[Ifeffit] distinguishing between actual shells and artifacts

[Voegelin Andreas]

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 

-----------------------------------------------
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
> 
> 
>