Wave property of electrons implies that they will show diffraction effects. Davisson and Germer demonstrated this by diffracting electrons from crystals. The law governing the diffraction from a crystal is obtained by requiring that electron waves reflected from the planes of atoms in a crystal interfere constructively (see figure).
If a strong diffraction peak is observed when electrons are incident at an angle $'i' from the normal to the crystal planes with distance 'd' between them (see figure), de Broglie wavelength {\lambda _{dB}} of electrons can be calculated by the relationship (n$ is an integer)