[Ifeffit] Problems in Energy calibration
leizhong8532 at gmail.com
Fri May 16 02:12:15 CDT 2014
Thank you so much for your generous sharing.
Have a nice weekend.
2014-05-15 9:36 GMT+02:00 Edmund Welter <edmund.welter at desy.de>:
> Dear Lei,
> > Q1. In two beam lines, for exactly the same MoS2 crystal, we got
> difference in XANES region. Spectrum from DESY has a weak pre-edge 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?
> If you measured the Mo K-edge at 20000 eV at DESY you were most probably
> using the 311 crystals (at least that is what I or one of my colleagues
> here would have suggested) As Matthew already mentioned the differences in
> the pre-edge region might be due to differences in the energy resolution
> (for instance if you used 111 crystals at ESRF).
> > 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?
> I am not sure if I understand exactly what you want to do. Anyway, if you
> find a difference of 2.5 eV between the edge position measured on the same
> sample at different beamlines it makes sense to define the spectra from one
> beamline to be "correct" and shift all spectra from the other beamline by
> the respective energy shift (here 2.5 eV). BUT (!) you must be sure that
> the shift is reproducible... If you measured reference spectra you can
> easily check if this is true, you should not observe any shift between the
> energy positions of you metal foil spectra. If you have no reference
> spectra you could trust encoder values (if you have them) or it becomes a
> religious thing and you just have to believe (and maybe convince others to
> believe too...;-)
> > 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?
> So you checked the reproducibility of your energy axis and you can be
> more or less sure that the energy axis did not shift during your
> measurements. Fine, so there is no need to re-calibrate your one ESRF
> spectrum with respect to another ESRF spectrum, but if you want to compare
> them with the DESY spectra you still have to shift either all the DESY
> spectra or all the ESRF spectra by 2.5 eV. And as Matthew already mentioned
> you should document what you did so that someone else can trace your energy
> positions back to a common standard (in your case the metal foil and the
> usually used k-edge position of 20000.0 eV from the orange book.
> Best regards
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