Opal-like Structure Research Articles

Structural colour in the brown algal genus Sporochnus (Sporochnales, Phaeophyceae)

ABSTRACT The colour produced by an object’s microstructure rather than by pigments is generally called structural colour. Various macroalgae have some mechanisms of structural colouration. The presence of structural colour in the brown algae is well known in the Dictyotales and Fucales but has recently been reported in the Sporochnales where Sporochnus dotyi has structures in the terminal assimilatory filaments (trichothallic hairs) that produce a pronounced green iridescence. Based on observations by light microscopy, the structural colour of this species was caused by iridescent bodies, 10–15 µm in diameter, within the cells of assimilatory filaments. In contrast, another Sporochnus species known as S. radiciformis in Japan (S. radiciformis auct. japon.) also contains iridescent bodies of 6–10 µm diameter in the assimilatory filaments, but no significant structural colour was observed. In epi-illumination observations using red, green and blue LED light sources, iridescent bodies of S. dotyi showed stronger reflection of green compared with red and blue, whereas the reflections were similar among those colours in S. radiciformis. Transmission electron microscopy (TEM) using a rapid freezing method revealed that homogeneous globules 130–160 nm in diameter were tightly packed inside the iridescent bodies of S. dotyi, whereas the sizes of the globules were markedly irregular in iridescent bodies of S. radiciformis. Therefore, we conclude that the structural colouration of S. dotyi is caused by the interference and diffraction of incident light caused by the crystal lattice-like structure of tightly packed and regularly arranged globules of homogeneous size in the iridescent bodies, which is similar to the mechanism causing iridescence in opal. A similar opal-like structure of iridescent bodies causing structural colouration was recently reported in Ericaria selaginoides, but that of S. dotyi lacked the dynamic shift of the globules shown in E. selaginoides that resulted in a change of the wavelength of reflected light.

Nanoscale Magnetic Arrays through Block Copolymer Templating of Polyoxometalates.

Magnetic nanoarrays promise to enable new energy-efficient computations based on spintronics or magnonics. In this work, we present a block copolymer-assisted strategy for fabricating ordered magnetic nanostructures on silicon and permalloy substrates. Block copolymer micelle-like structures were used as a template in which polyoxometalate (POM) clusters could assemble in an opal-like structure. A combination of microscopy and scattering techniques was used to confirm the structural and organizational features of the fabricated materials. The magnetic properties of these materials were investigated by polarized neutron reflectometry, nuclear magnetic resonance, and magnetometry measurements. The data show that a magnetic structural design was achieved and that a thin layer of patterned POMs strongly influenced an underlying permalloy layer. This work demonstrates that the bottom-up pathway is a potentially viable method for patterning magnetic substrates on a sub-100 nm scale, toward the magnetic nanostructures needed for spintronic or magnonic crystal devices.

Deposition of inverse opal-like TiO2 thin film with enhanced photoelectrochemical activity by a spin-coating combined with a dip-coating method

TiO2 thin films with an inverse opal-like structure have attracted considerable attention recently owing to their high potential for a range of applications. In this study, we demonstrated the possibility to deposit TiO2 thin films with an inverse opal-like structure from TiO2 nanoparticle-based slurry paste using a conventional spin-coating process. In addition, we also showed that the photoelectrochemical (PEC) performance of as-fabricated inverse opal-like TiO2 films can be further improved by the dip-coating process. In particular, dip-coated and untreated inverse opal-like TiO2 films exhibit photocurrent densities of ∼66.5 μA cm−2 and ∼40.9 μA cm−2 at 1.23 V versus RHE, respectively. A detailed physicochemical analysis revealed that photocurrent density enhancement (∼38.5%) in dip-coated inverse opal-like films can be attributed to a variety of factors including improved interconnection between TiO2 nanoparticles, higher crystallinity, decreased light reflection, and reduced charge carriers recombination. We strongly believe that these findings will be useful in the development of highly efficient third-generation solar cells, photocatalytic systems, electrochromic devices, and gas sensors.

Biocatalytic synthesis and ordered self-assembly of silica nanoparticles via a silica-binding peptide.

Achieving scalable and economic methods for manufacturing ordered structures of nanoparticles is an ongoing challenge. Ordered structures of SiO2 nanoparticles have gained increased attention due to the great potential they offer in filtering, separation, drug delivery, optics, electronics, and catalysis. Biomolecules, such as peptides and proteins, have been demonstrated to be useful in the synthesis and self-assembly of inorganic nanostructures. Herein, we describe a simple Stöber-based method wherein both the synthesis and the self-assembly of SiO2 nanoparticles can be facilitated by a silica-binding peptide (SiBP). We demonstrate that the SiBP acts as a multirole agent when used alone or in combination with a strong base catalyst (NH3). When used alone, SiBP catalyzes the hydrolysis of precursor molecules in a dose-dependent manner and produces 17-20 nm SiO2 particles organized in colloidal gels. When used in combination with NH3, the SiBP produces smaller and more uniformly distributed submicrometer particles. The SiBP also improves the long-range self-assembly of the as-grown particles into an opal-like structure by changing the surface charge, without any need for further modification or processing of the particles. The results presented here provide a biomimetic route to the single-step synthesis and assembly of SiO2 nanoparticles into colloidal gels or opal-like structures.

Preparation and properties of poly (vinylidene fluoride) membrane with inverse opal-like structure

Uniform pore size, high porosity and high flux are crucial to the application of membranes in separation. In this work, inspired by the special architecture of inverse opals (IOs)-a typical structure of photonic crystals (PCs), poly (vinylidene fluoride) (PVDF) membrane with uniform pore sizes, high porosity and high flux was fabricated by endowing the membrane with an IO-like structure, through sacrificing the template of SiO2 microspheres with HF. The sphericity and monodispersity of SiO2 microspheres were observed, the effects of HF on SiO2 microspheres and PVDF were studied, the membrane formation mechanism was investigated, and the membrane properties were discussed in detail. The results showed that during the membrane formation, SiO2 microspheres assembled from a disorder status into a relative ordered structure as PVDF polymer solidified, forming a relatively well-organized PVDF/SiO2 photonic crystals. Subsequently, the IO-like PVDF membranes were achieved after etching SiO2. The porosity and the pure water flux of the membrane could reach up to 76.77 % and 1145.92 L m-2h−1 respectively. The pore size of the membrane was uniform, thus exhibiting outstanding rejection of silica microspheres (almost 100 %) and excellent anti-fouling properties, which indicated IO-like PVDF membranes had great applications in separation. This study revealed a novel and facile method to modulate PVDF membranes into a uniform, highly porous and permeable microstructure.

Nitrogen/oxygen dual-doped hierarchical porous carbons with inverse opal-like structure for high performance supercapacitors

Heteroatom-doped activated carbons are ideal materials for energy storage devices. In this work, a series of nitrogen/oxygen codoped activated carbons with an inverse opal-like structure derived from cellulose diacetate are successfully synthesized through hydrothermal reaction and subsequent chemical activation during which the fluxing effect of KOH is discovered for the first time. The introduction of nitrogen and intrinsic oxygen (especially carbonyl and quinone groups) contributes to additional pseudocapacitance. The experimental results show that the obtained product delivers 400.3 F·g−1 at a current density of 1 A·g−1 in a three-electrode system and achieves extraordinary capacity retention of 90% after 10,000 charge-discharge cycles at 5 A·g−1. The energy density reaches as high as 8.8 Wh·kg−1 at a power density of 0.25 kW·kg−1 as symmetric supercapacitors, indicating a promising electrode material for high performance supercapacitors. The simple and cost-effective method requires no extra oxidation and excessive urea and thus provides new approaches for the future design of electrode materials.

Angle-dependent spectrum measurement of polystyrene opal-like structure described by Bragg-Snell diffraction and perturbed photonic band structure

Optical diffraction of opal structure, a colloidal photonic crystal, can be predicted by Bragg-Snell diffraction and photonic band structure. Theoretical prediction and optical measurement are frequently slightly different due to distance variation of particle packing. In this research, opal of 310 nm polystyrene beads was fabricated by self-assembly process and optically investigated in transmission spectra at varied angles. The measured spectra had less agreement to the Bragg-Snell prediction at large angle of detection. To explore influence of packing distance on optical response, photonic band structures were numerically simulated via plane-wave expansion method at presence of perturbed length in primitive lattice vectors. Extending each primitive vector with fixing others provided a different eigen-frequency of the first photonic band, although they had a symmetrical perturbation on (111) face-centered cubic. Perturbation on lattice length became much strong when the disturbing direction was out of eigenstate orientation plane.

A SiO2 Microcarrier with an Opal-like Structure for Cross-Linked Enzyme Immobilization.

The opal-like SiO2 microcarriers with different pore diameters named opal-SiO2I and opal-SiO2II were synthesized and utilized as microcarriers to immobilize Rhizopus oryzae lipase (ROL) and Aspergillus oryzae α-amylases (AOA). ROL and AOA can be more stably immobilized on the cross-linked SiO2 opals by neopentyl glycol diglycidyl ether (NGDE), which is the first attempt to use it as a cross-linking agent compared with glutaraldehyde. According to the morphology analysis, multiple layers of SiO2 monodisperse microspheres were regularly packed and formed an opal-like structure, and enzymes were well scattered and immobilized throughout the SiO2 opals. The results showed that the performance of enzymes immobilized on opal-SiO2II with a larger specific surface area was much better than that of opal-SiO2I. The enzyme activity of ROL@opal-SiO2II and AOA@opal-SiO2II cross-linked with 1% NGDE increased 5.32 and 9.32 times compared with their free counterpart, respectively. Furthermore, pH and thermal stability and reusability of ROL/AOA@opal-SiO2II were significantly improved and higher than those of ROL/AOA@opal-SiO2I and free enzymes. This study provides an easily obtained microcarrier opal-SiO2II, which shows potential for efficient different enzyme immobilizations and further industrial applications.

Optical response of inverse opal-like structures prepared from titanium dioxide with copper and nickel dopants

Inverse opals, as ordered macroporous structures, are widely used due to their interesting optical response. The addition of metal oxide dopants increases their optical absorption. However, with heavy dopant concentrations, the doped inverse opal is affected by structural damage and higher solid volume fractions. In this work, the effect of dopant concentration on inverse opals was investigated by doping copper and nickel into TiO2. The inverse opal-like structure was prepared by infiltrating TiO2 sol–gel into polystyrene microsphere opal templates and then baking at 500 °C. The polystyrene opal templates were constructed by self-assembly convective deposition with vibration assistance. The fluorescence emission from Cu d-states and defect states in doped TiO2 structures were studied. The emission for copper-doped TiO2 was observed at a wavelength of 520 nm with excitation at 410 nm. Although the characteristic emission of the dopants was readily observed, the overall fluorescence intensity of the doped TiO2 layer was much lower than that of the undoped TiO2 structure. Chemical compositions investigated by x-ray photoluminescence showed that the dopants disturbed the TiO2 bonds and created defect states. The reflection of the fabricated film under visible wavelength was stronger at higher dopant concentrations. These results are explained because the inverse opal has a higher solid content and the higher reflectivity is likely to be due to the rutile phase of TiO2.

Structure and phase regulation in MoxC (α-MoC1-x/β-Mo2C) to enhance hydrogen evolution

Non-precious metal-based efficient electrocatalysts with superior activity and stability for the hydrogen evolution reaction (HER) are useful in solving energy and environmental crises. Herein, monodisperse inverse opal-like MoxC (α-MoC1-x/β-Mo2C) nanospheres were synthesized via a facile strategy to adjust the intrinsic activity and maximize the exposed active sites. In particular, the MoxC-0.4 with the optimal composition of α-MoC1-x/β-Mo2C (0.56/0.44) demonstrated a superior HER performance in 0.5 M H2SO4 with a small Tafel slope of 48 mV dec−1 and remarkable stability. Such prominent performance not only benefits from the inverse opal-like structure that provides more active sites for HER, but also should be ascribed to the strong synergistic effect between α-MoC1-x and β-Mo2C. Based on theoretical calculations, it is further verified that the synergistic effect of MoxC-0.4 is originated from the optimization of interaction with the H* induced by the heterostructure. Furthermore, this work will broaden our vision for highly efficient hydrogen production by bridging the microscopic structure with macroscopic catalytic performance.

Macroporous Inverse Opal-like MoxC with Incorporated Mo Vacancies for Significantly Enhanced Hydrogen Evolution.

The hydrogen evolution reaction (HER) is one of the most important pathways for producing pure and clean hydrogen. Although platinum (Pt) is the most efficient HER electrocatalyst, its practical application is significantly hindered by high-cost and scarcity. In this work, an MoxC with incorporated Mo vacancies and macroporous inverse opal-like (IOL) structure (MoxC-IOL) was synthesized and studied as a low-cost efficient HER electrocatalyst. The macroporous IOL structure was controllably fabricated using a facile-hard template strategy. As a result of the combined benefits of the Mo vacancies and structural advantages, including appropriate hydrogen binding energy, large exposed surface, robust IOL structure and fast mass/charge transport, the synthesized MoxC-IOL exhibited significantly enhanced HER electrocatalytic performance with good stability, with performance comparable or superior to Pt wire in both acidic and alkaline solutions.

Nonlinear geometric scaling of coercivity in a three-dimensional nanoscale analog of spin ice

Magnetization hysteresis loops of a three-dimensional nanoscale analog of spin ice based on the nickel inverse opal-like structure (IOLS) have been studied at room temperature. The samples are produced by filling nickel into the voids of artificial opal-like films. The spin ice behavior is induced by tetrahedral elements within the IOLS, which have the same arrangement of magnetic moments as a spin ice. The thickness of the films vary from a two-dimensional, i.e., single-layered, antidot array to a three-dimensional, i.e., multilayered, structure. The coercive force, the saturation, and the irreversibility field have been measured in dependence of the thickness of the IOLS for in-plane and out-of-plane applied fields. The irreversibility and saturation fields change abruptly from the antidot array to the three-dimensional IOLS and remain constant upon further increase of the number of layers $n$. The coercive force ${H}_{c}$ seems to increase logarithmically with increasing $n$ as ${H}_{c}={H}_{c0}+\ensuremath{\alpha}ln(n+1)$. The logarithmic law implies the avalanchelike remagnetization of anisotropic structural elements connecting tetrahedral and cubic nodes in the IOLS. We conclude that the ``ice rule'' is the base of mechanism regulating this process.

Temperature behavior of the local magnetization vectors in ferromagnetic inverted opal-like structures

The behavior of magnetization in films of ferromagnetic inverted opal-like nanostructures based on cobalt and nickel is studied. The remagnetization curves M(H) and temperature dependences M(T) in the ranges of H from–50000 to +50000 Oe and T = 5–350 K are measured by magnetometry using a superconducting quantum interference device (SQUID-magnetometry). It is demonstrated that at T > 70 K, the total magnetization of the inverted nanostructures is composed of four local magnetizations, the vectors of which are oriented along the 〈111〉 anisotropy axes of a spatial opal-like structure. At low temperatures, the anisotropy of the film is found to make an additional significant contribution. The critical magnetic fields corresponding to reorientation of the local magnetization vectors along the 〈111〉 anisotropy axes are determined from the M(H) experimental curves. The data obtained for ferromagnetic inverted opal-like nanostructures are compared with the behavior of magnetization in continuous nickel and cobalt films.

Nanocasting hierarchical carbide-derived carbons in nanostructured opal assemblies for high-performance cathodes in lithium-sulfur batteries.

Silica nanospheres are used as templates for the generation of carbide-derived carbons with monodisperse spherical mesopores (d=20-40 nm) and microporous walls. The nanocasting approach with a polycarbosilane precursor and subsequent pyrolysis, followed by silica template removal and chlorine treatment, results in carbide-derived carbons DUT-86 (DUT=Dresden University of Technology) with remarkable textural characteristics, monodisperse, spherical mesopores tunable in diameter, and very high pore volumes up to 5.0 cm3 g(-1). Morphology replication allows these nanopores to be arranged in a nanostructured inverse opal-like structure. Specific surface areas are very high (2450 m2 g(-1)) due to the simultaneous presence of micropores. Testing DUT-86 samples as cathode materials in Li-S batteries reveals excellent performance, and tailoring of the pore size allows optimization of cell performance, especially the active center accessibility and sulfur utilization. The outstanding pore volumes allow sulfur loadings of 80 wt %, a value seldom achieved in composite cathodes, and initial capacities of 1165 mAh gsulfur(-1) are reached. After 100 cycle capacities of 860 mAh gsulfur(-1) are retained, rendering DUT-86 a high-performance sulfur host material.

Periodic order and defects in Ni-based inverse opal-like crystals on the mesoscopic and atomic scale

Thestructureofinverseopalcrystalsbasedonnickelwasprobedonthemesoscopicandatomiclevelsbyasetof complementary techniques such as scanning electron microscopy and synchrotron microradian and wide-angle diffraction. The microradian diffraction revealed the mesoscopic-scale face-centered-cubic (fcc) ordering of spherical voids in the inverse opal-like structure with unit cell dimension of 750 ± 10 nm. The diffuse scattering data were used to map defects in the fcc structure as a function of the number of layers in the Ni inverse opal-like structure. The average lateral size of mesoscopic domains is found to be independent of the number of layers. 3D reconstruction of the reciprocal space for the inverse opal crystals with different thickness provided an indirect study of original opal templates in a depth-resolved way. The microstructure and thermal response of the framework of the porous inverse opal crystal was examined using wide-angle powder x-ray diffraction. This artificial porous structure is built from nickel crystallites possessing stacking faults and dislocations peculiar for the nickel thin films.

Three-dimensional artificial spin ice in nanostructured Co on an inverse opal-like lattice

The evolution of the magnetic structure for an inverse opal-like structure under an applied magnetic field is studied by small-angle neutron scattering. The samples were produced by filling the voids of an artificial opal film with Co. It is shown that the local configuration of magnetization is inhomogeneous over the basic element of the inverse opal-like lattice structure (IOLS) but follows its periodicity. Applying the ``ice-rule'' concept to the structure, we describe the local magnetization of this ferromagnetic three-dimensional lattice. We have developed a model of the remagnetization process predicting the occurrence of an unusual perpendicular component of the magnetization in the IOLS which is defined only by the direction and strength of the applied magnetic field.

Polymerization of Ethylene over rac-Et(1-indenyl)2ZrCl2/MAO Catalyst Supported on Pseudo-Inverse Opal Silica Particles

The polymerization of ethylene with rac-Et(1-indenyl)2ZrCl2/MAO catalyst supported on ultraporous and spherical pseudo-inverse opal silica (PIOS) particles with unique morphology is reported. The novel silica particles with an inverse opal-like structure provide wide-open pore and surface structures favorable for the catalyst deposition and monomer access with minimal intraparticle diffusion resistance. The metallocene catalyst supported on the PIOS support exhibited very high initial catalyst activity and longer catalyst lifetime compared with conventional silica-supported catalysts. The experimental data that show the effects of support geometry on the catalytic activity, catalyst particle fragmentation, polymer particle morphology, and polymer molecular weight distribution in ethylene polymerization are presented.

Band gaps in phononic crystals: Generation mechanisms and interaction effects

A wide range of mesoscopic phononic materials can exhibit frequency bands where transmission is forbidden, i.e. band gaps. Three different mechanisms for their origin can be distinguished, namely Bragg, hybridization and weak elastic coupling effects. Characteristic properties of gaps of different origins are investigated and compared, for a 3D crystal of tungsten carbide beads in water, a 2D crystal of nylon rods in water, and a 3D opal-like structure of weakly sintered aluminum beads. For the second type of crystal, it is shown that Bragg and hybridization gaps can be overlapped, allowing the study of the interaction between these two mechanisms. Atypical dispersion characteristics are demonstrated near the resonance frequency.

Magnetic topology of Co-based inverse opal-like structures

The magnetic and structural properties of a cobalt inverse opal-like crystal have been studied by a combination of complementary techniques ranging from polarized neutron scattering and superconducting quantum interference device (SQUID) magnetometry to x-ray diffraction. Microradian small-angle x-ray diffraction shows that the inverse opal-like structure (OLS) synthesized by the electrochemical method fully duplicates the three-dimensional net of voids of the template artificial opal. The inverse OLS has a face-centered cubic (fcc) structure with a lattice constant of $640\ifmmode\pm\else\textpm\fi{}10$ nm and with a clear tendency to a random hexagonal close-packed structure along the $[111]$ axes. Wide-angle x-ray powder diffraction shows that the atomic cobalt structure is described by coexistence of 95% hexagonal close-packed and 5% fcc phases. The SQUID measurements demonstrate that the inverse OLS film possesses easy-plane magnetization geometry with a coercive field of 14.0 $\ifmmode\pm\else\textpm\fi{}$ 0.5 mT at room temperature. The detailed picture of the transformation of the magnetic structure under an in-plane applied field was detected with the help of small-angle diffraction of polarized neutrons. In the demagnetized state the magnetic system consists of randomly oriented magnetic domains. A complex magnetic structure appears upon application of the magnetic field, with nonhomogeneous distribution of magnetization density within the unit element of the OLS. This distribution is determined by the combined effect of the easy-plane geometry of the film and the crystallographic geometry of the opal-like structure with respect to the applied field direction.

Direct opal-like structures consisting of monodisperse polymer particles and synthesis of the related inverse structures

Three-dimensional periodic solid-state film structures with a face-centered cubic lattice and a high degree of perfection have been prepared from monodisperse particles of styrene copolymers with methacrylic acid. It has been shown that these structures can be successfully used not only as model objects for studying specific features of light propagation in photonic crystals but also as templates for synthesizing inverse opal-like structures. The influence of the degree of hydrophilization of the surface layer of polymer particles forming a polymer template and the template synthesis conditions on the quality of an inverse opal-like TiO2-based structure has been analyzed.