The 1927 Davisson–Germer experiment demonstrated diffraction of electrons from a nickel crystal. The scattered electrons formed intensity maxima at angles predicted by treating their de Broglie wavelengths as waves.
Clinton Davisson and Lester Germer were studying electron scattering at Bell Laboratories. Their accidental exposure of a nickel target to air changed the crystal structure; after heating the nickel to restore its crystalline arrangement, they observed a strong diffraction pattern. This unexpected result became evidence for electron wave behavior.
The measured wavelengths agreed with Louis de Broglie’s 1924 proposal that matter has wave properties. The experiment therefore helped confirm wave-particle duality, not just for light but for material particles as well.
Diffraction is not the same as ordinary reflection. A crystal’s regularly spaced atomic planes act like a three-dimensional grating, producing strong scattered beams only at particular angles and energies.