Sensitivity to surface structure in RHEED is due to the fact that the primary beam falls on the surface under study at a small grazing angle of 1-5º, and that only small angle diffraction beams are detected. As a result, throughout the free path the electrons remain in the thin surface region. For example, electrons with energy of 50-100 keV and a mean free path of about 100 nm at the angle of incidence of about 1o penetrate to a depth of less than 1 nm.

The figure shows the experimental arrangement for studying the surface by RHEED, in which a beam of high-energy electrons from an electron gun grazes the sample surface, and diffracted electron beams form the RHEED pattern on the fluorescent screen. As an example, the figure shows a RHEED pattern of atomically clean Si(111)7×7. The sample holder is placed on a platform that allows the sample to be rotated to obtain RHEED patterns from different azimuthal directions.

The RHEED method enables:

1) qualitative assessment of the structural perfection of the surface (a well-ordered surface gives a RHEED pattern with clear bright reflections and low background);

2) determination of the reciprocal lattice of the surface from the diffraction pattern geometry;

3) determination of the atomic structure of the surface by comparing the dependencies of the diffraction reflection intensity on the incidence angle of the primary electron beam (rocking curves), calculated for the structural models with dependencies obtained in the experiment;

4) determination of the structure of three-dimensional islands, formed on the surface;

5) control of the by-layer growth of epitaxial films with atomic precision using oscillation intensity values of the diffraction beam.