[Ifeffit] Ratio of peak amplitudes in R-space

Rana, Jatinkumar Kantilal jatinkumar.rana at helmholtz-berlin.de
Wed Sep 5 10:07:08 CDT 2012


Dear Christopher, Dear Scott,

Thank you so much for your valuable feedback.

I will now attempt to quantify the observed change in amplitude ratios by fitting data with theoretical standards.

With best regards,
Jatin




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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"
        <jatinkumar.rana at helmholtz-berlin.de>
To: "ifeffit at millenia.cars.aps.anl.gov"
        <ifeffit at millenia.cars.aps.anl.gov>
Subject: [Ifeffit] Ratio of peak amplitudes in R-space
Message-ID: <F11168F9CA572049ADA84F3072DE5DB135C7180D at didag2>
Content-Type: text/plain; charset="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 <patridge at buffalo.edu>
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] Ratio of peak amplitudes in R-space
Message-ID:
        <CAFAy88Eqj_RJLkEYNbDhn-yQc55uALhxfypE396oeRm3f7kb5w at mail.gmail.com>
Content-Type: text/plain; charset="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 at 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 at 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 <scalvin at sarahlawrence.edu>
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] Ratio of peak amplitudes in R-space
Message-ID: <59B5117D-3960-4548-A617-9EA4022AF78E at slc.edu>
Content-Type: text/plain; charset="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 <zhaomo1989 at postech.ac.kr>
To: ifeffit at millenia.cars.aps.anl.gov
Subject: [Ifeffit] How to write feff.inp file for CO adsorbed Cu?
Message-ID: <1346849234137.75822.postech at postech.ac.kr>
Content-Type: text/plain; charset="us-ascii"

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Message: 5
Date: Wed, 5 Sep 2012 09:25:53 -0400
From: Jason Gaudet <jason.r.gaudet at gmail.com>
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] How to write feff.inp file for CO adsorbed Cu?
Message-ID:
        <CANMcWtMPmowcQBAVU09+Pce3oBLM0nd23xy4krnZowad=0m0DQ at mail.gmail.com>
Content-Type: text/plain; charset="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 <zhaomo1989 at postech.ac.kr>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 at postech.ac.kr
>
>
>
> _______________________________________________
> Ifeffit mailing list
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________________________________

Helmholtz-Zentrum Berlin für 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
Geschäftsführung: 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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