Modeling and characterizing thin film nanostructures for ultra-hydrophobic surfaces with controlled optical scatter

摘要

We have developed a novel approach to design ultra-hydrophobic surfaces with optical quality. The nanostructure necessary for the functional effect is realized through enhanced nanoroughness of optical thin films. At the same time, the optical appearance must not be disturbed by scattering from the roughness. We have found that through wide-scale roughness analysis, applying white light interferometry, AFM and STM, and subsequent data reduction the roughness characteristics can be directly related to the wetting properties. As, on the other hand, vector scattering theories connect the roughness properties with scatter losses, a formalism has been established, where both the wetting properties and scattering behavior can be expressed within the same "language". Using this tool, the optical thin film design and the surface nanoroughness can be tailored to fulfill demands on wetting properties as well as on sufficient low scatter levels. For the deposition of high index single layers on Borofloat 33 substrates, qualified substrate-fihn-combinations are predicted by "virtual" coating simulations. Experiments with single oxide layer as test coatings yielded surfaces with a high water contact angle and light scatter losses below defined scatter thresholds.