Plasmonic coupling on dielectric nanowire core–metal sheath composites

Abstract

We have developed dielectric core/metal sheath nanowire (NW) composites for surface-enhanced Raman scattering (SERS), in which an electroless (EL) Ag plating approach was employed. The NW surface was uniformly covered with a high density of 3D silver islands, having a diameter in the 20-30 nm range and spaced less than approximately 10 nm apart. In comparison with the silver deposition via e-beam evaporation, the EL coating approach has the advantage of full metal coverage of the NWs. This approach also provides a fast and simple way to completely cover any nanostructures with Ag, including nanowires, regardless of the orientation or shape. SERS measurements were performed using benzene thiol and the SERS signal strength of the EL-coated NW composites was significantly greater than expected, since the surface plasmon resonance (SPR) of 20 nm Ag nanospheres is weak and in the UV, while our measurements were performed using a 514.5 nm laser line. However, we have modeled this system using our electric field calculations and the results indicate that the strong SERS signal is due to plasmonic coupling of neighboring closely spaced islands, as well as an enhanced substrate effect. In addition, the nanowire core serves as a template for the formation of these small, closely spaced Ag islands, resulting in the strong SERS signal.

Metal‐Dielectric‐CNT Nanowires for Femtomolar Chemical Detection by Surface Enhanced Raman Spectroscopy

“…Reports show that SERS performance could be augmented with increased roughness 18, 19. Compared to top‐down methods, bottom‐up non‐lithographic techniques such as nanowire array construction can provide even more increased roughness 20–23. Thus, herein proposed vertically aligned (VA) carbon nanotubes (CNTs) can offer an extremely dense and rough nanostructure as a viable template for the SERS substrate.…”

Femtomolar molecular detection with CNT based SERS substrate

“…[10,11] In this context, compared to top-down methods, bottom-up lithographyless fabrication techniques such as a nanowire array construction can provide much higher roughness, demonstrated by various nanowire-based SERS substrates. [12][13][14][15][16][17][18] It has also been reported that the crossings of separate nanowires (especially when they are in slight contact to one another) can result in great SERS enhancements. [19] In order to create a lot more nanowire junctions, each gold nanowire should become thinner.…”

Plasmonic Properties of Vertically Aligned Nanowire Arrays

“…In particular, NWs used for surface-enhanced Raman scattering (SERS) are of significant interest since SERS spectra can provide trace level detection and a chemical fingerprint by which a molecule can be identified. Several NWs types have been used to investigate the SERS effect, including silver NWs [6,7], gold NWs [8], semiconductor NWs [9], and dielectric NWs [10][11][12]. It has been demonstrated that the geometry of the nanowires and the orientation of the molecules play an important role in the SERS process [10][11][12][13][14].…”

“…Several NWs types have been used to investigate the SERS effect, including silver NWs [6,7], gold NWs [8], semiconductor NWs [9], and dielectric NWs [10][11][12]. It has been demonstrated that the geometry of the nanowires and the orientation of the molecules play an important role in the SERS process [10][11][12][13][14]. However, most of the reported NW structures were randomly distributed on a surface, where the largest SERS enhancements noted were in the NW crossing [10] and between the NW and the substrate [14].…”