Ring-shaped buckles in metal films induced by evaporation of micro-scaled silicone oil droplets

Abstract

We report on the spontaneous formation of ring-shaped buckles in cobalt films induced by evaporation of micro-scaled silicone oil droplets. Many small silicone oil droplets were generated on the glass substrate near a silicone oil reservoir during deposition. Due to the coffee ring effect, the silicone oil residue tends to gather at the droplet edges when the silicone oil evaporates, which results in the interfacial weakening and formation of ring-shaped buckles. The structural characteristics of the ring-shaped buckles have been investigated by atomic force microscopy, focused ion beam milling, numerical simulation and theoretic analysis. The maximum buckle height is found to increase approximately linearly with increasing the buckle width, but it is insensitive to the ring size. The structure characteristics of the ring-shaped buckles for small ratio of ring diameter to buckle width are also investigated by numerical simulation.