Spectroscopic Ellipsometry of Nickel Oxide/Zinc Oxide Artificial Superlattices

Abstract

Thin films of ZnO and NiO and their superlattices were made by an ion beam sputtering technique. The dielectric functions of these films were measured as a function of photon energy using a variable‐angle spectroscopic ellipsometer. Artificial superlattices were formed in [(NiO)12/(ZnO)6]10, [(NiO)6/(ZnO)4]16, and [(NiO)7/(ZnO)8]12 films, where ZnO had the rock salt structure rather than the wurtzite type of structure. The dielectric functions of these superlattices were markedly different from those of pure ZnO, NiO, and their mixtures. However, ZnO had the wurtzite type of structure in [(NiO)10/(ZnO)20]4. In this film, the epitaxial relation which enables the formation of an artificial superlattice was not observed between ZnO and NiO layers, and the dielectric function could be interpreted as a simple mixture of ZnO and NiO.