Wrinkle patterns of Fe films deposited on micro-scale silicone oil droplets

• Fe films were deposited on micro-scale silicone oil droplets by sputtering method.
• Wrinkle patterns form on smaller droplets while cracks form on larger droplets.
• Straight wrinkles form near droplet edge and labyrinths appear in the center.
• Wrinkle wavelength increases linearly with film thickness and droplet radius.
• Finite oil layer thickness has a significant influence on the wrinkle wavelength.

Continuous iron films that are deposited on silicone oil droplets with finite sizes and thicknesses by direct current magnetron sputtering and the ordered wrinkle patterns that resulted from thermal stress are investigated. Due to the edge effect, straight strip wrinkles form near the droplet edges, while disordered labyrinth wrinkles appear in the center regions of the droplets. When the distance from the droplet edge increases, the average wavelength of the wrinkles increases quickly first, and then it slows down gradually and finally reaches a saturation value. The saturation wavelength increases approximately linearly with increasing the droplet radius. Based on the geometrical characteristic of the silicone oil droplet, the evolution behaviors of the wrinkle wavelengths are discussed in the frame of stress theory.