Hi,
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 13308 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.
Thomas