# [Ifeffit] {Spam?} {Disarmed} How to do with diffraction peak

Matthew Marcus mamarcus at lbl.gov
Tue Dec 11 11:59:56 CST 2012

```I second that motion about the usefulness of multi-element detectors.  Some people suggest that because single-element detectors
can now count as fast as multi-element detectors used to and cover solid angle more efficiently, multi-element detectors are
obsolete.  My EXAFS data reduction software includes an option called 'deglitch with reference scalers'.  An example of how this works:
Suppose you have a 7-element detector (elements 0-6) and there's a Bragg peak in elements 4 and 5.  Now form the ratio 4/(0+1+2+3+6), where
the digits refer to element numbers.  Except for the Bragg peak, this ratio should be slowly-varying and almost devoid of EXAFS information
because everything in it should be proportional to the same signal.  Now, do the deglitch thing - fit this ratio to a smooth function
(I use a cubic polynomial) in a region outside the Bragg peak and replace the ratio in the Bragg region with the fit.  Then, in that region,
replace the signal from element 4 with (fitted)*(0+1+2+3+6).  Do the same with element 5.  What you've done is to reconstruct an estimate
of what elements 4,5 should have been doing with reference to the other elements.  Yes, you've faked some information, but much less than if
you had just 'papered over' the glitch region with a cubic on the sum.  This method allows you to deal with Bragg peaks in spectral regions
where there is detail without totally obliterating the signal you're after, but it only works if you have multiple elements.

OK, rant-mode off.
mam

On 12/10/2012 11:51 PM, "Dr. Dariusz A. Zając" wrote:
> Definitely XRD peaks are not EXAFS oscillations, thus you should exclude them from data analysis. The simplest way is to use deglitching tool from Athena. More complicated one is to subtract peaks (if you know very well their shapes). If you have still access to the experiment - tray to measure sample at different angle sample surface -detector, than you can shift the position of the diffraction peaks in energy scale. After merging of few of this scans you eliminate XRD peaks.
> Have you measured with one pixel fluorescence detector? For such experiments the use of multi-element detector can be also useful...
>
> regards
> kicaj
>
> p.s. I didnt check the attached file. Next time, please, give a link to a graph, not attach the file
>
> W dniu 12-12-11 08:08, Zhaomo Tian pisze:
>> Dear all,
>>
>> I got XAFS data for Ag with CO adsorption( using Ag K edge), Ag is thin film~300nm deposited on Si/SiO2 substrate. But in the original μ(E) spectra, from 25894-26044eV, four obvious diffraction peaks appear( I attached the file), and I guess they will influence the quality of fitting. Is there anyone who knows how to deal with these diffraction peak? Will it be corrected by smoothing or changing some origin data points in the original file? I want the modification that will not destroy data analysis later.
>>
>> Thanks for your help.
>>
>> *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
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>> e-mail: zhaomo1989 at postech.ac.kr <mailto:zhaomo1989 at postech.ac.kr>
>>
>>
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