A novel approach to extracting hardness of copper/niobium (Cu/Nb) multilayer films by removing the substrate effect

作者:Qiu, Y. H.; Bai, Q.; Fu, E. G.*; Wang, P. P.; Du, J. L.; Chen, X. F.; Xue, J. M.; Wang, Y. G.; Wang, X. J.
来源:Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2018, 724: 60-68.
DOI:10.1016/j.msea.2018.03.047

摘要

This article presents a novel method to eliminate the substrate effect in soft thin film on hard substrate by correcting the projected contact area in nanoindentation test. The hardness of sputtered Cu/Nb multilayer films on silicon substrate with different individual layer thickness was measured by nanoindentation in continuous stiffness mode (CSM) and was shown to be influenced by both indentation size effect (ISE) and substrate effect. Finite element modeling (FEM) and atomic force microscope (AFM) were used to investigate the influence of substrate to the hardness measurement, and the results showed that the hardness deviation induced by the substrate effect resulted from the pile-up can be reasonably removed. Silicon substrate was found to be crucial for the pile-up formation, as the vertical plastic flow of soft Cu/Nb film was restrained by hard silicon substrate with the increase of indentation depth. After applying our pile-up correction and revised Nix-Gao fitting, the hardness curves show a depth independent relation, which fulfills the requirement for accurate hardness measurement. We showed that the hardness deviation due to pile-up is about 14%. Meanwhile, some vague issues like the plateau region and "one-tenth rule" applied in many studies were discussed and clarified basing on our experimental and modeling results. The correcting methods and simulation results could be instructive and significant for nanoindentation hardness test of similar soft film on hard substrate system.

  • 出版日期2018-5-2
  • 单位北京大学; 区域光纤通信网与新型光纤通信系统国家重点实验室; 核物理与核技术国家重点实验室