FIELD EMISSION

also called Cold Emission, discharge of electrons from the surface of a material subjected to a strong electric field. In the absence of a strong electric field, an electron must acquire a certain minimum energy, called the work function, to escape through the surface of a given material, which acts as a barrier to electron passage. If the material is placed in an electric circuit that renders it strongly negative with respect to a nearby positive electrode (i.e., when it is subjected to a strong electric field), the work function is so lowered that some electrons will have sufficient energy to leak through the surface barrier. The resulting current of electrons through the surface of a material under the influence of a strong electric field is called field emission. This effect is utilized in the field-emission electron microscope, which in some instances achieves resolution of atomic dimensions. Field emission is sometimes called high-field emission to distinguish it from the Schottky effect (q.v.), which influences electron emission at lower values of the applied field. Positive ions (atoms that have lost at least one electron) also may be emitted from a solid subjected to a high electric field at its surface. See also thermionic emission.