Enhancing LSPR Sensitivity of Au Gratings through Graphene Coupling to Au Film

Abstract

A particular interesting plasmonic system is that of metallic nanostructures interacting with metal films. As the LSPR behavior of gold nanostructures (Au NPs) on the top of a gold thin film is exquisitely sensitive to the spacer distance of the film-Au NPs, we investigate in the present work the influence of a few-layered graphene spacer on the LSPR behavior of the NPs. The idea is to evidence the role of few-layered graphene as one of the thinnest possible spacer. We first show that the coupling to the Au film induces a strong lowering at around 507nm and sharpening of the main LSPR of the Au NPs. Moreover, a blue shift in the main LSP resonance of about 13 nm is observed in the presence of a few-layered graphene spacer when compared to the case where gold nanostructures are directly linked to a gold thin film. Numerical simulations suggest that this LSP mode is dipolar and that the hot spots of the electric field are pushed to the top corners of the NPs, which makes it very sensitive to surrounding medium optical index changes and thus appealing for sensing applications. A figure of merit (FoM) of such a system (gold/graphene/ Au NPs) is 2.8, as compared to 2.1 for gold/Au NPs either a 33% sensitivity gain and opens up new sensing strategies.The phenomenon of localized surface plasmon resonance (LSPR) has been extensively studied over the last decade (Mayer and H. Hafner, 2011, Szunerits andBoukherroub, 2012). Because of intense local electrical field enhancements and sharp resonance excitation peaks, metallic nanoparticles are of great interest for the development of chemical and biological sensors as well as their use as signal enhancers in surface-based spectroscopies (Haes and Van Duyne, 2002, Xu et al., 2012b). A particular interesting plasmonic system that has received somewhat less attention is that of metallic nanostructures interacting with metal films (He et al.,

Coupling between plasmonic films and nanostructures: from basics to applications

“…Wang et al, confirmed these results by focusing -both numerically and experimentally -on SERS gap modes when molecules are located in-between au NP dimmers and Au film [60]. As for LSP biosensors, T. Maurer and coworkers evidenced a FoM (figure of merit) as high as 2.8 for Au NP gratings -Au film systems coupled via a trilayer graphene spacer [61,62] exhibiting LSP at about 520 nm which ranks such LSP sensors among the more sensitive for those whose localized surface plasmon resonance is in the visible range [63]. Indeed, most of the interfaces with high FoM (4-16.5) [16,63,64] take advantage of the fact that higher sensitivities are achieved with plasmon bands in the near-infrared of the spectrum (850-1200 nm).…”

Plasmonic mode interferences and Fano resonances in Metal-Insulator- Metal nanostructured interface

“…Metal NPs/metal film were introduced as super absorbers 26 , optical absorbers using gap plasmon resonators 27 , and controlled reflectance surfaces through gap modes 28 . In addition, several groups have investigated the limit where the spacer layer is subnanometer with trilayer graphene 29 or even absent 20 , and revealed a plasmonic mode around 520 nm almost independent on the NP’s diameter or the grating periodicity, showing high potential for sensing applications with a figure of merit (FOM) ranging from 2 to 2.9.…”

Polarization Enhanced Charge Transfer: Dual-Band GaN-Based Plasmonic Photodetector

“…The presence of Au NPs increases reflectance in the visible region due to enhanced backward scattering by Au NPs. The broad peaks in green light region can be attributed to the dipole mode of LSPRs of Au NPs25. The LSPR peak for Au500C is more pronounced due to higher scattering efficiency of larger Au NPs26.…”