Tamm states and variety of their analogs in electrodynamics

The Tamm states [1] in quantum mechanics of bounded periodical crystals are well known special surface state of electrons concentrated in the vicinity of the crystal boundary. There are two physical reasons of electron localization near the surface: the electron motion outside, in the vacuum, is restricted by existing potential barrier connected with work function of a metal, while inside crystal the electronic motion is restricted if its energy belongs to an electron forbidden zone in periodic lattice. Tamm level shows itself as a very narrow level in the forbidden zone of electron spectra.