Re: [Ifeffit] Ifeffit Digest, Vol 156, Issue 4

I have an SDD and find very little strength in the escape peak or the Si Ka peak. I have seen Si from the sample. I can't speak to how well Si XAS works because my beamline doesn't go down that far. mam On 2/9/2016 10:25 AM, Pierre Lecante wrote:

Hi Pinit,

here is what you can expect from a SDD:

"At X-ray energies greater than silicon K absorption edge, which we have measured for crystalline silicon to be 1839 eV, the response function of the device shows two distinct peaks in addition to the primary one. One of them at energy /E/_/f/ = 1739 eV is due to the silicon fluorescent photons that have escaped far enough from the original site of interaction to be detected as a separate event. The other peak centered at energy /E/_/e/ = /E/_0 - /E/_/f/ , where /E/_0 is energy of the incident photon, is called an escape peak."

So, indeed this shouldn't be a concern if you had a perfect rejection of harmonics on your beamline; if not, inelastic scattering of harmonic by the sample, even rejected by energy analysis, should likely induce internal fluorescence and escape peaks not observed in TM. Just an hypothesis, but easy to check: presence or not of harmonic in your scattering.

Pierre

Le 02/02/2016 23:41, ifeffit-request@millenia.cars.aps.anl.gov a écrit :

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Today's Topics:

1. Re: Could you please give me some information? (Bruce Ravel) 2. Re: Athena with IOS "El Capitan" (Manuel Cossio Kohler) 3. Re: Athena with IOS "El Capitan" (Bruce Ravel) 4. Re: Athena with IOS "El Capitan" (Manuel Cossio Kohler)

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Message: 1 Date: Tue, 2 Feb 2016 15:30:45 -0500 From: Bruce Ravel To: pinit Cc: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Could you please give me some information? Message-ID:<56B111F5.7050108@bnl.gov> Content-Type: text/plain; charset=windows-1252; format=flowed

On 02/01/2016 11:58 PM, pinit wrote:

...

Dear Bruce,

I am Pinit from SLRI, Thailand. I have some questions concerning the Si-drift detector.

Could you give me some suggestions if Si-detector can detect the corrected Si K-edge or not? This is because I have seen a significant EXAFS signal (higher in amplitude in FT) measured by Si-drift detector differs from Lytle detector or ionization chambers (TM mode). Hi Pinit,

Nice to hear from you. I am CCing my answer to the Ifeffit Mailing List. Someone else may have more insight into your question than I do. You should CC the list in your response.

I'd probably need to know more about the sample and the nature of the measurement you made to understand why you are seeing a different signal with the Si drift detector.

Normally one would expect that he EXAFS would be /attenuated/ either due to self-absorption or due to the energy dependence of the I0 detector. That you are seeing a larger EXAFS signal with the Si-drift seems surprising.

One thing that occurs to me is that the Compton and elastic peaks probably overlap the Si K alpha ROI quite a bit, even extending into the EXAFS region. I would have thought that, too, would serve to attenuate the EXAFS (but maybe I am thinking about that wrongly).

Perhaps it would help to show us some of the data...?

B

-- Groupe MC2 CEMES-CNRS, 29 rue Jeanne Marvig, 31055 Toulouse Cedex 4, France Tel: +33 (0)5 62 25 78 51, Fax: +33 (0)5 62 25 79 99 Email:lecante@cemes.fr

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