Midinfrared Surface Waves on a High Aspect Ratio Nanotrench Platform

Abstract

Optical surface waves, highly localized modes bound to the surface of media, enable manipulation of light at nanoscale, thus impacting a wide range of areas in nanoscience. By applying metamaterials, artificially designed optical materials, as contacting media at the interface, we can significantly ameliorate surface wave propagation and even generate new types of waves. Here, we demonstrate that high aspect ratio (1 to 20) grating structures with plasmonic lamellas in deep nanoscale trenches, whose pitch is 1/10 -1/35 of a wavelength, function as a versatile platform supporting both surface and volume infrared waves. The surface waves exhibit a unique combination of properties, such as directionality, broadband existence (from 4 µm to at least 14 μm and beyond) and high localization, making them an attractive tool for effective control of light in an extended range of infrared frequencies. Main text 2Optical surface waves (SWs) arise at the interface of two dissimilar media with different types of permittivity or permeability 1 . Research on SWs has intensified in the last decade due to their unique properties of surface sensitivity, field localization, unusual dispersion and polarization properties at the nanoscale, stimulating the development of surface photonics 2 . The most studied SWs are surface plasmon-polaritons supported at the interfaces between metals and dielectrics 3 , which enable effective nanophotonic devices for sensing 4 , nano-guiding 5 , and imaging 6 based on near-field techniques. A newly emerging alternative is Dyakonov surface waves existing at the interfaces between anisotropic and isotropic dielectrics 7-10 . Up to present, various types of SWs have mostly been investigated individually. However, we can obtain new features by combining traits from various types of surface waves. This is where metamaterials, an artificially engineered materials and structures 11-13 , can play an essential role because in order to combine different SWs unprecedented and extreme optical parameters are often required. One example of such combined SWs on metamaterial structures are Dyakonov plasmons (DPs) 14,15 , a combination of surface plasmons and Dyakonov waves supported at the boundaries of hyperbolic metamaterials (HMMs) 16 . The diagonal components of the HMMs' permittivity tensors are of different signs, giving rise to hyperbolic iso-frequency contours in the k (wavevector) space accompanied by singularities in the density of optical states in an ideal lossless case. Natural material equivalents of HMMs are often referred to as indefinite media 17,18 . Characteristically, HMMs and their two-dimensional analogues of metasurfaces possess a unique combination of properties including unusually high wavevectors, optical density of states, and anisotropy. These feature lead to a wide variety of HMM potential applications such as broadband enhancement in the spontaneous emission for a single photon source 19,20 , sub-wavelength imaging 21 , sensing 22,23 , thermal engineering 19,20,24 , and steering of opti...

High Aspect Ratio Plasmonic Nanotrench Structures with Large Active Surface Area for Label-Free Mid-Infrared Molecular Absorption Sensing

“…Theoretically our AZO trench HMM supports bulk plasmon modes at 3 μm and above in a wide wavelength range. 42 Wavelengths longer than 3 μm cover most of the absorption bands of interesting/biologically relevant molecules. 3 Moreover, most of the important absorption resonances in the biomedical sensing are ranged between 2.5 and 10 μm (4000 to 1000 cm −1 ).…”

“…In this work, the process was fine-tuned in order to reduce this effect by minimizing the switching times and lowering the temperature. 42 Indeed, the resulting Si trench as depicted in Figure 1b has a very smooth sidewall surface suitable for subsequent ALD deposition. Fabricated Si templates were carefully investigated using SEM cross-sectional analysis.…”

Methodologies for On‐Demand Dispersion Engineering of Waves in Metasurfaces

“…First, by stacking and bending multilayers, one obtain the superlens, planar hyperlens, and curved hyperlenses . The hyperbolic dispersion in anisotropic metal–dielectric structures may lead to the formation of Dyakonov plasmons, which are similar to Dyakonov waves on anisotropic dielectric materials . Second, a 90° rotation of the multilayer would result a 1D grating, which can be either periodic or gradient.…”

Large‐Scale Plasmonic Hybrid Framework with Built‐In Nanohole Array as Multifunctional Optical Sensing Platforms

“…On the other hand, top‐down approaches including focused ion‐beam milling and e‐beam lithography (Figure 1 III) have been used to process most of the nanohole structures reported 20–22. The feature size down to ≈20 nm with perfect periodicity over hundreds of micrometers has been demonstrated, along with various geometries including elliptical or squared‐hole,22 double‐hole, patched nanohole arrays6,23 nanoscale‐voids,24 as well as nanotrenches 25,26. However, these top‐down lithography methods involve tedious writing and processing, and limited scalability.…”