electron diffraction

Electron diffraction is the bending and spreading of a beam of electrons as it passes through or reflects off a regular array of atoms, producing a pattern of bright spots or rings rather than a single blur. Diffraction is something only waves do, so seeing it from electrons is direct, hands-on evidence that matter has a wave nature. The pattern's geometry is governed by the electrons' de Broglie wavelength and the spacing of the atoms.

Because that wavelength can be made very short by speeding the electrons up, electron diffraction probes structures far finer than visible light can resolve. This is the working principle behind electron microscopes and behind techniques that map the atomic arrangement of crystals, surfaces, and even individual molecules. The same wave behaviour that once seemed a philosophical curiosity is now a routine tool of materials science and biology.

Conceptually, electron diffraction is the matter-wave twin of the double-slit experiment, just with a whole lattice of 'slits' instead of two. Fire the electrons one at a time and the rings still build up dot by dot, reaffirming that each electron interferes with itself. The phenomenon is among the most repeatable confirmations that the de Broglie relation holds for real particles.