Activation volume for inelastic deformation in polycrystalline Ag thin films

The low temperature (T<100°C) inelasticity of polycrystalline Ag thin films on oxidized Si substrates has been studied, and the results are expected to be representative of other metallic thin films (e.g. Cu and Au) on rigid substrates. Values of the activation volume for inelastic deformations have been obtained by measuring the rates of stress relaxation during isothermal annealing of films. In situ Transmission Electron Microscopy was used to study the characteristics of dislocation motion in films deposited on micromachined Si membranes. The values of the activation volume and the presence of jerky glide indicate thermally activated motion of dislocations through forest-dislocation obstacles. The mean distance between obstacles along the length of moving dislocations was found to be significantly smaller than the thickness of the film and the grain size, which explains why current models for dislocation-glide-mediated plasticity underestimate the strength of thin films.