NSLS-II Seminar

Because of their complex genesis, materials are commonly polycrystalline heterogeneous systems, with both chemical and structural heterogeneities at various scale-level. As most of the micro- and nano- analytical techniques relying on scanning instruments with a pencil-beam, XANES (X-ray Absorption Near Edge Structure) technique offers high spatial resolution but suffers from long acquisition times imposing practical limits on the field of view. Now, region of interest in samples are generally several orders of magnitude larger than the beam size.
Along this presentation, an overview will be given onto the on-going technical developments of the ESRF ID21-beamline Scanning Microscope, relating to detection (multi-elements detector, in-house developed WDX spectrometer) and optics (Fresnel zone plate, KB mirrors). Then, we will focus on an original setup developed and optimized to perform spectroscopic imaging on geomaterials, with relatively short acquisition time (≈1 h) and large field of view (0.5-2 mm2) while keeping a sub-micron resolution. The setup consists in coupling full-field absorption radiographies with a large parallel beam of hard X-rays, XANES and PIC (Polarization Imaging Contrast) techniques.
The potential of this combined approach will be demonstrated on metamorphic rocks. This non-invasive method enables 2D quantitative Fe3+/Fetotal estimates revealing subtle redox variations inside mineralogical phases. Moreover, besides providing crystalline orientations at the pixel scale, the PIC and XANES combination allowed to correct XANES estimates from polarization effects, which is a tricky but important task in polycrystalline materials.
Finally, the last application concerns an experimental study of a bentonite analog (clayey material) considered for nuclear wastes and CO2 storage. Mapping of the proportions of finely mixed phases at the µm3 scale were extracted from hyperspectral data acquired on a reference bentonite. The spatial repartition o