Structural evolution and control of Dutcher films

We report on numerical simulations of late stage undulation growth in Dutcher films. Dutcher films are ultrathin trilayer films consisting of a fluid layer sandwiched in between two solid layers. The van der Waals forces acting across the film can result in the spontaneous formation of surface undulations and corrugations. The complex interplay between the van der Waals forces, the elastic deformation of the solid layers and the fluid dynamics of the sandwiched fluid essentially selects a wavelength of undulation which grows most rapidly. We show how the lateral deformations in the solid layers can be obtained from the elastic stretching free energy as a function of the height variations. Furthermore, these lateral deformations can be shown to contribute to a pressure normal to the film which influences the dynamics of fluctuation growth. By taking into consideration the large-amplitude elastic stretching effects we simulate the late stages of undulation growth including the contact between the upper and lower solid layers. As the area of contact between the solid layers increases the fluid is corralled into isolated pockets. Because our numerical model captures the full elasticity of the solid layers we show how internal forces can be incorporated into the system. As a demonstration, we simulate the effects of thermal mismatch between a small region of the film and the surrounding matrix and show how concentric grooves can be formed in Dutcher films.