Sponsors:
 |
|
Organized by
the Institute of Experimental Physics, University of Bialystok
Krystyna Lawniczak-Jablonska, Poland
X-Ray Absorption Spectroscopy at Synchrotrons
Krystyna Lawniczak-Jablonska
Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warsaw, POLAND
-
Synchrotron radiation sources with very high radiation intensity in a broad range of energy, and with linear or circular polarization, have lead to the rapid development of X-ray Absorption Spectroscopy (XAS). The advanced analysis of X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectra offers a unique possibility for examining local structure. The most important feature of the x-ray absorption spectroscopy is the elemental sensitivity that allows to separate structural information concerning a particular element in a multi-element compound even if the content of this element is very low and the system is disordered. The physical background of XAS will be explained and the most important problems in experiments performance and data interpretation briefly discussed. The programs used for the data analysis will be presented on the example of materials interesting for spintronic.
Depending on the method used for data analysis and provided information the XAS is usually divided into XANES and EXAFS. The shape of the XANES spectra depends on the density of the unoccupied states in a given compound, and thus it can be considered as fingerprint of chemical bonds. The absorption edge energy can be correlated with charge transfer in the investigated element. In the case when a mixture of the several compounds containing the same element is present in the investigated sample, the analyzed spectrum is a weighted sum of the single-phase spectra of these compounds. This can be used for quantitative estimation of the concentration of particular phases in a sample.
The EXAFS oscillations are created in X-ray absorption process due to the scattering of internal photoelectrons on the neighboring atoms, therefore, the analysis of these oscillations is a source of information on a short-range order in the samples. This is of particular value in the case of investigation of buried low dimensional structures or dopants in the semiconductors.
Synchrotrons are modern, intense sources of continuous electromagnetic radiation emitted in the wide range of energy. The radiation range runs through the infrared, by the visible and vacuum ultraviolet up to soft and hard x-ray radiation. The radiation is emitted by the relativistic charged particles (electrons or positrons) with trajectories curved in the magnetic field. Almost 99% of particle energy is transferred to the emitting radiation, therefore the process is very effective as compare with x-ray tube. The brief descriptions of the synchrotron will be also given.
|
|
|
