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Secondary Electron Emission
If positive ions are accelerated by a space electric field in front of the cathode, and then positive ions with sufficient kinetic energy bombard the cathode surface, it is also possible that electrons are emitted from the cathode surface. The emitted electrons are usually called secondary electrons. This physical phenomenon of emitting electrons under the bombardment of positive ions is usually called secondary electron emission. However, not every positive ion that reaches the cathode can bombard an electron. The probability of emitting electrons is not only related to the properties and speed of the positive ions, but also to the electron work function of the cathode material. When the total energy (the sum of kinetic energy and ionization energy) obtained by the positive ions from the accelerating electric field is greater than twice the work function of the cathode material, one electron may escape from the cathode, while another electron is absorbed by the positive ions.
In this electron emission method, the cathode material does not need to be heated at all. Of course, due to the bombardment of positive ions, its temperature will also increase slightly. However, this temperature does not play a major role in the emission process. The reason for secondary electron emission is mainly due to the ionization energy of positive ions. Therefore, we also call this emission cold cathode emission. This secondary electron emission is the main emission form of the cathode of the glow discharge lamp.
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