Surface‐enhanced Raman scattering sensing on black silicon

Reactive ion etching was used to fabricate black‐Si over the entire surface area of 4‐inch Si wafers. After 20 min of the plasma treatment, surface reflection well below 2% was achieved over the 300–1000 nm spectral range. The spikes of the black‐Si substrates were coated by gold, resulting in an island film for surface‐enhanced Raman scattering (SERS) sensing. A detection limit of 1 × 10^?6 M (at count rate > 10² s^?1 . mW^?1) was achieved for rhodamine 6G in aqueous solution when drop cast onto a ～ 100‐nm‐thick Au coating. The sensitivity increases for thicker coatings. A mixed mobile‐on‐immobile platform for SERS sensing is introduced by using dog‐bone Au nanoparticles on the Au/black‐Si substrate. The SERS intensity shows a non‐linear dependence on the solid angle (numerical aperture of excitation/collection optics) for a thick gold coating that exhibits a 10 times higher enhancement. This shows promise for augmented sensitivity in SERS applications.