Hi Brandon, Will you send me your athena and artemis project files? Dr.sdkelly@gmail.com Shelly Sent from my Palm Pre on the Now Network from Sprint On Jun 7, 2011 2:09 PM, Andrew Korinda <a-korinda@northwestern.edu> wrote: Sorry Brandon, I see now everything I was asking for was I'm the first few emails. Enot is a local atomic shift in E0 as explained before. (sorry I'm not referencing, I only have my phone available this week) What I understand is you have set E0 to 27944 and 27950 then get Enot of -7 and -1 respectively. This leads to a local edge in the EXAFS equation of 27951 in both cases which is what I was getting at previously. But you say ~ so that means you have an real difference between the two, and the opposite of what I was thinking. Sorry if I caused any confusion. Andy Korinda On Jun 7, 2011 6:27 AM, "Brandon Reese" <bjreese@gmail.com> wrote:> 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@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@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@millenia.cars.aps.anl.gov >>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >>> >> >> >> _______________________________________________ >> Ifeffit mailing listIfeffit@millenia.cars.aps.anl.govhttp://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 >> >>