these phases, Ni2p binding energies differ substantially, and reflect primarily the nature of the ligand (O2−, OH−, SO4 2−) to which Ni is bonded. The influence of the ligand is the result of charge (electron) transfer from valence band bonding orbitals of dominantly ligand character, to unoccupied conduction band orbitals localized on Ni photoions. Relaxation energy resulting from charge transfer is acquired by the emitted photoelectron, thus Ni2p3/2 photopeak binding energies of these insulators reflect the nature of the ligand to which Ni is bonded. The Ni2p main peak binding energy of these conductors and insulators is a poor guide to Ni oxidation states. The Ni2p3/2 binding energies of insulators reflect, however, the nature of the ligand in the first coordination sphere of Ni. The intensity of the Doniach–Sunjic contribution to Ni2p XPS spectra of NiS and NiAs is dependent on the nature of the ligand. The Doniach–Sunjic contribution to ligand XPS core-level photopeaks (e.g., S2p of NiS and As3d of NiAs) has not been explained and is poorly understood.