Polarization-independent plasmonic subtractive color filtering in ultrathin Ag nanodisks with high transmission

Plasmonic Metamaterial Ag Nanostructures on a Mirror for Colorimetric Sensing

In this study, we demonstrate the localized surface plasmon resonance (LSPR) in the visible range by using nanostructures on mirrors. The nanohemisphere-on-mirror (NHoM) structure is based on random nanoparticles that were obtained by heat-treating silver thin films and does not require any top-down nanofabrication processes. We were able to successfully tune over a wide wavelength range and obtain full colors using the NHoM structures, which realized full coverage of the Commission Internationale de l'Eclairage (CIE) standard RGB (sRGB) color space. Additionally, we fabricated the periodic nanodisk-on-glass (NDoG) structure using electron beam lithography and compared it with the NHoM structure. Our analysis of dark-field microscopic images observed by a hyperspectral camera showed that the NHoM structure had less variation in the resonant wavelength by observation points compared with the periodic NDoG structure. In other words, the NHoM structure achieved a high color quality that is comparable to the periodic structure. Finally, we proposed colorimetric sensing as an application of the NHoM structure. We confirmed the significant improvement in performance of colorimetric sensing using the NHoM structure and succeeded in colorimetric sensing using protein drops. The ability to fabricate large areas in full color easily and inexpensively with our proposed structures makes them suitable for industrial applications, such as displays, holograms, biosensing, and security applications.

High-performance polarization-independent black phosphorus refractive index sensors enabled by a single-layer pattern design

The in-plane orientation-dependent electrical and optical properties of two-dimensional (2D) anisotropic materials attract significant attention because of the intriguing underlying physics. However, this feature limits their further development in polarization-independent applications such as refractive index sensors and light absorbers. In this paper, polarization-independent optical properties of black phosphorous (BP) metadevices are achieved by the design of a single-layer pattern of 2D anisotropic material. Finite-difference time-domain (FDTD) simulation results indicate that the absorption spectrum remains unchanged as the polarization angle of the incident light varies from 0° to 360°. The performance of the BP metadevices when used as refractive index sensors is also studied. The results show that the polarization-independent BP sensors exhibit high sensitivity and figures of merit (FOMs). This work opens up the possibility of fabricating optically polarization-independent devices based on a single-layer pattern of 2D anisotropic material.

Cavity-driven hybrid plasmonic ultra-narrow bandpass filter

We propose a novel compound grating structure that exhibits a tunable ultra-narrowband transmission in the near infrared regime. The thin microstructure can realize a steep wave form through a Fano-like resonance by coupling different propagation-type SPP modes and with a narrow line width formed by the energy band gap. Additionally, the out-of-band suppression is remarkably enhanced. It effectively solves the constraint relationship between high transmittance, narrow line width, and weak side peak of the plasmonic filter, and the structure is suitable for integration with detectors in the near infrared regime.

Spectral-Selective Plasmonic Polymer Nanocomposites Across the Visible and Near-Infrared

State-of-the-art commercial light-reflecting glass is coated with a metalized film to decrease the transmittance of electromagnetic waves. In addition to the cost of the metalized film, one major limitation of such light-reflecting glass is the lack of spectral selectivity over the entire visible and near-infrared (NIR) spectrum. To address this challenge, we herein effectively harness the transmittance, reflectance, and filtration of any wavelength across the visible and NIR, by judiciously controlling the planar orientation of two-dimensional plasmonic silver nanoplates (AgNPs) in polymer nanocomposites. In contrast to conventional bulk polymer nanocomposites where plasmonic nanoparticles are randomly mixed within a polymer matrix, our thin-film polymer nanocomposites comprise a single layer, or any desired number of multiple layers, of planarly oriented AgNPs separated by tunable spacings. This design employs a minimal amount of metal and yet efficiently manages light across the visible and NIR. The thin-film plasmonic polymer nanocomposites are expected to have a significant impact on spectral-selective light modulation, sensing, optics, optoelectronics, and photonics.

Fast and large-area fabrication of plasmonic reflection color filters by achromatic Talbot lithography

To overcome the limits of traditional technologies, which cannot achieve high resolution and high throughput simultaneously, here we propose, to the best of our knowledge, a novel method, i.e., achromatic Talbot lithography, to fabricate large-area nanopatterns fast and precisely. We successfully demonstrate reflection color filters with a maximum size of about 0.72×0.72  mm² with a time of only 20 s that have colors similar to simulations and small-area devices fabricated by electron beam lithography. These results indicate the possibility of large-scale fabrication of plasmonic color filters with high resolution efficiently by the achromatic Talbot lithography method.

Plasmonic metasurfaces for subtractive color filtering: optimized nonlinear regression models

We develop and explore a nonlinear regression modeling approach to designing subtractive color filters (SCFs) based on plasmonic metasurfaces. The approach opens up the possibility of rapidly choosing a desired optimized SCF design with high color saturation and brightness using an analytical expression. In this Letter, colors are produced by absorbing the light of specific wavelengths and reflecting the remaining spectrum with silver gap-plasmon nanoantennas deposited on a silver film. First, we design three different SCFs-yellow, magenta, and cyan. Then, by adjusting the design parameters of the nanoantennas, we optimize their high absorption resonance peaks (reflections dips), which are tunable over the visible spectrum. Finally, by using nonlinear regression analysis, we fit our results to a cubic regression model. Accordingly, a SCF for a color of choice can be designed in a straightforward way. This is a promising technique that provides a methodology to design preoptimized filters for practical applications such as color printing, high-resolution chromatic displays, and multi-spectral imaging.

Design of a plasmonic sensor based on a square array of nanorods and two slot cavities with a high figure of merit for glucose concentration monitoring

In this paper, a plasmonic nanosensor, by using a nanorod array in a square resonator coupled with two slot cavities, with properties for the detection of glucose concentration in water, is proposed and analyzed. We investigated the sensing feature by changing the concentration of the glucose from 0 to 60%. Obtained results show that, by placing different water samples in a square resonator and two cavities, resonance wavelengths can be changed. These resonances demonstrate different dependence on the glucose concentration of water samples. Further, varying the physical parameters of the configuration can also change the resonance wavelength and can be simply tuned. These features recommend flexibility to propose the structure. Simulation results show that the values of sensitivity and figure of merit can be obtained as 892 nm/RIU and 3.5×10⁶  RIU^-1, respectively, which can help researchers to discover applications in the plasmonic sensor domain.

Plasmonic- and dielectric-based structural coloring: from fundamentals to practical applications

Structural coloring is production of color by surfaces that have microstructure fine enough to interfere with visible light; this phenomenon provides a novel paradigm for color printing. Plasmonic color is an emergent property of the interaction between light and metallic surfaces. This phenomenon can surpass the diffraction limit and achieve near unlimited lifetime. We categorize plasmonic color filters according to their designs (hole, rod, metal-insulator-metal, grating), and also describe structures supported by Mie resonance. We discuss the principles, and the merits and demerits of each color filter. We also discuss a new concept of color filters with tunability and reconfigurability, which enable printing of structural color to yield dynamic coloring at will. Approaches for dynamic coloring are classified as liquid crystal, chemical transition and mechanical deformation. At the end of review, we highlight a scale-up of fabrication methods, including nanoimprinting, self-assembly and laser-induced process that may enable real-world application of structural coloring.

On the correlation of absorption cross-section with plasmonic color generation

Through numerical simulations, we investigate the correlation between the absorption cross-section and the color saturation of plasmonic nanostructures of varying density. Understanding this correlation, enables the prediction of an optimal nanostructure separation, or combinations of different nanostructure sizes for plasmonic color printing applications. Here, we use metal-insulator-metal (MIM) aluminum nanostructures that support gap-plasmons. Large absorption cross-sections were observed that exceed twelve times the physical cross-section of the nanostructure disks. We derive a set of equations to determine the optimal separation for a periodic array using the absorption cross-section of an individual structure to realize saturated colors. Using the optimum pitch and enabled by the large absorption cross-sections of our structures, we employ color mixing strategies to realize a wider color gamut. The simulated color gamut exceeds the sRGB gamut for some colors, and includes dark tones. Color mixing using structures with large absorption cross-sections is a practical approach to generate a broad range of colors, in comparison to fabricating structures with continuously varying sizes.

Plasmonic reflection color filters with metallic random nanostructures

We develop reflective color filters with randomly distributed nanodisks and nanoholes fabricated with hydrogen silsesquioxane and Ag films on silicon substrate. They exhibit high resolution, angle-independence and easily up-scalable fabrication, which are the most important factors for color filters for industrial applications. We uncover the underlying mechanism after systematically analyzing the localized surface plasmon polariton coupling in the electric-field distribution. The agreement of the experimental results with those from the simulation indicates that tunable colors across the visible spectrum can be obtained by simply varying the diameter of the nanodisks, promoting their applications.

High throughput fabrication of large-area plasmonic color filters by soft-X-ray interference lithography

Plasmonic color filters in mass production have been restricted from current fabrication technology, which impede their applications. Soft-X-ray interference lithography (XIL) has recently generated considerable interest as a newly developed technique for the production of periodic nano-structures with resolution theoretically below 4 nm. Here we ameliorate XIL by adding an order sorting aperture and designing the light path properly to achieve perfect-stitching nano-patterns and fast fabrication of large-area color filters. The fill factor of nanostructures prepared on ultrathin Ag films can largely affect the transmission minimum of plasmonic color filters. By changing the fill factor, the color can be controlled flexibly, improving the utilization efficiency of the mask in XIL simultaneously. The calculated data agree well with the experimental results. Finally, an underlying mechanism has been uncovered after systematically analyzing the localized surface plasmon polaritons (LSPPs) coupling in electric field distribution.

The Plasmonic Pixel: Large Area, Wide Gamut Color Reproduction Using Aluminum Nanostructures

We demonstrate a new plasmonic pixel (PP) design that produces a full-color optical response over macroscopic dimensions. The pixel design employs arrays of aluminum nanorods "floating" above their Babinet complementary screen, Concepts from conventional cyan magenta yellow key (CMYK) printing techniques and red green blue (RGB) digital displays are integrated with nanophotonic design principles and adapted to the production of PP elements. The fundamental PP color blocks of CMYK are implemented via a composite plasmonic nanoantenna/slot design and then mixed in a digital display analog 3 × 3 array to produce a broad-gamut PP. The PP goes beyond current investigations into plasmonic color production by enabling a broad color gamut and physically large plasmonic color features/devices/images. The use of nanorods also leads to a color response that is polarization tunable. Furthermore, devices are fabricated using aluminum and the fabrication strategy is compatible with inexpensive, rapid-throughput, nanoimprint approaches. Here we quantify, both computationally and experimentally, the performance of the PP. Spectral data from a test palette is obtained and a large area (>1.5 cm lateral dimensions) reproduction of a photograph is generated exemplifying the technqiue.