Fast and slow stress evolution mechanisms during interruptions of Volmer-Weber growth

The evolution of mechanical stress during Volmer-Weber growth of thin films is complex, often including a reversible stress evolution during interruptions of film deposition. The underlying mechanism for stress evolution during growth interruptions has been extensively debated, but remains unclear. In this work, in situ measurements of stress evolution during growth interruptions of various time scales, film thicknesses, and substrate temperatures were made during deposition of gold and nickel films. It was found that at least two mechanisms lead to the observed stress evolution, one fast (time constant ∼102s) and one slow (time constant ∼104s). The fast process is reversible and weakly dependent on the film thickness, while the slow process is irreversible and strongly dependent on the film thickness. It is shown that grain growth during growth interruptions can account for a significant portion of the stress change associated with the slow process. The fast reversible process is likely to be associated with reversible changes of the surface structure.