Recent Achievement and Perspectives in Synchrotron Radiation X-ray Absorption Spectroscopy

1. Recent Achievement and Perspectives in Synchrotron Radiation X-ray Absorption Spectroscopy Juris PuransInstitute of Solid State Physics University of Latvia, RigaSimone BénazethL.U.R.E.-Université Paris XI, 91405 OrsayCharles SouleauLaboratoire de Chimie Inorganique-UFR Pharmacie-Université ParisXI,E-mail: xas@latnet.lv Internet: www.dragon.lv/exafs

2. X-ray Absorption Spectroscopy Passed X-rays DCI Incident X-rays Absorption (XAS): Ir L3 - edge: E= 11210 eV Range: 11150 - 12000 eV SAMPLE IrO2 SuperACO Total Electron Yield (TEY): O K- edge: E= 530 eV Range: 520 - 570 eV XANES + EXAFS XANES

3. X-Ray absorption and fluorescence

4. XAS spectrum subdivided in its characteristic regions

5. Pre-edge and XANES regions • X-ray absorption pre-edge region extending a few eV below and above the edge is determined by the local density of vacant states in an absorbing atom; the region is very sensitive to the valence state of the an absorbing atom ( Cr3+/ Cr6+; V4+/ V5+; Fe2+/ Fe3+; Pb2+/Pb4+ etc.) • X-ray absorption near edge structure (XANES) region extending from the edge up to about 30-50 eV above it is determined by multiple-scattering effects (scattering of an excited photoelectron on several atoms); the region is very sensitive to the symmetry of polyhedra (first and second coordination shells); for crystalline materials the region contain information about the atomic structural organization over distances up to about 6-8 Å

6. * O K- edge XANES FMS calculations for c-IrO2 Dipole transitions: 1s(O)  np (n2) A: 5t2g(Ir) + 2p(O) B: 5eg (Ir) + 2p(O) *J. Purans, A. Kuzmin, Ph. Parent and C. Laffon, Electrochim. Acta 46 (2001) 1973-1976.

7. EXAFS region • extended x-ray absorption fine structure (EXAFS), extending from about 30-50 eV up to 1000 eV and more, above the edge; Fourier transform of the EXAFS oscillations gives a pattern close to the radial atomic distribution for crystalline materials; the region contain information about the atomic structural organisation over distances up to about 4-6 Å. This circumstance testified to the crystallographic origin of information contained in the EXAFS oscillations.

8. “white line”  5d-band “EDA” software package Dipole transitions: 2p3/2(Ir)  nd (n5) 1 shell Results for the 1st coordination shell Ir-O1: N R (Å) 2 (Å2) C3 (Å3) c-IrO2 6 1.98 0.0018 0 thin film 6 1.94 0.0048 - 8·10-4 6-8 shells thin film c-IrO2 Ir L3 - edge EXAFS

9. Elements Accessible by XAFS at Synchrotron Radiation Centers Daresbury and LURE

10. Basic Advantages of XAS Techniques

11. Basic Information Obtainable from XANES and EXAFS Studies

12. In situ XAFS/diffraction H10 LURE The aim of this experiment was to investigate the feasibility of high temperature in situ XAFS/diffraction to study the effect of progressive dehydration on the coordination of Ln3+ ions intercalated in montmorillonite and the associated collapse of the interlayer spacing. The samples were thin films (0.5 – 1mm) with the clay platelets oriented preferentially parallel to the film. The mosaic of the clay particles was sufficient to allow observation of the (001) reflection (interlayer spacing) with the film held at 30o to the incident beam. We were able to use this arrangement to make the first combined in situ EXAFS and diffraction measurements in transmission mode on the H10 beamline

13. Schematic cross-section perpendicular to the clay layers in Li-montmorillonite :  - oxygen atoms,  - hydrogen atoms

14. The temperature variation of (a) the diffraction pattern (001 reflection) of the Lu-montmorillonite sample, (b) the interlayer spacing d001, and (c) the raw absorption spectra for the Lu L3 edge.

15. In the second temperature range (80 - 135 °C) we observed a structural transformation of interlamellar Ce3+aqua ion complexes into intermediate type complexes of Ce3+ ions.  Ce3+ ions directly interact with the surface oxygen anions of the silicate sheets. The water coordination number decrease from eight to about five, structural disorder increase about three time (DW factor increase up to 0.0 35 Å2)

16. Third-generation SR Sources • At present, the third-generation SR sources ESRF (CEE); ALS and APS (USA); ELETTRA and DAFNE (Italy); SPRING8 (Japan) with radiation brightness up to ~1019 photons are in operation. Having high brightness and distinct linear or circular polarization, SR provides unique research possibilities.In particular, new XAS methods, which were developed for studying atomic and electronic structures in both the bulk and the surface layers of various thickness values, are as follows: • (i) fluorescent XAFS (FEXAFS) spectroscopy; • (ii) surface XAFS (SEXAFS) spectroscopy by measuring Auger electrons, the total or partial yield of the photoelectron current, the yield of the photoinduced ion desorption, and the total internal reflection; • (iii) XAFS spectroscopy of x-ray excited optical luminescence (XEOL); • (iv) the method of measuring the circular magnetic x-ray dichroism (CMXD) applicable to the investigation of the magnetic properties of materials; • (v) EXAFS spectroscopy by measuring the intensities of Bragg peaks-diffraction anomalous fine structure (DAFS).

17. CONCLUSIONS • The high penetration of hard X-ray at high photon energies also enables the non-destructive analysis at the K-absorption edges of the interior (mm) of archaeomaterials (see Pantos E. et all). On the other hand, the low penetration of soft X-ray at low photon energies enable the non-destructive analysis of the surface of materials (10-6-10-9m).