[Ifeffit] Ifeffit Digest, Vol 108, Issue 17

陈娟 cj071 at 163.com
Wed Feb 15 00:52:50 CST 2012


Dear Bruce

Thanks a lot for your suggestion. Yes, I did according your suggestion. I did the self-absorption correction and got the perfect spectrum as shown below.

 

However, for the pure standards without dilution by BN, How to do the self-absorption correction? For example, I try one, but cannot get the credible spectra. ForDibenzyl Disulfide, the formula should be (C14H14S2)0.5435(BN)0, no dilution. I put (C14H14S2)0.5435(BN)0 in, but the spectrum I got is




 

So can you tell me how to do the pure standards self-absorption correction using Athena?


Much appreciated.

Warm regards

Juan Chen





At 2012-02-15 02:00:01,ifeffit-request at millenia.cars.aps.anl.gov wrote:
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>Today's Topics:
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>   1. Re: fitting sulphur using standards by Athena (Bruce Ravel)
>   2. Re: fitting sulphur using standards by Athena (Matthew Marcus)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Tue, 14 Feb 2012 09:07:45 -0500
>From: Bruce Ravel <bravel at bnl.gov>
>To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
>Subject: Re: [Ifeffit] fitting sulphur using standards by Athena
>Message-ID: <201202140907.45529.bravel at bnl.gov>
>Content-Type: Text/Plain;  charset="utf-8"
>
>On Tuesday, February 14, 2012 07:55:54 am ?? wrote:
>> As I known, the spectra for standard diluted with BN and non-diluted are
>> different. The peak of the non-diluted is low due to self-absorption, as
>> shown in the figure below. S1 is non-diluted and s1_10 is diluted sulphur
>> to about 3%. For dilution, the position of the peak is also changed.
>> Therefore the non-diluted s1 spectra isnot the real spectra of
>> dibenzothiophene. The question is what percentage should I dilute the
>> standard to get the credible spectra for the standards?and how to explain
>> the peak position change? 
>
>Although this sort of thing can be approximated from tables of
>absorption coefficients, the advice I usually give to my users is to
>prepare a series of samples of diminishing concetrations and measure
>then.
>
>Having a good intuition for sample preparation and the effects of poor
>sample preparation is always important and even more so for low energy
>edges.  The best way to develop that intuition is by doing the
>experiment yourself.
>
>> Can I use Athena to counteract the self-absorption and get the
>> credible spectra for sdandards?
>
>Yes it can -- in principle.  Doing a good job of self absorption
>correction requires a lot of knowledge about your sample and its
>matrix -- often more than one has.
>
>The use of the self absorption tool is explained in the Athena
>document.  I have also written a lecture on this topic.  Go to 
>
>  https://github.com/bruceravel/XAS-Education/downloads
>
>and download the "selfabs.pdf" file.
>
>B
>
>
>-- 
>
> Bruce Ravel  ------------------------------------ bravel at bnl.gov
>
> National Institute of Standards and Technology
> Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
> Building 535A
> Upton NY, 11973
>
> My homepage:    http://xafs.org/BruceRavel
> EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter
>
>
>
>------------------------------
>
>Message: 2
>Date: Tue, 14 Feb 2012 07:33:38 -0800
>From: "Matthew Marcus" <mamarcus at lbl.gov>
>To: "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
>Subject: Re: [Ifeffit] fitting sulphur using standards by Athena
>Message-ID: <03B21711433A40B4AA45C3DE3410452A at als.lbl.gov>
>Content-Type: text/plain; format=flowed; charset="utf-8";
>	reply-type=original
>
>To reiterate a point which is often not understood - dilution won't fix overabsorption if the particles of the concentrated material 
>which are mixed in with the diluent are too big.  For concentrated S compounds, "too big" is in the low microns.
>When I run a S standard, I do it in total electron yield to avoid this problem.  When I fit a S spectrum, I use a crude 
>oveabsorption model with a single parameter which is treated as an unknown fitting parameter, with the assumption
>that the reference spectra were collected in a way which avoids overabsorption.
>    mam
>----- Original Message ----- 
>From: "Bruce Ravel" <bravel at bnl.gov>
>To: "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
>Sent: Tuesday, February 14, 2012 6:07 AM
>Subject: Re: [Ifeffit] fitting sulphur using standards by Athena
>
>
>> On Tuesday, February 14, 2012 07:55:54 am ?? wrote:
>>> As I known, the spectra for standard diluted with BN and non-diluted are
>>> different. The peak of the non-diluted is low due to self-absorption, as
>>> shown in the figure below. S1 is non-diluted and s1_10 is diluted sulphur
>>> to about 3%. For dilution, the position of the peak is also changed.
>>> Therefore the non-diluted s1 spectra isnot the real spectra of
>>> dibenzothiophene. The question is what percentage should I dilute the
>>> standard to get the credible spectra for the standards?and how to explain
>>> the peak position change?
>>
>> Although this sort of thing can be approximated from tables of
>> absorption coefficients, the advice I usually give to my users is to
>> prepare a series of samples of diminishing concetrations and measure
>> then.
>>
>> Having a good intuition for sample preparation and the effects of poor
>> sample preparation is always important and even more so for low energy
>> edges.  The best way to develop that intuition is by doing the
>> experiment yourself.
>>
>>> Can I use Athena to counteract the self-absorption and get the
>>> credible spectra for sdandards?
>>
>> Yes it can -- in principle.  Doing a good job of self absorption
>> correction requires a lot of knowledge about your sample and its
>> matrix -- often more than one has.
>>
>> The use of the self absorption tool is explained in the Athena
>> document.  I have also written a lecture on this topic.  Go to
>>
>>  https://github.com/bruceravel/XAS-Education/downloads
>>
>> and download the "selfabs.pdf" file.
>>
>> B
>>
>>
>> -- 
>>
>> Bruce Ravel  ------------------------------------ bravel at bnl.gov
>>
>> National Institute of Standards and Technology
>> Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
>> Building 535A
>> Upton NY, 11973
>>
>> My homepage:    http://xafs.org/BruceRavel
>> EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter
>>
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>> 
>
>
>
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>End of Ifeffit Digest, Vol 108, Issue 17
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