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 <mamar...@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@millenia.cars.aps.anl.gov >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> >> _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >
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