Adhesion energy and related plastic deformation mechanism of Cu/Ru nanostructured multilayer film

Sputter-deposited Cu/Ru nanolaminate composites with individual layer thickness as small as 1.5 nm were tested by nanoindentation probing to initiate and drive delamination. Focused ion beam (FIB) observations show the layer buckling and interface delamination with lateral crack along the interface between the multilayer and substrate. The buckling behaviors, dependent on the critical length scale, are rationalized in the light of the repeating structural unit in the coherent multilayer. In addition, due to the presence of the interfaces and constraints between the hetero-layers, the condition for plastic dissipation in multilayers shifts significantly from those of single layer films, therefore a modified energy-dissipative model has been employed to obtain the quantitative adhesion energy for Cu/Ru multilayer, which agrees well with previous reports on the Cu-based films adherent on rigid substrates. The present result provides meaningful adhesion energy estimates and helps to understand the underlying deformation mechanism in metallic multilayers.