[Ifeffit] Strange EXAFS oscillations, never seen before

[Rana, Jatinkumar Kantilal]

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



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