A numerical study on the effect of mobilities and initial profile in thin film morphology evolution

This paper presents a numerical method for simulating the morphology evolution of elastically stressed thin film due to surface diffusion and evaporation/condensation. Elastic stress field is solved by using boundary element method and morphology evolution is simulated by using an integral formulation, which does not require the calculation of surface curvature and has weaker requirement on the smoothness of surface than the formulation based on differential equations. As a model problem, surface morphology evolution of a stressed thin film is simulated to explore the similarity and difference between the surface grooves induced by surface diffusion and evaporation/condensation, the effect of the mobility ratio of two processes when they are concurrent, and the dependence of surface kinetic pathway on its initial profile. It is found that the grooves induced by surface diffusion and evaporation/condensation have different surface features: when two processes are concurrent but surface diffusion process is dominant, increasing the mobility of evaporation/condensation increases the time and groove depth needed to form surface cusps; an initially cracked surface could approach a flat surface first, then after a long slowly evolving period, it gradually develops sharp tips on the surface again. Simulations show that excessive surface area, due to small cracks, notches or other surface defects, could significantly delay the development of surface instability.