[Ifeffit] Athena: k-weight=3 in background removal problem

Kelly, Shelly D. SKelly at anl.gov
Tue Jul 8 08:52:51 CDT 2008


Hi Joseph,

I have a book chapter that explains how the different k-weighting affect
the chi(k) data produced in the background removal.  I'll send it to you
directly, so as not to fill up everyone's mail box.

Here is the reference for others that might be interested. 

Kelly, S.D., Hesterberg, D., and Ravel, B., in "Analysis of Soils and
Minerals Using X-ray Absorption Spectroscopy", (A.L. Ulery and L.R.
Drees, Eds.) p. 367. Soil Science Society of America, Madison, WI, USA,
2008.

Shelly

-----Original Message-----
From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Joseph
Washington
Sent: Tuesday, July 08, 2008 6:03 AM
To: ifeffit at millenia.cars.aps.anl.gov
Subject: Re: [Ifeffit] Athena: k-weight=3 in background removal problem

Hi Carlo,
Since much of our data is located at high k values, it would be an 
improvement to be using a high k weight in the background removal. 
Whether or not this will be a vast improvement might be questionable. My

main concern is why this occurs for all our Ge edge data  across the 
board, and if this is indicative of an underlying issue in data 
collection at the beamline or preprocessing.

Please see an attached project file containing some scans and a merge.

I appreciate the assistance,

Joseph

Carlo Segre wrote:
> 
> Hi Joseph:
> 
> On Mon, 7 Jul 2008, Joseph Washington wrote:
> 
>> Greetings all,
>> I am an APS user and a graduate of XAFS Summer School - class of 2007
:)
>>   We have been doing EXAFS analysis on Ge[2]Sb[2]Te[x] thin films. I
>> noticed that at the Ge edge in particular, the k-weight value used in
>> the background removal cannot equal 3, or else the background
function
>> no longer follows the data and oscillates wildly and/or it shoots up
at
>> the edge energy dominating the plot window. Values of 1 and 2 work
fine.
>> Even more puzzling is that this problem is inherent for the Ge edge
of
>> data taken over numerous runs, and for various samples (GST-224,
>> GST-225, 226, 227).
> 
> COuld you tell us why you would like to use a k-weight of 3 in the 
> background removal process?  I find that 1 (or 2 sometimes) is 
> sufficient to get a good result.  I just checked on a recent data set 
> and I agree that k-weight 1 nd 2 give nearly identical results but
that 
> k-weight 3 for the same parameters is slightly different.
> 
> It would help a lot if you oculd send a project file for us to look
at.
> 
> Carlo
> 

-- 
Joseph Washington
Research Assistant
Department of Physics
North Carolina State University
431 Riddick Hall
Raleigh, NC 27695-8202
email: jswashin at ncsu.edu




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