Showing papers on "Silicon dioxide published in 2013"

Oxidation and Volatilization of Silica-Formers in Water Vapor

Abstract: At high temperatures SiC and Si3N4 react with water vapor to form a silica scale. Silica scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming silica and the other removing silica, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved, After steady state is achieved, the oxide found on the surface is a constant thickness and recession of the underlying material occurs at a linear rate. The steady state oxide thickness, the time to achieve steady state, and the steady state recession rate can all be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate can also be determined from parameters that describe a water vapor-containing environment. Accordingly, maps have been developed to show these steady state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of silica formers in water-vapor containing environments such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si3N4

Aminosilane-Grafted Polymer/Silica Hollow Fiber Adsorbents for CO₂ Capture from Flue Gas

Abstract: Amine/silica/polymer composite hollow fiber adsorbents are produced using a novel reactive post-spinning infusion technique, and the obtained fibers are shown to capture CO2 from simulated flue gas. The post-spinning infusion technique allows for functionalization of polymer/silica hollow fibers with different types of amines during the solvent exchange step after fiber spinning. The post-spinning infusion of 3-aminopropyltrimethoxysilane (APS) into mesoporous silica/cellulose acetate hollow fibers is demonstrated here, and the materials are compared with hollow fibers infused with poly(ethyleneimine) (PEI). This approach results in silica/polymer composite fibers with good amine distribution and accessibility, as well as adequate porosity retained within the fibers to facilitate rapid mass transfer and adsorption kinetics. The CO2 adsorption capacities for the APS-infused hollow fibers are shown to be comparable to those of amine powders with similar amine loadings. In contrast, fibers that are spun with...

Silicon (100)/SiO2 by XPS

Abstract: Silicon (100) substrates are ubiquitous in microfabrication and, accordingly, their surface characteristics are important. Herein, we report the analysis of Si (100) via X-ray photoelectron spectroscopy (XPS) using monochromatic Al Kα radiation. Survey scans show that the material is primarily silicon and oxygen with small amounts of carbon, nitrogen, and fluorine contamination. The Si 2p region shows two peaks that correspond to elemental silicon and silicon dioxide. Using these peaks the thickness of the native oxide (SiO2) is estimated using the equation of Strohmeier. The oxygen peak is symmetric. These silicon wafers are used as the substrate for subsequent growth of templated carbon nanotubes in the preparation of microfabricated thin layer chromatography plates.

Oxygen Plasma and Humidity Dependent Surface Analysis of Silicon, Silicon Dioxide and Glass for Direct Wafer Bonding

Abstract: Surface and interface characteristics of substrates are critical for reliable wafer bonding. Understanding the elemental and compositional states of surfaces after various processing conditions is necessary when bonding dissimilar materials. Therefore, we investigated the elemental and compositional states of silicon (Si), silicon dioxide (SiO2) and glass surfaces exposed to oxygen reactive ion etching (O2 RIE) plasma followed by storage in controlled humidity and/or ambient atmospheric conditions to understand the chemical mechanisms in the direct wafer bonding. High-resolution X-ray Photoelectron Spectroscopy (XPS) spectra of O2 RIE treated Si, SiO2 and glass showed the presence of Si(-O)2 resulting in highly reactive surfaces. A considerable shift in the binding energies of Si(-O)2, Si(-O)4 and Si(-OH)x were observed only in Si due to plasma oxidation of the surface. The humidity and ambient storage of plasma activated Si and SiO2 increased Si(-OH)x due to enhanced sorption of hydroxyls. The amounts of Si(-O)2 and Si(-OH)x of Si varied in different humidity storage conditions which are attributed to crystal-orientation dependent surface morphology and oxidation. The O2 RIE plasma induced high surface reactivity and humidity induced Si(-OH)x can play an important role in the hydrophilic wafer bonding with low temperature heating. © 2013 The Electrochemical Society. [DOI: 10.1149/2.007312jss] All rights reserved.

Synergistic removal of Pb(II), Cd(II) and humic acid by Fe3O4@mesoporous silica-graphene oxide composites.

Abstract: The synergistic adsorption of heavy metal ions and humic acid can be very challenging. This is largely because of their competitive adsorption onto most adsorbent materials. Hierarchically structured composites containing polyethylenimine-modified magnetic mesoporous silica and graphene oxide (MMSP-GO) were here prepared to address this. Magnetic mesoporous silica microspheres were synthesized and functionalized with PEI molecules, providing many amine groups for chemical conjugation with the carboxyl groups on GO sheets and enhanced the affinity between the pollutants and the mesoporous silica. The features of the composites were characterized using TEM, SEM, TGA, DLS, and VSM measurements. Series adsorption results proved that this system was suitable for simultaneous and efficient removal of heavy metal ions and humic acid using MMSP-GO composites as adsorbents. The maximum adsorption capacities of MMSP-GO for Pb(II) and Cd (II) were 333 and 167 mg g−1 caculated by Langmuir model, respectively. HA enhances adsorption of heavy metals by MMSP-GO composites due to their interactions in aqueous solutions. The underlying mechanism of synergistic adsorption of heavy metal ions and humic acid were discussed. MMSP-GO composites have shown promise for use as adsorbents in the simultaneous removal of heavy metals and humic acid in wastewater treatment processes.

The comparative immunotoxicity of mesoporous silica nanoparticles and colloidal silica nanoparticles in mice.

Abstract: Background Mesoporous silica (MPS) nanoparticles (NPs), which have a unique pore structure and extremely large surface area and pore volume, have received much attention because of their biomedical application potential. Using MPS NPs for biomedical devices requires the verification of their biocompatibility because the surface area of NPs is one of the most important determinants of toxicity, including the cellular uptake and immune response. We have previously reported that the cytotoxicity and inflammation potential of MPS NPs have been shown to be lower than those of general amorphous colloidal silica (Col) NPs in macrophages, but the low cytotoxicity does not guarantee high biocompatibility in vivo. In this study, we compared the in vivo immunotoxicity of MPS and Col NPs in the mouse model to define the effects of pore structural conditions of silica NPs.

Ordered nanoporous silica as carriers for improved delivery of water insoluble drugs: a comparative study between three dimensional and two dimensional macroporous silica

Abstract: The goal of the present study was to compare the drug release properties and stability of the nanoporous silica with different pore architectures as a matrix for improved delivery of poorly soluble drugs. For this purpose, three dimensional ordered macroporous (3DOM) silica with 3D continuous and interconnected macropores of different sizes (200 nm and 500 nm) and classic mesoporous silica (ie, Mobil Composition of Matter [MCM]-41 and Santa Barbara Amorphous [SBA]-15) with well-ordered two dimensional (2D) cylindrical mesopores were successfully fabricated and then loaded with the model drug indomethacin (IMC) via the solvent deposition method. Scanning electron microscopy (SEM), N2 adsorption, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were applied to systematically characterize all IMC-loaded nanoporous silica formulations, evidencing the successful inclusion of IMC into nanopores, the reduced crystallinity, and finally accelerated dissolution of IMC. It was worth mentioning that, in comparison to 2D mesoporous silica, 3DOM silica displayed a more rapid release profile, which may be ascribed to the 3D interconnected pore networks and the highly accessible surface areas. The results obtained from the stability test indicated that the amorphous state of IMC entrapped in the 2D mesoporous silica (SBA-15 and MCM-41) has a better physical stability than in that of 3DOM silica. Moreover, the dissolution rate and stability of IMC loaded in 3DOM silica was closely related to the pore size of macroporous silica. The colorimetric 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Cell Counting Kit (CCK)-8 assays in combination with direct morphology observations demonstrated the good biocompatibility of nanoporous silica, especially for 3DOM silica and SBA-15. The present work encourages further study of the drug release properties and stability of drug entrapped in different pore architecture of silica in order to realize their potential in oral drug delivery.

Vertical integration of high-Q silicon nitride microresonators into silicon-on-insulator platform.

Abstract: We demonstrate a vertical integration of high-Q silicon nitride microresonators into the silicon-on-insulator platform for applications at the telecommunication wavelengths. Low-loss silicon nitride films with a thickness of 400 nm are successfully grown, enabling compact silicon nitride microresonators with ultra-high intrinsic Qs (~ 6 × 10(6) for 60 μm radius and ~ 2 × 10(7) for 240 μm radius). The coupling between the silicon nitride microresonator and the underneath silicon waveguide is based on evanescent coupling with silicon dioxide as buffer. Selective coupling to a desired radial mode of the silicon nitride microresonator is also achievable using a pulley coupling scheme. In this work, a 60-μm-radius silicon nitride microresonator has been successfully integrated into the silicon-on-insulator platform, showing a single-mode operation with an intrinsic Q of 2 × 10(6).

Improved Synthesis of Gold and Silver Nanoshells

Abstract: Metallic nanoshells have been in evidence as multifunctional particles for optical and biomedical applications. Their surface plasmon resonance can be tuned over the electromagnetic spectrum by simply adjusting the shell thickness. Obtaining these particles, however, is a complex and time-consuming process, which involves the preparation and functionalization of silica nanoparticles, synthesis of very small metallic nanoparticles seeds, attachment of these seeds to the silica core, and, finally, growing of the shells in a solution commonly referred as K-gold. Here we present synthetic modifications that allow metallic nanoshells to be obtained in a faster and highly reproducible manner. The main improved steps include a procedure for quick preparation of 2.3 ± 0.5 nm gold particles and a faster approach to synthesize the silica cores. An investigation on the effect of the stirring speed on the shell growth showed that the optimal stirring speeds for gold and silver shells were 190 and 1500 rpm, respective...

Adsorption behavior of a human monoclonal antibody at hydrophilic and hydrophobic surfaces.

Abstract: One aspiration for the formulation of human monoclonal antibodies (mAb) is to reach high solution concentrations without compromising stability. Protein surface activity leading to instability is well known, but our understanding of mAb adsorption to the solid-liquid interface in relevant pH and surfactant conditions is incomplete. To investigate these conditions, we used total internal reflection fluorescence (TIRF) and neutron reflectometry (NR). The mAb tested ("mAb-1") showed highest surface loading to silica at pH 7.4 (~12 mg/m(2)), with lower surface loading at pH 5.5 (~5.5 mg/m(2), further from its pI of 8.99) and to hydrophobized silica (~2 mg/m(2)). The extent of desorption of mAb-1 from silica or hydrophobized silica was related to the relative affinity of polysorbate 20 or 80 for the same surface. mAb-1 adsorbed to silica on co-injection with polysorbate (above its critical micelle concentration) and also to silica pre-coated with polysorbate. A bilayer model was developed from NR data for mAb-1 at concentrations of 50-5000 mg/L, pH 5.5, and 50-2000 mg/L, pH 7.4. The inner mAb-1 layer was adsorbed to the SiO₂ surface at near saturation with an end-on" orientation, while the outer mAb-1 layer was sparse and molecules had a "side-on" orientation. A non-uniform triple layer was observed at 5000 mg/L, pH 7.4, suggesting mAb-1 adsorbed to the SiO₂ surface as oligomers at this concentration and pH. mAb-1 adsorbed as a sparse monolayer to hydrophobized silica, with a layer thickness increasing with bulk concentration - suggesting a near end-on orientation without observable relaxation-unfolding.

Optical characterization of aminosilane-modified silicon dioxide surface for biosensing

Abstract: Silicon dioxide surfaces, functionalized by two aminosilane compounds (3-amino-propyl-triethoxysilane, APTES; 3-amino-propyl-dimethylethoxysilane, APDMES) both dissolved in different solvents (dry ethanol and toluene), have been investigated by standard techniques such as spectroscopic ellipsometry (SE), water contact angle (WCA), and atomic force microscopy (AFM). Silane thicknesses between 5 and 80 A have been found, depending on deposition conditions; surface wettabilities change, accordingly. These organic-inorganic interfaces have also been modified by a cross-linker (bis-sulfosuccinimidyl suberate) in order to covalently bind a fluorescein labeled protein A. The amount of protein linked to functional surfaces has been quantified by SE and fluorescence microscopy. These results could be very useful in developing new platforms for optical biosensing.

Hydrogen-atom-mediated electrochemistry

Abstract: Silicon dioxide thin films are widely used as dielectric layers in microelectronics and can also be engineered on silicon wafers. It seems counterintuitive that electrochemical reactions could occur on such an insulator without relying on tunnelling current. Here we report electrochemistry based on electron transfer through a thin insulating layer of thermally grown silicon dioxide on highly n-doped silicon. Under a negative electrical bias, protons in the silicon dioxide layer were reduced to hydrogen atoms, which served as electron mediators for electrochemical reduction. Palladium nanoparticles were preferentially formed on the dielectric layer and enabled another hydrogen-atom-mediated electrochemistry, as their surfaces retained many electrogenerated hydrogen atoms to act as a 'hydrogen-atom reservoir' for subsequent electrochemical reduction. By harnessing the precisely controlled electrochemical generation of hydrogen atoms, palladium-copper nanocrystals were synthesized without any surfactant or stabilizer on the silicon dioxide layer.

Hydrophobic core/hydrophilic shell structured mesoporous silica nanospheres: enhanced adsorption of organic compounds from water.

Abstract: Inspired by the structure features of micelle, we attempt to synthesize a novel functionalized mesoporous silica nanosphere consisting of a hydrophobic core and a hydrophilic shell. The obtained solid materials were structurally confirmed by N2 sorption, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Their compositions were characterized by Fourier transfer infrared spectroscopy (FT-IR), solid state NMR, X-ray photoelectron spectroscopy (XPS), and elemental analysis. Its fundamental properties such as dispersibility in water or organic phase, wettability, and adsorption ability toward hydrophobic organics in water were investigated. It was revealed that these important properties could be facilely adjusted through varying structure and composition. In particular, these materials showed much better adsorption ability toward hydrophobic organic molecules in water than conventional monofunctionalized mesoporous materials, owing to possessing the hydrophobic/hydrophilic domain-segregated...

Sub 2-μm macroporous silica particles derivatized for enhanced lectin affinity enrichment of glycoproteins.

Abstract: A new, mechanically stable silica microparticle with macrosized internal pores (1.6 μm particles with 100 nm pores) has been developed for chromatography. The particles are characterized by an exte...

Synergistic gelation of silica nanoparticles and a sorbitol-based molecular gelator to yield highly-conductive free-standing gel electrolytes.

Abstract: Lithium-ion batteries have emerged as the preferred type of rechargeable batteries, but there is a need to improve the performance of the electrolytes therein. Specifically, the challenge is to obtain electrolytes with the mechanical rigidity of solids but with liquid-like conductivities. In this study, we report a class of nanostructured gels that are able to offer this unique combination of properties. The gels are prepared by utilizing the synergistic interactions between a molecular gelator, 1,3:2,4-di-O-methyl-benzylidene-d-sorbitol (MDBS), and a nanoscale particulate material, fumed silica (FS). When MDBS and FS are combined in a liquid consisting of propylene carbonate with dissolved lithium perchlorate salt, the liquid electrolyte is converted into a free-standing gel due to the formation of a strong MDBS-FS network. The gels exhibit elastic shear moduli around 1000 kPa and yield stresses around 11 kPa-both values considerably exceed those obtainable by MDBS or FS alone in the same liquid. At the same time, the gel also exhibits electrochemical properties comparable to the parent liquid, including a high ionic conductivity (~5 × 10(-3) S/cm at room temperature) and a wide electrochemical stability window (up to 4.5 V).

DNA adsorption to and elution from silica surfaces: influence of amino acid buffers.

Abstract: Solid phase extraction and purification of DNA from complex samples typically requires chaotropic salts that can inhibit downstream polymerase amplification if carried into the elution buffer. Amino acid buffers may serve as a more compatible alternative for modulating the interaction between DNA and silica surfaces. We characterized DNA binding to silica surfaces, facilitated by representative amino acid buffers, and the subsequent elution of DNA from the silica surfaces. Through bulk depletion experiments, we found that more DNA adsorbs to silica particles out of positively compared to negatively charged amino acid buffers. Additionally, the type of the silica surface greatly influences the amount of DNA adsorbed and the final elution yield. Quartz crystal microbalance experiments with dissipation monitoring (QCM-D) revealed multiphasic DNA adsorption out of stronger adsorbing conditions such as arginine, glycine, and glutamine, with DNA more rigidly bound during the early stages of the adsorption process. The DNA film adsorbed out of glutamate was more flexible and uniform throughout the adsorption process. QCM-D characterization of DNA elution from the silica surface indicates an uptake in water mass during the initial stage of DNA elution for the stronger adsorbing conditions, which suggests that for these conditions the DNA film is partly dehydrated during the prior adsorption process. Overall, several positively charged and polar neutral amino acid buffers show promise as an alternative to methods based on chaotropic salts for solid phase DNA extraction.

Nitric oxide-releasing silica nanoparticle-doped polyurethane electrospun fibers.

Abstract: Electrospun polyurethane fibers doped with nitric oxide (NO)-releasing silica particles are presented as novel macromolecular scaffolds with prolonged NO-release and high porosity. Fiber diameter (119-614 nm) and mechanical strength (1.7-34.5 MPa of modulus) were varied by altering polyurethane type and concentration, as well as the NO-releasing particle composition, size, and concentration. The resulting NO-releasing electrospun nanofibers exhibited ~83% porosity with flexible plastic or elastomeric behavior. The use of N-diazeniumdiolate- or S-nitrosothiol-modified particles yielded scaffolds exhibiting a wide range of NO release totals and durations (7.5 nmol mg(-1)-0.12 μmol mg(-1) and 7 h to 2 weeks, respectively). The application of NO-releasing porous materials as coatings for subcutaneous implants may improve tissue biocompatibility by mitigating the foreign body response and promoting cell integration.

The effect of TEOS plasma parameters on the silicon dioxide deposition mechanisms

Abstract: In this study, the effects of tetraethyl orthosilicate (TEOS) plasma parameters on the silicon dioxide deposition mechanisms are studied. The films are deposited by the organometallic based plasma enhanced chemical vapour deposition method. The plasma generator is capacitively coupled radio frequency power source. The plasma is the mixture of organometallic TEOS vapour, oxygen and argon. The effects of the TEOS/O 2 pressure ratio (0.05–1.5), the applied power (100–400 W) and the argon gas percentage into the plasma (0–20) on the quality of the film are investigated. The film properties such as structure and chemical composition, surface topography are analysed by Fourier transform infrared spectroscopy and atomic force microscopy. In addition, the relation between the mechanism of deposition phenomenon and the process parameters is studied. It is found that in the deposition process the oxidation and the electron impact mechanisms determine the film characteristics as they can be controlled by adjusting the TEOS/O 2 pressure ratio, applied power and argon gas percentage.

Reversible and Cyclical Transformations between Solid and Hollow Nanostructures in Confined Reactions of Manganese Oxide and Silica within Nanosized Spheres

Abstract: Annealing of MnO@SiO2 nanospheres in a reducing gas environment resulted in the transformation of the core–shell structure into a hollow structure as a result of outward diffusion of MnO species into the thermodynamically more stable silicate phase. When the hollow silicate nanospheres were oxidized, the interior cavities were refilled with a Mn3O4 phase segregated from the silicate phase, and the hollow structure reverted to the initial core–shell structure. More interestingly, when catalytically active Pt nanocrystals were introduced into the manganese oxide/silica system, the Mn3O4 was readily reduced to the chemically reactive MnO, even at low temperature, which enabled reconversion of the solid nanospheres with a Mn3O4 core to hollow nanostructures during reductive annealing. Therefore, when MnO@SiO2/Pt(II) nanospheres were subjected to an oxidation/reduction cycle by repeatedly switching the flowing gas between air and hydrogen, the nanospheres underwent a reversible change between solid and hollow ...

Anodes including mesoporous hollow silicon particles and a method for synthesizing mesoporous hollow silicon particles

Abstract: Anodes including mesoporous hollow silicon particles are disclosed herein. A method for synthesizing the mesoporous hollow silicon particles is also disclosed herein. In one example of the method, a silicon dioxide sphere having a silicon dioxide solid core and a silicon dioxide mesoporous shell is formed. The silicon dioxide mesoporous shell is converted to a silicon mesoporous shell using magnesium vapor. The silicon dioxide solid core, any residual silicon dioxide, and any magnesium-containing by-products are removed to form the mesoporous, hollow silicon particle.

Influences of Surface Charge, Size, and Concentration of Colloidal Nanoparticles on Fabrication of Self-Organized Porous Silica in Film and Particle Forms

Abstract: Studies on preparation of porous material have attracted tremendous attention because existence of pores can provide material with excellent performances. However, current preparation reports described successful production of porous material with only partial information on charges, interactions, sizes, and compositions of the template and host materials. In this report, influences of self-assembly parameters (i.e., surface charge, size, and concentration of colloidal nanoparticles) on self-organized porous material fabrication were investigated. Silica nanoparticles (as a host material) and polystyrene (PS) spheres (as a template) were combined to produce self-assembly porous materials in film and particle forms. The experimental results showed that the porous structure and pore size were controllable and strongly depended on the self-assembly parameters. Materials containing highly ordered pores were effectively created only when process parameters fall within appropriate conditions (i.e., PS surface charge ≤ -30 mV; silica-to-PS size ratio ≤0.078; and silica-to-PS mass ratio of about 0.50). The investigation of the self-assembly parameter landscape was also completed using geometric considerations. Because optimization of these parameters provides significant information in regard to practical uses, results of this report could be relevant to other functional properties.