Sekundäärielektroneja

Sekundäärielektroneja are electrons that are ejected from a material's surface when primary electrons collide with it. This phenomenon is known as secondary electron emission. When energetic primary electrons strike a solid surface, they can transfer their kinetic energy to the electrons within the material. If this transferred energy is sufficient to overcome the material's work function, the electrons can escape from the surface and become secondary electrons.

The energy distribution of secondary electrons typically ranges from a few electron volts to a few tens of electron volts, with a peak at around 2-5 eV. The yield of secondary electrons, defined as the ratio of the number of secondary electrons emitted to the number of primary electrons incident, depends on the material, the energy of the primary electrons, and the angle of incidence. Generally, the secondary electron yield increases with primary electron energy up to a certain point, after which it begins to decrease.

Secondary electron emission has numerous applications. In electron microscopy, it is used to generate images of surfaces because secondary electrons are sensitive to the surface topography and composition. In vacuum tubes, secondary electron emission is exploited in devices like photomultiplier tubes and image intensifier tubes to amplify electron signals. It also plays a role in understanding plasma physics and radiation damage in materials. The study of secondary electron emission is crucial for fields ranging from materials science to astrophysics.