Nano-Scale Topographic Control of Polymer Surfaces via Buckling Instabilities

We have used a plasma-mediated cross-linking process to generate the patterns on polydimethylsiloxane (PDMS) thin film surfaces. Exposure to an argon plasma leads to the formation of a siloxane network in the near-surface region. The silica-like surface layer is put into compressive stress when the sample cools after removing it from the plasma chamber due to differential thermal contraction, leading to a buckling instability to reduce the stress. The resulting surface waves exhibit wavelengths and amplitudes down to ~ 700 nm and 10 nm respectively. The wavelength and amplitude are controlled by modifying the plasma exposure time and the initial PDMS film thickness. Atomic force microscopy is used to study the topography as a function of these parameters. Comparison to a recent model of the buckling of compressively stressed films on viscous substrates is presented, where we observe consistent qualitative agreement with the model.