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Effects of Microsphere Size on the Mechanical Properties of Photonic Crystals
摘要： Photonic crystal (PC) thin films that are self-assembled from different-sized silica microspheres were prepared for studying mechanical properties via nanoindentation at the submicron scale. We found that the silica photonic crystals (PCs) possessed a face-centered cubic (FCC) microstructure and their elastic modulus and hardness were in the range of ~1.81–4.92 GPa and 0.008–0.033 GPa, respectively. The calculated results proved that there were size-dependent properties in the silica PCs, in that the elastic modulus and hardness increased as the diameter decreased from 538 nm to 326 nm. After studying the total work and plastic work in the progressive deformation of silica PCs during the nanoindentation tests, we developed a two-stage deformation model to explain how the microsphere size affects the mechanical properties of PC thin films. The phenomenon of 'smaller is stronger' is mainly due to the energy consumption, which combines the effects of microstructure collapse, microsphere slide, and reduced porosity during the whole loading and unloading process. In addition, the results of numerical simulation matched the experimental data and reflected the energy change rules of PCs during the indentation process. Furthermore, the study affords useful guidance for constructing high-performance films with proper design and potential application in next-generation PC materials.
关键词： photonic crystals,deformation mechanism,nanoindentation,size-dependent
更新于2025-09-23 15:22:29
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Dynamic Emission Tuning of X-ray Radioluminescent Crystalline Colloidal Arrays: Coupling the Optical Stop Band with Sequential F?rster Resonance Energy Transfers
摘要： X-ray radiation exhibits diminished scattering and a greater penetration depth in tissue relative to the visible spectrum and has spawned new medical imaging techniques that exploit X-ray luminescence of nanoparticles. The majority of the nanoparticles finding applications in this field incorporate metals with high atomic numbers and pose potential toxicity effects. Here, a general strategy for the preparation of a fully organic X-ray radioluminescent colloidal platform that can be tailored to emit anywhere in the visible spectrum through a judicious choice in donor/acceptor pairing and multiple sequential F?rster resonance energy transfers (FRETs) is presented. This is demonstrated with three different types of ≈100 nm particles that are doped with anthracene as the scintillating molecule to “pump” subsequent FRET dye pairs that result in emissions from ≈400 nm out past 700 nm. The particles can be self-assembled in crystalline colloidal arrays, and the radioluminescence of the particles can be dynamically tuned by coupling the observed rejection wavelength with the dyes’ emission.
关键词： anthracene,F?rster resonance energy transfer,photonic crystals,X-ray radioluminescence,colloidal crystals
更新于2025-09-23 15:21:21
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Narrow Linewidth and Temperature Insensitive Blue Phase Liquid Crystal Films
摘要： Blue phase liquid crystal ?lms are quite useful in re?ective displays, ?exible photonic devices, and optical sensors. However, the effects of refractive index properties of re?lled liquid crystals and environment temperature on re?ection properties of blue phase liquid crystal ?lms are far from fully exploration. Herein, we demonstrate blue phase liquid crystal ?lms re?lled with different nematic liquid crystals. The effects of birefringence and average refractive index of re?lled nematic liquid crystals on the re?ection properties such as re?ectance, central wavelength, and linewidth of photonic band have been studies. The temperature effect on re?ectance and central wavelength has been studied. A narrow linewidth (19.4 nm) and temperature insensitivity blue phase liquid crystal ?lm has been fabricated by re?lling liquid crystals of DYX8013 with small birefringence. The narrow linewidth and excellent temperature insensitivity properties of BPLC ?lm can be applied in color re?ective display and ?exible photonic devices.
关键词： Photonic materials,photonic crystals
更新于2025-09-23 15:21:21
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High-performance and Multifunctional Colorimetric Humidity Sensors Based on Mesoporous Photonic Crystals and Nanogels
摘要： Colorimetric sensors, as a key branch of the application of photonic crystals (PCs), sets off enthusiasm of scientists to make research. Here, simple mesoporous and structurally colored one-dimensional photonic crystals (1DPCs) constructed by alternating assembly of poly(acrylamide-N,N'-methylene bisacrylamide) (P(AM-MBA)) nanogels and TiO2 nanoparticles are reported as high-performance colorimetric humidity sensors. The sensors with bright colors display rapid response to relative humidity (RH) change and reach sensing balance in 0.5 s. By varying RH from 47.0% to 89.3%, stopband of a sensor changes from 426 nm to 668 nm, almost spanning the whole visible range. Meanwhile, visual sensing of RH possesses good reversibility and repeatability. Moreover, the sensors with delicate patterns are facilely fabricated by partial UV photodegradation of the polymer layers with nano TiO2 as catalyst. The delicate patterns and backgrounds show different colors, and change color simultaneously and quickly by varying the ambient humidity. Accurate QR code pattern is also realized on the PC sensor, it is found successful reading of the data is only achieved by increasing RH to realize high color contrast between the code and background. Given their excellent properties, the porous hybrid PCs are promising as high-performance humidity sensors with potential display, decoration, information-storage and encryption functions.
关键词： colorimetric humidity sensors,photonic crystals,nanogels,patterning,mesoporous structure
更新于2025-09-23 15:21:21
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Towards silicon-based metamaterials
摘要： We study periodic lattices of silicon nanorods and introduce the concept of a phase diagram that characterizes a transition between the regimes of photonic crystals and dielectric metamaterials when the lattice spacing and operational wavelength vary. We find the conditions when a hexagonal periodic lattice of silicon nanorods can operate as a metamaterial described by averaged parameters. In general, we reveal that the metamaterial regime can be achieved for dielectric permittivity exceeding the value ε = 14, being commonly available for semiconductors in both visible and near-infrared frequency ranges. Thus, advanced semiconductor technologies can offer a versatile platform for novel designs of all-dielectric Mie-resonant metadevices.
关键词： phase diagram,photonic crystals,dielectric metamaterials,Mie resonances,silicon nanorods
更新于2025-09-23 15:21:21
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Design of a Wide Ranging Highly Sensitive Pressure Sensor Based on Two-Dimensional Photonic Crystals
摘要： A highly sensitive pressure sensor operating over a wide pressure range based on two-dimensional photonic crystals having a Mach-Zehnder interferometer structure has been developed. The plane wave expansion method (PWE) is used to determine the device operating wavelength range. The finite difference time domain method (FDTD) is used to calculate the device characteristic parameters such as the resonant frequency, the power transmission, and the sensitivity. The present sensor has two wide frequency ranges, a high sensitivity to refractive index changes and the highest detectable sensitivity pressure so far reported in the literature, that is, 25.06 nm/GPa. The present device has high and constant transmission power all over the entire pressure range 0 to 10 GPa. This is of practical importance since the constraints imposed on the sensing system (the light source and the photodetector) are the same.
关键词： Power transmission,Sensitivity,Mach-Zehnder interferometer,Pressure sensor,2-D photonic crystals,FDTD
更新于2025-09-23 15:21:21
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Holographic Fabrication and Optical Property of Graded Photonic Super-Crystals with a Rectangular Unit Super-Cell
摘要： Recently developed graded photonic super-crystals show an enhanced light absorption and light extraction efficiency if they are integrated with a solar cell and an organic light emitting device, respectively. In this paper, we present the holographic fabrication of a graded photonic super-crystal with a rectangular unit super-cell. The spatial light modulator-based pixel-by-pixel phase engineering of the incident laser beam provides a high resolution phase pattern for interference lithography. This also provides a flexible design for the graded photonic super-crystals with a different ratio of length over the width of the rectangular unit super-cell. The light extraction efficiency is simulated for the organic light emitting device, where the cathode is patterned with the graded photonic super-crystal. The high extraction efficiency is maintained for different exposure thresholds during the interference lithography. The desired polarization effects are observed for certain exposure thresholds. The extraction efficiency reaches as high as 75% in the glass substrate.
关键词： spatial light modulator,holographic lithography,organic light emitting device,photonic crystals,graded photonic super-crystals,extraction efficiency
更新于2025-09-23 15:21:01
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Optimization of PBG-Waveguides for Terahertz-Driven Electron Acceleration
摘要： The properties of 2-D photonic bandgap dielectric structures, also called photonic crystals, are numerically investigated to assist the design of waveguides for terahertz (THz)-driven linear electron acceleration. Given the broadband nature of the driving pulses in THz acceleration regimes, one design aim is to maximize the photonic bandgap width to allow propagation of the relevant frequencies within the photonic crystal linear defect waveguide. The proposed design is optimized to provide the best compromise between effective acceleration bandwidth and strong beam–wave interaction at the synchronism central frequency. Considerations on achieved acceleration bandwidth, accelerating voltage, and surface magnetic field are given to compare the proposed geometry to one of the main counterparts in the literature—the dielectric-lined waveguide.
关键词： Photonic crystals,terahertz (THz) electron acceleration,photonic-bandgap waveguides (PBG-Ws)
更新于2025-09-23 15:21:01
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Thermal darkening of one-dimensional photonic crystal containing tellurium suboxide
摘要： The purpose of this study is to experimentally and theoretically evaluate the optical properties of a one-dimensional photonic crystal (PC) with a defect layer before and after an annealing procedure. A sputtering technique with high index (TeOx) and low index (SiO2) materials was used to fabricate the 1D PC with a defect layer. The chemical and structural analysis of a single layer TeOx thin film was evaluated by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and X-Ray Diffraction (XRD). The optical constant of the single layer was also determined based on the envelope method from transmittance spectra measured by ultraviolet visible near-infrared spectrophotometry (UV-VIS-NIR). The measured reflectance spectra of the 1D PC were compared with the results simulated using the transfer matrix method (TMM) before and after the annealing procedure. A photonic bandgap (PBG) appears within the desired, near-infrared (NIR), region. The defect mode in the 1D PC was observed at λ = 1455 nm within the PBG of λ = 1235–1723 nm (Δλ = 488 nm). The reflectance spectra overall shifted toward longer wavelength due to thermal darkening effect resulting from the thermally induced optical property changes.
关键词： Photonic band gap,One-dimensional photonic crystals,Tellurium suboxide,Thermal darkening,Defect layer
更新于2025-09-23 15:21:01
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Synthesis of SiO <sub/>2</sub> @Ag core-shell photonic crystals for SERS application
摘要： Core-shell SiO2@Ag composite spheres with dense, complete and nanoscaled silver shell were prepared by using facile chemical reduction method. Self-assembly of the composite microspheres into 3D photonic crystals (PhCs) was carried out using the vertical deposition method. The core-shell PhCs composites were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy and energy dispersive X-ray spectroscopy (EDX). The results of amplification of Raman scattering by these composite substrates are presented.
关键词： SiO2@Ag,photonic crystals,SERS,core-shell,Raman scattering
更新于2025-09-23 15:21:01