CryoEXAFS

CryoEXAFS

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).

Figure 1 Scheme of the experimental setup for XAS at KMC-3 (CryoEXAFS) with cryogenic or in-situ (operando) ambient-temperature sample condition. Two energy-resolving 13-element fluorescence detectors (Ge and Si) can be used alternatively and facilitate switching between both types of experiments without rearrangements of the experimental set-up.

Figure 1 Scheme of the experimental setup for XAS at KMC-3 (CryoEXAFS) with cryogenic or in-situ (operando) ambient-temperature sample condition. Two energy-resolving 13-element fluorescence detectors (Ge and Si) can be used alternatively and facilitate switching between both types of experiments without rearrangements of the experimental set-up.


Liste von Publikationen

Methods

NEXAFS, EXAFS

Assigned to beamline(s)

Energy rangePolarisation
KMC-3 XPP 2 - 14 keVhorizontal
Station data
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.
Remote Access
Energy range 3 - 13 keV (extension to 2 keV in progress)
Monochromator Si (111)
Figure 2 KMC-3 CryoEXAFS experimental station a) with cryogenic condition utilizing the 13-element Si-drift SSD (Rayspec) that is flanged to the cyrostat, the same SSD is used in b) to acquire data using an electrochemical cell, the I1 ion chamber and I2 photodiode have been removed for this purpose. Using the yz-stage, the electrochemical cell can be aligned with the X-ray beam. See also Figure 1.

Figure 2 KMC-3 CryoEXAFS experimental station a) with cryogenic condition utilizing the 13-element Si-drift SSD (Rayspec) that is flanged to the cyrostat, the same SSD is used in b) to acquire data using an electrochemical cell, the I1 ion chamber and I2 photodiode have been removed for this purpose. Using the yz-stage, the electrochemical cell can be aligned with the X-ray beam. See also Figure 1.