Internal friction study of microplasticity in polycrystalline gold thin films

Amplitude-dependent internal friction in polycrystalline gold films 0.2–1.0 μm thick on silicon substrates has been studied with attention to the influence of a titanium-capping layer deposited on top of the gold films. Analysis of the amplitude-dependent internal friction provides the relation between the plastic strain of the order of 10−9 and the effective stress on dislocation motion. For the capped gold films, the microflow stress at a constant level of the plastic strain varies inversely with the film thickness, as in the case for aluminum films. The uncapped gold films, however, show a deviation from the inverse thickness relationship in the range thinner than 0.5 μm. Substantial strengthening for the thinner films with a capping layer is most likely attributed to the suppression of diffusional relaxation near the free surface during steady-state vibration.