Nondestructive Characterization of the Structure and Mechanical Properties of Metallic Superlattice Thin Films

Abstract

Superlattice thin films of Cu-Ni (50 atomic percent Cu-50 atomic percent Ni) with bilayer repeat lengths between 1.6 and 19.4 nm were produced by ion beam sputtering. The films were characterized by x-ray diffractometry, from which the bilayer repeat length and the average lattice parameter perpendicular to the plane of the film were determined. The average lattice parameter displayed a small increase as the bilayer repeat length was reduced. Films were also investigated using low load indentation methods. Such methods produce submicron deep indents, and leave most of the film unaffected, and as such can be considered nondestructive characterization techniques. A small enhancement above the rule of mixtures value of the effective elastic modulus of the films was observed (independent of the bilayer repeat length); however, a large enhancement in the hardness was measured for small bilayer repeat lengths. This hardness enhancement was attributed to an interface hardening effect. This behavior suggests that metallic superlattices may be have applications as high strength coatings or thin films.