The role of random nanostructures for the omnidirectional anti-reflection properties of the glasswing butterfly

Regeneration of Antifog Performance of Laser-Induced Copper-Based Micro-Nano Structured Surfaces by Rapid Thermal Treatment

In this investigation, the laser marker ablation technique was employed on Cu-coated glass to fabricate micro-nanostructured antifog glass. The resulting surfaces exhibited a quasi-periodic micron hillock-hollow structure with dispersed nanoparticles distributed throughout, which played a role in the antifog property and superhydrophilicity. However, airborne organic pollutant deposition degraded the superhydrophilicity of ablated glass surfaces and, therefore, their antifog performance, which cannot be circumvented. Conventionally, furnace annealing for at least 1 h was used to decompose the organic pollutants and restore the superhydrophilicity, limiting the throughput and application scenario. Remarkably, the rapid regeneration of this property was achieved through either a 5 min rapid thermal treatment at 400 °C or a 1 s flame treatment. These are interventions that are hitherto unreported. Such short and simple treatment methods underscore the potential of laser-ablated glass for diverse practical applications.

Highly flexible and transparent colorless polyimide substrate sandwiched between plasma polymerized fluorocarbon and InGaTiO for high performance flexible perovskite solar cells

We integrated transparent antireflective coatings and transparent electrodes onto flexible colorless polyimide (CPI) substrates to fabricate high-performance flexible perovskite solar cells. Multifunctional PPFC/CPI/IGTO substrates were fabricated by sputtering the optimal plasma-polymerized fluorocarbon (PPFC) antireflective coating and InGaTiO (IGTO) electrode films on both sides of the CPI substrate. By applying PPFC with a low refractive index (1.38) as an antireflective coating, the transparency of the PPFC/CPI/IGTO substrate increased by an additional 1.2%. In addition, owing to the amorphous characteristics of the PPFC and IGTO layers, the PPFC/CPI/IGTO substrate showed constant sheet resistance and transmittance change even after 10,000 cycles during the bending tests. The flexible perovskite solar cells, fabricated on the PPFC/CPI/IGTO substrate, exhibited an increase in current density of 1.48 mA/cm2 after the deposition of the PPFC antireflective coating. These results confirmed that the PPFC/CPI/IGTO substrate was durable against high-temperature treatment, flexible, and exhibited excellent electrical characteristics. This enhanced the efficiency and durability of the flexible perovskite solar cells. Moreover, the hydrophobic PPFC layer allowed the self-cleaning of inflexible perovskite solar cells. Given these attributes, the PPFC/CPI/IGTO structure has been recognized as a good choice for multifunctional substrates of flexible perovskite solar cells, presenting the potential for enhancing performance.

3D Intelligent Cloaked Vehicle Equipped with Thousand-Level Reconfigurable Full-Polarization Metasurfaces

A crucial aspect in shielding a variety of advanced electronic devices from electromagnetic detection involves controlling the flow of electromagnetic waves, akin to invisibility cloaks. Decades ago, the exploration of transformation optics heralded the dawn of modern invisibility cloaks, which has stimulated immense interest across various physical scenarios. However, most prior research is simplified to low-dimensional and stationary hidden objects, limiting their practical applicability in a dynamically changing world. This study develops a 3D large-scale intelligent cloak capable of remaining undetectable even in non-stationary conditions. By employing thousand-level reconfigurable full-polarization metasurfaces, this work has achieved an exceptionally high degree of freedom in sculpting the scattering waves as desired. Serving as the core computational unit, a hybrid inverse design enables the cloaked vehicle to respond in real-time, with a rapid reaction time of just 70 ms. These experiments integrate the cloaked vehicle with a perception-decision-control-execution system and evaluate its performance under random static positions and dynamic travelling trajectories, achieving a background scattering matching degree of up to 93.3%. These findings establish a general paradigm for the next generation of intelligent meta-devices in real-world settings, potentially paving the way for an era of "Electromagnetic Internet of Things."

Quintic refractive index profile-based funnel-shaped silicon antireflective structures for enhanced photodetector performance

Antireflection, vital in optoelectronics devices such as solar cells and photodetectors, reduces light reflection and increases absorption. Antireflective structures (ARS), a primary method by which to realize this effect, control the refractive index (RI) profile based on their shape. The antireflection efficiency depends on the refractive index profile, with the quintic RI profile being recognized as ideal for superior antireflection. However, fabricating nano-sized structures with a desired shape, particularly in silicon with a quintic RI profile, has been a challenge. In this study, we introduce a funnel-shaped silicon (Si) ARS with a quintic RI profile. Its antireflective properties are demonstrated through reflectance measurements and by an application to a photodetector surface. Compared to the film Si and cone-shaped ARS types, which are common structures to achieve antireflection, the funnel-shaped ARS showed reflectance of 4.24% at 760 nm, whereas those of the film Si and cone-shaped ARS were 32.8% and 10.6%, respectively. Photodetectors with the funnel-shaped ARS showed responsivity of 0.077 A/W at 950 nm, which is 19.54 times higher than that with the film Si and 2.45 times higher than that with the cone-shaped ARS.

Mechanically-Durable Antireflective Subwavelength Nanoholes on Glass Surfaces Using Lithography-Free Fabrication

Traditional multilayer antireflection (AR) surfaces are of significant importance for numerous applications, such as laser optics, camera lenses, and eyeglasses. Recently, technological advances in the fabrication of biomimetic AR surfaces capable of delivering broadband omnidirectional high transparency combined with self-cleaning properties have opened an alternative route toward realization of multifunctional surfaces which would be beneficial for touchscreen displays or solar harvesting devices. However, achieving the desired surface properties often requires sophisticated lithography fabrication methods consisting of multiple steps. In the present work, we show the design and implementation of mechanically robust AR surfaces fabricated by a lithography-free process using thermally dewetted silver as an etching mask. Both-sided nanohole (NH) surfaces exhibit transmittance above 99% in the visible or the near-infrared ranges combined with improved angular response at an angle of incidence of up to θi = 60°. Additionally, the NHs demonstrate excellent mechanical resilience against repeated abrasion with cheesecloth due to favorable redistribution of the shearing mechanical forces, making them a viable option for touchscreen display applications.

Multiple-pathways light modulation in Pleurosigma strigosum bi-raphid diatom

Ordered, quasi-ordered, and even disordered nanostructures can be identified as constituent components of several protists, plants and animals, making possible an efficient manipulation of light for intra- and inter- species communication, camouflage, or for the enhancement of primary production. Diatoms are ubiquitous unicellular microalgae inhabiting all the aquatic environments on Earth. They developed, through tens of millions of years of evolution, ultrastructured silica cell walls, the frustules, able to handle optical radiation through multiple diffractive, refractive, and wave-guiding processes, possibly at the basis of their high photosynthetic efficiency. In this study, we employed a range of imaging, spectroscopic and numerical techniques (including transmission imaging, digital holography, photoluminescence spectroscopy, and numerical simulations based on wide-angle beam propagation method) to identify and describe different mechanisms by which Pleurosigma strigosum frustules can modulate optical radiation of different spectral content. Finally, we correlated the optical response of the frustule to the interaction with light in living, individual cells within their aquatic environment following various irradiation treatments. The obtained results demonstrate the favorable transmission of photosynthetic active radiation inside the cell compared to potentially detrimental ultraviolet radiation.

Materials in Radiative Cooling Technologies

Radiative cooling (RC) is a carbon-neutral cooling technology that utilizes thermal radiation to dissipate heat from the Earth's surface to the cold outer space. Research in the field of RC has garnered increasing interest from both academia and industry due to its potential to drive sustainable economic and environmental benefits to human society by reducing energy consumption and greenhouse gas emissions from conventional cooling systems. Materials innovation is the key to fully exploit the potential of RC. This review aims to elucidate the materials development with a focus on the design strategy including their intrinsic properties, structural formations, and performance improvement. The main types of RC materials, i.e., static-homogeneous, static-composite, dynamic, and multifunctional materials, are systematically overviewed. Future trends, possible challenges, and potential solutions are presented with perspectives in the concluding part, aiming to provide a roadmap for the future development of advanced RC materials.

Rashba Metamaterials and Metasurfaces with Zero Reflectivity and Effect of Surface States in Ultrathin Metal Films

Metals, renowned for their high reflectivity, find extensive use in various technological applications, from mirrors to optical coatings in radars, telescopes, and mobile communications. However, their potential in antireflective coatings has remained largely untapped. In this study, we demonstrate that by applying an ultrathin metallic film onto an oxide layer, we can achieve a flawless optical surface with zero reflectivity. This phenomenon has been successfully observed across various metals, including Sn, Ag, Au, Pt, Bi, and Nb, showcasing its broad applicability. The underlying principle lies in the emergence of surface states, where the Rashba effect is strong, which give rise to the formation of Rashba metamaterial and metasurface (RMM) structures. Remarkably, these RMMs can be fine-tuned to act as high-resolution Veselago lenses. To illustrate, we achieved zero reflectivity with an RMM consisting of a 1 nm thick Sn metal film on a 1 nm Ge buffer, situated on a 60 nm Al2O3/Si substrate. Similar results were observed for other metals (Pt, Au, Ag, and Nb) and semimetals (Bi) by adjusting the film thickness to 2, 3, 5, 10, and 6 nm, respectively. The revelation of RMMs with zero reflectivity (R = 0) has tremendous potential to revolutionize optical device technologies, covering renewable energy, optoelectronics, and the telecommunications industry.

Recording animal-view videos of the natural world using a novel camera system and software package

Plants, animals, and fungi display a rich tapestry of colors. Animals, in particular, use colors in dynamic displays performed in spatially complex environments. Although current approaches for studying colors are objective and repeatable, they miss the temporal variation of color signals entirely. Here, we introduce hardware and software that provide ecologists and filmmakers the ability to accurately record animal-perceived colors in motion. Specifically, our Python codes transform photos or videos into perceivable units (quantum catches) for animals of known photoreceptor sensitivity. The plans and codes necessary for end-users to capture animal-view videos are all open source and publicly available to encourage continual community development. The camera system and the associated software package will allow ecologists to investigate how animals use colors in dynamic behavioral displays, the ways natural illumination alters perceived colors, and other questions that remained unaddressed until now due to a lack of suitable tools. Finally, it provides scientists and filmmakers with a new, empirically grounded approach for depicting the perceptual worlds of nonhuman animals.

High-Transmission Biomimetics Structural Surfaces Produced via Ultrafast Laser Manufacturing

Inspired by periodically aligned micro/nanostructures on biological surfaces, researchers have been fabricating biomimetic structures with superior performance. As a promising and versatile tool, an ultrafast laser combined with other forms of processing technology has been utilized to manufacture functional structures, e.g., the biomimetic subwavelength structures to restrain the surface Fresnel reflectance. In this review paper, we interpret the biomimetic mechanism of antireflective subwavelength structures (ARSSs) for high-transmission windows. Recent advances in the fabrication of ARSSs with an ultrafast laser are summarized and introduced. The limitations and challenges of laser processing technology are discussed, and the future prospects for advancement are outlined, too.

Analysis of the optical response of reptile tissues in the visible and UV applying the KKR method

Structural colors in nature are frequently produced by the ordered arrangement of nanoparticles. Interesting examples include reptiles and birds utilizing lattice-like formation of nanoparticles to produce a variety of colors. A famous example is the panther chameleon which is even able to change its color by actively varying the distance between guanine nanocrystals in its skin. Here, we demonstrate that the application of rigorous electromagnetic methods is important to determine the actual optical response of such biological systems. By applying the Korringa-Kohn-Rostoker (KKR) method we calculate the efficiencies of the reflected diffraction orders that can be viewed from directions other than the specular. Our results reveal that important characteristics of the reflectance spectra, especially within the ultraviolet (UV) and short visible wavelengths region, cannot be predicted by approximate models like the often-applied Maxwell-Garnett approach. Additionally, we show that the KKR method can be employed for the design of multi-layer structures with a desired optical response in the UV regime.

Tackling Multi-Physics Nano-Scale Phenomena in Capillary Force Lithography with Small Data by Hybrid Intelligence

The scientific community has been looking for novel approaches to develop nanostructures inspired by nature. However, due to the complicated processes involved, controlling the height of these nanostructures is challenging. Nanoscale capillary force lithography (CFL) is one way to use a photopolymer and alter its properties by exposing it to ultraviolet radiation. Nonetheless, the working mechanism of CFL is not fully understood due to a lack of enough information and first principles. One of these obscure behaviors is the sudden jump phenomenon-the sudden change in the height of the photopolymer depending on the UV exposure time and height of nano-grating (based on experimental data). This paper uses known physical principles alongside artificial intelligence to uncover the unknown physical principles responsible for the sudden jump phenomenon. The results showed promising results in identifying air diffusivity, dynamic viscosity, surface tension, and electric potential as the previously unknown physical principles that collectively explain the sudden jump phenomenon.

Pursuit of hidden rules behind the irregularity of nano capillary lithography by hybrid intelligence

Nature finds a way to leverage nanotextures to achieve desired functions. Recent advances in nanotechnologies endow fascinating multi-functionalities to nanotextures by modulating the nanopixel's height. But nanoscale height control is a daunting task involving chemical and/or physical processes. As a facile, cost-effective, and potentially scalable remedy, the nanoscale capillary force lithography (CFL) receives notable attention. The key enabler is optical pre-modification of photopolymer's characteristics via ultraviolet (UV) exposure. Still, the underlying physics of the nanoscale CFL is not well understood, and unexplained phenomena such as the "forbidden gap" in the nano capillary rise (unreachable height) abound. Due to the lack of large data, small length scales, and the absence of first principles, direct adoptions of machine learning or analytical approaches have been difficult. This paper proposes a hybrid intelligence approach in which both artificial and human intelligence coherently work together to unravel the hidden rules with small data. Our results show promising performance in identifying transparent, physics-retained rules of air diffusivity, dynamic viscosity, and surface tension, which collectively appear to explain the forbidden gap in the nanoscale CFL. This paper promotes synergistic collaborations of humans and AI for advancing nanotechnology and beyond.

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.

Bio-inspired optical structures for enhancing luminescence

Luminescence is an essential signal for many plants, insects, and marine organisms to attract the opposite sex, avoid predators, and so on. Most luminescent living organisms have ingenious optical structures which can help them get high luminescent performances. These remarkable and efficient structures have been formed by natural selection from long-time evolution. Researchers keenly observed the enhanced luminescence phenomena and studied how these phenomena happen in order to learn the characteristics of bio-photonics. In this review, we summarize the optical structures for enhancing luminescence and their applications. The structures are classified according to their different functions. We focus on how researchers use these biological inspirations to enhance different luminescence processes, such as chemiluminescence (CL), photoluminescence (PL), and electroluminescence (EL). It lays a foundation for further research on the applications of luminescence enhancement. Furthermore, we give examples of luminescence enhancement by bio-inspired structures in information encryption, biochemical detection, and light sources. These examples show that it is possible to use bio-inspired optical structures to solve complex problems in optical applications. Our work will provide guidance for research on biomimetic optics, micro- and nano-optical structures, and enhanced luminescence.

Recent advances in prevailing antifogging surfaces: structures, materials, durability, and beyond

In past decades, antifogging surfaces have drawn more and more attention owing to their promising and wide applications such as in aerospace, traffic transportation, optical devices, the food industry, and medical and other fields. Therefore, the potential hazards caused by fogging need to be solved urgently. At present, the up-and-coming antifogging surfaces have been developing swiftly, and can effectively achieve antifogging effects primarily by preventing fog formation and rapid defogging. This review analyzes and summarizes current progress in antifogging surfaces. Firstly, some bionic and typical antifogging structures are described in detail. Then, the antifogging materials explored thus far, mainly focusing on substrates and coatings, are extensively introduced. After that, the solutions for improving the durability of antifogging surfaces are explicitly classified in four aspects. Finally, the remaining big challenges and future development trends of the ascendant antifogging surfaces are also presented.

Predictive saccades and decision making in the beetle-predating saffron robber fly

Internal predictions about the sensory consequences of self-motion, encoded by corollary discharge, are ubiquitous in the animal kingdom, including for fruit flies, dragonflies, and humans. In contrast, predicting the future location of an independently moving external target requires an internal model. With the use of internal models for predictive gaze control, vertebrate predatory species compensate for their sluggish visual systems and long sensorimotor latencies. This ability is crucial for the timely and accurate decisions that underpin a successful attack. Here, we directly demonstrate that the robber fly Laphria saffrana, a specialized beetle predator, also uses predictive gaze control when head tracking potential prey. Laphria uses this predictive ability to perform the difficult categorization and perceptual decision task of differentiating a beetle from other flying insects with a low spatial resolution retina. Specifically, we show that (1) this predictive behavior is part of a saccade-and-fixate strategy, (2) the relative target angular position and velocity, acquired during fixation, inform the subsequent predictive saccade, and (3) the predictive saccade provides Laphria with additional fixation time to sample the frequency of the prey's specular wing reflections. We also demonstrate that Laphria uses such wing reflections as a proxy for the wingbeat frequency of the potential prey and that consecutively flashing LEDs to produce apparent motion elicits attacks when the LED flicker frequency matches that of the beetle's wingbeat cycle.

Exciting-frequency-adaptive amplitude/phase hybrid holographic inscription in plasmonic polymers

Plasmonic holography is generally regarded as an effective technology for 3D display that meets the requirements of the human visual system. However, low readout stability and large cross talk in the frequency field during a plasmonic photo-dissolution reaction set a huge obstacle for application of color holography. Herein, we propose a new, to the best of our knowledge, route toward producing exciting frequency sensitive holographic-inscription based on plasmonic nano-Ag adaptive growth. Donor-molecule-doped plasmonic polymers on polyethylene terephthalate substrates exhibit wide spectral response range, accurate optical frequency sensing, and bending durability. The resonant plasmonic particles act as optical antennas and transfer energy to surrounding organic matrices for nanocluster production and non-resonant particle growth. The surface relief hologram is also highly dependent on the excitation frequency, so we successfully obtain a controllable cross-periodic structure with amplitude/phase mixed information, as well as color holographic display. This work provides a bright way to high-density storage, information steganography, and virtual/augmented reality.

Biological and Bioinspired Thermal Energy Regulation and Utilization

The regulation and utilization of thermal energy is increasingly important in modern society due to the growing demand for heating and cooling in applications ranging from buildings, to cooling high power electronics, and from personal thermal management to the pursuit of renewable thermal energy technologies. Over billions of years of natural selection, biological organisms have evolved unique mechanisms and delicate structures for efficient and intelligent regulation and utilization of thermal energy. These structures also provide inspiration for developing advanced thermal engineering materials and systems with extraordinary performance. In this review, we summarize research progress in biological and bioinspired thermal energy materials and technologies, including thermal regulation through insulation, radiative cooling, evaporative cooling and camouflage, and conversion and utilization of thermal energy from solar thermal radiation and biological bodies for vapor/electricity generation, temperature/infrared sensing, and communication. Emphasis is placed on introducing bioinspired principles, identifying key bioinspired structures, revealing structure-property-function relationships, and discussing promising and implementable bioinspired strategies. We also present perspectives on current challenges and outlook for future research directions. We anticipate that this review will stimulate further in-depth research in biological and bioinspired thermal energy materials and technologies, and help accelerate the growth of this emerging field.

Multi-scale dissection of wing transparency in the clearwing butterfly Phanus vitreus

Optical transparency is rare in terrestrial organisms, and often originates through loss of pigmentation and reduction in scattering. The coloured wings of some butterflies and moths have repeatedly evolved transparency, offering examples of how they function optically and biologically. Because pigments are primarily localized in the scales that cover a colourless wing membrane, transparency has often evolved through the complete loss of scales or radical modification of their shape. Whereas bristle-like scales have been well documented in glasswing butterflies, other scale modifications resulting in transparency remain understudied. The butterfly Phanus vitreus achieves transparency while retaining its scales and exhibiting blue/cyan transparent zones. Here, we investigate the mechanism of wing transparency in P. vitreus by light microscopy, focused ion beam milling, microspectrophotometry and optical modelling. We show that transparency is achieved via loss of pigments and vertical orientation in normal paddle-like scales. These alterations are combined with an anti-reflective nipple array on portions of the wing membrane being more exposed to light. The blueish coloration of the P. vitreus transparent regions is due to the properties of the wing membrane, and local scale nanostructures. We show that scale retention in the transparent patches might be explained by these perpendicular scales having hydrophobic properties.

A theoretical approach to zero-reflection toroidal curved metasurfaces

In this paper, we investigate the electromagnetic response of metasurfaces due to excitation of the toroidal moment. A toroidal curved metasurface analyzad using a novel theoretical solution based on the Fourier analysis to evaluate the localized fields. Analyzing localized near-field interactions are crucial in investigating the excited trapped modes and enables us to optimize the reflection properties of the proposed metasurface. Optimization is accomplished using graphene layer and resulted a hybrid dielectric-graphene structure with near-zero reflection properties.

Unraveling Optical and Electrical Gains of Perovskite Solar Cells with an Antireflective and Energetic Cascade Electron Transport Layer

Electron transport layers (ETLs) are imperative in n-i-p structured perovskite solar cells (PSCs) because of their capability to affect light propagation, electron extraction, and perovskite crystallization, and any mismatch of optical constants, band position, and surface potential between the ETLs and the perovskites can cause unintentional optical and electrical losses. Herein, an antireflective and energetic cascade bilayer ETL with ubiquitously used SnO₂ and TiO₂ was constructed at 150 °C for PSCs, and the in-depth mechanism for performance improvement was systematically unraveled. It was revealed that the construction of an ETL with gradually increasing refractive indices can circumvent light reflection loss, resulting in enhanced photocurrent. The combined ETL forms an energetic cascade to promote electronic conductivity and facilitate electron extraction with reduced energy loss. Moreover, topologic perovskite growth with improved crystallinity and vertical orientation was preferred owing to the relative dewetting behavior, leading to reduced defect states and enhanced carrier mobility in the perovskite layer.

Soft Functionally Gradient Materials and Structures - Natural and Manmade: A Review

Functionally gradient materials (FGM) have gradual variations in their properties along one or more dimensions due to local compositional or structural distinctions by design. Traditionally, hard materials (e.g., metals, ceramics) are used to design and fabricate FGMs; however, there is increasing interest in polymer-based soft and compliant FGMs mainly because of their potential application in the human environment. Soft FGMs are ideally suitable to manage interfacial problems in dissimilar materials used in many emerging devices and systems for human interaction, such as soft robotics and electronic textiles and beyond. Soft systems are ubiquitous in everyday lives; they are resilient and can easily deform, absorb energy, and adapt to changing environments. Here, the basic design and functional principles of biological FGMs and their manmade counterparts are discussed using representative examples. The remarkable multifunctional properties of natural FGMs resulting from their sophisticated hierarchical structures, built from a relatively limited choice of materials, offer a rich source of new design paradigms and manufacturing strategies for manmade materials and systems for emerging technological needs. Finally, the challenges and potential pathways are highlighted to leverage soft materials' facile processability and unique properties toward functional FGMs.

Glasswing-Butterfly-Inspired Multifunctional Scleral Lens and Smartphone Raman Spectrometer for Point-of-Care Tear Biomarker Analysis

Augmenting contact lenses with sensing capabilities requires incorporating multiple functionalities within a diminutive device. Inspired by multifunctional biophotonic nanostructures of glasswing butterflies, a nanostructured scleral lens with enhanced optical, bactericidal, and sensing capabilities is reported. When used in conjunction with a smartphone-integrated Raman spectrometer, the feasibility of point-of-care applications is demonstrated. The bioinspired nanostructures made on parylene films are mounted on the anterior and posterior side of a scleral lens to create a nanostructured lens. Compared to unstructured parylene, nanostructured parylene minimizes glare by 4.3-fold at large viewing angles up to 80^o . When mounted on a scleral lens, the nanostructures block 2.8-fold more ultraviolet (UVA) light while offering 1.1-fold improved transmission in the visible regime. Furthermore, the nanostructures exhibit potent bactericidal activity against Escherichia coli, killing 89% of tested bacteria within 4 h. The same nanostructures, when gold-coated, are used to perform rapid label-free multiplex detection of lysozyme and lactoferrin, the protein biomarkers of the chronic dry eye disease, in whole human tears using drop-coating deposition Raman spectroscopy. The detection of both proteins in whole human tear samples from different subjects using the nanostructured lens produced excellent correlation with commercial enzyme-based assays while simultaneously displaying a 1.5-fold lower standard deviation.

Biomimicry in nanotechnology: a comprehensive review

Biomimicry has been utilized in many branches of science and engineering to develop devices for enhanced and better performance. The application of nanotechnology has made life easier in modern times. It has offered a way to manipulate matter and systems at the atomic level. As a result, the miniaturization of numerous devices has been possible. Of late, the integration of biomimicry with nanotechnology has shown promising results in the fields of medicine, robotics, sensors, photonics, etc. Biomimicry in nanotechnology has provided eco-friendly and green solutions to the energy problem and in textiles. This is a new research area that needs to be explored more thoroughly. This review illustrates the progress and innovations made in the field of nanotechnology with the integration of biomimicry.

Electron Tomography and Machine Learning for Understanding the Highly Ordered Structure of Leafhopper Brochosomes

Insects known as leafhoppers (Hemiptera: Cicadellidae) produce hierarchically structured nanoparticles known as brochosomes that are exuded and applied to the insect cuticle, thereby providing camouflage and anti-wetting properties to aid insect survival. Although the physical properties of brochosomes are thought to depend on the leafhopper species, the structure-function relationships governing brochosome behavior are not fully understood. Brochosomes have complex hierarchical structures and morphological heterogeneity across species, due to which a multimodal characterization approach is required to effectively elucidate their nanoscale structure and properties. In this work, we study the structural and mechanical properties of brochosomes using a combination of atomic force microscopy (AFM), electron microscopy (EM), electron tomography, and machine learning (ML)-based quantification of large and complex scanning electron microscopy (SEM) image data sets. This suite of techniques allows for the characterization of internal and external brochosome structures, and ML-based image analysis methods of large data sets reveal correlations in the structure across several leafhopper species. Our results show that brochosomes are relatively rigid hollow spheres with characteristic dimensions and morphologies that depend on leafhopper species. Nanomechanical mapping AFM is used to determine a characteristic compression modulus for brochosomes on the order of 1-3 GPa, which is consistent with crystalline proteins. Overall, this work provides an improved understanding of the structural and mechanical properties of leafhopper brochosomes using a new set of ML-based image classification tools that can be broadly applied to nanostructured biological materials.

Bioinspired Micro/Nanostructured Polyethylene/Poly(Ethylene Oxide)/Graphene Films with Robust Superhydrophobicity and Excellent Antireflectivity for Solar-Thermal Power Generation, Thermal Management, and Afterheat Utilization

The rational utilization and circulation of multiple energy sources is an effective way to address the crises of energy shortages and environmental pollution. Herein, microextrusion compression molding, an industrialized polymer molding technology that combines melt blending and compression molding, is proposed for the mass production of a bioinspired micro/nanostructured polyethylene/poly(ethylene oxide)/graphene (MN-PPG) film. The MN-PPG film exhibits robust shape stability, high storage energy density, and excellent thermal management capability owing to the cocontinuous network formed by poly(ethylene oxide) and the polyethylene matrix. The MN-PPG film has sufficient photothermal property due to the uniformly dispersed graphene nanosheets and the bioinspired surface micro/nanostructures. Interestingly, the MN-PPG film surface exhibits durable superhydrophobicity, acid/alkali resistance, and active deicing performance. Further, a multifunctional energy harvesting and circulation system was established by integrating the MN-PPG film, an LED chip, and a thermoelectric module. The hybrid system produced an open-circuit voltage of 315.4 mV and power output of 2.5 W m^-2 under 3 sun irradiation. Furthermore, the afterheat generated by the LED chips at night can be converted into electricity through thermoelectric conversion. The proposed method enables the large-scale fabrication of multifunctional phase change composites for energy harvesting in harsh environments.

Photonic nanostructures mimicking floral epidermis for perovskite solar cells

Here, we report photonic nanostructures replicated from the adaxial epidermis of flower petals onto light-polymerized coatings using low-cost nanoimprint lithography at ambient temperature. These multifunctional nanocoatings are applied to confer enhanced light trapping, water repellence, and UV light and environmental moisture protection features in perovskite solar cells. The former feature helps attain a maximum power conversion efficiency of 24.61% (21.01% for the reference cell) without any additional device optimization. Added to these merits, the nanocoatings also enable stable operation under AM 1.5G and UV light continuous illumination or in real-world conditions. Our engineering approach provides a simple way to produce multifunctional nanocoatings optimized by nature's wisdom.

Coscinodiscus diatom inspired bi-layered photonic structures with near-perfect absorptance Part II: hexagonal vs. square lattice-based structures

In this follow up of our previous work on bio-inspired photonics [Opt. Express28, 25007 (2020)10.1364/OE.399505], we present a detailed comparison between the absorption characteristics of hexagonal and square lattice oriented bi-layered photonic structures designed based on the morphology of Coscinodiscus diatom. It is well established that single layers of square lattice-based systems offer better light absorption characteristics than their hexagonal counterparts. However this study shows that superior performances are obtained with hexagonal lattices when bi-layered photonic structures mimicking Coscinodiscus diatom are designed. The finite difference time domain and effective medium approximation based numerical analysis of this work show that bi-layered structures containing hexagonal lattices exhibit tunable, near-perfect (∼95%) absorptance at around 426 nm wavelength up to about 60° angle of incidence, whereas for square lattice the absorptance goes below 85% (65%) for TM (TE) polarization. Moreover, depending on whether light is being incident onto smaller or larger pores of the bi-layered system, peak absorptance for hexagonal lattices is obtained to be nearly 4 times higher than the results obtained for the equivalent square lattices. Such characteristics make the hexagonal lattice-based structures more suitable for bi-facial light absorption related applications.

Nanochitin: Chemistry, Structure, Assembly, and Applications

Chitin, a fascinating biopolymer found in living organisms, fulfills current demands of availability, sustainability, biocompatibility, biodegradability, functionality, and renewability. A feature of chitin is its ability to structure into hierarchical assemblies, spanning the nano- and macroscales, imparting toughness and resistance (chemical, biological, among others) to multicomponent materials as well as adding adaptability, tunability, and versatility. Retaining the inherent structural characteristics of chitin and its colloidal features in dispersed media has been central to its use, considering it as a building block for the construction of emerging materials. Top-down chitin designs have been reported and differentiate from the traditional molecular-level, bottom-up synthesis and assembly for material development. Such topics are the focus of this Review, which also covers the origins and biological characteristics of chitin and their influence on the morphological and physical-chemical properties. We discuss recent achievements in the isolation, deconstruction, and fractionation of chitin nanostructures of varying axial aspects (nanofibrils and nanorods) along with methods for their modification and assembly into functional materials. We highlight the role of nanochitin in its native architecture and as a component of materials subjected to multiscale interactions, leading to highly dynamic and functional structures. We introduce the most recent advances in the applications of nanochitin-derived materials and industrialization efforts, following green manufacturing principles. Finally, we offer a critical perspective about the adoption of nanochitin in the context of advanced, sustainable materials.

Single-Step Fabrication of Longtail Glasswing Butterfly-Inspired Omnidirectional Antireflective Structures

Most bio-inspired antireflective nanostructures are extremely vulnerable and suffer from complicated lithography-based fabrication procedures. To address the issues, we report a scalable and simple non-lithography-based approach to engineer robust antireflective structures, inspired by the longtail glasswing butterfly, in a single step. The resulting two-dimensional randomly arranged 80/130/180 nm silica colloids, partially embedded in a polymeric matrix, generate a gradual refractive index transition at the air/substrate interface to suppress light reflection. Importantly, the randomly arranged subwavelength silica colloids display even better antireflection performance for large incident angles than that of two-dimensional non-close-packed silica colloidal crystals. The biomimetic coating is of considerable technological importance in numerous practical applications.

Ultra-Scratch-Resistant, Hydrophobic and Transparent Organosilicon-Epoxy-Resin Coating with a Double Cross-Link Structure

In this paper, an ultra-scratch-resistant, hydrophobic and transparent coating was fabricated by the sol–gel method using (3-Glycidyloxypropyl) triethoxysilane (GPTES) and curing agents. When the silanol was condensated, the ring-opening reaction of the epoxy groups also took place, which formed a double-cross-linked network (Si–O–Si and R3N). This network structure restricted the molecule chains from being twisted or dislocated, resulting in a great improvement of the abrasion resistance of the coating. A pencil hardness grade up to 8H was obtained. The coating also showed excellent stability after being soaked in pH = 2 and pH = 12 solutions, seawater and acetone, respectively. In addition, a water contact angle of 121° was obtained by post-treatment with hexamethyldisilazane (HMDS). The average transmittance of the coating reached to 90% in the wavelength range of 400~800 nm, nearly identical to the glass substrate. With multiple desirable properties and a simple fabrication process, this low-cost coating shows great potential in many practical applications.

Broadband Enhancement of Anti-reflectivity for a High Angle of Incidence Using Nanocone Geometry

The broadband antireflective (AR) effect for wide incident angles has a significant effect on the photoconversion efficiency of photovoltaics and visibility of large-format display panels. The fabrication of surface nanostructures has continued to attract research interest as an effective way to provide such optical performance. However, the effects of different nanostructure geometries are not fully understood, especially for wide-angle AR effects. In this work, we conduct a systematic analysis of the effect of periodic nanostructures such as nanocones (NCs) and inverted nanocones (INCs) on anti-reflectivity at high angles of incidence (AOIs) in terms of light scattering, guided-mode resonance (GMR), and internal reflections. NCs provide good coupling of light scattering and GMR because of their protruding geometry; hence, reduced reflectance can be obtained in the short wavelength region. Further, NCs exhibit relatively weaker GMR intensities and internal reflections, resulting in low reflectance in the long wavelength region. Therefore, NCs offer a superior broadband AR effect for high AOIs compared with INCs. Based on this analysis, we demonstrate an extremely low average reflectance (5.4%) compared to that of the bare substrate (34.7%) for the entire visible range at an AOI of 75° by fabricating NCs on both sides of the substrate.

Altering the Surface Properties of Metal Alloys Utilizing Facile and Ecological Methods

The development of a superhydrophobic and, even, water-repellent metal alloy surface is reported utilizing a simple, fast, and economical way that requires minimum demands on the necessary equipment and/or methods used. The procedure involves an initial irradiation of the metallic specimen using a femtosecond laser, which results in a randomly roughened surface, that is subsequently followed by placing the item in an environment under moderate vacuum (pressure 10^-2 mbar) and/or under low-temperature heating (at temperatures below 120 °C). The effects of both temperature and low pressure on the surface properties (water contact angle and contact angle hysteresis) are investigated and surfaces with similar superhydrophobicity are obtained in both cases; however, a significant difference concerning their water-repellent ability is obtained. The surfaces that remained under vacuum were water-repellent, exhibiting very high values of contact angle with a very low contact angle hysteresis, whereas the surfaces, which underwent thermal processing, exhibited superhydrophobicity with high water adhesion, where water droplets did not roll off even after a significant inclination of the surface. The kinetics of the development of superhydrophobic behavior was investigated as well. The findings were understood when the surface roughness characteristics were considered together with the chemical composition of the surface.

Cost-Effective Fabrication of Micro-Nanostructured Superhydrophobic Polyethylene/Graphene Foam with Self-Floating, Optical Trapping, Acid-/Alkali Resistance for Efficient Photothermal Deicing and Interfacial Evaporation

Solar evaporation is one of the most attractive and sustainable approaches to address worldwide freshwater scarcity. Unfortunately, it is still a crucial challenge that needs to be confronted when the solar evaporator faces harsh application environments. Herein, a promising polymer molding method that combines melt blending and compression molding, namely micro extrusion compression molding, is proposed for the cost-effective fabrication of lightweight polyethylene/graphene nanosheets (PE/GNs) foam with interconnected vapor escape channels and surface micro-nanostructures. A contact angle of 155 ± 2°, a rolling angle of 5 ± 1° and reflectance of ≈1.6% in the wavelength range of 300-2500 nm appears on the micro-nanostructured PE/GNs foam surface. More interestingly, the micro-nanostructured PE/GNs foam surface can maintain a robust superhydrophobic state under dynamic impacting, high temperature and acid-/alkali solutions. These results mean that the micro-nanostructured PE/GNs foam surface possesses self-cleaning, anti-icing and photothermal deicing properties at the same time. Importantly, the foam exhibits an evaporation rate of 1.83 kg m^-2 h^-1 under 1 Sun illumination and excellent salt rejecting performance when it is used as a self-floating solar evaporator. The proposed method provides an ideal and industrialized approach for the mass production of solar evaporators suitable for practical application environments.

Block Copolymer Nanopatterning for Nonsemiconductor Device Applications

Block copolymer (BCP) nanopatterning has emerged as a versatile nanoscale fabrication tool for semiconductor devices and other applications, because of its ability to organize well-defined, periodic nanostructures with a critical dimension of 5-100 nm. While the most promising application field of BCP nanopatterning has been semiconductor devices, the versatility of BCPs has also led to enormous interest from a broad spectrum of other application areas. In particular, the intrinsically low cost and straightforward processing of BCP nanopatterning have been widely recognized for their large-area parallel formation of dense nanoscale features, which clearly contrasts that of sophisticated processing steps of the typical photolithographic process, including EUV lithography. In this Review, we highlight the recent progress in the field of BCP nanopatterning for various nonsemiconductor applications. Notable examples relying on BCP nanopatterning, including nanocatalysts, sensors, optics, energy devices, membranes, surface modifications and other emerging applications, are summarized. We further discuss the current limitations of BCP nanopatterning and suggest future research directions to open up new potential application fields.

Analysis of Surface Patterns and Electric Field Simulation of Antireflective Green Lacewing Wings

The structural coloration and decoloration are problems of scientific interest for a long time. Hence, the fundamental investigations on structures and the optical properties of insect wings have been performed. As a part of such studies, we elucidate the optical properties of green lacewing wings via observation and simulation. First, we elucidate the surface pattern of green lacewing wings using a two-dimensional fast Fourier transform. A cross-shaped pattern of a Fourier spectrum is obtained, and the concise wing model with the surface protrusions arranged in a square grid on a base substrate is constructed in reference to the obtained Fourier spectrum. Next, we perform a finite-difference time-domain (FDTD) simulation to elucidate a light path through wings with and without surface protrusions. The FDTD simulation results indicate that the surface protrusions of a wing increase and decrease the intensity of the transmitted and reflected light, respectively, which is an antireflection behavior. This phenomenon was also observed in the case of 45° incident light. The intensity of transmitted light coupled to wings is induced by surface protrusions with a stepwise refractive index between air and a substrate, which induces antireflection. In particular, transmitted light is increased by the surface protrusions of wings in the range of 500-800 nm wavelength. The intensities of transmitted and reflected light are affected by the direction of incident electric field (polarization) in the case of wings with protrusions arranged in the same direction (parallel). Hence, the surface protrusions are arranged in a square grid to reduce the influence of the polarization direction.

Mimicry can drive convergence in structural and light transmission features of transparent wings in Lepidoptera

Müllerian mimicry is a positive interspecific interaction, whereby co-occurring defended prey species share a common aposematic signal. In Lepidoptera, aposematic species typically harbour conspicuous opaque wing colour patterns with convergent optical properties among co-mimetic species. Surprisingly, some aposematic mimetic species have partially transparent wings, raising the questions of whether optical properties of transparent patches are also convergent, and of how transparency is achieved. Here, we conducted a comparative study of wing optics, micro and nanostructures in neotropical mimetic clearwing Lepidoptera, using spectrophotometry and microscopy imaging. We show that transparency, as perceived by predators, is convergent among co-mimics in some mimicry rings. Underlying micro- and nanostructures are also sometimes convergent despite a large structural diversity. We reveal that while transparency is primarily produced by microstructure modifications, nanostructures largely influence light transmission, potentially enabling additional fine-tuning in transmission properties. This study shows that transparency might not only enable camouflage but can also be part of aposematic signals.

Bioinspiration as a method of problem-based STEM education: A case study with a class structured around the COVID-19 crisis

Bioinspiration is a promising lens for biology instruction as it allows the instructor to focus on current issues, such as the COVID-19 pandemic. From social distancing to oxygen stress, organisms have been tackling pandemic-related problems for millions of years. What can we learn from such diverse adaptations in our own applications? This review uses a seminar course on the COVID-19 crisis to illustrate bioinspiration as an approach to teaching biology content. At the start of the class, students mind-mapped the entire problem; this range of subproblems was used to structure the biology content throughout the entire class. Students came to individual classes with a brainstormed list of biological systems that could serve as inspiration for a particular problem (e.g., absorptive leaves in response to the problem of toilet paper shortages). After exploration of relevant biology content, discussion returned to the focal problem. Students dug deeper into the literature in a group project on mask design and biological systems relevant to filtration and transparency. This class structure was an engaging way for students to learn principles from ecology, evolution, behavior, and physiology. Challenges with this course design revolved around the interdisciplinary and creative nature of the structure; for instance, the knowledge of the participants was often stretched by engineering details. While the present class was focused on the COVID-19 crisis, a course structured through a bioinspired approach can be applied to other focal problems, or subject areas, giving instructors a powerful method to deliver interdisciplinary content in an integrated and inquiry-driven way.

Programmed Scale Detachment in the Wing of the Pellucid Hawk Moth, Cephonodes hylas: Novel Scale Morphology, Scale Detachment Mechanism, and Wing Transparency

No scales of most lepidopterans (butterflies and moths) detach from the wings through fluttering. However, in the pellucid hawk moth, Cephonodes hylas, numerous scales detach from a large region of the wing at initial take-off after eclosion; consequently, a large transparent region without scales appears in the wing. Even after this programmed detachment of scales (d-scales), small regions along the wing margin and vein still have scales attached (a-scales). To investigate the scale detachment mechanism, we analyzed the scale detachment process using video photography and examined the morphology of both d- and a-scales using optical and scanning electron microscopy. This study showed that d-scale detachment only occurs through fluttering and that d-scales are obviously morphologically different from a-scales. Although a-scales are morphologically common lepidopteran scales, d-scales have four distinctive features. First, d-scales are much larger than a-scales. Second, the d-scale pedicel, which is the slender base of the scale, is tapered; that of the a-scale is columnar. Third, the socket on the wing surface into which the pedicel is inserted is much smaller for d-scales than a-scales. Fourth, the d-scale socket density is much lower than the a-scale socket density. This novel scale morphology likely helps to facilitate scale detachment through fluttering and, furthermore, increases wing transparency.

Micropatterns Fabricated by Photodimerization-Induced Diffusion

Pattern technology plays an important role in the generation of microstructures with different functionalities and morphologies. In this report, a straightforward and versatile strategy is presented for spatially regulating the growth of a microstructure on a surface by the photodimerization of maleimide (MI). Upon exposure of ultraviolet (UV) light, photodimerization of MI in a film comprising furan-grafted polymer and bismaleimide (BMI) produces a chemical gradient, which can drive the diffusion of BMI from the unexposed to the exposed region and from the bottom to the surface, resulting in the growth of micropatterns. Sequential crosslinking induced by the Diels-Alder reaction between MI and furan maintains the stability of pattern shape. Theoretical modeling with reaction-diffusion equations reveal that as photodimerization moves the system far from thermodynamic equilibrium, the formation of a chemical potential gradient requires the redistribution of matter, resulting in the formation of topographies. Directional molecular motion induced by UV light can generate complex morphology, and produce materials with unique optical functions, such as charming-ordered gratings. This straightforward method of fabricating micropatterns by photodimerization-induced diffusion is successfully applied to patterned curved surfaces, microfluidic channels and encapsulation of integrated light emitting diode chips.

Bioinspired Multifunctional Glass Surfaces through Regenerative Secondary Mask Lithography

Nature-inspired nanopatterning offers exciting multifunctionality spanning antireflectance and the ability to repel water/fog, oils, and bacteria; strongly dependent upon nanofeature size and morphology. However, such patterning in glass is notoriously difficult, paradoxically, due to the same outstanding chemical and thermal stability that make glass so attractive. Here, regenerative secondary mask lithography is introduced and exploited to enable customized glass nanopillars through dynamic nanoscale tunability of the side-wall profile and aspect ratio (>7). The method is simple and versatile, comprising just two steps. First, sub-wavelength scalable soft etch masks (55-350 nm) are generated through an example of block copolymer micelles or nanoimprinted photoresist. Second, their inherent durability problem is addressed by an innovative cyclic etching, when the original mask becomes embedded within a protective secondary organic mask, which is tuned and regenerated, permitting dynamic nanofeature profiling with etching selectivity >1:32. It is envisioned that such structuring in glass will facilitate fundamental studies and be useful for numerous practical applications-from displays to architectural windows. To showcase the potential, glass features are tailored to achieve excellent broadband omnidirectional antireflectivity, self-cleaning, and unique antibacterial activity toward Staphylococcus aureus.

Understanding the structural diversity of chitins as a versatile biomaterial

Chitin is one of the most abundant biopolymers, and it has adopted many different structural conformations using a combination of different natural processes like biopolymerization, crystallization and non-equilibrium self-assembly. This leads to a number of striking physical effects like complex light scattering and polarization as well as unique mechanical properties. In doing so, chitin uses a fine balance between the highly ordered chain conformations in the nanofibrils and random disordered structures. In this opinion piece, we discuss the structural hierarchy of chitin, its crystalline states and the natural biosynthesis processes to create such specific structures and diversity. Among the examples we explored, the unified question arises from the generation of completely different bioarchitectures like the Christmas tree-like nanostructures, gyroids or helicoidal geometries using similar dynamic non-equilibrium growth processes. Understanding the in vivo development of such structures from gene expressions, enzymatic activities as well as the chemical matrix employed in different stages of the biosynthesis will allow us to shift the material design paradigms. Certainly, the complexity of the biology requires a collaborative and multi-disciplinary research effort. For the future's advanced technologies, using chitin will ultimately drive many innovations and alternatives using biomimicry in materials science. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Single-step-fabricated disordered metasurfaces for enhanced light extraction from LEDs

While total internal reflection (TIR) lays the foundation for many important applications, foremost fibre optics that revolutionised information technologies, it is undesirable in some other applications such as light-emitting diodes (LEDs), which are a backbone for energy-efficient light sources. In the case of LEDs, TIR prevents photons from escaping the constituent high-index materials. Advances in material science have led to good efficiencies in generating photons from electron-hole pairs, making light extraction the bottleneck of the overall efficiency of LEDs. In recent years, the extraction efficiency has been improved, using nanostructures at the semiconductor/air interface that outcouple trapped photons to the outside continuum. However, the design of geometrical features for light extraction with sizes comparable to or smaller than the optical wavelength always requires sophisticated and time-consuming fabrication, which causes a gap between lab demonstration and industrial-level applications. Inspired by lightning bugs, we propose and realise a disordered metasurface for light extraction throughout the visible spectrum, achieved with single-step fabrication. By applying such a cost-effective light extraction layer, we improve the external quantum efficiency by a factor of 1.65 for commercialised GaN LEDs, demonstrating a substantial potential for global energy-saving and sustainability.

Bioinspired Microstructured Polymer Surfaces with Antireflective Properties

Over the years, different approaches to obtaining antireflective surfaces have been explored, such as using index-matching, interference, or micro- and nanostructures. Structural super black colors are ubiquitous in nature, and biomimicry thus constitutes an interesting way to develop antireflective surfaces. Moth-eye nanostructures, for example, are well known and have been successfully replicated using micro- and nanofabrication. However, other animal species, such as birds of paradise and peacock spiders, have evolved to display larger structures with antireflective features. In peacock spiders, the antireflective properties of their super black patches arise from relatively simple microstructures with lens-like shapes organized in tightly packed hexagonal arrays, which makes them a good candidate for cheap mass replication techniques. In this paper, we present the fabrication and characterization of antireflective microarrays inspired by the peacock spider’s super black structures encountered in nature. Firstly, different microarrays 3D models are generated from a surface equation. Secondly, the arrays are fabricated in a polyacrylate resin by super-resolution 3D printing using two-photon polymerization. Thirdly, the resulting structures are inspected using a scanning electron microscope. Finally, the reflectance and transmittance of the printed structures are characterized at normal incidence with a dedicated optical setup. The bioinspired microlens arrays display excellent antireflective properties, with a measured reflectance as low as 0.042 ± 0.004% for normal incidence, a wavelength of 550 nm, and a collection angle of 14.5°. These values were obtained using a tightly-packed array of slightly pyramidal lenses with a radius of 5 µm and a height of 10 µm.

Tunable fabrication of biomimetic polypropylene nanopillars with robust superhydrophobicity and antireflectivity

The fine nanopillars on the natural cicada wing, which exhibits outstanding superhydrophobicity and anti-reflectivity, are carefully observed and analyzed. Here, a promising strategy by combining anodic aluminum oxide template and hot embossing is proposed for rapidly and efficiently mimicking the orderly and densely arranged nanopillars on the cicada wing surface to polypropylene (PP) surfaces. By adjusting the compression pressure, the nanostructures on the PP replica surface gradually evolve from nanoprotrusion-like features to nanopillar-like features so that a gradient wetting behavior from hydrophilicity to hydrophobicity and further to superhydrophobicity appears on the PP replica surfaces. Specifically, the biomimetic PP replica surface exhibits a contact angle of 159 ± 3° and a rolling angle of 8 ± 3° at a compression pressure of 15 MPa. Moreover, the biomimetic PP replica surface can stabilize its superhydrophobic state under a 1.96 kPa external pressure during the dynamic droplet impact. Besides robust dynamic superhydrophobicity, the biomimetic PP replica surface also demonstrated excellent anti-reflectivity because of the gradually changed effective refractive index. Therefore, the biomimetic PP replica inherits both the superhydrophobicity and anti-reflectivity of the natural cicada wing, which makes the products can effectively reduce the external damage when applied to agricultural films, dustproof films, and packaging materials.

Light Management with Natural Materials: From Whiteness to Transparency

The possibility of structuring material at the nanoscale is essential to control light-matter interactions and therefore fabricate next-generation paints and coatings. In this context, nature can serve not only as a source of inspiration for the design of such novel optical structures, but also as a primary source of materials. Here, some of the strategies used in nature to optimize light-matter interaction are reviewed and some of the recent progress in the production of optical materials made solely of plant-derived building blocks is highlighted. In nature, nano- to micrometer-sized structured materials made from biopolymers are at the origin of most of the light-transport effects. How natural photonic systems manage light scattering and what can be learned from plants and animals to produce photonic materials from biopolymers are discussed. Tuning the light-scattering properties via structural variations allows a wide range of appearances to be obtained, from whiteness to transparency, using the same renewable and biodegradable building blocks. Here, various transparent and white cellulose-based materials produced so far are highlighted.