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 x 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. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)