Silica Arrays Research Articles

Nanoimprinted patterned sapphire with silica array for efficient InGaN-based green mini-LEDs.

Here, we propose nanoimprinted patterned sapphire with a silica array (PSSA) with the aim to promote the efficiency of InGaN-based green (∼520 nm) mini-LEDs. According to x-ray diffraction measurements, the threading dislocation density of GaN epitaxial layers grown on nanoimprinted PSSA demonstrates a pronounced reduction compared with the epilayers on the conventional patterned sapphire substrate (PSS). Consequently, a mini-LED on PSSA exhibits a significantly boosted light output power (LOP) in comparison to a mini-LED on PSS. At 10 mA, the LOP of the mini-LED on PSS is 6.0 mW, and this is further improved to 6.8 mW for the mini-LED on PSSA. Moreover, the peak external quantum efficiencies of the mini-LEDs on PSS and PSSA are 41% and 47%, respectively. A three-dimensional (3D) finite-difference time-domain simulation demonstrates that the PSSA contributes enhanced light extraction for photons emitted from the active region. It is also highly feasible to use this nanoimprinted PSSA technology in red and blue mini-LEDs for the realization of full-color displays.

Spatial characterization of peptide nucleic acid molecularly imprinted inverse opal

The combination of molecularly imprinted polymers (MIPs) and inverse opals (IO) have been a point of interest in the past few years due to their potential in sensing applications. At the same time, peptide nucleic acid (PNA) is a stable analogue to natural occurring genetic material. In this study, we describe the preparation and characterization of a PNA imprinted matrix, based on the controlled self-assembly of organized silica particles (SiPs) arrays. The degree of organization of the silica arrays are compared to the organization of the cavities after the removal of the SiPs, using spatial statistical analysis. This analysis of the Voronoi tessellations, pair correlation functions and bond order showed that the successfully formed arrays contain a high degree of quasi-hexagonal (hexatic) organization of the cavities, with both global and local order. The adsorption analysis of the materials show potential for developing future materials with tunable structural reflective properties, such as on-site, color- changing genetic material sensor.Graphical abstract

Multi-Objective Optimization of Liquid Silica Array Lenses Based on Latin Hypercube Sampling and Constrained Generative Inverse Design Networks.

Injection molding process parameters have a great impact on plastic production quality, manufacturing cost, and molding efficiency. This study proposes to apply the method of Latin hypercube sampling, and to combine the response surface model and "Constraint Generation Inverse Design Network (CGIDN)" to achieve multi-objective optimization of the injection process, shorten the time to find the optimal process parameters, and improve the production efficiency of plastic parts. Taking the LSR lens array of automotive LED lights as the research object, the residual stress and volume shrinkage were taken as the optimization objectives, and the filling time, melt temperature, maturation time, and maturation pressure were taken as the influencing factors to obtain the optimization target values, and the response surface models between the volume shrinkage rate and the influencing factors were established. Based on the "Constraint-Generated Inverse Design Network", the optimization was independently sought within the set parameters to obtain the optimal combination of process parameters to meet the injection molding quality of plastic parts. The results showed that the optimal residual stress value and volume shrinkage rate were 11.96 MPa and 4.88%, respectively, in the data set of 20 Latin test samples obtained based on Latin hypercube sampling, and the optimal residual stress value and volume shrinkage rate were 8.47 MPa and 2.83%, respectively, after optimization by the CGIDN method. The optimal process parameters obtained by CGIDN optimization were a melt temperature of 30 °C, filling time of 2.5 s, maturation pressure of 40 MPa, and maturation time of 15 s. The optimization results were obvious and showed the feasibility of the data-driven injection molding process optimization method based on the combination of Latin hypercube sampling and CGIDN.

High Luminous Efficacy Phosphor-Converted Mass-Produced White LEDs Achieved by AlN Prebuffer and Transitional-Refraction-Index Patterned Sapphire Substrate.

Constant advance in improving the luminous efficacy (ηL) of nitride-based light-emitting diodes (LEDs) plays a critical role for saving measurable amounts of energy. Further development is motivated to approach the efficiency limit for this material system while reducing the costs. In this work, strategies of using thin AlN prebuffer and transitional-refraction-index patterned sapphire substrate (TPSS) were proposed, which pushed up the efficiency of white LEDs (WLEDs). The AlN prebuffer was obtained through physical vapor deposition (PVD) method and TPSS was fabricated by dry-etched periodic silica arrays covered on sapphire. Devices in mass production confirmed that PVD AlN prebuffer was able to improve the light output power (φe) of blue LEDs (BLEDs) by 2.53% while increasing the productivity by ~8% through shortening the growth time. Additionally, BLEDs on TPSS exhibited an enhanced top ηext of 5.65% in contrast to BLEDs on the conventional PSS through Monte Carlo ray-tracing simulation. Consequently, φe of BLEDs was experimentally enhanced by 10% at an injected current density (Jin) of 40 A/cm2. A peak ηL of 295.2 lm/W at a Jin of 0.9 A/cm2 and the representative ηL of 282.4 lm/W at a Jin of 5.6 A/cm2 for phosphor-converted WLEDs were achieved at a correlated color temperature of 4592 K.

Tunable ultra-high quality factor graphene absorber based on semicylindrical silica array and distributed Bragg reflector structure

We propose a tunable narrowband absorber by utilizing a graphene monolayer placed between a dielectric semicylindrical array and a multilayer silica/silicon distributed Bragg reflector (DBR) structure. The multi-band perfect absorption can be achieved due to the excitation of multiple resonant modes in the absorber, including the guided mode resonance of the dielectric silica array and BR-based guided mode resonance in the DBR structure. The ultra-high quality factor (Q) is mainly attributed to the low external leakage loss of the resonator and the low intrinsic loss of the graphene monolayer. Moreover, the Q-factor of absorption peaks can be tuned by electrically controlling the Fermi energy of graphene. The sensitivity of a spectral wavelength shift for the refractive index change of the resonator is up to 730 nm/RIU, and the figure of merit is 1043. The proposed graphene-based metamaterial offers potential applications for photodetectors, optical modulators, and sensors in the near infrared frequency regime.

Silver Nanoparticle-Decorated Silica Nanospheres and Arrays as Potential Substrates for Surface-Enhanced Raman Scattering.

Poly(vinylpyrrolidone) (PVP) was used as both a modifier and reductant to in situ deposit silver nanoparticles (denoted Ag NPs) on the surface of silica nanospheres (nanosilica or nano-SiO2), affording Ag-decorated nanosilica (denoted SiO2@Ag). The as-obtained SiO2@Ag composite can form silver nanoparticle-decorated silica nanosphere arrays (denoted SiO2@Ag arrays) via evaporation-induced self-assembly. The as-prepared SiO2@Ag composite and SiO2@Ag array were used as the SERS substrates to measure the Raman signals of the dilute solutions of rhodamine 6G (denoted R6G), an organic dye that is a potential pollutant to the environment. The findings indicate that the as-prepared SiO2@Ag composite and SiO2@Ag array as potential SERS substrates simultaneously exhibit a high degree of metal coverage and small size of Ag NPs as well as good stability and abundant “hot spots”, which contributes to their desired Raman enhancement capacities. For the detection of trace R6G, they provide a limit of detection of as low as 10–9–10–11 M as well as good reproducibility, showing promising potential for monitoring chemical and biological molecules.

Development of highly efficient ultraviolet LEDs on hybrid patterned sapphire substrates.

A hybrid patterned sapphire substrate (HPSS) aiming to achieve high-quality Al(Ga)N epilayers for the development of GaN-based ultraviolet light-emitting diodes (UV LEDs) has been prepared. The high-resolution X-ray diffraction measurements reveal that the Al(Ga)N epilayers grown on a HPSS and conventional patterned sapphire substrate (CPSS) have similar structural quality. More importantly, benefiting from the larger refractive index contrast between the patterned silica array and sapphire, the photons can escape from the hybrid substrate with an improved transmittance in the UV band. As a result, in comparison with the UV LEDs grown on the CPSS, the LEDs grown on the HPSS exhibit a significantly enhanced light output power by 14.5% and more than 22.9% higher peak external quantum efficiency, owing to the boost of the light extraction efficiency from the adoption of the HPSS which can be used as a promising substrate to realize high-efficiency and high-power UV LEDs of the future.

CO2 hydrogenation to dimethyl ether over In2O3 catalysts supported on aluminosilicate halloysite nanotubes

Abstract This work presents results on CO2 hydrogenation to dimethyl ether (DME) over bifunctional catalysts consisting of In2O3, supported on natural clay halloysite nanotubes (HNT), and HNT modified with Al-MCM-41 silica arrays. The catalysts were characterized by TEM, STEM, EDX-mapping, NH3-TPD, XRD, low-temperature nitrogen adsorption, TPO, and H2-TPR techniques. Catalytic properties of In2O3/HNT and In2O3/Al-MCM-41/HNT in the CO2 hydrogenation to DME were investigated in a fixed-bed continuous flow stainless steel reactor at 10–40 atm, in the temperature range of 200–300°C, at GHSV = 12,000 h−1 and molar ratio of H2:CO2 = 3:1. The best catalyst for CO2 hydrogenation was In2O3/Al-MCM-41/HNT that provided DME production rate 0.15 gDME·(gcat·h)−1 with DME selectivity 53% and at 40 bar, GHSV = 12,000 h−1, and T = 250°C. It was shown that In2O3/Al-MCM-41/HNT exhibited stable operation for at least 40 h on stream.

Strategically constructed patterned sapphire with silica array to boost substrate performance in GaN-based flip-chip visible light-emitting diodes

A strategically constructed substrate, patterned sapphire with silica array (PSSA), was developed to boost the efficiency of patterned sapphire substrate (PSS) in GaN-based light-emitting diodes (LEDs) application. The light output power of a flip-chip LED on PSSA improved by 16.5% at 120 mA than that of device grown on PSS. The XRD and STEM measurements revealed that the GaN epilayer grown on PSSA had better crystalline quality compared to the epilayer grown on PSS, which was the result of decreased misfit at coalescence boundary in the PSSA case. Moreover, the light extraction efficiency of the flip-chip LED on PSSA was significantly enhanced, benefiting from the small refractive-index contrast between the patterned silica array and air. This small refractive-index contrast also contributed to a more convergent emission pattern for the flip-chip LED on PSSA, as demonstrated by the far-field radiation pattern measurements. The discovery that PSSA could excel at defect suppression and light extraction revealed a new substrate platform for III-nitride optoelectronic devices.

Ruthenium Catalysts Templated on Mesoporous MCM-41 Type Silica and Natural Clay Nanotubes for Hydrogenation of Benzene to Cyclohexane

Mesoporous ruthenium catalysts (0.74–3.06 wt%) based on ordered Mobil Composition of Matter No. 41 (MCM-41) silica arrays on aluminosilicate halloysite nanotubes (HNTs), as well as HNT-based counterparts, were synthesized and tested in benzene hydrogenation. The structure of HNT core-shell silica composite-supported Ru catalysts were investigated by transmission electron microscopy (TEM), X-ray fluorescence (XRF) and temperature-programmed reduction (TPR-H2). The textural characteristics were specified by low-temperature nitrogen adsorption/desorption. The catalytic evaluation of Ru nanoparticles supported on both the pristine HNTs and MCM-41/HNT composite in benzene hydrogenation was carried out in a Parr multiple reactor system with batch stirred reactors (autoclaves) at 80 °C, a hydrogen pressure of 3.0 MPa and a hydrogen/benzene molar ratio of 3.3. Due to its hierarchical structure and high specific surface area, the MCM-41/HNT composite provided the uniform distribution and stabilization of Ru nanoparticles (NPs) resulted in the higher specific activity and stability as compared with the HNT-based counterpart. The highest specific activity (5594 h−1) along with deep benzene hydrogenation to cyclohexane was achieved for the Ru/MCM-41/HNT catalyst with a low metal content.

Boosted ultraviolet electroluminescence of InGaN/AlGaN quantum structures grown on high-index contrast patterned sapphire with silica array

Epitaxially grown high crystalline quality InGaN/AlGaN multiple quantum structures on patterned sapphire with silica array (PSSA) have been successfully demonstrated. In comparison to conventional epilayers grown on patterned sapphire substrate (PSS), we observed a reduced threading dislocation density in the films grown on PSSA, attributing to the preferable vertical growth mode and reduced misfit at the coalescence boundary. Furthermore, a significant enhancement in light extraction efficiency can be achieved from InGaN/AlGaN-based ultraviolet light-emitting diodes (UVLEDs) built on PSSA owing to the large refractive index contrast between the epilayers and PSSA. More photons can escape from the top and bottom of the device, which was confirmed by numerically modeling light propagation within such device architecture. Benefiting from the reduced threading dislocation density and enhanced light extraction efficiency, the external quantum efficiency (EQE) of the fabricated UVLEDs on PSSA was more than two times higher than that of devices on the conventional flat sapphire substrate and it was additionally enhanced by 26.1% in comparison to the devices fabricated on PSS under an injection current of 150 mA. Therefore, the successful demonstration of UVLED on PSSA provides an unprecedented opportunity in achieving higher electroluminescence performance in future solid-state UV light sources.

Ultrasensitive broadband infrared 4 × 4 Mueller-matrix ellipsometry for studies of depolarizing and anisotropic thin films

The authors present a second-generation broadband 4×4 Mueller-matrix (MM) ellipsometer for ultrasensitive infrared-spectroscopic (8000−800cm−1) studies of complex nanometer-thin films. In a modular design, the instrument employs retractable achromatic retarders and various sets of tandem polarizers. Using high-transmittance free-standing wire-grid polarizers, the device reaches an unparalleled precision of up to 5⋅10−5 in the important fingerprint region, even for block-offdiagonal MM elements. Broadband and signal-to-noise optimized access to the full 4×4 MM provides in-depth information on the sample’s polarimetric properties and opens the door for detailed explorations of depolarizing and anisotropic materials. The authors discuss examples of highly depolarizing nonuniform polyimide membranes, uniaxial-to-biaxial anisotropy changes in ultrathin polymer films, and azimuthal off-axis effects in 2D-structured silica arrays. Diverse optical modeling approaches based upon anisotropic layer stacks and rigorous coupled-wave analysis are used to quantify the optical, structural, and chemical properties of the sample.

Replicated Pattern Formation and Recognition Properties of 2,4-Dichlorophenoxyacetic Acid-Imprinted Polymers Using Colloidal Silica Array Molds.

Surface imprinting is an effective and simple method to fabricate and retain imprinted templates and recognizable nanocavities after template extraction. The imprinted effects can be controlled depending on the surface morphological changes. In general, a planar film has a limited area compared to a structured film with relatively higher surface-to-volume (S/V) ratio (A/A0), leading to the conventional sensing response upon the functionality of monomers in a fixed chemical composition. To increase the limited sensing properties and develop simple fabrication of porous arrays on a large area, we herein demonstrate the 2,4-dichlorophenoxyacetic acid (2,4-D, herbicide)-imprinted porous thin film lithographically patterned using photopolymerization and silica colloidal array as a master mold, derived by a unidirectional rubbing method. The resonant frequency changes with respect to the adsorption of 2,4-D molecules on a template-extracted porous poly(MAA-co-EGDMA) (MIP) film in a 10−1 mM aqueous solution of 2,4-D for 1 h, and when compared to the planar MIP film, the higher sensing response (Δf = −283 ± 7 Hz ≈ 1543 ± 38 ng/cm2) appears on the porous MIP film due to the specific recognition toward the more accessible templated cavities of the structured porous array, indicating an imprinting effect (If) value of 3.5. In addition, a higher selectivity for 2,4-D was also displayed on the porous MIP film compared to other herbicides. From these results, it was revealed that these improved sensing properties can be determined from the effects of various parameters (template functionality, film structuring, hydroxyl groups of silica colloids, etc.).

Dual-band near-perfect metamaterial absorber based on cylinder MoS[formula omitted]-dielectric arrays for sensors

As a two-dimensional (2D) material, the crystalline monolayer molybdenum disulfide (MoS2) has drawn extensive attention due to its interesting optical, mechanical and thermal properties compatible with many applications. Here, a dual-band perfect metamaterial absorber (PMA) composed of a simple periodically patterned cylinder/square MoS2-dielectric silica (SiO2) arrays supported by a metal ground plane is proposed and studied by using finite-difference time-domain (FDTD) simulations. Numerical results reveal that the absorption spectrum of the MoS2-based structure displays two perfect absorption peaks in the visible–NIR region. The interactions between electromagnetic waves and this PMA structure are analyzed through the field distributions and spectral responses in detail. It is also presented that the peak wavelengths can be tuned by manipulating related structural parameters. Compared with previous dual-band PMA, our absorber has only one shape that can greatly simplify the manufacturing process and the absorber is insensitive to the polarization of incident light. Furthermore, this PMA can work as a refractive index sensor with high performance due to its stable near-unity absorption.

Templated self-assembly of ordered mesoporous silica on clay nanotubes

A novel self-assembly strategy of ordered silica arrays on halloysite clay nanotubes allows us to obtain mesoporous MCM-41 materials with enhanced thermal and mechanical stability. The formation of a structured mesoporous silica phase on halloysite is based on the assembly of cationic amphiphilic molecules onto a negative nanotube surface. The resulting MCM-41/halloysite composite demonstrated thermal and mechanical stability up to 1100 °C and 500 MPa showing great potential for application of mesoporous materials as industrial catalyst carriers and adsorbents.

Perpendicular SiO2 cylinders fabricated from a self-assembled block copolymer as an adaptable platform

We discuss the formation of perpendicular cylinders from polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS), which were used to fabricate silica (SiO2) pillar arrays with an aspect ratio of 5. The solvent used in spin-coating solutions to form the initial films played an important role to lead the final morphology of the cylinders after solvent annealing. Tetrahydrofuran, a selective solvent for the major PS block, trapped PDMS spheres in isolation, opening a route to form highly aligned perpendicular cylinders after an induction period. Meanwhile, cyclohexane, a non-selective solvent, connected PDMS domains to some extent and provided a different route through which moderate regularity was achieved with gradual improvement. The transient morphological changes of the cylinders were precisely investigated using grazing-incidence small-angle X-ray scattering and scanning electron microscopy. The alignment of the final morphology of the cylinders was validated by reflectance and optical ellipsometry measurements. Oxygen plasma was used to completely remove organic substances and convert PDMS to SiO2, providing a platform suitable for various applications. As an example, a surface-enhanced Raman spectroscopy (SERS) platform was obtained by depositing gold on a perpendicular silica array. This platform exhibited substantial SERS enhancement using Rhodamine 6G as a probe molecule. Identical enhancements were observed throughout the platform, which was attributed to its uniform nanostructures.

Novel Biomimic Crystalline Colloidal Array for Fast Detection of Trace Parathion.

A novel gold doped inverse opal photonic crystal (IO PC) was successfully fabricated with combination of molecularly imprinted technical for the fast determination of parathion. First, a closest silica array arrangement behaved as the 3D photonic crystal precursors to build the opal photonic crystal (O PC). Second, the parathion-containing polymeric solution with gold nanoparticles was drawn into the 3D array cracks. After polymerization, the well-designed O PC was treated with HF solution for the etching of the silica skeleton. Finally, the template parathion was removed and the Au-MIP IO PCs were obtained. The morphology of SiO2 and Au NPs was characterized by transmission electron microscopy (TEM), and the eluted influence of the IO PCs was monitored by scanning electron microscopy (SEM). The cross-linking effect was well optimized according to the best spectrum signal of parathion. The as-synthesized Au-MIP IO PCs displayed the specificity toward parathion and the selectivity to other competitive pesticide molecules. The response time was only 5 min, and the parathion could be well detected from real water samples. The recoveries were between 95.5% and 101.5%.

Synthesis of biogenic silicon/silica (Si/SiO2) nanocomposites from rice husks and wheat bran through various microorganisms

Biosilification is an economically viable, energy saving and green approach for the commercial scale synthesis of oxide nanomaterials. The room temperature synthesis of oxide nanocomposites from cost effective agro-based waste is a particular example of biosilification. In this study, synthesis of Si/SiO2 nanocomposites from inexpensive agro-based waste material i.e. rice husks (RH) and wheat bran (WB) has been carried out by means of various eukaryotic microorganisms, i.e. Actinomycete, Fusarium oxysporum, Aspergillus niger, Trichoderma sp. and Penicillium sp., under ambient conditions. The XRD diffrectrograms represents that the synthesized nanomaterials exhibits silicon, amorphous silica and other crystal arrays such as cristobalite, trydimite and quartz, depending upon the type microorganism and time period used for extraction. All of the aforesaid microorganism bio transformed the naturally occurring amorphous silica to crystalline structures within the period of 24 h. However, the Actinomycete and Trichoderma sp. took 48 h in case of rice husks for biotransformation of naturally occurring plant silica to crystalline nanocomposite. While in case of wheat bran, Actinomycete and Trichoderma sp. took 24 h for biotransformation. The extracted nanocomposites exhibits band edge in the range 230–250 nm and blue emission. The procedure described in study can be used for commercial level production of Si/SiO2 nanocomposites from agro based waste materials.

Arrays of Hollow Silica Half‐Nanospheres Via the Breath Figure Approach

Breath figures (BFs) are patterns of liquid droplets that usually form upon condensation on a cold surface. Earlier work has shown that BFs can be used to produce continuous films of porous honeycomb‐structured patterns on various types of materials, paving the path to a number of important applications such as the manufacturing of highly ordered nano‐ and micron‐sized templates, micro lenses, and superhydrophobic coatings. It is worth noting, however, that few new findings have been reported in this area in recent years, limiting pursuits of novel architectures and key applications. In this report, an alternative method is described by which arrays of hollow silica half‐nanospheres can be produced via BF templates. In the present method, a chemical vapor deposition (CVD) protocol performed while the BF is formed on a glass substrate yields a nanostructured pattern of silica half‐spheres, which size (100–700 nm) and density across the glass surface vary with substrate modification and with the relative rates of water condensation and hydrolysis from silica precursors (a process carried out at room temperature). This method of forming arrays of hollow half‐nanospheres via the BF approach may be applicable to various other oxides and a broad range of substrates including large‐area flexible plastics.

High index of refraction nanosphere coatings for light trapping in crystalline silicon thin film solar cells

Dielectric nanospheres have emerged as a promising candidate for enhancing absorption in thin film photovoltaics. In this paper, we utilize numerical electrodynamic simulations to investigate the absorption enhancements achievable in crystalline Si (c-Si) thin films of thicknesses from 100 to 2000nm from 2-dimensional close-packed silica (SiO2), silicon nitride (Si3N4), and titania (TiO2) nanosphere array coatings. We demonstrate that dielectric nanospheres can enhance the absorption in c-Si thin films by coupling incident light to transverse electric (TE) waveguide modes in the c-Si thin film. While SiO2 nanosphere arrays may achieve enhancements of less than 10% compared to ideal double pass c-Si thin films, higher index of refraction nanospheres confine light more strongly such that more nanosphere resonances may couple to waveguide modes in the c-Si. Si3N4 nanospheres may enhance ultimate efficiencies by over 40% for thicknesses ≤800nm and TiO2 nanospheres by over 50% for thicknesses ≤700nm compared to thin film structures with perfect anti-reflection coatings. This light trapping approach increases the absorption in the photoactive region without introducing additional surfaces or interfaces that increase surface recombination.