[Ben Krasnow] has recently completed a home-built scanning electron microscope and has posted a video of it in action on his blog.
The build itself was done quite creatively using many off-the shelf components. We particularly like how long threaded brass rods were used not only for the supports, but also to maintain column alignment and fine-tune the spacing between the various beam focusing components. A large glass “bell jar” covers the entire apparatus and is sealed to the bottom plate when the air is removed from within by a mechanical vacuum pump.
In order to produce an image, an electron gun similar to one found in a conventional CRT television tube accelerates the electrons with a 5kV potential from the top of the microscope downwards through a long copper column. Along the way the beam is focused and manipulated by electronic lenses in much the same way that light would be handled by conventional optical lenses. Near the base of the main column there are electrostatic deflection plates placed orthogonally in the X and Y directions that allow for precise scanning of the beam across the sample’s surface. When this high-energy electron beam is scanned across the sample, scattering surface electrons are then picked up by a nearby detector consisting of a phosphor screen and photomultiplier – a system that supposedly allows for higher sensitivity than trying to measure the small numbers of electrons directly.
Although the resolution of the first few scans is only around 50uM, this early success clearly shows that the device functions as intended and will provide a great starting point for future refinement with the final goal being resolutions down to the 1uM range.
Despite Ben’s reassurance that the x-rays produced at this energy level won’t even penetrate the glass chamber, you can be sure that if we ever visit his garage we will definitely be donning some tin foil protection like these guys.