[Ifeffit] EXAFS signal from dopant atoms
brighton30 at 126.com
Thu Sep 17 11:21:44 CDT 2015
If it is possible to measure the EXAFS of B and/or C edges, you can also do a multiedge refinement like this paper.
发件人：Carlo Segre <segre at iit.edu>
主题：Re: [Ifeffit] EXAFS signal from dopant atoms
收件人："XAFS Analysis using Ifeffit"<ifeffit at millenia.cars.aps.anl.gov>
This only partly depends on the actual concentration of your dopant atom.
Just becuaseit is a low concentration does not mean the signal is
necessarily in the noise. If you set up your experiment correctly and
collect sufficient data you can get quite a good signal from even a low
What you will see in the EXAFS, if the structure is well-ordered, is the
fact that the C atom is surrounded by a bunch of A atoms at whatever
distance will be typical for a dopant atom of this kind. You will also
see further "shells" which will likely be mostly B atoms.
As you increase the concentration of C atoms, you might not see too much
difference in the near neighbor A atom environment but you will be seeing
a second shell with more and more C atoms replacing the B atoms.
There are many more nuances to this but it is not a great idea to put a
lot of presumptions into your structural model since you might bias the
results of the analysis.
On Thu, 17 Sep 2015, Eugenio Paris wrote:
> Dear all,
> I have a very general question about EXAFS analysis.
> Let's take as example a binary system AB in which i am substituting the
> atom B with another atom C so that we have AB(1-x)C(x). Let us imagine that
> we know the structure of binaries AB and AC with Rab and Rac atomic
> distances and we know that in AB(1-x)C(x) the substitutional site will be
> 100% the B-site.
> If I measure the EXAFS spectrum of atom C as a function of "x" what can I
> expect for the EXAFS oscillations? My idea is that when "x" is very small
> the EXAFS will be highly noisy and damped, while as "x" increases the
> oscillations will become more evident above the noise level.
> How to model this situation to get information on C-A bond? In Athena I can
> start with the .cif file of AC structure with full occupancy and obtain the
> distance and the DWF for the A-C bond but.. how to treat the
> signal-to-noise ratio? I mean, as "x" decreases I think there must be a
> leaking out of the EXAFS signal, should this effect be introduced in S0^2?
> Or can it affect the effective number of neighbors?
> Hope I explained myself,
> thank you!
> Eugenio Paris
> PhD student, University of Rome (Italy)
Carlo U. Segre -- Duchossois Leadership Professor of Physics
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498 Fax: 312.567.3494
segre at iit.edu http://phys.iit.edu/~segre segre at debian.org
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