Inverse opal photonic crystal of chalcogenide glass by solution processing

Chalcogenide opal and inverse opal photonic crystals were successfully fabricated by low-cost and low-temperature solution-based process, which is well developed in polymer films processing. Highly ordered silica colloidal crystal films were successfully infilled with nano-colloidal solution of the high refractive index As(30)S(70) chalcogenide glass by using spin-coating method. The silica/As-S opal film was etched in HF acid to dissolve the silica opal template and fabricate the inverse opal As-S photonic crystal. Both, the infilled silica/As-S opal film (Δn ~ 0.84 near λ=770 nm) and the inverse opal As-S photonic structure (Δn ~ 1.26 near λ=660 nm) had significantly enhanced reflectivity values and wider photonic bandgaps in comparison with the silica opal film template (Δn ~ 0.434 near λ=600 nm). The key aspects of opal film preparation by spin-coating of nano-colloidal chalcogenide glass solution are discussed. The solution fabricated "inorganic polymer" opal and the inverse opal structures exceed photonic properties of silica or any organic polymer opal film. The fabricated photonic structures are proposed for designing novel flexible colloidal crystal laser devices, photonic waveguides and chemical sensors.     

胶体晶体自组装排列进展

自组装排列胶体晶体是发展光子晶体等亚微米周期有序结构及新型光电子器件十分重要的环节.高电荷密度单分散胶体球在较弱的离子强度和稀浓度下会自发排列形成紧密堆积的周期性结构(ccp),常常是面心立方(fcc),科学家们以此为基础发展了多种结晶化胶体粒子的方法,包括重力场沉积、电泳沉积、胶体外延技术、垂直沉积、流通池、物理束缚排列及其他的许多方法.目前排列的胶体粒子基本为球形,材料也多为SiO2、PS、PMMA,此外一些复合粒子,主要为核壳粒子的排列这里也稍作介绍,这些方法及其变通的使用可以形成类蛋白石及反蛋白石结构,最终实现光子带隙及其它多种用途。     

Opal and inverse opal photonic crystals: Fabrication and characterization

Three-dimensional photonic crystals made of close-packed polymethylmethacrylate (PMMA) spheres or air spheres in silica, titania and ceria matrices have been fabricated and characterized using SEM, XRD, Raman spectroscopy and UV–Vis transmittance measurements. The PMMA colloidal crystals (opals) were grown by self-assembly from aqueous suspensions of monodisperse PMMA spheres with diameters between 280 and 415 nm. SEM confirmed the PMMA spheres crystallized uniformly in a face-centred cubic (fcc) array, and UV–Vis measurements show that the colloidal crystals possess pseudo photonic band gaps in the visible and near-IR regions. Inverse opals were prepared by depositing silica (SiO₂), titania (TiO₂) or ceria (CeO₂) in the voids of the PMMA colloidal crystals using sol-gel procedures, then calcining the resulting structure at 550 °C to remove the polymer template. The resulting macroporous materials showed fcc ordering of air spheres separated by thin frameworks of amorphous silica, nanocrystalline titania or nanocrystalline ceria particles, respectively. Optical measurements confirmed the photonic nature of the inverse opal arrays. UV–Vis data collected for the opals and inverse opals obeyed a modified Bragg’s law expression that considers both diffraction and refraction of light by the photonic crystal architectures. The versatility of the colloidal crystal template approach for the fabrication of macroporous oxide structures is demonstrated.     

三维SiO2欧泊模板溶剂热法制备硫化锌光子晶体

以单分散二氧化硅微球在重力场下自组装得到的三维有序欧泊(opal)为模板，采用溶剂热法在模板空隙内生长ZnS晶体，从而制备高质量的硫化锌基光子晶体. 通过X射线衍射(XRD)和Raman光谱证明ZnS晶体为闪锌矿结构且晶体质量较好，并对其生长机理进行了讨论. 通过场发射扫描电子显微镜(FESEM)和紫外-可见分光光度计对所合成的ZnS/opal复合物与ZnS反欧泊结构进行了表征，结果表明两种结构都保持了欧泊三维有序性，并且在Г-L方向(垂直于(111)方向)上出现了布拉格衍射峰，说明其具有良好的光子晶体特性.     

Pore-filling Three-dimensionally Ordered Macroporous Polyimide Composite Proton Conducting Membranes

The silica opal templates were prepared from three silica colloids of different diameters of 230 nm, 500 nm and 1.5 mm by a filtration route. The large-scale stable opal template membranes after sintering the deposited SiO2 opal template can be successfully obtained by optimizing the pH value and NaCl concentration in silica colloidal solutions. The three-dimensionally ordered macroporous(3DOM) polyimide membranes without crack were fabricated by reproducing the structure of silica opal template. We prepared the pore-filling composite proton exchange membranes by filling the 3DOM structure with proton conducting organosilane sol. The result indicates that the composite membranes exhibit higher water uptake than pure filling organosilane gel. The proton conductivity increased with the increasing of pore cell in composite membranes.     

Nanocomposites based on opal matrices and silica sols doped with rare earth compounds

Ordered 3D composites based on opal matrices and silica sols doped with rare earth elements have been prepared using colloidal chemistry methods. A uniform distribution of rare earth elements (which is important for avoiding luminescence concentration quenching) was achieved by means of repeated filling of the opal matrix interstitial space with silica sols doped with salts or oxides of rare earth elements. Trace amounts (10–30 ppm) of europium in a composite were shown to strongly affect optical properties of the material.     

Process optimization of sol–gel derived colloidal photonic crystals

Three-dimensional photonic bandgap structures have been synthesized by a colloidal/sol–gel route, starting with the self-organization of polystyrene microspheres into opals by dip-coating, sedimentation or vertical convective self-assembly, followed by sol–gel infiltration of the interstices with silica, titania or a silica-titania mixture, by dip-coating and removal of the polymeric template. The structural and optical properties of the opals and inverse opals prepared by this method have been studied by scanning electron microscopy and visible infra-red spectroscopies to assess the relationship between their structure and the photonic properties obtained. The optical transmission and reflection spectra of the opal and inverse opal structures have also been simulated by the Translight Software code, using the Transfer Matrix method, for different numbers of stacked layers, showing reasonable agreement with the experimental results. By optimizing the fabrication parameters, colloidal photonic crystals of good quality have been obtained, with reduced defect concentrations and increased mechanical strength.     

Doped colloidal photonic crystal structure with refractive index chirping to the [111] crystallographic axis

A three-dimensionally ordered array of close-packed colloidal spheres, a photonic crystal structure in which the refractive index of the medium interstitial lattice in a colloidal crystal spatially changes in the [111] crystallographic axis, is demonstrated. The colloidal photonic crystal structure with refractive index chirping was produced by infiltration of a monomer and organic dopants with a high refractive index into a silica opal, followed by interfacial gel polymerization. The resulting photonic crystal structure has a gradually varying stop band at each different (111) plane in the face-centered cubic (fcc) crystal structure at a normal incidence. This novel structure exhibited optical characteristics that have band-gap broadening by the superposition of stop bands at each plane of the crystal with different dielectric functions. Moreover, the refractive index perturbation in the [111] fcc opal also showed a defect state within a pseudo-photonic band gap. This new type of photonic crystal structure should be useful for the band-gap engineering of photonic-band-gap materials.     

Dry etching of colloidal crystal films

Two types of non-close-packed colloidal crystal films were prepared by etching the films made of polystyrene nanospheres using a hyperthermal neutral beam of oxygen gas. Etching without sintering above glass transition temperature of the polymer particles resulted in the non-close-packed structure of the nanospheres, in which polystyrene nanospheres in different lattice planes touched each other due to the reduction in the size of the nanospheres that occurred during the etching process. In contrast, a different non-close-packed structure with inter-connecting networks between etched nanospheres was generated by annealing of the colloidal crystal and a subsequent etching process. The photonic bandgap could be tuned during this dry etching of colloidal photonic crystals. This connected open structure could be used as a template for a silica inverse opal by chemical vapor deposition. An alternative dry etching process, reactive ion etching, mainly affected the morphology of particles near the top surface, and only a slight change in the stop band position of the colloidal crystal film was observed.     

Effect of anionic surfactants on synthesis and self-assembly of silica colloidal nanoparticles

Effects of the anionic surfactants, sodium dodecyl sulfate and sodium oleate, on the formation and properties of silica colloidal nanoparticles were investigated. At a concentration of approximately 1 x 10(-3) M, adsorption of anionic surfactants increased particle size, monodispersity, and negative surface charge density of synthesized silica particles. As uniformity of particle size and particle-particle interactions increase, colloidal photonic crystals readily self-assemble without extensive washing of the synthesized silica nanoparticles. The photonic crystals diffract light in the visible region according to Bragg's law. The assembled colloidal particle arrays exhibit a face-centered cubic structure in dried thin films. This study offers a new approach for producing ordered colloidal silica thin films.     

Synthesis and crystallization of hybrid spherical colloids composed of polystyrene cores and silica shells

The St?ber method has been adopted to prepare hybrid core-shell particles by coating the surfaces of monodisperse polystyrene beads with uniform silica shells. Polystyrene beads with diameters in the range of 0.1-1.0 microm have been successfully demonstrated for use with this process, and the thickness of the silica coating could be controlled in the range of 50-150 nm by adjusting the concentration of tetraethoxysilane, the deposition time, or both. The morphology and surface smoothness of the deposited silica were found to strongly depend on a number of parameters such as the surface functional groups on the polymer beads, the pH value of the medium, and the deposition time. Hollow spheres made of silica could be obtained by selectively removing the polymer cores via calcination in air at an elevated temperature or by wet etching with toluene. These core-shell colloids were also explored as building blocks to fabricate long-range ordered lattices (or colloidal crystals) that exhibited stop bands different from those assembled from spherical colloids purely made of either polystyrene or silica.     

胶态磁组装光子晶体及其离子强度响应

采用细乳液聚合方法合成了聚合物包覆的磁性复合纳米粒子(MCNPs),通过磁场诱导组装制备得到胶态磁组装光子晶体(CMA-PCs).透射电子显微镜(TEM)和扫描电子显微镜(SEM)表征结果表明,MCNPs具有规整的球形形貌和明显的核壳结构,并且单分散性较好,平均粒径为112 nm,聚合物壳层厚约10 nm.MCNPs在外界磁场的作用下可以快速(1 s)组装形成光子晶体结构.当离子强度在0.03~0.75 mmol/L范围内变化时,CMA-PCs的衍射色呈现从橙红色到紫色的变化,反射波长从607 nm蓝移至434 nm,并且离子强度的响应在10 s内即可达到平衡,表明制得的CMA-PCs可以作为化学传感器应用于离子强度的半定量检测,并且具有简便、快速及裸眼可视化检测的优点.     

红荧烯反蛋白石的制备及其光学性质研究

通过表面浸润法制备了红荧烯的反蛋白石结构,成功观测到其结构色,并检测出相对应反射光谱.此类方法可进一步拓展制备多种具有三维有序大孔结构的有机半导体材料,得到新的光电性质.     

无皂乳液聚合法制备聚甲基丙烯酸甲酯包覆厚度可控的纳米核-壳二氧化硅微球

用改进的Stöber法和无皂乳液聚合法制备窄分布的二氧化硅/PMMA核-壳纳米微球. 用改进的Stöber法将3-乙氧基甲基丙烯酸丙基硅烷(MPS)修饰在纳米的二氧化硅表面后, 用无皂乳液聚合法制备核-壳纳米微球. 该法简单有效且得到厚度均匀的聚合物包覆层. 随着单体MMA用量的增加, 用动态光散射法测量, PMMA壳层的厚度从6.4 nm增加到96.3 nm. 热重分析表明, PMMA的含量从22.25%增加到93.41%. 扫描电子显微镜和透射电子显微镜结果表明, 得到的是包覆良好、表面光滑的核-壳无机/聚合物纳米微球.     

Integration of self-assembled three-dimensional photonic crystals onto structured silicon wafers

We report on the fabrication of high-quality opaline photonic crystals from large silica spheres (diameter of 890 nm), self-assembled in hydrophilic trenches of silicon wafers by using a novel technique coined a combination of "lifting and stirring". The achievements reported here comprise a spatial selectivity of opal crystallization without special treatment of the wafer surface, a filling of the trenches up to the top, leading to a spatially uniform film thickness, particularly an absence of cracks within the size of the trenches, and finally a good 3D order of the opal lattice even in trenches with a complex confined geometry, verified using optical measurements. The opal lattice was found to match the pattern precisely in width as well as depth, providing an important step toward applications of opals in integrated optics.     

Synthesis of Cristobalite Containing Ordered Interstitial Mesopores using Crystallization of Silica Colloidal Crystals

Cristobalite with ordered interstitial dual-sized mesopores was synthesized through the crystallization of silica colloidal crystals composed of monodispersed amorphous silica nanoparticles. An aqueous solution containing both a flux (Na₂O) and a carbon precursor (an aqueous low-molecular weight phenolic resin) was infiltrated into the interstices of silica colloidal crystals. The organic fraction in the nanocomposite was further polymerized and subsequently carbonized in an Ar flow at 750 °C to reinforce the colloidal crystal structure. The thermal treatment resulted in the crystallization of the colloidal crystals into cristobalite while retaining the porous structure. The cristobalite-carbon nanocomposite was calcined in air to remove the carbon and create interstitial ordered mesopores in the cristobalite. The surfaces of crystalline mesoporous silica are quite different from those of various ordered mesoporous silica with amorphous frameworks; thus, the present findings will be useful for a precise understanding and control of the interfaces between the mesopores and silica networks.     

Self-assembled colloidal crystals from ZrO2 nanoparticles

Ordered three-dimensional (3-D) assemblies of nanocrystalline zirconia were synthesized from aqueous suspensions of ZrO(2) nanoparticles without the need for hydrocarbon surfactants or solvents to control colloidal crystal growth. Nanoparticles were suspended in mild acid and subsequently titrated from low to neutral pH. The solubility was reduced as the surfaces were neutralized, promoting assembly of the nanoparticles into ordered monoliths. TEM measurements indicated the formation of three-dimensional, hexagonal faceted, micrometer-sized colloidal crystals composed of 4 nm diameter ZrO(2) nanoparticles. Lacking organic surfactants, the colloidal crystals were exceptionally robust and were sintered at high temperatures (300-500 degrees C) for further stability. Small-angle X-ray scattering (SAXS) measurements demonstrate that the samples become progressively more amorphous above 350 degrees C, although some ordered domains of nanoparticles persist. Additionally, the heat treatment dramatically increases the surface area of the colloidal crystals as water and residual organics are desorbed, revealing highly controlled interstitial spaces and pores.     

TiO2掺杂调控聚苯乙烯微球折射率及胶体光子晶体结构色

胶体光子晶体由于其可调变的结构色在绿色印刷、印染等领域备受关注,而其光子带隙的宽度和位置由光子晶体的晶格参数(晶面间距,通常受胶体微球尺寸影响)和介质的折射率决定。现有人工胶体光子晶体主要基于SiO_2和高分子(如聚苯乙烯(PS)等)微球的组装制备,由于胶体微球材质种类有限,折射率调控受限,因而目前调控胶体光子晶体结构色主要靠改变胶体微球的尺寸来实现。本文首先制备高折射率(2.6)的TiO_2纳米晶,在乳液聚合制备单分散的PS(折射率1.6)微球过程中,将所制备的TiO_2纳米晶掺杂于PS微球中,通过TiO_2的掺杂量有效调控胶体微球的折射率,进而实现胶体光子晶体的结构色调控。以多色胶体光子晶体微球的水溶液为墨水,采用彩色喷墨打印技术打印了电脑设计的光子晶体彩画。本文发展的光子晶体结构色调控新技术拓展了胶体光子晶体的应用。     

MESO-STRUCTURED POLYMERIC HYDROGELS

Meso-structured (opal and inverse opal) polymeric hydrogels of varied morphology and composition wereprepared by using two methods: post-modification of the template-synthesized structured polymers and template-polymerization of functional monomers. A polyacrylic acid based inverse opal hydrogel was chosen to demonstrate its fastpH response by changing color, which is important in designing tunable photonic crystals. Template effects of the hydrogelson controlling structure of the template-synthesized inorganic materials were discussed. The catalytic effect of acid groups inthe templates was emphasized for a preferential formation of TiO_2 in the region containing acid groups, which allowedduplicating inorganic colloidal crytals from colloidal crystal hydrogels (or macroporous products from macroporoushydrogels) via one step duplication.     

Formation and drying of colloidal crystals using nanosized silica particles

Much interest has been generated in the fabrication of colloidal crystals from suspensions because of the promise of photonic band gap applications. However, since the case of small, nonsedimenting colloidal particles indeed remains rather rarely treated, spherical silica particles with diameters varying from 75 down to 20 nm have been used in the present work to fabricate colloidal crystals by drying the suspending liquid. Typical events that take place during the drying process of a particulate film, such as cracking, compaction and penetration of air into a porous network, have been evaluated using existing theories, and the maximum stress in the drying film could be approximated. Investigation on the dry film structure by scanning electron microscopy showed the arrangement of particles in a close-packed system. To interpret the formation of such crystals, the amplitudes of the interparticle and capillary forces have been estimated from existing models. The repulsive interparticle forces allow the particles to remain stable and thus rearrange up to fairly high particle concentration. These modeling results showed the dominance of the capillary contribution at the end of the drying process. Nitrogen adsorption/desorption measurements gave very coherent results regarding both pore volume and pore size of the dry particulate films when compared to the expected ordered packing arrangements.