electronbeam

An electron beam is a stream of electrons accelerated through a vacuum by an electric field, produced by an electron source such as a cathode. In typical devices, electrons are emitted from the cathode and accelerated to high energy by anode voltages or a sequence of electrodes. The beam travels in vacuum to minimize scattering and energy loss.

Emission mechanisms include thermionic emission (heated filament), field emission (sharp tip with strong electric field), and photoemission (illumination by photons). Beam energy ranges from tens of electronvolts in low-energy instruments to hundreds of megaelectronvolts in particle accelerators. Beam current and emittance determine brightness and focus; magnetic or electrostatic lenses shape and focus the beam, with aberrations setting practical limits on resolution.

When interacting with matter, electrons undergo elastic and inelastic scattering, producing signals such as backscattered electrons, secondary electrons, X-rays, or transmitted electrons. These interactions enable imaging and spectroscopy in electron microscopy and analysis, as well as material processing such as welding or surface modification.

Major applications include electron microscopes (transmission TEM, scanning SEM, and scanning TEM) for high-resolution imaging and spectroscopy; electron-beam lithography for nanoscale patterning; electron-beam welding and machining in manufacturing; and medical radiotherapy, where therapeutic electron beams penetrate tissue. In research, high-energy electron beams are used in accelerators and free-electron lasers.

Safety and handling: operation requires high voltage, high vacuum, and shielding to protect against ionizing radiation; hazards include electrical shock and exposure to X-rays at higher energies.

History: the electron was discovered by J. J. Thomson in 1897, leading to vacuum tubes, electron optics, and eventually electron microscopy in the 1930s and beyond.