Analyzing the mechanical behavior of thin films using nanoindentation, cantilever microbeam deflection, and finite element modeling

A comprehensive study was undertaken to identify the extent to which the mechanical properties of thin metal films on substrates could be determined quantitatively from instrumented sharp indentation. The mechanical behavior of thin Cu films on substrates was investigated using three different methods: nanoindentation, cantilever microbeam deflection, and microtensile testing. Finite element calculations of the nanoindentation and microbeam deflection experiments were conducted to extract yield strength and hardening modulus. Systematic experiments were performed to investigate the consistency of the different experimental techniques. The mechanical behavior of the Cu films was observed to depend on the film thickness. However, the results from finite element modeling of nanoindentation and microbeam deflection are quite different. In both cases, unique solutions for yield strength and hardening modulus were found. This is particularly noteworthy for the nanoindentation experiments; it is argued that the substrate destroys the self-similarity that is present during indentation of bulk material using a Berkovich tip. Microbeam deflection experiments seem to be more sensitive to the elastic–plastic transition, whereas the nanoindentation results describe the mechanical behavior at larger plastic strains. This is corroborated by microtensile tests.