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 Xray 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. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.