SPring-8, the large synchrotron radiation facility

Speaker : Prof. Weine Olovsson

Language : ENGLISH

Affiliation : Theoretical Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Sweden

Title : Theoretical core-level spectroscopy

Abstract :
By performing first-principles calculations for obtaining spectroscopic properties it is possible to investigate the electronic structure and bonding in a wide range of materials. Furthermore, the results can be used as a “fingerprint” in order to characterize different structures. In this presentation I will show different theoretical methodologies for core-level spectroscopy in comparison with experiment, for specific material studies.

Core-level binding energy shifts (CLSs) can be used as a sensitive probe of e.g. interface quality and intermixing of atoms. In substitutionally disordered alloys a so-called disorder broadening of the spectral core-line is expected due to the difference in the local chemical environment of the atoms. Also, one needs to consider lattice relaxation which can have a large effect in some systems. I will summarize some previous and new results focusing on disordered metallic alloys (e.g. AgPd) and interface systems (Ni/Cu/Ni) [1].

The most common methods to calculate the X-ray absorption near-edge structure (XANES) spectra are based on density functional theory (DFT) supercell techniques [2]. However, in order to carefully include the correlated motion of the core-hole and excited electron one needs to go beyond the single-particle picture. One way to do this is to use many-body perturbation theory by solving the Bethe-Salpeter equation (BSE). Here I will demonstrate results e.g. for the Li K-edge in Li-halides and Al L2,3-edge in different phases of AlN [3]. At present the BSE calculations are performed with the open source exciting-code [4].

It is a challenge to model amorphous structures and obtain representative XANES and extended x-ray absorption fine structure (EXAFS) spectra. Here I will demonstrate a computationally efficient way to do so with examples for Cr(1-x)C(x) surface alloys.

[1] W. Olovsson et al. J. Electron Spectroscopy Relat. Phenom. 178-9, 88 (2010)
[2] T. Mizoguchi et al. Micron 41, 695 (2010)
[3] W. Olovsson et al. Phys. Rev. B 83, 195206 (2011)
[4] http://exciting-code.org/

Organizer : Cui Yi Tao
Mail : yitaocui@spring8.or.jp
PHS : 3758