A large-area mesoporous array of magnetic nanostructure with perpendicular anisotropy integrated on Si wafers

Large-area, over several square centimeters, mesoporous array of magnetic nanostructure with perpendicular anisotropy is prepared by depositing Co/Pt multilayers (MLs) on a mesopore array of anodized alumina (AAO) fabricated on Si wafers. The MLs are mainly deposited on the top of AAO walls and perimeters of the pores; very small amounts of magnetic material reach the bottom due to the high aspect ratio of AAO. Consequently, ordered pores are present in the magnetic MLs. The mean pore diameter of the fabricated mesoporous array is 8.83?nm with a standard deviation of 3.16?nm and density of about 2.1 × 10(11)?cm(-2). The Co/Pt MLs deposited on AAO and Si both exhibit strong perpendicular magnetic anisotropy, but the perpendicular coercivity (H(c)) increases by 15 times on AAO compared to that on Si. On the other hand, the magnetic cluster size decreases from 1000?nm (on Si) to 100?nm due to the presence of high-density pores. The dramatic increase in H(c) and the decrease in magnetic cluster size suggest that the pores behave as effective pinning sites. The magnetization-switching characteristics of the fabricated porous structure are different from those of the continuous films or Stoner-Wohlfarth-type (S-W) particles. One of the potential applications of this mesoporous structure may be in the field of high-density magnetic data storage.     

Recent progress in mesoporous titania materials: adjusting morphology for innovative applications

Abstract

This review article summarizes recent developments in mesoporous titania materials, particularly in the fields of morphology control and applications. We first briefly introduce the history of mesoporous titania materials and then review several synthesis approaches. Currently, mesoporous titania nanoparticles (MTNs) have attracted much attention in various fields, such as medicine, catalysis, separation and optics. Compared with bulk mesoporous titania materials, which are above a micrometer in size, nanometer-sized MTNs have additional properties, such as fast mass transport, strong adhesion to substrates and good dispersion in solution. However, it has generally been known that the successful synthesis of MTNs is very difficult owing to the rapid hydrolysis of titanium-containing precursors and the crystallization of titania upon thermal treatment. Finally, we review four emerging fields including photocatalysis, photovoltaic devices, sensing and biomedical applications of mesoporous titania materials. Because of its high surface area, controlled porous structure, suitable morphology and semiconducting behavior, mesoporous titania is expected to be used in innovative applications.     

Characterization of mesoporous ZnO:SiO2 films obtained by the sol-gel method

ZnO:SiO₂ films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO₂ films are of great interest as catalyst and gas-sensing materials. The sol-gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films. The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO₂ films obtained by the sol-gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by X-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix were investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO₂ films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation. Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO₂ nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol-gel method.     

Ordered mesoporous silicon through magnesium reduction of polymer templated silica thin films

This paper describes the process of making ordered mesoporous silicon (Si) thin films. The process begins with mesoporous silica (SiO 2) thin films that are produced via evaporation induced self-assembly (EISA) using sol-gel silica precursors with a diblock copolymer template. This results in a film with a cubic lattice of 15 nm diameter pores and 10 nm thick walls. The silicon is produced through reduction of the silica thin films in a magnesium (Mg) vapor at 675 degrees C. Magnesium reduction preserves the ordered pore-solid architecture but replaces the dense silica walls with 10-17 nm silicon crystallites. The resulting porous silicon films are characterized by a combination of low and high angle X-ray diffraction, combined with direct SEM imaging. The result is a straightforward route to the production of ordered nanoporous silicon.     

Effective optical properties of highly ordered mesoporous thin films

This paper expands our previous numerical studies predicting the optical properties of highly ordered mesoporous thin films from two-dimensional (2D) nanostructures with cylindrical pores to three-dimensional (3D) structures with spherical pores. Simple, face centered, and body centered cubic lattices of spherical pores and hexagonal lattice of cylindrical pores were considered along with various pore diameters and porosities. The transmittance and reflectance were numerically computed by solving 3D Maxwell's equations for transverse electric and transverse magnetic polarized waves normally incident on the mesoporous thin films. The effective optical properties of the films were determined by an inverse method. Reflectance of 3D cubic mesoporous thin films was found to be independent of polarization, pore diameter, and film morphology and depended only on film thickness and porosity. By contrast, reflectance of 2D hexagonal mesoporous films with cylindrical pores depended on pore shape and polarization. The unpolarized reflectance of 2D hexagonal mesoporous films with cylindrical pores was identical to that of 3D cubic mesoporous films with the same porosity and thickness. The effective refractive and absorption indices of 3D films show good agreement with predictions by the 3D Maxwell-Garnett and nonsymmetric Bruggeman effective medium approximations, respectively.     

Photonic polymer replicas from distributed Bragg reflectors structured porous silicon

Well defined 1-dimentional (1-D) photonic crystals of polymer replicas have been successfully obtained. DBR porous silicon containing nanometer-scale pores are prepared by an anodic electrochemical etch of p(++)-type silicon wafer. The resulting DBR porous silicon film removed from the substrate by applying an electropolishing current has been thermally oxidized in the furnace at 400 degrees C for 3 h. Oxidized DBR PSi/polystyrene composite films are prepared by casting of polymer solution onto a free-standing porous silicon photonic crystal layer. Flexible photonic polymer replicas have been prepared after the removal of oxidized DBR PSi matrix in HF/H2O mixture solution. Polymer replicas exhibit a sharp resonance in the reflectivity spectrum. Optical characteristics of photonic polymer replica indicate that the surface of polymer film has a negative structure of DBR PSi. This replica is stable in aqueous solutions for several days without any degradation.     

Design and Application of Surface Modification at Molecular Scale

The structuring of surfaces on a nanoscale level-both chemically and topographically has become an increasingly relevant field of research in nanotechnology with widespread application potential in various fields of science ( e. g.surface engineering, electronics, biotechnology, optics). Two examples on surface modification at molecular scale with self-assembly monolayers are shown: ( 1 ) Chemically attaching ultra-thin polymer films through the self-assembly of silane fictionalized copolymer have been approved in this article. (2) The patterned films with microstructures on different substrates have been prepared through micro-contact printing technique and electro polymerization.     

Fabrication and optical properties of mesoporous SnO2 nanowire arrays

Large-scale SnO2 mesoporous nanowires have been successfully synthesized by an improved sol-gel method within the nanochannels of porous anodic alumina templates. In this method, chloride of stannic and urea are used as precursors, chloride of stannic is acting as source of tin ions, and urea offers a basic medium through its hydrolysis. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction are used to characterize the SnO2 mesoporous nanowires. It is found that the as-prepared nanowires consist of SnO2 nanoparticles and pores. They can be indexed as rutile structures and diameters are about 50-70 nm. The growth mechanism of the mesoporous nanowires is also been discussed. The band gap of the as-prepared mesoporous nanowires is 3.735 eV, determined by UV/visible absorption spectral results. The SnO2 mesoporous nanowires show strong and stable photoluminescence with emission peak centered at 3.730 eV, which has never been reported in nanowires. It could be attributed to the exciton recombination.     

Bio-inspired synthesis of mesoporous sílicas using large molecular weight poly-l-lysine at neutral pH

Among the various types of amorphous silica-based materials, those that have mesopores (pore widths between 2 and 50 nm) constitute an important group. Silica mesoporous materials have been considered in fields such as catalysis, adsorption, sensing, and electronics or, more recently in drug delivery. The synthesis of silica mesoporous materials usually involves corrosive reaction media and high temperatures. Nevertheless, some living organisms such as diatoms or sponges produce silica in non-corrosive environments and at ambient temperatures. Important progress has been achieved in the synthesis of silica-based materials by biomimetic or bio-inspired methodologies, but the number of studies that use biomolecules and address specifically the preparation of mesoporous materials is reduced. We report in this work, to our knowledge for the first time, a methodology to obtain mesoporous silicas that involves, simultaneously, a biomolecule (poly-l-lysine) and neutral pH. The prepared materials have pores with widths between 2 and 8 nm and specific surface areas between 232 and 616 m² g^?1.     

Application of the bimodal meso/macroporous composite synthesized from MCM-41 sol

A route to synthesize porous materials with a bimodal macro/mesoscopic pore system has been investigated in this work. Polystyrene with sub-micrometer size was used as a template in the synthesis. The resulting mesoporous silica wall replicated inversely the morphology of polystyrene template and had highly ordered three-dimensional arrays of macro pores. Large and moldable meso/macro porous silica monoliths could be obtained in centimeter scale by using monodispersed polystyrene beads and MCM-41 sol solutions. These bimodal structured porous silicates have been used as supports for asymmetric kinetic resolution of racemic epoxides to synthesize optically pure epoxide.     

Morphological and Optical Transformation of Gas Assisted Direct Laser Written Porous Silicon Films

Direct laser writing (DLW) of mesoporous porous silicon (PS) films is shown to selectively create spatially separated nitridized and carbonized features on a single film. Nitridized or carbonized features are formed during DLW at 405 nm in an ambient of nitrogen and propane gas, respectively. The range of laser fluence required to create varying feature sizes while avoiding damage to the PS film is identified. At high enough fluence, nitridation using DLW has been shown as an effective method for laterally isolating regions on the PS films. The efficacy in preventing oxidation once passivated is investigated via energy dispersive X-ray spectroscopy. Changes in composition and optical properties of the DL written films are investigated using spectroscopic analysis. Results show carbonized DLW regions have a much higher absorption than as-fabricated PS, attributed to pyrolytic carbon or transpolyacetylene deposits in the pores. Nitridized regions exhibit optical loss similar to previously published thermally nitridized PS films. This work presents methods to engineer PS films for a variety of potential device applications, including the application of carbonized PS to selectively engineer thermal conductivity and electrical resistivity and of nitridized PS to micromachining and selective modification of refractive index for optical applications.     

SiO_2含量对PI/SiO_2杂化薄膜性能的影响

聚酰亚胺与SiO2杂化形成的有机-无机杂化薄膜体现出了优异的综合性能,在催化与分离、微电子、光电和绝热材料等领域具有广泛的应用及发展潜力。杂化材料相关的研究也越来越多,就SiO2含量对聚酰亚胺/SiO2杂化薄膜的光、电、热和力学性能的影响进行综述,总结了杂化薄膜的性能随SiO2含量变化而变化的基本规律。     

新型纳米功能材料

讨论了纳米材料复合薄膜的结构和特性,涉及到与力学、防护、电池等特性有关的结构,重点分析了电学、光学、光电特性,如新型纳米线复合光电池,氧化锌(ZnO)纳米棒阵列的结构和荧光发射,以及金属纳米线阵列的制备和场发射特性.金属纳米线阵列场发射的高分辨,结构完美,工艺简单和极低的成本,有可能是未来平板显示器的重要组件.     

Displacement Current of Nanodendrimer

In the Langmuir-Blodgett (LB) technique, a monolayer on the water surface is transferred onto a substrate, which is raised and dipped through the surface. From this, multilayers can be obtained in which constituent molecules are periodically arranged. The LB technique has attracted considerable interest in the fabrication of electrical and electronic devices. Many researchers have investigated the electrical properties of monolayer and multiplayer films. Dendrimers represent a new class of synthetic macromolecules characterized by a regularly branched tree-like structure. Multiple branching yields a large number of chain ends that distinguish dendrimers from conventional star-like polymers and microgels. The azobenzene dendrimer is one of the dendritic macromolecules that include the azo-group exhibiting a photochromic character. Due to the presence of the charge transfer element of the azo-group and its rod-shaped structure, these compounds are expected to have potential interest in electronics and photoelectronics, especially in nonlinear optics. In the present paper, we give pressure stimulation to organic thin films and detect the induced displacement current.     

Confined palladium colloids in mesoporous frameworks for carbon nanotube growth

Palladium colloidal nanoparticles with an average size of approximately 2.4 nm have been incorporated into mesoporous inorganic thin films following a multistep approach. This involves the deposition of mesoporous titania thin films with a thickness of 200 nm by spin-coating on titanium plates with a superhydrophilic titania outer layer and activation by calcination in a vacuum furnace at 573 K. Nanoparticles have been confined within the porous titania network by dip-coating noble metal suspensions onto these mesoporous thin films. Finally, the resulting nanoconfined systems were used as substrates for the growth of oriented carbon nanotubes (CNTs) using plasma-enhanced chemical vapour deposition at 923 K in order to enhance their surface area. These CNTs were tested in the hydrogenation of phenylacetylene by hydrogen in a batch reactor. The initial reaction rate observed on a CNT/TiO₂ structured catalyst was considerably higher than that on 1 wt% Pd/TiO₂ thin films.     

New families of mesoporous materials

Abstract

Mesoporous materials have been paid much attention in both scientific researches and practical applications. In this review, we focus on recent developments on preparation and functionalization of new families of mesoporous materials, especially non-siliceous mesoporous materials invented in our research group. Replica synthesis is known as the method to synthesize mesoporous materials composed of various elements using originally prepared mesoporous replica. This strategy has been applied for the syntheses of novel mesoporous materials such as carbon nanocage and mesoporous carbon nitride. Carbon nanocage has a cage-type structure with huge surface area and pore volume, which exhibits superior capabilities for biomolecular adsorption. Mesoporous carbon nitride was synthesized, for first time, by using mixed material source of carbon and nitrogen simultaneously. As a totally new strategy for synthesis of mesoporous materials, the elemental substitution method has been recently proposed by us. Direct substitution of component elements in original mesoporous materials, with maintaining structural regularity, provided novel mesoporous materials. According to this synthetic strategy, mesoporous boron nitride and mesoporous boron carbon nitride have been successfully prepared, for first time. In addition to these material inventions, hybridization of high functional materials, such as biomaterials, to mesoporous structure has been also developed. Especially, immobilization of proteins in mesopores was systematically researched, and preparation of peptidehybridized mesoporous silica was demonstrated. These new families of mesoporous materials introduced in this review would have high potentials in future practical applications in wide ranges from electronics and photonics to environmental and medical uses.     

Wearable Large‐Scale Perovskite Solar‐Power Source via Nanocellular Scaffold

Dramatic advances in perovskite solar cells (PSCs) and the blossoming of wearable electronics have triggered tremendous demands for flexible solar‐power sources. However, the fracturing of functional crystalline films and transmittance wastage from flexible substrates are critical challenges to approaching the high‐performance PSCs with flexural endurance. In this work, a nanocellular scaffold is introduced to architect a mechanics buffer layer and optics resonant cavity. The nanocellular scaffold releases mechanical stresses during flexural experiences and significantly improves the crystalline quality of the perovskite films. The nanocellular optics resonant cavity optimizes light harvesting and charge transportation of devices. More importantly, these flexible PSCs, which demonstrate excellent performance and mechanical stability, are practically fabricated in modules as a wearable solar‐power source. A power conversion efficiency of 12.32% for a flexible large‐scale device (polyethylene terephthalate substrate, indium tin oxide‐free, 1.01 cm²) is achieved. This ingenious flexible structure will enable a new approach for development of wearable electronics.     

New families of mesoporous materials

Mesoporous materials have been paid much attention in both scientific researches and practical applications. In this review, we focus on recent developments on preparation and functionalization of new families of mesoporous materials, especially non-siliceous mesoporous materials invented in our research group. Replica synthesis is known as the method to synthesize mesoporous materials composed of various elements using originally prepared mesoporous replica. This strategy has been applied for the syntheses of novel mesoporous materials such as carbon nanocage and mesoporous carbon nitride. Carbon nanocage has a cage-type structure with huge surface area and pore volume, which exhibits superior capabilities for biomolecular adsorption. Mesoporous carbon nitride was synthesized, for first time, by using mixed material source of carbon and nitrogen simultaneously. As a totally new strategy for synthesis of mesoporous materials, the elemental substitution method has been recently proposed by us. Direct substitution of component elements in original mesoporous materials, with maintaining structural regularity, provided novel mesoporous materials. According to this synthetic strategy, mesoporous boron nitride and mesoporous boron carbon nitride have been successfully prepared, for first time. In addition to these material inventions, hybridization of high functional materials, such as biomaterials, to mesoporous structure has been also developed. Especially, immobilization of proteins in mesopores was systematically researched, and preparation of peptide-hybridized mesoporous silica was demonstrated. These new families of mesoporous materials introduced in this review would have high potentials in future practical applications in wide ranges from electronics and photonics to environmental and medical uses.     

Atmospheric plasma-calcination of mesoporous tungsten oxide utilizing plasma dielectric barrier discharge

The fabrication of mesoporous tungsten oxide films by spin-coating method followed by an atmospheric plasma-calcination method is described and discussed here. For the calcination process the dielectric barrier discharge system generating homogenous atmospheric plasma discharge was designed and used. By this method, large surface area mesoporous films, with disordered pores of average diameter size of about 4 to 5 nm were synthesized. All the plasma-calcined films exhibit amorphous structure. The process of calcination was evaluated by FT-IR spectroscopy and in comparison with other methods a very high speed of calcination process was achieved.     

A combined top-down and bottom-up approach to fabricate silica films with bimodal porosity

We report a method to fabricate silica films with bimodal porosity based on the surfactant-directed self-assembly process followed by post-treatment with reactive ion etching (RIE). By RIE of a surfactant-templated mesoporous silica film with a 3D hexagonal structure, vertically-etched pores with the size of several tens of nanometers and the depth of ca. 60 nm are generated, while the original caged mesopores (ca. 5 nm in size) are still retained in the unetched parts of the film. Pre-treatment of the mesoporous silica film by wet-etching to expose the pores on the surface, followed by sputter deposition of a Pt layer for partial masking, is crucial for the anisotropic etching of the film. Such a combined top-down and bottom up approach offers an opportunity to fabricate silica films with hierarchical pore architectures.