ID21 X-ray Microscopy Beamline
The X-ray micro-spectroscopy beamline ID21 enables identification down to a few ppm, and localization with a submicron beam of various elements, and with a higher sensitivity for low Z elements, from Na to Fe. These elemental mapping can be completed with spectroscopic analysis, performed on single points or as 2D images as well. The submitted proposals are mainly in the field of Environmental Science, Life Science and Cultural Heritage. Typical scientific questions concern the co-localization and/or speciation of trace elements in heterogeneous matrix at the micron scale.
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Synopsis
The ID21 X-ray microscopy beamline at the ESRF houses two microscopes: a scanning x-ray microscope (SXM) and an infra-red microscope (SR-FTIR microscope).
The SXM is designed for use over a relatively wide spectral range from 2 - 7.5 keV giving access to absorption edges from a wide range of elements of interest in life, materials and environmental sciences. For further details, please see the following periodic table. The microscope is designed to accept, apart from conventional absorption contrast imaging, a variety of complementary imaging modes, in particular spectromicroscopy using both fluorescence imaging and scanning of the primary X-ray probe energy for XANES imaging. The STXM itself works comparable to the different known scanning microscopes: The source - in this case the storage ring radiation emitted by the insertion device - is demagnified by a zone plate into a focal spot with a diameter below 1 micron. The sample is aligned in the focal plane of the zone plate and is scanned across the focal spot. The different signals from interaction of X-rays with matter like fluorescence, absorption or XAS can be detected with high spatial resolution.
Scientific Applications
Third generation synchrotron sources produce a beam of unprecedent quality: the extremely low emittance coupled with high brilliance together with the versatility of new insertion devices, offer the capability to control brightness, spectrum and polarisation, coherence and size of the beam. This means that X-ray microscopy techniques which have been intensively used in the soft X-ray region (see "Other X-ray microscopy groups") can now be extended, with the anticipation of very high
performance to higher photon energies. This enables new investigations: study of thicker specimens, access to K absorption edges of elements of major interest in the biological and materials sciences, in particular from Potassium to Chromium, access to M and L edges of heavy metals (i.e Au or Ag) for specimen labelling, and the use of X-ray fluorescence for trace element mapping.
Beamline Description
The beamline is a windowless UHV beamline - continuous with the storage ring vacuum - and therefore necessitates the use of UHV technology throughout. The white beam from the undulator source is conditioned in the lead shielded optics hutch principally by means of a fixed exit double mirror system acting as a low band pass filter. The glancing angle of this device can be varied from 7-20 mrad using either Rh, Si or Ni reflective coatings, thus allowing harmonic rejection factors greater than 1e-3 for any energy between 1-10 keV for spectroscopic experiments for total transmissions greater than 70 %. This system reduces the high energy content of the beam sufficiently to eliminate the need for lead shielding in the subsequent cabin. The Optics cabin houses a series of pre-focussing optics for the direct branch for use in combination with its monochromator. The beam passes afterwards in the experimental cabin for the SXM.
Complementary Information
Prof. John Rehr: seminar and practical on FEFF9
