Rapid and Large‐Scale Fabrication of Full Color Woodpile Photonic Crystals via Interference from a Conformal Multilevel Phase Mask

The practical use of photonic crystals with structural colors requires technology capable of rapidly producing large‐area, three‐dimensional (3D) periodic nanostructures. Until now, the fabrication of 3D photonic crystals has relied mainly on additive manufacturing and colloidal self‐assembly. These technologies have provided a useful academic platform based on precisely controlled 3D periodicity but have not evolved into mass production technology. Here, optical lithography for the rapid fabrication of large‐area 3D photonic crystals with structural colors is introduced. The key strategy is to incorporate two orthogonal line gratings (periodicity: 300 nm) made of an elastomer to create a conformal multilevel phase mask. When the mask is irradiated with a 355 nm laser, the five beam interference is established in the proximity region. The interlayer thickness between the two orthogonal line gratings controls the phase difference, which is closely related to the symmetry of the resulting 3D interference pattern. The interlayer thickness is designed to produce a woodpile structure with a planar periodicity of 300 nm and a vertical periodicity of 716 nm. The pattern area of the woodpile photonic crystal is expanded to 1 in². Red, green, and blue colors are experimentally realized by controlling the vertical shrinkage of the photoresist.     

Direct Transcription of Two‐Dimensional Colloidal Crystal Arrays into Three‐Dimensional Photonic Crystals

A simple protocol for the fabrication of three‐dimensional (3D) photonic crystals in silicon is presented. Surface structuring by nanosphere lithography is merged with a novel silicon etching method to fabricate ordered 3D architectures. The SPRIE method, sequential passivation reactive ion etching, is a one‐step processing protocol relying on sequential passivation and reactive ion etching reactions using C₄F₈ and SF₆ plasma chemistries. The diffusion of fresh reactants and etch product species inside the etched channels is found to play an important role affecting the structural uniformity of the designed structures and the etch rate drift is corrected by adjusting the reaction times. High quality photonic crystals are thus obtained by adding the third dimension to the two‐dimensional (2D) colloidal crystal assemblies through SPRIE. Careful adjustments of both mask design and lateral etch extent balance allow the implementation of even more complex functionalities including photonic crystal slabs and precise defect engineering. 3D photonic crystal lattices exhibiting optical stop‐bands in the infrared spectral region are demonstrated, proving the potential of SPRIE for fast, simple, and large‐scale fabrication of photonic structures.     

Beyond Seashells: Bioinspired 2D Photonic and Photoelectronic Devices

The discovery of novel materials that possess extraordinary optical properties are of special interest, as they inspire systems for next‐generation solar energy harvesting and conversion devices. Learning from nature has inspired the development of many photonic nanomaterials with fascinating structural colors. 2D photonic nanostructures, inspired by the attractive optical properties found on the inner surfaces of seashells, are fabricated in a facile and scalable way. The shells generate shining clusters for preying on phototactic creatures through interaction with incident solar light in water. By alternately depositing graphene and 2D ultrathin TiO₂ nanosheets to form 2D–2D heterostructures and homostructures, seashell‐inspired nanomaterials with well‐controlled parameters are successfully achieved. They exhibit exceptional interlayer charge transfer properties and ultrafast in‐plane electron mobility and present fascinating nacre‐mimicking optical properties and significantly enhanced light‐response behavior when acting as photoelectrodes. A window into the fabrication of novel 2D photonic structures and devices is opened, paving the way for the design of high‐performance solar‐energy harvesting and conversion devices.     

Control of Optical Hysteresis in Block Copolymer Photonic Gels: A Step Towards Wet Photonic Memory Films

Polystyrene‐block‐poly(2‐vinyl pyridine) (PS‐b‐P2VP) block copolymer photonic gels are fabricated that exhibit controllable optical hysteresis in response to a cyclic pH sweep. The optical hysteresis is tuned by controlling the ion‐pairing affinity between various anions and the protonated pyridinium ions on the P2VP block, which is highly dependent on the hydration energy of the ions, the dielectric constant of the solvent, and the ionic strength of the medium. The pH coercivity defining the magnitude of hysteresis of the photonic gels could be varied from 0.26 to 7.4. Photonic gel films with strong optical hysteresis can serve as wet photonic memory films where information can be cyclically recorded and erased at least 15 times and maintained for at least 96 h. The memory colors can be further tuned by selection of the copolymer molecular weight.     

不同背景介质下金属Cu光子晶体带隙

提出了一种利用全反射抑制二维光子晶体表面电磁波泄漏的方法,并计算了不同背景介质下的二维金属Cu光子晶体的带隙结构,得到了带隙结构与填充率间的关系曲线。计算方法采用时域有限差分,金属型光子晶体由Cu柱构成。分别计算了以空气为背景介质和以PMMA为背景介质的正方晶格金属型光子晶体的带隙结构。研究结果表明：以PMMA为背景介质的正方晶格金属型光子晶体与以空气为背景介质相比,第一带隙更窄,第二带隙中心频率更低,且在填充率大于0.70时将会出现第三带隙。这对进一步扩展这种光子晶体的应用具有良好的参考意义。     

Inverse‐Woodpile Photonic Band Gap Crystals with a Cubic Diamond‐like Structure Made from Single‐Crystalline Silicon

Three dimensional photonic band gap crystals with a cubic diamond‐like symmetry are fabricated. These so‐called inverse‐woodpile nanostructures consist of two perpendicular sets of pores in single‐crystal silicon wafers and are made by means of complementary metal oxide–semiconductor (CMOS)‐compatible methods. Both sets of pores have high aspect ratios and are made by deep reactive‐ion etching. The mask for the first set of pores is defined in chromium by means of deep UV scan‐and‐step technology. The mask for the second set of pores is patterned using an ion beam and carefully placed at an angle of 90° with an alignment precision of better than 30 nm. Crystals are made with pore radii between 135–186 nm with lattice parameters a = 686 and c = 488 nm such that a/c = √2; hence the structure is cubic. The crystals are characterized using scanning electron microscopy and X‐ray diffraction. By milling away slices of crystal, the pores are analyzed in detail in both directions regarding depth, radius, tapering, shape, and alignment. Using optical reflectivity it is demonstrated that the crystals have broad reflectivity peaks in the near‐infrared frequency range, which includes the telecommunication range. The strong reflectivity confirms the high quality of the photonic crystals. Furthermore the width of the reflectivity peaks agrees well with gaps in calculated photonic band structures.     

Freestanding Graphitic Carbon Nitride Photonic Crystals for Enhanced Photocatalysis

Graphitic carbon nitride (g‐C₃N₄) has attracted tremendous attention in photocatalysis due to its extraordinary features, such as good thermal and chemical stability, metal‐free composition, and easy preparation. However, the photocatalytic performance of g‐C₃N₄ is still restricted by the limited surface area, inefficient visible light absorption, and high recombination rate of photoinduced charge carriers. Herein, a facile synthesis to produce freestanding g‐C₃N₄ photonic crystals (PCs) by crack‐free, highly ordered colloid crystals templating is reported. The PC structure succeeded from the silica opals induces bicontinuous framework, stronger optical absorption, and increase in the lifetime of photoexcited charge carriers compared to that of the bulk g‐C₃N₄, while the chemical structure remains similar to that of the bulk g‐C₃N₄. As such, the g‐C₃N₄ PCs have a much higher photodegradation kinetic of methyl orange and photocatalytic hydrogen production rate which is nearly nine times the rate of bulk g‐C₃N₄.     

Tunable Colors in Opals and Inverse Opal Photonic Crystals

Colloidal photonic crystals and materials derived from colloidal crystals can exhibit distinct structural colors that result from incomplete photonic band gaps. Through rational materials design, the colors of such photonic crystals can be tuned reversibly by external physical and chemical stimuli. Such stimuli include solvent and dye infiltration, applied electric or magnetic fields, mechanical deformation, light irradiation, temperature changes, changes in pH, and specific molecular interactions. Reversible color changes result from alterations in lattice spacings, filling fractions, and refractive index of system components. This review article highlights the different systems and mechanisms for achieving tunable color based on opaline materials with close‐packed or non‐close‐packed structural elements and inverse opal photonic crystals. Inorganic and polymeric systems, such as hydrogels, metallopolymers, and elastomers are discussed.     

混合型Fe3O4@SiO2胶体光子晶体光传输特性的仿真分析

除了通过改变胶体粒子半径及晶格常数来实现对光子带隙的调控方式之外,能否利用不同尺寸粒子的混合精确控制胶体光子晶体的显色行为是人们关注的一个重要科学问题。在分析Fe₃O₄@SiO₂胶体光子晶体的带隙范围与介电常数、电磁波入射角度、晶格常数、颗粒尺寸、SiO₂包覆层厚度的依赖关系的基础上,利用数值仿真手段对不同尺寸粒子混合得到的光子晶体的光传输特性进行了研究。结果发现,两种粒径的磁性胶体粒子按不同质量比混合后,其光子带隙位置始终落在两种粒径胶体粒子各自形成光子晶体的带隙位置之间,且随着大粒径颗粒掺杂比的增加,反射光谱逐渐红移。这一结果证明混色原理对胶体光子晶体仍然是适用的。该结果对研究胶体光子晶体结构色的新型调控方式具有重要的参考价值。     

Highly Brilliant Noniridescent Structural Colors Enabled by Graphene Nanosheets Containing Graphene Quantum Dots

The most important properties of noniridescent structural colors of amorphous photonic structures (APS) are sufficient color brightness and saturation, which are difficult to be optimized simultaneously. Herein, highly saturated and brilliant noniridescent structural colors are achieved by introducing graphene nanosheets, which contain a fraction of graphene quantum dots (GQDs), into the short‐range ordered APS. The effective modulation of the photoluminescence (PL) of GQDs by the selective enhancement of absorption at the blue pseudo photonic bandgap edges of the APS boosts the PL with wavelength matching that of the photonic bandgap and thus enables high structural color brightness; the uniform light absorption of graphene nanosheets in the whole visible spectra contributes to the high color saturation. Furthermore, by using APS films with short‐range order as templates, a brilliant colorful humidity sensor is demonstrated. Compared with the conventional sensing platform based on photonic crystals, the humidity sensor with brilliant noniridescent structural colors is more convenient by avoiding the confusing color dependence on the viewing angles. The improvement in the structural color brightness of the APS films by facile graphene doping will facilitate their practical applications in fields of decorations, packaging, pigments, sensors, displays, or other color‐related areas.     

Lattice‐Registered Two‐Photon Polymerized Features within Colloidal Photonic Crystals and Their Optical Properties

In this work we demonstrate a significant advance in the introduction of embedded defects in 3D photonic crystals by means of two‐photon polymerization. We have developed the ability to precisely position embedded defects with respect to the lattice of 3D photonic crystals by imaging the structure concurrently with two‐photon writing. Defects are written with near‐perfect lattice registration and at specifically defined depths within the crystal. The effect of precise defect position on the optical response is investigated for embedded planar cavities written in a photonic crystal. The experimental data are compared to spectra calculated using the Scalar Wave Approximation (SWA).     

光子晶体微纳光纤的制备新方法及其特性研究

为了形成胶体晶体-微纳光纤结构,采用提拉生长法,将单分散的聚苯乙烯微球在微纳光纤表面自组装生长成胶体晶体,并用扫描电子显微镜和光谱仪对胶体晶体的显微形貌和透射光谱特性进行了表征。结果表明,聚苯乙烯微球有序堆积,自组装成胶体晶体,其结构为面心立方密排结构,表面为面心立方结构的[111]面。胶体晶体-微纳光纤的透射光谱在1400.8nm处有透射峰,对应于面心立方结构在[111]方向上的光子带隙。这种光子晶体微纳光纤在光纤传感器及滤波器方面有广阔的应用前景。     

硅树脂调制的可调光子晶体

文章提出一种利用硅树脂调节光子晶体光子带隙的方法,光子晶体波导是通过往二维正方形光子晶体的介质柱之间填充硅树脂得到的,利用温度场改变硅树脂的折射率.数值模拟结果表明:通过温度场可对这种光子晶体的禁带结构进行调节.这种可调光子晶体可应用于制作新颖的偏光片和光开关.     

Photocrosslinkable Nanocomposite Multilayers for Responsive 1D Photonic Crystals

A straightforward method to increase the refractive index of photocrosslinkable polymers by incorporation of high index inorganic nanoparticles is demonstrated and shown to enhance the reflection efficiency of thermochromic 1D photonic multilayers. The refractive index of spin‐coated and UV‐crosslinked films based on poly(para‐methyl styrene) (PpMS) copolymers is increased from 1.57 for the copolymer alone to as high as 1.67 for nanocomposite samples with a volume fraction of 0.38 of ZrO₂ nanoparticles. Thermochromic photonic multilayers consisting of alternating films of PpMS–ZrO₂ with poly(N‐isopropylacrylamide) (PNIPAM) copolymers shows the increases in reflectance as large as 2.5‐fold compared to PpMS/PNIPAM multilayers lacking particles. In addition, ZrO₂ nanoparticles are used to increase the refractive index of PNIPAM‐based films up to 1.68 with a volume fraction of 0.49 of nanoparticles, enabling the fabrication of alternating PNIPAM–ZrO₂/PNIPAM multilayers with a well‐defined Bragg peak that shifts from 635 nm at 6 °C to 410 nm at 48 °C, and reflectance intensities as high as ≈0.30.     

Design and realization of transparent solar modules based on luminescent solar concentrators integrating nanostructured photonic crystals

Herein, we present a prototype of a photovoltaic module that combines a luminescent solar concentrator integrating one‐dimensional photonic crystals and in‐plane CuInGaSe₂ (CIGS) solar cells. Highly uniform and wide‐area nanostructured multilayers with photonic crystal properties were deposited by a cost‐efficient and scalable liquid processing amenable to large‐scale fabrication. Their role is to both maximize light absorption in the targeted spectral range, determined by the fluorophore employed, and minimize losses caused by emission at angles within the escape cone of the planar concentrator. From a structural perspective, the porous nature of the layers facilitates the integration with the thermoplastic polymers typically used to encapsulate and seal these modules. Judicious design of the module geometry, as well as of the optical properties of the dielectric mirrors employed, allows optimizing light guiding and hence photovoltaic performance while preserving a great deal of transparency. Optimized in‐plane designs like the one herein proposed are of relevance for building integrated photovoltaics, as ease of fabrication, long‐term stability and improved performance are simultaneously achieved. © 2015 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.     

用平面波展开法计算二维方形光子晶体的带隙结构

用平面波展开法计算二维正方晶格光子晶体的带隙结构，对二维光子晶体的电磁波理论及周期介质中的Bloch波解进行了详细的推导，得出TE模和TM模下无缺陷时光子晶体的色散曲线，并设计了低频区域内具有较大带隙宽度的两种二维光子晶体的空间周期结构. 经过大量的计算，发现硅中的空气柱型光子晶体在红外波段TE模和TM模存在重叠的绝对光子带隙，并分别研究了空气中的硅介质柱和硅中的空气柱的TM模带隙宽度随空气柱半径和填充比变化的规律.     

Spray Synthesis of Photonic Crystal Based Automotive Coatings with Bright and Angular-Dependent Structural Colors

It is a challenge to prepare photonic crystal (PC) automotive coatings via spraying colloidal solutions because the fast fabrication tends to produce amorphous photonic crystals with faint colors. Here, a two-step spraying process followed by thermal curing is developed to prepare waterproof PC coatings with bright, uniform, and angular-dependent structural colors. The solvents in PC paint are studied to achieve a quick formation of liquid PC intermediate, which transformed into a highly crystalline PC coating. Thanks to the narrow and intense reflections, the as-made coatings present colors with high saturation, including the red/yellow/green/blue colors achieved by tuning the particle size, and many spectral/non-spectral colors via the mixing of base colors. Meanwhile, patterned or fully covered PC coatings with good chemical and mechanical stability can be prepared on different substrates, where the shiny colors changing with the viewing angles or the surface curvatures offer a new choice for personalized automotive coatings.     

入射角度对一维光子晶体禁带的调制研究

利用特征矩阵法,分别研究了不同偏振方式的波入射到光子晶体时,光子晶体的禁带随入射角度的变化.结果表明:不论是TM波入射还是TE波入射,随着入射角度的增大,光子晶体的带隙都向短波方向移动;TM波入射时,光子晶体的带隙随入射角度的增大而减小,而以TE波入射光子晶体时,随着入射角度的增大,光子晶体的带隙逐渐增大.     

Humidity‐Compensating Sensor for Volatile Organic Compounds Using Stacked Porous Silicon Photonic Crystals

One‐dimensional photonic crystals constructed from multilayered stacks of porous Si are used as sensors for gas‐phase volatile organic compounds (VOCs). The ability of a double‐stack structure to provide compensation for drift due to changing relative humidity (RH) is investigated. In this approach, two separate photonic crystals (dielectric stacks) are etched into a crystalline Si substrate, one on top of the other. The top stack is chemically modified to be hydrophobic (by hydrosilylation with dodecene) and the bottom stack is made hydrophilic (by hydrosilylation with undecylenic acid). It is shown that the optical spectrum of the double‐stack structure provides an effective means to discriminate VOCs from water vapor. In this approach, shifts in the peak frequencies from both photonic crystals are measured simultaneously. Because the two stacks respond differently to water and to VOC, the effect of changing humidity can be nulled by calculating the weighted difference between the two peak frequencies. Reliable determination of the concentration of VOC vapor in nitrogen over a range of RH values (25% < RH < 75%) is demonstrated. The ability of the double‐stack structure to discriminate between water vapor and VOCs is quantified for four different VOCs: toluene, dimethyl methylphosphonate (DMMP), heptane, and ethanol.     

PBG structures of novel two-dimensional annular photonic crystals with triangular lattice

The photonic band gap (PBG) structures of four types of annular photonic crystals (PCs) with inner-scatter of rectangular, square, hexagonal and circle shapes are respectively calculated by the plane wave expansion method. The optimal samples with the largest gap-midgap ratio for each structure are obtained by scanning the four parameters: filling ratio f, dielectric constant ɛ₁, rotating angle θ of inner-scatters and outside radius R of the air ring. The results show that the band gap can be further maximized by adjusting the structural parameters, and a wide PBG with the gap-midgap ratio of 20.4% is gained in the annular photonic crystal with rectangular inner-scatters.