Reflectance of surfactant-templated mesoporous silica thin films: Simulations versus experiments

In this study, cubic and hexagonal mesoporous amorphous silica thin films were synthesized using evaporation-induced self-assembly process followed by calcination leaving highly ordered spherical or cylindrical pores in a silica matrix. The films featured pores with diameter between 4 and 11 nm, lattice parameter from 7.8 to 24 nm, and porosity between 22% and 45%. All films were dehydrated prior to reflectance measurements except for one film which was fully hydrated. The present study compares the spectral reflectance measured experimentally between 400 and 900 nm with that computed numerically by solving three-dimensional Maxwell's equations in mesoporous silica thin films with the same morphology as those synthesized. The matrix was assumed to have the same optical properties as bulk fused silica. The pore optical properties were either those of air or liquid water whether the film was dehydrated or hydrated, respectively. Excellent agreement was found between experimental and numerical reflectance for both cubic and hexagonal mesoporous silica films. This study experimentally validates our simulation tool and offers the prospect of ab-initio design of nanocomposite materials with arbitrary optical properties without using effective medium approximation or mixing rules.     

气-液界面二元共沉积法制备三维有序大孔SiO2

采用乳液聚合法制备粒径为229nm的单分散聚苯乙烯(PS)微球,以单分散PS微球和粒径为10nm的硅溶胶为原料,采用蒸发自组装法在气-液界面上二元共沉积,制备了大孔SiO2材料。结果表明,当SiO2体积分数为11%时,大孔SiO2材料呈现有序规整的FCC结构,其填充率为42%,收缩率仅为2%。低温N2吸附表明该材料在大孔孔壁上存在6.4nm左右的介孔,是一种具有大孔/介孔复合孔道结构的功能材料。     

Functionalized cubic mesostructured silica films

Cubic Pm3n mesoporous silica films have been prepared on silicon wafers and quartz crystal microbalance (QCM) devices covered with gold electrodes by a spin-coating process from preformed silica/CTABr/ethanol/water assemblies under acidic conditions. Post-synthesis functionalization of mesoporous films with amino- and thiol-containing organosilanes is performed in order to modify the mesoporous surface for further confinement of nanoscale structures. The type of mesophase structure and the functionalization process was followed with surface sensitive techniques such as grazing incidence diffraction (GID), reflection-absorption FT-IR spectroscopy and gravimetric measurements by applying QCMs technique. Nitrogen sorption data using QCM devices were obtained for the calcined and functionalized mesoporous films.     

定向介孔薄膜制备的研究进展

定向介孔薄膜是指内部孔道沿着同一方向定向排列的介孔薄膜. 本文就定向介孔薄膜的制备方法特别是近几年内的进展进行了回顾和评述, 按形成介孔薄膜的机理总结出三类制备介孔薄膜的方法, 并且分析了薄膜制备过程中的影响因素, 从薄膜定向性的角度对制备介孔薄膜的研究进行了分析与展望, 提出了今后制备定向介孔薄膜的发展方向和研究热点.     

Nickel nanoparticles decoration of ordered mesoporous silica thin films for carbon nanotubes growth

We report in situ successive depositions of nickel nanoparticles and carbon nanotubes (CNTs) on ordered mesoporous silica films used as template for the catalyst particles. The mesoporous films are synthesized by the evaporation-induced self-assembly process from tetraethyl orthosilicate derived oligomers and a di-block copolymer from dip-coating deposition method. The substrates are decorated with Ni nanoparticles through Ion Beam Deposition and posterior annealing to induce metal coalescence in the mesoporous cavities. CNTs were then grown by Chemical Vapor Deposition in the presence of an electric field. These techniques provide a simple control method producing ordered arrangements of catalyst nanoparticles and ordered nanostructures for large area applications.     

Controlled Deposition of Silver Nanoparticles in Mesoporous Single‐ or Multilayer Thin Films: From Tuned Pore Filling to Selective Spatial Location of Nanometric Objects

Silver nanoparticle assemblies are embedded within mesoporous oxide thin films by an in situ mild reduction leading to nanoparticle–mesoporous oxide thin‐film composites (NP@MOTF). A quantitative method based on X‐ray reflectivity is developed and validated with energy dispersive spectroscopy in order to assess pore filling. The use of dilute formaldehyde solutions leads to control over the formation of silver nanoparticles within mesoporous titania films. Inclusion of silver nanoparticles in mesoporous silica requires more drastic conditions. This difference in reactivity can be exploited to selectively synthesize nanoparticles in a predetermined layer of a multilayered mesoporous stack leading to complex 1D‐ordered multilayers with precise spatial location of nanometric objects. The metal oxide nanocomposites synthesized have potential applications in catalysis, optical devices, surface‐enhanced Raman scattering, and metal enhancement fluorescence.     

蒸发诱导自组装仿生合成高有序度三维六方介孔氧化硅薄膜

借鉴自然界生物矿化的形成机理,利用蒸发诱导自组装(EISA)的方法,以十六烷基三甲基溴化铵(CTAB)为结构导向剂,正硅酸乙酯(TEOS)为硅源,通过浸渍提拉在普通玻璃片上制备出高有序度、三维六方结构的介孔氧化硅薄膜,通过XRD、TEM、低温N2吸附/脱附等方法对薄膜进行了表征,并初步讨论了形成三维六方结构的机理.     

An ordered Si nanowire with NiSi2 tip arrays as excellent field emitters

A method was developed to grow ordered silicon nanowire with NiSi(2) tip arrays by reacting nickel thin films on silica-coated ordered Si nanowire (NW) arrays. The coating of thin silica shell on Si NW arrays has the effect of limiting the diffusion of nickel during the silicidation process to achieve the single crystalline NiSi(2) NWs. In the meantime, it relieves the distortion of the NWs caused by the strain associated with formation of NiSi(2) to maintain the straightness of the nanowire and the ordering of the arrays. Other nickel silicide phases such as Ni(2)Si and NiSi were obtained if the silicidation processes were conducted on the ordered Si NWs without a thin silica shell. Excellent field emission properties were found for NiSi(2)/Si NW arrays with a turn on field of 0.82 V μm(-1) and a threshold field of 1.39 V μm(-1). The field enhancement factor was calculated to be about 2440. The stability test showed a fluctuation of about 7% with an applied field of 2.6 V μm(-1) for a period of 24 h. The excellent field emission characteristics are attributed to the well-aligned and highly ordered arrangement of the single crystalline NiSi(2)/Si heterostructure field emitters. In contrast to other growth methods, the present growth of ordered nickel silicide/Si NWs on silicon is compatible with silicon nanoelectronics device processes, and also provides a facile route to grow other well-aligned metal silicide NW arrays. The advantages will facilitate its applications as field emission devices.     

Si-supported mesoporous and microporous oxide interconnects as electrophoretic gates for application in microfluidic devices

Microfluidic analysis systems are becoming an important technology in the field of analytical chemistry. An expanding area is concerned with the control of fluids and species in microchannels by means of an electric field. This paper discusses a new class of Si-compatible porous oxide interconnects for gateable transport of ions. The integration of such thin oxide films in microfluidics devices has been hampered in the past by the compatibility of oxides with silicon technology. A general fabrication method is given for the manufacture of silicon microsieve support structures by micromachining, on which a thin oxide layer is deposited by the spin-coating method. The deposition method was used for constructing gamma-alumina, MCM-48 silica, and amorphous titania films on the support structures, from both water-based and solvent-based oxide sols. The final structures can be applied as microporous and mesoporous interconnecting walls between two microchannels. It is demonstrated that the oxide interconnects can be operated as ion-selective electrophoretic gates. The interconnects suppress Fick diffusion of both charged and uncharged species, so that they can be utilized as ionic gates with complete external control over the transport rates of anionic and cationic species, thus realizing the possibility for implementation of these Si-compatible oxide interconnects in microchip analyses for use as dosing valves or sensors.     

Hierarchical nanofabrication of microporous crystals with ordered mesoporosity

Shaped zeolite nanocrystals and larger zeolite particles with three-dimensionally ordered mesoporous (3DOm) features hold exciting technological implications for manufacturing thin, oriented molecular sieve films and realizing new selective, molecularly accessible and robust catalysts. A recognized means for controlled synthesis of such nanoparticulate and imprinted materials revolves around templating approaches, yet identification of an appropriately versatile template has remained elusive. Because of their highly interconnected pore space, ordered mesoporous carbon replicas serve as conceptually attractive materials for carrying out confined synthesis of zeolite crystals. Here, we demonstrate how a wide range of crystal morphologies can be realized through such confined growth within 3DOm carbon, synthesized by replication of colloidal crystals composed of size-tunable (about 10-40 nm) silica nanoparticles. Confined crystal growth within these templates leads to size-tunable, uniformly shaped silicalite-1 nanocrystals as well as 3DOm-imprinted single-crystal zeolite particles. In addition, novel crystal morphologies, consisting of faceted crystal outgrowths from primary crystalline particles have been discovered, providing new insight into constricted crystal growth mechanisms underlying confined synthesis.     

Preparation of conductive transparent adhesive films from carbon nanomaterials and polar acrylate

Electrically conductive optically clear adhesives (ECOCAs) were prepared using a nanostructured carbon material (CMK-3(150)) as a conductive filler. The mesoporous carbon material, CMK-3(150), was synthesized using an ordered mesoporous silica template to produce inverse replica ordered mesoporous carbon material with an approximately 10 nm pore diameter. An adhesive solution of acrylic monomers containing polar acrylate, CMK-3(150), and thermal initiator was reacted at 80 degrees C to prepare the ECOCA composite which had appropriate viscosity for further processing. The adhesive composite was adhered to various surfaces including ITO films upon thermal processing at 60 degrees C to afford a highly transparent and adhesive film. Tensile strength of the ECOCA films was increased with the contents of conductive filler up to 4 wt%. The percolation concentration of the CMK-3(150) in the composite was approximately 7 wt%, which is much less than those of typical conductive fillers. The optimum content of CMK-3(150) to assure optical clarity, tensile strength, and high conductivity was 2-3 wt%.     

Structure and optical properties of ordered mesoporous copper oxide–silica composite films

In this study, ordered mesoporous copper oxide–silica (CuO–SiO₂) composite films with CuO/SiO₂ molar ratio ≤6% have been prepared. Small-angle X-ray diffraction and transmission electron microscopy investigations show that the mesoporous CuO–SiO₂ composite films have a hexagonally ordered pore array nanostructure. Wide-angle X-ray diffraction analysis reveals that the copper oxide and silica in the composite films are non-crystalline. The non-crystalline CuO in the mesoporous composite films has an obvious blue-shift phenomenon of the absorption edge. The calculated band gap energy for CuO is 3.2?eV, which is much higher than its bulk counterparts (1.21–1.5?eV).     

Highly-ordered mesoporous titania thin films prepared via surfactant assembly on conductive indium-tin-oxide/glass substrate and its optical properties

Highly ordered mesoporous titanium dioxide (titania, TiO₂) thin films on indium-tin-oxide (ITO) coated glass were prepared via a Pluronic (P123) block copolymer template and a hydrophilic TiO₂ buffer layer. The contraction of the 3D hexagonal array of P123 micelles upon calcination merges the titania domains on the TiO₂ buffer layer to form mesoporous films with a mesochannel diameter of approximately 10 nm and a pore-to-pore distance of 10 nm. The mesoporous titania films on TiO₂-buffered ITO/glass featured an inverse mesospace with a hexagonally-ordered structure, whereas the films formed without a TiO₂ buffer layer had a disordered microstructure with submicron cracks because of non-uniform water condensation on the hydrophobic ITO/glass surface. The density of the mesoporous film was 83% that of a bulk TiO₂ film. The optical band gap of the mesoporous titania thin film was approximately 3.4 eV, larger than that for nonporous anatase TiO₂ (~ 3.2 eV), suggesting that the nanoscopic grain size leads to an increase in the band gap due to weak quantum confinement effects. The ability to form highly-ordered mesoporous titania films on electrically conductive and transparent substrates offers the potential for facile fabrication of high surface area semiconductive films with small diffusion lengths for optoelectronics applications.     

Control of wall thickness in the formation of ordered mesoporous silica films

Ordered mesoporous silica thin films using block copolymer have drawn an attention for low-k application due to its ordered pore structure. From the respect of dielectric and mechanical properties of the film, there is trade-off between pore size and wall thickness. In this work, factors for increase of wall thickness were investigated. It was found that body-centered cubic structure was maintained irrespective of the concentration of catalytic acid. The catalytic acid thickens the framework wall because counterion reduces the repulsion force between silicic acids. The highly ordered mesoporous silica films were obtained although high concentration of acid was added to the silica sol. However, wormlike micelle exists more with high HCl concentration due to fast gellation rate. And excess water, which has the role similar to the humid atmosphere, also increases the thickness of silica wall. However, large amount of excess water at the micelle interface disrupts organic-inorganic electrostatic interaction. As a conclusion, optimization of HCl concentration in the silica sol and control of humidity during spin coating can simultaneously increase the framework thickness while maintaining the pore periodicity.     

Observation of quantum confinement effect on ZnO embedded mesoporous silica

Nonionic surfactant as liquid organic template and tetraethoxysilane as silica precursor were used for the synthesis of mesoporous silica with ordered arrangement of nanopores (diameters are about 1-6 nm). The synthesized mesoporous silica was used as the template for the synthesis of ZnO nanoparticles using zinc acetylacetonate as ZnO precursor. The as synthesized ZnO incorporated in the mesoporous silica nanocomposite were analyzed using X-ray diffraction, TEM and Photoluminescent spectrum. ZnO introduction has no extensive influence on the mesoporous structure of silica. Quantum confinement effects are observed in the case of ZnO nanoparticles embedded in mesoporous silica. The particle size of ZnO is about 3.2 nm. The band gap is broadening to 3.47 eV.     

Synthesis of mesoporous silica with embedded nickel nanoparticles for catalyst applications

Here we describe a new route for the synthesis of nanometric Ni particles embedded in a mesoporous silica material with excellent potential for catalytic applications. Mesoporous silica with a surface area in the range of 202-280 m2/g, with narrow pore size distribution and Ni nanoparticles (particles in the range of 3-41 nm) were obtained in a direct process. A different approach was adopted to process such a nanocomposite. This new approach is based on the formation of a polymer with the silicon oxianion and nickel cation chelated to the macromolecule structure and on the control of the pyrolysis step. The CO/CO2 atmosphere resulting from the pyrolysis of the organic material promotes the reduction of the Ni citrate.     

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.     

New mesoporous silica/carbon composites by in situ transformation of silica template in carbon/silica nanocomposite

Hard template-based fabrication of mesoporous carbon unavoidably goes through the removal process of the template to generate template-free carbon replica, including troublesome disposal of template waste often accompanied by toxic etchant, which not only increases the fabrication cost of materials but also raises serious environmental concerns. As a novel strategy to overcome such problem, a direct in situ synthesis approach using silica waste in carbon/silica nanocomposite as a silica source and cetyltrimethylammonium bromide as a porogen under basic condition is reported in this study for the generation of a new composite composed of mesoporous MCM-41 silica and hollow carbon capsule. The resultant MCM-41/carbon capsule composite offers a 3-D interconnected multimodal pore system, which discloses a wide pore range of ordered uniform mesopores (ca 2.3?nm) resulting from MCM-41 silica and disordered uniform mesopores (ca 3.8?nm) and macropores (ca 300?nm) from hollow mesoporous carbon, respectively. The composite has a high specific surface area (ca 909?m²/g) and large pore volume (ca 0.73?cm³/g). The in situ transformation approach of silica waste into valuable mesoporous silica is considered as a promising scalable route for efficient new multi-functional composites useful for a wide range of applications such as adsorption of volatile organic compounds and radioactive wastes produced in a nuclear facility.     

偕胺肟基螯合氧化硅的合成及其Cu2+亲和性能

以氯化钾为晶体结构导向剂, 以正硅酸乙酯和2-氰乙基三乙氧基硅烷为硅源, 聚(乙二醇)-聚(丙二醇)-聚(乙二醇)三嵌段共聚物为模板剂, 合成了偕胺肟基螯合氧化硅(AO-SBA-15)。通过X射线衍射(XRD)、低温氮气吸附-脱附、傅里叶红外光谱(FT-IR)、Zeta电位分析和元素分析技术对样品的结构、孔性质和螯合官能团等进行了表征。XRD分析结果表明, 偕胺肟基螯合氧化硅材料具有有序的二维六方结构, 通过氮气物理吸附数据计算得到材料的平均孔径和比表面积分别为3.96 nm和435 m²/g。FT-IR分析表明将氰基成功地引入材料中并转化为偕胺肟基螯合官能团, 元素分析发现材料的偕胺肟基含量约为1.6 mmol/g, 此外, Zeta电位分析表明材料呈现电负性。相对未改性的氧化硅材料(SBA-15), AO-SBA-15对铜离子吸附容量提高了2倍; 相对氰基功能化氧化硅(CN-SBA-15), AO-SBA-15吸附容量提高了3.6倍。这表明通过引入偕胺肟基螯合官能团, SBA-15对铜离子的亲和力得到显著提高。     

Periodically ordered nanoscale islands and mesoporous films composed of nanocrystalline multimetallic oxides

Innovative strategies to produce well-defined nanoparticles and other nanostructures such as nanofibres, quantum wells and mesoporous materials have revitalized materials science for the potential benefit to society. Here, we report a controlled process, involving soft-chemistry-based deposition, template-assisted mesostructured growth, and tuned annealing conditions that allows the preparation of ordered mesoporous crystalline networks and mesostructured nano-island single layers, composed of multicationic metal oxides having perovskite, tetragonal or ilmenite structures. This strategy to obtain meso-organized multi-metal-oxide nanocrystalline films (M(3)NF) bridges the gap between conventional mesoporous materials and the remarkable properties of crystalline ternary or quaternary metallic oxides. Nanocrystalline mesoporous films with controlled wall thickness (10-20 nm) of dielectric SrTiO(3), photoactive MgTa(2)O(6) or ferromagnetic semi-conducting Co(x)Ti(1-x)O(2-x) were prepared by evaporation-induced self-assembly (EISA) using a specially designed non-ionic block-copolymer template. A tuned thermal treatment of the mesoporous films permits the transfer of the wall structure into nanocrystallites, with all tectonic units being tightly incorporated into mechanically stable ordered tri- or bidimensional nanocrystalline networks. This methodology should allow multifunctionalization, miniaturization and integration during development of devices such as smart sensors and actuators, better-performing photocatalysts, and fast electrochromic devices. On the other hand, organized arrays of dispersed ferromagnetic or ferroelectric nanoparticles are promising materials for spintronics and for cheap, non-volatile 'flash' memories.