Electron diffraction pattern. Demonstration of wave-particle duality. An electron gun has been fired at a thin sheet of graphite. The electrons passed through and hit a luminescent screen, producing the patterns of rings associated with diffraction. Diffraction occurs when a wave passes through an aperture similar in size to its wavelength. But electrons are particles, so should not exhibit the same phenomenon unless they can also behave like waves. De Broglie (1892- 1987) correctly deduced that this was the case and that particles have wavelengths inversely proportional to their momentum.