A Shop-Built Adapter Brings Transmission Imaging to a Scanning Electron Microscope

Makers who restore old scientific equipment sometimes end up pushing those machines into new roles. ProjectsInFlight fits that description after bringing a JEOL JSM-5200 scanning electron microscope back to life from a scrap pile.

Scanning electron microscopes work by zipping a narrow beam of electrons across the surface of a specimen. These electrons bounce off surface atoms and emit secondary electrons. Collecting all of those secondary electrons yields a highly detailed representation of the sample’s external form and roughness. However, the features you’re most interested in are often hidden beneath the surface. Transmission electron microscopes use electrons to penetrate ultra-thin materials. Any changes in density or material inside the sample affect how many electrons travel through, and a detector on the other end detects that pattern and translates it into an image of what’s going on inside.

Building on a scanning electron microscope to increase transmission capacity can be very expensive. That’s why ProjectsInFlight decided to be creative and build his own adapter from scratch using only basic machine tools. The adapter is a bespoke component that fits into the microscope chamber and perfectly aligns the sample. Then, a conductive barrier surrounds it, preventing secondary electrons bouncing off the surface from reaching the detector. A small mirror beneath the sample collects any electrons that pass through. These electrons bounce off the mirror, creating a new signal that the microscope’s standard detector can detect.

One of the most difficult jobs was to fit everything into the microscope chamber’s limited space. The standard sample holders took up too much space, so we had to create a custom plate out of thin metal to free up 14mm. The remaining components, such as the adjustable mirror mount and shield, were turned and milled from aluminum and brass. The most challenging element was figuring out how to change the mirror angle without repeatedly venting the entire chamber. So he designed a unique configuration that allows you to alter the tilt even after the suction is activated.

His initial test specimens were gold nanoparticles affixed to a standard electron microscopy grid, but the results were inconsistent at initially because some surface-generated signal was still reaching the detector. He repaired it by significantly beefing up the shield. With the shield in place, he could see the nanoparticles as distinct dark spots in the image. Because they appeared flat, we concluded that the contrast was created by electrons flowing through the particles rather than merely bouncing off the surface. The next object was a mosquito wing, and the thin sections of the wing allowed enough electrons to create a high internal contrast image. He could see small structures inside the wing that would have been invisible with a surface scan, and the best part was that the thicker areas of the wing blocked more electrons, allowing him to identify where the material was thickening or thinning.

However, this improvised adapter is not a replacement for a genuine transmission electron microscope. Those instruments have all sorts of fancy lenses and so on to make them much more powerful, but our adapter provides useful internal contrast for samples that can live with a bit less resolution. The best part is you won’t have to spend another small cash on a completely new instrument.
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