BM08 - XAFS/XRF (X-ray Absorption Fine Structure/X-ray Fluorescence) spectroscopy beamline

Beamline Optical Layout

The XAFS/XRF beamline is located at the bending-magnet port BM08 of the SESAME storage ring. The beamline optics uses horizontally a fan of 3.0 mrad of synchrotron radiation of the SESAME bending magnet (1.45 T magnetic field with a critical energy 6.05 keV). 

Front End

The first beamline element, after the photon shatter, is a water-cooled fixed mask, which defines the acceptance of the beam line (3.0 mrad horizontally and 0.6 mrad vertically) and reduces the heat load on the optical components by cutting off the off-axis radiation. This mask is followed by a pair of water-cooled white beam slits to define the primary beam size and a water-cooled copper rod equipped with three filters of different thickness for heat management. The beamline vacuum is separated from the ring vacuum by a CVD window (250 µm thickness). To further protect the storage ring vacuum from ruptures of the beam line vacuum a fast closing shutter is installed in the front-end section. Its sensor is placed just before the CVD window in the optical hutch. 

Beamline Optics 

The main elements are a fixed-exit double-crystal monochromator (DCM) located between a collimating and focusing cylindrically bent mirrors installed before and after the monochromator, respectively; each of the mirrors is double coated Si and Pt. The primary water-cooled slits are located at 12.8 m from the source after the fixed, they define the horizontal and vertical dimensions of the polychromatic beam impinging the collimating mirror (VCM, first mirror). diagnostic tools are installed after each major component such as beam position wire monitors located after the VCM and DCM and an x-ray sensitive screen that can be inserted just after the vertically focusing mirror (VFM, second mirror). Both mirrors are tilted to grazing angles (~ 2.8 mrad) in order to optimize simultaneously the angular acceptance of the incoming beam and the mirror reflectivity. Finally, a monochromatic shutter is installed at the end of the hutch for allowing the experimenter to access experimental hutches while keeping a constant heat load on the optics.

Experimental Station (End Station)

An optical table with 6-axis of freedom is used as support for different detectors (ICs, XRF detectors) as well as the support for some sample manipulator and other sample environment devises.

The standard sample manipulator consists of several modules including a horizontal and vertical translation stages as well as rotational stages covering 360° in addition to swivelling stage. The manipulator can take up to 10kg load and allow the installation and alignment of most in-situ experimental setups.

Detectors and experimental setup:

XAFS data can be collected in both transmission and fluorescence mode:

• Transmission mode:
  3 ionization chambers are used. Two ICs (15 cm) are used downstream and upstream the sample for recording I0 and It and a third one (30 cm) used for recording the reference.
• Fluorescence mode:
  Two detectors are available for use in fluorescence mode:
  
  Multi-element SDD state-of-the-art and unique fluorescence detector developed by INFN for samples with extreme low content (down to few ppm)
  
  
  • 64 elements
  • High count rate (~15 M cts/s)
  • Higher efficiency (low deadtime)
  
  
  •  
  Single element SDD for samples with concentration (>100 ppm)
  
  
  • 1 element D-XAS Ketek 
  • “DXP-Mercury” electronics from XIA
  • ICR (~1 Mcts/s)​​​​​​
  
  
  •  

X-ray Excited Optical Luminescence (XEOL)

XEOL is available at the end station of BM-08 XAFS/XRF beamline with emission spectra measurement capability under irradiation with X-ray beam. Combined with XAFS and XRF, the new technique enables users to probe optical channels in materials, and directly correlate them with the chemical composition, oxidation state/symmetry site, coordination geometry, and local atomic structure order of the photoabsorbers. The set-up can also accommodate a LASER source, provided by the users, allowing to measure emission spectra under simultaneous LASER excitation. This experimental setup was financially supported by International Atomic Energy Agency (IAEA).

Sample Environment

• LN2 Cryojet to cool down the sample to a temperature of about 95 K.
• Users can bring their own equipment for in-situ experiment (Cell, furnace, etc.) can be adapted to the beamline experimental station. 
  • Please note that the spatial resolution of the bam on sample doesn´t allow any experiment with small beam such as high-pressure using diamond cells or elemental XRF mapping. 
• All forms of samples are accepted whether solid (bulk or powder), liquid and/or gas. If holders do not exist yet at the beamline, they can be fabricated at the SESAME workshop.

Users are reminded that they should contact the XRF/XAFS beamline scientists when drafting their proposal to discuss the sample environments and beamline characteristcs.

Note: This input is synced with WayForLight.

• Sample Type: Crystal, Amorphous, Powder, Gel and Liquid.
• A modest set of tools for sample preparation can be used to prepare samples such as spatulas, balance, mortars, hydraulic press for pallets (12 mm dies), binders, etc. 

• Users are offered the help to calculate the thickness of the samples and to prepare pallets.
• Data are collected using a home developed (Python based) software.
• XAFS (XANES & EXAFS) data are saved in an ASCII format.
• XRF data are saved in JSON, CSV or HDF5 formats.

Many software can be used for Software for XAFS and XRF data analyses. Available on beamline platform are:

• Demeter (Free Software).
• WinXAS .
• FEFF6, FEFF7 (Free Software).
• PyMca (Free Software).