sekundääriemissioon

Sekundääriemissio, also known as secondary emission, is a phenomenon where electrons are emitted from a material when it is bombarded by primary charged particles, typically electrons or ions. These emitted electrons are called secondary electrons. The process is crucial in the operation of various electronic devices.

The number of secondary electrons emitted per incident primary particle is quantified by the secondary emission yield, often denoted by the Greek letter delta (δ). This yield is dependent on several factors, including the energy and type of the primary particle, the material properties of the target, and the angle of incidence. Different materials have varying secondary emission yields. For instance, materials with lower work functions and a higher density of electrons tend to exhibit higher secondary emission yields.

Secondary emission plays a significant role in vacuum tubes, such as photomultiplier tubes and cathode ray tubes, where it is used to amplify electron signals. In these applications, a primary electron beam strikes a dynode, causing the emission of multiple secondary electrons, which are then accelerated towards the next dynode or anode, leading to signal amplification.

However, secondary emission can also be an undesirable effect. In high-frequency circuits and high-power vacuum devices, uncontrolled secondary electron emission can lead to phenomena like secondary emission resonance, beam instability, and parasitic oscillations, which can degrade device performance. Understanding and controlling secondary emission is therefore essential for the design and optimization of many electronic systems.