Silica Opal Templates Research Articles

Three-dimensional opal-like photonic crystals made of diamond shells by chemical vapor deposition

3D ordered hollow diamond spheres packed into opal structure have been synthesized by chemical vapor deposition using silicon inverse opal template which, in turn, was produced by molding of a bulk silica opal template. These 3D diamond opals demonstrate optical properties of photonic crystal with Bragg reflection peak in the visible range. Numerical modeling of the reflection spectra is performed using a scattering matrix calculation, and agrees well with the measured Bragg peak positions. The porous structure consisting of nanocrystalline diamond shells with thickness of the order of 10 nm composes the light-weight material with density of ≈0.50 g/cm3. The diamond opals showed bright photoluminescence at 738 nm wavelength due to silicon-vacancy centers formation in course of the growth process. The diamond opals can be a new promising platform for versatile applications, primarily in photonics, due to wide transparency window, high chemical resistance and mechanical strength inherent to diamond.

Omnidirectional, Broadband, and Polarization‐Independent Near‐Perfect Light Absorption from Surface Plasmonic Excitation of a Corrugated Au–SiO2–Au Structure Fabricated with a Self‐Assembled Silica Opal Template

A corrugated metal–insulator–metal (cMIM) structural design for omnidirectional, broadband, and polarization‐independent near‐perfect light absorption (NPA) is proposed and demonstrated. The optimal structure consists of a (6 nm Au layer)–(70 nm SiO2 layer)–(90 nm Au layer) MIM structure on top of a self‐assembled silica opal template, which consists of monodisperse SiO2 nanospheres with an average diameter of 295 nm. The optical measurement demonstrates greater than 95% absorption for this optimal cMIM structure with incident light with wavelengths between 400 and 800 nm, and the incident angle varies from normal incidence to 60° off normal for both TE and TM polarizations. For the figure of merit (FOM) of the device performance, the spectral averaged absorption at normal incidence is calculated. The optimal cMIM structure demonstrates an FOM of 99.2%. Numerical simulations with rigorous coupling wave analysis (RCWA) and the finite difference time domain (FDTD) method to simulate the interaction between the incident light and the cMIM structure is carried out. The results qualitatively reproduce the structural dependence of the absorption of cMIM structures. They further indicate that multiple modes of surface plasmon polariton (SPP) excitation at various wavelengths are responsible for the NPA of the cMIM structure.

Synthesis and Modification of Macroporous Titania using Silver Nanoparticles

A synthesis method for preparing macroporous nitrogen and silver-modified titania via sol-gel route is presented. The addition of nitrogen and silver nanoparticles was carried out simultaneously with a hard templating technique using silica spheres packed into a three dimensional opal structure. The influence of such modifications on the optical and chemical properties of titania was evaluated using photocatalytic degradation under visible light. The macroporous opal templated samples in this work performed better than the commercial titania, Degussa P25. The highest photocatalytic enhancement, showing more than eight times higher activity than the non-modified titania, was achieved by the opal templated sample prepared with 1.0 mol % of silver. Although silver addition and macroporous templating enhanced the visible light activity, the most significant improvement was afforded by the utilization of the silica opal template that gave rise to high surface area (>100 m 2 g -1 ) and promoted the surface charge interaction.

Phototriggered Selective Actuation and Self‐Oscillating in Dual‐Phase Liquid Crystal Photonic Actuators

AbstractAmong different kinds of photoactuators available, those based on liquid‐crystal polymer networks (LCNs) are gathering a great deal of attention due to their fast response and versatility of structural design. However, only a few reports have focused on the phototriggered LCN actuators for complex actuation and multifunction properties. Here, a phototriggered LCN‐based photonic actuator with quasi‐bilayer structure that exhibits fast and reversible shape changes is created by infiltrating a LCN precursor–graphene oxide mixture into a silica opal template, ultraviolet photopolymerization, and removing the template. Particularly, the phototriggered selective actuation behavior is achieved in dual‐phase LCN‐based photonic actuators with macroscopically alternating nematic (N) and isotropic (I) phase, which enables versatile actuation modes and allows multiple shape changes. In addition, a two‐segmented, dual‐phase LCN‐based photonic actuator exhibits self‐oscillating motion when a responsive N‐phase region as localized active point is irradiated, which arises from the self‐shadowing of the passive I‐phase region. To demonstrate the potential application of this self‐oscillating motion behavior, a photoelectric energy conversion device that is capable of converting light energy to electric energy is constructed.

Label-free electrochemical immunoassay for neuron specific enolase based on 3D macroporous reduced graphene oxide/polyaniline film

The content of neuron specific enolase (NSE) in serum is considered to be an essential indicator of small cell lung cancer (SCLC). Here, a novel label-free electrochemical immunoassay for the detection of NSE based on the three dimensionally macroporous reduced graphene oxide/polyaniline (3DM rGO/PANI) film has been proposed. The 3DM rGO/PANI film was constructed by electrochemical co-deposition of GO and aniline into the interspaces of a sacrificial silica opal template modified Au slice. During the co-deposition, GO was successfully reduced by aniline and PANI could be deposited on the surfaces of rGO sheets. The ratio of rGO and PANI in the composite was also optimized to achieve the maximum electrochemical performance. The 3DM rGO/PANI composite provided larger specific surface area for the antibody immobilization, exhibited enhanced conductivity for electron transfer, and more important was that PANI acted as the electroactive probe for indicating the NSE concentration. Under the optimal conditions, a linear current response of PANI to NSE concentration was obtained over 0.5 pg mL−1-10.0 ng mL−1 with a detection limit of 0.1 pg mL−1. Moreover, the immunosensor showed excellent selectivity, good stability, satisfactory reproducibility and regeneration, and was employed to detect NSE in clinical serum specimens.

High thermal stability of three-dimensionally ordered nano-composite cathodes for solid oxide fuel cells

A non-close-packed (NCP) silica opal connected by cylindrical rods was prepared using a selective etching technique. Using sol-gel impregnation of the NCP silica opal template, La0.8Sr0.2MnO3/Zr0.84Y0.16O2 (LSM/YSZ) composite cathodes were fabricated for solid oxide fuel cells. The microstructure of the as-prepared cathode revealed three-dimensionally (3D) ordered hollow spheres connected by cylindrical tubes. Even after high-temperature sintering at 1000°C, the 3D ordered nano-network remained stable. Electrochemical impedance spectroscopy was used to study the oxygen reduction reaction kinetics of the 3D ordered LSM/YSZ electrode. The impedance behavior was similar to that of a mixed ionic-electronic conductor, different from the behavior of traditional micro-scaled LSM/YSZ electrodes. The nanometer-scale particle size and continuous nano-network are the main reasons for this divergence in behavior.

Ultrasensitive enzyme-free electrochemical immunoassay for free thyroxine based on three dimensionally ordered macroporous chitosan–Au nanoparticles hybrid film

The measurement of free thyroxine concentration in serum is considered to be an essential indicator of thyroid function. Here, a novel enzyme-free sandwich electrochemical immunosensor for the detection of FT4 antigen based on the immobilization of primary antibody (Ab1) on three dimensional ordered macroporous chitosan–Au nanoparticles hybrid (3DOM CS–AuNPs) film electrode, and magnetic multiwall carbon nanotubes (MMWCNTs) were used as label of secondary antibody (Ab2). The 3DOM CS–AuNPs film electrode was constructed by one-step electrodeposition of CS–AuNPs composite onto Au electrode with silica opal template. MMWCNTs were prepared by chemical co-precipitation of Fe2+ and Fe3+ salts on carboxylated MWCNTs. Ru(bpy)32+ labeled anti-FT4 (Ru(bpy)32+–Ab2) was covalently attached to MMWCNTs through the formation of amide bond between the carboxylic groups of MWCNTs and the amine groups of antibody. Under the optimal conditions, FT4 was detected in a concentration range from 0.71fgmL−1 to 1.15pgmL−1 with a correlation coefficient of 0.998 and a detection limit of 0.20fgmL−1. Moreover, the immunosensor showed excellent selectivity, good stability, satisfactory reproducibility and regeneration. Importantly, the developed method was used to assay clinical serum specimens, achieving a good relation with those obtained from the commercialized electrochemiluminescent method.

Coherent Phonon-Grain Boundary Scattering in Silicon Inverse Opals

We report measurements and modeling of thermal conductivity in periodic three-dimensional dielectric nanostructures, silicon inverse opals. Such structures represent a three-dimensional "phononic crystal" but affect heat flow instead of acoustics. Employing the Stober method, we fabricate high quality silica opal templates that on filling with amorphous silicon, etching and recrystallizing produce silicon inverse opals. The periodicities and shell thicknesses are in the range 420-900 and 18-38 nm, respectively. The thermal conductivity of inverse opal films are relatively low, ~0.6-1.4 W/mK at 300 K and arise due to macroscopic bending of heat flow lines in the structure. The corresponding material thermal conductivity is in the range 5-12 W/mK and has an anomalous ~T(1.8) dependence at low temperatures, distinct from the typical ~T(3) behavior of bulk polycrystalline silicon. Using phonon scattering theory, we show such dependence arising from coherent phonon reflections in the intergrain region. This is consistent with an unconfirmed theory proposed in 1955. The low thermal conductivity is significant for applications in photonics where they imply significant temperature rise at relatively low absorption and in thermoelectrics, where they suggest the possibility of enhancement in the figure of merit for polysilicon with optimal doping.

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.

Inverse Opal Carbons Derived from a Polymer Precursor as Electrode Materials for Electric Double-Layer Capacitors

Self-standing and macroporous carbon materials were prepared by using silica opals (colloidal crystal) as a template. Poly(furfuryl alcohol) was synthesized in the interstice of the silica colloidal crystals, followed by carbonization at . The silica templates were etched off to give inverse opal carbons. The inverse opal carbons were characterized by scanning electron micrograph (SEM), reflection spectroscopy, elemental analysis, infrared spectroscopy, X-ray diffraction, direct current conductivity, and -adsorption/desorption experiments. The SEM images and the reflection spectra indicated periodic porous structures that were negative structures of the silica opal templates. The inverse opal carbons were hard carbons, mainly consisting of amorphous incompletely graphitized structures, and have electronic conductivity of . The nitrogen adosorption/desorption experiments clarified that the carbons have large -BET (Brunauer-Emmett-Teller) specific surface area resulting from a lot of mesopores, in addition to macropores based on the silica templates. Electric double-layer charging and discharging of the carbons were studied in a tetraethylammonium tetrafluoroborate/propylene carbonate solution. The electric double-layer gravimetric capacitance and the coulombic efficiency of the inverse opal carbon electrodes in the solution increased with a decrease in the diameter of the silica spheres used for the opal templates and became superior to those of a typical activated carbon.

Optical properties of silica opal templates in the infrared and visible

Measurements of transmission and reflection from thick silica opal slabs were performed in the spectral range 0.3–3.5 μm. A wide transmission stop band due to photonic band gap with no signs of reentrance to high-transmission regime down to 0.3 μm was observed. In addition, a new stop band in the range 2.7–3.6 μm was observed, where the transmittance oscillates fringe like about a small level in spite of negligible dispersion and absorption. In the reflection measurements two strong rejection bands were observed around 9.0 μm and 20.9 μm, which are due to anomalous dispersion in SiO 2. The results obtained were explained using concepts of photonic band structure and photonic transport in disordered medium. An effective-medium theory was used to compute the infrared optical properties. A semi-quantitative agreement between the simulated and measured infrared reflectance was found.

A General Approach toward Opal–Inverse Opal Interlocked Materials

Opal–inverse opal interlocked composites consisting of opals of hollow spheres with window channels interlocked, have displayed new properties. A facile and general method has been reported to synthesize the ordered composites. Polymer shells are first grown onto the surface of a silica sphere of an opal template by ATRP, which is followed by a sequential modification of the shells resulting in functional groups. Composite shells are favorably synthesized within the functional polymer shells. After the removal of silica opal templates, opal–inverse opal interlocked structures with varied compositions of polymers, inorganic materials, and carbon are achieved.

Fabrication and Optical Properties of π-Conjugated Polymer Inverse Opal

Polymer inverse opals were fabricated by directly infiltrating a molten polymer into silica opal templates at an elevated temperature. The main-chain π-conjugated polymer, poly[2-(9',9'-dihexylfluorenyl)-1,4-phenylenevinylene] (DHF-PPV) was adopted for fabricating an inverse opal. The DHF-PPV inverse opal maintained well-defined periodic structures of the silica opal template, showing ordered and well-packed spherical air-pores by scanning electron microscopy. The DHF-PPV inverse opal showed an optical stop band based on the periodic pattern of the refractive index in the visible wavelength region. A dip in the photoluminescence spectrum resulting from the influence of the stop band was observed.

Novel Network Polymer for Templated Carbon Photonic Crystal Structures

Inverse opaline photonic crystal structures are created from carbon precursor polymer networks derived from the thermal Bergman cyclopolymerization of bis-ortho-diynyl arene (BODA) monomers. A new hydroxy-functional BODA monomer was prepared that exhibited excellent compatibility with silica opal templates. Monomer melt infiltration of the template, in situ thermal polymerization, and pyrolysis, followed by removal of the silica with HF affords a carbon inverse opal structure that conserves the original dimensions of the template. The photonic crystal was characterized by the reflectance spectra, and the refractive index of the carbon was estimated. The functionality of the carbon opal as a sensor element was demonstrated with water/acetonitrile mixtures and reveals a bandstop shift of 13 nm over a refractive index change of 0.011.

Optical and Crystallographic Properties of Inverse Opal Photonic Crystals Grown by Atomic Layer Deposition

ABSTRACTWe report a technique for the formation of infiltrated and inverse opal structures that produces high quality, low porosity conformal material structures. ZnS:Mn and TiO2 were deposited within the void space of an opal lattice by atomic layer deposition. The resulting structures were etched with HF to remove the silica opal template. Infiltrated and inverse opals were characterized by SEM, XRD, and transmission/reflection spectroscopy. The reflectance spectra exhibited features corresponding to strong low and high order photonic band gaps in the (111) direction (γ-L). In addition, deliberate partial infiltrations and multi-layered inverse opals have been formed. The effectiveness of a post-deposition heat treatment for converting TiO2 films to rutile was also studied.

Synthesis of inverse opals

Here we report different simple and inexpensive approaches to the fabrication of inverse opals originated from silica opal templates with sphere size in the range between 0.2 and 1.3 μm. The opal porous lattice is infiltrated with semiconductors (CdS, Ge, Si) as well as polymers by several methods such as chemical vapour deposition, chemical bath deposition, and hydrolysis. Afterwards the template is removed from the composite by a mild chemical etching method giving rise to an inverse opal. The periodicity of the template is chosen to guarantee that photonic gaps or pseudogaps are in the transparency region of the bulk-infiltrated material, which in the case of silicon and germanium can be easily integrated in the existing microelectronic technology.