Tunable localized surface plasmon resonances of asymmetricAu/SiO₂/Aucross-shape nanobars

Abstract

The plasmonic properties of asymmetric Au / SiO 2/ Au sandwiched cross-shape nanobars are investigated theoretically using the discrete dipole approximation (DDA) method. Two localized surface plasmon resonances are observed in the extinction spectra, which perform extreme sensitivity to the length and width of the nanobar and can be tuned easily throughout visible and into near-infrared spectral regions. The local electric fields around the nanobar are calculated and a pure electromagnetic Raman enhancement factor of about 106 can be achieved. In addition, compared to a monolayer gold nanobar, it exhibits more "hot spots" and stronger localized electric field enhancements. This plasmonic substrate provides potential applications in surface enhanced Raman scattering (SERS) and nonlinear optical devices.

Metal-dielectric-metal resonators with deep subwavelength dielectric layers increase the near-field SEIRA enhancement

“…In the M-D-M structure, the dielectric layer (Ag 2 O) effectively separates the two metallic silver layers in the vertical direction so that when the resonators are excited, two surface plasmon resonances are produced in the top and bottom layers creating a region of high E-field in the PMMA between the arcs of each ASRRs. In comparison with the fully metallic structure the plasmonic interaction between the two Ag layers in the M-D-M resonators amplifies the plasmonic excitation [29,31,33]. A similar enhancing effect was reported by measuring the SERS response of silver films sandwiching a thin silver-oxide layer, which peaked for 48 hours of air exposure between the two silver depositions [29].…”

“…For example, it was reported [29] that a very thin oxide layer sandwiched between silver films can increase the surface enhanced Raman scattering (SERS) signal up to 10 times with respect to bare silver films. Also, theoretical calculations predicted larger near-field enhancements for nanocrescents [30], bow ties [31], nanorods [32] and crossshaped nanobars [33] made by M-D-M structures with a silica core with respect to fully metallic structures of the same size. Similar single or multi-layered M-D-M structures such as fishnet [34], nanorods [35] and stacked plasmonic waveguides [36] have been known to exhibit negative refraction at optical frequencies.…”

“…The interference of the broader "bright" mode with the narrower "dark" mode [7,28] leads to Fano-shaped peaks that are sharper and have better Q than their symmetric counterparts because the dark-mode reduces the coupling with the free space and lowers the scattering losses [13,[25][26][27]. Another, less explored approach to increase the resonators sensitivity relies on metal-dielectric-metal (M-D-M) sandwich structures [29][30][31][32][33] as a mean to increase the plasmonic mode confinement and the enhancement in the near-field. For example, it was reported [29] that a very thin oxide layer sandwiched between silver films can increase the surface enhanced Raman scattering (SERS) signal up to 10 times with respect to bare silver films.…”