Superhydrophobic Hierarchical Silicon Structures: Fabrication and Property Characterization

Surface structuring is one of the most effective strategies for achieving water-repellent and self-cleaning surface properties of silicon surface. Here, through a silver nanoparticle-assisted HF/HNO
₃
etching process, we create a series of hierarchical silicon surface structures consisting of (110)-(100)-(110) oriented zigzag nanowires engraved in pyramids. The morphology of the hierarchical structure exhibits a strong dependence on the HNO3 concentration, which renders the hierarchical structures tunable and allows us to analyze the formation mechanism of the structures. The optimized hierarchical structure exhibits excellent superhydrophobic property, achieving a contact angle (CA) of 158° and CA hysteresis (CAH) of 1.2° without any surface treatment. The morphology-superhydrophobicity relation is systematically studied, based on which a microscopic model is proposed to describe how CA and CAH are affected by water penetration depth in the hierarchical structures.