Re: [Ifeffit] Ifeffit Digest, Vol 88, Issue 4

Dear Dominik, Thank you so very much for your detailed explanation about the effects of particle size on XAFS spectra. Warm wishes, Rana On 07.06.2010 19:00, ifeffit-request@millenia.cars.aps.anl.gov wrote:

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Today's Topics:

1. particle size effects on XAFS spectra (Jatinkumar Rana) 2. Re: particle size effects on XAFS spectra (Dominik Samuelis)

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Message: 1 Date: Mon, 07 Jun 2010 14:49:33 +0200 From: Jatinkumar Rana To: Ifeffit users Subject: [Ifeffit] particle size effects on XAFS spectra Message-ID:<4C0CEADD.8040600@helmholtz-berlin.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Dear Users,

I am working with the EXAFS technique for the characterization of my powder sample. I must admit that i am very much new to the technique and its analysis. I have read many tutorials on preparing sample for XAFS measurement (both transmission and fluoroscence). However, i am dealing with the powder having particle size much more smaller than one absorption length.

I would like to know will it create any destructive effect on my XAFS spectra ??

Many thanks in advance...

Warm wishes, Rana

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Message: 2 Date: Mon, 07 Jun 2010 15:21:14 +0200 From: Dominik Samuelis To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] particle size effects on XAFS spectra Message-ID:<4C0CF24A.10407@fkf.mpg.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Dear Rana,

yes, it will have effects on your XAFS spectra, but not really destructive. EXAFS only really vanishes if you have isolated atoms. As long as your particles still have several hundred atoms with some coordination shell-like ordering, EXAFS oscillations will show up.

However, the amplitude of the XAFS signals will be smaller than in bulk material, due to the lower average coordination number of the central atoms. If you e.g. have 5 nm particles (some 2000 atoms), already almost half of the atoms (~800) is sitting on the particle surface and therefore has a reduced coordination number.

There's a wealth of information in literature where people actually use this effect for determining the particle size from XAFS.

Another thing to keep in mind is that often it's not really clear how the surfaces of a particle looks like chemically - there might be adsorbates, or even passivation layers. If you're e.g. doing EXAFS on untreated 5nm Si particles, you can't really expect to see anything close to bulk Si, because the top layer might be SiO2

Best regards, Dominik

On 07.06.2010 14:49, Jatinkumar Rana wrote:

...

Dear Users,

I am working with the EXAFS technique for the characterization of my powder sample. I must admit that i am very much new to the technique and its analysis. I have read many tutorials on preparing sample for XAFS measurement (both transmission and fluoroscence). However, i am dealing with the powder having particle size much more smaller than one absorption length.

I would like to know will it create any destructive effect on my XAFS spectra ??

Many thanks in advance...

Warm wishes, Rana _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit