Enhanced Light–Matter Interactions in Graphene-Covered Gold Nanovoid Arrays

Abstract

The combination of graphene with noble-metal nanostructures is currently being explored for strong light-graphene interaction enhanced by plasmons. We introduce a novel hybrid graphene-metal system for studying light-matter interactions with gold-void nanostructures exhibiting resonances in the visible range. Strong coupling of graphene layers to the plasmon * To whom correspondence should be addressed † DTU Fotonik ‡ CNG ¶ Fudan University § DTU Nanotech CINF 1 modes of the nanovoid arrays results in significant frequency shifts of the underlying plasmon resonances, enabling more than 30% absolute light absorption in a single layer of graphene and up to 700-fold enhancement of the Raman response of the graphene. These new perspectives enable us to verify the presence of graphene on gold-void arrays and the enhancement even allows us to accurately quantify the number of layers. Experimental observations are further supported by numerical simulations and perturbation-theory analysis. The graphene gold-void platform is beneficial for sensing of molecules and placing R6G dye molecules on top of the graphene, we observe a strong enhancement of the R6G Raman fingerprints. These results pave the way toward advanced substrates for surface-enhanced Raman scattering (SERS) with potential for unambiguous single-molecule detection on the atomically well-defined layer of graphene.Graphene is an atomic monolayer formed by carbon hexagons, whose extraordinary electrical and optical properties have led to a range of promising optoelectronic devices, 1-3 such as photodetectors, 4 optical modulators, 5 and ultra-fast lasers. 6 However, all such devices suffer from the inherently weak interaction between pristine graphene and light (2.3% light absorption at normal incidence), therefore imposing substantial challenges and restrictions for many electro-optical and all-optical applications. 7,8 Doped graphene nanostructures which support surface plasmons in the teraherz and infrared regions offer an exciting route to increase the light-graphene interaction by confining the optical fields below the diffraction limit. 9-13 However, graphene is less attractive when the interband loss becomes large, and it effectively mimics a dielectric material in the visible and near-infrared frequencies. 14 One alternative way to enhance the light-graphene interaction in short wavelengths is the combination of graphene with conventional plasmonic nanostructures based on noble metals. 15 These graphene-plasmonic hybrid structures could be beneficial for both fields of investigation: first of all, graphene can influence the optical response of plasmonic structures leading to graphene-based tunable plasmonics, 16 and in turn, plasmonic nanostructures can dramatically enhance the local electric field, leading to strong light absorption and Raman signature of graphene layers.In this Letter, a novel platform based on graphene-covered gold nanovoid arrays (GNVAs) is 2 proposed to enhance the light-matter interaction in graphene-plasmonic hybrid str...

Graphene-plasmon polaritons: From fundamental properties to potential applications

“…In particular, interband and intraband transitions under optical excitation in graphene have been investigated. In the visible and nearinfrared ranges, interband transitions result in a constant absorption of ∼2.3% by single-layer graphene at normal incidence and modulation of infrared absorption by electrically tuning its Fermi level; the absorption can be further improved by applying graphene in designed optical cavities [32,110]. In the infrared and THz ranges, intraband transitions dominate, resulting in an optical conductivity well described by the Drude model [39].…”

Plasmon-driven reaction controlled by the number of graphene layers and localized surface plasmon distribution during optical excitation

“…In a graphene-mediated SERS (G-SERS) substrate [13][14][15][16][17][18] ; the monolayer graphene (1G) provides an atomically flat surface for Raman enhancement. Because the graphene surface is chemically inert, signals from G-SERS substrates have great advantages over normal SERS by providing cleaner vibrational information free from various metal-molecule interactions (molecules cannot interact with the chemically active metal by graphene-mediated interactions) and being more stable against photo-induced damage 13 .…”

Plasmons in metallic monolayer and bilayer transition metal dichalcogenides

“…We mention that the efficient coupling of 2D plasmons and light generally requires some kind of scattering of the light to overcome the momentum mismatch. 18 First-principles calculations of the q = 0 loss spectrum of several single-and bilayer TMDCs was recently reported in Ref. 19.…”