Preparation of Hydrophobic/Superhydrophobic Surface on Silicon Wafer by Reactive Ion Etching and Self-assembled Monolayers

Micro scale pillar arrays on silicon(100) wafer were generated by reactive ion etching. Three self-assembled monolayers(SAMs) were prepared on etched silicon wafer by self-assembled technique. The results show that four micro pillar arrays generated by reactive ion etching possess regular structures with diameter of 5 mu m, height of 10 mu m and spacing of 15-45 mu m. The water contact angles of silicon wafers increase significantly after SAMs deposition, in which maximum contact angle is abtained for 1H,1H,2H,2H-perfluorodecyltrichlorosilane(FDTS) deposition, medium for 1H,1H,2H,2H-perfluorooctyltrichlorosilane(FOTS) deposition and minimum for octadecyltrichlorosilane(ups) deposition. The measured contact angles larger than 150 degrees are close to the contact angles calculated with Cassei model. However, the measured contact angles less than 150 degrees approach the contact angles calculated with Wenzel model. Contact angles can be controlled by adjusting spacing of pillar array and choosing different SAMs. Atomic force microscope(AFM) measurement show that nano scale clusters on silicon wafers appear after SAMs deposition. Maximum contact angle of 156.0 degrees can be acquired in surface structure with micro pillar array and nano scale SAMs.