Hardness in Ag/Ni, Au/Ni and Cu/Ni multilayers

By use of nanoidentation, the hardness was measured in dc-magnetron sputterd Ag/Ni, Au/Ni and Cu/Ni multilayers as a function of the modulation period. In a limited modulation period range, the expression k*lambda**(-n) where k and n are fitting parameters and lambda is the modulation period, was fitted to the curves of hardness versus modulation period for the three types of multilayer. The exponent n of Ag/Ni was found to deviate by a factor of three from the n value of Au/Ni, which is surprising since no significant difference exists between the lattice parameters, shear moduli, morphologies and microstructures of the two systems. The results are discussed considering theoretical models and published experimental data.