[Ifeffit] Self absorption Correction

Jens Kruse jens.kruse at uni-rostock.de
Tue Feb 3 01:51:22 CST 2009


Hi,
Thanks Richard and Carlos for the the links.
But is the "Fluo"-Algorithm for self absorption correction also valid if 
I have the concentrated sample (standard) applied as a fine powder to a 
carbon tape or is it only valid for much much thicker samples?

thanks,
Jens
> ------------------------------
>
> Message: 4
> Date: Mon, 2 Feb 2009 09:51:10 -0500
> From: Richard Mayes <rtmayes at gmail.com>
> Subject: Re: [Ifeffit] Self absorption Correction
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Message-ID:
> 	<5a2a54820902020651nfaf1af7q4ec435fc207fc38a at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Jens,
>
> Since no one has answered yet, I'll chime in.  First let me direct you to a
> discussion of self-absorption and other sample-related distortions:
> http://www.xafs.org/Experiment/OverAbsorption  (this is a link from the
> tutorials page of www.xafs.org).
>
> As for your questions:
>
> I think that you should use the non-normalized XANES data to perform the SA
> correction.
>
> for the angle-in and angle-out meanings, see Grant Bunker's paper on
> self-absorption here:
> http://gbxafs.iit.edu/training/Self_Absorption_effects.pdf
>
> Now, how do you determine if you have self-absorption effects?  I have to
> defer here to those with more experience.  What you suggest sounds
> appropriate, but I'm not sure how you could determine this without studying
> multiple concentrations of your absorber and watch the signals, i.e. does a
> 10% increase in absorber concentration translate to a 10% increase in
> fluorescence yield (similar to what Matthew Marcus and Alain Manceau
> describe in their paper, from the over-absorption link above).
>
> HTH,
> -Rich
>
> On Fri, Jan 30, 2009 at 11:49 AM, Jens Kruse <jens.kruse at uni-rostock.de>wrote:
>
>   
>> Hi there,
>>
>> I have measured a pure reference compound with high absorber
>> concentration in fluorescence mode (P K-edge XANES).  I tried to use the
>> Self absorption correction  included in Athena but I don't really
>> understand the results.
>> Fist: Do I have to use the edge step normalized spectrum or the spectrum
>> without normalization ? I tried both and the results  of course a quite
>> different. I would rather use the not normalized spectrum.
>> Second: the value "Angel in"  is this the angle between the incident
>> beam and the sample surface" and "Angle out"  the angle between the
>> sample surface and the detector position?
>> Third: More general- How can I identify a spectrum suffering self
>> absorption? Just comparing the relative peak intensities of total
>> electron yield signal with the fluorescence yield signal ?
>>
>> thanks a lot for your comments,
>> cheers,
>>  Jens
>>
>> --
>> Jens Kruse
>> Institute for Land Use
>> Faculty for Agricultural and Environmental Sciences
>> Rostock University
>> Justus-von-Liebig-Weg 6
>> 18059 Rostock GERMANY
>> Phone: +49(0)381-498 3190
>>
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>
>>     
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> ------------------------------
>
> Message: 5
> Date: Mon, 02 Feb 2009 16:59:19 +0100
> From: Carlos Prieto <cprieto at icmm.csic.es>
> Subject: Re: [Ifeffit] Self absorption Correction
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Message-ID: <20090202155915.DFCAE9AD3E at estafeta.csic.es>
> Content-Type: text/plain; charset="iso-8859-1"; format=flowed
>
> Jens,
>
> Let me give you an old reference (but still 
> usefull) for the self absorption treatment:
>
> R. Casta?er and C. Prieto, "Fluorescence 
> detection of EXAFS in thin film samples", J. de 
> Phys. III (France), 7, 337-349 (1997).
>
> Best regards
>
> Carlos Prieto
>
> At 15:51 02/02/2009, you wrote:
>   
>> Jens,
>>
>> Since no one has answered yet, I'll chime 
>> in.  First let me direct you to a discussion of 
>> self-absorption and other sample-related 
>> distortions: 
>> <http://www.xafs.org/Experiment/OverAbsorption>http://www.xafs.org/Experiment/OverAbsorption 
>> (this is a link from the tutorials page of <http://www.xafs.org>www.xafs.org).
>>
>> As for your questions:
>>
>> I think that you should use the non-normalized 
>> XANES data to perform the SA correction.
>>
>> for the angle-in and angle-out meanings, see 
>> Grant Bunker's paper on self-absorption 
>> here: 
>> <http://gbxafs.iit.edu/training/Self_Absorption_effects.pdf>http://gbxafs.iit.edu/training/Self_Absorption_effects.pdf
>>
>> Now, how do you determine if you have 
>> self-absorption effects?  I have to defer here 
>> to those with more experience.  What you suggest 
>> sounds appropriate, but I'm not sure how you 
>> could determine this without studying multiple 
>> concentrations of your absorber and watch the 
>> signals, i.e. does a 10% increase in absorber 
>> concentration translate to a 10% increase in 
>> fluorescence yield (similar to what Matthew 
>> Marcus and Alain Manceau describe in their 
>> paper, from the over-absorption link above).
>>
>> HTH,
>> -Rich
>>
>> On Fri, Jan 30, 2009 at 11:49 AM, Jens Kruse 
>> <<mailto:jens.kruse at uni-rostock.de>jens.kruse at uni-rostock.de> wrote:
>> Hi there,
>>
>> I have measured a pure reference compound with high absorber
>> concentration in fluorescence mode (P K-edge XANES).  I tried to use the
>> Self absorption correction  included in Athena but I don't really
>> understand the results.
>> Fist: Do I have to use the edge step normalized spectrum or the spectrum
>> without normalization ? I tried both and the results  of course a quite
>> different. I would rather use the not normalized spectrum.
>> Second: the value "Angel in"  is this the angle between the incident
>> beam and the sample surface" and "Angle out"  the angle between the
>> sample surface and the detector position?
>> Third: More general- How can I identify a spectrum suffering self
>> absorption? Just comparing the relative peak intensities of total
>> electron yield signal with the fluorescence yield signal ?
>>
>> thanks a lot for your comments,
>> cheers,
>>  Jens
>>
>> --
>> Jens Kruse
>> Institute for Land Use
>> Faculty for Agricultural and Environmental Sciences
>> Rostock University
>> Justus-von-Liebig-Weg 6
>> 18059 Rostock GERMANY
>> Phone: +49(0)381-498 3190
>>
>> _______________________________________________
>> Ifeffit mailing list
>> <mailto:Ifeffit at millenia.cars.aps.anl.gov>Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>
>>
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>     
>
>
> ================================
> Carlos Prieto
> Instituto de Ciencia de Materiales de Madrid CSIC
> Cantoblanco, 28049 - MADRID (Spain)
> Tel.: 91 3349017
> e-mail: cprieto at icmm.csic.es
> ================================= 
>
>
>
>
> ------------------------------
>
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
>
> End of Ifeffit Digest, Vol 72, Issue 2
> **************************************
>
>   

-- 
Jens Kruse
Institute for Land Use
Faculty for Agricultural and Environmental Sciences
Rostock University
Justus-von-Liebig-Weg 6
18059 Rostock GERMANY
Phone: +49(0)381-498 3190 




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