[Ifeffit] distinguishing between actual shells and artifacts

Voegelin Andreas andreas.voegelin at env.ethz.ch
Wed Jan 14 09:56:40 CST 2009

Hi Hashem

You can copy-paste the respective EXAFS data in Athena and compare the backtransforms over the first shell, the first+second shell, the second shell.

By comparison of the backtransforms with each other and with the measured EXAFS, you can see where the second-shell contribution has its origin in k-space (note that the backtransform is not corrected for the window function).

For instance, if the second-shell signal adds to the spectrum in the low-k range (where noise should not be a problem), it is likely real and might result, e.g., from multiple scattering among first-shell O atoms. If the second-shell signal in the backtransform mainly contributes in the high-k range (where noise or glitches may be a problem), you may be able to see whether it falls together with obvious artefacts (such as glitches), or whether the backtransform matches spectral features that you consider to be real.


Andreas Voegelin, PhD
Soil Chemistry Group
Inst. of Biogeochemistry and Pollutant Dynamics
Dept. of Environmental Sciences
ETH Zurich
Universitätstrasse 16, CHN F24
CH-8092 Zürich, Switzerland
Phone: +41 44 633 61 47
Fax: +41 44 633 11 18
E-Mail: voegelin at env.ethz.ch
www: http://www.ibp.ethz.ch/people/andreavo


> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov 
> [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf 
> Of mstiet2 at lsu.edu
> Sent: Mittwoch, 14. Januar 2009 14:12
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: [Ifeffit] distinguishing between actual shells and artifacts
> Dear all,
> I am currently fitting first and second shells with Zn-O and 
> Zn-Zn paths,respectively. I get second shell features that 
> could be fit quite well, but I am not certain if they are 
> actually second shell features or possibly artifacts. For 
> some samples I get second shell features that I know should 
> not be present. What criteria would you use to distinguish 
> between artifacts and actual shells?
> Your assistance is appreciated.
> Hashem Stietiya
> Louisiana State University

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