Which edge is this for?  I'm guessing MoK since you talk about using a foil for calibration.

Could the problem be polarization?  Since MoS2 is a highly anisotropic material, you would expect strong dichroism in both XANES and EXAFS regions.

It's possible that the resolutions at the two beamlines are different, so that a weak pre-peak might not show on the worse one.

You said something about putting the foil in the sample position.  Was the data taken in transmission?  If in fluorescence, then it will be subject to over-absorption and the derivative
will look shifted to the left.  If in transmission, and you find that the calibration is stable, then I would think that it should be OK.  I work on a beamline with no
third foil and it works well.  Another way to check is to inspect I0 for monochromator glitches and see if they move.  You can use them as internal calibrants.

Whatever you do, note that different people use different reference values for edge energies, so whenever showing XANES or quoting energies, you should always make
clear that, for instance, the Mo K-edge for Mo foil was taken to be 20000.0eV (or whatever you use).
        mam

On 5/14/2014 1:23 PM, Lei Zhong wrote:

Dear all,

we had beam line time in DESY (Hamburg) and ERSF (Grenoble) for NiMo sulfided supported samples. In DESY we got quite nice foil reference but in ERSF we failed since the third chamber showed problems. Therefore, we have critical issues to do the energy calibration for spectra collected from ERSF. We collected spectra for MoS2 crystals. So we are thinking about if it is reasonable to compare the spectra of MoS2 for the energy shift and further apply the energy calibration. Would you please give me suggestions? Thank you in advance.

Q1. In two beam lines, for exactly the same MoS2 crystal, we got difference in XANES region. Spectrum from DESY has a weak preedge peak resolved in XANES while ERSF doesn't. And the derivative shape of the two spectra for MoS2 collected from two synchrotrons are not well overlapped. Is it acceptable?

Q2. I tried to overlay the first derivative of the two spectra of MoS2. There is a energy shift at 2.5 eV from the different synchrotrons if we take the one from DESY as standard. Can I apply the energy shift at 2.5 eV for MoS2 from ERSF and then overlay the first derivative of the other NiMo samples with MoS2 to get the energy calibration? Or should I apply 2.5 eV for all the NiMo sulfided samples?

Q3. Since we lost the signal for the foil reference in ERSF, we tried to put the foil in the sample position. The first derivatives of the foil spetra from time to time overlap quite well. Should we set the energy calibration at 0 according to the stable foil signal?

Sorry for the long email. Thank you for the time reading it. Hopefully I made the questions understandable to you. Looking forward to your answer!

Thanks.

Regards,
Lei
Technical University of Munich

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