Showing papers on "Silane published in 2008"

Attachment of 3-(Aminopropyl)triethoxysilane on Silicon Oxide Surfaces: Dependence on Solution Temperature

Abstract: Parameters important to the self-assembly of 3-(aminopropyl)triethoxysilane (APTES) on chemically grown silicon oxide (SiO2) to form an aminopropyl silane (APS) film have been investigated using in situ infrared (IR) absorption spectroscopy. Preannealing to ∼70 °C produces significant improvements in the quality of the film: the APS film is denser, and the Si−O−Si bonds between the molecules and the SiO2 surface are more structured and ordered with only a limited number of remaining unreacted ethoxy groups. In contrast, post-annealing the functionalized SiO2 samples after room temperature reaction with APTES (i.e., ex situ annealing) does not lead to any spectral change, suggesting that post-annealing has no strong effect on the horizontal polymerization as suggested earlier. Both IR and ellipsometry data show that the higher the solution temperature, the denser and thinner the APS layer is for a given immersion time. Finally, the APS layer obtained by preannealing the solution at 70 °C exhibits a better ...

How To Prevent the Loss of Surface Functionality Derived from Aminosilanes

Abstract: Aminosilanes are common coupling agents used to functionalize silica surfaces. A major problem in applications of 3-aminopropylsilane-functionalized silica surfaces in aqueous media was encountered: the loss of covalently attached silane layers upon exposure to water at 40 degrees C. This is attributed to siloxane bond hydrolysis catalyzed by the amine functionality. To address the issue of loss of surface functionality and to find conditions where hydrolytically stable amine-functionalized surfaces can be prepared, silanization with different types of aminosilanes was carried out. Hydrolytic stability of the resulting silane-derived layers was examined as a function of reaction conditions and the structural features of the aminosilanes. Silane layers prepared in anhydrous toluene at elevated temperature are denser and exhibit greater hydrolytic stability than those prepared in the vapor phase at elevated temperature or in toluene at room temperature. Extensive loss of surface functionality was observed in all 3-aminopropylalkoxysilane-derived layers, independent of the number and the nature of the alkoxy groups. The hydrolytic stability of aminosilane monolayers derived from N-(6-aminohexyl)aminomethyltriethoxysilane (AHAMTES) indicates that the amine-catalyzed detachment can be minimized by controlling the length of the alkyl linker in aminosilanes.

Superconductivity in hydrogen dominant materials: Silane

Abstract: The metallization of hydrogen directly would require pressure in excess of 400 gigapascals (GPa), out of the reach of present experimental techniques. The dense group IVa hydrides attract considerable attention because hydrogen in these compounds is chemically precompressed and a metallic state is expected to be achievable at experimentally accessible pressures. We report the transformation of insulating molecular silane to a metal at 50 GPa, becoming superconducting at a transition temperature of Tc = 17 kelvin at 96 and 120 GPa. The metallic phase has a hexagonal close-packed structure with a high density of atomic hydrogen, creating a three-dimensional conducting network. These experimental findings support the idea of modeling metallic hydrogen with hydrogen-rich alloy.

Surface modification of multi-walled carbon nanotubes using 3-aminopropyltriethoxysilane

Abstract: Multi-walled carbon nanotubes (MWCNTs) were functionalized via oxidation with a mixture of concentrated sulfuric acid and nitric acid. Thus functionalized nanotubes (f-MWCNTs) were silanized using a coupling agent, 3-Aminopropyltriethoxysilane (3-APTES). The f-MWCNTs and the reaction product of f-MWCNTs and 3-APTES (APTES–MWCNTs) were characterized by Fourier Transform Infrared Spectroscopy, Energy Dispersion Spectroscopy, Scanning Electron Microscopy, and Transmission Electron Microscopy. The results indicate the attachment of silane molecules on the surface of the functionalized MWCNTs. This silanization method allows for the improvement of the chemical compatibility of MWCNTs with specific polymers for application in nanotube-based polymer matrix composites.

Reverse microemulsion-mediated synthesis of silica-coated gold and silver nanoparticles.

Abstract: A reverse microemulsion method is reported for preparing monodispersed silica-coated gold (or silver) nanoparticles without the use of a silane coupling agent or polymer as the surface primer. This method enables a fine control of the silica shell thickness with nanometer precision. As compared to the Stober method reported for direct silica coating, which can only coat large gold particles (∼50 nm in diameter) at low concentrations (<1.5 × 1010 particles/mL), this new approach is capable of coating gold particles of a wide range of sizes (from 10 to 50 nm) at a much higher concentration (∼1.5 × 1013 particles/mL). Moreover, it enables straightforward surface functionalization via co-condensation between tetraethyl orthosilicate and another silane with the desired functional groups. The functional groups introduced by this method are readily accessible and thus useful for various applications.

Fabrication and interfacial modification of wood/recycled plastic composite materials

Abstract: In this study, wood/recycled plastic composite (WRPC) material was fabricated with post-consumer high density polyethylene (HDPE) and wood fiber using a single-screw extruder. To improve the interfacial adhesion between the wood fiber and the HDPE, a coupling agent, maleic anhydride modified polypropylene (MAPP), together with three surface treatments (an alkaline method, a silane method and an alkaline followed by silane method) were used to treat the wood fibers. The surface chemistry of the treated fibers was evaluated using FTIR techniques. The effects of wood fiber length, weight fraction and surface treatment on the mechanical properties of WRPC materials were investigated. Fracture surfaces of tested WRPC specimens were examined and the fracture mechanism of WRPC materials is also discussed in this paper. Test results indicate that WRPC material with wood fiber treated by the alkaline followed by silane treatment method together with the MAPP coupling agent possesses good mechanical properties. The content of wood fiber affects the flexural strength, flexural modulus, and impact strength of these WRPC materials.

Silane treatment of bagasse fiber for reinforcement of cementitious composites

Abstract: Silane coating of fibers is a promising process for improving durability and adhesion of vegetable fibers used as reinforcement material in a cementitious matrix. The work presented in this paper gives an insight into the effect of combining pyrolysis treatment with silane treatment. Indeed, this study focuses on silane treatment of unpyrolyzed and pyrolyzed sugar cane bagasse fibers with an alkyltrialkoxysilane (RSi(OR′)3), S1 or a dialkyldialkoxysilane (R2Si(OR″)2), S2. The silane solutions used vary from 0.5% to 8% by volume. This paper describes the effect of two silane compounds on parameters such as the porosity, dimension, morphology and hygroscopic character of silane-coated sugar cane bagasse fibers. Preliminary studies on natural fiber reinforced composite setting time show the importance of the silane chemistry/structure, for fiber treatments with silane solution containing up to 6% (volume percent) silane. In the case of composites reinforced with unpyrolyzed bagasse fibers, setting time increases with silane coating. Combining pyrolysis and silane treatment improve the water resistance of the fibers, which become more hydrophobic.

Thermal and Mechanical Properties of Wood Flour/Talc-filled Polylactic Acid Composites: Effect of Filler Content and Coupling Treatment:

Abstract: Wood flour (WF) and talc-filled polylactic acid (PLA) composites are prepared by melt compounding and injection molding. The effects of filler loading and silane treatment, the thermal and mechanical properties of the composites are studied. Loading of WF and WF/talc mixture into neat PLA results in a small decrease in the glass transition and crystalline temperatures of the composites. The use of WF, talc and silane in the composites causes successively larger decreased in the composite crystallinity. The addition of talc and silane to PLA/WF composites improved the tensile modulus. The tensile strength of the composites decreases slightly with the addition of talc, but it considerably improves with the use of 1 wt% silane. Morphological analysis shows improved interfacial bonding with silane treatment for the composites.

Pressure-induced metallization of silane

Abstract: There is a great interest in electronic transitions in hydrogen-rich materials under extreme conditions. It has been recently suggested that the group IVa hydrides such as methane (CH4), silane (SiH4), and germane (GeH4) become metallic at far lower pressures than pure hydrogen at equivalent densities because the hydrogen is chemically compressed in group IVa hydride compounds. Here we report measurements of Raman and infrared spectra of silane under pressure. We find that SiH4 undergoes three phase transitions before becoming opaque at 27–30 GPa. The vibrational spectra indicate the material transforms to a polymeric (framework) structure in this higher pressure range. Room-temperature infrared reflectivity data reveal that the material exhibits Drude-like metallic behavior above 60 GPa, indicating the onset of pressure-induced metallization.

Printable cross-linked polymer blend dielectrics. Design strategies, synthesis, microstructures, and electrical properties, with organic field-effect transistors as testbeds

Abstract: We report here the synthesis and dielectric properties of optimized, cross-linked polymer blend (CPB) dielectrics for application in organic field-effect transistors (OFETs). Novel silane cross-linking reagents enable the synthesis of CPB films having excellent quality and tunable thickness (from 10 to ∼500 nm), fabricated both by spin-coating and gravure-printing. Silane reagents of the formula X3Si−R−SiX3 (R = −C6H12− and X = Cl, OAc, NMe2, OMe, or R = −C2H4−O−C2H4− and X = OAc) exhibit tunable reactivity with hydroxyl-containing substrates. Dielectric films fabricated by blending X3Si−R−SiX3 with poly(4-vinyl)phenol (PVP) require very low-curing temperatures (∼110 °C) and adhere tenaciously to a variety of FET gate contact materials such as n+−Si, ITO, and Al. The CPB dielectrics exhibit excellent insulating properties (leakage current densities of 10−7 ∼ 10−8 A cm−2 at 2.0 MV/cm) and tunable capacitance values (from 5 to ∼350 nF cm−2). CPB film quality is correlated with the PVP-cross-linking reagent ...

Control of gold surface diffusion on Si nanowires

Abstract: Silicon nanowires (NW) were grown by the Vapour-Liquid-Solid (VLS) mechanism using gold as the catalyst and silane as the precursor. In this work we show that the diffusion of gold from the catalyst particle over the wire sidewalls can be controlled by adjusting growth parameters: partial silane pressure and growth temperature. The diameter of the NWs has also an effect. Gold diffusion results in the formation of gold clusters on the wire sidewalls (Figure 1). High Angle Annular Darkfield Scanning Transmission Electron Microscopy (HAADF STEM) and Scanning Electron Microscopy (SEM) were used to observe the presence or absence of gold clusters on the wire sidewall. In literature an influence of oxygen on the gold diffusion can be found [1].

Patterned epitaxial vapor-liquid-solid growth of silicon nanowires on Si(111) using silane

Abstract: We have carried out a detailed study on the vapour-liquid-solid growth of silicon nanowires (SiNWs) on (111)-oriented Si substrates using Au as catalytic seed material Arrays of individual seeds were patterned by electron-beam lithography, followed by Au evaporation and lift-off SiNWs were grown using diluted silane as precursor gas in a low-pressure chemical vapor deposition system The silane partial pressure, substrate temperature, and seed diameter were systematically varied to obtain the growth rate of the NWs and the rate of sidewall deposition Activation energies of 19kcal∕mol for the axial SiNW growth and 29kcal∕mol for the radial deposition on the SiNW surface are derived from the data SiNW growth at elevated temperatures is accompanied by significant Au surface diffusion, leading to a loss of Au from the tips of the SiNWs that depends on the layout and density of the Au seeds patterned In contrast to NWs grown from a thin-film-nucleated substrate, the deterministic patterning of identical A

Free‐radical‐promoted cationic photopolymerization under visible light in aerated media: New and highly efficient silane‐containing initiating systems

Abstract: New systems for the visible-light-induced polymerization of cationic resins working through a free-radical-promoted process are presented They are based on a photoinitiator (camphorquinone, isopropylthioxanthone, Eosin), a silane, and a diphenyl iodonium salt, the new compound being the silane The overall efficiency is strongly affected by the silane structure The rates of polymerization and final percent conversion are noticeably higher than those obtained in the presence of already studied reference systems Moreover, contrary to previously investigated free-radical-promoted cationic polymerizations, oxygen does not inhibit the process and an unusual enhancement of the polymerization kinetics is found in aerated conditions: such an observation seems to have never been reported so far The excited state processes and the role of oxygen as revealed by laser flash photolysis are discussed The particular behavior of the silyl radicals is outlined

Postassembly chemical modification of a highly ordered organosilane multilayer: new insights into the structure, bonding, and dynamics of self-assembling silane monolayers.

Abstract: Experimental evidence derived from a comprehensive study of a self-assembled organosilane multilayer film system undergoing a process of postassembly chemical modification that affects interlayer-located polar groups of the constituent molecules while preserving its overall molecular architecture allows a quantitative evaluation of both the degree of intralayer polymerization and that of interlayer covalent bonding of the silane headgroups in a highly ordered layer assembly of this type. The investigated system consists of a layer-by-layer assembled multilayer of a bifunctional n-alkyl silane with terminal alcohol group that is in situ converted, via a wet chemical oxidation process conducted on the entire multilayer, to the corresponding carboxylic acid function. A combined chemical-structural analysis of data furnished by four different techniques, Fourier transform infrared spectroscopy (FTIR), synchrotron X-ray scattering, X-ray photoelectron spectroscopy (XPS), and contact angle measurements, demonst...

Inorganic/Organic Hybrid Silica Nanoparticles as a Nitric Oxide Delivery Scaffold.

Abstract: The preparation and characterization of nitric oxide (NO)-releasing silica particles formed following the synthesis of N-diazeniumdiolate-modified aminoalkoxysilanes are reported. Briefly, an aminoalkoxysilane solution was prepared by dissolution of an appropriate amount of aminoalkoxysilane in a mixture of ethanol, methanol, and sodium methoxide (NaOMe) base. The silane solution was reacted with NO (5 atm) to form N-diazeniumdiolate NO donor moieties on the aminoalkoxysilanes. Tetraethoxy- or tetramethoxysilane (TEOS or TMOS) was then mixed with different ratios of N-diazeniumdiolate-modified aminoalkoxysilane (10–75 mol %, balance TEOS or TMOS). Finally, the silane mixture was added into ethanol in the presence of an ammonia catalyst to form NO donor silica nanoparticles via a sol–gel process. This synthetic approach allows for the preparation of NO delivery silica scaffolds with remarkably improved NO storage and release properties, surpassing all macromolecular NO donor systems reported to date with r...

High-rate deposition of microcrystalline silicon p-i-n solar cells in the high pressure depletion regime

Abstract: Hydrogenated microcrystalline silicon films (μc-Si:H) deposited at high deposition rates (∼2 nm/s) by means of the very-high-frequency (VHF) deposition technique in the high pressure depletion regime have been integrated into single junction p-i-n solar cells. It is demonstrated that μc-Si:H solar cells can be optimized using a twofold approach. First the bulk properties, deposited under steady-state plasma conditions, are optimized by monitoring the presence of crystalline grain boundaries in μc-Si:H. These hydrogenated crystalline grain boundaries can easily be detected via the crystalline surface hydrides contribution to the narrow high stretching modes by infrared transmission spectroscopy. The crystalline grain boundaries suffer from postdeposition oxidation which results in a reduced red response of the solar cell. The absence of these crystalline surfaces in an as-deposited μc-Si:H matrix reflects the device grade microcrystalline bulk material. Second, the prevention of silane backdiffusion from t...

Reduction of Ketones with Hydrocarbon-Soluble Calcium Hydride: Stoichiometric Reactions and Catalytic Hydrosilylation

Abstract: Reactions of the dimeric calcium hydride complex[(DIPP-nacnac)CaH·thf]2 {1; DIPP-nacnac = CH[(CMe)(2,6-iPr2C6H3N)]2} with the α-hydrogen containing ketones acetophenone, acetone, dibenzylketone and 2-adamantone are smooth. In most cases not only addition but also substantial enolization is observed as a side reaction and in some cases also aldol condensation was found. Despite this unselectivity, the addition products could be isolated crystalline pure. Crystal structures of [(DIPP-nacnac)CaOCH(Me)Ph]2 (3), [(DIPP-nacnac)CaOCH(CH2Ph)2]2 (6) and [(DIPP-nacnac)Ca(2-adamantoxide)]2 (7) have been determined. The calcium hydride complex 1 is an effective catalyst in the hydrosilylation of ketones. Independent from the silane/ketone ratio, a strong preference for formation of bis-alkoxy silanes [PhSiH(OR)2] is observed. In most cases no enoxy groups have been found in the product. This indicates that the mechanism does not involve addition of the calcium hydride to the ketone functionality. A concerted addition of silane to ketone through a six-coordinate hypervalent silicon intermediate is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)