We describe some aspects of the temperature-dependent and time-dependent deformation of gold thin films on silicon substrates. We show that plastic deformation of bare, unpassivated films at high temperatures is controlled both by dislocation plasticity and by diffusion of matter between the free surface of the film and the grain boundaries in the film. The presence of a passivting layer of tungsten on the surface of the film is shown to completely inhibit these diffusional processes, causing plasticity to be controlled by dislocation flow. Dislocation plasticity at high temperatures is largely athermal because the storage of dislocations at the film/substrate and film/passivation interfaces dominates the deformation resistance. The strength of passivated films also depends strongly on the film thickness. These properties differ significantly from those of bulk materials, for which deformation is samle size independent and strongly temperature dependent at high temperatures. Time-dependent stress relaxation of gold films at room temperature has also been observed and studie.d The stress in both passivated and unpassivated films is observed to fall logarithmically with time at a rate that is independent of the film thickness. This form of stress relaxation indicates an exponential dependence of the plastic strain rate on the stress in the film. This suggests that time-dependent deformation of gold thin films at room temperature may be controlled by thermally activated dislocation glide processes. A simple model of thermally activated dislocation glide past rectangular obstacles is used to describe the room temperature stress relaxation data.
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