The electron diffraction is a technique which makes it possible to study the structure and the symmetry of surfaces. This technique rests on the undulatory nature of the electrons and the strong interaction of those with the matter. The analysis of surface can be obtained by using electrons of low kinetic energy (50 eV < E < 100 eV) which have a mean free path or average distance between two inelastic scatterings lower than 1 nanometer. It corresponds to the LEED (Low Energy Electron Diffraction) technique. But one can also use high energy electrons (E > 1 keV), it is the case of RHEED (Reflexion High Energy Electron Diffraction) method. Taking into account the higher value of the mean free path, it is then necessary to work in grazing incidence to have only access to the structure of the surface atomic planes. Let us note that diffraction RHEED became an essential tool to follow the evolution of the growth in real time.
Low electron diffraction: LEED
The figure below schematizes the principle of the low electrons diffraction. In reciprocal space, the diffraction condition is graphically represented by the construction of the Ewald sphere. Diffraction takes place when the sphere of K = 2p /λ ray intercepts a node of the reciprocal lattice of the crystal. The diffraction pattern obtained then makes it possible to visualize the reciprocal space of the studied surface.