Transmittance modulation by gold nanoparticle mediated wet chemical etching of silica

Wet etching in hydrofluoric acid (HF) is one of the most common routes for the surface texturing of silica, leading to improved optical properties, which find applications in several fields. In this work, wet etching of silica is mediated by the deposition of chemically synthesized gold nanoparticles on the substrate. Nanoparticles of different sizes are coated on silica and act as a mask when etching using HF. The effect of parameters such as etching time, nanoparticle size, and HF concentration on the surface morphologies and transmittance are studied and correlated with the chemical etching mechanism. This work reveals that a proper choice of masking and etching conditions can reduce the optical transmission of silica. Etching leads to the formation of arrays of micron-size elongated pits. The pit width and surface roughness are found to increase with etching time and HF concentration, in turn leading to a decrease in transmittance. The results show that nanoparticle masking is an effective way to modulate silica etching and in turn, reduce the transmittance of the substrate.