As many of you know, the boundary fluorescence calculations shown in this window, which are accessed from the Standard application:



are based on the Penfluor/Fanal FORTRAN codes written by Cesc Salvat and Xavier Llovet. Penfluor (using Monte Carlo methods), calculates the primary and continuum x-ray productions from the primary electrons while Fanal (using analytical methods), calculates the fluorescence effects for boundary geometries (when the two phases are different) or for a bulk matrix (when the two phases are the same). This is described here and in the subsequent posts:

https://probesoftware.com/smf/index.php?topic=58.msg214#msg214

The thing is, even though the Penfluor code is based on Penepma, it parameterizes the results over 10 beam energies so there are some inaccuracies and more importantly it can only handle the simple mirror geometry of a vertical plane boundary.  The mistake I made was that until recently I had named the title of the window "Calculate Penepma 2012 Fluorescence Couple Profiles", so some people thought the GUI was running the full Penepma code.  But no it just utilizes the Penfluor/Fanal code.  But it gets one lots of results in minutes (assuming you have the PAR files already calculated for the selected materials).

For ultimate accuracy one should utilize the full Penepma Monte Carlo code GUI, because it can handle any boundary geometry, though it does take a lot longer. However one can create a bunch of input files that can be run as a batch. This is this the GUI window running the full Penepma FORTRAN code, which is opened when clicking the Penepma Monte Carlo menu in Standard:



Anyway, Xavier asked me to fix the title of the Penfluor/Fanal window as described above, so that is now done, and you can update to v. 12.8.2 any time using the Help menu in Probe for EPMA or CalcZAF.

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Subject: Job Posting for Scientist II - Electron Microscopy

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I wanted to update this topic with some actual photos of the mount because the best aspect of these acrylic mounts (see above post and login to see the attachment!) is that they are super easy to re-polish.

I'm sure most of us have had to deal with standard mounts where each standard material is individually mounted in a brass sleeve and then inserted in a multi-hole brass mount with a set screw for each standard. But this method requires that the brass sleeves and mount be completely disassembled and then each standard "tube" has to be polished separately. Then ultra-sonically cleaned because the epoxy tends to pull away from the inside of the brass sleeve when it originally was cured, resulting in a tiny gap that can collect polishing compounds and oils/solvents.

With these acrylic mounts seen here:



the epoxy completely adheres to the acrylic hole and when the mount is cured, the *entire* mount shrinks by a small amount. But no gaps or cracks!

So to clean these acrylic mounts one merely uses a little 0.05 um colloidial alumina (or silica) on a soft lap and polishes off the carbon (and any oxide buildup and/or beam damage), then just a quick rinse in ethanol (only use pure ethanol to avoid damaging the epoxy!), and then wipe clean with a KimWipe, and dry in a warming oven for a few minutes immediately prior to carbon coating.

This type of acrylic block makes it so easy to re-polish ones standards that you won't hesitate to do it when it needs to be done!  And if you look closely at the above photo you can see the carefully scribed vertices of a triangle which contain our three "fiducial" marks for quickly re-calibrating our digitized standard positions when the mount is replaced within the sample holder.

Another standard mounting method which we don't use, but which I have an example of, is similar to the acrylic mounting method, but the epoxy is filled with copper shavings and it has a metal outer sleeve. This mount was labeled the "MAC" mount (when I first arrived in Oregon) and I suspect it came with a very old microprobe many decades ago:



However, for whatever reason, our lab manager Julie Chouinard, had to vacuum re-impregnate it with epoxy because originally it did have some tiny cracks in a few places.  Now however, it works great for a quick re-polish.

We have such spectrometer from 2014 on our SXFiveFE.
I can tell you that I am having love-hate relation with it.

cons:
1) I think the mapping approach (on PC0) is better than Oxygen peak shift, it is not clear how much it is shifted, in case of mixed oxidation states the peak will be broadened. Generally I see O Ka shift to be really complicated to have any use.
2) on extended spectrometer the oxygen Ka is situated at the very edge of "spectrum", it is enough to get some mechanical de-calibration and oxygen peak is no more accessible (until Spectrometer is serviced).
3) Best spectral resolution (?) – only for Oxygen! Please mind, that normally TAP's suffer from too broad peaks - they (mounted diff. crystals) are normally smaller than PET or LiF and is further narrowed by blanking at the edges, so that there would be even narrower peaks and less overlaps. And here you have LTAP - at anything else than Oxygen (and Florine) with complicated composition that crystal is a complete nightmare! Well that can be mitigated a bit if You use ProbeSoftware and can use MAN background (unfortunately, we don't have ProbeSoftware), because it is impossible to find any place for classical background measurements for Si, Al, Mg, M lines of REE, Hf- W, Y, Sr, Rb. That spectrometer is idle for most of our analysis, unless very simple minerals are analysed.
4) If You are going to have LTAP, you can have only one more crystal mounted on the turret, large crystals are mounted only on the double and not quadruple turrets. Those actually are much better designed than new type (2014) quadruple, and so I would not fear for wires. We have this extended spectrometer with LTAP and LPC0. We are often switching and had no wire failure (differently than with quadruple turrets...)

pros:
1) I prefer this crystal over LPC0 for F measurements. Maybe I would have different opinion if I would use Probesoftware and its MAN background modeling, however with classical background measurement LTAP have enough of space (for F) out from interference for background measurement in complicated minerals (containing REE, Fe (try that on LPC0, PHA wont help you there)).
2) I think LTAP can have some potential for measuring Fe L lines for Fe oxidation state determination (it also suffers from similar uncertainties as Oxygen peak shift), That needs to be clarified. As for oxygen I find LPC0 quite impressive for that.

Concluding:
I would prefer instead of current extended spectrometer with x2 turret (LPC0, LTAP) - the spectrometer with x4 turret (TAP, PC0, PET). It would then could work, instead of being 90% of time idle.

Hi Dawn,
OK, I now see where you got the idea.

Yeah, he doesn't suggest using different electron energies for different coating thicknesses, but as I mentioned above, he states that the coating thickness affects the emission of high energy x-rays (in the case of Fe Ka) due to the drop in electron energy and therefore in low overvoltage situations, and for soft x-rays (in the case of Fe La) due to x-ray absorption by the coating.

And he goes on to say that therefore the unknown and standard need to have identical coating thicknesses (or as I said previously the different coating thicknesses need to be correctly specified in the correction software).

As Peter states in his conclusions:

Regardless of the methods used, care should be taken when carbon coating the samples to ensure that identical thickness are applied to both the standards and the unknowns, and the surfaces should be cleaned of any oxide layers or polishing residue.

I guess I would say that Peter and I are in complete agreement on this, I just added an additional alternative to simultaneous coating, that is if the coating thicknesses are different *and* also of known thicknesses, one can specify these different thicknesses in the correction procedure in Probe for EPMA.  Either way works fine.

I guess that's one good reason for polishing both the standards and unknowns, and coating them together, is that not only do you get similar coating thicknesses, but you are also get clean, (less) oxidized surfaces for ones metal standards. 

In practice I've found that our carbon evaporator coating thicknesses are quite reproducible using the method of red to blue color change on brass:

https://probesoftware.com/smf/index.php?topic=1252.0

That said, when I've needed to do careful measurements of oxygen at major level concentrations (where the standard dominates accuracy), I often re-polish and re-coat both the standards and unknowns together. But not always. We sometimes get uncoated metallurgical samples from some customers, and for those samples, we simply specify in PFE that the standards are coated with 20 nm of carbon and the unknowns are uncoated, and it seems to handle this nicely. Here is a detailed discussion on this very topic:

https://probesoftware.com/smf/index.php?topic=23.0

Hope this helps, and finally note that there's a typo in the pdf where Peter references fig 12, but I think he means fig 13 (as there is no fig 12!).

john