Fabrication and characterization of cerium-doped barium titanate inverse opal by sol-gel method

Cerium-doped barium titanate inverted opal was synthesized from barium acetate contained cerous acetate and tetrabutyl titanate in the interstitial spaces of a polystyrene (PS) opal. This procedure involves infiltration of precursors into the interstices of the PS opal template followed by hydrolytic polycondensation of the precursors to amorphous barium titanate and removal of the PS opal by calcination. The morphologies of opal and inverse opal were characterized by scanning electron microscope (SEM). The pores were characterized by mercury intrusion porosimetry (MIP). X-ray photoelectron spectroscopy (XPS) investigation showed the doping structure of cerium, barium and titanium. And powder X-ray diffraction allows one to observe the influence of doping degree on the grain size. The lattice parameters, crystal size and lattice strain were calculated by the Rietveld refinement method. The synthesis of cerium-doped barium titanate inverted opals provides an opportunity to electrically and optically engineer the photonic band structure and the possibility of developing tunable three-dimensional photonic crystal devices.     

Polymer-modified opal nanopores

The surface of nanopores in opal films, assembled from 205 nm silica spheres, was modified with poly(acrylamide) brushes using surface-initiated atom transfer radical polymerization. The colloidal crystal lattice remained unperturbed by the polymerization. The polymer brush thickness was controlled by polymerization time and was monitored by measuring the flux of redox species across the opal film using cyclic voltammetry. The nanopore size and polymer brush thickness were calculated on the basis of the limiting current change. Polymer brush thickness increased over the course of 26 h of polymerization in a logarithmic manner from 1.3 to 8.5 nm, leading to nanopores as small as 7.5 nm.     

Fabricating high-quality opal films with uniform structure over a large area

Films of opal, a colloidal crystalline lattice with closely packed structure, are anticipated to become a fundamental material in photonic crystal engineering. One of the technological issues is forming the opal film with a flat and uniform surface over a large area. This article describes a new and simple method for forming an opal film without special equipment. The opal film is formed by drying a colloidal suspension covered on a hydrophilic solid substrate. In the conventional method, a ring-shaped opal usually forms at the edge (contact line) of the suspension on the substrate. The new method improved the process of drying the colloidal suspension free from the ring formation. The driving force of this ring formation is based on capillary flow in the suspension from inside to outside because of the high evaporation rate at the contact line. To prevent capillary flow, the contact line of the suspension was covered with hydrophobic silicone liquid. As a result, ring formation was depressed and flat opal films with uniform structure were formed. The structure comprised cubic closely packed (111) planes, and the opal films were grown to grain sizes larger than 200 microm. In addition, the coating area of the opal film was greater than 75 cm2 using a 4-in. silicone wafer. This new method should be useful for coating high-quality opal film over large areas on solid substrates.     

Thickness measurement of colloidal opal crystal growth by Bragg reflection

This study investigates a simple method for thickness estimation with single layer accuracy for self-assembling opal crystals prepared by the dip-coating method. The thickness (number of layers) of the opal crystals was estimated by an analysis of the optical reflectance from s-polarization incident light, and then verified with SEM. The opal crystals were considered as periodic dielectric layers and were analyzed with the transfer matrix method. The reflectance simulation showed a good agreement with the experimental results. The lattice constant and the thickness were determined at the peak position and by the fringes of the reflection spectra, respectively.     

Post‐Deposition Opal Evolution

The formation of artificial opal films consists of wet opal deposition, drying, and possible transformations in the dry state. The processes after deposition, before the crystals lattice reaches its final equilibrium state, are studied herein. We follow the time evolution of the optical transmission spectra for polystyrene opals with different thicknesses. The evolution of the spectra shows pronounced changes in the Bragg peak position, width and height, as well as changes in the background and, in the beginning of the process, a band related to residual water in the sample. Therefore, a wet and a dry phase can be distinguished in the opal transformations. They are all connected to shrinkage and we associate one of them with a possible new sintering mechanism.     

Transformation of hydrogel-based inverse opal photonic sensors from FCC to L1(1) during swelling

The structural evolution of Bragg diffracting inverse opal hydrogel sensors during swelling is directly observed by two-photon laser scanning fluorescence microscopy and compared to predictions from finite element analysis. A fluorescently labeled pH-sensitive hydrogel is UV-polymerized in a dried polystyrene colloidal crystal template, which is etched to yield an inverse opal. Fluorescence imaging of the hydrogel at different pH values reveals an inhomogeneous deformation of the FCC array of aqueous pores. The pores elongate along the sample normal direction and collapse along the sample parallel directions, consistent with the Bragg response, which indicates a 1-D increase in the interlayer distance. Interconnects between the pores serve as anchor points during hydrogel expansion into the pores. Pinning of the hydrogel to the substrate causes a change of the hydrogel lattice symmetry during deformation, from FCC (ABC stacking) to L1(1) (ABCA'B'C' stacking). Reconstructed cross-sections confirm that a 1-D increase in the interlayer distance along the substrate normal direction is responsible for the diffraction response of an inverse opal hydrogel sensor. Comparison with predictions from finite element analysis shows qualitative agreement, although the experimental mesostructure is significantly more deformed than the calculated data, due to buckling in the experimental system that is not captured by the model.     

Surface-enhanced Raman scattering from silver-coated opals

We describe surface-enhanced Raman scattering measurements from a benzenethiol monolayer adsorbed on a silver-coated film that is, in turn, deposited on an artificial opal, where the latter is a close-packed three-dimensional dielectric lattice formed from polystyrene spheres. Data for a range of sphere sizes, silver film thicknesses, and laser excitation wavelengths are obtained. Enhancement factors can be in the range of 10(7). To partially explain these large enhancements, we have performed model finite-difference time domain simulations of the position-dependent electric fields generated at the opal surfaces for several experimentally studied laser wavelengths and sphere diameters.     

Fabrication of BaTiO3 Inverse Opal Photonic Crystal

The colloidal crystal template or opal with a closed-packed face centered cubic (fcc) lattice, was prepared from monodisperse polystyrene (PS) spheres by gravity sedimentation. The template was used for the generation of photonic crystal. The template provided void space for infiltration of liquid precursor composed of titanium butyloxide, barium acetate, ethanol, and acetic acid. The opal composite was hydrolyzed, dried, sintered by heating for completely removing PS spheres to form BaTiO3 photonic crystals with inverse opal structure. The PS spheres were replaced by air spheres, which interconnected each other through the windows on the BaTiO3 wall.So both the BaTiO3 wall and air void constitute continuous phases.     

PAM-PAA microgel inverse opal photonic crystal and pH response

The colloidal crystal template or opal with a closed-packed face-centered cubic (fcc) lattice was prepared from monodisperse polystyrene (PS) spheres by vertical sedimentation.The template provided void space for infiltration of monomer precursor composed of acrylate acid,acrylamide and ammonium persulfate,as well as microgel from the subsequent copolymerization.The sample was immersed in dimethylbenzene for completely removing PS spheres to form PAM inverse opal hydrogels (IOH_(PAM)) or PAM/PAA inverse opal hydrogels (IOH_(PAM/PAA)) photonic crystals.The PS spheres were replaced by air spheres,which interconnected each other through the windows.The study of responses to pH show that there are two peaks for both IOH_(PAM) and IOH_(PAM/PAA) films,but the IOH(PAM/PAA) peaks shift to higher pH,and the peaks are independent with the AA content. (?)2007 Xiao Dong Wang.Published by Elsevier B.V.on behalf of Chinese Chemical Society.All rights reserved.     

Optical, magnetic, and dielectric properties of opal matrices with intersphere nanocavities filled with crystalline multiferroic, piezoelectric, and segnetoelectric materials

The properties and structure of composites on the basis of the lattice packings of SiO₂ nanospheres (opal matrices), containing in intersphere nanocavities clusters of the crystal phases of multiferroics and piezoelectric and ferroelectric materials.     

Effect of additive triblock copolymer PEP-3100 on bottom-up filling in electroless copper plating

Bottom-up copper filling for different sub-micrometer trenches was investigated by electroless deposition technique using a PO-EO-PO triblock copolymer termed PEP-3100 as an additive. It was found that PEP-3100 (molecular weight 3100) had a strong inhibition for the electroless copper deposition. The bottom-up filling behavior of electroless copper bath for different trenches was investigated in a plating bath containing 1.0 mg l⁻¹ PEP-3100. The cross-section SEM observation indicated the trenches with different widths ranging from 100 to 380 nm were all filled completely by electroless copper.     

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.     

Carbon and carbon-silicon carbide nanocomposites with inverse opal structure

Synthesis, morphology, and structural characteristics of carbon and SiC/C nanocomposites with a lattice of inverse opal were investigated. Porous structure characteristics were determined by gas adsorption-desorption. Photoluminescence of SiC/C nanocomposites, induced by implantation of helium ions, and their structure revealed by high-resolution transmission electron microscopy were studied.     

Inverse opal carbons for counter electrode of dye-sensitized solar cells

We investigated the fabrication of inverse opal carbon counter electrodes using a colloidal templating method for DSSCs. Specifically, bare inverse opal carbon, mesopore-incoporated inverse opal carbon, and graphitized inverse opal carbon were synthesized and stably dispersed in ethanol solution for spray coating on a FTO substrate. The thickness of the electrode was controlled by the number of coatings, and the average relative thickness was evaluated by measuring the transmittance spectrum. The effect of the counter electrode thickness on the photovoltaic performance of the DSSCs was investigated and analyzed by interfacial charge transfer resistance (R(CT)) under EIS measurement. The effect of the surface area and conductivity of the inverse opal was also investigated by considering the increase in surface area due to the mesopore in the inverse opal carbon and conductivity by graphitization of the carbon matrix. The results showed that the FF and thereby the efficiency of DSSCs were increased as the electrode thickness increased. Consequently, the larger FF and thereby the greater efficiency of the DSSCs were achieved for mIOC and gIOC compared to IOC, which was attributed to the lower R(CT). Finally, compared to a conventional Pt counter electrode, the inverse opal-based carbon showed a comparable efficiency upon application to DSSCs.     

From planar defect in opal to planar defect in inverse opal

We demonstrate a facile method of fabricating opal and inverse opal structures with a planar defect. A single layer of silica beads was embedded into polystyrene opals by combining an inward-growing self-assembly method with spin-coating technique. After the infiltration of silica followed by the removal of the polystyrene beads by calcination, an inverted structure was obtained. The silica beads were connected together by the infiltrated silica, thus a solid silica phase with the silica beads as a planar defect embedded in the inverse silica opal was obtained. The thickness of the defect layer can be adjusted by changing the size of the silica beads. Scanning electron microscope images showed the good quality of the crystal and the uniformity of the defect layer. Optical transmission spectra indicated the existence of a defect state induced by the defect layer in both the opal and inverse opal structures. High-cost techniques such as lithography and chemical vapor deposition are not involved in the fabrication of inverse opals with planar defects.     

Application of a Fickian model of diffusion to the dehydration of graded specimens of a precious Australian sedimentary opal derived from Coober Pedy

A model developed for the estimation of the diffusion coefficient based on Fickian diffusion is applied to the dehydration of a Coober Pedy white play of colour (precious) opal using thermogravimetric analysis (TG). The model was originally applied to bulk and powdered opal (opal with no bulk). In this paper the opal was graded prior to TG analysis. The diffusion coefficient was calculated and is reported up to the critical point of water.     

Estimation of the diffusion coefficient of water evolved during the non-isothermal dehydration of Australian sedimentary opal

The dehydration of an opal specimen was investigated by thermogravimetric analysis (TG) in powder and bulk forms. The change in geometry resulted in a significant difference in the temperature range in which dehydration occurred with peak temperatures in the differential TG (DTG) curve for the hand ground opal at 203°C and for the bulk opal at 340°C. This difference was attributed to time taken for diffusion of free water in the bulk opal to the specimen surface prior to evolution as a registered mass loss. A model was proposed to account for the diffusion of water and was used to estimate the diffusion coefficient.     

Improved controllability of opal film growth using capillaries for the deposition process

A capillary deposition method for the preparation of opal and inverse opal films has been developed. By this method, one can control the film thickness and the crack arrangement in opal as well as inverse opal structures. This method combines tube capillarity with cell capillarity or with gravity depending on the stability of the suspensions. The combination of tube capillarity with cell capillarity is used to prepare opal films from stable suspensions. The tube capillary transports the suspension, while the cell capillary helps to assemble the spheres. The setup defines the drying fronts, thickness, and crack arrangements of the opal films. The combination of capillarity with gravity is useful for making opal films from unstable suspensions. Opal films of spheres with size up to 1 mum can be easily prepared from this combination. Here, the gravity influences the arrangement of the spheres. The two-capillary setup has also been used to infiltrate the opal films with a titania precursor. After calcination, inverse titania opal films with skeleton structure have been obtained.     

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.     

二氧化钛反蛋白石薄膜的制备及其在化学传感器中的应用

用提拉成膜法将单分散295 nm聚甲基丙烯酸甲酯(PMMA)胶体微球自组装成蛋白石光子晶体膜. 在PMMA蛋白石光子晶体膜的空隙里填充15 nm二氧化钛纳米颗粒, 经500 ℃的处理除去PMMA膜板, 制备出大面积, 结构均一的二氧化钛反蛋白石光子晶体膜. 扫描电子显微镜(SEM)观察和X射线光电能谱(XPS)分析表明, 这种二氧化钛反蛋白石光子晶体薄膜是六方紧密堆积. 用这种二氧化钛反蛋白石光子晶体膜对溶液折射率的检测实验表明该传感膜分辨率可达0.01.