Complete Optical Absorption in Periodically Patterned Graphene

Abstract

We demonstrate that 100% light absorption can take place in a single patterned sheet of doped graphene. General analysis shows that a planar array of small particles with losses exhibits full absorption under critical-coupling conditions provided the cross section of each individual particle is comparable to the area of the lattice unit cell. Specifically, arrays of doped graphene nanodisks display full absorption when supported on a substrate under total internal reflection and also when lying on a dielectric layer coating a metal. Our results are relevant for infrared light detectors and sources, which can be made tunable via electrostatic doping of graphene. DOI: 10.1103/PhysRevLett.108.047401 PACS numbers: 78.67.Wj, 42.25.Bs, 78.20.Ci Light absorption plays a central role in optical detectors and photovoltaics. Inspired by nature, two different routes have been investigated to achieve perfect absorption. (i) A first one consists in relying on diffusion in disordered lossy surfaces (e.g., black silver and carbon). Engineered materials have been synthesized following this solution to produce extraordinary broadband light absorption (e.g., dense arrays of carbon nanotubes [1]). (ii) A second approach consists in using ordered periodic structures, as found in some nocturnal insects, where they produce the moth eye effect [2]. This alternative has been pioneered by experimental and theoretical work showing total light absorption (TLA) in the visible using metallic gratings [3][4][5]. In this context, the Salisbury screen [6,7], consisting of a thin absorbing layer placed above a reflecting surface, has been known to produce TLA, and it can be integrated in thin structures using magnetic-mirror metamaterials [8]. Similar phenomena have been reported at infrared (IR) [9][10][11] and microwave [12,13] frequencies, including omnidirectional TLA [14], which has been realized by using periodic surfaces supporting localized plasmon excitations.The availability of high-quality graphene as a stable material with extraordinary (opto)electronic properties [15-17] makes a compelling case for exploring its ability to harvest light for potential application to optoelectronics, with the advantage of being optically tunable via electrostatic doping [18]. However, a single sheet of homogeneous graphene is poorly absorbing [19] (about 2.3% absorption), so the challenge is to transform it into a perfect absorber, for which we can rely on its power to host extremely confined plasmons [20,21].In this Letter, we show that a single sheet of doped graphene, patterned into a periodic array of nanodisks, exhibits 100% light absorption. We first discuss the extinction cross section of graphene disks (i.e., the sum of light absorption and elastic scattering), which can exceed by over an order of magnitude their geometrical area [21]. These disks therefore belong to the class of absorbing particles that can be arranged in periodic planar arrays such that their cross section exceeds the area of the unit cell. We further assume here that a...

Electronic modulation of infrared radiation in graphene plasmonic resonators

“…By choosing a dielectric that can withstand higher temperatures, such as SiO 2 or diamond-like carbon, devices displaying larger power modulation could be fabricated. Finally, devices fabricated with higher mobility graphene, less edge roughness and with circular resonator geometries (that is, non-polarized) have been predicted theoretically 31 to exhibit tunable absorptivity/ emissivity that can vary from 0 to 1 (that is, zero to total absorption) within a narrow frequency range. Such devices would display changes in absorbtivity that equal or exceed those provided by electrochromic devices 40 , while also providing potential for more operation cycles, and higher temperature and higher speeds of operation.…”

Graphene as a Tunable Anisotropic or Isotropic Plasmonic Metasurface

“…29 Alternatively, other works have shown coupling through relief corrugations or subwavelength gratings on which graphene is placed, [30][31][32][33][34] as well as patterned graphene structures including 1D arrays of micro-ribbons 13,35 and 2D arrangements of islands. 25,[36][37][38] In order to achieve a periodic doping in the graphene, the sheet can be biased with the spatially periodic electrostatic field generated by a periodically corrugated plane, either metallic or dielectric (see Fig. S2 in the SM).…”

“…Ref. 25. In addition, and in order to show that our results are general and our fundamental conclusions do not depend on the particular choice of parameters for graphene, we present results for graphene with α = 76 GHz/Ω and γ = 9.8 THz (µ = 0.65 eV, m = 1.6 × 10 3 cm 2 /V s and τ = 0.1 ps) in the SM, taken from experimental data 26 and used in Ref.…”

Plasmonics in atomically thin materials

“…This is the so-called Salisbury screen configuration, in which the film/metal-screen separation should be roughly λ/4n [85,86] (i.e., a phase of π is produced by the metallic reflection and another π contribution comes from phase associated with the round trip propagation between the film and the screen, assumed to be embedded in an environment of refractive index n). These ideas have been recently explored for graphene, leading to the prediction of complete optical absorption by a suitably patterned carbon layer [87,88], under the condition that the extinction cross-section per unit cell element is of the order of the unit cell area. The observation of electrically tunable large absorbance in patterned graphene has been recently accomplished [89,90].…”