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1

Surface studies of zinc oxide growth on Cu(110)  

NASA Astrophysics Data System (ADS)

Submonolayers to multilayers of zinc and oxygen deposited in UHV on Cu(110) were characterized by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and temperature programmed desorption (TPD) of CO, CO 2 and zinc. Carbon monoxide adsorbs will on copper at 150 K but only poorly on the oxides of copper and zinc. Carbon dioxide adsorbs on zinc oxide at 150 K but not on copper or oxidized copper. We used a combination of CO and CO 2 adsorption to follow the initial growth of two-dimensional ZnO x islands and the effect of heat and oxygen treatments on these two-dimensional islands. It is shown that heating above 300 K leads irreversibly to three-dimensional islands formation.

Fu, Sabrina S.; Somorjai, Gabor A.

1990-11-01

2

Anisotropic electric surface resistance of Cu(110)  

SciTech Connect

The electric surface resistance is measured without contacts by grazing incidence of p-polarized infrared (IR) radiation for the adsorbates CO and C{sub 2}H{sub 4}, which settle on top of the close packed atomic ridges of Cu(110) in the <1, -1, 0> direction. Surface resistance has only been observed for the IR electric currents in this direction. This can be explained by the assumption that IR induced currents in the <001> direction can only flow in the second and deeper layers of Cu(110). Therefore, in this direction, there is no friction with the adsorbates and hence no surface resistance.

Otto, A. [Institut f?r Physik der kondensierte Materie, Universit?t D?sseldorf D-40225, Germany; Lilie, P. [Synchrotron SOLEIL; Dumas, P. [Synchrotron SOLEIL; Hirschmugl, C. [University of Wisconsin-Milwaukee; Pilling, M. [University of Wisconsin-Milwaukee; Williams, Gwyn P. [JLAB

2007-08-01

3

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

4

Surface morphology after low coverage Pt deposition on Cu(110)  

NASA Astrophysics Data System (ADS)

The morphology of a Cu(110) surface after low coverage Pt atom deposition from the vapour phase is studied with thermal energy atom scattering (TEAS) in the temperature range of 200-800 K. Both cross section measurements and diffraction analysis reveal different structures. At low temperatures, isolated defects containing a metal adatom are observed. Between 350 and 650 K, experimental results suggest that these aggregates are dissociated, leaving behind them an almost flat surface patch with an incorporated Pt atom. Above 650 K, bulk dissolution of Pt occurs.

Hugenschmidt, Markus B.; de Beauvais, Christophe

1994-04-01

5

First principles study of properties of the oxidized Cu(100) and Cu(110)  

NASA Astrophysics Data System (ADS)

Copper based catalysts are of importance to a number of industrial processes including the synthesis of methanol, the reduction and decomposition of nitrogen oxides, and treatment of waste water. In copper catalysis surface oxidation and oxidic overlayers are believed to play a crucial role. In this work using density functional theory (DFT) within the generalized gradient approximation (GGA) we have studied the stability and associated electronic properties of the oxidized Cu(100) and Cu(110) surfaces. Especially, we have focused on studies of changes in the interlayer spacing, electron work function, binding energy, and density of states with oxygen coverage. We have examined the cases of various oxygen coverages of the non-reconstructed, missing row reconstructed Cu(100), and added row reconstructed Cu (110) surfaces. The first-principles calculations in this work have been performed using DMOl3 code. The obtained theoretical results have been compared with available experimental data.

Olenga, Antoine

6

Self-assembly of a halogenated molecule on oxide-passivated Cu(110).  

PubMed

The supramolecular self-assembly of brominated molecules was investigated and compared on Cu(110) and Cu(110)-O(2×1) surfaces under ultrahigh vacuum. By using scanning tunnelling microscopy, we show that brominated molecules form a disordered structure on Cu(110), whereas a well-ordered supramolecular network is observed on the Cu(110)-O(2×1) surface. The different adsorption behaviors of these two surfaces are described in terms of weakened molecule-substrate interactions on Cu(110)-O(2×1) as opposed to bare Cu(110). The effect of oxygen-passivation is to suppress debromination and it can be a convenient approach for investigating other self-assembly processes on copper-based substrates. PMID:23757211

El Garah, Mohamed; Lipton-Duffin, Josh; MacLeod, Jennifer M; Gutzler, Rico; Palmino, Frank; Luzet, Vincent; Chérioux, Frédéric; Rosei, Federico

2013-08-01

7

Growth of thin Fe/Fe2O3 films on the Cu(110) surface  

NASA Astrophysics Data System (ADS)

The growth of Fe/Fe-oxide double-layers on Cu(110) was studied with thermal energy atom scattering (TEAS), Auger electron spectroscopy, and low-energy electron diffraction (LEED). An iron film with a thickness of about 0.6 nm was evaporated at low temperature (130 K) on a smooth, well-ordered thin film of Fe2O3 prepared on Cu(110). This Fe film is disordered. Ordering of the film was observed at temperatures between 400 and 600 K. At 530 K, a structure corresponding to that of a well-ordered ?-Fe(001) surface was observed with TEAS and LEED. Clear evidence was found for a mixing of the Fe and Fe2O3 layers at the interface, already beginning at the deposition temperature of 130 K. With increasing temperature, the mixing of the Fe and Fe2O3 layers became gradually more effective until, at around 600 K, it was essentially completed. Upon annealing the sample to 1000 K the structure of the film changes and a very thin (less than 2 ML) FeO film on top of the Cu(110) surface is obtained.

Pflitsch, Christian; David, Rudolf; Verheij, Laurens K.; Franchy, René

2001-08-01

8

Interaction of Helium with a Metal Surface: Determination of Corrugation Profile of Cu(110)  

NASA Astrophysics Data System (ADS)

Starting from a microscopic description of the interaction of a helium atom with a metal surface, a simple approximate result is derived which shows that the lateral corrugation of the repulsive potential decreases exponentially with distance z from the surface. For Cu(110) this theory leads to an interaction potential that reproduces all the observed bound states and gives a quantitative fit of recent helium diffraction data taken at various incident energies and angles.

Harris, J.; Liebsch, A.

1982-08-01

9

Domain-wall pinning in uniaxial phases of Pb adlayers on a Cu(110) surface  

NASA Astrophysics Data System (ADS)

Submonolayers of Pb adsorbed on the Cu(110) surface form a series of uniaxial commensurate phases. We report the results of synchrotron x-ray scattering studies of the global phase behavior of this chemisorption system. We observe a floating-incommensurate to soliton-glass phase transition due to domain-wall pinning. The nature of this transition and other novel features revealed in this study are discussed in the context of current theories for strong adlayer systems.

Liang, K. S.; D'amico, K. L.; Lee, C. H.; Sheu, E. Y.

1990-12-01

10

LETTER TO THE EDITOR: Contrasting reaction pathways in methanol oxidation on Cu(110) studied by STM  

NASA Astrophysics Data System (ADS)

Scanning tunnelling microscopy (STM) has been employed in studying the adsorption and reaction of methanol and oxygen on Cu(110) during co-dosing. We have observed the production of formate c0953-8984/8/49/008/img1 and 0953-8984/8/49/008/img2 structures at 300 K during co-dosing. This strongly contrasts with the established case of sequential dosing, since oxygen 0953-8984/8/49/008/img3 precovered Cu(110) surfaces are seen to have negligible activity toward formate production when subsequently dosed with methanol. During co-dosing formate and methoxy groups are seen as the main reaction products while oxygen 0953-8984/8/49/008/img3 reconstructed areas poison the formate production channel. Competition for isolated oxygen adatoms between the O 0953-8984/8/49/008/img3 islands and methoxy groups is seen as determining the rate of formate production. Methanol rich gas mixtures have the highest efficiency for formate production whereas an oxygen rich gas phase composition does not produce formate due to preferential growth of O 0953-8984/8/49/008/img3 islands.

Poulston, S.; Jones, A. H.; Bennett, R. A.; Bowker, M.

1996-12-01

11

Thermally and Vibrationally Induced Tautomerization of Single Porphycene Molecules on a Cu(110) Surface  

NASA Astrophysics Data System (ADS)

We report the direct observation of intramolecular hydrogen atom transfer reactions (tautomerization) within a single porphycene molecule on a Cu(110) surface by scanning tunneling microscopy. It is found that the tautomerization can be induced via inelastic electron tunneling at 5 K. By measuring the bias-dependent tautomerization rate of isotope-substituted molecules, we can assign the scanning tunneling microscopy-induced tautomerization to the excitation of specific molecular vibrations. Furthermore, these vibrations appear as characteristic features in the dI/dV spectra measured over individual molecules. The vibrational modes that are associated with the tautomerization are identified by density functional theory calculations. At higher temperatures above ˜75K, tautomerization is induced thermally and an activation barrier of about 168 meV is determined from an Arrhenius plot.

Kumagai, Takashi; Hanke, Felix; Gawinkowski, Sylwester; Sharp, John; Kotsis, Konstantinos; Waluk, Jacek; Persson, Mats; Grill, Leonhard

2013-12-01

12

Many-body interactions and Rashba splitting of the surface state on Cu(110)  

NASA Astrophysics Data System (ADS)

Using high-resolution angle-resolved photoemission spectroscopy, we elucidate the Rashba splitting of ?kF=0.003 Å-1 near the Fermi level (EF) in the Shockley surface state of Cu(110) at the Y ¯ point of the surface Brillouin zone. The observed energy-band dispersion exhibits a kink structure at ˜-20 meV, which is a clear indication of band renormalization caused by an electron-phonon interaction. The electron-phonon coupling parameter is found to be ?ep=0.17±0.02 based on the experimentally obtained real part of the self-energy. First-principle calculations yield ?ep=0.160 and ?kF=0.004 Å-1 at EF, which are fully consistent with the experimental results. In addition, the contributions of the electron-electron and electron-phonon interactions to the linewidth of the surface state at the Y ¯ point are experimentally determined to be ?ee˜9 meV and ?ep˜7 meV, respectively. We demonstrate that the Rashba splitting must be resolved by photoemission line-shape analysis for an accurate determination of the electron self-energy and coupling parameters.

Jiang, J.; Tsirkin, S. S.; Shimada, K.; Iwasawa, H.; Arita, M.; Anzai, H.; Namatame, H.; Taniguchi, M.; Sklyadneva, I. Yu.; Heid, R.; Bohnen, K.-P.; Echenique, P. M.; Chulkov, E. V.

2014-02-01

13

Detection of disorder at a Cu(110) single-crystal surface by the use of ion scattering spectroscopy  

NASA Astrophysics Data System (ADS)

Impact Collision Ion Scattering Spectroscopy (ICISS) studies involving 3 keV 6Li + scattered from Cu(110) have demonstrated the existence of a disordered surface layer of Cu atoms on samples that displayed a sharp Low Energy Electron Diffraction (LEED) pattern. Additional annealing did not affect the LEED pattern, but the ICISS polar scans changed significantly until an ordered surface was achieved. The experimental data agreed quantitatively with Monte-Carlo calculations for scattering from the ordered surface. The calculations also demonstrated how disorder affects ICISS polar scans.

Yarmoff, Jory A.; Stanley Williams, R.

1986-01-01

14

Detection of disorder at a Cu(110) single-crystal surface by the use of ion scattering spectroscopy  

NASA Astrophysics Data System (ADS)

Impact Collision Ion Scattering Spectroscopy (ICISS) studies involving 3 keV 6Li + scattered from Cu(110) have demonstrated the existence of a disordered surface layer of Cu atoms on samples that displayed a sharp Low Energy Electron Diffraction (LEED) pattern. Additional annealing did not affect the LEED pattern, but the ICISS polar scans changed significantly until an ordered surface was achieved. The experimental data agreed quantitatively with Monte-Carlo calculations for scattering from the ordered surface. The calculations also demonstrated how disorder affects ICISS polar scans.

Yarmoff, Jory A.; Williams, R. Stanley

15

Adsorbate-induced surface stress and self-assembly of (2×1) O on Cu(110) measured with an STM  

NASA Astrophysics Data System (ADS)

The formation of the (2×1) oxygen stripe phase on Cu(110) at room temperature is imaged in situ with an STM and simultaneously a quantitative determination of the oxygen-induced surface stress is accomplished. The bending bar technique is utilized with the bending measured by the STM. We find that the difference ?? of the surface stresses of the (2×1)O phase on Cu(110) and the clean Cu(110) surface is compressive for both directions, which is in accordance with the adsorption of oxygen on other surfaces. The stress depends significantly on the coverage. Quantitative aspects of these results raise an interesting issue concerning the applicability of the Marchenko-Alerhand continuum model for the self-assembly of the stripe phase.

Bombis, Ch.; Moiseeva, M.; Ibach, H.

2005-12-01

16

Structural and vibrational properties of added-row reconstructions on O/Cu(110) and O/Ag(110) surfaces  

NASA Astrophysics Data System (ADS)

The geometry and vibrational frequency of (2×1) and (4×1) reconstructed structures of O/Cu(110) and O/Ag(110) systems have been calculated using a first-principles method. The calculated frequency shift between (2×1) and (4×1) is ca 1 meV on both copper and silver surfaces, being consistent with experimental values obtained so far. In contrast to a prediction by Schimizu and Tsukada [Surf. Sci. 295 (1993) L1017], we have found that the difference in the local structure between (2×1) and (4×1) is considerably small, indicating surface stress plays only a minor role in the frequency shift of oxygen vibration. The estimated effective charge on oxygen atom is consistent with the HREELS value reported by Vattuone et al. [Surf. Sci. 369 (1996) 336].

Katagiri, H.; Uda, T.; Terakura, K.

1999-04-01

17

C60/corannulene on Cu(110): a surface-supported bistable buckybowl-buckyball host-guest system.  

PubMed

Corannulene (COR) buckybowls were proposed as near ideal hosts for fullerene C60, but direct complexation of C60 and COR has remained a challenge in supramolecular chemistry. We report the formation of surface-supported COR-C60 host-guest complexes by deposition of C60 onto a COR lattice on Cu(110). Variable-temperature scanning tunneling microscopy studies reveal two distinctly different states of C60 on the COR host lattice, with different binding energies and bowl-ball separations. The transition from a weakly bound precursor state to a strongly bound host-guest complex is found to be thermally activated. Simple model calculations show that this bistability originates from a subtle interplay between homo- and heteromolecular interactions. PMID:18338886

Xiao, Wende; Passerone, Daniele; Ruffieux, Pascal; Aït-Mansour, Kamel; Gröning, Oliver; Tosatti, Erio; Siegel, Jay S; Fasel, Roman

2008-04-01

18

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

SciTech Connect

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

Ma Qiang; Zaera, Francisco [Department of Chemistry, University of California, Riverside, California 92521 (United States)

2013-01-15

19

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

SciTech Connect

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

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

2012-01-15

20

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

21

Chemisorption of Guanine on Cu(110)  

NASA Astrophysics Data System (ADS)

We use density functional theory (PBE) to calculate the adsorption of a guanine molecule on Cu(110). At saturation coverage, guanine adsorbs tilted with the oxygen atom strongly bound to one of the surface atoms at a height of 2.12 å above this surface atom with a binding energy of 430 meV/molecule. The substrate top layer atoms show a buckling of 0.22 å , while the molecule experiences a twist from the flat configuration in the gas phase. The dz^2 state of the copper atom -that is bound to the oxygen atom- presents an enhancement in its density near the Fermi level. We calculated a drop in the work function of 0.34 eV upon adsorption of guanine on Cu(110). These effects classify this system as chemisorption.

Matos, Jeronimo; Kara, Abdelkader

2011-03-01

22

Chemisorption of Anthracene on Cu(110)  

NASA Astrophysics Data System (ADS)

We use density functional theory (PBE) to calculate the adsorption of an Anthracene molecule on Cu(110). Anthracene adsorbs at a height of 2 å above the surface and has a binding energy of 562 meV/molecule. We also found noticeable changes in the atomic and electronic structures of both the molecule and the substrate. The molecule is bent while the surface atoms experience a buckling. The dz^2 state of the copper atoms that are directly under carbon atoms presents new states near the Fermi level. These effects, in addition to a change in the work function, classify this system as chemisorption. We also determined the barrier for diffusion along the Cu(110) channel to be 77 meV.

Matos, Jeronimo; Kara, Abdelkader

2011-03-01

23

Adsorption and reaction of sulfur dioxide with Cu(110) and Cu(110)-p(2×1)-O  

NASA Astrophysics Data System (ADS)

On Cu(110)-p(2×1)-O at 300 K SO2(g) reacts stoichiometrically with O(a) to form a surface covered with both c(4×2)-SO3 and p(2×2)-SO3 structures. With heating SO2(g) evolves from the surface in distinct reaction-limited states at 384 K, 425 K, and 470 K, and the surface reverts to its initially oxidized state. On Cu(110), SO2(g) adsorbs molecularly below 300 K; upon annealing to 300 K, the sulfur dioxide disproportionates according to 3SO2(a)-->S(a)+2SO3(a) with concomitant desorption of excess SO2(a). The surface formed in this manner exhibits large c(2×2)-S domains which encompass scattered c(4×2)-SO3 and p(2×2)-SO3 structures in a 1:2 coverage ratio. After being annealed to 400 K, the surface exhibits large p(2×2)-SO3 domains surrounding smaller c(4×2)-SO3 and c(2×2)-S islands. Continued heating past 400 K results in decomposition of sulfite according to SO3(a)-->SO2(g)+O(a), evolving sulfur dioxide at 470 K and leaving the surface covered with atomic sulfur and oxygen. Real-time STM images show the mobility of oxygen at island boundaries and the mobility of sulfite amid the p(2×1)-O structures. STM measurements suggest that the sulfite occupy four-fold hollow sites.

Alemozafar, Ali R.; Guo, Xing-Cai; Madix, Robert J.

2002-03-01

24

Growth and Stability of Ag Layers on Cu(110).  

National Technical Information Service (NTIS)

Combined surface science and high energy ion beam techniques have been used to characterize the composition, structure and thermal stability of Ag layers < 900A thick on Cu(110). A uniform Ag/Cu surface composite is formed for one monolayer coverage. Anal...

T. N. Taylor, M. A. Hoffbauer, C. J. Maggiore, J. G. Beery

1986-01-01

25

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

26

Chemical versus van der Waals Interaction: the role of the heteroatom in the flat absorption of aromatic molecules C6H6, C5NH5, and C4N2H4 on the Cu(110) surface.  

PubMed

We perform first-principles calculations aimed at investigating the role of a heteroatom such as N in the chemical and long-range van der Waals (vdW) interactions for a flat adsorption of several pi-conjugated molecules on the Cu(110) surface. Our study reveals that the alignment of the molecular orbitals at the adsorbate-substrate interface depends on the number of heteroatoms. As a direct consequence, the molecule-surface vdW interactions involve not only pi-like orbitals which are perpendicular to the molecular plane but also sigma-like orbitals delocalized in the molecular plane. PMID:19392392

Atodiresei, N; Caciuc, V; Lazi?, P; Blügel, S

2009-04-01

27

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

28

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

29

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

SciTech Connect

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

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

2007-05-16

30

Self-assembly of meta-aminobenzoate on Cu(110).  

PubMed

A variety of structures of meta-aminobenzoate molecules adsorbed on the Cu(110) surface have been characterized by scanning tunneling microscopy (STM) at a wide range of surface coverages, from a single molecule to saturated phases. At the start of molecular domain formation, individual molecules thermally diffuse to form chain structures via intermolecular hydrogen bonding. At higher surface coverages, there coexist three well-ordered phases, namely [Formula: see text] and chiral [Formula: see text] phases. The molecular orientation on the surface also varies with surface coverage. Flat-lying molecules are mainly observed at low surface coverage, while upright molecules start to appear as the surface becomes more highly covered. Our experimental findings and structural analysis are well supported by high-resolution STM images measured at 4.7 K and by molecular packing models with precise lattice parameters. PMID:19371044

Rabot, Caroline; Hori, Masafumi; Katano, Satoshi; Kim, Yousoo; Kawai, Maki

2009-05-19

31

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

32

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

PubMed

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. PMID:24908034

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

2014-06-01

33

The adsorption structure of glycine adsorbed on Cu(110); comparison with formate and {acetate}/{Cu(110) }  

NASA Astrophysics Data System (ADS)

The molecular orientation of an ordered monolayer of glycine adsorbed on Cu(110) has been studied using X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Fine Structure (NEXAFS), X-ray Photoelectron Diffraction (XPD), Low-Energy Electron Diffraction (LEED) and theoretical calculations. In particular, the NEXAFS results are discussed in terms of the spectra of the related molecules ammonia (NH 3), formate (HCOO), and acetate (CH 3COO) on Cu(110). Whereas the latter two molecules chemisorb in similar geometries, glycine is found to assume a very different chemisorption geometry. Formate and acetate bond through two equivalent oxygen atoms with the molecular plane oriented nearly perpendicular to the surface, aligned along the [11¯0]-azimuth. In the case of adsorbed glycine (NH 2CH 2COO), the azimuthal orientation is still present, i.e. the bonding oxygen atoms are aligned along the [11¯0]-azimuth, but the molecule is found to bend towards the surface. A second chemisorption bond is formed at the nitrogen end of the molecule, involving copper atoms in the neighboring [11¯0]-row. We therefore have the interesting case of a chemisorption bond involving different functional groups in the same molecule.

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

1998-06-01

34

Comparative study of phenol and thiophenol adsorption on Cu(110)  

NASA Astrophysics Data System (ADS)

Adsorption of phenol and thiophenol (benzenethiol) on Cu(110) is investigated by a scanning tunneling microscope and electron energy loss spectroscopy. Phenol adsorbs intact and forms a cyclic trimer at 78 K. It is dehydrogenated to yield a phenoxy (C6H5O) group at 300 K. On the other hand, thiophenol is dehydrogenated to a thiophenoxy (C6H5S) group even at 78 K. Both products are bonded via chalcogen atom to the short-bridge site with the phenyl ring oriented nearly parallel to the surface. The C6H5O and C6H5S groups are preferentially assembled into the chains along the [001] and [112] directions, respectively. Dipole-dipole interaction is responsible for the chain growth, while the chain direction is ruled by the steric repulsion between chalcogen atoms and adjacent phenyl ring. This work demonstrates a crucial role of chalcogen atom of phenol species in their overlayer growth on the surface.

Kitaguchi, Y.; Habuka, S.; Mitsui, T.; Okuyama, H.; Hatta, S.; Aruga, T.

2013-07-01

35

The interaction of NO, O 2 and CO with Cu(100) and Cu(110)  

NASA Astrophysics Data System (ADS)

Exposure of NO or O 2 to Cu(100) or Cu(110) (at temperatures between 370 and 670 K, pressures up to 0.1 Pa) leads to dissociative adsorption. Dissociation on Cu(110) is about an order of magnitude faster than on Cu(100). Saturation of the surface coverage (for both surfaces at about 0.42 monolayer) is followed by the structure-intensitive penetration of oxygen atoms into the crystal. Reduction proceeds via reaction of adsorped CO and adsorbed oxygen, the effect of nitrogen can be explained by site-blocking. Again, the reaction is about an order of magnitude faster on Cu(110) than on Cu(100). In the case of Cu(100) a transition from a disordered to an ordered overlayer is observed at a fractional surface coverage of about 0.3. Nitrogen desorption is more difficult from Cu(100) than from Cu(110). The desorption temperature depends on the presence of oxygen (adsorbed as well as penetrated). At high CO pressures the formation of isocyanate facilitates the desorption of nitrogen.

Balkenende, A. R.; den Daas, H.; Huisman, M.; Gijzeman, O. L. J.; Geus, J. W.

1991-06-01

36

Temperature Dependent Effects During Ag Deposition on Cu(110).  

National Technical Information Service (NTIS)

The composition, structure, and morphology of ultrathin films grown by Ag deposition on Cu(110) were monitored as a function of temperature using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and medium energy ion scattering (...

T. N. Taylor, R. E. Muenchausen, M. A. Hoffbauer, A. W. Denier van der Gon, J. F. van der Veen

1989-01-01

37

Water and ammonia on Cu{110}: comparative structure and bonding.  

PubMed

Water and ammonia are arguably the two most important inorganic molecular species in the modern world, and their interaction with metal surfaces is key to unlocking their further potential in a number of spheres. In this comparative study, conducted on the Cu{110} substrate, we present results from first-principles density functional theory that highlight the similarities and differences between these chemical cousins. We find that ammonia is less likely than water to undergo thermally induced partial dissociation, although we nevertheless identify the most likely product of electron-stimulated or defect-induced dissociation to be a surface amino species. We predict that ammonia, like water, will adopt a bilayer structure at high coverage, but that unlike water the net intermolecular interaction will be repulsive, despite the formation of a weak hydrogen-bonded network. Furthermore, we suggest that coadsorption of water and ammonia can give rise to an intimately mixed overlayer in which ammonia molecules are bound directly to the surface whilst water molecules are attached only via hydrogen bonds from below. PMID:23435594

Jones, Glenn; Jenkins, Stephen J

2013-04-01

38

Nanostripe Pattern of NaCl Layers on Cu(110)  

NASA Astrophysics Data System (ADS)

A sodium chloride monolayer on a Cu(110) surface gives rise to a highly corrugated periodic nanostripe pattern of the (100) lattice as observed by scanning tunneling microscopy and low-energy electron diffraction. As revealed by density-functional calculations, this pattern is a consequence of the frustration of the overlayer-substrate chemical bonding produced by epitaxial mismatch. The coexistence of regions of strong Cu-Cl covalent and weak nonbonding interactions leads to a chemically induced topographic modulation here realized in a two-dimensional dielectric. The carpetlike growth of the NaCl layer across Cu step edges induces a distinct contrast inversion in the stripe pattern as a result of the change in epitaxial relationship due to the stacking sequence of the (110) Cu layers. It is demonstrated that the competition between local substrate-overlayer and intraoverlayer interactions can support a well-defined heteroepitaxial relationship of a ionic dielectric film and a metal surface, with important consequences for the nanoscale morphology and related properties.

Wagner, M.; Negreiros, F. R.; Sementa, L.; Barcaro, G.; Surnev, S.; Fortunelli, A.; Netzer, F. P.

2013-05-01

39

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

40

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.

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

2014-01-01

41

A vibrational study of the hydrogen induced reconstructions on Cu(110)  

NASA Astrophysics Data System (ADS)

Hydrogen adsorbed at 100 K on Cu(110) induces a (1 × 3) surface reconstruction observable in LEED in the coverage region 0.2 > ? H > 0.8. Two loss peaks associated with the hydrogen adsorbed in this phase are observed in HREELS at 620 and 505 cm -1. These features persist throughout the coverage range 0.0 < ? H < 1.0. Additional losses associated with hydrogen on a (1 × 2) reconstructed surface appear at ? H > 0.8 where a conversion of the (1 × 3) to the (1 × 2) phase is evident in LEED. Hydrogen adsorption at 300 K leads directly to the (1 × 2) reconstructed phase observable in LEED over the coverage range 0.1 < ? H < 1.0 and exhibits associated HREELS losses at 765, 950 and 1150 cm -1. Heating the (1 × 3) phase formed at 100 K irreversibly produces the (1 × 2) reconstruction in the temperature range 140-190 K. We assign the modes observed in the (1 × 3) phase to hydrogen in a pseudo four-fold hollow site on a buckled reconstructed surface. The modes on the (1 × 2) phase are associated with hydrogen in a tilted trigonal site on a missing row reconstructed surface. The hydrogen site transition from (1 × 3) to (1 × 2) on Cu(110) is analogous to the behaviour in metal hydrides where a conversion from octahedral to tetrahedral hydrogen coordination occurs for increasing hydrogen concentrations.

Hayden, B. E.; Lackey, D.; Schott, J.

1990-12-01

42

Elementary process for CVD graphene on Cu(110): size-selective carbon clusters.  

PubMed

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

43

Oriented Growth of Cu(110) on YSi2-\  

NASA Astrophysics Data System (ADS)

The growth and diffusion characterization of Cu films on the YSi2-{x}(1\\bar{1}00)/Si(100) substrate are studied. On the YSi2-{x}(1\\bar{1}00) layer prepared using a thin template layer, highly oriented Cu(110) film growth is observed, and Cu diffusion through the YSi2- x layer and the subsequent Cu3Si formation occur at temperatures as low as 200° C. On the contrary, the growth of Cu with normal orientation is evident on the YSi2- x layer with poor epitaxial quality, and the out-diffusion of Si forms a Cu3Si layer on the YSi2- x layer. The film growth on YSi2- x layers is discussed on the basis of the lattice match between superlattice cells of Cu and YSi2- x, and the diffusion behavior is interpreted in terms of relaxation of the affinity of Cu for Si.

Nomura, Kouichi; Noya, Atsushi; Sasaki, Katsutaka; Sunaga, Kouji

1994-06-01

44

Cu-adatom-mediated bonding in close-packed benzoate/Cu(110)-systems.  

PubMed

Using UHV-STM investigations and density-functional theory calculations we prove the contribution of Cu-adatoms to the stabilization of a new high-density phase of benzoate molecules on a Cu(110) substrate. We show that two different chemical species, benzoate and benzoate Cu-adatoms molecules, build the new close-packed structure. Although both species bind strongly to the copper surface, we identify the benzoate Cu-adatoms molecules as the more mobile species on the surface due to their reduced dipole moment and their lower binding energy compared to benzoate molecules. Therefore, the self-assembly process is supposed to be mediated by benzoate Cu-adatom species, which is analogous to the gold-thiolate species on Au(111) surfaces. PMID:19177646

Lennartz, M Christina; Atodiresei, Nicolae; Muller-Meskamp, Lars; Karthauser, Silvia; Waser, Rainer; Blugel, Stefan

2009-01-20

45

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

Microsoft Academic Search

The persistent demand for cheaper and high efficient catalysts in industrial chemical synthesis, such as ammonia, and in novel energy applications, hydrogen generation and purification in fuel cells motivated us to study the fundamental interaction involved in water-Cu system, with an intension to examine Cu as a possible competitive candidate for cheaper catalysts. Water structure and dissociation kinetics on a

Jun Ren; Sheng Meng

2009-01-01

46

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

47

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

SciTech Connect

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

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

1989-01-01

48

First-principles study on the relaxed structures and electronic properties of Cu [110] nanowires  

NASA Astrophysics Data System (ADS)

Under the generalized gradient approximation (GGA), first-principles calculations are employed to study the structural stability of Cu nanowires (NWs) along the [110] direction by using the projector-augmented wave potential based on the density functional theory. With the first three diameters, we present different geometrical structures of Cu [110] NWs, formed by stacking of atomic polygons with rectangular or hexagonal cross sections perpendicular to the wire axis. For all sixsized NWs, the relaxed structures still have C2 symmetry and show a "round corner" phenomenon. The calculated binding energies and electronic band structures show that the hexagonal wire is not only more stable but also more metallic than the corresponding rectangular one. Therefore, the [110]-oriented Cu NWs are energetically more likely to have hexagonal cross sections perpendicular to the wire axis, in agreement with the experimental result. The vanishing of the neighbor atoms outside the NWs after being cleaved from the bulk crystal causes the "skin effect" phenomenon. In fact, the conclusions drawn here are applicable to not only NWs but also other surfaces, such as those of nanobelts, nanotubes, nanocables, clusters, thin films, and so on.

Sun, Yue; Zhang, Jian-Min; Xu, Ke-Wei

2012-10-01

49

Novel Mechanism for Molecular Self-Assembly on Metal Substrates: Unidirectional Rows of Pentacene on Cu(110) Produced by a Substrate-Mediated Repulsion  

Microsoft Academic Search

The formation of one-dimensional, unidirectional nanoscopic molecular structures by self-assembly on metal substrates with a long range ordering up to several hundred nanometers has been achieved by a novel mechanism, an oscillatory modulation of the adsorption energy due to charge-density waves related to a surface state. For the case of pentacene (C 22H 14) adsorbed on Cu(110), annealing at 400

S. Lukas; G. Witte; Ch. Wöll

2002-01-01

50

GaN epitaxy on Cu(110) by metal organic chemical vapor deposition  

NASA Astrophysics Data System (ADS)

We demonstrate that Cu can be a suitable substrate material for c-plane GaN epitaxy using metal organic chemical vapor deposition. By using a low temperature AlN buffer layer, Ga and Cu alloying can be prevented so that GaN layer can be grown on Cu at a temperature of 1000 °C. An epitaxial relation of GaN (0001)//Cu(110) is observed using cross-section transmission electron microscopy and electron back scatter diffraction studies. The single crystalline GaN epilayer shows a threading dislocation density of 3 × 109 cm-2 and strong band edge emission at room temperature. The site alignment between GaN (0001) and Cu(110) shows a mesh ratio of 4/3 and 5/3 in GaN [10-10] and GaN [-1100] directions, which is attributed to the epitaxial relation observed.

Li, Qiming; Figiel, Jeffery; Wang, George; Xu, Huiwen; Balakrishnan, Ganesh

2012-05-01

51

Kinetics of the reverse water-gas shift reaction over Cu(110)  

Microsoft Academic Search

The reverse water-gas shift reaction (COâ + Hâ â HâO + CO) has been studied over a clean Cu(110) single-crystal model catalyst at temperatures between 573 and 723 K. The steady-state kinetic measurements were carried out at medium pressures (10-2,000 Torr) in a microreactor after cleaning and characterization of the sample under UHV conditions. The Hâ\\/COâ-pressure ratios varied from 1,000:1

K. H. Ernst; C. T. Campbell; G. Moretti

1992-01-01

52

Structure of Oxide Surfaces  

NASA Astrophysics Data System (ADS)

Surfaces of metal oxides are of crucial importance for a variety of technological applications such as heterogeneous catalysis, thin film growth, gas sensing, and corrosion prevention. Due to the complexities of oxides in crystal structure and electronic structure, however, the surface science of oxides lags far behind that of metals or semiconductors. Conventional surface-science techniques are usually limited to surfaces of single crystals of conductors. Metal oxides are usually good insulators, making them difficult for conventional surface science techniques. On the other hand, the complex atomic structures of oxides results in too many structural parameters to be determined by spectroscopy or diffraction methods. We will show that the surface structure of oxides can be directly imaged and measured at the sub-angstrom scale using aberration-corrected transmission electron microscopy. The atomic positions of oxide surfaces can be measured to an accuracy of picometers, comparable to that obtained by conventional surface science techniques on single crystals.[4pt] [1] R. Yu, L.H. Hu, Z.Y. Cheng, Y.D. Li, H.Q. Ye, J. Zhu, Phys. Rev. Lett., 105, 226101 (2010).[0pt] [2] M.R. He, R. Yu, J. Zhu, Angew. Chem. Int. Ed., 124, 7864 (2012).

Yu, Rong

2013-03-01

53

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

NASA Astrophysics Data System (ADS)

The reactive system CH3OH/Cu(110) has been characterized by thermal desorption and infrared reflection-absorption spectroscopies. This provides the knowledge of the reactive system properties necessary for the interpretation of the ir photodesorption experimental results. These properties are the sticking coefficient of methanol on Cu(110) at 90 K, the monolayer density, the ir absorbance, and the structure of the adsorbate. In particular, ir spectroscopy demonstrates the possibility of thermally activating the crystallization of the amorphous adsorbate obtained upon condensation on Cu(110) at 90 K. The experimental setup used for the measurements of the photodesorption yield (YPD) makes use of an optical parametric oscillator generating ir pulses about 15 ns long and frequencies tunable from 2800 to 3450 cm.-1 This frequency range includes the ir bands corresponding to the asymmetric methyl and hydroxyl stretching modes. The ir YPD of amorphous and crystallized films have been measured as a function of the laser-beam frequency and fluence, of the substrate coverage, and of the temperature (from 90 to 120 K). The correspondence between the YPD spectra and the ir spectrum of liquid methanol indicates the occurrence of adsorbate melting during the photodesorption process. The saturable exponential evolution of the YPD as a function of the laser fluence reveals the thermal nature of the process. The YPD of the amorphous methanol thin films increases greatly upon their crystallization. This is tentatively explained as a consequence of a change in the film morphology. These experimental results are interpreted quantitatively in the framework of the thermal photodesorption mechanism due to the resonant substrate heating.

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

1992-04-01

54

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

55

The structure of methoxy species on Cu(110): A combined photoelectron diffraction and density functional theory determination  

NASA Astrophysics Data System (ADS)

The local structure of the methoxy species on Cu(110) has been investigated experimentally using chemical-state specific O 1s scanned-energy mode photoelectron diffraction (PhD), and also by density functional theory (DFT) calculations. The PhD data show a clear preference for adsorption with the O bonding atoms in short-bridge sites, though the best fit of multiple-scattering simulations to the experimental data is achieved with two slightly different short-bridge geometries. The DFT calculations also show that not only are the short-bridge sites energetically favoured in isolation, but that coordination to pairs of Cu adatoms has a similar energy. A structure consistent with both the PhD data and the DFT calculations is proposed for the previously-observed (5 × 2)pg ordered phase, based on methoxy species in short-bridge sites on pairs of Cu adatoms and on the underlying surface. Simulated scanning tunnelling microscopy images agree well with those observed experimentally, while the model is also shown to be consistent with the qualitative behaviour seen in early X-ray photoelectron diffraction (XPD) forward-scattering experiments.

Kreikemeyer Lorenzo, D.; Bradley, M. K.; Unterberger, W.; Duncan, D. A.; Lerotholi, T. J.; Robinson, J.; Woodruff, D. P.

2011-01-01

56

Molecular Assemblies on Oxide Surfaces.  

National Technical Information Service (NTIS)

Our focus for the past 3 years has been on developing a fundamental understanding of the chemical and physical properties of metal complexes on metal oxide surfaces. Carboxylate or phosphonate binding to metal oxide substrates provides a basis for formati...

T. J. Meyer

1998-01-01

57

Mechanisms for the near-UV photodissociation of CH3I on D2O/Cu(110)  

NASA Astrophysics Data System (ADS)

The system of CH3I adsorbed on submonolayer, monolayer, and multilayer thin films of D2O on Cu(110) has been studied by measuring the time of flight (TOF) distributions of the desorbing CH3 fragments after photodissociation using linearly polarized ? = 248 nm light. For multilayer D2O films (2-120 ML), the photodissociation is dominated by neutral photodissociation via the ``A-band'' absorption of CH3I. The polarization and angle dependent variation in the observed TOF spectra of the CH3 photofragments find that dissociation is largely via the 3Q0 excited state, but that also a contribution via the 1Q1 excitation can be identified. The photodissociation results also indicate that the CH3I adsorbed on D2O forms close-packed islands at submonolayer coverages, with a mixture of C-I bond axis orientations. For monolayer and submonolayer quantities of D2O we have observed a contribution to CH3I photodissociation via dissociative electron attachment (DEA) by photoelectrons. The observed DEA is consistent with delocalized photoelectrons from the substrate causing the observed dissociation- we do not find evidence for an enhanced DEA mechanism via the temporary solvation of photoelectrons in localized states of the D2O ice.

Miller, E. R.; Muirhead, G. D.; Jensen, E. T.

2013-02-01

58

Tailoring Graphene Morphology and Orientation on Cu(100), Cu(110), and Cu(111)  

NASA Astrophysics Data System (ADS)

Graphene CVD on Cu is phenomenologically complex, yielding diverse crystal morphologies, such as lobes, dendrites, stars, and hexagons, of various orientations. We present a comprehensive study of the evolution of these morphologies as a function of Cu surface orientation, pressure, H2:CH4, and nucleation density. Growth was studied on ultra-smooth, epitaxial Cu films inside Cu enclosures to minimize factors that normally complicate growth. With low H2:CH4, Mullins-Sekerka instabilities propagate to form dendrites, indicating transport limited growth. In LPCVD, the dendrites extend hundreds of microns in the 100, 111, and 110 directions on Cu(100), (110), and (111) and are perturbed by twin boundaries. In APCVD, multiple preferred dendrite orientations exist. With increasing H2:CH4, the dendritic nature of growth is suppressed. In LPCVD, square, rectangle, and hexagon crystals form on Cu(100), (110) and (111), reflecting the Cu crystallography. In APCVD, the morphology becomes hexagonal on each surface. If given ample time, every growth regime yields high-quality monolayers with D:G Raman ratio 0.1. The understanding gained here provides a framework to rationally tailor the graphene crystal morphology and orientation.

Jacobberger, Robert; Arnold, Michael

2013-03-01

59

Surface Nitriding and Oxidation of Nitinol  

Microsoft Academic Search

Nitinol has been widely employed in biomedical devices due to its unique mechanical properties such as superelasticity, shape memory, and good biocompatibility. However, nickel ion release from the surface of the Nitinol is an issue. Surface nitriding and oxidation was performed on the Nitinol specimens to develop a nickel-free oxide layer on the surface. Nitinol specimens were nitrided in nitrogen

Edin Bazochaharbakhsh

2011-01-01

60

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

61

Surface nitriding and oxidation of nitinol  

NASA Astrophysics Data System (ADS)

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

Bazochaharbakhsh, Edin

62

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

Microsoft Academic Search

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

Israel E. Wachs

1996-01-01

63

Surface modification to prevent oxide scale spallation  

SciTech Connect

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

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

2013-07-16

64

Surface oxidation of basalt glass\\/liquid  

Microsoft Academic Search

To evaluate surface oxidation of Fe2+-rich multi-component silicate glass, powder and pieces of natural basalt glass are heat-treated in Ar and subsequently investigated by Mössbauer spectroscopy to monitor the increase of Fe3+. Glass pieces show no increase in oxidation with time or temperature, suggesting that the oxygen potential between glass and Ar is insufficient to cause volume oxidation. In contrast,

Dorothee J. M. Burkhard; Torsten Scherer

2006-01-01

65

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

66

Tailoring Surface Reactivity of Metal Oxides  

NASA Astrophysics Data System (ADS)

Titanium oxide is receiving continued attention because of its importance as catalyst support, as a material to harvest solar energy for chemical transformations, and as a model metal oxide. In this talk, I will focus on the structure and defects (extrinsic and intrinsic) of less-studied TiO2 surfaces; i.e., rutile (011)-2x1 and anatase (101), and their influence on surface reactivity.

Diebold, Ulrike

2008-03-01

67

Surface Wrinkling on Polydimethylsiloxane Microspheres via Wet Surface Chemical Oxidation  

PubMed Central

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

2014-01-01

68

Local triboelectricity on oxide surfaces  

Microsoft Academic Search

:   In triboelectric phenomena, electric charges are transferred when two materials are touched or rubbed together. We present\\u000a in this paper a study of this effect performed on metallic oxides at the nanometric scale by an Atomic Force Microscope in\\u000a the resonant mode. We show that following the electrification processes, positive or negative charges can be deposited. From\\u000a our experimental

M. Saint Jean; S. Hudlet; C. Guthmann; J. Berger

1999-01-01

69

Acidity distribution on oxide surfaces  

Microsoft Academic Search

In the Benesi or n-butylamine titration method for measuring acid strength distributions, the assumption that both the n-butylamine titrant and the indicators are in adsorption equilibrium with surface acid sites, is invalid. This casts serious doubts on the use of the amine titration method for assessing surface acidity of petroleum catalysts. A series of bases of varying pK\\/sub a\\/ dissolved

Debba

1978-01-01

70

CO oxidation on PdO surfaces  

NASA Astrophysics Data System (ADS)

Density functional calculations were performed in order to investigate CO oxidation on two of the most stable bulk PdO surfaces. The most stable PdO(100) surface, with oxygen excess, is inert against CO adsorption, whereas strong adsorption on the stoichiometric PdO(101) surface leads to favorable oxidation via the Langmuir-Hinshelwood mechanism. The reaction with a surface oxygen atom has an activation energy of 0.66 eV, which is comparable to the lowest activation energies observed on metallic surfaces. However, the reaction rate may be limited by the coverage of molecular oxygen. Actually, the reaction with the site blocking molecular oxygen is slightly more favorable, enabling also possible formation of carbonate surface species at low temperatures. The extreme activity of strongly bonded surface oxygen atoms is more greatly emphasized on the PdO(100)-O surface. The direct reaction without adsorption, following the Eley-Rideal mechanism and taking advantage of the reaction tunnel provided by the adjacent palladium atom, has an activation energy of only 0.24 eV. The reaction mechanism and activation energy for the palladium activated CO oxidation on the most stable PdO(100)-O surface are in good agreement with experimental observations.

Hirvi, Janne T.; Kinnunen, Toni-Jani J.; Suvanto, Mika; Pakkanen, Tapani A.; Nørskov, Jens K.

2010-08-01

71

A study of nitric oxide adsorption on copper (100) and (110)  

NASA Astrophysics Data System (ADS)

The adsorption of nitric oxide on single crystal copper (100) and (110) surfaces has been studied with electron energy loss vibrational spectroscopy, low energy electron diffraction and thermal desorption spectroscopy. In the case of Cu(110), vibrational spectra confirm that molecular adsorption of NO occurs for very low exposures with a crystal temperature of 80 K. For exposures exceeding 2.2 L, dissociation occurs with atomic oxygen and nitrogen retained on the surface and located at the long bridge site. Vibrational frequencies obtained using two isotopic forms of NO, 14NO and 15NO, are assigned to the stretching and bending modes of NO and indicate a molecule strongly tilted relative to the surface normal in a predissociative state. Dissociation occurs at temperatures above 113 K with the atomic species again retained on the surface. Adsorption of nitric oxide on Cu(100) was found to be more complicated. Vibrational spectra indicate a difference in molecular species between low exposure (˜1 L) and high exposure (˜10 L) cases for T<100 K. Depending on exposure and temperature, evidence is found for the presence of N 2O, two forms of NO, O, and probably N 2. In contrast to adsorption of NO on Cu(110), a large fraction of the NO dissociates upon initial adsorption on Cu(100). All species containing nitrogen are found to desorb or dissociate below room temperature.

Wendelken, J. F.

72

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...

73

Surface oxidation of Permalloy thin films  

SciTech Connect

The chemical and magnetic structures of oxides on the surface of Permalloy Ni{sub 81}Fe{sub 19} films were investigated as functions of annealing time with x-ray and polarized neutron reflectometry. For annealing times of less than one hour, the oxide consisted of a 1.5-nm-thick layer of NiO on an Fe oxide layer that was in contact with Permalloy. The Fe oxide thickness increases with annealing time with a parabolic rate constant of 10{sup -18} cm{sup 2} s{sup -1} (for an annealing temperature of 373 K). The growth of the oxide layer is limited by the rate at which oxygen appears below the NiO layer. No portion of the oxide region was found to be ferromagnetically ordered for films annealed less than one hour. The growth of the Fe oxide region is well correlated with the measured increase of the second-order magnetic susceptibility for similarly prepared samples.

Fitzsimmons, M. R.; Crawford, T. M. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Silva, T. J. [National Institute of Standards and Technology, Boulder, Colorado 80303 (United States)

2006-01-01

74

Oxide-assisted laser surfacing of aluminum  

NASA Astrophysics Data System (ADS)

CO2 laser processing has been carried out on pure aluminum substrates for travel speeds from 0.3 to 6.1 mm/s, using laser powers of about 100 W or 300 W, with various preplaced single or mixed powders including CoO, NiO, SiO2, Fe2O3 or TiO2 usually combined with enough aluminum powder to permit complete reduction of the oxides. The 100 W laser experiments included low, normal and high gravity experiments. The resulting tracks were tested qualitatively for scratch resistance, and examined metallographically. Two types of surfacing were observed; continuous oxide layers produced by melting and an oxidation- reduction reaction of the original oxides with aluminum, and alloying of the substrate by elements reduced by the reaction. Low gravity experiments produced more uniform thicknesses and generally less cracking in the continuous oxides than normal or high gravity experiments. Alloying of the substrate ranged from almost 100% intermetallic layers at low laser powers and low travel speeds to complex mixtures and bands of different phases, depending on the temporal stability of the process, the powder composition and thickness, the laser power and travel speed. Optimization of the process could provide useful wear resistant coatings in a space environment.

Hoepp, E. E.; Kerr, Hugh W.

1996-04-01

75

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

76

Perfluorodiethoxymethane on nickel and nickel oxide surfaces  

SciTech Connect

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

Jacobson, J.

1994-03-03

77

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

78

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

79

Initial oxidation of MBE-grown Si( 100) surfaces  

NASA Astrophysics Data System (ADS)

We have investigated the initial oxidation of MBE-grown Si(100) surfaces with atomic flatness using X-ray photoemission spectroscopy (XPS) and reflection high energy electron diffraction (RHEED). It was found that the MBE-grown surfaces are inert and hardly oxidized even after exposure to molecular oxygen up to 1500 L at room temperature and that the oxygen coverage is saturated at 0.4 ML. At elevated temperatures, however, the surface oxidation was substantially promoted on the atomically flat surface. On the other hand, the oxidation was found to proceed on a deliberately corrugated Si surface prepared by a low temperature MBE growth, even at room temperature.

Hiroyuki, Yaguchi; Ken, Fujita; Susumu, Fukatsu; Yasuhiro, Shiraki; Ryoichi, Ito; Takayuki, Igarashi; Takeo, Hattori

1992-09-01

80

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

81

Engineering silicon oxide surfaces using self-assembled monolayers  

Microsoft Academic Search

Although a molecular monolayer is only a few nanometers thick it can completely change the properties of a surface. Molecular monolayers can be readily prepared using the Langmuir-Blodgett methodology or by chemisorption on metal and oxide surfaces. This Review focuses on the use of chemisorbed self-assembled monolayers (SAMs) as a platform for the functionalization of silicon oxide surfaces. The controlled

Steffen Onclin; Bart Jan Ravoo; David N. Reinhoudt

2005-01-01

82

Surface Oxides in P/M Aluminum Alloys  

NASA Astrophysics Data System (ADS)

Aluminum powder particles inherently exhibit a surface oxide layer because of the reactivity of aluminum with oxygen. This surface layer detrimentally affects mechanical properties when incompletely broken up or nonuniformly distributed during consolidation and hot working. The breakup of surface oxides depends on the degree of dehydration and constitutional changes occurring during degassing. When dehydrated completely, the surface oxide film is completely broken up during subsequent hot consolidation, particularly, if it contains fine crystalline oxides. Subsequent redistribution of the oxide is a direct function of processing parameters—deformation amounts and mode. This paper discusses the effect of the surface oxides on the mechanical properties and microstructure of both advanced high strength/corrosion resistant and elevated temperature aluminum powder metallurgy alloys.

Kim, Young-Won; Griffith, W. M.; Froes, F. H.

1985-08-01

83

Atomic-Scale Chemistry of Metal Surfaces.  

National Technical Information Service (NTIS)

The concept of pseudo-molecules is derived from reviewing the results of Scanning Tunneling Microscopy (STM) of metal surfaces. Ni(110), Cu(110), and Ag(110) surfaces exposed to H2 or O2 at room temperature reveal the formation of one-dimensional pseudo-m...

K. Tanaka

1993-01-01

84

Surface States Associated with Chemisorbed Species on Zinc Oxide.  

National Technical Information Service (NTIS)

The paper introduces a new method for measuring electronic energy levels (surface states) associated with foreign species on zinc oxide and describes early results. The method is based on electrostatic charging from the gas phase. The surface is shifted f...

S. R. Morrison

1968-01-01

85

Quantitative determination of the number of active surface sites and the turnover frequencies for methanol oxidation over metal oxide catalysts  

Microsoft Academic Search

A detailed study of the methanol chemisorption and oxidation processes on oxide surfaces allowed the development of a method to quantify the number of surface active sites (Ns) of metal oxide catalysts. In situ infrared analysis during methanol adsorption showed that molecular methanol and surface methoxy species are co-adsorbed on an oxide surface at room temperature, but only surface methoxy

Laura E Briand; William E Farneth; Israel E Wachs

2000-01-01

86

Surface modification of spherical magnesium oxide with ethylene glycol  

Microsoft Academic Search

The surface of spherical magnesium oxide has been modified with ethylene glycol in the presence of basic aqueous solution. Fourier transform infrared spectra have shown the presence of the graft group ethylene glycol on the surface of spherical magnesium oxide. In addition, this conclusion can also be drawn from appearance of new diffraction peak in X-ray diffraction pattern. Although magnesium

Jing Jin; Zhiping Zhang; Huilian Ma; Xianbo Lu; Jiping Chen; Qing Zhang; Haijun Zhang; Yuwen Ni

2009-01-01

87

Europa The Production of Oxidants in Europa' s Surface  

Microsoft Academic Search

The oxidants produced by radiolysis and photolysis in the icy surface of Europa may be nec- essary to sustain carbon-based biochemistry in Europa' s putative subsurface ocean. Because the subduction of oxidants to the ocean presents considerable thermodynamic challenges, we examine the formation of oxygen and related species in Europa' s surface ice with the goal of characterizing the chemical

R. E. JOHNSON; T. I. QUICKENDEN; P. D. COOPER; A. J. MCKINLEY; C. G. FREEMAN

88

Single-layer graphene oxide films on a silicon surface  

NASA Astrophysics Data System (ADS)

A method is proposed to produce large-area single-layer graphene oxide films on the surface of semiconductor silicon wafers by precipitation from aqueous suspensions. Graphene oxide is synthesized from natural crystalline graphite during chemical oxidation and represents a wide-gap insulator. Single-layer graphene with a homogeneous-fragment size up to 50 ?m can be formed by the reduction of graphene oxide films, and this size is significantly larger than those achieved to date.

Aleksenskii, A. E.; Brunkov, P. N.; Dideikin, A. T.; Kirilenko, D. A.; Kudashova, Yu. V.; Sakseev, D. A.; Sevryuk, V. A.; Shestakov, M. S.

2013-11-01

89

Oxide semiconductor film on amorphous insulating surface  

US Patent & Trademark Office Database

Objects are to provide a semiconductor device for high power application in which a novel semiconductor material having high productivity is used and to provide a semiconductor device having a novel structure in which a novel semiconductor material is used. The present invention is a vertical transistor and a vertical diode each of which has a stacked body of an oxide semiconductor in which a first oxide semiconductor film having crystallinity and a second oxide semiconductor film having crystallinity are stacked. An impurity serving as an electron donor (donor) which is contained in the stacked body of an oxide semiconductor is removed in a step of crystal growth; therefore, the stacked body of an oxide semiconductor is highly purified and is an intrinsic semiconductor or a substantially intrinsic semiconductor whose carrier density is low. The stacked body of an oxide semiconductor has a wider band gap than a silicon semiconductor.

2014-04-15

90

Effective surface oxidation of polymer replica molds for nanoimprint lithography  

PubMed Central

In nanoimprint lithography, a surface oxidation process is needed to produce an effective poly(dimethylsiloxane) coating that can be used as an anti-adhesive surface of template molds. However, the conventional photooxidation technique or acidic oxidative treatment cannot be easily applied to polymer molds with nanostructures since surface etching by UV radiation or strong acids significantly damages the surface nanostructures in a short space of time. In this study, we developed a basic oxidative treatment method and consequently, an effective generation of hydroxyl groups on a nanostructured surface of polymer replica molds. The surface morphologies and water contact angles of the polymer molds indicate that this new method is relatively nondestructive and more efficient than conventional oxidation treatments.

2012-01-01

91

Crystallographic Symmetry of Surface State Density in Thermally Oxidized Silicon  

Microsoft Academic Search

The detailed dependence of surface state density on crystallographic orientation was determined by measuring the ac metal-oxide-semiconductor conductance on the surface of a thermally oxidized single-crystal silicon hemisphere. It was found that the ?111? poles are located at maxima, the ?100? poles at minima, and the ?110? poles at saddle points in the surface state density distribution. The symmetry of

Emil Arnold; Joshua Ladell; Gerald Abowitz

1968-01-01

92

Kinetics of thermally oxidation of Ge(100) surface  

NASA Astrophysics Data System (ADS)

Thermal oxidation of a Ge(100) surface was investigated by using spectroscopic ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS). Ge oxide was grown in the temperature range of 375 to 550°C in dry-O2 ambience at atmospheric pressure. Although the Ge-oxide growth rate shows a linear relationship in a log-log plot at a fixed temperature, and the slope indicates an enhancement of GeO desorption at oxidation temperatures over 490°C. The GeO desorption was also confirmed from the XPS analysis of the Si surface which was oxidized simultaneously with the Ge(100) surface. Thus, the Ge thermal oxidation at atmospheric pressure cannot be explained simply by the Deal-Grove model, in which the contribution of thermal desorption of Ge monoxide must be taken into account.

Sahari, S. K.; Ohta, A.; Matsui, M.; Mishima, K.; Murakami, H.; Higashi, S.; Miyazaki, S.

2013-03-01

93

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

94

Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies  

PubMed Central

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

2008-01-01

95

High-Temperature Oxide Regrowth on Mechanically-Damaged Surfaces  

SciTech Connect

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

Blau, Peter Julian [ORNL; Lowe, Tracie M [ORNL

2008-01-01

96

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

97

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

NASA Astrophysics Data System (ADS)

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

Graham, Andrew M.; Bouwer, Edward J.

2012-04-01

98

Biomimetic surfaces of semiconducting metal oxides  

NASA Astrophysics Data System (ADS)

Metal oxides such as titanium dioxide and zink oxide are well-known semiconductors. They are used in various a wide variety of functional devices. The size and morphology of the material has a substantial effect on device performance. Here, we propose to manufacture a hierarchic assembly of nanomaterials on the micrometer scale to arrive at new functionalities for photonic devices. The construction of the materials follows a bottom-up assembly that mimics processes that occur in nature.

Orita, Kosuke; Karthaus, Olaf

2014-03-01

99

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

100

Formation of oxide films on the surface of tungsten disilicide during anodic oxidation  

Microsoft Academic Search

Oxide-layer formation on the surface of tungsten disilicide is studied during its electrochemical polarization in a 3% NaCl\\u000a solution at 20 C. It is indicated that the total thickness of the oxide layer that forms over a period of 90 min does not\\u000a exceed 10 nm. The following multistage mechanism of anodic oxidation is established: tungsten oxides (for example, W3O

A. D. Chirkin; V. A. Lavrenko; A. D. Panasyuk; V. N. Talash

2006-01-01

101

Ferrate (IV) as a Possible Oxidant on the Martian Surface  

NASA Astrophysics Data System (ADS)

Viking experiments showed that Martian soil has a very strong oxidant, which could be responsible for the results of experiments performed on Viking landers. These experiments were designed specifically to detect life on Mars. The nature of that oxidant was not determined during Viking mission. Later several groups tried to reconstruct Viking experiments and find out the nature of Martian oxidant. None of these attempts were completely successful. The general perception was that there are several chemically different oxidants on Martian surface. In this study we suggested that potassium ferrate K_2FeO_4 can be Martian oxidant responsible at least partially for the results of experiments on Viking landers. We characterized liquid and powder preparation of Fe (VI) with EPR, optical spectroscopy, Mossbauer spectroscopy, and by Fe-XANES. All properties of our preparations of (FeVI) are consistent with the proposal role of that compound as a strong oxidant on Martian surface.

Tsapin, Alexandre; Goldfeld, M. G.; McDonald, G. D.; Nealson, K. H.; Mohnke, J.; Moskovitz, B.; Solheid, P.; Kemner, K. H.; Orlandini, K.

102

First Principles Studies of Metal-Oxide Surfaces  

Microsoft Academic Search

The interest in first principles investigations of metal-oxide surfaces has been growing rapidly over the past 10 years. Several phenomena of vital importance for fundamental understanding of heterogeneous catalysis have been investigated, including the metal\\/metal-oxide interface and the interaction with adsorbates. This contribution reviews different implementations of the density functional theory frequently used in studies of metal-oxide properties. Computational results

Henrik Grönbeck

2004-01-01

103

Evolved gas analysis for examination of surface oxides on alloys  

Microsoft Academic Search

Temperature programmed reduction in a hydrogen flow with simultaneous evolved gas analysis was employed to determine surface oxides on oxide dispersion strengthened (ODS) nickel containing TiO2, A12O3 or Cr2O3 particles, and on a Ni-2OCr alloy, after exposure to air at elevated temperatures. Oxides on particles of water-atomized (WA) Ni-2OCr powder were analysed similarly. Significant differences in starting temperatures of the

D. B. Goldman

1985-01-01

104

Carrier Lifetime in Oxide Confined Vertical Cavity Surface Emitting Lasers  

SciTech Connect

The carrier lifetime in vertical cavity surface emitting lasers is determined for various oxide aperture sizes using turn-on delay measurements. The lifetime is relatively constant for large devices, but decreases for aperture sizes below 9 x 9 µm.

Allerman, A.A.; Choquette, K.D.; Fischer, A.J.; Geib, K.M.

1999-05-26

105

Electrodeposition of Co on oxide modified pSi surfaces  

Microsoft Academic Search

The influence of the first stages of anodic oxidation of p-Si on the mechanism of Co deposition was studied by means of electrochemical techniques and AFM. The surface transformation during the formation of a thin oxide layer on hydrogen-terminated Si was followed by capacitance measurements and related to changes of the electrodeposition mechanism. It was observed that the reduction of

A. G. Muñoz; G. Staikov

2006-01-01

106

Surface electronic structure of detonation nanodiamonds after oxidative treatment  

Microsoft Academic Search

X-ray absorption spectroscopy has been used for comparative study of electronic structure of detonation nanodiamonds (ND) purified using different oxidative treatments. The treatment of detonation soot with a mixture of nitric and sulphuric acids followed by ion exchange and ultrafiltration of hydrosol obtained was found to result in developing of ND surface coverage consisting of oxidized carbon species, which electronic

A. V. Okotrub; L. G. Bulusheva; I. S. Larionova; V. L. Kuznetsov; S. L. Molodtsov

2007-01-01

107

Surface Chemistry of Nano-Structured Mixed Metal Oxide Films.  

National Technical Information Service (NTIS)

We have synthesizes and studied nano-structured porous mixed metal oxide thin films with high surface area and catalytic activity. By temporally controlling the deposition of two different metals in low-pressure oxygen we synthesized mixed metal oxide cat...

C. B. Mullins

2012-01-01

108

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

109

Rates of oxidative weathering on the surface of Mars  

NASA Astrophysics Data System (ADS)

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.

110

Changes in surface chemistry of activated carbons by wet oxidation  

Microsoft Academic Search

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

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

2000-01-01

111

Enhanced acidity and pH-dependent surface charge characterization of successively oxidized graphite oxides  

Microsoft Academic Search

This pH-potentiometric study explores the factors influencing the surface charge developed in aqueous dispersions of graphite oxide (GO) after a series of oxidation treatments. Surface charging curves demonstrate that lamellar surfaces of GO are negatively charged in the entire pH range studied. While these curves were found to be independent from the concentration of the GO suspensions, they were greatly

Tamás Szabó; Etelka Tombácz; Erzsébet Illés; Imre Dékány

2006-01-01

112

Silicon Surface Potential Modified by Titanium Oxide.  

National Technical Information Service (NTIS)

Chemically vapor deposited (CVD) titanium oxide offers some utility in insulated-gate devices. Films 2000A thick show breakdown voltages as large as 10 volts. The capacitance-voltage curves have very low values of off-set from zero bias because of the hig...

D. R. Harbison H. L. Taylor

1969-01-01

113

Albumin adsorption on to aluminium oxide and polyurethane surfaces.  

PubMed

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

Sharma, C P; Sunny, M C

1990-05-01

114

Surface Oxidation Effects During Low Energy BF2+ Ion Implantation  

NASA Astrophysics Data System (ADS)

We present results on silicon wafer surface oxidation observed during low energy high dose BF2+ implantation. Experiments were performed on single-crystal and pre-amorphized silicon wafers that help elucidate the surface structure impact on boron distribution profiles and dose retention. Implanters with different architectures were compared including both single wafer and batch systems. It was found that the oxidation rate depends on implanter type and design, and that the surface oxide thickness is a linear function of implantation dose and time. Surface oxidation is significantly higher for batch systems compared to single wafer tools. This is due primarily to the significantly lower beam duty cycle on the batch implanter. The oxide thicknesses estimated from SIMS oxygen profiles are in agreement with ellipsometry measurements after spike annealing, and show a similar difference between single wafer and batch implanters. SIMS boron distribution profiles after implantation were compared and used to calculate retained dose. In the medium dose range (<=3×1014 at/cm2) the profiles from different implanters are well matched and the dose retention is close to 100%. For the higher dose range (>=3×1015 at/cm2) retention for the batch implanter is significantly less than the single wafer tool and depends on the wafer surface structure. A higher oxidation rate results in lower dopant activation and higher Rs value after spike annealing. For high implantation doses the single wafer system allows much higher dose retention and better boron activation after annealing.

Kondratenko, Serguei; Reece, Ronald N.; Hsu, P. K.; Zhao, Hongchen

2011-01-01

115

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

116

Heterogeneous nucleation of calcium oxalate on native oxide surfaces  

SciTech Connect

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

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

1994-04-01

117

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

118

Pulmonary effects of sulfur oxides on the surface of copper oxide aerosol  

SciTech Connect

The authors have developed a system that generates copper oxide aerosol similar to the primary emissions from smelters. The surface of the ultrafine copper oxide aerosol is coated with a layer of sulfur oxides consisting of sulfate, S(VI), and sulfite, S(IV). Guinea pigs were exposed to this sulfur oxide layered copper oxide aerosol, and pulmonary mechanical functions were measured by using the Amdur-Mead method. The concentration of sulfur oxides on the aerosol was determined by using a flame photometric detector system. Although sulfuric acid was not found in this system, S(IV) at concentrations as low as 0.36 mumol/m3 delivered as a surface layer caused prolonged changes in pulmonary mechanical functions.

Chen, L.C.; Peoples, S.M.; Amdur, M.O. (New York University Medical Center, Institute of Environmental Medicine, Tuxedo (United States))

1991-05-01

119

Surface oxidation of amorphous Ni?Zr alloys  

NASA Astrophysics Data System (ADS)

The surface oxidation behaviour of amorphous Ni 64Zr 36 and Ni 91Zr 9 was investigated in situ by XPS and UPS. Oxygen doses up to 2000 L (Langmuir units) were used to study the initial stages of oxidation of the clean surfaces in the temperature range from room temperature to 300°C. XPS core level binding energy shifts of Zr3d lines showed formation of zirconium oxides even at very low exposures. We observed different core level shifts of Zr3d in Ni 64Zr 36 and Ni 91Zr 9 indicating different stoichiometry of the oxides. A pronounced surface segregation of Zr was observed upon oxidation of the alloys. It is shown that this segregation is not a thermal but an oxygen induced phenomenon. The oxidation of Ni is strongly inhibited by Zr. Oxidation of Ni is only observed in Ni 91Zr 9 at 300°C after exposure to more than 1000 L O 2. In the UPS spectra we found a shift of the Ni3d band position towards lower binding energy which can be interpreted as a subsurface Ni enrichment of the amorphous alloys.

Walz, B.; Oelhafen, P.; Güntherodt, H.-J.; Baiker, A.

1989-07-01

120

The intermediate oxidation of the Pd(100) surface  

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

121

The reaction of vapor-deposited Al with Cu oxides  

SciTech Connect

Interfaces formed by controlled deposition of Al on Cu oxides at 300K have been characterized using Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). When Al is deposited onto a thin oxide grown on Cu(110) by atmospheric exposure, it completely scavenges the oxygen from the substrate material, increasing the O(1s) binding energy by 2.0 eV to give the value found for atmospheric oxidation of a thin Al film. Similar oxygen behavior is seen for Al deposition on sputter-deposited CuO with an enriched oxygen surface region, where multilayers of Al erase the shakeup satellites in the Cu(2p) region of the XPS spectrum to give features like those exhibited by Cu{sub 2}O or metallic Cu. Having calibrated the fluence of the Al source with Rutherford backscattering spectrometry, the attenuation of the Cu 2p{sub 1/2} satellite after approximately one monolayer of Al deposition is associated with the removal of oxygen from the top 20 {angstrom} of the CuO. Approximately 7--8 equivalent monolayers of Al are converted to an oxide in the initial rapid reaction process. Further deposition leads to progressive development of the metallic Al signature in both the XPS and AES spectra. These measurements clearly demonstrate the dominant role played by Al, a strong oxide former, when it is placed in intimate contact with the distinctively weaker Cu oxide. 9 refs., 5 figs.

Taylor, T.N.; Martin, J.A.

1990-01-01

122

Layer-by-layer deposition of praseodymium oxide on tin-doped indium oxide (ITO) surface  

Microsoft Academic Search

Praseodymium oxide as a thin film of controllable layer is known to display many unique physiochemical properties, which can be useful to ceramic, semiconductive and sensor industries. Here in this short paper, we describe a new chemical method of depositing praseodymium oxide on tin-doped indium oxide (ITO) surface using a layer-by-layer approach. The process is carried out by dipping the

S. Shrestha; C. M. Y. Yeung; F. Marken; C. E. Mills; S. C. Tsang

2007-01-01

123

Oxidation of silicon surface with atomic oxygen radical anions  

NASA Astrophysics Data System (ADS)

The surface oxidation of silicon (Si) wafers by atomic oxygen radical anions (O- anions) and the preparation of metal-oxide-semiconductor (MOS) capacitors on the O- -oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al28O64]4+.4O-(C12A7-O- for short). After it has been irradiated by an O- anion beam (0.5 ?A/cm2) at 300°C for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy (XPS) results reveal that the oxide layer is of a mixture of SiO2, Si2O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of < Al electrode/SiOx/SI > are investigated by measuring capacitance-voltage (C — V) and current-voltage (I — V) curves. The oxide charge density is about 6.0 × 1011 cm-2 derived from the C — V curves. The leakage current density is in the order of 10-6A/cm2 below 4MV/cm, obtained from the I — V curves. The O- anions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.

Wang, Lian; Song, Chong-Fu; Sun, Jian-Qiu; Hou, Ying; Li, Xiao-Guang; Li, Quan-Xin

2008-06-01

124

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

125

Microbial reduction of crystalline iron(III) oxides: Influence of oxide surface area and potential for cell growth  

Microsoft Academic Search

Quantitative aspects of microbial crystalline iron(III) oxide reduction were examined using a dissimilatory iron(III) oxide-reducing bacterium (Shewanella alga strain BrY). The initial rate and long-term extent of reduction of a range of synthetic iron(III) oxides were linearly correlated with oxide surface area. Oxide reduction rates reached an asymptote at cell concentrations in excess of =1 x 10⁹\\/m² of oxide surface.

Eric E. Roden; John M. Zachara

1996-01-01

126

Surface Properties of Photo-Oxidized Bituminous Coals: Final report  

SciTech Connect

Natural weathering has a detrimental effect on the hydrophobic nature of coal, which in turn can influence clean-coal recovery during flotation. Few techniques are available that can establish the quality of coal surfaces and that have a short analysis time to provide input for process control. Luminescence emissions which can be quantified with an optical microscope and photometer system, are measurably influenced by degree of weathering as well as by mild storage deterioration. In addition, it has been shown that when vitrinite is irradiated with a relatively high intensity flux of violet- or ultraviolet- light in the presence of air, photo-oxidation of the surface occurs. The combination of measuring the change in luminescence emission intensity with degree of surface oxidation provided the impetus for the current investigation. The principal aim of this research was to determine whether clear correlations could be established among surface oxygen functionality, hydrophobicity induced by photo-oxidation, and measurements of luminescence intensity and alteration. If successful, the project would result in quantitative luminescence techniques based on optical microscopy that would provide a measure of the changes in surface properties as a function of oxidation and relate them to coal cleanability. Two analytical techniques were designed to achieve these goals. Polished surfaces of vitrain bands or a narrow size fraction of powdered vitrain concentrates were photo-oxidized using violet or ultraviolet light fluxes and then changes in surface properties and chemistry were measured using a variety of near-surface analytical techniques. Results from this investigation demonstrate that quantitative luminescence intensity measurements can be performed on fracture surfaces of bituminous rank coals (vitrains) and that the data obtained do reveal significant variations depending upon the level of surface oxidation. Photo-oxidation induced by violet or ultraviolet light fluxes does result in a progressive and significant increase in the amount of near-surface oxygen concentration at about the same level regardless of bituminous coal rank. These incremental changes in oxygen concentration appear to lower the hydrophobicity as shown by contact angle measurements on polished surfaces. Although this influence diminished as coal rank increased, the level of oxygen uptake was about the same, suggesting that the type of oxygen functionality formed during oxidation may be of great importance in modifying surface hydrophobicity. Changes in functional-group chemistry, measured by a variety of near-surface techniques, showed a general increase in the concentration of carbonyl-containing groups while those of CH{sub 2} groups decreased. All of these observations follow the trends observed in previous investigations of naturally weathered coals. The photo-oxidation technique also resulted in the development of phenolic, ester and anhydride moieties instead of the expected emplacement of carboxylic acid groups which are normally associated with naturally weathered coals. The importance of this observation is that esters and anhydrides would result in a more hydrophobic surface in comparison to the more hydrophilic surface resulting from acid functionality. This observation is consistent with the results of film flotation of UV-irradiated powdered vitrain in which floatability was generally observed to increase with increasing photo- oxidation.

NONE

1998-09-01

127

Facile preparation of superhydrophobic surfaces based on metal oxide nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

128

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

Microsoft Academic Search

The surface chemistry and catalytic reactivity of transition metal oxides deposited on Rh and Pt substrates has been examined in order to establish the role of oxide-metal interactions in influencing catalytic activity. The oxides investigated included titanium oxide (TiOx), vanadium oxide (VOx), iron oxide (FeOx), zirconium oxide (ZrOx), niobium oxide (NbOx), tantalum oxide (TaOx), and tungsten oxide (WOx). The techniques

Boffa

1994-01-01

129

Oxygen segregation and oxidation on a copper surface  

NASA Astrophysics Data System (ADS)

The atom-probe field ion microscope was employed to study oxygen adsorption and oxidation on surfaces of two grades of copper: low-grade tough-pitch copper (99.9%) and high purity copper (99.999%). The source of the oxygen is the Cu 2O inclusions which were present in the low-grade tough-pitch copper. The 99.9% grade copper was annealed in ultra-high vacuum (UHV). During heating the Cu 2O inclusions dissolve and the oxygen content of the matrix increases. Surface enrichment of oxygen and oxide formation on the surface were found depending on the annealing conditions. No indication of oxidation and oxygen enrichment was found in the high purity copper (99.999%) under the same UHV conditions.

Hono, K.; Pickering, H. W.; Hashizume, T.; Kamiya, I.; Sakurai, T.

1989-04-01

130

Microwave surface impedance measurements on reduced graphene oxide  

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

131

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

132

Suppression of arsenopyrite surface oxidation by sol-gel coatings.  

PubMed

Oxidation of arsenopyrite (FeAsS) in mine tailings is considered as the major cause of arsenic release in groundwater around mineral mine sites. Oxidation rate is increased by the biooxidation of chemolithoautotrophic bacteria, such as Acidithiobacillus ferrooxidans via the adsorption mechanism. Hence, coating with thin films as a physical barrier for oxidants surrounding the mineral surface is one of the effective abatement strategies. In this work, we studied and characterized the formation of thin films using sol-gel on arsenopyrite and investigated the resistance of thin films to biological and chemical oxidations. We selected methyltrimethoxysilane (MTMOS), tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) and N-(2-aminoethyl)-3-aminopropyl trimethoxysilane (AAPS) as sol-gel precursors. MTMOS coating arsenopyrite particles at a H2O/Si molar ratio of 2 suppressed both biological oxidation and chemical oxidation and was superior to other alkoxysilane monomers. Factors involved in oxidation suppression are the crack-free morphology and the hydrophobicity of MTMOS coating. The Si-O-Si spectrum by Fourier transform infrared (FTIR) distinctly found for the MTMOS film is considered to indicate the formation of the networks of the film, and the Fe-O-Si spectrum confirmed the bonding of the film to the arsenopyrite surface. PMID:16233789

Khummalai, Nitinai; Boonamnuayvitaya, Virote

2005-03-01

133

Ozone oxidation of surface-adsorbed polycyclic aromatic hydrocarbons (PAHs): Role of PAH-surface interaction  

NASA Astrophysics Data System (ADS)

We examine the effects of substrate on the oxidation of surface-bound anthracene and pyrene by gas-phase O3 using density functional theory (B3LYP/6-31g**). We find that the PAH-substrate interaction may result in the inhibition of some oxidation pathways involving nonplanar intermediates. The energy penalty for partial detachment from the surface is estimated and accounted for in the thermodynamic analysis of the reaction pathways. For anthracene, at least one oxidation pathway may be inhibited by strong interaction with the surface, thus impacting the rate of anthraquinone formation and possibly the observed rate of anthracene loss due to oxidation. Furthermore, the formation of other nonplanar products which have been proposed previously may be inhibited. When larger PAHs such as pyrene are surface-adsorbed, ring-opening reactions that proceed via the Criegee mechanism may be inhibited.

McNeill, V. Faye; Chu, Sophie; Sands, Sophia; Tomasik, Michelle

2010-05-01

134

Topographic control on silicone surface using chemical oxidization method  

NASA Astrophysics Data System (ADS)

The paper describes a wet process for modifying the surface of polydimethylsiloxane (PDMS) using H 2SO 4/HNO 3 solutions. The oxidation on the surface of PDMS was confirmed by the examinations of Fourier transform infrared spectrometry (FTIR), contact angle of water drop and X-ray photoelectron spectroscopy (XPS). The hydrophobic surface of pristine PDMS was not only changed to hydrophilic, but also formed wrinkles on it after chemical modification. Bilayer systems, stiff oxidized PDMS layers were capped on soft PDMS foundations, would generate easily compressive stresses due to the large difference in volumetric contraction rates and led to form wrinkles on the surface. Experimental results demonstrated the periodicity of wrinkles was controllable by controlling the duration of oxidation. Therefore, wrinkles could be arranged orderly by the guidance of external forces before oxidization. The potential technology for generating and ordering wrinkles on the PDMS surface is valuable in the applications of pressure sensors, biology, micro-optics and nano-/micro-fabrication in the future.

Shih, Teng-Kai; Ho, Jeng-Rong; Chen, Chia-Fu; Whang, Wha-Tzong; Chen, Chien-Chung

2007-10-01

135

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

EPA Science Inventory

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

136

Surface fabrication of oxides via solution chemistry  

NASA Astrophysics Data System (ADS)

A template- and catalyst-free strategy has been successfully designed to prepare MgO and hydrated magnesium carbonate hydroxide (Mg 5(CO 3) 4(OH) 2·4H 2O) nanosheets with different patterns (such as chrysalides- and rose-like morphology) on the substrate surface. Experimental results reveal that the temperature and substrate allow us to tune the morphology of patterns. Mg 5(CO 3) 4(OH) 2·4H 2O thermodynamically prefers to grow into the sheet-like crystal at the current solution growth environment, which has been successfully explained by using the chemical bonding theory. The predicted morphology can accord well with the current experimental results. The obtained MgO and its precursor Mg 5(CO 3) 4(OH) 2·4H 2O with novel patterns might find enhanced applications in catalysis, refractory materials, plastics, fire retardants, and functional nanodevices.

Yan, Chenglin; Sun, Congting; Shi, Yong; Xue, Dongfeng

2008-04-01

137

The technology of chromium oxide passivation on stainless steel surface  

SciTech Connect

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

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

1993-06-01

138

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

139

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.

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

2014-01-01

140

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

141

Surface Morphological Studies on Cupric Oxide Thin Films  

NASA Astrophysics Data System (ADS)

Polycrystalline cupric oxide (CuO) thin films were deposited using alkaline solution bath employing cathodic electrodeposition method. The thin films were electrodeposited at various solution pH. The surface morphology and elemental analyzes of the films were studied using scanning electron microscopy and energy dispersive X-ray analysis (EDX), respectively. SEM studies revealed that the surface morphology could be tailored suitably by adjusting the pH value during deposition.

Mahalingam, T.; Dhanasekaran, V.; Ravi, G.; Vidhya, M. Sangeetha; Sasikumar, T.; Joycee, P.

2011-07-01

142

Pentacene ultrathin film formation on reduced and oxidized Si surfaces  

Microsoft Academic Search

We have compared the nucleation of pentacene on reduced and oxidized Si surfaces by a combination of x-ray reflectivity measurements and atomic force microscopy. For the reduced surface, the nucleation density is 0.007 mum-2. Second monolayer (ML) formation starts at a coverage of Theta=0.6 ML, and the first layer is completely closed at a total coverage of 2 ML. For

Ricardo Ruiz; Bert Nickel; Norbert Koch; Leonard C. Feldman; Richard F. Haglund; Antoine Kahn; Giacinto Scoles

2003-01-01

143

Surface textured molybdenum zinc oxide for light diffusion enhancement  

Microsoft Academic Search

Surface textures have been fabricated on a molybdenum doped zinc oxide (MZO) film using a shadow mask in a co-sputter process. The surface textures yielded 5.3% and 10.1% of light diffusion in the visible light region for MZO films with a thickness of 100 nm and 200 nm, respectively. Light diffusion in the near infra-red region was slightly less with 4.5% for

Ching-Ming Hsu; Hon-Bin Lin; Wen-Tuan Wu

2009-01-01

144

Low-Energy HELIUM(+) and LITHIUM(+) Ion Scattering from Surfaces  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. A 150^circ ion scattering spectrometer has been commissioned and utilized to investigate several adsorbate systems on Cu(110). Firstly, the experimental parameters were determined by using 3keV Li^+ ions in the ICISS mode to investigate the clean Cu(110) surface. The inelastic background normally observed in Li^+ ion scattering energy distributions was found to be more sensitive to the sublayer shadowing conditions than was the substrate's elastic scattering peak. Most of the observed lower layer scattering features corresponded to multiple scattering events. Using computer modelling it was deduced that for the clean Cu(110) surface the 1st to 2nd layer spacing was compressed by (8 +/- 3)%, and the 2nd to 3rd was expanded by (11 +/- 8)% compared to the bulk values. 3keV Li^+ and 2keV He ^+ ions were then used to study the Cu(110)(2 x 1)-O and Cu(110)(2 x 3)-N adsorbate systems. In the former case the Li^+ data exhibited a doubling of the Cu-Cu distance in the < 110> and the < 211 > azimuths and were found to favour a missing row type reconstruction, in which every other < 100> row had been removed. In addition, He^+to O scattering indicated that the oxygen atoms resides in the < 100> long bridge site (0.0 +/- 0.2)A above the surface. Li ^+ ion scattering from the Cu(110)(2 x 3)-N indicated a substantial reconstruction of the surface, with an apparent reduction in the Cu-Cu spacing in the < 110> azimuth and an increase in the < 211> azimuth. Many of the observations are found to be quantitatively consistent, and all are qualitatively consistent, with a reconstruction in which a local Cu(100)c(2 x 2)-N structure is formed. Additionally, the He ^+to N scattering results favour a N adsorption site slightly above the surface. Adsorption of Na, K and Cs onto Cu(110) at room temperature was studied using 1keV He^+ ions, 1keV Li^+ ions were used to investigate Cs adsorption. The intensity of the alkali elastic scattering signal exhibited a 'dip' with increasing alkali coverage. For lithium this was attributed to the change in the reionization probability with changes in the surface's work function. For helium this was thought to be due to changes in the neutralization mechanism within the alkali adlayer. Additionally, the alkali metal adsorbates induced an inelastic background in the He^+ ion energy distributions, and this is ascribed to changes in the neutralization probability as the ion returns through the alkali metal overlayer.

Ashwin, Mark John

1990-01-01

145

Surface modification of nickel based alloys for improved oxidation resistance  

SciTech Connect

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

Jablonski, Paul D.; Alman, David E.

2005-02-01

146

EPR study of the surface basicity of calcium oxide. 3. Surface reactivity and nonstoichiometry.  

PubMed

High surface area polycrystalline calcium oxide forms ozonide O3- ions upon O2 adsorption and NO3(2-) anions under low pressures of NO. Both radical anions, detected by electron paramagnetic resonance (EPR), are not observed in the case of the homologous magnesium oxide. This behavior reveals the presence, in CaO, of anomalies with respect to the ideal composition of an ionic oxide which are identified in terms of two main types of defects. The first type consists of positive holes dispersed in the bulk and originated by the unavoidable presence of Na+ ions in the composition of the solid. The decomposition of the surface ozonide shows the formation of a transient surface stabilized O- (the chemical notation of a positive hole associated to an oxide ion) which is for the first time reported at the surface of CaO. The second type of defect consists of surface peroxide groups (present at particular surface sites where they are formed by pairing of two distinct O-) which react with nitric oxide (NO) yielding NO3(2-) radical anions. The presence of peroxide is not related to the presence of impurities but, rather, to a certain propensity of the solid to form such ions at the surface along the dehydration process. PMID:16800495

Paganini, Maria Cristina; Chiesa, Mario; Dolci, Francesco; Martino, Paola; Giamello, Elio

2006-06-22

147

Assembly of coordination nanostructures via ligand derivatization of oxide surfaces.  

PubMed

A scheme is presented for the construction of coordination nanostructures on oxide surfaces (glass, Si/SiO2, quartz), based on application of epoxy-terminated monolayers as anchors for covalent grafting of ligands. Two ligands bearing amine groups were reacted with epoxysilane monolayers on oxide surfaces, providing ligand-terminated substrates. The ligands employed were (i) a pyridine moiety, used for subsequent binding of cobalt tetraphenylporphine (CoTPP), and (ii) deferoxamine (DFX), which contains hydroxamic acid moieties, used for subsequent construction of various Zr4+-based coordination layers. The results suggest that a dense ligand layer was obtained in both cases, allowing the formation of coordination overlayers on the oxide surfaces. The growth of coordinated layers was similar to analogous overlayers assembled on Au substrates, indicating that high ligand coverage is achieved by the epoxy-amine surface reaction. Epoxy-based functionalization of oxide substrates is a mild and efficient method for preparing high-quality coordination overlayers. Moreover, the method makes use of commercially available silane and amine reactants, providing the basis for wide application. PMID:16489798

Wanunu, Meni; Livne, Sivan; Vaskevich, Alexander; Rubinstein, Israel

2006-02-28

148

First principles studies of complex oxide surfaces and interfaces  

Microsoft Academic Search

Oxides enter our everyday life and exhibit an impressive variety of physical and chemical properties. The understanding of their behaviour, which is often determined by the electronic and atomic structures of their surfaces and interfaces, is a key question in many fields, such as geology, environmental chemistry, catalysis, thermal coatings, microelectronics, and bioengineering. In the last decade, first principles methods,

Claudine Noguera; Fabio Finocchi; Jacek Goniakowski

2004-01-01

149

The surface chemistry of multi-oxide silicates  

NASA Astrophysics Data System (ADS)

The surface chemistry of natural wollastonite, diopside, enstatite, forsterite, and albite in aqueous solutions was characterized using both electrokinetic techniques and surface titrations performed for 20 min in batch reactors. Titrations performed in such reactors allow determination of both proton consumption and metal release from the mineral surface as a function of pH. The compositions, based on aqueous solution analysis, of all investigated surfaces vary dramatically with solution pH. Ca and Mg are preferentially released from the surfaces of all investigated divalent metal silicates at pH less than ˜8.5-10 but preferentially retained relative to silica at higher pH. As such, the surfaces of these minerals are Si-rich and divalent metal poor except in strongly alkaline solutions. The preferential removal of divalent cations from these surfaces is coupled to proton consumption. The number of protons consumed by the preferential removal of each divalent cation is pH independent but depends on the identity of the mineral; ˜1.5 protons are consumed by the preferential removal of each Ca atom from wollastonite, ˜3 protons are consumed by the preferential removal of each Mg or Ca atom from diopside or enstatite, and ˜4 protons are consumed by the preferential removal of each Mg from forsterite. These observations are interpreted to stem from the creation of additional 'internal' adsorption sites by the preferential removal of divalent metal cations which can be coupled to the condensation of partially detached Si. Similarly, Na and Al are preferentially removed from the albite surface at 2 > pH > 11; mass balance calculations suggest that three protons are consumed by the preferential removal of each Al atom from this surface over this entire pH range. Electrokinetic measurements on fresh mineral powders yield an isoelectric point (pH IEP) 2.6, 4.4, 3.0, 4.5, and <1, for wollastonite, diopside, enstatite, forsterite, and albite, respectively, consistent with the predominance of SiO 2 in the surface layer of all of these multi-oxide silicates at acidic pH. Taken together, these observations suggest fundamental differences between the surface chemistry of simple versus multi-oxide minerals including (1) a dependency of the number and identity of multi-oxide silicate surface sites on the aqueous solution composition, and (2) the dominant role of metal-proton exchange reactions on the reactivity of multi-oxide mineral surfaces including their dissolution rate variation with aqueous solution composition.

Oelkers, Eric H.; Golubev, Sergey V.; Chairat, Claire; Pokrovsky, Oleg S.; Schott, Jacques

2009-08-01

150

Surface science investigations of oxidative chemistry on gold.  

PubMed

Because of gold's resistance to oxidation and corrosion, historically chemists have considered this metal inert. However, decades ago, researchers discovered that highly dispersed gold particles on metal oxides are highly chemically active, particularly in low-temperature CO oxidations. These seminal findings spurred considerable interest in investigations and applications of gold-based materials. Since the discovery of gold's chemical activity at the nanoscale, researchers found that bulk gold also has interesting catalytic properties. Thus, it is important to understand and contrast the intrinsic chemical properties of bulk gold with those of nanoparticle Au. Despite numerous studies, the structure and active site of supported Au nanoclusters and the active oxygen species remain elusive, and model studies under well-controlled conditions could help identify these species. The {111} facet has the lowest surface energy and is the most stable and prevalent configuration of most supported gold nanoparticles. Therefore, a molecular-level understanding of the physical properties and surface chemistry of Au(111) could provide mechanistic details regarding the nature of Au-based catalysts and lead to improved catalytic processes. This Account focuses on our current understanding of oxidative chemistry on well-defined gold single crystals, predominantly from recent investigations on Au(111) that we have performed using modern surface science techniques. Our model system strategy allows us to control reaction conditions, which assists in the identification of reaction intermediates, the determination of the elementary reaction steps, and the evaluation of reaction energetics for rate-limiting steps. We have employed temperature-programmed desorption (TPD), molecular beam reactive scattering (MBRS), and Auger electron spectroscopy (AES) to evaluate surface oxidative chemistry. In some cases, we have combined these results with density functional theory (DFT) calculations. By controlling the reaction parameters that determine product selectivity, we have examined the chemical properties of bulk gold. Based on our investigations, the surface-bound oxygen atoms are metastable at low temperature. We also demonstrate that the oxygen atoms and formed hydroxyls are responsible for some of the distinct chemical behavior of gold and participate in surface reactions either as a Brønsted base or a nucleophilic base. We observe similar reaction patterns on gold surfaces to those on copper and silver surfaces, suggesting that the acid-base reactions that have been observed on copper and silver may also occur on gold. Our model chemical studies on gold surfaces have provided intrinsic fundamental insights into high surface area gold-based catalysts and the origin of the reactive oxygen species. PMID:19588952

Gong, Jinlong; Mullins, C Buddie

2009-08-18

151

Simulation of the surface structure of lithium manganese oxide spinel  

NASA Astrophysics Data System (ADS)

Simulations of the surface structure of low-index surfaces of LiMn2O4 (LMO), a candidate Li-ion battery electrode material, have been performed within the GGA+U approximation, using the VASP code. Surfaces of (001), (110), and (111) orientation were considered, with at least two terminations treated in each case. A slab geometry was employed, with termination-layer vacancies introduced to remove the bulk dipole moment while maintaining ideal stoichiometry. To complement static-structure relaxation calculations, molecular-dynamics simulations were performed to explore the phase space of possible surface reconstructions. A reconstruction is predicted for the Mn-terminated (111) surface, in which the top layers mix in stoichiometric proportions to form an LMO termination layer with square-planar-coordinated Mn. Average surface Mn oxidation states are reduced, relative to the bulk, for all surfaces considered, as a consequence of the lower-energy cost of Jahn-Teller distortion at the surface. Threefold-coordinated surface Mn, found for two terminations, is divalent, which may enhance its vulnerability to dissolution. The Li-terminated (001) surface is lowest in energy, consistent with previous classical-potential simulations for MgAl2O4 that showed the Mg-terminated (001) surface to be lowest in energy.

Benedek, R.; Thackeray, M. M.

2011-05-01

152

Simulation of the surface structure of lithium manganese oxide spinel.  

SciTech Connect

Simulations of the surface structure of low-index surfaces of LiMn{sub 2}O{sub 4} (LMO), a candidate Li-ion battery electrode material, have been performed within the GGA+U approximation, using the VASP code. Surfaces of (001), (110), and (111) orientation were considered, with at least two terminations treated in each case. A slab geometry was employed, with termination-layer vacancies introduced to remove the bulk dipole moment while maintaining ideal stoichiometry. To complement static-structure relaxation calculations, molecular-dynamics simulations were performed to explore the phase space of possible surface reconstructions. A reconstruction is predicted for the Mn-terminated (111) surface, in which the top layers mix in stoichiometric proportions to form an LMO termination layer with square-planar-coordinated Mn. Average surface Mn oxidation states are reduced, relative to the bulk, for all surfaces considered, as a consequence of the lower-energy cost of Jahn-Teller distortion at the surface. Threefold-coordinated surface Mn, found for two terminations, is divalent, which may enhance its vulnerability to dissolution. The Li-terminated (001) surface is lowest in energy, consistent with previous classical-potential simulations for MgAl{sub 2}O{sub 4} that showed the Mg-terminated (001) surface to be lowest in energy.

Benedek, R.; Thackeray, M. M. (Chemical Sciences and Engineering Division)

2011-05-31

153

Modification of protein surface hydrophobicity and methionine oxidation by oxidative systems  

PubMed Central

Aging and some pathological conditions are associated with the accumulation of altered (inactive or less active) forms of enzymes. It was suggested that these age-related alterations reflect spontaneous changes in protein conformation and/or posttranslational modifications (e.g., oxidation). Because changes in protein conformations are often associated with changes in surface hydrophobicity, we have examined the effects of aging and oxygen radical-dependent oxidation on the hydrophobicity of rat liver proteins. As a measure of hydrophobicity, the increase in fluorescence associated with the binding of 8-anilino-1-naphthalene-sulfonic acid to hydrophobic regions on the proteins was used. By this criterion, the hydrophobicity of liver proteins of 24-month-old rats was 15% greater than that of 2-month-old animals. Exposure of liver proteins to a metal-catalyzed oxidation system (ascorbate/Fe(II)/H2O2) or a peroxyl radical generating system, 2,2?-azobis(2-amidino-propane) dihydrochloride (AAPH) led to increases of 2% or 30% in surface hydrophobicity, respectively. Treatment of liver proteins with the metal-catalyzed oxidation system led to a significant increase in reactive carbonyl content and to conversion of methionine residues to methionine sulfoxide residues. Treatment with AAPH led also to oxidation of methionine, tyrosine, and tryptophan residues and to the precipitation of some proteins. Dityrosine was detected in AAPH-treated protein, both the precipitate and supernatant fraction. The oxidation-dependent increase of hydrophobicity was correlated with an increase in the levels of methionine sulfoxide and dityrosine. These results suggest that oxidative modification of proteins may be responsible for the age-related increase of protein surface hydrophobicity in vivo, and that the oxidation of methionine by an oxidative system may be an important event for the change of protein conformation.

Chao, Chien-Chung; Ma, Yan-Shan; Stadtman, Earl R.

1997-01-01

154

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

155

Bacterial adhesion to glass and metal-oxide surfaces.  

PubMed

Metal oxides can increase the adhesion of negatively-charged bacteria to surfaces primarily due to their positive charge. However, the hydrophobicity of a metal-oxide surface can also increase adhesion of bacteria. In order to understand the relative contribution of charge and hydrophobicity to bacterial adhesion, we measured the adhesion of 8 strains of bacteria, under conditions of low and high-ionic strength (1 and 100 mM, respectively) to 11 different surfaces and examined adhesion as a function of charge, hydrophobicity (water contact angle) and surface energy. Inorganic surfaces included three uncoated glass surfaces and eight metal-oxide thin films prepared on the upper (non-tin-exposed) side of float glass by chemical vapor deposition. The Gram-negative bacteria differed in lengths of lipopolysaccharides on their outer surface (three Escherichia coli strains), the amounts of exopolysaccharides (two Pseudomonas aeruginosa strains), and their known relative adhesion to sand grains (two Burkholderia cepacia strains). One Gram positive bacterium was also used that had a lower adhesion to glass than these other bacteria (Bacillus subtilis). For all eight bacteria, there was a consistent increase in adhesion between with the type of inorganic surface in the order: float glass exposed to tin (coded here as Si-Sn), glass microscope slide (Si-m), uncoated air-side float glass surface (Si-a), followed by thin films of (Co(1-y-z)Fe(y)Cr(z))3O4, Ti/Fe/O, TiO2, SnO2, SnO2:F, SnO2:Sb, A1(2)O3, and Fe2O3 (the colon indicates metal doping, a slash indicates that the metal is a major component, while the dash is used to distinguish surfaces). Increasing the ionic strength from 1 to 100 mM increased adhesion by a factor of 2.0 +/- 0.6 (73% of the sample results were within the 95% CI) showing electrostatic charge was important in adhesion. However, adhesion was not significantly correlated with bacterial charge and contact angle. Adhesion (A) of the eight strains was significantly (P < 10(-25)) correlated with total adhesion free energy (U) between the bacteria and surface (A = 2162e(-1.8U)). Although the correlation was significant, agreement between the model and data was poor for the low energy surfaces (R2 = 0.68), indicating that better models or additional methods to characterize bacteria and surfaces are still needed to more accurately describe initial bacterial adhesion to inorganic surfaces. PMID:15261011

Li, Baikun; Logan, Bruce E

2004-07-15

156

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

157

Ultrathin chromium oxide films on the W(100) surface.  

PubMed

Ultrathin chromium oxide films were prepared on a W(100) surface under ultrahigh-vacuum conditions and investigated in situ by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy electron diffraction. The results show that, at Cr coverage of less than 1 monolayer, CrO2 is formed by oxidizing pre-deposited Cr at 300-320 K in approximately 10(-7) mbar oxygen. However, an increase of temperature causes formation of Cr2O3. At Cr coverage above 1 monolayer, only Cr2O3 is detected. PMID:16853718

Guo, Donghui; Guo, Qinlin; Altman, M S; Wang, E G

2005-11-10

158

Molecularly imprinted Ru complex catalysts integrated on oxide surfaces.  

PubMed

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

Muratsugu, Satoshi; Tada, Mizuki

2013-02-19

159

Study of tin oxide: Surface properties and palladium adsorption  

NASA Astrophysics Data System (ADS)

Surface properties of various single-crystalline SnO2 surfaces were studied and the growth of palladium was investigated in the low-coverage regime. Metal - oxide structures play an important role in microelectronics and nanotechnology. They are also widely used in catalysis. Small catalytically-active metal particles on metal oxide substrates are key features in the gas sensing mechanism: they dramatically increase the sensitivity and selectivity of solid-state gas sensors towards target gases. Tin Oxide is widely used in solid-state gas sensors for detection of combustible and toxic gases. Its sensitivity and selectivity strongly depends on catalytic dopants, such as Pd or Pt, on the surface of the material. Thus, the characterization of Pd growth on tin oxide may give new insights into the catalytic and gas sensing mechanisms, and also help to understand fundamental steps that lead to various metal-on-oxide growth modes. Upon deposition of Pd onto the reduced (101) surface of a SnO2 single crystal, 1D cluster growth was observed. Starting from very low coverages, one-dimensional Pd clusters grow on the terraces, which indicates that the Pd wets the reduced tin oxide surface. Pd deposition on the oxidized surface results in randomly distributed three-dimensional Pd clusters. The clusters are distributed at step edges and on terraces without any apparent preferential adsorption sites. The one-dimensional clusters are imaged in scanning tunneling microscopy (STM) as straight, parallel nanostructures oriented along the [-101] direction, all with the same characteristic width of 0.5 nm and a height of 1 monolayer (ML). X-ray photoelectron spectroscopy (XPS) experiments show no sign of Pd oxidation; i.e. Pd grows as a metal. There is a 0.5 eV shift in the Pd 3d 5/2 core level peak position to lower binding energy that occurs during the initial stages of the growth on the reduced surface. This is an indication of charge transfer from the Pd clusters to the substrate. Coverage-dependent Ultraviolet Photoelectron Spectroscopy (UPS) spectra show that, at submonolayer Pd coverages, a Pd 4d-derived peak appears at the same position (3eV from Fermi edge) in the band gap as the Sn surface state and shifts towards the Fermi edge as coverage increases. Angular resolved photoemission data of the valence band of the clean reduced SnO2 surface and the Pd dosed reduced surface shows a strong correlation between the Sn 5s derived surface state and the Pd 4d state. The position, as well as the shape of Pd 4d peak closely follows the position and the shape of the 5s derived Sn peak in both low-index directions. This is a sign of a strong electronic interaction, hybridization between Pd 4d and Sn 5s derived states. Scanning tunneling microscopy experiments on a clean, reduced SnO 2 (100)-(1x1) surface reveal surface defects with zero, one, and two dimensions. Point defects consist of missing SnO/SnO2 units. Line defects are probably crystallographic shear planes that extend to the surface and manifest themselves as rows of atoms, shifted half a unit cell along the [010] direction. Their ends act as preferential nucleation sites for the formation of Pd clusters upon vapor-deposition. Submonolayer coverages of Pd deposited on the reduced surface at room temperature by vapour deposition result in the formation of three-dimensional clusters nucleating on the terraces. Areas of a more reduced surface phase, i.e. elongated "holes", observed at the surface after annealing to higher temperatures, still with a (1x1) structure and a half-unit-cell deep, form at [001]-oriented step edges. Recently, the use of nanobelts and nanoribbons has been suggested as novel materials for gas sensing applications. The large surface-to-volume ratio of the semiconducting metal oxide nanobelts and the congruence of the carrier screening length with their lateral dimensions make them highly sensitive and efficient transducers of surface chemical processes into electrical signal. The surface morphology of an individual nanobelts (NB) was studied with STM. Atom

Katsiev, Khabiboulakh

160

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

161

Solid State, Surface and Catalytic Properties of Oxides. Progress Report, October 1, 1979-October 31, 1980.  

National Technical Information Service (NTIS)

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 ...

H. H. Kung

1980-01-01

162

The formation and fate of oxidants on icy satellite surfaces  

NASA Astrophysics Data System (ADS)

It is well known that the bombardment of ice covered surfaces in the outer solar system leads to chemical transformations and alteration of molecular compositions. Among the major radiolysis products remaining trapped within the ice are highly reactive, oxygen rich molecules and radicals. Studies of pure ices have revealed much information about production and survival of oxidants, but real systems are full of impurities and the ability of these oxidizers to react and alter other embedded impurities gives rise to significant indirect channels for radiation-induced chemistry. Observational and experimental evidence indicates that the presence of CO2 is correlated with carbonaceous surfaces rather than strictly the presence of carbon bearing molecules. Graphitic substrate interactions with ice overlayers impede oxidant formation by scavenging of reactively scattered O, O+, OH and other fast, hot fragments. These interfacial reactions consume graphitic and carbonaceous particles and produce formic acid, formaldehyde, CO and CO2. This talk will focus on the role of ice: grain interfacial reactions in determining the potential oxidant inventory.

Orlando, T. M.; Grieves, G. A.

2007-12-01

163

Optical measurements of surface oxide layer formation on metal films  

SciTech Connect

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

Scott, M.L.

1987-01-01

164

Random lasing from surface modified films of zinc oxide nanoparticles  

NASA Astrophysics Data System (ADS)

The photoluminescence properties of zinc oxide (ZnO) ceramic thin films, prepared by spin coating of ZnO nanoparticle aqueous suspensions, were studied with emphasis on the influence of film structure and surface morphology on the observation of random laser action. Surface processing employing laser annealing transforms the particulate grain structure of the as-deposited films into a porous channel-like network. This modification was shown to be critical for achieving random laser action as it favors efficient coupling of the pump light into the film material.

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

2005-07-01

165

Chemical modification of chromium oxide surfaces using organosilanes.  

PubMed

Alkylsiloxane layers that were prepared by reaction of alkyltrichlorosilanes, alkyltriethoxysilanes, and mono-, di- and trihydridoalkylsilanes with chromium oxide surfaces were assessed in terms of their hydrophobicity. Two general conditions were studied, in the vapor phase at elevated temperatures (70 degrees C) and in solution at 70 degrees C. The surfaces were characterized by contact angle analysis and X-ray photoelectron spectroscopy (XPS). The kinetics of the solution phase reactions of n-octadecylsilane and n-octadecyltrichlorosilane were also studied. Hydrophobic monolayers were achieved in all cases, but subtle differences in structure were found. PMID:19041983

Anac, Ilke; McCarthy, Thomas J

2009-03-01

166

MORPHOLOGICAL EVOLUTION OF Ti SURFACES DURING OXIDATION TREATMENT  

Microsoft Academic Search

Pure commercial titanium, a biocompatible titanium alloy and titanium samples produced by severe plastic deformation SPD) have been modified chemically to develop a thin, hydrated titanium oxide layer. The surface morphology and evolution of this morphology of four different Ti samples–-CP-Ti, Ti6Al4V, Ti-SPD1 and Ti-SPD8–-have been investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effects of

P. M. Nagy; B. Ferencz; E. Kálmán; B. Djuri?i?; R. Sonnleitner

2005-01-01

167

The technology of chromium oxide passivation on stainless steel surface  

Microsoft Academic Search

A complete chromium oxide (Cr[sub 2]O[sub 3]) passivation technology has been developed for stainless steel surfaces for use in high purity gas-delivery systems and process chambers. Starting with an electrochemical buffing (ECB) to add to electro-polished (EP) SUS316L stainless steel material, an optimal thermal treatment was found by using a gas mixture of 10% hydrogen, 1--10 ppm oxygen and argon

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

1993-01-01

168

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

SciTech Connect

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

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

2005-08-25

169

Charge-transfer doping by fullerenes on oxidized Si surfaces  

SciTech Connect

We have studied the charge transfer between various fullerenes (C{sub 60}, C{sub 78}, C{sub 84}, C{sub 60}F{sub 36}, and C{sub 60}F{sub 48}) and oxidized Si surfaces in order to evaluate their capability of charge-transfer doping to form ultrashallow junctions in Si. Although the lowest unoccupied molecular orbitals of these fullerene molecules in isolated states are higher in energy than the valence band maximum (VBM) of Si, the fullerenes C{sub 60}F{sub 36} and C{sub 60}F{sub 48}, which were deposited on oxidized Si substrates, captured electrons from the Si surfaces; this generated hole inversion layers. C{sub 60}, C{sub 78}, and C{sub 84} did not induce such electron transfer. From the densities of the generated holes, we estimated the acceptor levels of C{sub 60}F{sub 36} and C{sub 60}F{sub 48}, which were condensed on the oxidized Si surface, to be 5.6-5.7 and 5.2 eV below the vacuum level, respectively; these values are lower than the VBM of Si.

Tada, Tetsuya; Uchida, Noriyuki; Kanayama, Toshihiko; Hiura, Hidefumi; Kimoto, Kenji [Advanced Semiconductor Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan); Fundamental and Environmental Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501 (Japan); MIRAI, Association of Super-Advanced Electronics Technologies (ASET), AIST, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan)

2007-10-01

170

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

171

A Simple, Accurate Determination of Oxide PZC and the Strong Buffering Effect of Oxide Surfaces at Incipient Wetness  

Microsoft Academic Search

A special spear-tip semisolid electrode has been used to measure the pH of solid oxide-aqueous slurries at very high solid to liquid ratios. A simple non-Nernstian model of the oxide charging along with the experimental results demonstrate a very strong buffering effect of common oxide surfaces at high oxide content. This provides a simple, accurate measurement of oxide PZC which

John R. Regalbuto

1995-01-01

172

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

173

Conduction mechanism of oxide-nitride-oxide film formed on the rough polycrystalline silicon surface  

NASA Astrophysics Data System (ADS)

The conduction mechanism of oxide-nitride-oxide film formed on the rough polycrystalline silicon surface, which has non-uniform grain sizes, is studied. At the positive bias, Poole-Frenkel (PF) conduction of holes dominates in the total leakage current. At the negative bias, although the PF conduction of holes is dominant in the nitride, Fowler-Nordheim tunneling conduction of electrons also occurs at a higher electric field. This phenomenon is discussed with a model assuming an electric field concentration at the convex edge of the plate electrode, which is formed between neighboring grains.

Matsuo, Naoto; Sasaki, Akio

1996-03-01

174

Surface Oxidation Kinetics: A Scanning Tunneling Microscopy Experiment  

NASA Astrophysics Data System (ADS)

The study of surfaces and materials is underrepresented in the undergraduate chemistry curriculum. This is unfortunate because chemistry plays such a central role in the development of new materials. We have developed an undergraduate physical chemistry laboratory experiment in which students use the scanning tunneling microscope to study the oxidation of graphite by nitric oxide. The lab is designed to simulate a research experience. Each student is responsible for one part of the experiment and the whole class uses everyone's data for their analysis. A scanning tunneling microscope is used to measure the diameter of monolayer pits etched into the graphite by the nitric oxide. The results are both instructive and aesthetic. The data are used to determine the activation energy for the etching process. Several concepts that are explored from these results: crystallography, surface diffusion, bonding, defects, and reaction kinetics. We believe that the open-ended nature of both this experiment and the data analysis will result in better educated and more productive scientists.

Poler, Jordan C.

2000-09-01

175

How strain affects the reactivity of surface metal oxide catalysts.  

PubMed

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

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

2013-12-16

176

Attachment of pathogenic prion protein to model oxide surfaces.  

PubMed

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

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

2013-07-01

177

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

178

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

179

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

180

Surface engineering of iron oxide nanoparticles for targeted cancer therapy.  

PubMed

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 response. Of the nanomaterials studied, iron oxide nanoparticles have emerged as one of top candidates for cancer therapy. Their intrinsic superparamagnetism enables noninvasive magnetic resonance imaging (MRI), and their biodegradability is advantageous for in vivo applications. 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 the biological system, and a therapeutic payload that performs the designated function in vivo. Often, the design may include a targeting ligand that recognizes the receptors over-expressed on the exterior surface of 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 design of the iron oxide core to ensure its detection in MRI and the coatings that allow the nanoparticles 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 the employment of materials that promote desired intracellular trafficking and enable controlled drug release. The payload can be genes, proteins, chemotherapy drugs, or a combination of these molecules. Each type of therapeutic molecule requires a specific coating design to maximize the loading and to 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. We provide examples of how these design parameters have been implemented to produce SPIONs for specific therapeutic applications. Although there are still challenges to be addressed, SPIONs show great promise in the successful diagnosis and treatment of the most devastating cancers. Once the critical design parameters have been optimized, these nanoparticles, combined with imaging modalities, can serve as truly multifunctional theranostic agents that not only perform a therapeutic function but also provide instant clinical feedback, allowing the physician to adjust the treatment plan. PMID:21528865

Kievit, Forrest M; Zhang, Miqin

2011-10-18

181

Surface structures of supported tungsten oxide catalysts under dehydrated conditions  

Microsoft Academic Search

The molecular structures of the WO3\\/support (Al2O3, TiO2, Nb2O5, ZrO2, SiO2, and MgO) catalysts under in situ dehydrated conditions have been investigated by Raman spectroscopy. The series of catalysts was synthesized by the aqueous incipient wetness method. The WO3\\/support catalysts, with the exception of the WO3SiO2 and WO3MgO catalysts, possess a highly distorted, octahedrally coordinated surface tungsten oxide species with

Du Soung Kim; Marlene Ostromecki; Israel E. Wachs

1996-01-01

182

Surface oxidation effects on the optical properties of silicon nanocrystals  

NASA Astrophysics Data System (ADS)

We report first-principles calculations for optical absorption spectra of hydrogenated silicon clusters in the presence of oxygen on the surface. Our computational technique is based on linear-response theory within the time-dependent local-density approximation (TDLDA). The calculated spectra show that oxidation substantially reduces the size of optical gaps in silicon nanocrystals. This result may explain a seeming disagreement between the measured photoluminescence and theoretical predictions based on a quantum confinement model in the limit of small clusters.

Vasiliev, Igor; Chelikowsky, James R.; Martin, Richard M.

2002-03-01

183

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

NASA Astrophysics Data System (ADS)

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

Pradhan, Kallol

184

Surface morphology and structure of ultra-thin magnesium oxide grown on (100) silicon by atomic layer deposition oxidation  

Microsoft Academic Search

Ultra-thin magnesium oxide layers were elaborated by atomic layer deposition and oxidation process on silicon (100) starting from (2×1) thermally-reconstructed or hydrogen-terminated Si surfaces. Low-energy electron diffraction experiments show (2×3) and (3×3) reconstructions while depositing a magnesium monolayer on Si clean surfaces, and a 3-dimentional growth of the oxide as confirmed by ex-situ atomic force microscopy. For hydrogen-terminated or clean

N. Rochdi; K. Liudvikouskaya; M. Descoins; M. Raïssi; C. Coudreau; J.-L. Lazzari; H. Oughaddou; F. Arnaud D'Avitaya

2011-01-01

185

Effect of zirconium and molybdenum oxides on the surface and volume properties of an aluminocalcium oxide-fluoride melt  

NASA Astrophysics Data System (ADS)

The effect of additions of zirconium and molybdenum oxides on the surface tension and density of oxide-fluoride slags is studied by the method of the maximum pressure in a gas bubble. The obtained experimental and calculated results reveal a complex-forming character of the behavior of zirconium and molybdenum in oxide-fluoride slag melts, and they are used to estimate the sizes of the structural units present in the surface layer of the slags.

Agafonov, S. N.; Krasikov, S. A.

2013-02-01

186

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.

Kievit, Forrest M.; Zhang, Miqin

2011-01-01

187

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

PubMed

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

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

2000-11-01

188

Uranyl and arsenate cosorption on aluminum oxide surface  

NASA Astrophysics Data System (ADS)

In this study, we examined the effects of simultaneous adsorption of aqueous arsenate and uranyl onto aluminum oxide over a range of pH and concentration conditions. Arsenate was used as a chemical analog for phosphate, and offers advantages for characterization via X-ray absorption spectroscopy. By combining batch experiments, speciation calculations, X-ray absorption spectroscopy, and X-ray diffraction, we investigated the uptake behavior of uranyl, as well as the local and long-range structure of the final sorption products. In the presence of arsenate, uranyl sorption was greatly enhanced in the acidic pH range, and the amount of enhancement is positively correlated to the initial arsenate and uranyl concentrations. At pH 4-6, U L III- and As K-edge EXAFS results suggest the formation of surface-sorbed uranyl and arsenate species as well as uranyl arsenate surface precipitate(s) that have a structure similar to trögerite. Uranyl polymeric species or oxyhydroxide precipitate(s) become more important with increasing pH values. Our results provide the basis for predictive models of the uptake of uranyl by aluminum oxide in the presence of arsenate and (by analogy) phosphate, which can be especially important for understanding phosphate-based uranium remediation systems.

Tang, Yuanzhi; Reeder, Richard J.

2009-05-01

189

Photochemistry of adsorbed nitrate on aluminum oxide particle surfaces.  

PubMed

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

Rubasinghege, Gayan; Grassian, Vicki H

2009-07-01

190

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

SciTech Connect

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

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

2009-06-15

191

Influence of carbon–oxygen surface complexes on the surface acidity of tungsten oxide catalysts supported on activated carbons  

Microsoft Academic Search

Tungsten oxide catalysts supported on activated carbons were prepared by using tungsten hexacarbonyl, ammonium tungstate, and tungsten pentaethoxide as precursors. An activated carbon was obtained from olive stone by physical activation. A portion of this activated carbon was oxidized with ammonium peroxydisulfate in order to introduce different oxygen surface complexes. Subsequently, different portions of this oxidized activated carbon were heat

Carlos Moreno-Castilla; Agust??n F. Pérez-Cadenas; Francisco J. Maldonado-Hódar; Francisco Carrasco-Mar??n; José Luis G. Fierro

2003-01-01

192

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

193

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

194

Interaction of adsorbed organosilanes with polar zinc oxide surfaces: a molecular dynamics study comparing two models for the metal oxide surface  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations at 298 K are used to study the interaction of adsorbed silane molecules (octyltrihydroxysilane, butyltrihydroxysilane, aminopropyltrihydroxysilane and thiolpropyltrihydroxysilane) with the polar (0 0 0 1¯) zinc oxide surface. Special emphasis is placed on the influence of the metal oxide surface on the orientation and adsorption energy of the silanes. We compare a model of a reconstructed surface with a previous model using an ideal surface. Surface morphology is shown to have little effect on the orientation of silane adsorbates (except thiolpropyltrihydroxysilane) with the adsorption energy being correlated with the surface polarity.

Kornherr, Andreas; French, Samuel A.; Sokol, Alexey A.; Catlow, C. Richard A.; Hansal, Selma; Hansal, Wolfgang E. G.; Besenhard, Jürgen O.; Kronberger, Hermann; Nauer, Gerhard E.; Zifferer, Gerhard

2004-07-01

195

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

196

Characterization of the Oxidized CVD Diamond (100) Surfaces using STM, PEEM and XPS  

NASA Astrophysics Data System (ADS)

We have investigated atomic structures of B-doped microwave-plasma chemical-vapor-deposited (CVD) diamond (100) surfaces using an ultra-high-vacuum scanning tunneling microscope (STM), photoelectron emission microscopy (PEEM) and X-ray photoelectron spectroscopy (XPS). STM images taken from the diamond surfaces at the various oxidization stages reflected corresponding surface structures, from which the oxygen sites and oxidization process of the as-grown CVD diamond were discussed. PEEM images demonstrated a rather high electron emissivity of the as-grown CVD diamond surface and decreasing emissivities after light oxidization. XPS spectra taken from these surfaces demonstrated corresponding changes in shape with oxidization.

Nakamura, Jun; Ito, Toshimichi

197

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

198

Atomistic study of metal clusters supported on oxide surface  

NASA Astrophysics Data System (ADS)

Metal clusters on oxide surface are a widely studied topic in surface science and technology. In this work, we use the ab initio based pair potentials to study the shape evolution of these clusters with their width from 3 Å to 90 Å. The clusters have a basic polyhedron shape covered by (0 0 1) and (1 1 1) faces, with four undetermined parameters. The main purpose of this work is to determine the structure parameters numerically. Here, we use a combination of energy minimization calculation, least square method and Lagrange multiplier method, and go through a series of metals including Ag, Al, Au, Pd and Rh. As a result, we find that these clusters have a truncated octahedron structure on MgO(0 0 1) surface, with a square contact face for Ag, Al and Au, and an octagon one for Pd and Rh. Also, we see that misfit dislocation appears when the cluster becomes large, first at the edge, then inside the contact area.

Long, Y.; Chen, N. X.

199

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

200

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

201

Correlation between aSi:H surface oxidation process and the performance of MIS structures  

Microsoft Academic Search

In order to correlate the MIS devices performance with different surface oxidation methods, AFM, spectroscopic ellipsometry and infrared spectroscopy measurements were performed in a-Si:H films, before and after surface oxidation, using different oxidation techniques and oxides: thermal dry (in air), wet (in H2O2) and by oxygen plasma, while MIS (metal-insulator-semiconductor) devices were characterised by I–V curves, under dark and AM1.5

H. Águas; Y. Nunes; E. Fortunato; P. Gordo; M. Maneira; R. Martins

2001-01-01

202

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

PubMed

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

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

2013-10-23

203

Hydrophobicity of perfluoroalkyl isocyanate monolayers on oxidized aluminum surfaces.  

PubMed

Perfluoroalkyl isocyanate-derived monolayers were prepared on oxidized aluminum surfaces by chemical vapor deposition (CVD) of 1H,1H,2H,2H-perfluorodecyl isocyanate (CF(3)[CF(2)](7)CH(2)CH(2)N horizontal lineC horizontal lineO, i.e., R(F)-NCO). Two types of oxidized aluminum substrates were studied: electrochemically polished aluminum plates (Al(Al(2))(O(3))) and Al(Al(2))(O(3)) that was treated with boiling water ((BW)Al(Al(2))(O(3))). X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) confirmed that this CVD method produces a monolayer with a thickness of approximately 1.2 nm on Al(Al(2))(O(3)) through a carbamate linkage without discernible change in surface morphology. After monolayer deposition, hydrophilic Al(Al(2))(O(3)) surfaces become hydrophobic. Advancing and receding water contact angles are theta(A)/theta(R) = 125 degrees /103 degrees . AFM indicates that (BW)Al(Al(2))(O(3)) surfaces contain 10-15-nm-size pebble-like features. This is due to both chemical and physical erosion of the aluminum surface caused by the boiling water treatment. Due to the presence of these topographical features, the CVD of R(F)-NCO on (BW)Al(Al(2))(O(3)) induces superhydrophobicity (theta(A)/theta(R) = 167 degrees /165 degrees ). Al(Al(2))(O(3)) and (BW)Al(Al(2))(O(3)) based "control surfaces" were prepared with the conventional mono- and trifunctional organosilanes, 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (CF(3)[CF(2)](7)CH(2)CH(2)Si[CH(3)](2)Cl, R(F)-SiMe(2)Cl) and 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. In the case of R(F)-Si(OMe)(3), the theta(A)/theta(R) values for Al(Al(2))(O(3)) and (BW)Al(Al(2))(O(3)) are 125 degrees /110 degrees and 170 degrees /167 degrees , respectively. R(F)-SiMe(2)Cl-treated aluminum surfaces are much less hydrophobic. The theta(A)/theta(R) values for Al(Al(2))(O(3)) and (BW)Al(Al(2))(O(3)) are 107 degrees /69 degrees and 137 degrees /87 degrees , respectively. XPS analysis of surface coverage is consistent with the contact angle behavior and the water sensitivity. Stability of these three monolayers in water is in the order: R(F)-Si(OMe)(3) > R(F)-NCO > R(F)-SiMe(2)Cl. PMID:19432482

Hozumi, Atsushi; Kim, Bokyung; McCarthy, Thomas J

2009-06-16

204

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

PubMed

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

Lee, Myungjin; Kim, Kijeong; Lee, Hangil

2013-01-01

205

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

PubMed Central

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

2013-01-01

206

Surface area measurement of graphene oxide in aqueous solutions.  

PubMed

Graphene oxide (GO) forms persistent dispersions in aqueous solutions up to concentrations of 0.2 mg mL(-1). Addition of methylene blue (MB) to these aqueous dispersion of GO gives rise to the observation in optical spectroscopy of new absorption bands that are indicative of the formation of MB/GO conjugates. Four new absorption maxima have been characterized, and their intensity varies depending on the relative concentration of MB with respect to GO. Two of these bands appearing at 677 and 757 nm correspond to individual MB molecules adsorbed on neutral or acid sites of GO, respectively. Two other bands at 615 and 580 nm are attributable to adsorbed MB molecules showing interaction with other neighbor dye molecules at incomplete (615 nm) or complete (580 nm) surface coverage. Complete coverage of GO surface by MB causes the formation of a precipitate and the separation of the MB/GO conjugate. EDS mapping of carbon and sulfur atoms of MB/GO conjugate indicates the homogeneous distribution of MB molecules coating GO sheets. A simple and reliable protocol for surface area measurement and determination of the level of aggregation for GO dispersions in water has been proposed by determining the amount of MB that leads to the maximum intensity of the 580 nm band and precipitation of the MB/GO conjugate. Specific surface area as high as 736.6 m(2) g(-1) in the range of the theoretical value for GO has been experimentally measured for diluted GO solutions, but aggregation levels of 15% were estimated for GO concentration of 50 ?g mL(-1). PMID:24111520

Montes-Navajas, Pedro; Asenjo, Natalia G; Santamaría, Ricardo; Menéndez, Rosa; Corma, Avelino; García, Hermenegildo

2013-11-01

207

Surface plasmon resonance of gold and silver nanoparticle monolayers: effect of coupling and surface oxides  

NASA Astrophysics Data System (ADS)

Material properties are described by some physical parameters such as temperature or pressure. Optical properties of materials are very important for applications where is light as electromagnetic wave dominant. Behavior of the light in interaction with materials depends on refractive indices. These indices are same for various sizes of materials, but in nanoscale dimensions, they depend on some phenomena. Herein, we present the study of the silver (Ag) nanoparticle (NP) monolayer film and its dielectric properties. The aim of the study is to explain phenomenon why it is necessary to use effective material properties for Ag NPs, where these properties are size-dependent. The plasmonic properties of NP have been investigated by the finite domain time difference (FDTD) simulation methods. Although the good agreement of plasmonic resonances was found for gold (Au) NP film, a significant mismatch in the resonance energy for Ag NP film was observed. The deviation was assigned to the presence of silver oxide (Ag2O) in Ag NPs as a surface layer. This real structure of Ag NPs can be replaced by structure with suitable effective material properties. Results depict importance of the effective material properties in Ag NP film for reason of the presence of silver oxide. The Ag NPs with surface oxide exhibits linear tendency in the deviation of the effective dielectric function, which agrees with the experimental observations.

Kuzma, Anton; Chovan, Jozef; Uherek, František; Weis, Martin

2013-10-01

208

Surface characterization of plasma sprayed oxide materials: estimation of surface acidity using mass titration.  

PubMed

The aim of this study was to characterize the influence of plasma spraying on the point of zero charge (PZC) of Al2O3-, Cr2O3- and TiO2-based materials. PZC is one of the most important parameter, which describes the acidity of oxide material in aqueous environments. PZC values of several plasma sprayed oxides were determined using mass titration method. Studies were performed for initial spray powders and plasma sprayed coating materials. In addition, mass titration experiments were performed for water-washed and nonwashed samples. It was found that mass titration is a suitable method to estimate the surface acidity of relatively coarse sample powders. It was found for most of the studied materials that the limiting pH values (assumed to be close PZC) were close to those reported in literature for the PZC values of traditionally manufactured oxide materials. On the other hand, mass titration curves of some oxide samples showed unexpected deviation in curve shapes and limiting pH. These deviations were probably due to selective dissolution of sample contaminations or sample material. PMID:15271562

Harju, Mika; Levänen, Erkki; Mäntylä, Tapio

2004-08-15

209

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

SciTech Connect

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

Li, Wenbo; Zhu, Qiaozhi; Wang, Dejun, E-mail: dwang121@dlut.edu.cn [School of Electronic Science and Technology, Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024 (China)] [School of Electronic Science and Technology, Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024 (China); Zhao, Jijun [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), College of Advanced Science and Technology, Ministry of Education, Dalian 116024 (China)] [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), College of Advanced Science and Technology, Ministry of Education, Dalian 116024 (China)

2013-11-18

210

Probing surface band bending of surface-engineered metal oxide nanowires.  

PubMed

We in situ probed the surface band bending (SBB) by ultraviolet photoelectron spectroscopy (UPS) in conjunction with field-effect transistor measurements on the incompletely depleted ZnO nanowires (NWs). The diameter range of the NWs is ca. 150-350 nm. Several surface treatments (i.e., heat treatments and Au nanoparticle (NP) decoration) were conducted to assess the impact of the oxygen adsorbates on the SBB. A 100 °C heat treatment leads to the decrease of the SBB to 0.74 ± 0.15 eV with 29.9 ± 3.0 nm width, which is attributed to the removal of most adsorbed oxygen molecules from the ZnO NW surfaces. The SBB of the oxygen-adsorbed ZnO NWs is measured to be 1.53 ± 0.15 eV with 43.2 ± 2.0 nm width. The attachment of Au NPs to the NW surface causes unusually high SBB (2.34 ± 0.15 eV with the wide width of 53.3 ± 1.6 nm) by creating open-circuit nano-Schottky junctions and catalytically enhancing the formation of the charge O(2) adsorbates. These surface-related phenomena should be generic to all metal oxide nanostructures. Our study is greatly beneficial for the NW-based device design of sensor and optoelectronic applications via surface engineering. PMID:23092152

Chen, Cheng-Ying; Retamal, Jose Ramon Duran; Wu, I-Wen; Lien, Der-Hsien; Chen, Ming-Wei; Ding, Yong; Chueh, Yu-Lun; Wu, Chih-I; He, Jr-Hau

2012-11-27

211

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

Microsoft Academic Search

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

Bhabendra K. Pradhan; N. K. Sandle

1999-01-01

212

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

SciTech Connect

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

Boffa, A.B. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States). Materials Sciences Div.

1994-07-01

213

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

SciTech Connect

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

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

2010-01-01

214

In Situ Initial Surface Oxidation of Ti-44Al-11Nb Alloy at Room Temperature  

NASA Astrophysics Data System (ADS)

The in situ initial surface oxidation of polycrystalline Ti-44Al-11Nb (compositions are in atomic studied at room temperature in an ultra-high vacuum environment. Samples were cleaned by sputtering using 2.8 KV argon ions and the high-purity oxygen was carefully dosed onto sample surface. After each oxygen dosing the surface species, metallic states and oxidized states, were detected by X-ray Photoelectron Spectroscopy. Judged from the binding energy shifts and the concentration of oxidized species with respect to nominal composition of the alloy, Al metal is the easiest metal to be oxidized and Nb is the hardest one among these three metals. This study indicates that similar kinetics of oxidation process at room temperature is similar to that observed earlier at high temperature while Al atoms diffuse towards surface during the oxidation. Nb showed a lower oxidation rate with a different mechanism.

Wang, Paul W.; Woo, John; Avila, Marco; Garcia, Jorge; Varma, Shailendra K.; Bronson, Arturo

2002-03-01

215

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

216

Interaction of the reactants with the surface of an oxide catalyst under conditions of the oxidative ammonolysis of toluene  

SciTech Connect

The processes of separate and joint interaction of toluene, oxygen, and ammonia with the surface of a complex oxide catalyst were investigated by a pulsed method under nonsteady-state and steady-state conditions of the oxidative ammonolysis of toluene. It was shown that under steady-state conditions the formation of benzonitrile occurs according to a stepwise redox mechanism, and that of the products of profound oxidation occurs both according to a stepwise and according to associative mechanisms.

Guseinov, A.B.; Mamedov, E.A.; Pankrat'ev, Y.D.; Rizaev, R.G.

1985-08-01

217

Electroless coating of tungsten oxide on the surface of copper powder  

SciTech Connect

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

Ahn, Jae-Hoon; Lee, Jin-Kyu; Kim, Dong-Woo; Jung, Young-Soo; Kim, Gil-Pyo [Department of Chemical Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751 (Korea, Republic of); Baeck, Sung-Hyeon [Department of Chemical Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751 (Korea, Republic of)], E-mail: shbaeck@inha.ac.kr

2008-08-04

218

An investigation of molybdenum and molybdenum oxide catalyzed hydrocarbon formation reactions. [Surface chemistry of ethylene oxide on Pd(111)  

SciTech Connect

Progress was made in the following four areas: activity of model catalyst (Mo oxides) for olefin metathesis (2 C[sub 3]H[sub 6] [r arrow] C[sub 4]H[sub 8] + C[sub 2]H[sub 4]); kinetics of Mo(100)-catalyzed olefin metathesis; surface chemistry of ethylene oxide on Pd(111); and uv source construction.

Not Available

1993-01-01

219

Surface oxidation behavior of MgNd alloys  

NASA Astrophysics Data System (ADS)

The oxidation kinetics of MgNd alloys oxidized in pure O 2 at high temperatures has been investigated. The results revealed two stages of the reaction: A fast initial oxidation was followed by a slow oxide growth with a parabolic kinetics. For MgNd alloys (Nd = 25 wt.%), the oxidation rate increased with the enhancement of the oxidation temperature. A sudden ignition was found for this alloys oxidized at 873 K up to about 80 min. Moreover, the increase of the Nd content would harm the oxidation resistance of the MgNd alloys. By Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, it was found that a triplex structure of oxide film formed. The outer layer was composed of MgO, Nd 2O 3 and Nd(OH) 3, the middle layer mainly consisted of MgO and Nd 2O 3, and the inner layer was the transitional layer made of MgO, Nd 2O 3 and the content of the substrate. The protective oxidation was associated with the formation of the dense Nd 2O 3/MgO layer during isothermal oxidation process. The oxidation mechanisms for the formation of oxide film are discussed.

Wang, X. M.; Zeng, X. Q.; Wu, G. S.; Yao, S. S.; Li, L. B.

2007-09-01

220

Surfaces of reduced and oxidized SrTiO3 from atomic force microscopy  

Microsoft Academic Search

Measurements by atomic force microscopy are reported for (100) and (110) surfaces of SrTiO3 monocrystals prepared with different oxidizing and reducing conditions at elevated temperatures (800-1000 °C). The morphology of the surfaces turns out to be drastically altered for both oxidized and reduced crystals in comparison with the original stoichiometric surfaces. The observed changes on the surface of SrTiO3 due

K. Szot; W. Speier

1999-01-01

221

Investigation of Oxide Layer Structure on Niobium Surfaces using a Secondary Ion Mass Spectrometer  

Microsoft Academic Search

Oxide layer structure on the surfaces of niobium (Nb) can be studied by continuously monitoring peaks of the secondary ions of Nb and its relevant oxides as a function of time during depth profiling measurements employing a secondary ion mass spectrometer (SIMS). This is based on the fact that different oxides have different cracking patterns. This new approach is much

Andy T. Wu

2005-01-01

222

Investigation of oxide layer structure on niobium surface using a secondary ion mass spectrometry  

Microsoft Academic Search

Oxide layer structure on the surfaces of niobium (Nb) can be studied by continuously monitoring peaks of the secondary ions of Nb and its relevant oxides as a function of time during depth profiling measurements employing a secondary ion mass spectrometry (SIMS). This is based on the fact that different oxides have different cracking patterns. This new approach is much

A. T. Wu

2006-01-01

223

Oxide surface cleaning by an atmospheric pressure plasma  

Microsoft Academic Search

In this study, an atmospheric pressure plasma was generated using a dielectric barrier discharge (DBD) with a perforated dielectric covered electrode and its effect on the cleaning of organic materials on oxides such as indium tin oxide (ITO) and magnesium oxide (MgO) was investigated. He and O2 were used as the ignition gas and cleaning gas, respectively. In addition to

Chang Heon Yi; Chang Hyun Jeong; Yong Hyuk Lee; Young Wook Ko; Geun Young Yeom

2004-01-01

224

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

225

Investigation of Oxide Layer Structure on Niobium Surfaces using a Secondary Ion Mass Spectrometer  

SciTech Connect

Oxide layer structure on the surfaces of niobium (Nb) can be studied by continuously monitoring peaks of the secondary ions of Nb and its relevant oxides as a function of time during depth profiling measurements employing a secondary ion mass spectrometer (SIMS). This is based on the fact that different oxides have different cracking patterns. This new approach is much simpler and easier for studying oxide layer structure on Nb surfaces than the conventional approach through deconvolution of oxide peaks obtained from an x-ray photoemission spectrometer. Eventually it can be developed into an in-situ tool for monitoring the oxide layer structure on Nb surfaces prepared by various procedures. Preliminary results of SIMS measurements on the surfaces of Nb samples treated by buffered electropolishing and buffered chemical polishing will be reported.

Andy T. Wu

2005-07-10

226

Investigation of oxide layer structure on niobium surface using a secondary ion mass spectrometry  

NASA Astrophysics Data System (ADS)

Oxide layer structure on the surfaces of niobium (Nb) can be studied by continuously monitoring peaks of the secondary ions of Nb and its relevant oxides as a function of time during depth profiling measurements employing a secondary ion mass spectrometry (SIMS). This is based on the fact that different oxides have different cracking patterns. This new approach is much simpler and easier for studying oxide layer structure on Nb surfaces than the conventional approach through deconvolution of oxide peaks obtained from an X-ray photoelectron spectroscopy. Eventually the method described here can be developed into an in situ tool for monitoring the oxide layer structure on Nb surfaces prepared by various procedures. Preliminary results of SIMS measurements on the surfaces of Nb samples treated by buffered electropolishing and buffered chemical polishing will be reported.

Wu, A. T.

2006-07-01

227

Study and Investigation of the Dependence of Semiconductor Surface Stability on Oxide Growth.  

National Technical Information Service (NTIS)

Surface charge migration on the outer oxide surface was studied by means of the time dependence of charge and discharge currents of an MOS structure. The method was tested by placing a probe electrode on the oxide near the charging electrode and observing...

J. Lindmayer K. Lehovic

1967-01-01

228

SIMS studies of oxidation mechanisms and polysulfide formation in reacted sulfide surfaces  

Microsoft Academic Search

The surface oxidation of metal sulfides in air and aqueous solution is of central importance in mineral separation and environmental control of acid mine drainage. Mechanisms of oxidation, dissolution and surface restructuring have been extensively studied using XPS. High binding energy components in S 2p XPS spectra have been attributed to metal-deficiency, formation of polysulfide Sn2?, elemental sulfur and electronic

R. St. C. Smart; M. Jasieniak; K. E. Prince; W. M. Skinner

2000-01-01

229

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.

2010-01-01

230

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

SciTech Connect

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

Doyle, F.M.

1996-01-26

231

Oxidation of TiAl surface with hyperthermal oxygen molecular beams  

NASA Astrophysics Data System (ADS)

We report results of our detailed studies on the initial oxidation process of TiAl with a 2 eV hyperthermal oxygen molecular beam (HOMB) and thermal O2 in the backfilling. The oxidation processes are monitored by X-ray photoemission spectroscopy (XPS) measurements in conjunction with synchrotron radiation (SR). Oxidation of both Al and Ti occurs during the oxidation. The incident-energy and surface-temperature dependences of oxidation reveal that the precursor-mediated dissociative adsorption is the dominant initial step of oxidation in the thermal O2 backfilling. Thus, the efficiency of oxidation is higher for the thermal O2 backfilling than for the HOMB dose. The result is quite different from that on TiNi where the HOMB dose has the advantages in oxide layer growth at high O coverage. We succeeded in fabricating blue colored TiO2 and Al2O3 containing layers, combining HOMB and surface annealing.

Hashinokuchi, Michihiro; Tode, Mayumi; Yoshigoe, Akitaka; Teraoka, Yuden; Okada, Michio

2013-07-01

232

Dispersion and surface states of copper catalysts by temperature-programmed-reduction of oxidized surfaces (s-TPR)  

Microsoft Academic Search

Surface and sub-surface oxidation of dispersed copper phase by N2O adsorptive decomposition at controlled temperature followed by H2 temperature-programmed-reduction of the Cu2O surface layers formed (s-TPR) was performed on siliceous supported catalysts (ca. 6wt.% Cu). The combined analysis permitted to measure the copper dispersion and to identify different surface copper species. Copper dispersion parameters were calculated from the H2-uptakes in

Antonella Gervasini; Simona Bennici

2005-01-01

233

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

234

Chemical properties of oxidized silicon carbide surfaces upon etching in hydrofluoric acid.  

PubMed

Hydrogen termination of oxidized silicon in hydrofluoric acid results from an etching process that is now well understood and accepted. This surface has become a standard for studies of surface science and an important component in silicon device processing for microelectronics, energy, and sensor applications. The present work shows that HF etching of oxidized silicon carbide (SiC) leads to a very different surface termination, whether the surface is carbon or silicon terminated. Specifically, the silicon carbide surfaces are hydrophilic with hydroxyl termination, resulting from the inability of HF to remove the last oxygen layer at the oxide/SiC interface. The final surface chemistry and stability critically depend on the crystal face and surface stoichiometry. These surface properties affect the ability to chemically functionalize the surface and therefore impact how SiC can be used for biomedical applications. PMID:19919146

Dhar, Sarit; Seitz, Oliver; Halls, Mathew D; Choi, Sungho; Chabal, Yves J; Feldman, Leonard C

2009-11-25

235

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

236

Oxidation of Ge(100) and Ge(111) surfaces: an UPS and XPS study  

Microsoft Academic Search

In situ and ex situ oxidation studies are carried out on Ge(100) and Ge(111) employing techniques of ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS). In situ oxidation produces mainly GeO on both the surfaces. Ge 3d and 2p levels show a chemical shift of about 1.4 and 1.8 eV respectively corresponding to this oxide. GeO desorbs from the surface

K. Prabhakaran; T. Ogino

1995-01-01

237

Scanned Probe Oxidation on p GaAs(100) Surface with an Atomic Force Microscopy  

Microsoft Academic Search

Locally anodic oxidation has been performed to fabricate the nanoscale oxide structures on p-GaAs(100) surface, by using an atomic force microscopy (AFM) with the conventional and carbon nanotube (CNT)-attached probes.\\u000a The results can be utilized to fabricate the oxide nanodots under ambient conditions in noncontact mode. To investigate the\\u000a conversion of GaAs to oxides, micro-Auger analysis was employed to analyze

Sheng-Rui Jian; Jenh-Yih Juang

2008-01-01

238

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

239

Surface oxidation study of single wall carbon nanotubes  

NASA Astrophysics Data System (ADS)

Functionalization of single wall carbon nanotubes (SWCNTs) is desirable to enhance their ability to be incorporated into polymers and enhance their bonding with the matrix. One approach to carbon nanotube functionalization is by oxidation via a strong oxidizing agent or refluxing in strong acids. However, this approach can damage the nanotubes, leading to the introduction of defects and/or shorter nanotubes. Such damage can adversely affect the mechanical, thermal, and electrical properties. A more benign approach to nanotube functionalization has been developed involving photo-oxidation. Chemical analysis by XPS revealed that the oxygen content of the photo-oxidized SWCNTs was 11.3 at.% compared to 6.7 at.% for SWCNTs oxidized by acid treatment. The photo-oxidized SWCNTs produced by this method can be used directly in various polymer matrices or can be further modified by additional chemical reactions.

Lebrón-Colón, M.; Meador, M. A.; Lukco, D.; Solá, F.; Santos-Pérez, J.; McCorkle, L. S.

2011-11-01

240

Fundamental studies of electrochemically controlled surface oxidation and hydrophobicity of natural enargite.  

PubMed

The surface oxidation and hydrophobicity of natural enargite (Cu(3)AsS(4)) and the formation of oxidation species at the mineral surface have been examined by a novel experimental approach that combines electrochemical techniques and atomic force microscopy (AFM). This approach allows for in-situ, synchronized electrochemical control and examination of the oxidative surface morphology of enargite. Combined with ex-situ cryo X-ray photoelectron spectroscopy surface analysis, the surface speciation of enargite surface oxidation has been obtained, comparing the newly fractured natural enargite surface with those that have been electrochemically oxidized at pHs 4 and 10. At pH 4, surface layer formations consisting of metal-deficient sulfide and elemental sulfur were identified, associated with a limited increase in root-mean-square (rms) roughness (1.228 to 3.143 nm) and apparent heterogeneous distribution of surface products as demonstrated by AFM imaging. A mechanism of initial rapid dissolution of Cu followed by diffusion-limited surface layer deposition was identified. At pH 10, a similar mechanism was identified although the differences between the initial and diffusion-limited phases were less definitive. Surface species were identified as copper sulfate and copper hydroxide. A significant increase in surface roughness was found as rms roughness increased from 0.795 to 9.723 nm. Dynamic (receding) contact angle measurements were obtained by a droplet evaporation method. No significant difference in the contact angle on a surface oxidized at pH 10 and the freshly polished surface was found. A significant difference was found between the polished surface and that oxidized at pH 4, with an increase in contact angle of about 13° (46° to 59°) after oxidation. Competing effects of hydrophilic (copper oxides and hydroxides) and hydrophobic (elemental sulfur) species on the mineral surface under oxidizing conditions at pH 4 and the change in surface roughness at pH 10 may contribute to the observed effects of electrochemically controlled oxidation on enargite hydrophobicity. PMID:23331095

Plackowski, Chris; Hampton, Marc A; Nguyen, Anh V; Bruckard, Warren J

2013-02-19

241

TEMPO-mediated surface oxidation of cellulose whiskers  

Microsoft Academic Search

Cellulose whiskers resulting from HCl acid hydrolysis of tunicin were subjected to TEMPO-mediated oxidation under various conditions and the extent of the resulting oxidation was characterized by Fourier-transform infrared spectroscopy (FT-IR), conductimetry, X-Ray diffraction analysis and transmission electron microscopy (TEM). With degree of oxidation of up to 0.1 the samples kept their initial morphological integrity and native crystallinity, but at

Youssef Habibi; Henri Chanzy; Michel R. Vignon

2006-01-01

242

Depletion of surface accumulation charge in InN by anodic oxidation  

NASA Astrophysics Data System (ADS)

Si-doped InN layer by molecular beam epitaxy was subjected to anodic oxidation in 0.1 M potassium hydroxide (KOH) electrolyte and characterized by electrochemical methods to derive carrier profile at the InN surface. The obtained results were compared to the characteristics of a planar resistor structure and vertical metal-oxide-semiconductor (MOS) diodes with Ni-metal contacts on the oxidized InN. Both measurements in electrolyte and in air confirmed the formation of a surface oxide layer after the anodic treatment and depletion of the surface accumulation charge of the as-grown InN. The upward band bending of InN at the oxide interface was also concluded from the analysis of capacitance-voltage characteristics of the MOS diodes. Transmission electron microscopy revealed a nonuniform oxide layer containing porelike structures of a few nanometers in diameter.

Denisenko, A.; Pietzka, C.; Chuvilin, A.; Kaiser, U.; Lu, H.; Schaff, W. J.; Kohn, E.

2009-02-01

243

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

PubMed

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

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

2014-03-01

244

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

245

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

246

Surface and bulk aspects of mixed oxide catalytic nanoparticles: oxidation and dehydration of CH(3)OH by polyoxometallates.  

PubMed

The molecular structures and surface chemistry of mixed metal oxide heteropolyoxo vanadium tungstate (H(3+x)PW(12-x)V(x)O(40) with x = 0, 1, 2, and 3) Keggin nanoparticles (NPs), where vanadium is incorporated into the primary Keggin structure, and supported VO(x) on tungstophosphoric acid (TPA, H(3)PW(12)O(40)), where vanadium is present on the surface of the Keggin unit, were investigated with solid-state magic angle spinning (51)V NMR, FT-IR, in situ Raman, in situ UV-vis, CH(3)OH temperature-programmed surface reaction (TPSR), and steady-state methanol oxidation. The incorporated VO(x) unit possesses one terminal V horizontal lineO bond, four bridging V-O-W/V bonds, and one long V-O-P bond in the primary Keggin structure, and the supported VO(x) unit possesses a similar coordination in the secondary structure under ambient conditions. The specific redox reaction rate for VO(x) in the Keggin primary structure is comparable to that of bulk V(2)O(5) and the more active supported vanadium oxide catalysts. The specific acidic reaction rate for the WO(x) in the TPA Keggin, however, is orders of magnitude greater than found for bulk WO(3), supported tungsten oxide catalysts, and even the highly acidic WO(3)-ZrO(2) catalyst synthesized by coprecipitation of ammonium metatungstate and ZrO(OH)(2). From CH(3)OH-TPSR and in situ Raman spectroscopy it was found that incorporation of vanadium oxide into the primary Keggin structure is also accompanied by the formation of surface VO(x) species at secondary sites on the Keggin outer surface. Both CH(3)OH-TPSR and steady-state methanol oxidation studies demonstrated that the surface VO(x) species on the Keggin outer surface are significantly less active than the VO(x) species incorporated into the primary Keggin structure. The presence of the less active surface VO(x) sites in the Keggins, thus, decreases the specific reaction rates for both methanol oxidation and methanol dehydration. During methanol oxidation/dehydration (O(2)/CH(3)OH = 2.17, T = 225 degrees C), in situ UV-vis diffuse reflectance spectroscopy revealed that vanadium oxide is primarily present as the V(+5) cation, which reflects the Mars-van Krevelen redox mechanism and rapid reoxidation by molecular O(2). The bulk TPA Keggin structure becomes more disordered and less thermally stable as the vanadium content increases. Although surface polyaromatic carbon forms during methanol oxidation on the Keggin surfaces, its influence on the reaction kinetics seems minimal as the carbon content diminishes as the vanadium oxide content increases and the reaction temperature is raised. No relationships were found between the electronic structure (UV-vis E(g) values) and TOF(redox) and TOF(acid) (TOF = turnover frequency) kinetics, which reflect the complexity of H(3+x)PW(12-x)V(x)O(40) Keggins. The overall catalytic performance of the H(3+x)PW(12-x)V(x)O(40) Keggin materials results from a complex interplay among the presence of redox vanadium (as secondary surface VO(x) species and substituted VO(x) sites in the primary Keggin NP structure), structural disorder of the Keggin NPs, exposed surface acid and redox sites, and coke deposition. These new insights reveal that the Keggin heteropolyoxometallates are much more complex than originally thought and that care must be taken in using Keggins as model mixed metal oxide NPs in catalytic kinetic and theoretical studies because their surface and bulk structures are dynamic under the reaction conditions. PMID:19807071

Nakka, Lingaiah; Molinari, Julie E; Wachs, Israel E

2009-10-28

247

Controlled oxidative nanopatterning of microrough titanium surfaces for improving osteogenic activity.  

PubMed

To further enhance the biological properties of acid-etched microrough titanium surfaces, titania nanotextured thin films were produced by simple chemical oxidation, without significantly altering the existing topographical and roughness features. The nanotextured layers on titanium surfaces can be controllably varied by tuning the oxidation duration time. The oxidation treatment significantly reduced water contact angles and increased the surface energy compared to the surfaces prior to oxidation. The murine bone marrow stromal cells (BMSCs) were used to evaluate the bioactivity. In comparison, oxidative nanopatterning of microrough titanium surfaces led to improved attachment and proliferation of BMSCs. The rate of osteoblastic differentiation was also represented by the increased levels of alkaline phosphatase activity and mineral deposition. These data indicated that oxidative nanopatterning enhanced the biological properties of the microrough titanium surfaces by modulating their surface chemistry and nanotopography. Based on the proven mechanical interlocking ability of microtopographies, enhancement of multiple osteoblast functions attained by this oxidative nanopatterning is expected to lead to better implant osseointegration in vivo. PMID:24831082

Tan, Guoxin; Tan, Ying; Ni, Guoxin; Lan, Guobo; Zhou, Lei; Yu, Peng; Liao, Jingwen; Zhang, Yu; Yin, Zhaoyi; Wang, Hang; Ning, Chengyun

2014-08-01

248

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

249

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

NASA Astrophysics Data System (ADS)

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

Mema, Rediola

250

Silicon x-ray monochromator surfaces by independent oxidation and etching steps  

NASA Astrophysics Data System (ADS)

X-ray monochromators should ideally possess a surface that does not distort a diffracted beam. Beam distortions have been observed at the APS for rough surfaces. Mechanical polishing leaves sub-surface damage. The standard method to remove this damage is to wet etch Si crystals in a mixture of nitric acid and hydrofluoric acid. During the etch an oxide is produced and removed in the same acid bath. X-ray diffraction from a bulk reflection that is largely unaffected by strain can be obtained by this method. However, the smoothness is degraded to produce an orange-peel morphology. For the present study we carried out the oxidation and etching steps independently. By first growing an oxide layer in a furnace and subsequently etching away the the oxide layer, we find that sub-surface damage can be removed and the surface quality can be improved over that found with only wet etching.

Macrander, Albert; MacArthur, Kimberley; Maj, Josef; Qian, Jun; Linnen, Dan; Khachatryan, Ruben; Wieczorek, Michael; Conley, Ray; Genis, Alan

2009-03-01

251

Titanium oxide modeling and design for innovative biomedical surfaces: a concise review.  

PubMed

The natural oxide layer on implantable alloys insulates the reactive underlying metal from the physiological environment, preventing substrate corrosion and device failure. This type of oxide film has had a major role in the minimization of functional failure and toxic response after implantation in the first generation biomaterials. Recent advances in theoretical, computational, and experimental surface engineering tools provide the foundation for the design of novel devices with improved performances in this regard based on conventional implantable metal alloys. An increasing number of technologies provide the possibility of tailoring chemico-physical and morphological parameters of the surface oxide layers. For some applications, such as dental implants, surface modifications result in substantial innovation and economic success. However, the selection of novel surfaces is in general based on experimental studies and has a limited theoretical and computational foundation. In this review, we offer a perspective analysis of the correlation between theoretical studies and chemical surface modification technologies, with a special emphasis on titanium oxide on Ti alloys. Theoretical approaches for the surface behavior at an atomistic level of description are presented, together with some adsorption studies on a rutile surface. The role of chemical and electrochemical surface modification technologies in modifying the TiO(2) structure, morphology, and chemistry to tailor in vivo biological response is then briefly reviewed. Finally, we discuss the role of surface modeling as a powerful design tool for a new generation of implantable devices in which metal oxide surface can be tuned to yield specific biological response. PMID:23065887

De Nardo, Luigi; Raffaini, Giuseppina; Ebramzadeh, Edward; Ganazzoli, Fabio

2012-09-01

252

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

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

253

Polymer Brushes via Controlled, Surface-Initiated Atom Transfer Radical Polymerization (ATRP) from Graphene Oxide.  

PubMed

A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface-grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact. PMID:21590903

Lee, Sun Hwa; Dreyer, Daniel R; An, Jinho; Velamakanni, Aruna; Piner, Richard D; Park, Sungjin; Zhu, Yanwu; Kim, Sang Ouk; Bielawski, Christopher W; Ruoff, Rodney S

2010-02-01

254

Interactions of imidazolium-based ionic liquids with oxide surfaces controlled by alkyl chain functionalization.  

PubMed

From a different angle: Thin films of functionalized ionic liquids are deposited on cerium oxides following a surface science approach. The functionalization of the alkyl chain changes its orientation with respect to the surface plane from normal to parallel. This then leads to a different surface chemistry at higher temperatures. PMID:24123498

Schernich, Stefan; Laurin, Mathias; Lykhach, Yaroslava; Tsud, Nataliya; Sobota, Marek; Skála, Tomáš; Prince, Kevin C; Taccardi, Nicola; Wagner, Valentin; Steinrück, Hans-Peter; Matolín, Vladimír; Wasserscheid, Peter; Libuda, Jörg

2013-11-11

255

Surface modification of polymeric biomaterials with poly(ethylene oxide), albumin, and heparin for reduced thrombogenicity  

Microsoft Academic Search

Appropriate surface modification has significantly improved the blood compatibility of polymeric biomaterials. This article reviews methods of surface modification with water-soluble polymers, such as polyethylene oxide (PEO), albumin, and heparin. PEO is a synthetic, neutral, watersoluble polymer, while albumin and heparin are a natural globular protein and an anionic polysaccharide, respectively. When grafted onto the surface, all three macromolecules share

Mansoor Amiji

1993-01-01

256

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

NASA Astrophysics Data System (ADS)

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

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

2001-08-01

257

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

PubMed

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

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

2011-08-01

258

Adsorption of asphalt functionalities and oxidized asphalts on aggregate surfaces  

SciTech Connect

The adsorption of asphalt functionalities and asphalt oxidized to different degrees on real and model aggregates is investigated. The functionalities used are: nitrogen-base, phenolic, carboxylic acid, ester, ketone, sulfoxide, and polynuclear aromatic. Adsorption isotherms of these functionalities on porous silica show different affinity rankings dependent upon concentration. The competitive affinity ranking of the asphalt functionalities on dried silica is obtained. Asphalts oxidized to different degrees become adsorbed on different aggregates. On silica and alumina, the oxidized asphalts with viscosities of 32,000 and 126,000 poise are adsorbed less than AC-20. On limestone and sandstone, the adsorption of AC-20 and oxidized asphalts is concentration dependent; asphaltene adsorption followed the same trends.

Curtis, C.W.; Jeon, Y.W.; Clapp, D.J. (Auburn Univ., AL (USA). Dept. of Chemical Engineering)

1989-01-01

259

Heterogeneous nucleation of calcium oxalate on native oxide surfaces.  

National Technical Information Service (NTIS)

The aqueous deposition of calcium oxalate onto colloidal oxides has been studied as a model system for understanding heterogeneous nucleation processes of importance in biomimetic synthesis of ceramic thin films. Calcium oxalate nucleation has been monito...

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

1994-01-01

260

Methane oxidation at a surface-sealed boreal landfill  

Microsoft Academic Search

Methane oxidation was studied at a closed boreal landfill (area 3.9ha, amount of deposited waste 200,000 tonnes) equipped with a passive gas collection and distribution system and a methane oxidative top soil cover integrated in a European Union landfill directive-compliant, multilayer final cover. Gas wells and distribution pipes with valves were installed to direct landfill gas through the water impermeable

Juha Einola; Kai Sormunen; Anssi Lensu; Antti Leiskallio; Matti Ettala; Jukka Rintala

2009-01-01

261

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

Microsoft Academic Search

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

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

2010-01-01

262

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

263

Monitoring changes in surface and structural properties of porous carbons modified by different oxidizing agents  

SciTech Connect

A series of active carbons and carbon blacks was oxidized with various oxidizing agents such as hydrogen peroxide, perchloric acid, and nitric acid. Their surface and structural properties were evaluated by use of nitrogen and water vapor adsorption isotherms, as well as high-resolution thermogravimetry. A comparative analysis of differential thermogravimetric curves and adsorption isotherms of nitrogen and water vapor for the samples studied showed that the surface properties of oxidized carbons depend on the type of oxidizing agent as well as oxidation conditions. This comparison shows that the modification of carbons with concentrated nitric acid caused the most pronounced surface and structural changes. These changes were much smaller for the samples modified with perchloric acid and hydrogen peroxide.

Choma, J.; Burakiewicz-Mortka, W. [Military Technical Academy, Warsaw (Poland). Inst. of Chemistry] [Military Technical Academy, Warsaw (Poland). Inst. of Chemistry; Jaroniec, M.; Li, Z. [Kent State Univ., OH (United States). Dept. of Chemistry] [Kent State Univ., OH (United States). Dept. of Chemistry; Klinik, J. [Academy of Mining and Metallurgy, Cracow (Poland). Faculty of Fuels and Energy] [Academy of Mining and Metallurgy, Cracow (Poland). Faculty of Fuels and Energy

1999-06-15

264

Fourier transform infrared spectroscopic studies of surface-site probe species on metal oxide and pillared clay surfaces  

NASA Astrophysics Data System (ADS)

FTIR studies of adsorbed pyridine on several Pillared Interlayer Clay (PILC) and related oxide surfaces have been semi-quantitatively analyzed in terms of the ratio of Bronsted and Lewis adsorption site populations. Similar spectroscopic studies of adsorbed 2,2'-bipyridine on the pillared clays and the bulk metal oxides, that constitute the pillaring materials, were undertaken with a view to correlating the conformation of the base with the interpillar spacing.

Bagshaw, Stephen A.; Cooney, Ralph P.

1994-01-01

265

Xpd Study of Vanadium Oxide Films Grown on the SnO2(110) Surface  

NASA Astrophysics Data System (ADS)

The oxide phases formed upon annealing at 800 K of ultrathin vanadium films deposited on the SnO2(110) surface have been investigated by XPD and other techniques. We found that the annealing in vacuum of vanadium layers results in the oxidation of the metal carried out by lattice oxygen diffusing from the bulk of SnO2. The vanadium oxide phase formed in this way is epitaxially oriented with respect to the substrate and is covered by disordered layers of tin oxide. The XPD results rule out the formation of V-Sn mixed oxides. The simulation of the experimental XPD curves with SSC calculations performed for various structural models indicates that the product of the oxidation is a VOx ? 2 phase with a structure close to that of the rutile VO2(110) surface.

Atrei, A.; Bardib, U.; Cortigiani, B.; Rovida, G.

266

Polymeric heterogeneous catalysts of transition-metal oxides: surface characterization, physicomechanical properties, and catalytic activity.  

PubMed

We investigate the physicomechanical properties of polymeric heterogeneous catalysts of transition-metal oxides, specifically, the specific surface area, elongation at break, breaking strength, specific electrical resistance, and volume resistivity. Digital microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis are used to study the surfaces of the catalysts. The experimental results show that polymeric heterogeneous catalysts of transition-metal oxides exhibit high stability and can maintain their catalytic activity under extreme reaction conditions for long-term use. The oxidation mechanism of sulfur-containing compounds in the presence of polymeric heterogeneous catalysts of transition-metal oxides is confirmed. Microstructural characterization of the catalysts is performed by using X-ray computed tomography. The activity of various catalysts in the oxidation of sulfur-containing compounds is determined. We demonstrate the potential application of polymeric heterogeneous catalysts of transition-metal oxides in industrial wastewater treatment. PMID:24243767

Nhi, Bui Dinh; Akhmadullin, Renat Maratovich; Akhmadullina, Alfiya Garipovna; Samuilov, Yakov Dmitrievich; Aghajanian, Svetlana Ivanova

2013-12-16

267

Characterization of the ''clean-up'' of the oxidized Ge(100) surface by atomic layer deposition  

SciTech Connect

While the 'clean-up' effect on III-V substrates has recently been well documented interfacial reactions during atomic layer deposition (ALD) on Ge substrates are not fully explored. The 'clean-up' of Ge oxides is studied by interrupting the ALD process following individual precursor pulses for in situ monochromatic x-ray photoelectron spectroscopy analysis. Germanium oxides are found to be reduced by TMA and water, while an interfacial GeON layer is only affected by the initial TMA pulse. Oxide free germanium surfaces behave analogously to a surface with initial native oxides since they are oxidized measurably prior to the first TMA pulse due to residual oxidants in a commercial ALD chamber.

Milojevic, M.; Kim, J.; Wallace, R. M. [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75083 (United States); Contreras-Guerrero, R.; Lopez-Lopez, M. [Department of Physics, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14-740, Mexico D.F. 07000 (Mexico)

2009-11-23

268

Cyclic oxidation behavior of plasma surface chromising coating on titanium alloy Ti-6Al-4V  

NASA Astrophysics Data System (ADS)

The cyclic oxidation behavior of plasma surface chromising coating on titanium alloy (Ti-6Al-4V) was researched in air at 650 °C, 750 °C and 850 °C. A NiCrAlY coating was prepared by multi-arc ion plating as a comparison. The surface morphologies, microstructures and phases of both coatings before and after oxidation were investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometry (XRD). The results show that the chromising coating consisted of an outer layer of loose Cr deposition, an intermediate layer of compact Cr deposition and an inner Ti-Cr mutual diffusion layer. The multilayer oxide scales formed in the oxidation process, which has the better cyclic oxidation resistance compared with NiCrAlY thermal barrier coating. However, the brittleness of Ti(Cr, Al)2 laves phase resulted in spallation of oxide scales at 750 °C and 850 °C.

Wei, Dong-Bo; Zhang, Ping-Ze; Yao, Zheng-Jun; Zhou, Jin-Tang; Wei, Xiang-Fei; Zhou, Peng

2012-11-01

269

Surface oxide reduction and bilayer molecular assembly of a thiol-terminated organosilane on Cu  

NASA Astrophysics Data System (ADS)

We demonstrate the use of thiol-terminated organosilane to reduce the surface oxide and form a protective layer on Cu surfaces. The thiol termini of mercapto-propyl-trimethoxy-silane molecules reduce the copper oxide, and release disulfide- and sulfonate-terminated silanes. Unreacted mercaptosilanes and disulfides then assemble on the clean Cu surface forming a monolayer via chemisorption. The outward pointing methoxy groups react with other methoxysilane termini of sulfonated- and unreacted organosilanes, forming a molecular bilayer with Si-O-Si linkages between the two layers. These findings open up new possibilities for surface cleaning and passivating Cu interconnects with molecular nanolayers, and minimize surface-scattering-induced conductivity decrease in nanometer-thick Cu lines, without destructively etching the surface Cu oxide.

Ganesan, P. G.; Kumar, A.; Ramanath, G.

2005-07-01

270

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

271

Molecular Beam Study of CO Oxidation on a (111) Platinum Surface.  

National Technical Information Service (NTIS)

The heterogeneous oxidation of CO on epitaxially grown Pt(111) surfaces has been investigated using modulated molecular beam techniques. The overall reaction is apparently first order. The observance of higher order kinetics in these experiments is argued...

R. L. Palmer J. N. Smith

1973-01-01

272

Near-Field Spectroscopy of Selectively Oxidized Vertical Cavity Surface Emitting Lasers;Applied Physics Letters.  

National Technical Information Service (NTIS)

Selectively oxidized vertical cavity surface emitting lasers (VCSELs) have been studied by spectrally resolved near field scanning optical microscopy (NSOM). We have obtained spatially and spectrally resolved images of both subthreshold emission and lasin...

J. Kim J. T. Boyd Jackson Choquette

1999-01-01

273

The Identification of Stable Reaction Intermediates on Aluminum Oxide Surfaces with Inelastic Electron Tunneling Spectroscopy  

Microsoft Academic Search

The stable surface intermediates that were formed in several heterogeneous reactions on aluminum oxide films were identified with inelastic electron tunneling spectroscopy. The alumina films were synthesized by the plasma oxidation of aluminum metal films. The temperature and exposure dependent interaction of cyclopropane carboxylic acid with alumina films was studied. Cyclopropane carboxylate and n-butane carboxylate were the only adsorbed species

Michael Karpovich Templeton

1984-01-01

274

Investigation of Oxide Layer Structure on Niobium Surfaces Using a Secondary Ion Mass Spectrometer.  

National Technical Information Service (NTIS)

Oxide layer structure on the surfaces of niobium (Nb) can be studied by continuously monitoring peaks of the secondary ions of Nb and its relevant oxides as a function of time during depth profiling measurements employing a secondary ion mass spectrometer...

A. T. Wu

2005-01-01

275

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

276

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

SciTech Connect

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

McCafferty, E.; Wightman, J.P. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)] [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)

1997-10-15

277

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

278

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

279

Effect of oxidation on the wettability of poly(dimethylsiloxane) surfaces  

NASA Astrophysics Data System (ADS)

The wetting of amorphous poly(dimethylsiloxane) (PDMS) surfaces by water has been studied using molecular dynamics simulations. PDMS surfaces were generated by compressing a long PDMS chain between two elastic boundaries at atmospheric pressure. Oxidation of the PDMS surface, achieved in real systems by exposure to air plasma or corona discharge, was modeled by replacing methyl groups on the PDMS chain with hydroxyl groups. Three surfaces of varying degrees of oxidation were characterized by measuring the water contact angle and the roughness. The dependence of the microscopic contact angle on drop size was measured from time averaged density profiles. The macroscopic contact angle was measured directly using a cylindrical drop of infinite length with zero contact line curvature. The measured macroscopic contact angle ranged from approximately 125° on the untreated surface to 75° on the most oxidized surface studied. The line tension was found to increase with increasing degree of oxidation, from a negligible value on the untreated surface to approximately 5×10-11 J m-1 on the most heavily oxidized surface.

Schneemilch, M.; Quirke, N.

2007-09-01

280

Semiconductor aspects of the passive oxide film on aluminum as modified by surface alloying  

Microsoft Academic Search

For a series of binary aluminum surface alloys prepared by ion implantation, the critical pitting potential is a linear function of the isoelectric point of the oxide of the alloying element in the binary alloy. This follows by first showing that the critical pitting potential is a linear function of the flat-band potential of the oxide-covered surface. The flat-band potential

E McCafferty

2003-01-01

281

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

282

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

283

Observation of magnetic dead layers at the surface of iron oxide films  

Microsoft Academic Search

Depth profiles of the magnetization of sputtered films of Fe3O4 and its oxidized form, ?-Fe2O3, were obtained by the new polarized neutron reflection technique. We find that the magnetization of Fe3O4 is constant throughout the thickness (2600 A?) of the film except for a surface region about 25 A? deep corresponding to the surface roughness. In contrast the oxidized sample

S. S. P. Parkin; R. Sigsbee; R. Felicia; G. P. Felcher

1986-01-01

284

Observation of magnetic dead layers at the surface of iron oxide films  

Microsoft Academic Search

Depth profiles of the magnetization of sputtered films of FeâOâ and its oxidized form, ..gamma..-FeâOâ, were obtained by the new polarized neutron reflection technique. We find that the magnetization of FeâOâ is constant throughout the thickness (2600 A) of the film except for a surface region about 25 A deep corresponding to the surface roughness. In contrast the oxidized sample

S. S. P. Parkin; R. Sigsbee; R. Felici; G. P. Felcher

1986-01-01

285

Surface Characteristics and Bioactivity of Oxide Films with Haloid Ions Formed by Micro-Arc Oxidation on Titanium in Vitro  

Microsoft Academic Search

Ti-based implant materials have specific complications associated with their applications because of their unsatisfactory bioactivity. Hence, a surface which displays selective biointeractivity, i.e., enhancing the bioactivity of material but inhibiting pathogenic microbial adhesion, would be highly desirable. The aim of the present study was to investigate the effects of the haloid ions on the bioactivity of Ti oxide film via

Jianxue Li; Guofeng Wu; Jiang Jiang; Yimin Zhao

2011-01-01

286

Methane oxidation at a surface-sealed boreal landfill.  

PubMed

Methane oxidation was studied at a closed boreal landfill (area 3.9 ha, amount of deposited waste 200,000 tonnes) equipped with a passive gas collection and distribution system and a methane oxidative top soil cover integrated in a European Union landfill directive-compliant, multilayer final cover. Gas wells and distribution pipes with valves were installed to direct landfill gas through the water impermeable layer into the top soil cover. Mean methane emissions at the 25 measuring points at four measurement times (October 2005-June 2006) were 0.86-6.2 m(3) ha(-1) h(-1). Conservative estimates indicated that at least 25% of the methane flux entering the soil cover at the measuring points was oxidized in October and February, and at least 46% in June. At each measurement time, 1-3 points showed significantly higher methane fluxes into the soil cover (20-135 m(3) ha(-1) h(-1)) and methane emissions (6-135 m(3) ha(-1) h(-1)) compared to the other points (< 20 m(3) ha(-1) h(-1) and < 10 m(3) ha(-1) h(-1), respectively). These points of methane overload had a high impact on the mean methane oxidation at the measuring points, resulting in zero mean oxidation at one measurement time (November). However, it was found that by adjusting the valves in the gas distribution pipes the occurrence of methane overload can be to some extent moderated which may increase methane oxidation. Overall, the investigated landfill gas treatment concept may be a feasible option for reducing methane emissions at landfills where a water impermeable cover system is used. PMID:19264471

Einola, Juha; Sormunen, Kai; Lensu, Anssi; Leiskallio, Antti; Ettala, Matti; Rintala, Jukka

2009-07-01

287

Chapter 1 Surface Structure and Reactivity of Iron Oxide–Water Interfaces  

Microsoft Academic Search

The surface structure and composition of the three distinct iron-(hydr)oxide systems, goethite (100), hematite (11¯02), and magnetite (111) were determined under hydrated conditions at room temperature using crystal truncation rod (CTR) analysis. The prediction of surface protonation states and the overall chemical plausibility of the experimental surface models are performed using a bond-valence (BV) analysis. Further analysis of the surface

Sanjit K. Ghose; Sarah C. Petitto; Kunaljeet S. Tanwar; Cynthia S. Lo; Peter J. Eng; Anne M. Chaka; Thomas P. Trainor

2007-01-01

288

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

PubMed

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

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

2009-11-17

289

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

SciTech Connect

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

2013-04-19

290

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

291

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

292

Roles of Surface Steps on Pt Nanoparticles in Electro-oxidation of Carbon Monoxide and Methanol  

SciTech Connect

Design of highly active nanoscale catalysts for electro-oxidation of small organic molecules is of great importance to the development of efficient fuel cells. Increasing steps on single-crystal Pt surfaces is shown to enhance the activity of CO and methanol electro-oxidation up to several orders of magnitude. However, little is known about the surface atomic structure of nanoparticles with sizes of practical relevance, which limits the application of fundamental understanding in the reaction mechanisms established on single-crystal surfaces to the development of active, nanoscale catalysts. In this study, we reveal the surface atomic structure of Pt nanoparticles supported on multiwall carbon nanotubes, from which the amount of high-index surface facets on Pt nanoparticles is quantified. Correlating the surface steps on Pt nanoparticles with the electrochemical activity and stability clearly shows the significant role of surface steps in enhancing intrinsic activity for CO and methanol electro-oxidation. Here, we show that increasing surface steps on Pt nanoparticles of {approx}2 nm can lead to enhanced intrinsic activity up to {approx}200% (current normalized to Pt surface area) for electro-oxidation of methanol.

Lee, S.; Chen, S; Sheng, W; Yabuuchi, N; Kim, Y; Mitani, T; Vescovo, E; Shao-Horn, Y

2009-01-01

293

Roles of Surface Step on Pt Nanoparticles in Electro-oxidation of Carbon Monoxide and Methanol  

SciTech Connect

Design of highly active nanoscale catalysts for electro-oxidation of small organic molecules is of great importance to the development of efficient fuel cells. Increasing steps on single-crystal Pt surfaces is shown to enhance the activity of CO and methanol electro-oxidation up to several orders of magnitude. However, little is known about the surface atomic structure of nanoparticles with sizes of practical relevance, which limits the application of fundamental understanding in the reaction mechanisms established on single-crystal surfaces to the development of active, nanoscale catalysts. In this study, we reveal the surface atomic structure of Pt nanoparticles supported on multiwall carbon nanotubes, from which the amount of high-index surface facets on Pt nanoparticles is quantified. Correlating the surface steps on Pt nanoparticles with the electrochemical activity and stability clearly shows the significant role of surface steps in enhancing intrinsic activity for CO and methanol electro-oxidation. Here, we show that increasing surface steps on Pt nanoparticles of {approx}2 nm can lead to enhanced intrinsic activity up to {approx}200% (current normalized to Pt surface area) for electro-oxidation of methanol.

Lee, S.W.; Vescovo, E.; Chen, S.; Sheng, W.; Yabuuchi, N.; Kim, Y.T.; Mitani, T.; Shao-Horn, Y.

2009-10-13

294

In?Situ Observation of Surface Species on Iridium Oxide Nanoparticles during the Oxygen Evolution Reaction.  

PubMed

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

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

2014-07-01

295

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

296

Chemical reactions on metal oxide surfaces investigated by vibrational spectroscopy  

Microsoft Academic Search

The most successful method to unravel the microscopic mechanisms governing reactions in heterogeneous catalysis is the “surface science” approach which is based on well-controlled studies on model catalysts (usually single crystal surfaces) under ultrahigh vacuum (UHV) conditions [G. Ertl, Angew. Chem. 47 (2008) 3524]. In this review our recent vibrational spectroscopic studies on selected model reactions at various single-crystalline metal

Yuemin Wang; Christof Wöll

2009-01-01

297

Properties of clean and oxidized Ge surfaces at low temperatures  

NASA Astrophysics Data System (ADS)

Investigations of surface conductivity and photoconductivity carried out at helium temperature on the surfaces obtained by crystal cleavage in liquid helium, in ultra-high cryogenic vacuum, as well as under conditions of chemisorption of very low oxygen quantities have shown the existence of processes unknown before, and shed unexpected light on the problem of p-type layers in Ge crystals.

Zavaritskaya, E. I.

1994-04-01

298

Effect of surface stresses on CuO nanowire growth in the thermal oxidation of copper  

NASA Astrophysics Data System (ADS)

By exerting bending stresses on a metal surface, we show that in-plane tensile stresses can effectively promote CuO nanowire (NW) formation by significantly increasing the NW growth density during the oxidation of copper. It is found that the improved NW growth is associated with decreased size of oxide grains and increased number of grain boundaries in the underlying Cu 2O and CuO layers. These results are attributed to the effect of in-plane tensile stresses that result in fine grain structures in the underlying oxide layers, which facilitates the outward diffusion of Cu ions for enhanced oxide NW growth.

Mema, Rediola; Yuan, Lu; Du, Qingtian; Wang, Yiqian; Zhou, Guangwen

2011-08-01

299

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

300

In situ transmission infrared spectroscopy of high-kappa oxide atomic layer deposition onto silicon surfaces  

Microsoft Academic Search

Ultra-thin aluminum oxide (Al2O3) and hafnium oxide (HfO2) layers have been grown by atomic layer deposition (ALD) using tri-methyl-aluminum (TMA) and tetrakis-ethyl-methyl-amino-hafnium (TEMAH) respectively with heavy water (D2O) as the oxidizing agent. Several different silicon surfaces were used as substrates such as hydrogen terminated silicon (H\\/Si), SC2 (or RCA 2) cleaned native silicon oxide (SiO 2\\/Si), and silicon (oxy)nitride. In-situ

Ming-Tsung Ho

2008-01-01

301

Surface oxides of Ir(111) prepared by gas-phase oxygen atoms  

NASA Astrophysics Data System (ADS)

The Ir(111) surface is oxidized with gas-phase oxygen atoms under vacuum condition to achieve an oxidation level beyond its saturation coverage for chemisorption. Two surface oxides, rutile IrO2 of (100) domain and corundum Ir2O3 of (001) domain, have been grown at 550 K with different oxygen exposure of 3.6 × 105 L and 7.2 × 105 L respectively. The temperature programmed desorption (TPD) experiment of rutile IrO2(100) shows its desorption curve (at 4 K s- 1) peaks at 750 K, followed by a long tail of less pronounced desorption features. On the other hand, TPD of corundum Ir2O3(001) displays a symmetric trace, peaking at 880 K. Carbon monoxide titration experiments show that adsorbed CO reduces corundum Ir2O3(001) at 400 K, but CO does not adsorb on rutile IrO2(100) and no reduction reaction occurs. Evidently, among the two surface oxides, corundum Ir2O3(001) involves in catalysis of carbon monoxide oxidation, while rutile IrO2(100) does not. The formation of two surface oxides is also compared, we conclude that the atom arrangement favors Ir2O3(001) at the oxide/metal interface.

Chung, Wen-Hung; Tsai, Dah-Shyang; Fan, Liang-Jen; Yang, Yaw-Wen; Huang, Ying-Sheng

2012-12-01

302

Fragility of surface states and robustness of topological order in Bi2Se3 against oxidation.  

PubMed

Topological surface states are protected against local perturbations, but this protection does not extend to chemical reaction over the whole surface, as demonstrated by theoretical studies of the oxidation of Bi(2)Se(3) and its effects on the surface spin polarization and current. While chemisorption of O(2) largely preserves the topological surface states, reaction with atomic O removes the original surface states and yields two new sets of surface states. One set forms a regular Dirac cone but is topologically trivial. The other set, while topologically relevant, forms an unusual rounded Dirac cone. The details are governed by the hybridization interaction at the interface. PMID:22463655

Wang, Xiaoxiong; Bian, Guang; Miller, T; Chiang, T-C

2012-03-01

303

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

SciTech Connect

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

Jablonski, Paul D.; Alman, David E.; Kung, Steven C. (SOFCo-EFS, Alliance, OH)

2005-08-01

304

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

305

Simple quantification of surface carboxylic acids on chemically oxidized multi-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

The surface of multi-walled carbon nanotube (MWCNT) was chemically oxidized using nitric acid and sulfuric-nitric acid mixtures. Thermogravimetric analysis, transmission electron microscopy and infrared spectroscopy revealed that the use of acid mixtures led to higher degree of oxidation. More quantitative identification of surface carboxylic acids was carried out using X-ray photoelectron spectroscopy (XPS) and acid-base titration. However, these techniques are costly and require very long analysis times to promptly respond to the extent of the reaction. We propose a much simpler method using pH measurements and pre-determined pKa value in order to estimate the concentration of carboxylic acids on the oxidized MWCNT surfaces. The results from this technique were consistent with those obtained from XPS and titration, and it is expected that this simple quantification method can provide a cheap and fast way to monitor and control the oxidation reaction of MWCNT.

Gong, Hyejin; Kim, Seong-Taek; Lee, Jong Doo; Yim, Sanggyu

2013-02-01

306

Large area nanoscale patterning of silicon surfaces by parallel local oxidation.  

PubMed

The homogeneity and the reproducibility of parallel local oxidation have been improved by introducing a thin film of polymethylmethacrylate (PMMA) between the stamp and the silicon surface. The flexibility of the polymer film enables a homogeneous contact of the stamp with the silicon surface to be achieved. The oxides obtained yield better aspect ratios compared with the ones created with no PMMA layer. The pattern is formed when a bias voltage is applied between the stamp and the silicon surface for 1 min. The patterning can be done by a step and repeat technique and is reproducible across a centimetre length scale. Once the oxide nanostructures have been created, the polymer is removed by etching in acetone. Finally, parallel local oxidation is applied to fabricate silicon nanostructures and templates for the growth of organic molecules. PMID:19875876

Losilla, N S; Martínez, J; García, R

2009-11-25

307

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

308

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

PubMed

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

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

2013-05-28

309

Effect of surface acidity and basicity of aluminas on asphaltene adsorption and oxidation  

Microsoft Academic Search

This study investigates the effect of surface acidity and basicity of aluminas on asphaltene adsorption followed by air oxidation. Equilibrium batch adsorption experiments were conducted at 25°C with solutions of asphaltenes in toluene at concentrations ranging from 100 to 3000g\\/L using three conventional alumina adsorbents with different surface acidity. Data were found to better fit to the Freundlich isotherm model

Nashaat N. Nassar; Azfar Hassan; Pedro Pereira-Almao

2011-01-01

310

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

311

Modification of carbon steel surface by the Tenifer® process of nitrocarburizing and post-oxidation  

Microsoft Academic Search

The surface of the non-alloyed carbon steel was subjected to thermochemical modification by salt bath nitrocarburizing with or without post-oxidation based on the Tenifer procedure in order to improve mechanical properties, corrosion and wear resistance. Nitrocarburized layers were characterized by testing their basic properties (compound layer thickness, nitrocarburizing depth, surface hardness) according to current standards. Detailed estimation of the quality

K. Maruši?; H. Otma?i?; D. Landek; F. Cajner; E. Stupnišek-Lisac

2006-01-01

312

Improved surface morphology and texture of Ag films on indium tin oxide via Cu additions  

Microsoft Academic Search

The surface and texture properties of Ag(Cu) alloy thin films on indium tin oxide (ITO) has been investigated and compared to pure Ag thin films on ITO. Atomic force microscopy (AFM) and x-ray diffraction results of annealed films show differences in the evolution of surface morphology and texture with annealing. The presence of Cu atoms in the silver alters the

H. Han; Yeongseok Zoo; J. W. Mayer; T. L. Alford

2007-01-01

313

Surface treatments of indium tin oxide substrates: comprehensive investigation of mechanical, chemical, thermal, and plasma treatments  

Microsoft Academic Search

Various surface treatments significantly affect the work function and surface roughness of indium tin oxide (ITO), and thusly influence charge injection and overall performance of organic light emitting diodes (OLEDs). Large number of treatments, most commonly oxygen plasma treatment and UV-ozone treatment, have been proposed to improve characteristics of ITO. In this work, we have investigated a)mechanical treatments (mechanical rubbing,

Aleksandra B. Djurisic; TszWai Lau; Chung Yin Kwong; Weiling Guo; Yukun Bai; E. Herbert Li; Wai Kin Chan

2002-01-01

314

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

315

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

316

Surface Tension and Viscosity of Aluminum Oxide Nanofluids  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

317

Structure of ordered oxide on InAs(100) surface  

NASA Astrophysics Data System (ADS)

It was recently found that oxygen induces ordered reconstructions on several III-V surfaces. The most oxygen-rich reconstruction shows (3 × 1) periodicity. Based on first-principles investigations, a detailed atomic model is presented for this reconstruction. The uncommon periodicity is attributed to the highly stable Insbnd Osbnd In trilayer below surface which also leads to stabilizing additional bonds within the surface layer. The strain induced by the trilayer is more effectively accommodated within the (3 × 1) reconstruction than within the competing (2 × 1) reconstruction due to smaller number of dimers. It is proposed that the experimentally found semiconductivity is reached by substitutional atoms within the surface layer. Suitable substitution preserves the magnitude of the bulk band gap.

Punkkinen, M. P. J.; Laukkanen, P.; Lång, J.; Kuzmin, M.; Dahl, J.; Zhang, H. L.; Pessa, M.; Guina, M.; Vitos, L.; Kokko, K.

2012-12-01

318

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...

319

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

320

Specific ion binding influences on surface potential of chromium oxide  

Microsoft Academic Search

Colloidal force measurements as a function of pH can yield the isoelectric point (IEP) of a surface immersed in an electrolyte. The condition of surface charge-potential regulation imposed by the potential-dependent binding of H+ and counter-ions at the interface makes a detailed analysis of the electrostatic force non-trivial. In the current study, the specific ion binding of phosphate ions on

A. N Parbhu; J Soltis; L. Q Chen; J Atkin; S Hendy

2004-01-01

321

Wet etching of InSb surfaces in aqueous solutions: Controlled oxide formation  

NASA Astrophysics Data System (ADS)

This paper investigates the wet etching of InSb surfaces by two different oxidant agents: Br2 and H2O2 and the consecutive oxides generation onto the surfaces. The strong dependence between the chemical composition of the etching baths and the nature of the final surface chemistry of this low band-gap III-V semiconductor will be especially highlighted. One aqueous etching solution combined hydrobromic acid and Bromine (HBr-Br2:H2O) with adjusted concentrations. The other solution combines orthophosphoric and citric acids with hydrogen peroxide (H3PO4-H2O2:H2O). Depending on its composition, each formulation gave rise to variable etching rate. The dosage of Indium traces in the etching solution by atomic absorption spectroscopy (AAS) gives the kinetic variation of the dissolution process. The variations on etching rates are associated to the properties and the nature of the formed oxides on InSb surfaces. Surface characterization is specifically performed by X-ray photoelectron spectroscopy (XPS). A clear evidence of the differences between the formed oxides is highlighted. Atomic force microscopy is used to monitor the surface morphology and pointed out that very different final morphologies can be reached. This paper presents new results on the strong variability of the InSb oxides in relation with the InSb reactivity toward environment interaction.

Aureau, D.; Chaghi, R.; Gerard, I.; Sik, H.; Fleury, J.; Etcheberry, A.

2013-07-01

322

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

323

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

324

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

325

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

326

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

PubMed

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

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

2003-04-01

327

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

328

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

Microsoft Academic Search

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

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

1986-01-01

329

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

330

Evidence of alloy formation during reduction of platinized tin oxide surfaces  

NASA Technical Reports Server (NTRS)

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

Gardner, Steven D.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

1989-01-01

331

Chapter 1 Surface Structure and Reactivity of Iron Oxide-Water Interfaces  

Microsoft Academic Search

The surface structure and composition of the three distinct iron-(hydr)oxide systems, goethite (1 0 0), hematite (1{bar 1}02), and magnetite (1 1 1) were determined under hydrated conditions at room temperature using crystal truncation rod (CTR) analysis. The prediction of surface protonation states and the overall chemical plausibility of the experimental surface models are performed using a bond-valence (BV) analysis.

S. K. Ghose; S. C. Petitto; K. S. Tanwar; C. S. Lo; P. J. Eng; A. M. Chaka; T. P. Trainor

2008-01-01

332

Surface characterization of blood compatible amphiphilic graft copolymers having uniform poly(ethylene oxide) side chains  

Microsoft Academic Search

The surface characterization of poly(methyl methacrylate)-graft-poly(ethylene oxide) (PMMA-g-PEO) was investigated by XPS and contact-angle measurement, and its in vitro blood compatibility was assessed by plasma recalcification time measurement. The surface and bulk composition of different PMMA-g-PEO graft copolymer showed that PMMA segments were always enriched at the copolymer–air interface, but surface enrichment of PEO segments could occur in films of

Shengrong Guo; Liangjun Shen; Linxian Feng

2001-01-01

333

[A method of temperature measurement for hot forging with surface oxide based on infrared spectroscopy].  

PubMed

High temperature large forging is covered with a thick oxide during forging. It leads to a big measurement data error. In this paper, a method of measuring temperature based on infrared spectroscopy is presented. It can effectively eliminate the influence of surface oxide on the measurement of temperature. The method can measure the surface temperature and emissivity of the oxide directly using the infrared spectrum. The infrared spectrum is radiated from surface oxide of forging. Then it can derive the real temperature of hot forging covered with the oxide using the heat exchange equation. In order to greatly restrain interference spectroscopy through included in the received infrared radiation spectrum, three interference filter system was proposed, and a group of optimal gap parameter values using spectral simulation were obtained. The precision of temperature measurement was improved. The experimental results show that the method can accurately measure the surface temperature of high temperature forging covered with oxide. It meets the requirements of measurement accuracy, and the temperature measurement method is feasible according to the experiment result. PMID:22827063

Zhang, Yu-cun; Qi, Yan-de; Fu, Xian-bin

2012-05-01

334

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

NASA Technical Reports Server (NTRS)

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

Weber, Arthur L.

1995-01-01

335

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

NASA Technical Reports Server (NTRS)

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

Weber, Arthur L.

1995-01-01

336

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

NASA Technical Reports Server (NTRS)

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

Weber, Arthur L.

1994-01-01

337

Alternating current surface photovoltage in thermally oxidized chromium-contaminated n-type silicon wafers  

NASA Astrophysics Data System (ADS)

We investigated a variation of frequency-dependent alternating current (AC) surface photovoltages (SPVs) in thermally oxidized, chromium-contaminated, n-type silicon (Si) wafers. As previously reported, immediately after rinsing in Cr-contaminated solution, a Cr(OH)3-Si contact causes a Schottky-barrier-type AC SPV on n-type Si. Upon oxidation at 373 K for 10 min, the Schottky barrier collapses and, with further oxidation, a metal-induced negative oxide charge, due to atomic bridging of (CrOSi)- and/or CrO2- networks, definitely grows over time in SiO2. For samples oxidized at temperatures between 823 and 1023 K for 30 min, the observed AC SPV gives evidence that the metal-induced negative oxide charge causes a strongly inverted state of the Si surface. At oxidation temperatures higher than 1023 K and /or for an oxidation time longer than 60 min, the level height of the AC SPV is reduced, implying that the strongly inverted state changes into a less depleted state, whilst, finally, the AC SPV disappears. In this case, the collapse of the (CrOSi)- and/or CrO2- networks is anticipated, with a possible change into Cr2O3. The existence of the (CrOSi)- and/or CrO2- networks has also been confirmed in p-type Si wafers.

Shimizu, Hirofumi; Nagase, Shintarou; Ikeda, Masanori

2011-09-01

338

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.

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

2013-01-01

339

The roles of the surface oxide film and metal-oxide interfacial defects in corrosion initiation on aluminum  

NASA Astrophysics Data System (ADS)

In the first part, a mathematical model was developed for oxide thickness and faradaic current, assuming high-field conduction and a uniform oxide layer thickness, and incorporating as input the measured potential. Electrochemical current and potential transients were measured during anodic oxidation of aluminum. The ratio of the experimental faradaic current density to the predicted one using high field model, p, was calculated. The measured faradaic current is about 104 times smaller than that predicted by this model initially, but the two converge after the initial period of time when p approaches 1. This discrepancy may be caused by several reasons. Our nonuniform oxide thickness hypothesis was supported by: similar p˜x characteristics for the same film obtained from different polarization experiments, where x is the solid-state barrier layer thickness of the oxide film; model's capability of predicting film structure change due to pretreatment such as NaOH dissolution, H2SO4 immersion, and electropolishing; the capacity of predicting long-time current decays using high field model; the lower anodic current of the foils subjected a short anodic pulse previously. In the second part, the effect of H3PO4 immersion on pit nucleation on aluminum during anodic etching in hot HCl solution was investigated. It was found that the phosphoric acid immersion dramatically enhances the susceptibility of aluminum foil to anodic pitting corrosion, and the trend of the pit number density with the immersion time corresponds to decrease of surface oxide film thickness. AFM observation of the topography of foils which were experienced phosphoric acid treatment followed by oxide stripping in chromic-phosphoric acid solution revealed presence of cavities. PAS measurements show the existence of interfacial voids of nm dimensions, whose metallic surface is oxide-free. These defects can be introduced by electropolishing and H3PO4 immersion. The strong similarity between the surface cavities and the pits in terms of size, shape, and distribution suggests that interfacial voids may serve as pitting initiation sites. A phenomenological mechanism for pitting precursor site was proposed.

Wu, Huiquan

340

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

341

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

342

Physical and chemical analysis of elemental sulfur formation during galena surface oxidation.  

PubMed

The surface oxidation of sulfide minerals, such as galena (PbS), in aqueous solutions is of critical importance in a number of applications. A comprehensive understanding of the formation of oxidation species at the galena surface is still lacking. Much controversy over the nature of these oxidation products exists. A number of oxidation pathways have been proposed, and experimental evidence for the formation of elemental sulfur, metal polysulfides, and metal-deficient lead sulfides in acidic conditions has been shown and argued. This paper provides further insight into the electrochemical behavior of galena at pH 4.5. Utilizing a novel experimental system that combines in situ electrochemical control and AC mode atomic force microscopy (AFM) surface imaging, the formation and growth of nanoscopic domains on the galena surface are detected and examined at anodic potentials. AFM phase images indicate that these domains have different material properties to the underlying galena. Continued oxidation results in nanoscopic pitting and the formation of microscopic surface domains, which are confirmed to be elemental sulfur by Raman spectroscopy. Further clarification of the presence of elemental sulfur is provided by Cryo-XPS. Polysulfide and metal-deficient sulfide could not be detected within this system. PMID:21391636

Hampton, Marc A; Plackowski, Chris; Nguyen, Anh V

2011-04-01

343

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

344

Surface passivation using ultrathin AlNx film for Ge-metal-oxide-semiconductor devices with hafnium oxide gate dielectric  

NASA Astrophysics Data System (ADS)

A surface passivation method to improve the film quality of HfO2 gate dielectric on Ge substrate by using ultrathin AlNx layer is reported. Results show that the AlNx passivation layer is more effective in suppressing the GeOx formation at the HfO2/Ge interface, resulting in improved C-V characteristics, than surface nitridation-passivated Ge devices. In addition, a thermal stability study shows AlNx passivation is promising for future Ge metal-oxide-semiconductor devices.

Gao, Fei; Lee, S. J.; Pan, J. S.; Tang, L. J.; Kwong, Dim-Lee

2005-03-01

345

Kinetic Analysis of Gas Splitting on Oxide Surfaces for Solar Thermochemical Fuel Production  

NASA Astrophysics Data System (ADS)

Solar thermochemical cycles have the potential to convert solar energy into chemical fuels at high thermodynamic efficiency. This can be done by reducing an oxide at high temperature and oxidizing the reduced oxide at a lower temperature in H2O or CO2 to produce H2 or CO. The gas splitting reaction at low temperature is kinetically limited, possibly from slow kinetics of the surface processes. For example, the rate of H2O splitting over CeO2 is increased by the addition of a rhodium catalyst. Little is known about the gas splitting reactions at the atomic level. In this work we use density functional theory to investigate the mechanism for the gas splitting reactions on oxide surfaces such as CeO2 (111) or on precious metal catalyst particles such as Rh or Pt.

Hansen, Heine; Meredig, Bryce; Wolverton, Chris

2010-03-01

346

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

SciTech Connect

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

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

2011-04-15

347

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

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 coal 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 fourth quarter, characterization and oxidation tests were done on Upper Freeport coal from the Troutville {number sign}2 Mine, Clearfield County, Pennsylvania. In addition, standard test methods for characterizing pyrite-bearing materials were studied. 3 figs., 2 tabs.

Doyle, F.M.

1991-09-24

348

Surface chemistry of benzoyl compounds on oxides, an FT-IR study  

SciTech Connect

Adsorption and surface reactions on various oxides have been monitored by IR spectroscopy, with benzaldehyde, benzoic acid, methylphenylketone, and 2-phenyl-2-propanol. The oxides were chosen to represent typical adsorption properties (SiO[sub 2], [gamma]-Al[sub 2]O[sub 3], and [alpha]-Mn[sub 3]O[sub 4]). Surface reactions were observed at various temperatures, starting from room temperature. The results concern three points: (i) identification of adsorbed species, arising on different oxides under increasing temperatures; (ii) the possible sequence of reaction steps in the insertion (oxidation) or removal (reduction) of oxygen, into or from the molecules studied; and (iii) the conclusion that a Cannizzaro reaction is not likely so that the insertion (and removal) is most probably by the Mars and van Krevelen mechanism. 17 refs., 10 figs., 1 tab.

Koutstaal, C.A.; Angevaare, P.A.J.M.; Ponec, V. (Leiden Univ. (Netherlands))

1993-10-01

349

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

350

Relativistic potential energy surfaces of initial oxidations of Si(100) by atomic oxygen: The importance of surface dimer triplet state  

NASA Astrophysics Data System (ADS)

The non-relativistic and relativistic potential energy surfaces (PESs) of the symmetric and asymmetric reaction paths of Si(100)-2×1 oxidations by atomic oxygen were theoretically explored. Although only the singlet PES turned out to exist as a major channel leading to ``on-dimer'' product, both the singlet and triplet PESs leading to ``on-top'' products are attractive. The singlet PESs leading to the two surface products were found to be the singlet combinations (open-shell singlet) of the low-lying triplet state of surface silicon dimer and the ground 3P state of atomic oxygen. The triplet state of the ``on-top'' product can also be formed by the ground singlet state of the surface silicon dimer and the same 3P oxygen. The attractive singlet PESs leading to the ``on-dimer'' and ``on-top'' products made neither the intersystem crossings from triplet to singlet PES nor high energy 1D of atomic oxygen necessary. Rather, the low-lying triplet state of surface silicon dimer plays an important role in the initial oxidations of silicon surface.

Kim, Tae-Rae; Shin, Seokmin; Choi, Cheol Ho

2012-06-01

351

Protein-repellent silicon nitride surfaces: UV-induced formation of oligoethylene oxide monolayers.  

PubMed

The grafting of polymers and oligomers of ethylene oxide onto surfaces is widely used to prevent nonspecific adsorption of biological material on sensors and membrane surfaces. In this report, we show for the first time the robust covalent attachment of short oligoethylene oxide-terminated alkenes (CH(3)O(CH(2)CH(2)O)(3)(CH(2))(11)-(CH?CH(2)) [EO(3)] and CH(3)O(CH(2)CH(2)O)(6)(CH(2))(11)-(CH?CH(2)) [EO(6)]) from the reaction of alkenes onto silicon-rich silicon nitride surfaces at room temperature using UV light. Reflectometry is used to monitor in situ the nonspecific adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) onto oligoethylene oxide coated silicon-rich silicon nitride surfaces (EO(n)-Si(x)N(4), x > 3) in comparison with plasma-oxidized silicon-rich silicon nitride surfaces (SiO(y)-Si(x)N(4)) and hexadecane-coated Si(x)N(4) surfaces (C(16)-Si(x)N(4)). A significant reduction in protein adsorption on EO(n)-Si(x)N(4) surfaces was achieved, adsorption onto EO(3)-Si(x)N(4) and EO(6)-Si(x)N(4) were 0.22 mg m(-2) and 0.08 mg m(-2), respectively. The performance of the obtained EO(3) and EO(6) layers is comparable to those of similar, highly protein-repellent monolayers formed on gold and silver surfaces. EO(6)-Si(x)N(4) surfaces prevented significantly the adsorption of BSA (0.08 mg m(-2)). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity and static water contact angle measurements were employed to characterize the modified surfaces. In addition, the stability of EO(6)-Si(x)N(4) surfaces in phosphate-buffered saline solution (PBS) and alkaline condition (pH 10) was studied. Prolonged exposure of the surfaces to PBS solution for 1 week or alkaline condition for 2 h resulted in only minor degradation of the ethylene oxide moieties and no oxidation of the Si(x)N(4) substrates was observed. Highly stable antifouling coatings on Si(x)N(4) surfaces significantly broaden the application potential of silicon nitride-coated microdevices, and in particular of microfabricated filtration membranes. PMID:21309535

Rosso, Michel; Nguyen, Ai T; de Jong, Ed; Baggerman, Jacob; Paulusse, Jos M J; Giesbers, Marcel; Fokkink, Remko G; Norde, Willem; Schroën, Karin; van Rijn, Cees J M; Zuilhof, Han

2011-03-01

352

Surface and grain-boundary energies as well as surface mass transport in polycrystalline yttrium oxide  

Microsoft Academic Search

The sessile drop technique has been used to measure the temperature dependence of the contact angle, ?, of the liquid metals\\u000a Ag and Cu in contact with polycrystalline yttrium oxide (yttria, Y2O3) at the temperature range 1,333–1,773 K in Ar\\/4%H2 atmosphere. Combination of the experimental results with literature data taken for nonwetted and nonreactive oxide\\/liquid\\u000a metal systems permit the calculation of

G. Triantafyllou; G. N. Angelopoulos; P. Nikolopoulos

2010-01-01

353

Formation of channels for oxygen migration towards subsurface sites by CO oxidation and growth of the surface oxide phase on Ag( 0 0 1 )  

Microsoft Academic Search

The mechanism of oxygen incorporation in Ag is still poorly known. As recently demonstrated [Phys. Rev. B 63 (2001) R1404], oxygen adatoms removal by CO oxidation leaves the Ag(001) surface in a modified state in which oxygen segregation from the bulk and the formation of a surface oxide phase can be induced by further CO exposure. Here we show that

L. Savio; L. Vattuone; M. Rocca; F. Buatier de Mongeot; G. Comelli; A. Baraldi; S. Lizzit; G. Paolucci

2002-01-01

354

Low pressure oxidation of ordered Sn/Pd(110) surface alloys  

NASA Astrophysics Data System (ADS)

The reaction of oxygen at low pressure with the Sn/Pd(110) system has been examined by photoelectron spectroscopy using synchrotron radiation. The c(2 × 2) and (3 × 1) reconstructions of the Sn/Pd(110) surface at 0.5 and 0.7 monolayers (ML) Sn coverage and a 1.75 ML Sn overlayer on the Pd(110) surface after flashing to 470 K were studied. The Sn 4d core level is strongly affected by O2 adsorption while the Pd 3d core level shows very little change other than a decrease in intensity. Starting with a 10 L dose of oxygen, prominent changes in the spectra were observed for all Sn/Pd(110) surface alloys. Analysis of the Sn 4d core levels indicates that oxidation proceeds with the formation of well-defined states of Sn, which were identified as a Pd-Sn-O interface layer, SnO and SnO2 oxides. The valence band spectra confirm this assignment. The Sn2+ and Sn4+ component signals originate from the topmost surface layer, i.e. tin atoms in more highly oxidized states constitute the topmost surface layer on top of the Pd-Sn-O interface. The presence of a sub-surface PdSn intermetallic alloy facilitates the tin oxide formation; the Sn-O phase formation is accompanied by Pd-Sn bond dissociation.

Tsud, N.; Skála, T.; Šutara, F.; Veltruská, K.; Dudr, V.; Yoshitake, M.; Prince, K. C.; Matolín, V.

2009-05-01

355

Degradation of carbon tetrachloride by iron metal: Complexation effects on the oxide surface  

Microsoft Academic Search

Dehalogenation of chlorinated aliphatic contaminants at the surface of zero-valent iron metal (Fe0) is mediated by the thin film of iron (hydr)oxides found on Fe0 under environmental conditions. To evaluate the role this oxide film plays in the reduction of chlorinated methanes, carbon tetrachloride (CCl4) degradation by Fe0 was studied under the influence of various anions, ligands, and initial CCl4

Timothy L. Johnson; William Fish; Yuri A. Gorby; Paul G. Tratnyek

1998-01-01

356

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

357

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.

2010-01-01

358

Evaluation of Surface Acidity of Aluminum Oxide Film by Inelastic Electron Tunneling Spectroscopy  

Microsoft Academic Search

The surface acidity of aluminum oxide (AlOx) films was evaluated for the first time by inelastic electron tunneling (IET) spectroscopy using the Hammett indicators as probe molecules. The AlOx films were formed by oxidation of the aluminum films by DC glow discharge in oxygen atmosphere, and the indicators with pKa values ranging from -8.2 to +4.8 were used. The indicators,

Halal El Mouloudi; Haruo Takahashi; Hideki Haji; Akihiro Ooe; Hiroyuki Nishikawa; Takeo Iri

2003-01-01

359

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

Microsoft Academic Search

A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor\\u000a density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline\\u000a water layers are on the alloy surface in order to account for the relative inertness of the

Jiaying Cai; D. F. Gervasio

2010-01-01

360

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

Microsoft Academic Search

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

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

2008-01-01

361

Surface and catalytic properties of cobaltic oxide supported on an active magnesia  

Microsoft Academic Search

The surface and catalytic properties of Co3O4 loaded on MgO were investigated using nitrogen adsorption measurements conducted at ?196°C and oxidation of CO by O2 at 150–300°C. The amounts of cobaltic oxide were 23, 37.5 and 47.5 wt.% Co3O4. The supported samples were prepared by impregnating a known amount of magnesium carbonate with cobalt nitrate dissolved in the least amount

Gamil A. El-Shobaky; Nasr-Allah M. Deraz

2001-01-01

362

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

Microsoft Academic Search

Selective extraction techniques were used to assay the importance of specific solid phases in Pb binding by heterogeneous surface coating materials (biofilms) in Cayuga Lake, NY. Hydroxylamine hydrochloride (NH2OH·HC1) was used to extract easily reducible Mn oxides, and sodium dithionite (Na2S2O4) was used to extract Mn and Fe oxides in two sets of biofilm samples retrieved from the lake. Pb

Deming Dong; Louis A Derry; Leonard W Lion

2003-01-01

363

Chemical surface characterization of electrochemically and thermally oxidized boron-doped diamond film electrodes  

Microsoft Academic Search

In situ Cyclic Voltammetric analysis and ex situ X-ray Photoelectron Spectroscopy investigations have been carried out on highly boron-doped diamond film electrodes subjected to different oxidative treatments. Both the electrochemical and thermal oxidation modify, at different extent, the qualitative and quantitative chemical surface composition of the as prepared samples by partially converting the non diamond carbon species, for instance graphitic-like

Sergio Ferro; Maurizio Dal Colle; Achille De Battisti

2005-01-01

364

Surface texture in electrodeposited films of cuprous oxide  

Microsoft Academic Search

The polycrystalline films of Cu2O, prepared by electrodeposition, consist of grains with well-defined geometrical shapes. The size and the orientation of grains which define the surface texture can be controlled by controlling the deposition parameters. Grains with a size ranging from a few tenths of a micrometer to about 10µm and with a preferential orientation of the (1 0 0)

A. E. Rakhshani; J. Varghese

1988-01-01

365

A theoretical investigation on photocatalytic oxidation on the TiO2 surface  

NASA Astrophysics Data System (ADS)

The TiO2 photocatalytic oxidation mechanism was theoretically investigated by using long-range corrected time-dependent density functional theory (LC-TDDFT) with a cluster model of the anatase TiO2(001) surface. We found that LC-TDDFT with the cluster model quantitatively reproduces the photoexcitations of the TiO2 surface by calculating the electronic spectra of a clean TiO2 surface and one with oxygen defects. We calculated the electronic spectra of a molecularly adsorbed TiO2 surface for the adsorptions of phenol, methanol, and methane molecules as typical organic molecules. We obtained the surprising result that the main peak of the phenol-adsorbed TiO2 surface, which overlaps with the main peak of the clean TiO2 surface, corresponds to charge transfers from the phenol molecule to the TiO2 surface. This indicates that the TiO2 photocatalytic oxidation proceeds through direct charge transfer excitation from the substrate molecules to the TiO2 surface. In contrast, we found slight and no charge transfer for methanol and methane adsorption, respectively, in agreement with the experimental findings for their reactivities. In light of these results, we propose a new mechanism for heterogeneous TiO2 photocatalytic oxidations.

Suzuki, Satoshi; Tsuneda, Takao; Hirao, Kimihiko

2012-01-01

366

A theoretical investigation on photocatalytic oxidation on the TiO{sub 2} surface  

SciTech Connect

The TiO{sub 2} photocatalytic oxidation mechanism was theoretically investigated by using long-range corrected time-dependent density functional theory (LC-TDDFT) with a cluster model of the anatase TiO{sub 2}(001) surface. We found that LC-TDDFT with the cluster model quantitatively reproduces the photoexcitations of the TiO{sub 2} surface by calculating the electronic spectra of a clean TiO{sub 2} surface and one with oxygen defects. We calculated the electronic spectra of a molecularly adsorbed TiO{sub 2} surface for the adsorptions of phenol, methanol, and methane molecules as typical organic molecules. We obtained the surprising result that the main peak of the phenol-adsorbed TiO{sub 2} surface, which overlaps with the main peak of the clean TiO{sub 2} surface, corresponds to charge transfers from the phenol molecule to the TiO{sub 2} surface. This indicates that the TiO{sub 2} photocatalytic oxidation proceeds through direct charge transfer excitation from the substrate molecules to the TiO{sub 2} surface. In contrast, we found slight and no charge transfer for methanol and methane adsorption, respectively, in agreement with the experimental findings for their reactivities. In light of these results, we propose a new mechanism for heterogeneous TiO{sub 2} photocatalytic oxidations.

Suzuki, Satoshi [Department of Applied Chemistry, School of Engineering, University of Tokyo, Tokyo 113-8656 (Japan); Tsuneda, Takao; Hirao, Kimihiko [Advanced Science Institute, RIKEN, Wako, Saitama 351-0198 (Japan); CREST, Japan Science and Technology Agency (JST), Tokyo 113-8656 (Japan)

2012-01-14

367

Surface and Interface Structures of Crystalline Oxides on Silicon (COS)  

NASA Astrophysics Data System (ADS)

The structure of the Sr-covered Si(001) surface (the precursor to COS heteroepitaxy) is a matter of on-going scientific debate with experiment and theory casting opposing views. Real space Z-contrast imaging shows that half of the silicon atoms on the (001) surface are absent, and this has presented us with the intriguing question -- ``Where does the silicon go?''. A metallic surface termination of silicon was required in the layer-sequenced heteroepitaxy of COS. What has been common to all experimental realizations of the layer-sequenced COS structure, is the presence of hydrogen evolving from the metal sources during the film growth. We report here that this hydrogen has inadvertently played a pivotal role in defining the silicon termination and thus the evolution of the interface structure for COS. We will describe the thermodynamic basis for this hydrogen effect along with experimental and theoretical characterization of the structural details. Research sponsored jointly by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory under contract DE-AC05-00OR22725 with UT-Battelle, LLC and at the University of Tennessee under contract DE-FG02-01ER45937. Calculations have been performed on CCS supercomputers at Oak Ridge National Laboratory.

Walker, Fred; Buongiorno-Nardelli, Marco; McKee, Rodney

2006-03-01

368

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

369

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

370

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

Microsoft Academic Search

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

Chin-Chen Chiu

1994-01-01

371

Surface modification of oxide layer on Si using highly charged ions  

NASA Astrophysics Data System (ADS)

Surface modification using highly charged ions is presented. The surface of a Si wafer which is covered with a native oxide layer is used as a sample. The sample was irradiated with Ar11+ ions at a fluence of 1013-1014/cm2. The Ar11+ ions were obtained from an electron beam ion source (Kobe EBIS). The surface was investigated using secondary electron microscopy, X-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy. The obtained results suggest that the native oxide layer is sputtered by the irradiation of Ar11+ ions and that the structural modification makes the density of the oxide layer lower and the electric conductivity higher.

Sakurai, M.; Liu, S.; Sakai, S.; Ohtani, S.; Terui, T.; Sakaue, H. A.

2013-11-01

372

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

NASA Astrophysics Data System (ADS)

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

Lu, Weier

1995-01-01

373

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 though 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 to 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 ditch 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 one 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 immobilisation of dissolved P during the initial stage of the Fe(II) oxidation proces which results in P-depleted water before Fe(II) is competly 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 particulate 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.

2014-06-01

374

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

375

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

PubMed Central

Summary 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., F0, F+, F2+ 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 F2+-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide ?lms beyond imaging the topography of the surface atoms.

Konig, Thomas; Simon, Georg H; Heinke, Lars; Lichtenstein, Leonid

2011-01-01

376

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

377

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

PubMed

Gaseous HCl generated from a variety of sources is ubiquitous in both outdoor and indoor air. Oxides of nitrogen (NO(y)) are also globally distributed, because NO formed in combustion processes is oxidized to NO(2), HNO(3), N(2)O(5) and a variety of other nitrogen oxides during transport. Deposition of HCl and NO(y) 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 NO(2) or N(2)O(5) on solid substrates generates adsorbed intermediates that react with HCl to generate gaseous nitrosyl chloride (ClNO) and nitryl chloride (ClNO(2)), 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 ClNO(2) 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

2009-08-18

378

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.

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

2009-01-01

379

Selective growth of metallic nanostructures on surfaces patterned by AFM local anodic oxidation.  

PubMed

We report on an alternative approach for the fabrication of metallic nanostructures: a selective growth on silicon substrates patterned by local anodic oxidation using atomic force microscopy. Our method represents a maskless, four-step process which combines a top-down and bottom-up approach. The dimensions of both the oxide lines and metallic elements can be controlled during the technological process. In this paper we demonstrate the preparation of gallium and cobalt structures on silicon substrates but this method can be extended to other combinations of metals and substrates enabling thus the fabrication of ordered nanostructures of various compositions and properties on locally oxidized surfaces. PMID:19908470

Bartosík, Miroslav; Kolíbal, Miroslav; Cechal, Jan; Mach, Jindrich; Sikola, Tomás

2009-10-01

380

Surface electrochemical properties of mixed oxide ceramic membranes: Zeta-potential and surface charge density  

Microsoft Academic Search

The surface electrochemical properties of alumina based ceramic microfiltration membranes were studied by measuring electroosmotic rates and surface charge densities obtained from potentiometric titrations. The rate of electroosmosis, which determines the zeta-potential, was measured on the membrane itself, whereas the surface charge was titrated on a suspension obtained by crushing of the membrane. The zeta-potential was measured in the presence

M. Mullet; P. Fievet; J. C. Reggiani; J. Pagetti

1997-01-01

381

High-temperature Oxidation Behavior and Surface Roughness Evolution of VPS NiCrAlY Coating  

NASA Astrophysics Data System (ADS)

In this work, as a background to the development of high temperature environmental protection coating technology, the structural transformation of vacuum-plasma sprayed NiCrAlY coating has been studied, including the oxidation behavior, elastic modulus, microhardness, and surface roughness. Coating was oxidized isothermally at a 1,273 K for different time periods up to 1,000 h in order to form the oxide scale layer. The results showed that the oxide scale and weight gain increased proportional to the exposure time. The surface roughness and hardness decreased after isothermal exposure, but they are not proportional to the exposure time. The oxide scale growth was concentrated in the valleys of the surface at the early 1 h exposure (decreasing surface roughness), whereas the oxide scales over a longer perspective (time period), grew on the convex surface (increasing surface roughness).

Seo, D.; Ogawa, K.; Shoji, T.; Murata, S.

2008-03-01

382

Stable ag@oxides nanoplates for surface-enhanced Raman spectroscopy of amino acids.  

PubMed

Surface enhancement Raman scattering (SERS) is a powerful technique for detecting low-concentration analytes (chemicals and biochemicals). Herein, a high-performance SERS biosensing system has been created by using highly stable Ag@oxides nanoplates as enhancers. The Ag nanoplates were stabilized by coating a uniform ultrathin layer of oxides (SiO2 or TiO2) on the Ag surface through a simple sol-gel route. The thin oxide layer allows the plasmonic property of the original Ag nanoplates to be retained while preventing their contact with external etchants. The oxides provide an excellent platform for binding all kinds of molecules that contain a COOH group in addition to a SH group. We demonstrate that Ag@oxides have high performance with respect to the typical SERS molecule 4-ATP, which contains a typical SH group. Ag@oxides also can be directly employed for the SERS detection of amino acids. The highly stable Ag@oxides nanoplates are believed to hold great promise for fabricating a wide range of biosensors for the detection of many other biomolecules and may also find many interesting opportunities in the fields of biological labeling and imaging. PMID:24837067

Du, Peng; Ma, Lan; Cao, Yinghui; Li, Di; Liu, Zhenyu; Wang, Zhenxin; Sun, Zaicheng

2014-06-11

383

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

PubMed

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

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

2012-04-17

384

Ozone Oxidation of Self-Assembled Monolayers on SiOx-Coated Zinc Selenide Surfaces  

NASA Astrophysics Data System (ADS)

Airborne particles are important for visibility, human health, climate, and atmospheric reactions. Atmospheric particles contain a significant fraction of organics and such compounds present on airborne particles are susceptible to oxidation by atmospheric oxidants, such as OH, ozone, halogen atoms, and nitrogen trioxide. Oxidized organics associated with airborne particles are thought to be polar, hygroscopic species with enhanced cloud-nucleating properties. Oxide layers on silicon, or SiO2-coated substrates, act as models of environmentally relevant surfaces such as dust particles upon which organics adsorb. We have shown previously that ozone oxidation of unsaturated self-assembled monolayers (SAMs) on silicon attenuated total reflectance (ATR) crystals leads to the formation of carbonyl groups and micron-sized, hydrophobic organic aggregates surrounded by carbon depleted substrate that do not have increased water uptake as previously assumed. Reported here are further ATR-FTIR studies of the oxidation of alkene SAMs on ZnSe and SiO2-coated ZnSe. These substrates have the advantage that they transmit below 1500 cm-1, allowing detection of additional product species. These experiments show that the loss of C=C and formation of carbonyl groups is also accompanied by formation of a peak at 1110 cm-1, attributed to the secondary ozonide. Details concerning the products and mechanism of ozonolysis of alkene SAMs on surfaces based on these new data are presented and the implications for the oxidation of alkenes on airborne dust particles are discussed.

McIntire, T. M.; Ryder, O. S.; Finlayson-Pitts, B. J.

2008-12-01

385

Synthesis-dependent atomic surface structures of oxide nanoparticles.  

PubMed

Using SrTiO3 nanocuboids as a model system, we show with aberration-corrected high resolution electron microscopy at sub-Å resolution that surface relaxations or reconstructions are present on the nanocuboids, depending on the synthetic process. Oleic acid synthesis, acetic acid synthesis, and microwave-assisted acetic acid synthesis result in a SrO termination, TiO2-rich reconstruction, and mixed termination, respectively. The experimental atomic positions are in better agreement with density functional theory calculations using an exact-exchange corrected PBEsol functional than the Perdew-Burke-Ernzerhof (PBE) functional. PMID:24160614

Lin, Yuyuan; Wen, Jianguo; Hu, Linhua; Kennedy, Robert M; Stair, Peter C; Poeppelmeier, Kenneth R; Marks, Laurence D

2013-10-11

386

Electron stimulated desorption of hydronium ions from chromium oxide surfaces  

NASA Astrophysics Data System (ADS)

The mass spectral peak observed at 19 amu in residual gas analyzers at very high (<10-6 Torr) and ultrahigh vacuum (<10 -9 Torr) has often been attributed to fluorine. Using Fourier Transform Mass Spectrometry, the hydronium ion, H3O+, has been fully resolved from F+ and its correlation to water vapor concentration was determined to be linear as expected for a gas phase process. The comparison of the mass 19 signals for a conventional quadrupole mass spectrometer and a Fourier transform mass spectrometer on the same vacuum chamber indicated hydronium was the source of mass 19. The partial pressures of H2O in the very high vacuum range and higher suggest there is sufficient H2O density for the hydronium ions to form through ion-molecule interactions because hydronium formation was found to directly correlate with the H2O partial pressure. However, in a QMS at UHV, formation of H3O+ appears to occur principally by electron stimulated desorption (ESD). Introducing hydrogen into the system from 1 Langmuir exposure to saturation (1 x 10-6 Torr for 8 hours) increased the H3O + ESD yield detected by the QMS by as much as a factor of 10. The initial hydronium ESD cross section from a hydrogen saturated grid was estimated to be sigma ˜ 1 x 10-19, cm2. TOF-SIMS sputter yields from the stainless steel grid of a quadrupole mass spectrometer also showed small signals of H3O+, as well as its constituents (H+, O+ and OH) and a small amount of fluorine as F-, but no F+ or F+ complexes (HF+, etc.). Using x-ray photoelectron spectroscopy, a small amount (0.4%) of fluorine was found in the surface of stainless steel. Electron bombardment reduces the fluorine bound in surface complexes, but not metal halides found below the surface. However, heating the sample eliminated the F 1s signal entirely, indicating that fluorine is not likely to be the source of mass 19 in residual gas analysis. Also, changes in the spectral shoulders on the O 1s and Cr 2P3/2 peaks show that hydrogen dosing stainless steel and chromium increases the amount of hydroxides at the surface, while heating and electron bombardment reduce them.

Cole, Charles Randal

387

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

388

Surface structure of nickel oxide layers on a Rh(111) surface  

NASA Astrophysics Data System (ADS)

The formation of nickel oxide nanolayers by oxidizing Ni overlayers on Rh(111) has been investigated and their structures are reported as a function of the nickel coverage and oxygen pressure. Scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and diffraction (XPD), and high-resolution electron energy loss spectroscopy (HREELS) have been applied to characterize the structure and stoichiometry of the nickel oxide nanolayers. Several different phases have been observed depending on the strain state of the metallic Ni overlayers. For the pseudomorphic Ni monolayer, two distinctly different oxide phases with (6 × 1)-Ni5O5 and (2?3 × 2)-Ni8O10 structures have been identified at oxygen-poor (p = 5 × 10- 8 mbar) and oxygen-rich (p ? 1 × 10- 6 mbar) conditions, respectively. Above one monolayer, where the Ni layers are relaxed, bulk-like NiO(100) films form at the O-rich conditions, whereas chemisorbed-type p(2 × 2)Osbnd Ni(111) layers develop in the O-poor regime. X-ray photoelectron diffraction analysis has provided additional insight into the relaxation mechanism and the detailed atomic structure of the Ni-oxide nanolayers.

Gragnaniello, L.; Allegretti, F.; Zhan, R. R.; Vesselli, E.; Baraldi, A.; Comelli, G.; Surnev, S.; Netzer, F. P.

2013-05-01

389

Plasma decontamination of uranium oxide from stainless steel surfaces  

SciTech Connect

The U.S. Department of Energy (DOE) is expected to have 845000 m{sup 3} of transuranic (TRU) waste by the year 2000 that has accumulated during the development and assembly of the nation`s nuclear stockpile. The TRU disposal costs alone range up to $28000/m{sup 3}, which could be reduced to $1800/m{sup 3} or less by treating and converting the material to low-level waste. Plasma-based processes have been shown to remove plutonium and uranium surface contaminants from metallic components and could be used to treat TRU with significant cost avoidance, estimated at over $1.0 billion. Martz and Hess conducted the initial work of plutonium etching in low-power radio-frequency (rf) plasma with etch rates ranging from 0.007 to 0.025 kg/m{sup 2}{center_dot}h. Veilleux et al. reported that plasma decontamination of uranium from the interior of aluminum objects results in etch rates an order of magnitude greater. The current work reports on removal rates of uranium from stainless steel surfaces and includes estimates of the etch rates and characteristic times for removal.

Veilleux, J.M.; El-Genk, M.S. [Univ. of New Mexico, Albuquerque, NM (United States); Chamberlin, E.P. [Los Alamos National Lab., NM (United States)] [and others

1997-12-01

390

Radicals and Oxidants Instrument (ROXI) for Mars surface analyses  

NASA Astrophysics Data System (ADS)

Electron Paramagnetic Resonance (EPR) spectroscopy is likely the most sensitive technique for detection of elements and compounds with unpaired electrons. Typical analyses in the laboratory utilize a fixed microwave frequency and a scanning magnetic field to induce electron spin-state transitions in the sample. The location of the resonant absorption in the scan is a diagnostic property of the material, and the intensity of the signal is proportional to the concentration. We have developed a frequency scan EPR for planetary surface applications where a fixed magnetic field and tunable microwave sources are used to produce these characteristic resonant peaks. Our narrowband spectrometer covers 7.5 to 8.5 GHz at a field strength 2.8 kGauss and is specifically designed for the identification of organic radicals, minerals with radiation-induced defects, and reactive compounds in martian surface samples. Our wideband spectrometer covers 2.0 to 8.0 GHz at a field strength of 1.0 kGauss and is useful for the detection of paramagnetic cations. The detection limit of the narrowband and wideband spectrometers for species with unpaired electrons is 50 PPB and 1 PPM, respectively.

Yen, Albert S.; Kim, Soon S.

2004-12-01

391

Self-Assembled Monolayers on Aluminum and Copper Oxide Surfaces: Surface and Interface Characteristics, Nanotribological Properties, and Chemical Stability  

Microsoft Academic Search

The formation of self-assembled monolayer (SAM) films onto aluminum and copper oxide surfaces by reaction with 1H,1H,2H,2H-perfluorodecylphosphonic\\u000a acid (PFDP), octadecylphosphonic acid (ODP), decylphosphonic acid (DP), octylphosphonic acid (OP), and 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane\\u000a (PFMS) is discussed in this chapter. The properties and chemical stability of the films have been investigated using complementary\\u000a surface analysis techniques: X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM),

Enamul Hoque; James A. DeRose; Bharat Bhushan; Hans Jörg Mathieu

392

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

393

Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission  

SciTech Connect

Field emission on the inner surfaces of niobium superconducting radio frequency cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results* seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3 nm up to 460 nm. A home-made scanning field emission microscope was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The SFEM experimental results were analyzed in terms of surface morphology and oxide thickness of Nb samples and chemical composition and geographic shape of the emitters. A model based on the classic electromagnetic theory was developed trying to understand the experimental results. Possibly implications for Nb SRF cavity applications from this study will be discussed.

A.T. Wu, S. Jin, J.D. Mammosser, R.A. Rimmer, X.Y. Lu, K. Zhao

2011-09-01

394

Scanned Probe Oxidation on p-GaAs(100) Surface with an Atomic Force Microscopy  

NASA Astrophysics Data System (ADS)

Locally anodic oxidation has been performed to fabricate the nanoscale oxide structures on p-GaAs(100) surface, by using an atomic force microscopy (AFM) with the conventional and carbon nanotube (CNT)-attached probes. The results can be utilized to fabricate the oxide nanodots under ambient conditions in noncontact mode. To investigate the conversion of GaAs to oxides, micro-Auger analysis was employed to analyze the chemical compositions. The growth kinetics and the associated mechanism of the oxide nanodots were studied under DC voltages. With the CNT-attached probe the initial growth rate of oxide nanodots is in the order of ~300 nm/s, which is ~15 times larger than that obtained by using the conventional one. The oxide nanodots cease to grow practically as the electric field strength is reduced to the threshold value of ~2 × 107 V cm-1. In addition, results indicate that the height of oxide nanodots is significantly enhanced with an AC voltage for both types of probes. The influence of the AC voltages on controlling the dynamics of the AFM-induced nanooxidation is discussed.

Jian, Sheng-Rui; Juang, Jenh-Yih

2008-07-01

395

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

396

Mechanisms for formation and disruption of surface oxides: Final report  

SciTech Connect

Mill-annealed alloys 600, 690 and 800 were exposed to 10 and 50% caustic solutions containing 1% Na/sub 2/CO/sub 3/ to initiate IGA. IGA reproducibly occurred in all three alloys in the 10% caustic solution at 350/sup 0/C after a 240 h exposure and in the 50% caustic solution at 320/sup 0/C after a 120 h exposure. Reproducible IGA did not occur in the 10% caustic solution at 320/sup 0/C after a 120 h exposure. IGA was not observed in mill annealed plus thermally treated alloys 600 and 690 after exposure to any of the test conditions. IGA initiation was correlated with a dealloying mechanism in which the more active alloying metals, iron and chromium, selectively dissolve. Boric acid and calcium hydroxide additives were found to slow or prevent IGA by inhibiting dealloying. Titanates prevented IGA in alloys 600, 690 and 800, passivating the surface with a nickel titanate film.

Lumsden, J.B.

1987-08-01

397

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

398

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

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 term of the bulk and surface chemistry, the microstructure, and the semiconductor properties of the pyrite. During the twelfth quarter, wet and dry oxidation tests were done at room temperature on coal samples from the Pennsylvania State Coal Bank. Previous results had indicated that oxidation at high temperatures induced changes in surface properties through loss of volatiles. As-received and oxidized coal samples were studied by ion exchange methods to determine the carboxylate and phenolic group concentrations. Film flotation tests were done to characterize the floatability of as-received and oxidized coals. Surface area measurements were done on as-received coals.

Doyle, F.M.

1993-09-30

399

Improved performance of protected catecholic polysiloxanes for bio-inspired wet adhesion to surface oxides  

PubMed Central

A facile synthetic strategy for introducing catecholic moieties into polymeric materials based on a readily available precursor – eugenol – and efficient chemistries – tris(pentafluorophenyl)borane catalyzed silation and thiol-ene coupling is reported. Silyl-protection is shown to be critical for the oxidative stability of catecholic moieties during synthesis and processing which allows functionalized polysiloxane derivatives to be fabricated into 3-D microstructures as well as 2-D patterned surfaces. Deprotection gives stable catechol surfaces with adhesion to a variety of oxide surfaces being precisely tuned by the level of catechol incorporation. The advantage of silyl-protection for catechol functionalized polysiloxanes is demonstrated and represents a promising and versatile new platform for underwater surface treatments.

Heo, Jinhwa; Kang, Taegon; Jang, Se Gyu; Hwang, Dong Soo; Spruell, Jason M.; Killops, Kato L.; Waite, J. Herbert; Hawker, Craig J.

2012-01-01

400

Carbon monoxide oxidation over three different oxidation states of copper: Metallic copper, copper (I) oxide, and copper (II) oxide - a surface science and kinetic study  

Microsoft Academic Search

Reaction rates and activation energies were measured for carbon monoxide oxidation over thin films of metallic copper, copper (I) oxide, and copper (II) oxide grown on graphite. The reactions were carried out in the temperature range 200-350[degrees]C at total pressures of 100 Torr. Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the growth and oxidation

G. G. Jernigan; G. A. Somorjai

1994-01-01

401

Probing the electronic structure of early transition metal oxide clusters: Molecular models towards mechanistic insights into oxide surfaces and catalysis  

NASA Astrophysics Data System (ADS)

Selected recent works from the authors' laboratory on the intrinsic electronic and structural properties of early transition metal oxide clusters are reviewed. These clusters provide well-defined molecular models pertinent to mechanistic understandings of complex oxide surface chemistry and catalysis. The energy gap evolution with cluster size was probed for the stoichiometric (TiO 2) n-, (V 2O 5) n-, and (CrO 3) n- clusters, and each system was shown to approach the band gap of bulk oxides in a unique way. A variety of other model clusters have been characterized, such as the oxygen radical or diradical on a single W 6+ site in WO 4-/WO 4, the superoxide (WO 3) n(O 2-) complexes for dioxygen activation, and terminal versus bridging oxygen in M 3O 2- (M = Nb, Ta) clusters. Novel chemical bonding has been observed in a number of oxide clusters. The W 3O 9- and W 3O 92- clusters were found to possess d-orbital aromaticity, whereas ?-aromaticity was discovered in the Ta 3O 3- cluster.

Zhai, Hua-Jin; Wang, Lai-Sheng

2010-11-01

402

Composition and structure of iron oxidation surface layers produced in weak acidic solutions.  

PubMed

Although oxidation/passivation of iron in basic solution has been extensively investigated, there is very little information on iron corrosion in weak acidic solutions. In this work, iron surface composition and structure, produced in aerobic aqueous solutions ranging from pH 2 to 5, were determined in detail by the use of infrared external reflection spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The most striking observation is that at pH 2 and 3 almost all oxidized iron is dissolved in solution, whereas at pH 4 and 5 the product of iron oxidation is deposited on the iron surface in the form of lepidocrocite, gamma-FeOOH. Detailed iron surface and solution analyses allow the proposition of the following overall oxidation reactions: [EQUATION: SEE TEXT]. At pH 2 and 3, only a very thin surface layer consisting of FeO and Fe(OH)2 with polymeric structure is observed on the iron surface. The amounts of these surface species remain almost constant (2-5 nm) from the first minutes to a few hours of reaction, if pH is kept constant. Nevertheless, with time the akaganeite-like, beta-FeOOH structure is also detected. At pH 4 and 5, the amount of lepidocrocite deposited on the iron surface increases with reaction time. Detailed quantitative evaluation of the lepidocrocite produced at pH 5 and its surface distribution on iron was performed based on the comparison of infrared spectroscopic data with spectral simulation results of assumed surface structures. At pH 4 and 5 and a temperature of 40-50 degrees C, in addition to a very large amount of lepidocrocite other oxy-hydroxide surface species such as goethite (alpha-FeOOH) and feroxyhite (delta-FeOOH), were identified. Addition of Cl- ions to solution at 10(-3) M concentration at pH 5 increases the oxidation rate of iron by about 50%, and lepidocrocite remains the only oxidation product. Similarly, an addition of Fe2+ ions to solution at pH 5 very strongly enhances lepidocrocite formation as well as its conductivity. The latter finding is important for the possible application of metallic iron as a catalyst in redox reactions, for example, for decomposition of difficult-to-biodegrade water pollutants. PMID:15922350

Montes Atenas, Gonzalo; Mielczarski, Ela; Mielczarski, Jerzy A

2005-09-01

403

Thermal oxidation-resistant surface alloys processed by laser alloying on 35 NCD 16 ferritic steel  

Microsoft Academic Search

The hardness and the high-temperature oxidation resistance of the low-alloyed ferritic steel 35 NCD 16 (Fe-0.38 C-1.8 Cr-4 Ni, wt%) were increased by laser surface alloying of Cr3C2 or Cr3C2 and SiC. The obtained surface alloys always exhibit primary dendrites (? Fe solid solution with Cr and Si + martensite) and an interdendritic eutectic containing ? Fe + martensite +

E. Gemelli; A. Galerie; M. Caillet

1996-01-01

404

A highly selective ammonia gas sensor using surface-ruthenated zinc oxide  

Microsoft Academic Search

Preparation and characterisation of a highly selective surface-ruthenated zinc oxide sensor for ammonia in trace levels is demonstrated. The introduction of some RuO linkages on the surface of ZnO leads to a dramatic enhancement in the sensitivity (S) to 1000 ppm level of ammonia at 300°C (S=440) as compared to the similar response obtained for pure ZnO (S=1.5). A systematic

M Aslam; V. A Chaudhary; I. S Mulla; S. R Sainkar; A. B Mandale; A. A Belhekar; K Vijayamohanan

1999-01-01

405

AFM measurement of atomic-scale Si surface etching by active oxidation  

Microsoft Academic Search

Atomic-scale etching of a clean Si surface by active oxidation with oxygen molecules was examined using ex-situ atomic force microscopy (AFM). The etch rate was directly determined by measuring the etch depth with AFM. A SiO2 anti-etching mask was used on a H-terminated Si(001)-2×1:H surface prepared by low pH HF treatment followed by annealing in H2. The etch rate under

Y. Morita; S. Migita; W. Mizubayashi; H. Ota

2010-01-01

406

A room temperature etching route to tungsten oxide hydrate nanoplates with expanded surface area  

Microsoft Academic Search

Tungsten oxide hydrate nanoplates with expanded surface area have been synthesized through the acid treatment of tungstate?aluminum keggin nanocomposite. According to powder X-ray diffraction and W LIII-edge X-ray absorption spectroscopic analyses, X-ray amorphous nanocomposite is changed into crystalline WO3·2H2O upon the acidic etching of alumina component. Nitrogen adsorption?desorption isotherm and field emission-scanning electron microscopy measurements clearly demonstrated that the surface

Ah Reum Han; Seong-Ju Hwang; Hyun Jung; Jin-Ho Choy

2008-01-01

407

Structure and Surface and Catalytic Properties of Mg-Al Basic Oxides  

Microsoft Academic Search

Mg-Al mixed oxides with Mg\\/Al molar ratios of 0.5–9.0 were obtained by thermal decomposition of precipitated hydrotalcite precursors. The effect of composition on structure and surface and catalytic properties was studied by combining several characterization methods with ethanol conversion reactions. The nature, density, and strength of surface basic sites depended on the Al content. On pure MgO, strong basic sites

J. I. Di Cosimo; V. K. D??ez; M. Xu; E. Iglesia; C. R. Apestegu??a

1998-01-01

408

Formation and evolution of self-organized Au nanorings on indium-tin-oxide surface  

SciTech Connect

This work reports on the formation of Au nanoclusters and on their evolution in nanoring structures on indium-tin-oxide surface by sputtering deposition and annealing processes. The quantification of the characteristics of the nanorings (surface density, depth, height, and width) is performed by atomic force microscopy. The possibility to control these characteristics by tuning annealing temperature and time is demonstrated establishing relations which allow to set the process parameters to obtain nanostructures of desired morphological properties for various technological applications.

Ruffino, F.; Simone, F.; Grimaldi, M. G. [Dipartimento di Fisica e Astronomia, Universita di Catania, via S. Sofia 64, 95123 Catania (Italy); MATIS CNR-IMM, via S. Sofia 64, 95123 Catania (Italy); Crupi, I. [MATIS CNR-IMM, via S. Sofia 64, 95123 Catania (Italy)

2011-01-10

409

Ozone Oxidation of Endocrine Disruptors and Pharmaceuticals in Surface Water and Wastewater  

Microsoft Academic Search

The oxidative removal of a diverse group of trace organic contaminants from surface water and wastewater was evaluated using ozone (O3) and O3 combined with hydrogen peroxide (O3\\/H2O2). Target compounds included estrogenic and androgenic steroids, pharmaceuticals, pesticides, and industrial chemicals. Bench- and pilot- scale experiments were conducted with surface water spiked with the target compounds and wastewater effluent containing ambient

Shane A. Snyder; Eric C. Wert; David J. Rexing; Ronald E. Zegers; Douglas D. Drury

2006-01-01

410