Electronic surface states of ionic crystals

Abstract

This paper discusses the electronic behavior of the surface of insulating solids whose binding is at least partially ionic. The reference to ionic bonding is made for the sake of generality: all inorganic compound solids possess a certain degree of ionicity in their binding. Just as in bulk solids, the electronic states of the surface can be labeled either intrinsic or extrinsic. The intrinsic are the states that exist solely because of the termination of the lattice by the surface plane. The extrinsic may arise from any departure from the ideal periodicity of the lattice other than the presence of the surface itself. One important type of extrinsic surface state is that of a chemisorbed atom or molecule. This review discusses the physical origins of, as well as the interactions between, these two types of surface states.