A multichannel superconducting soft x-ray spectrometer for high-resolution spectroscopy of dilute samples

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Abstract
We have built a high-resolution high-efficiency superconductingsoft x-rayspectrometer for synchrotron-based fluorescence-detected absorption spectroscopy. The sensor is a 3×3 array of 200×200 μ m 2 superconducting Nb–Al–Al 2 O 3 – Al–Nb tunnel junctions with an energy resolution around 15 eV below 1 keV and a total count rate capability of ≈100 000 counts/s. This sensor array is cooled to ≈0.1 K by a two-stage adiabatic demagnetization refrigerator while held at the end of a 40-cm-long cold finger that can be inserted into an UHV sample chamber for x-ray fluorescence measurements. We present L-edge absorption spectra of dilute transition metals (≈few 100 ppm) and discuss spectrometer performance with respect to the analysis of metalloproteins.