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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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... One application with strong recent interest is structural colors arising from resonances that occur in the visible. 1 Utilized since ancient times, 2 such colors have advantages such as high stability compared to organic dyes and the possibility to "print" with very high resolution compared to ink. 1 Also, due to the strong interaction with light, ultrathin (<1 μm) nanostructures or "metasurfaces" are sufficient to generate vibrant colors. 3 Recently, there has also been an increased interest in active plasmonic devices, where the optical properties can be changed on demand. 4−8 In particular, tuning of structural colors in this manner is highly interesting for new types of displays. ...
... 5,12−15 Alternatively, inorganic electrochromic materials have been considered for display applications since the pioneering work of Deb. 16 Transition metal oxides, in particular, WO 3 , 17 have been frequently studied due to their application in electrochromic windows. 18 Just during the last year, there has been a strong interest in implementing inorganic materials for new types of electrochromic devices. ...
... Like in our initial work, 3 we use the L(λ) function representing photoptic vision (good illumination conditions) since this is the likely scenario for display of structural colors. ...
Article
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Plasmonic structural colors have recently received a lot of attention. For many applications there is a need to actively tune the colors after preparing the nanostructures, preferably with as strong changes in the optical response as possible. However, to date there is a lack of systematic investigations on how to enhance contrast in electrically induced color modulation. In this work we implement electrochromic films with plasmonic metasurfaces and compare systematically organic and inorganic materials, with the primary aim to maximize brightness and contrast in a reflective color display. We show nanostructures with good chromaticity and high polarization-insensitive reflectivity (~90%) that are electrochemically stable in a non-aqueous solvent. Methods are evaluated for reliable and uniform electropolymerization of the conductive polymer dimethylpropylenedioxythiophene (PProDOTMe2) on gold. The resulting organic films are well-described by Lambert-Beer formalism and the highest achievable contrast is easily determined in transmission mode. The optical properties of the inorganic option (WO3) require full Fresnel models due to thin film interference and the film thickness must be carefully selected in order to maintain the chromaticity of the metasurfaces. Still, the optimized fully inorganic device reaches the highest contrast of approximately 60% reflectivity change for all primary colors. The switching time is about an order of magnitude faster for the organic films (hundreds of ms). The bistability is very long (hours) for the inorganic devices and comparable for the polymers, which makes the power consumption essentially zero for maintaining the same state. Finally, we show that switching of the primary colors in optimized devices (both organic and inorganic) provides almost twice as high brightness and contrast compared to existing reflective display technologies with RGB subpixels created by color filters.
... However this limits their adoption since tuneability is limited and creating the forces required is nontrivial, particularly electrically. By contrast, combining plasmonic systems such as gratings [15] or thin-film cavities [16] with stimulus-responsive materials [1] such as electrochromic [2,[15][16][17][18] or phase change materials, [19][20][21][22] promises electrically-tunable color switching. However these devices are typically rigid and suffer from limited optical switching (solely "on-off" function), [15][16][17][18] long response times (multi-second) [22] and/or poor long-term reproducibility (<1 month). ...
... However this limits their adoption since tuneability is limited and creating the forces required is nontrivial, particularly electrically. By contrast, combining plasmonic systems such as gratings [15] or thin-film cavities [16] with stimulus-responsive materials [1] such as electrochromic [2,[15][16][17][18] or phase change materials, [19][20][21][22] promises electrically-tunable color switching. However these devices are typically rigid and suffer from limited optical switching (solely "on-off" function), [15][16][17][18] long response times (multi-second) [22] and/or poor long-term reproducibility (<1 month). ...
... By contrast, combining plasmonic systems such as gratings [15] or thin-film cavities [16] with stimulus-responsive materials [1] such as electrochromic [2,[15][16][17][18] or phase change materials, [19][20][21][22] promises electrically-tunable color switching. However these devices are typically rigid and suffer from limited optical switching (solely "on-off" function), [15][16][17][18] long response times (multi-second) [22] and/or poor long-term reproducibility (<1 month). [23] Large-area nanopatterning is another challenge confronting the fabrication of these flexible systems. ...
Article
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Plasmonic metafilms have been widely utilized to generate vivid colors, but making them both active and flexible simultaneously remains a great challenge. Here flexible active plasmonic metafilms constructed by printing electrochromic nanoparticles onto ultrathin metal films (<15 nm) are presented, offering low‐power electricallydriven color switching. In conjunction with commercially available printing techniques, such flexible devices can be patterned using lithography‐free approaches, opening up potential for fullyprinted electrochromic devices. Directional optical effects and dynamics show perceived upward and downward colorations can differ, arising from the dissimilar plasmonic mode excitation between nanoparticles and ultrathin metal films.
... Thus far, there are several classic reviews that are devoted to the field of dynamic plasmonics. 21,22 Several strategies have been proposed for dynamic plasmonics, including electrical controls by carrier doping (graphene) [23][24][25] or refractive index manipulation [liquid crystal (LC)] 26 with the applied voltage, chemical reactions by varying the pH value and biological species, [27][28][29][30] electrochemical redox reactions by manipulating structures or carrier-densities of plasmonic materials themselves or surrounding materials, [31][32][33][34][35][36][37] thermal stimuli by phase-change materials (such as vanadium dioxide) and thermo responsive polymer materials [such as poly(methyl methacrylate)], [38][39][40][41][42][43] mechanical strains by varying microstructures (such as period or distance between periodic plasmonic structures) through the flexible polymers substrate (such as polydimethylsiloxane), [44][45][46][47] optical excitations with photochromic molecules and quantum dots, [48][49][50][51] and magnetically driven approaches with magneto-plasmonic systems combining noble metals and ferromagnetic components (for example, Au-Fe 3 O 4 nanostructures). [52][53][54][55] Among the above-mentioned versatile dynamic-control strategies, electrochemically driven dynamic plasmonics, which serves as an intermediate approach between pure electric controls and chemical reactions, not only features flexible on-chip integration but also benefits from versatile chemical transformations, inspiring more extensive research interest and a broad range of potential applications. ...
... One of the most representative cases is the electrochromic materials, including inorganic tungsten oxide (WO 3 ) and organic polymers. 26,33,[86][87][88][89] Two effective strategies for dynamic control of the refractive index of electrochromic materials are ion insertion and redox reactions of polymers. Ion injection into the surrounding media can be a powerful way to electrically tune the plasmonic resonances. ...
... Another EC-based plasmonic coloration concept with potential applications for flexible plasmonic video displays and full-color electronic papers has been suggested by Xiong et al. (69). The authors electropolymerized thin layers of polypyrrole with thicknesses between 110 and 260 nm on a nanohole array residing on an Al 2 O 3 layer supported by Ag mirror (see Fig. 5B). ...
... Given the minimum pixel size of 10 m × 10 m or even below, the merged pixels are still on the order of 100 times smaller than those of current high-resolution displays. However, an ultrahigh resolution of 10,000 dpi can still be reached with plasmonic display devices (54,69). In contrast to the excellent resolution, the dynamic control of plasmonic colors strongly depends on the coloration concept and functional material (see Fig. 1, E to H). ...
Article
Full-text available
Displays are an indispensable medium to visually convey information in our daily life. Although conventional dye-based color displays have been rigorously advanced by world leading companies, critical issues still remain. For instance, color fading and wavelength-limited resolution restrict further developments. Plasmonic colors emerging from resonant interactions between light and metallic nanostructures can overcome these restrictions. With dynamic characteristics enabled by functional materials, dynamic plasmonic coloration may find a variety of applications in display technologies. In this review, we elucidate basic concepts for dynamic plasmonic color generation and highlight recent advances. In particular, we devote our review to a selection of dynamic controls endowed by functional materials, including magnesium, liquid crystals, electrochromic polymers, and phase change materials. We also discuss their performance in view of potential applications in current display technologies.
... Another prime application example of CPs is soft mechanical actuators for biomedical and applications. When immersed in an ionic solution, CPs can undergo dimensional changes in response to an electric charge, and consequently they are capable of transducing the electrochemical energy directly into mechanical work [6]. The latter can be converted into a variety of forms i.e. bending, linear or out of plane deformation according to the different device architectures [43 45]. ...
... CPs materials can have electrical properties similar to semiconductors and metals while their mechanical properties are relatively similar to conventional polymers [4]. Besides, their response to electrochemical oxidation or reduction can produce a reversible change in conductivity [5], color [6], wettability [7], and volume [8]. Such unique hybrid electronic-ionic conductivity, mechanical softness and biocompatibility make them favored candidates for a wide range of applications including neural interfaces, medical implants, biosensors, drug delivery systems and bioactive tissue engineering scaffolds [1,2,9 11]. ...
Article
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Conducting polymers are an exciting class of organic electronic materials, which have attracted an increasing interest in the fields of bioelectronics and their biomedical applications. Their unique features such as mixed ionic-electronic conductivity, good biocompatibility, as well as mechanical softness make them favored candidates for an effective conduit between the worlds of electronics and biology. In addition, the facile synthesis, simple functionalization, and ability to electronically control a range of physical and chemical properties of these materials has enabled considerable development for biorecognition and biosensors devices. In this review, we have turned our attention to recent progress in the tailoring of the conducting polymers functionalities, focusing especially on neural interfaces, molecularly imprinted conducting polymers for biorecognition and bioactive scaffolds for mechanotransduction in living cells.
... However, these approaches generally rely on the use of plasmonics, which comes with the drawback of substantial Ohmic losses in the visible region, which detrimentally affects the brightness and color performance. Other noteworthy strategies include employing electrochromic semi-conductors [30][31][32] or polymers 33 with optical properties that can be controlled electrically, and also the physical manipulation of the spatial locations of the metaatoms through the use of stretchable substrates 34 . ...
Article
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Taking inspiration from beautiful colors in nature, structural colors produced from nanostructured metasurfaces have shown great promise as a platform for bright, highly saturated, and high-resolution colors. Both plasmonic and dielectric materials have been employed to produce static colors that fulfil the required criteria for high-performance color printing, however, for practical applications in dynamic situations, a form of tunability is desirable. Combinations of the additive color palette of red, green, and blue enable the expression of further colors beyond the three primary colors, while the simultaneous intensity modulation allows access to the full color gamut. Here, we demonstrate an electrically tunable metasurface that can represent saturated red, green, and blue pixels that can be dynamically and continuously controlled between on and off states using liquid crystals. We use this to experimentally realize ultrahigh-resolution color printing, active multicolor cryptographic applications, and tunable pixels toward high-performance full-color reflective displays. Ellipsoidal-shaped Mie resonators are integrated with a liquid crystal cell to demonstrate electrically tunable reflective structural color metasurfaces that can be modulated continuously from bright spectral colors to dark blacks.
... Figure 2G implies the in situ transmission curve obtained when CV anode scanning (−0.8~0.1 V) was exerted on the nanohole electrode array in the NaClO 4 solution with the pyrrole monomer [110]. PPy has also been electropolymerized on the surface of plasmonic nanohole arrays to realize the reflection tuning of structural color with higher optical contrast [111,112]. As an electrochromic polymer material, poly(3,4-ethylene dioxythiophene) (PEDOT) is almost transparent in its oxidized state (conductive), and deep blue in its reduced state (insulating) when it is applied a voltage of 0.6 and −1 V, respectively. ...
Article
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With their ultrathin characteristics as well as the powerful and flexible capabilities of wavefront modulation, optical metasurfaces have brought a new understanding of the interaction between light and matter and provided a powerful way to constrain and manage light. However, the unmodifiable structures and the immutable materials used in the construction lead to the unsatisfactory applications in most functional devices. The emergence of tunable optical metasurfaces breaks the aforementioned limitations and enables us to achieve dynamic control of the optical response. The work in recent years has focused on achieving tunability of optical metasurfaces through material property transition and structural reconfiguration. In this review, some tunable optical metasurfaces in recent years are introduced and summarized, as well as the advantages and limitations of various materials and mechanisms used for this purpose. The corresponding applications in functional devices based on tunability are also discussed. The review is terminated with a short section on the possible future developments and perspectives for future applications.
... Tracking the LSPR shift and colorimetric responses are an established approach to various chemical sensors. Typically, chemical stimuli include humidity, pH, electrochemical reactions, ionic strength, and biological molecules (Gao et al., 2012;Byers et al., 2015;Xiong et al., 2016). The semiconducting polyaniline has great variations in its conductivity and dielectric properties upon protonation. ...
Article
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Plasmonic nanostructures, particularly of noble-metal Au and Ag, have attracted long-lasting research interests because of their intriguing physical and chemical properties. Under light excitation, their conduction electrons can form collective oscillation with the electromagnetic fields at particular wavelength, leading to localized surface plasmon resonance (LSPR). The remarkable characteristic of LSPR is the absorption and scattering of light at the resonant wavelength and greatly enhanced electric fields in localized areas. In response to the chemical and physical changes, these optical properties of plasmonic nanostructures will exhibit drastic color changes and highly sensitive peak shifts, which has been extensively used for biological imaging and disease treatments. In this mini review, we aim to briefly summarize recent progress of preparing responsive plasmonic nanostructures for biodiagnostics, with specific focus on cancer imaging and treatment. We start with typical synthetic approaches to various plasmonic nanostructures and elucidate practical strategies and working mechanism in tuning their LSPR properties. Current achievements in using responsive plasmonic nanostructures for advanced cancer diagnostics will be further discussed. Concise perspectives on existing challenges in developing plasmonic platforms for clinic diagnostics is also provided at the end of this review.
... Remarkably, Figure 3c shows that nanopixels with only 2 × 2 nanoantennae can exhibit vibrant alternating black-and-blue dots. The total area of such a nanopixel is 500 × 500 nm 2 , which is equivalent to a spatial resolution of around 50,000 dots per inch (dpi) and exceeds the reported values in the most recent literature [35][36][37][38][39][40] . This effect originates from the LSPR's high field confinement at the nanoantenna/air interface [41][42][43][44][45] . ...
Preprint
Plasmonic color generation utilizing ultra-thin metasurfaces as well as metallic nanoparticles hold a great promise for a wide range of applications, including color displays, data storage, and information encryption due to its high spatial resolution and mechanical/chemical stability. Most of the recently demonstrated systems generate static colors; however, more advanced applications such as data storage require fast and flexible means to tune the plasmonic colors, while keeping them vibrant and stable. Here, a surface-relief aluminum metasurface that reflects polarization-tunable plasmonic colors is designed and experimentally demonstrated. Excitation of localized surface plasmons encodes discrete combinations of the incident and reflected polarized light into diverse colors. A single storage unit - a nanopixel - stores a multiple-bit piece of information in the orientation of its constituent nanoantennae. This information is then reliably retrieved by inspecting the reflected color sequence with two linear polarizers. It is the broad color variability and high spatial resolution of the proposed encoding approach that supports a strong promise for rapid parallel read-out and encryption of high-density optical data. Our method also enables the robust generation of dynamic kaleidoscopic images with no detrimental "cross-talk" effect. The approach opens up a new route for advanced dynamic steganography, high-density parallel-access optical data storage, and optical information encryption.
... Given the minimum pixels size of 10 µm × 10 µm or even below, the merged pixels are still on the order of 100 times smaller than those of current high resolution displays. However, an ultra-high resolution of 10,000 dpi can still be reached with plasmonic display devices (54,69). In contrast to the excellent resolution, the dynamic control of plasmonic colors strongly depends on the coloration concept and functional material (see Fig. 1E-H). ...
Preprint
Full-text available
Displays are an indispensable medium to visually convey information in our daily life. Although conventional dye-based color displays have been rigorously advanced by world leading companies, critical issues still remain. For instance, color fading and wavelength-limited resolution restrict further developments. Plasmonic colors emerging from resonant interactions between light and metallic nanostructures can overcome these restrictions. With dynamic characteristics enabled by functional materials, dynamic plasmonic coloration may find a variety of applications in display technologies. In this review, we elucidate basic concepts for dynamic plasmonic color generation and highlight recent advances. In particular, we devote our review to a selection of dynamic controls endowed by functional materials, including magnesium, liquid crystals, electrochromic polymers, and phase change materials. We also discuss their performance in view of potential applications in current display technologies.
... 14 In addition, based on the resonance principle of nanostructures, the displayed colors cannot be switched without modifying the structure or environment. 24,32 Although dynamic color modulation has been realized based on the resonance principle of nanostructures with the assist of hydrogenation and dehydrogenation processes, 33,34 electrochromic oxides, 35 multidimensional hybridization, 36 and conjugated polymers, 37 the challenge remains that the dynamic plasmonic displays have substantially reduced spatial resolutions than the static images generated by subdiffraction-limited plasmonic pixels. 38 In addition, the responses of hydrogenation and electrochromic oxides are relatively slow. ...
... A single layer with uniform microsphere distribution will achieve the best Mie scattering intensity for the disordered structure. Meanwhile, the spraying method provides us a simple and efficient way to generate rainbow colors based on Mie scattering compared with complex designs and elaborate structures [36,37]. ...
Article
Structural color materials, which generate colors through the interaction between light and nano-microstructures, have always been research hotspots in the fields of display, anticounterfeiting and stimuli-responsive materials. Structural colors based on scattering have received increasing attention due to their wider viewing angles than that originating from the specular reflection of photonic crystals. However, the wide scattering spectrum of an amorphous structure leads to lower purity and brightness of the appeared colors. Few researchers have focused on the scattering of ordered structures due to their strong reflection and diffraction in the visible regions. In this work, by building ordered films (OFs) using SiO2 spheres (refractive index n = 1.46) with a diameter of 300–500 nm, for the first time, sharp scattering spectra with narrow full width at half-maximum (FWHM, 24 nm) were generated. Importantly, under ambient light, brilliant colors covering the entire visible region can be observed, and a formula was proposed to calculate the scattering spectra of OFs. Moreover, rainbow structural color was realized under irradiation of the nonparallel light, and full-spectrum structural color patterns were fabricated using building blocks with a single particle size by a spraying method. Finally, a composite structure was constructed to explore possibilities in the field of flexible transparent displays.
... These functions include diverging and converging of the electromagnetic wave front due to phase change [25], polarization control and switching based on Ge 2 Sb 2 Te 5 disks [26], diffraction-based spectral scatterrers [27], fullspectrum tunable bandgap and bandpass filters in the visible and near-infrared range [28], as well as chiral [29,30], nonlinear [31,32] and quantum [33] opti-cal effects. Due to their range of control on electromagnetic fields, metasurfaces have been used in the development of reflection-based displays and electronic paper [34][35][36][37], solar light concentrators in photovoltaic devices [38,39], biological and thermal sensors [40,41], with tunable-spectrum variations employing elastic materials [42], liquid crystals [43,44] and MEMS devices [45]. ...
Article
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In this paper, we theoretically investigate the spectroscopic properties of a simple hybrid metasurface consisting in a periodic array of a Si-Au pattern in the mid-infrared spectral region. Our simulations show that our hybrid metasurface exhibits a strong spectral absorption band in the 5.5μm−10μm region, by comparison to the typical Au-Au counterpart. A considerable improvement to the full-metal metasurface approach is that resonance in the mid-infrared is obtained with a pattern cell of just λ/1.5 instead of the typical λ/5 to λ/8 requirement that occurs in full-metal structures, which relaxes the manufacturing constraints. To fully characterize the surface around resonance, we also performed wave propagation and thermal deposition investigations, the latter of which allows predictions of the shift in the resonance frequency caused by thermal dilation. The proposed metasurface constitutes a good candidate for use in mid-infrared and thermal detection devices, and benefits from the advantages of on-chip integration and scalability in THz generation-detection systems.
... Compared to traditional FP MIM cavities, which produce dull band-stop reflected colors, the broadband absorption of these structures results in bright, band-pass reflectance peaks [15,17]. Self-assembled metasurfaces based on plasmonic nanoparticles offer further control over the absorption profile of the top layer (and resulting color response of the entire stack), while maintaining scalable device fabrication [17][18][19][20][21][22]. Franklin et al. recently demonstrated an innovative plasmonic MIM structure for display applications, which produced vivid, angle-independent reflective colors that were tuned by varying the nanoparticle size during deposition [19]. ...
Article
Dynamically reconfigurable structural colors are promising materials for new smart optical systems. However, improved reflected color quality (e.g., saturation, optical contrast, angular invariance) and larger tuning range/sensitivity are needed. Here, we demonstrate a vibrant, actively tunable system which meets these needs via coupling broadband plasmonic resonators to a responsive polymer film. Our structure consists of near-percolation gold nanoislands deposited on a poly[methyl methacrylate] (PMMA) spacer above a gold mirror, forming a Fabry-Pérot nanocavity. Broadband absorption in this system creates vivid reflected colors, while the polymer spacer enables continuous tuning over a wide color space. By exploiting swelling effects in PMMA, we show fast, reversible color switching in response to organic vapors. Our sensitive optical structure amplifies small vapor-induced changes in the spacer thickness, enabling naked-eye detection of changes as small as 10 nm. Additionally, optical absorption >99% yields modulation contrasts up to 80:1, opening the door to ultra-sensitive on-chip signal measurements, complementing the visual colorimetric readout. This structure has immediate implications for colorimetric bio/chemical sensing and may also find application to reflective displays and flexible/adaptive optical coatings.
... Coupled with increased photostability and the potential to engineer the polarization, phase, and amplitude of light, optical nanostructures can improve current displays and lead to novel forms. Several examples of nanostructure-integrated displays have been demonstrated, in which metallic nanostructures generate color (1)(2)(3) and are then combined with liquid crystal modes (4,5), electroactive polymers (6)(7)(8)(9), or phase-change materials (10) to modulate the amplitude of reflected/transmitted light. Alternatively, the plasmonic resonances of these metallic nanostructures can be tuned via liquid crystal orientation (11,12) (our previous work) or reversible chemical reactions (9,(13)(14)(15)(16)(17) to result in novel color-changing surfaces. ...
Article
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Nanostructured plasmonic materials can lead to the extremely compact pixels and color filters needed for next-generation displays by interacting with light at fundamentally small length scales. However, previous demonstrations suffer from severe angle sensitivity, lack of saturated color, and absence of black/gray states and/or are impractical to integrate with actively addressed electronics. Here, we report a vivid self-assembled nanostructured system which overcomes these challenges via the multidimensional hybridization of plasmonic resonances. By exploiting the thin-film growth mechanisms of aluminum during ultrahigh vacuum physical vapor deposition, dense arrays of particles are created in near-field proximity to a mirror. The sub-10-nm gaps between adjacent particles and mirror lead to strong multidimensional coupling of localized plasmonic modes, resulting in a singular resonance with negligible angular dispersion and ∼98% absorption of incident light at a desired wavelength. The process is compatible with arbitrarily structured substrates and can produce wafer-scale, diffusive, angle-independent, and flexible plasmonic materials. We then demonstrate the unique capabilities of the strongly coupled plasmonic system via integration with an actively addressed reflective liquid crystal display with control over black states. The hybrid display is readily programmed to display images and video.
... Metal nanostructures can be used as optical nanoantennas by converting free-space optical radiation into collective charge oscillations called plasmons 1 . Due to their ability to control light at the nanoscale, such systems have been utilized in areas including energy conversion [2][3][4] , biosensing [5][6][7][8][9] , display technologies [10][11][12][13] , ultrathin optical components [14][15][16][17][18] , and many others. However, light-matter interactions with conventional metal nanostructures are limited as it has proven unduly challenging to modify their static properties after fabrication 19 . ...
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Nanostructures of conventional metals offer manipulation of light at the nanoscale but are limited to static behavior due to their fixed material properties. To develop the next frontier of dynamic nanooptics and metasurfaces, we utilize the redox-tunable optical properties of conducting polymers, which were recently shown to be capable of sustaining plasmons in their most conducting oxidized state. Using nanodisks of poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) as a model system, we present the first electrically tunable conducting polymer nanooptical antennas. In addition to repeated on/off switching of the polymeric nanoantennas, we demonstrate the possibility for gradual electrical tuning of their nanooptical response, which was found to be related to the modulation of both density and mobility of the mobile polaronic charge carriers in the polymer. The presented concept takes important steps towards electrically tunable metasurfaces with truly dynamic optical nanoantenna pixels, with not only varying farfield but also tunable nearfield. The work paves the way for applications ranging from tunable flat metaoptics to adaptable smart windows.
... [10] These structures also enable a change of induced light angular moment um, [11] spins and/or quantum states, and provide applications in flat lenses, [12] holograms, [13] invisible clocks, [14] and photonic devices. [15] The light controlling capability of metasurfaces is strongly dependent on engineered nanostructures, especially their shape and material composition. [16] Metasurfaces with different dimensions have been fabricated using various nanofabrication methods including nanodisks by template stripping, [17] rod antenna by nanoimprint, [18] retroreflector by electron-beam (e-beam), [19] splitring resonators by nanosphere/ion-beam milling, [20] complex 3D structures by self-assembly approaches [21] and colloidal synthesis. ...
Article
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Metasurfaces are engineered nanostructured interfaces that extend photonic behavior of natural materials, and they spurred many breakthroughs in multiple fields, including quantum optics, optoelectronics and biosensing. Recent advances in metasurface nanofabrication enable precise manipulation of light–matter interactions at subwavelength scales. However, current fabrication methods are costly and timeconsuming and have a small active area with low reproducibility due to limitations in lithography, where sensing nanosized rare biotargets require a wide active surface area for efficient binding and detection. Here, we introduce a plastic-template tunable metasurface with a large active area, with periodic metal-dielectric layers to excite plasmonic Fano resonance transition providing multi-modal and multiplex sensing of small biotargets, such as proteins and viruses. The tunable Fano resonance feature of the metasurface is enabled via chemical etching steps to manage nanoperiodicity of the plastic template decorated with plasmonic layers and surronding dielectric medium. This metasurface integrated with microfluidics further enhances the light-matter interactions over a wide sensing area, extending data collection from 3-D to 4-D by tracking real-time biomolecular binding events. Overall, this work resolves cost and complexity related large-scale fabrication challenges and improves multi-layer sensitivity of detection in biosensing applications.
Article
Color generation based on strategically designed plasmonic nanostructures is a promising approach for display applications with unprecedented high-resolution. However, it is disadvantageous in that the optical response is fixed once the structure is determined. Therefore, high modulation depth with reversible optical properties, while maintaining its fixed nanostructure is a great challenge in nanophotonics. In this work, dynamic color tuning and switching using tungsten trioxide (WO3), a representative electrochromic material, is demonstrated with reflection-type and transmission-type optical devices. Thin WO3 films incorporated in simple stacked configurations undergo dynamic color change by the adjustment of their dielectric constant through the electrochromic principle. A large resonance wavelength shift up to 107 nm under an electrochemical bias of 3.2 V could be achieved by the reflection-type device. For the transmission-type device, on/off switchable color pixels with improved purity was demonstrated, of which transmittance is modulated by up to 1:4.04.
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Structural colors traditionally refer to colors arising from the interaction of light with structures with periodicities on the order of the wavelength. Recently, the definition has been broadened to include colors arising from individual resonators that can be subwavelength in dimension, e.g., plasmonic and dielectric nanoantennas. For instance, diverse metallic and dielectric nanostructure designs have been utilized to generate structural colors based on various physical phenomena, such as localized surface plasmon resonances (LSPRs), Mie resonances, thin-film Fabry–Pérot interference, and Rayleigh–Wood diffraction anomalies from 2D periodic lattices and photonic crystals. Here, we provide our perspective of the key application areas where structural colors really shine, and other areas where more work is needed. We review major classes of materials and structures employed to generate structural coloration and highlight the main physical resonances involved. We discuss mechanisms to tune structural colors and review recent advances in dynamic structural colors. In the end, we propose the concept of a universal pixel that could be crucial in realizing next-generation displays based on nanophotonic structural colors.
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With the rapid development of human society, consumer electronics have brought marvelous changes to human daily life, but they are accompanied by the much higher demand of display quality and visual experience. Therefore, ideal conversion among the three primary colors—red (R), green (G), and blue (B)—in a single pixel has been a better way to avoid the insurmountable technical barrier of subpixel technology of modern displays. Electrofluorochromic (EFC) materials capable of a novel luminescent switching, open a powerful way to design optoelectronic devices for displays and information storage etc. Colorful EFC devices, especially emitting the ideal three primary colors without subpixel technology, have been a challenge for years. Herein, a long‐awaited single‐pixel device with RGB color is fabricated successfully based on proton‐coupled electron transfer. The RGB EFC device exhibits outstanding EFC properties, such as low turn‐on voltage (+1.0 and −1.0 V), large color gamut, and good stability (500 cycles for each color). Prototypes of colorful alphanumeric displays are well demonstrated in a facile way. The success of this new exploration of single‐pixel RGB EFC device not only provides the possibility of full‐color emission in EFC devices, but also will widely broaden the EFC system and their applications.
Article
Plasmonic colors produced by metallic metasurfaces show subwavelength spatial resolution, material simplicity and durability. Compared to the colors created by plasmonic metasurfaces, plasmonic colors generated by colloidal plas-monic nanostructures are of narrower spectral linewidths, sharper and purer chromaticity. However, difficulties in the active control of plasmonic colors hinder the development from static plasmonic color pixels into dynamic plasmonic color devices. Moreover, functional plasmon-based applications usually involve plasmonic nanostructures supported on substrates that strongly alter the plasmonic far-field scattering properties. Au nanorings are emerging plasmonic nanostructures with an intriguing ring shape and controllable plasmon wavelengths. Herein we report on a study of the substrate effect on the far-field scattering properties of colloidal Au nanorings. The in-plane and out-of-plane plasmon modes of the Au nanorings deposited on metallic films can be excited in varying proportions, which are dependent on the incidence angle of light, producing distinct and controllable far-field scattering plasmonic colors. Color switching is further realized on the designed patterns made out of the Au nanorings by photolithography. Our study not only provides a fundamental understanding of the substrate effect on the plasmonic properties of uncommon metal nanostructures, but also opens the possibility for creating new functional metallic nanostructures for dynamic color devices and anti-counterfeiting applications.
Article
Plasmonic metasurfaces have attracted much attention for use in device applications over the past decade. Dynamic color tuning (DCT), where the displacement of periodic nanostructures is controlled to generate different colors in real time, is one of the great possibilities of plasmonic metasurfaces for optical strain sensors or display devices. In this study, an Al metasurface embedded in an elastomer nanosheet with film thickness 400 nm is fabricated by means of sacrificial release using a polyvinyl alcohol sacrificial layer. This plasmonic metasheet shows not only the seven colors produced by surface plasmons, but also DCT by stretching the elastomer nanosheet. Each pixel, designed with a grating period of 300–600 nm, emits the bright colors expected in electromagnetic simulation. Moreover, stretching the plasmonic metasheet demonstrates DCT from 495 to 660 nm in the visible light range. The freestanding metasheet with maximum thickness 400 nm may be easily integrated into any active device by post‐processing transfer. Stretching the metasheet requires an estimated × 10−3 lower force than previously reported for plasmonic metasurfaces, owing to a film thickness of only several hundreds of nanometers. These results facilitate the realization of microdevices with novel capabilities based on plasmonic metamaterials. Stretchable plasmonic metasurface with Al nanogratings embedded in a 400‐nm‐thick elastomer nanosheet emits bright colors generated by extraordinary optical transmission based on surface plasmon. This study demonstrates dynamic color tuning from 495 to 660 nm by sheet compression. The fabricated metasheet with high adhesiveness is expected to contribute to the realization of electronic skin devices.
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Reversible electrochemical mirror (REM) electrochromic devices with electrochemical tunability in multiple optical states are exciting alternatives to conventional electrochromic smart windows. Electrochromic devices are studied extensively, yet widespread adoptions have not been achieved due to problems associated with durability, switching speed, limited options on optical states, and cost. In this study, a REM electrochromic device based on CuSn alloy is developed, which offers highly reversible switching between transparent, greyish‐blue, and mirror states via reversible electrodeposition and dissolution. The alloying element, Sn acts as an electrochemical mediator, which facilitates the electrodeposition and dissolution of Cu. The CuSn‐based REM device shows superior cycling stability for 2400 cycles (transmittance mode) and 1000 cycles (reflectance mode). The electrodeposited CuSn alloy film is resistant to surface oxidation in ambient air, with a 2.9% difference in reflectance at 2000 nm after 3 days. In addition, the alloy film exhibits excellent NIR reflectance property with thermal modulation of 18.5 °C at a high temperature of 180 °C. The REM device with zero power consumption maintains its mirror state for at least 100 min, making it a promising candidate for energy‐efficient applications. The quasi‐solid‐state tristate reversible electrochemical mirror (REM) device offers highly reversible switching between transparent, greyish‐blue, and mirror states via reversible electrodeposition and dissolution. The REM shows superior thermal barrier property compared to the bare substrate. The extended memory effect of the REM device is achieved in the presence of quasi‐solid‐state polymer electrolyte.
Presentation
Electrochromic Polymer Switching in Nanostructured Plasmonic Environment
Article
Plasmonic color generation has attracted much research interest due to the unique optical properties of plasmonic nanocrystals that are promising for chromatic applications, such as flat-panel displays, smart windows and wearable devices. Low-cost, monodisperse plasmonic nanocrystals supporting strong localized surface plasmon resonances are favorable for the generation of plasmonic colors. However, many implementations so far have either a single static state or complexities in the particle alignment and switching mechanism for generating multiple displaying states. Herein we report on a facile and robust approach for realizing the electrochemical switching of plasmonic colors out of colloidal plasmonic nanocrystals. The metal nanocrystals are coated with a layer of polyaniline, whose refractive index and optical absorption are reversibly switched through the variation of an applied electrochemical potential. The change in the refractive index and optical absorption results in the modulation of the plasmonic scattering intensity with a depth of 11 dB. The electrochemical switching process is fast (~5 ms) and stable (over 1000 switching cycles). A device configuration is further demonstrated for switching plasmonic color patterns in a transparent electrochemical device, which is made from indium-tin-oxide electrodes and a polyvinyl alcohol solid electrolyte. Our control of plasmonic colors provides a favorable platform for engineering low-cost and high-performance miniaturized optical devices.
Article
Two types of thiophene derivatives, i.e., thiophene (T) and 3,4-ethylenedioxylthiophene (ET) with a single thiophene ring, and thieno[3,2-b]thiophene (TT) and 2,2′-bithiophene (BT) with double thiophene rings, have been inserted between the two pyridinium units of an octyl viologen (V). The effective conjugation lengths of the resulting thienoviologens TV, ETV, TTV, and BTV have been successfully extended. Unlike a traditional alkyl viologen, which always serves as a fluorescence quencher, all four thienoviologens exhibit intense photoluminescence (PL). The bathochromic shifts in both absorption and PL spectra are more pronounced in TTV and BTV with double thiophene rings as compared with TV and ETV with a single thiophene bridge. Moreover, upon applying a negative potential, all four thienoviologens display significant changes in both absorption and PL spectra, indicating their electrochromic (EC) and electrofluorochromic (EFC) properties. Additionally, the EC response can be found not only in the visible but also in the near-infrared (NIR) region. Although TTV and BTV with longer conjugated bridges exhibit more extended effective conjugation lengths and higher PL quantum yields, the EC and EFC devices based on TV and ETV gels display better performance than that for TTV and BTV owing to the faster charge and mass transport for smaller molecules. Consequently, a better comprehensive property is achieved by the ETV-based gel, which demonstrates fast coloration (1.9 s), high color contrast (87%), and high coloration efficiency (521 cm² C⁻¹) in the EC device with high fluorescence contrast ratio (Ion/Ioff = 221) in the EFC device. Furthermore, two smart windows have been fabricated to utilize their different driving potentials. Upon increasing the potential, the “window flower” in the first device blossoms out with gradually changing petal colors, while the other dual-functional smart window can be adjusted between flower decoration and light blocking functions.
Article
(Gold nanorod core)/(poly(3,4-ethylene-dioxythiophene) (PEDOT) shell) nanostructures are prepared by the surfactant-assisted oxidative polymerization of 3,4-ethylene-dioxythiophene on the surface of gold nanorods (NRs). The PEDOT shell exhibits distinct dielectric properties at doped and undoped states, which allows the manipulation of plasmonic responses of the Au nanorod core. The shift in plasmon resonance induced by the dedoping of PEDOT is found to be associated with the overlap between the plasmon resonance band of the core/shell nanostructure and the spectral region where the largest refractive index variation of PEDOT occurs, as well as with the type of the dedopant. Macroscopic two-dimensional (2D) monolayer arrays of core/shell nanostructures with controlled particle number densities are fabricated on indium tin oxide (ITO)-coated glass substrates by electrophoretic deposition. A reversible plasmonic shift of about 70 nm is obtained on the core/shell nanostructure monolayer array with a number density of around 18 particles per μm2. Our design of colloidal (Au nanorod core)/(PEDOT shell) nanostructures and their 2D monolayer arrays paves the way for the fabrication of high-performance plasmonic switches in large-scale practical usages as well as for the preparation of advanced, programmable chromic materials for a broad range of applications, such as smart windows, anti-counterfeiting tags, and medical and environmental sensors.
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Precise manipulation of light-matter interaction has enabled a wide variety of approaches to create bright and vivid structural colours. Techniques utilizing photonic crystals, Fabry-P\'erot cavities, plasmonics, or high-refractive index dielectric metasurfaces have been studied for applications ranging from optical coatings to reflective displays. However, complicated fabrication procedures for sub-wavelength nanostructures, limited active areas, and inherent absence of tunability with these approaches significantly impede their further developments towards flexible, large-scale, and switchable devices compatible with facile and cost-effective production. Herein, we present a way to generate structural colours based on conducting polymer thin films prepared on metallic surfaces via vapour phase polymerization and ultraviolet (UV) light patterning. Varying the UV dose leads to synergistic variation of film absorption and thickness, which generates controllable colours from violet to red. Together with greyscale photomasks this enables fabrication of high-resolution colour images using single exposure steps. We further demonstrate spatiotemporal tuning of the structurally coloured surfaces and images via electrochemical modulation of the polymer redox state. The simple structure, facile fabrication, wide colour gamut, and dynamic colour tuning make this concept competitive for future multi-functional and smart displays.
Article
Employing a silver nano semi-ellipsoid nanoarray with high symmetry into applications in plasmonic color printing, we fulfill printing images with colors independent of observing angles. Also, by decreasing the period of a nano semi-ellipsoid array into deep-subwavelength scales, we obtain high reflectivity over 50%, promising high efficiency for imaging generations. A facile technique based on the transfer of anodized aluminum oxide template is developed to fabricate the silver nano semi-ellipsoid nanoarray, realizing plasmonic color printing with features of low cost, scalable, full color and high flexibility. Our approach provides a feasible way to address the angle-dependent issue in the previous practice of plasmonic color printing, and boosts this field on its way to real-world commercial applications.
Article
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Precise manipulation of light–matter interactions has enabled a wide variety of approaches to create bright and vivid structural colors. Techniques utilizing photonic crystals, Fabry–Pérot cavities, plasmonics, or high‐refractive‐index dielectric metasurfaces have been studied for applications ranging from optical coatings to reflective displays. However, complicated fabrication procedures for sub‐wavelength nanostructures, limited active areas, and inherent absence of tunability of these approaches impede their further development toward flexible, large‐scale, and switchable devices compatible with facile and cost‐effective production. Here, a novel method is presented to generate structural color images based on monochromic conducting polymer films prepared on metallic surfaces via vapor phase polymerization and ultraviolet (UV) light patterning. Varying the UV dose enables synergistic control of both nanoscale film thickness and polymer permittivity, which generates controllable structural colors from violet to red. Together with grayscale photomasks this enables facile fabrication of high‐resolution structural color images. Dynamic tuning of colored surfaces and images via electrochemical modulation of the polymer redox state is further demonstrated. The simple structure, facile fabrication, wide color gamut, and dynamic color tuning make this concept competitive for applications like multifunctional displays. A UV light patterning method turns monochromic conducting polymers into multicolor images, using the UV dose to control structural coloration via both the film thickness and polymer permittivity. Electrochemical modulation of the conducting polymer redox states further enables dynamic tuning of the structurally colored images.
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Nanostructures of conventional metals offer manipulation of light at the nanoscale but are largely limited to static behavior due to fixed material properties. To develop the next frontier of dynamic nano‐optics and metasurfaces, this study utilizes the redox‐tunable optical properties of conducting polymers, as recently shown to be capable of sustaining plasmons in their most conducting oxidized state. Electrically tunable conducting polymer nano‐optical antennas are presented, using nanodisks of poly(3,4‐ethylenedioxythiophene:sulfate) (PEDOT:Sulf) as a model system. In addition to repeated on/off switching of the polymeric nanoantennas, the concept enables gradual electrical tuning of the nano‐optical response, which was found to be related to the modulation of both density and mobility of the mobile polaronic charge carriers in the polymer. The resonance position of the PEDOT:Sulf nanoantennas can be conveniently controlled by disk size, here reported down to a wavelength of around 1270 nm. The presented concept may be used for electrically tunable metasurfaces, with tunable farfield as well as nearfield. The work thereby opens for applications ranging from tunable flat meta‐optics to adaptable smart windows.
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Electrochromic devices with a wide color gamut distribution have long been sought after for non-emissive display technologies. The current state-of-the-art multicolor electrochromic displays utilize a single electrochromic layer, which restricts their color tunability within a linear or curved segment scope in International Commission on Illumination (CIE) color space and thus leads to limited color hues. Herein, it is demonstrated vivid electrochromic displays with broadened color hues via fabricating Zn-based multicolor electrochromic displays having 2D CIE color space tunability. In addition, it is revealed that a Fabry–Perot nanocavity structure can further tune the color hues via altering the coordinate of the 2D CIE color space. It is known that this is the first demonstration of 2D CIE color space tunability realization from a single transparent or reflective electrochromic device. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of electrochromic displays.
Article
Flexible devices play an important role in various fields such as electronics, industry, healthcare, military, space exploration, and so on. Traditional materials used for flexible devices include silicon, inorganic oxides, and polymers. However, these materials show some drawbacks such as high rigidity, low electrical conductivity, or being costly for large-scale manufacturing. Transition metal dichalcogenides (TMDs) have attracted great interest in the last decade due to their layered structures, and relevant publications have gained rapid growth. TMDs exhibit tunable properties as a function of layers. TMDs show semiconducting/metallic transition, direct/indirect band transition, strengthened flexibility, and increased transparency with the decreasing layer number. Such tunable properties of TMDs allow them to be promising materials for flexible devices. As part of this review, the initial discussion is on the structural information of TMDs. Subsequently, recent improved synthetic routes and phase engineering of TMDs will be introduced. Then, we introduce the studies and challenges of flexible and stretchable devices. And then we review some recent studies on TMD-based flexible devices, including transistors, energy storage devices, and sensors. In the end, some comprehensive discussion and perspectives for the future trend of flexible devices will be given.
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Reversible electrochemical mirror (REM) electrochromic devices based on reversible metal electrodeposition are exciting alternatives compared with conventional electrochromic because they offer electrochemical tunability in multiple optical states, long durability, and high contrast. Different from conventional electrochromic materials, of which the color change depends on the intercalation/deintercalation of ions into electrochromic films, the change in the optical states of REMs is based on the reversible electrodeposition and dissolution of metal. In this study, a REM electrochromic device with a Cu hybrid electrolyte composed of aqueous and nonaqueous components is proposed, which serves as an electrolyte reservoir that hosts Cu ions for reversible electrodeposition/dissolution. The hybrid electrolyte promotes the electrochemical reversibility of the Cu redox, an enhanced electrochromic performance, and a robust cycling stability of 5000 cycles (minor degradation of 4.71%). The investigation of the discharging/charging of the Cu hybrid REM device reveals that the Cl–/ClO– redox mechanism occurs at the cathode. Finally, an unprecedented dual-functional Cu hybrid REM energy storage device has been realized.
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Reflective displays or “electronic paper” technologies provide a solution to the high energy consumption of emissive displays by simply utilizing ambient light. However, it has proven challenging to develop electronic paper with competitive image quality and video speed capabilities. Here, the first technology that provides video speed switching of structural colors with high contrast over the whole visible is shown. Importantly, this is achieved with a broadband‐absorbing polarization‐insensitive electrochromic polymer instead of liquid crystals, which makes it possible to maintain high reflectivity. It is shown that promoting electrophoretic ion transport (drift motion) improves the switch speed. In combination with new nanostructures that have high surface curvature, this enables video speed switching (20 ms) at high contrast (50% reflectivity change). A detailed analysis of the optical signal during switching shows that the polaron formation starts to obey first order reaction kinetics in the video speed regime. Additionally, the system still operates at ultralow power consumption during video speed switching (<1 mW cm−2) and has negligible power consumption (<1 µW cm−2) in bistability mode. Finally, the fast switching increases device lifetime to at least 107 cycles, an order of magnitude more than state‐of‐the‐art. Electronic paper technologies are essential for reducing the energy consumption in future display devices. The first example of video speed switching of structural colors over the whole visible region is shown, while retaining high contrast. This is achieved with polarization‐insensitive metasurfaces and conjugated polymers, not liquid crystals. The lifetime is shown to be over ten million cycles.
Article
Dynamic structural color has attracted considerable attentions due to its good tunable characteristics. Here, an ultrathin asymmetric Fabry-Perot (FP)-type structural color with phase-change material VO2 cavity is proposed. The color-switching performance can be realized by temperature regulation due to the reversible monoclinic-rutile phase transition of VO2. The various, vivid structural color can be generated by simply changing the thickness of VO2 and Ag layers. Moreover, the simple structural configuration enables a large-scale, low-cost preparation on both rigid and flexible substrates. Accordingly, a flexible dynamic structural color membrane is adhered on a cup with a curved surface to be used for temperature perception. The proposed dynamic structural color has potential applications in anti-counterfeiting, temperature perception, camouflage coatings among other flexible optoelectronic devices.
Article
Structural color, which originates from the interaction between light and nanometer-scale structured materials, has the advantages of durability and environmentally friendly display compared with pigments and dyes. Large color gamut, high-speed, electrically-switching reflective structural color display is critical to the dynamically tunable reflective structural color devices. Here, we report a theoretical design of an electrically switching reflective structural color display device with a large color gamut (~ 157% sRGB, standard Red Green Blue) and high speed (> 10 MHz). Benefiting from the electric-switchable Epsilon-Near-Zero material and 1D dielectric grating with guided-mode resonance, the reflective display device can be electrically turned on or turned off by switching between a narrowband reflector and a transparent film. This design provides a promising solution towards the reflective color display, optical switches, spatial light modulators and so on.
Article
Next-generation color display entails miniaturization, reconfigurablity, flexibility, integration, and excellent workability. Recently, emerging 2D van der Waals materials offer a new opportunity to satisfy these requirements and attract intense attention, owing to their intrinsic in-plane anisotropy for polarization dependent photosensitivity, straightforward integration with complicated nanostructures, and efficient quantum confinement for good photodetecting performances. Nevertheless, reconfigurable color display in the visible region based on the 2D material stays elusive. Black phosphorus (BP) is a newly rising member of 2D family with intense optical anisotropy. Herein, the anisotropic BP crystals are explored as an optical dielectric for the visible spectrum, which possesses a polarization-dependent complex refractive index. A considerably large anisotropic ratio of BP enables polarized color displaying. It is experimentally and theoretically observed that the color from an air/BP/SiO2 multi-layered Fabry–Pérot cavity reversibly changes with the polarization angle, taking advantage of polarization-dependent complex refractive index of BP. The strategy offers a new prospect for developing next-generation polarization-dependent devices in data storage, anti-counterfeiting technologies, and color display.
Article
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The generation of pigment-free colors by nanostructures and subwavelength patterns has evolved in the last decade and outperformed the conventional paints in terms of durability, recyclability, and environmental friendliness. The recent progress in the field of structural coloration, particularly reflective coloration, offering a full-color gamut, has realized high-resolution printing, not attainable by the pigment paints. Herein, an overview of the various systems able to offer reflective coloration for a variety of optical applications with static and dynamic responses is presented. Specifically, an emphasis is given to recent works of the article's authors on the cooperative action of the disordered particles and dipoles that can generate specular reflective colors. In addition, further developments of reflective color nanosystems are discussed. In the first section, an overview of the recent progress in the field of plasmonic reflective structural coloration is provided. The second part of the article deals with the authors’ latest findings with respect to polarizonic color generation and its implementation in various areas ranging from environmental detection and biosensing to colored solar perfect absorbers. The report is wrapped up with an outlook and summary.
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The possibility of actively controlling structural colors has recently attracted a lot of attention, in particular for new types of reflective displays (electronic paper). However, it has proven challenging to achieve good image quality in such devices, mainly because many subpixels are necessary and the semitransparent counter electrodes lower the total reflectance. Here we present an inorganic electrochromic nanostructure based on tungsten trioxide, gold, and a thin platinum mirror. The platinum reflector provides a wide color range and makes it possible to “reverse” the device design so that electrolyte and counter electrode can be placed behind the nanostructures with respect to the viewer. Importantly, this makes it possible to maintain high reflectance regardless of how the electrochemical cell is constructed. We show that our nanostructures clearly outperform the latest commercial color e-reader in terms of both color range and brightness.
Article
Plasmonic metal nanostructures generate vivid colors with high spatial resolution. Active control of plasmonic pixels by electrical means, which is compatible with integrated circuit technologies, is a promising technique for dynamic full color reflective display. However, the development of electrical plasmonic display is still limited by the difficulties in cost‐effective construction of active plasmonic pixels over large areas. This study demonstrates the achievement of electrical plasmonic display in full color by electrophoretic movement control of plasmonic noble metal nanocrystals in an organic electrolyte solvent. The persistent issues of nanoparticle aggregation and irreversible deposition in electrophoresis are addressed through appropriate surface modifications of the plasmonic nanocrystals, enabling them as advantageous nanoscale colorful pigments with long‐term durability. A weak electric field therefore allows color display with high contrast, high saturation, and electrical reconfigurability. The ink containing plasmonic pigments is further assembled into microfluidic chips to display different characters. The strategy will pave the way towards the development of plasmonic electronic paper in full color. Electrical plasmonic display is achieved by reconfigurable electrophoretic movement control of noble metal nanocrystals in an organic electrolyte solvent. The noble metal nanocrystals serve as advantageous nanoscale colorful pigments with long‐term durability and mass production compatibility when their surfaces are modified by a hydrophobic coating. The technique is highly valuable in developing plasmonic electronic paper in full color.
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As an efficient patterning method for nanostructures, nanocolloidal lithography (NCL) presents a controllable and scalable means for achieving a uniform and good sidewall profile, and a high aspect ratio. While high selectivity between the etching mask and targeted materials is also essential for NCL-based precision nanophotonic structures, its realization in multi-material nanophotonic structures still remains a challenge due to the dielectric- or metallic-material-dependent etching selectivity. Here, dispersion-controlled Au-NCL is proposed, which enables high selectivity for Al and SiO2 over a Au nanoparticle (Au-NP) mask. Utilizing the proposed process, wafer-scale, uniformly dispersed multi-material nanopawn structures (Au-NPs/Al-SiO2 cylinders) on an Al ultrathin film are realized, obtaining excellent vertical sidewall (≈90°) and aspect ratio (>1). The high sidewall verticality and aspect ratio of the nanopawn structures support optical modes highly sensitive to the excitation direction of incident waves through the mixing of the interface-gap-assisted localized surface plasmons (GLSPs) formed in between the Au-NP and Al-disk interface, and plasmonic Fabry-Pérot (FP) modes formed in between the Al-disk and Al substrate; complementary spectral responses between reflected and scattered light are also demonstrated. As an application example, information encryption based on the triple-channel (i.e., reflection, scattering, and transmission) angle-dependent complementary-color responses is presented.
Article
Plasmonic color generation utilizing ultrathin metasurfaces as well as metallic nanoparticles holds a great promise for a wide range of applications including color displays, data storage, and information encryption due to its high spatial resolution and mechanical/chemical stability. Most of the recently demonstrated systems generate static colors; however, more advanced applications such as data storage require fast and flexible means to tune the plasmonic colors, while keeping them vibrant and stable. Here, a surface‐relief aluminum metasurface that reflects polarization‐tunable plasmonic colors is designed and experimentally demonstrated. Excitation of localized surface plasmons encodes discrete combinations of the incident and reflected polarized light into diverse colors. A single storage unit, namely a nanopixel, stores multiple‐bit information in the orientation of its constituent nanoantennae, which is conveniently retrived by inspecting the reflected color sequence with two linear polarizers. Owing to the broad color variability and high spatial resolution of the metasurface, the proposed encoding approach holds a strong promise for rapid parallel readout and encryption of high‐density optical data. The method also enables robust generation of dynamic kaleidoscopic images without the “cross‐talk” effect. The approach opens up a new route for advanced dynamic steganography, high‐density parallel‐access optical data storage, and optical information encryption. The proposed anisotropic metasurface has significant potential for high‐density optical data storage, dynamic color image display, and encryption. With the experimentally validated approach, diverse colors from individual plasmonic nanopixels are decoded. These colors, which depend on nanopixel anisotropy and the incident and reflected polarizations, can be obtained with a new integrated parallel readout scheme capable of reaching ultrafast speeds.
Article
Cephalopods offer a fascinating dynamic reflecting system to create desired colors and patterns through contracting and releasing their soft skins in response to environmental stimuli. Inspired by this natural display strategy, we designed a novel dynamic reflecting system based on pneumatic micro/nanoscale surface morphing. This system consists of a thin metal skin/elastomer bilayer modulated by a microfluidic-based gas injector. Benefited from the "wrinkled-specular" transition of the metal's surface under a small pneumatic actuation (4 kPa), an unprecedented reflectance contrast of 93 for broad-band (500-750 nm) modulation is achieved. This remarkable response also has excellent cycle stability (>2500 times) and fast response time (∼0.2 s). These advantages enable a robust and ultrasensitive optical gas pressure sensor with a sensitivity of 178 kPa-1, which is 3-4 orders of magnitude higher than those of conventional optical gas pressure sensors based on either a Fabry-Pérot interferometer or a Mach-Zehnder interferometer. Moreover, as proof-of-concept applications, we also experimentally demonstrated a curvature-variable convex mirror and noniridescent dynamic display, suggesting that our pneumatically dynamic reflecting system will potentially broaden the applications in adaptive optical devices, sensors, and displays.
Article
The electrochromic modulation of plasmonic metasurfaces showing structural colors is a promising strategy to realize dynamic electronic reflective displays. However, hybridizing electrochromic polymers with large-area plasmonic metasurfaces remains challenging. In this study, we present a poly(3,4-ethylenedioxythiophene) (PEDOT)-coated gold nanodisk (PCGN) metasurface, which is fabricated based on techniques of large-area anodic aluminum oxide template-assisted deposition and electrochemical polymerization. Experimental and numerical results demonstrated that fast and reversible electrochromic modulation was realized within the PCGN metasurface. The wavelength control of the localized surface plasmon resonance of the PCGN metasurface originated from the electrically driven refractive index change of the PEDOT layer. The PCGN metasurface is promising for the high yield manufacturing of devices applied in dynamic reflective displays.
Article
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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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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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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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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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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