By contrast, in the microscopic vacuum tubes, devices called field emitters shoot electrons from the most prominent tip of an array of tiny, unheated posts or pyramids. The electrons are torn from the tip by an enormous voltage produced when an external electric field becomes concentrated there. Field-emission research has intensified in the past decade because emitters can be used in flat displays for computers and other items. Another research team in 1991 reported sealing minuscule emitters inside an evacuated cavity, thus creating a vacuum tube, but it's not as small as the Cambridge tube, Akinwande says. The maximum current is low about 10 nanoamperes and too irregular, he says.
Vacuum tubes handle high-frequency signals better than semiconductor components do.
Unlike electrons in a semiconductor, which are slowed by collisions with crystal-lattice atoms, electrons in a tube fly unobstructed through the vacuum. Other possible roles include pressure and acceleration sensors and satellite microthrusters, Akinwande adds. References and sources for this article From Science News , Vol. Copyright 1999, Science Service.