[Wien] Difference among XAS, ELNES and EELS

[Ashley Harvey]

Dear BoKang,

Here is my slight & probably incomplete answer (I am not sure how  
much you already know):

XAS and EELS give very similar experimental spectra, and are based on  
similar physical processes, but not exactly the same.
In XAS, a photon is absorbed by the sample and, in transmission  
experiments, the resulting attenuation of the beam is measured while  
the photon energy is scanned (~ 0.2 - 40 keV depending on the  
beamline).  In EELS in a TEM, the electron beam is held at one energy  
(e.g. ~ 300 kV) and as electrons pass through the sample, energy is  
lost.    That energy loss is measured in Electron Energy Loss  
Spectroscopy (detection of ~ 0 - 2000 eV).
ELNES is a sub-set of EELS - the Energy Loss Near-Edge Structure,  
typically the part of the EEL spectrum < 50 eV beyond the edge  
onset.  The setup of the TEM can affect the EELS results, which is  
why there are adjustable parameters in the w2web TELNES window.
My impression is that in XAS the allowed electronic transitions are  
more strictly governed by the dipole selection rules, whereas in  
EELS, the rules can be bent a bit more depending on the experiment.   
However, I have not found a lot in literature that contrasts these  
two techniques - a lot of people just acknowledge that they are  
"basically the same."
In the end, I guess your question relates to simulating XAS or EELS  
with Wien2k.  I am not sure how the results differ between the two  
tasks, myself, but would be interested in the answer.

Hope this helps a little,
Ashley


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On Dec 4, 2007, at 2:05 PM, 波 康 wrote:

> Dear wien users,
>
>         Using WIEN2k code, we can calculate XAS and ELNES. I am  
> very confused, what's the differences among XAS, ELNES and EELS.  
> Could anyone tell me?
>
>        Any reply will be appreciated!
>
>                                                BoKang
>
>
>
> 进入雅虎游戏嘉年华，赢取液晶显示器！
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