Hell all I have the study for PtO nanoparticles with EXAFS. When I fitted the data to model, I had a problem for energy shift. I thought that the energy shift obtained from fitting must be below White line. However it was over white line. Although I removed background carefully and changed bond length in model, the energy shift was still big. I want to know other factors which affect energy shift.
Hi, could say more precise what kind of energy shift you are talking about? the position of the white line or the Enot in Artemis. How big it is? Which version of Feff do you use? What do you mean writing "removing background carefully"? Background in the EXAFS fit? Any pictures to illustrate problem are welcome W dniu 11-10-05 03:25, JeongEunSuk pisze:
Hell all I have the study for PtO nanoparticles with EXAFS. When I fitted the data to model, I had a problem for energy shift. I thought that the energy shift obtained from fitting must be below White line. However it was over white line. Although I removed background carefully and changed bond length in model, the energy shift was still big. I want to know other factors which affect energy shift.
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Thank Dariuz and Bruce. TiO is deposited on Si substrate and PtO is fabricated on TiO2. I measered EXAFS with Pt L3 edge(11563eV) and The model is decided from FEFF8.0. PtO has only fist shell like attached files So I chose the simple model with octahedral structure (probe atom Pt, others O) When the EXAFS was fitted by feffit, the variables were three eo(Enot in Artemis, energy shift), do1(distance factor), sigo1(debye-waller factor). the results of fit is as following variable best fit value uncertainty initial guess eo = 19.283398 1.726426 0.000000 do1 = -0.023227 0.009557 0.096000 sigo1 = 0.003790 0.000583 0.003047 r-factor: 11 reduced-chi square: 95 Energy shift by fit shows an amount of difference from Pt L3 edge. It is my problem. To reduce the energy shift, I tried to remove background carefully again and to change distance Pt-O. However the result was failed. Date: Wed, 5 Oct 2011 08:24:16 +0200 From: kicaj@ifj.edu.pl To: ifeffit@millenia.cars.aps.anl.gov Subject: Re: [Ifeffit] Energy shift Hi, could say more precise what kind of energy shift you are talking about? the position of the white line or the Enot in Artemis. How big it is? Which version of Feff do you use? What do you mean writing "removing background carefully"? Background in the EXAFS fit? Any pictures to illustrate problem are welcome W dniu 11-10-05 03:25, JeongEunSuk pisze: Hell all I have the study for PtO nanoparticles with EXAFS. When I fitted the data to model, I had a problem for energy shift. I thought that the energy shift obtained from fitting must be below White line. However it was over white line. Although I removed background carefully and changed bond length in model, the energy shift was still big. I want to know other factors which affect energy shift. _______________________________________________ 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
Your attachment do not help in this case... Do you know something more about sample? I suppose it is a thin layer. Have you checked if you have no defects, vacancies, etc? I suppose that you can follow instructions given in this post http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2009-January/008522.html but you can be also interested in this topic: http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2009-June/004293.html and especially in last posts. you can also try this suggestion http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2010-June/009471.html In general - could you precise, what is k_{min} for your fit, and did you use self consistent potential in calculations? W dniu 11-10-06 02:28, JeongEunSuk pisze:
Thank Dariuz and Bruce. TiO is deposited on Si substrate and PtO is fabricated on TiO2. I measered EXAFS with Pt L3 edge(11563eV) and The model is decided from FEFF8.0. PtO has only fist shell like attached files So I chose the simple model with octahedral structure (probe atom Pt, others O) When the EXAFS was fitted by feffit, the variables were three eo(Enot in Artemis, energy shift), do1(distance factor), sigo1(debye-waller factor). the results of fit is as following variable best fit value uncertainty initial guess eo = 19.283398 1.726426 0.000000 do1 = -0.023227 0.009557 0.096000 sigo1 = 0.003790 0.000583 0.003047 r-factor: 11 reduced-chi square: 95
Energy shift by fit shows an amount of difference from Pt L3 edge. It is my problem. To reduce the energy shift, I tried to remove background carefully again and to change distance Pt-O. However the result was failed.
------------------------------------------------------------------------ Date: Wed, 5 Oct 2011 08:24:16 +0200 From: kicaj@ifj.edu.pl To: ifeffit@millenia.cars.aps.anl.gov Subject: Re: [Ifeffit] Energy shift
Hi, could say more precise what kind of energy shift you are talking about? the position of the white line or the Enot in Artemis. How big it is? Which version of Feff do you use? What do you mean writing "removing background carefully"? Background in the EXAFS fit? Any pictures to illustrate problem are welcome
W dniu 11-10-05 03:25, JeongEunSuk pisze:
Hell all I have the study for PtO nanoparticles with EXAFS. When I fitted the data to model, I had a problem for energy shift. I thought that the energy shift obtained from fitting must be below White line. However it was over white line. Although I removed background carefully and changed bond length in model, the energy shift was still big. I want to know other factors which affect energy shift.
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_______________________________________________ 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
On Tuesday, October 04, 2011 09:25:18 pm JeongEunSuk wrote:
Hell all I have the study for PtO nanoparticles with EXAFS. When I fitted the data to model, I had a problem for energy shift. I thought that the energy shift obtained from fitting must be below White line. However it was over white line. Although I removed background carefully and changed bond length in model, the energy shift was still big. I want to know other factors which affect energy shift.
As Darek said, it is hard to know what you are talking about without some more information. There are a lot of things that can lead to weird values of E0 in an EXAFS fit, for instance: * You expect an oxide, but your sample has a large metallic component * You expect an oxide, but your sample has a large sulfide component * You run Feff on the Pt K edge rather than the Pt L3 edge, resulting in an incorrect phase shift in the theory * You mistyped a number while inputing crystal data into Atoms, resulting in icorrect distances in the feff.inp file * You took crystal data from an untrustworthy source, resulting in icorrect distances in the feff.inp file * Your material as a nanoparticle is substantially different from the bulk analogue I, of course, have no idea if any of those suggestions apply. The bottom line is that a disturbingly large E0 value is usually a suggestion that you have made an error of procedure or assumption while creating your fitting model. Sometimes it indicates a systematic problem in the data collection -- certain monochromator problems can introduce a periodic but non-EXAFS signal into the data. On occassion it even suggests a bug in the software -- but usually not. Usually there is some problem in the fitting model. I should also point out that going through the excercise of documenting the problem clearly, as Darek suggested, is valuable not only because it provides the information that makes it likely that someone can actually answer your question, but because doing so forces you to carefully examine your work, which may turn expose the problem. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter
participants (3)
-
"Dr. Dariusz A. Zając" -
Bruce Ravel -
JeongEunSuk