Manipulating disordered plasmonic systems by external cavity with transition from broadband absorption to reconfigurable reflection

Understanding the relationship between sequences and kinetics of DNA strand displacements

Precisely modulating the kinetics of toehold-mediated DNA strand displacements (TMSD) is essential for its application in DNA nanotechnology. The sequence in the toehold region significantly influences the kinetics of TMSD. However, due to the large sample space resulting from various arrangements of base sequences and the resulted complex secondary structures, such a correlation is not intuitive. Herein, machine learning was employed to reveal the relationship between the kinetics of TMSD and the toehold sequence as well as the correlated secondary structure of invader strands. Key factors that influence the rate constant of TMSD were identified, such as the number of free hydrogen bonding sites in the invader, the number of free bases in the toehold, and the number of hydrogen bonds in intermediates. Moreover, a predictive model was constructed, which successfully achieved semi-quantitative prediction of rate constants of TMSD even with subtle distinctions in toehold sequence.

A Mid-Infrared Perfect Metasurface Absorber with Tri-Band Broadband Scalability

Metasurfaces have emerged as a unique group of two-dimensional ultra-compact subwavelength devices for perfect wave absorption due to their exceptional capabilities of light modulation. Nonetheless, achieving high absorption, particularly with multi-band broadband scalability for specialized scenarios, remains a challenge. As an example, the presence of atmospheric windows, as dictated by special gas molecules in different infrared regions, highly demands such scalable modulation abilities for multi-band absorption and filtration. Herein, by leveraging the hybrid effect of Fabry-Perot resonance, magnetic dipole resonance and electric dipole resonance, we achieved multi-broadband absorptivity in three prominent infrared atmospheric windows concurrently, with an average absorptivity of 87.6% in the short-wave infrared region (1.4-1.7 μm), 92.7% in the mid-wave infrared region (3.2-5 μm) and 92.4% in the long-wave infrared region (8-13 μm), respectively. The well-confirmed absorption spectra along with its adaptation to varied incident angles and polarization angles of radiations reveal great potential for fields like infrared imaging, photodetection and communication.

Color Generation and Polarization-Sensitive Encryption by Laser Writing on Plasmonic Reflector Arrays

Plasmonic color printing presents a sustainable solution for vibrant and durable color reproduction by leveraging the light-manipulating properties of nanostructures. However, the fabrication of plasmonic nanostructures has posed challenges, hindering widespread adoption. In this paper, we introduce plasmonic reflector arrays (PRAs) composed of three layers─Ag nanoparticles (NPs), an Al2O3 spacer, and an Ag reflector─deposited via physical vapor deposition (PVD). By employing nanosecond and femtosecond laser writing techniques, we manipulate the surface morphology of silver nanoparticles on PRAs, resulting in a diverse range of structural colors that are both polarization-insensitive and polarization-sensitive. Furthermore, we demonstrate the versatility of nanosecond laser writing in creating intricate patterns on PRAs. Additionally, we propose a novel two-step method combining nanosecond and femtosecond laser processing to embed QR code patterns into PRAs, showcasing their potential for secure data encryption and transmission. This research underscores the promising applications of PRAs in advanced color printing and secure optical data encoding.

Illuminating Disorder: Optical Properties of Complex Plasmonic Assemblies

The optical properties of disordered plasmonic nanoparticle assemblies can be continuously tuned through the structural organization and composition of their colloidal building blocks. However, progress in the design and experimental realization of these materials has been limited by challenges associated with controlling and characterizing disordered assemblies and predicting their optical properties. This Perspective discusses integrated studies of experimental assembly of disordered optical materials, such as doped metal oxide nanocrystal gels and metasurfaces, with electromagnetic computations on large-scale simulated structures. The simulations prove vital for connecting experimental parameters to disordered structural motifs and optical properties, revealing structure-property relations that inform design choices. Opportunities are identified for optimizing optical property designs for disordered materials using computational inverse methods and tools from machine learning.

Meta-Structured Covalent Organic Framework Nanocoatings with Active and Angle-Independent Structural Coloration

High-performance multifunctional nanocoatings not only protect and enhance substrate materials but also offer additional functionalities. This demands a sophisticated coordination of the coating's inherent properties and microstructural features. Here, a multifunctional active nanocoating via meta-structural engineering of covalent organic framework (COF) deposition materials is presented. This COF nanocoating, characterized by well-defined micropores (1-2 nm), meta-structured textures (30-300 nm), tailored thickness (100-300 nm), and good uniformness, showcases a unique combination of angle-independent structural coloration and ultrafast responsiveness to gaseous stimuli. Remarkably, it demonstrates good compatibility with a wide range of inert substrate materials, from rigid ones like glass and metal to flexible elastomers and nanomaterial films of various shapes and sizes. This versatility enables the facile development of devices that can optically report information about their environments. Examples include chemically active coatings with ultrafast (≈10 ms) color-changing behaviors and programmable actuation behaviors upon exposure to gaseous stimuli, and mechanically active coatings that can detect substrate strain up to 50% yet maintain structural robustness and consistent coloration hue. It is believed that meta-structural engineering of COF nanocoatings on inert substrates can enable them to respond to environmental stimuli, potentially indicating a new trend in developing multifunctional materials and smart devices.

Development of Pd/In2O3 hybrid nanoclusters to optimize ethanol vapor sensing

In this study, we successfully synthesize palladium-decorated indium trioxide (Pd/In2O3) hybrid nanoclusters (NCs) using an advanced dual-target cluster beam deposition (CBD) method, a significant stride in developing high-performance ethanol sensors. The prepared Pd/In2O3 hybrid NCs exhibit exceptional sensitivity, stability, and selectivity to low concentrations of ethanol vapor, with a maximum response value of 101.2 at an optimal operating temperature of 260 °C for 6 at% Pd loading. The dynamic response of the Pd/In2O3-based sensor shows an increase in response with increasing ethanol vapor concentrations within the range of 50 to 1000 ppm. The limit of detection is as low as 24 ppb. The sensor exhibits a high sensitivity of 28.24 ppm-1/2, with response and recovery times of 2.7 and 4.4 seconds, respectively, for 100 ppm ethanol vapor. Additionally, the sensor demonstrates excellent repeatability and stability, with only a minor decrease in response observed over 30 days and notable selectivity for ethanol compared to other common volatile organic compounds. The study highlights the potential of Pd/In2O3 NCs as promising materials for ethanol gas sensors, leveraging the unique capabilities of CBD for controlled synthesis and the catalytic properties of Pd for enhanced gas-sensing performance.

Exploring the structural color of micro-nano composite gratings with FDTD simulation and experimental validation

The significance of micro-nano composite gratings (MNCGs) resides in their applications, including optical devices, sensors, and diffractive elements, which drive research interest in their diffraction characteristics. This study investigates both the diffraction characteristics of MNCGs and the factors that influence them by employing both Finite-Difference Time-Domain (FDTD) methods and experimental validation. The initial focus lies in deciphering the differences in diffraction characteristics between micro-gratings (MGs) and MNCGs by analyzing the coupling effects, diffraction order, color distribution, and intensity variation. Additionally, this research emphatically investigates five aspects to discover the influencing factors of MNCG's diffraction characteristics, such as the height, groove angle of MGs and the period, blaze angle, and height of nano-gratings (NGs). Results show that the structural coloration and saturation of MNCG surpass that of MG. NG plays the actual spectral role, and a reduction in the period of NG leads to enhanced splitting light capability of the white light. The optical detection tests validated the simulation results. The present study reveals the diffractive properties of MNCGs, providing technical insights for the design and processing of optically variable devices.

Resonant-Cavity-Enhanced Electrochromic Materials and Devices

With rapid advances in optoelectronics, electrochromic materials and devices have received tremendous attentions from both industry and academia for their strong potentials in wearable and portable electronics, displays/billboards, adaptive camouflage, tunable optics, and intelligent devices, etc. However, conventional electrochromic materials and devices typically present some serious limitations such as undesirable dull colors, and long switching time, hindering their deeper development. Optical resonators have been proven to be the most powerful platform for providing strong optical confinement and controllable lightmatter interactions. They generate locally enhanced electromagnetic near-fields that can convert small refractive index changes in electrochromic materials into high-contrast color variations, enabling multicolor or even panchromatic tuning of electrochromic materials. Here, resonant-cavity-enhanced electrochromic materials and devices, an advanced and emerging trend in electrochromics, are reviewed. In this review, w e will focus on the progress in multicolor electrochromic materials and devices based on different types of optical resonators and their advanced and emerging applications, including multichromatic displays, adaptive visible camouflage, visualized energy storage, and applications of multispectral tunability. Among these topics, principles of optical resonators, related materials/devices and multicolor electrochromic properties are comprehensively discussed and summarized. Finally, the challenges and prospects for resonant-cavity-enhanced electrochromic materials and devices are presented.

Single-Pixel-Adjustable Structural Color Fabricated Using a Spatially Modulated Femtosecond Laser

Structural colors provide a highly stable and ecofriendly dyeing mechanism. The ability to adjust structural colors by a single pixel enhances their flexibility and application range. However, achieving single-pixel control and dynamic adjustment of structural colors remain a challenge yet. In this study, we propose a coloring method involving microcurve surfaces fabricated using a spatially modulated femtosecond laser hybrid technology, which combines spatially modulated femtosecond laser-assisted wet etching and molding. The fabricated microcurve surface exhibits bright colors under white light irradiation, and the color of each pixel can be adjusted independently by changing the morphology of the modified region inside fused silica using a femtosecond laser. With the high flexibility of femtosecond laser fabrication, color lightness can be accurately controlled through the quantitative adjustment of the arrangement of microcurve surfaces in an array, and various color patterns can be fabricated through the programmable arrangement of different microcurve surfaces. Additionally, the color exhibits strong dynamic characteristics, that is, different colors correspond to different external forces.

Revisiting the Design Strategies for Metasurfaces: Fundamental Physics, Optimization, and Beyond

Over the last two decades, the capabilities of metasurfaces in light modulation with subwavelength thickness have been proven, and metasurfaces are expected to miniaturize conventional optical components and add various functionalities. Herein, various metasurface design strategies are reviewed thoroughly. First, the scalar diffraction theory is revisited to provide the basic principle of light propagation. Then, widely used design methods based on the unit-cell approach are discussed. The methods include a set of simplified steps, including the phase-map retrieval and meta-atom unit-cell design. Then, recently emerging metasurfaces that may not be accurately designed using unit-cell approach are introduced. Unconventional metasurfaces are examined where the conventional design methods fail and finally potential design methods for such metasurfaces are discussed.

Transfer-Printing Hydrogel-Based Platform for Moisture-Driven Dynamic Display and Optical Anti-Counterfeiting

Humidity-responsive materials offer a promising approach to achieving tunable metasurface systems due to their fast and reversible swelling responses to moisture, which enables many important applications, such as real-time humidity sensing, optical switches, dynamic displays, and optical information encryption. However, the humidity-responsive structural coloration generally cannot provide a high spatial resolution and requires a complex patterning process. Here, we present a scalable moisture-driven color-changing Fabry-Pérot (FP)-like cavity composed of a polyvinyl alcohol layer sandwiched between an upper gold nanoparticles assembly and a bottom gold mirror. Through nanoparticle contact printing, we pixelated these cavities with sub-micrometer sizes without crosstalk and achieved an ultrahigh display resolution of ∼400 nm. Meanwhile, these nanoparticle-based FP (NBFP) cavities exhibit more vibrant colors than those of conventional film-based ones due to broadband absorption of the disordered nanoparticle assembly. Moreover, the NBFP cavities exhibit a rapid response (<300 ms), benefiting from the membrane pores formed in the gaps between the adjacent nanoparticles. Finally, we demonstrated the applications of the NBFP cavities in optical anti-counterfeiting and dynamic multi-color printing. These results suggest that our approach will help to realize a colorful, fast, and ultrahigh-resolution dynamic display device in optical security and colorimetric sensing.

Broadband and Spectrally Selective Photothermal Conversion through Nanocluster Assembly of Disordered Plasmonic Metasurfaces

Plasmonic metasurfaces have been realized for efficient light absorption, thereby leading to photothermal conversion through nonradiative decay of plasmonic modes. However, current plasmonic metasurfaces suffer from inaccessible spectral ranges, costly and time-consuming nanolithographic top-down techniques for fabrication, and difficulty of scale-up. Here, we demonstrate a new type of disordered metasurface created by densely packing plasmonic nanoclusters of ultrasmall size on a planar optical cavity. The system either operates as a broadband absorber or offers a reconfigurable absorption band right across the visible region, resulting in continuous wavelength-tunable photothermal conversion. We further present a method to measure the temperature of plasmonic metasurfaces via surface-enhanced Raman spectroscopy (SERS), by incorporating single-walled carbon nanotubes (SWCNTs) as an SERS probe within the metasurfaces. Our disordered plasmonic system, generated by a bottom-up process, offers excellent performance and compatibility with efficient photothermal conversion. Moreover, it also provides a novel platform for various hot-electron and energy-harvesting functionalities.

Ultralight plasmonic structural color paint

All present commercial colors are based on pigments. While such traditional pigment-based colorants offer a commercial platform for large-volume and angle insensitiveness, they are limited by their instability in atmosphere, color fading, and severe environmental toxicity. Commercial exploitation of artificial structural coloration has fallen short due to the lack of design ideas and impractical nanofabrication techniques. Here, we present a self-assembled subwavelength plasmonic cavity that overcomes these challenges while offering a tailorable platform for rendering angle and polarization-independent vivid structural colors. Fabricated through large-scale techniques, we produce stand-alone paints ready to be used on any substrate. The platform offers full coloration with a single layer of pigment, surface density of 0.4 g/m², making it the lightest paint in the world.

Tailorable and Angle-Independent Colors from Synthetic Brochosomes

Although various artificial dyes and pigments have been invented, certain application fields need structural colors because they can last for centuries even under harsh conditions. Here, we report that the antireflective Ag brochosomes (soccer-ball-like microscale granules covered by nanobowls) become colorful when the nanobowls on the Ag brochosomes are filled by polystyrene (PS) nanospheres. The color originates from the enhanced electromagnetic resonances of the PS nanospheres by the surrounding metallic nanobowls, suggested by both the experimental and the simulation results. The color is determined by the size of the PS nanospheres. We can tailor the color simply by reducing the diameter of the PS nanospheres via the plasma etching treatment. The color intensity of the Ag brochosomes filled with PS nanospheres shows weak dependence on the observing angles, benefiting from their spherical shape. Plasma etching treatment of the Ag brochosomes filled with PS nanospheres through different masks can design various structural color patterns. The simple fabrication process and the easy processability make the Ag brochosomes filled with PS nanospheres have promising applications in the structural color fields.

Humidity-Responsive RGB-Pixels via Swelling of 3D Nanoimprinted Polyvinyl Alcohol

Humidity-responsive structural coloration is actively investigated to realize real-time humidity sensors for applications in smart farming, food storage, and healthcare management. Here, humidity-tunable nano pixels are investigated with a 700 nm resolution that demonstrates full standard RGB (sRGB) gamut coverage with a millisecond-response time. The color pixels are designed as Fabry-Pérot (F-P) etalons which consist of an aluminum mirror substrate, humidity-responsive polyvinyl alcohol (PVA) spacer, and a top layer of disordered silver nanoparticles (NPs). The measured volume change of the PVA reaches up to 62.5% when the relative humidity (RH) is manipulated from 20 to 90%. The disordered silver NP layer permits the penetration of water molecules into the PVA layer, enhancing the speed of absorption and swelling down to the millisecond level. Based on the real-time response of the hydrogel-based F-P etalons with a high-throughput 3D nanoimprint technique, a high-resolution multicolored color print that can have potential applications in display technologies and optical encryption, is demonstrated.

Scalable Hydrogel-Based Nanocavities for Switchable Meta-Holography with Dynamic Color Printing

Devices used for meta-optics display are currently undergoing a revolutionary transition from static to dynamic. Despite various tuning strategy demonstrations such as mechanical, electrical, optical, and thermal tunings, a longstanding challenge for their practical application has been the achievement of a conveniently accessible real-life tuning scheme for realizing versatile functionality dynamics outside the laboratory. In this study, we demonstrate a practical tuning strategy to realize a dynamic color printing with a switchable meta-holography exhibition based on hydrogel-based nanocavities. On the basis of the inflation sensitivity of a hydrogel to humidity alteration, its transmissive color was notably tuned from 450 to 750 nm. More intriguingly, by controlling the sample dry/immersed states in real time, we successfully enabled dual-channel switchable meta-holography. With the advantages of facile architecture, daily stimulus with large-area modulation, and high chromaticity, our proposed hydrogel-based nanocavities provide a promising path toward tunable display/encryption, optical sensors, and next-generation display technology.

Photonic and magnetic materials for on-demand local drug delivery

Nanomedicine has been considered a promising tool for biomedical research and clinical practice in the 21st century because of the great impact nanomaterials could have on human health. The generation of new smart nanomaterials, which enable time- and space-controlled drug delivery, improve the limitations of conventional treatments, such as non-specific targeting, poor biodistribution and permeability. These smart nanomaterials can respond to internal biological stimuli (pH, enzyme expression and redox potential) and/or external stimuli (such as temperature, ultrasound, magnetic field and light) to further the precision of therapies. To this end, photonic and magnetic nanoparticles, such as gold, silver and iron oxide, have been used to increase sensitivity and responsiveness to external stimuli. In this review, we aim to report the main and most recent systems that involve photonic or magnetic nanomaterials for external stimulus-responsive drug release. The uniqueness of this review lies in highlighting the versatility of integrating these materials within different carriers. This leads to enhanced performance in terms of in vitro and in vivo efficacy, stability and toxicity. We also point out the current regulatory challenges for the translation of these systems from the bench to the bedside, as well as the yet unresolved matter regarding the standardization of these materials.

Electrical devices designed based on inorganic clusters

The idea of exploring the bottom brink of material science has been carried out for more than two decades. Clusters science is the frontmost study of all nanoscale structures. Being an example of 0-dimensional quantum dot, nanocluster serves as the bridge between atomic and conventionally understood solid-state physics. The forming mechanism of clusters is found to be the mutual effects of electronic and geometric configuration. It is found that electronic shell structure influences the properties and geometric structure of the cluster until its size becomes larger, where electronic effects submerge in geometric structure. The discrete electronic structures depend on the size and conformation of clusters, which can be controlled artificially for potential device applications. Especially, small clusters with a size of 1-2 nm, whose electronic states are possibly discrete enough to overcome thermal fluctuations, are expected to build a single-electron transistor with room temperature operation. However, exciting as the progress may be seen, cluster science still falls within the territory of merely the extension of atomic and molecular science. Its production rate limits the scientific and potential application research of nanoclusters. It is suggested in this review that the mass-produce ability without losing the atomic precision selectivity would be the milestone for nanoclusters to advance to material science.

Giant mid-IR resonant coupling to molecular vibrations in sub-nm gaps of plasmonic multilayer metafilms

Nanomaterials capable of confining light are desirable for enhancing spectroscopies such as Raman scattering, infrared absorption, and nonlinear optical processes. Plasmonic superlattices have shown the ability to host collective resonances in the mid-infrared, but require stringent fabrication processes to create well-ordered structures. Here, we demonstrate how short-range-ordered Au nanoparticle multilayers on a mirror, self-assembled by a sub-nm molecular spacer, support collective plasmon-polariton resonances in the visible and infrared, continuously tunable beyond 11 µm by simply varying the nanoparticle size and number of layers. The resulting molecule-plasmon system approaches vibrational strong coupling, and displays giant Fano dip strengths, SEIRA enhancement factors ~ 10⁶, light-matter coupling strengths g ~ 100 cm^-1, Purcell factors ~ 10⁶, and mode volume compression factors ~ 10⁸. The collective plasmon-polariton mode is highly robust to nanoparticle vacancy disorder and is sustained by the consistent gap size defined by the molecular spacer. Structural disorder efficiently couples light into the gaps between the multilayers and mirror, enabling Raman and infrared sensing of sub-picolitre sample volumes.

Electrically switchable structural colors based on liquid-crystal-overlaid aluminum anisotropic nanoaperture arrays

Actively tunable or reconfigurable structural colors are highly promising in future development for high resolution imaging and displaying applications. To this end, we demonstrate switchable structural colors covering the entire visible range by integrating aluminum nanoaperture arrays with nematic liquid crystals. The geometrically anisotropic design of the nanoapertures provides strong polarization-dependent coloration. By overlaying a nematic liquid crystal layer, we further demonstrate switchable ability of the structural colors by either changing the polarization of the incident light or applying an external voltage. The switchable structural colors have a fast response time of 28 ms at a driving voltage of 6.5 V. Furthermore, colorful patterns are demonstrated by coding the colors with various dimensions of nanoaperture arrays with dual switching modes. Our proposed technique in this work provides a dual-mode switchable structural colors, which is highly promising for polarimetric displays, imaging sensors, and visual cryptography.

Disordered-nanoparticle-based etalon for ultrafast humidity-responsive colorimetric sensors and anti-counterfeiting displays

The development of real-time and sensitive humidity sensors is in great demand from smart home automation and modern public health. We hereby proposed an ultrafast and full-color colorimetric humidity sensor that consists of chitosan hydrogel sandwiched by a disordered metal nanoparticle layer and reflecting substrate. This hydrogel-based resonator changes its resonant frequency to external humidity conditions because the chitosan hydrogels are swollen under wet state and contracted under dry state. The response time of the sensor is ~10⁴ faster than that of the conventional Fabry-Pérot design. The origins of fast gas permeation are membrane pores created by gaps between the metal nanoparticles. Such instantaneous and tunable response of a new hydrogel resonator is then exploited for colorimetric sensors, anti-counterfeiting applications, and high-resolution displays.

Study on Spectral Selective Manipulation Characteristics of Surface Multilevel Micro-Nano Structures by FDTD Simulation

The optical filter based on the micro–nano structure on the material surface is an important optical device, which is widely used in many fields. The filter is fabricated on the substrate with different shapes and sizes of micro–nano array structure, and the wavelength selectivity is realized by adjusting the processing parameters. In this paper, the finite-difference time-domain (FDTD) method is used to simulate the spectral properties of periodic array structures on the Au surface, and the spectral response characteristics of different surface structural parameters to the incident light are obtained. The simulation results show that the periodic pore array has a directional modulation function on the reflectivity and transmittance of the material surface. In the same circular aperture array structure, the wavelength selection ability is proportional to the interval distance of the array period, but the transmission peak linewidth decreases with the increase of the interval distance. The structural spectrum of the cylindrical array is closely related to the structural period. The period of the array structure increases in proportion, the center wavelengths of the reflection and transmission peak of the spectrum are red-shifted. When the height of the array structure increases proportionally, the positions of the center wavelengths of the reflection and transmission peak remain almost unchanged. When the period of the array structure increases, the center wavelength of the reflection and transmission peaks appear red-shifted, and the line width is also narrowed. For the periodic ring array structure, as the inner diameter increases, the reflection peak is significantly red-shifted, and the smaller the ring width, the faster the red-shift of the reflection peak with the wavelength. By controlling the ratio of inner diameter-to-outer diameter, the spectral characteristics of the structured surface can be effectively controlled. These simulation results provide a basis for the preparation of optical filters in the future and a new idea for the study of micro–nano characteristic structures on the surface of materials.

Emerging Long-Range Order from a Freeform Disordered Metasurface

Recently, disordered metasurfaces have attracted considerable interest due to their potential applications in imaging, holography, and wavefront shaping. However, how to emerge long-range ordered phase distribution in disordered metasurfaces remains an outstanding problem. Here, a general framework is proposed to generate a spatially homogeneous in-plane phase distribution from a disordered metasurface, by engineering disorder parameters together with topology optimization. As a proof-of-concept demonstration, an all-dielectric disordered supercell metasurface with relatively homogeneous in-plane phase fluctuation is designed by disorder parameter engineering, manifesting as polarization conversion-dependent random scattering or unidirectional transmission. Then, a topology optimization approach is utilized to overcome the lattice coupling effect and to further improve the homogeneity of complex electric field fluctuation. In comparison with the initial supercell metasurface, both the phase fluctuation range and the relative efficiency of the topology-optimized freeform metasurface are significantly improved, leading to a long-range ordered electric field distribution. Moreover, three experimental realizations are performed, all of which agree well with the theoretical results. This methodology may inspire more exotic optical phenomena and find more promising applications in disordered metasurfaces and disordered optics.

Large-Scale and Wide-Gamut Coloration at the Diffraction Limit in Flexible, Self-Assembled Hierarchical Nanomaterials

Unveiling physical phenomena that generate controllable structural coloration is at the center of significant research efforts due to the platform potential for the next generation of printing, sensing, displays, wearable optoelectronics components, and smart fabrics. Colors based on e-beam facilities possess high resolutions above 100k dots per inch (DPI), but limit manufacturing scales up to 4.37 cm² , while requiring rigid substrates that are not flexible. State-of-art scalable techniques, on the contrary, provide either narrow gamuts or small resolutions. A common issue of current methods is also a heterogeneous resolution, which typically changes with the color printed. Here, a structural coloration platform with broad gamuts exceeding the red, green, and blue (RGB) spectrum in inexpensive, thermally resistant, flexible, and metallic-free structures at constant 101 600 DPI (at the diffraction limit), obtained via mass-production manufacturing is demonstrated. This platform exploits a previously unexplored physical mechanism, which leverages the interplay between strong scattering modes and optical resonances excited in fully 3D dielectric nanostructures with suitably engineered longitudinal profiles. The colors obtained with this technology are scalable to any area, demonstrated up to the single wafer (4 in.). These results open real-world applications of inexpensive, high-resolution, large-scale structural colors with broad chromatic spectra.

Revealing the Phase Segregation and Evolution Dynamics in Binary Nanoalloys via Electron Beam-Assisted Ultrafast Heating and Cooling

Gas-phase synthesized binary nanoparticles (NPs) possess ultraclean surfaces, which benefit versatile uses in sensors and catalysts. However, precise control of their configuration and properties is still a big challenge because the growth mechanism and phase evolution dynamics in these NPs are very hard to unveil. Here, we report a strategy to investigate the phase evolution dynamics in binary NPs by using e-beam assisted ultrafast local heating and cooling inside a transmission electron microscope. With this strategy, the phase segregation and corresponding shape evolution of PbBi NPs are in situ revealed. It is found that the as-prepared PbBi alloy NPs will transform into heterostructures under e-beam stimulated structural relaxation, leading to the formation of featured Janus configurations with faceted Bi polyhedron parts and intermetallic hemisphere parts. During phase segregation, Pb₁Bi₁ and Pb₇Bi₃ phases are captured and identified, and a model of phase and shape evolution of PbBi nanoalloys is developed and contrasted with that of their bulk counterparts. These findings benefit the understanding of the phase dynamics of binary NPs and can provide in-depth information for engineering their structures for practical applications.

Spectral Characteristics Simulation of Topological Micro-Nano Structures Based on Finite Difference Time Domain Method

Natural structural colors inspire people to obtain the technology of spectral characteristics by designing and preparing micro-nano structures on the material’s surface. In this paper, the finite difference time domain (FDTD) method is used to simulate the spectral selectivity of micro-nano grating on an Au surface, and the spectral response characteristics of different physical parameters to the incident light are obtained. The results show that, when the grating depth is shallow, the absorption peaks of TM polarized incident light on the material surface take on redshifts with the increase in the grating period. Meanwhile, when the depth-width ratio of the grating structure is high, the absorption peak appears in the reflection spectrum and presents a linear red shift with the increase in the grating period after the linearly polarized light TE wave incident on the surface of the micro-nano structure. At the same time, the wavelength of the absorption peak of the reflection spectrum and the grating period take on one-to-one correspondence relations, and when the TM polarized light is incident, the reflection spectrum exhibits obvious selective absorption characteristic peaks at certain grating periods (for example, when the period is 0.4 μm, there are three absorption peaks at the wavelengths of 0.7, 0.95, and 1.55 μm). These simulation results can provide a good theoretical basis for the preparation of micro-nano structures with spectral regulation function in the practical application.

Facile full-color printing with a single transparent ink

Structural colors are promising candidates for their antifading and eco-friendly characteristics. However, high cost and complicated processing inevitably hinder their development. Here, we propose a facile full-color structural-color inkjet printing strategy with a single transparent ink from the common polymer materials. This structural color arisen from total internal reflections is prepared by digitally printing the dome-shaped microstructure (microdome) with well-controlled morphology. By controlling the ink volume and substrate wettability, the microdome color can be continuously regulated across whole visible regions. The gamut, saturation, and lightness of the printed structural-color image are precisely adjusted via the programmable arrangement of different microdomes. With the advantages of simple manufacturing and widely available inks, this color printing approach presents great potential in imaging, decoration, sensing, and biocompatible photonics.

Vibrant reflective sensors with percolation film Fabry-Pérot nanocavities

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.

Shaping the Color and Angular Appearance of Plasmonic Metasurfaces with Tailored Disorder

The optical properties of plasmonic nanoparticle ensembles are determined not only by the particle shape and size but also by the nanoantenna arrangement. To investigate the influence of the spatial ordering on the far-field optical properties of nanoparticle ensembles, we introduce a disorder model that encompasses both "frozen-phonon" and correlated disorder. We present experimental as well as computational approaches to gain a better understanding of the impact of disorder. A designated Fourier microscopy setup allows us to record the real- and Fourier-space images of plasmonic metasurfaces as either RGB images or fully wavelength-resolved data sets. Furthermore, by treating the nanoparticles as dipoles, we calculate the electric field based on dipole-dipole interaction, extract the far-field response, and convert it to RGB images. Our results reveal how the different disorder parameters shape the optical far field and thus define the optical appearance of a disordered metasurface and show that the relatively simple dipole approximation is able to reproduce the far-field behavior accurately. These insights can be used for engineering metasurfaces with tailored disorder to produce a desired bidirectional reflectance distribution function.

Full Color and Grayscale Painting with 3D Printed Low-Index Nanopillars

Sculpting nanostructures into different geometries in either one or two dimensions produces a wide range of colorful elements in microscopic prints. However, achieving different shades of gray and control of color saturation remain challenging. Here, we report a complete approach to color and grayscale generation based on the tuning of a single nanostructure geometry. Through two-photon polymerization lithography, we systematically investigated color generation from the basic single nanopillar geometry in low-refractive-index (n < 1.6) material. Grayscale and full color palettes were achieved that allow decomposition onto hue, saturation, and brightness values. This approach enabled the "painting" of arbitrary colorful and grayscale images by mapping desired prints to precisely controllable parameters during 3D printing. We further extend our understanding of the scattering properties of the low-refractive-index nanopillar to demonstrate grayscale inversion and color desaturation and steganography at the level of single nanopillars.

Disorder-Induced Material-Insensitive Optical Response in Plasmonic Nanostructures: Vibrant Structural Colors from Noble Metals

Materials show various responses to incident light, owing to their unique dielectric functions. A well-known example is the distinct colors displayed by metals, providing probably the simplest method to identify gold, silver, and bronze since ancient times. With the advancement of nanotechnology, optical structures with feature sizes smaller than the optical wavelength have been routinely achieved. In this regime, the optical response is also determined by the geometry of the nanostructures, inspiring flourishing progress in plasmonics, photonic crystals, and metamaterials. Nevertheless, the nature of the materials still plays a decisive role in light-matter interactions, and this material-dependent optical response is widely accepted as a norm in nanophotonics. Here, a counterintuitive system-plasmonic nanostructures composed of different materials but exhibiting almost identical reflection-is proposed and realized. The geometric disorder embedded in the system overwhelms the contribution of the material properties to the electrodynamics. Both numerical simulations and experimental results provide concrete evidence of the insensitivity of the optical response to different plasmonic materials. The same optical response is preserved with various materials, providing great flexibility of freedom in material selection. As a result, the proposed configuration may shed light on novel applications ranging from Raman spectroscopy, photocatalysis, to nonlinear optics.

Artificial Structural Colors and Applications

Structural colors are colors generated by the interaction between incident light and nanostructures. Structural colors have been studied for decades due to their promising advantages of long-term stability and environmentally friendly properties compared with conventional pigments and dyes. Previous studies have demonstrated many artificial structural colors inspired by naturally generated colors from plants and animals. Moreover, many strategies consisting of different principles have been reported to achieve dynamically tunable structural colors. Furthermore, the artificial structural colors can have multiple functions besides decoration, such as absorbing solar energy, anti-counterfeiting, and information encryption. In the present work, we reviewed the typical artificial structural colors generated by multilayer films, photonic crystals, and metasurfaces according to the type of structures, and discussed the approaches to achieve dynamically tunable structural colors.

Black Au-Decorated TiO2 Produced via Laser Ablation in Liquid

The rational combination of plasmonic and all-dielectric concepts within hybrid nanomaterials provides a promising route toward devices with ultimate performance and extended modalities. Spectral matching of plasmonic and Mie-type resonances for such nanostructures can only be achieved for their dissimilar characteristic sizes, thus making the resulting hybrid nanostructure geometry complex for practical realization and large-scale replication. Here, we produced amorphous TiO₂ nanospheres decorated and doped with Au nanoclusters via single-step nanosecond-laser irradiation of commercially available TiO₂ nanopowders dispersed in aqueous HAuCl₄. Fabricated hybrids demonstrate remarkable light-absorbing properties (averaged value ≈96%) in the visible and near-IR spectral range mediated by bandgap reduction of the laser-processed amorphous TiO₂ as well as plasmon resonances of the decorating Au nanoclusters. The findings are supported by optical spectroscopy, electron energy loss spectroscopy, transmission electron microscopy, and electromagnetic modeling. Light-absorbing and plasmonic properties of the produced hybrids were implemented to demonstrate catalytically passive SERS biosensor for identification of analytes at trace concentrations and solar steam generator that permitted to increase water evaporation rate by 2.5 times compared with that of pure water under identical 1 sun irradiation conditions.

Bright Field Structural Colors in Silicon-on-Insulator Nanostructures

Structural coloration with artificially nanostructured materials is emerging as a prospective alternative to traditional pigments for the high resolution, sustainable recycling, and long-time durability. However, achieving bright field structural colors with dielectric nanostructures remains a great challenge due to the weak scattering in an asymmetric environment. Here, we demonstrate all-dielectric bright field structural colors with diffraction-limited resolution on the silicon-on-insulator platform. The backscattering is strongly enhanced from the constructive interference between Mie resonances of individual Si antennas and Fabry-Perot resonances supported by the SiO₂ layer. The fabricated colors with varying hues and saturations show strong insensitivity with respect to the interparticle spacing and, remarkably, the viewing angle under resonant conditions. Compared with creating a quasi-homogeneous environment, our strategy is solid and complementary metal-oxide semiconductor integrable, paving the way for practical applications of structural colors in nanoscale color printing, microdisplays, and imaging.

Self-assembled plasmonics for angle-independent structural color displays with actively addressed black states

Functional nanomaterials will enable the next generation of displays, detectors, and photovoltaic devices by interacting with light at subwavelength length scales. However, performance and practical integration with current electronic systems remain a scientific and engineering challenge. Here, we report the wafer-scale self-assembly/growth of nanoparticles which reproduce the cyan, magenta, and yellow color space. We explore the physics of the optical resonances and the advantageous properties they manifest for color filter technology, such as angle insensitivity and high saturation. The versatile formation process then enables integration with commercial devices to realize a hybrid, nanoparticle–liquid crystal reflective display.

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.