The internal friction in polycrystalline films (0.2 to 1.5μm-thick) on Si substrates was measured as a function of strain amplitude. It was found that the friction increased with increasing strain amplitude, but at amplitudes which were at least 2 orders of magnitude greater than those required for a similar increase in the bulk metal. An analysis of the amplitude-dependent internal friction indicated plastic strains which were of the order of 10-9, as a function of the effective stress on dislocation motion. Because the grain size was greater than the film thickness, the micro-flow stress at a given level of plastic strain varied inversely with the film thickness. The film thickness effect in the microplastic range was explained in terms of dislocation bowing.

Microplasticity of Copper Thin Films on Silicon Substrates. Y.Nishino, Y.Ota, T.Kawazoe: Philosophical Magazine Letters, 2001, 81[11], 743-50