(low-energy electron diffraction)
A technique used to study the structure of crystal surfaces and processes taking place on these surfaces. The surface is bombarded with a monochromatic electron beam 10−4 to 10−3 m in diameter, with energies between 6 and 600 V. The electrons are diffracted by the surface atoms and then collected on a fluorescent screen. Both the surface structure and changes that occur after chemisorption and surface reactions can be investigated in this way. It is necessary for the surface to be carefully cleaned and kept at ultrahigh vacuum pressure. Although many surfaces are altered by the electron beam and therefore cannot be studied using this method, there are enough surfaces and surface processes that can be studied using LEED to make it a very useful technique. Difficulties in interpreting LEED patterns arise as multiple-scattering theory, rather than single-scattering theory (as in X-ray or neutron scattering), is required. See also electron diffraction.