CryoEXAFS: X-ray absorption spectroscopy station with cryogenic or in-beam, operando electrochemistry sample conditions at BESSY II
The Cryo-EXAFS X-ray absorption spectroscopy (XAS) station at beamline KMC-3 at BESSY II was developed and is operated in a cooperation treaty between the FU Berlin, FB Physik (Prof. Holger Dau) and the HZB. The endstation is dedicated to XAS in a range of about 3-13 keV and is open for general user proposals since September 2016.
The Cryo-EXAFS station at beamline KMC-3 is a dedicated endstation to investigate the short-range environment around selected atomic species in condensed matter by X-ray Absorption Spectroscopy at low temperatures. This end-station provides possibility for EXAFS, XANES and X-ray fluorescence measurements in vacuum. The detector system consists of two ionization chambers, Si-PIN photodiode and 13-element detector (Ge and Si) with XIA electronics.
For details and current status of the experimental station contact the station manager.
The KMC-3 CryoEXAFS station offers XAS experiments in a 5-300 K cryogenic range (liquid Helium cryostat) as well as under in-beam, operando electrochemistry conditions (materials in solution or deposited on surfaces, for example electrodes). Both setups are installed in parallel to enable a rapid change from cryogenic to in-beam, operando electrochemistry mode (Figure 1). Both experiments at this bending magnet beamline are performed with a widened beam focus (several mm2 on the sample) thereby avoiding radiation-induced sample modifications (avoidance of radiation damage).
The general station setup includes a liquid-helium cryostat (Oxford, ca. 5-300 K), detectors (ion chambers, photodiodes) for transmission-mode XAS, as well as two retractable large-area energy-resolving detectors (liquid-nitrogen-cooled window-less 13-element Ge, Canberra; air/water-cooled Be-window 13-element Si-drift SSD, Rayspec) for fluorescence-mode XAS (up to ca. 400 kcps), which are operated via XIA DXP electronics and can be flanged to the cryostat for in-vacuum operation to yield maximum count rates (Figure 2a). Motorized y/z sample positioning is available for samples in the cryostat as well as in the in-beam, operando electrochemistry sample cells. Fast data acquisition/transfer hard- and software facilitates relatively rapid EXAFS scans, e.g. in ca. 3.0 min to k = 12 Å-1, as well as fluorescence data acquisition (e.g. at fixed energy) with the energy-resolving detectors with 1 ms per point or less for superior signal contrast in time-resolved applications. Typical applications for the cryogenic set-up are XAS experiments on biological materials (metalloproteins), (diluted) chemical solution samples, and solid-state materials. For the in-situ setup, sample cells and a potentiostat for in-beam electrochemistry are available and typical applications are XAS experiments on electrode-deposited metal catalyst films in contact with electrolyte at room temperature (Figure 2b).
Assigned to beamline(s)
|KMC-3 XPP||2 - 14 keV||horizontal|
|Temperature range||5 - 300 K|
|Pressure Range||The cryogenic setup is in vacuum with the sample in He gas environment. The in-beam, operando electrochemistry setup is under atmospheric conditions.|
|Detector||13-element detectors (Ge and Si) with XIA electronics, 3 ionization chambers, Si-PIN photodiodes, scintillation (photomultiplier) detector|
|Manipulators||Cryogenic and in-situ setup: y, z|
|Sample holder compatibility||For details, contact the station manager.|
|Energy range||3 - 13 keV (extension to 2 keV in progress)|