Microstructure and nanoindentation investigation of magnetron sputtering Ag/Co multilayers

The microstructure, hardness and elastic modulus of Ag/Co multilayers prepared by direct current magnetron sputtering were investigated by X-ray diffraction, transmission electron microscopy, and nanoindentation. The results show that all the multilayers have well compositionally modulation structure. A peak hardness of 4.9 GPa is obtained for periodicity of 7 nm, which is about 23% larger than the rule-of-mixture value, and it can be interpreted by elastic modulus mismatch between Ag and Co. For the multilayers with lower modulation period, Co layer grow into FCC structure together with Ag layer which would lead to hardness decrease. For the multilayers with periodicity large than 7 nm, the hardness decreases with increasing periodicity not obeying Hall–Petch relationship. The elastic modulus decreases with decreasing modulation period due to the compliant interface.