Silver macro-texture substrates fabricated by plasma selective etching for surface-enhanced Raman scattering

We have demonstrated a novel method to generate the nanostructured substrate that shows a large enhancement with a spatially uniform enhancement factor of approximately 106 in surface enhanced Raman scattering (SERS). The substrates are fabricated using plasma selective etching. First, the Al2O3TiC template which contains mixed Al2O3 and TiC grains with the diameters of similar to 400 nm is selected as a base plate. The Al2O3 and TiC grains have different physical properties, such as hardness, which corresponds to different etching rate in a plasma gas. Then, the Al2O3TiC substrate is selectively etched to generate a random macro-texture (MT) with different depths using the plasma of mixed gas of Ar and C2H4. Third, the MT substrate is deposited with a silver film (Ag). We further demonstrate that by varying the thickness of Ag layer, the EF is different which is confirmed by the plasmonic localized electric fields calculations using finite difference time domain. Finally, we combine this novel Ag MT substrate with ultrathin dielectric film, and the prepared substrates are coated with a 10 angstrom ta-C film. The 10 angstrom ta-C film can protect the oxygen-free Ag in air and prevent Ag ionizing in aqueous solutions. More importantly, the ultrathin ta-C can release the strongest plasmonic electric field to the outside of ta-C layer and get a higher electric field than the uncoated Ag substrate. We expect that this method has more potential applications in analytic assays using SERS technology. Copyright (c) 2012 John Wiley & Sons, Ltd.