Experiments with old tubes, Scanning electron microscope

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Re: Experiments with old tubes, Scanning electron microscope

Postby segelfam » Sat Oct 16, 2010 8:26 am

some more images from the vidicon-microscope.
A picture of a tick which was unlucky to cross our garden table and a operational amplfier. The first one is colored with 'Photo Shop' for nicer viewing
and the second allows to estimate the resolution which is arround 10 µm.
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Re: Experiments with old tubes, Scanning electron microscope

Postby Doug Coulter » Mon Oct 18, 2010 12:00 pm

This is really great stuff Thomas! Do you have an idea what's limiting the resolution? It seems very uniformly smeared, and so susceptible to a little unsharp masking kind of post processing to restore at least some more detail. Do you think it's space charge beam spreading, or just the fairly large cathode size? In other words, might it get better at lower beam current (or higher voltages etc)? This really seems like a much simpler way to "get in the game" than building something like that from scratch.

I tried some image improvement stuff on your image, but the jpeg artifacts also got "enhanced" so it would work a lot better on the raw image data. You can see the diagonal lines which I assume were from the jpeg process.
Scale and unsharp mask version from original jpg
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Experiments with old tubes, Scanning electron microscope

Postby segelfam » Wed Oct 20, 2010 1:41 am

I'm afraid the limiting resolution comes from the construction of the tube. The source is not the cathode but the crossover of the electronbeam just in front of the negativ biased wehnelt grid. The single lense is half the way between the crossover and the sample, so the demagnifiaction can't exceed 1:1. In real SEMs there are 2 to 3 lenses to reduce the source image and form the probe beam. If I compute the resolution of the vidicon I get some 10 µm, the tube is constructed for a scanning area 6,6 x 8,8 mm, resolution > 500 line.
It's interesting to compare the image of the µA709 with one made with a Hitachi SEM made in my work. The contrast of the aluminium metallisation is rather low, because the high energy electrons (20 kV) penetrates the thin layers, the 700 eV of my microscope gives much better contrast.

I think the lines You get in a edge enhanced images result from mains (50 Hz) interference not from the jpg-processing. But I can send You a not processed raw file. The sample currents a rather low, arround 1 nA so I have to amplify a bit and have some trouble with the mains hum. I would be better to use the normal scintillator, photomultiplier combination which easly allow megafold amplification without interference.
Another interesting experiment is to change the focus voltage a bit. So You focus not on the sample on the field mesh which covers the last electrode of the vidicon, the mesh is readily resolved in transmission mode. So perhaps I should remove the mesh and bring the sample into the vidicons tube. the distance to the lense would be smaller and the demagnification higher
mesh.jpg (10.39 KiB) Viewed 7588 times

But finally I think there's no way without using a tip electron gun to get sub micron probe size with only one lense.
Another interesting approach is the FIB ( focused ion beam ) with a liquid (gallium) ion source. A liquid gallium layer on the coarse tip forms a very fine tip because of the accelerating field (taylor cone) and can be used to get a very fine ion beam. Because of the liquid layer the tip is reformed all the time and rather stable, also at bad vacuum conditions. Like electrons the ion beam can be used for imaging.

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Re: Experiments with old tubes, Scanning electron microscope

Postby Joe Sousa » Sat Nov 06, 2010 6:02 pm

Very interesting use of CRT's. Thanks for sharing.

I read the German language web pages with the google translator.

The most straight-forward way to translate is to paste the desired url into this page:

There is also an instant translation button available in the google translation tools section, that can be placed in your bookmarks toolbar. This button is just a "favorite" link or Bookmark.
I just tried to find this button in the google web site and could not find it.

This what the button (bookmark) has in it's properties field:

Joe Sousa
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