electron diffraction
/ ih-LEK-tron dih-FRAK-shun /
We usually think of electrons as tiny bullets. But fire a beam of them at a thin, regular sheet of atoms and they fan out into the same kind of bright spotted pattern that waves make. Electron diffraction is this surprising behavior: electrons, like X-rays and neutrons, can act as waves and diffract off the orderly rows of a crystal.
The key fact is that any moving particle has a wavelength tied to its speed, and for electrons accelerated by a modest voltage that wavelength is even shorter than typical atomic spacings. So when an electron beam passes through a thin crystal, the scattered electron-waves reinforce in just the Bragg directions, producing spots or rings. Crucially, electrons interact with matter through their electric charge, far more strongly than X-rays do — meaning they scatter intensely but penetrate only a whisker-thin sample.
This matters because that strong interaction makes electrons ideal for the tiny and the thin: nanoparticles, surfaces, individual layers, and films too small to give a usable X-ray signal. The same beam can be focused with magnetic lenses to also form an image, which is why electron diffraction lives inside electron microscopes. The honest caveat: because electrons scatter so strongly, a wave often bounces more than once on its way through, which complicates turning the pattern into exact atomic positions compared with the cleaner X-ray case.
In 1927 Davisson and Germer bounced electrons off a nickel crystal and recorded bright peaks at exactly the angles a wave would give — the first direct proof that electrons are waves. Today the same trick inside a microscope reads off the atomic arrangement of a single grain of metal a few atoms thick.
The Davisson–Germer experiment: electrons scatter off a crystal like waves.
Electron diffraction does not contradict the idea of electrons as particles — it is the same wave–particle duality light shows. Each electron arrives as one tiny dot on the screen; the spotted pattern builds up only after many electrons have landed.