Improved SERS Intensity from Silver Coated Black Silicon by Tuning Surface Plasmons

An economical method of fabricating large-area (up to a 100-mm wafer) silver (Ag)-coated black silicon (BS) substrates is demonstrated by cryogenic deep reactive ion etching with inductively coupled plasma. This method enables a simple adjustment of the spike structure (e.g., height, width, sidewall slope and density of the spikes) on the silicon substrate, which thus offers the advantages of accurate tuning the density and amplitude of the localized surface plasmons after Ag coating. Using this method, an enhancement factor of 10⁹ is achieved for the probe molecule of rhodamine 6G (around two orders of magnitude higher than previous results based on Ag-coated BS) in surface-enhanced Raman scattering (SERS) measurement. The presented results pave the way to make Ag-coated BS substrates as economic and large-area platforms for diverse surface plasmon related applications (such as SERS and surface plasmon based biosensors).