(above): A polymer (PDMS) film is heated, exposed to a oxygen plasma (which creates a silica-like crust), and then cooled. The crust is under stress as it cools and so it must pucker, creating a system of waves on the surface.
(above): Additional structures (5-microns-high, 30-micron-wide circles spaced 70 microns apart) on the PDMS surface help to order the smaller wave structures.
reported by: Bowden et al., in Applied Physics Letters, 25 October 1999.
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