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Praseodymium XPS is typically performed on the Pr 3d orbitals. It will strongly overlap with the Cu 2p and I 3p photoemission, as well as weakly overlap with the Bi 4s emission, and augers from Cs, Mn and Ba when using Al X-rays (1486.7 eV). The binding energies of the metal and oxides may be found in Table 1. Note, the peak position of the oxides is that of the ‘m’ peak (see later section in this article).

Praseodymium metal comprises of a mostly singular asymmetric 3d_5/2 peak with a spin-orbit splitting to the 3d_3/2 of 20.2 eV.^(1,4) There are, however, small satellite peaks to lower binding energy due to the screened 3d⁹ 4f³ final state.⁽¹⁾ Additionally, the Pr 3d_3/2 photoemission does undergo splitting, thought to be a shake-up satellite in which an electron from the sd band during photoemission is excited into an empty 4f state (pulled below the Fermi level following photoemission) with the absence of this transition from the 3d_5/2 peak attributed to a lower ratio of this transition between 3d_5/2:3d_3/2.⁽¹⁾

Praseodymium metal comprises of a mostly singular asymmetric 3d_5/2 peak with a spin-orbit splitting to the 3d_3/2 of 20.2 eV.^(1,4) There are, however, small satellite peaks to lower binding energy due to the screened 3d⁹ 4f³ final state.⁽¹⁾ Additionally, the Pr 3d_3/2 photoemission does undergo splitting, thought to be a shake-up satellite in which an electron from the sd band during photoemission is excited into an empty 4f state (pulled below the Fermi level following photoemission) with the absence of this transition from the 3d_5/2 peak attributed to a lower ratio of this transition between 3d_5/2:3d_3/2.⁽¹⁾

Note for below: WordPress does not support underlining characters – so core holes will be described using a bold text-type rather than an underlined text-type. Apologies for the confusion.

The oxides of Pr are complicated by the presence of intense satellite features. Praseodymiuin ions in Pr₂O₃ are in a 4f² configuration in the ground state, however twin final states of 4f² and 4f³L (L = hole in O 2p valence band) cause each 3d photoemission to split into two, induced by a core-hole potential acting on the 4f electrons.⁽²⁾ PrO₂ in the ground state is a mixture of 4f¹ and 4f²L.⁽³⁾

Distinguishing between Pr³⁺ and Pr⁴⁺ by XPS can be challenging, due to the complex nature of final state effects in such systems, however, careful analysis of the Pr 3d_5/2 lineshape and high energy final state effects affords an appropriate methodology. Analysis of the 3d_5/2 photoemission reveals the presence of one photoemission peak (m) and one shake-down satellite (s) (Figure 2) at lower binding energy arising from a well screened 4f³ final state.

The ratio between these two peaks may be used as a semi-quantitative probe since it varies between Pr³⁺ and Pr⁴⁺, with Pr₂O₃ reporting a higher ratio of m:s than PrO₂ (table 2).⁽⁴⁾

Further support for the assignment of Pr⁴⁺ can be found in an an extra satellite peak, not observed in Pr or Pr2O₃, at ~967 eV arising from 3d4f¹ final states, although this photoemission is relatively weak and may be hard to justify in materials with a lower praesodymium content, especially since it may overlap with the O KLL auger (note, the Pr 3d_5/2 emission does also produce this peak in PrO₂, however it overlaps with the 3d4f²L, and 3d4f³L² peaks).⁽³⁾

References

1. Crecelius, G., et al. (1978). “Core-hole screening in lanthanide metals.” Physical Review B 18(12): 6519. Read it online here.
2. Ogasawara, H., et al. (1991). “Praseodymium 3d-and 4d-core photoemission spectra of Pr2O3.” Physical Review B 44(11): 5465. Read it online here.
3. Bianconi, A., et al. (1988). “Many-body effects in praesodymium core-level spectroscopies of PrO 2.” Physical Review B 38(5): 3433. Read it online here.
4. Lütkehoff, S., et al. (1995). “3d and 4d x-ray-photoelectron spectra of Pr under gradual oxidation.” Physical Review B 52(19): 13808. Read it online here.

Recommended reading

• Core level spectroscopy of solids