When a beam of electrons passes through a material, an electron-sensitive film placed beyond the sample will show, when developed, a pattern of concentric circles around the central intense electron beam. This phenomenon is due to the diffraction of the electron beam by the material through which it passes. C. Davisson (1881-1958), L. H. Germer (1896-1971), and George P. Thomson (1892-1975) used this method to prove the hypothesis of Louis de Broglie (1892-1987) that electrons have wave characteristics. Further research on electron diffraction showed that the angles of the diffracted electrons and the intensity of the diffracted electron beams can be used to determine the structure of the molecules of the gas.

Diffraction is a phenomenon that is characteristic of all types of waves. Perhaps the simplest case to understand is the diffraction of monochromatic light. Whenever an advancing wavefront of light encounters a barrier in...