ELECTRON DIFFRACTION

bending of a beam of electrons when passing near matter or through spacings in its submicroscopic structure that are comparable in size to the wavelength of an electron. According to the proposal (1924) of the French physicist Louis de Broglie, electrons and other particles have wavelengths that are inversely proportional to their momentum. Consequently, high-speed electrons have short wavelengths, a range of which are comparable to the spacings between atomic layers in crystals. A beam of such high-speed electrons should undergo diffraction, a characteristic wave effect, when directed through thin sheets of material or when reflected from the faces of crystals. Electron diffraction, in fact, was observed (1927) by C.J. Davisson and L.H. Germer in New York and by G.P. Thomson in Aberdeen, Scot., and the wave nature of electron beams was thereby experimentally established. As an analytic method, electron diffraction is used to identify a substance chemically or to locate the position of atoms in a substance. This information can be read from the patterns that are formed when various portions of the diffracted electron beam cross each other and by interference make a regular arrangement of impact positions, some where many electrons reach and some where few or no electrons reach. Recorded photographically or otherwise, such a distribution is called a diffraction pattern, which when properly interpreted yields information about the nature and structure of the gas, liquid, or solid that caused the electron diffraction.