Self‐Powered Humidity Sensor Using Chitosan‐Based Plasmonic Metal–Hydrogel–Metal Filters

Abstract

affects both its electrical conductivity and its absorption spectrum. These changes have obvious application as a sensor of relative humidity (RH).Structural colors found in nature [9] have received great scientific interest and been reproduced by diverse structural colors. [10][11][12] The simplest structural coloration mechanism consists of planar multilayered arrangements. [13][14][15][16][17] In particular, the metal-insulator-metal (MIM) configuration based on a Fabry-Pérot resonator has a high quality factor efficient band-pass filtering with scalability and cost-effective fabrication. [18][19][20] However, conventional planar MIM resonators lack tunable function, because the resonance depends only on the geometry and optical parameters of the insulating layer.Structural colors have been tuned using chemical, [21][22][23][24][25][26] mechanical, [27,28] or electrical stimuli, [29,30] polarization, [31,32] and phase-change materials. [33] However, tunable structural colors have a slow response, [21] complicated mechanism [27,28,33] and insufficient dynamic change. For those reasons, practical application of structural colors has been limited.In this work, we propose tunable color filter composed of MIM multilayer, in which the insulator is chitosan hydrogel. This color filter can serve as a humidity sensors when combined with a photovoltaic (PV) cell. The structure uses chitosan film sandwiched between two ultrathin silver (Ag) layers deposited on a glass substrate. The key element is the chitosan insulating layer, in which the effective optical thickness t eff and refractive index n c change in response to RH; this trait can be exploited to obtain optical tunability of the resonance wavelengths. The corresponding resonance peak shift induces output current change of a PV cell, which is proportional to a change in the RH value of the environment. The special features of the proposed sensor are simple development, incorporation into PV cell, and potentially zero power usage, that make it a promising material for devices that monitor RH in enclosed spaces, workplaces and storage areas. Results and Discussion Transfer-Matrix Method (TMM) Simulation of Ag-Chitosan-Ag Multilayer StructuresWe present a tunable MIM bandpass filter in which the sensitive insulating layer is composed of chitosan, which can adsorb A tunable Fabry-Pérot resonator is realized using metal-insulator-metal structure, in which the insulator is chitosan hydrogel. The chitosan swells in response to changes in relative humidity; this change affects transmissive structural color of the multilayer structure. This tunable resonator is utilized for a humidity sensor combined with a photovoltaic cell. The change in current through the photovoltaic cell provides rapid precise measurement of relative humidity, and the change in color of the multilayer provides an approximate, remotely-readable estimate. The response requires no power, so the device has numerous sensing applications.

Dispersion‐Controlled Gold–Aluminum–Silicon Dioxide–Aluminum Nanopawn Structures for Visible to NIR Light Modulation

“…Especially, for structures of high aspect ratio, the cylindrical FP cavity composed of Al-disk/SiO 2 -cylinder/Al-substrate supports cylinder height-dependent, strong reflectance dips (Figures 3c, 3d and Figure S13, Supporting Information for other cylinder heights). These reflectance dips (λ ≈ 460-560 nm) scale linearly with the height of the SiO 2 cylinder, and agree well with the theoretical results assuming flat-film FP resonator [36][37][38] (e.g., λ FP-dip = 490 nm at h = 180 nm and λ FP-dip = 590 nm at h = 215 nm). For scattering spectra, in contrast, with the absence of FP modes and excitation of asymmetric modes in the Al ultrathin film, the Al disk and Au-NPs together contribute to the reflection-complementary spectral responses (Figures 3e, 3f and Figure S14, Supporting Information for scattering with other cylinder heights).…”

Scalable and High-Throughput Top-Down Manufacturing of Optical Metasurfaces

“…They have been applied as high-resolution ultrathin lenses [ 1 , 2 ], as well as superlenses and hyperlenses that overcome diffraction limits [ 3 , 4 , 5 ]. Metasurfaces can also play the role of color filters, selectively transmitting or reflecting the specific wavelengths of incident light to produce the desired colors [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. Using a tunable polarization-dependent structural coloration, cryptography has been demonstrated to hide multiple pieces of information in one metasurface [ 6 , 9 ].…”

Extremely Polarized and Efficient Hot Electron Intraband Luminescence from Aluminum Nanostructures for Nonlinear Optical Encoding

“…The extremely polarized HEIL offers a mechanism for optical image encryption [ 38–41 ] of security information. As a demonstration, we encoded the Jinan University emblem in the prefabricated Al nanorod array though a bit by bit laser printing manner with a resolution of ≈800 nm.…”