A simple nanoindentation-based methodology to assess the strength of brittle thin films

In this work, we report a simple methodology to assess the mechanical strength of sub-micron brittle films. Nanoindentation of as-deposited tetrahedral amorphous carbon (ta-C) and Ti–Si–N nanocomposite films on silicon substrates followed by cross-sectional examination of the damage with a focused ion beam (FIB) miller allows the occurrence of cracking to be assessed in comparison with discontinuities (pop-ins) in the load–displacement curves. Strength is determined from the critical loads at which first cracking occurs using the theory of plates on a soft foundation. This methodology enables Weibull plots to be readily obtained, avoiding complex freestanding-film machining processes. This is of great relevance, since the mechanical strength of thin films ultimately controls their reliable use in a broad range of functional uses such as tribological coatings, magnetic drives, MEMS and biomedical applications.