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Sample records for oxidized cu110 surface

  1. Properties of the Oxidized Cu(110) Surface: The DFT study

    NASA Astrophysics Data System (ADS)

    Olenga, Antoine; Fazleev, N. G.

    2012-10-01

    The study of adsorption of oxygen on transition metal surfaces is important for the understanding of oxidation, heterogeneous catalysis, and metal corrosion. In this work we have studied from first principles the changes of electronic properties of the Cu(110) surface due to oxygen adsorption. Especially, we have focused on studies of changes in the work function, electronic density, interlayer spacing, density of states and band structure with oxygen coverage. Calculations of electronic properties from first principles have been also performed for the (110) and surface of Cu2O to use for comparison. The first-principles calculations in this work have been performed on the basis of the Density Functional Theory and using DMOl3 code. The obtained theoretical results have been compared with available experimental data.

  2. Optical signatures of thiolate/Cu(110) and S/Cu(110) surface structures

    NASA Astrophysics Data System (ADS)

    Martin, D. S.; Lane, P. D.; Isted, G. E.; Cole, R. J.; Blanchard, N. P.

    2010-08-01

    The optical properties of thiolate/Cu(110) and S/Cu(110) surfaces created by the adsorption of methanethiol and L-cysteine are investigated using reflection anisotropy spectroscopy (RAS). We find that characteristic optical signatures are obtained from these systems. The experimental RAS profiles are simulated using a four-phase model consisting of vacuum, anisotropic overlayer, anisotropic surface, and isotropic substrate. The results of the simulations suggest that a broad optical transition at 3.8 eV is associated with the thiolate/Cu(110) interface, consistent with recent first-principles calculations [S. D’Agostino , Phys. Rev. B 75, 195444 (2007)10.1103/PhysRevB.75.195444].

  3. Oxalic acid adsorption states on the clean Cu(110) surface

    NASA Astrophysics Data System (ADS)

    Fortuna, Sara

    2016-11-01

    Carboxylic acids are known to assume a variety of configurations on metallic surfaces. In particular oxalic acid on the Cu(110) surface has been proposed to assume a number of upright configurations. Here we explore with DFT calculations the possible structures that oxalic acid can form on copper 110 at different protonation states, with particular attention at the possibility of forming structures composed of vertically standing molecules. In its fully protonated form it is capable of anchoring itself on the surface thanks to one of its hydrogen-free oxygens. We show the monodeprotonated upright molecule with two oxygens anchoring it on the surface to be the lowest energy conformation of a single oxalic molecules on the Cu(110) surface. We further show that it is possible for this configuration to form dense hexagonally arranged patterns in the unlikely scenario in which adatoms are not involved.

  4. Adsorption of CO on Ni/Cu(110) bimetallic surfaces

    NASA Astrophysics Data System (ADS)

    Demirci, E.; Carbogno, C.; Groß, A.; Winkler, A.

    2009-08-01

    The adsorption behavior of CO on bimetallic Ni/Cu(110) surfaces has been studied experimentally by thermal-desorption spectroscopy and theoretically by density-functional theory (DFT) calculations. The bimetallic surfaces were produced either by evaporation of nickel or by decomposition of Ni(CO)4 on Cu(110). Adsorption of CO at 180 K on such a bimetallic surface yields three new adsorption states with adsorption energies between that of CO on clean Cu(110) and clean Ni(110). The new desorption peaks from the bimetallic surface, designated as β1-β3 , can be observed at 250, 300, and 360 K, respectively. These new states are most pronounced when (1)/(2) monolayer of nickel is present on the copper surface. DFT calculations, using the Vienna ab initio simulation package code, were performed to identify the most probable Ni/Cu atomic arrangements at the bimetallic surface to reconcile with the experimental results. It turned out that CO adsorption on nickel dimers consisting of in-surface and adjacent subsurface atoms can best explain the observed experimental data. The result shows that CO adsorption is determined by local (geometric) effects rather than by long-range (electronic) effects. These findings should contribute to a better understanding of tailoring catalytic processes with the help of bimetallic catalysts.

  5. A Window on Surface Explosions: Tartaric Acid on Cu(110)

    SciTech Connect

    Mhatre, B S; Pushkarev, V; Holsclaw, B; Lawton, T J; Sykes, E C. H.; Gellman, A J

    2013-04-18

    Autocatalytic reaction mechanisms are observed in a range of important chemical processes including catalysis, radical-mediated explosions, and biosynthesis. Because of their complexity, the microscopic details of autocatalytic reaction mechanisms have been difficult to study on surfaces and heterogeneous catalysts. Autocatalytic decomposition reactions of S,S- and R,R-tartaric acid (TA) adsorbed on Cu(110) offer molecular-level insight into aspects of these processes, which until now, were largely a matter of speculation. The decomposition of TA/Cu(110) is initiated by a slow, irreversible process that forms vacancies in the adsorbed TA layer, followed by a vacancy-mediated, explosive decomposition process that yields CO{sub 2} and small hydrocarbon products. Initiation of the explosive decomposition of TA/Cu(110) has been studied by measurement of the reaction kinetics, time-resolved low energy electron diffraction (LEED), and time-resolved scanning tunneling microscopy (STM). Initiation results in a decrease in the local coverage of TA and a concomitant increase in the areal vacancy concentration. Observations of explosive TA decomposition on the Cu(651)S surface suggest that initiation does not occur at structural defects in the surface, as has been suggested in the past. Once the vacancy concentration reaches a critical value, the explosive, autocatalytic decomposition step dominates the TA decomposition rate. The onset of the explosive decomposition of TA on Cu(110) is accompanied by the extraction of Cu atoms from the surface to form a (±6,7; {-+}2,1) overlayer that is readily observable using LEED and STM. The explosive decomposition step is second-order in vacancy concentration and accelerates with increasing extent of reaction.

  6. Water adsorbate influence on the Cu(110) surface optical response

    NASA Astrophysics Data System (ADS)

    Baghbanpourasl, Amirreza; Schmidt, Wolf Gero; Denk, Mariella; Cobet, Christoph; Hohage, Michael; Zeppenfeld, Peter; Hingerl, Kurt

    2015-11-01

    Surface reflectance anisotropy may be utilized for characterizing surfaces, interfaces, and adsorption structures. Here, the reflectance anisotropy and surface dielectric functions of the thermodynamically most favored water adsorbate structures on the Cu(110) surface (i.e. hexagonal bilayers, pentagonal chains, and partially dissociated water structures) are calculated from density-functional theory and compared with recent experimental data. It is shown that the water overlayer structures modify in a geometry-specific way the optical anisotropy of the bare surface which can be exploited for in situ determination of the adsorption structures. For hexagonal bilayer overlayer geometries, strong features in the vacuum ultraviolet region are predicted. The theoretical analysis shows a noticeable influence of intraband transitions also for higher photon energies and rather slight influences of the van der Waals interaction on the spectral signatures. Water induced strain effects on the surface optical response are found to be negligible.

  7. 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. PMID:25847844

  8. STM studies of the growth of the Si/Cu(110) surface alloy

    NASA Astrophysics Data System (ADS)

    Polop, C.; Sacedón, J. L.; Martín-Gago, J. A.

    1998-05-01

    The stages of the growth of the surface alloy c(2×2)-Si/Cu(110) have been analysed on the basis of scanning tunneling microscopy images and low electron energy diffraction (LEED) patterns. The formation of this interface goes through several stages as the Si coverage is increased. For a Si coverage ca 0.1 monolayer (ML), structured islands are observed on the surface. They are aligned along the < 1¯12> surface direction which corresponds to the Si-Si bonding direction in the atomic model. These islands grow and coalesce upon Si coverage, forming extended alloy areas. Defects, consisting of grouped atomic vacancies, along the < 1¯10> surface direction are observed at this stage of growth which are reflected on the corresponding LEED pattern as diffuse c(2×2) spots enlarged along the <001> surface direction. Complete and free of defects alloy terraces are observed for a Si coverage ca 0.5 ML, that is, when the completion of the overlayer alloy is attained. Atomic resolution STM images show a c(2×2) atomic arrangement which can be explained as a near coplanar substitution of Cu by Si atoms. Throughout the text the relationship between the growth stages and the perfection of the alloy layer is discussed.

  9. HRLEED study of the roughening transitions in Cu(110), Ni(110) and Ag(110) surfaces

    SciTech Connect

    Wang, K.; Montano, P.A. |

    1996-12-01

    The authors present the results of High Resolution Low Energy Electron Diffraction (HRLEED) measurements of the thermal roughening transition on Cu(110), Ag(110) and Ni(110) surfaces. They performed careful spot profile intensity measurements as a function of temperature. They observed a proliferation of steps along the (110) and (001) directions. In addition a strong deviation from a Debye model was observed in the scattered intensity of the Bragg reflections. This deviation from the harmonic approximation occurs well below the roughening transition temperature. The behavior of the three metal surfaces is qualitatively similar except for the transition temperatures. Ni shows the highest transition temperature (1,300 K), Cu is intermediate (1,000 K) and Ag has the lowest temperature (730 K). Analyzing the behavior of the (00) reflection intensity, and the evolution of the line shape as a function of the temperature, they found clear evidence of a roughening transition at the (110) surface. A lineshape analysis of the (00) reflection shows the transition from a Lorentzian lineshape to a power law. They also proved, based on the experimental data and a recent theoretical model, that there is a tremendous increase in step density and a decrease in the average terrace size as the temperature increases. They used STM to corroborate the HRLEED results at room temperature. They found excellent agreement.

  10. Experimental intensity analysis of second harmonic generation at the Cu(110) surface

    NASA Astrophysics Data System (ADS)

    Schwab, C.; Meister, G.; Woll, J.; Gerlach, A.; Goldmann, A.

    2000-06-01

    We have analyzed second harmonic generation (SHG) intensities from Cu(110) at fundamental wavelengths λ=1064 nm and between λ=650 and 540 nm. Experimentally the light incidence direction was chosen along the two inequivalent mirror planes of the surface lattice unit cell, and the linear polarizations of both input (fundamental) and output (frequency-doubled) radiation could be varied independently. At λ=1064 nm the relative sizes of the different components of the second-order susceptibility tensor are as follows: | χ zzz|=2490, | χ yzy|=139 and | χ zyy|=33.7. The remaining elements are below detection threshold: | χ xzx|<3 and | χ zxx|<3. This analysis is based on the use of Fresnel coefficients and bulk optical constants. The results indicate that SHG is dominated by transitions induced by the z-components of the incident electric field. However, the situation is completely different in the intensity maximum ( λ=600 nm) of a resonant intersurface band transition occurring around the Ȳ-point of the surface Brillouin zone: now SHG is dominated by the zyy tensor component, which exceeds both yzy and zzz, while again | χ zxx| and | χ xzx| are negligible. All available data, including temperature-dependent SHG studies of different authors, clearly show that contributions of electronic surface states to SHG intensities may be significant or even dominant. Therefore, a detailed quantitative understanding is a necessary condition for any analysis of adsorbate-induced SHG signals, since adsorbates can modify the surface electronic properties considerably. Our results furthermore indicate that the use of isotropic Fresnel coefficients to model the SHG-active electric fields is inadequate for a complete quantitative analysis.

  11. Effect of the structural anisotropy and lateral strain on the surface phonons of monolayer xenon on Cu(110)

    NASA Astrophysics Data System (ADS)

    Zeppenfeld, P.; Büchel, M.; David, R.; Comsa, G.; Ramseyer, C.; Girardet, C.

    1994-11-01

    The phonon-dispersion curves for a xenon monolayer adsorbed on Cu(110) have been measured using inelastic He scattering. The size and geometry of the substrate unit cell introduces an anisotropic distortion of the xenon monolayer, which is reflected in a strong deformation of the phonon-dispersion curves with respect to the floating two-dimensional (2D) xenon layer. This effect is reproduced in a 2D phonon calculation, based on the Lennard-Jones Xe pair potential. In this way a microscopic relationship between lattice strain, force constants, and surface stress can be established.

  12. Chemistry of Cu(acac){sub 2} on Ni(110) and Cu(110) surfaces: Implications for atomic layer deposition processes

    SciTech Connect

    Ma Qiang; Zaera, Francisco

    2013-01-15

    The thermal chemistry of copper(II)acetylacetonate, Cu(acac){sub 2}, on Ni(110) and Cu(110) single-crystal surfaces was probed under vacuum by using x-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Some data for acetylacetone (Hacac, CH{sub 3}COCH{sub 2}COCH{sub 3}) adsorbed on Ni(110) are also reported as reference. Chemical transformations were identified in several steps covering a temperature range from 150 K to at least 630 K. The desorption of Hacac and a 3-oxobutanal (CH{sub 3}COCH{sub 2}CHO) byproduct was observed first at 150 and 180 K on Ni(110) and at 160 and 185 K on Cu(110), respectively. Partial loss of the acetylacetonate (acac) ligands and a likely change in adsorption geometry are seen next, with the possible production of HCu(acac), which desorbs at 200 and 235 K from the nickel and copper surfaces, respectively. Molecular Cu(acac){sub 2} desorption is observed on both surfaces at approximately 300 K, probably from recombination of Cu(acac) and acac surface species. The remaining copper atoms on the surface lose their remaining acac ligands to the substrate and become reduced directly to metallic copper. At the same time, the organic ligands follow a series of subsequent surface reactions, probably involving several C-C bond-scissions, to produce other fragments, additional Hacac and HCu(acac) in the gas phase in the case of the copper surface, and acetone on nickel. A significant amount of acac must nevertheless survive on the surface to high temperatures, because Hacac peaks are seen in the TPD at about 515 and 590 K and the C 1s XPS split associated with acac is seen up to close to 500 K. In terms of atomic layer deposition processes, this suggests that cycles could be design to run at such temperatures as long as an effective hydrogenation agent is used as the second reactant to remove the surface acac as Hacac. Only a small fraction of carbon is left behind on Ni after heating to 800 K, whereas more carbon

  13. 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.

  14. Thermal chemistry of hydrazine on clean and oxygen- and water-predosed Cu(110) single-crystal surfaces

    NASA Astrophysics Data System (ADS)

    Yao, Yunxi; Zaera, Francisco

    2016-08-01

    The chemistry of hydrazine on Cu(110) single-crystal surfaces was probed under ultrahigh vacuum (UHV) conditions by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Survey TPD experiments identified molecular nitrogen and ammonia as the main desorbing products from thermal activation of the adsorbate, but small amounts of diazene and NH2· radicals were also detected. At saturation coverage, N2 production leads NH3 desorption by approximately 10 K (with TPD peaks at 350 K versus 360 K, respectively), indicating a preference for dehydrogenation over N-N bond scission steps, and additional nitrogen was seen at even lower temperatures (320 K) in experiments starting with even higher doses of hydrazine. On the other hand, the formation of NH3 and NH2·, which desorb in a wide range of temperatures between approximately 300 K and 700 K, dominates in experiments with low N2H4 doses, presumably because a stronger interaction of the N-N bond with the metal in the flat adsorption geometry expected at such low coverages. Dosing at room temperature seems to also facilitate the dissociative adsorption, albeit via dehydrogenation steps that lead to the subsequent production of more significant amounts of diazene and of molecular hydrogen (in addition to N2, NH3, and NH2·). Preadsorption of oxygen on the Cu(110) surface helps stabilize the hydrazine, increasing its desorption temperature and helping with the low-temperature (320 K) production of N2. Coadsorption of hydrazine with water leads to facile proton exchange, as indicated by the production of NH2D in TPD experiments with N2H4 + D2O. This isotope scrambling must occur at cryogenic temperatures because all water desorbs from the surface below 200 K and no other changes in surface chemistry are observed after that. The implications of all this chemistry to practical applications that may use hydrazine in surface reactions with copper, including its use as a reducing agent in atomic layer

  15. The synthesis of methanol and the reverse water-gas shift reaction over Zn-deposited Cu(100) and Cu(110) surfaces: comparison with Zn/Cu(111)

    NASA Astrophysics Data System (ADS)

    Nakamura, I.; Fujitani, T.; Uchijima, T.; Nakamura, J.

    1998-03-01

    The catalytic activity of Zn vapor-deposited Cu(100) and Cu(110) surfaces for methanol synthesis by the hydrogenation of CO 2 and the reverse water-gas shift reaction were studied using an XPS apparatus combined with a high-pressure flow reactor (18 atm). At a reaction temperature of 523 K, no promotional effect of Zn was observed for the methanol synthesis on both Zn/Cu(100) and Zn/Cu(110). The results were quite different from those for Zn/Cu(111), on which a significant promotion of methanol synthesis activity appeared to be due to the deposition of Zn, indicating that the promotional effect of Zn was sensitive to the surface structure of Cu. However, hysteresis was observed in the catalytic activity for methanol synthesis over the Zn/Cu(110) surface upon heating above 543 K in the reaction mixture. The activity became twice that measured before heating, which was close to the methanol synthesis activity of Zn/Cu(111) at the same Zn coverage. On the other hand, no such hysteresis was observed for the reverse water-gas shift reaction on Zn/Cu(110), indicating that the active site for methanol synthesis was not identical to that for the reverse water-gas shift reaction. In the post-reaction surface analysis, formate species was detected on both Zn/Cu(100) and Zn/Cu(110), whose coverage increased with increasing Zn coverage at 0< ΘZn<0.2. No correlation between the formate coverage and the methanol synthesis activity was obtained, which was in contrast to the results for Zn/Cu(111). Thus, the structure sensitivity observed in the catalytic activity of methanol synthesis over Zn-deposited Cu surfaces is ascribed to the significant difference in the reactivity of the formate intermediate.

  16. Adsorption and thermal chemistry of formic acid on clean and oxygen-predosed Cu(110) single-crystal surfaces revisited

    NASA Astrophysics Data System (ADS)

    Yao, Yunxi; Zaera, Francisco

    2016-04-01

    The thermal chemistry of formic acid on clean and oxygen-predosed Cu(110) single-crystal surfaces was studied under ultrahigh-vacuum (UHV) conditions by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Key results reported in the past were confirmed, including the partial switchover from H2 to H2O desorption upon oxygen addition on the surface and the development of a second decomposition regime at 420 K, in addition to the one observed at 460 K on the clean substrate. In addition, new observations were added, including the previously missed desorption of H2 at 420 K and the existence of a normal kinetic isotope effect in both TPD peaks. Peak fitting of the XPS data afforded the identification of an asymmetric geometry for the formate intermediate, which was established to form by 200 K, and the presence of coadsorbed molecular formic acid up to the temperatures of decomposition, probably in a second layer and held by hydrogen bonding. Quantitative analysis of the TPD data indicated a one-to-one correspondence between the increase in oxygen coverage beyond θO = 0.5 ML and a decrease in formic acid uptake that mainly manifests itself in a decrease in the decomposition seen in the 460 K TPD peak. All these observations were interpreted in terms of a simple decomposition mechanism involving hydrogen abstraction from adsorbed formate species, possibly aided by coadsorbed oxygen, and a change in reaction activation energy as a function of the structure of the oxygen overlayer, which reverts from a O-c(6 × 2) structure at high oxygen coverages to the O-(2 × 1) order seen at θO = 0.5 ML.

  17. Insight into the influence of liquid paraffin for methanol synthesis on Cu(110) surface using continuum and atomistic models

    NASA Astrophysics Data System (ADS)

    Jiao, Wei-Hong; Liu, Shi-Zhong; Zuo, Zhi-Jun; Ren, Rui-Peng; Gao, Zhi-Hua; Huang, Wei

    2016-11-01

    Methanol synthesis from CO/CO2 hydrogenation and water-gas shift (WGS) reaction on Cu(110) in liquid paraffin and vacuum have been systematically researched with density functional theory calculation (DFT). For methanol synthesis from CO hydrogenation, the reaction pathways in liquid paraffin and vacuum are CO + H → HCO → H2CO → H3CO → H3COH; in the case of WGS, the reaction pathways in liquid paraffin and vacuum are CO + 2H2O → CO + 2OH + 2H → CO + H2O + O + H2 → CO2 + H2O + H2; the reaction pathways of methanol synthesis from CO2 hydrogenation in liquid paraffin and vacuum are CO2 + H → HCOO → H2COO → H2CO → H3CO → H3COH and CO2 + H → HCOO → HCOOH → H2COOH → H3CO → H3COH, respectively. The result shows that liquid paraffin does not affect the reaction mechanisms of methanol synthesis from CO and WGS, but it changes the reaction mechanisms of methanol synthesis from CO2 hydrogenation. Hirshfeld charge and the d-band centers indicate that the catalytic activity of Cu(110) in liquid paraffin is smaller than that in vacuum. Our results also show that it is necessary to consider both continuum and atomistic models in the slurry bed.

  18. Two-dimensional unoccupied electronic band structure of clean Cu(110) and (1 × 2) Na/Cu(110)

    NASA Astrophysics Data System (ADS)

    Su, C.; Tang, D.; Heskett, D.

    1994-05-01

    Using the technique of angle-resolved inverse photoemission, we have measured the dispersion of an unoccupied Cu(110) surface state for the clean Cu(110) surface and for the (1 × 2) reconstructed Na/Cu(110) surface along the overlineΓ- overlineYandoverlineY- overlineS symmetry lines. The dispersion of the crystal-induced surface state of clean Cu(110) at 2.05 eV above the Fermi energy at the overlineY point of the SBZ is free-electron-like with an effective mass of (1.0 ± 0.2) me at the overlineY point, which is in good agreement with other experimental results as well as a theoretical calculation. This surface state shifts to 2.5 eV above the Fermi energy for the (1 × 2) phase of Na/Cu(110) with a coverage of 0.25 ML, and the dispersion along the overlineΓ- overlineY direction is considerably reduced compared to the clean surface. On the other hand, the dispersion of this state for (1 × 2) Na/Cu(110) (0.25 ML) along the overlineY- overlineS direction is close to that of clean Cu(110). We account for these results within a missing-row picture of the Na-induced reconstruction.

  19. Superatom orbitals of Sc₃N@C₈₀ and their intermolecular hybridization on Cu(110)-(2x1)-O surface

    SciTech Connect

    Huang, Tian; Zhao, Jin; Feng, Min; Petek, Hrvoje; Yang, Shangfeng; Dunsch, Lothar

    2010-02-24

    We investigate the electronic structure of an endohedral fullerene, Sc₃N@C₈₀, chemisorbed on Cu(110)-(2x1)-O surface by scanning tunneling microscopy and density-functional theory. Scanning tunneling microscopy and spectroscopy identify a series of delocalized atomlike superatom molecular orbitals (SAMOs) in the Sc₃N@C₈₀ and its aggregates. By contrast to C60, the encapsulated Sc₃N cluster in Sc₃N@C₈₀ distorts the nearly-spherical central potential of the carbon cage, imparting an asymmetric spatial distribution to the SAMOs. When Sc₃N@C₈₀ molecules form dimers and trimers, however, the strong intermolecular hybridization results in highly symmetric hybridized SAMOs with clear bonding and antibonding characteristics. The electronic-structure calculations on Sc3N@C80 and its aggregates confirm the existence of SAMOs and reproduce their hybridization as observed in the experiment.

  20. The unoccupied electronic structure of Na/Cu(110)

    NASA Astrophysics Data System (ADS)

    Tang, D.; Su, C.; Heskett, D.

    1993-10-01

    Using the technique of inverse photoemission spectroscopy (IPES), we have measured the unoccupied electronic states of sodium on Cu(110) as a function of Na dose on the Cu(110) surface at room temperature. An Na-induced state appears for Na coverages above 0.08 ML for normal incidence, which we assign as the Na unoccupied 3p level. A second peak appears for coverages greater than 1 ML near the overlineY point. The adsorption of Na also causes shifts and attenuation of Cu(110) surface states. We compare our results with studies of related systems.

  1. Role of the van der Waals interactions on the bonding mechanism of pyridine on Cu(110) and Ag(110) surface: First-principles study

    NASA Astrophysics Data System (ADS)

    Atodiresei, N.; Caciuc, V.; Franke, J.-H.; Blügel, S.

    2008-07-01

    We performed density-functional calculations aimed to investigate the adsorption mechanism of a single pyridine (C5H5N) molecule on Cu(110) and Ag(110) surfaces. Our ab initio simulations show that, in the ground state, the pyridine molecule adsorbs with its molecular plane perpendicular to these substrates and is oriented along the [001] direction. In this case, the bonding mechanism involves a σ bond through the lone-pair electrons of the nitrogen atom. When the heterocyclic ring is parallel to the surface, the bonding takes place via π -like molecular orbitals. However, depending on the position of the N atom on the surface, the planar adsorption configuration can relax to a perpendicular geometry. The role of the long-range van der Waals interactions on the adsorption geometries and energies was analyzed in the framework of the semiempirical method proposed by Grimme [J. Comput. Chem. 27, 1787 (2006)]. We demonstrate that these dispersion effects are very important for geometry and electronic structure of flat adsorption configurations.

  2. Growth models of coexisting p(2 × 1) and c(6 × 2) phases on an oxygen-terminated Cu(110) surface studied by noncontact atomic force microscopy at 78 K

    NASA Astrophysics Data System (ADS)

    Li, Yan Jun; Lee, Seung Hwan; Kinoshita, Yukinori; Ma, Zong Min; Wen, Huanfei; Nomura, Hikaru; Naitoh, Yoshitaka; Sugawara, Yasuhiro

    2016-05-01

    We present an experimental study of coexisting p(2 × 1) and c(6 × 2) phases on an oxygen-terminated Cu(110) surface by noncontact atomic force microscopy (NC-AFM) at 78 K. Ball models of the growth processes of coexisting p(2 × 1)/c(6 × 2) phases on a terrace and near a step are proposed. We found that the p(2 × 1) and c(6 × 2) phases are grown from the super Cu atoms on both sides of O–Cu–O rows of an atomic spacing. In this paper, we summarize our investigations of an oxygen-terminated Cu(110) surface by NC-AFM employing O- and Cu-terminated tips. Also, we state several problems and issues for future investigation.

  3. Growth models of coexisting p(2 × 1) and c(6 × 2) phases on an oxygen-terminated Cu(110) surface studied by noncontact atomic force microscopy at 78 K.

    PubMed

    Li, Yan Jun; Lee, Seung Hwan; Kinoshita, Yukinori; Ma, Zong Min; Wen, Huanfei; Nomura, Hikaru; Naitoh, Yoshitaka; Sugawara, Yasuhiro

    2016-05-20

    We present an experimental study of coexisting p(2 × 1) and c(6 × 2) phases on an oxygen-terminated Cu(110) surface by noncontact atomic force microscopy (NC-AFM) at 78 K. Ball models of the growth processes of coexisting p(2 × 1)/c(6 × 2) phases on a terrace and near a step are proposed. We found that the p(2 × 1) and c(6 × 2) phases are grown from the super Cu atoms on both sides of O-Cu-O rows of an atomic spacing. In this paper, we summarize our investigations of an oxygen-terminated Cu(110) surface by NC-AFM employing O- and Cu-terminated tips. Also, we state several problems and issues for future investigation. PMID:27067038

  4. Long Range Chiral Imprinting of Cu(110) by Tartaric Acid

    SciTech Connect

    Lawton, T J; Pushkarev, V; Wei, D; Lucci, F R; Sholl, D S; Gellman, A J; Sykes, E C. H.

    2013-10-31

    Restructuring of metals by chiral molecules represents an important route to inducing and controlling enantioselective surface chemistry. Tartaric acid adsorption on Cu(110) has served as a useful system for understanding many aspects of chiral molecule adsorption and ordering on a metal surface, and a number of chiral and achiral unit cells have been reported. Herein, we show that given the appropriate annealing treatment, singly deprotonated tartaric acid monolayers can restructure the Cu metal itself, and that the resulting structure is both highly ordered and chiral. Molecular resolution scanning tunneling microscopy reveals that singly deprotonated tartaric acid extracts Cu atoms from the Cu(110) surface layer and incorporates them into highly ordered, chiral adatom arrays capped by a continuous molecular layer. Further evidence for surface restructuring comes from images of atom-deep trenches formed in the Cu(110) surface during the process. These trenches also run in low symmetry directions and are themselves chiral. Simulated scanning tunneling microscopy images are consistent with the appearance of the added atom rows and etched trenches. The chiral imprinting results in a long-range, highly ordered unit cell covering the whole surface as confirmed by low energy electron diffraction. Details of the restructuring mechanism were further investigated via time-lapse imaging at elevated temperature. This work reveals the stages of nanoscale surface restructuring and offers an interesting method for chiral modification of an achiral metal surface.

  5. Autocatalytic water dissociation on Cu(110) at near ambient conditions

    SciTech Connect

    Mulleregan, Alice; Andersson, Klas; Ketteler, Guido; Bluhm, Hendrik; Yamamoto, Susumu; Ogasawara, Hirohito; Pettersson, Lars G.M.; Salmeron, Miquel; Nilsson, Anders

    2007-05-16

    Autocatalytic dissociation of water on the Cu(110) metal surface is demonstrated based on X-ray photoelectron spectroscopy studies carried out in-situ under near ambient conditions of water vapor pressure (1 Torr) and temperature (275-520 K). The autocatalytic reaction is explained as the result of the strong hydrogen-bond in the H{sub 2}O-OH complex of the dissociated final state, which lowers the water dissociation barrier according to the Broensted-Evans-Polanyi relations. A simple chemical bonding picture is presented which predicts autocatalytic water dissociation to be a general phenomenon on metal surfaces.

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

    NASA Astrophysics Data System (ADS)

    Shiotari, A.; Mitsui, T.; Okuyama, H.; Hatta, S.; Aruga, T.; Koitaya, T.; Yoshinobu, J.

    2014-06-01

    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-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.

  7. 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.

    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.

  8. Calculations of oxide formation on low-index Cu surfaces

    NASA Astrophysics Data System (ADS)

    Lian, Xin; Xiao, Penghao; Yang, Sheng-Che; Liu, Renlong; Henkelman, Graeme

    2016-07-01

    Density-functional theory is used to evaluate the mechanism of copper surface oxidation. Reaction pathways of O2 dissociation on the surface and oxidation of the sub-surface are found on the Cu(100), Cu(110), and Cu(111) facets. At low oxygen coverage, all three surfaces dissociate O2 spontaneously. As oxygen accumulates on the surfaces, O2 dissociation becomes more difficult. A bottleneck to further oxidation occurs when the surfaces are saturated with oxygen. The barriers for O2 dissociation on the O-saturated Cu(100)-c(2×2)-0.5 monolayer (ML) and Cu(100) missing-row structures are 0.97 eV and 0.75 eV, respectively; significantly lower than those have been reported previously. Oxidation of Cu(110)-c(6×2), the most stable (110) surface oxide, has a barrier of 0.72 eV. As the reconstructions grow from step edges, clean Cu(110) surfaces can dissociatively adsorb oxygen until the surface Cu atoms are saturated. After slight rearrangements, these surface areas form a "1 ML" oxide structure which has not been reported in the literature. The barrier for further oxidation of this "1 ML" phase is only 0.31 eV. Finally the oxidized Cu(111) surface has a relatively low reaction energy barrier for O2 dissociation, even at high oxygen coverage, and allows for facile oxidation of the subsurface by fast O diffusion through the surface oxide. The kinetic mechanisms found provide a qualitative explanation of the observed oxidation of the low-index Cu surfaces.

  9. Calculations of oxide formation on low-index Cu surfaces.

    PubMed

    Lian, Xin; Xiao, Penghao; Yang, Sheng-Che; Liu, Renlong; Henkelman, Graeme

    2016-07-28

    Density-functional theory is used to evaluate the mechanism of copper surface oxidation. Reaction pathways of O2 dissociation on the surface and oxidation of the sub-surface are found on the Cu(100), Cu(110), and Cu(111) facets. At low oxygen coverage, all three surfaces dissociate O2 spontaneously. As oxygen accumulates on the surfaces, O2 dissociation becomes more difficult. A bottleneck to further oxidation occurs when the surfaces are saturated with oxygen. The barriers for O2 dissociation on the O-saturated Cu(100)-c(2×2)-0.5 monolayer (ML) and Cu(100) missing-row structures are 0.97 eV and 0.75 eV, respectively; significantly lower than those have been reported previously. Oxidation of Cu(110)-c(6×2), the most stable (110) surface oxide, has a barrier of 0.72 eV. As the reconstructions grow from step edges, clean Cu(110) surfaces can dissociatively adsorb oxygen until the surface Cu atoms are saturated. After slight rearrangements, these surface areas form a "1 ML" oxide structure which has not been reported in the literature. The barrier for further oxidation of this "1 ML" phase is only 0.31 eV. Finally the oxidized Cu(111) surface has a relatively low reaction energy barrier for O2 dissociation, even at high oxygen coverage, and allows for facile oxidation of the subsurface by fast O diffusion through the surface oxide. The kinetic mechanisms found provide a qualitative explanation of the observed oxidation of the low-index Cu surfaces. PMID:27475390

  10. 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.; FOM-Instituut voor Atoom-en Molecuulfysica, Amsterdam )

    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.

  11. The stereoselective synthesis of dienes through dehalogenative homocoupling of terminal alkenyl bromides on Cu(110).

    PubMed

    Sun, Qiang; Cai, Liangliang; Ma, Honghong; Yuan, Chunxue; Xu, Wei

    2016-05-21

    We have successfully achieved the stereoselective synthesis of a specific cis-diene moiety through a dehalogenative homocoupling of alkenyl bromides on the Cu(110) surface, where the formation of a cis-form organometallic intermediate is the key to such a stereoselectivity as determined by DFT calculations. PMID:27063567

  12. Core-level photoemission and work-function investigation of Na on Cu(110)

    NASA Astrophysics Data System (ADS)

    Su, C.; Shi, X.; Tang, D.; Heskett, D.; Tsuei, K.-D.

    1993-10-01

    Core-level photoemission, low-energy electron diffraction (LEED), and work-function change measurements have been carried out to study the coverage dependence of Na/Cu(110) at room temperature. The results of LEED and work-function measurements are qualitatively similar to most other investigations of alkali-metal adsorption on fcc(110) metal surfaces. With LEED, we observed an alkali-metal-induced (1×2) reconstruction at intermediate coverage. We have performed a simple calculation to account for the work-function differences between Na/fcc(110) and Na/fcc(111) metal surfaces. The comparison of coverage-dependent core-level binding-energy shifts between Na/Cu(110) and Na/Cu(111) reveals that a low-coverage plateau in the curve of binding energy vs Na coverage for Na/Cu(110) is associated with the Na-induced reconstruction, and can be accounted for within a localized picture of the reconstruction.

  13. Photolysis of CH3I on Cu(110) at 337 nm: Direct and charge-transfer photodissociation

    NASA Astrophysics Data System (ADS)

    Johnson, C. C.; Jensen, E. T.

    2000-04-01

    The photochemistry of methyl iodide adsorbed on Cu(110) surfaces has been studied using time-of-flight mass spectrometry, temperature programmed desorption, and retarding potential spectroscopy. The λ=337 nm photodissociation of CH3I adsorbed on clean and iodided Cu(110) is found to have an increased cross section (by ˜2 orders of magnitude) and altered dynamics from that of the gas phase at the same wavelength. On the clean Cu(110) surface both enhanced neutral photodissociation and charge-transfer photodissociation processes are observed, the latter being ascribed to hot photoelectrons generated in the substrate. On the Cu(110)-I surface, only enhanced neutral photodissociation is observed and the CH3I molecules are found to be orientationally ordered with a 20° tilt in the [11¯0] azimuth. Further evidence of altered neutral photodissociation dynamics is found in the observed I/I* branching ratio. In contrast to earlier studies of adsorbed CH3I, the branching ratio is found to favor the higher energy I* dissociation pathway as compared to the gas phase. The altered neutral photodissociation dynamics are ascribed to changes in the CH3I excited state potential energy surfaces, caused by interactions with the copper-iodine interface.

  14. SEXAFS analysis of the Cu(110)-(2 × 3)-N structure

    NASA Astrophysics Data System (ADS)

    Wilde, L.; Pangher, N.; Haase, J.

    1996-02-01

    Surface-extended X-ray-absorption fine-structure measurements have been performed on the Cu(110)-(2 × 3)-N system. The data are consistent with a structural model in which nitrogen chemisorbs on a pseudo-(100) reconstructed and largely corrugated surface. The NCu bond length measures 1.89±0.03 Å. Nitrogen chemisorbs in five-fold coordinated sites close to the local plane formed by the four neighbouring surface Cu atoms. The reconstructed first Cu layer shows a corrugation of 0.64 Å (or 50% of the bulk interlayer spacing). Structural models with long-bridge adsorption sites can be safely excluded.

  15. Ab initio structural and electronic analysis of CH3SH self-assembled on a Cu(110) substrate

    NASA Astrophysics Data System (ADS)

    D'Agostino, S.; Chiodo, L.; Della Sala, F.; Cingolani, R.; Rinaldi, R.

    2007-05-01

    Ab initio Density Functional Theory calculations are here reported to characterize the adsorption of methanethiol at the Cu(110) surface. Theoretical results suggest that the binding of the adsorbate to the substrate is rather weak and the molecular geometry is correspondingly almost unaffected by the adsorption. Otherwise, when CH3SH deprotonates producing methanethiolate, a stronger chemical bond is realized between the sulfur atom of CH3S radical and Cu surface atoms. A detailed study of structural and electronic properties of methanethiolate on Cu(110) for a p(2×2) and a c(2×2) overlayer structure has been carried out. We find that, in the most stable configuration, the molecule adsorbs in the shortbridge site. The chemical bond arises due to a strong hybridization among p orbitals of sulfur and d states from the substrate, as it is deduced by an analysis of partial densities of states and charge densities.

  16. Magnetization dynamics of mixed Co-Au chains on Cu(110) substrate: Combined ab initio and kinetic Monte Carlo study

    NASA Astrophysics Data System (ADS)

    M. Tsysar, K.; V. Kolesnikov, S.; M. Saletsky, A.

    2015-09-01

    We present an investigation of the one-dimensional ferromagnetism in Au-Co nanowires deposited on the Cu(110) surface. By using the density functional theory, the influence of the nonmagnetic copper substrate Cu(110) on the magnetic properties of the bimetallic Au-Co nanowires is studied. The results show the emergence of magnetic anisotropy in the supported Au-Co nanowires. The magnetic anisotropy energy has the same order of magnitude as the exchange interaction energy between Co atoms in the wire. Our electronic structure calculation reveals the emergence of new hybridized bands between Au and Co atoms and surface Cu atoms. The Curie temperature of the Au-Co wires is calculated by means of kinetic Monte Carlo simulation. The strong size effect of the Curie temperature is demonstrated. Project supported by the Russian Foundation of Basic Researches.

  17. Structure and energetics of diphenylalanine self-assembling on Cu(110).

    PubMed

    Tomba, Giulia; Lingenfelder, Magalí; Costantini, Giovanni; Kern, Klaus; Klappenberger, Florian; Barth, Johannes V; Ciacchi, Lucio Colombi; De Vita, Alessandro

    2007-12-13

    We investigate the dynamical features of the adsorption of diphenylalanine molecules on the Cu(110) surface and of their assembling into supramolecular structures by a combination of quantum and classical atomistic modeling with dynamic scanning tunneling microscopy and spectroscopic experiments. Our results reveal a self-assembling mechanism in which isolated adsorbed molecules change their conformation and adsorption mode as a consequence of their mutual interactions. In particular, the formation of zwitterions after proton transfer between initially neutral molecules is found to be the key event of the assembling process, which stabilizes the supramolecular structures. Because of the constraints on the intermolecular bonds exerted by the surface-molecule interactions, the assembly process is strictly stereoselective, and may suggest a general model for patterning and functionalization of bare metal surfaces with short chiral peptides. PMID:17999478

  18. Adsorbed states of chlorophenol on Cu(110) and controlled switching of single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Okuyama, H.; Kitaguchi, Y.; Hattori, T.; Ueda, Y.; Ferrer, N. G.; Hatta, S.; Aruga, T.

    2016-06-01

    A molecular junction of substituted benzene (chlorophenol) is fabricated and controlled by using a scanning tunneling microscope (STM). Prior to the junction formation, the bonding geometry of the molecule on the surface is characterized by STM and electron energy loss spectroscopy (EELS). EELS shows that the OH group of chlorophenol is dissociated on Cu(110) and that the molecule is bonded nearly flat to the surface via an O atom, with the Cl group intact. We demonstrate controlled contact of an STM tip to the "available" Cl group and lift-up of the molecule while it is anchored to the surface via an O atom. The asymmetric bonding motifs of the molecule to the electrodes allow for reversible control of the junction.

  19. Adsorbed states of chlorophenol on Cu(110) and controlled switching of single-molecule junctions.

    PubMed

    Okuyama, H; Kitaguchi, Y; Hattori, T; Ueda, Y; Ferrer, N G; Hatta, S; Aruga, T

    2016-06-28

    A molecular junction of substituted benzene (chlorophenol) is fabricated and controlled by using a scanning tunneling microscope (STM). Prior to the junction formation, the bonding geometry of the molecule on the surface is characterized by STM and electron energy loss spectroscopy (EELS). EELS shows that the OH group of chlorophenol is dissociated on Cu(110) and that the molecule is bonded nearly flat to the surface via an O atom, with the Cl group intact. We demonstrate controlled contact of an STM tip to the "available" Cl group and lift-up of the molecule while it is anchored to the surface via an O atom. The asymmetric bonding motifs of the molecule to the electrodes allow for reversible control of the junction. PMID:27369529

  20. Imaging sequential dehydrogenation of methanol on Cu(110) with a scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Kitaguchi, Y.; Shiotari, A.; Okuyama, H.; Hatta, S.; Aruga, T.

    2011-05-01

    Adsorption of methanol and its dehydrogenation on Cu(110) were studied by using a scanning tunneling microscope (STM). Upon adsorption at 12 K, methanol preferentially forms clusters on the surface. The STM could induce dehydrogenation of methanol sequentially to methoxy and formaldehyde. This enabled us to study the binding structures of these products in a single-molecule limit. Methoxy was imaged as a pair of protrusion and depression along the [001] direction. This feature is fully consistent with the previous result that it adsorbs on the short-bridge site with the C-O axis tilted along the [001] direction. The axis was induced to flip back and forth by vibrational excitations with the STM. Two configurations were observed for formaldehyde, whose structures were proposed based on their characteristic images and motions.

  1. The onset of sub-surface oxidation induced by defects in a chemisorbed oxygen layer

    SciTech Connect

    Li, Jonathan; Li, Liang; Zhou, Guangwen

    2015-02-28

    We investigate the onset of internal oxidation of a Cu(110) surface induced by oxygen subsurface adsorption via defects in the Cu(110)–(2 × 1)–O chemisorbed layer. The presence of a boundary formed by merged add-row structure domains due to a mismatch of half unit-cell leads to preferred oxygen adsorption at the subsurface tetrahedral sites. The resulting distorted Cu–O tetrahedra along the domain boundary have comparable bond length and angles to those of the bulk oxide phase of Cu{sub 2}O. Our results indicate that the presence of defects in the oxygen-chemisorbed adlayer can lead to the internal oxidation via the formation of Cu{sub 2}O-like tetrahedra in between the topmost and second outermost atomic layers at the oxygen coverage θ = 0.53 and the second and third outermost atomic layers at θ = 0.56. These results show that the internal oxidation of a metal surface can occur in the very beginning of the oxygen chemisorption process enabled by the presence of defects in the oxygen chemisorbed layer.

  2. Theory of vibrationally assisted tunneling for hydroxyl monomer flipping on Cu(110)

    NASA Astrophysics Data System (ADS)

    Gustafsson, Alexander; Ueba, Hiromu; Paulsson, Magnus

    2014-10-01

    To describe vibrationally mediated configuration changes of adsorbates on surfaces we have developed a theory to calculate both reaction rates and pathways. The method uses the T-matrix to describe excitations of vibrational states by the electrons of the substrate, adsorbate, and tunneling electrons from a scanning tunneling probe. In addition to reaction rates, the theory also provides the reaction pathways by going beyond the harmonic approximation and using the full potential energy surface of the adsorbate which contains local minima corresponding to the adsorbates different configurations. To describe the theory, we reproduce the experimental results in [T. Kumagai et al., Phys. Rev. B 79, 035423 (2009), 10.1103/PhysRevB.79.035423], where the hydrogen/deuterium atom of an adsorbed hydroxyl (OH/OD) exhibits back and forth flipping between two equivalent configurations on a Cu(110) surface at T =6 K. We estimate the potential energy surface and the reaction barrier, ˜160 meV, from DFT calculations. The calculated flipping processes arise from (i) at low bias, tunneling of the hydrogen through the barrier, (ii) intermediate bias, tunneling electrons excite the vibrations increasing the reaction rate although over the barrier processes are rare, and (iii) higher bias, overtone excitations increase the reaction rate further.

  3. 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 π-π stacking, suggesting that this is an important contributor in the self-assembly process. PMID:25770505

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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 π-π stacking, suggesting that this is an important contributor in the self-assembly process.

  5. Trajectory analysis of low-energy and hyperthermal ions scattered from Cu(110)

    SciTech Connect

    McEachern, R. L.; Goodstein, D. M.; Cooper, B. H.

    1989-05-15

    We have investigated the trajectories of Na/sup +/ ions scattered from the Cu(110) surface in the <1/bar 1/0> and <001> azimuths for a range of incident energies from 56 eV to 4 keV. Our goal is to explain the trends observed in the energy spectra and determine what types of trajectories contribute to these spectra. Using the computer program SAFARI, we have performed simulations with trajectory analyses for 100-, 200-, and 400-eV scattering. We show results from the 100-eV simulations in both azimuths and compare them with the experimental data. The simulated energy spectra are in excellent agreement with the data. Ion trajectories and impact parameter plots from the simulations are used to determine the relative importance of different types of ion--surface-atom collisions. The simulations have shown that the striking differences observed in comparing the <1/bar 1/0> and <001> spectra are mostly due to ions which scatter from second-layer atoms. This system exhibits strong focusing onto the second-layer atoms by the first-layer rows, and the focusing is very sensitive to the spacing between the rows. At the lower beam energies, scattering from the second layer dominates the measured spectra.

  6. Trajectory analysis of low-energy and hyperthermal ions scattered from Cu(110)

    SciTech Connect

    McEachern, R.L.; Goodstein, D.M.; Cooper, B.H.

    1989-05-15

    Trajectories of Na{sup +} ions scattered from the Cu(110) surface in the <1 1bar 0> and <001> azimuths were studied for a range of incident energies from 56 eV to 4 keV. The goal is to explain the trends observed in the energy spectra and determine what types of trajectories contribute to these spectra. Using the computer program SAFARI, simulations were performed with trajectory analyses for 100-, 200-, and 400-eV scattering. We show results from the 100-eV simulations in both azimuths and compare them with the experimental data. The simulated energy spectra are in excellent agreement with the data. Ion trajectories and impact parameter plots from the simulations are used to determine the relative importance of different types of ion-surface-atom collisions. The simulations have shown that the striking differences observed in comparing the <1 1bar 0> and <001> spectra are mostly due to ions which scatter from second-layer atoms. This system exhibits strong focusing onto the second-layer atoms by the first-layer rows, and the focusing is very sensitive to the spacing between the rows. At the lower beam energies, scattering from the second layer dominates the measured spectra.

  7. Uracil on Cu(110): A quantitative structure determination by energy-scanned photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Duncan, D. A.; Unterberger, W.; Kreikemeyer-Lorenzo, D.; Woodruff, D. P.

    2011-07-01

    The local adsorption site of the nucleobase uracil on Cu(110) has been determined quantitatively by energy-scanned photoelectron diffraction (PhD). Qualitative inspection of the O 1s and N 1s soft x-ray photoelectron spectra, PhD modulation spectra, and O K-edge near-edge x-ray adsorption fine structure indicate that uracil bonds to the surface through its nitrogen and oxygen constituent atoms, each in near atop sites, with the molecular plane essentially perpendicular to surface and aligned along the close packed [1overline 1 0] azimuth. Multiple scattering simulations of the PhD spectra confirm and refine this geometry. The Cu-N bondlength is 1.96 ± 0.04 Å, while the Cu-O bondlengths of the two inequivalent O atoms are 1.93 ± 0.04 Å and 1.96 ± 0.04 Å, respectively. The molecule is twisted out of the [1overline 1 0]direction by 11 ± 5°.

  8. Effect of oxygen surfactant on the magnetic and structural properties of Co films grown on Cu(110)

    SciTech Connect

    Ling, W. L.; Qiu, Z. Q.; Takeuchi, O.; Ogletree, D. F.; Salmeron, M.

    2001-01-01

    It was found that atomically flat Co(110) films could be grown on Cu(110) using O as a surfactant. To obtain detailed knowledge on the effect of O on the growth, as well as on the magnetic properties of Co overlayer, we carried out an investigation on this system using Auger electron spectroscopy, low-energy electron diffraction, surface magneto-optic Kerr effect (SMOKE), and scanning tunneling microscopy. With O as a surfactant, the initial growth of Co (<1 ML) results in a flat monolayer structure. When the Co is thicker than 1 ML, three-dimensional clusters begin to form. These clusters become ordered islands at 3 ML Co and coalesce at {approx}5 ML Co. Above 5 ML Co, layer-by-layer growth resumes. No significant Cu segregation is observed. SMOKE studies at room temperature show that the Co film is magnetic above {approx}5 ML Co, with the magnetization easy axis along the [001] direction. On the other hand, without using oxygen as a surfactant, Co grows three-dimensionally on Cu(110). The Co overlayer has its easy magnetization axis along the [001] direction, but the onset of the magnetization was observed at 11 ML Co at room temperature.

  9. The adsorption geometry and chemical state of lysine on Cu{110}

    NASA Astrophysics Data System (ADS)

    Eralp, Tugce; Shavorskiy, Andrey; Held, Georg

    2011-02-01

    Chemisorbed layers of lysine adsorbed on Cu{110} have been studied using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. XPS indicates that the majority (70%) of the molecules in the saturated layer at room temperature (coverage 0.27 ML) are in their zwitterionic state with no preferential molecular orientation. After annealing to 420 K a less densely packed layer is formed (0.14 ML), which shows a strong angular dependence in the characteristic π-resonance of oxygen K edge NEXAFS and no indication of zwitterions in XPS. These experimental results are best compatible with molecules bound to the substrate through the oxygen atoms of the (deprotonated) carboxylate group and the two amino groups involving Cu atoms in three different close packed rows. This μ4 bonding arrangement with an additional bond through the ɛ-amino group is different from geometries previously suggested for lysine on Cu{110}.

  10. Electronic and structural properties at the interface between iron-phthalocyanine and Cu(110)

    SciTech Connect

    Hu, Fang; Fundamental Department, Ningbo Institute of Technology, Ningbo 315100 ; Mao, Hongying; Zhang, Hanjie; Wu, Ke; Cai, Yiliang; He, Pimo

    2014-03-07

    Electronic structure and adsorption geometry of Iron-Phthalocyanine (FePc) adsorbed on Cu(110) were investigated by using ultraviolet photoelectron spectroscopy (UPS) and first-principles density functional theory (DFT) calculations. The emission features α, β, γ, and δ originating from the FePc molecules in UPS spectra are located at 3.42, 5.04, 7.36, and 10.28 eV below Fermi level. The feature α is mostly deriving from Fe 3d orbital with some contributions from C 2p orbital. A considerable charge transfer from the Cu substrate to the Fe 3d orbital occurs upon the adsorption of FePc molecules. The angle-resolved UPS measurements indicate that FePc molecules adopt lying-down configurations with their molecular plane nearly parallel to the Cu(110) substrate at monolayer stage. In combination with the DFT calculations, the adsorption structure is determined to be that FePc molecule adsorbs on the top site of Cu(110) with an angle of 45° between the lobes of FePc and the [11{sup ¯}0] azimuth of the substrate.

  11. Iron oxide surfaces

    NASA Astrophysics Data System (ADS)

    Parkinson, Gareth S.

    2016-03-01

    The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe3O4), maghemite (γ-Fe2O3), haematite (α-Fe2O3), and wüstite (Fe1-xO) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. Fe diffuses in and out from the bulk in response to the O2 chemical potential, forming sometimes complex intermediate phases at the surface. For example, α-Fe2O3 adopts Fe3O4-like surfaces in reducing conditions, and Fe3O4 adopts Fe1-xO-like structures in further reducing conditions still. It is argued that known bulk defect structures are an excellent starting point in building models for iron oxide surfaces. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe3O4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment. It is also an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed. The best understood iron oxide surface at present is probably Fe3O4(100); the structure is

  12. Iron oxide surfaces

    NASA Astrophysics Data System (ADS)

    Parkinson, Gareth S.

    2016-03-01

    The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe3O4), maghemite (γ-Fe2O3), haematite (α-Fe2O3), and wüstite (Fe1-xO) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. Fe diffuses in and out from the bulk in response to the O2 chemical potential, forming sometimes complex intermediate phases at the surface. For example, α-Fe2O3 adopts Fe3O4-like surfaces in reducing conditions, and Fe3O4 adopts Fe1-xO-like structures in further reducing conditions still. It is argued that known bulk defect structures are an excellent starting point in building models for iron oxide surfaces. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe3O4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment. It is also an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed. The best understood iron oxide surface at present is probably Fe3O4(100); the structure is

  13. Structural and magnetic studies of fcc Fe films with self-organized lateral modulation on striped Cu(110)-O(2x1) substrates.

    SciTech Connect

    Li, D.

    1998-09-21

    Fcc Fe wedges of 0-12 monolayer (ML) were grown by means of molecular beam epitaxy onto a novel substrate: flat Cu(110) with an oxygen-induced, long-range ordered striped phase, and studied in-situ with medium energy electron diffraction (MEED) and the surface magneto-optical Kerr effect (SMOKE). In contrast to Fe growth on either clean or oxygen-saturated Cu(110), the films on the striped substrates retain a layer-by-layer growth mode up to 6-7 ML and are fcc at least up to 12 ML. In addition, satellite peaks were observed on both sides of the MEED (0,0) streak, indicating a long-range-ordered lateral modulation of the Fe surface. We postulate that the Fe films grow conformally onto the original striped substrate. SMOKE studies show that these fcc Fe wedges are ferromagnetic with an easy axis along the original stripes for Fe thickness > 4ML and a remnant magnetization that increases linearly with thickness beyond 4 ML.

  14. Control of the intermolecular coupling of dibromotetracene on Cu(110) by the sequential activation of C-Br and C-H bonds.

    PubMed

    Ferrighi, Lara; Píš, Igor; Nguyen, Thanh Hai; Cattelan, Mattia; Nappini, Silvia; Basagni, Andrea; Parravicini, Matteo; Papagni, Antonio; Sedona, Francesco; Magnano, Elena; Bondino, Federica; Di Valentin, Cristiana; Agnoli, Stefano

    2015-04-01

    Dibromotetracene molecules are deposited on the Cu(110) surface at room temperature. The complex evolution of this system has been monitored at different temperatures (i.e., 298, 523, 673, and 723 K) by means of a variety of complementary techniques that range from STM and temperature-programmed desorption (TPD) to high-resolution X-ray spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). State-of-the-art density-functional calculations were used to determine the chemical processes that take place on the surface. After deposition at room temperature, the organic molecules are transformed into organometallic monomers through debromination and carbon-radical binding to copper adatoms. Organometallic dimers, trimers, or small oligomers, which present copper-bridged molecules, are formed by increasing the temperature. Surprisingly, further heating to 673 K causes the formation of elongated chains along the Cu(110) close-packed rows as a consequence of radical-site migration to the thermodynamically more stable molecule heads. Finally, massive dehydrogenation occurs at the highest temperature followed by ring condensation to nanographenic patches. This study is a paradigmatic example of how intermolecular coupling can be modulated by the stepwise control of a simple parameter, such as temperature, through a sequence of domino reactions. PMID:25711882

  15. XPS and STM studies of the oxidation of hydrogen chloride at Cu(100) surfaces

    NASA Astrophysics Data System (ADS)

    Altass, Hatem; Carley, Albert F.; Davies, Philip R.; Davies, Robert J.

    2016-08-01

    The dissociative chemisorption of HCl on clean and oxidized Cu(100) surfaces has been investigated using x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Whereas the dissociation of HCl at the clean surface is limited to the formation of a (√ 2 × √ 2)-R45° Cl(a) monolayer, the presence of surface oxygen removes this barrier, leading to chlorine coverages up to twice that obtained at the clean surface. Additional features in the STM images that appear at these coverages are tentatively assigned to the nucleation of CuCl islands. The rate of reaction of the HCl was slightly higher on the oxidized surface but unaffected by the initial oxygen concentration or the availability of clean copper sites. Of the two distinct domains of adsorbed oxygen identified at room temperature on the Cu(100) surfaces, the (√ 2 × √ 2)-R45° structure reacts slightly faster with HCl than the missing row (√ 2 × 2 √ 2)-R45° O(a) structure. The results address the first stages in the formation of a copper chloride and present an interesting comparison with the HCl/O(a) reaction at Cu(110) surfaces, where oxygen also increased the extent of HCl reactions. The results emphasize the importance of the exothermic reaction to form water in the HCl/O(a) reaction on copper.

  16. Oxidation at Surfaces of Uranium Oxide Particles

    NASA Astrophysics Data System (ADS)

    Schueneman, Richard; Burgraff, Larry

    2001-04-01

    Uranium dioxide (UO2 (S)) is unstable in an oxidizing environment and oxidizes until covered with a layer of uranium trioxide (UO3 (C)). During the oxidation process, uranium cations change from U+4 to U+6 and the oxide crystal structure changes from face centered cubic to orthorhombic. Seven UO2(S) samples were prepared by pressing UO2 (S) powder into a tungsten screen and then subjected to five different temperatures and three partial pressures of oxygen. UO2 (S) oxidation was monitored with in situ photoluminescence (PL) spectroscopy. Quantitative oxidation data was obtained with secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). The in situ PL spectra did not identify UO3 (C) forming on the sample surfaces however, a new PL signature not associated with uranyl was observed. SIMS and XPS data from oxidized UO2 (S) samples indicated that at low temperatures, surface oxidation is kinetically limited and at high temperatures, surface oxidation is limited by diffusion. A model for the oxidation rate to UO3 (C) was not developed due to the temperature dependant oxidation process and high vacuum reduction of amorphous UO3 (A) present on the UO2 (S) sample surfaces prior to oxidation. A PL emission spectra intensity reduction was noticed on a UO3 (C) sample at room temperature under high vacuum. A reduction and re-oxidation of three additional UO3 (C) samples identified a kinetically irreversible reduction process for UO3(C) under high vacuum. A SIMS surface scan was performed on a fourth UO3(C) sample before and after exposure to ultra-high vacuum (10-8 torr) and the results suggest the reduction of UO3(C) to lower oxides (U3O8, U3O7 and UO2) at room temperature.

  17. X-ray emission spectroscopy applied to glycine adsorbed on Cu(110): An atom and symmetry projected view

    SciTech Connect

    Hasselstroem, J.; Karis, O.; Weinelt, M.

    1997-04-01

    When a molecule is adsorbed on a metal surface by chemical bonding new electronic states are formed. For noble and transition metals these adsorption-induced states overlap with the much more intense metal d-valence band, making them difficult to probe by for instance direct photoemission. However, it has recently been shown that X-ray emission spectroscopy (XES) can be applied to adsorbate systems. Since the intermediate state involves a core hole, this technique has the power to project out the partial density of states around each atomic site. Both the excitation and deexcitation processes are in general governed by the dipole selection rules. For oriented system, it is hence possible to obtain a complete separation into 2p{sub x}, 2p{sub y} and 2p{sub z} contributions using angular resolved measurements. The authors have applied XES together with other core level spectroscopies to glycine adsorption on Cu(110). Glycine (NH{sub 2}CH{sub 2}COOH) is the smallest amino acid and very suitable to study by core level spectroscopy since it has several functional groups, all well separated in energy by chemical shifts. Its properties are futhermore of biological interest. In summary, the authors have shown that it is possible to apply XES to more complicated molecular adsorbates. The assignment of different electronic states is however not as straight forward as for simple diatomic molecules. For a complete understanding of the redistribution and formation of new electronic states associated with the surface chemical bond, experimental data must be compared to theoretical calculations.

  18. Surface science studies of catalyzed methanol synthesis on model copper and Cu-Zn-O surfaces

    SciTech Connect

    Fu, Sabrina Su-Bin . Dept. of Chemistry Lawrence Berkeley Lab., CA )

    1991-06-01

    Cu-Zn-O surfaces that are catalysts for methanol synthesis from CO, CO{sub 2}, and H{sub 2} modeled using zinc oxide overlayers on copper single crystals. These studies were performed in ultra-high vacuum (UHV) utilizing Temperature Programmed Desorption, Auger Electron Spectroscopy, and Low Energy Electron Diffraction techniques. The chemisorption of O{sub 2}, CO, CO{sub 2}, and D{sub 2} were compared on a stepped on Cu(311), and a flat Cu(110). At low pressures ({approximately}10{sup {minus}6} Torr), Cu(311) was found to be much more reactive than Cu(110) for the dissociative adsorption of CO{sub 2} and D{sub 2}, and the formation of CO{sub 2} from surface oxygen and CO. Since these reactions are important in methanol synthesis, these results suggest that methanol synthesis over copper may be a structure sensitive reaction. The interaction of copper, zinc, and oxygen were examined by the deposition of submonolayers to multilayers of zinc and oxygen in UHV on Cu(110). The interaction of methanol with these model Cu-Zn-O surfaces was also studied. Oxygen was adsorbed onto these exposed copper part of the surface to form ZnO{sub x}/y ML O/Cu(110) surfaces. The roles of ZnO{sub x} islands and chemisorbed oxygen on copper were investigated by monitoring methanol decomposition, into surface formate and methoxy species, on these ZnO{sub x}/y ML O/Cu(11) surfaces.

  19. Insulating oxide surfaces and nanostructures

    NASA Astrophysics Data System (ADS)

    Goniakowski, Jacek; Noguera, Claudine

    2016-03-01

    This contribution describes some peculiarities of the science of oxide surfaces and nanostructures and proposes a simple conceptual scheme to understand their electronic structure, in the spirit of Jacques Friedel's work. Major results on the effects of non-stoichiometry and polarity are presented, for both semi-infinite surfaces and ultra-thin films, and promising lines of research for the near future are sketched. xml:lang="fr"

  20. Surface-Step-Induced Oscillatory Oxide Growth

    NASA Astrophysics Data System (ADS)

    Li, Liang; Luo, Langli; Ciston, Jim; Saidi, Wissam A.; Stach, Eric A.; Yang, Judith C.; Zhou, Guangwen

    2014-09-01

    We report in situ atomic-resolution transmission electron microscopy observations of the oxidation of stepped Cu surfaces. We find that the presence of surface steps both inhibits oxide film growth and leads to the oxide decomposition, thereby resulting in oscillatory oxide film growth. Using atomistic simulations, we show that the oscillatory oxide film growth is induced by oxygen adsorption on the lower terrace along the step edge, which destabilizes the oxide film formed on the upper terrace.

  1. Electron stimulated desorption studies of the adsorption and dynamics of molecules on a copper(110) single crystal surface

    NASA Astrophysics Data System (ADS)

    Mocuta, Dan Mihai

    This thesis describes studies of angular distributions produced by the electron stimulated desorption of ions and neutrals from adsorbates on a Cu(110) surface. A new technique, time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD), has been developed and several studies using this method are reported. The low frequency frustrated translation mode of a model system, low coverage CO/Cu(110), is analyzed using TOF-ESDIAD. A simplified model is used to extract the energies of this mode along the two crystal azimuthal directions. A first time measurement of an anisotropy of this mode in the two directions is reported. The same frustrated translational energies giving the same anisotropy have been measured in a helium atom scattering experiment in confirmation of the ESDIAD measurements. An analysis of the TOF distributions of species desorbing from CO/Cu(110) shows that these are Maxwellian. It is shown that CO* and CO+ have similar TOF distributions, indicating a common desorption channel for both species. The ability of ESDIAD to measure chemical bond directions has been put to use in the observation of interadsorbate interactions. It is shown that at high CO coverage on the Cu(110) surface, the CO molecules agglomerate in chains and tilt away from the surface normal. The same phenomenon is observed in the case of NH3, where H+ ions produced by rupturing the N-H bonds of this molecule are imaged. The NH3 molecules can be trapped in a tilted position by cooling the copper surface using liquid helium. It is shown that such a configuration is a precursor to the upright chemisorbed configuration, in which the molecules rotate around the C3v axis. Not only can we image using the electrons, but we can produce new species by electron bombardment. The dissociation of NH3 to NH2 and H has been induced by electrons and the formation of these products is witnessed using ESDIAD. The oxygen induced reconstruction of the Cu(110) surface is studied

  2. Atomistic details of oxide surfaces and surface oxidation: the example of copper and its oxides

    NASA Astrophysics Data System (ADS)

    Gattinoni, Chiara; Michaelides, Angelos

    2015-11-01

    The oxidation and corrosion of metals are fundamental problems in materials science and technology that have been studied using a large variety of experimental and computational techniques. Here we review some of the recent studies that have led to significant advances in our atomic-level understanding of copper oxide, one of the most studied and best understood metal oxides. We show that a good atomistic understanding of the physical characteristics of cuprous (Cu2O) and cupric (CuO) oxide and of some key processes of their formation has been obtained. Indeed, the growth of the oxide has been shown to be epitaxial with the surface and to proceed, in most cases, through the formation of oxide nano-islands which, with continuous oxygen exposure, grow and eventually coalesce. We also show how electronic structure calculations have become increasingly useful in helping to characterise the structures and energetics of various Cu oxide surfaces. However a number of challenges remain. For example, it is not clear under which conditions the oxidation of copper in air at room temperature (known as native oxidation) leads to the formation of a cuprous oxide film only, or also of a cupric overlayer. Moreover, the atomistic details of the nucleation of the oxide islands are still unknown. We close our review with a brief perspective on future work and discuss how recent advances in experimental techniques, bringing greater temporal and spatial resolution, along with improvements in the accuracy, realism and timescales achievable with computational approaches make it possible for these questions to be answered in the near future.

  3. Oxide driven strength evolution of silicon surfaces

    SciTech Connect

    Grutzik, Scott J.; Zehnder, Alan T.; Milosevic, Erik; Boyce, Brad L.

    2015-11-21

    Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations show that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.

  4. Oxide driven strength evolution of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Grutzik, Scott J.; Milosevic, Erik; Boyce, Brad L.; Zehnder, Alan T.

    2015-11-01

    Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations show that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.

  5. Surface-oxidized carbon black as a catalyst for the water oxidation and alcohol oxidation reactions.

    PubMed

    Suryanto, Bryan H R; Zhao, Chuan

    2016-05-11

    Carbon black (CB) is popularly used as a catalyst support for metal/metal oxide nanoparticles due to its large surface area, excellent conductivity and stability. Herein, we show that surface oxidized CB itself, after acidic treatment and electrochemical oxidation, exhibits significant catalytic activity for the electrochemical oxidation of water and alcohols. PMID:27097802

  6. Surface modification to prevent oxide scale spallation

    DOEpatents

    Stephens, Elizabeth V; Sun, Xin; Liu, Wenning; Stevenson, Jeffry W; Surdoval, Wayne; Khaleel, Mohammad A

    2013-07-16

    A surface modification to prevent oxide scale spallation is disclosed. The surface modification includes a ferritic stainless steel substrate having a modified surface. A cross-section of the modified surface exhibits a periodic morphology. The periodic morphology does not exceed a critical buckling length, which is equivalent to the length of a wave attribute observed in the cross section periodic morphology. The modified surface can be created using at least one of the following processes: shot peening, surface blasting and surface grinding. A coating can be applied to the modified surface.

  7. Electron stimulated oxidation of silicon surfaces

    SciTech Connect

    Munoz, M.C.; Sacedon, J.L.

    1981-04-15

    Experimental evidence of electron stimulated oxidation (ESO) has been given for Si(111) 7 x 7 surface. In a first stage, the oxide thickness as a function of time shows a linear relationship; in a second stage, the growth rate quickly decreases and a pressure dependent saturation oxide thickness is reached. During the oxidation process an electrical potential does exist across the oxide, as is required in the Cabrera--Mott theory. The linear kinetics and the electrical potential are shown to be explicable in terms of a modified coupled-current approach based on the Cabrera--Mott theory, provided a semiphenomenological pressure dependent parameter is included. This represents a contribution of the surface reaction to the transport equation. The saturation has been explained as due to the decrease of the negative surface charge (donor levels) which produces a decrease of the electron current.

  8. Platinum Attachments on Iron Oxide Nanoparticle Surfaces

    SciTech Connect

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

    2010-04-30

    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 Pt on iron oxide nanoparticles is limited by the wetting ability of the Pt (metal) on ceramic surfaces. A study of Pt nanoparticle attachment on iron oxide nanoparticle surfaces in an organic solvent is reported, which addresses the factors that promote or inhibit such attachment. It was discovered that the Pt attachment strongly depends on the capping molecules of the iron oxide seeds and the reaction temperature. For example, the attachment of Pt nanoparticles on oleic acid coated iron oxide nanoparticles was very challenging, because of the strong binding between the carboxylic groups and iron oxide surfaces. In contrast, when nanoparticles are coated with oleic acid/tri-n-octylphosphine oxide or oleic acid/oleylamine, a significant increase in Pt attachment was observed. Electronic structure calculations were then applied to estimate the binding energies between the capping molecules and iron ions, and the modeling results strongly support the experimental observations.

  9. Surface Wrinkling on Polydimethylsiloxane Microspheres via Wet Surface Chemical Oxidation

    PubMed Central

    Yin, Jian; Han, Xue; Cao, Yanping; Lu, Conghua

    2014-01-01

    Here we introduce a simple low-cost yet robust method to realize spontaneously wrinkled morphologies on spherical surfaces. It is based on surface chemical oxidation of aqueous-phase-synthesized polydimethylsiloxane (PDMS) microspheres in the mixed H2SO4/HNO3/H2O solution. Consequently, curvature and overstress-sensitive wrinkles including dimples and labyrinth patterns are successfully induced on the resulting oxidized PDMS microspheres. A power-law dependence of the wrinkling wavelength on the microsphere radius exists. The effects of experimental parameters on these tunable spherical wrinkles have been systematically investigated, when the microspheres are pre-deposited on a substrate. These parameters include the radius and modulus of microspheres, the mixed acid solution composition, the oxidation duration, and the water washing post-treatment. Meanwhile, the complicated chemical oxidation process has also been well studied by in-situ optical observation via the microsphere system, which represents an intractable issue in a planar system. Furthermore, we realize surface wrinkled topographies on the whole microspheres at a large scale, when microspheres are directly dispersed in the mixed acid solution for surface oxidation. These results indicate that the introduced wet surface chemical oxidation has the great potential to apply to other complicated curved surfaces for large-scale generation of well-defined wrinkling patterns, which endow the solids with desired physical properties. PMID:25028198

  10. Surface nitriding and oxidation of nitinol

    NASA Astrophysics Data System (ADS)

    Bazochaharbakhsh, Edin

    Nitinol has been widely employed in biomedical devices due to its unique mechanical properties such as superelasticity, shape memory, and good biocompatibility. However, nickel ion release from the surface of the Nitinol is an issue. Surface nitriding and oxidation was performed on the Nitinol specimens to develop a nickel-free oxide layer on the surface. Nitinol specimens were nitrided in nitrogen + 4% hydrogen at 800--1000°C for 10--30 min and further nitrided in nitrogen + 5% ammonia at 500--675°C for 0--30 min. The thickness and chemical composition, specifically the nickel content of the surface layer, were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The effect of the nitriding time and temperature on the thickness and chemical composition of the nitride layer was evaluated. Nitriding temperature was found to be more effective than nitriding time on the thickness of TiN layer. Titanium nitride, the dominant phase on the surface of the nitrided specimens, was nickel free. The nitrided Nitinol specimens were then oxidized at 675°C and 700°C for 30 and 60 min, respectively. The chemical composition and elemental depth profile showed that oxidizing Nitinol specimens with a 0.4 microm thick nitride layer on the surface did not provide a nickel-free oxide layer on the surface of the Nitinol. However, oxidizing the Nitinol specimens with a surface nitride layer that was thicker than 6 microm resulted in a nickel-free oxide layer.

  11. Surface protected lithium-metal-oxide electrodes

    DOEpatents

    Thackeray, Michael M.; Kang, Sun-Ho

    2016-04-05

    A lithium-metal-oxide positive electrode having a layered or spinel structure for a non-aqueous lithium electrochemical cell and battery is disclosed comprising electrode particles that are protected at the surface from undesirable effects, such as electrolyte oxidation, oxygen loss or dissolution by one or more lithium-metal-polyanionic compounds, such as a lithium-metal-phosphate or a lithium-metal-silicate material that can act as a solid electrolyte at or above the operating potential of the lithium-metal-oxide electrode. The surface protection significantly enhances the surface stability, rate capability and cycling stability of the lithium-metal-oxide electrodes, particularly when charged to high potentials.

  12. Surface chemistry and structure of beryllium oxide

    SciTech Connect

    Fuller, E.L. Jr.; Eager, M.H.; Smithwick, R.W. III; Smyrl, N.R.

    1982-02-01

    Detailed examination of nitrogen sorption isotherms related to the surface chemistry and structure of high-purity beryllium oxide and the products of alkali treatment aid in a better understanding of the topochemical problems encountered in the production of ceramic items. Details are corroborated by additional techniques: diffuse reflectance infrared Fourier transform (DRIFT); mercury intrusion porosimetry (MIP); and scanning electron microscopy (SEM). The results correlate well with studies on other oxides when the unique thermophysical properties of this material are considered.

  13. The surface chemistry of cerium oxide

    DOE PAGESBeta

    Mullins, David R.

    2015-01-29

    Our 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 focusmore » 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. We conducted surface science studies 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.« less

  14. The surface chemistry of cerium oxide

    SciTech Connect

    Mullins, David R.

    2015-01-29

    Our 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. We conducted surface science studies 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.

  15. SURFACE REACTIONS OF OXIDES OF SULFUR

    EPA Science Inventory

    Surface reactions of several sulfur-containing molecules have been studied in order to understand the mechanism by which sulfate ions are formed on atmospheric aerosols. At 25C the heterogeneous oxidation of SO2 by NO2 to sulfuric acid and sulfate ions occurred on hydrated silica...

  16. Advanced oxidation process sanitization of eggshell surfaces.

    PubMed

    Gottselig, Steven M; Dunn-Horrocks, Sadie L; Woodring, Kristy S; Coufal, Craig D; Duong, Tri

    2016-06-01

    The microbial quality of eggs entering the hatchery represents an important critical control point for biosecurity and pathogen reduction programs in integrated poultry production. The development of safe and effective interventions to reduce microbial contamination on the surface of eggs will be important to improve the overall productivity and microbial food safety of poultry and poultry products. The hydrogen peroxide (H2O2) and ultraviolet (UV) light advanced oxidation process is a potentially important alternative to traditional sanitizers and disinfectants for egg sanitation. The H2O2/UV advanced oxidation process was demonstrated previously to be effective in reducing surface microbial contamination on eggs. In this study, we evaluated treatment conditions affecting the efficacy of H2O2/UV advanced oxidation in order to identify operational parameters for the practical application of this technology in egg sanitation. The effect of the number of application cycles, UV intensity, duration of UV exposure, and egg rotation on the recovery of total aerobic bacteria from the surface of eggs was evaluated. Of the conditions evaluated, we determined that reduction of total aerobic bacteria from naturally contaminated eggs was optimized when eggs were sanitized using 2 repeated application cycles with 5 s exposure to 14 mW cm(-2) UV light, and that rotation of the eggs between application cycles was unnecessary. Additionally, using these optimized conditions, the H2O2/UV process reduced Salmonella by greater than 5 log10 cfu egg(-1) on the surface of experimentally contaminated eggs. This study demonstrates the potential for practical application of the H2O2/UV advanced oxidation process in egg sanitation and its effectiveness in reducing Salmonella on eggshell surfaces. PMID:27030693

  17. Surface effects in zinc oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Combe, Nicolas; Chassaing, Pierre-Marie; Demangeot, François

    2009-01-01

    Structural properties of zinc oxide nanoparticles are theoretically studied focusing on the effects induced by the surfaces. In this aim, we compare two models: an atomistic and an elastic model. Atomistic model uses a semiempirical potential: the shell model. Effects of surface relaxation and surface stress are taken into account in this model while they were not in the elastic model. Studying nanoparticles with sizes varying from 1.5 to 4.5 nm, we show that surface relaxation occurs on a typical length of about 1 nm in the vicinity of surfaces within the atomistic model. This significant length is due to the existence of long-range interaction forces in zinc oxide which is an ionocovalent material. Because this typical length is comparable to nanoparticle size, elasticity fails to reproduce correctly structural properties of the nanoparticles. As an illustration of structural properties changes by decreasing nanoparticles sizes, we study the nanoparticles acoustic vibrations eigenfrequencies focusing on the mostly observable modes by vibration spectroscopy. Differences between elasticity and atomistic calculations are attributed to surface effects. If elasticity acceptably provides vibration frequencies of most studied nanoparticles, it fails to reproduce them for nanoparticles with a size below an approximate value of 2.5 nm. We expect such effects to be experimentally observable.

  18. Surface Structure of Aerobically Oxidized Diamond Nanocrystals

    PubMed Central

    2015-01-01

    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 (λexcit = 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

  19. Oxygen Evolution Electrocatalysis on Cobalt Oxide surfaces

    NASA Astrophysics Data System (ADS)

    Bajdich, Michal; Norskov, Jens K.; García-Mota, Monica; Bell, Alexis T.

    2012-02-01

    The oxidation of water for hydrogen production using sunlight is of high importance to photo-fuel cell research. The electrochemical approach via heterogeneous catalysis to water splitting is a very promising route. The key challenge of this method lies in reduction of the loses, i.e., over-potential, for the oxygen evolution reaction (OER) on the anode. In this work, we investigate the dependence of theoretical over-potential of OER on type of anode by applying standard density functional theory (DFT). We attempt to explain recent experimental observation of enhanced activity on gold supported Cobalt Oxide surfaces [1]. We explore variety of possible CoO structures and associated surfaces which could emerge under operating conditions of catalyst. Finally, we also explore the influence of environment and admixtures of CoO with other elements. [4pt] [1] B.S. Yeo, A.T. Bell, AT, J. Am. Chem. Soc., 133, 5587-5593 (2011).

  20. 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

  1. Surface Stabilization Mechanisms in Metal Oxides

    NASA Astrophysics Data System (ADS)

    Becerra Toledo, Andres Enrique

    2011-07-01

    Metal oxide surfaces play a central role in modern applications, ranging from heterogeneous catalysis to electronic devices, yet little is known about the processes determining their structural stabilization. Several such stabilization mechanisms are explored via a combination of theoretical and experimental methods. The processes of periodic reconstruction, adsorption and segregation are studied through case studies of model material systems. The evaluation of structural models of periodic SrTiO3(001) reconstructions via bonding analysis and simulated scanning tunneling microscopy images supports the family of "DL" models terminating in two consecutive layers of TiO2 composition, and discards alternative proposals such as the models based on periodic Sr adatoms. Experimental and simulated scanning tunneling microscopy images and complementary spectroscopic data are used to determine the structure of linear Ti-rich SrTiO 3(001) nanostructures. The structural solution exemplifies the recurrence of locally stable motifs across numerous surfaces. In particular, the arrangement of edge-sharing TiO5 surface polyhedra is a trait is shared by (001) nanostructures and DL reconstructions. This is a flexible framework which allows for optimal bonding in surface atoms. Modeling of water adsorption on reconstructed SrTiO3(001) surfaces reveals that water plays two major roles in the stabilization of oxide surfaces: it may mediate the formation of certain ordered structures, or it may be part of the ultimately stable structures themselves. This can be understood in terms of the inevitable presence of chemisorbed water on defective surfaces. Since the surface mobility of cationic species is relatively low, the kinetics associated to water diffusion and desorption dominate the surface ordering process. High-temperature annealing of SrLaAlO4 single crystals leads to the segregation of SrO to the surfaces, in the form of islands. This process is in fact a bulk stabilization

  2. Polarity of oxide surfaces and nanostructures

    NASA Astrophysics Data System (ADS)

    Goniakowski, Jacek; Finocchi, Fabio; Noguera, Claudine

    2008-01-01

    Whenever a compound crystal is cut normal to a randomly chosen direction, there is an overwhelming probability that the resulting surface corresponds to a polar termination and is highly unstable. Indeed, polar oxide surfaces are subject to complex stabilization processes that ultimately determine their physical and chemical properties. However, owing to recent advances in their preparation under controlled conditions and to improvements in the experimental techniques for their characterization, an impressive variety of structures have been investigated in the last few years. Recent progress in the fabrication of oxide nano-objects, which have been largely stimulated by a growing demand for new materials for applications ranging from micro-electronics to heterogeneous catalysis, also offer interesting examples of exotic polar structures. At odds with polar orientations of macroscopic samples, some smaller size polar nano-structures turn out to be perfectly stable. Others are subject to unusual processes of stabilization, which are absent or not effective in their extended counterparts. In this context, a thorough and comprehensive reflexion on the role that polarity plays at oxide surfaces, interfaces and in nano-objects seems timely. This review includes a first section which presents the theoretical concepts at the root of the polar electrostatic instability and its compensation and introduces a rigorous definition of polar terminations that encompasses previous theoretical treatments; a second section devoted to a summary of all experimental and theoretical results obtained since the first review paper by Noguera (2000 J. Phys.: Condens. Matter 12 R367); and finally a discussion section focusing on the relative strength of the stabilization mechanisms, with special emphasis on ternary compound surfaces and on polarity effects in ultra-thin films.

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

    SciTech Connect

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

    2014-12-29

    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). As a result, 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.

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

    DOE PAGESBeta

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

    2014-12-29

    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 upmore » 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). As a result, 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.« less

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

    NASA Astrophysics Data System (ADS)

    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.

  6. 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

  7. Perfluorodiethoxymethane on nickel and nickel oxide surfaces

    SciTech Connect

    Jacobson, J.

    1994-03-03

    The interaction of perfluorodiethoxymethane with a nickel single crystal, Ni(100); a nickel crystal with chemisorbed oxygen, Ni(100)-c(2x2)O; and a nickel crystal with nickel oxide crystallites, NiO(100) is investigated in an ultra high vacuum environment using thermal desorption spectroscopy and high resolution electron energy loss spectroscopy. Nickel, a component of hard disk drives and stainless steel, is used to represent metal surfaces in these {open_quotes}real{close_quotes} systems. Perfluorodiethoxymethane is used in this study as a model compound of industrial perfluoropolyether lubricants. These lubricants are known for their exceptional stability, except in the presence of metals. Perfluorodiethoxymethane contains the acetal group (-OCF{sub 2}O-), believed to be particularly vulnerable to attack in the presence of Lewis acids. Since the surfaces studied show increasing Lewis acidity at the nickel atom sites, one might expect to see increasing decomposition of perfluorodiethoxymethane due to acidic attack of the acetal group. No decomposition of perfluorodiethoxymethane is observed on the clean Ni(100) surface, while more research is needed to determine whether a small decomposition pathway is observed on the oxygenated surfaces, or whether sample impurities are interfering with results. The strength of the bonding of perfluorodiethoxymethane to the surface is found to increase as the nickel atoms sites become more acidic in moving from Ni(100) to Ni (100)-c(2x2)O to NiO (100).

  8. Surface Structure of Aerobically Oxidized Diamond Nanocrystals

    DOE PAGESBeta

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

    2014-10-27

    Here 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 (λexcit = 633 nm) as well as carbon K-edge X-ray absorption spectra where the signature of a core–hole exciton is observed.more » Both spectroscopic features are similar to those of chemical vapor deposited (CVD) diamond but differ significantly from the spectra of detonation nanodiamond. Lastly, we discuss the importance of these findings to the functionalization of nanodiamond surfaces for biological labeling applications.« less

  9. Surface Structure of Aerobically Oxidized Diamond Nanocrystals

    SciTech Connect

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

    2014-10-27

    Here 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 (λexcit = 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. Lastly, we discuss the importance of these findings to the functionalization of nanodiamond surfaces for biological labeling applications.

  10. The oxidation and surface speciation of indium and indium oxides exposed to atmospheric oxidants

    NASA Astrophysics Data System (ADS)

    Detweiler, Zachary M.; Wulfsberg, Steven M.; Frith, Matthew G.; Bocarsly, Andrew B.; Bernasek, Steven L.

    2016-06-01

    Metallic indium and its oxides are useful in electronics applications, in transparent conducting electrodes, as well as in electrocatalytic applications. In order to understand more fully the speciation of the indium and oxygen composition of the indium surface exposed to atmospheric oxidants, XPS, HREELS, and TPD were used to study the indium surface exposed to water, oxygen, and carbon dioxide. Clean In and authentic samples of In2O3 and In(OH)3 were examined with XPS to provide standard spectra. Indium was exposed to O2 and H2O, and the ratio of O2 - to OH- in the O1s XPS region was used to monitor oxidation and speciation of the surface. HREELS and TPD indicate that water dissociates on the indium surface even at low temperature, and that In2O3 forms at higher temperatures. Initially, OH- is the major species at the surface. Pure In2O3 is also OH- terminated following water exposure. Ambient pressure XPS studies of water exposure to these surfaces suggest that high water pressures tend to passivate the surface, inhibiting extensive oxide formation.

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

    DOEpatents

    Singh, Prabhakar; Ruka, Roswell J.

    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.

  12. Energetics of nanoparticle oxides: interplay between surface energy and polymorphism†

    PubMed Central

    Navrotsky, Alexandra

    2003-01-01

    Many oxides tend to form different structures (polymorphs) for small particles. High temperature oxide melt solution calorimetry has been used to measure the enthalpy as a function of polymorphism and surface area for oxides of Al, Ti, and Zr. The results confirm crossovers in polymorph stability at the nanoscale. The energies of internal and external surfaces of zeolitic silicas with open framework structures are an order of magnitude smaller than those of oxides of normal density.

  13. Pretreatment of lubricated surfaces with sputtered cadmium oxide

    NASA Technical Reports Server (NTRS)

    Fusaro, Robert L. (Inventor)

    1991-01-01

    Cadmium oxide is used with a dry solid lubricant on a surface to improve wear resistance. The surface topography is first altered by photochemical etching to a predetermined pattern. The cadmium oxide is then sputtered onto the altered surface to form an intermediate layer to more tightly hold the dry lubricant, such as graphite.

  14. Structure and Bonding of Tungsten Oxide Clusters on Nanostructured Cu-O Surfaces

    SciTech Connect

    Wagner, Margareta; Surnev, Svetlozar; Ramsey, Michael; Barcaro, Giovanni; Sementa, Luca; Negreiros, Fabio R.; Fortunelli, Alessandro; Dohnalek, Zdenek; Netzer, Falko P.

    2011-12-01

    (WO3)3 gas-phase clusters generated via vacuum sublimation are deposited under UHV and low temperature (5 K) conditions on a Cu(110) 'stripe' phase consisting of alternating Cu-O (2x1) and clean Cu regions. STM imaging shows that the clusters adsorb as intact units on both substrates, and the suggested adsorption geometries are confirmed by density-functional (DF) simulations. On the clean surface the overall distortion is minor and we are able to image the nodal structure of an individual molecular orbital in the STM at low bias, whereas on the Cu-O surface both the clusters and the substrate are significantly distorted, due to the strong oxygen affinity of W atoms. On both surfaces cluster and Cu electronic states are appreciably mixed, and electron charge is donated by the surface to the cluster. The experimentally STS-determined DOS signature of the adsorption complex consists in two peaks across the Fermi energy and is well reproduced by the DF calculations.

  15. Generation of singlet oxygen on the surface of metal oxides

    NASA Astrophysics Data System (ADS)

    Kiselev, V. M.; Kislyakov, I. M.; Burchinov, A. N.

    2016-04-01

    Generation of singlet oxygen on the surface of metal oxides is studied. It is shown that, under conditions of heterogeneous photo-catalysis, along with the conventional mechanism of singlet oxygen formation due to the formation of electron-hole pairs in the oxide structure, there is an additional and more efficient mechanism involving direct optical excitation of molecular oxygen adsorbed on the oxide surface. The excited adsorbate molecule then interacts with the surface or with other adsorbate molecules. It is shown that, with respect to singlet oxygen generation, yttrium oxide is more than an order of magnitude more efficient than other oxides, including titanium dioxide.

  16. Surface chemistry of copper metal and copper oxide atomic layer deposition from copper(ii) acetylacetonate: a combined first-principles and reactive molecular dynamics study.

    PubMed

    Hu, Xiao; Schuster, Jörg; Schulz, Stefan E; Gessner, Thomas

    2015-10-28

    Atomistic mechanisms for the atomic layer deposition using the Cu(acac)2 (acac = acetylacetonate) precursor are studied using first-principles calculations and reactive molecular dynamics simulations. The results show that Cu(acac)2 chemisorbs on the hollow site of the Cu(110) surface and decomposes easily into a Cu atom and the acac-ligands. A sequential dissociation and reduction of the Cu precursor [Cu(acac)2 → Cu(acac) → Cu] are observed. Further decomposition of the acac-ligand is unfavorable on the Cu surface. Thus additional adsorption of the precursors may be blocked by adsorbed ligands. Molecular hydrogen is found to be nonreactive towards Cu(acac)2 on Cu(110), whereas individual H atoms easily lead to bond breaking in the Cu precursor upon impact, and thus release the surface ligands into the gas-phase. On the other hand, water reacts with Cu(acac)2 on a Cu2O substrate through a ligand-exchange reaction, which produces gaseous H(acac) and surface OH species. Combustion reactions with the main by-products CO2 and H2O are observed during the reaction between Cu(acac)2 and ozone on the CuO surface. The reactivity of different co-reactants toward Cu(acac)2 follows the order H > O3 > H2O. PMID:26399423

  17. TOPICAL REVIEW: Low-dimensional surface oxides in the oxidation of Rh particles

    NASA Astrophysics Data System (ADS)

    Mittendorfer, Florian

    2010-10-01

    The oxidation of rhodium particles leads to the formation of low-dimensional nanostructures, namely ultrathin oxide films and stripes adsorbed on the metallic surface. These structures display unique electronic and structural properties, which have been studied in detail experimentally and theoretically in recent years. In this review, the state of research on low-dimensional surface oxides formed on Rh surfaces will be discussed with a special focus on the contributions derived from computational approaches. Several points elucidating the novel properties of the surface oxides will be addressed: (i) the structural relation between the surface oxides and their bulk counterparts, (ii) the electronic properties of the low-dimensional oxide films and (iii) potential catalytic and electronic applications of the surface oxides.

  18. 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.

    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.

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

    SciTech Connect

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

    2014-09-29

    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.

  20. Surface and catalytic properties of doped tin oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Wang, Chien-Tsung; Lai, De-Lun; Chen, Miao-Ting

    2010-10-01

    Mixed oxides composed of Zn-Sn, Ti-Sn and V-Sn were prepared by a co-precipitation method and evaluated as catalysts for methanol oxidation in an ambient fixed-bed reactor. Surface analysis by X-ray photoelectron spectroscopy (XPS) revealed an electronic interaction between dopant and Sn atoms in the oxide structure and showed the formation of surface states associated with the dopants. Oxygen vacancies were present on the Zn-doped oxide, and the oxidation of methanol to carbon oxides was favored. The Ti-doped oxide exhibited a favorable selectivity to dimethyl ether, related to the oxygen anions near Ti centers. Vanadium dopants not only dramatically increased the catalytic activity but also promoted the partial oxidation of methanol to formaldehyde. Results demonstrate that the bridging dopant-O-Sn bond acts as active sites and influences product distribution.

  1. Characterization and stability of thin oxide films on plutonium surfaces

    NASA Astrophysics Data System (ADS)

    Flores, H. G. García; Roussel, P.; Moore, D. P.; Pugmire, D. L.

    2011-02-01

    X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were employed to study oxide films on plutonium metal surfaces. Measurements of the relative concentrations of oxygen and plutonium, as well as the resulting oxidation states of the plutonium (Pu) species in the near-surface region are presented. The oxide product of the auto-reduction (AR) of plutonium dioxide films is evaluated and found to be an oxide species which is reduced further than what is expected. The results of this study show a much greater than anticipated extent of auto-reduction and challenge the commonly held notion of the stoichiometric stability of Pu 2O 3 thin-films. The data indicates that a sub-stoichiometric plutonium oxide (Pu 2O 3 - y ) exists at the metal-oxide interface. The level of sub-stoichiometry is shown to depend, in part, on the carbidic contamination of the metal surface.

  2. Multiscale Investigations of the Early Stage Oxidation on Cu Surfaces

    NASA Astrophysics Data System (ADS)

    Zhu, Qing; Xiao, Penghao; Lian, Xin; Yang, Shen-Che; Henkelman, Grame; Saidi, Wissam; Yang, Judith; University of Pittsburgh Team; University of Texas at Austin Team

    Previous in situ TEM experiments have shown that the oxidation of the three low index Cu surfaces (100), (110) and (111) exhibit different oxide nucleation rates, and the resulting oxides have 3-dimensional (3D) island shapes or 2D rafts under different conditions. In order to better understand these results, we have investigated the early stages of Cu oxidation using a multiscale computational approach that employs density functional theory (DFT), reactive force field (ReaxFF), and kinetic Mote Carlo (KMC). With DFT calculation, we have compared O2 dissociation barriers on Cu (100), (110) and (111) surfaces at high oxygen coverage to evaluate the kinetic barrier of sublayer oxidization. We found that O2 dissociation barriers on Cu(111) surface are all lower than those on (110) and (100) surfaces. This trend agrees with experimental observations that (111) surface is easier to oxidize. These DFT calculated energy barriers are then incorporated into KMC simulations. The large scale ReaxFF molecular dynamics and KMC simulations detail the oxidation dynamics of the different Cu surfaces, and show the formation of various oxide morphologies that are consistent with experimental observations.

  3. Oxidized In-containing III-V(100) surfaces: Formation of crystalline oxide films and semiconductor-oxide interfaces

    NASA Astrophysics Data System (ADS)

    Punkkinen, M. P. J.; Laukkanen, P.; Lång, J.; Kuzmin, M.; Tuominen, M.; Tuominen, V.; Dahl, J.; Pessa, M.; Guina, M.; Kokko, K.; Sadowski, J.; Johansson, B.; Väyrynen, I. J.; Vitos, L.

    2011-05-01

    Previously found oxidized III-V semiconductor surfaces have been generally structurally disordered and useless for applications. We disclose a family of well-ordered oxidized InAs, InGaAs, InP, and InSb surfaces found by experiments. The found epitaxial oxide-III-V interface is insulating and free of defects related to the harmful Fermi-level pinning, which opens up new possibilities to develop long-sought III-V metal-oxide-semiconductor transistors. Calculations reveal that the early stages in the oxidation process include only O-III bonds due to the geometry of the III-V(100)c(8×2) substrate, which is responsible for the formation of the ordered interface. The found surfaces provide a different platform to study the oxidation and properties of oxides, e.g., the origins of the photoemission shifts and electronic structures, using surface science methods.

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

    NASA Astrophysics Data System (ADS)

    Wu, Wei; He, Quanguo; Jiang, Changzhong

    2008-10-01

    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.

  5. 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

  6. High-Temperature Oxide Regrowth on Mechanically-Damaged Surfaces

    SciTech Connect

    Blau, Peter Julian; Lowe, Tracie M

    2008-01-01

    Here we report the effects of mechanical damage from a sharp stylus on the regrowth of oxide layers on a Ni-based superalloy known as Pyromet 80A . It was found that the oxide that reformed on the damaged portion of a pre-oxidized surface differed from that which formed on undamaged areas after the equal exposures to elevated temperature in air. These findings have broad implications for modeling the processes of material degradation in applications such as exhaust valves in internal combustion engines because they imply that static oxidation data for candidate materials may not adequately reflect their reaction to operating environments that involve both mechanical contact and oxidation.

  7. 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 μM 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

  8. Oxide surfaces and metal/oxide interfaces studied by grazing incidence X-ray scattering

    NASA Astrophysics Data System (ADS)

    Renaud, Gilles

    Experimental determinations of the atomic structure of insulating oxide surfaces and metal/oxide interfaces are scarce, because surface science techniques are often limited by the insulating character of the substrate. Grazing incidence X-ray scattering (GIXS), which is not subject to charge effects, can provide very precise information on the atomic structure of oxide surfaces: roughness, relaxation and reconstruction. It is also well adapted to analyze the atomic structure, the registry, the misfit relaxation, elastic or plastic, the growth mode and the morphology of metal/oxide interfaces during their growth, performed in situ. GIXS also allows the analysis of thin films and buried interfaces, in a non-destructive way, yielding the epitaxial relationships, and, by variation of the grazing incidence angle, the lattice parameter relaxation along the growth direction. On semi-coherent interfaces, the existence of an ordered network of interfacial misfit dislocations can be demonstrated, its Burger's vector determined, its ordering during in situ annealing cycles followed, and sometimes even its atomic structure can be addressed. Careful analysis during growth allows the modeling of the dislocation nucleation process. This review emphasizes the new information that GIXS can bring to oxide surfaces and metal/oxide interfaces by comparison with other surface science techniques. The principles of X-ray diffraction by surfaces and interfaces are recalled, together with the advantages and properties of grazing angles. The specific experimental requirements are discussed. Recent results are presented on the determination of the atomic structure of relaxed or reconstructed oxide surfaces. A description of results obtained during the in situ growth of metal on oxide surfaces is also given, as well as investigations of thick metal films on oxide surfaces, with lattice parameter misfit relaxed by an array of dislocations. Recent work performed on oxide thin films having

  9. Surface characterization and reactivity of vanadium-tin oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Wang, Chien-Tsung; Chen, Miao-Ting; Lai, De-Lun

    2011-03-01

    Surface state and reactivity of vanadium-tin mixed oxide nanoparticles (V/Sn ratios 0.05-0.2) were characterized by spectroscopic techniques and catalytic measurements. Analyses by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS) revealed that the oxidation state and surface structure of vanadium oxide species and the electronic interaction between Sn and V atoms are dependent upon the vanadium content. These oxides were evaluated as catalysts for methanol oxidation in a fixed-bed reactor. Both reaction rate and formaldehyde selectivity increased with increasing the vanadium amount in catalyst. Results demonstrate that the V 5+ site in the bridging V-O-Sn structure exhibits a high redox activity to facilitate the transformation of adsorbed methoxy to formaldehyde and that the vanadium dispersion plays a crucial role in the surface reactivity. A mechanism that elucidates the catalytic redox process is proposed.

  10. Optical glass surfaces polishing by cerium oxide particles

    NASA Astrophysics Data System (ADS)

    Bouzid, D.; Belkhie, N.; Aliouane, T.

    2012-02-01

    The use of powders in metallic oxides as means of grinding and polishing of the optical glass components have seen recently a large application in optical industry. In fact, cerium oxide abrasive is more used in the optical glass polishing. It is used as grains abrasive in suspension or fixed abrasive (pellets); these pellets are manufactured from a mixture made of cerium oxide abrasive and a organic binder. The cerium oxide used in the experiments is made by (Logitech USA) of 99 % purity, the average grain size of the particle is 300 nm, the density being 6,74 g /cm3 and the specific surface is 3,3042 m2/g. In this study, we are interested in the surfaces quality of the optical glass borosilicate crown (BK7) polished by particles in cerium oxide bounded by epoxy. The surfaces of the optical glass treated are characterized by the roughness, the flatness by using the microscope Zygo and the SEM.

  11. Thermal instability of GaSb surface oxide

    NASA Astrophysics Data System (ADS)

    Tsunoda, K.; Matsukura, Y.; Suzuki, R.; Aoki, M.

    2016-05-01

    In the development of InAs/GaSb Type-II superlattice (T2SL) infrared photodetectors, the surface leakage current at the mesa sidewall must be suppressed. To achieve this requirement, both the surface treatment and the passivation layer are key technologies. As a starting point to design these processes, we investigated the GaSb oxide in terms of its growth and thermal stability. We found that the formation of GaSb oxide was very different from those of GaAs. Both Ga and Sb are oxidized at the surface of GaSb. In contrast, only Ga is oxidized and As is barely oxidized in the case of GaAs. Interestingly, the GaSb oxide can be formed even in DI water, which results in a very thick oxide film over 40 nm after 120 minutes. To examine the thermal stability, the GaSb native oxide was annealed in a vacuum and analyzed by XPS and Raman spectroscopy. These analyses suggest that SbOx in the GaSb native oxide will be reduced to metallic Sb above 300°C. To directly evaluate the effect of oxide instability on the device performance, a T2SL p-i-n photodetector was fabricated that has a cutoff wavelength of about 4 μm at 80 K. As a result, the surface leakage component was increased by the post annealing at 325°C. On the basis of these results, it is possible to speculate that a part of GaSb oxide on the sidewall surface will be reduced to metallic Sb, which acts as an origin of additional leakage current path.

  12. The chemistry and physics of zinc oxide surfaces

    NASA Astrophysics Data System (ADS)

    Wöll, Christof

    Metal oxides are virtually everywhere - only gold has the property not to form an oxide on its surface when exposed to the ambient. As a result, understanding the physics and chemistry of oxide surfaces is a topic of pronounced general interest and, of course, also a necessary prerequisite for many technical applications. The most important of these is certainly heterogeneous catalysis, but one has to realize that - under ambient conditions - virtually all phenomena occurring at liquid/metal and gas/metal interfaces are determined by the corresponding oxide. This applies in particular to friction phenomena, adhesion and corrosion. A necessary - but not necessarily sufficient - condition for unravelling the fundamentals governing this complex field is to analyze in some detail elementary chemical and physical processes at oxide surfaces. Although the Surface Science of metal surfaces has seen a major progress in the past decades, for oxides detailed experimental investigations for well-defined single crystal surfaces still represent a formidable challenge - mostly because of technical difficulties (charging), but to some extent also due to fundamental problems related to the stabilization of polar surfaces. As a result, the amount of information available for this class of materials is - compared to that at hand for metals - clearly not satisfactory. A particular disturbing lack of information is that about the presence of hydrogen at oxide surfaces - either as hydroxy-species or in form of metal hydrides. In the present review we will summarize recent experimental and theoretical information which has become available from single crystal studies on ZnO surfaces. While the number of papers dealing with another oxide, rutile TiO 2, is significantly larger (although titania does not exhibit a polar surface), also for zinc oxide a basis of experimental and theoretical knowledge as been accumulated, which - at least for the non-polar surfaces - allows to understand

  13. Halogens on Semiconductor Surfaces: Adsorption, Oxidation, and Etching.

    NASA Astrophysics Data System (ADS)

    Stepniak, Frank

    This dissertation presents studies of Si, GaAs, and InP surfaces following exposure to the halogens Cl _2 and Br_2. Synchrotron radiation photoemission is used to investigate the oxidation states of Si near the Si/SiO_2 interface as a function of Cl_2 exposure. Oxidation of highly ordered surfaces shows no dependence of the oxidation state concentration on Cl_2 inclusion in the gas mixture. For less-than-ideal Si surfaces, oxidation with O_2 -only results in a broader transition region, and presumably, inferior electrical properties. The addition of Cl_2 in the oxidizing gas reduced the concentration of intermediate oxides by a factor of two for these disordered starting Si surfaces. A new feature is also measured from Cl-Si bonds that we associate with passivation of Si defects at the oxide interface. The adsorption and reactivity of Br_2 and Cl_2 on GaAs(110) and InP(110) was studied in the temperature range of 25 K < T < 625 K with photoemission spectroscopy and scanning tunneling microscopy. Initial halogen adsorption was dissociative at all temperatures and we find that a simple model where the halogen atoms bond to a single Ga or As surface site can not account for the complex surface chemistry and morphology. Thermally-activated etching was observed after warming a surface with chemisorbed Br or Cl. Etching resulted from the formation and eventual temperature dependent desorption of the trihalides of Ga and As. For halogen exposures where T < 650 K, monohalide-like surface bonding persist during the etching process and the etched surface is rough. For T > 700 K, the surface is essentially free of halogen and etching occurs in a nearly layer-by-layer fashion.

  14. Improve oxidation resistance at high temperature by nanocrystalline surface layer.

    PubMed

    Xia, Z X; Zhang, C; Huang, X F; Liu, W B; Yang, Z G

    2015-01-01

    An interesting change of scale sequence occurred during oxidation of nanocrystalline surface layer by means of a surface mechanical attrition treatment. The three-layer oxide structure from the surface towards the matrix is Fe3O4, spinel FeCr2O4 and corundum (Fe,Cr)2O3, which is different from the typical two-layer scale consisted of an Fe3O4 outer layer and an FeCr2O4 inner layer in conventional P91 steel. The diffusivity of Cr, Fe and O is enhanced concurrently in the nanocrystalline surface layer, which causes the fast oxidation in the initial oxidation stage. The formation of (Fe,Cr)2O3 inner layer would inhabit fast diffusion of alloy elements in the nanocrystalline surface layer of P91 steel in the later oxidation stage, and it causes a decrease in the parabolic oxidation rate compared with conventional specimens. This study provides a novel approach to improve the oxidation resistance of heat resistant steel without changing its Cr content. PMID:26269034

  15. 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.

  16. Improve oxidation resistance at high temperature by nanocrystalline surface layer

    NASA Astrophysics Data System (ADS)

    Xia, Z. X.; Zhang, C.; Huang, X. F.; Liu, W. B.; Yang, Z. G.

    2015-08-01

    An interesting change of scale sequence occurred during oxidation of nanocrystalline surface layer by means of a surface mechanical attrition treatment. The three-layer oxide structure from the surface towards the matrix is Fe3O4, spinel FeCr2O4 and corundum (Fe,Cr)2O3, which is different from the typical two-layer scale consisted of an Fe3O4 outer layer and an FeCr2O4 inner layer in conventional P91 steel. The diffusivity of Cr, Fe and O is enhanced concurrently in the nanocrystalline surface layer, which causes the fast oxidation in the initial oxidation stage. The formation of (Fe,Cr)2O3 inner layer would inhabit fast diffusion of alloy elements in the nanocrystalline surface layer of P91 steel in the later oxidation stage, and it causes a decrease in the parabolic oxidation rate compared with conventional specimens. This study provides a novel approach to improve the oxidation resistance of heat resistant steel without changing its Cr content.

  17. Improve oxidation resistance at high temperature by nanocrystalline surface layer

    PubMed Central

    Xia, Z. X.; Zhang, C.; Huang, X. F.; Liu, W. B.; Yang, Z. G.

    2015-01-01

    An interesting change of scale sequence occurred during oxidation of nanocrystalline surface layer by means of a surface mechanical attrition treatment. The three-layer oxide structure from the surface towards the matrix is Fe3O4, spinel FeCr2O4 and corundum (Fe,Cr)2O3, which is different from the typical two-layer scale consisted of an Fe3O4 outer layer and an FeCr2O4 inner layer in conventional P91 steel. The diffusivity of Cr, Fe and O is enhanced concurrently in the nanocrystalline surface layer, which causes the fast oxidation in the initial oxidation stage. The formation of (Fe,Cr)2O3 inner layer would inhabit fast diffusion of alloy elements in the nanocrystalline surface layer of P91 steel in the later oxidation stage, and it causes a decrease in the parabolic oxidation rate compared with conventional specimens. This study provides a novel approach to improve the oxidation resistance of heat resistant steel without changing its Cr content. PMID:26269034

  18. The surface and materials science of tin oxide

    NASA Astrophysics Data System (ADS)

    Batzill, Matthias; Diebold, Ulrike

    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 also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO 2 surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn 4+ surface cations into a reduced surface with Sn 2+ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO 2. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO 2 are discussed and the few surface science studies of doped SnO 2 are reviewed. Epitaxial SnO 2 films may facilitate the surface science studies of doped films in the future. To this end film growth

  19. Structural and surface changes of copper modified manganese oxides

    NASA Astrophysics Data System (ADS)

    Gac, Wojciech; Słowik, Grzegorz; Zawadzki, Witold

    2016-05-01

    The structural and surface properties of manganese and copper-manganese oxides were investigated. The oxides were prepared by the redox-precipitation method. X-ray diffraction and electron microscopy studies evidenced transformation of cryptomelane-type nanoparticles with 1-D channel structure into the large MnO crystallites with regular rippled-like surface patterns under reduction conditions. The development of Cu/CuO nanorods from strongly dispersed species was evidenced. Coper-modified manganese oxides showed good catalytic performance in methanol steam reforming reaction for hydrogen production. Low selectivity to CO was observed in the wide range of temperatures.

  20. MOISTURE AND SURFACE AREA MEASUREMENTS OF PLUTONIUM-BEARING OXIDES

    SciTech Connect

    Crowder, M.; Duffey, J.; Livingston, R.; Scogin, J.; Kessinger, G.; Almond, P.

    2009-09-28

    To ensure safe storage, plutonium-bearing oxides are stabilized at 950 C for at least two hours in an oxidizing atmosphere. Stabilization conditions are expected to decompose organic impurities, convert metals to oxides, and result in moisture content below 0.5 wt%. During stabilization, the specific surface area is reduced, which minimizes readsorption of water onto the oxide surface. Plutonium oxides stabilized according to these criteria were sampled and analyzed to determine moisture content and surface area. In addition, samples were leached in water to identify water-soluble chloride impurity content. Results of these analyses for seven samples showed that the stabilization process produced low moisture materials (< 0.2 wt %) with low surface area ({le} 1 m{sup 2}/g). For relatively pure materials, the amount of water per unit surface area corresponded to 1.5 to 3.5 molecular layers of water. For materials with chloride content > 360 ppm, the calculated amount of water per unit surface area increased with chloride content, indicating hydration of hygroscopic salts present in the impure PuO{sub 2}-containing materials. The low moisture, low surface area materials in this study did not generate detectable hydrogen during storage of four or more years.

  1. 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

  2. Surface Morphology of Si(111) during Electrochemical Oxidation

    NASA Astrophysics Data System (ADS)

    Ando, A.; Miki, K.; Sakamoto, K.; Matsumoto, K.; Morita, Y.; Tokumoto, H.

    1997-03-01

    Topographical changes of hydrogen terminated Si(111) during electrochemical oxidation in a 0.2 M H_2SO4 aqueous solution have been investigated using atomic force microscopy (AFM). The hydrogen terminated surface with atomically flat terraces was prepared by dipping into a NH_4F aqueous solution. Electrochemical oxidation has been performed by a potentiostatic (constant potential) or a galvanostatic (constant current) method. AFM images show that the oxidation occured on the terraces and proceeded homogeneously. The surface became rough as the oxidation proceeded. However, step edges were still observed even after the charge of 50 mC/cm^2 was applied. Quantitative analysis of a relation between the charge and surface morphology will be discussed. the address below:

  3. New perspectives on thermal and hyperthermal oxidation of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Khalilov, Umedjon

    The growth of (ultra)thin silica (SiO2) layers on crystalline silicon (c-Si) and controlling the thickness of SiO2 is an important issue in the fabrication of microelectronics and photovoltaic devices (e.g., MOSFETs, solar cells, optical fibers etc.). Such ultrathin oxide can be grown and tuned even at low temperature (including room temperature), by hyperthermal oxidation or when performed on non-planar Si surfaces (e.g., Si nanowires or spheres). However, hyperthermal silica growth as well as small Si-NW oxidation in general and the initial stages in particular have not yet been investigated in full detail. This work is therefore devoted to controlling ultrathin silica thickness on planar and non-planar Si surfaces, which can open new perspectives in nanodevice fabrication. The simulation of hyperthermal (1-100 eV) Si oxidation demonstrate that at low impact energy (<10 eV), oxygen does not damage the Si surface and this energy region could thus beneficially be used for Si oxidation. In contrast to thermal oxidation, 10 eV species can directly oxidize Si subsurface layers. A transition temperature of about 700 K was found: below this temperature, the oxide thickness only depends on the impact energy of the impinging species. Above this temperature, the oxide thickness depends on the impact energy, type of oxidant and the surface temperature. The results show that control over the ultrathin oxide (a-SiO2) thickness is possible by hyperthermal oxidation of silicon surfaces at temperatures below the transition temperature. In small Si-NWs, oxidation is a self-limiting process that occurs at low temperature, resulting in small Si core - SiO2 shell (semiconductor + dielectric) or c-Si|SiOx| a-SiO2 nanowire, which has also being envisaged to be used as nanowire field-effect transistors and photovoltaic devices in near-future nanotechnology. Above the transition temperature such core-shell nanowires are completely converted to a-SiO2 nanowires. It can be concluded that

  4. Method of producing adherent metal oxide coatings on metallic surfaces

    DOEpatents

    Lane, Michael H.; Varrin, Jr., Robert D.

    2001-01-01

    Provided is a process of producing an adherent synthetic corrosion product (sludge) coating on metallic surfaces. The method involves a chemical reaction between a dry solid powder mixture of at least one reactive metal oxide with orthophosphoric acid to produce a coating in which the particles are bound together and the matrix is adherent to the metallic surface.

  5. OXYANION SORPTION TO HIGH SURFACE AREA IRON AND ALUMINUM OXIDES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sorption of selected oxyanions (Mo, As, and P) to high surface area iron and aluminum oxides was investigated using in situ Raman and ATR-FTIR spectroscopy, batch sorption methods, electrophoretic mobility measurements, and surface complexation modeling. In situ ATR-FTIR and Raman spectra were coup...

  6. Metal-oxide-semiconductor photocapacitor for sensing surface plasmon polaritons

    NASA Astrophysics Data System (ADS)

    Khalilzade-Rezaie, Farnood; Peale, Robert E.; Panjwani, Deep; Smith, Christian W.; Nath, Janardan; Lodge, Michael; Ishigami, Masa; Nader, Nima; Vangala, Shiva; Yannuzzi, Mark; Cleary, Justin W.

    2015-09-01

    An electronic detector of surface plasmon polaritons (SPP) is reported. SPPs optically excited on a metal surface using a prism coupler are detected by using a close-coupled metal-oxide-semiconductor capacitor. Semitransparent metal and graphene gates function similarly. We report the dependence of the photoresponse on substrate carrier type, carrier concentration, and back-contact biasing.

  7. Surface passivation of semiconducting oxides by self-assembled nanoparticles

    PubMed Central

    Park, Dae-Sung; Wang, Haiyuan; Vasheghani Farahani, Sepehr K.; Walker, Marc; Bhatnagar, Akash; Seghier, Djelloul; Choi, Chel-Jong; Kang, Jie-Hun; McConville, Chris F.

    2016-01-01

    Physiochemical interactions which occur at the surfaces of oxide materials can significantly impair their performance in many device applications. As a result, surface passivation of oxide materials has been attempted via several deposition methods and with a number of different inert materials. Here, we demonstrate a novel approach to passivate the surface of a versatile semiconducting oxide, zinc oxide (ZnO), evoking a self-assembly methodology. This is achieved via thermodynamic phase transformation, to passivate the surface of ZnO thin films with BeO nanoparticles. Our unique approach involves the use of BexZn1-xO (BZO) alloy as a starting material that ultimately yields the required coverage of secondary phase BeO nanoparticles, and prevents thermally-induced lattice dissociation and defect-mediated chemisorption, which are undesirable features observed at the surface of undoped ZnO. This approach to surface passivation will allow the use of semiconducting oxides in a variety of different electronic applications, while maintaining the inherent properties of the materials. PMID:26757827

  8. Surface passivation of semiconducting oxides by self-assembled nanoparticles

    NASA Astrophysics Data System (ADS)

    Park, Dae-Sung; Wang, Haiyuan; Vasheghani Farahani, Sepehr K.; Walker, Marc; Bhatnagar, Akash; Seghier, Djelloul; Choi, Chel-Jong; Kang, Jie-Hun; McConville, Chris F.

    2016-01-01

    Physiochemical interactions which occur at the surfaces of oxide materials can significantly impair their performance in many device applications. As a result, surface passivation of oxide materials has been attempted via several deposition methods and with a number of different inert materials. Here, we demonstrate a novel approach to passivate the surface of a versatile semiconducting oxide, zinc oxide (ZnO), evoking a self-assembly methodology. This is achieved via thermodynamic phase transformation, to passivate the surface of ZnO thin films with BeO nanoparticles. Our unique approach involves the use of BexZn1-xO (BZO) alloy as a starting material that ultimately yields the required coverage of secondary phase BeO nanoparticles, and prevents thermally-induced lattice dissociation and defect-mediated chemisorption, which are undesirable features observed at the surface of undoped ZnO. This approach to surface passivation will allow the use of semiconducting oxides in a variety of different electronic applications, while maintaining the inherent properties of the materials.

  9. 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.

  10. Heterogeneous nucleation of calcium oxalate on native oxide surfaces

    SciTech Connect

    Song, L.; Pattillo, M.J.; Graff, G.L.; Campbell, A.A.; Bunker, B.C.

    1994-12-31

    The aqueous deposition of calcium oxalate onto colloidal oxides has been studied as a model system for understanding heterogeneous nucleation processes of importance in biomimetic synthesis of ceramic thin films. Calcium oxalate nucleation has been monitored by measuring induction times for nucleation using Constant Composition techniques and by measuring nucleation densities on extended oxide surfaces using an atomic force microscope. Results show that the dependence of calcium oxalate nucleation on solution supersaturation fits the functional form predicted by classical nucleation theories. Anionic surfaces appear to promote nucleation better than cationic surfaces, lowering the effective energy barrier to heterogeneous nucleation.

  11. Phisicochemistry of alkaline-earth metals oxides surface

    NASA Astrophysics Data System (ADS)

    Ekimova, Irina; Minakova, Tamara; Ogneva, Tatyana

    2016-01-01

    The surface state of alkaline-earth metals and magnesium oxides obtained by means of commercial and laboratory ways has been studied in this paper. A complex of methods has been used for identification, determination of a phase composition and morphology of the samples. The high basic character of surface centres has been shown with the help of pH-metry and adsorption of indicators methods. Acid-basic parameters (pHt, pHiis, etc.) can be used for the estimation of a general acid-basic state of metal oxides samples surface and for the supposition about different nature and strength of acid-basic centres as well as for the initial control in the process of acid basic properties of solid oxides surface properties evaluation.

  12. Interaction of nanostructured metal overlayers with oxide surfaces

    NASA Astrophysics Data System (ADS)

    Fu, Qiang; Wagner, Thomas

    2007-11-01

    Interactions between metals and oxides are key factors to determine the performance of metal/oxide heterojunctions, particularly in nanotechnology, where the miniaturization of devices down to the nanoregime leads to an enormous increase in the density of interfaces. One central issue of concern in engineering metal/oxide interfaces is to understand and control the interactions which consist of two fundamental aspects: (i) interfacial charge redistribution — electronic interaction, and (ii) interfacial atom transport — chemical interaction. The present paper focuses on recent advances in both electronic and atomic level understanding of the metal-oxide interactions at temperatures below 1000 ∘C, with special emphasis on model systems like ultrathin metal overlayers or metal nanoclusters supported on well-defined oxide surfaces. The important factors determining the metal-oxide interactions are provided. Guidelines are given in order to predict the interactions in such systems, and methods to desirably tune them are suggested. The review starts with a brief summary of the physics and chemistry of heterophase interface contacts. Basic concepts for quantifying the electronic interaction at metal/oxide interfaces are compared to well-developed contact theories and calculation methods. The chemical interaction between metals and oxides, i.e., the interface chemical reaction, is described in terms of its thermodynamics and kinetics. We review the different chemical driving forces and the influence of kinetics on interface reactions, proposing a strong interplay between the chemical interaction and electronic interaction, which is decisive for the final interfacial reactivity. In addition, a brief review of solid-gas interface reactions (oxidation of metal surfaces and etching of semiconductor surfaces) is given, in addition to a comparison of a similar mechanism dominating in solid-solid and solid-gas interface reactions. The main body of the paper reviews

  13. A molecular catalyst for water oxidation that binds to metal oxide surfaces

    PubMed Central

    Sheehan, Stafford W.; Thomsen, Julianne M.; Hintermair, Ulrich; Crabtree, Robert H.; Brudvig, Gary W.; Schmuttenmaer, Charles A.

    2015-01-01

    Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. Here we describe how a molecular iridium catalyst for water oxidation directly and robustly binds to oxide surfaces without the need for any external stimulus or additional linking groups. On conductive electrode surfaces, this heterogenized molecular catalyst oxidizes water with low overpotential, high turnover frequency and minimal degradation. Spectroscopic and electrochemical studies show that it does not decompose into iridium oxide, thus preserving its molecular identity, and that it is capable of sustaining high activity towards water oxidation with stability comparable to state-of-the-art bulk metal oxide catalysts. PMID:25757425

  14. Comparison of thermal oxidation and plasma oxidation of 4H-SiC (0001) for surface flattening

    SciTech Connect

    Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya

    2014-03-10

    The thermal oxidation and water vapor plasma oxidation of 4H-SiC (0001) were investigated. The initial oxidation rate of helium-based atmospheric-pressure plasma oxidation was six times higher than that of thermal oxidation. The oxide-SiC interface generated by plasma oxidation became flatter with increasing thickness of the oxide, whereas the interface generated by thermal oxidation was atomically flat regardless of the oxide thickness. Many pits were generated on the thermally oxidized surface, whereas few pits were observed on the surface oxidized by plasma. After the oxide layer generated plasma oxidation was removed, an atomically flat and pit-free SiC surface was obtained.

  15. The intermediate oxidation of the Pd(100) surface

    NASA Astrophysics Data System (ADS)

    Mikkelsen, A.; Lundgren, E.; Gustafson, J.; Borg, M.; Andersen, J. N.

    2003-03-01

    The formation of oxides on metal surfaces has recently received much attention. Apart from the fundamental importance of the oxidation process, the interest is driven by the observation that oxides can play an important role in catalysis1, 2. The geometric structure of surface oxides can in some cases3 not be directly inferred from known bulk oxides. The surface structures formed by oxygen on Pd(100) have been studied by Scanning Tunneling Microscopy (STM), High Resolution Core-Level Spectroscopy (HRCLS) and Low Energy Electron Diffraction (LEED). It is shown that the structure determined in a recent LEED analysis4 of the Pd(100)- (root5xroot5)-O structure formed by adsorption of 0.8 ML of oxygen is difficult to reconcile with our STM and HRCLS data. New models for this surface oxide consistent with our experimental results are suggested. [1] Y. D. Kim, A. P. Seitsonen, S. Wendt, E. Lundgren, M. Schmid, P. Varga, A. Morgante, and G. Ertl., Science 287, 1474 (2000). [2] B. L. M. Hendriksen and J. W. M. Frenken, Phys. Rev. Lett. 89, 046101 (2002). [3] E. Lundgren,, G. Kresse, C. Klein, M. Borg, J.N. Andersen, M. De Santis, Y. Gauthier, C. Konvicka, M. Schmid, and P.Varga, Phys. Rev. Lett. 88 (2002) 246103 [4] M. Saidy, O.L. Warren, P.A. Thiel, and K.A.R. Mitchell, Surf. Sci. 494, L799 (2001).

  16. Surface structures of polar and non-polar metal oxides

    NASA Astrophysics Data System (ADS)

    Chamberlin, Sara E.

    Metal oxides have long been a challenge to surface science since many traditional surface techniques are often affected by their insulating nature. In particular, high current electron beams can cause charging effects in addition to potentially desorbing surface species and damaging the surface. The development of a low current, low energy electron diffraction (LEED) system has allowed us to investigate metal oxide surfaces while significantly limiting the above mentioned complications. This low current LEED system has been used to perform a structural LEED-IV study of the reconstructed TiO2(011)-(2x1) surface. This surface is known to experience significant oxygen desorption when exposed to high current electron beams. The low current LEED system was crucial to maintain confidence in the structure found, which generally agreed with recently published models, but did not confirm one key feature. The oxygen atoms at the surface were not found to be asymmetrically bonded, which has been thought to be the cause of this surface's enhanced photocatalytic activity. We have also used the low current LEED system to investigate the polar oxide surfaces of ZnO(000 1¯) and MgO(111)-(✓3x✓3)R30°. For Zn0(000 1¯) LEED-IV structural study was combined with Density Functional Theory (DFT) calculations to investigate the impact of hydrogen on the surface. Our results support a disordered, fractional coverage of hydrogen terminating the surface. MgO(111)-(✓3x✓3)R30° has proven to be a challenging reconstructed surface. Both LEED-IV and surface x-ray diffraction (SXRD) find that previously proposed models for the surface are not a good fit to the data, so other models have been explored. The SXRD data in particular suggest that the reconstruction is more than one atomic layer deep.

  17. A characterization study of a hydroxylated polycrystalline tin oxide surface

    NASA Technical Reports Server (NTRS)

    Hoflund, Gar B.; Grogan, Austin L., Jr.; Asbury, Douglas A.; Schryer, David R.

    1989-01-01

    In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 C causes a large reduction in the surface hydrogen concentration but not complete removal.

  18. Radiation induced chemical activity at iron and copper oxide surfaces

    NASA Astrophysics Data System (ADS)

    Reiff, Sarah C.

    The radiolysis of three iron oxides, two copper oxides, and aluminum oxide with varying amounts of water were performed using gamma-rays and 5 MeV 4He ions. The adsorbed water on the surfaces was characterized using temperature programmed desorption and diffuse reflectance infrared spectroscopy, which indicated that all of the oxides had chemisorbed water on the surface. Physisorbed water was observed on the Fe2O 3 and Al2O3 surfaces as well. Molecular hydrogen was produced from adsorbed water only on Fe2O3 and Al 2O3, while the other compounds did not show any hydrogen production due to the low amounts of water on the surfaces. Slurries of varying amounts of water were also examined for hydrogen production, and they showed yields that were greater than the yield for bulk water. However, the yields of hydrogen from the copper compounds were much lower than those of the iron suggesting that the copper oxides are relatively inert to radiation induced damage to nearby water. X-ray diffraction measurements did not show any indication of changes to the bulk crystal structure due to radiolysis for any of the oxides. The surfaces of the oxides were analyzed using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). For the iron samples, FeO and Fe3O4, Raman spectroscopy revealed areas of Fe2O3 had formed following irradiation with He ions. XPS indicated the formation of a new oxygen species on the iron oxide surfaces. Raman spectroscopy of the copper oxides did not reveal any changes in the surface composition, however, XPS measurements showed a decrease in the amount of OH groups on the surface of Cu2O, while for the CuO samples the amount of OH groups were found to increase following radiolysis. Pristine Al2O3 showed the presence of a surface oxyhydroxide layer which was observed to decrease following radiolysis, consistent with the formation of molecular hydrogen.

  19. 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.

  20. Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces

    SciTech Connect

    Uçar, A.; Çopuroğlu, M.; Suzer, S.; Baykara, M. Z.; Arıkan, O.

    2014-10-28

    We investigated the tribological interaction between polytetrafluoroethylene (PTFE) and silicon oxide surfaces. A simple rig was designed to bring about a friction between the surfaces via sliding a piece of PTFE on a thermally oxidized silicon wafer specimen. A very mild inclination (∼0.5°) along the sliding motion was also employed in order to monitor the tribological interaction in a gradual manner as a function of increasing contact force. Additionally, some patterns were sketched on the silicon oxide surface using the PTFE tip to investigate changes produced in the hydrophobicity of the surface, where the approximate water contact angle was 45° before the transfer. The nature of the transferred materials was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS results revealed that PTFE was faithfully transferred onto the silicon oxide surface upon even at the slightest contact and SEM images demonstrated that stable morphological changes could be imparted onto the surface. The minimum apparent contact pressure to realize the PTFE transfer is estimated as 5 kPa, much lower than reported previously. Stability of the patterns imparted towards many chemical washing processes lead us to postulate that the interaction is most likely to be chemical. Contact angle measurements, which were carried out to characterize and monitor the hydrophobicity of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO{sub 2} surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained.

  1. Reporting central tendencies of chamber measured surface emission and oxidation

    SciTech Connect

    Abichou, Tarek; Clark, Jeremy; Chanton, Jeffery

    2011-05-15

    Methane emissions, concentrations, and oxidation were measured on eleven MSW landfills in eleven states spanning from California to Pennsylvania during the three year study. The flux measurements were performed using a static chamber technique. Initial concentration samples were collected immediately after placement of the flux chamber. Oxidation of the emitted methane was evaluated using stable isotope techniques. When reporting overall surface emissions and percent oxidation for a landfill cover, central tendencies are typically used to report 'averages' of the collected data. The objective of this study was to determine the best way to determine and report central tendencies. Results showed that 89% of the data sets of collected surface flux have lognormal distributions, 83% of the surface concentration data sets are also lognormal. Sixty seven percent (67%) of the isotope measured percent oxidation data sets are normally distributed. The distribution of data for all eleven landfills provides insight of the central tendencies of emissions, concentrations, and percent oxidation. When reporting the 'average' measurement for both flux and concentration data collected at the surface of a landfill, statistical analyses provided insight supporting the use of the geometric mean. But the arithmetic mean can accurately represent the percent oxidation, as measured with the stable isotope technique. We examined correlations between surface CH{sub 4} emissions and surface air CH{sub 4} concentrations. Correlation of the concentration and flux values using the geometric mean proved to be a good fit (R{sup 2} = 0.86), indicating that surface scans are a good way of identifying locations of high emissions.

  2. Surface Properties of Photo-Oxidized Bituminous Coals: Final report

    SciTech Connect

    1998-09-01

    Natural weathering has a detrimental effect on the hydrophobic nature of coal, which in turn can influence clean-coal recovery during flotation. Few techniques are available that can establish the quality of coal surfaces and that have a short analysis time to provide input for process control. Luminescence emissions which can be quantified with an optical microscope and photometer system, are measurably influenced by degree of weathering as well as by mild storage deterioration. In addition, it has been shown that when vitrinite is irradiated with a relatively high intensity flux of violet- or ultraviolet- light in the presence of air, photo-oxidation of the surface occurs. The combination of measuring the change in luminescence emission intensity with degree of surface oxidation provided the impetus for the current investigation. The principal aim of this research was to determine whether clear correlations could be established among surface oxygen functionality, hydrophobicity induced by photo-oxidation, and measurements of luminescence intensity and alteration. If successful, the project would result in quantitative luminescence techniques based on optical microscopy that would provide a measure of the changes in surface properties as a function of oxidation and relate them to coal cleanability. Two analytical techniques were designed to achieve these goals. Polished surfaces of vitrain bands or a narrow size fraction of powdered vitrain concentrates were photo-oxidized using violet or ultraviolet light fluxes and then changes in surface properties and chemistry were measured using a variety of near-surface analytical techniques. Results from this investigation demonstrate that quantitative luminescence intensity measurements can be performed on fracture surfaces of bituminous rank coals (vitrains) and that the data obtained do reveal significant variations depending upon the level of surface oxidation. Photo-oxidation induced by violet or ultraviolet light

  3. Surface oxidability of pure liquid metals and alloys

    NASA Astrophysics Data System (ADS)

    Arato, E.; Bernardi, M.; Giuranno, D.; Ricci, E.

    2012-01-01

    The analysis of the oxygen-liquid metal interaction is a topic of particular technological interest. A deep knowledge of the kinetics and transport mechanisms involved in the oxidation phenomena is necessary: the effect of oxidation reactions taking place in the gas phase and the evaporation of oxides must be considered. This paper aims to review our works in order to provide a systematic analysis of the oxidation of pure metals and determine the most likely to keeping oxygen-free the surface in a binary alloy. In addition, the upgrading of this theoretical approach, here briefly described, is addressed to give a contribution to a better understanding of the evolution of oxidation phenomena close to the solid-liquid-gas interfaces.

  4. 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

  5. The oxidation state of the surface of Venus. [Abstract only

    NASA Technical Reports Server (NTRS)

    Fegley, B., Jr.; Klingelhofer, G.; Brackett, R. A.; Izenberg, N.

    1994-01-01

    We present experimental results showing that basalt is oxidized in CO-CO2 gas mixtures having CO number densities close to those (approximately 2 times higher) at the surface of Venus. The results suggest that the red color observed by Pieters et al at the Venera 9 and 10 landing sites is due to subaerial oxidation of Fe(2+)-bearing basalt on the surface of Venus, and that hematite, instead of magnetite, is present on the surface of Venus. Well-characterized basalt powder was iosthermally heated in 1000 ppm CO-CO2 gas mixtures at atmospheric pressure for several days. The starting material and reacted samples were analyzed by Mossbauer spectroscopy to determine the amount of Fe(2+) and Fe(3+) in the samples. X-ray diffraction and optical microscopy were also used to characterize samples. The basalt oxidation occurs because the CO and CO2 do not equilibrate in the gas mixture at the low temperatures used. Thus, the basalt reacts with the more abundant CO2 and is oxidized. We propose that the red color of the surface of Venus is due to failure of CO and CO2 to equilibrate with one another in the near-surface atmosphere of Venus, leading to subaerial oxidation of erupted Fe(2+)-bearing basalts. Our interpretation is supported by our studies of magnetite oxidation, which show that synthetic magnetite powders are oxidized to hematite in CO-CO2 gas mixtures inside the magnetite stability field, by our studies of pyrite decomposition, and by independent work on CO-CO2 equilibration in furnace gases.

  6. 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.

  7. Surface Chemistry and Properties of Oxides as Catalyst Supports

    SciTech Connect

    DeBusk, Melanie Moses; Narula, Chaitanya Kumar; Contescu, Cristian I

    2015-01-01

    Heterogeneous catalysis relies on metal-oxides as supports for the catalysts. Catalyst supports are an indispensable component of most heterogeneous catalysts, but the role of the support is often minimized in light of the one played by the catalytically active species it supports. The active species of supported catalysts are located on the surface of the support where their contact with liquid or gas phase reactants will be greatest. Considering that support plays a major role in distribution and stability of active species, the absorption and retention of reactive species, and in some cases in catalytic reaction, the properties and chemistry that can occur at the surface of an oxide support are important for understanding their impact on the activity of a supported catalyst. This chapter examines this rich surface chemistry and properties of oxides used as catalyst supports, and explores the influence of their interaction with the active species.

  8. Process of forming catalytic surfaces for wet oxidation reactions

    NASA Technical Reports Server (NTRS)

    Jagow, R. B. (Inventor)

    1977-01-01

    A wet oxidation process was developed for oxidizing waste materials, comprising dissolved ruthenium salt in a reactant feed stream containing the waste materials. The feed stream is introduced into a reactor, and the reactor contents are then raised to an elevated temperature to effect deposition of a catalytic surface of ruthenium black on the interior walls of the reactor. The feed stream is then maintained in the reactor for a period of time sufficient to effect at least partial oxidation of the waste materials.

  9. Enhanced photothermal effect of surface oxidized silicon nanocrystals anchored to reduced graphene oxide nanosheets

    NASA Astrophysics Data System (ADS)

    Afshani, Parichehr; Moussa, Sherif; Atkinson, Garrett; Kisurin, Vitaly Y.; Samy El-Shall, M.

    2016-04-01

    We demonstrate the coupling of the photothermal effects of silicon nanocrystals and graphene oxide (GO) dispersed in water. Using laser irradiation (532 nm or 355 nm) of suspended Si nanocrystals in an aqueous solution of GO, the synthesis of surface oxidized Si-reduced GO nanocomposites (SiOx/Si-RGO) is reported. The laser reduction of GO is accompanied by surface oxidation of the Si nanocrystals resulting in the formation of the SiOx/Si-RGO nanocomposites. The SiOx/Si-RGO nanocomposites are proposed as promising materials for photothermal therapy and for the efficient conversion of solar energy into usable heat for a variety of thermal and thermomechanical applications.

  10. Reaction of ethanol on oxidized and metallic cobalt surfaces

    NASA Astrophysics Data System (ADS)

    Hyman, Matthew P.; Vohs, John M.

    2011-02-01

    The reaction of ethanol on metallic and oxidized cobalt surfaces was studied using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) in order to determine the dependence of the reaction pathways on the cobalt oxidation state. The primary reaction for ethoxide species on metallic cobalt surfaces was decarbonylation producing CO, H 2 and carbon. This reaction was facile and occurred below 400 K. In contrast, CoO x surfaces which predominantly contained Co 2+ were selective for the dehydrogenation of ethoxide groups to produce acetaldehyde at 400 K. A fraction of the acetaldehyde molecules produced by this pathway were further oxidized to acetate which decomposed to produce CO 2 at 495 K. More highly oxidized Co surfaces that contained both CO 2+ and Co 3+ were active for the complete oxidation of ethanol producing CO, CO 2, and H 2O as the primary products. The insights that these results provide for understanding the mechanism of the steam reforming of ethanol on cobalt catalysts is discussed.

  11. Mechanical tearing of graphene on an oxidizing metal surface

    NASA Astrophysics Data System (ADS)

    George, Lijin; Gupta, Aparna; Shaina, P. R.; Das Gupta, Nandita; Jaiswal, Manu

    2015-12-01

    Graphene, the thinnest possible anticorrosion and gas-permeation barrier, is poised to transform the protective coatings industry for a variety of surface applications. In this work, we have studied the structural changes of graphene when the underlying copper surface undergoes oxidation upon heating. Single-layer graphene directly grown on a copper surface by chemical vapour deposition was annealed under ambient atmosphere conditions up to 400 °C. The onset temperature of the surface oxidation of copper is found to be higher for graphene-coated foils. Parallel arrays of graphene nanoripples are a ubiquitous feature of pristine graphene on copper, and we demonstrate that these form crucial sites for the onset of the oxidation of copper, particularly for ˜0.3-0.4 μm ripple widths. In these regions, the oxidation proceeds along the length of the nanoripples, resulting in the formation of parallel stripes of oxidized copper regions. We demonstrate from temperature-dependent Raman spectroscopy that the primary defect formation process in graphene involves boundary-type defects rather than vacancy or sp3-type defects. This observation is consistent with a mechanical tearing process that splits graphene into small polycrystalline domains. The size of these is estimated to be sub-50 nm.

  12. 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.

  13. Cr(OH)₃(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)₃(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 μM) was reacted with or without synthesized Cr(OH)₃(s) (1.0 g/L) at pH 7 – 9 under oxic or anoxic conditions. In the absence of Cr(OH)₃(s), homogeneous Mn(II) oxidation by dissolved O₂ 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)₃(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)₃(s) was readily oxidized by a newly formed Mn oxide as a result of Mn(II) oxidation catalyzed on Cr(OH)₃(s) surface. XANES analysis of the residual solids after the reaction between 1.0 g/L Cr(OH)₃(s) and 204 μM 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)₃(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)₃(s) that can be a source of Cr(VI) in the presence of dissolved Mn(II).

  14. Local anodic oxidation patterning of Au deposited Si surfaces.

    PubMed

    Vijaykumar, T; Kulkarni, G U

    2009-09-01

    Nanopatterning of Si(100) surfaces deposited with Au films from physical and chemical methods, has been carried out using a AFM set up mounted with a conducting tip. At a tip bias of -12 V, the LAO patterns drawn on various Au/SiOx surfaces have been compared with those on bare Si. The height of the oxide patterns is several times higher in the case of Au covered Si surfaces compared to patterns on bare Si surface. The enhancement in LAO is related to the catalytic activity of Au nanoparticulates at SiOx interface. PMID:19928226

  15. Surface oxide growth on platinum electrode in aqueous trifluoromethanesulfonic acid.

    PubMed

    Furuya, Yoshihisa; Mashio, Tetsuya; Ohma, Atsushi; Dale, Nilesh; Oshihara, Kenzo; Jerkiewicz, Gregory

    2014-10-28

    Platinum in the form of nanoparticles is the key and most expensive component of polymer electrolyte membrane fuel cells, while trifluoromethanesulfonic acid (CF3SO3H) is the smallest fluorinated sulfonic acid. Nafion, which acts as both electrolyte and separator in fuel cells, contains -CF2SO3H groups. Consequently, research on the electrochemical behaviour of Pt in aqueous CF3SO3H solutions creates important background knowledge that can benefit fuel cell development. In this contribution, Pt electro-oxidation is studied in 0.1 M aqueous CF3SO3H as a function of the polarization potential (E(p), 1.10 ≤ E(p) ≤ 1.50 V), polarization time (t(p), 10(0) ≤ t(p) ≤ 10(4) s), and temperature (T, 278 ≤ T ≤ 333 K). The critical thicknesses (X1), which determines the applicability of oxide growth theories, is determined and related to the oxide thickness (d(ox)). Because X1 > d(ox) for the entire range of E(p), t(p), and T values, the formation of Pt surface oxide follows the interfacial place-exchange or the metal cation escape mechanism. The mechanism of Pt electro-oxidation is revised and expanded by taking into account possible interactions of cations, anions, and water molecules with Pt. A modified kinetic equation for the interfacial place exchange is proposed. The application of the interfacial place-exchange and metal cation escape mechanisms leads to an estimation of the Pt(δ+)-O(δ-) surface dipole (μ(PtO)), and the potential drop (V(ox)) and electric field (E(ox)) within the oxide. The Pt-anion interactions affect the oxidation kinetics by indirectly influencing the electric field within the double layer and the surface oxide. PMID:25362330

  16. Surface oxide growth on platinum electrode in aqueous trifluoromethanesulfonic acid

    NASA Astrophysics Data System (ADS)

    Furuya, Yoshihisa; Mashio, Tetsuya; Ohma, Atsushi; Dale, Nilesh; Oshihara, Kenzo; Jerkiewicz, Gregory

    2014-10-01

    Platinum in the form of nanoparticles is the key and most expensive component of polymer electrolyte membrane fuel cells, while trifluoromethanesulfonic acid (CF3SO3H) is the smallest fluorinated sulfonic acid. Nafion, which acts as both electrolyte and separator in fuel cells, contains -CF2SO3H groups. Consequently, research on the electrochemical behaviour of Pt in aqueous CF3SO3H solutions creates important background knowledge that can benefit fuel cell development. In this contribution, Pt electro-oxidation is studied in 0.1 M aqueous CF3SO3H as a function of the polarization potential (Ep, 1.10 ≤ Ep ≤ 1.50 V), polarization time (tp, 100 ≤ tp ≤ 104 s), and temperature (T, 278 ≤ T ≤ 333 K). The critical thicknesses (X1), which determines the applicability of oxide growth theories, is determined and related to the oxide thickness (dox). Because X1 > dox for the entire range of Ep, tp, and T values, the formation of Pt surface oxide follows the interfacial place-exchange or the metal cation escape mechanism. The mechanism of Pt electro-oxidation is revised and expanded by taking into account possible interactions of cations, anions, and water molecules with Pt. A modified kinetic equation for the interfacial place exchange is proposed. The application of the interfacial place-exchange and metal cation escape mechanisms leads to an estimation of the Ptδ+-Oδ- surface dipole (μPtO), and the potential drop (Vox) and electric field (Eox) within the oxide. The Pt-anion interactions affect the oxidation kinetics by indirectly influencing the electric field within the double layer and the surface oxide.

  17. Interactions of Graphene Oxide Nanomaterials with Natural Organic Matter and Metal Oxide Surfaces

    EPA Science Inventory

    Interactions of graphene oxide (GO) with silica surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration a...

  18. The technology of chromium oxide passivation on stainless steel surface

    SciTech Connect

    Ohmi, Tadahiro; Ohki, Atsushi; Nakamura, Masakazu; Kawada, Koji; Watanabe, Tsuyoshi; Nakagawa, Yoshinori; Miyoshi, Shinji; Takahashi, Shinji; Chen, M.S.K. . Dept. of Electronics)

    1993-06-01

    A complete chromium oxide (Cr[sub 2]O[sub 3]) passivation technology has been developed for stainless steel surfaces for use in high purity gas-delivery systems and process chambers. Starting with an electrochemical buffing (ECB) to add to electro-polished (EP) SUS316L stainless steel material, an optimal thermal treatment was found by using a gas mixture of 10% hydrogen, 1--10 ppm oxygen and argon balance gas at 500C for 1 h. Five-day corrosion tests with HCl gas (containing 1.4 ppm moisture) at 5 kg/cm[sup 2] and 100C showed no sign of corrosion on the chromium oxide passivated surface. Chemical stability tests on this surface with silane specialty gas thermal decomposition also showed a remarkable noncatalytic activity compared with conventional surfaces.

  19. Oxidative nanopatterning of titanium generates mesoporous surfaces with antimicrobial properties

    PubMed Central

    Variola, Fabio; Zalzal, Sylvia Francis; Leduc, Annie; Barbeau, Jean; Nanci, Antonio

    2014-01-01

    Mesoporous surfaces generated by oxidative nanopatterning have the capacity to selectively regulate cell behavior, but their impact on microorganisms has not yet been explored. The main objective of this study was to test the effects of such surfaces on the adherence of two common bacteria and one yeast strain that are responsible for nosocomial infections in clinical settings and biomedical applications. In addition, because surface characteristics are known to affect bacterial adhesion, we further characterized the physicochemical properties of the mesoporous surfaces. Focused ion beam (FIB) was used to generate ultrathin sections for elemental analysis by energy-dispersive X-ray spectroscopy (EDS), nanobeam electron diffraction (NBED), and high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging. The adherence of Staphylococcus aureus, Escherichia coli and Candida albicans onto titanium disks with mesoporous and polished surfaces was compared. Disks with the two surfaces side-by-side were also used for direct visual comparison. Qualitative and quantitative results from this study indicate that bacterial adhesion is significantly hindered by the mesoporous surface. In addition, we provide evidence that it alters structural parameters of C. albicans that determine its invasiveness potential, suggesting that microorganisms can sense and respond to the mesoporous surface. Our findings demonstrate the efficiency of a simple chemical oxidative treatment in generating nanotextured surfaces with antimicrobial capacity with potential applications in the implant manufacturing industry and hospital setting. PMID:24872694

  20. Oxidative nanopatterning of titanium generates mesoporous surfaces with antimicrobial properties.

    PubMed

    Variola, Fabio; Zalzal, Sylvia Francis; Leduc, Annie; Barbeau, Jean; Nanci, Antonio

    2014-01-01

    Mesoporous surfaces generated by oxidative nanopatterning have the capacity to selectively regulate cell behavior, but their impact on microorganisms has not yet been explored. The main objective of this study was to test the effects of such surfaces on the adherence of two common bacteria and one yeast strain that are responsible for nosocomial infections in clinical settings and biomedical applications. In addition, because surface characteristics are known to affect bacterial adhesion, we further characterized the physicochemical properties of the mesoporous surfaces. Focused ion beam (FIB) was used to generate ultrathin sections for elemental analysis by energy-dispersive X-ray spectroscopy (EDS), nanobeam electron diffraction (NBED), and high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging. The adherence of Staphylococcus aureus, Escherichia coli and Candida albicans onto titanium disks with mesoporous and polished surfaces was compared. Disks with the two surfaces side-by-side were also used for direct visual comparison. Qualitative and quantitative results from this study indicate that bacterial adhesion is significantly hindered by the mesoporous surface. In addition, we provide evidence that it alters structural parameters of C. albicans that determine its invasiveness potential, suggesting that microorganisms can sense and respond to the mesoporous surface. Our findings demonstrate the efficiency of a simple chemical oxidative treatment in generating nanotextured surfaces with antimicrobial capacity with potential applications in the implant manufacturing industry and hospital setting. PMID:24872694

  1. Formation and stability of surface oxides and oxide surfaces of the O/Cu system: First-principles investigations

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

    Copper-based catalysts are important for several industrial reactions, e.g., the low-temperature water-gas-shift reaction and for methanol oxidation reactions. Despite this, very little is presently known about the surface structure, about the atomic and molecular processes involved and the associated reaction pathways. As a first step towards a microscopic understanding, we use density-functional theory to investigate chemisorption of oxygen on Cu(111), and the stability of surface oxides and oxide surfaces. Surface oxide structures are found to be energetically favoured over chemisorbed oxygen even at coverages as low as 116,L. Taking into account the pressure and temperature through the framework of ab initio thermodynamics [1,2] however, shows that for the conditions relevant to technical catalysis, bulk oxide structures are the appropriate ones to consider. Our results are compared to the behavior of other O/transition-metal systems. [1] K. Reuter, C. Stampfl and M. Scheffler, in Handbook of Materials Modeling, Volume 1, Fundamental Models and Methods, Sidney Yip (Ed). [2] C. Stampfl, Catal. Today 105, 17 (2005).

  2. 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.

  3. 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.

  4. 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

  5. Oxidation of a platinum microwire surface applied in glucose detection

    NASA Astrophysics Data System (ADS)

    Pham Xuan, Thanh Tung; Thanh Tuyen Le, Thi; Duy Tran, Phu; Van Pham, Binh; Hien Tong, Duy; Chien Dang, Mau

    2010-06-01

    In this paper, we report the results of the surface oxidation of platinum (Pt) microwires in aqueous sulfuric acid (H2SO4) solutions by using a cyclic voltammetry technique. The Pt microwire chips were scanned and applied with voltage potentials ranging from 0 to 1.4 V in the H2SO4 solution with concentrations from 0.0003 to 0.0018 M to find out the optimized concentration of sulfuric acid for the oxidation process. The cyclic voltammetry (CV) measurements show the oxidation peak at a potential range from 1.1 to 1.2 V. This is the peak of the interfacial place exchange of chemisorbed O (Ochem) and surface Pt atoms, resulting in the formation of a quasi-3D surface PtO lattice comprising Pt2+ and O2‑. The oxidized surface Pt microwires were then functionalized with a 3-aminopropyl triethoxy silane (APTES) and glucose oxidase (GOD) was immobilized onto the functionalized chips for further application in glucose detection. By using this process, Pt microwires have been used for the successful detection of glucose in solution with concentrations in the range of 4–20 mM.

  6. Electrochemically-Controlled Compositional Oscillations of Oxide Surfaces

    SciTech Connect

    Mutoro, Eva; Crumlin, Ethan; Pöpke, Hendrik; Luerssen, Bjoern; Amati, Matteo; Abyaneh, Majid; Biegalski, Michael D; Christen, Hans M; Gregoratti, Luca; Janek, Jürgen; Shao-Horn, Yang

    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.

  7. The role of probe oxide in local surface conductivity measurements

    SciTech Connect

    Barnett, C. J.; Kryvchenkova, O.; Wilson, L. S. J.; Maffeis, T. G. G.; Cobley, R. J.; Kalna, K.

    2015-05-07

    Local probe methods can be used to measure nanoscale surface conductivity, but some techniques including nanoscale four point probe rely on at least two of the probes forming the same low resistivity non-rectifying contact to the sample. Here, the role of probe shank oxide has been examined by carrying out contact and non-contact I V measurements on GaAs when the probe oxide has been controllably reduced, both experimentally and in simulation. In contact, the barrier height is pinned but the barrier shape changes with probe shank oxide dimensions. In non-contact measurements, the oxide modifies the electrostatic interaction inducing a quantum dot that alters the tunneling behavior. For both, the contact resistance change is dependent on polarity, which violates the assumption required for four point probe to remove probe contact resistance from the measured conductivity. This has implications for all nanoscale surface probe measurements and macroscopic four point probe, both in air and vacuum, where the role of probe oxide contamination is not well understood.

  8. Bacterial adhesion to glass and metal-oxide surfaces.

    PubMed

    Li, Baikun; Logan, Bruce E

    2004-07-15

    Metal oxides can increase the adhesion of negatively-charged bacteria to surfaces primarily due to their positive charge. However, the hydrophobicity of a metal-oxide surface can also increase adhesion of bacteria. In order to understand the relative contribution of charge and hydrophobicity to bacterial adhesion, we measured the adhesion of 8 strains of bacteria, under conditions of low and high-ionic strength (1 and 100 mM, respectively) to 11 different surfaces and examined adhesion as a function of charge, hydrophobicity (water contact angle) and surface energy. Inorganic surfaces included three uncoated glass surfaces and eight metal-oxide thin films prepared on the upper (non-tin-exposed) side of float glass by chemical vapor deposition. The Gram-negative bacteria differed in lengths of lipopolysaccharides on their outer surface (three Escherichia coli strains), the amounts of exopolysaccharides (two Pseudomonas aeruginosa strains), and their known relative adhesion to sand grains (two Burkholderia cepacia strains). One Gram positive bacterium was also used that had a lower adhesion to glass than these other bacteria (Bacillus subtilis). For all eight bacteria, there was a consistent increase in adhesion between with the type of inorganic surface in the order: float glass exposed to tin (coded here as Si-Sn), glass microscope slide (Si-m), uncoated air-side float glass surface (Si-a), followed by thin films of (Co(1-y-z)Fe(y)Cr(z))3O4, Ti/Fe/O, TiO2, SnO2, SnO2:F, SnO2:Sb, A1(2)O3, and Fe2O3 (the colon indicates metal doping, a slash indicates that the metal is a major component, while the dash is used to distinguish surfaces). Increasing the ionic strength from 1 to 100 mM increased adhesion by a factor of 2.0 +/- 0.6 (73% of the sample results were within the 95% CI) showing electrostatic charge was important in adhesion. However, adhesion was not significantly correlated with bacterial charge and contact angle. Adhesion (A) of the eight strains was

  9. Polarization-driven catalysis via ferroelectric oxide surfaces.

    PubMed

    Kakekhani, Arvin; Ismail-Beigi, Sohrab

    2016-07-20

    The surface chemistry and physics of oxide ferroelectric surfaces with a fixed polarization state have been studied experimentally for some time. Here, we discuss the possibility of using these materials in a different mode, namely under cyclically changing polarization conditions achievable via periodic perturbations by external fields (e.g., temperature, strain or electric field). We use Density Functional Theory (DFT) and electronic structure analysis to understand the polarization-dependent surface physics and chemistry of ferroelectric oxide PbTiO3 as an example of this class of materials. This knowledge is then applied to design catalytic cycles for industrially important reactions including NOx direct decomposition and SO2 oxidation into SO3. The possibility of catalyzing direct partial oxidation of methane to methanol is also investigated. More generally, we discuss how using ferroelectrics under cyclically changing polarization conditions can help overcome some of the fundamental challenges facing the catalysis community such as the limitations imposed by the Sabatier principle and scaling relations. PMID:27381676

  10. Mechanically reliable surface oxides for high-temperature corrosion resistance

    SciTech Connect

    Natesan, K.; Veal, B.W.; Grimsditch, M.; Renusch, D.; Paulikas, A.P.

    1995-05-01

    Corrosion is widely recognized as being important, but an understanding of the underlying phenomena involves factors such as the chemistry and physics of early stages of oxidation, chemistry and bonding at the substrate/oxide interface, role of segregants on the strength of that bond, transport processes through scale, mechanisms of residual stress generation and relief, and fracture behavior at the oxide/substrate interface. Because of this complexity a multilaboratory program has been initiated under the auspices of the DOE Center of Excellence for the Synthesis and Processing of Advanced Materials, with strong interactions and cross-leveraging with DOE Fossil Energy and US industry. Objective is to systematically generate the knowledge required to establish a scientific basis for designing and synthesizing improved protective oxide scales/coatings (slow-growing, adherent, sound) on high-temperature materials without compromising the requisite properties of the bulk materials. The objectives of program work at Argonne are to (1) correlate actual corrosion performance with stresses, voids, segregants, interface roughness, initial stages of oxidation, and microstructures; (2) study such behavior in growing or as-grown films; and (3) define prescriptive design and synthesis routes to mechanically reliable surface oxides. Several techniques, such as Auger electron spectroscopy, X-ray diffraction, X-ray grazing incidence reflectance, grazing-angle X-ray fluorescence, optical fluorescence, and Raman spectroscopy, are used in the studies. Tne project has selected Fe-25 wt.% Cr-20 wt.% Ni and Fe-Cr-Al alloys, which are chromia- and alumina-formers respectively, for the studies. This paper presents some of the results on early stages of oxidation and on surface segregation of elements.

  11. Surface characteristics and in vitro biocompatibility of a manganese-containing titanium oxide surface

    NASA Astrophysics Data System (ADS)

    Park, Jin-Woo; Kim, Youn-Jeong; Jang, Je-Hee

    2011-11-01

    This study investigated the surface characteristics and in vitro biocompatibility of a titanium (Ti) oxide layer incorporating the manganese ions (Mn) obtained by hydrothermal treatment with the expectation of utilizing potent integrin-ligand binding enhancement effect of Mn for future applications as an endosseous implant surface. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, optical profilometry and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The in vitro biocompatibility of the Mn-containing Ti oxide surface was evaluated in comparison with untreated bare Ti using a mouse calvaria-derived osteoblastic cell line (MC3T3-E1). The hydrothermal treatment produced a nanostructured Mn-incorporated Ti oxide layer approximately 0.6 μm thick. ICP-AES analysis demonstrated that the Mn ions were released from the hydrothermally treated surface into the solution. Mn incorporation notably decreased cellular attachment, spreading, proliferation, alkaline phosphatase activity, and osteoblast phenotype gene expression compared with the bare Ti surface (p < 0.05). The results indicate that the Mn-incorporation into the surface Ti oxide layer has no evident beneficial effects on osteoblastic cell function, but instead, actually impaired cell behavior.

  12. 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.

  13. Hydrogen passivation and ozone oxidation of silicon surface

    SciTech Connect

    Kurokawa, Akira; Nakamura, Ken; Ichimura, Shingo

    1998-12-31

    The oxidation of H/Si(100) and H/Si(111) with high concentration ozone gas was investigated with X-ray photoelectron spectroscopy (XPS). The ozone oxidation of partially hydride-covered surface was observed. The hydrogen termination reduced the rate of oxygen insertion into silicon backbond. The reduction of oxygen insertion rate by the H-termination for H/Si(100) was larger than that for H/Si(111). The dissociation rate of ozone molecule on H/Si was estimated to be {approx_equal}0.2 with a directional mass analyzer.

  14. Sorption, desorption, and surface oxidative fate of nicotine.

    PubMed

    Petrick, Lauren; Destaillats, Hugo; Zouev, Irena; Sabach, Sara; Dubowski, Yael

    2010-09-21

    Nicotine dynamics in an indoor environment can be greatly affected by building parameters (e.g. relative humidity (RH), air exchange rate (AER), and presence of ozone), as well as surface parameters (e.g. surface area (SA) and polarity). To better understand the indoor fate of nicotine, these parameter effects on its sorption, desorption, and oxidation rates were investigated on model indoor surfaces that included fabrics, wallboard paper, and wood materials. Nicotine sorption under dry conditions was enhanced by higher SA and higher polarity of the substrate. Interestingly, nicotine sorption to cotton and nylon was facilitated by increased RH, while sorption to polyester was hindered by it. Desorption was affected by RH, AER, and surface type. Heterogeneous nicotine-ozone reaction was investigated by Fourier transform infrared spectrometry with attenuated total reflection (FTIR-ATR), and revealed a pseudo first-order surface reaction rate of 0.035 +/- 0.015 min(-1) (at [O(3)] = 6 +/- 0.3 x 10(15) molecules cm(-3)) that was partially inhibited at high RH. Extrapolation to a lower ozone level ([O(3)] = 42 ppb) showed oxidation on the order of 10(-5) min(-1) corresponding to a half-life of 1 week. In addition, similar surface products were identified in dry and high RH using gas chromatography-mass spectrometry (GC-MS). However, FTIR analysis revealed different product spectra for these conditions, suggesting additional unidentified products and association with surface water. Knowing the indoor fate of condensed and gas phase nicotine and its oxidation products will provide a better understanding of nicotine's impact on personal exposures as well as overall indoor air quality. PMID:20582338

  15. 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

  16. Ammonia modification of oxide-free Si(111) surfaces

    NASA Astrophysics Data System (ADS)

    Chopra, Tatiana Peixoto; Longo, Roberto C.; Cho, Kyeongjae; Chabal, Yves J.

    2016-08-01

    Amination of surfaces is useful in a variety of fields, ranging from device manufacturing to biological applications. Previous studies of ammonia reaction on silicon surfaces have concentrated on vapor phase rather than wet chemical processes, and mostly on clean Si surfaces. In this work, the interaction of liquid and vapor-phase ammonia is examined on three types of oxide-free surfaces - passivated by hydrogen, fluorine (1/3 monolayer) or chlorine - combining infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and first-principles calculations. The resulting chemical composition highly depends on the starting surface; there is a stronger reaction on both F- and Cl-terminated than on the H-terminated Si surfaces, as evidenced by the formation of Si-NH2. Side reactions can also occur, such as solvent reaction with surfaces, formation of ammonium salt by-products (in the case of 0.2 M ammonia in dioxane solution), and nitridation of silicon (in the case of neat and gas-phase ammonia reactions for instance). Unexpectedly, there is formation of Si-H bonds on hydrogen-free Cl-terminated Si(111) surfaces in all cases, whether vapor phase of neat liquid ammonia is used. The first-principles modeling of this complex system suggests that step-edge surface defects may play a key role in enabling the reaction under certain circumstances, despite the endothermic nature for Si-H bond formation.

  17. Electrocatalytic oxygen evolution at surface-oxidized multiwall carbon nanotubes.

    PubMed

    Lu, Xunyu; Yim, Wai-Leung; Suryanto, Bryan H R; Zhao, Chuan

    2015-03-01

    Large-scale storage of renewable energy in the form of hydrogen (H2) fuel via electrolytic water splitting requires the development of water oxidation catalysts that are efficient and abundant. Carbon-based nanomaterials such as carbon nanotubes have attracted significant applications for use as substrates for anchoring metal-based nanoparticles. We show that, upon mild surface oxidation, hydrothermal annealing and electrochemical activation, multiwall carbon nanotubes (MWCNTs) themselves are effective water oxidation catalysts, which can initiate the oxygen evolution reaction (OER) at overpotentials of 0.3 V in alkaline media. Oxygen-containing functional groups such as ketonic C═O generated on the outer wall of MWCNTs are found to play crucial roles in catalyzing OER by altering the electronic structures of the adjacent carbon atoms and facilitates the adsorption of OER intermediates. The well-preserved microscopic structures and highly conductive inner walls of MWCNTs enable efficient transport of the electrons generated during OER. PMID:25658670

  18. Influence of Surface Morphology on the Antimicrobial Effect of Transition Metal Oxides in Polymer Surface.

    PubMed

    Oh, Yoo Jin; Hubauer-Brenner, Michael; Hinterdorfer, Peter

    2015-10-01

    In this study, the physical properties of transition metal oxide surfaces were examined using scanning probe microscopic (SPM) techniques for elucidating the antimicrobial activity of molybdenum trioxide (MoO3), tungsten trioxide (WO3), and zinc oxide (ZnO) embedded into the polymers thermoplastic polyurethane (TPU) and polypropylene (PP). We utilized atomic force microscopy (AFM) in the contact imaging mode and its derivative single-pass Kelvin probe force microscopy for investigating samples that were presumably identical in their compositions, but showed different antimicrobial activity in bacterial adhesion tests. Our results revealed that surfaces with larger roughness and higher surface potential variation showed stronger antimicrobial activities compared to smoother and homogeneously charge-distributed surfaces. In addition, capacitance gradient (dC/dZ) measurements were performed to elucidate the antimicrobial activity arising from the different dielectric behavior of the transition metal oxides in this heterogeneous polymer surface. We found that the nano-scale exposure of transition metal oxides on polymer surfaces provided strong antimicrobial effects. Applications arising from our studies will be useful for public and healthcare environments. PMID:26726428

  19. Interaction of D{sub 2}O with model oxide single crystal surfaces: Clean and oxidized W(110)

    SciTech Connect

    Herman, G.S.; Gallagher, M.C.; Joyce, S.

    1995-12-31

    It has been suggested that the interaction of D{sub 2}O with single crystal oxide surfaces are dominated by defects. To investigate this we have prepared and then characterized oxidized W(110) surfaces with Auger electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy. We have also used temperature programmed desorption (TPD) to investigate the interaction of D{sub 2}O with these surfaces. Results indicate that desorption of D{sub 2}O occurs from two states for both the clean and fully oxidized surface. The decomposition of D{sub 2}O was found to occur on the clean surface but not for the fully oxidized surface. This is evident from the observation of residual oxygen remaining on the clean surface after a TPD cycle as well as the observation of two different D{sub 2} desorption features for the clean surface. On the fully oxidized surface neither occur.

  20. Water-Mediated Proton Hopping on an Iron Oxide Surface

    SciTech Connect

    Merte, L. R.; Peng, Guowen; Bechstein, Ralf; Rieboldt, Felix; Farberow, Carrie A.; Grabow, Lars C.; Kudernatsch, Wilhelmine; Wendt, Stefen; Laegsgaard, E.; Mavrikakis, Manos; Besenbacher, Fleming

    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 H3O+-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO2(110), where water dissociation is a key step in proton diffusion.

  1. Stochastic stick-slip nanoscale friction on oxide surfaces.

    PubMed

    Craciun, A D; Gallani, J L; Rastei, M V

    2016-02-01

    The force needed to move a nanometer-scale contact on various oxide surfaces has been studied using an atomic force microscope and theoretical modeling. Force-distance traces unveil a stick-slip movement with erratic slip events separated by several nanometers. A linear scaling of friction force with normal load along with low pull-off forces reveals dispersive adhesive interactions at the interface. We model our findings by considering a variable Lennard-Jones-like interaction potential, which accounts for slip-induced variation of the effective contact area. The model explains the formation and fluctuation of stick-slip phases and provides guidelines for predicting transitions from stick-slip to continuous sliding on oxide surfaces. PMID:26751769

  2. Surface oxidation - A major sink for water on Mars

    NASA Technical Reports Server (NTRS)

    Huguenin, R. L.

    1976-01-01

    Surface oxidation irreversibly removes both oxygen and hydrogen from the Martian atmosphere at a rate of 10 million-100 billion per square centimeter per second. This rate corresponds to a net loss of 100 to 100,000 grams per square centimeter of H2O, if it is assumed that the loss rate is uniform over geologic time. Heretofore, exospheric escape was considered to be the principal irreversible sink for H2O, but the loss rate was estimated to be only 100 million per square centimeter per second. It is possible that surface oxidation may have had a minor effect on the supply of H2O in the regolith and polar caps.

  3. Band energy control of molybdenum oxide by surface hydration

    SciTech Connect

    Butler, Keith T. Walsh, Aron; Crespo-Otero, Rachel; Buckeridge, John; Scanlon, David O.; Bovill, Edward; Lidzey, David

    2015-12-07

    The application of oxide buffer layers for improved carrier extraction is ubiquitous in organic electronics. However, the performance is highly susceptible to processing conditions. Notably, the interface stability and electronic structure is extremely sensitive to the uptake of ambient water. In this study we use density functional theory calculations to asses the effects of adsorbed water on the electronic structure of MoO{sub x}, in the context of polymer-fullerene solar cells based on PCDTBT. We obtain excellent agreement with experimental values of the ionization potential for pristine MoO{sub 3} (010). We find that IP and EA values can vary by as much as 2.5 eV depending on the oxidation state of the surface and that adsorbed water can either increase or decrease the IP and EA depending on the concentration of surface water.

  4. Kinetics and Mechanisms of Ciprofloxacin Oxidation on Hematite Surfaces.

    PubMed

    Martin, Sébastien; Shchukarev, Andrey; Hanna, Khalil; Boily, Jean-François

    2015-10-20

    Adsorption of antibiotics at mineral surfaces has been extensively studied over the past 20 years, yet much remains to be learned on their interfacial properties and transformation mechanisms. In this study, interactions of Ciprofloxacin (CIP), a fluoroquinolone antibiotic with two sets of synthetic nanosized hematite particles, with relatively smooth (H10, 10-20 nm in diameter) and roughened (H80, 80-90 nm in diameter) surfaces, were studied by means of liquid chromatography (LC), mass spectrometry (MS), and spectroscopy (vibration and X-ray photoelectron). Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy provides evidence for inner-sphere bidentate complex formation of CIP at hematite surfaces in 0.01 M NaCl, irrespective of pH and particle size. ATR-FTIR spectroscopy also revealed that the sorbed mother CIP molecule decayed to other surface species over a period of at least 65 h. This was supported by the detection of three daughter products in the aqueous phase by LC/MS. The appearance of NH3(+) groups during the course of these experiments, revealed by cryogenic XPS, provides further evidence that CIP oxidation proceeds through an opening of piperazine ring via N-dealkylation. Additional in vacuo FTIR experiments under temperature-programmed desorption also showed that oxidation of sorbed byproducts were effectively degraded beyond 450 °C, a result denoting considerably strong (inter)molecular bonds of both mother and daughter products. This work also showed that rougher, possibly multidomainic particles (H80) generated slower rates of CIP decomposition but occurring through more complex schemes than at smoother particle surfaces (H10). This work thus uncovered key aspects of the binding of an important antibiotic at iron oxide surfaces, and therefore provided additional constraints to our growing understanding of the fate of emerging contaminants in the environment. PMID:26419340

  5. 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.

  6. The role of nitric oxide in ocular surface cells.

    PubMed

    Kim, Jae Chan; Park, Gun Sic; Kim, Jin Kook; Kim, Young Myeong

    2002-06-01

    The role of nitric oxide (NO) in the ocular surface remains unknown. We investigated the conditions leading to an increase of NO generation in tear and the main sources of NO in ocular surface tissue. We evaluated the dual action (cell survival or cell death) of NO depending on its amount. We measured the concentration of nitrite plus nitrate in the tears of ocular surface diseases and examined the main source of nitric oxide synthase (NOS). When cultured human corneal fibroblast were treated with NO producing donor with or without serum, the viabilities of cells was studied. We found that the main sources of NO in ocular surface tissue were corneal epithelium, fibroblast, endothelium, and inflammatory cells. Three forms of NOS (eNOS, bNOS, and iNOS) were expressed in experimentally induced inflammation. In the fibroblast culture system, the NO donor (SNAP, S-nitroso-N-acetyl-D, L-penicillamine) prevented the death of corneal fibroblast cells caused by serum deprivation in a dose dependent manner up to 500 micrometer SNAP, but a higher dose decreased cell viability. This study suggested that NO might act as a double-edged sword in ocular surface diseases depending on the degree of inflammation related with NO concentration. PMID:12068145

  7. Photocurrent spectroscopy of Ge nanoclusters grown on oxidized silicon surface

    NASA Astrophysics Data System (ADS)

    Mykytiuk, A. A.; Kondratenko, S. V.; Lysenko, V. S.; Kozyrev, Yu. N.

    2014-05-01

    Germanium (Ge) nanoclusters are grown by a molecular-beam epitaxy technique on chemically oxidized Si(100) surface at 700ºC. Evidence for long-term photoinduced changes of surface conductivity in structures with Ge nanoclusters (NCs) grown on silicon oxide is presented. Photoexcitation NCs or Si by quanta with different energy allows observing two non-equilibrium steady-states with excess and shortage of conductivity values as compare to equilibrium one. The persistent photoconductivity (PPC) behaviour was observed after interband excitation of electron-hole pairs in Si(001) substrate. This effect may be attributed to spatial carrier separation of photoexcited electron-hole pairs by macroscopic fields in the depletion layer of near-surface Si. Photoquenching of surface conductivity, driven by optical recharging of Ge NC's and Si/SiO2 interface states, is observed. Conductivity decay is discussed in the terms of hole`s accumulation by Ge-NC states enhancing the local-potential variations and, therefore, decreasing the surface conductivity of p-Si.

  8. 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

  9. Nano- and Micro-Scale Oxidative Patterning of Titanium Implant Surfaces for Improved Surface Wettability.

    PubMed

    Kim, In-hye; Son, Jun Sik; Choi, Seok Hwa; Kim, Kyo-han; Kwon, Tae-yub

    2016-02-01

    A simple and scalable surface modification treatment is demonstrated, in which nano- and microscale features are introduced into the surface of titanium (Ti) substrates by means of a novel and eco-friendly oxidative aqueous solution composed of hydrogen peroxide (H202) and sodium bicarbonate (NaHCO3). By immersing mirror-polished Ti discs in an aqueous mixture of 30 wt% H2O2/5 wt% NaHCO3 at 23 +/- 3 degrees C for 4 h, it was confirmed that this mixture is capable of generating microscale topographies on Ti surfaces. It also simultaneously formed nanochannels that were regularly arranged in a comb-like pattern on the Ti surface, thus forming a hierarchical surface structure. Further, these nano/micro-textured Ti surfaces showed great surface roughness and excellent wettability when compared with control Ti surfaces. This study demonstrates that a H2O2/NaHCO3 mixture can be effectively utilized to create reproducible nano/microscale topographies on Ti implant surfaces, thus providing an economical new oxidative solution that may be used effectively and safely as a Ti surface modification treatment. PMID:27433692

  10. Quantitative DEMS study of ethanol oxidation: effect of surface structure and Sn surface modification.

    PubMed

    Mostafa, Ehab; Abd-El-Latif, Abd-El-Aziz A; Ilsley, Richard; Attard, Gary; Baltruschat, Helmut

    2012-12-14

    Using the dual thin layer flow through cell, a semi-quantitative analysis of the volatile products during the electrooxidation of adsorbed and bulk solution of 0.01 M ethanol at polycrystalline platinum, smooth, roughened and Sn modified Pt(11,1,1), Pt(311) electrodes has been done by on-line differential electrochemical mass spectroscopy (DEMS). In addition to the current efficiency of CO(2), that of acetaldehyde was determined as a function of the flow rate. At polycrystalline platinum, ethanol oxidation produces only acetaldehyde; the amount of acetaldehyde further oxidized to acetic acid is negligible due to convection conditions. For comparison and for calibration purposes, i-propanol oxidation was examined for which acetone is the only oxidation product. At Pt(11,1,1), the main oxidation product is acetaldehyde. At Pt(311), in addition to acetaldehyde, acetic acid was also formed. Surface modification with Sn did not increase the reactivity of Pt(11,1,1) instead it led to inhibition of the ethanol oxidation. In the case of Pt(311), the onset potential of oxidation was shifted negatively by 0.2 V in the presence of Sn. The results of the potentiostatic measurements showed that this shift is not associated with the production of CO(2); rather acetic acid and acetaldehyde are the main oxidation products. PMID:23108295

  11. 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

  12. Adsorption of T4 bacteriophages on planar indium tin oxide surface via controlled surface tailoring.

    PubMed

    Liana, Ayu Ekajayanthi; Chia, Ed Win; Marquis, Christopher P; Gunawan, Cindy; Gooding, J Justin; Amal, Rose

    2016-04-15

    The work investigates the influence of surface physicochemical properties of planar indium tin oxide (ITO) as a model substrate on T4 bacteriophage adsorption. A comparative T4 bacteriophage adsorption study shows a significant difference in bacteriophage adsorption observed on chemically modified planar ITO when compared to similarly modified particulate ITO, which infers that trends observed in virus-particle interaction studies are not necessarily transferrable to predict virus-planar surface adsorption behaviour. We also found that ITO surfaces modified with methyl groups, (resulting in increased surface roughness and hydrophobicity) remained capable of adsorbing T4 bacteriophage. The adsorption of T4 onto bare, amine and carboxylic functionalised planar ITO suggests the presence of a unique binding behaviour involving specific functional groups on planar ITO surface beyond the non-specific electrostatic interactions that dominate phage to particle interactions. The paper demonstrates the significance of physicochemical properties of surfaces on bacteriophage-surface interactions. PMID:26851452

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

    SciTech Connect

    Minaye Hashemi, Fatemeh Sadat; Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne ; Thombare, Shruti; Brongersma, Mark L.; Morral, Anna Fontcuberta i; McIntyre, Paul C.; Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305

    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.

  14. Surface Proton Hopping and Coupling Pathway of Water Oxidation on Cobalt Oxide Catalyst

    NASA Astrophysics Data System (ADS)

    Pham, Hieu; Cheng, Mu-Jeng; Frei, Heinz; Wang, Lin-Wang

    We propose an oxidation pathway of water splitting on cobalt oxide surface with clear thermodynamic and kinetic details. The density-functional theory studies suggest that the coupled proton-electron transfer is not necessarily sequential and implicit in every elementary step of this mechanistic cycle. Instead, the initial O-O bond could be formed by the landing of water molecule on the surface oxos, which is then followed by the dispatch of protons through the hopping manner and subsequent release of di-oxygen. Our theoretical investigations of intermediates and transition states indicate that all chemical conversions in this pathway, including the proton transfers, are possible with low activation barriers, in addition to their favorable thermodynamics. Our hypothesis is supported by recent experimental observations of surface superoxide that is stabilized by hydrogen bonding to adjacent hydroxyl group, as an intermediate on fast-kinetics catalytic site.

  15. Atomistic Mechanism of Surface-Oxide Formation on Ru(0001)

    NASA Astrophysics Data System (ADS)

    Reuter, K.; Ganduglia-Pirovano, M. V.; Scheffler, M.; Stampfl, C.

    2001-03-01

    CO-oxidation catalysis on Ruthenium is a prime example of the pressure and materials gap in the sense, that a very low activity under UHV conditions is contrasted with very high turnover rates at high pressures. A recent experimental study has connected this change in activity with the formation of RuO_2(110) patches on the surface (H. Over et al., Science 287, 1474 (2000)). In order to analyze the atomistic mechanism behind this surface oxide formation, we perform density functional theory calculations for more and more O loaded Ru(0001) surfaces. After a full monolayer coverage on the surface has been reached, O starts to penetrate into the sample. Instead of diffusing further into the bulk, oxygen agglomerates in subsurface islands between the first and second substrate layers. These islands can be characterized as a O-Ru-O trilayer ``floating'' on top of the Ru(0001) substrate. Further O incorporation leads to a successive formation of such O-Ru-O trilayers, which at first remain in a CaF2 type stacking sequence. After a critical thickness has been exceeded, we finally observe a phase transition into the experimentally seen rutile RuO_2(110) structure.

  16. Surface activity of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers

    SciTech Connect

    Alexandridis, P.; Athanassiou, V.; Fukuda, Shinya; Hatton, T.A. )

    1994-08-01

    The surface tension of aqueous solutions of seven poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) Pluronic copolymers, covering a wide range of molecular weights (3400-14600) and PPO/PEO ratios (0.19-1.79), was determined over the 10[sup [minus]5]-10% w/v concentration range, at two temperatures (25 and 35[degree]C). Two breaks (changes in slope) were observed in the surface tension vs log concentration curve for most of the copolymers. The low-concentration break, occurring at bulk copolymer concentrations of approximately 10[sup [minus]3]%, is believed to originate from rearrangement of the copolymer molecules on the surface at complete coverage of the air/water interface. The breaks at the high-concentration part of the surface tension curve occurred at concentrations that correspond to the critical micellization concentration values as determined by a dye solubilization technique. The surface area per copolymer molecule, A, increased as a function of the number of EO segments, N[sub EO], obeying a scaling law (A [approx] N[sub EO][sup 1/2]) similar to that of lower molecular weight C[sub i]E[sub j] nonionic surfactants. 56 refs., 6 figs., 2 tabs.

  17. 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.

  18. How strain affects the reactivity of surface metal oxide catalysts.

    PubMed

    Amakawa, Kazuhiko; Sun, Lili; Guo, Chunsheng; Hävecker, Michael; Kube, Pierre; Wachs, Israel E; Lwin, Soe; Frenkel, Anatoly I; Patlolla, Anitha; Hermann, Klaus; Schlögl, Robert; Trunschke, Annette

    2013-12-16

    Highly dispersed molybdenum oxide supported on mesoporous silica SBA-15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2-2.5 Mo atoms nm(-2) ). X-ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO4 units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature-programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O-K-edge at high Mo loadings are explained by distorted MoO4 complexes. Limited availability of anchor silanol groups at high loadings forces the MoO4 groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity. PMID:24259425

  19. 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

  20. Oxide-Confined Vertical-Cavity Surface-Emitting Lasers

    NASA Astrophysics Data System (ADS)

    Liu, W. L.; Li, L.; Zhong, J. C.; Zhao, Y. J.; Zeng, L. N.; Yan, C. L.

    Novel distributed Bragg reflectors (DBRs) with 6-pair-GaAs/AlAs short period superlattice for the oxide-confined vertical-cavity surface-emitting lasers (VCSEL) are designed. They are for the VCSEL that emits at 840 nm and is grown with 34-period n-type mirrors, three-quantum-well active region, and 22-period p-type mirrors. In addition, a 35-nm-layer of Al0.98Ga0.02As was inserted in the top mirrors for being selectively oxidized. The maximum output power is more than 2 mW with low threshold current of about 2 mA. The fact that the device's threshold current in both CW and pulsed operation depends slightly on the operation temperature shows its higher characteristic temperature (T0).

  1. 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.

  2. Effect of surface roughness on the texture and oxidation behavior of Zircaloy-4 cladding tube

    NASA Astrophysics Data System (ADS)

    Akhiani, Hamed; Szpunar, Jerzy A.

    2013-11-01

    Conventional pressure water reactors like CANDU use Zircaloy-4 as a fuel cladding tube. Surface roughness that arises from the manufacturing process, pilgering, may alter these tubes' properties in various ways. This paper presents a comparative study of cladding tubes with different surface conditions in order to investigate their effect on the Zircaloy-4 substrate and oxide textures as well as the oxidation kinetic. The experimental results reveal that surface roughness affects the oxidation rate and weight gain of the cladding tubes. Although surface polishing slightly changes the substrate texture, it induces no significant change in the oxide texture. Moreover, oxidation time does not significantly change the preferred orientation of the zirconium oxide.

  3. Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis.

    PubMed

    Hozumi, Atsushi; McCarthy, Thomas J

    2010-02-16

    Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis for probe liquids were prepared by chemical vapor deposition (CVD) of bis((tridecafluoro-1,1,2,2,-tetrahydrooctyl)-dimethylsiloxy)methylsilane (CF(3)(CF(2))(5)CH(2)CH(2)Si(CH(3))(2)O)(2)SiCH(3)H, (R(F)Si(Me)(2)O)(2)SiMeH). Oxidized aluminum surfaces were prepared by photooxidation/cleaning of sputter-coated aluminum on silicon wafers (Si/Al(Al(2)(O(3)))) using oxygen plasma. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) confirmed that this facile CVD method produces a monolayer with a thickness of 1.1 nm on the Si/Al(Al(2)(O(3))) surface without a discernible change in surface morphology. After monolayer deposition, the hydrophilic Si/Al(Al(2)(O(3))) surface became both hydrophobic and oleophobic and exhibited essentially no contact angle hysteresis for water and n-hexadecane (advancing/receding contact angles (theta(A)/theta(R)) = 110 degrees/109 degrees and 52 degrees/50 degrees, respectively). Droplets move very easily on this surface and roll off of slightly tilted surfaces, independently of the contact angle (which is a practical definition of ultralyophobic). A conventional fluoroalkylsilane monolayer was also prepared from 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (CF(3)(CF(2))(7)CH(2)CH(2)Si(OCH(3))(3), R(F)Si(OMe)(3)) for comparison. The theta(A)/theta(R) values for water and n-hexadecane are 121 degrees/106 degrees and 76 degrees/71 degrees, respectively. The larger hysteresis values indicate the "pinning" of probe liquids, even though advancing contact angles are larger than those of the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers. The (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers have excellent hydrolytic stability in water. We propose that the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers are flexible and liquidlike and that drops in contact with these surfaces experience very low energy barriers between metastable states, leading to the

  4. Positive Biomechanical Effects of Titanium Oxide for Sandblasting Implant Surface as an Alternative to Aluminium Oxide.

    PubMed

    Gehrke, Sergio Alexandre; Taschieri, Silvio; Del Fabbro, Massimo; Coelho, Paulo Guilherme

    2015-10-01

    The aim of this study was to evaluate the physico-chemical properties and the in vivo host response of a surface sandblasted with particles of titanium oxide (TiO2) followed by acid etching as an alternative to aluminium oxide. Thirty titanium disks manufactured in the same conditions as the implants and 24 conventional cylindrical implants were used. Half of the implants had a machined surface (Gcon) while in the other half; the surface was treated with particles of TiO2 followed by acid etching (Gexp). Surface characterization was assessed by scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS), profilometry, and wettability. For the in vivo test, 12 implants of each group were implanted in the tibia of 6 rabbits, and were reverse torque tested after periods of 30 or 60 days after implantation. Following torque, SEM was utilized to assess residual bone-implant contact. The surface characterization by SEM showed a very homogeneous surface with uniform irregularities for Gexp and a small amount of residues of the blasting procedure, while Gcon presented a surface with minimal irregularities from the machining tools. Wettability test showed decreased contact angle for the Gcon relative to the Gexp. The Gexp removal torque at 30 and 60 days was 28.7%, and 33.2% higher relative to the Gcon, respectively. Blasting the surface with particles of TiO2 represents an adequate option for the surface treatment of dental implants, with minimal risk of contamination by the residual debris from the blasting procedure. PMID:24001048

  5. 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.

  6. How surface reparation prevents catalytic oxidation of carbon monoxide on atomic gold at defective magnesium oxide surfaces.

    PubMed

    Töpfer, Kai; Tremblay, Jean Christophe

    2016-07-21

    In this contribution, we study using first principles the co-adsorption and catalytic behaviors of CO and O2 on a single gold atom deposited at defective magnesium oxide surfaces. Using cluster models and point charge embedding within a density functional theory framework, we simulate the CO oxidation reaction for Au1 on differently charged oxygen vacancies of MgO(001) to rationalize its experimentally observed lack of catalytic activity. Our results show that: (1) co-adsorption is weakly supported at F(0) and F(2+) defects but not at F(1+) sites, (2) electron redistribution from the F(0) vacancy via the Au1 cluster to the adsorbed molecular oxygen weakens the O2 bond, as required for a sustainable catalytic cycle, (3) a metastable carbonate intermediate can form on defects of the F(0) type, (4) only a small activation barrier exists for the highly favorable dissociation of CO2 from F(0), and (5) the moderate adsorption energy of the gold atom on the F(0) defect cannot prevent insertion of molecular oxygen inside the defect. Due to the lack of protection of the color centers, the surface becomes invariably repaired by the surrounding oxygen and the catalytic cycle is irreversibly broken in the first oxidation step. PMID:27345190

  7. Electrochemical chlorine evolution at rutile oxide (110) surfaces.

    PubMed

    Hansen, Heine A; Man, Isabela C; Studt, Felix; Abild-Pedersen, Frank; Bligaard, Thomas; Rossmeisl, Jan

    2010-01-01

    Based on density functional theory (DFT) calculations we study the electrochemical chlorine evolution reaction on rutile (110) oxide surfaces. First we construct the Pourbaix surface diagram for IrO(2) and RuO(2), and from this we find the chlorine evolution reaction intermediates and identify the lowest overpotential at which all elementary reaction steps in the chlorine evolution reaction are downhill in free energy. This condition is then used as a measure for catalytic activity. Linear scaling relations between the binding energies of the intermediates and the oxygen binding energies at cus-sites are established for MO(2) (M being Ir, Ru, Pt, Ti). The linear relations form the basis for constructing a generalized surface phase diagram where two parameters, the potential and the binding energy of oxygen, are needed to determine the surface composition. We calculate the catalytic activity as function of the oxygen binding energy, giving rise to a Sabatier volcano. By combining the surface phase diagram and the volcano describing the catalytic activity, we find that the reaction mechanism differs depending on catalyst material. The flexibility in reaction path means that the chlorine evolution activity is high for a wide range of oxygen binding energies. We find that the required overpotential for chlorine evolution is lower than the overpotential necessary for oxygen evolution. PMID:20024470

  8. Step dynamics and oxide formation during CO oxidation over a vicinal Pd surface.

    PubMed

    Shipilin, Mikhail; Gustafson, Johan; Zhang, Chu; Merte, Lindsay Richard; Lundgren, Edvin

    2016-07-27

    In an attempt to bridge the material and pressure gaps - two major challenges for an atomic scale understanding of heterogeneous catalysis - we employed high-energy surface X-ray diffraction as a tool to study the Pd(553) surface in situ under changing reaction conditions during CO oxidation. The diffraction patterns recorded under CO rich reaction conditions are characteristic for the metallic state of the surface. In an environment with low excess of O2 over the reaction stoichiometry, the surface seems to accommodate oxygen atoms along the steps forming one or several subsequent adsorbate structures and rapidly transforms into a combination of (332), (111) and (331) facets likely providing the room for the formation of a surface oxide. For the case of large excess of O2, the diffraction data show the presence of a multilayer PdO with the [101] crystallographic direction parallel to the [111] and the [331] directions of the substrate. The reconstructions in O2 excess are to a large extent similar to those previously reported for pure O2 exposures by Westerström et al. [R. Westerström et al., Phys. Rev. B: Condens. Matter Mater. Phys., 2007, 76, 155410]. PMID:26805438

  9. Dopamine biosensor based on surface functionalized nanostructured nickel oxide platform.

    PubMed

    Roychoudhury, Appan; Basu, Suddhasatwa; Jha, Sandeep Kumar

    2016-10-15

    A dopamine biosensor has been developed using nickel oxide nanoparticles (NPs) and tyrosinase enzyme conjugate. Nickel oxide (NiO) NPs were synthesized by sol-gel method using anionic surfactant, sodium dodecyl sulphate (SDS), as template to control the size of synthesized nanoparticles. The structural and morphological studies of the prepared NPs were carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. Afterwards, tyrosinase enzyme molecules were adsorbed on NiO NPs surface and enzyme coated NPs were deposited on indium tin oxide (ITO) coated flexible polyethylene terephthalate (PET) substrate by solution casting method. The formation of enzyme-NPs conjugate was investigated by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) techniques and used in selective detection and estimation of neurochemical dopamine by electrochemical method. The fabricated Tyrosinase/NiO/ITO electrode exhibits high sensitivity of 60.2nA/µM in linear detection range (2-100μM) with a detection limit of 1.038μM. The proposed sensor had a response time of 45s, long shelf life (45 days) with good reproducibility and selectivity in presence of interfering substances and was validated with real samples. The tyrosinase enzyme functionalized NiO platform has good bio-sensing efficacy and can be used in detection of other catecholamines and phenolic neurochemicals. PMID:26626970

  10. The electrochemisty of surface modified <10 nm metal oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Roberts, Joseph J. P.

    Chapter One provides a general introduction of the research on metal oxide nanoparticles (MOx), highlighting their synthesis, surface modification, and functionalization. Emphasis is given to the different synthetic route for producing small (<10 nm) MOx nanoparticles with narrow size distributions. Different methods for modifying their surface with small organic molecules are discussed with focus given to silanes and phosphates. Furthermore, functionalizing surface modified nanoparticles for specific functions is addressed, with markers for analytically relevant nanoscale quantification being the primary focus. Chapter Two describes in detail the thermal degradation synthesis used for the generation of small MOx nanoparticles. It demonstrates the versatile of the synthesis by successfully synthesizing ZrO 2 and IrO2 nanoparticles. Preliminary work involving the formation of Bi2S3, Bi2O3, and RuO2 nanomaterials is also addressed. The solvothermal synthesis of indium tin oxide (ITO) is also shown for comparison to ITO produced by thermal degradation. Chapter Three details the surface modification of ITO nanoparticles and subsequent electrochemical tagging with a ferrocene moiety. ITO nanoparticles were synthesized via thermal degradation. These nanoparticles underwent a ligand exchange with a covalently binding mondentate silane terminated with a primary amine. Acyl chloride coupling between the amine and chlorocarbonylferrocene provided an electrochemical tag to quantify the level of surface modification. Electrochemisty of the quasi-diffusing nanoparticles was evaluated via cyclic voltammetry (CV), chronoamperometry (CA), and mircodisk electrode (microE) experiments. Chapter Four investigates spectroscopic tagging of ITO and ZrO2 nanoparticles as well as electrochemical tagging of ZrO 2 and IrO2 nanoparticles. An unbound azo-dye was synthesized and attempts were made to attach the dye to the surface of ITO nanoparticles. Imine couple between a spectroscopic tag

  11. Oxidic copper on the Au(111) surface: A theoretical surface science approach

    NASA Astrophysics Data System (ADS)

    Lee, Taehun; Lee, Yonghyuk; Kang, Kisung; Soon, Aloysius

    Recently, via reactive Cu deposition in an oxygen ambience, high quality gold-supported cuprous oxide (Cu2O) ultrathin nanofilms have been prepared as a model system to further such catalytic studies. Nonetheless, an accurate atomic picture of these ultrathin Cu2O nanofilms, which largely depends on its immediate oxygen environment, is currently lacking. In this work, we perform density-functional theory (DFT) calculations using the Vienna ab initio Simulation Package in combination with ab initio atomistic thermodynamics to investigate stability of Cu2O thin films on Au(111) as a function of oxygen chemical potential. Our results indeed show that some of the surface structures suggested in Ref. are energetically more stable than the traditional copper oxide thin film structures on copper substrate, and elucidated the electronic structure of these ultrathin copper oxide films on gold, in comparison with available experimental data.

  12. Photochemistry of adsorbed nitrate on aluminum oxide particle surfaces.

    PubMed

    Rubasinghege, Gayan; Grassian, Vicki H

    2009-07-01

    Nitrogen oxides, including nitrogen dioxide and nitric acid, react with mineral dust particles in the atmosphere to yield adsorbed nitrate. Although nitrate ion is a well-known chromophore in natural waters, little is known about the surface photochemistry of nitrate adsorbed on mineral particles. In this study, nitrate adsorbed on aluminum oxide, a model system for mineral dust aerosol, is irradiated with broadband light (lambda > 300 nm) as a function of relative humidity (RH) in the presence of molecular oxygen. Upon irradiation, the nitrate ion readily undergoes photolysis to yield nitrogen-containing gas-phase products including NO(2), NO, and N(2)O, with NO being the major product. The relative ratio and product yields of these gas-phase products change with RH, with N(2)O production being highest at the higher relative humidities. Furthermore, an efficient dark reaction readily converts the major NO product into NO(2) during post-irradiation. Photochemical processes on mineral dust aerosol surfaces have the potential to impact the chemical balance of the atmosphere, yet little is known about these processes. In this study, the impact that adsorbed nitrate photochemistry may have on the renoxification of the atmosphere is discussed. PMID:19534452

  13. Surface Phonon Dispersion of the Layered Transition-metal Oxides

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Ismail; Matzdorf, R.; Plummer, E. W.; Kimura, T.; Tokura, Y.

    2000-03-01

    Transition-metal oxides exhibit strong coupling between the charge and spin of the electrons and the lattice. Creating a surface by cleaving a single crystal breaks the symmetry of the lattice and disturbs the correlated system without changing the stoichiometry, providing the opportunity to study the response of electronic, structural, and magnetic properties. We have utilized electron-energy loss sprectroscopy (EELS) to study the electronic and lattice excitations of the Sr_2RuO4 and La_0.5Sr_1.5MnO4 surfaces. For both of these materials there are many more than three modes; three dominate surface optical phonons with small dispersion and with higher energies compared to those in the bulk materials. However, these phonons show completely different temperature dependence for different samples. The surface phonons become soft for Sr_2RuO4 while they become stiff for La_0.5Sr_1.5MnO4 with increasing temparature. The change of phonon energy of La_0.5Sr_1.5MnO4 with temperature is also in opposite direction to that of (La, Ca)MnO_4( Zhang et al., Surf. Sci. 393, 64(1997) * LMER Corp. for U.S. DOE under contract No. DE-AC05-96OR22464). These behaviors will be discussed in terms of the electronic, magnetic, and structural properties.

  14. Increased corrosion resistance of stent materials by converting current surface film of polycrystalline oxide into amorphous oxide.

    PubMed

    Shih, C C; Lin, S J; Chung, K H; Chen, Y L; Su, Y Y

    2000-11-01

    Current efforts of new stent technology have been aimed largely at the improvement of intravascular stent biocompatibility. Among the chemical characteristics of metallic stents, surface oxide corrosion properties are paramount. Using our unique technique, the currently marketed 316 L stainless steel and nitinol stent wires covered with polycrystalline oxide were chemically etched and then passivated to form amorphous oxide. Excellent metallic-stent corrosion resistance with an amorphous oxide surface was demonstrated in our previous in vitro study. For in vivo validation, we compared the corrosion behavior of different oxide surfaces on various forms of test wires in the abdominal aorta of mongrel dogs using open-circuit potential and cyclic anodic polarization measurements. After conduction, the retrieved test wires were observed under scanning electron microscope. No passivity breakdown was found for wires covered with amorphous oxide, while wires with polycrystalline oxide showed breakdown at potentials between +0.2 to + 0.6 V. It has been proven that severe pitting or crevice corrosion occurred on the surface of polycrystalline oxide, while the surface of amorphous oxide was free of degradations in our experiment. We have demonstrated that this amorphous oxide coating on metallic material provides better corrosion resistance, not only in vitro but also in vivo, and it is superior not only in strength safety but also in medical device biocompatibility. PMID:10951371

  15. Surface evolution at nanoscale during oxidation: A competing mechanism between local curvature effect and stress effect

    NASA Astrophysics Data System (ADS)

    Fang, Xufei; Li, Yan; Wang, Dan; Lu, Siyuan; Feng, Xue

    2016-04-01

    The process of surface evolution of a chemically etched stepped structure at nanoscale during oxidation at 600 °C is in situ and real time observed using scanning probe microscope, which is integrated in a nanoindentation equipment for high temperature test. Experimental results reveal that this curved stepped structure becomes flat after being oxidized for a short period of time. However, after a longer time of oxidation, it is observed that the originally flat surface near the stepped structure becomes rough. Analysis shows that such a surface evolution is attributed to the competition between the nanoscale curvature effect (related to surface energy) and the stress developed in the oxide film during oxidation (related to strain energy). It is demonstrated that both the surface energy and strain energy can modify the surface chemical potential, which acts as the driving force of the surface diffusion of oxygen and further affects the oxide formation on the surface.

  16. Surface and interfacial reaction study of InAs(100)-crystalline oxide interface

    SciTech Connect

    Zhernokletov, D. M.; Laukkanen, P.; Dong, H.; Brennan, B.; Kim, J.; Galatage, R. V.; Yakimov, M.; Tokranov, V.; Oktyabrsky, S.; Wallace, R. M.; Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080

    2013-05-27

    A crystalline oxide film on InAs(100) is investigated with in situ monochromatic x-ray photoelectron spectroscopy and low energy electron diffraction before and after in situ deposition of Al{sub 2}O{sub 3} by atomic layer deposition (ALD) as well as upon air exposure. The oxidation process leads to arsenic and indium trivalent oxidation state formation. The grown epitaxial oxide-InAs interface is stable upon ALD reactor exposure; however, trimethyl aluminum decreases oxidation states resulting in an unreconstructed surface. An increase in oxide concentration is also observed upon air exposure suggesting the crystalline oxide surface is unstable.

  17. Methane oxidation and methane fluxes in the ocean surface layer and deep anoxic waters

    NASA Technical Reports Server (NTRS)

    Ward, B. B.; Kilpatrick, K. A.; Novelli, P. C.; Scranton, M. I.

    1987-01-01

    Measured biological oxidation rates of methane in near-surface waters of the Cariaco Basin are compared with the diffusional fluxes computed from concentration gradients of methane in the surface layer. Methane fluxes and oxidation rates were investigated in surface waters, at the oxic/anoxic interface, and in deep anoxic waters. It is shown that the surface-waters oxidation of methane is a mechanism which modulates the flux of methane from marine waters to the atmosphere.

  18. 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

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

    SciTech Connect

    Sun, Shiyu; 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.

  20. 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.

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

    SciTech Connect

    Hoppe, Eric W.; Seifert, Allen; Aalseth, Craig E.; Bachelor, Paula P.; Day, Anthony R.; Edwards, Danny J.; Hossbach, Todd W.; Litke, Kevin E.; McIntyre, Justin I.; Miley, Harry S.; Schulte, Shannon M.; Smart, John E.; Warren, Glen A.

    2007-08-21

    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+/Cu2+ 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. © 2001 Elsevier Science. All rights reserved

  2. Behavior of Al on Clean and Oxidized GaAs(110) Surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Hyunwoo

    1993-04-01

    The adsorption of Al on clean and oxidized GaAs(110) surfaces was studied. The characteristics of an oxide surface formed in vacuum and during the chemical etching process of the tip have been investigated using the field desorption (FD) cleaning method and the retarding potential analyzer (RPA) equipped with an argon laser. The results obtained for the FD clean surface and on the oxidized surface are discussed in terms of the RPA threshold and work function change. The oxide films formed at relatively low temperatures on the GaAs(110) surface can easily be desorbed by FD. The intrinsic potential drops across the oxide surface disappear suddenly at a certain field value. This may indicate that the desorbed surface region is composed of a metallic species such as Ga. Changes in work function are observed but there is no change in the threshold values (Vth) with deposition of Al on the field-desorbed clean surface. The thick layers of Al on the oxidized surface completely cancel the effect of oxide on Vth, which decreases to the value of a metallic clean surface. In addition, the value of Vth decreases dramatically to that of a metallic clean surface by absorption of the laser beam on the oxidized surface, whereas only the thermal effect is seen on a metallic clean surface.

  3. High surface area, electrically conductive nanocarbon-supported metal oxide

    SciTech Connect

    Worsley, Marcus A.; Han, Thomas Yong-Jin; Kuntz, Joshua D.; Cervantes, Octavio; Gash, Alexander E.; Baumann, Theodore F.; Satcher, Jr., Joe H.

    2015-07-14

    A metal oxide-carbon composite includes a carbon aerogel with an oxide overcoat. The metal oxide-carbon composite is made by providing a carbon aerogel, immersing the carbon aerogel in a metal oxide sol under a vacuum, raising the carbon aerogel with the metal oxide sol to atmospheric pressure, curing the carbon aerogel with the metal oxide sol at room temperature, and drying the carbon aerogel with the metal oxide sol to produce the metal oxide-carbon composite. The step of providing a carbon aerogel can provide an activated carbon aerogel or provide a carbon aerogel with carbon nanotubes that make the carbon aerogel mechanically robust.

  4. High surface area, electrically conductive nanocarbon-supported metal oxide

    SciTech Connect

    Worsley, Marcus A; Han, Thomas Yong-Jin; Kuntz, Joshua D; Cervanted, Octavio; Gash, Alexander E; Baumann, Theodore F; Satcher, Jr., Joe H

    2014-03-04

    A metal oxide-carbon composite includes a carbon aerogel with an oxide overcoat. The metal oxide-carbon composite is made by providing a carbon aerogel, immersing the carbon aerogel in a metal oxide sol under a vacuum, raising the carbon aerogel with the metal oxide sol to atmospheric pressure, curing the carbon aerogel with the metal oxide sol at room temperature, and drying the carbon aerogel with the metal oxide sol to produce the metal oxide-carbon composite. The step of providing a carbon aerogel can provide an activated carbon aerogel or provide a carbon aerogel with carbon nanotubes that make the carbon aerogel mechanically robust.

  5. Interaction of ester functional groups with aluminum oxide surfaces studied using infrared reflection absorption spectroscopy.

    PubMed

    van den Brand, J; Blajiev, O; Beentjes, P C J; Terryn, H; de Wit, J H W

    2004-07-20

    The bonding of two types of ester group-containing molecules with a set of different oxide layers on aluminum has been investigated using infrared reflection absorption spectroscopy. The different oxide layers were made by giving typical surface treatments to the aluminum substrate. The purpose of the investigation was to find out what type of ester-oxide bond is formed and whether this is influenced by changes in the composition and chemistry of the oxide. The extent by which these bonded ester molecules resisted disbondment in water or substitution by molecules capable of chemisorption was also investigated. The ester groups were found to show hydrogen bonding with hydroxyls on the oxide surfaces through their carbonyl oxygens. For all oxides, the ester groups showed the same nu(C = O) carbonyl stretching vibration after adsorption, indicating very similar bonding occurs. However, the oxides showed differences in the amount of molecules bonded to the oxide surface, and a clear relation was observed with the hydroxyl concentration present on the oxide surface, which was determined from XPS measurements. The two compounds showed differences in the free to bonded nu(C = O) infrared peak shift, indicating differences in bonding strength with the oxide surface between the two types of molecules. The bonding of the ester groups with the oxide surfaces was found to be not stable in the presence of water and also not in the presence of a compound capable of chemisorption with the aluminum oxide surface. PMID:15248718

  6. 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

  7. Physicochemistry of the surface of and exoemission from magnesium oxide

    NASA Astrophysics Data System (ADS)

    Krylova, I. V.

    2010-02-01

    To optimize the processes of obtaining MgO with the highest possible exoemission intensity and time of decay, the influence of dehydration conditions and the subsequent adsorption of active gases (H2, O2, and H2O vapor) on its parameters was investigated. The nature of adsorption centers and exoemission is discussed, based on the results obtained using the latest literature data on dehydration processes, as are the formation of defects on the MgO surface (coloring centers) and their interaction with hydrogen and oxygen. Due to the introduction of exoemissionally active MgO in the manufacturing of plasma displays, the literature data dealing with the exposure of extremely active grains of oxide monocrystals containing exoemission centers (OH-groups) are examined.

  8. Molecular-level assemblies on metal oxide surfaces

    SciTech Connect

    Schoonover, J.R.; Bignozzi, C.; Meyer, T.

    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. Photochemistry of nitrate chemisorbed on various metal oxide surfaces.

    PubMed

    Lesko, Daniel M B; Coddens, Ellen M; Swomley, Hannah D; Welch, Rachel M; Borgatta, Jaya; Navea, Juan G

    2015-08-28

    Atmospheric aerosols are known to provide an important surface for gas-solid interfaces that can lead to heterogeneous reactions impacting tropospheric chemistry. In this work, α-Fe2O3, TiO2, γ-Al2O3, SiO2 and ZnO, common components of atmospheric aerosols, served as models to investigate the gas-solid interface of nitric acid with aerosols in the presence of simulated solar radiation. Adsorbed nitrate and gaseous products can be continuously monitored with infrared spectroscopy (IR). Kinetic studies of adsorbed species were carried out using attenuated total reflectance infrared spectroscopy (ATR-FTIR). Ex situ simultaneous infrared spectroscopy of gas-phase products using a 2 m long path cell allowed the detection of gaseous products at early stages of the heterogeneous photochemical reaction. In addition, photoactive gaseous products, such as HONO, were detected as gas analysis was carried out outside the region of irradiation. All reactions were found to be first order with respect to adsorbed nitric acid and yielded gas-phase products such as NO, NO2, N2O4, N2O, and HONO. While the correlation between semiconductor properties of the metal oxide and the heterogeneous photochemical rate constant (j) is not direct, the semiconductor properties were found to play a role in the formation of relatively high proportions of greenhouse gas nitrous oxide (N2O). PMID:26214064

  10. Superoleophobic textured copper surfaces fabricated by chemical etching/oxidation and surface fluorination.

    PubMed

    Ou, Junfei; Hu, Weihua; Liu, Sheng; Xue, Mingshan; Wang, Fajun; Li, Wen

    2013-10-23

    We report a convenient route to fabricate superoleophobic surfaces (abridged as SOS) on copper substrate by combining a two-step surface texturing process (first, the substrate is immersed in an aqueous solution of HNO3 and cetyltrimethyl ammonium bromide, and then in an aqueous solution of NaOH and (NH4)2S2O8) and succeeding surface fluorination with 1H,1H,2H,2H-perfluorodecanethiol (PFDT) or 1-decanethiol. The surface morphologies and compositions were characterized by field emission scanning electron microscopy and X-ray diffraction, respectively. The results showed that spherical micro-pits (SMP) with diameter of 50-100 μm were formed in the first step of surface texturing; in the second step, Cu(OH)2 or/and CuO with structures of nanorods/microflowers/microballs were formed thereon. The surface wettability was further assessed by optical contact angle meter by using water (surface tension of 72.1 mN m(-1) at 20°C), rapeseed oil (35.7 mN m(-1) at 20°C), and hexadecane (25.7 mN m(-1) at 20°C) as probe liquids. The results showed that, as the surface tension decreasing, stricter choosing of surface structures and surface chemistry are required to obtain SOS. Specifically, for hexadecane, which records the lowest surface tension, the ideal surface structures are a combination of densely distributed SMP and nanorods, and the surface chemistry should be tuned by grafted with low-surface-energy molecules of PFDT. Moreover, the stability of the so-fabricated sample was tested and the results showed that, under the testing conditions, superhydrophobicity and superoleophobicity may be deteriorated after wear/humidity resistance test. Such deterioration may be due to the loss of outermost PFDT layer or/and the destruction of the above-mentioned ideal surface structures. For UV and oxidation resistance, the sample remained stable for a period of 10 days. PMID:24073938

  11. The role of the substrate structure in the on-surface synthesis of organometallic and covalent oligophenylene chains.

    PubMed

    Dai, Jingya; Fan, Qitang; Wang, Tao; Kuttner, Julian; Hilt, Gerhard; Gottfried, J Michael; Zhu, Junfa

    2016-07-27

    The influences of the substrate structure on the formation of one-dimensional organometallic and covalent oligomers on a Cu(110) surface were studied using scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), and low energy electron diffraction (LEED) in ultrahigh vacuum (UHV). Vapor deposition of submonolayer 4,4''-dibromo-meta-terphenyl (DMTP) onto a Cu(110) surface at 300 K leads to scission of C-Br bonds and the formation of organometallic chains (cis/trans and all-trans) connected by C-Cu-C bonds. Larger islands (120 × 120 nm(2)) of all-trans zigzag organometallic chains as sole products were obtained by the deposition of DMTP onto Cu(110) held at 383 K. The domains are oriented along two directions with an angle of ±13° relative to the [0 0 1] direction due to the two-fold symmetry of the Cu(110) surface lattice. This study reveals at a sub-molecular level that the organometallic chains firstly lose copper atoms and then undergo C-C coupling into oligophenylene chains at a substrate temperature around 417 K. Annealing the large islands of organometallic chains at 458 K results in the formation of completely C-C covalently bonded zigzag oligophenylene chains. The zigzag angle of 125° slightly deviates from the ideal value of 120°. This is attributed to a stretching of the zigzag oligophenylene chains due to substrate template effects. PMID:27411742

  12. On the mechanism of carbon monoxide oxidation on the surface of gold nanoclusters supported on titanium oxide

    NASA Astrophysics Data System (ADS)

    Tvauri, I. V.; Remar, D. F.; Turiev, A. M.; Tsidaeva, N. I.; Fukutani, K.; Magkoev, T. T.

    2010-05-01

    The process of carbon monoxide (CO) oxidation on the surface of a system comprising nanodimensional gold clusters deposited onto thin films of titanium oxide of variable stoichiometry formed on a Re(1000) single crystal surface has been studied by methods of thermodesorption, IR, and X-ray photoelectron spectroscopy. It is established that oxygen contained in titanium oxide plays an important role in the conversion of CO into CO2. The efficiency of this process on the Au/TiO x ( x < 2) system surface is significantly higher that that on the Au/TiO2 system.

  13. Oxidation of step edges on vicinal 4H-SiC(0001) surfaces

    SciTech Connect

    Li, Wenbo; Zhu, Qiaozhi; Wang, Dejun; Zhao, Jijun

    2013-11-18

    The oxidation processes of stepped SiC(0001) surfaces are studied within the ab initio atomistic thermodynamics approach. Our calculations show that a one-dimensional -Si-O- chain structure as a precursor for oxide growth on stepped SiC surfaces is formed along the step edge, promoting further oxidation of the step edges. Following the modified Deal-Grove oxidation model, we also find that the oxidation rate at steps is higher than that at terraces by three orders of magnitude. These findings give a reasonable explanation for the oxide thickness fluctuation between the step and the terrace observed in the previous experiments.

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

    SciTech Connect

    Boffa, A B

    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.

  15. Modification of surface oxide layers of titanium targets for increasing lifetime of neutron tubes

    SciTech Connect

    Zakharov, A. M. Dvoichenkova, O. A.; Evsin, A. E.

    2015-12-15

    The peculiarities of interaction of hydrogen ions with a titanium target and its surface oxide layer were studied. Two ways of modification of the surface oxide layers of titanium targets for increasing the lifetime of neutron tubes were proposed: (1) deposition of an yttrium oxide barrier layer on the target surface; (2) implementation of neutron tube work regime in which the target is irradiated with ions with energies lower than 1000 eV between high-energy ion irradiation pulses.

  16. Modification of surface oxide layers of titanium targets for increasing lifetime of neutron tubes

    NASA Astrophysics Data System (ADS)

    Zakharov, A. M.; Dvoichenkova, O. A.; Evsin, A. E.

    2015-12-01

    The peculiarities of interaction of hydrogen ions with a titanium target and its surface oxide layer were studied. Two ways of modification of the surface oxide layers of titanium targets for increasing the lifetime of neutron tubes were proposed: (1) deposition of an yttrium oxide barrier layer on the target surface; (2) implementation of neutron tube work regime in which the target is irradiated with ions with energies lower than 1000 eV between high-energy ion irradiation pulses.

  17. 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.

  18. Bond selectivity in the dissociative adsorption of c-CH 2N 2 on single crystals: a comparative DFT-LSD investigation for Pd(110) and Cu(110)

    NASA Astrophysics Data System (ADS)

    Rochefort, Alain; McBreen, Peter H.; Salahub, Dennis R.

    1996-02-01

    A comparison between the reactivity of palladium and copper cluster models toward diazirine ( c-CH 2N 2) was made using the LCGTO-MCP-LSD method. Adsorption with the nitrogen pair directly over surface atoms (the μ-top site) is clearly more stable than when the NN pair is perpendicular to the rows of the (110) surface (the μ-bridge site). The NN bond is strongly affected by adsorption, a significant decrease of its bond order is observed for both palladium and copper. One main difference between palladium and copper with regards to the adsorption of c-CH 2N 2 is the magnitude of the MN bond order; palladium tends to form a stronger chemisorption bond than copper. A second difference is that partial occupation of the LUMO of diazirine only occurs for the copper cluster model systems. The concerted dissociation of CN bonds is energetically demanding but appears to be easier on Pd than on Cu by around 28 kcal mol -1. The study of electronically perturbed diazirine (excited, ionized or isomerized) provides insight on how chemisorption induces variations in bond lengths and vibrational frequencies as a result of charge transfer. The results of the calculations show that the μ-top adsorbed state is more similar to the n_ →π∗ first excited state of the free molecule than to the ionized state. A more striking result is obtained when the first excited states of the chemisorbed complexes are studied. A 0.4 eV electron excitation in the {c- CH2N2}/{Cu4} complex (μ-top) leads to a significant decrease of the bond order of the NN bond but does not induce even a small change for the {c- CH2N2}/{Pd4} complex. The calculations provide some insights on the markedly different bond scission selectivity observed in experimental studies of the thermal decomposition of diazirine on Pd and Cu surfaces. Experiments show that NN bond scission occurs with essentially 100% selectivity on copper, whereas NN bond retention as well as NN bond scission occurs on Pd(110).

  19. Electroless coating of tungsten oxide on the surface of copper powder

    SciTech Connect

    Ahn, Jae-Hoon; Lee, Jin-Kyu; Kim, Dong-Woo; Jung, Young-Soo; Kim, Gil-Pyo; Baeck, Sung-Hyeon

    2008-08-04

    Tungsten oxide was successfully deposited on the surface of copper powder and the thickness of coating layer was dependent on deposition time. Because a spontaneous reaction occurred on the interface between copper and tungsten-peroxo electrolyte, there was a maximum thickness that could be obtained, as confirmed from XRD and EDX results. Mesoporous tungsten oxide was also deposited using SDS as a structure directing agent. As-synthesized tungsten oxide was amorphous and, after calcination at 450 deg. C, crystallized tungsten oxide was produced. Compared to pure tungsten oxide, the tungsten oxide coated copper oxide showed enhanced absorption in the visible region.

  20. Adsorption of carbon oxide and nitrogen oxide molecules on the surface of the Ni/MgO(111) system

    NASA Astrophysics Data System (ADS)

    Magkoev, T. T.; Turiev, A. M.; Tsidaeva, N. I.; Pantileev, D. G.

    2009-10-01

    The coadsorption of carbon oxide (CO) and nitrogen oxide (NO) molecules on the surface of nickel nanoclusters formed on a thin magnesium oxide MgO(111) film grown on the Mo(110) face in an ultrahigh vacuum is studied by reflective infrared spectroscopy and thermodesorption spectroscopy (TDS). The adsorption of NO molecules is found to substantially change the state of the initially adsorbed CO molecules. The TDS and IR spectra suggest that the adsorption of NO molecules stimulates the surface migration of CO molecules from the surface of metallic clusters to the cluster-oxide interface, which is accompanied by a decrease in the angle of inclination of the molecular axis to the surface.

  1. 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.

  2. Surface composition and texture of titanium polished with colloidal silica suspension and chromic oxide slurry.

    PubMed

    Hossain, Awlad; Okawa, Seigo; Miyakawa, Osamu

    2005-09-01

    CP titanium was polished with a colloidal silica suspension and chromic oxide slurry under low and high pressures. The polished surfaces were characterized by means of EPMA and XPS. Irrespective of polishing pressure, colloidal silica suspension successfully created a mirror-like surface that was clean at EPMA level. However, XPS detected a small amount of silicon on the outermost surface. On the other hand, chromic oxide slurry under high pressure yielded a very uneven surface with numerous scratches. The EPMA and XPS results suggested the presence of chromium-containing species in the polished surface, which might include hydroxides as well as oxides. In addition, the level of oxygen concentration was noticeably raised, which probably resulted from the increase of surface oxide film thickness or the extension of oxide-to-metal transition zone. PMID:16279732

  3. 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.

  4. Surface plasmon resonance biochip based on ZnO thin film for nitric oxide sensing.

    PubMed

    Feng, Wei-Yi; Chiu, Nan-Fu; Lu, Hui-Hsin; Shih, Hsueh-Ching; Yang, Dongfang; Lin, Chii-Wann

    2008-01-01

    In this study, the design of a novel optical sensor that comprises surface plasmon resonance sensing chip and zinc oxide nano-film was proposed for the detection of nitric oxide gas. The electrical and optical properties of zinc oxide film vary in the presence of nitric oxide. This effect was utilized to prepare biochemical sensors with transduction based on surface plasmon resonance. Due to the refractive index of the transparent zinc oxide film that was deposited on the gold film, however, changes will be observed in the surface plasmon resonance spectra. For this reason, the thickness of zinc oxide film will be investigated and determined in this study. The interaction of nitric oxide with a 20 nm zinc oxide layer on gold leads to the shift of the resonance angle. The analysis on the reflectance intensity of light demonstrates that such effect is caused by the variation of conductivity and permittivity of zinc oxide film. Finally, a shift in surface plasmon resonance angle was measured in 25 ppm nitric oxide at 180 C and a calibration curve of nitride oxide concentration versus response intensity was successfully obtained in the range of 250 to 1000 ppm nitric oxide at lower temperature of 150 C. Moreover, these effects are quasi-reversible. PMID:19164025

  5. Study on Oxidation of Cu and Cu3Au Surfaces with Hyperthermal Oxygen Molecular Beam

    NASA Astrophysics Data System (ADS)

    Okada, Michio; Teraoka, Yuden

    Corrosion wastes more than a few percent of the world's GDP every year. The initial stage of the corrosion is one of the central topics in material science. The oxidation is one of the major corrosion processes of metals. Thus, the study of the oxidation process on metal surfaces is generally interesting in various fields of science and technology. The growth of a protective thin surface layer, which prevents further oxidation into bulk of a metal, requires the formation of a homogeneous film. One simple way for the protection of underlying metals is surface alloying, combining different substances to form multi-component surfaces. The surface alloying leads to the formation of a protective oxide layer due to the preferential oxidation of one component, possibly with surface segregation. Copper and copper alloys have wide industrial applications, and therefore are of interest for studies of oxidation mechanism, especially in the Cu2O formation. Cu forms the stable Cu2O, while Au does not form a stable oxide and is not soluble into stable Cu2O. Thus, the Cu-Au alloy system is ideal for investigating the effect of alloying on the formation of protective layer against further oxidation into bulk. Here, we introduce our recent comparative studies of the oxidation of Cu(100) and Cu3Au(100) with hyperthermal O2 molecular beam and discuss why Cu3Au(100) is protective against the oxidation.

  6. Interfacial electrochemistry of pyrite oxidation and flotation. 1: Effect of borate on pyrite surface oxidation

    SciTech Connect

    Wang, X.H.

    1996-03-25

    The interfacial chemistry of pyrite is of great industrial importance in complex sulfide ore flotation, coal desulfurization, acid mine drainage mitigation, and conversion of solar energy to electrical or chemical energy. Sodium tetraborate (Na{sub 2}B{sub 4}O{sub 7}) has been widely used as an electrolyte and pH buffer in studying the interfacial electrochemistry of sulfide minerals in relation to sulfide mineral flotation. In all the previous studies published so far, borate was regarded as an inert electrolyte/pH buffer, and its reactions with the sulfide minerals were completely overlooked. In this first part of this series papers, the complicating effects of borate on the interfacial electrochemistry of pyrite have been studied. In the borate solutions, the surface oxidation of pyrite is strongly enhanced. The first and rate-determining step of the reaction between borate and pyrite has been shown to be the following irreversible reaction: FeS{sub 2} + B(OH){sub 4}{sup {minus}} {yields} FeS{sub 2} {hor_ellipsis} [B(OH){sub 4}]{sub ads} + e. This reaction appears in the voltammogram as an anodic oxidation peak at potentials of more than 0.4 V lower than the commencement of pyrite oxidation in sodium perchlorate or nitrate electrolyte solutions. As the borate concentration increases, the peak current increases linearly, while the peak potential shifts positively at 240 mV per decade. On a rotating-disc electrode, the peak becomes a plateau. The limiting current density is a linear function of the square root of the rotation speed at relatively low rotation speeds. The Tafel slope is close to 240 mV per decade and is independent of the rotation speed and borate concentration. The results indicate that charge transfer coefficient is 0.25.

  7. Surface behaviour in deuterium permeation through erbium oxide coatings

    NASA Astrophysics Data System (ADS)

    Chikada, T.; Suzuki, A.; Adelhelm, C.; Terai, T.; Muroga, T.

    2011-06-01

    Suppression of tritium permeation through structural materials is essential in order to mitigate fuel loss and radioactivity concerns. Ceramic coatings have been investigated for over three decades as tritium permeation barriers (TPBs); however, a very limited number of investigations on the mechanism of hydrogen-isotope permeation through the coatings have been reported. In this study, deuterium permeation behaviour of erbium oxide coatings fabricated by filtered arc deposition on reduced activation ferritic/martensitic steels has been investigated. The samples coated on both sides of the substrates showed remarkably lower permeability than those coated on one side, and the maximum reduction efficiency indicated a factor of 105 compared with the substrate. The different permeation behaviour between the coatings facing the high and low deuterium pressure sides has been found by the crystal structure analysis and the evaluation of the energy barriers. It is suggested that the permeation processes on the front and back surfaces are independent, and the TPB efficiency of the samples coated on both sides can be expressed by a multiplication of that of each side.

  8. Electrospun nickel oxide nanofibers: Microstructure and surface evolution

    NASA Astrophysics Data System (ADS)

    Khalil, Abdullah; Hashaikeh, Raed

    2015-12-01

    Nickel oxide (NiO) nanofibers with controlled microstructure were synthesized through the electrospinning technique using a solution composed of nickel acetate and polyvinyl alcohol. The microstructure of NiO nanofibers was found to be highly dependent on nickel acetate concentration in the solution and the post-heat treatment. As the nickel acetate concentration increases, the crystallinity index of NiO nanofibers increases from nearly 50 percent to 90 percent and the average crystallite size in the nanofibers increases from about 20 nm to 30 nm. Further, it was found that annealing the nanofibers at 1000 °C for 2 h leads to nearly full crystallization of nanofibers with significant increase in the crystallite size to about 50 nm while maintaining the fibrous shape. For low nickel acetate concentration, and because of the small nanofibers size, the surface of the calcined nanofibers showed oxygen deficiency which promises a superior activity of these NiO nanofibers for catalytic and sensing applications.

  9. [Preparation of anodic oxidation layer on the surface of pure titanium and its biological activity study].

    PubMed

    Gao, Shuchun; Zhai, Yuchun; Hu, Jinling

    2010-09-01

    This paper introduces how TiO2 film was prepared on pure titanium by anodic oxidation. Surface morphology and composition of the oxide film were analyzed by SEM coupled with EDAX. The deposition ability of hydroxyapatite of the anodized titanium in simulated body fluid (SBF) at 37 degrees C was evaluated. The results indicated that the oxide film was rough and honeycomb holes, connecting with each other, could be found on the surface. The holes with the diameter of 1-2 microm were distributed uniformly, which was typical for anodic oxidation. After alkaline treatment, hydroxyapatite deposition on the oxidized specimens in SBF was improved significantly. PMID:21179705

  10. Study of the active surface on titanium oxide catalysts for the oxidation of hydrogen sulfide

    SciTech Connect

    Khanmamedov, T.K.; Kalinkin, A.V.; Rakhimova, N.R.

    1989-02-01

    A study was carried out on the change in the composition of a Ti-Mo-W catalyst depending on the conditions for their treatment by H/sub 2/S-SO/sub 2/ and H/sub 2/S-O/sub 2/ gas mixtures, which serve as models for the technological gases in Klaus apparatuses and the direct catalytic oxidation of H/sub 2/S. X-ray photoelectron spectroscopy was used to establish the formation of sulfur as S/sup 2/minus// and S/sup 6+/ on the surface. The presence of S/sup 6+/ along with the changes in E/sub b/ of the electrons in the T-Mo-W catalyst indicates the formation of MoS/sub 2/ and TiO(SO/sub 4/) species.

  11. Mechanism of the Initial Oxidation of Hydrogen andHalogen Terminated Ge(111) Surfaces in Air

    SciTech Connect

    Sun, Shiyu; Sun, Yun; Liu, Zhi; Lee, Dong-Ick; Pianetta, Piero; /SLAC, SSRL

    2006-08-23

    The initial stage of the oxidation of Ge(111) surfaces etched by HF, HCl and HBr solutions is systematically studied using synchrotron radiation photoelectron spectroscopy (SR-PES). We perform controlled experiments to differentiate the effects of different oxidation factors. SR-PES results show that both moisture and oxygen contribute to the oxidation of the surfaces; however, they play different roles in the oxidation process. Moisture effectively replaces the hydrogen and halogen termination layers with hydroxyl (OH), but hardly oxidizes the surfaces further. On the other hand, dry oxygen does not replace the termination layers, but breaks the Ge-Ge back bonds and oxidizes the substrates with the aid of moisture. In addition, room light enhances the oxidation rate significantly.

  12. Comparative temporal analysis of multiwalled carbon nanotube oxidation reactions: Evaluating chemical modifications on true nanotube surface

    NASA Astrophysics Data System (ADS)

    Pacheco, Flávia G.; Cotta, Alexandre A. C.; Gorgulho, Honória F.; Santos, Adelina P.; Macedo, Waldemar A. A.; Furtado, Clascídia A.

    2015-12-01

    The influence of extensive purification on oxidized multiwalled carbon nanotube surface composition was studied through the characterization and differentiation of the actual surface submitted to three oxidation methods: microwave-assisted acid oxidation, hydrogen peroxide reflux, and Fenton reaction. The oxidized samples were purified by a multi-step procedure including the sequential use of basic reflux and dispersion in dimethylformamide (DMF). The results showed a significant increase in the amount of oxidation debris with hydrogen peroxide and Fenton reaction times longer than 8 h and strong surface characteristic modification. With regard to sample purification, basic reflux led to a reduction in oxygenated group concentration of only 10% in the samples treated by acid oxidation. On the other hand, the subsequent use of DMF led to a further decrease in concentration of 39%, proving to be a more efficient method for the removal of oxidation debris.

  13. 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.

  14. Surface reconstruction evolution and anatase formation in the process of oxidation of titanium nitride film

    SciTech Connect

    Wu, S. X.; Liu, Y. J.; Xing, X. J.; Yu, X. L.; Xu, L. M.; Yu, Y. P.; Li, S. W.

    2008-03-15

    Titanium nitride film was grown on MgO(001) substrate by plasma-assisted molecular beam epitaxy and then oxidized by oxygen plasma. Reflection high-energy electron diffraction (RHEED) was employed to in situ monitor the process of growth and oxidation. After the TiN film was oxidized for a moment, spots among main streaks were observed in RHEED pattern, which should be attributed to the isolated surface reconstruction domains disorderedly distributing on flat surface. Subsequently, the spots gradually evolved to streaks so that more clear RHEED patterns of (2x1) surface reconstruction were observed. It was argued that the disordered and isolated reconstruction domains congregated to large domains or even perfect reconstruction surface with oxidation time evolving. After oxidation, a series of characterization methods were applied to study the TiO{sub 2} phase, which consistently confirmed that the phase of oxidized titanium nitride is anatase but not rutile.

  15. A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction.

    PubMed

    Eaker, Collin B; Khan, M Rashed; Dickey, Michael D

    2016-01-01

    Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension. Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries. Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( ̴500 mN/m to near zero). Furthermore, this method requires only a very modest potential (< 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests. PMID:26863045

  16. Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics. Final report

    SciTech Connect

    Doyle, F.M.

    1996-01-26

    Coal oxidation has been studies extensively in previous work. However, there is still no general agreement concerning the mechanisms of oxidation. Moreover, the oxidation behavior of coal and mineral matter have generally been regarded as separate processed. There is appreciable evidence that organic and inorganic oxidation process are actually coupled, consequently the changes in their surface properties induced by oxidation are difficult to predict. This makes the effectively of coal cleaning processes highly sensitive to the extent of weathering and oxidation that the coal has experienced. The objective of this research was to investigate the oxidation behavior of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with these surface properties that would influence the behavior in physical cleaning processes.

  17. Surface oxidation energetics and kinetics on MoS2 monolayer

    NASA Astrophysics Data System (ADS)

    KC, Santosh; Longo, Roberto C.; Wallace, Robert M.; Cho, Kyeongjae

    2015-04-01

    In this work, surface oxidation of monolayer MoS2 (one of the representative semiconductors in transition-metal dichalcogenides) has been investigated using density functional theory method. Oxygen interaction with MoS2 shows that, thermodynamically, the surface tends to be oxidized. However, the dissociative absorption of molecular oxygen on the MoS2 surface is kinetically limited due to the large energy barrier at low temperature. This finding elucidates the air stability of MoS2 surface in the atmosphere. Furthermore, the presence of defects significantly alters the surface stability and adsorption mechanisms. The electronic properties of the oxidized surface have been examined as a function of oxygen adsorption and coverage as well as substitutional impurities. Our results on energetics and kinetics of oxygen interaction with the MoS2 monolayer are useful for the understanding of surface oxidation, air stability, and electronic properties of transition-metal dichalcogenides at the atomic scale.

  18. Superhydrophilicity and antibacterial property of a Cu-dotted oxide coating surface

    PubMed Central

    2010-01-01

    Background Aluminum-made settings are widely used in healthcare, schools, public facilities and transit systems. Frequently-touched surfaces of those settings are likely to harbour bacteria and be a potential source of infection. One method to utilize the effectiveness of copper (Cu) in eliminating pathogens for these surfaces would be to coat the aluminum (Al) items with a Cu coating. However, such a combination of Cu and Al metals is susceptible to galvanic corrosion because of their different electrochemical potentials. Methods In this work, a new approach was proposed in which electrolytic plasma oxidation (EPO) of Al was used to form an oxide surface layer followed by electroplating of Cu metal on the top of the oxide layer. The oxide was designed to function as a corrosion protective and biocompatible layer, and the Cu in the form of dots was utilized as an antibacterial material. The antibacterial property enhanced by superhydrophilicity of the Cu-dotted oxide coating was evaluated. Results A superhydrophilic surface was successfully prepared using electrolytic plasma oxidation of aluminum (Al) followed by electroplating of copper (Cu) in a Cu-dotted form. Both Cu plate and Cu-dotted oxide surfaces had excellent antimicrobial activities against E. coli ATCC 25922, methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300 and vancomycin-resistant Enterococcus faecium (VRE) ATCC 51299. However, its Cu-dotted surface morphology allowed the Cu-dotted oxide surface to be more antibacterial than the smooth Cu plate surface. The enhanced antibacterial property was attributed to the superhydrophilic behaviour of the Cu-dotted oxide surface that allowed the bacteria to have a more effective killing contact with Cu due to spreading of the bacterial suspension media. Conclusion The superhydrophilic Cu-dotted oxide coating surface provided an effective method of controlling bacterial growth and survival on contact surfaces and thus reduces the risk of infection and

  19. In-situ X-ray photoelectron spectroscopy studies of water on metals and oxides at ambient conditions

    SciTech Connect

    Salmeron, Miquel; Yamamoto, S.; Bluhm, H.; Andersson, K.; Ketteler, G.; Ogasawara, H.; Salmeron, M.; Nilsson, A.

    2007-10-29

    X-ray photoelectron spectroscopy (XPS) is a powerful tool for surface and interface analysis, providing the elemental composition of surfaces and the local chemical environment of adsorbed species. Conventional XPS experiments have been limited to ultrahigh vacuum (UHV) conditions due to a short mean free path of electrons in a gas phase. The recent advances in instrumentation coupled with third-generation synchrotron radiation sources enables in-situ XPS measurements at pressures above 5 Torr. In this review, we describe the basic design of the ambient pressure XPS setup that combines differential pumping with an electrostatic focusing. We present examples of the application of in-situ XPS to studies of water adsorption on the surface of metals and oxides including Cu(110), Cu(111), TiO2(110) under environmental conditions of water vapor pressure. On all these surfaces we observe a general trend where hydroxyl groups form first, followed by molecular water adsorption. The importance of surface OH groups and their hydrogen bonding to water molecules in water adsorption on surfaces is discussed in detail.

  20. 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.

  1. Influence of controlled surface oxidation on the magnetic anisotropy of Co ultrathin films

    SciTech Connect

    Di, N.; Maroun, F. Allongue, P.; Kubal, J.; Zeng, Z.; Greeley, J.

    2015-03-23

    We studied the influence of controlled surface-limited oxidation of electrodeposited epitaxial Co(0001)/Au(111) films on their magnetic anisotropy energy using real time in situ magneto optical Kerr effect and density functional theory (DFT) calculations. We investigated the Co first electrochemical oxidation step which we demonstrate to be completely reversible and determined the structure of this oxide layer. We show that the interface magnetic anisotropy of the Co film increases by 0.36 erg/cm{sup 2} upon Co surface oxidation. We performed DFT calculations to determine the different surface structures in a wide potential range as well as the charge transfer at the Co surface. Our results suggest that the magnetic anisotropy change is correlated with a positive charge increase of 0.54 e{sup −} for the Co surface atom upon oxidation.

  2. Surface x-ray diffraction of complex metal oxide surfaces and interfaces--a new era

    SciTech Connect

    Schlepuetz, C. M.; Willmott, P. R.; Pauli, S. A.; Herger, R.; Martoccia, D.; Bjoerck, M.; Kumah, D.; Clarke, R.; Yacoby, Y.

    2009-01-29

    The availability of high-brilliance hard x-ray synchrotron radiation and the advent of novel photon counting area detectors have brought surface x-ray diffraction (SXRD) into a new era. It is now possible to record large numbers of structure factors with much improved reliability within reasonable beamtime durations. As a result, structural determination of the surfaces and interfaces of complex crystallographic systems and heterostructures has now become feasible, especially in conjunction with phase-retrieval methods. It is thereby hoped that detailed structural information will shed light on the unusual physical properties of these systems. Complex metal oxide systems investigated at the Materials Science beamline of the Swiss Light Source, including the surface of SrTiO{sub 3}, the interface between LaAlO{sub 3} and SrTiO{sub 3}, and the structure of YBa{sub 2}Cu{sub 3}O{sub 7} grown on NdGaO{sub 3}, SrTiO{sub 3}, and (LaSr)(AlTa)O{sub 3} will be presented as examples of what is now possible using SXRD.

  3. Friction-induced surface activity of some hydrocarbons with clean and oxide-covered iron

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1973-01-01

    Sliding friction studies were conducted on a clean and oxide-covered iron surface with exposure of that surface to various hydrocarbons. The hydrocarbons included ethane, ethylene ethyl chloride, methyl chloride, and vinyl chloride. Auger cylindrical mirror analysis was used to follow interactions of the hydrocarbon with the iron surface. Results with vinyl chloride indicate friction induced surface reactivity, adsorption to surface oxides, friction sensitivity to concentration and polymerization. Variation in the loads employed influence adsorption and accordingly friction. In contrast with ethyl and vinyl chloride, friction induced surface reactivity was not observed with ethane and ethylene.

  4. Robust hybrid elastomer/metal-oxide superhydrophobic surfaces.

    PubMed

    Hoshian, S; Jokinen, V; Franssila, S

    2016-08-21

    We introduce a new type of hybrid material: a nanostructured elastomer covered by a hard photoactive metal-oxide thin film resembling the exoskeleton of insects. It has extreme water repellency and fast self-recovery after damage. A new fabrication method for replicating high aspect ratio, hierarchical re-entrant aluminum structures into polydimethylsiloxane (PDMS) is presented. The method is based on a protective titania layer deposited by atomic layer deposition (ALD) on the aluminum template. The ALD titania transfers to the elastomeric scaffold via sacrificial release etching. The sacrificial release method allows for high aspect ratio, even 100 μm deep and successful release of overhanging structures, unlike conventional peeling. The ALD titania conformally covers the 3D multihierarchical structures of the template and protects the polymer during the release etch. Afterwards it prevents the high aspect ratio nanostructures from elasticity based collapse. The resulting nanostructured hybrid PDMS/titania replicas display robust superhydrophobicity without any further fluoro-coating or modification. Their mechanical and thermal robustness results from a thick nanostructured elastomeric layer which is conformally covered by ceramic titania instead of a monolayer hydrophobic coating. We have demonstrated the durability of these replicas against mechanical abrasion, knife scratches, rubbing, bending, peel tape test, high temperature annealing, UV exposure, water jet impingement and long term underwater storage. Though the material loses its superhydrophobicity in oxygen plasma exposure, a fast recovery from superhydrophilic to superhydrophobic can be achieved after 20 min UV irradiation. UV-assisted recovery is correlated with the high photoactivity of ALD titania film. This novel hybrid material will be applicable to the large area superhydrophobic surfaces in practical outdoor applications. PMID:27418238

  5. 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.

  6. A Molecular Dynamics Simulation Study on the Wetting Behavior of Water on Oxidized and Non-Oxidized atactic Polystyrene Surface

    NASA Astrophysics Data System (ADS)

    Bekele, Selemon; Tsige, Mesfin

    2013-03-01

    All-Atomistic Molecular dynamics simulations have been carried out to study the wetting of oxidized and non-oxidized atactic polystyrene (aPS) thin films by water droplets. The dependence of the contact angle on droplet size has been studied using spherical and hemispherical water droplets of varying sizes. The effect of oxidation of the aPS surface on the contact angle has been studied as a function of oxygen concentration. Oxidation of the aPs has been achieved by randomly replacing the ortho and/or meta hydrogen on the phenyl rings within 1 nm of the aPS surface by oxygen until the desired concentration of oxygen on the surface is reached. The simulated contact angle is found to decrease monotonically with oxygen concentration consistent with recent experimental results. We will present results on the variation of water contact angle with oxygen concentration on the aPS surface. In addition, the effect of oxidization on the roughness of the polystyrene surface, the ordering of the phenyl rings and the water molecules and the number of hydrogen bonding between water molecules and the polystrene at the interface have been investigated and will be presented. This work is supported by the NSF (DMR0847580).

  7. The oxidation of copper-indium diselenide surfaces

    SciTech Connect

    Diniz, A.S.A.C.

    1997-12-31

    The mechanisms, chemistry, structure and interface properties of native and grown oxides on CuInSe{sub 2} are presented. During thermal oxidation of this ternary semiconductor, the composition and the electrical properties are controlled, primarily by the temperature and duration of oxidation treatment. The oxygen reacts principally with In, leaving the Cu and Se to readjust at the interface to form a Cu{sub x}Se transition layer. The thermal oxide consists of an In{sub 2}O{sub 3} matrix and having either inclusion of Cu or SeO{sub 2} particles, depending on the precise formation conditions. The Cu{sub x}Se transition layer eventually acts as a barrier that prevents further oxidation of the underlying CuInSe{sub 2}.

  8. Aqueous stabilization of carbon nanotubes: effects of surface oxidization and solution chemistry.

    PubMed

    Bai, Yingchen; Wu, Fengchang; Lin, Daohui; Xing, Baoshan

    2014-03-01

    Surface oxygen functional groups can affect the morphological characteristics, aggregation kinetics, and adsorption capacity of multi-walled carbon nanotubes (MWCNTs). However, little is known about the quantitative relationship between oxygen content and the dispersion stability of MWCNTs. To investigate the effects of surface oxidization, MWCNTs were oxidized using concentrated H2SO4/HNO3 acids for 0, 1, 2, 4, and 8 h, respectively. Experimental results showed that the oxygen content of MWCNTs increased with surface oxidization time. Linear correlations were found to exist between the oxygen content, critical coagulation concentration (CCC) for NaCl, and critical coagulation pH values of MWCNTs detected by optical density at 800 nm. The CCC values for CaCl2 increased with oxygen contents for unmodified MWCNTs and lowly oxidized MWCNTs, while which decreased after further increasing the surface oxidization. CCC ratios in the presence of Ca(2+) to Na(+) were consistent with the empirical Schulze-Hardy rule for unmodified MWCNTs and lowly oxidized MWCNTs; however, which were much lower than the expected values for highly oxidized MWCNTs. Fulvic acid can clearly increase the stability of MWCNT suspension with unmodified MWCNTs and lowly oxidized MWCNTs, while it cannot affect the dispersion of highly oxidized MWCNTs. This study implied that the oxidation and presence of fulvic acid will possibly increase the mobility, exposure, bioavailability, and toxicity of MWCNTs. PMID:24323322

  9. Surface segregation and oxidation of Ti in a V-Ti alloy

    NASA Astrophysics Data System (ADS)

    Hayakawa, Ryo; Hatano, Yuji; Fujii, Katsuhiko; Fukumoto, Ken-ichi; Matsui, Hideki; Watanabe, Kuniaki

    2002-12-01

    The oxidation and reduction of surface oxides of the V-4%Ti alloy were examined by X-ray photoelectron spectroscopy. A specimen sheet of the alloy covered by oxide films was heated between 513 and 1223 K for 10 min in vacuum. Vanadium oxides started to be reduced to the metallic state at 673 K owing to oxygen dissolution in the bulk, while titanium remained in oxidized states up to 983 K. Titanium segregated to the surface above this temperature, and the surface concentration reached up to 40% at 1223 K. The specimen surface enriched in Ti was thus prepared and oxidized at 573 and 773 K under oxygen pressures between 10 -5 and 10 -3 Pa. At 573 K, titanium was selectively oxidized at 10 -5 Pa, while vanadium remained in a metallic state. Such selective oxidation of Ti took place also at 775 K under the pressure of 10 -4 Pa. Titanium segregating to the surface appeared to provide the barrier effect against tritium inventory and permeation under high temperature, low oxygen partial pressure conditions through selective oxidation.

  10. Early detection of oxidized surfaces using Shewanella oneidensis MR-1 as a tool.

    PubMed

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

    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 its nascent stages is a high priority for reasons that range from aesthetics to economics. Many bacteria in the facultatively aerobic genus Shewanella have the capacity to respire some metal oxides, such as iron oxide, by way of a variety of oxide-binding proteins lodged in their outer membrane. In this study, a rapid, cost-effective system for the specific early detection of a variety of oxidized steel surfaces is described, taking advantage of bacteria with natural affinities for iron oxides, to identify the sites of nascent corrosion. PMID:19165644

  11. Effect of Surface Oxidation on Interfacial Water Structure at a Pyrite (100) Surface as Studied by Molecular Dynamics Simulation

    SciTech Connect

    Jin, Jiaqi; Miller, Jan D.; Dang, Liem X.; Wick, Collin D.

    2015-06-01

    In the first part of this paper, a Scanning Electron Microscopy and contact angle study of a pyrite surface (100) is reported describing the relationship between surface oxidation and the hydrophilic surface state. In addition to these experimental results, the following simulated surface states were examined using Molecular Dynamics Simulation (MDS): fresh unoxidized (100) surface; polysulfide at the (100) surface; elemental sulfur at the (100) surface. Crystal structures for the polysulfide and elemental sulfur at the (100) surface were simulated using Density Functional Theory (DFT) quantum chemical calculations. The well known oxidation mechanism which involves formation of a metal deficient layer was also described with DFT. Our MDS results of the behavior of interfacial water at the fresh and oxidized pyrite (100) surfaces without/with the presence of ferric hydroxide include simulated contact angles, number density distribution for water, water dipole orientation, water residence time, and hydrogen-bonding considerations. The significance of the formation of ferric hydroxide islands in accounting for the corresponding hydrophilic surface state is revealed not only from experimental contact angle measurements but also from simulated contact angle measurements using MDS. The hydrophilic surface state developed at oxidized pyrite surfaces has been described by MDS, on which basis the surface state is explained based on interfacial water structure. The Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences (BES), of the DOE funded work performed by Liem X. Dang. Battelle operates the Pacific Northwest National Laboratory for DOE. The calculations were carried out using computer resources provided by BES.

  12. Process for growing a film epitaxially upon an oxide surface and structures formed with the process

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1998-01-01

    A process and structure wherein a film comprised of a perovskite or a spinel is built epitaxially upon a surface, such as an alkaline earth oxide surface, involves the epitaxial build up of alternating constituent metal oxide planes of the perovskite or spinel. The first layer of metal oxide built upon the surface includes a metal element which provides a small cation in the crystalline structure of the perovskite or spinel, and the second layer of metal oxide built upon the surface includes a metal element which provides a large cation in the crystalline structure of the perovskite or spinel. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  13. Process for growing a film epitaxially upon an oxide surface and structures formed with the process

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    1995-01-01

    A process and structure wherein a film comprised of a perovskite or a spinel is built epitaxially upon a surface, such as an alkaline earth oxide surface, involves the epitaxial build up of alternating constituent metal oxide planes of the perovskite or spinel. The first layer of metal oxide built upon the surface includes a metal element which provides a small cation in the crystalline structure of the perovskite or spinel, and the second layer of metal oxide built upon the surface includes a metal element which provides a large cation in the crystalline structure of the perovskite or spinel. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

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

    SciTech Connect

    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.

  16. d0 ferromagnetism in black phosphorous oxide caused by surface P-O bonds

    NASA Astrophysics Data System (ADS)

    Gui, Q. F.; Sun, L. L.; Liu, L. Z.; Wu, X. L.; Chu, Paul K.

    2016-02-01

    The room-temperature d0 ferromagnetism in black phosphorous (BP) oxide is investigated experimentally and theoretically. Electrochemical oxidation does not alter the single-crystal structure of BP and the degree of oxidation depends on the oxidation time, thereby resulting in changeable d0 ferromagnetism caused by surface P-O bonds. First-principles calculation reveals that different surface P-O bonds have different binding energies and contributions to the ferromagnetism and the bridge and dangling oxygen atoms are responsible for the observed ferromagnetism which stems from p orbital spin polarization of the oxygen and phosphorus atoms.

  17. Chemically modified Si(111) surfaces simultaneously demonstrating hydrophilicity, resistance against oxidation, and low trap state densities

    NASA Astrophysics Data System (ADS)

    Brown, Elizabeth S.; Hlynchuk, Sofiya; Maldonado, Stephen

    2016-03-01

    Chemically modified Si(111) surfaces have been prepared through a series of wet chemical surface treatments that simultaneously show resistance towards surface oxidation, selective reactivity towards chemical reagents, and areal defect densities comparable to unannealed thermal oxides. Specifically, grazing angle attenuated total reflectance infrared and X-ray photoelectron (XP) spectroscopies were used to characterize allyl-, 3,4-methylenedioxybenzene-, or 4-[bis(trimethylsilyl)amino]phenyl-terminated surfaces and the subsequently hydroxylated surfaces. Hydroxylated surfaces were confirmed through reaction with 4-(trifluoromethyl)benzyl bromide and quantified by XP spectroscopy. Contact angle measurements indicated all surfaces remained hydrophilic, even after secondary backfilling with CH3sbnd groups. Surface recombination velocity measurements by way of microwave photoconductivity transients showed the relative defect-character of as-prepared and aged surfaces. The relative merits for each investigated surface type are discussed.

  18. Effect of surface stresses and morphology modification on cupric oxide nanowire growth in the thermal oxidation of copper

    NASA Astrophysics Data System (ADS)

    Mema, Rediola

    Exerting in-plane tensile surface stress or modifying the morphology of the metal surface by forcibly propelling a stream of abrasive material into the surface (sandblasting) enhances nanowire growth by increasing the density of nanowires in the case of tensile stress, and increasing the density and length of nanowires in the case of sandblasting. This improved nanowire growth is attributed to the decreased size of the oxide grains and as a result, the increased number of grain boundaries in the underlying oxide layers, thus resulting in a facilitated outward diffusion of Cu ions for enhanced nanowire growth. These two very simple methods offer easy and inexpensive ways to generate dense, ultra-long CuO nanowires with larger aspect ratios, as well as shed more light on the growth mechanism of nanowires in the thermal oxidation of copper, which has been greatly debated thus far.

  19. Formation of surface oxides and Ag2O thin films with atomic oxygen on Ag(111)

    NASA Astrophysics Data System (ADS)

    Derouin, Jonathan; Farber, Rachael G.; Heslop, Stacy L.; Killelea, Daniel R.

    2015-11-01

    The nature of the oxygen species adsorbed to silver surfaces is a key component of the heterogeneously catalyzed epoxidation of ethylene and partial oxidation of methanol over silver catalysts. We report the formation of two different silver-oxygen species depending on the flux and energy of incident gas-phase oxygen atoms on an Ag(111) surface. A combination of surface science techniques was used to characterize the oxidized surfaces. Atomic oxygen was generated with an Ir filament; lower temperatures created surface oxides previously reported. When O was deposited with a higher filament temperature, the surface became highly corrugated, little subsurface oxygen was observed, and thin layers of Ag2O were likely formed. These results show that the energy and flux of oxygen are important parameters in the chemical identity and abundance of oxygen on silver surfaces and suggest that formation of the Ag2O thin film hinders formation of subsurface oxygen.

  20. Surface oxidation effect on the electrical behaviour of Bi2Te2Se nanoplatelets

    NASA Astrophysics Data System (ADS)

    Gehring, Pascal; Reusch, Frieder B.; Mashhadi, Soudabeh S.; Burghard, Marko; Kern, Klaus

    2016-07-01

    Charge transport in topological insulators is notably influenced by moisture and air in the surrounding environment. At present, however, little is known about the detailed composition of the oxidized surface and its impact on the electrical characteristics of these materials. Here, we investigate the surface oxide formation on the topological insulator Bi2Te2Se (BTS) and how this affects its electrical behavior. While ambient exposure of BTS nanoplatelets predominantly creates surface hydroxyl groups, oxygen plasma treatment yields a compact, few-nanometer thick surface oxide layer. The plasma causes p-type doping, accompanied by a decrease of the effective platelet thickness, the interplay of which is manifested in a resistance maximum as a function of plasma treatment time. It is furthermore demonstrated that the structural integrity of the plasma-derived surface oxide is sufficient to enable its use as a gate insulator layer in combination with a top gate.

  1. Surface oxidation effect on the electrical behaviour of Bi2Te2Se nanoplatelets.

    PubMed

    Gehring, Pascal; Reusch, Frieder B; Mashhadi, Soudabeh S; Burghard, Marko; Kern, Klaus

    2016-07-15

    Charge transport in topological insulators is notably influenced by moisture and air in the surrounding environment. At present, however, little is known about the detailed composition of the oxidized surface and its impact on the electrical characteristics of these materials. Here, we investigate the surface oxide formation on the topological insulator Bi2Te2Se (BTS) and how this affects its electrical behavior. While ambient exposure of BTS nanoplatelets predominantly creates surface hydroxyl groups, oxygen plasma treatment yields a compact, few-nanometer thick surface oxide layer. The plasma causes p-type doping, accompanied by a decrease of the effective platelet thickness, the interplay of which is manifested in a resistance maximum as a function of plasma treatment time. It is furthermore demonstrated that the structural integrity of the plasma-derived surface oxide is sufficient to enable its use as a gate insulator layer in combination with a top gate. PMID:27257792

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

    NASA Astrophysics Data System (ADS)

    Ricci, Pier Carlo; Carbonaro, C. M.; Corpino, R.; Chiriu, D.; Stagi, L.

    2014-10-01

    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 (TiO2) and in Iron oxide (Fe2O3): Maghemite is subjected to a phase transformation to α-Fe2O3 (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.

  3. Experimental estimation of oxidation-induced Si atoms emission on Si(001) surfaces

    SciTech Connect

    Ogawa, Shuichi Tang, Jiayi; Takakuwa, Yuji

    2015-08-15

    Kinetics of Si atoms emission during the oxidation of Si(001) surfaces have been investigated using reflection high energy electron diffraction combined with Auger electron spectroscopy. The area ratio of the 1 × 2 and the 2 × 1 domains on a clean Si(001) surface changed with the oxidation of the surface by Langmuir-type adsorption. This change in the domain ratio is attributed to the emission of Si atoms. We can describe the changes in the domain ratio using the Si emission kinetics model, which states that (1) the emission rate is proportional to the oxide coverage, and (2) the emitted Si atoms migrate on the surface and are trapped at S{sub B} steps. Based on our model, we find experimentally that up to 0.4 ML of Si atoms are emitted during the oxidation of a Si(001) surface at 576 °C.

  4. Surface effects in metal oxide-based nanodevices

    NASA Astrophysics Data System (ADS)

    Lien, Der-Hsien; Durán Retamal, José Ramón; Ke-Jian, Jr.; Kang, Chen-Fang; He-Hau, Jr.

    2015-11-01

    As devices shrink to the nanoscale, surface-to-volume ratio increases and the surface-environment interaction becomes a major factor for affecting device performance. The variation of electronic properties, including the surface band bending, gas chemisorption or photodesorption, native surface defects, and surface roughness, is called ``surface effects''. Such effects are ambiguous because they can be either negative or beneficial effects, depending on the environmental conditions and device application. This review provides an introduction to the surface effects on different types of nanodevices, offering the solutions to respond to their benefits and negative effects and provides an outlook on further applications regarding the surface effect. This review is beneficial for designing nano-enabled photodetectors, harsh electronics, memories, sensors and transistors via surface engineering.

  5. 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.

  6. Role of RuO2(100) in surface oxidation and CO oxidation catalysis on Ru(0001).

    PubMed

    Flege, Jan Ingo; Lachnitt, Jan; Mazur, Daniel; Sutter, Peter; Falta, Jens

    2016-01-01

    We have studied the oxidation of the Ru(0001) surface by in situ microscopy during exposure to NO2, an efficient source of atomic oxygen, at elevated temperatures. In a previous investigation [Flege et al., Phys. Rev. B: Condens. Matter Mater. Phys., 2008, 78, 165407], at O coverages exceeding 1 monolayer, using the combination of intensity-voltage (I(V)) low-energy electron microscopy (LEEM) and multiple scattering calculations for the (00) beam in the very-low-energy range (E≤ 50 eV) we identified three surface components during the initial Ru oxidation: a (1 × 1)-O chemisorption phase, the RuO2(110) oxide phase, and a surface oxide structure characterized by a trilayer O-Ru-O stacking. Here, we use dark-field LEEM imaging and micro-illumination low-energy electron diffraction in the range of 100 to 400 eV to show that this trilayer phase is actually a RuO2(100)-(1 × 1) phase with possibly mixed O and Ru surface terminations. This identification rationalizes the thermodynamic stability of this phase at elevated temperatures and is consistent with the observation of catalytic activity of the phase in CO oxidation. PMID:26601756

  7. Composition of Uranium Oxide Surface Layers Analyzed by m-Raman Spectroscopy

    SciTech Connect

    Siekhaus, W J

    2003-11-24

    Oxide thickness and composition averaged over a few square millimeter has been measured with nm thickness resolution by diffuse reflectance fourier transform infrared (FTIR) spectroscopy. {mu}-Raman spectroscopy has been done on powders and bulk samples in the past, and can now be done on surfaces layers with {micro}m lateral and depth resolution using con-focal microscopy. Here we apply con-focal-microscopy-based {mu}-Raman spectroscopy to a freshly polished/lightly oxidized and to heavily oxidized uranium to determine its sensitivity. The spectra show that {mu}-Raman spectroscopy does detect oxide thickness and oxide composition with high sensitivity.

  8. Long length oxide template for YBCO coated conductor prepared by surface-oxidation epitaxy method

    NASA Astrophysics Data System (ADS)

    Watanabe, Tomonori; Matsumoto, Kaname; Maeda, Toshihiko; Tanigawa, Toru; Hirabayashi, Izumi

    2001-08-01

    A 50 m long, biaxially textured NiO buffer layer for epitaxial growth ofYBa 2Cu 3O 7- δ (YBCO) film has been fabricated on the long cube textured nickel tape using surface-oxidation epitaxy (SOE) method. The SOE-NiO layers were highly {1 0 0} <0 0 1> textured. The full width at half maximum of 10-14.5° from X-ray φ-scan ( Δφ) was in the range of 10-14.5° through the whole length. The critical current density ( Jc) values exceeding 0.3 MA/cm 2 (77 K, 0 T) have been obtained in short samples of YBCO films on NiO/Ni tapes, by using thin MgO cap layer. Thirty meters long Ni-clad Ni-20wt.%Cr (Ni/NiCr) and Ni-clad austenitic stainless steel (Ni/SS) tapes were also prepared for YBCO coated conductors with higher strength and lower magnetism than those of pure nickel tape. Highly {1 0 0} <0 0 1> textured NiO layers were formed on those textured composite tapes by SOE method as same as on cube textured pure nickel tapes. YBCO films with Jc of 0.1 MA/cm 2 (77 K, 0 T) have been obtained on MgO/SOE-NiO layer of short Ni/NiCr composite tape.

  9. Zinc oxide nanorods modified indium tin oxide surface for amperometric urea biosensor.

    PubMed

    Palomera, Netzahualcóyotl; Balaguera, Marcia; Arya, Sunil K; Hernández, Samuel; Tomar, Maharaj S; Ramírez-Vick, Jaime E; Singh, Surinder P

    2011-08-01

    ZnO nanorods (ZnONR) grown onto indium-tin-oxide (ITO) coated glass surface using zinc nitrate hexahydrate/hexamethylenetetramine (HMT) in aqueous phase has been utilized for urea biosensor. Urease (Urs) was immobilized onto ZnONR/ITO at physiological pH via electrostatic interactions between Urs and ZnO to fabricate Urs/ZnONR/ITO bioelectrode. ZnONR/ITO electrode has been characterized using XRD, FE-SEM techniques and Urs/ZnONR/ITO bioelectrode using electrochemistry. The XRD and FE-SEM measurements confirm the formation of ZnO nanorods in wurtzite structure. Cyclic voltammetric and amperometric measurements on the Urs/ZnONR/ITO biolectrode for urea concentrations in the range of 1-20 mM reveal 0.4 microA mM(-1) sensitivity, with a response time of 3 seconds, and a detection limit of 0.13 mM. The Michaelis-Menten constant (Km) was calculated to be 9.09 mM. Results indicate that ZnO nanorods provide suitable microenvironment for urease immobilization and can be utilized in biosensor design and other biological applications. PMID:22103068

  10. Al-based thermal oxides in vertical cavity surface emitting lasers

    NASA Astrophysics Data System (ADS)

    Liliental-Weber, Zuzanna; Ruvimov, S.; Swider, W.; Washburn, Jack; Li, Meng; Li, Gabriel S.; Chang-Hasnain, Constance J.; Weber, Eicke R.

    1997-01-01

    The microstructure of wet oxidized layers for vertical cavity surface emitting lasers (VCSELS) was studied by transmission electron microscopy. These oxides were formed by reaction of AlxGa1-xAs(x approximately equals 0 - 0.2) with water vapor at elevated temperatures (approximately 400 - 450 degrees Celsius). Due to the excellent carrier confinement provided by the oxidized layer, VCSELS have very low threshold currents and high efficiencies. This study revealed the accumulation of excess As at the interfaces with the oxidized layers and occasionally at the sample surface. To avoid this As accumulation on the sample surface, GaInP layers were grown on top of AlGaAs/GaAs layers. In this case no As was found at the layer surface. In addition, substantial shrinkage was found after oxidation, and the formation of large pores at the interface between the oxide and the high Al content layer, which might be detrimental for the device performance. The dependence of the oxide and interface quality on the composition of the oxidized layers, oxidation time and temperature are discussed in relation to the optical quality of VCSELs.

  11. Structure of ultrathin oxide layers on metal surfaces from grazing scattering of fast atoms

    NASA Astrophysics Data System (ADS)

    Winter, H.; Seifert, J.; Blauth, D.; Busch, M.; Schüller, A.; Wethekam, S.

    2009-10-01

    The structure of ultrathin oxide layers grown on metal substrates is investigated by grazing scattering of fast atoms from the film surface. We present three recent experimental techniques which allow us to study the structure of ordered oxide films on metal substrates in detail. (1) A new variant of a triangulation method with fast atoms based on the detection of emitted electrons, (2) rainbow scattering under axial surface channeling conditions, and (3) fast atom diffraction (FAD) for studies on the structure of oxide films. Our examples demonstrate the attractive features of grazing fast atom scattering as a powerful analytical tool in surface physics.

  12. Mueller Matrix of Specular Reflection Using an Aluminum Grating Surface with Oxide Nanofilm.

    PubMed

    Qiu, Jun; Ran, Dongfang; Liu, Linhua; Hsu, Pei-Feng

    2016-06-01

    The accurate nondestructive and real-time determination of the critical dimensions of oxide nanofilms on periodic nanostructures has potential applications in nanofabrication techniques. Mueller ellipsometry is fast, accurate, nondestructive, and can be used in the ambient air. This study used the elements of a Mueller matrix of specular reflection, which is based on a Mueller ellipsometry method, to evaluate the thickness of an oxide nanofilm on an aluminum grating surface. By using non-traditional rigorous coupled-wave analysis (RCWA), we decomposed the Mueller matrix to obtain the relationship between the evaluated polarization properties of reflected light and the dimensions of oxide nanofilms on aluminum grating surfaces. We also quantitatively analyzed the Mueller matrix elements' variation due to the thicknesses of top, sidewall, and bottom oxides. We consider these oxide films are naturally formed and of nonuniform thickness on grating structures. The results show that the elements of Mueller matrix shift with the increasing of the uniform thickness of oxide at a fixed wavelength. Moreover, as oxide nanofilms on grating structures are nonuniform, the impact of the thickness of side wall oxide on the Mueller matrix elements is more obvious than that of top and bottom oxides at the relative larger incidence wavelength range. The finding of this work may facilitate the nondestructive and real-time measurement of the thickness of oxide nanofilms on metal gratings where the metal is easily oxidized. PMID:27129364

  13. Surface Reactions of Uranium Oxide Powder, Thin Films and Single Crystals

    SciTech Connect

    Idriss, H.

    2010-01-01

    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{sub 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.

  14. 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.

  15. Effects of additives on volume change on melting, surface tension, and viscosity of liquid aluminum oxide

    NASA Technical Reports Server (NTRS)

    Bates, J. L.; Rasmussen, J. J.

    1972-01-01

    The effects of various oxide additives on the volume change on melting, the surface tension, and the viscosity of liquid Al2O3 were studied. Additives of Sm2O3, MgO, and Y2O3 which form solid solutions, compounds, and multiphase solids with Al2O3 were studied. A review of the property data for Al2O3 and Al2O3 containing oxide additives is presented. Oxide additives to Al2O3 reduce the volume change on melting and with the exception of SiO2 lower the viscosity; surface tensions change with oxide additives, but changes vary with different container material. Viscosity and volume change on melting appeared to be significantly more important for studying the properties of liquid oxides than surface tension. Supercooling of 270 K of yttrium aluminum garnet was observed.

  16. Understanding Surface Processes on Mars Through Study of Iron Oxides/Oxyhydroxides: Clues to Surface Alteration and Aqueous Processes

    NASA Technical Reports Server (NTRS)

    Bishop, J. L.; Mancinelli, R. L.; Dyar, M. D.; Parente, M.; Drief, A.; Lane, M. D.; Murad, E.

    2006-01-01

    We are performing oxidation and reduction reactions on hydrated ferric oxide minerals in order to investigate how these might alter under a variety of conditions on the surface of Mars. Preliminary experiments on ferrihydrite and goethite showed that heating these minerals in a dry oxidizing environment produces fine-grained hematite, while heating these minerals in a reducing environment produces fine-grained magnetite. Under Mars-like oxidation levels this magnetite then oxidizes to maghemite. These reactions are dependent on the presence of water and organic material that can act as a reductant. We are using reflectance and Mossbauer spectroscopy to characterize the reaction products and TEM to analyze the sample texture. Our preliminary results indicate that magnetite and maghemite could be formed in the soil on Mars from ferrihydrite and goethite if organics were present on early Mars.

  17. Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure.

    PubMed

    Ta, D T; Tieu, A K; Zhu, H T; Kosasih, B

    2015-10-28

    A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe2O3(001), and Fe2O3(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength. PMID:26520538

  18. Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure

    NASA Astrophysics Data System (ADS)

    Ta, D. T.; Tieu, A. K.; Zhu, H. T.; Kosasih, B.

    2015-10-01

    A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe2O3(001), and Fe2O3(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength.

  19. Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure

    SciTech Connect

    Ta, D. T.; Tieu, A. K.; Zhu, H. T. Kosasih, B.

    2015-10-28

    A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe{sub 2}O{sub 3}(001), and Fe{sub 2}O{sub 3}(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength.

  20. A surface x-ray study of the structure and morphology of the oxidized Pd001 surface.

    PubMed

    Stierle, A; Kasper, N; Dosch, H; Lundgren, E; Gustafson, J; Mikkelsen, A; Andersen, J N

    2005-01-22

    The oxidation of Pd(100) and the formation of PdO was studied in situ using surface x-ray diffraction. A bulklike, epitaxial PdO film is formed at oxygen partial pressures beyond 1 mbar and sample temperatures exceeding 650 K. The main orientation is PdO(001)/Pd(001), based upon bulk reflections from the PdO film. By comparing with measurements from the Pd crystal truncation rods, we estimate an rms surface roughness of 6 A, in good agreement with previous high pressure scanning tunneling microscopy measurements. Finally, we observed the transformation from the (radical5 x radical5) surface oxide to PdO bulk oxide at 675 K and 50 mbar O(2) pressure. PMID:15740282

  1. Influence of surface oxidation on ion dynamics and capacitance in porous and nonporous carbon electrodes

    DOE PAGESBeta

    Dyatkin, Boris; Zhang, Yu; Mamontov, Eugene; Kolesnikov, Alexander I.; Cheng, Yongqiang; Meyer, III, Harry M.; Cummings, Peter T.; Gogotsi, Yury G.

    2016-04-07

    Here, we investigate the influence of surface chemistry and ion confinement on capacitance and electrosorption dynamics of room-temperature ionic liquids (RTILs) in supercapacitors. Using air oxidation and vacuum annealing, we produced defunctionalized and oxygen-rich surfaces of carbide-derived carbons (CDCs) and graphene nanoplatelets (GNPs). While oxidized surfaces of porous CDCs improve capacitance and rate handling abilities of ions, defunctionalized nonporous GNPs improve charge storage densities on planar electrodes. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) probed the structure, dynamics, and orientation of RTIL ions confined in divergently functionalized pores. Oxidized, ionophilic surfaces draw ions closer to pore surfaces andmore » enhance potential-driven ion transport during electrosorption. Molecular dynamics (MD) simulations corroborated experimental data and demonstrated the significance of surface functional groups on ion orientations, accumulation densities, and capacitance.« less

  2. Surface chemistry, reactivity, and pore structure of porous silicon oxidized by various methods.

    PubMed

    Riikonen, Joakim; Salomäki, Mikko; van Wonderen, Jessica; Kemell, Marianna; Xu, Wujun; Korhonen, Ossi; Ritala, Mikko; MacMillan, Fraser; Salonen, Jarno; Lehto, Vesa-Pekka

    2012-07-17

    Oxidation is the most commonly used method of passivating porous silicon (PSi) surfaces against unwanted reactions with guest molecules and temporal changes during storage or use. In the present study, several oxidation methods were compared in order to find optimal methods able to generate inert surfaces free of reactive hydrides but would cause minimal changes in the pore structure of PSi. The studied methods included thermal oxidations, liquid-phase oxidations, annealings, and their combinations. The surface-oxidized samples were studied by Fourier transform infrared spectroscopy, isothermal titration microcalorimetry, nitrogen sorption, ellipsometry, X-ray diffraction, electron paramagnetic resonance spectroscopy, and scanning electron microscopy imaging. Treatment at high temperature was found to have two advantages. First, it enables the generation of surfaces free of hydrides, which is not possible at low temperatures in a liquid or a gas phase. Second, it allows the silicon framework to partially accommodate a volume expansion because of oxidation, whereas at low temperature the volume expansion significantly consumes the free pore volume. The most promising methods were further optimized to minimize the negative effects on the pore structure. Simple thermal oxidation at 700 °C was found to be an effective oxidation method although it causes a large decrease in the pore volume. A novel combination of thermal oxidation, annealing, and liquid-phase oxidation was also effective and caused a smaller decrease in the pore volume with no significant change in the pore diameter but was more complicated to perform. Both methods produced surfaces that were not found to react with a model drug cinnarizine in isothermal titration microcalorimetry experiments. The study enables a reasonable choice of oxidation method for PSi applications. PMID:22671967

  3. 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.

  4. Enhanced arsenite removal through surface-catalyzed oxidative coagulation treatment.

    PubMed

    Li, Yue; Bland, Garret D; Yan, Weile

    2016-05-01

    Arsenic being a naturally-occurring groundwater contaminant is subject to stringent water quality regulations. Coagulation and adsorption are widely used methods to treat arsenic-contaminated water, however, these treatments have been reported to be less efficient for the removal of arsenite (As(III)) than arsenate (As(V)). In this study, the feasibility of in situ oxidation of As(III) during coagulation was investigated in two systems: Fe(II) or H2O2-assisted oxidative coagulation treatment using ferric chloride as the coagulant. This setup exploits the catalytic property of the fresh formed Fe(III) hydroxide colloids in coagulation suspension to mediate the production of reactive oxidants capable of As(III) oxidation. Fe(II)-assisted coagulation brought about small improvements in As(III) removal compared to treatment with Fe(III) coagulant alone, however, its arsenic removal efficiency is strongly dependent on pH (observed optimal pH = 7-9). Addition of H2O2 together with ferric chloride led to a significant enhancement in arsenic retention at pH 6-8, with final arsenic concentrations well below the U.S.EPA regulatory limit (10 μg/L). H2O2-assisted oxidative coagulation can attain reliable As(III) removal over a broad pH range of 4-9. Radical quenching experiments reveal the participation of superoxide radical in As(III) removal in the oxidative coagulation systems. Phosphate (at > 0.1 mM) strongly suppresses As(III) removal efficiency, whereas carbonate and humic acid pose a minor impact. Overall, the results suggest that a low dose addition of H2O2 along with ferric coagulant is a feasible method for the existing water treatment facilities to achieve improved As(III) removal efficiency. PMID:26897520

  5. Electrochemical oxide film formation at noble metals as a surface-chemical process

    NASA Astrophysics Data System (ADS)

    Conway, B. E.

    1995-08-01

    The mechanisms of electrochemical oxide film formation at noble metals are described and exemplified by the cases of Pt and Au, especially in the light of recent experimentation by means of cyclic voltammetry, ellipsometry and vacuum surface-science studies using LEED and AES. Unlike the mechanisms of base-metal oxidation, e.g., in corrosion processes, anodic oxide film formation at noble metals proceeds by surface chemical processes involving, initially, sub-monolayer, through monolayer, formation of 2-dimensional {OH}/{O} arrays. During such 2-d processes, place-exchange between electrosorbed OH or O species on the surface, and Pt or Au atoms within the surface lattice, takes place leading to a quasi-2-d compact film which then grows ultimately to a multilayer hydrous oxide film, probably by continuing injection of ions of the substrate metal and their migration through the growing film under the influence of the field. The initial, sub-monolayer stage of electrosorption of OH involves competitive chemisorption by anions, e.g. HSO 4-, ClO 4-, Cl -, which inhibits onset of the first stage of surface oxidation. These processes are demonstrable in experiments on single-crystal surfaces. The combination of such anion effects with place-exchange during the extension of the film, leads to a general mechanism of noble metal oxide film formation. The formation of the oxide films can be examined in detail by recording the distinguishable stages in the film's electrochemical reduction in linear-sweep voltammetry which is sensitive down to {OH}/{O} fractional coverages as low as 0.5% and over time-scales down to 50μs in experiments on time-evolution and transformation of the states of the oxide films. By means of LEED, AES and STM or AFM experiments, the reconstructions and perturbations (e.g. generation of stepped terraces) which oxide films cause on singlecrystal surfaces can be followed.

  6. 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

  7. Mechanism of oxidation protection of the Si(001) surface by sub-monolayer Sr template

    NASA Astrophysics Data System (ADS)

    Fredrickson, Kurt D.; Seo, Hosung; Demkov, Alexander A.

    2016-08-01

    We investigate theoretically the oxidation stability of the Si(001) (2 × 1) reconstructed surface passivated by Sr. Using density functional theory, we find that the Sr surface with ½ monolayer of Sr is protected against oxidation. The presence of Sr delays the oxidation of the surface dimer, and even when the dimer is oxidized, O does not react with the back-bond, preventing the unwanted vertical growth of SiO2. We also show that ¼ monolayer of Sr protects the Si surface in a different way. In the presence of ¼ monolayer of Sr, O atoms are attracted to the Sr-Si dimer complexes, thus preventing the formation of SiO2.

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

    SciTech Connect

    Flötotto, D. Wang, Z. M.; Jeurgens, L. P. H.; Mittemeijer, E. J.

    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.

  9. 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.

  10. Dynamic oxidation behavior of TD-NiCr alloy with different surface pretreatments

    NASA Technical Reports Server (NTRS)

    Young, C. T.; Tenney, D. R.; Herring, H. W.

    1975-01-01

    Oxidation tests of TD-NiCr alloy with different surface pretreatments were conducted in a Mach-5 arc-jet at 1200 C and 0.002 lb/sec flowing air environment. The mechanisms responsible for the observed oxidation behavior are examined. The presence of atomic oxygen in the air stream plays a significant role in determining the oxidation characteristic of the alloy. The rate of Cr2O3 vaporization by formation of volatile CrO3 is greatly enhanced by the flowing conditions. The typical microstructure of oxides formed in the dynamic tests consists of an external layer of NiO with a porous mushroom-type morphology, an intermediate layer of NiO and Cr2O3 oxide mixture, and a continuous inner layer of Cr2O3 in contact with the Cr-depleted alloy substrate. Three basic processes underlying the formation of mushroom-type NiO are identified and discussed. The oxidation rate is determined by the rate of vaporization of NiO. Surface pretreatment has a significant effect on the oxidation behavior of the alloy in the early stage of oxidation, but becomes less important as exposure time increases. Mechanical polishing induces surface recrystallization, but promotes the concurrence of external growth of NiO and internal oxidation of the alloy in the dynamic atmosphere.

  11. Determination of the surface isoelectric point of oxide films on metals by contact angle titration

    SciTech Connect

    McCafferty, E.; Wightman, J.P.

    1997-10-15

    The surface isoelectric point for the native air-formed oxide films on aluminum, chromium, and tantalum has been determined by measurement of contact angles at the hexadecane/aqueous solution interface as a function of pH of the aqueous phase. Application of Young`s equation, the Gibbs equation, and surface equilibria conditions for hydroxylated oxide films leads to a mathematical expression which shows that the contact angle goes through a maximum at the isoelectric point of the oxide. The experimentally determined isoelectric point of oxide-covered chromium is 5.2 to 5.3, of oxide-covered aluminum is 9.5, and of oxide-covered tantalum is approximately {minus}0.7. These values for the oxide films are within one to three pH units of the reported isoelectric points for the corresponding bulk oxide powders. The oxide-covered metal surfaces were cleaned by argon plasma treatment prior to measurement of contact angles, in that XPS measurements showed this treatment to be effective in reducing the thickness of the carbon contamination layer. In addition, interfacial tensions were measured at the hexadecane/aqueous solution interface and were observed to have only a slight dependence on the pH of the aqueous phase.

  12. 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.

  13. 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.

  14. Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces

    NASA Astrophysics Data System (ADS)

    McBriarty, Martin E.

    Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.

  15. Oxidation of cell surface thiol groups by contact sensitizers triggers the maturation of dendritic cells.

    PubMed

    Kagatani, Saori; Sasaki, Yoshinori; Hirota, Morihiko; Mizuashi, Masato; Suzuki, Mie; Ohtani, Tomoyuki; Itagaki, Hiroshi; Aiba, Setsuya

    2010-01-01

    p38 mitogen-activated protein kinase (MAPK) has a crucial role in the maturation of dendritic cells (DCs) by sensitizers. Recently, it has been reported that the oxidation of cell surface thiols by an exogenous impermeant thiol oxidizer can phosphorylate p38 MAPK. In this study, we examined whether sensitizers oxidize cell surface thiols of monocyte-derived DCs (MoDCs). When cell surface thiols were quantified by flow cytometry using Alexa fluor maleimide, all the sensitizers that we examined decreased cell surface thiols on MoDCs. To examine the effects of decreased cell surface thiols by sensitizers on DC maturation, we analyzed the effects of an impermeant thiol oxidizer, o-phenanthroline copper complex (CuPhen). The treatment of MoDCs with CuPhen decreased cell surface thiols, phosphorylated p38 MAPK, and induced MoDC maturation, that is, the augmentation of CD83, CD86, HLA-DR, and IL-8 mRNA, as well as the downregulation of aquaporin-3 mRNA. The augmentation of CD86 was significantly suppressed when MoDCs were pretreated with N-acetyl-L-cystein or treated with SB203580. Finally, we showed that epicutaneous application of 2,4-dinitrochlorobenzene on mouse skin significantly decreased cell surface thiols of Langerhans cells in vivo. These data suggest that the oxidation of cell surface thiols has some role in triggering DC maturation by sensitizers. PMID:19641517

  16. Surface thermal oxidation on titanium implants to enhance osteogenic activity and in vivo osseointegration.

    PubMed

    Wang, Guifang; Li, Jinhua; Lv, Kaige; Zhang, Wenjie; Ding, Xun; Yang, Guangzheng; Liu, Xuanyong; Jiang, Xinquan

    2016-01-01

    Thermal oxidation, which serves as a low-cost, effective and relatively simple/facile method, was used to modify a micro-structured titanium surface in ambient atmosphere at 450 °C for different time periods to improve in vitro and in vivo bioactivity. The surface morphology, crystallinity of the surface layers, chemical composition and chemical states were evaluated by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Cell behaviours including cell adhesion, attachment, proliferation, and osteogenic differentiation were observed in vitro study. The ability of the titanium surface to promote osseointegration was evaluated in an in vivo animal model. Surface thermal oxidation on titanium implants maintained the microstructure and, thus, both slightly changed the nanoscale structure of titanium and enhanced the crystallinity of the titanium surface layer. Cells cultured on the three oxidized titanium surfaces grew well and exhibited better osteogenic activity than did the control samples. The in vivo bone-implant contact also showed enhanced osseointegration after several hours of oxidization. This heat-treated titanium enhanced the osteogenic differentiation activity of rBMMSCs and improved osseointegration in vivo, suggesting that surface thermal oxidation could potentially be used in clinical applications to improve bone-implant integration. PMID:27546196

  17. Surface thermal oxidation on titanium implants to enhance osteogenic activity and in vivo osseointegration

    PubMed Central

    Wang, Guifang; Li, Jinhua; Lv, Kaige; Zhang, Wenjie; Ding, Xun; Yang, Guangzheng; Liu, Xuanyong; Jiang, Xinquan

    2016-01-01

    Thermal oxidation, which serves as a low-cost, effective and relatively simple/facile method, was used to modify a micro-structured titanium surface in ambient atmosphere at 450 °C for different time periods to improve in vitro and in vivo bioactivity. The surface morphology, crystallinity of the surface layers, chemical composition and chemical states were evaluated by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Cell behaviours including cell adhesion, attachment, proliferation, and osteogenic differentiation were observed in vitro study. The ability of the titanium surface to promote osseointegration was evaluated in an in vivo animal model. Surface thermal oxidation on titanium implants maintained the microstructure and, thus, both slightly changed the nanoscale structure of titanium and enhanced the crystallinity of the titanium surface layer. Cells cultured on the three oxidized titanium surfaces grew well and exhibited better osteogenic activity than did the control samples. The in vivo bone-implant contact also showed enhanced osseointegration after several hours of oxidization. This heat-treated titanium enhanced the osteogenic differentiation activity of rBMMSCs and improved osseointegration in vivo, suggesting that surface thermal oxidation could potentially be used in clinical applications to improve bone-implant integration. PMID:27546196

  18. Rates of oxidative weathering on the surface of Mars

    NASA Technical Reports Server (NTRS)

    Burns, Roger G.; Fisher, Duncan S.

    1993-01-01

    A model of acid weathering is proposed for the iron-rich basalts on Mars. Aqueous oxidation of iron sulfides released SO4(2-) and H(+) ions that initiated the dissolution of basaltic ferromagnesian silicates and released Fe(2+) ions. The Fe(2+) ions eventually underwent ferrolysis reactions and produced insoluble hydrous ferric oxide phases. Measurements of the time-dependence of acid weathering reactions show that pyrrhotite is rapidly converted to pyrite plus dissolved ferrous iron, the rate of pyrite formation decreasing with rising pH and lower temperatures. On Mars, oxidation rates of dissolved Fe(2+) ions in equatorial melt-waters in contact with the atmosphere are estimated to lie in the range 0.3-3.0 ppb Fe/yr over the pH range 2 to 6. Oxidation of Fe(2+) ions is estimated to be extremely slow in brine eutectic solutions that might be present on Mars and to be negligible in the frozen regolith.

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

    PubMed

    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 Al(2)O(3) (thickness, 0.4-0.7 nm) with 'nanocavities' (<2 nm in diameter) on a TiO(2) photocatalyst. The additional layers result in selectivity (up to 9:1) towards less hindered reactants in otherwise unselective, competitive photocatalytic oxidations and transfer hydrogenations. PMID:23174984

  20. 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.

  1. Rates of oxidative weathering on the surface of Mars

    NASA Astrophysics Data System (ADS)

    Burns, R. G.; Fisher, D. S.

    1993-02-01

    A model of acid weathering is proposed for the iron-rich basalts on Mars. Aqueous oxidation of iron sulfides released SO4(2-) and H(+) ions that initiated the dissolution of basaltic ferromagnesian silicates and released Fe(2+) ions. The Fe(2+) ions eventually underwent ferrolysis reactions and produced insoluble hydrous ferric oxide phases. Measurements of the time-dependence of acid weathering reactions show that pyrrhotite is rapidly converted to pyrite plus dissolved ferrous iron, the rate of pyrite formation decreasing with rising pH and lower temperatures. On Mars, oxidation rates of dissolved Fe(2+) ions in equatorial melt-waters in contact with the atmosphere are estimated to lie in the range 0.3-3.0 ppb Fe/yr over the pH range 2 to 6. Oxidation of Fe(2+) ions is estimated to be extremely slow in brine eutectic solutions that might be present on Mars and to be negligible in the frozen regolith.

  2. Influence of the surface morphology on the early stages of Cu oxidation

    NASA Astrophysics Data System (ADS)

    Luo, Langli; Kang, Yihong; Yang, Judith C.; Zhou, Guangwen

    2012-10-01

    The growth and morphological features of Cu films deposited on NaCl(1 0 0) by e-beam evaporation have been examined to evaluate the effect of various surface morphologies on the initial oxidation of Cu. It is shown that epitaxial Cu films with significantly reduced surface roughness can be achieved by first nucleating Cu seeds at 450 °C that favors epitaxial Cu grains which is followed by subsequent seed growth at 150 °C that favors smooth Cu film. The effect of the variations of the surface morphology of the resulting Cu films by the different growth conditions on the early stages oxidation of Cu films is examined by in situ transmission electron microscopy (TEM) and ex situ atomic force microscopy (AFM). It is shown that the changes in the surface morphologies of the Cu film result in distinct variations in the nucleation density and growth rates of oxide islands. Such correlation between the surface morphology and the initial oxidation behavior of the Cu films provides insights into understanding the microscopic processes of the transient oxidation of metals and for manipulating the initial oxide formation through surface treatments.

  3. Origin of complex impact craters on native oxide coated silicon surfaces

    SciTech Connect

    Samela, Juha; Nordlund, Kai; Popok, Vladimir N.; Campbell, Eleanor E. B.

    2008-02-15

    Crater structures induced by impact of keV-energy Ar{sub n}{sup +} cluster ions on silicon surfaces are measured with atomic force microscopy. Complex crater structures consisting of a central hillock and outer rim are observed more often on targets covered with a native silicon oxide layer than on targets without the oxide layer. To explain the formation of these complex crater structures, classical molecular dynamics simulations of Ar cluster impacts on oxide coated silicon surfaces, as well as on bulk amorphous silica, amorphous Si, and crystalline Si substrates, are carried out. The diameter of the simulated hillock structures in the silicon oxide layer is in agreement with the experimental results, but the simulations cannot directly explain the height of hillocks and the outer rim structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5 keV/atom Ar{sub 12} cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50 nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.

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

    SciTech Connect

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

    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.

  5. Surface band gaps and superexchange interaction in transition metal oxides

    SciTech Connect

    Pothuizen, J.J.M.; Cohen, O.; Sawatzky, G.A.

    1996-11-01

    In this paper, the authors discuss the change in the band gap of charge transfer insulators for different surface terminations. They have calculated the Madelung potential of the unreconstructed (100) surfaces of the rocksalt structured TM-O compounds (TM = Mn, Fe, Co and Ni). They also considered possible step defects on a (100) surface. The presented results are calculated in both the purely ionic case (TM{sup 2+}O{sup 2{minus}}) and in the strong ligand p - cation 4s,p hybridization (TM{sup 1+}O{sup 1{minus}}) case. In both cases the charge transfer gap, {Delta}, for the surface is reduced compared to the bulk value. As a consequence of this reduction there is a large increase of the surface superexchange interaction, J{sub sur}, and a decrease of the band gap.

  6. Oxide formation and alloying elements enrichment on TRIP steel surface during inter-critical annealing.

    PubMed

    Gong, Y F; Birosca, S; Kim, H S; De Cooman, B C

    2008-06-01

    The gas atmosphere in continuous annealing and galvanizing lines alters both composition and microstructure of the surface and sub-surface of sheet steels. The alloying element enrichments and the oxide morphology on transformation-induced plasticity steel surfaces are strongly influenced by the dew point of the furnace atmosphere and annealing temperature. The formation of a thin oxide film and enrichment of the alloying elements during annealing may result in surface defects on galvanized sheet products. The present contribution reports on the use of microanalysis techniques such as electron backscatter diffraction, glow discharge optical emission spectroscopy and electron probe micro-analysis for the detailed surface analysis of inter-critically annealed transformation-induced plasticity steel such as oxide phase determination, microstructure and microtexture evolutions. PMID:18503669

  7. Repassivation of titanium and surface oxide film regenerated in simulated bioliquid.

    PubMed

    Hanawa, T; Asami, K; Asaoka, K

    1998-06-15

    The change in potential during repassivation of titanium in artificial bioliquids was examined, and the regenerated surface oxide film on titanium was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy to elucidate the repassivation reaction of titanium in a biological system. The repassivation rate in Hanks' solution was slower than that in saline and was not influenced by the pH of the solution. This indicates that more titanium ions dissolve in a biological system than hitherto was predicted when the surface film is destroyed. Phosphate ions are taken up preferentially in the surface film during regeneration, and the film consists of titanium oxide and titanium oxyhydroxide containing titanium phosphate. Calcium ions and phosphate ions are adsorbed by the film after regeneration, and calcium phosphate or calcium titanium phosphate is formed at the outermost surface. Ions constituting Hanks' solution other than calcium and phosphate were absent from the surface oxide. PMID:9599028

  8. Obtaining composite Zr-Al-O coating on the surface of zirconium by microplasma oxidation

    SciTech Connect

    Gubaidulina, Tatiana A. E-mail: ostk@mail2000ru; Kuzmin, Oleg S. E-mail: ostk@mail2000ru; Fedorischva, Marina V. E-mail: kmp1980@mail.ru; Kalashnikov, Mark P. E-mail: kmp1980@mail.ru; Sergeev, Viktor P.

    2014-11-14

    The paper describes the application of the microplasma oxidation for production of Zr-Al-O composition on the surface of zirconium. Certification of a new-type power supply for depositing oxide ceramic coatings by microplasma oxidation was also carried out. The growth rate of Zr-Al-O coating amounted around 0.2 nm/s, which around 10 times exceeds that for depositing similar coatings using the similar equipment. We have studied the change of surface morphology and the chemical composition of the formed ceramic coating by means of EVO 50 scanning electron microscope and X-ray spectral analysis.

  9. Phase composition and structure of femtosecond laser-produced oxide layer on VT6 alloy surface

    NASA Astrophysics Data System (ADS)

    Kolobov, Yu R.; Zhidkov, M. V.; Golosov, E. V.; Vershinina, T. N.; Kudryashov, S. I.; Makarov, S. V.; Ionin, A. A.; Ligachev, A. E.

    2016-07-01

    The influence of femtosecond laser irradiation on the formation of an oxide layer on the surface of VT6 titanium alloy (Ti–6Al–4V) is studied. The structure, chemical and phase composition have been studied by x-ray diffraction, and scanning and transmission electron microscopy. The formation features of an oxide layer, which contains TiO2-rutile, TiO2-anatase Al2TiO5-aluminum titanate, Ti3O5-titanium oxide and TiO-titanium monoxide on the femtosecond laser-irradiation modified surface have been analyzed.

  10. In situ observation of surface species on iridium oxide nanoparticles during the oxygen evolution reaction.

    PubMed

    Sanchez Casalongue, Hernan G; Ng, May Ling; Kaya, Sarp; Friebel, Daniel; Ogasawara, Hirohito; Nilsson, Anders

    2014-07-01

    An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in situ by ambient-pressure X-ray photoelectron spectroscopy. Under OER conditions, iridium undergoes a change in oxidation state from Ir(IV) to Ir(V) that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH-mediated deprotonation mechanism. PMID:24889896

  11. 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

  12. Exclusively Gas-Phase Passivation of Native Oxide-Free Silicon(100) and Silicon(111) Surfaces.

    PubMed

    Tao, Ye; Hauert, Roland; Degen, Christian L

    2016-05-25

    Reactions in the gas phase are of primary technological importance for applications in nano- and microfabrication technology and in the semiconductor industry. We present exclusively gas-phase protocols to chemically passivate oxide-free Si(111) and Si(100) surfaces with short-chain alkynes. The resulting surfaces showed equal or better oxidation resistance than most existing liquid-phase-derived surfaces and rivaled the outstanding stability of a full-coverage Si(111)-propenyl surface.1,2 The most stable surface (Si(111)-ethenyl) grew one-fifth of a monolayer of oxide (0.04 nm) after 1 month of air exposure. We monitored the regrowth of oxides on passivated Si(111) and Si(100) surfaces by X-ray photoelectron spectroscopy (XPS) and observed a significant crystal-orientation dependence of initial rates when total oxide thickness was below approximately one monolayer (0.2 nm). This difference was correlated with the desorption kinetics of residual surface Si-F bonds formed during HF treatment. We discuss applications of the technology and suggest future directions for process optimization. PMID:27153212

  13. Surface photovoltage analysis of iron contamination in silicon processing and the relation to gate oxide integrity

    NASA Astrophysics Data System (ADS)

    Henley, Worth B.

    1995-09-01

    Surface photovoltage (SPV), a contactless optical technique for measuring minority carrier lifetime, is used to quantify the relationship between silicon iron contamination level and thin gate oxide integrity. Iron concentration levels in the range of 1 X 1010 cm-3 to 5 X 1013 cm-3 are evaluated for oxide thicknesses of 8 to 20 nm. Ramp voltage electrical breakdown and time dependant dielectric breakdown measurement on the iron contaminated gate oxide capacitors are reported. Distinct iron contamination threshold limits based on defect density and gate oxide integrity evaluate cleaning efficiencies and metallic cross contamination effects during thermal processing contamination. Iron-silicide precipitation kinetics are investigated by the lifetime analysis procedure.

  14. Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics

    SciTech Connect

    Doyle, F.M.

    1992-06-30

    during the seventh quarter, electrokinetic, humic acid extraction and film flotation tests were done on oxidized samples of Upper Freeport coal from the Troutville {number sign} 2 Mine, Clearfield County, Pennsylvania. Scanning electron microscopy and energy dispersive X-ray analysis was done to characterize the morphology and composition of the surface of as-received coal, oxidized coal, oxidized coal after extraction of humic acids and humic acid extracted from oxidized coal. In addition, electrochemical studies were done on electrodes prepared from coal pyrite samples.

  15. 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.

  16. Investigation of oxygen states and reactivities on a nanostructured cupric oxide surface

    NASA Astrophysics Data System (ADS)

    Svintsitskiy, D. A.; Stadnichenko, A. I.; Demidov, D. V.; Koscheev, S. V.; Boronin, A. I.

    2011-08-01

    Nanostructured copper (II) oxide was formed on clean copper foil at room temperature using activated oxygen produced by RF discharge. CuO particles of approximately 10-20 nm were observed on the surface by Scanning Tunneling Microscopy (STM). The copper states and oxygen species of the model cupric oxide were studied by means of X-ray Photoelectron Spectroscopy (XPS). These oxide particles demonstrated abnormally high reactivity with carbon monoxide (CO) at temperatures below 100 °C. The XPS data showed that the interaction of CO with the nanostructured cupric oxide resulted in reduction of the CuO particles to Cu 2O species. The reactivity of the nanostructured cupric oxide to CO was studied at 80 °C using XPS in step-by-step mode. The initial reactivity was estimated to be 5 × 10 -5 and was steadily reduced down to 5 × 10 -9 as the exposure was increased. O1s spectral analysis allowed us to propose that the high initial reactivity was caused by the presence of non-lattice oxygen states on the surface of the nanostructured CuO. We established that reoxidation of the partially reduced nanostructured cupric oxide by molecular oxygen O 2 restored the highly reactive oxygen form on the surface. These results allowed us to propose that the nanostructured cupric oxide could be used for low temperature catalytic CO oxidation. Some hypotheses concerning the nature of the non-lattice oxygen species with high reactivity are also discussed.

  17. Isothermal oxidation behavior and microstructure of plasma surface Ta coating on γ-TiAl

    SciTech Connect

    Song, Jian; Zhang, Ping-Ze Wei, Dong-Bo; Wei, Xiang-Fei; Wang, Ya

    2014-12-15

    The oxidation behavior of γ-TiAl with Ta surface coating fabricated by double glow plasma surface alloying technology was investigated by thermogravimetric method. Oxidation experiments were carried out at 750 °C and 850 °C in air for 100 h. The modification layer was comprised of deposition layer and diffusion layer, which metallurgically adhered to the substrate. Tantalum element decreased with the case depth. The oxidation morphology was studied by a scanning electron microscope and X-ray diffraction. The results highlighted that in the oxidizing process of the oxidation, the phase containing Ta-richer may restrain diffusing outward of the element Al in the matrix. Ti diffused outward, and formed the TiO{sub 2} scales, while the middle layer was rich in Al, and formed the continuous Al{sub 2}O{sub 3} scales after oxidation, which was effective to prevent further infiltration of oxygen atoms, and as a result the oxidation resistance increased immensely. - Highlights: • A Ta modified coating was prepared on γ-TiAl using DGP surface alloying technology. • The modification layer metallurgically adhered to the substrate. • The bonding force is about 60 N, satisfying the demands of practical use. • The oxidation resistance increased immensely at 750 °C and 850 °C.

  18. Scavenging of Cd through Fe/Mn oxides within natural surface coatings.

    PubMed

    Li, Yu; Huang, Guo-he; Zhang, Bai-yu; Guo, Shu-hai

    2006-01-01

    The dynamics of Cd scavenging from solutions by Fe/Mn oxides in natural surface coatings (NSCs) was investigated under laboratory conditions. Selective extraction methods were employed to estimate the contributions of Fe/Mn oxides, where hydroxylamine hydrochloride (0.01 mol/L NH2OH x HCl + 0.01 mol/L HNO3), sodium dithionite (0.4 mol/L Na2S2O4) and nitric acid (10% HNO3) were used as extraction reagents. The Cd scavenging was accomplished with developing periods of the NSCs (totally 21 data sets). The resulting process dynamics fitted well to the Elovich equation, demonstrating that the amount of Cd scavenged was proportional to the increments of Fe/Mn oxides that were accumulated in the NSCs. The amount of Cd bound to Fe oxides (M,,) and Mn oxides (MCdMn could be quantified by solving two equations based on the properties of two extraction reagents. The amount of Cd scavenged by Fe/Mn oxides could also be estimated using MCdFe and MCdMn, divided by the total amounts of Fe and Mn oxides in the NSCs, respectively. The results indicated that the Cd scavenging by Fe/Mn oxides was dominated by Fe oxides, with less roles attributed to Mn oxides. The estimated levels of Cd scavenging through Fe and Mn oxides agreed well with those predicted through additive-adsorption and linear-regression models. PMID:17294965

  19. Influence of growth ambient on the surface and structural properties of vanadium oxide nanorods

    NASA Astrophysics Data System (ADS)

    Tien, Li-Chia; Chen, Yu-Jyun

    2013-06-01

    The influence of growth ambient on the surface and structural properties of vanadium oxide nanorods have been studied by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS). The vanadium oxide nanorods, which were synthesized through an ambient controlled vapor transport process, exhibit different surface electronic properties depending upon the growth ambient. The Raman data indicates that the as-grown samples are orthorhombic V2O5 phase with a small variation of stoichiometry. Under highly oxidative conditions, nearly stoichiometry sample can be grown. If the samples were grown under less oxidizing conditions, an increase of structural disorder was observed. The observed V 2p core level spectra of both samples showed a single peak with chemical shifts corresponding to the V5+ and V4+. XPS results suggested that the highly oxidized vanadium ions (V5+) are gradually reduced to lower oxidation state (V4+) with the decreases of ambient oxygen levels during growth. The results clearly show that surface non-stoichiometry may be correlated with structural disorder of V2O5 nanorods. The growth ambient and post-annealing may influence the vanadium oxidation state and subsequent surface reactivity significantly.

  20. Thermal Stress of Surface Oxide Layer on Micro Solder Bumps During Reflow

    NASA Astrophysics Data System (ADS)

    Key Chung, C.; Zhu, Z. X.; Kao, C. R.

    2015-02-01

    Micro-bumps are now being developed with diameters smaller than 10 μm. At these dimensions, only very small amounts of solder are used to form the interconnections. Surface oxidation of such small micro-bumps is a critical issue. The key question is whether the oxide film on the solder bumps acts as a barrier to formation of solder joints. In this work, the mechanical stability of the oxide layer on solder bumps was investigated. Solder bumps with 35- μm radii were heated for different times. Auger electron spectroscopy was used to determine the thickness of the oxide layer on the solder bumps. Solder bumps with known oxide layer thicknesses were then heated in a low-oxygen environment (<50 ppm) until they melted. The mechanical stability of the oxide layer was observed by use of a high-speed camera. Results showed that a 14-nm-thick oxide layer on a solder bump of radius 35 μm was able to withstand the molten solder without cracking, leading to a non-wetting solder joint. A thermal stress model of the surface oxide layer revealed that the stress varied substantially with bump size and temperature, and increased almost linearly with temperature. Upon melting, the thermal stress on the oxide increased abruptly, because of the higher thermal expansion of molten solder compared with its solid state. On the basis of the experimental results and the thermal stress model of the oxide film, the maximum oxide thickness that can be tolerated to form a solder joint was determined, e.g. 14 nm oxide can support liquid solder, and thus lead to a non-wetting condition. This work provided a new method of determination of the maximum stress of oxide film for solder joint formation.

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

    SciTech Connect

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

    2014-10-28

    A six-dimensional potential energy hypersurface (PES) for two interacting rigid ethylene oxide (C{sub 2}H{sub 4}O) 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.

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

    PubMed

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

    2014-10-28

    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. PMID:25362314

  3. Controlling oxide surface dipole and reactivity with intrinsic nonstoichiometric epitaxial reconstructions

    NASA Astrophysics Data System (ADS)

    Kim, Seungchul; Sinai, Ofer; Lee, Chan-Woo; Rappe, Andrew M.

    2015-12-01

    The composition and reconstruction of oxide surfaces can be deterministically controlled via ambient conditions. We demonstrate that such intrinsic alterations can have a crucial effect on the surface dipole and reactivity, even for surfaces with the same crystallographic plane. The surface dipole potential drops of BaTiO3,SrTiO3,LaFeO3, and TiO2 surfaces with various reconstructions and compositions are shown to vary by as much as 5 V, leading to significant variation of the band edge positions at these surfaces. These variations are shown to correlate with the calculated oxygen binding energy, demonstrating how oxide surface reactivity can be substantially manipulated using environmental changes.

  4. 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.

  5. Enhanced magnetic properties of Fe soft magnetic composites by surface oxidation

    NASA Astrophysics Data System (ADS)

    Zhao, Guoliang; Wu, Chen; Yan, Mi

    2016-02-01

    Fe soft magnetic composites (SMCs) with low core loss were fabricated via surface oxidation of the Fe powders by H2O and O2 at elevated temperatures. Surface oxidation prevents magnetic dilution due to the formation of the ferromagnetic iron oxide coating layer, giving rise to high magnetic flux density and effective permeability of the SMCs compared with those fabricated with traditional phosphate coating. Mechanism of the oxidation process has been investigated where Fe3O4 forms by reactions of Fe with H2O and O2. The Fe3O4 coating layer tends to convert into γ-Fe2O3 with increased oxidation temperature and time. By controlling composition of the coating layer, low core loss of 688.9 mW/cm3 (measured at 50 mT and 100 kHz) and higher effective permeability of 88.3 can be achieved for the Fe SMCs.

  6. Determination of an oxide film on the surface of perlite steel

    SciTech Connect

    Krutikov, P.G.; Bykova, E.M.; Nemirov, N.V.; Papurin, N.M.

    1986-04-01

    When studying the formation of oxide films on the surface of circuits and systems in atomic and thermal power stations made of perlite steels, the need arises for the determination of the specific amount and thickness of oxide films. In order to reduce the error and the time required for such a determination, the authors have developed a new procedure, based on the selective dissolution of iron oxides with a proposed composition in the weak etching of themetal base. In this approach, the sample of perlite steel with the film is weighed before and after immersion in a solution of hydrochloric acid in acetone. The proposed procedure can be applied to dissolve dense oxide films. The total duration of a determination of the specific amount of oxide film on the surface of perlite steel by the proposed procedure is 20-25 minutes by using six samples at a time.

  7. Relationship between indium tin oxide surface treatment and hole injection in C60 modified devices

    NASA Astrophysics Data System (ADS)

    Kim, Sung Hyun; Jang, Jyongsik; Lee, Jun Yeob

    2006-12-01

    The effect of indium tin oxide (ITO) surface treatment on hole injection in organic light-emitting diode with C60 as a buffer layer on ITO was studied. Double surface dipole layer was induced on oxygen plasma treated ITO surface, while no dipole formation was observed on ITO without surface treatment. Interfacial energy barrier between ITO and hole transport layer was reduced by 0.4eV by C60 modification on oxygen plasma treated ITO surface, while there was no change of interfacial energy barrier by C60 on ITO without surface treatment.

  8. In-vacuum scattered light reduction with black cupric oxide surfaces for sensitive fluorescence detection.

    PubMed

    Norrgard, E B; Sitaraman, N; Barry, J F; McCarron, D J; Steinecker, M H; DeMille, D

    2016-05-01

    We demonstrate a simple and easy method for producing low-reflectivity surfaces that are ultra-high vacuum compatible, may be baked to high temperatures, and are easily applied even on complex surface geometries. Black cupric oxide (CuO) surfaces are chemically grown in minutes on any copper surface, allowing for low-cost, rapid prototyping, and production. The reflective properties are measured to be comparable to commercially available products for creating optically black surfaces. We describe a vacuum apparatus which uses multiple blackened copper surfaces for sensitive, low-background detection of molecules using laser-induced fluorescence. PMID:27250404

  9. 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...

  10. Electrically polarized micro-arc oxidized TiO2 coatings with enhanced surface hydrophilicity.

    PubMed

    Ma, Chufan; Nagai, Akiko; Yamazaki, Yuko; Toyama, Takeshi; Tsutsumi, Yusuke; Hanawa, Takao; Wang, Wei; Yamashita, Kimihiro

    2012-02-01

    The use of micro-arc oxidation titania (MAO TiO2) coatings to modify titanium surfaces improves the biocompatibility of implant surfaces. To obtain hydrophilic MAO TiO2 coating surfaces electric polarization, which induces surface electric fields in the materials and produces surface charges, was performed in this study. Electric polarization of the MAO TiO2 coatings was confirmed by measuring the thermally stimulated depolarization current. After electric polarization treatment the MAO TiO2 coatings did not exhibit any obvious changes in surface roughness, morphology, or phase components. X-ray photoelectron spectroscopy results indicated that electric polarization resulted in oxidation of the cathodic-faced surfaces and reduction of the anodic-faced surfaces. This result suggests that the existence of a concentration gradient of oxide ions/oxygen vacancies produced the stored space charge in the coatings. Reduction of the deionized water contact angle on the polarized MAO TiO2 surfaces was maintained for longer periods compared with the non-polarized surface. Our study demonstrated that metastable electric fields across the MAO TiO2 coating produced by electric polarization made it durably wettable by reducing the interfacial surface tension between the material and water. PMID:21971419

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

    SciTech Connect

    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 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.

  12. 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.

  13. Surface Oxidation of Ti-6Al-4V for Bio-Implant Application

    NASA Astrophysics Data System (ADS)

    Biswas, A.; Bhattacharjee, U.; Manna, I.; Dutta Majumdar, J.

    The present study aims at enhancing the wear resistance and biocompatibility of Ti-6Al-4V by forming a thin layer of oxide. Surface oxidation has been carried out by controlled heating of the surface of Ti-6Al-4V substrate in air at the temperature ranging from 400-600°C and time from 25-60 h. The phase formed under thermal oxidation was predominantly the rutile and anatase phase. The thickness of the oxide layer varied from 1.5-7.0 μm. The microhardness on the surface was significantly improved as compared to the as-received substrate. Both the corrosion resistance property and biocompatibility were improved.

  14. Surface modification of ferritic and Ni based alloys for improved oxidation resistance of SOFC interconnect applications

    SciTech Connect

    Jablonski, Paul D.; Alman, David E.; Kung, Steven C.

    2005-08-01

    This research is aimed at evaluating a surface modification of ferritic stainless steels (Type-430 and Crofer 22APU) and nickel-base alloys (Haynes 230) for use in the SOFC temperature range of 700 to 800°C. A surface treatment was devised to enhance the stability of the base metal oxide that forms and to reduce the oxidation rate of the materials at high temperature. Oxidation tests (in wet air; treated and untreated) were conducted at 800°C to evaulate the corrosion resistance of the alloys. It was found that the surface treatment improved the oxidation resistance of all the alloys tested. However, the treatment improved the performance of 430SS more than that of the other alloys.

  15. Cd adsorption properties of components in different freshwater surface coatings: the important role of ferromanganese oxides.

    PubMed

    Dong, Deming; Hua, Xiuyi; Li, Yu; Zhang, Jingjing; Yan, Dongxu

    2003-09-15

    Surface coatings developed in different natural waters were used to study the role of the composition of surface coatings in controlling Cd adsorption in aquatic environments. To investigate the adsorption property of each component, the method of extraction techniques followed by Cd adsorption and statistical analysis were employed. Hydroxylamine hydrochloride was used to remove Mn oxides selectively, sodium dithionite was used to remove Mn and Fe oxides, and oxalic acid was used to remove most metal oxides and part of the organic material. Adsorption of Cd to surface coatings was measured before and after extraction under controlled laboratory conditions. The observed Cd adsorptions to unextracted and extracted surface coatings were analyzed using nonlinear least-squares fitting to estimate the adsorption property of each surface coating constituent. In different waters, the relative contribution to Cd adsorption of each component was different, but in all the waters studied, ferromanganese oxides contributed most with lesser roles indicated for organic phase and Al oxides. The Cd adsorption ability of manganese oxides was significantly higher than that of the other components. PMID:14524442

  16. Oxidation of activated carbon fibers: Effect on pore size, surface chemistry, and adsorption properties

    SciTech Connect

    Mangun, C.L.; Benak, K.R.; Daley, M.A.; Economy, J.

    1999-12-01

    Activated carbon fibers (ACFs) were oxidized using both aqueous and nonaqueous treatments. As much as 29 wt% oxygen can be incorporated onto the pore surface in the form of phenolic hydroxyl, quinine, and carboxylic acid groups. The effect of oxidation on the pore size, pore volume, and the pore surface chemistry was thoroughly examined. The average micropore size is typically affected very little by aqueous oxidation while the micropore volume and surface area decreases with such a treatment. In contrast, the micropore size and micropore volume both increase with oxidation in air. Oxidation of the fibers produces surface chemistries in the pore that provide for enhanced adsorption of basic (ammonia) and polar (acetone) molecules at ambient and nonambient temperatures. The adsorption capacity of the oxidized fibers for acetone is modestly better than the untreated ACFs while the adsorption capacity for ammonia can increase up to 30 times compared to untreated ACFs. The pore surface chemical makeup was analyzed using elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS).

  17. 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.

  18. Chemical modification of oxidized and silicon oxide covered aluminium surfaces studied by FTIR/multiple specular reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Sondag, A. H.; Raas, M. C.; Touwslager, F. J.; Ponjee, J. J.

    1989-12-01

    Multiple Specular Reflectance (MSR) infrared reflection-absorption spectroscopy has been applied to study surface modification by organosilane (sub)monomolecular layers. The spectrum of octadecyldimethylmethoxysilane immobilized on an oxidized aluminium substrate is compared to the absorption spectra of the monomer and the disiloxane condensation product. Formation of hydroxyl groups on a Si02 covered aluminium substrate by a UV-ozon treatment is shown. Simultaneously, organic contaminants are removed from the surface by the UV-ozon treatment. The chemisorption of 3-methacryloxypropyldimethylethoxysilane on UV-ozon treated Si02 has been examined at different surface coverages. An increase of the number of organosilane species at the surface is accompanied by a decrease of surface hydroxyl groups.

  19. Deformation behavior of the oxide film on the surface of cold sprayed powder particle

    NASA Astrophysics Data System (ADS)

    Yin, Shuo; Wang, Xiaofang; Li, Wenya; Liao, Hanlin; Jie, Hongen

    2012-10-01

    In cold spraying, oxide-free interface is an important factor for metal-to-metal contact between powder particles and substrate, which determines the bonding strength and final coating quality. In this study, a systematic finite element analysis (FEA) is performed to examine the deformation behavior of the oxide film on an Al 6061-T6 particle surface after deposition. The simulation results show that the oxide film can be disrupted during the high velocity impact. Part of the cracked oxides remains at the interface and mainly accumulates at the central region after particle deposition. Substrate hardness, particle velocity and spray angle are found to influence the deformation behavior and final state of the oxide film. Besides, interparticle interaction is also investigated in the present work to clarify the deformation behavior of the oxide film inside the coating.

  20. Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface.

    PubMed

    Tsvetkov, Nikolai; Lu, Qiyang; Sun, Lixin; Crumlin, Ethan J; Yildiz, Bilge

    2016-09-01

    Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces are detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants (for example, ) by the positively charged oxygen vacancies () enriched at the surface. Here we show that reducing the surface concentration improves the oxygen surface exchange kinetics and stability significantly, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules. We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less reducible than Co on the B-site of LSC. By using ambient-pressure X-ray absorption and photoelectron spectroscopy, we proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while reducing the concentration of and making the LSC more oxidized at its surface. Consequently, we found that these less reducible cations significantly improve stability, with up to 30 times faster oxygen exchange kinetics after 54 h in air at 530 °C achieved by Hf addition onto LSC. Finally, the results revealed a 'volcano' relation between the oxygen exchange kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the chemical stability loss. PMID:27295099

  1. Surface Composition, Work Function, and Electrochemical Characteristics of Gallium-Doped Zinc Oxide

    SciTech Connect

    Ratcliff, E. L.; Sigdel, A. K.; Macech, M. R.; Nebesny, K.; Lee, P. A.; Ginley, D. S.; Armstrong, N. R.; Berry, J. J.

    2012-06-30

    Gallium-doped zinc oxide (GZO) possesses the electric conductivity, thermal stability, and earth abundance to be a promising transparent conductive oxide replacement for indium tin oxide electrodes in a number of molecular electronic devices, including organic solar cells and organic light emitting diodes. The surface chemistry of GZO is complex and dominated by the hydrolysis chemistry of ZnO, which influences the work function via charge transfer and band bending caused by adsorbates. A comprehensive characterization of the surface chemical composition and electrochemical properties of GZO electrodes is presented, using both solution and surface adsorbed redox probe molecules. The GZO surface is characterized using monochromatic X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy after the following pretreatments: (i) hydriodic acid etch, (ii) potassium hydroxide etch, (iii) RF oxygen plasma etching, and (iv) high-vacuum argon-ion sputtering. The O 1s spectra for the GZO electrodes have contributions from the stoichiometric oxide lattice, defects within the lattice, hydroxylated species, and carbonaceous impurities, with relative near-surface compositions varying with pretreatment. Solution etching procedures result in an increase of the work function and ionization potential of the GZO electrode, but yield different near surface Zn:Ga atomic ratios, which significantly influence charge transfer rates for a chemisorbed probe molecule. The near surface chemical composition is shown to be the dominant factor in controlling surface work function and significantly influences the rate of electron transfer to both solution and tethered probe molecules.

  2. 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

  3. Enhanced Lifetime of Polymer Solar Cells by Surface Passivation of Metal Oxide Buffer Layers.

    PubMed

    Venkatesan, Swaminathan; Ngo, Evan; Khatiwada, Devendra; Zhang, Cheng; Qiao, Qiquan

    2015-07-29

    The role of electron selective interfaces on the performance and lifetime of polymer solar cells were compared and analyzed. Bilayer interfaces consisting of metal oxide films with cationic polymer modification namely poly ethylenimine ethoxylated (PEIE) were found to enhance device lifetime compared to bare metal oxide films when used as an electron selective cathode interface. Devices utilizing surface-modified metal oxide layers showed enhanced lifetimes, retaining up to 85% of their original efficiency when stored in ambient atmosphere for 180 days without any encapsulation. The work function and surface potential of zinc oxide (ZnO) and ZnO/PEIE interlayers were evaluated using Kelvin probe and Kelvin probe force microscopy (KPFM) respectively. Kelvin probe measurements showed a smaller reduction in work function of ZnO/PEIE films compared to bare ZnO films when aged in atmospheric conditions. KPFM measurements showed that the surface potential of the ZnO surface drastically reduces when stored in ambient air for 7 days because of surface oxidation. Surface oxidation of the interface led to a substantial decrease in the performance in aged devices. The enhancement in the lifetime of devices with a bilayer interface was correlated to the suppressed surface oxidation of the metal oxide layers. The PEIE passivated surface retained a lower Fermi level when aged, which led to lower trap-assisted recombination at the polymer-cathode interface. Further photocharge extraction by linearly increasing voltage (Photo-CELIV) measurements were performed on fresh and aged samples to evaluate the field required to extract maximum charges. Fresh devices with a bare ZnO cathode interlayer required a lower field than devices with ZnO/PEIE cathode interface. However, aged devices with ZnO required a much higher field to extract charges while aged devices with ZnO/PEIE showed a minor increase compared to the fresh devices. Results indicate that surface modification can act as a

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

    SciTech Connect

    Masuda, Yoshitake 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.

  5. Surface Selective Oxidation of Sn-Added CMnSi TRIP Steel

    NASA Astrophysics Data System (ADS)

    Cho, Lawrence; Seo, Eun Jung; Jung, Geun Su; Suh, Dong Woo; De Cooman, Bruno C.

    2016-04-01

    The influence of the addition of Sn on the selective oxidation and the reactive wetting of CMnSi transformation-induced plasticity (TRIP) steels was studied by means of galvanizing simulator tests. A reference TRIP steel and TRIP steels containing Sn in the range of 0.05 to 1 wt pct were intercritically annealed at 1093 K (820 °C) in an N2+ 5 pct H2 gas atmosphere with a dew point of -60 °C. The thin-film oxides formed on the surface of the Sn-added CMnSi TRIP steel were investigated using transmission electron microscopy and 3-dimensional atom probe tomography. The addition of Sn (≥0.05 wt pct) changed the morphology of the xMnO·SiO2 surface oxides from a continuous film morphology to a lens-shaped island morphology. It also suppressed the formation of the Mn-rich oxides of MnO and 2MnO·SiO2. The changes in the morphology and chemistry of the surface oxides were clearly related to the surface segregation of Sn, which appeared to result in a decrease of the oxygen permeability at the surface. The formation of lens-shaped oxides improved the wettability of the CMnSi TRIP steel surface by the molten Zn. The improved wetting effect was attributed to an increased area fraction of the surface where the oxide layer was thinner. This enabled a direct, unhindered reaction between Fe and the Al in the liquid Zn and the formation of the inhibition layer in the initial stages of the hot dipping. The addition of a small amount of Sn was also found to decrease significantly the density of Zn-coating defects on CMnSi TRIP steel.

  6. Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

    NASA Astrophysics Data System (ADS)

    Weiss, Werner; Ranke, Wolfgang

    2002-03-01

    Metal-oxide-based catalysts are used for many important synthesis reactions in the chemical industry. A better understanding of the catalyst operation can be achieved by studying elementary reaction steps on well-defined model catalyst systems. For the dehydrogenation of ethylbenzene to styrene in the presence of steam both unpromoted and potassium promoted iron-oxide catalysts are active. Here we review the work done over unpromoted single-crystalline FeO(1 1 1), Fe3O4(1 1 1) and α- Fe2O3(0 0 0 1) films grown epitaxially on Pt(1 1 1) substrates. Their geometric and electronic surface structures were characterized by STM, LEED, electron microscopy and electron spectroscopic techniques. In an integrative approach, the interaction of water, ethylbenzene and styrene with these films was investigated mainly by thermal desorption and photoelectron emission spectroscopy. The adsorption-desorption energetics and kinetics depend on the oxide surface terminations and are correlated to the electronic structures and acid-base properties of the corresponding oxide phases, which reveal insight into the nature of the active sites and into the catalytic function of semiconducting oxides in general. Catalytic studies, using a batch-reactor arrangement at high gas pressures and post-reaction surface analysis, showed that only α- Fe2O3(0 0 0 1) containing surface defects is catalytically active, whereas Fe3O4(1 1 1) is always inactive. This can be related to the elementary adsorption and desorption properties observed in ultrahigh vacuum, which indicates that the surface chemical properties of the iron-oxide films do not change significantly across the “pressure-gap”. A model is proposed according to which the active site involves a regular acidic surface site and a defect site next to it. The results on metal-oxide surface chemistry also have implications for other fields such as environmental science, biophysics and chemical sensors.

  7. Hydrogen transport through oxide metal surface under atom and ion irradiation

    NASA Astrophysics Data System (ADS)

    Begrambekov, L.; Dvoychenkova, O.; Evsin, A.; Kaplevsky, A.; Sadovskiy, Ya; Schitov, N.; Vergasov, S.; Yurkov, D.

    2014-11-01

    Both the latest and earlier achieved results on gas exchange processes on metal surfaces (including stainless steel, titanium, zirconium, tungsten with deposited aluminum oxide coating) under hydrogen atom or plasma irradiation with occasional oxygen impurity are presented in the paper. Mechanisms and regularities of these processes are discussed. It is demonstrated that surface oxide layer properties as a diffusion barrier strongly depend on external influence on the surface. In particular, it is revealed that low energy hydrogen ion irradiation could slow down hydrogen desorption from metals. Hydrogen atom or ion irradiation combined with simultaneous oxygen admixture accelerates hydrogen desorption from metals.

  8. Influence of the Structure of the Titanium Oxide Coating Surface on Immunocompetent Tumor Cells

    NASA Astrophysics Data System (ADS)

    Khlusov, I. A.; Sharkeev, Yu. P.; Pichugin, V. F.; Legostaeva, E. V.; Litvinova, L. S.; Shupletsova, V. V.; Sokhonevich, N. A.; Khaziakhmatova, O. G.; Khlusova, M. Yu.; Gutor, S. S.; Tolkacheva, T. V.

    2016-03-01

    Results of a study of the properties of titanium oxide based coatings deposited on titanium substrates by microarc oxidation are presented that establish a relationship between physical and mechanical properties of the coating surface and their medical and biological properties. The required surface topography is formed by sandblasting of the substrate and is controlled by values of the roughness index Ra. A linear dependence of the amplitude of negative electrostatic potential of the oxide coating on the Ra value is established. The topography of the micro-arc coating surface determines its negative surface potential that apparently reduces the viability of the leukemia T cells of the Jurkat line via electrostatic and biological mechanisms unrelated to the generation of intracellular reactive oxygen species.

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

    SciTech Connect

    Salame, I.I.; Bandosz, T.J. |

    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).

  10. Dynamics of cathode spots in low-pressure arc plasma removing oxide layer on steel surfaces

    NASA Astrophysics Data System (ADS)

    Tang, Z. L.; Yang, K.; Liu, H. X.; Zhang, Y. C.; Li, H.; Zhu, X. D.

    2016-03-01

    The dynamics of cathode spots has been investigated in low-pressure arc plasma for removing oxide layer on low carbon steel surfaces. The motion of cathode spots was observed with a high speed camera, and the arc voltage was analyzed by fast Fourier transform. The spots move on clean steel surface as a random walk, and the low-frequency components dominated the voltage waveform. However, the spots on steel surfaces with oxide layer tend to burn on the rim of the eroded area formed in the previous arcing, and the low-frequency components decrease correspondingly. The "color" of the colored random noise for arc voltage varies from the approximate brown noise for clean steel surface to pink noise for thick oxide layer, where the edge effect of boundary is considered to play a significant role.

  11. Insight into magnetite's redox catalysis from observing surface morphology during oxidation.

    PubMed

    Nie, Shu; Starodub, Elena; Monti, Matteo; Siegel, David A; Vergara, Lucía; El Gabaly, Farid; Bartelt, Norman C; de la Figuera, Juan; McCarty, Kevin F

    2013-07-10

    We study how the (100) surface of magnetite undergoes oxidation by monitoring its morphology during exposure to oxygen at ~650 °C. Low-energy electron microscopy reveals that magnetite's surface steps advance continuously. This growth of Fe3O4 crystal occurs by the formation of bulk Fe vacancies. Using Raman spectroscopy, we identify the sinks for these vacancies, inclusions of α-Fe2O3 (hematite). Since the surface remains magnetite during oxidation, it continues to dissociate oxygen readily. At steady state, over one-quarter of impinging oxygen molecules undergo dissociative adsorption and eventual incorporation into magnetite. From the independence of growth rate on local step density, we deduce that the first step of oxidation, dissociative oxygen adsorption, occurs uniformly over magnetite's terraces, not preferentially at its surface steps. Since we directly observe new magnetite forming when it incorporates oxygen, we suggest that catalytic redox cycles on magnetite involve growing and etching crystal. PMID:23763580

  12. Surface Engineering of Core/Shell Iron/Iron Oxide Nanoparticles from Microemulsions for Hyperthermia

    PubMed Central

    Zhang, Guandong; Liao, Yifeng; Baker, Ian

    2011-01-01

    This paper describes the synthesis and surface engineering of core/shell-type iron/iron oxide nanoparticles for magnetic hyperthermia cancer therapy. Iron/iron oxide nanoparticles were synthesized from microemulsions of NaBH4 and FeCl3, followed by surface modification in which a thin hydrophobic hexamethyldisilazane layer - used to protect the iron core - replaced the CTAB coating on the particles. Phosphatidylcholine was then assembled on the nanoparticle surface. The resulting nanocomposite particles have a biocompatible surface and show good stability in both air and aqueous solution. Compared to iron oxide nanoparticles, the nanocomposites show much better heating in an alternating magnetic field. They are good candidates for both hyperthermia and magnetic resonance imaging applications. PMID:21833157

  13. Surface modification of alloys for improved oxidation resistance in SOFC applications

    SciTech Connect

    Alman, D.E.; Jablonski, P.D.; Kung, S.C.

    2006-11-01

    This research is aimed at improving the oxidation behavior of metallic alloys for SOFC application, by the incorporation of rare earths through surface treatments. This paper details the effect of such surface modification on the behavior of Crofer 22 APU, a ferritic steel designed specifically for SOFC application, and Type 430 stainless steel. Two pack cementation like treatments were used to incorporate Ce into the surface of the alloys. After 4000 hours of exposure at 800oC to air+3%H2O, the weight gain of Crofer 22APU samples that were Ce surface modified were less than half that of an unmodified sample, revealing the effectiveness of the treatments on enhancing oxidation resistance. For Type-430, the treatment prevented scale spalling that occurred during oxidation of the unmodified alloy.

  14. Modifying zirconia solid electrolyte surface property to enhance oxide transport

    SciTech Connect

    Liaw, B.Y.; Song, S.Y.

    1996-12-31

    Bismuth-strontium-calcium-copper oxide (Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}, BSCCO) is known for its high T{sub c} superconducting behavior and mixed conducting property. The applicability of similar high T{sub c} cuprates for intermediate-temperature solid oxide fuel cell (SOFC) application has been studied recently. We investigated the electrochemical behavior of several Ag{vert_bar}BSCCO{vert_bar}10 mol% yttria-stabilized zirconia (YSZ){vert_bar}Ag and Ag{vert_bar}YSZ{vert_bar}Ag cells using complex impedance spectroscopy. A highly uniform and porous microstructure was observed at the interface of the YSZ and BSCCO. The ionic conductivity determined from the Nyquest plots in the temperature range of 200-700{degrees}C agrees with the values reported in the literature. The specific resistance of the BSCCO{vert_bar}YSZ interface was also determined to be lower than those of the conventional manganite electrode, suggesting that BSCCO seems attractive for cathode applications in SOFC.

  15. Effects of different surfaces on the transport and deposition of ruthenium oxides in high temperature air

    NASA Astrophysics Data System (ADS)

    Vér, N.; Matus, L.; Pintér, A.; Osán, J.; Hózer, Z.

    2012-01-01

    In order to understand the behaviour of ruthenium oxides in the reactor coolant system during an air ingress accident, new tests were performed in the frame of the RUSET (RUthenium Separate Effect Test) experimental program. These aimed to ascertain the effects of different surfaces (quartz, stainless steel (SS), zirconium alloy, alumina, oxidised metal, and surfaces with Mo or Cs deposits) on the transport and decomposition of ruthenium oxides in air stream along the temperature gradient zone (1100-100 °C). The results demonstrated that the heterogeneous phase decomposition of RuO 3 and RuO 4 to RuO 2 is catalysed more efficiently by the quartz surface than by the SS or alumina surfaces. The presence of MoO 3 layers decreased the RuO x precipitation extent on all investigated surfaces. The trapping effect of Cs deposit on Ru in the temperature gradient zone was proved in the case of the SS surface. On the contrary, presence of Cs precipitate on alumina and especially on quartz surfaces was found to decrease their catalytic effect on the decomposition of ruthenium oxides, and thus increased the RuO 4 concentration in the outlet air. Similarly to the effect observed for Cs deposition, the presence of other fission products in the evaporation area (at 1100 °C) decreased the partial pressure of RuO 4 in the outlet air at the SS surface and increased it at quartz and alumina surfaces. When zirconium (E110) cladding material was placed in the temperature gradient zone, no Ru transmittance occurred until the high temperature end of the zirconium tube was completely oxidised. After the intense oxidation of E110, Ru release occurred only in the presence of other fission product species. Pre-oxidation of SS surfaces in steam had no significant effect on the Ru passage.

  16. 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 σ and π channels of adsorbates. Finally, we also present oxygen adsorption and oxygen vacancy formation energies in these oxide systems.

  17. Pb scavenging from a freshwater lake by Mn oxides in heterogeneous surface coating materials.

    PubMed

    Dong, Deming; Derry, Louis A; Lion, Leonard W

    2003-04-01

    Selective extraction techniques were used to assay the importance of specific solid phases in Pb binding by heterogeneous surface coating materials (biofilms) in Cayuga Lake, NY. Hydroxylamine hydrochloride (NH(2)OH.HC1) was used to extract easily reducible Mn oxides, and sodium dithionite (Na(2)S(2)O(4)) was used to extract Mn and Fe oxides in two sets of biofilm samples retrieved from the lake. Pb remaining after extraction was removed by extraction with 10% HNO(3), determined by analysis of Pb(208) using a sector field mass spectrometer with an inductively coupled plasma ion source (ICP-MS), and compared to the total extractable Pb. The results indicate that the greatest contribution to total Pb binding to the heterogeneous surface coating materials was from Mn oxides. Pb adsorption capacity of Mn oxides exceeded that of Fe oxides on a molar basis by approximately an order of magnitude. The high reactivity observed for natural Mn oxides indicates that they are biogenic in origin, consistent with expectations based on the relative biotic and abiotic rates of Mn(II) oxidation under circumneutral conditions. Collectively, these results confirm expectations based on prior observations of adsorption of added Pb by Cayuga Lake biofilms before and after selective extraction, and also confirm predictions for Pb phase association in the lake based on the behavior of laboratory surrogates for adsorptive surfaces. PMID:12600395

  18. 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.

  19. 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.

  20. 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.

  1. Magnetic iron oxide nanoparticles: Synthesis and surface coating techniques for biomedical applications

    NASA Astrophysics Data System (ADS)

    Sun, Sheng-Nan; Wei, Chao; Zhu, Zan-Zan; Hou, Yang-Long; Subbu, S. Venkatraman; Xu, Zhi-Chuan

    2014-03-01

    Iron oxide nanoparticles are the most popular magnetic nanoparticles used in biomedical applications due to their low cost, low toxicity, and unique magnetic property. Magnetic iron oxide nanoparticles, including magnetite (Fe3O4) and maghemite (γ-Fe2O3), usually exhibit a superparamagnetic property as their size goes smaller than 20 nm, which are often denoted as superparamagnetic iron oxide nanoparticles (SPIONs) and utilized for drug delivery, diagnosis, therapy, and etc. This review article gives a brief introduction on magnetic iron oxide nanoparticles in terms of their fundamentals of magnetism, magnetic resonance imaging (MRI), and drug delivery, as well as the synthesis approaches, surface coating, and application examples from recent key literatures. Because the quality and surface chemistry play important roles in biomedical applications, our review focuses on the synthesis approaches and surface modifications of iron oxide nanoparticles. We aim to provide a detailed introduction to readers who are new to this field, helping them to choose suitable synthesis methods and to optimize the surface chemistry of iron oxide nanoparticles for their interests.

  2. [A method of temperature measurement for hot forging with surface oxide based on infrared spectroscopy].

    PubMed

    Zhang, Yu-cun; Qi, Yan-de; Fu, Xian-bin

    2012-05-01

    High temperature large forging is covered with a thick oxide during forging. It leads to a big measurement data error. In this paper, a method of measuring temperature based on infrared spectroscopy is presented. It can effectively eliminate the influence of surface oxide on the measurement of temperature. The method can measure the surface temperature and emissivity of the oxide directly using the infrared spectrum. The infrared spectrum is radiated from surface oxide of forging. Then it can derive the real temperature of hot forging covered with the oxide using the heat exchange equation. In order to greatly restrain interference spectroscopy through included in the received infrared radiation spectrum, three interference filter system was proposed, and a group of optimal gap parameter values using spectral simulation were obtained. The precision of temperature measurement was improved. The experimental results show that the method can accurately measure the surface temperature of high temperature forging covered with oxide. It meets the requirements of measurement accuracy, and the temperature measurement method is feasible according to the experiment result. PMID:22827063

  3. Investigation of the Role of Surface Oxides in Catalysis by Gold Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shi, Hongqing; Stampfl, Catherine

    2007-03-01

    In contrast to the long held view that gold is catalytically inert, it is now well known that supported gold nanoparticles are notably more active than other transition metals for low temperature catalytic oxidation of CO, as well as promoting several other catalytic reactions [1]. This has stimulated huge efforts in an attempt to understand the mechanisms responsible for the high activity, including investigations into the nature of oxygen on gold surfaces [2]. Through density-functional theory and the approach of ab initio thermodynamics [3] we have found that on the gold (111) surface, thin oxide-like structures are significantly more stable for the pressure and temperature conditions of CO oxidation. The energetic preference for such partially oxidized gold, is in accord with very recent experimental results [4]. For the identified lowest energy surface oxide-like structure, we investigate the adsorption of CO on the surface and determine the reaction pathways for CO oxidation. [1] Haruta, Catal. J. New. Mater. Electro. Sys. 7, 163 (2004). [2] R. Meyer et al., Gold Bull. 37, 72 (2004), and references therein. [3] K. Reuter, C. Stampfl and M. Scheffler, in Handbook of Materials Modeling, Volume 1, Fundamental Models and Methods, Sidney Yip (Ed) 2005, 149-194. [4] L. Fu et al. J. Phys. Chem. B 109, 3704 (2005).

  4. Growth morphology of thin films on metallic and oxide surfaces.

    PubMed

    Krupski, Aleksander

    2014-02-01

    In this work we briefly review recent investigations concerning the growth morphology of thin metallic films on the Mo(110) and Ni3Al(111) surfaces, and Fe and copper phthalocyanine (C32H16N8Cu) on the Al2O3/Ni3Al(111) surface. Comparison of Ag, Au, Sn, and Pb growth on the Mo(110) surface has shown a number of similarities between these adsorption systems, except that surface alloy formation has only been observed in the case of Sn and Au. In the Pb/Mo(110) and Pb/Ni3Al(111) adsorption systems selective formation of uniform Pb island heights during metal thin film growth has been observed and interpreted in terms of quantum size effects. Furthermore, our studies showed that Al2O3 on Ni3Al(111) exhibits a large superstructure in which the unit cell has a commensurate relation with the substrate lattice. In addition, copper phthalocyanine chemisorbed weakly onto an ultra-thin Al2O3 film on Ni3Al(111) and showed a poor template effect of the Al2O3/Ni3Al(111) system. In the case of iron cluster growth on Al2O3/Ni3Al(111) the nucleation sites were independent of deposition temperature, yet the cluster shape showed a dependence. In this system, Fe clusters formed a regular hexagonal lattice on the Al2O3/Ni3Al(111). PMID:24445588

  5. Bacterial Biofilm Morphology on a Failing Implant with an Oxidized Surface: A Scanning Electron Microscope Study.

    PubMed

    Simion, Massimo; Kim, David M; Pieroni, Stefano; Nevins, Myron; Cassinelli, Clara

    2016-01-01

    This case report provided a unique opportunity to investigate the extent of microbiota infiltration on the oxidized implant surface that has been compromised by peri-implantitis. Scanning electron microscopic analysis confirmed the etiologic role of the bacteria on the loss of supporting structure and the difficulty in complete removal of bacterial infiltration on the implant surface. This case report emphasizes the need to perform definitive surface decontamination on failing dental implants prior to a regeneration procedure. PMID:27333005

  6. Methanol adsorption on magnesium oxide surface with defects: a DFT study

    NASA Astrophysics Data System (ADS)

    Branda, M. M.; Ferullo, R. M.; Belelli, P. G.; Castellani, N. J.

    2003-03-01

    The methanol adsorption on several defects of the magnesium oxide surface were studied. Structural and electronic study with geometrical optimization and natural bond orbital (NBO) analysis were performed using a density functional theory (DFT) method. Oxygen and magnesium with different coordination numbers have very different reactivity in this surface producing dissociated and non-dissociated species. These results are in agreement with infrared spectroscopy observations where CH 3OH, OCH 3 and OH species were found in defective MgO surfaces.

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

    NASA Technical Reports Server (NTRS)

    Gardner, Steven D.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

    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. Alternating current surface photovoltage in thermally oxidized chromium-contaminated n-type silicon wafers

    NASA Astrophysics Data System (ADS)

    Shimizu, Hirofumi; Nagase, Shintarou; Ikeda, Masanori

    2011-09-01

    We investigated a variation of frequency-dependent alternating current (AC) surface photovoltages (SPVs) in thermally oxidized, chromium-contaminated, n-type silicon (Si) wafers. As previously reported, immediately after rinsing in Cr-contaminated solution, a Cr(OH)3-Si contact causes a Schottky-barrier-type AC SPV on n-type Si. Upon oxidation at 373 K for 10 min, the Schottky barrier collapses and, with further oxidation, a metal-induced negative oxide charge, due to atomic bridging of (CrOSi)- and/or CrO2- networks, definitely grows over time in SiO2. For samples oxidized at temperatures between 823 and 1023 K for 30 min, the observed AC SPV gives evidence that the metal-induced negative oxide charge causes a strongly inverted state of the Si surface. At oxidation temperatures higher than 1023 K and /or for an oxidation time longer than 60 min, the level height of the AC SPV is reduced, implying that the strongly inverted state changes into a less depleted state, whilst, finally, the AC SPV disappears. In this case, the collapse of the (CrOSi)- and/or CrO2- networks is anticipated, with a possible change into Cr2O3. The existence of the (CrOSi)- and/or CrO2- networks has also been confirmed in p-type Si wafers.

  10. Resonance frequency and removal torque analysis of implants with turned and anodized surface oxides.

    PubMed

    Sul, Young-Taeg; Johansson, Carina B; Jeong, Youngsoo; Wennerberg, Ann; Albrektsson, Tomas

    2002-06-01

    The present experimental study was designed to address two issues. The first was to investigate whether oxide properties of titanium implants influenced bone tissue responses after an in vivo implantation time of six weeks. If such a result was found, the second aim was to investigate which oxide properties are involved in such bone tissue responses. Screw-shaped implants with a wide range of oxide properties were prepared by electrochemical oxidation methods, where the oxide thickness varied in the range of 200 nm to 1000 nm. The surface morphology was prepared in two substantially different ways, i.e. barrier and porous oxide film structures. The micropore structure revealed pore sizes of 8 microm in diameter, with a range in opening area from 1.27 microm 2 to 2.1 microm 2. Porosity ranged from 12.7% to 24.4%. The crystal structures of the titanium oxide were amorphous, anatase and a mixture of anatase and rutile type. The chemical compositions consisted mainly of TiO2. Surface roughness ranged from 0.96 microm to 1.03 microm (Sa). Each group of test samples showed its own, defined status with respect to these various parameters. The oxide properties of turned commercially pure titanium implants were used in the control group, which was characterized by an oxide thickness of 17.4 +/- 6.2 nm, amorphous type in crystallinity, TiO2 in chemical composition, and a surface roughness of 0.83 microm (Sa). Bone tissue responses were evaluated by resonance frequency measurements and removal torque tests that were undertaken six weeks after implant insertion in rabbit tibia. Implants that had an oxide thickness of approximately 600, 800 and 1000 nm demonstrated significantly stronger bone responses in the evaluation of removal torque values than did implants that had an oxide thickness of approximately 17 and 200 nm (P < 0.05). However, there were no difference between implants with oxide thicknesses of 17 and 200 nm (P = 0.99). It was concluded that oxide properties of

  11. Surface oxidation energetics and kinetics on MoS{sub 2} monolayer

    SciTech Connect

    KC, Santosh; Longo, Roberto C.; Wallace, Robert M.; Cho, Kyeongjae

    2015-04-07

    In this work, surface oxidation of monolayer MoS{sub 2} (one of the representative semiconductors in transition-metal dichalcogenides) has been investigated using density functional theory method. Oxygen interaction with MoS{sub 2} shows that, thermodynamically, the surface tends to be oxidized. However, the dissociative absorption of molecular oxygen on the MoS{sub 2} surface is kinetically limited due to the large energy barrier at low temperature. This finding elucidates the air stability of MoS{sub 2} surface in the atmosphere. Furthermore, the presence of defects significantly alters the surface stability and adsorption mechanisms. The electronic properties of the oxidized surface have been examined as a function of oxygen adsorption and coverage as well as substitutional impurities. Our results on energetics and kinetics of oxygen interaction with the MoS{sub 2} monolayer are useful for the understanding of surface oxidation, air stability, and electronic properties of transition-metal dichalcogenides at the atomic scale.

  12. Surface acidity of silica-titania mixed oxides

    SciTech Connect

    Odenbrand, C.U.I.; Brandin, J.G.M. ); Busca, G. )

    1992-06-01

    A study of the acidity of coprecipitated SiO[sub 2]-TiO[sub 2] oxides is presented. The amount of acidity has been determined by ammonia adsorption at 150 C. The acidity was also characterized by TPD of adsorbed ammonia and by infrared spectroscopy of various adsorbed probes, such as pivalonitrile, pyridine, ammonia, and n-butylamine. From the quantitative measurements of adsorption of ammonia and from TPD it was concluded that the SiO[sub 2]-TiO[sub 2] mixture can be regarded as a mechanical mixture of silica and titania. However, the IR investigation showed that Ti enters in small amounts into the silica framework. This results in formation of very strong Lewis acid sites, caused by incomplete tetrahedral coordination of Ti[sup 4[minus

  13. Zinc (hydr)oxide/graphite oxide/AuNPs composites: role of surface features in H₂S reactive adsorption.

    PubMed

    Giannakoudakis, Dimitrios A; Bandosz, Teresa J

    2014-12-15

    Zinc hydroxide/graphite oxide/AuNPs composites with various levels of complexity were synthesized using an in situ precipitation method. Then they were used as H2S adsorbents in visible light. The materials' surfaces were characterized before and after H2S adsorption by various physical and chemical methods (XRD, FTIR, thermal analysis, potentiometric titration, adsorption of nitrogen and SEM/EDX). Significant differences in surface features and synergistic effects were found depending on the materials' composition. Addition of graphite oxide and the deposition of gold nanoparticles resulted in a marked increase in the adsorption capacity in comparison with that on the zinc hydroxide and zinc hydroxide/AuNP. Addition of AuNPs to zinc hydroxide led to a crystalline ZnO/AuNP composite while the zinc hydroxide/graphite oxide/AuNP composite was amorphous. The ZnOH/GO/AuNPs composite exhibited the greatest H2S adsorption capacity due to the increased number of OH terminal groups and the conductive properties of GO that facilitated the electron transfer and consequently the formation of superoxide ions promoting oxidation of hydrogen sulfide. AuNPs present in the composite increased the conductivity, helped with electron transfer to oxygen, and prevented the fast recombination of the electrons and holes. PMID:25306297

  14. Rapid Covalent Modification of Silicon Oxide Surfaces through Microwave-Assisted Reactions with Alcohols.

    PubMed

    Lee, Austin W H; Gates, Byron D

    2016-07-26

    We demonstrate the method of a rapid covalent modification of silicon oxide surfaces with alcohol-containing compounds with assistance by microwave reactions. Alcohol-containing compounds are prevalent reagents in the laboratory, which are also relatively easy to handle because of their stability against exposure to atmospheric moisture. The condensation of these alcohols with the surfaces of silicon oxides is often hindered by slow reaction kinetics. Microwave radiation effectively accelerates this condensation reaction by heating the substrates and/or solvents. A variety of substrates were modified in this demonstration, such as silicon oxide films of various thicknesses, glass substrates such as microscope slides (soda lime), and quartz. The monolayers prepared through this strategy demonstrated the successful formation of covalent surface modifications of silicon oxides with water contact angles of up to 110° and typical hysteresis values of 2° or less. An evaluation of the hydrolytic stability of these monolayers demonstrated their excellent stability under acidic conditions. The techniques introduced in this article were successfully applied to tune the surface chemistry of silicon oxides to achieve hydrophobic, oleophobic, and/or charged surfaces. PMID:27396288

  15. 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

  16. Ion adsorption on metal oxide surface to hydrothermal conditions.

    SciTech Connect

    Wesolowski, D. J.; Machesky, M. L.; Ridley, M. K.; Palmer, D. A.; Zhang, Z.; Fenter, P.; Predota, M.; Vlcek, L.; ORNL; Illinois State Water Survey; Texsas Tech Univ.; Unv. of South Bohemia; Vanderbilt Univ.

    2008-01-01

    In this article, we review the sorption of multivalent cations on rutile (alpha-TiO2) powder surfaces in aqueous 1:1 electrolyte media from room temperature to 250 degrees C. All cations are shown to occupy 'inner sphere' sorption sites in contact with surface oxygens and hydroxyl groups, as well as the diffuse portion of the electrical double layer (EDL). Sorption is shown to increase strongly with increasing temperature, and the sorption affinity is strongly-related to cation radius and charge. Macroscopic powder pH-titration results obtained with ORNL's high temperature hydrogen electrode concentration cells can be rationalized with Gouy-Chapman-Stern models of the EDL, augmented by atomic-scale structural and proton affinity data from synchrotron X-ray studies and computational modeling approaches.

  17. Adsorption Structure of Nitric Oxide on the Pt(111) Surface

    NASA Astrophysics Data System (ADS)

    Matsumoto, Masuaki

    The adsorption structure of Pt(111) surface was studied by thermal desorption spectroscopy (TDS), infra-red absorption spectroscopy (IRAS), scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). LEED dynamical analysis, with the aid of other techniques, concluded that NO occupies the fcc hollow site at a low coverage, the fcc hollow and ontop sites at a medium coverage and the fcc hollow, ontop and hcp hollow sites at a high coverage, which is consistent with the other experimental and theoretical results. The desorption temperatures of NO on the fcc hollow (α species), ontop (β species) and hcp hollow sites (γ species) are 390, 300 and 200 K, respectively. The N-O stretching vibrations of each species are 1430-1490 cm-1, 1710 cm-1 and 1508 cm-1, respectively. Annealing to 250 K causes the desorption of the γ species, which results in the highly ordered two site occupied (α and β) surface. The high energy (>1 eV) electron injection from the STM tip causes the desorption of the β species, which enables us to get the surface of highly ordered α species. The mechanism of the desorption of the β species is the electron injection to the 2πa orbital, which has an anti-bonding character for the Pt-N bonding of the β species.

  18. 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.

  19. Characterization of a bioactive nanotextured surface created by controlled chemical oxidation of titanium

    NASA Astrophysics Data System (ADS)

    Yi, Ji-Hyun; Bernard, Caroline; Variola, Fabio; Zalzal, Sylvia F.; Wuest, James D.; Rosei, Federico; Nanci, Antonio

    2006-10-01

    Events at bone-implant interfaces are influenced by implant surface properties. Our previous work has revealed that osteogenic activity is enhanced by a nanotextured Ti surface, obtained by controlled chemical oxidation using a H 2SO 4/H 2O 2 mixture. To better understand the origin of this biological effect, we have carried out a characterization of the modified surface at the nanoscale. In particular, the morphology, structure, and chemical composition of the Ti surface were examined thoroughly. X-ray photoelectron spectroscopy (XPS), combined with grazing-angle Fourier-transform infrared (FTIR) spectroscopy, revealed that the oxidized Ti surface consists of almost pure TiO 2 with Ti:O ratio ranging between 1:2.02 and 1:2.08. Raman spectroscopy and X-ray diffraction (XRD) indicated that the chemically treated Ti surface is mainly composed of amorphous titania. Scanning electron microscopy (SEM) clearly showed that the treated Ti substrate becomes highly porous and has a surface consisting of nano-sized pits, which have average diameters and fractal dimensions ranging between 20-22 nm and 1.11-1.17, respectively. Atomic force microscopy (AFM) revealed a three-fold increase in surface roughness. The thickness of the oxide layer on the treated Ti surface is estimated to be ˜32-40 nm. Together, these observations provide a detailed characterization of chemically oxidized Ti surfaces at the nanoscale and offer new prospects for understanding and controlling the relationship between the properties of materials and their interactions with cells. Our work brings us closer to the creation of "intelligent" implant surfaces, capable of selectively influencing cell behavior.

  20. Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics. [Coal pyrite electrodes

    SciTech Connect

    Doyle, F.M.

    1992-01-01

    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 eighth quarter, wet chemical and dry oxidation tests were done on Upper Freeport coal from the Troutville [number sign]2 Mine, Clearfield County, Pennsylvania. In addition electrochemical experiments were done on electrodes prepared from Upper Freeport coal pyrite and Pittsburgh coal pyrite samples provided by the US Bureau of Mines, Pittsburgh Research Center, Pennsylvania.

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

    SciTech Connect

    Caron, A.; Louzguine-Luzguin, D. V.; Sharma, P.; Inoue, A.; Shluger, A.; Fecht, H.-J.

    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.

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

    SciTech Connect

    Garcia Rey, Natalia; Arnolds, Heike

    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.

  3. The Nature of Surface Oxides on Corrosion-Resistant Nickel Alloy Covered by Alkaline Water

    PubMed Central

    2010-01-01

    A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline water layers are on the alloy surface in order to account for the relative inertness of the nickel alloy in corrosive environments. PMID:20672134

  4. Protein-repellent silicon nitride surfaces: UV-induced formation of oligoethylene oxide monolayers.

    PubMed

    Rosso, Michel; Nguyen, Ai T; de Jong, Ed; Baggerman, Jacob; Paulusse, Jos M J; Giesbers, Marcel; Fokkink, Remko G; Norde, Willem; Schroën, Karin; van Rijn, Cees J M; Zuilhof, Han

    2011-03-01

    The grafting of polymers and oligomers of ethylene oxide onto surfaces is widely used to prevent nonspecific adsorption of biological material on sensors and membrane surfaces. In this report, we show for the first time the robust covalent attachment of short oligoethylene oxide-terminated alkenes (CH(3)O(CH(2)CH(2)O)(3)(CH(2))(11)-(CH═CH(2)) [EO(3)] and CH(3)O(CH(2)CH(2)O)(6)(CH(2))(11)-(CH═CH(2)) [EO(6)]) from the reaction of alkenes onto silicon-rich silicon nitride surfaces at room temperature using UV light. Reflectometry is used to monitor in situ the nonspecific adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) onto oligoethylene oxide coated silicon-rich silicon nitride surfaces (EO(n)-Si(x)N(4), x > 3) in comparison with plasma-oxidized silicon-rich silicon nitride surfaces (SiO(y)-Si(x)N(4)) and hexadecane-coated Si(x)N(4) surfaces (C(16)-Si(x)N(4)). A significant reduction in protein adsorption on EO(n)-Si(x)N(4) surfaces was achieved, adsorption onto EO(3)-Si(x)N(4) and EO(6)-Si(x)N(4) were 0.22 mg m(-2) and 0.08 mg m(-2), respectively. The performance of the obtained EO(3) and EO(6) layers is comparable to those of similar, highly protein-repellent monolayers formed on gold and silver surfaces. EO(6)-Si(x)N(4) surfaces prevented significantly the adsorption of BSA (0.08 mg m(-2)). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity and static water contact angle measurements were employed to characterize the modified surfaces. In addition, the stability of EO(6)-Si(x)N(4) surfaces in phosphate-buffered saline solution (PBS) and alkaline condition (pH 10) was studied. Prolonged exposure of the surfaces to PBS solution for 1 week or alkaline condition for 2 h resulted in only minor degradation of the ethylene oxide moieties and no oxidation of the Si(x)N(4) substrates was observed. Highly stable antifouling coatings on Si(x)N(4) surfaces significantly broaden the application potential of silicon

  5. Oxidation of nickel surfaces through the energetic impacts of oxygen molecules: Reactive molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Amiri, Negar; Behnejad, Hassan

    2016-04-01

    Molecular dynamics approach accompanied by reactive force field is used to study the characteristics of the oxide growth process on Ni(100) and Ni(111) surfaces at the temperatures of 300, 600, and 900 K and 5 eV as the energy of the O2 impacts. The exposure of Ni surfaces to the high-energy O2 impacts indicates that the primary oxide nuclei can be formed on any impact site. The results of kinetic studies clarify that the oxide growth kinetics cannot be accurately explained with the island growth model and increasing the surface temperature raises failure of the model. Under the present conditions, the growth kinetics is found to obey a Langmuir growth model. Increasing the surface temperature from 300 to 900 K results in ˜18.75% and ˜23% more oxygen consumption by (100) and (111) surfaces of Ni, respectively. The structure of nickel oxide (NiO) film formed after 200 successive O2 impacts per surface super-cell is investigated utilizing radial distribution functions and oxygen density profiles. These calculations demonstrate that the structure of the formed NiO film is amorphous. Moreover, the charge profiles in Ni/NiO system are illustrated and discussed.

  6. Oxidation of nickel surfaces through the energetic impacts of oxygen molecules: Reactive molecular dynamics simulations.

    PubMed

    Amiri, Negar; Behnejad, Hassan

    2016-04-14

    Molecular dynamics approach accompanied by reactive force field is used to study the characteristics of the oxide growth process on Ni(100) and Ni(111) surfaces at the temperatures of 300, 600, and 900 K and 5 eV as the energy of the O2 impacts. The exposure of Ni surfaces to the high-energy O2 impacts indicates that the primary oxide nuclei can be formed on any impact site. The results of kinetic studies clarify that the oxide growth kinetics cannot be accurately explained with the island growth model and increasing the surface temperature raises failure of the model. Under the present conditions, the growth kinetics is found to obey a Langmuir growth model. Increasing the surface temperature from 300 to 900 K results in ∼18.75% and ∼23% more oxygen consumption by (100) and (111) surfaces of Ni, respectively. The structure of nickel oxide (NiO) film formed after 200 successive O2 impacts per surface super-cell is investigated utilizing radial distribution functions and oxygen density profiles. These calculations demonstrate that the structure of the formed NiO film is amorphous. Moreover, the charge profiles in Ni/NiO system are illustrated and discussed. PMID:27083743

  7. Atomically flat reconstructed rutile TiO2(001) surfaces for oxide film growth

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Lee, S.; Vilmercati, P.; Lee, H. N.; Weitering, H. H.; Snijders, P. C.

    2016-02-01

    The availability of low-index rutile TiO2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxial growth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO2(001) surfaces can be prepared with an atomically ordered reconstructed surface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surface energy associated with the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxial growth of TiO2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.

  8. Surface passivation limited UO2 oxidative dissolution in the presence of FeS.

    PubMed

    Bi, Yuqiang; Hayes, Kim F

    2014-11-18

    Iron sulfide minerals produced during in situ bioremediation of U can serve as an oxygen scavenger to retard uraninite (UO2) oxidation upon oxygen intrusion. Under persistent oxygen supply, however, iron sulfides become oxidized and depleted, giving rise to elevated dissolved oxygen (DO) levels and remobilization of U(IV). The present study investigated the mechanism that regulates UO2 oxidative dissolution rate in a flow-through system when oxygen breakthrough occurred as a function of mackinawite (FeS) and carbonate concentrations. The formation and evolution of surface layers on UO2 were characterized using XAS and XPS. During FeS inhibition period, the continuous supply of carbonate and calcium in the influent effectively complexed and removed oxidized U(VI) to preserve an intermediate U4O9 surface. When the FeS became depleted by oxidization, a transient, rapid dissolution of UO2 was observed along with DO breakthrough in the reactor. This rate was greater than during the preceding FeS inhibition period and control experiments in the absence of FeS. With increasing DO, the rate slowed and the rate-limiting step shifted from surface oxidation to U(VI) detachment as U(VI) passivation layers developed. In contrast, increasing the carbonate concentrations facilitated detachment of surface-associated U(VI) complexes and impeded the formation of U(VI) passivation layer. This study demonstrates the critical role of U(VI) surface layer formation versus U(VI) detachment in controlling UO2 oxidative dissolution rate during periods of variable oxygen presence under simulated groundwater conditions. PMID:25322064

  9. A theoretical investigation on photocatalytic oxidation on the TiO{sub 2} surface

    SciTech Connect

    Suzuki, Satoshi; Tsuneda, Takao; Hirao, Kimihiko

    2012-01-14

    The TiO{sub 2} photocatalytic oxidation mechanism was theoretically investigated by using long-range corrected time-dependent density functional theory (LC-TDDFT) with a cluster model of the anatase TiO{sub 2}(001) surface. We found that LC-TDDFT with the cluster model quantitatively reproduces the photoexcitations of the TiO{sub 2} surface by calculating the electronic spectra of a clean TiO{sub 2} surface and one with oxygen defects. We calculated the electronic spectra of a molecularly adsorbed TiO{sub 2} surface for the adsorptions of phenol, methanol, and methane molecules as typical organic molecules. We obtained the surprising result that the main peak of the phenol-adsorbed TiO{sub 2} surface, which overlaps with the main peak of the clean TiO{sub 2} surface, corresponds to charge transfers from the phenol molecule to the TiO{sub 2} surface. This indicates that the TiO{sub 2} photocatalytic oxidation proceeds through direct charge transfer excitation from the substrate molecules to the TiO{sub 2} surface. In contrast, we found slight and no charge transfer for methanol and methane adsorption, respectively, in agreement with the experimental findings for their reactivities. In light of these results, we propose a new mechanism for heterogeneous TiO{sub 2} photocatalytic oxidations.

  10. Topological analysis of the metal-support interaction: the case of Pd atoms on oxide surfaces

    NASA Astrophysics Data System (ADS)

    Gomes, José R. B.; Illas, Francesc; Silvi, Bernard

    2004-04-01

    The metal support interaction was analyzed by means of AIM and ELF approaches taking Pd adsorbed on MgO(0 0 1), α-Al 2O 3 (0 0 0 1) and SiO 2 surfaces as examples of simple ionic, complex ionic and covalent oxide surfaces, respectively. On the most favorable adsorption sites, the polysynaptic basins found indicate the presence of chemical bonds. The basins populations are low in the case of the two ionic oxides while on a specific site of the SiO 2 surface, a polysynaptic basin with ˜2 electrons was found illustrating the variety and richness of the chemical bonding between a metal and an oxide.

  11. Electrocatalytic oxidation of formic acid at an ordered intermetallic PtBi surface.

    PubMed

    Casado-Rivera, Emerilis; Gál, Zoltán; Angelo, A C D; Lind, Cora; DiSalvo, Francis J; Abruña, Héctor D

    2003-02-17

    The electrocatalytic oxidation of formic acid at a PtBi ordered intermetallic electrode surface has been investigated using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and differential electrochemical mass spectrometry (DEMS). The results are compared to those at a polycrystalline platinum electrode surface. The PtBi electrode exhibits superior properties when compared to polycrystalline platinum in terms of oxidation onset potential, current density, and a much diminished poisoning effect by CO. Using the RDE technique, a value of 1.4 x 10(-4) cm s-1 was obtained for the heterogeneous charge transfer rate constant. The PtBi surface did not appear to be poisoned when exposed to a CO saturated solution for periods exceeding 0.5 h. The results for PtBi are discussed within the framework of the dual-path mechanism for the electrocatalytic oxidation of formic acid, which involves formation of a reactive intermediate and a poisoning pathway. PMID:12619419

  12. Enhanced electron-hole droplet emission from surface-oxidized silicon photonic crystal nanocavities.

    PubMed

    Sumikura, Hisashi; Kuramochi, Eiichi; Taniyama, Hideaki; Notomi, Masaya

    2016-01-25

    We have observed electron-hole droplet (EHD) emission enhanced by silicon photonic crystal (Si PhC) nanocavities with a surface oxide. The EHD is employed as a massive emitter that remains inside the nanocavity to achieve efficient cavity-emitter coupling. Time-resolved emission measurements demonstrate that the surface oxide greatly reduces the nonradiative annihilation of the EHDs and maintains them in the PhC nanocavities. It is found that the surface-oxidized Si PhC nanocavity enhances EHD emission in addition to the Purcell enhancement of the resonant cavity, which will contribute to works on Si light emission and the cavity quantum electrodynamics of electron-hole condensates. PMID:26832491

  13. Surface coordination number and surface redox couples on catalyst oxides, a new approach of the interpretation of activity and selectivity III. Interpretation of chemical and catalytic oxidation reactions on some oxides

    NASA Astrophysics Data System (ADS)

    Arnaud, Y. P.

    The concepts of surface coordination number n, and of surface redox couples MO [ n] /MO ( n+1) presented previously, are exploited to explain experimental results. Two cases are considered: reactions of chemical gaseous species such as CO, CO 2, H 2, H 2O,N 2O, propene and methanol on the surface of the oxides NiO, TiO 2, and Cr 2O 3, in the absence of oxygen: activated catalytic reactions of oxygen on reductive species such as CO, H 2,C 2H 6, and CH 3OH. The knowledge of the potential of surface redox couples permits a rationalization of the study of these reactions. The efficiency of the two concepts is obvious in many cases. For example, the origin of an athermal oxidative process occurring for the oxidations of CO or H 2 on TiO 2 is easily understood, as well as those of the poisoning of the catalysts or of the inactivity of a surface saturated by oxygen. In addition, the study of chemical reactions on the oxides confirms and completes the theoretical approach used. Particularly, the existence of the surface states, which are postulated in the case of Cr 2O 3, is corroborated by experimental observations concerning the number of surface states and the value of the chemical potentials. Even though the theory is based upon thermodynamical and structural data, it also leads to a better understanding of kinetic features.

  14. Electronic interactions and charge transfers of metal atoms and clusters on oxide surfaces.

    PubMed

    Pacchioni, Gianfranco

    2013-02-14

    Understanding the interaction of small metal clusters and isolated atoms with oxide surfaces is crucial in order to rationalize the properties of heterogeneous catalysts composed of sub-nanometer metal particles dispersed on an oxide support. The interaction with the oxide surface can significantly alter the original properties of the metal deposit. In particular, the occurrence and the direction of charge transfer at the metal/oxide interface determine the chemical activity of the supported catalyst. The charge transfer depends on a number of factors like the nature of the oxide (reducible or non-reducible), the surface exposed, the presence of defects, the nature of the supported metal, etc. In this article we describe the most important conceptual aspects of the electronic metal-support interaction, a phenomenon related to the direct modification of the metal nano-particle determined by the formation of chemical bonds at the interface with the oxide. For metal nano-particles with a size of about 1 nm or below these effects become dominant although difficult to identify experimentally. PMID:23287900

  15. Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy

    PubMed Central

    König, Thomas; Simon, Georg H; Heinke, Lars; Lichtenstein, Leonid

    2011-01-01

    Summary Surfaces of thin oxide films were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001) and line defects in aluminum oxide on NiAl(110), respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM) and the electronic structure by scanning tunneling spectroscopy (STS). On magnesium oxide, different color centers, i.e., F0, F+, F2+ and divacancies, have different effects on the contact potential. These differences enabled classification and unambiguous differentiation by KPFM. True atomic resolution shows the topography at line defects in aluminum oxide. At these domain boundaries, STS and KPFM verify F2+-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide films beyond imaging the topography of the surface atoms. PMID:21977410

  16. Chlorine activation indoors and outdoors via surface-mediated reactions of nitrogen oxides with hydrogen chloride

    PubMed Central

    Raff, Jonathan D.; Njegic, Bosiljka; Chang, Wayne L.; Gordon, Mark S.; Dabdub, Donald; Gerber, R. Benny; Finlayson-Pitts, Barbara J.

    2009-01-01

    Gaseous HCl generated from a variety of sources is ubiquitous in both outdoor and indoor air. Oxides of nitrogen (NOy) are also globally distributed, because NO formed in combustion processes is oxidized to NO2, HNO3, N2O5 and a variety of other nitrogen oxides during transport. Deposition of HCl and NOy onto surfaces is commonly regarded as providing permanent removal mechanisms. However, we show here a new surface-mediated coupling of nitrogen oxide and halogen activation cycles in which uptake of gaseous NO2 or N2O5 on solid substrates generates adsorbed intermediates that react with HCl to generate gaseous nitrosyl chloride (ClNO) and nitryl chloride (ClNO2), respectively. These are potentially harmful gases that photolyze to form highly reactive chlorine atoms. The reactions are shown both experimentally and theoretically to be enhanced by water, a surprising result given the availability of competing hydrolysis reaction pathways. Airshed modeling incorporating HCl generated from sea salt shows that in coastal urban regions, this heterogeneous chemistry increases surface-level ozone, a criteria air pollutant, greenhouse gas and source of atmospheric oxidants. In addition, it may contribute to recently measured high levels of ClNO2 in the polluted coastal marine boundary layer. This work also suggests the potential for chlorine atom chemistry to occur indoors where significant concentrations of oxides of nitrogen and HCl coexist. PMID:19620710

  17. High temperature oxidation behavior of AISI 304L stainless steel-Effect of surface working operations

    NASA Astrophysics Data System (ADS)

    Ghosh, Swati; Kumar, M. Kiran; Kain, Vivekanand

    2013-01-01

    The oxidation behavior of grade 304L stainless steel (SS) subjected to different surface finishing (machining and grinding) operations was followed in situ by contact electric resistance (CER) and electrochemical impedance spectroscopy (EIS) measurements using controlled distance electrochemistry (CDE) technique in high purity water (conductivity < 0.1 μS cm-1) at 300 °C and 10 MPa in an autoclave connected to a recirculation loop system. The results highlight the distinct differences in the oxidation behavior of surface worked material as compared to solution annealed material in terms of specific resistivity and low frequency Warburg impedance. The resultant oxide layer was characterized for (a) elemental analyses by glow discharge optical emission spectroscopy (GDOES) and (b) morphology by scanning electron microscopy (SEM). Oxide layers with higher specific resistivity and chromium content were formed in case of machined and ground conditions. Presence of an additional ionic transport process has also been identified for the ground condition at the metal/oxide interface. These differences in electrochemical properties and distinct morphological features of the oxide layer as a result of surface working were attributed to the prevalence of heavily fragmented grain structure and presence of martensite.

  18. Dependence of cryogenic strength of hydroxide catalysis bonded silicon on type of surface oxide

    NASA Astrophysics Data System (ADS)

    Beveridge, N. L.; van Veggel, A. A.; Cunningham, L.; Hough, J.; Martin, I. W.; Nawrodt, R.; Reid, S.; Rowan, S.

    2013-01-01

    Hydroxide catalysis bonding is a joining technique used in the construction of highly stable opto-mechanical systems including quasi-monolithic silica suspensions for first and second generation gravitational wave detectors. Future generations of detector are likely to operate at cryogenic temperatures necessitating a change in testmass/suspension material. A promising candidate material is silicon, which requires an oxide surface layer for hydroxide catalysis bonding to be reliable. Here, we present first results showing the influence of the type of oxide layer applied on bond strength, measured at room temperature and 77 K, and identify preferred oxide deposition methods.

  19. Ozone Oxidation of Self-Assembled Monolayers on SiOx-Coated Zinc Selenide Surfaces

    NASA Astrophysics Data System (ADS)

    McIntire, T. M.; Ryder, O. S.; Finlayson-Pitts, B. J.

    2008-12-01

    Airborne particles are important for visibility, human health, climate, and atmospheric reactions. Atmospheric particles contain a significant fraction of organics and such compounds present on airborne particles are susceptible to oxidation by atmospheric oxidants, such as OH, ozone, halogen atoms, and nitrogen trioxide. Oxidized organics associated with airborne particles are thought to be polar, hygroscopic species with enhanced cloud-nucleating properties. Oxide layers on silicon, or SiO2-coated substrates, act as models of environmentally relevant surfaces such as dust particles upon which organics adsorb. We have shown previously that ozone oxidation of unsaturated self-assembled monolayers (SAMs) on silicon attenuated total reflectance (ATR) crystals leads to the formation of carbonyl groups and micron-sized, hydrophobic organic aggregates surrounded by carbon depleted substrate that do not have increased water uptake as previously assumed. Reported here are further ATR-FTIR studies of the oxidation of alkene SAMs on ZnSe and SiO2-coated ZnSe. These substrates have the advantage that they transmit below 1500 cm-1, allowing detection of additional product species. These experiments show that the loss of C=C and formation of carbonyl groups is also accompanied by formation of a peak at 1110 cm-1, attributed to the secondary ozonide. Details concerning the products and mechanism of ozonolysis of alkene SAMs on surfaces based on these new data are presented and the implications for the oxidation of alkenes on airborne dust particles are discussed.

  20. 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 γ-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 “MEDС-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 MEDС-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 (MEDС-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

  1. Plasma decontamination of uranium oxide from stainless steel surfaces

    SciTech Connect

    Veilleux, J.M.; El-Genk, M.S.; Chamberlin, E.P.

    1997-12-01

    The U.S. Department of Energy (DOE) is expected to have 845000 m{sup 3} of transuranic (TRU) waste by the year 2000 that has accumulated during the development and assembly of the nation`s nuclear stockpile. The TRU disposal costs alone range up to $28000/m{sup 3}, which could be reduced to $1800/m{sup 3} or less by treating and converting the material to low-level waste. Plasma-based processes have been shown to remove plutonium and uranium surface contaminants from metallic components and could be used to treat TRU with significant cost avoidance, estimated at over $1.0 billion. Martz and Hess conducted the initial work of plutonium etching in low-power radio-frequency (rf) plasma with etch rates ranging from 0.007 to 0.025 kg/m{sup 2}{center_dot}h. Veilleux et al. reported that plasma decontamination of uranium from the interior of aluminum objects results in etch rates an order of magnitude greater. The current work reports on removal rates of uranium from stainless steel surfaces and includes estimates of the etch rates and characteristic times for removal.

  2. Iron oxidation kinetics and phosphorus immobilization at the groundwater-surface water interface

    NASA Astrophysics Data System (ADS)

    van der Grift, Bas; Rozemeijer, Joachim; Griffioen, Jasper; van der Velde, Ype

    2014-05-01

    Eutrophication of freshwater environments following diffuse nutrient loads is a widely recognized water quality problem in catchments. Fluxes of non-point P sources to surface waters originate from surface runoff and flow from soil water and groundwater into surface water. The availability of P in surface waters is controlled strongly by biogeochemical nutrient cycling processes at the soil-water interface. The mechanisms and rates of the iron oxidation process with associated binding of phosphate during exfiltration of anaerobic Fe(II) bearing groundwater are among the key unknowns in P retention processes in surface waters in delta areas where the shallow groundwater is typically pH-neutral to slightly acid, anoxic, iron-rich. We developed an experimental field set-up to study the dynamics in Fe(II) oxidation and mechanisms of P immobilization at the groundwater-surface water interface in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. The exfiltrating groundwater was captured in in-stream reservoirs constructed in the ditch. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and ditch water, we quantified Fe(II) oxidation kinetics and P immobilization processes across the seasons. This study showed that seasonal changes in climatic conditions affect the Fe(II) oxidation process. In winter time the dissolved iron concentrations in the in-stream reservoirs reached the levels of the anaerobic groundwater. In summer time, the dissolved iron concentrations of the water in the reservoirs are low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into the reservoirs. Higher discharges, lower temperatures and lower pH of the exfiltrated groundwater in winter compared to summer shifts the location of the redox transition zone

  3. Coupled ferric oxides and sulfates on the Martian surface.

    PubMed

    Bibring, J-P; Arvidson, R E; Gendrin, A; Gondet, B; Langevin, Y; Le Mouelic, S; Mangold, N; Morris, R V; Mustard, J F; Poulet, F; Quantin, C; Sotin, C

    2007-08-31

    The Mars Exploration Rover (MER), Opportunity, showed that layered sulfate deposits in Meridiani Planum formed during a period of rising acidic ground water. Crystalline hematite spherules formed in the deposits as a consequence of aqueous alteration and were concentrated on the surface as a lag deposit as wind eroded the softer sulfate rocks. On the basis of Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) orbital data, we demonstrate that crystalline hematite deposits are associated with layered sulfates in other areas on Mars, implying that Meridiani-like ground water systems were indeed widespread and representative of an extensive acid sulfate aqueous system. PMID:17673623

  4. Preparation of atomically flat rutile TiO2(001) surfaces for oxide film growth

    DOE PAGESBeta

    Wang, Yang; Lee, Shinbuhm; Vilmercati, P.; Lee, Ho Nyung; Weitering, Hanno; Snijders, Paul C.

    2016-01-01

    The availability of low-index rutile TiO2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxialgrowth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO2(001) surfaces can be prepared with an atomically ordered reconstructedsurface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surface energy associated withmore » the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxialgrowth of TiO2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.« less

  5. Surface Science Studies of Strong Metal-Oxide Interactions on Model Catalysts

    NASA Astrophysics Data System (ADS)

    Bowker, Michael; Bennett, Roger A.

    Here we report on recent model studies of a phenomenon known in catalysis as the “Strong Metal-Support Interaction” (SMSI for short). Decoration of the surfaces of precious metal single crystals, films, and nanoparticles supported on titania produces beautiful long-range ordered structures which can often be resolved at atomic resolution using scanning tunneling microscopy (STM). Such surfaces show reduced binding for CO and effectively lower the activity of the surface. Consideration is given to the cause and composition of the surface layer, that is, whether it is a kind of intermetallic layer, or is simply a thin layer of titanium (sub-)oxide.

  6. Microstructure and biocompatibility of titanium oxides produced on nitrided surface layer under glow discharge conditions.

    PubMed

    Czarnowska, E; Morgiel, J; Ossowski, M; Major, R; Sowinska, A; Wierzchon, T

    2011-10-01

    The disadvantages of titanium implants are their low wear resistance and the release of titanium elements into surrounding tissue. These can be eliminated by modifying the surface by surface engineering methods, among them nitriding under glow discharge conditions which allow to produce diffusive surface layers. Their combining with an oxide layer might be valuable for biological events occurring at the bone implant interface. The aim of this study was to enhance the titanium biomaterial performance via combining nitriding and oxidizing treatments in one process under glow discharge conditions. The oxynitrided surface layers were produced at 680 degrees C. The obtained layer was TiO + TiN + Ti2N + alphaTi(N) type and about 4-microm thick and was of diffusive character. This layer significantly increased wear resistance and slightly corrosion resistance compared to that of the reference titanium alloy. The produced titanium oxide was about 400-nm thick and built from fine crystallites. This oxide exhibits bioactivity in SBF (simulated body fluid). Osteoblasts of Saos-2 line incubated on this surface exhibited good adhesion and proliferation and ALP release comparable with cells cultured on the reference titanium alloy and TiN + Ti2N + alphaTi(N) surface layers. A quantitative analysis of blood platelets adhering to this layer revealed their highest amount in comparison to that on both the nitrided surface layer and titanium alloy. The presented study provided a simple and reproducible method of combining oxidizing and nitriding under glow discharge in one process. Experimental data in vitro suggests that titanium alloy oxynitriding under low temperatures at glow discharge conditions improves titanium alloy properties and biocompatibility and tissue healing. Therefore, the layer of TiO + TiN +Ti2N + alphaTi(N) type could be valuable for long-term bone implants. PMID:22400281

  7. Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission

    SciTech Connect

    A.T. Wu, S. Jin, J.D. Mammosser, R.A. Rimmer, X.Y. Lu, K. Zhao

    2011-09-01

    Field emission on the inner surfaces of niobium superconducting radio frequency cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results* seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3 nm up to 460 nm. A home-made scanning field emission microscope was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The SFEM experimental results were analyzed in terms of surface morphology and oxide thickness of Nb samples and chemical composition and geographic shape of the emitters. A model based on the classic electromagnetic theory was developed trying to understand the experimental results. Possibly implications for Nb SRF cavity applications from this study will be discussed.

  8. Aspects of native oxides etching on n-GaSb(1 0 0) surface

    NASA Astrophysics Data System (ADS)

    Cotirlan, C.; Ghita, R. V.; Negrila, C. C.; Logofatu, C.; Frumosu, F.; Lungu, G. A.

    2016-02-01

    Gallium antimonide (GaSb) is the basis of the most photovoltaic and thermophotovoltaic (TPV) systems and its innovative technological aspects based on modern ultra-high vacuum techniques are in trend for device achievement. The real surface of GaSb is modified by technological processes that can conduce to problems related to the reproducible control of its surface properties. The GaSb surface is reactive in atmosphere due to oxygen presence and exhibits a native oxide layer. The evolution of native oxides during the ion sputtering, chemical etching and thermal annealing processes for preparing the surface is presented in detailed way. Ratios of surface constituents are obtained by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS). Moreover, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM) and Low-Energy Electron Diffraction (LEED) are used for characterization. The surface stoichiometry is changed using a specific etchant (e.g. citric acid) at different etching time and is analyzed by ARXPS, SEM, EDS and AFM methods. The experimental results provide useful information regarding surface native oxides characteristics on n-GaSb(1 0 0) to be taken into account for development of low resistance contacts for TPV devices based on GaSb alloy.

  9. MicroRNA functionalized microporous titanium oxide surface by lyophilization with enhanced osteogenic activity.

    PubMed

    Wu, Kaimin; Song, Wen; Zhao, Lingzhou; Liu, Mengyuan; Yan, Jun; Andersen, Morten Østergaard; Kjems, Jørgen; Gao, Shan; Zhang, Yumei

    2013-04-10

    Developing biomedical titanium (Ti) implants with high osteogenic ability and consequent rigid osseointegration is a constant requirement from the clinic. In this study, we fabricate novel miRNA functionalized microporous Ti implants by lyophilizing miRNA lipoplexes onto a microporous titanium oxide surface formed by microarc oxidation (MAO). The microporous titanium oxide surface provides a larger surface area for miRNA loading and enables spatial retention of the miRNAs within the pores until cellular delivery. The loading of lipoplexes into the micropores on the MAO Ti surface is facilitated by the superhydrophilicity and Ti-OH groups gathering of the MAO surface after UV irradiation followed by lyophilization. A high miRNA transfection efficiency was observed in mesenchymal stem cells (MSCs) seeded onto the miRNA functionalized surface with no apparent cytotoxicity. When functionalizing the Ti surface with miR-29b that enhances osteogenic activity and antimiR-138 that inhibits miR-138 inhibition of endogenous osteogenesis, clear stimulation of MSC osteogenic differentiation was observed, in terms of up-regulating osteogenic expression and enhancing alkaline phosphatase production, collagen secretion and ECM mineralization. The novel miRNA functionalized Ti implants with enhanced osteogenic activity promisingly lead to more rapid and robust osseointegration of a clinical bone implant interface. Our study implies that lyophilization may constitute a versatile method for miRNA loading to other biomaterials with the aim of controlling cellular function. PMID:23459382

  10. Morphology of cerium oxide surfaces in an oxidzing enviroment:a first-principles investigation

    NASA Astrophysics Data System (ADS)

    Fronzi, Marco; Soon, Aloysius; Stampfl, Catherine; Delley, Bernard; Traversa, Enrico

    2007-03-01

    A good understanding of the stability and chemistry of CeO2 surfaces is crucial for a better designing of solid oxide fuel cells. As the first step, we use DFT [1] to study the structural and electronic ground state properties of bulk CeO2. various surface termination of the low-index surface of CeO2 are then investigated, namely the stoichiometric, metal- and oxygen- rich terminations, and defected surfaces. Using the concept of ab initio atomistic thermodynamics&[tilde;2], we calculate the surface free energy phase diagram. This allows us to identify and predict stable, and potentally catalytically important, structures. There is an evidence to suggest an interesting morphological change in the surface structures with varying oxygen concentration. Reaction pathways for methane oxidation on low energy cerium oxide surfaces are being investigated and will be reported.[1] Formulated in the DMol^3 code; B. Delley, J. Chem. Phys. 92, 508 (1990);ibid. 113, 7756 (2000).[2] K. Reuter, C. Stampfl and M. Scheffler, in Handbook of Materials Modeling, Volume 1, Fundamental Models and Methods, Sidney Yip (Ed)(2005).

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

    SciTech Connect

    Ricci, Pier Carlo Carbonaro, C. M. Corpino, R. Chiriu, D. Stagi, L.

    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 α−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.

  12. Surface Analysis of Micro-Arc Oxidized Coatings Deposited on cp-Ti

    NASA Astrophysics Data System (ADS)

    Kim, Yeon-Wook; Nam, Tae-Hyun

    The surface of commercially pure titanium (grade 4) was modified by micro-arc oxidation treatment. A porous TiO2 coating layer was formed on the Ti surface and its crystal structure was analyzed as rutile phase. Both the thickness of the TiO2 layer and the pore size on the surface were strongly dependent on the applied current density as well as the micro-arc oxidizing time during the oxidation treatment. When a current density of 50 mA/cm2 had been applied for 10 minutes, the thickness and the pore size of the oxide layer were 1.2 µm and 230 nm, respectively. The thickness and the pore size of the layer continued to increase with increasing the applied current density. The TiO2 passive layer of the titanium surface can attribute to the excellent biocompatibility and the formation of nano-sized pores may maximize the interlocking between mineralized bone and the surface of the Ti implant.

  13. 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

  14. The impact of the distributions of surface oxides and their migration on characterization of the heterogeneous carbon-oxygen reaction

    SciTech Connect

    Campbell, P.A.; Mitchell, R.E.

    2008-07-15

    A study was undertaken to characterize the impact of the heterogeneity and migration of surface oxides on the char oxidation process. The char employed in the study was subjected to a series of kinetics-limited oxidation tests in a pressurized thermogravimetric analyzer (PTGA). Temperature-programmed desorption and BET-CO{sub 2} gas adsorption tests were also performed in order to characterize surface oxide complexes and specific surface areas. In agreement with other studies, the experiments indicated that the surface-oxide populations may be characterized in terms of a distribution of desorption activation energies and that migration of the surface oxide complexes is significant. A heterogeneous reaction mechanism was developed to account for the observed rates of O{sub 2} adsorption, CO and CO{sub 2} desorption, and surface-oxide accumulation and was used in a numerical algorithm that modeled the PTGA reaction environment. Surface species were characterized by activation-energy-based distributions; allowance was made for the impact of surface area evolution on surface species concentrations. Analysis of calculated results indicate that a quasi-steady surface area assumption tends to underpredict surface species concentrations, especially at late conversions, but can overpredict these concentrations at early conversions. Calculated results also indicate that using less than five sites to approximate activation energy distributions yields results that are inconsistent with oxidation behaviors that are based on the full distributions. (author)

  15. Nitrogen-doped hierarchical porous carbon with high surface area derived from graphene oxide/pitch oxide composite for supercapacitors.

    PubMed

    Ma, Yuan; Ma, Chang; Sheng, Jie; Zhang, Haixia; Wang, Ranran; Xie, Zhenyu; Shi, Jingli

    2016-01-01

    A nitrogen-doped hierarchical porous carbon has been prepared through one-step KOH activation of pitch oxide/graphene oxide composite. At a low weight ratio of KOH/composite (1:1), the as-prepared carbon possesses high specific surface area, rich nitrogen and oxygen, appropriate mesopore/micropore ratio and considerable small-sized mesopores. The addition of graphene oxide plays a key role in forming 4 nm mesopores. The sample PO-GO-16 presents the characteristics of large surface area (2196 m(2) g(-1)), high mesoporosity (47.6%), as well as rich nitrogen (1.52 at.%) and oxygen (6.9 at.%). As a result, PO-GO-16 electrode shows an outstanding capacitive behavior: high capacitance (296 F g(-1)) and ultrahigh-rate performance (192 F g(-1) at 10 A g(-1)) in 6 M KOH aqueous electrolyte. The balanced structure characteristic, low-cost and high performance, make the porous carbon a promising electrode material for supercapacitors. PMID:26397915

  16. Development of highly faceted reduced graphene oxide-coated copper oxide and copper nanoparticles on a copper foil surface

    PubMed Central

    Matsumoto, Yasuhiro; Espinoza-Rivas, Andrés M; Pérez-Guzmán, Manuel A; Ortega-López, Mauricio

    2016-01-01

    Summary This work describes the formation of reduced graphene oxide-coated copper oxide and copper nanoparticles (rGO-Cu2ONPs, rGO-CuNPs) on the surface of a copper foil supporting graphene oxide (GO) at annealing temperatures of 200–1000 °C, under an Ar atmosphere. These hybrid nanostructures were developed from bare copper oxide nanoparticles which grew at an annealing temperature of 80 °C under nitrogen flux. The predominant phase as well as the particle size and shape strongly depend on the process temperature. Characterization with transmission electron microscopy and scanning electron microscopy indicates that Cu or Cu2O nanoparticles take rGO sheets from the rGO network to form core–shell Cu–rGO or Cu2O–rGO nanostructures. It is noted that such ones increase in size from 5 to 800 nm as the annealing temperature increases in the 200–1000 °C range. At 1000 °C, Cu nanoparticles develop a highly faceted morphology, displaying arm-like carbon nanorods that originate from different facets of the copper crystal structure. PMID:27547618

  17. Development of highly faceted reduced graphene oxide-coated copper oxide and copper nanoparticles on a copper foil surface.

    PubMed

    Ortega-Amaya, Rebeca; Matsumoto, Yasuhiro; Espinoza-Rivas, Andrés M; Pérez-Guzmán, Manuel A; Ortega-López, Mauricio

    2016-01-01

    This work describes the formation of reduced graphene oxide-coated copper oxide and copper nanoparticles (rGO-Cu2ONPs, rGO-CuNPs) on the surface of a copper foil supporting graphene oxide (GO) at annealing temperatures of 200-1000 °C, under an Ar atmosphere. These hybrid nanostructures were developed from bare copper oxide nanoparticles which grew at an annealing temperature of 80 °C under nitrogen flux. The predominant phase as well as the particle size and shape strongly depend on the process temperature. Characterization with transmission electron microscopy and scanning electron microscopy indicates that Cu or Cu2O nanoparticles take rGO sheets from the rGO network to form core-shell Cu-rGO or Cu2O-rGO nanostructures. It is noted that such ones increase in size from 5 to 800 nm as the annealing temperature increases in the 200-1000 °C range. At 1000 °C, Cu nanoparticles develop a highly faceted morphology, displaying arm-like carbon nanorods that originate from different facets of the copper crystal structure. PMID:27547618

  18. Adsorption of nitrogen oxide molecules to the surface of nanosized nickel clusters formed on the (111) surface of a magnesium oxide film

    NASA Astrophysics Data System (ADS)

    Remar, D. F.; Turiev, A. M.; Tsidaeva, N. I.; Magkoev, T. T.

    2010-10-01

    The properties of the systems formed on deposition of Ni atoms on the (111) surface of a MgO film of thickness equal to six monomolecular layers grown on a Mo(110) crystal face and the adsorption of NO nitrogen oxide molecules to the system surface have been studied by methods of electron spectroscopy (AES, XPES, LEED, LEIBSS) and reflective infrared absorption spectroscopy. On deposition of Ni atoms on the surface of MgO at a substrate temperature of 600 K, three-dimensional islands of Ni are formed. The subsequent adsorption of NO results in molecule dissociation even at 110 K. The efficiency of this process depends on the morphology of the Ni layer.

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

    SciTech Connect

    Kondratenko, Serguei; Hsu, P. K.; Zhao, Hongchen; 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.

  20. 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

  1. Photoemission and LEED study of the Sn/Rh(111) surface--early oxidation steps and thermal stability.

    PubMed

    Hanyš, Petr; Píš, Igor; Mašek, Karel; Sutara, František; Matolín, Vladimír; Nehasil, Václav

    2012-01-11

    We have deposited two monolayers of Sn onto Rh(111) single crystal. After the deposition, no ordered structure was revealed by low energy electron diffraction (LEED). We oxidized the obtained system in a low-pressure oxygen atmosphere at 420 K. The oxidized sample was then gradually heated to study the thermal stability of the oxide layer. We characterized the system by synchrotron radiation stimulated photoelectron spectroscopy and LEED. Valence band and core level photoelectron spectra of rhodium, tin and oxygen were used to study the oxidation of the Sn-Rh(111) surface and its behaviour upon annealing. A low stoichiometric oxide of Sn was created on the surface. The oxidation process did not continue towards creation of SnO(2) with higher oxygen dose. The annealing at 970 K caused decomposition of the surface oxide of Sn and creation of an ordered (√3 × √3)R30° Sn-Rh(111) surface alloy. PMID:22095587

  2. 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.

  3. Solid Oxide Fuel Cell Cathodes. Unraveling the Relationship Between Structure, Surface Chemistry and Oxygen Reduction

    SciTech Connect

    Gopalan, Srikanth

    2013-03-31

    In this work we have considered oxygen reduction reaction on LSM and LSCF cathode materials. In particular we have used various spectroscopic techniques to explore the surface composition, transition metal oxidation state, and the bonding environment of oxygen to understand the changes that occur to the surface during the oxygen reduction process. In a parallel study we have employed patterned cathodes of both LSM and LSCF cathodes to extract transport and kinetic parameters associated with the oxygen reduction process.

  4. Reduction of a thin chromium oxide film on Inconel surface upon treatment with hydrogen plasma

    NASA Astrophysics Data System (ADS)

    Vesel, Alenka; Mozetic, Miran; Balat-Pichelin, Marianne

    2016-11-01

    Inconel samples with a surface oxide film composed of solely chromium oxide with a thickness of approximately 700 nm were exposed to low-pressure hydrogen plasma at elevated temperatures to determine the suitable parameters for reduction of the oxide film. The hydrogen pressure during treatment was set to 60 Pa. Plasma was created by a surfaguide microwave discharge in a quartz glass tube to allow for a high dissociation fraction of hydrogen molecules. Auger electron depth profiling (AES) was used to determine the decay of the oxygen in the surface film and X-ray diffraction (XRD) to measure structural modifications. During hydrogen plasma treatment, the oxidized Inconel samples were heated to elevated temperatures. The reduction of the oxide film started at temperatures of approximately 1300 K (considering the emissivity of 0.85) and the oxide was reduced in about 10 s of treatment as revealed by AES. The XRD showed sharper substrate peaks after the reduction. Samples treated in hydrogen atmosphere under the same conditions have not been reduced up to approximately 1500 K indicating usefulness of plasma treatment.

  5. Determination of surface oxide compositions on Alloy 600 using Rutherford backscattering

    SciTech Connect

    Hanson, A.L.; Isaacs, H.S.; Kraner, H.W.

    1984-01-01

    The surface composition of oxides formed on Alloy 600 under conditions similar to those in the primary side of PWR heat exchangers has been studied as a function of potential using Rutherford backscattering and proton inelastic scattering. Electropolished samples of Alloy 600 were exposed at several potentials to a solution of 0.18M H/sub 3/BO/sub 3/(2000 ppM B) with 0.28M LiOH (1.4 ppM Li) at 300/sup 0/C for 450 hours. The potentials relative to an internal hydrogen electrode ranged from -.09 to 750 mV. RBS analysis showed little or no oxide formation on samples exposed at 0 mV. Above 0 mV oxide layers formed whose thicknesses increased with potential. In addition the RBS showed a significantly enhanced concentration of aluminum and silicon in oxide. Both the oxygen and the sum of the aluminum and silicon content appeared to maintain a fixed surface concentration independent of the oxide thickness. Boron and lithium concentration were analyzed with proton inelastic scattering. No lithium was found in any sample. The boron concentration was found to follow the thickness of the oxide.

  6. Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide

    SciTech Connect

    Kerr, A. J.; Chagarov, E.; Kaufman-Osborn, T.; Kummel, A. C.; Gu, S.; Wu, J.; Asbeck, P. M.; Madisetti, S.; Oktyabrsky, S.

    2014-09-14

    A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al{sub 2}O{sub 3} gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001)

  7. Determination of photoelectrochemical water oxidation intermediates on haematite electrode surfaces using operando infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Zandi, Omid; Hamann, Thomas W.

    2016-08-01

    Semiconductor electrodes capable of using solar photons to drive water-splitting reactions, such as haematite (α-Fe2O3), have been the subject of tremendous interest over recent decades. The surface has been found to play a significant role in determining the efficiency of water oxidation with haematite; however, previous works have only allowed hypotheses to be formulated regarding the identity of relevant surface species. Here we investigate the water-oxidation reaction on haematite using infrared spectroscopy under photoelectrochemical (PEC) water-oxidation conditions. A potential- and light-dependent absorption peak at 898 cm‑1 is assigned to a FeIV=O group, which is an intermediate in the PEC water-oxidation reaction. These results provide direct evidence of high-valent iron–oxo intermediates as the product of the first hole-transfer reaction on the haematite surface and represent an important step in establishing the mechanism of PEC water oxidation on semiconductor electrodes.

  8. Determination of photoelectrochemical water oxidation intermediates on haematite electrode surfaces using operando infrared spectroscopy.

    PubMed

    Zandi, Omid; Hamann, Thomas W

    2016-08-01

    Semiconductor electrodes capable of using solar photons to drive water-splitting reactions, such as haematite (α-Fe2O3), have been the subject of tremendous interest over recent decades. The surface has been found to play a significant role in determining the efficiency of water oxidation with haematite; however, previous works have only allowed hypotheses to be formulated regarding the identity of relevant surface species. Here we investigate the water-oxidation reaction on haematite using infrared spectroscopy under photoelectrochemical (PEC) water-oxidation conditions. A potential- and light-dependent absorption peak at 898 cm(-1) is assigned to a Fe(IV)=O group, which is an intermediate in the PEC water-oxidation reaction. These results provide direct evidence of high-valent iron-oxo intermediates as the product of the first hole-transfer reaction on the haematite surface and represent an important step in establishing the mechanism of PEC water oxidation on semiconductor electrodes. PMID:27442283

  9. 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

  10. Plasma surface oxidation of 316L stainless steel for improving adhesion strength of silicone rubber coating to metal substrate

    NASA Astrophysics Data System (ADS)

    Latifi, Afrooz; Imani, Mohammad; Khorasani, Mohammad Taghi; Daliri Joupari, Morteza

    2014-11-01

    Stainless steel 316L is one of the most widely used materials for fabricating of biomedical devices hence, improving its surface properties is still of great interest and challenging in biomaterial sciences. Plasma oxidation, in comparison to the conventional chemical or mechanical methods, is one of the most efficient methods recently used for surface treatment of biomaterials. Here, stainless steel specimens were surface oxidized by radio-frequency plasma irradiation operating at 34 MHz under pure oxygen atmosphere. Surface chemical composition of the samples was significantly changed after plasma oxidation by appearance of the chromium and iron oxides on the plasma-oxidized surface. A wettable surface, possessing high surface energy (83.19 mN m-1), was observed after plasma oxidation. Upon completion of the surface modification process, silicone rubber was spray coated on the plasma-treated stainless steel surface. Morphology of the silicone rubber coating was investigated by scanning electron microscopy (SEM). A uniform coating was formed on the oxidized surface with no delamination at polymer-metal interface. Pull-off tests showed the lowest adhesion strength of coating to substrate (0.12 MPa) for untreated specimens and the highest (0.89 MPa) for plasma-oxidized ones.

  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. In situ transmission infrared spectroscopy of high-kappa oxide atomic layer deposition onto silicon surfaces

    NASA Astrophysics Data System (ADS)

    Ho, Ming-Tsung

    Ultra-thin aluminum oxide (Al2O3) and hafnium oxide (HfO2) layers have been grown by atomic layer deposition (ALD) using tri-methyl-aluminum (TMA) and tetrakis-ethyl-methyl-amino-hafnium (TEMAH) respectively with heavy water (D2O) as the oxidizing agent. Several different silicon surfaces were used as substrates such as hydrogen terminated silicon (H/Si), SC2 (or RCA 2) cleaned native silicon oxide (SiO 2/Si), and silicon (oxy)nitride. In-situ transmission Fourier transform infrared spectroscopy (FTIR) has been adopted for the study of the growth mechanisms during ALD of these films. The vibrational spectra of gas phase TEMAH and its reaction byproducts with oxidants have also been investigated. Density functional theory (DFT) normal mode calculations show a good agreement with the experimental data when it is combined with linear wave-number scaling method and Fermi resonance mechanism. Ether (-C-O-C-) and tertiary alkylamine (N(R1R 2R3)) compounds are the two most dominant products of TEMAH reacting with oxygen gas and water. When ozone is used as the oxidant, gas phase CH2O, CH3NO2, CH3-N=C=O and other compounds containing -(C=O)- and --C-O-C- (or --O-C-) segments are observed. With substrate temperatures less than 400°C and 300°C for TMA and TEMAH respectively, Al oxide and Hf oxide ALD can be appropriately performed on silicon surfaces. Thin silicon (oxy)nitride thermally grown in ammonia on silicon substrate can significantly reduce silicon oxide interlayer formation during ALD and post-deposition annealing. The crystallization temperature of amorphous ALD grown HfO2 on nitridized silicon is 600°C, which is 100°C higher than on the other silicon surfaces. When HfO2 is grown on H/Si(111) at 100°C deposition temperature, minimum 5--10 ALD cycles are required for the full surface coverage. The steric effect can be seen by the evolution of the H-Si stretching mode at 2083 cm-1. The observed red shift of H-Si stretching to ˜ 2060 cm-1 can be caused by Si

  13. Surface functionalization of carbon nanofibers by sol gel coating of zinc oxide

    NASA Astrophysics Data System (ADS)

    Shao, Dongfeng; Wei, Qufu; Zhang, Liwei; Cai, Yibing; Jiang, Shudong

    2008-08-01

    In this paper the functional carbon nanofibers were prepared by the carbonization of ZnO coated PAN nanofibers to expand the potential applications of carbon nanofibers. Polyacrylonitrile (PAN) nanofibers were obtained by electrospinning. The electrospun PAN nanofibers were then used as substrates for depositing the functional layer of zinc oxide (ZnO) on the PAN nanofiber surfaces by sol-gel technique. The effects of coating, pre-oxidation and carbonization on the surface morphology and structures of the nanofibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM), respectively. The results of SEM showed a significant increase of the size of ZnO nanograins on the surface of nanofibers after the treatments of coating, pre-oxidation and carbonization. The observations by SEM also revealed that ZnO nanoclusters were firmly and clearly distributed on the surface of the carbon nanofibers. FTIR examination also confirmed the deposition of ZnO on the surface of carbon nanofibers. The XRD analysis indicated that the crystal structure of ZnO nanograins on the surface of carbon nanofibers.

  14. Intrinsic activity and poisoning rate for HCOOH oxidation on platinum stepped surfaces.

    PubMed

    Grozovski, Vitali; Climent, Víctor; Herrero, Enrique; Feliu, Juan M

    2010-08-21

    Pulsed voltammetry has been used to study formic acid oxidation on platinum stepped surfaces to determine the kinetics of the reaction and the role of the surface structure in the reactivity. From the current transients at different potentials, the intrinsic activity of the electrode through the active intermediate reaction path (j(theta = 0)), as well as the rate constant for the CO formation (k(ads)) have been calculated. The kinetics for formic acid oxidation through the active intermediate reaction path is strongly dependent on the surface structure of the electrode, with the highest activity found for the Pt(100) surface. The presence of steps, both on (100) and (111) terraces, does not increase the activity of these surfaces. CO formation only takes place in a narrow potential window very close to the local potential of zero total charge. The extrapolation of the results obtained with stepped surfaces with (111) terraces to zero step density indicates that CO formation should not occur on an ideal Pt(111) electrode. Additionally, the analysis of the Tafel slopes obtained for the different electrodes suggests that the oxidation of formic acid is strongly affected by the presence of adsorbed anions, hydrogen and water. PMID:20539876

  15. Effect of moisture on the surface free energy and acid-base properties of mineral oxides.

    PubMed

    Sun, Chenhang; Berg, John C

    2002-09-01

    Surface energetic properties of mineral oxides are important in many applications. Since oxide surfaces in practice have generally come in contact with water molecules, it is important to know how water coverage affects the surface properties. In this work, five oxide samples, namely MgO, Al2O3, TiO2, SnO2 and SiO2 are heat-treated to various extents, to produce different degrees of hydration, and characterized thereafter by inverse gas chromatography. Water contents of the treated samples are determined independently by Karl Fischer titration, and specific surface areas are measured by the BET method. The results show that in general as water coverage decreases, the Lifshitz-van der Waals component of the specific surface free energy (sigma(S)LW) increases, but the acid-base interaction potential (-deltaG(AB)) decreases. These attributes are more sensitive to changes in water coverage at lower coverages, where the surface is presumed to consist of patches of molecular water and unhydrated hydroxyl groups. PMID:12385377

  16. Effect of Reacting Surface Density on the Overall Graphite Oxidation Rate

    SciTech Connect

    Chang H. Oh; Eung Kim; Jong Lim; Richard Schultz; David Petti

    2009-05-01

    Graphite oxidation in an air-ingress accident is presently a very important issue for the reactor safety of the very high temperature gas cooled-reactor (VHTR), the concept of the next generation nuclear plant (NGNP) because of its potential problems such as mechanical degradation of the supporting graphite in the lower plenum of the VHTR might lead to core collapse if the countermeasure is taken carefully. The oxidation process of graphite has known to be affected by various factors, including temperature, pressure, oxygen concentration, types of graphite, graphite shape and size, flow distribution, etc. However, our recent study reveals that the internal pore characteristics play very important roles in the overall graphite oxidation rate. One of the main issues regarding graphite oxidation is the potential core collapse problem that may occur following the degradation of graphite mechanical strength. In analyzing this phenomenon, it is very important to understand the relationship between the degree of oxidization and strength degradation. In addition, the change of oxidation rate by graphite oxidation degree characterization by burn-off (ratio of the oxidized graphite density to the original density) should be quantified because graphite strength degradation is followed by graphite density decrease, which highly affects oxidation rates and patterns. Because the density change is proportional to the internal pore surface area, they should be quantified in advance. In order to understand the above issues, the following experiments were performed: (1)Experiment on the fracture of the oxidized graphite and validation of the previous correlations, (2) Experiment on the change of oxidation rate using graphite density and data collection, (3) Measure the BET surface area of the graphite. The experiments were performed using H451 (Great Lakes Carbon Corporation) and IG-110 (Toyo Tanso Co., Ltd) graphite. The reason for the use of those graphite materials is because

  17. Preparation of Thin Melanin-Type Films by Surface-Controlled Oxidation.

    PubMed

    Salomäki, Mikko; Tupala, Matti; Parviainen, Timo; Leiro, Jarkko; Karonen, Maarit; Lukkari, Jukka

    2016-04-26

    The preparation of thin melanin films suitable for applications is challenging. In this work, we present a new alternative approach to thin melanin-type films using oxidative multilayers prepared by the sequential layer-by-layer deposition of cerium(IV) and inorganic polyphosphate. The interfacial reaction between cerium(IV) in the multilayer and 5,6-dihydroxyindole (DHI) in the adjacent aqueous solution leads to the formation of a thin uniform film. The oxidation of DHI by cerium(IV) proceeds via known melanin intermediates. We have characterized the formed DHI-melanin films using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-vis spectroscopy, and spectroelectrochemistry. When a five-bilayer oxidative multilayer is used, the film is uniform with a thickness of ca. 10 nm. Its chemical composition, as determined using XPS, is typical for melanin. It is also redox active, and its oxidation occurs in two steps, which can be assigned to semiquinone and quinone formation within the indole structural motif. Oxidative multilayers can also oxidize dopamine, but the reaction stops at the dopamine quinone stage because of the limited amount of the multilayer-based oxidizing agent. However, dopamine oxidation by Ce(IV) was studied also in solution by UV-vis spectroscopy and mass spectrometry in order to verify the reaction mechanism and the final product. In solution, the oxidation of dopamine by cerium shows that the indole ring formation takes place already at low pH and that the mass spectrum of the final product is practically identical with that of commercial melanin. Therefore, layer-by-layer formed oxidative multilayers can be used to deposit functional melanin-type thin films on arbitrary substrates by a surface-controlled reaction. PMID:27049932

  18. A charge transport study in diamond, surface passivated by high-k dielectric oxides

    SciTech Connect

    Kovi, Kiran Kumar Majdi, Saman; Gabrysch, Markus; Isberg, Jan

    2014-11-17

    The recent progress in the growth of high-quality single-crystalline diamond films has sparked interest in the realization of efficient diamond power electronic devices. However, finding a suitable passivation is essential to improve the reliability and electrical performance of devices. In the current work, high-k dielectric materials such as aluminum oxide and hafnium oxide were deposited by atomic layer deposition on intrinsic diamond as a surface passivation layer. The hole transport properties in the diamond films were evaluated and compared to unpassivated films using the lateral time-of-flight technique. An enhancement of the near surface hole mobility in diamond films of up to 27% is observed when using aluminum oxide passivation.

  19. Ethanol oxidation on Pt single-crystal electrodes: surface-structure effects in alkaline medium.

    PubMed

    Busó-Rogero, Carlos; Herrero, Enrique; Feliu, Juan M

    2014-07-21

    Ethanol oxidation in 0.1 M NaOH on single-crystal electrodes has been studied using electrochemical and FTIR techniques. The results show that the activity order is the opposite of that found in acidic solutions. The Pt(111) electrode displays the highest currents and also the highest onset potential of all the electrodes. The onset potential for the oxidation of ethanol is linked to the adsorption of OH on the electrode surface. However, small (or even negligible) amounts of CO(ads) and carbonate are detected by FTIR, which implies that cleavage of the C-C bond is not favored in this medium. The activity of the electrodes diminishes quickly upon cycling. The diminution of the activity is proportional to the measured currents and is linked to the formation and polymerization of acetaldehyde, which adsorbs onto the electrode surface and prevents further oxidation. PMID:24782218

  20. Influence of surface defects and local structure on oxygenate reaction pathways over metal oxide surfaces

    NASA Astrophysics Data System (ADS)

    Cox, D. F.

    1993-07-01

    Complete thermal desorption and photoemission studies of seven molecules (methanol, formaldehyde, formic acid, isopropanol, acetone, water, and carbon monoxide) were completed on four different SnO2(110) surfaces (stoichiometric, reduced, slightly-defective, and highly-defective). Initial thermal desorption studies of acetic acid and propene were also done. Results indicate that different initial surface conditions can dramatically affect: (1) probability for heterolytic dissociation of Bronsted acids, (2) reaction kinetics for unimolecular decomposition of oxygenated surface intermediates, and (3) product selectivity.

  1. Chemical changes in secondary electron emission during oxidation of nickel /100/ and /111/ crystal surfaces

    NASA Technical Reports Server (NTRS)

    Holloway, P. H.; Hudson, J. B.

    1975-01-01

    Changes in the secondary electron spectra (which include chemical shifts of Auger transitions) between 0-70 eV during the oxidation of both (100) and (111) nickel surfaces are reported. The reaction sequence between oxygen and nickel is also briefly described. Emission rate changes are correlated with changes in the work function of the solid.

  2. Oxidation of the Ru(0001) surface covered by weakly bound, ultrathin silicate films

    NASA Astrophysics Data System (ADS)

    Emmez, Emre; Anibal Boscoboinik, J.; Tenney, Samuel; Sutter, Peter; Shaikhutdinov, Shamil; Freund, Hans-Joachim

    2016-04-01

    Bilayer silicate films grown on metal substrates are weakly bound to the metal surfaces, which allows ambient gas molecules to intercalate the oxide/metal interface. In this work, we studied the interaction of oxygen with Ru(0001) supported ultrathin silicate and aluminosilicate films at elevated O2 pressures (10- 5-10 mbar) and temperatures (450-923 K). The results show that the silicate films stay essentially intact under these conditions, and oxygen in the film does not exchange with oxygen in the ambient. O2 molecules readily penetrate the film and dissociate on the underlying Ru surface underneath. The silicate layer does however strongly passivate the Ru surface towards RuO2(110) oxide formation that readily occurs on bare Ru(0001) under the same conditions. The results indicate considerable spatial effects for oxidation reactions on metal surfaces in the confined space at the interface. Moreover, the aluminosilicate films completely suppress the Ru oxidation, providing some rationale for using crystalline aluminosilicates in anti-corrosion coatings.

  3. Oxidation of carbon fiber surfaces for use as reinforcement in high-temperature cementitious material systems

    DOEpatents

    Sugama, Toshifumi.

    1990-05-22

    The interfacial bond characteristics between carbon fiber and a cement matrix, in high temperature fiber-reinforced cementitious composite systems, can be improved by the oxidative treatment of the fiber surfaces. Compositions and the process for producing the compositions are disclosed. 2 figs.

  4. One-sided surface modification of cellulose fabric by printing a modified TEMPO-mediated oxidant.

    PubMed

    Fitz-Binder, Christa; Bechtold, Thomas

    2014-06-15

    One-sided surface oxidation of lyocell type cellulose fabric can be achieved by use of a modified TEMPO-mediated oxidation system. A borate-based buffer was used to maintain stable pH conditions and screen printing was applied to achieve oxidation on the fabric surface only. To formulate an applicable procedure, the TEMPO/NaBr/NaOCl system was split into two treatment steps: firstly, the fabric was impregnated with a buffered TEMPO/NaBr solution and dried, then a thickened NaOCl paste was printed on the fabric. FTIR-ATR spectra and methylene blue sorption experiments demonstrated successful modification on the printed side of the fabric. Substantial increases in carboxylic group content and water retention value were observed. The higher concentration of carboxylic groups on the fabric surface also led to a localised increase in binding capacity for Ca(2+)-ions. This new concept permits controlled oxidation of cellulose surfaces by printing techniques. PMID:24721061

  5. Oxidation of carbon fiber surfaces for use as reinforcement in high-temperature cementitious material systems

    DOEpatents

    Sugama, Toshifumi

    1990-01-01

    The interfacial bond characteristics between carbon fiber and a cement matrix, in high temperature fiber-reinforced cementitious composite systems, can be improved by the oxidative treatment of the fiber surfaces. Compositions and the process for producing the compositions are disclosed.

  6. 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.

  7. Effects of Oxide Surface on the Detonation Initiation of Energetic Materials from First Principles

    NASA Astrophysics Data System (ADS)

    Wang, Fenggong; Tsyshevsky, Roman; Kuklja, Maija; UMD Team

    Organic-inorganic interface provides both intrigues and opportunities for designing systems possessing properties and functionalities inaccessible by individual component. The electronic, catalytic, and defect properties of inorganic surfaces can affect the adsorption, chemical reaction, and photo-responsive properties of organic molecules. In particular, the presence of a particular oxide additive prompts the energy absorption for detonation initiation. Here, we choose the highly catalytic oxide TiO2 and explosive trinitrotoluene (TNT) as prototypical examples to explore the role of oxide surface on the detonation initiation of explosives from first principles. We show that the TNT-TiO2 (110) interface induces optical transitions between TiO2 and TNT, shifting the light absorption edge to lower energy. This helps to control the detonation initiation by laser light with a modest optical energy. In addition, the presence of surface oxygen vacancies leads to electron transfer from surface to molecule, facilitating the decomposition of TNT. Our results not only provide guidelines for designing a controllable oxide-explosive formulation that can be initiated by available lasers, but also help to understand interfaces with target properties and functionalities.

  8. Comparative study of metal adsorption on the metal and the oxide surfaces

    NASA Astrophysics Data System (ADS)

    Magkoev, T. T.; Vladimirov, G. G.; Remar, D.; Moutinho, A. M. C.

    2002-05-01

    Adsorption of Ti, Cr, Fe, Ni and Cu atoms at coverage not exceeding two monolayers on the surface of ultrathin (10-15 Å) alumina and magnesia films (γ-Al 2O 3(111) or α-Al 2O 3(1000) and MgO(111) grown on Mo(110) were studied in ultrahigh vacuum by means of electron spectroscopy techniques (Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), high resolution electron energy loss spectroscopy (HREELS), low energy electron diffraction (LEED), work function measurements and reflection absorption infrared spectroscopy (RAIRS)). At very low metal coverage and low substrate temperature (85 K) when the film can be viewed as consisting of separate adatoms and/or very small clusters the electronic properties of adatoms on the oxide films, on one hand, and on Mo(110) surface, on the other hand, are quite different. With increasing metal coverage, the properties on both the oxide and the metallic substrates change becoming similar at the coverage close to monolayer. On the Mo(110) surface the electronic properties change gradually with the metal coverage, whereas on the oxide there is a critical coverage of about 0.15 ML separating ionic and metallic adsorption of the metal species. It is shown that the lateral interaction of adatoms on the oxide surface plays a dominant role in the formation of the band-like structure of the adsorbed 2D film.

  9. Electrochemical oxidation of hydrazine and its derivatives on the surface of metal electrodes in alkaline media

    NASA Astrophysics Data System (ADS)

    Asazawa, Koichiro; Yamada, Koji; Tanaka, Hirohisa; Taniguchi, Masatoshi; Oguro, Keisuke

    Electrochemical oxidation of hydrazine and its derivatives on the surface of various metal electrodes in alkaline media was investigated. A comparison of various polycrystalline metal electrodes (Ni, Co, Fe, Cu, Ag, Au, and Pt) showed that Co and Ni electrodes have a lower onset potential for hydrazine oxidation than the Pt electrode. The onset oxidation potential of APA (aminopolyacrylamide), a hydrazine derivative (-0.127 V vs. reversible hydrogen electrode, RHE), was similar to that of hydrazine hydrate (-0.178 V vs. RHE) in the case of the Co electrode. APA oxidation was possible because of hydrazine desorption that was caused by APA hydrolysis. The hydrolysis reaction was brought about by a heat treatment. This result suggests that the hydrazine hydrolysis reaction of hydrazine derivatives makes it possible to store hydrazine hydrate safely.

  10. Effect of oxidization and chitosan on the surface activity of soy protein isolate.

    PubMed

    Wang, Wei; Li, Junsheng; Yan, Liujuan; Huang, Guoxia; Dong, Zhen

    2016-10-20

    The objective of this research was to study the effect of oxidization of performic acid and chitosan on the structure and surface properties of soy protein isolate. As the degree of oxidization increased, the emulsifying capacity and stability of all the oxidized soy protein isolate and chitosan (SPI/CHI) systems increased substantially, which were 29.7%, 31.7%, 34.1%, 31.9% and 31.9% respectively compared. Fluorescent spectrum showed that the fluorescence intensity of SPI/CHI conjugates decreased and the higher the oxidized degree was, the lower the fluorescence intensity. Results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the location of acidic bands of SPI/CHI conjugates moved upwards and broadened. Meanwhile, the basic bands lightened or even disappeared gradually as the oxidization increased. Scanning electron microscope (SEM) showed that the particles became lager as the degree of oxidization increased. Better thermostability of the oxidized SPI/CHI systems was shown in the differential scanning calorimetry (DSC). PMID:27474616

  11. Metal/Oxide Interface Nanostructures Generated by Surface Segregation for Electrocatalysis.

    PubMed

    Weng, Zhe; Liu, Wen; Yin, Li-Chang; Fang, Ruopian; Li, Min; Altman, Eric I; Fan, Qi; Li, Feng; Cheng, Hui-Ming; Wang, Hailiang

    2015-11-11

    Strong metal/oxide interactions have been acknowledged to play prominent roles in chemical catalysis in the gas phase, but remain as an unexplored area in electrocatalysis in the liquid phase. Utilization of metal/oxide interface structures could generate high performance electrocatalysts for clean energy storage and conversion. However, building highly dispersed nanoscale metal/oxide interfaces on conductive scaffolds remains a significant challenge. Here, we report a novel strategy to create metal/oxide interface nanostructures by growing mixed metal oxide nanoparticles on carbon nanotubes (CNTs) and then selectively promoting migration of one of the metal ions to the surface of the oxide nanoparticles and simultaneous reduction to metal. Employing this strategy, we have synthesized Ni/CeO2 nanointerfaces coupled with CNTs. The Ni/CeO2 interface promotes hydrogen evolution catalysis by facilitating water dissociation and modifying the hydrogen binding energy. The Ni/CeO2-CNT hybrid material exhibits superior activity for hydrogen evolution as a result of synergistic effects including strong metal/oxide interactions, inorganic/carbon coupling, and particle size control. PMID:26509583

  12. Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

    PubMed Central

    Piccinin, Simone; Sartorel, Andrea; Aquilanti, Giuliana; Goldoni, Andrea; Bonchio, Marcella; Fabris, Stefano

    2013-01-01

    Solar-to-fuel energy conversion relies on the invention of efficient catalysts enabling water oxidation through low-energy pathways. Our aerobic life is based on this strategy, mastered by the natural Photosystem II enzyme, using a tetranuclear Mn–oxo complex as oxygen evolving center. Within artificial devices, water can be oxidized efficiently on tailored metal-oxide surfaces such as RuO2. The quest for catalyst optimization in vitro is plagued by the elusive description of the active sites on bulk oxides. Although molecular mimics of the natural catalyst have been proposed, they generally suffer from oxidative degradation under multiturnover regime. Here we investigate a nano-sized Ru4–polyoxometalate standing as an efficient artificial catalyst featuring a totally inorganic molecular structure with enhanced stability. Experimental and computational evidence reported herein indicates that this is a unique molecular species mimicking oxygenic RuO2 surfaces. Ru4–polyoxometalate bridges the gap between homogeneous and heterogeneous water oxidation catalysis, leading to a breakthrough system. Density functional theory calculations show that the catalytic efficiency stems from the optimal distribution of the free energy cost to form reaction intermediates, in analogy with metal-oxide catalysts, thus providing a unifying picture for the two realms of water oxidation catalysis. These correlations among the mechanism of reaction, thermodynamic efficiency, and local structure of the active sites provide the key guidelines for the rational design of superior molecular catalysts and composite materials designed with a bottom–up approach and atomic control. PMID:23479603

  13. One step growth of protein antifouling surfaces: monolayers of poly(ethylene oxide) (PEO) derivatives on oxidized and hydrogen-passivated silicon surfaces.

    PubMed

    Cecchet, Francesca; De Meersman, Benoît; Demoustier-Champagne, Sophie; Nysten, Bernard; Jonas, Alain M

    2006-01-31

    We compare two routes for creating protein adsorption-resistant self-assembled monolayers (SAMs) by chemical modification of silicon surfaces with poly(ethylene oxide) (PEO) oligomeric derivatives. The first route involves the assembly of 2-methyl[(polyethyleneoxy)propyl]trichlorosilane (Cl3SiMPEO) films onto oxidized silicon surfaces (OH-SiO(x)) either by a liquid-phase process at room temperature or by a gas-phase process at 423 K, producing Si-O-Si bonds between the substrate and the organic layer. The second pathway makes use of the assembly of poly(ethylene glycol methyl ether) (MPEG) films onto hydrogen-passivated silicon surfaces (H-Si) using a liquid-phase process at 353 or 423 K, leading to the formation of Si-O-C bonds between the substrate and the organic layer. Structural investigation by X-ray reflectometry (XRR) reveals that the thickness and surface densities of the grafted PEO monolayers strongly depend on experimental conditions such as temperature and grafting time. Atomic force microscopy (AFM) shows that very smooth and homogeneous monolayers can be obtained with average roughnesses close to those measured on the corresponding bare substrates. Finally, the antifouling properties of the modified silicon surfaces were evaluated by X-ray photoelectron spectroscopy (XPS), using a membrane protein (P.69 antigen) as model protein. Both types of PEO monolayers exhibit excellent protein repellency, as soon as the grafting density is equal to or higher than 1.7 chains/nm2. PMID:16430281

  14. Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

    PubMed Central

    Ramana, CV; Becker, U; Shutthanandan, V; Julien, CM

    2008-01-01

    Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant increase in

  15. Biomembrane phospholipid-oxide surface interactions: crystal chemical and thermodynamic basis.

    PubMed

    Sahai, Nita

    2002-08-15

    Quartz has the least favored surface among many oxides for bacterial attachment and for lipid bilayer or micelle interactions. Tetrahedrally coordinated crystalline silica polymorphs are membranolytic toward liposomes, lysosomes, erythrocytes, and macrophages. Amorphous silica, the octahedral silica polymorph, (stishovite), and oxides such as Al2O3, Fe2 O3, and TiO2 are less cytotoxic. Existing theories for membrane rupture that invoke interactions between oxide surfaces and cell membrane phospholipids (PLs) do not adequately explain these differences in membranolytic potential of the oxides. The author presents a crystal chemical, thermodynamic model for the initial interaction of oxide surfaces with the quaternary ammonium component of the PL's polar head group. The model includes solvation energy changes and electrostatic forces during adsorption, represented by the dielectric constant of the solid and the charge-to-radius ratio of the adsorbing solute. The nature of oxide-solute interactions compared with oxide-water, solute-water, and water-water interactions determines the membranolytic activity of the oxide, where the solute is TMA+, the quaternary ammonium moeity. Significant membrane rupture, as on quartz, requires unfavorable adsorption entropy (DeltaS(ads,TMA+)<0) to maximize disruption of normal membrane structure and requires favorable Gibbs free energy of exchange between TMA+ and the ambient Na+ ions (DeltaG(exc,TMA+/Na+) = DeltaG(ads,TMA+)-DeltaG(ads,Na+)<0) to maximize the extent of membrane affected. For amorphous silica, DeltaS(ads,TMA+) >0, so disruption of structure is limited, even though G(exc,TMA+/Na+) is <0. Stishovite and other oxides have DeltaS(ads,TMA+) <0, but now DeltaG(exc,TMA+/Na+) is>0 at the acidic to circumneutral pHs of cellular and subcellular organelle fluids. The model predicts the correct sequence of membranolytic ability: quartz > or = amorphous SiO2 >Al2O3 >Fe2O3 >TiO2. The model thus explains the relatively poor adhesion

  16. Metal-oxide-semiconductor field effect transistor humidity sensor using surface conductance

    NASA Astrophysics Data System (ADS)

    Song, Seok-Ho; Yang, Hyun-Ho; Han, Chang-Hoon; Ko, Seung-Deok; Lee, Seok-Hee; Yoon, Jun-Bo

    2012-03-01

    This letter presents a metal-oxide-semiconductor field effect transistor based humidity sensor which does not use any specific materials to sense the relative humidity. We simply make use of the low pressure chemical vapor deposited (LPCVD) silicon dioxide's surface conductance change. When the gate is biased and then floated, the electrical charge in the gate is dissipated through the LPCVD silicon dioxide's surface to the surrounding ground with a time constant depending on the surface conductance which, in turn, varies with humidity. With this method, extremely high sensitivity was achieved—the charge dissipation speed increased thousand times as the relative humidity increased.

  17. 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.

  18. 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→π* (Cdbnd O) and 1s→σ* (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.

  19. Natural and pyrogenic humic acids at goethite and natural oxide surfaces interacting with phosphate.

    PubMed

    Hiemstra, Tjisse; Mia, Shamim; Duhaut, Pierre-Benoît; Molleman, Bastiaan

    2013-08-20

    Fulvic and humic acids have a large variability in binding to metal (hydr) oxide surfaces and interact differently with oxyanions, as examined here experimentally. Pyrogenic humic acid has been included in our study since it will be released to the environment in the case of large-scale application of biochar, potentially creating Darks Earths or Terra Preta soils. A surface complexation approach has been developed that aims to describe the competitive behavior of natural organic matter (NOM) in soil as well as model systems. Modeling points unexpectedly to a strong change of the molecular conformation of humic acid (HA) with a predominant adsorption in the Stern layer domain at low NOM loading. In soil, mineral oxide surfaces remain efficiently loaded by mineral-protected organic carbon (OC), equivalent with a layer thickness of ≥ ~0.5 nm that represents at least 0.1-1.0% OC, while surface-associated OC may be even three times higher. In natural systems, surface complexation modeling should account for this pervasive NOM coverage. With our charge distribution model for NOM (NOM-CD), the pH-dependent oxyanion competition of the organo-mineral oxide fraction can be described. For pyrogenic HA, a more than 10-fold increase in dissolved phosphate is predicted at long-term applications of biochar or black carbon. PMID:23875678

  20. Exposure of the hydrophobic components of porcine lung surfactant to oxidant stress alters surface tension properties.

    PubMed Central

    Gilliard, N; Heldt, G P; Loredo, J; Gasser, H; Redl, H; Merritt, T A; Spragg, R G

    1994-01-01

    We have tested the hypothesis that oxidation of lung surfactant results in loss of surface tension lowering function. Porcine lung surfactant was exposed to conditions known to cause lipid peroxidation (0.2 mM FeCl2 + 0.1 mM H2O2 or 5 microM CuCl2). Lipid peroxidation was verified by detection of conjugated dienes, thiobarbituric acid reactive substances, fluorescent products, hydroxy alkenals, and loss of unsaturated fatty acids. Exposed samples had significantly diminished surface tension lowering ability in vitro as measured in a bubble surfactometer. Samples exposed to FeCl2 + H2O2 had significantly diminished surface tension lowering ability in vivo as indicated by their reduced ability to improve lung compliance of surfactant-deficient fetal rabbits. Oxidation of phospholipid mixtures with surface tension lowering activity and containing unsaturated acyl groups resulted in partial loss of activity as determined in vitro. These results suggest that the effect of oxidants on lung surfactant function is due, in part, to effects on the phospholipid components and that acute pulmonary inflammation accompanied by oxygen radical production may result in surfactant lipid peroxidation and loss of surface tension lowering function. PMID:8200999

  1. Associative oxygen species on the oxidized silver surface formed under O 2 microwave excitation

    NASA Astrophysics Data System (ADS)

    Boronin, A. I.; Koscheev, S. V.; Murzakhmetov, K. T.; Avdeev, V. I.; Zhidomirov, G. M.

    2000-09-01

    The experimental methods of X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS, respectively) and the quantum mechanical calculations are applied for analysis of oxygen states on the silver oxide surface. At low temperatures ( T<470 K), the silver surface is intensively oxidized by a microwave oxygen discharge to form cuprite Ag 2O. Two adsorbed oxygen species of the atomic (dissociative) and molecular (associative) nature can be adsorbed on the cuprite Ag 2O surface. A comparison of the UPS data and the DFT calculations of molecular models Ag 2-O 2 and Ag 2-O 3 shows that the formation of ozonide-like structures is preferable to that of peroxide species. Thermal stability and the reaction probability of the adsorbed states are investigated.

  2. Sputtered cadmium oxide as a surface pretreatment for graphite solid-lubricant films

    NASA Technical Reports Server (NTRS)

    Fusaro, Robert L.

    1987-01-01

    Sputtered films of cadmium oxide were applied to sand blasted AISI 440C HT stainless steel disks as a surface pretreatment for the application of rubbed graphite films. Mixtures of cadmium oxide and graphite were applied to the nonpretreated sandblasted metal and evaluated. The results were compared to graphite films applied to other commercially available surface pretreatments. It is found that sputtered CdO pretreated surfaces increase the endurance lives of the graphite films and decrease the counterface steady state wear rate of the pins almost an order of magnitude compared to commercially available pretreatments. The CdO additions in general improved the tribological properties of graphite. The greatest benefit occurred when it was applied to the substrate rather than mixing it with the graphite and that sputtered films of CdO perform much better than rubbed CdO films.

  3. Sputtered cadmium oxide as a surface pretreatment for graphite solid lubricant films

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1986-01-01

    Sputtered films of cadmium oxide were applied to sand blasted AISI 440C HT stainless steel disks as a surface pretreatment for the application of rubbed graphite films. Mixtures of cadmium oxide and graphite were applied to the nonpretreated sandblasted metal and evaluated. The results were compared to graphite films applied to other commercially available surface pretreatments. It is found that sputtered CdO pretreated surfaces increase the endurance lives of the graphite films and decrease the counterface steady state wear rate of the pins almost an order of magnitude compared to commercially available pretreatments. The CdO additions in general improved the tribological properties of graphite. The greatest benefit occurred when it was applied to the substrate rather than mixing it with the graphite and that sputtered films of CdO perform much better than rubbed CdO films.

  4. [Distribution and Diversity of Ammonium-oxidizing Archaea and Ammonium-oxidizing Bacteria in Surface Sediments of Oujiang River].

    PubMed

    Li, Hu; Huang, Fu-yi; Su, Jian-qiang; Hong, You-wei; Yu, Shen

    2015-12-01

    Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) play important roles in the biogeochemical nitrogen cycle. Rivers are important ecosystems containing a large number of functional microbes in nitrogen cycle. In this study, denaturing gradient gel electrophoresis (DGGE ) and real-time quantitative PCR (qPCR) technology were used to analyze the distribution and diversity of AOA and AOB in sediments from Oujiang. The results showed that the AOA community structure was similar among various sites, while the AOB community structure was significantly different, in which all detected AOB sequences were classified into Nitrosospira and Nitrosomonas, and 90% affiliated to Nitrosospira. The community composition of AOA was influenced by NH₄⁺ and TS, in addition, the AOB composition was affected by NH₄⁺, EC, pH, NO₃⁻, TC and TN. Total sulfur (TS) and electrical conductivity (EC) were the major factors influencing the diversity of AOA and AOB, respectively. AOA abundance was significantly higher than that of AOB. EC, NH₄⁺-N and NO₃⁻-N were the main environmental factors affecting the abundance of AOA and AOB. This study indicated that the community composition and diversity of AOA and AOB were significantly influenced by environmental factors, and AOA might be dominant drivers in the ammonia oxidation process in Oujiang surface sediment. PMID:27012006

  5. Surface infra-red emission during alkali-metal incorporation at an oxide surface [rapid communication

    NASA Astrophysics Data System (ADS)

    Hou, Y.-C.; Jenkins, S. J.; King, D. A.

    2004-02-01

    Thermal emission of infra-red radiation from excited vibrational states is a sensitive probe of surface lattice dynamics, allowing the effects of adsorbed species to be studied in unprecedented detail. Here we examine the incorporation of adsorbed K into a NiO surface by following the formation of K 2O 2 and KNiO 2 through the evolution of the phonon spectrum. The resolution attained in the emission experiment yields new insight into processes of interdiffusion and growth. We identify O atoms as the mobile species at annealing temperatures up to 300 K, with K/Ni interdiffusion occurring after annealing at 600 K.

  6. 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.

  7. 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.

  8. Reduction of nitric oxide with carbon monoxide on the Al-Mo(110) surface alloy

    NASA Astrophysics Data System (ADS)

    Grigorkina, G. S.; Tvauri, I. V.; Kaloeva, A. G.; Burdzieva, O. G.; Sekiba, D.; Ogura, S.; Fukutani, K.; Magkoev, T. T.

    2016-05-01

    Coadsorption and reaction of carbon monoxide (CO) and nitric oxide (NO) on Al-Mo(110) surface alloy have been studied by means of Auger electron, reflection-absorption infrared and temperature programmed desorption spectroscopies (AES, RAIRS, TPD), low energy electron diffraction (LEED) and work function measurements. The Al-Mo(110) surface alloy was obtained by thermal annealing at 800 K of aluminum film deposited on Mo(110) held at room temperature. Upon annealing Al penetrates the surface, most likely forming stoichiometric hexagonal surface monolayer of the compound Al2Mo. The NO and CO adsorb molecularly on this alloy surface at 200 K, unlike totally dissociative adsorption on bare Mo(110) and Al(111) film. Adsorption of CO on NO precovered Al-Mo(110) substrate dramatically affects the state of NO molecules, most probably displacing them to higher-coordinated sites with their simultaneous tilting to the surface plane. Heating to about room temperature (320 K) causes reduction of nitric oxide with carbon monoxide, yielding CO2, and substrate nitridation. This behavior can be associated with the surface reconstruction providing additional Al/Mo interface reaction sites and change of the d-band upon alloying.

  9. Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species

    NASA Astrophysics Data System (ADS)

    Frunza, Stefan; Frunza, Ligia; Ganea, Constantin Paul; Zgura, Irina; Brás, Ana Rita; Schönhals, Andreas

    2016-02-01

    Surface layers have already been observed by broadband dielectric spectroscopy for composite systems formed by adsorption of rod-like cyanophenyl derivates as probe molecules on the surface of oxide particles. In this work, features of the surface layer are reported; samples with different amounts of the probe molecules adsorbed onto oxide (nano) particles were prepared in order to study their interactions with the surface. Thermogravimetric analysis (TGA) was applied to analyze the amount of loaded probe molecules. The density of the surface species ns was introduced and its values were estimated from quantitative Fourier transform infrared spectroscopy (FTIR) coupled with TGA. This parameter allows discriminating the composites into several groups assuming a similar interaction of the probe molecules with the hosts of a given group. An influence factor H is further proposed as the ratio of the number of molecules in the surface layer showing a glassy dynamics and the number of molecules adsorbed tightly on the surface of the support: It was found for aerosil composites and used for calculating the maximum filling degree of partially filled silica MCM-41 composites showing only one dielectric process characteristic for glass-forming liquids and a bulk behavior for higher filling degrees.

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

    PubMed

    Karthikeyan; Elliott; Chorover

    1999-01-01

    Isotherms were developed at pH 6.9 for adsorption (ADS) and coprecipitation (CPT) of Cu by hydrous oxides of Fe (HFO) and Al (HAO) to study the role of sorbate/sorbent ratio in metal cation removal. For low sorbate/sorbent conditions, HFO had a higher Cu retention capacity than HAO regardless of contact methodology. For either oxide, CPT was consistently more effective than ADS in removing Cu from solution. At high sorbate/sorbent ratios, surface precipitation dominates and the oxide's net cation retention capacity depends on the nature and solubility of the precipitate formed at the oxide-water interface. X-ray diffraction patterns and isotherms of HAO for both ADS and CPT suggest formation of a solid solution [e.g., CuAl2O4(s)] with dramatically lower solubility than Cu(OH)2(s) precipitated in bulk solution. In contrast, Cu precipitated on the HFO surface exhibited a solubility comparable to the bulk precipitated Cu(OH)2(s). Therefore, at high sorbate/sorbent ratios, HAO has a higher Cu "apparent" sorption capacity than HFO. The relative utility of these oxides as metal scavengers thus depends markedly on sorbate/sorbent conditions. Copyright 1999 Academic Press. PMID:9878138

  11. Experimental evaluation of the effects of quench rate and quartz surface area on homogeneous mercury oxidation

    SciTech Connect

    Andrew Fry; Brydger Cauch; Geoffrey D. Silcox; JoAnn S. Lighty; Constance L. Senior

    2007-07-01

    This paper presents a mercury oxidation data set suitable for validation of fundamental kinetic models of mercury chemistry and for mechanism development. Experimental facilities include a mercury reactor fitted with a 300-W, quartz-glass burner and a quartz reaction chamber. While operated with a temperature profile representative of a typical boiler, a residence time of 6 s was achieved. Participating reacting species (chlorine, mercury) were introduced through the burner to produce a radical pool representative of real combustion systems. Speciated mercury measurements were performed using a Tekran 2537A Analyzer coupled with a conditioning system. Homogeneous mercury reactions involving chlorine have been investigated under two different temperature profiles producing quench rates of -210 K/s and -440 K/s. The larger quench rate produced 52% greater total oxidation than the lower quench at chlorine concentrations of 200 ppm. The effect of reactor surface area on oxidation was also investigated. The quartz surfaces interacted with mercury only in the presence of chlorine and their overall effect was to weakly inhibit oxidation. The extent of oxidation was predicted using a detailed kinetic model. The model predicted the effects of quench rate and chlorine concentration shown in experimentation. 12 refs., 5 figs., 3 tabs.

  12. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

    NASA Astrophysics Data System (ADS)

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; Del Río, J. Antonio; Tagüeña-Martínez, Julia

    2016-04-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications.

  13. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

    PubMed Central

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; del Río, J. Antonio; Tagüeña-Martínez, Julia

    2016-01-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

  14. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry.

    PubMed

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; Del Río, J Antonio; Tagüeña-Martínez, Julia

    2016-01-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

  15. Influence of substrate preparation on the shaping of the topography of the surface of nanoceramic oxide layers

    NASA Astrophysics Data System (ADS)

    Bara, Marek; Kubica, Marek

    2014-02-01

    The paper discusses the shaping mechanism and changes occurring in the structure and topography of the surface of nanoceramic oxide layers during their formation. The paper presents the influence of substrate preparation on the surface topography of oxide layers. The layers were produced via hard anodizing on the EN AW-5251 aluminum alloy. The layers obtained were subjected to microscope examinations, image and chemical composition analyses, and stereometric examinations. Heredity of substrate properties in the topography of the surface of nanoceramic oxide layers formed as a result of electrochemical oxidation has been shown.

  16. 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−ɛ model, RNG k−ɛ model, realizable k−ɛ 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

  17. Oxidative stress and antioxidants at biosurfaces: plants, skin, and respiratory tract surfaces.

    PubMed Central

    Cross, C E; van der Vliet, A; Louie, S; Thiele, J J; Halliwell, B

    1998-01-01

    Atmospheric pollutants represent an important source of oxidative and nitrosative stress to both terrestrial plants and to animals. The exposed biosurfaces of plants and animals are directly exposed to these pollutant stresses. Not surprisingly, living organisms have developed complex integrated extracellular and intracellular defense systems against stresses related to reactive oxygen and nitrogen species (ROS, RNS), including O3 and NO2. Plant and animal epithelial surfaces and respiratory tract surfaces contain antioxidants that would be expected to provide defense against environmental stress caused by ambient ROS and RNS, thus ameliorating their injurious effects on more delicate underlying cellular constituents. Parallelisms among these surfaces with regard to their antioxidant constituents and environmental oxidants are presented. The reactive substances at these biosurfaces not only represent an important protective system against oxidizing environments, but products of their reactions with ROS/RNS may also serve as biomarkers of environmental oxidative stress. Moreover, the r