Pure‐Silica‐Zeolite MFI and MEL Low‐Dielectric‐Constant Films with Fluoro‐Organic Functionalization

The synthesis of organic‐functionalized pure‐silica‐zeolites (PSZs) with MFI‐ and MEL‐type structures for low‐k applications prepared through a direct‐synthesis method by adding a fluorinated silane to the synthesis solution is reported. The added fluorine functionality increases the hydrophobicity of the zeolites, which are characterized by scanning electron microscopy, X‐ray diffraction, ²⁹Si and ¹⁹F solid‐state NMR spectroscopy, nitrogen adsorption, and thermogravimetric analysis. The functionalized zeolite powders have low water content and calcined spin‐on films prepared from the functionalized nanoparticle suspensions exhibit higher water contact angles and lower k values (2.1 and 1.8 for the functionalized MFI‐ and MEL‐type zeolites, respectively) than PSZ films. The use of a direct‐synthesis method to decrease the moisture adsorption in the films eliminates the extra post‐spin‐on silylation steps that are traditionally used to render the zeolite films hydrophobic.     

Spin‐Coated Periodic Mesoporous Organosilica Thin Films—Towards a New Generation of Low‐Dielectric‐Constant Materials

Periodic mesoporous organosilica (PMO) thin films have been produced using an evaporation‐induced self‐assembly (EISA) spin‐coating procedure and a cationic surfactant template. The precursors are silsesquioxanes of the type (C₂H₅O)₃Si–R–Si(OC₂H₅)₃ or R′–[Si(OC₂H₅)₃]₃ with R = methene (–CH₂–), ethylene (–C₂H₂–), ethene (–C₂H₄–), 1,4‐phenylene (C₆H₄), and R′ = 1,3,5‐phenylene (C₆H₃). The surfactant is successfully removed by solvent extraction or calcination without any significant Si–C bond cleavage of the organic bridging groups R and R′ within the channel walls. The materials have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), and ²⁹Si and ¹³C magic‐angle spinning (MAS) NMR spectroscopy. The d‐spacing of the PMOs is found to be a function of R. Nanoindentation measurements reveal increased mechanical strength and stiffness for the PMOs with R = CH₂ and C₂H₄ compared to silica. Films with different organic‐group content have been prepared using mixtures of silsesquioxane and tetramethylorthosilicate (TMOS) precursors. The dielectric constant (k) is found to decrease with organic content, and values as low as 1.8 have been measured for films thermally treated to cause a “self‐hydrophobizing” bridging‐to‐terminal transformation of the methene to methyl groups with concomitant loss of silanols. Increasing the organic content and thermal treatment also increases the resistance to moisture adsorption in 60 and 80 %‐relative‐humidity (RH) environments. Methene PMO films treated at 500 °C are found to be practically unchanged after five days exposure to 80 % RH. These low dielectric constants, plus the good thermal and mechanical stability and the hydrophobicity suggest the potential utility of these films as low‐k layers in microelectronics.     

Nanoporous Low‐κ Polyimide Films via Poly(amic acid)s with Grafted Poly(ethylene glycol) Side Chains from a Reversible Addition–Fragmentation Chain‐Transfer‐Mediated Process

Thermally‐initiated living radical graft polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with ozone‐pretreated poly[N,N′‐(1,4‐phenylene)‐3,3′,4,4′‐benzophenonetetra‐carboxylic amic acid] (PAmA) via a reversible addition–fragmentation chain‐transfer (RAFT)‐mediated process was carried out. The chemical compositions and structures of the copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), and molecular weight measurements. The “living” character of the grafted PEGMA side chains was ascertained in the subsequent extension of the PEGMA side chains. Nanoporous low‐dielectric‐constant (low‐κ) polyimide (PI) films were prepared by thermal imidization of the PAmA graft copolymers under reduced argon pressure, followed by thermal decomposition of the side chains in air. The nanoporous PI films obtained from the RAFT‐mediated graft copolymers had well‐preserved PI backbones, porosity in the range of 5–17 %, and pore size in the range of 30–50 nm. The pores were smaller and the pore‐size distribution more uniform than those of the corresponding nanoporous PI films obtained via graft copolymers from conventional free‐radical processes. Dielectric constants approaching 2 were obtained for the nanoporous PI films prepared from the RAFT‐mediated graft copolymers.     

Nanoporous Ultra‐Low‐Dielectric‐Constant Fluoropolymer Films via Selective UV Decomposition of Poly(pentafluorostyrene)‐block‐Poly(methyl methacrylate) Copolymers Prepared Using Atom Transfer Radical Polymerization

Block copolymers of poly(pentafluorostyrene) (PFS) and poly(methyl methacrylate) (PMMA) (PFS‐b‐PMMA) have been synthesized using atom transfer radical polymerization (ATRP). Then, nanoporous fluoropolymer films have been prepared via selective UV decomposition of the PMMA blocks in the PFS‐b‐PMMA copolymer films. The chemical composition and structure of the PFS homopolymers and copolymers have been characterized using nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS), and molecular‐weight measurements. The cross‐sectional and surface morphologies of the PFS‐b‐PMMA copolymer films before and after selective UV decomposition of the PMMA blocks have been studied using field‐emission scanning electron microscopy (FESEM). The nanoporous fluoropolymer films with pore sizes in the range 30–50 nm and porosity in the range 15–40 % have been obtained from the PFS‐b‐PMMA copolymers of different PMMA content. Dielectric constants approaching 1.8 have been achieved in the nanoporous fluoropolymer films which contain almost completely decomposed PMMA blocks.     

Silica‐Gelatin Hybrids with Tailorable Degradation and Mechanical Properties for Tissue Regeneration

Nature has evolved mechanisms to create a diversity of specialized materials through nanoscale organization. Inspired by nature, hybrid materials are designed with highly tailorable properties, which are achieved through careful control of their nanoscale interactions. These novel materials, based on a silica‐gelatin hybrid system, have the potential to serve as a platform technology for human tissue regeneration. Covalent interactions between the inorganic and organic constituents of the hybrid are essential to enable the precise control of mechanical and dissolution properties. Furthermore, hybrid scaffold porosity is found to highly influence mechanical properties, to the extent where scaffolds of particular strength could be specified based on their porosity. The hybrids also demonstrate a non‐cytotoxic effect when mesenchymal stem cells are cultured on the material. Cytoskeletal proteins of the cells are imaged using actin and vimentin staining. It is envisaged these hybrid materials will find a diverse application in both hard and soft tissue regenerating scaffolds.     

Synthesis and Properties of Designed Low‐k Fluoro‐Copolyetherimides. Part 1

Polyetherimides are versatile melt‐processable engineering resins. A series of fluoro‐polyetherimides compositions based on diether‐containing diamines were designed on paper and their dielectric constants (ϵ′) estimated before their synthesis. Experimentally determined ϵ′ values were compared with the estimated values. The amorphous polyetherimides containing bis‐trifluoromethyl groups exhibited not only low dielectric constants—lower than those of the commercially available polyetherimide ULTEM 1000 and polyimide Kapton H at 1 kHz—but also excellent long‐term thermo‐oxidative stability and reduced water absorption relative to non‐fluorinated polyimides.     

Enhanced Dielectric and Electromechanical Responses in High Dielectric Constant All‐Polymer Percolative Composites

A type of all‐polymer percolative composite is introduced which exhibits a very high dielectric constant (> 7000). The experimental results also show that the dielectric behavior of this new class of percolative composites follows the predictions of the percolation theory and the analysis of conductive percolation phenomena. The very high dielectric constant of the all‐polymer composites, which are also very flexible and possesses an elastic modulus close to that of the insulation polymer matrix, makes it possible to induce a high electromechanical response under a very reduced electric field (a strain of 2.65 % with an elastic energy density of 0.18 J cm^–3 can be achieved under a field of 16 MV m^–1). Data analysis also suggests that within the composites, the non‐uniform local field distribution as well as interface effects can significantly enhance the strain responses. Furthermore, the experimental data as well as the data analysis indicate that conduction loss in the composites will not affect the strain hysteresis.     

Single Step Preparation of Novel Hydrophobic Composite Films for Low‐k Applications

Composite films with low dielectric constants (k) containing micro‐ and mesopores are synthesized from precursor solutions for the preparation of mesoporous silica and ethanolic suspensions of silicalite‐1 nanoparticles. The material contains silicalite‐1 nanoparticles (include nanocrystals and nanoslabs/intermediates) embedded in a randomly oriented matrix of highly porous mesoporous silica. Micropores result from the incorporated silicalite‐1 nanoparticles, while decomposition of the porogen F127 leads to additional mesopores. The porosity of the composite films increases from 9 to 60% with the increase in porogen loading, while in parallel the elastic modulus and hardness decrease. The elastic moduli of the films are in the range of 13–20 GPa. Hydrophobic surfaces of the composite films are obtained by introducing methyl triethoxysilane during the preparation of both precursor solutions, leading to the incorporation of ? CH₃ groups in the final composite films. These methyl groups are stable up to at least 500 °C. A low k value of approximately 2 is observed for films cured at 400 °C in N₂ flow, which is ideal for removing templates without decomposing methyl groups. Due to the intrinsic hydrophobicity of the material, post‐silylation is not required rendering the composite films attractive candidates for future low k materials.     

Hybrid Materials: Silica‐Gelatin Hybrids with Tailorable Degradation and Mechanical Properties for Tissue Regeneration (Adv. Funct. Mater. 22/2010)

Nature has evolved mechanisms to create a diversity of specialized materials through nanoscale organization. Inspired by nature, hybrid materials are designed with highly tailorable properties, which are achieved through careful control of their nanoscale interactions. These novel materials, based on a silica‐gelatin hybrid system, have the potential to serve as a platform technology for human tissue regeneration. Covalent interactions between the inorganic and organic constituents of the hybrid are essential to enable the precise control of mechanical and dissolution properties. Furthermore, hybrid scaffold porosity is found to highly influence mechanical properties, to the extent where scaffolds of particular strength could be specified based on their porosity. The hybrids also demonstrate a non‐cytotoxic effect when mesenchymal stem cells are cultured on the material. Cytoskeletal proteins of the cells are imaged using actin and vimentin staining. It is envisaged these hybrid materials will find a diverse application in both hard and soft tissue regenerating scaffolds.     

Probing the Effects of Nanoscale Architecture on the Mechanical Properties of Hexagonal Silica/Polymer Composite Thin Films

We examine the effects of controlling nanoscale architecture on the tensile properties of honeycomb‐structured silica/polymer composite films. The hexagonal films are produced using evaporation‐induced self‐assembly and uniaxially strained using a home‐built tensile testing apparatus. Significant differences in the yield strain, failure strain, and tensile moduli between the axes parallel and perpendicular to the film‐deposition direction are observed for the thinnest films examined and are attributed to anisotropy in the film nanostructure that is further characterized with transmission electron microscopy and atomic force microscopy. For properly oriented composites, these films have tensile moduli comparable to the Young's modulus of bulk silica but exhibit failure strains that are about an order of magnitude larger than those seen in typical bulk‐silica systems. The yielding and failure processes are explored using X‐ray diffraction and optical microscopy and are characterized by irreversible changes in the nanoscale architecture. We show that tuning the nanoscale architecture can provide control over the tensile properties of composites, allowing for materials with combinations of stiffness and elasticity unachievable in the analogous bulk systems.     

Synthesis of ZSM‐5 Films and Monoliths with Bimodal Micro/Mesoscopic Structures

A route to synthesize ZSM‐5 crystals with a bimodal micro/mesoscopic pore system has been developed in this study; the successful incorporation of the mesopores within the ZSM‐5 structure was performed using tetrapropylammonium hydroxide (TPAOH)‐impregnated mesoporous materials containing carbon nanotubes in the pores, which were encapsulated in the ZSM‐5 crystals during a solid rearrangement process within the framework. Such mesoporous ZSM‐5 zeolites can be readily obtained as powders, thin films, or monoliths.     

Facile Fabrication and Superparamagnetism of Silica‐Shielded Magnetite Nanoparticles on Carbon Nitride Nanotubes

Using conventional methods to synthesize magnetic nanoparticles (NPs) with uniform size is a challenging task. Moreover, the degradation of magnetic NPs is an obstacle to practical applications. The fabrication of silica‐shielded magnetite NPs on carbon nitride nanotubes (CNNTs) provides a possible route to overcome these problems. While the nitrogen atoms of CNNTs provide selective nucleation sites for NPs of a particular size, the silica layer protects the NPs from oxidation. The morphology and crystal structure of NP–CNNT hybrid material is investigated by transmission electron microscopy (TEM) and X‐ray diffraction. In addition, the atomic nature of the N atoms in the NP–CNNT system is studied by near‐edge X‐ray absorption fine structure spectroscopy (nitrogen K‐edge) and calculations of the partial density of states based on first principles. The structure of the silica‐shielded NP–CNNT system is analyzed by TEM and energy dispersive X‐ray spectroscopy mapping, and their magnetism is measured by vibrating sample and superconducting quantum interference device magnetometers. The silica shielding helps maintain the superparamagnetism of the NPs; without the silica layer, the magnetic properties of NP–CNNT materials significantly degrade over time.     

Thioether‐bridged Mesoporous Organosilicas: Mesophase Transformations Induced by the Bridged Organosilane Precursor

The achievement of structural control over thioether‐bridged mesoporous organosilicas is reported. The mesoporous materials have been synthesized by co‐condensation of bis[3‐(triethoxysilyl)propyl]tetrasulfide (TESPTS) and tetramethoxysilane (TMOS) in acetic acid/sodium acetate buffer solution (HAc–NaAc, pH 4.4), using the nonionic surfactant P123 as a template. The mesostructure of the material is mainly controlled by the molar ratio of TESPTS/TMOS in the initial gel mixture. A mesophase transformation, progressing from a highly ordered 2D hexagonal structure via a vesiclelike structure to a mesostructured cellular foam, can be clearly observed when the molar ratio of TESPTS/TMOS is increased in increments. Solid‐state NMR results show that TESPTS is not completely hydrolyzed and condensed at the applied buffer conditions. At low concentrations, the unhydrolyzed TESPTS can penetrate into the core of the surfactant micelles and change the packing parameter of the P123 surfactant. Above a certain concentration, the TESPTS can form a microemulsion with P123 surfactant molecules. Therefore, the vesiclelike structure or cellular foam structure can be synthesized by simply controlling the molar ratio of TESPTS/TMOS. This approach provides a novel method for the facile synthesis of organic–inorganic hybrid materials with a controllable mesostructure under mild synthetic conditions.     

Sub‐Micrometer Zeolite Films on Gold‐Coated Silicon Wafers with Single‐Crystal‐Like Dielectric Constant and Elastic Modulus

A low‐temperature synthesis coupled with mild activation produces zeolite films exhibiting low dielectric constant (low‐k) matching the theoretically predicted and experimentally measured values for single crystals. This synthesis and activation method allows for the fabrication of a device consisting of a b‐oriented film of the pure‐silica zeolite MFI (silicalite‐1) supported on a gold‐coated silicon wafer. The zeolite seeds are assembled by a manual assembly process and subjected to optimized secondary growth conditions that do not cause corrosion of the gold underlayer, while strongly promoting in‐plane growth. The traditional calcination process is replaced with a nonthermal photochemical activation to ensure preservation of an intact gold layer. The dielectric constant (k), obtained through measurement of electrical capacitance in a metal–insulator–metal configuration, highlights the ultralow k ≈ 1.7 of the synthetized films, which is among the lowest values reported for an MFI film. There is large improvement in elastic modulus of the film (E ≈ 54 GPa) over previous reports, potentially allowing for integration into silicon wafer processing technology.     

Magnetic‐Core/Porous‐Shell CoFe2O4/SiO2 Composite Nanoparticles as Immobilized Affinity Supports for Clinical Immunoassays

This study demonstrates a novel approach towards the development of advanced protein assay systems based on physically functionalized, magnetic‐core/porous‐shell CoFe₂O₄/SiO₂ composite nanoparticles. The preparation, characterization, and measurement of the relevant properties of the protein assay system is discussed, and the system is used for the detection of cancer antigen 15‐3 (CA 15‐3, used as a model here) in clinical immunoassays. The protein assay system, based on nanometer‐sized magnetic cores and silica shells, shows good adsorption properties for the selective attachment of CA 15‐3 antibodies specific to CA 15‐3. The core/shell nanostructures exhibit good magnetic properties, which enables their integration into a quartz crystal microbalance (QCM) detection cell with the help of a permanent magnet. Under optimal conditions, the resulting immunoassay system presents a good QCM response for the detection of CA 15‐3, and allows the detection of CA 15‐3 at concentrations as low as 1.5 U mL^–1 (U: units). Importantly, the proposed protein assay system can be extended to the detection of other antigens and biological compounds.     

Low‐Temperature Formation of Well‐Aligned Nanocrystalline Si/SiOx Composite Nanowires

Well‐aligned nanocrystalline (nc)‐Si/SiO_x composite nanowires have been deposited on various substrates at 120 °C using SiCl₄/H₂ in a hot‐filament chemical vapor deposition reactor. Structural and compositional analyses reveal that silicon nanocrystals are embedded in the amorphous SiO_x nanowires. The nc‐Si/SiO_x composite nanowires are transparent in the range 500–900 nm. Photoluminescence spectra of the nc‐Si/SiO_x composite nanowires have a broad emission band, ranging from 420 to 525 nm. Water vapor from the chamber wall plays a crucial role in the formation of the well‐aligned nanowires. A possible mechanism for the formation of the composite nanowires is suggested.     

Conductive Mesocellular Silica–Carbon Nanocomposite Foams for Immobilization,Direct Electrochemistry,and Biosensing of Proteins

A mesocellular silica–carbon nanocomposite foam (MSCF) is designed for the immobilization and biosensing of proteins. The as‐prepared MSCF has a highly ordered mesostructure, good biocompatibility, favorable conductivity and hydrophilicity, large surface area, and a narrow pore‐size distribution, as verified by transmission electron microscopy (TEM), IR spectroscopy, electrochemical impedance spectroscopy (EIS), nitrogen adsorption–desorption isotherms, pore size distribution plots, and water contact angle measurements. Using glucose oxidase (GOD) as a model, the MSCF is tested for immobilization of redox proteins and the design of electrochemical biosensors. GOD molecules immobilized in the mesopores of the MSCF show direct electrochemistry with a fast electron transfer rate (14.0 ± 1.7 s^–1) and good electrochemical performance. Based on a decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen, the proposed biosensor exhibits a linear response to glucose concentrations ranging from 50 μM to 5.0 mM with a detection limit of 34 μM at an applied potential of –0.4 V. The biosensor shows good stability and selectivity and is able to exclude interference from ascorbic acid (AA) and uric acid (UA) species that always coexist with glucose in real samples. The nanocomposite foam provides a good matrix for protein immobilization and biosensor preparation.     

Amphiphilic Poly(p‐phenylene)s for Self‐Organized Porous Blue‐Light‐Emitting Thin Films

Micro‐ and nanostructuring of conjugated polymers are of critical importance in the fabrication of molecular electronic devices as well as photonic and bandgap materials. The present report delineates the single‐step self‐organization of highly ordered structures of functionalized poly(p‐phenylene)s without the aid of either a controlled environment or expensive fabrication methodologies. Microporous films of these polymers, with a honeycomb pattern, were prepared by direct spreading of the dilute polymer solution on various substrates, such as glass, quartz, silicon wafer, indium tin oxide, gold‐coated mica, and water, under ambient conditions. The polymeric film obtained from C₁₂PPPOH comprises highly periodic, defect‐free structures with blue‐light‐emitting properties. It is expected that such microstructured, conjugated polymeric films will have interesting applications in photonic and optoelectronic devices. The ability of the polymer to template the facile micropatterning of nanomaterials gives rise to hybrid films with very good spatial dispersion of the carbon nanotubes.     

Water‐Stable,Magnetic Silica–Cobalt/Cobalt Oxide–Silica Multishell Submicrometer Spheres

A method to produce monodisperse magnetic composite spheres with diameters from less than 100 nm to more than 1 μm in water solution is reported. The spheres consist of a dielectric silica core and a cobalt/cobalt oxide shell which can be protected from further oxidation with an outer shell of silica or, alternatively, they can be covered with the polymer polyvinylpyrrolidone as a stabilizer. The formation of a uniform magnetic shell proceeds with the adsorption of metallic cobalt seeds, produced by the reduction of cobalt chloride with sodium borohydride, on a self‐assembled layer of polyelectrolytes on the silica core. In the second step, an outer silica shell can be formed by the hydrolysis and condensation of (3‐aminopropyl)trimethoxysilane and tetraethoxysilane. The double‐shell composite spheres show excellent sphericity, monodispersity, and a magnetic hysteresis loop at room temperature.     

Optically Functional Zeolites: Evaluation of UV and VUV Stimulated Photoluminescence Properties of Ce3+‐ and Tb3+‐doped Zeolite X

The optical properties of Tb³⁺/Ce³⁺ doped zeolites are elucidated with emphasis on ultraviolet (UV) and vacuum ultraviolet (VUV) excitation and luminescence. Ce³⁺ sensitized Tb³⁺ emission with quantum yields of 85 % may be obtained at 330 nm excitation. Low absorptivity at 254 nm due to low Ce³⁺ concentrations or low Ce³⁺/Tb³⁺ ratios, which are required for the suppression of UV components, restricts their applicability as phosphors for Hg‐based discharges, e.g., in conventional fluorescent lamps. Near band edge excitation at 172 nm revealed an immediate quantum yield of 50 % enabled by a zeolite → Ce³⁺ (5d¹) → Tb³⁺ (4f⁷5d¹) energy transfer channel, which may be exploited for the down‐conversion of the Xe₂ excimer emission.