Concept and demonstration of a low-cost compact electron microscope enabled by a photothermionic carbon nanotube cathode.

The scanning electron microscope (SEM) delivers high resolution, high depth of field, and an image quality as if microscopic objects are seen by the naked eye. This makes it not only a powerful scientific instrument, but a tool inherently applicable to nearly all fields of study and curiosity involving the small scale. However, SEMs have remained complex, expensive, and beyond the reach of many. To broaden access, we demonstrate an SEM using simple, low-cost, off-the-shelf components, and hobby-level electromechanics; this has been enabled by a thermionic electron source based on a carbon nanotube array excited by low optical power. The instrument offers sub-micrometer resolution, a depth of field of the order of a hundred micrometers, and an image quality comparable to commercial SEMs; it also tolerates poor vacuum and moist specimens, making it broadly applicable. It has a flexible design that lends itself to customization for different use scenarios. We describe the conceptual approach and high-level design in this paper; the detailed blueprints of our specific implementation are provided separately online. We hope that specialists and non-specialists alike will build variations that fit their own needs and interests, helping electron microscopy expand further into industry and society.