Coupling of Epsilon-Near-Zero Mode to Gap Plasmon Mode for Flat-Top Wideband Perfect Light Absorption

Abstract

Epsilon-near-zero (ENZ) materials, when probed at or near wavelengths corresponding to their zero permittivity crossing points, have unique and interesting properties that can be exploited for enhancing nanoscale light−matter interactions. Here, we experimentally show that over an order of magnitude increase in the absorption band of a periodically patterned metal− dielectric−metal structure can be obtained by integrating an indium tin oxide (ITO) subwavelength nanolayer into the insulating dielectric gap region. Through incorporation of a 12 nm thick ITO layer between the patterned gold nanodisks and the SiO 2 dielectric layer, a 240 nm wide, flat-top perfect (>98%) absorption centered at 1550 nm wavelength is enabled. The demonstrated wideband, perfect absorption resonance is shown to be due to coupling between the gap plasmon mode of the metasurface and the ENZ mode in the nanoscale ITO film.

Viscoelastic optical nonlocality of low-loss epsilon-near-zero nanofilms

“…The result is the enhancement of the normal electric-field component inside the film and the formation of an absorption peak in the spectrum 31 . Recently, a growing number of applications have been identified for ENZ materials, including structural color formation by metallic-network ENZ metamaterials 32 , enhanced absorption in thin-film photovoltaics 33 , record-efficient plasmonic photocatalysis for hydrogen production 34 , thermal radiation engineering 35 , and broadband perfect absorption in gap-plasmon metasurfaces 36 . So far, these phenomena have been discussed within the local approximation of the film’s dielectric constant, in which the relative permittivity depends only on the frequency, i.e., ε L (ω)= ε ′( ω ) + iε ′′( ω ).…”

Active metamaterial nearly perfect light absorbers: a review [Invited]

“…The right figure in this panel shows a SEM image of the MPA. In panel (b), an Au/SiO 2 /TiN MIM MPA is shown in which a thin film of ITO is implemented for broadening the absorption bandwidth of the MPA and can also be used for tuning purposes [134]. In (c) the schematic and SEM images of an AZO-based metamaterial are presented [135].…”

“…Moreover, it has been recently shown that [schematic depicted in Fig. 2(b)] by encapsulating a thin film of ITO between the top patterned layer and the bottom reflector in an MIM metamaterial absorber, it is possible to tunably broaden the absorption bandwidth of the metamaterial around 1.5 μm [134]. The physics behind this broadness is due to the coupling of the epsilon-near-zero mode to the gap plasmon mode supported by the metamaterial.…”

Tunable Electro- and All-Optical Switch Based on Epsilon-Near-Zero Metasurface

“…Recently, a novel class of materials with zero or near-zero permittivity at one or multiple wavelengths, known as epsilon-near-zero (ENZ) material, has become a research focus in photonics [10]- [13]. It has been reported that ENZ materials exhibit many extraordinary optical properties, including tunneling effects [14], transmission with constant phase [15], field enhancement [16], strong coupling phenomena [17] and large nonlinear responses [18], [19], etc. The ENZ material can be obtained in natural semiconductors or artificial metamaterials.…”