Excellent Antireflective Properties Research Articles

Wide-Spectrum Antireflective Properties of Germanium by Femtosecond Laser Raster-Type In Situ Repetitive Direct Writing Technique

A femtosecond laser raster-type in situ repetitive direct writing technique was used for the fabrication of anti-reflective microhole structures in Germanium (Ge) in the visible near-infrared range (300–1800 nm). This technique builds a layer of microstructured arrays on the surface of Ge, enabling Ge to exhibit excellent anti-reflective properties. The large-area micro-nanostructures of Ge were fabricated using femtosecond laser raster-type in situ repetitive direct writing. Ge microstructures are characterized by their structural regularity, high processing efficiency, high reproducibility, and excellent anti-reflective properties. Experimental test results showed that the average reflectance of the Ge microporous structure surface in the range of 300–1800 nm was 2.25% (the average reflectance of flat Ge was 41.5%), and the lowest reflectance was ~1.6%. This microstructure fabrication drastically reduced the optical loss of Ge, thus enhancing the photothermal utilization of Ge. The many nanoburrs and voids in the Ge microporous structure provided excellent hydrophobicity, with a hydrophobicity angle of up to 133 ± 2° (the hydrophobicity angle of flat Ge was 70 ± 2°). The high hydrophobicity angle allows for strong and effective self-cleaning performance. The femtosecond laser raster-type in situ repeatable direct writing technology has many desirable properties, including simplicity, high accuracy, flexibility, and repeatability, that make it one of the preferred choices for advanced manufacturing. The Ge micro-nanostructured arrays with excellent optical anti-reflective properties and hydrophobicity have become an attractive alternative to the current photo-thermal absorbers. It is expected to be used in many applications such as solar panels, photovoltaic sensors, and other optoelectronic devices.

Multifunctional capabilities of radio frequency sputtered GO-TiO2 nanocomposite ultra-thin films

The work presents the successful synthesis of ultra-thin Graphene Oxide-Titanium (GOT) nanocomposite films using radio frequency sputtering. It was employed a thorough characterization encompassing structural, optical, and morphological aspects, with a focus on practical applications such as photocatalysis, anti-corrosion, anti-reflective properties, and superhydrophobicity (PAAS). Notably, the GOT film exhibited outstanding photocatalytic efficiency, achieving a significant 96% photodegradation rate, and offering promise for environmental remediation. Additionally, it demonstrated excellent visible-light-induced photocatalytic disinfection against E. coli K12 contamination. Furthermore, the film displayed notable corrosion resistance, a fivefold improvement over pristine surfaces, and excellent anti-reflective properties with 98% transmittance in the visible light range, making it suitable for advanced optical devices with multifunctional benefits.

Coded meta-materials drivened by impedance-mismatch: Ultra-broadband anti-reflection and scattering field manipulation

The inability of existing electromagnetic wave absorbing materials (EAMs) to manipulate electromagnetic waves in multiple dimensions leads to the failure to satisfy the demands placed on electromagnetic (EM) defense technology by the current complex EM environment. To break this dilemma, this study focuses on the impedance properties of EAMs, conferring additional ability to disperse and deflect reflected waves by encoding EAMs with opposite phase responses in different impedance mismatch modes. Due to the synergy of both absorption and scattering mechanisms, the developed scattering metamaterial absorber exhibits excellent anti-reflection performance, with reflectivity below 0.1 in the 7.8–16.7 GHz at 2 mm thickness. Furthermore, a genetic algorithm is employed to tailor the desired scattering field to meet the stealth requirements of specific environments, allowing for the directional transmission of EM energy in the one-dimensional or homogeneous distribution in the three-dimensional. The proposed scattering metamaterial absorber constructed by coded EAMs exhibited excellent anti-reflection properties and environmental stealth adaptability, opening up new possibilities for the development of advanced EM defense technology.

Dual Porosity-Enhanced Antireflection Coatings with Continuous Gradient.

The incorporation of porous structures into films and coatings can transform their properties for applications in optics, separation, electronics, and energy generation and storage. Packing nanoparticles (NPs) is a versatile approach for fabricating nanoporous films with a tunable structure and properties. The mechanical fragility of NP packing-based films and coatings, however, significantly impedes their widespread utilization. Although infiltrating a polymer into the interstices of these NP packings has been shown to enhance their mechanical durability, this method completely eliminates the porosity of the structures, compromising their properties and functionality. This study presents a new approach to fabricate highly loaded porous nanocomposite films with a gradient in the refractive index by infiltrating subsaturating amounts of poly(methyl methacrylate) (PMMA) into disordered packings of hollow silica NPs. We demonstrate that dual porosity is a critical feature that enhances their antireflection (AR) and mechanical properties. The hollow cores of NPs prevent a substantial increase in the refractive index of the resulting films. Moreover, the interparticle voids allow for mechanical reinforcement to occur when the NP packings are infiltrated with PMMA, making them even more suitable for AR coatings. The refractive index and gradient across the nanocomposites can be tailored by adjusting the amount of PMMA infiltrated into the NP packing, the shape of hollow NPs, and the annealing time. The nanocomposite coatings with a continuous gradient in refractive index exhibit excellent AR properties and enhanced mechanical durability. Combined with the unique structural tunability afforded by the dual porosity, this approach provides a scalable and effective way to create robust and graded nanoporous structures for various applications.

Bioinspired Near-Full Transmittance MgF2 Window for Infrared Detection in Extremely Complex Environments

Due to the extreme complexity of the anti-reflective subwavelength structure (ASS) parameters and the drastic limitation of Gaussian beam manufacturing accuracy, it remains a great challenge to manufacture ASS with ultrahigh transmittance on the surface of infrared window materials (such as magnesium fluoride (MgF2)) directly by femtosecond laser. Here, a design, manufacturing, and characterization method that can produce an ultrahigh-performance infrared window by femtosecond laser Bessel beam is proposed. Inspired by the excellent anti-reflective and hydrophobic properties of the special structure of dragonfly wings, a similar structural pattern with grid-distributed truncated cones is designed and optimized for its corresponding parameters to achieve near-full transmittance. The desired submicron structures are successfully fabricated by a Bessel beam after effectively shaping the beam. As a practical application, the bioinspired ASS is manufactured on the surface of MgF2, achieving an ultrahigh transmittance of 99.896% in the broadband of 3–5 μm, ultrawide angle of incidence (over 70% at 75° incidence), and good hydrophobicity with a water contact angle of 99.805°. Results from infrared thermal imaging experiments show that the ultrahigh-transmittance MgF2 window has superior image acquisition and anti-interference performance (3.9–8.6% image contrast enhancement and more accurate image edge recognition) in an environment with multiple interfering factors, which may play a significant role in facilitating applications of infrared thermal imaging technologies in extremely complex environments.

Antireflective structured surface of chalcogenide glass fabricated using glass to glass molding

Chalcogenide (ChG) glasses with micro-nano structure arrays are increasingly demanded in infrared optical systems owing to their excellent antireflective properties, and can be mass-produced by precision glass molding (PGM). Nickel-phosphorus (Ni–P) plated molds are commonly used in the PGM process, but the Ni atoms tend to react with the ChG glass at high temperatures. In this study, we propose a novel two-step PGM process. A Ni–P mold is used to transfer antireflective micro-nano structure array to silicate glass. Then the silicate glass, which has a higher glass transition temperature (Tg) than the ChG glass, is used as the mold to replicate the antireflective structured surface to the ChG glass. The results show that the ChG glass micro-nano structure array has high forming accuracy and favorable infrared optical transmission characteristics. The silicate glass is proved to be an appropriate mold material for the ChG glass molding process. This work provides a novel type of the PGM techniques for ChG glass materials.

Enhanced Mechanical and Hydrophobic Antireflective Nanocoatings Fabricated on Polycarbonate Substrates by Combined Treatment of Water and HMDS Vapor.

Polycarbonate (PC) with high transmittance, stable mechanical performance and environmental resistance is crucial for practical applications. In this work, we report a method for the preparation of a robust antireflective (AR) coating by a simple dip-coating process of a mixed ethanol suspension consisting of tetraethoxysilane (TEOS) base-catalyzed silica nanoparticles (SNs) and acid-catalyzed silica sol (ACSS). ACSS greatly improved the adhesion and durability of the coating, and the AR coating exhibited high transmittance and mechanical stability. Water and hexamethyldisilazane (HMDS) vapor treatment were further employed to improve the hydrophobicity of the AR coating. The as-prepared coating exhibited excellent antireflective properties, with an average transmittance of 96.06% in the wavelength range of 400 to 1000 nm, which is 7.55% higher than the bare PC substrate. After sand and water droplet impact tests, the AR coating still maintained enhanced transmittance and hydrophobicity. Our method shows a potential application for the preparation of hydrophobic AR coatings on a PC substrate.

Comparative optical analysis of GaAs nanostructures for photovoltaic applications using finite element method

In this manuscript, a thorough comparative analysis of six GaAs based nanostructures (hollow and solid) is performed on the basis of their optical performance. These nanostructures are known to exhibit excellent anti-reflection properties, owing to their ability to generate a broadband absorption spectrum through efficient photon harvesting. Using the Finite Element Method (FEM) of the commercially available COMSOL Multiphysics package, the absorption characteristics, optical short circuit current density (JSC), electric field and photogeneration rates of six different nanostructures namely concentric nanocylinder (CNCy), hollow concentric nanocylinder (HCNCy), inverted nanopencil (INPe), hollow nanopencil (HNPe), nanorod + nanohemisphere (NR + NHe), and hollow nanorod + hollow nanohemisphere (HNR + HNHe) are computed. The optical performance of these nanostructures is largely dependent on their geometrical parameters such as filling ratio (FR = Diameter/Period), spacing and structural dimensions. The optimized values of these parameters can play a vital role in capturing the optical resonance modes by the nanostructures to produce absorption enhancement. It has been observed that the nanostructures with base diameter of 240 nm, period in the range of 300–350 nm and FR of 0.8 exhibit better optical characteristics. Optical JSC and optical efficiency of 29.45 mA cm−2 and 42.26%, respectively for CNCy nanostructure with FR of 0.8 and diameter of 240 nm is the highest among all the nanostructures. The effect of the angle of incidence of the photons striking the nanostructures on the average absorptance in both Transverse Electric (TE) and Transverse Magnetic (TM) modes are also investigated. In addition to this, we have also computed the effective refractive index for all the nanostructures using Maxwell Garnett formula in order to estimate the surface anti-reflection characteristics of these nanostructures.

Optimization Temperature Programming of Microwave-Assisted Synthesis ZnO Nanoneedle Arrays for Optical and Surface-Enhanced Raman Scattering Applications.

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.

Effect of Au film mask on antiwetting and antireflection properties of nanostructural polymer by plasma nanotexturing

Capacitively coupled radiofrequency plasma nanotexturing assisted by an Au film mask is carried out to fabricate the fluorocarbon-film decorated nanowires bundles from the semicrystalline polyethylene (PE) and amorphous PolyMethyl methacrylate (PMMA) subatrates. The spacing distance and height of the nanowires in a bundle on the PE and PMMA substrates are adjusted by the thickness of Au film mask. The complete rebound phenomenon occurs when the droplets impact with a high speed on the nanowire bundles. The nanowire bundles exhibit an improved superhydrophobicity. The narrow spacing distance between the nanowires is beneficial to the antiwetting of superhydrophobic surface. The low reflectivity of the nanowire bundles is also obtained with an incident light wavelength from 400 to 2000 nm. The antireflection property of the nanowire bundles is caused by the high height of nanowires in a bundle. The nanowire bundles on the PE and PMMA substrates prepared by the plasma nanotexturing assisted by the Au film mask have the excellent antiwetting and antireflection properties.

High Anti-Reflection Large-Scale Cup-Shaped Nano-Pillar Arrays via Thin Film Anodic Aluminum Oxide Replication.

Surface anti-reflection (AR) with nanometer-scaled texture has shown excellent light trapping performance involving optical devices. In this work, we developed a simple and lithography-free structure replication process to obtain large scale surface cup-shaped nano-pillar (CSNP) arrays for the first time. A method of depositing was used for pattern transfer based on PMMA pre-coated through-hole anodic aluminum oxide (AAO) thin film (~500 nm), and eventually, the uniformity of the transferred nanostructures was guaranteed. From the spectrum (250 nm~2000 nm) dependent measurements, the CSNP nanostructured Si showed excellent AR performance when compared with that of the single-polished Si. Moreover, the CSNP was found to be polarization insensitive and less dependent on incidence angles (≤80°) over the whole spectrum. To further prove the excellent antireflective properties of the CSNP structure, thin film solar cell models were built and studied. The maximum value of Jph for CSNP solar cells shows obvious improvement comparing with that of the cylinder, cone and parabola structured ones. Specifically, in comparison with the optimized Si3N4 thin film solar cell, an increment of 54.64% has been achieved for the CSNP thin film solar cell.

WS2/p-Si-based photocathodes with high activity originated from the unique vertical geometry of the 2D WS2 nanoplatelets

Earth-abundant two-dimensional (2D) materials-based photocathodes for solar hydrogen production may replace conventional noble metal-based ones when they can be grown with a proper orientation and dimension for efficient charge transfer and catalytic reactions. Here, we show that WS2 films can be grown as wafer-scale films with unique vertically aligned 2H-WS2 nanoplatelets using a single-step vacuum deposition process directly on substrates such as Si wafer and F-doped tin oxide (FTO)/glass. The as-grown WS2/p-Si shows enhanced photocathode performances that are attributed to the unique vertical WS2 nanoplatelet structure, which endows excellent antireflection properties (reflectance as low as ∼ 4%) for enhanced absorption, high photocurrent density (ca. 37 mA cm−2) at low overpotential optimized by controlled vertical length, and catalytically active WS2 edge-sites exposed to the surface for excellent catalytic hydrogen evolution reaction (HER). The results suggest that the nanostructured WS2/p-Si heterostructures are promising multi-functional photocathodes for solar hydrogen production with excellent stability for long-term operation in ambient condition.

Influence of metasurface pit structure on the anti-glare performance of display glass via high-throughput calculation

Recently more and more attentions have been drawn on the anti-glare property of display glass, which is directly related to visual health. However, it is still a big challenge to study the influence of the micron-size metasurface structure on the anti-glare property of glass by way of experiment. In this work, an ideal micron-size metasurface filled with uniform pits was firstly established on the display glass via the theoretical simulation. By using FDTD solutions software, the influences of the diameter (D) and depth (L) of the pits on anti-glare properties, such as reflectance and transmittance, electric field intensity distribution, energy flow density distribution, maximum reflection angle and maximum refraction angle, were investigated detailedly. Results show that a small size (less than 6 μm) of pits can promote the anti-reflectance, transmittance and anti-glare property of display glass. Meanwhile, when the diameter of pits matched well with the depth, namely D = 1/L = 0.3–0.4 μm, or D = 3/L = 0.6–1.1 μm, the color brightness and contrast of display glass were improved largely. The equivalent reflectance and equivalent transmittance can also be calculated at the wavelength of 200–1200 nm by using contour cloud map to find the optimal diameter and depth with good anti-glare performance. The distribution of electric field intensity and energy flow density at the specific wavelength which is equal or close to the size of the pits also help to illustrate the flash point position, and the short-range anti-reflection effect and long-range diffuse reflectance effect of metasurface pit structure. Specially, when the diameter is 3 μm and the depth is 0.6 μm, the maximum reflection angle is 113.8°, the maximum refraction angle is 138.6°, the equivalent reflectance is 3.58%, and the glass shows excellent anti-reflection and anti-glare properties, which make the display glass more comfortable and colorful.

Ultra-Low-Reflective, Self-Cleaning Surface by Fabrication Dual-Scale Hierarchical Optical Structures on Silicon

An integrated functional anti-reflective surface is of great significance for optical and optoelectronic devices. Hence, its preparation has attracted great attention from many researchers. This study combined wet alkaline etching approaches and reactive ion etching (RIE) techniques to create a dual-scale hierarchical anti-reflective surface on silicon substrates. The effect of RIE time on surface morphology and optical performance was investigated using multiple characterization forms. The optimal parameters for the fabrication of dual-scale structures by the composite etching process were explored. The silicon surface with a dual-scale structure indicated excellent anti-reflective properties (minimum reflectivity of 0.9%) in the 300 to 1100 nm wavelength range. In addition, the ultra-low reflection characteristic of the surface remained prominent at incident light angles up to 60°. The simulated spectra using the finite difference time domain (FDTD) method agreed with the experimental results. Superhydrophobicity and self-cleaning were also attractive properties of the surface. The functionally integrated surface enables silicon devices to have broad application prospects in solar cells, light emitting diodes (LEDs), photoelectric detectors, and outdoor equipment.

Boosting photoelectric performance of thin film GaAs solar cell based on multi-objective optimization for solar energy utilization

For enhancing the photoelectric performance of the GaAs photovoltaic cell, the non-dominated sorted genetic algorithm-II (NSGA-II) is employed to solve the multi-objective optimization problem, which consists of the thicknesses of active layer (GaAs) and three anti-reflection (AR) films (TiO2-HfO2-SiO2). Through maximizing (minimizing) the light absorption of photons with energies higher (lower) than the bandgap in the active layer directly and reducing the cost at the same time, the Pareto optimal solution is obtained. An increment in the absorptance, short circuit current and photoelectric conversion efficiency by 50%, 43.4% and 44.9% is achieved by the optimal GaAs solar cell due to excellent AR properties obtained by NSGA-II optimization. We systematically investigate the effects of carrier lifetime, surface recombination velocity, carrier mobility as well as doping concentration on the photovoltaic parameters, and acquire the limitations of these parameters. The strong robustness of the optimal GaAs solar cell enables it to be adapted to wide-angle sunlight incident, and the probability to achieve an absorptance of 0.963 is 97% even if there is a 20% machining error.

Coupled Superhydrophilic PMMA Film with Inverted Pyramid Microstructures for Antireflection and Antifogging Properties

Transparent substrates with antifogging and antireflection ability are of extreme significance for optical devices, because they alleviate performance loss and maintenance costs. Here, we reported that a multifunctional film, with excellent mechanical properties, can be fabricated on the PMMA surface via the micro-transfer printing method. In particular, the synergistic effect of the inverted pyramid microstructure and SiO2 nanoparticles gives the film excellent antireflective, superhydrophilic and antifogging properties, and the silica sol firmly adheres to the PMMA substrate via the silane coupling agent, which exhibits an encouraging prospect of practical applications from lenses for personal and sports eyewear to transparent displays and sensors, etc.

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.

Utilisation of transition metal chalcogenide MoSe2 as promising antireflective coating for achieving intensified light traption

At present scenario, engineering renewable energy sources with the view of attaining maximum efficiency is more important. The current research focusses on the synthesis and deposition of molybdenum diselenide over solar cell surface for achieving maximum light transmissivity.MoSe2 nanostructures synthesised through hydrothermal method exhibit excellent antireflection property. The developed transition metal chalcogenide is pelletised and sputter coated over solar cell substrate at regular intervals. Coated samples were analysed through various characterisation techniques from which S3 sample exhibited minimum light transmittance and electrical resistivity. The MoSe2 coating with 648 nm thickness reported maximum power conversion efficiency of 19.45 %.

Fabrication of antireflective hydrophobic periodic micro-hole structures on ZnS surface by femtosecond laser direct writing

ZnS has a promising wide range of applications in optical and optoelectronic areas. But the Fresnel reflection on ZnS surface reduces the transmittance of light and causes an obstacle in its applications. Thus, it is crucial to minimize the Fresnel reflection to promote the antireflection property. This paper demonstrates an effective way to fabricate antireflective periodic micro-hole structures on ZnS surface by femtosecond laser direct writing. The effects of laser power, scanning speed on the morphology of the holes are investigated. The fabricated structures exhibit an excellent antireflection property, and achieve more than 30% decrease in reflectance in the near-ultraviolet spectral wavelength range and near-infrared spectral region (200-800 nm), reducing 35% in 280 nm, especially. Besides, the prepared surface demonstrates effective performance concerning hydrophobicity with a contact angle of 107.4°, and the contact angle of unprocessed ZnS is 96.2°. These results show that the femtosecond laser can induce the antireflection and hydrophobic properties on the surface of ZnS, which has a potential application in outdoor optical and optoelectronic devices.

Hot embossing of moth eye-like nanostructure array on transparent glass with enhanced antireflection for solar cells

Antireflection (AR) silicon and glass surfaces are necessarily required for solar cells, because a reflective silicon solar cell with a glass covering will reflect a percentage of sunlight. In this work, we demonstrate a universal and scalable net-shape nanofabrication method for broadband nanostructured AR surface on transparent glass, intended for solar cell applications. Moth eye-like glass nanopillars with various diameters were successfully fabricated by a combination of precision hot embossing and ultrasonic vibration demolding process. The morphologies of nanopillars were detected to characterize different profiles formed by glass flow at elevated temperatures. Facile optical experiments were designed and conducted to measure the AR performance at varying wavelengths and angle of incidences and the proposed nanostructures exhibit excellent AR property. Additionally, a feasible optical modeling is developed and compared with the measurement to evaluate the theoretical optical behaviors of glass nanostructures based on their embossed shapes. The inexpensive and environmental hot embossing method with ultrasonic vibration demolding is expected to create AR glass nanostructured surfaces for widespread applications such as solar cells, displays and laser systems.