Effects of thickness on the characteristic length scale of dislocation plasticity in Ag thin films

The effects that film thickness has on the length scale over which dislocation motion takes place were studied to elucidate the origin of the thickness dependence of the strength of polycrystalline Ag thin films on substrates. At low temperatures (below 200°C), where dislocation-mediated plasticity is the dominant inelastic mechanism, the thickness dependence of two plasticity parameters, the activation volume and the length of mobile dislocation segments, was investigated. The experimental results indicate that the distance between pinning points along the length of mobile dislocations increases with film thickness, and that it is significantly smaller than the film thickness and the average grain size. The thickness-dependence of the length over which individual inelastic events occur, which is the characteristic length scale for dislocation plasticity, clarifies the origin of the dependence of the low-temperature strength of thin films on film thickness.