Plasmonic photocatalysis and SERS sensing using ellipsometrically modeled Ag nanoisland substrates.

Silver nano-islands are key platforms for plasmonic photocatalysis, SERS sensing and optical metamaterials due to their localized surface plasmon resonances. The low intrinsic loss in Ag enables high local electromagnetic field enhancements. Solution-based fabrication techniques, while cheap and compatible with high throughput, result in highly non-reproducible plasmonic substrates with wide sample-to-sample variability in geometry, optical resonances and Q-factors. Herein, we present a non-lithographic method of forming silver nano-islands based on sputter deposition of Ag films followed by elevated temperature annealing to induce spontaneous dewetting. The resulting plasmonic substrates show reproducible, well-defined LSPR resonances with high ensemble Q-factors whose optical properties could be modeled using spectroscopic ellipsometry to yield n and k values across the visible range. Our vacuum deposited Ag nanoislands demonstrated excellent photocatalytic activity for the transformation of 4-nitrobenzenethiol (4-NBT) and 4-aminothiophenol (PATP) into p,p'-dimercaptoazobenzene (DMAB).