Low Totals Across Metals Boundary

[jeb]

Hi All,
  So I have a problem I've been trying to figure out for a while now.  I have an annealed block of metals that I'm measuring traverses across the various systems on, the sample has blocks of Cr, Ni, Cu, Al, Fe, Co, and Ni (O was also analyzed for).  After having lots of magnetization issues, I finally had to give up on WDX and collected the data on the sample with EDX (the beam was being deflected too much). 

This worked out fine for every system except Ni-Cr.  I get ~100% totals for most of the traverse, except for the ~20 points near the boundary (1 micron spacing, so they are all within 10-20 microns of the boundary) where the totals drop to 92%.  There is some topography, but not 20 microns across worth and even when I just do a point manually making sure it's in focus first, I still get the low totals.  I see the same ~10% drop in both EDX and WDX (although all the totals are low with WDX) data.  If anything I had expected to see high totals near the boundary with these two metals.  Any ideas on what could be going on here?  I've tried about 5 traverses now and see the same thing every time.

[jeb]

Here's a graph if it helps to understand what I'm talking about:

[Probeman]

This worked out fine for every system except Ni-Cr.  I get ~100% totals for most of the traverse, except for the ~20 points near the boundary (1 micron spacing, so they are all within 10-20 microns of the boundary) where the totals drop to 92%.  There is some topography, but not 20 microns across worth and even when I just do a point manually making sure it's in focus first, I still get the low totals.  I see the same ~10% drop in both EDX and WDX (although all the totals are low with WDX) data.  If anything I had expected to see high totals near the boundary with these two metals.  Any ideas on what could be going on here?  I've tried about 5 traverses now and see the same thing every time.

Julie, Can you also post an EDS spectra from just outside each of the low totals and one from inside the low total?  I think we looked at oxygen and nitrogen contamination as an explanation?

I think we also looked at "anti" secondary fluorescence effects (due to a self fluorescing matrix adjacent to a material that does not contain the fluoresced element(s))?  And I think you found that these SF effects were minimal at most?
john