Graphene-coated holey metal films: Tunable molecular sensing by surface plasmon resonance

Abstract

† These authors contributed equally to this workWe report on the enhancement of surface plasmon resonances in a holey bidimensional grating of subwavelength size, drilled in a gold thin film coated by a graphene sheet. The enhancement originates from the coupling between charge carriers in graphene and gold surface plasmons. The main plasmon resonance peak is located around 1.5 µm. A lower constraint on the gold-induced doping concentration of graphene is specified and the interest of this architecture for molecular sensing is also highlighted. † These authors contributed equally to this work.PACS numbers: 78.67. Wj, 73.20.Mf, 42.79.Dj, 07.07.Df Plasmonic devices offer valuable platforms for a wide range of emerging molecular detection schemes. Among such applications, biosensors are very promising especially from the point of view of lab-on-a-chip (LOC) technologies. 1 Indeed, plasmon resonances are characterized by both a strong electric field and a great sensitivity to environmental conditions. As a consequence, adsorbed species can be detected through the resonance wavelength shift. In addition, the strong electric field enhancement allows for surface enhanced Raman spectroscopy, which can be used for single molecule detection. 2 Surface plasmons (SPs) require specific conditions to be excited. For instance, in the Kretschmann configuration, a light beam is totally internally reflected in a prism on which a metallic film is deposited and triggers the generation of SPs. 3 In a holey metal film, SPs can be excited by a normal incidence light beam. 4 Light is scattered due to the corrugations and the evanescent diffraction orders can excite SPs. 5 For a metallic layer accommodating an array of holes with subwavelength size, it is possible to probe SPs by simply measuring the intensity of the transmitted light. Such a simple configuration is much more practical in the LOC context and it has been widely studied since the pioneering work of Ebbesen et al. in 1998. 4 Recent theoretical works have shown that doping can induce SP modes in graphene. 6-8 Graphene, which appears as a monoatomic layer made of sp 2 carbon atoms in a hexagonal lattice configuration, presents a plethora of amazing properties. 9 In that context, SPs have been observed for graphene doped by charge transfer from metal thin films, 10-13 external atoms 14 or electrostatic gating 15,16 . It has been also suggested that SPs could be excited in graphene on a periodically structured * e-mail: michael.sarrazin@unamur.be substrate 17,18 or via regular patterns in graphene. [19][20][21][22][23][24][25] A recent experimental result showed that graphene SPs can be excited in a Kretschmann configuration using graphene deposited on a planar gold layer. 10 A different approach 26 was used in which SP resonance tunability was achieved by electromagnetic field coupling between a graphene sheet and SPs excited in gold nanoparticles.In the present work, we describe and study an opti-

Graphene–MoS2 hybrid nanostructures enhanced surface plasmon resonance biosensors

“…For instance, the charge carrier mobility of graphene is reported to be as high as 10 6 cm 2 V -1 s -1 [12]. Thus, when graphene layers are deposited on metallic thin films or functionalized with metallic nanoparticles (e.g., Au or Ag), strong coupling can be induced at the metallic/graphene interface due to the effective charge transfer and this generates a large electric field enhancement at the nanointerface [13][14][15][16][17][18]. The electric field excited on the metallic surface is an evanescent wave and is sensitive towards the refractive-index change of its surrounding media.…”

Plasmon dissipation in gapped graphene open systems at finite temperature

“…In order to tailor effectively the plasmon frequencies, graphene has been hybridized with prefabricated plasmonic nanoarrays and metamaterials [46][47][48] . Therefore, a thorough understanding of the dispersion and dissipation of plasmons in graphene interfacing with different kinds of substrates is necessary for designing innovative devices and their applications.…”

Probing Graphene χ(2) Using a Gold Photon Sieve

“…As shown hereafter, using a graphene-coated gold photon sieve enhances second harmonic (SH) conversion efficiency by up to two orders of magnitude, compared with bare flat gold, or, similarly, by up to an order of magnitude, compared with a bare gold photon sieve. This enhancement results from the propagation of surface plasmon polaritons (SPP) at the gold/graphene interface.Indeed, planar graphene in conjunction with metallic nanostructures enables localized electromagnetic hotspots to be created on the graphene sheet, thereby increasing light absorption by flat graphene above the classical value of 2.3% [16][17][18][19][20][21][22][23][24] . Moreover, it circumvents any momentum mismatch issues occurring with surface plasmon resonance (SPR) when the photon sieve SPP is excited from an optical illumination at normal incidence 4 .…”

“…A previous study details the fabrication method extensively 16 . The presence of defect-free single-layer graphene covering the sieve was verified by Raman spectroscopy (Figure 1c).…”

“…Here, the hybrid system is a photon sieve, i.e. a flat gold film, perforated according to a honeycomb nanohole pattern and coated with a graphene layer [12][13][14][15][16] . As shown hereafter, using a graphene-coated gold photon sieve enhances second harmonic (SH) conversion efficiency by up to two orders of magnitude, compared with bare flat gold, or, similarly, by up to an order of magnitude, compared with a bare gold photon sieve.…”