Modification Of SiO Research Articles

Controlled, Low-Coverage Metal Oxide Activation of Silicon for Organic Functionalization: Unraveling the Phosphonate Bond

Deposition of thin films and grafting of organic molecules on semiconductor surfaces, particularly oxide surfaces, are widely studied as means of passivation and functionalization for a variety of applications. However, organic functionalization of silicon oxide is challenging, as the currently used molecules (silanes and phosphonates) do not form layers that are stable in aqueous environments and present challenges during the grafting process. For instance, the chemical grafting of phosphonates requires high temperature (140 °C) to perform. Modification of SiO(2) surfaces with metal oxides is an attractive alternative since strong bonds can be established between metal oxides and relevant molecules (silanes, phosphonates). While such modification is possible using vapor-phase methods, such as atomic layer deposition and physical vapor-phase deposition, wet chemical processing is inexpensive and technologically very attractive. We describe here a simple wet chemical method to deposit an ultrathin layer of metal oxide/hydroxide groups. Further, using a model surface with exactly one-third monolayer OH groups on oxide-free Si surfaces, the precise adsorption geometry on single Al(OH)(3) groups is shown to be bidentate, and the distance between the Al and P atoms is determined to be the main influencing parameter for a thermodynamically stable formation of the Al-O-P bond.

Swift heavy ion-induced silicon dioxide nanostructuration: experimental observation of velocity effect

Thanks to atomic force microscope observation of swift heavy ion-induced structural modifications of SiO 2 -Si layer, we show that for a given linear energy transfer value the radial atomic modification along the ion track depends on the ion velocity regime.

Application of liquid phase deposition method for preparation of Co/ZrO x/SiO 2 catalyst with enhanced Fischer–Tropsch synthesis activity: Importance of Co–Zr interaction

Liquid phase deposition (LPD) method using (NH 4) 2ZrO(CO 3) 2 was applied to modifying chemical nature of SiO 2 surface with ZrO x species. ZrO x -modified SiO 2 was then impregnated with Co nitrate solution for preparation of Co/ZrO x /SiO 2 catalysts with 5 and 20 mass% Co loadings. Modification of SiO 2 surface with ZrO x using the LPD method enhanced FTS activity of the Co/ZrO x /SiO 2 catalysts under the reaction conditions of 503 K and 1.1 MPa. The LPD method was superior to other method reported previously such as impregnation and sol–gel methods in terms of surface modification of SiO 2 with ZrO x . H 2-TPR, XRD and hydrogen chemisorption measurements revealed that modification of SiO 2 surface with ZrO x using the LPD method enhanced dispersion of Co 0 without loss of high reducibility of Co. However, degree of Co 0 dispersion was less than that expected from enhancement of activity for the catalysts induced by ZrO x modification, indicating that turnover frequency (TOF) increased in the presence of ZrO x . This effect was particularly important for the catalyst with the low Co loading. Furthermore, in situ DRIFT measurement provided evidence for the formation of specific interaction of Co species with Si–OH and Zr–OH species in the Co/ZrO x /SiO 2 catalysts. It was suggested that the formation of such specific interaction was responsible for not only enhancement of Co 0 dispersion but also increase in TOF of the ZrO x modified catalysts.

SYNTHESIS OF 3-HEXANOYLTHIO-1-PROPYLTRIETHOXYSILANE AND ITS COUPLING EFFECT ON SOLUTION POLYMERIZED STYRENE-BUTADIENE RUBBER/SILICA COMPOUNDS

A novel coupling agent,3-hexanoylthio-1-propyltriethoxysilane(HXT),was synthesized through the reaction of 3-triethoxysiyl-1-propanethiol and hexanoyl chloride.HXT or bis-(triethoxysilylpropyl)disulfide(TESPD)as coupling agent were incorporated into solution polymerized styrene-butadiene rubber(SSBR)/silica(SiO_2)compounds.Dynamic rheological properties of the compounds were investigated by using an advanced rheomitric expended system(ARES).It is found incorporation of silane coupling agent into SSBR/SiO_2 compounds improved the elastic properties and wakened the Payne effect due to the surface modification of SiO_2 particles and the improved dispersion of the particles in the SSBR matrix.Compared with TESPD,HXT provides rubber compounds with higher critical strain value of Payne effect and lower storage modulus.In this aspect,HXT performs better than TESPD.This might be attributed to the combined effects of better rubber-filler interaction and better filler dispersion which are obtained when TESPD is replaced with HXT.

Fabrication of protein-anchoring surface by modification of Sio 2 with liposomal bilayer

SiO 2 surface was successfully modified with phospholipid bilayer for biocompatibility by covering the planar surface with vesicular liposomes. By applying heat to rupture the vesicle, they were converted into a planar form. To effectively decorate the bilayer with biological molecules such as a protein, BAM (biological anchor for membrane) was used as a linker. It is a linear assembly consisting of oleyl chain, polyethylene glycol, and NHS (N-hydroxysuccinimide). After a target protein (BSA) was conjugated with BAM by NHS replacement, the conjugate was effectively inserted to the phospholipid bilayer through the lipophilic interaction between the oleyl chain and the lipid bilayer. The entire process was monitored and quantitatively analyzed by QCM (quartz crystal microbalance). BSA–BAM conjugate showed approximately 12-fold higher binding efficiency to the lipid bilayer than BSA alone. From this result, we conclude that SiO 2 surface could be modified to a lipid bilayer surface so as to anchor a protein by the action of BAM.

Characterization of modified carbon paste electrode by using Salen Schiff base ligand immobilized on SiO 2–Al 2O 3 as a highly sensitive sensor for anodic stripping voltammetric determination of copper(II)

The wish of this work is to develop a Schiff base ligand covalently linked onto the SiO 2–Al 2O 3 mixed-oxide as a new modifier of carbon paste electrode for highly sensitive voltammetric determination of copper(II). It is also an easy and inexpensive way for determination of copper(II). For the preliminary screening purpose, the Schiff base ligand was prepared by modification of SiO 2–Al 2O 3 mixed-oxide and characterized by TG, CHN elemental analysis and FT-IR spectroscopy. Linear response to copper(II) was found in the 3.4 × 10 −10–3.3 × 10 −7 mol L −1 ( r 2 = 0.9994) concentration range, with a detection limit estimated at 1.8 × 10 −10 mol L −1 (3 S b/ m). The multiple determinations ( n = 3) of copper(II) in the concentration of 5.0 × 10 −4, 1.8 × 10 −5, 2.0 × 10 −7 and 1.0 × 10 −8 mol L −1, following a preconcentration detection–regeneration cycle, displayed a relative standard deviation of lower than 1.07%. The developed sensor could also be used to determine the copper(II) in tap water and real samples. The copper content of the samples were comparable with the results obtained through AAS method.

High selective SiO 2–Al 2O 3 mixed-oxide modified carbon paste electrode for anodic stripping voltammetric determination of Pb(II)

The main purpose of this study is to develop an inexpensive, simple, selective and especially highly selective modified mixed-oxide carbon paste electrode (CPE) for voltammetric determination of Pb(II). For the preliminary screening purpose, the catalyst was prepared by modification of SiO 2–Al 2O 3 mixed-oxide and characterized by TG, CHN elemental analysis and FTIR spectroscopy. Using cyclic voltammetry the electroanalytical characteristics of the catalyst have been determined, and consequently the modified mixed-oxide carbon paste electrode was constructed and applied for determination of Pb(II). The electroanalytical procedure for determination of the Pb(II) comprises two steps: the chemical accumulation of the analyte under open-circuit conditions followed by the electrochemical detection of the preconcentrated species using differential pulse anodic stripping voltammetry. During the preconcentration step, Pb(II) was accumulated on the surface of the modifier by the formation of a complex with the nitrogen atoms of the pyridyl groups in the modifier. The peak currents increases linearly with Pb(II) concentration over the range of 2.0 × 10 −9 to 5.2 × 10 −5 mol L −1 ( r 2 = 0.9995). The detection limit (three times signal-to-noise) was found to be 1.07 × 10 −9 mol L −1 Pb(II). The chemical and instrumental parameters have been optimized and the effect of the interferences has been determined. The Proposed method was used for determination of lead ion in the real samples.

Scanning spreading resistance microscopy of defect engineered low dose SIMOX samples

Modification of SiO 2 precipitate formation by defect engineering of SIMOX (separation by implanted oxygen) process was studied using cross section scanning spreading resistance microscopy (SSRM). Firstly, open volume defects, nanocavities, have been introduced by He + ion implantation in the region, where SiO 2 precipitates were subsequently formed. Secondly, dual (simultaneous) oxygen (O +) and silicon (Si +) implantation was used to modify SiO 2 reaction kinetics too. The results show that the He-induced nanocavities enhance the SiO 2 formation presumably releasing excess strain associated with Si oxidation, while the use of a dual O +/Si + beam do not influence significantly the oxidation kinetics in the initial state of the SIMOX process in our samples. Overall, SSRM was shown to be a suitable method for observation of the early stage of buried oxide formation in Si, since it measures the local resistivity, the main functional parameter of a SIMOX structure.

Catalytic Performance of Noble Metals Supported on Alumina-modified Silica Gel for Hydrodesulfurization Reaction

The catalytic activities and properties of noble metals (Pt, Pd, Rh, Ru) supported on silica gel (SiO 2 ) and alumina-modified silica gel (Al 2 O 3 -SiO 2 ) were investigated for the hydrodesulfurization of thiophene. Al 2 O 3 -SiO 2 was prepared by an impregnation method using aluminum nitrate (Al(NO 3 ) 3 · 9H 2 O) aqueous solution. Pt/ 8 wt%Al 2 O 3 -SiO 2 catalyst showed the highest activity for hydrodesulfurization of thiophene among various supported noble metal catalysts and this activity was higher than that of commercial CoMo/Al 2 O 3 hydrodesulfurization catalyst. The sulfur tolerance of noble metal/SiO 2 was enhanced by Al 2 O 3 modification of SiO 2 and Pt/8 wt%Al 2 O 3 -SiO 2 catalyst showed the highest sulfur tolerance among the supported noble metal catalysts. Pt/ 8 wt%Al 2 O 3 -SiO 2 catalyst had high hydrogenating ability for unsaturated C 4 hydrocarbons formed in the hydrodesulfurization of thiophene. The catalysts were characterized by 2-propanol dehydration, cumene cracking, XRD, H 2 adsorption and FT-IR. Dispersion of Pt on 8 wt%Al 2 O 3 -SiO 2 was remarkably higher than that on SiO 2 and the particle size of Pt on 8 wt%Al 2 O 3 -SiO 2 was the lowest among the supported noble metal catalysts. The acidity of 8 wt%Al 2 O 3 -SiO 2 was higher than that of SiO 2 . Furthermore, Bronsted acid sites were present on 8 wt%Al 2 O 3 -SiO 2 . FT-IR spectroscopy of thiophene adsorbed on 8 wt%Al 2 O 3 -SiO 2 support indicated that the thiophene molecule interacts with the Bronsted acid site on 8 wt%Al 2 O 3 -SiO 2 . The activity of the double-layer (Pt/SiO 2 + 8 wt%Al 2 O 3 -SiO 2 ) catalyst obtained experimentally was higher than that calculated. This suggests that spillover hydrogen was present on Pt/Al 2 O 3 -SiO 2 in the hydrodesulfurization of thiophene. Both the Bronsted acid sites of Al 2 O 3 -SiO 2 and the Pt particles in the Pt/Al 2 O 3 -SiO 2 catalyst act as active sites for the hydrodesulfurization of thiophene.

Etch Rate Modification of SiO[sub 2] by Ion Damage

Increased etch rate for implanted oxide with boron, phosphorus, arsenic, and argon is characterized for aqueous and vapor hydrofluoric acid (HF). Destruction by implantation of Si-O bonds makes oxide more reactive to HF. Water being reaction product and catalyst for oxide etching, its amount controls the reaction kinetic. In aqueous solution selectivity of four between implanted and unimplanted oxide is reached but increases up to 200 in vapor HF. In the case of HF etching under vapor phase the generated water increases the etch rate. This technique opens many process possibilities such as etch stop layer development, etching of buried trenches, definition of MEMS anchors, etc. (c) 2006 The Electrochemical Society.

Support and rhenium effects on the intrinsic site activity and methane selectivity of cobalt Fischer–Tropsch catalysts

Catalyst composition effects on site activity, active carbon coverage, and methane selectivity in the cobalt-catalyzed Fischer–Tropsch synthesis were examined using 12CO→ 13CO isotope transients at reaction steady state. All catalysts (18 total) were tested at identical conditions: 221 °C, 6.5 atm of H 2/CO/Ne=2/1/1. The intrinsic site activity of unsupported Co and Co-supported on SiO 2, TiO 2, and Al 2O 3 (Co dispersion < 10% ) varies within a relatively narrow band ( ∼ 2x maximum rate difference). Re present at a Re/Co weight ratio of 0.1 does not affect Fischer–Tropsch activity and selectivity. Since its own activity is 20 times lower than that of Co, Re does not appear to block or modify active Co sites. While Re and the above-noted three common oxide supports do not affect the Fischer–Tropsch activity and selectivity of the relatively large cobalt crystallites, some modifications of SiO 2 and Al 2O 3 supports (with MgO, Y 2O 3, ZnO, and Ce 2O 3, by coating and coprecipitation) reduce site activity by up to an order of magnitude. Interestingly, the reduced site activity does not measurably affect methane selectivity. For all catalysts, the observed site-activity differences, whether small or large, do not correlate with bulk composition, and are possibly the result of unidentified impurities introduced during catalyst preparation. These impurities affect the reactivity of both the adsorbed CO and the active carbon present on the catalyst: higher site activity correlates with higher active carbon reactivity. Although this correlation is strong, some variability in the CO/C ∗ reactivity ratio does occur. This variability appears to play a key role in methane selectivity, namely, higher values correlate with lower methane selectivity. These observations can be rationalized by our previously published simple kinetic model.

Formation Mechanism of Non-Metallic Inclusions in Different Stainless Steel Grades

In this study the processing routes of three different stainless steel grades were followed; during the reducing period in the AOD plant samplings of steel and slag and measurements of temperature and oxygen activities were performed. The goal was to develop tools for the improvement in the comprehension about the development of the non metallic inclusions in stainless steels. The inclusions in the steel samples were analysed by means of a SEM and then the evaluation of the oxide activities and phases present within them was performed with Thermocalc©. A model developed by Janke and co-workers was implemented in order to compute the activity of elements in the liquid steel. This is based on Wagner's formalism but it is more accurate for the steel baths where solutes are not at infinite dilution. This is the reason why Janke's formalism is better than the Wagner's one in the study of stainless steels, as they are high-alloy steels. It was found that Janke's formalism lacks reliability, when it neglects some strong interactions between two elements (e.g. O and another element having high affinity to oxygen).The activities of oxides at the equilibrium with the liquid metal were calculated and compared to those obtained from the Thermocalc©-based analysis of inclusions. From this comparison some hypotheses were made about the nucleation and modification of SiO 2 , Al 2 O 3 and Cr 2 O 3 . By making some variations to the model for the calculations of the oxides activity at the equilibrium with the steel bath, it has been also assessed how the model results are influenced by the choice of some thermodynamic parameters such as the interactions coefficients and the equilibrium constants.

The evolution of microstructure and surface bonding in SiO 2 aerogel film after plasma treatment using O 2, N 2, and H 2 gases

In this work, we investigated the effects of various gases (O 2, N 2, and H 2) plasma treatment on SiO 2 aerogel films in order to strengthen the film and improve the surface chemical bonding nature of the film. The plasma treatments could reduce the density of silanol (SiOH) and ethoxy (SiOR) groups. The physical, chemical, and electrical properties of SiO 2 aerogel film through curing with various plasma gases were evaluated. The modification of SiO 2 aerogel film by plasma gas treatment was related to the physical impingement effect of ions, chemical reaction, and irradiated vacuum UV.

Modification of SiO2 Surfaces by Reaction with Trialkoxymethanes and Triphenoxymethane

SiO2 (Aerosil) reacts with trialkoxymethanes and triaryloxymethanes (orthoformates) of the formula HC(OR)3, R = CH3, C2H5, n-C4H9, and C6H5. The modified surface was analyzed with IR and solid-state NMR spectroscopy and thermogravimetric analysis (TGA). The results show that only the alkyl (or aryl) residues are left on the surface (as part of alkoxy or aryloxy groups). Alkyl residues are more tightly bound to the surface than aryl residues. The reaction of SiO2 with trialkoxymethanes allows stable modifications with organic products in the range of monolayer coverage, with little effort.

Experimental evidence for changes during fossilization of radiolarian tests and implications for a model of biomineralization

This paper contains informations of two kinds: (1) observation on the effects of high-temperatures annealing on the organization of opaline radiolarian test that may simulate fossilization processes and (2) an hypothetical model for the processes of formation, preservation and destruction of radiolarian shells in geologic history, based on diverse published reports and observations of heat-treated skeletons. Biomineralization of radiolarian skeletons start with an appearance of some primary amorphous opal globules E (0.06–0.15 μm) on the hexagonal polysaccharide plates of the organic matrix. The finest globules E are grouped together, forming the globule units D (0.2–03 μm), which, in their turn, are united into a globule unit C (0.4–1 μm). The globule units C are grouped into the hexagonal prismatic units B (1–3 μm). The largest mineral units A (3–8 μm) are formed from the units B and pass throughout the whole shell wall. Besides that, every ultrastructural skeleton unit is surrounded by organic lamella. Therefore, the main tenent of biomineralization is corroborated: the existence of any skeleton as a single solid body is provided by the interactions of all ultrastructural skeleton elements through the unmineralized residual organic matrix. A common trend in the fossilization of skeletons is (1) destruction of the covering organic lamellae accompanied by disintegration of skeletons and (2) carbonization (tannage) of the residual organic matrix increasing a skeleton strength and silica transformation in the following successional: opal-opal-tridymite-tridymite-quartz. Initial stages of the secondary alteration of shells can be reconstructed by high-temperature annealing. As a result of experiment recent radiolarian tests were partially destroyed and showed increased pore sizes, thinning of shell wall and transformation of biogenic amorphous globules into opal-tridymite and even prismatic tridymite. The annealing of radiolarian tests from Early Permian outcrops show changing of pore sizes, cracking of skeletons along the largest ultrastructural units and besides that “guttering” of some primary globular shells and secondary crystallizing of others up to prismatic tridymite. Late Paleozoic radiolarians from deep drilling deposits can serve as an example of complete destruction of the carbonized organic lamellae, of an intergrowth of the mineral units and of substitution of prismatic low-temperature tridymite by dipyramidal-prismatic low-temperature quartz. Thus, modifications of SiO 2 possible can show a response to corresponding stages of lithogenesis: sedimentogenesis-diagenesis-early catagenesis-late catagenesis.

Modification of SiO through room-temperature plasma treatments, rapid thermal annealings, and laser irradiation in a nonoxidizing atmosphere.

We have studied the modification of a-SiO thin deposited films through Ar-plasma treatment at room temperature, through heating (rapid thermal annealing), or through irradiation (uv-laser treatment), in a nonoxidizing atmosphere. Rutherford backscattering spectroscopy, reflection high-energy electron diffraction, ir-absorption, and x-ray photoelectron spectroscopy techniques have been used in combination to investigate the atomic composition and the structural and chemical nature of SiO films after various nonoxidizing treatments. We show that the as-deposited oxide is not a mixture of Si and ${\mathrm{SiO}}_{2}$ and separates into phases as a result of processing. The effects of irradiation by low-energy electrons at room temperature (plasma treatment) are similar to those observed for high-temperature treatments. A possible microscopic mechanism, leading to silicon cluster growth, is proposed to explain the transition from a material rich in intermediate suboxides (as-deposited SiO) to the mixture structure (phase-separated Si and ${\mathrm{SiO}}_{2}$).

Properties of catalysts prepared by pyrolysis of Co 2(CO) 8 on silica containing surface Ti ions

Catalysts prepared by thermal decomposition of Co 2(CO) 8 on modified silica were studied by magnetic susceptibility and by IR and ESR spectroscopy, and were tested in CO hydrogenation. The modification of SiO 2 by Ti ions made it possible to diminish the size of metallic Co particles. The effect was the most pronounced for modification by hydride complexes of a low-valent titanium. An increase of Co dispersion was accompanied by a drop in the metal activity in CO hydrogenation and by a rise of the relative yield of light hydrocarbons and alcohols, especially that of ethanol.

“Paradox” of polymorphic modifications of SiO2 and the bulk role of Si and O in the crust and upper mantle

“Paradox” of polymorphic modifications of SiO₂ and the bulk role of Si and O in the crust and upper mantle