Full-photonic-bandgap structures for prospective dye-sensitized solar cells

The photonic bands of various TiO₂ photonic crystals filled with acetonitrile were investigated with the perspective for application to dye-sensitized solar cells. Finite-difference time-domain methods revealed that three-dimensional (3D) photonic crystals with diamond-log and inverse-diamond-log structures composed of TiO₂ and an electrolyte had full photonic band gaps under certain conditions. The quality factor of the band gap and the electrolyte filling factor of the structures were optimized. Moreover, with the consideration for easy fabrication of such photonic crystals, two-dimensional (2D) photonic crystals, i.e., TiO₂ slabs with square holes filled with electrolytes, were also investigated. Two-dimensional structures that have a full photonic band gap were also discovered. These discoveries may lead to early electrochemical applications of dye-sensitized photonic-crystal electrodes.     

Fabrication of TiO2–SiO2 Photonic Crystals with Diamond Structure

Ceramic photonic crystals with diamond structure were fabricated using stereolithography and successive sintering. The green body of an epoxy resin incorporating 10 vol% TiO₂–SiO₂ was formed by stereolithography and then heated in air at 1100°–1400°C for 2 h. The sintered products maintained the diamond structure with a linear shrinkage ratio of about 57% and a porosity of 38%. The ceramic photonic crystal with eight unit cells showed a photonic band gap at the center frequency of 23.5 GHz. This fabrication method of three-dimensional (3D) ceramic photonic crystals is applicable to other 3D structural ceramics and does not require any molding techniques.     

Smart Processing Development of Photonic Crystals and Fractals

A new concept of smart processing is proposed that can produce advanced materials and components by finely controlling processing energy and engineering structures. New functional components of 3D photonic crystals and fractals are demonstrated, which are constructed of dielectric ceramics and a polymer using a CAD/CAM stereolithography system. By modifying the structure of diamond-like photonic crystals using free-form fabrication, electromagnetic waves can be controlled, opening the way for new applications in communication and sensing technology. The photonic fractal, a new material that can strongly localize electromagnetic waves without reflection and transmission, will also lead to new applications in the energy and medical fields.     

Solvent-based paste extrusion solid freeforming

Solvent-based extrusion freeforming is capable of building complex ceramic 3D structures and can be used in the fabrication of hard and soft tissue scaffolds, photonic crystals for millimetre wave, ordered ceramic preforms for metal matrix composites, precise molten metal filters and potentially for terahertz bandgap metamaterials. This is a powder-based rapid prototyping process, the principle of which is the realization of liquid to solid transition through solvent evaporation in the presence of a binder. We describe the characteristics of pastes prepared from different powders, notably the rheological properties at different solvent fractions and illustrate some of the structures fabricated by this technique.     

基于聚合物的一维光子晶体研究进展

从一维光子晶体组装材料角度出发,总结分析了基于聚合物的有机/有机型和有机/无机杂化型一维光子晶体的结构特点、组装原理和方法、性能及应用。在有机/有机型一维光子晶体中,主要介绍了含有不同亲疏水链段的嵌段共聚物和含有可聚合双键的表面活性剂自组装形成的一维光子晶体。在有机/无机杂化型一维光子晶体中,既论述了基于聚合物、无机材料直接交替组装形成的多层膜,也讨论了基于两种无机材料组装,然后再填充柔性聚合物的一维光子晶体。通过对以上两类光子晶体材料的总结分析可知,基于聚合物材料制备的一维光子晶体可以实现多种功能,在柔性传感器、柔性光电器件、光子晶体纸、电子皮肤、3D打印等方面具有良好的应用前景。但目前基于聚合物的一维光子晶体存在组装均匀性有待提高、组装面积较小等问题,如何大规模制备均匀的功能性一维光子晶体是重要的研究方向,也是影响其实际应用的关键。     

陶瓷基光子晶体的研究进展

采用以陶瓷材料为母体制备光子晶体是光子晶体制备的一个重要研究发展方向.本文介绍了陶瓷基光子晶体的几种主要的制备方法以及光子晶体在微波和红外、可见光频段中的应用.基于功能陶瓷所具有丰富的光/电功能可以制备陶瓷基光子晶体,文中介绍了可调带隙光子晶体和光子晶体中自发辐射方面的一些研究成果.陶瓷基光子晶体由于具有折射率高,功能广泛,制备手段多样等特点,因而具有广泛的应用前景,如用作电场调节的光开关和在显示领域中基于光子晶体各向异性发光特点的具有定向光发射性能的光源.     

Recent advances in polymer colloidal crystal lasers

Colloids with a size in the nanometres to micrometres range are frequently used in both fundamental research and industrial applications. In this context, colloidal crystals (CCs)-3D ordered arrays of monodispersed colloidal microparticles with a diameter of several hundred nanometres-have garnered a great deal of attention in the intriguing research realm of photonic crystals (PCs) due to the feasible and high-throughput 3D-PC fabrication with CCs. For optoelectronic applications, it is of prime importance to construct 3D-PCs with photonic band-gaps (PBGs) in the visible wavelength range. With regard to photonic device applications, many reports have been made on a wide variety of optical reflection sensors and displays using CCs that shift the visible PBG wavelength in response to external stimuli. This Minireview describes the research progress in the investigation of CCs and their laser applications. We highlight not only the research background of CCs as 3D-PCs, but also new potential applications of CCs as flexible and widely tunable lasers by low-threshold optical excitation.     

Metal oxide one dimensional photonic crystals made by RF sputtering and spin coating

We report here the analysis of the light transmission properties of one dimensional photonic crystals made by multilayers of silicon dioxide and titanium dioxide. A precise fabrication by radiofrequency sputtering of a photonic crystal allows us to accurately model the transmission spectrum of the crystal, by taking into account the wavelength dependent refractive indexes of the materials. We found that, while the dispersion of silicon dioxide is in good agreement with data reported in literature, the dispersion of titanium dioxide is more critical. Using such dispersions we could fit the transmission spectra of silicon dioxide/titanium dioxide one dimensional photonic crystals made by spin coating layer deposition starting from nanoparticle colloidal dispersions. The fit takes into account the porosity of the layers and the losses due to Rayleigh scattering.     

胶晶模板法制备有序大孔炭材料研究进展

三维有序大孔炭材料（3DOCM）在光子晶体、催化剂载体、生物传感器和电极材料等方面具有潜在的应用前景，SiO2胶晶模板法是制备有序大孔炭材料的有效方法。制备步骤主要包括SiO2模板的组装、炭前驱填充及模板去除。本文综合所查文献，对有序大孔炭材料的制备及应用做了简要介绍。     

Constructing photocatalyst from β-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> photonic crystals for enhanced photocatalytic performance

Photonic crystals with highly ordered structure have presented a prospective application in the design of photocatalysts. Herein, we fabricated visible-light active β-Bi₂O₃ photonic crystals via a modified sandwich infiltration method. By using the acetylacetone-complexed metal ion precursors, pure β-Bi₂O₃ photonic crystals with highly ordered structure could be obtained at a calcination temperature of 400?°C. Benefited from the facilitated mass transport in the highly ordered structure, β-Bi₂O₃ photonic crystals exhibited higher photocatalytic activity towards organic pollutions degradation than porous β-Bi₂O₃ and β-Bi₂O₃ nanocrystals. Furthermore, the photonic band gap of β-Bi₂O₃ photonic crystals could be modulated to overlap its electronic band gap by changing the macropore diameter into 220 nm. Slow photon effect could be observed over the β-Bi₂O₃ photonic crystals with a pore diameter of 220 nm, which enhanced the electronic band gap absorption and further improved the corresponding photocatalytic activity. The enhanced activity stability of β-Bi₂O₃ photonic crystals could also be observed. Based on the detection of active species, the degradation mechanism over β-Bi₂O₃ photonic crystals was discussed. The fabrication of β-Bi₂O₃ photonic crystals in this study provides experimental guidance for developing photonic crystals with enhanced visible light absorption and photocatalytic activities.     

全光法制作三维光子晶体的研究进展

三维光子晶体作为一种新型材料已经得到了广泛的应用。用全光法制备三维光子晶体具有容易实现、成本低廉等优点。本文介绍了用光学方法制备三维光子晶体的几种方法。     

Highly flexible method for the fabrication of photonic crystal slabs based on the selective formation of porous silicon

ABSTRACT: A novel fabrication method of Si-photonic slabs based on the selective formation of porous silicon is reported. Free standing square lattices of cylindrical air holes embedded in a Si matrix can be achieved by proton beam irradiation followed by electrochemical etching of Si wafers. The Photonic Band structures of these slabs show several gaps for the two symmetry directions for reflection through the z-plane. The flexibility of the fabrication method for tuning the frequency range of the gaps over the near and mid infrared ranges is demonstrated. This tuneability can be achieved by simply adjusting the main parameters in the fabrication process such as the proton beam line spacing, proton fluence or anodization current density. Thus, the reported method opens a promising route towards the fabrication of Si-based photonic slabs, with high flexibility and compatible with the current microelectronics industry.     

光子晶体及SiO2光子晶体的制备技术

光子晶体是一种具有光子带隙的周期性电介质结构,落在光子带隙中的光将不能传播。由于其独特的调节光子传播状态的功能,成为实现光通讯和光子计算机的基础。SiO2胶体球作为胶体光子晶体的组成基元,具有广阔的应用前景。本文介绍了光子晶体的概念、特征与应用领域,以及SiO2光子晶体的制备技术。     

Strong Suppression and Enhancement of Photoluminescence in Zn2SiO4:Mn2+ Inverse Opal Photonic Crystals

Inverse opal photonic crystals based on a luminescent matrix of Mn²⁺-doped Zn₂SiO₄ were synthesized, and their photoluminescence was investigated using a fluorescence microscope and spectrometer. Strong suppression of the luminescence from the Zn₂SiO₄:Mn²⁺ matrix in certain directions was observed directly due to the overlap of the pseudo-photonic bandgap (PPBG) and the emission band. As a result, the luminescence in other orientations (outer of the PPBG) was enhanced significantly. This cost-effective, non-lithographic method to produce luminescent inverse opals is expected to be useful for the fabrication of anisotropic photonic crystal light sources for display applications.     

Nanoscale waveguiding methods

While 32 nm lithography technology is on the horizon for integrated circuit (IC) fabrication, matching the pace for miniaturization with optics has been hampered by the diffraction limit. However, development of nanoscale components and guiding methods is burgeoning through advances in fabrication techniques and materials processing. As waveguiding presents the fundamental issue and cornerstone for ultra-high density photonic ICs, we examine the current state of methods in the field. Namely, plasmonic, metal slot and negative dielectric based waveguides as well as a few sub-micrometer techniques such as nanoribbons, high-index contrast and photonic crystals waveguides are investigated in terms of construction, transmission, and limitations. Furthermore, we discuss in detail quantum dot (QD) arrays as a gain-enabled and flexible means to transmit energy through straight paths and sharp bends. Modeling, fabrication and test results are provided and show that the QD waveguide may be effective as an alternate means to transfer light on sub-diffraction dimensions.     

Preparation of a three‐dimensional ordered macroporous titanium dioxide material with polystyrene colloid crystal as a template

Polystyrene (PS) photonic colloid crystals were assembled from PS spheres prepared by emulsion‐free polymerization through an improved vertical deposition method that could shorten the assembly time efficiently. The monodispersity of the spheres was appraised according to the standard deviation. The results showed that the PS spheres had a high monodispersity with a standard deviation of 3.7% and a dispersion coefficient of 0.02. The morphology and bandgap structure were observed with scanning electron microscopy images and transmission spectra, respectively. The mechanism of vertical deposition was analyzed simply. As an application of PS colloid crystals, ordered macroporous TiO₂ photonic crystals were prepared, and the structure and properties of macroporous TiO₂ were also studied with various analytical methods, which provided some values for the fabrication of photonic crystals with a complete bandgap. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Photonic bandgap of inverse opals prepared from core-shell spheres

ABSTRACT: In this study we synthesized the monodispersed polystyrene (PS)-silica core-shell spheres with various shell thickness for the fabrication of photonic crystals. The shell thickness of spheres was controlled by the various additions of tetraethyl orthosilicate during the shell growth process. The shrinkage ratio of the inverse opal photonic crystals prepared from the core-shell spheres was significantly reduced from 14.7% to within 3%. We suspected that the improvement resulted from the confinement of silica to the contraction of PS space during calcination. Due to the shell effect, the inverse opals prepared from the core-shell spheres have the higher filling fraction and the larger wavelength of stop band maximum.     

Magnetic assembly route to colloidal responsive photonic nanostructures

Responsive photonic structures can respond to external stimuli by transmitting optical signals. Because of their important technological applications such as color signage and displays, biological and chemical sensors, security devices, ink and paints, military camouflage, and various optoelectronic devices, researchers have focused on developing these functional materials. Conventionally, self-assembled colloidal crystals containing periodically arranged dielectric materials have served as the predominant starting frameworks. Stimulus-responsive materials are incorporated into the periodic structures either as the initial building blocks or as the surrounding matrix so that the photonic properties can be tuned. Although researchers have proposed various versions of responsive photonic structures, the low efficiency of fabrication through self-assembly, narrow tunability, slow responses to the external stimuli, incomplete reversibility, and the challenge of integrating them into existing photonic devices have limited their practical application. In this Account, we describe how magnetic fields can guide the assembly of superparamagnetic colloidal building blocks into periodically arranged particle arrays and how the photonic properties of the resulting structures can be reversibly tuned by manipulating the external magnetic fields. The application of the external magnetic field instantly induces a strong magnetic dipole-dipole interparticle attraction within the dispersion of superparamagnetic particles, which creates one-dimensional chains that each contains a string of particles. The balance between the magnetic attraction and the interparticle repulsions, such as the electrostatic force, defines the interparticle separation. By employing uniform superparamagnetic particles of appropriate sizes and surface charges, we can create one-dimensional periodicity, which leads to strong optical diffraction. Acting remotely over a large distance, magnetic forces drove the rapid formation of colloidal photonic arrays with a wide range of interparticle spacing. They also allowed instant tuning of the photonic properties because they manipulated the interparticle force balance, which changed the orientation of the colloidal assemblies or their periodicity. This magnetically responsive photonic system provides a new platform for chromatic applications: these colloidal particles assemble instantly into ordered arrays with widely, rapidly, and reversibly tunable structural colors, which can be easily and rapidly fixed in a curable polymer matrix. Based on these unique features, we demonstrated many applications of this system, such as structural color printing, the fabrication of anticounterfeiting devices, switchable signage, and field-responsive color displays. We also extended this idea to rapidly organize uniform nonmagnetic building blocks into photonic structures. Using a stable ferrofluid of highly charged magnetic nanoparticles, we created virtual magnetic moments inside the nonmagnetic particles. This "magnetic hole" strategy greatly broadens the scope of the magnetic assembly approach to the fabrication of tunable photonic structures from various dielectric materials.     

High-temperature stable inverse opal photonic crystals via mullite-sol-gel infiltration of direct photonic crystals

Three-dimensionally ordered macroporous materials for photonic or refractory applications have been developed by an innovative approach based on mullite sol-gel infiltration of direct photonic crystals followed by burn-out and calcination. Direct photonic crystals were obtained using polystyrene spheres templates either by vertical convective self-assembly or by drop casting. The samples were then infiltrated by spin coating with mullite sol-gels prepared with two different compositions (74 wt.% Al₂O₃, 26 wt.% SiO₂ and 80 wt.% Al₂O₃, 20 wt.% SiO₂). The inverse opal photonic crystals prepared with both sol-gels presented a highly ordered porosity and the high-alumina composition showed stability up to 1500°C. After inversion of the structure (polymeric template burn-out), the high-alumina composition showed roundness of the PS templated pores closer to an ideal sphere (Ø = 0.967) when compared to the low-alumina composition (Ø = 0.954). Although the inverse opal photonic crystals did not present a photonic bandgap, they showed structural stability at high temperatures, which enable their application as refractory materials.     

Fabrication of Metallodielectric Photonic Crystals with a Diamond Structure and their Microwave Properties

Three-dimensional (3D) metallodielectric photonic crystals with a diamond structure were fabricated in order to investigate the formation of stop bands and the absorption ability for microwaves with the dielectric absorbing media embedded into the 3D metal lattice. First, the metallic photonic crystals were prepared by filling the epoxy molds formed by stereolithography with a metal alloy having a low melting point of 70°C, followed by removal of the molds. The metallodielectric photonic crystals were then fabricated by infiltrating the porous metal crystal with a SiC/polyester mixture. The lattice constant of photonic crystals was 15 mm. The effects of different aspect ratios of diamond lattice rods, number of metallic lattice units along Γ-L 〈1 1 1〉, Γ-X 〈1 0 0〉, and Γ-K 〈1 1 0〉 directions, and metallodielectric samples along the Γ-X 〈1 0 0〉 direction on the formation of stop band and microwave absorption ability were investigated in the frequency range from 3 to 30 GHz. Metallodielectric photonic crystals formed showed good absorption ability. The measured transmission spectra of the metallic and metallodielectric crystals agreed well with the simulation of the transmission line modeling method.