Hydrogel‐Based, Dynamically Tunable Plasmonic Metasurfaces with Nanoscale Resolution

Abstract

Flat metasurfaces with subwavelength meta‐atoms can be designed to manipulate the electromagnetic parameters of incident light and enable unusual light–matter interactions. Although hydrogel‐based metasurfaces have the potential to control optical properties dynamically in response to environmental conditions, the pattern resolution of these surfaces has been limited to microscale features or larger, limiting capabilities at the nanoscale, and precluding effective use in metamaterials. This paper reports a general approach to developing tunable plasmonic metasurfaces with hydrogel meta‐atoms at the subwavelength scale. Periodic arrays of hydrogel nanodots with continuously tunable diameters are fabricated on silver substrates, resulting in humidity‐responsive surface plasmon polaritons (SPPs) at the nanostructure–metal interfaces. The peaks of the SPPs are controlled reversibly by absorbing or releasing water within the hydrogel matrix, the matrix‐generated plasmonic color rendering in the visible spectrum. This work demonstrates that metasurfaces designed with these spatially patterned nanodots of varying sizes benefit applications in anti‐counterfeiting and generate multicolored displays with single‐nanodot resolution. Furthermore, this work shows system versatility exhibited by broadband beam‐steering on a phase modulator consisting of hydrogel supercell units in which the size variations of constituent hydrogel nanostructures engineer the wavefront of reflected light from the metasurface.

Direct‐Printing Hydrogel‐Based Platform for Humidity‐Driven Dynamic Full‐Color Printing and Holography

“…Regarding the cavity length evaluation, its refractive index was assumed to remain at a constant 1.51 in the numerical calculations, disregarding the minor index-alteration impact. [50] Sample Fabrications: For the MHMN platform preparation, Ag/PVA/Ag films were successively deposited on a silica substrate. For the hydrogel layer, the 10.7 wt% PVA solution was spin-coated onto the sample at the speed of 4000 rpm for 60 s to give a ≈460 nm thick hydrogel layer.…”

“…Regarding the cavity length evaluation, its refractive index was assumed to remain at a constant 1.51 in the numerical calculations, disregarding the minor index‐alteration impact. [ 50 ]…”

Transfer-Printing Hydrogel-Based Platform for Moisture-Driven Dynamic Display and Optical Anti-Counterfeiting

“…Compared with the conventional FBFP cavity, the NBFP cavity is constructed using a disorder AuNPs assembly instead of the gold film to improve its color vibrancy, response/recovery times, and spatial resolution. Generally, the fabrications of the conventional hydrogel-based FP cavities rely on the patterning of hydrogels [by electron beam lithography (EBL), , femtosecond laser pulse, interference lithography, and 3D printing] and metal depositions subsequently. Unfortunately, the direct metal depositions onto the patterned hydrogels will reshape their geometries (i.e., reduce the thicknesses of hydrogel structures due to the heat effect and partially cover their vertical sidewalls due to the divergence of the atomic beam), which enormously spoils the sample’s optical responses and spatial resolutions.…”

A Pitaya-Inspired Modular Cylindrical MOF-Based Capsule Design for Pesticide Signal Probes

“…Inspired by the unique self-protection strategies, designing a self-assembled modular capsule is of interest in material science. Both hydrogels and metal–organic frameworks (MOFs) have 3D porous structures, where hydrogels are soft wet materials with random polymer structures, − and MOFs are solid crystalline materials with definite frameworks, tunable surface groups, controllable pores, and adjustable sizes. − Purposefully, the capsules can combine new polymer materials with various fillers by adjusting the cross-linking strategy, and the synergy in the cross-linking networks to realize better properties. Recently, scientists developed a variety of MOF-based hydrogels, containing a (ZIF-8)/polysaccharide (sodium alginate-kappacarrageenan, SC) hydrogel bead, MOF-802@PVA hydrogel, gelatin/UiO-66-NO 2 , CaAlg-PET membrane, etc.…”