A simple guide to determine elastic properties of films on substrate from nanoindentation experiments

Several models have been developed to extract the intrinsic elastic modulus of thin films from the composite film/substrate modulus value obtained from indentation tests on coated systems. Either analytical, semi-analytical or empirical, they generally propose an expression of the composite modulus as a function of the film and substrate elastic moduli and of the film thickness. When the substrate properties and the film thickness are known, the expression without adjustable parameter contains only the film elastic modulus as unknown parameter, which can thus be deduced. In this paper, some models from the litterature are briefly described and compared with the easy-to-use model we have developed. Based on experimental results obtained with various film/substrate systems, this paper also aims to demonstrate that the error induced by the uncertainty in the knowledge of the substrate Young modulus value and in the film thickness value is often as large as the difference resulting from the choice of the model.