Hi,Jason!
I think you are really professional and pointed out the most important point at the beginning !
Actually I am really worried about my experiment too, I also have a doubt about whether I can see C or O contributions to the EXAFS in my sample.But I think maybe no one can give the answer for sure. So at least I need to try first and see. Actually the originality of my work is to study the electrochemical reduction of CO2 on metal electrodes. Since CO is noticed as an important adsorbed intermediate in the multistep reaction and only copper has been found to be unique among the metals in its ability to produce a high quantities of hydrocarbon fuels, i start to first investigate the interaction between adsorbed CO and copper.Thats why I believe that using EXAFS to study the chemisorbed CO gas-copper system will contribute to some reasonable explanation.
I sent you two references, in the first one there is evidence for CO adsorbed Ru taken at Ru k-edge,where CO is observed in EXAFS, and the second one SEXAFS study on CO adsorbed on Cu, but it is taken at oxygen K edge.I think even if there is not exact the same evidence with my system which is EXAFS on Cu k-edge of CO adsorbed Cu, but it may still work. Why do you think my experiment is not promising? Could you please explain some reasons to me? Is there any conditions for metal and adsorbed gas that their EXAFS signal can be detected? If there are,would you please to give me some modification of my experiment?
Thanks a million.
Best Regards,
------------ Original Message ------------
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To : ifeffit@millenia.cars.aps.anl.gov
Mail Subject : Ifeffit Digest, Vol 115, Issue 2
Sent : Wed, 05 Sep 2012 08:25:57 -0500
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Today's Topics:
1. Ratio of peak amplitudes in R-space (Rana, Jatinkumar Kantilal)
2. Re: Ratio of peak amplitudes in R-space (Christopher Patridge)
3. Re: Ratio of peak amplitudes in R-space (Scott Calvin)
4. How to write feff.inp file for CO adsorbed Cu? (Zhaomo Tian)
5. Re: How to write feff.inp file for CO adsorbed Cu? (Jason Gaudet)
----------------------------------------------------------------------
Message: 1
Date: Wed, 5 Sep 2012 12:01:01 +0000
From: "Rana, Jatinkumar Kantilal"
To: "ifeffit@millenia.cars.aps.anl.gov"
Subject: [Ifeffit] Ratio of peak amplitudes in R-space
Message-ID:
Content-Type: text/plain; Zharset="us-ascii"
Dear Ifeffit community,
I was wondering If I can make a qualitative comparison about the amplitude ratio of first two shells for various states of same sample ?
For example, I have a sample which is measured at various states, say A, B, C, D and E during any physical or chemical process.
I get systematic change in the ratio of first two peaks at each state. This could be interpreted either as change in disorder or as change in number of atoms associated with first two shells as a result of any physical or chemical change material has undergone.
As we know that amplitude of peak decreases with increase in distance from central absorber.
Can I compare the amplitude ratio of first two peaks for various states of same sample ??
Many thanks in advance !!!
With best regards,
Jatin
________________________________
Helmholtz-Zentrum Berlin f?r Materialien und Energie GmbH
Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V.
Aufsichtsrat: Vorsitzender Prof. Dr. Dr. h.c. mult. Joachim Treusch, stv. Vorsitzende Dr. Beatrix Vierkorn-Rudolph
Gesch?ftsf?hrung: Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas Frederking
Sitz Berlin, AG Charlottenburg, 89 HRB 5583
Postadresse:
Hahn-Meitner-Platz 1
D-14109 Berlin
http://www.helmholtz-berlin.de
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Message: 2
Date: Wed, 5 Sep 2012 08:28:27 -0400
From: Christopher Patridge
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Ratio of peak amplitudes in R-space
Message-ID:
Content-Type: text/plain; Zharset="iso-8859-1"
Jatin,
If these changes are systematic and you somewhat understand the physical or
chemical process associated with the sample, then why not just build a
model and do a structural fitting? A simple peak ratio comparison maybe
helpful but a much stronger argument and interpretation can be made if you
use a structural model to extract these comparisons....
several methods for building a model are available.
buena salud,
Chris Patridge
On Wed, Sep 5, 2012 at 8:01 AM, Rana, Jatinkumar Kantilal <
jatinkumar.rana@helmholtz-berlin.de> wrote:
> Dear Ifeffit community,
>
>
>
> I was wondering If I can make a qualitative comparison about the amplitude
> ratio of first two shells for various states of same sample ?
>
>
>
> For example, I have a sample which is measured at various states, say A,
> B, C, D and E during any physical or chemical process.
>
>
>
> I get systematic change in the ratio of first two peaks at each state.
> This could be interpreted either as change in disorder or as change in
> number of atoms associated with first two shells as a result of any
> physical or chemical change material has undergone.
>
>
>
> As we know that amplitude of peak decreases with increase in distance from
> central absorber.
>
>
>
> Can I compare the amplitude ratio of first two peaks for various states of
> same sample ??
>
>
>
> Many thanks in advance !!!
>
>
>
> With best regards,
>
> Jatin
>
>
>
>
>
> ------------------------------
>
> Helmholtz-Zentrum Berlin f?r Materialien und Energie GmbH
>
> Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher
> Forschungszentren e.V.
>
> Aufsichtsrat: Vorsitzender Prof. Dr. Dr. h.c. mult. Joachim Treusch, stv.
> Vorsitzende Dr. Beatrix Vierkorn-Rudolph
> Gesch?ftsf?hrung: Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas Frederking
>
> Sitz Berlin, AG Charlottenburg, 89 HRB 5583
>
> Postadresse:
> Hahn-Meitner-Platz 1
> D-14109 Berlin
>
> http://www.helmholtz-berlin.de
>
> _______________________________________________
> Ifeffit mailing list
> Ifeffit@millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
>
--
Christopher J. Patridge PhD.
Contact: (315)-529-0501
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Message: 3
Date: Wed, 5 Sep 2012 08:32:27 -0400
From: Scott Calvin
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Ratio of peak amplitudes in R-space
Message-ID: <59B5117D-3960-4548-A617-9EA4022AF78E@slc.edu>
Content-Type: text/plain; Zharset="iso-8859-1"
Hi Jatin,
It's really best to model such a system using Ifeffit or similar software. There's a lot that goes into peak height. For one thing, I'm assuming you're looking at the peak height in the magnitude of the Fourier transform. But the Fourier transform of the individual scattering paths is complex-valued, not positive-definite. Thus, two paths contributing at some value of R can sometimes result in less amplitude than either path alone. Depending on data ranges and windowing, there's likely to be some contribution from the path that you're thinking of as corresponding to the first peak at the R of the second, and vice-versa, and that contribution is not additive when viewed in the magnitude.
In addition, for the peak at higher-R there may be a significant contribution from multiple scattering.
It should also be noted that a single peak may be due to unresolved splitting. For example, a nearest-neighbor octahedron might be distorted, with different axial and radial distances. In a case like that, a change in the amount of distortion can have a dramatic effect on the height of the peak.
Having said that, you can make qualitative comparisons in a series like the one you describe. If you have a suspicion of what might be happening (change in coordination, change in disorder, change in splitting, etc.), then you can see it progress by just inspecting the graphs in the way you suggest, and could probably identify, e.g., a phase change. But for quantitative determinations, you really need to model the system.
--Scott Calvin
Sarah Lawrence College
On Sep 5, 2012, at 8:01 AM, Rana, Jatinkumar Kantilal wrote:
Dear Ifeffit community,
I was wondering If I can make a qualitative comparison about the amplitude ratio of first two shells for various states of same sample ?
For example, I have a sample which is measured at various states, say A, B, C, D and E during any physical or chemical process.
I get systematic change in the ratio of first two peaks at each state. This could be interpreted either as change in disorder or as change in number of atoms associated with first two shells as a result of any physical or chemical change material has undergone.
As we know that amplitude of peak decreases with increase in distance from central absorber.
Can I compare the amplitude ratio of first two peaks for various states of same sample ??
Many thanks in advance !!!
With best regards,
Jatin
------------------------------
Message: 4
Date: Wed, 05 Sep 2012 21:47:14 +0900
From: Zhaomo Tian
To: ifeffit@millenia.cars.aps.anl.gov
Subject: [Ifeffit] How to write feff.inp file for CO adsorbed Cu?
Message-ID: <1346849234137.75822.postech@postech.ac.kr>
Content-Type: text/plain; Zharset="us-ascii"
An HTML attachment was scrubbed...
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------------------------------
Message: 5
Date: Wed, 5 Sep 2012 09:25:53 -0400
From: Jason Gaudet
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] How to write feff.inp file for CO adsorbed Cu?
Message-ID:
Content-Type: text/plain; Zharset="iso-8859-1"
Hi Tian,
What leads you to believe you'd be able to see C or O contributions to the
EXAFS in your sample? CO probing of a catalyst during XAS measurements is
a pretty common experiment (although CO is often not a good probe molecule
for Cu...) but I'm having difficulty coming up with an example where the CO
itself was directly observed in EXAFS. Sulfur, sure, but CO? If your Cu
was monodisperse I suppose it would be less of a stretch to try, but if
you're talking about a Cu surface and expecting to separate Cu-C and Cu-Cu
contributions I'd be worried you may be far overestimating the capabilities
of your experiment.
If you have a cite that suggests this is feasible, it'd be news to me and
I'd be happy to read it.
-Jason
On Wed, Sep 5, 2012 at 8:47 AM, Zhaomo Tian wrote:
> Dear All!
>
> I am a beginner in this field and I have a difficulty in writing feff.inp
> file for my system.
>
> My system is CO gas adsorbed on metal (such as copper)surface and the
> experiment data will be taken on Cu k edge, since it is not crystalline
> structure, I may need to write my own feff.inp file instead of getting it
> from atoms.inp file. Is there anyone who knows how to create a structure
> for my system and how to calculate atomic coordinates of so many atoms?Or a
> simple structure includes only 4 atoms(2 Cu,1 C and 1 O is enough?) Then I
> am asking help for generating feff.inp file(especially all necessary atomic
> coordinates) for Cu-CO. If someone knows it, would you please give me a
> hand?
>
> Thanks a million
>
> Best Regards,
>
>
>
> *Tian Zhaomo*
>
> *M.S. candidate*
>
>
>
>
>
> *Lab. For Photosynthesis Materials and Devices*
>
> Department of Materials Science and Engineeing,POSTECH
>
> san 31, Hyoja-Dong, Nam-Gu,
> Pohang, 790-784, Republic of Korea
>
>
>
> office: +82-54-279-2827
>
> mobile: +82-10-7747-3790
>
> e-mail: zhaomo1989@postech.ac.kr
>
>
>
> _______________________________________________
> Ifeffit mailing list
> Ifeffit@millenia.cars.aps.anl.gov
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>
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