Waves (de Broglie Waves)
In 1923 in his dissertation, the physicist Louis de Broglie established a hypothesis which he could not prove experimentally at first. Based on the particle properties of light he reasoned that electrons need to show wave properties as well. He calculated the wavelength of a particle using the mass m and the velocity v as h/(m·v), an achievement for which he received the Nobel Prize in 1923.
In 1927, Davisson, Germer and Thomson proved experimentally the existence of de Broglie waves (matter waves) of the electron, using the diffraction by Ni crystals.