CryoEXAFS@KMC-3

EXAFS station with cryogenic or in-beam, operando electrochemistry sample conditions /KMC-3

The instrument CryoEXAFS (the name is historical) is dedicated to advanced X-ray absorption spectroscopy (XAS) techniques to investigate the short-range structure environment (up to ca. 10 Å) around selected atomic species and the redox state in condensed matter (e.g., proteins and synthetic molecules in solution, electrocatalytic films, battery cells, powder materials, etc.). It is installed at the tender/hard X-ray beamline KMC-3, which is equipped with two X-ray mirrors (Pt/Rh coated) for variable beam focus size (~0.35 - 5 mm) and variable spatial position to match the sample position, and a double-crystal monochromator with Si[111] and Si[311] crystal pairs (ca. 2 or 0.2 eV resolution).

XANES and EXAFS spectra can be collected in an energy range of ca. 2,050 eV to 21,000 eV (i.e., phosphorus to molybdenum K-edges and many L- or M-edges of heavier elements). XAS spectra can be collected in fluorescence mode with energy-resolving 7- or 13-element silicon-drift detectors or photodiode/scintillation detectors, or in transmission mode using ion chambers or PD detectors. The beamline has options for incident flux stabilization (MOSTAB) in detuned monochromator mode for harmonics suppression (i.e. at tender energies). 

4 main operation modes of the XAS experiment at KMC-3 are available to users:

1) Cryo-XAS in a ca. 5-310 K temperature range as provided by a closed-cycle liquid-helium cryostat with the sample held in a heat-exchange gas environment (typically helium at 100 mbar), to probe samples in a static state, as established e.g., using freeze-quench approaches or other treatments.

2) Operando-XAS at room temperature, typically for example on electrochemical or battery (flow-) cells, with samples operated in the X-ray beam using electrochemistry (potentiostats plus booster available) or light excitation (pulsed OPO-laser 400-2500 nm, pulsed LED-sources), to monitor changes in real time. Diverse sample (flow-) cells for electrochemistry are available at the beamline and users may also bring their own equipment.

3) Tender-energy XAS at room temperature (ca. 2-4 keV range) in a specialized sample chamber that can be evacuated or filled with inert gas, facilitating sample change in a few minutes, and using an ion chamber for I0-detection with thin foil windows (Mylar 3 µm), facilitating also operando (electrochemical) experiments.

4) Time-resolved XAS using rapid-scan spectra collection (minimally ca. 2 seconds for an EXAFS scan over 600 eV), to track e.g. redox and structure changes in materials during cyclic-voltammetry sweeps in minutes or light-induced changes, and collection of timescan traces at fixed excitation energies, for monitoring e.g. edge-energy shifts in real time (minimally ca. 0.1 ms per data point) during sample treatments. Both methods use the energy-resolving SD-detectors for superior fluorescence signal contrast also on relatively dilute samples.

Each two of the above experiments (i.e. tender-energy / cryo-XAS or cryo-XAS / operando-XAS) can be carried out in parallel, facilitating for example data collection during electrochemistry followed by low-temperature characterization of the sample. Radiation damage is not a problem, due to the usually large X-ray spot size on the sample (several mm2) and the moderate flux of the bending-magnet source. With a medium-thickness (electrochemical film) sample, delivering e.g. 100 kcps fluorescence per detector channel, good EXAFS spectra to k = 12 Å-1 can be collected within ca. 3 min in a single monochromator scan.

Selected Applications:
  • In-situ characterization of materials under catalysis conditions with low-temperature XAS data collection (freeze-quench approach)
  • Operando-XAS on electrocatalytic films for water oxidation (OER) or CO2-reduction (CO2RR) under electrochemistry conditions at room temperature
  • XAS on dilute-solution (1 mM) protein or synthetic-molecule samples at cryogenic conditions
  • Rapid-scan EXAFS (redox transitions and catalytic processes during cyclic voltammetry)
  • EXAFS as a function of chemical composition and/or temperature dependent EXAFS
Scheme of the experimental setup for XAS at KMC-3 with cryogenic or operando ambient-temperature sample conditions and two energy-resolving 7/13-element fluorescence SD-detectors.

Scheme of the experimental setup for XAS at KMC-3 with cryogenic or operando ambient-temperature sample conditions and two energy-resolving 7/13-element fluorescence SD-detectors.


Methods

EXAFS, NEXAFS, XRF

Remote access

not possible

Instrument data
trueXAS@KMC-3
Location (Pillar) 15.1
Phone (~49 30 8062-) 14695
Source D13.2 (Dipole)
Beam availability 24h/D
Monochromator Si[111] and Si[311]
Energy range (at experiment) 2.1 - 21 keV and 4.5 - 21 keV
Energy resolution DE/E ca. 2.5x10-4 and 0.5x10-4
Flux 1e11 photons/s (Si[111])
Polarisation horizontal
Focus size (hor. x vert.) 350 µm x 350 µm (up to ca. 5 x 2 mm)
Temperature range 5 - 310 K
Pressure range The cryogenic setup is in vacuum with the sample in (heat-exchange) He gas environment. The in-beam, operando (electrochemistry) setup is under atmospheric conditions. The tender-energy sample chamber (2-4 keV) can be evacuated (2 mbar) or filled with e.g. inert gas.
Detector 13- and 7-element detectors (Si-drift) with XIA electronics (DXP-XMAP, Falcon), 3 ionization chambers, Si-PIN photodiodes, scintillation (photomultiplier) detector
Manipulators Cryogenic and in-situ setup: y, z stages
Sample holder compatibility For details and specific demands, contact the instrument scientist.
Additional equipment Potentiostats (Biologic), pumps for e.g. electrolytes (up to 10 L/min, agressive media), continues and pulsed light sources for sample illumination (LED, OPO-laser)
Additional information Further details: beamline KMC-3 XPP
The XAS endstation at KMC-3. (clockwise) table with setup, lHe-cryostat, electrochemical flow-cell, I0 pressure & cryostat controls & Falcon electronics, tender-energy chamber, 7/13-element SDDs.

The XAS endstation at KMC-3. (clockwise) table with setup, lHe-cryostat, electrochemical flow-cell, I0 pressure & cryostat controls & Falcon electronics, tender-energy chamber, 7/13-element SDDs.


The XAS endstation at KMC-3 includes a closed-cycle liquid-helium cryostat (Oxford, ca. 5-310 K), detectors (ion chambers, photodiodes, scintillation/photomultiplier) for I0-detection and transmission-mode XAS, as well as two retractable large-area energy-resolving detectors (7- and 13-element Si-drift detectors, RaySpec) for fluorescence-mode XAS, which are operated via DXP-XMAP (</=0.5 Mcps ICR) or Falcon (</= 4 Mcps ICR) electronics (XIA) and can be flanged to the cryostat or the tender-energy sample chamber for in-vacuum operation to yield maximum count rates. Motorized y/z sample positioning is available for samples in the cryostat, tender-energy chamber, and in e.g. an electrochemical cell. The setup facilitates flexible accommodation of diverse user requirements. Fast data acquisition/transfer hard- and software facilitates allow rapid EXAFS scans in minimally 2 seconds (depending on the absolute energies) 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 setup are XAS experiments on biological materials (metalloproteins), (diluted) solutions of synthetic molecules, and solid-state materials. For the in-situ setup, sample cells and potentiostats for in-beam electrochemistry are available and typical applications are XAS experiments on electrode-deposited catalyst films in contact with electrolyte at room temperature or monitoring of charge/discharge cycles in battery cells.