Curved Crystal Transmission Optics for Energy-Dispersive X-ray Absorption Spectroscopy

Abstract

The development of a curved crystal monochromator of the Laue type for energy-dispersive X-ray absorption spectroscopy is presented. The quality of the X-ray absorption spectra at high photon energies is compared with spectra measured with silicon crystals in the more frequently used Bragg geometry. In the Bragg case, an asymmetric broadening of the reflectivity profile leads to strong distortions of the near-edge fine structure and to a reduction in spectral resolution. The reflectivity profiles of fiat and curved crystals for Laue and Bragg geometry have been calculated using dynamical theory and are compared with experimental data. The new optics have been used for in situ time-resolved X-ray absorption spectroscopy. An example of the application of the technique for the characterization of a Pd catalyst is given. The X-ray absorption fine structure at the Pd K-edge has been measured during the activation and during the heterogeneous catalytic oxidation of carbon monoxide.

Catalytic Methanol Oxidation over Copper: Observation of Reaction-Induced Nanoscale Restructuring by Means of In Situ Time-Resolved X-ray Absorption Spectroscopy

“…the provided synchrotron radiation photon energy ranges from 5 to 25 k eV. [15] The upstream optics consists of two X-ray focusing cooled mirrors. Both have three different stripes (Rh and Pt coating and a bare strip) allowing different cutoffs without changing the overall geometry of the beamline.…”

Turbo-XAS: dispersive XAS using sequential acquisition

“…A positionsensitive detector (PSD), consisting of a scintillator screen coupled to a CCD camera with a fast analog buffer, has been designed in order to reach such a time resolution (Koch et al, 1996). Thanks to the high¯ux available, both Bragg and Laue geometries (Hagelstein et al, 1995;San Miguel et al, 1998) for the polychromator crystal can be used, in order to cover the entire energy range from 5 to 27 keV with an optimized energy resolution.…”

The Time-resolved and Extreme-conditions XAS (TEXAS) facility at the European Synchrotron Radiation Facility: the energy-dispersive X-ray absorption spectroscopy beamline ID24

“…This geometry is ideally suited for the energy range 5-13 keV. At higher energies, penetration depth effects deteriorate both energy resolution and focal spot shape (Hagelstein et al, 1995;Sanchez del Rio et al, 2015). On branch EDXAS_L, a Si(111) polychromator crystal in Laue geometry (Poly_L) delivers larger spots, varying between 30 and 200 mm FWHM.…”