Chemie und Prozesstechnik
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Our aim is to develop a new method for full field X ray fluorescence imaging at the BAM line @ BESSY II. We will combine an energydispersive array detector for X rays with a coded aperture to get high resolution images . In coded aperture imaging , an object is projected through a mask , producing many overlapping images on the detector . The first part of the project is to perform raytracing simulations to get realistic data and to develop a reconstruction method that allows to get the Information about the investigated object out of the projected image .
The test material EDS-TM001 together with an accompanying software package, “EDX spectrometer check”, have been made available in 2009 by BAM to be employed by EDS (energy-dispersive X-ray spectrometer) users to check the performance of an EDS attached to the SEM. Particularly for test laboratories operating under accreditation schemes like ISO/IEC 17025, a periodical control of the critical instrumental parameters in end-user laboratories is required. With EDS-TM001 or EDS-TM002 (second generation) test material, this periodical check is simplified to the acquisition of only one 10 kV spectrum. The software “EDX spectrometer check” is destined to evaluate automatically this spectrum and determine the performance of the EDS in terms of energy resolution and calibration, as well as possible alteration of low-energy Efficiency due to detector contamination. Energy resolution can be compared with the specified values according to the international ISO standard ISO 15632:2012. EDS-TM is a synthetic material consisting of a 6 μm thick layer of C, Al, Mn, Cu and Zr deposited on a steel (in case of EDS-TM001) or silicon (in case of EDS-TM002) substrate. The chemical composition of EDS-TM was chosen such as to give nearly equal intensities of the low energy lines in a 10 kV spectrum, thus, making it very sensitive against spectrometer efficiency changes. Meanwhile, about 150 laboratories use the EDS-TM001 or EDS-TM002 test material for the periodical check of their EDS. A detailed description of the test material and software together with examples of application was published recently. New results and gained experiences will be presented as well. When the FWHM of the X-ray lines in the EDS-TM spectrum are determined, the spectrum background must be subtracted accurately. The applied physical background subtraction procedure is robust and takes into account the transmission of the detector window. While the previous version considers only Moxtek AP windows, the new version includes selection of silicon Nitride window and the case of windowless detector. Moreover, the new version allows importing of spectra in Bruker spx-format and EMSA/MSA files from EDAX TEAM software.
Windowless detectors have been also tested demonstrating long-term stability after repeated heating and cooling cycles. In this case, the appropriate Background subtraction is decisive for accurate detector characterization. Detailed results will be presented.
X-ray absorption fine structure (XAFS) spectroscopy is a powerful and widely used tool for material characterization. It is non-destructive, element-sensitive and requires no long-range order of the sample, making it suitable for the investigation of amorphous phases. XAFS includes the X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS), providing information about the electronical state of the absorbing atom and the spatial order of the neighboring atoms respectively.
Our new approach presented here is derived from the classical dispersive XAFS setup. The aim is to have a scanningless, stable and reproducible setup for applications, in which dynamic processes occur in the second time scale.
A broad polychromatic beam passes through the sample and is dispersed afterwards by a convexly bent Si (111) crystal. All energies are reflected under different angles and thus spatially separated, allowing a position sensitive detector to record a spectrum over the energy range of the incoming beam in a single shot.
Tests of this setup were performed at the BAMline @ BESSY-II (Berlin, Germany) with different metal foils. First in situ measurements comprised the investigation of the early stages of the zinc(II)2-methylimidazolate (ZIF-8) crystallization. This topic of metal-organic-frameworks (MOF) research is of interest for medical applications. Structural changes with a time resolution of 1 s could be followed. The second dimension of the broad beam can be used for a lateral resolution.
In this work, a new setup for dispersive XAFS measurements is presented. This reproducible and scanningfree setup yields both time- and laterally-resolved XAFS experiments in a ‘single-shot’. It allows a straightforward adjustment for probing different elements covering many relevant applications in materials science. An incoming energetic broadband beam is diffracted by a Si (111) crystal after passing through the sample and collected by an area sensitive detector. Depending on the energy range of the incoming beam, XANES and/or EXAFS spectra can be recorded with a time resolution down to 1 s. The feasibility of this setup was demonstrated at the BAMline at BESSY II (Berlin, Germany) with reference Fe and Cu foils and the results are hereby presented and discussed. Additionally, an application where time resolution on the second scale is required is briefly evaluated. The presented example concerns studying early stages of zinc(II)2-methylimidazolate (ZIF-8) crystallization. This is particularly important for biomedical applications.