Controlled Wrinkling Patterns in Periodic Thickness-Gradient Films on Polydimethylsiloxane Substrates

Area of Science:

• Materials Science
• Surface Engineering
• Thin Film Physics

Background:

• Surface wrinkling in film-substrate systems is crucial for science and engineering.
• Understanding wrinkling in heterogeneous systems with variable features remains challenging.

Purpose of the Study:

• To develop an unconventional strategy for preparing periodic thickness-gradient metal films on polydimethylsiloxane (PDMS) substrates.
• To investigate the modulation of surface wrinkles by copper grid structures and their position-dependence.

Main Methods:

• Utilized copper grids with orthometric copper wires as masks during sputtering to create periodic thickness gradients.
• Investigated spontaneous film formation and wrinkling phenomena during the sputtering process.
• Established a phase diagram correlating wrinkle morphology with mesh size and film thickness.

Main Results:

• Periodic thickness-gradient metal films spontaneously formed on PDMS substrates.
• Surface wrinkles were strongly modulated by copper grid structures and were position-dependent.
• A phase diagram showed evolution from labyrinth to herringbone to stripe wrinkling, and a wrinkling-free state with decreasing mesh size and/or increasing film thickness.

Conclusions:

• The study successfully prepared periodic thickness-gradient metal films using a novel masking technique.
• Copper grid structures significantly influence and control surface wrinkle morphology.
• The findings provide a framework for understanding and designing heterogeneous film wrinkling based on stress theory and numerical simulations.