X-ray Absorption Fine Structure Spectroscopy (XAFS) is a powerful technique to investigate local atomic geometry and the chemical state of the atoms of one specific element in almost any type of substance. It is particularly well suited to investigate materials that lack long-range order such as:
Samples with very low concentration (min. 500 ppm) can be measured in Fluorescence mode.
During an EXAFS scan, especially at lower energies (5-9 KeV), the monochromator makes a much larger movement of the Bragg angle (compared to higher energies) which causes a slight vertical displacement of the beam on the sample. A feedback system connected to a beam position monitor is used to keep the beam position fixed on the sample during the EXAFS scan by adjusting the gap between the two crystals of the monochromator.
This is only possible via collaboration with Prof. Laszlo Vincze, University of Ghent, Belgium, please also consult Dipanjan Banerjee prior to proposal.
The beam line is optimised for EXAFS/XANES but combined techniques can be useful for certain samples.
We have a 2D MAR detector that can be positioned at a fixed distance between 80cm and 350cm from the sample to acquire SAXS data during a XANES measurement. This sample-detector distance is calculated according to which absorption edge is being measured (the X-ray incident energy) and q-range of interest. We then trigger acquisition of the SAXS pattern at a specific incident X-ray energy during the XANES scan.
The Mythen 2D XRD detector has undergone a firmware upgrade and has been commissioned at the EXAFS line. It is now possible to collect XRD spectra at the peaks of interest simultaneously with XANES scans. Users are able to observe and record changes in the XRD peaks during in-situ catalysis reactions as a function of thermal treatment and gas flow. The Mythen XRD detector is not meant for a full scale XRD experiment and diffraction pattern analysis, for that users should consider going to a dedicated XRD beamline at ESRF.
It is possible to use both the 2D MAR detector and the 2D Mythen detector during XANES data collection as described above.
All chemical elements written with white fonts on coloured background can be studied at the DUBBLE XAFS station (see also the Note under the image). Among them, those already studied are underlined. To get the list of EXAFS/XANES publications corresponding to a given element, click on it in the image.
Note: To measure radioactive elements, you need to come to an agreement with the ESRF Safety group long before you apply for beamtime.
A beamline manual of BM26A is provided here. It gives all (or most of) the information a user may need to perform a successful experiment.