Beam diameter / Image Resolution

[Ben Buse]

Hi,

Inspired by Philip Gopon program to measure beam diameter

http://geoscience.wisc.edu/geoscience/research/facilities/electron-microprobe/software/

I've reproduced this for imagej. Using an SE image it will give you the beam diameter - if you measure across a sharp edge. Similarly if you measure a BSE or x-map signal across a sharp edge you get the resolution for the particular x-ray line.

I've currently set it to measure the distance between 10 and 90% intensity. But you can edit the macro script.

The script is shown below



Steps

As normal in imagej
(1) Open image
(2) Set image scale (otherwise distances in pixels)
(3) Draw line and plot profile (crtl-k)

The plugin
(4) Click on plugin.

The plugin should be stored in imagej plugin folder. Plugin attached

[John Donovan]

I made this topic "sticky"...

[Ben Buse]

Has anyone used David Joy's SMART marco for NIH image as described in this paper:

SMART – a program to measure SEM resolution and imaging performance

https://onlinelibrary.wiley.com/doi/full/10.1046/j.1365-2818.2002.01062.x

Where is it available, does it work with imagej?

Thanks

Ben

[Karsten Goemann]

Hi Ben,

Yes, I have. I got it directly from David Joy in a workshop.

It doesn't run in ImageJ as is, so when I retired by last Mac still running OS9 I tried to edit the code to use it in ImageJ. But didn't have much experience with ImageJ macros so I didn't get very far. I contacted David Joy a few years back but he wasn't planning to adapt it to ImageJ.

I think Brendan Griffin's SMARTer is an adaptation of SMART for ImageJ.

Cheers,
Karsten

[Ben Buse]

Hi Karsten,

Thanks, I'll ask Brendan Griffin

Ben

[ricounet67]

Can someone please share this plugin ?

[Stefan Baunack]

Hello,

there is a similar tool
SMART: Scanning Microscope Analysis and Resolution Test for DigitalMicrograph
http://www.dmscripting.com/smart.html

There's a free version of DigitalMicrograph, but it's very common in the TEM labs.
https://www.gatan.com/installation-instructions

Edit
Maybe you could ask here:https://forum.image.sc/,

Best regards
Stefan Baunack

[Nicholas Ritchie]

Following on with this conversation, I've got a question. 

Let's say I want to put down a microamp of current with a FEG microprobe.  Independent of whether I'd drill holes in my sample, what would be the minimum achievable spot size.   Is it possible on a FEG microprobe to get a 100 nm spot (or less) at 1 µA?

[Probeman]

Good question.  Are you asking from the perspective of an SE image and a 20/80 signal brightness profile?

Because as you well know, it depends on the signal being observed.

In other words, what sort of an SE imaging mode requires 1 uA of beam current?

[Karsten Goemann]

I think Nicholas may mean the beam diameter at the surface. This is relevant for analytical purposes as well, especially for lower kV on higher Z materials.

The achievable beam diameter will depend on the accelerating voltage as well.

On our 6 year old JEOL 8530F Plus I did for example some high resolution mapping on pyrite at 7 kV. At 500nA I got around 150 nm across a 20/80 signal brightness profile in SE images (haven't tried something fancy like SMART(er)). It doesn't quite go to 1 uA at 7 kV, maxes out at ~800 nA. It did 2.7 uA at 30 kV.

[sem-geologist]

Hi Nicolas,
I use time to time such currents on FE (Cameca SXFiveFE). Never had used any tool to find out what the spot size in reality is as it was clearly comparable with high resolution SEM, however not in standard user settable conditions. It is quite known that in normal conditions (using as intended by manufacturer) the resolution is worse than on Jeol SuperProbe...
But... I am not casual user which are happy being holded by hand. And I believe at max current it beats Jeol; especially at low voltages as be it 5kV or 30kV it is possible to stream all those electrons to the sample. Hearing from Karsten that there is such a strong handicap on Jeol in this regard, it just makes me more happy we have Cameca.

Anyway the trick and requirements is very simple.
1) Well maintained FE gun that includes: no ring-collapses, no arching, no poisoning.
2) decently physically centered column
3) ability to fiddle around manually with all lenses

If nr. 1 is met, then tip itself emits supper sharply round beam with no eye visible astigmatism. Moreover if tip is well maintained it can give about 0.1% beam stability/24h.

The idea is borrowed from Gemini columns (used by CZ FESEM's), where beam crosses only once - at surface of the sample. Crossing beam brings in astigmatism due to electron-electron interactions.

So the trick is to put zero strength on C2 lense (and probably C1 too if on Jeol, but I don't know if this trick is at all achievable there), and then rely on the integrated EL lense of the FE tip (again that needs user access, and other probes than Cameca deny it to user for that parameter) focusing the beam (with EL) up to moment of bypassing all apertures which is in axis of the column. The software and firmware will go nuts with C2 (and C1?) as zero and will give no magnification information as C2 and C3 values are used to calculate that. However the image will be as sharp as we see on our high resolution ZEISS FESEM's, thus closer to tens of nm, rather than hundreds. Again as there is no valid scale, I never tried to test it with any software, also seen no point in that.

Downsides of such trick:
* only the max current emitted from emitter (800-1.2µA, depends from setup); it is not possible to granularly tune that to particular value (actually it is but that will destabilize the emitter).
* WDS counting electronics will be enormously over-saturated for major elements. Even new dead time correction equations wont help.
* C3 will be working in different conditions than designed, long term stability of keeping such beam focused is unknown.

P.S. You wont drill the hole with such currents, if coating the sample with good coater in multi-pulse mode and mineral is resilient against electron beam. I.e. when applying 1µA beam on the rutile, I had never seen any disintegration spot mark. There are also some other minerals which can withstand insane amount of current.

[Probeman]

* WDS counting electronics will be enormously over-saturated for major elements. Even new dead time correction equations wont help.

Of course, measured count rate depends on the Bragg crystal diffraction intensity/sin theta and the emission line strength.  A weak emission line measured at high sin theta might still be possible in some analytical situations at such beam currents depending on the concentration. 

The logarithmic dead time expression is quantitative up to around 300 to 400 kcps, so as they say, "it depends".

https://epmalab.uoregon.edu/pdfs/Donovan-etal-DeadTime-2023.pdf

Cameca FEG operators: I would be very interested in reading a summary/timeline of Cameca's efforts to develop their FEG emitter. I know they had some troubles early on. Did these issues all get resolved eventually?  Is it still being offered on the shielded instrument?

[Anette von der Handt]

I cannot add any numbers to the high beam current side but I have some data at the low current side. When I got the new JEOL JXA-8530FPlus FEG-EPMA at the University of Minnesota, I went through the exercise of acquiring lots of SEI images of "Au-on-C" at various conditions to see how the image resolution/beam diameter changes across our most common analytical conditions.

I used WiscResolution to determine the beam diameter, it gives it for FWHM, 50:50 and 90:10. Below are some graphs using the FWHM data. I attached the spreadsheet with the actual data if somebody wants to play with it or compare it to their instrument. The dataset could be more complete but maybe it is of interest to see some actual numbers.

This is the change in beam diameter with increasing beam currents at 15kV. The biggest relative changes in beam diameter change occur at the low-beam current side.



This is a comparison of beam diameter at different accelerating voltages. The higher the beam current, the more the beam broadens at lower accelerating voltages.



And finally a comparison across different beam currents and accelerating voltages.

[Karsten Goemann]

Nice graphs Anette. Do you know if your new probe in Vancouver is similar, or have JEOL made changes/upgrades for the new series?

I'm not sure I would call the ability to do 800 nA at 7 kV a strong handicap! I was actually amazed when I did the tests back then, considering that it's a FEG (I was used to the beam currents you could get on SEM FEGs), how small the beam diameter still is at those sorts of settings, and it's always pretty much instantly stable, robust, and no real need to fiddle around with anything. I've never found myself needing more current on this machine.

In the end I did most of those pyrite maps at 7 kV 300 nA instead of 500 nA as the beam diameter is smaller and the analytical resolution of the resulting x-ray maps seemed visibly better because of that. Further reducing kV to 6 kV or lower seemed to reduce the overvoltage too much to still get decent count rates for some of the trace element peaks like Sb Lalpha. And yes, the pyrite itself seems happy with those sorts of conditions. The bigger problem was which minerals are surrounding it as they can be more beam sensitive. I did use weaker lines for the major elements such as Fe Ll for Fe and/or small/normal size monochromator crystals to avoid excessive count rates and the large crystals for the traces, but that was also before John developed the advanced dead time expressions.

[Nicholas Ritchie]

Thanks.  This information is helpful.   The intended use is to generate a point source of X-rays from a thin metallic film for an X-ray imaging system.

Anette, Your plots are really nice.  If I extrapolate the 25 keV data, it suggests that 100 nm might be doable. 
Karsten,  150 nm at 500nA and 7 kV seems pretty impressive performance.