Thermionically

Thermionically is an adverb describing a process or phenomenon that occurs through thermionic emission. Thermionic emission is the vaporization of material into a vacuum by heating it. When a material is heated to a sufficiently high temperature, electrons gain enough kinetic energy to overcome the material's work function and escape from its surface. This emission of electrons is known as thermionic emission.

The term "thermionically" is often used in contexts related to vacuum tubes and early electronics. For example, a cathode in a vacuum tube is heated to emit electrons thermionically, allowing current to flow through the device. Similarly, early light bulbs utilized a heated filament that emitted light and also electrons thermionically, although the primary purpose was illumination. The efficiency of thermionic emission depends on the material's work function and its temperature. Materials with lower work functions, such as thoriated tungsten or oxide-coated cathodes, are preferred for thermionic emission applications as they require less heat to achieve significant electron flow. The process is fundamental to the operation of many electronic components that were crucial in the development of radio, television, and computing before the widespread adoption of solid-state semiconductor devices.