Metastable deexcitation spectroscopy (MDS) is one of the most powerful techniques for studying electronic properties of the outermost layers of solid surfaces. Metastable atoms of rare gases impinge on solid surfaces and electrons are emitted as a result of electronic energy transfer. The principles of MDS applied to solid surfaces are described. Two mechanisms of deexcitation of metastable atoms are discussed in the cases of clean alkali and transition metal surfaces. The effects of adsorption of gases such as O and CO are also shown. Several applications of MDS are described for evaluation of new surface materials.
