Stable superhydrophobic si surface produced by using reactive ion etching process combined with hydrophobic coatings

A stable superhydrophobic and self-cleaning surface having a high contact angle (CA) greater than 153° was produced by using a reactive ion etching (RIE) process combined with hydrophobic coatings. It was found that the produced superhydrophobic and self-cleaning surface had a stable hierarchical structure similar to that observed on the surface of a lotus leaf. The single-crystalline silicon (Si) wafers were etched using a metal mesh in the RIE system. The CA on the etched Si surface decreases with increasing etching time, which agrees well with the dependence of the CA on the roughness factor predicted by Wenselʹs model. When the Si surface was coated with polytetrafluoroethylene (PTFE), it became hydrophobic. In particular, it was found that the Si etched for 20 min by the RIE process exhibited a superhydrophilic surface with a water CA lower than 30°, but when the PTFE was coated for over 3 min on the etched Si wafers, the Si surface could be transformed into a superhydrophobic surface (θ ≥ 153°) from a superhydrophilic surface (θ ≤ 3°). The root mean square (rms) roughness ranging from 0.25 μm to 0.4 μm.