Hydrophobic nanostructures fabricated by ferric nitrate etching method on single crystalline silicon surface

Abstract

To improve the hydrophobicity of the surfaces of single crystalline silicon (sc-Si) wafers, hierarchical structures were fabricated on the surfaces of sc-Si wafers by using Fe(NO3)3/HF mixed solution as an etchant. Scanning electron microscope, atomic force microscope and water contact angle were used to characterize the etching of sc-Si wafers. It was found that after the etching process the surface micro/nano-structures having hemispherical etched pits with needle-like folds can be formed and the surface of sc-Si wafers possess hydrophobicity. The concentration of Fe(NO3)3, etching temperature and etching time have important impacts on surface morphology and surface hydrophobicity of the sc-Si. Results showed that the surface water contact angle of etched sc-Si wafers decreased with the increase of the concentration of Fe(NO3)3. The surface water contact angle of the sc-Si wafer treated with 0.2 M of Fe(NO3)3 is highest (124.37°) and increased by 145.89% compared to that of control sc-Si wafers due to the smallest surface roughness and the most smooth surface. Surface wettability of sc-Si wafers varied from hydrophobic to hydrophilic as the etching temperature increasing from 30 °C to 70 °C. When the etching temperature was 30 °C and 70 °C, the surface water contact angle of sc-Si wafer was 142.32° and 13.86°, respectively. With the increase of the etching time, rough grooves formed on the surface of sc-Si wafers and the roughness changed larger. Hydrophobic surfaces with a water contact angle up to 144.50° were obtained at etching time of 30 min.