Inverse Opal Structure Research Articles

Silk fibroin scaffolds with inverse opal structure for bone tissue engineering.

How scaffold porosity, pore diameter and geometry influence cellular behavior is‐although heavily researched ‐ merely understood, especially in 3D. This is mainly caused by a lack of suitable, reproducible scaffold fabrication methods, with processes such as gas foaming, lyophilization or particulate leaching still being the standard. Here we propose a method to generate highly porous silk fibroin scaffolds with monodisperse spherical pores, namely inverse opals, and study their effect on cell behavior. These silk fibroin inverse opal scaffolds were compared to salt‐leached silk fibroin scaffolds in terms of human mesenchymal stem cell response upon osteogenic differentiation signals. While cell number remained similar on both scaffold types, extracellular matrix mineralization nearly doubled on the newly developed scaffolds, suggesting a positive effect on cell differentiation. By using the very same material with comparable average pore diameters, this increase in mineral content can be attributed to either the differences in pore diameter distribution or the pore geometry. Although the exact mechanisms leading to enhanced mineralization in inverse opals are not yet fully understood, our results indicate that control over pore geometry alone can have a major impact on the bioactivity of a scaffold toward stem cell differentiation into bone tissue. © 2016 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2074–2084, 2017.

Efficiency enhancement in solid state dye sensitized solar cells by including inverse opals with controlled layer thicknesses

The photoconversion efficiency of dye sensitized solar cells can be enhanced by the incorporation of light management nanostructures such as photonic crystals. Here, we present a facile route to incorporate titania inverse opals into solid state dye sensitized solar cells and report photoconversion efficiency enhancements of up to 56% compared with a model system without the inverse opal. Our approach is based on the precise design of titania inverse opals with a predetermined thickness that can be controlled at the individual layer level. By choosing an inverse opal exhibiting a photonic bandgap which overlaps the absorption bands of the dye, our results show that there is an optimal thickness of the inverse opal structure for maximum efficiency enhancement of the cell. This is the first experimental proof that the thickness of a titania inverse opal plays a pivotal role in cell efficiency enhancement in solid state dye sensitized solar cells.

High-temperature stable indium oxide photonic crystals: transducer material for optical and resistive gas sensing

Abstract. Indium oxide (In2O3) inverse opal is a promising new transducer material for resistive and optical gas sensors. The periodically ordered and highly accessible pores of the inverse opal allow the design of resistive sensors with characteristics independent of structure limitations, such as diffusion effects or limited conductivity due to constricted crosslinking. Additionally the photonic properties caused by the inverse opal structure can be utilized to read out the sensors' electronical state by optical methods. Typically semiconducting sensors are operated at high temperatures (> 300 °C). To maintain a good thermal stability of the transducer material during operation is a minimum requirement. We present results on the synthesis and investigation of the structural stability of the In2O3 inverse opal structure up to a temperature of 550 °C (limit of substrate material). As will be shown, their optical properties are maintained with only slight shifts of the photonic band gaps which can be explained by the results from the structural characterization using X-ray diffraction and electron microscopy combined with optical simulations.

Fabrication and Characterization of Monolithic 3D Amorphous Silicon Inverse-opal Photonic Materials with Magnesiothermic Reduction at a Lower Temperature

Background: Silicon photonic structures (PSs) with inverse opal structures are favored due to their high refractive index at optical frequencies. However, the fabrication of monoliths of 3D amorphous silicon (a-Si) inverse opals with large band-gaps and photoluminescence at optical frequencies especially in the visible range is rarely reported in literatures. Methods: The monoliths of the ordered 3D polystyrene colloidal crystals are immersed into tetraethyl-orthosilicate solution for several hours and then dried. The resulting monolith of latex/silica is calcinated under an oxygen flow. Using the porous silica as templates and reactants, a-Si photonic structures with a face centered cubic crystal lattice are obtained through a magnesiothermic reduction procedure. Results: Large-scale monoliths of a-Si photonic materials with inverse opal macro-porous hierarchical nanostructures have been fabricated. This successful fabrication is mainly attributed to the lower-temperature (605 ºC) and the disordered amorphous morphology for Si. The obtained 3D a-Si inverse opals are with a full band-gap at optical frequencies. Conclusion: This facile fabrication of large-scale amorphous Si photonic materials with well-tailored optical properties would greatly extend the applications of a-Si in optoelectronics and other fields. Keywords: Amorphous materials, magnesiothermic reduction, nanostructures, optical properties, photonic materials, silicon.

Patterned Photonic Nitrocellulose for Pseudo-Paper Microfluidics.

We report a pseudo-paper microfluidic chip based on patterned photonic nitrocellulose. The photonic nitrocellulose is fabricated using self-assembled monodisperse SiO2 nanoparticles as template. The SiO2 nanoparticles form a photonic crystal having a close-packed hexagonal structure in the microchannels, so the resulting nitrocellulose has a complementary inverse-opal structure. After lamination, a hollow channel is obtained that is partially filled with the photonic nitrocellulose. Owing to the highly ordered photonic structure of the pseudo-paper chip, the flow profile of aqueous solution wicking through the channel is more uniform than conventional paper microfluidic chip. It is also found that the wicking rate of aqueous solution can be easily manipulated by changing the diameter of the self-assembled monodisperse SiO2 nanoparticles, which determines the pore size of the photonic nitrocellulose. The fluorescent enhancement property of the photonic nitrocellulose is used to increase the fluorescent intensity for multiplex detection of two cancer biomarkers. Label-free detection of human immunoglobin G based on the structure color of the photonic nitrocellulose is also demonstrated.

Investigation and calculation of filling factor of SnO2 inverse opal

In the process of preparing inverse opal, the structure of inverse opal is affected by many factors, and the filling factor of inverse opal is difficult to directly test. In this paper, SnO2 inverse opal was prepared with the sol–gel method by cooperative opal template. The repetition times of the infiltrating precursor into the opal templates were investigated in detail. The band-gap positions of SnO2 inverse opal were tested. In order to prepare perfect inverse opal structure, the filling quantity of the precursor is greater, as the diameter of the PS microsphere of opal is bigger. The filling factor of air in inverse opal can be calculated with a formula derived from Bragg’s law. For inverse opal, the filling factor of air in inverse opal gradually enlarges as the diameter of the void increases.

Role of WO3 Layers Electrodeposited on SnO2 Inverse Opal Skeletons in Photoelectrochemical Water Splitting

Tin dioxide (SnO2) inverse opals (IOs) were developed by a spin-coating-assisted sol–gel process. The SnO2 IOs exhibited a pore size of ∼260 nm in the 370 nm sized polystyrene bead (PS) templates. Electrodes having a WO3 layer with a band gap (Eg) of 2.6 eV were electrodeposited on the SnO2 IOs under a constant potential (−0.47 VAg/AgCl), where the thickness of the WO3 layer depended on the applied charge amount for WO3 electrodeposition (200–800 mC/cm2). As a control sample, a pure WO3 IO film with the same thickness of ∼3.1 μm was also prepared by electrodeposition. The pore diameter of the SnO2 IO structure declined noticeably as the deposited charge amount of the WO3 layer increased from 200 to 800 mC/cm2, leading to eventual coverage of the SnO2 IO structure with the WO3 (800 mC/cm2) layer. Moreover, X-ray diffraction analysis indicated a steady increase of the signal intensity of the monoclinic WO3 planes as the deposited charge amount of the WO3 layer increased, indirectly indicating an increased l...

Enhancement of the near-infrared emission in novel quantum cutting SiO_2:Tb^3+, Yb^3+ thin films by Ag species

The SiO2: Tb, Yb thin films (or inverse opals) including Ag nanoparticles (NPs) were successfully synthesized by using the sol-gel method. The influence of Ag species on the photoluminescence (PL) property of SiO2: Tb, Yb, Ag material was investigated. Under 250 nm excitation, the visible-infrared (NIR) quantum cutting (QC) emission from Tb3+ and Yb3+ are greatly enhanced with formation of Ag NPs in SiO2 thin films. Meanwhile, an interesting broad excitation band which may be attributed to Ag nanoclusters of (Ag4)2+ tetramers is obtained by monitoring 977 nm emission of Yb3+. It is supposed that the (Ag4)2+ can pass energy to Yb3+ directly, where the energy transfer (ET) between (Ag4)2+ to the Yb3+ is suggested in a QC process. Moreover, we demonstrated that the Tb ions are required for the formation of the (Ag4)2+ in SiO2 glass hosts. In the SiO2: Tb, Yb, Ag inverse opals thin films, the QC emission intensity of Yb3+ is considerably improved by inhibiting the blue and green emission of Tb3+. The results demonstrated that the ET between Tb3+ and Yb3+ is enhanced. In addition, we not only observed the existence of (Ag4)2+, but also obtained ET from silver aggregates of (Ag2)+ to Tb3+ in the inverse opals under 377 nm excitation. The mechanism of visible-NIR QC emission of the SiO2: Tb, Yb, Ag films with inverse opal structure are discussed.

Performance enhancement of aqueous dye-sensitized solar cells via introduction of a quasi-solid-state electrolyte with an inverse opal structure

To bridge the gap in the power conversion efficiencies (PCEs) of aqueous and organic-solvent based dye-sensitized solar cells (DSCs), water-based electrolytes are exploited for a new role to enhance DSC performance. Hydrogels with an inverse opal structure (IOS) were prepared using various SiO2 opal films as templates. The gels were further used as a host for preparing fully water-based gel electrolytes with a photonic band gap (PBG) on which quasi-solid-state DSCs were fabricated. The current–voltage curves indicate that PCEs for the gel electrolytes with the IOS are superior to those for the reference gel electrolyte without the structure, and a maximum average PCE of 1.80% is achieved for the gel electrolytes with the PBG around 624nm, which is approximately 22% higher than the value for the reference gel electrolyte (1.48%). The action spectra reveal increases of the incident photo-to-current conversion efficiencies both in and beyond the PBG region, indicating that the back reflection and scattering of photons as a result of the IOS are significant for light-harvesting and PCE enhancement. The electrochemical impedance spectra further demonstrate that the IOS lowers the Warburg impedance and the resistance at the TiO2/electrolyte interface compared to the reference gel electrolyte. Furthermore, the durability of DSCs is improved by the gel electrolyte/TiO2 interface and the IOS.

Ag Nanoparticle/Polydopamine-Coated Inverse Opals as Highly Efficient Catalytic Membranes.

Polymeric three-dimensional inverse-opal (IO) structures provide unique structural properties useful for various applications ranging from optics to separation technologies. Despite vast needs for IO functionalization to impart additional chemical properties, this task has been seriously challenged by the intrinsic limitation of polymeric porous materials that do not allow for the easy penetration of waterborne moieties or precursors. To overcome this restriction, we present a robust and straightforward method of employing a dipping-based surface modification with polydopamine (PDA) inside the IO structures, and demonstrate their application to catalytic membranes via synthetic incorporation of Ag nanoparticles. The PDA coating offers simultaneous advantages of achieving the improved hydrophilicity required for the facilitated infiltration of aqueous precursors and successful creation of nucleation sites for a reduction of growth of the Ag nanoparticles. The resulting Ag nanoparticle-incorporated IO structures are utilized as catalytic membranes for the reduction of 4-nitrophenol to its amino derivatives in the presence of NaBH4. Synergistically combined characteristics of high reactivity of Ag nanoparticles along with a greatly enhanced internal surface area of IO structures enable the implementation of remarkably improved catalytic performance, exhibiting a good conversion efficiency greater than 99% while minimizing loss in the membrane permeability.

Synthesis of ZnO inverse opals with high crystalline quality by a three-dimensional colloidal crystal template-assisted hydrothermal method over a seed layer

In this paper, zinc oxide (ZnO) inverse opal structures were fabricated on a seed layer using three-dimensional (3D) colloidal crystal templates. The 3D colloidal crystal templates hindered the diffusion of zinc ions during hydrothermal growth thereby restricting the formation of porous ZnO structures at typical Zn2+ concentrations leading to rods. Instead of porous ZnO microstructures, ZnO nanobowl films were exclusively grown using the 3D colloidal templates on the photoresist-patterned seed layer at the initial Zn2+ concentrations. 3D porous ZnO with different filling fractions were successfully created by a hydrothermal method at a Zn2+ concentration of 0.15 M with different adjuvants. The addition of sodium citrate yielded ZnO having inverse opal structures and showing variable reflection peaks according to the photonic stop band, which were controlled by the diameter of the template colloidal spheres. ZnO inverse opals prepared with sodium citrate as an adjuvant also showed superior ultraviolet photoluminescence intensity values compared to their adjuvant-free and polyethylenimine counterparts. The hydrothermal method resulted in ZnO inverse opal structures with significantly enhanced crystalline quality compared to those prepared by electrodeposition methods. ZnO inverse opals prepared by large-diameter colloidal crystal templates showed slightly better properties than those prepared using small-diameter templates. The ZnO inverse opals conformally coated by a thin layer of TiO2 were used as photoanodes for water splitting. The ZnO inverse opals prepared by the hydrothermal method showed significantly higher photocurrent values than those synthesized by electrodeposition. These ZnO inverse opals showed maximum photocurrent values of ca. 0.9 mA cm−2 comparable to the best results of other ZnO-based microstructures.

Photoresponsive Liquid-Crystalline Polymer Films Bilayered with an Inverse Opal Structure

Photoresponsive Liquid-Crystalline Polymer Films Bilayered with an Inverse Opal Structure

Bilayer quantum dot-decorated mesoscopic inverse opals for high volumetric photoelectrochemical water splitting efficiency

We introduce a mesoscopic inverse opal structure sensitized by CdSe/CdS nanoparticle bilayer for use as water splitting electrodes.

Zintl Clusters as Wet‐Chemical Precursors for Germanium Nanomorphologies with Tunable Composition

Abstract[Ge9]4− Zintl clusters are used as soluble germanium source for a bottom–up fabrication of Ge nanomorphologies such as inverse opal structures with tunable composition. The method is based on the assembly and oxidation of [Ge9]4− clusters in a template mold using SiCl4, GeCl4, and PCl3 leading to Si and P‐containing Ge phases as shown by X‐ray diffraction, Raman spectroscopy, and energy‐dispersive X‐ray analysis. [Ge9]4− clusters are retained using ethylenediamine (en) as a transfer medium to a mold after removal of the solvent if water is thoroughly excluded, but are oxidized to amorphous Ge in presence of water traces. 1H NMR spectroscopy reveals the oxidative deprotonation of en by [Ge9]4−. Subsequent annealing leads to crystalline Ge. As an example for wet‐chemical synthesis of complex Ge nanomorphologies, we describe the fabrication of undoped and P‐doped inverse opal‐structured Ge films with a rather low oxygen contents. The morphology of the films with regular volume porosity is characterized by SEM, TEM, and grazing incidence small‐angle X‐ray scattering.

Zintl Clusters as Wet-Chemical Precursors for Germanium Nanomorphologies with Tunable Composition.

[Ge9](4-) Zintl clusters are used as soluble germanium source for a bottom-up fabrication of Ge nanomorphologies such as inverse opal structures with tunable composition. The method is based on the assembly and oxidation of [Ge9 ](4-) clusters in a template mold using SiCl4 , GeCl4 , and PCl3 leading to Si and P-containing Ge phases as shown by X-ray diffraction, Raman spectroscopy, and energy-dispersive X-ray analysis. [Ge9](4-) clusters are retained using ethylenediamine (en) as a transfer medium to a mold after removal of the solvent if water is thoroughly excluded, but are oxidized to amorphous Ge in presence of water traces. (1)H NMR spectroscopy reveals the oxidative deprotonation of en by [Ge9](4-). Subsequent annealing leads to crystalline Ge. As an example for wet-chemical synthesis of complex Ge nanomorphologies, we describe the fabrication of undoped and P-doped inverse opal-structured Ge films with a rather low oxygen contents. The morphology of the films with regular volume porosity is characterized by SEM, TEM, and grazing incidence small-angle X-ray scattering.

Self-assembly of plasmonic/excitonic silicon nanocrystals into photonic crystals

Abstract

Electrodeposited Structurally Stable V2O5 Inverse Opal Networks as High Performance Thin Film Lithium Batteries.

High performance thin film lithium batteries using structurally stable electrodeposited V2O5 inverse opal (IO) networks as cathodes provide high capacity and outstanding cycling capability and also were demonstrated on transparent conducting oxide current collectors. The superior electrochemical performance of the inverse opal structures was evaluated through galvanostatic and potentiodynamic cycling, and the IO thin film battery offers increased capacity retention compared to micron-scale bulk particles from improved mechanical stability and electrical contact to stainless steel or transparent conducting current collectors from bottom-up electrodeposition growth. Li(+) is inserted into planar and IO structures at different potentials, and correlated to a preferential exposure of insertion sites of the IO network to the electrolyte. Additionally, potentiodynamic testing quantified the portion of the capacity stored as surface bound capacitive charge. Raman scattering and XRD characterization showed how the IO allows swelling into the pore volume rather than away from the current collector. V2O5 IO coin cells offer high initial capacities, but capacity fading can occur with limited electrolyte. Finally, we demonstrate that a V2O5 IO thin film battery prepared on a transparent conducting current collector with excess electrolyte exhibits high capacities (∼200 mAh g(-1)) and outstanding capacity retention and rate capability.

High-performance characteristics of silicon inverse opal synthesized by the simple magnesium reduction as anodes for lithium-ion batteries

Inverse silicon opal (ISi) and carbon-coated inverse Si opal (C–ISi) structures are prepared from the simple thermal reduction method using magnesium and investigated as the anode materials in lithium-ion batteries. The ISi and C–ISi samples comprise continuously arranged inverse opal structures, constructed by Si nanoparticles. The macroporous structures in ∼1 μm range are favourable for lithium-ion transport and more importantly for absorbing volumetric change in the silicon nanoparticles. Moreover, the carbon coating on the inverse Si opal improves the electrical conductivity and acts as a mechanical buffer for the volume change. C–ISi sample shows a high capacity of 1550 mAh g−1 at the 100th cycle with very stable cycle retention, whereas the ISi and pristine Si samples show 1146.4 mAh g−1 and approximately zero, respectively, at the 100th cycle with rapid capacity fading. Surprisingly, the volumetric expansion of C–ISi electrode after 100th cycles is only 16.1%, which is as low as that for commercial graphite electrodes.

Chemically Patterned Inverse Opal Created by a Selective Photolysis Modification Process.

Anisotropic photonic crystal materials have long been pursued for their broad applications. A novel method for creating chemically patterned inverse opals is proposed here. The patterning technique is based on selective photolysis of a photolabile polymer together with postmodification on released amine groups. The patterning method allows regioselective modification within an inverse opal structure, taking advantage of selective chemical reaction. Moreover, combined with the unique signal self-reporting feature of the photonic crystal, the fabricated structure is capable of various applications, including gradient photonic bandgap and dynamic chemical patterns. The proposed method provides the ability to extend the structural and chemical complexity of the photonic crystal, as well as its potential applications.

SnO2 and F:SnO2 Inverse Opal Based Photoelectrochemcial Water Splitting

Nowadays, the exploration of new photoelectrode architectures to improve the light-harvesting and charge-collection properties of photoelectrochemical cells and related devices have been regarded as a challenging work. Here, we synthesized the inverse opal SnO2 for photoelectrochemical water splitting by the spin-coating method exploring the polystyrene beads with a size of approximately 350 nm. The SnO2 inverse opal structure shows the photonic crystal effect with a well-ordered hexagonal structure packing. Upon this film, the photoactive TiO2 layer with various thicknesses from 10 nm to 40 nm was deposited by atomic layer deposition. Herein, it is expected that an optimal TiO2 layer takes part in a role as a photoactive material. Adding to these results, the F doping on the SnO2 inverse opal film was also examined with the TiO2layers. These results were confirmed using Field-emission scanning electron microscopy, X-ray diffraction and ultraviolet-visible spectrophotometer. Detail results and discussion would be presented. Figure 1