Fast recovery of elastic constant in thin films studied by resonant-ultrasound spectroscopy

This paper reports incredibly large and rapid evolution of elastic constants in deposited copper and silver films observed by the resonant-ultrasound spectroscopy. The evolution begins just after stopping the deposition with the temperature dependent recovery rate. To explain the mechanism, we propose a model, where the elastic constants at grain boundary regions increase by 67% at least. Diffusion of atoms along the grain boundary region is a possible reason, and we confirm that the activation energy is much smaller than that for grain-boundary diffusion in bulk materials. These results are explained by drastic structure change at grain boundaries, being similar to phase transition from liquid into solid phase. (C) 2010 American Institute of Physics. [doi:10.1063/1.3407540]