Mechanism for grain size softening in nanocrystalline Zn

A technique (laser deposition of Zn/W multilayers) for producing stable nanocrystalline (nc) Zn films free of undesirable imperfections down to a grain size of d=6 nm is presented. These films exhibited grain size softening (inverse Hall-Petch effect) for dless than or equal to11 nm, providing support that this can be a real phenomenon in nc solids. The mechanism responsible for the softening was concluded to be thermally activated grain boundary shear. (C) 2002 American Institute of Physics.