Tailoring the robust superhydrophobic silicon textures with stable photodetection properties.

Surface hydrophobicity of silicon with sound durability under mechanical abrasion is highly desirable for practical needs. However, the reported micro-pyramid/nanowires structures suffer from the saturation characteristics of contact angle at around 132 degree, which impede the promotions toward reaching the state of superhydrophobicity. The present study focuses on the realization of two-scale silicon hierarchical structures prepared with the facile, rapid and large-area capable chemical etching methods without the need of lithographic patterning. The designed structures, with the well combination of microscale inverted pyramids and nanowire arrays, dramatically lead to the increased wetting angle of 157.2 degree and contact-angle hysteresis of 9.4 degree. In addition, the robustness test reveals that these hierarchical textures possess the narrow contact-angle change of 4 degree responding to the varied pH values, and maintain a narrow deviation of 2 degree in wetting angle after experiencing the abrasion test. Moreover, the highly stable photodetection characteristics of such two-scale structures were identified, showing the reliable photocurrents with less than 3% of deviation under wide range of environmental humidity. By adopting a simple chemical treatment, the wetting control is demonstrated for reliable transition of superhydrophobicity and superhydrophilicity.