| AVS 64th International Symposium & Exhibition | |
| Applied Surface Science Division | Tuesday Sessions |
| Session AS+MI+SS-TuM |
| Session: | Quantitative Surface Analysis: Effective Quantitation Strategies |
| Presenter: | C. Richard Brundle, C.R Brundle & Associates |
| Authors: | C.R. Brundle, C.R Brundle & Associates P.S. Bagus, University of North Texas |
| Correspondent: | Click to Email |
The “apparent” spin-orbit (S-O) splitting of metal cation core levels, observed by XPS for 3d transition metals, can vary with the ligand (anion) concerned, [1], even though true S-O splitting is an atomic property not depending on the atom’s environment. However, multiplet splittings of the core-level XPS of 3d cations depend on 3d shell occupation [1-3], so variation in this can alter the apparent S-O splitting. Such variation should have a consequence on the relative positions of the no-loss S-O component peak positions (ie the XPS “apparent” S-O splitting), via the well-established Mann and Aberg Sum Rule. [4]. Here we establish the importance of a mechanism that also contributes to changes in the multiplet splitting, and so in the apparent S-O splitting. This mechanism is covalent mixing of metal cation and ligand orbitals (for example Ref [5]), which alters the exchange integrals between core and valence electrons.
For a closed 3d shell, eg Ti4+ there is no possibility of multiplet splitting, but an apparent discrepancy in the S-O component intensity ratio has been reported (1), and an explanation proposed involving different intensity losses to shake-up satellites from each component. Our calculations indicate identical intensity losses, however, and a reanalysis of the experimental data indicates that the correct intensity ratio can be recovered by simply including the lifetime broadening of the 2p1/2 component, which results in overlap between it and the 2p3/2 component.
We present theoretical evidence, bare cation and cluster calculations, which provide quantitative estimates of the importance of various mechanisms for the covalency and for changes in apparent S-O splitting. These calculations allow comparison of “apparent S-O splitting” to “true” S-O splitting, the latter defined as the difference of the relativistic orbital energies of the S-O split levels. Furthermore, they permit establishing the differing importance of covalency for different ligands, and thus a connection to the observation of differences in core-level XPS for different ligands [6]. These effects also have a consequence for quantitative analysis using the 2p and 3p cation XPS peaks, which will be discussed.
1. S. A. Chambers, in Hard X-Ray Photoelectron Spectroscopy (HAXPES), edited by J. C. Woicik (Springer, Heidelberg, 2016), Vol. 59, p. 341
2. R. P. Gupta and S. K. Sen, Phys. Rev. B , 71 (1974)
3. R. P. Gupta and S. K. Sen, Phys. Rev. B , 15 (1975)
4. R. Manne and T. Åberg, Chem. Phys. Lett. , 282 (1970)
5. P. S. Bagus, E. S. Ilton, and C. J. Nelin, Surf. Sci. Rep. , 273 (2013)
6. M. Taguchi, T. Uozumi, and A. Kotani, J. Phys. Soc. Jpn. , 247 (1997)