Interfacial Model and Characterization for Nanoscale ReB2/TaN Multilayers at Desired Modulation Period and Ratios: First-Principles Calculations and Experimental Investigations

The interfacial structure of ReB2/TaN multilayers at varied modulation periods (Lambda) and modulation ratios (t(ReB2):t(TaN)) was investigated using key experiments combined with first-principles calculations. A maximum hardness of 38.7 GPa occurred at Lambda = 10 nm and t(ReB2):t(TaN) = 1:1. The fine nanocrystalline structure with small grain sizes remained stable for individual layers at Lambda = 10 nm and t(ReB2):t(TaN) = 1:1. The calculation of the interfacial structure model and interfacial energy was performed using the first principles to advance the in-depth understanding of the relationship between the mechanical properties, residual stresses, and the interfacial structure. The B-Ta interfacial configuration was calculated to have the highest adsorption energy and the lowest interfacial energy. The interfacial energy and adsorption energy at different t(ReB2):t(TaN) followed the same trend as that of the residual stress. The 9ReB(2)/21TaN interfacial structure in the B-Ta interfacial configuration was found to be the most stable interface in which the highest adsorption energy and the lowest interfacial energy were obtained. The chemical bonding between the neighboring B atom and the Ta atom in the interfaces showed both covalency and iconicity, which provided a theoretical interpretation of the relationship between the residual stress and the stable interfacial structure of the ReB2/TaN multilayer.