  Simultaneous superhydrophobic and visible range antireflective properties are
demonstrated in hydrothermally grown ZnO nanorods on chemically textured Si
surfaces. A drastic transformation of Si micro pyramids from hydrophobic to
superhydrophobic is observed by securing the formation of polycrystalline ZnO
nanorods at surfaces, showing an increment of apparent contact angle from 102
degree to 157 degree and further explained in the light of a decrease in solid
fractional surface area, according to the Cassie Baxter model. Moreover,
wurtzite phase of ZnO NRs is confirmed by the X ray diffraction and Raman
analysis. Such hierarchical structures further exhibit a large visible range
antireflection, 5 percentage, and correlated it to the variation in aspect
ratio of Si pyramids in conjunction with the formation of graded refractive
index. The combined superhydrophobic and large antireflection phenomenon in the
present dual scale structures is believed to be useful for Si based
photovoltaic applications.
