Band structure of photonic crystal fibers with silica rings in triangular lattice

The characteristics of the cladding band structure of air-core photonic crystal fibers with silica rings in triangular lattice are investigated by using a standard plane wave method. The numerical results show that light can be localized in the air core by the photonic band gaps of the fiber. By increasing the air-filling fraction, the band gap edges of the low frequency photonic band gaps shift to shorter wavelength, whereas the band gap width decreases linearly. In order to make a specified light fall in the low frequency band gaps of the fiber, the interplay of the silica ring spacing and the air-filling fraction is also analyzed. It shows that the silica ring spacing increases monotonously when the air-filling fraction is increased, and the spacing range increases exponentially. This type fiber might have potential in infrared light transmission.     

Measurements of sensitivity to hydrostatic pressure and temperature in highly birefringent photonic crystal fibers

We report on experimental studies of polarimetric sensitivity to hydrostatic pressure and temperature in two highly birefringent index guided photonic crystal fibers, in which birefringence is induced by one row of the cladding holes with diameters smaller than the other cladding holes. The sensitivity measurements were carried out in the spectral range from 0.6 μm to 1.6 μm. Our results show that absolute value of the polarimetric sensitivity to hydrostatic pressure can reach 23 rad/MPa × m, which is almost one order of magnitude higher than in conventional fibers with elliptical core. Simultaneously, polarimetric sensitivity to temperature is at least two orders of magnitude lower than in conventional highly birefringent fibers. Moreover, we proved experimentally that one of the investigated fibers is completely insensitive to temperature at certain wavelength.     

Deposition of silver nanoparticles on silica spheres via ultrasound irradiation

Silver-decorated silica spheres of submicrometer-sized silica spheres with a core-shell structure were obtained based on a seed-mediated growth process, where silver nanoparticles were firstly formed from reducing Ag⁺ to Ag⁰ in N,N-dimethylformamide (DMF) in the presence of poly(vinylpyrrolidone) (PVP) as protective agent under ultrasound irradiation, followed by the growth of silver shell served silver nanoparticles as nucleation sites and formaldehyde as reducer. The results revealed that the terms of PVP addition and ultrasonic surroundings had great influence on the fabrication of silver seeds.     

Synthesis and characterization of silica microspheres functionalized with porphyrin monolayer

A new type of inorganic and organic composite (SiO₂-MPS-TAPPI), oppositely charged meso-tetra-(4-trimethylaminophenyl)porphyrin iodide (TAPPI) bonded on the surface of silica microspheres coated with mercaptopropyltrimethoxysilane (MPS), was prepared by self-assembly method. The composite was tested by TEM, XRD and TG. The TEM images show that SiO₂-MPS microspheres in the composite are uniform. There are linkages among some different SiO₂-MPS microspheres. The XRD measurement bears out that the composite structure is the same with SiO₂-MPS. TG curves show that thermal stability of TAPPI assembled onto SiO₂-MPS microspheres is higher than that of TAPPI. Solid UV diffusion reflection spectra and fluorescence spectra are used to investigate the photophysical properties of the SiO₂-MPS-TAPPI composite. It is showed that the spectra of the composite exhibit significant enhancement of the spectra range. The strong interaction between TAPPI and SiO₂-MPS in the composite is responsible for the different spectra.     

Study on the silica hollow spheres by experiment and molecular simulation

This paper presents the synthesis, characterization and molecular simulation of the silica hollow spheres (SHSs). The SHSs have been prepared using a double-template method, in which the calcium carbonate nanoparticles (CaCO₃) serve as core templates and the cetyltrimethyl-ammonium bromide (CTAB) as wall structure-directing agents. The TEM, XRD, and nitrogen adsorption have been employed to characterize morphologies and structures of the SHSs. The experimental results indicate that the as-prepared sample has an average external diameter of about 85 nm and has occurrence of disordered mesopores in the walls. In the simulation, the SHSs have been modeled as cylindrical pore with pore size distribution according to the experimental data. A combined method of grand canonical Monte Carlo (GCMC) simulation and statistics integral equation (SIE) has been carried out to determine the pore size distribution (PSD) of the SHSs based on the experimental adsorption data of nitrogen at 77 K. The results show that the PSD simulated data are in a good agreement with the experiment, which means that the proposed model for the SHSs is reliable and the combined method of GCMC and SIE is powerful for evaluation of the PSD of the silica hollow spheres.     

超低密度SiO2气凝胶的制备及成型研究

 以正硅酸乙酯(TEOS)为硅源，采用酸碱二步催化溶胶-凝胶法，结合超临界干燥技术制备了超低密度SiO₂气凝胶,最低密度为3.4 mg/cm³；进一步结合成型工艺，在解决了模具设计和脱模技术后制备了具有不同密度的柱状和微型套筒样品，密度10～50 mg/cm³。研究了水、催化剂、稀释剂对二步溶胶-凝胶过程的影响，获得了制备低密度SiO₂气凝胶的最佳条件。利用扫描电镜、孔径分布及比表面积测试仪等对SiO₂气凝胶微结构进行了研究。结果表明，获得的超低密度SiO₂气凝胶具有较好的纳米网络，平均孔径18.9 nm，还具有高比表面积898 9 m²/g。     

A novel approach to fabrication of superparamagnetite hollow silica/magnetic composite spheres

We described a method for synthesizing hollow silica/magnetic composite spheres using sulfonic acid functionalized hollow silica spheres (SAFHSS) as templates. The Fe₃O₄ nanoparticles were deposited on or imbedded in the hollow silica shell by a precipitation reaction. The morphologies, composition and properties of the hollow composite spheres were characterized by transmission electron microscopy, Fourier transform infrared analysis, X-ray diffraction measurement and vibrating-sample magnetometry measurement. The results indicated crystal sizes and amount of the Fe₃O₄ nanoparticles on the SAFHSS. The magnetic properties of the hollow composite spheres were controlled by adjusting the proportion between Fe²⁺ and Fe³⁺ and iron ion total concentration. When appropriate loading species were added into the system, superparamagnetite hollow composite spheres were obtained. The method also could be applicable to prepare other superparamagnetite hollow silica/ferrite composite spheres.     

Liberations and twists of real and complex spheres

We study the 10 noncommutative spheres obtained by liberating, twisting, and liberating +twisting the real and complex spheres $S_{\mathbb{R}}^{N-1},S_{\mathbb{C}}^{N-1}$. At the axiomatic level, we show that, under very strong axioms, these 10 spheres are the only ones. Our main results concern the computation of the quantum isometry groups of these 10 spheres, taken in an affine real/complex sense. We formulate as well a proposal for an extended formalism, comprising 18 spheres.     

Preparation and optical properties of UV dye DMT-doped silica films

UV dye DMT-doped silica films were prepared by sol-gel process with dioxane as the cosolvent. Luminescence quenching was not observed even if the DMT concentration in the visibly transparent silica film is as high as 1.26×10⁻² M. The emission peaks centered at ∼375 nm for the films show red-shift of 35-45 nm, comparing with that of the cyclohexane solution of DMT. The fluorescence quantum efficiency of the films centered at ∼590 nm are larger than those at ∼375 nm.     

Preparation of monodisperse polystyrene/silica core-shell nano-composite abrasive with controllable size and its chemical mechanical polishing performance on copper

Monodisperse silica-coated polystyrene (PS) nano-composite abrasives with controllable size were prepared via a two-step process. Monodisperse positively charged PS colloids were synthesized via polymerization of styrene by using a cationic initiator. In the subsequent coating process, silica formed shell on the surfaces of core PS particles via the ammonia-catalyzed hydrolysis and condensation of tetraethoxysilane. Neither centrifugation/water wash/redispersion cycle process nor surface modification or addition surfactant was needed in the whole process. The morphology of the abrasives was characterized by scanning electron microscope. Transmission electron microscope and energy dispersive X-ray analysis results indicated that silica layer was successfully coated onto the surfaces of PS particles. Composite abrasive has a core-shell structure and smooth surface. The chemical mechanical polishing performances of the composite abrasive and conventional colloidal silica abrasive on blanket copper wafers were investigated. The root mean square roughness decreases from 4.27 nm to 0.56 nm using composite abrasive. The PS/SiO₂ core-shell composite abrasives exhibited little higher material removal rate than silica abrasives.     

Cavity mode control in side-coupled periodic waveguides: Theory and experiment

We demonstrate that the modes of coupled cavities created in periodic waveguides can depend critically on the longitudinal shift between the cavities. In the absence of such shift, the modes feature symmetric or antisymmetric profiles, and their frequency splitting generally increases as the cavities are brought closer. We show that the longitudinal shift enables flexible control over the fundamental modes, whose frequency detuning can be reduced down to zero. Our coupled-mode theory analysis reveals an intrinsic link between the mode tuning and the transformation of slow-light dispersion at the photonic band-edge. We illustrate our approach through numerical modeling of cavities created in arrays of dielectric rods, and confirm our predictions with experimental observations.     

非密堆积TiO2空心微球光子晶体的制备与能带分析

利用胶体自组装、高温烧结和HF酸刻蚀技术,制备了SiO₂微球非密堆积面心立方(FCC)结构的胶体晶体,并以此为模板,利用溶胶凝胶方法和NaOH湿法刻蚀技术制备了TiO₂空心微球非密堆积FCC结构光子晶体.利用电子显微镜分析了晶体的结构,用平面波展开法对该结构进行了能带计算与分析.计算结果表明,制备的TiO₂空心微球非密堆积FCC结构光子晶体在低能区的第二、第三能带之间除布里渊区的W点仍保持简并外,其余各点简并都已经消除. 关键词： 空心微球 非密堆积 光子晶体 光子带隙     

Numerical analysis of a temperature sensor based on the photonic band gap effect in a photonic crystal fiber

In this paper we investigate, by the plane wave expansion method and an analytical model, the temperature effect on the photonic band gap fiber, and we report on a numerical demonstration of a temperature sensor based on the photonic band gap (PBG) shift in a solid core photonic crystal fiber (PCF) infiltrated with a high refractive index oil. The bandwidth and the position of the central wavelength of the band gap are the parameters of interests for our temperature sensing purpose. Simulation results were found to be in excellent agreement with the refractive index scaling law and the highest sensitivity of 3.21?nm/°C was achieved, and it will be even higher than the grating based sensors written in PCFs with similar structure.     

一种可精确控制粒径的SiO2微球合成方法

用改进的种子法合成SiO₂微球. 微球生长过程中连续缓慢添加正硅酸乙酯,使用动态光散射法实时监控微球粒径的增长过程,调节正硅酸乙酯的添加,实现对粒径的精确控制. 为制备禁带位置位于1000 nm 的光子晶体,合成粒径为446 nm的SiO₂微球,微球粒径在4 h内从193 nm 增长到446 nm,远远快于传统种子法,微球粒径与目标粒径偏差为±5 nm. 制得的SiO₂微球被组装为光子晶体,其禁带位置恰好位于1000 nm.     

Preparation of silica nanowires using porous silicon as Si source

This very paper is focusing on the preparation of silica nano-wires via annealing porous silicon wafer at 1200 °C in H₂ atmosphere and without the assistant metal catalysts. X-ray diffraction, X-ray energy dispersion spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and selected area diffraction technology have been employed for characterizing the structures, the morphology and the chemical components of the nano-wires prepared, respectively. It is found that the diameter and the length of the nano-wires were about 100 nm and tens micron, respectively. Meanwhile, it is also necessary to be pointed out that silica NWs only formed in the cracks of porous wafers, where the stress induced both by the electro-chemical etching procedure for the porous silicon preparation and nanowires growth procedure is believed to be lower than that at the center of the island. Therefore, a stress-driven mechanism for the NWs growth model is proposed to explain these findings.     

Plasmonic structure generation by laser illumination of silica colloid spheres deposited onto prepatterned polymer-bimetal films

Plasmonic structures are prepared on bimetal films evaporated onto glass substrates applying a multi-step process, and atomic force microscopy is utilized to study the structures after each step. Sub-micrometer gratings are generated on polycarbonate films spin-coated onto silver-gold bimetal layers by interference lithography (IL) applying the fourth harmonics of a Nd:YAG laser. These polymer gratings are used as prepatterned templates in order to deposit silica colloid spheres by spin-coating. It is shown that the conditions of periodic silica sphere-array formation along the template valleys are sufficiently large grating modulation depth, appropriate ratio of silica sphere diameter to grating period, and optimized speed of spinning. The periodic silica sphere arrays are illuminated by a homogeneous KrF excimer laser beam, and periodically arrayed sub-wavelength holes are drilled into bimetal films via colloid sphere lithography (CSL). The characteristic dimensions of the resulted plasmonic structures are defined by the polymer grating period and by the silica colloid sphere diameter. Attenuated total reflection spectroscopy is performed exciting plasmons on different metal-dielectric interfacial structures by the second harmonic of a continuous Nd:YAG laser. The polar and azimuthal angle dependent grating-coupling and scattering effects of the complex periodic structures on the resonance characteristic of plasmons is demonstrated.     

二氧化硅人工蛋白石晶体（opal)的制备及其结构性质的研究

运用胶体化学法合成了尺寸可控的二氧化硅（SiO2）亚微米溶胶小球.透射电子显微镜（TEM）结果显示样品平均尺寸可从200nm变化至600nm，单分散性较高、平均标准偏差小于5％.通过自然沉积法，由溶胶SiO2小球自组织晶化制备了人工蛋白石晶体（opal晶体）结构.样品的剖面扫描电子显微镜（SEM）检测表明，样品为面心立方（fcc）结构.分析表明，较高的单分散性和缓慢的沉积过程是SiO2溶胶小球自组织晶化成三维有序结构的关键因素.反射谱中峰位在1320nm处的反射峰的出现，意味着样品在宏观尺度上的有序排列， 关键词： 亚微米二氧化硅溶胶小球 人工蛋白石晶体 方向带隙     

A photonic crystal biosensor with temperature dependency investigation of micro-cavity resonator

A two dimensional photonic crystal biosensor implemented by waveguides and microcavity is theoretically investigated. The designed structure has high quality factor about 15,000 and sensitivity approximately 141.67 nm/RIU, which are important parameters in biosensing applications. Also there is a linear dependency between resonant wavelength shift and refractive index changes. Since water is the main component of human organism, the temperature and wavelength dependence of proposed microcavity is investigated. The results show that the structure has good temperature stability. The temperature sensitivity is about −0.0142 nm/°C.     

Aging of starting solutions for nanoparticles synthesis with two different ultrasonication

Novel concept of aging starting solutions for nanoparticle synthesis and the application of two different sonication to aging is introduced. In sonoprocess of nanoparticles from liquid phase, it is usual to irradiate ultrasound to a reacting solution during synthesis. In this work, ultrasound is applied to a starting solution before synthesis. In case of the SiO₂ sphere synthesis, the aging process elongated the induction period of the precipitation, enlarge the sphere size, and enhanced the monodispersity of silica spheres. These effects were promoted by soft sonication at subtle power (~1 mW). In case of the TiO₂ sphere case, ordinary (cavitating) ultrasound during synthesis was found to be effective in more spherical shape. Also, the sonication to aging of the starting solution was useful for uniform spheres synthesis. Existence of miscible liquid such as water-ethanol and feasible relationship to the nucleation of nanoparticles are discussed.     

溶胶-凝胶工艺制备SiO2薄膜的结构控制和稳定性研究

 采用溶胶-凝胶工艺在酸性、碱性和碱/酸两步催化条件下制备纳米多孔结构的SiO₂薄膜。使用透射电子显微镜（TEM）、激光粒子分析仪测试了溶胶的微观结构和颗粒分布;使用反射式扫描椭偏仪、扫描电子显微镜（SEM）、原子力显微镜（AFM）测试了薄膜的光学性能和微观形貌。结果表明：通过改变溶胶-凝胶过程中的催化条件可控制薄膜微观结构和光学性能。溶胶在长期存贮期间符合镀膜的稳定性要求。