Photonic crystals with tunable optical stop band through monodispersed silica–polypyrrole core-shell spheres

We prepared monodispersed silica–polypyrrole core-shell spheres (SiO₂–Ppy) using adsorbed surfactant bilayers on silica as templates and demonstrated the construction of photonic crystal with tunable stop band from SiO₂–Ppy core-shell spheres. Since the photonic stop band is very dependent on the refractive index, it can be tuned by simply changing the refractive index of Ppy shell via changing doping level. In fact, the stop band was shifted about 15 nm when the photonic crystal was exposed to fuming sulfuric acid due to the change of the doping level of Ppy shell.     

大面积3D有序介孔二氧化钛薄膜光子晶体制备与性能研究

介绍了大面积有序反蛋白石结构介孔二氧化钛薄膜光子晶体制备与性能研究的进展.为了保证二氧化钛骨架结构的稳定性和有序度,从而使氧化钛介孔薄膜达到大面积结构均匀,在介孔薄膜制备过程中采用了几种新的工艺方法,其中包括二氧化硅晶体模板的应用和用NaOH溶液代替常用的HF溶液作为模板去除剂.制备的介孔二氧化钛薄膜光子晶体的面积达到厘米尺寸,二氧化钛骨架的填充率达到17.4%,薄膜制备过程中的收缩率<3%.薄膜透射光谱研究结果表明,这种大面积3D有序的反蛋白石结构介孔二氧化钛薄膜具有非常优良的光子带隙特性,有望成为一类具有非常好的发展和应用前景的光子晶体材料.     

Spontaneous emission of terbium complex in-filled in single-crystal colloidal multilayer

Highly monodisperse submicron-sized silica spheres were synthesized by a chemical method, and single-crystal colloidal multilayers were prepared by a vertical deposition technique. Rare earth complex Tb(ACAC)3phen was in-filled in this structure to investigate the photonic bandgap effect on the spontaneous emission. The photon density of states in the photonic crystal was calculated numerically to investigate the origin of the abnormally enhanced photoluminescence in the photonic bandgap region. Our results are suggestive of a new way to probe the position of fluorescent molecules in such photonic bandgap materials.     

Fabrication of photonic crystal heterostructures by a simple vertical deposition technique

This paper describes a facile method for the fabrication of photonic crystal heterostructures (PCHSs) composed of photonic crystals (PCs) of core–shell spheres with different diameters and effective refractive indexes. The PCs are fabricated by a simple vertical deposition technique. The PCs of monodisperse polystyrene/silica core–shell (PS@SiO₂) spheres or hollow silica spheres are used as substrates to fabricate PCHSs, respectively. The results indicate that the resultant PCHSs formed from PS@SiO₂ spheres or hollow silica spheres have a very high quality and a good adsorbing interface between the PCs. Transmission spectra show that there are two optical stop bands of the PCHSs, and the positions of optical stop bands are controlled by tuning the size and the effective refractive index of spheres. The PCHSs formed from hollow silica spheres may facilitate the development of the potential applications due to the novel properties of hollow silica spheres, such as, low density, low refractive index, and high specific surface area.     

Preparation and characterization of bowl-like porous ZnO film by electrodeposition using two-dimensional photonic crystal template

A rapid and low-cost method combining electrodeposition with two-dimensional (2D) photonic crystal template technique to prepare large scale bowl-like porous ZnO films is described. The 2D photonic crystal templates were fabricated by self-assembly of monodispersed polystyrene (PS) microspheres on indium-tin-oxide coated glass substrates using spinning coating method. The interstitial spaces among the spheres of the templates were filled with ZnO via electrodeposition from an aqueous solution containing 0.02 M zinc nitrate as electrolyte under a constant potential of ?1.0 V at 65 °C for 10 min. After removal of the PS photonic crystal template, bowl-like porous ZnO film was obtained. The entire process can be accomplished within 30 min. Scanning electron microscopic images showed good homogeneity in morphology, X-ray diffraction spectra demonstrated the wurtzite structure of the obtained ZnO film, and transmission electron microscopy indicated the single-crystallinity of the ZnO. Ultraviolet–visible (UV–vis) spectrophotometer was used to detect the absorption in UV–vis region of the PS template, opal ZnO-PS composite and inverse opal ZnO respectively. Two strong emission bands at 400 and 550 nm were displayed in photoluminescence spectrum.     

Normal-incidence reflection spectra of the (111) photonic opal surface in the regions of the first and second photonic band gaps

We have studied the reflection spectra of opal photonic crystals with air-or ethanol-filled pores at different diameters of the silica spheres. An experimental technique has been proposed which enables identification of both the first and second photonic band gaps in the reflection spectrum of opal. The ability to observe the second band gap allowed us to derive a dispersion relation for the refractive index of the infiltrated substance. The calculations were performed using a model for a one-dimensional periodic layered medium with two refractive indices. We obtained ω(k) dispersion curves for electromagnetic waves in a photonic crystal (at normal incidence). The ω(k) dispersion law was used to find a dispersion relation for the reflectance of the photonic crystal.     

Self-assembly of modified silica nanospheres at the liquid/liquid interface

A stabilized 2 or 3D silica sphere structure was successfully prepared by a 3-step method. First, the surfaces of silica spheres were modified with a functional silane coupling agent 3-methacryloxypropyltrimethoxysilane (γ-MPS); then, the surface-modified silica spheres were self-assembled at the liquid/liquid interface to fabricate a two- or three-dimensional ordered structure; and finally, the formed ordered structure was stabilized by a stable polymerization reaction among the modified silica spheres. The polymerized silica sphere film can be transferred from solution to quartz substrates without destroying its ordered structure. This ordered structure could be potentially used as a photonic band gap material or the template for fabrication of other highly ordered structures.     

A dual template method for synthesizing hollow silica spheres with mesoporous shells

PS/silica core/shell composites were synthesized by the modified Stöber method using polystyrene spheres and cetyltrimethylammonium bromide as dual templates under room temperature. The silicate species and the templates were self-assembled to form mesoporous silica shell on the surface of the PS spheres. Hollow silica spheres with mesoporous shell were obtained by removing the polymer core and the templates through calcination. The hollow silica spheres showed high specific surface area of 1099.5 m²/g and narrow pore size distribution centered at 2.31 nm.     

Characterisation of hollow Russian doll microspheres

Poly(1-methylpyrrol-2-yl)squaraine (PMPS) particles have been characterised using SEM. The PMPS particles were used as templates to prepare bare silica and iron–silica hollow spheres, which were characterised using TEM and SEM. The PMPS particles and the hollow spheres are not uniformly sized and are agglomerated. The hollow spheres with larger diameters (>900 nm) contain an internal ‘Russian doll’ structure. The iron–silica hollow spheres are fused to one another, and the hollow spheres have a heterogeneous wall thickness. The silica and iron–silica hollow spheres both aggregate by size. There are two different size populations (for the diameter) of the bare silica and iron–silica hollow spheres. The smaller silica spheres have thinner walls compared to the larger silica hollow spheres. The larger silica hollow spheres and the iron–silica hollow spheres have similar wall thicknesses. The iron compound in the iron–silica hollow spheres has an oxidation state of 3+ and is crystalline.     

Colloidal and transparent opal-matrix nanocomposites filled with europium-doped silica sols

Three-dimensional ordered opal-matrix composites filled with europium-doped silica sols have been produced using methods of colloid chemistry. According to elemental analysis data, the Eu concentration in the nanocomposites was ～30 ppm. A uniform europium distribution over the tetrahedral and octahedral pores of the 3D opal matrix was ensured by repeatedly filling the opal pores with silica sols doped with europium salts or europium oxide. Varying high-temperature annealing conditions, one can control the microstructure of 3D ordered nanocomposites, producing opaline and transparent photonic crystals. The microstructure of opal photonic crystals has the form of an ordered fcc lattice of amorphous silica spheres, whose tetrahedral and octahedral pores are filled with mesoporous europium-doped glass. Partial sintering of the silica spheres and mesoporous glass in transparent photonic crystals results in a periodic arrangement of quantum dots enriched in Eu-doped silica.     

Morphology of silica derived from various ammonium carboxylate templates

Synthesis of silica from tetraethyl orthosilicate (TEOS) in the presence of various ammonium carboxylate crystal templates was attempted and the effect of these templates on the shape and size of silica was investigated. The carboxylic acids examined immediately precipitated the crystals of their ammonium salts from ethanol and/or water by ammonia addition. The shape, size, and stability of thus formed crystal templates were varied depending on kinds of carboxylic acids and affected the morphology of TEOS-derived silica products. When the crystal templates formed were needle-like and less soluble, silica deposited not on the end faces but on the side faces of the crystals to form tubes with channels corresponding to the shape and size of the templates. On the other hand, when the crystal templates formed were particle-like with a few micron long and liable to re-dissolve into the solution, silica deposited on the whole surfaces of the templates. In this case, the morphology that silica particles with round edge were connected like twig was observed. It was also found that the size and its distribution of the silica tubes are variable to a certain extent by the reaction conditions such as acid and TEOS concentrations.     

Structured Porous Materials via Colloidal Crystal Templating: From Inorganic Oxides to Metals

The formation of nanostructured materials by using colloidal crystals as templates is a relatively new but rapidly growing area of materials science. Colloid crystalline templates are three‐dimensional close‐packed crystals of submicrometer spheres, whose long‐ranged ordered structure is replicated in a solid matrix, to yield materials with ordered pores. These materials hold promise for use as photonic crystals, advanced catalysts, and in a variety of other applications. Here we review the wide range of materials that have been made following the original synthesis of structured porous silica. This method has been recently modified to produce porous metals.     

Fabrication of hollow silica spheres and their application in polyacrylate film forming agent

Polystyrene (PS)/silica core/shell spheres were fabricated using mono-dispersed PS as templates by hydrolysis and condensation of two different silica precursors. The PS cores of PS/silica core/shell spheres were dissolved subsequently in the tetrahydrofuran medium to form mono-dispersed hollow silica spheres. The structures and morphologies of hollow silica spheres were characterized by scanning electron microscopy and transmission electron microscopy. Then, polyacrylate/hollow silica composite film forming agents were prepared via physical blending of polyacrylate and two different hollow silica spheres, and the water vapor permeability of their films were compared. The results showed that the structure of hollow silica spheres were very typical and obvious. The silica shell was continuous and uniform using tetraethylorthosilicate as precursor, which was accumulated by many silica seeds with size of 10–20 nm, and the thickness of silica shell was about 16.7 nm. However, the hollow silica spheres using tetraethylorthosilicate and vinyl triethoxysilane as precursors had mesoporous structure in the shell. The introduction of hollow silica spheres could significantly improve the water vapor permeability of polyacrylate film. At last, a possible mechanism for the formation of hollow silica spheres was proposed and the process of water vapor through polyacrylate/hollow silica composite films was modeled.     

Synthesis of hollow spheres with mesoporous silica nanoparticles shell

Hollow spheres with mesoporous silica nanoparticles shell were synthesized with the use of cetyltrimethylammonium bromide (CTAB) and polystyrene (PS) hollow spheres as dual templates. The key to this study is that the uneven surface of the template provides nucleation sites for mesoporous nanoparticles, resulting in the formation of hollow spheres with mesoporous silica nanoparticles shell. The final products with hierarchical mesopores can be obtained through a simple one-step approach.     

Fabrication of hollow silver spheres by MPTMS-functionalized hollow silica spheres as templates

In this study, we provide a strategy to prepare the hollow silver spheres by accumulating the silver nanoparticles on the surface of 3-mercaptopropyltrimethoxysilane (MPTMS)-functionalized silica as templates, which was accomplished by the chemisorption between silver nanoparticles and thiol groups. Then, the resulting hollow silver spheres were obtained through the chemical wet etching process with 10 M HF solution. In conventional method, the fabrication of hollow silver spheres from core-shell spheres was not easy due to the difficulties in retaining the shell structures during core removal. The method in this paper could overcome this limitation. The major focus of study is on understanding the mechanism of formation of the hollow silver spheres through the self-assembly behavior by chemisorption between silver nanoparticles and thiol groups. The silver-coated silica and hollow silver spheres were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and X-ray photoelectron spectroscopy (XPS).     

Sol-gel synthesis, microstructure and adsorption properties of hollow silica spheres

Spherical colloidal particles with a hollow interior and a mesoporous shell are particularly useful for drug delivery and release because such spheres combine the unique properties of hollow interior (for storing the drug) with mesoporous shell (for controlled release). Hollow silica spheres (HSS) with a mesoporous shell were prepared via a sol-gel process in the presence of dual templates polystyrene spheres and cetyltrimethylammonium bromide for creating the hollow core and mesopore shell. The effect of the ratio of silica precursor over polystyrene spheres on particle morphology and pore structure of the HSS was investigated. The adsorption kinetics of methyl blue on the HSS was evaluated and correlated with the mesoporous shell structure.     

Rapid fabrication of 2D and 3D photonic crystals and their inversed structures

In this paper a new technique is proposed for the fabrication of two-dimensional (2D) and three-dimensional (3D) photonic crystals using monodisperse polystyrene microspheres as the templates. In addition, the approaches toward the creation of their corresponding inversed structures are described. The inversed structures were prepared by subjecting an introduced silica source to a sol-gel process; programmed heating was then performed to remove the template without spoiling the inversed structures. Utilizing these approaches, 2D and 3D photonic crystals and their highly ordered inversed hexagonal multilayer or monolayer structures were obtained on the substrate.     

Sputtering fabrication of large scale ZnO nanobowl arrays using colloidal crystal templates

Ordered ZnO nanobowl arrays over cm2 areas were prepared by magnetron sputtering using the self-assembled polystyrene spheres arrays as templates. The process started with self-assembled sedimentation of there-dimensional (3D) hexagonal polystyrene sphere arrays. By depositing ZnO within the interstitials of 3D polystyrene colloidal crystal templates using magnetron sputtering, large-area ordered ZnO nanobowl sheets were prepared after removing the spheres by annealing. The whole nanobowl sheet could be lifted off, leaving accidentally observed inverse opal structures. The sizes of the nanobowls could be controlled by the size of the polystyrene spheres, the height of nanobowl sheets could be altered by changing sputtering parameters.     

The Langmuir‐Blodgett Approach to Making Colloidal Photonic Crystals from Silica Spheres

The area of colloidal photonic crystal research has attracted enormous attention in recent years as a result of the potential of such materials to provide the means of fabricating new or improved photonic devices. As an area where chemistry still predominates over engineering the field is still in its infancy in terms of finding real applications being limited by ease of fabrication, reproducibility and ‘quality’‐ for example the extent to which ordered structures may be prepared over large areas. It is our contention that the Langmuir‐Blodgett assembly method when applied to colloidal particles of silica and perhaps other materials, offers a way of overcoming these issues. To this end the assembly of silica and other particles into colloidal photonic crystals using the Langmuir‐Blodgett (LB) method is described and some of the numerous papers on this topic, which have been published, are reviewed. It is shown that the layer‐by‐layer control of photonic crystal growth afforded by the LB method allows for the fabrication of a range of novel, layered photonic crystals that may not be easily assembled using any other approach. Some of the more interesting of these structures, including so‐called heterostructured photonic crystals comprising of layers of spheres having different diameters are presented and their optical properties described. Finally, we offer our comments as to future applications of this interesting technology.     

单分散SiO_2/TiO_2/SiO_2多层复合微球的制备

采用一种以醇盐水解法为基础的生长硅溶胶的方法,制备了粒径为２００ｎｍ的单分散二氧化硅球形颗粒,并将其作为核心,利用常温连续进料的钛酸丁酯水解的多步法,在二氧化硅核心外经多次包覆形成厚层二氧化钛;在正硅酸乙酯的水解和陈化环境下,将上述ＴｉＯ２／ＳｉＯ２复合颗粒外再包覆一薄层二氧化硅,形成一种高折射率,可用于组装光子晶体的ＳｉＯ２／ＴｉＯ２／ＳｉＯ２多层复合微球．对该复合微球用重力沉降法、透射电镜法（ＴＥＭ）、Ｘ射线能谱分析法（ＥＤＳ）进行了表征．其中,重力沉降法是一种将Ｓｔｏｋｅｓ公式为基础推导的复合颗粒的粒径与沉降速度关系式所得的一系列数据进行拟合外延,来测定复合颗粒的粒径及包覆厚度的方法．