Multifunctional Silicon Surfaces with Enhanced Mechanical Resistance

Structuring silicon (Si) surfaces at the micro‐ and nanoscale is an effective strategy to achieve broadband antireflective behavior, essential for photonic and energy applications. Herein, scalable and low‐cost fabrication techniques including self‐assembly, metal dewetting, and nonchlorine dry etching are used to produce micro‐ and nanostructured Si surfaces with enhanced antireflective properties. Total reflectivity is reduced to below 4% for microstructures and down to 2% for nanostructures, resulting in a pronounced black silicon effect. These optical improvements are validated by finite‐difference time‐domain simulations, which closely match the experimental results. Despite the improved optical performance, surface structuring leads to increased fragility. To address this, a 200 nm conformal Al₂O₃ coating is applied via atomic layer deposition. Nanoscratch testing reveals significant mechanical reinforcement: critical load values tripled for microstructured surfaces and quadrupled for nanostructures. Notably, embedding the nanostructures beneath the coating preserves the low reflectivity while further enhancing durability. This multifunctional design approach enables the fabrication of surfaces that are both optically efficient and mechanically robust. Moreover, the fabrication techniques are compatible with large‐area processing, offering a promising pathway for industrial‐scale applications in advanced optical and energy systems.