Anisotropic, hierarchical surface patterns via surface wrinkling of nanopatterned polymer films.

By combining surface wrinkling and nanopatterned polymer films, we create anisotropic, hierarchical surfaces whose larger length-scale (wrinkling wavelength) depends intimately on the geometry and orientation of the smaller length-scale (nanopattern). We systematically vary the pattern pitch, pattern height, and residual layer thickness to ascertain the dependence of the wrinkling wavelength on the nanopattern geometry. We apply a composite mechanics model to gain a quantitative understanding of the relationship between the geometric parameters and the anisotropy in wrinkling wavelength. Additionally, these results shed light on the effect of surface roughness, as represented by the nanopattern, on the metrology of thin films via surface wrinkling.