Low‐Index‐Contrast Dielectric Lattices on Metal for Refractometric Sensing

Abstract

In this context, metal nanostructures with localized surface plasmon resonances (LSPRs) have attracted extensive attention. [2] LSPRs can be excited with wide-field normal-incidence illumination, and the optical setup for sensing can be simply constructed based on standard optical microscopes. [3] Periodic plasmonic nanostructures can offer additional advantages, [4] for example, a much narrower resonance linewidth (compared to LSPRs) that is beneficial for measuring a small spectral shift. However, the intense optical fields on the surface of plasmonic nanostructures can result in dissipative loss and lead to heating. Recently, periodic arrays of high-index dielectric nanostructures with collective resonances have been proposed as an alternative. [5-9] However, for periodic arrays of high-index dielectric nanostructures, even with broken inplane symmetry (so-called quasi-BIC; bound states in the continuum), [7,8] the bulk sensitivity (defined as the spectral shift upon the change in the bulk refractive index of the surrounding environment) is much lower than that of plasmonic arrays with the same lattice spacing. The collective lattice resonance stemming from the diffractive coupling in a periodic array of either metal [10-12] or high-index dielectric nanoparticles [13] requires a symmetric refractive-index environment between the bottom substrate and the upper cladding (e.g., aqueous buffers in sensing). [14-17] An asymmetric environment can inhibit long-range coupling between nanoparticles and suppress lattice resonances. In optical sensing, a periodic array of either metal or high-index dielectric nanoparticles is usually fabricated on a transparent substrate and exposed to solutions with different refractive indices. The index-mismatch between widely used quartz substrates (n ≈ 1.5) and aqueous buffers (n ≈ 1.33) can broaden the resonances and deteriorate the bulk sensitivity. [18] Although for sensing in aqueous buffers, one can find fluoropolymer (Cytop) with refractive index close to water to create a symmetric environment, [18,19] it is highly desirable to have a platform that can maintain high-quality resonances when subjected to a relatively large change in the bulk refractive index. (A symmetric refractive-index environment may not be required in a periodic structure with high-quality resonances of quasi-BIC type, for which the bulk sensitivity, however, is not high in the published literature. [7,8]) We recently reported that a hybrid system composed of low-index dielectric pillar arrays on a metal film can support This article reports refractometric sensing using two optical resonances of different types supported by TiO 2 nanopillar arrays on a gold film, which can be exposed to aqueous or organic environments. One lattice resonance, with enhanced electric fields extending into the surrounding environment, can maintain a quality factor Q > 200 when the bulk refractive index of the surrounding environment varies in a large range from 1.33 to 1.58. This lattice resonance exhibits not only sharp trans...

Resonant Metasurfaces for Spectroscopic Detection: Physics and Biomedical Applications

“…It demonstrates for the first time plasmonic sensing in three dimensions (3D) space, allowing simultaneous detection of local chemical or physical processes at different spatial locations. Subsequently, Dong et al proposed a hybrid metal-dielectric metasurface consisting of TiO 2 nanopillars arrays on a metallic reflector, supporting both SLR and plasmonic resonance modes [32]. The bulk sensitivities obtained experimentally were 449 nm/RIU and 273 nm/RIU, respectively.…”

“…In terms of miniaturized devices, the integration of metasurfaces with complementary metal-oxide-semiconductor (CMOS) or microfluidic systems offers the possibility of miniaturized devices [26][27][28]. From the perspective of functional enrichment multilayer metasurfaces [29,30], or hybrid metasurfaces [31,32] are used to obtain additional optical functionality. From the aspect of cost-effectiveness, wavelength-based interrogation is transformed into an intensity interrogation detection scheme to eliminate the need for cumbersome wavelength scanning or expensive spectrometers [27].…”

Loss‐induced phase transition in mid‐infrared plasmonic metamaterials for ultrasensitive vibrational spectroscopy

“…In terms of design constraints, the metamaterials, that is, artificial materials, can be engineered to achieve desired properties 44–49 . Approaches report that design constraint limitations can be bypassed by metamaterial structure optimization 50,51 . The first method is to increase light field strength by constructing narrow gaps between adjacent metamaterial pattern units 52,53 .…”

Polarization-Dependent Purcell Enhancement on a Two-Dimensional h-BN/WS2 Light Emitter with a Dielectric Plasmonic Nanocavity

“…On the basis of the coupling interaction between excitons of monolayer WS 2 and plasmons of the dielectric nanocavity, the emission intensity can be actively controlled by the orientation of linearly polarized light. In contrast to the strong-coupling regime of designed TMDCs/metal nanostructures, where the emission peak might split into two (known as Rabi splitting), the low-index dielectric nanostructure offers a sharp plasmonic resonance with small cavity line width and a remarkable Purcell enhancement is achieved at room temperature . In our devices, we develop a new platform for integrated nanoscale photonic emitters based on a silica-based chip.…”

“…In contrast to the strong-coupling regime of designed TMDCs/ metal nanostructures, where the emission peak might split into two (known as Rabi splitting), 28 the low-index dielectric nanostructure offers a sharp plasmonic resonance with small cavity line width and a remarkable Purcell enhancement is achieved at room temperature. 29 In our devices, we develop a new platform for integrated nanoscale photonic emitters based on a silica-based chip.…”