Ultrathin diamond-like carbon film coated silver nanoparticles-based substrates for surface-enhanced Raman spectroscopy.

We have demonstrated that by coating with a thin dielectric layer of tetrahedral amorphous carbon (ta-C), a biocompatible and optical transparent material in the visible range, the Ag nanoparticle-based substrate becomes extremely suitable for surface-enhanced Raman spectroscopy (SERS). Our measurements show that a 10 A or thicker ta-C layer becomes efficient to protect the oxygen-free Ag in air and prevent Ag ionizing in aqueous solutions. Furthermore, the Ag nanoparticles substrate coated with a 10 A ta-C film shows a higher enhancement of Raman signals than the uncoated substrate. These observations are further supported by our numerical simulations. We suggest that biomolecule detections in analytic assays could be easily realized using ta-C-coated Ag-based substrate for SERS especially in the visible range. The coated substrate also has higher mechanical stability, chemical inertness, and technological compliance, and may be useful, for example, to enhance TiO(2) photocatalysis and solar-cell efficiency by the surface plasmons.