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. 2020 Sep;200(5-6):479-484.
doi: 10.1007/s10909-020-02474-7. Epub 2020 Jul 4.

Feasibility of Laboratory-Based EXAFS Spectroscopy with Cryogenic Detectors

Simon J George  1 , Matthew H Carpenter  1 , Stephan Friedrich  2 , Robin Cantor  1
Affiliations

Feasibility of Laboratory-Based EXAFS Spectroscopy with Cryogenic Detectors

Simon J George et al. J Low Temp Phys. 2020 Sep.

Abstract

Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is a powerful technique that gives element-specific information about the structure of molecules. The development of a laboratory EXAFS spectrometer capable of measuring transmission spectra would be a significant advance as the technique is currently only available at synchrotron radiation lightsources. Here, we explore the potential of cryogenic detectors as the energy resolving component of a laboratory transmission EXAFS instrument. We examine the energy resolution, count-rate, and detector stability needed for good EXAFS spectra and compare these to the properties of cryogenic detectors and conventional X-ray optics. We find that superconducting tunnel junction (STJ) detectors are well-suited for this application.

Keywords: Cryogenic Detectors; EXAFS; STJ Detectors; XAS.

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Figures

Fig. 1
Fig. 1
EXAFS data extraction illustrated using experimental Fe K-edge data from Fe2(adt)(CO)6 (adt = the azadithiolate −SCH2NHCH2S−) [6] (Fig. 2 left). Left: The XAS absorption spectrum. A spline function is fitted to the X-ray edge to extract the post-edge oscillations. Center: The EXAFS spectrum is transformed into k-space and re-scaled by k3. Right: The EXAFS Fourier transform shows atoms as a function of distance from the absorbing element.
Fig. 2
Fig. 2
Structures and relevant distances used in this work. Left: Fe2(adt)(CO)6 [6]. Right: Cu(CQ)2; (CQ = clioquinol) [7].
Fig. 3
Fig. 3
Approaches to laboratory transmission EXAFS. Left: Using an energy-resolving crystal optic. A spectrum is collected one energy point at a time through a combined movement of the crystal, X-ray source and detector [8]. Right: Using an energy-resolving cryogenic detector. The entire spectrum is collected in a single X-ray exposure with no moving parts [9,10].
Fig. 4
Fig. 4
Simulated effect of energy resolution on the Cu K-edge EXAFS of Cu(CQ)2. Left: EXAFS spectrum convolved with Gaussian functions with increasing FWHM linewidths. Center: The corresponding Fourier transform with key interactions indicated. Elements in parentheses are multiple scattering intermediate atoms. Right: Plot of the intensity of the main peaks in the Fourier Transform as a function of simulated energy resolution.
Fig. 5
Fig. 5
Effect of adding Poissonian noise to the Fe EXAFS of 25 mM Fe2(adt)(CO)6 in acetonitrile (0.4% Fe). Left: Transmission. Center: EXAFS at different acquisition times. Right: Corresponding Fourier transform spectra.
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References

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