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

HI Haifeng, Suppose you measure Fe foil three times, and all three scans overlap. They are aligned. But suppose the edge positions are at 7116 eV instead of 7112 eV. The calibration is off. You can adjust to it, but, as Carlo mentioned, it is really an angle correction, not simply a shift in energy. It is better to have an accurate calibration to begin with, then aligned and calibrated would be the same. Note: Choice of target calibration can differ - some use the X-ray data booklet values http://xdb.lbl.gov/ and some use the Kraft  et al. values https://aip.scitation.org/doi/abs/10.1063/1.1146657 Just state which calibration you are using when presenting/publishing. -R. On 2018-07-27 10:32 AM, Haifeng Li wrote:

Hi, Robert,

Thanks for your help.

One more question. What is the real difference between calibration and alignment? Do they have specific meaning?

Thanks,

Haifeng

On Sun, Jul 22, 2018 at 5:45 PM, Robert Gordon mailto:ragordon@alumni.sfu.ca> wrote:

Hi Haifeng,

Here's my take on what you described:

Two sample to be studied at the same edge using the same reference. Three scans on A and three on B are done with simultaneous reference.

First: compare the three reference scans for A. If they agree, then compare the data scans. If they also look similar (i.e. no evidence of changing in the beam), you can merge the three data scans on A right away. If the references don't agree, then you determine by how much they differ (how much a correction would be needed to bring them into alignment) and apply that same correction to the data before merging. It is not meaningful to merge data that is not aligned. (If the sample scans show changes from scans 1  to 3, then you need to rethink how to do the measurements)

Repeat for B.

Now compare the merged (corrected beforehand if necessary) references for A and B. If they agree, you can compare data for A and B (merged) directly. If they do not, determine how much one reference differs from the other and apply that same correction to, say, B, that brings its reference into alignment with A's reference, and then compare A and B

You align the references between samples to the same value in order to do a meaningful comparison between them. If you report energy positions of features in your near-edge spectra, the reader would need to know to what energy those positions are referenced.

When possible, I recommend references that have tabulated edge values (i.e. metal foils). A reference need not be the same edge as the one being studied. For arsenic, as an example, the gold L3-edge is quite close to the As K-edge and serves as a good reference. If not possible to use a metal foil, use a reference that another interested researcher could readily obtain or has used. This allows for comparison of reproducibility. If your reference looks nothing like literature, you may have a problem with the beamline or in how you processed the data. This should be one of the first things you check when you start taking data at the beamlne.

You should also note how the beamline was calibrated when you did the measurements.

regards, Robert

On 2018-07-22 1:21 PM, 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

_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov mailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe:http://millenia.cars.aps.anl.gov/mailman/options/ifeffit http://millenia.cars.aps.anl.gov/mailman/options/ifeffit

_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov mailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit http://millenia.cars.aps.anl.gov/mailman/options/ifeffit

_______________________________________________ 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