June 2008


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Ellery Frahm <[log in to unmask]>
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JEOL-Focused Probe Users List <[log in to unmask]>
Thu, 12 Jun 2008 10:00:09 -0500
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Electron Microprobe Lab, University of Minnesota

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Hi Ron,

Thanks for your comments.

> I have had specimens that look OK and don't appear to charge but  
> gave low results.
> When I used my EDS/EDX detector and checked where the backgound x- 
> rays were going to zero counts at the high energy end (the Duane- 
> Hunt limit), I found that I had about 2kV of charge build up that  
> was decelerating the beam. The standards did not have this charging  
> problem. So I was effectively measuring standards at one voltage and  
> doing analysis at another. On my machine it's easy to do a  
> qualitative ED analysis while the probe is doing a WDS analysis.  
> Coating grounds the surface of the specimen but does not always  
> remove sub-surface charge build up.

Checking the DH limit is an excellent idea -- we'll have to check that  

> This has also caused me trouble before. My old 8800 JEOL (15 years)  
> uses Henke (1966) MACs for longer wavelenghts ( > 1.2nm) and  
> Heinrich (1966) MACs for shorter wavelenght x-rays. My newer 8200  
> EPMA (4 years) claims to use Henke (1966, 1982) for the longer  
> wavelenghts and the same Heinrich (1966) MACs for shorter wavelenght  
> x-rays. When I looked up the actual value in my new probe for O Ka  
> in Si I was given 8790.0, the same value John gave before as Bastin   
> 1992. I don't know the age of your probe, or what MACs it uses, but  
> changing MACs has affected my results (different sample) by about  
> the same amount you are talking about. You may be able to edit you  
> MAC table and recalculate to see if it makes a difference for you.

We have an 8900, but we also have the latest software updates, so I  
don't know if it still uses the original 8800 files or the newest 8200  
files.  I'm not sure if this could explain our low totals even when  
we're not measuring oxygen, but that's a very good question!  (Hint,  
hint: any JEOL folks want to chime in either on- or off-list?)