Chiral mesoporous materials based on the self-assembly

Ordered mesoporous materials with various structures are synthesized based on the self-assembly of surfactant and inorganic precursors and covered by several excellent reviews. However, less work has been directed to chiral structured mesoporous materials, although these could have wide-ranging applications on the manufacturing of enantio-pure chemicals and pharmaceuticals as catalysts and separation media with both shape selectivity and enantioselectivity. This short review will address the synthesis of chiral mesoporous materials by chiral organic compounds templating route, covering single and 2-dimensional ordered chiral channel mesoporous materials. Non-porous helical fiber, atomic-scale enantio-morphism and zeolite-like materials with three-dimensional helical pores are beyond the scope of this paper.     

Infrared ellipsometry characterization of porous silicon bragg reflectors

We investigate porous silicon Bragg reflectors in a nondestructive manner using variable angle-of-incidence infrared spectroscopic ellipsometry. In addition to the thickness, volume porosity, inhomogeneity, and optical anisotropy, properties of the solid content of the porous material are investigated in terms of dielectric function and surface chemistry. The material was found to have positive birefringence. The high sensitivity of the technique is employed to detect and identify infrared resonant absorptions related to different Si-H as well as Si-O-Si vibrational modes. The average electrical resistivity of the solid content of the porous material is determined to be 0.03 Omega cm, which is larger than the corresponding bulk value of 0.019 Omega cm. Furthermore the average carrier concentration in the porous material shows a decrease from 6.2 x 10(18) cm(-3) to 4 x 10(18) cm(-3).     

Graphoepitaxy of block-copolymer self-assembly integrated with single-step ZnO nanoimprinting

A highly efficient, ultralarge-area nanolithography that integrates block-copolymer lithography with single-step ZnO nanoimprinting is introduced. The UV-assisted imprinting of a photosensitive sol-gel precursor creates large-area ZnO topographic patterns with various pattern shapes in a single-step process. This straightforward approach provides a smooth line edge and high thermal stability of the imprinted ZnO pattern; these properties are greatly advantageous for further graphoepitaxial block-copolymer assembly. According to the ZnO pattern shape and depth, the orientation and lateral ordering of self-assembled cylindrical nanodomains in block-copolymer thin films could be directed in a variety of ways. Significantly, the subtle tunability of ZnO trench depth enabled by nanoimprinting, generated complex hierarchical nanopatterns, where surface-parallel and surface-perpendicular nanocylinder arrays are alternately arranged. The stability of this complex morphology is confirmed by self-consistent field theory (SCFT) calculations. The highly ordered graphoepitaxial nanoscale assembly achieved on transparent semiconducting ZnO substrates offers enormous potential for photonics and optoelectronics.     

High Q-factor distributed bragg reflector resonators with reflectors of arbitrary thickness

The Bragg reflection technique improves the Q-factor of a resonator by reducing conductor and dielectric losses. This is achieved by designing a low-loss inner resonant region (usually free space) surrounded by an outer anti-resonant region made of distributed Bragg reflector layers. In this paper we develop a simple non-Maxwellian model and apply it to design three distinct cylindrical Bragg resonators based on the same set of single-crystal sapphire plates and rings by changing only the dimension of the cavity that supports the structure. To accomplish this, the simple model allows an arbitrary thickness for either the horizontal or the cylindrical dielectric reflectors by relaxing the condition that they must be lambda/4 thick. The model also allows for higher-order field variations in both the resonant and the anti-resonant regions. The resonators were constructed and experimental results were compared with the simple model and the rigorous method of lines analysis. For the fundamental mode, an unloaded Q-factor of 234,000 at 9.7 GHz was obtained. This is larger than that for a whispering gallery mode resonator. The resonator also exhibited a greatly reduced spurious mode density when compared to an overmoded whispering gallery mode resonator.     

In situ electrochemical monitoring of selective etching in ordered mesoporous block-copolymer templates

We present a simple in situ electrochemical probe for the selective etching of the PLA component of thin film poly(4-fluorostyrene)-b-poly(D,L-lactide) (PFS-b-PLA) mesoporous block copolymer templates with a range of highly ordered microphase morphologies. Etching rates between 0.6 and 0.9 nm s?1 were measured in electric-field aligned standing PLA cylinders 12 nm wide and up to 800 nm long. The etching rate within a bicontinuous gyroid network morphology is comparable to that of the hexagonally ordered cylindrical array. A microphase-separated, nonaligned but film-spanning PLA pore structure is found in cylinder forming PFS-b-PLA films immediately after spin coating that could have applications in patterning of functional nanostructured arrays. Cross-film percolation of the PLA phase is confirmed electrochemically, with an etching rate approximately half that of the highly ordered morphologies. The etching rate is independent of template thickness in all three morphologies.     

Host-guest energetic nanocomposites based on self-assembly of multi-nitro organic molecules in nanochannels of mesoporous materials

Host-guest energetic nanocomposites have been synthesized by self-assembly of the high energy density compound HNIW in nanometer-scale channels of an ordered mesoporous material SBA-15. The complete impregnation of HNIW can be achieved in acetone solvent at ambient temperature, and the maximum amount was around 70 wt%. Structural characterizations were systematically provided by XRD, TEM, N(2) adsorption, TG, (13)C solid-state NMR and FT-IR. The tendency of multi-nitro organic molecules to self-assemble when the solvent evaporated has been described. Hydrogen bond interactions were considered as the main driving force, so the choices of matched host matrix and guest organic compounds were pivotal for implementing this process. The thermal properties of nanocomposites were measured by DSC analysis. Compared with pure HNIW and a physical mixture, the decomposition peak temperature of the confined crystals decreased about 11?°C, while the total amount of heat released slightly increased. This strategy can also be expanded to other similar host-guest systems.     

A study of distributed dielectric bragg reflectors for vertically emitting lasers of the near-IR range

Studies aimed at optimization of the design of a dielectric distributed Bragg reflector (DBR) produced by the reactive magnetron sputtering method for applications in near-IR vertical-cavity surface-emitting lasers with intracavity contacts (ICC-VCSELs) are carried out. It is shown that the reflectivity of the dielectric DBRs based on SiO₂/TiO₂ decreases due to the polycrystalline structure of the TiO₂ layers, which causes diffusive scattering of light. In contrast, amorphous Ta₂O₅ layers is characterized by a low surface roughness and low fluctuation in the refractive index. Single-mode ICC-VCSELs in the 980-nm spectral range with dielectric DBR based on SiO₂/Ta₂O₅ with a threshold current less than 0.27 mA, electric resistance of less than 200 Ω, and differential efficiency of more than 0.8 W/A are demonstrated.

     

Electrochemically assisted self-assembly of mesoporous silica thin films

Supported mesostructured thin films are of major importance for applications in optical, electrochemical and sensing devices. However, good performance is restricted to mesostructured phases ensuring good accessibility from the film surface, which would be straightforward with cylindrical pores oriented normal to the underlying support, but this remains challenging. Here, we demonstrate that electrochemistry is likely to induce self-assembly of surfactant-templated (organo)silica thin films on various conducting supports, homogeneously over wide areas. The method involves the application of a suitable cathodic potential to an electrode immersed in a surfactant-containing hydrolysed sol solution to generate the hydroxyl ions that are necessary to catalyse polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the electrode surface. The method is compatible with controlled and localized deposition on heterogeneous supports, opening the way to electrochemically driven nanolithography for designing complex patterns of widely accessible mesostructured materials.     

静电组装法制备介孔TiO_2

以TiCl4和(NH4)6Mo7O24·4H2O为原料,先通过水解、静电自组装和焙烧得到TiO2/MoO3,再用NaOH溶液溶解得到介孔TiO2。用X射线粉末衍射(XRD)、透射电镜(TEM)、X射线能量色散仪(EDX)、紫外-可见漫反射光谱(UV-DRS)和比表面及孔隙度分析仪(ASAP)对该材料进行表征,合成的介孔TiO2BET比表面积为241 m2/g,平均孔直径为3.5nm。通过光催化降解甲基橙实验,发现介孔TiO2具有较高光催化活性。     

Ultrasonic hydrophone based on short in-fiber bragg gratings

We investigate the feasibility of using in-fiber Bragg gratings for measuring acoustic fields in the megahertz range. We found that the acoustic coupling from the ultrasonic field to the grating leads to the formation of standing waves in the fiber. Because of these standing waves, the system response is complex and, as we show, the grating does not act as an effective probe. However, significant improvement in its performance can be gained by use of short gratings coupled with an appropriate desensitization of the fiber. A noise-limited pressure resolution of approximately 4.5 x 10(-3) atm/ radicalHz was found.     

表面活性剂模板法制备中孔材料的探索

自从发现M41S系列分子筛以来,人们对中孔材料进行了很多研究工作,包括合成、应用以及机理等方面的探索。在中孔材料的制备方面,由表面活性剂作模板剂来组装的方法有着重要的地位。本文回顾了近年来中孔材料制备技术方面的进展,主要包括各种各样的形成机理。以及如何控制孔径等主题。     

Wavelength division multiplexing based on apodized planar holographic Bragg reflectors

We report wavelength division multiplexing based on lithographically fabricated slab-waveguide-contained planar holographic Bragg reflectors (HBRs). Partial HBR diffractive contour writing and contour displacement are successfully demonstrated to enable precise bandpass engineering of multiplexer transfer functions and make possible compact-footprint devices based on hologram overlay. Four- and eight-channel multiplexers with channel spacings of approximately 50 and approximately 100 GHz, improved sidelobe suppression, and flattop passbands are demonstrated. When a second-order apodization effect, comprising effective waveguide refractive-index variation with written contour fraction, and the effect of hologram overlap on the hologram reflective amplitude are included in the simulation, excellent agreement between predicted and observed spectral passband profiles is obtained. With demonstrated simulation capability, the ability to fabricate general desired passband profiles becomes tractable.     

Tunable Bragg filters based on polymer swelling

We report on the optical properties of Bragg mirrors and filters fabricated from photo-cross-linked standard optical polymers. The transmittance spectra of these devices in the visible to near-infrared spectral range were measured. We demonstrate efficient tuning of the filter peak of the polymer Bragg filters over several hundred nanometers by adding organic solvents to the surrounding atmosphere of the filter. This represents what we believe to be a novel tuning principle for Bragg filters relying on the use of polymeric materials.     

Tunable synthesis of mesoporous titania with different morphologies for dye-sensitized solar cells

Different TiO₂ mesoporous structures, including core-shell spheres (CCSs) and micro-tubes (MTs), are synthesized through adjusting the pH of the solution using TiOSO₄ as titanium source in a hydrothermal route. TiO₂ CSSs with an average diameter of 1.3–3.5 μm exhibit excellent light scattering property and high specific surface area (177.63 m² g^?1). TiO₂ MTs show ultrahigh specific surface area of 276.03 m² g^?1. Dye-sensitized solar cell is fabricated using TiO₂ CSSs as the light scattering layer and TiO₂ nanoparticles (NPs) layer as the bottom layer. The efficiency of Cell-NPs + CSSs is up to 9.24% due to the good light scattering effect and excellent dye loading capacity. Furthermore, TiO₂ MTs are introduced to form the NPs/MTs bottom layer. The Cell-NPs/MTs + CSSs achieves an outstanding efficiency of 9.60% due to the further optimized electron transport path.     

Organosulfonic acid-functionalized mesoporous composites based on natural rubber and hexagonal mesoporous silica

This study is the first report on synthesis, characterization and catalytic application of propylsulfonic acid-functionalized mesoporous composites based on natural rubber (NR) and hexagonal mesoporous silica (HMS). In comparison with propylsulfonic acid-functionalized HMS (HMS-SO₃H), a series of NR/HMS-SO₃H composites were prepared via an in situ sol–gel process using tetrahydrofuran as the synthesis media. Tetraethylorthosilicate as the silica source, was simultaneously condensed with 3-mercaptopropyltrimethoxysilane in a solution of NR followed by oxidation with hydrogen peroxide to achieve the mesoporous composites containing propylsulfonic acid groups. Fourier-transform infrared spectroscopy and ²⁹Si MAS nuclear magnetic resonance spectroscopy results verified that the silica surfaces of the NR/HMS-SO₃H composites were functionalized with propylsulfonic acid groups and covered with NR molecules. After the incorporation of NR and organo-functional group into HMS, the hexagonal mesostructure remained intact concomitantly with an increased framework wall thickness and unit cell size, as evidenced by the X-ray powder diffraction analysis. Scanning electron microscopy analysis indicated a high interparticle porosity of NR/HMS-SO₃H composites. The textural properties of NR/HMS-SO₃H were affected by the amount of MPTMS loading to a smaller extent than that of HMS-SO₃H. NR/HMS-SO₃H exhibited higher hydrophobicity than HMS-SO₃H, as revealed by H₂O adsorption–desorption measurements. Moreover, the NR/HMS-SO₃H catalysts possessed a superior specific activity to HMS-SO₃H in the esterification of lauric acid with ethanol, resulting in a higher conversion level.     

Optical diodes and omnidirectional reflectors based on one-dimensional quasiperiodic photonic crystals

The optical properties of one-dimensional quasiperiodic photonic crystals with linear profiles of modulation parameters are considered. It is shown that such systems possess a wider photonic band gap as compared to the ideal periodic system and can be used as omnidirectional reflectors. The asymmetric profiles of parameters in these systems results in the appearance of nonreciprocity of a new type that makes possible their use as the ideal, purely optical diodes.     

混凝土结构的光纤光栅智能监测技术

根据混凝土结构的内部应变监测需要，提出了光纤光栅管式封装应变传感器，并对其传感特性进行了研究；探讨了光纤布拉格光栅传感元件在混凝土结构中的布设工艺，并用光纤光栅监测了水泥净浆的固化过程；用管式封装光纤光栅与裸光栅对钢筋温凝土梁进行了应变监测；最后将光纤光栅传感器成功地应用于黑大公路大桥。     

Design of omnidirectional reflectors based on a cascaded one-dimensional photonic crystal structure

The omnidirectional transmission properties of photonic heterostructures composed of cascaded one-dimensional photonic crystals (1DPCs) with the same materials and different thickness ratios of the alternate high- and low-refractive index layers were studied theoretically. A criterion for designing omnidirectional reflectors with a maximum bandgap width is presented for heterostructures with an arbitrary number of cascaded 1DPCs. Omnidirectional reflectors based on two and three cascaded 1DPCs are designed according to the criterion.     

Layer-by-layer self-assembly of multilayer films based on humic acid

Multilayer films consisting of negatively charged humic acid and positively charged polyelectrolyte have been fabricated on various substrates using the layer-by-layer self-assembly technique. The thickness (linearly increasing with the square root of NaCl concentration) and refractive index of the films determined by ellipsometry can be regulated by ionic strength through adjusting the coiling of the polyelectrolyte chains for assembly. The cone-shaped features on surface obtained by atomic force microscope are derived from the negatively charged colloidal humic acid binding with polyelectrolyte cation. The smooth features are corresponding to the dissociated humic acid with carboxylate ion (―COO⁻) electrostatically attracted on polyelectrolyte cation. These results are verified by Fourier transform infrared spectra. The linear dependence of the peak current on the square root of the scan rate revealed by the cyclic voltammetry indicates that the redox process at the electrode surface is diffusion-limited and the charge transport does not involve the film itself.     

基于光纤Bragg光栅的混凝土早期固化及应变过程研究

随着高强混凝土和高性能混凝土在实际工程中应用得越来越广泛,混凝土早期的收缩及早期开裂问题越来越引起人们的重视.本文根据光纤Bragg光栅的传感特性,针对混凝土材料的自身特点,系统地用裸光栅对非约束状态下及约束状态下的混凝土早期固化过程进行了内部温度及应变监测,探讨了光纤Bragg光栅传感元件在混凝土中的布设工艺和布设要求;最后,对不同状态下的被测对象的早期变形进行了对比研究.研究结果表明光纤Bragg光栅不仅可以进行混凝土内部温度及变形的测定,在非约束状态下,可以测出混凝土早期的自收缩;在约束状态下,通过测出的混凝土早期应变变化规律可以预测混凝土的开裂状态,而且可以对混凝土早期固化过程进行监测.