Solution processed nanomanufacturing of SERS substrates with random Ag nanoholes exhibiting uniformly high enhancement factors†
Achieving high Raman enhancement (SERS) that is relatively uniform over a large substrate area has been a major challenge in nanomanufacturing, as enhancement is localized around a plasmonic hotspot and hotspots are not usually spread uniformly over a substrate. Herein, we demonstrate a single-step, scalable method for the fabrication of Ag nanohole-based SERS substrates exhibiting ∼108 enhancement factors. The SERS enhancement of these substrates could be further augmented by approximately 4 times through interference effects involving an underlying SiO2 spacer of controlled thickness on the Si substrate, in agreement with FDTD simulations. Electrical activation by applying a short DC pulse across the Ag film and Si substrate resulted in ∼12% additional increase in the enhancement factor, while importantly the standard deviation of the signal across the 1 cm2 substrate decreased from 9.5% to 3.1%. Both these effects could be attributed to electromigration of the metal producing protrusions on the nanoparticle surfaces thus populating with the hotspots for high performance SERS. These relatively uniform and reproducible SERS-chips with high enhancement factors can potentially be used as highly sensitive multi-functional platforms for point-of-care diagnostics.