Formation of dielectric core/metal sheath nanowire composites and their application to SERS sensing

There has been significant interest in a variety of nanowire (NW) systems for various sensing applications. We had developed highly sensitive dielectric core/metal sheath nanowires composites which serve as surface-enhanced Raman scattering (SERS) substrates. Previously, our composites were fabricated using e-beam deposition, which has the problem of incomplete coverage. Here we report an electroless (EL) plating approach to cover the NWs with a silver sheath, producing the core/metal NW structures for the SERS measurements. In comparison with the common silver deposition via e-beam evaporation, electroless coating can result in the full metal coverage on NWs. Therefore, this approach provides a way to fully cover nanostructures with Ag, including NWs arrays, regardless of the orientations and shapes of the nanostructures. SERS measurements on EL produced Ag/NWs composites show stronger signals than those produced by e-beam evaporation. Electric field calculations suggest that the strong SERS signal is due to plasmonic coupling of neighboring closely spaced islands.