Re: [Ifeffit] Estimation of S02

Hi Matthias and Leandro, Thank you very much for your reply. I checked the DW-factor (MSRD) and found it also varies significantly depending on Fit k-weight as follows. kw amp ss 1 0.8145660 +/- 0.0486470 0.0073230 +/- 0.0005240 2 0.9230700 +/- 0.0673820 0.0082070 +/- 0.0005070 3 1.0439100 +/- 0.0854950 0.0089560 +/- 0.0005100 1,2,3 0.9081570 +/- 0.0722180 0.0081660 +/- 0.0005920 The correation between these variables reported by Artemis are very strong, especially for kw=3. kw corration between amp and ss 1 0.8469 2 0.8992 3 0.9543 1,2,3 0.8543 So, it seems to me that the amps obtaied by kw=1 and 1,2,3 with less degree are more reliable. If the DW-factor is fixed, for example, to ss = 0.008, the variation of amp become small as follows, kw amp ss 1 0.8674610 +/- 0.0296350 0.008 (fixed) 2 0.8984650 +/- 0.0260200 0.008 (fixed) 3 0.8998030 +/- 0.0327720 0.008 (fixed) 1,2,3 0.8898850 +/- 0.0325530 0.008 (fixed) But I don't know how to determine the appropriate DW-factor. Could you give me advice or comment on this problem? By the way, I attached the Athena project file of Zr-foil which I analyzed. I am glad if you kindly check it. Thank you for your coopration in advance, Best regards, Hiroshi Matthias Bauer wrote:

hi hiroshi, i did not have a look at the attached project, but what paramteres did you vary? even if you use different k-weightings, there is still the strong correlation of N,S02 and the Debye-Waller like factor. so as long as you do not keep two of these three on a certain value, your S02 might vary to some extend, which will be more significant for shells beyond the first one. anyway, it would be a great thing to hear some comment on a S02 value higher than one, which is by definition of S02 not possible. in most analyses the electron mean free path is not iterated, which can be an explanation of unphysical values of S02, but than it should be considered as a "net" factor accounting for both intrinsic and extrinsic losses. am i right? best regards matthias

Leandro Araujo wrote:

...

Hi Hiroshi,

your variation in SO2 does sound a bit too big, so I'll try to help adding my 50c and hopefully more people will jump in. It seems to me that your window in k-space is going a bit lower than it should - you seem to be including signal from the xanes region in your fit and that is not a good thing. I did some really quick fits using your project and just changing the window from k ~ 2-14 to k ~ 4.8-14. Then I got the following values: kw amp 1 1.0065350+/-0.0788250 2 1.0359800+/-0.0888140 3 1.0749950+/-0.0946640 1-3 1.0322490+/-0.0866650 That seems a more reasonable variation to me. But maybe I'm being tricked by the fact that you have a split first shell and the MSRDs are not supposed to be very similar... I would also suggest opening the r-window to the right side a little bit. (By the way, that "bump" in the FT at ~ 1 Angstrom seems unexpected for a Zr foil. Maybe check the background removal in Athena?)

The above comments obviously do not address the fundamental questions "why does SO2 change with k-weighting?" and "what's the best way to determine SO2?". This was intentional, since much better qualified people have previously written about it. My guess is that you will find something if you search previous threads in this mailing list. I would also suggest you check these sites: http://xafs.org/Tutorials http://cars9.uchicago.edu/iffwiki/FAQ/FeffitModeling

Hope this helps, Leandro

2008/10/7 Hiroshi Oji :

...

Dear all,

Could you give me some advice on estimating the intrinsic loss factor (S02)?

I am trying to estimate the S02 value in the curve-fitting analysis for Zr K-edge EXAFS.

To do this, I did the curve-fitting analysis on the first shell of Fourier transform of Zr-K EXAFS of Zr-foil by Artemis. However, there was a marked difference between the amps obtained by the fitting, depending on the "Fit k-weights" as follows.

kw amp 1 0.8145660 +/- 0.0486470 2 0.9230700 +/- 0.0673820 3 1.0439100 +/- 0.0854950 1,2,3 0.9081570 +/- 0.0722180

Is this a usual thing? I can't find the reasonable explanation why S02 depends on "Fit k-weights".

I attached the Artemis project file.

Thank you in advance for your cooperation.

Hiroshi Oji

========================================================= 　Hiroshi Oji, Dr. Industrial Application Division Japan Synchrotron Radiation Research Institute (JASRI) 1-1-1 Kouto, Sayo-cho Sayo-gun, Hyogo 679-5198 JAPAN E-mail oji-h@spring8.co.jp =========================================================

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