What is the electronic work function of an emitter material?
The electronic work function () of an emitter material is defined as the minimum amount of energy required to withdraw an electron completely from the surface of that material. It serves as a measure of how tightly a material holds its electrons, representing the energy difference between an electron inside the metal and one that is completely free.12
In the context of a thermionic power converter, the work function is a critical characteristic of the emitter material. Because the rate of electron emission decreases exponentially as the work function increases, it is desirable to select emitter materials with a small work function that can also operate reliably at high temperatures. Typical values for the work function of metals range from one to five electron volts. When electrons escape the emitter, they possess energy equal to this work function plus any additional kinetic energy they may have acquired.23