The effect of interface adhesion on buckling and cracking of hard thin films

In this paper, we demonstrate with our model-based simulations that the various buckling patterns with and without cracks, as experimentally observed in sputter-deposited Ti-Si-N films on Si substrates, could be reproduced and explained. The results show how the normal stiffness, the interfacial toughness and the normal strength of the cohesive interface determine the locations of the cracks. We believe that our results contribute to the advancement of the understanding of cracks location in buckles of hard thin films on rigid substrates.The physics behind the strain-released buckling patterns including telephone cords and straight-sided wrinkles with and without cracks, as experimentally observed in sputter-deposited Ti-Si-N thin films on Si substrates, are investigated with model-based simulations by varying the mechanical properties of the interface. Our calculations reveal that the location of the cracks depends on the normal stiffness, the interfacial toughness and the normal strength of the cohesive interface. These properties determine the geometrical shape of the buckles such as width, wavelength and deflection, and hence the local bending-induced tensile stresses. Buckling patterns with cracks at the apexes occur for low-stiffness interfaces as well as for high-stiffness interfaces with high toughness. On the other hand, cracks at the bottom of the buckles are more likely to occur for interfaces with high stiffness and low toughness. By using an elastic material model with a fracture criterion for brittle behavior, we demonstrate that the crack will follow the path where the bending-induced principal stress exceeds the flexural strength of the film.Australian Research Council (ARC) Centre of Excellence for Design in Light Metals (CE0561574). City University of Hong Kong SRG Grant (Project No. 7002755). National Natural Science Foundation of China under grant number 11232003