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To examine the permeability alterations in coal seams induced by liquid CO2 injection, we employed COMSOL simulations to recreate the flow, force, and temperature fields, along with the corresponding physical parameters of the geological formation. We established a mathematical model to track the evolution of the coal body's permeability, enabling us to capture the phase distribution of CO2, the dynamics of fluid transportation, and the coal body's mechanical responses during the liquid CO2 injection process. Our findings revealed that the coal seam undergoes significant changes due to low-temperature freezing and shrinkage, gas-liquid phase transitions, and expansion impacts from solid-liquid phase changes. These factors collectively modify the pore structure, subsequently influencing the coal seam's permeability. Notably, the coal body's permeability, influenced by the pore structure and the Klinkenberg effect, increases logarithmically with rising injection pressure and falling temperatures. The structural changes in the coal body are markedly impacted by seepage and phase change pressures, with the permeability enhancement from secondary phase changes being 2.28 times greater than that from primary phase changes, and five times greater than in scenarios without phase change. [ABSTRACT FROM AUTHOR]

Metamaterials (MTMs) are synthetic structures known for their ability to control electromagnetic wave propagation, offering innovative solutions for reducing the radar cross-section (RCS) of objects. This paper proposes an agile bilayer MTM to reduce the RCS. Each layer consists of identical agile MTM unit cells embedded with switches to achieve agility. Depending on the switch state, we can obtain two types of unit cells: connected (ON state) and disconnected (OFF state), which exhibit two different behaviors. The switches are controlled using an external command system. By independently adjusting the switching states (ON/OFF) of the two layers, six agile reflection frequency stop bands are generated, corresponding to the four possible configurations of ON–ON, ON–OFF, OFF–ON, and OFF–OFF, and their reflection and transmission ranges are controlled. This design has the capability to control six distinct frequency bands with a − 1- dBm RCS reduction, comprising two bands within the Ku-band (12–18 GHz) and four within the Ka-band (25–40 GHz). [ABSTRACT FROM AUTHOR]

Dust and other environmentally suspended particles deposited on the solar panels reduce the sunlight to photovoltaic cells, reducing the total energy outcome. A dust-reflecting coating keeps a cleaner surface, thus enhancing light absorption and improving the overall energy outcome. This study synthesized the sol–gel of SiO2, MgF2, and TiO2 and made the coating on the glass substrate by SiO2+MgF2, SiO2+TiO2, and MgF2+SiO2+TiO2 using sol–gel dip coating and spin coating method. Coatings that occurred on the glass sample surfaces were identified by using FTIR analysis. Five of the above six coatings made using different mixtures have increased transmittance than pure glass, while one SiO2+MgF2 spin coating reduced the transmittance. The minimum water contact angle of 37.69∘ was found on the SiO2+TiO2 spin-coated surface, and the maximum contact angle was 72.10∘ on the MgF2 dip-coated surface. This shows that the self-cleaning properties in SiO2+TiO2 spin-coated surfaces are maximum and minimum in MgF2 dip-coated surfaces. The angle found by the test shows that spin coating is a better technique than dip coating for hydrophilic surface coating. This was due to the more homogenous coating on the spin-coated sample surfaces. There was less accumulation of dust found on the coated surfaces compared to non-coated glass sample surfaces. [ABSTRACT FROM AUTHOR]

Artificial antireflective nanostructured surfaces, inspired by moth eyes, effectively reduce optical losses at interfaces, offering significant advantages in enhancing optical performance in various optoelectronic applications, including solar cells, light-emitting diodes, and cameras. However, their limited flexibility and low surface hardness constrain their broader use. In this study, we introduce a universal antireflective film by integrating nanostructures on both sides of a thin polycarbonate film. One side was thinly coated with Al2O3 for its high hardness, enhancing surface durability while maintaining flexibility. The opposite side was coated with SiO2 to optimize antireflective properties, making the film suitable for diverse environments (i.e., air, water, and adhesives). This dual-coating strategy resulted in a mechanically robust and flexible antireflective film with superior optical properties in various conditions. We demonstrated the universal capabilities of our antireflective film via optical simulations and experiments with the fabricated film in different environments. [ABSTRACT FROM AUTHOR]

This study presents an approach for fabricating super hydrophilic self-cleaning anti-fog micro-nano structures on silicon-coated glass utilizing a laser marking machine. The surface features a periodic microstructure interspersed with irregular nanoparticles, which contribute to its durable superhydrophilicity, maintaining a 0° contact angle for up to one year—the longest duration recorded to date. Moreover, it sustained its anti-fogging and self-cleaning abilities for 467 days, establishing the lengthiest duration for maintaining a 0° contact angle and retaining anti-fogging performance without visible deterioration. The sample also retained excellent anti-fogging and self-cleaning properties even after 43 days of outdoor exposure. Such remarkable performance was attributed not only to surface chemistry and roughness but also to the presence of dense, uniform, and minimally varying microstructures. The unique structure also enhanced the solar spectrum (AM 1.5) weighted average transmission by 3.84 % over control glass in the wavelength range of 400–1100 nm. It holds promising potential for use in automotive rearview mirrors, windows, and solar cells. [ABSTRACT FROM AUTHOR]

Photonic crystal (PhC) structures generated through periodic surface nanostructuring are pivotal for controlling light-matter interactions. These structures are essential for reducing high surface reflectivity in semiconductor optical devices, enhancing light absorption in photovoltaic cells, and improving light extraction in LEDs. Although various methods for PhC fabrication are well-documented, the use of single-pulse laser interference lithography (LIL) with commercial photoresists remains unexplored. Single nanosecond pulses for photoresist exposure offer significant advantages, including high throughput for large-scale patterning and reduced dependence on stable optical platforms. In this study, we used single-pulse LIL to fabricate antireflective PhC structures on GaAs substrates using a commercial photoresist. This process involved exposing the photoresist to single 7 nanosecond pulses at a wavelength of 355 nm, with relatively low energy levels. High-quality nanohole arrays were subsequently created via inductively coupled plasma (ICP) etching. Reflectivity analysis revealed that these structures reduced the average reflectance of GaAs to below 5% across the visible wavelength range of 450-700 nm. This work is crucial for optimizing current photonic technologies and advancing future devices with enhanced light management capabilities. [ABSTRACT FROM AUTHOR]

Abstract To examine the permeability alterations in coal seams induced by liquid CO2 injection, we employed COMSOL simulations to recreate the flow, force, and temperature fields, along with the corresponding physical parameters of the geological formation. We established a mathematical model to track the evolution of the coal body’s permeability, enabling us to capture the phase distribution of CO2, the dynamics of fluid transportation, and the coal body’s mechanical responses during the liquid CO2 injection process. Our findings revealed that the coal seam undergoes significant changes due to low-temperature freezing and shrinkage, gas-liquid phase transitions, and expansion impacts from solid-liquid phase changes. These factors collectively modify the pore structure, subsequently influencing the coal seam’s permeability. Notably, the coal body’s permeability, influenced by the pore structure and the Klinkenberg effect, increases logarithmically with rising injection pressure and falling temperatures. The structural changes in the coal body are markedly impacted by seepage and phase change pressures, with the permeability enhancement from secondary phase changes being 2.28 times greater than that from primary phase changes, and five times greater than in scenarios without phase change.

Antireflective (AR) coatings are widely used in the various applications of optical devices, flat panel displays, automotive windshields, and solar cell cover glasses. Usually, coatings with high transmittance and self-cleaning capability enhance solar cell efficiency. In this work, SnO2 thin film with TEOS, ITES, and MTES by spin coating was deposited on glass substrates and analyzed. The prepared films was characterized by Fourier Transform Infrared Spectroscopy, UV-visible spectroscopy, FESEM, and Water contact angle measurements (WCA). The prepared SnO2/TEOS/ITES and SnO2/TEOS/MTES films showed good optical transmittance of 92.46% and 92.56% with WCA of 9° and 92° respectively. The transmittance of the antireflective films was increased by 2% than the bare glass substrate. Also, the antifogging behavior of SnO2/TEOS/ITES film was examined. Furthermore, the self-cleaning ability of the coatings helps to maintain the efficiency of the solar cell even during dust exposure. Thus, the antireflection coating can be applied to enhance the efficiency of the photovoltaic system. [ABSTRACT FROM AUTHOR]

Antireflection surfaces are widely used in optical devices (such as vehicle display, solar cells, and architectural glass) to reduce the reflection and increase transmittance. Plasma etching shows great potential in making subwavelength antireflection structures for its advantage of scalable, low‐cost, and applicable in flexible substrates. Here, we demonstrate an antireflection nanostructure by O2 plasma etching on poly (ethylene terephthalate) (PET) substrate without additional corrosive gas species or antireflective coatings. Nanopores on the surface were formed due to the different etching rates of the organic region and silica region of the surface. The solar weighted average transmittance was improved from 91.6% to 94.8% for single‐side treated PET with silica antiblocking layer. The transmission increment was attributed to the gradient refractive index of the nanostructured surface due to the elimination of step discontinuity in refractive index. The result shows a highly efficient, eco‐friendly, solvent‐free, economical, and sputtering target‐free method for reducing the reflection and increasing the transmittance of the substrates. [ABSTRACT FROM AUTHOR]

The modulation of the surface of silicon stimulates its applications in optics (antireflection surface, solar cells, and photoelectric devices). In this work, an appropriate ratio of the O2 to SF6 plasma through reactive ion etching generated a double-layer Silicon nanograss (upper layerflocculent SiOxFy passivation; lower layerpointy silicon spike) on the surface of the silicon wafer. The height and density of Silicon nanograss can be controlled through process parameters (pressure, O2/SF6 ratio, and RF power), mask spacing, and a variety of assistant substrates. The underlying formation mechanisms of Silicon nanograss disclosed that the sputtering of Al substrate acts as a micromask, i.e., primarily responsible for the formation of Silicon nanograss. Considering an in-depth study, a simple, low-cost, and CMOS-compatible method for wafer-level preparation of Silicon nanograss is provided. Specifically, the Silicon nanograss exhibited excellent antireflection and enhanced absorption properties. This work contributes to micro-nano surface science accompanied by optical applications. [ABSTRACT FROM AUTHOR]

The application of antireflective (AR) films is a promising optical management strategy to improve the light utilization of perovskite solar cells (PSCs). Plumeria petals of different colors are employed as the master mold for the first time to prepare biomimetic AR films. Hierarchical morphologies replicated from the petals have a primary characteristic size in tens of micrometer scale. A strong scattering effect happens when the incident light hits the AR films, leading to a remarkably reduced reflectance with broadband enhancement of the transmission over the entire visible range. With the incorporation of the biomimetic AR film, the highest power conversion efficiency for PSCs reaches 23.56% with a large short‐circuit density (Jsc) of 26.54 mA cm−2, corresponding to an average enhancement of 6.17%. The enhancement effect is verified under 1.5G AM radiation with different tilted angles and warm white LED light source with different light intensities. Furthermore, optical simulations are performed to illustrate the structure–effective relationship. This work offers an interesting experience by learning from nature and provides valuable references for further refining the design of the AR films in micrometer scale. [ABSTRACT FROM AUTHOR]

In nature, leafhoppers cover their body surfaces with brochosomes as a protective coating. These leafhopper-produced brochosomes are hollow, buckyball-shaped, nanoscopic spheroids with through-holes distributed across their surfaces, representing a class of deployable optical materials that are rare in nature. Despite their discovery in the 1950s, it remains unknown why the sizes of brochosomes and their through-holes consistently fall within the range of hundreds of nanometers across different leafhopper species. Here, we demonstrate that the hierarchical geometries of brochosomes are engineered within a narrow size range with through-hole architecture to significantly reduce light reflection. By utilizing two-photon polymerization three-dimensional printing to fabricate high-fidelity synthetic brochosomes, we investigated the optical form-to-function relationship of brochosomes. Our results show that the diameters of brochosomes are engineered within a specific size range to maximize broadband light scattering, while the secondary through-holes are designed to function as short-wavelength, low-pass filters, further reducing light reflection. These synergistic effects enable brochosomes to achieve a substantial reduction in specular reflection, by up to approximately 80 to 94%, across a broadband wavelength range. Importantly, brochosomes represent a biological example demonstrating short-wavelength, low-pass filter functionality. Furthermore, our results indicate that the geometries of natural brochosomes may have evolved to effectively reduce reflection from ultraviolet to visible light, thereby enabling leafhoppers to evade predators whose vision spectrum encompasses both ultraviolet and visible light. Our findings offer key design insights into a class of deployable bioinspired optical materials with potential applications in omnidirectional antireflection coatings, optical encryption, and multispectral camouflage. [ABSTRACT FROM AUTHOR]

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All-angle wideband electromagnetic (EM) transparency for dual polarizations is desired for many practical applications. Conventionally, surface-mount anti-reflection materials or films are usually used to reduce the reflection and thus enhance transparency. In this paper, we propose to achieve wideband EM transparency under extreme angles for both TE- and TM-polarizations using embedded anti-reflection metasurface. The metasurface is composed of a pair of long and short metallic strips, which can introduce both plasma and lattice modes into the original half-wave wall. The plasma mode can create an angle-stable transmission peak at a lower frequency while the lattice mode renders a transmission peak under extreme angles at a higher frequency due to scattering cancellation between short strips and the substrate. By synergizing the plasma, half-wave, and lattice modes consecutively, wide-band transparency can be achieved under extreme angles for TE polarization. Due to the anisotropy of the metasurface, wideband transparency under TM-polarization is maintained. This finally enables us to obtain wideband EM transparency for dual polarizations under extreme angles. More importantly, the metasurface can also be customized to operate best under any given incident angle. Prototypes were designed, fabricated, and measured. Both the simulation and experiment results verify our method. This work provides an efficient route to wideband EM transparency under extreme angles and may find wide applications in communication, radar, and others. [ABSTRACT FROM AUTHOR]

Terahertz electromagnetic waves are widely used in various fields, but their practical application often suffers from significant interfacial losses. In this paper, we present a terahertz antireflection film based on an all-dielectric metasurface consisting of a zirconia microsphere array assembled using a template-assisted method. Simulations and experiments show that the film has a broadband, outstanding transmission-enhancing effect. Because the antireflection film has the advantages of ultralow cost, high compatibility, flexibility, and easy industrialization, it may have potential applications in various fields.

Artificial antireflective nanostructured surfaces, inspired by moth eyes, effectively reduce optical losses at interfaces, offering significant advantages in enhancing optical performance in various optoelectronic applications, including solar cells, light-emitting diodes, and cameras. However, their limited flexibility and low surface hardness constrain their broader use. In this study, we introduce a universal antireflective film by integrating nanostructures on both sides of a thin polycarbonate film. One side was thinly coated with Al2O3 for its high hardness, enhancing surface durability while maintaining flexibility. The opposite side was coated with SiO2 to optimize antireflective properties, making the film suitable for diverse environments (i.e., air, water, and adhesives). This dual-coating strategy resulted in a mechanically robust and flexible antireflective film with superior optical properties in various conditions. We demonstrated the universal capabilities of our antireflective film via optical simulations and experiments with the fabricated film in different environments.

Based on nanoimprint lithography and dry etching of stacked three-layer masks, we successfully prepared large-area periodic Al2O3 nanohole arrays on MgO (100) substrates. At 1550 nm, the nanohole arrays increased the interface transmittance of MgO (100) from 93.2% to above 98.8%. Postannealing at 700 °C, the interface transmittance decreased only to 97.8%. Compared with typical multilayer antireflection coating, it is simpler and easier to prepare. Nanoholes are arranged in a square lattice. The radius is 250 nm, the period is 350 nm, and the height is 200 nm. During the etching process, we eliminated the serious impact of shrinking the round hole into a gear hole caused by microloading. The processed nanohole is an inverted truncated cone with a verticality of 83.7°. In addition, the potential of Al2O3 nanohole arrays to interfere with interface reflections was effectively verified using spectrophotometry and the self-built low-reflectivity external cavity Fabry–Pérot interference platform. This research provides us with important solutions for developing Fabry–Pérot optical fiber devices with a higher demodulation accuracy. [ABSTRACT FROM AUTHOR]

Brochosomes, which are nanoscopic buckyball-shaped granules produced by leafhoppers, are one of the most intricate structures discovered in nature. Various functions of brochosomes have been proposed but only a few have been experimentally validated due to the challenge of fabricating their synthetic counterparts. Advancements in micro- and nanofabrication have recently led to the emergence of synthetic brochosomes, opening up new possibilities for innovative applications. This review explores the early discovery of natural brochosomes and their geometrical features, followed by the recent progress in fabricating synthetic brochosomes and their applications. Perspectives on future applications and challenges in the scalable manufacturing of synthetic brochosomes are discussed. [ABSTRACT FROM AUTHOR]

Developing high-performance, stable, and cost-effective photoelectrodes for hydrogen production has been a long-standing challenge. A promising approach has been to utilize photoelectrodes in a nanostructured architecture to improve optical absorption and charge collection. In this work we demonstrate the fabrication of highly ordered branched p-type Cadmium Telluride (CdTe) nanotube arrays and test their efficacy for hydrogen production. The branched CdTe nanotube arrays were fabricated using a combination of top down and bottom up approaches. The diameter and branch shape of vertically aligned CdTe nanotubes are controlled to increase the optical absorption due to the increased optical path length and to improve the charge carrier transfer due to the reduced transfer distance in the nanostructures for charge separation. The CdTe nanotubes with long and fine needle-like shaped branches show enhanced photoelectrochemical properties compared to those of broad-branched CdTe nanotubes. The optical absorption and charge transfer characteristics of a photoelectrochemical photoelectrode can be improved using narrow band-gap materials in well-designed nanostructures. [Display omitted] • Well-designed synthesis of branched CdTe nanotube array. • Improved photoelectrochemical properties in the branched CdTe nanotube photocathode. • Enhanced optical absorption/charge transfer in the needle-branched CdTe nanotube with the near-ideal antireflective surface. [ABSTRACT FROM AUTHOR]

In this study, we aim to optimize the process for developing antireflective and refractive-index-matching films on flexible substrates. The development of these films is crucial in light of the increasing demand in the market for flexible electronics, which are poised to be the next emerging technology and application after semiconductors and flat panel displays. Our research involves the production of these films by physical vapor deposition and sputtering techniques, which can also be applied to various optical thin films. The effectiveness of our coating process has been verified and refined on the basis of feedback. The results of this study are applicable to related industrial technologies and will contribute to improving industry competitiveness. [ABSTRACT FROM AUTHOR]

A transmission‐type all‐medium element is proposed to construct a coded metasurface. Due to the single‐layer metasurface unit structure, large reflection loss will be caused when the base plane is incident. In order to improve the efficiency of the coded metasurface device and reduce the reflection loss, the authors propose a double‐sided metasurface digital unit structure and introduces a wideband anti‐reflection pyramid microstructure to achieve significantly improved transmission characteristics. The optimized unit structure is coded and the coded metasurface is constructed. Different coding metasurface sequences are constructed based on 1‐bit, 2‐bit, and 3‐bit digital coding units. According to generalized Snell's law, the number of transmitted beams can be controlled. The authors introduce complex code addition theory to construct multifunctional beam control metasurface. Based on the far field scattering theory of metasurface, the addition theory of different sequences of transmission‐coded metasurface is analyzed. The addition operation of the superposition of two sets of symmetric double beams and two sets of ordinary double beams can be realized. Based on the analysis of far‐field scattering characteristics, the multifunctional coded metasurface is demonstrated, that is, multiple functions are simultaneously superimposed in one array without interference. [ABSTRACT FROM AUTHOR]

Recent research on combining photovoltaic (PV) modules with radiative sky cooling (RSC) technology has elicited much interest. Such cross‐disciplinary technology coupling provides a feasible approach to solar cells' nighttime applications. However, current commonly used radiative sky cooling materials' (RSCMs) conflict with the solar light harvesting and utilizing of PV module. The spectral selectivity characteristics of the strong transmission in the solar spectrum range (0.3–1.1 μm) and the enough emissivity within the atmosphere transparency window (8–13 μm) are the essential to develop the PV module‐usable RSC coating. Herein, antireflection (AR) structure optimize method and RSC coating design method are proposed to achieve nighttime RSC capacity with high solar radiation transmission property via the RSCM selection and light management, in the visible, near‐infrared, and midinfrared wavelength range, originating from the subwavelength optical effects of bioinspired AR design. A kind of double‐layer coating consisting of the PDMS substrate layer and SiO2 close‐packed hexagonal rotating parabolic body‐bioinspired moth‐eye structure cover layer is designed in this research. The coating has 0.997 average transmissivity characteristic in solar spectrum and can lower the PV cell temperature over 10.5 K than ambient at night. [ABSTRACT FROM AUTHOR]

Reflection occurs when light impinges on an interface between two distinct media. Suppression of the reflection is of paramount significance to practical applications in information transfer and conversion. While technologies such as the Brewster effect and material coatings are widely adopted to eliminate the wave reflection from purely spatial or temporal interfaces, how to eliminate the reflection from a spatiotemporal interface remains elusive. Here, a new type of spatiotemporal metamaterial that functions as a global and generalized perspective of quarter‐wave impedance transformers is presented. With the proper geometric design, the proposed spatiotemporal metamaterial can fully suppress the reflection, applicable to arbitrary modulation velocities. Importantly, the tunability of modulation velocity in the spatiotemporal metamaterial allows flexible frequency conversions in high efficiency, indicating that the spatiotemporal metamaterials are much more powerful than the purely spatial or temporal counterparts. These findings not only enhance the controllability of electromagnetic waves but also can be adapted to other classes of physical dynamics, including water surface waves, acoustic, and elastic. [ABSTRACT FROM AUTHOR]

Constructing nanostructured surfaces on the macro/micro-scale optical lens is of great importance in the improvement of light transmittance, reflection, and surface functionality of optical devices. In this paper, a flexible and novel material interface design and manufacturing method for hierarchical macro/nano optical glass lenses is proposed. To verify the feasibility of the presented manufacturing strategy, the deformation history and flow driving mechanism of multiscale structured surfaces during second hot embossing were studied by simulations and experiments. The results showed that solid-like glass preform exhibits a higher nanoscale deformation resistance and elastic recovery, which can reduce the distortion levels of the nanostructured surface. At small scales, molecular confinement greatly reduces the tectonic deformation of nanostructured surface at relatively low applied heat and pressure. However, beyond a specific thermal energy threshold, nanostructured convex surfaces are easily compressed into a smooth flattened surface. By collaborative control of embossing conditions, the nano-surface integrity of multiscale structured surface can be ensured during second hot embossing. Compared to the smooth macroscale optical lens, the hierarchical macro/nano glass lens exhibited better optical transmittance and antireflection properties. The proposed design and manufacturing strategy provides a facile and flexible solution for building the hierarchical macro/micro/nanostructure functional optics.

A visible–extended shortwave infrared indium gallium arsenide (InGaAs) focal plane array (FPA) detector is the ideal choice for reducing the size, weight and power (SWaP) of infrared imaging systems, especially in low-light night vision and other fields that require simultaneous visible and near-infrared light detection. However, the lower quantum efficiency in the visible band has limited the extensive application of the visible–extended InGaAs FPA. Recently, a novel optical metasurface has been considered a solution for a high-performance semiconductor photoelectric device due to its highly controllable property of electromagnetic wave manipulation. Broadband Mie resonator arrays, such as nanocones and nanopillars designed with FDTD methods, were integrated on a back-illuminated InGaAs FPA as an AR metasurface. The visible–extended InGaAs detector was fabricated using substrate removal technology. The nanostructures integrated into the Vis-SWIR InGaAs detectors could realize a 10–20% enhanced quantum efficiency and an 18.8% higher FPA response throughout the wavelength range of 500–1700 nm. Compared with the traditional AR coating, nanostructure integration has advantages, such as broadband high responsivity and omnidirection antireflection, as a promising route for future Vis-SWIR InGaAs detectors with higher image quality. [ABSTRACT FROM AUTHOR]

With chemical stability under high temperatures, dielectric materials can be idealized thermal emitters for different energy applications. However, dielectric materials do not support surface waves at near-infrared ranges for longer-distance thermal photon tunneling, which limits their applications in near-field thermal radiation. It is demonstrated in this study that thermal field amplification at near-infrared wavelengths at dielectric surfaces could be achieved through asymmetric Fabry–Perot resonance with anti-reflection coatings or 1D photonic crystal type structures. ⩾100 nm near-infrared thermal photon tunneling can be achieved when these thin film structures are added to the emitter and the collector surfaces. Among these two thin film structures, 1D photonic crystal type periodic structures constructed with the same high refractive index material as the emitter/collector material allow near-field thermal photon tunneling at large parallel wavenumbers. Moreover, the field amplification can be increased by adding more 1D photonic crystal layers to achieve even longer distances near field thermal photon tunneling. [ABSTRACT FROM AUTHOR]

Polysiloxane antireflective structures composed of tapered nanopillar arrays were prepared by nanoimprinting using anodic porous alumina molds with tapered pores. Because polysiloxane is a heat-resistant material, the resulting tapered nanopillar array structures were maintained even after heat treatment at 200 °C. In addition, no significant changes in antireflection properties were observed before and after heat treatment at 200 °C. These results indicate that the polysiloxane nanopillar arrays obtained in this study can be applied as heat-resistance antireflection structures. [ABSTRACT FROM AUTHOR]

Antireflective (AR) nanostructures offer an effective, broadband alternative to conventional AR coatings that could be used even under extreme conditions. In this publication, a possible fabrication process based on colloidal polystyrene (PS) nanosphere lithography for the fabrication of such AR structures on arbitrarily shaped fused silica substrates is presented and evaluated. Special emphasis is placed on the involved manufacturing steps in order to be able to produce tailored and effective structures. An improved Langmuir-Blodgett self-assembly lithography technique enabled the deposition of 200 nm PS spheres on curved surfaces, independent of shape or material-specific characteristics such as hydrophobicity. The AR structures were fabricated on planar fused silica wafers and aspherical planoconvex lenses. Broadband AR structures with losses (reflection + transmissive scattering) of <1% per surface in the spectral range of 750–2000 nm were produced. At the best performance level, losses were less than 0.5%, which corresponds to an improvement factor of 6.7 compared to unstructured reference substrates. [ABSTRACT FROM AUTHOR]

Advanced highly transparent films or membranes are required for diverse optical applications, including ophthalmology and the display industry. In general, bioinspired engineering is the most promising technology for obtaining highly transparent surfaces. This study proposes a novel perfluoropolyether (PFPE) highly transparent thin membrane with nanopatterns on both sides of the surface, inspired by the wings (clearwing) of Greta‐oto. PFPE is a superior material for achieving this goal because of its low refractive index and low surface energy. A clearwing‐inspired antireflective membrane (CAM) composed of PFPE is fabricated using a well‐designed polymer replica method. CAM exhibits outstanding optical properties and intriguing demonstrations of invisible trap sensors, both in air and water, with long‐term stability. [ABSTRACT FROM AUTHOR]

Currently, there is high demand for the development of a highly mass-producible technology for manufacturing moth-eye-structured films with an antireflection function. Conventional moth-eye-structured films have been produced by roll-to-roll (RTR) ultraviolet nanoimprint lithography (UV-NIL) using porous alumina, but the process of manufacturing the roll mold with aluminum is both complicated and time-consuming. To solve this problem, we proposed a sputtering process for forming a thin film of glassy carbon on a roll substrate and fabricated a moth-eye structure through the irradiation of oxygen plasma. A glassy carbon (GC) moth-eye-structure roll mold with a uniform reflectance of less than 0.1% over a length of 1560 mm was fabricated following this method. In addition, a superhydrophobic moth-eye-structured film was produced by RTR UV-NIL using the proposed roll mold, which exhibited a reflectance of 0.1%. In this study, a moth-eye-structure roll using porous alumina was compared with a film transferred from it. The GC moth-eye-structure roll mold was found to be superior in terms of antireflection, water repellency, and productivity. When the proposed large-area GC moth-eye-structured film was applied to window glass, significant anti-reflection and water-repellent functionalities were obtained. [ABSTRACT FROM AUTHOR]

Crystalline Si solar cells based on thin wafers, with thicknesses in the range of 5–50 μm, can find applications in a wide range of markets where flexibility and bendability are important. For these cells, avoiding standard macroscopic texture is desirable to increase structural integrity. Herein, a nanopatterned SiNx antireflection (AR) coating that consists of 174 nm‐radius and 118 nm‐high SiNx nanodisks arranged in a square lattice on a thin (59 nm) SiNx layer is introduced. This geometry combines Fabry–Pérot AR and forward scattering by a resonant Mie mode to achieve high transmission into the Si absorber over a broad spectral band. The nanostructured coating is patterned on a commercial interdigitated‐back‐contact (IBC) Si solar cell, experimentally demonstrating a short‐circuit current density (Jsc) of 36.9 mA cm−2, 2.3 mA cm−2 higher than for a single‐layer AR coated cell, and an efficiency of 16.3% at a thickness of around 100 μm. It is shown that light incoupling efficiency is comparable to that of pyramidal texturing, while the absorption in the infrared is lower, due to less‐effective light trapping. Overall, nanopatterned SiNx broadband AR coatings are an appealing option for improving light management in ultrathin solar cells and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

It is shown in this paper that a polymer, MA-PEG 1000-DGEBA (MP1D), exhibits antireflection, substrate-dependent photoluminescence (SDP), wide band-gap, and photoconduction characterization. MP1D was synthesized from maleic anhydride, polyethylene glycol 1000, and bisphenol-A diglycidyl ether. Self-assembled nanoparticles embedded in MP1D film and ranging from 2.5 to 31.6 nm are observed, which could be expected as scatterers to enhance light trapping and extraction. The size of the nanoparticle increases with the concentration of the MP1D solution. Besides solution concentration, the nanoparticle dimension could be modified by the chain length of polyethylene glycol in the polymer synthesis. The effects of solution concentration, annealing temperature, annealing period, and substrate on the photoluminescence (PL) of MP1D films are examined. Increasing solution concentration increases PL intensity. However, aggregation-caused quenching is explicit as the solution concentration exceeds 100 mM. PL intensity increases with annealing temperature, which could be attributed to crystallinity improvement. PL intensity increases with increasing the annealing period from 0.5 to 2 h. Nonetheless, as the annealing period exceeds 2 h, PL quenching is emerging, which could be due to aggregation. It is expected that MP1D could be a promising candidate for host materials and MP1D film could play a multifunctional role (antireflective and light-trapping functions) in optoelectronics. [ABSTRACT FROM AUTHOR]

[Display omitted] SiO 2 nanomaterials are widely used for antireflection and self-cleaning, but the preparation process is usually complex and time-consuming. Hence, we present a facile one-step synthesis of a hydrophobic two-dimensional SiO 2 nanomesh by tuning the reaction temperature using dodecylamine as a catalyst. SiO 2 nanomesh has the advantages of an adjustable refractive index, simple preparation process, and low cost, which affords both antireflection and self-cleaning functions for solar cells. Two types of perovskite solar cells were used to verify the stability and universality of the SiO 2 nanomesh coatings. The antireflection effect of the SiO 2 nanomesh is found to increase the current density of both perovskite solar cells fabricated at 500 °C and 150 °C, with the efficiency increased by 4.48% and 4.79%, respectively. [ABSTRACT FROM AUTHOR]

Antireflective metal surfaces have played an essential role in practical applications in the fields of photodetectors, infrared imaging, stray light shielding, photoelectric heat transfer equipment. In this work, a novel and convenient strategy for fabricating the black titanium alloy (Ti-6Al-4 V) surface with micro-nano-hierarchical structures by the nanosecond laser and hydrothermal treatment was proposed. The micro-protrusion array structures were constructed on titanium alloy surface by nanosecond laser, and then the nanoscale grasses structures grew on the micro-protrusion array structures after the hydrothermal treatment. The reflection of light was effectively limited by the micro-nano-hierarchical structures surface, and the average reflectance of the laser-processed surface was significantly reduced in the wavelength range of 250-2500 nm. The average reflectance of the micro-protrusion array structures surface decreased to 7.2% in the wavelength range of 250-800 nm, and 13.4% in the near IR. The average reflectance of the micro-protrusion and nanoscale grasses structures surface decreased to 2.5% in the wavelength range of 250-800 nm, and 4.6% in the near IR. In addition, the contact angle of the micro-nano-hierarchical structures surface reached 152.3° after the fluorination treatment and the self-cleaning test showed that the micro-nano-hierarchical structures surface had a good self-cleaning ability. This method of fabricating antireflective and self-cleaning surface demonstrated low cost, highly efficiency, and high controllability, and might potentially be utilized for industrial applications. [ABSTRACT FROM AUTHOR]

Nanostructure engineering has proven to be one of the most effective strategies to improve the efficiency of photoelectric devices. Herein, we numerically investigate and experimentally demonstrate a self-assembled silicon-based nanopillars and nanoholes structures, to improve the light absorption of photoelectric devices by an antireflection enhancement. The nanopillars and nanoholes structures are fabricated by the air–liquid interface self-assembly method based on polystyrene (PS) nanospheres. Additionally, the tunable antireflective properties with the different operation wavelength and nanostructures parameters have been discussed based on the Finite-Difference Time-Domain (FDTD) method. The experimental result shows that the self-assembled silicon-based nanopillars and nanoholes structures can achieve the lowest reflectivity of 1.42% (nanopillars) and 5.83% (nanoholes) in the wavelength range of 250–800 nm, which reduced 95.97% and 84.83%, respectively, compared with the plane silicon. The operation mechanism of the tunable antireflective property of self-assembled nanopillars and nanoholes structures is also analyzed in the simulation. Our study suggests that the self-assembled nanopillars and nanoholes structures are potentially attractive as improving efficiency of photoelectric devices. [ABSTRACT FROM AUTHOR]

Abstract Femtosecond laser machining of biomimetic micro/nanostructures with high aspect ratio (larger than 10) on ultrahard materials, such as sapphire, is a challenging task, because the uncontrollable surface damage usually results in poor surface structures, especially for deep scribing. Here, we report an inside-out femtosecond laser deep scribing technology in combination with etching process for fabricating bio-inspired micro/nanostructures with high-aspect-ratio on sapphire. To effectively avoid the uncontrollable damage at the solid/air interface, a sacrificial layer of silicon oxide was employed for surface protection. High-quality microstructures with an aspect ratio as high as 80:1 have been fabricated on sapphire surface. As a proof-of-concept application, we produced a moth-eye inspired antireflective window with sub-wavelength pyramid arrays on sapphire surface, by which broadband (3–5 μm) and high transmittance (98% at 4 μm, the best results reported so far) have been achieved. The sacrificial layer assisted inside-out femtosecond laser deep scribing technology is effective and universal, holding great promise for producing micro/nanostructured optical devices.

This study used a rapid and simple microwave-assisted synthesis method to grow ZnO nanoneedle arrays on the silicon substrate with the ZnO seed layer. The effects of reaction temperature and time on the lengths of ZnO nanoneedle arrays were investigated. The appropriate temperature programming step can grow the longer ZnO nanoneedle arrays at the same reaction time (25 min), which is 2.08 times higher than without the temperature programming step. The geometry of the ZnO nanoneedle arrays features a gradual decrease from the Si substrate to the surface, which provides an excellent progressive refractive index between Si and air, resulting in excellent antireflection properties over an extensive wavelength range. In addition, the ZnO nanoneedle arrays exhibit a suitable structure for uniform deposition of Ag nanoparticles, which can provide three-dimensional hot spots and surface active sites, resulting in higher surface-enhanced Raman scattering (SERS) enhancement, high uniformity, high reusability, and low detection limit for R6G molecule. The ZnO/Ag nanoneedle arrays can also reveal a superior SERS-active substrate detecting amoxicillin (10−8 M). These results are promising for applying the SERS technique for rapid low-concentration determination in different fields. [ABSTRACT FROM AUTHOR]

Commercial antireflective coatings (ARCs) on photovoltaic (PV) module glass can improve module power by 2.5%–3.0%, but their long‐term field performance requires additional study. In this paper, we investigate ARC performance on fielded modules using two nondestructive techniques: reflectance spectroscopy and RGB microscopy, finding a large variation in coating durability and performance. For new coatings, the fleet average nominal power enhancement is 2.8%. This power enhancement is observed to degrade at approximately −0.05%/year absolute over the first 8 years of fielding in arrays that are not regularly cleaned. Interferometry and imaging results imply that coating loss for these modules is due to slow chemical thinning of the initial 125 nm thick coating by 1.4 to 5.0 nm/year. Due to the physics of interference coatings, the performance loss is projected to accelerate as the coating is further thinned, resulting in a coating lifetime (time to 80% of initial performance) of 7.5 to 25 years. At the higher 5.0 nm/year coating loss rates, we estimate that −0.14%/year power degradation of the module can be attributed solely to ARC degradation over the first 20 years. Extreme coating loss is observed on some modules where after 8 years fielding, the coating can be completely removed with a single wet wipe with a lens tissue. A case study is also presented comparing ARC and noncoated modules installed at a single site in 2013. We find that the ARC modules have a 2.6% higher soiling power loss than the noncoated modules; this exceeds the ARC power enhancement of 2.4% and leads to the surprising conclusion that the ARC lowers production for modules in this location due to increased soiling. These results demonstrate that RGB microscopy is a powerful, field‐capable, and quantitative characterization technique for assessing degradation of PV module ARCs. [ABSTRACT FROM AUTHOR]

In monocrystalline Si solar cells, pyramidal surface textures with the size of a few micrometers (micropyramids) are commonly applied for light in‐coupling and trapping. Recently, there is a growing need to reduce the size of pyramids below 1 μm. Herein, an original method to fabricate nanometer‐sized pyramids (nanopyramids) featuring an average size of ≈500 nm or even smaller by using a simple one‐step Ag‐assisted solution process is proposed. The texture size can be controlled by the concentration of AgNO3 in the alkaline etching solution where the generated Ag nanoparticles act as an etching mask as well as promoting the detachment of H2 bubbles from the reacting Si surface. This process enables the formation of uniformly distributed Si nanopyramids with a lower reflectance below 10% and a smaller etching margin less than 1.7 μm compared with the conventional micropyramids. Silicon heterojunction solar cells employing Si nanopyramids outperform those with the conventional micropyramids owing to the reduced optical reflectance while preserving excellent surface passivation and carrier transport properties. These results demonstrate the advantages of our method and the high potential of Si nanopyramids for various applications such as thin crystalline Si solar cells and perovskite/Si tandem solar cells. [ABSTRACT FROM AUTHOR]

This paper reports on a facile bottom-up method for the direct integration of a silicon (Si)-magnesium silicide (Mg2Si) heterojunction solar cell (HSC) with a textured rear reflector made of stainless steel (SS). Modified wet chemical etching and post processing of SS substrates resulted in the formation of both a rough surface texture and diffusion barrier layer, consisting of magnetite (Fe3O4) with reduced optical reflection. Then, Si, Mg2Si and CaSi2 layers were stepwise thermally evaporated onto the textured SS surface. No traces of Fe and Cr silicide phases were detected by Raman spectroscopy, confirming effective suppression of impurity diffusion from the SS to the upper layers at least at temperatures required for Si deposition, as well as Mg2Si and CaSi2 formation. The obtained black-SS/Fe3O4/Si/Mg2Si/CaSi2 sample preserved, to some extent, its underlying textured morphology and demonstrated an averaged reflection of 15% over the spectral range of 200–1800 nm, while its prototype HSC possessed a wideband photoresponse with a photoelectric conversion efficiency of 7.5% under AM1.5 illumination. Moreover, Si layers deposited alone onto a black-SS substrate demonstrated competitive antireflection properties compared with black Si (b-Si) obtained by traditional top-down etching approaches, and hybrid b-Si/textured-SS structures with a glue-bonded interlayer. [ABSTRACT FROM AUTHOR]

The diffusion of uncured polydimethylsiloxane (PDMS) oligomers out of bulk PDMS elastomers is usually detrimental to many biomedical and microfluidic applications due to the inevitable contamination of the contacting fluids and substrates. Here, we transform this detrimental process into an enabling technology for achieving novel reconfigurable antireflection (AR) coatings, which are of great technological importance in the development of new nano-optical and optoelectronic applications. Self-assembled monolayer silica colloidal crystals are first used as sacrificial templates in fabricating nanoporous polymer AR coatings. When air in the templated nanopores is replaced with infused PDMS oligomers simply by pressing a PDMS stamp on a nanoporous AR film, the original antireflection conditions are lost, and the coating transforms from a low-reflection configuration to a high-reflection state. The original antireflection performance can be fully recovered by dissolving the infused oligomers in the appropriate solvents (e.g., hexane). This novel tuning mechanism for achieving reconfigurable AR properties has been confirmed by systematic investigations using various microscopes, optical spectroscopy, nanoindentation, thermomechanical tests, and X-ray photoelectron spectroscopy. Complex micropatterns with micrometer-scale spatial resolution and drastically different AR performances can be easily printed on nanoporous AR films by using a soft lithography-based microcontact printing process. Numerical finite-difference time-domain simulations match well with experimental antireflection measurements and reveal a linear relationship between the optical transmission and the amount of infused PDMS oligomers in nanopores.

Fine-tuning of microstructures enables the modulation of optical properties at multiple scales from metasurfaces to geometric optics. However, a dynamic system with a significant deformation range and topology transformation remains challenging. Owing to its magnetic controllability, ferrofluid has proven to be fertile ground for a wide range of engineering and technological applications. Here, we demonstrate a series of intelligent optical surfaces based on ferrofluid, through which multiple optical functions inspired by nature can be realized. The tunability is based on the topological transition of the ferrofluid between the flat state and cone array upon magnetic actuation. In the visible band, a tunable visual appearance is realized. In the mid-infrared band, active manipulation of reflection is realized based on the gradient-index (GRIN) effect. This system also features low latency response and straightforward manufacturability, and it may open opportunities for novel technologies such as smart windows, color displays, infrared camouflage, and other infrared-related technologies.

A visible–extended shortwave infrared indium gallium arsenide (InGaAs) focal plane array (FPA) detector is the ideal choice for reducing the size, weight and power (SWaP) of infrared imaging systems, especially in low-light night vision and other fields that require simultaneous visible and near-infrared light detection. However, the lower quantum efficiency in the visible band has limited the extensive application of the visible–extended InGaAs FPA. Recently, a novel optical metasurface has been considered a solution for a high-performance semiconductor photoelectric device due to its highly controllable property of electromagnetic wave manipulation. Broadband Mie resonator arrays, such as nanocones and nanopillars designed with FDTD methods, were integrated on a back-illuminated InGaAs FPA as an AR metasurface. The visible–extended InGaAs detector was fabricated using substrate removal technology. The nanostructures integrated into the Vis-SWIR InGaAs detectors could realize a 10–20% enhanced quantum efficiency and an 18.8% higher FPA response throughout the wavelength range of 500–1700 nm. Compared with the traditional AR coating, nanostructure integration has advantages, such as broadband high responsivity and omnidirection antireflection, as a promising route for future Vis-SWIR InGaAs detectors with higher image quality.

Antireflective (AR) nanostructures offer an effective, broadband alternative to conventional AR coatings that could be used even under extreme conditions. In this publication, a possible fabrication process based on colloidal polystyrene (PS) nanosphere lithography for the fabrication of such AR structures on arbitrarily shaped fused silica substrates is presented and evaluated. Special emphasis is placed on the involved manufacturing steps in order to be able to produce tailored and effective structures. An improved Langmuir-Blodgett self-assembly lithography technique enabled the deposition of 200 nm PS spheres on curved surfaces, independent of shape or material-specific characteristics such as hydrophobicity. The AR structures were fabricated on planar fused silica wafers and aspherical planoconvex lenses. Broadband AR structures with losses (reflection + transmissive scattering) of

• A new vibration assisted nanoimprinting method is proposed for face-to-face imprinting. • Vibration assisted-nanoimprinting can improve the filling rate of photoresist. • Vibration assisted-nanoimprinting can improve the hydrophobicity of microstructure surface. • Vibration assisted-nanoimprinting can improve the photovoltaic conversion efficiency of solar cells. To effectively improve the power conversion efficiency (PCE) of Si solar cells, vibration-assisted UV nanoimprint lithography based on piezoelectric driving is proposed to fabricate grating on Si solar cells. By applying piezoelectric vibration under the photoresist layer, vibration causes micro-displacement and micro-impact force, increasing the contact area between the photoresist and the grating's side wall and reducing surface tension. Meanwhile, the photoresist filling rate is increased by 25%. The effect of grating parameters on reflection is determined using Finite Difference Time Domain (FDTD), and grating with the best optical performance is optimized. In addition, the rationality of vibration introduction is verified by establishing a motion model, the influence of frequency and amplitude on the filling rate is analyzed using the finite element method, and a reasonable range of vibration parameters required by the experiment is obtained. Vibration-assisted UV nanoimprint is used to fabricate the periodic grating structures. PCE is increased by 25% when compared to bare Si solar cells. PCE of grating fabricated by vibration-assisted UV nanoimprint is increased by 4% when compared to traditional nanoimprint. The results show that vibration-assisted nanoimprint can efficiently and accurately fabricate periodic grating structures, resulting in improved Si solar cells performance. [ABSTRACT FROM AUTHOR]

The nanophotonic engineering of lightâ€"matter interactions has profoundly changed research behind the design and fabrication of optical materials and devices. Metasurfacesâ€"arrays of subwavelength nanostructures that interact resonantly with electromagnetic radiationâ€"have emerged as an integral nanophotonic platform for a new generation of ultrathin lenses, displays, polarizers and other devices. Their success hinges on advances in lithography and nanofabrication in recent decades. While existing nanolithography techniques are suitable for basic research and prototyping, issues of cost, throughput, scalability, and substrate compatibility may preclude their use for many metasurface applications. Patterning via spontaneous self-assembly of block copolymer thin films offers an enticing alternative for nanophotonic manufacturing that is rapid, inexpensive, and applicable to large areas and diverse substrates. This review discusses the advantages and disadvantages of block copolymer-based nanopatterning and highlights recent progress in their use for broadband antireflection, surface enhanced Raman spectroscopy, and other nanophotonic applications. Recent advances in diversification of self-assembled block copolymer nanopatterns and improved processes for enhanced scalability of self-assembled nanopatterning using block copolymers are also discussed, with a spotlight on directions for future research that would enable a wider array of nanophotonic applications. [ABSTRACT FROM AUTHOR]

In this article, the titanium‐oxo cluster containing bromine had been prepared by solvothermal synthesis, which was used to initiate the atom transfer radical polymerization of butyl methacrylate in order to obtain organic–inorganic hybrid materials. The structures and compositions of titanium‐oxo cluster and its hybrid materials were characterized by X‐ray photoelectron spectroscopy (XPS), 1H nuclear magnetic and infrared spectra tests. The hybrid materials with different molecular weights were dissolved in tetrahydrofuran and coated on the surface of polyethylene terephthalate (PET) film, which was used to study the surface properties. Compared with 89.7% light transmittance of the pure PET film, the light transmittance of the modified films was up to 93.3%. Meanwhile, the water contact angles of the modified films also significantly increased. It would be conducive to the self‐cleaning of the film surface. The coatings prepared by the static respiration diagram method had better hydrophobic effect and show the performance of light scattering. All of that could be proved through the scanning electron microscope (SEM) images. The elastic modulus and hardness of hybrid materials also change with the increase of molecular weight. In addition, the Tg of the hybrid materials increased, which means they have better thermal stability than that of Polybutylmethacrylate (PBMA). [ABSTRACT FROM AUTHOR]

Summary: We have experimentally demonstrated that slanted, kinked and straight silicon nanowire arrays form a broadband omnidirectional light‐harvesting structure. The unique design of kinked and slanted nanowires allows them to trap more light effectively across a wide wavelength range than straight silicon nanowires (SiNWs). We report that the light absorption in slanted, kinked and straight wires is enhanced by controlling their geometrical parameters. The p‐type SiNWs have less reflection than n‐type SiNWs due to their larger porosity gradient structure. Aperiodic and tapered slanted, kinked and straight SiNWs are remarkably photoactive and promising low‐cost materials for photoelectrochemical water splitting applications. [ABSTRACT FROM AUTHOR]