Full-field micro-XANES for 2D and 3D Chemical …...Full-field micro-XANES for 2D and 3D Chemical...
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Full-field micro-XANES for 2D and 3D Chemical State Imaging using a Novel Energy Dispersive CCD Detector Pieter TACK 1* , Jan GARREVOET 1 , Stephen BAUTERS 1 , Bart VEKEMANS 1 , Dipanjan BANERJEE 2 , Alessandro LONGO 2 , Wim BRAS 2 , Laszlo VINCZE 1 1 X-ray Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan 281 S12, B-9000 Ghent, Belgium 2 European Synchrotron Radiation Facility (ESRF), DUBBLE-CRG, FR-38043 Grenoble Cedex, France SLcam Setup at ESRF DUBBLE Beamline References Corresponding Author [1] Boone, M. N. et al. Nuclear Instruments and Methods in Physics Research A 2014, 735, 644-648. [2] Vekemans, B.; Vincze, L.; Brenker, F. E.; Adams, F. Journal of Analytical Atomic Spectrometry 2004, 19, 1302-1308. * Pieter Tack, X-ray Microspectroscopy and Imaging Group (XMI), Department of Analytical Chemistry, Ghent University, Krijgslaan 281 (S12), B-9000 Ghent, Belgium, [email protected] Abstract Chemical state imaging by emission mode of X-ray Absorption Near Edge Structure (XANES) spectroscopy is very much restricted by severe time constraints typically imposed by synchrotron radiation experiments because of the point by point measurement strategy of the X-ray Fluorescence (XRF) methodology. The introduction of a novel energy dispersive (ED) CCD detector, the SLcam, allows the simultaneous acquisition of 264×264 pixel XRF spectra constituting a full image view on sample areas from 12.7×12.7 mm² down to 2.1×2.1 mm² using dedicated X-ray optics, significantly speeding up the process of XANES imaging. This work presents the very first tests of the SLcam performed at the ESRF DUBBLE beamline (Grenoble, France) studying a model sample, and applying it for the investigation of a geological nitisol soil sample. XANES Imaging Fe foil Fe 2 O 3 Differential Imaging The Fe 0 /Fe 2 O 3 model sample consists of a 4 μm thin Fe foil and pure Fe 2 O 3 powder fixed on commercial tape. Transmission mode XANES measurements were performed on pure reference compound pellets. By differentiating between the Fe foil and Fe 2 O 3 curves, it is clear that imaging of the Fe-K α signal can differentiate between oxidation states. • 7120 eV: Fe 0 absorbs the most • 7143 eV: Fe 0 and Fe 3+ have equal absorbance Measure at each of both energies for 10 minutes and differentiate between the thusly obtained Fe-K α signal. 7075.5 eV - 7100.6 eV, 2.5 eV steps, 5 min/step 7102.7 eV - 7132.8 eV, 0.8 eV steps, 10 min/step 7134.9 eV - 7160.9 eV, 2.6 eV steps, 5 min/step Total time: 7 h 40 m Data reduction: PCA and K-means clustering Thickness sensitive self- absorption correction Conclusions Full-field fluorescence mode XANES imaging was demonstrated using the SLcam, by revealing oxidation state images of large sampled areas (12.7×12.7 mm² or 2.1×2.1 mm²) with microscopic resolution (48×48 μm² or 8×8 μm²) in less than 15 hours. Improvements are expected by using higher incident beam fluxes and using X-ray optics with higher transmission efficiency than the currently used polycapillary optics. A data reduction routine using a combination of PCA and K-means clustering was applied, successfully grouping pixels with similar XANES spectra. When investigating more compex samples, more efficient data processing strategies will be needed e.g. to differentiate between different chemical species with similar oxidation states. Full-field XANES imaging is now also possible for thin, diluted and thick, concentrated samples. Application: Nitisol Soil Sample Study: Fe 0 /Fe 2 O 3 Model Sample African soil, possibly enriched with volcanic ash particles, sectioned and applied to a glassy substrate. Kindly provided by Prof. Eric Van Ranst (UGent, geology and soil sciences) Question: study the Fe oxidation state distribution in an ‘ash particle’ and compare this to the surrounding matrix. XANES scan: 7075.5 eV - 7100.6 eV, 4.2 eV steps, 5 min/step 7102.7 eV - 7132.8 eV, 1.2 eV steps, 20 min/step 7134.9 eV - 7160.9 eV, 1.29 eV steps, 10 min/step Total time: 14 h 30 m • 2.1×2.1 mm² field of view • 8×8 μm² spatial resolution A broad X-ray beam is used to illuminate the sample with a shallow angle to increase the illuminated sample area. The SLcam views the sample from above, out of the plane of polarization. Scan over the incident X-ray beam energy with a Si(111) monochromator. • Monitor the X-ray fluorescence signal to extract the X-ray absorbance. 264×264 pixels, each detecting a full 1-20 keV ED spectrum • 450 μm silicon based pnCCD chip, 50 μm Be window • 400 Hz readout frequency • 48×48 μm² resolution: 12.7×12.7 mm² field of view • 8×8 μm² resolution: 2.1×2.1 mm² field of view (6:1 polycapillary optic) SLcam Si(111) Monochromator Sample mounted on a U-shaped holder, illuminated at a shallow angle Side View: SLcam Sample Stage 6:1 polycapillary optic
Transcript of Full-field micro-XANES for 2D and 3D Chemical …...Full-field micro-XANES for 2D and 3D Chemical...
Full-field micro-XANES for 2D and 3D Chemical State Imaging using a Novel Energy Dispersive CCD Detector
Pieter TACK1*, Jan GARREVOET1, Stephen BAUTERS1, Bart VEKEMANS1, Dipanjan BANERJEE2, Alessandro LONGO2, Wim BRAS2, Laszlo VINCZE1
1 X-ray Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan 281 S12, B-9000 Ghent, Belgium 2 European Synchrotron Radiation Facility (ESRF), DUBBLE-CRG, FR-38043 Grenoble Cedex, France
SLcam Setup at ESRF DUBBLE Beamline
References Corresponding Author [1] Boone, M. N. et al. Nuclear Instruments and Methods in Physics Research A 2014, 735, 644-648. [2] Vekemans, B.; Vincze, L.; Brenker, F. E.; Adams, F. Journal of Analytical Atomic Spectrometry 2004, 19, 1302-1308.
* Pieter Tack, X-ray Microspectroscopy and Imaging Group (XMI), Department of Analytical Chemistry, Ghent University, Krijgslaan 281 (S12), B-9000 Ghent, Belgium, [email protected]
Abstract
Chemical state imaging by emission mode of X-ray Absorption Near Edge Structure (XANES) spectroscopy is very much restricted by severe time constraints
typically imposed by synchrotron radiation experiments because of the point by point measurement strategy of the X-ray Fluorescence (XRF) methodology.
The introduction of a novel energy dispersive (ED) CCD detector, the SLcam, allows the simultaneous acquisition of 264×264 pixel XRF spectra constituting a
full image view on sample areas from 12.7×12.7 mm² down to 2.1×2.1 mm² using dedicated X-ray optics, significantly speeding up the process of XANES
imaging. This work presents the very first tests of the SLcam performed at the ESRF DUBBLE beamline (Grenoble, France) studying a model sample, and
applying it for the investigation of a geological nitisol soil sample.
XANES Imaging
Fe foil
Fe2O3
Differential Imaging The Fe0/Fe2O3 model sample consists of a 4 µm thin Fe foil and pure Fe2O3
powder fixed on commercial tape. Transmission mode XANES measurements were performed on pure
reference compound pellets. By differentiating between the Fe foil and Fe2O3 curves, it is clear that imaging of the Fe-Kα signal can differentiate between oxidation states.
• 7120 eV: Fe0 absorbs the most • 7143 eV: Fe0 and Fe3+ have equal absorbance
Measure at each of both energies for 10 minutes and differentiate between the thusly obtained Fe-Kα signal.
7075.5 eV - 7100.6 eV, 2.5 eV steps, 5 min/step 7102.7 eV - 7132.8 eV, 0.8 eV steps, 10 min/step 7134.9 eV - 7160.9 eV, 2.6 eV steps, 5 min/step
Total time: 7 h 40 m Data reduction: PCA and
K-means clustering Thickness sensitive self-
absorption correction
Conclusions
Full-field fluorescence mode XANES imaging was demonstrated using the SLcam, by revealing oxidation state images of large sampled areas (12.7×12.7 mm² or 2.1×2.1 mm²) with microscopic resolution (48×48 µm² or 8×8 µm²) in less than 15 hours. Improvements are expected by using higher incident beam fluxes and using X-ray optics with higher transmission efficiency than the currently used polycapillary optics. A data reduction routine using a combination of PCA and K-means clustering was applied, successfully grouping pixels with similar XANES spectra. When investigating more compex samples, more efficient data processing strategies will be needed e.g. to differentiate between different chemical species with similar oxidation states. Full-field XANES imaging is now also possible for thin, diluted and thick, concentrated samples.
Application: Nitisol Soil Sample Study: Fe0/Fe2O3 Model Sample
African soil, possibly enriched with volcanic ash particles, sectioned and applied to a glassy substrate. Kindly provided by Prof. Eric Van Ranst (UGent, geology and soil sciences)
Question: study the Fe oxidation state distribution in an ‘ash particle’ and compare this to the surrounding matrix.
XANES scan: 7075.5 eV - 7100.6 eV, 4.2 eV steps, 5 min/step 7102.7 eV - 7132.8 eV, 1.2 eV steps, 20 min/step 7134.9 eV - 7160.9 eV, 1.29 eV steps, 10 min/step
Total time: 14 h 30 m • 2.1×2.1 mm² field of view • 8×8 µm² spatial resolution
A broad X-ray beam is used to illuminate the sample with a shallow angle to
increase the illuminated sample area.
The SLcam views the sample from above, out of the plane of polarization.
Scan over the incident X-ray beam energy with a Si(111) monochromator.
• Monitor the X-ray fluorescence signal to extract the X-ray absorbance.
264×264 pixels, each detecting a full 1-20 keV ED spectrum
• 450 µm silicon based pnCCD chip, 50 µm Be window
• 400 Hz readout frequency
• 48×48 µm² resolution: 12.7×12.7 mm² field of view
• 8×8 µm² resolution: 2.1×2.1 mm² field of view (6:1 polycapillary optic)
SLcam
Si(111) Monochromator
Sample mounted on a U-shaped holder, illuminated at a
shallow angle
Side View:
SLcam
Sample Stage
6:1 polycapillary optic
