Solid-State Dewetting And Sublimation: A Phase Field Study Of The Competition Between Surface And Bulk Diffusion

We address the interplay between bulk/surface diffusion with applications to thin film dewetting and nanoparticle redistribution. Thereto, we build a multi-species phase field model tracking structural order and material density separately. The density field, representative of vacancy/interstitial (Frenkel) defects, allows a description of internal thermodynamics. This philosophy is a departure from conventional treatments within phase field models and provides a physical motivation of the order parameter and subsequent form of the mass mobility that differentiates bulk and surface diffusion. Subsequently, we illustrate the sublimation of a pure solid, comparing shrink rates against analytic theory when different diffusion modes are considered. Separately, we include substrate interactions and simplify the theory to a single component in the limit of an inactive substrate. We discuss shifts in the bulk thermodynamics near the substrate in the context of equilibrium contact angles. We believe such a model provides a quantitative means to explore the synthesis and degradation process of nano-catalysts and other thin film systems in future applications.