BM23 is the ESRF's general purpose X-ray absorption spectroscopy beamline. It is a mildy upgraded version of the former general purpose EXAFS beamline, which was dismounted from port BM29 and rebuilt on port BM23 in 2010. BM23 welcomed its first users in March 2011. It aims to meet the needs of the member countries in the area of conventional X-ray absorption spectroscopy. BM23 is designed to perform experiments which do not require the special characteristics of the other ESRF X-ray absorption instruments. The strengths to which BM23 operates arise from the intrinsic properties of the ESRF synchrotron, coupled with a bending magnet source and the high quality performance of the beamline's principle optical element, its monochromator. These strengths can be summarised as:

  • a very large operational energy range with reasonable X-ray flux: 4 keV to 74 keV
  • high energy resolution: typically a factor 3 to 5 better than the intrinsic spectral broadening at any K or L absorption edge
  • high spectral signal to noise ratio: above 7.0 * 10ˆ4 for well prepared samples
  • high beam stability: compatible with the demands of extreme sample environments such as pressure cells, where beam dimensions a few micron are required
  • a high level of automation
  • NEW: microXAS facility delivers spot of 3 x 3 microns2

X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) is a powerful structural technique to investigate the short-range environment around selected atomic species in condensed matter. While scanning the x-ray energy impinging onto the sample, a core level photoelectron is generated. This is scattered by the surroundings matter producing interference effects visible in the absorption cross-section and usually referred to as x-ray absorption fine structure (XAFS). The process itself is general and therefore fundamental to study structural properties in materials like:

  • liquids, molecular solutions, liquid crystals;
  • single- and poly-crystalline materials;
  • amorphous and highly disordered solids;
  • molecules and macromolecules containing metallic atoms or partially substituted with heavy atoms.

The energy range 4.5 keV < E < 74 keV is sufficient for K-edge studies of elements in the range 22 < Z < 76. For Z > 76 one must probe L-edges instead. The sample thicknesses for experiments are in the µm range for transmission experiments. However, thin film and/or dilute systems studies are still possible in fluorescence mode.

Scientific applications

The beamline is primarily used to investigate the electronic and local structure in crystalline, amorphous and liquid matter in a variety of thermodynamical and reaction conditions. 

Research at BM23 covers a variety of scientific domains, including solid state physics, materials science, geosciences, environmental science, solution chemistry, heterogeneous and homogeneous catalysis.

Chemistry

  • Heterogeoneous catalysis for the energy sector
  • In situ/operando time resolved studies of chemical and catalytic processes coupling X-ray absorption with infrared spectroscopy and mass spectrometry.

Matter at extreme pressures and temperatures

  • Studies of the local and electronic structure in solid and molten matter at high pressures and temperatures using the Diamond Anvil Cell or the Paris Edinburgh Press
  • Two dimensional speciation mapping with micron resolution within the diamond anvil cell.

Condensed matter physics, Material and Environmental science

  • Local and electronic structure characterization as a function of temperature for advanced materials: multiferroics, superconductors, etc.
  • Characterisation of electronic and local structure around impurities and/or trace elements in natural samples

X-ray techniques

Probes of local and electronic structure

  • X-ray absorption fine structure spectroscopy (XANES, EXAFS)

Probes of long range structure

  • Angle-resolved X-ray diffraction (XRD) – for complementary characterisation, if required

Detectors

  • Ion chambers
  • Si Vortex (Cubo, 1 mm chip thickness) combinable with a polycapillary half lens
  • Si Parker (2mm chip thickness)
  • Pilatus 1M XRD detector (Si)

Sample environment

  • MicroXAS station including optical microscope, compatible with fluorescence or transmission XAS
  • Diamond anvil cell and Paris-Edinburgh press for high pressure and temperature studies
  • Liquid He cryostats for transmission and fluorescence XAS
  • Different kinds of ovens (Tmax ~ 3000°C) compatible with transmission or fluorescence XAS
  • Different kinds of chemical reactors (capillary, pressed pellet, liquid cells)
  • IR spectrometer, UV-Vis spectrometer, mass spectrometer