Overlayer

An overlayer is a layer of adatoms adsorbed onto a surface, for instance onto the surface of a single crystal.

Overlayers on single crystals
Adsorbed layers on single crystal surfaces usually exhibit a long-range order. In other words, the adsorbed species forms a well-defined structure in the overlayer. Each particular structure exists only over a limited distance from the adsorbate's base surface. In some systems, a whole range of adsorbate structures forms as the overlayer gets thicker.