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A stress-relief model was developed to explain the phenomenon of spontaneous morphology change observed during room-temperature aging of electrodeposited copper and gold films. The model is based on excess vacancies due to which as-deposited films are initially expanded. These are gradually annihilated at the film surface. Quantitative modeling of vacancy diffusion revealed a well-defined vacancy-depleted zone near the film surface. A tensile stress developed in the near-surface region, the relaxation of which occurred with the formation of surface cracks or islands. The model is general and can be applied to both single-crystal and polycrystalline materials.
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Nakahara et al. (2006) studied this question.
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