The last time we used a scanning electron microscope (a SEM), it looked like something from a bad 1950s science fiction movie. These days SEMs, like the one at the IBM research center, look like computers with a big tank poised nearby. Interestingly, the SEM is so sensitive that it has to be in a quiet room to prevent sound from interfering with images.
As a demo of the machine’s impressive capability, [John Ott] loads two US pennies, one facing up and one face down. [John] notes that Lincoln appears on both sides of the penny and then proves the assertion correct using moderate magnification under the electron beam.
According to [Asianometry], no one believed in the scanning electron microscope. No one, that is, except [Charles Oatley].The video below tells the whole story.
The Cambridge graduate built radios during World War II and then joined Cambridge as a lecturer once the conflict was over. [Hans Busch] demonstrated using magnets to move electron beams, which suggested the possibility of creating a lens, and it was an obvious thought to make a microscope that uses electrons.
After all, electrons can have smaller wavelength than light, so a microscope using electrons could — in theory — image at a higher resolution. [Max Knoll] and [Ernst Ruska], in fact, developed the transmission electron microscope or TEM.
When we were in school, they always told us we can’t see atoms. If you have an electron microscope, then they were wrong. [AlphaPhoenix] has access to a scanning tunneling transmission electron microscope and he shows us some atoms in a very thin slice of a crystal.
Of course, you aren’t directly imaging the atoms. You are looking at the shadows of the atoms, but still. If you’ve never worked with a SEM or STEM before, there are plenty of little details that are interesting like the sample holders and the vacuum system.
Scanning electron microscopes are one of those niche instruments that most of us don’t really need all the time, but would still love to have access to once in a while. Although we’ve covered a few attempts at home-builds before, many have faltered, except this project over on Hackday.IO by user Vini’s Lab, which appears to be still under active development. The principle of the SEM is pretty simple; a specially prepared sample is bombarded with a focussed beam of electrons, that is steered in a raster pattern. A signal is acquired, using one of a number of techniques, such as secondary electrons (SE) back-scattered electrons (BSE) or simply the transmitted current into the sample. This signal can then be used to form an image of the sample or gather other properties.
Condenser assembly
The project is clearly in the early stages, as the author says, it’s a very costly thing to build, but already some of the machined parts are ready for assembly. Work has started on the drive electronics for the condenser stigmator. This part of the instrument takes the central part of the rapidly diverging raw electron beam that makes it through the anode, and with a couple of sets of octopole coil sets, and an aperture or two, selects only the central portion of the beam, as well as correcting for any astigmatism in the beam. By adjusting the relative currents through each of the coils, a quadrupole magnetic field is created, which counteracts the beam asymmetry.
Scanning control and signal acquisition are handled by a single dedicated card, which utilises the PIO function of a Raspberry Pi Pico module. The Pico can drive the scanning operation, and with an external FTDI USB3.0 device, send four synchronised channels of acquired sample data back to the host computer. Using PCIe connectors and mating edge connectors on the cards, gives a robust and cost effective physical connection. As can be seen from the project page, a lot of mechanical design is complete, and machining has started, so this is a project to keep an eye on in the coming months, and possibly years!
Electron microscopes were once the turf of research laboratories that could foot the hefty bill of procuring and maintaining such equipment. But old models have been finding their way into the hands of eager individuals who are giving us an inside look at the rare equipment. Before you start scouring Craigslist, go on a crash course of what you need to know with Adam McComb’s Hacker’s Guide to Electron Microscopy. He presented the talk at the 2018 Hackaday Superconference and the recording was just published, you’ll find it below.
When you’re a high schooler who built a semiconductor fab in your garage, what’s next on your agenda? Why, adding a scanning electron microscope to your lab, naturally. How silly of you to ask.
When last we stumbled across the goings on in the most interesting garage in New Jersey, [Sam Zeloof] was giving a tour of his DIY semiconductor fabrication lab and showing off some of the devices he’s made there, including diodes and MOSFETs. As impressive as those components are, it’s the equipment he’s accumulated that really takes our breath away. So adding an eBay SEM to the mix only seems a natural progression, and a good reason to use some of the high vacuum gear he has. The video below shows [Sam] giving a tour of the 1990s-vintage instrument and shows images of various copper-sputtered samples, including a tick, which is apparently the state bird of New Jersey.
SEM hacks are by no means common around here, but they’re not unheard of. [Ben Krasnow] has used his to image cutting tools and phonograph records in action, and there are a few homebrew SEMs kicking around too. But our hats are off to [Sam] for yet another acquisition and a great tutorial to boot.
I used to have access to some pretty nice Scanning Electron Microscopes (a SEM) at my day job. While they are a bit more complex than a 3D printer, they are awfully handy when you need them. [Adam Guilmet] acquired a scrapped unit and started trying to figure out how to breathe life into it. His realization was that a SEM isn’t all that complicated by today’s standards. So he has set out to take what he has learned and build one from scrap.
In all fairness, he has a long way to go and is looking for help. He currently says, “[T]his is being powered by fairy dust, unicorn farts, and a budget that would make the poorest of students look like Donald Trump.” Still, he’s collected a lot of interesting data and we hope he can build a team that can succeed.
