Harnessing surface wrinkling in film-substrate system by precisely controlling substrate modulus

Highlights: •Substrate elasticity was tuned by mixture of gel into polydimethylsiloxane. •Wrinkling spontaneously formed by deposition of metal films on soft substrates. •Two classes of wrinkling patterns with different features were observed. •Formation and evolution of wrinkling were discussed based on stress theory. -- Abstract: Wrinkled surfaces with controlled morphologies and sizes are quite useful for a wide range of applications including electronics, optics, bionics and metrology. Here we report on the controllable formation of surface wrinkling in metal films deposited on compliant substrates by precisely controlling substrate modulus. The wrinkling patterns are categorized as two classes of distinct features: G1 and G2 wrinkling. The G1 wrinkling emerges on very soft surfaces, originating from the surface instability of soft substrate during sputtering. The G2 wrinkling emerges on relatively stiff surfaces, originating from the thermal compression of film-substrate system after deposition. The size of G1 wrinkling decreases with increasing the substrate stiffness but is insensitive to the film thickness. The size of G2 wrinkling increases with increasing the film thickness or decreasing the substrate stiffness. The formation mechanisms and evolutional behaviors of the wrinkling patterns have been analyzed based on the stress model. The hydrophobicity of the wrinkled surfaces is also presented in this work.