1) Overlay 2) Protection 3) Protective cover 4) Protective covering 5) Sheathing 1) Overlay 2) Sheathing 
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 o...
• (n.) One who overlays; that with which anything is overlaid.
O'ver·lay'er noun One who overlays; that with which anything is overlaid.