Low-Energy Electron Diffraction

Abstract

The essential elements are an ultrahigh vacuum (UHV) chamber to preserve surface cleanliness, an electron gun to produce a collimated beam of electrons in the energy range 0 to 500 eV, a crystal holder and manipulator, and some means of observing the diffracted electrons, typically a fluorescent screen. Further details may be found elsewhere.^(1–3) The major difficulty is common to all surface experiments, namely, to keep the surface clean. The UHV chamber will normally contain an array of techniques for cleaning the surface (provision for heating the sample, ion bombardment) as well as some means of detecting impurities at the surface, usually by detection of Auger signals from adsorbed atoms. LEED is very sensitive to cleanliness of the surface and small amounts of contaminant can produce quite spurious results. Experiments conducted on clean, perfect, surfaces can produce a large amount of structural information of high precision. Obviously it is only possible to produce precise data for surfaces which are well defined in the first place.