How to use a line beam shape on a JEOL 8200 with PfE?

[Michael Lance]

Hello,

I would like to acquire a line scan perpendicular to an interface using a beam spot shaped like a 20 micron long line where the beam spot line is oriented parallel to the interface in order to average the composition along the interface direction somewhat. Within the JEOL software, I can make this shape by choosing the LSP (line) Scan Mode and a magnification of 6000X.

Should I just set up the spot shape using the JEOL interface and then unclick the Force Column Conditions button?

Thanks for your help.

-Michael

[Probeman]

Hi Michael,
You could, but you will get inaccurate results.  The reason is because the matrix corrections are non-linear, averaging photons introduces significant physics errors. What you want to do instead is average compositions (of individually quantified pixels).

Here is a topic that discusses this issue:

https://probesoftware.com/smf/index.php?topic=198.0

[Michael Lance]

Thanks for the warning.

This sample is a 1/2 mm thick homogeneous Fe-Al alloy that has been oxidized. I want to measure the Al depletion caused by oxidation across the entire sample thickness. The Al wt% will probably vary less than 1 wt% across the entire thickness, if at all. Moreover, the sample will be homogeneous along the 20 micron line spot that I would like to use.

I often work with homogeneous or pure alloys that have been oxidized or are bonded in a diffusion couple where I need to measure concentration profiles only in one direction and I would like a little averaging in the direction parallel to the interface. The concentration variation in the plane of the interface is (I presume?) less than the error introduced by the nonlinear matrix corrections.

This approach was also taken by this paper for measuring C and B in steel : https://www.corrosionjournal.org/doi/full/10.5006/3199.

Is turning off the Force Column Conditions the way to do this? Would you recommend not bothering to do this averaging and just stick with the point analysis?

[Probeman]

Hi Michael,
I agree that if the composition you are scanning the beam over is homogeneous enough to make the non-linear matrix effects insignificant, then there would not be any point in averaging the intensities over a scanned area.  Note however that matrix effects for oxygen are quite large in this matrix.

If I were tasked with this characterization I would probably acquire some rectangular x-ray maps across the interface and then fully quantify the pixels in CalcImage. Then perhaps use the "strip averaging" output method there.

If you want to utilize some special JEOL beam mode for "overscanning" in PFE, I would probably use the "Do Not Set Conditions During Acquisition" checkbox in Acquisition Options.  But again, I would avoid these "defocus beam" or "overscanning" methods due to the reasons discussed in the topic linked to above.
john