Re: [Ifeffit] Basic questions about the preliminary data processing in Athena

Hi, Carlo, Thanks for your physical explanation for the calibration. I have another question. I measured the same element at different beamlines. So if I want to compare different samples measured at different beamlines, how should I do for this situation given the possible different calibration methods? I know alignment is very important and just shifting the energy by calibrating would have issue. Here I mean different calibration methods is dedicated for my element ruthenium Ru with E0 of 22117 eV. The derivative curve show it has two peaks. One beamline used the first one for calibration. The other used the second. Another used the middle number between the two peaks by claiming that the peaks stand for oxidation state with one peak for one oxidation state and multiple peaks for multiple oxidation states. Here for Ru metal with one oxidation state, since the main peak splits into two, the middle energy between the two peaks was chose as the E0. Attached is the file of Ru foil for more information. I do not know which one should be right. In the manual, it shows choosing the first maximum point as the edge energy. How should I choose the edge energy? Maybe I think too much. It does not matter as the calibration is consistency. The reference data from different calibration methods can be aligned very well. This is another confusing part. Does the calibration would affect the alignment? Thanks in advance. Haifeng On Mon, Jul 23, 2018 at 10:48 AM, Carlo Segre wrote:

The calibration should be done at the beamline with a foil. Once that is done, then you don't really want to change it. Remember that just shifting the energy is not actually the correct way to do a shift. The energy shift is a non-linear function of the angle (Bragg's Law) and so when you shift energy you are really distorting Chi(k) since that is also a non-linear function of energy (E^1/2). Yes, it is usually a small effect but I prefer not to apply too many shifts in energy if possible.

I assume that the calibrate function is the same as the align except the E-shift is left at zero and a correction is applied permanently to the data.

Carlo

On Mon, 23 Jul 2018, Haifeng Li wrote:

Hi, Carlo,

...

Thanks for your answer.

I may ask you more questions. Why you do not recommend to calibrate the data? Calibration is used to find the E0 and match it to the literature data. What is the real difference between calibration and alignment?

Thanks,

Haifeng

On Sun, Jul 22, 2018 at 5:30 PM, Carlo Segre wrote:

...

Hello Haifeng:

Personally, I would not calibrate the data but merely align the references of A2 and A3 to the reference of A1 and similarly align B2 and B3 references to that of B1. Once merged, you can then aligh the reference of the merged B samples to that of the merged A samples.

If you keep the references then you can always align data taken at a leter time to these data sets. If the energy of your reference is a small bit off from the tabulated value, that is OK as long as all the data being compared has aligned references.

Carlo

On Sun, 22 Jul 2018, Haifeng Li wrote:

Dear ALL,

...

I am a beginner in Athena. Recently I got the spectra and I am confusing about the data calibration and alignment. The manual shows that calibrate the reference data of one scan and align other reference data to that calibrated one.

Here I want to show examples. I have two samples A and B, Each sample has three scans with the corresponding reference data. For sample A, 1st scan is calibrated and the other two scans are aligned to 1st scan. Then merge them into merged A. The same procedures for sample B and get merged B. If I want to compare XANES of sample A and B, do I need to align the merged reference data between A and B? If so, why? My understanding is that all scans (original data and merged data) in sample A and B are calibrated to standard edge energy. Why do they need to align?

I appreciate your help.

Thanks,

Haifeng

--

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@iit.edu http://phys.iit.edu/~segre segre@debian.org _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit

-- 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@iit.edu http://phys.iit.edu/~segre segre@debian.org