Which experiment, published in 1927, first clearly demonstrated electron diffraction from a crystal?

The Davisson–Germer experiment first clearly demonstrated electron diffraction from a crystal in 1927.

Clinton Davisson and Lester Germer directed electrons at a nickel crystal and measured the intensity of electrons scattered at different angles. Their results showed strong intensity peaks, just as wave diffraction theory predicts. The experiment provided decisive experimental support for Louis de Broglie’s proposal that matter has wave-like properties.

The result was especially important because electrons had long been treated as particles. Diffraction is normally associated with waves, so the observed pattern showed that quantum objects can display both particle and wave behavior. Davisson and Germer’s work also supported the wave mechanics developed by Erwin Schrödinger.

A common mix-up is with the Davisson–Germer experiment’s date: the decisive results were published in 1927, while related electron-diffraction work by George Paget Thomson was conducted independently. Davisson and Thomson shared the 1937 Nobel Prize in Physics for demonstrating the wave nature of electrons.