two measurements of the same compound in different beam-lines
Hi all! I have performed two independent XAFS measurements of Cr K-edge of the same Fe-Cr sample at two different beam-lines at SSRL. I have obtained the Fe-K edge data only once. The quality of data are different in each measurement. However, I cannot average spectra from different Cr-K measurements, and I don't know if I could take somehow advantage from having almost twice the information for the Cr- K adge, or I have to use only the better quality data and discard the other. What do you advice? If I can use both measurements, how can I do the fitting in Artemis? Thank you very much and all take care -- María Elena Dra. María Elena Montero Cabrera Departamento de Medio Ambiente y Energía Centro de Investigación en Materiales Avanzados (CIMAV) Miguel de Cervantes 120, Compl. Ind. Chihuahua Chihuahua CP 31109, Chih. México Tel (614) 4391123
Hi Maria, You have several choices. First, note that the merge function in Athena allows you to select options of weight by chi-noise, or weight by importance. If you weight by chi-noise, noisier data will be counted less. If you have some other way of estimating the quality of the data sets, you can enter different numbers in the "importance" field and then weight by importance. If working on two different beamlines, you might consider merging chi(k) data, rather than norm(E), as the backgrounds may be different. And mu(E) probably makes no sense at all. Another option is to obtain separate chi(k)'s, but then fit both spectra simultaneously in Artemis. The Artemis/Ifeffit default behavior in that case will be to use high-R noise for weighting, but you can override that by assigning an epsilon to each data set if you choose. This method has several advantages: it lets you see if one data set is fitting differently from the other; it lets you choose different k-ranges if noise begins dominating one data set at a lower value of k; it lets you use different values of S02 if there are pinhole, harmonic, or self-absorption effects; and it lets you use different values of delE0 if the data sets are hard to align properly. --Scott Calvin Sarah Lawrence College On Aug 12, 2010, at 8:44 PM, María Elena Montero Cabrera wrote:
Hi all! I have performed two independent XAFS measurements of Cr K-edge of the same Fe-Cr sample at two different beam-lines at SSRL. I have obtained the Fe-K edge data only once. The quality of data are different in each measurement. However, I cannot average spectra from different Cr-K measurements, and I don't know if I could take somehow advantage from having almost twice the information for the Cr- K adge, or I have to use only the better quality data and discard the other. What do you advice? If I can use both measurements, how can I do the fitting in Artemis? Thank you very much and all take care
-- María Elena
Dra. María Elena Montero Cabrera Departamento de Medio Ambiente y Energía Centro de Investigación en Materiales Avanzados (CIMAV) Miguel de Cervantes 120, Compl. Ind. Chihuahua Chihuahua CP 31109, Chih. México Tel (614) 4391123 _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Hi Scott,
Thanks a lot, Scott!
I didn't know about epsilon!
Take care
Maria Elena
2010/8/13 Scott Calvin
Hi Maria,
You have several choices. First, note that the merge function in Athena allows you to select options of weight by chi-noise, or weight by importance. If you weight by chi-noise, noisier data will be counted less. If you have some other way of estimating the quality of the data sets, you can enter different numbers in the "importance" field and then weight by importance.
If working on two different beamlines, you might consider merging chi(k) data, rather than norm(E), as the backgrounds may be different. And mu(E) probably makes no sense at all.
Another option is to obtain separate chi(k)'s, but then fit both spectra simultaneously in Artemis. The Artemis/Ifeffit default behavior in that case will be to use high-R noise for weighting, but you can override that by assigning an epsilon to each data set if you choose. This method has several advantages: it lets you see if one data set is fitting differently from the other; it lets you choose different k-ranges if noise begins dominating one data set at a lower value of k; it lets you use different values of S02 if there are pinhole, harmonic, or self-absorption effects; and it lets you use different values of delE0 if the data sets are hard to align properly.
--Scott Calvin Sarah Lawrence College
On Aug 12, 2010, at 8:44 PM, María Elena Montero Cabrera wrote:
Hi all!
I have performed two independent XAFS measurements of Cr K-edge of the same Fe-Cr sample at two different beam-lines at SSRL. I have obtained the Fe-K edge data only once. The quality of data are different in each measurement. However, I cannot average spectra from different Cr-K measurements, and I don't know if I could take somehow advantage from having almost twice the information for the Cr- K adge, or I have to use only the better quality data and discard the other. What do you advice? If I can use both measurements, how can I do the fitting in Artemis? Thank you very much and all take care
-- María Elena
Dra. María Elena Montero Cabrera Departamento de Medio Ambiente y Energía Centro de Investigación en Materiales Avanzados (CIMAV) Miguel de Cervantes 120, Compl. Ind. Chihuahua Chihuahua CP 31109, Chih. México Tel (614) 4391123 _______________________________________________ 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
-- María Elena Dra. María Elena Montero Cabrera Departamento de Medio Ambiente y Energía Centro de Investigación en Materiales Avanzados (CIMAV) Miguel de Cervantes 120, Compl. Ind. Chihuahua Chihuahua CP 31109, Chih. México Tel (614) 4391123
participants (2)
-
María Elena Montero Cabrera -
Scott Calvin