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Hacking the ISI-100A Scanning Electron Microscope - Focusing Coils

A project log for Open Source Freakin' Scanning Electron Microscope

You read that right.

Adam GuilmetAdam Guilmet 11/30/2016 at 07:120 Comments

So first thing on the way to getting this thing operational again is to figure out what the hell all these coils actually do. In the photos below, you can see the objective and the two condenser focusing coils. The coils look beefy but I'm guessing each of these coils would carry a maximum of a couple amps, as the feeding wires are only around 20 gauge and had a 8 foot run back to the original controller. As I have ZERO information on this SEM, most of the specs for the electronics is going to be pulled out of my nether regions and tweaked until it works, so if anyone has any better starting parameters, please share!

The assembly of the these is fairly straight forward; everything just stacks together on the steel beam tube. The great thing is that the only section in this assembly actually carrying high vacuum is this tube.

This is the business end of the stack. The entire stack is then inserted into a quite thick steel liner. The deflection and stigmator coils(more on those later) fit right inside the objective coil here. As of now, I'm still figuring out the pinout, field shape, etc.

Notice the coils are each fully surrounded by the steel jacket on the outside and the steel discs on the top and bottom, and that tube at the center is made of sections of a high-permeability copper alloy and steel. The copper affects the magnetic field relatively little so it effectively acts as the gap in the picture below. The gap is important to effectively 'shape' the electron beam to a tight point.

(from http://www.ammrf.org.au/myscope/tem/background/concepts/lenses/poleandcoil.php definitelyGO HERE if you want to learn more)


EDIT: Here's a better photo so you can see what I mean about the copper gaps

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