Sample records for oxidized cu110 surface

  1. Positron states and annihilation characteristics of surface-trapped positrons at the oxidized Cu(110) surface

    NASA Astrophysics Data System (ADS)

    Fazleev, N. G.; Olenga, Antoine; Weiss, A. H.

    2013-03-01

    The process by which oxide layers are formed on metal surfaces is still not well understood. In this work we present the results of theoretical studies of positron states and annihilation characteristics of surface-trapped positrons at the oxidized Cu(110) surface. An ab-initio investigation of stability and associated electronic properties of different adsorption phases of oxygen on Cu(110) has been performed on the basis of density functional theory and using DMOl3 code. The changes in the positron work function and the surface dipole moment when oxygen atoms occupy on-surface and sub-surface sites have been attributed to charge redistribution within the first two layers, buckling effects within each layer and interlayer expansion. The computed positron binding energy, positron surface state wave function, and annihilation probabilities of surface trapped positrons with relevant core electrons demonstrate their sensitivity to oxygen coverage, elemental content, atomic structure of the topmost layers of surfaces, and charge transfer effects. Theoretical results are compared with experimental data obtained from studies of oxidized transition metal surfaces using positron annihilation induced Auger electron spectroscopy. The process by which oxide layers are formed on metal surfaces is still not well understood. In this work we present the results of theoretical studies of positron states and annihilation characteristics of surface-trapped positrons at the oxidized Cu(110) surface. An ab-initio investigation of stability and associated electronic properties of different adsorption phases of oxygen on Cu(110) has been performed on the basis of density functional theory and using DMOl3 code. The changes in the positron work function and the surface dipole moment when oxygen atoms occupy on-surface and sub-surface sites have been attributed to charge redistribution within the first two layers, buckling effects within each layer and interlayer expansion. The computed positron binding energy, positron surface state wave function, and annihilation probabilities of surface trapped positrons with relevant core electrons demonstrate their sensitivity to oxygen coverage, elemental content, atomic structure of the topmost layers of surfaces, and charge transfer effects. Theoretical results are compared with experimental data obtained from studies of oxidized transition metal surfaces using positron annihilation induced Auger electron spectroscopy. This work was supported in part by the National Science Foundation Grant DMR-0907679.

  2. Surface-mediated isomerization and oxidation of allyl alcohol on Cu(110)

    SciTech Connect

    Brainard, R.L.; Peterson, C.G.; Madix, R.J. (Stanford Univ., CA (USA))

    1989-06-21

    Allyl alcohol reacts with clean and oxygen-covered Cu(110) surfaces to produce propanal, acrolein, n-propyl alcohol, and hydrogen under ultrahigh-vacuum conditions. Very small amounts of propylene and water are also formed. This pattern of reactivity contrasts sharply to the selective oxidation to acrolein observed on Ag(110). On the clean Cu(110) surface allyl alcohol undergoes O-H cleavage to form the surface alkoxide CH{sub 2}{double bond}CHCH{sub 2}O{sub (a)} and H{sub (a)}. The results suggest that the olefin in this species undergoes partial hydrogenation to the surface-bound oxametallacycles ({minus}CH{sub 2}CH{sub 2}CH{sub 2}O-){sub (a)} and ({minus}CH-(CH{sub 3})CH{sub 2}O-){sub (a)} and complete hydrogenation to CH{sub 3}CH{sub 2}CH{sub 2}O{sub (a)}. Propanal forms at 320 K via further reaction of these oxametallacycles. Evidence for a {pi}-bonded allyl oxide CH{sub 2}{double bond}CHCH{sub 2}O{sub (a)}, which is more stable than n-propoxide (CH{sub 3}CH{sub 2}CH{sub 2}O{sub (a)}) toward {beta}-hydride elimination, is presented. This allyl oxide decomposes at 370 K to form acrolein. The interaction of the double bond with the surface apparently restricts the interaction of the {beta}-C-H bond with the surface and increases the stability of this species. Propanal, acrolein, and H{sub 2} are formed at 435 K by a process thought to involve the thermal decomposition of ({minus}CH{sub 2}CH{sub 2}CH{sub 2}O-){sub (a)} by a {beta}-hydride elimination pathway. This dehydrogenation pathway exhibits an activation energy 8 kcal/mol greater than for acyclic alkoxides. The conversion of allyl alcohol to propanal and propyl alcohol obviously involves the hydrogenation of the double bond which, by comparison, does not occur for propylene coadsorbed with hydrogen under similar conditions on this surface.

  3. Oxygen chemisorption-induced surface phase transitions on Cu(110)

    NASA Astrophysics Data System (ADS)

    Liu, Qianqian; Li, Liang; Cai, Na; Saidi, Wissam A.; Zhou, Guangwen

    2014-09-01

    From an interplay between variable temperature scanning tunneling microscopy and density-functional theory calculations, the evolution of oxygen chemisorption-induced surface reconstructions of the Cu(110) surface is determined. The surface reconstructions proceed via a sequential pathway with increasing oxygen surface coverage. The (2 × 1) reconstruction occurs first and then transits to the c(6 × 2) phase with a higher oxygen coverage through a mechanism that consumes the existing (2 × 1) phase with the supply of Cu adatoms from step edges and terraces. The temperature dependence of the (2 × 1) ? c(6 × 2) transition demonstrates that the surface phase transition is an activated process for breaking up added Cu-O-Cu rows in the (2 × 1) structure. Comparison between the experimental observations and the theoretical surface phase diagram obtained from first-principles thermodynamic calculations reveals that the (2 × 1) ? c(6 × 2) transition takes place at the oxygen chemical potentials that are far above the chemical potential for Cu2O bulk oxide formation, reflecting the existence of kinetic limitations to the surface phase transition and the bulk oxide formation.

  4. First-principles study of water on Cu (110) surface

    NASA Astrophysics Data System (ADS)

    Ren, Jun; Meng, Sheng

    2009-03-01

    The persistent demand for cheaper and high efficient catalysts in industrial chemical synthesis, such as ammonia, and in novel energy applications, hydrogen generation and purification in fuel cells motivated us to study the fundamental interaction involved in water-Cu system, with an intension to examine Cu as a possible competitive candidate for cheaper catalysts. Water structure and dissociation kinetics on a model open metal surface: Cu (110), have been investigated in detail based on first-principles electronic structure calculations. We revealed that in both monomer and overlayer forms, water adsorbs molecularly, with a high tendency for diffusion and/or desorption rather than dissociation on clean surfaces at low temperature. With the increase of the water coverage on the Cu (110) surface, the H-bond pattern lowers the dissociation barrier efficiently. More importantly, if the water molecule is dissociated, the hydrogen atoms can diffuse freely along the [110] direction, which is very useful in the hydrogen collection. In addition, we extended to study water on other noble metal (110) surfaces. The result confirms that Cu (110) is the borderline between intact and dissociative adsorption, differing in energy by only 0.08 eV. This may lead to promising applications in hydrogen generation and fuel cells.

  5. The decomposition of nitrobenzene on a Cu(110) surface

    Microsoft Academic Search

    Q. Chen; B. G. Frederick; N. V. Richardson

    1999-01-01

    The decomposition of nitrobenzene on Cu(110) has been studied using Auger and high resolution electron energy loss spectroscopies. The Auger spectrum of the decomposed species indicates the presence of carbon and oxygen but no nitrogen. A direct comparison of the energy loss spectrum to that of phenol on Cu(110) excludes the decomposition of nitrobenzene to phenoxy. The difference between the

  6. Surface Chirality of Gly-Pro Dipeptide Adsorbed on a Cu(110) Surface.

    PubMed

    Cruguel, Hervé; Méthivier, Christophe; Pradier, Claire-Marie; Humblot, Vincent

    2015-07-01

    The adsorption of chiral Gly-Pro dipeptide on Cu(110) has been characterized by combining in situ polarization modulation infrared reflection absorption spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS). The chemical state of the dipeptide, and its anchoring points and adsorption geometry, were determined at various coverage values. Gly-Pro molecules are present on Cu(110) in their anionic form (NH2 /COO(-) ) and adsorb under a 3-point binding via both oxygen atoms of the carboxylate group and via the nitrogen atom of the amine group. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) have shown the presence of an extended 2D chiral array, sustained via intermolecular H-bonds interactions. Furthermore, due to the particular shape of the molecule, only one homochiral domain is formed, creating thus a truly chiral surface. Chirality 27:411-416, 2015. © 2015 Wiley Periodicals, Inc. PMID:25847844

  7. Chloride-induced morphology transformations of the Cu(110) surface in dilute HCl.

    PubMed

    Barati, Gholamreza; Solokha, Vladyslav; Wandelt, Klaus; Hingerl, Kurt; Cobet, Christoph

    2014-12-01

    Morphological changes of a bare Cu(110) substrate in 10 mM HCl aqueous solution have been studied using cyclic voltammetry (CV), electrochemical scanning tunneling microscopy (EC-STM), and reflectance anisotropy spectroscopy (RAS). At cathodic potentials more positive than the hydrogen evolution reaction, a bare copper surface (1 × 1) structure is found by EC-STM. At anodic potentials more negative than the copper(II) dissolution reaction, a furrowed structure is found. The governing factor that rules Cu(110)-Cl interface processes is discussed as an interplay among Cl(-) adsorption/desorption, the dynamic rearrangement of the surface atoms on the substrate, and strain in order to reduce the surface energy. The information provided by EC-STM and RAS complements that of CV, supplies detailed information on the surface morphology, and correlates peaking Faraday currents to structural modifications. Furthermore, RAS and EC-STM show changes in the surface appearance in a potential range where no specific charge transfer is observed. CV indicates that the Cu(110) surface chemistry compares much better to that of amorphous Cu than to that of the more stable (100) and (111) surfaces, respectively. PMID:25383708

  8. Dissociative chemisorption of H2 on the Cu(110) surface: a quantum and quasiclassical dynamical study.

    PubMed

    Kroes, G J; Pijper, E; Salin, A

    2007-10-28

    Six-dimensional quantum dynamical and quasiclassical trajectory (QCT) calculations are reported for the reaction and vibrationally inelastic scattering of (v = 0,1,j = 0) H(2) scattering from Cu(110), and for the reaction and rovibrationally elastic and inelastic scattering of (v = 1,j = 1) H(2) scattering from Cu(110). The dynamics results were obtained using a potential energy surface obtained with density functional theory using the PW91 functional. The reaction probabilities computed with quantum dynamics for (v = 0,1,j = 0) were in excellent agreement with the QCT results obtained earlier for these states, thereby validating the QCT approach to sticking of hydrogen on Cu(110). The vibrational de-excitation probability P(v=1,j = 0 --> v = 0) computed with the QCT method is in remarkably good agreement with the quantum dynamical results for normal incidence energies E(n) between 0.2 and 0.6 eV. The QCT result for the vibrational excitation probability P(v = 0,j = 0 --> v = 1) is likewise accurate for E(n) between 0.8 and 1 eV, but the QCT method overestimates vibrational excitation for lower E(n). The QCT method gives probabilities for rovibrationally (in)elastic scattering, P(v = 1,j = 1 --> v('),j(')), which are in remarkably good agreement with quantum dynamical results. The rotationally averaged, initial vibrational state-selective reaction probability obtained with QCT agrees well with the initial vibrational state-selective reaction probability extracted from molecular beam experiments for v = 1, for the range of collision energies for which the v=1 contribution to the measured total sticking probability dominates. The quantum dynamical probabilities for rovibrationally elastic scattering of (v = 1,j = 1) H(2) from Cu(110) are in good agreement with experiment for E(n) between 0.08 and 0.25 eV. PMID:17979386

  9. Temperature dependence of the surface free energy and surface stress: An atomistic calculation for Cu(110)

    E-print Network

    Mishin, Yuri

    Temperature dependence of the surface free energy and surface stress: An atomistic calculation is applied to compute the temperature dependencies of and for the 110 Cu surface using Monte Carlo temperature, eij is a strain tensor of the surface, and ij is the Kronecker sym- bol. Two of the Cartesian

  10. Thermal chemistry of copper(I)-N,N '-di-sec-butylacetamidinate on Cu(110) single-crystal surfaces

    SciTech Connect

    Ma Qiang; Zaera, Francisco; Gordon, Roy G. [Department of Chemistry, University of California, Riverside, California 92521 (United States); Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States)

    2012-01-15

    The surface chemistry of copper(I)-N,N'-di-sec-butylacetamidinate on Cu(110) single-crystal surfaces has been characterized under ultrahigh vacuum by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy. A series of thermal stepwise conversions were identified, starting with the partial dissociative adsorption of the copper acetamidinate dimers into a mixture of monomers and dimers on the surface. An early dissociation of a C-N bond leads to the production of N-sec-butylacetamidine, which is detected in TPD experiments in three temperature regimes, the last one centered around 480 K. Butene, and a small amount of butane, is also detected above approximately 500 K, and hydrogen production, an indication of dehydrogenation of surface fragments, is observed at 460, 550 and 670 K. In total, only about 10% of the initial copper(I)-N,N'-di-sec-butylacetamidinate adsorbed monolayer decomposes, and only about {approx}3% of carbon is left behind on the surface after heating to high temperatures. The implications of this surface chemistry to the design of chemical film growth processes using copper acetamidinates as precursors are discussed.

  11. Autocatalytic effect of Cu nano-islands on the reaction of water with the oxygen covered Cu(110) surface

    NASA Astrophysics Data System (ADS)

    Bobrov, Kirill; Guillemot, Laurent

    2013-05-01

    We present a detailed STM study on the reactivity to water of the oxygen covered Cu(110) surface at 200 K. This reactive interaction is known to produce hydroxyls. We found that the hydroxyl chemical state is a key factor regulating further chemical reactions and causing a strong re-structuring of the surface. Parts of the hydroxyls are originally produced on the surface in the form of highly mobile copper-hydroxyl [Cu-OH] complexes. We demonstrate that interaction of the [Cu-OH] complexes with the substrate governs the surface restructuring. The hydroxyl complexes can dissociate either on step sites of the surface, incorporating Cu to the substrate and releasing hydroxyls (OHs) either, remarkably, condensate on the terraces shaping two-dimensional monoatomic height Cu islands possessing under-coordinated sites at their borders. We show that nucleation and growth of these nanometer scaled islands significantly enhance the surface reactivity towards water. Indeed, the Cu islands providing under-coordinated sites enhance water adsorption and furthermore produce a local effect favoring diffusion of the water molecules towards the more reactive sites.

  12. Pentacene/Cu(110) interface formation monitored by in situ optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Liu, C. Y.; Fu, X.; Sun, L. D.; Zeppenfeld, P.

    2014-01-01

    The adsorption of pentacene on the Cu(110) surface has been investigated by reflectance difference spectroscopy (RDS) and spot profile analysis low energy electron diffraction (SPA-LEED). The sensitivity of RDS to electronic transitions involving both surface states and intramolecular transitions allows a close monitoring of the formation of interfacial electronic states and structural phase transitions of the pentacene monolayer on Cu(110).

  13. Tuning self-organized O/Cu(110) nanostructures by co-adsorption of sulfur

    NASA Astrophysics Data System (ADS)

    Wiame, Frédéric; Poulain, Clément; Budinská, Zuzana; Maurice, Vincent; Marcus, Philippe

    2015-06-01

    A method for tuning the nanostructures formed by self-organized growth of oxygen on Cu(110) surface is proposed. It is shown that the range of possible nanostructures, consisting in alternating stripes of bare and oxidized copper, can largely be extended by the co-adsorption of sulfur. The classical Marchenko-Vanderbilt model describing the nanostructuration was generalized in order to take into account the change in the surface properties induced by the presence of sulfur. This modified model enabled us to infer the expressions of the periodicity and width of the self-organized stripes as a function of the sulfur and oxygen coverages.

  14. Impact-collision ion-scattering spectroscopy of Cu(110) and Cu(110)-(2×1)-O using 5keV 6Li+

    Microsoft Academic Search

    Jory A. Yarmoff; Donna M. Cyr; Judy H. Huang; Sehun Kim; R. Stanley Williams

    1986-01-01

    Impact-collision ion-scattering spectroscopy was performed using 5-keV 6Li+ ions to study the Cu(110) and Cu(110)-(2×1)-O surfaces. Polar-angle scans were collected for scattering along the [11¯0], [11¯2], and [001] azimuths. These scans were quantitatively analyzed by comparing them to the results of an algorithm that combined a one-atom Monte Carlo computer simulation with various structural models to calculate trial polar scans.

  15. Impact-collision ion-scattering spectroscopy of Cu(110) and Cu(110)-(2 x 1)-O using 5keV ⁶Li\\/sup +

    Microsoft Academic Search

    J. A. Yarmoff; D. M. Cyr; J. H. Huang; S. Kim; R. S. Williams

    1986-01-01

    Impact-collision ion-scattering spectroscopy was performed using 5-keV ⁶Li\\/sup +\\/ ions to study the Cu(110) and Cu(110)-(2 x 1)-O surfaces. Polar-angle scans were collected for scattering along the (110), (112), and (001) azimuths. These scans were quantitatively analyzed by comparing them to the results of an algorithm that combined a one-atom Monte Carlo computer simulation with various structural models to calculate

  16. Co-adsorption of water and glycine on Cu{110}.

    PubMed

    Sacchi, Marco; Jenkins, Stephen J

    2014-04-01

    In this study, we use density functional theory (DFT) to investigate the surface co-adsorption of glycine with water on Cu{110}. Our results show that, under UHV conditions and for a wide range of temperatures, a pure glycine monolayer is more stable than either mixed gly-water phases or pure water (ice) monolayers, but for a high water pressure half-dissociated water layers can appear on the surface at low and medium temperatures. PMID:24556920

  17. Configuration change of NO on Cu(110) as a function of temperature

    SciTech Connect

    Shiotari, A.; Mitsui, T.; Okuyama, H., E-mail: hokuyama@kuchem.kyoto-u.ac.jp; Hatta, S.; Aruga, T. [Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan); Koitaya, T.; Yoshinobu, J. [The Institute for Solid State Physics, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

    2014-06-07

    The bonding structure of nitric oxide (NO) on Cu(110) is studied by means of scanning tunneling microscopy, reflection absorption infrared spectroscopy, and electron energy loss spectroscopy at 6–160 K. At low temperatures, the NO molecule adsorbs at the short bridge site via the N end in an upright configuration. At around 50 K, this turns into a flat configuration, in which both the N and O atoms interact with the surface. The flat configuration is characterized by the low-frequency N–O stretching mode at 855 cm{sup ?1}. The flat-lying NO flips back and forth when the temperature increases to ?80 K, and eventually dissociates at ?160 K. We propose a potential energy diagram for the conversion of NO on the surface.

  18. Effects of laser irradiation on the morphology of Cu(110)

    SciTech Connect

    Brandstetter, T.; Draxler, M.; Hohage, M.; Zeppenfeld, P.; Stehrer, T.; Heitz, J.; Georgiev, N.; Martinotti, D.; Ernst, H.-J. [Institut fuer Experimentalphysik, Johannes Kepler Universitaet Linz, A-4040 Linz (Austria); Institut fuer Angewandte Physik, Johannes Kepler Universitaet Linz, A-4040 Linz (Austria); CEA Saclay, DSM/Drecam/SPCSI, 91191 Gif sur Yvette (France)

    2008-07-15

    The effects of pulsed laser irradiation on the morphology of the Cu(110) surface were investigated by means of reflectance difference spectroscopy (RDS) and spot profile analysis low-energy electron diffraction (SPA-LEED). The laser light induces surface defects (adatoms and islands) as well as subsurface dislocation lines. The high surface mobility leads to efficient annealing of the surface defects even at room temperature, whereas the subsurface dislocation lines persist up to temperatures T>800 K. SPA-LEED profiles of the (00) diffraction spot from the laser irradiated surface suggest an anisotropic distribution of the subsurface line defects related to the geometry of the fcc easy glide system, which is corroborated by STM measurements. Comparative experiments using conventional Ar ion bombardment point out the distinctiveness of the morphological changes induced by laser irradiation.

  19. Temperature dependent effects during Ag deposition on Cu(110)

    SciTech Connect

    Taylor, T.N.; Muenchausen, R.E.; Hoffbauer, M.A.; Denier van der Gon, A.W.; van der Veen, J.F. (Los Alamos National Lab., NM (USA); FOM-Instituut voor Atoom-en Molecuulfysica, Amsterdam (Netherlands))

    1989-01-01

    The composition, structure, and morphology of ultrathin films grown by Ag deposition on Cu(110) were monitored as a function of temperature using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and medium energy ion scattering (MEIS). Aligned backscattering measurements with 150 keV He ions indicate that the Ag resides on top of the Cu and there is no significant surface compound formation. Measurements with LEED show that the Ag is initially confined to the substrate troughs. Further deposition forces the Ag out of the troughs and results in a split c(2 {times} 4) LEED pattern, which is characteristic of a distorted Ag(111) monolayer template. As verified by both AES and MEIS measurements, postmonolayer deposition of Ag on Cu(110) at 300K leads to a pronounced 3-dimensional clustering. Ion blocking analysis of the Ag clusters show that the crystallites have a (110)-like growth orientation, implying that the Ag monolayer template undergoes a rearrangement. These data are confirmed by low temperature LEED results in the absence of clusters, which indicate that Ag multilayers grow from a Ag--Cu interface where the Ag is captured in the troughs. Changes observed in the film structure and morphology are consistent with a film growth mechanism that is driven by overlayer strain response to the substrate corrugation. 16 refs., 4 figs.

  20. Rotationally anisotropic second-harmonic generation studies of the structure and electronic properties of bimetallic interfaces, Ag on Cu(110)

    SciTech Connect

    Hoffbauer, M.A.; McVeigh, V.J.

    1990-01-01

    Rotationally anisotropic surface second-harmonic generation (SHG) has been measured from a clean, well-ordered Cu(110) single-crystal surface as a function of both surface temperature and Ag coverage. For the clean Cu(110) surface, the temperature dependence of the SH response at a fixed azimuthal angle can be correlated with a surface phase transformation. A large decrease in the rotationally anisotropic SH response as a function of surface temperature can be related to changes in the surface disorder. The results are compared with other studies of Cu(110) surface structure using both x-ray and He-atom scattering. The rotationally anisotropic SH response has also been measured as a function of Ag coverage with the Cu(110) surface temperature fixed at 300 K. The results closely follow the formation of an ordered Ag(111)-like overlayer, the nucleation of three-dimensional Ag nanoclusters (<20 {angstrom} thick) that enhance the anisotropic SH response, and the subsequent growth of a {approximately}10 monolayer thick Ag film. Variations in the rotationally anisotropic SH response as a function of Ag coverage are used to separate the resonant surface electronic contributions to the nonlinear susceptibility of the interface. 22 refs., 4 figs.

  1. Energy and angular distributions of 100- to 400-eV Na+ scattered from Cu(110)

    NASA Astrophysics Data System (ADS)

    Adler, D. L.; Cooper, B. H.

    1991-02-01

    In this paper we present a detailed analysis of the energy and angular distributions of 100-, 200-, and 400-eV Na+ scattered from the Cu(110) surface. The spectra are analyzed using classical trajectory calculations with an improved ion-surface interaction potential. Qualitative features of the spectra can be reproduced using the chain model. Quantitative agreement between measured and simulated spectra is obtained with full-surface simulations, which include the thermal vibrations of the surface atoms. The trajectories are calculated using a potential constructed from a sum of (Na-Cu)+ Hartree-Fock pair potentials plus an attractive interaction. At lower beam energies, the contribution to the scattering potential from the long-range tails of the pair potentials becomes increasingly important in determining the positions of the rainbow angles. The tails are also responsible for the dramatic increase in ``focused'' scattering events at lower beam energies. The simulations provide the impact parameters for the detected ions. This information is used to determine the relative importance of zigzag, focused, and top-layer chainlike scattering events. By examining the trajectories of ions scattered into the forward and backward rainbow angles, the extreme sensitivity of the backward rainbow peak to surface thermal vibrations is explained. Lastly, angular spectra from chain and full-surface simulations are compared.

  2. Resonant ir laser stimulation of the desorption of methanol adsorbed on Cu(110)

    Microsoft Academic Search

    A. Peremans; A. Dereux; F. Maseri; J. Darville; J.-M. Gilles; J.-P. Vigneron

    1992-01-01

    The reactive system CH3OH\\/Cu(110) has been characterized by thermal desorption and infrared reflection-absorption spectroscopies. This provides the knowledge of the reactive system properties necessary for the interpretation of the ir photodesorption experimental results. These properties are the sticking coefficient of methanol on Cu(110) at 90 K, the monolayer density, the ir absorbance, and the structure of the adsorbate. In particular,

  3. Studies of the Ag/Cu(110) bimetallic interface using optical second-harmonic generation

    SciTech Connect

    Muenchausen, R.E.; Hoffbauer, M.A.; Taylor, T.N.

    1989-01-01

    Optical second harmonic generation (SHG) has recently been shown to be a sensitive, real-time, in situ probe for studying interfaces under many different environments. With regard to atomically clean well-characterized surfaces, SHG has been shown to be sensitive to submonolayer coverages of adsorbates, the structural symmetry or molecular arrangement on the surface, and the surface reordering observed during laser induced melting and recrystallization. Previous SHG studies of bimetallic systems have focused on alkali metal adsorption onto transition metal substrates. In these systems the observed SH response is enhanced by a factor of one thousand upon alkali adsorption, due to the large charge transfer to the substrate. We have chosen to study the growth of Ag overlayers on an atomically clean and well-characterized Cu(110) surface. The Ag overlayer growth on this substrate is known to have some interesting temperature dependent behavior that is typical for systems in which significant three-dimensional clustering is known to be important. Cu and Ag, while electronically similar, are immiscible near room temperature, hence there is no significant surface or bulk alloy formation. 16 refs., 4 figs., 1 tab.

  4. 1D self-assembly of chemisorbed thymine on Cu(110) driven by dispersion forces.

    PubMed

    Temprano, I; Thomas, G; Haq, S; Dyer, M S; Latter, E G; Darling, G R; Uvdal, P; Raval, R

    2015-03-14

    Adsorption of thymine on a defined Cu(110) surface was studied using reflection-absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and scanning tunnelling microscopy (STM). In addition, density functional theory (DFT) calculations were undertaken in order to further understand the energetics of adsorption and self-assembly. The combination of RAIRS, TPD, and DFT results indicates that an upright, three-point-bonded adsorption configuration is adopted by the deprotonated thymine at room temperature. DFT calculations show that the upright configuration adopted by individual molecules arises as a direct result of strong O-Cu and N-Cu bonds between the molecule and the surface. STM data reveal that this upright thymine motif self-assembles into 1D chains, which are surprisingly oriented along the open-packed [001] direction of the metal surface and orthogonal to the alignment of the functional groups that are normally implicated in H-bonding interactions. DFT modelling of this system reveals that the molecular organisation is actually driven by dispersion interactions, which cause a slight tilt of the molecule and provide the major driving force for assembly into dimers and 1D chains. The relative orientations and distances of neighbouring molecules are amenable for ?-? stacking, suggesting that this is an important contributor in the self-assembly process. PMID:25770505

  5. L-Methionine adsorption on Cu(110), binding and geometry of the amino acid as a function of coverage

    NASA Astrophysics Data System (ADS)

    Méthivier, Christophe; Humblot, Vincent; Pradier, Claire-Marie

    2015-02-01

    The adsorption of L-methionine on Cu(110) has been characterized by combining in situ Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) and X-ray Photoelectron Spectroscopy (XPS). Both the chemical state of the molecule, and its anchoring points were determined at various coverage values. Adsorbed methionine is anionic and first interacts with the copper surface via its sulfur and/or oxygen atoms, likely lying flat on the surface; at higher coverage, a stronger interaction of oxygen and nitrogen atoms with copper, evidenced by slight shifts of the XPS peaks, together with an angular dependence of the peak ratios, suggests that the molecule stands up on the surface, interacting with the surface via the N and O atoms but almost not anymore via its S atom. Last but not least, no multilayers were evidenced, and this was explained by the geometry of the molecules which leaves no groups accessible for intermolecular interactions.

  6. Structural Studies of Oxide Surfaces

    NASA Astrophysics Data System (ADS)

    Gustafsson, T.; Garfunkel, E.; Gusev, E. P.; Häberle, P.; Lu, H. C.; Zhou, J. B.

    We review some recent ion scattering experiments on the structure of oxide surfaces. We show that the MgO(100) surface exhibits very small surface distortions, in agreement with recent theoretical work. For the case of the oxidation of Si(100), we show that the oxidation proceeds in three different spatially separate regions, something which disagrees with the conventional model for silicon oxidation.

  7. DFT study of gas-phase adsorption of benzotriazole on Cu(111), Cu(100), Cu(110), and low coordinated defects thereon.

    PubMed

    Peljhan, Sebastijan; Kokalj, Anton

    2011-12-01

    The adsorption of benzotriazole--an outstanding corrosion inhibitor for copper--on Cu(111), Cu(100), Cu(110), and low coordinated defects thereon has been studied and characterized using density functional theory (DFT) calculations. We find that benzotriazole can either chemisorb in an upright geometry or physisorb with the molecular plane being nearly parallel to the surface. While the magnitude of chemisorption energy increases as passing from densely packed Cu(111) to more open surfaces and low coordinated defects, the physisorption energy is instead rather similar on all three low Miller index surfaces. It is pointed out that due to a large dipole moment of benzotriazole the dipole-dipole interactions are rather important. For perpendicular chemisorption modes the lateral repulsion is very long ranged, extending up to the nearest-neighbor distance of about 60 bohrs, whereas for parallel adsorption modes the lateral interactions are far less pronounced and the molecules experience a weak attraction at distances ?25 bohrs. The chemisorption energies were therefore extrapolated to zero coverage by a recently developed scheme and the resulting values are -0.60, -0.73, and -0.92 eV for Cu(111), Cu(100), and Cu(110), respectively, whereas the zero-coverage physisorption energy is about -0.7 eV irrespective of the surface plane. While the more densely packed surfaces are not reactive enough to interact with the molecular ?-system, the reactivity of Cu(110) appears to be at the onset of such interaction, resulting in a very stable parallel adsorption structure with an adsorption energy of -1.3 eV that is ascribed as an apparent chemisorption+physisorption mode. PMID:21997376

  8. Local chemical reaction of benzene on Cu(110) via STM-induced excitation

    NASA Astrophysics Data System (ADS)

    Komeda, T.; Kim, Y.; Fujita, Y.; Sainoo, Y.; Kawai, Maki

    2004-03-01

    We have investigated the mechanism of the chemical reaction of the benzene molecule adsorbed on Cu(110) surface induced by the injection of tunneling electrons using scanning tunneling microscopy (STM). With the dosing of tunneling electrons of the energy 2-5 eV from the STM tip to the molecule, we have detected the increase of the height of the benzene molecule by 40% in the STM image and the appearance of the vibration feature of the ?(C-H) mode in the inelastic tunneling spectroscopy (IETS) spectrum. It can be understood with a model in which the dissociation of C-H bonds occurs in a benzene molecule that induces a bonding geometry change from flat-lying to up-right configuration, which follows the story of the report of Lauhon and Ho on the STM-induced change of benzene on the Cu(100) surface. [L. J. Lauhon and W. Ho, J. Phys. Chem. A 104, 2463 (2000)]. The reaction probability shows a sharp rise at the sample bias voltage at 2.4 V, which saturates at 3.0 V, which is followed by another sharp rise at the voltage of 4.3 V. No increase of the reaction yield is observed for the negative sample voltage up to 5 eV. In the case of a fully deuterated benzene molecule, it shows the onset at the same energy of 2.4 eV, but the reaction probability is 103 smaller than the case of the normal benzene molecule. We propose a model in which the dehydrogenation of the benzene molecule is induced by the formation of the temporal negative ion due to the trapping of the electrons at the unoccupied resonant states formed by the ? orbitals. The existence of the resonant level close to the Fermi level (˜2.4 eV) and multiple levels in less than ˜5 eV from the Fermi level, indicates a fairly strong interaction of the Cu-?* state of the benzene molecule. We estimated that the large isotope effect of ˜103 can be accounted for with the Menzel-Gomer-Redhead (MGR) model with an assumption of a shallow potential curve for the excited state.

  9. Surface Oxidation of Liquid Sn

    SciTech Connect

    Grigoriev,A.; Shpyrko, O.; Steimer, C.; Pershan, P.; Ocko, B.; Deutsch, M.; Lin, B.; Meron, M.; Graber, T.; Gebhardt, J.

    2005-01-01

    We report the results of an X-ray scattering study that reveals oxidation kinetics and formation of a previously unreported crystalline phase of SnO at the liquid-vapour interface of Sn. Our experiments reveal that the pure liquid Sn surface does not react with molecular oxygen below an activation pressure of {approx}5.0 x 10{sup -6} Torr. Above that pressure a rough solid Sn oxide grows over the liquid metal surface. Once the activation pressure has been exceeded the oxidation proceeds at pressures below the oxidation pressure threshold. The observed diffraction pattern associated with the surface oxidation does not match any of the known Sn oxide phases. The data have an explicit signature of the face-centered cubic structure, however it requires lattice parameters that are about 9% smaller than those reported for cubic structures of high-pressure phases of Sn oxides.

  10. Hydrogen and coordination bonding supramolecular structures of trimesic acid on Cu(110).

    PubMed

    Classen, Thomas; Lingenfelder, Magalí; Wang, Yeliang; Chopra, Rishav; Virojanadara, Chariya; Starke, Ulrich; Costantini, Giovanni; Fratesi, Guido; Fabris, Stefano; de Gironcoli, Stefano; Baroni, Stefano; Haq, Sam; Raval, Rasmita; Kern, Klaus

    2007-12-13

    The adsorption of trimesic acid (TMA) on Cu(110) has been studied in the temperature range between 130 and 550 K and for coverages up to one monolayer. We combine scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), reflection absorption infrared spectroscopy (RAIRS), X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations to produce a detailed adsorption phase diagram for the TMA/Cu(110) system as a function of the molecular coverage and the substrate temperature. We identify a quite complex set of adsorption phases, which are determined by the interplay between the extent of deprotonation, the intermolecular bonding, and the overall energy minimization. For temperatures up to 280 K, TMA molecules are only partly deprotonated and form hydrogen-bonded structures, which locally exhibit organizational chirality. Above this threshold, the molecules deprotonate completely and form supramolecular metal-organic structures with Cu substrate adatoms. These structures exist in the form of single and double coordination chains, with the molecular coverage driving distinct phase transitions. PMID:17994713

  11. The electronic properties of Co nanowires on Cu(110)-p(2 × 3)N

    NASA Astrophysics Data System (ADS)

    Wedekind, Sebastian; Donati, Fabio; Oka, Hirofumi; Rodary, Guillemin; Sander, Dirk; Kirschner, Jürgen

    2012-11-01

    We present the first measurements of the differential conductance of Co wires grown on top of Cu(110)-p(2 × 3)N (Cu3N). We apply scanning tunneling spectroscopy (STS) in constant height and constant current mode to access the electronic density of states of the sample over a wide energy range. All measurements have been performed at 7 K. Our study reveals that the differential conductance of the Co wires is very similar to that of Cu3N. Spectra of the differential conductance measured on the Co wires and on Cu3N reveal that both systems exhibit the same characteristic features near + 1.8V and + 3.5 V.

  12. Vibrationally induced flip motion of a hydroxyl dimer on Cu(110)

    NASA Astrophysics Data System (ADS)

    Ootsuka, Yasuhiro; Frederiksen, Thomas; Ueba, Hiromu; Paulsson, Magnus

    2011-11-01

    Recent low-temperature scanning-tunneling microscopy experiments [T. Kumagai , Phys. Rev. BPLRBAQ0556-280510.1103/PhysRevB.79.035423 79, 035423 (2009)] observed the vibrationally induced flip motion of a hydroxyl dimer (OD)2 on Cu(110). We propose a model to describe two-level fluctuations and current-voltage characteristics of nanoscale systems that undergo vibrationally induced switching. The parameters of the model are based on comprehensive density functional calculations of the system’s vibrational properties. For the dimer (OD)2, the calculated population of the high- and low-conductance states, the I-V, dI/dV, and d2I/dV2 curves are in good agreement with the experimental results and underline the different roles played by the free and shared OD stretch modes of the dimer.

  13. Adsorption-geometry induced transformation of self-assembled nanostructures of an aldehyde molecule on Cu(110)

    NASA Astrophysics Data System (ADS)

    Zhang, Chi; Sun, Qiang; Sheng, Kai; Tan, Qinggang; Xu, Wei

    2014-09-01

    From an interplay of high-resolution STM imaging/manipulation and DFT calculations, we have revealed that different self-assembled nanostructures of BA molecules on Cu(110) are attributable to specific molecular adsorption geometries, and thus the corresponding intermolecular hydrogen bonding patterns. The STM manipulations demonstrate the feasibility of switching such weak-hydrogen-bonding patterns.From an interplay of high-resolution STM imaging/manipulation and DFT calculations, we have revealed that different self-assembled nanostructures of BA molecules on Cu(110) are attributable to specific molecular adsorption geometries, and thus the corresponding intermolecular hydrogen bonding patterns. The STM manipulations demonstrate the feasibility of switching such weak-hydrogen-bonding patterns. Electronic supplementary information (ESI) available: Supplementary STM images and DFT calculation results. See DOI: 10.1039/c4nr03754e

  14. Wettability of transition metal oxide surfaces

    Microsoft Academic Search

    Aiguo Feng; Benjamin J McCoy; Zuhair A Munir; Domenick Cagliostro

    1998-01-01

    The wettability of transition metal oxide surfaces (TiO2, ZrO2 and HfO2) by water was investigated by measuring the contact angles using the sessile drop method. The oxide surfaces were prepared by thermal oxidation of polished metal foils of Ti, Zr and Hf, which had been polished to different levels of surface roughness. The surfaces were also characterized by optical microscopy,

  15. Wave-vector-dependent symmetry analysis of a photoemission matrix element: The quasi-one-dimensional model system Cu(110)(2×1)O

    NASA Astrophysics Data System (ADS)

    Pforte, F.; Gerlach, A.; Goldmann, A.; Matzdorf, R.; Braun, J.; Postnikov, A.

    2001-04-01

    We derive orbital symmetry character from the study of peak intensities in angle-resolved photoemission spectra taken at different incidence angles of p-polarized light. Our method of analysis is tested at the oxygen-derived antibonding band on the Cu(110)(2×1)O surface. This band has an initial state energy Ei=-1.37 eV (T=300 K) at the Y¯ point and shows even symmetry with respect to the ?LUX mirror plane (along ?Y¯). The intensity analysis reveals that orbitals both of z-like (along surface normal) and y-like symmetry (y along the Cu-O chains) are mixed into this band. This interpretation is supported by several calculations. The ground-state symmetry character was studied by a full-potential linearized augmented plane-wave method using a seven-layer supercell geometry. For a direct comparison with the experimental intensities, photoemission spectra at the Y¯ point were calculated using the one-step model of photoemission. Our results contribute to a long-standing discussion about the orbital character of the even antibonding band. In particular we demonstrate that this kind of intensity analysis can supply valuable information about symmetry properties.

  16. Introduction to the Surface Spectra of Oxides

    SciTech Connect

    Baer, D.R. [William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington (United States)] [William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington (United States); Henrich, V.E. [Department of Applied Physics, Yale University, New Haven, Connecticut (United States)] [Department of Applied Physics, Yale University, New Haven, Connecticut (United States)

    1996-07-01

    Due to their technological importance and an increasing scientific interest, a set of data from oxide surfaces has been collected for publication in two special issues of {ital Surface Science Spectra}. This Introduction to these two special issues summarizes the data to be presented and provides short overviews of trends in both the physics and chemistry of metal-oxide surfaces and of some important aspects of the techniques used to examine these surfaces. The surface spectroscopies discussed in relation to oxides include: valence band photoemission (ultraviolet photoelectron spectroscopy and synchrotron based), core level photoemission (x-ray photoelectron spectroscopy, XPS), Auger electron spectroscopy (AES), (reflection) electron energy loss spectroscopy (R)EELS, high-resolution electron energy loss spectroscopy (HREELS), scanning probe methods, and ion scattering spectroscopy (ISS). Brief sections also discuss the nature of stoichiometric oxide surfaces, the physics and chemistry of defects on these surfaces, and adsorption on metal-oxide surfaces.{copyright} {ital 1998 American Vacuum Society.}

  17. Ultrasonically enhanced persulfate oxidation of polyethylene surfaces

    Microsoft Academic Search

    Fiona Keen

    1996-01-01

    The ultrasonically enhanced oxidation of polyethylene surfaces by potassium and ammonium persulfates is described. The use of ultrasound allows significant levels of surface modification to be achieved using these oxidizing agents under mild conditions. Changes in the water contact angle and attenuated total reflection infra-red spectra were used to follow the changes in surface chemistry. Variation of conditions such as

  18. Raman and IR studies of surface metal oxide species on oxide supports: Supported metal oxide catalysts

    Microsoft Academic Search

    Israel E. Wachs

    1996-01-01

    Raman and infrared spectroscopy provide complementary information about the nature of the surface metal oxide species present in supported metal oxide catalysts. This paper reviews the type of fundamental information that is typically obtained in Raman and IR characterization studies of supported metal oxide catalysts. The molecular structures of the surface metal oxide species are reflected in the terminal M=O

  19. Surface Wettability of Nanostructured Zinc Oxide Films

    Microsoft Academic Search

    Jie Han; Wei Gao

    2009-01-01

    Zinc oxide (ZnO) nanograin and nanorod films were prepared by magnetron sputter deposition and an aqueous solution growth\\u000a method. Their surface wettability was studied in relation to their surface morphologies. While the surfaces of both films\\u000a were hydrophobic, the nanorod films exhibited higher surface hydrophobicity. A superhydrophobic surface was obtained on a\\u000a ZnO nanorod film with a water contact angle

  20. The electrochemistry of surface oxidation of chalcopyrite

    Microsoft Academic Search

    T. Biegler; M. D. Horne

    1985-01-01

    Linear sweep voltammetry with a freshly renewed surface of a chalcopyrite (CuFeSâ) mineral electrode shows a small anodic prewave in acid electrolytes. The main anodic reaction, with complete dissolution of copper and iron, occurs at more positive potentials. Experiments under nitrogen show that the prewave is not a consequence of atmospheric oxidation during surface preparation. The prewave represents a surface

  1. Surface complexes of acrolein on oxide catalysts

    SciTech Connect

    Popova, G.Ya.; Davydov, A.A.; Andrushkevich, T.V.; Zakharov, I.I. [Boreskov Institute of Catalysis, Novosibirsk (Russian Federation)

    1995-01-01

    It is shown that acrolein can be adsorbed by different mechanisms on the surface of oxide catalysts with the formation of {sigma}- and {pi}-complexes, H-complexes with surface OH groups; a species bound via the carbonyl group (the dissociative form of adsorption); and oxidized fragments, such as surface acrylates, carboxylates, formylacetates, and malonates. On the basis of the quantum-chemical analysis of the acrolein interaction with the surface of oxide catalysts in combination with IR-spectroscopic, thermodesorption, and catalytic studies, a conclusion has been drawn that the formation of a certain surface species and its reactivity are determined by the nature of an adsorption site and by the reactivity of surface oxygen.

  2. Platinum attachments on iron oxide nanoparticle surfaces

    Microsoft Academic Search

    Soubantika Palchoudhury; Yaolin Xu; Wei An; C. Heath Turner; Yuping Bao

    2010-01-01

    Platinum nanoparticles supported on metal oxide surfaces have shown great potential as heterogeneous catalysts to accelerate electrochemical processes, such as the oxygen reduction reaction in fuel cells. Recently, the use of magnetic supports has become a promising research topic for easy separation and recovery of catalysts using magnets, such as Pt nanoparticles supported on iron oxide nanoparticles. The attachment of

  3. Ultrathin, ordered oxide films on metal surfaces

    NASA Astrophysics Data System (ADS)

    Chen, M. S.; Goodman, D. W.

    2008-07-01

    Metal oxides and oxide thin films are extensively used as active catalysts and catalytic supports, as well as in many other important technical applications. Unlike TiO2, which is a semiconductor and can be investigated using a variety of surface science techniques, most metal oxides are insulators, which seriously restricts their use as model surfaces with modern surface science techniques. This difficulty can be circumvented by synthesizing ultrathin oxide films a few nanometers in thickness with well-defined structures, that mimic the corresponding bulk oxides yet are thin enough to be sufficiently conducting. In this review, preparations, structures, electronic and chemical properties of four representative oxides, alumina, magnesium oxide, silica, and titania, are addressed. Of these MgO is found to grow in a layer-by-layer fashion, allowing preparation of crystalline thin film structures with varying thicknesses. Crystalline TiO2 and Ti2O3 can also be synthesized, whereas SiO2 and Al2O3, although amenable to synthesis as well-defined monolayer structures, have only been grown to date as amorphous multilayers.

  4. NORTHWESTERN UNIVERSITY Surface Stabilization Mechanisms in Metal Oxides

    E-print Network

    Shull, Kenneth R.

    NORTHWESTERN UNIVERSITY Surface Stabilization Mechanisms in Metal Oxides A DISSERTATION SUBMITTED Mechanisms in Metal Oxides Andrés E. Becerra Toledo Metal oxide surfaces play a central role in modern SrTiO3(001) surfaces reveals that water plays two major roles in the stabilization of oxide surfaces

  5. The surface chemistry of cerium oxide

    NASA Astrophysics Data System (ADS)

    Mullins, David R.

    2015-03-01

    This review covers the structure of, and chemical reactions on, well-defined cerium oxide surfaces. Ceria, or mixed oxides containing ceria, are critical components in automotive three-way catalysts due to their well-known oxygen storage capacity. Ceria is also emerging as an important material in a number of other catalytic processes, particularly those involving organic oxygenates and the water-gas shift reaction. Ceria's acid-base properties, and thus its catalytic behavior, are closely related to its surface structure where different oxygen anion and cerium cation environments are present on the low-index structural faces. The actual structure of these various faces has been the focus of a number of theoretical and experimental investigations. Ceria is also easily reducible from CeO2 to CeO2-X. The presence of oxygen vacancies on the surface often dramatically alters the adsorption and subsequent reactions of various adsorbates, either on a clean surface or on metal particles supported on the surface. Most surface science studies have been conducted on the surfaces of thin-films rather than on the surfaces of bulk single crystal oxides. The growth, characterization and properties of these thin-films are also examined.

  6. Epitaxial oxide growth on polar (111) surfaces

    NASA Astrophysics Data System (ADS)

    Blok, J. L.; Wan, X.; Koster, G.; Blank, D. H. A.; Rijnders, G.

    2011-10-01

    Obtaining atomically smooth surfaces and interfaces of perovskite oxide materials on polar (111) surfaces presents a particular challenge as these surfaces and interfaces will reconstruct. Here, the effect of the use of screening buffer layers on the epitaxial growth on such polar surfaces is investigated. Both transmission electron microscopy and in situ reflective high energy electron diffraction data imply that the buffer layers, SrRuO3 or LaAlO3, restore a near bulk-like termination at growth temperature, allowing for coherent growth of BiFeO3 and CaTiO3 for all deposited unit cell layers of the film material.

  7. Alkane activation on crystalline metal oxide surfaces.

    PubMed

    Weaver, Jason F; Hakanoglu, Can; Antony, Abbin; Asthagiri, Aravind

    2014-11-21

    Advances in the fundamental understanding of alkane activation on oxide surfaces are essential for developing new catalysts that efficiently and selectively promote chemical transformations of alkanes. In this tutorial review, we discuss the current understanding of alkane activation on crystalline metal oxide surfaces, and focus mainly on summarizing our findings on alkane adsorption and C-H bond cleavage on the PdO(101) surface as determined from model ultrahigh vacuum experiments and theoretical calculations. These studies show that alkanes form strongly-bound ?-complexes on PdO(101) by datively bonding with coordinatively-unsaturated Pd atoms and that these molecularly adsorbed species serve as precursors for C-H bond activation on the oxide surface. In addition to discussing the binding and properties of alkane ?-complexes on PdO(101), we also summarize recent advances in kinetic models to predict alkane dissociation rates on solid surfaces. Lastly, we highlight computations which predict that the formation and facile C-H bond activation of alkane ?-complexes also occurs on RuO2 and IrO2 surfaces. PMID:24480977

  8. The electrochemistry of surface oxidation of chalcopyrite

    SciTech Connect

    Biegler, T.; Horne, M.D.

    1985-06-01

    Linear sweep voltammetry with a freshly renewed surface of a chalcopyrite (CuFeS/sub 2/) mineral electrode shows a small anodic prewave in acid electrolytes. The main anodic reaction, with complete dissolution of copper and iron, occurs at more positive potentials. Experiments under nitrogen show that the prewave is not a consequence of atmospheric oxidation during surface preparation. The prewave represents a surface oxidation of chalcopyrite to form a thin passivating film. The charge passed in forming this film is around 2 mC cm/sup -2/ for a polishe surface. The prewave reaction is identified with the initial phase of the oxidative dissolution or leaching of chalcopyrite. Contrary to the reported behavior at 80/sup 0/C, the surface film is stable at 25/sup 0/C for long periods at open circuit Various evidence, including the relative charges passed in forming and then reducing the surface film, and the presence of dissolved copper, leads to the following suggested stoichiometry for the prewave reaction CuFeS/sub 2/ ..-->.. 0.75CuS + 0.25Cu/sup 2 +/ + Fe/sup 2 +/ + 1.25S + 2.5e. The product layer containing CuS and S is about 3 nm thick.

  9. Surface Ionization Gas Detection on Platinum and Metal Oxide Surfaces

    Microsoft Academic Search

    A. Hackner; A. Habauzit; G. Muller; E. Comini; G. Faglia; G. Sberveglieri

    2009-01-01

    Surface ionization (SI) gas detection experiments have been performed on platinum (Pt) and metal oxide (MOX) films. The probability of surface ion emission varies with temperature in an Arrhenius-type manner. Among all hydrocarbons studied so far those with amine functional groups exhibited the lowest activation energies allowing detection in the ppm concentration range at emitter operation temperatures of about 400degC.

  10. Geometrical Characterization of Adenine And Guanine on Cu(110) By NEXAFS, XPS, And DFT Calculation

    SciTech Connect

    Furukawa, M.; Yamada, T.; /Wako, RIKEN; Katano, S.; /tohoku U.; Kawai, M.; /Wako, RIKEN /Tokyo U.; Ogasawara, H.; /SLAC, SSRL; Nilsson, A.; /SLAC, SSRL /Stockholm U.

    2009-04-30

    Adsorption of purine DNA bases (guanine and adenine) on Cu(1 1 0) was studied by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine-structure spectroscopy (NEXAFS), and density-functional theory (DFT) calculation. At coverages near 0.2 monolayers, Angular-resolved NEXAFS analysis revealed that adenine adsorbates lie almost flat and that guanine adsorbates are tilted up on the surface with the purine ring parallel to the atom rows of Cu(1 1 0). Referring to the previous studies on pyrimidine DNA bases [M. Furukawa, H. Fujisawa, S. Katano, H. Ogasawara, Y. Kim, T. Komeda, A. Nilsson, M. Kawai, Surf. Sci. 532-535 (2003) 261], the isomerization of DNA bases on Cu(1 1 0) was found to play an important role in the adsorption geometry. Guanine, thymine and cytosine adsorption have an amine-type nitrogen next to a carbonyl group, which is dehydrogenated into imine nitrogen on Cu(1 1 0). These bases are bonded by the inherent portion of - NH-CO - altered by conversion into enolic form and dehydrogenation. Adenine contains no CO group and is bonded to Cu(1 1 0) by participation of the inherent amine parts, resulting in nearly flatly-lying position.

  11. The Characterisation of Uranium-Oxide Surfaces.

    NASA Astrophysics Data System (ADS)

    Holmes, Nigel Richard

    Available from UMI in association with The British Library. These studies show that x-ray photoelectron spectroscopy (X.p.s.) can be used to determine the overall oxidation state and the uranium valences present at the surface of a uranium oxide. By comparing the spectra recorded from an unknown oxide with those obtained from reference compounds it should be possible to predict the adopted structure type. X.p.s. cannot however distinguish between uranium oxides containing identical uranium oxidation states but different structures, such as the four UO_3 phases studied in this work. In the infra-red studies it was found that all of the uranium oxides studies had characteristic absorption spectra, and this can distinguish between samples with the same composition but different structures. In addition the layered structure oxides such as alpha-U_3O _6 and most of the UO_3 phases have strong vibrational absorptions which are absent in the spectra of the fluorite-type uranium oxides. This makes infra-red spectroscopy a useful technique for determining the types of oxides present in a partially oxidised sample. The X-ray diffraction (X.r.d.) studies in this work found that the initial oxidation product of UO_2 at temperatures between 125 ^circC and 135^ circC could be indexed on a cubic unit cell smaller than that of U_4O _9. From a comparison with previously reported data it was concluded that this oxide could be a low temperature alpha-U_3O _7 phase. By considering previously reported X.r.d. data for the uranium oxides it was also found that the structures could be divided into two general types, the fluorite structure typified by UO_2 and the layered structure typified by alpha-U_3O _6. From the close similarity of the hexagonally packed uranium planes present in both structure types a mechanism for the UO_2 to alpha-U_3O _6 phase transformation is proposed.

  12. Surface Structure of Aerobically Oxidized Diamond Nanocrystals.

    PubMed

    Wolcott, Abraham; Schiros, Theanne; Trusheim, Matthew E; Chen, Edward H; Nordlund, Dennis; Diaz, Rosa E; Gaathon, Ophir; Englund, Dirk; Owen, Jonathan S

    2014-11-20

    We investigate the aerobic oxidation of high-pressure, high-temperature nanodiamonds (5-50 nm dimensions) using a combination of carbon and oxygen K-edge X-ray absorption, wavelength-dependent X-ray photoelectron, and vibrational spectroscopies. Oxidation at 575 °C for 2 h eliminates graphitic carbon contamination (>98%) and produces nanocrystals with hydroxyl functionalized surfaces as well as a minor component (<5%) of carboxylic anhydrides. The low graphitic carbon content and the high crystallinity of HPHT are evident from Raman spectra acquired using visible wavelength excitation (?excit = 633 nm) as well as carbon K-edge X-ray absorption spectra where the signature of a core-hole exciton is observed. Both spectroscopic features are similar to those of chemical vapor deposited (CVD) diamond but differ significantly from the spectra of detonation nanodiamond. The importance of these findings to the functionalization of nanodiamond surfaces for biological labeling applications is discussed. PMID:25436035

  13. Compensation Mechanisms and Functionality of Transition Metal Oxide Surfaces and

    E-print Network

    Compensation Mechanisms and Functionality of Transition Metal Oxide Surfaces and Interfaces metal oxide surfaces and interfaces can lead to properties and functionality that are not observed-code on HLRBI and HLRBII. 1 Introduction The surfaces and interfaces of transition metal oxides represent

  14. Surface wettability of macroporous anodized aluminum oxide.

    PubMed

    Buijnsters, Josephus G; Zhong, Rui; Tsyntsaru, Natalia; Celis, Jean-Pierre

    2013-04-24

    The correlation between the structural characteristics and the wetting of anodized aluminum oxide (AAO) surfaces with large pore sizes (>100 nm) is discussed. The roughness-induced wettability is systematically examined for oxide films grown by a two-step, high-field anodization in phosphoric acid of three different concentrations using a commercial aluminum alloy. This is done for the as-synthesized AAO layers, after various degrees of pore widening by a wet chemical etching in phosphoric acid solution, and upon surface modification by either Lauric acid or a silane. The as-grown AAO films feature structurally disordered pore architectures with average pore openings in the range 140-190 nm but with similar interpore distances of about 405 nm. The formation of such AAO structures induces a transition from slightly hydrophilic to moderately hydrophobic surfaces up to film thicknesses of about 6 ?m. Increased hydrophobicity is obtained by pore opening and a maximum value of the water contact angle (WCA) of about 128° is measured for AAO arrays with a surface porosity close to 60%. Higher surface porosity by prolonged wet chemical etching leads to a rapid decrease in the WCA as a result of the limited pore wall thickness and partial collapse of the dead-end pore structures. Modification of the AAO surfaces by Lauric acid results in 5-30° higher WCA's, whereas near-superhydrophobicity (WCA ~146°) is realized through silane coating. The "rose petal effect" of strongly hydrophobic wetting with high adhesive force on the produced AAO surfaces is explained by a partial penetration of water through capillary action into the dead-end pore cavities which leads to a wetting state in-between the Wenzel and Cassie states. Moreover, practical guidelines for the synthesis of rough, highly porous AAO structures with controlled wettability are provided and the possibility of forming superhydrophobic surfaces is evaluated. PMID:23506401

  15. Modeling of surface oxidation and oxidation induced damage in metal matrix composites 

    E-print Network

    Ma, Xinzheng

    1995-01-01

    Surface oxidation in metal matrix composites (MMC's) is modeled by Fickian diffusion of oxygen in both the oxide layer and metal matrix. The oxidation process and the resulting immobilized oxygen at the interface is accounted for by the introduction...

  16. Modeling of surface oxidation and oxidation induced damage in metal matrix composites

    E-print Network

    Ma, Xinzheng

    1995-01-01

    Surface oxidation in metal matrix composites (MMC's) is modeled by Fickian diffusion of oxygen in both the oxide layer and metal matrix. The oxidation process and the resulting immobilized oxygen at the interface is accounted for by the introduction...

  17. Suppression of 90 spin switching in Co nanomagnets grown on the Cu,,110...-^21O surface

    E-print Network

    Xu, Yongbing

    , providing step-like edges for gas adsorption. The density of steps is similar to the density developing the 1-10 direction that provide ``step like'' edges for gas adsorption. Furthermore, it was found the specific adsorption sites preferred by the CO molecules in the first case while it displaces the CO gas

  18. Acceleration of Biochar Surface Oxidation during Composting?

    PubMed

    Wiedner, Katja; Fischer, Daniel; Walther, Sabine; Criscuoli, Irene; Favilli, Filippo; Nelle, Oliver; Glaser, Bruno

    2015-04-22

    Biochar composting experiments were performed to determine whether composting is a suitable method to accelerate biochar surface oxidation for increasing its reactivity. To assess the results, surface properties of Terra Preta (Brazil) and ancient charcoal pit (Northern Italy) biochars were additionally investigated. Calculation of O/C ratios by energy-dispersive X-ray spectroscopy demonstrated the anticipated increasing values from fresh biochars (0.13) to composted biochars (0.40), and finally charcoal pit biochars (0.54) and ancient Terra Preta biochars (0.64). By means of Fourier transformation infrared microscopy, formation of carboxylic and phenolic groups on biochars surface could be detected. Carboxylic acids of three composted biochars increased up to 14%, whereas one composted biochar showed a 21% lower proportion of carboxylic acids compared to the corresponding fresh biochar. Phenolic groups increased by 23% for the last mentioned biochar, and on all other biochars phenolic groups decreased up to 22%. Results showed that biochar surface oxidation can be accelerated through composting but still far away from ancient biochars. PMID:25802948

  19. Oxidation-driven surface dynamics on NiAl(100)

    PubMed Central

    Qin, Hailang; Chen, Xidong; Li, Liang; Sutter, Peter W.; Zhou, Guangwen

    2015-01-01

    Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling up of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). By comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps. PMID:25548155

  20. Oxide modified air electrode surface for high temperature electrochemical cells

    DOEpatents

    Singh, Prabhakar (Export, PA); Ruka, Roswell J. (Churchill Boro, Allegheny County, PA)

    1992-01-01

    An electrochemical cell is made having a porous cermet electrode (16) and a porous lanthanum manganite electrode (14), with solid oxide electrolyte (15) between them, where the lanthanum manganite surface next to the electrolyte contains a thin discontinuous layer of high surface area cerium oxide and/or praseodymium oxide, preferably as discrete particles (30) in contact with the air electrode and electrolyte.

  1. The surface and materials science of tin oxide

    Microsoft Academic Search

    Matthias Batzill; Ulrike Diebold

    2005-01-01

    The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are

  2. Kinetics of nitric oxide desorption from carbonaceous surfaces

    E-print Network

    Truong, Thanh N.

    Kinetics of nitric oxide desorption from carbonaceous surfaces Alejandro Montoya a , Fanor Mondrago of nitrogen-containing chars, the evolution of nitric oxide, (CNO) ! NO+(C*). Density functional theory.V. All rights reserved. Keywords: Nitric oxide; Carbonaceous surface; Chars 1. Introduction

  3. Antibacterial effects of zinc oxide nanorod surfaces.

    PubMed

    Jansson, Tobias; Clare-Salzler, Zachary J; Zaveri, Toral D; Mehta, Shahil; Dolgova, Natalia V; Chu, Byung-Hwan; Ren, Fan; Keselowsky, Benjamin G

    2012-09-01

    Antibacterial coating approaches are being investigated to modify implants to reduce bacterial adhesion and viability in order to reduce implant-associated infection. Nanostructured materials possess unique surface properties, and nanotopographic surfaces have been reported to modulate bacterial adhesion. Zinc oxide (ZnO) films presenting well-controlled nanorod surface structures have recently been developed. To assess the efficacy of ZnO nanorod surfaces as an anti-bacterial coating, we evaluated bacterial adhesion and viability, compared to sputtered ZnO substrates (a relatively flat control) and glass substrates (as a reference). Common implant-associated pathogens, Pseudomonas aeruginosa and Staphylococcus epidermidis were investigated. The number of adherent P. aeruginosa on ZnO nanorod surfaces was found to be reduced compared to glass and sputtered ZnO, while the adherent number of S. epidermidis on the ZnO nanorods was equivalent to glass. Regarding bacteria viability, the ZnO nanorod and sputtered ZnO surfaces demonstrated a modest, but significant bactericidal effect on adherent P. aeruginosa, killing 2.5-fold and 1.7-fold more over the number of dead P. aeruginosa on glass, respectively. A greater bactericidal effect of ZnO substrates on S. epidermidis was found, with sputtered ZnO and ZnO nanorod substrates killing -20-fold and 30-fold more over the number of dead S. epidermidis on glass, respectively. These data support the further investigation and optimization of ZnO nanorod coatings with potential for bacterial adhesion resistance and bactericidal properties. PMID:23035444

  4. Faraday Discussion # 114 The Surface Science of Metal Oxides

    E-print Network

    Jennison, Dwight R.

    -1- Faraday Discussion # 114 The Surface Science of Metal Oxides Ultrathin Alumina Film Al of common point defects in metal island nucleation on oxide terraces, and 3) the growth and morphology, they represent struc- tures which may be produced during the oxidation of Al metal, and are thus important

  5. Surface and sub-surface thermal oxidation of thin ruthenium films

    NASA Astrophysics Data System (ADS)

    Coloma Ribera, R.; van de Kruijs, R. W. E.; Kokke, S.; Zoethout, E.; Yakshin, A. E.; Bijkerk, F.

    2014-09-01

    A mixed 2D (film) and 3D (nano-column) growth of ruthenium oxide has been experimentally observed for thermally oxidized polycrystalline ruthenium thin films. Furthermore, in situ x-ray reflectivity upon annealing allowed the detection of 2D film growth as two separate layers consisting of low density and high density oxides. Nano-columns grow at the surface of the low density oxide layer, with the growth rate being limited by diffusion of ruthenium through the formed oxide film. Simultaneously, with the growth of the columns, sub-surface high density oxide continues to grow limited by diffusion of oxygen or ruthenium through the oxide film.

  6. Inverse gas chromatography investigation of oxidized polyolefins: surface properties.

    PubMed

    Voelkel, Adam; Strzemiecka, Beata; Marek, Adam Andrzej; Zawadiak, Jan

    2014-04-11

    Oxidized polyolefins were obtained in processes with the use of air or oxygen as oxidizing agent. The oxidation process caused partial polymer degradation and the change of the surface properties of examined materials. The magnitude of these changes was estimated by means of inverse gas chromatography. All oxidized materials were found to exhibit slightly acidic character. Surface properties strongly depend on the content of oxygen functional groups (oxidation degree) and type of initial material. The most active surfaces were found for oxidized polypropylene and polyethylene wax. The use of principal component analysis allowed to select four parameters offering complete information on the physiochemical character of examined materials (?S(D)), acid volume or saponification number, KA or KD and KA/KD. PMID:24636560

  7. Surface oxygen bond energy of Period IV transition metal oxides in the oxidation of carbon monoxide

    Microsoft Academic Search

    V. I. Marshneva; G. K. Boreskov

    1974-01-01

    The bond energies of oxygen have been determined by thermodesorption from Period IV transition metal oxides, both after treatment with oxygen and under steady state conditions of the catalytic oxidation of CO. With the exception of V2O5, there are several (2–3) forms of adsorbed oxygen with different bond energies on the surface of the oxide treated with oxygen.

  8. Surface Science Letters CO oxidation on ruthenium: The nature of the active catalytic surface

    E-print Network

    Goodman, Wayne

    in automotive catalytic converters, the reaction proceeds via the Langmuir­Hin- shelwood (L­H) mechanism betweenSurface Science Letters CO oxidation on ruthenium: The nature of the active catalytic surface D(110) The oxidation of CO, i.e. CO + 1=2O2 ! CO2, over metal surfaces is one of the most studied catalytic reactions

  9. Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

    PubMed Central

    2008-01-01

    Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed. PMID:21749733

  10. Development and Characterization of an Ultrathin Barium Oxide Film on a Surface Oxidized Ni(110) Substrate

    Microsoft Academic Search

    D. Vlachos; S. D. Foulias; M. Kamaratos

    2008-01-01

    In this work we develop an ultrathin barium oxide film by Ba adsorption on a pre?oxidized Ni(110) surface, and characterize it by means of Auger electron spectroscopy, low energy electron diffraction and work function measurements. The results show that the Ba adatoms reduce the NiO surface oxide forming an amorphous and incomplete BaO layer. At higher coverages, the Ba adsorbate

  11. Scanning tunneling microscopy and spectroscopy of oxide surfaces

    NASA Astrophysics Data System (ADS)

    Bonnell, Dawn A.

    1998-03-01

    Considerable progress has been made using scanning tunneling microscopy (STM) and tunneling spectroscopy (STS) to examine the atomic structures and properties of transition metal oxide surfaces. The surfaces are found to be very sensitive to thermochemical history; consequently a large variety of surface structures have been observed. This paper reviews the results to date of STM on single crystal transition metal oxides (excluding superconductors) and, while mentioning ambient analyses, will emphasize ultra high vacuum and atomic scale structural information of single crystal surfaces. First, a summary of salient features of oxide bulk and surface geometric and electronic structures is provided as a framework within which to discuss the STM results. The principles of STM and STS are reviewed with extensive discussion of special considerations for analyses of oxides, including effects of band bending and image interpretation. Variations of surface stoichiometry are illustrated with results on TiO 2 and SrTiO 3, for which the most data exist. The yet unresolved controversy regarding the basis of contrast in STM images of oxides is introduced explicitly into discussion of these results. Recent work on vanadyls and tungstate bronzes is also presented. First observations of the structures of local defects on surfaces, including vacancies, dopants, steps, and domain boundaries, are illustrated with results from ZnO, NiO, SrTiO 3, and TiO 2. Finally, the few studies of surface reactions are considered, including those of oxides with metals, with reducing gases, and with organic molecules.

  12. Mobility of Water on Oxide Surfaces Studied by QENS

    Microsoft Academic Search

    Mamontov

    2007-01-01

    Although neutron scattering is often considered a bulk probe, we demonstrate that the mobility of surface water on oxide nano-powders can be investigated using quasielastic neutron scattering. We discuss how the reduced number of hydrogen bonds per water molecule associated with surface confinement leads to a qualitative modification of single-particle translational dynamics compared to bulk water. The mobility of surface

  13. Dependence of thin-oxide films quality on surface microroughness

    Microsoft Academic Search

    Tadahiro Ohmi; Masayuki Miyashita; Mitsushi Itano; Takashi Imaoka; Ichiroh Kawanabe

    1992-01-01

    The effects of silicon surface microroughness on electrical properties of thin-oxide films, such as breakdown electric field intensity (EBD) and time-dependent dielectric breakdown (QBD), have been studied, where the microroughnesses of silicon and silicon dioxide surfaces are evaluated by the scanning tunneling microscope (STM) and the atomic force microscope (AFM), respectively. An increase of surface microroughness has been confirmed to

  14. Design and construction of rigs for studying surface condensation and creating anodized metal oxide surfaces

    E-print Network

    Sun, Wei-Yang

    2011-01-01

    This thesis details the design and construction of a rig for studying surface condensation and a rig for creating anodized metal oxides (AMOs). The condensation rig characterizes condensation for different surfaces; this ...

  15. Shape-selective sieving layers on an oxide catalyst surface

    E-print Network

    Mohseni, Hooman

    Shape-selective sieving layers on an oxide catalyst surface Christian P. Canlas1 , Junling Lu2 such as zeolites, metal­organic frameworks and mesostructured oxides are of immense practical utility for gas of molecules or can modify the product selectivity (regioselectivity or enantioselectivity) of catalyst sites

  16. Simulation of the formation of nanosize oxide structures by local anode oxidation of the metal surface

    NASA Astrophysics Data System (ADS)

    Avilov, V. I.; Ageev, O. A.; Blinov, Yu. F.; Konoplev, B. G.; Polyakov, V. V.; Smirnov, V. A.; Tsukanova, O. G.

    2015-05-01

    We propose a complex model of local anode oxidation of metals taking into account the processes occurring in the probe-substrate system in dry air, in water vapor, and in the water film adsorbed on the substrate surface. It is shown that local anode oxidation occurs due to generation of oxygen ions as a result of decomposition of water molecules in an electric field; the predominant source of oxidizer is the film of water adsorbed on the substrate surface. The results of numerical simulation of local anode oxidation of titanium demonstrate good correlation with experimental dependences of the height of oxide nanostructures on the duration of local anode oxidation, which confirms the effectiveness of the proposed model. Our results can be used in the development of technological processes of formation of elements of nanoelectronics by local anode oxidation.

  17. Rates of oxidative weathering on the surface of Mars

    NASA Technical Reports Server (NTRS)

    Burns, Roger G.

    1992-01-01

    Implicit in the mnemonic 'MSATT' (Mars surface and atmosphere through time) is that rates of surface processes on Mars through time should be investigated, including studies of the kinetics and mechanism of oxidative weathering reactions occurring in the Martian regolith. Such measurements are described. Two major elements analyzed in the Viking Lander XRF experiment that are most vulnerable to atmospheric oxidation are iron and sulfur. Originally, they occurred as Fe(2+)-bearing silicate and sulfide minerals in basaltic rocks on the surface of Mars. However, chemical weathering reactions through time have produced ferric- and sulfate-bearing assemblages now visible in the Martian regolith. Such observations raise several question about: (1) when the oxidative weathering reactions took place on Mars; (2) whether or not the oxidized regolith is a fossilized remnant of past weathering processes; (3) deducting chemical interactions of the ancient Martian atmosphere with its surface from surviving phases; (4) possible weathering reactions still occurring in the frozen regolith; and (5) the kinetics and mechanism of past and present-day oxidative reactions on Mars. These questions may be addressed experimentally by studying reaction rates of dissolution and oxidation of basaltic minerals, and by identifying reaction products forming on the mineral surfaces. Results for the oxidation of pyrrhotite and dissolved ferrous iron are reported.

  18. Changes in surface chemistry of activated carbons by wet oxidation

    Microsoft Academic Search

    C Moreno-Castilla; M. V López-Ramón; F Carrasco-Mar??n

    2000-01-01

    A series of activated carbons with different degrees of activation were oxidized with H2O2, (NH4)2S2O8 and HNO3 in order to introduce different oxygen surface complexes. Changes in the surface chemistry of the activated carbons after their oxidizing treatments were studied by different techniques including temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FTIR), titrations with HCl and

  19. Study of tin oxide: Surface properties and palladium adsorption

    Microsoft Academic Search

    Khabiboulakh Katsiev

    2008-01-01

    Surface properties of various single-crystalline SnO2 surfaces were studied and the growth of palladium was investigated in the low-coverage regime. Metal - oxide structures play an important role in microelectronics and nanotechnology. They are also widely used in catalysis. Small catalytically-active metal particles on metal oxide substrates are key features in the gas sensing mechanism: they dramatically increase the sensitivity

  20. Oxidative dissolution of pyrite surfaces by hexavalent chromium: Surface site saturation and surface renewal

    NASA Astrophysics Data System (ADS)

    Graham, Andrew M.; Bouwer, Edward J.

    2012-04-01

    In-situ reduction of toxic Cr(VI) to nontoxic Cr(III) represents an important natural attenuation process for Cr(VI)-impacted environments. This study investigates the stoichiometry and kinetics of Cr(VI) reduction by pyrite, a reduced iron-sulfur mineral ubiquitous in recent estuarine and marine sediments. Pyrite suspensions at surface loadings of 0.28-2.10 m2/L (typical of estuarine or marine sediments) were capable of completely reducing 7-120 ?M Cr(VI) on the timescale of minutes to days, with the time to reaction completion decreasing with increasing pyrite loading, decreasing initial Cr(VI) concentration, and decreasing suspension pH. Analysis of metal species (Cr and Fe) and sulfur species in solution and at the mineral surface indicated that Cr(VI) oxidatively dissolved the pyrite surface, releasing ferrous iron and sulfate into solution as the reaction progressed. Surface disulfide groups were postulated as the Cr(VI)-reactive surface entity. Net production or consumption of aqueous Fe(II) was shown to depend upon the relative rates of proton-promoted Fe(II) release, Fe(II) release due to oxidative dissolution of pyrite in the presence of Cr(VI), and Fe(II) consumption due to homogeneous reaction with Cr(VI). Kinetics of Cr(VI) reduction by pyrite displayed a biphasic pattern, and the time to reaction completion increased dramatically with increasing initial Cr(VI) concentration. Rapid Cr(VI) removal occurred early in the reaction progress, attributable to Cr(VI) loss under an adsorption-limited regime. Slow, approximately zero-order, Cr(VI) removal occurred over the bulk of the time courses, and corresponded to Cr(VI) removal under surface site saturation conditions. Stoichiometric Cr(VI) reduction was able to proceed under surface site limited conditions owing to regeneration of reactive surface sites following desorption/dissolution of oxidized surface products, as demonstrated in repeat Cr(VI)-spiking experiments. The role of surface passivation was evaluated by comparing rates of Cr(VI) reduction in the presence and absence of the Cr(III)-complexing agent citrate. While citrate addition significantly enhanced Cr(III) solubility, rates of Cr(VI) reduction were only marginally accelerated, suggesting that Cr(OH)3(s) coatings did not completely block access of Cr(VI) to reactive surface sites on pyrite. Given the rapid rates of Cr(VI) reduction with pyrite under pH and surface coverage conditions typical of natural environments, we propose that Cr(VI) reduction by pyrite be considered in fate and transport models for Cr in contaminated sediments.

  1. Mechanisms for the near-UV photodissociation of CH{sub 3}I on D{sub 2}O/Cu(110)

    SciTech Connect

    Miller, E. R.; Muirhead, G. D.; Jensen, E. T. [Physics Department, University of Northern British Columbia, 3333 University Way, Prince George, British Columbia V2N 4Z9 (Canada)

    2013-02-28

    The system of CH{sub 3}I adsorbed on submonolayer, monolayer, and multilayer thin films of D{sub 2}O on Cu(110) has been studied by measuring the time of flight (TOF) distributions of the desorbing CH{sub 3} fragments after photodissociation using linearly polarized {lambda} = 248 nm light. For multilayer D{sub 2}O films (2-120 ML), the photodissociation is dominated by neutral photodissociation via the 'A-band' absorption of CH{sub 3}I. The polarization and angle dependent variation in the observed TOF spectra of the CH{sub 3} photofragments find that dissociation is largely via the {sup 3}Q{sub 0} excited state, but that also a contribution via the {sup 1}Q{sub 1} excitation can be identified. The photodissociation results also indicate that the CH{sub 3}I adsorbed on D{sub 2}O forms close-packed islands at submonolayer coverages, with a mixture of C-I bond axis orientations. For monolayer and submonolayer quantities of D{sub 2}O we have observed a contribution to CH{sub 3}I photodissociation via dissociative electron attachment (DEA) by photoelectrons. The observed DEA is consistent with delocalized photoelectrons from the substrate causing the observed dissociation- we do not find evidence for an enhanced DEA mechanism via the temporary solvation of photoelectrons in localized states of the D{sub 2}O ice.

  2. Albumin adsorption on to aluminium oxide and polyurethane surfaces.

    PubMed

    Sharma, C P; Sunny, M C

    1990-05-01

    The changes in protein adsorption onto aluminium surfaces coated with different thicknesses of oxide layers were examined. The oxide layers on aluminium substrates were derived by the anodizing technique. Protein adsorption studies were conducted using 125I-labelled albumin and the amount of albumin adsorbed was estimated with the help of a gamma counter. An increase in albumin adsorption was observed on oxide layer coated aluminium surfaces. The effect of anti-Hageman factor on albumin and fibrinogen adsorption on to bare aluminium, oxide layer coated aluminium and bare polyether urethane urea surfaces was also investigated. It was observed that the presence of anti-Hageman factor increased the adsorption of albumin and fibrinogen on to all these substrates. PMID:2383620

  3. Nitric oxide adsorption at Pt(100) electrode surfaces

    Microsoft Academic Search

    A. Rodes; V. Climent; J. M. Orts; J. M. Pérez; A. Aldaz

    1998-01-01

    Nitric oxide adlayers formed at Pt(100) electrode surfaces have been characterized in situ by means of electrochemical and FTIR spectroscopic experiments. These adlayers can be reductively stripped from the electrode surface yielding dissolved ammonium as the main reduction product in acidic solution. From the voltammetric charge involved in this process the absolute NO coverage for the saturated adlayers has been

  4. Adsorption Mechanism(s) of Poly(Ethylene Oxide) on Oxide Surfaces

    Microsoft Academic Search

    Sharad Mathur; Brij Mohan Moudgil

    1997-01-01

    Adsorption of poly(ethylene oxide) (PEO) on various oxides and the flocculation behavior of PEO-coated particles was investigated to elucidate the polymer adsorption mechanism(s). It was determined that strong Bronsted acid sites on the surface interact with the ether oxygen of PEO, a Lewis base, to induce adsorption and subsequent flocculation of the substrate particles. In general highly acidic oxides of

  5. Surface Complexation of Actinides with Iron Oxides: Implications for Radionuclide Transport in Near-Surface Aquifers

    Microsoft Academic Search

    J. L. Jerden Jr; A. J. Kropf; Y. Tsai

    2005-01-01

    The surface complexation of actinides with iron oxides plays a key role in actinide transport and retardation in geosphere-biosphere systems. The development of accurate actinide transport models therefore requires a mechanistic understanding of surface complexation reactions (i.e. knowledge of chemical speciation at mineral\\/fluid interfaces). Iron oxides are particularly important actinide sorbents due to their pH dependent surface charges, relatively high

  6. A well-ordered surface oxide on Fe(110)

    NASA Astrophysics Data System (ADS)

    Soldemo, Markus; Niu, Yuran; Zakharov, Alexei; Lundgren, Edvin; Weissenrieder, Jonas

    2015-09-01

    A well-ordered surface oxide grown on Fe(110) has been studied using scanning tunneling microscopy (STM), low energy electron diffraction, low energy electron microscopy, and core level photoelectron spectroscopy. The iron oxide film exhibits wide terraces and is formed after exposure to 100-1000 L at 1 × 10- 6 mbar O2 and 400 °C. Two domains, mirror symmetric in the Fe(110)-lattice mirror symmetry planes but otherwise equal, are observed. The surface oxide forms a relatively large coincidence surface unit cell (16.1 Å × 26.5 Å). Imaging by STM reveals a strong bias dependence in the apparent height within the surface unit cell. The oxygen terminating atomic layer has a hexagonal atomic structure, FeO(111)-like, with the atomic spacing of 3.2 Å, that is expanded by ~ 6.3% relative to bulk FeO(111).

  7. Ab initio studies of propene epoxidation on oxidized silver surfaces.

    PubMed

    Molina, L M; López, M J; Alonso, J A

    2014-12-28

    Ab initio density functional simulations have been performed to study the adsorption of propene on partially oxidized silver surfaces and its interaction with surface oxygen. Two different adsorption conformations for propene are studied, with the molecule either intact or forming an Ag-C3H6-O oxymetallacycle (OMC) intermediate. Then, pathways for propene oxide, acrolein and propanone formation have been studied in detail, providing insight into the selectivity of the surfaces. We find that formation of acrolein must necessarily take place from OMC intermediates, requiring at least two neighbouring reactive surface oxygen anions. This suggests a strong relationship between the concentration of surface oxygen and the selectivity of these surfaces. PMID:25070620

  8. THIN-OXIDE MOS CAPACITANCE STUDIES OF FAST SURFACE STATES

    Microsoft Academic Search

    William R. Hunter; D. H. Eaton; C. T. Sah

    1970-01-01

    Fast surface states at the silicon-silicon dioxide interface have been studied using the MOS capacitor structure with a very thin oxide (50–100 Å), which greatly enhances the effect of the surface states on the capacitance-voltage characteristics. On p-type silicon, a surface-state distribution with a peak at 0.3 eV above the valence band is observed. Comparison of the experimental results with

  9. High Coverage Oxidation and diffusion on the Cu(001) Surface

    Microsoft Academic Search

    Willie Maddox; Nail Fazleev

    2010-01-01

    The structures formed on oxidized transition metal surfaces vary from simple adlayers of chemisorbed oxygen to more complex structures which result from the diffusion of oxygen into subsurface regions. In this paper, an ab-initio investigation of the stability and electronic structure of the Cu(001) missing row reconstructed surface at various surface and subsurface oxygen coverages ranging from 0.5 to 1.5

  10. Detection of DNA hybridization on indium tin oxide surfaces

    Microsoft Academic Search

    Selina Moses; Scott H. Brewer; Stephan Kraemer; Ryan R. Fuierer; Lisa B. Lowe; Chiamaka Agbasi; Marc Sauthier; Stefan Franzen

    2007-01-01

    Indium tin oxide (ITO) surfaces were modified with ssDNA by coupling oligonucleotides to a monolayer of 12-phosphonododecanoic acid (12-PDA) on ITO surfaces. This coupling involved the formation of an amide bond between the carboxylic acid moiety of 12-PDA to the amine group of a 5?-aminopropyl-labeled single strand of DNA. The self-assembled monolayer of 12-PDA and surface-attached oligonucleotides were characterized by

  11. Study of the oxidized surface layer of titanium after annealing

    Microsoft Academic Search

    V. V. Peshkov; V. N. Milyutin

    1984-01-01

    mined. Electron microscope study of the surface topography was carried out in an AMR-1000 SEM by a secondary electron scheme and with an accelerating voltage of 20 kV. The structure of the oxidized surface layer was evaluated at magnification of i0,000 times or more, and the titanium surface was shadowed with gold followed by earthing of the whole specimen. Phase

  12. Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies

    NASA Technical Reports Server (NTRS)

    Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

    1988-01-01

    The surface-catalyzed air oxidation reactions of fuel hydrazines were studied in a 6500-liter fluorocarbon-film chamber at 80 to 100 ppm concentrations. First-order rate constants for the reactions catalyzed by aluminum, water-damaged aluminum (Al/Al2O3), stainless steel 304L, galvanized steel and titanium plates with surface areas of 2 to 24 sq m were determined. With 23.8 sq m of Al/Al2O3 the surface-catalyzed air oxidation of hydrazine had a half-life of 2 hours, diimide (N2H2) was observed as an intermediate and traces of ammonia were present in the final product mixture. The Al/Al2O3 catalyzed oxidation of monomethylhydrazine yielded methyldiazine (HN = NCH3) as an intermediate and traces of methanol. Unsymmetrical dimethylhydrazine gave no detectable products. The relative reactivities of hydrazine, MMH and UDMH were 130 : 7.3 : 1.0, respectively. The rate constants for Al/Al2O3-catalyzed oxidation of hydrazine and MMH were proportional to the square of the surface area of the plates. Mechanisms for the surface-catalyzed oxidation of hydrazine and diimide and the formation of ammonia are proposed.

  13. Rate law analysis of water oxidation on a hematite surface.

    PubMed

    Le Formal, Florian; Pastor, Ernest; Tilley, S David; Mesa, Camilo A; Pendlebury, Stephanie R; Grätzel, Michael; Durrant, James R

    2015-05-27

    Water oxidation is a key chemical reaction, central to both biological photosynthesis and artificial solar fuel synthesis strategies. Despite recent progress on the structure of the natural catalytic site, and on inorganic catalyst function, determining the mechanistic details of this multiredox reaction remains a significant challenge. We report herein a rate law analysis of the order of water oxidation as a function of surface hole density on a hematite photoanode employing photoinduced absorption spectroscopy. Our study reveals a transition from a slow, first order reaction at low accumulated hole density to a faster, third order mechanism once the surface hole density is sufficient to enable the oxidation of nearest neighbor metal atoms. This study thus provides direct evidence for the multihole catalysis of water oxidation by hematite, and demonstrates the hole accumulation level required to achieve this, leading to key insights both for reaction mechanism and strategies to enhance function. PMID:25936408

  14. Rate Law Analysis of Water Oxidation on a Hematite Surface

    PubMed Central

    2015-01-01

    Water oxidation is a key chemical reaction, central to both biological photosynthesis and artificial solar fuel synthesis strategies. Despite recent progress on the structure of the natural catalytic site, and on inorganic catalyst function, determining the mechanistic details of this multiredox reaction remains a significant challenge. We report herein a rate law analysis of the order of water oxidation as a function of surface hole density on a hematite photoanode employing photoinduced absorption spectroscopy. Our study reveals a transition from a slow, first order reaction at low accumulated hole density to a faster, third order mechanism once the surface hole density is sufficient to enable the oxidation of nearest neighbor metal atoms. This study thus provides direct evidence for the multihole catalysis of water oxidation by hematite, and demonstrates the hole accumulation level required to achieve this, leading to key insights both for reaction mechanism and strategies to enhance function. PMID:25936408

  15. High-quality surface passivation by corona-charged oxides for semiconductor surface characterization

    SciTech Connect

    Schoefthaler, M.; Brendel, R.; Langguth, G.; Werner, J.H. [Max-Planck-Inst. fuer Festkoerperforschung, Stuttgart (Germany)

    1994-12-31

    A new surface passivation method using corona-charged oxides is discussed and applied to effective lifetime measurements by microwave-detected photoconductivity decay. Three lifetime measurements are required for evaluating surface recombination velocities and semiconductor bulk lifetimes in monocrystalline silicon wafers. Surface recombination velocities lower than 1 cm/s are achieved with corona passivation.

  16. Surface-confined atomic silver centers catalyzing formaldehyde oxidation.

    PubMed

    Hu, Pingping; Amghouz, Zakariae; Huang, Zhiwei; Xu, Fei; Chen, Yaxin; Tang, Xingfu

    2015-02-17

    Formaldehyde (HCHO) is a prior pollutant in both indoor and outdoor air, and catalytic oxidation proves the most promising technology for HCHO abatement. For this purpose, supported metal catalysts with single silver atoms confined at 4-fold O4-terminated surface hollow sites of a hollandite manganese oxide (HMO) as catalytic centers were synthesized and investigated in the complete oxidation of HCHO. Synchrotron X-ray diffraction patterns, X-ray absorption spectra, and electron diffraction tomography revealed that geometric structures and electronic states of the catalytic centers were tuned by the changes of HMO structures via controllable metal-support interactions. The catalytic tests demonstrated that the catalytically active centers with high electronic density of states and strong redox ability are favorable for enhancement of the catalytic efficiency in the HCHO oxidation. This work provides a strategy for designing efficient oxidation catalysts for controlling air pollution. PMID:25634796

  17. Autocatalytic and Cooperatively Stabilized Dissociation of Water on a Stepped Platinum Surface

    E-print Network

    processes, from catalysis to corrosion. Whereas water adlayers on atomically flat transition metal surfaces-metal interactions play a central role in many catalytic surface reactions, corrosion processes, and electrochemistry of water on high-symmetry surfaces of several transition metals, such as Cu(110) and (111), Pt(111), Pd(111

  18. Atomic probes of surface structure and dynamics. Technical progress report, September 15, 1991--September 14, 1992

    SciTech Connect

    Heller, E.J.; Jonsson, H.

    1992-12-31

    The following were studied: New semiclassical method for scattering calculations, He atom scattering from defective Pt surfaces, He atom scattering from Xe overlayers, thermal dissociation of H{sub 2} on Cu(110), spin flip scattering of atoms from surfaces, and Car-Parrinello simulations of surface processes.

  19. Oxidation-Resistant Surfaces For Solar Reflectors

    NASA Technical Reports Server (NTRS)

    Gulino, Daniel A.; Egger, Robert A.; Banholzer, William F.

    1988-01-01

    Thin films on silver provide highly-reflective, corrosion-resistant mirrors. Study evaluated variety of oxidation-resistant reflective materials for use in solar dynamic power system, one that generates electricity by focusing Sunlight onto reciever of heat engine. Thin films of platinum and rhodium deposited by ion-beam sputtering on various substrate materials. Solar reflectances measured as function of time of exposure to radio-frequency-generated air plasma. Several protective coating materials deposited on silver-coated substrates and exposed to plasma. Analyzed before and after exposure by electon spectroscopy for chemical analysis and by Auger spectroscopy.

  20. Facile preparation of superhydrophobic surfaces based on metal oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Bao, Xue-Mei; Cui, Jin-Feng; Sun, Han-Xue; Liang, Wei-Dong; Zhu, Zhao-Qi; An, Jin; Yang, Bao-Ping; La, Pei-Qing; Li, An

    2014-06-01

    A novel method for fabrication of superhydrophobic surfaces was developed by facile coating various metal oxide nanoparticles, including ZnO, Al2O3 and Fe3O4, on various substrates followed by treatment with polydimethylsiloxane (PDMS) via chemical vapor deposition (CVD) method. Using ZnO nanoparticles as a model, the changes in the surface chemical composition and crystalline structures of the metal oxide nanoparticles by PDMS treatment were investigated by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The results show that the combination of the improved surface roughness generated from of the nanoparticles aggregation with the low surface-energy of silicon-coating originated from the thermal pyrolysis of PDMS would be responsible for the surface superhydrophobicity. By a simple dip-coating method, we show that the metal oxide nanoparticles can be easily coated onto the surfaces of various textural and dimensional substrates, including glass slide, paper, fabric or sponge, for preparation of superhydrophobic surfaces for different purpose. The present strategy may provide an inexpensive and new route to surperhydrophobic surfaces, which would be of technological significance for various practical applications especially for separation of oils or organic contaminates from water.

  1. Cr(OH)?(s) Oxidation Induced by Surface Catalyzed Mn(II) Oxidation

    SciTech Connect

    Namgung, Seonyi; Kwon, M.; Qafoku, Nikolla; Lee, Gie Hyeon

    2014-09-16

    This study examined the feasibility of Cr(OH)?(s) oxidation mediated by surface catalyzed Mn(II) oxidation under common groundwater pH conditions as a potential pathway of natural Cr(VI) contaminations. Dissolved Mn(II) (50 ?M) was reacted with or without synthesized Cr(OH)?(s) (1.0 g/L) at pH 7 – 9 under oxic or anoxic conditions. In the absence of Cr(OH)?(s), homogeneous Mn(II) oxidation by dissolved O? was not observed at pH ? 8.0 for 50 d. At pH 9.0, by contrast, dissolved Mn(II) was completely removed within 8 d and precipitated as hausmannite. When Cr(OH)?(s) was present, this solid was oxidized and released substantial amounts of Cr(VI) as dissolved Mn(II) was added into the suspension at pH ? 8.0 under oxic conditions. Our results suggest that Cr(OH)?(s) was readily oxidized by a newly formed Mn oxide as a result of Mn(II) oxidation catalyzed on Cr(OH)?(s) surface. XANES analysis of the residual solids after the reaction between 1.0 g/L Cr(OH)?(s) and 204 ?M Mn(II) at pH 9.0 for 22 d revealed that the product of surface catalyzed Mn(II) oxidation resembled birnessite. The rate and extent of Cr(OH)?(s) oxidation was likely controlled by those of surface catalyzed Mn(II) oxidation as the production of Cr(VI) increased with increasing pH and initial Mn(II) concentrations. This study evokes the potential environmental hazard of sparingly soluble Cr(OH)?(s) that can be a source of Cr(VI) in the presence of dissolved Mn(II).

  2. Microwave surface impedance measurements on reduced graphene oxide

    NASA Astrophysics Data System (ADS)

    Hao, L.; Mattevi, C.; Gallop, J.; Goniszewski, S.; Xiao, Y.; Cohen, L.; Klein, N.

    2012-07-01

    Here we report a non-contact method for microwave surface impedance measurements of reduced graphene oxide samples using a high Q dielectric resonator perturbation technique, with the aim of studying the water content of graphene oxide flakes. Measurements are made before, during and after heating and cooling cycles. We have modelled plane wave propagation of microwaves perpendicular to the surface of graphene on quartz substrates, capacitively coupled to a dielectric resonator. Analytical solutions are derived for both changes in resonant frequency and microwave loss for a range of water layer thicknesses. In this way we have measured the presence of adsorbed water layers in reduced graphene oxide films. The water can be removed by low temperature annealing on both single and multilayer samples. The results indicate that water is intercalated between the layers in a multilayer sample, rather than only being adsorbed on the outer surfaces, and it can be released by applying a mild heating.

  3. Surface chemistry dependence of native oxidation formation on silicon nanocrystals

    SciTech Connect

    Liptak, R. W.; Campbell, S. A. [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Kortshagen, U. [Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2009-09-15

    The growth of silicon oxide on bare and SF{sub 6}-etched silicon nanocrystals (Si-NCs), which were synthesized by an all gas phase approach, was investigated by examining the surface chemistry and optical properties of the NCs over time. Consistent with previous work in the low temperature oxidation of silicon, the oxidation follows the Cabrera-Mott mechanism, and the measured data are well fitted to the Elovich equation. The use of the SF{sub 6} plasma is found to reduce the surface Si-H bond density and dramatically increase the monolayer growth rate. This is believed to be due to the much larger volatility of Si-F bonds compared to Si-H bonds on the surface of the NC.

  4. Surface binding vs. sequestration; the uptake of benzohydroxamic acid at iron(III) oxide surfaces 

    E-print Network

    Tasker, Peter; Harris, S.G.; Brechin, E.K.; White, Fraser J; Rio-Echevarria I.M.

    2008-01-01

    Benzohydroxamic acid is shown to be an unexpectedly good ligand for iron(III) oxides, favouring surface attachment to the formation of trisbenzohydroxamato complexes, which are known to have very high thermodynamic stability ...

  5. Electrochemical oxidation of carbon fibers: Properties, surface chemistry and morphology

    NASA Astrophysics Data System (ADS)

    Jiang, Wenbo

    1999-10-01

    A series of PAN-based T300 carbon fibers was continuously, electrochemically oxidized in aqueous and organic media. A 30% fiber weight loss was obtained at an extent of oxidation of 10,600 C/g. Acidic functional groups were produced on fiber surfaces in amounts from 0 to 2640 mumol/g as the extent of oxidation increased from 0 to 10600 C/g. These surface functions were further reacted with diethylenetriamine to introduce amine functions onto fibers. The oxidation extended far deeper than the XPS detection limit (<100 A). N 2 BET at 77K gave very low fiber specific surface area in contrast to CO2 DR measurements at 273 K which confirmed large increases in surface area with oxidation. No heavy damage or macro-/mesopores were found in scanning electron micrographs. An ultramicropore structure was characterized by the CO2 DR method combined with nonlocal density functional theory. The average pore diameter was about 1.2 nm with a dominant pore diameter of 0.4 nm. CCl4, methylene blue, I2, AgNO3, and Ni(NO3)2 adsorption studies were performed. A pH-dependent swelling model was discussed. In basic media, a solvation/swelling process allows small molecules to penetrate the microporous channels and react with fiber functional groups. A remote site silver reduction/adsorption model was confirmed based upon high AgNO3 adsorption and qualitative experiments. Single filament breaking and fragmentation tests and fiber/epoxy composite mechanical tests were conducted. Fiber/epoxy matrix adhesion was improved by oxidation although the fiber tensile strength decreased. Post-heat treatment causes further weight loss and the loss of oxygen-containing surface functional groups.

  6. Electronic structure of the surfaces of layered copper oxides

    SciTech Connect

    Prosandeyev, S.A.; Tennenboum, I.M. [Department of Physics, Rostov State University, 5 Zorge Street, 344104 Rostov on Don (Russian Federation)] [Department of Physics, Rostov State University, 5 Zorge Street, 344104 Rostov on Don (Russian Federation)

    1995-08-01

    The electronic structure of the surfaces of layered copper oxides has been investigated in the framework of a tight-binding model together with the unrestricted Hartree-Fock method. The main element of the layered copper oxides, namely the CuO{sub 2} layer, was supposed to lie parallel with the surface, as well as to be trimmed at a boundary of crystal. In the former case, the electrons at the surface were considered to be in an additional (surface) potential. A mode of the calculation of this potential has been developed on the basis of a method being similar to Ewald`s transformation. As an example, the surface of La{sub 2}CuO{sub 4} was studied. In the latter case, when the CuO{sub 2} layer is semi-infinite due to its cutting at the surface, the formation of electronic surface bands was carefully investigated. Both the metal and dielectric phases were examined. For the metal phase, we took into account the possible freezing of the spin-density wave at the surface. In all the cases, surface bands were present in the vicinity of the Fermi level. They had inherent, in the one-dimensional systems, peculiarities.

  7. Understanding Metal Oxide Surfaces at the Atomic Scale: STM Investigations of Bulk-defect Dependent Surface Processes

    E-print Network

    Diebold, Ulrike

    Understanding Metal Oxide Surfaces at the Atomic Scale: STM Investigations of Bulk-defect Dependent of oxygen vacancies which migrate from the bulk to the surface. INTRODUCTION Metal oxides are fascinating. The surface and interface properties of metal oxides play a role in all these applications, and sometimes even

  8. Surface modification of nickel based alloys for improved oxidation resistance

    SciTech Connect

    Jablonski, Paul D.; Alman, David E.

    2005-02-01

    The present research is aimed at the evaluation of a surface modification treatment to enhance the high temperature stability of nickel-base superalloys. A low Coefficient Thermal Expansion (CTE ~12.5x10-6/°C) alloy based on the composition (in weight %) of Ni-22Mo-12.5Cr was produced by Vacuum Induction Melting and Vacuum Arc Melting and reduced to sheet by conventional thermal-mechanical processing. A surface treatment was devised to enhance the oxidation resistance of the alloys at high temperature. Oxidation tests (in dry and wet air; treated and untreated) were conducted 800°C to evaluate the oxidation resistance of the alloys. The results were compared to the behavior of Haynes 230 (Ni-22Cr) in the treated and untreated conditions. The treatment was not very effective for Haynes 230, as this alloy had similar oxidation behavior in both the treated and untreated conditions. However, the treatment had a significant effect on the behavior of the low CTE alloy. At 800°C, the untreated Ni-12.5Cr alloy was 5 times less oxidation resistant than Haynes 230. However, in the treated condition, the Ni-12.5Cr alloy had comparable oxidation resistance to the Haynes 230 alloy.

  9. Random lasing from surface modified films of zinc oxide nanoparticles

    Microsoft Academic Search

    A. Stassinopoulos; R. N. Das; E. P. Giannelis; S. H. Anastasiadis; D. Anglos

    2005-01-01

    The photoluminescence properties of zinc oxide (ZnO) ceramic thin films, prepared by spin coating of ZnO nanoparticle aqueous suspensions, were studied with emphasis on the influence of film structure and surface morphology on the observation of random laser action. Surface processing employing laser annealing transforms the particulate grain structure of the as-deposited films into a porous channel-like network. This modification

  10. Influence of mineral oil and additives on microhardness and surface chemistry of magnesium oxide (001) surface

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Shigaki, H.; Buckley, D. H.

    1982-01-01

    X-ray photoelectron spectroscopy analyses and hardness experiments were conducted with cleaved magnesium oxide /001/ surfaces. The magnesium oxide bulk crystals were cleaved into specimens along the /001/ surface, and indentations were made on the cleaved surface in laboratory air, in nitrogen gas, or in degassed mineral oil with and without an additive while not exposing specimen surface to any other environment. The various additives examined contained sulfur, phosphorus, chlorine, or oleic acid. The sulfur-containing additive exhibited the highest hardness and smallest dislocation patterns evidencing plastic deformation; the chlorine-containing additive exhibited the lowest hardness and largest dislocation patterns evidencing plastic deformation. Hydrocarbon and chloride (MgCl2) films formed on the magnesium oxide surface. A chloride film was responsible for the lowest measured hardness.

  11. Ruthenium Oxide Surface Chemistry Surface Coordination Chemistry: Dihydrogen

    E-print Network

    . The combination of low-temperature ultrahigh vacuum experiments in conjunction with density-functional theory (DFT concurrently with dissociation of the ligand. The discovery of h2 -H2 (dihydrogen) complexes, in which the HÀH by exposing the Ru(0001) surface of a single crystal to O2 (1 107 L; 1 L = 1.3 10À6 mbars) at 700 K.[7

  12. Emerging Applications of Liquid Metals Featuring Surface Oxides

    PubMed Central

    2014-01-01

    Gallium and several of its alloys are liquid metals at or near room temperature. Gallium has low toxicity, essentially no vapor pressure, and a low viscosity. Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface. The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance. Here, we show that this solid oxide “skin” enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects. PMID:25283244

  13. Probing the tunable surface chemistry of graphene oxide.

    PubMed

    Liu, Zhen; Liu, Jingquan; Li, Da; Francis, Paul S; Barnett, Neil W; Barrow, Colin J; Yang, Wenrong

    2015-06-23

    The determination of oxygen content, hydrophobicity and reduction efficiency of graphene oxide (GO) are difficult tasks because of its heterogeneous structure. Herein, we describe a novel approach for the detailed understanding of the surface chemistry of GO by studying the interactions between [Ru(bpy)3](2+) and GO. PMID:26062770

  14. Is Silica Really an Anomalous Oxide? Surface Acidity and Aqueous

    E-print Network

    Sahai, Nita

    Is Silica Really an Anomalous Oxide? Surface Acidity and Aqueous Hydrolysis Revisited N I T A S A H, polarizability, ionicity, electronegativity, and local charge densities. Silica is acidic (PZC acidity depends largely on high values of the s/r ratio. The dielectric constant of the solid affects

  15. Distinct Duplex Oxide Scale of Surface-Oxidized Co-Cr Film Observed by Auger Electron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kitakami, Osamu; Ogawa, Yoichi; Daimon, Hideo; Maro, Tsuyoshi

    1991-03-01

    The structure of a surface-oxidized Co-Cr film for perpendicular magnetic recording media is investigated by Auger electron spectroscopy. It is found that an oxidized Co-Cr film has a distinct duplex oxide scale on its surface when oxidation is carried out at relatively high temperature (˜ 400°C). From the outermost surface of the film, a CoO-dominant oxide scale and Cr2O3-dominant oxide scale are formed on the Co-Cr alloy film in order.

  16. Electron stimulated oxidation of the Ni(111) surface: Dependence on substrate temperature and incident electron energy

    E-print Network

    Sibener, Steven

    Electron stimulated oxidation of the Ni(111) surface: Dependence on substrate temperature 29 March 1995 The effect of surface temperature on the rate of oxidation of the Ni 111 surface synergistic effect in the oxidation of this surface at low temperature and under irra- diation from

  17. The effect of antioxidants on the surface oxidation and surface cracking of crosslinked polydimethylsiloxane

    Microsoft Academic Search

    K. Fateh-Alavi; M. Gallstedt; U. W. Gedde

    2001-01-01

    Crosslinked polydimethylsiloxanes with three different chain-breaking antioxidants (Irganox 1076, Irganox 565 and Tinuvin 770) were exposed to air plasma (GHz), and the surface structures of the exposed samples were assessed by contact angle measurements, X-ray photoelectron spectroscopy, optical and scanning electron microscopy, and surface profilometry before and after uniaxial stretching. It was found that samples containing antioxidants oxidized more slowly

  18. Reactions of metal ions at surfaces of hydrous iron oxide

    USGS Publications Warehouse

    Hem, J.D.

    1977-01-01

    Cu, Ag and Cr concentrations in natural water may be lowered by mild chemical reduction involving ferric hydroxide-ferrous ion redox processes. V and Mo solubilities may be controlled by precipitation of ferrous vanadate or molybdate. Concentrations as low as 10-8.00 or 10-9.00 M are readily attainable for all these metals in oxygen-depleted systems that are relatively rich in Fe. Deposition of manganese oxides such as Mn3O4 can be catalyzed in oxygenated water by coupling to ferrous-ferric redox reactions. Once formed, these oxides may disproportionate, giving Mn4+ oxides. This reaction produces strongly oxidizing conditions at manganese oxide surfaces. The solubility of As is significantly influenced by ferric iron only at low pH. Spinel structures such as chromite or ferrites of Cu, Ni, and Zn, are very stable and if locally developed on ferric hydroxide surfaces could bring about solubilities much below 10-9.00 M for divalent metals near neutral pH. Solubilities calculated from thermodynamic data are shown graphically and compared with observed concentrations in some natural systems. ?? 1977.

  19. Electrochemically-Controlled Compositional Oscillations of Oxide Surfaces

    SciTech Connect

    Mutoro, Eva [Massachusetts Institute of Technology (MIT); Crumlin, Ethan [Massachusetts Institute of Technology (MIT); Pöpke, Hendrik [Institute of Physical Chemistry, Justus-Liebig-University Giessen; Luerssen, Bjoern [Institute of Physical Chemistry, Justus-Liebig-University Giessen; Amati, Matteo [Sincrotrone Trieste Elettra; Abyaneh, Majid [Sincrotrone Trieste, Basovizza, Italy; Biegalski, Michael D [ORNL; Christen, Hans M [ORNL; Gregoratti, Luca [Sincrotrone Trieste, Basovizza, Italy; Janek, Jürgen [Institute of Physical Chemistry, Justus-Liebig-University Giessen; Shao-Horn, Yang [Massachusetts Institute of Technology (MIT)

    2012-01-01

    Perovskite oxides can exhibit a wide range of interesting characteristics such as being catalytically active and electronically and/or ionically conducting, and thus they have been used in a number of solid-state devices such as solid oxide fuel cells and sensors. As the surface compositions of perovskites can greatly influence the catalytic properties, knowing and controlling their surface chemistries is crucial to enhance device performance. In this study, we demonstrate that the surface strontium (Sr) and cobalt (Co) concentrations of perovskite-based thin films can be controlled reversibly at elevated temperatures by applying small electrical potential biases. The surface chemistry changes of La0.8Sr0.2CoO3 (LSC113), LaSrCoO4 (LSC214), and LSC214-decorated LSC113 films (LSC113/214) were investigated in situ by utilizing synchrotron-based X-ray photoelectron spectroscopy (XPS), where the largest changes of surface Sr was found for the LSC113/214 surface. These findings offer the potential of reversibly controlling the surface functionality of perovskites.

  20. Giant and switchable surface activity of liquid metal via surface oxidation

    PubMed Central

    Khan, Mohammad Rashed; Eaker, Collin B.; Bowden, Edmond F.; Dickey, Michael D.

    2014-01-01

    We present a method to control the interfacial tension of a liquid alloy of gallium via electrochemical deposition (or removal) of the oxide layer on its surface. In sharp contrast with conventional surfactants, this method provides unprecedented lowering of surface tension (?500 mJ/m2 to near zero) using very low voltage, and the change is completely reversible. This dramatic change in the interfacial tension enables a variety of electrohydrodynamic phenomena. The ability to manipulate the interfacial properties of the metal promises rich opportunities in shape-reconfigurable metallic components in electronic, electromagnetic, and microfluidic devices without the use of toxic mercury. This work suggests that the wetting properties of surface oxides—which are ubiquitous on most metals and semiconductors—are intrinsic “surfactants.” The inherent asymmetric nature of the surface coupled with the ability to actively manipulate its energetics is expected to have important applications in electrohydrodynamics, composites, and melt processing of oxide-forming materials. PMID:25228767

  1. Giant and switchable surface activity of liquid metal via surface oxidation.

    PubMed

    Khan, Mohammad Rashed; Eaker, Collin B; Bowden, Edmond F; Dickey, Michael D

    2014-09-30

    We present a method to control the interfacial tension of a liquid alloy of gallium via electrochemical deposition (or removal) of the oxide layer on its surface. In sharp contrast with conventional surfactants, this method provides unprecedented lowering of surface tension (? 500 mJ/m(2) to near zero) using very low voltage, and the change is completely reversible. This dramatic change in the interfacial tension enables a variety of electrohydrodynamic phenomena. The ability to manipulate the interfacial properties of the metal promises rich opportunities in shape-reconfigurable metallic components in electronic, electromagnetic, and microfluidic devices without the use of toxic mercury. This work suggests that the wetting properties of surface oxides--which are ubiquitous on most metals and semiconductors--are intrinsic "surfactants." The inherent asymmetric nature of the surface coupled with the ability to actively manipulate its energetics is expected to have important applications in electrohydrodynamics, composites, and melt processing of oxide-forming materials. PMID:25228767

  2. Radiation Induced Surface Activity Phenomenon: 1. Report - Surface Wettability on Metal Oxides

    SciTech Connect

    Yasuyuki Imai; Tatsuya Koga; Tomoji Takamasa [Tokyo University of Mercantile Marine, 2-1-6 Etchu-jima, Koto-Ku, Tokyo 135-8533 (Japan); Koji Okamoto [University of Tokyo (Japan); Susumu Uematsu [Advanced Maritime Transport Technology Department, National Maritime Research Institute, Mitaka, Tokyo 181-0004 (Japan)

    2002-07-01

    Improving the limit of boiling heat transfer or critical heat flux requires that the cooling liquid can contact the heating surface, or a high-wettability, highly hydrophilic heating surface, even if a vapor bubble layer is generated on the surface. We investigated surface wettability using metal oxides irradiated by gamma rays in room condition. Contact angle, an indicator of macroscopic wettability, was measured by image processing of the images obtained by a CCD video camera. The results showed that the surface wettability on oxide metal pieces of titanium, zircaloy No. 4, SUS-304 and copper improved significantly by Radiation Induced Surface Activity (RISA) phenomenon. Highly hydrophilic conditions on the test pieces were achieved after 500 kGy irradiation of {sup 60}Co gamma ray. (authors)

  3. Macromolecular surface design: photopatterning of functional stable nitrile oxides.

    PubMed

    Altintas, Ozcan; Glassner, Mathias; Rodriguez-Emmenegger, Cesar; Welle, Alexander; Trouillet, Vanessa; Barner-Kowollik, Christopher

    2015-05-01

    The efficient trapping of photogenerated thioaldehydes with functional shelf-stable nitrile oxides in a 1,3-dipolar cycloaddition is a novel and versatile photochemical strategy for polymer end-group functionalization and surface modification under mild and equimolar conditions. The modular ligation in solution was followed in detail by electrospray ionization mass spectrometry (ESI-MS). X-ray photoelectron spectroscopy (XPS) was employed to analyze the functionalized surfaces, whereas time-of-flight secondary-ion mass spectrometry (ToF-SIMS) confirmed the spatial control of the surface functionalization using a micropatterned shadow mask. Polymer brushes were grown from the surface in a spatially confined regime by surface-initiated atom transfer radical polymerization (SI-ATRP) as confirmed by TOF-SIMS, XPS as well as ellipsometry. PMID:25784598

  4. Controllably interfacing with metal: a strategy for enhancing CO oxidation on oxide catalysts by surface polarization.

    PubMed

    Bai, Yu; Zhang, Wenhua; Zhang, Zhenhua; Zhou, Jie; Wang, Xijun; Wang, Chengming; Huang, Weixin; Jiang, Jun; Xiong, Yujie

    2014-10-22

    Heterogeneous catalysis often involves charge transfer from catalyst surface to adsorbed molecules, whose activity thus depends on the surface charge density of catalysts. Here, we demonstrate a unique solution-phase approach to achieve controllable interfacial lengths in oxide-metal hybrid structures. Resulting from their different work functions, surface polarization is induced by the Ag-CuO interface and acts to tailor the surface charge state of CuO. As a result, the designed hybrid catalysts exhibit enhanced intrinsic activities in catalyzing CO oxidation in terms of apparent activation energy, as compared with their counterparts. Moreover, the CO conversion rate can be enhanced by maximizing the Ag-CuO interfacial length and thus the number of active sites on the CuO. This work provides a new strategy for tuning catalytic performance by controlling interface in hybrid catalysts. PMID:25296380

  5. Optimum conditions for fabricating superhydrophobic surface on copper plates via controlled surface oxidation and dehydration processes

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Li, Wen; Ma, Fumin; Yu, Zhanlong; Ruan, Min; Ding, Yigang; Deng, Xiangyi

    2013-09-01

    The superhydrophobic surfaces on copper substrate were fabricated by direct oxidation and dehydration processes, and the reaction and modification conditions were optimized. Firstly, the oxidation conditions including the concentrations of K2S2O8 and NaOH, the oxidation time were studied. It is found that the superhydrophobicity would be better if the copper plates were oxidized in 0.06 M K2S2O8 and 3.0 M NaOH solution at 65 °C for 35 min. Then, the modification conditions including modifier concentration and modification time were investigated. The results showed that 5 wt% lauric acid and 1 h modification time were suitable modification conditions for preparing copper-based superhydrophobic surfaces. The surface fabricated under optimized conditions displayed excellent superhydrophobicity of high water contact angle of 161.1° and a low contact angle hysteresis of 2.5°. The surface microstructure and composition of the superhydrophobic surfaces were also characterized by SEM and FT-IR. It is found that the highly concentrated micro/nanostructured sheets and the low surface energy materials on the surface should be responsible for the high superhydrophobicity.

  6. Molecularly imprinted Ru complex catalysts integrated on oxide surfaces.

    PubMed

    Muratsugu, Satoshi; Tada, Mizuki

    2013-02-19

    Selective catalysis is critical for the development of green chemical processes, and natural enzymes that possess specialized three-dimensional reaction pockets with catalytically active sites represent the most sophisticated systems for selective catalysis. A reaction space in an enzyme consists of an active metal center, functional groups for molecular recognition (such as amino acids), and a surrounding protein matrix to prepare the reaction pocket. The artificial design of such an integrated catalytic unit in a non-enzymatic system remains challenging. Molecular imprinting of a supported metal complex provides a promising approach for shape-selective catalysis. In this process, an imprinted cavity with a shape matched to a template molecule is created in a polymer matrix with a catalytically active metal site. In this Account, we review our studies on molecularly imprinted metal complex catalysts, focusing on Ru complexes, on oxide surfaces for shape-selective catalysis. Oxide surface-attached transition metal complex catalysts not only improve thermal stability and catalyst dispersion but also provide unique catalytic performance not observed in homogeneous precursors. We designed molecularly imprinted Ru complexes by using surface-attached Ru complexes with template ligands and inorganic/organic surface matrix overlayers to control the chemical environment around the active metal complex catalysts on oxide surfaces. We prepared the designed, molecularly imprinted Ru complexes on SiO(2) surfaces in a step-by-step manner and characterized them with solid-state (SS) NMR, diffuse-reflectance (DR) UV-vis, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller isotherm (BET), X-ray fluorescence (XRF), and Ru K-edge extended X-ray absorption fine structure (EXAFS). The catalytic performances of these Ru complexes suggest that this process of molecular imprinting facilitates the artificial integration of catalytic functions at surfaces. Further advances such as the imprinting of a transition state structure or the addition of multiple binding sites could lead to systems that can achieve 100% selective catalysis. PMID:23030829

  7. Effects of oxidation on surface heterogeneity of carbosils

    NASA Astrophysics Data System (ADS)

    Charmas, B.; Leboda, R.; Gérard, G.; Villiéras, F.

    2002-08-01

    Carbon-silica adsorbents (carbosils), prepared by pyrolysis of methylene chloride (CH 2Cl 2) on the surface of a porous silica gel, were subjected to an oxidizing hydrothermal treatment (HTT) at 200 °C, using a hydrogen peroxide water solution as a modification medium. Conventional nitrogen adsorption volumetry and low-pressure argon and nitrogen adsorption techniques were used to analyze and compare textural properties and surface heterogeneity of initial and hydrothermally treated samples. In the presence of carbon, the mesoporous network of silica gel is protected from the massive collapse generally observed after oxidizing HTT. For carbosils, some changes occur during HTT, leading to a slight decrease of specific surface areas accompanied by an increase in mean mesopore size. The argon and nitrogen condensation energy distributions, derived from low-pressure adsorption experiments, indicate that both silica and pyrocarbon materials were modified during HTT. Depolymerization and recondensation processes occur for silica, creating new silica surfaces. These processes are responsible of the decrease in specific surface areas. For pyrocarbon, similar depolymerization and recondensation processes probably occur, creating new and high-energy surface sites.

  8. Effects of surface oxide formation on germanium nanowire band-edge photoluminescence

    SciTech Connect

    Minaye Hashemi, Fatemeh Sadat [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States) [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland); Thombare, Shruti; Brongersma, Mark L. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States)] [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Morral, Anna Fontcuberta i [Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland)] [Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland); McIntyre, Paul C. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States) [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305 (United States)

    2013-06-24

    The effect of intentional surface oxide formation on band-edge photoluminescence (PL) of Ge nanowires was investigated. Thermal oxidation in molecular O{sub 2} was used to produce a surface oxide layer on assemblies of single crystal nanowires grown by the vapor-liquid-solid method. With increasing oxidation of the wires, the band-edge PL associated with the indirect gap transition becomes more intense. X-ray photoelectron spectroscopy confirms the formation of an increasingly GeO{sub 2}-like surface oxide under annealing conditions that enhance the indirect-gap PL, consistent with surface oxide passivation of nonradiative recombination centers initially present on the nanowire surface.

  9. Nitric Oxide Production from Surface Recombination of Oxygen and Nitrogen Atoms

    E-print Network

    Martín, Pino

    1 Nitric Oxide Production from Surface Recombination of Oxygen and Nitrogen Atoms Dusan A. Pejakovi;2 Abstract Experimental results are presented that support the surface-catalyzed production of nitric oxide

  10. Water-mediated proton hopping on an iron oxide surface.

    PubMed

    Merte, Lindsay R; Peng, Guowen; Bechstein, Ralf; Rieboldt, Felix; Farberow, Carrie A; Grabow, Lars C; Kudernatsch, Wilhelmine; Wendt, Stefan; Lægsgaard, Erik; Mavrikakis, Manos; Besenbacher, Flemming

    2012-05-18

    The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion. PMID:22605771

  11. Creating a Stable Oxide at the Surface of Black Phosphorus.

    PubMed

    Edmonds, M T; Tadich, A; Carvalho, A; Ziletti, A; O'Donnell, K M; Koenig, S P; Coker, D F; Özyilmaz, B; Neto, A H Castro; Fuhrer, M S

    2015-07-15

    The stability of the surface of in situ cleaved black phosphorus crystals upon exposure to atmosphere is investigated with synchrotron-based photoelectron spectroscopy. After 2 days atmosphere exposure a stable subnanometer layer of primarily P2O5 forms at the surface. The work function increases by 0.1 eV from 3.9 eV for as-cleaved black phosphorus to 4.0 eV after formation of the 0.4 nm thick oxide, with phosphorus core levels shifting by <0.1 eV. The results indicate minimal charge transfer, suggesting that the oxide layer is suitable for passivation or as an interface layer for further dielectric deposition. PMID:26126232

  12. Optical measurements of surface oxide layer formation on metal films

    SciTech Connect

    Scott, M.L.

    1987-01-01

    We have employed two optical techniques which give complementary indications of the formation of monolayers of oxide on freshly evaporated aluminum and silicon thin films. Visible ellipsometry is utilized to observe the growth of the initial monolayer of oxide on these films. From these data, we deduce the pressure and coverage dependence as well as the growth rate for the initial monolayer arising from these surface reactions. In addition, extreme ultraviolet (xuv) reflectance vs angle of incidence measurements at 58.4 nm wavelength clearly indicate the growth of oxide on the surface of our freshly deposited aluminum and silicon films as well. We have utilized this reflectance data to deduce the optical constants of aluminum and silicon at 58.4 nm. We find that previous xuv measurements of these optical constants were hampered by the presence of oxides. We also determined that the xuv reflectivity performance of aluminum films freshly deposited in our uhv system does not degrade appreciably when stored for four weeks in a helium atmosphere of 2 x 10/sup -9/ Torr. 11 refs., 7 figs., 1 tab.

  13. Surface modification of hydrophobic iron oxide nanoparticles for clinical applications

    Microsoft Academic Search

    Kyoungja Woo; Jangwon Hong

    2005-01-01

    Monodisperse superparamagnetic iron oxide nanoparticles (SPIONs) were prepared by thermal decomposition of Fe(CO)5 and by consecutive aeration in organic medium. The resultant hydrophobic SPION surface was modified to be hydrophilic via Fe-S covalent bond with bi-functional 3-mercaptopropionic acid and then, the terminal carboxylic acid group was esterified with dextran for biocompatibility. Analysis by water dispersity, transmission electron microscopy, X-ray diffraction,

  14. Surface oxide debonding in field assisted powder sintering

    Microsoft Academic Search

    K. R Anderson; J. R Groza; M Fendorf; C. J Echer

    1999-01-01

    Field activated sintering techniques (FAST) have been applied to two high-temperature powder materials: tungsten and NiAl. High and atomic resolution electron microscopy (HREM\\/ARM) of tungsten powder sintered via FAST showed essentially clean boundaries. Analytical transmission electron microscopy (TEM) of FAST sintered NiAl also showed boundaries free of surface oxide layer(s). However, small alumina precipitates were found at and near prior

  15. New advanced surface modification technique: titanium oxide ceramic surface implants: long-term clinical results

    NASA Astrophysics Data System (ADS)

    Szabo, Gyorgy; Kovacs, Lajos; Barabas, Jozsef; Nemeth, Zsolt; Maironna, Carlo

    2001-11-01

    The purpose of this paper is to discuss the background to advanced surface modification technologies and to present a new technique, involving the formation of a titanium oxide ceramic coating, with relatively long-term results of its clinical utilization. Three general techniques are used to modify surfaces: the addition or removal of material and the change of material already present. Surface properties can also be changed without the addition or removal of material, through the laser or electron beam thermal treatment. The new technique outlined in this paper relates to the production of a corrosion-resistant 2000-2500 A thick, ceramic oxide layer with a coherent crystalline structure on the surface of titanium implants. The layer is grown electrochemically from the bulk of the metal and is modified by heat treatment. Such oxide ceramic-coated implants have a number of advantageous properties relative to implants covered with various other coatings: a higher external hardness, a greater force of adherence between the titanium and the oxide ceramic coating, a virtually perfect insulation between the organism and the metal (no possibility of metal allergy), etc. The coated implants were subjected to various physical, chemical, electronmicroscopic, etc. tests for a qualitative characterization. Finally, these implants (plates, screws for maxillofacial osteosynthesis and dental root implants) were applied in surgical practice for a period of 10 years. Tests and the experience acquired demonstrated the good properties of the titanium oxide ceramic-coated implants.

  16. Surface impedance of the high-Tc oxide superconductors

    SciTech Connect

    Hylton, T.L.; Beasley, M.R.; Kapitulnik, A.; Carini, J.P.; Drabeck, L.

    1988-01-01

    We review briefly our results on measurements of the millimeter wave surface impedance of ceramic, thin film and single crystal samples of the high-Tc oxide superconductors. The observed losses and temperature dependences do not agree with BCS theory. We discuss our recent measurements of single crystal Bi(2)CaSr(2)Cu(2)O(x) and the effect of the application of a perpendicular magnetic field. We consider the possibilities of intrinsic and defect mechanisms to explain our observations. In particular, we discuss the effects of weakly coupled granular films on surface impedance.

  17. Functionalization to control microstructural, optical, electronic and wetting properties of metal oxide surfaces

    Microsoft Academic Search

    Jagdeep Singh

    2010-01-01

    This thesis focuses on engineering the surface chemistry of oxide surfaces in order to control their microstructural, optical, electronic and wetting properties. Several different types of experiments have been performed to tailor the properties of silicon oxide, titanium dioxide, and zinc oxide surfaces. Applications of this work include organic electronics, sensors and nanomanufacturing. Adsorption of 3-mercaptopropyltrimethoxysilane (MPS) on hydroxylated silicon

  18. SURFACE COMPLEXATION OF ACTINIDES WITH IRON OXIDES: IMPLICATIONS FOR RADIONUCLIDE TRANSPORT IN NEAR-SURFACE AQUIFERS

    SciTech Connect

    J.L. Jerden Jr.; A.J. Kropf; Y. Tsai

    2005-08-25

    The surface complexation of actinides with iron oxides plays a key role in actinide transport and retardation in geosphere-biosphere systems. The development of accurate actinide transport models therefore requires a mechanistic understanding of surface complexation reactions (i.e. knowledge of chemical speciation at mineral/fluid interfaces). Iron oxides are particularly important actinide sorbents due to their pH dependent surface charges, relatively high surface areas and ubiquity in oxic and suboxic near-surface systems. In this paper we present results from field and laboratory investigations that elucidate the mechanisms involved in binding uranium and neptunium to iron oxide mineral substrates in near neutral groundwaters. The field study involved sampling and characterizing uranium-bearing groundwaters and solids from a saprolite aquifer overlying an unmined uranium deposit in the Virginia Piedmont. The groundwaters were analyzed by inductively coupled mass spectrometry and ion chromatography and the aquifer solids were analyzed by electron microprobe. The laboratory study involved a series of batch sorption tests in which U(VI) and Np(V) were reacted with goethite, hematite and magnetite in simulated groundwaters. The pH, ionic strength, aging time, and sorbent/sorbate ratios were varied in these experiments. The oxidation state and coordination environment of neptunium in solutions and sorbents from the batch tests were characterized by X-ray absorption spectroscopy (XAS) at the Advanced Photon Source, Argonne National Laboratory. Results from this work indicate that, in oxidizing near-surface aquifers, the dissolved concentration of uranium may be limited to less than 30 parts per billion due to uptake by iron oxide mineral coatings and the precipitation of sparingly soluble U(VI) phosphate minerals. Results from the batch adsorption tests showed that, in near neutral groundwaters, a significant fraction of the uranium and neptunium adsorbed as strongly bound surface complexes that were not removed (desorbed) when the sorbents were resuspended in dilute groundwater. The XAS results indicate that at pH 7.0-8.0 neptunium adsorbs to goethite as a neptunyl(V) complex and to magnetite as an inner-sphere Np(lV) complex with a Np-Fe distance of approximately 3.5 angstroms. These findings demonstrate that the presence of iron oxides in oxidizing near-surface aquifers may significantly retard actinide transport and that future reactive-transport models for actinides should therefore account for irreversible sorption processes.

  19. Inhibition of Sulfide Mineral Oxidation by Surface Coating Agents: Batch

    NASA Astrophysics Data System (ADS)

    Choi, J.; Ji, M. K.; Yun, H. S.; Park, Y. T.; Gee, E. D.; Lee, W. R.; Jeon, B.-H.

    2012-04-01

    Mining activities and mineral industries have impacted on rapid oxidation of sulfide minerals such as pyrite (FeS2) which leads to Acid Mine Drainage (AMD) formation. Some of the abandoned mines discharge polluted water without proper environmental remediation treatments, largely because of financial constraints in treating AMD. Magnitude of the problem is considerable, especially in countries with a long history of mining. As metal sulfides become oxidized during mining activities, the aqueous environment becomes acid and rich in many metals, including iron, lead, mercury, arsenic and many others. The toxic heavy metals are responsible for the environmental deterioration of stream, groundwater and soils. Several strategies to remediate AMD contaminated sites have been proposed. Among the source inhibition and prevention technologies, microencapsulation (coating) has been considered as a promising technology. The encapsulation is based on inhibition of O2 diffusion by surface coating agent and is expected to control the oxidation of pyrite for a long time. Potential of several surface coating agents for preventing oxidation of metal sulfide minerals from both Young-Dong coal mine and Il-Gwang gold mine were examined by conducting batch experiments and field tests. Powdered pyrite as a standard sulfide mineral and rock samples from two mine outcrops were mixed with six coating agents (KH2PO4, MgO and KMnO4 as chemical agents, and apatite, cement and manganite as mineral agents) and incubated with oxidizing agents (H2O2 or NaClO). Batch experiments with Young-Dong coal mine samples showed least SO42- production in presence of KMnO4 (16% sulfate production compared to no surface coating agents) or cement (4%) within 8 days. In the case of Il-Gwang mine samples, least SO42- production was observed in presence of KH2PO4 (8%) or cement (2%) within 8 days. Field-scale pilot tests at Il-Gwang site also showed that addition of KH2PO4 decreased sulfate production from 200 to 13 mg L-1 and reduced Cu and Mn from 8 and 3 mg L-1 to below the detection limits, respectively. The experimental results suggested that the amendment of surface coating agents can be a promising alternative for inhibition of sulfide oxidation at AMD sites.

  20. Mobility of Water on Oxide Surfaces Studied by QENS

    SciTech Connect

    Mamontov, Eugene [ORNL

    2007-01-01

    Although neutron scattering is often considered a bulk probe, we demonstrate that the mobility of surface water on oxide nano-powders can be investigated using quasielastic neutron scattering. We discuss how the reduced number of hydrogen bonds per water molecule associated with surface confinement leads to a qualitative modification of single-particle translational dynamics compared to bulk water. The mobility of surface water in zirconium oxide with two hydration layers present is discussed in detail. The outer hydration layer exhibits translational dynamics on the time scale of tens of picoseconds, and thus can be studied using time-of-flight neutron spectrometry. The translational dynamics of the inner hydration layer in the range of hundreds of picoseconds can be assessed with backscattering neutron spectrometry. Interestingly, despite being slower by two orders of magnitude, the translational motion of the molecules of the inner hydration layer may share more common traits with bulk water compared to the motion of the outer hydration layer, the dynamics of which is slower than that of bulk water by just one order of magnitude. Similar to bulk water, the temperature dependence of the residence time for the water molecules of the inner hydration layer is non-Arrhenius, and can be described by a Vogel-Fulcher-Tammann (VFT) law. On the other hand, the molecules of the outer hydration layer demonstrate Arrhenius-type temperature dependence indicative of thermally activated surface jump diffusion. Our recent study of surface water on cerium oxide, which exhibits faster dynamics compared to water on zirconium oxide, has ventured into the low-temperature region (down to 200 K). Below 215 K, we have found a deviation from the VFT temperature dependence for the residence time indicative of a surprise "fragile"-to-"strong" transition in the surface water. While "fragile"-to-"strong" transition has been predicted in supercooled bulk water, there has been no prediction of such a transition in surface water. We discuss the links between our results and recent work on hydration water in carbon nanotubes and proteins.

  1. Growth and surface structure of vanadium oxide on anatase (001)

    SciTech Connect

    Gao, Weiwei; Wang, Chong M.; Wang, Huiqiong; Henrich, Victor E.; Altman, Eric I.

    2004-06-20

    Oxygen plasma assisted molecular beam epitaxy (OPA-MBE) of vanadium oxide on (1?4)-reconstructed anatase (001) thin films was studied using reflection high energy electron diffraction (RHEED), low energy electron diffraction (LEED), x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), x-ray diffraction (XRD), and transmission electron microscopy (TEM). XPS and UPS results showed that the vanadium was predominantly in the 5+ oxidation state after deposition of a monolayer at 525 K. After 1 ML of vanadia was deposited, the anatase (1?4)/(4?1) LEED and RHEED patterns were replaced by (1?1) patterns indicating that the vanadia lifts the reconstruction and suggesting that the monolayer is pseudomorphic. At 525 K, the V?? oxidation state predominated in thicker films, however, no discernible LEED or RHEED patterns were seen after a few monolayers were deposited indicating that V?O? epitaxy cannot be continued beyond 1 ML. When the growth temperature was increased to 750 K, RHEED patterns indicated no change in the surface structure after more than 20 ML of vanadia were deposited. Under these conditions, XPS peak positions were consistent with VO?. After growth at 775 K a c(2x2) LEED pattern attributed to half a monolayer of adsorbed oxygen on the VO? surface was observed. The surface characterization data all pointed towards pseudomorphic growth of VO? with a half monolayer of capping oxygen allowing the monolayer to achieve the V?O? stoichiometry while maintaining the anatase structure. Bulk XRD data, however, were consistent with VO? (B), V?O??, and rutile VO? none of which expose surfaces with the periodicity observed with RHEED and LEED. The reasons for the differences between the surface and bulk characterization are discussed.

  2. Enhanced biogenic emissions of nitric oxide and nitrous oxide following surface biomass burning

    NASA Technical Reports Server (NTRS)

    Anderson, Iris C.; Levine, Joel S.; Poth, Mark A.; Riggan, Philip J.

    1988-01-01

    Recent measurements indicate significantly enhanced biogenic soil emissions of both nitric oxide (NO) and nitrous oxide (N2O) following surface burning. These enhanced fluxes persisted for at least six months following the burn. Simultaneous measurements indicate enhanced levels of exchangeable ammonium in the soil following the burn. Biomass burning is known to be an instantaneous source of NO and N2O resulting from high-temperature combustion. Now it is found that biomass burning also results in significantly enhanced biogenic emissions of these gases, which persist for months following the burn.

  3. Influence of corrosive solutions on microhardness and chemistry of magnesium oxide /001/ surfaces

    NASA Technical Reports Server (NTRS)

    Ishigaki, H.; Miyoshi, K.; Buckley, D. H.

    1982-01-01

    X-ray photoelectron spectroscopy analyses and hardness experiments were conducted on cleaved magnesium oxide /001/ surfaces. The magnesium oxide bulk crystals were cleaved to specimen size along the /001/ surface, and indentations were made on the cleaved surface in corrosive solutions containing HCl, NaOH, or HNO3 and in water without exposing the specimen to any other environment. The results indicated that chloride (such as MgCl2) and sodium films are formed on the magnesium oxide surface as a result of interactions between an HCl-containing solution and a cleaved magnesium oxide surface. The chloride films soften the magnesium oxide surface. In this case microhardness is strongly influenced by the pH value of the solution. The lower the pH, the lower the microhardness. Sodium films, which are formed on the magnesium oxide surface exposed to an NaOH containing solution, do not soften the magnesium oxide surface.

  4. Oxidation of low density lipoproteins by myeloperoxidase at the surface of endothelial cells: an additional mechanism to subendothelium oxidation

    Microsoft Academic Search

    K. Zouaoui Boudjeltia; N. Moguilevskyf; I. Legssyer; S. Babar; M. Guillaume; P. Delree; M. Vanhaeverbeek; D. Brohee; J. Ducobue; C. Remacle

    2004-01-01

    The present paradigm of atherogenesis proposes that low density lipoproteins (LDL) are trapped in subendothelial space of the vascular wall where they are oxidized. Myeloperoxidase (MPO) plays a key role in oxidative damage. We propose that LDL oxidation by myeloperoxidase (Mox-LDL) could occur at the surface of the endothelial cells and not restricted to the subendothelial space. The triad constituted

  5. Attachment of Pathogenic Prion Protein to Model Oxide Surfaces

    PubMed Central

    Jacobson, Kurt H.; Kuech, Thomas R.; Pedersen, Joel A.

    2014-01-01

    Prions are the infectious agents in the class of fatal neurodegenerative diseases known as transmissible spongiform encephalopathies, which affect humans, deer, sheep, and cattle. Prion diseases of deer and sheep can be transmitted via environmental routes, and soil is has been implicated in the transmission of these diseases. Interaction with soil particles is expected to govern the transport, bioavailability and persistence of prions in soil environments. A mechanistic understanding of prion interaction with soil components is critical for understanding the behavior of these proteins in the environment. Here, we report results of a study to investigate the interactions of prions with model oxide surfaces (Al2O3, SiO2) using quartz crystal microbalance with dissipation monitoring and optical waveguide light mode spectroscopy. The efficiency of prion attachment to Al2O3 and SiO2 depended strongly on pH and ionic strength in a manner consistent with electrostatic forces dominating interaction with these oxides. The N-terminal portion of the protein appeared to facilitate attachment to Al2O3 under globally electrostatically repulsive conditions. We evaluated the utility of recombinant prion protein as a surrogate for prions in attachment experiments and found that its behavior differed markedly from that of the infectious agent. Our findings suggest that prions preferentially associate with positively charged mineral surfaces in soils (e.g., iron and aluminum oxides). PMID:23611152

  6. The Reduction of Aqueous Metal Species on the Surfaces of Fe(II)-Containing Oxides: The Role of Surface Passivation

    USGS Publications Warehouse

    White, A.F.; Peterson, M.L.

    1998-01-01

    The reduction of aqueous transition metal species at the surfaces of Fe(II)- containing oxides has important ramifications in predicting the transport behavior in ground water aquifers. Experimental studies using mineral suspensions and electrodes demonstrate that structural Fe(II) heterogeneously reduces aqueous ferric, cupric, vanadate and chromate ions on magnetite and ilmenite surfaces. The rates of metal reduction on natural oxides is strongly dependent on the extent of surface passivation and redox conditions in the weathering environment. Synchrotron studies show that surface oxidation of Fe(II)-containing oxide minerals decreases their capacity for Cr(VI) reduction at hazardous waste disposal sites.

  7. Reflection spectra and magnetochemistry of iron oxides and natural surfaces

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.

    1978-01-01

    The magnetic properties and spectral characteristics of iron oxides are distinctive. Diagnostic features in reflectance spectra (0.5 to 2.4 micron) for alpha Fe2O3, gamma Fe2O3, and FeOOH include location of Fe3(+) absorption features, intensity ratios at various wavelengths, and the curve shape between 1.2 micron and 2.4 micron. The reflection spectrum of natural rock surfaces are seldom those of the bulk rock because of weathering effects. Coatings are found to be dominated by iron oxides and clay. A simple macroscopic model of rock spectra (based on concepts of stains and coatings) is considered adequate for interpretation of LANDSAT data. The magnetic properties of materials associated with specific spectral types and systematic changes in both spectra and magnetic properties are considered.

  8. Molecular dynamics simulation of electric field effects on surface diffusion and surface oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Waigen

    Scope and Method of Study: Classical molecular dynamics method with charge transferable ES+EAM (Streitz-Mintmire) potential has been employed to study surface diffusion and surface oxidation on FCC metal surfaces under the influence of applied electric field. The potential parameters are firstly optimized by fitting to structural and elastic properties. Diffusion barriers for adatoms and monovacancy are calculated as the optimized energy differences at adsorption site and symmetric transition states. The static barriers are comparable to activation energy derived from Arrhenius equation in dynamic simulations. External electric field is simulated by including the interactions of ionic charges q and field E. In simulating surface diffusions, electric field is modeled as exponential decreasing function. In oxidation simulation, the field is applied via a bias voltage across the sample and electric field in each finite difference grid is calculated by solving the Kirchhoff's law for circuit equations. The field in each grid is updated with time according to the local composition. Heat diffusion equation is numerically solved and the temperature in the dynamic simulations is updated via an ad hoc loop. Findings and Conclusions: Hopping and exchange mechanisms have different reactions to external field. Exchange barrier increases with field and hopping barrier decreases with field, but with a smaller slope. If the exchange barrier is preferred at zero field, there is a chance that at higher field the two barriers will have crossover and we will observe a mechanism change. This mechanism change is found in Pt/Pt(100) system and confirms previous experimental observations with FIM. If the hopping barrier is preferred at zero field, the diffusion will be promoted by the field but the two barriers will never have crossover at positive electric field. Electric field has limited effect on vacancy diffusion barriers, and adding solute Al to Cu(111) surface cannot improve the lifetime of the interconnects. In metal surface oxidation, electric field and temperature are both important and can enhance the oxide thickness. The miscrostructure of the oxide is dramatically changed by electric field and high temperature, including oxide density, bond length, Al-O pair distribution, coordination number. Our results show the oxide growth can be controlled via electric field and temperature. Our current simulation method provides a new method to study inhomogeneous systems.

  9. Growth of Zinc oxide thin films on polar oxide surfaces by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Pradhan, Kallol

    Polar heterointerfaces of MgO(111) and the II-VI semiconductor ZnO are of technological interest for transparent conducting electrode applications. Growth and structure of thin films on polar surfaces can be different than on non-polar surfaces due to the large surface energy of polar surfaces. We have grown ZnO on unreconstructed MgO(111)-(1x1)-OH terminated and reconstructed MgO(111)-(?3x?3)R30° polar oxide surfaces using atomic layer deposition. A homemade UHV-interfaced viscous-flow atomic layer deposition (ALD) reactor with in-situ quartz crystal monitor was used to grow ZnO thin films on the MgO(111) substrates. Surface morphology studies revealed that the surface roughness increases with ZnO film thickness and that reconstructed MgO(111) is a better substrate for production of smooth ZnO films. Thin-film structural analysis revealed that ZnO thin films are polycrystalline, having the wurtzite structure, with preferential growth along the c-axis. ZnO grown on MgO(111)-(?3x?3)R30° substrates show strong preferential growth along the polar (002) direction. In contrast, growth along the non-polar (100) and (101) directions is also observed when grown on MgO(111)-(1x1) substrates. These observations indicate the crystal orientation during ALD ZnO growth depends not only on temperature but also on the surface terminations and symmetry of the substrates. We also investigated the growth of ALD ZnO on polar 6H-SiC(0001) substrates and non-polar MgO(100), alpha-Al2O3(0001) and oxidized Si(100). Our study revealed that, for non-polar substrates, ALD ZnO grows along the non-polar (100) and (101) directions along with the polar (002) direction. Highly c-axis-oriented ALD ZnO thin film growth on 6H-SiC(0001) indicates that lattice matched substrates favor growth of high-quality ALD ZnO. Finally, we investigated ZnO thin film growth on unreconstructed MgO(111)-(1x1)-OH terminated and reconstructed MgO(111)-(?3x?3)R30° polar oxide surfaces using pulsed-laser deposition (PLD). Structural studies revealed that surface termination affects the PLD ZnO growth similar to the way it affected ALD ZnO growth.

  10. Surface characterization and mechanical property evaluation of thermally oxidized Ti-6Al-4V

    SciTech Connect

    Biswas, Amit [Department of Metal. and Maters. Engg., I. I. T. Kharagpur, W. B. - 721302 (India); Dutta Majumdar, Jyotsna, E-mail: jyotsna@metal.iitkgp.ernet.in [Department of Metal. and Maters. Engg., I. I. T. Kharagpur, W. B. - 721302 (India)

    2009-06-15

    The present study concerns development of a thin and adherent oxide film on the surface of Ti-6Al-4V by thermal oxidation. Thermal oxidation was carried out over a range of temperature between 400 to 600 deg. C and a time from 25 h to 60 h. A detailed characterization of the surface and cross section of the oxidized surface was carried out by optical/scanning electron microscopy and X-ray diffraction techniques. Finally, the mechanical properties of the oxidized surface in terms of microindentation hardness and wear resistance were evaluated as a function of oxidation parameters. Surface oxidation of Ti-6Al-4V at 600 deg. C for 36 h offered a defect free oxide scale with improved hardness and wear resistance.

  11. Roles of Oxygen and Water Vapor in the Oxidation of Halogen Terminated Ge(111) Surfaces

    SciTech Connect

    Sun, Shiyu; /Stanford U., Phys. Dept.; Sun, Yun; Liu, Zhi; Lee, Dong-Ick; Pianette, Piero; /SLAC, SSRL

    2006-12-18

    The initial stage of the oxidation of Cl and Br terminated Ge(111) surfaces is studied using photoelectron spectroscopy. The authors perform controlled experiments to differentiate the effects of different factors in oxidation, and find that water vapor and oxygen play different roles. Water vapor effectively replaces the halogen termination layers with the hydroxyl group, but does not oxidize the surfaces further. In contrast, little oxidation is observed for Cl and Br terminated surfaces with dry oxygen alone. However, with the help of water vapor, oxygen oxidizes the surface by breaking the Ge-Ge back bonds instead of changing the termination layer.

  12. Surface Science Letters Synthesis of well-ordered ultra-thin titanium oxide films

    E-print Network

    Goodman, Wayne

    Surface Science Letters Synthesis of well-ordered ultra-thin titanium oxide films on Mo(112) M microscopy (STM); X-ray photoelectron spectroscopy (XPS); Titanium oxide; Surface structure, morphology oxide systems, titanium dioxide has served as the prototypical reducible 0039-6028/$ - see front matter

  13. Role of Surface Precipitation in Copper Sorption by the Hydrous Oxides of Iron and Aluminum

    E-print Network

    Chorover, Jon

    Role of Surface Precipitation in Copper Sorption by the Hydrous Oxides of Iron and Aluminum K. G precipitation; sorption; isotherms; X-ray diffraction; hydrous iron oxide; hydrous aluminum oxide; copper. INTRODUCTION Hydrous oxides of iron (HFO) and aluminum (HAO) are important mineral components of natural

  14. Creation of Exotic Features in Metal Oxides by Surface Treatment for Enhanced Gas Sensing

    E-print Network

    Azad, Abdul-Majeed

    Creation of Exotic Features in Metal Oxides by Surface Treatment for Enhanced Gas Sensing Majed of oxide ceramics, we have developed a technique based on rigorous thermodynamic consideration of the metal/metal or air, the metal oxide of interest is reduced and re-oxidized by exposing it to a well-defined pO2

  15. Control of Chemical States on Locally Anode-Oxidized Si Surfaces

    NASA Astrophysics Data System (ADS)

    Kashiwase, Yuta; Oya, Takahide; Ogino, Toshio

    2008-07-01

    We have demonstrated that chemical states on the anode-oxidized Si surfaces prepared by atomic force microscopy (AFM) can be controlled by selecting the appropriate applied voltage for the oxidation. The frictional force on the oxidized surface formed at relatively low voltages (4.5-9 V) was large, whereas that at relatively high voltages (9-10 V) was small. This is due to a difference in the hydrophilicity of the surfaces. Octadecyltrichlorosilane (OTS) films were formed only on the oxidized surface prepared at the low voltages. Since OTS molecules require OH groups to form a film, the hydrophilicity originates from OH group termination of the surfaces. Therefore, the oxide surface is terminated with OH groups when the applied voltage is relatively low. When the applied voltage is relatively high, it is speculated that the oxide surface is covered with Si-O-Si groups instead of OH groups.

  16. Diphosphine Dioxide Cages and Hydrogen Peroxide Adducts of Phosphine Oxides: Syntheses and Applications in Surface Science 

    E-print Network

    Hilliard, Casie Renee

    2013-12-09

    Understanding the adsorption of phosphine oxides on silica surfaces has a threefold incentive. (a) Efficiently removing phosphine oxides from reaction mixtures is crucial after many synthetic procedures, for example the ...

  17. Water-hydroxyl phases on an open metal surface: breaking the ice rules Matthew Forster,a

    E-print Network

    Alavi, Ali

    Water-hydroxyl phases on an open metal surface: breaking the ice rules Matthew Forster,a Rasmita catalyzed redox reactions, yet establishing the phase diagram for water/hydroxyl adsorption on metal and density functional theory calculations, we report the phase diagram for water/hydroxyl on Cu(110

  18. Effect of photoirradiation on potassium persulfate-surface oxidation of low-density polyethylene film

    Microsoft Academic Search

    Hitoshi Kubota; Yayoi Hariya; Shin-ichi Kuroda; Takashi Kondo

    2001-01-01

    Surface oxidation of low-density polyethylene (PE) film (thickness=30 ?m) with potassium persulfate (KPS) was investigated at 50°C in water. The surface oxidation was followed by ATR-IR measurement of the oxidized PE film, where the absorbance ratio of the carbonyl group at 1716 cm?1 to the methylene group at 1460 cm?1 was used as a measure of the oxidation. The absorbance

  19. The aniline-to-azobenzene oxidation reaction on monolayer graphene or graphene oxide surfaces fabricated by benzoic acid

    PubMed Central

    2013-01-01

    The oxidation of aniline to azobenzene was conducted in the presence of either monolayer graphene (EG) or graphene-oxide-like surface, such as GOx, under ultra-high vacuum conditions maintaining a 365-nm UV light exposure to enhance the oxidation reaction. The surface-bound products were investigated using micro Raman spectroscopy, high-resolution photoemission spectroscopy, and work function measurements. The oxygen carriers present on the GOx surfaces, but not on the EG surfaces, acted as reaction reagents to facilitate the oxidation reaction from aniline to azobenzene. Increasing the aniline concentration at 300 K confirmed that the exchange ratio from the aniline to the azobenzene was enhanced, as determined by the intensity ratio between the aniline- and azobenzene-induced N 1 s core-level spectra. The work function changed dramatically as the aniline concentration increased, indicating that the aniline on the GOx surface conveyed n-type doping characteristics at a low coverage level. A higher aniline concentration increased the p-type doping character by increasing the azobenzene concentration on the GOx surface. A comparison of the oxidation reactivity of aniline molecules on the EG or GOx surfaces revealed the role of the oxygen carriers on the GOx surfaces in the context of catalytic oxidation. PMID:24229051

  20. Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

    PubMed Central

    Blinn, Kevin S.; Li, Xiaxi; Liu, Mingfei; Bottomley, Lawrence A.; Liu, Meilin

    2012-01-01

    Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode. PMID:23023264

  1. Probing and mapping electrode surfaces in solid oxide fuel cells.

    PubMed

    Blinn, Kevin S; Li, Xiaxi; Liu, Mingfei; Bottomley, Lawrence A; Liu, Meilin

    2012-01-01

    Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen (1-7). The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion(2). Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation(8-12). It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition(8, 10, 13, 14) ("coking") and sulfur poisoning(11, 15) and the manner in which surface modifications stave off this degradation(16). The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated(17-22). In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode. PMID:23023264

  2. Transition metal oxides deposited on rhodium and platinum: Surface chemistry and catalysis

    SciTech Connect

    Boffa, A B [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1994-07-01

    The surface chemistry and catalytic reactivity of transition metal oxides deposited on Rh and Pt substrates has been examined in order to establish the role of oxide-metal interactions in influencing catalytic activity. The oxides investigated included titanium oxide (TiOx), vanadium oxide (VOx), iron oxide (FeOx), zirconium oxide (ZrOx), niobium oxide (NbOx), tantalum oxide (TaOx), and tungsten oxide (WOx). The techniques used to characterize the sample included AES, XPS, LEED, TPD, ISS, and STM. After characterization of the surface in UHV, the sample was enclosed in an atmospheric reaction cell to measure the influence of the oxide deposits on the catalytic activity of the pure metal for CO and CO{sub 2} hydrogenation. The oxide deposits were found to strongly enhance the reactivity of the Rh foil. The rates of methane formation were promoted by up to 15 fold with the maximum in rate enhancement occurring at oxide coverages of approximately 0.5 ML. TiOx TaOx, and NbOx were the most effective promoters and were stable in the highest oxidation states during both reactions (compared to VOx, WOx, and FeOx). The trend in promoter effectiveness was attributed to the direct relationship between oxidation state and Lewis acidity. Bonding at the metal oxide/metal interface between the oxygen end of adsorbed CO and the Lewis acidic oxide was postulated to facilitate C-O bond dissociation and subsequent hydrogenation. 192 refs.

  3. Effect of different oxidizing agent treatments on the surface properties of activated carbons

    Microsoft Academic Search

    Bhabendra K. Pradhan; N. K. Sandle

    1999-01-01

    Two commercially available activated carbon (activated charcoal cloth (ACC) and activated granular carbon(AGC)) were oxidized with different oxidizing agents viz., HNO3, H2O2 and (NH4)2S2O8, in order to introduce surface oxygen complexes. The effect of the oxidizing agent treatment on the surface chemical nature and surface texture were characterized by ultimate elemental analysis, bulk chemical analysis, FTIR, XRD and nitrogen adsorption

  4. Start | Author Index 699-28 Impact of Mineral Surface Modification on As(III) Oxidation by Mn(IV) Oxides.

    E-print Network

    Sparks, Donald L.

    Start | Author Index 699-28 Impact of Mineral Surface Modification on As(III) Oxidation by Mn(III) mobilization. Future studies will investigate As(III) oxidation by biogenic Mn(IV) oxides. See more of

  5. A surface science investigation of silicon carbide: Oxidation, crystal growth and surface structural analysis

    SciTech Connect

    Powers, J.M.

    1991-11-01

    For the semiconductor SiC to fulfill its potential as an electronic material, methods must be developed to produce insulating surface oxide layers in a reproducible fashion. Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) were used to investigate the oxidation of single crystal {alpha}-SiC over a wide temperature and O{sub 2} pressure range. The {alpha}-SiC surface becomes graphitic at high temperatures and low O{sub 2} pressures due to Si and SiO sublimation from the surface. Amorphous SiO{sub 2} surface layers from on {alpha}-SiC at elevated O{sub 2} pressures and temperatures. Both the graphitization and oxidation of {alpha}-SiC appears to be enhanced by surface roughness. Chemical vapor deposition (CVD) is currently the preferred method of producing single crystal SiC, although the method is slow and prone to contamination. We have attempted to produce SiC films at lower temperatures and higher deposition rates using plasma enhanced CVD with CH{sub 3}SiH{sub 3}. Scanning AES, XPS and scanning electron microscopy (SEM) were utilized to study the composition and morphology of the deposited Si{sub x}C{sub y}H{sub z} films as a function of substrate temperature, plasma power and ion flux bombardment of the film during deposition. High energy ion bombardment during deposition was found to increase film density and substrate adhesion while simultaneously reducing hydrogen and oxygen incorporation in the film. Under all deposition conditions the Si{sub x}C{sub y}H{sub z} films were found to be amorphous, with the ion bombarded films showing promise as hard protective coatings. Studies with LEED and AES have shown that {beta}-SiC (100) exhibits multiple surface reconstructions, depending on the surface composition. These surface reconstructions possess substantially different surface reactivities at elevated temperatures, which can complicate the fabrication of metal on SiC junctions.

  6. Characterization of the thrombogenic potential of surface oxides on stainless steel for implant purposes

    NASA Astrophysics Data System (ADS)

    Shih, Chun-Che; Shih, Chun-Ming; Su, Yea-Yang; Chang, Mau-Song; Lin, Shing-Jong

    2003-12-01

    Marketed stents are manufactured from various metals and passivated with different degrees of surface oxidation. The functional surface oxides on the degree of antithrombotic potential were explored through a canine femoral extracorporeal circuit model. Related properties of these oxide films were studied by open-circuit potential, current density detected at open-circuit potential, the electrochemical impedance spectroscopy, transmission electron microscopy, Auger spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. Experimental evidences showed that blood clot weight after a 30-min follow-up was significantly lower for the stainless steel wire passivated with amorphous oxide (AO) compared to the wire passivated with polycrystalline oxide (PO) or commercial as-received wire coils (AS). Surface characterizations showed that a stable negative current density at open-circuit potential and a significant lower potential were found for the wire surface passivated with AO than for the surface passivated with PO. Time constant of AO is about 25 times larger than that of polycrystalline oxide. Significant difference in oxide grain sizes was found between PO and AO. Surface chemistries revealed by the AES and XPS spectra indicated the presence of a Cr- and oxygen-rich surface oxide for AO, and a Fe-rich and oxygen-lean surface oxide for PO. These remarkable characteristics of AO surface film might have a potential to provide for excellent antithrombotic characteristics for the 316L stainless steel stents.

  7. Cleaning and passivation of copper surfaces to remove surface radioactivity and prevent oxide formation

    NASA Astrophysics Data System (ADS)

    Hoppe, E. W.; Seifert, A.; Aalseth, C. E.; Bachelor, P. P.; Day, A. R.; Edwards, D. J.; Hossbach, T. W.; Litke, K. E.; McIntyre, J. I.; Miley, H. S.; Schulte, S. M.; Smart, J. E.; Warren, G. A.

    2007-08-01

    High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited on surfaces can represent the largest remaining background. To control these backgrounds, a copper cleaning chemistry has been developed. Designed to replace an effective, but overly aggressive concentrated nitric acid etch, this peroxide-based solution allows for a more controlled cleaning of surfaces. The acidified hydrogen peroxide solution will generally target the Cu +/Cu 2+ species which are the predominant surface participants, leaving the bulk of copper metal intact. This preserves the critical tolerances of parts and eliminates significant waste disposal issues. Accompanying passivation chemistry has also been developed that protects copper surfaces from oxidation. Using a high-activity polonium surface spike, the most difficult-to-remove daughter isotope of radon, the performance of these methods are quantified.

  8. Molecular-level assemblies on metal oxide surfaces

    SciTech Connect

    Schoonover, J.R.; Bignozzi, C. [Univ. of Ferrara (Italy); Meyer, T. [Univ. of North Carolina, Chapel Hill, NC (United States)

    1996-07-01

    This is the final report of a one-year, Laboratory-Directed Research and Development project at the Los Alamos National Laboratory (LANL). The objective of this project was to explore molecular-level assemblies based on polypyridyl transition metal complexes attached to metal oxide surfaces to provide the basis for applications such as energy conversion and electricity generation, photoremediation of hazardous waste, chemical sensors, and optical storage and photorefractive devices for communications and optical computing. We have elucidated the fundamental factors that determine the photochemistry and photophysics of a series of these photoactive inorganic complexes in solution and on metal oxide substrates by exploiting our unique transient laser capabilities. This data is being utilized to design and fabricate molecular-level photonic devices. The rich chemistry of transition metal polypyridyl complexes can be utilized to prepare molecular assemblies having well-defined redox or excited-state properties that can be finely tuned to produce desired materials properties. We plan to explore other novel applications such as photorefractive switches and optical sensors using this molecular engineering approach.

  9. Decontamination of U-metal Surface by an Oxidation Etching System

    SciTech Connect

    Stout, R B; Kansa, E J; Shaffer, R J; Weed, H C

    2000-12-18

    A surface oxidation treatment is described to remove surface contamination from uranium (U) metal and/or hydrides of uranium and heavy metals (HM) from U-metal parts. In the case of heavy metal atomic contamination on a surface, and potentially several atomic layers beneath, the surface oxidation treatment combines both chemical and chemically driven mechanical processes. The chemical process is a controlled temperature-time oxidization process that creates a thin film of uranium oxide (UO{sub 2} and higher oxides) on the U-metal surface. The chemically driven mechanical process is strain induced by the volume increase as the U-metal surface transforms to a UO{sub 2} surface film. These volume strains are sufficiently large to cause surface failure spalling/scale formation and thus, removal of a U-oxide film that contains the HM-contaminated surface. The case of a HM-hydride surface contamination layer can be treated similarly by using inert hot gas to decompose the U-hydrides and/or HM-hydrides that are contiguous with the surface. A preliminary analysis to design and to plan for a sequence of tests is developed. The tests will provide necessary and sufficient data to evaluate the effective implementation and operational characteristics of a safe and reliable system. The following description is limited to only a surface oxidation process for HM-decontamination.

  10. Oxygen Reduction Kinetics Enhancement on a 2 Heterostructured Oxide Surface for Solid Oxide Fuel Cells

    SciTech Connect

    Crumlin, Ethan [Massachusetts Institute of Technology (MIT); Mutoro, Eva [ORNL; Ahn, Sung Jin [Massachusetts Institute of Technology (MIT); Jose la O', Gerardo [Massachusetts Institute of Technology (MIT); Leonard, Donovan N [ORNL; Borisevich, Albina Y [ORNL; Biegalski, Michael D [ORNL; Christen, Hans M [ORNL; Shao-Horn, Yang [Massachusetts Institute of Technology (MIT)

    2010-01-01

    Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of {approx}85 nm thick La{sub 0.8}Sr{sub 0.2}CoO{sub 3-{delta}} (LSC{sub 113}) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia (YSZ) substrates is dramatically enhanced ({approx} 3-4 orders of magnitude above bulk LSC{sub 113}) by surface decorations of (La{sub 0.5}Sr{sub 0.5}){sub 2}CoO{sub 4{+-}{delta}} (LSC{sub 214}) with coverage in the range from {approx}0.1 to {approx}15 nm. Their surface and atomic structures were characterized by atomic force, scanning electron, and scanning transmission electron microscopy, and the ORR kinetics were determined by electrochemical impedance spectroscopy. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSC{sub 113}/LSC{sub 214} regions, which were shown to be atomically sharp.

  11. Effect of oxidizing medium and heat treatment on stoichiometry of ZnSe crystal surface

    NASA Astrophysics Data System (ADS)

    Sotnikov, V. T.; Dobrotvorskiy, S. S.

    1984-10-01

    The chemical composition of ZnSe crystals at the surface after heat treatment under vacuum, without and with an oxidizing medium, was studied by both Auger electron spectroscopy and secondary ion mass spectroscopy. Heating without oxidation resulted in a higher surface concentration of Se atoms, these excess Se atoms being accompanied by Na, K. Li, Cs impurity atoms. Surface oxidation was effected plainly with commercial oxygen at room temperature, with traces of water vapor as well as with stimulation and intensification by electron bombardment. The spectra of Auger electrons and the kinetics of these spectra under the various conditions of heat treatment reveal intense oxidation and hydrolysis of the Zn Se surface, accompanied by a decrease of the Se surface concentration and an increase of the Zn surface concentration along with formation of ZnOH and Zn(OH)2 hydroxides indicated by the ion mass spectra. The spectra also indicate a thermomechanical mechanism of oxidation during electron bombardment.

  12. Hydrophobic cotton textile surfaces using an amphiphilic graphene oxide (GO) coating

    NASA Astrophysics Data System (ADS)

    Tissera, Nadeeka D.; Wijesena, Ruchira N.; Perera, J. Rangana; de Silva, K. M. Nalin; Amaratunge, Gehan A. J.

    2015-01-01

    We report for the first time hydrophobic properties on cotton fabric successfully achieved by grafting graphene oxide on the fabric surface, using a dyeing method. Graphite oxide synthesized by oxidizing natural flake graphite employing improved Hummer's method showed an inter layer spacing of ?1 nm from XRD. Synthesized graphite oxide was exfoliated in water using ultrasound energy to obtain graphene oxide (GO). AFM data obtained for the graphene oxide dispersed in an aqueous medium revealed a non-uniform size distribution. FTIR characterization of the synthesized GO sheets showed both hydrophilic and hydrophobic functional groups present on the nano sheets giving them an amphiphilic property. GO flakes of different sizes were successfully grafted on to a cotton fabric surface using a dip dry method. Loading different amounts of graphene oxide on the cotton fiber surface allowed the fabric to demonstrate different degrees of hydrophobicity. The highest observed water contact angle was at 143° with the highest loading of graphene oxide. The fabric surfaces grafted with GO also exhibits adhesive type hydrophobicity. Microscopic characterization of the fiber surface using SEM and AFM reveals the deposition of GO sheets on the fiber surface as a conformal coating. Analysis of the fabric surface using UV-vis absorption allowed identification of the ratio of hydrophobic to hydrophilic domains present on the GO coated cotton fabric surface. Hydrophobic properties on cotton fabric are ascribed to two dimensional amphiphilic properties of deposited GO nano sheets, which successfully lower the interfacial energy of the fabric surface.

  13. Advanced Surface Modification of Indium Tin Oxide for Improved Charge Injection in Organic Devices

    E-print Network

    Schwartz, Jeffrey

    Advanced Surface Modification of Indium Tin Oxide for Improved Charge Injection in Organic Devices and involves sequential formation of a monolayer of a -conjugated organic semiconductor on the indium tin oxide, indium tin oxide, ITO) and cathode of organic light emitting diodes (OLEDs), or at electrodes in other

  14. Electrodeposited ruthenium oxide thin films for supercapacitor: Effect of surface treatments

    E-print Network

    Chow, Lee

    Electrodeposited ruthenium oxide thin films for supercapacitor: Effect of surface treatments V Supercapacitor is similar to a regular capacitor in operation; however, it offers a very high capacitance for supercapacitor should be able to get oxidized and reduce reversibility between various oxidation states [1

  15. Surfactant Organic Molecules Restore Magnetism in Metal-Oxide Nanoparticle Surfaces

    E-print Network

    Pennycook, Steve

    Surfactant Organic Molecules Restore Magnetism in Metal-Oxide Nanoparticle Surfaces Juan Salafranca ingredient in the fabrication of nanoparticles with optimal magnetic properties. KEYWORDS: Ferrites, metal-oxide nanoparticles, magnetism, electron magnetic chiral dichroism, electron energy loss spectroscopy Metal-oxide

  16. Adsorption and oxidation of methanol and ethanol on the surface of metallic and ceramic catalysts

    NASA Astrophysics Data System (ADS)

    Kirillov, Sviatoslav A.; Tsiakaras, Panagiotis E.; Romanova, Irina V.

    2003-06-01

    A short review of results obtained in latest infrared and Raman studies, with special reference to in situ measurements and first-principles quantum-mechanical investigations of adsorption and oxidation of alcohol molecules over different (metallic, semiconductor and oxide) surfaces and metal/oxide interfaces is presented, and differences and similarities in the behaviour of methanol and ethanol are discussed.

  17. Surface and sub-surface reactions during low temperature aluminium oxide atomic layer deposition on fiber-forming polymers

    E-print Network

    Khan, Saad A.

    , but the coating structure depends strongly on the starting polymer composition. For the weakly interacting interactions between depositing species and the polymer surface or chain.7­11 While studies addressingSurface and sub-surface reactions during low temperature aluminium oxide atomic layer deposition

  18. Soot Surface Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix I

    NASA Technical Reports Server (NTRS)

    Xu, F.; El-Leathy, A. M.; Kim, C. H.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2003-01-01

    Soot surface oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round fuel jets burning in coflowing dry air considering acetylene-nitrogen, ethylene, propyiene-nitrogen, propane and acetylene-benzene-nitrogen in the fuel stream. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2, C2H6, C3H6, C3H8, and C6H6) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption and flow velocities by laser velocimetry. For present test conditions, it was found that soot surface oxidation rates were not affected by fuel type, that direct rates of soot surface oxidation by O2 estimated from Nagle and Strickland-Constable (1962) were small compared to observed soot surface oxidation rates because soot surface oxidation was completed near the flame sheet where O2 concentrations were less than 3% by volume, and that soot surface oxidation rates were described by the OH soot surface oxidation mechanism with a collision efficiency of 0.14 and an uncertainty (95% confidence) of +/- 0.04 when allowing for direct soot surface oxidation by O2, which is in reasonably good agreement with earlier observations of soot surface oxidation rates in both premixed and diffusion flames at atmospheric pressure.

  19. Atomistic simulations of surface segregation of defects in solid oxide electrolytes

    E-print Network

    Cai, Wei

    ) are widely used electrolyte materials for solid oxide fuel cells (SOFCs) due to their high ionic conductivAtomistic simulations of surface segregation of defects in solid oxide electrolytes Hark B. Lee is important in fuel cell applications because it can affect the near-surface chemical reactions and ionic

  20. Phase-transformation dynamics in the oxides on the surface of nickel electrodes in alkaline electrolyte

    Microsoft Academic Search

    A. M. Ivanov; L. O. Favorskaya; L. A. Salnikov; L. P. Timofeeva

    1986-01-01

    Optical surface characteristics of plate-type nickel electrodes have been investigated in alkaline electrolyte under different conditions: storage in the electrolyte, dc operation, and ac operation. It is shown that the dynamics of the optical properties of the surface oxides on nickel can nicely be interpreted with the two-layer model of oxide films.

  1. Phase-transformation dynamics in the oxides on the surface of nickel electrodes in alkaline electrolyte

    SciTech Connect

    Ivanov, A.M.; Favorskaya, L.O.; Sal'nikov, L.A.; Timofeeva, L.P.

    1986-04-01

    Optical surface characteristics of plate-type nickel electrodes have been investigated in alkaline electrolyte under different conditions: storage in the electrolyte, dc operation, and ac operation. It is shown that the dynamics of the optical properties of the surface oxides on nickel can nicely be interpreted with the two-layer model of oxide films.

  2. Conduction and Gas–Surface Reaction Modeling in Metal Oxide Gas Sensors

    Microsoft Academic Search

    Brian Chwieroth; Bruce R. Patton; Yunzhi Wang

    2001-01-01

    A phenomenological approach to the operation of metal oxide gas sensors, the Integrated Reaction Conduction (IRC) model, is proposed which integrates the gas-surface reactions with the electrical conduction process in a weakly sintered, porous metal oxide. An effective medium approximation is employed to relate the mesoscopic microstructure and the carrier depletion at the granular surface to the macroscopic electrical conduction.

  3. The surface and materials science of tin oxide Matthias Batzill *, Ulrike Diebold

    E-print Network

    Diebold, Ulrike

    the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by whichReview The surface and materials science of tin oxide Matthias Batzill *, Ulrike Diebold Department properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science

  4. A chemical approach to understanding oxide surfaces James A. Enterkin a,b,c

    E-print Network

    Marks, Laurence D.

    A chemical approach to understanding oxide surfaces James A. Enterkin a,b,c , Andres E. Becerra-Toledo d , Kenneth R. Poeppelmeier a,b,c , Laurence D. Marks c,d, a Chemical Sciences and Engineering Keywords: Bond valence sum Coordination Chemical bond Surface structure Metal oxide Chemical bonding has

  5. Atmospheric and electrochemical oxidation of the surface of chalcopyrite (CuFeS 2)

    Microsoft Academic Search

    Q. Yin; G. H. Kelsall; D. J. Vaughan; K. E. R. England

    1995-01-01

    Atmospheric and electrochemical oxidation of the surface of chalcopyrite has been investigated using electrochemical techniques with subsequent surface analysis by X-ray photoelectron spectroscopy (XPS) and aqueous phase analysis by inductively coupled plasma-atomic emission spectrometry (ICPAES). The extent of atmospheric oxidation of chalcopyrite was assessed qualitatively by measuring the increase in the open circuit potential; quantitative estimation was made either by

  6. Influence of acidic surface oxides of activated carbon on gas adsorption characteristics

    Microsoft Academic Search

    H. Tamon; M. Okazaki

    1996-01-01

    An activated carbon was oxidized by HNO3 at boiling temperature. The influence of acidic surface oxides of the activated carbon was experimentally studied on the adsorption characteristics of eleven different gases or vapors. In the adsorption of cyclohexane, benzene, 2-propanol and 2-butanol, the adsorption capacity decreased greatly with oxidizing the carbon by 13.2 N HNO3. This was because the surface

  7. Surface-Modified Carbon Nanotubes Catalyze Oxidative Dehydrogenation of n-Butane

    Microsoft Academic Search

    Jian Zhang; Xi Liu; Raoul Blume; Aihua Zhang; Robert Schlögl; Dang Sheng Su

    2008-01-01

    Butenes and butadiene, which are useful intermediates for the synthesis of polymers and other compounds, are synthesized traditionally by oxidative dehydrogenation (ODH) of n-butane over complex metal oxides. Such catalysts require high O2\\/butane ratios to maintain the activity, which leads to unwanted product oxidation. We show that carbon nanotubes with modified surface functionality efficiently catalyze the oxidative dehydrogenation of n-butane

  8. Atomistic modeling of ultra-thin surface oxide growth on a ternary alloy : oxidation of Al-Ni-Fe.

    SciTech Connect

    Byoungseon, J.; Sankaranarayanan, S. K. R. S.; Ramanathan, S. (Center for Nanoscale Materials); (Harvard Univ.)

    2011-04-14

    By employing variable-charge molecular dynamics, surface oxide film growth on aluminum-nickel-iron alloys has been studied at 300 and 600 K. The dynamics of oxidation and oxide growth is strongly dependent on the composition of the initial alloy and the ambient temperature. Higher content of Ni and Fe in Al alloys is found to reduce the oxide growth kinetics; 15% Ni + 15% Fe Al alloy yielded 30-40% less growth at 400 ps oxygen exposure compared to pure Al. We observe dopant segregation, which disrupts the interaction between O atoms and Al atoms in the alloy, leading to a nonlinear oxide growth profile in the case of ternary Al-Ni-Fe alloy. Compared to oxidation at 300 K, 30% more oxide layer was yielded at 600 K, due to the elevated temperature. The simulated oxide kinetics indicates that the growth rate of anion surpasses the cation rate with higher sensitivity to the stoichiometry of the base metal substrate. Charge state analysis provides insights into the evolution of cation and anion species as the oxide layer grows. In particular, due to higher correlation, Fe shows a high rate of oxidation when the content is high, whereas the rate of Ni oxidation is consistently low. Density profile analysis suggests the segregation of dopant atoms below the growing ultrathin oxide layer, showing the presence of a layer-by-layer mode of oxide layer even with disordered structure. Coordination number (Z, the number of oxygen atoms around an aluminum atom) of aluminum oxide has been used to identify how the initial oxidation transitions into equilibrated states. Z = 3 is dominant in the early stages of oxidation and at the interface between oxide and bulk substrate, but it transitions quickly to Z = 4 (45%) and 5 (35%) as the oxide equilibrates and approaches its self-limiting thickness. Even though growth kinetics is dependent on the base metal stoichiometry, the composition of the oxide microstructure is not significantly affected, primarily segregating dopant elements, i.e., Ni and Fe outside of the oxide layer.

  9. Surface Catalysis and Oxidation on Stagnation Point Heat Flux Measurements in High Enthalpy Arc Jets

    NASA Technical Reports Server (NTRS)

    Nawaz, Anuscheh; Driver, David M.; Terrazas-Salinas

    2013-01-01

    Heat flux sensors are routinely used in arc jet facilities to determine heat transfer rates from plasma plume. The goal of this study is to assess the impact of surface composition changes on these heat flux sensors. Surface compositions can change due to oxidation and material deposition from the arc jet. Systematic surface analyses of the sensors were conducted before and after exposure to plasma. Currently copper is commonly used as surface material. Other surface materials were studied including nickel, constantan gold, platinum and silicon dioxide. The surfaces were exposed to plasma between 0.3 seconds and 3 seconds. Surface changes due to oxidation as well as copper deposition from the arc jets were observed. Results from changes in measured heat flux as a function of surface catalycity is given, along with a first assessment of enthalpy for these measurements. The use of cupric oxide is recommended for future heat flux measurements, due to its consistent surface composition arc jets.

  10. Surface intermediates in selective olefin oxidation and ammoxidation

    SciTech Connect

    Burrington, J.D.; Kartisek, C.T.; Grasselli, R.K.

    1983-02-01

    An investigation of the mechanism of the oxidation and ammoxidation of propylene was made. The products of the above reactions were acrylonitrile and acrolein for ammoxidation and oxidation, respectively. Also, the ammoxidation and oxidation of allyl alcohol, allyl amine, and their allylic deuterium substituted analogues was studied. It was concluded that oxidation and ammoxidation of propylene have the same rate determining step. Other conclusions about the reaction intermediates were also made.

  11. Surface Kinetics of Copper Oxidation Investigated by In Situ Ultra-high Vacuum Transmission Electron Microscopy.

    PubMed

    Yang, Judith C.; Bharadwaj, Mridula D.; Zhou, Guangwen; Tropia, Lori

    2001-11-01

    We review our studies of the initial oxidation stages of Cu(001) thin films as investigated by in situ ultra-high vacuum transmission electron microscopy. We present our observations of surface reconstruction and the nucleation to coalescence of copper oxide during in situ oxidation in O2. We have proposed a semi-quantitative model, where oxygen surface diffusion is the dominant mechanism of the initial oxidation stages of Cu. We have also investigated the effect of water vapor on copper oxidation. We have observed that the presence of water vapor in the oxidizing atmosphere retards the rate of Cu oxidation and Cu2O is reduced when exposed directly to steam. PMID:12597793

  12. Metastable surface oxide on CoGa(100): Structure and stability

    NASA Astrophysics Data System (ADS)

    Vlad, A.; Stierle, A.; Marsman, M.; Kresse, G.; Costina, I.; Dosch, H.; Schmid, M.; Varga, P.

    2010-03-01

    We investigated the structure and formation of a surface oxide and bulk ?-Ga2O3 on CoGa(100) from ultrahigh vacuum to 1 bar oxygen pressure in a temperature range from 300 to 1040 K. We combined in situ surface x-ray diffraction with scanning tunneling microscopy, atomic force microscopy, and density-functional theory calculations. We find that the two-dimensional epitaxial surface oxide layer exhibits a p2mm symmetry with an additional mirror plane as compared to the bulk oxide. The surface oxide layer is found to form under metastable conditions at an oxygen chemical potential ˜1.6eV above the stability limit for bulk ?-Ga2O3 . The formation of the bulk oxide is kinetically hindered by the presence of the oxygen-terminated surface oxide, which most likely hampers dissociative oxygen chemisorption. We observe that below 620 K, the surface oxide is surprisingly stable at 1 bar oxygen pressure. Substrate faceting accompanies the bulk oxide formation at temperatures higher than 1020 K.

  13. Ab initio atomistic thermodynamics study on the oxidation mechanism of binary and ternary alloy surfaces.

    PubMed

    Liu, Shi-Yu; Liu, Shiyang; Li, De-Jun; Wang, Sanwu; Guo, Jing; Shen, Yaogen

    2015-02-14

    Utilizing a combination of ab initio density-functional theory and thermodynamics formalism, we have established the microscopic mechanisms for oxidation of the binary and ternary alloy surfaces and provided a clear explanation for the experimental results of the oxidation. We construct three-dimensional surface phase diagrams (SPDs) for oxygen adsorption on three different Nb-X(110) (X = Ti, Al or Si) binary alloy surfaces. On the basis of the obtained SPDs, we conclude a general microscopic mechanism for the thermodynamic oxidation, that is, under O-rich conditions, a uniform single-phase SPD (type I) and a nonuniform double-phase SPD (type II) correspond to the sustained complete selective oxidation and the non-sustained partial selective oxidation by adding the X element, respectively. Furthermore, by revealing the framework of thermodynamics for the oxidation mechanism of ternary alloys through the comparison of the surface energies of two separated binary alloys, we provide an understanding for the selective oxidation behavior of the Nb ternary alloy surfaces. Using these general microscopic mechanisms, one could predict the oxidation behavior of any binary and multi-component alloy surfaces based on thermodynamics considerations. PMID:25681933

  14. [Surface chemical behavior of 2,4-dichlorophenol in presence of metal oxides].

    PubMed

    Lin, Qi; Wu, Jianyang; Chen, Yingxu; Jin, Haifeng

    2005-04-01

    To understand the surface chemistry of phenolic pollutants in the presence of metal oxides, this paper studied the reactions of 2,4-dichlorophenol with metal oxides in a kinetic and batch experiment. The results showed that amorphous ferric oxyhydroxide, goethite, delta-MnO2 and alpha-MnO2 were the potential oxidizing agents of natural and xenobiotic organic compounds. The oxidation rate of 2,4-DCP on the surface of these metal oxides was in order of delta-MnO2 > alpha-MnO2 > iron oxides. It was observed from the pseudo-first-order kinetics that the reaction rates of manganese oxides were 3-50 times higher than those of iron oxides, and delta-MnO2 had a 1.5-3.2 times higher reaction rate than alpha-MnO2. Root exudates had a significant effect on the oxidation ability of metal oxides through changing the surface characteristics or involving in the reaction process. Upon the addition of ryegrass root exudates, the oxidation of 2,4-DCP was decreased in the suspension of alpha-MnO2 while increased in that of delta-MnO2. The coexistence of Cu probably influenced the oxidation process of 2,4-DCP on the surface of metal oxides. A greater negative effect of Cu on the oxidation of 2,4-DCP was also observed in the suspension of delta-MnO2 due to its strong adsorption toward Cu, as compared with that of alpha-MnO2. PMID:16011168

  15. Chemistry and mineralogy of oxidation products on the surface of the Hoba nickel-iron meteorite

    NASA Astrophysics Data System (ADS)

    Golden, D. C.; Ming, D. W.; Zolensky, M. E.

    1995-07-01

    An oxide layer adjacent to the surface of the Hoba Ni-Fe meteorite was analyzed chemically and mineralogically. Maghemite, magnetite, goethite and lepidocrocite were the main Fe minerals found in the oxide layer surrounding Hoba. Most of the Ni from the unweathered original meteorite was distributed among the above minerals with spinel-type oxides (maghemite and magnetite) having the largest Ni fraction. Some Ni migrated to the limestone in which the meteorite is embedded. No evidence for zaratite or akaganeite was found in the oxide layer. Sulfate derived from the oxidation of troilite precipitated as gypsum. Phosphate accumulation in limestone in contact with the meteorite is probably due to phosphate adsorbed on Fe-oxides. Maghemite with some magnetite was the oxidation product immediately next to the meteorite metal surface, which accommodated most of the Ni and Fe from the meteorite into its structure. Upon oxidation, some of the Ni, which was incorporated into calcite, was released. Cobalt associated with the oxides stayed within the oxide structure regardless of the oxidation state and did not migrate to the limestone. This suggests that Co may be a good tracer for oxides of meteoritic origin.

  16. Electron spectroscopy of single crystal and polycrystalline cerium oxide surfaces

    Microsoft Academic Search

    D. R Mullins; S. H Overbury; D. R Huntley

    1998-01-01

    Valence band photoemission (XPS), valence band electron energy loss spectroscopy (EELS), Ce3d and 4d XPS, O1s XPS and O1s X-ray absorption (XAS) have been investigated for oxidized and sputtered single crystal CeO2 films and for oxidized Ce foil. Features were identified that distinguish between the Ce4+ or Ce3+ oxidation states. Ce4+ was identified by the highest binding energy peaks in

  17. Effect of surface roughness on leakage current and corrosion resistance of oxide layer on AZ91 Mg alloy prepared by plasma electrolytic oxidation

    Microsoft Academic Search

    Bongyoung Yoo; Ki Ryoung Shin; Duck Young Hwang; Dong Heon Lee; Dong Hyuk Shin

    2010-01-01

    The influence of the surface roughness of Mg alloys on the electrical properties and corrosion resistance of oxide layers obtained by plasma electrolytic oxidation (PEO) were studied. The leakage current in the insulating oxide layer was enhanced by increasing the surface roughness, which is a favorable characteristic for the material when applied to hand-held electronic devices. The variation of corrosion

  18. Surface study of the oxidation of type 304L stainless steel at 600 K in air

    SciTech Connect

    Allen, G.C.; Dyke, J.M.; Harris, S.J.; Morris, A.

    1988-06-01

    The oxidation of type 304L stainless steel at 600 K in air was studied using a number of surface-analytical techniques, including Auger electron spectroscopy (AES), scanning electron microscopy with energy-dispersive analysis of X-rays (SEM-EDAX), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS). Spectral analysis showed that a duplex oxide was formed, the outer layer of which formed rapidly and was essentially iron (III) oxide. Beneath this was a mixed iron-chromium oxide. SIMS sputter-profile curves showed region of relatively low iron concentration in the oxide film at the metal-oxide interface. This resulted from the rapid diffusion of iron within the oxide film. The oxide grain boundaries were examined using SEM-EDAX. Higher chromium and silicon levels were detected in these regions compared with the corresponding grain centers. AES indicated the presence of silicon as SiO/sub 2/.

  19. Structure of adsorption layers and conformation transformations of ethylhydroxyethylcellulose on surfaces of titanium and iron oxides

    NASA Astrophysics Data System (ADS)

    Bulychev, N. A.; Fomin, V. N.; Malyukova, E. B.; Ur'ev, N. B.

    2011-01-01

    Regularities of the adsorption of ethylhydroxyethylcellulose (EHEC) hydrophilic polymer on a surface of inorganic pigments of TiO2 and Fe2O3 were investigated by infrared spectroscopy. It was found that the adsorption interaction between EHEC and a surface of oxides is accompanied by conformation transformations of the adsorbed molecules of EHEC. The means by which macromolecules bind with active centers on a surface of metal oxides and the influence of the oxides' nature on the EHEC macromolecule conformation transformations determining the structure of the adsorption layer upon adsorption were established.

  20. The energy evolution of surface plasmons on an oxidized aluminum surface: the role of the atomic polarizability of oxygen adsorbates and the thickness of the oxide layer

    NASA Astrophysics Data System (ADS)

    Li, Jiang-Tao; Parisi, Jason; Wang, Zhen-Bin; Pu, Yi-Kang

    2014-10-01

    The energy evolution of surface plasmons on an aluminum surface during the oxidation process is investigated using electron energy loss spectroscopy (EELS) and x-ray photoemission spectroscopy (XPS). The surface plasmon energy is determined from the location of the surface plasmon loss peak in the EELS spectra; at the same time, the total oxygen coverage (in the submonolayer regime) and the oxide layer thickness (in the multilayer regime) are obtained from the peak profiles of O 1s and Al 2p photoemission lines in the XPS spectra. In the submonolayer regime, the surface plasmon energy slightly decreases with the total oxygen coverage ? when ? ? 1, and the rate of decrease becomes larger as ? increases. This behaviour can be explained by a frequency-dependent polarizability model adopted in this work. In the multilayer regime, the surface plasmon energy decreases with the oxide layer thickness dox, and the rate of decrease becomes smaller as dox increases. The behaviour can be interpreted using a classical electromagnetic model. Based on this model, the relative dielectric constant of the oxide layer should be 3.9 ± 0.1 in the energy range of 7–8.5 eV.

  1. Surface-active products from oxidation of catalytic naphtha and subsequent sulfonation of the oxidation product

    Microsoft Academic Search

    E. A. Drizo; L. A. Gnusareva; G. S. Ushakova; N. A. Gafarova

    1968-01-01

    1.The processes of oxidation of catalytic cracking naphtha and sulfonating the oxidation products have been studied with the objective of preparing flotation agents.2.Optimum oxidation conditions have been found: temperature, 130–135°C; duration, 7–9 h; catalyst, manganese naphthenate in an amount of 1% by wt.; air input, 3.5–4 liters\\/kg per min.3.Optimum conditions of sulfonating the oxidate have been found: temperature during additon

  2. Tailoring the surface properties of Ti6Al4V by controlled chemical oxidation

    E-print Network

    . Many methods have been used to modify surfaces to enhance tissue re- pair events, such as sand activity at the surface of implants, mainly by modifying their topography and physicochemical propertiesTailoring the surface properties of Ti6Al4V by controlled chemical oxidation Fabio Variola a,b , Ji

  3. Vibrational Relaxation of Carbon-Dioxide at Lithium FLUORIDE(100) and Aluminum-Oxide Surfaces

    Microsoft Academic Search

    Jeanne Carol Sawicki

    1989-01-01

    The vibrational relaxation of CO_2 (101) at LiF(100) and aluminum oxide surfaces has been investigated by laser induced fluorescence. For these experiments, carbon dioxide is introduced to a cell, where the cell walls form the surface being studied. Laser radiation passing through the cell prepares the (101) state of the molecule, which subsequently collides with the surface and may lose

  4. Structure Sensitivity of Photochemical Oxidation and Reduction Reactions on SrTiO3 Surfaces

    E-print Network

    Rohrer, Gregory S.

    Structure Sensitivity of Photochemical Oxidation and Reduction Reactions on SrTiO3 Surfaces) on the surface. Mi- croscopic analysis has been used to relate the rates of these two reactions to the structure and the composition of the termination layer does not influence this reaction. On the polar (111) surface

  5. Influence of process conditions on the surface oxidation of silicon nitride green compacts

    Microsoft Academic Search

    S. M. CASTANHO; R MORENO; J. L. G FIERRO

    1997-01-01

    The surface chemistry of silicon nitride is strongly influenced by the processing environment. Mixing and forming steps can modify the oxidation state at the surface of the particle. The aim of the present investigation is to determine the possible changes and interactions on the surface of the particle induced during processing by different techniques of formation, such as isostatic pressing

  6. Durability of self-assembled monolayers on aluminum oxide surface for determining surface wettability

    NASA Astrophysics Data System (ADS)

    Lee, Jaejun; Bong, Jihye; Ha, Young-Geun; Park, Sangyoon; Ju, Sanghyun

    2015-03-01

    The durable non-wettability of functionalized aluminum oxide (Al2O3) thin films coated with two different self-assembled monolayers (SAMs), phosphonic acid (HDF-PA) and trichlorosilane (HDF-S), was investigated by a water flow test method. After exposing the surface to 5 L of water droplets, the contact angle of HDF-S coated Al2O3 thin films remained at the initial value of ?102.7°, while the contact angle of HDF-PA coated Al2O3 thin films decreased from an initial value of ?99.9° to a value of ?69.3°. Thermal annealing effect at various temperature post formation of the self-assembled HDF-PA on the Al2O3 were investigated and shown to enhance the durability of SAMs with a constant contact angle (?100°) annealed at 100-150 °C.

  7. Surface reactions of uranium oxide powder, thin films and single crystals

    NASA Astrophysics Data System (ADS)

    Idriss, H.

    2010-03-01

    The review deals with surface reactions of the complex uranium oxide systems with relevance to catalysis and the environment. After a brief introduction on the properties of uranium oxides, the focus of the review is on surface science studies of defined structures of uranium oxides which are entirely on UO 2 because of the lack of available model on other uranium oxide systems. Powder work is also included as it has given considerable information related to the dynamics between the many phases of uranium oxides. Many chemical reactions are mapped and these include water dissociative adsorption and reaction, CO oxidation and reductive coupling, as well as the reaction of oxygen containing organic compounds such as alcohols, aldehydes, ketones and carboxylic acids in addition to a few examples of sulfur and nitrogen containing compounds.

  8. Methoxychlor and Estradiol Induce Oxidative Stress DNA Damage in the Mouse Ovarian Surface Epithelium

    Microsoft Academic Search

    Daniel A. Symonds; Istvan Merchenthaler; Jodi A. Flaws

    2008-01-01

    Estrogenic compounds such as 17b-estradiol (E2) and methoxy- chlor (MXC) induce oxidative stress damage in breast cells and mouse ovarian follicles, respectively. However, little is known about whether estrogenic compounds cause oxidative stress in the ovarian surface epithelium (OSE). Thus, this work tested the hypothesis that E2 and MXC cause oxidative stress in the OSE. To test this hypothesis, we

  9. Chemical and spectroscopic studies of metal oxide surfaces D. W. Goodman

    E-print Network

    Goodman, Wayne

    Chemical and spectroscopic studies of metal oxide surfaces D. W. Goodman Department of Chemistry Thin oxide films e.g., 5­10 nm of SiO2, Al2O3, NiO, MgO supported on a refractory metal substrate e.g., Mo, W, Ta, Re have been prepared by deposition of the oxide metal precursor in a background of oxygen

  10. Phosphonate-anchored thin films on titanium and niobium oxide surfaces: Fabrication and characterization

    Microsoft Academic Search

    Racheli Adadi; Gilad Zorn; Reuven Brener; Irena Gotman; Elazar Y. Gutmanas; Chaim N. Sukenik

    2010-01-01

    Phosphonate-anchored thin films form on various metal oxide substrates. This paper compares structural details of these covalently anchored films on the oxidized surfaces of titanium, niobium and a Ti45Nb alloy. This is made possible by a sample configuration wherein the alkylphosphonates are coated onto a thin film of metal which is sputtered onto a double-side-polished silicon wafer and then oxidized.

  11. Influence of a Cerium surface treatment on the oxidation behavior of type 347 stainless steel

    SciTech Connect

    Alman, D.E.; Jablonski, P.D.

    2007-04-01

    A surface treatment was applied to the surface of Type 347 stainless steel to enhance oxidation resistance. The treatment consisted of dip coating coupons in a CeO2 and halide activator slurry, followed by a thermal treatment at 900C in an inert atmosphere for 12 hours. Cyclical oxidation tests were conducted at 800C in either dry air or air+3%H2O. In dry air, the treatment reduced the oxidation rate (reduced the magnitude of weight gain) of the alloy by a factor of three. Protective chromium based oxide and spinel ((Mn,Cr)3O4 and (Cr,Fe)2O3) phases formed on the surface of the untreated and treated alloy. More significantly, the treatment suppressed the oxide scale spallation that occurred upon cyclical exposure of this alloy to moist air. In moist air, less protective chromite (FeCr2O4), magnetite (Fe+2Fe2+3O4), and hematite (Fe2O3) formed as oxide products on the surface of the base alloy. The treated alloy did not spall during exposure to moist air, and interestingly, the treated alloy possessed similar oxidation rates (magnitude of weight gain) in both moist and dry air. The same protective chromium based oxide and spinel ((Mn,Cr)3O4 and (Cr,Fe)2O3) phases formed on the surface of the treated alloy exposed to both moist and dry air. In the aggressive moist environment, the Ce surface treatment suppressed the formation of less protective iron-oxides, and concomitant oxide scale spallation during thermal cycling.

  12. The effect of surface oxides on multi-walled carbon nanotube aqueous colloidal properties

    NASA Astrophysics Data System (ADS)

    Smith, Billy

    Carbonaceous nanomaterials are being produced and integrated into consumer products and specialized applications at an accelerating rate. Recently, however, concerns have increased about the environmental, health and safety risks of these nanomaterials, particularly those chemically functionalized to enhance their aqueous colloidal stability and biocompatibility. In this dissertation research, I have investigated the role that surface-oxide concentration plays in the aqueous colloidal stability of multi-walled carbon nanotubes (MWCNTs), a prominent class of engineered nanomaterials. To vary the concentration of surface oxides on the MWCNTs' surface, pristine (unmodified) tubes were treated with a wet-chemical oxidant (e.g., HNO3, H2SO4 /HNO3, KMnO4); the concentration of surface oxides imparted was measured by x-ray photoelectron spectroscopy (XPS). In conjunction with XPS, previously developed chemical derivatization techniques were used to determine the distribution of hydroxyl, carboxyl, and carbonyl functional groups present on the MWCNTs' surface. The length distribution and structural integrity of pristine and oxidized MWCNTs were characterized using atomic force microscopy and transmission electron microscopy, respectively. To examine the aqueous colloidal stability and aggregation properties of oxidized MWCNTs, sedimentation and time-resolved dynamic light scattering (TR-DLS) experiments were conducted on neat (i.e., ideal) suspensions prepared by prolonged sonication of MWCNTs in Milli-Q water. Over a range of environmentally relevant pH values (4--9) and electrolyte (NaCL, CaCl2) concentrations (0.001--1.000 M), the aggregation and colloidal properties of MWCNTs were found to agree with the basic tenants of DLVO theory, in that ( i) more highly oxidized, negatively charged MWCNTs remained stable over a wider range of solution conditions than lowly oxidized tubes, ( ii) oxidized MWCNTs adhered to the empirical Schulze-Hardy rule, and (iii) in early-time aggregation experiments, MWCNTs exhibited reaction- and diffusion-limited aggregation regimes. Structure-property relationships developed during this dissertation research showed that linear correlations existed between MWCNT colloidal stability, XPS measured surface oxidation, and the solution pH. Comparisons between surface charge titrations and electrophoretic mobility (EM) measurements showed that MWCNT colloidal stability was more strongly correlated with surface charge than EM. Analysis of chemical derivatization results indicated that carboxylic functionalities on the MWCNT's surface played a dominate role regulating colloidal stability; however, stronger correlations were observed when colloidal stability was compared to the overall level of surface oxidation. To complement the investigations conducted under ideal solution conditions, the effect that natural organic matter (NOM---an ubiquitous environmental macromolecule) had on the MWCNT's colloidal properties were examined. Before conducting aggregation experiments, a series of NOM adsorption studies were performed. In the first study, NOM adsorption as a function of MWCNT surface oxide concentration was evaluated. Results showed a systematic decrease in NOM adsorption with increasing surface oxidation. In parallel, the sorption of NOM by pristine MWCNTs and a set of highly oxidized tubes was examined under different solution conditions (i.e., pH and ionic strength). NOM adsorption onto pristine MWCNTs was negligibly affected by the solution conditions while NOM sorption by the oxidized MWCNTs increased with increasing ionic strength and decreasing pH. The colloidal stability of MWCNTs was greatly enhanced in the presence of NOM due to steric stabilization, as expected. However, bench top sedimentation and TR-DLS studies indicated that the colloidal stability of lowly oxidized MWCNTs could exceed that of oxidized MWCNTs at environmentally relevant NOM concentrations (˜3 mg/L). Sorption data was used to rationalize these results, in that, because lowly oxidized MWCNTs adsorb more NOM than highly oxidize

  13. Intrinsic stress evolution during amorphous oxide film growth on Al surfaces

    SciTech Connect

    Flötotto, D., E-mail: d.floetotto@is.mpg.de; Wang, Z. M.; Jeurgens, L. P. H. [Max Planck Institute for Intelligent Systems (former Max Planck Institute for Metals Research), Heisenbergstraße 3, D-70569 Stuttgart (Germany); Mittemeijer, E. J. [Max Planck Institute for Intelligent Systems (former Max Planck Institute for Metals Research), Heisenbergstraße 3, D-70569 Stuttgart (Germany); Institute for Materials Science, University of Stuttgart (Germany)

    2014-03-03

    The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al{sub 2}O{sub 3} films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively.

  14. Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides

    E-print Network

    Lee, Wonyoung

    As the oxygen reduction reaction (ORR) becomes more critical for development of solid oxide fuel cells (SOFCs) that operate at 500-700 °C, the correlation between the surface chemistry and electrochemical performance is ...

  15. Electronic structure of perovskite oxide surfaces at elevated temperatures and its correlation with oxygen reduction reactivity

    E-print Network

    Chen, Yan, Ph. D. Massachusetts Institute of Technology

    2014-01-01

    The objective is to understand the origin of the local oxygen reduction reaction (ORR) activity on the basis of the local electronic structure at the surface of transition metal oxides at elevated temperatures and in oxygen ...

  16. Modification of implant material surface properties by means of oxide nano-structured coatings deposition

    NASA Astrophysics Data System (ADS)

    Safonov, Vladimir; Zykova, Anna; Smolik, Jerzy; Rogowska, Renata; Lukyanchenko, Vladimir; Kolesnikov, Dmitrii

    2014-08-01

    The deposition of functional coatings on the metal surface of artificial joints is an effective way of enhancing joint tribological characteristics. It is well-known that nanostructured oxide coatings have specific properties advantageous for future implant applications. In the present study, we measured the high hardness parameters, the adhesion strength and the low friction coefficient of the oxide magnetron sputtered coatings. The corrosion test results show that the oxide coating deposition had improved the corrosion resistance by a factor of ten for both stainless steel and titanium alloy substrates. Moreover, the hydrophilic nature of coated surfaces in comparison with the metal ones was investigated in the tensiometric tests. The surfaces with nanostructured oxide coatings demonstrated improved biocompatibility for in vitro and in vivo tests, attributed to the high dielectric constants and the high values of the surface free energy parameters.

  17. Effects of surface area and oxygen vacancies on ceria in CO oxidation: Differences and relationships

    Microsoft Academic Search

    Yi Liu; Cun Wen; Yun Guo; Guanzhong Lu; Yanqin Wang

    2010-01-01

    Many properties of ceria, such as surface area, defects, and exposed crystal faces, were found to influence the CO oxidation performance of the ceria. Nevertheless, the relations of these properties, which will facilitate the understanding of the catalytic role of ceria in CO oxidation, have not been studied. In this study, the ceria catalysts, HY and CA, were synthesized by

  18. Early detection of oxidized surfaces using Shewanella oneidensis MR1 as a tool

    Microsoft Academic Search

    M. S. Waters; E. C. Salas; S. D. Goodman; F. E. Udwadia; K. H. Nealson

    2009-01-01

    Corrosion is a natural global problem of immense importance. Oxidation of iron and steel not only compromises the structural stability of a widely used and versatile material but it also creates an abrasive compound (iron oxide) that can score the surfaces of metals, rendering them useless for the purpose for which they were designed. Clearly, the identification of corrosion in

  19. A Surface Precipitation Model for the Sorption of Cations on Metal Oxides

    E-print Network

    Morel, François M. M.

    A Surface Precipitation Model for the Sorption of Cations on Metal Oxides KEVIN J. FARLEY, ~ DAVID metallic oxides, as homogeneous phases or more commonly as coatings on other solid particles, are dominant to describethe equilibrium sorption of metal cations on amorphous iron hydroxide is demonstrated. The model can

  20. Chemical modification of carbon fiber surfaces by nitric acid oxidation followed by reaction with tetraethylenepentamine

    Microsoft Academic Search

    C. U. Pittman; G.-R. He; B. Wu; S. D. Gardner

    1997-01-01

    Amino groups react rapidly with both isocyanates and epoxides. Thus, to prepare carbon fibers which might exhibit enhanced adhesion to both polyurethanes and epoxy resin matrices, attempts were made to introduce a high surface amine concentration onto high-strength carbon fibers (derived from PAN) by nitric acid oxidation followed by reaction with excess tetraethylenepentamine (TEPA). Fibers were oxidized with concentrated (70%)

  1. A novel strategy for surface modification of superparamagnetic iron oxide nanoparticles for lung cancer imaging

    E-print Network

    Gao, Jinming

    and targeted therapy of lung cancer. Recently, superparamagnetic nanoparticles (e.g., Fe3O4,3­5 MnFe2O4 6A novel strategy for surface modification of superparamagnetic iron oxide nanoparticles for lung Superparamagnetic iron oxide (SPIO) nanoparticles are widely used in magnetic resonance imaging (MRI) as versatile

  2. Further studies of the effects of oxidation on the surface properties of coal and coal pyrite

    SciTech Connect

    Herrera, M.N.

    1994-12-31

    The objective of this research was to investigate the oxidation behavior of coal and coal pyrite and to correlate the changes in the surface properties induced by oxidation, along with the intrinsic physical and chemical properties of these organic and inorganic materials, with the behavior in physical coal cleaning processes. This provide more fundamental knowledge for understanding the way in which different factors interact in a medium as heterogeneous as coal. Fourteen coal samples of different ranks ranging from high to medium sulfur content were studied by dry oxidation tests at different temperatures and humidities, and by wet oxidation tests using different oxidizing agents. The concentration of surface oxygen functional groups was determined by ion-exchange methods. The changes in the coal composition with oxidation were analyzed by spectroscopic techniques. The wettability of as-received and oxidized coal and coal pyrite samples was assessed by film flotation tests. The electrokinetic behavior of different coals and coal pyrite samples was studied by electrokinetic tests using electrophoresis. Possible oxidation mechanisms have been proposed to explain the changes on the coal surface induced by different oxidation treatments.

  3. Surface Functionalization of Oxide-Covered Zinc and Iron with Phosphonated Phenylethynyl Phenothiazine.

    PubMed

    Rechmann, Julian; Sarfraz, Adnan; Götzinger, Alissa C; Dirksen, Elena; Müller, Thomas J J; Erbe, Andreas

    2015-07-01

    Phenothiazines are redox-active, fluorescent molecules with potential applications in molecular electronics. Phosphonated phenylethynyl phenothiazine can be easily obtained in a four-step synthesis, yielding a molecule with a headgroup permitting surface linkage. Upon modifying hydroxylated polycrystalline zinc and iron, both covered with their respective native oxides, ultrathin organic layers were formed and investigated by use of infrared (IR) reflection spectroscopy, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), contact angle measurement, and ellipsometry. While stable monolayers with upright oriented organic molecules were formed on oxide-covered iron, multilayer formation is observed on oxide-covered zinc. ToF-SIMS measurements reveal a bridging bidentate bonding state of the organic compound on oxide-covered iron, whereas monodentate complexes were observed on oxide-covered zinc. Both organically modified and unmodified surfaces exhibit reactive wetting, but organic modification makes the surfaces initially more hydrophobic. Cyclic voltammetry (CV) indicates redox activity of the multilayers formed on oxide-covered zinc. On the other hand, the monolayers on oxide-covered iron desorb after electrochemical modifications in the state of the oxide, but are stable at open circuit conditions. Exploiting an electronic coupling of phenothiazines to oxides may thus assist in corrosion protection. PMID:26057456

  4. Synthesis and characterization of surface oxide films on CoGa(100)

    NASA Astrophysics Data System (ADS)

    Nerko, Danielle C.; Axnanda, Stephanus; Lofaro, John C.; Zhou, Wei-Ping; White, Michael G.

    2013-10-01

    It has been shown that a Ga2O3 film forms on the surface of CoGa alloy crystals when exposed to oxygen (Pan, 2001 and Vlad, 2010). In this work we report the results of the characterization of surface oxides on CoGa(100) using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and ion scattering spectroscopy (ISS). The oxides were synthesized using either O2 or NO2 as the oxidant at 300 K or in excess of 700 K. ISS scans showed that cobalt was always present in the top surface layer regardless of oxidation conditions. XPS showed that depending on the oxidant and the temperature, the composition of the oxide films vary depending on oxidation treatment, with some oxides being nearly all Ga2O3 and ordered with a sharp LEED pattern consisting of (2 × 1) domains rotated by 90º and others being Co-Ga mixed oxides that gave no diffraction pattern.

  5. Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics. Technical progress report

    SciTech Connect

    Doyle, F.M.

    1995-05-31

    The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical cleaning processes. Work during the nineteenth quarter has concluded studies of the surface functional groups produced on coal by severe thermal and chemical oxidation, and on investigating the partition of metal ions between such strongly oxidized coal samples and aqueous solutions. This partitioning behavior was being followed to obtain further information on the chemistry of the coal surfaces after different oxidation treatments. Adsorption isotherms for the uptake of Cd{sup 2+} on coal oxidized by different methods were obtained, and these and the Cu{sup 2+} adsorption isotherms reported in the last report have been scrutinized, and interpreted more exhaustively. The apparent discrepancies noted in the last report for the analysis of surface functional groups have been investigated further. The adsorption behavior has been related to the surface chemistry of Upper Freeport coal oxidized by different methods.

  6. Surface modifications of iron oxide nanoparticles for biological applications

    E-print Network

    Insin, Numpon

    2011-01-01

    Iron oxides magnetic nanoparticles (MPs) of high crystallinity, high magnetization, and size-monodispersity were synthesized with oleic acid as their native ligands. These hydrophobic and non-functionalized MPs have magnetic ...

  7. Solid State, Surface and Catalytic Studies of Oxides

    SciTech Connect

    Kung, H. H.

    2004-11-23

    This project investigates the catalytic properties of oxides for the selective oxidative dehydrogenation of light alkanes and for hydrocarbon reduction of NO{sub x}. Various vanadium oxide based catalysts were investigated to elucidate the relationship between the chemical and structural properties of the catalysts and their selectivity for the formation of alkenes. It was found that vanadium oxide units that are less reducible give higher selectivities. For hydrocarbon reduction of NO{sub x}, it was found that alumina-based catalysts can be effective at higher temperatures than the corresponding zeolite-based catalysts. On some catalysts, such as SnO{sub 2}/Al{sub 2}O{sub 3}. Ag/Al{sub 2}O{sub 3}, the alumina participates directly in the reaction, making the catalyst bifunctional. These results are useful in research to improve the performance of this stress of catalysts.

  8. Surface Nanocrystallization of 310S Stainless Steel and Its Effect on Oxidation Behavior

    Microsoft Academic Search

    Z. Liu; Y. He; W. Gao

    1998-01-01

    Two techniques, unbalanced magnetron sputter deposition and high-energy short-pulsed plasma discharge, have been used to produce\\u000a a nanocrystalline surface on AISI 310S stainless steel specimens. The\\u000a average grain size after surface modification was estimated as ~100 nm by using atomic force microscopy.\\u000a Cyclic oxidation was performed at 1000C with treated and untreated 310S stainless steel specimens.\\u000a The oxide products formed

  9. Surface nanocrystallization of 310s stainless steel and its effect on oxidation behavior

    Microsoft Academic Search

    Z. Liu; Y. He; W. Gao

    1998-01-01

    Two techniques, unbalanced magnetron sputter deposition and high-energy short-pulsed plasma discharge, have been used to produce\\u000a a nanocrystalline surface on AISI310S stainless steel specimens. The average grain size after surface modification was estimated\\u000a as ?100 nm by using atomic force microscopy. Cyclic oxidation was performed at 1000 ?C with treated and untreated 310S stainless\\u000a steel specimens. The oxide products formed

  10. Growth and surface structure of vanadium oxide on anatase (001)

    Microsoft Academic Search

    Weiwei Gao; Chong M. Wang; Huiqiong Wang; Victor E. Henrich; Eric I. Altman

    2004-01-01

    Oxygen plasma assisted molecular beam epitaxy (OPA-MBE) of vanadium oxide on (1?4)-reconstructed anatase (001) thin films was studied using reflection high energy electron diffraction (RHEED), low energy electron diffraction (LEED), x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), x-ray diffraction (XRD), and transmission electron microscopy (TEM). XPS and UPS results showed that the vanadium was predominantly in the 5+ oxidation

  11. High-Temperature Oxide Regrowth on Mechanically Damaged Surfaces

    Microsoft Academic Search

    Peter Julian Blau; Tracie M Brummett

    2008-01-01

    X-ray elemental maps are used with single-point abrasion tests of a nickel-based superalloy, exposed to air at 850 °C, to\\u000a demonstrate how high-temperature oxidation products form differently on damaged and non-damaged tribosurfaces. These findings\\u000a complement previous work on the nature of sliding combined with oxidation. Results have implications for modeling the wear\\u000a processes of exhaust valves in internal combustion engines.

  12. Adsorption of V on a Hematite (0001) Surface and its Oxidation: Submonolayer Coverage

    SciTech Connect

    Jin, J.; Ma, X.; Kim, C.-Y.; Ellis, D.E.; Bedzyk, M.J. (NWU)

    2008-10-06

    The adsorption of submonolayer V on an idealized model hematite (0 0 0 1) surface and subsequent oxidation under atomic O adsorption are studied by density functional theory. The preferred adsorption sites, adsorption energy and configuration changes due to V and O adsorption are investigated. It is found that in most cases V forms threefold bonds with surface O atoms, inducing a large geometry change at the hematite surface and near surface region and a bond stretch between surface Fe and O. The adsorption energy is mainly decided by interplay between adsorbed metal-surface oxygen bonding and adsorbed metal - subsurface metal interaction. The relative energy of subsequent O adsorption and geometry depends on the reformed V/hematite structure. Electronic properties such as projected densities of states and chemical state change upon V adsorption are studied through both periodic slab and embedded cluster localized orbital calculations; both strong vanadium-oxygen and vanadium-iron interactions are found. While V generally donates electrons to a hematite surface, causing nearby Fe to be partially reduced, the Fe and V oxidization state depends very much on the coverage and detailed adsorption configuration. When the V/hematite system is exposed to atomic O, V is further oxidized and surface/near surface Fe is re-oxidized. Our theoretical results are compared with X-ray surface standing wave and X-ray photoelectron spectroscopic measurements. The influence of d-electron correlation on the predicted structures is briefly discussed, making use of the DFT + U scheme.

  13. Oxide contacts in organic photovoltaics: characterization and control of near-surface composition in indium-tin oxide (ITO) electrodes.

    PubMed

    Armstrong, Neal R; Veneman, P Alex; Ratcliff, Erin; Placencia, Diogenes; Brumbach, Michael

    2009-11-17

    The recent improvements in the power conversion efficiencies of organic photovoltaic devices (OPVs) promise to make these technologies increasingly attractive alternatives to more established photovoltaic technologies. OPVs typically consist of photoactive layers 20-100 nm thick sandwiched between both transparent oxide and metallic electrical contacts. Ideal OPVs rely on ohmic top and bottom contacts to harvest photogenerated charges without compromising the power conversion efficiency of the OPV. Unfortunately, the electrical contact materials (metals and metal oxides) and the active organic layers in OPVs are often incompatible and may be poorly optimized for harvesting photogenerated charges. Therefore, further optimization of the chemical and physical stabilities of these metal oxide materials with organic materials will be an essential component of the development of OPV technologies. The energetic and kinetic barriers to charge injection/collection must be minimized to maximize OPV power conversion efficiencies. In this Account, we review recent studies of one of the most common transparent conducting oxides (TCOs), indium-tin oxide (ITO), which is the transparent bottom contact in many OPV technologies. These studies of the surface chemistry and surface modification of ITO are also applicable to other TCO materials. Clean, freshly deposited ITO is intrinsically reactive toward H(2)O, CO, CO(2), etc. and is often chemically and electrically heterogeneous in the near-surface region. Conductive-tip atomic force microscopy (C-AFM) studies reveal significant spatial variability in electrical properties. We describe the use of acid activation, small-molecule chemisorption, and electrodeposition of conducting polymer films to tune the surface free energy, the effective work function, and electrochemical reactivity of ITO surfaces. Certain electrodeposited poly(thiophenes) show their own photovoltaic activity or can be used as electronically tunable substrates for other photoactive layers. For certain photoactive donor layers (phthalocyanines), we have used the polarity of the oxide surface to accelerate dewetting and "nanotexturing" of the donor layer to enhance OPV performance. These complex surface chemistries will make oxide/organic interfaces one of the key focal points for research in new OPV technologies. PMID:19728725

  14. Metal pulled-off effect: A unique explanation of different oxidation process on Cu and Al surfaces

    NASA Astrophysics Data System (ADS)

    Zhu, Junyi; Kang, Joongoo; Wei, Su-Huai

    2012-02-01

    One interesting oxidation phenomenon is the difference of the oxidation of Cu and Al. Cu forms disordered domains, large surface reconstructions and oxide islands on the surface with some O atoms diffuse into inner layers to further oxidize inner Cu atoms. Al forms a dense oxide layer which protects the inner Al atoms from oxidation. In this talk, we demonstrate a possible electronic origin of this oxidation difference by using the first-principles method to calculate the initial oxidation of different metal surfaces and nanoclusters. On Cu 55 Icosahedron surface, we found that 2 O atoms at neighboring sites form a structure with a Cu atom in the middle pulled off from the surface. We also found the similar pull-offs on Cu, Pd, Zn surfaces, but not on Al surface, which is not a transition metal. This pulled off effect is explained by the strong metal d and O p coupling. We also checked different O concentration on Cu (111) surface and on Cu cluster surface and found that O atoms form chain or ring like structures. Our first principle molecular dynamic calculation confirms that these structures are stable. With this pull-off effect, additional O atoms can further oxidize inner Cu atoms and make Cu relative easy to oxidize. This finding enhances the scientific understanding of the initial oxidation of metallic nano-particles and surfaces, which may have important applications in catalysis, thermal storage and other surface science fields.

  15. Characterization of oxide on the water-atomized FeMn powder surface

    NASA Astrophysics Data System (ADS)

    Long, An Ping; Li, Song Lin; Wang, Hang; Chen, HuiZhu

    2014-03-01

    The characterization of surface oxides composition and the depth distribution of oxides in water-atomized steel powder is vital to adjust the reduction condition for sufficient removal of the oxides. To systematically analyze the composition, depth distribution and morphology of surface oxides in water-atomized low alloy steel powder containing manganese (0.3 wt.%), X-ray photoelectron spectroscopy (XPS) combined with Ar-cluster-ion sputtering, X-ray diffraction (XRD), scanning electron microscope (SEM) and energy disperse spectroscopy (EDS) were utilized. The results show that surface oxygen exists in the form of "Oxides Island", and the surface oxygen content is much higher than the bulk. In the unreduced powder, the oxygen-rich surface layer contains 67% of total oxygen within a depth of 1800 nm (0.072R, R denotes the radius of the powder); while for the reduced powder, the oxygen-rich surface layer contains 28% of the total oxygen in the powder within a depth of 80 nm (0.0032R). The oxygen depth distribution curves fit well with exponential decay function as Y = f(x) = A1exp(- x/t1) + A2exp(- x/t2) + y0. The oxides mainly exist in the forms of ?-Fe2O3, FeO, Mn2O3 and MnO in the unreduced powder and ?-Fe2O3, FeO, Mn2O3 in the reduced powder.

  16. Characterization of surface-modified ceria oxide nanoparticles synthesized continuously in supercritical methanol

    Microsoft Academic Search

    Bambang Veriansyah; Jae-Duck Kim; Byoung Koun Min; Young Ho Shin; Youn-Woo Lee; Jaehoon Kim

    2009-01-01

    Surface-modified ceria oxide (CeO2) nanoparticles were synthesized continuously in supercritical methanol at 400°C, 30MPa and a residence time of ?40s using a flow type reactor system. Oleic acid and decanoic acid were used as the surface modifiers. Transmission electron microscopy (TEM) showed that the surface modifiers changed drastically the shape and size of the nanoparticles. When 0.3M of the surface

  17. Continuous synthesis of surface-modified zinc oxide nanoparticles in supercritical methanol

    Microsoft Academic Search

    Bambang Veriansyah; Jae-Duck Kim; Byoung Koun Min; Young Ho Shin; Youn-Woo Lee; Jaehoon Kim

    2010-01-01

    Continuous synthesis of surface-modified zinc oxide (ZnO) nanoparticles was examined using surface modifiers (oleic acid and decanoic acid) in supercritical methanol at 400°C, 30MPa and a residence time of ?40s. Wide angle X-ray diffraction (WAXD) analysis revealed that the surface-modified nanoparticles retained ZnO crystalline structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the surface modifiers changed

  18. Theoretical studies of positron states and annihilation characteristics at the oxidized Cu(100) surface

    SciTech Connect

    Fazleev, N. G. [Department of Physics, Box 19059, University of Texas at Arlington, Arlington Texas 76019 (United States) and Institute of Physics, Kazan Federal University, Kremlevskaya18, Kazan 420008 (Russian Federation); Weiss, A. H. [Department of Physics, Box 19059, University of Texas at Arlington, Arlington Texas 76019 (United States)

    2013-04-19

    In this work we present the results of theoretical studies of positron surface and bulk states and annihilation probabilities of surface-trapped positrons with relevant core electrons at the oxidized Cu(100) surface under conditions of high oxygen coverage. An ab-initio study of the electronic properties of the Cu(100) missing row reconstructed surface at various on surface and sub-surface oxygen coverages has been performed on the basis of the density functional theory (DFT) using the Dmol3 code and the generalized gradient approximation (GGA). Surface structures in calculations have been constructed by adding oxygen atoms to various surface hollow and sub-surface octahedral sites of the 0.5 monolayer (ML) missing row reconstructed phase of the Cu(100) surface with oxygen coverages ranging from 0.5 to 1.5 ML. The charge redistribution at the surface and variations in atomic structure and chemical composition of the topmost layers associated with oxidation and surface reconstruction have been found to affect the spatial extent and localization of the positron surface state wave function and annihilation probabilities of surface trapped positrons with relevant core electrons. Theoretical results are compared with experimental data obtained from studies of oxidation of the Cu(100) surface using positron annihilation induced Auger electron spectroscopy (PAES). It has been shown that positron annihilation probabilities with Cu 3s and 3p core electrons decrease when total (on-surface and sub-surface) oxygen coverage of the Cu(100) surface increases up to 1 ML. The calculations show that for high oxygen coverage when total oxygen coverage is 1. 5 ML the positron is not bound to the surface.

  19. Facile surface PEGylation via tyrosinase-catalyzed oxidative reaction for the preparation of non-fouling surfaces.

    PubMed

    Lee, Yunki; Park, Kyung Min; Bae, Jin Woo; Park, Ki Dong

    2013-02-01

    The control of biological interactions that occur at material-cell/blood interfaces is of great importance to help maximize in vitro and in vivo performance of biomedical devices. PEGylation has been extensively used as an effective surface modification tool that can alter biological responses on device surfaces. Herein, we report a new surface PEGylation method using a tyrosinase-catalyzed oxidative reaction. Tyramine (TA), an enzymatically active phenolic compound, was chemically conjugated to methoxy poly(ethylene glycol) (mPEG). Surface immobilization of mPEG-TA onto various substrates was accomplished simply and rapidly by adding tyrosinase under mild conditions. It was shown that the water contact angles on all surfaces modified with mPEG-TA were decreased, indicating successful introduction of hydrophilic PEG. In addition, the X-ray photoelectron spectroscopy (XPS) spectra demonstrated the differences in the atomic composition on the TiO(2) surface after treatment with mPEG-TA. Non-fouling surfaces prevent non-specific interactions with proteins and cells; consistently, the PEGylated TiO(2) surface clearly showed a decrease in both levels of bovine serum albumin (BSA) adsorption and NIH3T3 cell attachment. Therefore, the facile surface PEGylation using a tyrosinase-catalyzed oxidative reaction should be useful for designing non-fouling surfaces of biomedical devices. PMID:23104029

  20. Surface oxide on thin films of yttrium hydride studied by neutron reflectometry

    NASA Astrophysics Data System (ADS)

    Mongstad, T.; Platzer-Björkman, C.; Mæhlen, J. P.; Hauback, B. C.; Karazhanov, S. Zh.; Cousin, F.

    2012-05-01

    The applicability of standard methods for compositional analysis is limited for H-containing films. Neutron reflectometry is a powerful, non-destructive method that is especially suitable for these systems due to the large negative scattering length of H. In this work, we demonstrate how neutron reflectometry can be used to investigate thin films of yttrium hydride. Neutron reflectometry gives a strong contrast between the film and the surface oxide layer, enabling us to estimate the oxide thickness and oxygen penetration depths. A surface oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride films.

  1. High-Resolution Electron Energy Loss Studies of Oxygen, Hydrogen, Nitrogen, Nitric Oxide, and Nitrous Oxide Adsorption on Germanium Surfaces.

    NASA Astrophysics Data System (ADS)

    Entringer, Anthony G.

    The first high resolution electron energy loss spectroscopy (HREELS) studies of the oxidation and nitridation of germanium surfaces are reported. Both single crystal Ge(111) and disordered surfaces were studied. Surfaces were exposed to H, O_2, NO, N _2O, and N, after cleaning in ultra-high vacuum. The Ge surfaces were found to be non-reactive to molecular hydrogen (H_2) at room temperature. Exposure to atomic hydrogen (H) resulted hydrogen adsorption as demonstrated by the presence of Ge-H vibrational modes. The HREEL spectrum of the native oxide of Ge characteristic of nu -GeO_2 was obtained by heating the oxide to 200^circC. Three peaks were observed at 33, 62, and 106 meV for molecular oxygen (O_2) adsorbed on clean Ge(111) at room temperature. These peaks are indicative of dissociative bonding and a dominant Ge-O-Ge bridge structure. Subsequent hydrogen exposure resulted in a shift of the Ge-H stretch from its isolated value of 247 meV to 267 meV, indicative of a dominant +3 oxidation state. A high density of dangling bonds and defects and deeper oxygen penetration at the amorphous Ge surface result in a dilute bridge structure with a predominant +1 oxidation state for similar exposures. Molecules of N_2O decompose at the surfaces to desorbed N_2 molecules and chemisorbed oxygen atoms. In contrast, both oxygen and nitrogen are detected at the surfaces following exposure to NO molecules. Both NO and N_2O appear to dissociate and bond at the top surface layer. Molecular nitrogen (N_2) does not react with the Ge surfaces, however, a precursor Ge nitride is observed at room temperature following exposure to nitrogen atoms and ions. Removal of oxygen by heating of the NO-exposed surface to 550^circC enabled the identification of the Ge-N vibrational modes. These modes show a structure similar to that of germanium nitride. This spectrum is also identical to that of the N-exposed surface heated to 550^circC. Surface phonon modes of the narrow-gap semiconducting compounds Mg _2Sn, Mg_2Ge and Mg _2Si were detected at 29, 32, and 40 meV, respectively. The native oxide of all three show a dominant Mg-O mode at 80 meV. Probable Sn-O, Ge-O, and Si-O modes are also identified. Complete removal of the oxide layer was accomplished only on the Mg_2 Si surface but resulted in no noticeable change in the energy of the surface phonon. Results are compared to the known bulk optical properties of these compounds.

  2. Fe(VI) as a Possible Oxidant on the Martian Surface

    NASA Technical Reports Server (NTRS)

    Tsapin, A. I.; Goldfeld, M. G.; McDonald, G. D.; Nealson, K. H.

    1999-01-01

    The essential findings of the three biological experiments (Gas Exchange, Labeled Released, and Pyrolitic Release) aboard the Viking Mars landers were the discovery of the presence of one or more strong oxidants on the Martian surface. The Gas Exchange experiments showed that wetting Martian soil leads to the evolution of oxygen, while in the Labeled Release experiment addition of a nutrient solution containing C-14-labeled formate, glycine, lactate, alanine, and glycolic acid induced CO2 evolution. A general consensus was reached that all data taken together pointed to the presence on Martian surface of a strong oxidant, or most probably several different types of oxidants. Several candidates have been proposed as oxidants, including superoxides, hydrogen peroxide, and iron oxides (possibly gamma-Fe2O3). Additional information is contained in the original extended abstract.

  3. Modification on surface oxide layer structure and surface morphology of niobium by gas cluster ion beam treatments

    SciTech Connect

    A. T. Wu, D. R. Swenson, Z. Insepov

    2010-09-01

    Recently, it was demonstrated that significant reductions in field emission on Nb surfaces could be achieved by means of a new surface treatment technique called gas cluster ion beam (GCIB). Further study as shown in this paper revealed that GCIB treatments could modify surface irregularities and remove surface asperities leading to a smoother surface finish as demonstrated through measurements using a 3D profilometer, an atomic force microscope, and a scanning electron microscope. These experimental observations were supported by computer simulation via atomistic molecular dynamics and a phenomenological surface dynamics. Measurements employing a secondary ion mass spectrometry found that GCIB could also alter Nb surface oxide layer structure. Possible implications of the experimental results on the performance of Nb superconducting radio frequency cavities treated by GCIB will be discussed. First experimental results on Nb single cell superconducting radio frequency cavities treated by GCIB will be reported.

  4. Surface-catalyzed air oxidation reactions of hydrazines: Tubular reactor studies

    NASA Technical Reports Server (NTRS)

    Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

    1988-01-01

    The surface-catalyzed air oxidation reactions of hydrazine, monomethylhydrazine, unsymmetrical dimethylhydrazine, symmetrical dimethylhydrazine, trimethylhydrazine and tetramethylhydrazine were investigated in a metal-powder packed turbular flow reactor at 55 plus or minus 3 C. Hydrazine was completely reacted on all surfaces studied. The major products of monomethylhydrazine (MMH) oxidation were methanol, methane and methyldiazene. The di-, tri- and tetra-methyl hydrazines were essentially unreactive under these conditions. The relative catalytic reactivities toward MMH are: Fe greater than Al2O3 greater than Ti greater than Zn greater than 316 SS greater than Cr greater than Ni greater than Al greater than 304L SS. A kinetic scheme and mechanism involving adsorption, oxidative dehydrogenation and reductive elimination reactions on a metal oxide surface are proposed.

  5. Surface nanocrystallization of 310S stainless steel and its effect on oxidation behavior

    SciTech Connect

    Liu, Z.; He, Y.; Gao, W. [Univ. of Auckland (New Zealand). Dept. of Chemical and Materials Engineering] [Univ. of Auckland (New Zealand). Dept. of Chemical and Materials Engineering

    1998-02-01

    Two techniques, unbalanced magnetron sputter deposition and high-energy short-pulsed plasma discharge, have been used to produce a nanocrystalline surface on AISI 310S stainless steel specimens. The average grain size after surface modification was estimated as {approximately} 100 nm by using atomic force microscopy. Cyclic oxidation was performed at 1,000 C with treated and untreated 310S stainless steel specimens. The oxide products formed on the specimens consisted of an outer spinel layer that was rich in chromium, iron, manganese, and nickel, and an inner chromium-rich layer. It was found that the concentrations of iron and manganese in the outer layer of treated specimens were higher, and adherence of the scale was better in the treated specimens. The observed oxidation behavior can be explained by the increase of the creep diffusion rate in the fine oxide scale formed on the nanocrystalline surfaces.

  6. Surface nanocrystallization of 310s stainless steel and its effect on oxidation behavior

    NASA Astrophysics Data System (ADS)

    Liu, Z.; He, Y.; Gao, W.

    1998-02-01

    Two techniques, unbalanced magnetron sputter deposition and high-energy short-pulsed plasma discharge, have been used to produce a nanocrystalline surface on AISI310S stainless steel specimens. The average grain size after surface modification was estimated as ˜100 nm by using atomic force microscopy. Cyclic oxidation was performed at 1000 °C with treated and untreated 310S stainless steel specimens. The oxide products formed on the specimens consisted of an outer spinel layer that was rich in chromium, iron, manganese, and nickel, and an inner chromium-rich layer. It was found that the concentrations of iron and manganese in the outer layer of treated specimens were higher, and adherence of the scale was better in the treated specimens. The observed oxidation behavior can be explained by the increase of the creep diffusion rate in the fine oxide scale formed on the nanocrystalline surfaces.

  7. Oxygen adsorption and stability of surface oxides on Cu(111) : A first-principles investigation

    NASA Astrophysics Data System (ADS)

    Soon, Aloysius; Todorova, Mira; Delley, Bernard; Stampfl, Catherine

    2006-04-01

    As a first step towards gaining microscopic understanding of copper-based catalysts, e.g., for the low-temperature water-gas shift reaction and methanol oxidation reactions, we present density-functional theory calculations investigating the chemisorption of oxygen, and the stability of surface oxides on Cu(111) . We report atomic geometries, binding energies, and electronic properties for a wide range of oxygen coverages, in addition to the properties of bulk copper oxide. Through calculation of the Gibbs free energy, taking into account the temperature and pressure via the oxygen chemical potential, we obtain the (p,T) phase diagram of O/Cu(111) . Our results show that for the conditions typical of technical catalysis the bulk oxide is thermodynamically most stable. If, however, formation of this fully oxidized surface is prevented due to a kinetic hindering, a thin surface-oxide structure is found to be energetically preferred compared to chemisorbed oxygen on the surface, even at very low coverage. Similarly to the late 4d transition metals (Ru, Rh, Pd, Ag), sub-surface oxygen is found to be energetically unfavorable.

  8. Oxygen diffusion at surface reduction in catalysts for selective oxidation

    Microsoft Academic Search

    O. Yu. Ovsitser; V. D. Sokolovskii

    1993-01-01

    The coefficient of oxygen diffusion and the activation energy for diffusion have been measured for the series of oxide catalysts of selective oxidation of organic compounds (Sm-Mg-O, Sm-O; V-P-O, Sn-Sb-O, Sn-Bi-O, Fe-Sb-O, Bi-Sb-O). The rates of oxygen diffusion under catalytic conditions have been compared with the reaction rates. For all studied systems (except Sm-O and Sm-Mg-O) at optimal operative temperatures

  9. Interaction of Fe(II) with phosphate and sulfate on iron oxide surfaces

    NASA Astrophysics Data System (ADS)

    Hinkle, Margaret A. G.; Wang, Zimeng; Giammar, Daniel E.; Catalano, Jeffrey G.

    2015-06-01

    Sulfate and phosphate, oxoanions common in natural systems, affect iron oxide growth and dissolution processes, the adsorption behavior of divalent cations, and iron oxide phase transformations. These oxoanions may thus influence Fe(II) adsorption behavior and subsequently alter the mechanisms and products of Fe(II)-catalyzed Fe(III) oxide recrystallization processes, such as trace metal repartitioning. In this study, the macroscopic and molecular-scale effects of the coadsorption of Fe(II) and sulfate or phosphate onto Fe(III) oxide surfaces were investigated. Macroscopic adsorption edges show that both sulfate and phosphate increase Fe(II) adsorption and that Fe(II) increases sulfate and phosphate adsorption. Attenuated total reflectance Fourier transform infrared spectroscopy shows that the cooperative adsorption behavior of oxoanions and aqueous Fe(II) likely results from a combination of ternary complexation and electrostatic interactions. Surface complexation modeling requires the inclusion of ternary complexes to simulate all conditions of the macroscopic data, further suggesting that these oxoanions and Fe(II) form ternary complexes on Fe(III) oxide surfaces. Despite clear evidence in previous research for Fe(II) oxidation upon adsorption on iron oxide surfaces, this work shows that Fe(II) also displays macroscopic and molecular-scale behaviors associated with divalent (i.e., non-oxidative) cation adsorption. Prior work has shown that metal release from iron oxides caused by ET-AE reactions is directly proportional to the macroscopically-determined Fe(II) surface coverage. Predicting the effects of sulfate and phosphate on processes controlled by ET-AE reactions at redox interfaces, such as mineral phase transformations and trace element repartitioning, may thus not require the explicit consideration of electron transfer processes.

  10. Interaction mechanisms of near-surface quantum wells with oxidized and H-passivated AlGaAs surfaces

    NASA Astrophysics Data System (ADS)

    Emiliani, V.; Bonanni, B.; Presilla, C.; Capizzi, M.; Frova, A.; Chang, Ying-Lan; Tan, I.-Hsing; Merz, J. L.; Colocci, M.; Gurioli, M.

    1994-05-01

    The tunneling mechanism of electrons and holes to surface states from near-surface Al0.3Ga0.7As/GaAs quantum wells has been investigated by steady-state and time-resolved photoluminescence spectroscopy, near liquid-helium temperature, of the excitonic e1-hh1 transition in the well. The ensemble of the data, taken over a wide range of optical excitation levels, for various values of the tunneling-barrier thickness, and before and after passivation of the surface by hydrogen, allows a description both of the details of the tunneling mechanism and of the character and behavior of relevant surface states. The main results are summarized as follows: (i) steady-state tunneling is ambipolar, namely, separate for electrons and holes, rather than excitonic; (ii) Spicer's advanced unified defect model for an oxidized GaAs surface, antisite-As donors as dominating surface traps, provides an appropriate description of the state distribution at the interface between AlGaAs and its oxide; (iii) hole accumulation in surface states, resulting from the nominally different unipolar tunneling probability for the two carriers (and increasing with excitation level), generates a dipole electric field across the tunneling barrier, extending into the well; (iv) hydrogenation efficiently passivates electron trapping in surface states, but not hole tunneling and the consequent generation of a surface field by illumination; (v) the experimental findings agree with a model for ambipolar tunneling based on a self-consistent quantum-mechanical approach.

  11. FT-IR study of the adsorption and transformation of formaldehyde on oxide surfaces

    SciTech Connect

    Busca, G.; Lamotte, J.; Lavalley, J.C.; Lorenzelli, V.

    1987-08-19

    The adsorption of formaldehyde on different oxides (silica, pure and fluorided alumina, magnesia, titania, thoria, zirconia, and iron oxide) has been studied by FT-IR spectroscopy in the temperature range 170-570 K. The following adsorbed species have been identified and characterized spectroscopically: (i) physisorbed HCHO, (ii) coordinated HCHO, (iii) dioxymethylene, (iv) polyoxymethylene, (v) formate ions, and (vi) methoxy groups. On silica at 170 K formaldehyde physisorbs on surface OH groups and, by warming, polymerizes producing linear polyoxymethylene. On ionic oxides at about 250 K dioxymethylene is always observed, generally together with variable amounts of the linear polymer that has been isolated on magnesia at 170 K. Heating up to or above room temperature results in the disproportionation of dioxymethylene into formate and methoxide groups, probably via a Cannizzaro-type mechanism. Such a route probably parallels an oxidative route, involving direct oxidation of dioxymethylene into formates, as observed on iron oxide.

  12. Surface modification of silicon oxide with trialkoxysilanes toward close-packed monolayer formation.

    PubMed

    Tanaka, Mutsuo; Sawaguchi, Takahiro; Kuwahara, Masashi; Niwa, Osamu

    2013-05-28

    In order to scrutinize potential of trialkoxysilanes to form close-packed monolayer, surface modification of silicon oxide was carried out with the trialkoxysilanes bearing a ferrocene moiety for analysis by electrochemical methods. As it was found that hydrogen-terminated silicon reacts with trialkoxysilane through natural oxidation in organic solvents, where the silicon oxide layer is thin enough to afford conductivity for electrochemical analysis, hydrogen-terminated silicon wafer was immersed in trialkoxysilane solution for surface modification without oxidation treatment. Cyclic voltammetry measurements to determine surface concentrations of the immobilized ferrocene-silane on silicon surface were carried out with various temperature, concentration, solvent, and molecular structure, while the blocking effect in the cyclic voltammogram was investigated to obtain insight into density leading to the close-packed layer. The results suggested that a monolayer modification tended to occur under milder conditions when the ferrocene-silane had a longer alkyl chain, and formation of a close-packed layer to show significant blocking effect was observed. However, the surface modification proceeded even when surface concentration of the immobilized ferrocene-silane was greater than that expected for the monolayer. On the basis of these tendencies, the surface of silicon oxide modified with trialkoxysilane is considered to be a partial multilayer rather than monolayer although a close-packed layer is formed. This result is supported by the comparison with carbon surface modified with ferrocene-diazonium, in which a significant blocking effect was observed when surface concentrations of the immobilized ferrocene moiety are lower than that for silicon oxide modified with ferrocene-silane. PMID:23668922

  13. Antibacterial Efficacy of Iron-Oxide Nanoparticles against Biofilms on Different Biomaterial Surfaces

    PubMed Central

    Thukkaram, Monica; Sitaram, Soundarya; Kannaiyan, Sathish kumar; Subbiahdoss, Guruprakash

    2014-01-01

    Biofilm growth on the implant surface is the number one cause of the failure of the implants. Biofilms on implant surfaces are hard to eliminate by antibiotics due to the protection offered by the exopolymeric substances that embed the organisms in a matrix, impenetrable for most antibiotics and immune cells. Application of metals in nanoscale is considered to resolve biofilm formation. Here we studied the effect of iron-oxide nanoparticles over biofilm formation on different biomaterial surfaces and pluronic coated surfaces. Bacterial adhesion for 30?min showed significant reduction in bacterial adhesion on pluronic coated surfaces compared to other surfaces. Subsequently, bacteria were allowed to grow for 24?h in the presence of different concentrations of iron-oxide nanoparticles. A significant reduction in biofilm growth was observed in the presence of the highest concentration of iron-oxide nanoparticles on pluronic coated surfaces compared to other surfaces. Therefore, combination of polymer brush coating and iron-oxide nanoparticles could show a significant reduction in biofilm formation. PMID:25332720

  14. CO Oxidation on the Pd(111) Surface Zhiyao Duan and Graeme Henkelman*

    E-print Network

    Henkelman, Graeme

    . INTRODUCTION Pd is a widely used catalyst in catalytic converters for the oxidation of CO and unburnt fuel catalytically relevant gas-phase conditions. Three-fold oxygen atoms in the surface are found to react with gas, will dramatically influence the catalytic reaction mechanism. Due to the complex nature of the catalyst surface

  15. Diphosphine Dioxide Cages and Hydrogen Peroxide Adducts of Phosphine Oxides: Syntheses and Applications in Surface Science

    E-print Network

    Hilliard, Casie Renee

    2013-12-09

    the P=O group for probing the surface acidity of oxides. (c) Most importantly, getting more insight regarding the nature of the P=O/surface interaction. Hereby, the mobility of the adsorbed species is of fundamental interest. In the classical 31P MAS...

  16. The influence of titanium oxide nanocoatings on the surface quality of glass products for electronic devices

    Microsoft Academic Search

    A. A. Malkov; E. A. Sosnov; A. A. Malygin; N. A. Kulikov; G. L. Brusilovsky; E. G. Kalinikos

    2006-01-01

    The formation of a defect-free continuous titanium oxide coating on the surface of borosilicate glass in the course of synthesis\\u000a by the molecular layering method is revealed using atomic-force microscopy. This coating ensures a significant decrease in\\u000a the roughness of the initial surface.

  17. ADSORPTION OF ASPHALT FUNCTIONALITIES AND OXIDIZED ASPHALTS ON AGGREGATE SURFACES

    Microsoft Academic Search

    Christine W. Curtis; Young Woong Jeon; Douglas J. Clapp

    1989-01-01

    The adsorption of asphalt functionalities and asphalt oxidized to different degrees on real and model aggregates has been investigated. The functionalities used were: nitrogen-base, phenolic, carboxylic acid, ester, ketone, sulfoxide, and polynuclear aromatic. Adsorption isotherms of these functionalities on porous silica showed different affinity rankings dependent upon concentration. The competitive affinity ranking of the asphalt functionalities on dried silica was

  18. Shape-selective sieving layers on an oxide catalyst surface

    NASA Astrophysics Data System (ADS)

    Canlas, Christian P.; Lu, Junling; Ray, Natalie A.; Grosso-Giordano, Nicolas A.; Lee, Sungsik; Elam, Jeffrey W.; Winans, Randall E.; van Duyne, Richard P.; Stair, Peter C.; Notestein, Justin M.

    2012-12-01

    New porous materials such as zeolites, metal-organic frameworks and mesostructured oxides are of immense practical utility for gas storage, separations and heterogeneous catalysis. Their extended pore structures enable selective uptake of molecules or can modify the product selectivity (regioselectivity or enantioselectivity) of catalyst sites contained within. However, diffusion within pores can be problematic for biomass and fine chemicals, and not all catalyst classes can be readily synthesized with pores of the correct dimensions. Here, we present a novel approach that adds reactant selectivity to existing, non-porous oxide catalysts by first grafting the catalyst particles with single-molecule sacrificial templates, then partially overcoating the catalyst with a second oxide through atomic layer deposition. This technique is used to create sieving layers of Al2O3 (thickness, 0.4-0.7 nm) with ‘nanocavities’ (<2 nm in diameter) on a TiO2 photocatalyst. The additional layers result in selectivity (up to 9:1) towards less hindered reactants in otherwise unselective, competitive photocatalytic oxidations and transfer hydrogenations.

  19. Surface modification of zinc oxide nanoparticles by aminopropyltriethoxysilane

    Microsoft Academic Search

    F Grasset; N Saito; D Li; I Sakaguchi; N Ohashi; H Haneda; T Roisnel; S Mornet; E Duguet

    2003-01-01

    Commercial zinc oxide nanoparticles (20–30 nm) were coated by aminopropyltriethoxysilane (APTES) under varying environments. Three different processes, acidic, basic and toluene were used. The effects of coating conditions (acidic, basic and toluene) on the grafting, structural and optical properties of these nanoparticles were studied. In the three cases, it was possible to control the coating and according to X-ray diffraction,

  20. Aqueous phase deposition of dense tin oxide films with nano-structured surfaces

    SciTech Connect

    Masuda, Yoshitake, E-mail: masuda-y@aist.go.jp; Ohji, Tatsuki; Kato, Kazumi

    2014-06-01

    Dense tin oxide films were successfully fabricated in an aqueous solution. The pH of the solutions was controlled to pH 1.3 by addition of HCl. Precise control of solution condition and crystal growth allowed us to obtain dense tin oxide films. Concave–convex surface of fluorine-doped tin oxide (FTO) substrates was entirely-covered with the continuous films. The films were about 65 nm in thickness and had nano-structured surfaces. Morphology of the films was strikingly different from our previous reported nano-sheet assembled structures. The films were not removed from the substrates by strong water flow or air blow to show strong adhesion strength. The aqueous solution process can be applied to surface coating of various materials such as nano/micro-structured surfaces, particles, fibers, polymers, metals or biomaterials. - Graphical abstract: Dense tin oxide films of 65 nm were successfully fabricated in an aqueous solution. They had nano-structured surfaces. Concave-convex substrates were entirely-covered with the continuous films. - Highlights: • Dense tin oxide films of 65 nm were successfully fabricated in an aqueous solution. • They had nano-structured surfaces. • Concave–convex substrates were entirely-covered with the continuous films.

  1. Study of water adsorption on activated carbons with different degrees of surface oxidation

    SciTech Connect

    Salame, I.I.; Bandosz, T.J. [City Coll. of New York, NY (United States). Dept. of Chemistry] [City Coll. of New York, NY (United States). Dept. of Chemistry; [City Univ. of New York, NY (United States). Graduate School

    1999-02-15

    A carbon of wood origin was oxidized with different oxidizing agents (nitric acid, hydrogen peroxide, and ammonium persulfate). The microstructural properties of the starting material and the oxidized samples were characterized using sorption of nitrogen. The surface acidity was determined using Boehm titration and potentiometric titration. The changes in the surface chemistry were also studied by diffuse reflectance FTIR. Water adsorption isotherms were measured at three different temperatures close to ambient (relative pressure from 0.001 to 0.3). From the isotherms the heats of adsorption were calculated using a virial equation. The results indicated that the isosteric heats of water adsorption are affected by the surface heterogeneity only at low surface coverage. In all cases the limiting heat of adsorption was equal to the heat of water condensation (45 kJ/mol).

  2. Surface energetics of alkaline-earth metal oxides: Trends in stability and adsorption of small molecules

    NASA Astrophysics Data System (ADS)

    Bajdich, Michal; Nørskov, Jens K.; Vojvodic, Aleksandra

    2015-04-01

    We present a systematic theoretical investigation of the surface properties, stability, and reactivity of rocksalt type alkaline-earth metal oxides including MgO, CaO, SrO, and BaO. The accuracy of commonly used exchange-correlation density functionals (LDA, PBE, RPBE, PBEsol, BEEF-vdW, and hybrid HSE) and random-phase approximation (RPA) is evaluated and compared to existing experimental values. Calculated surface energies of the four most stable surface facets under vacuum conditions, the (100) surface, the metal and oxygen terminated octopolar (111), and the (110) surfaces, exhibit a monotonic increase in stability from MgO to BaO. On the MgO(100) surface, adsorption of CO, NO, and CH4 is characterized by physisorption while H2O chemisorbs, which is in agreement with experimental findings. We further use the on-top metal adsorption of CO and NO molecules to map out the surface energetics of each alkaline-earth metal oxide surface. The considered functionals all qualitatively predict similar adsorption energy trends. The ordering between the adsorption energies on different surface facets can be attributed to differences in the local geometrical surface structure and the electronic structure of the metal constituent of the alkaline-earth metal oxide. The striking observation that CO adsorption strength is weaker than NO adsorption on the (100) terraces as the period of the alkaline-earth metal in the oxide increases is analyzed in detail in terms of charge redistribution within the ? and ? channels of adsorbates. Finally, we also present oxygen adsorption and oxygen vacancy formation energies in these oxide systems.

  3. Prebiotic Oxidative Polymerization of 2,3 Dimercaptopropanol on the Surface of Iron(III) Hydroxide Oxide

    NASA Technical Reports Server (NTRS)

    Weber, Arthur L.

    1994-01-01

    The oxidation of 2,3-Dimercapto-1-propanol by ferric ions on the surface of iron (III) hydroxide oxide yielded polydisulfide polymers. This polymerization occured readily at low dithiol concentration under mild aqueous conditions. Polydisulfide polymers up to the 15-mer were synthesized from 1 mM dithiol in 5 ml water reacted with iron (III) hydroxide oxide (20 mg, 160 micro mole Fe) for 3 days under anaerobic conditions at 40 C and pH 4. About 91% of the dithiol was converted to short soluble oligomers and 9% to insoluble larger oligomers that were isolated with the mineral phase. Reactions at higher dithiol concentrations with the same ratio of dithiol to mineral gave a higher yield of the larger insoluble oligomers. The relationship of these results to prebiotic polymer synthesis will be discussed.

  4. Prebiotic polymerization: Oxidative polymerization of 2, 3-dimercapto-1-propanol on the surface of iron(III) hydroxide oxide

    NASA Technical Reports Server (NTRS)

    Weber, Arthur L.

    1995-01-01

    The oxidation of 2, 3-dimercapto-1-propanol by ferric ions on the surface of iron(III) hydroxide oxide (Fe(OH)O) yielded polydisulfide oligomers. This polymerization occurred readily at low dithiol concentration under mild aqueous conditions. Polydisulfide polymers up to the 15-mer were synthesized from 1 mM dithiol in 5 ml water reacted with iron(III) hydroxide oxide (20 mg, 160 micromole Fe) for 3 days under anaerobic conditions at 40 C and pH 4. About 91% of the dithiol was converted to short soluble oligomers and 9% to insoluble larger oligomers that were isolated with the Fe(OH)O phase. Reactions carried out at the same ratio of dithiol to Fe(OH)O but at higher dithiol concentrations gave higher yields of the larger insoluble oligomers. The relationship of these results to prebiotic polymer synthesis is discussed.

  5. Prebiotic Polymerization: Oxidative Polymerization of 2,3 Dimercapto-1- Propanol on the Surface of Iron(III) Hydroxide Oxide

    NASA Technical Reports Server (NTRS)

    Weber, Arthur L.

    1995-01-01

    The oxidation of 2,3-dimercapto-1-propanol by ferric ions on the surface of iron(III) hydroxide oxide (Fe(OH)O) yielded polydisulfide oligomers. This polymerization occurred readily at low dithiol concentration under mild aqueous conditions. Polydisulfide polymers up to the 15-mer were synthesized from 1 mM dithiol in 5 ml water reacted with iron(III) hydroxide oxide (20 mg, 160 micromole Fe) for 3 days under anaerobic conditions at 40 C and pH 4. About 91% of the dithiol was converted to short soluble oligomers and 9% to insoluble larger oligomers that were isolated with the FE(OH)O phase. Reactions carried out at the same ratio of dithiol to FE(OH)O but at higher dithiol concentrations gave higher yields of the larger insoluble oligomers. The relationship of these results to prebiotic polymer synthesis is discussed.

  6. Oxygen Reduction Kinetics Enhancement on a 2 Heterostructured Oxide Surface for Solid Oxide Fuel Cells

    Microsoft Academic Search

    Ethan Crumlin; Eva Mutoro; Sung Jin Ahn; Gerardo Jose la O; Donovan N Leonard; Albina Y Borisevich; Michael D Biegalski; Hans M Christen; Yang Shao-Horn

    2010-01-01

    Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of 85 nm thick La{sub 0.8}Sr{sub 0.2}CoO{sub 3-} (LSC) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia

  7. Evidence of alloy formation during reduction of platinized tin oxide surfaces

    SciTech Connect

    Gardner, S.D.; Hoflund, G.B.; Davidson, M.R. (Univ. of Florida, Gainesville (USA)); Schryer, D.R. (NASA Langley Research Center, Hampton, VA (USA))

    1989-01-01

    Ion scattering spectroscopy, Auger electron spectroscopy, and electron spectroscopy for chemical analysis have been used to examine a platinized tin oxide catalyst surface before, during, and after reduction by annealing under vacuum at 250 to 450 C. These techniques were then used to examine the reduced surface after a room-temperature, low-pressure oxygen exposure. The spectral results and the behavior of the reduced surface toward oxygen exposure both indicate that a Pt/Sn alloy is produced during reduction.

  8. A critical study of the role of the surface oxide layer in titanium bonding

    NASA Technical Reports Server (NTRS)

    Dias, S.; Wightman, J. P.

    1982-01-01

    The molecular understanding of the role which the surface oxide layer of the adherend plays in titanium bonding is studied. The effects of Ti6-4 adherends pretreatment, bonding conditions, and thermal aging of the lap shear specimens were studied. The use of the SEM/EDAX and ESCA techniques to study surface morphology and surface composition was emphasized. In addition, contact angles and both infrared and visible reflection spectroscopy were used in ancillary studies.

  9. Ester oxidation on an aluminum surface using chemiluminescence

    NASA Technical Reports Server (NTRS)

    Jones, William R., Jr.; Meador, Michael A.; Morales, Wilfredo

    1986-01-01

    The oxidation characteristics of a pure ester (trimethyolpropane triheptanoate) were studied by using a chemiluminescence technique. Tests were run in a thin film microoxidation apparatus with an aluminum alloy catalyst. Conditions included a pure oxygen atmosphere and a temperature range of 176 to 206 C. Results indicated that oxidation of the ester (containing .001 M diphenylanthracene as an intensifier) was accompanied by emission of light. The maximum intensity of light emission was a function of the amount of ester, the concentration of intensifier, and the test temperature. The induction period, or the time to reach one-half of maximum intensity was inversely proportional to test temperature. Decreases in light emission at the later stages of a test were caused by depletion of the intensifier.

  10. Surface oxidation of NiTi shape memory alloy

    Microsoft Academic Search

    G. S Firstov; R. G Vitchev; H Kumar; B Blanpain; J Van Humbeeck

    2002-01-01

    Mechanically polished NiTi alloy (50at% Ni) was subjected to heat treatment in air in the temperature range 300–800°C and characterised by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Thermogravimetry measurements were carried out to investigate the kinetics of oxidation. The results of thermodynamic calculations were compared to the experimental observations. It was found that NiTi alloy

  11. Intermolecular potential energy surface and thermophysical properties of ethylene oxide

    NASA Astrophysics Data System (ADS)

    Crusius, Johann-Philipp; Hellmann, Robert; Hassel, Egon; Bich, Eckard

    2014-10-01

    A six-dimensional potential energy hypersurface (PES) for two interacting rigid ethylene oxide (C2H4O) molecules was determined from high-level quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the MP2 and CCSD(T) levels of theory was utilized to determine interaction energies for 10178 configurations of two molecules. An analytical site-site potential function with 19 sites per ethylene oxide molecule was fitted to the interaction energies and fine tuned to agree with data for the second acoustic virial coefficient from accurate speed of sound measurements. The PES was validated by computing the second virial coefficient, shear viscosity, and thermal conductivity. The values of these properties are substantiated by the best experimental data as they tend to fall within the uncertainty intervals and also obey the experimental temperature functions, except for viscosity, where experimental data are insufficient. Due to the lack of reliable data, especially for the transport properties, our calculated values are currently the most accurate estimates for these properties of ethylene oxide.

  12. Nanoscale analysis of surface oxides on ZnMgAl hot-dip-coated steel sheets.

    PubMed

    Arndt, M; Duchoslav, J; Itani, H; Hesser, G; Riener, C K; Angeli, G; Preis, K; Stifter, D; Hingerl, K

    2012-05-01

    In this work, the first few nanometres of the surface of ZnMgAl hot-dip-galvanised steel sheets were analysed by scanning Auger electron spectroscopy, angle-resolved X-ray photoelectron spectroscopy and atomic force microscopy. Although the ZnMgAl coating itself is exhibiting a complex micro-structure composed of several different phases, it is shown that the topmost surface is covered by a smooth, homogeneous oxide layer consisting of a mixture of magnesium oxide and aluminium oxide, exhibiting a higher amount of magnesium than aluminium and a total film thickness of 4.5 to 5 nm. Especially by the combined analytical approach of surface-sensitive methods, it is directly demonstrated for the first time that within surface imprints--created by industrial skin rolling of the steel sheet which ensures a smooth surface appearance as well as reduced yield-point phenomenon--the original, smooth oxide layer is partly removed and that a layer of native oxides, exactly corresponding to the chemical structure of the underlying metal phases, is formed. PMID:22086398

  13. Surface characterization of oxidized myofibrils using X-ray photoelectron spectroscopy and scanning electron microscopy.

    PubMed

    Sun, Weizheng; Li, Qingyun; Zhou, Feibai; Zhao, Haifeng; Zhao, Mouming

    2014-07-30

    The functional properties of myofibrils depend largely on their surface characteristics. Changes in surface characteristics of myofibrils after chemical oxidation were elucidated using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. Myofibrils were oxidized by a hydroxyl radical generating system. Lipid oxidation and phospholipid distribution were altered during the oxidative processing. Results from particle size analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and salt solubility indicated that protein cross-linking and fragmentation occurred during the oxidation of myofibrils. XPS analysis of C 1s, N 1s, and O 1s spectra suggested that surface chemical function concentrations changed significantly because of the modification of amino acid side chains that rendered protein cross-links and fragmentation and phospholipid alteration. Analysis of the correlation between the surface chemical composition and parameters of particle size distributions confirmed that protein carbonylation and phospholipid alteration were involved in protein surface modification. Results of the microstructure analysis were in agreement with those of particle size and XPS analysis. PMID:25005710

  14. Elucidation of the reaction mechanism during the removal of copper oxide by halogen surfactant at the surface of copper plate

    NASA Astrophysics Data System (ADS)

    Yokoyama, Shun; Takahashi, Hideyuki; Itoh, Takashi; Motomiya, Kenichi; Tohji, Kazuyuki

    2013-01-01

    Although copper nanoparticles have various attractive properties, electrical applications of these was not achieved because of its surface oxide layer which prohibited electrical conduction. Thus, it can be considered that a new elimination method of the oxide on Cu surface, which simultaneously provide the resistance to re-oxidized, should be developed. In this study, the reaction between the metal oxide on Cu plate surface and halogen surfactant was introduced into development as a new elimination method of surface oxide layer. Since electrochemical and surface analysis are effective for analyzing the reaction mechanism which expected to be the reduction reaction of the oxide on metal surface, Cu electrode, which represented material of Cu nanoparticles surface, was used for the reaction mechanism analysis. The oxide is removed by controlling the temperature and selecting the optimal combination of solvents and the halogen surfactant (TIC). Results of electrochemical measurements strongly suggest that the chemical reaction between the oxides on the surface with the halogen surfactant is a substitution reaction which converts Cu oxide to Cu bromide, and continuously formed Cu bromide was dissolved into solvent. Totally, the oxide on the Cu surface was successfully eliminated.

  15. Influence of surface oxidation on thermal shock resistance and flexural strength of SiC\\/Al 2 O 3 composites

    Microsoft Academic Search

    Chin-Chen Chiu

    1994-01-01

    It is known that SiC whisker\\/Al2O3 matrix composites can oxidize in air at high temperature and then form oxidation layers on their surfaces. Oxidation treatment has been experimentally performed in air at 1450 °C for a pre-determined time. The results show that the surface layer is in a state of compressive residual stress. The oxidized specimens have better resistance to

  16. SPECTROSCOPIC STUDY OF SURFACE REDOX REACTIONS WITH MANGANESE OXIDES

    EPA Science Inventory

    Redox reactions involving soil minerals and materials are important processes in environmental chemistry, but unfortunately they only have been characterized in the solution phase. he lack of a suitable method has prevented investigations of the mineral surface component of redox...

  17. Surface Tension and Viscosity of Aluminum Oxide Nanofluids

    NASA Astrophysics Data System (ADS)

    Zhu, D. S.; Wu, S. Y.; Wang, N.

    2010-03-01

    Nanofluid is a kind of new engineering material consisting of solid nanoparticles with sizes typically of 1-100 nm suspended in base fluids. Due to the importance of thermophysical property on the heat transfer behavior of fluids, the surface tension and viscosity of Al2O3-H2O nanofluids were investigated. The tests of nanoparticle concentrations ranged from 0 g/l to 1 g/l. The measurements of surface tension and viscosity were equipments based on the maximum bubble pressure method and a capillary viscometer, respectively. The results showed that the surface tension and the viscosity of nanofluids are both highly dependent on the temperature, which is the same to those of water. Because the nanoparticle concentration studied in this work is very low, so there is no obvious change for the viscosity and a maximum enhancement only about 5% for surface tension is obtained at a concentration of 1 g/l.

  18. Diffuse Reflectance Fourier Transform Infrared Spectroscopic Study of Chemical Bonding and Hydrothermal Stability of an Aminosilane on Metal Oxide Surfaces

    Microsoft Academic Search

    Somsak Naviroj; Jack L Koenig; Hatsuo Ishida

    1985-01-01

    Fourier transform infrared spectroscopy was used to study the metal oxide\\/silane interface. Structures of ?-aminopropyldimethylethoxysilane (?-APDMES) coupling agent on the surface of metal oxide powders are proposed. The structures depend on the surface characteristics of the substrate. The amine group of the silane molecule forms a hydrogen bond with the silica surface. The enhanced intensity of the amine band around

  19. Growth Law of the Oxide Film Formed on the Tin Plated Contact Surface and Its Contact Resistance Characteristic

    Microsoft Academic Search

    Yuuya Nabeta; Yasushi Saitoh; Shigeru Sawada; Yasuhiro Hattori; Terutaka Tamai

    2009-01-01

    Tin plating has been applied widely to electrical connectors to save the cost for electromechanical devices. However, the tin plated surface covered with oxide film is fundamentally different from gold plated surfaces. The oxide film prevents the surface from corrosion. When the film is interposed between contact interface, contact resistance increases. It is necessary to break down mechanically to obtain

  20. Surface silver clusters as oxidation catalysts on semiconductor gas sensors

    Microsoft Academic Search

    Jianping Zhang; Konrad Colbow

    1997-01-01

    We have investigated silver clusters on SnO2 thin-film surfaces by scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and X-ray diffraction (XRD). These clusters act as catalytic activators on SnO2 gas sensors and improve sensor performance for H2 detection compared to untreated surfaces. The sensitivity is found to be dependent on the operating temperature of the sensors and the amount

  1. Oxidation of formic acid on the Pt(111) surface in the gas phase.

    PubMed

    Gao, Wang; Keith, John A; Anton, Josef; Jacob, Timo

    2010-09-28

    Formic acid (HCOOH) oxidation on Pt(111) under gas-phase conditions is a benchmark heterogeneous catalysis reaction used to probe electro-catalytic HCOOH conversion in fuel cells, itself an important reaction in energy conversion. We used density functional theory (DFT) calculations to elucidate the fundamental oxidation mechanisms of HCOOH in the gas phase, determining the relative strengths of chemical interactions between HCOOH oxidation intermediates and the Pt(111) surface. We focused on investigating how water and adsorption coverage affects reaction intermediate structures and transition states. Our results show that adsorbed HCOO is a reactive intermediate in gas phase, and co-adsorbed water plays a key role in HCOOH oxidation influencing the structure of reaction intermediates and reaction barriers on Pt(111). The simulations show the preferred catalytic pathway is qualitatively dependent on surface coverage. These results provide a conceptual basis to better interpret its complicated experimental reaction kinetics. PMID:20714626

  2. The surface modification of fluorine-doped tin oxide by the underpotential deposition of noble metals

    SciTech Connect

    Colton, R.H.; Hager, H.E.

    1986-12-01

    The surface modification of fluorine-doped tin oxide by the underpotential deposition of noble metals (Rh, Ru, Pd, Pt, and Au) strongly influences the rate of sulfide-polysulfide reduction at the SnO/sub 2/ electrode. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy are used to characterize as-prepared and surface modified tin oxide preceding and following electrode operation. The noble metal coverages follow the relative ordering: Au, Pt < Ru, Pd < Rh, showing an identical trend as the observed enhancement effects. Depth profile analysis shows that rhodium is found more than 100A into the tin oxide film. This spatial distribution is apparently an artifact of the columnar SnO/sub 2/ structure. The XPS atom bonding peaks for the noble metals are shifted from the peak values associated with metallic states by an amount which is dependent on the exposure history of the tin oxide and yet independent of the noble metal species.

  3. Effect of surface oxidation on the nm-scale wear behavior of a metallic glass

    SciTech Connect

    Caron, A.; Louzguine-Luzguin, D. V. [WPI-AIMR, Tohoku University, Sendai 980-8577 (Japan); Sharma, P.; Inoue, A. [IMR, Tohoku University, Sendai 980-8577 (Japan); Shluger, A. [WPI-AIMR, Tohoku University, Sendai 980-8577 (Japan); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Fecht, H.-J. [WPI-AIMR, Tohoku University, Sendai 980-8577 (Japan); IMNM, University of Ulm, D-89081 Ulm (Germany); Institute of Nanotechnology, Research Center of Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany)

    2011-04-15

    Metallic glasses are good candidates for applications in micromechanical systems. With size reduction of mechanical components into the micrometer and submicrometer range, the native surface oxide layer starts playing an important role in contact mechanical applications of metallic glasses. We use atomic force microscopy to investigate the wear behavior of the Ni{sub 62}Nb{sub 38} metallic glass with a native oxide layer and with an oxide grown after annealing in air. After the annealing, the wear rate is found to have significantly decreased. Also the dependency of the specific wear on the velocity is found to be linear in the case of the as spun sample while it follows a power law in the case of the sample annealed in air. We discuss these results in relation to the friction behavior and properties of the surface oxide layer obtained on the same alloy.

  4. Studies of the kinetics and mechanisms of perfluoroether reactions on iron and oxidized iron surfaces

    NASA Technical Reports Server (NTRS)

    Napier, Mary E.; Stair, Peter C.

    1992-01-01

    Polymeric perfluoroalkylethers are being considered for use as lubricants in high temperature applications, but have been observed to catalytically decompose in the presence of metals. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to explore the decomposition of three model fluorinated ethers on clean polycrystalline iron surfaces and iron surfaces chemically modified with oxygen. Low temperature adsorption of the model fluorinated ethers on the clean, oxygen modified and oxidized iron surfaces was molecular. Thermally activated defluorination of the three model compounds was observed on the clean iron surface at remarkably low temperatures, 155 K and below, with formation of iron fluoride. Preferential C-F bond scission occurred at the terminal fluoromethoxy, CF3O, of perfluoro-1-methoxy-2-ethoxy ethane and perfluoro-1-methoxy-2-ethoxy propane and at CF3/CF2O of perfluoro-1,3-diethoxy propane. The reactivity of the clean iron toward perfluoroalkylether decomposition when compared to other metals is due to the strength of the iron fluoride bond and the strong electron donating ability of the metallic iron. Chemisorption of an oxygen overlayer lowered the reactivity of the iron surface to the adsorption and decomposition of the three model fluorinated ethers by blocking active sites on the metal surface. Incomplete coverage of the iron surface with chemisorbed oxygen results in a reaction which resembles the defluorination reaction observed on the clean iron surface. Perfluoro-1-methoxy-2-ethoxy ethane reacts on the oxidized iron surface at 138 K, through a Lewis acid assisted cleavage of the carbon oxygen bond, with preferential attack at the terminal fluoromethoxy, CF3O. The oxidized iron surface did not passivate, but became more reactive with time. Perfluoro-1-methoxy-2-ethoxy propane and perfluoro-1,3-diethoxy propane desorbed prior to the observation of decomposition on the oxidized iron surface.

  5. Water-gas shift activity of Cu surfaces and Cu nanoparticles supported on metal oxides

    Microsoft Academic Search

    J. A. Rodriguez; P. Liu; X. Wang; W. Wen; J. Hanson; J. Hrbek; M. Pérez; J. Evans

    2009-01-01

    Oxide supported Cu catalysts show significant activity for the water-gas shift reaction (WGS, CO+H2O?H2+CO2) but their performance is not fully understood and is highly dependent on the synthesis conditions or the nature of the oxide support. This article describes a series of new studies examining the water-gas shift activity of Cu\\/MgO(100) surfaces and compares it to the activities found for

  6. Kinetics of laser-induced surface melting and oxide removal in single-crystalline Ge

    Microsoft Academic Search

    J. Solís; F. Vega; C. N. Afonso

    1996-01-01

    The process of oxide removal in crystalline Ge using a pulsed ultraviolet laser has been studied by means of real-time reflectivity measurements with nanosecond resolution. The interaction of laser radiation with a clean, oxide-free surface has been characterized and the inhomogeneous and homogeneous energy density melting thresholds of c-Ge for 193rnm radiation have been determined. The values are 180 and

  7. Stability and Degradation Processes of Pentaerythritol Tetranitrate (PETN) on Metal Oxide Surfaces

    Microsoft Academic Search

    Melissa Mileham; Jonathan Burk; Preya Bhavsar; A. E. Stiegman; Michael P. Kramer

    2008-01-01

    The chemical stability of pentaerythritol tetranitrate (PETN) when placed in physical contact with metal oxides is investigated. In this study, PETN was placed on the surfaces of a range of microcrystalline metal oxides including MnO2, CuO, MoO3, WO3, Bi2O3, SnO2, and Fe2O3 in coverages of 1–3.5 monolayers by a wet impregnation technique. Samples were then placed in a controlled temperature

  8. Effect of surface condition on the oxidation behaviour of MCrAlY coatings

    Microsoft Academic Search

    A. Gil; V. Shemet; R. Vassen; M. Subanovic; J. Toscano; D. Naumenko; L. Singheiser; W. J. Quadakkers

    2006-01-01

    Coatings of the MCrAlY type (M=Ni, Co) are commonly used as overlay coatings and as bond coats (BC's) for ceramic thermal barrier coatings (TBC's) in industrial gas turbines. During high temperature service the MCrAlY coatings form aluminium based surface oxide scales. The technologically most relevant properties of the oxide scales, growth rate and adherence do not only depend on the

  9. Endocrine Disrupting Compounds in Surface Water and Their Degradation by Advanced Oxidation Process with Ozone

    Microsoft Academic Search

    Ramiro Vallejo Rodríguez; Alberto López López

    \\u000a This chapter presents the state-of-the-art techniques for identification and analysis of endocrine disrupting compounds (EDCs) and their degradation by advanced oxidation processes (AOPs). The document arises from a research project oriented towards developing a pilot-level technology for advanced oxidation\\u000a using ozone for the degradation of EDCs present in surface water. Today EDCs are an environmental and public health problem.\\u000a Their

  10. Enhanced ultraviolet sensitivity of zinc oxide nanoparticle photoconductors by surface passivation

    Microsoft Academic Search

    Liqiao Qin; Christopher Shing; Shayla Sawyer; Partha S. Dutta

    2011-01-01

    Zinc oxide nanoparticles were created by a top-down wet-chemical etching process and then coated with polyvinyl-alcohol (PVA), exhibiting sizes ranging from 10 to 120nm with an average size approximately 80nm. The PVA layer provides surface passivation of zinc oxide nanoparticles. As a result of PVA coating, enhancement in ultraviolet emission and suppression of parasitic green emission is observed. Photoconductors fabricated

  11. Stabilization of catalytically active Cu? surface sites on titanium-copper mixed-oxide films.

    PubMed

    Baber, Ashleigh E; Yang, Xiaofang; Kim, Hyun You; Mudiyanselage, Kumudu; Soldemo, Markus; Weissenrieder, Jonas; Senanayake, Sanjaya D; Al-Mahboob, Abdullah; Sadowski, Jerzy T; Evans, Jaime; Rodriguez, José A; Liu, Ping; Hoffmann, Friedrich M; Chen, Jingguang G; Stacchiola, Darío J

    2014-05-19

    The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper-based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu(+) cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed-metal oxide with a Cu(+) terminated surface that is highly active for CO oxidation. PMID:24719231

  12. Surface modification of Cu(In,Ga)Se{sub 2} thin films during aqueous oxidation etch

    SciTech Connect

    Canava, B.; Guillemoles, J.F.; Lincot, D.; Vedel, J.; Ardelean, H.; Malengreau, F. [Ecole Nationale Superieure de Chimie, Paris (France)

    1998-12-31

    The control of the barrier height at the Cu(In,Ga)Se{sub 2}(CIGS)/CdS interface, via the chemical state of the CIGs surface, is a key to improve solar cell performances. In this paper chemical modifications have been achieved by the electrochemical method, by varying both the pH of the solution and the applied potential. It is shown that the potential for electrochemical oxidation depends on the pH, in good agreement with the thermodynamic predictions. The resulting surface composition of CIGS, analyzed by XPS, also depends on the pH. Contact Potential Differences (CPD) and Surface photovoltage (SPV) measurements show that the electronic properties of the CIGS surface are modified. The important result is that the oxidation leads to the formation of permanent positive surface charges, which increase the band bending up to 0.20 V in a direction favorable for the solar cell performances.

  13. Hot hole-induced dissociation of NO dimers on a copper surface

    NASA Astrophysics Data System (ADS)

    García Rey, Natalia; Arnolds, Heike

    2011-12-01

    We use reflection-absorption infrared spectroscopy (RAIRS) to study the photochemistry of NO on Cu(110) in the UV-visible range. We observe that the only photoactive species of NO on Cu(110) is the NO dimer, which is asymmetrically bound to the surface. RAIRS shows that photoinduced dissociation proceeds via breaking of the weak N-N bond of the dimer, photodesorbing one NOg to the gas phase and leaving one NOads adsorbed on the surface in a metastable atop position. We model the measured wavelength-dependent cross sections assuming both electron- and hole-induced processes and find that the photochemistry can be described by either electron attachment to a level 0.3 eV above the Fermi energy EF or hole attachment to a level 2.2 eV below EF. While there is no experimental or theoretical evidence for an electron attachment level so close to EF, an occupied NO-related molecular orbital is known to exist at EF - 2.52 eV on the Cu(111) surface [I. Kinoshita, A. Misu, and T. Munakata, J. Chem. Phys. 102, 2970 (1995)]. We, therefore, propose that photoinduced dissociation of NO dimers on Cu(110) in the visible wavelength region proceeds by the creation of hot holes at the top of the copper d-band.

  14. Hot hole-induced dissociation of NO dimers on a copper surface

    SciTech Connect

    Garcia Rey, Natalia; Arnolds, Heike [Surface Science Research Centre, University of Liverpool, Oxford Road, Liverpool L69 3BX (United Kingdom)

    2011-12-14

    We use reflection-absorption infrared spectroscopy (RAIRS) to study the photochemistry of NO on Cu(110) in the UV-visible range. We observe that the only photoactive species of NO on Cu(110) is the NO dimer, which is asymmetrically bound to the surface. RAIRS shows that photoinduced dissociation proceeds via breaking of the weak N-N bond of the dimer, photodesorbing one NO{sub g} to the gas phase and leaving one NO{sub ads} adsorbed on the surface in a metastable atop position. We model the measured wavelength-dependent cross sections assuming both electron- and hole-induced processes and find that the photochemistry can be described by either electron attachment to a level 0.3 eV above the Fermi energy E{sub F} or hole attachment to a level 2.2 eV below E{sub F}. While there is no experimental or theoretical evidence for an electron attachment level so close to E{sub F}, an occupied NO-related molecular orbital is known to exist at E{sub F}- 2.52 eV on the Cu(111) surface [I. Kinoshita, A. Misu, and T. Munakata, J. Chem. Phys. 102, 2970 (1995)]. We, therefore, propose that photoinduced dissociation of NO dimers on Cu(110) in the visible wavelength region proceeds by the creation of hot holes at the top of the copper d-band.

  15. Reactions of formaldehyde and methanol on clean, carburized and oxidized Mo(100) surfaces

    NASA Astrophysics Data System (ADS)

    Ko, E. I.; Madix, R. J.

    1981-12-01

    The reactions of formaldehyde and methanol have been studied on clean, carburized, and oxidized Mo(100) surfaces using temperature programmed reaction spectroscopy (TPRS). The thermal cracking of ethylene at 550 K and the adsorption of molecular oxygen at 1050 K were used to carburize and oxidize, respectively, the clean surface to saturation. Both the carbide and oxide surfaces showed (1×1) LEED features. Methanol decomposed to give hydrogen atoms and methoxy intermediates upon adsorption on the clean Mo(100) surface at 200 K. The methoxy intermediate was stable up to 340 K. Adsorbed carbon and oxygen suppressed the dissociation of the hydroxyl hydrogen from the alcohol and yielded a significantly different activity and selectivity compared to the very reactive clean surface. The binding energies for both formaldehyde and methanol on the three surfaces were similar, demonstrating the weak sensitivity of donor-acceptor bonds to surface modifiers. The results in this study were very similar to those previously observed for W(100) though different adlayer structures were present. This similarity suggested that the modification in surface reactivity was primarily a compositional effect.

  16. Atomic resolution non-contact atomic force microscopy of clean metal oxide surfaces.

    PubMed

    Lauritsen, J V; Reichling, M

    2010-07-01

    In the last two decades the atomic force microscope (AFM) has become the premier tool for topographical analysis of surface structures at the nanometre scale. In its ultimately sensitive implementation, namely dynamic scanning force microscopy (SFM) operated in the so-called non-contact mode (NC-AFM), this technique yields genuine atomic resolution and offers a unique tool for real space atomic-scale studies of surfaces, nanoparticles as well as thin films, single atoms and molecules on surfaces irrespective of the substrate being electrically conducting or non-conducting. Recent advances in NC-AFM have paved the way for groundbreaking atomic level insight into insulator surfaces, specifically in the most important field of metal oxides. NC-AFM imaging now strongly contributes to our understanding of the surface structure, chemical composition, defects, polarity and reactivity of metal oxide surfaces and related physical and chemical surface processes. Here we review the latest advancements in the field of NC-AFM applied to the fundamental atomic resolution studies of clean single crystal metal oxide surfaces with special focus on the representative materials Al(2)O(3)(0001), TiO(2)(110), ZnO(1000) and CeO(2)(111). PMID:21386455

  17. In situ high temperature microscopy study of the surface oxidation and phase transformations in titanium alloys.

    PubMed

    Malinov, S; Sha, W; Voon, C S

    2002-09-01

    Two popular commercial titanium alloys, Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.08Si, were used for in situ high temperature microscopy study. The experiments were performed on an optical microscope equipped with high temperature stage using both normal and florescence lights. Two kinds of experiments were performed, at continuous heating/cooling with different rates and in isothermal conditions at different temperatures. The changes taking place on the sample surface during the experiments were monitored. The morphology of the alpha ==> beta ==> alpha phase transformation was recorded at different heat treatment conditions using the effect of thermal etching. An effect of sample surface oxidation and deoxidation was observed during continuous heating. The appearance and disappearance of ordered titanium oxides Ti3O and Ti2O are discussed based on the phase equilibrium diagram. The kinetics of the surface oxidation was monitored in both isothermal and continuous cooling conditions. PMID:12230486

  18. Structure and the catalysis mechanism of oxidative chlorination in nanostructural layers of a surface of alumina

    PubMed Central

    2014-01-01

    On the basis of X-ray diffraction and mass spectrometric analysis of carrier ?-Al2O3 and catalysts CuCl2/CuCl on its surface, the chemical structure of the active centers of two types oxidative chlorination catalysts applied and permeated type of industrial brands “Harshow” and “MED?-B” was investigated. On the basis of quantum-mechanical theory of the crystal, field complexes were detected by the presence of CuCl2 cation stoichiometry and structure of the proposed model crystal quasichemical industrial catalyst permeated type MED?-B for oxidative chlorination of ethylene. On the basis of quantum-mechanical calculations, we propose a new mechanism of catalysis crystal quasichemical oxidative chlorination of ethylene reaction for the catalysts of this type (MED?-B) and confirmed the possibility of such a mechanism after the analysis of mass spectrometric studies of the active phase (H2 [CuCl4]) catalyst oxidative chlorination of ethylene. The possibility of the formation of atomic and molecular chlorine on the oxidative chlorination of ethylene catalyst surface during Deacon reaction was displaying, which may react with ethylene to produce 1,2-dichloroethane. For the active phase (H [CuCl2]), catalyst offered another model of the metal complex catalyst oxidative chlorination of ethylene deposited type (firm ‘Harshow,’ USA) and the mechanism of catalysis of oxidative chlorination of ethylene with this catalyst. PMID:25258594

  19. Structure and the catalysis mechanism of oxidative chlorination in nanostructural layers of a surface of alumina

    NASA Astrophysics Data System (ADS)

    Kurta, Sergiy A.; Mykytyn, Igor M.; Tatarchuk, Tetiana R.

    2014-07-01

    On the basis of X-ray diffraction and mass spectrometric analysis of carrier ?-Al2O3 and catalysts CuCl2/CuCl on its surface, the chemical structure of the active centers of two types oxidative chlorination catalysts applied and permeated type of industrial brands "Harshow" and "MEDR-B" was investigated. On the basis of quantum-mechanical theory of the crystal, field complexes were detected by the presence of CuCl2 cation stoichiometry and structure of the proposed model crystal quasichemical industrial catalyst permeated type MEDR-B for oxidative chlorination of ethylene. On the basis of quantum-mechanical calculations, we propose a new mechanism of catalysis crystal quasichemical oxidative chlorination of ethylene reaction for the catalysts of this type (MEDR-B) and confirmed the possibility of such a mechanism after the analysis of mass spectrometric studies of the active phase (H2 [CuCl4]) catalyst oxidative chlorination of ethylene. The possibility of the formation of atomic and molecular chlorine on the oxidative chlorination of ethylene catalyst surface during Deacon reaction was displaying, which may react with ethylene to produce 1,2-dichloroethane. For the active phase (H [CuCl2]), catalyst offered another model of the metal complex catalyst oxidative chlorination of ethylene deposited type (firm `Harshow,' USA) and the mechanism of catalysis of oxidative chlorination of ethylene with this catalyst.

  20. Oxide properties of a gamma titanium aluminide: A surface science study

    SciTech Connect

    Taylor, T.N.; Paffett, M.T.

    1991-01-01

    The surface properties of oxides grown on a gamma titanium aluminide (2 at. % Nb) have been examined using a x-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectroscopy (SIMS). An oxide formed on the sample during air exposure at room temperature was thermally destabilized in ultra-high vacuum. The heating largely decomposed the advanced Ti oxidation states to give a predominate +2 valence configuration at 600{degrees}C, while the Al oxide was somewhat enhanced for the same treatment. Growth of a post chemisorption oxide for various temperatures and exposure times at pressures {le} 10{sup {minus}6} Torr oxygen revealed the progressive development of Ti and AL oxide. At a temperature of 600{degrees}C the Ti component was greatly enhanced relative to the Al content in the surface region. This separation of Ti from Al was clearly visible in SIMS measurements. The development and thermal stability of these oxides is in agreement with the heats of formation and available valence states for the two majority components in the material. 12 refs., 4 figs.

  1. Evaluating the electrochemical capacitance of surface-charged nanoparticle oxide coatings.

    PubMed

    Leonard, Kevin C; Suyama, Wendy E; Anderson, Marc A

    2012-04-17

    While transition metal oxides have been thoroughly investigated as coatings for electrochemical capacitors due to their pseudocapacitance, little work has been done investigating other oxide coatings. There exists a whole class of nanoporous oxides typically synthesized by sol-gel chemistry techniques that have very high differential capacitance. This high differential capacitance has been attributed to the surface potential of these materials and the close approach of counterions near the surface of these oxides. This study focuses on investigating the electrochemical capacitance of non-transition metal oxide nanoparticle coatings when deposited on supporting electrodes. Here, we show that, by adding coatings of SiO(2), AlOOH, TiO(2), and ZrO(2) nanoparticles to graphite support electrodes, we can increase the electrochemical capacitance. We also show that the measured electrochemical capacitance of these oxide-coated electrodes directly relates to the electrophoretic mobility of these materials with the lowest values in capacitance occurring at or near the respective isoelectric pH (pH(IEP)) of each oxide. PMID:22428877

  2. Surface aspects of hydrogen photogeneration on titanium oxides

    NASA Astrophysics Data System (ADS)

    Wagner, F. T.; Ferrer, S.; Somorjai, G. A.

    1980-07-01

    The effects of surface platinization on photoactivity are discussed and evidence for a thermal reaction between Pd and TiO2 surfaces is given. No Auger detectable changes in surfaces composition correlate with the higher rates of hydrogen photogeneration on metal-free SrTiO3 observed in highly concentrated aqueous alkaline electrolyte. Platinized crystals and photoelectrochemical cells show similar enhancement of photoactivity at high hydroxide concentrations. Although no hydrogen photogeneration is seen from water vapor at pressures up to 20 Torr on crystals near room temperatures, hydrogen photogeneration does occur on prereduced crystals at temperatures where oxygen diffusion into the bulk is rapid. Kinetics of hole transfer or hydroxylation may determine the overall reaction rate at zero applied potential.

  3. Interaction of cobalt with a stainless steel oxide surface

    SciTech Connect

    Taylor, J.B. (British Nuclear Fuels PLC, Risley (England))

    1991-01-01

    The deposition of radioactive cobalt ions from aqueous solutions in the pH range from 1 to 12 onto the internal surface of a stainless steel vessel or pipework can lead to the buildup of tenacious surface activity. For liquid streams of low specific activity (measured in becquerels per millilitre), the surface activity buildup may create a more dominant gamma radiation field than the activity suspended in the liquid. Failure to adequately predict this buildup for an operational nuclear plant can lead to an underestimate of potential gamma dose rates. This may lead to an economic penalty if additional shielding or other protective measures are necessary following plant operation. A theoretical method of determining the cobalt mass/activity deposition from aqueous liquor onto stainless steel is outlined in this paper. A validation of the method is given, and the limits of its application are discussed.

  4. STM Image Contrast Interpretation and its Role in Determining the Structure of Transition Metal Oxide Surfaces

    NASA Astrophysics Data System (ADS)

    Lu, Weier

    1995-01-01

    The surfaces of transition metal oxides play a critical role in many applications such as heterogeneous catalysis, gas detection, thermionic emission, electrolysis, and photolysis. Understanding the mechanisms of such surface processes requires a detailed knowledge of the surface microscopic structure. Since its invention in the early 1980's, scanning tunneling microscopy (STM) has come to be a popular tool for oxide surface studies. However, despite some experimental successes, interpretation of the contrast in STM images of metal oxides has remained challenging due to the numerous contributing factors such as nonstoichiometry, structural complexity, surface disorder, and uncertainties regarding the bonding and termination layers in such multicomponent systems. In this thesis work, a computer simulation scheme that explores these effects separately has been developed to assist the interpretation of atomic-scale contrast in STM images. A semiquantitative technique, based on the one -dimensional square well tunneling model, is used to simulate constant current STM images. This model provides an efficient mechanism to test and explore effects of various ill-defined experimental parameters. The method was applied to the atomic-scale resolution STM study of three transition metal oxides: {rm M_{x}WO _3} (M=Rb, Na), {rm Mo_{18}O_{52}}, and V_2{rm O}_5. Our observations include surface termination layer variations, surface ordering, surface relaxations, surface steps caused by crystallographic shear (CS) planes, surface oxygen vacancies and other defects. In each case, the competition between geometric and electronic contributions to the image contrast is evident. Tunneling spectroscopy experiments and calculations were also performed on the sodium tungsten bronzes and the implication to their electronic structures is discussed.

  5. In situ passivation of GaAs surface with aluminum oxide with MOVPE

    NASA Astrophysics Data System (ADS)

    Terada, Yuki; Deura, Momoko; Shimogaki, Yukihiro; Sugiyama, Masakazu; Nakano, Yoshiaki

    2008-11-01

    In situ passivation of GaAs surface subsequent to the growth in a metalorganic vapor phase epitaxy (MOVPE) reactor has been made possible using trimethylaluminum (TMAl). The adsorption layer on GaAs, presumably consisting of aluminum and the decomposition product of TMAl, was oxidized upon exposure to air to form thin AlO x layer. TMAl supply of only 0.5 monolayer completely prevented the oxidation of As on the surface, as confirmed by XPS. The passivation layer mostly prevented the oxidation of As upon O 2 annealing for 5 min at 250 °C. For the successful passivation, complete desorption of excess As on the GaAs surface was essential prior to the injection of TMAl. Otherwise, AlAs layer was formed and arsenic oxide was inevitably formed. The optimum length of H 2 purge to desorb As was determined to be 2 min with in situ surface monitoring using reflectance anisotropy spectroscopy (RAS). This passivation method, combined with the succeeding deposition of Al 2O 3 as a gate dielectric in a different reactor, provides the GaAs/gate interface without As-oxide. The method is applicable to the MOVPE growth of electron channel layers containing As for III-V metal-insulator-semiconductor field effect transistors (MISFETs).

  6. Reduction of a polar oxide surface in a strong DC-field

    NASA Astrophysics Data System (ADS)

    Steurer, Wolfram; Surnev, Svetlozar; Barcaro, Giovanni; Fortunelli, Alessandro; Netzer, Falko P.

    2011-03-01

    Polar oxide surfaces are of fundamental scientific interest because of their inherent instability in bulk samples on electrostatic grounds. Here we report first experimental evidence of field-induced reduction of a polar oxide surface by applying homogeneous external DC-fields. Ultrathin Ni-oxide nanostructures immersed into an Ag(100) substrate have been grown by reactive evaporation and have subsequently been exposed to electric fields in the range of 0.5-1.6 V/nm. We achieve such high fields in a setup resembling a plate capacitor where the Ag(100) substrate (with the deposited NiO film) acts as the cathode with a counter electrode placed 800nm apart. For fields exceeding the threshold of 0.9 V/nm, oxygen atoms are torn away from the surface, thus, efficiently reducing the initially highly-ordered Ni-oxide film. The remaining Ni atoms on the surface are highly mobile and cluster together. No oxide reduction occurs if the field polarity is inverted. This work is supported by the ERC Advanced Grant ``SEPON.''

  7. Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics. Technical progress report, [June--August 1993

    SciTech Connect

    Doyle, F.M.

    1993-09-30

    The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical cleaning processes. The results will provide fundamental insight into oxidation, in term of the bulk and surface chemistry, the microstructure, and the semiconductor properties of the pyrite. During the twelfth quarter, wet and dry oxidation tests were done at room temperature on coal samples from the Pennsylvania State Coal Bank. Previous results had indicated that oxidation at high temperatures induced changes in surface properties through loss of volatiles. As-received and oxidized coal samples were studied by ion exchange methods to determine the carboxylate and phenolic group concentrations. Film flotation tests were done to characterize the floatability of as-received and oxidized coals. Surface area measurements were done on as-received coals.

  8. SemiEmpirical Molecular Modeling of Ionic Liquid Tribology: Ionic Liquid–Aluminum Oxide Surface Interactions

    Microsoft Academic Search

    W. Robert Carper; Phillip G. Wahlbeck; Naveed S. Nooruddin

    The interactions between the selected ionic liquids (ILs) and aluminum oxide surfaces are modeled in this report using theoretical\\u000a methods. A wide range of ILs and their interactions with an aluminum oxide surface are modeled using the PM5 semi-empirical\\u000a method. The ILs modeled in this study contain imidazolium (C3, 4, 6, 8 or 10mim) or ammonium cations including (C6H13)3NH+, (C8H17)3NH+,

  9. SURFACE TENSION OF SOME LIQUID OXIDES AND THEIR TEMPERATURE COEFFICIENTS

    Microsoft Academic Search

    W. D. KINGERY

    1959-01-01

    Surface-tension data are reported for liquid AlâOâ, Bâ; Oâ, GeOâ, Pââsub 5\\/, and SiOâ. Abnormal positive ; temperature coefficients for Bââsub 3\\/, GeOâ, and SiOâ are ; shown to be due mainly to changes in the liquid structure (dissociation) with ; temperature. (auth);

  10. Surface Mn(II) oxidation actuated by a multicopper oxidase in a soil bacterium leads to the formation of manganese oxide minerals.

    PubMed

    Zhang, Zhen; Zhang, Zhongming; Chen, Hong; Liu, Jin; Liu, Chang; Ni, Hong; Zhao, Changsong; Ali, Muhammad; Liu, Fan; Li, Lin

    2015-01-01

    In this manuscript, we report that a bacterial multicopper oxidase (MCO266) catalyzes Mn(II) oxidation on the cell surface, resulting in the surface deposition of Mn(III) and Mn(IV) oxides and the gradual formation of bulky oxide aggregates. These aggregates serve as nucleation centers for the formation of Mn oxide micronodules and Mn-rich sediments. A soil-borne Escherichia coli with high Mn(II)-oxidizing activity formed Mn(III)/Mn(IV) oxide deposit layers and aggregates under laboratory culture conditions. We engineered MCO266 onto the cell surfaces of both an activity-negative recipient and wild-type strains. The results confirmed that MCO266 governs Mn(II) oxidation and initiates the formation of deposits and aggregates. By contrast, a cell-free substrate, heat-killed strains, and intracellularly expressed or purified MCO266 failed to catalyze Mn(II) oxidation. However, purified MCO266 exhibited Mn(II)-oxidizing activity when combined with cell outer membrane component (COMC) fractions in vitro. We demonstrated that Mn(II) oxidation and aggregate formation occurred through an oxygen-dependent biotic transformation process that requires a certain minimum Mn(II) concentration. We propose an approximate electron transfer pathway in which MCO266 transfers only one electron to convert Mn(II) to Mn(III) and then cooperates with other COMC electron transporters to transfer the other electron required to oxidize Mn(III) to Mn(IV). PMID:26039669

  11. Surface Mn(II) oxidation actuated by a multicopper oxidase in a soil bacterium leads to the formation of manganese oxide minerals

    PubMed Central

    Zhang, Zhen; Zhang, Zhongming; Chen, Hong; Liu, Jin; Liu, Chang; Ni, Hong; Zhao, Changsong; Ali, Muhammad; Liu, Fan; Li, Lin

    2015-01-01

    In this manuscript, we report that a bacterial multicopper oxidase (MCO266) catalyzes Mn(II) oxidation on the cell surface, resulting in the surface deposition of Mn(III) and Mn(IV) oxides and the gradual formation of bulky oxide aggregates. These aggregates serve as nucleation centers for the formation of Mn oxide micronodules and Mn-rich sediments. A soil-borne Escherichia coli with high Mn(II)-oxidizing activity formed Mn(III)/Mn(IV) oxide deposit layers and aggregates under laboratory culture conditions. We engineered MCO266 onto the cell surfaces of both an activity-negative recipient and wild-type strains. The results confirmed that MCO266 governs Mn(II) oxidation and initiates the formation of deposits and aggregates. By contrast, a cell-free substrate, heat-killed strains, and intracellularly expressed or purified MCO266 failed to catalyze Mn(II) oxidation. However, purified MCO266 exhibited Mn(II)-oxidizing activity when combined with cell outer membrane component (COMC) fractions in vitro. We demonstrated that Mn(II) oxidation and aggregate formation occurred through an oxygen-dependent biotic transformation process that requires a certain minimum Mn(II) concentration. We propose an approximate electron transfer pathway in which MCO266 transfers only one electron to convert Mn(II) to Mn(III) and then cooperates with other COMC electron transporters to transfer the other electron required to oxidize Mn(III) to Mn(IV). PMID:26039669

  12. Reduction of aqueous transition metal species on the surfaces of Fe(II)-containing oxides

    USGS Publications Warehouse

    White, A.F.; Peterson, M.L.

    1996-01-01

    Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1-7 at 25??C. For an aqueous transition metal m, such reactions are 3[Fe2+Fe3+2]O4(magnetite) + 2/nmz ??? 4[Fe3+2]O3(maghemite) + Fe2+ + 2/nmz-n and 3[Fe2+Ti]O3(ilmenite) + 2/nmz ??? Fe3+2Ti3O9(pseudorutile) + Fe2+ + 2/nmz-n, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] ??? [Fe(III)] is -0.34 to -0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe2+ (-0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 ?? 10-10 mol m-2 s-1. Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe2+ is oxidized homogeneously in solution to Fe3+. X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental solution. In contrast, magnetite weathered under oxidizing vadose conditions show minimum reactivity toward chromate ions. The ability of Fe(II) oxides to reduce transition metals in soils and groundwaters will be strongly dependent on the redox environment.

  13. Surface-charge measurements in microgap dielectric barrier discharge using bismuth silicon oxide crystals

    NASA Astrophysics Data System (ADS)

    Mukaigawa, S.; Matsuda, H.; Fue, H.; Takahashi, R.; Takaki, K.; Fujiwara, T.

    2013-06-01

    A surface-charge measurement system based on the Pockels effect in bismuth silicon oxide dielectric crystals was constructed for measuring the surface-charge density of the dielectrics in the microgap dielectric barrier discharge. We re-examined the calculation methods of the surface-charge density from the voltage applied to the BSO crystal, obtained by laser interferometry. The charge calculated using the circuit equation coincided with the that obtained using the discharge current. Under certain experimental conditions, the maximum values of the surface charge density in the discharge cell with and without a protection glass were +2.0 and +2.5 nC/cm2, respectively.

  14. FT-IR characterization of adsorption complexes on magnesium oxide surfaces

    NASA Astrophysics Data System (ADS)

    Echterhoff, R.; Knözinger, E.

    1988-05-01

    Different hydration and hydroxylation states of surfaces of highly dispersed magnesium oxide were subjected to a detailed FT-IR spectroscopic analysis using the transmission technique. Thermal desorption and time resolved adsorption studies on a time-scale of seconds enabled a great variety of surface hydroxyl species to be characterized. Additional information on some of these species was obtained by probing the surface with ammonia. Based on data obtained with the aid of modern FT-IR technology the previously published assignment of the NH bending region in the system MgO/NHa was revised. This leads to a new description of the respective surface complexes.

  15. Redox activity of surface oxygen anions in oxygen-deficient perovskite oxides during electrochemical reactions.

    PubMed

    Mueller, David N; Machala, Michael L; Bluhm, Hendrik; Chueh, William C

    2015-01-01

    Surface redox-active centres in transition-metal oxides play a key role in determining the efficacy of electrocatalysts. The extreme sensitivity of surface redox states to temperatures, to gas pressures and to electrochemical reaction conditions renders them difficult to investigate by conventional surface-science techniques. Here we report the direct observation of surface redox processes by surface-sensitive, operando X-ray absorption spectroscopy using thin-film iron and cobalt perovskite oxides as model electrodes for elevated-temperature oxygen incorporation and evolution reactions. In contrast to the conventional view that the transition metal cations are the dominant redox-active centres, we find that the oxygen anions near the surface are a significant redox partner to molecular oxygen due to the strong hybridization between oxygen 2p and transition metal 3d electronic states. We propose that a narrow electronic state of significant oxygen 2p character near the Fermi level exchanges electrons with the oxygen adsorbates. This result highlights the importance of surface anion-redox chemistry in oxygen-deficient transition-metal oxides. PMID:25598003

  16. Modifications of oxidized Zircaloy-4 surface in contact with radiolysed wet air

    NASA Astrophysics Data System (ADS)

    Guipponi, C.; Millard-Pinard, N.; Bérerd, N.; Serris, E.; Pijolat, M.; Peres, V.; Wasselin-Trupin, V.

    2012-02-01

    In the framework of radioactive waste geological disposal, the long term evolution of the nuclear wastes packages and the release of the radionuclides from the wastes have to be studied. Regarding compacted wastes (cladding tubes) coming from reprocessing of spent fuel, the Zircaloy-4 (zirconium alloy) cladding tubes have been activated and oxidized in reactors. In the disposal, the radioactive waste is exposed to humid air in a first phase and to water after the resaturation phase. In order to better assess the degradation process of these nuclear waste package, the influence of wet air proton radiolysis on the behavior of surface oxidized Zircaloy-4 has been investigated. Radiolysis experiments were performed using an irradiation cell which is associated to an extracted beam. Samples are exposed to wet air, under and without radiolysis, during 12 and 24 h. The water partial pressure has been fixed at 6 and 50 mbar in order to have, respectively, localized adsorbed water molecules and a thin film of adsorbed water. Before and after each treatment, sample surfaces were characterized by X-ray Photoelectron Spectroscopy (XPS) in order to identify the elements at the topmost surface of the solid. The wet air radiolysis causes changes at the surface of oxidized Zircaloy-4 and influences the corrosion phenomenon. Indeed, an enrichment of tin and the presence of nitrogen species were observed. It could be due to the formation of tritin(II) tetrahydroxide dinitrate and a Zr 4+ tetramer on the topmost oxide surface.

  17. Surface effects and phase stability in metal oxides nanoparticles under visible irradiation

    SciTech Connect

    Ricci, Pier Carlo, E-mail: carlo.ricci@dsf.unica.it; Carbonaro, C. M., E-mail: carlo.ricci@dsf.unica.it; Corpino, R., E-mail: carlo.ricci@dsf.unica.it; Chiriu, D., E-mail: carlo.ricci@dsf.unica.it; Stagi, L., E-mail: carlo.ricci@dsf.unica.it [Dipartimento di Fisica, Universitá degli Studi di Cagliari, S.P. Monserrato-Sestu Km 0,700, 09042 Monserrato (Canada) (Italy)

    2014-10-21

    The light induced phase transformation between stable phases of metal oxides nanoparticles is analyzed. The surrounding atmosphere as well as the defect density at the surface play a fundamental role. It has been found that in oxygen poor chamber atmosphere the phase transformation is favored, while the phase transition cannot be achieved if the defects at the surface are properly passivated. The phase transition is activated by intragap irradiation, able to activate the F- center at the surface connected to oxygen vacancies, and promoting the activation of the surface and the nucleation of neighboring crystallites. The phase transition was studied in Titanium oxide (TiO{sub 2}) and in Iron oxide (Fe{sub 2}O{sub 3}): Maghemite is subjected to a phase transformation to ??Fe{sub 2}O{sub 3} (hematite), Anatase nanoparticles converts to Rutile. The general mechanism of the phase transition and, more in general, the possibility to optically control the surface activity of metal oxides is discussed.

  18. Influences of various Pt dopants over surface platinized TiO2 on the photocatalytic oxidation of nitric oxide.

    PubMed

    Wang, Haiqiang; Wu, Zhongbiao; Liu, Yue; Wang, Yuejun

    2009-02-01

    Various surface platinized TiO(2) were prepared by four different preparation methods and investigated with respect to their behaviors in UV photocatalytic oxidation of nitric oxide. The physicochemical properties of the Pt modified TiO(2) were investigated by X-ray diffraction analysis, X-ray photoelectron spectrum analysis, transmission electron microscopy, and photoluminescence spectra. From the experimental results, it was found that new electronic states were observed above the valence bands of PtOx-TiO(2) and PtClx-TiO(2). And the lifetime of electrons and holes was found prolonged in the PtOx-TiO(2) catalysts. The activity tests showed that the dopants existed as metallic Pt and platinum chloride had little contribution to the photocatalytic oxidation of NO in gas phase. However, the dopant which existed as PtOx could improve the NO photocatalytic oxidation efficiency and the reaction rate. The photocatalytic activity of the 0.05 at% PtOx-TiO(2) was nearly three times higher than that of the pure Degussa P25 with an inlet NO concentration of 200 ppm. PMID:19091376

  19. Unveiling and controlling the electronic structure of oxidized semiconductor surfaces: Crystalline oxidized InSb(100)(1 Ã-- 2)-O

    NASA Astrophysics Data System (ADS)

    Lâng, J. J. K.; Punkkinen, M. P. J.; Tuominen, M.; Hedman, H.-P.; Vähä-Heikkilä, M.; Polojärvi, V.; Salmi, J.; Korpijärvi, V.-M.; Schulte, K.; Kuzmin, M.; Punkkinen, R.; Laukkanen, P.; Guina, M.; Kokko, K.

    2014-07-01

    The exothermic nature of oxidation causes nearly all semiconductor applications in various fields like electronics, medicine, photonics, and sensor technology to acquire an oxidized semiconductor surface part during the application manufacturing. The significance of understanding and controlling the atomic scale properties of oxidized semiconductor surfaces is expected to increase even further with the development of nanoscale semiconductor crystals. The nature of oxidized semiconductor layers is, however, hard to predict and characterize as they are usually buried and amorphous. To shed light on these issues, we pursue a different approach based on oxidized III-V semiconductor layers that are crystalline. We present a comprehensive characterization of oxidized crystalline InSb(100)(1×2)-O layers by ab initio calculations, photoelectron spectroscopy, scanning tunneling microscopy, and spectroscopy, and demonstrate the electronic band structures of different oxidized phases of the semiconductor, which elucidate the previous contradictory semiconductor-oxidation effects. At 0.5 monolayer (ML) oxidation, oxygen atoms tend to occupy subsurface Sb sites, leading to metallic states in the semiconductor band gap, which arise from top dimers. When the oxidation is increased to the 1.0-2.0 ML concentration, oxygen occupies also interstitial sites, and the insulating band structure without gap states is stabilized with unusual occupied In dangling bonds. In contrast, the 2.5-3.0 ML oxide phases undergo significant changes toward a less ordered structure. The findings suggest a methodology for manipulating the electronic structure of oxidized semiconductor layers.

  20. Surface Oxidation Effects During Low Energy BF{sub 2}{sup +} Ion Implantation

    SciTech Connect

    Kondratenko, Serguei [Axcelis Technologies, 108 Cherry Hill Drive, Beverly, MA 01915 (United States); Hsu, P. K.; Zhao, Hongchen [Axcelis Technologies, 19F Kirin Plaza, 666 Gubei Road, Shanghai, China 200336 (China); Reece, Ronald N.

    2011-01-07

    We present results on silicon wafer surface oxidation observed during low energy high dose BF{sub 2}{sup +} implantation. Experiments were performed on single-crystal and pre-amorphized silicon wafers that help elucidate the surface structure impact on boron distribution profiles and dose retention. Implanters with different architectures were compared including both single wafer and batch systems. It was found that the oxidation rate depends on implanter type and design, and that the surface oxide thickness is a linear function of implantation dose and time. Surface oxidation is significantly higher for batch systems compared to single wafer tools. This is due primarily to the significantly lower beam duty cycle on the batch implanter. The oxide thicknesses estimated from SIMS oxygen profiles are in agreement with ellipsometry measurements after spike annealing, and show a similar difference between single wafer and batch implanters. SIMS boron distribution profiles after implantation were compared and used to calculate retained dose. In the medium dose range ({<=}3x10{sup 14} at/cm{sup 2}) the profiles from different implanters are well matched and the dose retention is close to 100%. For the higher dose range ({>=}3x10{sup 15} at/cm{sup 2}) retention for the batch implanter is significantly less than the single wafer tool and depends on the wafer surface structure. A higher oxidation rate results in lower dopant activation and higher Rs value after spike annealing. For high implantation doses the single wafer system allows much higher dose retention and better boron activation after annealing.

  1. Nonthermal desorption from surfaces of ices and other oxides

    NASA Astrophysics Data System (ADS)

    Madey, Theodore E.

    2001-03-01

    Non-thermal DIET processes at surfaces (desorption induced by electronic transitions) may affect both terrestrial and planetary atmospheres. One case concerns observations of neutral sodium and potassium vapor in the tenuous atmospheres of the planet Mercury and the Moon, as well as Jupiter's icy satellite, Europa. In a series of model experiments, we find strong evidence that non-thermal processes - mainly photon-stimulated desorption (PSD) by UV photons - play a dominant role in desorption of Na atoms from the lunar surface, and may affect Na and K in the other atmospheres also. The second case involves measurements that may impact on understanding the destruction of ozone-depleting chlorofluorocarbons (CFCs) in the earth's upper atmosphere, via electron-induced processes on ice particles in polar stratospheric clouds. We observe giant Cl^- and F^- enhancements by several orders of magnitude in electron-stimulated desorption (ESD) of a fractional monolayer of CF_2Cl2 coadsorbed with water ice and ammonia ice on a metal surface at ~25 K, respectively. The negative-ion enhancements are attributed to dissociation of CF_2Cl2 by capture of low-energy secondary electrons trapped by coadsorbed polar water or ammonia.

  2. Chemisorption of pyridine and pyrrole on iron oxide surfaces studied by XPS

    NASA Astrophysics Data System (ADS)

    Pan, Fu-Ming; Stair, Peter C.; Fleisch, Theo H.

    1986-11-01

    Adsorption of pyridine and pyrrole on model iron oxide surfaces has been studied by X-ray photoelectron spectroscopy. At room temperature both molecules adsorb with their molecular identity intact. Upon heating above 320 K pyridine decomposes on the surface whereas pyrrole desorbs intact at 345 K. The bonding of pyridine and pyrrole to the surface at room temperature is studied by monitoring the change in measured N(1s) and C(1s) binding energies between gas-phase molecules and the monolayer phase at room temperature. The results suggest that pyridine bonds via electron donation from the non-bonding nitrogen lone pair to the surface while pyrrole bonds via electron donation from a ?-bonding orbital to the surface. The differences in surface bonding are interpreted in the context of the concept of Lewis acids and bases applied to surfaces.

  3. Improved performance of protected catecholic polysiloxanes for bio-inspired wet adhesion to surface oxides

    PubMed Central

    Heo, Jinhwa; Kang, Taegon; Jang, Se Gyu; Hwang, Dong Soo; Spruell, Jason M.; Killops, Kato L.; Waite, J. Herbert; Hawker, Craig J.

    2012-01-01

    A facile synthetic strategy for introducing catecholic moieties into polymeric materials based on a readily available precursor – eugenol – and efficient chemistries – tris(pentafluorophenyl)borane catalyzed silation and thiol-ene coupling is reported. Silyl-protection is shown to be critical for the oxidative stability of catecholic moieties during synthesis and processing which allows functionalized polysiloxane derivatives to be fabricated into 3-D microstructures as well as 2-D patterned surfaces. Deprotection gives stable catechol surfaces with adhesion to a variety of oxide surfaces being precisely tuned by the level of catechol incorporation. The advantage of silyl-protection for catechol functionalized polysiloxanes is demonstrated and represents a promising and versatile new platform for underwater surface treatments. PMID:23181614

  4. EMSL Research and Capability Development Proposals Accurate Embedded-Cluster Modeling of Insulators: Applications to Metal Oxide Surface

    E-print Network

    to understanding, controlling, and designing molecular interactions and transformations for new energy sources: Applications to Metal Oxide Surface Chemistry and Surface Excitation Processes Project Duration: May 2008 accurate quantum mechanical methods. Implementing various embedding approaches allows us to tackle

  5. Self-Assembled Monolayers on Aluminum and Copper Oxide Surfaces: Surface and Interface Characteristics, Nanotribological Properties, and Chemical Stability

    Microsoft Academic Search

    Enamul Hoque; James A. DeRose; Bharat Bhushan; Hans Jörg Mathieu

    The formation of self-assembled monolayer (SAM) films onto aluminum and copper oxide surfaces by reaction with 1H,1H,2H,2H-perfluorodecylphosphonic\\u000a acid (PFDP), octadecylphosphonic acid (ODP), decylphosphonic acid (DP), octylphosphonic acid (OP), and 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane\\u000a (PFMS) is discussed in this chapter. The properties and chemical stability of the films have been investigated using complementary\\u000a surface analysis techniques: X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM),

  6. Antimony(III) Oxide Film on a Cellulose Fiber Surface: Preparation and Characterization of the Composite.

    PubMed

    Toledo, Eduardo A.; Gushikem, Yoshitaka; de Castro, Sandra C.

    2000-05-15

    Cellulose/antimony(III) oxide composites, Cel/Sb(2)O(3), with oxide loadings of 1.7, 5.4, and 9.2 wt% were prepared by reacting the precursor SbCl(3) reagent with cellulose in dry ethanol solution. The reaction of the Lewis acid and the cellulose fibers occurred at the~amorphous domains of the biopolymer, increasing the crystallinity degree of the composite compared with that of the untreated cellulose. The scanning electron microscopy images and metal mapping for all samples showed that the oxide film layer uniformly covered the fiber surfaces with no detectable agglomerates of the oxide particles. The synchrotron X-ray diffraction patterns indicated that the antimony oxide film was obtained as a crystalline phase with orthorombic structure. The atomic ratios of O/Sb, determined by X-ray photoelectron spectroscopy, indicated that, for Cel/Sb(2)O(3) samples with 9.3 wt% loading, the fiber surface is nearly saturated by the oxide layer. The thermal stability of Cel/Sb(2)O(3) compared to that of untreated cellulose is practically unaffected. Copyright 2000 Academic Press. PMID:11254285

  7. Chemistry of sulfur oxides on transition metal surfaces: BOC-MP analysis

    Microsoft Academic Search

    Harrell Sellers; Evgeny Shustorovich

    1997-01-01

    The bond order conservation-Morse potential (BOC-MP) method proved to be versatile and useful in analyzing chemisorption and reactivity on transition metal surfaces [1–3]. Most recently, we have applied the BOC-MP method to analyze surface chemistry of sulfur oxides on the Cu and Ni group metals [4,5]. We have calculated the reaction energetics (heats of adsorption, reaction enthalpies and intrinsic activation

  8. Surface plasmon dispersion analysis in the metal-oxide-metal tunnel diode

    NASA Technical Reports Server (NTRS)

    Donohue, J. F.; Wang, E. Y.

    1987-01-01

    A detailed model of surface plasmon dispersion in the metal-oxide-metal tunnel diode is presented in order to clarify the spectral emission from this diode. The model predicts the location of the spectral peaks and the emission between the peaks by considering the effects of retardation on the surface plasmon. A nonradiative mode is found to play a major role in the transition from the visible to UV peaks in the diode spectra.

  9. Surface modification of zinc oxide nanoparticle by PMAA and its dispersion in aqueous system

    Microsoft Academic Search

    Erjun Tang; Guoxiang Cheng; Xiaolu Ma; Xingshou Pang; Qiang Zhao

    2006-01-01

    Commercial zinc oxide nanoparticles were modified by polymethacrylic acid (PMAA) in aqueous system. The hydroxyl groups of nano-ZnO particle surface can interact with carboxyl groups (COO–) of PMAA and form poly(zinc methacrylate) complex on the surface of nano-ZnO. The formation of poly(zinc methacrylate) complex was testified by Fourier-transform infrared spectra (FT-IR). Thermogravimetric analysis (TGA) indicated that PMAA molecules were absorbed

  10. Surface treatment effects of indium–tin oxide in organic light-emitting diodes

    Microsoft Academic Search

    S. Jung; N. G Park; M. Y Kwak; B. O Kim; K. H Choi; Y. J Cho; Y. K Kim

    2003-01-01

    Effects of mechanically polished and annealed indium–tin oxide (ITO) substrate in tris-(8-hydroxyquinoline) aluminum (Alq3)-based light-emitting diodes were studied. It was found that roughness and oxygen content at ITO surface were reduced after the mechanical polishing. The organic light-emitting diodes (OLEDs) fabricated on the polished ITO surface showed 10 times better electroluminescence and current injection than the OLEDs based on as-received

  11. Thermal oxidation of cleft surface of InSe single crystal

    Microsoft Academic Search

    O. A. Balitskii; R. V. Lutsiv; V. P. Savchyn; J. M. Stakhira

    1998-01-01

    The thermal oxidation processes of cleft surface of InSe single crystals in the temperature range from 200 to 615°C have been investigated. We used the cathodoluminescence and X-ray diffraction methods. We established that adsorption processes were activated and defect creation on the cleft InSe surface begun at the low temperatures. The formation of In2Se3 and In2(SeO4)3 phases took place at

  12. Ozone Oxidation of Endocrine Disruptors and Pharmaceuticals in Surface Water and Wastewater

    Microsoft Academic Search

    Shane A. Snyder; Eric C. Wert; David J. Rexing; Ronald E. Zegers; Douglas D. Drury

    2006-01-01

    The oxidative removal of a diverse group of trace organic contaminants from surface water and wastewater was evaluated using ozone (O3) and O3 combined with hydrogen peroxide (O3\\/H2O2). Target compounds included estrogenic and androgenic steroids, pharmaceuticals, pesticides, and industrial chemicals. Bench- and pilot- scale experiments were conducted with surface water spiked with the target compounds and wastewater effluent containing ambient

  13. Influence of Surface Oxide of Sputtered TaN on Displacement Plating of Cu

    NASA Astrophysics Data System (ADS)

    Wang, Zenglin; Sakaue, Hiroyuki; Shingubara, Shoso; Takahagi, Takayuki

    2003-04-01

    Copper can be deposited on TaN by displacement electroless plating when a surface oxide layer is removed by wet chemical etching. For application to ultralarge-scale integrated (ULSI) interconnection technology in which very thin TaN barrier films are used, it is essential to form a stable TaN film with minimal native oxide thickness. In this study, we investigated surface oxidation of sputtered TaN films kept in air atmosphere by X-ray photoelectron spectroscopy (XPS) analysis. TaN films were sputtered in a mixture of Ar and N2 gases, where Ar partial pressure was kept constant at 3.0 mTorr and N2 partial pressure was varied. When N2 partial pressure was lower than 0.5 mTorr, surface oxidation of the TaN films advanced with time. However, when N2 partial pressure was higher than this value, oxidation of TaN film stopped at one monolayer. We confirmed that the redox potentials of TaN films formed with N2 partial pressures higher than 0.5 mTorr are lower than that of Cu, which suggests that displacement plating of Cu is possible on TaN films with thickness smaller than 10 nm.

  14. Surface oxidation of tin chalcogenide nanocrystals revealed by 119Sn-Mössbauer spectroscopy.

    PubMed

    de Kergommeaux, Antoine; Faure-Vincent, Jérôme; Pron, Adam; de Bettignies, Rémi; Malaman, Bernard; Reiss, Peter

    2012-07-18

    Narrow band gap tin(II) chalcogenide (SnS, SnSe, SnTe) nanocrystals are of high interest for optoelectronic applications such as thin film solar cells or photodetectors. However, charge transfer and charge transport processes strongly depend on nanocrystals' surface quality. Using (119)Sn-Mössbauer spectroscopy, which is the most sensitive tool for probing the Sn oxidation state, we show that SnS nanocrystals exhibit a Sn((IV))/Sn((II)) ratio of around 20:80 before and 40:60 after five minutes exposure to air. Regardless of the tin or sulfur precursors used, similar results are obtained using six different synthesis protocols. The Sn((IV)) content before air exposure arises from surface related SnS(2) and Sn(2)S(3) species as well as from surface Sn atoms bound to oleic acid ligands. The increase of the Sn((IV)) content upon air exposure results from surface oxidation. Full oxidation of the SnS nanocrystals without size change is achieved by annealing at 500 °C in air. With the goal to prevent surface oxidation, SnS nanocrystals are capped with a cadmium-phosphonate complex. A broad photoluminescence signal centered at 600 nm indicates successful capping, which however does not reduce the air sensitivity. Finally we demonstrate that SnSe nanocrystals exhibit a very similar behavior with a Sn((IV))/Sn((II)) ratio of 43:57 after air exposure. In the case of SnTe nanocrystals, the ratio of 55:45 is evidence of a more pronounced tendency for oxidation. These results demonstrate that prior to their use in optoelectronics further surface engineering of tin chalcogenide nanocrystals is required, which otherwise have to be stored and processed under inert atmosphere. PMID:22691030

  15. Characterization of High Surface Area Zr-Ce (1:1) Mixed Oxide Prepared by a Microemulsion Method

    E-print Network

    a surface redox reactivity higher than that of the CeO2 single oxide. Introduction Cerium oxide is a common to the particular ability of CeO2 to undergo rapid reduction/ oxidation cycles, has been shown to be of major

  16. Activated carbon enhanced ozonation of oxalate attributed to HO oxidation in bulk solution and surface oxidation: effect of activated carbon dosage and pH.

    PubMed

    Xing, Linlin; Xie, Yongbing; Minakata, Daisuke; Cao, Hongbin; Xiao, Jiadong; Zhang, Yi; Crittenden, John C

    2014-10-01

    Ozonation of oxalate in aqueous phase was performed with a commercial activated carbon (AC) in this work. The effect of AC dosage and solution pH on the contribution of hydroxyl radicals (HO) in bulk solution and oxidation on the AC surface to the removal of oxalate was studied. We found that the removal of oxalate was reduced by tert-butyl alcohol (tBA) with low dosages of AC, while it was hardly affected by tBA when the AC dosage was greater than 0.3g/L. tBA also inhibited ozone decomposition when the AC dosage was no more than 0.05g/L, but it did not work when the AC dosage was no less than 0.1g/L. These observations indicate that HO in bulk solution and oxidation on the AC surface both contribute to the removal of oxalate. HO oxidation in bulk solution is significant when the dosage of AC is low, whereas surface oxidation is dominant when the dosage of AC is high. The oxalate removal decreased with increasing pH of the solution with an AC dosage of 0.5g/L. The degradation of oxalate occurs mainly through surface oxidation in acid and neutral solution, but through HO oxidation in basic bulk solution. A mechanism involving both HO oxidation in bulk solution and surface oxidation was proposed for AC enhanced ozonation of oxalate. PMID:25288554

  17. First-principles studies of polar oxide surfaces and hetero-interfaces

    NASA Astrophysics Data System (ADS)

    Pande, Kanupriya

    Metal oxide surfaces and interfaces are important in several fields of research and have technological applications ranging from catalysis, electronics, magnetic recording and solid-state physics. In this context, polar oxide surfaces and interfaces have interesting, and novel properties due to their unique local atomic and electronic structure. Conventional wisdom based on classical electrostatic theory suggests that polar surfaces are unstable due to the presence of a diverging potential along the surface normal. However, real systems are not made up of rigid charges, even if the lattice is rigid, and the quantum or electronic degrees of freedom are able to efficiently stabilize polar systems. This dissertation presents a first-principles study of the atomic and electronic structure, energetics and growth of polar oxide surfaces and interfaces by using MgO(111) as a model polar surface and Fe2O 3(0001)/MgO(111) as a model polar hetero-interface. The inherent difference in the structure of non-polar MgO(001) and polar MgO(111) surfaces results in different epitaxial growth mechanisms that are sensitive to experimental conditions. Growth of the MgO(111) surface follows a complicated thermodynamic pathway and is highly dynamic in nature due to large, but meta-stable, relaxations of Mg and O atoms at the surface and near sub-surface. Similarly, the polarity of the MgO(111) substrate has a marked effect on the growth of Fe2O 3(0001) films in that it results in drastic structural relaxations leading to a complete rearrangement of Fe and O stacking at the interface. The results of our study suggest that the stabilization of the polar interface and screening of the dipole field occur due to the combined effect of electronic and structural relaxations.

  18. The interaction of water with environmentally relevant surfaces

    SciTech Connect

    Andersson, K.; Yamamoto, S.; Ketteler, G.; Starr, D.E.; Nilsson, A.; Salmeron, M.; Bluhm, H.

    2006-04-05

    Probing the coverage and chemical speciation of molecules at surfaces are of fundamental interest in molecular environmental science. The concentration of water and its dissociation fragments at surfaces affect many highly important interfacial chemical processes and there exist no previous quantitative determinations of the coverage of water on clean metal surfaces at near ambient conditions. We have utilized Ambient Pressure Photoelectron Spectroscopy (AP-PES) to study the water/Cu(111) and Cu(110) systems at pressures up to 1 Torr in the temperature range 270-470 K.

  19. Control of carbon nanotube handedness using a supramolecular chiral surface.

    PubMed

    Picaud, F; Herlem, G; Girardet, C

    2011-10-21

    Sorting diameter and handedness of carbon nanotubes still appears as an important challenge in nanotechnology. In this context, supramolecular structures formed by self-assembled chiral molecules deposited on well-defined metal surfaces can be used to discriminate the two isomers of carbon nanotubes. Calculations are carried out to determine the adsorption energy of nanotube enantiomers on alaninate coated Cu(110) surface. The results show a significant discrimination of the L and R handed isomers by such a surface and an additional selectivity in terms of small and large tube diameters. PMID:22029330

  20. Oxidation of the surface of A15 Nb/sub 3/Ge

    SciTech Connect

    Ihara, H.; Kimura, Y.; Yamazaki, M.; Gonda, S.

    1983-01-01

    An oxide layer grown on the A15 Nb/sub 3/Ge surface after exposing to pure oxygen is found to be mainly Nb/sub 2/O/sub 5/ from the in situ observation of x-ray photoelectron spectroscopy. The thickness of the Nb/sub 2/O/sub 5/ layer varies with the oxidation time by following the logarithmic-growth-law. The oxide layer serves as a protective stable film with a thickness of around 1.5 nm. Beneath the oxide layer a Nb-deficient layer occurs in a thickness of 2 nm due to the preferential diffusion of Nb atoms. This is caused by the contact potential difference between Nb/sub 3/Ge and adsorbed oxygen layer and the ionization potential difference between Nb and Ge atoms.

  1. Localized surface plasmon sensing based investigation of nanoscale metal oxidation kinetics

    NASA Astrophysics Data System (ADS)

    Malasi, A.; Sachan, R.; Ramos, V.; Garcia, H.; Duscher, G.; Kalyanaraman, R.

    2015-05-01

    The localized surface plasmon resonance (LSPR) of nanoparticles can be a powerful and sensitive probe of chemical changes in nanoscale volumes. Here we have used the LSPR of silver (Ag) to study the oxidation kinetics of nanoscopic volumes of cobalt (Co) metal. Bimetal nanoparticles of the immiscible Co–Ag system prepared by pulsed laser dewetting were aged in ambient air and the resulting changes to the LSPR signal and bandwidth were used to probe the oxidation kinetics. Co was found to preferentially oxidize first. This resulted in a significant enhancement by a factor of 8 or more in the lifetime of stable Ag plasmons over that of pure Ag. Theoretical modeling based on optical mean field approximation was able to predict the oxidation lifetimes and could help design stable Ag-based plasmonic nanoparticles for sensing applications.

  2. Influence of surface mechanical attrition treatment on the oxidation behavior of 316L stainless steel at 750°C

    NASA Astrophysics Data System (ADS)

    Benafia, S.; Retraint, D.; Panicaud, B.; Grosseau Poussard, J. L.

    2014-08-01

    In this paper, the effects of Surface Mechanical Attrition Treatment on the high- temperature oxidation of AISI 316L austenitic stainless steel are investigated. Samples treated with different conditions were oxidized at 750°C in order to study the effect of this type of nanocrystallisation on the oxidation resistance of the alloy concerned. X-ray diffraction and in- situ Raman spectroscopy were used to identify the oxides formed at the surface. The results indicate the presence of hematite, magnetite and chromium oxides. Experimental results obtained by Raman spectroscopy were also used to study the stress evolution in Cr2O3 films during isothermal conditions.

  3. FTIR Spectroscopic Analysis of Surface Oxidation Reactions During Ozonation of Fossil Resin and Coal

    Microsoft Academic Search

    Q. YU; K. BUKKA; Y. YE; J. D. MILLER

    1992-01-01

    Diffuse and specular reflectance FTIR analysis both fossil resin (resinite) and coal has been carried out to study surface oxidation reactions which occur during the selective flotation of fossil resin from coal by ozone conditioning. It was found from the FTIR spectra that ozonation of both fossil resin and coal causes an increase in the peak intensity associated with stretching

  4. Role of oxide surface in coordination chemistry of transition metal ions in catalytic systems

    Microsoft Academic Search

    L. Bonneviot; M. Curie

    1988-01-01

    On going from the solution into the bulk of an oxide through the fluid-solid interface, it is possible to encounter four types of coordina- tion chemistry (CC) for a transition metal ion (TMI) : solution coordina- tion chemistry, extraframework ion CC, surface framework ion CC and solid state CC. In each case, the reactivity of the TMI is discussed on

  5. Surface defects and arc generation in reactive magnetron sputtering of aluminium oxide thin films

    Microsoft Academic Search

    K Koski; J Hölsä; P Juliet

    1999-01-01

    Arcing phenomena and defect density on the surface of aluminium oxide thin films have been investigated as a function of process parameters such as pulsing frequency, substrate bias voltage, target voltage and sputtering gas pressure. The thin films were deposited by direct current reactive magnetron sputtering techniques. The deposition of the thin films was controlled by target voltage. A pulsed

  6. Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications

    Microsoft Academic Search

    Ajay Kumar Gupta; Mona Gupta

    2005-01-01

    Superparamagnetic iron oxide nanoparticles (SPION) with appropriate surface chemistry have been widely used experimentally for numerous in vivo applications such as magnetic resonance imaging contrast enhancement, tissue repair, immunoassay, detoxification of biological fluids, hyperthermia, drug delivery and in cell separation, etc. All these biomedical and bioengineering applications require that these nanoparticles have high magnetization values and size smaller than 100nm

  7. Surface modification of iron oxide nanoparticles and their conjuntion with water soluble polymers for biomedical application

    Microsoft Academic Search

    Nguyen Thanh Huong; Lam Thi Kieu Giang; Nguyen Thanh Binh; Le Quoc Minh

    2009-01-01

    Superparamagnetic iron oxide nanoparticles (SPION) coated with suitable bio-compatible substances have been used in biomedicine, particularly in magnetic resonance imaging (MRI), tissue engineering, and hyperthermia and drug delivery. In this study, we describe the synthesis of SPION and its surface modification for in-vitro experiments. The particle diameter and structure were estimated by FESEM, TEM, XRD analyses. The saturation magnetization was

  8. Formation and reactivity of surface-bound high oxidation state Ruthenium-oxo complexes.

    SciTech Connect

    Hornstein, B. J. (Brooks J.); Dattelbaum, D. M. (Dana M.); Schoonover, J. R. (Jon R.); Meyer, T. J. (Thomas J.)

    2004-01-01

    Ruthenium polypyridyl oxalate complexes are precursors to high oxidation state species that can catalyze the oxidation of a variety of substrates. Covalent attachment of these reactive species to surfaces such at ZrO{sub 2} or TiO{sub 2} inhibit catalyst deactivation and provide supports from which to build electrocatalytic and photoelectrocatalytic devices. Unfortunately, few details of the effects of surface binding on reactivity are available in the literature. To this end, precursors such as, Ru(H{sub 2}O{sub 3}Ptpy)(C{sub 2}O{sub 4})(H{sub 2}O) and (C{sub 2}O{sub 4})(H{sub 2}O{sub 3}Ptpy)Ru-O-Ru(H{sub 2}O{sub 3}Ptpy)(C{sub 2}O{sub 4}) (tpy is terpyridine) have been synthesized and attached to TiO{sub 2}. Quantitative surface binding studies were carried out and acid catalyzed solvolysis was used to form the aqua species. The complexes were oxidized with Ce(IV) to their high-valent analogs and their reactivity toward selected substrates was tested. These studies not only provide information about the effects of surface binding on the reactivity of metal oxides but also have implications for the development of light-driven catalysts.

  9. Surface Plasmon Resonance (SPR) Electron and Energy Transfer in Noble Metal-Zinc Oxide Composite Nanocrystals

    E-print Network

    Kim, Tae-Geun

    Surface Plasmon Resonance (SPR) Electron and Energy Transfer in Noble Metal-Zinc Oxide Composite tagging, drug delivery, chemical sensors, catalysts, and photovoltaics.9­11 ZnO is a wide energy band gap is beneficial to light absorption/emission or electron transfer. Nanometer-scale noble metals have been

  10. ROLE OF SURFACE COMPLEXED IRON IN OXIDANT GENERATION AND LUNG INFLAMMATION INDUCED BY SILICATES

    EPA Science Inventory

    The hypothesis was tested that silica and silicate dusts complex iron on their surface and that this iron increases 1) in vitro oxidant generation, and mediator release by alveolar macrophages, and 2) acute inflammatory lung injury. ilica and silicates were found to complex more ...

  11. Quantitative determination of elemental sulfur at the arsenopyrite surface after oxidation by ferric iron: mechanistic implications

    Microsoft Academic Search

    Molly M. McGuire; Jillian F. Banfield; Robert J. Hamers

    2001-01-01

    : The elemental sulfur formed at the arsenopyrite surface after oxidation by ferric iron was quantitatively measured by extraction in perchloroethylene and subsequent quantitative analysis by HPLC. Reactions with ferric iron in perchloric acid solutions or in sulfuric acid solutions (both at pH = 1 and 42°C, which approximate extreme acid mine drainage conditions) produced elemental sulfur in quantities greater

  12. Surface and lightning sources of nitrogen oxides over the United States: Magnitudes, chemical evolution, and outflow

    E-print Network

    Jacob, Daniel J.

    commercial aircraft. We show that regional lightning is the dominant source of this upper tropospheric NOxSurface and lightning sources of nitrogen oxides over the United States: Magnitudes, chemical; accepted 5 January 2007; published 18 April 2007. [1] We use observations from two aircraft during

  13. INFLUENCE OF TEMPERATURE ON NICKEL SORPTION ON CLAY MINERAL AND OXIDE SURFACES. K. G. Scheckel1

    E-print Network

    Sparks, Donald L.

    INFLUENCE OF TEMPERATURE ON NICKEL SORPTION ON CLAY MINERAL AND OXIDE SURFACES. K. G. Scheckel1- mation of metal precipitates. However, the influence of temperature on the kinetic formation of these metal pre- cipitates has not been studied. The effect of temperature on reaction rates is well known

  14. Tip-induced nano-writing/machining of Si and DLC surfaces ``anodic'' versus thermal oxidation?

    NASA Astrophysics Data System (ADS)

    Myhra, S.; Watson, G. S.

    2005-08-01

    Tip-induced oxidative manipulation of conducting surfaces, e.g., Si and some metals, has conventionally been described by a field-induced anodic mechanism. Likewise, in the case of electrically conducting graphitic and diamond-like carbon (DLC) films, tip-induced conversion of carbon to CO2 was initially thought to be due to an ionisation process. There is now mounting evidence for thermal activation playing an important role. The state of the tip is a critical, but largely disregarded, factor in such experiments. The present project has been prepared and characterized by I V analysis, tips with different initial characteristics (e.g., H-termination , Au-coating, native oxide). Likewise, several surfaces have been prepared (e.g., Si plus termination by either native or thermal oxide, or plus H-termination, DLC and Au), and also subjected to I V analysis. The resultant point-contact characteristics were found to range from ohmic to non-ohmic (the latter due to either direct or Fowler Nordheim tunnelling). The various combinations were tested with respect to oxidative yield and tip durability. It was found that the presence of a tunnelling barrier at the point of contact is essential for enhancing yield. Tip durability, on the other hand, is promoted by the barrier being located in the surface thus localizing thermal deposition in the surface rather than in the tip.

  15. Reconstructing Earth's Surface Oxidation Across The Archean- Proterozoic Transition

    NASA Astrophysics Data System (ADS)

    Kaufman, A. J.; Guo, Q.; Strauss, H.; Schröder, S.; Gutzmer, J.; Wing, B. A.; Baker, M.; Bekker, A.; Jin, Q.; Kim, S.; Farquhar, J.

    2010-12-01

    The Archean-Proterozoic transition is characterized by the widespread deposition of organic-rich shale, sedimentary iron formation, glacial diamictite, and marine carbonates recording profound carbon isotope anomalies, but notably lacks bedded evaporites. All deposits reflect environmental changes in oceanic and atmospheric redox states, in part associated with Earth’s earliest ice ages. Time-series data for multiple sulfur isotopes from carbonate associated sulfate as well as sulfides in the glaciogenic Duitschland Formation of the Transvaal Supergroup, South Africa, capture the concomitant buildup of sulfate in the ocean and the loss of mass independent sulfur isotope fractionation. This is arguably associated with the atmospheric rise of oxygen (as well as the protective ozone layer) coincident with profound changes in ocean chemistry and biology. The loss of the MIF signal within the Duitschland succession is in phase with the earliest recorded positive carbon isotope anomaly, convincingly linking these environmental perturbations to the Great Oxidation Event (ca. 2.3 Ga). The emergence of cyanobacteria and oxygenic photosynthesis may be associated with a geochemical “whiff of oxygen” recorded in 2.5 Ga sediments. If true, the delay in the GOE can then be understood in terms of a finite sink for molecular oxygen - ferrous iron, which was abundant in deep Neoarchean seawater and sequestered in a worldwide episode of iron formation deposition ending shortly before accumulation of the Duitschland Formation. Insofar as early Paleoproterozoic glaciation is associated with oxygenation of a methane-rich atmosphere, we conclude that Earth’s earliest ice age(s) and the onset of a modern and far more energetic carbon cycle are directly related to the global expansion of cyanobacteria that released oxygen to the environment, and of eukaryotes that respired it.

  16. Aqueous aggregation and surface deposition processes of engineered superparamagnetic iron oxide nanoparticles for environmental applications.

    PubMed

    Li, Wenlu; Liu, Di; Wu, Jiewei; Kim, Changwoo; Fortner, John D

    2014-10-21

    Engineered, superparamagnetic, iron oxide nanoparticles (IONPs) have significant potential as platform materials for environmental sensing, imaging and remediation due to their unique size, physicochemical and magnetic properties. To this end, controlling the size and surface chemistry of the materials is crucial for such applications in the aqueous phase, and in particular, for porous matrixes with particle-surface interaction considerations. In this study, superparamagnetic, highly monodispersed 8 nm IONPs were synthesized and transferred into water as stable suspensions (remaining monodispersed) by way of an interfacial oleic acid bilayer surface. Once stabilized and characterized, particle-particle and model surface interactions (deposition and release) were quantitatively investigated and described systematically as a function of ionic strength (IS) and type with time-resolved dynamic light scattering (DLS), zeta potential, and real-time quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The critical coagulation concentration (CCC) for oleic acid bilayer coated iron oxide nanoparticles (OA-IONPs) were determined to be 710 mM for NaCl (matching DLVO predictions) and 10.6 mM for CaCl2, respectively. For all conditions tested, surface deposition kinetics showed stronger, more favorable interactions between OA-IONPs and polystyrene surfaces compared to silica, which is hypothesized to be due to increased particle-surface hydrophobic interactions (when compared to silica surfaces). PMID:25222070

  17. A new strategy to grow polymer brush on graphene oxide surface through microwave assisted polymer synthesis

    NASA Astrophysics Data System (ADS)

    Park, Min Su; Ramaraj, B.; Yoon, Kuk Ro

    2012-09-01

    Herein, we report a method for growing polymers directly from the surface of graphene oxide (GPO). In this method, surface-initiated, microwave irradiation supported polymerization of benzyl chloride carrying vinylates was carried out from the surface of graphene oxide (GPO) for tailoring surface properties of GPO. This synthetic method consists of two important steps: first, the graphene was converted into GPO, then vinylbenzyl chloride (VBC) was polymerized on the surface of GPO by microwave induced irradiation polymerization. The structure and properties of the resultant polymeric conjugates were characterized by a range of characterization techniques viz.: Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The FT-IR analysis of polymeric conjugates shows infrared (IR) peaks characteristic of VBC on the surface of GPO. TGA reveals enhanced thermal stability for GPO surface polymerized with VBC. EDX and XPS analysis shows signal corresponding to the chloride with reduction in oxygen percentage and increase in carbon percentage. SEM and TEM images visually show the presence of PVBC polymer layer on GPO surface.

  18. Interaction of Aqueous Chromium Ions with Iron Oxide Surfaces

    SciTech Connect

    Brown, G. E.; Chambers, Scott A.; Amonette, James E.; Rustad, James R.; Kendelewicz, Thomas; Liu, Ping; Doyle, C. S.; Grolimund, D.; Foster, Nancy S.; Joyce, Stephen A.; Thevuthasan, Suntharampillai

    2000-05-01

    To gain a more fundamental understanding of abiotic processes controlling reduction reactions of aqueous chromate and dichromate ions (Cr(VI)aq) in subsurface environments, we carried out molecular-level experimental and modeling studies of the interaction of water and Cr(VI)aq with well-characterized single crystal samples of synthetic and natural hematite and magnetite. A reductionist approach was adopted in which simplified model systems of increasing complexity were studied. Photoemission spectroscopy (PES), photo-electron diffraction, and vacuum STM were used to characterize the composition, atomic structure, and morpho-logy of clean surfaces of ?-Fe?O?(0001) and Fe?O?(100) grown by molecular beam epitaxy on single crystal substrates of ?-Al?O?(0001) and MgO(100), respectively.

  19. On the surface magnetism induced atypical ferromagnetic behavior of cerium oxide (CeO2) nanoparticles

    NASA Astrophysics Data System (ADS)

    Sakara, M.; Arumugam, S.; Tripathy, S.; Balakumar, S.

    2012-06-01

    An investigation was made on the intrinsic ferromagnetic behavior of nano sized cerium oxide (ceria). The nanosized ceria was prepared by modified sol gel method with crystallite size around 7nm. Structural analysis was done by XRD which showed a single phase, impurity free fluorite type crystal structured of nano ceria. The morphological analysis by FESEM technique showed agglomerated nature of nanoparticles due to their high surface energy. The surface and bulk information was obtained from UV and visible Raman analysis. From Raman studies it was observed that the large surface defect which was the prime reason for the induced surface magnetism in the nano ceria. From magnetization studies by VSM, it was found that if magnetism was associated with the surface defects of the material. The ferromagnetic behavior of nanosized ceria is still under debate. An attempt has taken to explain the same with emphasizing the surface magnetism of ceria nanoparticles.

  20. Spatially-resolved modeling of electric double layers and surface chemistry for the hydrogen oxidation reaction in

    E-print Network

    Litster, Shawn

    HOR with the three elementary steps for hydrogen oxidation reaction on Pt surface: ( )2H +2Pt 2 HSpatially-resolved modeling of electric double layers and surface chemistry for the hydrogen oxidation reaction in water-filled platinum-carbon electrodes Iryna V. Zenyuk and Shawn Litster Department

  1. The influence of surface oxides on the distribution and release of nickel from Nitinol wires.

    PubMed

    Shabalovskaya, Svetlana A; Tian, He; Anderegg, James W; Schryvers, Dominique U; Carroll, William U; Van Humbeeck, Jan

    2009-02-01

    The patterns of Ni release from Nitinol vary depending on the type of material (Ni-Ti alloys with low or no processing versus commercial wires or sheets). A thick TiO(2) layer generated on the wire surface during processing is often considered as a reliable barrier against Ni release. The present study of Nitinol wires with surface oxides resulting from production was conducted to identify the sources of Ni release and its distribution in the surface sublayers. The chemistry and topography of the surfaces of Nitinol wires drawn using different techniques were studied with XPS and SEM. The distribution of Ni into surface depth and the surface oxide thickness were evaluated using Auger spectroscopy, TEM with FIB and ELNES. Ni release was estimated using either ICPA or AAS. Potentiodynamic potential polarization of selected wires was performed in as-received state with no strain and in treated strained samples. Wire samples in the as-received state showed low breakdown potentials (200 mV); the improved corrosion resistance of these wires after treatment was not affected by strain. It is shown how processing techniques affect surface topography, chemistry and also Ni release. Nitinol wires with the thickest surface oxide TiO(2) (up to 720 nM) showed the highest Ni release, attributed to the presence of particles of essentially pure Ni whose number and size increased while approaching the interface between the surface and the bulk. The biological implications of high and lasting Ni release are also discussed. PMID:18996586

  2. Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO

    NASA Technical Reports Server (NTRS)

    Drawdy, Jean E.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

    1990-01-01

    Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions.

  3. Surface and interface analysis of poly-hydroxyethylmethacrylate-coated anodic aluminium oxide membranes

    NASA Astrophysics Data System (ADS)

    Ali, Nurshahidah; Duan, Xiaofei; Jiang, Zhong-Tao; Goh, Bee Min; Lamb, Robert; Tadich, Anton; Poinern, Gérrard Eddy Jai; Fawcett, Derek; Chapman, Peter; Singh, Pritam

    2014-01-01

    The surface and interface of poly (2-hydroxyethylmethacrylate) (PHEMA) and anodic aluminium oxide (AAO) membranes were comprehensively investigated using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. It was found that 1s??* (Cdbnd O) and 1s??* (Csbnd O) transitions were dominant on the surface of both bulk PHEMA polymer and PHEMA-surface coated AAO (AAO-PHEMA) composite. Findings from NEXAFS, Fourier-Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses suggest the possibility of chemical interaction between carbon from the ester group of polymer and AAO membrane.

  4. The Study of Oxidation on TiAl Surface with Photoemission Spectroscopy in Conjunction with Synchrotron Radiation

    NASA Astrophysics Data System (ADS)

    Hashinokuchi, Michihiro; Sumimoto, Yuichi; Tode, Mayumi; Harries, James; Okada, Michio; Teraoka, Yuden; Kasai, Toshio

    The oxidation processes on a TiAl surface induced by a hyperthermal O2 molecular beam (HOMB) with a translational energy of 2.2 eV was studied by X-ray photoemission spectroscopy in conjunction with synchrotron radiation. At a surface temperature of 300 K, the simultaneous growth of Al and Ti oxides accompanied with the segregation of Al2O3 near the surface was observed. The efficiency of oxidation for the HOMB incidence was smaller than that for O2 backfilling (25 meV). Furthermore, the chemical compositions of oxide species (Al2O3, Ti2O3, TiO2) on the TiAl surface were independent of the translational energy of incident O2 molecule. The present results suggest that the oxidation on TiAl surface proceed via precursor molecular states.

  5. Surface modification, heterojunctions, and other structures: composing metal oxide nanocrystals for chemical sensors

    NASA Astrophysics Data System (ADS)

    Epifani, Mauro; Comini, Elisabetta; Díaz, Raül; Genç, Aziz; Arbiol, Jordi; Andreu, Teresa; Siciliano, Pietro; Faglia, Guido; Morante, Joan R.

    2014-03-01

    The modification of the surface reception properties of nanocrystalline structures is of great interest in environmental, catalysis and energy related applications. For instance, an oxide surface covered with a layer of another oxide opens the possibility of creating the nanosized counterparts of bulk catalytic systems. A relevant example is the TiO2-WO3, which is an active catalysts in a broad range of reactions. The chemical synthesis of the colloidal, nanocrystalline version of such system will first be exposed, by coupling suitable sol-gel chemistry with solvothermal processing. Then, the range of obtained structures will be discussed, ranging from WOx-surface modified TiO2 to TiO2-WO3 heterojunctions. The complex structural evolution of the materials will be discussed, depending on the W concentration. A summary of the acetone sensing properties of these systems will be shown. In particular, the surface activation of the otherwise almost inactive pure TiO2 by surface deposition of WO3-like layers will be highlighted. Addition of the smallest W concentration boosted the sensor response to values comparable to those of pure WO3, ranging over 2-3 orders of magnitude of conductance variation in presence of ethanol or acetone gases. Simple analysis of the sensing data will evidence that the combination of such nanocrystalline oxides results in catalytic activation effects, with exactly opposite trend, with respect to pure TiO2, of the activation energies and best responses.

  6. Occurrence of surface polysulfides during the interaction between ferric (hydr)oxides and aqueous sulfide.

    PubMed

    Wan, Moli; Shchukarev, Andrey; Lohmayer, Regina; Planer-Friedrich, Britta; Peiffer, Stefan

    2014-05-01

    Polysulfides are often referred to as key reactants in the sulfur cycle, especially during the interaction of ferric (hydr)oxides and sulfide, forming ferrous-sulphide minerals. Despite their potential relevance, the extent of polysulfide formation and its relevance for product formation pathways remains enigmatic. We applied cryogenic X-ray Photoelectron Spectroscopy and wet chemical analysis to study sulfur oxidation products during the reaction of goethite and lepidocrocite with aqueous sulfide at different initial Fe/S molar ratios under anoxic conditions at neutral pH. The higher reactivity of lepidocrocite leads to faster and higher electron turnover compared to goethite. We were able to demonstrate for the first time the occurrence of surface-associated polysulfides being the main oxidation products in the presence of both minerals, with a predominance of disulfide (S2(2-)(surf)), and elemental sulfur. Concentrations of aqueous polysulfide species were negligible (<1%). With prior sulfide fixation by zinc acetate, the surface-associated polysulfides could be precipitated as zerovalent sulfur (S°), which was extracted by methanol thereafter. Of the generated S°, 20-34% were associated with S2(2-)(surf). Varying the Fe/S ratio revealed that surface polysulfide formation only becomes dominant when the remaining aqueous sulfide concentration is low (<0.03 mmol L(-1)). We hypothesize these novel surface sulfur species, particularly surface disulfide, to act as pyrite precursors. We further propose that these species play an overlooked role in the sulfur cycle. PMID:24735157

  7. XPS and UPS in situ study of oxygen thermal desorption from nanocrystalline diamond surface oxidized by different process

    Microsoft Academic Search

    G. Speranza; S. Torrengo; A. Miotello; L. Minati; I. Bernagozzi; M. Ferrari; M. Dipalo; E. Kohn

    2011-01-01

    The chemistry of oxygen bonding on the diamond surface is a rich area of surface science research. It is well known that different surface terminations lead to strong variation of the material work function. This effect in diamond assumes peculiar consequences. In fact the oxidized diamond surface is hydrophilic, due to the high work function it shows a positive electron

  8. Selective surface modification of lithographic silicon oxide nanostructures by organofunctional silanes

    PubMed Central

    von Borczyskowski, Christian; Graaf, Harald

    2013-01-01

    Summary This study investigates the controlled chemical functionalization of silicon oxide nanostructures prepared by AFM-anodization lithography of alkyl-terminated silicon. Different conditions for the growth of covalently bound mono-, multi- or submonolayers of distinctively functional silane molecules on nanostructures have been identified by AFM-height investigations. Routes for the preparation of methyl- or amino-terminated structures or silicon surfaces are presented and discussed. The formation of silane monolayers on nanoscopic silicon oxide nanostructures was found to be much more sensitive towards ambient humidity than, e.g., the silanization of larger OH-terminated silica surfaces. Amino-functionalized nanostructures have been successfully modified by the covalent binding of functional fluorescein dye molecules. Upon excitation, the dye-functionalized structures show only weak fluorescence, which may be an indication of a relatively low surface coverage of the dye molecules on length scale that is not accessible by standard AFM measurements. PMID:23616941

  9. Adsorption of V on a Hematite (0001) Surface and its Oxidation: Monolayer Coverage

    SciTech Connect

    Jin, J.; Ma, X.; Kim, C.-Y.; Ellis, D.E.; Bedzyk, M.J. (NWU)

    2008-10-06

    The adsorption of a monolayer of V on idealized Fe- and oxygen-terminated hematite (0 0 0 1) surfaces and subsequent oxidation under atomic O adsorption are studied by density functional theory. Theoretical results are compared with X-ray surface standing wave and X-ray photoelectron spectroscopic measurements, and interpreted in the light of data on sub-monolayer coverages. Near-surface Fe reduction under V adsorption and accompanying structural relaxation are examined. These effects and subsequent response to oxidation, are found to be highly site specific. A full monolayer of oxygen leads to a V{sup 5+} state and reoxidation of subsurface Fe to the trivalent state, seen in both theory and experiment.

  10. Density functional theory study of the oxidation of ammonia on the IrO2(110) surface.

    PubMed

    Wang, Chia-Ching; Siao, Shih Syong; Jiang, Jyh-Chiang

    2011-12-01

    In this study, we employed density functional theory (DFT) to investigate the oxidation of ammonia (NH(3)) on the IrO(2)(110) surface. We characterized the possible reaction pathways for the dehydrogenation of NH(x) species (x = 1-3) and for the formation of the oxidation products N(2), N(2)O, NO, NO(2), and H(2)O. The presence of oxygen atoms on coordinatively unsaturated sites (O(cus)) of the oxygen-rich IrO(2)(110) surface promotes the oxidation of NH(3) on the surface. In contrast, NH(3) molecules prefer undergoing desorption over oxidation on the stoichiometric IrO(2)(110) surface. Moreover, the O(cus) atoms are also the major oxidants leading to the formation of oxidation products; none of the oxidations mediated by the bridge oxygen atoms were favorable reactions. The energy barrier for formation of H(2)O as a gaseous oxidation product on the IrO(2)(110) surface is high (from 1.83 to 2.29 eV), potentially leading to the formation of nitrogen-atom-containing products at high temperature. In addition, the selectivity toward the nitrogen-atom-containing products is dominated by the coverage of O(cus) atoms on the surface; for example, a higher coverage of O(cus) atoms results in greater production of nitrogen oxides (NO, NO(2)). PMID:22047008

  11. Propene oxidation over Cu[sub 2]O single-crystal surfaces: A surface science study of propene activation at 1 atm and 300 K

    SciTech Connect

    Schulz, K.H.; Cox, D.F. (Virginia Polytechnic Institute and State Univ., Blacksburg, VA (United States))

    1993-10-01

    Propene oxidation was studied on Cu[sub 2]O single-crystal surfaces using XPS and TDS in ultrahigh vacuum (UHV) following propene exposures at 300 K and atmospheric pressure. Three different Cu[sub 2]O surfaces were examined: A Cu[sup +]-terminated (100) surface, an oxygen-terminated (100) surface, and a (111) surface with accessible copper cations and lattice oxygen. Selective oxidation to acrolein is promoted by coordinately unsaturated surface lattice oxygen. No clear correlation between the formation of partial oxidation products and oxygen coordination was observed. Both selective and nonselective oxidation products are formed from lattice oxygen. The propene oxidation pathway proceeds through an allyloxy (CH[sub 2][double bond]CHCH[sub 2]O-) species where oxygen insertion occurs prior to the second hydrogen abstraction over Cu[sub 2]O. This conclusion was reached by comparing the propene TDS results from atmospheric pressure exposures with UHV allyl alcohol and acrolein thermal desorption data. The selective oxidation process over Cu[sub 2]O is subject to a [open quotes]pressure gap[close quotes] at 300 K with oxygen insertion occurring at higher pressures, presumably because of translational and collisional activation. However, the subsequent steps in the selective oxidation pathway can be effectively modeled by dissociative adsorption of oxygenates under UHV to simulate the oxygenated surface intermediates. 34 refs., 8 figs., 1 tab.

  12. Surface-oxidation-induced phase separation in FeMn thin films

    NASA Astrophysics Data System (ADS)

    Lefakis, H.; Huang, T. C.; Alexopoulos, P.

    1988-11-01

    Films of Fe50Mn50, 700 Å thick, were deposited on glass substrates by diode rf sputtering. Auger electron spectroscopy, and x-ray fluorescence analysis verified the film composition and x-ray diffraction determined the crystalline phase to be ?-Mn(Fe), a complex bcc-like structure and a considerable deviation from that dictated by the equilibrium binary phase diagram. The films were annealed for 1 h at 260 °C and 10-7, 10-5, and 10-2 Torr. Auger depth profile analysis showed that (a) while no further oxidation (than that induced by ambient exposure) occurred during annealing at the lowest pressure, severe film oxidation took place at the highest pressure and (b) preferential surface oxidation of Mn resulted in a layered structure consisting of a surface Mn- and oxygen-rich layer followed by a region (deeper into the film) depleted in Mn and Fe enriched. The crystalline phases present were determined by x-ray diffraction analysis to be MnO (fcc) and ?-Fe(Mn) (bcc). Magnetic measurements of the oxidized films revealed that they displayed in-plane isotropic ferromagnetic properties, with 4?Ms˜15-18 kG for the most extensively oxidized films.

  13. Methanol oxidation on (2 × 1)Pt(110): formaldehyde on a stepped surface

    NASA Astrophysics Data System (ADS)

    Wang, J.; DeAngelis, M. A.; Zaikos, D.; Setiadi, M.; Masel, R. I.

    1994-10-01

    In 1897 Sabatier and Severins found that methanol could be selectively oxidized to formaldehyde over a platinum catalyst. However, no one has since been able to produce a platinum catalyst which showed significant selectivity toward formaldehyde production. In this study methanol oxidation on (2 × 1)Pt(110) was examined to see if the (2 × 1)Pt(110) surface showed any unusual selectivity for formaldehyde production. It is found that when a monolayer of methanoi is adsorbed onto a 100 K oxygen covered (2 × 1)Pt(110) sample and then the sample is flashed, part of the methanol reacts and part desorbs. Up to 35% of the methanol which reacts is oxidized to formaldehyde, with the rest reacting to form CO, CO 2, hydrogen, water and adsorbed hydrocarbons. By comparison previous workers found that little formaldehyde production is seen during methanol oxidation on Pt(111). This result shows that the (2 × 1)Pt(110) surface is more selective than any other face of platinum examined so far for oxidation of methanol to formaldehyde. However, the selectivity is still low in comparison to the selectivity of Sabatier and Severins' platinum catalyst or of silver.

  14. Oxidation of elemental mercury by chlorine: Gas phase, Surface,and Photo-induced reaction pathways

    SciTech Connect

    Yan, Nai-Qiang; Liu, Shou-Heng; Chang, Shih-Ger

    2004-10-22

    Accurate oxidation rate constants of mercury gas are needed for determining its dispersion and lifetime in the atmosphere. They would also help in developing a technology for the control of mercury emissions from coal-fired power plants. However, it is difficult to establish the accurate rate constants primarily due to the fact that mercury easily adsorbs on solid surface and its reactions can be catalyzed by the surface. We have demonstrated a procedure that allows the determination of gas phase, surface-induced, and photo-induced contributions in the kinetic study of the oxidation of mercury by chlorine gas. The kinetics was studied using reactors with various surface to volume ratios. The effect of the surface and the photo irradiation on the reaction was taken into consideration. The pressure dependent study revealed that the gas phase oxidation was a three-body collision process. The third order rate constant was determined to be 7.5({+-}0.2) x 10{sup -39} mL{sup 2} molecules{sup -2}s{sup -1} with N{sub 2} as the third body at 297 {+-} 1 K. The surface induced reaction on quartz window was second order and the rate constant was 2.7 x 10{sup -17} mL{sup 2} molecules{sup -1} cm{sup -2} sec. Meanwhile, the 253.7 nm photon employed for mercury detection was found to accelerate the reaction. The utilization efficiency of 253.7 nm photon for Hg{sup 0} oxidation was 6.7 x 10{sup -4} molecules photon{sup -1} under the conditions employed in this study.

  15. Interaction and reactivity of nitric oxide and carbon monoxide on ruthenium surfaces

    SciTech Connect

    Quick, E.E.

    1980-03-01

    A multifaceted investigation of the reduction of nitric oxide by carbon monoxide using a ruthenium (102) single crystal catalyst in the pressure range 10/sup -3/ to 10 Torr and temperature range of 300 to 475/sup 0/C has been undertaken. Kinetic and isotopic results indicate that the reaction products CO/sub 2/ and N/sub 2/ were produced via two reaction mechanisms. Using a reducing gas mixture (low P/sub NO//P/sub CO/ ratio) a two site mechanism was operative involving NO dissociation. The carbon monoxide kinetic order varied from +1 to -3 and the nitric oxide order varied from +1 to 0. The catalyst under these conditions was determined to be metallic ruthenium with oxygen bonded within the first surface layer. The oxygen was unreactive and formed a (1 x 3)-0 LEED pattern. Under oxidizing conditions (high P/sub NO//P/sub CO/ ratio) the catalyst was ruthenium dioxide and the functional mechanism under these reaction conditions yielded a nitric oxide order of +2 to -4. Inclusion of a site poisoning mechanism under reducing conditions and an RuO/sub 2/ growth mechanism involving ruthenium cation transfer under oxidizing conditions into the kinetic rate laws led to an overall rate law which could be fit to the carbon monoxide and nitric oxide order plots. Using isotopically oxygen labelled reactants, it was observed that the three possible isotopes of carbon dioxide were produced. A ..gamma..-CO surface species is postulated as an intermediate in the exchange process. The reaction was observed to be initially surface structure insensitive and the reaction kinetics were derived using a Langmuir-Hinshelwood formalism.

  16. TiO2-Al2O3 binary mixed oxide surfaces for photocatalytic NOx abatement

    NASA Astrophysics Data System (ADS)

    Soylu, Asli Melike; Polat, Meryem; Erdogan, Deniz Altunoz; Say, Zafer; Y?ld?r?m, Cansu; Birer, Özgür; Ozensoy, Emrah

    2014-11-01

    TiO2-Al2O3 binary oxide surfaces were utilized in order to develop an alternative photocatalytic NOx abatement approach, where TiO2 sites were used for ambient photocatalytic oxidation of NO with O2 and alumina sites were exploited for NOx storage. Chemical, crystallographic and electronic structure of the TiO2-Al2O3 binary oxide surfaces were characterized (via BET surface area measurements, XRD, Raman spectroscopy and DR-UV-Vis Spectroscopy) as a function of the TiO2 loading in the mixture as well as the calcination temperature used in the synthesis protocol. 0.5 Ti/Al-900 photocatalyst showed remarkable photocatalytic NOx oxidation and storage performance, which was found to be much superior to that of a Degussa P25 industrial benchmark photocatalyst (i.e. 160% higher NOx storage and 55% lower NO2(g) release to the atmosphere). Our results indicate that the onset of the photocatalytic NOx abatement activity is concomitant to the switch between amorphous to a crystalline phase with an electronic band gap within 3.05-3.10 eV; where the most active photocatalyst revealed predominantly rutile phase together and anatase as the minority phase.

  17. Computational Fluid Dynamics Simulation of Flows in an Oxidation Ditch Driven by a New Surface Aerator

    PubMed Central

    Huang, Weidong; Li, Kun; Wang, Gan; Wang, Yingzhe

    2013-01-01

    Abstract In this article, we present a newly designed inverse umbrella surface aerator, and tested its performance in driving flow of an oxidation ditch. Results show that it has a better performance in driving the oxidation ditch than the original one with higher average velocity and more uniform flow field. We also present a computational fluid dynamics model for predicting the flow field in an oxidation ditch driven by a surface aerator. The improved momentum source term approach to simulate the flow field of the oxidation ditch driven by an inverse umbrella surface aerator was developed and validated through experiments. Four kinds of turbulent models were investigated with the approach, including the standard k?? model, RNG k?? model, realizable k?? model, and Reynolds stress model, and the predicted data were compared with those calculated with the multiple rotating reference frame approach (MRF) and sliding mesh approach (SM). Results of the momentum source term approach are in good agreement with the experimental data, and its prediction accuracy is better than MRF, close to SM. It is also found that the momentum source term approach has lower computational expenses, is simpler to preprocess, and is easier to use. PMID:24302850

  18. Production of hydroxyapatite layers on the plasma electrolytically oxidized surface of titanium alloys.

    PubMed

    Lugovskoy, Alex; Lugovskoy, Svetlana

    2014-10-01

    Hydroxyapatite (HA) is a bioactive material that is widely used for improving the osseointegration of titanium dental implants. Titanium can be coated with HA by various methods, such as chemical vapor deposition (CVD), thermal spray, or plasma spray. HA coatings can also be grown on titanium surfaces by hydrothermal, chemical, and electrochemical methods. Plasma electrolytic oxidation (PEO), or microarc oxidation (MAO), is an electrochemical method that enables the production of a thick porous oxide layer on the surface of a titanium implant. If the electrolyte in which PEO is performed contains calcium and phosphate ions, the oxide layer produced may contain hydroxyapatite. The HA content can then be increased by subsequent hydrothermal treatment. The HA thus produced on titanium surfaces has attractive properties, such as a high porosity, a controllable thickness, and a considerable density, which favor its use in dental and bone surgery. This review summarizes the state of the art and possible further development of PEO for the production of HA on Ti implants. PMID:25175246

  19. Association of uranium with iron oxides typically formed on corroding steel surfaces.

    PubMed

    Dodge, C J; Francis, A J; Gillow, J B; Halada, G P; Eng, C; Clayton, C R

    2002-08-15

    Decontamination of metal surfaces contaminated with low levels of radionuclides is a major concern at Department of Energy facilities. The development of an environmentally friendly and cost-effective decontamination process requires an understanding of their association with the corroding surfaces. We investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces. Uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite. X-ray diffraction confirmed the mineralogical form of the oxide. EXAFS analysis at the U L(III) edge showed that uranium was present in hexavalent form as a uranyl oxyhydroxide species with goethite, maghemite, and magnetite and as a bidentate inner-sphere complex with ferrihydrite and lepidocrocite. Iron was present in the ferric form with ferrihydrite, goethite, lepidocrocite, and maghemite; whereas with magnetite and green rust II, both ferrous and ferric forms were present with characteristic ferrous:total iron ratios of 0.65 and 0.73, respectively. In the presence of the uranyl ion, green rust II was converted to magnetite with concomitantreduction of uranium to its tetravalent form. The rate and extent of uranium dissolution in dilute HCl depended on its association with the oxide: uranium present as oxyhydroxide species underwent rapid dissolution followed by a slow dissolution of iron; whereas uranium present as an inner-sphere complex with iron resulted in concomitant dissolution of the uranium and iron. PMID:12214641

  20. Laser-Surface Alloying of Nimonic 80 with Silicon and Aluminum and its Oxidation Behavior

    NASA Astrophysics Data System (ADS)

    Majumdar, Jyotsna Dutta; Manna, Indranil

    2012-10-01

    In the current study, laser-surface alloying (LSA) of Nimonic 80 (a Ni-based superalloy) was conducted using a high-power continuous wave (CW) CO2 laser by simultaneous feeding of predetermined proportion of elemental Si and Al powders with an Ar shroud. After LSA, the microstructure of the alloyed zone was carefully analyzed and found to consist of several intermetallic phases of Ni and Si. The microhardness of the alloyed zone was significantly increased to 500 VHN compared with 250 VHN of the as-received substrate. The high-temperature oxidation resistance of the laser-surface-alloyed specimens (under isothermal conditions) was improved (at temperature ranges between 1223 K and 1423 K [950 °C and 1150 °C]) compared with as-received Nimonic. Even though LSA enhanced resistance to oxidation up to a limited period, continued exposure to extended hours (at a given temperature) led to spallation of scale. It seems that a SiO2-rich adherent scale is responsible for enhanced protection against oxidation in the laser-surface-alloyed specimens. However, the presence of Al2O3 in the oxide film enhances the resistance to spallation by increasing the scale adherence at a higher temperature. The results are supported by a suitable thermodynamic calculation.

  1. Functionalization to control microstructural, optical, electronic and wetting properties of metal oxide surfaces

    NASA Astrophysics Data System (ADS)

    Singh, Jagdeep

    This thesis focuses on engineering the surface chemistry of oxide surfaces in order to control their microstructural, optical, electronic and wetting properties. Several different types of experiments have been performed to tailor the properties of silicon oxide, titanium dioxide, and zinc oxide surfaces. Applications of this work include organic electronics, sensors and nanomanufacturing. Adsorption of 3-mercaptopropyltrimethoxysilane (MPS) on hydroxylated silicon oxide substrates by immersion in MPS solution or exposure to MPS vapor has been compared using X-ray photoelectron spectroscopy (XPS). To aid the interpretation, MPS has also been cryogenically condensed in ultrahigh vacuum (UHV) onto gold surfaces. Condensation of MPS vapor on gold in the absence of water does not result in MPS polymerization, as evidenced by multilayer desorption upon warming to room temperature. The C1s XPS spectrum has been used to infer the relative abundance of methoxy groups. Vapor-deposition on hydroxylated silicon oxide leads to an unpolymerized MPS monolayer consisting of molecules with two methoxy groups. UV induced hydrophilicity of titanium dioxide surfaces could possibly be used to provide a means of registration and alignment in high-rate nanomanufacturing applications or to induce transfer of nanoelements. In order to understand the nature and magnitude of intermolecular forces, force-distance curves have been measured on TiO2. Toward the goal of possibly using light to induce nanoparticle transfer, force curves have been recorded using an SiO2 colloidal probe before and after irradiating the TiO 2 surface with UV light. In order to eliminate the effects of capillary forces, the relative humidity has been kept below 1% by flowing either N 2 or N2/O2 (1:1) into the AFM chamber. In a dry nitrogen environment, no difference is observed in adhesive forces measured with and without UV exposure. Gold-coated atomic force microscope (AFM) tips functionalized with amine-, hydroxyl, carboxylic acid, and methyl-terminated alkanethiol molecules have been used to probe the adhesive forces of polystyrene and poly(acrylic acid) films in dry air (relative humidity < 0.5%). XPS and contact angle measurements confirm the quality and uniformity of similarly treated gold surfaces and the polymer films. XPS indicates that the amine-functionalized thiol films are protonated and comprised of multilayers. Toward the goal of modifying its optical properties, ZnO nanorod surfaces have been modified using 3-mercaptopropyltriethoxysilane (MPTES) and 1-propanethiol (PPT), and XPS has been used to investigate the changes occurring on the nanorods after surface modification. XPS reveals that in the case of MPTES-modified nanorods, bonding occurs via both S-Zn and Si-O-Zn bond formation. For comparison, 3-mercaptopropyltrimethoxysilane (MPTMS), dodecanethiol and methanethiol have been adsorbed on sputter-cleaned Zn-terminated ZnO (0001) in ultrahigh vacuum (UHV). In this case, XPS indicates that bonding of thiols on ZnO surfaces occurs via S-Zn bond formation. Photoluminescence spectroscopy has been used to study the effect of surface functionalization on the optical properties of the nanorods. MPTES- and PPT-functionalized nano-ZnO show an increase in intensity of the UV emission peak relative to the unfunctionalized nanorods due to reduced probability of surface dependent non-radiative processes. A decrease in the visible peak in both cases is believed to be due to passivation of surface defects. A simple method for encapsulating zinc oxide nanoparticles within an organic matrix has been discovered that consists of dispersing them in an ethanolic solution, adding an organothiol and stirring while heating. Electron microscopy, photoemission, Raman spectroscopy and thermal gray metric analyses demonstrate that partial dissolution of the oxide occurs accompanied by encapsulation within a matrix consisting of a 1:2 zinc-thiol complex. Using this methodology, it is possible to surround ZnO within diverse matrices, including fluorescent ones. (Abstract shorte

  2. Cs promoted oxidation of Zn and Cu?Zn surfaces: a combined experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Chaturvedi, Sanjay; Rodriguez, JoséA.; Hrbek, Jan

    1997-07-01

    The interaction of O 2 with Zn, {Cs}/{Zn} and {Cs}/{CuZn} surfaces was investigated using photoemission and ab initio self-consistent-field (SCF) calculations. On zinc films, the sticking probability of O 2 is extremely low (10 -3-10 -2), and O 2 exposures in the range of 10 3 to 10 4 langmuirs are necessary to produce a significant adsorption of oxygen and the transformation of metallic zinc into zinc oxide. The presence of sub monolayer coverages of cesium enhances the oxidation rate of zinc by 2-3 orders of magnitude. In the {Cs}/{Zn} system, the alkali atom donates electrons to zinc. This charge transfer facilitates the formation of Zn?O 2 dative bonds and breaking of the O?O bond. For the coadsorption of Cs and O 2 on Zn(001), the larger the electron transfer from Zn into the O 2 (1 ?g) orbitals, the bigger the adsorption energy of the molecule and the elongation of the O?O bond. In general, cesium does not promote the oxidation of copper. In the {Cs}/{CuZn} system, copper withdraws electrons from zinc. The presence of copper in the {Cs}/{CuZn} system inhibits the oxidation of the Zn component compared with the {Cs}/{Zn} system by lowering the electron density on the Zn atoms. After exposing the {Cs}/{CuZn} system to O 2, zinc is oxidized at a rate that is larger than that found for clean CuZn surfaces and smaller than seen in {Cs}/{Zn} surfaces. Molecular hydrogen is found to have no effect on oxidized Cu, Zn and CuZn films. However, atomic hydrogen reduces ZnO to metallic zinc and CuO to Cu 2O. In the oxidized CuZn alloy, CuO is reduced first followed by the reduction of ZnO. A comparison of the behavior of O 2/Cs/Zn and H 2O/Cs/Zn systems shows that while O 2 causes severe oxidation of Cs promoted Zn surfaces, H 2O has little or no effect.

  3. Prediction of iodide adsorption on oxides by surface complexation modeling with spectroscopic confirmation.

    PubMed

    Nagata, Takahiro; Fukushi, Keisuke; Takahashi, Yoshio

    2009-04-15

    A deficiency in environmental iodine can cause a number of health problems. Understanding how iodine is sequestered by materials is helpful for evaluating and developing methods for minimizing human health effects related to iodine. In addition, (129)I is considered to be strategically important for safety assessment of underground radioactive waste disposal. To assess the long-term stability of disposed radioactive waste, an understanding of (129)I adsorption on geologic materials is essential. Therefore, the adsorption of I(-) on naturally occurring oxides is of environmental concern. The surface charges of hydrous ferric oxide (HFO) in NaI electrolyte solutions were measured by potentiometric acid-base titration. The surface charge data were analyzed by means of an extended triple-layer model (ETLM) for surface complexation modeling to obtain the I(-) adsorption reaction and its equilibrium constant. The adsorption of I(-) was determined to be an outer-sphere process from ETLM analysis, which was consistent with independent X-ray absorption near-edge structure (XANES) observation of I(-) adsorbed on HFO. The adsorption equilibrium constants for I(-) on beta-TiO(2) and gamma-Al(2)O(3) were also evaluated by analyzing the surface charge data of these oxides in NaI solution as reported in the literature. Comparison of these adsorption equilibrium constants for HFO, beta-TiO(2), and gamma-Al(2)O(3) based on site-occupancy standard states permitted prediction of I(-) adsorption equilibrium constants for all oxides by means of the Born solvation theory. The batch adsorption data for I(-) on HFO and amorphous aluminum oxide were reasonably reproduced by ETLM with the predicted equilibrium constants, confirming the validity of the present approach. Using the predicted adsorption equilibrium constants, we calculated distribution coefficient (K(d)) values for I(-) adsorption on common soil minerals as a function of pH and ionic strength. PMID:19176225

  4. Thermo-oxidation of DIII-D codeposits on open surfaces and in simulated tile gaps

    NASA Astrophysics Data System (ADS)

    Davis, J. W.; Tsui, C. K.; Chung, G. A.; Fitzpatrick, B. W. N.; Haasz, A. A.

    2011-08-01

    This work extends previous thermo-oxidation studies [R. Ochoukov, A.A. Haasz, J.W. Davis, Phys. Scr. T124 (2006) 27; A.A. Haasz, C.K. Tsui, J.W. Davis, R. Ochoukov, Phys. Scr. T128 (2007) 55] of DIII-D codeposits to provide reference data prior to performing in situ thermo-oxidation in DIII-D. The present results confirm that codeposit removal by oxidation in dry air or a mixture of O2-He gas is equally effective as in pure O2, given equivalent O2 partial pressures. We have also demonstrated that increasing the oxidation time to 48 h (compared with 2-8 h [R. Ochoukov, A.A. Haasz, J.W. Davis, Phys. Scr. T124 (2006) 27; A.A. Haasz, C.K. Tsui, J.W. Davis, R. Ochoukov, Phys. Scr. T128 (2007) 55]) does not compensate for 'less severe' oxidation conditions of (i) 'low pressure' (0.021 kPa O2 partial pressure) at 'high temperature' (623 K) and (ii) 'low temperature' (523 K) at 'high pressure' (17 kPa O2 partial pressure). The new results also show that thermo-oxidation is equally effective in removing codeposits from open surfaces and from tile gaps accessible by narrow (˜1 mm) passageways, and have extended the range of the linear relationship between D removal rates and inherent D content.

  5. Sputtering and native oxide formation on (110) surfaces of Cd(1-x)Mn(x)Te

    NASA Technical Reports Server (NTRS)

    Neff, H.; Lay, K. Y.; Abid, B.; Lange, P.; Lucovsky, G.

    1986-01-01

    Native oxides on the surface of Cd(1-x)Mn(x)Te (X between 0 and 0.7) have been analyzed on the basis of X-ray photoemission spectroscopy measurements. Depth profile analysis revealed a significant increase in the thickness at higher Mn concentrations and a strong Mn segregation to the surface, respectively. Sputter-induced damage on cleaved (110)-oriented surfaces was analyzed by photoreflectance and photoluminescence measurements. The damage was found to be larger on CdTe than on the alloy. Thermal annealing showed nearly complete restoration for the surface of the alloy, while CdTe revealed irreversible modifications in the near-surface regime upon sputtering and post annealing.

  6. Studies of Oxidation of the Cu(100) Surface Using Low Energy Positrons

    SciTech Connect

    Fazleev, N. G. [University of Texas at Arlington, Arlington Texas 76019 (United States); Kazan State University, Kazan 420008 (Russian Federation); Maddox, W. B.; Nadesalingam, M.; Rajeshwar, K.; Weiss, A. H. [University of Texas at Arlington, Arlington Texas 76019 (United States)

    2009-03-10

    Changes in the surface of an oxidized Cu(100) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the positron annihilation induced Cu M{sub 2,3}VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The intensity then decreases monotonically as the annealing temperature is increased to {approx}600 deg. C. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. Possible explanation for the observed behavior of the intensity of positron annihilation induced Cu M{sub 2,3}VV Auger peak with changes of the annealing temperature is proposed.

  7. Surface chemistry of Cr(III) oxidation and precipitation on Mn(IV) oxides Gautier Landrot, landrot@udel.edu, Department of Plant and Soil Sciences and Center for Critical Zone Research, University of

    E-print Network

    Sparks, Donald L.

    Surface chemistry of Cr(III) oxidation and precipitation on Mn(IV) oxides GEOC 29 Gautier Landrot, Newark, DE 19717. The main soil components that oxide Cr(III) to the more hazardous chromium species Cr(VI) are manganese oxides. With hydrous manganese oxide (HMO) and birnessite, Cr(III) may react in two steps: a first

  8. Competitive adsorption of dopamine and rhodamine 6G on the surface of graphene oxide.

    PubMed

    Ren, Hui; Kulkarni, Dhaval D; Kodiyath, Rajesh; Xu, Weinan; Choi, Ikjun; Tsukruk, Vladimir V

    2014-02-26

    Competitive adsorption-desorption behavior of popular fluorescent labeling and bioanalyte molecules, Rhodamine 6G (R6G) and dopamine (DA), on a chemically heterogeneous graphene oxide (GO) surface is discussed in this study. Individually, R6G and DA compounds were found to adsorb rapidly on the surface of graphene oxide as they followed the traditional Langmuir adsorption behavior. FTIR analysis suggested that both R6G and DA molecules predominantly adsorb on the hydrophilic oxidized regions of the GO surface. Thus, when R6G and DA compounds were adsorbed from mixed solution, competitive adsorption was observed around the oxygen-containing groups of GO sheets, which resulted in partial desorption of R6G molecules from the surface of GO into the solution. The desorbed R6G molecules can be monitored by fluorescence change in solution and was dependent on the DA concentration. We suggest that the efficient competitive adsorption of different strongly bound bioanalytes onto GO-dye complex can be used for the development of sensitive and selective colorimetric biosensors. PMID:24494630

  9. Excellent c-Si surface passivation by low-temperature atomic layer deposited titanium oxide

    NASA Astrophysics Data System (ADS)

    Liao, Baochen; Hoex, Bram; Aberle, Armin G.; Chi, Dongzhi; Bhatia, Charanjit S.

    2014-06-01

    In this work, we demonstrate that thermal atomic layer deposited (ALD) titanium oxide (TiOx) films are able to provide a—up to now unprecedented—level of surface passivation on undiffused low-resistivity crystalline silicon (c-Si). The surface passivation provided by the ALD TiOx films is activated by a post-deposition anneal and subsequent light soaking treatment. Ultralow effective surface recombination velocities down to 2.8 cm/s and 8.3 cm/s, respectively, are achieved on n-type and p-type float-zone c-Si wafers. Detailed analysis confirms that the TiOx films are nearly stoichiometric, have no significant level of contaminants, and are of amorphous nature. The passivation is found to be stable after storage in the dark for eight months. These results demonstrate that TiOx films are also capable of providing excellent passivation of undiffused c-Si surfaces on a comparable level to thermal silicon oxide, silicon nitride, and aluminum oxide. In addition, it is well known that TiOx has an optimal refractive index of 2.4 in the visible range for glass encapsulated solar cells, as well as a low extinction coefficient. Thus, the results presented in this work could facilitate the re-emergence of TiOx in the field of high-efficiency silicon wafer solar cells.

  10. Oxidation- and organic-molecule-induced changes of the Si surface optical anisotropy: ab initio predictions

    NASA Astrophysics Data System (ADS)

    Schmidt, W. G.; Fuchs, F.; Hermann, A.; Seino, K.; Bechstedt, F.; Paßmann, R.; Wahl, M.; Gensch, M.; Hinrichs, K.; Esser, N.; Wang, S.; Lu, W.; Bernholc, J.

    2004-10-01

    In the last couple of years there has been much methodological and computational progress in the modelling of optical properties from first principles. Reflectance anisotropy spectra (RAS) can now be calculated with true predictive power and can thus be used to draw conclusions directly on the surface geometry. In the present work we study two potentially very interesting applications for RAS: the oxidation of Si(001) and the functionalization of the Si surface with organic molecules. Our calculations confirm experimental indications that the polarity of the interface-induced optical anisotropy is reversed layer by layer with increasing oxide thickness. The oscillation of the RAS amplitude should thus allow for the quantitative monitoring of the vertical progression of the oxidation. Our results for Si(001) surfaces modified by cyclopentene and 9,10-phenanthrenequinone adsorption show a strong sensitivity of the RAS signal with respect to the adsorption geometry. Comparison with experimental data shows that cyclopentene most probably adsorbs via a cycloaddition reaction with the Si surface dimers, while phenanthrenequinone seems to adsorb across two Si dimers.

  11. Electric field effects in transition metal oxides, their surfaces and heterostructures

    NASA Astrophysics Data System (ADS)

    Held, Karsten

    2015-03-01

    Modern computational tools such as density functional theory and its merger with dynamical mean field theory are nowadays inevitable for the modeling and understanding of oxides, their heterostructures and surfaces. In this talk, I will concentrate on the impact of electric fields, how they affect the physical properties and how to make use of them. Substantial internal electric fields are created at polar surfaces, and even for an isopolar-interface the electronic reconstruction can lead to a charge transfer and hence a dipole field. Such internal fields can be employed to efficiently separate electrons and holes in a oxide solar cell. Even if the polar dipole field is compensated by a surface reconstruction, a local surface potential remains, and makes SrTiO3 (110) the arguably simplest 2 dimensional electron gas (2DEG). External electric fields, on the other hand, can trigger ``gigantic'' responses, since correlated oxides are prone to small perturbations. For example, a field effect Mott transistor can be realized in a few layers of SrVO3 with ideal on-off (metal-insulator) switching properties; and interfacing a ferroelectric, BaTiO3, plus a 2DEG with large spin-orbit coupling, BaOsO3, allows for a giant switchable Rashba effect. Support by the ERC through Grant Agreement No. 306447 is gratefully acknowledged.

  12. Conversion of a solid surface from super-hydrophobic to super-hydrophilic by photocatalytic remote oxidation and photocatalytic lithography

    Microsoft Academic Search

    Wakana Kubo; Tetsu Tatsuma

    2005-01-01

    A super-hydrophobic surface, of which contact angle was 151°, was obtained by modifying a SiO2 microparticle film-coated glass plate with octadecyltriethoxysilane (ODS). The super-hydrophobic surface was converted to super-hydrophilic by remote oxidation using a TiO2 photocatalyst for 40min, due to oxidative decomposition of the ODS monolayer. The increase in the wettability of the super-hydrophobic surface with water was faster than

  13. Early stages of the oxidation of metal surfaces. [photoelectron spectroscopy of zinc oxide

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Johnson, K. H.

    1978-01-01

    Photoemission cross sections were calculated for the ZnO4(-6) cluster using the self consistent-chi alpha- scattered wave theory to display the main features of the ultraviolet and X-ray photoemission data from ZnO. A solid model is suggested for an absolute photoemission intensity comparison resulting in chi alpha intensities which are roughly 70% of the experimental values. Together with the experimental data, the calculations allow a complete determination of the electronic structure of a ZnO surface.

  14. Enhanced Cell Integration to Titanium Alloy by Surface Treatment with Microarc Oxidation: A Pilot Study

    PubMed Central

    Lim, Young Wook; Kwon, Soon Yong; Sun, Doo Hoon; Kim, Hyoun Ee

    2009-01-01

    Microarc oxidation (MAO) is a surface treatment that provides nanoporous pits, and thick oxide layers, and incorporates calcium and phosphorus into the coating layer of titanium alloy. We presumed such modification on the surface of titanium alloy by MAO would improve the ability of cementless stems to osseointegrate. We therefore compared the in vitro ability of cells to adhere to MAOed titanium alloy to that of two different types of surface modifications: machined and grit-blasted. We performed energy-dispersive x-ray spectroscopy and scanned electron microscopy investigations to assess the structure and morphology of the surfaces. Biologic and morphologic responses to osteoblast cell lines (SaOS-2) were then examined by measuring cell proliferation, cell differentiation (alkaline phosphatase activity), and ?v?3 integrin. The cell proliferation rate, alkaline phosphatase activity, and cell adhesion in the MAO group increased in comparison to those in the machined and grit-blasted groups. The osteoblast cell lines of the MAO group were also homogeneously spread on the surface, strongly adhered, and well differentiated when compared to the other groups. This method could be a reasonable option for treating the surfaces of titanium alloy for better osseointegration. PMID:19434468

  15. Surface oxidation of GaN(0001): Nitrogen plasma-assisted cleaning for ultrahigh vacuum applications

    SciTech Connect

    Gangopadhyay, Subhashis [Institute of Solid State Physics, University of Bremen, P.O. Box 330440, 28334 Bremen, Germany and Department of Physics, Birla Institute of Technology and Science, Pilani, 333031 Rajasthan (India); Schmidt, Thomas, E-mail: tschmidt@ifp.uni-bremen.de; Kruse, Carsten; Figge, Stephan; Hommel, Detlef; Falta, Jens [Institute of Solid State Physics, University of Bremen, P.O. Box 330440, 28334 Bremen (Germany)

    2014-09-01

    The cleaning of metal-organic vapor-phase epitaxial GaN(0001) template layers grown on sapphire has been investigated. Different procedures, performed under ultrahigh vacuum conditions, including degassing and exposure to active nitrogen from a radio frequency nitrogen plasma source have been compared. For this purpose, x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and scanning tunneling microscopy have been employed in order to assess chemical as well as structural and morphological surface properties. Initial degassing at 600?°C under ultrahigh vacuum conditions only partially eliminates the surface contaminants. In contrast to plasma assisted nitrogen cleaning at temperatures as low as 300?°C, active-nitrogen exposure at temperatures as high as 700?°C removes the majority of oxide species from the surface. However, extended high-temperature active-nitrogen cleaning leads to severe surface roughening. Optimum results regarding both the removal of surface oxides as well as the surface structural and morphological quality have been achieved for a combination of initial low-temperature plasma-assisted cleaning, followed by a rapid nitrogen plasma-assisted cleaning at high temperature.

  16. Cleaning and passivation of copper surfaces to remove surface radioactivity and prevent oxide formation

    Microsoft Academic Search

    Eric W. Hoppe; Allen Seifert; Craig E. Aalseth; Paula P. Bachelor; Anthony R. Day; Danny J. Edwards; Todd W. Hossbach; Kevin E. Litke; Justin I. McIntyre; Harry S. Miley; Shannon M. Schulte; John E. Smart; Glen A. Warren

    2007-01-01

    High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited

  17. The Interaction of Vibrationally Excited Hydrogen with a Copper Surface

    NASA Astrophysics Data System (ADS)

    Parhikhteh, Hadi

    1995-01-01

    The survival probability of H_2 (v = 1, J = 1) scattered from a clean Cu(110) surface has been measured and compared with the survival probability of hydrogen molecules in the ground state to show the role of vibrational energy of the incident molecules. For a translational energy of 78 meV, H_2(v = 0, J = 1) had a ratio of scattered flux/incident flux = 1.01 +/-.01. The same quantity for vibrationally excited molecules was measured to be 0.74 +/- 0.13. The effect of surface coverage on the reflectivity has been studied and possible loss channels are discussed.

  18. Surface Adsorption of Iron Oxide Minerals for Phenol and Dissolved Organic Matter

    NASA Astrophysics Data System (ADS)

    WU, Honghai; LIN, Yiying; WU, Jiayi; ZENG, Lixuan; ZENG, Dingcai; DU, Juan

    The aim of this article is to research the eco-mineralogical development by investigating the adsorption of iron oxide minerals for phenol and dissolved organic matter (DOM). The multiple mechanisms of surface adsorption associated with the iron minerals can coexist, mainly depending on the solution chemistry as well as the physicochemical properties of adsorbates and minerals. The adsorption study was conducted by batch equilibrium techniques. The results showed that the adsorption of goethite and hematite for phenol is weak in acidic and mild acidic media, and that the phenol adsorption isotherms can be fitted well by Langmuir equation with a correlation coefficient of R > 0.985. Therefore, the phenol adsorption was subjected to a surface physical adsorption model, whereas the sorption of goethite for the DOM was stronger along with the DOM sorption fractionation. The DOM sorption fractionation was controlled simultaneously by multi-mechanisms in acidic and neutral media, mainly including "surface ligand exchange", "hydrophobic force", and "van der Waals forces" models. Moreover, the DOM sorption isotherms can be fitted well by linear and Freundlich equations with correlation coefficients, R > 0.92, but not by Langmuir equation ascribed to low concentration of DOM used in this article. The effect of the mineral surface charge on adsorption was significant, especially when pH of the solution neared pH pzc (pH for point of zero charge); the phenol and the hydrophobic DOM molecule and/or fraction can preferentially adsorb onto iron oxide minerals because of the decrease in thickness; even the binding of the water film over the iron minerals disappear. However, the phenol adsorption can be impacted more significantly because of its simple adsorption model, therefore, its pH-dependence adsorption curve showed a peak value at pH 7 -8 near the pH pzc. In general, surface complexation reaction of iron oxides can occur especially in acidic and mild acidic media. However, under the condition of pH 7.5 or so of this study, though the surface ligand exchange may have been still functional, the predominant adsorption mechanisms of DOM onto goethite would be mainly based on the "hydrophobic force" and "van der Waals forces" models. Moreover, the adsorption isotherm of DOM was almost linear (Freundlich equation fitting constant n = 1.02), accounting for the importance of the later two types of adsorption models in the DOM adsorption. Of course, the surface sorption reactions of iron oxide minerals play an important role in regulating immobility and fate of pollutants and natural organic matter in red soils that contain low content of organic matter but high content of iron oxide minerals.

  19. Possible oxidants at Mars surface and their impact on organic matter

    NASA Astrophysics Data System (ADS)

    Noblet, A.; Coll, P. J.; Szopa, C.; Stalport, F.

    2010-12-01

    In 1976, the Viking probes did not provide any results demonstrating the presence of extant life or even organic molecules in the soil samples collected at their landing sites, unlikely to what it could be expected at that time. The results obtained by the biological experiments on board of Viking probes have been discussed for a long time. The most relevant hypothesis is the presence of oxidants in the martian soil. Klein et al. (1978) proposed different oxidizing agents among which “superoxides”, hydrogen peroxide and iron oxides. The presence of H2O2 has been confirmed by its detection in the atmosphere (Clancy et al. 2004; Encrenaz et al. 2004). Moreover, the recent detection of perchlorate by the Phoenix mission confirms the oxidants hypothesis (Hecht et al. 2009). We propose here a review of oxidants potentially present in the martian environment, focusing on their formation pathways and their reactivity on organic molecules. It appears that a synergy between atmosphere, soil, UV radiation and water ice content in the soil could lead to the formation of very reactive species able to degrade organic matter at the surface. Several oxidants could diffuse or directly be formed in the subsurface and thus potentially lead to organic degradation in depth (see the figure). This review work could give guidelines on the oxidizing potential of the martian surface/subsurface and could estimate the stability of organic matter under these conditions. Based on this review work, we have developed an experimental device (MOMIE for Martian Organic Molecules Irradiation and Evolution) to simulate the formation of oxidants in the martian environment and their impact on organic matter. This laboratory experiment will help to determine the fate of organic matter at the martian surface and to define the most relevant detection protocol to highlight organic molecules at Mars by the future in-situ missions. Clancy, R.T., et al., 2004. Icarus 168:116-121 ; Encrenaz, T., et al., 2004. Icarus 170:424-429 ; Hecht, M.H., et al., 2009. Science 325:64-67 ; Klein, H.P., 1978. Icarus 34:666-674.

  20. Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces.

    PubMed

    Jogikalmath, G; Stuart, J K; Pungor, A; Hlady, V

    1999-08-01

    Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the ?m-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of ?-glycidoxypropyltrimethoxy silane (GPS) to glass decreased the pull-off forces relative to the clean glass and made the surface more uniform. The subsequent hydrolysis of the terminal epoxide groups resulted in a larger surface heterogeneity which was modeled by two populations of the terminal hydroxyl groups, each with its own distribution of adhesion forces and force variance. The activation of the hydroxyls with carbonyldiimmidazole (CDI) healed the surface and lowered its adhesion, however, the force variance remained rather large. Finally, the grafting of the ?,?-diamino poly(ethyleneoxide) chains to the CDI-activated glass largely eliminated adhesion except at a few discrete regions. The adhesion on the PEO grafted layer followed the Poisson distribution of the pull-off forces. With the exception of the glass surface, a correlation between the water contact angles and the mean pull-off forces measured with the Si(3)N(4) tip surfaces was found for all modified glass surfaces. PMID:22267896

  1. Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces

    PubMed Central

    Jogikalmath, G.; Stuart, J.K.; Pungor, A.; Hlady, V.

    2012-01-01

    Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the ?m-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of ?-glycidoxypropyltrimethoxy silane (GPS) to glass decreased the pull-off forces relative to the clean glass and made the surface more uniform. The subsequent hydrolysis of the terminal epoxide groups resulted in a larger surface heterogeneity which was modeled by two populations of the terminal hydroxyl groups, each with its own distribution of adhesion forces and force variance. The activation of the hydroxyls with carbonyldiimmidazole (CDI) healed the surface and lowered its adhesion, however, the force variance remained rather large. Finally, the grafting of the ?,?-diamino poly(ethyleneoxide) chains to the CDI-activated glass largely eliminated adhesion except at a few discrete regions. The adhesion on the PEO grafted layer followed the Poisson distribution of the pull-off forces. With the exception of the glass surface, a correlation between the water contact angles and the mean pull-off forces measured with the Si3N4 tip surfaces was found for all modified glass surfaces. PMID:22267896

  2. Control of selectivity in allylic alcohol oxidation on gold surfaces: the role of oxygen adatoms and hydroxyl species.

    PubMed

    Mullen, Gregory M; Zhang, Liang; Evans, Edward J; Yan, Ting; Henkelman, Graeme; Mullins, C Buddie

    2015-02-14

    Gold catalysts display high activity and good selectivity for partial oxidation of a number of alcohol species. In this work, we discuss the effects of oxygen adatoms and surface hydroxyls on the selectivity for oxidation of allylic alcohols (allyl alcohol and crotyl alcohol) on gold surfaces. Utilizing temperature programmed desorption (TPD), reactive molecular beam scattering (RMBS), and density functional theory (DFT) techniques, we provide evidence to suggest that the selectivity displayed towards partial oxidation versus combustion pathways is dependent on the type of oxidant species present on the gold surface. TPD and RMBS results suggest that surface hydroxyls promote partial oxidation of allylic alcohols to their corresponding aldehydes with very high selectivity, while oxygen adatoms promote both partial oxidation and combustion pathways. DFT calculations indicate that oxygen adatoms can react with acrolein to promote the formation of a bidentate surface intermediate, similar to structures that have been shown to decompose to generate combustion products over other transition metal surfaces. Surface hydroxyls do not readily promote such a process. Our results help explain phenomena observed in previous studies and may prove useful in the design of future catalysts for partial oxidation of alcohols. PMID:25588689

  3. Sub-surface oxide features at the aluminum-sapphire interface after low temperature annealing

    NASA Astrophysics Data System (ADS)

    Dutta, Sreya

    This work focuses on the formation of sub-surface oxide features that form at the aluminum-sapphire interface during a low temperature heat-treatment. The features consist of two parts, stable alpha-alumina ridges on the substrate, and faceted pyramidal structures composed of thin, low-temperature oxide shells that are bounded by the ridges. It is surprising to observe the formation of thermodynamically stable alpha-alumina at a low temperature. The ridges are epitaxial with the (0001) sapphire substrate and the overlying metal. The pyramidal features resemble closely the Wulff shape in aluminum. Experiments show that these features are underlying the annealing hillocks. This work is a detailed study of such oxide interfacial features associated with hollow hillocks. At the annealing temperatures (below the melting point of aluminum), the aluminum thin film is subjected to compressive stresses arising from the thermal expansion coefficient mismatch and this is aided by dewetting at the aluminum-sapphire interface. Creep cavitation and grain boundary sliding are postulated to help in the cavity formation. Annealing holes are also observed in the thin films. Two different types of holes are seen: dendritic branched holes and hexagonal faceted holes (drums). At lower temperature and thickness, dendritic holes are seen to be formed at the grain boundaries. The drums form within the grains at higher temperatures and in thicker films. The drums have a surface oxide layer suspended on the top. It is postulated that clustering of vacancies due to the presence of irregularities, defects, and dislocations at the interface as well as dewetting causes the nucleation of the drums at the interface. Numerous hillock-hole couples were seen. Thinning of the metal in areas near the hillocks could possibly aid in the hole formation process. It is speculated that the hole growth occurred during the cooling stage when the film was subjected to tensile stresses. Another interesting aspect of the study is that the features at the interface are somehow getting oxidized. Annealing holes surrounding the hillocks are suspected of playing a role in the subsurface oxygen transport. Calculations of diffusion coefficients needed to form the oxide features, generate unrealistically high diffusion coefficient values for interfacial, amorphous/gamma alumina, and grain boundary diffusion mechanisms at these low temperatures. Oxygen permeation through the oxide drum shells and especially through the interfacial oxide can be a possible transport path. It is also postulated that easy transport paths, like cracks or orifices on the drums or hillocks, could contribute to the oxidation process.

  4. Self-assembly and oligomerization of alkyne-terminated molecules on metal and oxide surfaces.

    PubMed

    Vyklický, Libor; Afzali-Ardakani, Ali; Kagan, Cherie R

    2005-12-01

    We report the self-assembly and subsequent oligomerization of organic molecules based on terthiophenes bearing a terminal alkyne moiety. Molecules with thioacetate and phosphonic acid functional groups were synthesized, enabling molecular self-assembly on metal (Au and Pd) and metal oxide [Al(2)O(3), HfO(2), and indium tin oxide (ITO)] surfaces, respectively. The molecules were assembled from solution and then oligomerized using either 2,5-norbornadiene-rhodium(I) chloride dimer or UV light. UV-vis and infrared absorption spectroscopies and electrochemical techniques show that the molecules assemble to form dense monolayers on the substrate surfaces and oligomerize under the action of a catalyst or UV light. PMID:16316082

  5. Prediction of Surface and pH-Specific Binding of Peptides to Metal and Oxide Nanoparticles

    NASA Astrophysics Data System (ADS)

    Heinz, Hendrik; Lin, Tzu-Jen; Emami, Fateme Sadat; Ramezani-Dakhel, Hadi; Naik, Rajesh; Knecht, Marc; Perry, Carole C.; Huang, Yu

    2015-03-01

    The mechanism of specific peptide adsorption onto metallic and oxidic nanostructures has been elucidated in atomic resolution using novel force fields and surface models in comparison to measurements. As an example, variations in peptide adsorption on Pd and Pt nanoparticles depending on shape, size, and location of peptides on specific bounding facets are explained. Accurate computational predictions of reaction rates in C-C coupling reactions using particle models derived from HE-XRD and PDF data illustrate the utility of computational methods for the rational design of new catalysts. On oxidic nanoparticles such as silica and apatites, it is revealed how changes in pH lead to similarity scores of attracted peptides lower than 20%, supported by appropriate model surfaces and data from adsorption isotherms. The results demonstrate how new computational methods can support the design of nanoparticle carriers for drug release and the understanding of calcification mechanisms in the human body.

  6. Surface modification of iron oxide nanoparticles and their conjuntion with water soluble polymers for biomedical application

    NASA Astrophysics Data System (ADS)

    Thanh Huong, Nguyen; Thi Kieu Giang, Lam; Thanh Binh, Nguyen; Minh, Le Quoc

    2009-09-01

    Superparamagnetic iron oxide nanoparticles (SPION) coated with suitable bio-compatible substances have been used in biomedicine, particularly in magnetic resonance imaging (MRI), tissue engineering, and hyperthermia and drug delivery. In this study, we describe the synthesis of SPION and its surface modification for in-vitro experiments. The particle diameter and structure were estimated by FESEM, TEM, XRD analyses. The saturation magnetization was characterized. SPION with a mean size of 12 nm have been prepared under N2 atmosphere, with support of natural polymeric starch, by controlling chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts ratios of Fe2+ and Fe3+. The surface of SPION-nanoparticles was treated with a coordinatable agent for higher dispersion ability in water and remaining the superparamagnetic behavior. The prepared iron oxide nanoparticles were coated with starch, dextran, PEG or MPEG to extend the application potential in the quite different engineering field of nano biomedicine.

  7. Laser-assisted chemical cleaning of thin oxide films on carbon steel surfaces

    NASA Astrophysics Data System (ADS)

    Lim, Hyunkyu; Kim, Dongsik

    2003-11-01

    This paper introduces a novel laser chemical process for removing thin oxide films on low-carbon steel surfaces by combining laser-induced shock waves and chemical etching technique that is used in the conventional oxide-scale removal process. In the proposed process, a Q-switched Nd:YAG laser (wavelength 1064 nm, FWHM 6 ns) pulse is focused onto the liquid surface and subsequently induces optical breakdown in the acid solution, producing intense pressure waves. The pressure waves act as a non-contact oxide-film breaker and increases the removal rate. It has been demonstrated that the novel process leads to substantial enhancement of the oxide-film removal, compared with the conventional solvent-based cleaning technique. The removal rate has been measured quantitatively employing an optical microscope, a scanning electron microscope, and energy-dispersive X-ray analysis. Parametric study has been performed to reveal the effect of pressure pulse, laser pulse number, acid concentration, reaction time on the efficiency of scale removal. It is shown that the laser-assisted process can lower the acid concentration, with the cleaning efficiency unchanged or even improved. The results demonstrates a technical feasibility of utilizing the method for industrial applications that required enhanced scale-removal rate or reduced use of toxic chemicals.

  8. Precious metal-free catalyst for purification of automotive exhausts: NO dissociation on Cu oxide surfaces

    NASA Astrophysics Data System (ADS)

    Kasai, Hideaki; Padama, Allan Abraham; Moreno, Joaquin Lorenzo

    2014-03-01

    The dissociation of NOx molecule on catalysts is the rate-limiting step for its reduction process and is the subject of recent investigations related to exhaust gas purification. Three-way catalysts which are composed of Rh, Pd and Pt, are known to work well for such purpose; however, their expensive cost hinders their applicability. In this work, Computational Materials Design based on density functional theory was employed to test the efficiency of Cu-based catalysts for NO dissociation. It was found that the dissociation path of NO on Cu-terminated Cu2O(111) and CuO(110) surfaces is comparable with Rh(111). This is attributed to the modified electronic structure of the surface Cu atoms of Cu oxides in comparison with Cu(111). The calculated NO dissociation barriers are lower and the binding energies of co-adsorbed N and O atoms are weaker on Cu oxides than on Rh(111), which is favorable for subsequent reactions. Our experimental collaborator had also verified that Cu oxides can be better catalysts than Rh, Pd and Pt for the purification of exhaust gases. The details of this work and the oxidation of CO in the presence of dissociated NO will be discussed in the meeting.

  9. Site-selective surface reactions: nitric oxide reduction on Mo(110).

    PubMed

    Queeney, K; Friend, C M

    2000-11-01

    The catalytic reduction of NO(x) compounds formed in combustion processes is a critical factor in maintaining a clean environment. The introduction of the "catalytic converter" has been extremely effective in reducing these pollutants in automobile exhaust over the last two decades. Nevertheless, new environmental regulations have necessitated the development of processes that operate over a wider range of conditions and that are more efficient, so that NOx emissions can be reduced further. The need for new catalysts and processes has motivated a considerable number of studies of NO reduction using metal oxides as catalysts. In order to better understand the mechanisms for NO reduction on oxides, we have systematically studied the reactions of NO on thin-film oxides grown on Mo(110). By using a thin-film oxide, we are able to change the type of coordination sites that are available for NO binding and to use surface-sensitive spectroscopies to identify intermediates on the surface. We specifically explore the role of low-temperature NO coupling to a dinitrosyl species in our work and contrast this reaction to the higher temperature process, NO dissociation followed by nitrogen atom coupling. PMID:23696302

  10. Chemically patterned, metal oxide based surfaces produced by photolithographic techniques for studying protein- and cell-surface interactions I: Microfabrication and surface characterization.

    PubMed

    Winkelmann, M; Gold, J; Hauert, R; Kasemo, B; Spencer, N D; Brunette, D M; Textor, M

    2003-03-01

    Chemical patterns on smooth wafer substrates comprising areas with two different metals have been produced by vacuum metal deposition and photolithographic techniques. The combination of metals has been chosen from the series titanium (Ti), aluminium (Al), vanadium (V) and niobium (Nb), producing patterns (dots and stripes with dimensions of 50, 100 and 150 micrometer) with one of the metals as the background and with the second metal (foreground pattern) deposited on the background metal. The structure and chemical composition of the patterned surfaces were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy and imaging time-of-flight secondary-ion mass spectrometry. The surfaces proved to be geometrically well defined with the expected surface-chemical composition, i.e. a surface oxide (passive) film essentially composed of TiO(2),Al(2)O(3),V(2)O(5), or Nb(2)O(5). Ti/Ti patterned surfaces were produced as controls and found to show no chemical composition contrast. The surface roughness of the pattern was greater than that of the background by a factor of 2-3, but was still extremely smooth with Ra<2nm. The patterns serve as model surfaces for studying in vitro the behaviour of cells as well as the adsorption of serum proteins on different metal oxides, which will be reported in a companion paper. These surfaces can be used to compare and contrast the response of osteoblasts to Ti and other alloy components, such as Al, V, or Nb, which are used in load-bearing medical implants. PMID:12527254

  11. Tailoring of structure, surface, and luminescence properties of nanodiamonds using rapid oxidative treatment

    NASA Astrophysics Data System (ADS)

    Mona, J.; Perevedentseva, E.; Karmenyan, A.; Liou, H.-M.; Kang, T.-Y.; Cheng, C.-L.

    2013-03-01

    Precise surface functional groups, low sp2 content, and controlled size of agglomerates are the major concerns for using nanodiamonds (NDs) successfully in many biological applications. In this context, we report on the surface modifications of NDs carried out in the temperature range from 450 °C to 750 °C via rapid thermal annealing (RTA). Advantage of RTA is that one can obtain sufficient quantity of final sample. Effects on the ND's surfaces have been scrutinized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence, and time-resolved photoluminescence spectroscopy. FTIR shows red-shift in C=O stretching frequency at 450 °C while at 550 °C and above the surface functional groups are either reduced or completely removed. Raman spectrum shows red-shift and peak broadening of diamond peak with increasing temperature from R.T. to 550 °C. The band characteristic to the graphite at 1585 cm-1 is not observed for oxidative temperatures at 550 °C and 650 °C. Raman measurements indicate that the size and surface of NDs are modified. Intriguingly, sharp increase in the PL intensity has been observed at 450 °C, while PL intensity decreases gradually at 550 °C and 650 °C. Comparison of the lifetime decay profile approximated with two exponential components, for the NDs, before and after oxidative treatments at 450 °C indicates that the photoluminescence decay is highly sensitive to the surface modifications due to oxidation. Substantial changes in the luminescence and its decay provide useful insights into the role of the graphite and disordered carbon shell.

  12. Oxidative decolorization of direct light red F3B dye at natural manganese mineral surface

    Microsoft Academic Search

    Ruixia Liu; Hongxiao Tang

    2000-01-01

    In this paper, the characteristics of natural manganese mineral collected from Guangxi Province, China, including crystalline properties, elemental composition, organic substrates content (0.17%) and BET surface area (29.8 m2\\/g), were determined. By X-ray powder diffraction and fluorescence spectrograph analysis, it is shown that manganese oxide in the natural mineral exists in the crystal structure of ?-Mn2O3 and the contents of manganese

  13. Characterization of modified surface of indium tin oxide film during process of laser patterning

    Microsoft Academic Search

    JiNan Zeng; Hwee L. Koh; ZhongMin Ren; Wen D. Song; Yongfeng Lu

    2002-01-01

    Effect of excimer laser irradiation at different fluences on Indium-Tin-Oxide films has been studied with the use of optical transmission, XRD, Mirco-Raman spectra and XPS. Surface modification at low fluence of 154mJ\\/cm2 is observed to cause the increase of optical transmittance at initial several pulses of UV laser. At moderate fluence of 239mJ\\/cm2, UV laser irradiation results in apparent coloration

  14. Fabrication of a super-hydrophobic nanofibrous zinc oxide film surface by electrospinning

    Microsoft Academic Search

    Bin Ding; Tasuku Ogawa; Jinho Kim; Kouji Fujimoto; Seimei Shiratori

    2008-01-01

    We report a new approach for fabricating a super-hydrophobic nanofibrous zinc oxide (ZnO) film surface. The pure poly(vinyl alcohol) (PVA) and composite PVA\\/ZnO nanofibrous films can be obtained by electrospinning the PVA and PVA\\/zinc acetate solutions, respectively. After the calcination of composite fibrous films, the inorganic fibrous ZnO films with a reduced fiber diameter were fabricated. The wettability of three

  15. Oxidation mechanism of the ammonium-fluoride-treated Si(100) surface

    SciTech Connect

    Kluth, G.J.; Maboudian, R. [Department of Chemical Engineering, University of California, Berkeley, California 94720 (United States)] [Department of Chemical Engineering, University of California, Berkeley, California 94720 (United States)

    1996-11-01

    High-resolution electron energy loss (HREEL) spectroscopy, Auger electron spectroscopy, and low-energy electron diffraction have been employed to examine the initial oxidation stage of ammonium-fluoride-treated Si(100) surfaces exposed to air. The NH{sub 4}F treatment results in a hydrogen-terminated surface, as shown by the presence of the Si{endash}H stretch (2100 cm{sup {minus}1}), SiH{sub 2} scissor (910 cm{sup {minus}1}), and SiH bend (650 cm{sup {minus}1}) in the HREEL spectra. Initial oxidation on this surface occurs through oxygen insertion in the silicon backbonds, as indicated by the presence of the asymmetric bridge-bonded oxygen stretch in the region between 1060 and 1160 cm{sup {minus}1}. Oxygen is observed in both surface and bulk bridge-bonding sites for even the shortest air exposures, suggesting that initial oxygen uptake is not taking place in a layer-by-layer fashion. Auger electron spectroscopy shows a slow uptake of oxygen over the first few days of air exposure, followed by more rapid oxidation. Over the first two weeks of air exposure, the Si{endash}H stretch at 2100 cm{sup {minus}1} gradually disappears, accompanied by the appearance of oxygen backbonded Si{endash}H peaks around 2250 cm{sup {minus}1}. This behavior indicates that, despite the increase in oxygen uptake, the hydrogen termination remains intact, and further confirms that oxygen uptake occurs through insertion in the silicon backbonds. Water is found to play a significant role in the initial oxidation. {copyright} {ital 1996 American Institute of Physics.}

  16. The Pd( 1 0 0 )– ( 5 × 5 ) R27°-O surface oxide revisited

    Microsoft Academic Search

    M. Todorova; E. Lundgren; V. Blum; A. Mikkelsen; S. Gray; J. Gustafson; M. Borg; J. Rogal; K. Reuter; J. N. Andersen; M. Scheffler

    2003-01-01

    Combining high-resolution core-level spectroscopy, scanning tunneling microscopy and density-functional theory calculations we reanalyze the Pd(100)–(5×5)R27°-O surface oxide phase. We find that the prevalent structural model, a rumpled PdO(001) film suggested by previous low energy electron diffraction (LEED) work [Surf. Sci. 494 (2001) L799], is incompatible with all three employed methods. Instead, we suggest the two-dimensional film to consist of a

  17. Identification of defect sites on oxide surfaces by metastable impact electron spectroscopy

    Microsoft Academic Search

    S. Wendt; Y. D. Kim; D. W. Goodman

    2003-01-01

    In this review, thin films of SiO2 on Mo(112) and MgO(100) on Mo(100) have been characterized using metastable impact electron and ultraviolet photoelectron spectroscopies (metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy). The electronic and chemical properties of the thin films are identical to those of the corresponding bulk oxides. For different prepared defective SiO2 surfaces, additional features are

  18. Calorimetric study of the reactions of n-alkylphosphonic acids with metal oxide surfaces

    Microsoft Academic Search

    Jaime M. Ferreira; Stephen Marcinko; Richard Sheardy; Alexander Y. Fadeev

    2005-01-01

    The reaction enthalpies for the solution-phase self-assembly of n-alkylphosphonic acids on the surfaces of TiO2 and ZrO2 have been determined using isothermal titration calorimetry at 298 K. The reaction enthalpies were negative (exothermic) for methyl- and n-octylphosphonic acids and positive (endothermic) for n-octadecylphosphonic acid with both metal oxides. The enthalpy\\/energy analysis showed that the net enthalpy of the formation of

  19. Light Management in Transparent Conducting Oxides by Direct Fabrication of Periodic Surface Arrays

    NASA Astrophysics Data System (ADS)

    Eckhardt, S.; Sachse, C.; Lasagni, A. F.

    Line- and hexagonal-like periodic textures were fabricated on aluminium zinc oxide (AZO) using direct laser interference patterning method. It was found that hexagonally patterned surfaces show a higher performance in both transparency and diffraction properties compared to line-like textured and non-patterned substrates. Furthermore, the electrical resistance of the processed AZO coated substrates remained below the tolerance values for transparent conducting electrodes.

  20. Voltammetry of copper oxide micro-particles immobilised on diatomite surface

    Microsoft Academic Search

    Šebojka Komorsky-Lovri?; Ljiljana Marini?-Pajc; Neven Tadej; Alka J. M. Horvat; Jasenka Petran

    2008-01-01

    Copper oxide micro-particles immobilised on diatomite surface were prepared by coating diatomite from the solution of copper(II) salts under the room conditions followed by a thermal transformation or sintering at the two different temperatures (900°C and 1100°C). The purpose of these investigations was to develop a method for detection and identification of copper on a modified diatomite. Characterisation of copper-modified

  1. Surface treatment of Indium Tin Oxide (ITO) thin films synthesized by chemical solution deposition

    Microsoft Academic Search

    Young-Hoon Yun; Jin-Woo Choi; Sung-Churl Choi

    Indium tin oxide (ITO) thin films were synthesized on glass substrates by chemical solution deposition from starting materials of Indium (III) acetylacetonate and Tin (IV) iso-propoxide. The ITO films were fired in a temperature range of 400 oC to 600 oC and annealed under N2 gas at 500 oC. The effects of surface chemical treatment on the sheet resistance of

  2. Synthesis, characterization, and photocatalytic activities of titanate nanotubes surface-decorated by zinc oxide nanoparticles

    Microsoft Academic Search

    Li Shi Wang; Ming Wei Xiao; Xin Jian Huang; Yan Dan Wu

    2009-01-01

    Nanoscaled zinc oxide (ZnO) particles with different amounts are coated on titanate nanotubes (TNTs) by a facile chemical method at room temperature. The characterizations of XPS, TEM, XRD and UV–vis spectra confirm that pure hexagonal wurtzite ZnO nanoparticles with an average size of about 9nm are distributed on the surfaces of TNTs evenly and attached strongly. The photocatalytic activities of

  3. XAFS study on the local atomic structures of cerium-oxide nanoparticles with surface coatings

    Microsoft Academic Search

    Zhonghua Wu; Jing Zhang; Xing Chen; Zhongjun Chen; Minhua Sun; Ziyu Wu; Lin Guo

    2005-01-01

    Four kinds of cerium oxide nanoparticles coated, respectively, with Sodium bis(2-ethylhexyl) sulfosuccinate (AOT), cetyltrimethyl ammonium bromide (CTAB), poly vinyl pyrrolidone (PVP) and those (naked) without surface coating were prepared using chemical method. The particle sizes were identified to be 2–3nm by using transmission electron microscope (TEM) and x-ray diffraction (XRD). Mixed valences of Ce3+ and Ce4+ were detected by x-ray

  4. Biologically inspired tunable hydrophilic\\/hydrophobic surfaces: a copper oxide self-assembly multitier approach

    Microsoft Academic Search

    Bong June Zhang; Jiyeon Park; Kwang J Kim; Hyungkee Yoon

    2012-01-01

    In this study, a fabrication method for biologically inspired superhydrophobic micro- and nano-structured tier surfaces, each made of a self-assembled copper oxide, is presented. The method is controllable and applicable to bulk production when compared to existing high-end fabrication techniques. By modulating wet chemistry, different shapes and scales of tier structures were created. We demonstrated that their wetting behaviors are

  5. Impact of aircraft and surface emissions of nitrogen oxides on tropospheric ozone and global warming

    Microsoft Academic Search

    Colin Johnson; Jim Henshaw; Gordon McLnnes

    1992-01-01

    ACTUAL and potential increases in aircraft traffic are causing concern about the effects of aircraft exhaust emission on atmos-pheric chemistry. Model results1-3 and measurements4-6 in the Northern Hemisphere have shown that growth in surface emissions of nitrogen oxides and hydrocarbons leads to increases in concentration of tropospheric ozone. Tropospheric ozone is toxic to plants, humans and other organisms, and it

  6. Effects of Laser Surface Modification of Nimonic with Aluminum on Oxidation Behavior

    Microsoft Academic Search

    G. P. Rodriguez; I. García; J. Damborenea

    2002-01-01

    Using a high-power CO2 laser, aluminum-surface alloying was carried out on a nickel-base superalloy (Nimonic 80A) with the aim of improving its oxidation resistance. After the treatment, scanning-electron microscopy (SEM) studies show the alloy area to have a two-phase structure of Ni solid solution and Ni3Al intermetallic. These layers were subsequently subjected to a laser-remelting treatment with different beam-scanning speeds

  7. Adsorption of Anionic–Cationic Surfactant Mixtures on Metal oxide Surfaces

    Microsoft Academic Search

    A. Upadhyaya; E. J. Acosta; J. F. Scamehorn; D. A. Sabatini

    2007-01-01

    This research evaluates the adsorption of anionic and cationic surfactant mixtures on charged metal oxide surfaces (i.e.,\\u000a alumina and silica). For an anionic-rich surfactant mixture below the CMC, the adsorption of anionic surfactant was found\\u000a to substantially increase with the addition of low mole fractions of cationic surfactant. Two anionic surfactants (sodium\\u000a dodecyl sulfate and sodium dihexyl sulfosuccinate) and two

  8. Energy dependence of the trapping of uranium atoms by aluminum oxide surfaces

    NASA Technical Reports Server (NTRS)

    Librecht, K. G.

    1979-01-01

    The energy dependence of the trapping probability for sputtered U-235 atoms striking an oxidized aluminum collector surface at energies between 1 eV and 184 eV was measured. At the lowest energies, approximately 10% of the uranium atoms are not trapped, while above 10 eV essentially all of them stick. Trapping probabilities averaged over the sputtered energy distribution for uranium incident on gold and mica are also presented.

  9. Surface nanostructuring by ion-induced localized plasma expansion in zinc oxide

    SciTech Connect

    El-Said, A. S., E-mail: elsaid@kfupm.edu.sa, E-mail: a.s.el-said@hzdr.de [Physics Department, King Fahd University of Petroleum and Minerals, Dhahran 31261 (Saudi Arabia); Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01328 Dresden (Germany); Physics Department, Faculty of Science, Mansoura University, 35516 Mansoura (Egypt); Moslem, W. M. [Department of Physics, Faculty of Science, Port Said University, Port Said 42521 (Egypt); Centre for Theoretical Physics, British University in Egypt (BUE), El-Shorouk City, Cairo (Egypt); Djebli, M. [Theoretical Physics Laboratory, Faculty of Physics USTHB, B.P. 32 Bab Ezzour, 16079 Algiers (Algeria)

    2014-06-09

    Creation of hillock-like nanostructures on the surface of zinc oxide single crystals by irradiation with slow highly charged ions is reported. At constant kinetic energy, the nanostructures were only observed after irradiation with ions of potential energies above a threshold between 19.1?keV and 23.3?keV. The size of the nanostructures increases as a function of potential energy. A plasma expansion approach is used to explain the nanostructures creation. The calculations showed that the surface nanostructures became taller with the increase of ionic temperature. The influence of charged cluster formation and the relevance of their polarity are discussed.

  10. Surface component distribution in a vanadium-molybdenum oxide catalyst for making acrylic acid from acrolein

    SciTech Connect

    Zazhigalov, V.A.; Kholyavenko, K.M.

    1986-11-01

    A scanning electron microscope and microprobe analyzer have been used to examine the surfaces of vanadium-molybdenum catalysts on aerosil. It is found that the phase VMo/sub 3/O/sub 11/ is formed, which is dispersed on the SiO/sub 2/. MoO/sub 3/ crystals of various shapes occur at the surface of the dispersed phase. It is suggested that this catalyst is highly active in oxidizing acrolein to acrylic acid because of the presence of VMo/sub 3/O/sub 11/.

  11. Surface impedance studies of the high-T/sub c/ oxide superconductors

    SciTech Connect

    Hylton, T.L.; Beasley, M.R.; Kapitulnik, A.; Carini, J.P.; Drabeck, L.; Gruner, G.

    1989-03-01

    The authors briefly review results on measurements of the millimeter wave surface impedance of ceramic, thin film and single crystal samples of the high-T/sub c/ oxide superconductors. The observed losses and temperature dependences do not agree with BCS theory. They discuss recent measurements of single crystal Bi/sub 2/CaSr/sub 2/Cu/sub s/O/sub x/ and the effect of the application of a perpendicular magnetic field. They consider the possibilities of intrinsic and defect mechanisms to explain the observations. In particular, they discuss the effects of weakly coupled granular films on surface impedance.

  12. Graphoepitaxy of sexithiophene on thermally oxidized silicon surface with artificial periodic grooves

    SciTech Connect

    Ikeda, Susumu; Saiki, Koichiro; Tsutsui, Ken; Edura, Tomohiko; Wada, Yasuo; Miyazoe, Hiroyuki; Terashima, Kazuo; Inaba, Katsuhiko; Mitsunaga, Toru; Shimada, Toshihiro [Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8561 (Japan); Nanotechnology Research Laboratory, Waseda University, Wasedatsurumaki-cho, Shinjuku-ku, Tokyo 162-0041 (Japan); Department of Advanced Materials Science, Graduate School of Frontier Sciences, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8561 (Japan); Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666 (Japan); Department of Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2006-06-19

    Graphoepitaxial growth of a sexithiophene (6T) thin film was achieved on a thermally oxidized silicon surface with artificial periodic grooves. The surface structure was fabricated by electron beam lithography and the thin film was grown by molecular beam deposition. A well-pronounced, in-plane oriented component ([010]{sub 6T} parallel grooves) was identified by grazing incidence x-ray diffraction, though there also existed some randomly oriented 6T grains. Presence of the graphoepitaxial component was also confirmed by results of the orientational analysis of atomic force microscopy images. It was shown that the in-plane orientation control of organic semiconductors is possible using graphoepitaxy.

  13. Plastic deformation of a magnesium oxide 001-plane surface produced by cavitation

    NASA Technical Reports Server (NTRS)

    Hattori, S.; Miyoshi, K.; Buckley, D. H.; Okada, T.

    1986-01-01

    An investigation was conducted to examine plastic deformation of a cleaved single-crystal magnesium oxide 001-plane surface exposed to cavitation. Cavitation damage experiments were carried out in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (2 mm) to the surface of the cleaved specimen. The dislocation-etch-pit patterns induced by cavitation were examined and compared with that of microhardness indentations. The results revealed that dislocation-etch-pit patterns around hardness indentations contain both screw and edge dislocations, while the etch-pit patterns on the surface exposed to cavitation contain only screw dislocations. During cavitation, deformation occurred in a thin surface layer, accompanied by work-hardening of the ceramic. The row of screw dislocations underwent a stable growth, which was analyzed crystallographically.

  14. Superhydrophobic surfaces using selected zinc oxide microrod growth on ink-jetted patterns.

    PubMed

    Myint, Myo Tay Zar; Kitsomboonloha, Rungrot; Baruah, Sunandan; Dutta, Joydeep

    2011-02-15

    The synthesis and properties of superhydrophobic surfaces based on binary surface topography made of zinc oxide (ZnO) microrod-decorated micropatterns are reported. ZnO is intrinsically hydrophilic but can be utilized to create hydrophobic surfaces by creating artificial roughness via microstructuring. Micron scale patterns consisting of nanocrystalline ZnO seed particles were applied to glass substrates with a modified ink-jet printer. Microrods were then grown on the patterns by a hydrothermal process without any further chemical modification. Water contact angle (WCA)(1) up to 153° was achieved. Different micro array patterned surfaces with varying response of static contact angle or sessile droplet analysis are reported. PMID:21109250

  15. Raman Spectroscopy as a Probe of Surface Oxides and Hydrides on Niobium

    SciTech Connect

    J. Zasadzinski, B. Albee, S. Bishnoi, C. Cao, G. Ciovati, L.D. Cooley, D.C. Ford, Th. Proslier

    2011-07-01

    Raman microscopy/spectroscopy has been used in conjunction with AFM, tunneling and magnetic susceptibility to identify surface oxides and hydrides on annealed, recrystallized foils of high purity Nb and on single crystals of cavity grade Nb. Cold worked regions of the Nb foil as well as rough regions near grain boundaries showed clear evidence of ordered hydride phases which were identified by VASP phonon calculations. Cold worked regions also displayed enhanced surface paramagnetism. Surface enhanced Raman spectra have also been obtained using 1.0 nm Au depositon. The SERS spectra reveal hydride molecular species which are not observable by conventional Raman. These results indicate that Raman is a useful probe of Nb surfaces relevant for cavity performance

  16. Oxidation resistance of 9-12% Cr steels: effect of rare earth surface treatment

    SciTech Connect

    Dogan, Omer N.; Alman, David A.; Jablonski, Paul D.

    2005-02-01

    Medium Cr steels have been used in fossil fired power plants for many years because of their excellent high temperature stability and mechanical properties. The environment in a fossil fired power plant is extremely aggressive in terms of corrosion, especially oxidation. This is only accelerated as the operating temperature increases to 650C and beyond. For any new steel to be qualified for power plant use, in addition to adequate strength at the operating temperature, material wastage from all corrosion processes must be kept to a minimum acceptable level. The use of medium Cr steels provides a means to improve overall corrosion resistance. Three medium Cr are under development for use as high temperature power plant steels: 0.08C-(9-12)Cr-1.2Ni-0.7Mo-3.0Cu-3.0Co-0.5Ti. Oxidation tests were performed on the steels for times greater than 1000 hours in order to determine the oxidation kinetics and extent of material wastage. Also, rare earth oxides were incorporated into the outer surface layers of the steels to see if the oxidation resistance could be improved. These results will be compared to current power plant steels.

  17. Solid state chemistry of nitrogen oxides--part II: surface consumption of NO2.

    PubMed

    Ioppolo, S; Fedoseev, G; Minissale, M; Congiu, E; Dulieu, F; Linnartz, H

    2014-05-14

    Nitrogen oxides are considered to be important astrochemical precursors of complex species and prebiotics. However, apart from the hydrogenation of solid NO that leads to the surface formation of hydroxylamine, little is known about the full solid state reaction network involving both nitrogen and oxygen. Our study is divided into two papers, hereby called Part I and Part II. In the accompanying paper, we investigate the surface reactions NO + O/O2/O3 and NO + N with a focus on the formation of NO2 ice. Here, we complement this study by measurements of the surface destruction of solid NO2, e.g., NO2 + H/O/N. Experiments are performed in two separate ultra-high vacuum setups and therefore under different experimental conditions to better constrain the experimental results. Surface reaction products are monitored by means of Fourier Transform Reflection Absorption Infrared Spectroscopy (FT-RAIRS) and Temperature Programmed Desorption (TPD) techniques using mass spectrometry. The surface destruction of solid NO2 leads to the formation of a series of nitrogen oxides such as NO, N2O, N2O3, and N2O4 as well as HNO, NH2OH, and H2O. When NO2 is mixed with an interstellar more relevant apolar (i.e., CO) ice, solid CO2 and HCOOH are also formed due to interactions between different reaction routes. The astrophysical implications of the full nitrogen and oxygen reaction network derived from Parts I and II are discussed. PMID:24671439

  18. Study of hydrocarbon adsorption on oxide catalysts by IR spectroscopy: XIX. Propylene adsorption on a Bi-Mo oxide catalyst and the nature of surface sites

    SciTech Connect

    Davydov, A.A. [Boreskov Institute of Catalysis, Novosibirsk (Russian Federation)

    1994-07-01

    The nature of surface sites and propylene adsorption on stoichiometric bismuth molybdate are studied by FTIR spectroscopy. Lewis and Broensted acid centers are revealed at the oxidized catalyst surface using IR spectra of adsorbed ammonia. Lewis acid sites are shown to interact with strong electron-donor ligands (NH{sub 3}), but they do not interact with weak ligands (CO, C{sub 2}H{sub 4}, C{sub 3}H{sub 6}). Weak proton acid sites are found only at the surface of the oxidized sample.

  19. Surface-directed synthesis of erbium-doped yttrium oxide nanoparticles within organosilane zeptoliter containers.

    PubMed

    Englade-Franklin, Lauren E; Morrison, Gregory; Verberne-Sutton, Susan D; Francis, Asenath L; Chan, Julia Y; Garno, Jayne C

    2014-09-24

    We introduce an approach to synthesize rare earth oxide nanoparticles using high temperature without aggregation of the nanoparticles. The dispersity of the nanoparticles is controlled at the nanoscale by using small organosilane molds as reaction containers. Zeptoliter reaction vessels prepared from organosilane self-assembled monolayers (SAMs) were used for the surface-directed synthesis of rare earth oxide (REO) nanoparticles. Nanopores of octadecyltrichlorosilane were prepared on Si(111) using particle lithography with immersion steps. The nanopores were filled with a precursor solution of erbium and yttrium salts to confine the crystallization step to occur within individual zeptoliter-sized organosilane reaction vessels. Areas between the nanopores were separated by a matrix film of octadecyltrichlorosilane. With heating, the organosilane template was removed by calcination to generate a surface array of erbium-doped yttria nanoparticles. Nanoparticles synthesized by the surface-directed approach retain the periodic arrangement of the nanopores formed from mesoparticle masks. While bulk rare earth oxides can be readily prepared by solid state methods at high temperature (>900 °C), approaches for preparing REO nanoparticles are limited. Conventional wet chemistry methods are limited to low temperatures according to the boiling points of the solvents used for synthesis. To achieve crystallinity of REO nanoparticles requires steps for high-temperature processing of samples, which can cause self-aggregation and dispersity in sample diameters. The facile steps for particle lithography address the problems of aggregation and the requirement for high-temperature synthesis. PMID:25163977

  20. Role of surface exposed tryptophan as substrate generators for the antibody catalyzed water oxidation pathway.

    PubMed

    Sreedhara, Alavattam; Lau, Kimberly; Li, Charlene; Hosken, Brian; Macchi, Frank; Zhan, Dejin; Shen, Amy; Steinmann, Daniel; Schöneich, Christian; Lentz, Yvonne

    2013-01-01

    The reaction of singlet oxygen with water to form hydrogen peroxide was catalyzed by antibodies and has been termed as the antibody catalyzed water oxidation pathway (ACWOP) (Nieva and Wentworth, Trends Biochem. Sci. 2004, 29, 274-278; Nieva et al. Immunol. Lett. 2006, 103, 33-38). While conserved and buried tryptophans in the antibody are thought to play a major role in this pathway, our studies with a monoclonal antibody, mAb-1 and its mutant W53A, clearly demonstrate the role of surface-exposed tryptophans in production of hydrogen peroxide, via the photo-oxidation pathway. Reactive oxygen species (ROS) such as singlet oxygen and superoxide were detected and site-specific tryptophan (Trp53) oxidation was observed under these conditions using RP-HPLC and mass spectrometry. The single mutant of the surface exposed Trp53 to Ala53 (W53A) results in a 50% reduction in hydrogen peroxide generated under these conditions, indicating that surface exposed tryptophans are highly efficient in transferring light energy to oxygen and contribute significantly to ROS generation. ACWOP potentially leads to the chemical instability of mAb-1 via the generation of ROS and is important to consider during clinical and pharmaceutical development of mAbs. PMID:23136850

  1. Spatial Separation of Photochemical Oxidation and Reduction Reactions on the Surface of Ferroelectric BaTiO3

    E-print Network

    Rohrer, Gregory S.

    LETTERS Spatial Separation of Photochemical Oxidation and Reduction Reactions on the Surface reaction products are deposited on the surface in patterns that correspond to the underlying ferroelectric and holes migrate to the solid surface, where they can participate in reactions with adsorbed species. One

  2. Abnormal increase of time of oxygen diffusion with oxidation of silicon surface under action of powerful laser pulses

    Microsoft Academic Search

    Alexander F. Banishev; Vladimir S. Golubev; Alexei Y. Kremnev

    2000-01-01

    The paper presents an investigation of deformation response of monocrystalline silicon surface to the action of short laser pulses in the air and in vacuum P approximately equals 10-2 Torr. An anomalously continuous change of the surface relief was identified on irradiation in the air. The observable phenomenon is explained by oxidation of surface layer, enriched with defects.

  3. Formation, stability, and solubility of metal oxide nanoparticles: Surface entropy, enthalpy, and free energy of ferrihydrite

    NASA Astrophysics Data System (ADS)

    Hiemstra, Tjisse

    2015-06-01

    Ferrihydrite (Fh) is an excellent model for understanding nanoparticle behavior in general. Moreover, Fh is one of the most important Fe (hydr) oxides in nature. Fh particles can be extremely small leading to a very high reactive surface area that changes its chemical potential, strongly affecting the solubility, nucleation, and stability. These characteristics can be coupled to the interfacial Gibbs free energy, being ? = 0.186 ± 0.01 J m-2 for Fh. The surface free energy has a relatively large contribution of surface entropy (-TSsurf = +0.079 ± 0.01 J m-2). The surface entropy is primarily related to the formation of surface groups by chemisorption of water (-17.1 J mol-1 K-1), for Fh equivalent with +0.064 ± 0.002 J m-2 at a surface loading NH2O = 12.6 ?mol m-2. The entropy contribution of physisorbed water has been estimated by analyzing, as model, the surface enthalpy, entropy, and Gibbs free energy of the principal interfaces of H2O, i.e. ice-water-gas. It is about 20% of the contribution of chemisorbed water. The surface enthalpy of Fh is exceptionally low (Hsurf = +0.107 ± 0.01 J m-2), which can be explained by surface depletion (SD) of relatively unstable Fe polyhedra, or similarly, by additional surface loading of the non-depleted mineral core with specific Fe polyhedra for stabilization. The experimental enthalpy of Fh formation varies linearly with the surface area and correctly predicts the enthalpy value for the mineral core (-405.2 ± 1.2 kJ mol FeO3/2), being similar to the literature value for Fh as virtual bulk material (-406.7 ± 1.5 kJ mol FeO3/2) obtained with MO/DFT computations. The thermochemical quantities of the mineral core and surface are essentially the same for the entire range of Fh samples, in line with the SD model. The solubility of Fh suspensions as a whole may differ from the behavior of individual particles due to polydispersity. For 2-line Fh, the overall solubility is log Kso ? -38.5 ± 0.1 and for prolongedly aged 6-line Fh, log Kso ? -39.5 ± 0.1. The smallest Fh particles in a suspension react according to the Ostwald-Freundlich equation (RT?lnKso = 2/3 ?A), but the suspension as a whole apparently reacts according to the Ostwald equation (RT?lnKso = ?A). This difference can be explained by the observed linear relation between the minimum (dmin) and mean (dmean) particle size (dmin = 2/3 dmean) in Fh suspensions. With best estimates for the surface entropy of goethite, hematite, and lepidocrocite, predictions show that Fh becomes thermodynamically unstable above a diameter of ?8.0 nm at 298 K, allowing formation of nano-goethite and nano-hematite, as experienced experimentally at Ostwald ripening. More generally, one observes that metal (hydr) oxides with the highest chemical stability also have the highest mean surface Gibbs free energy, which can be considered as the scientific explanation of the empirical rule of Ostwald-Lussac. In addition, it is shown that the surface Gibbs free energies of metal (hydr) oxides increase with the mean metal coordination number of oxygen in the lattices following the order: oxides > oxyhydroxides > hydroxides.

  4. Surface Oxide Net Charge of a Titanium Alloy; Comparison Between Effects of Treatment With Heat or Radiofrequency Plasma Glow Discharge

    PubMed Central

    MacDonald, Daniel E.; Rapuano, Bruce E.; Schniepp, Hannes C.

    2010-01-01

    In the current study, we have compared the effects of heat and radiofrequency plasma glow discharge (RFGD) treatment of a Ti6Al4V alloy on the physico-chemical properties of the alloy’s surface oxide. Titanium alloy (Ti6Al4V) disks were passivated alone, heated to 600 °C, or RFGD plasma treated in pure oxygen. RFGD treatment did not alter the roughness, topography, elemental composition or thickness of the alloy’s surface oxide layer. In contrast, heat treatment altered oxide topography by creating a pattern of oxide elevations approximately 50–100 nm in diameter. These nanostructures exhibited a three-fold increase in roughness compared to untreated surfaces when RMS roughness was calculated after applying a spatial high-pass filter with a 200 nm cutoff wavelength. Heat treatment also produced a surface enrichment in aluminum and vanadium oxides. Both RFGD and heat treatment produced similar increases in oxide wettability. Atomic force microscopy (AFM) measurements of metal surface oxide net charge signified by a long range force of attraction to or repulsion from a (negatively charged) silicon nitride AFM probe were also obtained for all three experimental groups. Force measurements showed that the RFGD-treated Ti6Al4V samples demonstrated a higher net positive surface charge at pH values below 6 and a higher net negative surface charge at physiological pH (pH values between 7 and 8) compared to control and heat-treated samples These findings suggest that RFGD treatment of metallic implant materials can be used to study the role of negatively charged surface oxide functional groups in protein bioactivity, osteogenic cell behavior and osseointegration independently of oxide topography. PMID:20880672

  5. CO-oxidation on surface hematite in hot atmospheres of rocky planets

    NASA Astrophysics Data System (ADS)

    Grenfell, John Lee; Stock, Joachim W.; Patzer, A. Beate C.

    2013-08-01

    Hematite surface minerals can play a key role for the stability in hot, CO2 exoplanetary atmospheres. In a previous work we applied a heterogeneous mechanism for the oxidation of atmospheric CO(g) into CO2(g) occurring on the surface of hematite to planetary atmospheres. In that work we calculated CO2(g) production rates via this "hematite mechanism" for specific planetary atmospheric scenarios both in and out of the Solar System. We perform a general parameter study of the hematite mechanism in which we change key initial variables (CO and O2 gas-phase abundances) and temperature, pressure covering the diverse range of conditions for terrestrial planetary atmospheres; we investigate the response of the CO(g) oxidation rate and hence discuss the implications for the atmospheric CO2(g) budget. We apply a numerical integration scheme based on the Gear method to a system of seven chemical equations to investigate the rate of CO(g) oxidation via the hematite mechanism. Results suggest the mechanism has a potentially important influence on the evolution of hot atmospheres of terrestrial-type planets, especially for temperatures above about 550 K. The abundance of CO(g) was found to be not important for the rate of CO oxidation, whereas the abundance of O2(g) begins to play a role above about 10-5 volume mixing ratio. Above about 550 K, the efficiency of CO(g) oxidation increases because the rate determining step involving CO2 desorption is faster. Subsequently switching off the rather uncertain rate of diffusion of O atoms from the crystal bulk to the surface led to a strong lowering in reaction rates and a stronger dependency of the CO(g) oxidation rate upon O2(g). For example, on increasing the volume mixing ratio of O2(g) from 10-5 to 10-4 for a scenario without diffusion (with Venus-like surface conditions) the percentage conversion of initial CO(g) into CO2(g) increased from ~30% up to ~60%.

  6. Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics. [Quarterly] technical progress report, April--June 1993

    SciTech Connect

    Doyle, F.M.

    1993-06-30

    The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical cleaning processes. The results will provide fundamental insight into oxidation, in terms of the bulk and surface chemistry, the microstructure, and the semiconductor properties of the pyrite. During the eleventh quarter, dry thermal oxidation tests were done on coal samples from the Pennsylvania State Coal Bank. As-received and oxidized coal samples were studied by ion-exchange methods to determine the carboxylate and phenolic group concentrations. Film flotation tests were done to characterize the flotability of as-received and oxidized coals. In addition, electrokinetic tests were done on different coals, to obtain information pertinent to the selection of flotation reagents. DRIFT analysis was done to characterize the structure of coals.

  7. Surface Instability in High Surface Area Complex Oxides: BaTiO3 Study

    Microsoft Academic Search

    Nobuo Sakurai; Vincent Bojan; Josh J. Stapleton; Gai-Ying Yang; Clive A. Randall; Youichi Mizuno; Hirokazu Chazono

    2009-01-01

    High quality BaTiO3 powders that were synthesized with hydrothermal and solid state methods are characterized with respect to surface chemistry. Different characterization techniques are used to obtain a physical picture for the BaTiO3 powders with respect to different synthesis routes and thermal histories. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) are

  8. Effect of Chemical Compositions and Surface Morphologies of MCrAlY Coating on Its Isothermal Oxidation Behavior

    NASA Astrophysics Data System (ADS)

    Li, Yong; Li, Chang-Jiu; Zhang, Qiang; Xing, Lu-Kuo; Yang, Guan-Jun

    2011-01-01

    Chemical composition and surface morphology of MCrAlY coatings are factors which influence the oxidation behavior and the thermal durability of thermal barrier coatings. In this study, Cold-sprayed Ni20Cr10AlY and Ni23Co20Cr8.5Al4.0Ta0.6Y coatings with polished surfaces were employed to study the effect of composition on the oxidation behavior. The cold-sprayed MCrAlY coatings at the as-sprayed and shot-peened surface conditions, along with the low pressure plasma-sprayed MCrAlY coating with sputters adhered weakly on the surface, were employed to investigate the effects of surface morphologies of MCrAlY coatings on their oxidation behavior. Cold-sprayed Ni20Cr10AlY coating exhibited a two-stage oxidation behavior and a higher TGO growth rate than that of the cold-sprayed Ni23Co20Cr8.5Al4.0Ta0.6Y coating at the rapid growth stage. After 10-h oxidation, the TGO on the as-cold-sprayed coating surface was mainly constituted by Al2O3, while the TGO on the coating surface attached with sputters was composed of Al2O3 and Cr/Ni-oxides. After 500-h oxidation, Cr2O3 and porous spinel appeared in the TGO on the surface of the as-cold-sprayed coatings with different compositions. The growth of Cr/Ni-oxides was attributed to the Al depletion. The content of spinel decreased on the cold-sprayed NiCrAlY with a shot-peened surface compared with the as-sprayed coating.

  9. Activation of H(2) oxidation at sulphur-exposed Ni surfaces under low temperature SOFC conditions.

    PubMed

    Deleebeeck, Lisa; Shishkin, Maxim; Addo, Paul; Paulson, Scott; Molero, Hebert; Ziegler, Tom; Birss, Viola

    2014-05-28

    Ni-YSZ (yttria-stabilized zirconia) cermets are known to be very good anodes in solid oxide fuel cells (SOFCs), which are typically operated at 700-1000 °C. However, they are expected to be increasingly degraded as the operating temperature is lowered in the presence of H2S (5-10 ppm) in the H2 fuel stream. However, at 500 to 600 °C, a temperature range rarely examined for sulphur poisoning, but of great interest for next generation SOFCs, we report that H2S-exposed Ni-YSZ anodes are catalytic towards the H2 oxidation reaction, rather than poisoned. By analogy with bulk Ni3S2/YSZ anodes, shown previously to enhance H2 oxidation kinetics, it is proposed that a thin layer of Ni sulphide, akin to Ni3S2, is forming, at least at the triple point boundary (TPB) region under our conditions. To explain why Ni3S2/YSZ is so active, it is shown from density functional theory (DFT) calculations that the O(2-) anions at the Ni3S2/YSZ TPB are more reactive towards hydrogen oxidation than is O(2-) at the Ni/YSZ TPB. This is accounted for primarily by structural transformations of Ni3S2 during H2 oxidation, rather than by the electronic properties of this interface. To understand why a thin layer of Ni3S2 could form when a single monolayer of sulphur on the Ni surface is the predicted surface phase under our conditions, it is possible that the reaction of H2 with O(2-), forming water, prevents sulphur from re-equilibrating to H2S. This may then promote Ni sulphide formation, at least in the TPB region. PMID:24718381

  10. Surface properties of photo-oxidized bituminous coals. Technical progress report, October--December 1995

    SciTech Connect

    Mitchell, G.; Polat, H.; Davis, A.; Chander, S.

    1996-02-01

    During this report period, polished blocks of coal containing 3--4 mm wide vitrain bands were prepared for contact angle measurements of fresh and photo-oxidized surfaces using the advancing-drop technique. Contact angles were measured on two of the coals collected for this study, (the Ohio No. 4a (DECS-33) and Lower Kittanning (PSOC-1562) seams) and the results added to those presented in the last quarterly report. Although the new data give additional variation to the sample set, they are consistent with the original observations, i.e., that contact angle is influenced by irradiation time and coal rank. Using the maximum change in contact angle measured between fresh and photo-oxidized surfaces, a linear decrease is observed with increasing rank resulting from 5 and 10 minutes of irradiation. The magnitude of the decrease in contact angle diminishes with increasing rank. Also during this period, an ultraviolet spotlight was evaluated as a means of irradiating powdered vitrain. This 100 watt, long wavelength (366 nm) ultraviolet lamp is to be used in place of the optical microscope system to establish the influence of surface photo-oxidation on the flotation characteristics of vitrain concentrates. A series of experiments was designed to determine the magnitude of change in the luminescence intensity (at 600 nm measured in the optical microscope) with exposure to the ultraviolet light with time for vitrinite from different rank coals. The authors have established that there is a significant decrease in luminescence intensity with time of exposure which diminishes slightly as rank increases. The ultraviolet light appears to provide a level of photo-oxidation that is a factor of 10 lower than that obtained with their optical microscope system.

  11. Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

    NASA Astrophysics Data System (ADS)

    Khan, Sami; Azimi, Gisele; Yildiz, Bilge; Varanasi, Kripa K.

    2015-02-01

    Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ˜3 and a water contact angle of ˜15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (˜2.2) and becomes hydrophobic (contact angle of ˜104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. This study provides insight into the role of surface relaxation on the wettability of REOs.

  12. Laser induced surface structuring and ion conversion in the surface oxide of titanium: possible implications for the wetability of laser treated implants.

    PubMed

    Forsgren, Johan; Paz, María Dolores; León, Betty; Engqvist, Håkan

    2013-01-01

    In the present study, commercially pure titanium was irradiated with UV-light with varying wavelengths using a Q-switched Nd:YAG-laser. This was performed in order to investigate if a laser treatment can be employed to rapidly introduce hydrophilic properties to titanium surfaces, which is believed to facilitate protein adsorption and cell attachment. It was demonstrated that irradiation with 355 nm light (10 Hz, 90 mJ/shot) for 1 min or more caused an ion conversion of Ti(4+) to Ti(3+) sites in the surface oxide which lead to an increase in hydrophilicity of the surface. Furthermore, shorter irradiation times at 355 nm caused a surface structuring that gave rise to an unexpected and unstable hydrophobic state at the surface. Irradiation with 266 nm light (10 Hz, 40 mJ/shot) did not introduce any ion conversion in the surface oxide, nor did it give rise to any hydrophobicity of the surface. PMID:23053809

  13. Oxidation of formic acid on platinum surfaces decorated with cobalt(III) macrocyclic complexes

    NASA Astrophysics Data System (ADS)

    Stevanovi?, S.; Babi?-Samardžija, K.; Sovilj, S. P.; Tripkovi?, A.; Jovanovi?, V. M.

    2009-09-01

    Platinum electrode decorated with three different mixed-ligand cobalt(III) complexes of the general formula [Co(Rdtc)cyclam](ClO4)2 [cyclam = 1,4,8,11-tetraazacyclotetradecane, Rdtc- = morpholine-(Morphdtc), piperidine-(Pipdtc), and 4-methylpiperidine-(4-Mepipdtc) dithiocarbamates, respectively] was used to study oxidation of formic acid in acidic solution. The complexes were adsorbed on differently prepared Pt surfaces, at open circuit potential. The preliminary results show increased catalytic activity of Pt for formic acid oxidation with complex ion adsorbed on the polycrystalline surfaces. The increase in catalytic activity depends on the structure of the complex applied and follows the order of metal-coordinated bidentate ligand as Morphdtc > Pipdtc > 4-Mepipdtc. Based on IR and NMR data, the main characteristics of the Rdtc ligands do not vary dramatically, but high symmetry of the corresponding complexes decreases in the same order. Accordingly, the complexes are distinctively more mobile, causing chemical interactions to occur on the surface with appreciable speed and enhanced selectivity. The effect of the complexes on catalytic activity presumably depends on structural changes on Pt surfaces caused by their adsorption.

  14. Influence of surface properties of zinc oxide nanoparticles on their cytotoxicity.

    PubMed

    Altunbek, Mine; Baysal, Asl?; Çulha, Mustafa

    2014-09-01

    The toxicity of nanoparticles (NPs) depends on several factors including size, shape, surface properties and chemical nature of the NPs. The release of toxic ions due to the dissolution of NPs is another important factor. In addition, impurities or reaction products from synthesis procedures on the NP surfaces may contribute to the toxicity. Zinc oxide nanoparticles (ZnO NPs) are one of the unique NPs showing toxicity through all of these mentioned factors. In this study, we demonstrate that the treatment of the ZnO NPs with hydrogen peroxide (H2O2) alters the surface properties of the ZnO NPs by decomposing organic impurities remained from synthesis procedures. The changes on the surface chemistry and properties of the ZnO NPs influence their behavior in cell culture media and the NPs-cell interactions. Finally, a decrease in the cytotoxicity of H2O2 treated ZnO NPs is observed on HDF and A549 cells through the decrease of the membrane damage and oxidative stress. PMID:25042418

  15. The structures of hexadecylamine films adsorbed on iron-oxide surfaces in dodecane and hexadecane.

    PubMed

    Doig, Michael; Camp, Philip J

    2015-02-21

    Molecular-dynamics simulations are used to gain insights on recent sum-frequency spectroscopy and polarised neutron reflectometry measurements of the structure of hexadecylamine films adsorbed on iron-oxide surfaces in dodecane and hexadecane. Simulations were carried out under quiescent and high-shear conditions. Mass-density profiles, molecular-height and molecular-orientation probability distribution functions, and in-layer radial distribution functions were calculated. The simulation results show that at high surface coverage, the film thickness is about 15 Å, and that the molecules are mainly pointing upwards from the surface at an angle of 40-50°. The results are compared critically against published experimental results, and the agreement is found to be good. The in-layer ordering of the hexadecylamine head-group atoms is found to be dictated by the crystalline structure of the iron-oxide surface, but this influence rapidly diminishes along the molecular backbone. The tail-group atoms show almost no positional ordering. Finally, an example calculation of the kinetic friction coefficient under high-shear conditions is presented. The lateral (friction) force is measured as a function of the normal (applied) force, and the kinetic friction coefficient is determined to be about 0.09, which is typical for this kind of system. PMID:25607715

  16. Effect of surface acidity and basicity of aluminas on asphaltene adsorption and oxidation.

    PubMed

    Nassar, Nashaat N; Hassan, Azfar; Pereira-Almao, Pedro

    2011-08-01

    This study investigates the effect of surface acidity and basicity of aluminas on asphaltene adsorption followed by air oxidation. Equilibrium batch adsorption experiments were conducted at 25°C with solutions of asphaltenes in toluene at concentrations ranging from 100 to 3000 g/L using three conventional alumina adsorbents with different surface acidity. Data were found to better fit to the Freundlich isotherm model showing a multilayer adsorption. Results showed that asphaltene adsorption is strongly affected by the surface acidity, and the adsorption capacities of asphaltenes onto the three aluminas followed the order acidic>basic and neutral. Asphaltenes adsorbed over aluminas were subjected to oxidation in air up to 600°C in a thermogravimetric analyzer to study the catalytic effect of aluminas with different surface acidity. A correlation was found between Freundlich affinity constant (1/n) and the catalytic activity. Basic alumina that has the lowest 1/n value, depicting strongest interactions, has the highest catalytic activity, followed by neutral and acidic aluminas, respectively. PMID:21571295

  17. A molecular beacon biosensor based on the nanostructured aluminum oxide surface.

    PubMed

    Che, Xiangchen; He, Yuan; Yin, Haocheng; Que, Long

    2015-10-15

    A new class of molecular beacon biosensors based on the nanostructured aluminum oxide or anodic aluminum oxide (AAO) surface is reported. In this type of sensor, the AAO surface is used to enhance the fluorescent signals of the fluorophore-labeled hairpin DNA. When a target DNA with a complementary sequence to that of the hairpin DNA is applied on the sensor, the fluorophores are forced to move away from the AAO surface due to the hybridization between the hairpin DNA and the target DNA, resulting in the significant decrease of the fluorescent signals. The observed signal reduction is sufficient to achieve a demonstrated detection limit of 10nM, which could be further improved by optimizing the AAO surface. The control experiments have also demonstrated that the bioassay used in the experiments has excellent specificity and selectivity, indicating the great promise of this type of sensor for diagnostic applications. Since the arrayed AAO micropatterns can be fabricated on a single chip in a cost-effective manner, the arrayed sensors could provide an ideal technical platform for studying fundamental biological process and monitoring disease biomarkers. PMID:25988788

  18. Toxicity Assessment of Silica Coated Iron Oxide Nanoparticles and Biocompatibility Improvement by Surface Engineering

    PubMed Central

    Malvindi, Maria Ada; De Matteis, Valeria; Galeone, Antonio; Brunetti, Virgilio; Anyfantis, George C.; Athanassiou, Athanassia; Cingolani, Roberto; Pompa, Pier Paolo

    2014-01-01

    We have studied in vitro toxicity of iron oxide nanoparticles (NPs) coated with a thin silica shell (Fe3O4/SiO2 NPs) on A549 and HeLa cells. We compared bare and surface passivated Fe3O4/SiO2 NPs to evaluate the effects of the coating on the particle stability and toxicity. NPs cytotoxicity was investigated by cell viability, membrane integrity, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) assays, and their genotoxicity by comet assay. Our results show that NPs surface passivation reduces the oxidative stress and alteration of iron homeostasis and, consequently, the overall toxicity, despite bare and passivated NPs show similar cell internalization efficiency. We found that the higher toxicity of bare NPs is due to their stronger in-situ degradation, with larger intracellular release of iron ions, as compared to surface passivated NPs. Our results indicate that surface engineering of Fe3O4/SiO2 NPs plays a key role in improving particles stability in biological environments reducing both cytotoxic and genotoxic effects. PMID:24465736

  19. Investigations of adsorption sites on oxide surfaces using solid-state NMR and TPD-IGC

    NASA Astrophysics Data System (ADS)

    Golombeck, Rebecca A.

    The number and chemical identity of reactive sites on surfaces of glass affects the processing, reliability, and lifetime of a number of important commercial products. Surface site densities, distributions, and structural identities are closely tied to the formation and processing of the glass surface, and exert a direct influence on strength and coating performance. The surface of a glass sample may vary markedly from the composition and chemistry of the bulk glass. We are taking a physicochemical approach to understanding adsorption sites on pristine multicomponent glass fibers surfaces, directly addressing the effect of processing on surface reactivity. This project aimed to understand the energy distributions of surface adsorption sites, the chemical/structural identity of those sites, and the relationship of these glasses to glass composition, thermal history, and in future work, surface coatings. We have studied the bulk and surface structure as well as the surface reactivity of the glass fibers with solid-state nuclear magnetic resonance (NMR) spectroscopy, inverse gas chromatography (IGC), and computational chemistry methods. These methods, solid-state NMR and IGC, typically require high surface area materials; however, by using probe molecules for NMR experiments or packing a column at high density for IGC measurements, lower surface area materials, such as glass fibers, can be investigated. The glasses used within this study were chosen as representative specimens of fibers with potentially different reactive sites on their surfaces. The two glass compositions were centered around a nominal E-glass, which contains very little alkali cations and mainly alkaline earth cations, and wool glass, which contains an abundance of alkali cations. The concentration of boron was varied from 0 to 8 mole % in both fiber compositions. Fibers were drawn from each composition at a variety of temperatures and draw speeds to provide a range of glass samples with varying diameters and thermal histories. The bulk structural features in both compositions of glass fibers were identified using high-resolution 29Si, 27Al, and 11B magic-angle spinning (MAS) NMR spectroscopic measurements. In multi-component glasses, the determination of silicon, aluminum, and boron distributions becomes difficult due to the competitive nature of the network-modifying oxides among the network-forming oxides. In pure silicates, 29Si MAS NMR can often resolve resonances arising from silicate tetrahedron having varying numbers of bridging oxygens. In aluminoborosilicate glasses, aluminum is present in four-, five-, and six- coordination with oxygen as neighbors. The speciation of the aluminum can be determined using 27Al MAS NMR. The fraction of tetrahedral boron species in the glass fibers were measured using 11B MAS NMR, which is typically used to study the short-range structure of borate containing glasses such as alkali borate, borosilicate, and aluminoborosilicate glasses. While solid-state NMR is a powerful tool for elucidating bonding environments and coordination changes in the glass structure, it cannot quantitatively probe low to moderate surface area samples due to insufficient spins. Chemical probes either physisorbed or chemisorbed to the fiber's surface can increase the surface selectivity of NMR for analysis of samples with low surface areas and provide information about the local molecular structure of the reactive surface site. Common chemical probe molecules contain NMR active nuclei such as 19F or may be enriched with 13C. A silyating agent, (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS), reacts with reactive surface hydroxyls, which can be quantified by utilizing the NMR active nucleus (19F) contained in the probe molecule. The observed 19F MAS NMR peak area is integrated and compared against a standard of known fluorine spins (concentration), allowing the number of reactive hydroxyl sites to be quantified. IGC is a method used to study the surface properties of a material by examining the retention behavior of a probe molecule. The I

  20. Chemisorption and anodic oxidation of aromatic molecules on Pd electrode surfaces: studies by UHV-EC-STM

    E-print Network

    Chen, Xiaole

    2006-04-12

    The chemisorption and anodic oxidation of hydroquinone (H2Q) and benzoquinone (BQ) at palladium electrode surfaces was studied by a combination of electrochemistry (EC), Auger electron spectroscopy (AES), high-resolution electron...

  1. Chemisorption and anodic oxidation of aromatic molecules on Pd electrode surfaces: studies by UHV-EC-STM 

    E-print Network

    Chen, Xiaole

    2006-04-12

    The chemisorption and anodic oxidation of hydroquinone (H2Q) and benzoquinone (BQ) at palladium electrode surfaces was studied by a combination of electrochemistry (EC), Auger electron spectroscopy (AES), high-resolution electron...

  2. Chemistry of sulfur oxides on transition metal surfaces: a bond order conservation-Morse potential modeling perspective

    Microsoft Academic Search

    Harrell Sellers; Evgeny Shustorovich

    1996-01-01

    We have employed the bond order conservation-Morse potential (BOC-MP) method to analyze the chemistry of sulfur oxides on the copper and nickel group metals. Specifically, we have calculated the reaction energetics (heats of adsorption, reaction enthalpies and intrinsic activation barriers) of the decomposition and oxidation of sulfur dioxide at low coverages on fcc (111) surfaces of Cu, Ag, Au, Ni,

  3. Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along a climosequence

    Microsoft Academic Search

    Chih-Hsin Cheng; Johannes C. Lehmann; Mark H. Engelhard

    2008-01-01

    The aim of this work was to investigate changes in molecular form and surface charge of black carbon (BC) due to long-term natural oxidation and to examine how climatic and soil factors affect BC oxidation. Black C was collected from 11 historical charcoal blast furnace sites with a geographic distribution from Quebec, Canada, to Georgia, USA, and compared to BC

  4. Effects of prior surface damage on high-temperature oxidation of Fe-, Ni-, and Co-based alloys

    SciTech Connect

    Blau, Peter Julian [ORNL; Lowe, Tracie M [ORNL; Pint, Bruce A [ORNL

    2009-01-01

    Multi-component metallic alloys have been developed to withstand high-temperature service in corrosive environments. Some of these applications, like exhaust valve seats in internal combustion engines, must also resist sliding, impact, and abrasion. The conjoint effects of temperature, oxidation, and mechanical contact can result in accelerated wear and the formation of complex surface layers whose properties differ from those of the base metal and the oxide scale that forms in the absence of mechanical contact. The authors have investigated the effects of prior surface damage, produced by scratch tests, on the localized reformation of oxide layers. Three high-performance commercial alloys, based on iron, nickel, and cobalt, were used as model materials. Thermogravimetric analysis (TGA) was used to determine their static oxidation rates at elevated temperature (850o C). A micro-abrasion, ball-cratering technique was used to measure oxide layer thickness and to compare it with TGA results. By using taper-sectioning techniques and energy-dispersive elemental mapping, a comparison was made between oxide compositions grown on non-damaged surfaces and oxides that formed on grooves produced by a diamond stylus. Microindentation and scratch hardness data revealed the effects of high temperature exposure on both the substrate hardness and the nature of oxide scale disruption. There were significant differences in elemental distribution between statically-formed oxides and those that formed on scratched regions

  5. Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics. Technical progress report, May 31, 1995

    SciTech Connect

    Doyle, F.M.

    1995-12-31

    The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical cleaning processes. Work during the nineteenth quarter has concluded studies of the surface functional groups produced on coal by severe thermal and chemical oxidation, and on investigating the partition of metal ions between such strongly oxidized coal samples and aqueous solutions. This partitioning behavior was being followed to obtain further information on the chemistry of the coal surfaces after different oxidation treatments. Adsorption isotherms for the uptake of Cd{sup 2+} on coal oxidized by different methods were obtained, and these and the Cu{sup 2+} adsorption isotherms reported in the last report have been scrutinized, and interpreted more exhaustively. The apparent discrepancies noted in the last report for the analysis of surface functional groups have been investigated further. The adsorption behavior has been related to the surface chemistry of Upper Freeport coal oxidized by different methods.

  6. Performance enhancement for solid oxide fuel cells using electrolyte surface modification

    NASA Astrophysics Data System (ADS)

    Dai, Hailu; He, Shoucheng; Chen, Han; Yu, Shancheng; Guo, Lucun

    2015-04-01

    The yttria-stabilized zirconia electrolyte surface is properly modified to improve the performance of solid oxide fuel cells. Compared with conventional electrolytes, the surface-modified ones can provide more active reaction sites and anchor better to the cathode layer, which is demonstrated in electrochemical impedance spectroscopy studies. Both ohmic and polarization resistances are dramatically reduced for the modified fuel cell, which increases the fuel cell performance by more than 150%: from 40 to 101 mW cm-2 at 800 °C. The low polarization resistance of 0.73 ? cm2 that is obtained in this study is also remarkable because it is lower than that for similar cathode compositions in the literature. The results indicate that the surface modification method can effectively reduce the electrode polarization resistance and significantly improve the fuel cell performance.

  7. Surface diffusion control of the photocatalytic oxidation in air/TiO2 heterogeneous reactors

    E-print Network

    Tsekov, R

    2015-01-01

    The diffusion of superoxide radical anions on the surface of TiO2 catalysts is theoretically considered as an important step in the kinetics of photocatalytic oxidation of toxic pollutants. A detailed analysis is performed to discriminate the effects of rotation, anion and adsorption bonds vibrations on the diffusion coefficient. A resonant dependence of the diffusivity on the lattice parameters of the TiO2 surface is discovered showing that the most rapid diffusion takes place when the lattice parameters are twice larger than the bond length of the superoxide radical anions. Whereas the rotation and vibrations normal to the catalyst surface are important, the anion bond vibrations do not affect the diffusivity due to their low amplitudes as compared to the lattice parameters.

  8. Surface Decoration of MgO Nanocubes with Sulfur Oxides: Experiment and Theory.

    PubMed

    Sternig, Andreas; Diwald, Oliver; Gross, Silvia; Sushko, Peter V

    2013-04-18

    We investigated the effect of surface sulfate formation on the structure and spectroscopic properties of MgO nanocubes using X-ray diffraction, electron microscopy, several spectroscopic techniques, and ab initio calculations. After CS2 adsorption and oxidative treatment at elevated temperatures the MgO particles remain cubic and retain their average size of ?6 nm. Their low coordinated surface elements (corners and edges) were found to bind sulfite and sulfate groups even after annealing up to 1173 K. The absence of MgO corner specific photoluminescence emission bands at 3.4 and 3.2 eV substantiates that sulfur modifies the electronic properties of characteristic surface structures, which we attribute to the formation of (SO3)(2-) and (SO4)(2-) groups at corners and edges. Ab initio calculations support these conclusions and provide insight into the local atomic structures and spectroscopic properties of these groups. PMID:23616910

  9. Efficient catalysts for olefins from alkanes: sol–gel synthesis of high surface area nano scale mixed oxide clusters

    Microsoft Academic Search

    C. Trionfetti; I. V. Babich; K. Seshan; L. Lefferts

    2006-01-01

    High surface area nano scale Li\\/MgO oxide clusters with low lithium loadings are prepared by sol–gel method. Appreciable amounts\\u000a of lithium present can be incorporated into the magnesia gel during preparation and retained in the oxide matrix after gel\\u000a combustion. This limits presence of free lithium phases and helps prevent the associated sintering and loss of surface area\\u000a during thermal

  10. Bulk and surface structure and composition of V–Sb mixed-oxide catalysts for the ammoxidation of propane

    Microsoft Academic Search

    H. W Zanthoff; W Grünert; S Buchholz; M Heber; L Stievano; F. E Wagner; G. U Wolf

    2000-01-01

    Vanadium–antimony mixed oxides, which are active and selective catalysts for the ammoxidation of propane to acrylonitrile, were obtained via different preparation routes and studied with a number of bulk and surface-sensitive techniques to elucidate the bulk composition of these complex materials and the character of their exposed surfaces. The V–Sb oxides were prepared via a redox reaction between NH4VO3 and

  11. Mechanisms of Arsenic Adsorption on Amorphous Oxides Evaluated Using Macroscopic Measurements, Vibrational Spectroscopy, and Surface Complexation Modeling

    Microsoft Academic Search

    Sabine Goldberg; Cliff T. Johnstony

    2001-01-01

    Arsenic adsorption on amorphous aluminum and iron oxides was investigated as a function of solution pH, solution ionic strength, and redox state. In this study in situ Raman and Fourier transform infrared (FTIR) spectroscopic methods were combined with sorption techniques, electrophoretic mobility measurements, and surface complexation modeling to study the interaction of As(III) and As(V) with amorphous oxide surfaces. The

  12. Thermal stability of uniform silver clusters prepared on oxidized silicon and aluminum surfaces by electron beam lithography in oxidizing and reducing ambients

    Microsoft Academic Search

    M. X. Yang; P. W. Jacobs; C. Yoon; L. Muray; E. Anderson; D. T. Attwood; G. A. Somorjai

    1997-01-01

    100 and 750 nm silver nanoclusters are fabricated on oxidized silicon and aluminum surfaces by electron beam lithography.\\u000a Silver nanoclusters are characterized by atomic force microscopy, scanning electron microscopy, scanning Auger electron microscopy\\u000a and high-resolution optical microscopy. The ordered structure of silver nanoclusters facilitates a thermal stability study\\u000a in both reducing and oxidizing conditions. In reducing conditions, silver clusters are

  13. Bisphenol A Adsorption Onto Metals Oxides and Organic Materials in the Natural Surface Coatings Samples (NSCSs) and Surficial Sediments (SSs): Inhibition for the Importance of Mn Oxides

    Microsoft Academic Search

    Yu Li; Na Li; Dan Chen; Xiaoli Wang; Zili Xu; Deming Dong

    2009-01-01

    Selective extraction techniques followed by batch adsorption experiments and statistical analyses were employed to investigate\\u000a the adsorption behavior of bisphenol A (BPA) onto the natural surface coatings samples (NSCSs) and surficial sediments (SSs)\\u000a and estimate the relative contribution of components (i.e. Fe oxides, Mn oxides, organic materials and residues) to the total\\u000a BPA adsorption. The results indicate that nonlinear Langmuir

  14. Antioxidant properties of cerium oxide nanocrystals as a function of nanocrystal diameter and surface coating.

    PubMed

    Lee, Seung Soo; Song, Wensi; Cho, Minjung; Puppala, Hema L; Nguyen, Phuc; Zhu, Huiguang; Segatori, Laura; Colvin, Vicki L

    2013-11-26

    This work examines the effect of nanocrystal diameter and surface coating on the reactivity of cerium oxide nanocrystals with H2O2 both in chemical solutions and in cells. Monodisperse nanocrystals were formed in organic solvents from the decomposition of cerium precursors, and subsequently phase transferred into water using amphiphiles as nanoparticle coatings. Quantitative analysis of the antioxidant capacity of CeO2-x using gas chromatography and a luminol test revealed that 2 mol of H2O2 reacted with every mole of cerium(III), suggesting that the reaction proceeds via a Fenton-type mechanism. Smaller diameter nanocrystals containing more cerium(III) were found to be more reactive toward H2O2. Additionally, the presence of a surface coating did not preclude the reaction between the nanocrystal surface cerium(III) and hydrogen peroxide. Taken together, the most reactive nanoparticles were the smallest (e.g., 3.8 nm diameter) with the thinnest surface coating (e.g., oleic acid). Moreover, a benchmark test of their antioxidant capacity revealed these materials were 9 times more reactive than commercial antioxidants such as Trolox. A unique feature of these antioxidant nanocrystals is that they can be applied multiple times: over weeks, cerium(IV) rich particles slowly return to their starting cerium(III) content. In nearly all cases, the particles remain colloidally stable (e.g., nonaggregated) and could be applied multiple times as antioxidants. These chemical properties were also observed in cell culture, where the materials were able to reduce oxidative stress in human dermal fibroblasts exposed to H2O2 with efficiency comparable to their solution phase reactivity. These data suggest that organic coatings on cerium oxide nanocrystals do not limit the antioxidant behavior of the nanocrystals, and that their redox cycling behavior can be preserved even when stabilized. PMID:24079896

  15. Reaction of tributyl phosphite with oxidized iron: surface and tribological chemistry.

    PubMed

    Gao, Feng; Furlong, Octavio; Kotvis, Peter V; Tysoe, Wilfred T

    2004-08-31

    The surface chemistry of a model lubricant additive, tributyl phosphite (TBPi), is investigated on Fe3O4 in ultrahigh vacuum. A portion of the TBPi desorbs molecularly following adsorption at approximately 200 K, the remainder decomposing either by C-O bond scission to form 1-butyl species or by P-O bond cleavage to form butoxy species. Adsorbed butyl species either undergo beta-hydride elimination to desorb 1-butene or decompose to deposit carbon and hydrogen on the surface. The resulting adsorbed hydrogen reacts with the oxide to desorb water or with the butoxy species to form 1-butanol. Butoxy species are stable up to approximately 600 K at which temperature they also undergo beta-hydride elimination to form butanal and the released hydrogen reacts with other butoxy species to form 1-butanol. Only a small amount of carbon is deposited onto the surface following adsorption at approximately 200 K, which then desorbs as CO above approximately 750 K. Adsorbing TBPi at 300 K results in the deposition of more carbon and an Auger depth profile reveals that the carbon is located predominantly on the surface, while the phosphorus is rather uniformly distributed throughout the oxide film. This result is in accord with previous near-edge X-ray absorption fine structure measurements, which show the formation of phosphates and polyphosphate glasses. The resulting tribological film appears to be composed of a relatively hard polyphosphate glass formed by rapid diffusion of POx species into the oxide, covered by a low shear strength graphitic layer. PMID:15323502

  16. Surface-Localized Spermidine Protects the Pseudomonas aeruginosa Outer Membrane from Antibiotic Treatment and Oxidative Stress

    PubMed Central

    Johnson, Lori; Mulcahy, Heidi; Kanevets, Uliana; Shi, Yan

    2012-01-01

    Extracellular DNA acts as a cation chelator and induces the expression of antibiotic resistance genes regulated by Mg2+ levels. Here we report the characterization of novel DNA-induced genes in Pseudomonas aeruginosa that are annotated as homologs of the spermidine synthesis genes speD (PA4773) and speE (PA4774). The addition of sublethal concentrations of DNA and membrane-damaging antibiotics induced expression of the genes PA4773 to PA4775, as shown using transcriptional lux fusions and quantitative RT-PCR. Exogenous polyamine addition prevented DNA- and peptide-mediated gene induction. Mutation of PA4774 resulted in an increased outer membrane (OM) susceptibility phenotype upon polymyxin B, CP10A, and gentamicin treatment. When the membrane-localized fluorescent probe C11-BODIPY581/591 was used as an indicator of peroxidation of membrane lipids, the PA4774::lux mutant demonstrated an increased susceptibility to oxidative membrane damage from H2O2 treatment. Addition of exogenous polyamines protected the membranes of the PA4774::lux mutant from polymyxin B and H2O2 treatment. Polyamines from the outer surface were isolated and shown to contain putrescine and spermidine by using high-performance liquid chromatography and mass spectrometry. The PA4774::lux mutant did not produce spermidine on the cell surface, but genetic complementation restored surface spermidine production as well as the antibiotic and oxidative stress resistance phenotypes of the membrane. We have identified new functions for spermidine on the cell surface and propose that polyamines are produced under Mg2+-limiting conditions as an organic polycation to bind lipopolysaccharide (LPS) and to stabilize and protect the outer membrane against antibiotic and oxidative damage. PMID:22155771

  17. Enhancing the mechanical and biological performance of a metallic biomaterial for orthopedic applications through changes in the surface oxide layer by nanocrystalline surface modification.

    PubMed

    Bahl, Sumit; Shreyas, P; Trishul, M A; Suwas, Satyam; Chatterjee, Kaushik

    2015-04-24

    Nanostructured metals are a promising class of biomaterials for application in orthopedics to improve the mechanical performance and biological response for increasing the life of biomedical implants. Surface mechanical attrition treatment (SMAT) is an efficient way of engineering nanocrystalline surfaces on metal substrates. In this work, 316L stainless steel (SS), a widely used orthopedic biomaterial, was subjected to SMAT to generate a nanocrystalline surface. Surface nanocrystallization modified the nature of the oxide layer present on the surface. It increased the corrosion-fatigue strength in saline by 50%. This increase in strength is attributed to a thicker oxide layer, residual compressive stresses, high strength of the surface layer, and lower propensity for intergranular corrosion in the nanocrystalline layer. Nanocrystallization also enhanced osteoblast attachment and proliferation. Intriguingly, wettability and surface roughness, the key parameters widely acknowledged for controlling the cellular response remained unchanged after nanocrystallization. The observed cellular behavior is explained in terms of the changes in electronic properties of the semiconducting passive oxide film present on the surface of 316L SS. Nanocrystallization increased the charge carrier density of the n-type oxide film likely preventing denaturation of the adsorbed cell-adhesive proteins such as fibronectin. In addition, a net positive charge developed on the otherwise neutral oxide layer, which is known to facilitate cellular adhesion. The role of changes in the electronic properties of the oxide films on metal substrates is thus highlighted in this work. This study demonstrates the advantages of nanocrystalline surface modification by SMAT for processing metallic biomaterials used in orthopedic implants. PMID:25833718

  18. Low temperature formation of electrode having electrically conductive metal oxide surface

    DOEpatents

    Anders, Simone (Albany, CA); Anders, Andre (Albany, CA); Brown, Ian G. (Berkeley, CA); McLarnon, Frank R. (Orinda, CA); Kong, Fanping (Berkeley, CA)

    1998-01-01

    A low temperature process is disclosed for forming metal suboxides on substrates by cathodic arc deposition by either controlling the pressure of the oxygen present in the deposition chamber, or by controlling the density of the metal flux, or by a combination of such adjustments, to thereby control the ratio of oxide to metal in the deposited metal suboxide coating. The density of the metal flux may, in turn, be adjusted by controlling the discharge current of the arc, by adjusting the pulse length (duration of on cycle) of the arc, and by adjusting the frequency of the arc, or any combination of these parameters. In a preferred embodiment, a low temperature process is disclosed for forming an electrically conductive metal suboxide, such as, for example, an electrically conductive suboxide of titanium, on an electrode surface, such as the surface of a nickel oxide electrode, by such cathodic arc deposition and control of the deposition parameters. In the preferred embodiment, the process results in a titanium suboxide-coated nickel oxide electrode exhibiting reduced parasitic evolution of oxygen during charging of a cell made using such an electrode as the positive electrode, as well as exhibiting high oxygen overpotential, resulting in suppression of oxygen evolution at the electrode at full charge of the cell.

  19. Surface adsorption of organoarsenic roxarsone and arsanilic acid on iron and aluminum oxides.

    PubMed

    Chen, Wan-Ru; Huang, Ching-Hua

    2012-08-15

    Aromatic organoarsenicals roxarsone (ROX) and p-arsanilic acid (ASA) are common feed additives for livestock and could be released into the environment via animal manure and agricultural runoff. To evaluate their environmental fate, the adsorption behavior of ROX and ASA was investigated with two common soil metal oxides, goethite (FeOOH) and aluminum oxide (Al(2)O(3)), under different reactant loading, water pH and competing ion conditions. ROX and ASA exhibit essentially identical adsorption characteristics. FeOOH and Al(2)O(3) exhibit similar adsorption trends for both organoarsenicals; however, the adsorption efficiency on the surface site basis was about three times lower for Al(2)O(3) than for FeOOH. The adsorption reaction is favorable at neutral and acidic pH. Phosphate and natural organic matter significantly interfere with aromatic arsenical adsorption on both metal oxides, whereas sulfate and nitrate do not. Pre-adsorbed aromatic arsenicals can be quickly but not completely displaced by phosphate, indicating that ion exchange is not the only mechanism governing the adsorption process. The adsorption envelope was successfully modeled by a diffuse double layer surface complexation model, identifying the critical role of di-anionic organoarsenic species in the adsorption. Results of this research can help predict and control the mobility of aromatic arsenicals in the environment. PMID:22695387

  20. Fabrication of free standing anodic titanium oxide membranes with clean surface using recycling process.

    PubMed

    Meng, Xianhui; Lee, Tae-Young; Chen, Huiyu; Shin, Dong-Wook; Kwon, Kee-Won; Kwon, Sang Jik; Yoo, Ji-Beom

    2010-07-01

    Large area of self-organized, free standing anodic titanium oxide (ATO) nanotube membranes with clean surfaces were facilely prepared to desired lengths via electrochemical anodization of highly pure Ti sheets in an ethylene glycol electrolyte, with a small amount of NH4F and H2O at 50 V, followed by self-detachment of the ATO membrane from the Ti substrate using recycling processes. In the first anodization step, the nanowire oxide layer existed over the well-arranged ATO nanotube. After sufficiently rinsing with water, the whole ATO layer was removed from the Ti sheet by high pressure N2 gas, and a well-patterned dimple layer with a thickness of about 30 nm existed on the Ti substrate. By using these naturally formed nano-scale pits as templates, in the second and third anodization process, highly ordered, vertically aligned, and free standing ATO membranes with the anodic aluminum oxide (AAO)-like clean surface were obtained. The inter-pore distance and diameter was 154 +/- 2 nm and 91+/- 2 nm, the tube arrays lengths for 25 and 46 hours were 44 and 70 microm, respectively. The present study demonstrates a simple approach to producing high quality, length controllable, large area TiO2 membrane. PMID:21128409

  1. Osteoblast cell adhesion and viability on nanostructured surfaces of porous titanium oxide layer.

    PubMed

    Song, Yo-Han; An, Ji-Hae; Seo, Young-Woo; Moon, Won-Jin; Park, Yeong-Joon; Song, Ho-Jun

    2014-08-01

    Surface characteristics and osteoblast cell functions were investigated for the nano-structured oxide layer on commercially pure titanium (CP-Ti) fabricated using microarc oxidation (MAO) and hydrothermal treatment (HT) methods. Ti-MAO-135HT, Ti-MAO-150HT, and Ti-MAO-175HT groups were fabricated by hydrothermally treating the MAO-treated specimens (Ti-MAO) in phosphorus-containing alkaline solution at temperatures of 135, 150, or 175 °C, respectively. After hydrothermal treatment, a nanosheet-shaped morphology, nano-needles and nanorods were observed on the porous surface of the Ti-MAO-135HT, Ti-MAO-150HT and Ti-MAO-175HT groups, respectively. The roughness was not significantly different for all groups. However the contact angle decreased dramatically as the hydrothermal temperature increased. The osteoblastic cell adhesion and viability of the Ti-MAO-150HT and Ti-MAO-175HT groups were significantly lower compared to those of the Ti-MAO group. This study showed that nano-topology formed on micro porous oxide layer was more important than hydrophilicity in its effect upon initial osteoblastic cell functions. PMID:25935989

  2. Solid state chemistry of nitrogen oxides--part I: surface consumption of NO.

    PubMed

    Minissale, M; Fedoseev, G; Congiu, E; Ioppolo, S; Dulieu, F; Linnartz, H

    2014-05-14

    The role of nitrogen and oxygen chemistry in the interstellar medium is still rather poorly understood. Nitric oxide, NO, has been proposed as an important precursor in the formation of larger N- and O-bearing species, such as hydroxylamine, NH2OH, and nitrogen oxides, NO2 and N2O. The topic of this study is the solid state consumption of NO via oxygenation and the formation of NO2 and other nitrogen oxides (ONNO2 and N2O4) under conditions close to those encountered on icy grains in quiescent interstellar clouds. In our experiments nitric oxide and oxygen allotropes (O, O2, and O3) or N atoms are co-deposited under ultra-high vacuum conditions on different substrates (silicate, graphite, compact ASW ice, and gold) at temperatures ranging between 10 and 35 K. Reaction products are monitored via Fourier Transform Reflection Absorption Infrared Spectroscopy (FT-RAIRS) and Temperature Programmed Desorption (TPD) using mass spectrometry. We find that NO2 is efficiently formed in NO + O/O2/O3/N solid surface reactions. These are essentially barrier free and offer a pathway for the formation of NO2 in space. Nitrogen dioxide, however, has not been astronomically detected, contradicting the efficient reaction channel found here. This is likely due to other pathways, including regular hydrogenation reactions, as discussed separately in part II of this study. PMID:24671412

  3. Ferrate(VI) as a possible oxidant on the Martian surface.

    SciTech Connect

    Tsapin, A. I.; Goldfeld, M. G.; McDonald, G. D.; Nealson, K. H.; Mohnke, J.; Moskovitz, B.; Solheid, P.; Kemner, K. M.; Orlandini, K.; Environmental Research; Jet Propulsion Lab.; Univ. of Minnesota

    2000-01-01

    Viking 'Biological' experiments (Oyama et al. 1976, Levin & Straat 1977) revealed an unexpected chemical activity in the surfam material, which in some ways resembled biology but was ultimately explained by a rather complex chemistry. It was shown, in these experiments that moisturizing Martian soil resulted in oxygen evolution, while addition of a bacterial nutrient solution (14G formate, glycine, lactate, etc.) released 14C02, dong with some oxygen. These observations indicated the presence of a strong oxidant on Martian surface, or, most probably, several different oxidants (Klein 1978). The nature of the oxidants in Mars soil, and their distribution, are important for choosing Martian landing sites. Iron as an one of the most abundant elements in Martian soil, deserves attention in this context, since it has a whole set of oxidation states, from 0 to +6, even though in terrestrial conditions only Fe(O), Fe(+2) and Fe(+3) are commonly found. Fe(+4, +5) are unstable, but Fe(+6) has been characterized in some detail. Though it was never identified as a natural compound on the Earth, it is stable enough under some conditions (highly alkaline solutions, lack of reductants, dry atmosphere, low temperature) that are not normally encountered in the terrestrial environment, but still can be considered as a possibility in Martian soil. Here are discussed ferrate(VI) formation and accumulation in Martian soil, and experimental data are presented on the spectral characterization and chemical behavior under conditions simulating the Viking 'biological experiments'.

  4. Stability and Transport of Graphene Oxide Nanoparticles in Groundwater and Surface Water

    PubMed Central

    Lanphere, Jacob D.; Rogers, Brandon; Luth, Corey; Bolster, Carl H.; Walker, Sharon L.

    2014-01-01

    Abstract The effects of groundwater and surface water constituents (i.e., natural organic matter [NOM] and the presence of a complex assortment of ions) on graphene oxide nanoparticles (GONPs) were investigated to provide additional insight into the factors contributing to fate and the mechanisms involved in their transport in soil, groundwater, and surface water environments. The stability and transport of GONPs was investigated using dynamic light scattering, electrokinetic characterization, and packed bed column experiments. Stability results showed that the hydrodynamic diameter of the GONPs at a similar ionic strength (2.1±1.1?mM) was 10 times greater in groundwater environments compared with surface water and NaCl and MgCl2 suspensions. Transport results confirmed that in groundwater, GONPs are less stable and are more likely to be removed during transport in porous media. In surface water and MgCl2 and NaCl suspensions, the relative recovery was 94%±3% indicating that GONPs will be very mobile in surface waters. Additional experiments were carried out in monovalent (KCl) and divalent (CaCl2) salts across an environmentally relevant concentration range (0.1–10?mg/L) of NOM using Suwannee River humic acid. Overall, the transport and stability of GONPs was increased in the presence of NOM. This study confirms that planar “carbonaceous-oxide” materials follow traditional theory for stability and transport, both due to their response to ionic strength, valence, and NOM presence and is the first to look at GONP transport across a wide range of representative conditions found in surface and groundwater environments. PMID:25053876

  5. Oxidation states of GaAs surface and their effects on neutral beam etching during nanopillar fabrication

    NASA Astrophysics Data System (ADS)

    Thomas, C.; Tamura, Y.; Syazwan, M. E.; Higo, A.; Samukawa, S.

    2014-05-01

    We have investigated a new process for fabricating GaAs sub-20 nm nanopillars that uses a top-down combination of a bio-template and damage-free neutral beam etching. A two-dimensional array of nanoparticles composed of a protein shell embedded with a metal oxide core was formed on the top of a GaAs surface treated by neutral beam oxidation. Because of device requirements, three low-temperature oxygen techniques were investigated for removing the protein shell prior to the etching process: oxygen radical, oxygen neutral beam, and low-temperature oxygen annealing in vacuum (LT-OAV). X-ray photoelectron spectroscopy was used to monitor the effects of the different treatments on the GaAs surface. While the three processes could efficiently remove a protein shell, subsequent oxidation of the GaAs surface showed some differences in the oxide layer composition. Therefore, LT-OAV was selected considering its lower gallium oxide formation. A hydrogen radical process was then performed at temperatures lower than 400 °C to remove the oxide layer prior to etching. This process completely removed arsenide oxide and only residual gallium oxide was found on the surface afterwards. Etching was performed using a pure chlorine neutral beam of GaAs samples with metal oxide core etching masks. We found that control of the Ga-oxide amount on the surface is the key parameter for controlling the diameter and the density of nanopillars. Finally, high-aspect ratio nanopillars using stacked layers of GaAs and AlGaAs were obtained and showed no damage layer.

  6. Surface analysis of a nano-sized oxide formed on alloy 600 in a high temperature/pressure aqueous solution.

    PubMed

    Kim, Dong-jin; Lim, Yun Soo; Kwon, Hyuk Chul; Hwang, Seong Sik; Kim, Hong Pyo

    2010-01-01

    Even though nickel based Alloy 600 (Ni 75 wt%, Cr 15 wt% and Fe 10 wt%) shows superior corrosion and mechanical properties, numerous corrosion problems, caused by a long time exposure of more than 30 years under a high temperature and high pressure water chemical environment have occurred. Especially, a lead induced stress corrosion cracking (SCC) has been a very important issue. A SCC is deeply related to a nano-sized oxide properties, formed on an Alloy 600 surface, because a crack initiates and propagates through a breakdown and modification of a thin surface oxide formed naturally on Alloy 600 in an aqueous solution. Therefore an investigation of an oxide properties would provide key information to elucidate the mechanism of a SCC and to establish a countermeasure. In the present work, a surface oxide film formed on Alloy 600 in an aqueous solution at 315 degrees C without/with a lead oxide and nickel boride as a SCC accelerator and an inhibitor, respectively, was analyzed by using a transmission electron microscopy, equipped with an energy dispersive X-ray spectroscopy and an X-ray photoelectron spectroscopy, equipped with an ion sputter for a depth profiling. In both the ammonia solutions without/with NiB, a duplex oxide layer was formed, i.e., a porous outer oxide mainly composed of NiO and Ni(OH)2 and a relatively dense inner Cr2O3 layer. Lead was incorporated into the oxide layer leading to a Cr depletion in the oxide layer and a passivity degradation. The passivity of the surface oxide was increased when NiB was added into a solution with PbO, which was in accordance with the increase of the SCC resistance. Passivity degradation by lead and the inhibitive mechanism of nickel boride were explained by a defect chemistry in an oxide semiconductor and an adhesion preference as a function of the wetting angle, respectively. PMID:20352815

  7. Methoxychlor and estradiol induce oxidative stress DNA damage in the mouse ovarian surface epithelium.

    PubMed

    Symonds, Daniel A; Merchenthaler, Istvan; Flaws, Jodi A

    2008-09-01

    Estrogenic compounds such as 17beta-estradiol (E(2)) and methoxychlor (MXC) induce oxidative stress damage in breast cells and mouse ovarian follicles, respectively. However, little is known about whether estrogenic compounds cause oxidative stress in the ovarian surface epithelium (OSE). Thus, this work tested the hypothesis that E(2) and MXC cause oxidative stress in the OSE. To test this hypothesis, we employed an improved mouse tissue culture assay in which OSE cells were treated with hydrogen peroxide (H2O2; positive control), MXC, or E(2) +/- the anti-oxidant vitamin E, or progesterone. The cells then were subjected to a novel direct immunofluorescent assay in which cells in the microtiter plate were reacted with antibodies that detect oxidative damage to DNA (8-hydroxy-2'-deoxyguanosine). The signal was identified with a tyramide Alexa Fluor fluorescent probe and quantified by microfluorimetry. Correction for cellularity was carried out for each well with a fluorescent DNA dye system (CyQuant) at a different wavelength. After 24 h, the mean Alexa Fluor CyQuant ratio was 11.3 +/- 0.9 for controls, 132 +/- 15 for H2O2 treated positive control cells (p < or = 0.01 from control), 105 +/- 6.6 for E(2) treated cells (p < or = 0.01 from control), and 64 +/- 5.1 for MXC-treated cells (p < or = 0.01 from control). After 72 h, the mean ratio was 121 +/- 10.6 for controls, 391 +/- 23 for H2O2 treated cells (p < or = 0.01 from control), 200 +/- 15 for E(2) treated cells (p < or = 0.03), and 228 +/- 21 for MXC-treated cells (p < or = 0.01). Further, vitamin E, but not progesterone, protected OSE cells from E(2)- and MXC-induced oxidative damage. This study demonstrates the feasibility of direct immunofluorescent quantitation of DNA adducts in cell cultures without DNA extraction. Moreover, these data indicate that E(2) and MXC produce oxidative DNA damage in the OSE, and that this damage is prevented by the anti-oxidant vitamin E. PMID:18502743

  8. Thermal and photochemical reactions of NO2 on chromium(III) oxide surfaces at atmospheric pressure.

    PubMed

    Nishino, Noriko; Finlayson-Pitts, Barbara J

    2012-12-01

    While many studies of heterogeneous chemistry on Cr(2)O(3) surfaces have focused on its catalytic activity, less is known about chemistry on this surface under atmospheric conditions. We report here studies of the thermal and photochemical reactions of NO(2) on Cr(2)O(3) at one atm in air. In order to follow surface species, the interaction of 16-120 ppm NO(2) with a 15 nm Cr(2)O(3) thin film deposited on a germanium crystal was monitored in a flow system using attenuated total reflectance (ATR) coupled to a Fourier transform infrared (FTIR) spectrometer. Gas phase products were monitored in the effluent of an ~285 ppm NO(2)-air mixture that had passed over Cr(2)O(3) powder in a flow system. A chemiluminescence NO(y) analyzer, a photometric O(3) analyzer and a long-path FTIR spectrometer were used to probe the gaseous products. In the absence of added water vapor, NO(2) formed nitrate (NO(3)(-)) ions coordinated to Cr(3+). These surface coordinated NO(3)(-) were reversibly solvated by water under humid conditions. In both dry and humid cases, nitrate ions decreased during irradiation of the surface at 302 nm, and NO and NO(2) were generated in the gas phase. Under dry conditions, NO was the major gaseous product while NO(2) was the dominant species in the presence of water vapor. Heating of the surface after exposure to NO(2) led to the generation of both NO(2) and NO under dry conditions, but only NO(2) in the presence of water vapor. Elemental chromium incorporated into metal alloys such as stainless steel is readily oxidized in contact with ambient air, forming a chromium-rich metal oxide surface layer. The results of these studies suggest that active photo- and thermal chemistry will occur when boundary layer materials containing chromium(III) or chromium oxide such as stainless steel, roofs, automobile bumpers etc. are exposed to NO(2) under tropospheric conditions. PMID:23090708

  9. Strontium oxide segregation at SrLaAlO4 surfaces A.E. Becerra-Toledo , L.D. Marks

    E-print Network

    Marks, Laurence D.

    Strontium oxide segregation at SrLaAlO4 surfaces A.E. Becerra-Toledo , L.D. Marks Northwestern surfaces We report observable segregation of strontium oxide at the surface of strontium lanthanum-dispersive X-ray spectroscopy showed that Sr and O segregation occurs on strontium lanthanum aluminate surfaces

  10. Inhibited phase behavior of gas hydrates in graphene oxide: influences of surface and geometric constraints.

    PubMed

    Kim, Daeok; Kim, Dae Woo; Lim, Hyung-Kyu; Jeon, Jiwon; Kim, Hyungjun; Jung, Hee-Tae; Lee, Huen

    2014-11-01

    Porous materials have provided us unprecedented opportunities to develop emerging technologies such as molecular storage systems and separation mechanisms. Pores have also been used as supports to contain gas hydrates for the application in gas treatments. Necessarily, an exact understanding of the properties of gas hydrates in confining pores is important. Here, we investigated the formation of CO2, CH4 and N2 hydrates in non-interlamellar voids in graphene oxide (GO), and their thermodynamic behaviors. For that, low temperature XRD and P-T traces were conducted to analyze the water structure and confirm hydrate formation, respectively, in GO after its exposure to gaseous molecules. Confinement and strong interaction of water with the hydrophilic surface of graphene oxide reduce water activity, which leads to the inhibited phase behavior of gas hydrates. PMID:25232710

  11. Electronic structure of nitinol surfaces oxidized by low-energy ion bombardment

    NASA Astrophysics Data System (ADS)

    Petravic, M.; Varasanec, M.; Peter, R.; Kavre, I.; Metikos-Hukovic, M.; Yang, Y.-W.

    2014-06-01

    We have studied the electronic structure of nitinol exposed to low-energy oxygen-ion bombardment, using x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. XPS spectra reveal a gradual transformation of nitinol surfaces into TiO2 with increased dose of implanted oxygen. No oxidation of Ni atoms has been detected. NEXAFS spectra around O K-edge and Ti L2,3-edge, reflecting the element-specific partial density of empty electronic states, exhibit features, which can be attributed to the creation of molecular orbitals, crystal field splitting, and the absence of long-range order, characteristic of the amorphous TiO2. Based on these results, we discuss the oxidation kinetics of nitinol under low-energy oxygen-ion bombardment.

  12. Method and apparatus for detecting the presence and thickness of carbon and oxide layers on EUV reflective surfaces

    DOEpatents

    Malinowski, Michael E.

    2005-01-25

    The characteristics of radiation that is reflected from carbon deposits and oxidation formations on highly reflective surfaces such as Mo/Si mirrors can be quantified and employed to detect and measure the presence of such impurities on optics. Specifically, it has been shown that carbon deposits on a Mo/Si multilayer mirror decreases the intensity of reflected HeNe laser (632.8 nm) light. In contrast, oxide layers formed on the mirror should cause an increase in HeNe power reflection. Both static measurements and real-time monitoring of carbon and oxide surface impurities on optical elements in lithography tools should be achievable.

  13. Production and Wear Behavior of Tribofilms by Supplying Oxide Nanoparticles on Rubbing Steel Surfaces

    NASA Astrophysics Data System (ADS)

    Kato, Hirotaka

    This study demonstrates wear-protective tribofilms produced by supplying nanometer-sized oxide particles on rubbing steel surfaces. Particularly, the influence of the type of supplied oxide, atmosphere and applied load in the tribofilm production process, on the behavior of tribofilm formation and the wear of the tribofilms have been investigated in detail. Tribofilms were produced by supplying CuO (mean particle diameter: 48 nm), Fe2O3 (30 nm) or Bi2O3 (51 nm) oxide particles in a normal laboratory atmosphere of air or in a vacuum (8×10-4 Pa) by using a pin-on-disc friction method. The material used for the pin and disc specimens was normalized 0.45 mass% carbon steel. The produced tribofilms were examined by a CCD microscope and a SEM equipped with an EDX. The wear properties of the tribofilms were tested by using the same pin-on-disc machine in air. It has been found that the tribofilms produced by supplying Bi2O3 particles were thicker and wider compared with those produced by supplying CuO or Fe2O3 particles. The tribofilms produced by supplying CuO, Fe2O3 or Bi2O3 oxide particles reduced the wear considerably. Particularly, the tribofilms produced by supplying Bi2O3 particles on a disc surface showed mild wear throughout the wear test, resulting in a very small wear volume. Moreover, the tribofilms produced in a vacuum showed longer sliding distance of the transition from mild to severe wear than those produced in air, owing to the dense structure and the wide area of the produced tribofilms.

  14. Solid-State 17O NMR Study of Benzoic Acid Adsorption On Metal Oxide Surfaces

    SciTech Connect

    Hagaman, Edward {Ed} W [ORNL; Chen, Banghao [ORNL; Jiao, Jian [ORNL; Parsons, Williams [Oak Ridge National Laboratory (ORNL)

    2012-01-01

    Solid-state 17O NMR spectra of 17O-labeled benzoic and anisic acids are reported and benzoic acid is used to probe the surface of metal oxides. Complexes formed when benzoic acid is dry-mixed with mesoporous silica, and nonporous titania and alumina are characterized. Chemical reactions with silica are not observed. The nature of benzoic acid on silica is a function of the water content of the oxide. The acid disperses in the pores of the silica if the silica is in equilibrium with ambient laboratory humidity. The acid displays high mobility as evidenced by a liquid-like, Lorentzian resonance. Excess benzoic acid remains as the crystalline hydrogen-bonded dimer. Benzoic acid reacts with titania and alumina surfaces in equilibrium with laboratory air to form the corresponding titanium and aluminum benzoates. In both materials the oxygen of the 17O-labeled acid is bound to the metal, showing the reaction proceeds by bond formation between oxygen deficient metal sites and the oxygen of the carboxylic acid. 27Al MAS NMR confirms this mechanism for the reaction on alumina. Dry mixing of benzoic acid with alumina rapidly quenches pentacoordinate aluminum sites, excellent evidence that these sites are confined to the surface of the alumina particles.

  15. Evaluation of surface modifications for oxidation protection of vanadium-base alloys in helium-cooled blanket designs

    NASA Astrophysics Data System (ADS)

    Tobin, A.; Busch, G.

    1986-11-01

    Vanadium-base alloys are currently being considered for application to high-temperature helium-cooled fusion reactor blanket designs. A major drawback is their known sensitivity to low levels of oxidizing impurities that would normally be present as water vapor in the helium coolant gas. Although baseline data on the oxidation resistance of vanadium alloys are lacking, protection of vanadium alloy surfaces exposed to the helium coolant will probably be necessary for contiuous blanket operation at temperatures above 875 K. Surface alloying of vanadium-base alloys appears to be a feasible method of creating an oxidation-resistant surface. To examine this approach, a series of V-15Cr-5Ti alloy sheet specimens was surface alloyed with chromium. Oxidation tests were then conducted in flowing helium containing up to 100 vppm H 2O. Temperatures up to 925 K and times up to 1000 h were utilized. Control samples of unmodified V-15Cr-5Ti and a Type 316 stainless steel were also included. Significant reductions in oxygen pickup were observed with surface-alloyed specimens. These results suggest that surface alloying techniques offer great promise for protecting vanadium alloy surfaces against oxidation at blanket operating temperatures.

  16. Induced increase in surface work function and surface energy of indium tin oxide-doped ZnO films by (NH4)2Sx treatment

    Microsoft Academic Search

    Chia-Lung Tsai; Yow-Jon Lin; Ping-Hsun Wu; Shu-You Chen; Day-Shan Liu; Jia-Huang Hong; Chia-Jyi Liu; Yu-Tai Shih; Jie-Min Cheng; Hsing-Cheng Chang

    2007-01-01

    The effects of (NH4)2Sx treatment on the surface electronic properties of the thin indium tin oxide (ITO)-doped ZnO films have been examined in this study. According to the experimental results, we found that the formation of S-metal bonds and the removal of oxygen vacancies near the (NH4)2Sx-treated ITO-doped ZnO surface could lead to an increase in the surface energy and

  17. Surface modification of coir fibre involving oxidation of lignins followed by reaction with furfuryl alcohol: Characterization and stability

    NASA Astrophysics Data System (ADS)

    Saw, Sudhir Kumar; Sarkhel, Gautam; Choudhury, Arup

    2011-02-01

    In this study, the chemical treatment of the coir fibres was executed through oxidation with aqueous ClO2 followed by grafting with furfuryl alcohol (FA), leading to create a coating around the fibres more compatible with the polymeric matrices. The ClO2 was used to oxidize mainly phenolic syringyl and guaiacyl units of the lignin polymer to create quinones, which were characterized by UV-vis spectroscopy and Fourier transform infrared spectroscopy. In addition, the surface features of modified fibres were studied using scanning electron microscopy. The extent of FA-grafting was found higher (weight gain 17.7%) for oxidized fibre compared to those for non-oxidized fibre (weight gain 2.2%). The surface modification with FA-grafting reduced the hydrophilicity of the coir fibre, as confirm by the dynamic contact angle and water absorption measurements. The thermal and mechanical properties of untreated, oxidized and FA-grafted coir fibres were evaluated and compared.

  18. Adsorption and Reaction of NO on Oxidized and Reduced SrTiO{sub 3} (100) Surfaces

    SciTech Connect

    Azad, Samina; Szanyi, Janos; Peden, Charles HF.; Wang, Li Q.

    2003-07-01

    Adsorption and reaction of NO on oxidized and reduced SrTiO{sub 3}(100) surfaces have been studied using temperature programmed desorption (TPD). Major desorption peaks for NO from the fully oxidized surface as found at 140 and 260 K, along with a long tail that continues up to 500 K. The desorption features at 140 and 260 K correspond to activation energies of 36 and 66 kJ/mol, respectively, using a simple Redhead analysis. NO reacts non-dissociatively on the fully oxidized surface. Reactivity of reduced SrTiO{sub 3}(100) is relatively higher than that of the fully oxidized surface and is influenced by the adsorption temperature of the NO molecules on the surface. NO and N{sub 2}O are the major desorption products following adsorption of NO on the reduced surface at 110 K. Desorption of N{sub 2}O from significantly reduced SrTiO{sub 3}(100) indicates that the oxygen atoms of the adsorbed NO molecules are preferentially extracted by the surface oxygen vacancy sites whereas the surface oxidizes as a result of the de-oxygenation of the adsorbates. Adsorption of NO on the reduced surface at 297 K is followed by breakage of the N-O bond producing adsorbed N and O atoms and recombination of these ad-species results in desorption of NO and N{sub 2} from this surface. Adsorption of NO on the significantly reduced surface at 200 K is followed by desorption of NO, N{sub 2} and N{sub 2}O as TPD products and the reactivity of this surface at 200 K presumable is a composite of the behavior observed for NO adsorption at 110 and 297 K.

  19. Adsorption and reaction of NO on oxidized and reduced SrTiO3(100) surfaces

    NASA Astrophysics Data System (ADS)

    Azad, S.; Szanyi, J.; Peden, C. H. F.; Wang, L.-Q.

    2003-07-01

    Adsorption and reaction of NO on oxidized and reduced SrTiO3(100) surfaces have been studied using temperature programmed desorption (TPD). Major desorption peaks for NO from the fully oxidized surface are found at 140 and 260 K, along with a long tail that continues up to 500 K. The desorption features at 140 and 260 K correspond to activation energies of 36 and 66 kJ/mol, respectively, using a simple Redhead analysis. NO reacts nondissociatively on the fully oxidized surface. Reactivity of reduced SrTiO3(100) is relatively higher than that of the fully oxidized surface and is influenced by the adsorption temperature of the NO molecules on the surface. NO and N2O are the major desorption products following adsorption of NO on the reduced surface at 110 K. Desorption of N2O from significantly reduced SrTiO3(100) indicates that the oxygen atoms of the adsorbed NO molecules are preferentially extracted by the surface oxygen vacancy sites, whereas the surface oxidizes as a result of the deoxygenation of the adsorbates. Adsorption of NO on the reduced surface at 297 K is followed by breakage of the N-O bond producing adsorbed N and O atoms and recombination of these adspecies results in desorption of NO and N2 from this surface. Adsorption of NO on the significantly reduced surface at 200 K is followed by desorption of NO, N2, and N2O as TPD products and the reactivity of this surface at 200 K presumably is a composite of the behavior observed for NO adsorption at 110 and 297 K.

  20. Vibrational spectra of CO adsorbed on oxide thin films: A tool to probe the surface defects and phase changes of oxide thin films

    SciTech Connect

    Savara, Aditya, E-mail: savaraa@ornl.gov [Chemical Sciences Division, Oak Ridge National Lab, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831 (United States)

    2014-03-15

    Thin films of iron oxide were grown on Pt(111) single crystals using cycles of physical vapor deposition of iron followed by oxidative annealing in an ultrahigh vacuum apparatus. Two procedures were utilized for film growth of ?15–30 ML thick films, where both procedures involved sequential deposition+oxidation cycles. In procedure 1, the iron oxide film was fully grown via sequential deposition+oxidation cycles, and then the fully grown film was exposed to a CO flux equivalent to 8 × 10{sup ?7} millibars, and a vibrational spectrum of adsorbed CO was obtained using infrared reflection-absorption spectroscopy. The vibrational spectra of adsorbed CO from multiple preparations using procedure 1 show changes in the film termination structure and/or chemical nature of the surface defects—some of which are correlated with another phase that forms (“phase B”), even before enough of phase B has formed to be easily detected using low energy electron diffraction (LEED). During procedure 2, CO vibrational spectra were obtained between deposition+oxidation cycles, and these spectra show that the film termination structure and/or chemical nature of the surface defects changed as a function of sequential deposition+oxidation cycles. The authors conclude that measurement of vibrational spectra of adsorbed CO on oxide thin films provides a sensitive tool to probe chemical changes of defects on the surface and can thus complement LEED techniques by probing changes not visible by LEED. Increased use of vibrational spectra of adsorbed CO on thin films would enable better comparisons between films grown with different procedures and by different groups.