Scalable Fabrication of Super-Liquid-Repellent Surfaces Enabled by Overhanging PTFE Nanospikes on Needle-Like Microstructures

We present a scalable strategy for fabricating super-liquid-repellent surfaces by depositing polytetrafluoroethylene (PTFE) onto black silicon (bSi) substrates. Needle-like microstructures were initially fabricated on a Si wafer via fluorine plasma etching using plasma-based ion implantation and deposition (PBII&D). Subsequent thermal evaporation of PTFE formed overhanging nanospikes on the needle-like microstructures of bSi, resulting in a composite solid-air interface characteristic of the Cassie-Baxter state. The engineered surfaces exhibited outstanding repellency to various liquids, including water (<i>θ</i>^<i>*</i> = 172°, <i>θ_roll-off</i> = 4°), diethylene glycol (<i>θ^*</i> = 168°, <i>θ_roll-off</i> = 4.4°), hexadecane, and commercial ink for large-format inkjet printing. To extend this functionality to diverse substrates, we employed a supplementary approach using Si-based amorphous films, such as a-C:H:Si:O films, deposited using hexamethyldisiloxane as a precursor gas. Needle-like microstructures were successfully replicated using a-C:H:Si:O films via plasma etching under conditions identical to those used for bSi substrates. PTFE deposition on these replicated structures achieved comparable liquid-repellent performance, demonstrating the feasibility of integrating hierarchical bSi-inspired morphologies on diverse materials. The combined use of scalable techniques, such as PBII&D and thermal evaporation, enables large-area fabrication of robust liquid-repellent surfaces for industrial applications.