[Ifeffit] Estimation of S02
Hiroshi Oji
oji-h at spring8.or.jp
Wed Oct 8 10:47:16 CDT 2008
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 <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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>>> Ifeffit mailing list
>>> Ifeffit at millenia.cars.aps.anl.gov
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>>>
>>>
>>>
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陰地 宏
（財）高輝度光科学研究センター（JASRI）
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E-mail: oji-h at spring8.or.jp
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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