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Abstract

method provides high polarization-independent resonant reflection (>90% in air), good contrast (30–50%), fast response times (ms regime), ultralow power consumption (<0.5 mW cm −2), and long-term stability. We also show that plasmonic metasur-faces containing pixels of the primary colors red–green–blue (RGB) give the same reflectivity and contrast as ink produced by an ordinary printer. Finally, we show how the RGB pixels can produce secondary colors and display-size images which can be switched on/off. Our plasmonic metasurfaces contain three solid films (Figure 1a). During fabrication, a 150 nm silver film was first deposited on the substrate to provide a high base reflection. The subsequent alumina spacer layer tuned the reflective color by Fabry–Pérot interference. [6] Next, short-range ordered 150 nm nanoholes in a 20 nm gold film (Figure 1b) were prepared on alumina by colloidal self-assembly and tape stripping. [18] The fabrication consisted of parallel processing steps [19] compatible with large areas and plastic supports, which made the material flexible by hand (Figure 1c). We generated a color palette by varying the alumina thickness [20] from 40 to 95 nm and found that the primary colors red, green, and blue (RGB samples, Figure 1d) corresponded to an alumina thickness of 48, 93, and 83 nm respectively. The high resonant reflectivity (Figure 1e) confirmed the clear colors of the plasmonic metasurfaces. The gold film is necessary to create coloration because the absorption of silver is very low in the visible [21] and since there is no transmission through the thick mirror layer all visible wavelengths would then be reflected. Further, the nanohole array in the thin gold film enhances the coloration since it enables coupling to surface plasmons [22,23] and provides strong resonant scattering. [18] Although we could also generate colors by only a gold film without holes on the silver and alumina layers, such thin film multilayers do not support plasmon excitation under ordinary illumination and cannot scatter light. This limited the possibility to tune the reflection spectrum and resulted in more diffuse colors since only absorption [21] (and not scattering) could contribute (Figure 1c). By dark-field illumination we verified that the three RGB structures with nanoholes scattered their complementary colors at high angles (Figure S1, Supporting Information). We also analyzed the reflectivity for increasing incident angle (Figure S2, Supporting Information) and found that the viewing angle could be up to ≈60° with correct color appearance. To switch the colors on and off, the tunable optical absorption of conjugated polymers was utilized. [24] Doped polypyrrole films [25] were first electropolymerized [26] on the nanostructures arrays simply by applying +0.57 V versus Ag/AgCl in a solution containing NaDBS and pyrrole. [25] This process was monitored by combined electrochemical and plasmonic sensing

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... Plasmonics, with the unique capability of focusing light into subwavelength scale, offers a promising solution for high-resolution display [23][24][25][26][27][28], featuring prominently compared with other structure color materials like all-dielectric metasurfaces, semiconductors and phase change materials [29][30][31][32][33][34][35]. In addition, external electrical (such as nanostructured noble metal deposition [36]), chemical or other stimuluses can be more effective to enable dynamic displays with respect to dielectric-based nanophotonic counterparts [37][38][39][40][41][42][43][44][45][46]. On the other hand, as the lightest metal, lithium (Li) metal has long been regarded as the holy grail of high-energy-density anode materials [10,12], with the high specific capacity (3860 mAh g -1 ) and the lowest electrochemical potential (−3.04 V versus the standard hydrogen electrode). ...
... Taking the average energy efficiency (~ 56.70%) of our prototype device, for example, the specific energy consumption is ~ 0.390 mW cm -2 without optimization, which is at least one order of magnitude lower than the commercial active matrix organic light-emitting diode (AMOLED) (at the brightness of 160 cd cm -2 and Contrast Ratio of 10000:1) or several times lower than the electronic paper display (EPD) system [37,47]. Moreover, if the display is operated at a static coloration state, the specific energy consumption can be even three times lower (0.105 mW cm -2 , see METHODS for detailed explanations). ...
... consumption, response speed, compactness/thickness, and eye protection. [37,[47][48][49][50] Finally, the pixel-scaling limit of the proposed lithium plasmonic device is experimentally evaluated and shown in Fig. 5e and Supplementary Fig. 16. Full-color pixels with different sizes (decreasing from 20 m to 1 m) and different colors in a square shape can be observed using a conventional optical microscope, unraveling that the full-color pixel size can be down to 1 m even in the complicated liquid surroundings (~ less than one half of that of metasurface counterpart reported thus far [8]). ...
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Display and power supply have been two essential and independent cornerstones of modern electronics. Here we report a lithium plasmon based low-powered dynamic color display with intrinsic dual functionalities, the plasmonic display and energy recycling unit, through the electric-driven transformation of nanostructured lithium metals. Dynamic color displays are enabled by plasmonic transformation through electrodeposition (electrostripping) of the lithium metals during the charging (discharging) processes, while the consumed energy for coloring can be retrieved in the inverse processes respectively. The energy recycling of lithium metals makes the energy consumption of the display device down to 0.390 mW cm−2 (0.105 mW cm−2) for the active (static) coloration state of a proof-of-concept display/battery device, which approaches nearly-zero-energy-consumption towards the near-100%-energy-efficiency limit of commercial lithium batteries. Combining the subwavelength feature of plasmonics with the effective energy recycling, the lithium plasmon based dynamic display offers a promising route towards next-generation integrated photonic devices, with intriguing advantages of low energy consumption, small footprint and high resolution.
... Importantly, it is possible to prepare different electrochromic materials on different structurally colored pixels in a display device. Using electropolymerization, there is not even a need for lithography steps to achieve this goal: if individual pixels or segments can be electronically addressed, one can synthesize conductive polymers on them selectively [10]. Thus, instead of using a single polymer (or metal oxide) for all pixels/colors and aim for high-contrast broadband switching, there is a clear value in finding different polymers that provide maximum contrast only in a spectral region corresponding to a single color. ...
... For instance, a device with red, green and blue (RGB) pixels could have three different polymers, each giving maximum contrast for one primary color ( Figure 1). While polymers such as polypyrrole [10] (PPy), poly(3,4-ethylenedioxythiophene) [11] (PEDOT) and poly(dimethylpropylenedioxythiophene) In a reflective display where color mixing is achieved by subpixels (here RGB), performance can be increased by using different electrochromic materials for the different primary colors, since no single material is "perfect broadband". In particular, there is a need to find good materials for switching blue pixels with high contrast. ...
... To implement PProDOP with plasmonic structural colors, we prepared metal-insulator-metal nanostructures with nanohole arrays as described previously [9][10][11] and then polymerized the PProDOP on the top gold film with nanoholes. The fabrication process is described in Figure 4A. ...
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Recent advances in nanofabrication technologies have enabled new ways to produce structural colors. By combining nanofabrication methods, it is possible to integrate electrochromic materials with the nanostructures, which enable electrical tuning of the colors and thus new types of reflective displays. Previous work has shown high quality colors and high switching contrast in general. However, so far the intensity modulation has always been more limited in the blue. In this work we prepare blue structural colors and synthesize films of an electrochromic polymer (PProDOP) that is optimized for high contrast in this spectral region. A protocol for electropolymerization of PProDOP on gold surfaces is presented. The polymer films are shown to follow Lambert–Beer behavior and can provide up to 75% contrast (difference in transmittivity). On blue nanostructures, the reflectivity can be modulated with a contrast of 50%, which is a considerable improvement in comparison with previous work. The results presented here should be useful for electrochromic or other electro-optical devices operating in the blue spectral region.
... The realization of such dynamic structural colour is crucial for extending functionality beyond merely static images to include animations. Commonly reported approaches involve empolying active materials that respond to physical or chemical principles to alter the refractive index or size of nanoresonators [16][17][18][19][20][21][22][23][24], or to change the refractive index of the background of nanostructures [25][26][27][28][29][30][31][32]. Previous studies on dynamic structural colours have two main limitations: (1) Most studies have focused on transitions to different colours rather than ON/OFF colour switching [19-27, 30, 31]. ...
... For real applications, it is essential to have several basic colours (such as red, green, and blue) that can be turned on and off, along with their combinations, similar to the principle of commercialized displays. (2) The materials used for colour reproduction and the active materials used for colour control are different [28,29,32]. Adding other types of materials for active control could introduce compatibility issues or compromise the desired optical properties, potentially reducing the overall efficiency or reliability of the color-changing process. ...
Preprint
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Colour printing based on metallic or dielectric nanostructures has revolutionized colour science due to its unprecedented subwavelength resolution. Evidently, the evolution towards the active control of such structural colours with smart materials is in progress for real applications. Here we experimentally demonstrate a large colour gamut with high intensity and purity, as well as its switching on and off based solely on tungsten trioxide (WO3) cylindrical resonators. The strong resonances in the visible spectral range in these WO3 metasurfaces can be reversibly switched on and off due to its electrochromism by applying alternating voltages of +2.0 V and -0.3 V. Our approach opens up possibilities for the functional diversification of commercial smart windows, as well as the development of new display technologies in the future.
... Therefore, the structure needs to be able to transition between two or even multiple chromatic states under external stimulation, forming a controllable dynamic structural color. Many methods have been studied to achieve dynamic structural color, such as color change induced by chemical reactions [23,24], force-induced color change [25,26], electrically induced color change [27][28][29], and phase-change material color change [30][31][32][33][34]. However, the reaction time of reversible electrochemical deposition operations is relatively long, slowing the refresh rate [23,24]. ...
... The color performance will significantly weaken after a period of compression or stretching [25,26]. Additionally, the device for electrically induced color change is relatively complex, and its production is more difficult [27][28][29]. ...
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Tunable structural color has gained significant attention due to its dynamic characteristics. However, conventional devices are usually regulated only in their color capabilities by structural parameters, restricting real-time dynamic applications. In this study, we propose an ultra-thin asymmetric Fabry–Perot cavity patterned with phase-change materials (MPMP). The reversible phase transition of VO2 induces changes in the MPMP’s optical performance, enabling color mode switching through temperature control and resulting in rapid color conversion and low-temperature regulation. By adjusting relevant structural parameters of the VO2 layer and nanodiscs, the color performance range can be tailored. Through numerical investigations, we demonstrate that MPMP can produce stable transformation of dynamic structural colors by harnessing the phase-change effect. Our research unveils new possibilities for applications such as anti-counterfeiting, bio/chemical sensing, and temperature sensing.
... We prepare these nanostructures by combining established low-cost nanofabrication techniques (schematic of fabrication process in Fig. S1). Compared to our previous work 22,23,24 , we use here a 'reversed' design which generates the re ective colors from the glass side. This design hides the electrolyte and counter-electrode behind the re ective colors, which improves the total re ectivity of real devices 25 . ...
... Part of the re ected light was collected by an optical ber and analyzed by a spectrometer (B&WTek CypherX). In order to get accurate absolute re ectivities, the mirror used to obtain reference intensities was also measured in the CM-700d instrument, as explained previously 23 . ...
Preprint
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Dynamically-tunable reflective structural colors are attractive for reflective displays (electronic paper). However, it has been challenging to tune a thin layer of structural color across the full red-green-blue (RGB) basis set of colors at video rates and with long-term stability. Here, this is achieved through a hybrid cavity built from metal-insulator-metal (MIM) ‘nano-caves’ and an electrochromic polymer (PProDOTMe 2 ). The reflective colors are modulated by electrochemically doping/dedoping the polymer. Compared with traditional subpixel-based systems, this hybrid structure provides high reflectivity (> 40%) due to its ‘monopixel’ nature, and switches at video rates. The polymer bistability helps deliver ultralow power consumption (~ 2.5 mW cm − 2 ) for video display applications and negligible values (~ 3 µW cm − 2 ) for static images, compatible with fully-photovoltaic powering. In addition, the color uniformity of the hybrid material is excellent (over cm − 2 ) and the scalable fabrication enables large-area production.
... The reflection of the cavity is first determined through the thickness of a dielectric Al 2 O 3 layer placed between an Ag mirror and an Au NHA. By adjusting the period of the array, the plasmonic NHA is designed to have a spectral overlap with the F-P resonance [81,84]. The plasmonic NHA exhibited insignificant change in the reflectivity for viewing angles between 0 • and 45 • . ...
... The main conclusions that can be drawn are that while both technologies provide low power consumption at operating voltage below ±2 V and are scalable for large-scale production, a major drawback to overcome is that all investigated devices to date used liquid electrolytes, which limits their potential for integration into e-readers or similar [15,30,85], such a platform shows tremendous promise in replacing common e-readers based on e-ink and OLED displays wherever switching speeds are less important than energy consumption. While OLED displays require a power density of roughly 15 mW/cm 2 and e-readers about 3 mW/cm 2 , plasmonic cavity devices have shown to be a lot more energy efficient (P < 1 mW/cm 2 ) [84]. However, full color modulation is necessary to even compete with LED displays. ...
Article
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Research regarding electrochromic (EC) materials, such materials that change their color upon application of an electrochemical stimulus, has been conducted for centuries. However, most recently, increasing efforts have been put into developing novel solutions to utilize these on-off switching materials in advanced nanoplasmonic and nanophotonic devices. Due to the significant change in dielectric properties of oxides such as WO 3 , NiO, Mn 2 O 3 and conducting polymers like PEDOT:PSS and PANI, EC materials have transcended beyond simple smart window applications and are now found in plasmonic devices for full-color displays and enhanced modulation transmission and photonic devices with ultra-high on-off ratios and sensing abilities. Advancements in nanophotonic ECDs have further decreased EC switching speed by several orders of magnitude, allowing integration in real-time measurement and lab-on-chip applications. The EC nature of such nanoscale devices promises low energy consumption with low operating voltages paired with bistability and long lifetimes. We summarize these novel approaches to EC device design, lay out the current short comings and draw a path forward for future utilization.
... Particularly in the field of displays, hybrid nanomaterials-combining tunable conjugated polymers or semiconductors as color modulators with metallic nanostructures-have demonstrated the ability to modulate the intensity or the reflected colors of subpixels (15,16). These technologies significantly enhance the color gamut, reflectivity, and optical contrast of E-paper and enable video display functionality (17,18,19,20). However, due to limitations in structure, materials, and fabrication methods, the pixel sizes of these hybrid nanomaterials remain in the range of tens to hundreds of micrometres, making it challenging to achieve ultrahigh-resolution displays (21,22,23). ...
Preprint
As demand for immersive experiences grows, displays are moving closer to the eye with smaller sizes and higher resolutions. However, shrinking pixel emitters reduce intensity, making them harder to perceive. Electronic Papers utilize ambient light for visibility, maintaining optical contrast regardless of pixel size, but cannot achieve high resolution. We show electrically tunable meta-pixels down to ~560 nm in size (>45,000 PPI) consisting of WO3 nanodiscs, allowing one-to-one pixel-photodetector mapping on the retina when the display size matches the pupil diameter, which we call Retina Electronic Paper. Our technology also supports video display (25 Hz), high reflectance (~80%), and optical contrast (~50%), which will help create the ultimate virtual reality display.
... In comparison with traditional pigment-based coloring methods, structural colors offer notable advantages such as long-term stability, environmental friendliness, ease of manufacturing, and slim dimensions [8][9][10][11]. Various resonant mechanisms are used by researchers to create vibrant structural colors including plasma resonance [12][13][14][15], guided mode resonance [16][17][18], and Mie resonance [19][20][21][22][23][24]. However, these technologies typically require nanoscale array patterns or gratings that often involve complex photolithography processes along with reactive ion etching (RIE) and other fabrication procedures which make them cost-prohibitive for large-area applications requiring high volume production [25][26][27]. ...
Article
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A novel approach is proposed for generating reflective angle-insensitive structural colors with high purity, high brightness, and a wide color gamut in an asymmetric Fabry-Perot structure based on an ultra-thin bilayer absorber composed of Ni and Ge2Sb2Te5. The bilayer absorber is designed to have broadband absorption, enhancing the optical absorption across the entire visible spectrum and suppressing the reflection of complementary colors, thereby improving the color purity of reflective colors. By constructing a simplified five-layer structure and controlling only the thickness of the oxide layers, different colors can be achieved while maintaining high levels for all colors. The prepared structural color devices (yellow, cyan, magenta, green, blue, and purple) demonstrate exceptional angle-robust appearance within an incident light range of 0°–60° with reflection peaks exceeding 80%, as demonstrated theoretically and experimentally. This device offers a simple yet effective structure that utilizes a novel material combination and enables cost-effective mass production through just one coating run process. It holds significant potential for diverse applications in micro-nano displays, anti-counterfeiting, color filters, printing, illumination systems, and decorations.
... 8,15 In particular, electrical plasmon resonance control has been a popular research topic because of its many advantages such as high repeatability, fast response time, and compatibility for implementation in microdevices. Electrically dynamic tuning of plasmon resonance has been proposed and developed using liquid crystals (LCs), 2,5,7,8,16−21 conductive polymers, 22,23 organic electrolyte solvents, 3,24,25 and microelectromechanical system (MEMS) technology. 26,27 It is expected to lead to practical applications in ultracompact spectrometers and tunable color filters for multi-or hyperspectral image sensors with high light utilization efficiency. ...
Article
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We experimentally demonstrated electrical plasmonic color modulation by combining a nematic-phase liquid crystal (LC) layer and a silver nanocube (AgNC) monolayer. The color modulation LC/AgNC device was fabricated by filling LCs with negative dielectric anisotropy onto a densely assembled AgNC monolayer. The transmitted light color through the LC/AgNC device was modulated between green and magenta by applying voltages of 0–15 V. The peaks and dips in the transmission spectrum of the LC/AgNC device at wavelengths of 500–600 nm were switched with voltage. The switching effect of light transmission in the green region was achieved by overlapping the plasmon resonance of the AgNC monolayer and multiple transmittance peaks caused by the birefringence of the LC layer. In addition, the color inversion appeared at cross-Nicole and parallel-Nicole because the LC layer functioned like a half-wave plate due to birefringence. The electrical modulation of the plasmonic color with LCs has a high implementation capability in microdevices and is anticipated to be applied in display devices or color filters.
... Copyright 2015, IOP Science. Reproduced with permission [31]. Copyright 2016 Wiley-VCH. ...
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Multifunctional electrochromic-induced rechargeable aqueous batteries (MERABs) integrate electrochromism and aqueous ion batteries into one platform, which is able to deliver the conversion and storage of photo-thermal-electrochemical sources. Aqueous ion batteries compensate for the drawbacks of slow kinetic reactions and unsatisfied storage capacities of electrochromic devices. On the other hand, electrochromic technology can enable dynamically regulation of solar light and heat radiation. However, MERABs still face several technical issues, including a trade-off between electrochromic and electrochemical performance, low conversion efficiency and poor service life. In this connection, novel device configuration and electrode materials, and an optimized compatibility need to be considered for multidisciplinary applications. In this review, the unique advantages, key challenges and advanced applications are elucidated in a timely and comprehensive manner. Firstly, the prerequisites for effective integration of the working mechanism and device configuration, as well as the choice of electrode materials are examined. Secondly, the latest advances in the applications of MERABs are discussed, including wearable, self-powered, integrated systems and multisystem conversion. Finally, perspectives on the current challenges and future development are outlined, highlighting the giant leap required from laboratory prototypes to large-scale production and eventual commercialization.
... Reversible switching or tuning of these localized optical resonances is necessary to realize display functionality [11,12]. So far, various tuning approaches have been explored in the literature, such as chemical reactions [13], thermal annealing process [6,[14][15][16], phase transition [17][18][19][20], mechanical stress [21][22][23], temperature change [24][25][26], hydrolysis [27], optical excitation [28], and electrical voltage [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. ...
Article
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Electrical switching of nanophotonic structural color elements is a promising approach towards addressable color switching pixels for next generation reflective displays. However, electrical switching between the primary colors to colorless near-white state remains a challenge. Here, we present a reversible electrical switching approach, relying on the electrocoagulation of Ag nanoparticles between silicon nanostructures that support Mie resonances. The electrodeposited Ag nanoparticles enable the excitation of the hybrid plasmon-Mie resonance as supported on Ag-silicon nanostructures, resulting in a large spectral transformation. Importantly, this process is reversible. This device design outperforms other designs in terms of electrotonic color control since it is highly stable and reliable for use in high-resolution reflective displays, such as colored electronic papers and smart display glass, where the combination is scalable to other nanostructure designs and electrolytic solutions.
... Both PPy and PEDOT tune over narrower wavelength ranges than PANI, making their color dynamics harder to recognize by eye from their DF images (Figure 2b and SI Figure S4). Although not as good as Au@ PANI in color dynamics for display applications, 5,6 Au@PPy and Au@PEDOT have been used in switching devices 21,22 as their absorption varies with their different redox states. Further FDTD simulations from different nanostructure configurations show the NPoM geometry gives consistent near-field enhancements in the gap, providing reliability for quantitative analysis of these polymers (SI Figure S3). ...
Article
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Conducting polymers are a key component for developing wearable organic electronics, but tracking their redox processes at the nanoscale to understand their doping mechanism remains challenging. Here we present an in-situ spectro-electrochemical technique to observe redox dynamics of conductive polymers in an extremely localized volume (<100 nm3). Plasmonic nanoparticles encapsulated by thin shells of different conductive polymers provide actively tuned scattering color through switching their refractive index. Surface-enhanced Raman scattering in combination with cyclic voltammetry enables detailed studies of the redox/doping process. Our data intriguingly show that the doping mechanism varies with polymer conductivity: a disproportionation mechanism dominates in more conductive polymers, while sequential electron transfer prevails in less conductive polymers.
... The two Al coating films are sufficiently spaced apart to prevent plasmonic coupling while effectively supporting the buildup of resonant fields within the crystalline silicon nano-resonator. A series of color filters shown in Fig. 13 J o u r n a l P r e -p r o o f posed an approach to suppress high-order multipoles and weak their confinement via replacing the high-contrast boundaries with index-matched boundaries 178 . The index matching is accomplished by inserting anti-reflection layers between the resonator and the boundaries. ...
... At present, electrochromic technology has a wide application prospect in the fields of smart window, display, electronic paper, military camouflage and so on. [4][5][6][7][8] Among the electrochromic materials, transition metal oxides (WO 3 , MoO 3 , Nb 2 O 5 , V 2 O 5 , NiO, etc.) have been identified as the most promising EC materials due to their fast redox reaction, higher coloration efficiency, and pleasing cyclic stability. 9,10 Among them, WO 3 , as the earliest electrochromic material, is a typical representative of cathodic electrochromic oxides with the advantages of high coloring efficiency, good reversibility, fast response, long life and low cost. ...
Article
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In this paper, nickel oxide films were deposited on ITO-coated glass substrates by DC magnetron sputtering at different pressures(1.2Pa~3.0Pa). The effects of sputtering pressure on microstructure and electrochromic properties of nickel oxide films were investigated. The film thickness was measured by a surface profilometer. The crystal structure and surface morphology of the films were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochromic properties of the films were studied by combining UV-visible spectrophotometer with electrochemical workstation. The results showed that the nickel oxide film obtained the best surface morphology (uniform grain size and the fewer surface cracks) and outstanding electrochromic performances, including large transmittance modulation (ΔT=57.19%), high coloration efficiency (CE=33.59cm2C-1) and fast switching speed (tc=4.63s, tb=4.87s) at a wavelength of 550 nm when the sputtering pressure was 2.4 Pa. And after 500 electrochemical cycles, the transmittance modulation could continue to increase to 61.49% and the coloration efficiency can still be maintained at about 28.21cm2C-1, which showed excellent cycling durability.
Article
Self-powered electrochromic devices (SECDs) that employ metal electrodes have attracted considerable attention owing to their low voltage, low energy consumption, and ability to function independently from external power supplies; however,...
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Inorganic electrochromic (EC) devices with vibrant multicolor variations are at the forefront of EC technology and play a crucial role in display applications. Expanding the dynamic color gamut of a single EC device has long been a subject of investigation. Herein, a design is presented that employs vanadium oxide (VO x ) as the EC layer and tungsten (W) as the reflective layer to construct an asymmetric Fabry–Pérot (F–P) nanocavity, enabling wide color gamut EC displays. By leveraging the different thicknesses of VO x , this design allows for a range of color changes from yellow and orange to magenta, purple, blue, cyan, and green through dynamic EC modulation. Notably, a typical single W‐VO x (150 nm) F–P nanocavity demonstrates an impressive modulation range of 110 nm, exceeding the capabilities of existing F–P nanocavities. In‐depth structural analysis reveals that the insertion and extraction of Li ⁺ ions significantly influence the microstructure and optical properties of VO x film, allowing for greater refractive index adjustment than WO 3 . This facilitates precise control and expansion of the nanocavity's color range through interference effects. This study provides a new perspective for developing dynamically adjustable wide color gamut EC displays and highlights their potential applications in flexible display technologies.
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Conjugated polymers with delocalized polarons and near‐infrared (IR) absorption properties are promising materials for applications in electrochemical devices. However, the poor stability of low bandgap polymers in electrochemical redox conditions limits the realization of such devices. Herein, a new family of near‐IR absorbing conjugated polymers based on diketopyrrolopyrrole (DPP) derivatives with methoxy substituents to achieve reversible p‐type electrochemical doping with bistable near‐IR electrochromism is designed. The extent of volumetric doping in various electrolytes using cyclic voltammetry and spectroelectrochemistry for optimal electrochemical kinetics and near‐IR contrast is systematically investigated. Further, the spray‐coated films of polymers display high open circuit memory as the methoxylation is increased on the polymer backbone. The contrasting electrochromic memory and kinetics observed for these polymers are mainly ascribed to two factors; i) the effect of backbone structure on the spatial extent of polaron delocalization, and ii) the ionization energy of the polymers. The utility of DPP‐based polymers as energy‐efficient electrochromic optical attenuators (EVOAs) with high near‐IR coloration efficiencies, and an optical attenuation value of 5.1 dB at 1.3 and 1.5 µm wavelengths is demonstrated. Furthermore, the experimental findings are corroborated with theoretical studies to establish that the polaron delocalization length is central to the performance of the device.
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Thin polymer films (TPFs) are indispensable elements in numerous technologies ranging from liquid encapsulation to biotechnology to electronics. However, their production typically relies on wet chemistry involving organic solvents or chemical vapor deposition, necessitating elaborate equipment and often harsh conditions. Here, an eco‐friendly, fast, and facile synthesis of water‐templated interfacial polymers based on cyanoacrylates (superglues, CAs) that yield thin films with tailored properties is demonstrated. Specifically, by exposing a cationic surfactant‐laden water surface to cyanoacrylate vapors, surfactant‐modulated anionic polymerization produces a manipulable thin polymer film with a thickness growth rate of 8 nm min⁻¹. Furthermore, the shape and color of the film are precisely controlled by the polymerization kinetics, wetting conditions, and/or exposure to patterned light. Using various interfaces as templates for film growth, including the free surface of drops and soap bubbles, the developed method advantageously enables in situ packaging of chemical and biological cargos in liquid phase as well as the encapsulation of gases within solidified bubbles. Simple, versatile, and biocompatible, this technology constitutes a potent platform for programmable coating and soft/smart encapsulation of fluids.
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Electrochromism is a technology that affects the reflectivity and color types of materials by applying an external voltage change, which has been gradually applied in mobile phones, automobiles and buildings...
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Electrically‐induced oblique helicoidal cholesterics (ChOH) are attractive for use in reflective displays due to tunable photonic band gap (PBG) in a broad spectral range and natural eye‐friendly feature. However, the lack of a stable liquid crystal (LC) material system with a wide temperature range and unknown driver architecture hinder the implementation of the ChOH‐based reflective displays. Here, a prototype for a full‐color reflective display device based on electrically‐tunable ChOH‐LC is demonstrated. In the comparison of ChOH‐S1, S2 and S3 samples, the electric‐field‐induced ChOH in the ChOH‐S3 exhibits intense Bragg reflection and a tunable PBG in the extended temperature range from 19.5 °C to 30 °C. Particularly, the resulting device exhibits a lower driving voltage and a relatively larger color gamut for the full‐color reflective displays. On this basis, the display patterns with variable colors are demonstrated via the direct addressing mode. Furthermore, a proof‐of‐concept of the full‐color reflective display is demonstrated with red‐green‐blue pixeled images serving as the active panels. Ultimately, by regulating the electric field strength dependent on the ambient temperature, a stable and vivid effect of the ChOH device on the actual environment is shown. This work provides valuable insight for the development of ChOH‐based reflective displays.
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The fusion of electrochromic technology with optical resonant cavities presents an intriguing innovation in the electrochromic field. However, this fusion is mainly achieved in liquid electrolyte‐based or sol–gel electrolyte‐based electrochromic devices, but not in all‐solid‐state electrochromic devices, which have broader industrial applications. Here, a new all‐solid‐state electrochromic device is demonstrated with a metal–dielectric–metal (MDM) resonant cavity, which can achieve strong thin‐film interference effects through resonance, enabling the device to achieve unique structural colors that have rarely appeared in reported all‐solid‐state electrochromic devices, such as yellow green, purple, and light red. The color gamut of the device can be further expanded due to the adjustable optical constants of the electrochromic layer. What is more, this device exhibits remarkable cycling stability (maintaining 84% modulation capability after 7200 cycles), rapid switching time (coloration in 2.6 s and bleaching in 2.8 s), and excellent optical memory effect (only increasing by 13.8% after almost 36 000 s). In addition, this exquisite structural design has dual‐responsive anti‐counterfeiting effects based on voltage and angle, further demonstrating the powerful color modulation capability of this device.
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Reflective pixels made by plasmonic metasurfaces and tuned by electrochromics exhibit significant potential to be used as flexible, polychromatic, electronic paper. This is attributed to their high reflectivity, low power consumption, and ultrathin dimensions. However, to date, only single pixels of electrochromics combined with plasmonics have been demonstrated. To make a graphical display, pixels in a matrix are required. A matrix configuration that has been successful for emissive displays such as liquid crystal displays (LCD) and organic light emitting-diodes (OLED) is the active matrix. Active matrix configurations consist of thin-film transistors (TFT) in an array where the transistors block unwanted signals. In this study, we demonstrate the suitability of a commercial, flexible TFT array as a substrate for depositing plasmonic metasurfaces in a red, green, and blue subpixel configuration. The conjugated polymer PProDOT-Me2 can be directly polymerized onto selected pixels from a monomer solution and individual pixels can be controlled. We demonstrate the ability of the TFT array to function both in an electrochemical 3-electrode setup and as a 2-electrode flexible device.
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Active plasmonic nanostructures have attracted tremendous interest in nanophotonics and metamaterials owing to the dynamically switchable capabilities of plasmonic resonances. In this study, tunable hybrid plasmon resonances (HPR) of sodium metasurfaces through heat‐initiated structural transformation is experimentally demonstrated. A HPR is formed by coupling surface plasmon polaritons (SPP) and gap plasmon resonances (GPR), whose resonant wavelengths are highly sensitive to gaseous nanogaps. By carefully manipulating the thermo‐assisted spin‐coating process and post‐thermal treatment, tuning of the HPR is achieved because of the phase transition between the antidome and nanodome structural profiles of liquid sodium inside the patterned fused silica substrates. Furthermore, the figure of merit of the heat initiated variable structure‐spectrum is demonstrated that is highly dependent on the size of the substrate patterns, based on which temperature‐sensitive plasmonic color and “invisible ink” of sodium metasurfaces are demonstrated. These findings can lead to new solutions for manipulating low‐cost and high‐performance active plasmonic devices.
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The introduction of metamaterials into electrochromic (EC) displays has recently inspired a great breakthrough in the EC field, as this can offer a variety of new attractive features, from a very wide gamut of colors to very fast switching times. However, such metamaterial-based EC displays still face significant constraints when developing from single electrodes to full devices, because other supportive components in devices, such as counter electrodes and electrolytes, significantly affect light propagation and the subsequent perceived color quality in metamaterial-based EC devices. Herein, we report a new, cost-effective device design structured around a new type of porous metamaterial to circumvent the critical problem in metamaterial-based EC displays. Owing to its unique design, the metamaterial-based EC device achieves good color quality with no drop in brightness or shift in color chromaticity when compared with a single electrode. Moreover, the porous metamaterial-based EC device can exhibit non-iridescence and be viewed from a wide range of angles (5°-85°) and has fast switching response (2.4 and 2.5 s for coloration and bleaching, respectively), excellent cycling performance (at least 2000 cycles), and extremely low power consumption (4.0 mW/cm2 ). This article is protected by copyright. All rights reserved.
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Electrochromic (EC) materials and devices, whose optical properties (color, reflectance, emittance, etc.) can be manipulated by switching a low-voltage bias, show great promise in many applications such as smart windows,...
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Tunable metal‐insulator‐metal (MIM) Fabry‐Pérot cavities that can dynamically control light enable novel sensing, imaging, and display applications. However, the realization of dynamic cavities incorporating stimuli‐responsive materials pose a significant engineering challenge. Current approaches rely on refractive index modulation and suffer from low dynamic tunability, high losses, limited spectral ranges and require liquid and hazardous materials for operation. To overcome these challenges, a new tuning mechanism employing reversible mechanical adaptations of a polymer network is proposed and dynamic tuning of optical resonances is demonstrated. Solid‐state temperature‐responsive optical coatings are developed by preparing a monodomain nematic liquid crystalline network (LCN) and are incorporated between metallic mirrors to form active optical microcavities. LCN microcavities offer large, reversible and highly linear spectral tuning of Fabry‐Pérot resonances reaching wavelength‐shifts up to 40 nm via thermo‐mechanical actuation while featuring outstanding repeatability and precision over more than 100 heating‐cooling cycles. This degree of tunability allows for reversible switching between the reflective and the absorbing states of the device over the entire visible and near‐infrared spectral regions, reaching large changes in reflectance with modulation efficiency ΔR = 79%. This article is protected by copyright. All rights reserved
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Thermoelectric (TE) devices exhibit considerable application potential in Internet of Things and personal health monitoring systems. However, TE self‐powered devices are expensive and their fabrication process is complex. Therefore, large‐scale preparation of the TE devices remains challenging. In this work, simple screen‐printing technology was used to fabricate a user‐friendly and high‐performance paper‐based TE device, which can be used in both stamp‐like paper‐based TE generators and infrared displays. When used as a paper‐based TE generator, an output power of 940.8 μW was achieved with a temperature difference of 40 K. The programmable infrared pattern based on the TE array display could be used to realize encryption and anti‐counterfeiting properties. Moreover, a visual extraction algorithm was used to develop a mobile application for processing and decoding the infrared quick response code information. Our findings offer an exciting approach to using paper‐based TEGs in applications such as energy harvesting devices, optical encryption, anti‐counterfeiting, and dynamic infrared display. This article is protected by copyright. All rights reserved
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Most organic semiconductors (OSCs) consist of conjugated skeletons with flexible peripheral chains. Their weak intermolecular interactions from dispersion and induction forces result in environmental susceptibilities and are unsuitable for many multifunctional applications where direct exposure to external environments is unavoidable, such as gas absorption, chemical sensing, and catalysis. To exploit the advantages of inorganic semiconductors in OSCs, ion‐in‐conjugation (IIC) materials are proposed. An IIC material refers to any conjugated material (molecules, polymers, and crystals) in Kekule's structural formula containing stoichiometric ionic states in its conjugated backbone in the electronic ground state. In this review, the definitions, structures, synthesis, properties, and applications of IIC materials are described briefly. Four types of IIC material, including zwitterionic conjugated molecules/polymers, conjugated ionic dyes, π‐d conjugated molecules and polymers, and coordinatively doped polymers, are reported. Their applications in gas sensing, humidity sensing, resistive memory devices, and thermal/photo‐/electro‐catalysis are demonstrated. The challenges and opportunities for future research are also discussed. It is expected that this work will inspire the design of new organic electronic information materials.
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Molecular plasmonics, the area which deals with the interactions between surface plasmons and molecules, has received enormous interest in fundamental research and found numerous technological applications. Plasmonic metamaterials, which offer rich opportunities to control the light intensity, field polarization, and local density of electromagnetic states on subwavelength scales, provide a versatile platform to enhance and tune light-molecule interactions. A variety of applications, including spontaneous emission enhancement, optical modulation, optical sensing, and photoactuated nanochemistry, have been reported by exploiting molecular interactions with plasmonic metamaterials. In this paper, we provide a comprehensive overview of the developments of molecular plasmonics with metamaterials. After a brief introduction to the optical properties of plasmonic metamaterials and relevant fabrication approaches, we discuss light-molecule interactions in plasmonic metamaterials in both weak and strong coupling regimes. We then highlight the exploitation of molecules in metamaterials for applications ranging from emission control and optical modulation to optical sensing. The role of hot carriers generated in metamaterials for nanochemistry is also discussed. Perspectives on the future development of molecular plasmonics with metamaterials conclude the review. The use of molecules in combination with designer metamaterials provides a rich playground both to actively control metamaterials using molecular interactions and, in turn, to use metamaterials to control molecular processes.
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Dynamically controllable reflective structural colors have been garnering growing attention due to increasing commercial interests in smart displays (e.g., colorimetric labels), colored e-readers, etc. To comply with the requirements of future displays, several strategies have been proposed by various research groups to achieve wide color tuning ranges in the visible regime, high on/off contrast ratios, and fast response times. In this review, we first introduce ways to create optical resonances including plasmonic, photonic, and plasmonic-photonic hybrid structures that form the basis of color generation. We then outline strategies that control the refractive index contrast between the system and the surrounding as a means to actively change the reflective structural colors, backed with representative examples from the literature. Finally, we provide a comparison of dynamic structural colors based on various switching mechanisms summarizing performance metrics that are important for future displays, and conclude with an outlook on current challenges.
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Manufacturing cost is a major concern for electrochromic device (ECD) applications in smart windows for energy saving and low-carbon economy. Fully printing instead of a vacuum-based chemical vapor deposition (CVD) process is favored for large-scale fabrication of ECDs. To adapt to the screen printing process, a UV curable solid-state electrolyte based on lithium bis(trifluoromethane-sulfonyl) imide (LiTFSI) was specially formulated. It contains poly(ethylene glycol) diacrylate (PEG-DA), LiTFSI, water, and ethyl acetate. The optimized ECDs have achieved a 0.6 s bleaching time at 0.6 V and a 1.4 s coloring time at -0.5 V. The ECDs also exhibited excellent stability, which could endure 100 000 cycles of color switching while still maintaining 35% of transmittance change at a 550 nm wavelength. A demo ECD has been fabricated with a screen printed electrolyte, exhibiting stable switching between the clear state and patterned color state.
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With vibrant colours and simple, room-temperature processing methods, electrochromic polymers have attracted attention as active materials for flexible, low-power-consuming devices. However, slow switching speeds in devices realized to date, as well as the complexity of having to combine several distinct polymers to achieve a full-colour gamut, have limited electrochromic materials to niche applications. Here we achieve fast, high-contrast electrochromic switching by significantly enhancing the interaction of light-propagating as deep-subwavelength-confined surface plasmon polaritons through arrays of metallic nanoslits, with an electrochromic polymer-present as an ultra-thin coating on the slit sidewalls. The switchable configuration retains the short temporal charge-diffusion characteristics of thin electrochromic films, while maintaining the high optical contrast associated with thicker electrochromic coatings. We further demonstrate that by controlling the pitch of the nanoslit arrays, it is possible to achieve a full-colour response with high contrast and fast switching speeds, while relying on just one electrochromic polymer.
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Plasmonic colour printing has drawn wide attention as a promising candidate for the next-generation colour-printing technology. However, an efficient approach to realize full colour and scalable fabrication is still lacking, which prevents plasmonic colour printing from practical applications. Here we present a scalable and full-colour plasmonic printing approach by combining conjugate twin-phase modulation with a plasmonic broadband absorber. More importantly, our approach also demonstrates controllable chromotropic capability, that is, the ability of reversible colour transformations. This chromotropic capability affords enormous potentials in building functionalized prints for anticounterfeiting, special label, and high-density data encryption storage. With such excellent performances in functional colour applications, this colour-printing approach could pave the way for plasmonic colour printing in real-world commercial utilization.
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This paper provides an overview of the main manufacturing technologies of displays, focusing on those with low and ultra-low levels of power consumption, which make them suitable for current societal needs. Considering the typified value obtained from the manufacturer's specifications, four technologies—Liquid Crystal Displays, electronic paper, Organic Light-Emitting Display and Electroluminescent Displays—were selected in a first iteration. For each of them, several features, including size and brightness, were assessed in order to ascertain possible proportional relationships with the rate of consumption. To normalize the comparison between different display types, relative units such as the surface power density and the display frontal intensity efficiency were proposed. Organic light-emitting display had the best results in terms of power density for small display sizes. For larger sizes, it performs less satisfactorily than Liquid Crystal Displays in terms of energy efficiency.
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Structural colour arising from nanostructured metallic surfaces offers many benefits compared to conventional pigmentation based display technologies, such as increased resolution and scalability of their optical response with structure dimensions. However, once these structures are fabricated their optical characteristics remain static, limiting their potential application. Here, by using a specially designed nanostructured plasmonic surface in conjunction with high birefringence liquid crystals, we demonstrate a tunable polarization-independent reflective surface where the colour of the surface is changed as a function of applied voltage. A large range of colour tunability is achieved over previous reports by utilizing an engineered surface which allows full liquid crystal reorientation while maximizing the overlap between plasmonic fields and liquid crystal. In combination with imprinted structures of varying periods, a full range of colours spanning the entire visible spectrum is achieved, paving the way towards dynamic pixels for reflective displays.
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With the advancement of wireless networks and cloud computing, people are becoming increasingly surrounded by a variety of displays rich electronic devices: TV, Phone, Pad, Notebook and other portable or wearable devices. These electronic products put high demands on the quality of the visual interface. Paper-like displays are reflective and do not require a backlight. They have received much attention after electrophoretic-based electronic paper displays were commercialized in 2004. Paper-like displays combine excellent reading experience with ultra-low power consumption. In particular, their outdoor readability is superior to transmissive liquid crystal displays (LCDs) and organic light emitting devices (OLEDs). In this paper, we give an overview on various paper-like display technologies with emphasis of the status and future development of electrophoretic display and electrofluidic display principles. We focus on both technologies because electrophoretic displays have been commercialized successfully, and electrofluidic display has high potential to deliver video and full color.
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Recent developments in color filtering and display technologies focus predominantly on high resolution, color vibrancy, high efficiency, and slim dimensions. To achieve these goals, metallic nanostructures have attracted extensive research interest due to their abilities to manipulate the properties of light through surface plasmon resonances. In this paper, we will review recent representative developments in plasmonic color engineering at the nanoscale using subwavelength nanostructures, demonstrating their great potential in high-resolution and high-fidelity color rendering, spectral filtering applications, holography, three-dimensional stereoscopic imaging, etc.
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Micro-actuators have been developed that exploit the electrochemically induced volume change of the electro-active polymer polypyrrole. The strain regime is inherently complex at a physical level and whilst volume change can be estimated indirectly using, for instance, bending beam theory, such methods become unreliable for large deflections owing to limitations in the mathematical model. A new non-contact measuring technique based on laser micrometry is presented to characterize the time-dependent expansion of electro-active films such as polypyrrole. Measurements have been made which demonstrate that the observed strain is dependent on film thickness. The new measurement technique is straightforward to perform and it is anticipated that it can be used for future materials development and performance assessment, including long-term stability evaluations and operational failure studies of the films.
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pi-Conjugated polymers that are electrochemically cycled in ionic liquids have enhanced lifetimes without failure (up to 1 million cycles) and fast cycle switching speeds (100 ms). We report results for electrochemical mechanical actuators, electrochromic windows, and numeric displays made from three types of pi-conjugated polymers: polyaniline, polypyrrole, and polythiophene. Experiments were performed under ambient conditions, yet the polymers showed negligible loss in electroactivity. These performance advantages were obtained by using environmentally stable, room-temperature ionic liquids composed of 1-butyl-3-methyl imidazolium cations together with anions such as tetrafluoroborate or hexafluorophosphate.
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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 CMYK printing techniques and 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 nano-antenna/slot design, and then mixed in a digital display analog 3x3 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 nano-rods 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 technique.
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A continuous-gradient approach of material evaporation is employed to fabricate nanostructures with varying geometric parameters such as thickness, lateral positioning, and orientation on a single substrate. The method developed for mask-lithography allows continuous tuning of the physical properties of a sample. The technique is highly valuable in simplifying the overall optimization process for constructing metasurfaces.
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Table of contents entry Nanoparticles of different materials, shapes, and sizes are integrated into plasmonic atoms and molecules of defined shape and location through sequential directed self-assembly following a single patterning step. A rational tuning of the emitted color across the visible range of the electromagnetic spectrum and switchable polarization properties are demonstrated. Self-assembled plasmonic pixels provide tunable, stable, and switchable optical responses.
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Colour generation by plasmonic nanostructures and metasurfaces has several advantages over dye technology: reduced pixel area, sub-wavelength resolution and the production of bright and non-fading colours. However, plasmonic colour patterns need to be pre-designed and printed either by e-beam lithography (EBL) or focused ion beam (FIB), both expensive and not scalable processes that are not suitable for post-processing customization. Here we show a method of colour printing on nanoimprinted plasmonic metasurfaces using laser post-writing. Laser pulses induce transient local heat generation that leads to melting and reshaping of the imprinted nanostructures. Depending on the laser pulse energy density, different surface morphologies that support different plasmonic resonances leading to different colour appearances can be created. Using this technique we can print all primary colours with a speed of 1 ns per pixel, resolution up to 127,000 dots per inch (DPI) and power consumption down to 0.3 nJ per pixel.
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Chromatic devices such as flat panel displays could, in principle, be substantially improved by incorporating aluminum plasmonic nanostructures instead of conventional chromophores that are susceptible to photo-bleaching. In nanostructure form, aluminum is capable of producing colors that span the visible region of the spectrum while contributing exceptional robustness, low cost, and streamlined manufacturability compatible with semiconductor manufacturing technology. However, individual aluminum nanostructures alone lack the vivid chromaticity of currently available chromophores because of the strong damping of the aluminum plasmon resonance in the visible region of the spectrum. In recent work, we showed that pixels formed by periodic arrays of Al nanostructures yield far more vivid coloration than the individual nanostructures. This progress was achieved by exploiting far-field diffractive coupling, which significantly suppresses the scattering response on the long-wavelength side of plasmonic pixel resonances. In the present work, we show that by utilizing another collective coupling effect, Fano interference, it is possible to substantially narrow the short-wavelength side of the pixel spectral response. Together, these two complementary effects provide unprecedented control of plasmonic pixel spectral lineshape, resulting in aluminum pixels with far more vivid, monochromatic coloration across the entire RGB color gamut than previously attainable. We further demonstrate that pixels designed in this manner can be used directly as switchable elements in liquid crystal displays and determine the minimum and optimal numbers of nanorods required in an array to achieve good color quality and intensity.
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Electrochromic materials display reversible color change upon electrochemical cycling. Within the last two decades there has been growing interest in the electrochromic properties of polypyrroles. In this article, we highlight and provide insight about the electrochromic properties of polypyrroles in terms of their structure-property relationships without the intention of providing a complete chronological order.
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We introduce the first plasmonic palette utilizing color generation strategies for photorealistic printing with aluminum nanostructures. Our work expands the visible color space through spatially mixing and adjusting the nanoscale spacing of discrete nanostructures. With aluminum as the plasmonic material, we achieved enhanced durability and dramatically-reduced materials costs with our nanostructures compared to commonly-used plasmonic materials such as gold and silver, as well as size regimes scalable to higher-throughput approaches such as photolithography and nanoimprint lithography. These advances could pave the way toward a new generation of low-cost, high-resolution, plasmonic color printing with direct applications in security tagging, cryptography, and information storage.
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Practical guest-host devices, in which dichroic dye molecules follow electrical switching of a liquid crystal host, remain elusive for decades despite promising efficient displays and emergent applications such as smart windows. This is mainly because of poor stability, surface precipitation, and limited means for property engineering of the dyes. To overcome these challenges, we develop plasmonic metal nanoparticle analogs of dichroic guest-host liquid crystals. Nematic dispersions of aligned anisotropic gold nanoparticles are obtained by polymer passivation of their surfaces to impose weak tangential boundary conditions for orientation of anisotropic host molecules. Control of the ensuing surface interactions leads to long-range ordered colloidal dispersions, allowing for collective optical and electrical switching of rod- and platelet-like nanoparticles. This facile control of mesostructured plasmonic medium's optical properties in visible and infrared spectral ranges is of interest for many applications.
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A novel type of plasmonic nanopore array in a metal–insulator–metal thin film is presented. The optical properties of this structure are described using a generic theoretical framework for surface waves in a coupled multilayer system. The characteristic spacing (short-range order) of the pores enables grating-type coupling to hybridized surface plasmons, with stronger coupling to some modes than others. The nature of the optical resonances and their excitation mechanisms can be conceptually understood from a charge distribution argument. The experimental results are further verified by numerical simulations, which also enable visualization of the near field. This study illustrates the surface plasmon characteristics (sensitive to periodicity) of the extinction maximum in the asymmetric spectral resonance induced by aperture arrays, while the transmission maximum corresponds to a resonance of localized character (sensitive to pore shape). Finally, the use of these nanopores for sensing applications through changes in the refractive index is evaluated.
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(Gold nanorod core)/(polyaniline shell) nanostructures are prepared for functioning as active plasmonic switches. The single core/shell nanostructures exhibit a remarkable switching performance, with the modulation depth and scattering peak shift reaching 10 dB and 100 nm, respectively. The nanostructures are also deposited on substrates to form macroscale monolayers with remarkable ensemble plasmonic switching performances.
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Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.
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The optical constants n and k were obtained for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV. The film-thickness range was 185-500 Å. Three optical measurements were inverted to obtain the film thickness d as well as n and k. The estimated error in d was ± 2 Å, and that in n, k was less than 0.02 over most of the spectral range. The results in the film-thickness range 250-500 Å were independent of thickness, and were unchanged after vacuum annealing or aging in air. The free-electron optical effective masses and relaxation times derived from the results in the near infrared agree satisfactorily with previous values. The interband contribution to the imaginary part of the dielectric constant was obtained by subtracting the free-electron contribution. Some recent theoretical calculations are compared with the results for copper and gold. In addition, some other recent experiments are critically compared with our results.
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We have developed a color and flexible electronic paper display using electronic liquid powder. Novel types of color display either colored powder or color filter are discussed. We have also developed a flexible display with low cost substrate films with a high throughput roll-to-roll manufacturing system. These technologies enable QR-LPD® to be used widely as an electronic paper display.
Article
Over the past twenty years, polypyrrole has appeared as the most extensively studied conducting polymer. However, despite the volume of work already done in this area, there has been little focus put on the mechanism of polypyrrole synthesis, especially concerning the most efficient method, electropolymerization. Numerous analytical techniques have been used to study polypyrrole electrodeposition and/or doping. However, the mechanism itself is still a controversial subject as there is not one mechanism which is universally accepted. The mechanism proposed by Diaz is the one most commonly referred to in the literature although several other mechanisms are not lacking in support. The controversy lies in the initiation step as each mechanism proposes a different way of beginning the reaction, varying between electron transfer, proton transfer and direct radical pyrrole formation. Without considering the initiation step, there are many other factors including electrolyte, solvent, temperature and pH which can influence the reaction mechanism during the electropolymerization of pyrrole, thus impacting the characteristics of the polymer formed at the electrode.
Article
By combining an electronically conductive polymer, a solid state polymer electrolyte and a metal oxide (vanadium oxide), a solid state electrochemical cell was constructed. The optical absorption of the cell could easily be changed by changing the applied cell potential. The polymeric materials used have the advantage of very easy fabrication of thin films: spin-coating or solution-casting for poly(3-octylthiophene) and template polymerization for polypyrrole. Owing to the difference in coulombic capacity and coloration efficiency between the metal oxide and the conjugated polymer, the optical changes of the cell are mainly due to optical changes of the polymer. Thus, this technique can also be used for studying the doping process of the polymer and the stability of the states induced by doping.
Article
We present the fabrication and optical characterization of plasmonic nanostructures consisting of nanohole arrays in two thin films, a metal and a dielectric. A novel method called mask-on-metal colloidal lithography is used to prepare high aspect ratio holes, providing efficient mass fabrication of stable structures with close to vertical walls and without the need for an adhesion layer under the metal. Our approach for understanding the transmission properties is based on solving the dispersions of the guided modes supported by the two films and calculating the influence from interference. The methodology is generic and can be extended to multilayered films. In particular, the influence from coupling to waveguide modes is discussed. We show that by rational design of structural dimensions it is possible to study only bonding surface plasmons and the associated hole transmission maximum. Further, numerical simulations with the multiple multipole program provide good agreement with experimental data and enable visualization of the asymmetric near field distribution in the nanohole arrays, which is focused to the interior of the "nanowells". The refractometric sensitivity is evaluated experimentally both by liquid bulk changes and surface adsorption. We demonstrate how the localized mode provides reasonably good sensitivity in terms of resonance shift to molecular binding inside the voids. Importantly, high resolution sensing can be accomplished also for the surface plasmon mode, despite its extremely low figure of merit. This is accomplished by monitoring the coupling efficiency of light to plasmons instead of conventional sensing which is based on changes in plasmon energy. We suggest that these nanohole structures can be used for studying molecular transport through nanopores and the behavior of molecules confined in volumes of approximately one attoliter.
Article
Elastic scattering measurements show that isolated nanometric holes in optically thin Au films exhibit a localized surface plasmon resonance in the red to near-infrared region. The hole plasmon red shifts with increasing hole diameter or increasing refractive index of the surrounding medium, analogous to a dipolar particle plasmon. A pronounced blue shift is observed when the distance between holes is decreased, indicating an enhanced coupling between holes mediated by surface plasmon polaritons of the intervening flat film surface.
Article
Conjugated polymers such as polypyrrole (PPy) have potential use as artificial muscles or in microsystems such as valves for microfluid handling. One of the most important parameters in such uses is the magnitude of volume change during associated redox processes; however, until now, estimates have varied greatly. Atomic force microscopy is reported here as allowing direct measurement of the in situ thickness change during oxidation and reduction of thin films of PPy doped with dodecylbenzenesulfonate.
Article
Many nanotechnological devices are based on implementing electrochemistry with plasmonic nanostructures, but these systems are challenging to understand. We present a detailed study of the influence of electrochemical potentials on plasmon resonances, in the absence of surface coatings and redox active molecules, by synchronized voltammetry and spectroscopy. The experiments are performed on gold nanodisks and nanohole arrays in thin gold films, which are fabricated by improved methods. New insights are provided by high resolution spectroscopy and variable scan rates. Furthermore, we introduce new analytical models in order to understand the spectral changes quantitatively. In contrast to most previous literature, we find that the plasmonic signal is caused almost entirely by the formation of ionic complexes on the metal surface, most likely gold chloride in this study. The refractometric sensing effect from the ions in the electric double layer can be fully neglected, and the charging of the metal gives a surprisingly small effect for these systems. Our conclusions are consistent for both localized nanoparticle plasmons and propagating surface plasmons. We consider the results in this work especially important in the context of combined electrochemical and optical sensors.
Article
The new international standards, which define a standard observer, three standard illuminants, standard conditions of illuminating and viewing opaque specimens, a standard for evaluating the brightness factor of opaque specimens, and a standard trichromatic system for the expression of colour measurements, are stated and their origin explained. In addition to the numerical tables which are appended to the resolutions setting up these standards, there are given a table specifying the trichromatic coordinates for the standard observer of all spectral colours at wave-length intervals of 1 mμ, tables to facilitate the calculation of the standard coordinates and the brightness factor of a material illuminated by any one of the three standard illuminants from spectrophotometric measurements on the material, and a table giving the coordinates of some stimuli of special importance on the N.P.L. system, the standard system, and another system which occurs in the resolutions. Some new colorimetric terms are proposed, partly to avoid misinterpretation and partly to meet new needs. The theory of colour transformations, and points which arise in the application of the system and in the calibration of instruments, are discussed.
Article
It has for many years been an ambition of researchers in display media to create a flexible low-cost system that is the electronic analogue of paper. In this context, microparticle-based displays have long intrigued researchers. Switchable contrast in such displays is achieved by the electromigration of highly scattering or absorbing microparticles (in the size range 0.1-5μm), quite distinct from the molecular-scale properties that govern the behaviour of the more familiar liquid-crystal displays. Microparticle-based displays possess intrinsic bistability, exhibit extremely low power d.c. field addressing and have demonstrated high contrast and reflectivity. These features, combined with a near-lambertian viewing characteristic, result in an `ink on paper' look. But such displays have to date suffered from short lifetimes and difficulty in manufacture. Here we report the synthesis of an electrophoretic ink based on the microencapsulation of an electrophoretic dispersion. The use of a microencapsulated electrophoretic medium solves the lifetime issues and permits the fabrication of a bistable electronic display solely by means of printing. This system may satisfy the practical requirements of electronic paper.
Article
Biosensing with nanoholes is one of the most promising applications of nanoplasmonic devices. The sensor properties, however, are complex due to coupled resonances through propagating and localized surface plasmons. This Full Paper demonstrates experimental and simulation studies on different plasmonic hole systems, namely various patterns of circular holes in gold films. In contrast to most previous work, here, the challenging situation of optically thin films is considered. The refractive-index-sensing properties, such as sensitive locations in the nanostructure and sensitive spectral features, are investigated. The multiple multipole program provides the complete field distribution in the nanostructure for different wavelengths. It is shown that the spectral feature most sensitive to refractive-index changes is the extinction minimum, rather than the maximum. The results are consistent with theory for perfect electrical conductors. The spectral response is investigated for molecular adsorption at different positions inside or outside a hole. Furthermore, the optical properties of nanohole arrays with long-range and short-range order are compared and found to demonstrate remarkable similarities. Our results help to predict the resonance wavelengths of nanoholes with arbitrary patterns, including short-range order. The results presented here are highly important since they extend and challenge several aspects of the current understanding of plasmon resonances in nanohole arrays. These theoretical models, simulation results, and experimental data together help provide the understanding necessary for the development of efficient biomolecular analysis tools based on metallic nanoholes.
Article
Due to the continuously increasing demand for ultimate miniaturization of electronic and photonic systems, molecular electronics and plasmonic devices are currently booming as alternative technologies because of their very promising potential in writing, reading, storing, and processing information at the nanoscale. Conducting polymers or oligomers have been proposed and used as basic building blocks in molecular and plastic electronics since the end of the 80s. Plasmonics is, on the other hand, an emerging branch of photonics which uses nanostructured materials that support surface plasmons. Among plasmonic devices, active plasmonic devices are still lacking. In this work, we report on new active molecular plasmonic devices in which the electrochemical switching of a nanometric film of conductive polymer between its reduced and oxidized state is used in order to control, switch, and modulate localized surface plasmon (LSP) resonance of gold nanoparticle arrays.
Article
The colorimetric variations induced upon changes in interfacial refractive index of nanoscale noble metal structures exhibiting localized surface plasmon resonance (LSPR) provides a convenient means of label-free, affinity-based detection of biomolecular recognition reactions. However, despite being similar in nature to conventional SPR, LSPR has so far suffered from significantly lower data quality in terms of its signal-to-noise ratio (S/N) in typical biomolecular recognition analysis. In this work, generic data analysis algorithms and a simple experimental setup that provide a S/N upon protein binding that is comparable to that of state-of-the art SPR systems are presented. Specifically, it is demonstrated how temporal variations (rate approximately 0.5 Hz) in parameters proportional to the resonance peak position can be recorded simultaneously, yielding a peak position precision of <5 x 10(-4) nm and an extinction noise level of <5 x 10(-6) absorbance units (Abs). This, in turn, is shown to provide a S/N of approximately 2000 (equivalent to a detection limit of <0.1 ng/cm(2)) for typical protein binding reactions. Furthermore, the importance of utilizing changes in both peak position and magnitude is highlighted by comparing different LSPR active noble metal architectures that respond differently to bulk and interfacial refractive index changes.
Article
The conjugated polymer polypyrrole undergoes a volume change of several percent when its oxidation state is changed electrochemically by the application of voltages between 0 and -1 V (versus Ag/AgCl). This volume change is due to ion movements in or out of the polymer film. Bilayers of polypyrrole and gold undergo a large bending and can deliver high force. They can thus function as hinges to lift rigid components. In this work, we demonstrate that silicon plates produced by reactive ion etching can be lifted by such PPy/Au hinges. The strength and efficiency of these bilayers are also determined
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