Grain growth in thin films – When the third dimension matters

The tendency for lowering Gibbs free energy drives the complex three-dimensional process of grain boundary motion. The evolution of the grain structure is governed by the interplay between the preservation of the local balance in the grain boundary network with respect to, for example, dihedral angles along triple lines, and the overall volume conservation. Grain growth has traditionally been studied primarily in two dimensions. Experimental analyses of two-dimensional sections have been conducted, and corresponding numerical simulations in two dimensions have been performed. Such two-dimensional simulations have persisted for thin films up until recently. We demonstrate that the three-dimensional grain boundary motion in thin films cannot be modeled by two-dimensional considerations. In order to achieve that goal, we discuss the evolution of a three-dimensional grain structure in a highly textured thin film with one particularly large grain added. The migration of its boundary depends strongly on both, the location of the particular grain and the morphology of the matrix grains. Such a dependence can indeed only be captured in three dimensions.