Fältemissionskällor

Fältemissionskällor, often referred to as field emission sources, are devices that emit electrons into a vacuum when subjected to a strong electric field. This phenomenon, known as field emission, occurs when the electric field is intense enough to lower the potential energy barrier at the surface of a material, allowing electrons to tunnel out.

The primary components of a field emission source typically include a sharp tip or edge made of a conductive material, often a metal or a semiconductor, and a gate electrode. The tip is usually designed to have a very small radius of curvature, which concentrates the electric field at its apex, thereby reducing the voltage required for emission. The gate electrode, positioned close to the tip, is used to apply the necessary electric field.

Field emission sources have found applications in various technologies. One significant use is in field emission displays (FEDs), where emitted electrons strike phosphors to generate light. They are also employed in electron microscopes, particularly scanning electron microscopes (SEMs) and transmission electron microscopes (TEMs), where the high brightness and small source size of field emission guns (FEGs) enable higher resolution imaging. Other applications include vacuum electronic devices like klystrons and traveling wave tubes, as well as in X-ray sources and ion sources.

The advantages of field emission sources include their ability to produce a high current density, excellent coherence of the electron beam, and relatively low operating temperatures compared to thermionic emission sources. However, challenges exist, such as the need for ultra-high vacuum environments to prevent contamination and arcing, and the potential for tip degradation over time.