Evaluation of incipient plasticity from interfaces between ultra-thin gold films and compliant substrates

Nanoindentation experiments were conducted for 30 nm-thick Au films on two types of substrates, polyimide (compliant) and glass (stiff), to clarify the dominant mechanics of incipient plasticity from the interface. A high resolved shear stress τr could be effectively applied to the Au/polyimide interface due to the compliant substrate, and plastic deformation was initiated at the interface. The critical resolved shear stress τcrss at the interface was determined to have a value of 0.4 ∼ 0.5 GPa. On the other hand, in Au/glass, τr peaked within the Au film, and the maximum values were 1.1 ∼ 2.2 GPa depending on the tip radius, whereas the values of τr at the Au/glass interface were almost identical at 0.5 ∼ 0.7 GPa. Therefore, plastic deformation might be initiated from the Au/glass interface. The values of τcrss for heterogeneous nucleation at the interfaces were smaller than that for homogeneous nucleation in the Au films.