Strange EXAFS oscillations, never seen before
Dear all, I observed strange EXAFS oscillations in my data up to about 1000 eV beyond the K-edge, I would like to share this situation with you and hope to get some feedback. Please find attached the athena project file of the data. The chemical composition of the material is (Fe0.5Cu0.5)Sn5. The EXAFS sample was prepared by taking the material equal to 2 absorption lengths at the Cu K-edge, mixing it with graphite and pressing into the pellet, which was sealed between the Kapton tape. The measurements were carried out at the Cu K-edge of the material in the transmission mode at the beamline 5BM of APS. Here are my concerns: (1) In the athena project file, the data files "Cu_S1_scan003" and "Cu_S1_scan004" are the two scans of the same sample measured one after the other. As can be seen, there are strong oscillations even at 1000 eV from the Cu K-edge, which is strange because generally EXAFS oscillations "wash out" as we go higher in energy. Nevertheless, the two scans appear reproducible. (2) Once I removed the sample and remeasured it after some time (because I did not believe the previous 2 scans), I found completely different data (i.e., data "Cu_S1_scan005"). (3) The Cu reference foil measured simultaneously along with the sample for each of these scans appear quite reproducible. I am puzzled as to what can contribute to such effects. I have never seen such effects before. We can rule out the possibility of beam damage, since I have measured up to 3 scans (25 min per scan) and they all look reproducible. However, once I remove the sample and remeasure it after some time to reproduce the previous 3 scans, the scan looks totally different. Also, we can rule out the chemical instability of the material, since the material is quite air-stable. I have measured a series of samples with this composition and all of them have the same effect. I would very much appreciate your feedback! Best regards Jatin ________________________________ Helmholtz-Zentrum Berlin für Materialien und Energie GmbH Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V. Aufsichtsrat: Vorsitzender Dr. Karl Eugen Huthmacher, stv. Vorsitzende Dr. Jutta Koch-Unterseher Geschäftsführung: Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas Frederking Sitz Berlin, AG Charlottenburg, 89 HRB 5583 Postadresse: Hahn-Meitner-Platz 1 D-14109 Berlin http://www.helmholtz-berlin.de
Hi Rana: I agree. The data is basically unusable as it is. You clearly have issues in the background (look at the oscillations in the pre-edge area) and the three data sets are different from each other which is another clue. It looks like you have transmission data with a very samll edge jump (0.09) which is sort of marginal for XANES much less EXAFS at 5BM). In addition, your sample probably has pinholes and is not uniform. You should be taking this data in fluorescence with such a small amount of sample unless you have an absolutely uniform sample. Carlo On Sun, 19 Mar 2017, Lorenzo Stievano wrote:
Dear Rana,
you seem to have real EXAFS oscillations up to k=9, then there are surely some artefacts in your spectra, which are unusable from that point on. In fact, if you limit your spline range to 9 in Athena, you get oscillations that look real and seem to have some sense.
These artefacts are probably of experimental origin (shit happens), I do not think you can do much about them,with the exception of remesuring your spectra.
Yours sincerely,
Lorenzo
Le 19/03/2017 à 17:13, Rana, Jatinkumar Kantilal a écrit :
Dear all, I observed strange EXAFS oscillations in my data up to about 1000 eV beyond the K-edge, I would like to share this situation with you and hope to get some feedback. Please find attached the athena project file of the data.
The chemical composition of the material is (Fe0.5Cu0.5)Sn5. The EXAFS sample was prepared by taking the material equal to 2 absorption lengths at the Cu K-edge, mixing it with graphite and pressing into the pellet, which was sealed between the Kapton tape.
The measurements were carried out at the Cu K-edge of the material in the transmission mode at the beamline 5BM of APS.
Here are my concerns:
(1) In the athena project file, the data files "Cu_S1_scan003" and "Cu_S1_scan004" are the two scans of the same sample measured one after the other. As can be seen, there are strong oscillations even at 1000 eV from the Cu K-edge, which is strange because generally EXAFS oscillations "wash out" as we go higher in energy. Nevertheless, the two scans appear reproducible.
(2) Once I removed the sample and remeasured it after some time (because I did not believe the previous 2 scans), I found completely different data (i.e., data "Cu_S1_scan005").
(3) The Cu reference foil measured simultaneously along with the sample for each of these scans appear quite reproducible.
I am puzzled as to what can contribute to such effects. I have never seen such effects before.
We can rule out the possibility of beam damage, since I have measured up to 3 scans (25 min per scan) and they all look reproducible. However, once I remove the sample and remeasure it after some time to reproduce the previous 3 scans, the scan looks totally different.
Also, we can rule out the chemical instability of the material, since the material is quite air-stable.
I have measured a series of samples with this composition and all of them have the same effect.
I would very much appreciate your feedback!
Best regards Jatin
____________________________________________________________________________
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V.
Aufsichtsrat: Vorsitzender Dr. Karl Eugen Huthmacher, stv. Vorsitzende Dr. Jutta Koch-Unterseher Geschäftsführung: Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas Frederking
Sitz Berlin, AG Charlottenburg, 89 HRB 5583
Postadresse: Hahn-Meitner-Platz 1 D-14109 Berlin
http://www.helmholtz-berlin.de
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-- [IMAGE]
Lorenzo Stievano Professeur Tel : +33(0) 4 67 14 33 46 aime.icgm.fr/spip.php?article102
[IMAGE]
Institut Charles Gerhardt Montpellier UMR 5253 CNRS-UM-ENSCM Université de Montpellier, Place E. Bataillon, Bât 15, cc 1502 34095 Montpellier cedex 5 - France
-- Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair, Department of Chemistry Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://phys.iit.edu/~segre segre@debian.org
participants (3)
-
Carlo Segre -
Lorenzo Stievano -
Rana, Jatinkumar Kantilal