THIN METALLIC LAYERS IN SCANNING-TUNNELING-MICROSCOPY

If a metallic overlayer is very thin, its surface electronic structure will be different from that of a thick slab of the same metal. Notably, surface band gaps and certain surface states need a minimum thickness of the crystal structure underneath to be fully developed. If the overlayer thickness is less than that, then the surface electronic properties will be thickness-dependent. A metallic overlayer which is atomically flat on the surface, but which covers a step in the interface, will have different electronic structures on the two sides of the step. This paper investigates if, and under what conditions, such a behaviour can be picked up by a scanning tunneling microscope (STM). This is done by calculating STM data for Ag/Pd(111), Ag/Pd(100), and Cu/Ni(100). The results show tip height changes in the order of 0.1 angstrom for layer thicknesses of up to four monolayers.