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Antireflective Coatings for Glass and Transparent Polymers
Abstract
Antireflective coatings (ARCs) are applied to reduce surface reflections. We review coatings that reduce the reflection of the surface of the transparent substrates float glass, polyethylene terephthalate, poly(methyl methacrylate), and polycarbonate. Three main coating concepts exist to lower the reflection at the interface of a transparent substrate and air: multilayer interference coatings, graded index coatings, and quarter-wave coatings. We introduce and discuss these three concepts, and zoom in on porous quarter-wave coatings comprising colloidal particles. We extensively discuss the four routes for introducing porosity in quarter-wave coatings through the use of colloidal particles, which have the highest potential for application: (1) packing of dense nanospheres, (2) integration of voids through hollow nanospheres, (3) integration of voids through sacrificial particle templates, and (4) packing of nonspherical nanoparticles. Finally, we address the remaining challenges in the field of ARCs, and elaborate on potential strategies for future research in this area.
... When antireflection properties are needed over a wide wavelength range or wide angles of incidence light, special multilayer coatings have to be designed. [15] When very low reflectance at one wavelength is needed, a stack of low and higher refractive index material layers of /4 optical thickness are used. The optimal ratio of the refractive indices of the materials is dictated by Equation 3, when light propagates from air to the material with a low refractive index (n L ) and then to the material with a higher refractive index (n H ). For example, in the case of a glass substrate and MgF 2 as the low-index material, the refractive index of the other material should be 1.70. ...
... The optimal ratio of the refractive indices of the materials is dictated by Equation 3, when light propagates from air to the material with a low refractive index (n L ) and then to the material with a higher refractive index (n H ). For example, in the case of a glass substrate and MgF 2 as the low-index material, the refractive index of the other material should be 1.70. [15] Figure 2 illustrates the refractive indices of some metal fluoride and oxide thin films at different wavelength ranges. ...
Metal fluoride thin films are important materials in a multitude of applications. Currently, they are mostly used in optics, but their potential in energy harvesting and storage is recognized as well. Atomic layer deposition (ALD) is an advanced thin film deposition method that has an ever‐increasing role in microelectronics. The assets of ALD are its capability to produce uniform, stoichiometric, and pure films with precise thickness control even on top of complicated structures, such as high aspect ratio trenches. These characteristics can be beneficial in applications of metal fluoride thin films but so far ALD of metal fluorides has remained much less studied and used than ALD of metal oxides, nitrides, sulfides, and pure metals. This review aims to motivate research on ALD of metal fluorides by surveying potential applications for ALD metal fluoride thin films and coatings. The basics of luminescent applications, antireflection coatings, and lithium‐ion batteries will be discussed. Next, the fundamentals of ALD will be presented followed by a comprehensive summary of the metal fluoride ALD processes published so far.
... A solar glass with a low iron content is commonly used as the top cover of PV modules with a transmittance of approximately 91%-92% [2]. This means that around 8%-9% of light is reflected between the two surfaces of the cover glass due to the difference in refractive index of the air and the cover glass [3]. Consequently, the use of a cover glass significantly reduces the efficiency of the solar cell. ...
... In addition to SiO 2 passivating the surface of glass, it exhibits a high scratch resistance and chemical stability at high temperatures, while TiO 2 is known for its chemical stability, mechanical hardness, and low moisture absorption [16]. Thus, the refractive index can be tuned by applying a coating SiO 2 -TiO 2 [3]. Several techniques have been used to deposit SiO 2 /TiO 2 films such as sputtering, chemical vapor deposition (CVD), atomic layer deposition (ALD), chemical spray pyrolysis (CSP), and pulsed laser deposition (PLD) [17,18]. ...
... Over the course of the last century, synthetic polymers have revolutionized our daily lives. The profound impact of synthetic polymers on various aspects of modern life such as medical implants [1,2], food packaging [3,4], coatings [5][6][7][8], automotive parts [9,10], cosmetics [11][12][13], drug delivery [14,15], and many others [16,17], and emphasizes the growing interest in stimuli-responsive (smart) polymers. The development of stimuli-responsive (smart) polymers is of broad interest because of their ability to respond to changes in the local environment, such as light [18,19], heat [20], pH [21][22][23], and mechanical force [24][25][26]. ...
... Reprinted with permission from ref. [83]. 6 Advances in Polymer Technology to 50°C. However, the reformed Eu3+ emission was recovered upon cooling ( Figure 10). ...
The widespread discourse on the circular economy has fueled a growing demand for polymeric materials characterized by mechanical robustness, sustainability, renewability, and the ability to mend defects. Such materials can be crafted using dynamic covalent bonds, albeit rarely or more efficiently through noncovalent interactions. Metal–ligand interactions, commonly employed by living organisms to adapt to environmental changes, play a pivotal role in this endeavor. Metallosupramolecular polymers (MSPs), formed through the incorporation of metal–ligand interactions, present a versatile platform for tailoring physicochemical properties. This review explores recent advancements in MSPs achieved through the assembly of (macro)monomers via reversible metal–ligand interactions. Various strategies and pathways for synthesizing these materials are discussed, along with their resulting properties. The review delves into the stimuli-responsive behavior of coordination metal–ligand polymers, shedding light on the impact of the core employed in MSPs. Additionally, it examines the influence of parameters such as solvent choice and counter-ions on the supramolecular assemblies. The ability of these materials to adapt their properties in response to changing environmental conditions challenges the traditional goal of creating stable materials, marking a paradigm shift in material design.
... Furthermore, carefully designing the photonic elements of ARCs (such as materials, geometry, and arrangement) provides the opportunity to enable control of the scattering, polarization, angle dependence, and light propagation within Si PV modules. [17][18][19][20] Previous reports to this attempt includes ARC having photonic elements of inverted pyramids, moth-eyes, nanopillars, micro-nanoporous inclusion, photonic crystals, and micro-lens. [14][15][16][17][18][19][20] Most of them are demonstrated in laboratory scale and do not have rigorous explanation of effectiveness for such improvement as well as feasibility especially when translating to larger-scale PVs. ...
... [17][18][19][20] Previous reports to this attempt includes ARC having photonic elements of inverted pyramids, moth-eyes, nanopillars, micro-nanoporous inclusion, photonic crystals, and micro-lens. [14][15][16][17][18][19][20] Most of them are demonstrated in laboratory scale and do not have rigorous explanation of effectiveness for such improvement as well as feasibility especially when translating to larger-scale PVs. ...
Antireflective coating helps to reduce reflectance losses, thereby improving photovoltaic (PV) efficiency. Improving PV efficiency while maintaining low innovation cost has been a challenging task for the PV industry, especially in the case of monocrystalline silicon. Herein, the feasibility of integrating polydimethylsiloxane foil onto the protecting glass of an n‐type tunnel oxide–passivated contact silicon cell is studied. The foil is made using a polymer molding technique with digital video disk templates. On average, the foil provides 5.2% total reflectance and 93.5% total transmission. Under 1 sun illumination, the cell's power‐conversion efficiency increases by 12% (among the highest improvement), from 17.3% to 19.3%, in the presence of foil. A combined set of optical spectroscopy and simulation data shows that this improvement is due not only to the index‐matched medium, but also to forward scattering that increases broadband light transmission to the silicon cell through the foil which is different to the prevalent light‐trapping mechanism. The foil is also evaluated under different illumination conditions (indoors and outdoors), which show that the cell's power output nearly doubles at dimmer illumination levels and is stable under a fluctuating light source. While effective, the feasibility of antireflective foil should be reexamined further.
... Antireflection (AR) coatings are widely used to reduce the reflection and increase transmission in a wide range of industries [1,2] such as displays, buildings, lenses, and photovoltaics. Reflection is usually undesirable because of its detrimental effects on optical systems. ...
... Sol-gel process produced antireflection coatings are frequently made of a packing of silica nanoparticles [2,11,[18][19][20]. Hollow silica nanospheres are one of the most promising materials for antireflection coatings [3,4,15,[21][22][23][24], due to their ultra-low refractive index, outstanding chemical stability, corrosion and heat resistance, and significant hardness. ...
Fabrication parameters of antireflection films made of spin coating hollow SiO2 nanospheres were investigated. The film thickness, film morphology and optical properties of the antireflection films were observed dependent on speed of spin coating. With a proper coating speed to produce film of desirable thickness, the antireflection film shows transmittance of 98.7% at λ = 550 nm. We applied a two-step coating to serve as an alternative way for fabrication of hollow SiO2 nanospheres antireflection films. For the antireflection films made by the two-step coating, a relatively improved uniformity in surface morphology and decrease in diffuse reflectance were found. The results suggest using the two-step coating method can be beneficial for uniformity in film morphology and optical properties of the antireflection films.
... In order to further increase the transmittance of light, while reducing reflectance to a minimum, different strategies have been employed. These strategies rely on depositing thin film ARC on the surface of the material, as well as modifying their surface roughness by creating micro and nano-structures or generating nano-particles on the surface [5]. Thin film ARC are made of single-layer or multi-layer films with different refractive indices (RI), which reduces the reflection due to the destructive interference of the multiple wavefronts reflected at each interface [6,7]. ...
... Multilayer ARC have been applied to glass optics for decades [5,8], with TiO 2 and SiO 2 being the most used materials, which are typically stacked in a layered structure with other materials such as ZnO, WO 3 , Cr 2 O 3 , VO 3 , Al 2 O 3 , and MgF 2 [9]. On the other hand, studies that describe ARC on polymer substrates report that these systems may present thermal limitations, due to the low vitric point of the substrates, and that they also can interact with plasma which can lead to adhesion modifications [8]. ...
In this work, we investigated the transmission enhancement of a polycarbonate substrate (PC) at the beginning of
the near-infrared part of the electromagnetic spectrum, by incorporating anti-reflective coatings (ARC) on the
surface. Thin film ARC formed by combining layers of SiO2, TiO2, and SiNx were studied, and the influence of the
layers thickness on the optical response of the systems was explored, with the objective of keeping the fabrication
process simple, while maintaining high levels of light transmission. Moreover, we compare the results obtained
with the thin film ARC with those for a more complex system formed by a hexagonal array of nanopillars.
Transmission values close to 100% were theoretically predicted for both systems and experimentally measured
with the thin film ARC. Additionally, we report a superamphiphilic behaviour for the thin film ARC studied
experimentally, after contact angle measurements, which renders self-cleaning properties to the surface of the
systems.
... This method enhances transmittance by alternately stacking materials with low and high refractive in-dices. The PVD method achieves excellent quality by finely adjusting the thickness of the deposition sample [19,20], allowing precise control of the refractive index. However, vacuum deposition, a key aspect of PVD, is costly, significantly increasing the price of cover glass materials. ...
Currently, coating with anti-reflective materials is an attractive approach to improve the quality of screen-based displays. In this study, mesoporous silica particles were systematically synthesized as a function of surfactant (i.e., CTAC-cetyltrimethylammonium chloride) concentration to serve as main coating fillers possessing low refractive indices. Precisely changing the amount of the CTAC surfactant, silica sol with an average diameter of 50 nm exhibits distinctively different specific surface areas, pore size, and pore volume. Prior to the preparation of final coating solutions containing these silica particle fillers, the percentage of solid content was optimized on a glass slide. The use of 50 wt% solid content exhibited the highest transmittance of light. Among various content levels of silica sol, the use of 3.5 wt% of silica particles in the solid content displayed the highest transmittance (i.e., best anti-reflectiveness). Under the almost identical coating layers prepared with the fixed amount of silica particles possessing different surface areas, pore size, and pore volume, it appears that the largest pore volume played the most important role in improving the anti-reflective properties. Experimentally understanding the key feature of low-refractive filler materials under the optimized conditions could provide a clear view to develop highly effective anti-reflective materials for various display applications.
... According to the optical theory, the holes could not result in obvious Mie scattering of visible light because their size was smaller than 80 nm. [39] The oblique-sectional SEM images could better display the internal nanostructure of composite coatings. In the first row of Figure 5, obvious lamellar nanostructure and cavities coexisted in all the three composite coatings. ...
Developing siloxane‐based coatings with excellent water vapor barrier ability is of great importance due to their wide applications for various optical‐related fields. To improve the water vapor barrier ability of polysilsesquioxane coatings, this research proposes a strategy of introducing carbon quantum dots (CQDs) into organic‐bridged polysilsesquioxane coatings to enhance their water vapor barrier property. The CQDs are prepared by the pyrolysis of citric acid and then the composite coatings are prepared by thioether‐ester‐bridged silsesquioxane precursor in situ hydrolysis and condensation in the presence of CQDs. The experimental results show that the CQDs disperse well in the polysilsesquioxane matrix which is conducive to provide long diffusion pathway of water vapor molecules and also introduce individual “bubble pores” into the composite coatings. Thus‐obtained composite coatings not only show fivefold enhancement in water vapor barrier ability compared to the polysilsesquioxane coating without CQDs, but also perform good light transparence and good UV radiation‐resistant property, which would satisfy the requirements of optical‐related moisture‐resistant application fields.
... Three primary applications of HRIPs are as follows: (1) thin film coating/layer applications, (2) self-standing lenses, and (3) optical waveguides. Thin-film applications include encapsulants for organic light-emitting diodes (OLEDs), 15,16 microlenses for charge-coupled devices (CCDs), complementary metal oxide semiconductors (CMOS), 17 and antireflective coatings, 18 all of which are generally used in the visible light region and require thin, high-RI coatings/lenses to improve device efficiency and reduce film thickness. Because such materials are used in thin film states, transparency should be guaranteed with a few-micrometer thickness, but ultrahigh RI exceeding 1.71.8 is required from RI-matching aspects. ...
High refractive index polymers (HRIPs) are essential materials for many optical applications, including organic light-emitting diodes (OLEDs), charge-coupled devices (CCDs), complementary metal oxide semiconductors (CMOS), eyeglasses, and optical waveguides. Various molecular designs, synthetic routes, and material preparation methods have been reported to increase the refractive index (RI) of polymers; however, increasing the RI using only organic (and classical) components is difficult. Other properties, such as low or high Abbe numbers (RI dispersion), low birefringence, and high transparency, are also required for HRIPs depending on the intended wavelength usage, which ranges from visible to infrared (IR) light and X-ray applications. This review summarizes the recent developments in HRIPs, including their synthesis, properties, and applications, and provides future prospects for achieving HRIPs with the desired performances.
... AR coatings based on ''Moth-eye'' and multiple interference films have been investigated, and several techniques to produce them have already been demonstrated [106,107]. These and other results are fascinating; however, as PVs should withstand weathering for at least a few decades, it is fundamental to investigate the durability of these coatings under the most distinct climatic and meteorological conditions and specific conditions caused by regionally located situations. ...
... Polycarbonate (PC) has become one of the most widely used optical plastic materials because of its high transmittance, outstanding impact resistance, good temperature resistance and excellent toughness [1][2][3][4]. For shatterproof glass, eyeglasses, optical lenses and other optics that need to improve sunlight transmittance while reducing sunlight reflection, one of the best methods to increase the effectiveness of light usage is to apply antireflective (AR) coatings on the surface of optical components [5][6][7]. Different physical and chemical techniques have been employed to prepare antireflective coatings, including chemical vapor deposition [8], vacuum vapor deposition [9], nanoscale etching [10], layer-by-layer assembly [11] and sputtering [12]. However, the application of AR coatings is limited by the particular equipment, environmental requirements and intricate operating procedures required for these methods. ...
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.
... AR coatings based on "Moth-eye" and multiple interference films have been investigated, and several techniques to produce them have already been demonstrated [90,91]. These and other results are fascinating; however, as PVs should withstand weathering for at least a few decades, it is fundamental to investigate the durability of these coatings [92,93]. ...
... [13][14][15][16][17][18][19][20][21][22] The main energy loss in transforming solar energy into electrical energy is attributed to the Shockley-Queisser (S-Q) limit, i.e., non-absorption of low-energy photons and the thermal loss of high-energy photons. [2,23] The optical loss occurred due to the photons that cannot be gathered by the perovskite layer or converted into photo carriers. Consequently, this loss has a lasting impact on light absorption and photocurrent (J ph ) of the active layer of PSCs. ...
It is anticipated that perovskite solar cells (PSCs) will overtake other products in the market for next‐generation photovoltaics. The optical loss, however, continues to be a flaw that restricts the photocurrent (Jph) of PSCs. Mesoporous antireflection coatings (ARCs), both monolayer and multilayer, are designed using a combination of the finite element method and equivalent medium theory, and ARCs models are merged with PSCs. In the current work, mesoporous ARCs are made, the optical performance of the device is evaluated using optical modeling, and then the ARCs are integrated into solar cells. The simulation results show that the Jph of planar inverted PSCs can increase to 24.00 mA cm−2 when the front surface of PSCs adopts mesoporous ARC (via parameter optimization and sensible arrangement and combination). An increase of 0.98 mA cm−2 in Jph of PSCs is observed in comparison with flat ARC (23.02 mA cm−2). The strong light transmission and low reflection properties of the mesoporous ARCs are confirmed by the optimized solution. It is important to note that the first fusion of mesoporous and multilayer ARC offers a fresh approach to the development of perovskite and perovskite/silicon tandem solar cells with extremely high efficiency. Numerical simulation techniques are utilized to design mesoporous antireflective coatings with exceptional light‐trapping properties. By optimizing the material, size, and arrangement of the coatings, perovskite solar cells with mesoporous antireflective coatings on their front surface exhibit superior optical performance compared to conventionally structured planar perovskite photovoltaic devices. These findings present a viable strategy for creating ultrahigh‐performance photovoltaic devices.
... Dans ce cas, l'empilement consiste en une succession de couches d'indice de réfraction élevé puis faible disposant chacune d'une épaisseur bien spécifique (Fig.I.11.b). Des interférences destructives sont alors générées sur un plus large domaine spectral, améliorant l'efficacité de l'effet antireflet [73]. Toutefois, optimiser un traitement multicouche s'avère complexe. ...
De nos jours, des matériaux innovants sont de plus en plus recherchés pour créer de nouveaux traitements photoniques différenciants. La nanostructuration des couches minces, omniprésente dans notre quotidien (médical, biomimétisme), est un moyen de rupture technologique. L’étude des propriétés optiques contrôlées par la nanostructuration de surface via la technique de dépôt PVD en incidence oblique (Oblique-Angle Deposition) est principalement adressée dans cette thèse. Cette technologie efficace et originale forme des architectures 3D nanoporeuses utilisées dans de nombreux domaines d’application (biomatériaux, capteurs). Son avantage majeur réside dans la grande modularité des indices de réfraction accessibles par un contrôle précis de la porosité des couches via les conditions de dépôt. La morphologie du film peut également être influencée en changeant l’orientation du porte-échantillons in situ lors du dépôt, ce qui permet de contrôler l'indice de réfraction dans les trois dimensions de la couche. Les films résultants sont complexes (anisotropie, gradients de porosité, diffusion) et nécessitent donc une caractérisation optique avancée. Des moyens uniques d’élaboration ont permis de contrôler précisément la croissance des nanostructures et de développer de nouvelles morphologies.De parfaites corrélations ont été démontrées entre nanostructures et propriétés optiques. La diffusion de ces nanostructures a également été étudiée par éléments finis pour optimiser les performances optiques des traitements de surface. Leur empilement a été maitrisé, ce qui a permis de les intégrer dans des designs multicouches de fonctions optiques nouvelles ou existantes de hautes performances. Les traitements antireflets large bande dans le Visible-SWIR, de 400 à 1800 nm, ont été optimisés en développant leur omnidirectionnalité.L’ensemble du travail a permis d’élargir l’utilisation de la technique OAD à une nouvelle application : les filtres polarimétriques.
... These coatings are designed to offer innovative functions such as antibacterial, self-cleaning, self-healing, super-hard, solar reflecting, pollutants removal, anti-ultraviolet (anti-UV) radiation, super hydrophilic behaviour, and radar absorption for desired end-user applications. Numerous aggressive substances have the potential to disrupt coating performance (Buskens et al. 2016;Deng et al. 2011;Yang et al. 2019). Giving coatings multifunctional character is a relatively new way of reducing or resolving many of these issues, and as a consequence, coatings now respond adequately to environmental changes, mechanical or chemical damage, and other threats. ...
... To ensure a high transmittance of light, low-refractive nanoporous singlelayer films are applied to the glass. For example, the literature discusses optical single-layer quarter-wave antireflection coatings based on nanoporous silicon dioxide obtained from sol compositions of a special chemical content, and also considers the technological parameters of the coating process and the temperature regime of gel annealing [10][11][12][13][14][15][16][17][18]. ...
In this work, nanoporous antireflective coatings on silicate glass were obtained from silicon dioxide sol compositions by the sol-gel method in the presence of quaternary ammonium salt (tetrabutylammonium bromide) at different annealing temperatures (200–250 °C). Varying the salt concentration from 3 to 5 wt.%, we achieved the transmittance of the coatings of about 97% at 250 °C in comparison with 91% for clean glass in the wavelength range from 400 to 1100 nm. The addition of gold nanoparticles to the composition containing 5 wt.% tetrabutylammonium bromide allowed us to decrease the annealing temperature to 200 °C, preserving the transmittance at the level of 96.5%. For this case, the optimal concentration of gold nanoparticles is determined (2.6 × 10⁻⁹ mol/mL). According to the SEM analysis, the obtained antireflective coatings contain pores with a minimum area size up to 4 nm².
... Polymers with high values of refractive index (n D ), particularly n D > 1.60, have a wide range of applications, including antireflection coatings, [1,2] optical lenses, [3] light-emitting diodes, [4][5][6][7] 3D printing materials, [8,9] and nanoimprinting materials, [10][11][12][13][14] and there is great interest in the development of higherrefractive-index polymers. ...
We examined the radical polymerization of 2,4,6‐triiodophenyl acrylate (TIPA), the chain‐transfer radical polymerization of TIPA in the presence of 4,4‐thiobisbenzenethiol (TBBT) or 4‐mercaptopyridine (MP), and the radical copolymerization of TIPA with 2‐hydroxyethyl acrylate (HEA) or 2‐(2‐ethoxyethoxy) ethyl acrylate (EEA), using AIBN as an initiator at 60 °C for 20 h. These reactions afforded poly(TIPA), TBBT‐poly(TIPA)m, MP‐poly(TIPA)m poly(TIPAm‐co‐HEAn) and poly(TIPAm‐co‐EEAn), respectively, with Mn values in the range of 3,180 to 46,550, in satisfactory yields. MP‐poly(TIPA)41 (Mn=6,880), poly(TIPA88‐co‐HEA12) (Mn=11,300), and poly(TIPA85‐co‐EEA15) (Mn=19,200) showed film‐forming ability, although poly(TIPA) and TBBT‐poly(TIPA)m did not. Among them, poly(TIPA85‐co‐EEA15) showed high values of refractive index (n) and Abbe number (ν), i. e., n=1.850 and ν=20.7.
... Each film in a coating must have its refractive index in between that of the substrate and the ambient and thus a large range of materials can be required for the coatings to be effective over a significant bandwidth. Porous layers formed by leeching or by coating have also been demonstrated as films of adjustable refractive index [2,[6][7][8]. Surface structuring is an alternative method whereby structures (typically sub-wavelength) are formed on the surface of the substrate either by etching or by coating [5,[9][10][11][12]. ...
A method for producing large-area, broadband, quasi-omnidirectional low-reflectivity glass surfaces is presented. Using block copolymer patterning and inductively coupled plasma etching, near-periodic arrays of pillars are formed in glass. The patterned surface has reflectivity < 0.5%—almost an order of magnitude smaller than plain glass—with a bandwidth of ∼300 nm. Substrates etched on both sides transmit > 99.5% across the wavelength range 850–1200 nm, with > 99% down to λ = 650 nm. The process is demonstrated on a 5 cm diameter fused silica wafer and high transmittance is maintained up to at least 70∘ incidence. The resulting substrates might find application as lab optics (windows, lenses, etc) display screens for televisions, computers, phones, and as encapsulants for optoelectronic devices.
Antireflective (AR) coatings are indispensable for optimizing light energy capture in transparent materials and mitigating glare-induced hazards. However, current nanoporous coatings suffer from small pore sizes (2–10 nm) that are...
The chapter titled, “Optical and Photonic Applications,” describes the numerous and vital functions that thin films play in the domains of optics and photonics. In this chapter, various uses of thin films including antireflection coatings, optical filters, mirrors, and photovoltaics are explained. Reflective coatings are necessary mostly antireflective to reduce the amount of light that is reflected back by the optical surface and increase the amount that is transmitted through lenses and other optical parts. Multilayer thin films used in optical filters permit or reject certain wavelengths of light which is vital in imaging as well as telecommunication. Moreover, the chapter explores the application of thin films in the construction of mirrors especially in delivering high reflectivity and at the same time improving their life span. Thin films are used in photovoltaics to produce high-performing solar cells by changing sunlight into electricity in a more efficient and economical way. In this chapter, the authors illustrate detailed descriptions of these applications which unveiled the role of thin film as a central factor in the progression of the optical and photonic elements, stimulating advancement and enhanced performance in numerous devices and systems. The discussed information provides a deep insight into the possibilities of thin-film applications in modern optical and photonic engineering.
Feynman's statement, “There is plenty of room at the bottom”, underscores vast potential at the atomic scale, envisioning microscopic machines. Today, this vision extends into 3D space, where thousands of atoms and molecules are volumetrically patterned to create light‐driven technologies. To fully harness their potential, 3D designs must incorporate high‐refractive‐index elements with exceptional mechanical and chemical resilience. The frontier, however, lies in creating spatially patterned micro‐optical architectures in glass and ceramic materials of dissimilar compositions. This multi‐material capability enables novel ways of shaping light, leveraging the interaction between diverse interfaced chemical compositions to push optical boundaries. Specifically, it encompasses both multi‐material integration within the same architectures and the use of different materials for distinct architectural features in an optical system. Integrating fluid handling systems with two‐photon lithography (TPL) provides a promising approach for rapidly prototyping such complex components. This review examines single and multi‐material TPL processes, discussing photoresin customization, essential physico‐chemical conditions, and the need for cross‐scale characterization to assess optical quality. It reflects on challenges in characterizing multi‐scale architectures and outlines advancements in TPL for both single and spatially patterned multi‐material structures. The roadmap provides a bridge between research and industry, emphasizing collaboration and contributions to advancing micro‐optics.
Fluoropolymers possess among the lowest indexes of refraction for dense, continuous materials, but their crystallinity typically leads to light scattering and haze. In this work, we studied poly(1H,1H,2H,2H-perfluorodecyl acrylate) (pPFDA) as a low-index fluoropolymer and successfully suppressed its crystallization while preserving its desirable low index of refraction (1.36 at 633 nm wavelength) and hydrophobicity (water contact angle of 122°). This was achieved through copolymerization between the hydrophobic 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) and N-vinylpyrrolidone (NVP) using initiated chemical vapor deposition (iCVD). The resulting copolymer p(PFDA-co-VP) film was smooth (roughness <2 nm), highly transparent, thermally robust, and mechanically flexible. This contrasted with pPFDA homopolymer films, which were rough (roughness >30 nm), hazy, and disintegrated at 70 °C due to melting. Moreover, the copolymerization resulted in a 16-fold improvement in the deposition kinetics. To demonstrate its excellent performance in practical applications, the low-index copolymer was paired with a high-index poly(divinylbenzene) (pDVB) (n633 = 1.59) to build a six-layer interference coating. A six-layer fully polymeric interference coating with precise, independent control of each individual layer’s thickness was prepared for the first time by iCVD. Optimized for broadband antireflection, it reduced the surface reflectance to 1% over the entire visible spectrum, while withstanding large mechanical strain.
Superhydrophobic surfaces have attracted tremendous attention due to their intriguing lotus‐leaf‐like water‐repelling phenomenon and wide applications, however, most superhydrophobic coatings are prepared with environmentally unfriendly organic solvents and suffer from poor mechanical strength. To solve these issues, waterborne recoatable superhydrophobic (WRSH) coatings are developed based on a novel self‐synthesized water‐soluble fluorinated acrylic polymer and hydrophobic modified silica nanoparticles. The trade‐off between waterborne and superhydrophobicity is well mediated by protonation and deprotonation of the fluorinated acrylic polymer. When the coating is damaged, it can be easily repaired and recoated using WRSH coatings without the need to remove the damaged superhydrophobic layer, providing a sustainable and environmentally friendly solution for maintaining a superhydrophobic surface. The coating exhibits good mechanical properties with the WRSH coating maintaining mechanical stability even after abrasion with 2000 mesh sandpaper for 20 m or impact from 100 g of sand. Additionally, the visible light transmittance of WRSH coating glass reaches as high as ≈94.0%, which is superior to the bare glass of ≈91.7%. Moreover, the WRSH coatings exhibit excellent self‐cleaning performance and anti‐dust performance when applied on solar panels.
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.
Antireflective coatings play an important role in various optical devices. Herein, we developed omnidirectional antireflective coatings fabricated with charged chitin nanofibers (ChNFs) through layer-by-layer (LbL) self-assembly technology. The charged ChNFs were prepared from chitin with modifications of esterification (negatively charged) and esterification followed partial deacetylation (positively charged), respectively, through ultrasonic treatment. The effects of concentration of the ChNF suspensions and number of bilayers on thickness, refractive index and antireflective capacity of the ChNF coatings were investigated. Refractive index of the ChNF coatings can be manipulated by changing concentration of the ChNF suspensions. Thickness of the ChNF coatings depends on number of bilayers and concentration of the ChNF suspensions. The ChNF coating on a glass substrate with 5 bilayers fabricated using the suspensions with concentration 0.1% had a refractive index of 1.36 and yielded 4% gain in transmittance compared to the glass at the wavelength of 550 nm. This work demonstrates that charged ChNFs are promising building blocks to fabricate antireflective coatings on large size substrates with high efficiency and low cost through LbL self-assembly.
In this paper, a sol–gel method was adopted, using tetraethyl orthosilicate (TEOS) as a precursor, to prepare hollow silica spheres through alkali-catalyzed sol, and further to form a long-chain structure through acid catalysis. The alkali-aluminosilicate glass is coated with hollow silica spheres by a dip coating method, and the anti-reflection (AR) nanostructured silica coatings with different thicknesses and porosities are obtained. The prepared hollow silica spheres have an inner diameter of 20 nm and a wall thickness of 6–20 nm. The average transmittance of the coating at normal incidence within the wavelength range of 300–900 nm is between 94 and 96.9%, a great improvement compared with 91.8% of the substrate. Hollow spherical and long-chain structure of silica is conducive to film formation on the glass surface and endows the film with a high mechanical strength. After 60 friction cycles, the average transmittance is only decreased by 0.6%.Graphical abstract
Industries and researchers have been continuously advancing the coolants and lubricants that cope up with the industrial demand in terms of performance, quality and cost without compromising the sustainability requirements like eco-elimination, operator friendly, easier maintenance, treatment, etc. This work discusses the efficacy of nanoparticle-based enhancement in the performance of cutting fluids. Furthermore, it discusses the preparation, lubrication, heat transfer mechanisms, application method and performance of different nano-enhanced lubricants and/or coolants. It also discusses synergistic relationship analysis among various process variables, physicochemical properties, machining mechanisms, and performance. Finally, the future development directions are put forward aiming at current performance limitations of these nano-cutting fluids, which can be taken up for further research.
A design of coating with single, double, and three-layers for allyl diglycol carbonate (CR-39) spectacle lenses has been done. The coating included anti-reflection (AR) layers for back and front surfaces which allow the transmission to reach 99 % of incident light on the eye. This design shows spectacle lenses of higher contrast images, decreasing ghost images, and little driving glare at night as well as more cosmetic. The anti-reflection layers increased scratch resistance, and cleanability, and make lenses nearly invisible and durable Keywords: AR coating, thin-film coating, plastic glasses, hard multi-coating.
Siloxane-based hybrid materials with lamellar nanostructure have great potential to be water vapor barrier layer for electronic devices and photovoltaic cells encapsulation. Improving water vapor barrier ability was still a big challenge. This research article proposed a facile one-pot methodology to prepare vesicles/lamellae mixed matrix organic-bridged polysilsesquioxane (BPSQ) composite coatings with excellent water vapor barrier performance. The composite coatings were fabricated from three thioether-ester-briged silsesquioxane by sol-gel method in the presence of phytic acid. Phytic acid not only acted as catalyst to catalyze the hydrolysis and condensation reactions of silsesquioxane precursors, but also formed vesicles in ethanol solution. Experimental evidence demonstrated that vesicles size mainly influenced the barrier property of composite coatings, and with bigger vesicles, the composite coating showed 10-fold enhancement in water vapor barrier ability compared to the corresponding BPSQ coating with only lamellar nanostructure. Moreover, the vesicles/lamellae composite coatings displayed outstanding transparency and flexibility which would meet the requirements of optical related moisture resistant application fields.
Developing siloxane-based hybrid coatings with excellent water vapor barrier performance remains a great challenge. The water vapor barrier ability of siloxane-based coatings can be effectively improved by tailoring the chemical structure of silane precursors. In this article, three thioether-ester-bridged polysilsesquioxane (BPSQ) coatings were fabricated from bridged silsesquioxane precursors by sol-gel method involving hydrolysis and condensation reactions. The bridged silsesquioxane (BSQ) precursors were synthesized by (3-mercaptopropyl)trimethoxysilane (MPTMS) and reagents with molecular structure containing C=C groups via a facile thiol-ene click reaction. Experimental evidence obtained from FT-IR and NMR techniques confirmed the bridged molecular structure of BSQ precursors. The results obtained from XRD, SEM and TEM proved that the BPSQ coatings had short range ordered and long range disordered lamellar structure parallel to the substrate. These lamellar BPSQ coatings performed better water vapor barrier ability with WVTR of 3 ~ 7 g·cm⁻²·d⁻¹ in comparison to polymer and silica-based hybrid coatings. Of them, MA-BPSQ coating performed the best water vapor barrier ability. The chemical structure of bridged organic chain had great effect on the distance of lamellar nanostructure, which played a key role in improving water vapor barrier property of BPSQ coatings.
Moth-eye nanostructures are amongst the most remarkable surfaces in nature because of their multi-functionality including antireflection, self-cleaning and bactericidal ability. Moth-eye surfaces consist of subwavelength arrays of tapered nanostructures that are challenging to reproduce artificially. Nanoimprint lithography is probably one of the most suited technologies for this purpose. However, the poor mechanical resilience and durability of the polymeric nanocones when exposed to the environment, hinders their use in actual applications. To overcome these limitations, this work demonstrates the use of a thin oxide coating over the polymer moth-eye features imprinted on poly methyl methacrylate (PMMA) films. Particularly TiO2 conformal thin film coatings are deposited by unipolar pulsed dc magnetron sputtering over the antireflective nanopatterns acting as encapsulant. The coating, while preserving the antireflective properties, protects the nanostructures against mechanical scratching and improves substantially their thermal stability to over 250 oC. Furthermore, the TiO2 layer provides additional photoinduced self-cleaning functionality and at the same time it protects the matrix from UV photodegradation. The robust and durable antireflective surfaces developed here may find application on solar cells covers, flat panel displays or on optical components.
This paper reviews the current progress in mathematical modeling of anti-reflective subwavelength structures. Methods covered include effective medium theory (EMT), finite-difference time-domain (FDTD), transfer matrix method (TMM), the Fourier modal method (FMM)/rigorous coupled-wave analysis (RCWA) and the finite element method (FEM). Time-based solutions to Maxwell's equations, such as FDTD, have the benefits of calculating reflectance for multiple wavelengths of light per simulation, but are computationally intensive. Space-discretized methods such as FDTD and FEM output field strength results over the whole geometry and are capable of modeling arbitrary shapes. Frequency-based solutions such as RCWA/FMM and FEM model one wavelength per simulation and are thus able to handle dispersion for regular geometries. Analytical approaches such as TMM are appropriate for very simple thin films. Initial disadvantages such as neglect of dispersion (FDTD), inaccuracy in TM polarization (RCWA), inability to model aperiodic gratings (RCWA), and inaccuracy with metallic materials (FDTD) have been overcome by most modern software. All rigorous numerical methods have accurately predicted the broadband reflection of ideal, graded-index anti-reflective subwavelength structures; ideal structures are tapered nanostructures with periods smaller than the wavelengths of light of interest and lengths that are at least a large portion of the wavelengths considered.
Anti-reflective coatings (ARCs) are used to lower the reflection of light on the surface of a substrate. Here, we demonstrate that the two main drawbacks of moth eye-structured ARCs—i.e., the lack of suitable coating materials and a process for large area, high volume applications—can be largely eliminated, paving the way for cost-efficient and large-scale production of durable moth eye-structured ARCs on polymer substrates. We prepared moth eye coatings on polymethylmethacrylate (PMMA) and polycarbonate using wafer-by-wafer step-and-flash nano-imprint lithography (NIL). The reduction in reflection in the visible field achieved with these coatings was 3.5% and 4.0%, respectively. The adhesion of the coating to both substrates was good. The moth eye coating on PMMA demonstrated good performance in three prototypical accelerated ageing tests. The pencil hardness of the moth eye coatings on both substrates was <4B, which is less than required for most applications and needs further optimization. Additionally, we developed a roll-to-roll UV NIL pilot scale process and produced moth eye coatings on polyethylene terephthalate (PET) at line speeds up to two meters per minute. The resulting coatings showed a good replication of the moth eye structures and, consequently, a lowering in reflection of the coated PET of 3.0%.
This Feature Article discusses two biomimetic aspects of functional particle surface assembly: the fabrication of biologically inspired structures from particles and the arrangement of particles on biomimetic templates. The first part discusses the creation of primary patterns by convective assembly and adsorption of particles that can be modified by a combination of etching and growth steps. Resulting structures mimic moth eyes, Lotus leaves, and the Gecko's adhesive structures, for example. The second part focusses on template assisted self-assembly (TASA) of particles. Herein, biological examples are inspiring in terms of structure formation related processes, rather than in terms of functionality. Template formation is a major bottleneck TASA. It is illustrated how bio-inspired wrinkling processes help overcoming this problem and can be employed for forming highly ordered functional nanoparticle assemblies.
The authors report a simple self-assembly technique for fabricating antireflection coatings that mimic antireflective moth eyes. Wafer-scale, nonclose-packed colloidal crystals with remarkable large hexagonal domains are created by a spin-coating technology. The resulting polymer-embedded colloidal crystals exhibit highly ordered surface modulation and can be used directly as templates to cast poly(dimethylsiloxane) (PDMS) molds. Moth-eye antireflection coatings with adjustable reflectivity can then be molded against the PDMS master. The specular reflection of replicated nipple arrays matches the theoretical prediction using a thin-film multilayer model. These biomimetic films may find important technological application in optical coatings and solar cells.
A nanoimprint process that presses a mold into a thin thermoplastic polymer film on a substrate to create vias and trenches with a minimum size of 25 nm and a depth of 100 nm in the polymer has been demonstrated. Furthermore, the imprint process has been used as a lithography process to fabricate sub‐25 nm diameter metal dot arrays of a 100 nm period in a lift‐off process. It was found that the nanostructures imprinted in the polymers conform completely with the geometry of the mold. At present, the imprinted size is limited by the size of the mold being used; with a suitable mold, the imprint process should mold sub‐10 nm structures with a high aspect ratio in polymers. The nanoimprint process offers a low cost method for mass producing sub‐25 nm structures and has the potential to become a key nanolithography method for future manufacturing of integrated circuits and integrated optics. © 1995 American Institute of Physics.
Recently, our group reported synthesis routes for sub-micron sized hollow, and nanoporous phenylsiloxane spheres, in which phenyltrimethoxysilane is applied as surfmer. Here, we present insights into the surfactant formed through hydrolytic conversion of phenyltrimethoxysilane, and factors influencing the particle architecture.
In this paper, we present a simple method to fabricate the antireflective porous surface on sodalime glass using a single step HF-vapor phase etching method. Under optimal conditions, both-sides etched glass substrate exhibited a broadband enhancement in the transmittance with maximum transmittance as high as 99.2% at ∼500 nm with extremely low diffusive scattering. The measured transmittance exceeds by ∼7.6% as compared to plain glass (91.6%). X-ray photoelectron spectroscopy results confirmed the formation of a fluoride layer comprising of NaF and CaF2 on sodalime glass substrate after etching. Field emission scanning electron microscopy results showed the formation of porous structure with randomly distributed pores of size <150 nm. The refractive index of the porous fluoride layer was found to be 1.28 and lowest reflectance of 0.6% has been achieved. Moreover, reflection (measured at 500 nm) remains below 1.5% over a range of incident angles (8–48°), which is ascribed to the fact that refractive index follows a gradual change in the nanoporous surface. The theoretical transmittance of the optimized etched glass determined by finite difference time domain simulation shows a good agreement with the experimental results. The silicon solar cell covered with both-sides optimized etched glass showed a relative increase of ∼4% in power conversion efficiency as compared to a solar cell covered with a plain glass.
A cost effective, facile and scalable method to fabricate the stable broadband antireflective (AR) surface on glass substrates for solar energy applications is still a challenge. In this paper, we have demonstrated a simple and non-lithographic method to fabricate the broadband quasi-omnidirectional AR nanoporous surface on glass substrates by hydrofluoric (HF) acid based vapor phase etching method. Both-sides etched sodalime glass substrate under optimized conditions showed broadband enhanced transmittance with maximum total transmittance of ~97% at 598. nm. The measured transmittance exceeds by ~5.4% as compared to plain glass (91.6%). Field emission scanning electron microscopy results showed that an AR nanoporous surface with graded porosity was formed on sodalime glass substrate after etching. Due to the graded porosity, the fabricated nanoporous surface on sodalime glass substrate showed excellent broadband enhanced transmittance, and exhibited low reflectance <2.8% over a wide range of incidence angles (8-48°). The mechanism of nanostructured surface formation and the effect of etching parameters on transmittance have been discussed in detail. To get more insight, the theoretical transmittance of the optimized sample has been determined by finite difference time domain simulation, which confirms a good agreement of AR property with the experimental results. Furthermore, these AR nanoporous surface showed good adhesion property, excellent thermal and chemical stability, and exhibited outstanding stability against outdoor exposure. These properties signify its strong potential in various solar energy devices.
The use of cellulose nanocrystals (CNCs) in optical materials has been extensively studied. Key in most applications reported to date is the chiral nematic ordering of CNCs. Here, we demonstrate that random packing of silicated CNCs can also yield materials with interesting optical properties, i.e., highly porous, ultra-low refractive index coatings. Needle-shaped CNCs with an aspect ratio of 25 were extracted from Avicel, and subsequently covered with a silica layer. In one single dip coating step, highly porous coatings of CNC-silica core-shell particles were deposited on glass slides and silicon wafers. The lowest refractive index achieved was 1.03, which corresponds to a porosity of 94%; the thickness of these coatings ranged from 101 nm to 239 nm. The substrates, coated with a layer of CNC-silica core-shell particles, were heated to 450 °C for two hours. Cellulose was removed through pyrolysis, which resulted in porous coatings of sub-micron sized hollow silica rods. The porosity increase generated through pyrolysis of cellulose, however, was largely compensated by the decrease in packing porosity due to shrinkage of the coating.
More than 90% of the Dutch greenhouse area is covered with single glass. Energy losses through the covering are high during the heating period (winter) but energy requirements are also high during the cooling period (summer) in the case of semi-closed greenhouses. Until now, light losses of insulating coverings prevented growers from using double glass or plastic film. However, increasing energy prices allow new developments. Wageningen UR Greenhouse Horticulture studied the possibilities to use modern glass coatings to increase light transmission and save energy. Several glass types (standard glass, 90+ glass, low-iron glass) were covered with different anti-reflection coatings from different producers. Double glasses were produced; their optical properties were determined. It was possible to produce double glasses with new coatings having a higher light transmission than traditional single greenhouse glass (83-85% for hemispherical (diffuse) light, compared to 82-83% for traditional single glass) and a k-value of 3.6 W m-2 K-1 (compared to7.6 W m-2 K-1 of a traditional single glass). Other double glasses were produced using a combination of anti-reflection and modern low-emission coatings, reaching an even lower k-value of ≈2.4 W m-2 K-1, however, showing a slight light loss (78.5% for hemispherical (diffuse) light). Calculations of greenhouse climate (temperature, humidity, CO2) and energy consumptions year-round were carried out with a validated dynamic climate model. Additionally the effects on tomato production (dry matter) were calculated for the different prototypes of coated and insulated glass. Double materials show the highest energy saving with 25-33%, depending on the composition but also low-emission coatings on single glass decrease the energy use with 15-20%. Economic calculations with current tomato and energy prices showed that single and double glasses with anti-reflection coating currently have the highest potential.
During the last years it has been shown that diffuse light is advantageous for many greenhouse crops. Modern greenhouse covering materials are able to transform direct sunlight into diffuse light. After entering the greenhouse sunlight is scattered and penetrates into the crop, where it is absorbed and used for photosynthesis. Experimental research with different crops (e.g., tomato, cucumber, roses) over the last years showed an improved production under diffuse light conditions, expressed in growth rate or yield of up to 10% in The Netherlands. In the last five years different glass producers have put a lot of effort in development of diffusing greenhouse covering materials. Different structures have been developed and applied on glass for greenhouse application. Glass surface treatments result in regular or irregular patterns on glass such as matt/matt, prismatic, satin, texture and v-grooves. Next to that micro structures are combined with nanostructures, such as anti-reflection treatments (AR), in order to improve light transmission into the greenhouse. It can be shown that material development was able to improve hemispherical light transmission of diffuse glasses by at least 5% in 2013 compared to before 2007, glasses with larger hemispherical transmission and highly diffusing properties are available. Earlier an evaluation method for diffuse materials had been proposed. That method is mainly based on a measurement of the so-called hemispherical light transmission and haze. New possibilities in material technology and increasing knowledge of the relation of diffuse light and crop reactions caused a need to extend evaluation methods. Measuring spatial distribution of transmitted light is suggested next to measuring angular and spectral light transmission. Different new diffuse materials of different producers are measured and evaluated. The results show that diffuse glasses differ in haze and hemispherical light transmission. As well, the choice of basic glass material as the type of anti-reflection treatment are main causes of light spectrum changes. Diffuse structures alone do not cause differences in spectral light transmission. Different structures and AR treatments result in different angular light transmission, which explains differences in hemispherical light transmission. Measurements of spatial light transmission show that many diffusing glasses only cause a narrow light scattering pattern so far.
Colloidal monolayers represent a versatile material class to fabricate nanostructures with high quality. The length scale of the nanostructured film is given by the size of the colloidal nanoparticles. Importantly, colloidal monolayers, though being of hexagonally close packed symmetry, still embody a high amount of free volume. This reduces the effective refractive index of thin colloidal monolayer films significantly. For particles and periodicities <200 nm, the heterogeneous layer can be approximated by an effective medium theory. The amount of free volume can be further fine-tuned by a controlled size reduction of the constituting spheres, for instance by plasma etching. This can be utilized to realize an optimum refractive index for the application of colloidal monolayers as antireflective (AR) coatings. In contrast, previously reported >200 nm monolayers demonstrate distinct extinction peaks due to grating diffraction. Rational design by the use of differently sized particles further allows shifting the best performance across the visible spectrum. Colloidal monolayers, though representing single-layer AR coatings, exhibit broadband AR properties and are ideally suited to demonstrate the influence of refractive index and layer thickness, independently.
Antireflection coatings have received a great importance due to their ability to enhance the efficiency of the solar cells and solar selective coatings by minimizing the reflections of the incident light from the front surface. In this study, a silica (SiO2) sol, prepared using sol–gel process, was deposited on cleaned glass substrates by dip coating method and subjected to heat treatment at 400 °C. The thickness and porosity of the coating were optimized to achieve high transmittance. The thickness was optimized by varying the lifting speed of the substrate from the sol. The porosity was induced in the coating by using polymeric additives and through heat treatments. The optimized single layer SiO2 coating on cleaned glass substrate exhibited a maximum transmittance of 97.5% at λ=500 nm wavelength. The hybrid sol was found to give reproducible coatings up to a period of 30 days when stored at 16 °C. The present process provides a simple and cost effective method for the preparation of antireflection coatings, which have huge potential to enhance the efficiency of solar cells, receiver tubes and other solar devices.
We present a facile route for the synthesis of sub-micron sized hollow and multiporous organosilica spheres, which is based on an oil-in-water emulsion and merely uses one organosilica precursor - phenyl trimethoxysilane - that serves as monomer, precursor for a surface active species and oil phase.
A double-layer broadband antireflective (AR) coating was prepared on glass substrate via sol-gel process using two kinds of acid-catalyzed TEOS-derived silica sols. The relative dense layer with a porosity of ~10% was obtained from an as-prepared sol, while the porous layer with a porosity of ~55% was from a modified one with block copolymer (BCP) Pluronic F127 as template which results in abundant ordered mesopores. The two layers give rise to a reasonable refractive index gradient from air to the substrate and thus high transmittance in a wide wavelength range; and both of them have the same tough skeleton despite of different porosity, for which each single-layer and the double-layer coatings all behaved well in the mechanical property tests. The high transmittance and the strong ability of resisting abrasion make this coating promising for applications in some harsh conditions. In addition, the preparation is simple, low-cost, time-saving and flexible for realizing the optical property.
A graded-index anti-reflection coating with high optical transmittance, a rapid anti-fogging capability, and excellent robustness is fabricated via the stacking of Si-containing block copolymers and simple oxidation. The porosity in the nanostructured silica layers can easily be controlled by changing the fraction of the Si-containing block in the block copolymers. The high optical transparency can be maintained in harsh chemical, mechanical, and thermal environments, suggesting that the coating will be especially advantageous for outdoor applications.
A series of colloidal nanocomposite dispersions are synthesized by alcoholic dispersion polymerization of styrene in the presence of an ultrafine silica sol. The original core/shell polystyrene/silica nanocomposite particles have mean diameters ranging from 321 to 471 nm, as determined by dynamic light scattering. Upon calcination of the polystyrene cores, some shrinkage occurs but intact hollow silica shells are observed by transmission electron microscopy. On visual inspection, these silica residues display remarkable colors that vary depending on the particle diameter. When examined in transmittance mode (i.e., with an illuminated background) the silica powders appear yellow to red in color, but when viewed in reflectance (i.e., with a dark background) relatively intense blue/green colors are observed. The latter phenomenon has been analyzed by visible reflectance spectroscopy and the reflectance maximum depends on the dimensions of the silica shell, which are in turn dictated by the initial nanocomposite particle diameter. Small-angle X-ray scattering is used to determine the packing density of the silica nanoparticles, both in the original polystyrene/silica nanocomposite particles and in the calcined silica shells. Combined with geometrical considerations, this allows the equivalent uniform silica shell thickness to be calculated for a particulate silica shell and this parameter is then related to the theoretical predictions made by Retsch et al. for hollow particles comprising uniform silica shells (see Retsch, M.; Schmelzeisen, M.; Butt, H. J.; Thomas, E. L. Nano Lett., 2011, 11, 1389).
We report broadband and quasi-omnidirectional antireflective (AR) structures inspired to the nipple arrays of moth eyes. These nanocoatings, based on thin elastomeric films, are prepared by simple self-assembly processing of a co-polymer specifically designed to this purpose, and PDMS replica molding. Typically, their surface is covered by a compact distribution of hemispherical nanodomes of about 250 nm in diameter and about 100 nm in height. When these novel nanostructures are applied on a single glass surface, a maximum of 2% transmission enhancement (equivalent to a 50% reduction of the reflected component) towards wavelengths ranging from visible to near IR region is obtained. A considerable AR power is observed also at a wide range of incident angles ranging from normal to 50°. These properties could be attributed to an optimized graded refractive index profile resulting from the randomly distributed and close-packed nanodomes. Moreover, thanks to their elastomeric nature, these crack-free films can be easily applied on glass, as stickers, and periodically replaced, thus offering the possibility of easy dirt removal from an optical device.
An omnidirectional antireflection (AR) coating for a deep-ultraviolet (UV) AR band is designed and fabricated on the sapphire substrate of a deep-UV flip-chip light-emitting diode (LED) device. The two-layer AR coating uses the tailored- and low-refractive index nanoporous alumina fabricated by glancing-angle deposition methodology. The AR coating effectively matches the refractive indices between the air and sapphire substrate. At close-to-normal angles of incidence, this AR coating almost completely eliminates the Fresnel reflection at the sapphire/air interface of the deep-UV LED device. The resulting improvement of the light-extraction efficiency by 8% is in good agreement with the simulation results. For a total thickness of 172 nm for the two-layer AR coating, extinction was negligible (<2%). The results show that nanoporous alumina thin films are excellent tailored- and low-refractive index thin film materials for high-performance deep-UV AR coating applications.
We report the effect of nanocone arrays (NCAs) as an antireflection coating (ARC) of encapsulation coverglasses on the device performance of encapsulated III–V InGaP/GaAs/Ge triple-junction (TJ) solar cells. The NCAs were fabricated on the single-side surface of glasses using the gold nanopatterns (i.e., nanoclusters) prepared by the glancing angle deposition technique without additional thermal treatment and the subsequent dry etching. Their wetting behavior and optical properties, together with a theoretical prediction using the rigorous coupled-wave analysis method, were investigated. The NCAs ARC coverglass exhibited a much lower water contact angle (θCA) of <5° (i.e., superhydrophilic surface) and higher solar weighted transmittance (SWT) of ~95.9% over a wide wavelength region of 300–1800 nm at normal incidence compared to the bare coverglass (i.e., θCA~63° and SWT ~92.8%). The use of the NCAs ARC coverglass in encapsulated III–V InGaP/GaAs/Ge TJ solar cells led to the higher short circuit current density (Jsc) of 14.22 mA/cm2 and thus improved the conversion efficiency (η) to 32.07% (cf., Jsc=13.84 mA/cm2 and η=30.6% for the cell with the bare coverglass). For incident angle-dependent solar cell characteristics, it also showed a superior solar power conversion property in wide incident light angles of 20–80°.
The non-collapsed hollow polymeric nanoparticles with shell thicknesses in the order of 10 nm are prepared by interfacially confined reversible addition fragmentation transfer (RAFT) miniemulsion polymerization. The void fraction and average diameter of the hollow polymeric nanoparticles could be largely tuned up to 0.58 and from 68 nm to 180 nm, respectively. The non-collapsed hollow polymeric nanoparticles could be a building block for nanoporous materials, which hold promise in many fields such as anti-reflection coatings, ultra-thermal insulation materials, catalysis and sensors.
A new sol-gel method for the preparation of optical SiO2 and TiO2 multilayer coatings has been developed. As an example, a 3-layer antireflective (AR-filter) coating and a 5-layer NIR reflective coating on glass are described. For the preparation, a nanoparticulate TiO2 sol was synthesized by hydrolysis and condensation of tetraisopropylorthotitanate and complex formation with methacrylic acid. A SiO2 nanoparticulate sol was synthesized analogeously with tetraethoxysilane (TEOS) as the precursor. By mixing both sols in different ratios, layers with tunable refractive index between 1.46 and 2.2 could be obtained on glass after thermal densification at 450°C for 15 min. Three layers (SiO2-TiO2, TiO2, SiO2) were deposited by dip-coating with subsequent UV-curing, and the layer-stack was thermally densified at 450 C. The so obtained AR-filter shows a reflection of ≤2% in the wavelength range between 380 and 610 nm, ≤1% between 450 and 560 nm and 0% at 550 nm. The AR filter shows very good abrasion resistance and scratch hardness, since only 3% haze is obtained after 1000 cycles of Taber test and the AR filter does not show any damage after 300 cycles of rubber test. The high abrasion resistance can be attributed to the surprisingly low surface roughness (about 6 nm) of the filter. The mechanical and optical properties of the AR filter did not change after sun test with 760 W/m2 for 320 h and after boiling water test for 11 days.
Nanostructured antireflective surfaces were fabricated by the deposition of monodispersed silica nanoparticles on a glass substrate by electrostatic attraction between charged colloidal particles and charged polyelectrolyte multilayers. The effects of particle size and surface nanoparticle density on the antireflective properties of the nanostructured surfaces were investigated by the analysis of their reflection/transmission spectra and examination of their surface morphology. It was found that the nanostructured surfaces with particles of ∼120nm in diameter yielded the most suitable performance for antireflection with respect to the visible-light region. The nanoparticle coatings revealed reflective properties similar to homogeneous porous layers. However, in comparing the simulation analysis to the experimental results, it was found inappropriate that an NP coating is entirely regarded as a homogenous porous layer.
THE problem of surface reflexion from lenses has led1 to the development of multilayer interference structures which can suppress the reflexion from glass surfaces by a factor of 10 or more throughout the visible spectrum. But observations on the corneas of nocturnal insects indicate that nature may have anticipated the problems2. Electron microscope studies of the corneal lenses of moths reveal that the outer surface is covered in a regular array of conical protuberances, typically of about 200 nm height and spacing. Bernhard2 proposed that the function of this structure might be to suppress reflexions by effectively proving a graded transition of refractive index between the air and the cornea. The proposal was substantiated by measurements with microwave radiation reflected from a model of the array, scaled up appropriately for the longer wavelengths.
We propose a roll-to-roll UV imprint lithography tool as a way to pattern flexible PET foil with μm-resolution. As a way to overcome dimensional instability of the foil and its effect on overlay, a self-align approach was investigated, that permits to make several layers in a single lithography step. Flexible Ni-stamps were used, with a single level and with 2 levels. The stamps were fabricated on wafers using conventional optical lithography and Si etching. Thin Ni replica, both single and multilevel, were obtained by electroplating using a thickness of 50μm. The flexible Ni stamps were attached on the main drum that is placed on a conventional roll-to-roll machine. Resist was dispensed drop by drop by valve-jet nozzle using solvent-free UV resist. The imprint speed was of 0.35m/min, using a UV illumination of 2W. Fifty imprints were made in a row, equivalent to 20m foil length. High imprint quality was observed with good reproducibility. All features type were replicated, from 500μm contact pads to 800nm wide trenches and 1μm wide lines. A resolution of 800nm in 1μm thick resist was obtained for single level imprint. Multi-level imprints (2 levels) show the same quality in replication with a resolution of 1μm.
a b s t r a c t Many recent studies have focused on enhancing the efficiency of optical devices such as light-emitting diodes (LEDs). However, optical device efficiency decreases when generated light passes through the LED packaging material. Herein, we developed a technique to improve the efficiency of LED packages and the external efficiency of the optical devices, which were packaged. Specifically, anti-reflection patterns consisting of moth-eye structures were used to prevent internal reflection from the surface of the LED package. These nanosized conical structures were fabricated with nano-imprint lithography, which is a next-generation lithography technology. Fine nanosized moth-eye patterns were formed on the surface of an LED package, increasing its efficiency by 3.27%. Ó 2013 Published by Elsevier B.V.
We report the fabrication of a nanometric multi-scale rough, transparent and anti-reflective zinc oxide (ZnO) superhydrophobic coating on TiAlN/TiAlON/Si3N4 spectrally selective solar absorber surface, which has been developed previously for solar thermal power generation applications. The optimized ZnO superhydrophobic coating on the absorber surface demonstrates extraordinary water repellency (with contact angle >155°), improved absorptance (>0.96) and excellent broadband anti-reflection in the visible range of the solar spectrum. The multi-functional ZnO coating was stable up to 450 °C (in air and vacuum), indicating its reliability for high temperature photothermal conversion applications.
Sintered targets of ZrO2 and Al2O3 are ablated by KrF excimer laser radiation. The processing gas atmosphere consists of O-2 at pressures of 0.1-50 Pa. The films of 100nm-10 mu m in thickness are deposited on polymethylmechacrylate (PMMA), polycarbonate (PC) and glass (fused silica) substrates. Analytical techniques used for the determination of structural characteristics of the films are optical and electron microscopy. The thickness and the complex refractive index are determined by ellipsometry. The optical film thickness, reflectivity and transmittivity of the films at different wavelengths are determined in situ and ex situ using optical spectroscopy. The hardness and elastic modulus of the films are investigated using nano-indentation. The investigations concentrate on the influence of the oxygen pressure, the target-to-substrate distance and the laser fluence on the refractive index of the films, which is correlated with the film density. The compaction of the films is achieved by particles impinging with kinetic energies above 30 eV on the growing surface. Dense (94% of the bulk density), transparent and hard (Vickers hardness 1200, elastic modulus 190 GPa) alumina films 2-10 mu m in thickness have been deposited on glass substrates. Alumina films thicker than 500 nm deposited on PMMA or PC substrates delaminate due to large compressive stress in the films. Multilayer systems of alumina and zirconia are deposited on micro-optics of PMMA, as antireflective coatings in the spectral range lambda= 800-900 nm yielding a transmittance >99%.
Porous sol−gel silica films are prepared using different PMMA latex nanoparticles, 30−80 nm in diameter, as sacrificial templates. By changing the size and the content of the latex particles in the deposited silica sol, it was possible for the first time to tailor the porosity of the sol−gel films (uniform pore size and porous fraction from 0.10 to 0.74) independently of their thickness. This is the consequence of a low microporosity in the silica walls as shown by the correspondence between the measured porous fraction after calcination and the starting latex volume fraction. No ethanol capillary condensation occurs in these films before high partial pressure (above 0.9), leading to a stable refractive index that can be tuned in a large range (from 1.15 to 1.40 at 600 nm). A porosity percolation transition with the opening of the extrinsic pore interconnection was observed at a pore fraction threshold of about 0.40 for different sizes of the initial template. Below the threshold, the films showed a closed porosity structure with a low stable refractive index (down to 1.29 at 600 nm), opening the way to their use for antireflective applications.
We report here a self-cleaning particle coating with antireflection (AR) properties. The coatings were prepared by (1) depositing SiO2 single-layered particle coatings on polyelectrolyte-modified glass substrates through electrostatic attraction, (2) subsequently depositing another layer of TiO2 nanoparticles through electrostatic attraction, and (3) removing the polymer by calcination at 500 °C. The AR effect of the coatings was studied with transmission spectra collected at normal incidence. The self-cleaning properties of the coatings were studied by the change of the water contact angle on octadodecyldimethylchlorosilane-modified coatings under 1.0 mW cm-2 ultraviolet light. Both the AR and self-cleaning properties of the coatings were dependent on the concentration of colloidal TiO2 solution used in the preparation. However, excellent surface wettability of the coatings for water was obtained, independent of the preparation conditions. The experimental findings are discussed in terms of the special structure of the particle coatings.
a b s t r a c t The superhydrophobic surfaces have drawn lot of interest, in both academic and industries because of optically transparent, adherent and self-cleaning behavior. Surface chemical composition and mor-phology plays an important role in determining the superhydrophobic nature of coating surface. Such concert of non-wettability can be achieved, using surface modifying reagents or co-precursor method in sol–gel process. Attempts have been made to increase the hydrophobicity and optical trans-parency of methyltrimethoxysilane (MTMS) based silica coatings using polymethylmethacrylate (PMMA) instead of formal routes like surface modification using silylating reagents. The optically transparent, superhydrophobic uniform coatings were obtained by simple dip coating method. The molar ratio of MTMS:MeOH:H 2 O was kept constant at 1:5.63:1.58, respectively with 0.5 M NH 4 F as a catalyst and the weight percent of PMMA varied from 1 to 8. The hydrophobicity of silica coatings was analyzed by FTIR and contact angle measurements. These substrates exhibited 91% optical transmittance as compared to glass and water drop contact angle as high as 171 ± 1 • . The effect of humidity on hydrophobic nature of coating has been studied by exposing these films at relative humidity of 90% at constant tempera-ture of 30 • C for a period of 45 days. The micro-structural studies carried out by transmission electron microscopy (TEM).
Porous polymer films that can be employed for broadband and omnidirectional antireflection coatings are successfully shown. These films form a gradient-refractive-index structure and are achieved by spin-coating the solution of a polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA)/PMMA blend onto an octadecyltrichlorosilane (OTS)-modified glass substrate. Thus, a gradient distribution of PMMA domains in the vertical direction of the entire microphase-separated film is obtained. After those PMMA domains are removed, a PS porous structure with an excellent gradient porosity ratio in the vertical direction of the film is formed. Glass substrates coated with such porous polymer film exhibit both broadband and omnidirectional antireflection properties because the refractive index increases gradually from the top to the bottom of the film. An excellent transmittance of >97% for both visible and near-infrared (NIR) light is achieved in these gradient-refractive-index structures. When the incident angle is increased, the total transmittance for three different incident angles is improved dramatically. Meanwhile, the film possesses a color reproduction character in the visible light range.
Convective assembly at high volume fraction was used to deposit silica nanoparticle coatings onto glass and silicon substrates. By allowing control of the film structure and thickness, this technique provides a means for making large-scale coatings with antireflective properties. The reflectance was reduced by 50% for silicon (at 600 nm) and by 70% for single glass/air surface. Microstructural investigations using SEM, AFM, profilometry, and ellipsometry provided good correlation to the observed macroscopic optical properties. By virtue of the coatings' uniformity, the reflectance and transmission spectra from both substrates could be modeled well by classical reflection relations, using a volume-averaged refractive index. Data analysis showed that the relatively high packing fraction in nanocoatings made from monodisperse spheres is responsible for the limit on antireflective capabilities. To overcome this restriction, low-density silica coatings were made from binary colloidal mixtures of different diameter SiO 2 particles. The packing fraction of these coatings was further optimized to yield 88% maximal reduction in the reflectance of glass surfaces. The technique is simple, inexpensive, and scalable.
Optical reflection, or in other words the loss of reflection, from a surface becomes increasingly crucial in determining the extent of the light-matter interaction. The simplest example of using an anti-reflecting (AR) surface is possibly the solar cell that incorporates an AR coating to harvest sunlight more effectively. Researchers have now found ways to mimic biological structures, such as moth eyes or cicada wings, which have been used for the AR purpose by nature herself. These nanoscopic biomimetic structures lend valuable clues in fabricating and designing gradient refractive index materials that are efficient AR structures. The reflectance from a selected sub-wavelength or gradient index structures have come down to below 1% in the visible region of the spectrum and efforts are on to achieve broader bands of such enhanced AR regime. In addition to the challenge of broader bands, the performance of AR structures is also limited by factors such as omnidirectional properties and polarization of incident light. This review presents selected state-of-the-art AR techniques, reported over the last half a century, and their guiding principles to predict a logical trend for future research in this field.
Various optical elements with subwavelength structured surfaces have been developed. The periods of the subwavelength structures are too short to generate diffracted light waves. But the structures are equivalent to refractive index materials with form birefringence. Many new optical elements are realized using the artificial refractive indices of these subwavelength structures. Some typical elements are described here in the passive element regime, and fabrication methods of the elements are explained.
This paper reports on anti-reflective (AR) and antireflective-antistatic (ARAS) coatings on glass prepared by reactive sputtering using a special twin magnetron device powered with a mid frequency generator (this device is commercially known as TwinMag). Single SiO2 and TiO2 layers as well as complete AR and ARAS systems have been prepared on large scale flat substrates and 17″ curved computer and TV screens. The morphology, crystal structure and the optical constants of the individual layers and the reflection spectra of different layer systems are investigated.
In this work an innovative antireflection coating technology for photovoltaic modules based on remote plasma-enhanced chemical vapour deposition of porous SiO2 films is presented. We show that the proposed technology has the potential to significantly improve the performance of photovoltaic modules by effectively reducing the optical losses of the air/glass interface. As a result, the transmission of a glass pane measured at a single wavelength was increased from 91.7% to 100% by a single-layer porous SiO2 antireflection coating on both sides of the glass pane. Furthermore, a double-layer porous SiO2 antireflection coating on both sides of the glass pane increased the transmission weighted with the AM1.5G spectrum in the 400–1150 nm wavelength region from 91.6% to the remarkably high value of 99.4%.
Numerous effective medium models have been proposed for the effective optical properties of nanoporous media. However, validations of these models against experimental data are often contradictory and inconclusive. This issue was numerically investigated by solving the two-dimensional Maxwell's equations in non-absorbing nanoporous thin films with various morphologies. It was found that below a certain critical film thickness, the effective index of refraction depends on the porosity and on the pore size, shape and spatial distribution. For thick enough films the effective index of refraction depends solely on porosity and on the indices of refraction of the two constitutive phases. The numerical results agree very well with a recent model obtained by applying the Volume Averaging Theory to the Maxwell's equations. However, commonly used models systematically and sometimes significantly underpredict the numerical results.
An industrial sol–gel process to coat solar glass with a porous SiO2 antireflection (AR) layer has been recently developed. This paper presents the first detailed study obtained on sets of commercial multicrystalline silicon solar cells encapsulated with patterned low-iron glasses, with or without this AR coating. Measurements under standard test conditions (STC) show a current gain of 2.65% with the AR glass, whereas an additional current gain is obtained at high light incidence angle. Based on the mini-module results and on the outdoor monitoring of test modules to evaluate temperature effects, simulations were performed to asses the yearly photovoltaic energy yield gain at different locations. A significant energy yield increase of 3.4–3.7% is expected with the new AR glass.
Traditionally, various vacuum-based processes, depending on material systems and properties, and chemical etching process have been used for producing different types of anti-reflection (AR) coating on different substrate materials. In this paper, the development of sol–gel derived AR coating on different substrates for various applications in the past 40 years are reviewed. These coatings possess good uniformity in thickness and properties which have met requirements for various applications. The major approaches to fabricate AR coating and their characteristics have been discussed. This paper outlines the major solution coating processes and design principles of AR coatings. Major fabrication processes used in AR coating technologies have been compared. Different solution chemistries developed for producing different materials for AR coating preparation have been extensively reviewed. The optical performance of different types of sol–gel-derived AR coatings have been summarized and comparison to the commercial AR coating produced by traditional technologies have been discussed. The sol–gel AR coating has been shown to possess comparable or superior performance to those produced by vacuum-based processes.
The collective mechanical behavior of multilayer colloidal arrays of hollow silica nanoparticles (HSNP) is explored under spherical nanoindentation through a combination of experimental, numerical, and theoretical approaches. The effective indentation modulus E(ind) is found to decrease with an increasing number of layers in a nonlinear manner. The indentation force versus penetration depth behavior for multilayer hollow particle arrays is predicted by an approximate analytical model based on the spring stiffness of the individual particles and the multipoint, multiparticle interactions as well as force transmission between the layers. The model is in good agreement with experiments and with detailed finite element simulations. The ability to tune the effective indentation modulus, E(ind), of the multilayer arrays by manipulating particle geometry and layering is revealed through the model, where E(ind) = (0.725m(-3/2) + 0.275)E(mon) and E(mon) is the monolayer modulus and m is number of layers. E(ind) is seen to plateau with increasing m to E(ind_plateau) = 0.275E(mon) and E(mon) scales with (t/R)(2), t being the particle shell thickness and R being the particle radius. The scaling law governing the nonlinear decrease in indentation modulus with an increase in layer number (E(ind) scaling with m(-3/2)) is found to be similar to that governing the indentation modulus of thin solid films E(ind_solid) on a stiff substrate (where E(ind_solid) scales with h(-1.4) and also decreases until reaching a plateau value) which also decreases with an increase in film thickness h. However, the mechanisms underlying this trend for the colloidal array are clearly different, where discrete particle-to-particle interactions govern the colloidal array behavior in contrast to the substrate constraint on deformation, which governs the thickness dependence of the continuous thin film indentation modulus.
An environmentally benign surface modification process for plastic films was demonstrated by fabricating composite coatings through layer-by-layer assembly with green solid materials: aqueous dispersions of two kinds of crystalline polysaccharide nanofibrils. Anionic cellulose nanofibrils were obtained by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation of native cellulose, while cationic β-chitin nanofibrils were prepared by the protonation of squid pen chitin. Uniform layer depositions, driven by electrostatic attraction and enhanced by hydrogen bonding, were observed on silicon wafers and then reproduced onto poly(ethylene terephthalate) films. Contact angle measurements and dyeing tests on the resulting films revealed their hydrophilic nature and the sorption of both charged and uncharged substances. Antireflection properties were also confirmed via the light transmittance measurements. As might be presumed from all these properties, this composite coating exhibited its unique behavior largely due to its structure, which was distinct from both those of nanofibril cast films and polymer films.
Mesoporous silica nanoparticles are used to fabricate antireflectance coatings on glass substrates. The combination of mesoporous silica nanoparticles in conjunction with a suitable binder material allows mechanically robust single layer coatings with a reflectance <0.1% to be produced by simple wet processing techniques. Further advantages of these films is that their structure results in broadband antireflective properties with a reflection minimum that can tuned between 400 nm and 1900 nm. The ratio of binder material to mesoporous nanoparticles allows control of the refractive index. In this report, we discuss how control of the structural properties of the coatings allows optimization of the optical properties.
Based on conventional colloidal nanosphere lithography, we experimentally demonstrate novel graded-index nanostructures for broadband optical antireflection enhancement including the near-ultraviolet (NUV) region by integrating residual polystyrene antireflective (AR) nanoislands coating arrays with silicon nano-conical-frustum arrays. This is a feasible optimized integration method of two major approaches for antireflective surfaces: quarter-wavelength AR coating and biomimetic moth's eye structure.
This paper reviews the progress made recently in synthesis and applications of spherical silica micro/nanomaterials with multilevel (hierarchical) structures. The spherical silica micro/nanomaterials with hierarchical structures are classified into four main structural categories that include (1) hollow mesoporous spheres, (2) core-in-(hollow porous shell) spheres, (3) hollow spheres with multiple porous shells and (4) hierarchically porous spheres. Due to the complex structures and being focused on spherical silica micro/nanomaterials, some novel methods based on the combination of two routine methods or two surfactants, and some special synthetic strategies are proposed to produce the spherical silica micro/nanomaterials with hierarchical structures. Compared with the same-sized solid, porous or hollow silica spheres, these fantastic spherical silica micro/nanomaterials with hierarchical structures exhibit enhanced properties which may enable them to be used in broad and promising applications as ideal scaffolds (carriers) for biological, medical, and catalytic applications.
Inorganic hollow spheres have attracted considerable interest due to their singular properties and wide range of potential applications. In this critical review, we provide a comprehensive overview of the preparation and applications of inorganic hollow spheres. We first discuss the syntheses of inorganic hollow spheres by use of polymers, inorganic nonmetals, metal-based hard templates, small-molecule emulsion, surfactant micelle-based soft-templates, and the template-free approach. For each method, a critical comment is given based on our knowledge and related research experience. We go on to discuss some important applications of inorganic hollow spheres in 0D, 2D, and 3D arrays. We conclude this review with some perspectives on the future research and development of inorganic hollow spheres (235 references).
Automated spray-layer-by-layer (LbL) assembly was used to create highly reflective structurally colored thin films with high reflectance at near-UV light wavelengths. Reflectance peaks were tuned by fabricating alternating stacks of high (TiO(2) nanoparticles) and low (SiO(2) nanoparticles) refractive index materials using a non-quarter-wave design. Spray-assembled multilayer heterostructures fabricated with up to 840 individual polymer or nanoparticle deposition steps presented similar roughness and refractive index values compared to Bragg stacks obtained via immersion LbL assembly. Such complex multilayer heterostructures, however, could be fabricated in significantly shorter times; the time required to deposit a complete bilayer was only about 90 s, compared to 36 min for the immersion assembly of the same system. Optimization of the experimental parameters was performed to achieve uniform coatings and relatively smooth interfaces and surfaces. We observed that the spraying times of the nanoparticle and polymer solutions are the main parameters that determine the thickness, optical properties, and uniformity of the assembled films. Ellipsometry, atomic force microscopy (AFM), UV-vis spectroscopy, and transmission electron microscopy (TEM) were used to characterize the samples. The nanoparticle thin films were iridescent and presented relatively narrow peaks of high reflectance (∼90%) at visible and near-UV wavelengths of light.
Robust transparent superhydrophobic coatings are advantageous for convenient and cost-effective maintenance of a variety of surfaces. Until now most coatings suffer from poor mechanical stability. Based on porous silica capsules we developed an easy to apply method to overcome these limitations. The coating is not only mechanically robust but also highly transparent as demonstrated by applying it to organic solar cells, keeping its high performance unaltered.