In 1923, Louis Victor Pierre-Raymond de Broglie postulated that since light particles had also been shown to exhibit wave characteristics, perhaps other particles, such as the electron, might as well. From relativity, he knew that the momentum of a photon was: E = pc. Substituting the energy in one equation with the energy of the other and solving for wavelength (), he found: = h/p = h/mv. However, from the photoelectric effect, he knew: E = hc/.

This postulate was verified later by the Davisson-Germer experiment. This used the concept of constructive interference resulting from the path length difference that incident beams travel when hitting a lattice structure. If the electrons did not behave as waves, no constructive interference would be seen and thus no maximum (or minimum) intensities would be measured. However, if the electrons did behave as waves, there would be a maximum intensity at an angle related to the distance between the lattice layers of the scattering material.

The electrons were accelerated by a potential of 54 V and were incident on a nickel plate. The intensity of scattered electrons was determined by measuring the current produced. A plot of current versus detection angle was then plotted. The electrons were scattered through a wide range of angles, but a maximum intensity was seen at 50°. Since the distance between the layers of the nickel lattice was 2.15Å, a wavelength based on the experiment of 1.65Å was calculated. Using the de Broglie wavelength equation, a wavelength of 1.67Å was predicted, thus proving that indeed, electrons behave as waves: = 2.15Å sin(50°) = 1.65Å. Thus the electron was shown to behave as a wave as well as a particle.