Atomistic simulations of stress and microstructure evolution during polycrystalline Ni film growth

Abstract

Film stress and microstructure evolution during the growth of a Ni bicrystal film are investigated by molecular dynamics simulations. The nominal surface orientation of the growing film was (111) and the grain boundaries are Σ79 symmetrical tilt grain boundaries. The growth mode is layer by layer; two-dimensional (2D) islands nucleate on the surface, grow, and coalesce into complete layers. Grain-boundary migration near the free surface is observed as boundaries are dragged by step edges of growing 2D islands. Simulations show that the film stress-thickness product is compressive and oscillatory with a period that is approximately equal to one monolayer. Adatoms are observed to incorporate into grain boundaries and exert compressive strain on neighboring grains. Theoretical modeling demonstrates incorporated atoms are a primary source of the observed compressive stress during growth and gives predictions in very good agreement with simulation results. The oscillatory stress-thickness product is shown to be related to atoms diffusing into the grain boundary from the surface and out of the grain boundary onto the surface. © 2009 The American Physical Society.