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Oxide Surface (oxide + surface)
Kinds of Oxide Surface Selected AbstractsDiffusion versus Desorption: Complex Behavior of H Atoms on an Oxide SurfaceCHEMPHYSCHEM, Issue 2 2008X.-L. Yin Dr. Adsorption of atomic hydrogen on single-crystalline rutile TiO2(110)-(1×1) (see picture) at room temperature leads to ordered H adlayers with (1×1) periodicity and many vacancies. Unexpectedly, almost no recombinative desorption of H2 (or H2O) occurs on heating to above 600 K, because the activation energy of 1.11 eV for H atoms migrating into the bulk is significantly smaller as shown by DFT calculations. [source] Silicon-Assisted Direct Covalent Grafting on Metal Oxide Surfaces: Synthesis and Characterization of Carboxylate N,N,-Ligands on TiO2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2010Henri Arzoumanian Abstract The easy covalent bonding of an OH-bearing molecule onto a metal oxide surface can be done by transesterifying a trimethylsilylated hydroxy function with the surface OH groups. This results in the grafting of the organic molecule directly on the matrix, accompanied by the formation of trimethylsilanol, which can easily be eliminated as volatile hexamethyldisiloxane and water. This was accomplished on a TiO2 matrix with three carboxylic acids: acetic, isonicotinic, and 2,2,-bipyridyl-4,4,-dicarboxylic acids. The N,N,-immobilized ligand was then used for a dioxidomolybdenum entity and tested as such at room temperature and under atmospheric pressure O2 oxidation of ethylbenzene. All intermediates and grafted species were fully characterized by 13CMAS NMR spectroscopy, and thermogravimetric and elemental analysis. [source] Vapor-Phase Deposition of Monofunctional Alkoxysilanes for Sub-Nanometer-Level Biointerfacing on Silicon Oxide SurfacesADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Brian Dorvel Abstract Improving the performance and lowering the analyte detection limits of optical and electronic biosensors is essential for advancing wide ranging applications in diagnostics and drug discovery. Most sensing methods require direct linkage of a recognition element and a sensor, which is commonly accomplished through an organic monolayer interface. Alkoxyorganosilanes are typically used to prepare sensor surfaces on dielectric oxides. However, many silanes lead to roughened or thick interfaces that degrade device sensitivity. Here, controlled vapor phase deposition of monoalkoxysilanes is found to lead to monolayers resistant to elevated temperatures and extreme pH conditions. The formation of high density, subnanometer monolayers is demonstrated by ellipsometry, XPS, and AFM. The uniform attachment of these monofunctional silanes to such biosensing platforms as microarrays, field effect devices, and the formation of surface enhanced Raman spectroscopy substrates is demonstrated. The advantages of using this silane deposition protocol for the above technologies are also discussed. [source] Rapid Microfluidic Generation of Patterned Aldehydes from Hydroxy-Terminated Self-Assembled Monolayers for Ligand and Cell Immobilization on Optically Transparent Indium Tin Oxide SurfacesADVANCED MATERIALS, Issue 30 2009Abigail Pulsipher Selective immobilization of a wide range of ligands on an indium tin oxide (ITO) surface is demonstrated. A chemoselective immobilization strategy to tailor ITO surfaces is developed by selectively oxidizing hydroxyl-terminated phosphonate self-assembled monolayers (SAMs) to aldehyde-presenting SAMs using microfluidic channels and then reacting with oxyamine-containing ligands , all on a chip. [source] Evidence for a Size-Selective Adsorption Mechanism on Oxide Surfaces: Pd and Au atoms on SiO2/Mo(112)CHEMPHYSCHEM, Issue 10 2008Stefan Ulrich Sieving single atoms: The binding of single metal atoms to thin SiO2 films grown on Mo(112) depends on the size of the adatom. While Pd atoms are able to pass the nanopores in the silica network (see figure) and strongly bind to the Mo,SiO2 interface, Au atoms are too big for a penetration and interact only with line defects in the oxide surface. [source] Zeta Potential Measurement in Catalyst PreparationsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2005J. B. Stelzer Abstract Oxide surfaces are covered with hydroxyl groups. In contact with water, positive or negative surface charges can be developed. The surface charge of oxide particles can be fine-tuned by changing the calcination temperature of the oxides before dispersion in water or by variation of the suspension pH. Strong negative or positive surface charges stabilize a suspension and avoid particle aggregation. Nano-structured catalysts suspended in water show surface charges different from those of compact TiO2. For spray drying, the cationic or anionic additives used have to be strongly attached via electrostatic forces to the surface of the suspended oxide particles. When noble metal complexes have to be brought to the support surface, the positively or negatively charged complexes must have an opposite charge relative to the surface charge. Zeta potential measurements can solve these problems. [source] Silicon-Assisted Direct Covalent Grafting on Metal Oxide Surfaces: Synthesis and Characterization of Carboxylate N,N,-Ligands on TiO2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2010Henri Arzoumanian Abstract The easy covalent bonding of an OH-bearing molecule onto a metal oxide surface can be done by transesterifying a trimethylsilylated hydroxy function with the surface OH groups. This results in the grafting of the organic molecule directly on the matrix, accompanied by the formation of trimethylsilanol, which can easily be eliminated as volatile hexamethyldisiloxane and water. This was accomplished on a TiO2 matrix with three carboxylic acids: acetic, isonicotinic, and 2,2,-bipyridyl-4,4,-dicarboxylic acids. The N,N,-immobilized ligand was then used for a dioxidomolybdenum entity and tested as such at room temperature and under atmospheric pressure O2 oxidation of ethylbenzene. All intermediates and grafted species were fully characterized by 13CMAS NMR spectroscopy, and thermogravimetric and elemental analysis. [source] A study of the factors controlling the adsorption of Cr(III) on modified montmorillonitesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2001A. Bakhti Summary We have examined the way that the metallic ion Cr(III) is held by Na-montmorillonite and alumina pillared clay. We used several physico-chemical methods of analysis (X-ray powder diffraction, infrared absorption spectrometry, thermal analysis and chemical composition) to determine the structural formula of the Na-montmorillonite, and to clarify the effect of the introduction of the Al13 polycations between the clay layers on its physico-chemical and structural properties. Our results show that the strength of chromium retention increases with pH. This effect is more marked in pillared than in unpillared clays. It seems that the mechanism of fixing of the metallic cations on pillared clays is more complex than a simple cationic exchange and involves the surface groups of the pillars. In other words, chromium adsorption on pillared montmorillonite is more like adsorption on an amphoteric oxide surface (such as Al2O3) than on a non-pillared clay. Etude des facteurs contrôlant l'adsorption de Cr(III) sur des montmorillonites modifiées Résumé Nous avons examiné les possibilités de fixation de l'ion métallique Cr(III) sur une montmorillonite sodique et pontée. Les différentes analyses physico-chimiques (Rayons-X, Spectroscopie Infrarouge, Analyse Thermique Différentielle et composition chimique) ont permis d'une part, d'établir la formule structurale de l'argile sodique et d'autre part de mettre en évidence l'effet du pontage de l'argile par des polycations hydroxyaluminiques sur ses propriétés physico-chimiques et structurales. Nos résultats montrent que le pouvoir de rétention du chrome augmente avec le pH. Ce paramètre affecte davantage son comportement dans les argiles pontées. Il apparaît que le mécanisme de fixation du Cr(III) sur les argiles à piliers est différent d'un simple échange cationique. L'adsorption dans ce cas met en jeu les groupements de la surface des piliers. En d'autres termes, le mécanisme d'adsorption des cations du chrome sur une montmorillonite pontée se rapproche de l'adsorption sur une surface d'oxyde amphotère (tel que Al2O3) plutôt que l'adsorption sur une argile non pontée. [source] Influence of Dielectric Surface Chemistry on the Microstructure and Carrier Mobility of an n-Type Organic SemiconductorADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Parul Dhagat Abstract This paper examines the microstructure evolution of 3,4,9,10-perylene-tetracarboxylic bis-benzimidazole (PTCBI) thin films resulting from conditions imposed during film deposition. Modification of the silicon dioxide interface with a hydrophobic monolayer (octadecyltrichlorosilane (OTS-18)) alters the PTCBI growth habit by changing the unit cell contact plane. PTCBI films deposited on oxide surface have an orientation of (011), while films atop OTS-treated oxide surface have a preferred orientation of (001). The quality of the self assembled monolayer does not appear to influence the PTCBI growth preference significantly yet it enhances the carrier mobility, suggesting that charge traps are adequately passivated due to uniform monolayer coverage. High-quality monolayers result in n-type carrier mobility values of 0.05,cm2V,1s,1 Increasing the substrate temperature during PTCBI film deposition correlates with an increase in mobility that is most significant for films deposited on OTS-treated surface. [source] Novel Structural Modulation in Ceramic Sensors Via Redox Processing in Gas BuffersINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2006Abdul-Majeed Azad High selectivity, enhanced sensitivity, short response time, and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. As the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, high aspect ratio and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of "oxygen deprivation," with exotic morphological features, has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of potential semiconducting ceramic oxide-based carbon monoxide and hydrogen sensors with enhanced characteristics. [source] Patterned Gold-Nanoparticle Monolayers Assembled on the Oxide of Silicon,ADVANCED MATERIALS, Issue 12 2005W. Foster Patterned monolayers of gold nanoparticles are selectively formed on Hf4+ -modified silicon dioxide. The 1.5,nm diameter particles are functionalized with a phosphonic acid ligand shell and assembled from solution on a native oxide surface that has been patterned with Hf4+ ions, as shown in the Figure. This system integrates nanoscale components and lithographic patterning. The technique used is precise and compatible with other lithographic techniques. [source] Alveolar ridge augmentation using implants coated with recombinant human growth/differentiation factor-5: histologic observationsJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 8 2010Giuseppe Polimeni Polimeni G, Wikesjö UME, Susin C, Qahash M, Shanaman RH, Prasad HS, Rohrer MD, Hall J. Alveolar ridge augmentation using implants coated with recombinant human growth/differentiation factor-5: histologic observations. J Clin Periodontol 2010; 37: 759-768 doi: 10.1111/j.1600-051X.2010.01579.x. Abstract Objectives: In vitro and in vivo preclinical studies suggest that growth/differentiation factor-5 (GDF-5) may induce local bone formation. The objective of this study was to evaluate the potential of recombinant human GDF-5 (rhGDF-5) coated onto an oral implant with a purpose-designed titanium porous oxide surface to stimulate local bone formation including osseointegration and vertical augmentation of the alveolar ridge. Materials and Methods: Bilateral, critical-size, 5 mm, supraalveolar peri-implant defects were created in 12 young adult Hound Labrador mongrel dogs. Six animals received implants coated with 30 or 60 ,g rhGDF-5, and six animals received implants coated with 120 ,g rhGDF-5 or left uncoated (control). Treatments were alternated between jaw quadrants. The mucoperiosteal flaps were advanced, adapted, and sutured to submerge the implants for primary intention healing. The animals received fluorescent bone markers at weeks 3, 4, 7, and 8 post-surgery when they were euthanized for histologic evaluation. Results: The clinical examination showed no noteworthy differences between implants coated with rhGDF-5. The cover screw and implant body were visible/palpable through the alveolar mucosa for both rhGDF-5-coated and control implants. There was a small increase in induced bone height for implants coated with rhGDF-5 compared with the control, induced bone height averaging (±SD) 1.6±0.6 mm for implants coated with 120 ,g rhGDF-5 versus 1.2±0.5, 1.2±0.6, and 0.6±0.2 mm for implants coated with 60 ,g rhGDF-5, 30 ,g rhGDF-5, or left uncoated, respectively (p<0.05). Bone formation was predominant at the lingual aspect of the implants. Narrow yellow and orange fluorescent markers throughout the newly formed bone indicate relatively slow new bone formation within 3,4 weeks. Implants coated with rhGDF-5 displayed limited peri-implant bone remodelling in the resident bone; the 120 ,g dose exhibiting more advanced remodelling than the 60 and 30 ,g doses. All treatment groups exhibited clinically relevant osseointegration. Conclusions: rhGDF-5-coated oral implants display a dose-dependent osteoinductive and/or osteoconductive effect, bone formation apparently benefiting from local factors. Application of rhGDF-5 appears to be safe as it is associated with limited, if any, adverse effects. [source] Evidence for a Size-Selective Adsorption Mechanism on Oxide Surfaces: Pd and Au atoms on SiO2/Mo(112)CHEMPHYSCHEM, Issue 10 2008Stefan Ulrich Sieving single atoms: The binding of single metal atoms to thin SiO2 films grown on Mo(112) depends on the size of the adatom. While Pd atoms are able to pass the nanopores in the silica network (see figure) and strongly bind to the Mo,SiO2 interface, Au atoms are too big for a penetration and interact only with line defects in the oxide surface. [source] Creating metal-spiked bed sediments: A case study from Orewa estuary, New Zealand,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2008Xueqiang Lu Abstract Spiking sediments to achieve target concentrations of heavy metal pollutants is a key step in sediment toxicity tests. It is difficult, however, to ensure that metals in an artificially spiked sediment will behave naturally. A method has been developed in the present study to create Cu-, Pb-, and Zn-spiked sediments in which naturally occurring adsorption onto sediment surfaces is the dominant process binding the metals and in which precipitation of readily redissolved minerals and other metal-bearing phases (artifacts of the spiking procedure) are avoided. Uncontaminated bed sediment from an intertidal mudflat in the Orewa estuary, New Zealand, was characterized in terms of existing metal content, optimal adsorption pH, and adsorption capacity. Competitive adsorption between Cu and Pb as well as complexation by seawater anions only slightly affected metal adsorption from seawater. Surface complexation modeling indicated that iron oxide surfaces in the sediment likely were dominating metal adsorption processes. Spiking experiments were designed using these established adsorption characteristics but with significantly higher (>100-fold) concentrations of sediments and dissolved metals and a liquid to solid (L:S) ratio of approximately 5.5. An equilibration time of at least 36 h was required to achieve a reproducible target metal concentration, which could be reliably predicted from the L:S ratio and the initial metal concentration in the spiking solution. Adsorption equilibrium remained the process governing metal binding to the sediment, and no indication was observed that the adsorption capacity of the sediment had been exceeded or that additional metal-bearing phases had been formed. [source] Synthesis and Characterisation of a New Cu(O2CNAllyl2)2 Carbamato Complex and an Unusual Polymeric CuI Complex [CuI4Cl4(NHAllyl2)4]n: New Insights into Metal Carbamato ChemistryEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Alberto Albinati Abstract Transition-metal N,N -dialkylcarbamato complexes represent an interesting class of compounds that can be conveniently used as precursors for the controlled formation of inorganic compounds, typically oxides. They can also be used as convenient precursors for chemical grafting of metal oxides on oxide surfaces as well as for the synthesis of inorganic,organic hybrid materials. In this last case, the presence of double bonds on the complex would enable its covalent embedding into a polymer matrix through reaction with suitable monomers. To this aim, we addressed the synthesis of an allyl-functionalised copper carbamato complex. During the synthesis of the N,N -diallylcarbamato complex Cu(O2CNAllyl2)2 (Cu1), the formation of the crystalline and unusual polymeric CuI complex [CuI4Cl4(NHAllyl2)4]n (Cu2) was observed. The new compound was characterised by X-ray single crystal diffraction and FTIR, 1H and 13C NMR spectroscopic analysis. In an attempt to investigate the redox mechanism and the equilibria leading to the formation of the observed unusual CuI polymeric complex, gas chromatography coupled with mass spectrometry (GC,MS) experiments were carried out, which allowed us to identify 3,4-dimethylpyrrole as the oxidation product of the reaction, leading to the reduction of CuII to CuI.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Retarded surface photovoltage response from dye molecules adsorbed on metal oxide surfacesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2004Th. DittrichArticle first published online: 11 AUG 200 Abstract A retarded surface photovoltage response has been observed on metal oxide layers (SnO2:F, TiO2) covered with adsorbed dye molecules while only the dye molecules were excited by short laser pulses. The retardation ranged between 30 and 570 ns depending on the nature of the metal oxide and on surface treatment. Therefore, charge separation in space of electrons injected from dye molecules into metal oxides is strikingly different from ultrafast electron injection measured by time-resolved optical techniques. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A comparative ab initio study of Cu overlayers on BaTiO3(001) and MgO(001) substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008Yu. F. Zhukovskii Abstract In order to compare Cu adhesion upon two kinds of perfect cubic (001) oxide surfaces: (i) TiO2 - and BaO-terminated substrates of partly covalent BaTiO3 and (ii) highly ionic MgO substrate, we have performed DFT-LCAO calculations using a hybrid B3PW Hamiltonian. 2D symmetrical slabs used here contain seven BaTiO3 and five MgO substrate layers covered on both sides by submonolayers of ordered Cu atoms. The Cu periodic coverage density atop the surface oxygen anions was varied from 1/8 to 1/2 monolayer. Copper bonding on the BaTiO3(001) surface has been found to be noticeably stronger than that on ionic MgO(001). Cu adatoms attract the electron density from BaO-terminated and donate it towards TiO2 -terminated BaTiO3(001) substrates, respectively, by an amount that is about threefold larger than for a Cu/MgO(001) interface. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Molecular and biomolecular interfaces to metal oxide semiconductorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Robert J. Hamers Abstract Previous work has shown that organic alkenes will graft to covalent semiconductors such as diamond and silicon. Here, we demonstrate that organic alkenes can be grafted to the surfaces of metal oxide semiconductors, including TiO2 in nanocrystalline thin films and as single-crystal anatase(001) epitaxial films grown on SrTiO3(001) substrates. The resulting layers can be used as a starting point for linking biomolecules such as DNA to metal oxide surfaces. Initial results are presented showing that this chemistry can also be applied to graft molecular layers to zirconium oxide thin films. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Volcano Relation for the Deacon Process over Transition-Metal OxidesCHEMCATCHEM, Issue 1 2010Felix Studt Dr. Abstract We establish an activity relation for the heterogeneous catalytic oxidation of HCl (the Deacon Process) over rutile transition-metal oxide catalysts by combining density functional theory calculations (DFT) with microkinetic modeling. Linear energy relations for the elementary reaction steps are obtained from the DFT calculations and used to establish a one-dimensional descriptor for the catalytic activity. The descriptor employed here is the dissociative chemisorption energy of oxygen. It is found that the commonly employed RuO2 catalyst is close to optimal, but that there could still be room for improvements. The analysis suggests that oxide surfaces which offer slightly weaker bonding of oxygen should exhibit a superior activity to that of RuO2. [source] Selective Deposition of Ultrathin Poly(p -xylene) Films on Dielectrics Versus Copper SurfacesCHEMICAL VAPOR DEPOSITION, Issue 5 2004J.J. Senkevich Ultrathin films of poly(p -xylylene) are selectively deposited on oxide surfaces but not on air exposed copper. The polymers are deposited under conditions favorable for forming highly conformal ultrathin films appropriate for ,pore sealing' the surface of ultra-low , dielectrics. Variable angle spectroscopic ellipsometry is used to measure the polymer deposit on SiO2, and shows the lack of deposition on air-exposed copper. X-ray photoelectron spectroscopic analysis of the copper samples shows deposition of adventitious carbon on the metal surface, and confirms that no polymer deposition occurs. [source] Acid,Base Bifunctional Catalytic Surfaces for Nucleophilic Addition ReactionsCHEMISTRY - AN ASIAN JOURNAL, Issue 8-9 2008Ken Motokura Dr. Abstract This article illustrates the modification of oxide surfaces with organic amine functional groups to create acid,base bifunctional catalysts, summarizing our previous reports and also presenting new data. Immobilization of organic amines as bases on inorganic solid,acid surfaces afforded highly active acid,base bifunctional catalysts, which enabled various organic transformations including CC coupling reactions, though these reactions did not proceed with either the homogeneous amine precursors or the acidic supports alone. Spectroscopic characterization, such as by solid-state MAS NMR and FTIR, revealed not only the interactions between acidic and basic sites but also bifunctional catalytic reaction mechanisms. [source] | |||||||||||||||||||