Feasibility of Laboratory-Based EXAFS Spectroscopy with Cryogenic Detectors
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Feasibility of Laboratory‑Based EXAFS Spectroscopy with Cryogenic Detectors Simon J. George1 · Matthew H. Carpenter1 · Stephan Friedrich2 · Robin Cantor1 Received: 26 July 2019 / Accepted: 15 May 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
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 detectors are well-suited for this application. Keywords Cryogenic detectors · EXAFS · STJ detectors · XAS
1 Introduction In this paper, we explore whether a practical laboratory spectrometer for extended X-ray absorption fine structure (EXAFS) can be built using a cryogenic detector as the energy-resolving component. EXAFS spectroscopy gives element-specific structural information about molecules [1–3]. The term “EXAFS” describes the oscillations that extend over 1000 eV above an X-ray edge in an X-ray absorption spectroscopy (XAS) measurement (Fig. 1 left). These oscillations arise from interference between the emitted photoelectron waves from X-ray absorption and those
* Simon J. George [email protected] Robin Cantor [email protected] 1
STAR Cryoelectronics, Santa Fe, NM 87508, USA
2
Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
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Vol.:(0123456789)
Journal of Low Temperature Physics
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
backscattered from nearby atoms, and they can be analyzed to give the number, distances and element-type of atoms within approximately 7 Å of the absorbing atom. The extraction of EXAFS data from an XAS spectrum is illustrated in Fig. 1. Note that EXAFS spectra are typically plotted against the photoelectron wave vector k (in Å−1) and since the intensity of the EXAFS oscillations reduce substantially with increasing k, spectra are typically multiplied by k3 for clarity (Fig. 1 center). The Fourier transform of an EXAFS spectrum (Fig. 1 right) is a plot of magnitude against distance from the absorbing atom, with peaks corresponding to neighboring atoms.
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