Plasmonic colours are structural colours that emerge from resonant interactions between light and metallic nanostructures. The engineering of plasmonic colours is a promising, rapidly emerging research field that could have a large technological impact. We highlight basic properties of plasmonic colours and recent nanofabrication developments, comparing technology-performance indicators for traditional and nanophotonic colour technologies. The structures of interest include diffraction gratings, nanoaperture arrays, thin films, and multilayers and structures that support Mie resonances and whispering-gallery modes. We discuss plasmonic colour nanotechnology based on localized surface plasmon resonances, such as gap plasmons and hybridized disk–hole plasmons, which allow for colour printing with sub-diffraction resolution. We also address a range of fabrication approaches that enable large-area printing and nanoscale lithography compatible with complementary metal-oxide semiconductor technologies, including nanoimprint lithography and self-assembly. Finally, we review recent developments in dynamically reconfigurable plasmonic colours and in the laser-induced post-processing of plasmonic colour surfaces. Plasmonic colours can be used to colour large surfaces, can be mass-produced and dynamically reconfigured, and can provide sub-diffraction resolution. In this Review, basic properties of plasmonic colours, different platforms supporting them and recent developments in the field are discussed.

Plasmonic colour generation

Plasmonic effects associated with metallic nanostructures have been widely studied for color generation. It became apparent that highly saturated and bright colors are hard to obtain, and very small nanostructures need to be fabricated. To address this issue, in this study, we employ metal–insulator–metal sandwich nanodisks that support enhanced in-phase electric dipole modes, which are blue-shifted with respect to a single metal disk. The blue shift enables the generation of short wavelength colors with larger nanostructures. The radiation modes hybridize with the Wood’s anomaly in periodic structures, creating narrow and high-resonance peaks in the reflection and deep valleys in the transmission spectra, thus producing vivid complementary colors in both cases. Full colors can be achieved by tuning the radius of the nanodisks and the periodicity of the arrays. Good agreement between simulations and experiments is demonstrated and analyzed in CIE1931, sRGB, and HSV color spaces. The presented method has p...

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Full Color Generation Using Silver Tandem Nanodisks.

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.

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

Dynamic, colour-changing surfaces have many applications including displays, wearables and active camouflage. Plasmonic nanostructures can fill this role by having the advantages of ultra-small pixels, high reflectivity and post-fabrication tuning through control of the surrounding media. However, previous reports of post-fabrication tuning have yet to cover a full red-green-blue (RGB) colour basis set with a single nanostructure of singular dimensions. Here, we report a method which greatly advances this tuning and demonstrates a liquid crystal-plasmonic system that covers the full RGB colour basis set, only as a function of voltage. This is accomplished through a surface morphology-induced, polarization-dependent plasmonic resonance and a combination of bulk and surface liquid crystal effects that manifest at different voltages. We further demonstrate the system’s compatibility with existing LCD technology by integrating it with a commercially available thin-film-transistor array. The imprinted surface interfaces readily with computers to display images as well as video. Tuning of plasmonic nanostructures has yet to cover a full colour basis set with a single nanostructure. Franklinet al. demonstrate a liquid crystal-plasmonic system that covers the full red-green-blue colour basis set as a function of voltage and which can be actively addressed with thin-film-transistor technology.

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Actively addressed single pixel full-colour plasmonic display.

Optical metasurfaces, composed of ultrathin subwavelength meta-atoms, have enabled flat-optics and corresponding flat optical components such as ultrathin lenses, color filters, and absorbers Among the plethora of applications currently attracting great interest, next generation display techniques could further benefit from metasurface technology Thanks to relatively simple mechanisms of amplitude and phase modulation of light by the meta-atoms, many of the recent research achievements in metasurfaces are related to display applications In this Perspective, we focus on metasurface holograms and colorations for projective and reflective display techniques First, we briefly introduce the working mechanism of metasurface holograms and colorations and review state-of-the-art techniques in each field from perspective of materials, functionalities, and fabrication methodologies toward real-life display applications Finally, we conclude on the potential outcome and outlook on this technology and highlight t

Outfitting Next Generation Displays with Optical Metasurfaces

We present transmissive plasmonic structural colors from subwavelength nanohole arrays with bottom metal disks for scaled-up manufacturing by nanoimprint lithography (NIL). Comprehensive theoretical and experimental studies are carried out to understand the specific extraordinary optical transmission behavior of the structures with such bottom metal disks. Distinctive colors covering the entire visible spectrum can be generated by changing the structural dimensions of hole arrays in Ag covered by the metal disks. The plasmonic energy hybridization theory is applied to explain the unstable color output with shallow holes so that a large processing window during NIL could be achieved for mass production. A high-resolution of 127,000 dots per inch is demonstrated with potential applications, including color filters and displays, high-resolution color printing, CMOS color imaging, and anti-counterfeiting.

High-resolution plasmonic structural colors from nanohole arrays with bottom metal disks.

Inspired by the structural color from the multilayer nanophotonic structures in Morpho butterfly wing scales, 3D lamellae layers in dielectric polymers (polymethyl methacrylate, PMMA) with n ∼ 1.5 were designed and fabricated by standard top-down electron beam lithography with one-step exposure followed by an alternating development/dissolution process of PMMA/LOR (lift-off resist) multilayers. This work offers direct proof of the structural blue/green color via lithographically-replicated PMMA/air multilayers, analogous to those in real Morpho butterfly wings. The success of nanolithography in this work for the 3D lamellae structures in dielectric polymers not only enables us to gain deeper insight into the mysterious blue color of the Morpho butterfly wings, but also breaks through the bottleneck in technical development toward broad applications in gas/liquid sensors, 3D meta-materials, coloring media, and infrared imaging devices, etc.

Lithographically-generated 3D lamella layers and their structural color

Processing study of SU-8 pillar profiles with high aspect ratio by electron-beam lithography

We report our work on the development of subwavelength gold pillar arrays as local surface plasmonic (LSP) resonators for sensor applications. These arrays are fabricated by electron beam lithography combined with electroplating. The conical shape, instead of flat one, on the top of Au pillars, induced by uneven current density in the plating, may affect the LSP resonance (LSPR). This paper aims to carry out a systematic study of LSPR behavior in nanopillar arrays with both flat and conical shapes on the top, trying to prove the feasibility of the developed nanoprocess. Both numerical simulations by the finite-difference time-domain (FDTD) method and experimental characterization on fabricated LSP resonators for reflectance spectra were carried out. Our experiments indicate that the fabricated nanopillar arrays in Au demonstrate the promising capability of refractive index sensing with sensitivity of 270 nm/refractive index unit. FDTD simulation of electric field density in the gap between pillars reveals the correlation between the resonant absorption of the incident light and the standing waves of localized surface plasmon polaritons in the gaps of the pillar array, despite the conical shape of the pillars. Moreover, it was discovered that the resonant absorption becomes stronger when the light incident angle is increased. The proposed nanoprocess for pillar arrays should possess great prospects for manufacturing Au pillars with high aspect ratio for achieving higher sensitivity at an economical cost.

Jianpeng Liu

Papers

High-resolution plasmonic structural colors from nanohole arrays with bottom metal disks.

Lithographically-generated 3D lamella layers and their structural color

Processing study of SU-8 pillar profiles with high aspect ratio by electron-beam lithography

Gold nanopillar arrays as biosensors fabricated by electron beam lithography combined with electroplating

Ultra-tall sub-wavelength gold nano pillars for high sensitive LSPR sensors