| AVS 63rd International Symposium & Exhibition | |
| Applied Surface Science | Monday Sessions |
| Session AS-MoM |
| Session: | Quantitative Surface Analysis: New Ways to Perform Old Tricks |
| Presenter: | Alberto Herrera-Gomez, CINVESTAV-Queretaro, Mexico |
| Authors: | A. Herrera-Gomez, CINVESTAV-Queretaro, Mexico D. Cabrera-German, CINVESTAV-Queretaro, Mexico J.A. Huerta-Ruelas, CICATA-Unidad Queretaro, Mexico M. Bravo-Sanchez, IPICYT, Mexico |
| Correspondent: | Click to Email |
The peak-asymmetry commonly found in core level photoemission spectra, especially from transition metals and their oxides, has been described in a number of ways. Doniach and Sunjic (DS) [1] proposed that the asymmetry is due to a “combination of the Kondo effect and a transient and singular re-adjustment of the ground state of the entire Fermi gas to the presence of the effective potential of the hole.” The argument was done for metals since the phenomenon requires occupation at the Fermi level. The proposed line-shape, which is extensively employed for peak-fitting, has important shortcomings. The form is not integrable (the area under it is infinite) for any possible value of the associated asymmetry parameter. Since integrability is paramount for composition analysis, the DS line-shape can only be employed in qualitative studies. Another proposed source is the divergence of the energy loss function at zero-loss [2]. Although this argument could apply to both metals and insulators, the divergence in turn causes a divergence in the calculated spectrum, forcing the near-zero loss region to be cut during integration.
A very extended view is that the skewedness is caused by the multiplet structure. Each multiplet component is considered as symmetric and the apparent asymmetry is due to the presence of components of different intensities near each other. In this way it has been possible to qualitatively reproduce the main features (satellites) of a number of materials. An excellent example is the work of Fujii et al. [3] for the Fe 2p spectrum for iron in Fe2O3 and in Fe3O4. As shown in their Fig. 3 and 10, the components are many and distributed with no apparent order. Since the intrinsic width of each component is much larger than the separation among them, it is impossible to experimentally resolve them. In addition, it would not make sense to try to construct a “fundamental” asymmetric line-shape.
Thereupon, we present a practical asymmetric line-shape, the double-Lorentzian (DL) [4], that minimizes the number of parameters employed for fitting complex spectra with apparent peak-asymmetries. The fits are clearly superior than those employing DS and also lacks for the integrability problem. Through DL it is possible to fit theoretical spectra, allowing for the quantitative comparison between the predicted and the experimental data.
1. S. Doniach and M. Sunjic, J. Phys. C 3, 285 (1970).
2. A.C. Simonsen, F. Yubero, S. Tougaard. Phys. Rev. B 56, p. 1612 (1997).
3. T. Fujii, F.M.F. de Groot, G. a Sawatzky, F.C. Voogt, T. Hibma, K. Okada. Phys. Rev. B. 59 (1999) 3195–3202.
4. http://www.qro.cinvestav.mx/~aherrera/reportesInternos/doubleLorentzian.pdf.