Exploiting Nanoroughness on Holographically Patterned Three‐Dimensional Photonic Crystals

The fabrication of three‐dimensional (3D) diamond photonic crystals with controllable nanoroughness (≤120 nm) on the surface from epoxy‐functionalized cyclohexyl polyhedral oligomeric silsesquioxanes (POSS) is reported. The nanoroughness is generated on the 3D network due to microphase separation of the polymer chain segments in a nonsolvent during the rinsing step in holographic lithography process. The degree of roughness can be tuned by the crosslinking density of the polymer network, which is dependent on the loading of photoacid generators, the exposure dosage, and the choice of developer and rinsing solvent. Because the nanoroughness size is small, it does not affect the photonic band gap position of the photonic crystal in the infrared region. The combination of periodic microstructure and nanoroughness, however, offers new opportunities to realize superhydrophobicity and enhanced dye adsorption in addition to the photon management in the 3D photonic crystal.     

Light‐Induced Color Change in the Sapphirinid Copepods: Tunable Photonic Crystals

Light‐induced tunable photonic systems are rare in nature, and generally beyond the state‐of‐the‐art in artificial systems. Sapphirinid male copepods produce some of the most spectacular colors in nature. The male coloration, used for communication purposes, is structural and is produced from ordered layers of guanine crystals separated by cytoplasm. It is generally accepted that the colors of the males are related to their location in the epipelagic zone. By combining correlative reflectance and cryoelectron microscopy image analyses, together with optical time lapse recording and transfer matrix modeling, it is shown that male sapphirinids have the remarkable ability to change their reflectance spectrum in response to changes in the light conditions. It is also shown that this color change is achieved by a change in the thickness of the cytoplasm layers that separate the guanine crystals. This change is reversible, and is both intensity and wavelength dependent. This capability provides the male with the ability to efficiently reflect light under certain conditions, while remaining transparent and hence camouflaged under other conditions. These copepods can thus provide inspiration for producing synthetic tunable photonic arrays.     

光子晶体内的慢光及其应用

光子晶体是一种具有周期性介电结构的人造材料,具有独特的光子带隙特性,能控制光子的运动状态,是慢光实现的最佳材料系统之一.从多角度描述了光子晶体内产生慢光效应的物理机理,并给出了光子晶体内慢光效应的研究进展状况和主要研究方向,最后讨论了其潜在应用.     

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.     

含缺陷一维光子晶体电场分布研究

文章给出了任意入射角时光在一维光子晶体中的透射率及电场分布的解析式,研究了不同的入射角、入射光角频率、缺陷层折射率及光子晶体周期数对含缺陷的一维光子晶体场强分布的影响,同时研究了缺陷层的吸收系数对光子晶体透射率及场强分布的影响,所得到的一些结论为光子晶体的制备及应用提供新的有价值的理论依据。     

介电常数对比和填充率对光子晶体中光子禁带和局域态的调节

用有限时域差分法(FDTD)和Padé近似分析了二维光子晶体的能带结构和缺陷引起的局域态.针对介电常数对比和填充率对完整光子晶体中光子禁带以及缺陷态的影响作了研究.计算了不同缺陷的光子晶体模式的振荡频率和质量因子.数值模拟的结果表明通过改变介电参数对比和填充率可以实现对光子禁带的位置、宽度、数目以及对缺陷态的调整.     

介电常数对比和填充率对光子晶体中光子禁带和局域态的调节

用有限时域差分法(FDTD)和Padé近似分析了二维光子晶体的能带结构和缺陷引起的局域态.针对介电常数对比和填充率对完整光子晶体中光子禁带以及缺陷态的影响作了研究.计算了不同缺陷的光子晶体模式的振荡频率和质量因子.数值模拟的结果表明通过改变介电参数对比和填充率可以实现对光子禁带的位置、宽度、数目以及对缺陷态的调整.     

光子晶体的制备方法与应用

简要列出了光子晶体的制备方法,应用研究方面介绍了光子晶体光纤和波导、激光器、高效发光二极管等。     

Scalable Nanowire Photonic Crystals: Molding the Light Emission of InGaN

To date, there have been no efficient semiconductor light emitters operating in the green and amber wavelengths. This study reports on the synthesis of InGaN nanowire photonic crystals, including dot‐in‐nanowires, nanotriangles, and nanorectangles with precisely controlled size, spacing, and morphology, and further demonstrates that bottom‐up InGaN photonic crystals can exhibit highly efficient and stable emission. The formation of stable and scalable band edge modes in defect‐free InGaN nanowire photonic crystals is directly measured by cathodoluminescence studies. The luminescence emission, in terms of both the peak position (λ ≈ 505 nm) and spectral linewidths (full‐width‐half‐maximum ≈ 12 nm), remains virtually invariant in the temperature range of 5–300 K and under excitation densities of 29 W cm^?2 to 17.5 kW cm^?2. To the best of our knowledge, this is the first demonstration of the absence of Varshni and quantum‐confined Stark effects in wurtzite InGaN light emitters—factors that contribute significantly to the efficiency droop and device instability under high‐power operation. Such distinct emission properties of InGaN photonic crystals stem directly from the strong Purcell effect, due to efficient coupling of the spontaneous emission to the highly stable and scalable band‐edge modes of InGaN photonic crystals, and are ideally suited for uncooled, high‐efficiency light‐emitting‐diode operation.     

一维光子晶体中光场局域态特性的研究

给出了任意入射角的一维光子晶体透射率及场强分布解析式,分别研究了缺陷层的吸收系数对光子晶体透射率、场强分布的影响,同时研究了不同的入射角、缺陷层折射率、光子晶体周期数及光子晶体结构形式对场强分布的影响。得到了一些新的有价值的结论,为光子晶体的制备及应用提供了理论依据。     

Designing Multicolor Micropatterns of Inverse Opals with Photonic Bandgap and Surface Plasmon Resonance

Structural coloration provides unique features over chemical coloration, such as nonfading, color tunability, and high color brightness, rendering it useful in various optical applications. To develop the structural colors, two different mechanisms of coloration–photonic bandgap (PBG) and surface plasmon resonance (SPR)–have been separately utilized. In this work, a new method is suggested to create structurally colored micropatterns by regioselectively employing SPR in a single film of inverse opal with PBG. The inverse opals are prepared by thermal embedding of opal into a negative photoresist and its subsequent removal. The inverse opals have a hexagonal array of open pores on the surface which serves as a template to make SPR‐active nanostructures through a directional deposition of gold, a perforated gold film and an array of curved gold disks are formed. With a shadow mask lithographically prepared, the gold is regioselectively deposited on the surface of the inverse opal, which results in two distinct regions of gold‐free inverse opal with PBG and gold nanostructure with SPR. As PBG and SPR develop their own structural colors respectively, the resultant micropatterns exhibit pronounced dual colors. More importantly, the micropatterns show the distinguished optical response for evaporation of volatile liquids that occupy the pores.     

光子晶体结构、制备技术和应用进展

介绍了光子晶体的结构、制备技术和应用方面的最新进展。继金刚石结构之后,又证实了圆木堆积、反蛋白石和矩形螺旋结构具有完全光子带隙。光子晶体的制备技术大体可分为微电子制备技术、自组装技术与层层叠加技术,三者各有优缺点。光子晶体在光子晶体光纤、光子晶体激光器、光子晶体波导等众多领域有着广阔的应用前景。     

Bio‐Inspired Photonic Materials: Prototypes and Structural Effect Designs for Applications in Solar Energy Manipulation

Natural creatures have evolved elaborate photonic nanostructures on multiple scales and dimensions in a hierarchical, organized way to realize controllable absorption, reflection, or transmitting the desired wavelength of the solar spectrum. A bio‐inspired strategy is a powerful and promising way for solar energy manipulation. This feature article presents the state‐of‐the‐art progress on bio‐inspired photonic materials on this particular application. The article first briefly recalls the physical origins of natural photonic effects and catalogues the typical natural photonic prototypes including light harvesting, broadband reflection, selective reflection, and UV/IR response. Next, typical applications are categorized into two primary areas: solar energy utilization and reflection. Recent advances including solar‐to‐electricity, solar‐to‐fuels, solar‐thermal (e.g., photothermal converters, infrared detectors, thermoelectric materials, smart windows, and solar steam generation) are highlighted in the first part. Meanwhile, solar energy reflection involving infrared stealth, radiative cooling, and micromirrors are also addressed. In particular, this article focuses on bioinspired design principles, structural effects on functions, and future trends. Finally, the main challenges and prospects for the next generation of bioinspired photonic materials are discussed, including new design concepts, emerging ideas, and possible strategies.     

Differences of Band Gap Characteristics of Square and Triangular Lattice Photonic Crystals in Terahertz Range

Band gap characteristics of the photonic crystals in terahertz range with square lattice and triangular lattice of GaAs cylinders are comparatively studied by means of plane wave method (PWM). The influence of the radius on the band gap width is analyzed and the critical values where the band gap appears are put forward. The results show that the maximum band gap width of photonic crystal with triangular lattice of GaAs cylinders is much wider than that of photonic crystal with square lattice. The research provides a theoretic basis for the development of t rahertz (THz) devices.     

Differences of Band Gap Characteristics of Square and Triangular Lattice Photonic Crystals in Terahertz Range

Band gap characteristics of the photonic crystals in terahertz range with square lattice and triangular lattice of GaAs cylinders are comparatively studied by means of plane wave method （PWM）. The influence of the radius on the band gap width is analyzed and the critical values where the band gap appears are put forward. The results show that the maximum band gap width of photonic crystal with triangular lattice of GaAs cylinders is much wider than that of photonic crystal with square lattice. The research provides a theoretic basis for the development of terahertz （THz） devices.     

Biopolymer Templated Glass with a Twist: Controlling the Chirality,Porosity, and Photonic Properties of Silica with Cellulose Nanocrystals

A detailed investigation of the formation and properties of mesoporous silica templated by the chiral nematic liquid crystal phase of cellulose nanocrystals (CNCs) is presented. Under appropriate conditions, CNCs co‐assemble with silica up to loadings of ≈60 wt% to give composite films with periodic chiral nanostructures. The periodicity of these films can be readily controlled to obtain materials that selectively reflect light with wavelengths ranging from ≈400–1400 nm. The co‐assembly of CNCs and silica into ordered chiral nematic structures is demonstrated to occur within a narrow window of pH and is affected by aging: a slow rate of silica condensation appears to be vital for the formation of well‐ordered materials. CNCs can be removed from the composite films by calcination or acid hydrolysis to give high surface area chiral nematic mesoporous silica (CNMS) with tunable pore diameters. The combination of mesoporosity and chiral nematic ordering in CNMS enables it to be used in a unique way for refractometric sensing applications. It is shown that, when using circular dichroism (CD) signals to monitor the chiral photonic properties of CNMS, variations in refractive index can be detected based on changes of both CD signal intensity and peak position with good sensitivity.     

Creation of Nanotips on ITO Electrode by Nanoparticle Deposition: An Easy Way to Enhance the Performance of Electrically Responsive Photonic Crystal and Fabricate Electrically Triggered Anticounterfeiting Tags

Electrically responsive photonic crystals (ERPC) are promising materials for electrophoretic displays, smart windows, and tunable optical devices. However, the high working voltage limits the application of most polar ERPCs because it damages color saturation, response stability, and reversibility. Herein, an easy but general method based on the modification of electrodes with nanoparticles is developed to improve ERPC's performance. The deposition of Au, Cu, or Cu₂O nanoparticles created nanotip structures on the electrode, which enhanced the charge injection and local electric field strength, lowered 43% of the working voltage, and increased the color saturation. Meanwhile, the lowered voltage inhibited the electrodeposition of colloidal particles and the electrochemical reaction, which also improved the stability and reversibility of the electrical response. Based on the region-selective modification of the electrode and the resulting asymmetric electrical response, an electrically triggered tag with a “pattern showing/hiding” effect is fabricated for anticounterfeiting purposes.     

Simultaneous Tenfold Brightness Enhancement and Emitted‐Light Spectral Tunability in Transparent Ambipolar Organic Light‐Emitting Transistor by Integration of High‐k Photonic Crystal

In organic light‐emitting transistors, the structural properties such as the in‐plane geometry and the lateral charge injection are the key elements that enable the monolithic integration of multiple electronic, optoelectronic, and photonic functions within the same device. Here, the realization of highly integrated multifunctional optoelectronic organic device is reported by introducing a high‐capacitance photonic crystal as a gate dielectric into a transparent single‐layer ambipolar organic light‐emitting transistor (OLET). By engineering the photonic crystal multistack and bandgap, it is showed that the integration of the photonic structure has a twofold effect on the optoelectronic performance of the device, i.e., i) to modulate the spectral profile and outcoupling of the emitted light and ii) to enhance the transistor source–drain current by a 25‐fold factor. Consequently, the photonic‐crystal‐integrated OLET shows an order of magnitude higher emitted power and brightness with respect to the corresponding polymer‐dielectric device, while presenting as‐designed electroluminescence spectral and spatial distribution. The results validate the efficacy of the proposed approach that is expected to unravel the technological potential for the realization of highly integrated optoelectronic smart systems based on organic light‐emitting transistors.     

Dramatic Tuning of the Topological Hall Effect in AxRhO2 (A = K,Rb, and Cs) Crystals by Electron Concentration or Cation

Topological Hall effect, being an unconventional anomalous Hall effect, is originated from the real-space Berry curvature caused by the nontrivial topological spin textures in materials. Manipulations of nontrivial magnetic structure and related topological Hall effect are very important for the study of the chiral magnet. Herein, it is experimentally observed that the significant topological Hall conductivity σ_xy in antiferromagnetic K_0.5RhO₂ can reach 3.5% of ν = 1 quantum conductivity below 20 K. Furthermore, by adjusting the concentration of K-cation different from 0.5 in K_xRhO₂ or substituting the K cations by Rb or Cs to form Rb_0.5RhO₂ or Cs_0.5RhO₂, it is observed that the topological Hall effect is much weakened or even disappeared. This evolution, verified by the theoretical calculations, is attributed to the unstable ground state of the non-coplanar spin structure in K_xRhO₂ (x = 0.4 and 0.6) and Cs_0.5RhO₂. The significantly tunable topological Hall effect in A_xRhO₂ makes it prospective on logical/sensor devices of spintronics.