Plasticity Effects on Interfacial Fracture of Thin Gold Films

A systematic study of interfacial fracture energies of thin gold films as a function of film thickness is presented in this paper. The films were sputter deposited onto sapphire substrates to thicknesses ranging from 10 nm to 200 nm. Nanoindentation was used to measure mechanical properties and combined with stressed overlayers to trigger delamination and buckling. Fracture energies and interfacial fracture energies were then obtained from the buckles using mechanics-based models. The results showed that measured fracture energies decreased with decreasing film thickness to a lower limiting value near 1.5 J/m for film thicknesses up to 40 nm with a mode I normal component equal to 0.6 J/m. The normal component equals the true work of adhesion and governs delamination. The shear component is composed of contributions from the test technique and crack tip plasticity which varied with film thickness.