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Chemical speciation with X-ray emission and absorption spectroscopy

Especially in the field of geology and catalysis there is need of the investigation of chemical species of different kinds of samples. In this case, the chemical species means the chemical state, such as different oxidations states of the same atom (for example Fe, FeO, Fe2O3), or the orientation within a molecule.

Both of these properties are accessible with X-ray Emission (XES) and Absorption fine structure (XAFS) spectroscopy, but due to the small changes in corresponding energy levels in the range of a few eV, the needed spectral resolving power is very high. This is the reason why these measurements are usually carried out at synchrotron radiation (SR) sources, which combines a high flux with a very good spectral resolving power up to E/delta E = 10000, which means that you can resolve 0.8 eV at the energy of the copper Kα emission line duplet.

To transfer this method to the laboratory wavelength dispersive spectrometers based on the von Hamos geometry were designed and build up, that are capable to perform these kinds of measurements in the laboratory.

To ensure the necessarily high efficiency of the spectrometer due to the low brilliant laboratory sources, Highly Annealed Pyrolytic Graphite (HAPG) mosaic crystals are used as the dispersive element. These crystals have the highest integral reflectivity among all known crystals and provide a spectral resolving power of approximately E/delta E = 2000 in first and E/delta E = 4000 in second order of reflection.

Point of contact: Christopher Schlesiger, Wolfgang Malzer

Relevant publications:

L. Anklamm, C. Schlesiger, W. Malzer, D. Grötzsch, M. Neitzel and B. Kanngießer, Rev. Sci. Instrum. 85, 053110 (2014)

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