Wetting behavior of silicon nanowires array fabricated by Metal-assisted chemical etching

A silicon (Si) substrate exhibits a hydrophobic surface (contact angle, CA similar to 90.2 degrees), and upon anodization, the porous Si (PSi) also possesses a hydrophobic surface (CA similar to 142.4 degrees). Silicon nanowires (SiNWs) array, also known as black silicon, exhibits lotus effect, i.e., water droplet role-over the surface without penetrating inside the surface. An array of SiNWs, fabricated by metal-assisted chemical etching (MACE) of Si, act as a superhydrophobic surface (i.e., CA > 150 degrees) without using any functionalization material. The MACE fabricates etched-Si, using PSi substrate that also possesses a superhydrophobic surface. Trapped air, present among the conical tips of the densely formed SiNWs array, reduces the solid-liquid contact area and improves the de-wetting behavior. The trapped air increases on increasing the length of SiNWs, which further enhances the de-wetting behavior. The wetting behavior changes to hydrophobic/hydrophilic when kept for a longer duration due to the aging effect. Oxidation causes aging and changes the conical/dendrite structure of the SiNWs/etched-Si surface. The Fourier transform infrared spectroscopy confirms the hydrogen passivation on the surfaces of SiNWs because of HF etching and highly oxidized surfaces due to the effect of aging. Copyright (C) 2022 Elsevier Ltd. All rights reserved.