Answer

In 1927, Clinton Davisson and Lester Germer fired electrons at a nickel crystal and observed diffraction patterns identical to those produced by X-rays, directly confirming de Broglie's hypothesis that particles have wave properties. This was the first experimental proof of matter wave interference, a cornerstone of quantum mechanics. The other experiments, while historically important, demonstrated different quantum phenomena such as electron charge, spin quantization, and photon-electron scattering.