Fabrication of optical hydrophobic metasurfaces resembling the surface structure of Peruvian lily flower petals

Abstract

Optical metasurfaces are inscribed in surface relief on azobenzene molecular glass thin films following double and triple sequential exposures to laser interference patterns with very close periodicities, resulting in two-fold and three-fold hierarchical Moiré gratings respectively. These metasurfaces formed due to the unique photomechanical effect in azobenzene materials, in which molecules migrate from zones of high to low laser irradiance. The laser interference patterns were obtained using a Lloyd mirror interferometer and a continuous wave laser having a wavelength of 532 nm and an irradiance of 200 mW/cm2. The resulting optical metasurfaces, which resembled surface features of a Peruvian lily flower petal, were characterized using atomic force microscopy, optical microscopy and surface profilometry techniques. It was found that the highly-customizable surface characteristics of the resulting metasurfaces can significantly alter their hydrophobicity.