Evaluating modulus and hardness enhancement in evaporated Cu/W multilayers

The microstructure, hardness and elastic modulus of Cu/W multilayers prepared by evaporation deposition were investigated by X-ray diffraction, transmission electron microscopy and nanoindenation. The results show that the multilayers with good modulation structure have asymmetrical interfaces. The W on Cu interfaces are relatively sharp, while the Cu on W interfaces are diffuse, with significant intermixing. The intermixing results in compression of the out-of-plane interplanar spacing of the W layer. The compression increases with decreasing periodicity and leads to modulus enhancement. The hardness values also increase with decreasing periodicity, which is interpreted by the Lehoczky model.