On the relation between morphology and elastic properties in amorphous columnar thin films

The optical, electromagnetic and mechanical properties of thin films (TFs) are directly correlated to their morphology at the nanoscale. This, in concert with the fact that new deposition techniques are enabling the growth of thin films with very complex morphologies, there is an increasing interest in model-based simulation (MBS) for the design of engineering structures (including nanostructures), and increasing computer speeds are beginning to make MBS an effective design tool capable of bridging the nanoscale with the continuum scale, has made it increasingly important to understand how the nanostructure of a thin film impacts its properties at all length scales. The authors have developed the capability to determine the mechanical properties of thin films with amorphous nanostructure by combining molecular dynamics, i.e., position of particles (e.g., atoms or molecules) and their interatomic potential(s), with continuum mechanics principles. This work concerns the application of this capability to determine mechanical properties, such as stability and distributions of elastic modules and residual stresses, to thin films grown via physical vapor deposition (PVD) under conditions in which the deposition angle of the incident species is not normal to the substrate. Deposition in this manner results in an amorphous thin film with a porous, columnar nanostructure, whose morphology depends primarily on the deposition angle. In this presentation, we will focus on the exploration of the relationship between the deposition angle in PVD and the resulting mechanical properties of the film for important species such as MgF2 and GaN. The films are created via molecular dynamics simulations using potentials available in the literature. The resulting mechanical properties are then obtained by an approach that bridges length scales from the discrete to the continuum. (author)