[Ifeffit] Estimation of S02

Matthias Bauer matthias.bauer at ipc.uni-stuttgart.de
Wed Oct 8 05:27:42 CDT 2008


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 <oji-h at spring8.or.jp>:
>   
>> 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 at spring8.co.jp
>> =========================================================
>>
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>>
>>     
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