Au NPs were synthesized by a seed-mediated method starting with HAuCl 4 .3H 2 O (99.99%, Alfa Aesar) and trisodium citrate (95%, Merck) as described in Thomas et al. thomas2022combined and Bastus et al. bastus2011kinetically. Silica substrates of size 1 × 1.5 cm 2 , with a thickness of 1.1 mm, were used as substrates for the etching experiments. 3-aminopropyl-trimethoxy silane (APTMS, 99%, sigma), ethanol (premium grade, Heyman), and de-ionized water (18.2 MΩ cm) were used for silanization of silica to help in the coating of the Au NPs. An aqueous solution of HF (48%, EMPARTA ACS) was used for etching the substrate. All chemicals were used as purchased. Both APTMS and Au NPs were coated using a dip-coater (Apex instruments, Xdip-SV1DH). The transmittance of the substrates were measured in a UV-VIS absorption spectrophotometer (Jasco, V-650). A high-resolution scanning electron microscope (Apreo S) was used for imaging the fabricated surface structures. The roughness of the etched substrates was measured using a profilometer (Bruker ContourGT).