[Ifeffit] Problems in Energy calibration

Lei Zhong leizhong8532 at gmail.com
Wed May 14 16:05:43 CDT 2014


Sorry. It is the Mo K-edge.

The spectra for the foil was taken in transmission. And I will check the
monochromator when I am in the office tomorrow morning. Thank you very much
for the quick response and your helpful comments.

Regards,

Lei



2014-05-15 4:43 GMT+08:00 Matthew Marcus <mamarcus at lbl.gov>:

> 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
>>
>>
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>
>>  _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20140515/150a22be/attachment.html>


More information about the Ifeffit mailing list