How does Electron Beam Evaporation work?
Evaporation takes place under vacuum, typically 10E-5 or deeper. A current (5 to 10 kV) is sent through a tungsten filament and heats it to the point where thermionic emission of electrons takes place. The filament is located in an area outside the deposition zone, in order to avoid contamination. The electrons are focused and directed toward the evaporant by means of permanent magnets or electromagnets.
As the electron beam hits the surface of the evaporant, the kinetic energy of its motion is transformed to heat via the impact. While the energy given off by a single electron is small, there are lots of them. The overall energy released is quite high – often more than several million watts per square inch. Compare that to the heat given off by a 100 watt bulb and it is easy to understand that the hearth which holds the evaporant must be water-cooled to keep from melting.
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