Making the Electron Microscope(asimov.press)
asimov.press
Making the Electron Microscope
https://www.asimov.press/p/electron-microscope
9 comments
Really nicely-done article. I suppose that if there was any resentment on Ruska's part over losing the patent race to Ruedenberg, it was smoothed over when he (and not Ruedenberg) was awarded the physics Nobel.
It would have been interesting to hear why Ruedenberg wasn't considered for the prize.
It would have been interesting to hear why Ruedenberg wasn't considered for the prize.
I am a cryo-electron microscopist (TEM), will keep an eye on this thread in case there's any specific questions.
(Also have done Xray crystallography)
(Also have done Xray crystallography)
Are there any new developments on the technical side of microscopy such as new materials or techniques? What journals or trade papers are reliable in researching this information?
How does one become a microscopist as a profession? It seems like a specialized field with a narrow entry point and a lot of hoops.
How does one become a microscopist as a profession? It seems like a specialized field with a narrow entry point and a lot of hoops.
On the technical side, yes. The biggest new developments I can quickly think of are:
1) Cold field emission guns. The big challenge of an electron source is producing a coherent beam - that is a beam that comes off the tip one electron at a time, at the same location, the same angle, and with the same energy. The cooler the tip runs, the more coherent it tends to be. This has made a big difference and is just now widely commercially available.
2) Narrow pole-piece gap. The sample on most TEMs sits sandwiched between two objective lenses that operate in tandem - these are typically called twin objectives. The upper one ensures the beam is parallel, which primarily results in uniform defocus (or focus if one so desires) across the image. The lower one is responsible for image formation and initial magnification (actually, all of your resolution essentially). The gap between them is responsible for your primary aberrations: spherical and chromatic. Reducing this gap reduces the total aberrations in the image.
I will side bar that the physics of a microscope are not really holding it back from what I'm doing - generating structures of biomolecules. Really, I'm more limited by the camera technology than anything, because the cameras simply aren't performant enough to dose the images to the level I'd like, to collect as many images as possible in as short a time as possible. Fundamentally, I tend to be limited by number of observations.
For the really cutting edge stuff...check out ptychography:
https://en.wikipedia.org/wiki/Ptychography
>How does one become a microscopist as a profession? It seems like a specialized field with a narrow entry point and a lot of hoops.
There are basically two routes for TEM - material science, or biochemistry. The way to become a microscopist for me was to show up at a University that had a grant for a microscope, but no one to operate it. :)
In general, universities operate TEM cores, frequently called bioimaging or something. (Structural biology if it's newer although that's just one application among many). Frequently there are positions for all education levels - bachelor's through PhD, depending on what one wants to do. Training is a mix of hands on (interfacing with complicated systems) and theoretical (physics and image formation). Typically the operators aren't the most theoretical, but have a lot of very niche practical knowledge you only get from being around broken microscopes.
1) Cold field emission guns. The big challenge of an electron source is producing a coherent beam - that is a beam that comes off the tip one electron at a time, at the same location, the same angle, and with the same energy. The cooler the tip runs, the more coherent it tends to be. This has made a big difference and is just now widely commercially available.
2) Narrow pole-piece gap. The sample on most TEMs sits sandwiched between two objective lenses that operate in tandem - these are typically called twin objectives. The upper one ensures the beam is parallel, which primarily results in uniform defocus (or focus if one so desires) across the image. The lower one is responsible for image formation and initial magnification (actually, all of your resolution essentially). The gap between them is responsible for your primary aberrations: spherical and chromatic. Reducing this gap reduces the total aberrations in the image.
I will side bar that the physics of a microscope are not really holding it back from what I'm doing - generating structures of biomolecules. Really, I'm more limited by the camera technology than anything, because the cameras simply aren't performant enough to dose the images to the level I'd like, to collect as many images as possible in as short a time as possible. Fundamentally, I tend to be limited by number of observations.
For the really cutting edge stuff...check out ptychography:
https://en.wikipedia.org/wiki/Ptychography
>How does one become a microscopist as a profession? It seems like a specialized field with a narrow entry point and a lot of hoops.
There are basically two routes for TEM - material science, or biochemistry. The way to become a microscopist for me was to show up at a University that had a grant for a microscope, but no one to operate it. :)
In general, universities operate TEM cores, frequently called bioimaging or something. (Structural biology if it's newer although that's just one application among many). Frequently there are positions for all education levels - bachelor's through PhD, depending on what one wants to do. Training is a mix of hands on (interfacing with complicated systems) and theoretical (physics and image formation). Typically the operators aren't the most theoretical, but have a lot of very niche practical knowledge you only get from being around broken microscopes.
Mostly used for biological targets, laser induced ultrasound is pretty impressive.
I found it interesting that electron microscopes might also be called electron-accidental-cnc-machines
Interesting how they continued manufacturing these during ww2
Wonder what it'd take to make a tachiyon microscope? :)
Ben Krasnow (Applied Science) has a few videos and blog posts on the topic[0,1,2]. The Tungsten Filaments can be expensive, but I sent an email to the company and they sent me some samples to play with. It's been years so I forgot who I contacted. I tried the Nalgene bottle method but honestly I could not get it to hold a tight enough vacuum. The electron beam was very unstable and it is just really hard to purge and backfill the "chamber". The hardest part is getting the beam control circuit. I never got that refined myself for clear images, but I'm sure I could have gotten it with more time (it was a DIY work project so other things took priorities[3]). For our purposes the beam mattered more, so we went with what we could get. But even "failing" I learned a lot and it was a ton of fun. It's pretty exciting to get a beam to produce.
And keep in mind, even if you do get it fully running you shouldn't expect it to be anywhere near on par with the professional ones. Machining is great these days and we have a lot of advantages we can leverage as even hobbyists that shops couldn't get even a few decades ago, but we're talking about a high precision machine.
If the idea of having one for fun excites you, then it is worth the go. It was one of the most fun things I've ever made (maybe only next to a sputtering gun, which was very successful). If you can CAD, do some basic electronics, have a lot of patience, and a decent vacuum pump[4], then you should give it a go.
[0] https://www.youtube.com/watch?v=ZIJ1jI1xDhY
[1] https://www.youtube.com/watch?v=VdjYVF4a6iU
[2] https://benkrasnow.blogspot.com/2014/04/electron-beam-contro...
[3] Resources were tight enough that I think I could have done better if I decided to fund it myself. Big thing I would say is that whenever working with vacuum stuff don't take shortcuts. It's better to act like a perfectionist as it'll save you time in the long run. When you're working with tiny things, well... the little things matter lol
[4] I mean a vacuum pump, not a roughing pump. You don't need a turbo, but you do need a high vacuum.