Full-field XANES

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Introduction

 

Fullfieldschema.png

Image from De Andrade et al. 2011, Anal. Chem, 83.

 

The X-ray absorption near-edge spectroscopy (XANES) full-field imaging station operates in the 2-9 keV energy range and allows for the simultaneous acquisition of up to 4.10 6 XANES spectra over large sample areas with preserved sub-micron spatial resolution. The XANES full-field imaging station is based on a 2D detector able to record in one shot an entire absorption image. It is designed to perform submicrometric XANES analysis in transmission mode on major elements (in bold on periodic table) of large samples (up to 2mm2 FOV). For each energy point across a given K- or L- edge, a magnified 2D transmission image of the sample is acquired by a camera coupled to an X-ray scintillator and magnifying visible light optics. Then a “flat field image” recorded with the sample out of the X-ray beam is used for normalization.

 


XANES_periodictable-1.png

 

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X-ray Source

 

The ESRF machine is routinely operated at 6 GeV electron energy with a maximum current of 200 mA. The horizontal source emittance is 3.8 10-9 m.rad and the coupling is usually 1%. Beamline ID21 is installed on a 4.8 m long low beta straight (small source but larger divergence). The larger horizontal divergence limits the heat load on the first optical components by spreading the power over a larger surface.

 

RMS Photon source parameters
  7.0 keV 2.0 keV
Horizontal source size [µm] 50 50
Vertical source size [µm] 4.1 4.6
Horizontal source divergence [µrad] 108 109
Vertical source divergence [µrad] 10.8 19.8

 

The straight section is equipped with 3 different insertion devices: Two in-phase 42 period undulators and one 32 period. The two U42 can be used simultaneously for a gain in flux of at least a factor of 2 . The U32 offers a significant gain for the analysis of 3d transition metals (4-8KeV) as it provides two times more flux compared to a single U42.

 

On–axis brilliance of the fundamental (n=1) and third harmonic (n=3) of the insertion devices used on ID21.

 

ID21 is a windowless UHV beamline. The white beam from the undulatory source is conditioned in the lead shielded optics hutch principally by means of a fixed exit double mirror system (M0), acting as a low band-pass filter. The grazing angle of this device can be varied from 7 to 20 mad using either Rh, Si, or Ni reflective coatings. The Si coating is usually used to cover the 2-4 KeV range, the Ni coating to cover the 4-7.5 KeV, and Rh for energies higher than 7.5 KeV.

 

M0primarymirror.png

 

 

Double Crystal Monochromator

   

A fixed exit double crystal monochromator (DCM) from Kohzu is used In the energy range (2-9keV). This monochromator is operating with two Si<111> crystals and two Si<220> crystals. This fixed exit monochromator allows "easy" energy scanning with very little exit beam movement or loss of parallelism. In order to minimize the effect of any residual beam movement during the energy scan, the device is positioned as close as possible to the SXM in the experimental cabin. This monochromator can be used either in focussed or unfocussed beam conditions.

 

Energy resolution with available DCM crystals at ID21
Energy Si(111) Si(220)
2.1 0.41  
2.5 0.52  
3.3 0.69 0.3
3.9 0.8 0.35
4.5 0.92 0.40
4.8 0.97 0.43
5.1 1.03 0.45
5.4 1.08 0.47
5.7 1.14 0.51
6 1.17 0.52
6.6 1.3 0.57
7.2 1.42 0.62
8 1.56 0.69
  kohzu.jpg (kohzu)

 

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Sample Chamber

 

 

Fullfield_chamber.png

The full-field chamber is connected to the ID21 SXM chamber through a vacuum valve. The sample stage consists of two translation stages (26 mm range in the horizontal and vertical directions) on top of which a fast vertical translation is mounted. The fast vertical sample motion is used to move out the sample from the x-ray beam for flat field acquisitions, and then to move it back in front of the beam (the escape range is ~  10 mm). The sample holder is also compatible with a small rotation stage (SmarAct) than can be used to perform polarization contrast imaging.

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Detection system

 

The scintillator (Lu2SiO5:Tb, 10 μm thick) is located less than 2 mm from the sample to limit phase contrast features generated by the sample heterogeneities. The support of the scintillator is directly mounted on the viewport holder that ensures the air-vacuum interface. A 2D detector coupled to a long working distance optical objective records the magnified transmission image of the sample. Pixel size ranging from 0.3 μm to 1.4 μm and fields of view from 600 μm2 up to 2 mm2 can be ontained using the 20x and 10x optical objectives available at ID21. The set-up is compatible with both scientific CMOS PCO.edge camera and in-house developed CCD FReLoN E2V camera.

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References and examples

 

  • Fayard, B.; Pouyet, E.; Berruyer, G.; Bugnazet, D.; Cornu, C.; Cotte, M.; De Andrade, V.; Di Chiaro, F.; Hignette, O.; Kieffer, J.; Martin, T.; Papillon, E.; Salomé, M.; A Sole, V. The new ID21 XANES full-field end-station at ESRF. Journal of Physics: Conference Series 425 (2013) 192001. DOI 1088/1742-6596/425/19/192001
  • Meirer, F.; Liu, Y.; Pouyet, E.; Fayard, B.; Cotte, M.; Sanchez, C.; Andrews, J.; Mehta, A.; Sciau, P. Full-field XANES analysis of Roman ceramics to estimate firing conditions- A novel probe to study hierarchical firing conditions- Anovel probe to study hierarchical heterogenous materials. J. Anal. At. Spectrom.,  2013, 28, 1870-1883. (ESRF spotlight on science in 2013)
  • Pouyet, E.; Cotte, M.; Fayard, B.; Salome, M.; Meirer, F.; Mehta, A.; Uffelman, E.S. 2D X-ray and FTIR micro-analysis of the degradation of cadmium yellow pigment in paintings of Henri Matisse. Appl. Phys. A, Vols. DOI 10.1007/s00339-015-9239-4, 2015.

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