[Ifeffit] Question about shift in E0
Brandon Reese
bjreese at gmail.com
Tue Jun 7 05:25:42 CDT 2011
I was using feff6. Does your comment mean that when fitting Enot with Feff6,
the results should be considered unreliable? I assumed the 0.5 eV shift in
the mu spectra was small enough that the spectrum could be considered
essentially at the same energy. That is why I was surprised with the
(somewhat) larger shift in Artemis.
Andy, are you asking what the difference is between E0-Enot for the two
samples? If I picked E0 to be 27944 for all the samples( a round number near
the 1st derv peak), Artemis would fit Enot to be ~5.5 for one group of
samples and ~7 for the other group. Approximately the same offset was
present if I let the parameters get chosen automatically, regardless of the
absolute E0 (within reason). Is this what you were asking, or did I
misunderstand?
Brandon
Andy, E0-Enot came out to be 2794
2011/6/7 "Dr. Dariusz A. Zając" <kicaj at ifj.edu.pl>
> **
> Hi Brandon,
> that was a reason why I wanted to clarify which parameters you use.
> E0 (as a Fermi level) in Athena can be taken (but do not must) as a valence
> state of measured ion for K edges, whereas in Artemis delE0 can correspond
> to the potential of the one of nearest atoms to the measured one. If you
> talk about Artemis and calculations, would be also helpful to know the
> version of feff. It is known that for version up to 6. can be problem with
> fitting values of Enot. And of course Matt answered you more clearly...
> The difference of 0.5eV between spectra of reference sample can be simply
> related with the energy resolution of the beam (beamline).
>
> Maybe this will helps you more:
> http://cars9.uchicago.edu/pipermail/ifeffit/2004-June/005607.html
> http://cars9.uchicago.edu/pipermail/ifeffit/2006-February/006811.html
>
> kicaj
>
> W dniu 11-06-07 00:46, Brandon Reese pisze:
>
> Kicaj and Matt,
>
> Thanks for the replies. It is certainly reasonable to ask about the
> experimental setup, that seems like a good first place to look for oddities.
> Sorry about using E0 in two different contexts (Athena and Artemis). I'll
> switch to using E0 for the chosen parameter in Athena's background
> subtraction and Enot for the guess parameter in Artemis.
>
> I aligned the scans in Athena using the reference foil absorption edge. I
> ended up shifting the scans in energy by ~1 eV or less based on the
> reference foil. I then set the E0 parameter in Athena to the peak of the
> first derivative. This value varied by about 0.5 eV (or less) between the
> different samples. This is what I considered when I made the statement about
> not seeing the oxidation change in the XANES. There is a shift of about 4 eV
> compared to the reference foil, which I would expect because I am looking at
> oxides.
>
> I then extracted the chi(k) into Artemis, and used the same Feff
> calculations/paths for each sample. In the Artemis fits I am seeing Enot
> shifts of 1-2 eV, which is a fair bit larger than the error bars. If I chose
> E0 at peak of the first derivative the Enot came out to be ~7 eV. Since this
> seemed a little on the big side, I also tried setting E0 to be the top of
> the white line, in that case Enot came out to be ~1 eV. The Enot shift
> between samples was about the same either way. Could an argument be made
> that there is a small shift in the overall oxidation state of the films,
> possibly contributing to the changes in the conductivity changes in the
> films? Does anyone have any references about using Enot shifts in this way?
>
> Scott - The amplitudes of the XANES features are very close. in the
> normalized spectrum the difference practically 0, and in the derivative the
> amplitudes are ~5% off. There is bit larger of a difference in amplitude
> between the samples (in fluorescence) and a pure In2O3 powder (in
> transmission) of ~10% in the first derivative. The samples are sputtered
> from oxide sources, so the presence of metallic In should be pretty small. I
> am interested about your comment on the relative sizes of the first
> derivative peaks. Comparing my samples to the foil the oxide peak amplitude
> is bigger than the metal peak by 10% or so. Could this be due to the
> differences between fluorescence and transmission or not optimizing the
> experiment to measure the foil? Or could it be due to something else more
> heinous?
>
> I noticed on individual fits that the dR for the first shell came out
> nearly the same (2.162 +/- .007 vs. 2.164) on the two samples, while the
> Enot's had the 1-2 eV shift between the samples. I tried to fit the two
> types of samples simultaneously while constraining the dR's (and a few 2nd
> shell parameters) to be equal to each other and letting the Enot's float.
> The relative Enot values came out close to what they were before. If I let
> dR values fit independantly, there was no real change present. In other
> words the multiple data set fit just made my EB's a bit smaller, but the
> relative shifts stayed about the same.
>
> Would there be some reasonable way in a multi-data set fit to constrain the
> Enot's?
>
> Brandon
>
> On Mon, Jun 6, 2011 at 9:04 AM, Matt Newville <newville at cars.uchicago.edu>wrote:
>
>> HI Brandon,
>>
>> If I understand right (and to echo Darius's questions), it seems like
>> you measure samples with a metal reference, and aligned the spectra in
>> Athena so that the references matched. That's a fine way to go. I
>> would ask: how big were the needed energy shifts?
>> Are the experimental mu(E) spectra aligned well at this point? If
>> you're studying metal oxides with different oxygen content, you might
>> very well see oxidation in the XANES. If I understand correctly,
>> you're saying you don't see this.
>>
>> Then, you extracted the chi(k) from the aligned spectra. How much did
>> E0 vary for the shifted spectra in this background-subtraction step?
>>
>> Then, you pulled these chi(k) into Artemis, and see different E0
>> shifts in the fits. This E0 is a little different, in that it is the
>> E0 shift applied to the Feff calculation to match the experimental
>> spectra. If you use different paths or different calculations, such
>> E0 shifts might happen, and wouldn't be highly meaningful.
>>
>> I know that's not a complete answer, but hopefully that and Darius's
>> questions will help,
>>
>> --Matt
>>
>> PS on Q2: 1/ (kR)^2 vs 1 / kR^2
>>
>> This is probably either a typo, or a different convention based on the
>> definition of f(k) as the electron scattering amplitude. In the Feff
>> world, it should be 1/kR^2, but using 1/(kR)^2 would just map f(k) to
>> k*f(k).
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>
>
>
> _______________________________________________
> Ifeffit mailing listIfeffit at millenia.cars.aps.anl.govhttp://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
>
>
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20110607/bf4b168c/attachment.html>
More information about the Ifeffit
mailing list