[Ifeffit] Questions about Athena and XANES

[Jeff Terry]

Hi Jenny,

I just wanted to add a bit to Matt's answer on TEY vs FY and suggest a  
couple of reference for you.

There are three contributions to the TEY: photoelectrons, Auger  
Electrons, and secondary electrons. The secondary electrons will  
typically determine the maximum depth that you can observe in a TEY  
measurement. There is a good description of this in Jo Stohr's book,  
NEXAFS Spectroscopy which can be seen at google books.
http://tiny.cc/44VGq

There is also a quick synopsis of the book at: http://www-ssrl.slac.stanford.edu/stohr/nexafs.htm
At this site, there is a photoelectron spectrum showing the relative  
intensity of Auger and Photopeaks. The secondaries are roughly a  
factor of 100 more intense than the other contributions.

It is possible to measure both TEY and Auger electron yield (AEY) and  
you will see that the AEY is more surface sensitive that TEY.  
Measuring AEY requires an analyzer capable of discriminating the  
electron energy. AEY is typically performed at lower photon energies  
as there are not too many electron energy analyzers at hard x-ray  
facilities.

It is actually pretty difficult to try to calculate the maximum  
analysis depth for TEY because of the three different contributions.  
Here is an attempt to understand the probe depth of TEY but neglects  
secondary electrons: http://www.icdd.com/resources/axa/vol44/v44_058.pdf

For the K-edges in the hard x-ray regime, with TEY it would not be  
unrealistic to expect probe depths on the order of 1000 angstroms (100  
nm).

Jeff

On Feb 20, 2008, at 6:33 PM, Jenny Cai wrote:

> Hi all,
>
> Could someone please answer my questions? I would really appreciate  
> your help.
>
> 1. For linear combination fitting, there are three indicators for  
> the goodness of fitting: R-factor, chi-square and reduced chi- 
> square. Could anyone tell me how they work?
>
> 2. Since TEY is sensitive for the surface and FY for the bulk (and  
> surface?), species detected by TEY should be also detected by FY,  
> right?
>
> 3. How to calculate the maximum analysis depths for TEY and FY?
>
> Thank you in advance.
>
>
> Jenny Cai
>
>
>
>
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