Electron Beam Coating is a process is based on evaporation in a vacuum to produce thin films. The electron beam as an energy carrier serves to heat the evaporant in the crucible directly. Electron beam is generated in the electron gun, and by suitable focussing and deflection, is passed through the work chamber to the evaporant.
Both the work chamber and the beam generating system are evacuated to enable generation and unimpeded propagation of electron beams. When the beam hits the evaporant, the kinetic energy is converted into heat (useful energy and evaporation) and losses encountered are back scattered electrons, secondary electrons, thermionic electrons and X-radiation.
Fig. 8.4 shows the principle of electron beam evaporation. Plant consists of a work chamber with a vaccum pumping system, a crucible for an evaporant, an electron gun, a shutter, and a substrate with its fixtures and heating appliance.
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The evaporant is heated by the beam that impinges directly into its surface. The surface is therefore brought to such a high temperature that it becomes the source of a vapour stream. The substrate to be coated is arranged in this vapour stream, and part of the vapour condenses on it in the form of a thin film. Evaporation from cooled crucible allows the production of high purity films because reactions with the crucible walls are avoided almost completely.