Nasty Boundary Fluorescence Analytical Situations

[Anette von der Handt]

As always, the Edinburgh SIMS lab webpage on epoxies is useful here. They don't have absolute Cl concentrations but they identify the epoxy resins with elevated Cl contents.

https://www.ed.ac.uk/geosciences/about/facilities/all/ionprobe/instrument-capabilities-and-sample-requirements/specimen-requirements/epoxy-resins/results/compositions

It is not trivial in some cases. I definitely ran into this problem when doing analyses of apatite grain mounts where the apatites would get more Cl-rich towards the rims, although that was probably more a problem of mixed analyses than secondary fluorescence.

[Probeman]

Interesting.

Any ideas on how we could measure some epoxy Cl concentrations?

[Probeman]

The Athens 2022 EPMA just concluded and there were questions about how to correct data for modeled secondary fluorescence effects.

This post here provides one example:

https://probesoftware.com/smf/index.php?topic=58.msg5603#msg5603

It should be noted however, that ideally one should perform a matrix correction after the concentrations have been modified after this subtraction as the "apparent" concentration of the fluoresced element is of course not actually present in the matrix. However, so long as the subtracted concentration is a fraction of a percent the effect should be minimal, particularly on the measured element itself.

In fact the CalcZAF software actually includes this matrix iteration in the secondary fluorescence correction based on defined distances from the boundary. See here for details:

https://probesoftware.com/smf/index.php?topic=58.msg223#msg223

Unfortunately this SF subtraction/iteration GUI not yet implemented in the Probe for EPMA software, though soon perhaps.

But it should also be pointed out that the modeled secondary fluorescence concentrations from Fanal or Penepma are only accurate for EDS detectors (without any Bragg defocusing) and WDS detectors in the two directions parallel to the spectrometer orientation. This is described by Ben Buse in the paper linked to this post here:

https://probesoftware.com/smf/index.php?topic=1447.msg10718#msg10718

To avoid this WDS defocusing effect on the secondary fluorescence from a boundary, one should orient the sample so the boundary is parallel to the spectrometer orientation, hence one of the reasons we are trying to document this spectrometer orientation in JEOL and Cameca microprobes.

[Probeman]

Llovet et al. (2022), just published a new paper on correction of secondary boundary fluorescence effects near grain boundaries. 

If you ever perform trace/minor element analysis near a boundary, then you should read this new paper attached below (login to see attachments).

I also include one other earlier paper on this subject that is referenced in the above new paper.