Matter Waves

De Broglie postulated that matter such as electrons should exhibit the wave particle duality just as light does.

He theorised that electrons would have a wavelength inversely proportional to its momentum, and that its kinetic energy would be directly proportional to its frequency.

The observation of electron diffraction patterns, similar to that of x-rays (where each have equivalent wavelengths) provided experimental confirmation of De Broglie's theoretical prediction.