increase in the discharge of electrons from the surface of a heated material by application of an electric field that reduces the value of the energy required for electron emission. The minimum energy required for an electron to escape the surface of a specific material, called the work function, is supplied by the heat. A very weak electric field may be applied that simply sweeps the already emitted electrons away from the surface of the material. When the field is increased, a point is reached for quite moderate fields at which the value of the work function itself is lowered. As the applied field (voltage) is further increased, the work function continues to decrease, so that the electron emission current continues to increase. At very high values of the applied field, however, the electron emission undergoes an excessive increase because of the onset of a different type of emission, called high-field emission or, simply, field emission. The effect is named after its discoverer, the German physicist Walter Schottky.