Knowledge Base

Analysis of lanthanum by XPS is typically performed on the 3d orbitals, which may overlap with Fe 2s, In 3s as well as the KLL auger from flourine and the Ce LMM auger if using Al X-rays (1486.7 eV). Additionally, the La M_4,5N_4,5N_4,5 auger overlaps with the La 3d peaks when using Al X-rays which may complicate peak analysis (can be separately modeled using a twin X-ray source).

Lanthanum metal consists of a typical asymmetric doublet with a spin-orbit separation of 17 eV.⁽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.

Lanthanum compounds however, undergo peak splitting and each spin-orbit coupled peak appears as a doublet (Figure 1). In general, this is due to the formation of one poorly screened final state (ground state – 4fⁿ(3dⁿ) – cf⁰) and one well-screened final state due to conduction band to 4f charge transfer screening (4fⁿ⁺¹(3dⁿ⁺¹⁺) – cf¹L).⁽²⁾

Figure 1: La₂O₃ (green) and Lanthanum acetate sesquihydrate (red)⁽³⁾

The energy separation between the two maxima changes between the oxide and hydroxide, and in fact is often used as a simple method for determining chemical state (Table 1).⁽⁵⁾

Table 1: Peak separation energies for lanthanum oxide and hydroxide

Interestingly, no spin orbit splitting may be observed for the La 4p region due to a Coster-Kronig process⁽⁸⁾ but further splittings enable this region to be of use when dealing with lanthanum in XPS (Figure 3).⁽⁴⁾

References

1. Kumar, R., et al. (1984). “Surface recoiling, XPS and UPS study of chemisorption of H2, O2 and H2O on lanthanum.” Surface science 147(1): 37-47. Read it online here.
2. Suzuki, S., et al. (1974). “X-ray photoemission spectra of 4d and 3d electrons in lanthanum-and cerium-halides.” Journal of the Physical Society of Japan 37(5): 1334-1340. Read it online here.
3. Data acquired by HarwellXPS
4. Sunding, M., et al. (2011). “XPS characterisation of in situ treated lanthanum oxide and hydroxide using tailored charge referencing and peak fitting procedures.” Journal of Electron Spectroscopy and Related Phenomena 184(7): 399-409. Read it online here.
5. Mickevičius, S., et al. (2007). “The Surface Hydro-Oxidation of LaNiO_ {3-x} Thin Films.” Acta Physica Polonica A 1(112): 113-120. Read it online here.
6. Teterin, Y. A., et al. (2004). “Secondary electronic processes and the structure of X-ray photoelectron spectra of lanthanides in oxygen-containing compounds.” Journal of Electron Spectroscopy and Related Phenomena 137: 607-612. Read it online here.
7. Siegmann, H., et al. (1978). “Self-Restoring of the Active Surface in the Hydrogen Sponge La Ni 5.” Physical review letters 40(14): 972. Read it online here.
8. Mullica, D., et al. (1993). “The X-ray photoemission spectra of La (OH) 3.” Journal of Electron Spectroscopy and Related Phenomena 61(3-4): 337-355. Read it online here.

Recommended reading

1. Sunding, M., et al. (2011). “XPS characterisation of in situ treated lanthanum oxide and hydroxide using tailored charge referencing and peak fitting procedures.” Journal of Electron Spectroscopy and Related Phenomena 184(7): 399-409. – Excellent discussion on the origin of photoemissions within La compounds as well as charge referencing challenging materials.