Dear list, I enclose an Athena project with a XAFS spectrum of Co3O4 with a metallic Co reference. Athena by default has chosen E0 at the absolute maximun of the derivative curve (at 7727.8eV) which in my opinion is too high because it is at the white line zone. I believe that E0 should be the previous maximun in the derivative at around 7722eV, which would be at the rising edge. Am I wrong? I would appreciate some help with the criterion to determine the right value. Yours, Jesús
Dear Jesús, Why will you choose the maximum at 7722 eV? I will choose the first one (ignoring the pre-edge), around 7718 eV. The problem here, could be that in Co3O4 you have one atom of Co(II) and two of Co(III) so, there are absorbing at different energies. But the EXAFS is common so, and error will happen no matter which maximum you choose. I have a CoO spectra and the maximums of the derivative (again ignoring the pre-edge) appear at 7717, 7721 and 7725 eV. If you had a Co2O3 spectra (I don't) you can compare and decide to choose the E0 which is closer to that of the Co2O3 as in Co3O4 you have more Co(III). Also, if you make three copies of the spectra and select a different E0 for each one you can see how it affect the x(k) and the Fourier transform (to R). The first E0 (7718 eV) make x(k) to have higher intensity (resulting in higher intensity of peaks in R). But the third one (7722) creates an extra feature below 1 in the R space (for k range 3-9 or 3-10). Usually I will just choose the first one or, compare some and see what happen. Probably, the different will not so high to make you worry too much. Regards, Manuel On 25/10/2017 17:11, Jesús Eduardo Vega Castillo wrote:
_________________________________________________________________
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I enclose an Athena project with a XAFS spectrum of Co3O4 with a metallic Co reference. Athena by default has chosen E0 at the absolute maximun of the derivative curve (at 7727.8eV) which in my opinion is too high because it is at the white line zone.
I believe that E0 should be the previous maximun in the derivative at around 7722eV, which would be at the rising edge.
Am I wrong?
I would appreciate some help with the criterion to determine the right value.
Yours,
Jesús
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Thank you very much Manuel,
2017-10-27 6:41 GMT-03:00 Manuel MONTE CABALLERO
Dear Jesús,
Why will you choose the maximum at 7722 eV? I will choose the first one (ignoring the pre-edge), around 7718 eV.
The problem here, could be that in Co3O4 you have one atom of Co(II) and two of Co(III) so, there are absorbing at different energies. But the EXAFS is common so, and error will happen no matter which maximum you choose. I have a CoO spectra and the maximums of the derivative (again ignoring the pre-edge) appear at 7717, 7721 and 7725 eV. If you had a Co2O3 spectra (I don't) you can compare and decide to choose the E0 which is closer to that of the Co2O3 as in Co3O4 you have more Co(III).
Also, if you make three copies of the spectra and select a different E0 for each one you can see how it affect the x(k) and the Fourier transform (to R). The first E0 (7718 eV) make x(k) to have higher intensity (resulting in higher intensity of peaks in R). But the third one (7722) creates an extra feature below 1 in the R space (for k range 3-9 or 3-10).
Usually I will just choose the first one or, compare some and see what happen. Probably, the different will not so high to make you worry too much.
Regards,
Manuel
On 25/10/2017 17:11, Jesús Eduardo Vega Castillo wrote:
_________________________________________________________________
* WARNING:* Viruses are often found in attached files of type document (.xls .doc etc.) and compressed (.zip .rar etc.). Please be *EXTREMELY* careful when opening this kind of file. In case of doubt, please contact the sender for confirmation. _________________________________________________________________ Dear list,
I enclose an Athena project with a XAFS spectrum of Co3O4 with a metallic Co reference. Athena by default has chosen E0 at the absolute maximun of the derivative curve (at 7727.8eV) which in my opinion is too high because it is at the white line zone.
I believe that E0 should be the previous maximun in the derivative at around 7722eV, which would be at the rising edge.
Am I wrong?
I would appreciate some help with the criterion to determine the right value.
Yours,
Jesús
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participants (2)
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Jesús Eduardo Vega Castillo -
Manuel MONTE CABALLERO