[Ifeffit] [HOWTO] converting experimental mu(E) in cm^-1

mauro at rulp.org mauro at rulp.org
Thu May 13 01:53:21 CDT 2004


Hi Matt,

On Wed, May 12, 2004 at 01:41:49PM -0500, Matt Newville wrote:
>  
> But to do the self-absorption corrections on a well-characterized
> sample, you can use tabulated cross-sections (using barns/atoms is
> HIGHLY recommended over cm^2/gr or cm^-1 unless you have a pure
> compound: densities do not add!), and scale the XAFS wiggles to the
> edge jump of the absorbing atom.  That assumes that the tabulated
> value for mu are correct except that they ignore the XAFS.

Ok, this is what I normally do "by hand". The first part of my question - if
this is right - has been widely answered by you and Tsu-Chien. The second
part concerned if someone has already written a routine that can match the
tabulated cross-sections and the XAFS one automatically and then write out a
file containing the scaled XAFS.

> 
> I'm not sure I understand 'standing-wave-assisted EXAFS'.  I'd
> interpret this to mean the measurements are done near the critical
> angle to control the penetration depth. Is that right?  If so, and
> if you're asking for advice on self-absorption corrections, you'd
> need to give more details layer thickness, and measurement geometry.

Yes, you are right. For standing-wave-assisted EXAFS I mean fluorescence
measurements done at gracing-incidence. In multilayers a standing wave field
occurs for reflection at the first Bragg reflection order, so a defined
shift of the standing wave field position leads to different weights of
absorption.

The experimental setup is phi+theta=90deg with a Ge detector (13 elements),
incidence angle (theta) in the range 0.400-0.700deg. Samples are 10-periods
multilayers with the following structure:

SiO_2(15A)/[Si(42A)/Mo(28A)]_10/Si_substrate

I would like to simulate (and then correct) the selfabsorption in these
samples but applying the standard formula doesn't work. In my opinion, I
think that this is due to the fact that the field intensity in the sample is
not exponentially decaying but oscillating+exponentially-decaying (because
it is a standing wave field).

Thanks,
Mauro

--
  Mauro Rovezzi <mauro at rulp.org> - Physics student
  University of Rome "Tor Vergata", ESRF Beamline BM8 - GILDA 


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