Optical properties of nanoparticle-based metallodielectric inverse opals

Metallodielectric inverse opals were prepared by co-crystallizing silica-coated gold nanoparticles and polymer spheres, followed by removal of the crystal template. The inverse opals exhibit a distinct reflectance peak, which results from Bragg diffraction due to the highly ordered 3D macroporous structure. Photonic band-structure calculations indicate that the characteristic reflectance peaks observed are signatures of the directional gap at the L point. It is demonstrated that the optical properties (the position and magnitude of the electromagnetic bandgaps) of the gold-silica nanocomposite inverse opals can be engineered by varying the nanoparticle morphology (core size and shell thickness) and/or the nanoparticle volume-filling ratio of the composite. The use of metallodielectric nanoparticles to form inverse opals offers a versatile approach to prepare photonic materials that may exhibit absolute bandgaps.     

Colloidal crystal templating of three-dimensionally ordered macroporous solids: materials for photonics and beyond

This review discusses strategies for the synthesis of three-dimensionally ordered macroporous (3DOM) solids (inverse opals) by colloidal crystal templating. Compositions of 3DOM structures include simple and ternary oxides, chalcogenides, non-metallic and metallic elements, hybrid organo-silicates, and polymers. A wide range of 3DOM synthesis techniques, including sol–gel chemistry, polymerization, salt-precipitation and chemical conversion, chemical vapor deposition, spray pyrolysis, ion spraying, laser spraying, nanocrystal deposition and sintering, oxide and salt reduction, electrodeposition, electroless deposition, fabrication from core-shell spheres, and patterning methods, as well as templating using inverse opal molds to produce new opal compositions are reviewed. Potential uses of 3DOM solids, including photonic crystal, optical, catalytic, and bioglass applications are briefly discussed.     

Modulation of Multiscale 3D Lattices through Conformational Control: Painting Silk Inverse Opals with Water and Light

Structural proteins from naturally occurring materials are an inspiring template for material design and synthesis at multiple scales. The ability to control the assembly and conformation of such materials offers the opportunity to define fabrication approaches that recapitulate the dimensional hierarchy and structure–function relationships found in nature. A simple and versatile directed assembly method of silk fibroin, which allows the design of structures across multiple dimensional scales by generating and tuning structural color in large‐scale, macro defect‐free colloidally assembled 3D nanostructures in the form of silk inverse opals (SIOs) is reported. This approach effectively combines bottom‐up and top‐down techniques to obtain control on the nanoscale (through silk conformational changes), microscale (through patterning), and macroscale (through colloidal assembly), ultimately resulting in a controllable photonic lattice with predefined spectral behavior, with a resulting palette spanning almost the entire visible range. As a demonstration of the approach, examples of “multispectral” SIOs, paired with theoretical calculations and analysis of their response as a function of changes of lattice constants and refractive index contrast are illustrated.     

Photoluminescence and energy transfer investigation from SiO2: Tb,Au inverse opals to rhodamine-B dyes

Energy transfer has attracted extensive attention due to its widespread applications in medical diagnostics, DNA analysis and lighting devices. There are few reports on the energy transfer from rare earth ions to dyes. In the present work, the SiO₂:Tb inverse opals with and without Au nanoparticles were prepared, and the organic rhodamine-B (RhB) dyes were filled into the voids of SiO₂:Tb inverse opals. Non-radiative and radiative energy transfer processes from the SiO₂:Tb inverse opals to the RhB were observed. The influence of Au nanoparticles and photonic band gap on the energy transfer from SiO₂:Tb inverse opals to the RhB was investigated. The Au nanoparticles enhanced energy transfer was observed due to the surface plasmon resonance effects of the Au nanoparticles. When the emission peaks from the SiO₂:Tb inverse opal is overlapped with the photonic band gap, the emission suppression of the SiO₂:Tb inverse opal as well the emission enhancement of the RhB dyes were obtained, which is attributed to improved energy transfer caused by the photonic band gap. The steady state rate equations were used to explain enhancement of energy transfer caused by the photonic band gap.     

Lithographically Encrypted Inverse Opals for Anti‐Counterfeiting Applications

Colloidal photonic crystals possess inimitable optical properties of iridescent structural colors and unique spectral shape, which render them useful for security materials. This work reports a novel method to encrypt graphical and spectral codes in polymeric inverse opals to provide advanced security. To accomplish this, this study prepares lithographically featured micropatterns on the top surface of hydrophobic inverse opals, which serve as shadow masks against the surface modification of air cavities to achieve hydrophilicity. The resultant inverse opals allow rapid infiltration of aqueous solution into the hydrophilic cavities while retaining air in the hydrophobic cavities. Therefore, the structural color of inverse opals is regioselectively red‐shifted, disclosing the encrypted graphical codes. The decoded inverse opals also deliver unique reflectance spectral codes originated from two distinct regions. The combinatorial code composed of graphical and optical codes is revealed only when the aqueous solution agreed in advance is used for decoding. In addition, the encrypted inverse opals are chemically stable, providing invariant codes with high reproducibility. In addition, high mechanical stability enables the transfer of the films onto any surfaces. This novel encryption technology will provide a new opportunity in a wide range of security applications.     

Interconversion of inverse opals of electrically conducting doped titanium oxides and nitrides

There is a need for conducting, porous, and chemically stable materials for technologies including, but not limited to, fuel cells, solar cells, and batteries. The need for catalyst support materials that are more durable than carbon black in fuel cells motivated previous studies of the synthesis, characterization, and corrosion resistance of Ti(0.7) W(0.3) O(2) nanoparticles. However, because even higher porosity and increased electrical conductivity are desired, processes were developed to prepare rutile phase Ti(0.7) W(0.3) O(2) and cubic Ti(0.7) W(0.3) N in inverse opal morphologies from a precursor inverse opal of very poorly conducting, amorphous Ti(0.7) W(0.3) O(2.3) . Inverse opals have been explored for a variety of applications from catalysis to photonics, and inverse opals of both oxides and nitrides have been reported. By synthesizing highly conducting mixed-metal oxides and mixed-metal nitrides, the applications of inverse opals can be broadened. Herein, the synthesis and characterization of polystyrene-templated, single-phase, crystalline inverse opals of Ti(0.7) W(0.3) O(2) are reported. These conducting inverse opals can subsequently be converted to inverse opals of Ti(0.7) W(0.3) N and then fully oxidized back to inverse opals of the original insulating, amorphous Ti(0.7) W(0.3) O(2.3) . Such changes in composition and crystal structure, while successfully retaining the inverse opal morphology without the use of a supporting template during the conversion, have not been previously reported.     

Gems of Chemistry and Physics: Macroporous Metal Oxides with 3D Order

Naturally occurring gem opals would seem to be the inspiration for the recent explosion of work on three‐dimensionally ordered macroporous, or “3DOM” materials. Myriad techniques have been developed for the creation of 3DOM products. This work focuses on ordered metal oxides and the effects that the chemistry behind precursors and template removal have on the phase and composition of the end product. Structural features that affect the materials' photonic, optical, catalytic, and magnetic properties are discussed.     

Simulation and fabrication of binary colloidal photonic crystals and their inverse structures

Theoretical and experimental investigations have demonstrated that full bandgaps are not easy to achieve in the face-centered cubic (fcc) unary and binary structures; even for unary inverse opals with high refractive index network, the bandgaps are not as large as 1D or 2D structures. In this work, we simulated the bandgap of a binary inverse opal, which is over 16% larger than that of a unary inverse crystal. Two kinds of binary colloidal crystals and their inverse structures have been fabricated by a horizontal deposition method.     

Confinement Catalysis with 2D Materials for Energy Conversion

The unique electronic and structural properties of 2D materials have triggered wide research interest in catalysis. The lattice of 2D materials and the interface between 2D covers and other substrates provide intriguing confinement environments for active sites, which has stimulated a rising area of “confinement catalysis with 2D materials.” Fundamental understanding of confinement catalysis with 2D materials will favor the rational design of high‐performance 2D nanocatalysts. Confinement catalysis with 2D materials has found extensive applications in energy‐related reaction processes, especially in the conversion of small energy‐related molecules such as O₂, CH₄, CO, CO₂, H₂O, and CH₃OH. Two representative strategies, i.e., 2D lattice‐confined single atoms and 2D cover‐confined metals, have been applied to construct 2D confinement catalytic systems with superior catalytic activity and stability. Herein, the recent advances in the design, applications, and structure–performance analysis of two 2D confinement catalytic systems are summarized. The different routes for tuning the electronic states of 2D confinement catalysts are highlighted and perspectives on confinement catalysis with 2D materials toward energy conversion and utilization in the future are provided.     

Emerging Porous Two-Dimensional Materials: Current Status,Existing Challenges,and Applications

Two-Dimensional (2D) materials have attracted immense attention in recent years. These materials have found their applications in various fields, such as catalysis, adsorption, energy storage, and sensing, as they exhibit excellent physical, chemical, electronic, photonic, and biological properties. Recently, researchers have focused on constructing porous structures on 2D materials. Various strategies, such as chemical etching and template-based methods, for the development of surface pores are reported, and the porous 2D materials fabricated over the years are used to develop supercapacitors and energy storage devices. Moreover, the lattice structure of the 2D materials can be modulated during the construction of porous structures to develop 2D materials that can be used in various fields such as lattice defects in 2D nanomaterials for enhancing biomedical performances. This review focuses on the recently developed chemical etching, solvent thermal synthesis, microwave combustion, and template methods that are used to fabricate porous 2D materials. The application prospects of the porous 2D materials are summarized. Finally, the key scientific challenges associated with developing porous 2D materials are presented to provide a platform for developing porous 2D materials.     

反蛋白石结构光子晶体及其应用的研究

反蛋白石结构光子晶体因具有完全光子带隙、制备材料广泛、特殊的周期结构、大的比表面积和连通的孔洞结构,近年来在自发辐射的调制、提高光催化反应速率和染料敏化太阳能电池反应速率等领域成为研究热点之一,并且在光、电、催化、传感、显示、检测等领域有着巨大的应用价值。介绍了反蛋白石结构光子晶体的基本概念及制备方法,阐述了反蛋白石结构在材料自发辐射的调制、能量传递的调制、促进物理化学反应、外界环境响应材料等方面的作用及其应用。     

三维有序纳米光子晶体的缺陷及其形成机理

通过纳米小球自组装的方法制备获得了三维有序结构的聚苯乙烯（PS）蛋白石光子晶体.利用扫描电子显微镜（SEM）对蛋白石光子晶体的微观形貌进行表征,并利用透射光谱对蛋白石进行光学表征.结果表明,胶体自组装能够形成点缺陷、等边三角线缺陷和等边立方体缺陷,通过对最低能量和机理的探讨,得出导致这些缺陷形成的原因是折射率差异和光子带隙（PBG）位置的蓝移.     

Color tunability of upconversion emission in YBO3: Yb, Er inverse opal

Upconversion (C) light-emitting photonic band gap materials (YBO₃: Yb, Er) with inverse opal structure were prepared by a self-assembly technique in combination with a sol-gel method. The effect of the photonic stop-band on the upconversion luminescence of Er³⁺ ions has been investigated in the YBO₃: Yb, Er inverse opals. Significant suppression of the green or red UC emission was detected if the photonic band-gap overlaps with the Er³⁺ ions emission band. We successfully achieved the color tuning of the UC optical properties of the inverse opal by controlling the structure of the photonic crystal.     

Strain Engineering of 2D Materials: Issues and Opportunities at the Interface

Triggered by the growing needs of developing semiconductor devices at ever‐decreasing scales, strain engineering of 2D materials has recently seen a surge of interest. The goal of this principle is to exploit mechanical strain to tune the electronic and photonic performance of 2D materials and to ultimately achieve high‐performance 2D‐material‐based devices. Although strain engineering has been well studied for traditional semiconductor materials and is now routinely used in their manufacturing, recent experiments on strain engineering of 2D materials have shown new opportunities for fundamental physics and exciting applications, along with new challenges, due to the atomic nature of 2D materials. Here, recent advances in the application of mechanical strain into 2D materials are reviewed. These developments are categorized by the deformation modes of the 2D material–substrate system: in‐plane mode and out‐of‐plane mode. Recent state‐of‐the‐art characterization of the interface mechanics for these 2D material–substrate systems is also summarized. These advances highlight how the strain or strain‐coupled applications of 2D materials rely on the interfacial properties, essentially shear and adhesion, and finally offer direct guidelines for deterministic design of mechanical strains into 2D materials for ultrathin semiconductor applications.     

3D Heteroatom‐Doped Carbon Nanomaterials as Multifunctional Metal‐Free Catalysts for Integrated Energy Devices

Sustainable and cost‐effective energy generation has become crucial for fulfilling present energy requirements. For this purpose, the development of cheap, scalable, efficient, and reliable catalysts is essential. Carbon‐based heteroatom‐doped, 3D, and mesoporous electrodes are very promising as catalysts for electrochemical energy conversion and storage. Various carbon allotropes doped with a variety of heteroatoms can be utilized for cost‐effective mass production of electrode materials. 3D porous carbon electrodes provide multiple advantages, such as large surface area, maximized exposure to active sites, 3D conductive pathways for efficient electron transport, and porous channels to facilitate electrolyte diffusion. However, it is challenging to synthesize and functionalize isotropic 3D carbon structures. Here, various synthesis processes of 3D porous carbon materials are summarized to understand how their physical and chemical properties together with heteroatom doping dictate the electrochemical catalytic performance. Prospects of attractive 3D carbon structural materials for energy conversion and efficient integrated energy systems are also discussed.     

Photonic crystals and photonic structures

This paper reviews the state-of-the-art of photonic band gap materials, addressing separately the spectral ranges of microwaves and optics. In the microwave domain, applications seem to emerge in particular, thanks to the recent breakthrough of metallo-dielectric structures. In the optical domain, 3D structures have been recently demonstrated in the infrared. In the mean time, refractive index engineering of a variety of complex structures involving photonic band gap reflections as well as more classical Fresnel confinement of light is now underway for the study of quantum electrodynamics in the solid state.     

Bioinspired 2D Nanomaterials for Sustainable Applications

The increasing demand for constructing ecological civilization and promoting socially sustainable development has encouraged scientists to develop bioinspired materials with required properties and functions. By bringing science and nature together, plenty of novel materials with extraordinary properties can be created by learning the best from natural species. In combination with the exceptional features of 2D nanomaterials, bioinspired 2D nanomaterials and technologies have delivered significant achievements. Here, the progress over the past decade in bioinspired 2D photonic structures, energy nanomaterials, and superwetting materials, is summarized, together with the challenges and opportunities in developing bioinspired materials for sustainable energy and environmental technologies.     

Flexible photonic crystals for strain sensing

Three-dimensional (3-D) photonic crystals (PCs) have been studied as possible strain sensing materials, based on strain-induced stop band frequency shifting. Self-assembly of polystyrene microspheres, achieved by sedimentation over a flexible polyimide tape substrate whose surface hydrophilicity was optimized in order to achieve maximum wettability, led to an organized 3-D direct opal template. This was infiltrated with a silica sol-gel solution by dip-coating or by chemical vapour deposition and an inverse opal structure was ultimately obtained by chemical dissolution of the polymer template. The structural and optical properties of these PCs have been studied by scanning electron microscopy (FE-SEM) and UV/visible spectroscopy under variable degrees of strain. FE-SEM showed the presence of ordered domains up to ∼30 μm². A mechano-optical effect was evidenced by strain-induced shifting of the photonic stop band peak wavelength of the direct, infiltrated and inverse opals up to 50 nm in transmission mode, due to changes in interplanar spacing upon bending the flexible PCs. Optical response strain cycles were studied, suggesting the possible use of these structures in reversible photonic strain sensors integrated in sensor/actuator devices.     

Interactions of low-power photons with natural opals—PBG materials,photonic control,natural metamaterials,spontaneous laser emissions,and band-gap boundary responses

One overall goal of this research was to examine types of naturally-occurring opals that exhibit photonic control to learn about previously-unknown properties of naturally occurring photonic control that may be developed for broader applications. Three different photon sources were applied consecutively to three different types of natural, flawless, gem-quality precious opals. Two photon sources were lasers (green and red) and one was simulated daylight tungsten white. As each type of precious opal was exposed to each of the photon sources, the respective refractions, reflections, and transmissions were studied. This research is the first to show that applying various pleochroic and laser photon sources to these types of opals revealed significant information regarding naturally occurring photonic control, metamaterials, spontaneous laser emissions, and microspheroid cluster (inter-PBG zone) boundary effects. Plus, minimizing ambient light and the use of low power photon sources were critical to observing the properties regarding this photonic materials research. This research yielded information applicable to the development of materials to advance applications and devices of photonics, phononics, optoelectronics, nanomaterials, and metamaterials.     

2D Oxide Nanomaterials to Address the Energy Transition and Catalysis

2D oxide nanomaterials constitute a broad range of materials, with a wide array of current and potential applications, particularly in the fields of energy storage and catalysis for sustainable energy production. Despite the many similarities in structure, composition, and synthetic methods and uses, the current literature on layered oxides is diverse and disconnected. A number of reviews can be found in the literature, but they are mostly focused on one of the particular subclasses of 2D oxides. This review attempts to bridge the knowledge gap between individual layered oxide types by summarizing recent developments in all important 2D oxide systems including supported ultrathin oxide films, layered clays and double hydroxides, layered perovskites, and novel 2D‐zeolite‐based materials. Particular attention is paid to the underlying similarities and differences between the various materials, and the subsequent challenges faced by each research community. The potential of layered oxides toward future applications is critically evaluated, especially in the areas of electrocatalysis and photocatalysis, biomass conversion, and fine chemical synthesis. Attention is also paid to corresponding novel 3D materials that can be obtained via sophisticated engineering of 2D oxides.