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Electron Microprobe Lab, University of Minnesota

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     One "simple" way for a user to get low totals on EMP is to have  
the sample out of focus during the analysis.  We find some students  
focusing with BSE or in transmitted light instead of reflected light,  
or simply failing to check focus.  With the SX-100 we use an autofocus  
system but some students turn off that option.  Once the low total is  
obtained, one should immediately check in reflected light to see if  
the sample is still in focus after the analysis before moving the  
     Another problem is that students (and sometimes their advisors)  
handle the sample, imparting oils to the carbon coat and causing  
charging that is difficult to see if the sample doesn't fluoresce (or  
we find that the user pays no attention to the flickering or moving  
luminescence!).  One can find salt crystals in swirls in some cases.   
The only check for that is to repolish, reclean (a step that lots of  
folks forget), recoat, and then immediately reanalyze.  I find that  
many students or faculty pick up their coated samples with thumb and  
forefinger pinching the flat glass slide rather than squeezing in from  
the sides.