MECHANICAL-PROPERTIES OF EPITAXIAL TIN/(V0.6NB0.4)N SUPERLATTICES MEASURED BY NANOINDENTATION

We have used nanoindentation to measure the mechanical properties of epitaxial TiN/(V0.6Nb0.4)N superlattices, grown on MgO(100), as a function of the wavelength lambda. The V/Nb ratio within the VNbN layers was chosen to provide a lattice match with TiN, minimizing effects resulting from coherency strains. For lambda greater-than-or-equal-to 4 nm, the hardness was found to be significantly enhanced relative to a homogeneous reference film of the same average composition. For lambda < 4 nm, the hardness decreased to a value close to that of the reference film. The elastic modulus was found to be constant for lambda greater-than-or-equal-to 4 nm, at a value close to that predicted by the law of mixtures. For samples with lambda = 2.3 and 2.8 nm, there was a 15 % decrease in modulus. The observed variations appear not to be an effect of interfacial strain. Possible mechanisms are discussed.