Scientists at the National Institute of Standards and Technology (NIST) and the University of Maryland, College Park, have built a practical, high-efficiency nanostructured electron source. Described in the journal Nanotechnology, this new, patent-pending technology could lead to improved microwave communications and radar, and more notably to new and improved X-ray imaging systems for security and health-care applications.
While thermionic electron sources such as the hot filaments inside cathode ray tubes have largely been replaced by LEDs and liquid crystals for display screens and televisions, they are still used to produce microwaves for radar and X-rays for medical imaging. Thermionic sources use an electric current to boil electrons off the surface of a wire filament, similar to the way an incandescent light bulb uses an electric current to heat a wire filament until it glows.
And like an incandescent light bulb, thermionic sources are generally not very energy efficient. It takes a lot of power to boil off the electrons, which spew in every direction. Those that aren't lost have to be captured and focused using a complicated system of electric and magnetic fields. Field emission electron sources require much less power and produce a much more directional and easily controllable stream of electrons.
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