Crack progression and interface debonding in brittle/ductile nanoscale multilayers

Crack initiation and progression have been studied in nanoscale brittle/ductile multilayers of Cu and Si. Variations in the interface debond energy on the cracking behavior have been examined by using thin interlayers comprising either Cr (strong interface) or Au (weak interface). For strongly bonded Cr interfaces, it has been found that cracks forming in the Si invariably extend through the Cu layers, despite the ductile rupture characteristics of the Cu. This behavior occurs even when the Cu layers comprise more than 70% of the multilayer volume. It also contrasts with the crack arrest capabilities exhibited by relatively thick ductile layers (∼10-100 μm). The disparity in behavior is attributed to the relatively large cracking strain required for the thin brittle layers. Weak Au interfaces result in debonding which, in turn, can suppress the propagation of cracks into adjacent layers. However, when the interface includes strongly bonded sections, the debond arrests, and often kinks into the attached Si. In this case, cracking still progresses sequentially through the Si layers. Careful control of the interface debond energy is needed to fully suppress crack progression in nanoscale multilayers.