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1

Image formation and contrast inversion in noncontact atomic force microscopy imaging of oxidized Cu(110) surfaces  

NASA Astrophysics Data System (ADS)

Joint experimental and theoretical investigation of image formation in noncontact atomic force microscopy (NC-AFM) of the c(6 × 2) and p(2 × 1) phases of the Cu(110):O surface is presented. We proposed previously that the c(6 × 2) reconstruction of the Cu(110):O surface may serve as a reference system allowing chemical identification of the tip apex atom during the course of NC-AFM experiments. The identification is possible due to the fact that two most likely possible contrasts that could be observed after intermittent contacts of the tip with the surface were found which can be attributed to the tip being either terminated by Cu or O atoms. In this paper the idea of exploiting the Cu(110):O surface in NC-AFM studies is further developed. Specifically, (i) we show that there must be an image contrast inversion when the c(6 × 2) surface reconstruction is scanned depending on the tip-surface distance: at the usual imaging conditions, at tip-sample distances of 2-5 Å, the previously reported contrast is observed; however, an opposite contrast is observed for larger separations with one of the two tip terminations. (ii) We study in detail also the image contrast formation of the p (2×1) surface, which is another common surface reconstruction, and show that tip identification for it is not possible. (iii) Finally, we discuss here possible effects of the actual tip atomic structure on the NC-AFM image. In particular, we show that the O-terminated tip will remain such even after picking up a Cu atom from the surface, experimentally a frequently observed process. Hence this type of the tip modification would only affect secondary features in the image.

Bamidele, J.; Kinoshita, Y.; Turanský, R.; Lee, S. H.; Naitoh, Y.; Li, Y. J.; Sugawara, Y.; Štich, I.; Kantorovich, L.

2014-07-01

2

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

SciTech Connect

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.

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

2013-04-18

3

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

PubMed

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

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

2014-12-01

4

Localized reaction at a smooth metal surface: p-diiodobenzene at Cu(110).  

PubMed

Halogenation at a semiconductor surface follows simple dynamics characterized by "localized reaction" along the direction of the halide bond being broken. Here we extend the study of halide reaction dynamics to the important environment of a smooth metal surface, where greater product mobility would be expected. Extensive examination of the physisorbed reagent and chemisorbed products from two successive electron-induced reactions showed, surprisingly, that for this system product localization and directionality described the dynamics at a metal. The reagent was p-diiodobenzene on Cu(110) at 4.6 K. The first C-I bond-breaking yielded chemisorbed iodophenyl and I-atom(#1), and the second yielded phenylene and I-atom(#2). The observed collinear reaction resulted in secondary encounters among products, which revealed the existence of a surface-aligned reaction. The molecular dynamics were well explained by a model embodying a transition between an a priori ground state and a semiempirical ionic state, which can be generally applied to electron-induced chemical reactions at surfaces. PMID:22563977

Leung, Lydie; Lim, Tingbin; Ning, Zhanyu; Polanyi, John C

2012-06-01

5

Non-isotropic surface diffusion of lead on Cu(110): a molecular dynamics study  

NASA Astrophysics Data System (ADS)

By using numerical simulation we have studied the diffusion of isolated lead atoms on Cu(110). The calculations rely on a phenomenological many-body potential derived in the framework of the second-moment approximation of the tight-binding method, with parameters fitted on the physical properties of the bulk crystals of copper and lead and to the copper-lead phase diagram. Static calculations, at T=0 K, provide the energy and relaxed atomic positions of the equilibrium and saddle-point configurations of various possible diffusion mechanisms. In spite of the large miscibility gap present in the lead-copper phase diagram, we find that insertion of a lead adatom into the uppermost copper surface layer is a thermodynamically favoured process. Molecular dynamics calculations show that inserted lead atoms diffuse via an exchange mechanism with copper adatoms and via jumps in adatom position along the open [1¯10] direction. These results confirm previously published experimental observations. They also confirm the validity of a statistical model that was developed to account for these observations. The quantity governing the variation of diffusion anisotropy with temperature is the difference Er- Ej between the activation energies for the insertion of a lead atom in the copper plane and for its jumps in adatom position. The value of this difference, as determined in the static simulations, compares very well with what can be deduced from experimental observations. The agreement is also very good concerning the value of the main diffusion barrier, which is the energy associated with the de-insertion of a lead atom. Simulations performed in the temperature range 400-700 K show that multiple jumps occur frequently. Their frequency increases with temperature, thus leading to lead diffusion that is more anisotropic and more steeply dependent on temperature than could be expected from the static calculations.

Prévot, G.; Cohen, C.; Schmaus, D.; Pontikis, V.

2000-07-01

6

Adsorption geometry of 4-picoline chemisorbed on the Cu(110) surface: a study of forces controlling molecular self-assembly.  

PubMed

The adsorption of 4-picoline (4-methylpyridine) on the Cu(110) surface has been studied with time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD) and other methods. Using deuterium labeling in the methyl group and hydrogen labeling on the aromatic ring, it has been possible to separately monitor by TOF-ESDIAD the C-D bond directions and the C-H bond directions in the adsorbed molecule. These triangulation measurements have led to a detailed understanding of the conformation of the adsorbed molecule relative to the Cu(110) crystal lattice, allowing one to witness changes in the molecular conformation as adsorbate-adsorbate interactional effects take place for increasing coverages. At low coverages, the molecule adsorbs by the N atom at an atop Cu site with the aromatic ring parallel to the <001> azimuth and with the molecular axis inclined 33 (+/- 5) degrees along the <001> azimuth. As rows of 4-picoline molecules form long range ordered chain structures oriented along the <112> azimuth, the aromatic ring twists 29 degrees about the inclined molecular axis as a result of forces between the adsorbate molecules. The initial tilting of the molecular axis at low coverage is likely due to the interaction of the positive-outward dipole with its image in the substrate. The ring twist may result from dipoleminus signdipole forces between the adsorbate molecules in the rows formed tending to form nested parallel pyridine rings. These studies are the first to apply the TOF-ESDIAD method for the measurement of the direction of chemical bonds at more than one molecular location within an adsorbed molecule and the new method is named electron stimulated desorption-molecular triangulation (ESD-MT). The results obtained give information of importance in understanding the factors which control conformational effects during the molecular self-assembly of complex adsorbed molecules on surfaces. PMID:11890829

Lee, J-G; Ahner, J; Yates, J T

2002-03-20

7

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)

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< ?Zn<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.

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

1998-03-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

9

Bonding and ordering of decacyclene molecules on Cu(110) studied by scanning tunneling microscopy  

NASA Astrophysics Data System (ADS)

We have studied the adsorption of decacyclene (DC) molecules on a Cu(110) surface. The results are compared to previous studies of hexa-tert-butyl decacyclene (HtBDC) also on Cu(110). Opposite to HtBDC, the DC molecules do not induce any restructuring of the Cu(110) surface and no ordered structures are observed at low coverages. This difference is discussed in terms of molecule-substrate and molecule-molecule interactions. Close to full monolayer coverage, DC molecules are forced into ordered arrangements. The ordered structures with different molecule density are described in a model.

Schunack, M.; Laegsgaard, E.; Stensgaard, I.; Besenbacher, F.

2002-11-01

10

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

SciTech Connect

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.

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

2013-10-31

11

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

PubMed

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

Sacchi, Marco; Jenkins, Stephen J

2014-04-01

12

Reflectance difference spectroscopy of water on Cu(110)  

NASA Astrophysics Data System (ADS)

The adsorption of H2O on Cu(110) was probed by means of reflectance difference spectroscopy (RDS) in the energy range between 1.5 and 9.3 eV and by scanning tunneling microscopy (STM). The adsorption of water on the pristine Cu(110) substrate mainly induces changes in the Cu surface state related optical transitions. Furthermore, the H2O adsorbate modifies the Cu bulk transitions. In particular, our investigations demonstrate that the coverage-dependent phase transition from 1D pentamer chains to a (7 × 8) superstructure can be monitored by means of RDS. In the vacuum-UV range, new RD features assigned to Cu bulk transitions were detected. Adsorption on the metal surface strongly modifies or quenches the H2O HOMO-LUMO transition, whereby a distinct RD feature of the water molecules themselves in the vacuum-UV range is absent.

Denk, M.; Hohage, M.; Sun, L. D.; Zeppenfeld, P.; Esser, N.; Cobet, C.

2014-09-01

13

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

SciTech Connect

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

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

2014-06-07

14

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

15

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

SciTech Connect

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.

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

2008-07-15

16

Identification of active oxygen on Cu 110 using low temperature scanning tunneling microscopy  

NASA Astrophysics Data System (ADS)

Using a low temperature scanning tunneling microscope (STM) we have imaged isolated oxygen-related features on the unreconstructed surface between (2 × 1)-O regions on Cu{110}. On the assumption that these are individual oxygen atoms, they appear to occupy mostly hollow sites in the troughs. We suggest that such adatoms constitute an active form of oxygen known to participate readily in deprotonation reactions on copper surfaces.

Buisset, J.; Rust, H.-P.; Schweizer, E. K.; Cramer, L.; Bradshaw, A. M.

1996-04-01

17

The bonding of simple carboxylic acids on Cu(110)  

NASA Astrophysics Data System (ADS)

We present a study of the bonding of formate (HCOO) and acetate (CH3COO) chemisorbed on Cu(110) using core level spectroscopies in combination with theoretical calculations. For the first time, we apply x-ray emission spectroscopy (XES) to these systems. When XES is used in conjunction with x-ray absorption spectroscopy (XAS) and ab initio calculations, new information about the electronic interaction in the adsorbate-substrate system is provided. In particular, we have used the azimuthal orientation of the COO-surface bond on the (110) surface, to make a complete partition into x, y, and z orbital contributions. The surface bond is found to be predominantly ionic. For the case of adsorbed formate, the covalent bonding is dominated by 6a1/7a1, (?)-type, frontier orbitals, interacting with the Cu valence band. The resulting hybrid orbitals form a distribution of states that cross the Fermi level. The contribution from adsorbate ?-type orbitals is small. The chemical bond formation of adsorbed acetate is very similar to that of formate. In addition, states with metal character have been identified for the outermost CH3-group of acetate. These are delocalized states of mainly local ?-character. The spectral features due to states of local ?-character in the adsorbed acetate are well described within the framework of hyperconjugation.

Karis, O.; Hasselström, J.; Wassdahl, N.; Weinelt, M.; Nilsson, A.; Nyberg, M.; Pettersson, L. G. M.; Stöhr, J.; Samant, M. G.

2000-05-01

18

Stranski-Krastanov growth of para-sexiphenyl on Cu(110)-(2×1)O revealed by optical spectroscopy.  

PubMed

We have studied the growth of para-sexiphenyl (p-6P) on the Cu(110)-(2×1)O surface using reflectance difference spectroscopy (RDS) in combination with scanning tunneling microscopy (STM). The evolution of the optical anisotropy reveals that the growth of p-6P on the Cu(110)-(2×1)O surface at room temperature follows the Stranski-Krastanov growth mode with a two monolayer thick wetting layer. During all stages of growth, the p-6P molecules are well orientated with their long molecular axis aligned parallel to the Cu-O rows along the [001] direction of the Cu(110) substrate. The high packing density of the p-6P molecules in the first and second monolayer evidenced by RDS and STM is believed to be responsible for the switch from layer-by-layer to three-dimensional island growth. PMID:20941450

Sun, Lidong; Weidlinger, Günther; Denk, Mariella; Denk, Richard; Hohage, Michael; Zeppenfeld, Peter

2010-11-28

19

Elementary Process for CVD Graphene on Cu(110): Size-selective Carbon Clusters  

NASA Astrophysics Data System (ADS)

Revealing the graphene growth mechanism at the atomic-scale is of great importance for achieving high quality graphene. However, the lack of direct experimental observation and density functional theory (DFT) verification hinders a comprehensive understanding of the structure of the carbon clusters and evolution of the graphene growth on surface. Here, we report an in-situ low-temperature scanning tunneling microscopy (LT-STM) study of the elementary process of chemical vapor deposition (CVD) graphene growth via thermal decomposition of methane on Cu(110), including the formation of monodispersed carbon clusters at the initial stage, the graphene nucleation and the ripening of graphene islands to form continuous graphene film. STM measurement, supported by DFT calculations, suggests that the carbon clusters on the surface are C2H5. It is found that graphene layers can be joined by different domains, with a relative misorientation of 30°. These graphene layers can be decoupled from Cu(110) through low temperature thermal cycling.

Zhang, Jialin; Wang, Zhunzhun; Niu, Tianchao; Wang, Shengnan; Li, Zhenyu; Chen, Wei

2014-03-01

20

Adsorbate site determination with the scanning tunneling microscope: C2H4 on Cu\\{110\\}  

NASA Astrophysics Data System (ADS)

Scanning tunneling microscopy at T=4 K has been used to determine directly the binding site of a molecule chemisorbed on a metal surface, namely, ethene on Cu<110>, by simultaneous imaging of the adsorbate and the underlying lattice. The molecule is found to bond in the short bridge site on the close-packed rows with its C-C axis oriented in the <110> direction.

Buisset, J.; Rust, H.-P.; Schweizer, E. K.; Cramer, L.; Bradshaw, A. M.

1996-10-01

21

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

SciTech Connect

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

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

1990-01-01

22

Oxide surfaces.  

PubMed

Although the history of metal oxides and their surfaces goes back several decades to landmark studies, such as Mott and Peierls' explanation of electrical insulation in materials that are predicted in band theory to be conducting, or the observation by Morin of the superfast metal-to-insulator transition in vanadium dioxide, it is only in the last two decades that the world of condensed matter physics has become increasingly dominated by research into complex metal oxides. This has been driven most notably by an attempt to better understand and describe the fundamental physical processes behind their seemingly endless spectrum of properties, which in turn has also led to the discovery of novel phenomena, most prominently demonstrated by the discovery of high-temperature superconductivity in 1986, colossal magnetoresistance in 1994, and most recently, the formation of a two-dimensional conducting layer at the interface between two band insulators in 2004. One important reason why metal oxides, particularly in the form of thin films, have become such a popular subject for basic condensed matter research is that they offer a uniquely versatile materials base for the development of novel technologies. They owe this versatility both to the many different elemental combinations that lead to structurally similar forms, and also to the fact that in many cases, the strong interaction between the valence electrons means that there is a subtle interplay between structure and magnetic and electronic properties. This aspect has led in recent years to the birth or renaissance of research fields such as spintronics, orbital ordering, and multiferroics. Surfaces and interfaces are especially interesting in these strongly-correlated electron systems, where the rearrangement of electrical charge resulting from a minimization of surface or interfacial energy can have unexpected and often exciting consequences. Indeed, as the drive to miniaturize devices well below the micron size continues, the fraction of material constituting `non-bulklike' properties is becoming increasingly significant. On the other hand, the degree of sophistication needed to understand and predict these complex systems has driven a complementary thrust in theoretical modelling, beginning as long ago as 1963, with Hubbard's addition to the tight-binding model of the formulation of conduction in terms of a hopping integral. The present level of understanding is now so advanced that theory and experiment are no longer so distinct, both gaining further insights from one another. The aim of this special issue in the Journal of Physics: Condensed Matter is to convey to the reader the most up-to-date understanding of the physics of the surfaces, interfaces, and thin films of complex metal oxides, in a clear and accessible manner. The order of the 16 contributions reflects the broad range of disciplines within this field, beginning with general considerations and theoretical models, continuing with film growth techniques and characterization, and concluding with material types and devices. It is fairly safe to assume that research in this area will enjoy as illustrious and long-lived a future as it has had a past. As such, it is hoped that this contribution will accurately reflect this status in the first decade of the 21st Century and long provide a reference for physicists continuing on this exciting Odyssey. PMID:21694334

Willmott, Phil

2008-07-01

23

Elementary Process for CVD Graphene on Cu(110): Size-selective Carbon Clusters  

PubMed Central

Revealing the graphene growth mechanism at the atomic-scale is of great importance for achieving high quality graphene. However, the lack of direct experimental observation and density functional theory (DFT) verification hinders a comprehensive understanding of the structure of the carbon clusters and evolution of the graphene growth on surface. Here, we report an in-situ low-temperature scanning tunneling microscopy (LT-STM) study of the elementary process of chemical vapor deposition (CVD) graphene growth via thermal decomposition of methane on Cu(110), including the formation of monodispersed carbon clusters at the initial stage, the graphene nucleation and the ripening of graphene islands to form continuous graphene film. STM measurement, supported by DFT calculations, suggests that the carbon clusters on the surface are C2H5. It is found that graphene layers can be joined by different domains, with a relative misorientation of 30°. These graphene layers can be decoupled from Cu(110) through low temperature thermal cycling. PMID:24651211

Zhang, Jialin; Wang, Zhunzhun; Niu, Tianchao; Wang, Shengnan; Li, Zhenyu; Chen, Wei

2014-01-01

24

The electronic structure and adsorption geometry of L-histidine on Cu(110).  

PubMed

The adsorption of L-histidine on clean and oxygen-covered Cu(110) surfaces has been studied by soft X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The valence band spectra, carbon, nitrogen and oxygen 1 s XPS and N K edge absorption spectra were measured for submonolayer, monolayer, and multilayer films. The spectra provide a detailed picture of the electronic structure and adsorption geometry at each coverage. In the monolayer, the histidine molecules are randomly oriented, in contrast to the submonolayer regime, where the molecules are coordinated to the copper surface with the imidazole functional group nearly parallel to, and strongly interacting with, the surface. The pi*/sigma* intensity ratio in NEXAFS spectra at the nitrogen edge varies strongly with angle, showing the imidazole ring is oriented. Adsorption models are proposed. PMID:18834171

Feyer, Vitaliy; Plekan, Oksana; Skála, Tomás; Cháb, Vladimír; Matolín, Vladimír; Prince, Kevin C

2008-10-30

25

Orientation and bonding of benzoic acid, phthalic anhydride and pyromellitic dianhydride on Cu(110)  

NASA Astrophysics Data System (ADS)

The interaction of the polyimide precursor pyromellitic dianhydride (PMDA), and the related compounds benzoic acid and phthalic anhydride, with Cu(110) has been studied by high resolution electron energy loss spectroscopy (HREELS). For benzoic acid, deprotonation of the carboxylic acid group occurs on adsorption leading to the formation of a surface benzoate species (C 6H 5COO-). Bonding to the surface occurs through a carboxylate linkage via two equivalent oxygen atoms. The HREEL spectrum is characterised by an intense dipole active band, the symmetric O?C?O stretching vibration, at ˜ 1420 cm -1. The plane of the carboxylate group is aligned perpendicular to the surface as is the plane of the benzene ring. A similar species is found following exposure of Cu(110) to phthalic anhydride. The carboxylate linkage results from disruption of the anhydride ring with loss of the C?O character (C 6H 4COO-). In the case of the dianhydride species PMDA, only one of the anhydride units is used in bonding to the surface; the second unit points away from the surface and is characterised by the symmetric anhydride stretch at 1255 cm -1 and weak OO stretching vibrations at ˜ 1850 cm -1. In both cases, changes in the intensity of some of the bands compared with benzoic acid suggest that the carboxylate group is tilted away from the surface normal due to an interaction between one of the carbons of the aromatic ring and the copper surface. This implies that the plane of the aromatic ring is now twisted out of the plane of the carboxylate group and, although still perpendicular to the surface, the axis is tilted to allow one of the ?-carbon atoms to interact with the surface. In all cases, off-specular measurements at a primary electron energy of ˜ 8 eV are dominated by the intense C?H stretching vibration. Measurements of the intensity of this mode, in the surface benzoate species, as a function of incident electron energy suggest that excitation of this mode occurs via a resonance scattering mechanism.

Frederick, B. G.; Ashton, M. R.; Richardson, N. V.; Jones, T. S.

1993-07-01

26

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

NASA Astrophysics Data System (ADS)

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 ~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 ~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.

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

2001-01-01

27

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

SciTech Connect

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.

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

2001-01-01

28

Oxide surface science.  

PubMed

Most metals are oxidized under ambient conditions, and metal oxides show interesting and technologically promising properties. This has motivated much recent research on oxide surfaces. The combination of scanning tunneling microscopy with first-principles density functional theory-based computational techniques provides an atomic-scale view of the properties of metal-oxide materials. Surface polarity is a key concept for predicting the stability of oxide surfaces and is discussed using ZnO as an example. This review also highlights the role of surface defects for surface reactivity, and their interplay with defects in the bulk, for the case of TiO(2). Ultrathin metal-oxide films, grown either through reactive evaporation on metal single crystals or through oxidation of metal alloys (such as Al(2)O(3)/NiAl), have gained popularity as supports for planar model catalysts. The surface oxides that form upon oxidation on Pt-group metals (e.g., Ru, Rh, Pd, and Pt) are considered as model systems for CO oxidation. PMID:20055675

Diebold, Ulrike; Li, Shao-Chun; Schmid, Michael

2010-01-01

29

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

30

Edge-on bonding of benzene molecules in the second adsorbed layer on Cu(110).  

PubMed

The bilayer of benzene on Cu(110) was studied with temperature-programmed desorption (TPD), time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD), and scanning tunneling microscopy (STM). TPD spectra show that three well-defined adsorption states exist. The alpha layer corresponds to the first layer containing flat-lying benzene molecules. As coverage increases, the beta layer forms on top of the alpha layer, and eventually, a multilayer, gamma, forms. TPD measurements show that the number of benzene molecules in the beta layer is equal to the number of benzene molecules in the alpha layer. ESDIAD measurements establish that the orientation of the benzene molecules in the beta layer is edge-on, with two C-H bonds directed toward the surface. STM images of the beta layer reveal closely spaced edge-on benzene molecules arranged in repeating hexagons, as well as loosely spaced benzene molecules with greater apparent height, which are also edge-on species. Correlation between the different measurements suggests a structural model for the benzene bilayer. PMID:16898704

Lee, Junseok; Dougherty, Daniel B; Yates, John T

2006-08-17

31

Thermal excitation of rotation of the methyl group in chemisorbed acetate on Cu(110)  

SciTech Connect

The adsorption of acetic acid on the Cu(110) surface has been investigated by the time-of-flight electron stimulated desorption ion angular distribution technique by observing H{sup +}(D{sup +}) ions from the methyl groups. The activated conversion of acetic acid to acetate has been witnessed by observing the formation of oriented acetate species. It has been found that the activation energy for acetate formation varies from 0.39{+-}0.06 eV at low coverage to 1.1{+-}0.1 eV at high coverage, possibly because of acetic acid stabilization at high coverage by hydrogen bonding. Methyl groups are oriented with one C-H bond azimuthally directed in the <11(bar sign)0> direction. At high coverage, the methyl groups are tilted slightly in the <11(bar sign)0> direction due to repulsive acetate-acetate interactions. The activated rotation of the methyl groups on adsorbed acetate is clearly observed by the electron stimulated desorption ion angular distribution method and the barrier height for CH{sub 3} rotation is estimated to be 12{+-}6 meV, and for CD{sub 3} groups to be 7{+-}4 meV. The small inverse D isotope effect is postulated to be caused by higher amplitude CH{sub 3} wagging motions compared to CD{sub 3}, which permit slightly higher hyperconjugation for CH{sub 3} as this group interacts with the anchoring carboxyl group. (c) 2000 American Institute of Physics.

Lee, J.-G. [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Ahner, J. [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Mocuta, D. [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Denev, S. [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Yates, J. T. Jr. [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)

2000-02-15

32

Thermal excitation of rotation of the methyl group in chemisorbed acetate on Cu(110)  

NASA Astrophysics Data System (ADS)

The adsorption of acetic acid on the Cu(110) surface has been investigated by the time-of-flight electron stimulated desorption ion angular distribution technique by observing H+(D+) ions from the methyl groups. The activated conversion of acetic acid to acetate has been witnessed by observing the formation of oriented acetate species. It has been found that the activation energy for acetate formation varies from 0.39±0.06 eV at low coverage to 1.1±0.1 eV at high coverage, possibly because of acetic acid stabilization at high coverage by hydrogen bonding. Methyl groups are oriented with one C-H bond azimuthally directed in the <11¯0> direction. At high coverage, the methyl groups are tilted slightly in the <11¯0> direction due to repulsive acetate-acetate interactions. The activated rotation of the methyl groups on adsorbed acetate is clearly observed by the electron stimulated desorption ion angular distribution method and the barrier height for CH3 rotation is estimated to be 12±6 meV, and for CD3 groups to be 7±4 meV. The small inverse D isotope effect is postulated to be caused by higher amplitude CH3 wagging motions compared to CD3, which permit slightly higher hyperconjugation for CH3 as this group interacts with the anchoring carboxyl group.

Lee, J.-G.; Ahner, J.; Mocuta, D.; Denev, S.; Yates, J. T.

2000-02-01

33

Dynamics of quantum tunneling: Effects on the rate and transition path of OH on Cu(110)  

NASA Astrophysics Data System (ADS)

Recent low-temperature scanning-tunneling microscopy experiments [T. Kumagai , Phys. Rev. B 79, 035423 (2009)] observed the possible quantum tunneling of hydroxyl groups between two equivalent adsorption configurations on Cu(110). Here we analyze the quantum nuclear tunneling dynamics of hydroxyl on Cu(110) using density-functional theory based techniques. We calculate classical, semiclassical, and quantum-mechanical transition rates for the flipping of OH between two degenerate energy minima. The classical transition rate is essentially zero at the temperatures used in experiment and the tunneling rate along the minimum-energy path is also much too low compared to experimental observations. When tunneling is taken into account along a direct path connecting the initial and final states with only a minimum amount of the oxygen movement the transition rate obtained is in much better agreement with experiment, suggesting quantum tunneling effects cause a deviation of the reaction coordinate from the classical transition path.

Davidson, Erlend R. M.; Alavi, Ali; Michaelides, Angelos

2010-04-01

34

Mode-selective electron-phonon coupling in laser photoemission on Cu(110)  

NASA Astrophysics Data System (ADS)

By combining density functional perturbation theory (DFPT) calculations and laser photoemission spectroscopy (LPES) experiments, we have clarified the selective coupling between low-energy photoelectrons and subsurface phonon modes. A step structure resulting from the inelastic scattering of photoelectrons appeared at 14.7 meV below the Fermi level in the LPES of Cu(110). We found that the inelastic step originates from an indirect excitation in which the electron is excited by the low-energy photon near the Y¯ point and then scattered to the ?¯ point by phonon modes that are predominantly present in the subsurface region.

Minamitani, Emi; Arafune, Ryuichi; Yamamoto, Mayuko Q.; Takagi, Noriaki; Kawai, Maki; Kim, Yousoo

2013-12-01

35

The dynamics of quantum tunneling: effects on the rate and transition path of OH on Cu(110)  

NASA Astrophysics Data System (ADS)

The quantum tunneling of hydrogen is important to many scientific disciplines. Through well-defined experiments at surfaces with for example scanning-tunneling microscopy (STM) it is possible to understand the fundamental mechanisms involved at the atomic level. Recent STM experiments have identified OH on Cu(110) as an interesting model system in which the low temperature dynamics is entirely dominated by proton tunneling. Here we report the results from our analysis of the quantum nuclear tunneling dynamics of this system using density functional theory based techniques. We present computed classical, semi-classical and quantum mechanical transition rates for the flipping of OH between two degenerate energy minima. The classical transition rate is essentially zero at the temperatures used in experiment, and the tunneling rate along the minimum energy path is also much too low compared to experimental observations. However when tunneling is taken into account along a direct path connecting the initial and final states with only a small amount of the oxygen movement the transition rate obtained is in much better agreement with experiment, suggesting quantum tunneling effects cause a deviation of the reaction coordinate from the classical transition path.

Davidson, Erlend; Alavi, Ali; Michaelides, Angelos

2010-03-01

36

Diffraction of helium from Cu(110), (113), (115) and (117); Interaction potential and surface crystallography  

NASA Astrophysics Data System (ADS)

We present data obtained by helium scattering on different faces of copper: (110), (113), (115) and (117). It is shown that they are well fitted by model potentials, a corrugated Morse (CMP) for all faces and a modified form (MCMP) for the low corrugated (110) and (113) faces. Then, the isopotentials Z E( R) , representing the effective corrugation for an incident helium atom of energy E are compared to those resulting from a method of superposition of atomic densities calculated in two different ways. So, starting from the tables of atomic wave functions given by Clementi and Roetti, a good agreement is obtained with experiment, provided that the proportionality constant between the potential and the electronic density is taken to be ? = 600 eV03.

Gorse, D.; Salanon, B.; Fabre, F.; Kara, A.; Perreau, J.; Armand, G.; Lapujoulade, J.

1984-11-01

37

Effect of Surface Oxide Transformation on CO Oxidation  

NASA Astrophysics Data System (ADS)

Under sub-atmospheric conditions, many metal catalyst surfaces for CO oxidation transform to the oxide phase with higher catalytic activity than chemisorbed oxygen. The surface phase transformation from metal to its oxide could be by collective oxidation of the adsorbed oxygen sites as soon as their coverage reaches a global critical threshold, or such oxidation may be restricted to small patches of the surface, which is driven by the local coverage. In this communication, we investigate the effect of the latter on the phase diagram and the CO2 production rate behavior using a kinetic Monte Carlo surface reaction lattice gas model for CO oxidation.

Sinha, I.; Mukherjee, A. K.

2015-02-01

38

Surface-step-induced oscillatory oxide growth.  

PubMed

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. PMID:25302908

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

2014-09-26

39

LETTER TO THE EDITOR Surface Precipitation Reactions on Oxide Surfaces  

E-print Network

LETTER TO THE EDITOR Surface Precipitation Reactions on Oxide Surfaces Retention of heavy metal such processes. However, various mechanisms have been proposed for the sorption of cationic heavy metals on oxide of hydrolyzable metal ions on oxide surfaces. ©1992 Academic Press, Inc. The mechanisms of metal ion retention

Sparks, Donald L.

40

Oxide dispersed copper alloys by surface oxidation  

Microsoft Academic Search

A series of Cu-Al and Cu-Ni-Al alloys, inert gas atomized, as -44 ? powders, were converted to submicron thick flakes covered\\u000a by copper oxide and aluminum oxide in varying amounts, depending on the initial aluminum content. The flake powders were either\\u000a hydrogen reduced to eliminate copper oxide, or were reacted in a hot inert gas to increase the Al2O3 content

William F. Schilling; Nicholas J. Grant

1970-01-01

41

Oxide dispersed copper alloys by surface oxidation  

Microsoft Academic Search

A series of Cu-Al and Cu-Ni-Al alloys, inert gas atomized, as -44 mu powders, were converted to submicron thick flakes covered by copper oxide and aluminum oxide in varying amounts, depending on the initial aluminum content. The flake powders were either hydrogen reduced to eliminate copper oxide, or were reacted in a hot inert gas to increase the Al2O3 content

William F. Schilling; Nicholas J. Grant

1970-01-01

42

Surface-oxidized carbon fibers: I. Surface structure and chemistry  

Microsoft Academic Search

The surface structure and chemistry of various surface oxidized HT carbon fibers, an IM and a HM carbon fiber were studied by SEM, STM, CAM (contact angle measurement), XPS and TPD with special reference to adsorbed oxidation products and adsorbed water. It is shown that a real image of surface structure and surface chemistry is only obtained after removal of

U. Zielke; K. J. Hüttinger; W. P. Hoffman

1996-01-01

43

Wettability of transition metal oxide surfaces  

Microsoft Academic Search

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

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

1998-01-01

44

Ultrasonically enhanced persulfate oxidation of polyethylene surfaces  

Microsoft Academic Search

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

Fiona Keen

1996-01-01

45

Surface Precipitation of Hydrolyzable Metal Ions on Oxide Surfaces  

E-print Network

Surface Precipitation of Hydrolyzable Metal Ions on Oxide Surfaces S. E. Fendorf Heavy metalO2 and TiO2 near and beyond monolayer coverage. Surface precipitation of Al(III) and La(III) was observed on MnO2, but was not apparent on TiO2 nor in bulk solution. Al(III) formed a surface precipitate

Sparks, Donald L.

46

Thermal chemistry of copper(I)-N,N 0 -di-sec-butylacetamidinate on Cu(110)  

E-print Network

92521 Roy G. Gordon Department of Chemistry and Chemical Biology, Harvard University, Cambridge solid films of metals, oxides, nitrides, and other materials is an essential step in the manufacturing of appropriate precursors for CVD processes.5 A large number of metallo-organic compounds have been tested

47

Platinum attachments on iron oxide nanoparticle surfaces  

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

48

Platinum Attachments on Iron Oxide Nanoparticle Surfaces  

SciTech Connect

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.

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

2010-04-30

49

Platinum attachments on iron oxide nanoparticle surfaces  

Microsoft Academic Search

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

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

2010-01-01

50

Surface Wrinkling on Polydimethylsiloxane Microspheres via Wet Surface Chemical Oxidation  

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

51

Surface wrinkling on polydimethylsiloxane microspheres via wet surface chemical oxidation.  

PubMed

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

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

2014-01-01

52

ESCA study of oxidized wood surfaces  

SciTech Connect

Results of a preliminary study of the surface of wood exposed to outdoor weathering as well as to UV irradiation showed that ESCA provides valuable information and insight into the manifestation of weathering and photooxidation. From the ESCA spectra, the increase in signal intensities of carbon-oxygen bonds and oxygen-carbon-oxygen bonds (or unsaturated carbon oxygen bond) and oxygen-to-carbon ratio, and the decrease in carbon-carbon and carbon-hydrogen bonds of weathered and UV-irradiated wood surfaces suggested that wood surface was oxidized. Nevertheless, it was a superficial effect. Only a slow oxidation was observed at 100 ..mu..m under the exposed wood surfaces. From the oxygen-to-carbon ratio data, it revealed that weathered wood surface was rich in cellulose, poor in lignin. The leached-away degradation products from weathered wood surface accounted for the discrepancy between the ESCA line shapes of UV-irradiated and weathered wood surfaces.

Hon, D.N.S.

1984-09-01

53

Structure and oxidation at quasicrystal surfaces  

Microsoft Academic Search

We have investigated the atomic and electronic structure, chemical composition, and oxidation characteristics of the surfaces of icosahedral, Al-rich quasicrystals, using a variety of surface-sensitive techniques (LEED, XPS, STM, AES). We have systematically investigated the way that these traits vary with preparation conditions (e.g. sputtering and then annealing to various temperatures, vs. fracture), with surface symmetry (e.g. 2f vs. 3f

Patricia A Thiel

2004-01-01

54

Structure and oxidation at quasicrystal surfaces  

NASA Astrophysics Data System (ADS)

We have investigated the atomic and electronic structure, chemical composition, and oxidation characteristics of the surfaces of icosahedral, Al-rich quasicrystals, using a variety of surface-sensitive techniques (LEED, XPS, STM, AES). We have systematically investigated the way that these traits vary with preparation conditions (e.g. sputtering and then annealing to various temperatures, vs. fracture), with surface symmetry (e.g. 2f vs. 3f vs. 5f surfaces), and with bulk composition (e.g. i-Al-Pd-Mn vs. i-Al-Cu-Fe). We have also compared our results for the quasicrystals with results for crystalline approximants and other related crystalline phases. Our main conclusions are that, under specific conditions of sputter-annealing, the bulk atomic and electronic structures of the clean quasicrystal propagate to the surface. Also, the oxidation chemistry is dominated by that of the primary constituent, aluminum.

Thiel, Patricia A.

2004-08-01

55

Alkane activation on crystalline metal oxide surfaces.  

PubMed

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

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

2014-11-21

56

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...

57

Surface wettability of macroporous anodized aluminum oxide.  

PubMed

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

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

2013-04-24

58

Oxidation-driven surface dynamics on NiAl(100)  

PubMed Central

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

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

2015-01-01

59

Oxidation-driven surface dynamics on NiAl(100).  

PubMed

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

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

2015-01-13

60

Electrolysis of water on (oxidized) metal surfaces  

NASA Astrophysics Data System (ADS)

Density functional theory calculations are used as the basis for an analysis of the electrochemical process, where by water is split to form molecular oxygen and hydrogen. We develop a method for obtaining the thermochemistry of the electrochemical water splitting process as a function of the bias directly from the electronic structure calculations. We consider electrodes of Pt(1 1 1) and Au(1 1 1) in detail and then discuss trends for a series of different metals. We show that the difficult step in the water splitting process is the formation of superoxy-type (OOH) species on the surface by the splitting of a water molecule on top an adsorbed oxygen atom. One conclusion is that this is only possible on metal surfaces that are (partly) oxidized. We show that the binding energies of the different intermediates are linearly correlated for a number of metals. In a simple analysis, where the linear relations are assumed to be obeyed exactly, this leads to a universal relationship between the catalytic rate and the oxygen binding energy. Finally, we conclude that for systems obeying these relations, there is a limit to how good a water splitting catalyst an oxidized metal surface can become.

Rossmeisl, J.; Logadottir, A.; Nørskov, J. K.

2005-12-01

61

The surface and materials science of tin oxide  

Microsoft Academic Search

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

Matthias Batzill; Ulrike Diebold

2005-01-01

62

Oxide modified air electrode surface for high temperature electrochemical cells  

DOEpatents

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.

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

1992-01-01

63

Pretreatment of lubricated surfaces with sputtered cadmium oxide  

NASA Technical Reports Server (NTRS)

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.

Fusaro, Robert L. (inventor)

1991-01-01

64

Silicon surfaces : metallic character, oxidation and adhesion A. Cros (*)  

E-print Network

707 Silicon surfaces : metallic character, oxidation and adhesion A. Cros (*) IBM T.J. Watson of an ordered or disordered noble metal (Ag, Au) monolayer on the Si(111) surface has a great influence on the growth mode ofmetal atoms and the oxidation ofthe silicon surface atoms. These phenomena are discussed

Paris-Sud XI, Université de

65

Microwave properties of thermochromic metal oxide surfaces  

NASA Astrophysics Data System (ADS)

Thermochromic metal oxides with a Mott transition, such as vanadium dioxide (VO II) exhibit an extensive alteration in their infrared reflectivity when heated above the transition temperature. For VO II the infrared reflectivity increases as the material becomes more metal-like above the transition temperature at 68°C. Given these dynamic electromagnetic properties in the IR-range, it is interesting to study the reflection of the material also in other wavelength ranges. The microwave properties of VO II as a function of temperature have been investigated here. Measurements were made with an automated network analyzer combined with an electrical heating unit. Reflection properties of VO II in the microwave region were determined. Above the transition temperature, an increase in the reflection of the surface was observed. The VO II became more metal-like in the whole measured microwave frequency range, as in the infrared region. It is concluded that VO II not only can be used to adapt the thermal emissivity of a surface but also to control the microwave reflectivity. Possible applications are switchable radomes, switchable radarabsorbers and heat protection for antenna apertures.

Ousbäck, Jan-Olof; Kariis, Hans

2006-09-01

66

Oxidation of a polycrystalline titanium surface by oxygen and water  

NASA Astrophysics Data System (ADS)

Reactions of a well-characterized polycrystalline titanium surface with oxygen and water molecules at 150-850 K were studied in UHV by X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS) and Fourier transform reflectance-absorption infrared spectroscopy (FT-RAIRS). At 150 K, O 2 oxidizes Ti 0 to Ti IV, Ti III and Ti II, but Ti exposure to H 2O at this temperature produces only Ti II species. At temperatures above 300 K, further oxidation of Ti by H 2O was observed. Maximum oxidation by either molecule is achieved at 550-600 K. Upon heating the oxidized titanium above 850 K, the oxide layer is completely reduced to Ti 0. Hydroxyl species are identified on the Ti surface after reaction with H 2O; they appear to be mostly hydrogen bonded between 250 and 350 K, and isolated in the 450-650 K surface temperature range. Depth profiling of the O 2-oxidized Ti surface shows that Ti IV/Ti III species account for about 20% of the total thickness of the oxide layers and are located near the surface, while Ti II has a broader distribution, and is concentrated close to the oxide-metal interface. The OH group concentration is maximized at 550 K on the sample surface and accounts for about 16% of the total surface oxygen, with a decreasing concentration of OH into the bulk of the titanium oxides.

Lu, Gang; Bernasek, Steven L.; Schwartz, Jeffrey

2000-06-01

67

Oxidation of heated diamond C(100):H surfaces  

NASA Astrophysics Data System (ADS)

This paper extends a previous study (Pehrsson and Mercer, submitted to Surf. Sci.) on unheated, hydrogenated, natural diamond (100) surfaces oxidized with thermally activated oxygen (O ?2). In this paper, the oxidation is performed at substrate temperatures from Tsub=24 to 670°C. The diamond surface composition and structure were then investigated with high resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and low energy electron diffraction (LEED). The oxygen coverage ( ?) increased in two stages, as it did during oxidation at T<80°C. However, there are fundamental differences between the oxidation of nominally unheated and heated diamond surfaces. This difference is attributed to simultaneous adsorption and rapid desorption of oxygen species at higher temperatures; the desorption step is much slower without heating. The initial oxidation rates were similar regardless of the substrate temperatures, but the peak coverage ( ?) was lower at higher temperatures. For example, ? plateaued at 0.4±0.1 ML at 600°C. The lower saturation coverage is again attributed to oxygen desorption during oxidation. Consistent results were obtained on fully oxidized surfaces, which when heated in vacuum to Tsub=600°C, lost ˜60% of their adsorbed oxygen. ELS revealed few C?C dimers on the oxidized surfaces, and more graphitization than on unheated surfaces. Oxidation at elevated temperatures also increased the carbonyl to ether ratio, reflecting etching-induced changes in the types of surface sites. The carbonyl and C-H stretch frequencies increased with oxygen dose due to formation of higher oxidation states and/or hydrogen bonding between adjacent groups. The oxygen types did not interconvert when the oxidized surfaces were heated in vacuum. Oxygen desorption generated a much more reactive surface than heating-induced dehydrogenation of the smooth, hydrogenated surface.

Pehrsson, Pehr E.; Mercer, Thomas W.

2000-07-01

68

Solid state, surface and catalytic properties of oxides  

NASA Astrophysics Data System (ADS)

In the past year, efforts were directed to: (1) continue to elucidate the relationship between the surface structure of ZnO and the surface chemistry; (2) attempt to understand the relationship between the bulk structure and the selectivity in the oxidation of butene on iron oxide; and (3) explore the use of electrostatic potential argument to explain the formation of new acid sites in a dilute oxide solution. Progress in these areas is described.

Kung, H. H.

1984-09-01

69

Highly Oxidizing Surface Radicals in Lunar Dust  

NASA Astrophysics Data System (ADS)

Lunar rocks are generally believed to be very "dry" with little or no evidence for hydroxyl as indicators of traces of dissolved H2O. The absence of hydroxyl, however, is not a sure sign of the absence of dissolved H2O. The reason is that hydroxyl pairs in the structure of host minerals, O3X-OH HO-XO3, with X=Si4+, Al3+ etc., tend to undergo an electronic rearrangement (redox conversion) in the course of which two oxygen anions are oxidized from the 2- to the 1- valence, forming a peroxy link, O3X-OO-XO3, plus an H2 molecule. If the H2 molecules diffuse out (which they are expected to do from lunar rocks and lunar fines over the course of 4 Gyrs), the peroxy links remain as the only "memory" of a former solute H2O content. Hard UV causes peroxy links to dissociate. In the process an electron from a neighboring O2- jumps into the broken peroxy bond. This is equivalent to forming an O-, e.g. a defect electron in the oxygen anion sublattice. Such defect electrons, also known as positive holes or pholes for short, represent highly mobile charge carriers. When trapped at the surface of dust grains, these charge carriers turn into highly reactive, highly oxidizing O- radicals, which are of concern because of their toxicity when lunar dust is inhaled by astronauts. We propose a device to measure the UV-activation of peroxy links by dusting lunar fines onto a polyethylene base plate with Au electrodes sputtered onto both ends and an ammeter connecting the two electrodes. One end of the dust layer will be exposed to the ambient UV radiation, while the remainder will be shaded. During the lunar night no current is expected to flow between the two Au electrodes. During passage through the night-day terminator, a current is expected to flow between the Au electrodes carried by defect electrons activated in the irradiated portion of the dust layer. Such a current would be an indicator that lunar fines and, by implication, lunar rocks contain peroxy links as a memory of a former solute H2O content.

Kulahci, I.; Freund, F. T.; Bose, M.; Loftus, D. J.

2007-12-01

70

Anchoring of alkylphosphonic derivatives molecules on copper oxide surfaces  

NASA Astrophysics Data System (ADS)

In this study, a new approach of copper surface modification, taking advantage of the oxide layer naturally present, is proposed using phosphonic acids derivatives. Phosphonic acids are a class of molecules particularly known for their spontaneous self-assembly on oxidized substrates. On this basis, copper substrates chemically oxidized using H 2O 2 (5%) were successfully modified with n-dodecylphosphonic acid and 1-pyrrolyl-10-decanephosphonic acids. The oxidation state of copper substrate, just after chemical oxidation, was probed by XPS and PM-IRRAS. Surface characterization was completed by contact angle and AFM measurements. Molecular integrity, alkyl chain ordering and wettability were evaluated for both elaborated coatings. The panel of characterization tools used demonstrates the efficient grafting of phosphonic acid compounds on oxidized copper surfaces. The grafting mode appears similar for both investigated molecules and is evaluated as a tridentate mode.

Fonder, Grégory; Minet, Isabelle; Volcke, Cédric; Devillers, Sébastien; Delhalle, Joseph; Mekhalif, Zineb

2011-05-01

71

Inverse gas chromatography investigation of oxidized polyolefins: surface properties.  

PubMed

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

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

2014-04-11

72

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

E-print Network

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

Goodman, Wayne

73

Surface characterization of electrochemically oxidized carbon fibers  

Microsoft Academic Search

High strength PAN-based carbon fibers were continuously electrochemically oxidized by applying current to the fibers serving as an anode in 1% wt aqueous KNO3. Progressive fiber weight loss occurred with increasing extents of electrochemical oxidation. XPS studies (C 1s and O 1s) indicated that the oxygen\\/carbon atomic ratio rose rapidly to 0.24 as the extent of electrochemical oxidation was increased

Z. R. Yue; W. Jiang; L. Wang; S. D. Gardner; C PITTMANJR

1999-01-01

74

Structure and Reactivity of Surface Oxides on Pt(110) during Catalytic CO Oxidation  

SciTech Connect

We present the first structure determination by surface x-ray diffraction during the restructuring of a model catalyst under reaction conditions, i.e., at high pressure and high temperature, and correlate the restructuring with a change in catalytic activity. We have analyzed the Pt(110) surface during CO oxidation at pressures up to 0.5 bar and temperatures up to 625 K. Depending on the O{sub 2}/CO pressure ratio, we find three well-defined structures: namely, (i) the bulk-terminated Pt(110) surface, (ii) a thin, commensurate oxide, and (iii) a thin, incommensurate oxide. The commensurate oxide only appears under reaction conditions, i.e., when both O{sub 2} and CO are present and at sufficiently high temperatures. Density functional theory calculations indicate that the commensurate oxide is stabilized by carbonate ions (CO{sub 3}{sup 2-}). Both oxides have a substantially higher catalytic activity than the bulk-terminated Pt surface.

Ackermann, M.D. [ESRF, 6, rue Jules Horowitz, F-38043 Grenoble cedex (France); Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden (Netherlands); Pedersen, T.M.; Hammer, B. [Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Hendriksen, B.L.M.; Bobaru, S.C.; Frenken, J.W.M. [Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden (Netherlands); Robach, O. [CEA-Grenoble DRFMC/SI3M/PCM17, rue des Martyrs, 38054 Grenoble cedex 9 (France); Popa, I.; Kim, H. [ESRF, 6, rue Jules Horowitz, F-38043 Grenoble cedex (France); Quiros, C. [Departamento de Fisica, Faculdad de Ciencias, Universidad de Oviedo, Avda. Calvo Sotelo, s/n, 33007 Oviedo (Spain); Ferrer, S. [CELLS - ALBA, Edifici Ciencies Nord. Modul C-3 centra, Campus Universitari de Bellaterra, Universita Autonoma de Barcelona, 08193 Bellaterra (Spain)

2005-12-16

75

Comment on "Catalytic Activity of the Rh Surface Oxide: CO Oxidation over Rh(111)  

E-print Network

Comment on "Catalytic Activity of the Rh Surface Oxide: CO Oxidation over Rh(111) under Realistic. Obviously, during the rapid increase in the CO2 formation rate between 170 and 230 °C, the catalytic surface study is considerably restricted (TOF 25) by the overall pressure (due to the He makeup gas used

Goodman, Wayne

76

Interactions of graphene oxide nanomaterials with natural organic matter and metal oxide surfaces.  

PubMed

Interactions of graphene oxide (GO) nanomaterials with natural organic matter (NOM) and metal oxide surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Three different types of NOM were studied: Suwannee River humic and fulvic acids (SRHA and SRFA) and alginate. Aluminum oxide surface was used as a model metal oxide surface. Deposition trends show that GO has the highest attachment on alginate, followed by SRFA, SRHA, and aluminum oxide surfaces, and that GO displayed higher interactions with all investigated surfaces than with silica. Deposition and release behavior of GO on aluminum oxide surface is very similar to positively charged poly-L-lysine-coated surface. Higher interactions of GO with NOM-coated surfaces are attributed to the hydroxyl, epoxy, and carboxyl functional groups of GO; higher deposition on alginate-coated surfaces is attributed to the rougher surface created by the extended conformation of the larger alginate macromolecules. Both ionic strength (IS) and ion valence (Na(+) vs Ca(2+)) had notable impact on interactions of GO with different environmental surfaces. Due to charge screening, increased IS resulted in greater deposition for NOM-coated surfaces. Release behavior of deposited GO varied significantly between different environmental surfaces. All surfaces showed significant release of deposited GO upon introduction of low IS water, indicating that deposition of GO on these surfaces is reversible. Release of GO from NOM-coated surfaces decreased with IS due to charge screening. Release rates of deposited GO from alginate-coated surface were significantly lower than from SRHA and SRFA-coated surfaces due to trapping of GO within the rough surface of the alginate layer. PMID:25026416

Chowdhury, Indranil; Duch, Matthew C; Mansukhani, Nikhita D; Hersam, Mark C; Bouchard, Dermont

2014-08-19

77

Electron spectroscopic studies of perfect and defect metal oxide surfaces  

Microsoft Academic Search

A number of surface sensitive electron spectroscopic techniques have been used during the last few years to study the geometric and electronic structure of well characterized surfaces of metal oxide single crystals. For rocksalt monoxides, the (100) surface has been found to be very nearly a truncation of the bulk lattice; only qualitativelow energy electron diffraction (LEED) measurements have been

Victor E. Henrich

1987-01-01

78

Effects of anodic oxidation parameters on a modified titanium surface.  

PubMed

Anodic oxidation is an electrochemical treatment that can be used to control the thickness of an oxide layer formed on a titanium surface. This procedure has the advantage of allowing the ions contained in an electrolyte to deposit onto the oxide layer. The characteristics of a layer treated with anodic oxidation can vary according to the type and concentration of the electrolytes as well as the processing variables used during anodic oxidation. In this study, the constant electrolyte for anodic oxidation was a mixed solution containing 0.02 M DL-alpha-glycerophosphate disodium salt and 0.2M calcium acetate. Anodic oxidation was carried out at different voltages, current densities, and duration of anodic oxidation. The results showed that the current density and variation in the duration of anodic oxidation did not have a large effect on the change in the characteristics of the layer. On the other hand, the size of the micropores was increased with increasing voltage of anodic oxidation, and anatase and rutile phases were found to co-exist in the porous titanium dioxide layer. In addition, the thickness of the oxide layer on titanium and the characteristic of corrosion resistance increased with increasing voltage. The MTT test showed that the cell viability was increased considerably as a result of anodic oxidation. The anodizing voltage is an important parameter that determines the characteristics of the anodic oxide layer of titanium. PMID:17595033

Park, Il Song; Lee, Min Ho; Bae, Tae Sung; Seol, Kyeong Won

2008-02-01

79

Reporting central tendencies of chamber measured surface emission and oxidation.  

PubMed

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(4) emissions and surface air CH(4) concentrations. Correlation of the concentration and flux values using the geometric mean proved to be a good fit (R(2)=0.86), indicating that surface scans are a good way of identifying locations of high emissions. PMID:20933379

Abichou, Tarek; Clark, Jeremy; Chanton, Jeffery

2011-05-01

80

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

E-print Network

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

Sun, Wei-Yang

2011-01-01

81

Application of Surface Spectroscopies and Microscopies to Elucidate Sorption Mechanisms on Oxide Surfaces  

E-print Network

Application of Surface Spectroscopies and Microscopies to Elucidate Sorption Mechanisms on Oxide structure (EXAFS) spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), high a system and thus obtain detailed information of reactions mechanisms. Surface spectroscopies

Sparks, Donald L.

82

Surface Oxidation and Dissolution of Metal Nanocatalysts in Acid Medium  

E-print Network

the main features of the oxidation phenomena observed experimentally, it is concluded that the dissolution mechanism of metal atoms involves: 1) Surface segregation of alloy atoms, 2) oxygen absorption into the subsurface of the catalyst, and 3) metal...

Callejas-Tovar, Juan

2012-10-19

83

Formation of Surface Oxides on 13% Chromium Stainless Steel  

Microsoft Academic Search

The objective with this work was to get a better understanding of the formation of protective surface oxides on 13% chromium steel in formation water. Formation of oxide was studied by an electrochemical quartz crystal micro balance (EQCM) and dynamic and potentiostatic polarization. The EQCM samples were produced by pulse laser deposition (PLD) of about 200 nm alloy on the

Ole Øystein KNUDSEN; Thomas M. DEVINE

84

Rates of oxidative weathering on the surface of Mars  

NASA Technical Reports Server (NTRS)

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.

Burns, Roger G.

1992-01-01

85

Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms  

E-print Network

Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms Gordon E of Clean Metal Oxide Surfaces 83 2.1. The Nature of Defects on Metal Oxide Surfaces 83 2.2. Overview of UHV Surface Science Methods Used To Study Clean Metal Oxide Surfaces 84 2.3. Geometric and Electronic

Goodman, Wayne

86

The surface and materials science of tin oxide  

NASA Astrophysics Data System (ADS)

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 on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO 2 surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized.

Batzill, Matthias; Diebold, Ulrike

87

Surface-catalyzed singlet oxygen production on iodine oxide films  

NASA Astrophysics Data System (ADS)

Enhanced production of singlet oxygen, O2(a1?g), was observed by reaction of O2/He discharge effluents on an iodine oxide film surface in a microwave discharge-flow reactor at 320 K. We observed a two-fold increase in the O2(a) yields over discharge-generated amounts for non-catalytic conditions. The iodine oxide surface appears to catalyze the heterogeneous reaction to form O2(a) with high collision efficiency. The observed catalytic effect could significantly benefit the development of electrically driven oxygen-iodine laser systems, and may also have implications for the chemistry of atmospheric iodine oxide aerosol.

Lee, Seonkyung; Terry Rawlins, W.; Davis, Steven J.

2009-02-01

88

MOISTURE AND SURFACE AREA MEASUREMENTS OF PLUTONIUM-BEARING OXIDES  

SciTech Connect

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.

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

2009-09-28

89

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

SciTech Connect

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.

Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya, E-mail: yamamura@upst.eng.osaka-u.ac.jp [Research Center for Ultra-precision Science and Technology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)] [Research Center for Ultra-precision Science and Technology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)

2014-03-10

90

Surface oxides of the oxygen copper system: Precursors to the bulk oxide phase?  

NASA Astrophysics Data System (ADS)

To gain an initial understanding of the copper-based catalysts in commercially important chemical reactions such as the oxygen-assisted water-gas shift reaction, we performed density-functional theory calculations, investigating the interaction of oxygen and copper, focusing on the relative stability of surface oxides and oxide surfaces of the O/Cu system. By employing the technique of " ab initio atomistic thermodynamics", we show that surface oxides are only metastable at relevant pressures and temperatures of technical catalysis, with no stable chemisorption phase observed even at very low coverage. Although exhibiting only metastability, these surface oxides resemble the bulk oxide material both geometrically and electronically, and may serve as a precursor phase before onset of the bulk oxide phase. Having identified the bulk oxide as the most stable phase under realistic catalytic conditions, we show that a Cu 2O(1 1 1) surface with Cu vacancies has a lower free energy than the stoichiometric surface for the considered range of oxygen chemical potential and could be catalytically relevant.

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

2007-12-01

91

New perspectives on thermal and hyperthermal oxidation of silicon surfaces  

NASA Astrophysics Data System (ADS)

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 an accurate control over the interfacial stress by choosing a suitable oxidation temperature and Si-NW diameter can lead to precise nanoscale control over the Si-core radius. All investigations were carried out by applying molecular dynamics calculations using the ReaxFF potential, allowing a accurately study of the underpinning physical and chemical processes.

Khalilov, Umedjon

92

Method of producing adherent metal oxide coatings on metallic surfaces  

DOEpatents

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.

Lane, Michael H. (Clifton Park, NY); Varrin, Jr., Robert D. (McLean, VA)

2001-01-01

93

Oxidative etching of cleaved synthetic diamond {1 1 1} surfaces  

Microsoft Academic Search

In this study, three commonly used methods for oxidative etching of diamond {111} faces are compared: gas phase etching using `dry' oxygen, gas phase etching using an oxygen\\/water vapour mixture and liquid etching in molten potassium nitrate. The synthetic diamond surfaces are prepared by cleavage. The morphology of the surfaces is studied using atomic force microscopy and the kinetics of

F. K. de Theije; E. van Veenendaal; W. J. P. van Enckevort; E. Vlieg

2001-01-01

94

Some kinetic aspects of unsteady-state partial oxidation reactions. Dynamic processes on metal oxide surfaces  

Microsoft Academic Search

It is shown that steady-state kinetic data do not allow the discrimination between the redox and associated mechanisms of the partial oxidation reactions. A discrimination between these mechanisms was performed using transient experiments. The obtained rate expressions are in agreement with experimental kinetic data for catalytic partial oxidation of o-xylene.An influence of the conjugate oxidation of a catalyst surface on

Yuri I. Pyatnitsky; Nina I. Ilchenko

1996-01-01

95

Microwave properties of thermochromic metal oxide surfaces  

Microsoft Academic Search

Thermochromic metal oxides with a Mott transition, such as vanadium dioxide (VO2) exhibit an extensive alteration in their infrared reflectivity when heated above the transition temperature. For VO2 the infrared reflectivity increases as the material becomes more metal-like above the transition temperature at 68°C. Given these dynamic electromagnetic properties in the IR-range, it is interesting to study the reflection of

Jan-Olof Ousbäck; Hans Kariis

2006-01-01

96

A characterization study of a hydroxylated polycrystalline tin oxide surface  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

97

Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

98

Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces  

NASA Astrophysics Data System (ADS)

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 SiO2 surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained.

Uçar, A.; ?opuro?lu, M.; Baykara, M. Z.; Ar?kan, O.; Suzer, S.

2014-10-01

99

Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces.  

PubMed

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 SiO2 surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained. PMID:25362327

Uçar, A; Çopuro?lu, M; Baykara, M Z; Ar?kan, O; Suzer, S

2014-10-28

100

Reporting central tendencies of chamber measured surface emission and oxidation  

SciTech Connect

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.

Abichou, Tarek, E-mail: abichou@eng.fsu.edu [Department of Civil and Environmental Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310 (United States); Clark, Jeremy [Department of Civil and Environmental Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310 (United States); Chanton, Jeffery, E-mail: jchanton@fsu.edu [Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL 32306-4327 (United States)

2011-05-15

101

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

Microsoft Academic Search

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

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

2001-01-01

102

Surface oxidation of Zircaloy-4 at 600 K by adsorbed oxygen, nitric oxide, and sulfur dioxide  

NASA Astrophysics Data System (ADS)

Understanding and controlling the formation of surface oxides on Zircaloy-4 (Zry-4) surfaces in the presence of nitrogen or sulfur at high temperatures is of interest in applications where this alloy serves as a structural material. In this article we monitor the adsorption of gases on Zry-4 surfaces at 600 K using Auger electron spectroscopy. We find that sulfur dioxide (SO 2), nitric oxide (NO), and isotopic oxygen ( 18O 2) all result in the formation of surface oxides. The presence of sulfur on the surface is reflected both in an increase in the intensity of the overlapping [Zr(MNV) + S(LMM)] feature and its shift toward higher kinetic energies. On the other hand, since oxide formation results in shifts of the Zr(MNV) Auger transition toward lower energies, opposite to what the presence of sulfur does, we also obtain useful information from the Zr(MNN) transition. Although exposure to oxygen results in the largest oxygen concentration near the surface, all the three adsorbates shift the Zr(MNN) feature by about 1.5-2.0 eV, indicative of surface oxidation.

Stojilovic, N.; Ramsier, R. D.

2006-04-01

103

Surface-confined atomic silver centers catalyzing formaldehyde oxidation.  

PubMed

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

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

2015-02-17

104

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

105

Microwave surface impedance measurements on reduced graphene oxide.  

PubMed

Here we report a non-contact method for microwave surface impedance measurements of reduced graphene oxide samples using a high Q dielectric resonator perturbation technique, with the aim of studying the water content of graphene oxide flakes. Measurements are made before, during and after heating and cooling cycles. We have modelled plane wave propagation of microwaves perpendicular to the surface of graphene on quartz substrates, capacitively coupled to a dielectric resonator. Analytical solutions are derived for both changes in resonant frequency and microwave loss for a range of water layer thicknesses. In this way we have measured the presence of adsorbed water layers in reduced graphene oxide films. The water can be removed by low temperature annealing on both single and multilayer samples. The results indicate that water is intercalated between the layers in a multilayer sample, rather than only being adsorbed on the outer surfaces, and it can be released by applying a mild heating. PMID:22728562

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

2012-07-20

106

Process of forming catalytic surfaces for wet oxidation reactions  

NASA Technical Reports Server (NTRS)

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.

Jagow, R. B. (inventor)

1977-01-01

107

Cr(OH)3(s) Oxidation Induced by Surface Catalyzed Mn(II) Oxidation  

SciTech Connect

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 ?M) 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 ?M Mn(II) at pH 9.0 for 22 d revealed that the product of surface catalyzed Mn(II) oxidation resembled birnessite. The rate and extent of Cr(OH)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).

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

2014-09-16

108

ESCA study of oxidized wood surfaces  

Microsoft Academic Search

Results of a preliminary study of the surface of wood exposed to outdoor weathering as well as to UV irradiation showed that ESCA provides valuable information and insight into the manifestation of weathering and photooxidation. From the ESCA spectra, the increase in signal intensities of carbon-oxygen bonds and oxygen-carbon-oxygen bonds (or unsaturated carbon oxygen bond) and oxygen-to-carbon ratio, and the

David N.-S. Hon

1984-01-01

109

``Phenylpicrylhydrazyl'' on n-type Oxidic Surfaces  

Microsoft Academic Search

MANY organic compounds have a relatively stable electron spin resonance signal1-6 even at room temperature when adsorbed on a surface. In all these cases, the radical is a positive ion formed as a result of charge transfer with an appropriate site on the adsorbent. Recently, we have found that 1-phenyl-2-picrylhydrazine adsorbed on an anatase sample of high area shows an

Dwarika N. Misra

1967-01-01

110

Investigation of the Si(111) surface in uhv: oxidation and the effect of surface phosphorus  

SciTech Connect

We have studied the initial stages of oxidation, the segregation of phosphorus, and the effect of phosphorus on oxidation of the Si(111) 7 x 7 surface using optical second-harmonic generation. We have also observed a (..sqrt..3 x ..sqrt..3)R30/sup 0/ LEED pattern for P on Si(111).

Tom, H.W.K.; Zhu, X.D.; Shen, Y.R.; Somorjai, G.A.

1984-06-01

111

Surface oxide growth on platinum electrode in aqueous trifluoromethanesulfonic acid  

NASA Astrophysics Data System (ADS)

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 Pt?+-O?- surface dipole (?PtO), 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.

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

2014-10-01

112

Surface oxide growth on platinum electrode in aqueous trifluoromethanesulfonic acid.  

PubMed

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(?+)-O(?-) surface dipole (?(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

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

2014-10-28

113

Cr(OH)3(s) oxidation induced by surface catalyzed Mn(II) oxidation.  

PubMed

We 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 ?M) was reacted with or without synthesized Cr(OH)3(s) (1.0 g/L) at pH 7.0-9.0 under oxic or anoxic conditions. Homogeneous Mn(II) oxidation by dissolved O2 was not observed at pH ? 8.0 for 50 days. At pH 9.0, by contrast, dissolved Mn(II) was completely removed within 8 days 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. Production of Cr(VI) was attributed to Cr(OH)3(s) oxidation by a newly formed Mn oxide via Mn(II) oxidation catalyzed on Cr(OH)3(s) surface. XANES results indicated that this surface-catalyzed Mn(II) oxidation produced a mixed valence Mn(III/IV) solid phase. Our results suggest that toxic Cr(VI) can be naturally produced via Cr(OH)3(s) oxidation coupled with the oxidation of dissolved Mn(II). In addition, this study evokes the potential environmental hazard of sparingly soluble Cr(OH)3(s), which has been considered the most common and a stable remediation product of Cr(VI) contamination. PMID:25144300

Namgung, Seonyi; Kwon, Man Jae; Qafoku, Nikolla P; Lee, Giehyeon

2014-09-16

114

Oxidative nanopatterning of titanium generates mesoporous surfaces with antimicrobial properties  

PubMed Central

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

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

2014-01-01

115

Oxidative nanopatterning of titanium generates mesoporous surfaces with antimicrobial properties.  

PubMed

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

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

2014-01-01

116

Effect of dipolar fields, surface termination, and surface orientation on photochemical reactions on transition metal oxides  

NASA Astrophysics Data System (ADS)

Experiments have been conducted to determine the effects of dipolar fields, surface termination, and surface orientation on the photochemical reactivity of several transition metal oxides. These compounds include BaTiO3, SrTiO3, BaTi4O9, Sr2Nb2O 7, and Sr2Ta2O7 which were studied as polycrystalline ceramics, single crystals, micron-sized faceted particles, or some combination of these forms. The reduction of Ag+ from an aqueous AgNO3 solution (Ag0 product) and the oxidation of Pb2+ from an aqueous lead acetate solution (PbO 2 product) were selected as probe reactions because they leave insoluble products on the oxide surfaces. The reactivity of ferroelectric BaTiO3 was dominated by the effect of dipolar fields on the transport of photogenerated charge carriers. Silver was reduced on domains with a positive surface charge while lead was oxidized on domains with a negative surface charge. This reactivity implies that the dipolar field in individual domains drives photogenerated charge carriers to oppositely charged surfaces. This reaction mechanism results in a physical separation of the photogenerated charge carriers and the locations of the oxidation and reduction half reactions on the catalyst surface. Experiments performed on polycrystalline ceramics, single crystals, and micron-sized particles all showed this domain specific reactivity. SrTiO3 has the ideal cubic perovskite structure from which the tetragonally distorted ferroelectric BaTiO3 phase is derived. Polished and annealed surfaces of randomly oriented grain surfaces were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. Surfaces with the complex {100} facet were found to be the most active for Ag reduction. Single crystal studies also showed that the nonpolar (100) surface is the most reactive and that the composition of the termination layer does not influence this reaction. However, the polar (111) and (110) surfaces had a non-uniform distribution of reaction products. For these orientations, the location of the reduction and oxidation reactions is determined by the chemical and charge terminations of the different terraces or facets. The reactivity for silver reduction on the faceted particles is ranked as (100) > (111) > (110) while the (100) surface was least reactive for lead oxidation. Overall, these results show that the photochemical reactivity of SrTiO3 is anisotropic and that on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. (Abstract shortened by UMI.)

Giocondi, Jennifer Lynn

117

Effect of Annealing on Slightly Oxidized Silicon Surface  

NASA Astrophysics Data System (ADS)

We investigated the effect of annealing on slightly oxidized silicon surfaces by using atomic force microscopy (AFM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The very thin oxide films (˜1 nm) were made by chemical treatment for three kinds of samples. One of them was p-type Si(100) wafer, the others were heavily phosphorus-doped Si(100) wafers made by ion implantation and low pressure chemical vapor deposition. These samples were annealed at low temperature (700°C˜900°C) in ultra high vacuum. AFM measurements showed that RMS roughness of all surfaces after annealing in UHV was several times as much as that of the surfaces right after chemical treatment. The morphology of every sample after oxide silicon desorbed by annealing revealed dot shape. And the morphology of p-type Si(100) after annealing at 730°C resembled that of heavily phosphorus-doped Si(100) made by ion implantation after annealing at 830°C. AES and XPS measurements showed that the difference of annealing temperature for these samples was due to the difference of their oxide thickness and the quality of their oxides.

Kakimoto, Masashi; Sano, Yuichi; Kamiura, Yoshitomo; Mizokawa, Yusuke

118

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

NASA Technical Reports Server (NTRS)

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.

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

1982-01-01

119

Solid state, surface and catalytic properties of oxides. Progress report, October 1, 1979October 31, 1980  

Microsoft Academic Search

Fundamental studies on oxide catalysts have been conducted with emphasis on the investigation of the properties of anion and cation vacancies on an oxide surface, on the characterization of an adsorbed oxygen species on an oxide, and on the determination of surface cation densities in solid oxide solutions. An automically well ordered surface of ZnO has been successfully prepared on

Kung

1980-01-01

120

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

E-print Network

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

Diebold, Ulrike

121

Evidence concerning oxidation as a surface reaction in Baltic amber.  

PubMed

The aim of this study was to provide evidence about oxidation as a surface reaction during degradation of Baltic amber. A clear understanding of the amber-oxygen interaction modalities is essential to develop conservation techniques for museum collections of amber objects. Pellet-shaped samples, obtained from pressed amber powder, were subjected to accelerated thermal ageing. Cross-sections of the pellets were analyzed by infrared micro-spectroscopy, in order to identify and quantify changes in chemical properties. The experimental results showed strong oxidation exclusively at the exterior part of cross-sections from samples subjected to long-term thermal ageing, confirming that oxidation of Baltic amber starts from the surface. PMID:22277623

Pastorelli, Gianluca; Richter, Jane; Shashoua, Yvonne

2012-04-01

122

Evidence concerning oxidation as a surface reaction in Baltic amber  

NASA Astrophysics Data System (ADS)

The aim of this study was to provide evidence about oxidation as a surface reaction during degradation of Baltic amber. A clear understanding of the amber-oxygen interaction modalities is essential to develop conservation techniques for museum collections of amber objects. Pellet-shaped samples, obtained from pressed amber powder, were subjected to accelerated thermal ageing. Cross-sections of the pellets were analyzed by infrared micro-spectroscopy, in order to identify and quantify changes in chemical properties. The experimental results showed strong oxidation exclusively at the exterior part of cross-sections from samples subjected to long-term thermal ageing, confirming that oxidation of Baltic amber starts from the surface.

Pastorelli, Gianluca; Richter, Jane; Shashoua, Yvonne

2012-04-01

123

Emerging applications of liquid metals featuring surface oxides.  

PubMed

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

Dickey, Michael D

2014-11-12

124

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

E-print Network

. LITERATURE REVIEW 2. 1. Oxidation Mechanism of Titanium Alloys 4 2. 2. Stress and Effective Properties Analysis in MMC with Surface Oxidation. . . . 9 3. MODELING OF OXIDATION BY FICKIAN DIFFUSION PROBLEM . . . . 10 3. 1. Diffusion Equations 3. 2... of the applied loading is evaluated for a SiC/Ti-15-3 four-ply laminate loaded in tension. In the temperature range considered in this study (500'C to 800'C), the titanium is susceptible to oxygen diffusion which chemically forms a brittle thermodynainically...

Ma, Xinzheng

2012-06-07

125

Isopropanol oxidation by pure metal oxide catalysts: number of active surface sites and turnover frequencies  

Microsoft Academic Search

The objective of the present study was to determine the number of active surface sites and their nature, redox or acidic, for bulk metal oxide catalysts using isopropanol as a chemical probe molecule. Isopropanol oxidation activity on the following metal oxides was investigated: MgO, CaO, SrO, BaO, Y2O3, La2O3, CeO2, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, Cr2O3, MoO3, WO3, Mn2O3,

Deepak Kulkarni; Israel E. Wachs

2002-01-01

126

Reactions of metal ions at surfaces of hydrous iron oxide  

USGS Publications Warehouse

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

Hem, J.D.

1977-01-01

127

Electrochemically-Controlled Compositional Oscillations of Oxide Surfaces  

SciTech Connect

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.

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

2012-01-01

128

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

NASA Astrophysics Data System (ADS)

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 ?m 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.

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

2011-11-01

129

Infrared Characterization of Biotinylated Silicon Oxide Surfaces, Surface Stability and Specific Attachment of Streptavidin  

PubMed Central

Biotinylation of silicon oxide surfaces, surface stability and evolution of these functionalized surfaces under bio-specific attachment of streptavidin were studied using Fourier Transform Infrared Spectroscopy. Adsorption and stability of species or changes in the resulting surfaces were monitored after each step of the attachment processes. The silicon oxide surface was initially derivatized by 3-aminopropyltriethoxysilane (APTES) and the quality of the 3-aminopropylsiloxane (APS) surface was monitored using the Si-O-Si and Si-O-C region of its vibrational spectrum. A strong correlation between surface quality and pre-silanization atmospheric moisture content was established. The vibrational fingerprint of biotinylation was determined, both for physisorption and chemisorption to the surface. A new band (i.e. not previous associated with biotin) at ~1250 cm?1 was identified as a vibrational mode of the biotin ureido group, making it possible to track changes in the biotinylated surface in the presence of streptavidin. Some of the biotin ureido at the surface was found to be affected by the protein adsorption and rinse steps while remaining chemisorbed to the surface. The stability of the APS was found to impact the behavior of the biotinylated surface (measured using the Si-O-Si/Si-O-C and ~1250 cm?1 absorption bands respectively). PMID:19489542

Lapin, Norman A.; Chabal, Yves J.

2009-01-01

130

Initial Stages of Oxidation of IRON(100) Surface  

NASA Astrophysics Data System (ADS)

Oxygen/metal systems are involved in several important areas, such as catalytic oxidation, corrosion processes and surface magnetism. As an example of one important system the surface structure and oxidation of the iron/oxygen system are of interest. AES, XPS, and LEED have been used to determine the initial uptake of oxygen, crystallographic structure of chemisorbed oxygen, and final state of the oxide. The AES measurements, which agree well with results of XPS, show three regions of oxygen adsorption. The chemisorption of oxygen is followed by oxide formation and oxide growth. The initial oxygen uptake curve increases rapidly with exposure and becomes flat at around 6 L, and then increases nonlinearly. The sticking coefficient corresponding to the oxygen uptake curve decreases rapidly to a minimum at around 6 L oxygen exposure. Beyond this exposure, the sticking coefficient increases to a maximum at around 20L and decreases again. LEED patterns of clean Fe(100) and chemisorbed oxygen on Fe(100) are p(1 x 1). According to results using the Fe MVV transition, we have found that the final state of oxide is Fe _2O_3 at room temperature. The photoemission extended x-ray absorption fine structure (PEXAFS) technique has been used to investigate the structures of the clean Fe(100) surface and the oxide formed on the Fe(100) surface. This is the first successful PEXAFS measurement using a photopeak of a single crystal substrate. PEXAFS is a powerful tool for surface study because of its surface sensitivity due to the short electron escape depth (about 5A) and its chemical sensitivity permitting selective study of each element in different chemical environments. An Fe 3p core level shift of 2.6(3) eV is observed at the surface of Fe(100) exposed to 50L, 100L and 500L of oxygen. We measured PEXAFS using Fe 3p unshifted and chemically shifted peaks, in constant initial state(CIS) spectroscopy. We determined Fe-Fe distances in the clean iron, and Fe-O and Fe-Fe separations in the oxide. The results for clean Fe(100) are 2.47(4), 2.85(4), 4.01(7), and 4.71(7) A for the 1st, 2nd, 3rd, and 4th nearest neighbor Fe-Fe distances, respectively, which agree well with the known bulk values. The two Fe-O distances and the Fe-Fe distance of the oxide are 2.01(4), 4.48(7) and 3.31(6) A, respectively. These results are also in agreement with the known values of the bulk gamma-Fe_2 O_3. The surface extended electron energy loss fine structure technique, which has the advantage of greater accessibility than synchrotron radiation, also has been applied to the structural study. The correct distances are obtained from SEELFS above the Fe 3p edge using phase shifts calculated with the curve wave approximation but not the plane wave approximation.

Park, Yong Seob

131

Comparison Between Crystalline and Amorphous Surfaces of Transition Metal Oxide Water Oxidation Catalysts: a Theoretical Perspective  

NASA Astrophysics Data System (ADS)

Amorphous films of transition-metal oxide water oxidation catalysts (WOCs) often show an enhanced catalytic activity compared to their crystalline counterparts [1-4]. In particular, in the case of cobalt-oxide based WOCs the observed similarity in their electrochemical properties and catalytic activity, under oxidative conditions, has been correlated with the formation of similar amorphous surface morphologies, suggesting the presence of a common, catalytically active amorphous structural motif [3,4]. We present ab initio calculations of cobalt oxide based material surfaces and we compare the electronic properties of crystalline and amorphous surfaces, with the aim of identifying differences related to their different catalytic activity.[4pt] [1] Blakemore, J. D., Schley, N. D., Kushner-Lenhoff, M. N., Winter, A. M., D'Souza, F., Crabtree, R. H., and Brudvig, G. W. Inorg. Chem. 51, 7749 (2012); [2] Tsuji, E., Imanishi, A., Fukui, K.-I. and Nakato, Y. Electrochimica Acta 56, 2009 (2011); [3] Jia, H., Stark, J., Zhou, L. Q., Ling, C., Takeshi, S., and Markin, Z. RSC Advances 2, 10874 (2012); [4] Lee, S. W., Carlton, C., Risch, M., Surendranath, Y., Chen, S., Furutsuki, S., Yamada, A., Nocera, D. G., and Shao-Horn, Y. J. Am. Chem. Soc. 134, 16959 (2012).

Skone, Jonathan H.; Galli, Giulia

2013-03-01

132

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

SciTech Connect

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.

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

2013-06-24

133

Water-Mediated Proton Hopping on an Iron Oxide Surface  

SciTech Connect

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.

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

134

Water-mediated proton hopping on an iron oxide surface.  

PubMed

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

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

2012-05-18

135

Colloids and Surfaces B: Biointerfaces 36 (2004) 8190 Bacterial adhesion to glass and metal-oxide surfaces  

E-print Network

Colloids and Surfaces B: Biointerfaces 36 (2004) 81­90 Bacterial adhesion to glass and metal-oxide, The Pennsylvania State University, University Park, PA 16802, USA Accepted 4 May 2004 Abstract Metal oxides can. However, the hydrophobicity of a metal-oxide surface can also increase adhesion of bacteria. In order

136

Molecular cluster models of aluminum oxide and aluminum hydroxide surfaces  

Microsoft Academic Search

Ab initio, molecular orbital calculations for two different Hartree-Fock basis levels were performed on clusters in the system Al-O-H, and tested by comparing derived vibrational frequencies to the measured values for aluminum oxides and aluminum oxyhydroxide minerals. Models were chosen to reflect surface groups that may be present on aluminous minerals such as a-Al2O3 (corundum) and Al(OH)3 (gibbsite). Protonation and

J. D. KUBICKI; S. E. APITZ

1998-01-01

137

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

NASA Astrophysics Data System (ADS)

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.

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

2001-11-01

138

Inhibition of Sulfide Mineral Oxidation by Surface Coating Agents: Batch  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

139

Adhesion mechanisms of thin polymer films on inorganic oxide surfaces  

NASA Astrophysics Data System (ADS)

This study focuses on the chemical and microstructural mechanisms that govern the adhesion of a model interface between a low dielectric constant insulating polymer and the native silicon dioxide surface of silicon. Interface adhesion was quantitatively characterized with a fracture mechanics-based method that allows accurate and repeatable measurement of the interface resistance to fracture under mixed-mode loading conditions. We studied reinforcement of the model interface by chemical modification via silane coupling agents. Specifically, we investigated the effect of two commercially available coupling agent formulations, one with an amine, the other with a vinyl end-group functionality. The vinylsilane was found to be the most effective adhesion promoter. We furthermore discovered that the two materials formed thin films of drastically different morphologies when deposited via spin-coating on oxidized silicon surfaces. The aminosilane exhibited islands and incomplete surface coverage, whereas the vinysilane exhibited smooth morphology. The improved adhesion obtained via the latter was thus interpreted as the combined effect of superior surface wetting and film uniformity on one hand, and chemical affinity with the polymer on the other. We further developed a novel method for characterizing fractional surface coverage via angle-resolved X-ray photoelectron spectroscopy (AR-XPS). Results obtained from this method were found to be in good agreement with results obtained via contact angle experiments. The AR-XPS approach is very powerful and can be used to characterize both surface and buried films with island microstructures. An alternative approach of interface reinforcement is microstructural modification by introducing controlled roughness or porosity. The success of such engineering strategies depends on the structural properties of the resulting porous surface and control over these properties is particularly important. To that end, we proposed and demonstrated the use of self-assembling template-assisted mesoporous oxide films to generate porous oxide surfaces with excellent control over the structural properties. We further demonstrated that such films are capable of significantly improving the adhesive strength of the model organic/inorganic interface of interest. The combination of mesoporous surface morphology with silane coupling agent chemistry is a very powerful and versatile interface engineering strategy, applicable to a variety of technological and biomedical applications.

Pantelidis, Dimitrios

140

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

NASA Astrophysics Data System (ADS)

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.

Akhiani, Hamed; Szpunar, Jerzy A.

2013-11-01

141

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

NASA Technical Reports Server (NTRS)

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.

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

1982-01-01

142

Reflection spectra and magnetochemistry of iron oxides and natural surfaces  

NASA Technical Reports Server (NTRS)

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.

Wasilewski, P.

1978-01-01

143

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

USGS Publications Warehouse

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

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

1998-01-01

144

Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis.  

PubMed

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 formation of nonhysteretic ultralyophobic surfaces. PMID:20030348

Hozumi, Atsushi; McCarthy, Thomas J

2010-02-16

145

Surface x-ray diffraction study on polar oxide surface and interface  

NASA Astrophysics Data System (ADS)

An atomic scale study of surface/interface structure is required to properly understand physical and chemical phenomena such as crystal growth, lubrication and electrochemistry. The stability of polar oxide surface has long been an interesting question. A bulk-terminated polar oxide surface comprises alternating layers of opposite charges, thus resulting in diverging surface energies. In order to reduce the surface energy, various reconstruction-stabilized MgO (111) surfaces have been reported experimentally. However, the atomic structure of the MgO (111)rt3xrt3R30° reconstructed surface remains unclear. Using a third-generation X-ray source is one of the feasible methodologies to probe such a system due to its increase of sensitivity on the interface layer. Surface X-ray diraction (SXRD) experiments were performed for the MgO(111) rt3xrt3R30° reconstructed surface at Advanced Photon Source, Argonne National Laboratory. The sample surface was prepared at home laboratory by annealing in a tube furnace for 36hrs at 1050°C, with N2 blowing at rate 1 to 2 scft. Crystal truncation rod (CTR) and super structure rod (SSR) measurements were acquired in both the absence and presence of a thin layer of water, obtained by compressing the bulk water layer with a thin Kapton sheet. A differential evolution algorithm, GenX, was used to search for the appropriate atomic model of reconstructed structure. Some reasonable models are presented and discussed with quantitative calculation of optimizing parameters (R factor and chi square). Preliminary SXRD results of the dry surface and solid-liquid interface are compared. This determination will shed light on whether physical (as opposed to chemical) factors are operant in the formation of ice-like layers.

Han, Wei

146

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

SciTech Connect

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.

Zhernokletov, D. M. [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States)] [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States); Laukkanen, P. [Department of Physics and Astronomy, University of Turku, Turku FI-20014 (Finland)] [Department of Physics and Astronomy, University of Turku, Turku FI-20014 (Finland); Dong, H.; Brennan, B.; Kim, J. [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States)] [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Galatage, R. V. [Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States)] [Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Yakimov, M.; Tokranov, V.; Oktyabrsky, S. [College of Nanoscale Science and Engineering, University at Albany-SUNY, Albany, New York 12203 (United States)] [College of Nanoscale Science and Engineering, University at Albany-SUNY, Albany, New York 12203 (United States); Wallace, R. M. [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States) [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States); Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States)

2013-05-27

147

Enhanced Remote Photocatalytic Oxidation on Surface-Fluorinated TiO 2  

Microsoft Academic Search

The mobile nature of active oxygen species generated on the UV-illuminated TiO2 surface is now well- recognized. Surface oxidants not only migrate two-dimensionally but also desorb from the surface to be air-borne oxidants. The remote photocatalytic oxidation (PCO) of stearic acids over the surface-fluorinated TiO2 (F-TiO2) film was carried out in the ambient air to study the effects of fluorination

Jong Sung Park; Wonyong Choi

2004-01-01

148

Oxidative etching of cleaved synthetic diamond {1 1 1} surfaces  

NASA Astrophysics Data System (ADS)

In this study, three commonly used methods for oxidative etching of diamond {1 1 1} faces are compared: gas phase etching using `dry' oxygen, gas phase etching using an oxygen/water vapour mixture and liquid etching in molten potassium nitrate. The synthetic diamond surfaces are prepared by cleavage. The morphology of the surfaces is studied using atomic force microscopy and the kinetics of the reactions is determined by measuring the decrease in thickness of the diamond. The atomic arrangement of the {1 1 1} surfaces etched in oxygen/water is studied using surface X-ray diffraction. Upon dry oxygen etching, the {1 1 1} faces are roughened and become morphologically unstable. This observation conflicts with standard theory, which predicts {1 1 1} to be a stable F-face that should etch via a layer mechanism. A possible explanation for this is chemical roughening. The addition of water vapour to the oxygen has a dramatic effect on the etching mechanism of the {1 1 1} faces. Now etching proceeds via a layer mechanism involving monoatomic steps. Shallow etch pits are formed, of which the slope increases for increasing etching temperature. Surface X-ray diffraction experiments show that the surface is -OH terminated. For potassium nitrate etching, the {1 1 1} face etches also via a layer mechanism and triangular etch pits with rounded corners are formed, having point or flat bottoms. This etching technique appears to be the best method to reveal different types of defects ending on diamond {1 1 1} surfaces.

de Theije, F. K.; van Veenendaal, E.; van Enckevort, W. J. P.; Vlieg, E.

2001-10-01

149

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

E-print Network

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

Goodman, Wayne

150

Estimation of surface precipitation constants for sorption of divalent metals onto hydrous ferric oxide and calcite  

E-print Network

oxide and calcite Chen Zhu * Department of Geology and Planetary Science, University of Pittsburgh for modeling surface precipitation of divalent metals, M2+ , onto hydrous ferric oxide and calcite were+ . D 2002 Elsevier Science B.V. All rights reserved. Keywords: Surface adsorption; Iron oxide; Calcite

Polly, David

151

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

E-print Network

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

Chorover, Jon

152

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

E-print Network

Electrodeposited ruthenium oxide thin films for supercapacitor: Effect of surface treatments V,2]. The examples include transition metal oxides and conducting polymers [3­6]. Ruthenium oxide (RuO2ÁxH2O films [10]. Several studies are reported to improve the specific capacitance of ruthenium oxide

Chow, Lee

153

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

E-print Network

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

Azad, Abdul-Majeed

154

Surface engineering of iron oxide nanoparticles for targeted cancer therapy  

PubMed Central

Conspectus Nanotechnology provides a flexible platform for the development of effective therapeutic nanomaterials that can interact specifically with a target in a biological system and provoke a desired biological response. Of the nanomaterials studied, iron oxide nanoparticles have emerged as one of top candidates for cancer therapy due to their intrinsic superparamagnetism that enables no-invasive magnetic resonance imaging (MRI) and biodegradability favorable for in vivo application. A therapeutic superparamagnetic iron oxide nanoparticle (SPION) typically consists of three primary components: an iron oxide nanoparticle core that serves as both a carrier for therapeutics and contrast agent for MRI, a coating on the iron oxide nanoparticle that promotes favorable interactions between the SPION and biological system, and a therapeutic payload that performs designated function in vivo. Often, a targeting ligand is also included in the design that recognizes the receptors over-expressed on cancer cells. The body is a highly complex system that imposes multiple physiological and cellular barriers to foreign objects. Thus, the success of a therapeutic SPION largely relies on the proper design of the iron oxide core to ensure MRI detectability and more critically, the coating to render the ability to bypass these barriers. Strategies to bypass the physiological barriers such as liver, kidneys, and spleen, involve tuning the overall size and surface chemistry of the SPION to maximize blood half-life and facilitate the navigation in the body. Strategies to bypass cellular barriers include the use of targeting agents to maximize uptake of the SPION by cancer cells, and employing materials that promote desired intracellular trafficking and enable controlled drug release. The payload can be genes, proteins, chemotherapy drugs, or a combination of them. Each therapeutic requires a specific coating design to maximize the loading and achieve effective delivery and release. In this Account, we discuss the primary design parameters in developing therapeutic SPIONs with a focus on surface coating design to overcome the barriers imposed by the body’s defense system and provide examples of how these design parameters have been implemented to produce therapeutic SPIONs for specific therapeutic applications. Although there are still challenges to be addressed, SPIONs show great promise in successful diagnosis and treatment of the most devastating cancers. Once critical design parameters have been optimized, these nanoparticles, combined with imaging modalities, can serve as a truly multi-functional theranostic agent that not only performs a therapeutic function, but provides instant treatment feedback for the physician to adjust the treatment plan. PMID:21528865

Kievit, Forrest M.; Zhang, Miqin

2011-01-01

155

The electrochemisty of surface modified <10 nm metal oxide nanoparticles  

NASA Astrophysics Data System (ADS)

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 and ZrO2 nanoparticles was also explored, but resulted in very low surface coverages. ZrO2 nanoparticles were also ferrocene tagged using previously discussed siloxane chemistry as well as a new route using click chemistry with an azo-phosphate ligand. A similar approach was taken with hydrolytically synthesized IrO 2 and is included for comparison. Chapter Five studies the multivalent electrochemistry of 4 nm magnetite nanoparticles. These nanoparticles are synthesized via thermal degradation and capped with citric acid to make them water soluble. pH dependent electrochemistry was discovered and characterized using cyclic voltammetry, chronoamperometry, and rotating disk electrode experiments. Two separate electrochemical species are present and undergo two irreversible, but separate electrochemical reactions; Fe(II) ? Fe (III) and Fe(III) ? Fe(II).

Roberts, Joseph J. P.

156

TEMPO-oxidized Nanocelluloses: Surface Modification and use as Additives in Cellulosic Nanocomposites.  

E-print Network

??The process of TEMPO-mediated oxidation has gained broad usage towards the preparation of highly charged, carboxyl-functionalized polysaccharides. TEMPO-oxidized nanocelluloses (TONc) of high surface charge and… (more)

Johnson, Richard Kwesi

2010-01-01

157

Probing and mapping electrode surfaces in solid oxide fuel cells.  

PubMed

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

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

2012-01-01

158

Oxide treatments of Al 2024 for adhesive bonding- surface characterization  

NASA Astrophysics Data System (ADS)

A study was made to characterize the surface of oxides formed on Al 2024 in comparison to those formed on Al 1100, using Auger, ESCA, SIMS, FTIR and SEM/EDAX techniques. The pretreatments studied were chromate conversion coating, chromic acid anodizing and sulfuric acid anodizing. The specimens were evaluated as treated and after exposure to laboratory conditions ( T=25?3°C and relative humidity of 60?10%) for 6 months. In addition, a new surface pretreatment was studied, which was based on McDonnell Douglas P.S. 13201 specification. Adhesive bond strength of silicone rubbers and epoxy adhesives to pretreated Al 2024 was determined, using single lap joint specimens. It was shown that the main difference between the anodic coatings on Al 1100 and Al 2024 was the presence of copper on the surface in the latter. The presence of copper led us to postulate the mechanism of polymerization inhibition of 2 parts polysiloxane adhesive. The most suitable treatments for adhesive joining were found to be chromic acid sealed or unsealed anodizing for both Al 2024 and Al 1100. Our standard chromic acid anodizing gave higher bond strength for aluminum-adhesive joints than the "Douglas" process. as determined with several epoxy adhesives. Correlation between microscopic and macroscopic phenomena was established.

Fin, N.; Dodiuk, H.; Yaniv, A. E.; Drori, L.

1987-03-01

159

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

SciTech Connect

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.

Powers, J.M.

1991-11-01

160

High surface area, electrically conductive nanocarbon-supported metal oxide  

DOEpatents

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.

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

161

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

SciTech Connect

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

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

162

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

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

163

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

NASA Astrophysics Data System (ADS)

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.

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

2009-10-01

164

Decontamination of U-metal Surface by an Oxidation Etching System  

SciTech Connect

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.

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

2000-12-18

165

The adsorption of hyperbranched polymers on silicon oxide surfaces.  

PubMed

The electrostatic interaction between quarternised hyperbranched polymers (polyesteramides) and a silicon oxide (SiO2) surface has been studied via adsorption studies with quartz crystal microbalance instrument with dissipation (QCM-D). Frequency shift (Deltaf) results show that the increase in both pH and salt concentration positively affect the adsorbed amount of these polymers, calculated by Sauerbrey equation, on the QCM crystal. The adsorbed amount of HA1 (with lower molecular weight and higher charge density) was lower than that of HA2 (with higher molecular weight and lower charge density) in all experiments. It was also observed that there are no significant changes in the dissipation after adsorption of these polymers. This indicated that both hyperbranched polymers formed rigid adsorbed layers on the negative SiO2 surface. Additionally, the results were compared with adsorption of poly-DADMAC and the results showed that the hyperbranched polymers formed thicker and more rigid layers as compared with the poly-DADMAC. PMID:16820163

Ondaral, Sedat; Wågberg, Lars; Enarsson, Lars-Erik

2006-09-01

166

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

SciTech Connect

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.

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

2007-10-29

167

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

168

Surface Modification of Ti Dental Implants by Grit-Blasting and Micro-Arc Oxidation  

Microsoft Academic Search

The osseointegration capability of titanium implants is related to their chemical composition and surface roughness. The combination of grit-blasting and micro-arc oxidation had been used to produce the improved implant surfaces. The ceramic particles were projected to titanium implants at high velocity to get high surface roughness. Then the surface of implants was modified by micro-arc oxidation treatment. A porous

Yeon-Wook Kim

2010-01-01

169

Correlation and surface effects in vanadium oxides S. Schwieger, M. Potthoff, and W. Nolting  

E-print Network

Correlation and surface effects in vanadium oxides S. Schwieger, M. Potthoff, and W. Nolting modifications in the spectra from vanadium oxides such as (V,Cr)2O3 or (Sr,Ca)VO3. The effective mass transitions are caused by correlations. Typical ma- terials that show such behavior are vanadium oxides

Potthoff, Michael

170

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

NASA Technical Reports Server (NTRS)

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.

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

171

Microstructure of oxide layers formed on zirconium alloy by air oxidation, uniform corrosion and fresh-green surface modification  

NASA Astrophysics Data System (ADS)

Cladding materials with superior corrosion resistance and anti-hydrogen pickup have been developed for high burnup nuclear fuel. We have suggested a surface modification of the cladding materials for this purpose and invented a new surface modification method "Fresh-Green". The Fresh-Green treatment oxidizes and carbonizes a material surface in the same process. Zircaloy-2 with the Fresh-Green treatment showed the improvement of corrosion resistance in autoclave tests. In order to investigate the effect of surface modifications on the corrosion resistance, a synchrotron radiation experiment and a TEM observation were performed on different oxide layers formed on Zircaloy-2. The oxide layers were formed by air-oxidation, an autoclave test and the Fresh-Green treatment. Crystal structures of all the samples were transformed as Zr > Zr 3O > tetragonal ZrO 2 > monoclinic ZrO 2 from the matrix to the surface. Columnar grains of monoclinic zirconia were arranged unidirectionally in the Fresh-Green oxide layer treated at a low temperature. Diffusing capacity for oxygen influenced the crystal structure of the oxide layers.

Sawabe, Takashi; Sonoda, Takeshi; Furuya, Masahiro; Kitajima, Shoichi; Kinoshita, Motoyasu; Tokiwai, Moriyasu

2011-12-01

172

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

NASA Astrophysics Data System (ADS)

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 ?m. The microhardness on the surface was significantly improved as compared to the as-received substrate. Both the corrosion resistance property and biocompatibility were improved.

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

173

The Behavior of Surface Oxide Film on Ruthenium and Rhodium Plated Contacts  

Microsoft Academic Search

Although a surface oxide film on platinum-metal contacts is effective in preventing these contacts from polymerizing organic materials, it causes an increase in contact resistance. It is important to determine the thickness of surface oxide film which effectly prevents organic polymerization without causing a significant increase in contact resistance. Auger Electron Spectroscopy is used here to determine the thicknesses of

T. Umemoto; T. Takeuchi; R. Tanaka

1978-01-01

174

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

E-print Network

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

Marks, Laurence D.

175

X-ray photoelectron and scanning auger electron spectroscopic studies of oxidized graphite electrode surfaces  

Microsoft Academic Search

The surfaces of electrochemically modified graphite electrodes have been studied using ESCA, scanning Auger microscopy, and chemical titration. Quantitative evaluation of surface functionalities after electro-oxidation in sulfuric acid provides an understanding of their mechanistic role in synthetic uses of the carbon electrode. Specifically concentrations of acid and phenolic groups are correlated with the level of oxidation on the electrode. A

Joseph H. Wandass; J. A. Jr. Gardello; N. L. Weinberg; M. E. Bolster; L. Jr. Salvati

1987-01-01

176

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

PubMed Central

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 spread of bacteria-related diseases particularly in moist or wet environments. PMID:20843373

2010-01-01

177

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

SciTech Connect

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.

Wang, X.H. [Univ. of Kentucky, Lexington, KY (United States)] [Univ. of Kentucky, Lexington, KY (United States)

1996-03-25

178

Oxidation of ultrathin copper layers on zinc oxide polar surfaces: unoccupied electronic states  

NASA Astrophysics Data System (ADS)

Total current spectroscopy (TCS) was used to study an evolution of unoccupied states through the process of thin-layer copper deposition and its oxidation on polar ZnO(0001) and 0953-8984/9/35/005/img9 surfaces. Zn-derived and O-derived unoccupied bands were identified in the TC spectrum at 7.7 and 9.8 eV, respectively, from the clean and well ordered polar ZnO faces, while the spectra from a thin CuO layer reveal an intensive fine structure in the 6 - 25 eV energy range above the Fermi level, which is discussed in comparison with previously reported results of experimental and theoretical investigations. The obtained data provide additional information on the energy location of the edges of unoccupied bands in CuO in the 6 - 25 eV range relative to 0953-8984/9/35/005/img10.

Komolov, S. A.; Lazneva, E. F.; Egebjerg, T.; Møller, P. J.

1997-09-01

179

Surface characterisation of dextran-coated iron oxide nanoparticles prepared by laser pyrolysis and coprecipitation  

NASA Astrophysics Data System (ADS)

The favoured mechanism of adsorption of dextran on the surface of maghemite nanoparticles (5 nm) prepared by laser pyrolysis seems to be the collective hydrogen bonding between dextran hydroxyl groups and iron oxide particle surface. After heating, the formation of a surface complex between the polysaccharide oxygen atoms and the surface iron atoms gave rise to a stronger bonding.

Carmen Bautista, M.; Bomati-Miguel, Oscar; del Puerto Morales, María; Serna, Carlos J.; Veintemillas-Verdaguer, Sabino

2005-05-01

180

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

NASA Technical Reports Server (NTRS)

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.

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

2013-01-01

181

Influence of surface defects and local structure on acid/base properties and oxidation pathways over metal oxide surfaces. Final report, June 1990--January 1997  

SciTech Connect

This final report covers work done during project period one and project period two. All the work in project period one was focused on the selective oxidation of oxygenated hydrocarbons over the SnO{sub 2}(110) single crystal surface. In project period two, the emphasis was on the acid/base properties of SnO{sub 2}(110) as well as two different Cu{sub 2}O single crystal surfaces. Prior to the summary of results, a description of these different surfaces is given as background information. Results are described for the dissociation and reaction of Bronsted acids (methanol, formic acid, water, formaldehyde, acetone, propene, acetic acid, and carbon monoxide). Results from project period two include: ammonia adsorption, CO{sub 2} adsorption, propene adsorption and oxidation, with tin oxides; complimentary work with copper oxides; and STM investigations.

Cox, D.F.

1997-12-31

182

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

SciTech Connect

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

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

2011-04-14

183

Surface complexation and oxidation of Sn(II) by nanomagnetite.  

PubMed

The long-lived fission product 126Sn is of substantial interest in the context of nuclear waste disposal in deep underground repositories. However, the prevalent redox state, the aqueous speciation as well as the reactions at the mineral-water interface under the expected anoxic and reducing conditions are a matter of debate. We therefore investigated the reaction of Sn(II) with a relevant redox-reactive mineral, magnetite (Fe(II)Fe(III)2O4) at <2 ppmv O2, and monitored Sn uptake as a function of pH and time. Tin redox state and local structure were investigated by Sn–K X-ray absorption spectroscopy (XAS). We observed a rapid uptake (<30 min) and oxidation of Sn(II) to Sn(IV) by magnetite. The local structure determined by XAS showed two Sn–Fe distances of about 3.15 and 3.60 Å in line with edge and corner sharing arrangements between octahedrally coordinated Sn(IV) and the magnetite surface, indicative of formation of tetradentate inner-sphere complexes between pH 3 and 9. Based on the EXAFS-derived surface structure, we could successfully model the sorption data with two different complexes, (Magn_sO)4Sn(IV)(OH)2–2 (logK(2,0)(–2) ?14.97 ± 0.35) prevailing from pH 2 to 9, and (Magn_sO)4Sn(IV)(OH)2Fe (logK(2,1)(0) ?17.72 ± 0.50), which forms at pH > 9 by coadsorption of Fe(II), thereby increasing sorption at this high pH. PMID:24147605

Dulnee, Siriwan; Banerjee, Dipanjan; Merkel, Broder J; Scheinost, Andreas C

2013-11-19

184

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

NASA Technical Reports Server (NTRS)

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.

Buckley, D. H.

1973-01-01

185

Effect of the surface oxidation of LiBH(4) on the hydrogen desorption mechanism.  

PubMed

The surface oxidation behavior of LiBH(4) and NaBH(4) was investigated in view of the formation and structure of the surface oxidation and its effect on the hydrogen desorption kinetics. The sample surfaces were intentionally modified by exposure to oxygen in the pressure range from 10(-10) mbar up to 200 mbar. The induced surface changes were systematically studied by means of X-ray photoelectron spectroscopy. NaBH(4) shows a low reactivity with oxygen, while LiBH(4) oxidizes rapidly, accompanied by surface segregation of Li. The hydrogen desorption kinetics of LiBH(4) were studied by thermal desorption spectroscopy with particular emphasis on the analysis of the desorbed gases, i.e. diborane and hydrogen. The surface oxidation induces the formation of a Li(2)O layer on LiBH(4), significantly reduces the desorption of diborane, and enhances the rate of hydrogen desorption. PMID:20657909

Kato, Shunsuke; Bielmann, Michael; Borgschulte, Andreas; Zakaznova-Herzog, Valentina; Remhof, Arndt; Orimo, Shin-Ichi; Züttel, Andreas

2010-09-28

186

Oxidation of Hg 1?x Cd x Te studied with surface sensitive techniques  

Microsoft Academic Search

We report the use of surface sensitive electron spectroscopies to monitor the initial steps of formation of a native oxide\\u000a on atomically clean cleaved Hgl-xCdxTe single crystal surfaces in ultrahigh vacuum (UHV). Here the oxide is formed by oxygen excited by the presence of an operating\\u000a ion gauge. During the reaction, the composition of the surface region of the substrate

P. Morgen; J. A. Silberman; I. Lindau; W. E. Spicer; J. A. Wilson

1982-01-01

187

Oxidation characteristics of the electron beam surface-treated Alloy 617 in high temperature helium environments  

NASA Astrophysics Data System (ADS)

The oxidation characteristics of the electron beam surface-treated Alloy 617, which has an Al-rich surface layer, were evaluated in high temperature helium environments. Isothermal oxidation tests were performed in helium (99.999% purity) and VHTR-helium (helium of prototypical VHTR chemistry containing impurities like CO, CO2, CH4, and H2) environments at 900 °C for up to 1000 h. The surface-treated Alloy 617 showed an initial transient oxidation stage followed by the steady-state oxidation in all test environments. In addition, the steady-state oxidation kinetics of the surface-treated Alloy 617 was 2-order of magnitude lower than that of the as-received Alloy 617 in both helium environments as well as in air. The improvement in oxidation resistance was primarily due to the formation of the protective Al2O3 layer on the surface. The weight gain was larger in the order of air, helium, and VHTR-helium, while the parabolic rate constants (kp) at steady-state were similar for all test environments. In both helium environments, the oxide structure consisted of the outer transition Al2O3 with a small amount of Cr2O3 and inner columnar structured Al2O3 without an internal oxide. In the VHTR-helium environment, where the impurities were added to helium, the initial transient oxidation increased but the steady state kinetics was not affected.

Lee, Ho Jung; Sah, Injin; Kim, Donghoon; Kim, Hyunmyung; Jang, Changheui

2015-01-01

188

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

DOEpatents

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.

McKee, Rodney Allen (Kingston, TN); Walker, Frederick Joseph (Oak Ridge, TN)

1998-01-01

189

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

DOEpatents

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.

McKee, Rodney A. (Kingston, TN); Walker, Frederick J. (Oak Ridge, TN)

1995-01-01

190

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

PubMed

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

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

2015-02-14

191

High-energy-surface engineered metal oxide micro- and nanocrystallites and their applications.  

PubMed

Because many physical and chemical processes occur at surfaces, surface atomic structure is a critical factor affecting the properties of materials. Due to the presence of high-density atomic steps and edges and abundant unsaturated coordination sites, micro- and nanocrystallites with high-energy surfaces usually exhibit greater reactivity than those with low-energy surfaces. However, high-energy crystal surfaces are usually lost during crystal growth as the total surface energy is minimized. Therefore, the selective exposure of high-energy facets at the surface of micro- and nanocrystallites is an important and challenging research topic. Metal oxides play important roles in surface-associated applications, including catalysis, gas sensing, luminescence, and antibiosis. The synthesis of metal oxide micro- and nanocrystallites with specific surfaces, particularly those with high surface energies, is more challenging than the synthesis of metal crystals due to the presence of strong metal-oxygen bonds and diverse crystal structures. In this Account, we briefly summarize recent progress in the surface-structure-controlled synthesis of several typical metal oxide micro- and nanocrystallites, including wurtzite ZnO, anatase TiO2, rutile SnO2, and rocksalt-type metal oxides. We also discuss the improvement of surface properties, focusing on high-energy surfaces. Because of the huge quantity and diverse structure of metal oxides, this Account is not intended to be comprehensive. Instead, we discuss salient features of metal oxide micro- and nanocrystallites using examples primarily from our group. We first discuss general strategies for tuning the surface structure of metal oxide micro- and nanocrystallites, presenting several typical examples. For each example, we describe the basic crystallographic characteristics as well as the thermodynamic (i.e., tuning surface energy) or kinetic (i.e., tuning reaction rates) strategies we have used to synthesize micro- and nanocrystallites with high surface energies. We discuss the structural features of the specific facets and analyze the basis for the enhanced performance of the metal oxide micro- and nanocrystallites in water splitting, the degradation of organic pollutants, gas sensing, catalysis, luminescence, and antibiosis. Finally, we note the future trends in high-energy-facet metal oxide micro- and nanocrystallite research. A comprehensive understanding of the properties of metal oxide micro- and nanocrystallites with high-energy crystal surfaces and related synthetic strategies will facilitate the rational design of functional nanomaterials with desired characteristics. PMID:24341353

Kuang, Qin; Wang, Xue; Jiang, Zhiyuan; Xie, Zhaoxiong; Zheng, Lansun

2014-02-18

192

The Martian oxygen surface sink and its implications for the oxidant extinction depth  

NASA Astrophysics Data System (ADS)

Based on the evolution of the atmosphere-surface-interaction of Mars, one might expect a large oxygen surface sink over geologic time-scales. Due to intense oxidation of inorganic matter this led to the formation of considerable amounts of sulfates and ferric oxides on Mars. To model this effect several factors have to be under consideration: Inorganic composition of the Martian soil, amount of incorporated oxygen, meteoritic gardening, and the oxidant extinction depth. The oxygen incorporation has further implications for the assumed oxidant extinction depth, which is an important parameter to determine required sampling depths on Mars to find putative organic material.

Kolb, C.; Lammer, H.; Abart, R.; Ellery, A.; Edwards, H. G. M.; Cockell, C. S.; Patel, M. R.

2002-11-01

193

Ir-Surface enriched porous Ir-Co oxide hierarchical architecture for high performance water oxidation in acidic media.  

PubMed

The large-scale application of acidic water electrolysis as a viable energy storage technology has been hindered by the high demand of precious metal oxides at anode to catalyze the oxygen evolution reaction (OER). We report an Ir-Co binary oxide electrocatalyst for OER fabricated by a multistep process of selective leaching of Co from Co-rich composite oxides prepared through thermal decomposition. The stepwise leaching of the Co component from the composites leads to the formation of macro- and mesoscale voids walled by a cross-linked nanoporous network of rod- and wedge-like building units of Ir-Co binary oxide with a rutile phase structure and an Ir-enriched surface. In comparison, Ir-Co binary oxide with similar composition prepared by direct thermal decomposition method exhibits a loose nanoparticle aggregation morphology with a Co-enriched surface. The cross-linked porous Ir-Co binary oxide from selective leaching is about 3-fold more active for the OER than that from direct thermal decomposition. Compared with pure IrO2 from thermal decomposition, the Co-leached binary oxide is ca. two times more active and is much more durable during continuous oxygen evolution under a constant potential of 1.6 V, thus showing a possibility of reducing the demand of the expensive and scarce Ir in OER electrocatalyst for acidic water splitting. PMID:24984084

Hu, Wei; Zhong, Huawei; Liang, Wei; Chen, Shengli

2014-08-13

194

Oxidation of Germanium and Silicon surfaces (100): a comparative study through DFT methodology  

NASA Astrophysics Data System (ADS)

Density Functional Theory calculations are used to map out the preferential oxygen molecule adsorption sites and oxygen atom incorporation on germanium (100) surface. A comparison with primary oxidation mechanisms encountered in pure silicon and silicon germanium (100) surfaces is presented here. This study highlights opposite substrates behaviors facing oxygen molecule adsorption: 1/ surface germanium atoms move from their crystalline positions to adapt to the approaching oxygen molecule resulting in adsorbed peroxide bridge configuration, whereas oxygen molecule is fully dissociated in strand configuration on a silicon surface 2/ oxygen atoms tend to avoid each other on germanium surface whereas oxide nucleus can be observed on silicon surface even at the early steps of the oxidation process. Results show that germanium surface appears to be less reactive than the silicon substrate towards molecular oxygen species.

Mastail, C.; Bourennane, I.; Estève, A.; Landa, G.; Djafari Rouhani, M.; Richard, N.; Hémeryck, A.

2012-12-01

195

Patterning surface oxide nanostructures using atomic force microscope local anodic oxidation  

Microsoft Academic Search

We show how the analysis of the current detected during the fabrication of titanium oxide dots by AFM local anodic oxidation allows the determination of the optimal duration of bias voltage for obtaining nanostructures with higher aspect ratio. Experimental conditions to fabricate oxide dots and lines are discussed. Finally, we demonstrate that proper values of scan rate and period of

Tae Young Kim; Ermanno Di Zitti; Davide Ricci; Silvano Cincotti

2008-01-01

196

Vacancy segregation in the initial oxidation stages of the TiN(100) surface.  

PubMed

The well-known corrosion resistance and biocompatibility of TiN depend on the structural and chemical properties of the stable oxide film that forms spontaneously on its surface after exposure to air. In the present work, we focus on the atomistic structure and stability of the TiN(100) surface in contact with an oxidizing atmosphere. The early oxidation stages of TiN(100) are investigated by means of first-principles molecular dynamics (FPMD). We observe selective oxidation of Ti atoms and formation of an ultrathin Ti oxide layer, while Ti vacancies are left behind at the metal/oxide interface. Within the formalism of ab initio thermodynamics we compute the segregation energies of vacancies and vacancy clusters at the metal/oxide interface, comparing the stability of the system obtained by FPMD simulations with ideally reconstructed models. We find that the localization of Ti vacancies in the thin oxide layer and at the TiN/oxide interface is thermodynamically stable and may account for the early removal of N atoms from the interface by segregation of N vacancies from the bulk reservoir. We suggest that superficial oxidation may proceed along two distinct possible pathways: a thermodynamically stable path along the potential energy minimum surface and a metastable, kinetically driven path that results from the high heat release during the dissociation of O(2). PMID:19355771

Zimmermann, Janina; Finnis, Mike W; Ciacchi, Lucio Colombi

2009-04-01

197

Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides Wonyoung Lee and Bilge Yildiz  

E-print Network

Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides Wonyoung Lee is important to understand and enable design of cathode materials with optimal surface chemistry. Recently we segregation, a detrimental process on the surface of perovskite cathodes (1). Motivated by those results, here

Yildiz, Bilge

198

Effect of surface charge and electrode material on the size-dependent oxidation of surface-attached metal nanoparticles.  

PubMed

Here we report on the size-dependent oxidation of Au nanoparticles (NPs) electrodeposited directly on indium tin oxide-coated glass (glass/ITO) electrodes as compared to those chemically synthesized and electrostatically or drop-cast deposited onto aminopropyltriethoxysilane (APTES)-modified, mercaptopropyltrimethoxysilane (MPTMS)-modified, or unmodified glass/ITO electrodes. The peak oxidation potential (Ep) of 54 nm diameter Au NPs shifts by as much as 155 mV negative when deposited electrostatically on the highly positively charged glass/ITO/APTES surface and oxidized at low pH as compared to their oxidation on more neutral glass/ITO or glass/ITO/MPTMS surfaces at all pH's and on glass/ITO/APTES at neutral pH. Electrodeposited Au NPs on glass/ITO of similar size also oxidize at more positive potentials due to the neutral electrode surface charge. Ag NPs show a similar charge dependence on their Ep. Interestingly, the Ep value of Au and Ag NPs smaller than about 10 nm in diameter is independent of surface charge. The Ep of 9 nm diameter citrate-capped Ag NPs attached to Au, Pt, glassy carbon (GC), and glass/ITO electrodes electrostatically through short amine-terminated organic linkers depends on the electrode material, following the order (vs Ag/AgCl) of Au (384 ± 7 mV) ? Pt (373 ± 12 mV) > GC (351 ± 2 mV) > glass/ITO (339 ± 1 mV). The underlying electrode material affects the Ag NP Ep even though the NPs are not directly interacting with it. In addition to size, the electrode material and its surface charge have a strong influence on the oxidation potential of surface-confined metallic nanostructures. PMID:25260111

Masitas, Rafael A; Khachian, Irina V; Bill, Bryan L; Zamborini, Francis P

2014-11-01

199

Quantitative surface structure determination using in situ high-energy SXRD: Surface oxide formation on Pd(100) during catalytic CO oxidation  

NASA Astrophysics Data System (ADS)

We have performed a quantitative structure determination of the ?{5}×?{5}R27° surface oxide, formed on Pd(100) under semi-realistic conditions for catalytic CO oxidation, using in situ high-energy surface X-ray diffraction. We describe the experiment and the extraction of quantitative data in detail. The structural results are in agreement with previous reports of a system consisting of a single layer of PdO(101) formed in pure O2 on top of Pd(100) and studied under ultra-high vacuum conditions.

Shipilin, Mikhail; Hejral, Uta; Lundgren, Edvin; Merte, Lindsay R.; Zhang, Chu; Stierle, Andreas; Ruett, Uta; Gutowski, Olof; Skoglundh, Magnus; Carlsson, Per-Anders; Gustafson, Johan

2014-12-01

200

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

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

201

Analysis of surface oxides on an Fe12Cr alloy by reduction in a hydrogen flow  

Microsoft Academic Search

I have previously used a temperature-programmed reduction in hydrogen to identify surface oxides on nickel base alloys [1]. The reduction onset temperature of oxides depends on the cation-oxygen bond strength [2-6]. Sufficiently large differences in the reduction onset temperatures make identification of oxides possible [7-9]. The amount of water vapour produced as a result of the reduction is directly proportional

D. B. Goldman

1989-01-01

202

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

E-print Network

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

Goodman, Wayne

203

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

Microsoft Academic Search

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

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

2010-01-01

204

Surface modifications of iron oxide nanoparticles for biological applications  

E-print Network

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

Insin, Numpon

2011-01-01

205

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

SciTech Connect

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.

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

2007-04-01

206

Surface Attachment of Ammonia-Oxidizing Bacteria in Soil  

Microsoft Academic Search

Indigenous ammonia-oxidizing bacteria (AOB) in a clay loam soil were extremely difficult to release from soil particles compared\\u000a to most heterotrophic bacteria; less than 1% of indigenous AOB (estimated as potential ammonia oxidation rate) were extractable\\u000a by the dispersion-density-gradient centrifugation technique. This is at least 10-fold less than the extractability of heterotrophic\\u000a bacteria. Urea applications to the same soil induced

Å. Aakra; M. Hesselsøe; L. R. Bakken

2000-01-01

207

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces  

SciTech Connect

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.

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

2014-03-03

208

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

209

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

E-print Network

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

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

2014-01-01

210

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces  

NASA Astrophysics Data System (ADS)

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 Al2O3 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.

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

2014-03-01

211

External noise-induced phenomena in CO oxidation on single crystal surfaces  

E-print Network

small. Random patterns "raindrop patterns" observed in catalytic CO oxidation on Pt 110 at high pressure of external noise on minimalistic models for the catalytic CO oxidation on Ir 111 and Pt 111 is studied on the complex behavior of catalytic surface reactions has become a challenge in recent years. In general, the ef

Toral, Raúl

212

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

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

213

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

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

214

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

SciTech Connect

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.

Herrera, M.N.

1994-12-31

215

Enhanced Cell Integration to Titanium Alloy by Surface Treatment with Microarc Oxidation: A Pilot Study  

Microsoft Academic Search

Microarc oxidation (MAO) is a surface treatment that provides nanoporous pits, and thick oxide layers, and incorporates calcium\\u000a and phosphorus into the coating layer of titanium alloy. We presumed such modification on the surface of titanium alloy by\\u000a MAO would improve the ability of cementless stems to osseointegrate. We therefore compared the in vitro ability of cells to\\u000a adhere to

Young Wook Lim; Soon Yong Kwon; Doo Hoon Sun; Hyoun Ee Kim; Yong Sik Kim

2009-01-01

216

The impact of ultraviolet light on bacterial adhesion to glass and metal oxide-coated surface  

Microsoft Academic Search

Biofouling of glass and quartz surfaces can be reduced when the surface is coated with photocatalytically active metal oxides, such as TiO2 (anatase form) or SnO2. We measured the attachment of eight strains of bacteria to these two metal oxides (TiO2 and SnO2), and to an uncoated glass (control; designated Si-m) before and after exposure to UV light at wavelengths

Baikun Li; Bruce E. Logan

2005-01-01

217

X-ray photoelectron and scanning auger electron spectroscopic studies of oxidized graphite electrode surfaces  

SciTech Connect

The surfaces of electrochemically modified graphite electrodes have been studied using ESCA, scanning Auger microscopy, and chemical titration. Quantitative evaluation of surface functionalities after electro-oxidation in sulfuric acid provides an understanding of their mechanistic role in synthetic uses of the carbon electrode. Specifically concentrations of acid and phenolic groups are correlated with the level of oxidation on the electrode. A plateau is reached at between 4 and 22 C/cm/sup 2/.

Wandass, J.H.; Gardello, J.A. Jr.; Weinberg, N.L.; Bolster, M.E.; Salvati, L. Jr.

1987-11-01

218

Anion Adsorption on Oxide Surfaces: Inclusion of the Water  

E-print Network

surfaces (3), binding of medical implants in the human body (4), and theories about the origin of life (5 on thestructureandnumberofsurfacespecies,theirprotonation states, and even the proportion of inner- to outer-sphere surface complexes (6

Sverjensky, Dimitri A.

219

Origin of complex impact craters on native oxide coated silicon surfaces  

SciTech Connect

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.

Samela, Juha; Nordlund, Kai; Popok, Vladimir N.; Campbell, Eleanor E. B. [Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 Espoo (Finland); Department of Physics, Gothenburg University, 41296 Gothenburg (Sweden); Department of Physics, Gothenburg University, 41296 Gothenburg, Sweden and School of Chemistry, Edinburgh University, West Mains Road, Edinburgh EH9 3JJ, Scotland (United Kingdom)

2008-02-15

220

Outer Cell Surface Components Essential for Fe(III) Oxide Reduction by Geobacter metallireducens  

PubMed Central

Geobacter species are important Fe(III) reducers in a diversity of soils and sediments. Mechanisms for Fe(III) oxide reduction have been studied in detail in Geobacter sulfurreducens, but a number of the most thoroughly studied outer surface components of G. sulfurreducens, particularly c-type cytochromes, are not well conserved among Geobacter species. In order to identify cellular components potentially important for Fe(III) oxide reduction in Geobacter metallireducens, gene transcript abundance was compared in cells grown on Fe(III) oxide or soluble Fe(III) citrate with whole-genome microarrays. Outer-surface cytochromes were also identified. Deletion of genes for c-type cytochromes that had higher transcript abundance during growth on Fe(III) oxides and/or were detected in the outer-surface protein fraction identified six c-type cytochrome genes, that when deleted removed the capacity for Fe(III) oxide reduction. Several of the c-type cytochromes which were essential for Fe(III) oxide reduction in G. metallireducens have homologs in G. sulfurreducens that are not important for Fe(III) oxide reduction. Other genes essential for Fe(III) oxide reduction included a gene predicted to encode an NHL (Ncl-1–HT2A–Lin-41) repeat-containing protein and a gene potentially involved in pili glycosylation. Genes associated with flagellum-based motility, chemotaxis, and pili had higher transcript abundance during growth on Fe(III) oxide, consistent with the previously proposed importance of these components in Fe(III) oxide reduction. These results demonstrate that there are similarities in extracellular electron transfer between G. metallireducens and G. sulfurreducens but the outer-surface c-type cytochromes involved in Fe(III) oxide reduction are different. PMID:23183974

Smith, Jessica A.; Lovley, Derek R.

2013-01-01

221

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

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

223

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

PubMed

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

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

2013-02-01

224

Modeling and experimental studies of oxide covered metal surfaces  

SciTech Connect

The collaborative research effort of the Aqueous Group of the Corrosion Research Center has focussed on the physical, chemical, and electronic structure of native and anodically grown TiO{sub 2} films. The stability of Ti in corrosive environments is due entirely to the presence of the oxide film; thus, our goal is to correlate measurable structural parameters of the oxide film with the corrosion resistance that it imparts to the base metal. The fundamental nature of both theoretical and experimental approaches taken in studying TiO{sub 2} films will allow key factors underlying oxide film stability to be identified and translated to other materials. 44 refs., 1 tab., 7 figs.

Smyrl, W.H.; Halley, J.W.; Oriani, R.A.; White, H.S. (Minnesota Univ., Minneapolis, MN (USA). Corrosion Research Center); Toney, M.F.; Melroy, O.R. (International Business Machines Corp., Armonk, NY (USA))

1990-01-01

225

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

NASA Astrophysics Data System (ADS)

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

Entringer, Anthony G.

226

Controllable sealing of leaky alumina films on NiAl(100) surface by catalytic oxidation  

NASA Astrophysics Data System (ADS)

We show the oxide films grown by saturated dosing of oxygen on NiAl(100) is leaky, i.e., it has no apparent effect blocking deposited Co from diffusion into the bulk. We then show the easy paths for diffusion (presumably the boundaries between the oxide stripes) can be sealed by an oxidation process catalyzed by Co nanoparticles. Once sealed, the temperature range in which Co nanoparticles persist on the surface is extended by 400 K (up to 1100 K). Such "leak tight" oxide films could serve as better corrosion barrier and insulting layers.

Liu, Kuan-Te; Chen, Jian-Wei; Liao, Yu-Wen; Lin, Wen-Chin; Wu, Chii-Bin; Kuo, Chien-Cheng; Lin, Minn-Tsong; Song, Ker-Jar

2014-01-01

227

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

NASA Astrophysics Data System (ADS)

Micro-bumps are now being developed with diameters smaller than 10 ?m. 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- ?m 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 ?m 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.

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

2015-02-01

228

Ordered oxide layers on the pentagonal surface of AlPdMn quasicrystal  

NASA Astrophysics Data System (ADS)

Recently, we reported the structural investigation of the oxide layers grown on the pentagonal surface of icosahedral Al70Pd20Mn10 quasicrystal based on low-energy electron diffraction. The oxide layer was described to consist of five twin domains rotated by 2?/5 with respect to each other in accordance with the symmetry of the quasicrystalline substrate each of which having one twofold-symmetry direction of the substrate as a mirror plane. Here, we discuss the oxidation process in more detail and report the growth of different oxide structures depending on the sample temperature and its pretreatment. At room temperature, amorphous oxide layers form. In contrast five distinct and few-nanometer-large domains possessing an internal hexagonal structure with substantial amount of contribution from antiphase domain boundaries grow at 700-800 K for small and large coverage. In an intermediate range, a mixture of antiphase domain-boundary contributions and fractional-order spots characteristic to a 23(1×1)R±30° reconstruction of the surface oxide layer is found which additionally stabilized the interface. The previously reported twin-domain model, which was derived after an ion bombardment of the preoxidized surface with subsequent reoxidation, is identified as an oxide layer grown on the (110) surface of a crystalline Al50(PdMn)50 alloy as a result of the sputtering.

Burkardt, S.; Erbudak, M.

2010-02-01

229

Rates of oxidative weathering on the surface of Mars  

NASA Technical Reports Server (NTRS)

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.

Burns, Roger G.; Fisher, Duncan S.

1993-01-01

230

Shape-selective sieving layers on an oxide catalyst surface.  

PubMed

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

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

231

Rates of oxidative weathering on the surface of Mars  

NASA Astrophysics Data System (ADS)

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.

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

1993-02-01

232

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

233

Ferrous iron oxidation under acidic conditions - The effect of ferric oxide surfaces  

NASA Astrophysics Data System (ADS)

In this study, the kinetics of Fe(II) oxidation in the presence of the iron oxyhydroxides ferrihydrite, Si-ferrihydrite, schwertmannite, lepidocrocite and goethite are investigated over the pH range 4-5.5. Despite limited sorption of Fe(II), the rate of Fe(II) oxidation is up to 70-fold faster than in the absence of any Fe oxyhydroxide phase over pH 4.5-5.5. Enhanced Fe(II) oxidation was minor or negligible at pH 4 with undetectable amounts of Fe(II) adsorbed to the iron oxyhydroxides at this pH. Heterogeneous rate constants derived from kinetic modeling were normalized to the concentration of adsorbed Fe(II) and deviated by no more than 13.8% at pH 4.5, 5 and 5.5, indicating that oxidation is proportional to the concentration of adsorbed Fe(II). Average rate constants were found to be: 2.12 ± 0.20, 1.30 ± 0.09, 1.69 ± 0.22, 1.20 ± 0.08 and 0.68 ± 0.09 M-1 s-1 for ferrihydrite, goethite, lepidocrocite, schwertmannite and Si-ferrihydrite, respectively. The role of reactive oxygen species, such as hydrogen peroxide, the hydroxyl radical and superoxide, towards the overall oxidation of Fe(II) was examined but found to have only a minor impact on Fe(II) oxidation when compared to the effect of heterogeneous oxidation.

Jones, Adele M.; Griffin, Phillipa J.; Collins, Richard N.; Waite, T. David

2014-11-01

234

Desorption process of GaAs surface native oxide controlled by direct Ga-beam irradiation  

NASA Astrophysics Data System (ADS)

In this study, the native oxide desorption process at GaAs(1 0 0) surface triggered by direct Ga molecular beam irradiation was investigated at a temperature of 440°C in order to maintain surface flatness prior to molecular beam epitaxy (MBE). The oxide desorption process associated with the change in compositional and structural surface properties was characterized by in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM). With an increase in irradiated Ga dose, it is shown that an initial halo RHEED pattern from the native oxide layer transforms to a streaky one, indicating the desorption process taking place in a two-dimensional way with a decrease in oxide layer thickness. At a critical dose of 5.5×10 15 cm -2, which is confirmed by the change in RHEED intensities, the oxide layer is fully removed in conjunction with the smoothest surface morphology. Then the surface turns into a dark RHEED pattern corresponding to the accumulation of excess Ga in the form of droplets. The development of those surface properties monitored by RHEED is in good agreement with the change in root mean square (RMS) value of surface roughness obtained from AFM images. The minimum RMS roughness obtained is at the critical Ga dose, which is accurately controlled by RHEED measurements. The surface morphology treated at the critical Ga dose at 440°C is maintained even after high-temperature annealing at 600°C without causing deep pit. Therefore, the direct Ga-beam irradiation on GaAs oxide at 440°C is considered to be an effective method providing a deoxidized smooth surface prior to MBE growth without the need of a buffer layer.

Asaoka, Y.

2003-04-01

235

Cobalt(III) complexes as functional ligands for metal (oxide) surfaces.  

PubMed

Co(III) polyamine complexes with either two or three labile coordination sites bind strongly to high surface area metal oxides such as goethite or aluminium trihydroxide, and have been shown to act as passivating agents for aluminium flake in aqueous media, in addition to providing a potential method for surface functionalisation. PMID:22908118

Cooper, Rachel J; Jane, Reuben T; Jeffs, Thomas E; Hartshorn, Richard M; Tasker, Peter A

2012-10-01

236

Titanium implants with oxidized surfaces: the background and long-term results  

Microsoft Academic Search

The purpose of this paper is to give an overview of different implant surface modification technologies—including the presentation of a new technique, involving the formation of a ceramic titanium oxide coating. Three techniques are used to modify metal surfaces: (1) addition of material, (2) removal of material and (3) modification of material already present, e.g. by means of laser or

Christian Toth; György Szabó; Lajos Kovács; Kálmán Vargha; József Barabás; Zsolt Németh

2002-01-01

237

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

E-print Network

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

Henkelman, Graeme

238

Effects of electrolyzed oxidizing water on reducing Listeria monocytogenes contamination on seafood processing surfaces  

Microsoft Academic Search

The effects of electrolyzed oxidizing (EO) water on reducing Listeria monocytogenes contamination on seafood processing surfaces were studied. Chips (5×5 cm2) of stainless steel sheet (SS), ceramic tile (CT), and floor tile (FT) with and without crabmeat residue on the surface were inoculated with L. monocytogenes and soaked in tap or EO water for 5 min. Viable cells of L.

Chengchu Liu; Jingyun Duan; Yi-Cheng Su

2006-01-01

239

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

SciTech Connect

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.

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

240

A study of adsorption of fully atomistic oligomers on aluminum oxide surfaces  

Microsoft Academic Search

Phosphate oligomers are widely applied as important primers in coating on aluminum oxide surfaces. Detailed conformational properties of these oligomers upon adsorbing onto the substrates provides insight into the process of the adsorption as well as the ability of the coatings to prevent water and other small molecules diffusion. The values of the binding energies per unit surface area can

Qiyun Emily Ou

1997-01-01

241

Surfactant Organic Molecules Restore Magnetism in Metal-Oxide Nanoparticle Surfaces  

E-print Network

Surfactant Organic Molecules Restore Magnetism in Metal-Oxide Nanoparticle Surfaces Juan Salafranca, Nashville, Tennessee 37235, United States *S Supporting Information ABSTRACT: The properties of magnetic nanoparticles tend to be depressed by the unavoidable presence of a magnetically inactive surface layer. However

Pennycook, Steve

242

Surface rumpling of a (Ni, Pt)Al bond coat induced by cyclic oxidation  

Microsoft Academic Search

The surface of an initially flat, platinum-modified nickel aluminide bond coat formed on a single crystal superalloy is shown to progressively roughen (“rumple”) with thermal cycling in air. Far less surface roughening occurs after isothermal oxidation or after the same number of thermal cycles but with a shorter high-temperature exposure in each cycle. Mechanisms of the observed rumpling and the

V. K Tolpygo; D. R Clarke

2000-01-01

243

Quantitative measurement of the surface silicon interstitial boundary condition and silicon interstitial injection into silicon during oxidation  

E-print Network

Quantitative measurement of the surface silicon interstitial boundary condition and silicon interstitial injection into silicon during oxidation M. S. Carroll* and J. C. Sturm Department of Electrical the oxidation of silicon, interstitials are generated at the oxidizing surface and diffuse into the silicon

244

Graphene Oxide: Surface Activity and Two-Dimensional By Franklin Kim, Laura J. Cote, and Jiaxing Huang*  

E-print Network

Graphene Oxide: Surface Activity and Two-Dimensional Assembly By Franklin Kim, Laura J. Cote in graphite oxide has been rapidly growing, largely towards graphene-related applications such as transistors of a graphite oxide single layer, now often termed graphene oxide (GO), is around 1 nm, as measured by atomic

Huang, Jiaxing

245

Hydrogen transport through oxide metal surface under atom and ion irradiation  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

246

Ester oxidation on an aluminum surface using chemiluminescence  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

247

Effects of surface charges of graphene oxide on neuronal outgrowth and branching.  

PubMed

Graphene oxides with different surface charges were fabricated from carboxylated graphene oxide by chemical modification with amino- (-NH2), poly-m-aminobenzene sulfonic acid- (-NH2/-SO3H), or methoxyl- (-OCH3) terminated functional groups. The chemically functionalized graphene oxides and the carboxylated graphene oxide were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, UV-Vis spectrometry, ? potential measurements, field emission scanning electron microscopy, and contact angle analyses. Subsequently, the resulting graphene oxides were used as substrates for culturing primary rat hippocampal neurons to investigate neurite outgrowth and branching. The morphological features of neurons that directly reflect their potential capability in synaptic transmission were characterized. The results demonstrate that the chemical properties of graphene oxide can be systematically modified by attaching different functional groups that confer known characteristics to the substrate. By manipulating the charge carried by the functionalized graphene oxides, the outgrowth and branching of neuronal processes can be controlled. Compared with neutral, zwitterionic, or negatively charged graphene oxides, positively charged graphene oxide was found to be more beneficial for neurite outgrowth and branching. The ability to chemically modify graphene oxide to control neurite outgrowth could be implemented clinically, especially in cases wherein long-term presence of outgrowth modulation is necessary. PMID:24162459

Tu, Qin; Pang, Long; Chen, Yun; Zhang, Yanrong; Zhang, Rui; Lu, Bingzhang; Wang, Jinyi

2014-01-01

248

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

PubMed

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 ?-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

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

249

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

SciTech Connect

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).

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

1999-02-15

250

Intermolecular potential energy surface and thermophysical properties of ethylene oxide.  

PubMed

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

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

2014-10-28

251

Intermolecular potential energy surface and thermophysical properties of ethylene oxide  

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

252

Aspirin degradation in surface-charged TEMPO-oxidized mesoporous crystalline nanocellulose.  

PubMed

TEMPO-mediated surface oxidation of mesoporous highly crystalline Cladophora cellulose was used to introduce negative surface charges onto cellulose nanofibrils without significantly altering other structural characteristics. This enabled the investigation of the influence of mesoporous nanocellulose surface charges on aspirin chemical stability to be conducted. The negative surface charges (carboxylate content 0.44±0.01 mmol/g) introduced on the mesoporous crystalline nanocellulose significantly accelerated aspirin degradation, compared to the starting material which had significantly less surface charge (0.06±0.01 mmol/g). This effect followed from an increased aspirin amorphisation ability in mesopores of the oxidized nanocellulose. These results highlight the importance of surface charges in formulating nanocellulose for drug delivery. PMID:24291076

Carlsson, Daniel O; Hua, Kai; Forsgren, Johan; Mihranyan, Albert

2014-01-30

253

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

NASA Astrophysics Data System (ADS)

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.

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

2012-01-01

254

Monday, November 5, 2007 -9:30 AM Real-Time Surface-Chemistry of Arsenite Oxidation by Hydrous Manganese Oxide.  

E-print Network

Monday, November 5, 2007 - 9:30 AM 91-1 Real-Time Surface-Chemistry of Arsenite Oxidation by Hydrous Manganese Oxide. Matthew Ginder-Vogel and Donald L. Sparks. University of Delaware, 152 Townsend Hall, Dept of Plant and Soil Sciences, Newark, DE 19716 Arsenite (As(III)) oxidation to arsenate (As

Sparks, Donald L.

255

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...

256

Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex  

PubMed Central

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

Piccinin, Simone; Sartorel, Andrea; Aquilanti, Giuliana; Goldoni, Andrea; Bonchio, Marcella; Fabris, Stefano

2013-01-01

257

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

NASA Technical Reports Server (NTRS)

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.

Dias, S.; Wightman, J. P.

1982-01-01

258

Surface Electronic Structure and Chemisorption on Corundum Transition-Metal Oxides  

Microsoft Academic Search

The surface electronic structures of all of the conducting corundum oxides of the fourth-period transition -metals have been studied using an ultra-high vacuum (UHV), multiple-technique surface analysis system. This system, which permits comprehensive determination of surface properties, includes ultra-violet and x-ray photoemission, low energy electron diffraction (LEED), Auger electron spectroscopy, and electron energy-loss spectroscopy. The complementary nature of the information

Richard Leigh Kurtz

1983-01-01

259

Hydration of calcium oxide surface predicted by reactive force field molecular dynamics.  

PubMed

In this work, we present the parametrization of Ca-O/H interactions within the reactive force field ReaxFF, and its application to study the hydration of calcium oxide surface. The force field has been fitted using density functional theory calculations on gas phase calcium-water clusters, calcium oxide bulk and surface properties, calcium hydroxide, bcc and fcc Ca, and proton transfer reactions in the presence of calcium. Then, the reactive force field has been used to study the hydration of the calcium oxide {001} surface with different water contents. Calcium oxide is used as a catalyzer in many applications such as CO(2) sequestration and biodiesel production, and the degree of surface hydroxylation is a key factor in its catalytic performance. The results show that the water dissociates very fast on CaO {001} bare surfaces without any defect or vacancy. The surface structure is maintained up to a certain amount of water, after which the surface undergoes a structural rearrangement, becoming a disordered calcium hydroxyl layer. This transformation is the most probable reason for the CaO catalytic activity decrease. PMID:22316164

Manzano, Hegoi; Pellenq, Roland J M; Ulm, Franz-Josef; Buehler, Markus J; van Duin, Adri C T

2012-03-01

260

Surface modification of surface sol–gel derived titanium oxide films by self-assembled monolayers (SAMs) and non-specific protein adsorption studies  

Microsoft Academic Search

Biological events occurring at the implant–host interface, including protein adsorption are mainly influenced by surface properties of the implant. Titanium alloys, one of the most widely used implants, has shown good biocompatibility primarily through its surface oxide. In this study, a surface sol–gel process based on the surface reaction of metal alkoxides with a hydroxylated surface was used to prepare

Maria Advincula; Xiaowu Fan; Jack Lemons; Rigoberto Advincula

2005-01-01

261

Adsorption of Pb, Cd to Fe, Mn oxides in natural freshwater surface coatings developed in different seasons.  

PubMed

Metal oxides( Fe, Mn oxides) in natural surface coatings(biofilms and associated minerals) are believed to play a significant role in the fate and transport of trace metal in aquatic environments. Seasonal variation of Fe, Mn oxides and organic materials in surface coatings, which were developed periodically on glass slides in Nanhu Lake, Jilin Province, China over the time frame of three seasons, was investigated in order to understand the influence of metal oxides on Pb and Cd adsorption to heterogeneous surface coating materials (biofilm). Pb and Cd adsorption was measured under controlled laboratory conditions(mineral salts solution with defined speciation, ionic strength 0.05 mol/L, 25 degrees C and pH 6.0). The classical Langmuir adsorption isotherm was applied to estimate equilibrium coefficients of Pb and Cd adsorption to the surface coatings. In general, components in the surface coatings varied greatly with seasons altering and obtained higher concentrations in summer while the content of iron oxides always exceeded that of manganese oxides. Correlation analyses between the maximum adsorption of Pb and Cd and components in the surface coatings developed periodically indicated that Pb phase association with Mn oxides and Cd phase association with Fe oxides as well as Mn oxides were statistically significant. Effect of Mn oxides on Cd adsorption was confirmed in view of its higher content in the surface coatings. The importance of ferromanganese oxides for Pb and Cd adsorption to the natural surface coatings developed in different seasons was evidenced. PMID:15900753

Dong, De-ming; Yang, Fan; Li, Yu; Hua, Xiu-yi; Lü, Xiao-jun; Zhang, Jing-jing

2005-01-01

262

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

PubMed

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

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

2012-05-01

263

Surface functionalization of fluorine-doped tin oxide samples through electrochemical grafting.  

PubMed

Transparent conductive oxides are emerging materials in several fields, such as photovoltaics, photoelectrochemistry, and optical biosensing. Their high chemical inertia, which ensured long-term stability on one side, makes challenging the surface modification of transparent conductive oxides; long-term robust modification, high yields, and selective surface modifications are essential prerequisite for any further developments. In this work, we aim at inducing chemical functionality on fluorine-doped tin oxide surfaces (one of the most inexpensive transparent conductive oxide) by means of electrochemical grafting of aryl diazonium cations. The grafted layers are fully characterized by photoemission spectroscopy, cyclic voltammetry, and atomic force microscopy showing linear correlation between surface coverage and degree of modification. The electrochemical barrier effect of modified surfaces was studied at different pH to characterize the chemical nature of the coating. We showed immuno recognition of biotin complex built onto grafted fluorine-doped tin oxides, which opens the perspective of integrating FTO samples with biological-based devices. PMID:24171474

Lamberti, F; Agnoli, S; Brigo, L; Granozzi, G; Giomo, M; Elvassore, N

2013-12-26

264

Iron oxidation kinetics and phosphate immobilization along the flow-path from groundwater into surface water  

NASA Astrophysics Data System (ADS)

The retention of phosphorus in surface waters through co-precipitation of phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich groundwater is not well understood. We developed an experimental field set-up to study Fe(II) oxidation and P immobilization along the flow-path from groundwater into surface water 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. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and surface water, we investigated Fe(II) oxidation kinetics and P immobilization processes. The oxidation rate inferred from our field measurements closely agreed with the general rate law for abiotic oxidation of Fe(II) by O2. Seasonal changes in climatic conditions affected the Fe(II) oxidation process. Lower pH and lower temperatures in winter (compared to summer) resulted in low Fe oxidation rates. After exfiltration to the surface water, it took a couple of days to more than a week before complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates were much higher. The Fe concentrations in the exfiltrated groundwater were low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into a ditch. While the Fe oxidation rates reduce drastically from summer to winter, P concentrations remained high in the groundwater and an order of magnitude lower in the surface water throughout the year. This study shows very fast immobilization of dissolved P during the initial stage of the Fe(II) oxidation process which results in P-depleted water before Fe(II) is completely depleted. This cannot be explained by surface complexation of phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox gradients seems an important geochemical mechanism in the transformation of dissolved phosphate to structural phosphate and, therefore, a major control on the P retention in natural waters that drain anaerobic aquifers.

van der Grift, B.; Rozemeijer, J. C.; Griffioen, J.; van der Velde, Y.

2014-11-01

265

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

266

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

NASA Technical Reports Server (NTRS)

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.

Napier, Mary E.; Stair, Peter C.

1992-01-01

267

Oxidation of coal and coal pyrite mechanisms and influence on surface characteristics. [Coal pyrite electrodes  

SciTech Connect

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.

Doyle, F.M.

1992-01-01

268

The formation of a surface layer during microarc oxidation of aluminum alloys  

NASA Astrophysics Data System (ADS)

The formation of a surface layer during microarc oxidation has been investigated. The results of experimental studies aimed at determining the structure and composition of oxide coatings on aluminum alloys are presented. The studies found out that, in contrast to existing ideas about the initial stages of micro-arc oxidation, a "barrier layer" grows unevenly over the sample area and there is no clear boundary between a pre-spark and a spark mode of the process. Uneven growth of a " barrier layer " is connected with different distribution of electric field on the surface of a sample and different concentration of electrolyte components. Depending on the electrolytes used the inside coating layers consist mainly of aluminium oxide, and the outer layers contain components formed as a result of thermochemical transformation of the electrolyte.

Mikheev, A. Ye; Girn, A. V.; Vakhteev, E. V.; Alekseeva, E. G.; Ravodina, D. V.

2015-01-01

269

Oxidized GaN(0001) Surfaces studied by Scanning Tunneling Microscopy and Spectroscopy and by First-Principles Theory  

E-print Network

1 Oxidized GaN(0001) Surfaces studied by Scanning Tunneling Microscopy and Spectroscopy Abstract Oxidized Ga-polar GaN surfaces have been studied both experimentally and theoretically. For in tunneling spectroscopy revealed a surface band gap with size close to that of GaN, indicating that any

Feenstra, Randall

270

The Nature of Surface Oxides on Corrosion-Resistant Nickel Alloy Covered by Alkaline Water  

PubMed Central

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

2010-01-01

271

Surface properties of zirconium oxide and its catalytic activity for isomerization of 1-butene  

Microsoft Academic Search

Surface properties of zirconium oxide and its catalytic activity for isomerization of 1-butene isomerization, and its cis\\/trans selectivity were tested on catalysts calcined at 300°⁻⁹°°sup 0\\/C and correlated to the acidity, measured by IR spectroscopy of adsorbed pyridine; basicity measured by adsorption of COâ or ESR spectroscopy of adsorbed diphenylamine and oxygen; oxidizing sites, measured by ESR spectroscopy of adsorbed

Y. Nakano; T. Iizuka; H. Hattori; K. Tanabe

1979-01-01

272

Formation of titanium oxide films on the surface of porous silicon carbide  

Microsoft Academic Search

The influence of rapid thermal annealing (RTA) on the properties of a titanium film on the surface of porous silicon carbide\\u000a is considered. It is shown that an increase in the RTA temperature to 900°C stabilizes the phase composition of the forming\\u000a titanium oxide over the film, which is identified as rutile. Due to the formation of titanium oxide nanoclusters

Yu. Yu. Bacherikov; N. L. Dmitruk; R. V. Konakova; O. S. Kondratenko; V. V. Milenin; O. B. Okhrimenko; L. M. Kapitanchuk; A. M. Svetlichnyi; N. N. Moskovchenko

2008-01-01

273

New surface treatment using shot blast for improving oxidation resistance of TiAl-base alloys  

Microsoft Academic Search

A new surface treatment using shot blasts with WO3 powder has been developed. This has been most effective in improving the cyclic oxidation resistance of TiAl-base alloy in air and in a diesel engine exhaust gas atmosphere of up to 1223 K. This effect is attributed to the formation of an Al2O3 layer in an oxidation atmosphere. The above layer

Hiroyuki Kawaura; Hiroshi Kawahara; Kazuaki Nishino; Takashi Saito

2002-01-01

274

Ordered oxide layers on the pentagonal surface of AlPdMn quasicrystal  

Microsoft Academic Search

Recently, we reported the structural investigation of the oxide layers grown on the pentagonal surface of icosahedral Al70Pd20Mn10 quasicrystal based on low-energy electron diffraction. The oxide layer was described to consist of five twin domains rotated by 2pi\\/5 with respect to each other in accordance with the symmetry of the quasicrystalline substrate each of which having one twofold-symmetry direction of

S. Burkardt; M. Erbudak

2010-01-01

275

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

SciTech Connect

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.

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

2011-12-14

276

Characterization study of native oxides on GaAs(100) surface by XPS  

NASA Astrophysics Data System (ADS)

In order to know more about the surface state of GaAs(100) epitaxial wafer during a storage period of two years, the XPS analysis was carried out four times on the surface, respectively polished by chemical etching, stored in desiccator for half a year, one year and two years. The results indicated that even after cleaned by proper etchant solutions, the fresh surface was slightly oxidized with Ga2O3, As2O3 and organic contaminant. The epi-wafer was always exposed to air during the storage period, so more and more oxides turned out. The mixed oxide layer comprised of C-OR, COOR, Ga2O3, As2O3 and As2O5 appeared after only half a year. In the ageing process of two years, the oxide types of gallium or arsenic did not change with stable content of Ga2O3 and remarkably fluctuating relative contents of As2O3 and As2O5. Based on the intensity ratio of Ga 3d-Ga2O3 to Ga 3d-GaAs, the thickness of oxide layer was estimated. The oxide layer generated after chemical polishing was very thin, just only 0.435nm thick, and then it grew rapidly, approximately 1.822nm after one year while almost no change any more subsequently. It was indicated that after the epi-wafer was stored for one year, because of volatile As2O3 or As2O5, there remained a large amount of Ga2O3 in oxide layer, which prevented the reactions between bulk material and oxide layer with oxygen. So native oxide layer plays a role as passive film to protect epi-wafer against the environment during a long storage period.

Feng, Liu; Zhang, Lian-dong; Liu, Hui; Gao, Xiang; Miao, Zhuang; Cheng, Hong-chang; Wang, Long; Niu, Sen

2013-08-01

277

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

PubMed

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

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

2014-05-19

278

Surface-modified carbon nanotubes catalyze oxidative dehydrogenation of n-butane.  

PubMed

Butenes and butadiene, which are useful intermediates for the synthesis of polymers and other compounds, are synthesized traditionally by oxidative dehydrogenation (ODH) of n-butane over complex metal oxides. Such catalysts require high O2/butane ratios to maintain the activity, which leads to unwanted product oxidation. We show that carbon nanotubes with modified surface functionality efficiently catalyze the oxidative dehydrogenation of n-butane to butenes, especially butadiene. For low O2/butane ratios, a high selectivity to alkenes was achieved for periods as long as 100 hours. This process is mildly catalyzed by ketonic CO groups and occurs via a combination of parallel and sequential oxidation steps. A small amount of phosphorus greatly improved the selectivity by suppressing the combustion of hydrocarbons. PMID:18832641

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

2008-10-01

279

First Principles Studies of Water and Ice on Oxide Surfaces  

E-print Network

and donate H bonds) of the hydroxylated kaolinite surface is key to its many properties with regard to water and recombination of the water molecules within the dimers. Overall, it is hoped that these studies shed new light background 20 3.1 Electronic structure theory . . . . . . . . . . . . . . . . . . . . . . . 20 3.1.1 Born

Alavi, Ali

280

Photoemission of surface oxides and hydrides of delta plutonium  

NASA Astrophysics Data System (ADS)

High resolution photoelectron spectroscopy (PES) studies were conducted on a gallium stabilized ?-phase plutonium sample cleaned by laser ablation and gas dosed with O 2 and H 2. The measurements were made with an instrument resolution of 60 meV with the sample at 300 K, 77 K and 10 K. The PES data under these experimental conditions strongly support an idealized model with Pu 2O 3 growth on the metal followed by PuO 2 growth on the Pu 2O 3 layer at low temperature. In vacuum, the PuO 2 reduces to Pu 2O 3 at room temperature at a pressure of 6 × 10 -11 Torr. In the case of H 2 dosing of the surface at low temperature, the hydrogen appears to penetrate the surface and disrupt the electronic structure of the valence band as evidenced by a drop in intensity of the peak at E F which is not accompanied by a drop in the main 5f manifold at ˜1 eV. Studies were also carried out on the dosing of hydrogen on surfaces already dosed with both 0.5 L (Pu 2O 3) and 10 L (PuO 2) oxygen films and show that hydrogen penetrates the 0.5 L Pu 2O 3 covered surface.

Butterfield, M. T.; Durakiewicz, T.; Guziewicz, E.; Joyce, J. J.; Arko, A. J.; Graham, K. S.; Moore, D. P.; Morales, L. A.

2004-11-01

281

An unusual surface peroxiredoxin protects invasive Entamoeba histolyticafrom oxidant attack  

Microsoft Academic Search

Peroxiredoxins are an important class of antioxidant enzymes found from Archaea to humans, which reduce and thereby detoxify peroxides and peroxynitrites. The major thiol-containing surface antigen of the invasive ameba, Entamoeba histolytica, is a peroxiredoxin and is likely to be important during the transition from the anaerobic environment of the large intestine to human tissues. The closely related species, Entamoeba

Min-Ho Choia; Dana Sajed; Leslie Poole; Ken Hirata; Scott Herdman; Bruce E. Torian; Sharon L. Reed

2005-01-01

282

Oxidation of graphitic carbon on a Pt(111) surface  

NASA Astrophysics Data System (ADS)

The interaction of graphitic carbon with dissociatively adsorbed oxygen was investigated by thermal desorption mass spectroscopy (TDS), Auger electron spectroscopy (AES) and measurements of the change ?? of the work function ?. Carbon coverages on the Pt(111) surface were produced by different C 2H 4 exposures at 850 K, resulting in immobile graphite islands. The reaction of the carbon atoms at the boundaries of these islands with mobile oxygen adatoms yields the formation and desorption of CO 2 (550-800 K) and CO (700-1100 K). The time te, for a complete removal of the carbon depends strongly on the initial carbon coverage and is proportional to the reciprocal oxygen partial pressure, whereas for T ? 700 K te does not depend significantly on the surface temperature. The experimental results can be described quantitatively by a model considering the linear decrease of the oxygen sticking coefficient with growing carbon coverage. The comparison of the results with those for the reaction between sulfur and oxygen on a Pt(111) surface [Surface Sci. 136 (1984) 243] demonstrates the different poisoning effects of carbon and sulfur.

Schäfer, L.; Wassmuth, H.-W.

1989-01-01

283

Growth morphology of thin films on metallic and oxide surfaces.  

PubMed

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

Krupski, Aleksander

2014-02-01

284

Faraday Discussion # 114 The Surface Science of Metal Oxides  

E-print Network

. Jennison# and A. Bogicevic Surface and Interface Sciences Department 1114 Sandia National Laboratories island nucleation. Common point defects (vacancies, pairs of vacancies, and water by-products) were and growth on -Al2O3(0001) was investi- gated. While Born-Haber calculations show wetting

Jennison, Dwight R.

285

Modification of the sintering kinetics of palladium by a surface oxide  

NASA Astrophysics Data System (ADS)

The presence of a surface oxide layer on palladium powders gives rise to a densification-free sintering process controlled by a surface diffusion mechanism with an activation energy of 59.2 kJ/mol-1. At temperatures above the oxide dissociation temperature in air, 1062 K, palladium powders sinter with an activation energy of 120.4 kJ/mol"1, indicative of a grain boundary diffusion. At T < 1061 K and under a 10-8 atm vacuum, sintered powders showed densification but with an activation energy too high to be grain boundary diffusion-related. These results are interpreted in terms of the role of the surface oxide and are compared with previously published results on the sintering of Pd.

Higgins, P. K.; Munir, Z. A.

1981-09-01

286

High temperature oxidation behavior of AISI 304L stainless steel-Effect of surface working operations  

NASA Astrophysics Data System (ADS)

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 ?S 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.

Ghosh, Swati; Kumar, M. Kiran; Kain, Vivekanand

2013-01-01

287

Chlorine activation indoors and outdoors via surface-mediated reactions of nitrogen oxides with hydrogen chloride  

PubMed Central

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

Raff, Jonathan D.; Njegic, Bosiljka; Chang, Wayne L.; Gordon, Mark S.; Dabdub, Donald; Gerber, R. Benny; Finlayson-Pitts, Barbara J.

2009-01-01

288

Surface patterning of mesoporous niobium oxide films for solar energy conversion.  

PubMed

An array of periodic surface features were patterned on mesoporous niobium oxide films by a soft-lithographic technique with the goal of constructing a photonic crystal (PC) structure on the back side of the oxide. The oxide films, fabricated by mixing sol-gel derived niobium oxide nanoparticles and hydroxypropyl cellulose, were employed as photoelectrodes in dye-sensitized solar cells (DSSCs), and their performance evaluated against their flat counterparts. The surface patterns were imprinted using a photocurable perfluoropolyether (PFPE) soft-replica of a silicon master with a two-dimensional array of cylindrical posts (200 nm (D) × 200 nm (H)) in hexagonal geometry. The PC on the niobium oxide surface caused large changes in optical measurements, particularly in the blue wavelengths. To evaluate the optical effect on solar energy conversion, the incident photon-to-current conversion efficiency (IPCE) was measured in the patterned devices and the control group. The IPCE of patterned niobium oxide anodes exhibited a relative enhancement in photocurrent generation over the wavelength range corresponding to the higher absorption in optical measurements. PMID:23534849

Ok, Myoung-Ryul; Ghosh, Rudresh; Brennaman, M Kyle; Lopez, Rene; Meyer, Thomas J; Samulski, Edward T

2013-04-24

289

Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy.  

PubMed

Surfaces of thin oxide ?lms 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., F(0), F(+), F(2+) and divacancies, have different effects on the contact potential. These differences enabled classi?cation 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 F(2+)-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 ?lms beyond imaging the topography of the surface atoms. PMID:21977410

König, Thomas; Simon, Georg H; Heinke, Lars; Lichtenstein, Leonid; Heyde, Markus

2011-01-01

290

Increased reactivity and in vitro cell response of titanium based implant surfaces after anodic oxidation.  

PubMed

In the quest for improved bone growth and attachment around dental implants, chemical surface modifications are one possibility for future developments. The biological properties of titanium based materials can be further enhanced with methods like anodic polarization to produce an active rather than a passive titanium oxide surface. Here we investigate the formation of hydroxide groups on sand blasted and acid etched titanium and titanium-zirconium alloy surfaces after anodic polarization in an alkaline solution. X-ray photoelectron spectroscopy shows that the activated surfaces had increased reactivity. Furthermore the activated surfaces show up to threefold increase in OH(-) concentration in comparison to the original surface. The surface parameters Sa, Sku, Sdr and Ssk were more closely correlated to time and current density for titanium than for titanium-zirconium. Studies with MC3T3-E1 osteoblastic cells showed that OH(-) activated surfaces increased mRNA levels of osteocalcin and collagen-I. PMID:23912792

Walter, M S; Frank, M J; Sunding, M F; Gómez-Florit, M; Monjo, M; Bucko, M M; Pamula, E; Lyngstadaas, S P; Haugen, H J

2013-12-01

291

Enhanced ultraviolet sensitivity of zinc oxide nanoparticle photoconductors by surface passivation  

NASA Astrophysics Data System (ADS)

Zinc oxide nanoparticles were created by a top-down wet-chemical etching process and then coated with polyvinyl-alcohol (PVA), exhibiting sizes ranging from 10 to 120 nm with an average size approximately 80 nm. The PVA layer provides surface passivation of zinc oxide nanoparticles. As a result of PVA coating, enhancement in ultraviolet emission and suppression of parasitic green emission is observed. Photoconductors fabricated using the PVA coated zinc oxide nanoparticles exhibited a ratio of ultraviolet photo-generated current to dark current as high as 4.5 × 104, 5 times better than that of the devices fabricated using uncoated ZnO nanoparticles.

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

2011-01-01

292

Formation of titanium oxide films on the surface of porous silicon carbide  

NASA Astrophysics Data System (ADS)

The influence of rapid thermal annealing (RTA) on the properties of a titanium film on the surface of porous silicon carbide is considered. It is shown that an increase in the RTA temperature to 900°C stabilizes the phase composition of the forming titanium oxide over the film, which is identified as rutile. Due to the formation of titanium oxide nanoclusters under the action of RTA, an additional photoluminescence band arises near 2.5 eV. Based on Auger spectrometry data, a multilayer model to calculate the optical parameters of titanium oxide films covering porous silicon carbide is suggested.

Bacherikov, Yu. Yu.; Dmitruk, N. L.; Konakova, R. V.; Kondratenko, O. S.; Milenin, V. V.; Okhrimenko, O. B.; Kapitanchuk, L. M.; Svetlichnyi, A. M.; Moskovchenko, N. N.

2008-09-01

293

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

PubMed

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

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

2014-01-01

294

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

PubMed Central

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

2014-01-01

295

Surface acidity of silica-titania mixed oxides  

SciTech Connect

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

Odenbrand, C.U.I.; Brandin, J.G.M. (Lund Univ. (Sweden)); Busca, G. (Univ. di Genova (Italy))

1992-06-01

296

Reduction of nitric oxide with carbon monoxide on the Rh(100) single-crystal surface  

SciTech Connect

The reduction of nitric oxide with carbon monoxide has been investigated on the Rh(100) single-crystal surface. Steady-state kinetic measurements, at 688 K and in the pressure range 1.0 to 1800 Pa, indicate that this process proceeds via a Langmuir-Hinshelwood-type mechanism and is selective toward the production of N/sub 2/ and CO/sub 2/. The carbon monoxide kinetic order varied continuously from +1 to -1 as the partial pressure of CO was increased from 1 to 250 Pa, at a constant NO partial pressure of 57.5 Pa. In a similar manner, the nitric oxide kinetic order varied continuously from +3/2 to -1 as the partial pressure of NO was increased from 1 to 1800 Pa, at a constant CO partial pressure of 44.0 Pa. The catalyst surface was characterized with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and thermal desorption spectroscopy (TDS). Initial Auger analysis revealed surface contamination by sulfur, phosphorus, and boron. These contaminants were removed via cycles of argon ion bombardment, reactive ion bombardment, and high-temperature annealing. Nitric oxide adsorbed with a high sticking coefficient and formed a c(2 x 2) ordered overlayer at saturation. The nitric oxide adsorbate dissociated upon slow stepwise heating as indicated by the production of a surface oxide and disappearance of surface nitrogen. Thermal desorption experiments at a faster heating rate indicated, however, that most of the adsorbed nitric oxide desorbed molecularly in a first-order process with a peak at 401 K during the temperature flash. Carbon monoxide adsorbs molecularly in two distinct sites with desorption from both following first-order kinetics with TDS peaks at 373 and 425 K. A kinetic model was developed which is consistent with both the steady-state kinetic and surface characterization results.

Hendershot, R.E.; Hansen, R.S.

1986-03-01

297

Iron oxidation kinetics and phosphorus immobilization at the groundwater-surface water interface  

NASA Astrophysics Data System (ADS)

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, with Fe(II) oxidation taking place in the soil surrounding the ditch during summer and in the surface water during winter. The dynamics in Fe(II) oxidation did not affect the dissolved P concentrations. The dissolved P concentrations of the in-stream reservoirs water were an order of magnitude lower than observed in the groundwater and have no seasonal trend. Our data showed preferential binding of P during initial stage of the Fe(II) oxidation process, indicating the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at the groundwater-surface water interface is an important geochemical mechanism in the transformation of dissolved phosphate to particulate phosphate and therefore a major control on the P retention in natural waters that drain anaerobic aquifers.

van der Grift, Bas; Rozemeijer, Joachim; Griffioen, Jasper; van der Velde, Ype

2014-05-01

298

Passivation of SiC device surfaces by aluminum oxide  

NASA Astrophysics Data System (ADS)

A steady improvement in material quality and process technology has made electronic silicon carbide devices commercially available. Both rectifying and switched devices can today be purchased from several vendors. This successful SiC development over the last 25 years can also be utilized for other types of devices, such as light emitting and photovoltaic devices, however, there are still critical problems related to material properties and reliability that need to be addressed. This contribution will focus on surface passivation of SiC devices. This issue is of utmost importance for further development of SiC MOSFETs, which so far has been limited by reliability and low charge carrier surface mobilities. Also bipolar devices, such as BJTs, LEDs, or PV devices will benefit from more efficient and reliable surface passivation techniques in order to maintain long charge carrier lifetimes. Silicon carbide material enables the devices to operate at higher electric fields, higher temperatures and in more radiation dense applications than silicon devices. To be able to utilize the full potential of the SiC material, it is therefore necessary to develop passivation layers that can sustain these more demanding operation conditions. In this presentation it will also be shown that passivation layers of Al2O3 deposited by atomic layer deposition have shown superior radiation hardness properties compared to traditional SiO2-based passivation layers.

Hallén, A.; Usman, M.; Suvanam, S.; Henkel, C.; Martin, D.; Linnarsson, M. K.

2014-03-01

299

Ultrasmooth reaction-sintered silicon carbide surface resulting from combination of thermal oxidation and ceria slurry polishing.  

PubMed

An ultrasmooth reaction-sintered silicon carbide surface with an rms roughness of 0.424 nm is obtained after thermal oxidation for 30 min followed by ceria slurry polishing for 30 min. By SEM-EDX analysis, we investigated the thermal oxidation behavior of RS-SiC, in which the main components are Si and SiC. As the oxidation rate is higher in the area with defects, there are no scratches or cracks on the surface after oxidation. However, a bumpy structure is formed after oxidation because the oxidation rates of Si and SiC differ. Through a theoretical analysis of thermal oxidation using the Deal-Grove model and the removal of the oxide layer by ceria slurry polishing in accordance with the Preston equation, a model for obtaining an ultrasmooth surface is proposed and the optimal processing conditions are presented. PMID:23787665

Shen, Xinmin; Dai, Yifan; Deng, Hui; Guan, Chaoliang; Yamamura, Kazuya

2013-06-17

300

Mechanism of the initial stage of the oxidation of the clean and precovered with nonmetals iron surface  

SciTech Connect

The oxidation of the iron surface has been studied using the Auger electron spectroscopy method, particularly the intermediate state of the process proceedings between a monolayer of oxygen and an oxide layer. The oxidation of the clean iron surface has been compared to that of the iron surface precovered with carbon, sulfur, nitrogen, and phosphorus. The monolayer of carbon or nitrogen does not affect the rate of the oxidation process; however the monolayer of sulfur or phosphorus inhibits the oxidation. The mechanism of the oxidation stage between the monolayer of oxygen and the oxide layer has been elucidated taking into account the incorporation of oxygen atoms into the first iron layer. The concentration of defects in the bidimensional adsorbate layer has been taken into consideration. The number of surface defects in the 2D lattice of sulfur or phosphorus is 20 times lower than in the layer of oxygen.

Narkiewicz, U.; Arabczyk, W.

1999-08-31

301

Photoemission and LEED study of the Sn/Rh(111) surface—early oxidation steps and thermal stability  

NASA Astrophysics Data System (ADS)

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 SnO2 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.

Hanyš, Petr; Píš, Igor; Mašek, Karel; Šutara, František; Matolín, Vladimír; Nehasil, Václav

2012-01-01

302

Photoemission and LEED study of the Sn/Rh(111) surface--early oxidation steps and thermal stability.  

PubMed

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

Hanyš, Petr; Píš, Igor; Mašek, Karel; Sutara, František; Matolín, Vladimír; Nehasil, Václav

2012-01-11

303

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

304

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

PubMed

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

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

2015-01-01

305

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

306

Surface Analysis of Micro-Arc Oxidized Coatings Deposited on cp-Ti  

NASA Astrophysics Data System (ADS)

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.

Kim, Yeon-Wook; Nam, Tae-Hyun

307

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

308

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

USGS Publications Warehouse

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

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

1996-01-01

309

Monte Carlo simulations of catalytic CO oxidation on fractal surfaces of dimension between two and three  

NASA Astrophysics Data System (ADS)

We present a method for generating fractal surfaces of dimension between two and three. By using the method, five fractal surfaces with dimension 2.262, 2.402, 2.524, 2.631, and 2.771 are created. For each of these surfaces, the reaction of carbon monoxide and oxygen is simulated by using a Monte Carlo method based on the ZGB model [Phys. Rev. Lett. 24 (1986) 2553]. The results show that the catalytic CO oxidation proceeds more efficiently on a surface with higher fractal dimension. It is also found that as the fractal dimension of the surface becomes higher, the first-order kinetic phase transition point (y 2) is shifted to a higher partial pressure of CO. This implies that poisoning of the catalyst surface due to CO segregation sets in at a higher CO partial pressure for surfaces with more complexity.

Park, Hwangseo; Kim, Hojing; Lee, Sangyoub

1997-05-01

310

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

311

Surface plasmon dispersion analysis in the metal-oxide-metal tunnel diode  

NASA Technical Reports Server (NTRS)

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.

Donohue, J. F.; Wang, E. Y.

1987-01-01

312

Role of surface precipitation in copper sorption by the hydrous oxides of iron and aluminum  

SciTech Connect

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., CuAl{sub 2}O{sub 4}(s)] with dramatically loser solubility than Cu(OH){sub 2}(s) precipitated in bulk solution. In contrast, Cu precipitated on the HFO surface exhibited a solubility comparable to the bulk precipitated Cu(OH){sub 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.

Karthikeyan, K.G.; Elliott, H.A.; Chorover, J. [Pennsylvania State Univ., University Park, PA (United States)] [Pennsylvania State Univ., University Park, PA (United States)

1999-01-01

313

Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide.  

PubMed

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-Al2O3 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). PMID:25217942

Kerr, A J; Chagarov, E; Gu, S; Kaufman-Osborn, T; Madisetti, S; Wu, J; Asbeck, P M; Oktyabrsky, S; Kummel, A C

2014-09-14

314

Determination of surface oxide compositions on Alloy 600 using Rutherford backscattering  

SciTech Connect

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.

Hanson, A.L.; Isaacs, H.S.; Kraner, H.W.

1984-01-01

315

Oxygen interaction with the Pd(112) surface: From chemisorption to bulk oxide formation  

NASA Astrophysics Data System (ADS)

We investigated the interaction of oxygen with the Pd(112) surface from ultrahigh vacuum up to 5 mbars oxygen partial pressure in a temperature range from 523 to 673 K. We combined in situ surface x-ray diffraction with scanning tunneling microscopy, high-resolution core-level spectroscopy, and low-energy electron diffraction. A structural model of the clean Pd(112) is proposed based on the x-ray-diffraction data. The morphology of the Pd(112) surface is strongly influenced by the oxidation conditions: at 673 K, upon exposure to oxygen at pressures from 2×10-8 to 5×10-5 mbar, the (112) surface undergoes a massive rearrangement and (113)- and (335)-type facets are formed. Further increase of the O2 partial pressure leads to a new rearrangement into (111)- and (113)-type facets. This is in contrast to the previous observation that (112) facets are stabilized on MgO supported Pd nanoparticles under oxygen exposure [P. Nolte, A. Stierle, N. Kasper, N. Y. Jin-Phillipp, N. Jeutter, and H. Dosch, Nano Lett.NALEFD1530-698410.1021/nl2023564 11, 4697 (2011)]. Based on the core-level spectroscopy and scanning tunneling microscopy measurements, the transition from chemisorbed oxygen to surface oxide formation was identified to take place at pressures of 10-3 mbar O2 and 623 K. Kinetic barriers for the formation of the PdO bulk oxide are observed to be reduced compared to low index Pd surfaces.

Vlad, Alina; Stierle, Andreas; Westerström, Rasmus; Blomberg, Sara; Mikkelsen, Anders; Lundgren, Edvin

2012-07-01

316

First-principles studies of polar oxide surfaces and hetero-interfaces  

NASA Astrophysics Data System (ADS)

Metal oxide surfaces and interfaces are important in several fields of research and have technological applications ranging from catalysis, electronics, magnetic recording and solid-state physics. In this context, polar oxide surfaces and interfaces have interesting, and novel properties due to their unique local atomic and electronic structure. Conventional wisdom based on classical electrostatic theory suggests that polar surfaces are unstable due to the presence of a diverging potential along the surface normal. However, real systems are not made up of rigid charges, even if the lattice is rigid, and the quantum or electronic degrees of freedom are able to efficiently stabilize polar systems. This dissertation presents a first-principles study of the atomic and electronic structure, energetics and growth of polar oxide surfaces and interfaces by using MgO(111) as a model polar surface and Fe2O 3(0001)/MgO(111) as a model polar hetero-interface. The inherent difference in the structure of non-polar MgO(001) and polar MgO(111) surfaces results in different epitaxial growth mechanisms that are sensitive to experimental conditions. Growth of the MgO(111) surface follows a complicated thermodynamic pathway and is highly dynamic in nature due to large, but meta-stable, relaxations of Mg and O atoms at the surface and near sub-surface. Similarly, the polarity of the MgO(111) substrate has a marked effect on the growth of Fe2O 3(0001) films in that it results in drastic structural relaxations leading to a complete rearrangement of Fe and O stacking at the interface. The results of our study suggest that the stabilization of the polar interface and screening of the dipole field occur due to the combined effect of electronic and structural relaxations.

Pande, Kanupriya

317

Effect of Reacting Surface Density on the Overall Graphite Oxidation Rate  

SciTech Connect

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 their chemical and mechanical characteristics are well identified by the previous investigations, and therefore it was convenient for us to access the published data, and to apply and validate our new methodologies. This paper presents preliminary results of compressive strength vs. burn-off and surface area density vs. burn-off, which can be used for the nuclear graphite selection for the NGNP.

Chang H. Oh; Eung Kim; Jong Lim; Richard Schultz; David Petti

2009-05-01

318

Effect of surface ZnO coatings on oxidation and thermal stability of zinc films  

NASA Astrophysics Data System (ADS)

The effect of thin ZnO coatings grown on Zn films on further oxidation and thermal stability of Zn films deposited on Mo(110) substrate was in situ investigated under ultrahigh vacuum by photoelectron spectrometries and low-energy electron diffraction. The results indicated that ZnO layers formed by oxidizing Zn films had at least a thickness of 3-5 monolayers. Further oxidation of Zn films was confined by as-formed ZnO coatings due to a surface passivation. It was of advantage to explain the difficulty in growing low oxygen-deficient ZnO films. The surface ZnO coatings strongly enhanced the thermal stability of Zn films, which was useful for understanding the underlying application of Zn/ZnO materials, such as Zn/ZnO nanocables with Zn core and ZnO shell.

Xue, M. S.; Li, W.; Wang, F. J.

2010-08-01

319

Oxide-free InSb (100) surfaces by molecular hydrogen cleaning  

SciTech Connect

We report that annealing of an oxidized InSb (100) single-crystal sample at 250 deg. C under molecular hydrogen flow [molecular hydrogen cleaning (MHC)] results in complete desorption of the surface oxides. Following this process, the surface morphology is found to be very smooth at the nanometric scale without any droplet structure and a nearly 1:1 In:Sb stoichiometry. MHC was applied to remove the native oxide of an epi-ready InSb(100) substrate used for molecular beam epitaxy growth of InSb films. These results suggest that MHC of InSb can be used as a very effective cleaning process for epitaxial film growth.

Tessler, R.; Saguy, C.; Klin, O.; Greenberg, S.; Weiss, E.; Akhvlediani, R.; Edrei, R.; Hoffman, A. [Physics Department, Technion--Israel Institute of Technology, Haifa 32000 (Israel); SCD-Semi-conductor Devices, Haifa 31201 (Israel); Chemistry Department, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

2006-01-16

320

Tailoring the surface properties of Ti6Al4V by controlled chemical oxidation  

E-print Network

activity at the surface of implants, mainly by modifying their topography and physicochemical properties modification; Titanium alloy; Titanium oxide 1. Introduction Titanium and its alloys are widely used biocompatibility, and high corro- sion resistance. An important feature of Ti-based materials is their air

321

Oxidation of carbon fiber surfaces for use as reinforcement in high-temperature cementitious material systems  

DOEpatents

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.

Sugama, Toshifumi (Mastic Beach, NY)

1990-01-01

322

Oxidation of carbon fiber surfaces for use as reinforcement in high-temperature cementitious material systems  

DOEpatents

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.

Sugama, Toshifumi.

1990-05-22

323

Surface diffusion upon oxygen isotopic exchange on oxide-supported metal nanoclusters  

Microsoft Academic Search

A newly developed real-time kinetic model is presented. The model was used for the characterization of supported metal catalysts' properties in the oxygen isotopic exchange reaction. This model is based on rate equations and includes several elementary processes: adsorption on the metal nanoclusters, reactions on the metal nanoclusters, desorption from the metal nanoclusters, surface and bulk diffusion on\\/in the oxide

A Galdikas; C Descorme; D Duprez

2004-01-01

324

Particle size associated with the surface oxides on low enriched uranium metal plates  

Microsoft Academic Search

Inhalation of respirable particulates of uranium is a radiological concern during the industrial processes used to manufacture nuclear fuels. An investigation of some exposures to Low Enriched Uranium (LEU) indicated that intakes occurred from the inhalation of surface oxide (Uâ, Oâ) particulates covering some LEU metal plates. Measurements of the size distributions of the respirable UâOâ particles were made by

S. H. Linauskas; F. Szostak; A. Trivedi

1996-01-01

325

Atomistic simulations of surface segregation of defects in solid oxide electrolytes  

E-print Network

pronounced dopant segregation in GDC than in YSZ, even though the size mismatch between dopant and hostAtomistic simulations of surface segregation of defects in solid oxide electrolytes Hark B. Lee online 22 January 2010 Abstract We performed atomistic simulations of yttria-stabilized zirconia (YSZ

Cai, Wei

326

Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications  

Microsoft Academic Search

Superparamagnetic iron oxide nanoparticles (SPION) with appropriate surface chemistry have been widely used experimentally for numerous in vivo applications such as magnetic resonance imaging contrast enhancement, tissue repair, immunoassay, detoxification of biological fluids, hyperthermia, drug delivery and in cell separation, etc. All these biomedical and bioengineering applications require that these nanoparticles have high magnetization values and size smaller than 100nm

Ajay Kumar Gupta; Mona Gupta

2005-01-01

327

Tip-induced nano-writing/machining of Si and DLC surfaces ``anodic'' versus thermal oxidation?  

NASA Astrophysics Data System (ADS)

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.

Myhra, S.; Watson, G. S.

2005-08-01

328

Role of oxide surface in coordination chemistry of transition metal ions in catalytic systems  

Microsoft Academic Search

On going from the solution into the bulk of an oxide through the fluid-solid interface, it is possible to encounter four types of coordina- tion chemistry (CC) for a transition metal ion (TMI) : solution coordina- tion chemistry, extraframework ion CC, surface framework ion CC and solid state CC. In each case, the reactivity of the TMI is discussed on

L. Bonneviot; M. Curie

1988-01-01

329

Ozone and nitrogen oxides in surface air in Russia: TROICA experiments  

Microsoft Academic Search

The results of measurements of surface ozone and nitrogen oxides concentrations over the continental regions of Russia are discussed. The measurements were done during 10 TROICA experiments (Transcontinental Observations Into the Chemistry of the Atmosphere). The TROICA experiment started in 1995. By the present moment ten expeditions along the Trans-Siberian railroad from Moscow to Vladivostok (around 9300 km) are carried

N. Pankratova; N. Elansky; I. Belikov; R. Shumskiy

2009-01-01

330

Changes in ?-sialon suspension behaviour due to surface oxidation, milling, surfactant and sintering additive  

Microsoft Academic Search

Results of a study of the behaviour of aqueous suspensions of carbothermally prepared ?-sialon are presented. The influence of an oxidation treatment, attrition milling, sintering additive (Y2O3) and addition of a deflocculant (Dolapix CE 64) on the stabilisation behaviour of the suspensions was studied. Obtained results show that the surface properties of ?-sialon particles are affected, as expected, by the

AA Kudyba-Jansen; M. Muurmans; M. Almeida; J. Laven; HTJM Hintzen; R. Metselaar

2000-01-01

331

Manganese Peroxidase Degrades Pristine but Not Surface-Oxidized (Carboxylated) Single-Walled Carbon Nanotubes  

E-print Network

about the biotransformation potential of single-walled carbon nanotubes (SWNTs). In this study, we, and mechanical properties.1 Single-walled carbon nanotubes (SWNTs) are particularly attractive for potentialManganese Peroxidase Degrades Pristine but Not Surface-Oxidized (Carboxylated) Single-Walled Carbon

Alvarez, Pedro J.

332

Electrochemical reduction of porous 17 kg uranium oxide pellets by selection of an optimal cathode/anode surface area ratio  

NASA Astrophysics Data System (ADS)

This study examines how the cathode/anode surface area ratio affects the electrochemical reduction of uranium oxide in a molten Li 2O-LiCl electrolyte. A bench-scale test showed that a low cathode/anode surface area ratio is helpful for efficiently attaining a high current density and producing metallic uranium from uranium oxide in an Li 2O-LiCl electrolyte. A 17 kg uranium oxide electrolysis cell was set up with a cathode/anode surface area ratio of 2.6, and uranium oxide was successfully reduced to metallic uranium.

Choi, Eun-Young; Hur, Jin-Mok; Choi, In-Kyu; Kwon, Seon Gil; Kang, Dae-Seung; Hong, Sun Seok; Shin, Ho-Sup; Yoo, Min A.; Jeong, Sang Mun

2011-11-01

333

Influence of substrate preparation on the shaping of the topography of the surface of nanoceramic oxide layers  

NASA Astrophysics Data System (ADS)

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.

Bara, Marek; Kubica, Marek

2014-02-01

334

Molecular-level chemistry of model single-crystal oxide surfaces with model halogenated compounds  

NASA Astrophysics Data System (ADS)

Synchrotron-based X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD) and low energy electron diffraction (LEED) have been used to investigate, at a molecular level, the chemistry of different terminations of single crystal iron-oxide surfaces with probe molecules (CCl4 and D2O). Comparisons of the reactivity of these surfaces towards CCl4, indicate that the presence of an uncapped surface Fe cation (strong Lewis acid site) and an adjacent oxygen site capped by that cation can effect the C-Cl bond cleavage in CCl4, resulting in dissociatively adsorbed Cl-adatoms and carbon-containing fragments. If in addition to these sites, an uncapped surface oxygen (Lewis base) site is also available, the carbon-containing moiety can then move that site, coordinate itself with that uncapped oxygen, and stabilize itself. At a later step, the carbon-containing fragment may form a strong covalent bond with the uncapped oxygen and may even abstract that surface oxygen. On the other hand, if an uncapped oxygen is not available to stabilize the carbon-containing fragment, the surface coordination will not occur and upon the subsequent thermal annealing of the surface the Cl-adatoms and the carbon-containing fragments will recombine and desorb as CCl4. Finally, the presence of surface deuteroxyls blocking the strong Lewis acid and base sites of the reactive surface, passivates this surface. Such a deuteroxylated surface will be unreactive towards CCl 4. Such a molecular level understanding of the surface chemistry of metal-oxides will have applications in the areas of selective catalysis, including environmental catalysis, and chemical sensor technology.

Adib, Kaveh

335

Carbon contamination and oxidation of Au surfaces under extreme ultraviolet radiation: An x-ray photoelectron spectroscopy study  

E-print Network

.5 nm) and high chemical resistance in corrosive environments,12 EUV-induced carbon contamination is oneCarbon contamination and oxidation of Au surfaces under extreme ultraviolet radiation: An x 2012) Extreme ultraviolet (EUV) radiation-induced carbon contamination and oxidation of Au surfaces

Harilal, S. S.

336

Bovine Bone Screws: Metrology and Effects of Chemical Processing and Ethylene Oxide Sterilization on Bone Surface and Mechanical Properties  

Microsoft Academic Search

We assess the effects of chemical processing, ethylene oxide sterilization, and threading on bone surface and mechanical properties of bovine undecalcified bone screws. In addition, we evaluate the possibility of manufacturing bone screws with predefined dimensions. Scanning electronic microscopic images show that chemical processing and ethylene oxide treatment causes collagen fiber amalgamation on the bone surface. Processed screws hold higher

D. P. Haje; J. B. Volpon; C. A. Moro

2009-01-01

337

Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO  

NASA Technical Reports Server (NTRS)

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.

Drawdy, Jean E.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

1990-01-01

338

Surface and interface analysis of poly-hydroxyethylmethacrylate-coated anodic aluminium oxide membranes  

NASA Astrophysics Data System (ADS)

The surface and interface of poly (2-hydroxyethylmethacrylate) (PHEMA) and anodic aluminium oxide (AAO) membranes were comprehensively investigated using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. It was found that 1s??* (Cdbnd O) and 1s??* (Csbnd O) transitions were dominant on the surface of both bulk PHEMA polymer and PHEMA-surface coated AAO (AAO-PHEMA) composite. Findings from NEXAFS, Fourier-Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses suggest the possibility of chemical interaction between carbon from the ester group of polymer and AAO membrane.

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

339

Natural and pyrogenic humic acids at goethite and natural oxide surfaces interacting with phosphate.  

PubMed

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

Hiemstra, Tjisse; Mia, Shamim; Duhaut, Pierre-Benoît; Molleman, Bastiaan

2013-08-20

340

Occurrence of surface polysulfides during the interaction between ferric (hydr)oxides and aqueous sulfide.  

PubMed

Polysulfides are often referred to as key reactants in the sulfur cycle, especially during the interaction of ferric (hydr)oxides and sulfide, forming ferrous-sulphide minerals. Despite their potential relevance, the extent of polysulfide formation and its relevance for product formation pathways remains enigmatic. We applied cryogenic X-ray Photoelectron Spectroscopy and wet chemical analysis to study sulfur oxidation products during the reaction of goethite and lepidocrocite with aqueous sulfide at different initial Fe/S molar ratios under anoxic conditions at neutral pH. The higher reactivity of lepidocrocite leads to faster and higher electron turnover compared to goethite. We were able to demonstrate for the first time the occurrence of surface-associated polysulfides being the main oxidation products in the presence of both minerals, with a predominance of disulfide (S2(2-)(surf)), and elemental sulfur. Concentrations of aqueous polysulfide species were negligible (<1%). With prior sulfide fixation by zinc acetate, the surface-associated polysulfides could be precipitated as zerovalent sulfur (S°), which was extracted by methanol thereafter. Of the generated S°, 20-34% were associated with S2(2-)(surf). Varying the Fe/S ratio revealed that surface polysulfide formation only becomes dominant when the remaining aqueous sulfide concentration is low (<0.03 mmol L(-1)). We hypothesize these novel surface sulfur species, particularly surface disulfide, to act as pyrite precursors. We further propose that these species play an overlooked role in the sulfur cycle. PMID:24735157

Wan, Moli; Shchukarev, Andrey; Lohmayer, Regina; Planer-Friedrich, Britta; Peiffer, Stefan

2014-05-01

341

Interfacial interactions of polymer coatings with oxide-free phosphate films on metal surfaces  

NASA Astrophysics Data System (ADS)

A method for producing thin oxide-free phosphate films using an easier process than those previously reported is described. The process is carried out under ambient conditions using aqueous phosphoric acid. The chemistry of the phosphated surface prepared by the process and the interaction of this surface with a thin film of polyvinyl alcohol (PVA) are examined with the purpose of evaluating the potential of this film to serve as an adhesion promoting layer. The surface chemical changes are monitored by core and valence band x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, with the resultant spectra compared to those from band structure calculations. Valance band photoemission interpreted by band structure calculations can be used to study the interfaces involved, and proves to be a very effective tool for conclusively identifying the surface species present. The process for forming oxide-free phosphate films forms the same surface chemistry as previously reported for other processes. PVA is found to strongly interact with the oxide-free phosphate film on aluminum metal illustrating the potential of such films as adhesion promoters.

Wang, Yuqing; Sherwood, Peter M. A.

2003-07-01

342

Oxidation of arsenopyrite and deposition of gold on the oxidized surfaces: A scanning probe microscopy, tunneling spectroscopy and XPS study  

NASA Astrophysics Data System (ADS)

We have used ex situ atomic force microscopy (AFM), scanning tunneling microscopy and spectroscopy (STM/STS) and X-ray photoelectron spectroscopy (XPS) to study the surfaces of natural arsenopyrite samples that were electrochemically polarized in 1 M HCl, or leached in acidic solutions containing ferric iron salts, and then reacted with aqueous gold (III) chloride at ambient temperatures. For arsenopyrite oxidized on a positive-going potential sweep, progressively increasing amounts of surface Fe(III)-O and As-O species, and of S/Fe and S/As ratios in a non-stoichiometric sulfidic layer were found. The products formed in the sweep to a potential of 0.6 V (Ag/AgCl) of the passivity region are shaped in about 100 nm protrusions of two sorts, which are arranged in micrometer-size separate areas, while they are largely mixed at higher, "transpassive" potentials. The quantities of surface alteration substances notably decrease after leaching in ferric chloride and ferric sulfate acidic solutions. Passivation of arsenopyrite was suggested to associate with the disordered, metal-deficient surface layer having moderate excess of sulfur rather than with the products of arsenopyrite oxidation. Exposure of arsenopyrite to 10 -5-10 -3 M AuCl4- (pH 2) solutions results in the deposition of 8-50 nm gold particles; only a small fraction of the gold is present as Au(I)-S species. The electrochemical oxidation at 0.6 V or ageing of arsenopyrite in air promotes the subsequent gold deposition; in contrast, the amount of Au deposited on arsenopyrite that was treated by leaching in ferric chloride and sulfate solutions was about 10 times smaller than with polished arsenopyrite samples. It has been concluded that reducing agents formed as intermediates of arsenopyrite decomposition facilitate the Au 0 cementation although other factors related to the surface state of the arsenopyrite play a role as well. A decrease in the tunneling current magnitudes with decreasing the Au 0 particle size has been revealed using STS. This effect along with the increase by 0.2-0.5 eV in the XPS Au 4f binding energies were tentatively ascribed to retarding the electron transitions by emerging electrostatic charge on gold nanoparticles (Coulomb blockade). Possible mechanisms for the effects, and their potential role in the deposition and hydrometallurgy of "invisible" gold are discussed.

Mikhlin, Yuri L.; Romanchenko, Alexander S.; Asanov, Igor P.

2006-10-01

343

Sputtered cadmium oxide as a surface pretreatment for graphite solid-lubricant films  

NASA Technical Reports Server (NTRS)

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.

Fusaro, Robert L.

1987-01-01

344

Selective surface modification of lithographic silicon oxide nanostructures by organofunctional silanes  

PubMed Central

Summary This study investigates the controlled chemical functionalization of silicon oxide nanostructures prepared by AFM-anodization lithography of alkyl-terminated silicon. Different conditions for the growth of covalently bound mono-, multi- or submonolayers of distinctively functional silane molecules on nanostructures have been identified by AFM-height investigations. Routes for the preparation of methyl- or amino-terminated structures or silicon surfaces are presented and discussed. The formation of silane monolayers on nanoscopic silicon oxide nanostructures was found to be much more sensitive towards ambient humidity than, e.g., the silanization of larger OH-terminated silica surfaces. Amino-functionalized nanostructures have been successfully modified by the covalent binding of functional fluorescein dye molecules. Upon excitation, the dye-functionalized structures show only weak fluorescence, which may be an indication of a relatively low surface coverage of the dye molecules on length scale that is not accessible by standard AFM measurements. PMID:23616941

von Borczyskowski, Christian; Graaf, Harald

2013-01-01

345

Effect of oxidation–reduction surface treatment on the electrochemical behavior of PAN-based carbon fibers  

Microsoft Academic Search

The relationship between surface functionality and electrochemical properties of polyacrylonitrile (PAN)-based carbon fibers (CFs) differentiated by the modification treatment was studied. Oxidative and non-oxidative treatments (i.e. oxidation with ammonium peroxydisulfate (1 M (NH4)2S2O8), and heating in hydrogen and argon atmosphere) were used for the modification. The chemical character of the CF surface was estimated by using the titration method and

Yu. V. Basova; H. Hatori; Y. Yamada; K. Miyashita

1999-01-01

346

Generalized molybdenum oxide surface chemical state XPS determination via informed amorphous sample model  

NASA Astrophysics Data System (ADS)

Accurate elemental oxidation state determination for the outer surface of a complex material is of crucial importance in many science and engineering disciplines, including chemistry, fundamental and applied surface science, catalysis, semiconductors and many others. X-ray photoelectron spectroscopy (XPS) is the primary tool used for this purpose. The spectral data obtained, however, is often very complex and can be subject to incorrect interpretation. Unlike traditional XPS spectra fitting procedures using purely synthetic spectral components, here we develop and present an XPS data processing method based on vector analysis that allows creating XPS spectral components by incorporating key information, obtained experimentally. XPS spectral data, obtained from series of molybdenum oxide samples with varying oxidation states and degree of crystallinity, were processed using this method and the corresponding oxidation states present, as well as their relative distribution was elucidated. It was shown that monitoring the evolution of the chemistry and crystal structure of a molybdenum oxide sample due to an invasive X-ray probe could be used to infer solutions to complex spectral envelopes.

Baltrusaitis, Jonas; Mendoza-Sanchez, Beatriz; Fernandez, Vincent; Veenstra, Rick; Dukstiene, Nijole; Roberts, Adam; Fairley, Neal

2015-01-01

347

Experimental evaluation of the effects of quench rate and quartz surface area on homogeneous mercury oxidation  

SciTech Connect

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.

Andrew Fry; Brydger Cauch; Geoffrey D. Silcox; JoAnn S. Lighty; Constance L. Senior [University of Utah, Salt Lake City, UT (United States). Department of Chemical Engineering

2007-07-01

348

Hydrophobic/superhydrophobic oxidized metal surfaces showing negligible contact angle hysteresis.  

PubMed

Dynamic wettability of oxidized metal (aluminum and titanium) surfaces could be tuned by chemical vapor deposition (CVD) of 1,3,5,7-tetramethylcyclotetrasiloxane (D(4)(H)). This facile CVD method produces not only monomeric layers but also particulate films by changing the CVD temperature, resulting in a marked difference in the final wetting properties. In the samples prepared at 80°C for ~3 days, D(4)(H) layers with thicknesses of ~0.5 nm were formed on the surfaces without discernible change in surface morphology, as evidenced by X-ray photoelectron spectroscopy and atomic force microscopy. After this D(4)(H) monomeric layer formation, the hydrophilic oxidized aluminum and titanium surfaces became hydrophobic (advancing/receding water contact angles (?(A)/?(R))=102-104°/99-102°) showing essentially negligible contact angle hysteresis. Performing CVD of D(4)(H) at 180°C for ~1 day produced opaque film with particulate morphologies with diameters in the range of 500 nm to 4 ?m observed on the surfaces. This geometric morphology enhanced the surface hydrophobicity (?(A)/?(R)=163°/160-161°). Droplets on these negligible-hysteresis surfaces moved very easily without "pinning". PMID:20970808

Hozumi, Atsushi; Cheng, Dalton F; Yagihashi, Makoto

2011-01-15

349

The effect of boron oxide on the composition, structure, and adsorptivity of glass surfaces  

NASA Astrophysics Data System (ADS)

Boron oxide has been added to commercial silicate glasses for many years to aid in lowering melting temperatures, lowering thermal expansion, and controlling chemical durability. The fact that simple borate glasses have rather high thermal expansion and low chemical durability attests to the unique influence of boron oxide additions upon the properties of silicate glasses. However, the impact of boron oxide additions upon surface properties of multicomponent borosilicates such as adsorption and reactivity is not yet well understood. In particular, the presence of multiple coordination states for boron is expected to introduce adsorption sites with different acidic or basic behavior, but their existence is yet unproven. To investigate these effects, multicomponent sodium aluminosilicate glasses have been prepared with varying sodium and boron concentrations and drawn into moderately high-surface-area continuous filament fibers. A relatively new technique, boron K-edge Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is applied to study the local boron coordination at fracture and melt-derived fiber surfaces of these glasses. This structural information is combined with surface compositional information by X-ray Photoelectron Spectroscopy (XPS) to characterize the local atomic structure of boron at the as-formed glass surface. Finally, this information is used to interpret the adsorptivity of these as-formed and leached surfaces toward short-chain alcohol molecules through a new Inverse Gas Chromatography---Temperature Programmed Desorption (IGC-TPD) experiment. The results clearly show that boron additions to alkali-free glass surfaces introduce a unique adsorption site which is not present on boron-free glass surfaces and is easily removed by leaching in acidic solutions.

Schaut, Robert A.

350

TiO2-Al2O3 binary mixed oxide surfaces for photocatalytic NOx abatement  

NASA Astrophysics Data System (ADS)

TiO2-Al2O3 binary oxide surfaces were utilized in order to develop an alternative photocatalytic NOx abatement approach, where TiO2 sites were used for ambient photocatalytic oxidation of NO with O2 and alumina sites were exploited for NOx storage. Chemical, crystallographic and electronic structure of the TiO2-Al2O3 binary oxide surfaces were characterized (via BET surface area measurements, XRD, Raman spectroscopy and DR-UV-Vis Spectroscopy) as a function of the TiO2 loading in the mixture as well as the calcination temperature used in the synthesis protocol. 0.5 Ti/Al-900 photocatalyst showed remarkable photocatalytic NOx oxidation and storage performance, which was found to be much superior to that of a Degussa P25 industrial benchmark photocatalyst (i.e. 160% higher NOx storage and 55% lower NO2(g) release to the atmosphere). Our results indicate that the onset of the photocatalytic NOx abatement activity is concomitant to the switch between amorphous to a crystalline phase with an electronic band gap within 3.05-3.10 eV; where the most active photocatalyst revealed predominantly rutile phase together and anatase as the minority phase.

Soylu, Asli Melike; Polat, Meryem; Erdogan, Deniz Altunoz; Say, Zafer; Y?ld?r?m, Cansu; Birer, Özgür; Ozensoy, Emrah

2014-11-01

351

Computational Fluid Dynamics Simulation of Flows in an Oxidation Ditch Driven by a New Surface Aerator  

PubMed Central

Abstract In this article, we present a newly designed inverse umbrella surface aerator, and tested its performance in driving flow of an oxidation ditch. Results show that it has a better performance in driving the oxidation ditch than the original one with higher average velocity and more uniform flow field. We also present a computational fluid dynamics model for predicting the flow field in an oxidation ditch driven by a surface aerator. The improved momentum source term approach to simulate the flow field of the oxidation ditch driven by an inverse umbrella surface aerator was developed and validated through experiments. Four kinds of turbulent models were investigated with the approach, including the standard k?? model, RNG k?? model, realizable k?? model, and Reynolds stress model, and the predicted data were compared with those calculated with the multiple rotating reference frame approach (MRF) and sliding mesh approach (SM). Results of the momentum source term approach are in good agreement with the experimental data, and its prediction accuracy is better than MRF, close to SM. It is also found that the momentum source term approach has lower computational expenses, is simpler to preprocess, and is easier to use. PMID:24302850

Huang, Weidong; Li, Kun; Wang, Gan; Wang, Yingzhe

2013-01-01

352

Ultra-thin metal oxide based light controlled converter for sensing surface chemicals  

NASA Astrophysics Data System (ADS)

The thin film technology is used to intentionally combine functional properties of metal oxides at the nanoscale. An ultra thin construction of metal oxide layers is sandwiched between the metal contacts and a system with the gas sensitivity is made and characterized. The built in potential differences in the construction results a combination of the photovoltaic effect and the electrical response to the gas-surface interaction. The response is detected at the ambient temperature, it is sufficiently fast for the practical purposes and is reversible without and with assistance of light even if the response memristance exists. The parameters of the sensor can be intentionally modified by the thin film technology.

Å etkus, ArÅ«nas; Bukauskas, Virginijus; Mironas, Audružis; Vaškelis, Å. arÅ«nas

2014-08-01

353

Electrochemical Reduction of CO2 to CH3OH at Copper Oxide Surfaces  

SciTech Connect

The direct reduction of CO{sub 2} to CH{sub 3}OH is known to occur at several types of electrocatalysts including oxidized Cu electrodes. In this work, we examine the yield behavior of an electrodeposited cuprous oxide thin film and explore relationships between surface chemistry and reaction behavior relative to air-oxidized and anodized Cu electrodes. CH{sub 3}OH yields (43 ?mol cm{sup ?2} h{sup ?1}) and Faradaic efficiencies (38%) observed at cuprous oxide electrodes were remarkably higher than air-oxidized or anodized Cu electrodes suggesting Cu(I) species may play a critical role in selectivity to CH{sub 3}OH. Experimental results also show CH{sub 3}OH yields are dynamic and the copper oxides are reduced to metallic Cu in a simultaneous process. Yield behavior is discussed in comparison with photoelectrochemical and hydrogenation reactions where the improved stability of Cu(I) species may allow continuous CH{sub 3}OH generation.

Le, Minh; Ren, Maoming; Zhang, Ziyu; Sprunger, Phillip T.; Kurtz, Richard L.; Flake, John C.

2011-01-01

354

Oxidation-Induced Whisker Growth on the Surface of Sn-6.6(La, Ce) Alloy  

NASA Astrophysics Data System (ADS)

During solidification of rare-earth (RE)-containing Sn-6.6(La, Ce) alloys, (La0.93Ce0.07)Sn3 intermetallic clusters form in the near ?-Sn matrix. These (La0.93Ce0.07)Sn3 intermetallics oxidize predominately after air storage at room temperature for short time periods. Accompanying the oxidation reaction, tin sprouts appear on the outer surface of the intermetallic clusters. Increasing the storage time at room temperature leads to the formation of thread-like tin whiskers. In specimens stored at 150°C in an air furnace, only a small amount of tin sprouts can be found in the interior regions of the oxidized (La0.93Ce0.07)Sn3 intermetallics. However, many coarse tin hillocks formed around the intermetallic clusters. The driving force for whisker growth is the compressive stress induced by the volume expansion of (La0.93 Ce0.07)Sn3, which extrudes the tin atoms released by the oxidation reaction of these RE intermetallics. In addition, the huge compressive stress accumulated by the volume expansion of the drastically oxidized RE intermetallics during 150°C air storage extrudes the Sn-6.6(La, Ce) matrix around the RE oxides to form the coarse hillocks.

Chuang, Tung-Han; Lin, Hsiu-Jen; Chi, Chih-Chien

2007-12-01

355

The growth and evolution of thin oxide films on delta-plutonium surfaces  

SciTech Connect

The common oxides of plutonium are the dioxide (PuO{sub 2}) and the sesquioxide (Pu{sub 2}O{sub 3}). The structure of an oxide on plutonium metal under air at room temperature is typically described as a thick PuO{sub 2} film at the gas-oxide interface with a thinner PuO{sub 2} film near the oxide-metal substrate interface. In a reducing environment, such as ultra high vacuum, the dioxide (Pu{sup 4+}; O/Pu = 2.0) readily converts to the sesquioxide (Pu{sup 3+}; O/Pu = 1.5) with time. In this work, the growth and evolution of thin plutonium oxide films is studied with x-ray photoelectron spectroscopy (XPS) under varying conditions. The results indicate that, like the dioxide, the sesquioxide is not stable on a very clean metal substrate under reducing conditions, resulting in substoichiometric films (Pu{sub 2}O{sub 3-y}). The Pu{sub 2}O{sub 3-y} films prepared exhibit a variety of stoichiometries (y = 0.2-1) as a function of preparation conditions, highlighting the fact that caution must be exercised when studying plutonium oxide surfaces under these conditions and interpreting resulting data.

Garcia Flores, Harry G [Los Alamos National Laboratory; Pugmire, David L [Los Alamos National Laboratory

2009-01-01

356

Identifying active surface phases for metal oxide electrocatalysts: a study of manganese oxide bi-functional catalysts for oxygen reduction and water oxidation catalysis.  

PubMed

Progress in the field of electrocatalysis is often hampered by the difficulty in identifying the active site on an electrode surface. Herein we combine theoretical analysis and electrochemical methods to identify the active surfaces in a manganese oxide bi-functional catalyst for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). First, we electrochemically characterize the nanostructured ?-Mn(2)O(3) and find that it undergoes oxidation in two potential regions: initially, between 0.5 V and 0.8 V, a potential region relevant to the ORR and, subsequently, between 0.8 V and 1.0 V, a potential region between the ORR and the OER relevant conditions. Next, we perform density function theory (DFT) calculations to understand the changes in the MnO(x) surface as a function of potential and to elucidate reaction mechanisms that lead to high activities observed in the experiments. Using DFT, we construct surface Pourbaix and free energy diagrams of three different MnO(x) surfaces and identify 1/2 ML HO* covered Mn(2)O(3) and O* covered MnO(2), as the active surfaces for the ORR and the OER, respectively. Additionally, we find that the ORR occurs through an associative mechanism and that its overpotential is highly dependent on the stabilization of intermediates through hydrogen bonds with water molecules. We also determine that OER occurs through direct recombination mechanism and that its major source of overpotential is the scaling relationship between HOO* and HO* surface intermediates. Using a previously developed Sabatier model we show that the theoretical predictions of catalytic activities match the experimentally determined onset potentials for the ORR and the OER, both qualitatively and quantitatively. Consequently, the combination of first-principles theoretical analysis and experimental methods offers an understanding of manganese oxide oxygen electrocatalysis at the atomic level, achieving fundamental insight that can potentially be used to design and develop improved electrocatalysts for the ORR and the OER and other important reactions of technological interest. PMID:22990481

Su, Hai-Yan; Gorlin, Yelena; Man, Isabela C; Calle-Vallejo, Federico; Nørskov, Jens K; Jaramillo, Thomas F; Rossmeisl, Jan

2012-10-28

357

Sputtering and native oxide formation on (110) surfaces of Cd(1-x)Mn(x)Te  

NASA Technical Reports Server (NTRS)

Native oxides on the surface of Cd(1-x)Mn(x)Te (X between 0 and 0.7) have been analyzed on the basis of X-ray photoemission spectroscopy measurements. Depth profile analysis revealed a significant increase in the thickness at higher Mn concentrations and a strong Mn segregation to the surface, respectively. Sputter-induced damage on cleaved (110)-oriented surfaces was analyzed by photoreflectance and photoluminescence measurements. The damage was found to be larger on CdTe than on the alloy. Thermal annealing showed nearly complete restoration for the surface of the alloy, while CdTe revealed irreversible modifications in the near-surface regime upon sputtering and post annealing.

Neff, H.; Lay, K. Y.; Abid, B.; Lange, P.; Lucovsky, G.

1986-01-01

358

Indium tin oxide exhibiting high poly-crystallinity on oxygen plasma-treated polyethylene terephthalate surface  

PubMed Central

Low-resistivity indium tin oxide [ITO] film was successfully deposited on oxygen plasma-treated polyethylene terephthalate [PET] surfaces at room temperature. X-ray diffraction [XRD] measurements demonstrated that the film deposited on the PET surface that had not been treated with oxygen plasma had an amorphous structure. In contrast, after the low-power oxygen plasma treatment of the PET surface, the ITO film deposited on the PET surface had a poly-crystalline structure due to interactions between electric dipoles on the PET surface and electric dipoles in the ITO film. The minimum resistivity of the poly-crystalline ITO was about 3.6 times lower than that of the amorphous ITO film. In addition, we found that the resistivity of ITO film is proportional to the intensity of the (400) line in the film's XRD spectra. PMID:22330878

2012-01-01

359

Early stages of the oxidation of metal surfaces. [photoelectron spectroscopy of zinc oxide  

NASA Technical Reports Server (NTRS)

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.

Gatos, H. C.; Johnson, K. H.

1978-01-01

360

The growth of cobalt oxides on HOPG and SiO2 surfaces: A comparative study  

NASA Astrophysics Data System (ADS)

The growth of cobalt oxides by reactive thermal evaporation of metallic cobalt on highly oriented pyrolytic graphite (HOPG) and SiO2 (X cut quartz surface), in an oxygen atmosphere at room temperature, has been chemically and morphologically studied by means of X-ray photoelectron spectroscopy and atomic force microscopy. The chemical analysis, which also includes cluster calculations, reveals that for the early deposition stages on both substrates, Co2 + species are stabilized at the surface up to a coverage which depends on the substrate. Further coverages lead to the formation of the spinel oxide Co3O4. The results are discussed in terms of the dependence of the surface energy on the size of the CoO deposited moieties. On the other hand, it has been found that the initial way of growth of cobalt oxides on HOPG is of Stranski-Krastanov mode whereas on SiO2 the growth is of Volmer-Weber mode. The differences in the growth morphology have been discussed in terms of the surface diffusivity of the CoO deposits on the substrates.

Díaz-Fernández, D.; Méndez, J.; Bomatí-Miguel, O.; Yubero, F.; Mossanek, R. J. O.; Abbate, M.; Domínguez-Cañizares, G.; Gutiérrez, A.; Tougaard, S.; Soriano, L.

2014-06-01

361

Excellent c-Si surface passivation by low-temperature atomic layer deposited titanium oxide  

SciTech Connect

In this work, we demonstrate that thermal atomic layer deposited (ALD) titanium oxide (TiO{sub x}) films are able to provide a—up to now unprecedented—level of surface passivation on undiffused low-resistivity crystalline silicon (c-Si). The surface passivation provided by the ALD TiO{sub x} films is activated by a post-deposition anneal and subsequent light soaking treatment. Ultralow effective surface recombination velocities down to 2.8?cm/s and 8.3?cm/s, respectively, are achieved on n-type and p-type float-zone c-Si wafers. Detailed analysis confirms that the TiO{sub x} films are nearly stoichiometric, have no significant level of contaminants, and are of amorphous nature. The passivation is found to be stable after storage in the dark for eight months. These results demonstrate that TiO{sub x} films are also capable of providing excellent passivation of undiffused c-Si surfaces on a comparable level to thermal silicon oxide, silicon nitride, and aluminum oxide. In addition, it is well known that TiO{sub x} has an optimal refractive index of 2.4 in the visible range for glass encapsulated solar cells, as well as a low extinction coefficient. Thus, the results presented in this work could facilitate the re-emergence of TiO{sub x} in the field of high-efficiency silicon wafer solar cells.

Liao, Baochen, E-mail: liaobaochen@nus.edu.sg [Solar Energy Research Institute of Singapore, National University of Singapore, 7 Engineering Drive 1, Singapore 117574 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); A*STAR Institute of Materials Research and Engineering (IMRE), 3 Research Link, Singapore 117602 (Singapore); Hoex, Bram [Solar Energy Research Institute of Singapore, National University of Singapore, 7 Engineering Drive 1, Singapore 117574 (Singapore); Aberle, Armin G.; Bhatia, Charanjit S., E-mail: elebcs@nus.edu.sg [Solar Energy Research Institute of Singapore, National University of Singapore, 7 Engineering Drive 1, Singapore 117574 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Chi, Dongzhi [A*STAR Institute of Materials Research and Engineering (IMRE), 3 Research Link, Singapore 117602 (Singapore)

2014-06-23

362

Quantitative analysis of chemical interaction and doping of the Si(111) native oxide surface with tetrafluorotetracyanoquinodimethane  

NASA Astrophysics Data System (ADS)

The charge-transfer states and the carrier concentration of the native oxide Si(111) surface adsorbed with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) were investigated by X-ray photoelectron spectroscopy (XPS) and independently driven four-probe electrical conductivity measurements. The XPS results show that F4-TCNQ molecules are involved in charge transfer with the SiO2/Si(111) surface. The Si 2p XPS spectra and the surface photovoltage shift provide the evidences of (i) change in the oxidation states at the SiO2-Si(111) interface region and (ii) formation of a p-type space charge layer (SCL) with a hole concentration of 1.7 × 1010 cm-2, respectively. The four-probe I-V measurements also support the formation of the p-type SCL, and the estimated hole concentration of 2.0 × 1010 cm-2 agrees well with the XPS results. The estimated SCL hole concentrations were much smaller than the excess charge density in the F4-TCNQ layer, of the order of 1013 cm-2, suggesting that most of charges were localized as the oxidation states at the SiO2-Si(111) interface region. The present quantitative methods ensure precise determination of the doping concentration near the surface region.

Yoshimoto, Shinya; Furuhashi, Masayuki; Koitaya, Takanori; Shiozawa, Yuichiro; Fujimaki, Kazutaka; Harada, Yosuke; Mukai, Kozo; Yoshinobu, Jun

2014-04-01

363

Quantitative analysis of chemical interaction and doping of the Si(111) native oxide surface with tetrafluorotetracyanoquinodimethane  

SciTech Connect

The charge-transfer states and the carrier concentration of the native oxide Si(111) surface adsorbed with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F{sub 4}-TCNQ) were investigated by X-ray photoelectron spectroscopy (XPS) and independently driven four-probe electrical conductivity measurements. The XPS results show that F{sub 4}-TCNQ molecules are involved in charge transfer with the SiO{sub 2}/Si(111) surface. The Si 2p XPS spectra and the surface photovoltage shift provide the evidences of (i) change in the oxidation states at the SiO{sub 2}-Si(111) interface region and (ii) formation of a p-type space charge layer (SCL) with a hole concentration of 1.7?×?10{sup 10}?cm{sup ?2}, respectively. The four-probe I–V measurements also support the formation of the p-type SCL, and the estimated hole concentration of 2.0?×?10{sup 10}?cm{sup ?2} agrees well with the XPS results. The estimated SCL hole concentrations were much smaller than the excess charge density in the F{sub 4}-TCNQ layer, of the order of 10{sup 13}?cm{sup ?2}, suggesting that most of charges were localized as the oxidation states at the SiO{sub 2}-Si(111) interface region. The present quantitative methods ensure precise determination of the doping concentration near the surface region.

Yoshimoto, Shinya, E-mail: yosshi@issp.u-tokyo.ac.jp; Furuhashi, Masayuki; Koitaya, Takanori; Shiozawa, Yuichiro; Fujimaki, Kazutaka; Harada, Yosuke; Mukai, Kozo; Yoshinobu, Jun [The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

2014-04-14

364

How surface potential determines the kinetics of the first hole transfer of photocatalytic water oxidation.  

PubMed

Interfacial hole transfer between n-SrTiO3 and OH(-) was investigated by surface sensitive transient optical spectroscopy of an in situ photoelectrochemical cell during water oxidation. The kinetics reveal a single rate constant with an exponential dependence on the surface hole potential, spanning time scales from 3 ns to 8 ps over a ?1 V increase. A voltage- and laser illumination-induced process moves the valence band edge at the n-type semiconductor/water interface to continuously change the surface hole potential. This single step of the water oxidation reaction is assigned to the first hole transfer h(+) + OH(-) ? OH(•). The kinetics quantify how much a change in the free energy difference driving this first hole transfer reduces the activation barrier. They are also used to extrapolate the kinetic rate due to the activation barrier when that free energy difference is zero, or the Nernstian potential. This is the first time transient spectroscopy has enabled the separation of the first hole transfer from the full four hole transfer cycle and a direct determination of these two quantities. The Nernstian potential for OH(-)/OH(•) is also suggested, in rough agreement with gas-phase studies. The observation of a distinct, much longer time scale upon picosecond hole transfer to OH(-) suggests that a dominant, more stable intermediate of the water oxidation reaction, possibly a surface bound oxo, may result. PMID:25029360

Waegele, Matthias M; Chen, Xihan; Herlihy, David M; Cuk, Tanja

2014-07-30

365

Strong reciprocal interaction between polarization and surface stoichiometry in oxide ferroelectrics.  

PubMed

We present a systematic evaluation of the effects of polarization switchability on surface structure and stoichiometry in BaTiO3 and PbTiO3 ferroelectric oxides. We show that charge passivation, mostly by ionic surface reconstructions, is the driving force for the stability of the surfaces, which suggests that varying the substrate polarization offers a new mechanism for controlling surface reconstructions in polar systems and inducing highly nonstoichiometric structures. Conversely, for thin-films the chemical environment can drive polarization switching via induced compositional changes on the surface. We find that the value of the oxygen partial pressure for the positive-to-negative polar transition is in good agreement with the recent experimental value for thin-film PbTiO3. For BaTiO3, we show that it is harder for oxygen control to drive polar transition because it is more difficult to reduce. This study opens up the possibility of real-time control of structure and composition of oxide surfaces. PMID:25322070

Saidi, Wissam A; Martirez, John Mark P; Rappe, Andrew M

2014-11-12

366

Helium-surface interaction potential: Determination and applications  

NASA Astrophysics Data System (ADS)

Extensive interest in the field of elastic helium atom-surface scattering is due to encouraging progress made for surface structure determination. An important ingredient in this development is a reliable atom-surface interaction potential. We briefly review the theoretical activity in this area and present our results for the He-Cu(110) interaction potential. From these studies we conclude that the Esbjerg-Nørskov relation between helium-surface repulsive potential and the surface charge density works well. The addition of the Zaremba-Kohn attractive part to the calculated repulsive part completely specifies the total interaction potential. We also reconcile different values for the Cu(110) corrugation obtained with and without using the Esbjerg-Nørskov relation. For application purposes we find that the Esbjerg-Nørskov relation with charge densities derived from atomic superposition is more convenient to use. We illustrate this by examining chemisorption of oxygen on Ni(001). For this a p(2 × 2) structure at low exposures changes to a c(2 × 2) at higher exposures. There have been conflicting suggestions about the vertical height for oxygen in the two phases. We compare our calculated corrugations with Rieder's data and conclude that in both phases oxygen is at a vertical distance of about 0.9 Å. Chlorine adsorption on Ag(001) is another system for which He diffraction work of Cardillo et al. has clearly distinguished between two competing structural alternatives. Another application is taken to show how helium diffraction can give site specific information. Here we study the He-H/Pt(111) system and demonstrate that H chemisorbs on a three-fold hcp site at a vertical distance of about 1 Å on Pt(111). As a last example, we present some new results for the Cu(110)-O(2 × 1) system. In particular, we show that He diffraction results are in agreement with the recent findings of EXAFS measurements.

Batra, Inder P.

1984-12-01

367

Oxidation and Metal-Insertion in Molybdenite Surfaces: Evaluation of Charge-Transfer Mechanisms and Dynamics  

SciTech Connect

Molybdenum sulfide (MoS2), an important representative member of the layered transition-metal dichalcogenides, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and industrial science and technology. 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. On the other hand understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is quite important to utilize these minerals in technological applications. Furthermore, such a detailed investigation of thermal oxidation behavior and intercalation process will provide a basis to further explore and model the mechanism of adsorption of metal ions on to geomedia. Therefore, the present work was performed to understand the oxidation and intercalation processes of molybdenite surfaces. The results obtained, using a wide variety of analytical techniques, are presented and discussed in this paper.

Ramana, Chintalapalle V.; Becker, U.; Shutthanandan, V.; Julien, C. M.

2008-06-05

368

Effects of electrolyzed oxidizing water on reducing Listeria monocytogenes contamination on seafood processing surfaces.  

PubMed

The effects of electrolyzed oxidizing (EO) water on reducing Listeria monocytogenes contamination on seafood processing surfaces were studied. Chips (5 x 5 cm(2)) of stainless steel sheet (SS), ceramic tile (CT), and floor tile (FT) with and without crabmeat residue on the surface were inoculated with L. monocytogenes and soaked in tap or EO water for 5 min. Viable cells of L. monocytogenes were detected on all chip surfaces with or without crabmeat residue after being held at room temperature for 1 h. Soaking contaminated chips in tap water resulted in small-degree reductions of the organism (0.40-0.66 log cfu/chip on clean surfaces and 0.78-1.33 log cfu/chip on dirty surfaces). Treatments of EO water significantly (p<0.05) reduced L. monocytogenes on clean surfaces (3.73 log on SS, 4.24 log on CT, and 5.12 log on FT). Presence of crabmeat residue on chip surfaces reduced the effectiveness of EO water on inactivating Listeria cells. However, treatments of EO water also resulted in significant reductions of L. monocytogenes on dirty surfaces (2.33 log on SS and CT and 1.52 log on FT) when compared with tap water treatments. The antimicrobial activity of EO water was positively correlated with its chlorine content. High oxidation-reduction potential (ORP) of EO water also contributed significantly to its antimicrobial activity against L. monocytogenes. EO water was more effective than chlorine water on inactivating L. monocytogenes on surfaces and could be used as a chlorine alternative for sanitation purpose. Application of EO water following a thorough cleaning process could greatly reduce L. monocytogenes contamination in seafood processing environments. PMID:16219378

Liu, Chengchu; Duan, Jingyun; Su, Yi-Cheng

2006-02-15

369

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions.  

PubMed

We report a mild and straightforward one-step chemical surface functionalization of indium tin oxide (ITO) electrodes by redox-active molecules bearing an organophosphoryl anchoring group (i.e., alkyl phosphate or alkyl phosphonate group). The method takes advantage of simple passive adsorption in an aqueous solution at room temperature. We show that organophosphorus compounds can adsorb much more strongly and stably on an ITO surface than analogous redox-active molecules bearing a carboxylate or a boronate moiety. We provide evidence, through quantitative electrochemical characterization (i.e., by cyclic voltammetry) of the adsorbed organophosphoryl redox-active molecules, of the occurrence of three different adsorbate fractions on ITO, exhibiting different stabilities on the surface. Among these three fractions, one is observed to be strongly chemisorbed, exhibiting high stability and resistance to desorption/hydrolysis in a free-redox probe aqueous buffer. We attribute this remarkable stability to the formation of chemical bonds between the organophosphorus anchoring group and the metal oxide surface, likely occurring through a heterocondensation reaction in water. From XPS analysis, we also demonstrate that the surface coverage of the chemisorbed molecules is highly affected by the degree of surface hydroxylation, a parameter that can be tuned by simply preconditioning the freshly cleaned ITO surfaces in water. The lower the relative surface hydroxide density on ITO, the higher was the surface coverage of the chemisorbed species. This behavior is in line with a chemisorption mechanism involving coordination of a deprotonated phosphoryl oxygen atom to the non-hydroxylated acidic metal sites of ITO. PMID:25611977

Forget, Amélie; Limoges, Benoît; Balland, Véronique

2015-02-17

370

Surface chemistry of the atomic layer deposition of metals and group III oxides  

NASA Astrophysics Data System (ADS)

Atomic Layer Deposition (ALD) is a thin-film growth technique offering precise control of film thickness and the ability to coat high-aspect-ratio features such as trenches and nanopowders. Unlike other film growth techniques, ALD does not require harsh processing conditions and is not limited by line-of-sight deposition. Emerging applications for ALD materials include semiconductor devices, gas sensors, and water-diffusion barriers. The chemistry behind ALD involves understanding how the precursors interact with surfaces to deposit the desired material. All ALD precursors need to be stable on the substrate to ensure self-limiting behavior yet reactive enough to be easily removed with the second reagent. Recent precursor development has provided many volatile organometallic compounds for most of the periodic table. As the number of precursors increases, proper precursor choice becomes crucial. This is because the film properties, growth rates, and growth temperature vary widely between the precursors. Many of the above traits can be predicted with knowledge of the precursor reaction mechanisms. This thesis aims to link surface reaction mechanisms to observed growth and nucleation trends in metal and oxide ALD systems. The first portion of this thesis explores the mechanisms of two ALD oxide systems. First, I examine the mechanism of ALD alumina with ozone. Ozone is used as an oxidant in the semiconductor industry because the deposited Al 2O3 films possess better insulating properties and ozone is easier to purge from a vacuum system. FT-IR analysis reveals a complicated array of surface intermediates such as formate, carbonate, and methoxy groups that form during Al2O3 growth with ozone. Next, a new method to deposit thin films of Ga2O3 is introduced. Gallium oxide is a transparent conducting oxide that needs expensive solid precursors to be deposited by ALD. I show that trimethylgallium is a good high-temperature ALD precursor that deposits films of Ga2O 3 with low impurities and a good growth rate. The second section of this thesis focuses on two metal ALD systems. One major drawback of metal ALD systems is their inability to nucleate on many oxide surfaces. This greatly limits the applications of metal ALD for interconnects and flexible electrodes. The first emphasis is an on a new palladium ALD system using palladium (II) hexafluoroacetylaceonate (Pd(hfac)2) and formalin. FT-IR studies show that the Pd(hfac)2 dissociatively adsorbs, releasing free hfacH molecules that bind to Lewis acid sites on the alumina. The observed nucleation period of Pd is linked to surface poisoning by hfacH. In a related experiment, I use trimethylaluminum exposures to remove excess hfacH from the surface. Trimethylaluminum is able to ligand exchange an easier to remove methyl group with the surface hfacH, This treatment causes palladium to nucleate much more rapidly and deposit at lower temperatures. Finally, I examine ToRuS, a new precursor solution for Ru ALD. ToRuS, a solution of RuO4 in perfluoroethers, deposits ruthenium faster and at lower temperatures than all other Ru precursors. The mechanism for deposition and role of the perfluoroethers, however, is poorly understood. In the first study, I couple FT-IR spectroscopy with ab-initio calculations to identify the surface species formed when the perfluoroether solvent adsorbs on alumina. These surface species bind strongly to the alumina surface, creating a nonpolar, fluorinated layer. I then use these results to understand how ToRuS deposits Ru films. The fluorinated layer solvates RuO4, stabilizing it near the surface until it can be reduced by H2 gas. FT-IR and XPS analysis shows that the fluorinated layer does not leave carbonaceous impurities on the ruthenium surface or impedes metal deposition.

Goldstein, David Nathan

371

Surface Binding and Organization of Sensitizing Dyes on Metal Oxide Single Crystal Surfaces  

SciTech Connect

Even though investigations of dye-sensitized nanocrystalline semiconductors in solar cells has dominated research on dye-sensitized semiconductors over the past two decades. Single crystal electrodes represent far simpler model systems for studying the sensitization process with a continuing train of studies dating back more than forty years. Even today single crystal surfaces prove to be more controlled experimental models for the study of dye-sensitized semiconductors than the nanocrystalline substrates. We analyzed the scientific advances in the model sensitized single crystal systems that preceded the introduction of nanocrystalline semiconductor electrodes. It then follows the single crystal research to the present, illustrating both their striking simplicity of use and clarity of interpretation relative to nanocrystalline electrodes. Researchers have employed many electrochemical, photochemical and scanning probe techniques for studying monolayer quantities of sensitizing dyes at specific crystallographic faces of different semiconductors. These methods include photochronocoulometry, electronic spectroscopy and flash photolysis of dyes at potential-controlled semiconductor electrodes and the use of total internal reflection methods. In addition, we describe the preparation of surfaces of single crystal SnS2 and TiO2 electrodes to serve as reproducible model systems for charge separation at dye sensitized solar cells. This process involves cleaving the SnS2 electrodes and a photoelectrochemical surface treatment for TiO2 that produces clean surfaces for sensitization (as verified by AFM) resulting in near unity yields for electron transfer from the molecular excited dyes into the conduction band.

Parkinson, Bruce

2010-06-04

372

Surface modification of iron oxide nanoparticles and their conjuntion with water soluble polymers for biomedical application  

NASA Astrophysics Data System (ADS)

Superparamagnetic iron oxide nanoparticles (SPION) coated with suitable bio-compatible substances have been used in biomedicine, particularly in magnetic resonance imaging (MRI), tissue engineering, and hyperthermia and drug delivery. In this study, we describe the synthesis of SPION and its surface modification for in-vitro experiments. The particle diameter and structure were estimated by FESEM, TEM, XRD analyses. The saturation magnetization was characterized. SPION with a mean size of 12 nm have been prepared under N2 atmosphere, with support of natural polymeric starch, by controlling chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts ratios of Fe2+ and Fe3+. The surface of SPION-nanoparticles was treated with a coordinatable agent for higher dispersion ability in water and remaining the superparamagnetic behavior. The prepared iron oxide nanoparticles were coated with starch, dextran, PEG or MPEG to extend the application potential in the quite different engineering field of nano biomedicine.

Thanh Huong, Nguyen; Thi Kieu Giang, Lam; Thanh Binh, Nguyen; Minh, Le Quoc

2009-09-01

373

A novel ellipsometer for measuring thickness of oxide layer on the surface of silicon sphere  

NASA Astrophysics Data System (ADS)

The Avogadro constant NA is used as one of the several possible routes to redefinition of the kilogram in metrology today. Usually in order to accurately determine NA, the volume of a perfect single crystal silicon sphere of nearly 1 kg mass should be measured with a high relative uncertainty, i.e. about 1×10 -8. However, the oxide layer grown on the surface of the silicon sphere causes a remarkable systematic difference between the measured and real diameters. A novel ellipsometer has been developed to determine the thickness of the oxide layer accurately and automatically. The arrangement of this instrument is suitable for measuring the layer on the sphere surface. What's more, the measuring is faster by optimizing the parameters and developing the algorithm of calculating the thickness and refractive index of the oxide layer. The preliminary simulation result has present. Thus, the uncertainty of the diameter measurement caused by the oxide layer can be observably reduced. And the further improving of this ellipsometer is discussed in the end.

Zhang, Jitao; Li, Yan

2008-03-01

374

Silicon surface deoxidation using strontium oxide deposited with the pulsed laser deposition technique.  

PubMed

The epitaxial growth of functional oxides on silicon substrates requires atomically defined surfaces, which are most effectively prepared using Sr-induced deoxidation. The manipulation of metallic Sr is nevertheless very delicate and requires alternative buffer materials. In the present study the applicability of the chemically much more stable SrO in the process of native-oxide removal and silicon-surface stabilization was investigated using the pulsed-laser deposition technique (PLD), while the as-derived surfaces were analyzed in situ using reflection high-energy electron diffraction and ex situ using X-ray photoelectron spectroscopy, X-ray reflectivity, and atomic force microscopy. After the deposition of the SrO over Si/SiO2, in a vacuum, different annealing conditions, with the temperature ranging up to 850 °C, were applied. Because the deposition took place in a vacuum, a multilayer composed of SrO, Sr-silicate, modified Si, and Si as a substrate was initially formed. During the subsequent annealing the topmost layer epitaxially orders in the form of islands, while a further increase in the annealing temperature induced rapid desorption and surface deoxidation, leading to a 2 × 1 Sr-reconstructed silicon surface. However, the process is accompanied by distinctive surface roughening, and therefore the experimental conditions must be carefully optimized to minimize the effect. The results of the study revealed, for the first time, an effective pathway for the preparation of a SrO-induced buffer layer on a silicon substrate using PLD, which can be subsequently utilized for the epitaxial growth of functional oxides. PMID:25249034

Jovanovi?, Zoran; Spreitzer, Matjaž; Kova?, Janez; Klement, Dejan; Suvorov, Danilo

2014-10-22

375

Compositional Tuning of Ultrathin Surface Oxides on Metal and Alloy Substrates Using Photons: Dynamic Simulations and Experiments  

SciTech Connect

Oxide synthesis with controlled functional properties is desirable for a plethora of applications but is elusive due to oxide growth kinetics. Here, we report on the ability to modify the structure and composition of ultra-thin oxides grown on Ni-Al alloy surfaces at room temperature utilizing photon illumination. Atomistic simulations that take into account dynamic charge transfer predict that the electric field produced across an oxide film in photon-assisted synthesis overcomes the activation energy barrier for ionic migration, leading to enhanced oxidation kinetics and oxygen incorporation into the oxide, enabling us to control the oxide composition at atomic length scales. Experiments (near-edge x-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy) indicate that the native oxide on 5%Ni-Al alloy is primarily composed of aluminum oxide with no nickel oxide whereas the photon-assisted oxide comprises of both aluminum oxide and nickel oxide. The ability to tune the composition at the atomic scale of the ultra-thin oxide films leads to excellent passivity as verified from polarization experiments.

Chang, Chia-Lin; Sankaranarayanan, Subramanian; Ruzmetov, Dmitry; Engelhard, Mark H.; Kaxiras, Efthimios; Ramanathan, Shriram

2010-02-02

376

Oxidation mechanism of the ammonium-fluoride-treated Si(100) surface  

SciTech Connect

High-resolution electron energy loss (HREEL) spectroscopy, Auger electron spectroscopy, and low-energy electron diffraction have been employed to examine the initial oxidation stage of ammonium-fluoride-treated Si(100) surfaces exposed to air. The NH{sub 4}F treatment results in a hydrogen-terminated surface, as shown by the presence of the Si{endash}H stretch (2100 cm{sup {minus}1}), SiH{sub 2} scissor (910 cm{sup {minus}1}), and SiH bend (650 cm{sup {minus}1}) in the HREEL spectra. Initial oxidation on this surface occurs through oxygen insertion in the silicon backbonds, as indicated by the presence of the asymmetric bridge-bonded oxygen stretch in the region between 1060 and 1160 cm{sup {minus}1}. Oxygen is observed in both surface and bulk bridge-bonding sites for even the shortest air exposures, suggesting that initial oxygen uptake is not taking place in a layer-by-layer fashion. Auger electron spectroscopy shows a slow uptake of oxygen over the first few days of air exposure, followed by more rapid oxidation. Over the first two weeks of air exposure, the Si{endash}H stretch at 2100 cm{sup {minus}1} gradually disappears, accompanied by the appearance of oxygen backbonded Si{endash}H peaks around 2250 cm{sup {minus}1}. This behavior indicates that, despite the increase in oxygen uptake, the hydrogen termination remains intact, and further confirms that oxygen uptake occurs through insertion in the silicon backbonds. Water is found to play a significant role in the initial oxidation. {copyright} {ital 1996 American Institute of Physics.}

Kluth, G.J.; Maboudian, R. [Department of Chemical Engineering, University of California, Berkeley, California 94720 (United States)] [Department of Chemical Engineering, University of California, Berkeley, California 94720 (United States)

1996-11-01

377

Impact of aircraft and surface emissions of nitrogen oxides on tropospheric ozone and global warming  

Microsoft Academic Search

ACTUAL and potential increases in aircraft traffic are causing concern about the effects of aircraft exhaust emission on atmos-pheric chemistry. Model results1-3 and measurements4-6 in the Northern Hemisphere have shown that growth in surface emissions of nitrogen oxides and hydrocarbons leads to increases in concentration of tropospheric ozone. Tropospheric ozone is toxic to plants, humans and other organisms, and it

Colin Johnson; Jim Henshaw; Gordon McLnnes

1992-01-01

378

Surface conductivity of the single crystal aluminum oxide in vacuum and caesium vapors  

SciTech Connect

Results of measurements of surface conductivity of single-crystal aluminum oxide samples in vacuum and cesium vapors at T=620{endash}830 K and P{sub Cs}=0.13{endash}2 Pa are shown in the paper. Analysis of caesium vapor influence is carried out and ultimate characteristics of samples conductivity under operation conditions in thermionic nuclear power system (NPP) TFE are estimated. {copyright} {ital 1996 American Institute of Physics.}

Vasilchenko, A.V.; Izhvanov, O.L. [INERTEK (TOPAZ-2 Project), 901 University Blvd. SE, Albuquerque, New Mexico 87106-4439 (United States)

1996-03-01

379

Thermal desorption spectroscopy from the surfaces of metal-oxide-semiconductor nanostructures.  

PubMed

An experimental setup, which combines direct heating and temperature measurement of metal nanofilms allowing temperature programmed desorption experiments is described. This setup enables the simultaneous monitoring of the thermal desorption flux from the surface of chemi-electric devices and detection of chemically induced hot charge carriers under UHV conditions. This method is demonstrated for the case of water desorption from a Pt/SiO2-n-Si metal-oxide-semiconductor nanostructure. PMID:25362420

Meyburg, Jan Philipp; Nedrygailov, Ievgen I; Hasselbrink, Eckart; Diesing, Detlef

2014-10-01

380

Analysis of a conducting channel at the native zinc oxide surface  

Microsoft Academic Search

The electrical properties of high-resistivity zinc oxide (ZnO) bulk and epi-samples are strongly influenced by the sample ambient. Bulk samples that are highly resistive in ambient air can be reversibly transformed into a high conducting state under vacuum. As an explanation we suggest a conducting electron channel at the ZnO surface. Under vacuum this channel appears upon annealing. Exposure to

Oliver Schmidt; Arnd Geis; Peter Kiesel; Chris. G. Van de Walle; Noble M. Johnson; Andrey Bakin; Andreas Waag; Gottfried H. Döhler

2006-01-01

381

Thermal desorption spectroscopy from the surfaces of metal-oxide-semiconductor nanostructures  

NASA Astrophysics Data System (ADS)

An experimental setup, which combines direct heating and temperature measurement of metal nanofilms allowing temperature programmed desorption experiments is described. This setup enables the simultaneous monitoring of the thermal desorption flux from the surface of chemi-electric devices and detection of chemically induced hot charge carriers under UHV conditions. This method is demonstrated for the case of water desorption from a Pt/SiO2-n-Si metal-oxide-semiconductor nanostructure.

Meyburg, Jan Philipp; Nedrygailov, Ievgen I.; Hasselbrink, Eckart; Diesing, Detlef

2014-10-01

382

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

SciTech Connect

During the ninth quarter, 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. Scanning electron microscopy and energy dispersive X-ray analysis were done to characterize the morphology and composition of the surface of as-received coal, oxidized coal and coal pyrite. In addition, electrokinetic tests were done on Upper Freeport coal pyrite.

Doyle, F.M.

1992-01-01

383

Energy dependence of the trapping of uranium atoms by aluminum oxide surfaces  

NASA Technical Reports Server (NTRS)

The energy dependence of the trapping probability for sputtered U-235 atoms striking an oxidized aluminum collector surface at energies between 1 eV and 184 eV was measured. At the lowest energies, approximately 10% of the uranium atoms are not trapped, while above 10 eV essentially all of them stick. Trapping probabilities averaged over the sputtered energy distribution for uranium incident on gold and mica are also presented.

Librecht, K. G.

1979-01-01

384

Superhydrophobic surfaces using selected zinc oxide microrod growth on ink-jetted patterns.  

PubMed

The synthesis and properties of superhydrophobic surfaces based on binary surface topography made of zinc oxide (ZnO) microrod-decorated micropatterns are reported. ZnO is intrinsically hydrophilic but can be utilized to create hydrophobic surfaces by creating artificial roughness via microstructuring. Micron scale patterns consisting of nanocrystalline ZnO seed particles were applied to glass substrates with a modified ink-jet printer. Microrods were then grown on the patterns by a hydrothermal process without any further chemical modification. Water contact angle (WCA)(1) up to 153° was achieved. Different micro array patterned surfaces with varying response of static contact angle or sessile droplet analysis are reported. PMID:21109250

Myint, Myo Tay Zar; Kitsomboonloha, Rungrot; Baruah, Sunandan; Dutta, Joydeep

2011-02-15

385

Interactions of water, methanol and diethyl ether molecules with the surface of oxidized activated carbon  

NASA Astrophysics Data System (ADS)

Two samples of oxidized activated carbon of wood origin were used as adsorbents of water, methanol, and diethyl ether. Structural and chemical characteristics of the samples' surfaces were obtained using adsorption of nitrogen and Boehm titration. The adsorption isotherms of water and methanol were measured using a volumetric apparatus whereas the adsorption of diethyl ether was studied by means of inverse gas chromatography at finite concentration. Then the isotherms at three different temperatures were used to calculate the isosteric heats of adsorption. The results showed that the strength of interaction depends on the porosity of the sample and its surface chemistry. The effect of surface chemistry and the presence of oxygenated groups are predominant in the case of water and the least important in the case of diethyl ether. This is the result of the chemical nature of the molecules, their sizes, and the relative strengths of the dispersive interactions in small pores in comparison with hydrogen bonding to surface functional groups.

Salame, Issa I.; Bandosz, Teresa J.

386

Raman Spectroscopy as a Probe of Surface Oxides and Hydrides on Niobium  

SciTech Connect

Raman microscopy/spectroscopy has been used in conjunction with AFM, tunneling and magnetic susceptibility to identify surface oxides and hydrides on annealed, recrystallized foils of high purity Nb and on single crystals of cavity grade Nb. Cold worked regions of the Nb foil as well as rough regions near grain boundaries showed clear evidence of ordered hydride phases which were identified by VASP phonon calculations. Cold worked regions also displayed enhanced surface paramagnetism. Surface enhanced Raman spectra have also been obtained using 1.0 nm Au depositon. The SERS spectra reveal hydride molecular species which are not observable by conventional Raman. These results indicate that Raman is a useful probe of Nb surfaces relevant for cavity performance

J. Zasadzinski, B. Albee, S. Bishnoi, C. Cao, G. Ciovati, L.D. Cooley, D.C. Ford, Th. Proslier

2011-07-01

387

Noisy CO oxidation on Iridium(111) surfaces. Experiments explained by theory under realistic assumptions  

NASA Astrophysics Data System (ADS)

Noise is an everywhere phenomenon. Its influence could be described theoretically quite easily, but is hard to measure in an experiment. Catalytic reactions on surfaces can be described by nonlinear reaction-diffusion equations. For one of such surface reactions - CO oxidation on Iridium(111) surfaces - the probability distribution of CO2 rates around the mean value - showing the influence of noise - could be measured directly in a ultra high vacuum (UHV) experiment. This opens the way to address such a fundamental phenomenon like noise by all three modern methods of physics - experimental, computational and analytical. We show the measured effect of colored noise on a bistable surface reaction and explain all observations directly with the underlying theoretical description - the Langmuir-Hinshelwood reaction scheme - by solving the equations under realistic assumptions. It is a great pleasure to dedicate this work to Prof. Dr. Helmut R. Brand on the occasion of his 60th birthday.

Wehner, S.; Cisternas, J.; Descalzi, O.; Küppers, J.

2014-01-01

388

Solubility and Surface Adsorption Characteristics of Metal Oxides to High Temperature  

SciTech Connect

The interaction of high temperature aqueous solutions with mineral surfaces plays a key role in many aspects of fossil, geothermal and nuclear energy production. This is an area of study in which the subsurface geochemical processes that determine brine composition, porosity and permeability changes, reservoir integrity, and fluid flow rates overlap with the industrial processes associated with corrosion of metal parts and deposition of solids in pipes and on heat exchanger surfaces. The sorption of ions on mineral surfaces is also of great interest in both the subsurface and ''above ground'' regimes of power production, playing a key role in subsurface migration of contaminants (nuclear waste disposal, geothermal brine re-injection, etc.) and in plant operations (corrosion mitigation, migration of radioactive metals from reactor core to heat exchanger, etc.). In this paper, results of the solubility and surface chemistry of metal oxides relevant to both regimes are summarized.

D.J. Wesolowski; M.L. Machesky; S.E. Ziemniak; C. Xiao; D.A. Palmer; L.M. Anovitz; P. Benezeth

2001-05-04

389

Plastic deformation of a magnesium oxide 001-plane surface produced by cavitation  

NASA Technical Reports Server (NTRS)

An investigation was conducted to examine plastic deformation of a cleaved single-crystal magnesium oxide 001-plane surface exposed to cavitation. Cavitation damage experiments were carried out in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (2 mm) to the surface of the cleaved specimen. The dislocation-etch-pit patterns induced by cavitation were examined and compared with that of microhardness indentations. The results revealed that dislocation-etch-pit patterns around hardness indentations contain both screw and edge dislocations, while the etch-pit patterns on the surface exposed to cavitation contain only screw dislocations. During cavitation, deformation occurred in a thin surface layer, accompanied by work-hardening of the ceramic. The row of screw dislocations underwent a stable growth, which was analyzed crystallographically.

Hattori, S.; Miyoshi, K.; Buckley, D. H.; Okada, T.

1986-01-01

390

The binding of phosphonic acids at aluminium oxide surfaces and correlation with passivation of aluminium flake.  

PubMed

Measurements of adsorption isotherms of a series of thirteen mono- and di-phosphonic acids have shown that these bind strongly to the surface of high surface area aluminium trihydroxide. The incorporation of such phosphonates into a suspension of aluminium flake in an aqueous medium, modelling the continuous phase of a water-based paint, greatly suppresses the evolution of hydrogen. Whilst strong binding of the phosphonate to aluminium oxides is an essential criterion for good passivation, other factors such as the hydrophobicity of the ligand are also important in suppressing hydrogen-evolution. PMID:17372645

Cooper, Rachel J; Camp, Philip J; Henderson, David K; Lovatt, Paul A; Nation, David A; Richards, Stuart; Tasker, Peter A

2007-04-01

391

Analysis of surface potential and photocatalytic activity of Au-graphene oxide nanocomposites  

NASA Astrophysics Data System (ADS)

Surface potential of chemically synthesized graphene oxide (GO) and gold nanoparticles decorated GO (Au-GO) have been measured using scanning Kelvin probe (SKP) microscope. The Raman spectra of GO and Au-GO confirms presence of D and G peaks of GO. The intensity of both the peaks gets enhanced in case of Au-GO. The enhancement is due to surface enhanced Raman scattering (SERS) of GO. Such type of composite material has been used as a photocatalyst for degradation of Rhodamine B dye molecules. The degradation rate constant was found to be 1.6 × 10-2 min-1 in visible light.

Patel, Arun Singh; Mishra, Mukesh; Mohanty, T.

2014-04-01

392

Surface structures of (Hg, T1)-based oxides studied by high-resolution electron microscopy  

Microsoft Academic Search

Surface structures of the (Hg,T1)-based superconducting and related oxides were studied by high-resolution electron microscopy. The {100} planes of the 1201-type structure were found to be stable, and Hg0.5Tl0.5Ba2CuO5 showed a preferred atomic surface consisting of Ba layers. The {001} planes were also stable in HgTlBa2CuOx and TlBa2CaCu2O7. The present work indicates that the stable {100} planes of (Hg,Tl)-based superconducting

Takeo Oku; Satoru Nakajima

1998-01-01

393

Surface nanostructuring by ion-induced localized plasma expansion in zinc oxide  

SciTech Connect

Creation of hillock-like nanostructures on the surface of zinc oxide single crystals by irradiation with slow highly charged ions is reported. At constant kinetic energy, the nanostructures were only observed after irradiation with ions of potential energies above a threshold between 19.1?keV and 23.3?keV. The size of the nanostructures increases as a function of potential energy. A plasma expansion approach is used to explain the nanostructures creation. The calculations showed that the surface nanostructures became taller with the increase of ionic temperature. The influence of charged cluster formation and the relevance of their polarity are discussed.

El-Said, A. S., E-mail: elsaid@kfupm.edu.sa, E-mail: a.s.el-said@hzdr.de [Physics Department, King Fahd University of Petroleum and Minerals, Dhahran 31261 (Saudi Arabia); Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01328 Dresden (Germany); Physics Department, Faculty of Science, Mansoura University, 35516 Mansoura (Egypt); Moslem, W. M. [Department of Physics, Faculty of Science, Port Said University, Port Said 42521 (Egypt); Centre for Theoretical Physics, British University in Egypt (BUE), El-Shorouk City, Cairo (Egypt); Djebli, M. [Theoretical Physics Laboratory, Faculty of Physics USTHB, B.P. 32 Bab Ezzour, 16079 Algiers (Algeria)

2014-06-09

394

Oxidation resistance of 9-12% Cr steels: effect of rare earth surface treatment  

SciTech Connect

Medium Cr steels have been used in fossil fired power plants for many years because of their excellent high temperature stability and mechanical properties. The environment in a fossil fired power plant is extremely aggressive in terms of corrosion, especially oxidation. This is only accelerated as the operating temperature increases to 650C and beyond. For any new steel to be qualified for power plant use, in addition to adequate strength at the operating temperature, material wastage from all corrosion processes must be kept to a minimum acceptable level. The use of medium Cr steels provides a means to improve overall corrosion resistance. Three medium Cr are under development for use as high temperature power plant steels: 0.08C-(9-12)Cr-1.2Ni-0.7Mo-3.0Cu-3.0Co-0.5Ti. Oxidation tests were performed on the steels for times greater than 1000 hours in order to determine the oxidation kinetics and extent of material wastage. Also, rare earth oxides were incorporated into the outer surface layers of the steels to see if the oxidation resistance could be improved. These results will be compared to current power plant steels.

Dogan, Omer N.; Alman, David A.; Jablonski, Paul D.

2005-02-01

395

Recent advances in surface chemistry strategies for the fabrication of functional iron oxide based magnetic nanoparticles  

NASA Astrophysics Data System (ADS)

The synthesis of superparamagnetic nanostructures, especially iron-oxide based nanoparticles (IONPs), with appropriate surface functional groups has been intensively researched for many high-technological applications, including high density data storage, biosensing and biomedicine. In medicine, IONPs are nowadays widely used as contrast agents for magnetic resonance imaging (MRI), in hyperthermia therapy, but are also exploited for drug and gene delivery, detoxification of biological fluids or immunoassays, as they are relatively non-toxic. The use of magnetic particles in vivo requires IONPs to have high magnetization values, diameters below 100 nm with overall narrow size distribution and long time stability in biological fluids. Due to the high surface energies of IONPs agglomeration over time is often encountered. It is thus of prime importance to modify their surface to prevent aggregation and to limit non-specific adsorption of biomolecules onto their surface. Such chemical modifications result in IONPs being well-dispersed and biocompatible, and allow for targeted delivery and specific interactions. The chemical nature of IONPs thus determines not only the overall size of the colloid, but also plays a significant role for in vivo and in vitro applications. This review discusses the different concepts currently used for the surface functionalization and coating of iron oxide nanoparticles. The diverse strategies for the covalent linking of drugs, proteins, enzymes, antibodies, and nucleotides will be discussed and the chemically relevant steps will be explained in detail.

Turcheniuk, Kostiantyn; Tarasevych, Arkadii V.; Kukhar, Valeriy P.; Boukherroub, Rabah; Szunerits, Sabine

2013-10-01

396

Recent advances in surface chemistry strategies for the fabrication of functional iron oxide based magnetic nanoparticles.  

PubMed

The synthesis of superparamagnetic nanostructures, especially iron-oxide based nanoparticles (IONPs), with appropriate surface functional groups has been intensively researched for many high-technological applications, including high density data storage, biosensing and biomedicine. In medicine, IONPs are nowadays widely used as contrast agents for magnetic resonance imaging (MRI), in hyperthermia therapy, but are also exploited for drug and gene delivery, detoxification of biological fluids or immunoassays, as they are relatively non-toxic. The use of magnetic particles in vivo requires IONPs to have high magnetization values, diameters below 100 nm with overall narrow size distribution and long time stability in biological fluids. Due to the high surface energies of IONPs agglomeration over time is often encountered. It is thus of prime importance to modify their surface to prevent aggregation and to limit non-specific adsorption of biomolecules onto their surface. Such chemical modifications result in IONPs being well-dispersed and biocompatible, and allow for targeted delivery and specific interactions. The chemical nature of IONPs thus determines not only the overall size of the colloid, but also plays a significant role for in vivo and in vitro applications. This review discusses the different concepts currently used for the surface functionalization and coating of iron oxide nanoparticles. The diverse strategies for the covalent linking of drugs, proteins, enzymes, antibodies, and nucleotides will be discussed and the chemically relevant steps will be explained in detail. PMID:24091568

Turcheniuk, Kostiantyn; Tarasevych, Arkadii V; Kukhar, Valeriy P; Boukherroub, Rabah; Szunerits, Sabine

2013-11-21

397

A Slightly Oxidizing Etchant for Polishing of CdTe and CdZnTe Surfaces  

NASA Astrophysics Data System (ADS)

New iodine-evolving etching solutions were developed for surface treatment of CdTe and CdZnTe crystals. The nature of the chemical dissolution of CdTe samples with (100), (110), and (111) orientations, and also of (211) Cd0.96Zn0.04Te samples, in KIO3-KI-lactic acid solution was studied. It was established that this dissolution is diffusion controlled. Surface roughness measurements revealed highly polishing properties of the etchant. A study of the chemical composition and structure of the (211)B Cd0.96Zn0.04Te surfaces etched under different conditions was carried out. The thickness of the Te oxide layer was evaluated in the course of heating in vacuum. KIO3-KI-lactic acid treatment appears to be preferable in terms of elimination of Te oxides from the surface as compared with standard Br2-methanol solution. The etching compositions were shown to be useful for chemical polishing of CdTe-based surfaces.

Ivanits'ka, V. G.; Moravec, P.; Tomashik, V. M.; Mašek, K.; Tomashik, Z. F.; Franc, J.; Grill, R.; Höschl, P.

2013-11-01

398

Atomistic and electronic structure calculation of defects at the surfaces of oxides  

NASA Astrophysics Data System (ADS)

We present the results of simulations using both atomistic and density functional theory (DFT) approaches that illustrate the uses of these techniques for investigating the structure and electronic structure of defects at the surfaces of oxides. Atomistic simulation studies of the low index surfaces of spinel (MgAl2O4) will show the role of vacancy configuration and surface rearrangement. Atomistic and DFT studies on Li doped MgO illustrate the importance of both the defect structure and its effect of morphology. We will also illustrate using DFT electronic defects at the surface of CeO2 , which are of great importance in redox reactions and catalytic activity. Finally we will present a novel atomistic approach for predicting the structure of supported oxide nanoclusters giving rise to a wide range of defects including a range of surface terminations, grain formation, mixed screw edge dislocations and misfit dislocations. We will illustrate this using the structure of a BaO supported MgO nanocluster.

Watson, G. W.

399

From novel PtSn/Pt(110) surface alloys to SnOx/Pt(110) nano-oxides  

NASA Astrophysics Data System (ADS)

UHV evaporation of Sn on (1 × 2) Pt(110), followed by UHV annealing, provides three different PtSn/Pt(110) surface alloys, each characterized by a specific low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) pattern. When annealed in a controlled oxygen background, the PtSn/Pt(110) surface alloys can be transformed into SnOx/Pt(110) nano-oxides. This paper reports the experimental phase diagram of the metallic and oxidized surface superstructures. PtSn surface alloys prepared by Sn evaporation in UHV and annealing on Pt(110) SnOx nano-oxides by thermal treatment of surface alloys in an oxygen background LEED and STM reported for each different phases Surface roughening is obtained after surface alloy preparation.

Zheng, Jian; Agnoli, Stefano; Artiglia, Luca; Sedona, Francesco; Di Marino, Marco; Sambi, Mauro; Granozzi, Gaetano

2013-09-01

400

Cell surface characteristics enable encrustation-free survival of neutrophilic iron-oxidizing bacteria  

NASA Astrophysics Data System (ADS)

Microbial growth in mineralizing environments depends on the cells' ability to evade surface precipitation. Cell-mineral interactions may be required for metabolism, but if unmoderated, cells could become encrusted, which would limit diffusion of nutrients and waste across cell walls. A combination of cell surface charge and hydrophobicity could enable the survival of microbes in such environments by inhibiting mineral attachment. To investigate this mechanism, we characterized the surfaces of two neutrophilic iron-oxidizing bacteria (FeOB): Mariprofundus ferrooxydans, a Zetaproteobacterium from Fe(II)-rich submarine hydrothermal vents and a Betaproteobacterium Gallionellales strain R-1, recently isolated from a ferrous groundwater seep. Both bacteria produce iron oxyhydroxides, yet successfully escape surface encrustation while inhabiting milieu where iron minerals are also produced by abiotic processes. SEM-EDX and TEM-EELS analyses of cultured bacteria revealed no iron on the cell surfaces. Zeta potential measurements showed that these bacteria have very small negative surface charge (0 to -4 mV) over a pH range of 4-9, indicating near-neutrally charged surfaces. Water contact angle measurements and thermodynamic calculations demonstrate that both bacteria and abiotically-formed Fe oxhydroxides are hydrophilic. Extended-DLVO calculations showed that hydrophilic repulsion between cells and minerals dominates over electrostatic and Lifshitz-van der Waals interactions. This leads to overall repulsion between microbes and minerals, thus preventing surface encrustation. Low surface charge and hydrophilicity (determined by microbial adhesion to hydrocarbon assay) were common features for both live and azide-inhibited cells, which shows that surface characteristics do not depend on active metabolism. It is remarkable that these two phylogenetically-distant bacteria from different environments employ similar adaptations to prevent surface mineralization. Our results confirm that surface characteristics can be a mechanism for survival in mineralizing environments. We predict that biotechnological applications such as bioremediation and microbial mineral carbon sequestration will benefit from microbes that can similarly avoid encrustation.

Saini, G.; Chan, C. S.

2011-12-01

401

Highly active surfaces for CO oxidation on Rh, Pd, and Pt  

NASA Astrophysics Data System (ADS)

Studies show that the rate of CO oxidation on Pt-group metals at temperatures between 450 and 600 K and pressures between 1 and 300 Torr increases markedly with an increase in the O 2/CO ratio above 0.5. The catalytic surfaces, formed at discrete O 2/CO ratios >0.5, exhibit rates 2-3 orders of magnitude greater than those rates observed for stoichiometric reaction conditions and similar reactant pressures or previously in ultrahigh vacuum studies at any reactant conditions and extrapolate to the collision limit of CO in the absence of mass transfer limitations. The O 2/CO ratios required to achieve these so-called "hyperactive" states (where the reaction probabilities of CO are thought to approach unity) for Rh, Pd, and Pt relate directly to the adsorption energies of oxygen, the heats of formation of the bulk oxides, and the metal particle sizes. Auger spectroscopy and X-ray photoemission spectroscopy reveal that the hyperactive surfaces consist of approximate 1 ML of surface oxygen. In situ polarization modulation reflectance absorption infrared spectroscopy measurements coupled with no detectable adsorbed CO. In contrast, under stoichiometric O 2/CO conditions and similar temperatures and pressures, Rh, Pd, and Pt are essentially saturated with chemisorbed CO and exhibit far less activity for CO oxidation.

Chen, M. S.; Cai, Y.; Yan, Z.; Gath, K. K.; Axnanda, S.; Goodman, D. Wayne

2007-12-01

402

Reactive molecular dynamics study of chloride ion interaction with copper oxide surfaces in aqueous media.  

PubMed

Using reactive force-field (ReaxFF) and molecular dynamics simulation, we study atomistic scale chloride ion adsorption and transport through copper oxide thin films under aqueous conditions. The surface condition of passive oxide film plays a key role in chloride ion adsorption and facilitates initial adsorption when surface corrosion resistance is low. Using implemented surface defects, the structural evolution of the copper oxide film from thinning to breakdown is investigated. In addition to chemical thinning of passive film, extended defects in the metal substrate are observed, at high concentration of adsorbed chloride ions. The initial stage of breakdown is associated with rapid depletion of adjacent chloride ions, which creates a locally deficient environment of chloride ions in the solution. The dissolved copper cations gain higher charge upon interaction with chloride ions. Owing to the increased Coulomb interactions resulted from dissolved copper ions and locally low density of chloride ions, far-field chloride ions would diffuse into the local corrosion sites, thereby promoting further corrosion. PMID:22373345

Jeon, Byoungseon; Sankaranarayanan, Subramanian K R S; van Duin, Adri C T; Ramanathan, Shriram

2012-03-01

403

Evaluation of springtime nitrogen oxide and oxidant data from a suburban/rural northeast USA surface site. [PRECP  

SciTech Connect

Full characterization of the air chemistry (gases, particles and meteorology) was accomplished for a rural site in Bucks County, PA during April 1985, in connection with PRECP field experiments. Data from continuous monitoring of nitrogen oxides (NO/sub y/), nitric acid, ozone and SO/sub 2/ are used in this evaluation along with PAN analyses every 30 min, meteorological data from surface observations and a single theodolite radiosonde system, and selected aerosol compositions and gaseous aldehyde data. Limited precipitation composition data from a manual sequential sampler is available including common ions, dissolved SO/sub 2/ and H/sub 2/O/sub 2/. Correlation matrices, averaged diurnal trends, and pollution roses will be presented indicating strong relationships between ozone and the secondary nitrogen oxide species, HNO/sub 3/ and PAN. Periods of impact from the greater Philadelphia and New York source regions can be identified from NO/sub y/ and SO/sub 2/ data, but anticyclonic flow in aged air masses advected from the west resulted in the major importation of secondary nitrogen(V) and sulfur(VI) species (HNO/sub 3/, PAN and aerosol sulfate) to this site. 16 refs.

Tanner, R.L.; Roberts, J.M.; Gaffney, J.S.; Sisterson, D.L.

1988-03-01

404

Electric double layer at metal oxide surfaces: Static properties of the cassiterite - Water Interface  

SciTech Connect

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively charged variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).

Vlcek, Lukas [ORNL; Zhang, Zhan [Argonne National Laboratory (ANL); Machesky, Michael L. [Illinois State Water Survey, Champaign, IL; Wesolowski, David J [ORNL

2007-04-01

405

Electric double layer at metal oxide surfaces:static properties of the cassiterite-water interface.  

SciTech Connect

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively charged variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).

Vlcek, L.; Zhang, Z.; Machesky, M .L.; Fenter, P.; Rosenqvist, J.; Wesolowski, D. J.; Anovitz, L. M.; Predota, M.; Cummings, P. T.; Vanderbilt Univ.; ORNL; Univ. of South Bohimia; Illinois State Water Survey

2007-03-24

406

Stability of phosphonic acid self-assembled monolayers on amorphous and single-crystalline aluminum oxide surfaces in aqueous solution.  

PubMed

The formation of octadecylphosphonic acid (ODPA) self-assembled monolayers (SAMs) and their stability in water has been studied on four distinctly different aluminum oxide surfaces. The aim was to improve the understanding of the state of binding between the phosphonic acid to the oxide surface and how this interaction depends on the structure and termination of the oxide surface. Single crystalline Al(2)O(3)(0001) and Al(2)O(3)(1102) surfaces were compared to amorphous oxide passive films on aluminum and physical vapor deposited (PVD) amorphous aluminum oxide films on gold. The monolayers were adsorbed from ethanol solution, characterized by means of high-resolution in situ atomic force microscopy (AFM), contact angle measurements, polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and proved to be self-assembled. On Al(2)O(3)(1102) surfaces and amorphous Al(2)O(3) surfaces, the ODPA self-assembled monolayers showed high stability in aqueous environments. However, the adsorbed ODPA monolayers were substituted by the adsorption of interfacial water on the Al(2)O(3)(0001) surface via the intermediate formation of micelles. The different stability of the monolayers in aqueous environments is explained by the variation of interfacial binding states ranging from ionic interactions between phosphonate groups and the positively charged hydrolytated oxide surface to directed coordination bonds between the phosphonate group and Al ions. PMID:20000361

Thissen, Peter; Valtiner, Markus; Grundmeier, Guido

2010-01-01

407

High temperature steam oxidation of Al3Ti-based alloys for the oxidation-resistant surface layer on Zr fuel claddings  

NASA Astrophysics Data System (ADS)

We investigated the feasibility to apply Al3Ti-based alloys as the surface layer for improving the oxidation resistance of Zr fuel claddings under accident conditions. Two types of Al3Ti-based alloys with the compositions of Al-25Ti-10Cr and Al-21Ti-23Cr in atomic percent were prepared by arc-melting followed by homogenization annealing at 1423 K for 48 h. Al-25Ti-10Cr alloy showed an L12 quasi-single phase microstructure with a lot of needle-shaped minor phase and pores. Al-21Ti-23Cr alloy consisted of an L12 matrix and Cr2Al as the second phase. Al3Ti-based alloys showed an extremely low oxidation rate in a 1473 K steam for up to 7200 s when compared to Zircaloy-4. Both alloys exhibited almost the same oxidation rate in the early stage of oxidation, but Al-25Ti-10Cr showed a little lower oxidation rate after 4000 s than Al-21Ti-23Cr. The difference in the oxidation rate between two types of Al3Ti-based alloys was too marginal to distinguish the oxidation behavior of each alloy. The resultant oxide exhibited almost the same characteristics in both alloys even though the microstructure was explicitly distinguished from each other. The crystal structure of the oxide formed up to 2000 s was identified as Al2O3 in both alloys. The oxide morphology consisted of columnar grains whose length was almost identical to the average oxide thickness. On the basis of the results obtained, it is considered that Al3Ti-based alloy is one of the promising candidates for the oxidation-resistant surface layer on Zr fuel claddings.

Park, Jeong-Yong; Kim, Il-Hyun; Jung, Yang-Il; Kim, Hyun-Gil; Park, Dong-Jun; Choi, Byung-Kwon

2013-06-01

408

Anaerobic methane oxidation may be more prevalent in surface soils than was originally thought  

NASA Astrophysics Data System (ADS)

Anaerobic oxidation of methane (CH4) (AOM) is a process that was first reported to occur in deep anoxic marine sediments. In this environment, CH4 is oxidized with sulphate (SO42-) as the terminal electron acceptor. It is mediated by a syntrophic consortium formed by SO42- reducing bacteria and anaerobic CH4 oxidizing Archaea, or by the latter alone. Since this landmark discovery, AOM was found to occur in other environments including freshwater lake sediments and water columns, mud volcanoes, landfill leachate, deep buried Holocene sediments and hydrocarbon contaminated aquifers. All of these situations are very specific and point to AOM as being primarily occurring in highly reducing conditions. Thus, observations of AOM in surface soils with fluctuating REDOX conditions are relatively scarce, although a few independent studies have reported AOM in surface peatlands as well as in a forest soil. Furthermore, AOM may follow different pathways, such as via the coupled oxidation of CH4 and reduction of manganese (Mn(IV)) or iron (Fe(III)), or by a lone denitrifying species that converts nitrite to nitric oxide in order to generate O2 that is then used internally to oxidize CH4. Thus, the goal of our study was to determine whether AOM is more prevalent than was thought in hydromorphic surface soils across different environments, and whether the addition of NO3- or SO4= as alternative electron acceptors may stimulate the process. We collected samples from 3 peatland soils in Scotland, 2 acid-sulphate soils in Finland, and shore sediments of 15 drained fish ponds in the Czech Republic. Subsamples were incubated in the absence of O2 and amended with either NO3-, SO42-, or left unamended (control). The net flux of CH4 and CO2 were assessed by gas chromatography after 2, 20, 40 and 60 days. We also used a 13C-CH4 isotope dilution technique to determine gross production and consumption rates of CH4. We detected AOM in all of our soils, with oxidation rates ranging between 0.001 and 37.28 nmol g-1 day-1, suggesting that AOM may be more ubiquitous than was originally thought. On the other hand, no clear patterns emerged as to the effects of NO3- or SO42- amendments on this process.

Gauthier, Mathieu; Bradley, Robert L.; Šimek, Miloslav

2013-04-01

409

As(V) and As(III) reactions on pristine pyrite and on surface-oxidized pyrite.  

PubMed

Reactions of As(III) and As(V) with pyrite were investigated using pristine pyrite (produced and reacted in a rigorously anoxic environment with P(O2)<10(-8)atm) and using surface-oxidized pyrite (produced under anoxic conditions, exposed to air, then stored and reacted under ri