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Sample records for si o2 synthesis

  1. SiO2@TiO2 Coating: Synthesis, Physical Characterization and Photocatalytic Evaluation

    A. Rosales

    2018-03-01

    Full Text Available Use of silicon dioxide (SiO2 and titanium dioxide (TiO2 have been widely investigated individually in coatings technology, but their combined properties promote compatibility for different innovative applications. For example, the photocatalytic properties of TiO2 coatings, when exposed to UV light, have interesting environmental applications, such as air purification, self-cleaning and antibacterial properties. However, as reported in different pilot projects, serious durability problems, associated with the adhesion between the substrate and TiO2, have been evidenced. Thus, the aim of this work is to synthesize SiO2 together with TiO2 to increase the durability of the photocatalytic coating without affecting its photocatalytic potential. Therefore, synthesis using sonochemistry, synthesis without sonochemistry, physical characterization, photocatalytic evaluation, and durability of the SiO2, SiO2@TiO2 and TiO2 coatings are presented. Results indicate that using SiO2 improved the durability of the TiO2 coating without affecting its photocatalytic properties. Thus, this novel SiO2@TiO2 coating shows potential for developing long-lasting, self-cleaning and air-purifying construction materials.

  2. Synthesis of TiO2-doped SiO2 composite films and its applications

    Wintec

    structure of the titanium oxide species in the TiO2-doped SiO2 composite films and the photocatalytic reactiv- ity in order to ... gaku D-max γA diffractometer with graphite mono- chromized ... FT–IR absorption spectra of TiO2-doped SiO2 com-.

  3. Synthesis of metallic nanoparticles in SiO2 matrices

    Gutierrez W, C.; Mondragon G, G.; Perez H, R.; Mendoza A, D.

    2004-01-01

    Metallic nanoparticles was synthesized in SiO 2 matrices by means of a process of two stages. The first one proceeded via sol-gel, incorporating the metallic precursors to the reaction system before the solidification of the matrix. Later on, the samples underwent a thermal treatment in atmosphere of H 2 , carrying out the reduction of the metals that finally formed to the nanoparticles. Then it was detected the presence of smaller nanoparticles than 20 nm, dispersed and with the property of being liberated easily of the matrix, conserving a free surface, chemically reactive and with response to external electromagnetic radiation. The system SiO 2 -Pd showed an important thermoluminescent response. (Author)

  4. Tunable Synthesis of SiC/SiO2 Heterojunctions via Temperature Modulation

    Wei Li

    2018-05-01

    Full Text Available A large-scale production of necklace-like SiC/SiO2 heterojunctions was obtained by a molten salt-mediated chemical vapor reaction technique without a metallic catalyst or flowing gas. The effect of the firing temperature on the evolution of the phase composition, microstructure, and morphology of the SiC/SiO2 heterojunctions was studied. The necklace-like SiC/SiO2 nanochains, several centimeters in length, were composed of SiC/SiO2 core-shell chains and amorphous SiO2 beans. The morphologies of the as-prepared products could be tuned by adjusting the firing temperature. In fact, the diameter of the SiO2 beans decreased, whereas the diameter of the SiC fibers and the thickness of the SiO2 shell increased as the temperature increased. The growth mechanism of the necklace-like structure was controlled by the vapor-solid growth procedure and the modulation procedure via a molten salt-mediated chemical vapor reaction process.

  5. One-pot synthesis of Ag-SiO2-Ag sandwich nanostructures

    Li Chaorong; Mei Jie; Li Shuwen; Lu Nianpeng; Wang Lina; Chen Benyong; Dong Wenjun

    2010-01-01

    Ag-SiO 2 -Ag sandwich nanostructures were prepared by a facile one-pot synthesis method. The Ag core, SiO 2 shell and Ag nanoparticle shell were all synthesized with polyvinylpyrrolidone, catalysed by ammonia, in the one-pot reaction. The polyvinylpyrrolidone, acting as a smart reducing agent, reduced the Ag + to Ag cores and Ag shells separately. Furthermore, the polyvinylpyrrolidone served as a protective agent to prevent the silver cores from aggregating. The SiO 2 shell and outer layer Ag nanoparticles were obtained when tetraethyl orthosilicate and ammonia were added to the silver core solution. Ammonia, acting as the catalyst, accelerated the hydrolysis of the tetraethyl orthosilicate to SiO 2 , which coated the silver cores. Furthermore, Ag(NH 3 ) 2 + ions were formed when aqueous ammonia was added to the solution, which increased the reduction capability. Then the polyvinylpyrrolidone reduced the Ag(NH 3 ) 2 + ions to small Ag nanoparticles on the surface of the Ag-SiO 2 and formed Ag-SiO 2 -Ag sandwich structures with a standard deviation of less than 4%. This structure effectively prevented the Ag nanoparticles on the silica surface from aggregating. Furthermore, the Ag-SiO 2 -Ag sandwich structures showed good catalysis properties due to the large surface area/volume value and activity of surface atoms of Ag particles.

  6. Synthesis of crystalline Ge nanoclusters in PE-CVD-deposited SiO2 films

    Leervad Pedersen, T.P.; Skov Jensen, J.; Chevallier, J.

    2005-01-01

    The synthesis of evenly distributed Ge nanoclusters in plasma-enhanced chemical-vapour-deposited (PE-CVD) SiO2 thin films containing 8 at. % Ge is reported. This is of importance for the application of nanoclusters in semiconductor technology. The average diameter of the Ge nanoclusters can...

  7. Synthesis, characterization, and thermal stability of SiO2/TiO2/CR-Ag multilayered nanostructures

    Díaz, Gabriela; Chang, Yao-Jen; Philipossian, Ara

    2018-06-01

    The controllable synthesis and characterization of novel thermally stable silver-based particles are described. The experimental approach involves the design of thermally stable nanostructures by the deposition of an interfacial thick, active titania layer between the primary substrate (SiO2 particles) and the metal nanoparticles (Ag NPs), as well as the doping of Ag nanoparticles with an organic molecule (Congo Red, CR). The nanostructured particles were composed of a 330-nm silica core capped by a granular titania layer (10 to 13 nm in thickness), along with monodisperse 5 to 30 nm CR-Ag NPs deposited on top. The titania-coated support (SiO2/TiO2 particles) was shown to be chemically and thermally stable and promoted the nucleation and anchoring of CR-Ag NPs, which prevented the sintering of CR-Ag NPs when the structure was exposed to high temperatures. The thermal stability of the silver composites was examined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Larger than 10 nm CR-Ag NPs were thermally stable up to 300 °C. Such temperature was high enough to destabilize the CR-Ag NPs due to the melting point of the CR. On the other hand, smaller than 10 nm Ag NPs were stable at temperatures up to 500 °C because of the strong metal-metal oxide binding energy. Energy dispersion X-ray spectroscopy (EDS) was carried out to qualitatively analyze the chemical stability of the structure at different temperatures which confirmed the stability of the structure and the existence of silver NPs at temperatures up to 500 °C.

  8. Sol-gel synthesis of TiO2-SiO2 photocatalyst for β-naphthol photodegradation

    Qourzal, S.; Barka, N.; Tamimi, M.; Assabbane, A.; Nounah, A.; Ihlal, A.; Ait-Ichou, Y.

    2009-01-01

    Silica gel supported titanium dioxide particles (TiO 2 -SiO 2 ) prepared by sol-gel method was as photocatalyst in the degradation of β-naphthol in water under UV-illumination. The prepared sample has been characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The supported catalyst had large surface area and good sedimentation ability. The photodegradation rate of β-naphthol under UV-irradiation depended strongly on adsorption capacity of the catalyst, and the photoactivity of the supported catalyst was much higher than that of the pure titanium dioxides. The experiments were measured by high performance liquid chromatography (HPLC). The photodegradation rate of β-naphthol using 60% TiO 2 -SiO 2 particles was faster than that using TiO 2 'Degussa P-25', TiO 2 'PC-50' and TiO 2 'Aldrich' as photocatalyst by 2.7, 4 and 7.8 times, respectively. The kinetics of photocatalytic β-naphthol degradation was found to follow a pseudo-first-order rate law. The effect of the TiO 2 loading on the photoactivity of TiO 2 -SiO 2 particles was also discussed. With good photocatalytic activity under UV-irradiation and the ability to be readily separated from the reaction system, this novel kind of catalyst exhibited the potential effective in the treatment of organic pollutants in aqueous systems.

  9. Synthesis of hybrid cellulose nanocomposite bonded with dopamine SiO2/TiO2 and its antimicrobial activity

    Ramesh, Sivalingam; Kim, Gwang-Hoon; Kim, Jaehwan; Kim, Joo-Hyung

    2015-04-01

    Organic-inorganic hybrid material based cellulose was synthesized by the sol-gel approach. The explosion of activity in this area in the past decade has made tremendous progress in industry or academic both fundamental understanding of sol-gel process and applications of new functionalized hybrid materials. In this present research work, we focused on cellulose-dopamine functionalized SiO2/TiO2 hybrid nanocomposite by sol-gel process. The cellulose-dopamine hybrid nanocomposite was synthesized via γ-aminopropyltriethoxysilane (γ-APTES) coupling agent by in-situ sol-gel process. The chemical structure of cellulose-amine functionalized dopamine bonding to cellulose structure with covalent cross linking hybrids was confirmed by FTIR spectral analysis. The morphological analysis of cellulose-dopamine nanoSiO2/TiO2 hybrid nanocomposite materials was characterized by XRD, SEM and TEM. From this different analysis results indicate that the optical transparency, thermal stability, control morphology of cellulose-dopamine-SiO2/TiO2 hybrid nanocomposite. Furthermore cellulose-dopamine-SiO2/TiO2 hybrid nanocomposite was tested against pathogenic bacteria for antimicrobial activity.

  10. Room temperature synthesis of porous SiO2 thin films by plasma enhanced chemical vapor deposition

    Barranco Quero, Ángel; Cotrino Bautista, José; Yubero Valencia, Francisco; Espinós, J. P.; Rodríguez González-Elipe, Agustín

    2004-01-01

    Synthesis of porous SiO2 thin films in room temperature was carried out using plasma enhanced chemical vapor deposition (CVD) in an electron cyclotron resonance microwave reactor with a downstream configuration.The gas adsorption properties and the type of porosity of the SiO2 thin films were assessed by adsorption isotherms of toluene at room temperature.The method could also permit the tailoring synthesis of thin films when both composition and porosity can be simultaneously and independent...

  11. Kinetics of acetic acid synthesis from ethanol over a Cu/SiO2 catalyst

    Voss, Bodil; Schjødt, Niels Christian; Grunwaldt, Jan-Dierk

    2011-01-01

    The dehydrogenation of ethanol via acetaldehyde for the synthesis of acetic acid over a Cu based catalyst in a new process is reported. Specifically, we have studied a Cu on SiO2 catalyst which has shown very high selectivity to acetic acid via acetaldehyde compared to competing condensation routes....... In light of this, an observed intrinsic activity difference between whole catalyst pellets and crushed pellets may be explained by the Cu crystal size and growth rate being functions of the catalyst particle size and time....

  12. Synthesis And Characterization Of SiO2, SnO2 And TiO2 Metal Oxide Shells Covering Cu2O Particles

    Yu Ri

    2015-06-01

    Full Text Available In this work is described a means of improving the chemical stability of Cu2O@SiO2, Cu2O@SnO2 and Cu2O@TiO2 materials. The SiO2, SnO2 and TiO2 coated samples were stable from pH 3 to pH 10 for up to seven days. To determine the stability of the coated nanoparticles, and their colloidal solutions under acidic and basic conditions, colloidal nanoparticle solutions with various pH values were prepared and monitored over time. Details of the effect of variations in pH on the phase stability of core-shell type Cu2O were characterized using transmission electron microscopy and X-ray diffraction.

  13. Novel polyester/SiO2 nanocomposite membranes: Synthesis, properties and morphological studies

    Ahmadizadegan, Hashem; Esmaielzadeh, Sheida

    2018-06-01

    In this paper, a new type of soluble polyester/silica (PE/SiO2) hybrid was prepared by the ultrasonic irradiation process. The coupling agent γ-glycidyloxypropyltrimethoxysilane (GOTMS) was chosen to enhance the compatibility between the polyester (PE) and silica (SiO2). Furthermore, the effects of the coupling agent on the morphologies and properties of the PE/SiO2 hybrids were investigated using UV-vis and FT-IR spectroscopies and FE-SEM. The densities and solubilities of the PE/SiO2 hybrids were also measured. The results show that the size of the silica particle was markedly reduced by the introduction of the coupling agent, which made the PE/SiO2 hybrid films become transparent. Furthermore, thermal stability, residual solvent in the membrane film and structural ruination of membranes were analyzed by thermal gravimetric analysis (TGA). The effects of SiO2 nanoparticles on the glass transition temperature (Tg) of the prepared nanocomposites were studied by differential scanning calorimetry (DSC). Moreover, their mechanical properties were also characterized. It can be observed that the Young's moduli (E) of the hybrid films increase linearly with the silica content. The results obtained from gas permeation experiments with a constant pressure setup showed that adding SiO2 nanoparticles to the polymeric membrane structure increased the permeability of the membranes.

  14. Synthesis of SiCN@TiO2 core-shell ceramic microspheres via PDCs method

    Liu, Hongli; Wei, Ning; Li, Jing; Zhang, Haiyuan; Chu, Peng

    2018-02-01

    A facile and effective polymer-derived ceramics (PDCs) emulsification-crosslinking-pyrolysis method was developed to fabricate SiCN@TiO2 core-shell ceramic microspheres with polyvinylsilazane (PVSZ) and tetrabutyl titanate (TBT) as precursors. The TBT: PVSZ mass ratios, emulsifier concentrations and the pyrolysis temperature were examined as control parameters to tune the size and morphology of microspheres. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the synthesized SiCN@TiO2 microspheres to be comprised of SiCN core coated with TiO2 crystals, with an average size of 0.88 μm when pyrolyzed at 1400 °C. The analysis of Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) ensured that SiCN@TiO2 core-shell ceramic microspheres composed of rutile TiO2, β-SiC and Si3N4 crystalline phases, The thermal properties were characterized by thermogravimetric analysis (TGA). The obtained SiCN@TiO2 core-shell ceramic microspheres were the promising candidate of the infrared opacifier in silica aerogels and this technique can be extended to other preceramic polymers.

  15. Synthesis of Porous SiO2 Microspheres by Soft Template%软模板合成多孔 SiO2微球

    王克; 肖树秀; 柏永清; 刘朴; 马丽红; 苏碧桃

    2009-01-01

    以CTAB为软模板在水-乙醇体系中合成了SiO2微球.SEM结果表明,本实验制得的SiO2微球表面具有褶皱、内部有很多空隙;催化剂碱的种类、反应体系的温度、CTAB的加入量均对SiO2微球的表观形貌有着较大的影响.

  16. Facile synthesis of microporous SiO2/triangular Ag composite nanostructures for photocatalysis

    Sirohi, Sidhharth; Singh, Anandpreet; Dagar, Chakit; Saini, Gajender; Pani, Balaram; Nain, Ratyakshi

    2017-11-01

    In this article, we present a novel fabrication of microporous SiO2/triangular Ag nanoparticles for dye (methylene blue) adsorption and plasmon-mediated degradation. Microporous SiO2 nanoparticles with pore size aminopropyl) trimethoxysilane) to introduce amine groups. Amine-functionalized microporous silica was used for adsorption of triangular silver (Ag) nanoparticles. The synthesized microporous SiO2 nanostructures were investigated for adsorption of different dyes including methylene blue, congo red, direct green 26 and curcumin crystalline. Amine-functionalized microporous SiO2/triangular Ag nanostructures were used for plasmon-mediated photocatalysis of methylene blue. The experimental results revealed that the large surface area of microporous silica facilitated adsorption of dye. Triangular Ag nanoparticles, due to their better charge carrier generation and enhanced surface plasmon resonance, further enhanced the photocatalysis performance.

  17. Synthesis of unidirectional structures of SiO2-Ag using Au nanoparticles as nucleation centers

    Villa S, G.; Mendoza A, D.; Gutierrez W, C.; Perez H, R.

    2008-01-01

    This paper reports a method to synthesize Ag unidirectional structures covered with SiO 2 by sol-gel technique using Au nanoparticles as nucleation centers of the unidirectional structures. In the first phase unidirectional structures of SiO 2 -Ag CI are obtained by sol-gel, using TEOS as a precursor of metallic structures (Ag) and the incorporation of Au nanoparticles as nucleation centers for growth of unidirectional structures. In the second stage, one-way systems are subjected to thermal treatment in H 2 atmosphere for obtain AG 0 particles through mechanisms that diffusion and coalescence of silver to form structures that have a thin cover of SiO 2 . Analysis by scanning electron microscopy, transmission and atomic force microscopy allowed to determine the chemical composition and microstructural properties of unidirectional systems SiO 2 -Ag. (Author)

  18. Nano-Ticl 4 .SiO 2 : a Versatile and Efficient Catalyst for Synthesis of ...

    Nano-TiCl4.SiO2 has been found to be an extremely efficient catalyst for the preparation of 3,4-dihydropyrimidinones/thiones via three-component reactions of an aldehyde, β-ketoester or β-diketone and urea or thiourea under mild conditions. Nano-TiCl4.SiO2 as a solid Lewis acid has been synthesized by reaction of ...

  19. Synthesis of geopolymer from spent FCC: Effect of SiO2/Al2O<3 and Na2O/SiO2 molar ratios

    Trochez, J. J.

    2015-03-01

    Full Text Available This paper assesses the feasibility of using a spent fluid catalytic cracking catalyst (SFCC as precursor for the production of geopolymers. The mechanical and structural characterization of alkali-activated SFCC binders formulated with different overall (activator + solid precursor SiO2/Al2O3 and Na2O/SiO2 molar ratios are reported. Formation of an aluminosilicate ‘geopolymer’ gel is observed under all conditions of activation used, along with formation of zeolites. Increased SiO2/Al2O3 induces the formation of geopolymers with reduced mechanical strength, for all the Na2O/SiO2 ratios assessed, which is associated with excess silicate species supplied by the activator. This is least significant at increased alkalinity conditions (higher Na2O/SiO2 ratios, as larger extents of reaction of the spent catalyst are achieved. SiO2/Al2O3 and Na2O/SiO2 ratios of 2.4 and 0.25, respectively, promote the highest compressive strength (67 MPa. This study elucidates the great potential of using SFCC as precursor to produce sustainable ceramic-like materials via alkali-activation.Este artículo estudia la factibilidad de usar un catalizador gastado del proceso de craqueo (SFCC para la producción de geopolímeros. Se evalúan las características mecánicas y estructurales de los geopolímeros producidos con diferentes relaciones molares (activador + precursor solido de SiO2/Al2O3 y Na2O/SiO2. La formación de un gel geopolimérico de tipo aluminosilicato se observa a las diferentes condiciones evaluadas, así como la formación de zeolitas. Un incremento en la relación SiO2/Al2O3 genera geopolímeros de baja resistencia mecánica, a las diferentes relaciones molares Na2O/SiO2 evaluadas, como consecuencia del exceso de especies silicato provenientes del activador. Este efecto es menos significativo al incrementar las condiciones de alcalinidad (mayores relaciones Na2O/SiO2, ya que un mayor grado de reacción del catalizador gastado es alcanzado. Las

  20. Synthesis and characterization of polyurethane/CdS-SiO 2 nanocomposites via ultrasonic process

    Chen, Jing; Zhou, Yu-Ming; Nan, Qiu-Li; Ye, Xiao-Yun; Sun, Yan-Qing; Wang, Zhi-Qiang; Zhang, Shi-Ming

    2008-12-01

    In this study, the high-intensity ultrasound was applied in the preparation of chiral polyurethane/CdS-SiO 2 nanocomposites. The polyurethane/CdS-SiO 2 nanocomposites were analyzed by powder X-ray diffraction, thermogravimetric analysis (TGA), TEM and SEM. The results indicated that the heat stability of the nanocomposites was improved in the presence of CdS-SiO 2 core-shell nanoparticles. The infrared emissivity (8-14 μm) study revealed that the nanocomposites possessed much lower infrared values compared with those of the neat polymers and nanoparticles, respectively. A possible mechanism of ultrasonic induced composite reaction was proposed based on the experimental results.

  1. Synthesis and characterization of polyurethane/CdS-SiO2 nanocomposites via ultrasonic process

    Chen Jing; Zhou Yuming; Nan Qiuli; Ye Xiaoyun; Sun Yanqing; Wang Zhiqiang; Zhang Shiming

    2008-01-01

    In this study, the high-intensity ultrasound was applied in the preparation of chiral polyurethane/CdS-SiO 2 nanocomposites. The polyurethane/CdS-SiO 2 nanocomposites were analyzed by powder X-ray diffraction, thermogravimetric analysis (TGA), TEM and SEM. The results indicated that the heat stability of the nanocomposites was improved in the presence of CdS-SiO 2 core-shell nanoparticles. The infrared emissivity (8-14 μm) study revealed that the nanocomposites possessed much lower infrared values compared with those of the neat polymers and nanoparticles, respectively. A possible mechanism of ultrasonic induced composite reaction was proposed based on the experimental results.

  2. One-pot synthesis of Au@SiO2 catalysts: A click chemistry approach

    Solovyeva, Vera A.

    2014-10-13

    Using the copper-catalyzed azide-alkyne cycloaddition "click" reaction, a library of triazole amphiphiles with a variety of functional polar "heads" and hydrophobic or superhydrophobic "tails" was synthesized. The amphiphiles were evaluated for their ability to stabilize small Au nanoparticles, and, at the same time, serve as templates for nanocasting porous SiO2. One of the Au@SiO2 materials thus prepared was found to be a highly active catalyst for the Au nanoparticle-catalyzed regioselective hydroamination of alkynes.

  3. One-pot synthesis of Au@SiO2 catalysts: A click chemistry approach

    Solovyeva, Vera A.; Vu, Khanh B.; Merican, Zulkifli; Sougrat, Rachid; Rodionov, Valentin O.

    2014-01-01

    Using the copper-catalyzed azide-alkyne cycloaddition "click" reaction, a library of triazole amphiphiles with a variety of functional polar "heads" and hydrophobic or superhydrophobic "tails" was synthesized. The amphiphiles were evaluated for their ability to stabilize small Au nanoparticles, and, at the same time, serve as templates for nanocasting porous SiO2. One of the Au@SiO2 materials thus prepared was found to be a highly active catalyst for the Au nanoparticle-catalyzed regioselective hydroamination of alkynes.

  4. Synthesis, characterization and electroanalytical application of a new SiO2/SnO2 carbon ceramic electrode

    Arguello, Jacqueline; Magosso, Herica A.; Landers, Richard; Pimentel, Vinicius L.; Gushikem, Yoshitaka

    2010-01-01

    A new SiO 2 /SnO 2 carbon ceramic composite was prepared by the sol-gel method, and its potential application in electrochemistry as a novel electrode material has been studied. The prepared xerogel was structurally and electrochemically characterized by scanning electron microscopy coupled to energy dispersive spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and cyclic voltammetry. The composite was pressed in a rigid disk-shape and used as a conductive substrate to immobilize a water-soluble organic-inorganic hybrid polymer, 3-n-propyl-4-picolinium chloride silsesquioxane. The oxidation of nitrite was studied on this polymer film coated electrode in aqueous solution using cyclic voltammetry and differential pulse voltammetry. This modified electrode exhibited a better defined voltammetric peak shifted negatively about 60 mV. The linear detection limit found for nitrite was from 1.3 x 10 -5 to 1.3 x 10 -3 mol l -1 and the detection limit was 3.3 x 10 -6 mol l -1 .

  5. BF3.SiO2: an efficient catalyst for the synthesis of azo dyes at room temperature

    Bi Bi Fatemeh Mirjalili

    2012-07-01

    Full Text Available A rapid one-pot method has been developed for the synthesis of azo dyes via ‎sequential diazotization–diazo coupling of aromatic amines with coupling agents at room ‎temperature in the presence of BF3.SiO2 as acidic catalyst. The obtained aryl diazonium salts bearing silica supported boron tri-flouride counter ion‎ was sufficiently stable to be kept at room ‎temperature in the dry state.‎

  6. Synthesis and Luminescence Properties of Yellow-emitting SiO2/Zn2SiO4: Mn Nanocomposite

    Karim OMRI

    2014-05-01

    Full Text Available Yellow light emitting Mn2+-doped b-Zn2SiO4 phosphor nanoparticles embedded in SiO2 host matrix, were prepared by a simple solid-phase reaction under natural atmosphere at 1500 °C for 2 hours after the incorporation of manganese doped zinc oxide nanoparticles in silica using sol-gel method. The SiO2/Zn2SiO4:Mn nanocomposite was characterized by X-ray diffraction (XRD, transmission electron microscopy (TEM, scanning electron microscopy (SEM and photoluminescence (PL. The nanopowder was crystallized in triclinic b-Zn2SiO4 phase with a particles size varies between 70 nm and 84 nm. The SiO2/b-Zn2SiO4:Mn nanocomposite exhibited a broad yellow emission band at 575 nm under UV excitation light. The dependence of the intensity and energy position of the obtained PL band on measurement temperature and power excitation will be discussed.

  7. TiO2 nanoparticles supported on the Fe3O4@SiO2 nanocomposites: a novel magnetic nanocatalyst for the synthesis of 2-aminothiazoles

    Safari, Javad; Abedi-Jazini, Zahra; Zarnegar, Zohre; Sadeghi, Masoud

    2015-01-01

    Nano TiO 2 supported on the Fe 3 O 4 @SiO 2 nanocomposites is introduced as a novel catalyst for the environmental synthesis of 2-aminothiazoles in PEG-200 as a green medium at room temperature. In this reaction, thiourea and N-bromosuccinimide were reacted with various ketones affording the desired 2-aminothiazole compounds. This green protocol has promising features for the reaction response such as simple procedure, high yields, and the ease of separation of pure product, short reaction time, and convenient manipulation. This catalyst was easily separated by an external magnet, and the recovered catalyst was reused several times without any significant loss of activity.Graphical abstract

  8. Synthesis of ZnFe2O4/SiO2 composites derived from a diatomite template.

    Liu, Zhaoting; Fan, Tongxiang; Zhou, Han; Zhang, Di; Gong, Xiaolu; Guo, Qixin; Ogawa, Hiroshi

    2007-03-01

    A novel porous ZnFe2O4/SiO2 composite product has been generated with a template-directed assembly method from porous diatomite under different synthesis conditions, such as precursor concentrations (metallic nitrates), calcination temperature and diatomite type. The phase composition and morphology of all the materials were examined by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results indicated that an inherited hierarchical porous structure from the diatomite template can be obtained, and the synthesis conditions were found to have clear effects on the formation of the ZnFe2O4/SiO2 composite. The ideal composite of ZnFe2O4/SiO2 can be obtained through optimization of diatomite template type, precursor solution and calcination temperature. Furthermore, the adsorption abilities of two types of diatomites were analyzed in detail using FTIR spectra and nitrogen adsorption measurements etc, which proved that A-diatomite (Shengzhou-diatomite) is better than B-diatomite (Changbai-diatomite) on the aspect of adsorbing Zn and Fe ions, and of forming the ZnFe2O4.

  9. Microwave-assisted synthesis and characterization of poly(acrylic)/SiO2-TiO2 core-shell nanoparticle hybrid thin films

    Chien, Wen-Chen; Yu, Yang-Yen; Chen, Po-Kan; Yu, Hui-Huan

    2011-01-01

    In this study, poly(acrylic)/SiO 2 -TiO 2 core-shell nanoparticle hybrid thin films were successfully synthesized by microwave-assisted polymerization. The coupling agent 3-(trimethoxysilyl) propyl methacrylate (MSMA) was hydrolyzed with colloidal SiO 2 -TiO 2 core-shell nanoparticles, and then polymerized with two acrylic monomers and initiator to form a precursor solution. The results of this study showed that the spin-coated hybrid films had relatively good surface planarity, high thermal stability, a tunable refractive index (1.525 2 -TiO 2 core-shell nanoparticle hybrid thin films, for potential use in optical applications.

  10. TiO2/SiO2 prepared via facile sol-gel method as an ideal support for green synthesis of Ag nanoparticles using Oenothera biennis extract and their excellent catalytic performance in the reduction of 4-nitrophenol

    Bahar Khodadadi

    2017-01-01

    Full Text Available In the present study, the extract of the plant of Oenothera biennis was used to green synthesis of silver nanoparticles (Ag NPs as an environmentally friendly, simple and low cost method. And Additionally, TiO2/SiO2 was prepared via facile sol-gel method using starch as an important, naturally abundant organic polymer as an ideal support. The Ag NPs/TiO2/SiO2 as an effective catalyst was prepared through reduction of Ag+ ions using Oenothera biennis extract as the reducing and stabilizing agent and Ag NPs immobilization on TiO2/SiO2 surface in the absence of any stabilizer or surfactant. Several techniques such as FT-IR spectroscopy, UV-Vis spectroscopy, X-ray Diffraction (XRD, sScanning eElectron mMicroscopy (FE-SEM, Eenergy dDispersive X-ray sSpectroscopy (EDS, and Ttransmission Eelectron Mmicroscopy (TEM were used to characterize TiO2/SiO2, silver nanoparticles (Ag NPs, and Ag NPs/TiO2/SiO2. Moreover, the catalytic activity of the Ag NPs/ TiO2/SiO2 was investigated in the reduction of 4-nitrophenol (4-NP at room temperature. On the basis of the results, the Ag NPs/TiO2/SiO2 was found to be high catalytic activity highly active catalyst according to the experimental results in this study. In addition, Ag NPs/TiO2/SiO2 can be recovered and reused several times in the reduction of 4-NP with no significant loss of catalytic activity.

  11. Design and Synthesis of Hierarchical SiO2@C/TiO2 Hollow Spheres for High-Performance Supercapacitors.

    Zhang, Ying; Zhao, Yan; Cao, Shunsheng; Yin, Zhengliang; Cheng, Li; Wu, Limin

    2017-09-06

    TiO 2 has been widely investigated as an electrode material because of its long cycle life and good durability, but the relatively low theoretical capacity restricts its practical application. Herein, we design and synthesize novel hierarchical SiO 2 @C/TiO 2 (HSCT) hollow spheres via a template-directed method. These unique HSCT hollow spheres combine advantages from both TiO 2 such as cycle stability and SiO 2 with a high accessible area and ionic transport. In particular, the existence of a C layer is able to enhance the electrical conductivity. The SiO 2 layer with a porous structure can increase the ion diffusion channels and accelerate the ion transfer from the outer to the inner layers. The electrochemical measurements demonstrate that the HSCT-hollow-sphere-based electrode manifests a high specific capacitance of 1018 F g -1 at 1 A g -1 which is higher than those for hollow TiO 2 (113 F g -1 ) and SiO 2 /TiO 2 (252 F g -1 ) electrodes, and substantially higher than those of all the previously reported TiO 2 -based electrodes.

  12. Effect of Lanthanum as a Promoter on Fe-Co/SiO2 Catalyst for Fischer-Tropsch Synthesis

    Ali Abbasi

    2014-03-01

    Full Text Available Iron-Cobalt catalyst is well known from both operational and economical aspects for Fischer-Tropsch synthesis. Effort to increase the efficiency of this kind of catalyst is an important research topic. In this work, the effect of lanthanum on characteristic behavior, conversion and selectivity of a Fe-Co/SiO2 Fischer-Tropsch catalyst was studied. The Fe-Co-La/SiO2 Catalysts were prepared using an incipient wetness impregnation method. These catalysts were then characterized by XRF-EDAX, BET and TPR techniques, and their performance were evaluated in a lab-scale reactor at 250ºC, H2/CO = 1.8 of molar ratio, 16 barg pressure and GHSV=600 h-1. TPR analysis showed that the addition of La lowered the reduction temperature of Fe-Co catalyst, and due to a lower temperature, the sintering of the catalyst can be mitigated. Furthermore, from the micro reactor tests (about 4 days, it was found that lanthanum promoted catalyst had higher selectivity toward hydrocarbons, and lower selectivity toward CO2.Received: 8th July 2013; Revised: 18th November 2013; Accepted: 1st December 2013[How to Cite: Abbasi, A., Ghasemi, M., Sadighi, S. (2014. Effect of Lanthanum as a Promoter on Fe-Co/SiO2 Catalyst for Fischer-Tropsch Synthesis. Bulletin of Chemical Reaction Engineering & Catalysis, 9 (1: 23-27. (doi:10.9767/bcrec.9.1.5142.23-27][Permalink/DOI: http://dx.doi.org/10.9767/bcrec.9.1.5142.23-27

  13. Synthesis of biogenic silicon/silica (Si/SiO2) nanocomposites from rice husks and wheat bran through various microorganisms

    Kaur, Taranjot; Pal Singh, Gurwinder; Kaur, Gurneet; Kaur, Sukhvir; Gill, Prabhjot Kaur

    2016-08-01

    Biosilification is an economically viable, energy saving and green approach for the commercial scale synthesis of oxide nanomaterials. The room temperature synthesis of oxide nanocomposites from cost effective agro-based waste is a particular example of biosilification. In this study, synthesis of Si/SiO2 nanocomposites from inexpensive agro-based waste material i.e. rice husks (RH) and wheat bran (WB) has been carried out by means of various eukaryotic microorganisms, i.e. Actinomycete, Fusarium oxysporum, Aspergillus niger, Trichoderma sp. and Penicillium sp., under ambient conditions. The XRD diffrectrograms represents that the synthesized nanomaterials exhibits silicon, amorphous silica and other crystal arrays such as cristobalite, trydimite and quartz, depending upon the type microorganism and time period used for extraction. All of the aforesaid microorganism bio transformed the naturally occurring amorphous silica to crystalline structures within the period of 24 h. However, the Actinomycete and Trichoderma sp. took 48 h in case of rice husks for biotransformation of naturally occurring plant silica to crystalline nanocomposite. While in case of wheat bran, Actinomycete and Trichoderma sp. took 24 h for biotransformation. The extracted nanocomposites exhibits band edge in the range 230-250 nm and blue emission. The procedure described in study can be used for commercial level production of Si/SiO2 nanocomposites from agro based waste materials.

  14. Sustainable synthesis of magnetically separable SiO2/Co@Fe2O4 nanocomposite and its catalytic applications for the benzimidazole synthesis

    Jithendra Kumara, K. S.; Krishnamurthy, G.; Sunil Kumar, N.; Naik, Nagaraja; Praveen, T. M.

    2018-04-01

    The Co(II) and Fe(III) centres magnetically separable two new mesoporous nanocatalyst were synthesised via chemical synthesis method. The transmission electron microscopic studies (TEM) show that, the particles are spherical shape with mean size of 20 nm. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) reveals that SiO2 is coating on the surface of the cobalt ferrate nanoparticle (CoFe2O4). The SiO2 coating is efficiently preventing the aggregated collision of nanoparticles. Magnetic measurements show that diamagnetic character of the SiO2 is unaffected to the coercivity of SiO2 coated CoFe2O4 particles. In addition, these nanoparticles are used as nanocatalyst for high yielding, facile and expeditious synthesis of various functionalized 2-arylbenzimidazoles via one-pot condensation. The cascade including imine formation, cyclization, condensation, and aromatization occurs, without addition of any reducing or oxidizing agents. In all situations, the desired product was synthesised with excellent yield. The shorter reaction time, mild reaction condition, simplicity, non-toxicity, safe reaction and easy workup are the impotent merits of this protocol.

  15. Electrochemical synthesis of 1D core-shell Si/TiO2 nanotubes for lithium ion batteries

    Kowalski, Damian; Mallet, Jeremy; Thomas, Shibin; Nemaga, Abirdu Woreka; Michel, Jean; Guery, Claude; Molinari, Michael; Morcrette, Mathieu

    2017-09-01

    Silicon negative electrode for lithium ion battery was designed in the form of self-organized 1D core-shell nanotubes to overcome shortcomings linked to silicon volume expansion upon lithiation/delithiation typically occurring with Si nanoparticles. The negative electrode was formed on TiO2 nanotubes in two step electrochemical synthesis by means of anodizing of titanium and electrodeposition of silicon using ionic liquid electrolytes. Remarkably, it was found that the silicon grows perpendicularly to the z-axis of nanotube and therefore its thickness can be precisely controlled by the charge passed in the electrochemical protocol. Deposited silicon creates a continuous Si network on TiO2 nanotubes without grain boundaries and particle-particle interfaces, defining its electrochemical characteristics under battery testing. In the core-shell system the titania nanotube play a role of volume expansion stabilizer framework holding the nanostructured silicon upon lithiation/delithiation. The nature of Si shell and presence of titania core determine stable performance as negative electrode tested in half cell of CR2032 coin cell battery.

  16. Synthesis and characterization of ion-implanted Pt nanocrystals in SiO2

    Giulian, R.; Kluth, P.; Johannessen, B.; Araujo, L.L.; Llewellyn, D.J.; Cookson, D.J.; Ridgway, M.C.

    2007-01-01

    Pt nanocrystals (NCs) produced by ion implantation in SiO 2 films were investigated by Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The implantations were performed at liquid nitrogen temperature using energies between 3.4 and 5.6 MeV and an ion fluence range of 2-30 x 10 16 cm -2 and were followed by annealing in forming gas (95% N 2 , 5% H 2 ) for one hour at temperatures between 500 and 1100 deg. C. TEM analysis revealed that the NCs are spherical in shape. The mean size of the NCs annealed at 1100 deg. C varied between 2.8 and 3.6 nm for the highest and lowest fluences, respectively, as determined with both TEM and SAXS. In contrast to previous studies on ion implanted metal NCs, larger Pt NCs are located far beyond the Pt peak concentration, potentially the result of a strongly defect mediated NC nucleation

  17. Metal Fe3+ ions assisted synthesis of highly monodisperse Ag/SiO2 nanohybrids and their antibacterial activity

    Zhang, Nianchun; Xue, Feng; Yu, Xiang; Zhou, Huihua; Ding, Enyong

    2013-01-01

    Graphical abstract: TEM images of the Ag/SiO 2 -2 nanohybrids. The homogeneous and more mono-disperse Ag nanoparticles deposit on SiO 2 spheres. Through this method, Ag nanoparticles are easily formed on the surface of SiO 2 compared to other methods. Highlights: ► We prepared homogeneous and mono-dispersed Ag/SiO 2 -2 nanohybrids by adding Fe 3+ ions. ► The Ag/SiO 2 -2 nanohybrids had core(SiO 2 )-shell(Ag) structure. ► The Ag/SiO 2 -2 nanohybrids exhibited excellent antibacterial activity against bacteria. ► The reaction temperature was lower and the yield of Ag/SiO 2 -2 nanohybrids were higher. - Abstract: Highly monodispersed Ag/SiO 2 nanohybrids with excellent antibacterial property were synthesized by using DMF as a reducing agent and employing an additional redox potential of metal Fe 3+ ion as a catalytic agent. The obtained Ag/SiO 2 -2 nanohybrids of about 240 nm were highly monodispersity and uniformity by adding trace Fe 3+ ions into the reaction which Ag + reacted with N,N-dimethyl formamide (DMF) at 70 °C. Compared to the conventional techniques, which need long time and high temperature for silica coating of Ag nanoparticles, this new method was capable of synthesizing monodispersed, uniform, high yield Ag/SiO 2 nanohybrids. The electron was transferred from the Fe 2+ ion to the Ag + ion to accelerate the nucleation of silver nanoparticles. The chemical structures, morphologies and properties of the Ag/SiO 2 nanohybrids were characterized by X-ray diffraction (XRD), (High-resolution, Scanning transmission) transmission electron microscopy (TEM, HRTEM and STEM), and X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy (UV–vis) and test of antibacterial. The results demonstrated that the silver nanoparticles supported on the surface of SiO 2 spheres in Ag/SiO 2 -2 nanohybrids structure, the Ag nanoparticles were homogeneous and monodispersed. The results also indicated that the Ag/SiO 2 -2 nanohybrid had excellent antibacterial.

  18. Synthesis of Vertically-Aligned Carbon Nanotubes from Langmuir-Blodgett Films Deposited Fe Nanoparticles on Al2O3/Al/SiO2/Si Substrate.

    Takagiwa, Shota; Kanasugi, Osamu; Nakamura, Kentaro; Kushida, Masahito

    2016-04-01

    In order to apply vertically-aligned carbon nanotubes (VA-CNTs) to a new Pt supporting material of polymer electrolyte fuel cell (PEFC), number density and outer diameter of CNTs must be controlled independently. So, we employed Langmuir-Blodgett (LB) technique for depositing CNT growth catalysts. A Fe nanoparticle (NP) was used as a CNT growth catalyst. In this study, we tried to thicken VA-CNT carpet height and inhibit thermal aggregation of Fe NPs by using Al2O3/Al/SiO2/Si substrate. Fe NP LB films were deposited on three typed of substrates, SiO2/Si, as-deposited Al2O3/Al/SiO2/Si and annealed Al2O3/Al/SiO2/Si at 923 K in Ar atmosphere of 16 Pa. It is known that Al2O3/Al catalyzes hydrocarbon reforming, inhibits thermal aggregation of CNT growth catalysts and reduces CNT growth catalysts. It was found that annealed Al2O3/Al/SiO2/Si exerted three effects more strongly than as-deposited Al2O3/Al/SiO2/Si. VA-CNTs were synthesized from Fe NPs-C16 LB films by thermal chemical vapor deposition (CVD) method. As a result, at the distance between two nearest CNTs 28 nm or less, VA-CNT carpet height on annealed Al2O3/Al/SiO2/Si was about twice and ten times thicker than that on SiO2/Si and that on as-deposited Al2O3/Al/SiO2/Si, respectively. Moreover, distribution of CNT outer diameter on annealed Al2O3/Al/SiO2/Si was inhibited compared to that on SiO2/Si. These results suggest that since thermal aggregation of Fe NPs is inhibited, catalyst activity increases and distribution of Fe NP size is inhibited.

  19. Synthesis and microwave absorption enhancement of Fe-doped NiO@SiO2@graphene nanocomposites

    Wang, Lei; Huang, Ying; Ding, Xiao; Liu, Panbo; Zong, Meng; Wang, Yan

    2013-01-01

    Highlights: • Fe-doped NiO@SiO 2 @graphene composites have excellent microwave performance. • The reflection loss of Fe doped NiO@SiO 2 @graphene was below −10 dB in 7–11 GHz. • The maximum absorption of Fe-doped NiO@SiO 2 @graphene was −51.2 dB at 8.6 GHz. -- Abstract: Fe-doped NiO@SiO 2 @graphene nanocomposites have been successfully fabricated for the first time, in which Fe-doped NiO nanoparticles are about 3 nm in diameter. In order to measure their electromagnetic properties, Fe-doped NiO@SiO 2 @graphene (25 wt%) wax composites were then prepared. The experimental results show that Fe-doped NiO@SiO 2 @graphene nanocomposites exhibit significantly enhanced microwave absorption performance in terms of both the maximum reflection loss value and the absorption bandwidth in comparison with NiO@SiO 2 @graphene. The maximum reflection loss of Fe-doped NiO@SiO 2 @graphene nanocomposites can reach −51.2 dB at 8.6 GHz with a thickness of 4 mm, and the absorption bandwidth with the reflection loss below −10 dB is 4 GHz (from 7 to 11 GHz). Therefore, this kind of nanocomposites may have the potential as high-efficient absorbers for microwave absorption applications

  20. Ethanol-to-Butadiene Conversion over SiO2-MgO Catalysts: Synthesis-Structure-Performance Relationships

    Angelici, C.

    2015-01-01

    The work presented in this PhD Thesis provides new insights into the underlying reasons that make SiO2-MgO materials excellent catalysts for the ethanol-to-butadiene Lebedev process. In particular, the preparation technique of choice affects the structural properties of the resulting SiO2-MgO

  1. Synthesis of Hollow Nanotubes of Zn2SiO4 or SiO2: Mechanistic Understanding and Uranium Adsorption Behavior.

    Tripathi, Shalini; Bose, Roopa; Roy, Ahin; Nair, Sajitha; Ravishankar, N

    2015-12-09

    We report a facile synthesis of Zn2SiO4 nanotubes using a two-step process consisting of a wet-chemical synthesis of core-shell ZnO@SiO2 nanorods followed by thermal annealing. While annealing in air leads to the formation of hollow Zn2SiO4, annealing under reducing atmosphere leads to the formation of SiO2 nanotubes. We rationalize the formation of the silicate phase at temperatures much lower than the temperatures reported in the literature based on the porous nature of the silica shell on the ZnO nanorods. We present results from in situ transmission electron microscopy experiments to clearly show void nucleation at the interface between ZnO and the silica shell and the growth of the silicate phase by the Kirkendall effect. The porous nature of the silica shell is also responsible for the etching of the ZnO leading to the formation of silica nanotubes under reducing conditions. Both the hollow silica and silicate nanotubes exhibit good uranium sorption at different ranges of pH making them possible candidates for nuclear waste management.

  2. Synthesis of NiO-TiO2 hybrids/mSiO2 yolk-shell architectures embedded with ultrasmall gold nanoparticles for enhanced reactivity

    Fang, Jiasheng; Zhang, Yiwei; Zhou, Yuming; Zhao, Shuo; Zhang, Chao; Huang, Mengqiu; Gao, Yan

    2017-08-01

    Novel NiO-TiO2 hybrids/mSiO2 yolk-shell architectures loaded with ultrasmall Au nanoparticles (STNVS-Au) were developed via the rational synthetic strategy. The hierarchical yolk-shell nanostructures (STNVS) with high surface areas were constructed by a facile "bottom-up" assembly process using SiO2 materials and polymer resins as cores/shells and sacrificial templates, accompanied by a simple hydrothermal incorporation of NiO into uniform amorphous TiO2 layers that were converted to NiO-anatase TiO2 p-n heterojunction hybrids. Then, numerous sub-3 nm Au nanoparticles were post encapsulated within STNVS nanostructures through the low-temperature hydrogen reduction based on the unique deposition-precipitation method with Au(en)2Cl3 compounds as gold precursors. The NiO-TiO2 hybrids alloying with Au nanoparticles were effectively protected and entrapped within STNVS architectures, and interacted with outer mSiO2-Au shells, which comprised the powerful STNVS-Au yolk-shell nanoreactors and produced stronger configural synergies in enhancing the heterogeneous catalysis. Into catalyzing the reduction of 4-nitrophenol to 4-aminophenol, the STNVS-Au was shown with outstanding activity and reusability, and its pristine morphology was well retained during the recycling process.

  3. Synthesis of mesoporous SiO2–ZnO nanocapsules: encapsulation of small biomolecules for drugs and “SiOZO-plex” for gene delivery

    Kumar, Vijay Bhooshan; Annamanedi, Madhavi; Prashad, Muvva Durga; Arunasree, Kalle M.; Mastai, Yitzhak; Gedanken, Aharon; Paik, Pradip

    2013-01-01

    This work presents a new synthesis of mesoporous SiO 2 –ZnO composite nanocapsules with sizes of 90–150 nm and represents their applications in encapsulation of small biomolecules (fluorescent molecules, drugs, and DNA) for uses in medical biotechnology (e.g., drug and gene delivery) for the first time. The nanocapsule size and morphology have been confirmed through the HRSEM and HRTEM. The mesoporous structure of the novel materials has been confirmed through both BET and HRTEM, and the pore diameter observed to be ca. 2–8 nm with an average diameter of 5.1 nm. The BET surface area of mesoporous SiO 2 –ZnO was found to be ∼230 m 2 g −1 . Three different types of pores were detected through HRTEM: type-I, normal pores in silica matrix, pore with ZnO nanoparticles at the boundary (type-II) and type-III, the pores with tiny ZnO nanoparticles (∼5–7 nm) inside them. To demonstrate the biocompatibility and cell viability of the nanocapsules, normal and cancerous lymphocyte cells have been chosen and investigated in a systematic way. Fluorescent dye (Rhodamine 6G), anticancer drug e.g., Doxorubicin (DOX) were loaded in all types of pores, and EtBr-labeled DNA molecules were loaded efficiently into the mesopores of second and third types of the composite nanocapsules to manifest the characteristic of mesoporous, and to find out its loading efficacy. The release kinetics of Rhodamine 6G and DOX were studied. The results highlight the potential of novel functional mesoporous SiO 2 –ZnO nanoparticles for using as the carrier of drugs and formation of “SiOZO-plex”, a complex of mesoporous SiO 2 –ZnO with DNA for gene delivery applications.Graphical Abstract

  4. Synthesis and structure of nanomaterials in the system K2O-Nb2O5-SiO2

    Georgi Chernev

    2009-06-01

    Full Text Available The aim of the present work is synthesis of ferroelectric nanomaterials, in the K2O-Nb2O5-SiO2 system via solgel method and studying the processes of formation and structure of the synthesized ferroelectric nanomaterials. The structure of synthesized materials has been studied by means of the following methods: EDS, XRD, FT-IR, SEM and AFM. The results obtained showed that the structure of the investigated compositions does not depend on the niobium content and all the samples keep their amorphous nature at room temperature. The surface structure shows random distribution of different kinds of aggregates with dimensions about 200–500 nm. The presence of a hybrid nanostructure with well-defi ned nanounits having special geometry is clearly observed.

  5. Sol-gel synthesis and structure of La2O3–CoO–SiO2 powders

    Lachezar Radev

    2008-12-01

    Full Text Available LaCoO3 powders are studied because they exhibit interesting electrical, magnetic and catalytic properties. In this paper, new synthesized La2O3-CoO-SiO2 powders with different quantity of silica were prepared via solgel method in aqua media, starting from metal nitrates with different chelating agents. The relation between the reaction in solution, crystallization pathway and morphology were discussed. In LaCoO3-SiO2 powders, depending on the content of SiO2 and the treatment temperature (700–1100°C, different crystalline phases (LaCoO3, Co2SiO4 and La9.31(SiO46O2 were observed with the crystallite sizes ranging from 50 to 100 nm. It was proved that chemical composition and nature of used additives has influence on the phase formation and structure of obtained nanomaterials.

  6. Synthesis and characterization of erbium-doped SiO2 nanoparticles fabricated by using reverse micelle and sol-gel processing

    Park, Hoyyul; Bae, Dongsik

    2012-01-01

    Erbium-doped SiO 2 nanoparticles have been synthesized using a reverse micelle technique combined with metal-alkoxide hydrolysis and condensation. The sizes and the morphologies of the erbium-doped SiO 2 nanoparticles could be changed by varying the molar ratio of water to surfactant. The sizes and the morphologies of the erbium-doped SiO 2 nanoparticles were examined by using a transmission electron microscope. The average size of synthesized erbium-doped SiO 2 nanoparticles was approximately 20 - 25 nm and that of the erbium particles was 3 - 5 nm. The effects of the synthesis parameters, such as the molar ratio of water to surfactant, are discussed.

  7. Synthesis of Nanoscale CaO-Al2O3-SiO2-H2O and Na2O-Al2O3-SiO2-H2O Using the Hydrothermal Method and Their Characterization

    Jingbin Yang

    2017-06-01

    Full Text Available C-A-S-H (CaO-Al2O3-SiO2-H2O and N-A-S-H (Na2O-Al2O3-SiO2-H2O have a wide range of chemical compositions and structures and are difficult to separate from alkali-activated materials. Therefore, it is difficult to analyze their microscopic properties directly. This paper reports research on the synthesis of C-A-S-H and N-A-S-H particles with an average particle size smaller than 300 nm by applying the hydrothermal method. The composition and microstructure of the products with different CaO(Na2O/SiO2 ratios and curing conditions were characterized using XRD, the RIR method, FTIR, SEM, TEM, and laser particle size analysis. The results showed that the C-A-S-H system products with a low CaO/SiO2 ratio were mainly amorphous C-A-S-H gels. With an increase in the CaO/SiO2 ratio, an excess of Ca(OH2 was observed at room temperature, while in a high-temperature reaction system, katoite, C4AcH11, and other crystallized products were observed. The katoite content was related to the curing temperature and the content of Ca(OH2 and it tended to form at a high-temperature and high-calcium environment, and an increase in the temperature renders the C-A-S-H gels more compact. The main products of the N-A-S-H system at room temperature were amorphous N-A-S-H gels and a small amount of sodalite. An increase in the curing temperature promoted the formation of the crystalline products faujasite and zeolite-P. The crystallization products consisted of only zeolite-P in the high-temperature N-A-S-H system and its content were stable above 70%. An increase in the Na2O/SiO2 ratio resulted in more non-bridging oxygen and the TO4 was more isolated in the N-A-S-H structure. The composition and microstructure of the C-A-S-H and N-A-S-H system products synthesized by the hydrothermal method were closely related to the ratio of the raw materials and the curing conditions. The results of this study increase our understanding of the hydration products of alkali

  8. Ultrasound promoted and SiO2/CCl3COOH mediated synthesis of 2 ...

    First one-pot synthesis of 2-aryl-1-arylmethyl-1H- benzimidazole derivatives from ... to promote chemical reactions is called sonochemistry .... −1): 1615, 2845, 2980, 3036, 3067; 1H NMR (500MHz,. CDCl3):δ 5.38 (s, 2H, CH2), 6.65 (d, J = 8.0 ...

  9. Catalyst synthesis PD/SiO2 and PD/C by irradiation microwave method

    Sant'Anna, L.S.; Franceschi, E.; Egues, S.; Santos, M.L.; Dariva, C.; Borges, G.R.

    2016-01-01

    The synthesis of nanoparticulate materials has been developed over the years, in order to propose new routes or routes more efficient in the process. The application of microwave irradiation applied in this work allowed to show that metal catalysts may be generated in a faster reaction time compared to conventional mechanical agitation techniques. Catalysts using palladium acetate (OAc) 2 supported on charcoal and commercial silica were synthesized. The solvent used for the preparation was 40 ml of ethanol at a temperature of 100 ° C and 300 W power. The synthesis time was 2 to 5 minutes. The synthesized material was calcined and characterized by ICP, XRD, TEM and BET obtained metal content ranged from 1.1 to 4.1% of the metal support. The particle size was between 7 and 9 nm. The surface areas of the carriers were reduced on its surface due to the metal impregnation. (author)

  10. Synthesis and Physicochemical Characterization of Mesoporous SiO2 Nanoparticles

    Dharani Das

    2014-01-01

    Full Text Available There exists a knowledge gap in understanding potential toxicity of mesoporous silica nanoparticles. A critical step in assessing toxicity of these particles is to have a wide size range with different chemistries and physicochemical properties. There are several challenges when synthesizing mesoporous silica nanoparticles over a wide range of sizes including (1 nonuniform synthesis protocols using the same starting materials, (2 the low material yield in a single batch synthesis (especially for particles below 60–70 nm, and (3 morphological instability during surfactant removal process and surface modifications. In this study, we synthesized a library of mesoporous silica nanoparticles with approximate particle sizes of 25, 70, 100, 170, and 600 nm. Surfaces of the silica nanoparticles were modified with hydrophilic-CH2–(CH22–COOH and relatively hydrophobic-CH2–(CH210–COOH functional groups. All silica nanoparticles were analysed for morphology, surface functionality, surface area/pore volume, surface organic content, and dispersion characteristics in liquid media. Our analysis revealed the synthesis of a spectrum of monodisperse bare and surface modified mesoporous silica nanoparticles with a narrow particle size distribution and devoid of cocontaminants critical for toxicity studies. Complete physicochemical characterization of these synthetic mesoporous silica nanoparticles will permit systematic toxicology studies for investigation of structure-activity relationships.

  11. Synthesis and Characterization of Ti-Phenyl at SiO2 Core-Shell Nanoparticles Catalyst

    Syamsi Aini; Jon Efendi; Syamsi Aini; Jon Efendi

    2012-01-01

    This study highlights the potential use of Ti-Phenyl at SiO 2 core-shell nanoparticles as heterogeneous catalysis in oxidation reaction. The Ti-Phenyl at SiO 2 was synthesized by reduction of TiCl 4 and diazonium salt with sodium borohydride to produce phenyl titanium nanoparticles (Ti-Phenyl), followed by the silica shell coating using tetraethyl orthosilicate (TEOS). The Ti-Phenyl at SiO 2 nanoparticles were characterized by Fourier transform infrared (FTIR) spectrometer, diffuse reflectance (DR) UV-visible spectrometer, thermogravimetric analyzer (TGA), X-ray diffraction (XRD) spectrometer, field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The core-shell size of Ti-Phenyl at SiO 2 was in the range of 40 to 100 nm with its core composed with an agglomeration of Ti-Phenyl. The Ti-Phenyl at SiO 2 was active as a catalyst in the liquid phase epoxidation of 1-octene with aqueous hydrogen peroxide as an oxidant. (author)

  12. Preparation and characterization of Fe–V/TiO2SiO2 nanocatalyst ...

    Administrator

    to silica mole ratio, synthesis temperature and heating rate of calcination on the structure ... 2 wt% of zinc (all on weight percent) supported on TiO2SiO2 with synthesis temperature of ... (TEOS) and titanium isopropoxide (TIP) have been dis-.

  13. Synthesis, Characterization, and Catalytic Ability of U3O8/SiO2 Nocomposite Materials

    Green, Fatima

    Applications of uranium oxide nanoparticles as oxidative catalysts is a field uncommonly studied. In the past, little research has been done to study the potential of this material for room temperature, catalytic breakdown of organic pollutants. Due to an increase in the presence of these pollutants in surface water, an effort to study these reactions in aqueous solution has been a high priority. To further enhance the properties of the nanoparticles, synthesis was performed using the sol-gel method. Characterization of the material was carried out using, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction, (XRD) and transmission electron microscopy (TEM). This material has proven to be pure, crystalline alpha-phase U3O8 with an average particle size of 27 nm. Based on previous studies, we hypothesized that under ambient conditions our synthesized material will be able to effectively breakdown organic molecules in aqueous solution. Catalytic studies were monitored using titration techniques with oxalic acid as a model system. The decomposition percentages varied based on amounts of nanocomposite used and temperature controls.

  14. In situ synthesis and properties of self-reinforced Si3N4–SiO2 ...

    reinforced glass–ceramic composites were obtained without any β -Si 3 N 4 seed crystal. These composites with different compositions were prepared in a nitrogenatmosphere for comparison of phase transformation and mechanical properties.

  15. Au nanoparticles decorated SiO2 nanowires by dewetting on curved surfaces: facile synthesis and nanoparticles–nanowires sizes correlation

    Ruffino, F.; Grimaldi, M. G.

    2013-01-01

    We report a solid-state synthesis for SiO 2 nanowires (NWs) (up to 20 microns in length and from about 40 to about 150 nm in diameter) coated by Au nanoparticles (NPs) (from about 20 to about 80 nm in diameter). This protocol is based on three steps: (1) large area production of very long SiO 2 NWs on a Si surface exploiting a simple Au/Si solid-state reaction at high temperature; (2) coating of the SiO 2 NWs by a Au film of desired thickness using sputtering depositions; and (3) a thermal process to induce a dewetting process of the Au-film coating the SiO 2 NWs to obtain Au NPs on the curved surface of the NWs. The morphology evolution of the SiO 2 NWs was followed, in each step, by scanning electron microscopy analyses. They allowed to correlate the evolution of the NPs size with the NWs sizes for different thicknesses of the starting Au-film coating the NWs and different annealing temperatures of the dewetting process. Some theoretical concepts, related to the dewetting process of a film on a curved surface were used to describe the experimental data. The main advantages of the proposed protocols include: (i) simplicity and low-cost (it is based only on sputtering depositions and thermal processes), and (ii) versatility based on the possibility of tuning Au-film thickness and annealing temperature to tune the NPs–NWs sizes ratio. These advantages can make this technique suitable for the mass production of Au NPs-coated SiO 2 NWs toward applications in electronic devices, biosensors, and nanoscale optical devices

  16. High-temperature synthesis of highly hydrothermal stable mesoporous silica and Fe-SiO2 using ionic liquid as a template

    Liu, Hong; Wang, Mengyang; Hu, Hongjiu; Liang, Yuguang; Wang, Yong; Cao, Weiran; Wang, Xiaohong

    2011-01-01

    Mesoporous silicas and Fe-SiO 2 with worm-like structures have been synthesized using a room temperature ionic liquid, 1-hexadecane-3-methylimidazolium bromide, as a template at a high aging temperature (150-190 o C) with the assistance of NaF. The hydrothermal stability of mesoporous silica was effectively improved by increasing the aging temperature and adding NaF to the synthesis gel. High hydrothermally stable mesoporous silica was obtained after being aged at 190 o C in the presence of NaF, which endured the hydrothermal treatment in boiling water at least for 10 d or steam treatment at 600 o C for 6 h. The ultra hydrothermal stability could be attributed to its high degree of polymerization of silicate. Furthermore, highly hydrothermal stable mesoporous Fe-SiO 2 has been synthesized, which still remained its mesostructure after being hydrothermally treated at 100 o C for 12 d or steam-treated at 600 o C for 6 h. -- Graphical abstract: Worm-like mesoporous silica and Fe-SiO 2 with high hydrothermal stability have been synthesized using ionic liquid 1-hexadecane-3-methylimidazolium bromide as a template under the assistance of NaF at high temperature. Display Omitted Research highlights: → Increasing aging temperature improved the hydrothermal stability of materials. →Addition of NaF enhanced the polymerization degree of silicates. → Mesoporous SiO 2 and Fe-SiO 2 obtained have remarkable hydrothermal stability.

  17. Synthesis of mesoporous TS-1 using a hybrid SiO2–TiO2 xerogel for catalytic oxidative desulfurization

    Yang, Seung-Tae; Jeong, Kwang-Eun; Jeong, Soon-Yong; Ahn, Wha-Seung

    2012-01-01

    Graphical abstract: Display Omitted Highlights: ► Meso-TS-1 catalyst was synthesized using a SiO 2 –TiO 2 xerogel with an organosilane precursor. ► Hierarchical pore structure was confirmed by characterization of the materials. ► Catalytic activity was tested using oxidative desulfurization of the model sulfur compounds. ► Meso-TS-1 demonstrated significantly improved catalytic activity than TS-1. -- Abstract: Mesoporous TS-1 (M-TS-1) was synthesized using a hybrid SiO 2 –TiO 2 xerogel combined with an organosilane precursor. Prepared samples were characterized by XRD, UV–vis spectroscopy, SEM, and N 2 adsorption–desorption measurement. M-TS-1, prepared in 2 days, showed high crystallinity and the best textural properties among the samples. The N 2 adsorption–desorption isotherms of M-TS-1 exhibited a hysteresis loop at pressure higher than P/P 0 = 0.4, clearly indicating the existence of mesopores. M-TS-1 has significantly larger mesopore volume (0.48 cm 3 /g) than that of conventional TS-1 (0.07 cm 3 /g), and showed a narrow peak centered at ca. 6.3 nm. In the oxidative desulfurization reaction, M-TS-1 was more active than conventional TS-1 at the same Ti-loading; M-TS-1 produced a dibenzothiophene (DBT) conversion of 96%, whereas conventional TS-1 produced a final DBT conversion of 5.6% after a reaction time of 180 min. Oxidative desulfurization over TS-1 was influenced both by electron density and steric hindrance in the sulfur compounds tested.

  18. Low temperature synthesis of non-crystaline solids of the system SrO-SiO2

    Yamane, M.; Kojima, T.

    1981-01-01

    Non-crystalline solids within the liquid-liquid immiscibility region in the system SrO-SiO 2 have been prepared from a gel obtained by the hydrolysis of silicon tetramethoxide with an aqueous solution of strontium nitrate. The gel which was porous and translucent at room temperature increased in transparency with heating due to the collapse of micropores until it became completely clear. The gel became opaque again due to the precipitation of α-quartz at higher temperatures. The critical temperatures below which clear solids were obtained fell on a line connecting the glass transition temperatures of vitreous silica and those of SrO-SiO 2 glass prepared by melting. The density and refractive index of the pore-free, clear glassy solid, changed continuously with the SrO content along lines connecting those of vitreous silica and SrO-SiO 2 glasses of high SrO content prepared by melting. The maximum amount of Sr 2+ which could be introduced using an aqueous solution as the starting material corresponded to a composition of 10 SrO x 90 SiO 2 by weight. (orig.)

  19. Synthesis of Cu/SiO2 Core-Shell Particles Using Hyperbranched Polyester as Template and Dispersant

    Han, Wensong

    2017-07-01

    Third-generation hyperbranched polyester (HBPE3) was synthesized by stepwise polymerization with N, N-diethylol-3-amine methylpropionate as AB2 monomer and pentaerythritol as core molecule. Then, Cu particles were prepared by reduction of copper nitrate with ascorbic acid in aqueous solution using HBPE3 as template. Finally, Cu/SiO2 particles were prepared by coating silica on the surface of Cu particles. The structure and morphology of the samples were characterized by Fourier-transform infrared (FT-IR) spectrometry, x-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results confirmed the formation of the silica coating on the surface of Cu and that the Cu/SiO2 particles had spherical shape with particle size in the range of 0.8 μm to 2 μm. Compared with pure Cu, the synthesized Cu/SiO2 core-shell particles exhibited better oxidation resistance at high temperature. Moreover, the oxidation resistance of the Cu/SiO2 particles increased significantly with increasing tetraethyl orthosilicate (TEOS) concentration.

  20. Ruthenium Modification on Mn and Zr-Modified Co/SiO2 Catalysts for Slurry-Phase Fischer-Tropsch Synthesis

    Tomohisa Miyazawa

    2015-01-01

    Full Text Available The addition of Ru to Mn and Zr-modified Co/SiO2 catalysts, while applying different preparation orders and loading amounts, was investigated as a means of enhancing the Fischer-Tropsch synthesis reaction. The coimpregnation of Zr/SiO2 with Co, Mn and Ru gave the most attractive catalytic properties. This can be attributed to the higher dispersion of Co metal resulting from the coimpregnation of Co and Mn as well as enhanced reducibility due to the presence of Ru. The addition of a moderate amount of Ru together with the appropriate order of addition affected both the Co reducibility and the catalytic activity, primarily because of increased reducibility. The addition of even 0.1 wt.% Ru resulted in an obvious enhancement of Fischer-Tropsch synthesis activity.

  1. Synthesis and optical properties of SiO2–Al2O3–MgO–K2CO3–CaO ...

    Synthesis and optical properties of SiO 2 –Al 2 O 3 –MgO–K 2 CO 3 –CaO–MgF 2 –La 2 O 3 glasses. C R GAUTA. Volume 39 Issue 3 June 2016 pp 677-682 ... Author Affiliations. C R GAUTA1. Advanced Glass and Glass Ceramic Research Laboratory, Department of Physics, University of Lucknow, Lucknow 226007, India ...

  2. Synthesis and characterization of the Pt/SiO2 nanocomposite by the sol-gel method

    A. Salabat

    2011-01-01

    Full Text Available The silica supported platinum nanoparticles was synthesized by using the sol-gel method. The possibility of using diamminedinitro platinum (II as Pt precursor and effect of metal precursor concentration on the final Pt nanoparticle size was investigated. A stable silica sol was prepared via hydrolysis of tetraethyl orthosilicate (TEOS as a metal alcoxide and condensation reaction. Subsequently, diamminedinitro platinum (II was added to sol to form the Pt/silica sol. After drying and calcination of the sol, the Pt/SiO2 nanocpmposite has been obtained. Crystallographic information and crystalline size of the synthesized Pt/SiO2 were determined by X-ray diffraction (XRD method. Morphology of the nanoparticles and hydrogen-bonding interaction between silanol groups and amine ligands were characterized by SEM and Fourier transform infrared (FTIR spectra, respectively. Transmission Electron Microscopy (TEM was employed in evaluating the distribution and size of the platinum nanoparticles in the silica.

  3. Synthesis and effect of copper incorporation on the thermoluminescence and structural properties of SiO2 particles

    Burruel I, S. E.; Cruz V, C.; Salas J, Ch. J.; Bernal, R.; Garcia H, A. R.; Castano, V. M.

    2015-10-01

    Full text: In this work, we evaluated the effect of Cu-dopant concentration in SiO 2 particles on structural and thermoluminescence (Tl) properties, prepared by the sol-gel technique. Tl studies in silica samples containing Cu show an important enhancement of their Tl response when compared with pure silica samples. In the copper doped silica a prominent Tl peak is observed, the glow curve was observed between 70 and 450 degrees C after exposure to beta irradiation. The maximum temperature of the glow peak centered at around 140 degrees C shifts to higher values and the intensity enhancement with increasing Cu content, this glow curve is surely composed of several overlapped individual Tl peaks. Also, the particle size is affected by the concentration of Cu dopant. In the case SiO 2 , only is observed a glow peak centered to 95 degrees C, which is interesting for non-Tl dosimetry of ionizing radiation, which is based in detecting the afterglow response following exposure to radiation. The dose response of SiO 2 :Cu showed a linear behaviour in the interval studied with no saturation evidence until 6.4 kGy, which makes this material suitable and promising for medical, industrial and also space dosimetry applications. (Author)

  4. Synthesis and electrochemical characterization of hybrid membrane Nafion-SiO2 for application as polymer electrolyte in PEM fuel cell

    Dresch, Mauro Andre

    2009-01-01

    In this work, the effect of sol-gel synthesis parameters on the preparation and polarization response of Nafion-SiO 2 hybrids as electrolytes for proton exchange membrane fuel cells (PEMFC) operating at high temperatures (130 degree C) was evaluated. The inorganic phase was incorporated in a Nafion matrix with the following purposes: to improve the Nafion water uptake at high temperatures (> 100 degree C); to increase the mechanical strength of Nafion and; to accelerate the electrode reactions. The hybrids were prepared by an in-situ incorporation of silica into commercial Nafion membranes using an acid-catalyzed sol-gel route. The effects of synthesis parameters, such as catalyst concentration, sol-gel solvent, temperature and time of both hydrolysis and condensation reactions, and silicon precursor concentration (Tetraethyl orthosilicate - TEOS), were evaluated as a function on the incorporation degree and polarization response. Nafion-SiO 2 hybrids were characterized by gravimetry, thermogravimetric analysis (TGA), scanning electron microscopy and X-ray dispersive energy (SEM-EDS), electrochemical impedance spectroscopy (EIS), and X-ray small angle scattering (SAXS). The hybrids were tested as electrolyte in single H 2 /O 2 fuel cells in the temperature range of 80 - 130 degree C and at 130 degree C and reduced relative humidity (75% and 50%). Summarily, the hybrid performance showed to be strongly dependent on the synthesis parameters, mainly, the type of alcohol and the TEOS concentration. (author)

  5. LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Synthesis of bulk SiO2 : MxOy materials in a steady-state laser plume

    Lebedev, V. F.

    1997-01-01

    An analysis was made of the conditions of existence of a two-component steady-state laser plume in atmospheric air. Such a plume is used in single-stage synthesis of bulk molten materials belonging to the SiO2 : MxOy system. Targets of the SiO2 : M type (metal foil and a silica glass rod) and doping elements with boiling points below and above the boiling point of silica glass are discussed. The regimes and efficiency of steady-state transfer of the dopants are considered. The efficiency of transfer of metal oxides during growth of samples with the aid of a cw CO2 laser is reported to be ~0.05, 0.4, and 0.75g min-1 kW-1 when the mass dopant concentration is ~8%, 20%, and 60% for the oxides of Ti, Cu, and Ni, respectively.

  6. Sol-gel synthesis and characterization of single-phase Ni ferrite nanoparticles dispersed in SiO2 matrix

    Nadeem, K.; Traussnig, T.; Letofsky-Papst, I.; Krenn, H.; Brossmann, U.; Wuerschum, R.

    2010-01-01

    Nanoparticles of NiFe 2 O 4 dispersed in SiO 2 (25 wt%) matrix were synthesized by sol-gel method using tetraethyl orthosilicate (TEOS), as a precursor for SiO 2 . The sol-gel method for nanocomposites normally provides multi-phase nanoparticles. We investigated by a synopsis of different analysis methods, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SQUID-magnetometry, how the various chemical phases are transformed to a single-phase spinel structure during the various stages of annealing from 300 to 900 o C. We have developed a full phase diagram of chemical phases as a function of annealing temperature. The average particle size lies in the range 16-27 nm. The chemical phases formed below 900 o C are NiFe, NiO, γ-Fe 2 O 3 , α-Fe 2 O 3 , and NiFe 2 O 4 , respectively. The role of the TEOS prepared SiO 2 matrix is to restrict the particle size in a small range in order to rule out particle size effects. In the mid-infrared, a shift of the vibrational Fe-O bond is observed from 568 to 586 cm -1 for annealing between 500 and 700 o C which indicates an increasing NiFe 2 O 4 phase formation. A systematic study of coercivity field (ranging from 32 to 200 Oe) and saturation magnetic moment (ranging from 12.2 to 32.1 emu/g) for differently annealed samples supports our findings about the evolution of single-phase NiFe 2 O 4 at 900 o C. The opposite trend of saturation magnetic moment and coercivity with respect to annealing temperature clearly separates the different phases of metallic, antiferromagnetic, and finally single-phase spinel NiFe 2 O 4 .

  7. Sol-Gel synthesis of MgO-SiO2 glass compositions having stable liquid-liquid immiscibility

    Bansal, Narottam P.

    1987-01-01

    MgO-SiO2 glasses containing up to 15 mol % MgO, which could not have been prepared by the conventional glass melting method due to the presence of stable liquid-liquid immiscibility, were synthesized by the sol-gel technique. Clear and transparent gels were obtained from the hydrolysis and polycondensation of silicon tetraethoxide (TEOS) and magnesium nitrate hexahydrate when the water/TEOS mole ratio was four or more. The gelling time decreased with increase in magnesium content, water/TEOS ratio, and reaction temperature. Magnesium nitrate hexahydrate crystallized out of the gels containing 15 and 20 mol % MgO on slow drying. This problem was partially alleviated by drying the gels quickly at higher temperatures. Monolithic gel samples were prepared using glycerol as the drying control additive. The gels were subjected to various thermal treatments and characterized by several methods. No organic groups could be detected in the glasses after heat treatments to approx. 800 C, but trace amounts of hydroxyl groups were still present. No crystalline phase was found from X-ray diffraction in the gel samples to approx. 890 C. At higher temperatures, alpha quartz precipitated out as the crystalline phase in gels containing up to 10 mol % MgO. The overall activation energy for gel formation in 10MgO-90SiO2 (mol %) system for water/TEOS mole ratio of 7.5 was calculated to be 58.7 kJ/mol.

  8. Synthesis and Performance of an Acrylamide Copolymer Containing Nano-SiO2 as Enhanced Oil Recovery Chemical

    Zhongbin Ye

    2013-01-01

    Full Text Available A novel copolymer containing nano-SiO2 was synthesized by free radical polymerization using acrylamide (AM, acrylic acid (AA, and nano-SiO2 functional monomer (NSFM as raw materials under mild conditions. The AM/AA/NSFM copolymer was characterized by infrared (IR spectroscopy, 1H NMR spectroscopy, elemental analysis, and scanning electron microscope (SEM. It was found that the AM/AA/NSFM copolymer exhibited higher viscosity than the AM/AA copolymer at 500 s−1 shear rate (18.6 mPa·s versus 8.7 mPa·s. It was also found that AM/AA/NSFM could achieve up to 43.7% viscosity retention rate at 95°C. Mobility control results indicated that AM/AA/NSFM could establish much higher resistance factor (RF and residual resistance factor (RRF than AM/AA under the same conditions (RF: 16.52 versus 12.17, RRF: 3.63 versus 2.59. At last, the enhanced oil recovery (EOR of AM/AA/NSFM was up to 20.10% by core flooding experiments at 65°C.

  9. SiO2@FeSO4 nano composite: A recoverable nano-catalyst for eco-friendly synthesis oximes of carbonyl compounds

    Mostafa Karimkoshteh

    2016-01-01

    Full Text Available Various aldoximes and ketoximes synthesis of corresponding aldehydes and ketones in the presence of SiO2@FeSO4 nano composite as recoverable nano catalyst and NH2OH·HCl. The SiO2@FeSO4 nano composite system was carried out between 10 to 15 min in oil bath (70-80 °C under solvent-free condition in excellent yields in addition this protocol can be used for industrial scales. This method offers some advantages in term of clean reaction conditions, easy work-up procedure, short reaction time, applied to convert α-diketones to α-diketoximes (as longer than other carbonyl compounds, α,β-unsaturated aldehydes and ketones to corresponding oximes and suppression of any side product. So we think that NH2OH•HCl/SiO2@FeSO4 nano composite system could be considered a new and useful addition to the present methodologies in this area. Structure of products and nano composite elucidation was carried out by 1H NMR, 13C NMR, FT-IR, scanning electron microscopy (SEM.

  10. Efficient one-pot sonochemical synthesis of thickness-controlled silica-coated superparamagnetic iron oxide (Fe3O4/SiO2) nanospheres

    Abbas, Mohamed; Abdel-Hamed, M. O.; Chen, Jiangang

    2017-12-01

    A facile and eco-friendly efficient sonochemical approach was designed for the synthesis of highly crystalline Fe3O4 and Fe3O4/SiO2 core/shell nanospheres in single reaction. The generated physical properties (shock waves, microjets, and turbulent flows) from ultrasonication as a consequence of the collapse of microbubbles and polyvinylpyrrolidone (PVP) as a chemical linker were found to play a crucial role in the successful formation of the core/shell NPs within short time than the previously reported methods. Transmission electron microscopy revealed that a uniform SiO2 shell is successfully coated over Fe3O4 nanospheres, and the thickness of the silica shell could be easily controlled in the range from 5 to 15 nm by adjusting the reaction parameters. X-ray diffraction data were employed to confirm the formation of highly crystalline and pure phase of a cubic inverse spinel structure for magnetite (Fe3O4) nanospheres. The magnetic properties of the as-synthesized Fe3O4 and Fe3O4/SiO2 core/shell nanospheres were measured at room temperature using vibrating sample magnetometer, and the results demonstrated a high magnetic moment values with superparamagnetic properties.

  11. Synthesis and characterization of novel Cu(II) complex coated Fe3O4@SiO2 nanoparticles for catalytic performance

    Nasrollahzadeh, Mahmoud; Sajjadi, Mohaddeseh; Khonakdar, Hossein Ali

    2018-06-01

    In this study, a convenient method for the synthesis of arylaminotetrazoles has been developed using a copper (II)-aminotetrazole complex immobilized on silica-coated Fe3O4 (Fe3O4@SiO2) nanoparticles (Fe3O4@SiO2-aminotet-Cu(II)) as a novel and efficient magnetically catalyst. The constructed superparamagnetic core-shell nanoparticles were successfully prepared, as proven using different spectroscopic techniques such as fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscope (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetry and differential thermogravimetry (TG-DTG) and vibrating sample magnetometer (VSM) analysis. The applicability of Fe3O4@SiO2-aminotet-Cu(II) magnetic catalyst allows the efficient synthesis of a variety of arylaminotetrazoles from the reaction between various arylcyanamides with sodium azide in high yields. The effect of catalyst loading was investigated. In addition, the reaction mechanism for the synthesis of arylaminotetrazoles was reasonably proposed. Results show that the 1-aryl-5-amino-1H-tetrazole (B isomer) and 5-arylamino-1H-tetrazole (A isomer) can be obtained from the arylcyanamides carrying electron-donating and electron-withdrawing substituents, respectively. This procedure offers a simple methodology, relatively short reaction times, easy work-up, high yields of the products and a cleaner reaction with elimination of hydrazoic acid (HN3). Moreover, catalyst can be conveniently recovered through the use of external magnet and reused for at least 6 times without any significant loss of its activity.

  12. Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO2/SiO2 stack tunnel dielectrics for memory application

    Gloux Florence

    2011-01-01

    Full Text Available Abstract Ge nanocrystals (Ge-NCs embedded in SiN dielectrics with HfO2/SiO2 stack tunnel dielectrics were synthesized by utilizing low-energy (≤5 keV ion implantation method followed by conventional thermal annealing at 800°C, the key variable being Ge+ ion implantation energy. Two different energies (3 and 5 keV have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge+-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO2/SiO2/Si metal-insulator-semiconductor (MIS memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 × 1016 cm-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of ± 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices.

  13. Synthesis of C14/Fe3O4@SiO2 and Its Performance in Removing Uranium (VI from Aqueous Solutions and Real Wastewater Using Benzamide

    Zohreh Akbari Jonoosh

    2016-09-01

    Full Text Available Uranium separation and removal are important from environmental, public health, and strategic veiwpoints. Scientits have put great efforts to develop technologies for uranium removal and regeneration because of its important applications and beneficial uses. In this study, efforts have been made to synthesize a modified form of Fe3O4@SiO2 and benzamide uranium complexes that can be exploited to remove and adsorb uranium onto an adsorbent that can be recycled. In the first step, Fe3O4@SiO2 was synthesized and later modified with trimethoxysilane. The adsorbent was subsequently characterized by SEM and FTIR.  In a second step, experiments were performed to determine optimum stirring speed, contact time, ion strength, and adsorbent reusability. Finally, the performance of the adsorbent was tested in samples of real wastewater. SEM and FTIR analyses confirmed the satisfactory synthesis and modification of Fe3O4@SiO2 Nps. Statistical analyses revealed that although contact time, ion strength, and stirring speed were effective in adsorbent performance, they only led to a removal enhancement of 5% and a decrease of only 17% with increasing RPM to 250 and the enhancement of ion strength to 1.5M. The highest U(VI removal efficiency in the synthetic solution was found to be 97%, which reduced to 49% in real wastewater samples. It was concluded that the nano-composite C14/SiO2_Fe3O4 adsorbent with its magnetic core and resistant surface not only offers the possibility for easy separation of urnaium from solutions but is also reusable and is only slightly affected by changes in stirring speed or ion strength. It, therefore, has a good capability for use as a U(VI adsorbent in wastewater treatment.

  14. Synthesis and Characterization of Modified Epoxy Resins by Silicic Acid Tetraethyl Ester and Nano-SiO2

    李海燕; 张之圣

    2004-01-01

    A kind of modified epoxy resins was obtained by condensation of epoxy resin with silicic acid tetraethyl ester(TEOS) and nano-SiO2. The reactions were performed with hydrochloric acid as a catalyst at 63 °C.The structure, thermal stability and morphological characteristics of the modified epoxy resins were studied through infrared spectra(FT-IR) analysis, thermogravimetric (TG) analysis and scanning electron microscopy respectively. It has been found from the IR and TG study that modified epoxy resins have greater thermal stability than epoxy resins, and its thermal stability has been improved by the formation of inter-crosslinked network structure. The modified epoxy resins exhibit heterogeneous morphology and heterogeneity increases with more TEOS feeding, which in turn confirms the formation of inter-crosslinked network structure in modified epoxy resins.

  15. Use of MnO2 and MnO2 SiO2 for sorbing of Sr-90 from liquid rad waste

    Subiarto; Las, Thamzil; Aan BH, Martin; Utomo, Cahyo Hari

    1998-01-01

    The synthesis of MnO 2 adsorbent and MnO 2 -SiO 2 composite has been done. MnO 2 synthesis is done by the reaction of KMnO 4 , Mn(NO 3 ) 2 .4H 2 O and Na 2 S 2 O 4 ( MnO 2 -A, MnO 2 -B, and MnO 2 -T ). MnO 2 . SiO 2 is made from KMnO 4 , Na 2 SiO 3 , and H 2 O 2 . The result obtained show the best Sr-90 sorption by MnO 2 -A with Kd = 2085.63 ml/g, by MnO 2 -L with Kd = 755.09 ml/g, and by MnO 2 - SiO 2 composite with Kd = 1466.51 ml/g. From this result, we can conclude that MnO 2 -SiO 2 can be expanded for Sr-90 sorption from liquid radioactive waste. (author)

  16. Photoluminescence of Er-doped Si-SiO2 and Al-Si-SiO2 sputtered thin films

    Rozo, C.; Fonseca, L.F.; Jaque, D.; Sole, J.Garcia

    2008-01-01

    Er-doped Si-SiO 2 and Al-Si-SiO 2 films have been deposited by rf-sputtering being annealed afterwards. Annealing behavior of the Er 3+ : 4 I 13/2 → 4 I 15/2 emission of Er-doped Si-SiO 2 yields a maximum intensity for annealing at 700-800 deg. C. 4 I 13/2 → 4 I 15/2 peak emission for Er-doped Al-Si-SiO 2 at 1525 nm is shifted from that for Er-doped Si-SiO 2 at 1530 nm and the bandwidth increases from 29 to 42 nm. 4 I 13/2 → 4 I 15/2 emission decays present a fast decaying component related to Er ions coupled to Si nanoparticles, defects, or other ions, and a slow decaying component related to isolated Er ions. Excitation wavelength dependence and excitation power dependence for the 4 I 13/2 → 4 I 15/2 emission correspond with energy transfer from Si nanoparticles. Populating of the 4 I 11/2 level in Er-doped Si-SiO 2 involves branching and energy transfer upconversion involving two or more Er ions. Addition of Al reduces the populating of this level to an energy transfer upconversion involving two ions

  17. Synthesis of mullite (3Al2O32SiO2) from local kaolin for radiation shielding

    Ripin, Azuhar; Mohamed, Faizal; Aman, Asyraf

    2018-04-01

    Raw kaolin from Kota Tinggi, Johor was used in this study to produce ceramic mullite (3Al2O22SiO2) for radiation shielding materials. In this work, an attempt was made to study the potential of local minerals to be used as a shielding barrier for diagnostic radiology radiation facilities in hospitals and medical centers throughout Malaysia. The conventional ceramic processing route was employed in the study using different pressing strength and sintering time. The obtained samples were characterized using X-ray diffractometer (XRD) for phase identification of each of the samples. The lead equivalent (LE) test was carried out using 15.05 mCi Cobalt-57 with gamma energy of 122 keV to compute the abilities of the mullite ceramic samples to attenuate the radiation. XRD patterns of prepared ceramics revealed the presence of orthorhombic mullite, hexagonal quartz and orthorhombic sillimanite structures. Furthermore, the radiation test displayed the ability of ceramics to shield of 70 % of gamma radiation at the distance of 60 cm from the radiation source. The highest lead equivalent thickness is 1.0 mm Pb and the lowest is about 0.06 mm Pb. From the result, it is shown that the ceramic has the potential to use as a shielding barrier in diagnostic radiology facilities due to the ability of reducing the radiation dose up to 70 % from its initial value.

  18. In-situ synthesis of SiO2@MOF composites for high-efficiency removal of aniline from aqueous solution

    Han, Tongtong; Li, Caifeng; Guo, Xiangyu; Huang, Hongliang; Liu, Dahuan; Zhong, Chongli

    2016-12-01

    A series of SiO2@aluminum-MOF(MIL-68) composites with different SiO2 loadings have been synthesized by a simple and mild compositing strategy for high-efficiency removal of aniline. As evidenced from SEM and TEM images as well as the particle size distribution, the incorporation of SiO2 can improve the dispersity of MIL-68(Al) in composites, and result in the smaller particle size than that of pristine MIL-68(Al). Besides, the adsorption of aniline over SiO2, MIL-68(Al), the physical mixture of these two materials, and SiO2@MIL-68(Al) composites was investigated comparatively, demonstrating a relatively high adsorption capacity (531.9 mg g-1) of 7% SiO2@MIL-68(Al) towards aniline. Combining the ultrafast adsorption dynamics (reaching equilibrium within 40 s) and great reusability, 7% SiO2@MIL-68(Al) shows excellent adsorption performance. This indicates that the SiO2@MIL-68(Al) composites possess great potential applications as a kind of fascinating adsorbent in water pollution protection.

  19. Bio-template-assisted synthesis of hierarchically hollow SiO2 microtubes and their enhanced formaldehyde adsorption performance

    Le, Yao; Guo, Daipeng; Cheng, Bei; Yu, Jiaguo

    2013-01-01

    The indoor air quality is crucial for human health, taking into account that people often spend more than 80% of their time in houses, offices and cars. Formaldehyde (HCHO) is a major pollutant and long-term exposure to HCHO may cause health problems such as nasal tumors and skin irritation. In this work, for the first time, hierarchically hollow silica microtubes (HHSM) were synthesized by a simple sol–gel and calcination method using cetyltrimethyl ammonium bromide (CTAB) and bio-template poplar catkin (PC) as co-templates and the PC/SiO 2 weight ratio R was varied from 0, 0.1, 0.3 and 1. The prepared samples were further modified with tetraethylenepentamine (TEPA) and characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), and N 2 physisorption techniques. This was followed by formaldehyde adsorption tests at ambient temperature. The results showed that all the prepared HHSM samples contained small mesopores with peak pore size at ca. 2.5 nm and large several tens of nanometer-sized pores on the tube wall. The R exhibited an obvious influence on specific surface areas and the sample prepared at R = 0.3 exhibited highest specific surface area (896 m 2 /g). All the TEPA-modified samples exhibited enhanced formaldehyde adsorption performance. The maximum HCHO adsorption capacity (20.65 mg/g adsorbent) was achieved on the sample prepared at R = 0.3 and modified by 50 wt.% TEPA. The present study will provide new insight for the utilization of bio-template used for the fabrication of inorganic hollow tubes with high HCHO adsorption performance for indoor air purification.

  20. Electronic states at Si-SiO2 interface introduced by implantation of Si in thermal SiO2

    Kalnitsky, A.; Poindexter, E.H.; Caplan, P.J.

    1990-01-01

    Interface traps due to excess Si introduced into the Si-SiO 2 system by ion implantation are investigated. Implanted oxides are shown to have interface traps at or slightly above the Si conduction band edge with densities proportional to the density of off-stoichiometric Si at the Si-SiO 2 interface. Diluted oxygen annealing is shown to result in physical separation of interface traps and equilibrium substrate electrons, demonstrating that ''interface'' states are located within a 0.5 nm thick layer of SiO 2 . Possible charge trapping mechanisms are discussed and the effect of these traps on MOS transistor characteristics is described using a sheet charge model. (author)

  1. Synthesis of pigments of Fe2O3·SiO2 system, with Ca, Mg, or Co oxide additions

    Tsvetan Dimitrov

    2017-03-01

    Full Text Available The present research work is based on the comparative evaluation of the Ca, Mg, and Co dopant impact on the properties of new ceramic pigments from the system Fe2O3·SiO2 obtained via classical ceramic technology. This approach enabled determination of the optimal temperature for the synthesis and the most appropriate mineralizer. The obtained specimens were submitted to systematical analysis, including X-ray Diffraction (XRD spectroscopy, Electron Paramagnetic Resonance (EPR analysis and Mössbauer spectroscopy for crystalline phase determination. The color characteristics are quantified by spectrophotometric measurements. The pigments particle size has been determined by Scanning Electron Microscopy (SEM, combined by Energy Dispersion X-ray spectroscopy (EDX. The obtained results enabled to determine the correlation between the calcination temperature and the phase compositions of the obtained pigments. In addition, some interesting magnetic properties were detected for the Co-doped composition.

  2. Synthesis of pigments of Fe2O3·SiO2 system, with Ca, Mg, or Co oxide additions

    Dimitrov, T.; Kozhukharov, S.; Velinov, N.

    2017-07-01

    The present research work is based on the comparative evaluation of the Ca, Mg, and Co dopant impact on the properties of new ceramic pigments from the system Fe2O3·SiO2 obtained via classical ceramic technology. This approach enabled determination of the optimal temperature for the synthesis and the most appropriate mineralizer. The obtained specimens were submitted to systematical analysis, including X-ray Diffraction (XRD) spectroscopy, Electron Paramagnetic Resonance (EPR) analysis and Mössbauer spectroscopy for crystalline phase determination. The color characteristics are quantified by spectrophotometric measurements. The pigments particle size has been determined by Scanning Electron Microscopy (SEM), combined by Energy Dispersion X-ray spectroscopy (EDX). The obtained results enabled to determine the correlation between the calcination temperature and the phase compositions of the obtained pigments. In addition, some interesting magnetic properties were detected for the Co-doped composition. (Author)

  3. Nano-sized Fe-metal catalyst on ZnO-SiO2: (photo-assisted deposition and impregnation) Synthesis routes and nanostructure characterization

    Mohamed, R.M.; Al-Rayyani, M.A.; Baeissa, E.S.; Mkhalid, I.A.

    2011-01-01

    Highlights: → We prepared Fe/ZnO-SiO 2 by two methods. → We tested photocatalytic activity for degradation of methylene blue dye. → We controlled band gap and size. → We found activity of Fe/ZnO-SiO 2 prepared by PAD is hightest photocatalytic activity. - Abstract: A nano-sized Fe metal on ZnO-SiO 2 was synthesized using the photo-assisted deposition (PAD) and impregnation routes. The obtained samples were characterized by a series of techniques including X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy, N 2 adsorption, extended X-ray absorption fine structure (EXAFS), and transmission electron microscopy (TEM). Photocatalytic reactivity using Fe-ZnO-SiO 2 catalysts under visible-light condition on the degradation of methylene blue dye was evaluated. The results of characterization reveal, a notable photocatalytic activity of PAD:Fe-ZnO-SiO 2 which was about 9 and 12 times higher than that of Img:Fe-ZnO-SiO 2 and ZnO-SiO 2 , respectively.

  4. Synthesis of PANi-SiO2 Nanocomposite with In-Situ Polymerization Method: Nanoparticle Silica (NPS) Amorphous and Crystalline Phase

    Munasir; Luvita, N. R. D.; Kusumawati, D. H.; Putri, N. P.; Triwikantoro; Supardi, Z. A. I.

    2018-03-01

    Silica which is synthesized from natural materials such as Bancar Tuban’s sand composited with Polyaniline (PANi), where the silica used are silica has an amorphous phase and cristobalite phase. In this research, the composite method used is in- situ polymerization, which is silica entered during the fabrication of PANi, then automatically silica will be substitute into the chain bonding of PANi. The aim of this research is to find out the results of a composite process using in-situ methods as well as differences in the morphology of PANi/a- SiO2 and PANi/c-SiO2. For the characterization of samples tested in the form of FTIR to determine the functional groups of the composite and SEM to determine the morphology of the sample. From the test results of FTIR are known composite possibility has occurred because there are several functional groups belonging to silica also functional groups belonging polyaniline, functional group that’s happened in wave numbers were almost identical between PANi/a-SiO2 and PANi/c-SiO2, but there are little differences were seen in the form of a graph generated from the peak and intensity that occurred charts for PANi/c-SiO2 has peak more pointed or sharp compared to PANi/a-SiO2 because that bond of crystal is strong, stiff and has a larger particle size than the amorphous composite. Then from the data of SEM seen clearly their morphological differences between PANi/a-SiO2 and PANi/c-SiO2 where polyaniline is composited with amorphous silica will have a fault that is not uniform or irregular different from PANi/c -SiO2 has a regular fault and this is corresponding with the nature of the typical structure of amorphous and crystalline.

  5. Synthesis, structural characterization and dielectric properties of Nb doped BaTiO3/SiO2 core–shell heterostructure

    Cernea, M.; Vasile, B.S.; Boni, A.; Iuga, A.

    2014-01-01

    Highlights: • Optimal parameters for preparation by sol–gel of core–shell (BT-Nb 0.005 )/SiO 2 are presented in this paper. • Single crystalline BT-Nb 0.005 /SiO 2 core–shell composite with ∼34 nm shell thick was prepared. • The core–shell ceramic exhibits good dielectric properties and ferroelectric characteristics. -- Abstract: Perovskite complex ceramic oxides, BaTiO 3 doped with 0.5 mol%Nb 2 O 5 and then nanocoated with SiO 2 (abbreviated as BT-Nb 0.005 /SiO 2 ) was successful prepared using conventional sol–gel processing. Phase composition, particle morphology, structure, and electric properties of BT-Nb 0.005 core and BT-Nb 0.005 /SiO 2 core–shell were examined and compared, using X-ray diffraction, transmission electron microscopy and, dielectric and ferroelectric measurements. Core–shell composite with well-defined perovskite tetragonal phase of BaTiO 3 was achieved. Furthermore, single crystalline BT-Nb 0.005 /SiO 2 core–nanoshell heterostructure with ∼34 nm shell thick was prepared, which is a novelty in ferroelectrics field. The ferroelectric quality of BT-Nb 0.005 has suffered an alteration when the (BT-Nb 0.005 )/SiO 2 core–shell heterostructure was realized. One-dimensional BT-Nb 0.005 /SiO 2 core–shell heterostructure exhibits an improvement of dielectric losses and a decrease of dielectric constant, compared to uncoated BT-Nb 0.005 . The (BT-Nb 0.005 )/SiO 2 core–shell material could be interesting for application in the composite capacitors

  6. Photoemission study on electrical dipole at SiO_2/Si and HfO_2/SiO_2 interfaces

    Fujimura, Nobuyuki; Ohta, Akio; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

    2017-01-01

    Electrical dipole at SiO_2/Si and HfO_2/SiO_2 interfaces have been investigated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. From the analysis of the cut-off energy for secondary photoelectrons measured at each thinning step of a dielectric layer by wet-chemical etching, an abrupt potential change caused by electrical dipole at SiO_2/Si and HfO_2/SiO_2 interfaces has been clearly detected. Al-gate MOS capacitors with thermally-grown SiO_2 and a HfO_2/SiO_2 dielectric stack were fabricated to evaluate the Al work function from the flat band voltage shift of capacitance-voltage (C-V) characteristics. Comparing the results of XPS and C-V measurements, we have verified that electrical dipole formed at the interface can be directly measured by photoemission measurements. (author)

  7. Positron annihilation at the Si/SiO2 interface

    Leung, T.C.; Weinberg, Z.A.; Asoka-Kumar, P.; Nielsen, B.; Rubloff, G.W.; Lynn, K.G.

    1992-01-01

    Variable-energy positron annihilation depth-profiling has been applied to the study of the Si/SiO 2 interface in Al-gate metal-oxide-semiconductor (MOS) structures. For both n- and p-type silicon under conditions of negative gate bias, the positron annihilation S-factor characteristic of the interface (S int ) is substantially modified. Temperature and annealing behavior, combined with known MOS physics, suggest strongly that S int depends directly on holes at interface states or traps at the Si/SiO 2 interface

  8. Ag-Decorated Fe3O4@SiO2 Nanorods: Synthesis, Characterization, and Applications in Degradation of Organic Dyes

    Chao Li

    2016-01-01

    Full Text Available Well-dispersed Ag nanoparticles (NPs are successfully decorated on Fe3O4@SiO2 nanorods (NRs via a facile step-by-step strategy. This method involves coating α-Fe2O3 NRs with uniform silica layer, reduction in 10% H2/Ar atmosphere at 450°C to obtain Fe3O4@SiO2 NRs, and then depositing Ag NPs on the surface of Fe3O4@SiO2 NRs through a sonochemical step. It was found that the as-prepared Ag-decorated magnetic Fe3O4@SiO2 NRs (Ag-MNRs exhibited a higher catalytic efficiency than bare Ag NPs in the degradation of organic dye and could be easily recovered by convenient magnetic separation, which show great application potential for environmental protection applications.

  9. Synthesis and crystal structure of alkali metal diamido dioxosilicates M2SiO2(NH2)2 with M corresponds to K, Rb and Cs

    Jacobs, H.; Mengis, H.

    1993-01-01

    SiO 2 - α-quartz - reacts with alkali metal amides MNH 2 (M corresponds to K, Rb, and Cs) in molar ratios from 1:2 to 1:10 at 450 C ≤ T ≤ 600 C and P(NH 3 ) = 6 kbar in autoclaves to diamidodioxosilicates M[SiO 2 (NH 2 ) 2 ]. Crystals of the colourless compounds which hydrolyze rapidly were investigated by X-ray methods. (orig.)

  10. Facile and efficient synthesis of the surface tantalum hydride (≡SiO)2TaIIIH and tris-siloxy tantalum (≡SiO)3TaIII starting from novel tantalum surface species (≡SiO)TaMe4 and (≡SiO)2TaMe 3

    Chen, Yin

    2014-03-10

    By grafting of TaMe5 (1) on the surface of silica partially dehydroxylated at 500 C (silica500), a mixture of (≡SiO)TaMe4 (2a; major, 65 ± 5%) and (≡SiO) 2TaMe3 (2b; minor, 35 ± 5%) was produced, which has been characterized by microanalysis, IR, and SS NMR (1H, 13C, 1H-13C HETCOR, proton double and triple quantum). After grafting, these surface organometallic compounds are more stable than the precursor TaMe5. Treatment of 2a,b with water and H 2 resulted in the formation of methane in amount of 3.6 ± 0.2 and 3.4 ± 0.2 mol/grafted Ta, respectively. 2a,b react with H2 (800 mbar) to form (≡SiO)2TaH. After (≡SiO) 2TaH was heated to 500 C under hydrogen or vacuum, [(≡SiO) 3Ta][≡SiH] was produced, and the structure was confirmed by IR, NMR, and EXAFS. Considering the difficulty of the previous preparation method, these syntheses represent a facile and convenient way to prepare tantalum surface species (≡SiO)2TaH and (≡SiO)3Ta via the intermediate of the new surface organometallic precursors: (≡SiO)TaMe4/(≡SiO)2TaMe3. (≡SiO)2TaH and (≡SiO)3Ta exhibit equal reactivities in alkane metathesis and ethylene polymerization in comparison to those in previous reports. © 2014 American Chemical Society.

  11. Facile and efficient synthesis of the surface tantalum hydride (≡SiO)2TaIIIH and tris-siloxy tantalum (≡SiO)3TaIII starting from novel tantalum surface species (≡SiO)TaMe4 and (≡SiO)2TaMe 3

    Chen, Yin; Ould-Chikh, Samy; Abou-Hamad, Edy; Callens, Emmanuel; Mohandas, Janet Chakkamadathil; Khalid, Syed M.; Basset, Jean-Marie

    2014-01-01

    By grafting of TaMe5 (1) on the surface of silica partially dehydroxylated at 500 C (silica500), a mixture of (≡SiO)TaMe4 (2a; major, 65 ± 5%) and (≡SiO) 2TaMe3 (2b; minor, 35 ± 5%) was produced, which has been characterized by microanalysis, IR, and SS NMR (1H, 13C, 1H-13C HETCOR, proton double and triple quantum). After grafting, these surface organometallic compounds are more stable than the precursor TaMe5. Treatment of 2a,b with water and H 2 resulted in the formation of methane in amount of 3.6 ± 0.2 and 3.4 ± 0.2 mol/grafted Ta, respectively. 2a,b react with H2 (800 mbar) to form (≡SiO)2TaH. After (≡SiO) 2TaH was heated to 500 C under hydrogen or vacuum, [(≡SiO) 3Ta][≡SiH] was produced, and the structure was confirmed by IR, NMR, and EXAFS. Considering the difficulty of the previous preparation method, these syntheses represent a facile and convenient way to prepare tantalum surface species (≡SiO)2TaH and (≡SiO)3Ta via the intermediate of the new surface organometallic precursors: (≡SiO)TaMe4/(≡SiO)2TaMe3. (≡SiO)2TaH and (≡SiO)3Ta exhibit equal reactivities in alkane metathesis and ethylene polymerization in comparison to those in previous reports. © 2014 American Chemical Society.

  12. Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.

    Zhang, Kunhao; Zhao, Ziyan; Wu, Zhonghua; Zhou, Ying

    2015-01-01

    In this paper, the Co@SiO2 core-shell nanoparticles were prepared by the sol-gel method. The oxidization of Co core nanoparticles was studied by the synchrotron radiation-based techniques including in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) up to 800°C in air and N2 protection conditions, respectively. It was found that the oxidization of Co cores is undergoing three steps regardless of being in air or in N2 protection condition. In the first step ranging from room temperature to 200°C, the Co cores were dominated by Co(0) state as well as small amount of Co(2+) ions. When temperature was above 300°C, the interface between Co cores and SiO2 shells was gradually oxidized into Co(2+), and the CoO layer was observed. As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO. Nevertheless, the oxidization kinetics of Co cores is different for the Co@SiO2 in air and N2 gas conditions. Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells. However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

  13. A novel approach for the synthesis of ultrathin silica-coated iron oxide nanocubes decorated with silver nanodots (Fe3O4/SiO2/Ag) and their superior catalytic reduction of 4-nitroaniline

    Abbas, Mohamed; Torati, Sri Ramulu; Kim, Cheolgi

    2015-07-01

    A novel sonochemical approach was developed for the synthesis of different core/shell structures of Fe3O4/SiO2/Ag nanocubes and SiO2/Ag nanospheres. The total reaction time of the three sonochemical steps for the synthesis of Fe3O4/SiO2/Ag nanocubes is shorter than that of the previously reported methods. A proposed reaction mechanism for the sonochemical functionalization of the silica and the silver on the surface of magnetic nanocubes was discussed in detail. Transmission electron microscopy revealed that the surface of Fe3O4/SiO2 nanocubes was decorated with small Ag nanoparticles of approximately 10-20 nm in size, and the energy dispersive spectroscopy mapping analysis confirmed the morphology of the structure. Additionally, X-ray diffraction data were used to confirm the formation of both phases of a cubic inverse spinel structure for Fe3O4 and bcc structures for Ag in the core/shell structure of the Fe3O4/SiO2/Ag nanocubes. The as-synthesized Fe3O4/SiO2/Ag nanocubes showed a high efficiency in the catalytic reduction reaction of 4-nitroaniline to 4-phenylenediamine and a better performance than both Ag and SiO2/Ag nanoparticles. The grafted silver catalyst was recycled and reused at least fifteen times without a significant loss of catalytic efficiency.A novel sonochemical approach was developed for the synthesis of different core/shell structures of Fe3O4/SiO2/Ag nanocubes and SiO2/Ag nanospheres. The total reaction time of the three sonochemical steps for the synthesis of Fe3O4/SiO2/Ag nanocubes is shorter than that of the previously reported methods. A proposed reaction mechanism for the sonochemical functionalization of the silica and the silver on the surface of magnetic nanocubes was discussed in detail. Transmission electron microscopy revealed that the surface of Fe3O4/SiO2 nanocubes was decorated with small Ag nanoparticles of approximately 10-20 nm in size, and the energy dispersive spectroscopy mapping analysis confirmed the morphology of the

  14. Solvent-Free Synthesis of Aryl Iodide Using Nano SiO2/HIO4 as a Reusable Acid Catalyst

    A. Bamoniri

    2014-07-01

    Full Text Available An efficient and environmentally benign   method for the synthesis of aryl iodides have been developed by diazotization of aromatic amines with NaNO2 and nanosilica periodic acid (nano-SPIA as a green catalyst via grinding followed by a sandmeyer iodination by KI under solvent-free conditions at room temperature. The ensuing aryl diazonium salts supported on nano-SPIA were sufficiently stable to be kept at room temperature in the dry state. This method is a novel, efficient, eco-friendly route for solvent-free synthesis of aryl iodides.

  15. Synthesis of Y2O3-ZrO2-SiO2 composite coatings on carbon fiber reinforced resin matrix composite by an electro-plasma process

    Zhang, Yuping; Lin, Xiang; Chen, Weiwei; Cheng, Huanwu; Wang, Lu

    2016-05-01

    In the present paper the Y2O3-ZrO2-SiO2 composite coating was successfully synthesized on carbon fiber reinforced resin matrix composite by an electro-plasma process. The deposition process, microstructures and oxidation resistance of the coatings with different SiO2 concentrations were systematically investigated. A relatively dense microstructure was observed for the Y2O3-ZrO2-SiO2 composite coating with the SiO2 concentration above 5 g/L. The coating exhibited very good oxidation resistance at 1273 K with the mass loss rate as low as ∼30 wt.%, compared to 100 wt.% of the substrate. The formation of the ceramic composites was discussed in detail based on the electrochemical mechanism and the deposition dynamics in order to explain the effect of the plasma discharge. We believe that the electro-plasma process will find wide applications in preparing ceramics and coatings in industries.

  16. Synthesis of TiO2 nanoparticles containing Fe, Si, and V using multiple diffusion flames and catalytic oxidation capability of carbon-coated nanoparticles

    Ismail, Mohamed

    2016-01-19

    Titanium dioxide (TiO2) nanoparticles containing iron, silicon, and vanadium are synthesized using multiple diffusion flames. The growth of carbon-coated (C–TiO2), carbon-coated with iron oxide (Fe/C–TiO2), silica-coated (Si–TiO2), and vanadium-doped (V–TiO2) TiO2 nanoparticles is demonstrated using a single-step process. Hydrogen, oxygen, and argon are utilized to establish the flame, with titanium tetraisopropoxide (TTIP) as the precursor for TiO2. For the growth of Fe/C–TiO2 nanoparticles, TTIP is mixed with xylene and ferrocene. While for the growth of Si–TiO2 and V–TiO2, TTIP is mixed with hexamethyldisiloxane (HMDSO) and vanadium (V) oxytriisopropoxide, respectively. The synthesized nanoparticles are characterized using high-resolution transmission electron microscopy (HRTEM) with energy-filtered TEM for elemental mapping (of Si, C, O, and Ti), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption BET surface area analysis, and thermogravimetric analysis. Anatase is the dominant phase for the C–TiO2, Fe/C–TiO2, and Si–TiO2 nanoparticles, whereas rutile is the dominant phase for the V–TiO2 nanoparticles. For C–TiO2 and Fe/C–TiO2, the nanoparticles are coated with about 3-5-nm thickness of carbon. The iron-based TiO2 nanoparticles significantly improve the catalytic oxidation of carbon, where complete oxidation of carbon occurs at a temperature of 470 °C (with iron) compared to 610 °C (without iron). Enhanced catalytic oxidation properties are also observed for model soot particles, Printex-U, when mixed with Fe/C-TiO2. With regards to Si–TiO2 nanoparticles, a uniform coating of 3 to 8 nm of silicon dioxide is observed around the TiO2 particles. This coating mainly occurs due to variance in the chemical reaction rates of the precursors. Finally, with regards to V–TiO2, vanadium is doped within the TiO2 nanoparticles as visualized by HRTEM and XPS further confirms the formation of

  17. Synthesis of TiO2 nanoparticles containing Fe, Si, and V using multiple diffusion flames and catalytic oxidation capability of carbon-coated nanoparticles

    Ismail, Mohamed; Memon, Nasir K.; Hedhili, Mohamed N.; Anjum, Dalaver H.; Chung, Suk-Ho

    2016-01-01

    Titanium dioxide (TiO2) nanoparticles containing iron, silicon, and vanadium are synthesized using multiple diffusion flames. The growth of carbon-coated (C–TiO2), carbon-coated with iron oxide (Fe/C–TiO2), silica-coated (Si–TiO2), and vanadium-doped (V–TiO2) TiO2 nanoparticles is demonstrated using a single-step process. Hydrogen, oxygen, and argon are utilized to establish the flame, with titanium tetraisopropoxide (TTIP) as the precursor for TiO2. For the growth of Fe/C–TiO2 nanoparticles, TTIP is mixed with xylene and ferrocene. While for the growth of Si–TiO2 and V–TiO2, TTIP is mixed with hexamethyldisiloxane (HMDSO) and vanadium (V) oxytriisopropoxide, respectively. The synthesized nanoparticles are characterized using high-resolution transmission electron microscopy (HRTEM) with energy-filtered TEM for elemental mapping (of Si, C, O, and Ti), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption BET surface area analysis, and thermogravimetric analysis. Anatase is the dominant phase for the C–TiO2, Fe/C–TiO2, and Si–TiO2 nanoparticles, whereas rutile is the dominant phase for the V–TiO2 nanoparticles. For C–TiO2 and Fe/C–TiO2, the nanoparticles are coated with about 3-5-nm thickness of carbon. The iron-based TiO2 nanoparticles significantly improve the catalytic oxidation of carbon, where complete oxidation of carbon occurs at a temperature of 470 °C (with iron) compared to 610 °C (without iron). Enhanced catalytic oxidation properties are also observed for model soot particles, Printex-U, when mixed with Fe/C-TiO2. With regards to Si–TiO2 nanoparticles, a uniform coating of 3 to 8 nm of silicon dioxide is observed around the TiO2 particles. This coating mainly occurs due to variance in the chemical reaction rates of the precursors. Finally, with regards to V–TiO2, vanadium is doped within the TiO2 nanoparticles as visualized by HRTEM and XPS further confirms the formation of

  18. Facile Synthesis of SiO2@C Nanoparticles Anchored on MWNT as High-Performance Anode Materials for Li-ion Batteries

    Zhao, Yan; Liu, Zhengjun; Zhang, Yongguang; Mentbayeva, Almagul; Wang, Xin; Maximov, M. Yu.; Liu, Baoxi; Bakenov, Zhumabay; Yin, Fuxing

    2017-07-01

    Carbon-coated silica nanoparticles anchored on multi-walled carbon nanotubes (SiO2@C/MWNT composite) were synthesized via a simple and facile sol-gel method followed by heat treatment. Scanning and transmission electron microscopy (SEM and TEM) studies confirmed densely anchoring the carbon-coated SiO2 nanoparticles onto a flexible MWNT conductive network, which facilitated fast electron and lithium-ion transport and improved structural stability of the composite. As prepared, ternary composite anode showed superior cyclability and rate capability compared to a carbon-coated silica counterpart without MWNT (SiO2@C). The SiO2@C/MWNT composite exhibited a high reversible discharge capacity of 744 mAh g-1 at the second discharge cycle conducted at a current density of 100 mA g-1 as well as an excellent rate capability, delivering a capacity of 475 mAh g-1 even at 1000 mA g-1. This enhanced electrochemical performance of SiO2@C/MWNT ternary composite anode was associated with its unique core-shell and networking structure and a strong mutual synergistic effect among the individual components.

  19. Efficient FeCl3/SiO2 as heterogeneous nanocatalysis for the synthesis of benzimidazoles under mild conditions

    Taher, Mohammad Ali; Karami, Changiz; Arabi, Mehdi Sheikh; Ahmadian, Hossein; Karami, Yasaman

    2016-11-01

    Iron(III) supported on nano silica as a new catalyst has been synthesized. Structural properties of this complex have been studied by TEM, SEM and EDX. The average crystalline size of Iron(III) supported on nano silica is 30-50 nm. Catalytic activity of this catalyst has been investigated by synthesis of benzimidazoles from 1, 2-diaminobenzene and aromatic aldehydes, and also the other variables investigated such as the amount of catalyst, reaction temperature and the effect of various solvents are also studied. The present procedure offers several advantages such as short reaction time, simple workup, recovery and reusability of the catalyst.

  20. Synthesis and Characterization of Nafion-SiO2 Composite Membranes as an Electrolyte for Medium Temperature and Low Relative Humidity

    Mahreni Mahreni

    2011-12-01

    Full Text Available The weakness of the Nafion membrane as electrolyte of PEMFC associated with physical properties that is easy to shrink at temperatures above 80°C due to dehydration. Shrinkage will decrease the conductivity and membrane damage. Nafion-SiO2 composite membranes can improve membrane stability. The role of SiO2 in the Nafion clusters is as water absorbent cause the membrane remains wet at high temperatures and low humidity and conductivity remains high. The results showed the content of 2.8 wt% of SiO2 in the Nafion membrane, the conductivity of composite membrane is higher than the pure Nafion membrane that are 0.127 S cm-1 in dry conditions and 0.778 S cm-1 in wet conditions at room temperature. Compared with the pure Nafion membrane conductivity are 0.0661 S cm-1 and 0.448 S cm-1 respectively in dry and wet conditions.

  1. Microwave-assisted synthesis of SiO2 nanoparticles and its application on the flame retardancy of poly styrene and poly carbonate nanocomposites

    A. Esmaeili-Bafghi-Karimabad

    2015-07-01

    Full Text Available Various morphologies of silica nanoparticles were synthesized by a microwave-assisted Pechini method. Silica nanostructures were synthesized via a fast reaction between tetra ethyl ortho silicate and ammonia at presence citric acid and other effective agents in Pechini procedure. Then for preparation of polymer-matrix nanocomposites, SiO2 nanoparticles were added to poly carbonate (PC and poly styrene (PS matrices. Nanostructures were characterized by X-ray diffraction (XRD, scanning electron microscopy (SEM and Fourier transform infrared (FT-IR. The influence of SiO2 nanostructures on the flame retardancy of the polymeric matrix was studied using UL- 94 analysis. Our results show that the SiO2 nanostructure can enhance the flame retardant property of the poly carbonate matrix. PC shows better flame retardancy compare to poly styrene.

  2. Synthesis of Ni-SiO2/silicalite-1 core-shell micromembrane reactors and their reaction/diffusion performance

    Khan, Easir A.

    2010-12-15

    Core-shell micromembrane reactors are a novel class of materials where a catalyst and a shape-selective membrane are synergistically housed in a single particle. In this work, we report the synthesis of micrometer -sized core-shell particles containing a catalyst core and a thin permselective zeolite shell and their application as a micromembrane reactor for the selective hydrogenation of the 1-hexene and 3,3-dimethyl-1-butene isomers. The bare catalyst, which is made from porous silica loaded with catalytically active nickel, showed no reactant selectivity between hexene isomers, but the core-shell particles showed high selectivities up to 300 for a 1-hexene conversion of 90%. © 2010 American Chemical Society.

  3. Facile synthesis of 1-naphthol azo dyes with nano SiO2/HIO4 under solvent-free conditions

    A.R. Pourali

    2013-09-01

    Full Text Available Nano-silica supported periodic acid (nano-SPIA has been utilized as a heterogeneous reagent for a highly efficient and one pot synthesis of azo dyes based on 1-naphthol under solvent-free conditions at room temperature. This method has some advantages, the reaction workup is very easy and the catalyst can be easily separated from the reaction mixture and one-pot procedure. The related products have been obtained in good to excellent yields, high purity and short reaction times. The structures of the products have been characterized by several techniques using UV-Vis, FT-IR, 1H NMR, 13C NMR and mass spectra.DOI: http://dx.doi.org/10.4314/bcse.v27i3.13

  4. Synthesis and luminescent properties of CaCO3:Eu3+@SiO2 phosphors with core-shell structure

    Liu, Min; Kang, Ming; Chen, Kexu; Mou, Yongren; Sun, Rong

    2018-03-01

    Integrating the processes of preparation of CaCO3:Eu3+ and its surface-coating, core-shell structured CaCO3:Eu3+@SiO2 phosphors with red emission were synthesized by the carbonation method and surface precipitation procedure using sodium silicate as silica source. The phase structure, thermal stability, morphology and luminescent property of the as-synthesized samples were characterized by X-ray diffraction, Fourier transform infrared spectrum, thermal analysis, field-emission scanning electron microscopy, transmission electron microscope and photoluminescence spectra. The experimental results show that Eu3+ ions as the luminescence center are divided into two types: one is at the surface of the CaCO3 and the other inhabits the site of Ca2+. For CaCO3:Eu3+@SiO2 phosphors, the SiO2 layers are continuously coated on the surface of CaCO3:Eu3+ and show a typical core-shell structure. After coated with SiO2 layer, the luminous intensity and the compatibility with the rubber matrix increase greatly. Additionally, the luminous intensity increases with the increasing of Eu3+ ions concentration in CaCO3 core and concentration quenching occurs when Eu3+ ions concentration exceeds 7.0 mol%, while it is 5.0 mol% for CaCO3:Eu3+ phosphors. Therefore, preparation of CaCO3:Eu3+@SiO2 phosphors can not only simplify the experimental process through integrating the preparation of CaCO3:Eu3+ and SiO2 layer, but also effectively increase the luminous intensities of CaCO3:Eu3+ phosphors. The as-obtained phosphors may have potential applications in the fields of optical materials and functional polymer composite materials, such as plastics and rubbers.

  5. Synthesis and Characterization of V2O5/SiO2 Nanoparticles as Efficient Catalyst for Aromatization 1,4 Dihydropyridines

    Farzaneh, F.; Zamanifar, E.; Jafari Foruzin, L.; Ghandi, M.

    2012-01-01

    V 2 O 5 /SiO 2 nanoparticles was prepared via an one-pot sol gel method from vanadyl- acetylacetonate and tetraethyl orthosilicate in refluxing MeOH, followed by calcination at 700 °C for 2 hours. The resultant nanoparticles was characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, TGA and FTIR techniques. Rapid and efficient aromatization of 1,4-dihydropyridines catalyzed by V 2 O 5 /SiO 2 nanoparticles is described in this presentation.

  6. High Ionic Conductivity of Composite Solid Polymer Electrolyte via In Situ Synthesis of Monodispersed SiO2 Nanospheres in Poly(ethylene oxide).

    Lin, Dingchang; Liu, Wei; Liu, Yayuan; Lee, Hye Ryoung; Hsu, Po-Chun; Liu, Kai; Cui, Yi

    2016-01-13

    High ionic conductivity solid polymer electrolyte (SPE) has long been desired for the next generation high energy and safe rechargeable lithium batteries. Among all of the SPEs, composite polymer electrolyte (CPE) with ceramic fillers has garnered great interest due to the enhancement of ionic conductivity. However, the high degree of polymer crystallinity, agglomeration of ceramic fillers, and weak polymer-ceramic interaction limit the further improvement of ionic conductivity. Different from the existing methods of blending preformed ceramic particles with polymers, here we introduce an in situ synthesis of ceramic filler particles in polymer electrolyte. Much stronger chemical/mechanical interactions between monodispersed 12 nm diameter SiO2 nanospheres and poly(ethylene oxide) (PEO) chains were produced by in situ hydrolysis, which significantly suppresses the crystallization of PEO and thus facilitates polymer segmental motion for ionic conduction. In addition, an improved degree of LiClO4 dissociation can also be achieved. All of these lead to good ionic conductivity (1.2 × 10(-3) S cm(-1) at 60 °C, 4.4 × 10(-5) S cm(-1) at 30 °C). At the same time, largely extended electrochemical stability window up to 5.5 V can be observed. We further demonstrated all-solid-state lithium batteries showing excellent rate capability as well as good cycling performance.

  7. Synthesis, characterization and in vitro bioactivity of sol-gel-derived SiO2-CaO-P2O5-MgO bioglass

    Saboori, A.; Rabiee, M.; Moztarzadeh, F.; Sheikhi, M.; Tahriri, M.; Karimi, M.

    2009-01-01

    In this study, the synthesis of SiO 2 -CaO-P 2 O 5 -MgO bioactive glass was performed by the sol-gel method. Sol-gel-derived bioglass material was produced both in powder and in discs form by uniaxial pressing, followed by sintering at 700 deg. C. The obtained material was evaluated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analyses. The biocompatibility evaluation of the formed glass was assessed through in vitro cell culture [alkaline phosphatase (AP) activity of osteoblasts] experiments and immersion studies in simulated body fluid (SBF) for different time intervals while monitoring the pH changes and the concentration of calcium, phosphorus and magnesium in the SBF medium. The SEM, XRD and FTIR studies were conducted before and after soaking of the material in SBF. At first, an amorphous calcium phosphate was formed; after 7 days this surface consisted of deposited crystalline apatite. The present investigation also revealed that the sol-gel derived quaternary bioglass system has the ability to support the growth of human fetal osteoblastic cells (hFOB 1.19). Finally, this material proved to be non-toxic and compatible for the proposed work in segmental defects in the goat model in vivo

  8. The ceramic SiO2 and SiO2-TiO2 coatings on biomedical Ti6Al4VELI titanium alloy

    Surowska, B.; Walczak, M.; Bienias, J.

    2004-01-01

    The paper presents the study of intermediate SiO 2 and SiO 2 -TiO 2 sol-gel coatings and dental porcelain coatings on Ti6Al4VELI titanium alloy. Surface microstructures and wear behaviour by pin-on-disc method of the ceramic coatings were investigated. The analysis revealed: (1) a compact, homogeneous SiO 2 and SiO 2 -TiO 2 coating and (2) that intermediate coatings may provide a durable joint between metal and porcelain, and (3) that dental porcelain on SiO 2 and TiO 2 coatings shows high wear resistance. (author)

  9. Synthesis and applications of crack-free SiO2 monolith containing CdSe/ZnS quantum dots as passive lighting sources.

    Yi, Dong Kee

    2008-09-01

    A reverse microemulsion technique has been used to synthesize quantum dot nanocomposites within a SiO2 surface coating. With this approach, the unique optical properties of the CdSe/ZnS quantum dots were preserved. CdSe/ZnS/SiO2 nanoparticles were homogeneously distributed in a tetramethyl orthosilicate ethanol solution and gelation process was initiated within a 10 min, and was left over night at room temperature and dried fully to achieve a solid SiO, monolith. The resulting monolith was transparent and fluorescent under ultraviolet (UV) lamp. Moreover the monolith produced was crack-free. Further studies on the photo stability of the monolith were performed using a high power UV LED device. Remarkably, quantum dots in the SiO, monolith showed better photo stability compared with those dispersed in a polymer matrix.

  10. Synthesis of bioactive poly(ethylene glycol)/SiO2-CaO-P2O5 hybrids for bone regeneration

    Liu Wei; Wu Xiaohong; Zhan Hongbing; Yan Fuhua

    2012-01-01

    Poly(ethylene glycol) (PEG)/SiO 2 -CaO-P 2 O 5 hybrid xerogels were prepared using a room temperature sol-gel process. The advantage of this hybrid material over conventional composites is the molecular scale interactions between the bioactive inorganic components and the biodegradable organic components. Since PEG was added into the sol when the hydrolysis of tetraethoxysilane occurred, the molecular chain of PEG was penetrated into the SiO 2 networks to form a semi-IPN structure. Due to the excellent biocompatibility and aqueous solubility of PEG molecules, as well as the bioactivity of the inorganic components, the biological and mechanical properties of this hybrid xerogel exhibit great potential for bone regeneration applications. The formation of hydroxyapatite was observed when the xerogel was immersed into simulated body fluid, demonstrating good bioactivity of the hybrid. The cell toxicity test also demonstrated that the hybrid material is suitable for the proliferation of MC3T3-E1 cells. Thus, the PEG/SiO 2 -CaO-P 2 O 5 hybrid xerogel has great potential to meet the demands of bone regeneration materials. - Highlights: ► PEG was penetrated into the SiO 2 networks to form a semi-IPN structure. ► This hybrid xerogel exhibit great potential for bone regeneration applications. ► SEM micrographs confirm the bioactivity of the samples.

  11. Synthesis and Characterization of SiO2@Y2MoO6:Eu3+ Core-Shell Structured Spherical Phosphors by Sol-Gel Process.

    Li, G Z; Liu, F H; Chu, Z S; Wu, D M; Yang, L B; Li, J L; Wang, M N; Wang, Z L

    2016-04-01

    SiO2@Y2MoO6:Eu3+ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO2@Y2MoO6:Eu3+ core-shell phosphors. The XRD results demonstrated that the Y2MoO6:Eu3+ layers on the SiO2 spheres crystallized after being annealed at 700 °C and the crystallinity increased with raising the annealing temperature. The obtained core-shell phosphors have spherical shape with narrow size distribution (average size ca. 640 nm), non-agglomeration, and smooth surface. The thickness of the Y2MoO6:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (70 nm for four deposition cycles). The Eul+ shows a strong PL emission (dominated by 5D0-7F2 red emission at 614 nm) under the excitation of 347 nm UV light. The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.

  12. Synthesis, characterization, and 3D-FDTD simulation of Ag@SiO2 nanoparticles for shell-isolated nanoparticle-enhanced Raman spectroscopy.

    Uzayisenga, Viviane; Lin, Xiao-Dong; Li, Li-Mei; Anema, Jason R; Yang, Zhi-Lin; Huang, Yi-Fan; Lin, Hai-Xin; Li, Song-Bo; Li, Jian-Feng; Tian, Zhong-Qun

    2012-06-19

    Au-seed Ag-growth nanoparticles of controllable diameter (50-100 nm), and having an ultrathin SiO(2) shell of controllable thickness (2-3 nm), were prepared for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Their morphological, optical, and material properties were characterized; and their potential for use as a versatile Raman signal amplifier was investigated experimentally using pyridine as a probe molecule and theoretically by the three-dimensional finite-difference time-domain (3D-FDTD) method. We show that a SiO(2) shell as thin as 2 nm can be synthesized pinhole-free on the Ag surface of a nanoparticle, which then becomes the core. The dielectric SiO(2) shell serves to isolate the Raman-signal enhancing core and prevent it from interfering with the system under study. The SiO(2) shell also hinders oxidation of the Ag surface and nanoparticle aggregation. It significantly improves the stability and reproducibility of surface-enhanced Raman scattering (SERS) signal intensity, which is essential for SERS applications. Our 3D-FDTD simulations show that Ag-core SHINERS nanoparticles yield at least 2 orders of magnitude greater enhancement than Au-core ones when excited with green light on a smooth Ag surface, and thus add to the versatility of our SHINERS method.

  13. Synthesis and optical characterization of C-SiO2 and C-NiO sol-gel composite films for use as selective solar absorbers

    Makiwa, G

    2008-08-01

    Full Text Available The authors present a cheaper and environmentally friendly method to fabricate efficient spectrally selective solar absorber materials. The sol-gel technique was used to fabricate carbon-silica (C-SiO2) and carbon-nickel oxide (C-NiO) composite...

  14. Total Ionizing Dose Effects of Si Vertical Diffused MOSFET with SiO2 and Si3N4/SiO2 Gate Dielectrics

    Jiongjiong Mo

    2017-01-01

    Full Text Available The total ionizing dose irradiation effects are investigated in Si vertical diffused MOSFETs (VDMOSs with different gate dielectrics including single SiO2 layer and double Si3N4/SiO2 layer. Radiation-induced holes trapping is greater for single SiO2 layer than for double Si3N4/SiO2 layer. Dielectric oxidation temperature dependent TID effects are also studied. Holes trapping induced negative threshold voltage shift is smaller for SiO2 at lower oxidation temperature. Gate bias during irradiation leads to different VTH shift for different gate dielectrics. Single SiO2 layer shows the worst negative VTH at VG=0 V, while double Si3N4/SiO2 shows negative VTH shift at VG=-5 V, positive VTH shift at VG=10 V, and negligible VTH shift at VG=0 V.

  15. Ordered micro/macro porous K-OMS-2/SiO2 nanocatalysts: Facile synthesis, low cost and high catalytic activity for diesel soot combustion

    Yu, Xuehua; Zhao, Zhen; Wei, Yuechang; Liu, Jian

    2017-04-01

    A series of novel oxide catalysts, which contain three-dimensionally ordered macroporous (3DOM) and microporous structure, were firstly designed and successfully synthesized by simple method. In the as-prepared catalysts, 3DOM SiO2 is used as support and microporous K-OMS-2 oxide nanoparticles are supported on the wall of SiO2. 3DOM K-OMS-2/SiO2 oxide catalysts were firstly used in soot particle oxidation reaction and they show very high catalytic activities. The high activities of K-OMS-2/SiO2 oxide catalysts can be assigned to three possible reasons: macroporous effect of 3DOM structure for improving contact between soot and catalyst, microporous effect of K-OMS-2 for adsorption of small gas molecules and interaction of K and Mn for activation of gas molecules. The catalytic activities of catalysts are comparable to or even higher than noble metal catalyst in the medium and high temperature range. For example, the T50 of K-OMS-2/SiO2-50, 328 °C, is much lower than those of Pt/Al2O3 and 3DOM Au/LaFeO3, 464 and 356 °C,respectively. Moreover, catalysts exhibited high catalytic stability. It is attributed to that the K+ ions are introduced into the microporous structure of OMS-2 and stabilized in the catalytic reaction. Meanwhile, the K+ ions play an important role in templating and stabilizing the tunneled framework of OMS-2.

  16. Synthesis of functionalized 3D porous graphene using both ionic liquid and SiO2 spheres as ``spacers'' for high-performance application in supercapacitors

    Li, Tingting; Li, Na; Liu, Jiawei; Cai, Kai; Foda, Mohamed F.; Lei, Xiaomin; Han, Heyou

    2014-12-01

    In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO2 spheres as ``spacers''. In the synthesis, the introduction of dual ``spacers'' effectively enlarged the interspace between graphene sheets and suppressed their re-stacking. In addition, the IL also acted as a structure-directing agent playing a crucial role in inducing the formation of unique 3D architectures. Consequently, fast electron/ion transport channels were successfully constructed and numerous oxygen-containing groups on graphene sheets were effectively reserved, which had unique advantages in decreasing ion diffusion resistance and providing additional pseudocapacitance. As expected, the obtained material exhibited superior specific capacitance and rate capability compared to single ``spacer'' designed electrodes and simultaneously maintained excellent cycling stability. In particular, there was nearly no loss of its initial capacitance after 3000 cycles. In addition, we further assembled a symmetric two-electrode device using the material, which showed outstanding flexibility and low equivalent series resistance (ESR). More importantly, it was capable of yielding a maximum power density of about 13.3 kW kg-1 with an energy density of about 7.0 W h kg-1 at a voltage of 1.0 V in 1 M H2SO4 electrolyte. All these impressive results demonstrate that the material obtained by this approach is greatly promising for application in high-performance supercapacitors.In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO2 spheres as ``spacers''. In the synthesis, the introduction of dual ``spacers'' effectively enlarged the interspace between graphene sheets

  17. Ordering at Si(111)/o-Si and Si(111)/SiO2 Interfaces

    Robinson, I. K.; Waskiewicz, W. K.; Tung, R. T.

    1986-01-01

    X-ray diffraction has been used to measure the intensity profile of the two-dimensional rods of scattering from a single interface buried inside a bulk material. In both Si(111)/a-Si and Si(111)/SiO2 examples there are features in the perpendicular-momentum-transfer dependence which are not expec...... are not expected from an ideal sharp interface. The diffraction profiles are explained by models with partially ordered layers extending into the amorphous region. In the Si(111)/a-Si case there is clear evidence of stacking faults which are attributed to residual 7×7 reconstruction....

  18. Synthesis of functionalized 3D porous graphene using both ionic liquid and SiO2 spheres as "spacers" for high-performance application in supercapacitors.

    Li, Tingting; Li, Na; Liu, Jiawei; Cai, Kai; Foda, Mohamed F; Lei, Xiaomin; Han, Heyou

    2015-01-14

    In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO2 spheres as "spacers". In the synthesis, the introduction of dual "spacers" effectively enlarged the interspace between graphene sheets and suppressed their re-stacking. In addition, the IL also acted as a structure-directing agent playing a crucial role in inducing the formation of unique 3D architectures. Consequently, fast electron/ion transport channels were successfully constructed and numerous oxygen-containing groups on graphene sheets were effectively reserved, which had unique advantages in decreasing ion diffusion resistance and providing additional pseudocapacitance. As expected, the obtained material exhibited superior specific capacitance and rate capability compared to single "spacer" designed electrodes and simultaneously maintained excellent cycling stability. In particular, there was nearly no loss of its initial capacitance after 3000 cycles. In addition, we further assembled a symmetric two-electrode device using the material, which showed outstanding flexibility and low equivalent series resistance (ESR). More importantly, it was capable of yielding a maximum power density of about 13.3 kW kg(-1) with an energy density of about 7.0 W h kg(-1) at a voltage of 1.0 V in 1 M H2SO4 electrolyte. All these impressive results demonstrate that the material obtained by this approach is greatly promising for application in high-performance supercapacitors.

  19. Synthesis and characterization of Al2O3 and SiO2 films with fluoropolymer content using rf-plasma magnetron sputtering technique

    Islam, Mohammad; Inal, Osman T.

    2008-01-01

    Pure and molecularly mixed inorganic films for protection against atomic oxygen in lower earth orbit were prepared using radio-frequency (rf) plasma magnetron sputtering technique. Alumina (Al 2 O 3 ) and silica (SiO 2 ) films with average grain size in the range of 30-80 nm and fully dense or dense columnar structure were synthesized under different conditions of pressure and power. Simultaneous oxide sputtering and plasma polymerization (PP) of hexafluoropropylene (HFP) led to the formation of molecularly mixed films with fluoropolymer content. The degree of plasma polymerization was strongly influenced by total chamber pressure and the argon to HFP molar ratio (n Ar /n M ). An order of magnitude increase in pressure due to argon during codeposition changed the plasma-polymerization mechanism from radical-chain- to radical-radical-type processes. Subsequently, a shift from linear CH 2 group based chain polymerization to highly disordered fluoropolymer content with branching and cross-linking was observed. Fourier transform infrared spectroscopy studies revealed chemical interaction between depositing SiO 2 and PP-HFP through appearance of absorption bands characteristic of Si-F stretching and expansion of SiO 2 network. The relative amount and composition of plasma-polymerized fluoropolymer in such films can be controlled by changing argon to HFP flow ratio, total chamber pressure, and applied power. These films offer great potential for use as protective coatings in aerospace applications

  20. Nano-TiCl4.SiO2: A Versatile and Efficient Catalyst for Synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes

    B. F. Mirjalili; A. Bamoniri; L. Zamani

    2013-01-01

    Nano-silica supported titanium tetrachloride (TiCl4.SiO2) was prepared and used as an acid catalyst for the 14-aryl or alkyl-14H-dibenzo[a,,j]xanthenesreaction under solvent-free conditions. Compared to the classical 14-aryl or alkyl-14H-dibenzo[a,j]xanthenesreaction conditions, this method consistently has the advantage of excellent yields, mild reaction conditions, ease of workup, survival of different functional groups and short reaction times.

  1. Nano-TiCl4.SiO2: A Versatile and Efficient Catalyst for Synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes

    B. F. Mirjalili

    2013-12-01

    Full Text Available Nano-silica supported titanium tetrachloride (TiCl4.SiO2 was prepared and used as an acid catalyst for the 14-aryl or alkyl-14H-dibenzo[a,,j]xanthenesreaction under solvent-free conditions. Compared to the classical 14-aryl or alkyl-14H-dibenzo[a,j]xanthenesreaction conditions, this method consistently has the advantage of excellent yields, mild reaction conditions, ease of workup, survival of different functional groups and short reaction times.

  2. Synthesis of Si, N co-Doped Nano-Sized TiO2 with High Thermal Stability and Photocatalytic Activity by Mechanochemical Method

    Peisan Wang

    2018-05-01

    Full Text Available Τhe photocatalytic activity in the range of visible light wavelengths and the thermal stability of the structure were significantly enhanced in Si, N co-doped nano-sized TiO2, and synthesized through high-energy mechanical milling of TiO2 and SiO2 powders, which was followed by calcination at 600 °C in an ammonia atmosphere. High-energy mechanical milling had a pronounced effect on the mixing and the reaction between the starting powders and greatly favored the transformation of the resultant powder mixture into an amorphous phase that contained a large number of evenly-dispersed nanocrystalline TiO2 particles as anatase seeds. The experimental results suggest that the elements were homogeneously dispersed at an atomic level in this amorphous phase. After calcination, most of the amorphous phase was crystallized, which resulted in a unique nano-sized crystalline-core/disordered-shell morphology. This novel experimental process is simple, template-free, and provides features of high reproducibility in large-scale industrial production.

  3. Novel Cu@SiO2/bacterial cellulose nanofibers: Preparation and excellent performance in antibacterial activity

    Ma, Bo; Huang, Yang; Zhu, Chunlin; Chen, Chuntao; Chen, Xiao; Fan, Mengmeng; Sun, Dongping

    2016-01-01

    The antibacterial composite based on bacterial cellulose (BC) was successfully prepared by in-situ synthesis of SiO 2 coated Cu nanoparticles (Cu@SiO 2 /BC) and its properties were characterized. Its chemical structures and morphologies were evaluated by Fourier transformation infrared spectrum (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the SiO 2 coated Cu particles were well homogeneously precipitated on the surface of BC. The Cu@SiO 2 /BC was more resistant to oxidation than the Cu nanoparticles impregnated into BC (Cu/BC) and then Cu@SiO 2 /BC could prolong the antimicrobial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). - Graphical abstract: Schematic illustration of the preparation of Cu@SiO 2 /BC. Due to its unique structure, the Cu@SiO 2 /BC membrane shows excellent antibacterial effects and can be used for a long time. - Highlights: • This work paves the novel way to fabricate antibacterial nanomaterial with good efficiency. • We prepare the antibacterial membrane based on bacterial cellulose by in-situ synthesis of SiO 2 -coated Cu nanoparticles. • The antibacterial membrane is more resistant to oxidation and can prolong the antimicrobial activity.

  4. Nonvolatile field effect transistors based on protons and Si/SiO2Si structures

    Warren, W.L.; Vanheusden, K.; Fleetwood, D.M.; Schwank, J.R.; Winokur, P.S.; Knoll, M.G.; Devine, R.A.B.

    1997-01-01

    Recently, the authors have demonstrated that annealing Si/SiO 2 /Si structures in a hydrogen containing ambient introduces mobile H + ions into the buried SiO 2 layer. Changes in the H + spatial distribution within the SiO 2 layer were electrically monitored by current-voltage (I-V) measurements. The ability to directly probe reversible protonic motion in Si/SiO 2 /Si structures makes this an exemplar system to explore the physics and chemistry of hydrogen in the technologically relevant Si/SiO 2 structure. In this work, they illustrate that this effect can be used as the basis for a programmable nonvolatile field effect transistor (NVFET) memory that may compete with other Si-based memory devices. The power of this novel device is its simplicity; it is based upon standard Si/SiO 2 /Si technology and forming gas annealing, a common treatment used in integrated circuit processing. They also briefly discuss the effects of radiation on its retention properties

  5. Preparation and Characterization of Fluorescent SiO2 Microspheres

    Xu, Cui; Zhang, Hao; Guan, Ruifang

    2018-01-01

    Fluorescent compound without typical fluorophores was synthesized with citric acid (CA) and aminopropyltriethoxysilane (APTS) firstly, and then it was grafted to the surface of the prepared SiO2 microspheres by chemical reaction. The fluorescent SiO2 microspheres with good fluorescent properties were obtained by optimizing the reaction conditions. And the morphology and structure of the fluorescent SiO2 microspheres have been characterized by scanning electron microscopy (SEM) and fourier transform infrared (FTIR) spectroscopy. The results showed that the preparation of fluorescent SiO2 microspheres have good monodispersity and narrow particle size distribution. Moreover, the fluorescent SiO2 microspheres can be applied to detect Fe3+ in aqueous solution, prepare fluorescent SiO2 rubber, and have potential to be applied in the fluorescent labeling and fingerprint appearing technique fields.

  6. The Effect of SiO2 Shell on the Suppression of Photocatalytic Activity of TiO2 and ZnO Nanoparticles

    Lee, Min Hee; Lee, Choon Soo; Patil, Umakant Mahadev; Kochuveedu, Saji Thomas

    2012-01-01

    In this study, we investigate the potential use of TiO 2 SiO 2 and ZnO SiO 2 core/shell nanoparticles (NPs) as effective UV shielding agent. In the typical synthesis, SiO 2 was coated over different types of TiO 2 (anatase and rutile) and ZnO by sol-gel method. The synthesized TiO 2 SiO 2 and ZnO SiO 2 Nps were characterized by UV-Vis, XRD, Sem and TEM. The UV-vis absorbance and transmittance spectra of core shell NPs showed an efficient blocking effect in the UV region and more than 90% transmittance in the visible region. XRD and SAED studies confirmed the formation of amorphous SiO 2 coated over the TiO 2 and ZnO NPs. The FESEM and TEM images shows that coating of SiO 2 over the surface of anatase, rutile TiO 2 and ZnO NPs resulted in the increase in particle size by ∼30 nm. In order to study the UV light shielding capability of the samples, photocatalytic degradation of methylene blue dye on TiO 2 SiO 2 and ZnO SiO 2 NPs was performed. Photocatalytic activity for both types of TiO 2 NPs was partially suppressed. In comparison, the photocatalytic activity of ZnO almost vanished after the SiO 2 coating

  7. Precipitation of amorphous SiO2 particles and their properties

    S. Musić

    2011-03-01

    Full Text Available The experimental conditions were optimized for the synthesis of amorphous SiO2 particles by the reaction of neutralization of sodium silicate solution with H2SO4 solution. Amorphous SiO2 particles were characterized by XRD, FT-IR, FE-SEM, EDS and microelectrophoresis. The amorphous peak was located at 2θ = 21.8º in the XRD pattern. Primary SiO2 particles were ~ 15 to ~ 30 nm in size and they aggregated into bigger particles. Amorphous SiO2 particles showed a specific surface area up to 130 m²g-1, dependent on the parameters of the precipitation process. The EDS spectrum of amorphous SiO2 particles did not show contamination with sulfate or other ions, which cannot be excluded in traces. pHzpc =1.7 was obtained by microelectrophoresis.

  8. Core/shell structured ZnO/SiO2 nanoparticles: Preparation, characterization and photocatalytic property

    Zhai Jing; Tao Xia; Pu Yuan; Zeng Xiaofei; Chen Jianfeng

    2010-01-01

    ZnO nanoparticles were prepared by a simple chemical synthesis route. Subsequently, SiO 2 layers were successfully coated onto the surface of ZnO nanoparticles to modify the photocatalytic activity in acidic or alkaline solutions. The obtained particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS) and zeta potential. It was found that ultrafine core/shell structured ZnO/SiO 2 nanoparticles were successfully obtained. The photocatalytic performance of ZnO/SiO 2 core/shell structured nanoparticles in Rhodamine B aqueous solution at varied pH value were also investigated. Compared with uncoated ZnO nanoparticles, core/shell structured ZnO/SiO 2 nanoparticles with thinner SiO 2 shell possess improved stability and relatively better photocatalytic activity in acidic or alkaline solutions, which would broaden its potential application in pollutant treatment.

  9. Sum Frequency Generation Vibrational Spectroscopy of 1,3-Butadiene Hydrogenation on 4 nm Pt@SiO 2 , Pd@SiO 2 , and Rh@SiO 2 Core–Shell Catalysts

    Krier, James M.

    2015-01-14

    © 2014 American Chemical Society. 1,3-Butadiene (1,3-BD) hydrogenation was performed on 4 nm Pt, Pd, and Rh nanoparticles (NPs) encapsulated in SiO2 shells at 20, 60, and 100 °C. The core-shells were grown around polyvinylpyrrolidone (PVP) coated NPs (Stöber encapsulation) prepared by colloidal synthesis. Sum frequency generation (SFG) vibrational spectroscopy was performed to correlate surface intermediates observed in situ with reaction selectivity. It is shown that calcination is effective in removing PVP, and the SFG signal can be generated from the metal surface. Using SFG, it is possible to compare the surface vibrational spectrum of Pt@SiO2 (1,3-BD is hydrogenated through multiple paths and produces butane, 1-butene, and cis/trans-2-butene) to Pd@SiO2 (1,3-BD favors one path and produces 1-butene and cis/trans-2-butene). In contrast to Pt@SiO2 and Pd@SiO2, SFG and kinetic experiments of Rh@SiO2 show a permanent accumulation of organic material.

  10. Hazards of TiO2 and amorphous SiO2 nanoparticles

    Reijnders, L.; Kahn, H.A.; Arif, I.A.

    2012-01-01

    TiO2 and amorphous SiO2 nanoparticles have been described as ‘safe’, ‘non-toxic’ and ‘environment friendly’ in scientific literature. However, though toxicity data are far from complete, there is evidence that these nanoparticles are hazardous. TiO2 nanoparticles have been found hazardous to humans

  11. Effect of Number of Various-Type Acid Sites Located on 20 % Co/ZrO2SiO2 Sample Surface on Parameters of Catalytic Process in Synthesis of High-Octane Motor Fuel Components

    A. P. Nesenchouk

    2011-01-01

    Full Text Available The paper considers an effect of ZrO2 content in 20%Co/xZrO2∙(100 – xSiO2 (x = 0, 10, 15, 25, 30, 40 and 100 mass percent catalyst carriers on their catalytic properties. Temperature programmed desorption of NH3 has made it possible to determine relations between their acid and catalytic properties. The paper reveals the TPD spectrum is the result of 4 overlapping peaks originating during NH3 desorption from the respective groups of acid sites. Total acidity of samples and contribution of separate acid site groups into the given acidity have been have been determined in the paper. The paper contains graphical dependences of a various-type acid site number on  content of zirconium oxide in the carrier. Correlations between change in various-type acid site number and catalytic process parameters (CO conversion, C5+ hydrocarbon output and  C5+ isoparaffin output have been found in the paper. The paper shows that the highest values of CO conversion and C5+ hydrocarbon output correspond to maximum number of acid sites, and that number accounts for a peak of desorbed ammonia at Tmax = 122 °C, while the lowest isoparaffin output corresponds to minimum number of acid sites, which characterizes a peak of desorbed ammonia at Tmax = 224–257 °C. 

  12. Reliability implications of defects in high temperature annealed Si/SiO2/Si structures

    Warren, W.L.; Fleetwood, D.M.; Shaneyfelt, M.R.; Winokur, P.S.; Devine, R.A.B.; Mathiot, D.; Wilson, I.H.; Xu, J.B.

    1994-01-01

    High-temperature post-oxidation annealing of poly-Si/SiO 2 /Si structures such as metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field effect transistors is known to result in enhanced radiation sensitivity, increased 1/f noise, and low field breakdown. The authors have studied the origins of these effects from a spectroscopic standpoint using electron paramagnetic resonance (EPR) and atomic force microscopy. One result of high temperature annealing is the generation of three types of paramagnetic defect centers, two of which are associated with the oxide close to the Si/SiO 2 interface (oxygen-vacancy centers) and the third with the bulk Si substrate (oxygen-related donors). In all three cases, the origin of the defects may be attributed to out-diffusion of O from the SiO 2 network into the Si substrate with associated reduction of the oxide. The authors present a straightforward model for the interfacial region which assumes the driving force for O out-diffusion is the chemical potential difference of the O in the two phases (SiO 2 and the Si substrate). Experimental evidence is provided to show that enhanced hole trapping and interface-trap and border-trap generation in irradiated high-temperature annealed Si/SiO 2 /Si systems are all related either directly, or indirectly, to the presence of oxygen vacancies

  13. Potential energy landscape of an interstitial O2 molecule in a SiO2 film near the SiO2/Si(001) interface

    Ohta, Hiromichi; Watanabe, Takanobu; Ohdomari, Iwao

    2008-10-01

    Potential energy distribution of interstitial O2 molecule in the vicinity of SiO2/Si(001) interface is investigated by means of classical molecular simulation. A 4-nm-thick SiO2 film model is built by oxidizing a Si(001) substrate, and the potential energy of an O2 molecule is calculated at Cartesian grid points with an interval of 0.05 nm in the SiO2 film region. The result shows that the potential energy of the interstitial site gradually rises with approaching the interface. The potential gradient is localized in the region within about 1 nm from the interface, which coincides with the experimental thickness of the interfacial strained layer. The potential energy is increased by about 0.62 eV at the SiO2/Si interface. The result agrees with a recently proposed kinetic model for dry oxidation of silicon [Phys. Rev. Lett. 96, 196102 (2006)], which argues that the oxidation rate is fully limited by the oxidant diffusion.

  14. Synthesis of chelating agent free-solid phase extractor (CAF-SPE) based on new SiO2/Al2O3/SnO2 ternary oxide and application for online preconcentration of Pb2+ coupled with FAAS

    Tarley, César R.T.; Scheel, Guilherme L.; Zappielo, Caroline D.; Suquila, Fabio A.C.; Ribeiro, Emerson S.

    2018-01-01

    A new online solid phase preconcentration method using the new SiO 2 /Al2O 3 /SnO 2 ternary oxide (designated as SiAlSn) as chelating agent free-solid phase extractor (CAF-SPE) coupled to flame atomic absorption spectrometry (FAAS) for Pb 2+ determination at trace levels in different kind of samples is proposed. The solid adsorbent has been characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence spectroscopy (XRF) and textural data. The method involves the preconcentration using time-based sampling of Pb 2+ solution at pH 4.3 through 100.0 mg of packed adsorbed into a mini-column under flow rate of 4.0 mL min -1 during 5 min. The elution step was accomplished by using 1.0 mol L -1 HCl. A wide range of analytical curve (5.0-400.0 μg L -1 ), high enrichment factor (40.5), low consumption index (0.5 mL) and low limits of quantification and detection, 5.0 and 1.5 μg L -1 , respectively, were obtained with the developed method. Practical application of method was tested on water samples, chocolate powder, Ginkgo biloba and sediment (certified reference material). On the basis of the results, the SiAlSn can be considered an effective adsorbent belonging to the class of CAF-SPE for Pb 2+ determination from different matrices. (author)

  15. Comparisons between TiO2- and SiO2-flux assisted TIG welding processes.

    Tseng, Kuang-Hung; Chen, Kuan-Lung

    2012-08-01

    This study investigates the effects of flux compounds on the weld shape, ferrite content, and hardness profile in the tungsten inert gas (TIG) welding of 6 mm-thick austenitic 316 L stainless steel plates, using TiO2 and SiO2 powders as the activated fluxes. The metallurgical characterizations of weld metal produced with the oxide powders were evaluated using ferritoscope, optical microscopy, and Vickers microhardness test. Under the same welding parameters, the penetration capability of TIG welding with TiO2 and SiO2 fluxes was approximately 240% and 292%, respectively. A plasma column made with SiO2 flux exhibited greater constriction than that made with TiO2 flux. In addition, an anode root made with SiO2 flux exhibited more condensation than that made with TiO2 flux. Results indicate that energy density of SiO2-flux assisted TIG welding is higher than that of TiO2-flux assisted TIG welding.

  16. Synthesis and Cell Seeding Assessment of Novel Biphasic Nano Powder in the CaO–MgO–SiO2 System for Bone Implant Application

    Kazem Marzban

    2017-02-01

    Full Text Available Objective(s: CaO–MgO–SiO2 system bioceramics possess good characteristics for hard tissue engineering applications. The aim of the study was to synthesize the nano powder by using a sol-gel method and evaluate of bioactivity in the cells culture. Methods: To characterize of powder X-ray diffraction (XRD, transmission electron microscopy (TEM and to evaluate the bioactivity sample cell seeding and methylthiazol tetrazolium (MTT assay were performed. Results: X-ray diffraction (XRD analysis showed that the biphasic powder was obtained at 1300°C for 2 h by using a sol-gel method. Transmission electron microscopy (TEM image showed that powder particle size was about 45 nm. Besides, cell culture results indicated that the percentage of viability values was increased by the extension of period. Conclusions: found that the sample is cytocompatible and has cell proliferation potential in culture medium. The present study demonstrates that, the biphasic CaO–MgO–SiO2 system can be used to achieve novel bioactive materials for bone implant application.

  17. Simple and efficient synthesis of copper(II)-modified uniform magnetic Fe3O4@SiO2 core/shell microspheres for immobilization of cellulase

    Li, Shi-Kuo; Hou, Xiao-Cheng; Huang, Fang-Zhi; Li, Chuan-Hao; Kang, Wen-Juan; Xie, An-Jian; Shen, Yu-Hua

    2013-11-01

    In this paper, we reported a simple and efficient protocol for preparation of Cu2+-modified magnetic Fe3O4@SiO2 core/shell microspheres for immobilization of cellulase. The uniform magnetic Fe3O4@SiO2 core/shell microspheres with a thin shell of 20 nm were synthesized through a solvothermal method followed by a sol-gel process. An amino-terminated silane coupling agent of (3-aminopropyl)triethoxysilane (APTS) was then grafted on them for capturing Cu2+ ions. The reaction process is very simple, efficient, and economical. Noticeably, the content of Cu2+ ions on the magnetic core/shell microspheres can reach 4.6 Wt%, endowing them possess as high immobilization capacity as 225.5 mg/g for cellulase. And the immobilized cellulase can be retained over 90 % on the magnetic microspheres after six cycles. Meanwhile, the magnetic microspheres decorated with Cu2+ ions show a superparamagnetic character with a high magnetic saturation of 58.5 emu/g at room temperature, suggesting conveniently and rapidly recycle the enzyme from solution. This facile, recyclable, high immobilization capacity and activity strategy may find potential applications in enzyme catalytic reactions with low cost.

  18. Simple and efficient synthesis of copper(II)-modified uniform magnetic Fe3O4@SiO2 core/shell microspheres for immobilization of cellulase

    Li, Shi-Kuo; Hou, Xiao-Cheng; Huang, Fang-Zhi; Li, Chuan-Hao; Kang, Wen-Juan; Xie, An-Jian; Shen, Yu-Hua

    2013-01-01

    In this paper, we reported a simple and efficient protocol for preparation of Cu 2+ -modified magnetic Fe 3 O 4 @SiO 2 core/shell microspheres for immobilization of cellulase. The uniform magnetic Fe 3 O 4 @SiO 2 core/shell microspheres with a thin shell of 20 nm were synthesized through a solvothermal method followed by a sol–gel process. An amino-terminated silane coupling agent of (3-aminopropyl)triethoxysilane (APTS) was then grafted on them for capturing Cu 2+ ions. The reaction process is very simple, efficient, and economical. Noticeably, the content of Cu 2+ ions on the magnetic core/shell microspheres can reach 4.6 Wt%, endowing them possess as high immobilization capacity as 225.5 mg/g for cellulase. And the immobilized cellulase can be retained over 90 % on the magnetic microspheres after six cycles. Meanwhile, the magnetic microspheres decorated with Cu 2+ ions show a superparamagnetic character with a high magnetic saturation of 58.5 emu/g at room temperature, suggesting conveniently and rapidly recycle the enzyme from solution. This facile, recyclable, high immobilization capacity and activity strategy may find potential applications in enzyme catalytic reactions with low cost

  19. One-step synthesis, toxicity assessment and degradation in tumoral pH environment of SiO2@Ag core/shell nanoparticles

    De Matteis, Valeria; Rizzello, Loris; Di Bello, Maria Pia; Rinaldi, Rosaria

    2017-06-01

    The unique physicochemical properties of SiO2@Ag core/shell nanoparticles make them a promising tool in nanomedicine, where they are used as nanocarriers for several biomedical applications, including (but not restricted to) cancer treatment. However, a comprehensive estimation of their potential toxicity, as well as their degradation in the tumor microenvironment, has not been extensively addressed yet. We investigated in vitro the viability, the reactive oxygen species (ROS) production, the DNA damage level, and the nanoparticle uptake on HeLa cells, used as model cancer cells. In addition, we studied the NPs degradation profile at pH 6.5, to mimic the tumor microenvironment, and at the neutral and physiological (pH 7-7.4). Our experiments demonstrate that the silver shell dissolution is promoted under acidic conditions, which could be related to cell death induction. Our evidences demonstrate that SiO2@Ag nanoparticles possess the ability of combining an effective cancer cell treatment (through local silver ions release) together with a possible controlled release of bioactive compounds encapsulated in the silica as future application.

  20. Design of laser-driven SiO2-YAG:Ce composite thick film: Facile synthesis, robust thermal performance, and application in solid-state laser lighting

    Xu, Jian; Liu, Bingguo; Liu, Zhiwen; Gong, Yuxuan; Hu, Baofu; Wang, Jian; Li, Hui; Wang, Xinliang; Du, Baoli

    2018-01-01

    In recent times, there have been rapid advances in the solid-state laser lighting technology. Due to the large amounts of heat accumulated from the high flux laser radiation, color conversion materials used in solid-state laser lighting devices should possess high durability, high thermal conductivity, and low thermal quenching. The aim of this study is to develop a thermally robust SiO2-YAG:Ce composite thick film (CTF) for high-power solid-state laser lighting applications. Commercial colloidal silica which was used as the source of SiO2, played the roles of an adhesive, a filler, and a protecting agent. Compared to the YAG:Ce powder, the CTF exhibits remarkable thermal stability (11.3% intensity drop at 200 °C) and durability (4.5% intensity drop after 1000 h, at 85 °C and 85% humidity). Furthermore, the effects of the substrate material and the thickness of the CTF on the laser lighting performance were investigated in terms of their thermal quenching and luminescence saturation behaviors, respectively. The CTF with a thickness of 50 μm on a sapphire substrate does not show luminescence saturation, despite a high-power density of incident radiation i.e. 20 W/mm2. These results demonstrate the potential applicability of the CTF in solid-state laser lighting devices.

  1. Crystallization behavior of Li2O-SiO2, Na2O-SiO2 and Na2O-CaO-SiO2 glasses; Li2O-SiO2, Na2O-SiO2, Na2O-CaO-SiO2 kei glass no kessho sekishutsu kyodo

    Tsutsumi, K.; Otake, J.; Nagasaka, T.; Hino, M. [Tohoku University, Sendai (Japan)

    1998-06-01

    It has been known that crystallization of mold powder is effective on the disturbance of heat transfer between mold and solidified shell in production of middle carbon steel slabs in continuous casting process. But it has not yet been made clear which composition of mold powder is the most suitable for crystallization. The crystallization behavior of Li2O-SiO2, Na2O-SiO2 and Na2O-CaO-SiO2 glasses was observed by differential thermal analysis (DTA) and hot-thermocouple methods with DTA in the present work. As a result, addition of alkaline metal and alkaline earth metal oxides to SiO2 increased the critical cooling rate for glass formation in binary system of Li2O-SiO2 and Na2O-SiO2 and Li2O-SiO2 system crystallized easier than Na2O-SiO2 system. In ternary system of Na2O-CaO-SiO2, addition of Na2O hurried the critical cooling rate at CaO/SiO2=0.93 mass ratio, but the rate was almost constant in the composition range of more than 15 mass% Na2O. The slag of CaO/SiO2=0.93 made the rate faster than the slag of CaO/SiO2=0.47 at constant content of 10mass% Na2O. 17 refs., 10 figs., 3 tabs.

  2. Multifunctional Roles of TiO 2 Nanoparticles for Architecture of Complex Core−Shells and Hollow Spheres of SiO 2 −TiO 2 −Polyaniline System

    Wang, Dan Ping; Zeng, Hua Chun

    2009-01-01

    to prepare inorganic-polymer nanocomposites. In this work, we explore the roles of metal-oxide nanoparticles (anatase TiO2) in the area of constructional synthesis of highly complex core-shell and hollow sphere nanostructures comprising SiO2, TiO2

  3. Alpha-particle irradiation induced defects in SiO2 films of Si-SiO2 structures

    Koman, B.P.; Gal'chynskyy, O.V.; Kovalyuk, R.O.; Shkol'nyy, A.K.

    1996-01-01

    The aim of the work was to investigate alpha-particle irradiation induced defects in Si-SiO 2 structures by means of the thermostimulated discharge currents (TSDC) analysis. The object of investigation were (p-Si)-SiO 2 structures formed by a combined oxidation of the industrial p-Si wafers in dry and wet oxygen at temperature of 1150 C. The TSD currents were investigated in the temperature range between 90 and 500 K under linear heating rate. Pu 238 isotopes were the source of alpha-particles with an energy of 4-5 MeV and a density of 5.10 7 s -1 cm -2 . The TSD current curves show two peculiar maxima at about 370 and 480 K. Alpha-particle irradiation doesn't affect the general shape of the TSDC curves but leads to a shift of the maximum at 370 K and reduces the total electret charge which is accumulated in the Si-SiO 2 structures during polarization. The energy distribution function of the defects which are involved in SiO 2 polarization has been calculated. It showes that defects with activation energies of about 0.8 and 1.0 eV take part in forming the electret state, and these activation energies have certain energy distributions. It has been found that the TSDC maximum at 370 K has space charge nature and is caused by migration of hydrogen ions. In irradiated samples hydrogen and natrium ions localize on deeper trapping centres induced by alpha-particle irradiation. (orig.)

  4. Fabrication and properties of highly luminescent materials from Tb(OH)3-SiO2 and Tb(OH)3-SiO2:Eu3+ nanotubes

    Tran Thu Huong; Tran Kim Anh; Le Quoc Minh

    2009-01-01

    Luminescent nanomaterials with one-dimensional (1D) structures have attracted much attention due to their unique properties and potential applications in nanophotonics and nanobiophotonics. In this paper, we report a synthesis of terbium - hydroxide - at - silica Tb(OH) 3 -SiO 2 and Tb(OH) 3 -SiO 2 :Eu 3+ nanotubes. Terbium - hydroxide tubes were synthesized by soft template method. The size of the tubes can be controlled precisely and have outer diameters ranging from 80 to 120 nm, wall thickness of about 30 nm, and lengths ranging from 300 to 800 nm. To fabricate core/shell materials, the seed growth method is used. FESEM, X-ray diffraction, Raman spectra of Tb(OH) 3 and Tb(OH) 3 -SiO 2 nanotubes were investigated. The photoluminescence (PL) spectrum of Tb(OH) 3 under 325 nm excitation consists of four main peaks at 488, 542, 582, and 618 nm. Furthermore, a preliminary suggestion for the mechanism of growth of the Tb(OH) 3 nanotubes using the soft - template synthesis technique has been proposed. The PL intensity from Tb(OH) 3 -SiO 2 or Tb(OH) 3 -SiO 2 :Eu 3+ nanotubes is much stronger than that of Tb(OH) 3 .

  5. Synthesis of Fe5C2@SiO2 core@shell nanoparticles as a potential candidate for biomedical application

    Ahmadpoor, Fatemeh; Shojaosadati, Seyed Abbas; Delavari H, Hamid; Christiansen, Gunna; Saber, Reza

    2018-05-01

    A new strategy for water-dispersibility of hydrophobic carbide nanostructures was proposed. In this regard, hydrophobic Fe5C2 nanoparticles (NPs) with size ranging 25–40 nm were synthesized and coated with 12–15 nm silica shell for biomedical applications. X-ray diffraction (XRD) results revealed that Fe5C2 NPs with monoclinic structure were successfully prepared. The crystalline structure of Fe5C2 NPs was remained unchanged and saturation magnetization of core remained nearly constant after coating with silica shell. Moreover, Raman spectroscopy identified D-band of amorphous carbon shells which was also confirmed by transmission electron microscopy (TEM). Finally, Fe5C2@SiO2 core@shell NPs demonstrated no significant cytotoxicity and appropriate heat generating which makes them a promising candidate for magnetic fluid hyperthermia applications.

  6. PAC study in the HfO2-SiO2 system

    Chain, C.Y.; Damonte, L.C.; Ferrari, S.; Munoz, E.; Torres, C. Rodriguez; Pasquevich, A.F.

    2010-01-01

    A high-k HfO 2 /SiO 2 gate stack is taking the place of SiO 2 as a gate dielectric in field effect transistors. This fact makes the study of the solid-state reaction between these oxides very important. Nanostructure characterization of a high-energy ball milled and post-annealed equimolar HfO 2 and amorphous SiO 2 powder mixture has been carried out by perturbed angular correlations (PAC) technique. The study was complemented with X-ray diffraction and positron annihilation lifetime spectroscopy (PALS). The experimental results revealed that the ball milling of equimolar mixtures increases the defects concentration in hafnium oxide. No solid-state reaction occurred even after 8 h of milling. The formation of HfSiO 4 (hafnon) was observed in the milled blends annealed at high temperatures.The PAC results of the milled samples are compared with those obtained for pure m-ZrO 2 subjected to high-energy ball milling and with reported microstructure data for the system ZrO 2 -SiO 2 .

  7. Dependence of Photocatalytic Activity of TiO2-SiO2 Nanopowders

    M. Riazian

    2014-10-01

    Full Text Available Structural properties and chemical composition change the photocatalytic activity in TiO2-SiO2 nanopowder composite. The SiO2-TiO2 nanostructure is synthesized based on sol–gel method. The nanoparticles are characterized by x-ray fluorescents (XRF, x- ray diffraction (XRD, tunneling electron microscopy (TEM, field emission scanning electron microscopy (FE-SEM, UV-vis. Spectrophotometer and furrier transmission create infrared absorption (FTIR techniques. The rate constant k for the degradation of methylen blue in its aqueous solution under UV irradiation is determined as a measure of photocatalytic activity. Dependence between photocatalytic activity and SiO2 content in the composite is determined. Rate constant k is found dependent on the content of SiO2 in the composite that calcined at 900 oC. The addition of low composition SiO2 to the TiO2 matrix (lower than 45% enhances the photocatalytic activity due to thermal stability and increasing in the surface area. The effects of chemical compositions on the surface topography and the crystallization of phases are studied.

  8. Synthesis of raspberry-like monodisperse magnetic hollow hybrid nanospheres by coating polystyrene template with Fe(3)O(4)@SiO(2) particles.

    Wang, Chunlei; Yan, Juntao; Cui, Xuejun; Wang, Hongyan

    2011-02-01

    In this paper, we present a novel method for the preparation of raspberry-like monodisperse magnetic hollow hybrid nanospheres with γ-Fe(2)O(3)@SiO(2) particles as the outer shell. PS@Fe(3)O(4)@SiO(2) composite nanoparticles were successfully prepared on the principle of the electrostatic interaction between negatively charged silica and positively charged polystyrene, and then raspberry-like magnetic hollow hybrid nanospheres with large cavities were achieved by means of calcinations, simultaneously, the magnetite (Fe(3)O(4)) was transformed into maghemite (γ-Fe(2)O(3)). Transmission electron microscopy (TEM) demonstrated that the obtained magnetic hollow silica nanospheres with the perfect spherical profile were well monodisperse and uniform with the mean size of 253nm. The Fourier transform infrared (FTIR) spectrometry, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) provided the sufficient evidences for the presence of Fe(3)O(4) in the silica shell. Moreover, the magnetic hollow silica nanospheres possessed a characteristic of superparamagnetic with saturation magnetization value of about 7.84emu/g by the magnetization curve measurement. In addition, the nitrogen adsorption-desorption measurement exhibited that the pore size, BET surface area, pore volume of magnetic hollow silica nanospheres were 3.5-5.5nm, 307m(2)g(-1) and 1.33cm(3)g(-1), respectively. Therefore, the magnetic hollow nanospheres possess a promising future in controlled drug delivery and targeted drug applications. Copyright © 2010 Elsevier Inc. All rights reserved.

  9. Facile synthesis of highly biocompatible folic acid-functionalised SiO2 nanoparticles encapsulating rare-earth metal complexes, and their application in targeted drug delivery.

    Xu, Xiuling; Hu, Fan; Shuai, Qi

    2017-11-14

    Mesoporous silica core-shell nanospheres encapsulating a rare-earth metal complex (RC) were first synthesised through a facile W/O (water in oil) inverse microemulsion method. In order to achieve targeted complex delivery, folic acid (FA) was used as the targeting component due to its high affinity for over-expressed folate receptors (FRs) in cancer cells. The RC 2 @SiO 2 -FA nanospheres were characterised via ultraviolet-visible light absorption spectroscopy (UV-vis spectroscopy), dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A microwave method was used to synthesise five RC cores based on 4-chlorophenoxyacetic acid, and their crystal structures were further confirmed using X-ray diffraction. The five RC cores have the following chemical formulae: [Er 2 (p-CPA) 6 (H 2 O) 6 ] RC 1 , [Ho 2 (p-CPA) 6 (H 2 O) 6 ] RC 2 , [Sm(p-CPA) 3 (H 2 O)] RC 3 , [Pr(p-CPA) 3 (H 2 O)]·3H 2 O RC 4 and [Ce(p-CPA) 3 (H 2 O) 2 ]·2H 2 O RC 5 . The carboxyl groups showed two kinds of coordination modes, namely μ 2 -η 1 :η 1 and μ 2 -η 1 :η 2 , among RC 1 -RC 5 . The flexible -OCH 2 COO- spacer group, which can undergo rotation of its C-O and C-C bonds, offered great potential for structural diversity. In vivo experiments revealed that the nanospheres exhibited no obvious cytotoxicity on HepG2 cells and 293 T cells, even at concentrations of up to 80 μg mL -1 . Nevertheless, all of the RC cores showed a certain degree of anti-tumour efficacy; in particular, RC 2 showed the strongest cytotoxicity against HepG2 cells. Interestingly, the cytotoxicity of all of the RC 2 @SiO 2 -FA nanospheres was higher than that of lone RC 2 . These types of FA-targeted mesoporous silica nanocarriers can be used for the delivery of anti-tumour RC, and provide a basis for the further study of affordable non-platinum-based complexes.

  10. Internal Friction of (SiO2)1-x (GeO2)x Glasses

    Kosugi , T.; Kobayashi , H.; Kogure , Y.

    1996-01-01

    Internal friction of (SiO2)1-x (GeO2)x glasses (x = 0, 5, 10, 24 and 100 mole%) is measured at temperatures between 1.6 and 280 K. The data are filted with the equations for thermally activated relaxation with distributing activation energies in symmetrical double-well potentials. From the determined relaxation strength spectra for each sample, the contributions from each type of microscopic structural units are calculated assuming that transverse motion of the bridging O atom in Si-O-Si, Si-...

  11. Stability analysis of SiO2/SiC multilayer coatings

    Fu Zhiqiang; Jean-Charles, R.

    2006-01-01

    The stability behaviours of SiC coatings and SiO 2 /SiC coatings in helium with little impurities are studied by HSC Chemistry 4.1, the software for analysis of Chemical reaction and equilibrium in multi-component complex system. It is found that in helium with a low partial pressure of oxidative impurities under different total pressure, the key influence factor controlling T cp of SiC depends is the partial pressure of oxidative impurities; T cp of SiC increases with the partial pressure of oxidative impurities. In helium with a low partial pressure of different impurities, the key influence factor of T cs of SiO 2 are both the partial pressure of impurities and the amount of impurities for l mol SiO 2 ; T cs of SiO 2 increases with the partial pressure of oxidative impurities at the same amount of the impurities for 1 mol SiO 2 while it decreases with the amount of the impurities for 1 mm SiO 2 at the same partial pressure of the impurities. The influence of other impurities on T cp of SiC in He-O 2 is studied and it is found that CO 2 , H 2 O and N-2 increase T cp of SiC in He-O 2 while H 2 , CO and CH 4 decrease T cp of SiC He-O 2 . When there exist both oxidative impurities and reductive impurities, their effect on T cs of SiO 2 can be suppressed by the other. In HTR-10 operation atmosphere, SiO 2 /SiC coatings can keep stable status at higher temperature than SiC coatings, so SiO 2 /SiC coatings is more suitable to improve the oxidation resistance of graphite in HTR-10 operation atmosphere compared with SiC coatings. (authors)

  12. Enhanced Photocatalytic Activity of ZrO2-SiO2 Nanoparticles by Platinum Doping

    Mohammad W. Kadi

    2013-01-01

    Full Text Available ZrO2-SiO2 mixed oxides were prepared via the sol-gel method. Photo-assisted deposition was utilized for doping the prepared mixed oxide with 0.1, 0.2, 0.3, and 0.4 wt% of Pt. XRD spectra showed that doping did not result in the incorporation of Pt within the crystal structure of the material. UV-reflectance spectrometry showed that the band gap of ZrO2-SiO2 decreased from 3.04 eV to 2.48 eV with 0.4 wt% Pt doping. The results show a specific surface area increase of 20%. Enhanced photocatalysis of Pt/ZrO2-SiO2 was successfully tested on photo degradation of cyanide under illumination of visible light. 100% conversion was achieved within 20 min with 0.3 wt% of Pt doped ZrO2-SiO2.

  13. Preparation of TiO2-SiO2 composite photocatalysts for environmental applications

    Paušová, Š.; Krýsa, J.; Jirkovský, Jaromír; Prevot, V.; Mailhot, G.

    2014-01-01

    Roč. 89, č. 8 (2014), s. 1129-1135 ISSN 0268-2575 Institutional support: RVO:61388955 Keywords : photocatalysis * TiO2/SiO2 * composite Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.349, year: 2014

  14. Catalytic combustion of trichloroethylene over TiO2-SiO2 supported catalysts

    Kulazynski, M.; van Ommen, J.G.; Trawczynski, J.; Walendziewski, J.

    2002-01-01

    Combustion of trichloroethylene (TCE) on Cr2O3, V2O5, Pt or Pd catalysts supported on TiO2-SiO2 as a carrier has been investigated. It was found that oxide catalysts are very active but their activity quickly diminishes due to loss of the active component, especially at higher reaction temperatures

  15. Stability of trapped electrons in SiO2

    Fleetwood, D.M.; Winokur, P.S.; Flament, O.; Leray, J.L.

    1998-01-01

    Electron trapping near the Si/SiO 2 interface plays a crucial role in mitigating the response of MOS devices to ionizing radiation or high-field stress. These electrons offset positive charge due to trapped holes, and can be present at densities exceeding 10 12 cm -2 in the presence of a similar density of trapped positive charge. The nature of the defects that serve as hosts for trapped electrons in the near-interfacial SiO 2 is presently unknown, although there is compelling evidence that these defects are often intimately associated with trapped holes. This association is depicted most directly in the model of Lelis et al., which suggests that trapped electrons and holes occupy opposite sides of a compensated E center in SiO 2 . Charge exchange between electron traps and the Si can occur over a wide range of time scales, depending on the trap depth and location relative to the Si/SiO 2 interface. Here the authors report a detailed study of the stability of electron traps associated with trapped holes near the Si/SiO 2 interface

  16. Effect of Ti content in the photo catalytic behavior of Fe/TiO2-SiO2 systems

    Leon C, A.; Portillo V, N.; Hernandez P, I.; May L, M.; Gonzalez R, L.; Luna P, R.; Suarez P, R.

    2013-01-01

    In this work we report the synthesis of Fe/TiO 2 -SiO 2 systems with different concentrations of TiO 2 in order to determine the influence of titanium content on the structural, textural, optical properties and their photo catalytic behavior. The materials were synthesized by the sol-gel method and their modification was carried out by incipient impregnation. All samples were characterized be means of X-ray diffraction, N 2 physisorption (Bet method), Dr-UV-Vis and Raman spectroscopy. The modifications of the structural and optical properties are discussed on the basis of long-range order reduction, suggesting the formation of highly dispersed TiO 2 species. On the other hand, it was observed that the energy of the optical band gap decreases by introducing Fe. On the basis of these phenomena, the photo catalytic activity was measured, employing the degradation of orange II azo dye as a model reaction. (Author)

  17. Effect of SiO 2-ZrO 2 supports prepared by a grafting method on hydrogen production by steam reforming of liquefied natural gas over Ni/SiO 2-ZrO 2 catalysts

    Seo, Jeong Gil; Youn, Min Hye; Song, In Kyu

    SiO 2-ZrO 2 supports with various zirconium contents are prepared by grafting a zirconium precursor onto the surface of commercial Carbosil silica. Ni(20 wt.%)/SiO 2-ZrO 2 catalysts are then prepared by an impregnation method, and are applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of SiO 2-ZrO 2 supports on the performance of the Ni(20 wt.%)/SiO 2-ZrO 2 catalysts is investigated. SiO 2-ZrO 2 prepared by a grafting method serves as an efficient support for the nickel catalyst in the steam reforming of LNG. Zirconia enhances the resistance of silica to steam significantly and increases the interaction between nickel and the support, and furthermore, prevents the growth of nickel oxide species during the calcination process through the formation of a ZrO 2-SiO 2 composite structure. The crystalline structures and catalytic activities of the Ni(20 wt.%)/SiO 2-ZrO 2 catalysts are strongly influenced by the amount of zirconium grafted. The conversion of LNG and the yield of hydrogen show volcano-shaped curves with respect to zirconium content. Among the catalysts tested, the Ni(20 wt.%)/SiO 2-ZrO 2 (Zr/Si = 0.54) sample shows the best catalytic performance in terms of both LNG conversion and hydrogen yield. The well-developed and pure tetragonal phase of ZrO 2-SiO 2 (Zr/Si = 0.54) appears to play an important role in the adsorption of steam and subsequent spillover of steam from the support to the active nickel. The small particle size of the metallic nickel in the Ni(20 wt.%)/SiO 2-ZrO 2 (Zr/Si = 0.54) catalyst is also responsible for its high performance.

  18. Interactions of atomic hydrogen with amorphous SiO2

    Yue, Yunliang; Wang, Jianwei; Zhang, Yuqi; Song, Yu; Zuo, Xu

    2018-03-01

    Dozens of models are investigated by the first-principles calculations to simulate the interactions of an atomic hydrogen with a defect-free random network of amorphous SiO2 (a-SiO2) and oxygen vacancies. A wide variety of stable configurations are discovered due to the disorder of a-SiO2, and their structures, charges, magnetic moments, spin densities, and density of states are calculated. The atomic hydrogen interacts with the defect-free a-SiO2 in positively or negatively charged state, and produces the structures absent in crystalline SiO2. It passivates the neutral oxygen vacancies and generates two neutral hydrogenated E‧ centers with different Si dangling bond projections. Electron spin resonance parameters, including Fermi contacts, and g-tensors, are calculated for these centers. The atomic hydrogen interacts with the positive oxygen vacancies in dimer configuration, and generate four different positive hydrogenated defects, two of which are puckered like the Eγ‧ centers. This research helps to understand the interactions between an atomic hydrogen, and defect-free a-SiO2 and oxygen vacancies, which may generate the hydrogen-complexed defects that play a key role in the degeneration of silicon/silica-based microelectronic devices.

  19. Implantation of P ions in SiO2 layers with embedded Si nanocrystals

    Kachurin, G.A.; Cherkova, S.G.; Volodin, V.A.; Kesler, V.G.; Gutakovsky, A.K.; Cherkov, A.G.; Bublikov, A.V.; Tetelbaum, D.I.

    2004-01-01

    The effect of 10 13 -10 16 cm -2 P ions implantation and of subsequent annealing on Si nanocrystals (Si-ncs), formed preliminarily in SiO 2 layers by the ion-beam synthesis, has been studied. Photoluminescence (PL), Raman spectroscopy, high resolution electron microscopy (HREM), X-Ray Photoelectron Spectroscopy (XPS) and optical absorption were used for characterizations. The low fluence implantations have shown even individual displacements in Si-ncs quench their PL. Restoration of PL from partly damaged Si-ncs proceeds at annealing less than 1000 deg. C. In the low fluence implanted and annealed samples an increased Si-ncs PL has been found and ascribed to the radiation-induced shock crystallization of stressed Si nanoprecipitates. Annealing at temperatures under 1000 deg. C are inefficient when P ion fluences exceed 10 14 cm -2 , thus becoming capable to amorphize Si-ncs. High crystallization temperature of the amorphized Si-ncs is attributed to a counteraction of their shell layers. After implantation of the highest P fluences an enhanced recovery of PL was found from P concentration over 0.1 at.%. Raman spectroscopy and HREM showed an increased Si-ncs number in such layers. The effect resembles the impurity-enhanced crystallization, known for heavily doped bulk Si. This effect, along with the data obtained by XPS, is considered as an indication P atoms are really present inside the Si-ncs. However, no evidence of free electrons appearance has been observed. The fact is explained by an increased interaction of electrons with the donor nuclei in Si-ncs

  20. Tunable graphene doping by modulating the nanopore geometry on a SiO2/Si substrate

    Lim, Namsoo; Yoo, Tae Jin; Kim, Jin Tae; Pak, Yusin; Kumaresan, Yogeenth; Kim, Hyeonghun; Kim, Woochul; Lee, Byoung Hun; Jung, Gun Young

    2018-01-01

    A tunable graphene doping method utilizing a SiO2/Si substrate with nanopores (NP) was introduced. Laser interference lithography (LIL) using a He–Cd laser (λ = 325 nm) was used to prepare pore size- and pitch-controllable NP SiO2/Si substrates

  1. Multifunctional Roles of TiO 2 Nanoparticles for Architecture of Complex Core−Shells and Hollow Spheres of SiO 2 −TiO 2 −Polyaniline System

    Wang, Dan Ping

    2009-10-27

    Nanoparticles are often used as seeds to grow one-dimensional nanomaterials or as core materials to prepare core-shell nanostructures. On the other hand, the presynthesized inorganic nanoparticles can also be used as starting building blocks to prepare inorganic-polymer nanocomposites. In this work, we explore the roles of metal-oxide nanoparticles (anatase TiO2) in the area of constructional synthesis of highly complex core-shell and hollow sphere nanostructures comprising SiO2, TiO2, and polyaniline (PAN). In particular, multifunctional roles of oleate-surfactant-protected TiO2 nanoparticles have been revealed in this study: they provide starting sites for polymerization of aniline on the surface of SiO2 mesospheres; they land on the inner surface of polyaniline shell to form a secondary material phase; they work as initial crystalline seeds for homogeneous growth of interior TiO2 shell; and they serve as primary nanobuilding blocks to form exterior TiO2 shell on the polyaniline via self-assembly. With the assistance of the TiO2 nanoparticles, a total of six complex core-shell and hollow sphere nanocomposites (SiO 2/TiO2, SiO2/TiO2/PAN, SiO 2/TiO2/PAN/TiO2, TiO2/PAN, TiO 2/PAN/TiO2, and TiO2/TiO2) have been made in this work through controlled self-assembly, templating growth, polymerization, and homogeneous seeded growth. Applicability of these nanostructures in photocatalytic applications has also been demonstrated by our preliminary investigations. The easy separation of used catalysts after reaction seems to be advantageous because of relatively large external diameters of the lightweight nanocomposites. © 2009 American Chemical Society.

  2. Preliminary study in development of glass-ceramic based on SiO2-LiO2 system, starting of different SiO2 starting powders

    Daguano, J.K.M.F.; Santos, F.A.; Santos, C.; Marton, L.F.M.; Conte, R.A.; Rodrigues Junior, D.; Melo, F.C.L.

    2009-01-01

    In this work, lithium disilicate glass-ceramics were developed starting of the rice ash- SiO 2 and Li 2 CO 3 powders. The results were compared with glass ceramics based on the lithium disilicate obtained by commercial SiO 2 powders. Glass were melted at 1580 deg C, and annealed at 850 deg C. X-Ray diffraction and scanning electron microscopy were used for characterization of the materials, and hardness and fracture toughness were evaluated using Vickers indentation method. Glasses with amorphous structure were obtained in both materials. After annealing, 'rice-ash' samples presented Li 2 SiO 3 and residual SiO 2 as crystalline phases. On the other side, commercial SiO 2 - Samples presented only Li 2 Si 2 O 5 as crystalline phases and the better results of hardness and fracture toughness. (author)

  3. Dielectric properties of PMMA-SiO2 hybrid films

    Morales-Acosta, M. D.; Quevedo-Ló pez, Manuel Angel Quevedo; Alshareef, Husam N.; Gnade, Bruce E.; Ramí rez-Bon, Rafael

    2010-01-01

    Organic-inorganic hybrid films were synthesized by a modified sol-gel process. PMMASiO2 films were prepared using methylmethacrylate (MMA), tetraethil-orthosilicate (TEOS) as silicon dioxide source, and 3-trimetoxi-silil-propil-methacrylate (TMSPM) as coupling agent. FTIR measurements were performed on the hybrid films to confirm the presence of PMMA-SiO2 bonding. In addition, metal-insulator-metal (MIM) devices were fabricated to study the dielectric constant of the films as function of frequency (1 KHz to 1 MHz). Electrical results show a weak trend of the dielectric constant of the hybrid films with MMA molar ratio. More importantly, the PMMA-SiO2 hybrid films showed a higher dielectric constant than SiO2 and PMMA layers, which is likely due to the presence of additional C-O-C bond. © (2010) Trans Tech Publications.

  4. Dielectric properties of PMMA-SiO2 hybrid films

    Morales-Acosta, M. D.

    2010-03-01

    Organic-inorganic hybrid films were synthesized by a modified sol-gel process. PMMASiO2 films were prepared using methylmethacrylate (MMA), tetraethil-orthosilicate (TEOS) as silicon dioxide source, and 3-trimetoxi-silil-propil-methacrylate (TMSPM) as coupling agent. FTIR measurements were performed on the hybrid films to confirm the presence of PMMA-SiO2 bonding. In addition, metal-insulator-metal (MIM) devices were fabricated to study the dielectric constant of the films as function of frequency (1 KHz to 1 MHz). Electrical results show a weak trend of the dielectric constant of the hybrid films with MMA molar ratio. More importantly, the PMMA-SiO2 hybrid films showed a higher dielectric constant than SiO2 and PMMA layers, which is likely due to the presence of additional C-O-C bond. © (2010) Trans Tech Publications.

  5. Hydrogen and chlorine detection at the SiO2/Si interface

    Tsong, I.S.T.; Monkowski, M.D.; Monkowski, J.R.; Wintenberg, A.L.; Miller, P.D.; Moak, C.D.

    1981-01-01

    Hydrogen and chlorine depth profiles were obtained on a series of silicon oxides thermally grown in HCl/O 2 and Cl 2 /O 2 ambients at 1100 0 C for 15 minutes using the 19 F nuclear reaction and SIMS techniques. The data show close correlation between the H and Cl profiles in both the HCl/O 2 and Cl 2 /O 2 oxides. While the H and Cl appear to be enriched at the SiO 2 /Si interface of the HCl/O 2 oxides, they are higher in concentration and more evenly distributed in the oxide bulk of the Cl 2 /O 2 oxides

  6. Heat stability evaluations of Co/SiO2 multilayers

    Ishino, Masahiko; Koike, Masato; Kanehira, Mika; Satou, Futami; Terauchi, Masami; Sano, Kazuo

    2008-01-01

    The heat stability of Co/SiO 2 multilayers was evaluated. Co/SiO 2 multilayer samples were deposited on Si substrate by means of an ion beam sputtering method, and annealed at temperatures from 100degC to 600degC in a vacuum furnace. For the structural and optical evaluations, small angle x-ray diffraction (XRD) measurements, soft x-ray reflectivity measurements, and transmission electron microscopy (TEM) observations were carried out. As the results, the Co/SiO 2 multilayer samples annealed up to 400degC maintained the initial multilayer structures, and kept almost the same soft x-ray reflectivities as that of the as-deposited Co/SiO 2 multilayer sample. A deterioration of the multilayer structure caused by the growth of Co grains was found on the Co/SiO 2 multilayer samples annealed over 500degC, and the soft x-ray reflectivity dropped in accordance with the deterioration of the multilayer structure. (author)

  7. Synthesis of CaO-SiO2-P2O5 mesoporous bioactive glasses with high P2O5 content by evaporation induced self assembly process.

    Zhao, Shan; Li, Yanbao; Li, Dongxu

    2011-02-01

    Mesoporous bioactive glasses (MBGs) of the CaO-SiO(2)-P(2)O(5) system containing relatively high P(2)O(5) contents (10-30 mol%) were prepared from a sol-gel. An evaporation-induced self-assembly (EISA) technique was used with poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (EO(20)-PO(70)-EO(20), P123) acting as a template. The structural, morphological and textural properties of MBGs were investigated by small-angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and a N(2) sorption/desorption technique. SAXRD and TEM results display the reduced long-range ordering of mesopores with increasing P(2)O(5) content. N(2) sorption/desorption analysis shows that all three samples exhibit a type IV isotherm with type H1 hysteresis loops, characteristic of independent cylindrical slim pore channels and this material has a Barret-Joyner-Halenda (BJH) model pore size of ~4 nm and BET specific surface area ~430 m(2)/g. NMR results indicate a more condensed framework for samples with 30 mol% P(2)O(5) than samples with 10 mol% P(2)O(5). For in vitro bioactivity tests where samples were soaked in simulated body fluid (SBF), samples with 30 mol% P(2)O(5) showed higher crystallinity than those with lower P(2)O(5) contents Silicon concentration increased in SBF solution during the soaking period, which indicates MBGs can be degradable in SBF solution.

  8. Refractories in the Al2O3-ZrO2-SiO2 system

    Banerjee, S.P.; Bhadra, A.K.; Sircar, N.R.

    1978-01-01

    The effect of addition of ZrO 2 in different proportions in the refractories of the Al 2 O 3 -SiO 2 system was studied. The investigation was confined to two broad ranges of compositions incorporating zirconia (15-30 percent and 80-85 percent) in the Al 2 O 3 -ZrO 2 -SiO 2 system. The overall attainment of properties is dependent upon the mode of fabrication and firing, and bears a relationship with the phase assemblages and the relative proportion thereof. Of the different characteristics, the trend of dissociation of zircon has been found to be specially significant vis-a-vis the temperature of firing and thermal shock resistance. Reassociation of the dissociated products has been ascribed to bring forth improved resistance to thermal spalling. The different products developed during this investigation are considered to be very promising which find useful applications in view of the properties attained by them. (auth.)

  9. Sorption and physical properties of Mn O2-Si O2 composite

    Labayru M, R.; Correa N, M.; Andalaft J, E.

    1992-01-01

    These results show that the addition of silica improve the sorption and mechanical properties of Mn O 2 -Si O 2 composite. This ion-exchange material has an high Sr adsorption capacity still in the presence of Cs and Al, its capacity being higher than that of commercially available products. The particle size distribution of the ground solid is homogeneous ranging from 90 to 600 μm. The largest particle size fraction is directly proportional to the amount of silica. (author)

  10. Ultrahigh broadband photoresponse of SnO2 nanoparticle thin film/SiO2/p-Si heterojunction.

    Ling, Cuicui; Guo, Tianchao; Lu, Wenbo; Xiong, Ya; Zhu, Lei; Xue, Qingzhong

    2017-06-29

    The SnO 2 /Si heterojunction possesses a large band offset and it is easy to control the transportation of carriers in the SnO 2 /Si heterojunction to realize high-response broadband detection. Therefore, we investigated the potential of the SnO 2 nanoparticle thin film/SiO 2 /p-Si heterojunction for photodetectors. It is demonstrated that this heterojunction shows a stable, repeatable and broadband photoresponse from 365 nm to 980 nm. Meanwhile, the responsivity of the device approaches a high value in the range of 0.285-0.355 A W -1 with the outstanding detectivity of ∼2.66 × 10 12 cm H 1/2 W -1 and excellent sensitivity of ∼1.8 × 10 6 cm 2 W -1 , and its response and recovery times are extremely short (oxide or oxide/Si based photodetectors. In fact, the photosensitivity and detectivity of this heterojunction are an order of magnitude higher than that of 2D material based heterojunctions such as (Bi 2 Te 3 )/Si and MoS 2 /graphene (photosensitivity of 7.5 × 10 5 cm 2 W -1 and detectivity of ∼2.5 × 10 11 cm H 1/2 W -1 ). The excellent device performance is attributed to the large Fermi energy difference between the SnO 2 nanoparticle thin film and Si, SnO 2 nanostructure, oxygen vacancy defects and thin SiO 2 layer. Consequently, practical highly-responsive broadband PDs may be actualized in the future.

  11. Pd/CeO2/SiC Chemical Sensors

    Lu, Weijie; Collins, W. Eugene

    2005-01-01

    The incorporation of nanostructured interfacial layers of CeO2 has been proposed to enhance the performances of Pd/SiC Schottky diodes used to sense hydrogen and hydrocarbons at high temperatures. If successful, this development could prove beneficial in numerous applications in which there are requirements to sense hydrogen and hydrocarbons at high temperatures: examples include monitoring of exhaust gases from engines and detecting fires. Sensitivity and thermal stability are major considerations affecting the development of high-temperature chemical sensors. In the case of a metal/SiC Schottky diode for a number of metals, the SiC becomes more chemically active in the presence of the thin metal film on the SiC surface at high temperature. This increase in chemical reactivity causes changes in chemical composition and structure of the metal/SiC interface. The practical effect of the changes is to alter the electronic and other properties of the device in such a manner as to degrade its performance as a chemical sensor. To delay or prevent these changes, it is necessary to limit operation to a temperature sensor structures. The present proposal to incorporate interfacial CeO2 films is based partly on the observation that nanostructured materials in general have potentially useful electrical properties, including an ability to enhance the transfer of electrons. In particular, nanostructured CeO2, that is CeO2 with nanosized grains, has shown promise for incorporation into hightemperature electronic devices. Nanostructured CeO2 films can be formed on SiC and have been shown to exhibit high thermal stability on SiC, characterized by the ability to withstand temperatures somewhat greater than 700 C for limited times. The exchanges of oxygen between CeO2 and SiC prevent the formation of carbon and other chemical species that are unfavorable for operation of a SiC-based Schottky diode as a chemical sensor. Consequently, it is anticipated that in a Pd/CeO2/SiC Schottky

  12. Reduced cobalt phases of ZrO2 and Ru/ZrO2 promoted cobalt catalysts and product distributions from Fischer–Tropsch synthesis

    Kangvansura, Praewpilin; Schulz, Hans; Suramitr, Anwaraporn; Poo-arporn, Yingyot; Viravathana, Pinsuda; Worayingyong, Attera

    2014-01-01

    Highlights: • Ru/ZrO 2 , ZrO 2 promoted Co/SiO 2 for FTS were reduced by time resolved XANES. • Reduced catalysts resulted from XANES reduction showed the mixed phases of Co, CoO. • The highest percentages of CoO resulted from the high ZrO 2 promoted Co/SiO 2 . • Product distributions of 1-alkenes, iso-alkanes indicated sites for FTS and the 2° reaction. • Alkene readsorption were high corresponding to the high CoO forming branched alkanes. - Abstract: Co/SiO 2 catalysts were promoted with 4% and 8% ZrO 2 . Small amounts (0.07%) of Ru were impregnated onto 4%ZrO 2 /Co/SiO 2 . Catalysts resulting from time-resolved XANES reduction showed mixed phases of Co and CoO, with the highest percentages of Co resulting from Ru/4%ZrO 2 /Co/SiO 2 and the highest percentages of CoO resulting from 8%ZrO 2 /Co/SiO 2 . Product distributions of n-alkanes, iso-alkanes and alkenes during Fischer–Tropsch Synthesis (FTS) were used to investigate the catalyst performance of 4%ZrO 2 /Co/SiO 2 8%ZrO 2 /Co/SiO 2 and Ru/4%ZrO 2 /Co/SiO 2 . FTS steady state was studied by growth probabilities of n-alkane products. No 1-alkene was produced from Ru/4%ZrO 2 /Co/SiO 2 , indicating high availability of Fischer–Tropsch sites for long chain hydrocarbon growth, despite high methanation. Branched alkanes produced from the secondary reaction were related to the high CoO percentages on 8%ZrO 2 /Co/SiO 2 . Alkene readsorption sites were high, corresponding to the high CoO percentages, causing a high probability of forming branched alkane products

  13. The effect of rare earth dopants on the structure, surface texture and photocatalytic properties of TiO2-SiO2 prepared by sol-gel method

    Mohamed, R.M.; Mkhalid, I.A.

    2010-01-01

    The sol-gel method was successfully used to prepare a series of TiO 2 -SiO 2 and rare earth (RE) (La 3+ , Nd 3+ , Sm 3+ , Gd 3+ )-doped TiO 2 -SiO 2 nanoparticles at a doping level of 3 atomic percent. The structural features of parent TiO 2 -SiO 2 and RE-TiO 2 -SiO 2 fired at 550 o C have been investigated by XRD, UV-diffuse reflection, SEM and nitrogen adsorption measurements at -196 o C. XRD data verified the formation of typical characteristic anatase form in all the prepared RE-doped TiO 2 -SiO 2 samples. In comparison with the pure TiO 2 -SiO 2 samples (ca. 35 nm in diameter), the RE-TiO 2 -SiO 2 samples have relatively small particle size indicating that the doping with RE metal ions can improve the particle morphology, and retard the grain growth of TiO 2 -SiO 2 during heat treatment. The results indicated that Gd 3+ doped TiO 2 -SiO 2 has the lowest bandgap and particle size compared with pure TiO 2 -SiO 2 and other nanoparticles of RE-doped TiO 2 -SiO 2 . The highest surface area (S BET ) and pore volume (V p ) values were recorded for Gd-TiO 2 -SiO 2 as well. The effect of doping on the photoactivity was evaluated by the photocatalytic degradation of EDTA as a probe reaction. Among all the pure and RE-doped TiO 2 -SiO 2 , Gd 3+ -TiO 2 -SiO 2 performed the highest catalytic activity towards the tested reaction. That might be due to its special characteristics of particle size, surface texture and bandgap properties. Details of the synthesis procedure and results of the characterization studies of the produced RE-TiO 2 -SiO 2 are presented in this paper.

  14. Density-functional theory molecular dynamics simulations of a-HfO2/a-SiO2/SiGe and a-HfO2/a-SiO2/Ge with a-SiO2 and a-SiO suboxide interfacial layers

    Chagarov, Evgueni A.; Kavrik, Mahmut S.; Fang, Ziwei; Tsai, Wilman; Kummel, Andrew C.

    2018-06-01

    Comprehensive Density-Functional Theory (DFT) Molecular Dynamics (MD) simulations were performed to investigate interfaces between a-HfO2 and SiGe or Ge semiconductors with fully-stoichiometric a-SiO2 or sub-oxide SiO interlayers. The electronic structure of the selected stacks was calculated with a HSE06 hybrid functional. Simulations were performed before and after hydrogen passivation of residual interlayer defects. For the SiGe substrate with Ge termination prior to H passivation, the stacks with a-SiO suboxide interlayer (a-HfO2/a-SiO/SiGe) demonstrate superior electronic properties and wider band-gaps than the stacks with fully coordinated a-SiO2 interlayers (a-HfO2/a-SiO2/SiGe). After H passivation, most of the a-HfO2/a-SiO2/SiGe defects are passivated. To investigate effect of random placement of Si and Ge atoms additional simulations with a randomized SiGe slab were performed demonstrating improvement of electronic structure. For Ge substrates, before H passivation, the stacks with a SiO suboxide interlayer (a-HfO2/a-SiO/Ge) also demonstrate wider band-gaps than the stacks with fully coordinated a-SiO2 interlayers (a-HfO2/a-SiO2/Ge). However, even for a-HfO2/a-SiO/Ge, the Fermi level is shifted close to the conduction band edge (CBM) consistent with Fermi level pinning. Again, after H passivation, most of the a-HfO2/a-SiO2/Ge defects are passivated. The stacks with fully coordinated a-SiO2 interlayers have much stronger deformation and irregularity in the semiconductor (SiGe or Ge) upper layers leading to multiple under-coordinated atoms which create band-edge states and decrease the band-gap prior to H passivation.

  15. A sensitive optical sensor based on DNA-labelled Si@SiO2 core ...

    2017-10-31

    Oct 31, 2017 ... Si@SiO2 core–shell nanoparticles were proposed for the development of fluorescent mercury ... orophores, due to their unique optical properties, such as .... were made by evaporating one drop of the sample solution on.

  16. Preparation and Characterization of SiO2/SiCN Core-shell Ceramic Microspheres

    ZHANG Hai-yuan

    2017-05-01

    Full Text Available The SiO2/PSN core-shell microspheres were prepared via an emulsion reaction combined with the polymer-derived ceramics (PDCs method using polysilazane (PSN in situ polymerization on the surface of SiO2 modified by silane coupling agents MPS, followed by pyrolysis process to obtain SiO2/SiCN core-shell ceramic microspheres. The effects of raw mass ratio, curing time and pyrolysis temperature on the formation and the morphology of core-shell microspheres were studied. The morphology, chemical composition and phase transformation were characterized by SEM, EDS, TEM, FT-IR and XRD. The results show that after reaction for 4h at 200℃, SiO2 completely coated PSN forms a core-shell microsphere with rough surface when the mass ratio of SiO2 and PSN is 1:4; when pyrolysis temperature is at 800-1200℃, amorphous SiO2/SiCN core-shell ceramic microspheres are prepared; at 1400℃, the amorphous phase partially crystallizes to produce SiO2, SiC and Si3N4 phase.

  17. Incorporation of sol-gel SnO2:Sb into nanoporous SiO2

    Canut, B.; Blanchin, M.G.; Ramos-Canut, S.; Teodorescu, V.; Toulemonde, M.

    2006-01-01

    Silicon oxide films thermally grown on Si(1 0 0) wafers were irradiated with 200 MeV 197 Au ions in the 10 9 -10 1 cm -2 fluence range. The targets were then etched at room temperature in aqueous HF solution (1 vol.%) for various durations. Atomic force microscopy (AFM) in the tapping mode was used to probe the processed surfaces. Conical holes with a low size dispersion were evidenced. Their surface diameter varies between 20 and 70 nm, depending on the etching time. Sol-gel dip coating technique, associated with a further annealing treatment performed at 500 o C for 15 min, was used to fill the nanopores created in SiO 2 with a transparent conductive oxide (SnO 2 doped with antimony). Transmission electron microscopy (TEM) performed on cross-sectional specimen showed that SnO 2 :Sb crystallites of ∼5 nm mean size are trapped in the holes without degrading their geometry

  18. Si nanocrystals embedded in SiO2: Optical studies in the vacuum ultraviolet range

    Pankratov, V.; Osinniy, Viktor; Kotlov, A.

    2011-01-01

    done. It is demonstrated that the experimentally determined blueshift of the photoluminescence excitation and absorption spectra is larger than the theoretical predictions. The influence of point defects in the SiO2 matrix on the optical and luminescence properties of the embedded Si nanocrystals...... is discussed. Moreover, it is demonstrated that no energy transfer takes place between the SiO2 and Si nanocrystals when the excitation energy is higher than the band-to-band transition energy in SiO2....

  19. Self-aligned indium–gallium–zinc oxide thin-film transistors with SiNx/SiO2/SiNx/SiO2 passivation layers

    Chen, Rongsheng; Zhou, Wei; Zhang, Meng; Kwok, Hoi-Sing

    2014-01-01

    Self-aligned top-gate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) with SiN x /SiO 2 /SiN x /SiO 2 passivation layers are developed in this paper. The resulting a-IGZO TFT exhibits high reliability against bias stress and good electrical performance including field-effect mobility of 5 cm 2 /Vs, threshold voltage of 2.5 V, subthreshold swing of 0.63 V/decade, and on/off current ratio of 5 × 10 6 . With scaling down of the channel length, good characteristics are also obtained with a small shift of the threshold voltage and no degradation of subthreshold swing. The proposed a-IGZO TFTs in this paper can act as driving devices in the next generation flat panel displays. - Highlights: • Self-aligned top-gate indium–gallium–zinc oxide thin-film transistor is proposed. • SiN x /SiO 2 /SiN x /SiO 2 passivation layers are developed. • The source/drain areas are hydrogen-doped by CHF3 plasma. • The devices show good electrical performance and high reliability against bias stress

  20. New fundamental defects in a-SiO2

    Karna, S.P.; Kurtz, H.A.; Shedd, W.M.; Pugh, R.D.; Singaraju, B.K.

    1999-01-01

    Throughout the three decades of research into radiation-induced degradation of metal-oxide-semiconductor (MOS) devices, investigators understood that point defects in the Si-SiO 2 structure (localized deviations from stoichiometrically pure Si and SiO 2 ) are responsible for many observed anomalies. Basic research in this area has progressed along two tracks: (i) differentiating the anomalies based upon subtle differences in their characteristic behavior, and (ii) precise description of the defects responsible for the anomalous behavior. These two research tracks are complementary since often a discovery in one area provides insight and ultimately leads to discoveries in the other. Here, the atomic structure and spin properties of two previously undescribed amorphous silicon dioxide fundamental point defects have been characterized for the first time by ab initio quantum mechanical calculations. Both defects are electrically neutral trivalent silicon centers in the oxide. One of the defects, the X-center, is determined to have an O 2 Sitriple b ondSi ↑ atomic structure. The other defect, called the Y-center, is found to have an OSi 2 triple b ondSi ↑ structure. Calculated electronic and electrical properties of the new defect centers are consistent with the published characteristics of the oxide switching trap or border trap precursors

  1. Association behaviour of 241Am(III) on SiO2(amorphous) and SiO2(quartz) colloids

    Degueldre, C.; Wernli, B.

    1993-01-01

    SiO 2 colloids have been identified as a potential vector for enhancing radionuclide transport in granitic groundwater and in concrete pore water. The sorption behaviour of 241 Am(III) on SiO 2 colloids was studied as a function of americium concentration pH (5-12), colloid concentration, ionic strength, temperature and SiO 2 allotropic species. The Am(III) sorption mechanism on amorphous silica is different from that on quartz. For SiO 2(amorphous) solution, the variation of log K p (ml g -1 ) with pH is linear (pH=5-9) with a slope of +1 indicating a one proton exchange mechanism. The colloid concentration (ppm) affects the sorption and log K p 3.7-0.67 log [SiO 2 ] (pH = 6). K p increases insignificantly when the ionic strength decreases. It shows no significant variation, however, with the Am concentration. On amorphous silica, the Am(III) sorption is driven by proton exchange from the silanol groups. For SiO 2 (quartz), log K p is constant over a large range of quartz concentration in suspension and the variation of log K p with pH is about linear (pH = 5-12), with a slope of 0.28, indicating a more complex exchange mechanism. Reactions taking into account the interaction of positive Am(OH) w (3-w)+ species on to the negatively charged quartz surface are suggested. (author)

  2. Enhancement of photocatalytic properties of TiO2 nanoparticles doped with CeO2 and supported on SiO2 for phenol degradation

    Hao, Chunjing; Li, Jing; Zhang, Zailei; Ji, Yongjun; Zhan, Hanhui; Xiao, Fangxing; Wang, Dan; Liu, Bin; Su, Fabing

    2015-01-01

    Highlights: • CeO 2 -TiO 2 /SiO 2 composites were prepared via a facile co-precipitation method. • Introduction of SiO 2 support increases the dispersion of CeO 2 -TiO 2 . • CeO 2 -TiO 2 /SiO 2 exhibits an enhanced photocatalytic efficiency for phenol degradation. • Ce 3+ /Ce 4+ pair coexisting in CeO 2 improves electron–hole pairs separation efficiency. - Abstract: A series of CeO 2 -TiO 2 and CeO 2 -TiO 2 /SiO 2 composites were prepared with TiCl 4 and Ce (NO 3 ) 3 ·6H 2 O as precursors via a facile co-precipitation method. The obtained samples were characterized by various techniques such as X-ray diffraction (XRD), nitrogen adsorption (N 2 -BET), Fourier transformation infrared spectrum (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis spectroscopy measurements. The results indicated that TiO 2 doped with CeO 2 and supported on SiO 2 could reduce the crystallite size, inhibit the phase transformation, enhance the thermal stability, and effectively extend the spectral response from UV to visible range. When applied to the phenol photodegradation on a homemade batch reactor with an external cooling jacket, the CeO 2 -TiO 2 /SiO 2 catalysts exhibited significantly enhanced photodegradation efficiency in comparison with commercial Degussa P25 and CeO 2 -TiO 2 . The unique catalytic properties of CeO 2 -TiO 2 /SiO 2 were ascribed to improved electron–hole pairs separation efficiency and formation of more reactive oxygen species owing to the presence of Ce 3+ /Ce 4+ , as well as high dispersion of active component of CeO 2 -TiO 2 as a result of the introduction of SiO 2 support. Furthermore, the catalysts can be easily recovered from the reaction solution by centrifugation and reused for four cycles without significant loss of activity

  3. Potentiodynamical deposition of nanostructured MnO2 film at the assist of electrodeposited SiO2 as template

    Wu, Lian-Kui; Xia, Jie; Hou, Guang-Ya; Cao, Hua-Zhen; Tang, Yi-Ping; Zheng, Guo-Qu

    2016-01-01

    Highlights: • MnO 2 -SiO 2 composite film is prepared by potentiodynamical deposition. • Hierarchical porous MnO 2 films is obtained after the etching of SiO 2 . • The obtained MnO 2 film electrode exhibit high specific capacitance. - Abstract: We report a novel silica co-electrodeposition route to prepare nanostructured MnO 2 films. Firstly, MnO 2 -SiO 2 composite film was fabricated on a stainless steel substrate by potentiodynamical deposition, i.e. cyclic deposition, and then the SiO 2 template was removed by simple immersion in concentrated alkaline solution, leading to the formation of a porous MnO 2 (po-MnO 2 ) matrix. The structure and morphology of the obtained films were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical properties of the po-MnO 2 film were evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS). Results showed that this porous MnO 2 derived from the MnO 2 -SiO 2 composite film exhibits good electrochemical performance for potential use as a supercapacitor material.

  4. Cathodoluminescence properties of SiO2:Pr3+and ZnO.SiO2:Pr3+ phosphor nanopowders

    Mhlongo, GH

    2010-10-01

    Full Text Available regardless of the incorporation of Pr3+ and nanocrystalline ZnO or annealing at 600 °C. The particles were mostly spherical and agglomerated as confirmed by Field Emission Scanning Electron Microscopy. Thermogravimetric analysis of dried gels performed... Science, vol. 45(19): 5228-5236 Cathodoluminescence properties of SiO2:Pr 3+and ZnO·SiO2:Pr 3+ phosphor nanopowders G. H. Mhlongo, O. M. Ntwaeaborwa, M. S. Dhlamini, H. C. Swart, K. T. Hillie ABSTRACT: The successful incorporation of Zn...

  5. Target swapping in PLD: An efficient approach for CdS/SiO2 and CdS:Ag(1%)/SiO2 nanocomposite thin films with enhanced luminescent properties

    Saxena, Nupur; Kumar, Pragati; Gupta, Vinay

    2017-01-01

    A novel synthesis method for luminescent and by-products (like CdO) free CdS/SiO 2 and CdS:Ag(1%)/SiO 2 (i.e. 1%Ag doped CdS/SiO 2 ) nanocomposite thin films at room temperature by pulsed laser deposition is reported. Targets of CdS, CdS:Ag(1%) and SiO 2 are used to deposit CdS/SiO 2 and CdS:Ag(1%)/SiO 2 nanocomposite thin films by swapping them at a frequency ratio of 2:8 laser pulses/sec. X-ray photoelectron spectroscopy analysis ensures the ratio of CdS to SiO 2 in nanocomposite as 21:79 which is nearly same as the ratio of incident pulses/sec (i.e. 2:8) on the two targets. Transmission electron micrographs visualize the formation of CdS/ CdS:Ag(1%) nanocrystals in nanocomposite systems after annealing at 500 °C. Highly intense and broad red emission is achieved from CdS/SiO 2 and CdS:Ag(1%)/SiO 2 nanocomposites. The efficiencies of emission from pristine CdS:SiO 2 and CdS:Ag(1%)/SiO 2 nanocomposites are found to be enhanced by approximately two times as compared to sole nanocrystalline CdS and CdS:Ag(1%) thin films respectively and further enhanced upto 7 times on annealing the nanocomposite systems at 500 °C. - Graphical abstract: A modified synthesis method for luminescent and by-products (like CdO) free undoped &1% Ag doped CdS/SiO 2 (deposit CdS/SiO 2 and CdS:Ag(1%)/SiO 2 ) nanocomposite thin films at room temperature by pulsed laser deposition is reported. Targets of CdS or CdS:Ag(1%) and SiO 2 are used to deposit CdS/SiO 2 and CdS:Ag(1%)/SiO 2 nanocomposite thin films by swapping them at a frequency of 2:8 pulses/sec. X-ray photoelectron spectroscopy analysis ensures the ratio of CdS to SiO 2 in nanocomposite as 21:79 which is nearly same as the ratio of incident pulses/sec (2:8) on the two targets. Transmission electron micrographs visualize the formation of CdS nanocrystals in nanocomposite systems after annealing at 500 °C. Intense and broad red emission is achieved from deposit CdS/SiO 2 and CdS:Ag(1%)/SiO 2 nanocomposites. The efficiency of

  6. Positron annihilation in SiO 2-Si studied by a pulsed slow positron beam

    Suzuki, R.; Ohdaira, T.; Uedono, A.; Kobayashi, Y.

    2002-06-01

    Positron and positronium (Ps) behavior in SiO 2-Si have been studied by means of positron annihilation lifetime spectroscopy (PALS) and age-momentum correlation (AMOC) spectroscopy with a pulsed slow positron beam. The PALS study of SiO 2-Si samples, which were prepared by a dry-oxygen thermal process, revealed that the positrons implanted in the Si substrate and diffused back to the interface do not contribute to the ortho-Ps long-lived component, and the lifetime spectrum of the interface has at least two components. From the AMOC study, the momentum distribution of the ortho-Ps pick-off annihilation in SiO 2, which shows broader momentum distribution than that of crystalline Si, was found to be almost the same as that of free positron annihilation in SiO 2. A varied interface model was proposed to interpret the results of the metal-oxide-semiconductor (MOS) experiments. The narrow momentum distribution found in the n-type MOS with a negative gate bias voltage could be attributed to Ps formation and rapid spin exchange in the SiO 2-Si interface. We have developed a two-dimensional positron lifetime technique, which measures annihilation time and pulse height of the scintillation gamma-ray detector for each event. Using this technique, the positronium behavior in a porous SiO 2 film, grown by a sputtering method, has been studied.

  7. HfO2 and SiO2 as barriers in magnetic tunneling junctions

    Shukla, Gokaran; Archer, Thomas; Sanvito, Stefano

    2017-05-01

    SiO2 and HfO2 are both high-k, wide-gap semiconductors, currently used in the microelectronic industry as gate barriers. Here we investigate whether the same materials can be employed to make magnetic tunnel junctions, which in principle can be amenable for integration in conventional Si technology. By using a combination of density functional theory and the nonequilibrium Green's functions method for quantum transport we have studied the transport properties of Co [0001 ] /SiO2[001 ] /Co [0001 ] and Fe [001 ] /HfO2[001 ] /Fe [001 ] junctions. In both cases we found a quite large magnetoresistance, which is explained through the analysis of the real band structure of the magnets and the complex one of the insulator. We find that there is no symmetry spin filtering for the Co-based junction since the high transmission Δ2' band crosses the Fermi level, EF, for both spin directions. However, the fact that Co is a strong ferromagnet makes the orbital contribution to the two Δ2' spin subbands different, yielding magnetoresistance. In contrast for the Fe-based junction symmetry filtering is active for an energy window spanning between the Fermi level and 1 eV below EF, with Δ1 symmetry contributing to the transmission.

  8. Diffusive charge transport in graphene on SiO 2

    Chen, J.-H.; Jang, C.; Ishigami, M.; Xiao, S.; Cullen, W. G.; Williams, E. D.; Fuhrer, M. S.

    2009-07-01

    We review our recent work on the physical mechanisms limiting the mobility of graphene on SiO 2. We have used intentional addition of charged scattering impurities and systematic variation of the dielectric environment to differentiate the effects of charged impurities and short-range scatterers. The results show that charged impurities indeed lead to a conductivity linear in density ( σ(n)∝n) in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates; increased dielectric screening reduces the scattering from charged impurities, but increases the scattering from short-range scatterers. We evaluate the effects of the corrugations (ripples) of graphene on SiO 2 on transport by measuring the height-height correlation function. The results show that the corrugations cannot mimic long-range (charged impurity) scattering effects, and have too small an amplitude-to-wavelength ratio to significantly affect the observed mobility via short-range scattering. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a resistivity that is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO 2 substrate give rise to an activated, carrier density-dependent resistivity. Together the results paint a complete picture of charge carrier transport in graphene on SiO 2 in the diffusive regime.

  9. Friction and wear properties of ZrO2/SiO2 composite nanoparticles

    Li Wei; Zheng Shaohua; Cao Bingqiang; Ma Shiyu

    2011-01-01

    In this article, the lubrication properties of ZrO 2 /SiO 2 composite nanoparticles modified with aluminum zirconium coupling agent as additives in lubricating oil under variable applied load and concentration fraction were reported. It was demonstrated that the modified nanoparticles as additives in lubrication can effectively improve the lubricating properties. Under an optimized concentration of 0.1 wt%, the average friction coefficient was reduced by 16.24%. This was because the nanoparticles go into the friction zone with the flow of lubricant, and then the sliding friction changed to rolling friction with a result of the reduction of the friction coefficient.

  10. Selective adsorption of thiophenic compounds from fuel over TiO2/SiO2 under UV-irradiation.

    Miao, Guang; Ye, Feiyan; Wu, Luoming; Ren, Xiaoling; Xiao, Jing; Li, Zhong; Wang, Haihui

    2015-12-30

    This study investigates selective adsorption of thiophenic compounds from fuel over TiO2/SiO2 under UV-irradiation. The TiO2/SiO2 adsorbents were prepared and then characterized by N2 adsorption, X-ray diffraction and X-ray photoelectron spectroscopy. Adsorption isotherms, selectivity and kinetics of TiO2/SiO2 were measured in a UV built-in batch reactor. It was concluded that (a) with the employment of UV-irradiation, high organosulfur uptake of 5.12 mg/g was achieved on the optimized 0.3TiO2/0.7SiO2 adsorbent at low sulfur concentration of 15 ppmw-S, and its adsorption selectivity over naphthalene was up to 325.5; (b) highly dispersed TiO2 served as the photocatalytic sites for DBT oxidation, while SiO2 acted as the selective adsorption sites for the corresponding oxidized DBT using TiO2 as a promoter, the two types of active sites worked cooperatively to achieve the high adsorption selectivity of TiO2/SiO2; (c) The kinetic rate-determining step for the UV photocatalysis-assisted adsorptive desulfurization (PADS) over TiO2/SiO2 was DBT oxidation; (d) consecutive adsorption-regeneration cycles suggested that the 0.3TiO2/0.7SiO2 adsorbent can be regenerated by acetonitrile washing followed with oxidative air treatment. This work demonstrated an effective PADS approach to greatly enhance adsorption capacity and selectivity of thiophenic compounds at low concentrations for deep desulfurization under ambient conditions. Copyright © 2015 Elsevier B.V. All rights reserved.

  11. Preparation, Characterization and Thermal Degradation of Polyimide (4-APS/BTDA/SiO2 Composite Films

    Arash Dehzangi

    2012-04-01

    Full Text Available Polyimide/SiO2 composite films were prepared from tetraethoxysilane (TEOS and poly(amic acid (PAA based on aromatic diamine (4-aminophenyl sulfone (4-APS and aromatic dianhydride (3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA via a sol-gel process in N-methyl-2-pyrrolidinone (NMP. The prepared polyimide/SiO2 composite films were characterized using X-ray diffraction (XRD, Fourier transform infrared spectroscopy (FTIR, scanning electron microscope (SEM and thermogravimetric analysis (TGA. The FTIR results confirmed the synthesis of polyimide (4-APS/BTDA and the formation of SiO2 particles in the polyimide matrix. Meanwhile, the SEM images showed that the SiO2 particles were well dispersed in the polyimide matrix. Thermal stability and kinetic parameters of the degradation processes for the prepared polyimide/SiO2 composite films were investigated using TGA in N2 atmosphere. The activation energy of the solid-state process was calculated using Flynn–Wall–Ozawa’s method without the knowledge of the reaction mechanism. The results indicated that thermal stability and the values of the calculated activation energies increased with the increase of the TEOS loading and the activation energy also varied with the percentage of weight loss for all compositions.

  12. Photocatalytic Removal of Phenol under Natural Sunlight over N-TiO2-SiO2 Catalyst: The Effect of Nitrogen Composition in TiO2-SiO2

    Viet-Cuong Nguyen

    2009-01-01

    Full Text Available In this present work, high specific surface area and strong visible light absorption nitrogen doped TiO2-SiO2 photocatalyst was synthesized by using sol-gel coupled with hydrothermal treatment method. Nitrogen was found to improve the specific surface area while it also distorted the crystal phase of the resulting N-TiO2-SiO2 catalyst. As the N/ (TiO2-SiO2 molar ratio was more than 10%, the derived catalyst presented the superior specific surface area up to 260 m2/g. Nevertheless, its photoactivity towards phenol removal was observed to significantly decrease, which could results from the too low crystallinity. The nitrogen content in N-TiO2-SiO2 catalyst was therefore necessary to be optimized in terms of phenol removal efficiency and found at ca. 5%. Under UVA light and natural sunlight irradiation of 80 min, N(5%-TiO2-SiO2 catalyst presented the phenol decomposition efficiencies of 68 and 100%, respectively. It was also interestingly found in this study that the reaction rate was successfully expressed using a Langmuir-Hinshelwood (L-H model, indicating the L-H nature of photocatalytic phenol decomposition reaction on the N-TiO2-SiO2 catalyst.

  13. Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

    Marszałek, Konstanty; Winkowski, Paweł; Jaglarz, Janusz

    2014-01-01

    Investigations of bilayer and trilayer Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10-3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al2O3, 0.6 nm - 0.8 nm/s for HfO2 and 0.6 nm/s for SiO2. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al2O3/SiO2 and 78 nm/156 nm/78 nm for Al2O3/HfO2/SiO2. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.

  14. Tunable graphene doping by modulating the nanopore geometry on a SiO2/Si substrate

    Lim, Namsoo

    2018-02-28

    A tunable graphene doping method utilizing a SiO2/Si substrate with nanopores (NP) was introduced. Laser interference lithography (LIL) using a He–Cd laser (λ = 325 nm) was used to prepare pore size- and pitch-controllable NP SiO2/Si substrates. Then, bottom-contact graphene field effect transistors (G-FETs) were fabricated on the NP SiO2/Si substrate to measure the transfer curves. The graphene transferred onto the NP SiO2/Si substrate showed relatively n-doped behavior compared to the graphene transferred onto a flat SiO2/Si substrate, as evidenced by the blue-shift of the 2D peak position (∼2700 cm−1) in the Raman spectra due to contact doping. As the porosity increased within the substrate, the Dirac voltage shifted to a more positive or negative value, depending on the initial doping type (p- or n-type, respectively) of the contact doping. The Dirac voltage shifts with porosity were ascribed mainly to the compensation for the reduced capacitance owing to the SiO2–air hetero-structured dielectric layer within the periodically aligned nanopores capped by the suspended graphene (electrostatic doping). The hysteresis (Dirac voltage difference during the forward and backward scans) was reduced when utilizing an NP SiO2/Si substrate with smaller pores and/or a low porosity because fewer H2O or O2 molecules could be trapped inside the smaller pores.

  15. The Degradation Behavior of SiCf/SiO2 Composites in High-Temperature Environment

    Yang, Xiang; Cao, Feng; Qing, Wang; Peng, Zhi-hang; Wang, Yi

    2018-04-01

    SiCf/SiO2 composites had been fabricated efficiently by Sol-Gel method. The oxidation behavior, thermal shock property and ablation behavior of SiCf/SiO2 composites was investigated. SiCf/SiO2 composites showed higher oxidation resistance in oxidation atmosphere, the flexural strength retention ratio was larger than 90.00%. After 1300 °C thermal shock, the mass retention ratio was 97.00%, and the flexural strength retention ratio was 92.60%, while after 1500 °C thermal shock, the mass retention ratio was 95.37%, and the flexural strength retention ratio was 83.34%. After 15 s ablation, the mass loss rate was 0.049 g/s and recession loss rate was 0.067 mm/s. The SiO2 matrix was melted in priority and becomes loosen and porous. With the ablation going on, the oxides were washed away by the shearing action of the oxyacetylene flame. The evaporation of SiO2 took away large amount of heat, which is also beneficial to the protection for SiCf/SiO2 composites.

  16. Synthesis, surface modification/decoration of luminescent–magnetic core/shell nanomaterials, based on the lanthanide doped fluorides (Fe3O4/SiO2/NH2/PAA/LnF3)

    Runowski, Marcin; Lis, Stefan

    2016-01-01

    The synthesized magnetite nanoparticles (10–15 nm) were successfully coated with amine modified silica nanoshell, which led to the formation of core/shell type nanostructures (30–50 nm). The as-prepared nanoparticles were surface modified with polyacrylic acid (PAA) via electrostatic interactions of –NH 2 and –COOH groups. Afterwards, the surface PAA molecules acted as complexing agents of the introduced lanthanide (Ln 3+ ) ions. Subsequently, the as-prepared nanostructures were surface decorated with luminescent LnF 3 nanoparticles, forming Eu 3+ or Tb 3+ doped Fe 3 O 4 /SiO 2 /NH 2 /PAA/LnF 3 nanomaterials (50–100 nm). The obtained luminescent–magnetic products exhibited simultaneously bright red or green emission under UV lamp irradiation (λ ex =254 nm), and a response for the applied magnetic field (strong magnet attracts the colloidal particles, dispersed in aqueous medium). After the synthesis, properties of the nanomaterials were investigated by powder X-ray diffraction (XRD) technique, transmission electron microscopy (TEM), infrared spectroscopy (IR) and spectrofluorometry (analysis of excitation/emission spectra and luminescence decay curves). Such advanced nanomaterials can be potentially used in multimodal imaging, targeted therapies and as multifunctional contrast agents, novel luminescent–magnetic tracers, protection of documents, etc. - Highlights: • Luminescent–magnetic nanomaterials Fe 3 O 4 /SiO 2 /NH 2 /PAA/LnF 3 were synthesized. • Core/shell nanostructures were obtained by surface modification of nanoparticles. • Luminescent lanthanide fluoride nanoparticles doped with Eu 3+ and Tb 3+ ions. • Multifunctional core/shell nanostructures exhibited red or green emission. • Nanomaterials formed stable aqueous colloids.

  17. Gel electrolytes based on poly(acrylonitrile)/sulpholane with hybrid TiO2/SiO2 filler for advanced lithium polymer batteries

    Kurc, Beata

    2014-01-01

    Highlights: • Paper describes properties of gel electrolyte based on PAN with TMS and TiO 2 -SiO 2 . • The TiO 2 -SiO 2 oxide composite was precipitated in the emulsion system and used as the fillers. • The capacity of the graphite anode depends on the current rate and the amount of TiO 2 -SiO 2 . • For PE3 electrolyte was obtained practical capacity more than 90% of the theoretical capacity. - Abstract: This paper describes the synthesis and properties of a new type of ceramic fillers for composite polymer gel electrolytes. Hybrid TiO 2 -SiO 2 ceramic powders have been obtained by co-precipitation from titanium(IV) sulfate solution using sodium silicate as the precipitating agent. The resulting submicron-size powders have been applied as fillers for composite polymer gel electrolytes for Li-ion batteries based on polyacrylonitrile (PAN) membranes. The powders and gel electrolytes have been examined structurally and electrochemically, showing favorable properties in terms of electrolyte uptake and electrochemical characteristics in Li-ion cells

  18. Optical properties of ZrO2, SiO2 and TiO2-SiO2 xerogels and coatings doped with Eu3+ and Eu2+

    Gonçalves Rogéria R.

    1999-01-01

    Full Text Available Eu3+ doped bulk monoliths and thin films were obtained by sol-gel methods in the ZrO2, SiO2 and SiO2-TiO2 systems. Eu3+ 5D0 ® 7FJ emission and decay time characteristics were measured during the entire experimental preparation route from the initial sol to the final xerogels. The crystalline phases identified were tetragonal ZrO2 and mixtures of rutile and anatase TiO2 at high temperature treatments in bulk samples. Good quality thin films were obtained for all systems by dip-coating optical glasses (Schott BK270. The same spectroscopic features were observed either for the bulk monoliths or the films. By appropriate heat treatments under H2 atmosphere Eu2+ containing samples could be obtained in the SiO2-TiO2 system.

  19. Laser conditioning effect on HfO2/SiO2 film

    Wei Yaowei; Zhang Zhe; Liu Hao; Ouyang Sheng; Zheng Yi; Tang Gengyu; Chen Songlin; Ma Ping

    2013-01-01

    Laser conditioning is one of the important methods to improve the laser damage threshold of film optics. Firstly, a large aperture laser was used to irradiate the HfO 2 /SiO 2 reflectors, which were evaporated from hafnia and silica by e-beam. Secondly, a laser calorimeter was used to test the film absorption before and after laser irradiation. Focused ion beam (FIB) was few reported using on laser film, it was used to study the damage morphology and explore the cause of damage. The shooting of the partial ejection on nodule was obtained for the first time, which provided the basis for study the damage process. The results show that film absorption was decreased obviously after the laser irradiation, laser conditioning can raise the laser damage threshold by the 'cleaning mechanism'. For the HfO 2 /SiO 2 reflectors, laser conditioning was effective to eject the nodules on substrate. It resulted from the nodule residue not to affect the subsequent laser. In addition, laser conditioning was not effective to the nodule in the film, which might be from the material spatter in coating process. In this case, other method could be used to get rid of the nodules. (authors)

  20. Study of Si/Si, Si/SiO2, and metal-oxide-semiconductor (MOS) using positrons

    Leung, To Chi.

    1991-01-01

    A variable-energy positron beam is used to study Si/Si, Si/SiO 2 , and metal-oxide-semiconductor (MOS) structures. The capability of depth resolution and the remarkable sensitivity to defects have made the positron annihilation technique a unique tool in detecting open-volume defects in the newly innovated low temperature (300C) molecular-beam-epitaxy (MBE) Si/Si. These two features of the positron beam have further shown its potential role in the study of the Si/SiO 2 . Distinct annihilation characteristics has been observed at the interface and has been studied as a function of the sample growth conditions, annealing (in vacuum), and hydrogen exposure. The MOS structure provides an effective way to study the electrical properties of the Si/SiO 2 interface as a function of applied bias voltage. The annihilation characteristics show a large change as the device condition is changed from accumulation to inversion. The effect of forming gas (FG) anneal is studied using positron annihilation and the result is compared with capacitance-voltage (C-V) measurements. The reduction in the number of interface states is found correlated with the changes in the positron spectra. The present study shows the importance of the positron annihilation technique as a non-contact, non-destructive, and depth-sensitive characterization tool to study the Si-related systems, in particular, the Si/SiO 2 interface which is of crucial importance in semiconductor technology, and fundamental understanding of the defects responsible for degradation of the electrical properties

  1. Lithium superionic conductor Li9.42Si1.02P2.1S9.96O2.04 with Li10GeP2S12-type structure in the Li2S–P2S5–SiO2 pseudoternary system: Synthesis, electrochemical properties, and structure–composition relationships

    Satoshi Hori

    2016-12-01

    Full Text Available Lithium superionic conductors with the Li10GeP2S12 (LGPS-type structure are promising materials for use as solid electrolytes in next-generation lithium batteries. A novel member of the LGPS family, Li9.42Si1.02P2.1S9.96O2.04, and its solid solutions were synthesised by quenching from 1273 K in the Li2S–P2S5–SiO2 pseudoternary system. The material exhibited an ionic conductivity as high as 3.2×10−4 S cm−1 at 298 K, as well as the high electrochemical stability to lithium metal, which was improved by the introduction of oxygen into the LGPS-type structure. An all-solid-state cell with a lithium metal anode and Li9.42Si1.02P2.1S9.96O2.04 as the separator showed excellent performance with a high coulomb efficiency of 100%. Thus, oxygen doping is an effective way of improving the electrochemical stability of LGPS-type structure.

  2. Positron annihilation spectroscopy of the interface between nanocrystalline Si and SiO2

    Pi, X.D.; Coleman, P.G.; Harding, R.; Davies, G.; Gwilliam, R.M.; Sealy, B.J.

    2003-01-01

    Positron annihilation spectroscopy has been employed to study changes in the interface region between nanocrystalline Si and SiO 2 , following annealing between 400 deg. C and 900 deg. C in nitrogen or oxygen. With the support of photoluminescence spectroscopy we find that nitrogen and oxygen are trapped in voids at the interface at low temperatures. At temperatures above 700 deg. C both nitrogen and oxygen react with Si nanocrystals, and the resulting volume increase introduces stress in the SiO 2 matrix which is relaxed by the shrinkage of its intrinsic open volume. Oxygen appears to enhance Si diffusion in SiO 2 so that the agglomeration of Si nanocrystals occurs more readily during annealing in oxygen than in nitrogen

  3. Ge nanocrystals embedded in ultrathin Si3N4 multilayers with SiO2 barriers

    Bahariqushchi, R.; Gundogdu, Sinan; Aydinli, A.

    2017-04-01

    Multilayers of germanium nanocrystals (NCs) embedded in thin films of silicon nitride matrix separated with SiO2 barriers have been fabricated using plasma enhanced chemical vapor deposition (PECVD). SiGeN/SiO2 alternating bilayers have been grown on quartz and Si substrates followed by post annealing in Ar ambient from 600 to 900 °C. High resolution transmission electron microscopy (HRTEM) as well as Raman spectroscopy show good crystallinity of Ge confined to SiGeN layers in samples annealed at 900 °C. Strong compressive stress for SiGeN/SiO2 structures were observed through Raman spectroscopy. Size, as well as NC-NC distance were controlled along the growth direction for multilayer samples by varying the thickness of bilayers. Visible photoluminescence (PL) at 2.3 and 3.1 eV with NC size dependent intensity is observed and possible origin of PL is discussed.

  4. Fabrication of Carbon Nanotube/SiO2and Carbon Nanotube/SiO2/Ag Nanoparticles Hybrids by Using Plasma Treatment

    Li Haiqing

    2009-01-01

    Full Text Available Abstract Based on plasma-treated single wall carbon nanotubes (SWCNTs, SWCNT/SiO2and thiol groups-functionalized SWCNT/SiO2hybrids have been fabricated through a sol–gel process. By means of thiol groups, Ag nanoparticles have been in situ synthesized and bonded onto the SiO2shell of SWCNT/SiO2in the absence of external reducing agent, resulting in the stable carbon nanotube/SiO2/Ag nanoparticles hybrids. This strategy provides a facile, low–cost, and green methodology for the creation of carbon nanotube/inorganic oxides-metal nanoparticles hybrids.

  5. Sol-Gel Synthesis and Characterization of Ba1-xGdxTiO3+δ Thin Films on SiO2/Si Substrates Using Spin-Coating Technique

    Yen Chin TEH

    2017-02-01

    Full Text Available Ba1-xGdxTiO3+δ, at x = 0, 0.05, 0.1, 0.15, 0.2, (BGT thin films have been fabricated on SiO2/Si substrate using Sol-Gel method. The microstructure and surface morphology of the fabricated films have been investigated using X-ray diffraction (XRD and atomic force microscopy (AFM. The XRD results show that the fabricated films are crystalline with perovskite structure. There is a shifting of the preferred peak at 31.5o to a higher angle as the doping ratio increases suggesting a distortion lattice exists in the films, which could be due to the substitution of Gd3+ ions into Ba-site. The decreasing of lattice constants confirms the substitution of Gd3+ in BaTiO3 lattice structure. The microstrain and dislocation density are found to be increased with the increase of Gd3+ doping, which attributed to the reduction of lattice volume that due to the ionic size mismatch effect. The AFM results show decreasing trend in both average grain size and roughness parameters. Therefore, the microstructure and surface morphology of BGT samples is strongly dependent on the Gd3+ doping concentration that mainly due to the difference ionic radius substitution.DOI: http://dx.doi.org/10.5755/j01.ms.23.1.13954

  6. Passivation of pigment-grade TiO2 particles by nanothick atomic layer deposited SiO2 films

    King, David M; Liang Xinhua; Weimer, Alan W; Burton, Beau B; Akhtar, M Kamal

    2008-01-01

    Pigment-grade TiO 2 particles were passivated using nanothick insulating films fabricated by atomic layer deposition (ALD). Conformal SiO 2 and Al 2 O 3 layers were coated onto anatase and rutile powders in a fluidized bed reactor. SiO 2 films were deposited using tris-dimethylaminosilane (TDMAS) and H 2 O 2 at 500 deg. C. Trimethylaluminum and water were used as precursors for Al 2 O 3 ALD at 177 deg. C. The photocatalytic activity of anatase pigment-grade TiO 2 was decreased by 98% after the deposition of 2 nm SiO 2 films. H 2 SO 4 digest tests were performed to exhibit the pinhole-free nature of the coatings and the TiO 2 digest rate was 40 times faster for uncoated TiO 2 than SiO 2 coated over a 24 h period. Mass spectrometry was used to monitor reaction progress and allowed for dosing time optimization. These results demonstrate that the TDMAS-H 2 O 2 chemistry can deposit high quality, fully dense SiO 2 films on high radius of curvature substrates. Particle ALD is a viable passivation method for pigment-grade TiO 2 particles

  7. High-dose MeV electron irradiation of Si-SiO2 structures implanted with high doses Si+

    Kaschieva, S.; Angelov, Ch; Dmitriev, S. N.

    2018-03-01

    The influence was studied of 22-MeV electron irradiation on Si-SiO2 structures implanted with high-fluence Si+ ions. Our earlier works demonstrated that Si redistribution is observed in Si+-ion-implanted Si-SiO2 structures (after MeV electron irradiation) only in the case when ion implantation is carried out with a higher fluence (1016 cm-2). We focused our attention on the interaction of high-dose MeV electron irradiation (6.0×1016 cm-2) with n-Si-SiO2 structures implanted with Si+ ions (fluence 5.4×1016 cm-2 of the same order magnitude). The redistribution of both oxygen and silicon atoms in the implanted Si-SiO2 samples after MeV electron irradiation was studied by Rutherford back-scattering (RBS) spectroscopy in combination with a channeling technique (RBS/C). Our results demonstrated that the redistribution of oxygen and silicon atoms in the implanted samples reaches saturation after these high doses of MeV electron irradiation. The transformation of amorphous SiO2 surface into crystalline Si nanostructures (after MeV electron irradiation) was evidenced by atomic force microscopy (AFM). Silicon nanocrystals are formed on the SiO2 surface after MeV electron irradiation. The shape and number of the Si nanocrystals on the SiO2 surface depend on the MeV electron irradiation, while their size increases with the dose. The mean Si nanocrystals height is 16-20 nm after irradiation with MeV electrons at the dose of 6.0×1016 cm-2.

  8. Silica-modified luminescent LaPO4 :Eu@LaPO4 @SiO2 core/shell nanorods: Synthesis, structural and luminescent properties.

    Ansari, Anees A

    2018-02-01

    Monoclinic-type tetragonal LaPO 4 :Eu (core) and LaPO 4 :Eu@LaPO 4 (core/shell) nanorods (NRs) were successfully prepared using a urea-based co-precipitation process under ambient conditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol-gel process to improve their solubility and colloidal stability in aqueous and non-aqueous media. The prepared nano-products were systematically characterized by X-ray diffraction pattern, transmission electron microscopy, energy dispersive X-ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nano-products were in the range 80-120 nm and 10-15 nm, respectively. High solubility of the silica-modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO 4 and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic-based biomedical applications. Copyright © 2017 John Wiley & Sons, Ltd.

  9. The structure modification of Si-SiO2 irradiated by Fe+ ion

    Jin Tao; Ma Zhongquan; Guo Qi

    1992-01-01

    The effect of the iron ion implantation on the oxide surface and SiO 2 -Si interface of MOS structure was studied by X-ray photo-electron spectroscopy (XPS), and the chemical states of compounds formed were examined. The results obtained show that in the surface layers of SiO 2 the pure Si micro-regions are formed under the implantation and the interface layers of SiO 2 the pure Si micro-regions are formed under the implantation and the interface thickness is almost doubled that leads to failure of MOS capacitors. The physical and chemical mechanisms of MOS structure change by Fe + ion implantation are also discussed and analyzed

  10. Adsorption of uranyl in SiO2 porous glass

    Benedetto, F. E.; Prado, M. O.

    2013-01-01

    Vitreous SiO 2 porous matrices can be used in many applications involving the uptake of chemical species on its solid surface. In this work, vitreous silica sponges were prepared from a sodium borosilicate glass manufactured in our laboratory. The product obtained was then separated into phases with subsequent leaching of the soluble phase rich in B and Na. The resulting porous matrices have a specific surface of 35 m2/gr. Adsorption of uranyl ions onto the SiO 2 porous surface was studied to evaluate the use of this material as a filter for treatment of uranium containing water. The effects of contact time, adsorbent mass and equilibrium concentration of solution were studied. The porous adsorbent exhibits a pseudo-second-order kinetic behavior. The sponges with adsorbed uranium were thermally sealed as a way of U immobilization. Retention of uranium was confirmed during the matrix sealing by TGA. Uranium concentration before and after adsorption tests were made by means of ICP-OES. For uranium concentration of 800 ppm, 72 hours contact time and pH of 3.5, the amount of uranium adsorbed was 21.06 ± 0.02 mg U per gram of vitreous porous SiO 2 . (author)

  11. Effect of oxide charge trapping on x-ray photoelectron spectroscopy of HfO2/SiO2/Si structures

    Abe, Yasuhiro; Miyata, Noriyuki; Suzuki, Haruhiko; Kitamura, Koji; Igarashi, Satoru; Nohira, Hiroshi; Ikenaga, Eiji

    2009-01-01

    We examined the effects of interfacial SiO 2 layers and a surface metal layer on the photoelectron spectra of HfO 2 /SiO 2 /Si structures by hard X-ray photoemission spectroscopy with synchrotron radiation as well as conventional X-ray photoelectron spectroscopy (XPS). The Hf 4f and Hf 3d photoelectron peaks broadened and shifted toward a higher binding energy with increasing thickness of the interfacial SiO 2 layer, even though photoelectrons may have been emitted from the HfO 2 layer with the same chemical composition. Thinning the interfacial Si oxide layer to approximately one monolayer and depositing a metal layer on the HfO 2 surface suppressed these phenomena. The O 1s photoelectron spectra revealed marked differences between the metal- and nonmetal-deposited HfO 2 /SiO 2 /Si structures; HfO 2 and SiO 2 components in the O 1s photoelectron spectra for the metal-deposited structures were observed at reasonably separated binding energies, but those for the nonmetal-deposited structures were not separated clearly. From this behavior concerning the effects of interfacial SiO 2 and surface metal layers, we concluded that the Hf 4f, Hf 3d, and O 1s spectra measured from the HfO 2 /SiO 2 /Si structures did not reflect actual chemical bonding states. We consider that potential variations in the HfO 2 film owing to charge trapping strongly affect the measured photoelectron spectra. On the basis of angle-resolved XPS measurements, we propose that positive charges are trapped at the HfO 2 surface and negative charges are trapped inside the HfO 2 layer. (author)

  12. Investigation of hydrogen and chlorine at the SiO2/Si interface

    Tsong, I.S.T.; Monkowski, M.D.; Monkowski, J.R.; Miller, P.D.; Moak, C.D.; Appleton, B.R.; Wintenberg, A.L.

    1980-01-01

    Silicon oxides thermally grown in H 2 O, O 2 , HCl/O 2 and Cl 2 /O 2 ambients were analyzed, via 1 H( 19 F,αγ) 16 O nuclear reaction and SIMS, for the presence of hydrogen. In addition, those oxides grown in HCl/O 2 and Cl 2 /O 2 ambients were analyzed with SIMS for the presence of chlorine. The SIMS data show that the hydrogen levels in these oxides were below the limit of detection for nuclear reaction experiments. The 35 Cl + depth-profiles show that chlorine is enriched at the SiO 2 interface for the HCl/O 2 grown oxides while it is more evenly distributed in oxide bulk in the Cl 2 /O 2 grown samples

  13. Natural CaO-TiO2-SiO2 based ceramics

    Jelena Pantić

    2011-06-01

    Full Text Available Lešnica river deposits consist of a large number of minerals of different grain sizes including sphene. Since it is very difficult to obtain pure monophase titanite by different synthetic routes (sol-gel, coprecipitation, combustion, spray pyrolysis and hydrothermal method, the aim of this work was to study the structure of the sphene from the Lešnica river deposits and possibility of using it as a natural precursor for CaO-TiO2-SiO2 based ceramics. The sphene from Lešnica was analyzed by different methods: tristimulus colorimetry, infrared spectroscopy, electron microprobe and X-ray single crystal diffraction. It was confirmed that Al, Fe, Mn and P are present in the sphene structure and proposed that corresponding structural formula could be: (Ca2+1.008 Mn2+0.0021.010(Ti4+0.901 Fe3+0.033 Al3+0.060 P5+0.0010.995 Si4+1.024 O2-5.

  14. Making MgO/SiO2 Glasses By The Sol-Gel Process

    Bansal, Narottam P.

    1989-01-01

    Silicon dioxide glasses containing 15 mole percent magnesium oxide prepared by sol-gel process. Not made by conventional melting because ingredients immiscible liquids. Synthesis of MgO/SiO2 glass starts with mixing of magnesium nitrate hexahydrate with silicon tetraethoxide, both in alcohol. Water added, and transparent gel forms. Subsequent processing converts gel into glass. Besides producing glasses of new composition at lower processing temperatures, sol-gel method leads to improved homogeneity and higher purity.

  15. On formation of silicon nanocrystals under annealing SiO2 layers implanted with Si ions

    Kachurin, G.A.; Yanovskaya, S.G.; Volodin, V.A.; Kesler, V.G.; Lejer, A.F.; Ruault, M.-O.

    2002-01-01

    Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence have been used to study the formation of silicon nanocrystals in SiO 2 implanted with Si ions. Si clusters have been formed at once in the postimplanted layers, providing the excessive Si concentration more ∼ 3 at. %. Si segregation with Si-Si 4 bonds formation is enhanced as following annealing temperature increase, however, the Raman scattering by Si clusters diminishes. The effect is explained by a transformation of the chain-like Si clusters into compact phase nondimensional structures. Segregation of Si nanoprecipitates had ended about 1000 deg C, but the strong photoluminescence typical for Si nanocrystals manifested itself only after 1100 deg C [ru

  16. Role of yttria-stabilized zirconia produced by ion-beam-assisted deposition on the properties of RuO2 on SiO2/Si

    Jia, Q.X.; Arendt, P.; Groves, J.R.; Fan, Y.; Roper, J.M.; Foltyn, S.R.

    1998-01-01

    Highly conductive biaxially textured RuO 2 thin films were deposited on technically important SiO 2 /Si substrates by pulsed laser deposition, where yttria-stabilized zirconia (YSZ) produced by ion-beam-assisted-deposition (IBAD) was used as a template to enhance the biaxial texture of RuO 2 on SiO 2 /Si. The biaxially oriented RuO 2 had a room-temperature resistivity of 37 μΩ-cm and residual resistivity ratio above 2. We then deposited Ba 0.5 Sr 0.5 TiO 3 thin films on RuO 2 /IBAD-YSZ/SiO 2 /Si. The Ba 0.5 Sr 0.5 TiO 3 had a pure (111) orientation normal to the substrate surface and a dielectric constant above 360 at 100 kHz. copyright 1998 Materials Research Society

  17. Silicon (100)/SiO2 by XPS

    Jensen, David S.; Kanyal, Supriya S.; Madaan, Nitesh; Vail, Michael A.; Dadson, Andrew; Engelhard, Mark H.; Linford, Matthew R.

    2013-09-25

    Silicon (100) wafers 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 K radiation. Survey scans show that the material is primarily silicon and oxygen, and 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) was estimated using the equation of Strohmeier.1 The oxygen peak is symmetric. The material shows small amounts of carbon, fluorine, and nitrogen contamination. These silicon wafers are used as the base material for subsequent growth of templated carbon nanotubes.

  18. C-A-S-H synthesis and thermodynamics modelling in CaO-Al2O3-SiO2-H2O system

    Haas, J.; Pochard, I.; Nonat, A.

    2015-01-01

    Ordinary Portland cement (OPC) is being increasingly replaced by blended cements, where part of the clinker is replaced by secondary cementitious materials (SCM) such as blast furnace or fly ash. The use of SCM enables to achieve various aims as the cost reduction by recovery of by-products, the CO 2 emission reduction, the obtaining of specific properties as low pH. So, blended cements are more and more current in different fields as civil engineering and nuclear waste repository. The use of silica and/or aluminium rich SCMs directly impacts the amount and the kind of hydrates formed, hence the volume and the porosity and finally the durability of these materials. Aluminates containing hydrates formation is not well understood. Al content can result from Al-uptake in C-S-H due to Al-substitution of Si-tetrahedra to well crystallised hydrates like straetlingite or katoite phases. This study proposes a surface dependant thermodynamic model to predict and to correlate the Al-uptake (substitution) of C-A-S-H with solutions representative of that of cement pores chemistry. For this purpose, pure C-A-S-H alkali-free were synthesized in diluted suspensions. On one hand, hydrates and their solutions were characterized at equilibrium. On the other hand, thermodynamics modelling were performed from these collected data to describe C-A-S-H in the equilibrium solutions. These results allowed evaluating the Al-availability in the cementitious system and especially for aluminates containing hydrates precipitation. (authors)

  19. The influence of phosphorus precursors on the synthesis and bioactivity of SiO2-CaO-P 2O 5 sol-gel glasses and glass-ceramics.

    Siqueira, Renato Luiz; Zanotto, Edgar Dutra

    2013-02-01

    Bioactive glasses and glass-ceramics of the SiO(2)-CaO-P(2)O(5) system were synthesised by means of a sol-gel method using different phosphorus precursors according to their respective rates of hydrolysis-triethylphosphate (OP(OC(2)H(5))(3)), phosphoric acid (H(3)PO(4)) and a solution prepared by dissolving phosphorus oxide (P(2)O(5)) in ethanol. The resulting materials were characterised by differential scanning calorimetry and thermogravimetry, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and by in vitro bioactivity tests in acellular simulated body fluid. The different precursors significantly affected the main steps of the synthesis, beginning with the time required for gel formation. The most striking influence of these precursors was observed during the thermal treatments at 700-1,200 °C that were used to convert the gels into glasses and glass-ceramics. The samples exhibited very different mineralisation behaviours; especially those prepared using the phosphoric acid, which had a reduced onset temperature of crystallisation and an increased resistance to devitrification. However, all resulting materials were bioactive. The in vitro bioactivity of these materials was strongly affected by the heat treatment temperature. In general, their bioactivity decreased with increasing treatment temperature. For crystallised samples obtained above 900 °C, the bioactivity was favoured by the presence of two crystalline phases: wollastonite (CaSiO(3)) and tricalcium phosphate (α-Ca(3)(PO(4))(2)).

  20. Modeling and optimization of Fischer-Tropsch synthesis over Co-Mn-Ce/SiO_2 catalyst using hybrid RSM/LHHW approaches

    Zohdi-Fasaei, Hossein; Atashi, Hossein; Farshchi Tabrizi, Farshad; Mirzaei, Ali Akbar

    2017-01-01

    Operating conditions considerably affect the energy required for Fischer-Tropsch synthesis, depending on the catalyst composition and reactor type (catalyst system). This paper reports the use of cobalt-manganese-cerium supported on silica as a novel CO hydrogenation catalyst, to produce hydrocarbons in a fixed bed micro-reactor. Response surface methodology (RSM) was applied to study the effects of temperature, pressure, feed ratio and their interactions on CO consumption rate, and the selectivity of light olefins (light olefinity), methane and C_5_+ hydrocarbons. Quadratic mathematical models adequately described the responses in this catalyst system. According to Langmuir Hinshelwood Hougen Watson (LHHW) approach, kinetic mechanism of the reaction was found to be an associative adsorption of H_2 and CO. Statistical analysis demonstrated that pressure and feed ratio were the most important factors for the production of C_5_+ and light alkenes, respectively. Model graphs indicated that minimum methane selectivity was achieved at 523.15 k and 2 bar. The maximum amounts of light olefins and heavier hydrocarbons were obtained at H_2/CO = 1 and H_2/CO = 2, respectively. Characterization of precursor and calcined catalyst (before and after the reaction) was carried out using SEM and BET techniques. - Highlights: • The performance of a new catalytic system was studied using RSM as a research plan. • Interactions between significant factors were investigated using mathematical models. • Based on LHHW approach, kinetic mechanism was molecular adsorptions of H_2 and CO. • RSM rate expression was in consistent with the LHHW kinetic model. • Hybrid RSM/LHHW is promising for optimization, mechanism and selectivity studies.

  1. Study of SiO2/PMMA/CE tri-component interpenetrating polymer network composites

    Wang Junlong; Wang Chuang; Jiao Gengsheng; Wang Qiuya

    2010-01-01

    A technology of conjugated tri-component interpenetrating polymer networks was applied to synthesize a nano-SiO 2 /polymethylmethacrylate (PMMA)/cyanate (CE) composite through an asynchronous synthesis way. The microstructure of the composite was characterized using infrared spectroscopy (IR) and transmission electron microscopy (TEM). The mechanical properties were measured in German-made DL-1000B and XCL-40 universal material test machines, respectively. Results showed that both the impact strength and the flexural strength were in the optimum status when 3% SiO 2 /PMMA/CE was chosen as a sample with the PMMA/CE ratio of 20/80. Compared with the strengths of pure cyanate, those of the composite were raised by 137.28% and 31.29%, respectively. When 3% nano-SiO 2 was added, the impact strength was increased by 29.96% and the flexural strength by 20.05%, compared with the strengths of polymers without SiO 2 . Analysis and measurements by IR and TEM indicated that no chemical reactions took place among components in the composite. The interpenetration of the conjugated tri-component improved the loading capacity of the polymer, hence the toughness enhancement of cyanate.

  2. Improving Passivation Process of Si Nanocrystals Embedded in SiO2 Using Metal Ion Implantation

    Jhovani Bornacelli

    2013-01-01

    Full Text Available We studied the photoluminescence (PL of Si nanocrystals (Si-NCs embedded in SiO2 obtained by ion implantation at MeV energy. The Si-NCs are formed at high depth (1-2 μm inside the SiO2 achieving a robust and better protected system. After metal ion implantation (Ag or Au, and a subsequent thermal annealing at 600°C under hydrogen-containing atmosphere, the PL signal exhibits a noticeable increase. The ion metal implantation was done at energies such that its distribution inside the silica does not overlap with the previously implanted Si ion . Under proper annealing Ag or Au nanoparticles (NPs could be nucleated, and the PL signal from Si-NCs could increase due to plasmonic interactions. However, the ion-metal-implantation-induced damage can enhance the amount of hydrogen, or nitrogen, that diffuses into the SiO2 matrix. As a result, the surface defects on Si-NCs can be better passivated, and consequently, the PL of the system is intensified. We have selected different atmospheres (air, H2/N2 and Ar to study the relevance of these annealing gases on the final PL from Si-NCs after metal ion implantation. Studies of PL and time-resolved PL indicate that passivation process of surface defects on Si-NCs is more effective when it is assisted by ion metal implantation.

  3. Enhanced PEC performance of nanoporous Si photoelectrodes by covering HfO2 and TiO2 passivation layers.

    Xing, Zhuo; Ren, Feng; Wu, Hengyi; Wu, Liang; Wang, Xuening; Wang, Jingli; Wan, Da; Zhang, Guozhen; Jiang, Changzhong

    2017-03-02

    Nanostructured Si as the high efficiency photoelectrode material is hard to keep stable in aqueous for water splitting. Capping a passivation layer on the surface of Si is an effective way of protecting from oxidation. However, it is still not clear in the different mechanisms and effects between insulating oxide materials and oxide semiconductor materials as passivation layers. Here, we compare the passivation effects, the photoelectrochemical (PEC) properties, and the corresponding mechanisms between the HfO 2 /nanoporous-Si and the TiO 2 /nanoporous-Si by I-V curves, Motte-schottky (MS) curves, and electrochemical impedance spectroscopy (EIS). Although the saturated photocurrent densities of the TiO 2 /nanoporous Si are lower than that of the HfO 2 /nanoporous Si, the former is more stable than the later.

  4. Enhanced PEC performance of nanoporous Si photoelectrodes by covering HfO2 and TiO2 passivation layers

    Xing, Zhuo; Ren, Feng; Wu, Hengyi; Wu, Liang; Wang, Xuening; Wang, Jingli; Wan, Da; Zhang, Guozhen; Jiang, Changzhong

    2017-03-01

    Nanostructured Si as the high efficiency photoelectrode material is hard to keep stable in aqueous for water splitting. Capping a passivation layer on the surface of Si is an effective way of protecting from oxidation. However, it is still not clear in the different mechanisms and effects between insulating oxide materials and oxide semiconductor materials as passivation layers. Here, we compare the passivation effects, the photoelectrochemical (PEC) properties, and the corresponding mechanisms between the HfO2/nanoporous-Si and the TiO2/nanoporous-Si by I-V curves, Motte-schottky (MS) curves, and electrochemical impedance spectroscopy (EIS). Although the saturated photocurrent densities of the TiO2/nanoporous Si are lower than that of the HfO2/nanoporous Si, the former is more stable than the later.

  5. Electrochemical and optical properties of CeO2-SnO2 and CeO2-SnO2:X (X = Li, C, Si films

    Berton Marcos A.C.

    2001-01-01

    Full Text Available Thin solid films of CeO2-SnO2 (17 mol% Sn and CeO2-SnO2:X (X = Li, C and Si were prepared by the sol-gel route, using an aqueous-based process. The addition of Li, C and Si to the precursor solution leads to films with different electrochemical performances. The films were deposited by the dip-coating technique on ITO coated glass (Donnelly Glass at a speed of 10 cm/min and submitted to a final thermal treatment at 450 °C during 10 min in air. The electrochemical and optical properties of the films were determined from the cyclic voltammetry and chronoamperometry measurements using 0.1 M LiOH as supporting electrolyte. The ion storage capacity of the films was investigated using in situ spectroelectrochemical method and during the insertion/extraction process the films remained transparent. The powders were characterized by thermal analysis (DSC/TGA and X-ray diffraction.

  6. RBS characterization of the deposition of very thin SiGe/SiO2 multilayers by LPCVD

    Munoz-Martin, A.; Climent-Font, A.; Rodriguez, A.; Sangrador, J.; Rodriguez, T.

    2005-01-01

    Multilayer structures consisting of several alternated layers of SiGe and SiO 2 with thickness ranging from 2 or Si as well as the deposition of SiO 2 on Si show negligible incubation times. The deposition of SiO 2 on SiGe, however, exhibits an incubation time of several minutes, which would be related to the oxidation of the surface necessary for the SiO 2 deposition to start. In all cases the film thickness increases linearly with deposition time, thus allowing the growth rates to be determined. These data allow the deposition process of these very thin layers to be accurately controlled

  7. Facile hydrothermal synthesis of CeO2 nanopebbles

    Administrator

    However, to the best of our knowledge the reports on the synthesis of CeO2 ... The base pressure of the XAS chamber was in the range of 10–8 Pa. A Shimadzu ... scopy was investigated to confirm the crystalline quality of CeO2 nanopebbles.

  8. Ce O2-Zr O2 powder synthesis by alcohol dehydration of aqueous salt solutions

    Andrade Nono, M.C. de

    1993-01-01

    A method for the precipitation of Ce O 2 -Zr O 2 powder is reported. It involves the powder synthesis by precipitation from an aqueous of Y and Zr sulphates in ethanol and isopropanol followed by calcination. The powder characteristics and their relations with the green compaction and densification by sintering are shown and discussed. It is observed that the ethanol gives powders with the best compaction and sintering behavior. (author)

  9. Study of temperature-dependent charge conduction in silicon-nanocrystal/SiO_2 multilayers

    Mavilla, Narasimha Rao; Chavan, Vinayak; Solanki, Chetan Singh; Vasi, Juzer

    2016-01-01

    Silicon-nanocrystals (Si-NCs) realized by SiO_x _ 8 MV/cm; independent of temperature), while for lower electric fields (5–8 MV/cm) at higher temperatures, the trap-related Generalized Poole–Frenkel (GPF) is dominant. This signified the role of traps in modifying the conduction in bulk ICPCVD SiO_2 films. We then present the conduction in ML samples. For multilayer samples with SiO_2 sublayer thickness of 1.5 nm and 2.5 nm, Direct Tunneling (DT) is observed to be dominant, while for SiO_2 sublayer thickness of 3.5 nm, Space Charge Limited Conduction (SCLC) with exponential trap distribution is found to be the dominant conduction mechanism. This signifies the role of traps in modifying the conduction in Si-NC multilayer samples and SiO_2 sublayer thickness dependence. - Highlights: • Electrical conduction in SiO_2 film & Si-nanocrystal layers (Si-NCs) is reported. • SiO_2/SiO_x multilayer based Si-NCs were realized by Inductively Coupled plasma CVD. • For SiO_2 film, Fowler–Nordheim tunneling & Generalized Poole–Frenkel are observed. • For Si-NCs with thin SiO_2 sublayers (< 2.5 nm) Direct Tunneling is dominant. • For Si-NCs with 3.5 nm SiO_2 sublayers Space Charge Limited Conduction is dominant.

  10. Lithium Superionic Conductor Li9.42Si1.02P2.1S9.96O2.04 with Li10GeP2S12-Type Structure in the Li2S–P2S5–SiO2 Pseudoternary System: Synthesis, Electrochemical Properties, and Structure–Composition Relationships

    Hori, Satoshi; Suzuki, Kota; Hirayama, Masaaki; Kato, Yuki; Kanno, Ryoji

    2016-01-01

    Lithium superionic conductors with the Li 10 GeP 2 S 12 (LGPS)-type structure are promising materials for use as solid electrolytes in the next-generation lithium batteries. A novel member of the LGPS family, Li 9.42 Si 1.02 P 2.1 S 9.96 O 2.04 (LSiPSO), and its solid solutions were synthesized by quenching from 1273 K in the Li 2 S–P 2 S 5 –SiO 2 pseudoternary system. The material exhibited an ionic conductivity as high as 3.2 × 10 −4 S cm −1 at 298 K, as well as the high electrochemical stability to lithium metal, which was improved by the introduction of oxygen into the LGPS-type structure. An all-solid-state cell with a lithium metal anode and LSiPSO as the separator showed excellent performance with a high reversibility of 100%. Thus, oxygen doping is an effective way of improving the electrochemical stability of LGPS-type structure.

  11. Crystallization behaviour of nanostructured hybrid SiO2-TiO2 gel glasses to nanocomposites.

    Tsvetelina, Gerganova; Yordanka, Ivanova; Yuliya, Vueva; Miranda, Salvado Isabel M; Helena, Fernandes Maria

    2010-04-01

    The crystallization behaviour of hybrid SiO2-TiO2 nanocomposites derived from titanosiloxanes by sol-gel method has been investigated depending on the type of siloxane precursor and the pirolysis temperature. The resulting hybrid titanosiloxanes, crosslinked with trimethylsilil isocyanate (nitrogen-modified) or methyltrietoxisilane (carbon-modified), were pirolyzed in an inert atmosphere in the temperature range between 600 to 1100 degrees C in order to form C-(N)-Si-O-TiO2 nanocomposites. By means of XRD, FTIR, 29Si NMR, SEM, TEM and AFM investigations have been established that the transformation of the nanostructured SiO2-TiO2 hybrid materials into nanocomposites as well as the crystalline size depend on the titanium content and the type of cross-linking agents used in the synthesizes.

  12. Photo-induced tunneling currents in MOS structures with various HfO2/SiO2 stacking dielectrics

    Chin-Sheng Pang

    2014-04-01

    Full Text Available In this study, the current conduction mechanisms of structures with tandem high-k dielectric in illumination are discussed. Samples of Al/SiO2/Si (S, Al/HfO2/SiO2/Si (H, and Al/3HfO2/SiO2/Si (3H were examined. The significant observation of electron traps of sample H compares to sample S is found under the double bias capacitance-voltage (C-V measurements in illumination. Moreover, the photo absorption sensitivity of sample H is higher than S due to the formation of HfO2 dielectric layer, which leads to larger numbers of carriers crowded through the sweep of VG before the domination of tunneling current. Additionally, the HfO2 dielectric layer would block the electrons passing through oxide from valance band, which would result in less electron-hole (e−-h+ pairs recombination effect. Also, it was found that both of the samples S and H show perimeter dependency of positive bias currents due to strong fringing field effect in dark and illumination; while sample 3H shows area dependency of positive bias currents in strong illumination. The non-uniform tunneling current through thin dielectric and through HfO2 stacking layers are importance to MOS(p tunneling photo diodes.

  13. Synthesis, characterization, and immune efficacy of layered double hydroxide@SiO2 nanoparticles with shell-core structure as a delivery carrier for Newcastle disease virus DNA vaccine

    Zhao K

    2015-04-01

    Full Text Available Kai Zhao,1,* Guangyu Rong,1,2,* Chen Guo,1 Xiaomei Luo,1 Hong Kang,1 Yanwei Sun,1,3 Chunxiao Dai,4 Xiaohua Wang,1 Xin Wang,1 Zheng Jin,4 Shangjin Cui,3 Qingshen Sun1 1Key Laboratory of Microbiology, School of Life Science, Heilongjiang University, Harbin, People’s Republic of China; 2Department of Avian Infectious Disease, Shanghai Veterinary Research Institute of Chinese Academy of Agricultural Sciences, Shanghai, People’s Republic of China; 3Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute of Chinese Academy of Agricultural Sciences, Harbin, People’s Republic of China; 4Key Laboratory of Chemical Engineering Process and Technology for High-efficiency Conversion, Heilongjiang University, Harbin, People’s Republic of China *These authors contributed equally to this work Abstract: Layered double hydroxide (LDH@SiO2 nanoparticles were developed as a delivery carrier for the plasmid DNA expressing the Newcastle disease virus F gene. The LDH was hydrotalcite-like materials. The plasmid DNA encapsulated in the LDH@SiO2 nanoparticles (pFDNA-LDH@SiO2-NPs was prepared by the coprecipitation method, and the properties of pFDNA-LDH@SiO2-NPs were characterized by transmission electron microscopy, zeta potential analyzer, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. The results demonstrated that the pFDNA-LDH@SiO2-NPs had a regular morphology and high stability with a mean diameter of 371.93 nm, loading capacity of 39.66%±0.45%, and a zeta potential of +31.63 mV. A release assay in vitro showed that up to 91.36% of the total plasmid DNA could be sustainably released from the pFDNA-LDH@SiO2-NPs within 288 hours. The LDH@SiO2 nanoparticles had very low toxicity. Additionally, their high transfection efficiency in vitro was detected by fluorescent microscopy. Intranasal immunization of specific pathogen-free chickens with pFDNA-LDH@SiO2-NPs

  14. Enhanced the hydrophobic surface and the photo-activity of TiO2-SiO2 composites

    Wahyuni, S.; Prasetya, A. T.

    2017-02-01

    The aim of this research is to develop nanomaterials for coating applications. This research studied the effect of various TiO2-SiO2 composites in acrylic paint to enhance the hydrophobic properties of the substrate. Titanium dioxide containing silica in the range 20-35 mol% has been synthesized using sol-gel route. The XRD’s spectra show that increasing SiO2 content in the composite, decreasing its crystalline properties but increasing the surface area. TiO2-SiO2 composite was dispersed in acrylic paint in 2% composition by weight. The largest contact angle was 70, which produced by the substrate coated with TS-35-modified acrylic paint. This study also investigated the enhanced photo-activity of TiO2-SiO2 modified with poly-aniline. The XRD spectra show that the treatment does not change the crystal structure of TiO2. The photo-activity of the composite was evaluated by degradation of Rhodamine-B with visible light. The best performance of the degradation process was handled by the composite treated with 0.1mL anilines per gram of TiO2-SiO2 composite (TSP-A). On the other side, the contact angle 70 has not shown an excellent hydrophobic activity. However, the AFM spectra showed that nanoroughness has started to form on the surface of acrylic paint modified with TiO2-SiO2 than acrylic alone.

  15. Do SiO 2 and carbon-doped SiO 2 nanoparticles melt? Insights from QM/MD simulations and ramifications regarding carbon nanotube growth

    Page, Alister J.; Chandrakumar, K. R. S.; Irle, Stephan; Morokuma, Keiji

    2011-05-01

    Quantum chemical molecular dynamics (QM/MD) simulations of pristine and carbon-doped SiO 2 nanoparticles have been performed between 1000 and 3000 K. At temperatures above 1600 K, pristine nanoparticle SiO 2 decomposes rapidly, primarily forming SiO. Similarly, carbon-doped nanoparticle SiO 2 decomposes at temperatures above 2000 K, primarily forming SiO and CO. Analysis of the physical states of these pristine and carbon-doped SiO 2 nanoparticles indicate that they remain in the solid phase throughout decomposition. This process is therefore one of sublimation, as the liquid phase is never entered. Ramifications of these observations with respect to presently debated mechanisms of carbon nanotube growth on SiO 2 nanoparticles will be discussed.

  16. Influence of Poly (Ethylene Glycol) and Oleylamine on the Formation of Nano to Micron Size Spherical SiO2 Particles

    We report an eco-friendly synthesis of well–controlled, nano-to-micron-size, spherical SiO2 particles using non-hazardous solvent and a byproducts-producing system. It was found that the morphology and size of spherical SiO2 particles are controlled by adjusting the concentration...

  17. Efficient photocatalytic activity with carbon-doped SiO2 nanoparticles

    Zhang, Dongen

    2013-01-01

    Photocatalysis provides a \\'green\\' approach to completely eliminate various kinds of contaminants that are fatal for current environmental and energy issues. Semiconductors are one of the most frequently used photocatalysts as they can absorb light over a wide spectral range. However, it is also well known that naked SiO2 is not an efficient photocatalyst due to its relatively large band gap, which could only absorb shortwave ultraviolet light. In this report, nanoscale particles of carbon-doped silicon dioxide (C-doped SiO2) for use in photocatalysis were successfully prepared by a facile one-pot thermal process using tetraethylorthosilicate (TEOS) as the source of both silicon and carbon. These particles were subsequently characterized by thermogravimetric analysis, X-ray diffraction, standard and high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The C-doped SiO2 displayed outstanding photocatalytic properties, as evidenced by its catalysis of Rhodamine B degradation under near-UV irradiation. We propose that carbon doping of the SiO2 lattice creates new energy states between the bottom of the conduction band and the top of the valence band, which narrows the band gap of the material. As a result, the C-doped SiO2 nanoparticles exhibit excellent photocatalytic activities in a neutral environment. The novel synthesis reported herein for this material is both energy efficient and environmentally friendly and as such shows promise as a technique for low-cost, readily scalable industrial production. © 2013 The Royal Society of Chemistry.

  18. Reaction mechanisms at 4H-SiC/SiO2 interface during wet SiC oxidation

    Akiyama, Toru; Hori, Shinsuke; Nakamura, Kohji; Ito, Tomonori; Kageshima, Hiroyuki; Uematsu, Masashi; Shiraishi, Kenji

    2018-04-01

    The reaction processes at the interface between SiC with 4H structure (4H-SiC) and SiO2 during wet oxidation are investigated by electronic structure calculations within the density functional theory. Our calculations for 4H-SiC/SiO2 interfaces with various orientations demonstrate characteristic features of the reaction depending on the crystal orientation of SiC: On the Si-face, the H2O molecule is stable in SiO2 and hardly reacts with the SiC substrate, while the O atom of H2O can form Si-O bonds at the C-face interface. Two OH groups are found to be at least necessary for forming new Si-O bonds at the Si-face interface, indicating that the oxidation rate on the Si-face is very low compared with that on the C-face. On the other hand, both the H2O molecule and the OH group are incorporated into the C-face interface, and the energy barrier for OH is similar to that for H2O. By comparing the calculated energy barriers for these reactants with the activation energies of oxide growth rate, we suggest the orientation-dependent rate-limiting processes during wet SiC oxidation.

  19. Supercritical Flow Synthesis of TiO2

    Hellstern, Henrik Christian; Becker, Jacob; Hald, Peter

    2014-01-01

    A new, up-scaled supercritical flow synthesis apparatus has been constructed in Aarhus. A module based system allows for a range of parameter studies with improved parameter control. The dual-reactor setup enables both single phase and core-shell nanoparticle synthesis. TiO2 is a well-known mater...

  20. Role of the SiO2 buffer layer thickness in the formation of Si/SiO2/nc-Ge/SiO2 structures by dry oxidation

    Kling, A.; Ortiz, M.I.; Prieto, A.C.; Rodriguez, A.; Rodriguez, T.; Jimenez, J.; Ballesteros, C.; Soares, J.C.

    2006-01-01

    Nanomemories, containing Ge-nanoparticles in a SiO 2 matrix, can be produced by dry thermal oxidation of a SiGe layer deposited onto a Si-wafer with a barrier SiO 2 layer on its top. Rutherford backscattering spectrometry has been used to characterize the kinetics of the oxidation process, the composition profile of the growing oxide, the Ge-segregation and its diffusion into the barrier oxide in samples with thin and thick barrier oxide layers. The Ge segregated during the oxidation of the SiGe layer diffuses into the barrier oxide. In the first case the diffusion through the thin oxide is enhanced by the proximity of the substrate that acts as a sink for the Ge, resulting in the formation of a low Ge concentration SiGe layer in the surface of the Si-wafer. In the second case, the Ge-diffusion progresses as slowly as in bulk SiO 2 . Since barrier oxide layers as thin as possible are favoured for device fabrication, the structures should be oxidized at lower temperatures and the initial SiGe layer thickness reduced to minimize the Ge-diffusion

  1. Formation of SiO2/polytetrafluoroethylene hybrid superhydrophobic coating

    Zheng Yansheng; He Yi; Qing Yongquan; Zhuo Zhihao; Mo Qian

    2012-01-01

    Highlights: ► The coating showed the water contact angle of 165° and the water sliding angle of 6°. ► The hierarchical structure with the low surface energy leads to surface superhydrophobicity. ► We demonstrated a simple yet efficient approach to preparing superhydrophobic surface. - Abstract: Superhydrophobic coating has been fabricated on the glass substrates with modified SiO 2 sol and polytetrafluoroethylene emulsion through a sol–gel process. SiO 2 sol was modified with γ-glycidoxypropyl trimethoxysilane. The coatings were characterized by water contact angle measurement, Scanning electron microscope, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy and thermal synthetic analysis. The experimental results show that coatings exhibited superhydrophobic and heat-resistant property with a water average contact angle of 156° and sliding angle of 6°, coating has a rough surface with both micro- and nanoscale structures, γ-glycidoxypropyl trimethoxysilane enhanced the hydrophobicity of the coatings. Low surface energy of polymer and special structure of the coatings were responsible for the hydrophobic of the surfaces.

  2. Effect of Commercial SiO2 and SiO2 from rice husk ash loading on biodegradation of Poly (lactic acid) and crosslinked Poly (lactic acid)

    Prapruddivongs, C.; Apichartsitporn, M.; Wongpreedee, T.

    2017-09-01

    In this work, biodegradation behavior of poly (lactic acid) (PLA) and crosslinked PLA filled with two types of SiO2, precipitated SiO2 (commercial SiO2) and SiO2 from rice husk ash, were studied. Rice husks were first treated with 2 molar hydrochloric acid (HCl) to produce high purity SiO2, before burnt in a furnace at 800°C for 6 hours. All components were melted bending by an internal mixer then hot pressed using compression molder to form tested specimens. FTIR spectra of SiO2 and PLA samples were investigated. The results showed the lack of silanol group (Si-OH) of rice husk ash after steric acid surface modification, while the addition of particles can affect the crosslinking of the PLA. For biodegradation test by evaluating total amount of carbon dioxide (CO2) evolved during 60 days incubation at a controlled temperature of 58±2°C, the results showed that the biodegradation of crosslinked PLA occurred slower than the neat PLA. However, SiO2 incorporation enhanced the degree of biodegradation In particular, introducing commercial SiO2 in PLA and crosslinked PLA tended to clearly increase the degree of biodegradation as a consequence of the more accelerated hydrolysis degradation.

  3. Study of Stress Migration Failure in SiLKTM/SiO2 Hybrid Cu Interconnects

    Tsuchikawa, Haruo; Nakamura, Tomoji; Suzuki, Takashi; Mori, Hiroko; Shono, Ken

    2004-01-01

    Stress migration (SM) behavior is studied for a 130nm-node SiLK TM /SiO2 hybrid structure in which the interlevel dielectrics (ILD) consist of SiLK TM for trench levels and SiO2 for via levels. The failure rate dependence on the temperature, line width and circuit is examined in detail. Furthermore, an effect of dielectric deposition process on the reliability of the hybrid interconnects is investigated. It has been found that SM behavior is essentially similar to that reported in Cu/SiO2 systems. It has also been clarified that SiO2 PVD conditions at via level had a large impact on the failure rate. Therefore, the control of ILD deposition conditions is found to be one of the key factors in suppressing the SM failure. In order to examine the effect of the PVD conditions, the residual stress in vias were measured by using X-ray diffraction method. The results show that σx (the stress component parallel to the surface) in vias greatly depends on the PVD conditions. Then, the relationship between the PVD conditions and the SM failure rate is clarified

  4. Phonon spectra in SiO2 glasses

    Perez R, J.F.; Jimenez S, S.; Gonzalez H, J.; Vorobiev, Y.V.; Hernandez L, M.A.; Parga T, J.R.

    1999-01-01

    Phonon spectra in SiO 2 sol-gel made glasses annealed under different conditions are investigated using infrared absorption and Raman scattering. These data are compared with those obtained in commercial optical-quality quartz. All the materials exhibit the same phonon bands, the exact position and the intensity depend on the measuring technique and on the sample preparation method. The phonon spectra in this material are interpreted on the basis of a simple quasi-linear description of elastic waves in an O-Si-O chain. It is shown that the main features observed in the range 400-1400 cm -1 can be predicted using a quasi-linear chain model in which the band at 1070 cm -1 is assigned to the longitudinal optical waves in the O-Si-O chain with the smallest possible wavelength at the Brillouin zone boundary, the band located around 450 cm -1 is assigned to the transversal optical waves and the band at 800 cm -1 to the longitudinal acoustical waves with the same wavelength. The degree of structural disorder can be also deduced within the framework of the proposed model. (Author)

  5. Slow positron studies of hydrogen activation/passivation on SiO2/Si(100) interfaces

    Lynn, K.G.; Asoka-Kumar, P.

    1991-01-01

    The hydrogen atoms are one of the most common impurity species found in semiconductor systems owing to its large diffusivity, and are easily incorporated either in a controlled process like in ion implantation or in an uncontrolled process like the one at the fabrication stage. Hydrogen can passivate dangling bonds and dislocations in these systems and hence can be used to enhance the electrical properties. In a SiO 2 /Si system, hydrogen can passivate electronic states at the interface and can alter the fixed or mobile charges in the oxide layer. Since hydrogen is present in almost all of the environments of SiO 2 /Si wafer fabrication, the activation energy of hydrogen atoms is of paramount importance to a proper understanding of SiO 2 /Si based devices and has not been measured on the technologically most important Si(100) face. There are no direct, nondestructive methods available to observe hydrogen injection into the oxide layer and subsequent diffusion. This study uses the positrons as a ''sensitive'', nondestructive probe to observe hydrogen interaction in the oxide layer and the interface region. We also describe a new way of characterizing the changes in the density of the interface states under a low-temperature annealing using positrons. 9 refs., 6 figs

  6. Slow positron studies of hydrogen activation/passivation on SiO2/Si(100) interfaces

    Lynn, K. G.; Asoka-Kumar, P.

    The hydrogen atoms are one of the most common impurity species found in semiconductor systems owing to its large diffusivity, and are easily incorporated either in a controlled process like in ion implantation or in an uncontrolled process like the one at the fabrication stage. Hydrogen can passivate dangling bonds and dislocations in these systems and hence can be used to enhance the electrical properties. In a SiO2/Si system, hydrogen can passivate electronic states at the interface and can alter the fixed or mobile charges in the oxide layer. Since hydrogen is present in almost all of the environments of SiO2/Si wafer fabrication, the activation energy of hydrogen atoms is of paramount importance to a proper understanding of SiO2/Si based devices and has not been measured on the technologically most important Si(100) face. There are no direct, nondestructive methods available to observe hydrogen injection into the oxide layer and subsequent diffusion. The positrons are used as a 'sensitive', nondestructive probe to observe hydrogen interaction in the oxide layer and the interface region. A new way is described of characterizing the changes in the density of the interface states under a low temperature annealing using positrons.

  7. Preparation and electrocatalytic properties of Pt-SiO2 nanocatalysts for ethanol electrooxidation.

    Liu, B; Chen, J H; Zhong, X X; Cui, K Z; Zhou, H H; Kuang, Y F

    2007-03-01

    Due to their high stability in general acidic solutions, SiO(2) nanoparticles were selected as the second catalyst for ethanol oxidation in sulfuric acid aqueous solution. Pt-SiO(2) nanocatalysts were prepared in this paper. The micrography and elemental composition of Pt-SiO(2) nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The electrocatalytic properties of Pt-SiO(2) nanocatalysts for ethanol oxidation were investigated by cyclic voltammetry. Under the same Pt loading mass and experimental conditions for ethanol oxidation, Pt-SiO(2) nanocatalysts show higher activity than PtRu/C (E-Tek), Pt/C (E-Tek), and Pt catalysts. Additionally, Pt-SiO(2) nanocatalysts possess good anti-poisoning ability. The results indicate that Pt-SiO(2) nanocatalysts may have good potential applications in direct ethanol fuel cells.

  8. Annealing characteristics of SiO2-Si structures after incoherent light pulse processing

    Sieber, N.; Klabes, R.; Voelskow, M.; Fenske, F.

    1982-01-01

    The behaviour of oxide charges and interface charges in boron implanted and non-implanted SiO 2 -Si structures as well as the electrical activation of the dopants by the action of incoherent light pulses was studied. Depth profiles of electrically active boron ions are presented for different annealing conditions as measured by the pulsed C-V method. It can be concluded that exposure of MOS structures to intense radiation of flash lamps does not increase the fixed charge and the fast state density at the SiO 2 -Si interface if optimal annealing conditions (energy densities) are employed. Low dose boron implanted silicon can be electrically activated without diffusion or segregation of dopants

  9. Photocatalytic activity of Ti3+ self-doped dark TiO2 ultrafine nanorods, grey SiO2 nanotwin crystalline, and their composite under visible light

    Zhang, Renhui; Yang, Yingchang; Leng, Senlin; Wang, Qing

    2018-04-01

    Efficient electron-holes separation is of crucial importance for the improvement of photocatalytic activity for photocatalytic reaction. In this work, dark TiO2 (D-TiO2) nanorods, grey SiO2 (G-SiO2) and D-TiO2/G-SiO2 composite with surface defects are synthesized. We report that the efficiency of photo-generated electrons and holes separation is well enhanced by introducing G-SiO2 into D-TiO2 lattice. Using first-principles method, we find that surface defects (O or Si vacancy) can be conducive to improving the optical absorption under visible-light region. Combination of the experimental results, for D-TiO2/G-SiO2 composite, the surface defects of TiO2 nanocrystallines can significantly improve the photocatalytic efficiency.

  10. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    Wei-Ting eLai

    2016-02-01

    Full Text Available We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5−90 nm, the SiO2 thickness (3−4 nm, and as well the SiGe-shell thickness (2−15 nm has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5 in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge MOS nanoelectronic and nanophotonic applications.

  11. Study of hydrogen interaction with SiO2/Si(100) system using positrons

    Asoka-Kumar, P.; Lynn, K.G.; Leung, T.C.; Nielsen, B.; Wu, X.Y.

    1991-01-01

    We describe positron annihilation studies of SiO 2 /Si(100) structures having 100-nm-thick oxide grown by plasma enhanced chemical vapor deposition. A normalized shape parameter is used to characterize the positron annihilation spectra. Activation and passivation of interface states by atomic hydrogen are demonstrated by repeated vacuum anneal and atomic hydrogen exposure. Hydrogen activation energy is derived for one of the samples as 2.02±0.07 eV

  12. Nucleation of C60 on ultrathin SiO2

    Conrad, Brad; Groce, Michelle; Cullen, William; Pimpinelli, Alberto; Williams, Ellen; Einstein, Ted

    2012-02-01

    We utilize scanning tunneling microscopy to characterize the nucleation, growth, and morphology of C60 on ultrathin SiO2 grown at room temperature. C60 thin films are deposited in situ by physical vapor deposition with thicknesses varying from <0.05 to ˜1 ML. Island size and capture zone distributions are examined for a varied flux rate and substrate deposition temperature. The C60 critical nucleus size is observed to change between monomers and dimers non-monotonically from 300 K to 500 K. Results will be discussed in terms of recent capture zone studies and analysis methods. Relation to device fabrication will be discussed. doi:10.1016/j.susc.2011.08.020

  13. Effects of four step sintering on Y2O3: SiO2 nanocomposite

    Ahlawat, Rachna

    2015-01-01

    Need for high performance materials for advanced applications have led to the development of new concepts in materials design processing and their fabrication. The development of nanocrystalline materials with improved and novel properties is an important turning point in materials research. In present work, we report synthesis and structural characterization of Y 2 O 3 : SiO 2 nanocomposite. Sol-gel technique is being used to prepare-Y 2 O 3 SiO 2 nanocomposite due to its effectiveness in preparing samples with good mixing of starting materials and at relatively low reaction temperature. We have used Y(NO 3 ) 3 .4H 2 O and TEOS as precursors and followed usual approach of sol-gel technique, the final product of Y 2 O 3 : SiO 2 nanocomposite is obtained in the form of powder. The powder samples were sintered at different temperature for different time durations in programmable muffle furnace. The samples were characterized by complementary techniques as X-Ray Diffraction (XRD), Fourier Transforms Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). (author)

  14. Atomic state and characterization of nitrogen at the SiC/SiO2 interface

    Xu, Y.; Garfunkel, E. L.; Zhu, X.; Lee, H. D.; Xu, C.; Shubeita, S. M.; Gustafsson, T.; Ahyi, A. C.; Sharma, Y.; Williams, J. R.; Lu, W.; Ceesay, S.; Tuttle, B. R.; Pantelides, S. T.; Wan, A.; Feldman, L. C.

    2014-01-01

    We report on the concentration, chemical bonding, and etching behavior of N at the SiC(0001)/SiO 2 interface using photoemission, ion scattering, and computational modeling. For standard NO processing of a SiC MOSFET, a sub-monolayer of nitrogen is found in a thin inter-layer between the substrate and the gate oxide (SiO 2 ). Photoemission shows one main nitrogen related core-level peak with two broad, higher energy satellites. Comparison to theory indicates that the main peak is assigned to nitrogen bound with three silicon neighbors, with second nearest neighbors including carbon, nitrogen, and oxygen atoms. Surprisingly, N remains at the surface after the oxide was completely etched by a buffered HF solution. This is in striking contrast to the behavior of Si(100) undergoing the same etching process. We conclude that N is bound directly to the substrate SiC, or incorporated within the first layers of SiC, as opposed to bonding within the oxide network. These observations provide insights into the chemistry and function of N as an interface passivating additive in SiC MOSFETs

  15. Anomalous defect processes in Si implanted amorphous SiO2, II

    Fujita, Tetsuo; Fukui, Minoru; Okada, Syunji; Shimizu-Iwayama, Tsutomu; Hioki, Tatsumi; Itoh, Noriaki

    1994-01-01

    Aanomalous features of the defects in Si implanted amorphous SiO 2 are reported. The numbers of E 1 prime centers and B 2 centers are found to increase monotonically with implanted Si dose, in contrast to the saturating feature of these numbers in Ar implanted samples. Moreover, when H ions are implanted in amorphous SiO 2 predamaged by Si implantation, both of the density and the number of E 1 prime centers increase and they reach a constant value at a small H dose. We point out that these anomalies can be explained in terms of the difference in the cross-section for defect annihilation in the specimens implanted with Si ions and other ions, in accordance with the homogeneous model proposed by Devine and Golanski. We consider that the main mechanism of defect annihilation is the recombination of an E 1 prime center and an interstitial O, which is stabilized by an implanted Si, reducing the cross-section in Si-implanted specimens. ((orig.))

  16. Nanocrystal in Er3+-doped SiO2-ZrO2 Planar Waveguide with Yb3+ Sensitizer

    Razaki, N. Iznie; Jais, U. Sarah; Abd-Rahman, M. Kamil; Bhaktha, S. N. B.; Chiasera, A.; Ferrari, M.

    2010-01-01

    Higher doping of Er 3+ in glass ceramic waveguides would cause concentration and pair-induced quenching which lead to inhomogeneous line-width of luminescence spectrum thus reduce output intensity. Concentration quenching can be overcome by introducing ZrO 2 in the glass matrix while co-doping with Yb 3+ which acts as sensitizer would improve the excitation efficiency of Er 3+ . In this study, SiO 2 -ZrO 2 planar waveguides having composition in mol percent of 70SiO 2 -30ZrO 2 doped with Er 3+ and co-doped with Yb 3+ , were prepared via sol-gel route. Narrower and shaper peaks of PL and XRD shows the formation of nanocrystals. Intensity is increase with addition amount of Yb 3+ shows sensitizing effect on Er 3+ .

  17. Formation of radiative centers in SiO2 by tin high-dose implantation

    Komarov, F.F.; Parkhomenko, I.N.; Vlasukova, L.A.; Mil'chanin, O.V.; Mokhovikov, M.A.; Wendler, E.; Wesch, W.

    2013-01-01

    The structural transformations in SiO 2 layers implanted with high fluence of Sn ions have been investigated. It has been found that post-implantation annealing results in the β-Sn precipitation as well as the formation of SnO 2 -enriched regions in SiO 2 :Sn matrix. The intensive emission in the range of photon energies 1.5 – 3.5 eV is registered for the implanted and annealed samples. We attribute it to the oxygen deficiency centers created in the SiO 2 :Sn matrix and at the 'nanocluster/SiO 2 ' interfaces. (authors)

  18. Photocatalytic application of TiO2/SiO2-based magnetic nanocomposite (Fe3O4@SiO2/TiO2 for reusing of textile wastewater

    Laleh Enayati Ahangar

    2016-01-01

    Full Text Available In this research we have developed a treatment method for textile wastewater by TiO2/SiO2-based magnetic nanocomposite. Textile wastewater includes a large variety of dyes and chemicals and needs treatments. This manuscript presents a facile method for removing dyes from the textile wastewater by using TiO2/SiO2-based nanocomposite (Fe3O4@SiO2/TiO2 under UV irradiation. This magnetic nanocomposite, as photocatalytically active composite, is synthesized via solution method in mild conditions. A large range of cationic, anionic and neutral dyes including: methyl orange, methylene blue, neutral red, bromocresol green and methyl red are used for treatment investigations. Neutral red and bromocresol green have good results in reusing treatment. The high surface area of nanocomposites improve the kinetic of wastewater treatment. In this method, by using the magnetic properties of Fe3O4 nanoparticles, TiO2-based photocatalyst could be separated and reused for 3 times. The efficiency of this method is respectively 100% and 65% for low concentration (10 ppm and high concentration (50 ppm of neutral red and bromocrosol green after 3 h treatment. The efficiency of treatment using the second used nanocomposite was 90% for 10 ppm of the same dyes.

  19. Electronic states of SiO2-MxOy (MxOy=P205, TiO2 and ZrO2) glasses

    Kowada, Y [Hyogo Univ. of Teacher Education, Hyogo (Japan); Adachi, H [Kyoto Univ. (Japan). Faculty of Engineering; Minami, T [Univ. of Osaka Prefecture, Osaka (Japan). Faculty of Engineering

    1993-12-01

    Using the sol-gel method the surface of metal and glass substrates can be modified. For example, stainless steel sheets coated with the SiO2-ZrO2 glass films have higher resistance to corrosion and oxidation. The coating films contain high concentration of alkali ions diffusing from the glass substrates. It suggests that the sodium ions are trapped strongly within the coating films and are blocked to further diffuse to the surface. This behavior must be associated with the chemical bonding around the sodium ions in the SiO2-TiO2 and SiO2-ZrO2 films. For better understanding of the chemical bonding in the glasses, the electronic states of the SiO2-MxOy glasses were calculated by means of the DV-Xa cluster method. In this paper, the calculation method is explained, the results are discussed and the conclusion is stated. 17 refs., 6 figs.

  20. Thickness and composition of ultrathin SiO2 layers on Si

    van der Marel, C; Verheijen, M.A.; Tamminga, Y; Pijnenburg, RHW; Tombros, N; Cubaynes, F

    2004-01-01

    Ultrathin SiO2 layers are of importance for the semiconductor industry. One of the techniques that can be used to determine the chemical composition and thickness of this type of layers is x-ray photoelectron spectroscopy (XPS). As shown by Seah and Spencer [Surf. Interface Anal. 33, 640 (2002)], it

  1. Realization of Colored Multicrystalline Silicon Solar Cells with SiO2/SiNx:H Double Layer Antireflection Coatings

    Minghua Li

    2013-01-01

    Full Text Available We presented a method to use SiO2/SiNx:H double layer antireflection coatings (DARC on acid textures to fabricate colored multicrystalline silicon (mc-Si solar cells. Firstly, we modeled the perceived colors and short-circuit current density (Jsc as a function of SiNx:H thickness for single layer SiNx:H, and as a function of SiO2 thickness for the case of SiO2/SiNx:H (DARC with fixed SiNx:H (refractive index n=2.1 at 633 nm, and thickness = 80 nm. The simulation results show that it is possible to achieve various colors by adjusting the thickness of SiO2 to avoid significant optical losses. Therefore, we carried out the experiments by using electron beam (e-beam evaporation to deposit a layer of SiO2 over the standard SiNx:H for 156×156 mm2 mc-Si solar cells which were fabricated by a conventional process. Semisphere reflectivity over 300 nm to 1100 nm and I-V measurements were performed for grey yellow, purple, deep blue, and green cells. The efficiency of colored SiO2/SiNx:H DARC cells is comparable to that of standard SiNx:H light blue cells, which shows the potential of colored cells in industrial applications.

  2. Physical and Electrical Properties of SiO2 Layer Synthesized by Eco-Friendly Method

    Kim, Jong-Woong; Kim, Young-Seok; Hong, Sung-Jei; Hong, Tae-Hwan; Han, Jeong-In

    2010-05-01

    SiO2 thin film has a wide range of applications, including insulation layers in microelectronic devices, such as semiconductors and flat panel displays, due to its advantageous characteristics. Herein, we developed a new eco-friendly method for manufacturing SiO2 nanoparticles and, thereby, SiO2 paste to be used in the digital printing process for the fabrication of SiO2 film. By excluding harmful Cl- and NO3- elements from the SiO2 nanoparticle synthetic process, we were able to lower the heat treatment temperature for the SiO2 precursor from 600 to 300 °C and the diameter of the final SiO2 nanoparticles to about 14 nm. The synthesized SiO2 nanoparticles were dispersed in an organic solvent with additives to make a SiO2 paste for feasibility testing. The SiO2 paste was printed onto a glass substrate to test the feasibility of using it for digital printing. The insulation resistance of the printed film was high enough for it to be used as an insulation layer for passivation.

  3. Processing of SiO2 protective layer using HMDS precursor by combustion CVD.

    Park, Kyoung-Soo; Kim, Youngman

    2011-08-01

    Hexamethyldisilazane (HMDS, [(CH3)3Si]2NH) was used as a precursor to form SiO2 protective coatings on IN738LC alloys by combustion chemical vapor deposition (CCVD). SEM and XPS showed that the processed coatings were composed mainly of SiO2. The amount of HMDS had the largest effect on the size of the SiO2 agglomerates and the thickness of the deposited coatings. The specimens coated with SiO2 using the 0.05 mol/l HMDS solution showed a significantly higher temperature oxidation resistance than those deposited under other conditions.

  4. Thickness and composition of ultrathin SiO2 layers on Si

    Marel, C. van der; Verheijen, M.A.; Tamminga, Y.; Pijnenburg, R.H.W.; Tombros, N.; Cubaynes, F.

    2004-01-01

    Ultrathin SiO 2 layers are of importance for the semiconductor industry. One of the techniques that can be used to determine the chemical composition and thickness of this type of layers is x-ray photoelectron spectroscopy (XPS). As shown by Seah and Spencer [Surf. Interface Anal. 33, 640 (2002)], it is not trivial to characterize this type of layer by means of XPS in a reliable way. We have investigated a series of ultrathin layers of SiO 2 on Si (in the range from 0.3 to 3 nm) using XPS. The samples were also analyzed by means of transmission electron microscopy (TEM), Rutherford backscattering (RBS), and ellipsometry. The thickness of the SiO 2 layers (d) was determined from the XPS results using three different approaches: the 'standard' equation (Seah and Spencer) for d, an overlayer-substrate model calculation, and the QUASES-Tougaard [Surf. Interface Anal. 26, 249 (1998), QUASES-Tougaard: Software package for Quantitative Analysis of Surfaces by Electron Spectroscopy, version 4.4 (2000); http://www.quases.com] method. Good agreement was obtained between the results of XPS analyses using the 'standard' equation, the overlayer-substrate model calculation, and RBS results. The QUASES-Tougaard results were approximately 62% above the other XPS results. The optical values for the thickness were always slightly higher than the thickness according to XPS or RBS. Using the model calculation, these (relatively small) deviations from the optical results could be explained as being a consequence of surface contaminations with hydrocarbons. For a thickness above 2.5 nm, the TEM results were in good agreement with the results obtained from the other techniques (apart from QUASES-Tougaard). Below 2.5 nm, significant deviations were found between RBS, XPS, and optical data on the one hand and TEM results on the other hand; the deviations became larger as the thickness of the SiO 2 decreased. This effect may be related to interface states of oxygen, which have been

  5. Heterogeneous Ag-TiO2-SiO2 composite materials as novel catalytic systems for selective epoxidation of cyclohexene by H2O2.

    Xin Wang

    Full Text Available TiO2-SiO2 composites were synthesized using cetyl trimethyl ammonium bromide (CTAB as the structure directing template. Self-assembly hexadecyltrimethyl- ammonium bromide TiO2-SiO2/(CTAB were soaked into silver nitrate (AgNO3 aqueous solution. The Ag-TiO2-SiO2(Ag-TS composite were prepared via a precipitation of AgBr in soaking process and its decomposition at calcination stage. Structural characterization of the materials was carried out by various techniques including X-ray diffraction (XRD, scanning electron microscopy (SEM, transmission electron microscopy (TEM, N2 adsorption-desorption and ultraviolet visible spectroscopy (UV-Vis. Characterization results revealed that Ag particles were incorporated into hierarchical TiO2-SiO2 without significantly affecting the structures of the supports. Further heating-treatment at 723 K was more favorable for enhancing the stability of the Ag-TS composite. The cyclohexene oxide was the major product in the epoxidation using H2O2 as the oxidant over the Ag-TS catalysts. Besides, the optimum catalytic activity and stability of Ag-TS catalysts were obtained under operational conditions of calcined at 723 K for 2 h, reaction time of 120 min, reaction temperature of 353 K, catalyst amount of 80 mg, aqueous H2O2 (30 wt.% as oxidant and chloroform as solvent. High catalytic activity with conversion rate up to 99.2% of cyclohexene oxide could be obtainable in water-bathing. The catalyst was found to be stable and could be reused three times without significant loss of catalytic activity under the optimized reaction conditions.

  6. Laser-controlled stress of Si nanocrystals in a free-standing Si /SiO2 superlattice

    Khriachtchev, Leonid; Räsänen, Markku; Novikov, Sergei

    2006-01-01

    We report laser manipulations with stress at the nanoscale level. The continuous-wave Ar+ laser radiation melts Si nanocrystals in a free-standing Si /SiO2 superlattice. Silicon crystallization from the liquid phase leads to a compressive stress, which can be accurately tuned in the 3GPa range using laser annealing below the Si melting temperature and then recovered by laser annealing above the melting temperature. This allows investigations of various phenomena as a function of stress and makes a case of Si-nanocrystal memory with very long retention time, which can be written, erased, and read by optical means.

  7. Laser-controlled stress of Si nanocrystals in a free-standing Si/SiO2 superlattice

    Khriachtchev, Leonid; Raesaenen, Markku; Novikov, Sergei

    2006-01-01

    We report laser manipulations with stress at the nanoscale level. The continuous-wave Ar + laser radiation melts Si nanocrystals in a free-standing Si/SiO 2 superlattice. Silicon crystallization from the liquid phase leads to a compressive stress, which can be accurately tuned in the 3 GPa range using laser annealing below the Si melting temperature and then recovered by laser annealing above the melting temperature. This allows investigations of various phenomena as a function of stress and makes a case of Si-nanocrystal memory with very long retention time, which can be written, erased, and read by optical means

  8. Thermal stability of Cu/α-Ta/SiO2/Si structures

    Yuan, Z.L.; Zhang, D.H.; Li, C.Y.; Prasad, K.; Tan, C.M.

    2004-01-01

    The thermal stability of the Cu/α-Ta/SiO 2 /Si structures is investigated. Tantalum oxides are first observed at the interface between Cu and Ta due to residual oxygen in the annealing ambient at low annealing temperatures (about 600 deg. C). Ternary Cu-Ta oxides and/or Ta oxides rather than Cu oxides are found at the Cu top layer on account of the out diffusion of Ta. After high temperature annealing (up to 750 deg. C), polycrystalline Tantalum oxides (Ta 2 O 5 ) and Ta-rich silicides (Ta 5 Si 3 ) are found as dominant products due to the dissociation of SiO 2 . A severe intermixing of Cu, Ta and SiO 2 was observed after 800 deg. C annealing. First a drop and then an increase in sheet resistances were observed, the former possibly resulting from grain growth and impurities removal in Cu films, and the latter from the reduction of Cu thickness and formation of high resistivity products. The α-Ta films with a thickness of 25 nm have good barrier effectiveness up to 750 deg. C. The degradation of α-Ta film is mainly caused by self oxidation, silicidation and bidirectional diffusion

  9. Experimental observations of the chemistry of the SiO2/Si interface

    Grunthaner, F. J.; Maserjian, J.

    1977-01-01

    Changes in silicon surface preparation prior to thermal oxidation are shown to leave a signature by altering the final SiO2/Si interface structure. Surface analytical techniques, including XPS, static SIMS, ion milling, and newly developed wet-chemical profiling procedures are used to obtain detailed information on the chemical structure of the interface. The oxides are shown to be essentially SiO2 down to a narrow transitional interface layer (3-7 A). A number of discrete chemical species are observed in this interface layer, including different silicon bonds (e.g., C-, OH-, H-) and a range of oxidation states of silicon (0 to +4). The effect of surface preparation and the observed chemical species are correlated with oxide growth rate, surface-state density, and flatband shifts after irradiation.

  10. Effect of Different Nano-Sized Silica Sols as Supports on the Structure and Properties of Cu/SiO2 for Hydrogenation of Dimethyl Oxalate

    Chuancai Zhang

    2017-02-01

    Full Text Available Cu/x-SiO2 catalysts with 4, 10, and 20 nm silica sols as supports was produced by ammonia evaporation method and characterized. Different nano-sized silica sols as supports significantly affected the structure and catalytic properties of the copper catalysts for ethylene glycol synthesis from dimethyl oxalate. Compared with Cu/20-SiO2 and Cu/4-SiO2 catalysts, the catalytic performance and stability of Cu/10-SiO2 catalyst were greatly enhanced. The Cu/10-SiO2 catalyst showed 99.9% conversion with 94% EG selectivity and a lifetime of over 3080 h if it is calculated by industrial weight liquid hourly space velocity (WLHSV of 0.5 h−1. The Cu/10-SiO2 catalyst has one of the longest lifetimes among the catalysts and is a good alternative catalyst for this reaction. Improvement in the catalytic performance and stability of Cu/10-SiO2 is attributed to the proper SBET, Dp and larger dispersion of copper. In addition, the supports of Cu/10-SiO2 catalyst have smaller particles than that of Cu/20-SiO2; thus, the migration and growth of copper species in catalysts are restrained during the reaction.

  11. Interfacial microstructure of NiSi x/HfO2/SiO x/Si gate stacks

    Gribelyuk, M.A.; Cabral, C.; Gusev, E.P.; Narayanan, V.

    2007-01-01

    Integration of NiSi x based fully silicided metal gates with HfO 2 high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi x film. Ni content varies near the NiSi/HfO x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi x /HfO 2 interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi x /HfO x was found higher than that of poly-Si/HfO 2 , likely due to compositional non-uniformity of NiSi x . No intermixing between Hf, Ni and Si beyond interfacial roughness was observed

  12. Influence of SiO2 Addition on Properties of PTFE/TiO2 Microwave Composites

    Yuan, Ying; Wang, Jie; Yao, Minghao; Tang, Bin; Li, Enzhu; Zhang, Shuren

    2018-01-01

    Composite substrates for microwave circuit applications have been fabricated by filling polytetrafluoroethylene (PTFE) polymer matrix with ceramic powder consisting of rutile TiO2 ( D 50 ≈ 5 μm) partially substituted with fused amorphous SiO2 ( D 50 ≈ 8 μm) with composition x vol.% SiO2 + (50 - x) vol.% TiO2 ( x = 0, 3, 6, 9, 12), and the effects of SiO2 addition on characteristics such as the density, moisture absorption, microwave dielectric properties, and thermal properties systematically investigated. The results show that the filler was well distributed throughout the matrix. High dielectric constant ( ɛ r > 7.19) and extremely low moisture absorption (ceramic particles served as barriers and improved the thermal stability of the PTFE polymer, retarding its decomposition. The temperature coefficient of dielectric constant ( τ ɛ ) of the composites shifted toward the positive direction (from - 309 ppm/°C to - 179 ppm/°C) as the SiO2 content was increased, while the coefficient of thermal expansion remained almost unchanged (˜ 35 ppm/°C).

  13. Synthesis of polyaniline/ZrO 2 nanocomposites and their ...

    Home; Journals; Bulletin of Materials Science; Volume 39; Issue 3. Synthesis of polyaniline/ZrO 2 nanocomposites and their performance in AC conductivity and electrochemical supercapacitance. B P PRASANNA D N AVADHANI H B MURALIDHARA K CHAITRA VINNY ROSE THOMAS M REVANASIDDAPPA N ...

  14. Surface spins disorder in uncoated and SiO2 coated maghemite nanoparticles

    Zeb, F.; Nadeem, K.; Shah, S. Kamran Ali; Kamran, M.; Gul, I. Hussain; Ali, L.

    2017-01-01

    We studied the surface spins disorder in uncoated and silica (SiO 2 ) coated maghemite (γ-Fe 2 O 3 ) nanoparticles using temperature and time dependent magnetization. The average crystallite size for SiO 2 coated and uncoated nanoparticles was about 12 and 29 nm, respectively. Scanning electron microscopy (SEM) showed that the nanoparticles are spherical in shape and well separated. Temperature scans of zero field cooled (ZFC)/field cooled (FC) magnetization measurements showed lower average blocking temperature (T B ) for SiO 2 coated maghemite nanoparticles as compared to uncoated nanoparticles. The saturation magnetization (M s ) of SiO 2 coated maghemite nanoparticles was also lower than the uncoated nanoparticles and is attributed to smaller average crystallite size of SiO 2 coated nanoparticles. For saturation magnetization vs. temperature data, Bloch's law (M(T)= M(0).(1− BT b )) was fitted well for both uncoated and SiO 2 coated nanoparticles and yields: B =3×10 −7 K -b , b=2.22 and B=0.0127 K -b , b=0.57 for uncoated and SiO 2 coated nanoparticles, respectively. Higher value of B for SiO 2 coated nanoparticles depicts decrease in exchange coupling due to enhanced surface spins disorder (broken surface bonds) as compared to uncoated nanoparticles. The Bloch's exponent b was decreased for SiO 2 coated nanoparticles which is due to their smaller average crystallite size or finite size effects. Furthermore, a sharp increase of coercivity at low temperatures (<25 K) was observed for SiO 2 coated nanoparticles which is also due to contribution of increased surface anisotropy or frozen surface spins in these smaller nanoparticles. The FC magnetic relaxation data was fitted to stretched exponential law which revealed slower magnetic relaxation for SiO 2 coated nanoparticles. All these measurements revealed smaller average crystallite size and enhanced surface spins disorder in SiO 2 coated nanoparticles than in uncoated γ-Fe 2 O 3 nanoparticles

  15. Concentration effect of Tm3+ on cathodoluminescence properties of SiO2: Tm3+ and SiO2:Ho3+, Tm3+ systems

    Dhlamini, MS

    2012-05-01

    Full Text Available .physb.2011.09.091 Concentration effect of Tm3+ on cathodoluminescence properties of SiO2: Tm 3+ and SiO2:Ho 3+, Tm3+ systems M.S. Dhlamini, G.H. Mhlongo, H.C. Swart, O.M. Ntwaeaborwa, K.T. Hillie ABSTRACT: Cathodoluminescence (CL) properties of Si...O2 powders activated with thulium (Tm3+) and holmium (Ho3+) ions prepared by a sol–gel process were investigated. Different molar concentrations of Tm3+ co-doped with Ho3+ were studied. The 460 nm peak was monitored and the influence of the beam...

  16. Study of Direct-Contact HfO2/Si Interfaces

    Noriyuki Miyata

    2012-03-01

    Full Text Available Controlling monolayer Si oxide at the HfO2/Si interface is a challenging issue in scaling the equivalent oxide thickness of HfO2/Si gate stack structures. A concept that the author proposes to control the Si oxide interface by using ultra-high vacuum electron-beam HfO2 deposition is described in this review paper, which enables the so-called direct-contact HfO2/Si structures to be prepared. The electrical characteristics of the HfO2/Si metal-oxide-semiconductor capacitors are reviewed, which suggest a sufficiently low interface state density for the operation of metal-oxide-semiconductor field-effect-transistors (MOSFETs but reveal the formation of an unexpected strong interface dipole. Kelvin probe measurements of the HfO2/Si structures provide obvious evidence for the formation of dipoles at the HfO2/Si interfaces. The author proposes that one-monolayer Si-O bonds at the HfO2/Si interface naturally lead to a large potential difference, mainly due to the large dielectric constant of the HfO2. Dipole scattering is demonstrated to not be a major concern in the channel mobility of MOSFETs.

  17. Synthesis of Fe3O4@SiO2@OSi(CH2)3NHRN(CH2PPh2)2PdCl2 type nanocomposite complexes: Highly efficient and magnetically-recoverable catalysts in vitamin K3 synthesis.

    Uruş, Serhan

    2016-12-15

    The synthesis of aminomethylphosphine-metal complexes have opened a new perspective to the catalytic applications of organic compounds. Magnetic Fe3O4 nano-core was synthesized using the closed quartz tube with Teflon cover and microwaved 200°C for 1h with power controlled instrument set to max. 600W. Novel nano-composite supported; Fe3O4@SiO2(CH2)3NHArN(CH2PPh2)2 and Fe3O4@SiO2(CH2)3N(CH2PPh2)2 type bis(diphenylphosphinomethyl)amino ligands and their Pd(II) complexes have been synthesized and characterized with FT-IR, SEM, EDX, TEM, UV-Visible, XRD and TG/DTA techniques. All the complexes were used as heterogeneous catalysts in the oxidation of 2-methyl naphthalene (2MN) to 2-methyl-1, 4-naphthoquinone (vitamin K3, menadione, 2MNQ) in the presence of hydrogen peroxide and acetic acid. Selectivity reached about 55-60% with a conversion of 90-96% using the nano-magnetite supported aminomethylphosphine-Pd(II) complexes. The complexes were very active in three times in the catalytic recycling experiments in five catalytic cycles. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. Trapping time of excitons in Si nanocrystals embedded in a SiO2 matrix

    de Jong, E. M. L. D.; de Boer, W. D. A. M.; Yassievich, I. N.; Gregorkiewicz, T.

    2017-05-01

    Silicon (Si) nanocrystals (NCs) are of great interest for many applications, ranging from photovoltaics to optoelectonics. The photoluminescence quantum yield of Si NCs dispersed in SiO2 is limited, suggesting the existence of very efficient processes of nonradiative recombination, among which the formation of a self-trapped exciton state on the surface of the NC. In order to improve the external quantum efficiency of these systems, the carrier relaxation and recombination need to be understood more thoroughly. For that purpose, we perform transient-induced absorption spectroscopy on Si NCs embedded in a SiO2 matrix over a broad probe range for NCs of average sizes from 2.5 to 5.5 nm. The self-trapping of free excitons on surface-related states is experimentally and theoretically discussed and found to be dependent on the NC size. These results offer more insight into the self-trapped exciton state and are important to increase the optical performance of Si NCs.

  19. Structural and optical properties of SiC-SiO2 nanocomposite thin films

    Bozetine, I.; Keffous, A.; Kaci, S.; Menari, H.; Manseri, A.

    2018-03-01

    This study deals with the deposition of thin films of a SiC-SiO2nanocomposite deposited on silicon substrates. The deposition is carried out by a co-sputtering RF magnetron 13.56 MHz, using two targets a polycristallin 6H-SiC and sprigs of SiO2. In order to study the influence of the deposition time on the morphology, the structural and optical properties of the thin films produced, two series of samples were prepared, namely a series A with a 30 min deposition time and a series B of one hour duration. The samples were investigated using different characterization techniques such as Scanning Electron Microscope (SEM), X-ray Diffraction (DRX), Fourier Transform Infrared Spectroscopy (FTIR), Secondary Ion Mass Spectrometry (SIMS) and photoluminescence. The results obtained, reveal an optical gap varies between 1.4 and 2.4 eV depending on the thickness of the film; thus depending on the deposition time. The SIMS profile recorded the presence of oxygen (16O) on the surface, which the signal beneath the silicon signal (28Si) and carbon (12C) signals, which confirms that the oxide (SiO2) is the first material deposited at the interface film - substrate with an a-OSiC structure. The photoluminescence (PL) measurement exhibits two peaks, centred at 390 nm due to the oxide and at 416 nm due probably to the nanocrystals of SiC crystals, note that when the deposition time increases, the intensity of the PL drops drastically, result in agreement with dense and smooth film.

  20. Photochemical process of divalent germanium responsible for photorefractive index change in GeO2-SiO2 glasses.

    Sakoh, Akifumi; Takahashi, Masahide; Yoko, Toshinobu; Nishii, Junji; Nishiyama, Hiroaki; Miyamoto, Isamu

    2003-10-20

    The photoluminescence spectra of the divalent Ge (Ge2+) center in GeO2-SiO2 glasses with different photosensitivities were investigated by means of excitation-emission energy mapping. The ultraviolet light induced photorefractivity has been correlated with the local structure around the Ge2+ centers. The glasses with a larger photorefractivity tended to exhibit a greater band broadening of the singlet-singlet transition on the higher excitation energy side accompanied by an increase in the Stokes shifts. This strongly suggests the existence of highly photosensitive Ge2+ centers with higher excitation energies. It is also found that the introduction of a hydroxyl group or boron species in GeO2-SiO2 glasses under appropriate conditions modifies the local environment of Ge2+ leading to an enhanced photorefractivity.

  1. Resonant tunneling with high peak to valley current ratio in SiO2/nc-Si/SiO2 multi-layers at room temperature

    Chen, D. Y.; Sun, Y.; He, Y. J.; Xu, L.; Xu, J.

    2014-01-01

    We have investigated carrier transport in SiO 2 /nc-Si/SiO 2 multi-layers by room temperature current-voltage measurements. Resonant tunneling signatures accompanied by current peaks are observed. Carrier transport in the multi-layers were analyzed by plots of ln(I/V 2 ) as a function of 1/V and ln(I) as a function of V 1/2 . Results suggest that besides films quality, nc-Si and barrier sub-layer thicknesses are important parameters that restrict carrier transport. When thicknesses are both small, direct tunneling dominates carrier transport, resonant tunneling occurs only at certain voltages and multi-resonant tunneling related current peaks can be observed but with peak to valley current ratio (PVCR) values smaller than 1.5. When barrier thickness is increased, trap-related and even high field related tunneling is excited, causing that multi-current peaks cannot be observed clearly, only one current peak with higher PVCR value of 7.7 can be observed. While if the thickness of nc-Si is large enough, quantum confinement is not so strong, a broad current peak with PVCR value as high as 60 can be measured, which may be due to small energy difference between the splitting energy levels in the quantum dots of nc-Si. Size distribution in a wide range may cause un-controllability of the peak voltages

  2. Surface properties of SiO2 with and without H2O2 treatment as gate dielectrics for pentacene thin-film transistor applications

    Hung, Cheng-Chun; Lin, Yow-Jon

    2018-01-01

    The effect of H2O2 treatment on the surface properties of SiO2 is studied. H2O2 treatment leads to the formation of Si(sbnd OH)x at the SiO2 surface that serves to reduce the number of trap states, inducing the shift of the Fermi level toward the conduction band minimum. H2O2 treatment also leads to a noticeable reduction in the value of the SiO2 capacitance per unit area. The effect of SiO2 layers with H2O2 treatment on the behavior of carrier transports for the pentacene/SiO2-based organic thin-film transistor (OTFT) is also studied. Experimental identification confirms that the shift of the threshold voltage towards negative gate-source voltages is due to the reduced number of trap states in SiO2 near the pentacene/SiO2 interface. The existence of a hydrogenated layer between pentacene and SiO2 leads to a change in the pentacene-SiO2 interaction, increasing the value of the carrier mobility.

  3. The application of Cu/SiO2 catalytic system in chemical mechanical planarization based on the stability of SiO2 sol

    Li Yan; Liu Yuling; Wang Aochen; Yang Zhixin; Sun Mingbin; Cheng Chuan; Zhang Yufeng; Zhang Nannan

    2014-01-01

    There is a lot of hydroxyl on the surface of nano SiO 2 sol used as an abrasive in the chemical mechanical planarization (CMP) process, and the chemical reaction activity of the hydroxyl is very strong due to the nano effect. In addition to providing a mechanical polishing effect, SiO 2 sol is also directly involved in the chemical reaction. The stability of SiO 2 sol was characterized through particle size distribution, zeta potential, viscosity, surface charge and other parameters in order to ensure that the chemical reaction rate in the CMP process, and the surface state of the copper film after CMP was not affected by the SiO 2 sol. Polarization curves and corrosion potential of different concentrations of SiO 2 sol showed that trace SiO 2 sol can effectively weaken the passivation film thickness. In other words, SiO 2 sol accelerated the decomposition rate of passive film. It was confirmed that the SiO 2 sol as reactant had been involved in the CMP process of copper film as reactant by the effect of trace SiO 2 sol on the removal rate of copper film in the CMP process under different conditions. In the CMP process, a small amount of SiO 2 sol can drastically alter the chemical reaction rate of the copper film, therefore, the possibility that Cu/SiO 2 as a catalytic system catalytically accelerated the chemical reaction in the CMP process was proposed. According to the van't Hoff isotherm formula and the characteristics of a catalyst which only changes the chemical reaction rate with out changing the total reaction standard Gibbs free energy, factors affecting the Cu/SiO 2 catalytic reaction were derived from the decomposition rate of Cu (OH) 2 and the pH value of the system, and then it was concluded that the CuSiO 3 as intermediates of Cu/SiO 2 catalytic reaction accelerated the chemical reaction rate in the CMP process. It was confirmed that the Cu/SiO 2 catalytic system generated the intermediate of the catalytic reaction (CuSiO 3 ) in the CMP process

  4. Characterization of Ni-P-SiO2 nano-composite coating on magnesium

    Sadreddini, S.; Salehi, Z.; Rassaie, H.

    2015-01-01

    In this study, the effects of SiO2 nanoparticles added to the electroless Ni-P coating were studied. The surface morphology, corrosion behavior, hardness and porosity of Ni-P-SiO2composite were investigated. The related microstructure was investigated through field emission scanning electron microscopy (FESEM) and the amount of SiO2 was examined by Energy Dispersive Analysis of X-ray (EDX). The corrosion behavior was evaluated through electrochemical impedance spectroscopy (EIS) and polarization techniques. The results illustrated that with increasing the quantity of the SiO2 nanoparticles, the corrosion rate decreased and the hardness increased.

  5. Magnetic SiO2/Fe3O4 colloidal crystals

    Huang, C-K; Hou, C-H; Chen, C-C; Tsai, Y-L; Chang, L-M; Wei, H-S; Hsieh, K-H; Chan, C-H

    2008-01-01

    We proposed a novel technique to fabricate colloidal crystals by using monodisperse SiO 2 coated magnetic Fe 3 O 4 (SiO 2 /Fe 3 O 4 ) microspheres. The magnetic SiO 2 /Fe 3 O 4 microspheres with a diameter of 700 nm were synthesized in the basic condition with ferric sulfate, ferrous sulfate, tartaric acid and tetraethyl orthosilicate (TEOS) in the reaction system. Monodisperse SiO 2 /Fe 3 O 4 superparamagnetic microspheres have been successfully used to fabricate colloidal crystals under the existing magnetic field

  6. Adsorption of cationic dye on a biohybrid SiO2-alginate

    Barrón Zambrano, J A; Ávila Ortega, A; Muñoz Rodríguez, D; Carrera Figueiras, C; López-Pérez, A J

    2013-01-01

    In this work, a biohybrid material based on SiO 2 -alginate was obtained and its properties of adsorption evaluated using methylene blue as a model dye. The experimental results showed that the biohybrid SiO 2 -alginate has a higher adsorption ability compared to their base compounds (SiO 2 and alginate). Methylene blue adsorption is pH dependent, resulting in a maximum adsorption at pH = 8. The sorption kinetics rate is similar to SiO 2 . Kinetic data were fitted to a model of pseudosecond order. The experimental isotherms fit well the Langmuir model.

  7. Effects of nano-SiO2 on the adsorption of chiral metalaxyl to agricultural soils.

    Huang, Junxing; Liang, Chuanzhou; Zhang, Xu

    2017-06-01

    The application of nanotechnology in agriculture, pesticide delivery and other related fields increases the occurrence of engineered nanoparticles (ENPs) in soil. Since ENPs have larger surface areas and normally a high adsorption capacity for organic pollutants, they are thought to influence the transport of pesticides in soils and thereafter influence the uptake and transformation of pesticides. The adsorption pattern of racemic-metalaxyl on agricultural soils including kinetics and isotherms changed in the presence of nano-SiO 2 . The adsorption of racemic-metalaxyl on agricultural soil was not enantioselective, in either the presence or the absence of SiO 2 . The adsorption of racemic-metalaxyl on SiO 2 decreased to some extent in soil-SiO 2 mixture, and the absolute decrease was dependent on soil properties. The decreased adsorption of metalaxyl on SiO 2 in soil-SiO 2 mixture arose from the competitive adsorption of soil-dissolved organic matter and the different dispersion and aggregation behaviors of SiO 2 in the presence of soil. Interactions between SiO 2 and soil particles also contributed to the decreased adsorption of metalaxyl on SiO 2 , and the interactions were analyzed by extended Derjaguin-Landau-Verwey-Overbeek theory. The results showed that the presence of nano-particles in soils could decrease the mobility of pesticides in soils and that this effect varied with different soil compositions. Copyright © 2017 Elsevier Ltd. All rights reserved.

  8. Theoretical prediction of Grüneisen parameter for SiO_2.TiO_2 bulk metallic glasses

    Singh, Chandra K.; Pandey, Brijesh K.; Pandey, Anjani K.

    2016-01-01

    The Grüneisen parameter (γ) is very important to decide the limitations for the prediction of thermoelastic properties of bulk metallic glasses. It can be defined in terms of microscopic and macroscopic parameters of the material in which former is based on vibrational frequencies of atoms in the material while later is closely related to its thermodynamic properties. Different formulation and equation of states are used by the pioneer researchers of this field to predict the true sense of Gruneisen parameter for BMG but for SiO_2.TiO_2 very few and insufficient information is available till now. In the present work we have tested the validity of two different isothermal EOS viz. Poirrior-Tarantola EOS and Usual-Tait EOS to predict the true value of Gruneisen parameter for SiO_2.TiO_2 as a function of compression. Using different thermodynamic limitations related to the material constraints and analyzing obtained result it is concluded that the Poirrior-Tarantola EOS gives better numeric values of Grüneisen parameter (γ) for SiO_2.TiO_2 BMG.

  9. Effects of deposition rates on laser damage threshold of TiO2/SiO2 high reflectors

    Yao Jianke; Xu Cheng; Ma Jianyong; Fang Ming; Fan Zhengxiu; Jin Yunxia; Zhao Yuanan; He Hongbo; Shao Jianda

    2009-01-01

    TiO 2 single layers and TiO 2 /SiO 2 high reflectors (HR) are prepared by electron beam evaporation at different TiO 2 deposition rates. It is found that the changes of properties of TiO 2 films with the increase of rate, such as the increase of refractive index and extinction coefficient and the decrease of physical thickness, lead to the spectrum shift and reflectivity bandwidth broadening of HR together with the increase of absorption and decrease of laser-induced damage threshold. The damages are found of different morphologies: a shallow pit to a seriously delaminated and deep crater, and the different amorphous-to-anatase-to-rutile phase transition processes detected by Raman study. The frequency shift of Raman vibration mode correlates with the strain in film. Energy dispersive X-ray analysis reveals that impurities and non-stoichiometric defects are two absorption initiations resulting to the laser-induced transformation.

  10. Positive magnetoresistance in Co40Fe40B20/SiO2/Si heterostructure

    Zhang, Y.

    2016-07-20

    Current-perpendicular-to-plane electronic transport properties and magnetoresistance of amorphous Co40Fe40B20/SiO2/Si heterostructures are investigated systematically. A backward diode-like rectifying behavior was observed due to the formation of a Schottky barrier between Co40Fe40B20 and Si. The junction resistance shows a metal-insulator transition with decreasing temperature in both the forward and reverse ranges. A large positive magnetoresistance (MR) of ∼2300% appears at 200 K. The positive MR can be attributed to the magnetic-field-controlled impact ionization process of carriers. MR shows a temperature-peak-type character under a constant bias current, which is related to the spin-dependent barrier in the Si near the interface. © CopyrightEPLA, 2016.

  11. Positive magnetoresistance in Co40Fe40B20/SiO2/Si heterostructure

    Zhang, Y.; Mi, W. B.; Zhang, Xixiang

    2016-01-01

    Current-perpendicular-to-plane electronic transport properties and magnetoresistance of amorphous Co40Fe40B20/SiO2/Si heterostructures are investigated systematically. A backward diode-like rectifying behavior was observed due to the formation of a Schottky barrier between Co40Fe40B20 and Si. The junction resistance shows a metal-insulator transition with decreasing temperature in both the forward and reverse ranges. A large positive magnetoresistance (MR) of ∼2300% appears at 200 K. The positive MR can be attributed to the magnetic-field-controlled impact ionization process of carriers. MR shows a temperature-peak-type character under a constant bias current, which is related to the spin-dependent barrier in the Si near the interface. © CopyrightEPLA, 2016.

  12. Synthesis and characterization of erbium-doped SiO2-TiO2 thin films prepared by sol-gel and dip-coating techniques onto commercial glass substrates as a route for obtaining active GRadient-INdex materials

    Gómez-Varela, Ana I.; Castro, Yolanda; Durán, Alicia; De Beule, Pieter A.A.; Flores-Arias, María T.; Bao-Varela, Carmen

    2015-01-01

    In this work, SiO 2 -TiO 2 films doped with erbium were prepared by dip-coating sol-gel process onto commercial glass substrates. The surface morphology of the films was characterized using atomic force microscopy, while thickness, refractive index, extinction coefficient and porosity of the films were determined by ellipsometric measurements in a wavelength region of 400-1000 nm. Optical constants and porosity were found to vary with erbium concentration. The proof of principle presented in this paper is applicable to systems of different nature by tailoring the sol-gel precursors in such a way that active GRadient-INdex media described by a complex, parabolic-like refractive index distribution for beam shaping purposes is obtained. - Highlights: • Sol-gel route for preparation of active GRadient-INdex materials is proposed. • SiO 2 -TiO 2 films doped with erbium were prepared by dipping onto commercial glasses. • Morphological and optical characterization of the samples was performed. • Optical constants and porosity were found to vary with erbium concentration. • Refractive index diminishes with dopant content; the contrary occurs for porosity

  13. Beyond sixfold coordinated Si in SiO2 glass at ultrahigh pressures.

    Prescher, Clemens; Prakapenka, Vitali B; Stefanski, Johannes; Jahn, Sandro; Skinner, Lawrie B; Wang, Yanbin

    2017-09-19

    We investigated the structure of SiO 2 glass up to 172 GPa using high-energy X-ray diffraction. The combination of a multichannel collimator with diamond anvil cells enabled the measurement of structural changes in silica glass with total X-ray diffraction to previously unachievable pressures. We show that SiO 2 first undergoes a change in Si-O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. Si-O bond length shows first an increase due to the fourfold to sixfold coordination change and then a smaller linear decrease up to 172 GPa. We reconcile the changes in relation to the oxygen-packing fraction, showing that oxygen packing decreases at ultrahigh pressures to accommodate the higher than sixfold Si-O coordination. These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures.

  14. Formation of metallic Si and SiC nanoparticles from SiO2 particles by plasma-induced cathodic discharge electrolysis in chloride melt

    Tokushige, M.; Tsujimura, H.; Nishikiori, T.; Ito, Y.

    2013-01-01

    Silicon nanoparticles are formed from SiO 2 particles by conducting plasma-induced cathodic discharge electrolysis. In a LiCl–KCl melt in which SiO 2 particles were suspended at 450 °C, we obtained Si nanoparticles with diameters around 20 nm. During the electrolysis period, SiO 2 particles are directly reduced by discharge electrons on the surface of the melt just under the discharge, and the deposited Si atom clusters form Si nanoparticles, which leave the surface of the original SiO 2 particle due to free spaces caused by a molar volume difference between SiO 2 and Si. We also found that SiC nanoparticles can be obtained using carbon anode. Based on Faraday's law, the current efficiency for the formation of Si nanoparticles is 70%

  15. Synthesis and green up-conversion fluorescence of colloidal La0.78Yb0.20Er0.02F3/SiO2 core/shell nanocrystals

    Wang Yan; Qin Weiping; Zhang Jisen; Cao Chunyan; Zhang Jishuang; Jin Ye; Zhu Peifen; Wei Guodong; Wang Guofeng; Wang Lili

    2007-01-01

    Water-soluble PVP-stabilized hexagonal-phase La 0.78 Yb 0.20 Er 0.02 F 3 nanocrystals (NCs) were synthesized by hydrothermal method. The NCs were coated with a very thin silica shell, and amino groups were introduced to the surface of silica shells by copolymerization of 3-aminopropyl(triethoxy)silane. The core/shell NCs can be dispersed in ethanol and water to form stable colloidal solution. The transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the core/shell materials. In addition, the green up-conversion fluorescence mechanism of La 0.78 Yb 0.20 Er 0.02 F 3 /SiO 2 NCs was studied with a 980-nm diode laser as excitation source. The water solubility, small core/shell particles size, and well colloidal stability mean the green up-conversion fluorescence NCs have potential applications in bioassay. - Graphical abstract: Colloidal La 0.78 Yb 0.20 Er 0.02 F 3 /SiO 2 Core/Shell nanocrystals (NCs) were synthesized and the free amino groups were introduced to the surface of silica shells by copolymerization 3-aminopropyl(triethoxy)silane. The NCs can be dispersed in ethanol and water to form stable colloidal solution. In addition, the NCs exhibit green up-conversion fluorescence under 980-nm excitation

  16. In Situ Synthesis of Poly(methyl methacrylate/SiO2 Hybrid Nanocomposites via “Grafting Onto” Strategy Based on UV Irradiation in the Presence of Iron Aqueous Solution

    Hong Zhang

    2012-01-01

    Full Text Available Poly(methyl methacrylate/SiO2 (PMMA/SiO2 hybrid composites were prepared via “grafting onto” strategy based on UV irradiation in the presence of iron aqueous solution. Two steps were used to graft polymethyl methacrylate (PMMA onto the surface of nanosilica, anchoring 3-(methacryloxy propyl trimethoxysilane (MPTS onto the surface of nanosilica to modify it with double bonds, and then grafting PMMA onto the surface of nanosilica with FeCl3 as photoinitiator. The products were characterized by FT-IR, TGA, TEM, DLS, and XPS. The results showed that it is easy to graft PMMA onto the surface of nanosilica under UV irradiation, and the hybrid particles are monodisperse and have core-shell structure with nanosilica as the core and PMMA layers as the shell. Furthermore, the products initiated by FeCl3 have higher monomer conversion, percent grafting, and better monodispersion compared with the products initiated by traditional photoinitiator such as 2-hydroxy-4-(2-hydroxyethoxy-2-methyl-propiophenone (Irgacure 2959.

  17. Study of strained-Si p-channel MOSFETs with HfO2 gate dielectric

    Pradhan, Diana; Das, Sanghamitra; Dash, Tara Prasanna

    2016-10-01

    In this work, the transconductance of strained-Si p-MOSFETs with high-K dielectric (HfO2) as gate oxide, has been presented through simulation using the TCAD tool Silvaco-ATLAS. The results have been compared with a SiO2/strained-Si p-MOSFET device. Peak transconductance enhancement factors of 2.97 and 2.73 has been obtained for strained-Si p-MOSFETs in comparison to bulk Si channel p-MOSFETs with SiO2 and high-K dielectric respectively. This behavior is in good agreement with the reported experimental results. The transconductance of the strained-Si device at low temperatures has also been simulated. As expected, the mobility and hence the transconductance increases at lower temperatures due to reduced phonon scattering. However, the enhancements with high-K gate dielectric is less as compared to that with SiO2.

  18. Characterization of modified SiC@SiO2 nanocables/MnO2 and their potential application as hybrid electrodes for supercapacitors.

    Zhang, Yujie; Chen, Junhong; Fan, Huili; Chou, Kuo-Chih; Hou, Xinmei

    2015-12-14

    In this research, we demonstrate a simple route for preparing SiC@SiO2 core-shell nanocables and furthermore obtain SiC@SiO2 nanocables/MnO2 as hybrid electrodes for supercapacitors using various modified methods. The modified procedure consists of mild modifications using sodium hydroxide as well as UV light irradiation and deposition of MnO2. The morphology and microstructural characteristics of the composites are investigated using XRD, XPS, FE-SEM with EDS and TEM. The results indicate that the surfaces of modified SiC@SiO2 nanocables are uniformly coated with a MnO2 thin layer. The electrochemical behaviors of the hybrid electrodes are systematically measured in a three-electrode system using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The resultant electrode presents a superb charge storage characteristic with a large specific capacitance of 276.3 F g(-1) at the current density of 0.2 A g(-1). Moreover, the hybrid electrode also displays a long cycle life with a good capacitance retention (∼92.0%) after 1000 CV cycles, exhibiting a promising potential for supercapacitors.

  19. Design of flexible PANI-coated CuO-TiO2-SiO2 heterostructure nanofibers with high ammonia sensing response values

    Pang, Zengyuan; Nie, Qingxin; Lv, Pengfei; Yu, Jian; Huang, Fenglin; Wei, Qufu

    2017-06-01

    We report a room-temperature ammonia sensor with extra high response values and ideal flexibility, including polyaniline (PANI)-coated titanium dioxide-silicon dioxide (TiO2-SiO2) or copper oxide-titanium dioxide-silicon dioxide (CuO-TiO2-SiO2) composite nanofibers. Such flexible inorganic TiO2-SiO2 and CuO-TiO2-SiO2 composite nanofibers were prepared by electrospinning, followed by calcination. Then, in situ polymerization of aniline monomers was carried out with inorganic TiO2-SiO2 and CuO-TiO2-SiO2 composite nanofibers as templates. Gas sensing tests at room temperature indicated that the obtained CuO-TiO2-SiO2/PANI composite nanofibers had much higher response values to ammonia gas (ca. 45.67-100 ppm) than most of those reported before as well as the prepared TiO2-SiO2/PANI composite nanofibers here. These excellent sensing properties may be due to the P-N, P-P heterojunctions and a structure similar to field-effect transistors formed on the interfaces between PANI, TiO2, and CuO, which is p-type, n-type, and p-type semiconductor, respectively. In addition, the prepared free-standing CuO-TiO2-SiO2/PANI composite nanofiber membrane was easy to handle and possessed ideal flexibility, which is promising for potential applications in wearable sensors in the future.

  20. Effects of SiO2 and TiO2 fillers on thermal and dielectric properties ...

    Administrator

    eco-friendly bismuth glass microcomposites of plasma display panels. SHIV PRAKASH SINGH ... MS received 12 November 2008; revised 18 March 2009. Abstract. The effects .... In view of above, in this paper we report the effects of. SiO2 (amorphous) ..... mic Membrane Sections of this institute for carrying out the XRD and ...

  1. Core shell structured nanoparticles of Eu3+ doped SnO2 with SiO2 shell: luminescence studies

    Ningthoujam, R.S.; Sudarsan, V.; Kulshreshtha, S.K.

    2005-01-01

    Re dispersible SnO 2 nanoparticles with and without Eu 3+ doping nanoparticles were prepared at 185 deg C by the urea hydrolysis of Sn 4+ in ethylene glycol medium. X-ray diffraction and 119 Sn MAS NMR studies of these particles revealed that these nanoparticles are crystalline with Cassiterite structure having an average crystallite size of 7 nm. Undoped SnO 2 gave a emission peak centered around 470 nm characteristic of the traps present in the nanoparticles. For Eu 3+ doped samples, emission around 590 and 615 nm was observed on both direct excitation as well as indirect excitation through traps, indicating that there is an energy transfer between the traps present in the nanoparticles and Eu 3+ ions. The asymmetric ratio of luminescence (relative intensity ratio of 590 to 615 nm transitions) has been found to be 1.2. For SnO 2 :Eu(5%)-SiO 2 nanoparticles, the asymmetric ratio of luminescence change significantly indicating the formation of nanoparticles with SnO 2 :Eu(5%) core covered with SiO 2 shell. (author)

  2. Study of SiO2-Si and metal-oxide-semiconductor structures using positrons

    Leung, T. C.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K. G.

    1993-01-01

    Studies of SiO2-Si and metal-oxide-semiconductor (MOS) structures using positrons are summarized and a concise picture of the present understanding of positrons in these systems is provided. Positron annihilation line-shape S data are presented as a function of the positron incident energy, gate voltage, and annealing, and are described with a diffusion-annihilation equation for positrons. The data are compared with electrical measurements. Distinct annihilation characteristics were observed at the SiO2-Si interface and have been studied as a function of bias voltage and annealing conditions. The shift of the centroid (peak) of γ-ray energy distributions in the depletion region of the MOS structures was studied as a function of positron energy and gate voltage, and the shifts are explained by the corresponding variations in the strength of the electric field and thickness of the depletion layer. The potential role of the positron annihilation technique as a noncontact, nondestructive, and depth-sensitive characterization tool for the technologically important, deeply buried interface is shown.

  3. Study of SiO2-Si and metal-oxide-semiconductor structures using positrons

    Leung, T.C.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K.G.

    1993-01-01

    Studies of SiO 2 -Si and metal-oxide-semiconductor (MOS) structures using positrons are summarized and a concise picture of the present understanding of positrons in these systems is provided. Positron annihilation line-shape S data are presented as a function of the positron incident energy, gate voltage, and annealing, and are described with a diffusion-annihilation equation for positrons. The data are compared with electrical measurements. Distinct annihilation characteristics were observed at the SiO 2 -Si interface and have been studied as a function of bias voltage and annealing conditions. The shift of the centroid (peak) of γ-ray energy distributions in the depletion region of the MOS structures was studied as a function of positron energy and gate voltage, and the shifts are explained by the corresponding variations in the strength of the electric field and thickness of the depletion layer. The potential role of the positron annihilation technique as a noncontact, nondestructive, and depth-sensitive characterization tool for the technologically important, deeply buried interface is shown

  4. BAND ALIGNMENT OF ULTRATHIN GIZO/SiO2/Si HETEROSTRUCTURE DETERMINED BY ELECTRON SPECTROSCOPY

    Hee Jae Kang2

    2011-11-01

    Full Text Available Amorphous GaInZnO (GIZO thin films are grown on SiO2/Si substrate by the RF magnetron sputtering method. By thecombination of measured band gaps from reflection energy loss spectroscopy (REELS spectra and valence band fromX-ray photo-electron spectroscopy (XPS spectra, we have demonstrated the energy band alignment of GIZO thin films.The band gap values are 3.2 eV, 3.2 eV, 3.4eV and 3.6eV for the concentration ratios of Ga: In: Zn in GIZO thin filmsare 1:1:1, 2:2:1, 3:2:1 and 4:2:1, respectively. These are attributed to the larger band gap energy of Ga2O3 comparedwith In2O3 and ZnO. The valence band offsets (ΔEv decrease from 2.18 to 1.68 eV with increasing amount of Ga inGIZO thin films for GIZO1 to GIZO4, respectively. These experimental values of band gap and valence band offsetwill provide the further understanding in the fundamental properties of GIZO/SiO2/Si heterostructure, which will beuseful in the design, modeling and analysis of the performance devices applications.

  5. Magneto-transport phenomena in metal/SiO2/n(p)-Si hybrid structures

    Volkov, N. V.; Tarasov, A. S.; Rautskii, M. V.; Lukyanenko, A. V.; Bondarev, I. A.; Varnakov, S. N.; Ovchinnikov, S. G.

    2018-04-01

    Present review touches upon a subject of magnetotransport phenomena in hybrid structures which consist of ferromagnetic or nonmagnetic metal layer, layer of silicon oxide and silicon substrate with n- or p-type conductivity. Main attention will be paid to a number gigantic magnetotransport effects discovered in the devices fabricated on the base of the M/SiO2/n(p)-Si (M is ferromagnetic or paramagnetic metal) hybrid structures. These effects include bias induced dc magnetoresistance, gigantic magnetoimpedance, dc magnetoresistance induced by an optical irradiation and lateral magneto-photo-voltaic effect. The magnetoresistance ratio in ac and dc modes for some of our devices can exceed 106% in a magnetic field below 1 T. For lateral magneto-photo-voltaic effect, the relative change of photo-voltage in magnetic field can reach 103% at low temperature. Two types of mechanisms are responsible for sensitivity of the transport properties of the silicon based hybrid structures to magnetic field. One is related to transformation of the energy structure of the (donor) acceptor states including states near SiO2/n(p)-Si interface in magnetic field. Other mechanism is caused by the Lorentz force action. The features in behaviour of magnetotransport effects in concrete device depend on composition of the used structure, device topology and experimental conditions (bias voltage, optical radiation and others). Obtained results can be base for design of some electronic devices driven by a magnetic field. They can also provide an enhancement of the functionality for existing sensors.

  6. Silicon electrodeposition from chloride-fluoride melts containing K2SiF6 and SiO2

    Zhuk Sergey I.

    2017-01-01

    Full Text Available Silicon electrodeposition on glassy carbon from the KF-KCl-K2SiF6, KF-KCl-K2SiF6-KOH and KF-KCl-K2SiF6-SiO2 melts was studied by the cyclic voltammetry. Тhe electroreduction of Si(IV to metallic Si was observed as a single 4-electron wave under all considered conditions. The reactions of cathode reduction of silicon from fluoride and oxyfluoride complexes were suggested. It was shown that the process can be controlled by the preliminary transformation of SiO44- to SiF62- and SiOxFyz-. The influence of the current density on structure and morphology of silicon deposits obtained during galvanostatic electrolysis of the KF-KCl-K2SiF6-SiO2 melt was studied.

  7. Volume labeling with Alexa Fluor dyes and surface functionalization of highly sensitive fluorescent silica (SiO2) nanoparticles

    Wang, Wei; Nallathamby, Prakash D.; Foster, Carmen M.; Morrell-Falvey, Jennifer L.; Mortensen, Ninell P.; Doktycz, Mitchel J.; Gu, Baohua; Retterer, Scott T.

    2013-10-01

    A new synthesis approach is described that allows the direct incorporation of fluorescent labels into the volume or body of SiO2 nanoparticles. In this process, fluorescent Alexa Fluor dyes with different emission wavelengths were covalently incorporated into the SiO2 nanoparticles during their formation by the hydrolysis of tetraethoxysilane. The dye molecules were homogeneously distributed throughout the SiO2 nanoparticles. The quantum yields of the Alexa Fluor volume-labeled SiO2 nanoparticles were much higher than nanoparticles labeled using conventional organic dyes. The size of the resulting nanoparticles was controlled using microemulsion reaction media with sizes in the range of 20-100 nm and a polydispersity of cultured macrophages. Differences in particle agglomeration and cell association were clearly associated with differences in observed nanoparticle toxicity. The capacity to maintain particle fluorescence while making significant changes to surface chemistry makes these particles extremely versatile and useful for studies of particle agglomeration, uptake, and transport in environmental and biological systems.A new synthesis approach is described that allows the direct incorporation of fluorescent labels into the volume or body of SiO2 nanoparticles. In this process, fluorescent Alexa Fluor dyes with different emission wavelengths were covalently incorporated into the SiO2 nanoparticles during their formation by the hydrolysis of tetraethoxysilane. The dye molecules were homogeneously distributed throughout the SiO2 nanoparticles. The quantum yields of the Alexa Fluor volume-labeled SiO2 nanoparticles were much higher than nanoparticles labeled using conventional organic dyes. The size of the resulting nanoparticles was controlled using microemulsion reaction media with sizes in the range of 20-100 nm and a polydispersity of cultured macrophages. Differences in particle agglomeration and cell association were clearly associated with differences in

  8. Photocatalytic properties of Au-deposited mesoporous SiO_2–TiO_2 photocatalyst under simultaneous irradiation of UV and visible light

    Okuno, T.; Kawamura, G.; Muto, H.; Matsuda, A.

    2016-01-01

    Mesoporous SiO_2 templates deposited TiO_2 nanocrystals are synthesized via a sol–gel route, and Au nanoparticles (NPs) are deposited in the tubular mesopores of the templates by a photodeposition method (Au/SiO_2–TiO_2). The photocatalytic characteristics of Au/SiO_2–TiO_2 are discussed with the action spectra of photoreactions of 2-propanol and methylene blue. Photocatalytic activities of SiO_2–TiO_2 under individual ultraviolet (UV) and visible (Vis) light illumination are enhanced by deposition of Au NPs. Furthermore, Au/SiO_2–TiO_2 shows higher photocatalytic activities under simultaneous irradiation of UV and Vis light compared to the activity under individual UV and Vis light irradiation. Since the photocatalytic activity under simultaneous irradiation is almost the same as the total activities under individual UV and Vis light irradiation, it is concluded that the electrons and the holes generated by lights of different wavelengths are efficiently used for photocatalysis without carrier recombination. - Graphical abstract: This graphic shows the possible charge behavior in Au/SiO_2–TiO_2 under independent light irradiation of ultraviolet and visible light irradiation. Both reactions under independent UV and Vis light irradiation occurred in parallel when Au/SiO_2–TiO_2 photocatalyst was illuminated UV and Vis light simultaneously, and then photocatalytic activity is improved by simultaneous irradiation. - Highlights: • Au nanoparticles were deposited in mesoporous SiO_2–TiO_2 by a photodeposition method. • Photocatalytic activity under UV and Vis light was enhanced by deposition of Au. • Photocatalytic activity of Au/SiO_2–TiO_2 was improved by simultaneous irradiation.

  9. SiO 2/SiC interface proved by positron annihilation

    Maekawa, M.; Kawasuso, A.; Yoshikawa, M.; Itoh, H.

    2003-06-01

    We have studied positron annihilation in a Silicon carbide (SiC)-metal/oxide/semiconductor (MOS) structure using a monoenergetic positron beam. The Doppler broadening of annihilation quanta were measured as functions of the incident positron energy and the gate bias. Applying negative gate bias, significant increases in S-parameters were observed. This indicates the migration of implanted positrons towards SiO 2/SiC interface and annihilation at open-volume type defects. The behavior of S-parameters depending on the bias voltage was well correlated with the capacitance-voltage ( C- V) characteristics. We observed higher S-parameters and the interfacial trap density in MOS structures fabricated using the dry oxidation method as compared to those by pyrogenic oxidation method.

  10. SiO2/SiC interface proved by positron annihilation

    Maekawa, M.; Kawasuso, A.; Yoshikawa, M.; Itoh, H.

    2003-01-01

    We have studied positron annihilation in a Silicon carbide (SiC)-metal/oxide/semiconductor (MOS) structure using a monoenergetic positron beam. The Doppler broadening of annihilation quanta were measured as functions of the incident positron energy and the gate bias. Applying negative gate bias, significant increases in S-parameters were observed. This indicates the migration of implanted positrons towards SiO 2 /SiC interface and annihilation at open-volume type defects. The behavior of S-parameters depending on the bias voltage was well correlated with the capacitance-voltage (C-V) characteristics. We observed higher S-parameters and the interfacial trap density in MOS structures fabricated using the dry oxidation method as compared to those by pyrogenic oxidation method

  11. Assembly of Fe3O4 nanoparticles on SiO2 monodisperse spheres

    Assembly of Fe3O4 nanoparticles on SiO2 monodisperse spheres. K C BARICK and D BAHADUR*. Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay,. Mumbai 400 076, India. Abstract. The assembly of superparamagnetic Fe3O4 nanoparticles on submicroscopic SiO2 ...

  12. Excimer laser crystallization of InGaZnO4 on SiO2 substrate

    Chen, T.; Wu, M.Y.; Ishihara, R.; Nomura, K.; Kamiya, T.; Hosono, H.; Beenakker, C.I.M.

    2011-01-01

    In this paper, we were able to crystallize InGaZnO4 (IGZO) by excimer laser on SiO2 substrate. It was observed that uniform [0001] textured polycrystalline IGZO film has been obtained without any grain boundaries and oxygen vacancies on SiO2 substrate. This process is very promising in fabricating

  13. Hopping conduction on PPy/SiO2 nanocomposites obtained via in situ emulsion polymerization

    Rubinger, C.P.L.; Costa, L.C.; Carvalho Esteves, de A.C.; Barros-Timmons, A.M.M.V.

    2008-01-01

    This work describes the preparation and electrical characterization of conducting polypyrrole (PPy) and silica nanocomposites. Four samples were investigated: (i) pure PPy, (ii) PPy-covered SiO2 spherical nanoparticles, (iii) PPy-covered SiO2 spherical nanoparticles modified with

  14. Water droplet behavior on superhydrophobic SiO2 nanocomposite films during icing/deicing cycles

    Lazauskas, A.; Guobiene, A.; Prosycevas, I.; Baltrusaitis, V.; Grigaliunas, V.; Narmontas, P.; Baltrusaitis, Jonas

    2013-01-01

    This work investigates water droplet behavior on superhydrophobic (water contact angle value of 162 ± 1°) SiO2 nanocomposite films subjected to repetitive icing/deicing treatments, changes in SiO2 nanocomposite film surface morphology and their non-wetting characteristics. During the experiment,

  15. TiO2, SiO2 and ZrO2 Nanoparticles Synergistically Provoke Cellular Oxidative Damage in Freshwater Microalgae

    Yinghan Liu

    2018-02-01

    Full Text Available Metal-based nanoparticles (NPs are the most widely used engineered nanomaterials. The individual toxicities of metal-based NPs have been plentifully studied. However, the mixture toxicity of multiple NP systems (n ≥ 3 remains much less understood. Herein, the toxicity of titanium dioxide (TiO2 nanoparticles (NPs, silicon dioxide (SiO2 NPs and zirconium dioxide (ZrO2 NPs to unicellular freshwater algae Scenedesmus obliquus was investigated individually and in binary and ternary combination. Results show that the ternary combination systems of TiO2, SiO2 and ZrO2 NPs at a mixture concentration of 1 mg/L significantly enhanced mitochondrial membrane potential and intracellular reactive oxygen species level in the algae. Moreover, the ternary NP systems remarkably increased the activity of the antioxidant defense enzymes superoxide dismutase and catalase, together with an increase in lipid peroxidation products and small molecule metabolites. Furthermore, the observation of superficial structures of S. obliquus revealed obvious oxidative damage induced by the ternary mixtures. Taken together, the ternary NP systems exerted more severe oxidative stress in the algae than the individual and the binary NP systems. Thus, our findings highlight the importance of the assessment of the synergistic toxicity of multi-nanomaterial systems.

  16. Evaluation of micro-abrasion-corrosion on SiO2-TiO2-ZrO2 coatings synthesized by the sol-gel method

    Bautista Ruiz, J.; Aperador, W.; Caballero Gómez, J.

    2016-02-01

    The medical science and the engineering, work to improve the materials used in the manufacture of joint implants, since they have a direct impact on the quality of people life. The surgical interventions are increasing worldwide with a high probability of a second or even a third intervention. Around these circumstances, it was evaluated the behaviour against microabrasion-corrosion phenomena on SiO2 TiO2 ZrO2 coatings, synthesized by the sol-gel method with concentration of the Si/Ti/Zr precursors: 10/70/20 and 10/20/70. The coatings were deposited on AISI 316 LVM stainless steel substrates. The morphological characterization of the wear was made by AFM techniques. It was observed that the coatings with higher levels of titanium have a good response to the phenomena of microabrasion-corrosion.

  17. In vivo immuno-reactivity analysis of the porous three-dimensional chitosan/SiO2 and chitosan/SiO2 /hydroxyapatite hybrids.

    Guo, Mengxia; Dong, Yifan; Xiao, Jiangwei; Gu, Ruicai; Ding, Maochao; Huang, Tao; Li, Junhua; Zhao, Naru; Liao, Hua

    2018-05-01

    Inorganic/organic hybrid silica-chitosan (CS) scaffolds have promising potential for bone defect repair, due to the controllable mechanical properties, degradation behavior, and scaffold morphology. However, the precise in vivo immuno-reactivity of silica-CS hybrids with various compositions is still poorly defined. In this study, we fabricated the three-dimensional (3D) interconnected porous chitosan-silica (CS/SiO 2 ) and chitosan-silica-hydroxyapatite (CS/SiO 2 /HA) hybrids, through sol-gel process and 3D plotting skill, followed by the naturally or freeze drying separately. Scanning electron microscopy demonstrated the hybrids possessed the uniform geometric structure, while, transmission electron microscopy displayed nanoscale silica, or HA nanoparticles dispersed homogeneously in the CS matrix, or CS/silica hybrids. After intramuscular implantation, CS/SiO 2 and CS/SiO 2 /HA hybrids triggered a local and limited monocyte/macrophage infiltration and myofiber degeneration. Naturally dried CS/SiO 2 hybrid provoked a more severe inflammation than the freeze-dried ones. Dendritic cells were attracted to invade into the implants embedded-muscle, but not be activated to prime the adaptive immunity, because the absence of cytotoxic T cells and B cells in muscle received the implants. Fluorescence-activated cell sorting (FACS) analysis indicated the implanted hybrids were incapable to initiate splenocytes activation. Plasma complement C3 enzyme linked immunosorbent assay (ELISA) assay showed the hybrids induced C3 levels increase in early implanting phase, and the subsequent striking decrease. Thus, the present results suggest that, in vivo, 3D plotted porous CS/SiO 2 and CS/SiO 2 /HA hybrids are relatively biocompatible in vivo, which initiate a localized inflammatory procedure, instead of a systematic immune response. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1223-1235, 2018. © 2018 Wiley Periodicals, Inc.

  18. Molybdenum oxide supported on silica (MoO3/SiO2): an efficient and reusable catalyst for the synthesis of 1,8-dioxodecahydroacridines under solvent-free conditions

    Khojastehnezhad, A.; Vafaei, M.; Moeinpour, F.

    2014-01-01

    Silica supported molybdenum oxide (MoO 3 /SiO 2 ) was found to be and efficient, eco-friendly and heterogeneous catalyst for the multicomponent reaction of aromatic aldehydes, dimedone and ammonium acetate or aromatic amines under solvent-free conditions to afford the corresponding 1,8-dioxodecahydroacridines in high yields. The catalyst can be easily recovered and reused for several times without considerable loss of activity. Furthermore, the present method offers several advantages, such as an easy experimental and work-up procedures, short reaction times and good to excellent yields. For the characterization were used: Fourier transform infrared spectroscopy (Ft-IR), X-ray diffraction and scanning electron microscopy analyses. (Author)

  19. Synthesis, bioactivity and preliminary biocompatibility studies of glasses in the system CaO-MgO-SiO2-Na2O-P2O5-CaF2.

    Tulyaganov, D U; Agathopoulos, S; Valerio, P; Balamurugan, A; Saranti, A; Karakassides, M A; Ferreira, J M F

    2011-02-01

    New compositions of bioactive glasses are proposed in the CaO-MgO-SiO(2)-Na(2)O-P(2)O(5)-CaF(2) system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO(4)) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts' cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C).

  20. Synthesis and characterization of 64SiO2-26CaO-5P2O5-5CuO bioactive composition for the growth of hydroxyapatite layer by XRD, Raman and pH studies

    Kaur, Pardeep; Singh, K. J.

    2016-05-01

    Bioactive sample with the nominal composition of 64SiO2-26CaO-5P2O5-5CuO has been prepared in the laboratory by using the sol-gel technique. The bioactivity of the prepared sample has been analyzed by using the Tris Simulated Body Fluid which has also been prepared in the laboratory. XRD and Raman techniques have been employedto probe the formation of hydroxyapatite layer. pH studies has also been undertaken to check the acidic/non-acidic behavior of sample. Growth of hydroxyapatite layer has been observed after one day on the surface of the sample. Moreover, sample has been observed to be non-acidic in nature.

  1. Self-Ordered Voids Formation in SiO2 Matrix by Ge Outdiffusion

    B. Pivac; P. Dubček; J. Dasović; H. Zorc; S. Bernstorff; J. Zavašnik; B. Vlahovic

    2018-01-01

    The annealing behavior of very thin SiO2/Ge multilayers deposited on Si substrate by e-gun deposition in high vacuum was explored. It is shown that, after annealing at moderate temperatures (800°C) in inert atmosphere, Ge is completely outdiffused from the SiO2 matrix leaving small (about 3 nm) spherical voids embedded in the SiO2 matrix. These voids are very well correlated and formed at distances governed by the preexisting multilayer structure (in vertical direction) and self-organization ...

  2. Investigation of γ-radiation defect formation at the Si-SiO2 interface

    Zaynabidinov, S.; Yulchiev, Sh.; Aliev, R.

    2004-01-01

    Full text: In work the results of an experimental research of process radiating defects formation on border are submitted undressed Si-SiO 2 at γ-radiation of the silicon MOS structures. As against similar researches the basic attention is given on the analysis of generation-recombination characteristics of structures, that allowed to establish character of the defects formation both on border undressed Si-SiO 2 , and in about border of Si. In experiments the structures received by thermal oxidation at T=1000 deg. C in environment of dry oxygen n-Si substrates with specific resistance ρ=0.3 Ω·cm are used. The thickness of oxygen layer made ∼0.1 μm. The test MOS-structures with an aluminium electrode and area ∼0.01 cm 2 irradiated with γ-quanta from the 60 Co source by a dose of 10 6 rad. The choice of a dose of an radiation is caused by that at such dose the essential increase of concentration of superficial defects is observed, and at the same time there are no significant changes of parameters of a substrate because of formation of point defects in volume of silicon. The generation characteristics of structures such, as speed of superficial generation s and time of life τ g of carriers of a charge in about surface before and after an radiation defined by a method isothermal relaxation of nonequilibrium high-frequency capacity. The relaxation of nonequilibrium capacity registered at submission on translating structure in a condition of deeper inversion. Such mode of measurement allows to neglect the contribution which is brought in recharged of superficial condition in superficial generation currents. Are received relaxation dependence of structures before and after an radiation, and also spectra of distribution of density of superficial condition on width of the forbidden zone Si dN ss /dE. The increase at 12-15 of time of concentration of superficial condition with E=E c -(0.18±0.03) eV in the irradiated structures is established. Such condition is

  3. Investigation on the utilization of ZrO2-SiO2 composite microspheres for Sr+2 sorption synthesized via sol-gel method

    Sert, S.; Tel, H.; Altas, Y.; Eral, M.; Cetinkaya, B.; Inan, S.; Kasap, S.

    2009-01-01

    Multivalence metal ion's oxides and hydro oxides show high adsorption capacity. These are selective to some kind of ions and show thermal, chemical and radiation resistance. Because of these properties they can be used as a adsorbent for radioactive waste management. It is known that the mix oxide's acidic and basic surface sides and textural (surface area, por side and volume) properties related to mix oxide composition. The previously works shown that the ZrO 2 have high adsorption capacity for Sr + 2. Additionally ZrO 2 is used in production of heat resistance materials, glass and ceramic industries due to it's high melting point. Generally inorganic adsorbents which are crystal forms have low surface area. It is needed that the materials have high surface area and appropriate por size to targeted molecules for take inside adsorbent, in the practical adsorption proses. It is thought that the addition of oxide which has high surface area ( SiO 2 etc.) to between material layer increase it's surface area. Some works showed that the silica increase surface area when mixed Ti in materials structure. Sol-jell proses is a method which is show homogen hetero metal oxide bounds distribution and give advantages to prepare multicomponent oxide materials. In this study, ZrO 2 -SiO 2 -TiO 2 composite microspheres were synthesized by sol-gel method. In synthesis proses; peristaltic pump, nozzle-vibrator system and glass column were used. The optimum Sr 2 + adsorption conditions were determined by 'Central Composite Design' (CCD). Thermodynamic parameters related to adsorption such as ΔHo, ΔSo and ΔGo were calculated. The adsorption data have been interpreted in terms of Langmuir, Freundlich and D-R isotherms.

  4. Effect of hydrostatic pressure on photoluminescence spectra from structures with Si nanocrystals fabricated in SiO2 matrix

    Zhuravlev, K.S.; Tyschenko, I.E.; Vandyshev, E.N.; Bulytova, N.V.; Misiuk, A.; Rebohle, L.; Skorupa, W.

    2002-01-01

    The effect of hydrostatic pressure applied at high temperature on photoluminescence of Si-implanted SiO 2 films was studied. A 'blue'-shift of PL spectrum from the SiO 2 films implanted with Si + ions to total dose of 1.2x10 17 cm -2 with increase in hydrostatic pressure was observed. For the films implanted with Si + ions to a total dose of 4.8x10 16 cm -2 high temperature annealing under high hydrostatic pressure (12 kbar) causes a 'red'-shift of photoluminescence spectrum. The 'red' photoluminescence bands are attributed to Si nanocrystals while the 'blue' ones are related to Si nanocrystals of reduced size or chains of silicon atoms or Si-Si defects. A decrease in size of Si nanocluster occurs in result of the pressure-induced decrease in the diffusion of silicon atoms. (author)

  5. Changes in the microbiological and chemical characteristics of white bread during storage in paper packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2.

    Peter, Anca; Mihaly-Cozmuta, Leonard; Mihaly-Cozmuta, Anca; Nicula, Camelia; Ziemkowska, Wanda; Basiak, Dariusz; Danciu, Virginia; Vulpoi, Adriana; Baia, Lucian; Falup, Anca; Craciun, Grigore; Ciric, Alexandru; Begea, Mihaela; Kiss, Claudia; Vatuiu, Daniela

    2016-04-15

    Microbiological and chemical characteristics of white bread during storage in paper-packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2 were investigated. The whiteness and the water retention of the modified packages were slightly superior to those exhibited by the reference sample, as the color of the composite was lighter. The water retention was very good especially for the Ag/TiO2-SiO2-paper. These improvements can be associated with the high specific surface area and with the low agglomeration tendency of Ag nanoparticles in comparison with the Au ones. The preservation activity of the composites for the bread storage is positively influenced by photoactivity and presence of nano-Ag. Packages Ag/TiO2-SiO2-paper and Ag/N-TiO2-paper can find their applicability for extending the shelf life of bread by 2 days as compared with the unmodified paper-package. No influence of the Au/TiO2 on the extending the shelf life of bread was observed. Copyright © 2015 Elsevier Ltd. All rights reserved.

  6. Catalytic Performance of Fe-Mn/SiO2 Nanocatalysts for CO Hydrogenation

    Mostafa Feyzi

    2013-01-01

    Full Text Available A series of x(Fe, Mn/SiO2 nanocatalysts (x=5, 10, 15, 20, 25, and 30 wt.% were prepared by sol-gel method and studied for the light olefins production from synthesis gas. It was found that the catalyst containing 20 wt.% (Fe, Mn/SiO2 is an optimal nano catalyst for production of C2–C4 olefins. Effects of sulfur treatment on the catalyst performance of optimal catalyst have been studied by espousing different volume fractions of H2S in a fixed bed stainless steel reactor. The results show that the catalyst treated with 6 v% of H2S had high catalytic performance for C2–C4 light olefins production. The best operational conditions were H2/CO = 3/2 molar feed ratio at 260°C and GHSV = 1100 h−1 under 1 bar total pressure. Characterization of catalysts was carried out using X-ray diffraction (XRD, scanning electron microscopy (SEM, transmission electron microscopy (TEM, and surface area measurements.

  7. Irradiation-induced hardening/softening in SiO2 studied with instrumented indentation

    Nakano, Shinsuke; Muto, Shunsuke; Tanabe, Tetsuo

    2005-01-01

    To understand the plastic deformation mechanism of SiO 2 polytypes, we measured the mechanical parameters of He + -irradiated crystalline SiO 2 (α-quartz, c-SiO 2 ) and vitreous SiO 2 (silica glass, v-SiO 2 ) as functions of the irradiation dose, by using the instrumented indentation method combined with a finite-element analysis. We extracted the effects of local rotation and bending of the SiO 4 framework (the degree of local structural freedom), which play key roles in the plastic deformation, and expressed the hardness change with a simple formula. For v-SiO 2 , the changes in the density and the number of broken bonds correlated well with the change in the degree of freedom. In contrast, for c-SiO 2 the present formulation was insufficient to fully express the hardness change in the structural disordering regime. The structure change by irradiation peculiar to this material is discussed, based on the theoretical formulation

  8. Effect of SiO2 addition and gamma irradiation on the lithium borate glasses

    Raut, A. P.; Deshpande, V. K.

    2018-01-01

    The physical properties like density, glass transition temperature (Tg), and ionic conductivity of lithium borate (LB) glasses with SiO2 addition were measured before and after gamma irradiation. Remarkable changes in properties have been obtained in the physical properties of LB glasses with SiO2 addition and after gamma irradiation. The increase in density and glass transition temperature of LB glasses with SiO2 addition has been explained with the help of increase in density of cross linking due to SiO4 tetrahedra formation. The increase in ionic conductivity with SiO2 addition was explained with the help of ‘mixed glass former effect’. The increase in density and Tg of LB glasses with SiO2 addition after gamma irradiation has been attributed to fragmentation of bigger ring structure into smaller rings, which increases the density of cross linking and hence compaction. The exposure of gamma irradiation has lead to decrease in ionic conductivity of LB glasses with SiO2 addition. The atomic displacement caused by gamma irradiation resulted in filling of interstices and decrease in trapping sites. This explains the obtained decrease in ionic conductivity after gamma irradiation of glasses. The obtained results of effect of SiO2 addition and gamma irradiation on the density, Tg and ionic conductivity has been supported by FTIR results.

  9. Coupling behaviors of graphene/SiO2/Si structure with external electric field

    Onishi, Koichi; Kirimoto, Kenta; Sun, Yong

    2017-02-01

    A traveling electric field in surface acoustic wave was introduced into the graphene/SiO2/Si sample in the temperature range of 15 K to 300 K. The coupling behaviors between the sample and the electric field were analyzed using two parameters, the intensity attenuation and time delay of the traveling-wave. The attenuation originates from Joule heat of the moving carriers, and the delay of the traveling-wave was due to electrical resistances of the fixed charge and the moving carriers with low mobility in the sample. The attenuation of the external electric field was observed in both Si crystal and graphene films in the temperature range. A large attenuation around 190 K, which depends on the strength of external electric field, was confirmed for the Si crystal. But, no significant temperature and field dependences of the attenuation in the graphene films were detected. On the other hand, the delay of the traveling-wave due to ionic scattering at low temperature side was observed in the Si crystal, but cannot be detected in the films of the mono-, bi- and penta-layer graphene with high conductivities. Also, it was indicated in this study that skin depth of the graphene film was less than thickness of two graphene atomic layers in the temperature range.

  10. Effects of Mev Si Ions and Thermal Annealing on Thermoelectric and Optical Properties of SiO2/SiO2+Ge Multi-nanolayer thin Films

    Budak, S.; Alim, M. A.; Bhattacharjee, S.; Muntele, C.

    Thermoelectric generator devices have been prepared from 200 alternating layers of SiO2/SiO2+Ge superlattice films using DC/RF magnetron sputtering. The 5 MeV Si ionsbombardmenthasbeen performed using the AAMU Pelletron ion beam accelerator to formquantum dots and / or quantum clusters in the multi-layer superlattice thin films to decrease the cross-plane thermal conductivity, increase the cross-plane Seebeck coefficient and increase the cross-plane electrical conductivity to increase the figure of merit, ZT. The fabricated devices have been annealed at the different temperatures to tailor the thermoelectric and optical properties of the superlattice thin film systems. While the temperature increased, the Seebeck coefficient continued to increase and reached the maximum value of -25 μV/K at the fluenceof 5x1013 ions/cm2. The decrease in resistivity has been seen between the fluence of 1x1013 ions/cm2 and 5x1013 ions/cm2. Transport properties like Hall coefficient, density and mobility did not change at all fluences. Impedance spectroscopy has been used to characterize the multi-junction thermoelectric devices. The loci obtained in the C*-plane for these data indicate non-Debye type relaxation displaying the presence of the depression parameter.

  11. Scratch resistance of SiO2 and SiO2 - ZrO2 sol-gel coatings on glass-ceramic obtained by sintering

    Soares, V. O.; Soares, P.; Peitl, O.; Zanotto, E. D.; Duran, A.; Castro, Y.

    2013-01-01

    The sol-gel process is widely used to obtain coatings on glass-ceramic substrates in order to improve the scratch and abrasion resistance, also providing a bright and homogeneous appearance of a glaze avoiding expensive final polishing treatments. This paper describes the preparation of silica and silica / zirconia coatings by sol-gel method on Li 2 O-Al 2 O3-SiO 2 (LAS) glassceramic substrates produced by sintering. The coatings were deposited by dip-coating on LAS substrates and characterized by optical microscopy and spectral ellipsometry. On the other hand, hardness and elastic modulus, coefficient of friction and abrasion and scratch resistance of the coatings were determined and compared with the substrate properties. Coatings deposited on LAS glass-ceramic confere the substrate a bright and homogeneous aspect, similar to a glaze, improving the appearance and avoiding the final polishing. However these coatings do not increase the scratch resistance of the substrate only equaling the properties of the glass-ceramic. (Author)

  12. Synthesis and characterization of a binary oxide ZrO2–TiO2 and its ...

    Administrator

    Synthesis and characterization of a binary oxide ZrO2–TiO2 and its application in ... Solar cells based on dye-sensitized TiO2 nanoparticles were first developed by Grätzel ... cells, resulting in high Jsc (short-circuit current density),. *Author for .... simple method to study dye sensitization of semiconduc- tors. It is found that the ...

  13. Annealing behavior of oxygen in-diffusion from SiO2 film to silicon substrate

    Abe, T.; Yamada-Kaneta, H.

    2004-01-01

    Diffusion behavior of oxygen at (near) the Si/SiO 2 interface was investigated. We first oxidized the floating-zone-grown silicon substrates, and then annealed the SiO 2 -covered substrates in an argon ambient. We examined two different conditions for oxidation: wet and dry oxidation. By the secondary-ion-mass spectrometry, we measured the depth profiles of the oxygen in-diffusion of these heat-treated silicon substrates: We found that the energy of dissolution (in-diffusion) of an oxygen atom that dominates the oxygen concentration at the Si/SiO 2 interface depends on the oxidation condition: 2.0 and 1.7 eV for wet and dry oxidation, respectively. We also found that the barrier heights for the oxygen diffusion in argon anneal were significantly different for different ambients adopted for the SiO 2 formation: 3.3 and 1.8 eV for wet and dry oxidation, respectively. These findings suggest that the microscopic behavior of the oxygen atoms at the Si/SiO 2 interface during the argon anneal depends on the ambient adopted for the SiO 2 formation

  14. Materiais SiO2-TiO2 para a degradação fotocatalítica de diuron

    Arthur Alaím Bernardes

    2011-01-01

    Full Text Available SiO2-TiO2 materials prepared by sol-gel method were evaluated in the photocatalytic degradation of diuron. The materials were prepared with and without surfactant cetyltrimethylammonium chloride at different temperatures (25, 50 and 100 ºC. The samples were characterized by N2 adsorption-desorption measurements, scanning electron microscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy and infrared diffuse reflectance spectroscopy. The results showed that the materials synthesized with the surfactant had higher surface areas and band-gap values similar to anatase. All materials were more active than the commercial catalyst P-25 and better performance was achieved using the surfactant in the material synthesis.

  15. Influence of phosphorous precursors on spectroscopic properties of Er3+-activated SiO2-HfO2-P2O5 planar waveguides

    Vasilchenko, I; Carpentiero, A; Chiappini, A; Chiasera, A; Ferrari, M; Vaccari, A; Lukowiak, A; Righini, G C; Vereshagin, V

    2014-01-01

    (70-x)SiO 2 -30HfO 2 -xP 2 O 5 (x= 5, 10 mol %) glass planar waveguides activated by 0.5 mol% Er 3 + ions were prepared by sol-gel route. Several phosphorous precursors have been investigated for the synthesis of a dielectric stable sol useful for the realization of planar waveguides. The waveguides were investigated by different diagnostic techniques. The optical properties such as refractive index, thickness, number of propagating modes and attenuation coefficient were measured at 632.8 and 543.5 nm by prism coupling technique. Transmission measurements were carried out in order to assess the transparency of the deposited films. Photoluminescence measurements and lifetime decay curves of the Er 3 + transition (4 I 13/2 → 4 I 15/2 ) were performed in order to investigate the role of P 2 O 5

  16. High-efficient production of SiC/SiO2 core-shell nanowires for effective microwave absorption

    Zhong, Bo; Sai, Tianqi; Xia, Long; Yu, Yuanlie; Wen, Guangwu

    2017-01-01

    In the current report, we have demonstrated that the high-efficient production of SiC/SiO2 core-shell nanowires can be achieved through the introduction of trace of water vapor during the chemical vapor deposition process. The yield of the SiC/SiO2 core-shell nanowires is dramatically improved due to the introduction of water vapor. The SiC/SiO2 core-shell nanowires exhibit an excellent microwave absorption property in the frequency range of 2.0–18.0GHz with a very low weight percentage of 0.50wt.% in the absorbers. A minimum reflection loss value of −32.72dB (>99.99% attenuation) at 13.84GHz has been observed with the absorber thickness of 3.0mm. Moreover, the SiC/SiO2 core-shell nanowires based absorber can reach an effective absorption bandwidth (<−10dB) of 5.32GHz with the absorber thickness of 3.5mm. Furthermore, a possible absorption mechanism is also proposed in detail for such effective attenuation of microwave which can be attributed to the dielectric loss and magnetic loss of SiC/SiO2 core-shell nanowires.

  17. High-efficient production of SiC/SiO2 core-shell nanowires for effective microwave absorption

    Zhong, Bo

    2017-02-21

    In the current report, we have demonstrated that the high-efficient production of SiC/SiO2 core-shell nanowires can be achieved through the introduction of trace of water vapor during the chemical vapor deposition process. The yield of the SiC/SiO2 core-shell nanowires is dramatically improved due to the introduction of water vapor. The SiC/SiO2 core-shell nanowires exhibit an excellent microwave absorption property in the frequency range of 2.0–18.0GHz with a very low weight percentage of 0.50wt.% in the absorbers. A minimum reflection loss value of −32.72dB (>99.99% attenuation) at 13.84GHz has been observed with the absorber thickness of 3.0mm. Moreover, the SiC/SiO2 core-shell nanowires based absorber can reach an effective absorption bandwidth (<−10dB) of 5.32GHz with the absorber thickness of 3.5mm. Furthermore, a possible absorption mechanism is also proposed in detail for such effective attenuation of microwave which can be attributed to the dielectric loss and magnetic loss of SiC/SiO2 core-shell nanowires.

  18. Formation of thin DLC films on SiO2/Si substrate using FCVAD technique

    Bootkul, D.; Intarasiri, S.; Aramwit, C.; Tippawan, U.; Yu, L.D.

    2013-01-01

    Diamond-like carbon (DLC) films deposited on SiO 2 /Si substrate are attractive for novel sensitive and selective chemical sensors. According to the almost never ending of size reduction, a nm-thickness layer of the film is greatly required. However, formation of such a very thin DLC film on SiO 2 /Si substrate is challenging. In this experiment, DLC films were formed using our in-house Filtered Cathodic Vacuum Arc Deposition (FCVAD) facility by varying the bias voltage of 0 V, −250 V and −450 V with the arc voltage of 350 V, 450 V, 550 V, 650 V and 750 V for 10 min. Raman spectroscopy was applied for characterization of the film qualities and Transmission Electron Microscopy (TEM) was applied for cross sectional analysis. Results showed that films of thickness ranging from 10–50 nm were easily acquired depending on deposition conditions. Deconvolution of Raman spectra of these samples revealed that, when fixing the substrate bias but increasing the arc voltage from 350 to 750 V, the ratio between D-peak and G-peak intensity, namely I D /I G ratio, tended to reduce up to the arc voltage of 450 V, then increased up to the arc voltage of 650 V and finally decreased again. On the other hand, when fixing the arc voltage, the I D /I G ratio tended to decrease continuously as the increasing of bias voltage. It can be concluded that the bonding structure would evolve from a graphitic-like structure to a diamond-like structure as the substrate bias increases. Additionally, the sp 3 site should be maximized at the arc voltage ∼450 V for fixed bias voltage. It is expected that, at −450 V bias and 450 V arc, sp 3 fractions could be higher than 60%. However, in some cases, e.g. at low arc voltages, voids formed between the film and the amorphous SiO 2 substrate. Electron energy loss spectroscopy (EELS) of the C edge across the DLC indicated that the thicker DLC film had uniform chemistry and structure, whereas the thin DLC film showed changes in the edge shape

  19. Enhanced antioxidation and microwave absorbing properties of SiO2-coated flaky carbonyl iron particles

    Zhou, Yingying; Xie, Hui; Zhou, Wancheng; Ren, Zhaowen

    2018-01-01

    SiO2 was successfully coated on the surface of flaky carbonyl iron particles using a chemical bath deposition method in the presence of 3-aminopropyl triethoxysilane (APTES). The morphologies, composition, valence states of elements, as well as antioxidation and electromagnetic properties of the samples were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and microwave network analyzer. TG curve shows the obvious weight gain of carbonyl iron was deferred to 360 °C after SiO2-coated, which can be ascribed to the exits of SiO2 overlayer. Compared with the raw carbonyl iron, SiO2-coated sample shows good wave absorption performance due to its impedance matching. The electromagnetic properties of raw and SiO2-coated carbonyl iron particles were characterized in X band before and after heat treatment at 250 °C for 10 h. It was established that SiO2-coated carbonyl iron demonstrate good thermal stability, indicating SiO2-coating is useful in the usage of microwave absorbers operating at temperature up to 250 °C.

  20. Organic/inorganic composite membranes based on polybenzimidazole and nano-SiO2

    Pu Hongting; Liu Lu; Chang Zhihong; Yuan Junjie

    2009-01-01

    Organic/inorganic composite membranes based on polybenzimidazole (PBI) and nano-SiO 2 were prepared in this work. However, the preparation of PBI/SiO 2 composite membrane is not easy since PBI is insoluble in water, while nano-SiO 2 is hydrophilic due to the hydrophilicity of nano-SiO 2 and water-insolubility of PBI. Thus, a solvent-exchange method was employed to prepare the composite membrane. The morphology of the composite membranes was studied by scanning electron microscopy (SEM). It was revealed that inorganic particles were dispersed homogenously in the PBI matrix. The thermal stability of the composite membrane is higher than that of pure PBI, both for doped and undoped membranes. PBI/SiO 2 composite membranes with up to 15 wt% SiO 2 exhibited improved mechanical properties compared with PBI membranes. The proton conductivity of the composite membranes containing phosphoric acid was studied. The nano-SiO 2 in the composite membranes enhanced the ability to trap phosphoric acid, which improved the proton conductivity of the composite membranes. The membrane with 15 wt% of inorganic material is oxidatively stable and has a proton conductivity of 3.9 x 10 -3 S/cm at 180 deg. C.

  1. Characterization of the implantation damage in SiO2 with x-ray photoelectron spectroscopy

    Ajioka, T.; Ushio, S.

    1986-01-01

    X-ray photoelectron spectroscopy (XPS) has been applied to characterize the damage introduced into SiO 2 by ion implantation. By measuring the peak width of Si/sub 2p/ from SiO 2 which corresponds to perturbation of the SiO 2 network, good depth profiles of the damage have been obtained for implanted samples and subsequently annealed samples. The results show that the damage distributed more widely than that calculated from energy deposition and that the perturbation of the network is caused not only by radiation damage but also by the existence of impurities in the network. It has been found that the XPS method is effective to understand the atomic structure, and thus, electrical properties of SiO 2

  2. Self-Ordered Voids Formation in SiO2 Matrix by Ge Outdiffusion

    B. Pivac

    2018-01-01

    Full Text Available The annealing behavior of very thin SiO2/Ge multilayers deposited on Si substrate by e-gun deposition in high vacuum was explored. It is shown that, after annealing at moderate temperatures (800°C in inert atmosphere, Ge is completely outdiffused from the SiO2 matrix leaving small (about 3 nm spherical voids embedded in the SiO2 matrix. These voids are very well correlated and formed at distances governed by the preexisting multilayer structure (in vertical direction and self-organization (in horizontal direction. The formed films produce intensive photoluminescence (PL with a peak at 500 nm. The explored dynamics of the PL decay show the existence of a very rapid process similar to the one found at Ge/SiO2 defected interface layers.

  3. PECVD SiO2 dielectric for niobium Josephson IC process

    Lee, S.Y.; Nandakumar, V.; Murdock, B.; Hebert, D.

    1991-01-01

    PECVD SiO 2 dielectric has been evaluated as an insulator for a Nb-based, all-refractory Josephson integrated circuit process. First, the properties of PECVD SiO 2 films were measured and compared with those of evaporated SiO films. Second, the PECVD SiO 2 dielectric film was used in our Nb-based Josephson integrated circuit process. The main problem was found to be the deterioration of the critical temperature of the superconducting niobium adjacent to the SiO 2 . The cause and a solution of the problem were investigated. Finally, a Josephson integrated sampler circuit was fabricated and tested. This paper shows acceptable junction I-V characteristics and a measured time resolution of a 4.9 ps pulse in liquid helium

  4. Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting.

    Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

    2016-02-07

    We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ∼20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

  5. Direct observation of ozone formation on SiO2 surfaces in O2 discharges

    Marinov, D.; Guaitella, O.; Booth, J. P.; Rousseau, A.

    2013-01-01

    Ozone production is studied in a pulsed O2 discharge at pressures in the range 1.3-6.7 mbar. Time-resolved absolute concentrations of O3 and O are measured in the post-discharge using UV absorption spectroscopy and two-photon absorption laser-induced fluorescence. In a bare silica discharge tube ozone is formed mainly by three-body gas-phase recombination. When the tube surface is covered by a high specific surface silica catalyst heterogeneous formation becomes the main source of ozone. The efficiency of this surface process increases with O2 pressure and is favoured by the presence of OH groups and adsorbed H2O on the surface. At p = 6.7 mbar ozone production accounts for up to 25% of the atomic oxygen losses on the surface.

  6. Direct observation of ozone formation on SiO2 surfaces in O2 discharges

    Marinov, D; Guaitella, O; Booth, J P; Rousseau, A

    2013-01-01

    Ozone production is studied in a pulsed O 2 discharge at pressures in the range 1.3-6.7 mbar. Time-resolved absolute concentrations of O 3 and O are measured in the post-discharge using UV absorption spectroscopy and two-photon absorption laser-induced fluorescence. In a bare silica discharge tube ozone is formed mainly by three-body gas-phase recombination. When the tube surface is covered by a high specific surface silica catalyst heterogeneous formation becomes the main source of ozone. The efficiency of this surface process increases with O 2 pressure and is favoured by the presence of OH groups and adsorbed H 2 O on the surface. At p = 6.7 mbar ozone production accounts for up to 25% of the atomic oxygen losses on the surface.

  7. Performance of NiFe2O4-SiO2-TiO2 Magnetic Photocatalyst for the Effective Photocatalytic Reduction of Cr(VI in Aqueous Solutions

    Mike O. Ojemaye

    2017-01-01

    Full Text Available Investigation into the reduction of Cr(VI in aqueous solution was carried out through some batch photocatalytic studies. The photocatalysts used were silica coated nickel ferrite nanoparticles (NiFe2O4-SiO2, nickel ferrite titanium dioxide (NiFe2O4-TiO2, nickel ferrite silica titanium dioxide (NiFe2O4-SiO2-TiO2, and titanium dioxide (TiO2. The characterization of the materials prepared via stepwise synthesis using coprecipitation and sol-gel methods were carried out with the aid of X-ray diffraction (XRD, transmission electron microscopy (TEM, scanning electron microscopy (SEM, Fourier transform infrared (FTIR spectroscopy, thermal gravimetric analysis (TGA, and vibrating sample magnetometry (VSM. The reduction efficiency was studied as a function of pH, photocatalyst dose, and contact time. The effects of silica interlayer between the magnetic photocatalyst materials reveal that reduction efficiency of NiFe2O4-SiO2-TiO2 towards Cr(VI was higher than that of NiFe2O4-TiO2. However, TiO2 was observed to have the highest reduction efficiency at all batch photocatalytic experiments. Kinetics study shows that photocatalytic reduction of Cr(VI obeyed Langmuir-Hinshelwood model and first-order rate kinetics. Regenerability study also suggested that the photocatalyst materials can be reused.

  8. Alkali passivation mechanism of sol-gel derived TiO2-SiO2 films coated on soda-lime-silica glass substrates

    Matsuda, A; Matsuno, Y; Katayama, S; Tsuno, T [Nippon Steel Glass Co. Ltd., Tokyo (Japan); Toge, N; Minami, T [University of Osaka Prefecture, Osaka (Japan). College of Engineering

    1992-09-01

    TiO2-SiO2 films prepared by the sol-gel method serves as an effective alkali passivation layer on a soda-lime-silica glass substrate and the film is superior to a sol-gel derived pure SiO2 film from the view point of weathering resistance improvement. To clarify the reason, alkali passivation mechanism of sol-gel derived TiO2-SiO2 glass films with different TiO2 contents coated on a soda-lime-silica glass substrate was studied by SIMS (secondary ion mass spectroscopy) and XPS (X-ray photoelectron spectroscopy) analyses, and compared with the results of a sol-gel derived pure SiO2 film. As a result, the following conclusions were obtained: An increase in TiO2 content in the TiO2 SiO2 film increases the sodium concentration in the film, which was induced by sodium migration from the glass substrate during the heat-treatment. Because of the presence of sodium the TiO2 -SiO2 films serve not as a barrier but as an effective getter of alkali ions and thereby effectively improve the weathering resistance Of the glass substrate. 10 refs., 6 figs.

  9. Densification of ∼5 nm-thick SiO_2 layers by nitric acid oxidation

    Choi, Jaeyoung; Joo, Soyeong; Park, Tae Joo; Kim, Woo-Byoung

    2017-01-01

    Highlights: • Leakage current density of the commercial PECVD grown ∼5 nm SiO_2 layer has been decreased about three orders of magnitude by densification. • The densification of SiO_2 layer is achieved by high oxidation ability of O·. • Densities of suboxide, fixed charge (N_f) and defect state (N_d) in SiO_2/Si interface are decreased by NAOS and PMA. • Tunneling barrier height (Φ_t) is increased because of the increase of atomic density in SiO_2 layer. - Abstract: Low-temperature nitric acid (HNO_3) oxidation of Si (NAOS) has been used to improve the interface and electrical properties of ∼5 nm-thick SiO_2/Si layers produced by plasma-enhanced chemical vapor deposition (PECVD). Investigations of the physical properties and electrical characteristics of these thin films revealed that although their thickness is not changed by NAOS, the leakage current density at a gate bias voltage of −1 V decreases by about two orders of magnitude from 1.868 × 10"−"5 A/cm"2. This leakage current density was further reduced by post-metallization annealing (PMA) at 250 °C for 10 min in a 5 vol.% hydrogen atmosphere, eventually reaching a level (5.2 × 10"−"8 A/cm"2) approximately three orders of magnitude less than the as-grown SiO_2 layer. This improvement is attributed to a decrease in the concentration of suboxide species (Si"1"+, Si"2"+ and Si"3"+) in the SiO_2/Si interface, as well as a decrease in the equilibrium density of defect sites (N_d) and fixed charge density (N_f). The barrier height (Φ_t) generated by a Poole-Frenkel mechanism also increased from 0.205 to 0.371 eV after NAOS and PMA. The decrease in leakage current density is therefore attributed to a densification of the SiO_2 layer in combination with the removal of OH species and increase in interfacial properties at the SiO_2/Si interface.

  10. Mechanochemically conjugated PMHS/nano-SiO 2 hybrid and subsequent optimum grafting density study

    Lin, Jinbin; Chen, Hongling; Yuan, Yongbing; Ji, Yan

    2011-08-01

    In this paper, we reported the preparation of poly(methylhydrosiloxane) (PMHS)/SiO 2 hybrid particles by mechanochemical method based on high energy ball milling (HEBM). The obtained hybrid particles were characterized by Fourier transform infrared (FT-IR) spectroscopy, 29Si CP (cross-polarization) MAS NMR, viscosity measurement, particle size distribution, thermal analysis (TGA, DSC and DTG), static contact angle (CA), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). FT-IR and 29Si CP MAS NMR spectra indicate that PMHS is chemically anchored onto the surface of nano-SiO 2. Viscosity measurement, particle size distribution, FE-SEM and TEM demonstrate that an appropriate grafting density optimizes the dispersion of nanoparticles in poly(dimethylsiloxane) (PDMS) matrix, so lower viscosity can be achieved. Too high or too low grafting density may only achieve suboptimal and poor dispersions. The optimum grafting density of PMHS on nano-SiO 2 was determined by thermal analysis, with approximately 0.0531 PMHS/nm 2. Static contact angle measurement indicates that the water contact angle of hybrid particles is modulated by changing the grafting density of PMHS on nano-SiO 2. The CA value of PMHS/SiO 2 hybrid with optimum grafting density is 139.4°, and the highest CA value of PMHS/SiO 2 hybrid is approximately 158.2°.

  11. Network rigidity and properties of SiO2 and GeO2 glasses under pressure.

    Trachenko, Kostya; Dove, Martin T; Brazhkin, Vadim; El'kin, F S

    2004-09-24

    We report in situ studies of SiO2 glass under pressure and find that temperature-induced densification takes place in a pressure window. To explain this effect, we study how rigidity of glasses changes under pressure, with rigidity percolation affecting the dynamics of local relaxation events. We link rigidity percolation in glasses to other effects, including a large increase of crystallization temperature and logarithmic relaxation under pressure.

  12. Improved thermal conductivity of TiO2-SiO2 hybrid nanofluid in ethylene glycol and water mixture

    Hamid, K. A.; Azmi, W. H.; Nabil, M. F.; Mamat, R.

    2017-10-01

    The need to study hybrid nanofluid properties such as thermal conductivity has increased recently in order to provide better understanding on nanofluid thermal properties and behaviour. Due to its ability to improve heat transfer compared to conventional heat transfer fluids, nanofluids as a new coolant fluid are widely investigated. This paper presents the thermal conductivity of TiO2-SiO2 nanoparticles dispersed in ethylene glycol (EG)-water. The TiO2-SiO2 hybrid nanofluids is measured for its thermal conductivity using KD2 Pro Thermal Properties Analyzer for concentration ranging from 0.5% to 3.0% and temperature of 30, 50 and 70°C. The results show that the increasing in concentration and temperature lead to enhancement in thermal conductivity at range of concentration studied. The maximum enhancement is found to be 22.1% at concentration 3.0% and temperature 70°C. A new equation is proposed based on the experiment data and found to be in good agreement where the average deviation (AD), standard deviation (SD) and maximum deviation (MD) are 1.67%, 1.66% and 5.13%, respectively.

  13. Self-Compacting Concrete Incorporating Micro-SiO2 and Acrylic Polymer

    Ali Heidari

    2014-01-01

    Full Text Available This study examined the effects of using acrylic polymer and micro-SiO2 in self-compacting concrete (SCC. Using these materials in SCC improves the characteristics of the concrete. Self-compacting samples with 1-2% of a polymer and 10% micro-SiO2 were made. In all cases, compressive strength, water absorption, and self-compacting tests were done. The results show that adding acrylic polymer and micro-SiO2 does not have a significant negative effect on the mechanical properties of self-compacting concrete. In addition using these materials leads to improving them.

  14. Self-Compacting Concrete Incorporating Micro-SiO2 and Acrylic Polymer

    Heidari, Ali; Zabihi, Marzieh

    2014-01-01

    This study examined the effects of using acrylic polymer and micro-SiO2 in self-compacting concrete (SCC). Using these materials in SCC improves the characteristics of the concrete. Self-compacting samples with 1-2% of a polymer and 10% micro-SiO2 were made. In all cases, compressive strength, water absorption, and self-compacting tests were done. The results show that adding acrylic polymer and micro-SiO2 does not have a significant negative effect on the mechanical properties of self-compa...

  15. Analysis of SiO2 nanoparticles binding proteins in rat blood and brain homogenate

    Shim KH

    2014-12-01

    Full Text Available Kyu Hwan Shim,1 John Hulme,1 Eun Ho Maeng,2 Meyoung-Kon Kim,3 Seong Soo A An1 1Department of Bionano Technology, Gachon Medical Research Institute, Gachon University, Sungnam-si, 2Department of Analysis, KTR, Kimpo, Gyeonggi-do, 3Department of Biochemistry and Molecular Biology, Korea University Medical School and College, Seoul, South Korea Abstract: A multitude of nanoparticles, such as titanium oxide (TiO2, zinc oxide, aluminum oxide, gold oxide, silver oxide, iron oxide, and silica oxide, are found in many chemical, cosmetic, pharmaceutical, and electronic products. Recently, SiO2 nanoparticles were shown to have an inert toxicity profile and no association with an irreversible toxicological change in animal models. Hence, exposure to SiO2 nanoparticles is on the increase. SiO2 nanoparticles are routinely used in numerous materials, from strengthening filler for concrete and other construction composites, to nontoxic platforms for biomedical application, such as drug delivery and theragnostics. On the other hand, recent in vitro experiments indicated that SiO2 nanoparticles were cytotoxic. Therefore, we investigated these nanoparticles to identify potentially toxic pathways by analyzing the adsorbed protein corona on the surface of SiO2 nanoparticles in the blood and brain of the rat. Four types of SiO2 nanoparticles were chosen for investigation, and the protein corona of each type was analyzed using liquid chromatography-tandem mass spectrometry technology. In total, 115 and 48 plasma proteins from the rat were identified as being bound to negatively charged 20 nm and 100 nm SiO2 nanoparticles, respectively, and 50 and 36 proteins were found for 20 nm and 100 nm arginine-coated SiO2 nanoparticles, respectively. Higher numbers of proteins were adsorbed onto the 20 nm sized SiO2 nanoparticles than onto the 100 nm sized nanoparticles regardless of charge. When proteins were compared between the two charges, higher numbers of proteins were

  16. Cytotoxicity and effect on GJIC of SiO2 nanoparticles in HL-7702 cells

    Pan Tao; Jin Minghua; Liu Xiaomei; Du Zhongjun; Zhou Xianqing; Huang Peili; Sun Zhiwei

    2013-01-01

    Objective: To study the cytotoxicity and effect on gap junction intracellular communication (GJIC) of SiO 2 nanoparticles in HL-7702 cells, and to provide experimental basis for toxicity assessment and the security applications of SiO 2 nanoparticles. Methods: Transmission electron microscope (TEM) was used to characterize two kinds of SiO 2 nanoparticles, verifying their size, dispersion and shape; dynamic light scattering (DLS) method was used to analyze the water dispersion and culture medium dispersion of the SiO 2 nanoparticles; MTT assay was carried out to examine the cytotoxicities of the two sizes SiO 2 nanoparticles on the cells; lactate dehydrogenase (LDH) release assay was performed to examine the integrity nano of the cell membrane; Scrape-loading and dye transfer assay was performed to examine the effect of SiO 2 nanoparticles on GJIC. Results: Based on the result of TEM, two kinds of SiO 2 nanoparticles were spherically shaped, uniformly sized and sporadically dispersed; the statistical analysis results showed the diameters of the two nanoparticles were (447.60±20.78) nm and (67.42±5.69) nm, respectively, thus they could be categorized as submicron scale and nano scale. The DLS method results manifested that the hydration nanoparticle sizes of the two SiO 2 nanoparticles were (684.37±18.76) nm, (128.31±7.64) nm in high purity water and (697.02±19.57) nm, (133.74±8.97) nm in RPMI-1640 solution, all the two nanoparticles were well dispersed without aggregation. MTT assay indicated that 24 h after treatment of SiO 2 nanoparticles, the cell viabilities were affected by both the size and the dose of the SiO 2 nanoparticles; the higher the dose was, the less viability the cells exhibited. Moreover, the nano scale particles inflicted more damage to the cells. LDH release assay indicated that the SiO 2 particles could also damage the cell membrane in a dose-dependent and size-dependent way. Scrape-loading and dye transfer assay indicated that the nano

  17. Effect of Si implantation on the microstructure of silicon nanocrystals and surrounding SiO2 layer

    Ross, G.G.; Smirani, R.; Levitcharsky, V.; Wang, Y.Q.; Veilleux, G.; Saint-Jacques, R.G.

    2005-01-01

    Si nanocrystals (Si-nc) embedded in a SiO 2 layer have been characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For local Si concentration in excess 8 x 10 21 Si + /cm 3 , the size of the Si-nc was found to be ∼3 nm and comparatively homogeneous throughout the whole implanted layer. For local Si concentration in excess of ∼2.4 x 10 22 Si + /cm 3 , the Si-nc diameter ranges from ∼2 to ∼12 nm in the sample, the Si-nc in the middle region of the implanted layer being bigger than those near the surface and the bottom of the layer. Also, Si-nc are visible deeper than the implanted depth. Characterization by XPS shows that a large quantity of oxygen was depleted from the first ∼25 nm in this sample (also visible on TEM image) and most of the SiO 2 bonds have been replaced by Si-O bonds. Experimental and simulation results suggest that a local Si concentration in excess of ∼3 x 10 21 Si/cm 3 is required for the production of Si-nc

  18. Ultrathin Microporous SiO2 Membranes Photodeposited on Hydrogen Evolving Catalysts Enabling Overall Water Splitting

    Bau, Jeremy A.

    2017-10-17

    Semiconductor systems for photocatalytic overall water splitting into H2 and O2 gases typically require metal cocatalyst particles, such as Pt, to efficiently catalyze H2 evolution. However, such metal catalyst surfaces also serve as recombination sites for H2 and O2, forming H2O. We herein report the photon-induced fabrication of microporous SiO2 membranes that can selectively restrict passage of O2 and larger hydrated ions while allowing penetration of protons, water, and H2. The SiO2 layers were selectively photodeposited on Pt nanoparticles on SrTiO3 photocatalyst by using tetramethylammonium (TMA) as a structure-directing agent (SDA), resulting in the formation of core–shell Pt@SiO2 cocatalysts. The resulting photocatalyst exhibited both improved overall water splitting performance under irradiation and with no H2/O2 recombination in the dark. The function of the SiO2 layers was investigated electrochemically by fabricating the SiO2 layers on a Pt electrode via an analogous cathodic deposition protocol. The uniform, dense, yet amorphous layers possess microporosity originating from ring structures formed during the hydrolysis of the silicate precursor in the presence of TMA, suggesting a double-role for TMA in coordinating silicate to cathodic surfaces and in creating a microporous material. The resulting layers were able to function as a molecular sieve, allowing for exclusive H2 generation while excluding unwanted side reactions by O2 or ferricyanide. The SiO2 layer is stable for extended periods of time in photocatalytic conditions, demonstrating promise as a nontoxic material for selective H2 evolution.

  19. Ultrathin Microporous SiO2 Membranes Photodeposited on Hydrogen Evolving Catalysts Enabling Overall Water Splitting

    Bau, Jeremy A.; Takanabe, Kazuhiro

    2017-01-01

    Semiconductor systems for photocatalytic overall water splitting into H2 and O2 gases typically require metal cocatalyst particles, such as Pt, to efficiently catalyze H2 evolution. However, such metal catalyst surfaces also serve as recombination sites for H2 and O2, forming H2O. We herein report the photon-induced fabrication of microporous SiO2 membranes that can selectively restrict passage of O2 and larger hydrated ions while allowing penetration of protons, water, and H2. The SiO2 layers were selectively photodeposited on Pt nanoparticles on SrTiO3 photocatalyst by using tetramethylammonium (TMA) as a structure-directing agent (SDA), resulting in the formation of core–shell Pt@SiO2 cocatalysts. The resulting photocatalyst exhibited both improved overall water splitting performance under irradiation and with no H2/O2 recombination in the dark. The function of the SiO2 layers was investigated electrochemically by fabricating the SiO2 layers on a Pt electrode via an analogous cathodic deposition protocol. The uniform, dense, yet amorphous layers possess microporosity originating from ring structures formed during the hydrolysis of the silicate precursor in the presence of TMA, suggesting a double-role for TMA in coordinating silicate to cathodic surfaces and in creating a microporous material. The resulting layers were able to function as a molecular sieve, allowing for exclusive H2 generation while excluding unwanted side reactions by O2 or ferricyanide. The SiO2 layer is stable for extended periods of time in photocatalytic conditions, demonstrating promise as a nontoxic material for selective H2 evolution.

  20. Transfer free graphene growth on SiO2 substrate at 250 °C

    Vishwakarma, Riteshkumar; Rosmi, Mohamad Saufi; Takahashi, Kazunari; Wakamatsu, Yuji; Yaakob, Yazid; Araby, Mona Ibrahim; Kalita, Golap; Kitazawa, Masashi; Tanemura, Masaki

    2017-03-01

    Low-temperature growth, as well as the transfer free growth on substrates, is the major concern of graphene research for its practical applications. Here we propose a simple method to achieve the transfer free graphene growth on SiO2 covered Si (SiO2/Si) substrate at 250 °C based on a solid-liquid-solid reaction. The key to this approach is the catalyst metal, which is not popular for graphene growth by chemical vapor deposition. A catalyst metal film of 500 nm thick was deposited onto an amorphous C (50 nm thick) coated SiO2/Si substrate. The sample was then annealed at 250 °C under vacuum condition. Raman spectra measured after the removal of the catalyst by chemical etching showed intense G and 2D peaks together with a small D and intense SiO2 related peaks, confirming the transfer free growth of multilayer graphene on SiO2/Si. The domain size of the graphene confirmed by optical microscope and atomic force microscope was about 5 μm in an average. Thus, this approach will open up a new route for transfer free graphene growth at low temperatures.

  1. UV-VUV laser induced phenomena in SiO2 glass

    Kajihara, Koichi; Ikuta, Yoshiaki; Oto, Masanori; Hirano, Masahiro; Skuja, Linards; Hosono, Hideo

    2004-01-01

    Creation and annihilation of point defects were studied for SiO 2 glass exposed to ultraviolet (UV) and vacuum UV (VUV) lights to improve transparency and radiation toughness of SiO 2 glass to UV-VUV laser light. Topologically disordered structure of SiO 2 glass featured by the distribution of Si-O-Si angle is a critical factor degrading transmittance near the fundamental absorption edge. Doping with terminal functional groups enhances the structural relaxation and reduces the number of strained Si-O-Si bonds by breaking up the glass network without creating the color centers. Transmittance and laser toughness of SiO 2 glass for F 2 laser is greatly improved in fluorine-doped SiO 2 glass, often referred as 'modified silica glass'. Interstitial hydrogenous species are mobile and reactive at ambient temperature, and play an important role in photochemical reactions induced by exposure to UV-VUV laser light. They terminate the dangling-bond type color centers, while enhancing the formation of the oxygen vacancies. These findings are utilized to develop a deep-UV optical fiber transmitting ArF laser photons with low radiation damage

  2. Structural studies of gels and gel-glasses in the SiO2-GeO2 system using vibrational spectroscopy

    Mukherjee, Shyama P.; Sharma, Shiv K.

    1986-01-01

    GeO2 gel and gels in the SiO2-GeO2 system synthesized by the hydrolytic polycondensation of metal alkoxides have been studied by infrared and Raman spectroscopic techniques. The molecular structures, hydroxyl contents, and crystallinity of gels and gel-glasses in relation to the thermal history and GeO2 concentration were investigated. The binary compositions having up to 70 mol percent GeO2 were examined.

  3. Biomedical bandpass filter for fluorescence microscopy imaging based on TiO2/SiO2 and TiO2/MgF2 dielectric multilayers

    Butt, M A; Fomchenkov, S A; Verma, P; Khonina, S N; Ullah, A

    2016-01-01

    We report a design for creating a multilayer dielectric optical filters based on TiO 2 and SiO 2 /MgF 2 alternating layers. We have selected Titanium dioxide (TiO 2 ) for high refractive index (2.5), Silicon dioxide (SiO 2 ) and Magnesium fluoride (MgF 2 ) as a low refractive index layer (1.45 and 1.37) respectively. Miniaturized visible spectrometers are useful for quick and mobile characterization of biological samples. Such devices can be fabricated by using Fabry-Perot (FP) filters consisting of two highly reflecting mirrors with a central cavity in between. Distributed Bragg Reflectors (DBRs) consisting of alternating high and low refractive index material pairs are the most commonly used mirrors in FP filters, due to their high reflectivity. However, DBRs have high reflectivity for a selected range of wavelengths known as the stopband of the DBR. This range is usually much smaller than the sensitivity range of the spectrometer range. Therefore a bandpass filters are required to restrict wavelength outside the stopband of the FP DBRs. The proposed filter shows a high quality with average transmission of 97.4% within the passbands and the transmission outside the passband is around 4%. Special attention has been given to keep the thickness of the filters within the economic limits. It can be suggested that these filters are exceptional choice for florescence imaging and Endoscope narrow band imaging. (paper)

  4. Thermodynamics of Bi2O3-SiO2 system

    Onderka B.

    2017-01-01

    Full Text Available Thermodynamic properties of the liquid Bi2O3-SiO2 solutions were determined from the results of the electrochemical measurements by use of the solid oxide galvanic cells with YSZ (Yttria-Stabilized-Zirconia electrolyte. Activities of Bi2O3 in the solutions were determined for 0.2, 0.3, 0.4, and 0.5 SiO2 mole fractions in the temperature range 1073-1293 K from measured electromotive force (e.m.f of the solid electrolyte galvanic cell: Bi, Bi2O3-SiO2 | YSZ | air (pO2 = 0.213 bar Additionally, heat capacity data obtained for two solid phases 6Bi2O3•SiO2 and 2Bi2O3•3SiO2 were included into optimization of thermodynamic properties of the system. Optimization procedure was supported by differential thermal analysis (DTA data obtained in this work as well as those accepted from the literature. Using the data obtained in this work, and the information about phase equilibria found in the literature, binary system Bi2O3-SiO2 was assessed with the ThermoCalc software.

  5. Semiconductor nanocrystals formed in SiO2 by ion implantation

    Zhu, J.G.; White, C.W.; Budai, J.D.; Withrow, S.P.; Chen, Y.

    1994-11-01

    Nanocrystals of group IV (Si, Ge and SiGe), III-V (GaAs), and II-VI (CdSe) semiconductor materials have been fabricated inside SiO 2 by ion implantation and subsequent thermal annealing. The microstructure of these nanocrystalline semiconductor materials has been studied by transmission electron microscopy (TEM). The nanocrystals form in near-spherical shape with random crystal orientations in amorphous SiO 2 . Extensive studies on the nanocrystal size distributions have been carried out for the Ge nanocrystals by changing the implantation doses and the annealing temperatures. Remarkable roughening of the nanocrystals occurs when the annealing temperature is raised over the melting temperature of the implanted semiconductor material. Strong red photoluminescence peaked around 1.67 eV has been achieved in samples with Si nanocrystals in SiO 2

  6. Light-emitting Si films formed by neutral cluster deposition in a thin O2 gas

    Honda, Y.; Takei, M.; Ohno, H.; Shida, S.; Goda, K.

    2005-01-01

    We have fabricated the light-emitting Si-rich and oxygen-rich amorphous SiO 2 (a-SiO 2 ) films using the neutral cluster deposition (NCD) method without and with oxygen gas admitted, respectively, and demonstrate for the first time that these films show a photoluminescent feature. The Si thin films were observed by atomic force microscopy and high-resolution transmission electron microscopy, and analyzed by means of X-ray photoelectron spectroscopy, photoluminescence (PL) and FTIR-attenuated total reflection measurements. All of the PL spectra show mountainous distribution with a peak around 620 nm. It is found that the increase in the oxygen termination in the a-SiO 2 films evidently makes the PL intensity increase. It is demonstrated that NCD technique is one of the hopeful methods to fabricate light-emitting Si thin films

  7. Efectos de fotodegradación propiciados por recubrimientos de TiO2 y TiO2-SiO2 obtenidos por Sol-Gel

    Rodriguez Paez, J. E.

    2008-10-01

    Full Text Available Photodegradation effect is widely used for water purification this contributes to preservation and protection of environment. Titanium oxide, (TiO2, is a compound that shows up this phenomenon. TiO2 is a semiconductor which may degradate pollutants through of a oxidation process. It permit the treatment of the residual water. It this work we has conformed coatings of TiO2 y TiO2-SiO2, utilized Sol-Gel method and investigated the degradation of the blue Methylene. For this, we introduced these coatings in the blue methylene solution which was illuminated with radiation of λ=365nm to activate its photocatilist properties. The structures of the coatings were characterized using Atomic Force Microscopy (AFM and X-ray Photoelectron Spectroscopy (XPS.El efecto de fotodegradación es ampliamente utilizado para la purificación del agua, acción que contribuye a la conservación y protección del medio ambiente; el óxido de titanio (TiO2 es uno de los semiconductores que pueden degradar contaminantes mediante procesos de oxidación, lo que lo hace apto para el tratamiento de aguas residuales. En este trabajo se conformaron recubrimientos de TiO2 y TiO2-SiO2, por el método Sol-Gel, y se estudio la degradación que experimentaba una solución de azul de metileno al introducirle estos recubrimientos e iluminarlos con una radiación de λ=365nm para activar su propiedad fotocatalítica. Los recubrimientos fueron caracterizados microestructuralmente utilizando Microscopía de Fuerza Atómica (MFA y Espectroscopía de Fotoelectrones de rayos X (XPS. Los resultados obtenidos de los ensayos de fotodegradación indican que los recubrimientos con una cantidad pequeña de silicio presentan un mayor efecto de fotodegradación indicando que el silicio puede generar puntos de anclaje que facilitan las reacciones de fotocatálisis. Por otro lado, la formación de centros activos, constituidos principalmente por carbono, también contribuyeron al desarrollo de estas

  8. Formation, structure, and phonon confinement effect of nanocrystalline Si1-xGex in SiO2-Si-Ge cosputtered films

    Yang, Y.M.; Wu, X.L.; Siu, G.G.; Huang, G.S.; Shen, J.C.; Hu, D.S.

    2004-01-01

    Using magnetron cosputtering of SiO 2 , Ge, and Si targets, Si-based SiO 2 :Ge:Si films were fabricated for exploring the influence of Si target proportion (P Si ) and annealing temperature (Ta) on formation, local structure, and phonon properties of nanocrystalline Si 1-x Ge x (nc-Si 1-x Ge x ). At low P Si and Ta higher than 800 deg. C, no nc-Si 1-x Ge x but a kind of composite nanocrystal consisting of a Ge core, GeSi shell, and amorphous Si outer shell is formed in the SiO 2 matrix. At moderate P Si , nc-Si 1-x Ge x begins to be formed at Ta=800 deg. C and coexists with nc-Ge at Ta=1100 deg. C. At high P Si , it was disclosed that both optical phonon frequency and lattice spacing of nc-Si 1-x Ge x increase with raising Ta. The possible origin of this phenomenon is discussed by considering three factors, the phonon confinement, strain effect, and composition variation of nc-Si 1-x Ge x . This work will be helpful in understanding the growth process of ternary GeSiO films and beneficial to further investigations on optical properties of nc-Ge 1-x Si x in the ternary matrix

  9. Synthesis, cytotoxicity, and hydroxyapatite formation in 27-Tris-SBF for sol-gel based CaO-P2O5-SiO2-B2O3-ZnO bioactive glasses.

    Kaur, Gurbinder; Pickrell, G; Kimsawatde, G; Homa, D; Allbee, H A; Sriranganathan, N

    2014-03-18

    CaO-P2O5-SiO2-B2O3-ZnO bioactive glasses were prepared via an optimized sol-gel method. The current investigation was focused on producing novel zinc based calcium phosphoborosilicate glasses and to evaluate their mechanical, rheological, and biocompatible properties. The morphology and composition of these glasses were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The particle size, mechanical and flexural strength was also determined. Furthermore, the zeta potential of all the glasses were determined to estimate their flocculation tendency. The thermal analysis and weight loss measurements were carried out using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) respectively. For assessing the in-vitro bioactive character of synthesized glasses, the ability for apatite formation on their surface upon their immersion in simulated body fluid (SBF) was checked using SEM and pH measurements. MTS assay cytotoxicity assay and live-dead cell viability test were conducted on J774A.1 cells murine macrophage cells for different glass concentrations.

  10. Mechanisms and selectivity for etching of HfO2 and Si in BCl3 plasmas

    Wang Chunyu; Donnelly, Vincent M.

    2008-01-01

    The authors have investigated plasma etching of HfO 2 , a high dielectric constant material, and poly-Si in BCl 3 plasmas. Etching rates were measured as a function of substrate temperature (T s ) at several source powers. Activation energies range from 0.2 to 1.0 kcal/mol for HfO 2 and from 0.8 to 1.8 kcal/mol for Si, with little or no dependence on source power (20-200 W). These low activation energies suggest that product removal is limited by chemical sputtering of the chemisorbed Hf or Si-containing layer, with a higher T s only modestly increasing the chemical sputtering rate. The slightly lower activation energy for HfO 2 results in a small improvement in selectivity over Si at low temperature. The surface layers formed on HfO 2 and Si after etching in BCl 3 plasmas were also investigated by vacuum-transfer x-ray photoelectron spectroscopy. A thin boron-containing layer was observed on partially etched HfO 2 and on poly-Si after etching through HfO 2 films. For HfO 2 , a single B(1s) feature at 194 eV was ascribed to a heavily oxidized species with bonding similar to B 2 O 3 . B(1s) features were observed for poly-Si surfaces at 187.6 eV (B bound to Si), 189.8 eV, and 193 eV (both ascribed to BO x Cl y ). In the presence of a deliberately added 0.5% air, the B-containing layer on HfO 2 is largely unaffected, while that on Si converts to a thick layer with a single B(1s) peak at 194 eV and an approximate stoichiometry of B 3 O 4 Cl

  11. Determination of optimum Si excess concentration in Er-doped Si-rich SiO2 for optical amplification at 1.54 μm

    Savchyn, Oleksandr; Coffey, Kevin R.; Kik, Pieter G.

    2010-01-01

    The presence of indirect Er 3+ excitation in Si-rich SiO 2 is demonstrated for Si-excess concentrations in the range of 2.5-37 at. %. The Si excess concentration providing the highest density of sensitized Er 3+ ions is demonstrated to be relatively insensitive to the presence of Si nanocrystals and is found to be ∼14.5 at. % for samples without Si nanocrystals (annealed at 600 deg. C) and ∼11.5 at. % for samples with Si nanocrystals (annealed at 1100 deg. C). The observed optimum is attributed to an increase in the density of Si-related sensitizers as the Si concentration is increased, with subsequent deactivation and removal of these sensitizers at high Si concentrations. The optimized Si excess concentration is predicted to generate maximum Er-related gain at 1.54 μm in devices based on Er-doped Si-rich SiO 2 .

  12. Suspended HfO2 photonic crystal slab on III-nitride/Si platform

    Wang, Yongjin; Feng, Jiao; Cao, Ziping; Zhu, Hongbo

    2014-01-01

    We present here the fabrication of suspended hafnium oxide (HfO 2 ) photonic crystal slab on a III-nitride/Si platform. The calculations are performed to model the suspended HfO 2 photonic crystal slab. Aluminum nitride (AlN) film is employed as the sacrificial layer to form air gap. Photonic crystal patterns are defined by electron beam lithography and transferred into HfO 2 film, and suspended HfO 2 photonic crystal slab is achieved on a III-nitride/Si platform through wet-etching of AlN layer in the alkaline solution. The method is promising for the fabrication of suspended HfO 2 nanostructures incorporating into a III-nitride/Si platform, or acting as the template for epitaxial growth of III-nitride materials. (orig.)

  13. Seed-mediated photodeposition route to Ag-decorated SiO2@TiO2 microspheres with ideal core-shell structure and enhanced photocatalytic activity

    Ma, Jianqi; Guo, Xiaohua; Ge, Hongguang; Tian, Guanghui; Zhang, Qiang

    2018-03-01

    Ag-decorated SiO2@TiO2 microspheres (SiO2@TiO2-Ag) with ideal core-shell structure and enhanced photocatalytic activity were successfully fabricated by combining both coating anatase TiO2 on the surface of SiO2 spheres and subsequent depositing face-centered cubic Ag nanoparticles (NPs) on the coated TiO2 surface via novel sol-gel method and Ag-seed-mediated photodeposition (PD) route, respectively. The morphology, structure, composition and optical properties of the resulting composites were characterized in detail. The results reveal that the monodisperse SiO2 spheres of ∼260 nm were covered uniformly and perfectly by the TiO2 nanoparticle coating layer with the thickness of ca. 55 nm by the novel sol-gel method. Further, homogeneously and highly dispersed Ag NPs with an average size of 8 ± 1.5 nm were strongly anchored onto the TiO2 surface in SiO2@TiO2 core-shell spheres by the modified PD process (Ag-seed-mediated PD route), whereas polydispersed Ag aggregates and detached Ag NPs were irregularly deposited over the TiO2 surface in previous works, which is the inherent problem and has not been effectively solved for depositing noble metal NPs such as Au, Ag, Pt, Pd on TiO2 surface by conventional PD method. The formation mechanism of small and uniformly dispersed Ag NPs with narrow size distribution via the modified PD method is tentatively explained by both nucleation kinetics and growth kinetics. The key reason is that the pre-deposited seeds firmly tethered on SiO2@TiO2 spheres served as nucleation sites and anchoring points for the further nucleation and subsequent growth of Ag via photoreduction of Ag+.

  14. Preparation, characterization and application of dispersible and spherical Nano-SiO2@Copolymer nanocomposite in leather tanning

    Pan, Hui; Li, Guang-Long; Liu, Rui-Qi; Wang, Su-Xia; Wang, Xiao-Dong

    2017-12-01

    Dispersible and spherical silica nanoparticles (nano-SiO2) were prepared with tetraethyl silicate and different surface-modifiers via a simple method. The silica nanoparticles surface-modified with methacryloxy (propyl) trimethoxysilane (denoted as MPS-SiO2), dimethyl diallyl ammoniumchloride (denoted as DMDAAC-SiO2) and poly (methacrylic acid) (denoted as PMAA-SiO2) which are known as hydrophobic, amphiphilic and hydrophilic modifiers, respectively, exhibited excellent dispersibility in various solvents or polymer matrix. The obtained bare silica nanoparticles, MPS-SiO2, DMDAAC-SiO2 and PMAA-SiO2 were characterized by Fourier transform infrared spectra (FTIR), thermogravimetric analysis (TGA), transmission electron microscope (TEM) and scanning electron microscope (SEM). A series of nanocomposites (denoted as SiO2/P, MPS-SiO2/P, DMDAAC-SiO2/P and PMAA-SiO2/P, respectively) were also prepared with the bare or surface-modified silica nanoparticles and methacrylic acid-co-acrylamide-co-acrylonitrile-co-salicylic acid tetrabasic copolymer (denoted as PMAAS) and applied in leather tanning. Compared with those of the leather tanned with the commercial acrylic resin (CHINATAN OM) and pure tetrabasic copolymer tanning agents, the physical and mechanical properties, rheological properties and thermal stabilities of the leather treated with SiO2/P, MPS-SiO2/P, DMDAAC-SiO2/P or PMAA-SiO2/P founded to be improved in a significant way. Moreover, the highest shrinkage temperature of the wet-white sheepskin tanned with PMAA-SiO2/P reached to 76 °C and the thickness increase reached to 105%.

  15. Efficient photocatalytic activity with carbon-doped SiO2 nanoparticles

    Zhang, Dongen; Wu, Jinbo; Zhou, Bingpu; Hong, Yaying; Li, Shunbo; Wen, Weijia

    2013-01-01

    by thermogravimetric analysis, X-ray diffraction, standard and high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The C-doped SiO2 displayed outstanding photocatalytic properties, as evidenced by its catalysis of Rhodamine B

  16. Photoluminescence from ZnO-SiO2 opals with different sphere diameters and thicknesses

    Yang Yingling; Yan Hongwei; Fu Zhengping; Yang Beifang; Xia Linsheng; Wang Zhen; Zuo Jian; Yu Shijun; Fu Shengquan; Li Fanqing

    2007-01-01

    We systematically investigated the photoluminescence (PL) and transmittance characteristics of ZnO-SiO 2 opals with varied positions of the stop-band and film thicknesses. An improved ultraviolet (UV) luminescence was observed from ZnO-SiO 2 composites over pure ZnO nanocrystals under 325 nm He-Cd laser excitation at room temperature. The UV PL of ZnO nanocrystals in SiO 2 opals with stop-bands center of 410 nm is sensitive to the thickness of opal films, and the UV PL intensity increases with the film thickness increasing. The PL spectra of ZnO nanocrystals in SiO 2 opals with stop-bands center of 570 nm show a suppression of the weak visible band. The experimental results are discussed based on the scattering and/or absorbance in opal crystals

  17. Fabrication and Surface Properties of Composite Films of SAM/Pt/ZnO/SiO 2

    Yao, Ke Xin; Zeng, Hua Chun

    2008-01-01

    Through synthetic architecture and functionalization with self-assembled monolayers (SAMs), complex nanocomposite films of SAM/Pt/ZnO/SiO2 have been facilely prepared in this work. The nanostructured films are highly uniform and porous, showing a

  18. Preparation and characterization of DLC/SiO2/Al2O3 nanofiltration ...

    MS received 12 July 2012; revised 27 September 2012 ... support were deposited using plasma-enhanced chemical vapour deposi- ... the nanofiltration membrane with DLC/SiO2/Al2O3 were observed at various annealing temperatures.

  19. Effect of water layer at the SiO2/graphene interface on pentacene morphology.

    Chhikara, Manisha; Pavlica, Egon; Matković, Aleksandar; Gajić, Radoš; Bratina, Gvido

    2014-10-07

    Atomic force microscopy has been used to examine early stages of pentacene growth on exfoliated single-layer graphene transferred to SiO2 substrates. We have observed 2D growth with mean height of 1.5 ± 0.2 nm on as-transferred graphene. Three-dimensional islands of pentacene with an average height of 11 ± 2 nm were observed on graphene that was annealed at 350 °C prior to pentacene growth. Compellingly similar 3D morphology has been observed on graphene transferred onto SiO2 that was treated with hexamethyldisilazane prior to the transfer of graphene. On multilayer graphene we have observed 2D growth, regardless of the treatment of SiO2. We interpret this behavior of pentacene molecules in terms of the influence of the dipolar field that emerges from the water monolayer at the graphene/SiO2 interface on the surface energy of graphene.

  20. Experimental determination of nanofluid specific heat with SiO2 nanoparticles in different base fluids

    Akilu, S.; Baheta, A. T.; Sharma, K. V.; Said, M. A.

    2017-09-01

    Nanostructured ceramic materials have recently attracted attention as promising heat transfer fluid additives owing to their outstanding heat storage capacities. In this paper, experimental measurements of the specific heats of SiO2-Glycerol, SiO2-Ethylene Glycol, and SiO2-Glycerol/Ethylene Glycol mixture 60:40 ratio (by mass) nanofluids with different volume concentrations of 1.0-4.0% have been carried out using differential scanning calorimeter at temperatures of 25 °C and 50 °C. Experimental results indicate lower specific heat capacities are found with SiO2 nanofluids compared to their respective base fluids. The specific heat was decreasing with the increase of concentration, and this decrement depends on upon the type of the base fluid. It is observed that temperature has a positive impact on the specific heat capacity. Furthermore, the experimental values were compared with the theoretical model predictions, and a satisfactory agreement was established.

  1. Porous asymmetric SiO2-g-PMMA nanoparticles produced by phase inversion

    Munirasu, Selvaraj; Nunes, Suzana Pereira

    2014-01-01

    of functionalized nanoparticles in different solvents and immersion in water. The resulting asymmetrically porous morphology and nanoparticle assembly was characterized by scanning electron and atomic force microscopy. The PMMA functionalized SiO2 hybrid material

  2. Sequential Condensation and Hydrodeoxygenation Reaction of Furfural-Acetone Adduct over Mix Catalysts Ni/SiO2 and Cu/SiO2 in Water

    Siti Mariyah Ulfa

    2018-05-01

    Full Text Available Sequential condensation and hydrodeoxygenation reaction were perform using autoclave batch reactor in the presence of water as a solvent. The condensation of furfural and acetone was performed using MgO catalyst followed by hydrodeoxygenation using mix catalyst Ni/SiO2 and Cu/SiO2. The catalyst was prepared by wet-impregnation method and analyzed by XRD, SEM-EDX as well as BET surface. Condensation of furfural and acetone in 1:2 mol ratio was carried out by reflux gave 4-(2-furyl-3-buten-2-one and 1,5-bis-(2-furanyl-1,4-pentadien-3-one. The condensation product was then subjected for hydrodeoxygenation using batch reactor, catalyzed by mixed Ni/SiO2 and Cu/SiO2 at 150 and 180 °C for 2 h. The product identified as alkane derivatives with the conversion at 38.83 and 50.35%, respectively. The selectivity of hydrocarbon is 61.39% at 150 °C and 16.55% at 180 °C. Increasing the reaction temperature to 200 °C did not give any products except the recovery of the precursor. It showed that higher temperature enhanced the catalyst activity but the selectivity is controlled by low reaction temperature.

  3. Estimation of the depth resolution of secondary ion mass spectrometry at the interface SiO2/Si

    Kocanda, J.; Fesič, V.; Veselý, M.; Breza, J.; Kadlečíková, M.

    1995-08-01

    Similarities between the processes that occur during sputtering of monocrystalline Si by reactive O2+ primary ions and the interface SiO2/monocrystalline Si by noble gas ions (e.g., by Ar+) have motivated us to utilize the semiempirical model of P. C. Zalm and C. J. Vriezema [Nucl. Instrum. Methods B 67, 495 (1992)], modified later by M. Petravić, B. G. Svensson, and J. S. Williams [Appl. Phys. Lett. 62, 278 (1993)] to calculate the decay length λb, as defined by J. B. Clegg [Surf. Interface Anal. 10, 322 (1987)], at the SiO2/Si interface. The measured and calculated results agree remarkably well. Inconsistency observed to be larger than 100% for glancing incidence angles confirms limitations of this model that were admitted already by its authors.

  4. Effect of Nano-SiO2 on the Hydration and Microstructure of Portland Cement

    Liguo Wang

    2016-12-01

    Full Text Available This paper systematically studied the modification of cement-based materials by nano-SiO2 particles with an average diameter of about 20 nm. In order to obtain the effect of nano-SiO2 particles on the mechanical properties, hydration, and pore structure of cement-based materials, adding 1%, 3%, and 5% content of nano-SiO2 in cement paste, respectively. The results showed that the reaction of nano-SiO2 particles with Ca(OH2 (crystal powder started within 1 h, and formed C–S–H gel. The reaction speed was faster after aging for three days. The mechanical properties of cement-based materials were improved with the addition of 3% nano-SiO2, and the early strength enhancement of test pieces was obvious. Three-day compressive strength increased 33.2%, and 28-day compressive strength increased 18.5%. The exothermic peak of hydration heat of cement increased significantly after the addition of nano-SiO2. Appearance time of the exothermic peak was advanced and the total heat release increased. Thermogravimetric-differential scanning calorimetry (TG-DSC analysis showed that nano-SiO2 promoted the formation of C–S–H gel. The results of mercury intrusion porosimetry (MIP showed that the total porosity of cement paste with 3% nano-SiO2 was reduced by 5.51% and 5.4% at three days and 28 days, respectively, compared with the pure cement paste. At the same time, the pore structure of cement paste was optimized, and much-detrimental pores and detrimental pores decreased, while less harmful pores and innocuous pores increased.

  5. Magnetic porous PtNi/SiO2 nanofibers for catalytic hydrogenation of p-nitrophenol

    Guan, Huijuan; Chao, Cong; Kong, Weixiao; Hu, Zonggao; Zhao, Yafei; Yuan, Siguo; Zhang, Bing

    2017-06-01

    In this work, the mesoporous SiO2 nanofibers from pyrolyzing precursor of electrospun nanofibers were employed as support to immobilize PtNi nanocatalyst (PtNi/SiO2 nanofibers). AFM, XRD, SEM, TEM, XPS, ICP-AES and N2 adsorption/desorption analysis were applied to systematically investigate the morphology and microstructure of as-prepared products. Results showed that PtNi alloy nanoparticles with average diameter of 18.7 nm were formed and could be homogeneously supported on the surface of porous SiO2 nanofiber, which further indicated that the SiO2 nanofibers with well-developed porous structure, large specific surface area, and roughened surface was a benefit for the support of PtNi alloy nanoparticles. The PtNi/SiO2 nanofibers catalyst exhibited an excellent catalytic activity towards the reduction of p-nitrophenol, and the catalyst's kinetic parameter ( k n = 434 × 10-3 mmol s-1 g-1) was much higher than those of Ni/SiO2 nanofibers (18 × 10-3 mmol s-1 g-1), Pt/SiO2 nanofibers (55 × 10-3 mmol s-1 g-1) and previous reported PtNi catalysts. The catalyst could be easily recycled from heterogeneous reaction system based on its good magnetic properties (the Ms value of 11.48 emu g-1). In addition, PtNi/SiO2 nanofibers also showed an excellent stability and the conversion rate of p-nitrophenol still could maintain 94.2% after the eighth using cycle.

  6. Effect of Nano-SiO2 on the Hydration and Microstructure of Portland Cement

    Wang, Liguo; Zheng, Dapeng; Zhang, Shupeng; Cui, Hongzhi; Li, Dongxu

    2016-01-01

    This paper systematically studied the modification of cement-based materials by nano-SiO2 particles with an average diameter of about 20 nm. In order to obtain the effect of nano-SiO2 particles on the mechanical properties, hydration, and pore structure of cement-based materials, adding 1%, 3%, and 5% content of nano-SiO2 in cement paste, respectively. The results showed that the reaction of nano-SiO2 particles with Ca(OH)2 (crystal powder) started within 1 h, and formed C–S–H gel. The reaction speed was faster after aging for three days. The mechanical properties of cement-based materials were improved with the addition of 3% nano-SiO2, and the early strength enhancement of test pieces was obvious. Three-day compressive strength increased 33.2%, and 28-day compressive strength increased 18.5%. The exothermic peak of hydration heat of cement increased significantly after the addition of nano-SiO2. Appearance time of the exothermic peak was advanced and the total heat release increased. Thermogravimetric-differential scanning calorimetry (TG-DSC) analysis showed that nano-SiO2 promoted the formation of C–S–H gel. The results of mercury intrusion porosimetry (MIP) showed that the total porosity of cement paste with 3% nano-SiO2 was reduced by 5.51% and 5.4% at three days and 28 days, respectively, compared with the pure cement paste. At the same time, the pore structure of cement paste was optimized, and much-detrimental pores and detrimental pores decreased, while less harmful pores and innocuous pores increased. PMID:28335369

  7. Development of nano SiO2 incorporated nano zinc phosphate coatings on mild steel

    Tamilselvi, M.; Kamaraj, P.; Arthanareeswari, M.; Devikala, S.; Selvi, J. Arockia

    2015-01-01

    Highlights: • Nano SiO 2 incorporated nano zinc phosphate coating on mild steel was developed. • Coatings showed enhanced corrosion resistance. • The nano SiO 2 is adsorbed on mild steel surface and become nucleation sites. • The nano SiO 2 accelerates the phosphating process. - Abstract: This paper reports the development of nano SiO 2 incorporated nano zinc phosphate coatings on mild steel at low temperature for achieving better corrosion protection. A new formulation of phosphating bath at low temperature with nano SiO 2 was attempted to explore the possibilities of development of nano zinc phosphate coatings on mild steel with improved corrosion resistance. The coatings developed were studied by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Electrochemical measurements. Significant variation in the coating weight, morphology and corrosion resistance was observed as nano SiO 2 concentrations varied from 0.5–4 g/L. The results showed that, the nano SiO 2 in the phosphating solution changed the initial potential of the interface between mild steel substrate and phosphating solution and reduce the activation energy of the phosphating process, increase the nucleation sites and yielded zinc phosphate coatings of higher coating weight, greater surface coverage and enhanced corrosion resistance. Better corrosion resistance was observed for coatings derived from phosphating bath containing 1.5 g/L nano SiO 2 . The new formulation reported in the present study was free from Ni or Mn salts and had very low concentration of sodium nitrite (0.4 g/L) as accelerator

  8. Characterization of defects in Si and SiO2-Si using positrons

    Asoka-Kumar, P.; Lynn, K.G.

    1993-01-01

    Positron annihilation spectroscopy of overlayers, interfaces, and buried regions of semiconductors has seen a rapid growth in recent years. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites, and can be used to probe defect concentrations in a range inaccessible to conventional defect probes. Some of the recent success of the technique in examining low concentrations of point defects in technologically important Si-based structures is discussed

  9. High reflectivity YDH/SiO2 distributed Bragg reflector for UV-C wavelength regime

    Alias, Mohd Sharizal

    2018-02-15

    A distributed Bragg reflector (DBR) composed of Y2O3-doped HfO2 (YDH)/SiO2 layers with high reflectivity spectrum centered at a wavelength of ~240 nm is deposited using radio-frequency magnetron sputtering. Before the DBR deposition, optical properties for a single layer of YDH, SiO2, and HfO2 thin films were studied using spectroscopic ellipsometry and spectrophotometry. To investigate the performance of YDH as a material for the high refractive index layer in the DBR, a comparison of its optical properties was made with HfO2 thin films. Due to larger optical bandgap, the YDH thin films demonstrated higher transparency, lower extinction coefficient, and lower absorption coefficient in the UV-C regime (especially for wavelengths below 250 nm) compared to the HfO2 thin films. The deposited YDH/SiO2 DBR consisting of 15 periods achieved a reflectivity higher than 99.9% at the wavelength of ~240 nm with a stopband of ~50 nm. The high reflectivity and broad stopband of YDH/SiO2 DBRs will enable further advancement of various photonic devices such as vertical-cavity surface-emitting lasers, resonant-cavity light-emitting diodes, and resonant-cavity photodetectors operating in the UV-C wavelength regime.

  10. High reflectivity YDH/SiO2 distributed Bragg reflector for UV-C wavelength regime

    Alias, Mohd Sharizal; Alatawi, Abdullah; Wong, Ka Chun; Tangi, Malleswararao; Holguin Lerma, Jorge Alberto; Stegenburgs, Edgars; Shakfa, Mohammad Khaled; Ng, Tien Khee; Rahman, Abdul; Alyamani, Ahmed; Ooi, Boon S.

    2018-01-01

    A distributed Bragg reflector (DBR) composed of Y2O3-doped HfO2 (YDH)/SiO2 layers with high reflectivity spectrum centered at a wavelength of ~240 nm is deposited using radio-frequency magnetron sputtering. Before the DBR deposition, optical

  11. The high temperature synthesis of CsAlSiO 4-ANA, a new polymorph in the system Cs 2OAl 2O 3SiO 2. I. The end member of ANA type of zeolite framework

    Dimitrijevic, R.; Dondur, V.; Petranovic, N.

    1991-12-01

    High temperature phase transformations of Cs + exchanged zeolites were investigated. Above 1000°C, CsX, CsY (FAU), and Cs, ZK-4 (LTA) frameworks recrystallized in a pollucite phase. A Cs + loaded mordenite recrystallized at 1300°C in the orthorhombic CsAlSi 5O 12 phase. A Cs + exchanged zeolite A at 960°C recrystallized in a mixture of two polymorphic CsAlSiO 4 phases having different (Al,Si)O 4 frameworks. The unstable orthorhombic CsAlSiO 4ABW phase has a topotactic transition at 1150°C into an ordered low CsAlSiO 4-ANA framework. Further calcination produces, at 1200°C, transformation of the low CsAlSiO 4-ANA phase to the more stable high CsAlSiO 4-ANA polymorph having cubic ( a 0 = 13.6595 (5) Å) symmetry and an ordered SiAl distribution. The crystal structure of high CsAlSiO 4ANA, a new polymorph in the system Cs 2OAl 2O 3SiO 2, was determined using X-ray Rietveld analyses and 29Si MAS NMR spectroscopy.

  12. Improving Passivation Process of Si Nano crystals Embedded in SiO2 Using Metal Ion Implantation

    Bornacelli, J.; Esqueda, J.A.R.; Fernandez, L.R.; Oliver, A.

    2013-01-01

    We studied the photoluminescence (PL) of Si nano crystals (Si-NCs) embedded in SiO 2 obtained by ion implantation at MeV energy. The Si-NCs are formed at high depth (1-2 μm) inside the SiO 2 achieving a robust and better protected system. After metal ion implantation (Ag or Au), and a subsequent thermal annealing at 600°C under hydrogen-containing atmosphere, the PL signal exhibits a noticeable increase. The ion metal implantation was done at energies such that its distribution inside the silica does not overlap with the previously implanted Si ion . Under proper annealing Ag or Au nanoparticles (NPs) could be nucleated, and the PL signal from Si-NCs could increase due to plasmonic interactions. However, the ion-metal-implantation-induced damage can enhance the amount of hydrogen, or nitrogen, that diffuses into the SiO 2 matrix. As a result, the surface defects on Si-NCs can be better passivated, and consequently, the PL of the system is intensified. We have selected different atmospheres (air, H 2 /N 2 and Ar) to study the relevance of these annealing gases on the final PL from Si-NCs after metal ion implantation. Studies of PL and time-resolved PL indicate that passivation process of surface defects on Si-NCs is more effective when it is assisted by ion metal implantation.

  13. Oxide Structure Dependence of SiO2/SiOx/3C-SiC/n-Type Si Nonvolatile Resistive Memory on Memory Operation Characteristics

    Yamaguchi, Yuichiro; Shouji, Masatsugu; Suda, Yoshiyuki

    2012-11-01

    We have investigated the dependence of the oxide layer structure of our previously proposed metal/SiO2/SiOx/3C-SiC/n-Si/metal metal-insulator-semiconductor (MIS) resistive memory device on the memory operation characteristics. The current-voltage (I-V) measurement and X-ray photoemission spectroscopy results suggest that SiOx defect states mainly caused by the oxidation of 3C-SiC at temperatures below 1000 °C are related to the hysteresis memory behavior in the I-V curve. By restricting the SiOx interface region, the number of switching cycles and the on/off current ratio are more enhanced. Compared with a memory device formed by one-step or two-step oxidation of 3C-SiC, a memory device formed by one-step oxidation of Si/3C-SiC exhibits a more restrictive SiOx interface with a more definitive SiO2 layer and higher memory performances for both the endurance switching cycle and on/off current ratio.

  14. Co-electrospinning fabrication and photocatalytic performance of TiO2/SiO2 core/sheath nanofibers with tunable sheath thickness

    Cao, Houbao; Du, Pingfan; Song, Lixin; Xiong, Jie; Yang, Junjie; Xing, Tonghai; Liu, Xin; Wu, Rongrong; Wang, Minchao; Shao, Xiaoli

    2013-01-01

    Graphical abstract: - Highlights: • The core–sheath TiO 2 /SiO 2 nanofibers were fabricated by co-electrospinning technique. • The catalytic property of nanofibers with different sheath thickness was studied. • The potential methods of improving catalytic efficiency are suggested. - Abstract: In this paper, core/sheath TiO 2 /SiO 2 nanofibers with tunable sheath thickness were directly fabricated via a facile co-electrospinning technique with subsequent calcination at 500 °C. The morphologies and structures of core/sheath TiO 2 /SiO 2 nanofibers were characterized by TGA, FESEM, TEM, FTIR, XPS and BET. It was found that the 1D core/sheath nanofibers are made up of anatase–rutile TiO 2 core and amorphous SiO 2 sheath. The influences of SiO 2 sheath and its thickness on the photoreactivity were evaluated by observing photo-degradation of methylene blue aqueous solution under the irradiation of UV light. Compared with pure TiO 2 nanofibers, the core/sheath TiO 2 /SiO 2 nanofibers performed a better catalytic performance. That was attributed to not only efficient separation of hole–electron pairs resulting from the formation of heterojunction but also larger surface area and surface silanol group which will be useful to provide higher capacity for oxygen adsorption to generate more hydroxyl radicals. And the optimized core/sheath TiO 2 /SiO 2 nanofibers with a sheath thickness of 37 nm exhibited the best photocatalytic performance

  15. Cotton fabric finishing with TiO2/SiO2 composite hydrosol based on ionic cross-linking method

    Xu, Z.J.; Tian, Y.L.; Liu, H.L.; Du, Z.Q.

    2015-01-01

    Highlights: • We studied the cotton finishing with TiO 2 /SiO 2 based on ionic cross-linking method. • The samples treated with CHTAC had lower value of whiteness. • The samples treated with BTCA achieved higher crease recovery angle and lower tensile strength. • The ionic cross-linking treatment (CHTAC + BTCA + TiO 2 /SiO 2 ) was better than with TiO 2 /SiO 2 sol alone. - Abstract: Cotton fabric was successfully modified by 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHTAC), 1,2,3,4-butanetetracarboxylic acid (BTCA) and TiO 2 /SiO 2 sol. Self-cleaning characteristic was investigated using a Color Measuring and Matching System with 6 h sunlight irradiation. And the stability of TiO 2 /SiO 2 coatings was explored by measuring the washing fastness and wrinkle resistance of treated cotton samples. In addition, whiteness index, crease recovery angle and tensile strength retention (%) of treated samples were evaluated. Moreover, the morphology, structure change and crystallinity of samples were observed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. The results revealed that the samples treated with CHTAC had lower value of whiteness index as compared with original cotton fabric. It was also found that samples treated with BTCA achieved higher crease recovery angle and lower tensile strength. Moreover, the treatment of CHTAC and BTCA had adverse effect on the crystallinity of cotton samples, as treated samples had lower crystallinity in comparison with raw cotton fabrics. Nevertheless, the stability of self-cleaning coatings was better for samples treated with ionic cross-linking treatment (CHTAC + BTCA + TiO 2 /SiO 2 ) than samples treated with TiO 2 /SiO 2 sol alone. Furthermore, compared with original samples the UV-blocking property of ionic cross-linking treated samples was obviously enhanced

  16. Self assembly of SiO2-encapsulated carbon microsphere composites

    Yang Yongzhen; Song Jingjing; Han Yanxing; Guo Xingmei; Liu Xuguang; Xu Bingshe

    2011-01-01

    SiO 2 was firstly coated onto the surface of carbon microspheres (CMSs) using tetraethyl orthosilicate (TEOS) as precursor by Stoeber method. Then SiO 2 -encapsulated CMS (CMS-SiO 2 ) composites were self-assembled by vertical deposition, in which the effects of deposition temperature and suspension concentration on the quality of self-assembling film were investigated. Morphologies and structures of the samples were characterized by field emission scanning electron microscopy, Fourier transformation infrared spectrometry, X-ray diffraction and thermogravimetry. The results show that uniform CMS-SiO 2 composites with good mono-dispersion were prepared by Stober method with 0.5 g of CMSs, 2 mL of TEOS, 30 mL of ammonia and 12 h of reaction time, the CMSs-based films with ordered and denser structure were prepared by vertical deposition using CMS-SiO 2 composites as monodipersion spheres under suspension concentration of 1 wt% and deposition temperature of 50 deg. C. The ultraviolet-visible absorption measurement shows that the absorbance of CMS-SiO 2 composite films grew steadily with increasing suspension concentration.

  17. Effect of SiO2 passivation overlayers on hillock formation in Al thin films

    Kim, Deok-kee

    2012-01-01

    Hillock formation in Al thin films with varying thicknesses of SiO 2 as a passivation layer was investigated during thermal cycling. Based on the stress measurements and the number of hillocks, 250 nm thick SiO 2 was thick enough to suppress the hillock formation and the suppression of hillock at 250 nm passivation and the lack of suppression at thinner passivation is related to the presence/absence of protection against the diffusive flow of atoms from the surrounding area to the surface due to the biaxial compressive stresses present in the film through the weak spots in the passivation layer. The stress state of Al films measured during annealing (the driving force for hillock formation) did not vary much with SiO 2 thickness. A small number of hillocks formed during the plasma enhanced chemical vapor deposition of SiO 2 overlayers at 300 °C. - Highlights: ► We examined the effect of SiO 2 overlayers on hillock formation in Al thin films. ► Thin overlayers were not effective in suppressing diffusive flow to the surface. ► A thick overlayer suppressed the diffusive flow from the interior to the surface. ► The stress state of Al films did not vary much with SiO 2 passivation thickness. ► High mechanical strength provided a large driving force for the large grain growth.

  18. Screen-Printed Photochromic Textiles through New Inks Based on SiO2@naphthopyran Nanoparticles.

    Pinto, Tânia V; Costa, Paula; Sousa, Céu M; Sousa, Carlos A D; Pereira, Clara; Silva, Carla J S M; Pereira, Manuel Fernando R; Coelho, Paulo J; Freire, Cristina

    2016-10-26

    Photochromic silica nanoparticles (SiO 2 @NPT), fabricated through the covalent immobilization of silylated naphthopyrans (NPTs) based on 2H-naphtho[1,2-b]pyran (S1, S2) and 3H-naphtho[2,1-b]pyran (S3, S4) or through the direct adsorption of the parent naphthopyrans (1, 3) onto silica nanoparticles (SiO 2 NPs), were successfully incorporated onto cotton fabrics by a screen-printing process. Two aqueous acrylic- (AC-) and polyurethane- (PU-) based inks were used as dispersing media. All textiles exhibited reversible photochromism under UV and solar irradiation, developing fast responses and intense coloration. The fabrics coated with SiO 2 @S1 and SiO 2 @S2 showed rapid color changes and high contrasts (ΔE* ab = 39-52), despite presenting slower bleaching kinetics (2-3 h to fade to the original color), whereas the textiles coated with SiO 2 @S3 and SiO 2 @S4 exhibited excellent engagement between coloration and decoloration rates (coloration and fading times of 1 and 2 min, respectively; ΔE* ab = 27-53). The PU-based fabrics showed excellent results during the washing fastness tests, whereas the AC-based textiles evidenced good results only when a protective transfer film was applied over the printed design.

  19. Characterization of Ni–P–SiO2 nano-composite coating on magnesium

    Sadreddini, S.; Salehi, Z.; Rassaie, H.

    2015-01-01

    Highlights: • The enhancement of SiO 2 nanoparticles in the bath up to 12.5 g/l, increased the amount of coating particles to 4.62 wt%. • Better corrosion resistance and lower porosity could be obtained by expansion prevention of corrosion cavity with deposition of nanoparticles in the coating. • Microhardness increases with increasing the SiO 2 particles concentration. - Abstract: In this study, the effects of SiO 2 nanoparticles added to the electroless Ni–P coating were studied. The surface morphology, corrosion behavior, hardness and porosity of Ni–P–SiO 2 composite were investigated. The related microstructure was investigated through field emission scanning electron microscopy (FESEM) and the amount of SiO 2 was examined by Energy Dispersive Analysis of X-ray (EDX). The corrosion behavior was evaluated through electrochemical impedance spectroscopy (EIS) and polarization techniques. The results illustrated that with increasing the quantity of the SiO 2 nanoparticles, the corrosion rate decreased and the hardness increased

  20. Coupling between Ge-nanocrystals and defects in SiO2

    Skov Jensen, J.; Franzo, G.; Leervad Petersen, T.P.; Pereira, R.; Chevallier, J.; Christian Petersen, M.; Bech Nielsen, B.; Nylandsted Larsen, A.

    2006-01-01

    Room temperature photoluminescence (PL) at around 600 nm from magnetron-sputtered SiO 2 films co-doped with Ge is reported. The PL signal is observed in pure SiO 2 , however, its intensity increases significantly in the presence of Ge-nanocrystals (Ge-nc). The PL intensity has been optimized by varying the temperature of heat treatment, type of gas during heat treatment, concentration of Ge in the SiO 2 films, and gas pressure during deposition. Maximum intensity occurs when Ge-nc of around 3.5 nm are present in large concentration in SiO 2 layers deposited at fairly high gas pressure. Based on time resolved PL, and PL measurements after α-particle irradiation or H passivation, we attribute the origin of the PL to a defect in SiO 2 (probably an O deficiency) that is excited through an energy transfer from Ge-nc. There is no direct PL from the Ge-nc; however, there is a strong coupling between excitons created in the Ge-nc and the SiO 2 defect

  1. SiO2 stabilized Pt/C cathode catalyst for proton exchange membrane fuel cells

    Zhu Tong; Du Chunyu; Liu Chuntao; Yin Geping; Shi Pengfei

    2011-01-01

    This paper describes the preparation of SiO 2 stabilized Pt/C catalyst (SiO 2 /Pt/C) by the hydrolysis of alkoxysilane, and examines the possibility that the SiO 2 /Pt/C is used as a durable cathode catalyst for proton exchange membrane fuel cells (PEMFCs). TEM and XRD results revealed that the hydrolysis of alkoxysilane did not significantly change the morphology and crystalline structure of Pt particles. The SiO 2 /Pt/C catalyst exhibited higher durability than the Pt/C one, due to the facts that the silica layers covered were beneficial for reducing the Pt aggregation and dissolution as well as increasing the corrosion resistance of supports, although the benefit of silica covering was lower than the case of Pt/CNT catalyst. Also, it was observed that the activity of the SiO 2 /Pt/C catalyst for the oxygen reduction reaction was somewhat reduced compared to the Pt/C one after the silica covering. This reduction was partially due to the low oxygen kinetics as revealed by the rotating-disk-electrode measurement. Silica covering by hydrolysis of only 3-aminopropyl trimethoxysilane is able to achieve a good balance between the durability and activity, leading to SiO 2 /Pt/C as a promising cathode catalyst for PEMFCs.

  2. Ag/SiO2 surface-enhanced Raman scattering substrate for plasticizer detection

    Wu, Ming-Chung; Lin, Ming-Pin; Lin, Ting-Han; Su, Wei-Fang

    2018-04-01

    In this study, we demonstrated a simple method of fabricating a high-performance surface-enhanced Raman scattering (SERS) substrate. Monodispersive SiO2 colloidal spheres were self-assembled on a silicon wafer, and then a silver layer was coated on it to obtain a Ag/SiO2 SERS substrate. The Ag/SiO2 SERS substrates were used to detect three kinds of plasticizer with different concentrations, namely, including bis(2-ethylhexyl)phthalate (DEHP), benzyl butyl phthalate (BBP), and dibutyl phthalate (DBP). The enhancement of Raman scattering intensity caused by surface plasmon resonance can be observed using the Ag/SiO2 SERS substrates. The Ag/SiO2 SERS substrate with a 150-nm-thick silver layer can detect plasticizers, and it satisfies the detection limit of plasticizers at 100 ppm. The developed highly sensitive Ag/SiO2 SERS substrates show a potential for the design and fabrication of functional sensors to identify the harmful plasticizers that plastic products release in daily life.

  3. SiO2-supported Pt particles studied by electron microscopy

    Wang, D.; Penner, S.; Su, D.S.; Rupprechter, G.; Hayek, K.; Schloegl, R.

    2003-01-01

    Regularly grown Pt particles supported by amorphous SiO 2 were heated in hydrogen at 873 K after an oxidising treatment. The morphological and structural changes were studied by electron microscopy. Platinum silicides Pt 3 Si with L1 2 (Cu 3 Au) structure, monoclinic Pt 3 Si and tetragonal Pt 12 Si 5 were identified after the treatment. The mechanisms of coalescence of the particles and the formation of irregular large particles are suggested. A topotactic structural transformation accompanied with the migration of Si from the substrate to the particles are suggested to take place during Pt 3 Si formation

  4. Characterization of remote O2-plasma-enhanced CVD SiO2/GaN(0001) structure using photoemission measurements

    Truyen, Nguyen Xuan; Ohta, Akio; Makihara, Katsunori; Ikeda, Mitsuhisa; Miyazaki, Seiichi

    2018-01-01

    The control of chemical composition and bonding features at a SiO2/GaN interface is a key to realizing high-performance GaN power devices. In this study, an ∼5.2-nm-thick SiO2 film has been deposited on an epitaxial GaN(0001) surface by remote O2-plasma-enhanced chemical vapor deposition (O2-RPCVD) using SiH4 and Ar/O2 mixture gases at a substrate temperature of 500 °C. The depth profile of chemical structures and electronic defects of the O2-RPCVD SiO2/GaN structures has been evaluated from a combination of SiO2 thinning examined by X-ray photoelectron spectroscopy (XPS) and the total photoelectron yield spectroscopy (PYS) measurements. As a highlight, we found that O2-RPCVD is effective for fabricating an abrupt SiO2/GaN interface.

  5. Study on spectroscopic properties and effects of tungsten ions in 2Bi2O3-3GeO2/SiO2 glasses.

    Yu, Pingsheng; Su, Liangbi; Cheng, Junhua; Zhang, Xia; Xu, Jun

    2017-04-01

    The 2Bi 2 O 3 -3GeO 2 /SiO 2 glass samples have been prepared by the conventional melt quenching technique. XRD patterns, absorption spectra, excitation-emission spectra and Raman measurements were utilized to characterize the synthesized glasses. When substitute SiO 2 for GeO 2 , the 0.4Bi 2 O 3 -(0.4-0.1)GeO 2 -(0.2-0.5)SiO 2 glasses exhibit strong emission centered at about 475nm (under 300nm excitation), and the decay constants are within the scope of 20-40ns. W doping into 2Bi 2 O 3 -3SiO 2 glass could increase the emission intensity of 470nm, and the W-doped 2Bi 2 O 3 -3SiO 2 glass has shown another emission at about 433nm with much shorter decay time (near 10ns). The 2Bi 2 O 3 -3GeO 2 /SiO 2 glass system could be the possible candidate for scintillator in high energy physics applications. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. Stability and kinetics of point defects in SiO2 and in SiC

    Roma, G.

    2012-01-01

    This document is conceived as an overview of Guido Roma's research achievements on defects stability and kinetics in two materials of interest in nuclear science and for many other application domains: silicon dioxide and silicon carbide. An extended summary in french is followed by the main document, in english. Chapter 1 describes the context, introduces the approach and explains the choice of silicon dioxide and silicon carbide. Chapter 2 discusses several approximations and specific issues of the application of Density Functional Theory to point defects in non-metallic materials for the study of defects energetics and diffusion. Chapter 3 is devoted to native defects in silicon dioxide and the understanding of self-diffusion in crystalline and amorphous SiO 2 . Chapter 4 summarises the results on native defects and palladium impurities in silicon carbide. A conclusion, including suggestions for future developments, closes the main part of the document. (author) [fr

  7. Emission Mechanisms of Si Nanocrystals and Defects in SiO2 Materials

    José Antonio Rodríguez

    2014-01-01

    Full Text Available Motivated by the necessity to have all silicon optoelectronic circuits, researchers around the world are working with light emitting silicon materials. Such materials are silicon dielectric compounds with silicon content altered, such as silicon oxide or nitride, enriched in different ways with Silicon. Silicon Rich Oxide or silicon dioxide enriched with silicon, and silicon rich nitride are without a doubt the most promising materials to reach this goal. Even though they are subjected to countless studies, the light emission phenomenon has not been completely clarified. So, a review of different proposals presented to understand the light emission phenomenon including emissions related to nanocrystals and to point defects in SiO2 is presented.

  8. Comparison of interfaces for (Ba,Sr)TiO3 films deposited on Si and SiO2/Si substrates

    Suvorova, N.A.; Lopez, C.M.; Irene, E.A.; Suvorova, A.A.; Saunders, M.

    2004-01-01

    (Ba,Sr)TiO 3 (BST) thin films were deposited by ion sputtering on both bare and oxidized Si. Spectroscopic ellipsometry results have shown that a SiO 2 underlayer of nearly the same thickness (2.6 nm in average) is found at the Si interface for BST sputter depositions onto nominally bare Si, 1 nm SiO 2 on Si or 3.5 nm SiO 2 on Si. This result was confirmed by high-resolution electron microscopy analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO 2 . Using the conductance method, capacitance-voltage measurements show a decrease in the interface trap density D it of an order of magnitude for oxidized Si substrates with a thicker SiO 2 underlayer. Further reduction of D it was achieved for the capacitors grown on oxidized Si and annealed in forming gas after metallization

  9. Comparison of interfaces for (Ba,Sr)TiO3 films deposited on Si and SiO2/Si substrates

    Suvorova, N. A.; Lopez, C. M.; Irene, E. A.; Suvorova, A. A.; Saunders, M.

    2004-03-01

    (Ba,Sr)TiO3(BST) thin films were deposited by ion sputtering on both bare and oxidized Si. Spectroscopic ellipsometry results have shown that a SiO2 underlayer of nearly the same thickness (2.6 nm in average) is found at the Si interface for BST sputter depositions onto nominally bare Si, 1 nm SiO2 on Si or 3.5 nm SiO2 on Si. This result was confirmed by high-resolution electron microscopy analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO2. Using the conductance method, capacitance-voltage measurements show a decrease in the interface trap density Dit of an order of magnitude for oxidized Si substrates with a thicker SiO2 underlayer. Further reduction of Dit was achieved for the capacitors grown on oxidized Si and annealed in forming gas after metallization.

  10. Synthesis and physico-chemical characterization of CeO2/ZrO2-SO42- mixed oxides

    Hernandez E, J. M.; Silva R, R.; Garcia A, R.; Garcia S, L. A.; Handy, B. E.; Cardenas G, G.; Cueto H, A.

    2012-01-01

    Environmentally friendly solid-acid catalysts CeO 2 /ZrO 2 -SO 4 2- were prepared by the sol gel method varying CeO 2 content (10, 20 and 30 wt %) and using sulfation in situ, maintaining the sulfate ions amount present in the materials at 20 wt %. ZrO 2 and ZrO 2 -SO 4 2- were also prepared for comparison proposes using the same synthesis method. The materials were characterized by X-ray diffraction, nitrogen physisorption, potentiometric titration with n-butylamine, decomposition of 2-propanol and n-pentane isomerization. The specific surface area of ZrO 2 -SO 4 2- was high (160 m 2 /g) compared with the unmodified ZrO 2 (80 m 2 /g), however this area decreased with increasing the CeO 2 content (37-100 m 2 /g). There was no significant effect of CeO 2 on the tetragonal structure of ZrO 2 -SO 4 2- . The variation of acid sites amount runs parallel to the change of specific surface area. The acid sites amount decreased with increasing cerium oxide content. The decomposition of 2-propanol results fundamentally in the formation of dehydration products such as propylene and diisopropyl ether, both involving acid sites. In addition, a good performance during the n-pentane isomerization was observed for these materials. The selectivity towards isopentane reaches 84% when the Pt/CeO 2 /ZrO 2 -SO 4 2- catalyst with the highest CeO 2 content was used. (Author)

  11. Removal of Hazardous Pollutants from Wastewaters: Applications of TiO2-SiO2 Mixed Oxide Materials

    Shivatharsiny Rasalingam

    2014-01-01

    Full Text Available The direct release of untreated wastewaters from various industries and households results in the release of toxic pollutants to the aquatic environment. Advanced oxidation processes (AOP have gained wide attention owing to the prospect of complete mineralization of nonbiodegradable organic substances to environmentally innocuous products by chemical oxidation. In particular, heterogeneous photocatalysis has been demonstrated to have tremendous promise in water purification and treatment of several pollutant materials that include naturally occurring toxins, pesticides, and other deleterious contaminants. In this work, we have reviewed the different removal techniques that have been employed for water purification. In particular, the application of TiO2-SiO2 binary mixed oxide materials for wastewater treatment is explained herein, and it is evident from the literature survey that these mixed oxide materials have enhanced abilities to remove a wide variety of pollutants.

  12. Thermal Annealing Effect on Optical Properties of Binary TiO2-SiO2 Sol-Gel Coatings

    Xiaodong Wang

    2012-12-01

    Full Text Available TiO2-SiO2 binary coatings were deposited by a sol-gel dip-coating method using tetrabutyl titanate and tetraethyl orthosilicate as precursors. The structure and chemical composition of the coatings annealed at different temperatures were analyzed by Raman spectroscopy and Fourier Transform Infrared (FTIR spectroscopy. The refractive indices of the coatings were calculated from the measured transmittance and reflectance spectra. An increase in refractive index with the high temperature thermal annealing process was observed. The Raman and FTIR results indicate that the refractive index variation is due to changes in the removal of the organic component, phase separation and the crystal structure of the binary coatings.

  13. Crystallization Mechanism and Kinetics of BaO-Li2O-ZrO2-SiO2 Glasses

    Cristian Berto da Silveira

    2002-03-01

    Full Text Available Differential thermal analysis and scanning electron microscopy were used to determine the influence of the addition of BaO on the crystallization mechanism of Li2O-ZrO2-SiO2 systems. As the concentration of BaO in the samples increased, a transition occurred in the predominant crystallization mechanism, which passed from superficial to volumetric. To determine the maximum nucleation rate, the crystallization kinetics of the sample containing 20 mole % BaO, which showed the most uniform crystallization, was studied by counting the nuclei with an image analyzer. The first nuclei appeared at the first endothermic inflection point (at the start of Tg, at 440 °C, while the maximum number of nuclei was counted at the midpoint of the glass transition region (446 °C. These results are similar to those observed for other materials that crystallize in volume, and confirm scanning electron microscopy data.

  14. Light coupling and distribution for Si3N4/SiO2 integrated multichannel single-mode sensing system

    Kaźmierczak, Andrzej; Dortu, Fabian; Schrevens, Olivier; Giannone, Domenico; Bouville, David; Cassan, Eric; Gylfason, Kristinn B.; Sohlström, Hans; Sanchez, Benito; Griol, Amadeu; Hill, Daniel

    2009-01-01

    We present an efficient and highly alignment-tolerant light coupling and distribution system for a multichannel Si3N4/SiO2 single-mode photonics sensing chip. The design of the input and output couplers and the distribution splitters is discussed. Examples of multichannel data obtained with the system are given.

  15. Highly sensitive work function hydrogen gas sensor based on PdNPs/SiO2/Si structure at room temperature

    G. Behzadi pour

    Full Text Available In this study, fabrication of highly sensitive PdNPs/SiO2/Si hydrogen gas sensor using experimental and theoretical methods has been investigated. Using chemical method the PdNPs are synthesized and characterized by X-ray diffraction (XRD. The average size of PdNPs is 11 nm. The thickness of the oxide film was 20 nm and the surface of oxide film analyzed using Atomic-force microscopy (AFM. The C-V curve for the PdNPs/SiO2/Si hydrogen gas sensor in 1% hydrogen concentration and at the room temperature has been reported. The response time and recovery time for 1% hydrogen concentration at room temperature were 1.2 s and 10 s respectively. The response (R% for PdNPs/SiO2/Si MOS capacitor hydrogen sensor was 96%. The PdNPs/SiO2/Si MOS capacitor hydrogen sensor showed very fast response and recovery times compared to SWCNTs/PdNPs, graphene/PdNPs, nanorod/PdNPs and nanowire/PdNPs hydrogen gas sensors. Keywords: Sensitive, Oxide film, Capacitive, Resistance

  16. SHS synthesis of Si-SiC composite powders using Mg and reactants from industrial waste

    Chanadee, Tawat

    2017-11-01

    Si-SiC composite powders were synthesized by self-propagating high-temperature synthesis (SHS) using reactants of fly ash-based silica, sawdust-based activated carbon, and magnesium. Fly ash-based silica and sawdust-based activated carbon were prepared from coal mining fly ash and Para rubber-wood sawdust, respectively. The work investigated the effects of the synthesis atmosphere (air and Ar) on the phase and morphology of the SHS products. The SHS product was leached by a two-step acid leaching processes, to obtain the Si-SiC composite powder. The SHS product and SHS product after leaching were characterized by X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectrometry. The results indicated that the SHS product synthesized in air consisted of Si, SiC, MgO, and intermediate phases (SiO2, Mg, Mg2SiO4, Mg2Si), whereas the SHS product synthesized in Ar consisted of Si, SiC, MgO and a little Mg2SiO4. The SiC content in the leached-SHS product was higher when Ar was used as the synthesis atmosphere. As well as affecting the purity, the synthesis atmospheres also affected the average crystalline sizes of the products. The crystalline size of the product synthesized in Ar was smaller than that of the product synthesized in air. All of the results showed that fly ash and sawdust could be effective waste-material reactants for the synthesis of Si-SiC composite powders.

  17. Preparation of Microkernel-Based Mesoporous (SiO2-CdTe-SiO2)@SiO2 Fluorescent Nanoparticles for Imaging Screening and Enrichment of Heat Shock Protein 90 Inhibitors from Tripterygium Wilfordii.

    Hu, Yue; Miao, Zhao-Yi; Zhang, Xiao-Jing; Yang, Xiao-Tong; Tang, Ying-Ying; Yu, Sheng; Shan, Chen-Xiao; Wen, Hong-Mei; Zhu, Dong

    2018-05-01

    The currently utilized ligand fishing for bioactive molecular screening from complex matrixes cannot perform imaging screening. Here, we developed a new solid-phase ligand fishing coupled with an in situ imaging protocol for the specific enrichment and identification of heat shock protein 90 (Hsp 90) inhibitors from Tripterygium wilfordii, utilizing a multiple-layer and microkernel-based mesoporous nanostructure composed of a protective silica coating CdTe quantum dot (QD) core and a mesoporous silica shell, i.e., microkernel-based mesoporous (SiO 2 -CdTe-SiO 2 )@SiO 2 fluorescent nanoparticles (MMFNPs) as extracting carries and fluorescent probes. The prepared MMFNPs showed a highly uniform spherical morphology, retention of fluorescence emission, and great chemical stability. The fished ligands by Hsp 90α-MMFNPs were evaluated via the preliminary bioactivity based on real-time cellular morphology imaging by confocal laser scanning microscopy (CLSM) and then identified by mass spectrometry (MS). Celastrol was successfully isolated as an Hsp 90 inhibitor, and two other specific components screened by Hsp 90α-MMFNPs, i.e., demecolcine and wilforine, were preliminarily identified as potential Hsp 90 inhibitors through the verification of strong affinity to Hsp 90 and antitumor bioactivity. The approach based on the MMFNPs provides a strong platform for imaging screening and discovery of plant-derived biologically active molecules with high efficiency and selectivity.

  18. Sponge-like Si-SiO2 nanocomposite—Morphology studies of spinodally decomposed silicon-rich oxide

    Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.; Mikolajick, T.

    2013-09-01

    Sponge-like Si nanostructures embedded in SiO2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.

  19. Sponge-like Si-SiO2 nanocomposite—Morphology studies of spinodally decomposed silicon-rich oxide

    Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.; Mikolajick, T.

    2013-01-01

    Sponge-like Si nanostructures embedded in SiO 2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO 2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations

  20. Integrated nanophotonic hubs based on ZnO-Tb(OH3/SiO2 nanocomposites

    Lin Yu

    2011-01-01

    Full Text Available Abstract Optical integration is essential for practical application, but it remains unexplored for nanoscale devices. A newly designed nanocomposite based on ZnO semiconductor nanowires and Tb(OH3/SiO2 core/shell nanospheres has been synthesized and studied. The unique sea urchin-type morphology, bright and sharply visible emission bands of lanthanide, and large aspect ratio of ZnO crystalline nanotips make this novel composite an excellent signal receiver, waveguide, and emitter. The multifunctional composite of ZnO nanotips and Tb(OH3/SiO2 nanoparticles therefore can serve as an integrated nanophotonics hub. Moreover, the composite of ZnO nanotips deposited on a Tb(OH3/SiO2 photonic crystal can act as a directional light fountain, in which the confined radiation from Tb ions inside the photonic crystal can be well guided and escape through the ZnO nanotips. Therefore, the output emission arising from Tb ions is truly directional, and its intensity can be greatly enhanced. With highly enhanced lasing emissions in ZnO-Tb(OH3/SiO2 as well as SnO2-Tb(OH3/SiO2 nanocomposites, we demonstrate that our approach is extremely beneficial for the creation of low threshold and high-power nanolaser.

  1. Annealing of TiO2 Films Deposited on Si by Irradiating Nitrogen Ion Beams

    Yokota, Katsuhiro; Yano, Yoshinori; Miyashita, Fumiyoshi

    2006-01-01

    Thin TiO2 films were deposited on Si at a temperature of 600 deg. C by an ion beam assisted deposition (IBAD) method. The TiO2 films were annealed for 30 min in Ar at temperatures below 700 deg. C. The as-deposited TiO2 films had high permittivities such 200 εo and consisted of crystallites that were not preferentially oriented to the c-axis but had an expanded c-axis. On the annealed TiO2 films, permittivities became lower with increasing annealing temperature, and crystallites were oriented preferentially to the (110) plane

  2. Quantitative SIMS analysis of SiGe composition with low energy O2+ beams

    Jiang, Z.X.; Kim, K.; Lerma, J.; Corbett, A.; Sieloff, D.; Kottke, M.; Gregory, R.; Schauer, S.

    2006-01-01

    This work explored quantitative analyses of SiGe films on either Si bulk or SOI wafers with low energy SIMS by assuming a constant ratio between the secondary ion yields of Si + and Ge + inside SiGe films. SiGe samples with Ge contents ranging from 15 to 65% have been analyzed with a 1 keV O 2 + beam at normal incidence. For comparison, the samples were also analyzed with RBS and/or AES. The Ge content as measured with SIMS, based on a single SiGe/Si or SiGe/SOI standard, exhibited good agreement with the corresponding RBS and AES data. It was concluded that SIMS was capable of providing accurate characterization of the SiGe composition with the Ge content up to 65%

  3. A facile approach to fabricate Au nanoparticles loaded SiO2 microspheres for catalytic reduction of 4-nitrophenol

    Tang, Mingyi; Huang, Guanbo; Li, Xianxian; Pang, Xiaobo; Qiu, Haixia

    2015-01-01

    Hydrophilic and biocompatible macromolecules were used to improve and simplify the process for the fabrication of core/shell SiO 2 @Au composite particles. The influence of polymers on the morphology of SiO 2 @Au particles with different size of SiO 2 cores was analyzed by transmission electron microscopy and scanning electron microscopy. The optical property of the SiO 2 @Au particles was studied with UV–Vis spectroscopy. The results indicate that the structure and composition of macromolecules affect the morphology of Au layers on SiO 2 microspheres. The SiO 2 @Au particles prepared in the presence of polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP) have thin and complete Au nanoshells owing to their inducing act in preferential growth of Au nanoparticles along the surface of SiO 2 microspheres. SiO 2 @Au particles can be also prepared from SiO 2 microspheres modified with 3-aminopropyltrimethoxysilane in the presence of PVA or PVP. This offers a simple way to fabricate a Au layer on SiO 2 or other microspheres. The SiO 2 @Au particles demonstrated high catalytic activity in the reduction of 4-nitrophenol. - Highlights: • Facile direct deposition method for Au nanoparticles on silica microspheres. • Influence of different types of macromolecule on the formation of Au shell. • High catalytic performance of Au nanoparticles on silica microspheres

  4. SiO2 on silicon: behavior under heavy ion irradiation

    Rotaru, C.

    2004-03-01

    Heavy ion irradiation was performed on a-SiO 2 layers deposited on Si. Damage of the surface was studied by means of Atomic Force Microscopy. Hillocks appear for an electronic stopping power higher than 16 keV/nm. The height of the hillocks decreases with the thickness of the oxide layer. Infrared Spectroscopy studies show that the damage threshold for a-SiO 2 is at an electronic stopping power of 2 keV/nm. Therefore it is probable that the origin of the hillocks comes from the silicon layer. This could be explain within the frame of thermal spike model. The theoretical thresholds are 8 keV/nm and 1.8 keV/nm for silicon and a-SiO 2 respectively. Chemical etching after irradiation gives a technical possibility to create nano-pits, whose size and shape can be controlled. Additionally, these structures allowed to determine the AFM tip radius. (author)

  5. The Role of SiO2 Gas in the Operation of Anti-Corrosion Coating Produced by PVD

    Meysam Zarchi

    2015-09-01

    Full Text Available This study examined theSiO2 gas present in the coatings used in corrosion industry.These layers have been created by physical vapor deposition (PVD, with an appropriate performance. Sublimation of SiO2is used to protect PVD aluminum flakes from water corrosionand to generate highly porous SiO2 flakes with holes in the nanometer range. SiOx/Al/SiOx sandwiches were made as well as Ag loaded porous SiO2 as antimicrobial filler.

  6. Microwave assisted highly efficient one-pot multi-component synthesis of novel 2-(tetrasubstituted-1H-pyrrol-3-yl-4H-chroman-4-ones catalyzed by heterogeneous reusable silica gel supported polyphosphoric acid (PPA/SiO2

    Sumit Kumar

    2018-02-01

    Full Text Available A solvent-free, eco-friendly and facile approach for the synthesis of highly functionalized tetrasubstituted pyrroles has been reported through one-pot four-component reaction of aldehyde, amine, nitroalkane and 1,3-diketone using silica gel supported polyphosphoric acid (PPA–SiO2 under microwave condition. The reaction occured through the in situ formation of β-keto enamine and nitrostyrene analog following Michael addition and finally intramolecular annulation affording the products in good yields. The key features of the present method include clean reaction, mild conditions, low catalyst loading, straightforward, high to excellent yields, short reaction time, avoiding use of harmful metal catalyst and organic solvent, environmentally friendly compared to the existing methods, recovery and reusability of catalyst and easy workup procedure.

  7. Selective epitaxial growth properties and strain characterization of Si1- x Ge x in SiO2 trench arrays

    Koo, Sangmo; Jang, Hyunchul; Ko, Dae-Hong

    2017-04-01

    In this study, we investigated the formation of a Si1- x Ge x fin structure in SiO2 trench arrays via an ultra-high-vacuum chemical-vapor deposition (UHV-CVD) selective epitaxial growth (SEG) process. Defect generation and microstructures of Si1- x Ge x fin structures with different Ge concentrations ( x = 0.2, 0.3 and 0.45) were examined. In addition, the strain evolution of a Si1- x Ge x fin structure was analyzed by using reciprocal space mapping (RSM). An (111) facet was formed from the Si1- x Ge x epi-layer and SiO2 trench wall interface to minimize the interface and the surface energy. The Si1- x Ge x fin structures were fully relaxed along the direction perpendicular to the trenches regardless of the Ge concentration. On the other hand, the fin structures were fully or partially strained along the direction parallel to the trenches depending on the Ge concentration: fully strained Si0.8Ge0.2 and Si0.7Ge0.3, and a Si0.55Ge0.45 strain-relaxed buffer. We further confirmed that the strain on the Si1- x Ge x fin structures remained stable after oxide removal and H2/N2 post-annealing.

  8. Unraveling the role of SiC or Si substrates in water vapor incorporation in SiO 2 films thermally grown using ion beam analyses

    Corrêa, S. A.; Soares, G. V.; Radtke, C.; Stedile, F. C.

    2012-02-01

    The incorporation of water vapor in SiO 2 films thermally grown on 6H-SiC(0 0 0 1) and on Si (0 0 1) was investigated using nuclear reaction analyses. Water isotopically enriched in deuterium ( 2H or D) and in 18O was used. The dependence of incorporated D with the water annealing temperature and initial oxide thickness were inspected. The D amount in SiO 2/SiC structures increases continuously with temperature and with initial oxide thickness, being incorporated in the surface, bulk, and interface regions of SiO 2 films. However, in SiO 2/Si, D is observed mostly in near-surface regions of the oxide and no remarkable dependence with temperature or initial oxide thickness was observed. At any annealing temperature, oxygen from water vapor was incorporated in all depths of the oxide films grown on SiC, in contrast with the SiO 2/Si.

  9. Hydrodeoxygenation of lignin-derived phenolic compounds to hydrocarbons over Ni/SiO2-ZrO2 catalysts.

    Zhang, Xinghua; Zhang, Qi; Wang, Tiejun; Ma, Longlong; Yu, Yuxiao; Chen, Lungang

    2013-04-01

    Inexpensive non-sulfided Ni-based catalysts were evaluated for hydrodeoxygenation (HDO) using guaiacol as model compound. SiO2-ZrO2 (SZ), a complex oxide synthesized by precipitation method with different ratio of Si/Zr, was impregnated with Ni(NO3)2·6H2O and calcined at 500°C. Conversion rates and product distribution for guaiacol HDO at 200-340°C were determined. Guaiacol conversion reached the maximum at 300°C in the presence of Ni/SZ-3. When HDO reaction was carried out with real lignin-derived phenolic compounds under the optimal conditions determined for guaiacol, the total yield of hydrocarbons was 62.81%. These hydrocarbons were comprised of cyclohexane, alkyl-substituted cyclohexane and alkyl-substituted benzene. They have high octane number, would be the most desirable components for fungible liquid transportation fuel. Copyright © 2013 Elsevier Ltd. All rights reserved.

  10. Regulating effect of SiO2 interlayer on optical properties of ZnO thin films

    Xu, Linhua; Zheng, Gaige; Miao, Juhong; Su, Jing; Zhang, Chengyi; Shen, Hua; Zhao, Lilong

    2013-01-01

    ZnO/SiO 2 nanocomposite films with periodic structure were prepared by electron beam evaporation technique. Regulating effect of SiO 2 interlayer with various thicknesses on the optical properties of ZnO/SiO 2 thin films was investigated deeply. The analyses of X-ray diffraction show that the ZnO layers in ZnO/SiO 2 nanocomposite films have a wurtzite structure and are preferentially oriented along the c-axis while the SiO 2 layers are amorphous. The scanning electron microscope images display that the ZnO layers are composed of columnar grains and the thicknesses of ZnO and SiO 2 layers are all very uniform. The SiO 2 interlayer presents a significant modulation effect on the optical properties of ZnO thin films, which is reflected in the following two aspects: (1) the transmittance of ZnO/SiO 2 nanocomposite films is increased; (2) the photoluminescence (PL) of ZnO/SiO 2 nanocomposite films is largely enhanced compared with that of pure ZnO thin films. The ZnO/SiO 2 nanocomposite films have potential applications in light-emitting devices and flat panel displays. -- Highlights: ► ZnO/SiO 2 nanocomposite films with periodic structure were prepared by electron beam evaporation technique. ► The SiO 2 interlayer presents a significant modulation effect on the optical properties of ZnO thin films. ► The photoluminescence of ZnO/SiO 2 nanocomposite films is largely enhanced compared with that of pure ZnO thin films. ► The ZnO/SiO 2 nanocomposite films have potential applications in light-emitting devices and flat panel displays

  11. HIDROGENACIÓN DE CROTONALDEHÍDO SOBRE CATALIZADORES Ir/TiO2-SiO2

    HUGO ROJAS

    2009-01-01

    Full Text Available Se estudió la hidrogenación de crotonaldehído en fase líquida, sobre catalizadores Ir/TiO2-SiO2; este aldehído es altamente contaminante y proviene de fuentes tan diversas como humo de tabaco, gases de escape de motores de gasolina o diesel y humo de combustión de madera [1]. El objetivo principal de esta investigación fue la obtención del alcohol insaturado (crotil alcohol. A partir de los estudios realizados logró demostrarse que un aumento en el contenido de TiO2, lo mismo que la reducción de los catalizadores a altas temperaturas favorece parámetros como selectividad hacia el producto de interés, actividad catalítica y en general se logró mejorar de manera notable los niveles de conversión. El comportamiento observado se atribuyó principalmente a la fuerte influencia del efecto SMSI (Strong Metal Support Interaction, presente a altas temperaturas en óxidos parcialmente reducibles.

  12. Stability of Trapped Electrons in SiO(2)

    Fleetwood, D.M.; Winokur, P.S.

    1999-01-01

    Thermally stimulated current and capacitance voltage methods are used to investigate the thermal stability of trapped electrons associated with radiation-induced trapped positive charge in metal-oxide-semiconductor capacitors. The density of deeply trapped electrons in radiation-hardened 45 nm oxides exceeds that of shallow electrons by a factor of ∼3 after radiation exposure, and by up to a factor of 10 or more during biased annealing. Shallow electron traps anneal faster than deep traps, and seem to be at least qualitatively consistent with the model of Lelis et al. Deeper traps maybe part of a fundamentally distinct dipole complex, and/or have shifted energy levels that inhibit charge exchange with the Si

  13. Effect of interfacial SiO2- y layer and defect in HfO2- x film on flat-band voltage of HfO2- x /SiO2- y stacks for backside-illuminated CMOS image sensors

    Na, Heedo; Lee, Jimin; Jeong, Juyoung; Kim, Taeho; Sohn, Hyunchul

    2018-03-01

    In this study, the effect of oxygen gas fraction during deposition of a hafnium oxide (HfO2- x ) film and the influence of the quality of the SiO2- y interlayer on the nature of flat-band voltage ( V fb) in TiN/HfO/SiO2- y /p-Si structures were investigated. X-ray photoemission spectroscopy analysis showed that the non-lattice oxygen peak, indicating an existing oxygen vacancy, increased as the oxygen gas fraction decreased during sputtering. From C- V and J- E analyses, the V fb behavior was significantly affected by the characteristics of the SiO2- y interlayer and the non-lattice oxygen fraction in the HfO2- x films. The HfO2- x /native SiO2- y stack presented a V fb of - 1.01 V for HfO2- x films with an oxygen gas fraction of 5% during sputtering. Additionally, the V fb of the HfO2- x /native SiO2- y stack could be controlled from - 1.01 to - 0.56 V by changing the deposition conditions of the HfO2- x film with the native SiO2- y interlayer. The findings of this study can be useful to fabricate charge-accumulating layers for backside-illuminated image sensor devices.

  14. Application of core–shell-structured CdTe-SiO2 quantum dots synthesized via a facile solution method for improving latent fingerprint detection

    Gao Feng; Han Jiaxing; Lv Caifeng; Wang Qin; Zhang Jun; Li Qun; Bao Liru; Li Xin

    2012-01-01

    Fingerprint detection is important in criminal investigation. This paper reports a facile powder brushing technique for improving latent fingerprint detection using core–shell-structured CdTe-SiO 2 quantum dots (QDs) as fluorescent labeling marks. Core–shell-structured CdTe-SiO 2 QDs are prepared via a simple solution-based approach using NH 2 NH 2 ·H 2 O as pH adjustor and stabilizer, and their application for improving latent fingerprint detection is explored. The obtained CdTe-SiO 2 QDs show spherical shapes with well-defined core–shell structures encapsulating different amounts of QDs depending on the type of the pH adjustor and stabilizer. Moreover, the fluorescence of CdTe-SiO 2 QDs is largely enhanced by surface modification of the SiO 2 shell. The CdTe-SiO 2 QDs overcome the oxidation problem of pure CdTe QDs in air, thus affording better variability with strong adhesive ability, better resolution, and bright emission colors for practical application in latent fingerprint detection. In comparison with the conventional fluorescence powders, silver powders, and others, the effectiveness of CdTe-SiO 2 QD powders for detection of latent fingerprints present on a large variety of object surfaces is greatly improved. The synthesis method for CdTe-SiO 2 QDs is simple, cheap, and easy for large-scale production, and thus offers many advantages in the practical application of fingerprint detection.

  15. Characterisation of NdFeB thin films prepared on (100)Si substrates with SiO2 barrier layers

    Sood, D.K.; Muralidhar, G.K.

    1998-01-01

    This work presents a systematic study of the deposition and characterization of NdFeB films on substrates of Si(100) and of SiO2 layer thermally grown on Si(100) held at RT, 360 deg C or 440 deg C. The post-deposition annealing is performed at 600 or 800 deg C in vacuum. The films are characterised using the analytical techniques of RBS, SIMS, XRD, OM and SEM. Results indicate that SiO2 is, in deed, an excellent diffusion barrier layer till 600 deg C but becomes relatively less effective at 800 deg C. Without this barrier layer, interdiffusion at the Si-NdFeB film interface leads to formation of iron silicides, α-Fe and B exclusion from the diffusion zone, in competition with the formation of the magnetic NdFeB phase. (authors)

  16. Processes and procedures for a thin film multilevel hybrid circuit metallization system based on W--Au/SiO2/Al/SiO2

    Hampy, R.E.; Knauss, G.L.; Komarek, E.E.; Kramer, D.K.; Villanueva, J.

    1976-04-01

    The processes and procedures developed for the deposition and photodefinition of a W-Au/SiO 2 /Al/SiO 2 hybrid circuit metallization system for the SLL Micro Actuator are described. The metallization system affords a high degree of miniaturization and permits effective interconnection of a mixture of semiconductor devices and passive components with both gold and aluminum terminations without creating undesirable gold-aluminum interfaces. Sputtered tungsten-gold is the first level conductor except at crossovers where tungsten only is used and aluminum is the second level conductor. Silicon dioxide serves as an insulator between the tungsten and aluminum for crossovers. Vias in the insulating layer permit tungsten-aluminum interconnections where desired. A second layer of silicon dioxide is deposited over the metallization and opened for all gold and aluminum bonding pads. Substrates used were polished sapphire and fine grained alumina. The metallization is capable of withstanding processing temperatures up to 400 0 C for short times

  17. High photocatalytic activity of hierarchical SiO2@C-doped TiO2 hollow spheres in UV and visible light towards degradation of rhodamine B.

    Zhang, Ying; Chen, Juanrong; Hua, Li; Li, Songjun; Zhang, Xuanxuan; Sheng, Weichen; Cao, Shunsheng

    2017-10-15

    Ongoing research activities are targeted to explore high photocatalytic activity of TiO 2 -based photocatalysts for the degradation of environmental contaminants under UV and visible light irradiation. In this work, we devise a facile, cost-effective technique to in situ synthesize hierarchical SiO 2 @C-doped TiO 2 (SCT) hollow spheres for the first time. This strategy mainly contains the preparation of monodisperse cationic polystyrene spheres (CPS), sequential deposition of inner SiO 2 , the preparation of the sandwich-like CPS@SiO 2 @CPS particles, and formation of outer TiO 2 . After the one-step removal of CPS templates by calcination at 450°C, hierarchical SiO 2 @C-doped TiO 2 hollow spheres are in situ prepared. The morphology, hierarchical structure, and properties of SCT photocatalyst were characterized by TEM. SEM, STEM Mapping, BET, XRD, UV-vis spectroscopy, and XPS. Results strongly confirm the carbon doping in the outer TiO 2 lattice of SCT hollow spheres. When the as-synthesized SCT hollow spheres were employed as a photocatalyst for the degradation of Rhodamine B under visible-light and ultraviolet irradiation, the SCT photocatalyst exhibits a higher photocatalytic activity than commercial P25, effectively overcoming the limitations of poorer UV activity for many previous reported TiO 2 -based photocatalysts due to doping. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Synthesis, Characterization and Properties of CeO2-doped TiO2 Composite Nanocrystals

    Oman ZUAS

    2013-12-01

    Full Text Available Pure TiO2 and CeO2-doped TiO2 (3 % CeO2-97 %TiO2 composite nanocrystals were synthesized via co-precipitation method and characterized using TGA, XRD, FTIR, DR-UV-vis and TEM. The XRD data revealed that the phase structure of the synthesized samples was mainly in pure anatase having crystallite size in the range of 7 nm – 11 nm. Spherical shapes with moderate aggregation of the crystal particles were observed under the TEM observation. The presence of the CeO2 at TiO2 site has not only affected morphologically but also induced the electronic property of the TiO2 by lowering the band gap energy from 3.29 eV (Eg-Ti to 3.15 eV (Eg-CeTi. Performance evaluation of the synthesized samples showed that both samples have a strong adsorption capacity toward Congo red (CR dye in aqueous solution at room temperature experiment, where  the capacity of the CeTi was higher than the Ti sample. Based on DR-UV data, the synthesized samples obtained in this study may also become promising catalysts for photo-assisted removal of synthetic dye in aqueous solution. DOI: http://dx.doi.org/10.5755/j01.ms.19.4.2732

  19. First investigations on the quaternary system Na2O-K2O-CaO-SiO2: synthesis and crystal structure of the mixed alkali calcium silicate K1.08Na0.92Ca6Si4O15

    Kahlenberg, Volker; Mayerl, Michael Jean-Philippe; Schmidmair, Daniela; Krüger, Hannes; Tribus, Martina

    2018-04-01

    In the course of an exploratory study on the quaternary system Na2O-K2O-CaO-SiO2 single crystals of the first anhydrous sodium potassium calcium silicate have been obtained from slow cooling of a melt in the range between 1250 and 1050 °C. Electron probe micro analysis suggested the following idealized molar ratios of the oxides for the novel compound: K2O:Na2O:CaO:SiO2 = 1:1:12:8 (or KNaCa6Si4O15). Single-crystal diffraction measurements on a crystal with chemical composition K1.08Na0.92Ca6Si4O15 resulted in the following basic crystallographic data: monoclinic symmetry, space group P 21/ c, a = 8.9618(9) Å, b = 7.3594(6) Å, c = 11.2453(11) Å, β= 107.54(1)°, V = 707.2(1) Å3, Z = 2. Structure solution was performed using direct methods. The final least-squares refinement converged at a residual of R(|F|) = 0.0346 for 1288 independent reflections and 125 parameters. From a structural point of view, K1.08Na0.92Ca6Si4O15 belongs to the group of mixed-anion silicates containing [Si2O7]- and [SiO4]-units in the ratio 1:2. The mono- and divalent cations occupy a total of four crystallographically independent positions located in voids between the tetrahedra. Three of these sites are exclusively occupied by calcium. The fourth site is occupied by 54(1)% K and 46%(1) Na, respectively. Alternatively, the structure can be described as a heteropolyhedral framework based on corner-sharing silicate tetrahedra and [CaO6]-octahedra. The network can build up from kröhnkite-like [Ca(SiO4)2O2]-chains running along [001]. A detailed comparison with other A2B6Si4O15-compounds including topological and group-theoretical aspects is presented.

  20. SiO2-induced release of sVEGFRs from pulmonary macrophages.

    Chao, Jie; Lv, Yan; Chen, Jin; Wang, Jing; Yao, Honghong

    2018-01-01

    The inhalation of silicon dioxide (SiO 2 ) particles causes silicosis, a stubborn pulmonary disease that is characterized by alveolar inflammation during the early stage. Soluble cytokine receptors (SCRs) play important roles in regulating inflammation by either attenuating or promoting cytokine signaling. However, the role of SCRs in silicosis remains unknown. Luminex assays revealed increased soluble vascular endothelial growth factor receptor (sVEGFR) family levels in the plasma of silicosis patients. In an enzyme-linked immunosorbent assay (ELISA), cells from the differentiated human monocytic cell line U937 released sVEGFR family proteins after exposure to SiO 2 (50μg/cm 2 ). Further Western blot experiments revealed that VEGFR expression was also elevated in U937 cells. In contrast, levels of sVEGFR family members did not change in the supernatants of human umbilical vein endothelial cells (HUVECs) after exposure to SiO 2 (50μg/cm 2 ). Interestingly, VEGFR expression in HUVECs decreased after SiO 2 treatment. In a scratch assay, HUVECs exhibited cell migration ability, indicating the acquisition of mesenchymal properties. Our findings highlight the important role of sVEGFRs in both inflammation and fibrosis induced by SiO 2 , suggesting a possible mechanism for the fibrogenic effects observed in pulmonary diseases associated with fibrosis. Copyright © 2017 Elsevier B.V. All rights reserved.

  1. The improvement of SiO2 nanotubes electrochemical behavior by hydrogen atmosphere thermal treatment

    Spataru, Nicolae; Anastasescu, Crina; Radu, Mihai Marian; Balint, Ioan; Negrila, Catalin; Spataru, Tanta; Fujishima, Akira

    2018-06-01

    Highly defected SiO2 nanotubes (SiO2-NT) were obtained by a simple sol-gel procedure followed by calcination. Boron-doped diamond (BDD) polycrystalline films coated with SiO2-NT were used as working electrodes and, unexpectedly, cyclic voltammetric experiments have shown that the concentration of both positive and negative defects at the surface is high enough to enable redox processes involving positively charged Ru(bpy)32+/3+ to occur. Conversely, no electrochemical activity was put into evidence for Fe(CN)63-/4- species, most likely as a result of the strong electrostatic repulsion exerted by the negatively charged SiO2 surface. The concentration of surface defects was further increased by a subsequent thermal treatment in a hydrogen atmosphere which, as EIS measurements have shown, significantly promotes Ru(bpy)32+ anodic oxidation. Digital simulation of the voltammetric responses demonstrated that this treatment does not lead to a similar increase of the number of electron-donor sites. It was also found that methanol anodic oxidation at hydrogenated SiO2-NT-supported platinum results in Tafel slopes of 116-220 mV decade-1, comparable to those reported for both conventional PtRu and Pt-oxide catalysts.

  2. CoFe2O4-SiO2 Composites: Preparation and Magnetodielectric Properties

    T. Ramesh

    2016-01-01

    Full Text Available Cobalt ferrite (CoFe2O4 and silica (SiO2 nanopowders have been prepared by the microwave hydrothermal (M-H method using metal nitrates as precursors of CoFe2O4 and tetraethyl orthosilicate as a precursor of SiO2. The synthesized powders were characterized by XRD and FESEM. The (100-x (CoFe2O4 + xSiO2 (where x = 0%, 10%, 20%, and 30% composites with different weight percentages have been prepared using ball mill method. The composite samples were sintered at 800°C/60 min using the microwave sintering method and then their structural and morphological studies were investigated using X-ray diffraction (XRD, Fourier transformation infrared (FTIR spectra, and scanning electron microscopy (SEM, respectively. The effect of SiO2 content on the magnetic and electrical properties of CoFe2O4/SiO2 nanocomposites has been studied via the magnetic hysteresis loops, complex permeability, permittivity spectra, and DC resistivity measurements. The synthesized nanocomposites with adjustable grain sizes and controllable magnetic properties make the applicability of cobalt ferrite even more versatile.

  3. Modulation of the thermoluminescence glow curve of sol-gel synthesized SiO2 and Si O-2:Eu through thermal annealing

    Salas J, Ch. J.; Cruz V, C.; Bernal, R.; Castano, V. M.

    2015-10-01

    Full text: Due to the increasing use of ionizing radiations, is necessary to monitor the radiation fields and exposure doses in facilities in which they are used. Different facilities or applications involve the use of different radiation and doses, and the sort of needed dosimetry also varies. Sometimes a conventional thermoluminescence (Tl) dosimetry satisfy the requirements since the record of the accumulated dose in a time interval is enough, but other cases could require for real-time measurement of a radiation field, being required a non-Tl dosimetric technique. On the other hand, different applications involve the use of different dose ranges, and so dosimeters with different sensitivities are needed. To solve the diverse needs of radiation detectors and dosimeters, a lot of phosphors materials has been characterized concerning their dosimetric capabilities. For medical application, biocompatible materials are desirable. In this work, we present experimental evidence that Sol-Gel synthesized SiO 2 and SiO 2 :Eu phosphors exhibit Tl glow curves composed by the superposition of several individual glow peaks each located at different temperature ranging from values below 100 up to temperatures greater than 400 degrees C, whose relative sensitivities can be modified by subjecting the phosphors to different thermal annealing. By modulating the relative intensities of the individual Tl peaks, glow curves with different shapes are obtained in such a way that SiO 2 and SiO 2 :Eu can be used to develop dosimeters useful for different dose ranges, and for both, conventional thermoluminescence dosimetry and non-thermoluminescence afterglow-based) dosimetry. (Author)

  4. Influence of SiO2 coating on dielectric property of TiC reinforced PVDF composite%SiO2涂层对TiC/PVDF复合材料介电性能的影响研究

    贺新福; 吴红菊; 刘天涯; 冉安; 周文英

    2017-01-01

    为降低碳化钛(TiC)/聚偏氟乙烯(PVDF)体系的介电损耗,通过溶胶-凝胶法在TiC粒子表面包覆SiO2绝缘层,形成SiO2@TiC核壳结构粒子,再与PVDF复合,制备出SiO2@TiC/PVDF复合材料.研究结果表明,TiC表面成功包覆上SiO2涂层;在质量分数为9%的TiC或SiO2@TiC总用量时,SiO2@TiC/PVDF的损耗因子相比TiC/PVDF明显降低,随SiO2包覆量的增加,SiO2@TiC/PVDF的介电常数、损耗因子和电导率均下降;包覆量相同时,随SiO2@TiC粒子含量增加,SiO2@TiC/PVDF的介电常数、电导率、损耗因子均逐步增大.

  5. A novel ITO/AZO/SiO2/p-Si frame SIS heterojunction fabricated by magnetron sputtering

    He, Bo; Wang, HongZhi; Li, YaoGang; Ma, ZhongQuan; Xu, Jing; Zhang, QingHong; Wang, ChunRui; Xing, HuaiZhong; Zhao, Lei; Rui, YiChuan

    2013-01-01

    Highlights: •Because the ITO/AZO double films lead to a great decrease of the lateral resistance. •The photon current can easily flow through top film entering the Cu front contact. •High photocurrent is obtained under a reverse bias. -- Abstract: The novel ITO/AZO/SiO 2 /p-Si SIS heterojunction has been fabricated by low temperature thermal oxidation an ultrathin silicon dioxide and RF sputtering deposition ITO/AZO double films on p-Si (1 0 0) polished substrate. The microstructural, optical and electrical properties of the ITO/AZO antireflection films were characterized by XRD, SEM, UV–VIS spectrophotometer, four point probe and Hall effect measurement, respectively. The results show that ITO/AZO films are of good quality. And XPS was carried out on the ultrathin SiO 2 film. The heterojunction shows strong rectifying behavior under a dark condition, which reveals that formation of a diode between AZO and p-Si. The ideality factor and the saturation current of this diode is 2.7 and 8.68 × 10 −5 A, respectively. High photocurrent is obtained under a reverse bias when the crystalline quality of ITO/AZO double films is good enough to transmit the light into p-Si. We can see that under reverse bias conditions the photocurrent of ITO/AZO/SiO 2 /p-Si SIS heterojunction is much higher than the photocurrent of AZO/SiO 2 /p-Si SIS heterojunction. Because the high quality crystallite and the good conductivity of ITO film which prepared by magnetron-sputtering on AZO film lead to a great decrease of the lateral resistance. The photon induced current can easily flow through ITO layer entering the Cu front contact. Thus, high photocurrent is obtained under a reverse bias

  6. Reflection Enhancement Using TiO2/SiO2 Bilayer Films Prepared by Cost-Effective Sol-gel Method

    R. Ajay Kumar

    2017-04-01

    Full Text Available Multilayer dielectric thin film structure has been demanded for its application in optoelectronic devices such as optical waveguides, vertical cavity surface-emitting devices, biosensors etc. In this paper, we present the fabrication and characterization of bilayer thin films of TiO2/SiO2 using sol-gel spin coating method. Ellipsometer measurement showed refractive index values 1.46, 2.1 corresponding to the SiO2 and TiO2 films respectively. The FTIR transmittance peaks observed at ~970 cm-1, ~1100 cm-1 and ~1400 cm-1 are attributed to the Ti-O-Si, Si-O-Si and Ti-O-Ti bonds respectively. Maximum reflectance is observed from two bilayer film structure which can be further optimized to get the high reflection to a broad wavelength range.

  7. Whiter, brighter, and more stable cellulose paper coated with TiO2 /SiO2 core/shell nanoparticles using a layer-by-layer approach.

    Cheng, Fei; Lorch, Mark; Sajedin, Seyed Mani; Kelly, Stephen M; Kornherr, Andreas

    2013-08-01

    To inhibit the photocatalytic degradation of organic material supports induced by small titania (TiO2 ) nanoparticles, four kinds of TiO2 nanoparticles, that is, commercial P25-TiO2 , commercial rutile phase TiO2 , rutile TiO2 nanorods and rutile TiO2 spheres, prepared from TiCl4 , were coated with a thin, but dense, coating of silica (SiO2 ) using a conventional sol-gel technique to form TiO2 /SiO2 core/shell nanoparticles. These core/shell particles were deposited and fixed as a very thin coating onto the surface of cellulose paper samples by a wet-chemistry polyelectrolyte layer-by-layer approach. The TiO2 /SiO2 nanocoated paper samples exhibit higher whiteness and brightness and greater stability to UV-bleaching than comparable samples of blank paper. There are many potential applications for this green chemistry approach to protect cellulosic fibres from UV-bleaching in sunlight and to improve their whiteness and brightness. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. XPS studies of SiO2 surface layers formed by oxygen ion implantation into silicon

    Schulze, D.; Finster, J.

    1983-01-01

    SiO 2 surface layers of 160 nm thickness formed by 16 O + ion implantation into silicon are examined by X-ray photoelectron spectroscopy measurements into the depth after a step-by-step chemical etching. The chemical nature and the thickness of the transition layer were determined. The results of the XPS measurements show that the outer surface and the bulk of the layers formed by oxygen implantation and subsequent high temperature annealing consist of SiO 2 . There is no evidence for Si or SiO/sub x/ (0 2 and Si is similar to that of thin grown oxide layers. Only its thickness is somewhat larger than in thermal oxide

  9. Self-organization of nanocluster δ-layers at ion-beam-mixed Si-SiO2 interfaces

    Roentzsch, L.

    2003-11-01

    This diploma thesis presents experimental evidence of a theoretical concept which predicts the self-organization of δ-layers of silicon nanoclusters in the buried oxide of a MOS-like structure. This approach of ''bottom-up'' structuring might be of eminent importance in view of future semiconductor memory devices. Unconventionally, a 15 nm thin SiO 2 layer, which is enclosed by a 50 nm poly-Si capping layer and the Si substrate, is irradiated with Si + ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiO x (x 2 matrix at a distance of ∼3 nm from the Si substrate. The physical mechanisms of ion mixing of the two Si-SiO 2 interfaces and subsequent phase separation, which result in the desired sample structure, are elucidated from the viewpoint of computer simulations. In addition, experimental evidence is presented based on various methods, including TEM, RBS, and SIMS. A novel method of Si nanocluster decoration is of particular importance which applies Ge as contrast enhancing element in TEM studies of tiny Si nanoclusters. (orig.)

  10. Sensing performance of plasma-enhanced chemical vapor deposition SiC-SiO2-SiC horizontal slot waveguides

    Pandraud, G.; Margallo-Balbas, E.; Sarro, P.M.

    2012-01-01

    We have studied, for the first time, the sensing capabilities of plasma-enhanced chemical vapor deposition (PECVD) SiC-SiO2-SiC horizontal slot waveguides. Optical propagation losses were measured to be 23.9 dB?cm for the quasi-transverse magnetic mode. To assess the potential of this device as a

  11. Defect layer in SiO2-Sic interface proved by a slow positron beam

    Maekawa, M.; Kawasuso, A.; Yoshikawa, M.; Miyashita, A.; Suzuki, R.; Ohdaira, T.

    2006-01-01

    The structure of the SiO 2 -4ph-SiC interface layer produced by dry oxidation has been studied by positron annihilation spectroscopy using slow positron beams. From Doppler broadening measurements, the interface layer was clearly distinguished from the SiO 2 and SiC layers and was observed to be defective. At the interface layer, a single long positron lifetime of 451 ps, which is close to the second lifetime in the SiO 2 layer, was obtained, thus suggesting that the structure of the interface layer resembles an amorphous SiO 2 network. A comparison was made between the obtained electron momentum distribution at the interface layer and the theoretical calculation. It was found that positrons annihilate with oxygen valence electrons. By annealing after the oxidation, the annihilation probability of the positrons with oxygen valence electrons and the number of interface traps decreased in the same temperature range, thus suggesting a correlation between interface traps and positron annihilation sites

  12. Fluorocarbon based atomic layer etching of Si_3N_4 and etching selectivity of SiO_2 over Si_3N_4

    Li, Chen; Metzler, Dominik; Oehrlein, Gottlieb S.; Lai, Chiukin Steven; Hudson, Eric A.

    2016-01-01

    Angstrom-level plasma etching precision is required for semiconductor manufacturing of sub-10 nm critical dimension features. Atomic layer etching (ALE), achieved by a series of self-limited cycles, can precisely control etching depths by limiting the amount of chemical reactant available at the surface. Recently, SiO_2 ALE has been achieved by deposition of a thin (several Angstroms) reactive fluorocarbon (FC) layer on the material surface using controlled FC precursor flow and subsequent low energy Ar"+ ion bombardment in a cyclic fashion. Low energy ion bombardment is used to remove the FC layer along with a limited amount of SiO_2 from the surface. In the present article, the authors describe controlled etching of Si_3N_4 and SiO_2 layers of one to several Angstroms using this cyclic ALE approach. Si_3N_4 etching and etching selectivity of SiO_2 over Si_3N_4 were studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Surface chemistries of Si_3N_4 were investigated by x-ray photoelectron spectroscopy (XPS) after vacuum transfer at each stage of the ALE process. Since Si_3N_4 has a lower physical sputtering energy threshold than SiO_2, Si_3N_4 physical sputtering can take place after removal of chemical etchant at the end of each cycle for relatively high ion energies. Si_3N_4 to SiO_2 ALE etching selectivity was observed for these FC depleted conditions. By optimization of the ALE process parameters, e.g., low ion energies, short ESLs, and/or high FC film deposition per cycle, highly selective SiO_2 to Si_3N_4 etching can be achieved for FC accumulation conditions, where FC can be selectively accumulated on Si_3N_4 surfaces. This highly selective etching is explained by a lower carbon consumption of Si_3N_4 as compared to SiO_2. The comparison of C_4F_8 and CHF_3 only showed a difference in etching selectivity for FC depleted conditions. For FC accumulation conditions

  13. Synthesis of ceramic powders of La9,56 (SiO4)6O2,34 and La9,8Si5,7MgO,3O26,4 by modified sol-gel process

    Lira, Sabrina Lopes; Paiva, Mayara Rafaela Soares; Misso, Agatha Matos; Elias, Daniel Ricco; Yamagata, Chieko

    2012-01-01

    Lanthanum silicate oxyapatite materials are promising for application as electrolyte in solid oxide fuel cells because of high ionic conductivity at temperatures between 600 deg C and 800 deg C. In this work, oxyapatites with the composition La 9,56 (SiO 4 ) 6 O 2,34 , and La 9,8 Si 5,7 Mg 0,3 O 26,4 were synthesized by using the sol-gel method, followed by precipitation. Initially, the gel of silica was synthesized from sodium silicate solution, by acid catalysis using lanthanum and magnesium chloride solution. Then, the La and Mg hydroxides were precipitated with NaOH in the gel. The powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and measurements of specific surface area. The crystalline oxyapatite phase of La 9,56 (SiO 4 ) 6 O 2,34 , and was La 9,8 Si 5,7 Mg 0,3 O 26,4 obtained by calcination at 900 deg C for 2 and 1h respectively (author)

  14. Enhanced formation of Ge nanocrystals in Ge : SiO2 layers by swift heavy ions

    Antonova, I V; Volodin, V A; Marin, D M; Skuratov, V A; Smagulova, S A; Janse van Vuuren, A; Neethling, J; Jedrzejewski, J; Balberg, I

    2012-01-01

    In this paper we report the ability of swift heavy Xe ions with an energy of 480 MeV and a fluence of 10 12 cm -2 to enhance the formation of Ge nanocrystals within SiO 2 layers with variable Ge contents. These Ge-SiO 2 films were fabricated by the co-sputtering of Ge and quartz sources which followed various annealing procedures. In particular, we found that the irradiation of the Ge : SiO 2 films with subsequent annealing at 500 °C leads to the formation of a high concentration of nanocrystals (NCs) with a size of 2-5 nm, whereas without irradiation only amorphous inclusions were observed. This effect, as evidenced by Raman spectra, is enhanced by pre-irradiation at 550 °C and post-irradiation annealing at 600 °C, which also leads to the observation of room temperature visible photoluminescence. (paper)

  15. Investigation of luminescence properties in SiO2: Tb, Yb upconversion inverse opal

    Yang Zhengwen; Yan Dong; Song Zhiguo; Zhou Dacheng; Yu Xue; Yang Yong; Yin Zhaoyi; Yan Lei; Wang Rongfei; Wu Hangjun; Qiu Jianbei

    2012-01-01

    The SiO 2 : Tb, Yb inverse opals with photonic band gap at 465 or 543 nm were prepared, and an effect of photonic band gap on upconversion spontaneous emission from Tb 3+ was investigated. The results show that the photonic band gap has a significant influence on the upconversion emission of the SiO 2 : Tb, Yb inverse opals. The upconversion luminescence of the Tb 3+ ions is suppressed in the inverse opal compared with the luminescence of that of the reference sample. - Highlights: ► Upconversion emission from Tb 3+ was observed in the SiO 2 : Tb, Yb inverse opal. ► UC emission of Tb 3+ was modulated by controlling the structure of inverse opal. ► UC emission of Tb 3+ was depressed in the inverse opal.

  16. Fundamental characteristics study of anion-exchange PVDF-SiO(2) membranes.

    Zuo, Xingtao; Shi, Wenxin; Yu, Shuili; He, Jiajie

    2012-01-01

    A new type of poly(vinylidene fluoride)(PVDF)-SiO(2) hybrid anion-exchange membrane was prepared by blending method. The anion-exchange groups were introduced by the reaction of epoxy groups with trimethylamine (TMA). Contact angle between water and the membrane surface was measured to characterize the hydrophilicity change of the membrane surface. The effects of nano-sized SiO(2) particles in the membrane-forming materials on the membrane mechanical properties and conductivity were also investigated. The experimental results indicated that PVDF-SiO(2) anion-exchange membranes exhibited better water content, ion-exchange capacity, conductivity and mechanic properties, and so may find potential applications in alkaline membrane fuel cells and water treatment processes.

  17. Ion assisted deposition of SiO2 film from silicon

    Pham, Tuan. H.; Dang, Cu. X.

    2005-09-01

    Silicon dioxide, SiO2, is one of the preferred low index materials for optical thin film technology. It is often deposited by electron beam evaporation source with less porosity and scattering, relatively durable and can have a good laser damage threshold. Beside these advantages the deposition of critical optical thin film stacks with silicon dioxide from an E-gun was severely limited by the stability of the evaporation pattern or angular distribution of the material. The even surface of SiO2 granules in crucible will tend to develop into groove and become deeper with the evaporation process. As the results, angular distribution of the evaporation vapor changes in non-predicted manner. This report presents our experiments to apply Ion Assisted Deposition process to evaporate silicon in a molten liquid form. By choosing appropriate process parameters we can get SiO2 film with good and stable property.

  18. Defects in electron irradiated vitreous SiO2 probed by positron annihiliation

    Uedono, Akira; Tanigawa, Shoichiro; Kawano, Takao; Itoh, Hisayoshi

    1994-01-01

    Defects in 3 MeV electron irradiated vitreous SiO 2 (v-SiO 2 ) were probed by the positron annihilation technique. For unirradiated v-SiO 2 specimens, almost all positrons were found to annihilate from positronium (Ps) states. This high formation probability of Ps was attributed to the trapping of positrons by open-space defects. The formation probability of Ps was decreased by the electron irradiation. The observed inhibition of the Ps formation was attributed to the trapping of positrons by point defects introduced and/or activated by the irradiation. From measurements of the lifetime distribution of Ps, it was found that, by the electron irradiation, the mean size of open-space defects was decreased and the size distribution of such defects was broadened. (Author)

  19. Superhydrophobicity and regeneration of PVDF/SiO2 composite films

    Liu, Tao; Li, Xianfeng; Wang, Daohui; Huang, Qinglin; Liu, Zhen; Li, Nana; Xiao, Changfa

    2017-02-01

    Superhydrophobicity of polymers is easily destroyed by careless touching due to the softness of microstructures. In this study, based on a well-constructed polyvinylidene fluoride (PVDF) surface, a novel superhydrophobic PVDF/SiO2 composite film was fabricated by adding hydrophobic SiO2 nanoparticle and solvent into a coagulation bath. The water contact angle of the composite film reached 162.3° and the sliding angle was as low as 1.5°. More importantly, the composite film could be regenerated only through immersing the composite film in the designed regeneration agent. The composition of the designed regeneration agent ensured that SiO2 nanoparticles were firmly adhered on the film surface even under the ultrasonic cleaning. Hence, the superhydrophobicity and self-cleaing property could be regenerated and maintained effectively, and moreover, these propeties could resist a proper pressure. In addition, after many rubbing-regenerating cycles, the regeneration method was still valid.

  20. The hydrophobic and omnidirectional antireflection coating of SiO2 nanospheres with C18-TEOS

    Hsu, Cheng-Chih; Lan, Wen-Lin; Chen, Nien-Po; Wu, Chyan-Chyi

    2014-06-01

    This paper demonstrates the antireflection coating of SiO2 nanospheres applied to cover glass by using the optimal spin-coating method. Because of the hydrolysis and condensation reactions between the SiO2 nanosphere antireflection (AR) coating and n-octadecyltriethoxysilane solution (C18-TEOS), the contact angle of the AR coating with hydrophobic treatment is improved approximately 38%, and the moisture-resistance remains unchanged, which preserved similar transmittance for six weeks. Furthermore, the AR coating with hydrophobic treatment exhibits approximately 3% and 7% improvement in the transmittance at normal and oblique incidence, respectively. The hydrophobic and omnidirectional AR coating with nanoscale SiO2 particles can be fabricated using the proposed simple and economical method.

  1. SiO2 coating of silver nanoparticles by photoinduced chemical vapor deposition

    Boies, Adam M; Girshick, Steven L; Roberts, Jeffrey T; Zhang Bin; Nakamura, Toshitaka; Mochizuki, Amane

    2009-01-01

    Gas-phase silver nanoparticles were coated with silicon dioxide (SiO 2 ) by photoinduced chemical vapor deposition (photo-CVD). Silver nanoparticles, produced by inert gas condensation, and a SiO 2 precursor, tetraethylorthosilicate (TEOS), were exposed to vacuum ultraviolet (VUV) radiation at atmospheric pressure and varying temperatures. The VUV photons dissociate the TEOS precursor, initiating a chemical reaction that forms SiO 2 coatings on the particle surfaces. Coating thicknesses were measured for a variety of operation parameters using tandem differential mobility analysis and transmission electron microscopy. The chemical composition of the particle coatings was analyzed using energy dispersive x-ray spectrometry and Fourier transform infrared spectroscopy. The highest purity films were produced at 300-400 0 C with low flow rates of additional oxygen. The photo-CVD coating technique was shown to effectively coat nanoparticles and limit core particle agglomeration at concentrations up to 10 7 particles cm -3 .

  2. Core–shell-typed Ag-SiO2 nanoparticles as solar selective coating materials

    Gao, Tao; Jelle, Bjørn Petter; Gustavsen, Arild

    2013-01-01

    Silver (Ag) nanoparticles with typical diameter of about 50 nm have been prepared via a polyol process. The as-prepared Ag nanoparticles are well crystallized and exhibit a characteristic surface plasmon resonance (SPR) band centered at ∼423 nm. The SPR band shows a strong dependence on the sizes of Ag nanoparticles and the types of the dielectric medium. Core–shell-typed Ag-SiO 2 nanoparticles have also been prepared by depositing a thin layer (∼25 nm) of silica on Ag nanoparticles. The core–shell-typed Ag-SiO 2 nanoparticles show similar optical behaviors (absorption, transmission, and reflection) but enhanced stability compared to those of the Ag nanoparticles, indicating that the core–shell-typed Ag-SiO 2 nanoparticles may be used as solar selective coating materials for architectural window applications.

  3. Preparation, characterization and infrared emissivity study of helical polyurethane-SiO2 core-shell composite

    Wang Zhiqiang; Zhou Yuming; Yao Qingzhao; Sun Yanqing

    2009-01-01

    Helical polyurethane-SiO 2 (HPU-SiO 2 ) core-shell composite was prepared after surface modification of SiO 2 nanoparticles. HPU-SiO 2 was characterized by Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet (UV) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified SiO 2 . HPU-SiO 2 composite exhibits clearly core-shell structure. The ultraviolet absorption and crystallizability of HPU-SiO 2 are changed due to the shell of helical polyurethane, which possesses regular single-handed conformation and inter-chain hydrogen bonds. The infrared emissivity of HPU-SiO 2 was also investigated. The result indicates that the interfacial interactions between organic shell and inorganic core induce the infrared emissivity value being reduced from 0.781 for SiO 2 to 0.503 for HPU-SiO 2 .

  4. Electro-codeposition of Ni-SiO2 nanocomposite coatings from deep eutectic solvent with improved corrosion resistance

    Li, Ruiqian; Hou, Yuanyuan; Liang, Jun

    2016-03-01

    Electro-codeposition of nano-sized SiO2 particles into the metal matrix in aqueous solution is generally difficult. In this paper, the nano-sized SiO2 particles were successfully codeposited in the Ni matrix from a choline chloride (ChCl)/ethylene glycol (EG) based deep eutectic solvent (DES) by pulse electro-codeposition. The effects of nano-sized SiO2 particles on electrochemical behaviour of Ni(II) were investigated. The microstructure, composition and corrosion resistance of pure Ni and Ni-SiO2 nanocomposite coatings were explored. Results showed that the SiO2 nanoparticles exhibited excellent dispersion stability in ChCl:2EG DES without any stabilizing additives and the presence of SiO2 nanoparticles have significant effects on the nucleation mechanism of Ni. The maximum content of SiO2 nanoparticles in composite coatings can achieve 4.69 wt.%, which closes to the level of co-deposition micro-sized SiO2 particles from aqueous solution. The Ni-SiO2 nanocomposite coatings exhibit much better corrosion resistance than pure Ni coating, and the corrosion resistance performance increases with increasing SiO2 content in the composite coatings.

  5. Microwave electromagnetic and absorption properties of SiO2/C core/shell composites plated with metal cobalt

    Shen, Guozhu; Fang, Xumin; Wu, Hongyan; Wei, Hongyu; Li, Jingfa; Li, Kaipeng; Mei, Buqing; Xu, Yewen

    2017-04-01

    A facile method has been developed to fabricate magnetic core/shell SiO2/C/Co sub-microspheres via the pyrolysis of SiO2/PANI (polyaniline) and electroless plating method. The electromagnetic parameters of these SiO2/C and SiO2/C/Co composites were measured and the microwave reflection loss properties were evaluated in the frequency range of 2-18 GHz. The results show that the dielectric loss of SiO2/C composite increases with the increase of carbonization temperature and the magnetic loss enhances due to the deposition of cobalt on the SiO2/C sub-microspheres. The reflection loss results exhibit that the microwave absorption properties of the SiO2/C/Co composites are more excellent than those of SiO2/C composites for each thickness. The maximum effective absorption bandwidth (reflection loss ≤ -10 dB) arrives at 5.0 GHz (13.0-18 GHz) for SiO2/C/Co composite with 1.5 mm of thickness and the minimum reflection loss value is -24.0 dB at 5.0 GHz with 4.0 mm of thickness. The microwave loss mechanism of the SiO2/C/Co composites was also discussed in this paper.

  6. High Photocatalytic Activity of Fe3O4-SiO2-TiO2 Functional Particles with Core-Shell Structure

    Chenyang Xue

    2013-01-01

    Full Text Available This paper describes a novel method of synthesizing Fe3O4-SiO2-TiO2 functional nanoparticles with the core-shell structure. The Fe3O4 cores which were mainly superparamagnetic were synthesized through a novel carbon reduction method. The Fe3O4 cores were then modified with SiO2 and finally encapsulated with TiO2 by the sol-gel method. The results of characterizations showed that the encapsulated 700 nm Fe3O4-SiO2-TiO2 particles have a relatively uniform size distribution, an anatase TiO2 shell, and suitable magnetic properties for allowing collection in a magnetic field. These magnetic properties, large area, relative high saturation intensity, and low retentive magnetism make the particles have high dispersibility in suspension and yet enable them to be recovered well using magnetic fields. The functionality of these particles was tested by measuring the photocatalytic activity of the decolouring of methyl orange (MO and methylene blue (MB under ultraviolet light and sunlight. The results showed that the introduction of the Fe3O4-SiO2-TiO2 functional nanoparticles significantly increased the decoloration rate so that an MO solution at a concentration of 10 mg/L could be decoloured completely within 180 minutes. The particles were recovered after utilization, washing, and drying and the primary recovery ratio was 87.5%.

  7. Pt/MOx/SiO2, Pt/MOx/TiO2, and Pt/MOx/Al2O3 Catalysts for CO Oxidation

    Hongmei Qin

    2015-04-01

    Full Text Available Conventional supported Pt catalysts have often been prepared by loading Pt onto commercial supports, such as SiO2, TiO2, Al2O3, and carbon. These catalysts usually have simple metal-support (i.e., Pt-SiO2 interfaces. To tune the catalytic performance of supported Pt catalysts, it is desirable to modify the metal-support interfaces by incorporating an oxide additive into the catalyst formula. Here we prepared three series of metal oxide-modified Pt catalysts (i.e., Pt/MOx/SiO2, Pt/MOx/TiO2, and Pt/MOx/Al2O3, where M = Al, Fe, Co, Cu, Zn, Ba, La for CO oxidation. Among them, Pt/CoOx/SiO2, Pt/CoOx/TiO2, and Pt/CoOx/Al2O3 showed the highest catalytic activities. Relevant samples were characterized by N2 adsorption-desorption, X-ray diffraction (XRD, transmission electron microscopy (TEM, H2 temperature-programmed reduction (H2-TPR, X-ray photoelectron spectroscopy (XPS, CO temperature-programmed desorption (CO-TPD, O2 temperature-programmed desorption (O2-TPD, and CO2 temperature-programmed desorption (CO2-TPD.

  8. The photodeposition of surface plasmon Ag metal on SiO2@α-Fe2O3 nanocomposites sphere for enhancement of the photo-Fenton behavior

    Uma, Kasimayan; Arjun, Nadarajan; Pan, Guan-Ting; Yang, Thomas C.-K.

    2017-12-01

    In this study, a simple sol-gel method was used for the synthesis of a core-shell structure of SiO2@α-Fe2O3 nanocomposites for employment as a visible light photocatalyst. It was observed that Ag nanoparticles about 20 nm in size were successfully deposited on the surface of the SiO2@α-Fe2O3 nanocomposites. The photocatalytic activity of the Ag-SiO2@α-Fe2O3 nanocomposites catalyst was investigated by observing the degradation of methylene blue (MB) dye in a photo-Fenton process. The results showed that the Ag nanoparticles acted as centers for photo induced electron transfer. The catalytic activity in the SiO2@α-Fe2O3 nanocomposites were enhanced due to the plasmoni c effect of Ag metal under visible light irradiation. The addition of H2O2 played an important role, generating more OH radicals which improved the photo-Fenton catalytic activity, resulting in quicker degradation of the MB dye using the Ag-SiO2@α-Fe2O3 nanocomposite catalyst.

  9. Influence of substrate treatment on the growth of advanced core–shell alloys and compounds of FeSi@SiO2 and SiO2 nanowires

    Thabethe, S

    2014-12-01

    Full Text Available Advanced core–shell FeSi@SiO(subx) nanowires are observed when FeCl(sub3) vapour is made to flow over a SiO(sub2)/Si substrate at 1100 degress C. The thickness of the SiO(subx) sheath (d0) is found to depend inversely as the period of time of HF...

  10. Thermal stability of polyoxometalate compound of Keggin K8[2-SiW11O39]∙nH2O supported with SiO2

    Yunita Sari M A

    2017-06-01

    Full Text Available Synthesis through sol-gel method and characterization of polyoxometalate compound of K8[b2-SiW11O39]∙nH2O supported with SiO2 have been done. The functional groups of polyoxometalate compound  was characterized by FT-IR spectrophotometer for the fungtional groups and the degree’s of crystalinity  using XRD. The acidity of K8[b2-SiW11O39]∙nH2O/SiO2 was determined qualitative analysis using ammonia and pyridine adsorption and the quantitative analysis using potentiometric titration method. The results of FT-IR spectrum of K8[b2-SiW11O39]∙nH2O appeared at  wavenumber 987.55 cm-1 (W=O, 864.11 cm-1 (W-Oe-W, 756.1 cm-1 (W-Oc-W, 3425.58 cm-1 (O-H, respectively and spectrum of  K8[b2-SiW11O39]SiO2 appeared at wavenumber  956.69 cm-1 (W=O, 864.11 cm-1 (W-Oe-W, 3448.72 cm-1 (O-H, respectively. The diffraction of XRD pattern of K8[b2-SiW11O39]∙nH2O and K8[b2-SiW11O39]∙nH2O/SiO2 compounds show high crystalinity. The acidic properties showed K8[b2-SiW11O39]∙nH2O/SiO2 more acidic compared to K8[b2-The SiW11O39]∙nH2O. The qualitative analysis showed pyridine compound adsorbed more of polyoxometalate compound of K8[b2-SiW11O39]∙nH2O/SiO2. Analysis of stability showed that the K8[b2-SiW11O39]∙nH2O/SiO2 at temperature 500°C has structural changes compare to 200-400oC which was indicated from vibration at wavenumber 800-1000 cm-1. Keywords : K8[b2-SiW11O39]∙nH2O, polyoxometalate, SiO2.

  11. Characterization of Chemical Vapor Deposited Tetraethyl Orthosilicate based SiO2 Films for Photonic Devices

    Jhansirani KOTCHARLAKOTA

    2016-05-01

    Full Text Available Silicon has been the choice for photonics technology because of its cost, compatibility with mass production and availability. Silicon based photonic devices are very significant from commercial point of view and are much compatible with established technology. This paper deals with deposition and characterization of SiO2 films prepared by indigenously developed chemical vapor deposition system. Ellipsometry study of prepared films showed an increase in refractive index and film thickness with the increment in deposition temperature. The deposition temperature has a significant role for stoichiometric SiO2 films, FTIR measurement has shown the three characteristics peaks of Si-O-Si through three samples prepared at temperatures 700, 750 and 800 °C while Si-O-Si stretching peak positions were observed to be shifted to lower wavenumber in accordance to the temperature. FESEM analysis has confirmed the smooth surface without any crack or disorder while EDX analysis showed the corresponding peaks of compositional SiO2 films.DOI: http://dx.doi.org/10.5755/j01.ms.22.1.7245

  12. Effect of re-oxidation annealing process on the SiO2/SiC interface characteristics

    Yan Hongli; Jia Renxu; Tang Xiaoyan; Song Qingwen; Zhang Yuming

    2014-01-01

    The effect of the different re-oxidation annealing (ROA) processes on the SiO 2 /SiC interface characteristics has been investigated. With different annealing processes, the flat band voltage, effective dielectric charge density and interface trap density are obtained from the capacitance—voltage curves. It is found that the lowest interface trap density is obtained by the wet-oxidation annealing process at 1050 °C for 30 min, while a large number of effective dielectric charges are generated. The components at the SiO 2 /SiC interface are analyzed by X-ray photoelectron spectroscopy (XPS) testing. It is found that the effective dielectric charges are generated due to the existence of the C and H atoms in the wet-oxidation annealing process. (semiconductor technology)

  13. Study on the technique for precision measurement of density of SiO_2 foam shells

    Ma Xiaojun; Gao Dangzhong; Meng Jie

    2013-01-01

    The measuring method based on vertical scanning interference and combined with the relation between refraction index and density of SiO_2 foam shells is introduced, and the relation is analyzed according to formulas of Lorentz-Lorenz and Gladstone-Dale. The experimental result and measuring uncertainty evaluation indicate that the precision measurement of density of low density SiO_2 foam shells can be realized by using the vertical scanning interference technique and combining with Gladstone and Dale analysis method, and the measuring uncertainty is about 5%. (authors)

  14. Chemical effects in ion mixing of a ternary system (metal-SiO2)

    Banwell, T.; Nicolet, M.-A.; Sands, T.; Grunthaner, P. J.

    1987-01-01

    The mixing of Ti, Cr, and Ni thin films with SiO2 by low-temperature (- 196-25 C) irradiation with 290 keV Xe has been investigated. Comparison of the morphology of the intermixed region and the dose dependences of net metal transport into SiO2 reveals that long range motion and phase formation probably occur as separate and sequential processes. Kinetic limitations suppress chemical effects in these systems during the initial transport process. Chemical interactions influence the subsequent phase formation.

  15. Chemical modifications of Au/SiO2 template substrates for patterned biofunctional surfaces.

    Briand, Elisabeth; Humblot, Vincent; Landoulsi, Jessem; Petronis, Sarunas; Pradier, Claire-Marie; Kasemo, Bengt; Svedhem, Sofia

    2011-01-18

    The aim of this work was to create patterned surfaces for localized and specific biochemical recognition. For this purpose, we have developed a protocol for orthogonal and material-selective surface modifications of microfabricated patterned surfaces composed of SiO(2) areas (100 μm diameter) surrounded by Au. The SiO(2) spots were chemically modified by a sequence of reactions (silanization using an amine-terminated silane (APTES), followed by amine coupling of a biotin analogue and biospecific recognition) to achieve efficient immobilization of streptavidin in a functional form. The surrounding Au was rendered inert to protein adsorption by modification by HS(CH(2))(10)CONH(CH(2))(2)(OCH(2)CH(2))(7)OH (thiol-OEG). The surface modification protocol was developed by testing separately homogeneous SiO(2) and Au surfaces, to obtain the two following results: (i) SiO(2) surfaces which allowed the grafting of streptavidin, and subsequent immobilization of biotinylated antibodies, and (ii) Au surfaces showing almost no affinity for the same streptavidin and antibody solutions. The surface interactions were monitored by quartz crystal microbalance with dissipation monitoring (QCM-D), and chemical analyses were performed by polarization modulation-reflexion absorption infrared spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS) to assess the validity of the initial orthogonal assembly of APTES and thiol-OEG. Eventually, microscopy imaging of the modified Au/SiO(2) patterned substrates validated the specific binding of streptavidin on the SiO(2)/APTES areas, as well as the subsequent binding of biotinylated anti-rIgG and further detection of fluorescent rIgG on the functionalized SiO(2) areas. These results demonstrate a successful protocol for the preparation of patterned biofunctional surfaces, based on microfabricated Au/SiO(2) templates and supported by careful surface analysis. The strong immobilization of the biomolecules resulting from the described

  16. A microbiological evaluation of SiO2-coated textiles in hospital interiors

    Mogensen, Jeppe; Jørgensen, Poul-Erik; Thomsen, Trine Rolighed

    2016-01-01

    . From this perspective, the purpose of this paper is therefore to address focus on alternative passive coatings that without actively killing the bacteria provide a hydrophobic and easy-to-clean textile surface. The paper relates to an in-situ study evaluating the effect and cleaning potential of SiO2...... contact plates through a three-week period. By determining the level of contamination on these surfaces, the study illustrates that the SiO2-coated textile is possible to clean to an acceptable level below the critical limit value of 2,5 Colony Forming Units (CFU) per cm2. In comparison, the traditional...

  17. Bond length contraction in Au nanocrystals formed by ion implantation into thin SiO2

    Kluth, P.; Johannessen, B.; Giraud, V.; Cheung, A.; Glover, C.J.; Azevedo, G. de M; Foran, G.J.; Ridgway, M.C.

    2004-01-01

    Au nanocrystals (NCs) fabricated by ion implantation into thin SiO 2 and annealing were investigated by means of extended x-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy. A bond length contraction was observed and can be explained by surface tension effects in a simple liquid-drop model. Such results are consistent with previous reports on nonembedded NCs implying a negligible influence of the SiO 2 matrix. Cumulant analysis of the EXAFS data suggests surface reconstruction or relaxation involving a further shortened bond length. A deviation from the octahedral closed shell structure is apparent for NCs of size 25 A

  18. 120 MeV Ag ion induced effects in Au/HfO2/Si MOSCAPs

    Manikanthababu, N.; Prajna, K.; Pathak, A. P.; Rao, S. V. S. Nageswara

    2018-05-01

    HfO2/Si thinfilms were deposited by RF sputtering technique. 120 MeV Ag ion irradiation has been used to study the electrical properties of Au/HfO2/Si MOSCAPs. SHI (120 MeV Ag) induced annealing, defects creation and intermixing effects on the electrical properties of these systems have been studied. Here, we have observed that the high electronic excitation can cause a significant reduction of leakage currents in these MOSCAP devices. Various quantum mechanical tunneling phenomenon has been observed from the I-V characteristics.

  19. Positron trap centers in x-ray and γ-ray irradiated SiO2

    Khatri, R.; Asoka-Kumar, P.; Nielsen, B.; Roellig, L.O.; Lynn, K.G.

    1993-01-01

    Using Doppler broadening annihilation spectroscopy, we investigated the properties of irradiated samples of SiO 2 /Si(100) with 117 nm thick oxide layer, grown in dry O 2 on p- and n-type substrates. These samples were irradiated with γ rays and x rays at doses in the range of 7x10 4 --9x10 6 rad and 50--2000 mJ/cm 2 , respectively. The changes observed in the Doppler broadening line shape parameter after irradiation and its recovery during isochronal annealing were used to obtain an activation energy of 1.48--1.61 eV required for annealing the defects

  20. Facile hydrothermal synthesis of CeO 2 nanopebbles

    Cerium oxide (CeO2) nanopebbles have been synthesized using a facile hydrothermal method. X-ray diffraction pattern (XRD) and transmission electron microscopy analyses confirm the presence of CeO2 nanopebbles. XRD shows the formation of cubic fluorite CeO2 and the average particle size estimated from the ...

  1. The electrorheological properties of nano-sized SiO2 particle materials doped with rare earths

    Liu Yang; Liao Fuhui; Li Junran; Zhang Shaohua; Chen Shumei; Wei Chenguan; Gao Song

    2006-01-01

    Electrorheological (ER) materials of pure SiO 2 and SiO 2 doped with rare earths (RE = Ce, Gd, Y) (non-metallic glasses (silicates)) were prepared using Na 2 SiO 3 and RECl 3 as starting materials. The electrorheological properties are not enhanced by all rare earth additions. The material doped with Ce exhibits the best ER performance

  2. Viscosity Measurements of "FeO"-SiO2 Slag in Equilibrium with Metallic Fe

    Chen, Mao; Raghunath, Sreekanth; Zhao, Baojun

    2013-06-01

    The current study delivered the measurements of viscosities in the system "FeO"-SiO2 in equilibrium with metallic Fe in the composition range between 15 and 40 wt pct SiO2. The experiments were carried out in the temperature range of 1473 K to 1773 K (1200 °C to 1500 °C) using a rotational spindle technique. An analysis of the quenched sample by electron probe X-ray microanalysis (EPMA) after the viscosity measurement enables the composition and microstructure of the slag to be directly linked with the viscosity. The current results are compared with available literature data. The significant discrepancies of the viscosity measurements in this system have been clarified. The possible reasons affecting the accuracy of the viscosity measurement have been discussed. The activation energies derived from the experimental data have a sharp increase at about 33 wt pct SiO2, which corresponds to the composition of fayalite (Fe2SiO4). The modified quasi-chemical model was constructed in the system "FeO"-SiO2 to describe the current viscosity data.

  3. SiO2 Glass Density to Lower-Mantle Pressures

    Petitgirard, Sylvain; Malfait, Wim J.; Journaux, Baptiste

    2017-01-01

    and present Earth. SiO2 is the main constituent of Earth's mantle and is the reference model system for the behavior of silicate melts at high pressure. Here, we apply our recently developed x-ray absorption technique to the density of SiO2 glass up to 110 GPa, doubling the pressure range...... for such measurements. Our density data validate recent molecular dynamics simulations and are in good agreement with previous experimental studies conducted at lower pressure. Silica glass rapidly densifies up to 40 GPa, but the density trend then flattens to become asymptotic to the density of SiO2 minerals above 60...... GPa. The density data present two discontinuities at similar to 17 and similar to 60 GPa that can be related to a silicon coordination increase from 4 to a mixed 5/6 coordination and from 5/6 to sixfold, respectively. SiO2 glass becomes denser than MgSiO3 glass at similar to 40 GPa, and its density...

  4. Characterization and optimization of cathodic conditions for H2O2 synthesis in microbial electrochemical cells

    Cathode potential and O2 supply methods were investigated to improve H2O2 synthesis in an electrochemical cell, and optimal cathode conditions were applied for microbial electrochemical cells (MECs). Using aqueous O2 for the cathode significantly improved current density, but H2...

  5. Preparation and development of FeS2 Quantum Dots on SiO2 nanostructures immobilized in biopolymers and synthetic polymers as nanoparticles and nanofibers catalyst for antibiotic degradation.

    Gao, Wei; Razavi, Razieh; Fakhri, Ali

    2018-03-22

    The FeS 2 Quantum Dots (QDs) decorated SiO 2 nanostructure were prepared by hydrothermal synthesis method. Chitosan and polypyrrole as polymers were used for the immobilization process. The characteristic structure of prepared samples was analyzed using several techniques such as X-ray diffraction, scanning and transmittance electron microscopy, photoluminescence and UV-vis spectroscopy. The mean crystallite sizes of FeS 2 QDs/SiO 2 nanocomposites, FeS 2 QDs/SiO 2 -chitosan nanocomposites and FeS 2 QDs/SiO 2 -polypyrrole nanohybrids are 56.12, 76.38, and 83.24nm, respectively. The band gap energy of FeS 2 QDs/SiO 2 nanocomposites, FeS 2 QDs/SiO 2 -chitosan nanocomposites and FeS 2 QDs/SiO 2 -polypyrrole nanohybrids were found out to be 3.0, 2.8, and 2.7eV, respectively. The photocatalysis properties were investigated by degradation of ampicillin under UV light illumination. The effect of experimental variables, such as, pH and time, on photo-degradation efficiency was studied. The results show that the three prepared samples nanopowders under UV light was in pH3 at 60min. As it could be seen that the amount of ampicillin degradation was increased with the loading of FeS 2 QDs on SiO 2 and FeS 2 QDs/SiO 2 on chitosan nanoparticles and polypyrrole nanofiber. The antibacterial experiment was investigated under visible light illumination and the FeS 2 QDs/SiO 2 -chitosan nanocomposites and FeS 2 QDs/SiO 2 -polypyrrole nanohybrids demonstrate good antibacterial compared to FeS 2 QDs/SiO 2 nanocomposites. Copyright © 2018 Elsevier B.V. All rights reserved.

  6. Fourier transform infrared spectroscopic study of gamma irradiated SiO2 nanoparticles

    Huseynov, Elchin; Garibov, Adil; Mehdiyeva, Ravan; Huseynova, Efsane

    2018-03-01

    In the present work, nano SiO2 particles are investigated before and after gamma irradiation (25, 50, 75, 100 and 200 kGy) using Fourier transform infrared (FTIR) spectroscopy method for the wavenumber between 400-4000 cm-1. It is found that as a result of spectroscopic analysis, five new peaks have appeared after gamma radiation. Two of new obtained peaks (which are located at 687 cm-1 and 2357 cm-1 of wavenumber) were formed as a result of gamma radiation interaction with Si-O bonds. Another three new peaks (peaks appropriate to 941, 2052 and 2357 cm-1 values of wavenumber) appear as a result of interaction of water with nano SiO2 particles after gamma irradiation. It has been defined as asymmetrical bending vibration, symmetrical bending vibration, symmetrical stretching vibration and asymmetrical stretching vibration of Si-O bonds appropriate to peaks.

  7. Lowered operation voltage in Pt/SBi2Ta2O9/HfO2/Si ferroelectric-gate field-effect transistors by oxynitriding Si

    Horiuchi, Takeshi; Takahashi, Mitsue; Li, Qiu-Hong; Wang, Shouyu; Sakai, Shigeki

    2010-01-01

    Oxynitrided Si (SiON) surfaces show smaller subthreshold swings than do directly nitrided Si (SiN) surfaces when used in ferroelectric-gate field-effect transistors (FeFETs) having the following stacked-gate structure: Pt/SrBi 2 Ta 2 O 9 (SBT)/HfO 2 /Si. SiON/Si substrates for FeFETs were prepared by rapid thermal oxidation (RTO) in O 2 at 1000 °C and subsequent rapid thermal nitridation (RTN) in NH 3 at various temperatures in the range 950–1150 °C. The electrical properties of the Pt/SBT/HfO 2 /SiON/Si FeFET were compared with those of reference FETs, i.e. Pt/SBT/HfO 2 gate stacks formed on Si substrates subjected to various treatments: SiN x /Si formed by RTN, SiO 2 /Si formed by RTO and untreated Si. The Pt/SBT/HfO 2 /SiON/Si FeFET had a larger memory window than all the other reference FeFETs, particularly at low operation voltages when the RTN temperature was 1050 °C

  8. Self induced gratings in ternary SiO2:SnO2:Na2O bulk glasses by UV light seeding.

    Lancry, M; Douay, M; Niay, P; Beclin, F; Menke, Y; Milanese, D; Ferraris, M; Poumellec, B

    2005-09-05

    The diffraction efficiency of gratings written in ternary SnO2:SiO2:Na2O bulk glasses rises dramatically with time after the occultation of the cw 244nm light used to write the thick hologram. This self-induced behavior lasts for several hours and ultimately leads to refractive index changes as high as 3 10-3.

  9. Metabolomic effects of CeO2, SiO2 and CuO metal oxide nanomaterials on HepG2 cells

    U.S. Environmental Protection Agency — The data set is a matrix of cellular biochemical (metabolites) in HepG2 cells treated with various metal oxide nanomaterials composed of CeO2, SiO2 and CuO. This...

  10. Above room temperature ferromagnetism in Si:Mn and TiO(2-delta)Co.

    Granovsky, A; Orlov, A; Perov, N; Gan'shina, E; Semisalova, A; Balagurov, L; Kulemanov, I; Sapelkin, A; Rogalev, A; Smekhova, A

    2012-09-01

    We present recent experimental results on the structural, electrical, magnetic, and magneto-optical properties of Mn-implanted Si and Co-doped TiO(2-delta) magnetic oxides. Si wafers, both n- and p-type, with high and low resistivity, were used as the starting materials for implantation with Mn ions at the fluencies up to 5 x 10(16) cm(-2). The saturation magnetization was found to show the lack of any regular dependence on the Si conductivity type, type of impurity and the short post-implantation annealing. According to XMCD Mn impurity in Si does not bear any appreciable magnetic moment at room temperature. The obtained results indicate that above room temperature ferromagnetism in Mn-implanted Si originates not from Mn impurity but rather from structural defects in Si. The TiO(2-delta):Co thin films were deposited on LaAlO3 (001) substrates by magnetron sputtering in the argon-oxygen atmosphere at oxygen partial pressure of 2 x 10(-6)-2 x 10(-4) Torr. The obtained transverse Kerr effect spectra at the visible and XMCD spectra indicate on intrinsic room temperature ferromagnetism in TiO(2-delta):Co thin films at low (< 1%) volume fraction of Co.

  11. Comparative study of neurologic effects of nano-TiO2 versus SiO2 after direct intracerebral exposure in mice

    Balvay, A; Bencsik, A; Thieriet, N; Lakhdar, L

    2013-01-01

    Titanium and silicon dioxide nanoparticles (TiO 2 and SiO 2 NPs) are now in daily use in many commercial products of which food, sunscreens, toothpastes or cosmetics. However, their effects on human body, especially on the central nervous system, are still unclear. The aim of this study was to determine whether direct exposition of the brain to TiO 2 and SiO 2 NPs results in alternations in nervous system function. C57Bl6 mice were exposed to 5 and 10 μg doses of TiO 2 and SiO 2 NPs through intracerebroventricular administration using a stereotaxic approach. Then the neurologic effects were investigated using motor performance parameters, measured on a rotarod at 20 rpm or at an accelerating rod (from 4 to 40 rpm). Before and after injection, motor activity is registered individually for each mouse exposed, once a week, for 8 weeks. Besides, a group of 3 mice is culled at 1, 2, 3, 4 and 8 weeks after exposure in order to study the time dependant effect on the histopathology of the brain (gliosis, inflammatory process...). Both rotarod tests (accelerating and at 20 rpm) showed that TiO 2 and SiO 2 NPs exposure could significantly impair the motor performances, even several weeks after initial acute exposure. The first examination of the brain histopathology revealed microglial activation. As it appeared to grow throughout the brain in a time dependant manner this suggests the induction of a long lasting neuroinflammation. These primary findings indicated that exposure to TiO 2 and SiO 2 NPs could possibly impair the locomotor ability and this deficit may be possibly attributed at least to an inflammatory process maintained till 8 weeks after exposure in the mouse brain. To fully investigate the neurotoxicological consequences of TiO 2 and SiO 2 NPs exposure, brain contents in these NPs will be also investigated as well as other alterations like neurotransmitter levels. These preliminary data already underline the necessity of more in vivo studies to better

  12. Comparative study of neurologic effects of nano-TiO2 versus SiO2 after direct intracerebral exposure in mice

    Balvay, A.; Thieriet, N.; Lakhdar, L.; Bencsik, A.

    2013-04-01

    Titanium and silicon dioxide nanoparticles (TiO2 and SiO2 NPs) are now in daily use in many commercial products of which food, sunscreens, toothpastes or cosmetics. However, their effects on human body, especially on the central nervous system, are still unclear. The aim of this study was to determine whether direct exposition of the brain to TiO2 and SiO2 NPs results in alternations in nervous system function. C57Bl6 mice were exposed to 5 and 10 μg doses of TiO2 and SiO2 NPs through intracerebroventricular administration using a stereotaxic approach. Then the neurologic effects were investigated using motor performance parameters, measured on a rotarod at 20 rpm or at an accelerating rod (from 4 to 40 rpm). Before and after injection, motor activity is registered individually for each mouse exposed, once a week, for 8 weeks. Besides, a group of 3 mice is culled at 1, 2, 3, 4 and 8 weeks after exposure in order to study the time dependant effect on the histopathology of the brain (gliosis, inflammatory process...). Both rotarod tests (accelerating and at 20 rpm) showed that TiO2 and SiO2 NPs exposure could significantly impair the motor performances, even several weeks after initial acute exposure. The first examination of the brain histopathology revealed microglial activation. As it appeared to grow throughout the brain in a time dependant manner this suggests the induction of a long lasting neuroinflammation. These primary findings indicated that exposure to TiO2 and SiO2 NPs could possibly impair the locomotor ability and this deficit may be possibly attributed at least to an inflammatory process maintained till 8 weeks after exposure in the mouse brain. To fully investigate the neurotoxicological consequences of TiO2 and SiO2 NPs exposure, brain contents in these NPs will be also investigated as well as other alterations like neurotransmitter levels. These preliminary data already underline the necessity of more in vivo studies to better characterize TiO2

  13. Study on the structure of Co/ZrO2-SiO2 catalysts by XAFS

    Gao Haiyan; Xiang Hongwei; Li Yongwang; Sun Yuhan; Liu Tao; Xie Yaning; Hu Tiandou

    2002-01-01

    The Co-based catalysts have been extensively used in converting CO to longer chain hydrocarbons which can then be hydrocracked to diesel oil with high grade. SiO 2 is one of the most commonly used carriers for Co-based catalysts. It is showed that commercial silica carrier after modification can lead to much high reaction activity and selectivity to heavy hydrocarbons. But the structure of Co-based catalysts supported on the modified carrier has not been clearly understood. XAFS is used to investigate the change of structure of cobalt species in Co-based catalysts supported on modified carriers. The result from XAFS indicate that the structure of Co-based catalysts supported on modified carrier has certain change in comparison with Co-based catalyst supported on commercial silica. The interaction between carrier and metal is woken in the modified catalysts. Especially, the structure of catalysts after reduction have distinct difference. The extent of reduction in modified catalysts is much more than the catalyst supported on commercial silica. Cobalt species of the catalyst supported commercial silica after reduction dose exist mainly in the form of cobalt metal forms and may exist in the form of Co 2 SiO 4 surface compound

  14. Composite SiOx/hydrocarbon plasma polymer films prepared by RF magnetron sputtering of SiO2 and polyimide

    Drabik, M.; Kousal, J.; Pinosh, Y.; Choukourov, A.; Biederman, H.; Slavínská, D.; Macková, Anna; Boldyryeva, Hanna; Pešička, J.

    2007-01-01

    Roč. 81, č. 7 (2007), s. 920-927 ISSN 0042-207X Institutional research plan: CEZ:AV0Z10480505 Keywords : composite films * magnetron * sputtering * polyimide * SiO2 Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 0.881, year: 2007

  15. H2O incorporation in the phosphorene/a-SiO2 interface: a first-principles study.

    Scopel, Wanderlã L; Souza, Everson S; Miwa, R H

    2017-02-22

    Based on first-principles calculations, we investigate (i) the energetic stability and electronic properties of single-layer phosphorene (SLP) adsorbed on an amorphous SiO 2 surface (SLP/a-SiO 2 ), and (ii) the further incorporation of water molecules at the phosphorene/a-SiO 2 interface. In (i), we find that the phosphorene sheet binds to a-SiO 2 through van der Waals interactions, even in the presence of oxygen vacancies on the surface. The SLP/a-SiO 2 system presents a type-I band alignment, with the valence (conduction) band maximum (minimum) of the phosphorene lying within the energy gap of the a-SiO 2 substrate. The structure and the surface-potential corrugations promote the formation of electron-rich and electron-poor regions on the phosphorene sheet and at the SLP/a-SiO 2 interface. Such charge density puddles are strengthened by the presence of oxygen vacancies in a-SiO 2 . In (ii), because of the amorphous structure of the surface, we consider a number of plausible geometries for H 2 O embedded in the SLP/a-SiO 2 interface. There is an energetic preference for the formation of hydroxyl (OH) groups on the a-SiO 2 surface. Meanwhile, in the presence of oxygenated water or interstitial oxygen in the phosphorene sheet, we observe the formation of metastable OH bonded to the phosphorene, and the formation of energetically stable P-O-Si chemical bonds at the SLP/a-SiO 2 interface. Further x-ray absorption spectra simulations are performed, which aim to provide additional structural/electronic information on the oxygen atoms forming hydroxyl groups or P-O-Si chemical bonds at the interface region.

  16. Tunneling magnetoresistance of ultra-thin Co-SiO2 granular films with narrow current channels

    Honda, S.; Hirata, M.; Ishimaru, M.

    2005-01-01

    We have constructed the tunneling magnetoresistance (TMR) junction of AuCr/SiO 2 /Co-SiO 2 /SiO 2 /AuCr with narrow current channels, where the TMR occurs in the Co-SiO 2 layer with 10-50 nm thickness. The magnetic properties are independent of thickness, while the TMR properties depend fairly on thickness. The current (I)-bias voltage (V B ) curve is nonlinear, namely the differential resistivity decreases with increasing V B , and also the magnetoresistance ratio decreases

  17. Novel hydrophobic PDVB/R-SiO2 for adsorption of volatile organic compounds from highly humid gas stream.

    Lu, Han-feng; Cao, Jie-jing; Zhou, Ying; Zhan, De-li; Chen, Yin-fei

    2013-11-15

    A novel organic-inorganic hydrophobic polydivinylbenzene-silica adsorbent (PDVB/R-SiO2) was successfully prepared by introducing a specific amount of divinylbenzene and solvent (i.e., tetrahydrofuran) to SiO2pores and initiating polymerization under solvothermal conditions. New smaller structures and surface areas were formed in the SiO2 pores. The PDVB/R-SiO2-0.5 samples exhibited a bimodal pore size distribution with both SiO2 micropores/mesopores (0.5-2.0 nm) and mesopores (2.0-5.0 nm). The surface areas increased from 116 m(2)/g (SiO2) to 246 m(2)/g. The breakthrough curves of toluene adsorption indicated that the amount adsorbed on PDVB/R-SiO2-0.5 was 12 times higher than that on SiO2. The highly humid environment exhibited no effect on adsorption because the surface of PDVB was functionalized. The adsorbed toluene was easily desorbed in hot N2 stream at 100 °C. After 10 adsorption-desorption cycles, PDVB/R-SiO2-0.5 continued exhibiting excellent adsorption, indicating superior structural and regeneration abilities. Copyright © 2013 Elsevier B.V. All rights reserved.

  18. Upgrading pyrolysis bio-oil through hydrodeoxygenation (HDO) using non-sulfided Fe-Co/SiO2 catalyst

    Cheng, Shouyun; Wei, Lin; Julson, James; Rabnawaz, Muhammad

    2017-01-01

    Highlights: • Fe-Co/SiO 2 catalyst with medium acidity was more effective for bio-oil upgrading. • Co-loading of Fe and Co on SiO 2 support improved catalyst performance. • Catalyst showing the best catalytic activity had a Fe/Co mole ratio of 1. • Biofuel produced by Fe-Co(1)/SiO 2 had the higher hydrocarbons content at 22.44%. • The mechanism of bio-oil HDO on Fe-Co/SiO 2 catalysts is proposed. - Abstract: Hydrodeoxygenation (HDO) is an effective route to upgrade bio-oil to hydrocarbon bio-oil, but the development of efficient catalysts for bio-oil HDO still remains a challenge. In this study, non-sulfided Fe-Co/SiO 2 catalysts were used to upgrade bio-oil using HDO. A series of Fe-Co/SiO 2 catalysts with different Fe/Co mole ratios were prepared, characterized and evaluated. The Fe and/or Co loading did not change SiO 2 crystalline structure. The Fe and/or Co metals increased the amount and strength of Fe-Co/SiO 2 catalyst acidity. Physicochemical properties of upgraded bio-oils produced using Fe-Co/SiO 2 catalysts such as water content, total acid number, viscosity and higher heating values improved in comparison to raw bio-oil. Bimetallic Fe-Co/SiO 2 catalysts resulted in better HDO performance than monometallic Fe/SiO 2 or Co/SiO 2 catalysts. This was due to the synergistic effect of Fe and Co occurring on the SiO 2 support. Fe-Co/SiO 2 catalyst having medium amount of acidity was more effective for bio-oil upgrading. The highest hydrocarbons content produced using Fe-Co(1)/SiO 2 catalyst was 22.44%. The mechanism of bio-oil HDO on Fe-Co/SiO 2 catalysts is proposed.

  19. Structural colors of the SiO2/polyethyleneimine thin films on poly(ethylene terephthalate) substrates

    Jia, Yanrong; Zhang, Yun; Zhou, Qiubao; Fan, Qinguo; Shao, Jianzhong

    2014-01-01

    The SiO 2 /polyethyleneimine (PEI) films with structural colors on poly(ethylene terephthalate) (PET) substrates were fabricated by an electrostatic self-assembly method. The morphology of the films was characterized by Scanning Electron Microscopy. The results showed that there was no distinguishable multilayered structure found of SiO 2 /PEI films. The optical behaviors of the films were investigated through the color photos captured by a digital camera and the color measurement by a multi-angle spectrophotometer. Different hue and brightness were observed at various viewing angles. The structural colors were dependent on the SiO 2 particle size and the number of assembly cycles. The mechanism of the structural colors generated from the assembled films was elucidated. The morphological structures and the optical properties proved that the SiO 2 /PEI film fabricated on PET substrate formed a homogeneous inorganic/organic SiO 2 /PEI composite layer, and the structural colors were originated from single thin film interference. - Highlights: • SiO 2 /PEI thin films were electrostatic self-assembled on PET substrates. • The surface morphology and optical behavior of the film were investigated. • The structural colors varied with various SiO 2 particle sizes and assembly cycles. • Different hue and lightness of SiO 2 /PEI film were observed at various viewing angles. • Structural color of the SiO 2 /PEI film originated from single thin film interference

  20. More accurate definition of liquation dome in Na2O-B2O3-SiO2 system

    Alekseeva, Z.D.; Mazurin, O.V.; Aver'yanov, V.I.; Galakhov, F.Ya.

    1977-01-01

    The liquation region in the system Na 2 O-B 2 O 3 -SiO 2 was investigated. The liquation temperatures were determined by the boundary of disappearance of opalescence in specimens with pre-induced opalescence. Extrapolation of the concentration dependences of the liquation temperature along sections with a constant SiO 2 content to a point indicates that with a SiO 2 content of 20-40% the liquation boundary in the system B 2 O 3 -SiO 2 hardly lies above 450 deg C