Preparation of Hydrophobic Porous Silicon by Metal-Assisted Etching with Pd-Catalyst

Abstract

The process of the porous silicon layer formation by metal-assisted etching of single-crystal Si with the resistivity of ρ = 0.01 Ω cm, coated with thin Pd-film up to 100 nm thick, in HF/H₂O₂/H₂O solution is studied. The porous silicon is studied by scanning electron microscopy and gravimetric analysis. The dependence of the silicon dissolution rate on the HF concentration, in the presence and in the absence of the Pd-film, is investigated. The anodic current facilitating the Si dissolution in the HF solutions of different concentration is studied. By using sessile drop method, the porous silicon formed by the Pd-assisted anodic etching was shown to be superhydrophobic. The porous Si wetting angle reached 172°. The free surface energy for the porous layers and the water surface tension at the porous Si are calculated. The modified Si-surfaces may found their possible use in robotics.