Organosilane Sources Research Articles

Approach to achieve controlled particle size synthesis of non-polar functionalised siloxane particles using a one-pot synthesis

The homogeneous addition of functional silanes dissolved in a co-solvent such as ethanol has been shown to change particle growth mechanisms as well as control over particle size and dispersity, especially for non-polar silanes. Highly monodisperse size-controlled silica particles from 50 to over 1000 nm bearing thiol, vinyl, phenyl, propyl, cyanopropyl and chloropropyl R group functionality were synthesised directly from the corresponding single organosilane source. Observing particle growth over time revealed that it proceeded by a conventional Stöber process, where silane monomers and oligomers add to nucleation sites, resulting in particle growth. Scale-up of the homogeneous mixing approach produced gram quantities of particles without affecting size, size dispersion or functionality under good mixing. The presence and functionality of the surface R groups were confirmed by a simple second addition of reactive molecules to the particle synthesis liquor, resulting in theoretical maximum attachment densities.

A one-step co-condensation method for the synthesis of well-defined functionalized mesoporous SBA-15 using trimethallylsilanes as organosilane sources.

A new method for the preparation of well-defined functionalized mesoporous SBA-15 has been developed by a one-step co-condensation method using trimethallylsilanes as organosilane sources. This new method enables the incorporation of various bulky organic functional groups with long alkyl chain tethers into the mesoporous silica network.

Synthesis, characterization and reactive separation activity of acid-functionalized silicalite-1 catalytic membrane in m-xylene isomerization

Propylsulfonic acid-functionalized silicalite-1 membrane and arenesulfonic acid-functionalized silicalite-1 membrane were synthesized over α-alumina support via one-step in situ hydrothermal crystallization and subsequent post-synthesis modification. Propylsulfonic acid-functionalized silicalite-1 membrane was synthesized using 3-mercaptopropyltrimethoxysilane (3MP) as an organosilane source whereas for arenesulfonic acid silicalite-1 membrane, phenethyltrimethoxysilane (PE) was used as an organosilane source. The acid capacity of the membrane was varied by adjusting the concentration of organosilane from 5 mol% to 20 mol%. The membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen gas permeation. Ammonia temperature-programmed desorption (NH 3-TPD) and Fourier transform infrared spectroscopy (FT-IR) showed the presence of strong Brönsted acid sites in both membranes. The total acid capacity increased with increase in organosilane concentration in the synthesis mixture. Both membranes were tested for their catalytic activity in m-xylene isomerization reaction in the temperature range of 355–450 °C. Due to higher acid density, arenesulfonic acid-functionalized silicalite-1 membrane gave higher catalytic activity compared to propylsulfonic acid-functionalized silicalite-1 membrane. At 450 °C, m-xylene conversion of 57% with 33% p-xylene yield was achieved using arenesulfonic acid-functionalized silicalite-1 membrane with 15 mol% of phenethyltrimethoxysilane, while m-xylene conversion of 46% with 28% p-xylene yield was achieved using propylsulfonic acid-functionalized silicalite-1 membrane with 15 mol% of 3-mercaptopropyltrimethoxysilane. The enhancement in p-xylene yield was due to the simultaneous isomerization reaction and separation of the reaction products through the catalytic membrane. Both catalytic membranes exhibited good structural stability after subjected to isomerization reaction study for 120 h.

Propylsulfonic acid-functionalized partially crystalline silicalite-1 materials: synthesis and characterization

Propylsulfonic acid-functionalized partially crystalline silicalite-1 materials were synthesized via one step co-condensation technique by varying the molar ratio of organosilane source, 3-mercaptopropyltrimethoxysilane (3MP) to tetraethylorthosilicate (TEOS) in the range of 0.05–0.30, and subsequent oxidation of thiol group to propylsulfonic acid using hydrogen peroxide (H2O2). These materials were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and nitrogen adsorption–desorption method. The structure of these materials was determined by Fourier transform infrared spectroscopy (FT-IR) and 29Si and 13C solid state NMR. XRD results show that % crystallinity of the materials decreased with the increase in 3MP concentration in the synthesis mixture. Selected area electron diffraction (SAED) showed the presence of crystalline and amorphous phases in the samples. An amorphous phase was formed when 3MP concentration was 30 mol% of the total silica source. After elimination of the structure directing agent (SDA) by calcination at 420 °C, thermogravimetric analysis (TGA) shows that the structure was thermally stable up to 550 °C. Ammonia temperature-programmed desorption (NH3-TPD) shows that the acid capacity of these materials was in the range of 1.19–1.83 mmol H+/g, which shows that these materials could be used as potential heterogeneous acid catalyst.

Synthesis, structure and acid characteristics of partially crystalline silicalite-1 based materials

A series of partially crystalline silicalite-1 based materials were synthesized by varying the molar ratio of organosilane source, phenethyltrimethoxysilane (PE) to tetraethylorthosilicate (TEOS) in the range of 0.05–0.50, using one step co-condensation hydrothermal synthesis method. The phenethyl group was subsequently sulfonated to arenesulfonic acid group following strong acid treatment. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and desorption and elemental analysis. The structure of these materials was determined by Fourier transform infrared spectroscopy (FTIR), 29Si and 13C solid state NMR. The % crystallinity of the partially crystalline silicalite-1 as determined from XRD was in the range of 33–73%. The average crystallite size decreased with the increase of PE concentration in the synthesis mixture. The thermogravimetric analysis shows that the structures were thermally stable up to 550 °C after elimination of the structure directing agents (SDAs) by calcination at 420 °C. The acid capacities of these materials ranged from 2.52 to 6.63 mmol H +/g.

Improving Adsorbent Properties of Cage-like Ordered Amine Functionalized Mesoporous Silica with Very Large Pores for Bioadsorption

In this paper, we report the successful synthesis of amine-functionalized FDU-12-type mesoporous silica with a very large pore (30.2 nm) and a highly ordered mesostructure by using 3-aminopropyltriethoxysilane (APTES) as an organosilane source. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements confirmed that the materials possessed a face-centered cubic (space group Fm3m) mesostructure. Different techniques were used to obtain a significant pore and entrance size enlargement: low synthesis temperature and high hydrothermal treatment temperature. The amount of amine organosilane influenced the mesostructure of the mesoporous silica. It was found that the addition of inorganic salt (KCl) could help to maintain an ordered structure of the large pore mesoporous material. X-ray photoelectron spectroscopy (XPS), solid-state magic-angle spinning (MAS) 13C nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) verified the incorporation of amine functional groups on the surface of the materials. The addition of amine organosilane extended the synthesis temperature domain of ordered FDU-12 materials. The amine functional group significantly enhanced the adsorption capacity of the mesoporous materials, e.g., the amine functionalized mesoporous silica had 8-fold higher bovine serum albumin (BSA) adsorption capacity than that of the unfunctionalized one. It also had 2 times higher adsorption capacity for large cellulase enzymes. The amine functional group introduced positively charged groups on the surface of the mesoporous silica, which created strong electrostatic interactions between the protein and the silica.

Spectroscopic Ellipsometry of 3C-SiC Thin Films Grown on Si Substrates Using Organosilane Sources

Dielectric function spectra of 3C-SiC films on Si substrates in the energy region of 0.73–6.43 eV were measured by spectroscopic ellipsometry. Hexamethyldisilane (Si2(CH3)6) and tetraethylsilane (Si(C2H5)4) were used as safe organosilane sources for the growth of SiC films. The measured spectra were compared with those of 3C-SiC on a Si(001) substrate grown with disilane (Si2H6). First, the pseudodielectric function spectra gave a shoulder structure corresponding to the direct X5–X1 interband transition in the Brillouin zone. Secondly, the dielectric function of 3C-SiC was determined by applying a four-layer model in which we took into account the surface roughness and mixed crystals of a carbonized interface layer. Finally, the third-derivative lineshape of the imaginary part ε2 of the complex-dielectric function provided the values of the interband transition energy Eg and the broadening parameter Γ for the X5–X1 interband transition. The measured values of Γ indicated that the crystalline quality of SiC films grown using organosilane sources is comparable to that of SiC films grown using Si2H6.

Epitaxial Growth of 3C-SiC on Si(111) Using Tetraethylsilane and Prevention of Void Formation at Heterointerfaces

The surface morphology and crystalline quality of 3C-SiC films on Si(111) substrates were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy, where tetraethylsilane (TES, Si(C2H5)4) was first used as a safety source for the growth of SiC films. While TES was expected to be the safest in various organosilane sources, it was essentially anticipated that the high C/Si ratio in TES results in deposition of carbon-rich SiC films, preventing single crystal formation. In raising the temperature after carbonization, voids appeared at the interface of SiC/Si, causing the formation of hillocks on the grown SiC films. The formation of voids and hillocks was prevented by adjusting the TES flow rate and time in the heating process to the growth temperature, leading to the growth of SiC films with a good surface morphology. As a result, it was shown that single crystal epitaxial films could be obtained in the growth of SiC films using TES, and yet a high density of stacking faults resided at the SiC/Si interface.

二段階プラズマプロセスによる超はっ水高分子基板の作製

The wettability of a solid surface is governed by two factors, that is, its surface morphology and composition. Ultra water-repellent polymeric substrates [poly(ethylene naphthalate) and polystyrene] have been fabricated while retaining their transparency by a two-step plasma process combining oxygen plasma etching and plasma-enhanced chemical vapor deposition (PECVD). In order to avoid optical scattering, appropriate nanotextures were prepared on the polymeric substrates through the oxygen plasma etching. Subsequently, a hydrophobic layer was coated on the nanotextured surfaces by PECVD using an organosilane source. The modified surfaces were certainly ultra-water-repellent, showing water contact angles greater than 150°.

Epitaxial Growth of 3C-SiC on Si(111) Using Hexamethyldisilane and Tetraethylsilane

Hexamethyldisilane (HMDS, Si2(CH3)6) and tetraethylsilane (TES, Si(C2H5)4) were used as safe organosilane sources for the chemical vapor deposition of SiC films on Si(111) substrates. The surface morphology and crystalline quality of SiC films were investigated. On increasing temperature in H2 ambient after carbonization, voids appeared at the interface of SiC/Si causing the formation of hillocks on the grown SiC films. The formation of voids was prevented by supplying C3H8 and HMDS or TES during the heating process to the growth temperature, leading to the growth of SiC films with a good surface morphology. In the case of TES, the excess carbon incorporated in the film due to the high C/Si ratio was removed by reducing TES flow rate. It was found that the control of the flow rate of organosilane sources during heating plays a vital role in the formation of a high-quality SiC film with a smooth surface.

Properties of a-Si 1 −x C x:H thin films deposited from the organosilane Triethylsilane

We deposited carbon-rich a-Si 1 −x C x :H thin films from the liquid organosilane source Triethylsilane (C 2 H 5) 3-Si–H (TrES) in a PECVD process at 13.56 MHz. These films generally show a photoluminescence in the visible spectral range when excited with ultraviolet light. By increasing the substrate temperature from room temperature up to 300°C we can red shift the PL peak energy and also the optical Tauc gap. Furthermore, an increase in the film density and correspondingly in the refractive index is observed. FTIR measurements show that these films have a polymer–like character for all temperatures under investigation. The hydrogen concentration is calculated from the stretching modes of CH n and SiH n groups, respectively, and is shown to decrease with substrate temperature. We also show that the amount of hydrogen bonded to carbon decreases with respect to that bonded to silicon with substrate temperature.

Influence of thermal annealing on the ultraviolet stability of a-SiC:H thin films deposited from liquid organosilanes

The photoluminescence (PL) of a-SiC:H thin films, deposited in a plasma enhanced chemical vapor deposition process from liquid organosilane sources degrades under ultraviolet (UV) exposure (325 nm). UV illumination reduces the PL intensity of as-grown films usually to one-half of the initial intensity. The UV-induced decay of the PL follows a stretched exponential time dependence. Annealing of the films at about 400°C in nitrogen atmosphere increases both the UV stable and the unstable part of the PL, by a factor 1.5 to 3 dependent on the starting material. We have investigated the annealing behaviour for different starting materials. Best results with respect to reproducible UV-stable PL are obtained for hexamethyldisilazane. Infrared absorption spectra indicate that the UV exposure is accompanied by photo-oxidation, while annealing in inert gas atmosphere results in a decrease of hydrogen-related vibrations. We discuss the structural changes in the a-SiC:H thin films caused by UV illumination and by thermal annealing on the basis of the spectroscopic investigations.

Light generation and transportation in luminescent a-SiC:H thin film waveguides

Carbon-rich films were deposited from liquid organosilane sources tetramethylsilane (TMS), hexamethyldisilane (HMDS) and hexamethyldisilazane (HMDSN). These films generally show efficient photoluminescence (PL) at room temperature (RT), when excited with ultraviolet (UV) light. For certain preparation conditions the self-absorption in the low energy wing of the PL can be reduced below 1 cm −1. This property together with a sufficiently high index of refraction allows for a waveguide operation mode, where the guided light is generated in the waveguide itself via PL. Particularly, a thermal post-treatment of the deposited films has a major influence on the self-absorption and on the PL.