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1

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

2

Cyclic dipeptide immobilization on Au(111) and Cu(110) surfaces.  

PubMed

Soft X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy have been used to probe the electronic and adsorption properties of two cyclic dipeptides, i.e. cyclo(glycyl-histidyl) and cyclo(phenylalanyl-prolyl), on Au(111) and Cu(110) surfaces. The core level spectra show chemical shifts which indicate weak chemisorption on Au(111), and stronger chemisorption on the Cu(110) surface, mainly via one of the nitrogen atoms in the central rings of both molecules, and nitrogen in the imidazole ring of cyclo(glycyl-histidyl). From the angular dependence of the NEXAFS spectra at the O and N K-edges, we conclude that both dipeptides have a preferred orientation on the two surfaces. PMID:24584969

Plekan, Oksana; Feyer, Vitaliy; Ptasi?ska, Sylwia; Tsud, Nataliya; Prince, Kevin C

2014-04-14

3

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

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

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

6

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

7

Influence of aggregation, defects, and contaminant oxygen on water dissociation at Cu(110) surface: A theoretical study  

Microsoft Academic Search

The DFT-PW91 slab model approach is employed to investigate the influence of aggregation, surface defects, and contaminant oxygen on water dissociation on Cu(110) at low temperatures. The dissociation barriers of water in various aggregate states are calculated in the range of 60-75 kJ\\/mol on the clean surfaces, in nice agreement with the experimentally determined values. It is revealed that the

Qian-Lin Tang; Zhao-Xu Chen

2007-01-01

8

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

E-print Network

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

Mishin, Yuri

9

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

10

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

11

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

12

Morphology of Pd multilayers on Cu(110)  

NASA Astrophysics Data System (ADS)

The growth of Pd films deposited on a Cu(110) single crystal surface and the resulting morphology of the film structure has been followed by STM for deposition at 310 K. For ˜1 ML films an ordered (2×1) surface alloy is formed which is also visible in LEED. The surface morphology is, however, not flat but has roughened step edges, raised islands and smaller trenches. For increased coverages of Pd the growth shifts to the formation of rectangular multilayered Pd islands. Upon annealing, AES shows a preferential segregation of Cu to the surface region that accompanies a flattening of the surface morphology in STM. Annealing thick films (>4 ML) to 603 K produces a surface morphology with larger flat terraces and small islands that have rough, non-crystallographically aligned step edges. With further annealing to 723 K these surfaces also display large-scale 'banding' in the STM images that we attribute to stress relaxation between the CuPd alloy and Cu.

Bennett, R. A.; Poulston, S.; Price, N. J.; Reilly, J. P.; Stone, P.; Barnes, C. J.; Bowker, M.

1999-08-01

13

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

Microsoft Academic Search

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 HO-OH complex of the dissociated final state, which lowers the water dissociation

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

2007-01-01

14

LEEM study of nucleation, growth, and decay of Ag nanowires on Cu(110)  

Microsoft Academic Search

Low energy electron microscopy (LEEM) has been used to study the nucleation, growth, and ripening of Ag nanowires on Cu(110). Previous STM and LEED studies of Ag on the Cu(110) surface have shown that for a Ag coverage of below 0.3 ML, Ag forms a surface alloy, followed by the formation of a 2D Ag(111) flat superstructure through dealloying at

Indrajith Senevirathne; Ezra Bussmann; Gary Kellogg; Richard Kurtz; Phillip Sprunger

2007-01-01

15

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

16

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

SciTech Connect

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

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

1990-01-01

17

c2 2 Water-Hydroxyl Layer on Cu(110): AWetting Layer Stabilized by Bjerrum Defects Matthew Forster,1  

E-print Network

by spontaneous dissociation of water. Although formation of water-hydroxyl wetting layers has been in- tensivelycð2 � 2� Water-Hydroxyl Layer on Cu(110): AWetting Layer Stabilized by Bjerrum Defects Matthew the composition and stability of mixed water-hydroxyl layers is a key step in describing wetting and how surfaces

Alavi, Ali

18

LEEM study of nucleation, growth, and decay of Ag nanowires on Cu(110)  

NASA Astrophysics Data System (ADS)

Low energy electron microscopy (LEEM) has been used to study the nucleation, growth, and ripening of Ag nanowires on Cu(110). Previous STM and LEED studies of Ag on the Cu(110) surface have shown that for a Ag coverage of below 0.3 ML, Ag forms a surface alloy, followed by the formation of a 2D Ag(111) flat superstructure through dealloying at one monolayer. For Ag coverages above 1.3 ML , nanowires of Ag(110), with widths/heights of 12 nm / 2nm, grow along the [110] crystallographic direction with highly anisotropic aspect ratios. LEEM reveals that Ag initially alloys at Cu/Ag step edges producing a distortion of the steps. Upon deposition above 1 ML, nucleation of Ag nanowires was observed across terraces, however nucleation still occurred at defect and step edges. LEEM showed that the nanowires grow to micron lengths and have highly anisotropic aspect ratios. Annealing above 573K resulted in rapid Oswald ripening of nanowires to Ag clusters of several micron dimensions. Quantitative details of the growth and decay mechanisms will be discussed. Sandia Corporation is a Lockheed Martin Company, for the US DOE's NNSA under Contract DE-AC04-94AL85000. Work was supported CINT-U2006A123 and NSF-DMR-0504654.

Senevirathne, Indrajith; Bussmann, Ezra; Kellogg, Gary; Kurtz, Richard; Sprunger, Phillip

2007-03-01

19

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

PubMed

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

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

2008-10-30

20

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

NASA Astrophysics Data System (ADS)

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

Gustafsson, Alexander; Ueba, Hiromu; Paulsson, Magnus

2014-10-01

21

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

SciTech Connect

It was found that atomically flat Co(110) film could be grown on Cu(110) using O as a surfactant. To obtain detailed knowledge on the effect of O on the growth, as well as on the magnetic properties of Co overlayer, we carried out an investigation on this system using Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), Surface Magneto-Optic Kerr Effect (SMOKE), and Scanning Tunneling Microscopy (STM). With O as a surfactant, the initial growth of Co (< 1 ML) results in a flat monolayer structure. When the Co is thicker than 1 ML, three-dimensional clusters begin to form. These clusters become ordered islands at 3 ML Co and coalesce at about 5 ML Co. Above 5 ML Co, layer-by-layer growth resumes. No Cu segregation is observed. SMOKE studies at room temperature show that the Co film is magnetic above about 5 ML Co, with the magnetization easy axis along the [001] direction. On the other hand, without using oxygen as a surfactant, Co grows three-dimensionally on Cu(110). The Co overlayer has its easy magnetization axis along the [001] direction, but the onset of the magnetization was observed at 11 ML Co at room temperature.

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

2000-04-13

22

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

SciTech Connect

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

Li, D.

1998-09-21

23

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

PubMed

From an interplay of high-resolution STM imaging/manipulation and DFT calculations, we have revealed that different self-assembled nanostructures of BA molecules on Cu(110) are attributable to specific molecular adsorption geometries, and thus the corresponding intermolecular hydrogen bonding patterns. The STM manipulations demonstrate the feasibility of switching such weak-hydrogen-bonding patterns. PMID:25145767

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

2014-10-01

24

"Magic" vicinal zinc oxide surfaces.  

PubMed

The structure of (0001) oriented ZnO single crystal surfaces is investigated by scanning tunneling microscopy. Depending on the preparation conditions, faceting of the crystals into large areas of {101¯4} surface orientation occurs. This restructuring of the surface is shown to be a consequence of dipole compensation and charge neutralization. A new stabilization mechanism of polar oxide surfaces is found which is based on the formation of vicinal surfaces with special electronic and structural properties. PMID:24010455

Zheng, Hao; Gruyters, Markus; Pehlke, Eckhard; Berndt, Richard

2013-08-23

25

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

26

Surface-Step-Induced Oscillatory Oxide Growth  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

27

Surface-step-induced oscillatory oxide growth.  

PubMed

We report in situ atomic-resolution transmission electron microscopy observations of the oxidation of stepped Cu surfaces. We find that the presence of surface steps both inhibits oxide film growth and leads to the oxide decomposition, thereby resulting in oscillatory oxide film growth. Using atomistic simulations, we show that the oscillatory oxide film growth is induced by oxygen adsorption on the lower terrace along the step edge, which destabilizes the oxide film formed on the upper terrace. PMID:25302908

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

2014-09-26

28

Copper(110) surface in thermodynamic equilibrium with water vapor studied from first principles  

E-print Network

at the oxygen. They observed dissociative adsorption of water, occurring at temperatures above 90 K. Preference water monolayer. Yamamoto et al. [14] ascribed the wettability of Cu(110) to partial dissociation of water molecules on this surface. An autocatalytic water dissociation on Cu(110) at near ambient

Schmidt, Wolf Gero

29

Epitaxial oxide growth on polar (111) surfaces  

Microsoft Academic Search

Obtaining atomically smooth surfaces and interfaces of perovskite oxide materials on polar (111) surfaces presents a particular challenge as these surfaces and interfaces will reconstruct. Here, the effect of the use of screening buffer layers on the epitaxial growth on such polar surfaces is investigated. Both transmission electron microscopy and in situ reflective high energy electron diffraction data imply that

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

2011-01-01

30

Surface Precipitation of Hydrolyzable Metal Ions on Oxide Surfaces  

E-print Network

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

Sparks, Donald L.

31

Initial oxidation of polycrystalline Permalloy surface  

NASA Astrophysics Data System (ADS)

X-ray photoelectron spectroscopy (XPS) and work-function measurements were used in combination to investigate the initial steps of Permalloy (Ni 80Fe 20) oxidation at room temperature. They showed that, after oxygen saturation, the surface is covered by nickel oxide (NiO), nickel hydroxide (Ni(OH) 2) and iron oxides (Fe xO y), and there is no preferential oxidation. Iron oxidation proceeds through the formation of FeO (Fe 2+) followed with Fe 2O 3 growth (Fe 3+). The oxidation is governed by a dissociative Langmuir-type oxidation: the sticking coefficient is decreasing over oxygen exposure. Oxidation continues by oxygen dissolution into the first layers to form a nano-oxide of about 8 Å in thickness.

Salou, M.; Lescop, B.; Rioual, S.; Lebon, A.; Youssef, J. Ben; Rouvellou, B.

2008-09-01

32

Surface modification to prevent oxide scale spallation  

DOEpatents

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

33

Surface Wrinkling on Polydimethylsiloxane Microspheres via Wet Surface Chemical Oxidation  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

34

Surface plasmon resonance in conducting metal oxides  

Microsoft Academic Search

We report the initial observation of surface plasmon resonance (SPR) in a conducting metal oxide thin film. The SPR phenomenon has been observed by attenuated total reflection of near-infrared radiation and is in agreement with electron energy loss spectroscopy measurements. To date, only metals are known to exhibit surface plasmon resonance and only noble metals have practical application. According to

Crissy Rhodes; Stefan Franzen; Jon-Paul Maria; Mark Losego; Donovan N. Leonard; Brian Laughlin; Gerd Duscher; Stephen Weibel

2006-01-01

35

Epitaxial oxide growth on polar (111) surfaces  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

36

Alkane activation on crystalline metal oxide surfaces.  

PubMed

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

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

2014-10-20

37

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...

38

Reversible oriented surface immobilization of functional proteins on oxide surfaces.  

PubMed

Reversible and oriented immobilization of proteins in a functionally active form on solid surfaces is a prerequisite for the investigation of molecular interactions by surface-sensitive techniques. We demonstrate a method generally applicable for the attachment of proteins to oxide surfaces. A nitrilotriacetic acid group serving as a chelator for transition metal ions was covalently bound to the surface via silane chemistry. Reversible binding of the green fluorescent protein, modified with a hexahistidine extension, was monitored in situ using total internal reflection fluorescence. The association constant and kinetic parameters of the binding process were determined. The reversible, directed immobilization of proteins on surfaces as described here opens new ways for structural investigation of proteins and receptor-ligand interactions. PMID:9183172

Schmid, E L; Keller, T A; Dienes, Z; Vogel, H

1997-06-01

39

Patterning pentacene surfaces by local oxidation nanolithography.  

PubMed

Sequential and parallel local oxidation nanolithographies have been applied to pattern pentacene samples by creating a variety of nanostructures. The sequential local oxidation process is performed with an atomic force microscope and requires the application of a sequence of voltage pulses of 36V for 1ms. The parallel local oxidation process is performed by using a conductive and patterned stamp. Then, a voltage pulse is applied between the stamp and the pentacene surface. Patterns formed by arrays of parallel lines covering 1mm(2) regions and with a periodicity of less than 1microm have been generated in a few seconds. We also show that the patterns can be used as templates for the deposition of antibodies. PMID:20226594

Losilla, N S; Martinez, J; Bystrenova, E; Greco, P; Biscarini, F; García, R

2010-05-01

40

Surface aspects of bismuth-metal oxide catalysts  

SciTech Connect

A series of conventional and model bismuth-metal oxide catalysts (vanadates, molybdates, tungstates, and niobates) were physically and chemically characterzied (Raman spectroscopy, BET, XPS, and methanol oxidation) to obtain additional insights into the structure-reactivity relationships of such catalytic materials. The reactivity for methanol oxidation over the conventional bismuth-metal oxide catalysts was found to be primarily related to the surface area of the oxide catalysts and was essentially independent of the near surface composition and the bulk structure. The selectivity for methanol oxidation over the conventional bismuth-metal oxide catalysts was essentially found not to be a function of the surface area, the near surface composition, and the bulk structure. A series of model bismuth-metal oxide catalysts was synthesized by depositing metal oxides on the surface of a bismuth oxide support. The model studies demonstrated that two-dimensional metal oxide overlayers are not stable on the bismuth oxide support and readily react to form bulk bismuth-metal oxide compounds upon heating. Furthermore, the model studies revealed that these bulk bismuth-metal oxide compounds are related to the active sites for the partial oxidation reaction. In situ Raman spectroscopy in methanol/oxygen, methanol, and oxygen reaction environments with helium as the diluent revealed no additional information regarding the nature of the active site. It was found that only highly crystalline bismuth-metal oxide phases are selective for the partial oxidation of methanol to formaldehyde. Thus, selective bismuth-metal oxide catalysts will always possess highly crystalline metal oxide phases containing extremely low surface areas which make it difficult to obtain fundamental surface information about the outermost layers. 48 refs., 11 figs., 9 tabs.

Arora, N.; Deo, G.; Wachs, I.E. [Lehigh Univ., Bethlehem, PA (United States)] [and others] [Lehigh Univ., Bethlehem, PA (United States); and others

1996-03-01

41

Surface oxidation of liquid Sn Alexei Grigoriev a,*  

E-print Network

Review Copy 1 Surface oxidation of liquid Sn Alexei Grigoriev a,* , Oleg Shpyrko b , Christoph-ray scattering study that reveals oxidation kinetics and formation of a previously unreported crystalline phase solid Sn oxide grows over the liquid metal surface. Once the activation pressure has been exceeded

Grigoriev, Alexei

42

Surface Chemistry of Supported Chromium Oxide on Lanthanum Carbonate  

Microsoft Academic Search

The surface chemistry of supported chromium oxide on lanthanum carbonate has been studied by TPD, FTIR, XPS, and electrophoretic measurement techniques. The active center for the oxidative dehydrogenation of isobutane to isobutylene was identified as a chromate species bound to the surface of lanthanum carbonate. This species was formed as a result of interaction between chromium oxide and lanthanum carbonate

Manh Hoang; Anthony E. Hughes; Joseph F. Mathews; Kerry C. Pratt

1997-01-01

43

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

44

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

SciTech Connect

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

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

2011-12-01

45

Atomic hydrogen modification of copper surfaces studied by helium atom scattering  

NASA Astrophysics Data System (ADS)

The structure and bonding of single crystal copper surfaces under irradiation by H atoms is investigated by helium atom scattering under UHV conditions. The effect of H atoms on Cu?Cu bonding is deduced from the temperature dependence of the intensity of the specular He reflection from a clean Cu(110) surface and for irradiation with an effusive H atom beam. The Debye temperature deduced from the attenuation of the specular reflection decreases from 340 ± 10 K to 287 ± 10 K upon exposure to hydrogen atoms, implying a decrease in the surface Rayleigh phonon frequency by the H?Cu interaction. Also, the chemical reduction of a Cu(100)-(2 2× 2) R45°- O surface by irradiation with H atoms at 723 K is investigated. H atoms are shown to be an effective means for removing oxide impurities from Cu surfaces.

Miyake, T.; Petek, H.

1997-11-01

46

Oxidation of graphite surface: the role of water  

E-print Network

Based on density functional calculations, we demonstrate a significant difference in oxidation patterns between graphene and graphite and the formation of defects after oxidation. Step-by-step modeling demonstrates that oxidation of 80% of the graphite surface is favorable. Oxidation above half of the graphite surface significantly decreases the energy costs of vacancy formation with CO2 production. The presence of water is crucial in the transformation of epoxy groups to hydroxyl, the intercalation with further bundle and exfoliation. In water-rich conditions, water intercalates graphite at the initial stages of oxidation and oxidation, which is similar to the oxidation process of free-standing graphene; in contrast, in water-free conditions, large molecules intercalate graphite only after oxidation occurs on more than half of the surface.

Boukhvalov, D W

2014-01-01

47

Surface and sub-surface thermal oxidation of thin ruthenium films  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

48

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

E-print Network

707 Silicon surfaces : metallic character, oxidation and adhesion A. Cros (*) IBM T.J. Watson on the growth mode ofmetal atoms and the oxidation ofthe silicon surface atoms. These phenomena are discussed long range order or not has a great importance. There are at least two cases where basic properties

Paris-Sud XI, Université de

49

Surface and catalytic properties of doped tin oxide nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

50

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

SciTech Connect

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

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

2013-02-28

51

Solid state, surface and catalytic properties of oxides  

NASA Astrophysics Data System (ADS)

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

Kung, H. H.

1984-09-01

52

Surface oxidation of the icosahedral Ag-In-Yb quasicrystal  

Microsoft Academic Search

The oxidation of the high-symmetry surfaces of a single grain icosahedral (i) Ag-In-Yb quasicrystal has been studied using x-ray photoemission spectroscopy. The oxidation was carried out in vacuum, air, and water. It is found that air exposure results in the same degree of oxidation as exposure to oxygen in vacuum. The oxidation in water is more effective. Among the three

P. J. Nugent; G. Simutis; V. R. Dhanak; R. McGrath; M. Shimoda; C. Cui; A. P. Tsai; H. R. Sharma

2010-01-01

53

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

54

Adsorption of bovine serum albumin onto metal oxide surfaces  

Microsoft Academic Search

The adsorption of bovine serum albumin (BSA) on surfaces of silicon dioxide (silica), titanium dioxide (titania), zirconium oxide (zirconia), and aluminium oxide (alumina) was studied as a function of pH. The adsorption isotherms for these metal oxides showed well-defined saturation plateaus in the pH range of 3.5 to 9.0. On positively charged metal oxides the isotherms showed a steeper initial

Satoshi Fukuzaki; Hiromi Urano; Kazuya Nagata

1996-01-01

55

TOPICAL REVIEW: Surface oxides on close-packed surfaces of late transition metals  

NASA Astrophysics Data System (ADS)

In recent years, the formation of thin, well-ordered but complex surface oxides on late transition metals has been discovered. The driving force for this line of research has been the strong incentive to increase the partial pressure of oxygen from ultra-high vacuum to conditions more relevant for heterogeneous catalysis. Here we review the present status of the research field. Compared to oxygen adatom superstructures, the structure of the surface oxides has proven to be extremely complex, and the investigations have therefore relied on a combination of several experimental and theoretical techniques. The approach to solving the structures formed on close-packed surfaces of Pd and Rh is presented in some detail. Focusing on the structures found, we show that the surface oxides share some general properties with the corresponding bulk oxides. Nevertheless, of all surface oxide structures known today, only the two-dimensional surface oxides on Pd(100) and Pt(110) have the same lattice as the bulk oxides (PdO and PtO, respectively). In addition to two-dimensional oxides, including the O-Rh-O trilayers found on Rh, one-dimensional oxides were observed at ridges or steps of open surfaces such as (110) or vicinal surfaces. Finally, we briefly report on a few studies of the reactivity of surface oxides with well-known structure.

Lundgren, Edvin; Mikkelsen, Anders; Andersen, Jesper N.; Kresse, Georg; Schmid, Michael; Varga, Peter

2006-08-01

56

Nanoscale oxidation and complex oxide growth on single crystal iron surfaces and external electric field effects.  

PubMed

Oxidation of iron surfaces and oxide growth mechanisms have been studied using reactive molecular dynamics. Oxide growth kinetics on Fe(100), (110), and (111) surface orientations has been investigated at various temperatures and/or an external electric field. The oxide growth kinetics decreases in the order of (110), (111), and (100) surfaces at 300 K over 1 ns timescale while higher temperature increases the oxidation rate. The oxidation rate shows a transition after an initial high rate, implying that the oxide formation mechanism evolves, with iron cation re-ordering. In early stages of surface oxide growth, oxygen transport through iron interstitial sites is dominant, yielding non-stoichiometric wüstite characteristics. The dominant oxygen inward transport decreases as the oxide thickens, evolving into more stoichiometric oxide phases such as wüstite or hematite. This also suggests that cation outward transport increases correspondingly. In addition to oxidation kinetics simulations, formed oxide layers have been relaxed in the range of 600-1500 K to investigate diffusion characteristics, fitting these results into an Arrhenius relation. The activation energy of oxygen diffusion in oxide layers formed on Fe(100), (110), and (111) surfaces was estimated to be 0.32, 0.26, and 0.28 eV, respectively. Comparison between our modeling results and literature data is then discussed. An external electric field (10 MV cm(-1)) facilitates initial oxidation kinetics by promoting oxygen transport through iron lattice interstitial sites, but reaches self-limiting thickness, showing that similar oxide formation stages are maintained when cation transport increases. The effect of the external electric field on iron oxide structure, composition, and oxide activation energy is found to be minimal, whereas cation outward migration is slightly promoted. PMID:23247653

Jeon, Byoungseon; Van Overmeere, Quentin; van Duin, Adri C T; Ramanathan, Shriram

2013-02-14

57

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

58

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. PMID:21749733

2008-01-01

59

Nano-confined water on surfaces of metal oxide nanoparticles  

Microsoft Academic Search

Nanolayers of water interacting with metal oxide surfaces demonstrate physical properties that are significantly different from those of bulk water and ice. Our recent water adsorption experiments suggest that the entropy of surface water is lower than those of bulk water and ice implying restricted motion of the water on the surface. We have studied dynamics of water on nanoparticles

Andrey Levchenko; Juliana Boerio-Goates; Brian Woodfield; Alexander Kolesnikov; Nancy Ross; David Wesolowski; David Cole; Alexandra Navrotsky

2008-01-01

60

Surface catalysis of water oxidation by the blue ruthenium dimer.  

PubMed

Single-electron activation of multielectron catalysis has been shown to be viable in catalytic water oxidation with stepwise proton-coupled electron transfer, leading to high-energy catalytic precursors. For the blue dimer, cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(H(2)O)(bpy)(2)](4+), the first well-defined molecular catalyst for water oxidation, stepwise 4e(-)/4H(+) oxidation occurs to give the reactive precursor [(O)Ru(V)ORu(V)(O)](4+). This key intermediate is kinetically inaccessible at an unmodified metal oxide surface, where the only available redox pathway is electron transfer. We report here a remarkable surface activation of indium-tin oxide (In(2)O(3):Sn) electrodes toward catalytic water oxidation by the blue dimer at electrodes derivatized by surface phosphonate binding of [Ru(4,4'-((HO)(2)P(O)CH(2))(2)bpy)(2)(bpy)](2+). Surface binding dramatically improves the rate of surface oxidation of the blue dimer and induces water oxidation catalysis. PMID:20377256

Jurss, Jonah W; Concepcion, Javier C; Norris, Michael R; Templeton, Joseph L; Meyer, Thomas J

2010-05-01

61

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

62

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

PubMed

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

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

2014-08-19

63

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

64

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

Microsoft Academic Search

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

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

2008-01-01

65

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.

66

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

E-print Network

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

Sun, Wei-Yang

2011-01-01

67

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

68

Step like surface potential on few layered graphene oxide  

NASA Astrophysics Data System (ADS)

We report surface potential maps of few layered graphene oxide films on different substrates. Kelvin probe force microscopy images reveal that the surface potential decreases in steps with increasing number of layers on the substrate until five layers are reached, where it saturates to a constant value. This intrinsic behavior is smeared out in the presence of ambient humidity where the surface potential is shielded by the presence of a thin water layer on the surface. This effect can be exploited to quickly determine the number of layers of graphene oxide on a substrate.

Jaafar, M.; López-Polín, G.; Gómez-Navarro, C.; Gómez-Herrero, J.

2012-12-01

69

The surface and materials science of tin oxide  

NASA Astrophysics Data System (ADS)

The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO 2 surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn 4+ surface cations into a reduced surface with Sn 2+ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO 2. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO 2 are discussed and the few surface science studies of doped SnO 2 are reviewed. Epitaxial SnO 2 films may facilitate the surface science studies of doped films in the future. To this end film growth on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO 2 surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized.

Batzill, Matthias; Diebold, Ulrike

70

MOISTURE AND SURFACE AREA MEASUREMENTS OF PLUTONIUM-BEARING OXIDES  

SciTech Connect

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

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

2009-09-28

71

New perspectives on thermal and hyperthermal oxidation of silicon surfaces  

NASA Astrophysics Data System (ADS)

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

Khalilov, Umedjon

72

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

Microsoft Academic Search

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

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

2005-01-01

73

Photo-oxidation of hydrogen passivated silicon surfaces  

NASA Astrophysics Data System (ADS)

Conventional and synchrotron photoelectron spectroscopy and a custom experimental setup are used to investigate how factors present in cleanrooms, including UV light, O2, and H2O, lead to contamination of the hydrogen passivated surface. Experimental results indicate that both the H-Si(111) and the Hx-Si(100) surfaces oxidize when exposed to UV light in the presence of O2 only, H2O only, or both O2 and H2O. We propose that UV light assists in the photo-oxidation of hydrogen terminated silicon surfaces by cleaving the H-Si bond. This process generates silicon surface radicals that can then be scavenged by either O2 to form Si-O-O· or by H2O to form Si-OH. Results also show that oxide contamination is most significant when the surface is exposed to both O2 and H2O (humid air) in the presence of UV light. In this humid air case, the water molecule is expected to more readily react with silicon surface radicals than the oxygen molecule. Polarization of the surface by the Si-OH bonding is thought to weaken the Si-Si backbond and make incorporation of oxygen, by O2, more energetically favorable. UV light also assist the oxidation process by providing the energy required for a successful electron transfer between the substrate and the O2 molecule. This electron transfer process creates reactive O2- species. This dissertation also shows that the extent of silicon surface photo-oxidation depends on the surface preparation condition which is determined by the concentration of HF used to hydrogen passivate the surface. Results show that the 250:1HF solution does not as effectively hydrogen passivate the Si(100) surface as does the 50:1HF solution. Comparison of the SR-PES Si(2p) spectra indicates that the 250:1HF prepared surface has a lower density of hydrides than the 50:1HF prepared surface. The study of how surface microstructure is affected by silicon processing conditions, obtained through XPS and SR-PES analysis, provides crucial information to the research community and to the silicon industry whose success depends on controlling the state of the silicon surface. Contrary to common understanding, the silicon surface can be kept oxidation-free for an extended period of time. Therefore, the need to clean silicon at the point-of-use has been eliminated.

Morse, Kathleen Anne

74

Interaction of nanostructured metal overlayers with oxide surfaces  

NASA Astrophysics Data System (ADS)

Interactions between metals and oxides are key factors to determine the performance of metal/oxide heterojunctions, particularly in nanotechnology, where the miniaturization of devices down to the nanoregime leads to an enormous increase in the density of interfaces. One central issue of concern in engineering metal/oxide interfaces is to understand and control the interactions which consist of two fundamental aspects: (i) interfacial charge redistribution — electronic interaction, and (ii) interfacial atom transport — chemical interaction. The present paper focuses on recent advances in both electronic and atomic level understanding of the metal-oxide interactions at temperatures below 1000 ?C, with special emphasis on model systems like ultrathin metal overlayers or metal nanoclusters supported on well-defined oxide surfaces. The important factors determining the metal-oxide interactions are provided. Guidelines are given in order to predict the interactions in such systems, and methods to desirably tune them are suggested. The review starts with a brief summary of the physics and chemistry of heterophase interface contacts. Basic concepts for quantifying the electronic interaction at metal/oxide interfaces are compared to well-developed contact theories and calculation methods. The chemical interaction between metals and oxides, i.e., the interface chemical reaction, is described in terms of its thermodynamics and kinetics. We review the different chemical driving forces and the influence of kinetics on interface reactions, proposing a strong interplay between the chemical interaction and electronic interaction, which is decisive for the final interfacial reactivity. In addition, a brief review of solid-gas interface reactions (oxidation of metal surfaces and etching of semiconductor surfaces) is given, in addition to a comparison of a similar mechanism dominating in solid-solid and solid-gas interface reactions. The main body of the paper reviews experimental and theoretical results from the literature concerning the interactions between metals and oxides (TiO 2, SrTiO 3, Al 2O 3, MgO, SiO 2, etc.). Chemical reactions, e.g., redox reactions, encapsulation reactions, and alloy formation reactions, are highlighted for metals in contact with mixed conducting oxides of TiO 2 and SrTiO 3. The dependence of the chemical interactions on the electronic structure of the contacting metal and oxide phases is demonstrated. This dependence originates from the interplay between interfacial space charge transfer and diffusion of ionic defects across interfaces. Interactions between metals and insulating oxides, such as Al 2O 3, MgO, and SiO 2, are strongly confined to the interfaces. Literature results are cited which discuss how the metal/oxide interactions vary with oxide surface properties (surface defects, surface termination, surface hydroxylation, etc.). However, on the surfaces of thin oxide films grown on conducting supports, the effect of the conducting substrates on metal-oxide interactions should be carefully considered. In the summary, we conclude how variations in the electronic structure of the metal/oxide junctions enable one to tune the interfacial reactivity and, furthermore, control the macroscopic properties of the interfaces. This includes strong metal-support interactions (SMSI), catalytic performance, electrical, and mechanical properties.

Fu, Qiang; Wagner, Thomas

2007-11-01

75

A characterization study of a hydroxylated polycrystalline tin oxide surface  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

76

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

E-print Network

stable compound of rutile TiO, when the oxygen concentration reaches a critical value. Therefore, subsequent thermal residual stresses develop due to the coefficient of therinal expansion mismatch between the matrix and the oxide. In addition, growth... on the surface of titanium showed that the scale primarily consists of TiO, in the rutile form, although there are diverse explanations of the oxidation kinetics (Wagner, 1951, Kofstad, 1966). Wagner describes a simple example of oxidation as a reaction...

Ma, Xinzheng

2012-06-07

77

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

78

Thermostimulated surface segregation in complex ferroelectric oxides  

Microsoft Academic Search

Thermostimulated surface segregation of intrinsic elements is studied in BaTiO3, SrTiO3, PbTiO3, PbFe1\\/2Nb1\\/2O3, Pb5Ge3O11, LiNbO3, KNbO3, Gd2Mo4O12, Bi4Ti3O12. The surface composition in terms of temperature, levels of reversible and irreversible segregation, the segregating cations were determined by the in situ Auger electron spectroscopy technique.

Yu. Y. A. Tomashpolsky

1989-01-01

79

The interaction of uranium metal with nitrogen oxides: The formation of an oxynitride surface layer  

Microsoft Academic Search

The interaction of nitric oxide, nitrogen dioxide and nitrous oxide with a polycrystalline uranium surface has been investigated at 298K. The surface composition and electronic structure of the developing oxide films were studied using X-ray and ultraviolet photoelectron spectroscopy. Nitrous oxide adsorbs dissociatively leaving only oxygen adsorbed on the uranium surface. Nitric oxide and nitrogen dioxide also adsorb dissociatively but

Albert F. Carley; Paul Nevitt; Paul Roussel

2008-01-01

80

Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

81

Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces.  

PubMed

We investigated the tribological interaction between polytetrafluoroethylene (PTFE) and silicon oxide surfaces. A simple rig was designed to bring about a friction between the surfaces via sliding a piece of PTFE on a thermally oxidized silicon wafer specimen. A very mild inclination (?0.5°) along the sliding motion was also employed in order to monitor the tribological interaction in a gradual manner as a function of increasing contact force. Additionally, some patterns were sketched on the silicon oxide surface using the PTFE tip to investigate changes produced in the hydrophobicity of the surface, where the approximate water contact angle was 45° before the transfer. The nature of the transferred materials was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS results revealed that PTFE was faithfully transferred onto the silicon oxide surface upon even at the slightest contact and SEM images demonstrated that stable morphological changes could be imparted onto the surface. The minimum apparent contact pressure to realize the PTFE transfer is estimated as 5 kPa, much lower than reported previously. Stability of the patterns imparted towards many chemical washing processes lead us to postulate that the interaction is most likely to be chemical. Contact angle measurements, which were carried out to characterize and monitor the hydrophobicity of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO2 surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained. PMID:25362327

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

2014-10-28

82

Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces  

NASA Astrophysics Data System (ADS)

We investigated the tribological interaction between polytetrafluoroethylene (PTFE) and silicon oxide surfaces. A simple rig was designed to bring about a friction between the surfaces via sliding a piece of PTFE on a thermally oxidized silicon wafer specimen. A very mild inclination (˜0.5°) along the sliding motion was also employed in order to monitor the tribological interaction in a gradual manner as a function of increasing contact force. Additionally, some patterns were sketched on the silicon oxide surface using the PTFE tip to investigate changes produced in the hydrophobicity of the surface, where the approximate water contact angle was 45° before the transfer. The nature of the transferred materials was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS results revealed that PTFE was faithfully transferred onto the silicon oxide surface upon even at the slightest contact and SEM images demonstrated that stable morphological changes could be imparted onto the surface. The minimum apparent contact pressure to realize the PTFE transfer is estimated as 5 kPa, much lower than reported previously. Stability of the patterns imparted towards many chemical washing processes lead us to postulate that the interaction is most likely to be chemical. Contact angle measurements, which were carried out to characterize and monitor the hydrophobicity of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO2 surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained.

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

2014-10-01

83

A method of measuring heat fluxes across nickel surfaces using the metal oxide on the surface  

Microsoft Academic Search

The feasibility of using the semiconducting oxide film on a metal surface to measure the heat flux through that surface and to measure the temperature of the surface has been demonstrated for nickel. The output compares favourably with other available heat flux meters.

P L Weickhardt; I M Ritchie; R J Batterham; D G Wood

1969-01-01

84

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

85

A computational study of the mechanism of CO oxidation by a ceria supported surface rhodium oxide layer.  

PubMed

A mechanism of CO oxidation by a thin surface oxide of Rh supported on ceria is proposed: CO is oxidized by the Rh-oxide film, which is subsequently reoxidized by a ceria surface O atom. The proposed mechanism is supported by in situ Raman spectroscopic investigations. PMID:23549301

Song, Weiyu; Jansen, Antonius P J; Degirmenci, Volkan; Ligthart, D A J Michel; Hensen, Emiel J M

2013-05-10

86

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

87

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

SciTech Connect

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

Heller, E.J.; Jonsson, H.

1992-12-31

88

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...

89

Surface oxide growth on platinum electrode in aqueous trifluoromethanesulfonic acid  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

90

Oxidative nanopatterning of titanium generates mesoporous surfaces with antimicrobial properties  

PubMed Central

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

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

2014-01-01

91

Introduction: Surface Chemistry of Oxides Understanding the surface chemistry of oxide materials  

E-print Network

, sorbents, and solid reactants. Thin films of oxides must be designed and grown for everything from medical devices, reflective and protective coatings, optical, electro-optic and opto-electric devices, and adhesives. The synthesis, stabilization, and utilization of oxide-based composite materials

Campbell, Charles T.

92

Surface nature of nanoparticle gold\\/iron oxide aerogel catalysts  

Microsoft Academic Search

The aerogel catalysts investigated are constituted by two chemically different nanoparticle systems consisting of the gold phase and the iron oxide support. High-resolution transmission electronic microscopy (HRTEM) showed an increased surface roughness for aerogel particles with higher gold loading. X-ray photoelectron spectroscopy (XPS) revealed increases in the surface coverage of hydroxyl groups and the Fe2+\\/Fe3+ ratio due to the addition

Chien-Tsung Wang; Shih-Hung Ro

2006-01-01

93

Ellipsometric study of anodic oxide films formed on niobium surfaces  

Microsoft Academic Search

.   Anodic oxide films formed potentiostatically on niobium surfaces, from open circuit potential (OCP) to 10 V, were studied\\u000a by performing in situ and ex situ ellipsometric measurements. The kinetics of the film thickness growth in 1 M H2SO4 and complex indices of refraction of these films were determined. A strong influence of the surface preparation conditions\\u000a on the complex refractive indices

Irena Lj. Arsova; Abdurauf R. Prusi; Ljubomir D. Arsov

2003-01-01

94

Design of oxide electrodes with large surface area  

Microsoft Academic Search

In order to design Ru-based oxide-coated catalyst electrodes with a large surface area, the following five methods were evaluated and the electrochemically active surface area of the electrodes were compared. (1) The addition of sodium carbonate to an alcoholic dipping solution for a dip-coated RuO2\\/Ti electrode; (2) the preparation of RuO2–MOx (M, dopant metal)\\/Ti electrodes by dip-coating method; (3) the

Y Takasu; Y Murakami

2000-01-01

95

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

96

Samarium- and ytterbium-promoted oxidation of silicon and gallium arsenide surfaces  

SciTech Connect

A method is described for promoting oxidation of a silicon or gallium arsenide surface comprising: depositing a ytterbium overlayer on the silicon or gallium arsenide surface prior to the oxidation of the surface.

Franciosi, A.

1989-02-21

97

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

98

Emerging applications of liquid metals featuring surface oxides.  

PubMed

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

Dickey, Michael D

2014-11-12

99

Emerging Applications of Liquid Metals Featuring Surface Oxides  

PubMed Central

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

2014-01-01

100

Is Silica Really an Anomalous Oxide? Surface Acidity and Aqueous  

E-print Network

of silicaonthesurfaceacidityversusaqueousaciditycorrelation developed for metal oxides, by considering the solvation energy change in the protonation reaction implemented through the dielectric constant (1/ k) and the electrostatic energy change through the Pauling acidity mainly by reflecting the nature of water-surface interactions. Solids with large values of k

Sahai, Nita

101

First Principles Studies of Water and Ice on Oxide Surfaces  

E-print Network

the fundamental properties of water adsorption, dissociation, and proton transfer on oxide surfaces. These studies reveal that the water adsorption energy and the tendency to dissociate both increase as one moves down transfer within clusters of just two water molecules, made possible by facile dissociation

Alavi, Ali

102

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

103

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

104

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

105

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

PubMed

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

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

2014-09-30

106

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

107

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

SciTech Connect

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

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

2002-07-01

108

Role of oxidation on surface conductance of the topological insulator Bi2Te2Se  

NASA Astrophysics Data System (ADS)

We investigated the effect of surface oxides on charge transport properties in a topological insulator (Bi2Te2Se) using conductive probe atomic force microscopy in an ultrahigh vacuum environment. Uniform distribution of the measured friction and current were observed over a single quintuple layer terrace after exposure to the ambient environment, which is an indication of uniform surface oxide coverage. An oxide-free topological insulator surface was exposed using tip-induced etching. By comparing surface conduction on a fresh surface versus a surface exposed to air, we observed a minor change in resistance when surface oxide was present. The current density varied with applied load on the oxidized surface, which implies that the topological surface states respond to tip-induced pressure even though surface oxide is present. From these results, we conclude that surface oxidation in air has a negligible effect on surface conductance in topological insulators.

Hwang, Jin Heui; Park, Joonbum; Kwon, Sangku; Kim, Jun Sung; Park, Jeong Young

2014-12-01

109

Vanadium surface oxides on Pd(111):??A structural analysis  

NASA Astrophysics Data System (ADS)

Scanning tunneling microscopy studies of vanadium oxides grown on Pd(111) show interesting structures especially in the low-coverage region. Evaporation of V in an oxygen background at elevated sample temperature (250 °C) results in the formation of a nonperiodic honeycomb-like structure growing from the steps, which starts to transform into an ordered phase at a vanadium coverage of ?0.2 ML (monolayer). At 0.31 ML the entire surface is covered by this well-ordered open (4×4) structure. Annealing this structure in H2 atmosphere transforms the phase into a V2O3 surface oxide with (2×2) periodicity, whose optimal coverage is reached at 0.5 ML vanadium. Models for both ordered structures have been suggested before on the basis of ab initio density-functional theory (DFT) calculations and molecular-dynamics simulations and these models are now unambiguously confirmed by quantitative low-energy electron-diffraction (LEED) analyses. In the (4×4) phase, the V atoms are surrounded by four oxygen atoms in an unusual tetrahedral coordination leading to a V5O14 stoichiometry. This tetrahedral coordination allows the oxide to adopt open loosely packed two-dimensional (2D) and 1D structures, which are stabilized by the surface-oxide interface energy. Furthermore, it is shown that state of the art DFT calculations can indeed predict complex structures exactly as well as that modern quantitative LEED is capable of dealing with very large unit cells.

Klein, C.; Kresse, G.; Surnev, S.; Netzer, F. P.; Schmid, M.; Varga, P.

2003-12-01

110

Immobilization of antibodies onto gold and titanium oxide surfaces  

NASA Astrophysics Data System (ADS)

The immobilization of antibodies onto surfaces by means of a reactive polymer has been studied. Two types of surfaces, gold and titanium oxide, were investigated. After modification with a suitable reagent bearing amino group, these surfaces are able to link covalently the reactive polymer through its N-hydroxysuccinimide carbonate functions. After polymer immobilization, a reaction between antibody and the remaining reactive sites on the polymer can take palce. This permits a covalent binding of biomolecules to the surface. The resulting biosensor is stable and specific. Another approach has been used for immobilization of antibodies: it involves a modification of the polymer with sulfonate groups and fixation of tetravalent metal ions. The resulting biosensor can recognize specifically the corresponding antigen and the regeneration of the surface between polymer and antibody layers is possible.

Millot, Marie-Claude; Martin, Francoise; Omont, Juliette; Sebille, Bernard; Levy, Yves

1995-09-01

111

Adsorption of phosphonic and ethylphosphonic acid on aluminum oxide surfaces  

NASA Astrophysics Data System (ADS)

Phosphonic acid and ethylphosphonic acid chemisorbed on aluminum oxide surfaces have been investigated using a density-functional based tight-binding method. We have in particular focused on hydroxylated surface models based on corundum ?-AlO (0 0 0 1), bayerite ?-Al(OH) (0 0 1) and boehmite ?-AlOOH (0 1 0). On these we have studied monodentate, bidentate and tridentate adsorption of the acids on all possible adsorption sites on the surfaces considering different surface coverages. By comparing the energies of the adsorption complexes we determined the favored adsorption sites for each coordination mode and surface structure. We found that the preference of an adsorption site is strongly influenced by its geometry and the regioselectivity increases when going from mono- to tridentate adsorption complexes. Moreover, the ethyl chain has no influence on the selection of the preferred adsorption sites.

Luschtinetz, Regina; Oliveira, Augusto F.; Frenzel, Johannes; Joswig, Jan-Ole; Seifert, Gotthard; Duarte, Helio A.

2008-04-01

112

Hydrogen passivation and ozone oxidation of silicon surface  

SciTech Connect

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

Kurokawa, Akira; Nakamura, Ken; Ichimura, Shingo [Electrotechnical Lab., Tsukuba (Japan)

1998-12-31

113

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

E-print Network

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

Sibener, Steven

114

The effect of surface treatment on the oxidation of ferritic stainless steels used for solid oxide fuel cell interconnects  

Microsoft Academic Search

Ferritic stainless steels are candidate interconnect materials for solid oxide fuel cells (SOFC); however, the oxidation resistance of commercial stainless steels within the operating temperature range of 700–800°C is not adequate. A relatively thick, poorly conducting oxide layer forms on the surface of the stainless steel interconnect, decreasing cell performance. One way of modifying the oxidation behaviour of an alloy

L. Cooper; S. Benhaddad; A. Wood; D. G. Ivey

2008-01-01

115

Controllably Interfacing with Metal: A Strategy for Enhancing CO Oxidation on Oxide Catalysts by Surface Polarization.  

PubMed

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

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

2014-10-22

116

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

Microsoft Academic Search

For the semiconductor SiC to fulfill its potential as an electronic material, methods must be developed to produce insulating surface oxide layers in a reproducible fashion. Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and x ray photoelectron spectroscopy (XPS) were used to investigate the oxidation of single crystal alpha-SiC over a wide temperature and O2 pressure range. The

J. M. Powers

1991-01-01

117

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

118

Observations of Electron Irradiation Effects at Transition Metal Oxide Surfaces.  

NASA Astrophysics Data System (ADS)

In this dissertation the effects of electron irradiation on several maximally-valent transition-metal oxides have been investigated using a combination of surface profile imaging, selected-area-electron diffraction, optical diffractograms, and electron-energy-loss spectroscopy. It was found that the surfaces of TiO_2, Nb _2O_5, V_2 O_5 and Ti_2 Nb_{10}O _{29} were reduced to the corresponding binary oxide phase inside a 400keV high-resolution electron microscope during observation at high magnification and high current density (5-50A/cm^2). These reduced surface phases, which are all based on cubic rock -salt structures, grow with a well-defined three-dimensional epitaxial relationship with the bulk oxide. Certain structural features of the epitaxy were found to be common to the oxides studied and computer-drawn models of the crystalline structures were used to gain insight into the atomic rearrangements which took place during the monoxide growth. In the case of WO_3, for which no stable monoxide phase has been reported, the striking similarity in the epitaxial growth of a surface phase led to the proposal of a novel monoxide phase. The metallic conductivity of each of these monoxide phases was considered to be significant in terms of the mechanism which is proposed to initiate the electron-stimulated-desorption of oxygen from the original oxides. Evidence for a current density threshold for the accumulation of the monoxide phase and observation of recrystallization below this threshold are reported. In contrast, in response to extremely high-current density irradiation (10 ^3-10^4A/cm ^2), the surfaces of these oxides developed sputter pits and were reduced beyond the monoxide phase. These observations were repeated for TiO_2 in a ultra-high-vacuum microscope. Secondary electron images, high-angle annular dark-field images and EELS confirmed that the improved vacuum did not affect substantially the beam-induced reactions.

McCartney, Martha Rogers

119

Water-Mediated Proton Hopping on an Iron Oxide Surface  

SciTech Connect

The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H3O+-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO2(110), where water dissociation is a key step in proton diffusion.

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

2012-05-18

120

Water-mediated proton hopping on an iron oxide surface.  

PubMed

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

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

2012-05-18

121

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

122

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

NASA Astrophysics Data System (ADS)

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

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

2001-11-01

123

Photocurrent spectroscopy of Ge nanoclusters grown on oxidized silicon surface  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

124

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

125

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

NASA Astrophysics Data System (ADS)

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(IV) 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.

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

2005-12-01

126

Inhibition of Sulfide Mineral Oxidation by Surface Coating Agents: Batch  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

127

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

Microsoft Academic Search

In this study, the design of a novel optical sensor that comprises surface plasmon resonance sensing chip and zinc oxide nano-film was proposed for the detection of nitric oxide gas. The electrical and optical properties of zinc oxide film vary in the presence of nitric oxide. This effect was utilized to prepare biochemical sensors with transduction based on surface plasmon

Wei-Yi Fenga; Nan-Fu Chiub; Hui-Hsin Lub; Hsueh-Ching Shihc; Dongfang Yangd; Chii-Wann Lina

2008-01-01

128

Mobility of Water on Oxide Surfaces Studied by QENS  

SciTech Connect

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

Mamontov, Eugene [ORNL

2007-01-01

129

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

SciTech Connect

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

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

2004-06-20

130

Thiolsulfinates/Thiolsulfonates  formation:  X-ray photoelectron spectroscopy (XPS) of oxidized thiols on flat surfaces.  

E-print Network

?? In order  to  find  another way to fix peptides      on      surfaces      we      study      the      chemical      and      electro      oxidation       of      a      Silicon      flat      surface  … (more)

Lebrun, Delphine

2010-01-01

131

Shape and surface structure of gold nanoparticles under oxidizing conditions  

NASA Astrophysics Data System (ADS)

We perform density-functional theory calculations to investigate the adsorption of oxygen at the Au(100) and Au(110) surfaces. For the clean surfaces, we find that the added-row (5×1)/Au(100) structure is more stable than the unreconstructed (1×1)/Au(100) surface and the missing-row (2×1)/Au(110) structure is more stable than the unreconstructed (1×1)/Au(110) surface, which is consistent with experimental results. For oxygen adsorption on Au(100), the most stable structure is predicted to be a low coverage ( ˜0.1 ML) on the added-row reconstructed surface, while for adsorption on Au(110), the most stable configuration of those considered is a (2×1) missing-row structure with 1 ML coverage of oxygen. From these results, together with those of our previous investigations into the O/Au(111) system, we use the Wulff construction to predict the nanoparticle shape as a function of oxygen chemical potential, which we correlate with pressure (p) and temperature (T) . For low values of the oxygen chemical potential ( <-0.6eV , corresponding, e.g., to p=1atm and T>600K ), the nanoparticle consists of clean (111) facets. For slightly higher values, clean (111) facets still dominate but there are small regions of (110) facets, which are covered with the (2×1)-2O reconstruction. With progressively increasing values of the chemical potential (e.g., from -0.4to-0.18eV , corresponding to, e.g., p=1atm and T=420-200K ), the (111) facets become covered with a thin oxide-like structure, and the (110) regions with the (2×1)-2O/(110) surface reconstruction become larger and finally dominate. These findings indicate that for low temperature oxidation reactions, where gold nanoparticles have been reported to be surprisingly active, such thin “surface-oxide-like” structures on the (111) and (110) surfaces could possibly play a role in the behavior of the nanogold catalysts.

Shi, Hongqing; Stampfl, Catherine

2008-03-01

132

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

133

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

NASA Astrophysics Data System (ADS)

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

Akhiani, Hamed; Szpunar, Jerzy A.

2013-11-01

134

Photoinduced oxidation of the insecticide phenothrin on soil surfaces.  

PubMed

Photodegradation profiles of the pyrethroid insecticide phenothrin on a moistened U.S. soil thin layer was investigated by using its predominant component, the 1R-trans-isomer (I), under continuous exposure to light at >290 nm from a xenon arc lamp. Its degradation was moderately accelerated by irradiation with half-lives of 5.7-5.9 days (dark control 21-24 days), mainly via successive oxidation of the 2-methylprop-1-enyl group and ester cleavage followed by mineralization to carbon dioxide. Spectroscopic and cochromatographic analyses showed that the major degradates were the alcohol and ketone derivatives of I formed via photoinduced oxidation of the 2-methylprop-1-enyl group by singlet oxygen. The photoinduced generation of singlet oxygen in/on the soil surface was confirmed by using chemical trapping reactions together with ESR spectroscopy. PMID:21877720

Suzuki, Yusuke; Lopez, Andrea; Ponte, Marian; Fujisawa, Takuo; Ruzo, Luis O; Katagi, Toshiyuki

2011-09-28

135

Effect of Surface Roughness on the Oxidation Behavior of the Ni-Base Superalloy ME3  

Microsoft Academic Search

Ni-base superalloys are used in applications, such as jet aircraft engines and power production facilities that require excellent\\u000a elevated temperature oxidation resistance. This present work evaluated the effect of surface roughness on the oxidation behavior\\u000a of the Ni-base superalloy ME3. Isothermal oxidation tests were performed in air at different times to investigate the oxide\\u000a growth kinetics. The surface oxides were

Jeffrey L. Evans

2010-01-01

136

Effect of Surface Roughness on the Oxidation Behavior of the Ni-Base Superalloy ME3  

Microsoft Academic Search

Ni-base superalloys are used in applications, such as jet aircraft engines and power production facilities that require excellent elevated temperature oxidation resistance. This present work evaluated the effect of surface roughness on the oxidation behavior of the Ni-base superalloy ME3. Isothermal oxidation tests were performed in air at different times to investigate the oxide growth kinetics. The surface oxides were

Jeffrey L. Evans

2010-01-01

137

Surface and bulk electronic structure of bixbyite transparent conducting oxides  

NASA Astrophysics Data System (ADS)

Subsolidus phase relationships within the ZnO-In2O 3-SnO2 system at 1275°C were established by conventional solid state reaction methods. No new compounds or structures were observed within the ternary diagram. Equilibrium in the ZnO-corner, between the homologous compounds and the spinel phase, was found difficult to achieve. This problem was overcome by utilizing mixtures of the k=11 (ZnO)11In2 O3 homologous series compound plus spinels with high indium content. The defect chemistry and surface electronic properties of the zinc- and tin- co-doped In2O3, In(2-2 x)SnxZn xO3 (x=0-0.40) or ZITO, were investigated. The ZITO material is an n-type conductor and carriers are generated via an inherent cation off-stoichiometry of tin donors to zinc acceptors, i.e., n=Sn•In -Z? In > 0. pO2-dependent conductivity and thermopower measurements completed on a bulk specimen of the terminal ZITO composition showed the presence of the Frank and Kostlin1 neutral defect cluster, 2Sn•In Öi x, which is also prevalent in ITO. Photoelectron spectroscopy studies were made of the surfaces of bulk ceramic pellet specimens of ZITO. Small variations were seen in the Fermi level position and core level binding energies upon oxidation and reduction. The surfaces of the bulk specimens were rich in zinc as well as oxygen. The 'surface oxygen enrichment' was observed as a shoulder on the high binding energy side of the O1s core level emission. Sputter depth-profiling showed that the features characteristic of the 'surface oxygen enrichment' are mostly removed after one minute of sputtering. In addition, no variation in the Fermi level position was seen upon going from a significantly zinc-rich to a slightly tin-rich surface. In situ thin film deposition and annealing of ZITO films were carried out, and analyzed by XPS/UPS without breaking vacuum. Deposition under different oxygen contents leads to differences in the Fermi level position and core level binding energies consistent with changes in the concentration of Frank and Kostlin1 neutral defect clusters, 2Sn•In Oï x, affecting the carrier content in ZITO (i.e., reducing conditions result in high EF, oxidizing conditions result in low EF). In addition, significant reversible changes in the Fermi level and core level binding energies of 300-600 meV upon oxidation and reduction annealing were seen. These changes were attributed to changes in the concentration of the Frank and Kostlin1 neutral defect cluster, which affects the carrier content. Ex situ annealing of a previously in situ deposited film in air for 48 hours at 450°C created the 'surface oxygen enrichment' observed on bulk ceramic specimens. Subsequent in situ oxidation and reduction annealings no longer resulted in the large variations of the Fermi level or core level binding energies that were seen for the same treatments completed on in situ deposited films. It was suggested that the surface oxygen enrichment inhibits the oxygen exchange necessary for changes in the Fermi level position in ZITO.

Harvey, Steven Paul

138

Energetic Surface Smoothing of Complex Metal-Oxide Thin Films  

SciTech Connect

A novel energetic smoothing mechanism in the growth of complex metal-oxide thin films is reported from in situ kinetic studies of pulsed laser deposition of La{sub 1-x}Sr{sub x}MnO{sub 3} on SrTiO{sub 3}, using x-ray reflectivity. Below 50% monolayer coverage, prompt insertion of energetic impinging species into small-diameter islands causes them to break up to form daughter islands. This smoothing mechanism therefore inhibits the formation of large-diameter 2D islands and the seeding of 3D growth. Above 50% coverage, islands begin to coalesce and their breakup is thereby suppressed. The energy of the incident flux is instead rechanneled into enhanced surface diffusion, which leads to an increase in the effective surface temperature of {delta}T{approx_equal}500 K. These results have important implications on optimal conditions for nanoscale device fabrication using these materials.

Willmott, P.R.; Herger, R.; Schlepuetz, C.M.; Martoccia, D.; Patterson, B.D. [Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen (Switzerland)

2006-05-05

139

Energetic surface smoothing of complex metal-oxide thin films.  

PubMed

A novel energetic smoothing mechanism in the growth of complex metal-oxide thin films is reported from in situ kinetic studies of pulsed laser deposition of on , using x-ray reflectivity. Below 50% monolayer coverage, prompt insertion of energetic impinging species into small-diameter islands causes them to break up to form daughter islands. This smoothing mechanism therefore inhibits the formation of large-diameter 2D islands and the seeding of 3D growth. Above 50% coverage, islands begin to coalesce and their breakup is thereby suppressed. The energy of the incident flux is instead rechanneled into enhanced surface diffusion, which leads to an increase in the effective surface temperature of DeltaT approximately 500 K. These results have important implications on optimal conditions for nanoscale device fabrication using these materials. PMID:16712314

Willmott, P R; Herger, R; Schlepütz, C M; Martoccia, D; Patterson, B D

2006-05-01

140

Altering Iron Oxide Nanoparticle Surface Properties Induce Cortical Neuron Cytotoxicity  

PubMed Central

Superparamagnetic iron oxide nanoparticles, with diameters in the range of a few tens of nanometers, display the ability to cross the blood-brain barrier and are envisioned as diagnostic and therapeutic tools in neuro-medicine. However, despite the numerous applications being explored, insufficient information is available on their potential toxic effect on neurons. While iron oxide has been shown to pose a decreased risk of toxicity, surface functionalization, often employed for targeted delivery, can significantly alter the biological response. This aspect is addressed in the present study, which investigates the response of primary cortical neurons to iron oxide nanoparticles with coatings frequently used in biomedical applications: aminosilane, dextran, and polydimethylamine. Prior to administering the particles to neuronal cultures, each particle type was thoroughly characterized to assess the (1) size of individual nanoparticles, (2) concentration of the particles in solution and (3) agglomeration size and morphology. Culture results show that polydimethylamine functionalized nanoparticles induce cell death at all concentrations tested by swift and complete removal of the plasma membrane. Aminosilane coated particles affected metabolic activity only at higher concentrations while leaving the membrane intact and dextran-coated nanoparticles partially altered viability at higher concentrations. These findings suggest that nanoparticle characterization and primary cell-based cytotoxicity evaluation should be completed prior to applying nanomaterials to the nervous system. PMID:22111864

Rivet, Christopher J.; Yuan, Yuan; Borca-Tasciuc, Diana-Andra; Gilbert, Ryan J.

2014-01-01

141

Ceramic oxides: Surfaces and amorphous/crystalline interfaces  

NASA Astrophysics Data System (ADS)

Model studies have been carried out to further the basic understanding of ceramic oxide surfaces and the interface between ceramic oxides and amorphous films. Boundary-migration studies using model geometries of alumina and rutile bicrystals have been carried out. In the case of the rutile boundary, migration proceeds faster near the surface, while in the alumina bicrystal migration proceeds faster away from the boundary. A solution/reprecipitation mechanism is proposed for the alumina case, while a mechanism similar to diffusion-induced grain boundary migration (DIGM) is proposed for the rutile case. Three distinct faceting behaviors for the m-plane of alumina have been identified. The low-energy configuration was observed within a glass droplet whereas higher-energy configurations were observed outside dewet droplets and within a migrating grain boundary. These high-energy configurations are due to kinetic limitations. A method for monitoring the evolution of faceting over the course of several heat treatments has been developed which uses a combination of visible-light microscopy (VLM) and atomic-force microscopy (AFM) with the aid of fiducial marks (indentations) as reference markers. Grooves at migrating grain boundaries in high-purity alumina have been studied using a combination of VLM, AFM, and transmission electron microscopy (TEM) through a progression of heat treatments at 1650°C. The partial angles of grooves that developed at migrating grain boundaries were found to be asymmetric compared with those that developed at stationary boundaries. The wetting behavior of an amorphous SiO2 film on single-crystal substrates of TiO2 has been extensively studied. A model involving the initiation of an instability due to surface-tension gradients is proposed as the mechanism for the complex patterns observed. It is proposed that the surface-tension gradients are caused by the changing composition of the SiO 2 thin film due to dissolution of the TiO2 substrate into the film. Surfaces of ceria (CeO2) particles have been studied by electron energy-loss spectroscopy. All the ceria particles analyzed contained Ce 3+ at the surface. Cation impurities were enriched at the surface of the particles. Time series investigations indicate that fluorine substitutes on the oxygen sublattice and is charged balanced by some cerium changing from Ce4+ to Ce3+.

Gilliss, Shelley Rae

142

Uranyl and Arsenate Cosorption on Aluminum Oxide Surface  

SciTech Connect

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{sub 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 tr{umlt o}gerite. 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, Y.; Reeder, R

2009-01-01

143

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

SciTech Connect

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

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

2013-05-27

144

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

SciTech Connect

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

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

2006-12-18

145

Effect of surface physics of metal oxides on the ability to form metallic nanowires  

NASA Astrophysics Data System (ADS)

Through the control of surface physics of oxide films, nanowires of various metals can be readily grown on the surface of oxide films without templates and surfactants. To clarify how the characteristics of oxides affect the formation of metallic nanowires, this report investigated the influence of the surface physical characteristics, including morphological, electrical, optical and hydrophilic properties of the metal oxide substrates (TiO2, CeO2, and indium tin oxide), on the yield of Ag and Pt nanowires. In addition to the surface roughness, photo-induced defects were suggested to be the key factor dominating the number of nucleation sites and thus the population of nanowires.

Song, Jenn-Ming; Chen, Shih-Yun; Shen, Yu-Lin; Tsai, Chi-Hang; Feng, Shih-Wei; Tung, Hsien-Tse; Chen, In-Gann

2013-11-01

146

Surface oxidation of liquid Sn Alexei Grigoriev a,*, Oleg Shpyrko b  

E-print Network

Surface oxidation of liquid Sn Alexei Grigoriev a,*, Oleg Shpyrko b , Christoph Steimer a , Peter S-ray scattering study that reveals oxidation kinetics and formation of a previously unreported crystalline phase a rough solid Sn oxide growsover the liquid metal surface. Once the activation pressure has been

Pershan, Peter S.

147

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

Microsoft Academic Search

Marketed stents are manufactured from various metals and passivated with different degrees of surface oxidation. The functional surface oxides on the degree of antithrombotic potential were explored through a canine femoral extracorporeal circuit model. Related properties of these oxide films were studied by open-circuit potential, current density detected at open-circuit potential, the electrochemical impedance spectroscopy, transmission electron microscopy, Auger spectroscopy

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

2003-01-01

148

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

149

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells  

PubMed Central

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

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

2012-01-01

150

Surface Science Letters Initial oxidation stages of hydrogen-and styrene-terminated Si(100) surfaces: A  

E-print Network

Surface Science Letters Initial oxidation stages of hydrogen- and styrene-terminated Si(100- and styrene-terminated Si(100)-2Ã?1 films in O2 atmosphere at 500 K using molecular dynamics (MD) simulations of these reactions leads to increased amorphization of the surface as the oxidation proceeds. In the case of styrene

Ciobanu, Cristian

151

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

SciTech Connect

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

Powers, J.M.

1991-11-01

152

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.

153

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

E-print Network

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

Hilliard, Casie Renee

2013-12-09

154

Activation of carbon dioxide on metal and metal oxide surfaces  

SciTech Connect

The environmental concern about the impact of CO{sub 2} has grown recently due to its rapidly increasing concentration. Deforestation strongly affects the natural reduction of CO{sub 2} by water into carbohydrates by photosynthesis. Industrial utilization of CO{sub 2} by heterogeneous catalytic reactions can be one of the effective ways to cut the CO{sub 2} level. The first step in catalytic reaction of CO{sub 2} is the adsorption. The objective of this study is to investigate the adsorption of CO{sub 2} on the Rh/Al{sub 2}O{sub 3} surfaces. Rh is selected for this study because of its unique activity to catalyze a number of CO{sub 2} related reactions. In situ infrared results show that CO{sub 2} adsorbed on the alumina oxide support as bidentate carbonate and non-coordinated carbon which are the dominant species during the CO{sub 2} adsorption.

Tan, C.D.; Chuang, S.S.C. [Univ. of Akron, OH (United States). Dept. of Chemical Engineering

1995-12-31

155

Surface Oxide Film Entrainment Mechanisms in Shape Casting Running Systems  

NASA Astrophysics Data System (ADS)

During the transient phase of filling a casting running system, surface turbulence can cause the entrainment of oxide films into the bulk liquid. Research has shown that these are detrimental to the material’s integrity. Common mechanisms for this entrainment include returning waves, arising during filling of the runner bar, and plunging jets, found when pouring into a basin. One of these, the returning wave, has been studied in greater depth, using real-time X-ray and process modeling techniques alongside the application of physical principals. It has been concluded that when developed, returning waves cannot attain the more stable and less entraining tranquil flow regime desirable in the running system of castings.

Reilly, C.; Green, N. R.; Jolly, M. R.

2009-12-01

156

Surface plasmon enhancement of broadband photoluminescence emission from graphene oxide  

NASA Astrophysics Data System (ADS)

The photoluminescence (PL) emission studies of both graphene oxide (GO) and partially reduced graphene oxide (rGO) have been investigated. It has been observed that GO has broadband emission from the green to near infrared range and upon reduction rGO shows blue PL emission. The broadband PL emission is due to the recombination of the electron-hole pair in the sp2 domain embedded within the sp3 matrix. The broadband PL emission also suggests the existence of various sizes of the sp2 domain within the same matrix. Furthermore, PL emission from GO in the presence of an Au metal thin film has been investigated. It has been observed that the entire broadband emission from GO in the green to near infrared wavelength region is enhanced significantly at room temperature. The Au-GO interface exhibits surface plasmon resonance in the visible wavelength region and is responsible for over 10 fold enhancement in the photoluminescence at ~2.36 eV. The electrical property measurements on the GO and rGO thin films suggested that the rGO exhibits significantly higher electrical conductivity compared to that of the GO thin film. Furthermore, the GO thin film exhibits semiconducting behaviour. These properties make the material quite suitable for fabrication of new generation photonic devices.

Neogi, A.; Karna, S.; Shah, R.; Phillipose, U.; Perez, J.; Shimada, R.; Wang, Z. M.

2014-09-01

157

Frequency-selective surface coupled metal-oxide-metal diodes  

NASA Astrophysics Data System (ADS)

Metal-Oxide-Metal diodes offer the possibility of directly rectifying infrared radiation. To be effective for sensing or energy harvesting they must be coupled to an antenna which produces intense fields at the diode. While antennas significantly increase the effective capture area of the MOM diode, it is still limited and maximizing the captured energy is still a challenging goal. In this work we investigate integrating MOM diodes with a slot antenna Frequency Selective Surface (FSS). This maximizes the electromagnetic capture area while minimizing the transmission line length which helps reduce losses because metal losses are much lower at DC than at infrared frequencies. Our design takes advantage of a single self-aligned patterning step using shadow evaporation. The structure is optimized at 10.6 µm to have less than 2% reflection (polarization sensitive) and simulations predict that 70% of the incident energy is dissipated into the oxide layer. Initial experimental results fabricated with e-beam lithography are presented and the diode coupled FSS is shown to produce a polarization sensitive unbiased DC short circuit current. This work is promising for both infrared sensing and imaging as well as direct conversion of thermal energy.

Kinzel, Edward C.; Brown, Robert L.; Ginn, James C.; Lail, Brian A.; Slovick, Brian A.; Boreman, Glenn D.

2013-06-01

158

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

159

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. PMID:24229051

2013-01-01

160

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

161

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

162

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

163

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

164

Abiotic formation of elemental selenium and role of iron oxide surfaces Yu-Wei Chen a  

E-print Network

Abiotic formation of elemental selenium and role of iron oxide surfaces Yu-Wei Chen a , Hoang: Elemental selenium Abiotic reduction Surface catalysis Laboratory simulation Lake sediments a b s t r a c

Belzile, Nelson

165

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

166

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

E-print Network

by Hydrous Manganese Oxide. Matthew Ginder-Vogel and Donald L. Sparks. University of Delaware, 152 Townsend(V)) by manganese(IV) oxide is an important reaction impacting the natural cycling of As. The aresenite species(III) on the surface of manganese oxides has been well characterized; however, the surface chemistry of the oxidation

Sparks, Donald L.

167

Energy distribution of surface acid sites of metal oxides  

SciTech Connect

The acid site strength distributions of {gamma}-Al{sub 2}O{sub 3}, BeO, Nb{sub 2}O{sub 5}, TiO{sub 2}, WO{sub 3}, and ZrO{sub 2} surfaces were evaluated starting from volumetric and calorimetric experimental data of ammonia adsorption collected at 80 and 150{degrees}C. A mathematical model was employed to describe the behavior of the adsorbate-adsorbent system. The model took into account a discrete inhomogeneity of the surface. A fitting procedure applied to both the isotherms and the integral heat curves of ammonia adsorption, at the two above temperatures, permitted the determination of the thermodynamic parameters characteristic of the different types of site. The number, n{sub max,i}, the adsorption equilibrium constant, b{sub i}, as well as a new parameter termed the {open_quotes}half-coverage temperature at unit pressure{close_quotes}, T{degrees}{sub 1/2,i}, of each type of acid site were obtained. All the oxides showed a significant amount of acid sites with ammonia enthalpy of adsorption {Delta}{sub a}H{sub i} at -40 kJ/mol corresponding to hydrogen-bonded ammonia. Three types of more energetic sites, with {Delta}{sub a}H{sub i} ranging from -280 to -160 kJ/mol, were found for {gamma}-Al{sub 2}O{sub 3}, Nb{sub 2}O{sub 5}, TiO{sub 2}, and ZrO{sub 2}. Sites with {Delta}{sub a}H{sub i} of -280 and-200 kJ/mol were found for BeO and WO{sub 3}. Mean molar adsorption entropies were also determined, and the values obtained are typical of immobile or localized adsorption. 26 refs., 10 figs., 2 tabs.

Carniti, P.; Gervasini, A. [Universita di Milano (Italy)] [Universita di Milano (Italy); Auroux, A. [Institut de Recherches sur la Catalyse, Villeurbanne (France)] [Institut de Recherches sur la Catalyse, Villeurbanne (France)

1994-12-01

168

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

169

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

E-print Network

for elemental semiconductors or metals. Local imperfections such as point or line defects, step edges focuses on two aspects of bulk-dependent processes, the high-temperature re-oxidation of reduced singleUnderstanding Metal Oxide Surfaces at the Atomic Scale: STM Investigations of Bulk-defect Dependent

Diebold, Ulrike

170

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

SciTech Connect

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

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

2006-08-23

171

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

SciTech Connect

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

Wu, S. X.; Liu, Y. J.; Xing, X. J.; Yu, X. L.; Xu, L. M.; Yu, Y. P.; Li, S. W. [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Zhongshan University, Guangzhou 510275 (China)

2008-03-15

172

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

E-print Network

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

Marks, Laurence D.

173

Generation of active oxygen species on solid surfaces. Opportunity for novel oxidation technologies over zeolites  

Microsoft Academic Search

Generation of surface oxygen species and their role in partial oxidation reactions catalyzed by metal oxides are discussed. Main attention is paid to a new concept related to a recent discovery of remarkable ability of Fe complexes stabilized in a ZSM-5 matrix to generate a new form of surface oxygen (?-oxygen) from N2O. At room temperature, ?-oxygen exhibits a high

Gennady I. Panov; Anthony K. Uriarte; Mikhail A. Rodkin; Vladimir I. Sobolev

1998-01-01

174

Atomistic simulations of surface segregation of defects in solid oxide electrolytes  

E-print Network

Atomistic simulations of surface segregation of defects in solid oxide electrolytes Hark B. Lee) are widely used electrolyte materials for solid oxide fuel cells (SOFCs) due to their high ionic conductiv transport of the electrolytes. A clear understanding of surface segregation will also shed light

Cai, Wei

175

Fluxing of protective oxide scales on superalloys via a thermal surface tension gradient  

Microsoft Academic Search

An oxide fluxing model involving continuous dissolution and reprecipitation of oxide scales via a thermal surface tension effect is postulated to explain hot corrosion of high teperature alloys and coatings in gas turbines. It is demonstrated that due to the existence of a thermal surface tension gradient, a molten alkali salt film condensed on a turbine vane or blade can

S. K. Lau; S. C. Singhal

1983-01-01

176

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

PubMed Central

Background Aluminum-made settings are widely used in healthcare, schools, public facilities and transit systems. Frequently-touched surfaces of those settings are likely to harbour bacteria and be a potential source of infection. One method to utilize the effectiveness of copper (Cu) in eliminating pathogens for these surfaces would be to coat the aluminum (Al) items with a Cu coating. However, such a combination of Cu and Al metals is susceptible to galvanic corrosion because of their different electrochemical potentials. Methods In this work, a new approach was proposed in which electrolytic plasma oxidation (EPO) of Al was used to form an oxide surface layer followed by electroplating of Cu metal on the top of the oxide layer. The oxide was designed to function as a corrosion protective and biocompatible layer, and the Cu in the form of dots was utilized as an antibacterial material. The antibacterial property enhanced by superhydrophilicity of the Cu-dotted oxide coating was evaluated. Results A superhydrophilic surface was successfully prepared using electrolytic plasma oxidation of aluminum (Al) followed by electroplating of copper (Cu) in a Cu-dotted form. Both Cu plate and Cu-dotted oxide surfaces had excellent antimicrobial activities against E. coli ATCC 25922, methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300 and vancomycin-resistant Enterococcus faecium (VRE) ATCC 51299. However, its Cu-dotted surface morphology allowed the Cu-dotted oxide surface to be more antibacterial than the smooth Cu plate surface. The enhanced antibacterial property was attributed to the superhydrophilic behaviour of the Cu-dotted oxide surface that allowed the bacteria to have a more effective killing contact with Cu due to spreading of the bacterial suspension media. Conclusion The superhydrophilic Cu-dotted oxide coating surface provided an effective method of controlling bacterial growth and survival on contact surfaces and thus reduces the risk of infection and spread of bacteria-related diseases particularly in moist or wet environments. PMID:20843373

2010-01-01

177

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

178

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

179

Surfactant-assisted growth of anodic nanoporous niobium oxide with a grained surface  

Microsoft Academic Search

Nanoporous niobium oxide film with a maximum thickness of 520nm was prepared by anodizing niobium in a mixture of 1wt% HF, 1M H3PO4, and a small amount of Sodium Dodecyl Sulfate (SDS) surfactant. The porosity of the anodic niobium oxide prepared without SDS is irregular with the surface of the oxide suggesting a grained surface pattern rather than an ordered

Jeong Eun Yoo; Jinsub Choi

2010-01-01

180

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

181

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

182

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

NASA Astrophysics Data System (ADS)

The availability of high-brilliance hard x-ray synchrotron radiation and the advent of novel photon counting area detectors have brought surface x-ray diffraction (SXRD) into a new era. It is now possible to record large numbers of structure factors with much improved reliability within reasonable beamtime durations. As a result, structural determination of the surfaces and interfaces of complex crystallographic systems and heterostructures has now become feasible, especially in conjunction with phase-retrieval methods. It is thereby hoped that detailed structural information will shed light on the unusual physical properties of these systems. Complex metal oxide systems investigated at the Materials Science beamline of the Swiss Light Source, including the surface of SrTiO3, the interface between LaAlO3 and SrTiO3, and the structure of YBa2Cu3O7 grown on NdGaO3, SrTiO3, and (LaSr)(AlTa)O3 will be presented as examples of what is now possible using SXRD.

Schlepü; tz, C. M.; Willmott, P. R.; Pauli, S. A.; Herger, R.; Martoccia, D.; Björck, M.; Kumah, D.; Clarke, R.; Yacoby, Y.

2009-01-01

183

Electron spectroscopy of single crystal and polycrystalline cerium oxide surfaces  

Microsoft Academic Search

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

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

1998-01-01

184

Influence of thermal oxidation on surface and thermo-mechanical properties of polyethylene  

Microsoft Academic Search

Blown low density polyethylene (LDPE) films added with oxo-biodegradable additive containing pro-oxidant were subjected to\\u000a thermo-oxidation in an oven at 70 °C for varying time periods. The changes in mechanical and surface properties were studied\\u000a using tensile strength, elongation at break, wettability, surface morphology using SEM, surface topology by AFM, functional\\u000a groups by FTIR spectroscopy, absorbance spectra by UV-Vis spectroscopy. The

Balasubramanian Suresh; S. Maruthamuthu; Alika Khare; N. Palanisamy; V. S. Muralidharan; R. Ragunathan; M. Kannan; K. Navaneetha Pandiyaraj

185

An STM study of the initial oxidation of single-crystalline zirconium surfaces  

NASA Astrophysics Data System (ADS)

The microstructural development of thin (thickness < 10 nm) oxide layers grown on Zr surfaces by thermal oxidation was investigated by in-vacuo STM and XPS. To this end, single-crystalline Zr(0001) and Zr(101¯0) surfaces were prepared under UHV conditions by a cyclic treatment of ion-sputtering and in-vacuo annealing steps and then exposed to dry O2(g) in the temperature range of 300-450 K (at pO2 = 1×10- 4 Pa). Oxidation proceeds by the fast formation of a dense arrangement of tiny oxide nuclei, which cover the entire Zr surface. The initial oxide cluster size is about 1.2 ± 0.1 nm. The transport processes on the oxidizing surface become promoted with increasing temperature and thereby the oxide clusters rearrange into bigger agglomerates with increasing oxidation time. At the same time, a long-range atomic order develops in the oxide overgrowths, as evidenced from the emergence of a bonding/non-bonding fine structure in the resolved oxide-film upper valence band, as measured in-situ by XPS.

Bakradze, Georgijs; Jeurgens, Lars P. H.; Mittemeijer, Eric J.

2012-05-01

186

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

187

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

188

Finite element modelling of surface roughness transfer and oxide scale micro deformation in metal manufacturing process  

NASA Astrophysics Data System (ADS)

In the paper, the micro deformation of oxide scale in hot strip rolling has been investigated with considering the friction effect. The finite element simulation of the micro deformation of oxide scale has been successfully conducted, and the calculated surface roughness is compared with the measured value, which shows a good agreement. A crystal plasticity finite element method (CPFEM) model was also successfully developed to analyse the surface roughness transfer during metal manufacturing. The simulation results show a good agreement with the experimental results in the flattening of surface asperity, and the surface roughness decreases significantly with an increase of reduction. This study also indicates that the lubrication can delay surface asperity flattening.

Jiang, Zhengyi; Wei, Dongbin; Li, Heijie

2013-05-01

189

Characterization of High Surface Area Zr-Ce (1:1) Mixed Oxide Prepared by a Microemulsion Method  

E-print Network

a surface redox reactivity higher than that of the CeO2 single oxide. Introduction Cerium oxide is a commonCharacterization of High Surface Area Zr-Ce (1:1) Mixed Oxide Prepared by a Microemulsion Method A oxide with ca. a 1:1 atomic ratio is prepared by a microemulsion method and studied by X-ray diffraction

190

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

PubMed

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

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

2014-11-01

191

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

E-print Network

.1.1. MgO and CaO 93 3.1.2. R-Al2O3 95 3.1.3. TiO2 (Rutile) 95 3.1.4. TiO2 (Anatase) 97 3.1.5. R-Fe2O3 97 3.4. Imperfections on Oxide Surfaces 91 2.4.1. Bulk Point Defects 91 2.4.2. Steps, Kinks, and Point Defects 92 3 of Clean Metal Oxide Surfaces 83 2.1. The Nature of Defects on Metal Oxide Surfaces 83 2.2. Overview of UHV

Goodman, Wayne

192

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

193

Surface modifications of iron oxide nanoparticles for biological applications  

E-print Network

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

Insin, Numpon

2011-01-01

194

Solid State, Surface and Catalytic Studies of Oxides  

SciTech Connect

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

Kung, H. H.

2004-11-23

195

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

196

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

197

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

SciTech Connect

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

Idriss, H.

2010-01-01

198

The surface chemistry of multi-oxide silicates  

Microsoft Academic Search

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 20min 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

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

2009-01-01

199

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

200

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

PubMed

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

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

2012-07-17

201

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

202

Speciation of adsorbed yttrium and rare earth elements on oxide surfaces  

E-print Network

Speciation of adsorbed yttrium and rare earth elements on oxide surfaces Wojciech Piasecki, Dimitri 10 June 2008 Abstract The distribution of yttrium and the rare earth elements (YREE) between natural investigate the applicability of the X-ray results to rare earth elements and to several oxides in addition

Sverjensky, Dimitri A.

203

Characterization of a bioactive nanotextured surface created by controlled chemical oxidation of titanium  

E-print Network

Elsevier B.V. All rights reserved. Keywords: Nanotopography; Titanium oxides; Chemical oxidation; SEM; AFM Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2006.07.053 * Corresponding author. Tel.: +1 514 343.elsevier.com/locate/susc Surface Science 600 (2006) 4613­4621 #12;from a recent animal study show that nanotextured Ti im- proves

204

Identification of defect sites on oxide surfaces by metastable impact electron spectroscopy  

E-print Network

a suitable substrate, epitaxially grown oxide thin films of MgO, Al2O3, and TiO2 have been synthesized predictions of additional occupied states in the band-gap due to point defects. Extended defect sites on SiO2Identification of defect sites on oxide surfaces by metastable impact electron spectroscopy S

Goodman, Wayne

205

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

206

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

207

Determination of the Surface Isoelectric Point of Oxide Films on Metals by Contact Angle Titration  

PubMed

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 though 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 -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. Copyright 1997 Academic Press. Copyright 1997Academic Press PMID:9398416

McCafferty; Wightman

1997-10-15

208

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

Microsoft Academic Search

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

Baikun Li; Bruce E. Logan

2005-01-01

209

Compositional Control of Surface Oxides on Metal Alloys using Photons: Dynamic Simulations and Experiments  

SciTech Connect

We report on the ability to modify the structure and composition of ultrathin oxides grown on Ni and Ni-Al alloy surfaces at room temperature utilizing photon illumination. We find that the nickel-oxide formation is enhanced in the case of oxidation under photo-excitation. The enhanced oxidation kinetics of nickel in 5% Ni-Al alloy is corroborated by experimental and simulation studies of natural and photon-assisted oxide growth on pure Ni(100) surfaces. In case of pure Ni substrates, combined x-ray photoelectron spectroscopy analysis, and atomic force microscope current mapping support the deterministic role of the structure of nickel passive-oxide films on their nanoscale corrosion resistance. Atomistic simulations involving dynamic charge transfer predict that the applied electric field overcomes the activation-energy barrier for ionic migration, leading to enhanced oxygen incorporation into the oxide, enabling us to tune the mixed-oxide composition at atomic length scales. Atomic scale control of ultrathin oxide structure and morphology in the case of pure substrates as well as compositional tuning of complex oxide in the case of alloys leads to excellent passivity as verified from potentiodynamic polarization experiments.

Chang, C.; Sankaranarayanan, S; Ruzmetov, D; Engelhard, M; Kaxiras, E; Ramanathan, S

2010-01-01

210

Characterization of oxide on the water-atomized FeMn powder surface  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

211

Self-inhibition of water dissociation on magnesium oxide surfaces  

Microsoft Academic Search

Hydroxylated MgO surfaces have been prepared by exposure to water vapour of MgO crystals at room temperature. High hydroxyl coverages were achieved on freshly cleaved surfaces. However, upon adsorption–desorption cycles of the hydroxyl adlayer, the ability of the MgO surfaces to dissociate water was seen to be dramatically inhibited. Reduced reactivities have also been observed on both air- and water-exposed

D. Abriou; J. Jupille

1999-01-01

212

Simulation of the surface structure of lithium manganese oxide spinel  

Microsoft Academic Search

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

R. Benedek; M. M. Thackeray

2011-01-01

213

Rates of oxidative weathering on the surface of Mars  

NASA Technical Reports Server (NTRS)

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

Burns, Roger G.; Fisher, Duncan S.

1993-01-01

214

Anion Adsorption on Oxide Surfaces: Inclusion of the Water  

E-print Network

surfaces (3), binding of medical implants in the human body (4), and theories about the origin of life (5). Recently, increasing numbers of in situ infrared and X-ray spectroscopic studies have definitively of dipolar molecules to or from a charged surface also involves electrostatic work (29); however, this work

Sverjensky, Dimitri A.

215

Determination of an oxide film on the surface of perlite steel  

SciTech Connect

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

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

1986-04-01

216

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

217

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

218

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

219

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

220

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

SciTech Connect

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

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

1998-02-01

221

Reactive molecular dynamic simulations of early stage of wet oxidation of Si (001) surface  

NASA Astrophysics Data System (ADS)

We have investigated the initial stage of oxidation of Si (001) surface by water (H2O) molecules using reactive molecular dynamics (MD) simulation at 300 K and 1200 K without any external constraint on the water molecules. Previously, reported water reaction behaviors on silicon surface by ab initio calculations or experimental observations were reproduced by the present MD simulation. The present simulation further revealed that the hydrogen atom in H2O is more attractive than oxygen atom in O2 to bond with Si, such that it accelerates the dissociation process of H2O. It was also observed that the oxidation reaction was enhanced with increased number of the supplied water molecules. It was suggested that the repulsion between water molecules and their fragments facilitates the dissociation of both water molecules and hydroxyl decomposition on the Si surface. Therefore, the wet oxidation behavior appeared to have more temperature dependence even in the early stage of oxidation.

Pamungkas, Mauludi Ariesto; Kim, Byung-Hyun; Lee, Kwang-Ryeol

2013-08-01

222

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

223

A Chemical Approach to Understanding Oxide Surface Structure and Reactivity  

NASA Astrophysics Data System (ADS)

Transmission electron microscopy and diffraction are powerful tools for solving complex structural problems. They complement other analytical techniques, such as x-ray diffraction, elucidating problems which cannot be solved by other techniques. One area where they are of particularly great value is in the determination of surface structures. The research presented herein uses electron microscopy and diffraction as the primary experimental techniques in the development of a chemistry of surface structures. High-resolution electron microscopy revealed that the La4Cu 3MoO12 structure has turbostratic disorder and a lower symmetry space group (Pm) than was previously found. The refinement of the x-ray data was significantly improved by using a disordered model and the Pm space group. A bond valence analysis confirmed that the disordered structure is the superior model. Strontium titanate, SrTiO3, single crystal surfaces were examined principally via transmission electron diffraction. A homologous series with intergrowths was discovered on the (110) surface of strontium titanate, marking the first time that these important concepts of solid state chemistry have been found at the surface. Atmospheric adsorbates, such as H2O and CO2, were found to help to stabilize undercoordinated surface structures on the (100) surface. It was shown that chemical bonding, bond valence, atomic coordination, and stoichiometry greatly influence the development of surface structures. Additionally, such chemistry based analysis was demonstrated to be able to predict surface structure stability and reactivity. Application of a modified Wulff construction to the observed shape of strontium titanate nanocuboids revealed that the surface structure and particle stoichiometry are interlinked, with control over one allowing equally precise control over the other. Platinum nanoparticles on the strontium titanate nanocuboids were shown via high resolution electron microscopy to have cube-on-cube epitaxy, with the shape of the platinum nanoparticles governed by the Winterbottom construction. Precise modification of the support surface will therefore allow engineering of supported metal particles with precise control over which facets are exposed. These results suggest that control over the support surface chemistry can be used to engineer thermodynamically stable, face selective catalysts.

Enterkin, James Andrew

224

Vanadium surface oxides on Pd(111): A structural analysis  

Microsoft Academic Search

Scanning tunneling microscopy studies of vanadium oxides grown on Pd(111) show interesting structures especially in the low-coverage region. Evaporation of V in an oxygen background at elevated sample temperature (250 °C) results in the formation of a nonperiodic honeycomb-like structure growing from the steps, which starts to transform into an ordered phase at a vanadium coverage of ≈0.2 ML (monolayer).

C. Klein; G. Kresse; S. Surnev; F. P. Netzer; M. Schmid; P. Varga

2003-01-01

225

Energetic Surface Smoothing of Complex Metal-Oxide Thin Films  

Microsoft Academic Search

A novel energetic smoothing mechanism in the growth of complex metal-oxide thin films is reported from in situ kinetic studies of pulsed laser deposition of La1-xSrxMnO3 on SrTiO3, using x-ray reflectivity. Below 50% monolayer coverage, prompt insertion of energetic impinging species into small-diameter islands causes them to break up to form daughter islands. This smoothing mechanism therefore inhibits the formation

P. R. Willmott; R. Herger; C. M. Schlepütz; D. Martoccia; B. D. Patterson

2006-01-01

226

Energetic Surface Smoothing of Complex Metal-Oxide Thin Films  

Microsoft Academic Search

A novel energetic smoothing mechanism in the growth of complex metal-oxide thin films is reported from in situ kinetic studies of pulsed laser deposition of La{sub 1-x}SrâMnOâ on SrTiOâ, using x-ray reflectivity. Below 50% monolayer coverage, prompt insertion of energetic impinging species into small-diameter islands causes them to break up to form daughter islands. This smoothing mechanism therefore inhibits the

P. R. Willmott; R. Herger; C. M. Schlepuetz; D. Martoccia; B. D. Patterson

2006-01-01

227

Surface oxidation of NiTi shape memory alloy  

Microsoft Academic Search

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

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

2002-01-01

228

Intermolecular potential energy surface and thermophysical properties of ethylene oxide.  

PubMed

A six-dimensional potential energy hypersurface (PES) for two interacting rigid ethylene oxide (C2H4O) molecules was determined from high-level quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the MP2 and CCSD(T) levels of theory was utilized to determine interaction energies for 10178 configurations of two molecules. An analytical site-site potential function with 19 sites per ethylene oxide molecule was fitted to the interaction energies and fine tuned to agree with data for the second acoustic virial coefficient from accurate speed of sound measurements. The PES was validated by computing the second virial coefficient, shear viscosity, and thermal conductivity. The values of these properties are substantiated by the best experimental data as they tend to fall within the uncertainty intervals and also obey the experimental temperature functions, except for viscosity, where experimental data are insufficient. Due to the lack of reliable data, especially for the transport properties, our calculated values are currently the most accurate estimates for these properties of ethylene oxide. PMID:25362314

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

2014-10-28

229

Intermolecular potential energy surface and thermophysical properties of ethylene oxide  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

230

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

PubMed

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

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

2014-01-01

231

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

PubMed Central

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

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

2014-01-01

232

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

SciTech Connect

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

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

2012-06-30

233

The interaction of metal oxide surfaces with complexing agents dissolved in water  

Microsoft Academic Search

Upon exposure to liquid water or to aqueous solutions, the surfaces of metal oxide particles or films undergo a series of chemical reactions that are dictated to a large extent by the chemistry of the metal ions involved. These reactions involve surface hydroxylation and hydration (dissociative and non-dissociative water chemisorption), chemisorption of solutes and charge transfer reactions. The present review

M. A. Blesa; A. D. Weisz; P. J. Morando; J. A. Salfity; G. E. Magaz; A. E. Regazzoni

2000-01-01

234

Structure Sensitivity of Photochemical Oxidation and Reduction Reactions on SrTiO3 Surfaces  

E-print Network

and water purifiers,4 ­ 6 self-cleaning surface treatments,7 and water photolysis catalysts8,9 are examples species. When these reactions occur on the surface of an oxide pigment particle embedded in a composite of photochemical reactions on BaTiO3 sur- faces indicate that internal dipolar fields can drive photogenerated

Rohrer, Gregory S.

235

Assembly of Linear Nano-Chains from Iron Oxide Nanospheres with Asymmetric Surface Chemistry  

Microsoft Academic Search

Besides the multifunctionality, another equally important aspect of nanoparticles is their engineerability to control the geometrical and chemical properties during fabrication. In this work, we exploited this aspect to define asymmetric surface chemistry of an iron oxide nanosphere by controlling the topology of ligand expression on its surface resulting in a particle with two faces, one displaying only amines and

Pubudu M. Peiris; Erik Schmidt; Michael Calabrese; Efstathios Karathanasis; Meni Wanunu

2011-01-01

236

ANRV408-PC61-07 ARI 14 October 2009 17:16 Oxide Surface Science  

E-print Network

oxidation of metal alloys (such as Al2O3/NiAl), have gained popularity as supports for planar model: density functional theory 1. INTRODUCTION Surface science is the study of solid surfaces under well-controlled improved the accuracy of theoretical predictions, and in combination with the expansion of computing power

Diebold, Ulrike

237

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

238

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...

239

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

240

Simulation of oxidation of carbon particles at the surface of mixed oxide catalysts  

Microsoft Academic Search

A model of catalytic oxidation of a cylindrical carbon particle was suggested. The model considers the rate of layer-by-layer\\u000a burning of the particle, variation of its geometry, and remote action of the catalyst. A software for calculations was developed;\\u000a the data obtained correlate well with the experimental data for catalysts based on lanthanum cesium vanadate. The kinetics\\u000a of carbon oxidation

A. A. Ostroushko; M. Yu. Sennikov; M. O. Tonkushina

2007-01-01

241

Peculiar surface-interface properties of nanocrystalline ceria-cobalt oxides with enhanced oxygen storage capacity.  

PubMed

Peculiar surface-interface properties of nanocrystalline ceria-cobalt oxides were evidenced by X-ray diffraction, transmission electron microscopy and X-ray absorption spectroscopy. It was found that cobalt foreign cations modify the surface oxygen vacancies of ceria at the atomic level, inducing the exposure of well-defined reactive faces between the ceria-host and the cobalt oxide interface. These modifications of the surface-interface structure promoted a remarkable increase in the oxygen storage capacity of ceria nanocrystals. PMID:25231060

Qiu, Nan; Zhang, Jing; Wu, Ziyu

2014-11-01

242

Delivering octadecylphosphonic acid self-assembled monolayers on a Si wafer and other oxide surfaces.  

PubMed

We describe a simple experimental approach for delivering self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) on many oxide surfaces using a nonpolar medium with a dielectric constant around 4 (e.g., trichloroethylene). This approach readily results in the formation of full-coverage OPA SAMs on a wide variety of oxide surfaces including cleaved mica, Si wafer, quartz, and aluminum. Especially, the availability of delivering full-coverage OPA SAM on a Si wafer is unique, as no OPA SAMs at all could be formed on a Si wafer when using a polar OPA solution. The reason a nonpolar solvent is superior lies in the very fact that the hydrophilic OPA headgroup tends to escape from the nonpolar solution and is thus enriched at the medium-air interface. It is these OPA headgroups seeking a hydrophilic surface that make possible the well-controlled OPA monolayer on an oxide surface. PMID:17048932

Nie, Heng-Yong; Walzak, Mary J; McIntyre, N Stewart

2006-10-26

243

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

PubMed Central

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

Zhang, Guandong; Liao, Yifeng; Baker, Ian

2011-01-01

244

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

245

Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along a climosequence  

E-print Network

Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along oxidation and to examine how climatic and soil factors affect BC oxidation. Black C was collected from 11. The results showed that the historical BC samples were substantially oxidized after 130 years in soils

Lehmann, Johannes

246

Reaction of neptunium with molecular and atomic oxygen: Formation and stability of surface oxides  

NASA Astrophysics Data System (ADS)

The surface reactions of thin films of Np metal with molecular and atomic oxygen were investigated by X-ray and Ultra-Violet Photoelectron Spectroscopy (XPS and UPS, respectively). Goal of this work was to study the entire range of oxides, starting with the very early reaction stages, in presence of metal, up to the highest possible oxides, reached at saturation under highly reactive, oxidative conditions. Emphasis was given to the surface layers, whose properties often differ from the bulk, and which are directly involved in corrosion processes of solids. Molecular O 2 reacts readily with the metallic neptunium surface to form the sesquioxide and dioxide. The sesquioxide is observed as thin 'bulk' species of up to nine monolayers thickness. A higher oxide, identified as Np 2O 5, is formed when the NpO 2 surface is exposed to atomic oxygen. It is stable under UHV conditions up to a temperature of about 200 °C. The high oxide, Np 2O 5, is still capable of chemisorbing further oxygen. This is shown in UPS spectra by the additional O-2p line at 5-6 eV BE, superimposing onto the valence band (VB). The formation of both a lower (Np 2O 3) and higher oxide (Np 2O 5) besides the dioxide is discussed in the framework of ongoing 5f localization throughout the actinide series.

Seibert, A.; Gouder, T.; Huber, F.

2009-06-01

247

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

NASA Astrophysics Data System (ADS)

Iron oxide nanoparticles are the most popular magnetic nanoparticles used in biomedical applications due to their low cost, low toxicity, and unique magnetic property. Magnetic iron oxide nanoparticles, including magnetite (Fe3O4) and maghemite (?-Fe2O3), usually exhibit a superparamagnetic property as their size goes smaller than 20 nm, which are often denoted as superparamagnetic iron oxide nanoparticles (SPIONs) and utilized for drug delivery, diagnosis, therapy, and etc. This review article gives a brief introduction on magnetic iron oxide nanoparticles in terms of their fundamentals of magnetism, magnetic resonance imaging (MRI), and drug delivery, as well as the synthesis approaches, surface coating, and application examples from recent key literatures. Because the quality and surface chemistry play important roles in biomedical applications, our review focuses on the synthesis approaches and surface modifications of iron oxide nanoparticles. We aim to provide a detailed introduction to readers who are new to this field, helping them to choose suitable synthesis methods and to optimize the surface chemistry of iron oxide nanoparticles for their interests.

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

2014-03-01

248

Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces  

Microsoft Academic Search

Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the ?m-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of ?-glycidoxypropyltrimethoxy silane (GPS) to

G Jogikalmath; J. K Stuart; A Pungor; V Hlady

1999-01-01

249

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

250

Laser-induced hydrophobicity on single crystal zinc oxide surface  

NASA Astrophysics Data System (ADS)

Highly hydrophobic surface of ZnO crystal substrate is prepared easily and rapidly by KrF excimer laser irradiation. The water contact angle is increased from 70° to approximately 120°. Through the XRD, AFM, XPS measurements and the Cassie-Baxter model analysis, it is indicated that the unique micro-nano fluctuant surface structure induced by laser irradiation is the prominent factor to the great increase of the water CA. The annealing treatments for the irradiated sample are carried out both in oxygen and vacuum atmosphere. It is found that the adsorption of oxygen atoms on the roughened surface could make the CA decrease abruptly at the first beginning, and after being stored at ambient atmosphere, the CA would reconvert to the value of the freshly irradiated sample gradually. It probably provides a convenient method for rapid conversion of the wettability through excimer laser irradiation and post annealing treatment.

Xie, Sijing; Zhao, Yan; Jiang, Yijian

2012-12-01

251

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

PubMed

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

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

2012-03-01

252

Metal oxide surfaces and their interactions with aqueous solutions and microbial organisms  

SciTech Connect

During the past decade, interest in chemical reactions occurring at metal oxide-aqueous solution interfaces has increased significantly because of their importance in a variety of fields, including atmospheric chemistry, heterogeneous catalysis and photocatalysis, chemical sensing, corrosion science, environmental chemistry and geochemistry, metallurgy and ore beneficiation, metal oxide crystal growth, soil science, semiconductor manufacturing and cleaning, and tribology. This review begins with a consideration of the structure (both geometric and electronic) and properties of clean metal oxide surfaces (section 2). Section 3 considers the interaction of water vapor with metal oxide surfaces. The largest section of the paper, section 4, addresses the interactions that occur when metal oxides are immersed in liquid water. The dissolution and growth of metal oxides in aqueous solutions are addressed in section 5. Section 6 considers biotic processes involving bacterial utilization and production of metal oxides. The various theoretical approaches that are being used to interpret and predict the structure and properties of metal oxide-aqueous interfaces are described in section 7. Section 8 then considers the challenges that face this emerging field and the future directions in which research must go if answers to the important unanswered questions are to be obtained. 600 refs.

Brown, G.E. Jr. [Stanford Univ., CA (United States)] [Stanford Univ., CA (United States); Henrich, V.E. [Yale Univ., New Haven, CT (United States)] [Yale Univ., New Haven, CT (United States); Casey, W.H. [Univ. of California, Davis, CA (United States). Dept. of Land, Air, and Water Resources] [and others] [Univ. of California, Davis, CA (United States). Dept. of Land, Air, and Water Resources; and others

1999-01-01

253

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

PubMed

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

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

2014-07-30

254

Stability, structure, and electronic properties of chemisorbed oxygen and thin surface oxides on Ir(111)  

NASA Astrophysics Data System (ADS)

Iridium-based catalysts are widely used in several important chemical reactions. Despite this, very little is known about the surface structure of the catalyst and the atomic and molecular processes involved. As a first step towards a microscopic understanding, we use density-functional theory, coupled with ab initio atomistic thermodynamics [1], to investigate chemisorption of oxygen on Ir(111), and the stability of surface oxides. We find for on-surface adsorption, oxygen prefers the fcc-hollow site for all coverages considered, where with increasing coverage, the adsorption energy decreases substantially. Subsurface adsorption is found to be highly unfavourable. The most favourable surface-oxide-like structure has a tri-layer-like (O-Ir-O) configuration, which however, the (p,T) phase diagram predicts is only metastable. For practically all conditions, except ultra-high vacuum, the bulk oxide is thermodynamically the most stable, and the only other stable phase predicted is the on-surface (2x2)-O structure for coverage 0.25 ML [2]. These studies point to the possible importance of oxidized iridium for heterogeneous oxidation reactions. [1] C. Stampfl, Catal. Today 105, 17 (2005). [2] H. Zhang, A. Soon, B. Delley and C. Stampfl, submitted to Phys. Rev. B.

Zhang, H.; Soon, A.; Delley, B.; Stampfl, C.

2008-03-01

255

Growth morphology of thin films on metallic and oxide surfaces.  

PubMed

In this work we briefly review recent investigations concerning the growth morphology of thin metallic films on the Mo(110) and Ni3Al(111) surfaces, and Fe and copper phthalocyanine (C32H16N8Cu) on the Al2O3/Ni3Al(111) surface. Comparison of Ag, Au, Sn, and Pb growth on the Mo(110) surface has shown a number of similarities between these adsorption systems, except that surface alloy formation has only been observed in the case of Sn and Au. In the Pb/Mo(110) and Pb/Ni3Al(111) adsorption systems selective formation of uniform Pb island heights during metal thin film growth has been observed and interpreted in terms of quantum size effects. Furthermore, our studies showed that Al2O3 on Ni3Al(111) exhibits a large superstructure in which the unit cell has a commensurate relation with the substrate lattice. In addition, copper phthalocyanine chemisorbed weakly onto an ultra-thin Al2O3 film on Ni3Al(111) and showed a poor template effect of the Al2O3/Ni3Al(111) system. In the case of iron cluster growth on Al2O3/Ni3Al(111) the nucleation sites were independent of deposition temperature, yet the cluster shape showed a dependence. In this system, Fe clusters formed a regular hexagonal lattice on the Al2O3/Ni3Al(111). PMID:24445588

Krupski, Aleksander

2014-02-01

256

Synthesis and surface characterization of todorokite-type microporous manganese oxides: implications for shape-selective oxidation catalysts  

Microsoft Academic Search

Various todorokite-type Mn(IV)-oxides, namely, Mg-, Ni- and Cu-todorokite, were synthesized via hydrothermal treatment of corresponding buserites. The bulk chemical and phase compositions, crystalline structure, particle morphology and thermal stability, were determined by means of atomic absorption spectroscopy, X-ray powder diffractometry, infrared spectroscopy, and thermogravimetry. The surface chemical composition, texture and structure were assessed using X-ray photoelectron spectroscopy, nitrogen sorptiometry, and

Fakhreia A Al-Sagheer; Mohamed I Zaki

2004-01-01

257

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

NASA Technical Reports Server (NTRS)

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

Napier, Mary E.; Stair, Peter C.

1992-01-01

258

Laser direct writing of oxide structures on hydrogen-passivated silicon surfaces  

NASA Astrophysics Data System (ADS)

A focused laser beam has been used to induce oxidation of hydrogen-passivated silicon. The scanning laser beam removes the hydrogen passivation locally from the silicon surface, which immediately oxidizes in air. The process has been studied as a function of power density and excitation wavelength on amorphous and crystalline silicon surfaces in order to determine the depassivation mechanism. The minimum linewidth achieved is about 450 nm using writing speeds of up to 100 mm/s. The process is fully compatible with local oxidation of silicon by scanning probe lithography. Wafer-scale patterns can be generated by laser direct oxidation and complemented with nanometer resolution by scanning probe techniques. The combined micro- and nanoscale pattern can be transferred to the silicon in a single etching step by either wet or dry etching techniques.

Müllenborn, M.; Birkelund, K.; Grey, F.; Madsen, S.

1996-11-01

259

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

260

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

261

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

262

Computerized infrared spectroscopic study of surface reactions on selected lanthanide oxides  

Microsoft Academic Search

The natures of adsorption sites on LaâOâ, NdâOâ, and selected praseodymium oxides were investigated by examining surface reactions of probe molecules using computerized transmission ir spectroscopy on unsupported samples. Additionally, the rehydration\\/dehydration behavior and crystallographic phase transitions of these oxides were examined in pretreatment temperature experiments involving rehydration of the sesquioxides to hydroxides by water exposure. Following rehydration of LaâOâ

Dellisante

1982-01-01

263

Facile Fabrication of Gold Nanoparticle-Titanium Oxide Alternate Assemblies by Surface Sol-Gel Process  

Microsoft Academic Search

Multistructured assemblies consisting of gold nanoparticles and titanium oxide were alternately fabricated by a surface sol-gel process. First, a quartz glass substrate was immersed into an organic solution of titanium butoxide [Ti(OBu)4]. Then, the substrate was rinsed with water, and dried in air, giving ultra-thin titanium oxide [Ti(O)]-modified quartz glass substrate. This modified glass substrate was immersed into an aqueous

Taichi Arakawa; Tomoaki Kawahara; Tsuyoshi Akiyama; Sunao Yamada

2007-01-01

264

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

265

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

PubMed Central

A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline water layers are on the alloy surface in order to account for the relative inertness of the nickel alloy in corrosive environments. PMID:20672134

2010-01-01

266

The reactivity of CO2 and H2 at trapped electron sites at an oxide surface.  

PubMed

We investigate the reactivity to H2 of a chemisorbed CO2 species at electron traps on oxide surfaces, taking the single electron F(+) oxygen vacancy of the MgO(100) terrace as a model system. We find that multiple hydrogen addition steps form three interacting catalytic cycles, leading to the evolution of formaldehyde, methanol or methane. Our results have general implications for the reactivity of CO2 on metal oxides. PMID:25103599

Downing, C A; Sokol, A A; Catlow, C R A

2014-10-21

267

Titania surface modification and photovoltaic characteristics with tungsten oxide  

Microsoft Academic Search

WO3-coated TiO2 film was prepared by depositing TiO2 suspension containing small amounts of ammonium tungstate solution. The morphology and structure of the samples were characterized with high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL) emission spectrum. The results showed that WO3 formed a coating layer on surface of TiO2 and significantly reduced the

Ping Cheng; ChangSheng Deng; DaNian Liu; XiaMing Dai

2008-01-01

268

Roughening of Pt nanoparticles induced by surface-oxide formation.  

PubMed

Using density functional theory (DFT) and thermodynamic considerations we studied the equilibrium shape of Pt nanoparticles (NPs) under electrochemical conditions. We found that at very high oxygen coverage, obtained at high electrode potentials, the experimentally-observed tetrahexahedral (THH) NPs consist of high-index (520) faces. Since high-index surfaces often show higher (electro-)chemical activity in comparison to their close-packed counterparts, the THH NPs can be promising candidates for various (electro-)catalytic applications. PMID:23303314

Zhu, Tianwei; Hensen, Emiel J M; van Santen, Rutger A; Tian, Na; Sun, Shi-Gang; Kaghazchi, Payam; Jacob, Timo

2013-02-21

269

NORTHWESTERN UNIVERSITY Oxide Surfaces in Practical and Model Catalytic Systems  

E-print Network

structures and dynamics of Mg3(VO4)2, LaAlO3, SrTiO3, and -Fe2O3/Fe3O4 are investigated under a variety oxygen atoms. The c(6Ã?2) is a reconstruction of the SrTiO3 (001) surface that is formed between 1050 of conditions and by a range of experimental and computational techniques. The structure and morphology of La

Shull, Kenneth R.

270

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

271

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

272

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

PubMed

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

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

2013-12-01

273

Surface Passivation Limited UO2 Oxidative Dissolution in the Presence of FeS.  

PubMed

Iron sulfide minerals produced during in situ bioremediation of U can serve as an oxygen scavenger to retard uraninite (UO2) oxidation upon oxygen intrusion. Under persistent oxygen supply, however, iron sulfides become oxidized and depleted, giving rise to elevated dissolved oxygen (DO) levels and remobilization of U(IV). The present study investigated the mechanism that regulates UO2 oxidative dissolution rate in a flow-through system when oxygen breakthrough occurred as a function of mackinawite (FeS) and carbonate concentrations. The formation and evolution of surface layers on UO2 were characterized using XAS and XPS. During FeS inhibition period, the continuous supply of carbonate and calcium in the influent effectively complexed and removed oxidized U(VI) to preserve an intermediate U4O9 surface. When the FeS became depleted by oxidization, a transient, rapid dissolution of UO2 was observed along with DO breakthrough in the reactor. This rate was greater than during the preceding FeS inhibition period and control experiments in the absence of FeS. With increasing DO, the rate slowed and the rate-limiting step shifted from surface oxidation to U(VI) detachment as U(VI) passivation layers developed. In contrast, increasing the carbonate concentrations facilitated detachment of surface-associated U(VI) complexes and impeded the formation of U(VI) passivation layer. This study demonstrates the critical role of U(VI) surface layer formation versus U(VI) detachment in controlling UO2 oxidative dissolution rate during periods of variable oxygen presence under simulated groundwater conditions. PMID:25322064

Bi, Yuqiang; Hayes, Kim F

2014-11-18

274

X-ray Photoelectron Spectroscopy Studies of Oxidized and Reduced CeO?(111) Surfaces  

SciTech Connect

We have studied the electronic structure of oxidized and reduced CeO? (111) surfaces using X-ray photoelectron spectroscopy (XPS). The 50 nm thick Co?(111) film was grown on a YSZ(111) substrate using oxygen plasma assisted molecular beam epitaxy (OPA-MBE). This film has been characterized using in-situ RHEED (reflection high energy electron diffraction) and ex-situ XRD (X-ray diffraction), HRTEM (high resolution transmission electron microscopy) and RBS (Rutherford backscattering spectroscopy). The lattice mismatch between CeO?(111) and YSZ(111) is less than 5% and yields a flat surface that is comprised of an equivalent number of Ce?? and O?? ions. Oxidation with O? at 773 K under UHV conditions was sufficient to fully oxidize the CeO?(111). Surface reduction was carried out by annealing in UHV at 973 K.

Engelhard, Mark H.; Azad, Samina; Peden, Charles HF; Thevuthasan, Suntharampillai

2004-12-01

275

The influence of metal oxide additives on the molecular structures of surface tungsten oxide species on alumina. II. In situ conditions  

Microsoft Academic Search

The dehydrated Raman spectra of unpromoted WO3\\/Al2O3 indicate that the tungsten oxide surface species have the mono-oxo structure and are present as tetrahedrally coordinated monomers at low loadings and as a mixture of tetrahedrally and octahedrally coordinated surface polymers at high loadings. The effect of introducing secondary metal oxide additives to WO3\\/Al2O3 catalysts, where tungsten oxide is present as a

Marlene M. Ostromecki; Loyd J. Burcham; Israel E. Wachs

1998-01-01

276

Quantum states of a hydrogen atom adsorbed on Cu(100) and (110) surfaces  

NASA Astrophysics Data System (ADS)

Quantum states of a hydrogen atom adsorbed on Cu(100) and Cu(110) are studied theoretically. In calculating eigenenergies and wave functions of hydrogen atom motion, three-dimensional adiabatic potential energy surfaces (PESs) are constructed within density functional theory and the Schrödinger equation for hydrogen atom motion on the PESs is solved by the variation method. The wave function on Cu(100) indicates a localized mode on the hollow (HL) site at the ground state. Wave functions of the first few excited states indicate vibrational modes on the HL site and suggest migration from an HL site to a neighboring HL site over the bridge (BR) site. In the case of Cu(110) , the ground state wave function is spread from the short bridge (SB) site and to the pseudothreefold (PT) site. The first few excited states are vibrational modes centered at the SB and long bridge (LB) sites. The excited state wave function of the hydrogen atom motion on Cu(110) show isotope effects as follows. The fourth excited state wave function for the H atom motion shows a localized character on the LB site, and those for D and T atom motion show vibrational modes parallel to the surface. On the other hand, the fifth excited state wave functions for D and T atom motion show localized characters on the LB site and that for H atom motion shows a vibrational mode parallel to the surface. Our calculated eigenenergies of the hydrogen atom motion in excited states on Cu(100) and Cu(110) are fairly in agreement with their corresponding experimental findings.

Ozawa, Nobuki; Roman, Tanglaw; Nakanishi, Hiroshi; Diño, Wilson Agerico; Kasai, Hideaki

2007-03-01

277

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

278

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

PubMed Central

Gaseous HCl generated from a variety of sources is ubiquitous in both outdoor and indoor air. Oxides of nitrogen (NOy) are also globally distributed, because NO formed in combustion processes is oxidized to NO2, HNO3, N2O5 and a variety of other nitrogen oxides during transport. Deposition of HCl and NOy onto surfaces is commonly regarded as providing permanent removal mechanisms. However, we show here a new surface-mediated coupling of nitrogen oxide and halogen activation cycles in which uptake of gaseous NO2 or N2O5 on solid substrates generates adsorbed intermediates that react with HCl to generate gaseous nitrosyl chloride (ClNO) and nitryl chloride (ClNO2), respectively. These are potentially harmful gases that photolyze to form highly reactive chlorine atoms. The reactions are shown both experimentally and theoretically to be enhanced by water, a surprising result given the availability of competing hydrolysis reaction pathways. Airshed modeling incorporating HCl generated from sea salt shows that in coastal urban regions, this heterogeneous chemistry increases surface-level ozone, a criteria air pollutant, greenhouse gas and source of atmospheric oxidants. In addition, it may contribute to recently measured high levels of ClNO2 in the polluted coastal marine boundary layer. This work also suggests the potential for chlorine atom chemistry to occur indoors where significant concentrations of oxides of nitrogen and HCl coexist. PMID:19620710

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

2009-01-01

279

Photoinduced desorption of sulfur from gold nanoparticles loaded on metal oxide surfaces.  

PubMed

We now report photoinduced sulfur desorption from the surfaces of Au nanoparticles loaded on metal oxides. This reaction occurs in water at ordinary temperature and pressure. Nanometer-sized Au particles have been formed on the surfaces of various metal oxides by deposition-precipitation (Au/oxides). Elemental sulfur (S8) is selectively adsorbed on the Au nanoparticle surfaces of Au/oxides in an atomic state at a coverage of (theta) 1/3. Irradiation (lambdaex > 300 nm) of the sulfur adsorbed Au/anatase TiO2 in water has led to reductive desorption of the sulfurs at room temperature. Electrochemical measurements using Au/oxides indicate that the driving force for this reaction is the photoinduced upward shift of Fermi energy of the metal oxide-supported Au nanoprticles. This study will open up a novel and wide application of heterogeneous photocatalysis for thermal catalysts. PMID:15584715

Tada, Hiroaki; Soejima, Tetsuro; Ito, Seishiro; Kobayashi, Hisayoshi

2004-12-15

280

Preparation of self-organized porous anodic niobium oxide microcones and their surface wettability  

Microsoft Academic Search

Porous anodic niobium oxide with a pore size of ?10nm was formed at 10V in glycerol electrolyte containing 0.6moldm?3 K2HPO4 and 0.2moldm?3 K3PO4 at 433K. After prolonged anodizing for 5.4ks, niobium oxide microcones develop on the surface. X-ray diffraction patterns of the anodized specimens revealed that the initially formed anodic oxide is amorphous, but an amorphous-to-crystalline transition occurs during anodizing.

Y. Oikawa; T. Minami; H. Mayama; K. Tsujii; K. Fushimi; Y. Aoki; P. Skeldon; G. E. Thompson; H. Habazaki

2009-01-01

281

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

282

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

PubMed Central

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

2014-01-01

283

Scanning tunneling microscopy study of oxide nucleation and oxidation-induced roughening at elevated temperatures on the Si(001)-(2×1) surface  

NASA Astrophysics Data System (ADS)

Room temperature scanning tunneling microscopy images of Si(001)-(2×1) surfaces exposed to O2 at pressures 1×10-8surface roughening via formation of long step ``fingers'' and multilevel Si islands. This is caused by nucleation of oxide clusters, which pin step edges during oxidation-induced surface etching. The nucleation rate Jox (estimated by counting pinning sites) was found to scale as Pmox, with m>=2. This is consistent with a simple model in which two diffusing surface oxygen species are required to nucleate a stable oxide cluster.

Seiple, J. V.; Pelz, J. P.

1994-08-01

284

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

285

Surface characterization of Laponite-Poly(ethylene oxide) nanocomposite films  

NASA Astrophysics Data System (ADS)

The aim of the present work is to understand how ionic strength of precursor polymer-clay gels influences the final structure of multilayered nanocomposite films fabricated from such gels. We have prepared three aqueous precursor gels containing 3wt% LRD, 2wt% PEO and 95wt% water, in which the salt concentrations were kept at 0X, 1X and 3X with X = 5.57 * 10^- 5 g NaCl/mL. The Laponite (LRD) - PEO multilayered films (LRD60%-PEO40%) were fabricated by manually spreading and drying each gel on a glass slide. Prior to the AFM measurements the polymer-clay composite films where freeze-dried by immersion in liquid nitrogen until they were totally degassed. Frozen samples where then fractured and left for additional drying for 24 hours in a desiccator. The imaging procedure employed here was tapping-mode AFM. Distinct features were identified on the layered transversal surface of the films, and were attributed to the different salt concentrations in the samples. Addition of salt increases the adhesion and compactness properties of the nanoparticles, as a more uniform side surface can be observed after freeze-fracturing the materials.

Stefanescu, Eduard A.; Negulescu, Ioan I.; Daly, William H.; Donose, Bogdan C.; Nguyen, Anh V.

2008-03-01

286

Surface Science Studies of Strong Metal-Oxide Interactions on Model Catalysts  

NASA Astrophysics Data System (ADS)

Here we report on recent model studies of a phenomenon known in catalysis as the “Strong Metal-Support Interaction” (SMSI for short). Decoration of the surfaces of precious metal single crystals, films, and nanoparticles supported on titania produces beautiful long-range ordered structures which can often be resolved at atomic resolution using scanning tunneling microscopy (STM). Such surfaces show reduced binding for CO and effectively lower the activity of the surface. Consideration is given to the cause and composition of the surface layer, that is, whether it is a kind of intermetallic layer, or is simply a thin layer of titanium (sub-)oxide.

Bowker, Michael; Bennett, Roger A.

287

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

NASA Astrophysics Data System (ADS)

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

Park, Hwangseo; Kim, Hojing; Lee, Sangyoub

1997-05-01

288

The role of oxygen vacancies on ceria surfaces in the oxidation of carbon monoxide  

NASA Astrophysics Data System (ADS)

Computer simulation techniques are used to model the surfaces of ceria, paying special attention to the effects of surface structures and energetics on catalytic activity. Three surfaces of CeO 2 have been investigated for both their structure and relative stability. The results show that the three low energy surfaces are the (111), (110) and (310) with the first of these three being the most stable. These surfaces will dominate the morphology of the material. Defects including oxygen vacancies and reduced cerium ions are found to be more stable at the surfaces than in the bulk of the crystal. Finally, we show that the ready formation of oxygen vacancies on the (110) and (310) surfaces of CeO 2 significantly promotes the oxidation of carbon monoxide.

Sayle, T. X. T.; Parker, S. C.; Catlow, C. R. A.

1994-09-01

289

Interaction of Aqueous Chromium Ions with Iron Oxide Surfaces  

SciTech Connect

To gain a more fundamental understanding of abiotic processes controlling reduction reactions of aqueous chromate and dichromate ions (Cr(VI)aq) in subsurface environments, we carried out molecular-level experimental and modeling studies of the interaction of water and Cr(VI)aq with well-characterized single crystal samples of synthetic and natural hematite and magnetite. A reductionist approach was adopted in which simplified model systems of increasing complexity were studied. Photoemission spectroscopy (PES), photo-electron diffraction, and vacuum STM were used to characterize the composition, atomic structure, and morpho-logy of clean surfaces of ?-Fe?O?(0001) and Fe?O?(100) grown by molecular beam epitaxy on single crystal substrates of ?-Al?O?(0001) and MgO(100), respectively.

Brown, G. E.; Chambers, Scott A.; Amonette, James E.; Rustad, James R.; Kendelewicz, Thomas; Liu, Ping; Doyle, C. S.; Grolimund, D.; Foster, Nancy S.; Joyce, Stephen A.; Thevuthasan, Suntharampillai

2000-05-01

290

Effects of surface size on minimalistic stochastic models for the catalytic CO oxidation  

NASA Astrophysics Data System (ADS)

The impact of surface size on two minimalistic models for the bistable CO oxidation is analytically studied. A simple model for the catalytic CO oxidation on nanoscale surfaces is analyzed by the chemical master equation. The analytical results predict a shift of the bistable region and cusp point in the global bifurcation diagram as a function of surface size. A reaction-diffusion stochastic model consisting of a collection of reactive subdomains locally coupled by CO diffusion is also considered. A local description of fluctuations can be obtained after applying a Weiss-type mean-field approximation. This approximation predicts, for infinitely many subdomains, a break of ergodicity and a bifurcation behavior like in first-order phase transitions as a function of surface size and coupling parameter. Analytical results are compared with Gillespie-type Monte Carlo simulations.

Pineda, M.; Imbihl, R.; Schimansky-Geier, L.

2010-03-01

291

Plasma surface oxidation of 316L stainless steel for improving adhesion strength of silicone rubber coating to metal substrate  

NASA Astrophysics Data System (ADS)

Stainless steel 316L is one of the most widely used materials for fabricating of biomedical devices hence, improving its surface properties is still of great interest and challenging in biomaterial sciences. Plasma oxidation, in comparison to the conventional chemical or mechanical methods, is one of the most efficient methods recently used for surface treatment of biomaterials. Here, stainless steel specimens were surface oxidized by radio-frequency plasma irradiation operating at 34 MHz under pure oxygen atmosphere. Surface chemical composition of the samples was significantly changed after plasma oxidation by appearance of the chromium and iron oxides on the plasma-oxidized surface. A wettable surface, possessing high surface energy (83.19 mN m-1), was observed after plasma oxidation. Upon completion of the surface modification process, silicone rubber was spray coated on the plasma-treated stainless steel surface. Morphology of the silicone rubber coating was investigated by scanning electron microscopy (SEM). A uniform coating was formed on the oxidized surface with no delamination at polymer-metal interface. Pull-off tests showed the lowest adhesion strength of coating to substrate (0.12 MPa) for untreated specimens and the highest (0.89 MPa) for plasma-oxidized ones.

Latifi, Afrooz; Imani, Mohammad; Khorasani, Mohammad Taghi; Daliri Joupari, Morteza

2014-11-01

292

Flow induced surface enrichment of poly(ethylene-block-ethylene oxide) on polypropylene by capillary rheometer  

NASA Astrophysics Data System (ADS)

In this study, we prepared polypropylene (PP) blends with commercially available amphiphilic diblock copolymer poly(ethylene- block-ethylene oxide) (P(E- b-EO)). Selective surface enrichment of the diblock copolymer used was observed only on the PP blend extrudates which were prepared using capillary rheometer with different wall shear rates showing that flow processes play an enormous role in surface migration.

Özen, Ilhan; Rustal, Claude; Dirnberger, Klaus; Fritz, Hans-Gerhard; Eisenbach, Claus Dieter

2011-03-01

293

Indium-tin-oxide nanowhiskers crystalline silicon photovoltaics combining micro- and nano-scale surface textures  

Microsoft Academic Search

In this work, we present a solution that employs combined micro- and nano-scale surface textures to increase light harvesting in the near infrared for crystalline silicon photovoltaics, and discuss the associated antireflection and scattering mechanisms. The combined surface textures are achieved by uniformly depositing a layer of indium-tin-oxide nanowhiskers on passivated, micro-grooved silicon solar cells using electron-beam evaporation. The nanowhiskers

C. H. Chang; M. H. Hsu; W. L. Chang; W. C. Sun; Peichen Yu

2011-01-01

294

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

NASA Technical Reports Server (NTRS)

A detailed model of surface plasmon dispersion in the metal-oxide-metal tunnel diode is presented in order to clarify the spectral emission from this diode. The model predicts the location of the spectral peaks and the emission between the peaks by considering the effects of retardation on the surface plasmon. A nonradiative mode is found to play a major role in the transition from the visible to UV peaks in the diode spectra.

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

1987-01-01

295

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

PubMed

A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001). PMID:25217942

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

2014-09-14

296

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

NASA Astrophysics Data System (ADS)

A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001).

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

2014-09-01

297

Direct evidence of active surface reconstruction during oxidative dehydrogenation of propane over VMgO catalyst  

SciTech Connect

This paper presents a thorough investigation of an optimized VMgO catalyst (14 wt% V) for the oxidative dehydrogenation of propane, carried out in order to elucidate the nature and behavior of the active surface. The catalyst morphology and the surface composition are studied by means of HREM, XPS, UV-vis, XRD, and in-situ electrical conductivity techniques, as a function of the gaseous environments of the catalyst. The active surface is shown to be essentially a monolayer of amorphous VO{sub 4}{sup 3{minus}} units scattered over the magnesia as isolated and polymeric species. These surface vanadia units are found to stabilize an unusual polar (111) orientation of MgO up to temperatures of 800 C. A direct and outstanding evidence of a totally reversible phenomenon of order/disorder restructuration of this V overlayer is provided in conjunction with the redox state of the surface depending on the properties of the surrounding atmosphere (reductive or oxidative). These fast surface phenomena are assumed to determine the elementary steps of propane activation within the overall oxidative dehydrogenation of propane (ODHP) process.

Pantazidis, A.; Mirodatos, C. [C.N.R.S., Villeurbanne (France). Inst. de Recherches sur la Catalyse] [C.N.R.S., Villeurbanne (France). Inst. de Recherches sur la Catalyse; Burrows, A.; Kiely, C.J. [Univ. of Liverpool (United Kingdom). Dept. of Materials Science and Engineering] [Univ. of Liverpool (United Kingdom). Dept. of Materials Science and Engineering

1998-07-25

298

Structures and stabilities of gold oxide films on gold surfaces in O2 atmosphere  

NASA Astrophysics Data System (ADS)

The structures and stabilities of gold oxide films on gold surfaces in O2 atmosphere are investigated by a combination of thermodynamics and density functional theory (DFT) calculations. It is predicted that the stability of a gold oxide film on a gold surface depends on the formation energy of an isolated gold oxide film, the lattice mismatch, and the oxygen coverage. These predictions are subsequently confirmed by DFT calculations and thermodynamic analysis. The calculation results also display that the dual chain structure is stable on most gold surfaces at low oxygen chemical potential except on a Au(111) surface, on which the graphene-like 12 MR structure is more stable. While at the high oxygen chemical potential, the connected dual chain structure is the most stable structure because of the highest oxygen coverage and the lowest formation energy. The phase transformation point from the dual chain structure to the connected dual chain structure on a gold surface depends on the lattice mismatch between the connected dual chain and a gold surface.

Sun, Keju; Kohyama, Masanori; Tanaka, Shingo; Takeda, Seiji

2014-10-01

299

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

NASA Astrophysics Data System (ADS)

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

Pande, Kanupriya

300

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

NASA Astrophysics Data System (ADS)

Ultra-thin aluminum oxide (Al2O3) and hafnium oxide (HfO2) layers have been grown by atomic layer deposition (ALD) using tri-methyl-aluminum (TMA) and tetrakis-ethyl-methyl-amino-hafnium (TEMAH) respectively with heavy water (D2O) as the oxidizing agent. Several different silicon surfaces were used as substrates such as hydrogen terminated silicon (H/Si), SC2 (or RCA 2) cleaned native silicon oxide (SiO 2/Si), and silicon (oxy)nitride. In-situ transmission Fourier transform infrared spectroscopy (FTIR) has been adopted for the study of the growth mechanisms during ALD of these films. The vibrational spectra of gas phase TEMAH and its reaction byproducts with oxidants have also been investigated. Density functional theory (DFT) normal mode calculations show a good agreement with the experimental data when it is combined with linear wave-number scaling method and Fermi resonance mechanism. Ether (-C-O-C-) and tertiary alkylamine (N(R1R 2R3)) compounds are the two most dominant products of TEMAH reacting with oxygen gas and water. When ozone is used as the oxidant, gas phase CH2O, CH3NO2, CH3-N=C=O and other compounds containing -(C=O)- and --C-O-C- (or --O-C-) segments are observed. With substrate temperatures less than 400°C and 300°C for TMA and TEMAH respectively, Al oxide and Hf oxide ALD can be appropriately performed on silicon surfaces. Thin silicon (oxy)nitride thermally grown in ammonia on silicon substrate can significantly reduce silicon oxide interlayer formation during ALD and post-deposition annealing. The crystallization temperature of amorphous ALD grown HfO2 on nitridized silicon is 600°C, which is 100°C higher than on the other silicon surfaces. When HfO2 is grown on H/Si(111) at 100°C deposition temperature, minimum 5--10 ALD cycles are required for the full surface coverage. The steric effect can be seen by the evolution of the H-Si stretching mode at 2083 cm-1. The observed red shift of H-Si stretching to ˜ 2060 cm-1 can be caused by Si-H...Hf interactions or by the dielectric screening effect of as-grown high-kappa moiety. A summary of local bonding models with vibrational mode assignments of the adsorbed TMA and TEMAH on silicon surfaces is presented based on the analysis of the substructure of silicate interfacial band at 900--1100 cm-1.

Ho, Ming-Tsung

301

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

SciTech Connect

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

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

2006-01-16

302

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

NASA Astrophysics Data System (ADS)

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

Tessler, R.; Saguy, C.; Klin, O.; Greenberg, S.; Weiss, E.; Akhvlediani, R.; Edrei, R.; Hoffman, A.

2006-01-01

303

Research of surface-oxidation epitaxy of NiO films on cube textured Ni tapes  

NASA Astrophysics Data System (ADS)

Thin films of NiO were fabricated in air by surface-oxidation epitaxy (SOE) on biaxially-textured Ni substrate, for use as buffer layers for YBCO coated conductors. The surface-oxidation conditions such as the temperature and the reaction time, as well as the cooling rate, play a determining role in the process of epitaxial growth of the NiO layer. A continuous, biaxially-aligned textured NiO layer, was obtained for a 10 min oxidation in air at 1120 °C, and a cooling rate of 150 K/h. The roughness of the NiO layer is mostly controlled by a coarsening of some NiO grains.

Shi, D. Q.; Ionescu, M.; McKinnon, J.; Chen, W. M.; Dou, S. X.

2002-05-01

304

ROLE OF SURFACE COMPLEXED IRON IN OXIDANT GENERATION AND LUNG INFLAMMATION INDUCED BY SILICATES  

EPA Science Inventory

The hypothesis was tested that silica and silicate dusts complex iron on their surface and that this iron increases 1) in vitro oxidant generation, and mediator release by alveolar macrophages, and 2) acute inflammatory lung injury. ilica and silicates were found to complex more ...

305

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

E-print Network

Abstract The study of tin oxide is motivated by its applications as a solid state gas sensor material+ sur- face cations depending on the oxygen chemical potential of the system. Reduction of the surface response are not the lattice oxygen concentration but chemisorbed (or iono- sorbed) oxygen and other

Diebold, Ulrike

306

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

DOEpatents

The interfacial bond characteristics between carbon fiber and a cement matrix, in high temperature fiber-reinforced cementitious composite systems, can be improved by the oxidative treatment of the fiber surfaces. Compositions and the process for producing the compositions are disclosed.

Sugama, Toshifumi (Mastic Beach, NY)

1990-01-01

307

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

DOEpatents

The interfacial bond characteristics between carbon fiber and a cement matrix, in high temperature fiber-reinforced cementitious composite systems, can be improved by the oxidative treatment of the fiber surfaces. Compositions and the process for producing the compositions are disclosed. 2 figs.

Sugama, Toshifumi.

1990-05-22

308

INFLUENCE OF TEMPERATURE ON NICKEL SORPTION ON CLAY MINERAL AND OXIDE SURFACES. K. G. Scheckel1  

E-print Network

INFLUENCE OF TEMPERATURE ON NICKEL SORPTION ON CLAY MINERAL AND OXIDE SURFACES. K. G. Scheckel1- mation of metal precipitates. However, the influence of temperature on the kinetic formation of these metal pre- cipitates has not been studied. The effect of temperature on reaction rates is well known

Sparks, Donald L.

309

Interaction of cobalt atoms with an oxidized Si(111)7 × 7 surface  

NASA Astrophysics Data System (ADS)

The interaction of cobalt atoms with a Si(111)7 × 7 surface subjected to in situ oxidation in an oxygen atmosphere at a pressure of 10-5 Pa, an exposure of 20 L, and a temperature of 500°C is studied by high-decomposition (100 meV) photoelectron spectroscopy using synchrotron radiation. This surface treatment is shown to form an oxide film, which has a complex composition, occupies about 80% of the substrate surface, and has a thickness of ˜6 Å. At room temperature and a coverage of up to six monolayers, cobalt atoms are found to migrate to free (unoxidized) silicon surface spots rather than being adsorbed on the formed oxide layer. In these spots, a thin layer of cobalt disilicide first forms and a Co-Si solid solution then grows on it. Some cobalt atoms penetrate under the oxide layer and form a three-component Co-Si-O interfacial phase and a metastable cobalt disilicide with a CsCl-type structure at the SiO x -Si interface.

Gomoyunova, M. V.; Voistrik, T. E.; Pronin, I. I.

2009-05-01

310

A Laboratory Evaluation of Wipe Testing Based on Lead Oxide Surface Contamination  

Microsoft Academic Search

Although wipe testing has been used extensively as a measure of surface contamination in industrial hygiene, few scientific studies have been reported to validate the procedure with respect to quantitative recovery, repeatability or methodology. Consequently, a laboratory evaluation of wipe testing with particular attention to the OSHA procedure was undertaken using lead oxide dust as the test contaminant. A dust

CHAIYUTH CHAVALITNITIKUL; LESTER LEVIN

1984-01-01

311

Chemical changes in secondary electron emission during oxidation of nickel /100/ and /111/ crystal surfaces  

NASA Technical Reports Server (NTRS)

Changes in the secondary electron spectra (which include chemical shifts of Auger transitions) between 0-70 eV during the oxidation of both (100) and (111) nickel surfaces are reported. The reaction sequence between oxygen and nickel is also briefly described. Emission rate changes are correlated with changes in the work function of the solid.

Holloway, P. H.; Hudson, J. B.

1975-01-01

312

Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications  

Microsoft Academic Search

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

Ajay Kumar Gupta; Mona Gupta

2005-01-01

313

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

Microsoft Academic Search

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

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

2009-01-01

314

Thickness of surface thin oxide layers determined by impedance spectroscopy using silicon/oxide/electrolyte (SOE) structures  

NASA Astrophysics Data System (ADS)

The differential capacitance of SiO 2 ultra-thin layers on Si substrate is greatly sensitive to the space charge generated within the semiconductor. In the potential scan, the determination of the capacitance/voltage characteristics in MOS devices is hindered by the high value of the tunneling leakage current. In this work, the difficulty was overcome by careful measurement of the impedance diagrams using a semiconductor/oxide/electrolyte (SOE) structure, under zero current flow. Depending on the bias potential we obtained RC equivalent circuits corresponding either to the depletion layer or to the oxide dielectric film. A novel aspect of the work is that both R and C components were derived from the data processing. In a previous work the investigation was focussed on the depletion layer, and lead to values of the resistance term in the range of a few k? to a few M? cm 2, while the capacitance value was a few 10 -2 ?F cm -2. These results were consistent with a theoretical treatment of the bias voltage dependence of the charge distribution near the flatband potential, and constitute a new technique for the determination of the fb potential versus a reference electrode. The present work is devoted to the electrical properties of the Si surface oxide layer. The leakage resistance term of the thermal oxide layer, a few nm thick, was found equal to several 10 8 ? cm 2. But, the electric field within the semiconductor is not effective for the full charge of the oxide capacitance even when the polarization creates an accumulation layer. In accordance with the computed electric field within the semiconductor, the right value of the capacitance can be reached easily when the wafer is submitted to light radiation and provided the polarization of the substrate is such as to generate an inversion layer. This property leads to an accurate method for ultra-thin insulators characterization excluding tunnel leakage current.

Chemla, M.; Bertagna, V.; Erre, R.; Rouelle, F.; Petitdidier, S.; Levy, D.

2004-04-01

315

Aqueous aggregation and surface deposition processes of engineered superparamagnetic iron oxide nanoparticles for environmental applications.  

PubMed

Engineered, superparamagnetic, iron oxide nanoparticles (IONPs) have significant potential as platform materials for environmental sensing, imaging and remediation due to their unique size, physicochemical and magnetic properties. To this end, controlling the size and surface chemistry of the materials is crucial for such applications in the aqueous phase, and in particular, for porous matrixes with particle-surface interaction considerations. In this study, superparamagnetic, highly monodispersed 8 nm IONPs were synthesized and transferred into water as stable suspensions (remaining monodispersed) by way of an interfacial oleic acid bilayer surface. Once stabilized and characterized, particle-particle and model surface interactions (deposition and release) were quantitatively investigated and described systematically as a function of ionic strength (IS) and type with time-resolved dynamic light scattering (DLS), zeta potential, and real-time quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The critical coagulation concentration (CCC) for oleic acid bilayer coated iron oxide nanoparticles (OA-IONPs) were determined to be 710 mM for NaCl (matching DLVO predictions) and 10.6 mM for CaCl2, respectively. For all conditions tested, surface deposition kinetics showed stronger, more favorable interactions between OA-IONPs and polystyrene surfaces compared to silica, which is hypothesized to be due to increased particle-surface hydrophobic interactions (when compared to silica surfaces). PMID:25222070

Li, Wenlu; Liu, Di; Wu, Jiewei; Kim, Changwoo; Fortner, John D

2014-10-21

316

Surface modification of tin oxide by VUV rays and charge particle treatment: An effective method to improve the efficiency of surface catalytic behavior  

NASA Astrophysics Data System (ADS)

Plasma processing is a promising method to modify the chemical and physical properties of the semiconductor oxide surfaces. However, the tuning of surface characteristics is also influenced by plasma-emitted VUV and UV radiations. Different combinations of argon and oxygen partial pressures were applied in the capacitively coupled plasma. The highest surface conductivity was achieved with increasing plasma power, which was attributed to the interstitial defects with increased Tamm states created by the following two processes. First, the charge particle bombardment on the oxide surface, which etches the surface atoms and second, the absorption of VUV and UV radiation in the exposed layers of tin oxide nanoflakes scission the covalent bonds connecting the Sn-O atoms. The catalytic behavior of the tin oxide nanoflakes towards reducing gases have been studied as the function of Ar-O partial pressures, plasma power and voltage, and the ambient sensing temperature. Modified surface characteristics were also supported by SEM, TEM and XPS analysis.

Ganesan, Rajesh; Tolner, Harm

2011-11-01

317

On the Relation Between Oxide Ridge Evolution and Alloy Surface Grain Boundary Disorientation in Fe22 wt % Cr Alloys  

E-print Network

On the Relation Between Oxide Ridge Evolution and Alloy Surface Grain Boundary Disorientation in Fe Technology Laboratory, Albany, Oregon 97321-2198, USA Oxide ridges formed during the transient stage oxidation of the scale evolution in iron alloys containing 22 wt % Cr that were held at 800°C in dry air

Laughlin, David E.

318

Surface Instability in High Surface Area Complex Oxides: BaTiO3 Study  

NASA Astrophysics Data System (ADS)

High quality BaTiO3 powders that were synthesized with hydrothermal and solid state methods are characterized with respect to surface chemistry. Different characterization techniques are used to obtain a physical picture for the BaTiO3 powders with respect to different synthesis routes and thermal histories. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) are used to understand the BaTiO3 powders after heat and humidity treatments. Formation of amorphous and crystalline BaCO3 in local heterogeneous regions depletes the surrounding surface of Ba ions to create larger areas that are Ti-rich. BaCO3 formation and adventitious carbon adsorption occur extremely quickly on the surface of crushed single-crystal BaTiO3 powder, but for manufactured powders, the degree of carbonate formation and the impact on surface stoichiometry varies with thermal history.

Sakurai, Nobuo; Bojan, Vincent; Stapleton, Josh J.; Yang, Gai-Ying; Randall, Clive A.; Mizuno, Youichi; Chazono, Hirokazu

2009-06-01

319

Influence of surface defects and local structure on oxygenate reaction pathways over metal oxide surfaces  

SciTech Connect

Work during the last year (August 1991 to July 1992) has concentrated on completing the previously initiated studies of the surface chemistry of C{sub 1} oxygenates on particularly methanol SnO{sub 2}(110) and beginning studies of C{sub 2}oxygenate surface chemistry. During the remaining six months of the second budget period, the C{sub 2} studies will be continued.

Cox, D.F.

1992-07-01

320

Activated carbon enhanced ozonation of oxalate attributed to HO oxidation in bulk solution and surface oxidation: Effect of activated carbon dosage and pH.  

PubMed

Ozonation of oxalate in aqueous phase was performed with a commercial activated carbon (AC) in this work. The effect of AC dosage and solution pH on the contribution of hydroxyl radicals (HO) in bulk solution and oxidation on the AC surface to the removal of oxalate was studied. We found that the removal of oxalate was reduced by tert-butyl alcohol (tBA) with low dosages of AC, while it was hardly affected by tBA when the AC dosage was greater than 0.3g/L. tBA also inhibited ozone decomposition when the AC dosage was no more than 0.05g/L, but it did not work when the AC dosage was no less than 0.1g/L. These observations indicate that HO in bulk solution and oxidation on the AC surface both contribute to the removal of oxalate. HO oxidation in bulk solution is significant when the dosage of AC is low, whereas surface oxidation is dominant when the dosage of AC is high. The oxalate removal decreased with increasing pH of the solution with an AC dosage of 0.5g/L. The degradation of oxalate occurs mainly through surface oxidation in acid and neutral solution, but through HO oxidation in basic bulk solution. A mechanism involving both HO oxidation in bulk solution and surface oxidation was proposed for AC enhanced ozonation of oxalate. PMID:25288554

Xing, Linlin; Xie, Yongbing; Minakata, Daisuke; Cao, Hongbin; Xiao, Jiadong; Zhang, Yi; Crittenden, John C

2014-10-01

321

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

NASA Technical Reports Server (NTRS)

Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions.

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

1990-01-01

322

Influence of surface mechanical attrition treatment on the oxidation behavior of 316L stainless steel at 750°C  

NASA Astrophysics Data System (ADS)

In this paper, the effects of Surface Mechanical Attrition Treatment on the high- temperature oxidation of AISI 316L austenitic stainless steel are investigated. Samples treated with different conditions were oxidized at 750°C in order to study the effect of this type of nanocrystallisation on the oxidation resistance of the alloy concerned. X-ray diffraction and in- situ Raman spectroscopy were used to identify the oxides formed at the surface. The results indicate the presence of hematite, magnetite and chromium oxides. Experimental results obtained by Raman spectroscopy were also used to study the stress evolution in Cr2O3 films during isothermal conditions.

Benafia, S.; Retraint, D.; Panicaud, B.; Grosseau Poussard, J. L.

2014-08-01

323

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

NASA Technical Reports Server (NTRS)

Sputtered films of cadmium oxide were applied to sand blasted AISI 440C HT stainless steel disks as a surface pretreatment for the application of rubbed graphite films. Mixtures of cadmium oxide and graphite were applied to the nonpretreated sandblasted metal and evaluated. The results were compared to graphite films applied to other commercially available surface pretreatments. It is found that sputtered CdO pretreated surfaces increase the endurance lives of the graphite films and decrease the counterface steady state wear rate of the pins almost an order of magnitude compared to commercially available pretreatments. The CdO additions in general improved the tribological properties of graphite. The greatest benefit occurred when it was applied to the substrate rather than mixing it with the graphite and that sputtered films of CdO perform much better than rubbed CdO films.

Fusaro, Robert L.

1987-01-01

324

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

NASA Technical Reports Server (NTRS)

Sputtered films of cadmium oxide were applied to sand blasted AISI 440C HT stainless steel disks as a surface pretreatment for the application of rubbed graphite films. Mixtures of cadmium oxide and graphite were applied to the nonpretreated sandblasted metal and evaluated. The results were compared to graphite films applied to other commercially available surface pretreatments. It is found that sputtered CdO pretreated surfaces increase the endurance lives of the graphite films and decrease the counterface steady state wear rate of the pins almost an order of magnitude compared to commercially available pretreatments. The CdO additions in general improved the tribological properties of graphite. The greatest benefit occurred when it was applied to the substrate rather than mixing it with the graphite and that sputtered films of CdO perform much better than rubbed CdO films.

Fusaro, R. L.

1986-01-01

325

Spin alignment of surface oxidized CoxNi1-x/Cu(001)  

NASA Astrophysics Data System (ADS)

We investigated the ferromagnetic (FM)/antiferromagnetic (AF) spin alignment of a 13 monolayer oxidized CoxNi1-x/Cu(001) (x = 0 or 0.05) surface by X-ray magnetic circular dichroism and X-ray magnetic linear dichroism photoemission electron microscopy (XMCD-PEEM and XMLD-PEEM). Surface NiO and the underlying Ni (CoxNi1-x) were found to be AF and FM by analyzing the gray scale of XMLD-PEEM and XMCD-PEEM images; this indicates the spin orientation with respect to the polarization of the incident X-ray. We found both collinear and perpendicular alignment of the FM and AF spins. This suggests that the AF NiO is magnetically random, resulting in coercivity enhancement without exchange bias in the surface-oxidized CoxNi1-x/Cu(001) films.

Shih, Ying-Ta; Tsai, Chung-Wei; Su, Chien-Yu; Pan, Wei; Wei, Der-Hsin; Chan, Yuet-Loy; Chang, Hui-Ching

2013-05-01

326

Selective surface modification of lithographic silicon oxide nanostructures by organofunctional silanes.  

PubMed

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

Baumgärtel, Thomas; von Borczyskowski, Christian; Graaf, Harald

2013-01-01

327

Selective surface modification of lithographic silicon oxide nanostructures by organofunctional silanes  

PubMed Central

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

von Borczyskowski, Christian; Graaf, Harald

2013-01-01

328

Control of morphology and surface wettability of anodic niobium oxide microcones formed in hot phosphate–glycerol electrolytes  

Microsoft Academic Search

We report the fabrication of superhydrophobic surfaces with a hierarchical morphology by self-organized anodizing process. Simply by anodizing of niobium metal in hot phosphate–glycerol electrolyte, niobium oxide microcones, consisting of highly branched oxide nanofibers, develop on the surface. The size of the microcones and their tip angles are controlled by changing the applied potential difference in anodizing and the water

Shu Yang; Hiroki Habazaki; Takashi Fujii; Yoshitaka Aoki; Peter Skeldon; George E. Thompson

2011-01-01

329

Covalent attachment of porphyrins and ferrocenes to electrode surfaces through direct anodic oxidation of terminal ethynyl groups.  

PubMed

One with the surface: A method is presented for electrode modification with terminal alkynes and alkenes. Direct oxidation of these moieties leads to efficient grafting onto glassy carbon, gold, platinum, and indium tin oxide surfaces. Various ferrocenes and 5,10,15,20-(4-ethynylphenyl)porphyrin were attached in this way. PMID:24127205

Sheridan, Matthew V; Lam, Kevin; Geiger, William E

2013-12-01

330

Laboratory evaluation of wipe testing based on lead oxide surface contamination  

SciTech Connect

Although wipe testing has been used extensively as a measure of surface contamination in industrial hygiene, few scientific studies have been reported to validate the procedure with respect to quantitative recovery, repeatability or methodology. Consequently, a laboratory evaluation of wipe testing with particular attention to the OSHA procedure was undertaken using lead oxide dust as the test contaminant. A dust dispersion system was devised using a Wright dust feeder to produce relatively uniform surface concentrations in an aerosol chamber. Wipe materials included moistened filter paper, commercial paper towels, adhesive paper labels and adhesive tape. The quantitative recovery and repeatability of the wipe procedures were related to surface concentrations and the operational and material variables. Significant improvements in recoveries of up to 90% can be obtained with good repeatability for removable lead oxide dust on non-porous surfaces using moist paper on a fixed test surface area. For porous surfaces, which show significantly lower recovery by all methods, adhesive sampling materials applied at maximum pressure provided an optimum recovery of 77%. The importance of reliable surface contamination measurements in assessing potential health hazards underscores the desirability of improving the demonstrated deficiencies of the OSHA and other wipe sampling procedures.

Chavalitnitikul, C.; Levin, L.

1984-05-01

331

Oxidation of elemental mercury by chlorine: Gas phase, Surface,and Photo-induced reaction pathways  

SciTech Connect

Accurate oxidation rate constants of mercury gas are needed for determining its dispersion and lifetime in the atmosphere. They would also help in developing a technology for the control of mercury emissions from coal-fired power plants. However, it is difficult to establish the accurate rate constants primarily due to the fact that mercury easily adsorbs on solid surface and its reactions can be catalyzed by the surface. We have demonstrated a procedure that allows the determination of gas phase, surface-induced, and photo-induced contributions in the kinetic study of the oxidation of mercury by chlorine gas. The kinetics was studied using reactors with various surface to volume ratios. The effect of the surface and the photo irradiation on the reaction was taken into consideration. The pressure dependent study revealed that the gas phase oxidation was a three-body collision process. The third order rate constant was determined to be 7.5({+-}0.2) x 10{sup -39} mL{sup 2} molecules{sup -2}s{sup -1} with N{sub 2} as the third body at 297 {+-} 1 K. The surface induced reaction on quartz window was second order and the rate constant was 2.7 x 10{sup -17} mL{sup 2} molecules{sup -1} cm{sup -2} sec. Meanwhile, the 253.7 nm photon employed for mercury detection was found to accelerate the reaction. The utilization efficiency of 253.7 nm photon for Hg{sup 0} oxidation was 6.7 x 10{sup -4} molecules photon{sup -1} under the conditions employed in this study.

Yan, Nai-Qiang; Liu, Shou-Heng; Chang, Shih-Ger

2004-10-22

332

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

NASA Astrophysics Data System (ADS)

This thesis focuses on engineering the surface chemistry of oxide surfaces in order to control their microstructural, optical, electronic and wetting properties. Several different types of experiments have been performed to tailor the properties of silicon oxide, titanium dioxide, and zinc oxide surfaces. Applications of this work include organic electronics, sensors and nanomanufacturing. Adsorption of 3-mercaptopropyltrimethoxysilane (MPS) on hydroxylated silicon oxide substrates by immersion in MPS solution or exposure to MPS vapor has been compared using X-ray photoelectron spectroscopy (XPS). To aid the interpretation, MPS has also been cryogenically condensed in ultrahigh vacuum (UHV) onto gold surfaces. Condensation of MPS vapor on gold in the absence of water does not result in MPS polymerization, as evidenced by multilayer desorption upon warming to room temperature. The C1s XPS spectrum has been used to infer the relative abundance of methoxy groups. Vapor-deposition on hydroxylated silicon oxide leads to an unpolymerized MPS monolayer consisting of molecules with two methoxy groups. UV induced hydrophilicity of titanium dioxide surfaces could possibly be used to provide a means of registration and alignment in high-rate nanomanufacturing applications or to induce transfer of nanoelements. In order to understand the nature and magnitude of intermolecular forces, force-distance curves have been measured on TiO2. Toward the goal of possibly using light to induce nanoparticle transfer, force curves have been recorded using an SiO2 colloidal probe before and after irradiating the TiO 2 surface with UV light. In order to eliminate the effects of capillary forces, the relative humidity has been kept below 1% by flowing either N 2 or N2/O2 (1:1) into the AFM chamber. In a dry nitrogen environment, no difference is observed in adhesive forces measured with and without UV exposure. Gold-coated atomic force microscope (AFM) tips functionalized with amine-, hydroxyl, carboxylic acid, and methyl-terminated alkanethiol molecules have been used to probe the adhesive forces of polystyrene and poly(acrylic acid) films in dry air (relative humidity < 0.5%). XPS and contact angle measurements confirm the quality and uniformity of similarly treated gold surfaces and the polymer films. XPS indicates that the amine-functionalized thiol films are protonated and comprised of multilayers. Toward the goal of modifying its optical properties, ZnO nanorod surfaces have been modified using 3-mercaptopropyltriethoxysilane (MPTES) and 1-propanethiol (PPT), and XPS has been used to investigate the changes occurring on the nanorods after surface modification. XPS reveals that in the case of MPTES-modified nanorods, bonding occurs via both S-Zn and Si-O-Zn bond formation. For comparison, 3-mercaptopropyltrimethoxysilane (MPTMS), dodecanethiol and methanethiol have been adsorbed on sputter-cleaned Zn-terminated ZnO (0001) in ultrahigh vacuum (UHV). In this case, XPS indicates that bonding of thiols on ZnO surfaces occurs via S-Zn bond formation. Photoluminescence spectroscopy has been used to study the effect of surface functionalization on the optical properties of the nanorods. MPTES- and PPT-functionalized nano-ZnO show an increase in intensity of the UV emission peak relative to the unfunctionalized nanorods due to reduced probability of surface dependent non-radiative processes. A decrease in the visible peak in both cases is believed to be due to passivation of surface defects. A simple method for encapsulating zinc oxide nanoparticles within an organic matrix has been discovered that consists of dispersing them in an ethanolic solution, adding an organothiol and stirring while heating. Electron microscopy, photoemission, Raman spectroscopy and thermal gray metric analyses demonstrate that partial dissolution of the oxide occurs accompanied by encapsulation within a matrix consisting of a 1:2 zinc-thiol complex. Using this methodology, it is possible to surround ZnO within diverse matrices, including fluorescent ones. (Abstract shorte

Singh, Jagdeep

333

Association of uranium with iron oxides typically formed on corroding steel surfaces.  

PubMed

Decontamination of metal surfaces contaminated with low levels of radionuclides is a major concern at Department of Energy facilities. The development of an environmentally friendly and cost-effective decontamination process requires an understanding of their association with the corroding surfaces. We investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces. Uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite. X-ray diffraction confirmed the mineralogical form of the oxide. EXAFS analysis at the U L(III) edge showed that uranium was present in hexavalent form as a uranyl oxyhydroxide species with goethite, maghemite, and magnetite and as a bidentate inner-sphere complex with ferrihydrite and lepidocrocite. Iron was present in the ferric form with ferrihydrite, goethite, lepidocrocite, and maghemite; whereas with magnetite and green rust II, both ferrous and ferric forms were present with characteristic ferrous:total iron ratios of 0.65 and 0.73, respectively. In the presence of the uranyl ion, green rust II was converted to magnetite with concomitantreduction of uranium to its tetravalent form. The rate and extent of uranium dissolution in dilute HCl depended on its association with the oxide: uranium present as oxyhydroxide species underwent rapid dissolution followed by a slow dissolution of iron; whereas uranium present as an inner-sphere complex with iron resulted in concomitant dissolution of the uranium and iron. PMID:12214641

Dodge, C J; Francis, A J; Gillow, J B; Halada, G P; Eng, C; Clayton, C R

2002-08-15

334

Production of hydroxyapatite layers on the plasma electrolytically oxidized surface of titanium alloys.  

PubMed

Hydroxyapatite (HA) is a bioactive material that is widely used for improving the osseointegration of titanium dental implants. Titanium can be coated with HA by various methods, such as chemical vapor deposition (CVD), thermal spray, or plasma spray. HA coatings can also be grown on titanium surfaces by hydrothermal, chemical, and electrochemical methods. Plasma electrolytic oxidation (PEO), or microarc oxidation (MAO), is an electrochemical method that enables the production of a thick porous oxide layer on the surface of a titanium implant. If the electrolyte in which PEO is performed contains calcium and phosphate ions, the oxide layer produced may contain hydroxyapatite. The HA content can then be increased by subsequent hydrothermal treatment. The HA thus produced on titanium surfaces has attractive properties, such as a high porosity, a controllable thickness, and a considerable density, which favor its use in dental and bone surgery. This review summarizes the state of the art and possible further development of PEO for the production of HA on Ti implants. PMID:25175246

Lugovskoy, Alex; Lugovskoy, Svetlana

2014-10-01

335

Surface cleaning effects on reliability for devices with ultrathin oxides or oxynitrides  

NASA Astrophysics Data System (ADS)

A new wafer cleaning procedure has been developed for ultra-thin thermal oxidation process (oxides (48 angstrom) and oxynitrides grown in N2O (42 angstrom) were prepared using this new cleaning and other commonly used cleaning methods to investigate the effects of surface preparation on dielectric integrity. It has been found that this two-dip method produces dielectrics with reduced leakage current and stress-induced leakage current, which are believed to be the critical parameters for ultrathin oxides. Furthermore, this new cleaning procedure improves both intrinsic and defect-related breakdown as well as the uniformity of the current- voltage characteristics across a 4-inch wafer. The methanol/HF dip time has also been optimized. The improvement is believed to be due to enhanced silicon surface passivation by hydrogen, the reduced surface micro-roughness and the absence of native oxide.

Lai, Kafai; Hao, Ming-Yin; Chen, Wei-Ming; Lee, Jack C.

1994-09-01

336

Laser-Surface Alloying of Nimonic 80 with Silicon and Aluminum and its Oxidation Behavior  

NASA Astrophysics Data System (ADS)

In the current study, laser-surface alloying (LSA) of Nimonic 80 (a Ni-based superalloy) was conducted using a high-power continuous wave (CW) CO2 laser by simultaneous feeding of predetermined proportion of elemental Si and Al powders with an Ar shroud. After LSA, the microstructure of the alloyed zone was carefully analyzed and found to consist of several intermetallic phases of Ni and Si. The microhardness of the alloyed zone was significantly increased to 500 VHN compared with 250 VHN of the as-received substrate. The high-temperature oxidation resistance of the laser-surface-alloyed specimens (under isothermal conditions) was improved (at temperature ranges between 1223 K and 1423 K [950 °C and 1150 °C]) compared with as-received Nimonic. Even though LSA enhanced resistance to oxidation up to a limited period, continued exposure to extended hours (at a given temperature) led to spallation of scale. It seems that a SiO2-rich adherent scale is responsible for enhanced protection against oxidation in the laser-surface-alloyed specimens. However, the presence of Al2O3 in the oxide film enhances the resistance to spallation by increasing the scale adherence at a higher temperature. The results are supported by a suitable thermodynamic calculation.

Majumdar, Jyotsna Dutta; Manna, Indranil

2012-10-01

337

Surface analysis reveals biogenic oxidation of sub-bituminous coal by Pseudomonas fluorescens.  

PubMed

Direct analysis of the colonised surface on coal using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) revealed the nature of bacteria-mediated oxidation at the coal surface. Unique oxidation peaks generated by the presence of Pseudomonas fluorescens on coal was shown through ATR-FTIR measurements, and ATR-FTIR imaging illustrated that this peak was only observed within the region of coal colonised by bacteria. Contact angle measurements and surface free energy of adhesion calculations showed that the adhesion between P. fluorescens and coal was thermodynamically favourable, and scanning electron microscopy (SEM) exhibited individual cell or monolayer cluster attachment on coal. Furthermore, Gaussian peak fitting of peroxidase-treated coal ATR-FTIR spectra revealed that peroxidase or related enzymes produced by P. fluorescens may be responsible for coal oxidation. This study demonstrated the usefulness and practicality of ATR-FTIR for analysing coal oxidation by P. fluorescens and may well be applied to other microbe-driven modifications of coal for its rapidity and reliability. PMID:24898633

Hazrin-Chong, Nur Hazlin; Marjo, Christopher E; Das, Theerthankar; Rich, Anne M; Manefield, Mike

2014-07-01

338

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

NASA Technical Reports Server (NTRS)

Photoemission cross sections were calculated for the ZnO4(-6) cluster using the self consistent-chi alpha- scattered wave theory to display the main features of the ultraviolet and X-ray photoemission data from ZnO. A solid model is suggested for an absolute photoemission intensity comparison resulting in chi alpha intensities which are roughly 70% of the experimental values. Together with the experimental data, the calculations allow a complete determination of the electronic structure of a ZnO surface.

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

1978-01-01

339

Studies on the Surface Chemistry of Oxide Films Formed on IN738LC Superalloy at Elevated Temperatures in Dry Air  

Microsoft Academic Search

The oxidation behavior of IN-738LC was studied to develop high-temperature materials for low cost and highly efficient turbine systems. The present study was undertaken to investigate the kinetics and the surface chemistry of the oxide films formed during isothermal oxidation of IN-738LC superalloy in the temperature range 1123–1223 K in dry air. The oxidation kinetics followed the parabolic law. The

S. Seal; S. C. Kuiry; Leyda A. Bracho

2001-01-01

340

CO Oxidation Facilitated by Robust Surface States on Au-Covered Topological Insulators  

SciTech Connect

Surface states the electronic states emerging as a solid material terminates at a surface are usually vulnerable to contaminations and defects. The robust topological surface state(s) (TSS) on the three-dimensional topological insulators provide a perfect platform for exploiting surface states in less stringent environments. Employing first-principles density functional theory calculations, we demonstrate that the TSS can play a vital role in facilitating surface reactions by serving as an effective electron bath. We use CO oxidation on gold-covered Bi2Se3 as a prototype example, and show that the robust TSS can significantly enhance the adsorption energy of both CO and O2 molecules, by promoting different directions of electron transfer. The concept of TSS as an electron bath may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis.

Chen, Hua [University of Tennessee, Knoxville (UTK); Zhu, Wenguang [ORNL; Xiao, Di [ORNL; Zhang, Zhenyu [University of Science and Technology, Beijing, China

2011-01-01

341

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

PubMed Central

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

2012-01-01

342

Electron-induced surface reactivity modification in Zinc oxide-based thin films  

SciTech Connect

Chemical surface reactivity is a key parameter in modern microelectronic and display technology that is defined by basic physical interactions at the liquid etcher/material surface interface. We apply recently developed low-energy electron irradiation method for surface modification of zinc oxide-based thin films affording to vary physical processes at the liquid agent/material surface interface/and widely tune its chemical reactivity. Electron irradiation leads to the formation of ultrathin layer on irradiated surface, without generation of volumetric defects, and preserves original optical and conductive properties. The method allows fabrication of high-resolution patterned templates with modified chemical etching resistance for the fabrication of three-dimensional patterned arrays.

Sabayev, V.; Aronov, D.; Rosenman, G. [Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); Oster, L. [Sami Shamoon Academic College of Engineering, Beer-Sheva 84100 (Israel)

2008-10-06

343

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

344

Eu oxides on Ni(100): Polar surfaces, magic clusters and structures with large lattice dilation  

NASA Astrophysics Data System (ADS)

Sub-monolayers of Eu oxide were grown on Ni(100) and analysed by means of in-situ scanning tunnelling microscopy and low energy electron diffraction. For changes of the O2 pressure not more than a factor of two, four different surface phases were found which consist of EuO(111), 'magic' clusters and two 2-dimensional nano-layers without a counterpart in bulk Eu oxides. A structural model for one of the latter phases suggests an O-O nearest neighbour (NN) distance of 4.4 Å — considerably larger than the 3.64 Å for bulk EuO.

Förster, Daniel F.; Klinkhammer, Jürgen; Michely, Thomas

2012-07-01

345

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

SciTech Connect

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

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

2009-01-01

346

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

SciTech Connect

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

Parkinson, Bruce

2010-06-04

347

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

348

A Simple Nanoscale Interface Directs Alignment of a Confluent Cell Layer on Oxide and Polymer Surfaces  

PubMed Central

Templating of cell spreading and proliferation is described that yields confluent layers of cells aligned across an entire two-dimensional surface. The template is a reactive, two-component interface that is synthesized in three steps in nanometer thick, micron-scaled patterns on silicon and on several biomaterial polymers. In this method, a volatile zirconium alkoxide complex is first deposited at reduced pressure onto a surface pattern that is prepared by photolithography; the substrate is then heated to thermolyze the organic ligands to form surface-bound zirconium oxide patterns. The thickness of this oxide layer ranges from 10 to 70 nanometers, which is controlled by alkoxide complex deposition time. The oxide layer is treated with 1,4-butanediphosphonic acid to give a monolayer pattern whose composition and spatial conformity to the photolithographic mask are determined spectroscopically. NIH 3T3 fibroblasts and human bone marrow-derived mesenchymal stem cells attach and spread in alignment with the pattern without constraint by physical means or by arrays of cytophilic and cytophobic molecules. Cell alignment with the pattern is maintained as cells grow to form a confluent monolayer across the entire substrate surface. PMID:23936630

Donnelly, Patrick E.; Jones, Casey M.; Bandini, Stephen B.; Singh, Shivani; Schwartz, Jeffrey; Schwarzbauer, Jean E.

2013-01-01

349

Strong Reciprocal Interaction between Polarization and Surface Stoichiometry in Oxide Ferroelectrics.  

PubMed

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

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

2014-11-12

350

Modular "click" chemistry for electrochemically and photoelectrochemically active molecular interfaces to tin oxide surfaces.  

PubMed

We demonstrate the use of "click" chemistry to form electrochemically and photoelectrochemically active molecular interfaces to SnO(2) nanoparticle thin films. By using photochemical grafting to link a short-chain alcohol to the surface followed by conversion to a surface azide group, we enable use of the Cu(I)-catalyzed azide-alkyne [3 + 2] cycloaddition (CuAAC) reaction, a form of "click" chemistry, on metal oxide surfaces. Results are shown with three model compounds to test the surface chemistry and subsequent ability to achieve electrochemical and photoelectrochemical charge transfer. Surface-tethered ferrocene groups exhibit good electron-transfer characteristics with thermal rates estimated at >1000 s(-1). Time-resolved surface photovoltage measurements using a ruthenium terpyridyl coordination compound demonstrate photoelectron charge transfer on time scales of nanoseconds or less, limited by the laser pulse width. The results demonstrate that the CuAAC "click" reaction can be used to form electrochemically and photoelectrochemically active molecular interfaces to SnO(2) and other metal oxide semiconductors. PMID:21766849

Benson, Michelle C; Ruther, Rose E; Gerken, James B; Rigsby, Matthew L; Bishop, Lee M; Tan, Yizheng; Stahl, Shannon S; Hamers, Robert J

2011-08-01

351

Chemically patterned, metal oxide based surfaces produced by photolithographic techniques for studying protein- and cell-surface interactions I: Microfabrication and surface characterization.  

PubMed

Chemical patterns on smooth wafer substrates comprising areas with two different metals have been produced by vacuum metal deposition and photolithographic techniques. The combination of metals has been chosen from the series titanium (Ti), aluminium (Al), vanadium (V) and niobium (Nb), producing patterns (dots and stripes with dimensions of 50, 100 and 150 micrometer) with one of the metals as the background and with the second metal (foreground pattern) deposited on the background metal. The structure and chemical composition of the patterned surfaces were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy and imaging time-of-flight secondary-ion mass spectrometry. The surfaces proved to be geometrically well defined with the expected surface-chemical composition, i.e. a surface oxide (passive) film essentially composed of TiO(2),Al(2)O(3),V(2)O(5), or Nb(2)O(5). Ti/Ti patterned surfaces were produced as controls and found to show no chemical composition contrast. The surface roughness of the pattern was greater than that of the background by a factor of 2-3, but was still extremely smooth with Ra<2nm. The patterns serve as model surfaces for studying in vitro the behaviour of cells as well as the adsorption of serum proteins on different metal oxides, which will be reported in a companion paper. These surfaces can be used to compare and contrast the response of osteoblasts to Ti and other alloy components, such as Al, V, or Nb, which are used in load-bearing medical implants. PMID:12527254

Winkelmann, M; Gold, J; Hauert, R; Kasemo, B; Spencer, N D; Brunette, D M; Textor, M

2003-03-01

352

Adsorption and dissociation of methanol on the fully oxidized and partially reduced (111) cerium oxide surface: dependence on the configuration of the cerium 4f electrons  

SciTech Connect

The adsorption and dissociation of methanol on the fully oxidized and partially reduced (111) cerium oxide surface is studied using the PW91 functional as well as the PW91+U scheme. We investigate the influence of the detailed electronic structure of the Ce 4f band on the chemistry of methanol on the surface. For the partially reduced surface we obtain a spin delocalized, a ferromagnetic, and an anti-ferromagnetic solution. We find that the qualitative conclusions are independent of the surface type used. Methanol adsorption is exothermic on the fully oxidized as well as on the partially reduced surface. Also dissociation of methanol on the surface is exothermic but strongly enhanced by the presence of a vacancy. We localize an on-top methoxy species as a dissociation product on the fully oxidized surface and a triply bridged methoxy species on the partially reduced surface where the methoxy oxygen partly fills the oxygen vacancy in the surface. Adsorption energies are influenced by the introduction of the repulsive Hubbard (U) term. On the other hand, relative surface stabilities like dissociation energies are less sensitive.

Beste, Ariana [ORNL; Mullins, David R [ORNL; Overbury, Steven {Steve} H [ORNL; Harrison, Robert J [ORNL

2008-01-01

353

Helium-surface interaction potential: Determination and applications  

NASA Astrophysics Data System (ADS)

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

Batra, Inder P.

1984-12-01

354

Analysis of protein solvent accessible surfaces by photochemical oxidation and mass spectrometry.  

PubMed

Protein surfaces are important in most biological processes, including protein-protein interactions, enzymatic catalysis, and protein-ligand binding. We report a method in which hydroxyl radicals generated by a rapid-UV irradiation of a 15% hydrogen peroxide solution were utilized to oxidize specific amino acid side chains of two model proteins (lysozyme, beta-lactoglobulin A), according to the residues' chemical reactivities and the solvent accessibility of the reactive carbons and sulfurs in the residue. Oxidized peptides generated by tryptic digestion were identified by electrospray-Fourier transform mass spectrometry. The specific sites of the stable modification were then identified by reverse-phase liquid chromatography coupled to quadropole ion trap tandem mass spectrometry. The solvent accessibility of the residue was shown to directly affect the rate of oxidation by this method (with the exception of methionine), supporting its use as a rapid measure of the solvent accessibility of specific residues, and in some cases, individual atoms. PMID:14750862

Sharp, Joshua S; Becker, Jeffrey M; Hettich, Robert L

2004-02-01

355

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

SciTech Connect

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

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

2008-06-05

356

Evaluation of lipid oxidative stress status and inflammation in atopic ocular surface disease  

PubMed Central

Background Although the oxidative stress status in atopic skin disease has been reported to be elevated, there are still no studies related to the status of oxidative stress in atopic ocular surface disease. The purpose of this study was to evaluate the ocular surface lipid oxidative stress status and inflammation in atopic keratoconjunctivitis (AKC) patients and normal subjects. Methods Twenty eight eyes of 14 patients (9 males, 5 females) with AKC and 18 eyes of 9 age and sex matched (4 males and 5 females) normal healthy controls were examined in this prospective study. The severity of atopic dermatitis (AD) was scored by the SCORing Atopic Dermatitis (SCORAD) index. All subjects underwent Schirmer test, tear film break up time (BUT), fluorescein/Rose Bengal stainings, tear collection, and brush cytology from the upper palpebral conjunctiva. The brush cytology samples were stained with Diff-Quik for differentiation of inflammatory cells and immunohistochemistry (IHC) staining with HEL (hexanoyl-lysine) and 4-HNE (4-hydroxy-2-nonenal) to study lipid oxidation. HEL and cytokine (interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-?), interferon-gamma (IFN-?)) levels were measured by enzyme-linked immunosorbent assay (ELISA) from tear samples of AKC patients and control subjects. Toluidine Blue and IHC staining with HEL, 4-HNE and cluster of differentiation 45 (CD45) were performed on papillary samples of AKC patients. This study was conducted in compliance with the “Declaration of Helsinki.” Results The tear stability and vital staining scores were significantly worse in eyes of AKC patients (p<0.05) compared to the controls. Inflammatory cells and positively stained conjunctival epithelial cells for HEL and 4-HNE showed a significant elevation in brush cytology samples of AKC patients. Significantly higher levels of HEL and cytokines were detected in tears of AKC patients compared to controls. Papillary specimens also revealed many CD45 inflammatory cells as well as many cells positively stained with HEL and 4-HNE in IHC. A strong significant linear positive correlation between conjunctival inflammation and epithelial lipid oxidative stress status was observed. Conjunctival lipid oxidative stress also correlated strongly with tear HEL levels and epithelial damage scores. Conclusions The ocular surface disease in AKC was characterized by marked tear instability, ocular surface epithelial damage, increase in inflammatory infiltrates and presence of increased lipid oxidation. PMID:21139696

Wakamatsu, Tais H.; Ayako, Igarashi; Takano, Yoji; Matsumoto, Yukihiro; Ibrahim, Osama M.A.; Okada, Naoko; Satake, Yoshiyuki; Fukagawa, Kazumi; Shimazaki, Jun; Tsubota, Kazuo; Fujishima, Hiroshi

2010-01-01

357

Magnesium surface segregation and oxidation in Al–Mg alloys studied with local probe scanning Auger-scanning electron microscopy  

Microsoft Academic Search

Magnesium surface segregation and oxidation were investigated in Al–Mg alloys with a surface texture characterized by branched and dendritic disordered features of low Mg concentration having a lateral 2-D fractal dimension DB?1.77. Phase separation of areas with high (?38% at.) and low (?14% at.) Mg content allows direct observation of distinct differences in Mg surface segregation and oxidation across disordered

D. T. L. van Agterveld; G. Palasantzas; J. Th. M. De Hosson

1999-01-01

358

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

PubMed

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

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

2014-10-22

359

Surface-initiated synthesis of poly(3-methylthiophene) from indium tin oxide and its electrochemical properties.  

PubMed

Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm. Electrochemical oxidative doping of these films was used to manipulate their near surface composition and effective work function. Doped states of the P3MT film are maintained even after the sample is removed from solution and potential control confirming the robustness of the films. Such materials with controllable thicknesses and electronic properties have the potential to be useful as interlayer materials for organic electronic applications. PMID:22149001

Doubina, Natalia; Jenkins, Judith L; Paniagua, Sergio A; Mazzio, Katherine A; MacDonald, Gordon A; Jen, Alex K-Y; Armstrong, Neal R; Marder, Seth R; Luscombe, Christine K

2012-01-24

360

Effect of surface oxide on the melting behavior of lead-free solder nanowires and nanorods  

NASA Astrophysics Data System (ADS)

Lead-free nanosolders have shown promise in nanowire and nanoelectronics assembly. Among various important parameters, melting is the most fundamental property affecting the assembly process. Here we report that the melting behavior of tin and tin/silver nanowires and nanorods can be significantly affected by the surface oxide of nanosolders. By controlling the nanosolder reflow atmosphere using a flux, the surface oxide of the nanowires/nanorods can be effectively removed and complete nanosolder melting can be achieved. The complete melting of the nanosolders leads to the formation of nanoscale to microscale spherical solder balls, followed by Ostwald ripening phenomenon. The contact angle of the microscale solder balls formed on Si substrate was measured by direct electron microscopic imaging. These results provide new insights into micro- and nanoscale phase transition and liquid droplet coalescence from nanowires/nanorods to spheroids, and are relevant to nanoscale assembly and smaller ball grid array formation.

Gao, Fan; Rajathurai, Karunaharan; Cui, Qingzhou; Zhou, Guangwen; NkengforAcha, Irene; Gu, Zhiyong

2012-07-01

361

The Performance of Ce Surface Treated Ferritic Stainless Steels for Solid Oxide Fuel Cell Interconnects  

SciTech Connect

This research deals with the effect of a Ce surface treatment on the behavior of Fe-Cr-Mn ferritic stainless steels which may have application in SOFC technology. This treatment consisted of applying a slurry of CeO2 and a halide activator to the surface of coupons. After the slurry dried the coupons were heated to 900C in a controlled atmosphere furnace for 12 hours. The effectiveness of the treatment on commercial (Type 409 (12Cr), Type 430 (18Cr), Crofer 22APU (22Cr), Type 446(26Cr)) and experimental (NETL F9 (12Cr) and NETL F5 (22Cr)) alloys as a function of Cr content will be presented. The oxidation behavior of the alloys was assessed by exposing coupons (untreated and treated) to moist air at 800C. Area specific resistance (ASR) was measured at 800C. In general, the rare earth treatment effectively reduced the oxidation rate, resulting in thinner oxide scales and less internal oxidation.

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

2007-09-01

362

Characterization of surface and photooxidative properties of supported metal oxide photocatalysts using solid-state NMR.  

PubMed

In situ solid-state NMR (SSNMR) methodologies have been used to investigate the surface properties and photooxidative reactivities of a number of metal oxide photocatalysts. Adsorption of ethanol on single monolayers of TiO2, SnO2, V205, and WO3 supported on porous Vycor glass results in the formation of hydrogen-bonded ethanol species and metal-bound ethoxide species. The chemical shift of the metal-bound ethoxide species varies with the metal oxide catalyst while the chemical shift of the hydrogen-bonded species is independent of the metal oxide. X-ray powder diffraction, UV-VIS spectroscopy, and SSNMR investigations of ethanol adsorption show that increasing the number of monolayers of TiO2 on the Vycor surface changes the morphology of the catalyst from amorphous at a single monolayer coverage to anatase at a four monolayer coverage. The rate of photocatalytic oxidation of ethanol, acetone, and 2-propanol also increases with increasing TiO2 monolayer coverage. PMID:11993648

Pilkenton, S; Xu, W; Raftery, D

2001-01-01

363

Surface modification of Ti{sub 3}Al for improved oxidation resistance  

SciTech Connect

Ti{sub 3}Al has very attractive properties such as low density and high temperature mechanical strength for elevated temperature structural applications. Its major drawback however, is poor oxidation resistance at temperatures above 600{degrees}C. Potential use of Ti{sub 3}Al in high temperature applications depends on its protection from excessive oxidation. To this effect, Al{sub 2}O{sub 3} and Al{sub 3}Ti were selected as coating materials chemically compatible with Ti{sub 3}Al. Al{sub 2}O{sub 3} acts as a protective layer on the surface of Ti{sub 3}Al and is impervious to oxygen diffusion. Al{sub 3}Ti is resistant to high temperatures and also protects the Ti{sub 3}Al substrate by forming an oxide layer consisting primarily of Al{sub 2}O{sub 3}. In this study, Al{sub 2}O{sub 3} was plasma sprayed onto the surface of Ti{sub 3}Al, while the Al{sub 3}Ti was applied by laser melting. Effectiveness of the coatings were investigated after 10 hours of cyclic oxidation.

Vaidya, R.U.; Zurek, A.K.; Castro, R. [Los Alamos National Lab., NM (United States); Sin, Y.W.; Subramanian, K.N. [Michigan State Univ., East Lansing, MI (United States). Dept. of Materials Science and Mechanics

1993-08-01

364

Preparation of water-dispersible graphene by facile surface modification of graphite oxide  

NASA Astrophysics Data System (ADS)

Water-dispersible graphene was prepared by reacting graphite oxide and 6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS). X-ray diffraction study showed that the basal reflection (002) peak of graphite oxide was absent in the ANS-functionalized graphene (ANS-G), indicating crystal layer delamination. Ultraviolet-visible spectral data were recorded to assess the solubility of the ANS-G in water. Fourier transform infrared spectral analysis suggested the attachment of ANS molecules to the surface of graphene. Raman and x-ray photoelectron spectroscopy revealed that oxygen functionality in the graphite oxide had been removed during reduction. Atomic force microscopy found that the thickness of ANS-G in water was about 1.8 nm, much higher than that of single layer graphene. Thermal stability measurements also indicated successful removal of oxygen functionality from the graphite oxide and the attachment of thermally unstable ANS to the graphene surfaces. The electrical conductivity of ANS-G, determined by a four-point probe, was 145 S m - 1 at room temperature.

Kuila, Tapas; Khanra, Partha; Bose, Saswata; Kim, Nam Hoon; Ku, Bon-Cheol; Moon, Bongho; Lee, Joong Hee

2011-07-01

365

Advances in surface-oxidation epitaxy processed substrates for YBa 2Cu 3O 7- ? film  

NASA Astrophysics Data System (ADS)

The preparation of long oxide template using surface-oxidation epitaxy (SOE) method and the deposition of oxide cap layer and YBa 2Cu 3O 7- ? (YBCO) film on it have been studied for the fabrication of coated conductors. In SOE process, Cr-oxide behaves as a barrier against Cr contamination with SOE-NiO layer in high strength and low magnetism Ni-clad Ni-20wt.%Cr (Ni/NiCr) tape. MgO cap layer makes SOE-processed tape surface smooth with the average roughness of a few nm. The critical current ( Ic) of 8 A (the critical current density ( Jc) of 0.2 MA/cm 2) was obtained for the YBCO film deposited on a 10 cm long×5 mm width SOE-processed tape with MgO cap layer in a short sample cut from a 10 cm long specimen. Jc exceeding 0.1 MA/cm 2 was obtained for YBCO film on SrTiO 3 cap layer and CeO 2 one of SOE-processed tape.

Watanabe, T.; Wada, K.; Ohashi, Y.; Ozaki, M.; Yamamoto, K.; Maeda, T.; Hirabayashi, I.

2002-10-01

366

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

NASA Astrophysics Data System (ADS)

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

Salame, Issa I.; Bandosz, Teresa J.

367

Mechanism of Surface Morphology Development of Tin Oxide Transparent Conductive Films  

NASA Astrophysics Data System (ADS)

The surface morphology of tin oxide transparent conductive films deposited by chemical vapor deposition was studied. The development of surface crystallites was observed, and the change in the crystalline orientations was evaluated at several stages of film growth. The prismatic and triangular pyramidal-shaped crystallites on the surface were characterized as (200) and (110) oriented, respectively, based on the knowledge of crystal habit appearing on cassiterite mineral crystals and periodic bond chain theory. The prismatic shape consisted of flat 110, while the triangular pyramidal shape consisted of two 101 and one rough surface, which is brought about by the imperfectness of the kinked 111. Although these two orientations exist in films from the initial growth stage, switching of the most dominant crystalline orientation from (110) to (200) occurs as the morphology of the film changes from an isolated island to competitive growths.

Matsui, Yuji; Matsuishi, Kiyoto; Kojima, Seiji

2012-02-01

368

Molecular functionalization of tantalum oxide surface towards development of apatite growth  

NASA Astrophysics Data System (ADS)

We have studied the apatite growth dynamics on tantalum oxide surfaces. This nucleation is obtained via an organosilane intermediate layer between the apatite and the substrate surface. Four organosilane layers (differing by their terminal functionality) were investigated. Their characterization with atomic force microscopy and other techniques such as X-ray photoelectron spectroscopy (XPS) and wetting measurements highlighted the influence of the organosilane terminal groups on the apatite growth rates. Results revealed that apatite is indeed growing faster on phosphate terminal groups than on the three other groups studied (vinyl, hydroxyl and carboxyl).

Aubry, D.; Volcke, C.; Arnould, Ch.; Humbert, C.; Thiry, P. A.; Delhalle, J.; Mekhalif, Z.

2009-02-01

369

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

370

Mechanical properties of chitosan\\/bamboo charcoal composite films made with normal and surface oxidized charcoal  

Microsoft Academic Search

Chitosan\\/bamboo charcoal composite films were prepared by blending chitosan with either virgin bamboo charcoal or bamboo charcoal modified by nitric acid oxidation to provide more hydrophilic regions on the bamboo charcoal surface. Investigation of the physical properties of these composite films revealed that the tensile strength and Young’s modulus of the chitosan films were enhanced in a dose-dependent manner by

Walaikorn Nitayaphat; Nantana Jiratumnukul; Sireerat Charuchinda; Siriwan Kittinaovarat

2009-01-01

371

Corrosion resistance and surface biocompatibility of a microarc oxidation coating on a Mg–Ca alloy  

Microsoft Academic Search

The Mg–Ca alloy system has been proposed as a potential new kind of degradable biomaterial with possible application within bone. Here microarc oxidation (MAO) coatings were fabricated on top of a Mg–Ca alloy using different applied voltages and the effect of applied voltage on the surface morphology and phase constitution, hydrogen evolution, pH variation in the immersion solution and in

X. N. Gu; N. Li; W. R. Zhou; Y. F. Zheng; X. Zhao; Q. Z. Cai; Liquan Ruan

2011-01-01

372

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

Microsoft Academic Search

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

Colin Johnson; Jim Henshaw; Gordon McLnnes

1992-01-01

373

The structure and surface acidity of zirconia-supported tungsten oxides  

Microsoft Academic Search

The structure and surface acidity of zirconia-supported tungsten oxide are studied by using BET, XRD, FT Raman, Tian–Calvet\\u000a microcalorimetry as well as XPS. Three different crystal forms of ZrO2 and their hydroxide precursors were prepared in a controllable way. It was found that the starting material and preparing\\u000a conditions used have a significant effect on the structure of ZrO2 obtained.

Weijie Ji; Jingqiu Hu; Yi Chen

1998-01-01

374

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

SciTech Connect

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

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

1996-03-01

375

Highly oriented, self-assembled alkanephosphate monolayers on tantalum(V) oxide surfaces  

Microsoft Academic Search

Octadecyl phosphoric acid ester has been found to produce oriented, well-ordered monolayers on a flat tantalum(V) oxide surface, via self-assembly from a heptane\\/propan-2-ol solution. By means of contact angle, optical waveguide lightmode spectroscopy (OWLS), near-edge X-ray absorption fine structure spectroscopy (NEXASFS), and X-ray photoelectron spectroscopy (XPS) measurements, it has been shown that these layers closely resemble those formed by the

Dorothee Brovelli; G. Haehner; Laurence Ruiz; Rolf Hofer; Gerolf Kraus; Adrian Waldner; Johanna Schlösser; Peter Oroszlan; Markus Ehrat; Nicholas D. Spencer

1999-01-01

376

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

NASA Technical Reports Server (NTRS)

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

Librecht, K. G.

1979-01-01

377

Fatigue behavior of carburized steel with internal oxides and nonmartensitic microstructure near the surface  

Microsoft Academic Search

The characteristic fatigue behavior of carburized and quenched steel with internal oxides and non-martensitic microstructure\\u000a near the surface was presented through rotating bending fatigue test. The S-N diagram revealed two knees and the specimens\\u000a continued to fail over 107 stress cycles. The fatigue limit could not be obtained even at 108 stress cycles. The test results were compared to those

Takeshi Naito; Hideo Ueda; Masao Kikuchi

1984-01-01

378

Solid state chemistry of nitrogen oxides--part II: surface consumption of NO2.  

PubMed

Nitrogen oxides are considered to be important astrochemical precursors of complex species and prebiotics. However, apart from the hydrogenation of solid NO that leads to the surface formation of hydroxylamine, little is known about the full solid state reaction network involving both nitrogen and oxygen. Our study is divided into two papers, hereby called Part I and Part II. In the accompanying paper, we investigate the surface reactions NO + O/O2/O3 and NO + N with a focus on the formation of NO2 ice. Here, we complement this study by measurements of the surface destruction of solid NO2, e.g., NO2 + H/O/N. Experiments are performed in two separate ultra-high vacuum setups and therefore under different experimental conditions to better constrain the experimental results. Surface reaction products are monitored by means of Fourier Transform Reflection Absorption Infrared Spectroscopy (FT-RAIRS) and Temperature Programmed Desorption (TPD) techniques using mass spectrometry. The surface destruction of solid NO2 leads to the formation of a series of nitrogen oxides such as NO, N2O, N2O3, and N2O4 as well as HNO, NH2OH, and H2O. When NO2 is mixed with an interstellar more relevant apolar (i.e., CO) ice, solid CO2 and HCOOH are also formed due to interactions between different reaction routes. The astrophysical implications of the full nitrogen and oxygen reaction network derived from Parts I and II are discussed. PMID:24671439

Ioppolo, S; Fedoseev, G; Minissale, M; Congiu, E; Dulieu, F; Linnartz, H

2014-05-14

379

A Slightly Oxidizing Etchant for Polishing of CdTe and CdZnTe Surfaces  

NASA Astrophysics Data System (ADS)

New iodine-evolving etching solutions were developed for surface treatment of CdTe and CdZnTe crystals. The nature of the chemical dissolution of CdTe samples with (100), (110), and (111) orientations, and also of (211) Cd0.96Zn0.04Te samples, in KIO3-KI-lactic acid solution was studied. It was established that this dissolution is diffusion controlled. Surface roughness measurements revealed highly polishing properties of the etchant. A study of the chemical composition and structure of the (211)B Cd0.96Zn0.04Te surfaces etched under different conditions was carried out. The thickness of the Te oxide layer was evaluated in the course of heating in vacuum. KIO3-KI-lactic acid treatment appears to be preferable in terms of elimination of Te oxides from the surface as compared with standard Br2-methanol solution. The etching compositions were shown to be useful for chemical polishing of CdTe-based surfaces.

Ivanits'ka, V. G.; Moravec, P.; Tomashik, V. M.; Mašek, K.; Tomashik, Z. F.; Franc, J.; Grill, R.; Höschl, P.

2013-11-01

380

Atomistic and electronic structure calculation of defects at the surfaces of oxides  

NASA Astrophysics Data System (ADS)

We present the results of simulations using both atomistic and density functional theory (DFT) approaches that illustrate the uses of these techniques for investigating the structure and electronic structure of defects at the surfaces of oxides. Atomistic simulation studies of the low index surfaces of spinel (MgAl2O4) will show the role of vacancy configuration and surface rearrangement. Atomistic and DFT studies on Li doped MgO illustrate the importance of both the defect structure and its effect of morphology. We will also illustrate using DFT electronic defects at the surface of CeO2 , which are of great importance in redox reactions and catalytic activity. Finally we will present a novel atomistic approach for predicting the structure of supported oxide nanoclusters giving rise to a wide range of defects including a range of surface terminations, grain formation, mixed screw edge dislocations and misfit dislocations. We will illustrate this using the structure of a BaO supported MgO nanocluster.

Watson, G. W.

381

Cell surface characteristics enable encrustation-free survival of neutrophilic iron-oxidizing bacteria  

NASA Astrophysics Data System (ADS)

Microbial growth in mineralizing environments depends on the cells' ability to evade surface precipitation. Cell-mineral interactions may be required for metabolism, but if unmoderated, cells could become encrusted, which would limit diffusion of nutrients and waste across cell walls. A combination of cell surface charge and hydrophobicity could enable the survival of microbes in such environments by inhibiting mineral attachment. To investigate this mechanism, we characterized the surfaces of two neutrophilic iron-oxidizing bacteria (FeOB): Mariprofundus ferrooxydans, a Zetaproteobacterium from Fe(II)-rich submarine hydrothermal vents and a Betaproteobacterium Gallionellales strain R-1, recently isolated from a ferrous groundwater seep. Both bacteria produce iron oxyhydroxides, yet successfully escape surface encrustation while inhabiting milieu where iron minerals are also produced by abiotic processes. SEM-EDX and TEM-EELS analyses of cultured bacteria revealed no iron on the cell surfaces. Zeta potential measurements showed that these bacteria have very small negative surface charge (0 to -4 mV) over a pH range of 4-9, indicating near-neutrally charged surfaces. Water contact angle measurements and thermodynamic calculations demonstrate that both bacteria and abiotically-formed Fe oxhydroxides are hydrophilic. Extended-DLVO calculations showed that hydrophilic repulsion between cells and minerals dominates over electrostatic and Lifshitz-van der Waals interactions. This leads to overall repulsion between microbes and minerals, thus preventing surface encrustation. Low surface charge and hydrophilicity (determined by microbial adhesion to hydrocarbon assay) were common features for both live and azide-inhibited cells, which shows that surface characteristics do not depend on active metabolism. It is remarkable that these two phylogenetically-distant bacteria from different environments employ similar adaptations to prevent surface mineralization. Our results confirm that surface characteristics can be a mechanism for survival in mineralizing environments. We predict that biotechnological applications such as bioremediation and microbial mineral carbon sequestration will benefit from microbes that can similarly avoid encrustation.

Saini, G.; Chan, C. S.

2011-12-01

382

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

SciTech Connect

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

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

2005-02-01

383

Ion beam deposition and surface characterization of thin multi-component oxide films during growth.  

SciTech Connect

Ion beam deposition of either elemental targets in a chemically active gas such as oxygen or nitrogen, or of the appropriate oxide or nitride target, usually with an additional amount of ambient oxygen or nitrogen present, is an effective means of depositing high quality oxide and nitride films. However, there are a number of phenomena which can occur, especially during the production of multicomponent films such as the ferroelectric perovskites or high temperature superconducting oxides, which make it desirable to monitor the composition and structure of the growing film in situ. These phenomena include thermodynamic (Gibbsian), and oxidation or nitridation-driven segregation, enhanced oxidation or nitridation through production of a highly reactive gas phase species such as atomic oxygen or ozone via interaction of the ion beam with the target, and changes in the film composition due to preferential sputtering of the substrate via primary ion backscattering and secondary sputtering of the film. Ion beam deposition provides a relatively low background pressure of the sputtering gas, but the ambient oxygen or nitrogen required to produce the desired phase, along with the gas burden produced by the ion source, result in a background pressure which is too high by several orders of magnitude to perform in situ surface analysis by conventional means. Similarly, diamond is normally grown in the presence of a hydrogen atmosphere to inhibit the formation of the graphitic phase.

Krauss, A.R.; Im, J.; Smentkowski, V.; Schultz, J.A.; Auciello, O.; Gruen, D.M.; Holocek, J.; Chang, R.P.H.

1998-01-13

384

Reactive molecular dynamics study of chloride ion interaction with copper oxide surfaces in aqueous media.  

PubMed

Using reactive force-field (ReaxFF) and molecular dynamics simulation, we study atomistic scale chloride ion adsorption and transport through copper oxide thin films under aqueous conditions. The surface condition of passive oxide film plays a key role in chloride ion adsorption and facilitates initial adsorption when surface corrosion resistance is low. Using implemented surface defects, the structural evolution of the copper oxide film from thinning to breakdown is investigated. In addition to chemical thinning of passive film, extended defects in the metal substrate are observed, at high concentration of adsorbed chloride ions. The initial stage of breakdown is associated with rapid depletion of adjacent chloride ions, which creates a locally deficient environment of chloride ions in the solution. The dissolved copper cations gain higher charge upon interaction with chloride ions. Owing to the increased Coulomb interactions resulted from dissolved copper ions and locally low density of chloride ions, far-field chloride ions would diffuse into the local corrosion sites, thereby promoting further corrosion. PMID:22373345

Jeon, Byoungseon; Sankaranarayanan, Subramanian K R S; van Duin, Adri C T; Ramanathan, Shriram

2012-03-01

385

Surface-directed synthesis of erbium-doped yttrium oxide nanoparticles within organosilane zeptoliter containers.  

PubMed

We introduce an approach to synthesize rare earth oxide nanoparticles using high temperature without aggregation of the nanoparticles. The dispersity of the nanoparticles is controlled at the nanoscale by using small organosilane molds as reaction containers. Zeptoliter reaction vessels prepared from organosilane self-assembled monolayers (SAMs) were used for the surface-directed synthesis of rare earth oxide (REO) nanoparticles. Nanopores of octadecyltrichlorosilane were prepared on Si(111) using particle lithography with immersion steps. The nanopores were filled with a precursor solution of erbium and yttrium salts to confine the crystallization step to occur within individual zeptoliter-sized organosilane reaction vessels. Areas between the nanopores were separated by a matrix film of octadecyltrichlorosilane. With heating, the organosilane template was removed by calcination to generate a surface array of erbium-doped yttria nanoparticles. Nanoparticles synthesized by the surface-directed approach retain the periodic arrangement of the nanopores formed from mesoparticle masks. While bulk rare earth oxides can be readily prepared by solid state methods at high temperature (>900 °C), approaches for preparing REO nanoparticles are limited. Conventional wet chemistry methods are limited to low temperatures according to the boiling points of the solvents used for synthesis. To achieve crystallinity of REO nanoparticles requires steps for high-temperature processing of samples, which can cause self-aggregation and dispersity in sample diameters. The facile steps for particle lithography address the problems of aggregation and the requirement for high-temperature synthesis. PMID:25163977

Englade-Franklin, Lauren E; Morrison, Gregory; Verberne-Sutton, Susan D; Francis, Asenath L; Chan, Julia Y; Garno, Jayne C

2014-09-24

386

Oxidation of CO on surface hematite in high CO2 atmospheres  

E-print Network

We propose a mechanism for the oxidation of gaseous CO into CO2 occurring on the surface mineral hematite (Fe2O3(s)) in hot, CO2-rich planetary atmospheres, such as Venus. This mechanism is likely to constitute an important source of tropospheric CO2 on Venus and could at least partly address the CO2 stability problem in Venus' stratosphere, since our results suggest that atmospheric CO2 is produced from CO oxidation via surface hematite at a rate of 0.4 Petagrammes (Pg) CO2 per (Earth) year on Venus which is about 45% of the mass loss of CO2 via photolysis in the Venusian stratosphere. We also investigated CO oxidation via the hematite mechanism for a range of planetary scenarios and found that modern Earth and Mars are probably too cold for the mechanism to be important because the rate-limiting step, involving CO(g) reacting onto the hematite surface, proceeds much slower at lower temperatures. The mechanism may feature on extrasolar planets such as Gliese 581c or CoRoT-7b assuming they can maintain solid ...

Grenfell, John Lee; Patzer, A Beate C; Gebauer, Stefanie; Rauer, Heike

2010-01-01

387

Electric double layer at metal oxide surfaces: Static properties of the cassiterite - Water Interface  

SciTech Connect

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively charged variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).

Vlcek, Lukas [ORNL; Zhang, Zhan [Argonne National Laboratory (ANL); Machesky, Michael L. [Illinois State Water Survey, Champaign, IL; Wesolowski, David J [ORNL

2007-04-01

388

Electric double layer at metal oxide surfaces:static properties of the cassiterite-water interface.  

SciTech Connect

The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively charged variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths based on ab initio calculations and H-bond configurations as inputs led to the prediction of a pH of zero net-proton induced surface charge (pH{sub pzc}) that agrees very well with those determined experimentally (about 4.4 at 298 K).

Vlcek, L.; Zhang, Z.; Machesky, M .L.; Fenter, P.; Rosenqvist, J.; Wesolowski, D. J.; Anovitz, L. M.; Predota, M.; Cummings, P. T.; Vanderbilt Univ.; ORNL; Univ. of South Bohimia; Illinois State Water Survey

2007-03-24

389

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

SciTech Connect

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

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

2010-02-02

390

Surface chemistry of Cr(III) oxidation and precipitation on Mn(IV) oxides Gautier Landrot, landrot@udel.edu, Department of Plant and Soil Sciences and Center for Critical Zone Research, University of  

E-print Network

Surface chemistry of Cr(III) oxidation and precipitation on Mn(IV) oxides GEOC 29 Gautier Landrot, Newark, DE 19717. The main soil components that oxide Cr(III) to the more hazardous chromium species Cr(VI) are manganese oxides. With hydrous manganese oxide (HMO) and birnessite, Cr(III) may react in two steps: a first

Sparks, Donald L.

391

Surface preparation effects on efficient indium-tin-oxide-CdTe and CdS-CdTe heterojunction solar cells  

Microsoft Academic Search

The effects of CdTe surface preparation and subsequent junction formation have been investigated through characterization of ITO\\/CdTe and CdS\\/CdTe heterojunction solar cells formed by electron beam evaporation of indium-tin-oxide (ITO) and CdS onto single crystal p-type CdTe. Surfaces investigated include air-cleaved (110) surfaces, bromine-in-methanol etched (110) and (111) surfaces, and teh latter surfaces subjected to a hydrogen heat treatment. Both

J. G. Werthen; A. L. Fahrenbruch; R. H. Bube; J. C. Zesch

1983-01-01

392

Anaerobic methane oxidation may be more prevalent in surface soils than was originally thought  

NASA Astrophysics Data System (ADS)

Anaerobic oxidation of methane (CH4) (AOM) is a process that was first reported to occur in deep anoxic marine sediments. In this environment, CH4 is oxidized with sulphate (SO42-) as the terminal electron acceptor. It is mediated by a syntrophic consortium formed by SO42- reducing bacteria and anaerobic CH4 oxidizing Archaea, or by the latter alone. Since this landmark discovery, AOM was found to occur in other environments including freshwater lake sediments and water columns, mud volcanoes, landfill leachate, deep buried Holocene sediments and hydrocarbon contaminated aquifers. All of these situations are very specific and point to AOM as being primarily occurring in highly reducing conditions. Thus, observations of AOM in surface soils with fluctuating REDOX conditions are relatively scarce, although a few independent studies have reported AOM in surface peatlands as well as in a forest soil. Furthermore, AOM may follow different pathways, such as via the coupled oxidation of CH4 and reduction of manganese (Mn(IV)) or iron (Fe(III)), or by a lone denitrifying species that converts nitrite to nitric oxide in order to generate O2 that is then used internally to oxidize CH4. Thus, the goal of our study was to determine whether AOM is more prevalent than was thought in hydromorphic surface soils across different environments, and whether the addition of NO3- or SO4= as alternative electron acceptors may stimulate the process. We collected samples from 3 peatland soils in Scotland, 2 acid-sulphate soils in Finland, and shore sediments of 15 drained fish ponds in the Czech Republic. Subsamples were incubated in the absence of O2 and amended with either NO3-, SO42-, or left unamended (control). The net flux of CH4 and CO2 were assessed by gas chromatography after 2, 20, 40 and 60 days. We also used a 13C-CH4 isotope dilution technique to determine gross production and consumption rates of CH4. We detected AOM in all of our soils, with oxidation rates ranging between 0.001 and 37.28 nmol g-1 day-1, suggesting that AOM may be more ubiquitous than was originally thought. On the other hand, no clear patterns emerged as to the effects of NO3- or SO42- amendments on this process.

Gauthier, Mathieu; Bradley, Robert L.; Šimek, Miloslav

2013-04-01

393

Influence of CrN surface compound on the initial stages of high temperature oxidation of ferritic stainless steel  

NASA Astrophysics Data System (ADS)

Segregation phenomena and formation of surface compounds on Fe-17Cr (ferritic stainless steel) were studied at temperatures up to 800 °C upon annealing and kinetically controlled oxidation by photoelectron spectroscopy and inelastic electron background analysis. The results revealed the formation of a chromium nitride surface compound during annealing in ultrahigh vacuum at temperatures exceeding 527 °C. Surface enrichment of P, As, and other trace elements became more prominent at higher temperatures approaching 800 °C. It was found that nitrogen was buried below the surface oxide layer during oxygen exposure, yet it had little effect on the rate of oxidation. However, the formation of CrN surface compound promoted the selective oxidation of Cr initially, which is of great importance in processing and application environments involving high temperature and controlled atmosphere conditions.

Ali-Löytty, H.; Jussila, P.; Hirsimäki, M.; Valden, M.

2011-06-01

394

Desorption of InSb(001) native oxide and surface smoothing induced by low temperature annealing under molecular hydrogen flow  

NASA Astrophysics Data System (ADS)

The preparation of InSb (001) oxygen-free surfaces by thermal annealing at relatively low temperatures under molecular hydrogen flow is reported. This process is compared with thermal oxide desorption (TOD) at 400°C under ultrahigh vacuum conditions. Molecular hydrogen cleaning (MHC) at substrate temperature of 250°C and at hydrogen pressure of 5×10-6Torr resulted in complete desorption of the native oxide layer. Furthermore, no carbon contamination was observed on the surface following this treatment. The surface morphology of the samples following this process was found to be very smooth without any droplet structure. The In:Sb surface stoichiometry was nearly 1:1 along the MHC process. In addition, annealing the sample at 400°C in vacuum after oxide removal by MHC maintains the smoothness and the stoichiometry of the surface. In contrast, TOD at 400°C of an oxidized InSb surface in vacuum does not result in complete oxide removal from the surface. Furthermore, small droplets associated with In are produced at this annealing temperature. The surface stoichiometry shows In enrichment after TOD in vacuum above 360°C. The surface composition and chemical bonding were monitored by Auger electron spectroscopy and x-ray photoelectron spectroscopy as a function of process parameters. The surface morphology was analyzed by atomic force microscopy.

Tessler, R.; Saguy, C.; Klin, O.; Greenberg, S.; Weiss, E.; Akhvlediani, R.; Edrei, R.; Hoffman, A.

2007-01-01

395

Enzymatic activity and catalytic hydrogen evolution in reduced and oxidized urease at mercury surfaces.  

PubMed

It was originally shown [10] that urease retains its enzymatic activity when adsorbed at bare mercury and solid amalgam surfaces. However the opinion later prevailed that, when adsorbed at bare metal electrodes, proteins are irreversibly denatured. Here we confirm that urease is enzymatically active at a bare solid amalgam surface as found by Santhanam et al., and we show that this enzyme is equally active at a thiol-modified amalgam surface. We also show that it is the reduced form of urease, which is enzymatically active at Hg surfaces. Oxidation of the protein, resulting in formation of disulfide bonds, strongly decreases the enzyme activity. Using constant current chronopotentiometric stripping (CPS) we show that the exposure of surface-attached urease to negative potentials results in the protein unfolding. The extent of the unfolding depends upon the amount of time for which the protein is exposed to negative potentials, and at very short times this unfolding can be avoided. At thiol-modified Hg surfaces the protein is less vulnerable to the effects of the electric field. We conclude that the loss of enzymatic activity, resulting from a 10 min exposure of the protein to -0.58 V, is not due to reduction of the disulfide bonds as suggested by Santhanam et al. This loss is probably a result of protein reorientation, due to reduction of the Hg-S bonds (formed by accessible cysteines), followed by prolonged electric field effect on the surface-attached protein. PMID:23856228

Cernocká, Hana; Ostatná, Veronika; Pale?ek, Emil

2013-07-30

396

Producing ultra-thin silica coatings on iron-oxide nanoparticles to improve their surface reactivity  

NASA Astrophysics Data System (ADS)

The reactivity of the relatively inert surfaces of iron-oxide magnetic nanoparticles can be significantly improved by coating the surfaces with silica. Unfortunately, however, this nonmagnetic silica layer tends to dilute the magnetic properties of the nanoparticles. Therefore, the silica layer should be as continuous, homogeneous, and as thin as possible. In this investigation we coated superparamagnetic maghemite nanoparticles by hydrolysis and the polycondensation of tetraethyl orthosilicate (TEOS), with the ethanol solution of TEOS being added to a stable suspension of citric acid-coated nanoparticles. The influences of the various parameters of the procedure on the quality of the coatings were systematically evaluated. The quality of the silica layer was characterized using electron microscopy and by performing leaching of the nanoparticles in HCl, while the surface reactivity was tested by grafting (3-aminopropyl) triethoxysilane (APS) onto the nanoparticles. We observed that the surface concentration of the grafted APS strongly increased when the nanoparticles were coated with a silica layer. The choice of experimental conditions for the coating procedure that favors the heterogeneous nucleation of silica on the surfaces of the nanoparticles enabled the preparation of very thin silica layers, less than 2 nm thick. By decreasing the amount of added TEOS to correspond to a monolayer of -Si-OH at the nanoparticles' surfaces, their surface reactivity could be very much improved, and with a reduction in their magnetization of only ˜10%.

Kralj, Slavko; Makovec, Darko; ?ampelj, Stanislav; Drofenik, Miha

2010-07-01

397

Surface properties of photo-oxidized bituminous coals. Technical progress report, October--December 1995  

SciTech Connect

During this report period, polished blocks of coal containing 3--4 mm wide vitrain bands were prepared for contact angle measurements of fresh and photo-oxidized surfaces using the advancing-drop technique. Contact angles were measured on two of the coals collected for this study, (the Ohio No. 4a (DECS-33) and Lower Kittanning (PSOC-1562) seams) and the results added to those presented in the last quarterly report. Although the new data give additional variation to the sample set, they are consistent with the original observations, i.e., that contact angle is influenced by irradiation time and coal rank. Using the maximum change in contact angle measured between fresh and photo-oxidized surfaces, a linear decrease is observed with increasing rank resulting from 5 and 10 minutes of irradiation. The magnitude of the decrease in contact angle diminishes with increasing rank. Also during this period, an ultraviolet spotlight was evaluated as a means of irradiating powdered vitrain. This 100 watt, long wavelength (366 nm) ultraviolet lamp is to be used in place of the optical microscope system to establish the influence of surface photo-oxidation on the flotation characteristics of vitrain concentrates. A series of experiments was designed to determine the magnitude of change in the luminescence intensity (at 600 nm measured in the optical microscope) with exposure to the ultraviolet light with time for vitrinite from different rank coals. The authors have established that there is a significant decrease in luminescence intensity with time of exposure which diminishes slightly as rank increases. The ultraviolet light appears to provide a level of photo-oxidation that is a factor of 10 lower than that obtained with their optical microscope system.

Mitchell, G.; Polat, H.; Davis, A.; Chander, S.

1996-02-01

398

Oxide Particle Size, Loading, and Specific Surface Area Effects on Adsorption Isotherms  

NASA Astrophysics Data System (ADS)

The specific surface area of mineral particles is usually determined by the BET gas adsorption isotherm method, and is a key property needed to normalize surface concentrations, mineral dissolution and growth rates, etc. per surface area, in studies of mineral surface reactions. However, aggregation and settling of particles could affect the available surface area for surface reactions, thus influencing the measured adsorption isotherms and surface reaction rates, with significant implications for the interpretation of the data. In this study, we have examined the effects of particle loading (mass of oxide per liter of solution) and size (micron- versus nanometer-sized) on adsorption isotherms of dipalmitoylphosphatidylcholine (DPPC), a common cell-membrane phospholipid (PL), at pH 7.2 and 55°C. The oxides included two nanoparticulate amorphous silicas, one nanoparticulate anatase (b-TiO2), and micron-sized quartz (a-SiO2), rutile (a-TiO2) and corundum (a-Al2O3). Phospholipids are amphiphilic molecules that comprise biological cell membranes, and self-assemble to vesicles in solution, serving as model proto-cells for studies relating to the origin of cellularity in the early evolution of life. The interactions and stability of PL vesicles and bilayers adsorbed at mineral surfaces has relevance for understanding the potential role of minerals in promoting or inhibiting the evolution of cellularity. Amphipihile-mineral interactions are also relevant for bacterial cell surfaces in contact with soil minerals. We have previously established the effects of oxide mineral surface chemistry and PL head-group chemistry on adsorption and self-assembly (Oleson and Sahai, 2008a). In the present work, adsorption isotherms apparently showed less DPPC adsorption at higher particle loadings for micron-sized particles, indicating that a greater fraction of the suspended solid settles out, so that the specific surface area available for adsorption is less than that used for normalizing the adsorption isotherms. This effect is most apparent at higher solution concentrations of DPPC. The effect of particle aggregation on supression of isotherms is even more pronounced when comparing micron- versus nanometer-sized particles, with much lower apparent adsorption on the nanometer sized particles. Particle size analyses by HRTEM and Dynamic Light Scattering suggest that the amorphous silica and anatase nanoparticles aggregate into secondary particles of size from ~ 100-1000s of nanometers. There is considerably less aggregation of the micrometer-sized quartz and rutile. Furthermore, the extent of nanoparticle aggregation depends on the solution pH and ionic strength, which affect surface charge and van der Waals forces, as expected rom DLVO theory. Aggregation of the nanoparticles reduces the available surface area for adsorption than the specific surface area value used for the isotherms. Our results have implications beyond the adsorption of PLs. For any surface studies involving particle suspensions, our data indicate the critical need to determine (a) the particular mass loading for micron-sized particles that minimizes settling, (b) secondary particle size of aggregated nanoparticles, and (c) to develop relationships between particle size, shape, and effective specific surface area.

Giuffre, A. J.; Oleson, T. A.; Xu, J.; Zhang, N.; Sahai, N.

2008-12-01

399

Effects of Water Adsorption and Surface Oxidation on the Electrical Conductivity of Silicon Nanocrystal Films  

NASA Astrophysics Data System (ADS)

Electrical conductivities of thin films of silicon nanocrystals (4-6 nm) exhibit high sensitivity to water vapor. Specifically, water adsorption on the surface of silicon nanocrystal (NC) films increases their electrical conductivity by a factor of four at room temperature and an order of magnitude at 175 K. The increase in conductivity is reversible and can manifest as peaks or hysteresis loops in temperature-dependent conductivity measurements even when the measurements are conducted under vacuum at 10-5 Torr and in the presence of only residual amounts of water vapor. Hydrogen-terminated silicon nanocrystals are easily oxidized to form submonolayer to monolayer of chemically bound oxygen on their surfaces when annealed at 300°C in a glovebox with 0.1 ppm of water vapor. Annealing under vacuum at 300°C retains H-passivation without oxidation. The electrical conductivity of films made from hydrogen-terminated silicon nanocrystals is 200 times higher than the electrical conductivity of films made from silicon nanocrystals with a monolayer of chemically bound oxygen. However, the conductivities of both types of films increase upon adsorption of water on the nanocrystal surfaces. These findings underscore the importance of controlling silicon nanocrystal surfaces in determining the electrical properties of their thin films.

Rastgar, Neema

400

Oxidation of formic acid on platinum surfaces decorated with cobalt(III) macrocyclic complexes  

NASA Astrophysics Data System (ADS)

Platinum electrode decorated with three different mixed-ligand cobalt(III) complexes of the general formula [Co(Rdtc)cyclam](ClO4)2 [cyclam = 1,4,8,11-tetraazacyclotetradecane, Rdtc- = morpholine-(Morphdtc), piperidine-(Pipdtc), and 4-methylpiperidine-(4-Mepipdtc) dithiocarbamates, respectively] was used to study oxidation of formic acid in acidic solution. The complexes were adsorbed on differently prepared Pt surfaces, at open circuit potential. The preliminary results show increased catalytic activity of Pt for formic acid oxidation with complex ion adsorbed on the polycrystalline surfaces. The increase in catalytic activity depends on the structure of the complex applied and follows the order of metal-coordinated bidentate ligand as Morphdtc > Pipdtc > 4-Mepipdtc. Based on IR and NMR data, the main characteristics of the Rdtc ligands do not vary dramatically, but high symmetry of the corresponding complexes decreases in the same order. Accordingly, the complexes are distinctively more mobile, causing chemical interactions to occur on the surface with appreciable speed and enhanced selectivity. The effect of the complexes on catalytic activity presumably depends on structural changes on Pt surfaces caused by their adsorption.

Stevanovi?, S.; Babi?-Samardžija, K.; Sovilj, S. P.; Tripkovi?, A.; Jovanovi?, V. M.

2009-09-01

401

Toxicity Assessment of Silica Coated Iron Oxide Nanoparticles and Biocompatibility Improvement by Surface Engineering  

PubMed Central

We have studied in vitro toxicity of iron oxide nanoparticles (NPs) coated with a thin silica shell (Fe3O4/SiO2 NPs) on A549 and HeLa cells. We compared bare and surface passivated Fe3O4/SiO2 NPs to evaluate the effects of the coating on the particle stability and toxicity. NPs cytotoxicity was investigated by cell viability, membrane integrity, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) assays, and their genotoxicity by comet assay. Our results show that NPs surface passivation reduces the oxidative stress and alteration of iron homeostasis and, consequently, the overall toxicity, despite bare and passivated NPs show similar cell internalization efficiency. We found that the higher toxicity of bare NPs is due to their stronger in-situ degradation, with larger intracellular release of iron ions, as compared to surface passivated NPs. Our results indicate that surface engineering of Fe3O4/SiO2 NPs plays a key role in improving particles stability in biological environments reducing both cytotoxic and genotoxic effects. PMID:24465736

Malvindi, Maria Ada; De Matteis, Valeria; Galeone, Antonio; Brunetti, Virgilio; Anyfantis, George C.; Athanassiou, Athanassia; Cingolani, Roberto; Pompa, Pier Paolo

2014-01-01

402

Spectra investigation on surface characteristics of graphene oxide nanosheets treated with tartaric, malic and oxalic acids.  

PubMed

The surface characteristics of graphene oxide nanosheets (GO) treated respectively with tartaric acid, malic acid and oxalic acid, have been investigated by mainly using optical spectroscopic methods including Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-visible (UV-Vis) absorption and Raman spectroscopy. Additionally, the electrochemical property of the products has also been studied. The data revealed that oxygen-containing groups such as OH, COOH and CO on the GO surface have been almost removed and thus reduced graphene oxide nanosheets (RGN) were obtained. Interestingly, the number of sp(2) domains of RGN increases as treated by tartaric acidsurface conjugated degree alteration. We claim that the difference in both SH and IC among these acids is the main reason for the diverse surface characteristics as well as the improved Cs of the RGN. PMID:24161864

Teng, Xiyao; Yan, Manqing; Bi, Hong

2014-01-24

403

Ozone oxidation of oleic acid surface films decreases aerosol cloud condensation nuclei activity  

NASA Astrophysics Data System (ADS)

Heterogeneous oxidation of aerosols composed of pure oleic acid (C18H34O2, an unsaturated fatty acid commonly found in continental and marine aerosol) by gas-phase O3 is known to increase aerosol hygroscopicity and activity as cloud condensation nuclei (CCN). Whether this trend is preserved when the oleic acid is internally mixed with other electrolytes is unknown and addressed in this study. We quantify the CCN activity of sodium salt aerosols (NaCl and Na2SO4) internally mixed with sodium oleate (SO) and oleic acid (OA). We find that particles containing roughly one monolayer of SO/OA show similar CCN activity to pure salt particles, whereas a tenfold increase in organic concentration slightly depresses CCN activity. O3 oxidation of these multicomponent aerosols has little effect on the critical diameter for CCN activation for unacidified particles at all conditions studied, and the activation kinetics of the CCN are similar in each case to those of pure salts. SO-containing particles which are acidified to atmospherically relevant pH before analysis in order to form oleic acid, however, show depressed CCN activity upon oxidation. This effect is more pronounced at higher organic concentrations. The behavior after oxidation is consistent with the disappearance of the organic surface film, supported by Köhler Theory Analysis (KTA). The ?-Köhler calculations show a small decrease in hygroscopicity after oxidation. The important implication of this finding is that oxidative aging may not always enhance the hygroscopicity of internally mixed inorganic-organic aerosols.

Schwier, A. N.; Sareen, N.; Lathem, T. L.; Nenes, A.; McNeill, V. F.

2011-08-01

404

Iron oxide and hydroxide precipitation from ferrous solutions and its relevance to Martian surface mineralogy  

NASA Astrophysics Data System (ADS)

Experiments were performed to examine if the ubiquitousness of a weak magnetic component in all Martian surface fines tested with the Viking Landers can be attributed to ferric iron precipitation in aqueous solution under oxidizing conditions at neutral pH. Ferrous solutions were mixed in deionized water and