[Ifeffit] Strange EXAFS oscillations, never seen before

[Carlo Segre]

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
> 
> 
> 
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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 at iit.edu   http://phys.iit.edu/~segre   segre at debian.org