Low temperature viscoelasticity in nanocrystalline nickel films

Metals typically do not exhibit viscoelastic deformation. However, grain size effects can render grain boundaries in nanocrystalline metals viscous. Modeling the nanocrystallites as linear elastic elements embedded in a viscous network of grain boundaries, the overall response of nanocrystalline metals can be viscoelastic even at lower temperatures. To investigate this hypothesis, we measured viscoelastic response of 100 nm thick freestanding nickel films at temperatures up to 425 K. Experimental results show about two orders of magnitude lower viscosity compared to the bulk, suggesting that diffusion enhanced mobility of grain boundary atoms may be responsible for such pronounced viscoelasticity.