Note: This page contains sample records for the topic oxidized cu110 surface from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

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

NASA Astrophysics Data System (ADS)

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

Olenga, Antoine; Fazleev, N. G.

2012-10-01

2

Magnetic properties of 3d transition metal-phthalocyanine molecules on oxided Cu(110) surface  

NASA Astrophysics Data System (ADS)

After being extensively interesting topics in both fundamental researches and application practices for a decade, spintronics is now on its way of diversity. Molecular spintronics has attracted much attention in recent years, due to the accelerating miniaturization of electronic devices. In this work, based on first-principles calculations, we studied the electronic and magnetic properties of both isolated metal-phthalocyanines (commonly referred to as MPc) molecules (M=Mn, Fe and Co) and a single MPc molecule adsorbed on oxided Cu(110) [O-Cu(110)] surface. We find that the easy axis of FePc molecule switches from in-plane direction to perpendicular direction when it is adsorbed on O-Cu(110) surface. However, such a switch of direction of magnetization could not be observed for MnPc and CoPc molecules which are two neighbors of FePc with one electron less and more, respectively. Furthermore, we find that the magnetization of these MPc molecules on O-Cu(110) surface are rather stable, so they could not be altered by moderate hole/electron doping. The eg orbitals (dxz and dyz) of MPc molecules are found to be crucial for their magnetization on O-Cu(110) surface. Acknowledgement. This work was supported by DOE Grant DE-FG02-05ER46237.

Hu, Jun; Wu, Ruqian

2012-02-01

3

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

SciTech Connect

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

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

1989-06-21

4

Insights into surface reactivity: formic acid oxidation on Cu(110) studied using STM and a molecular beam reactor  

Microsoft Academic Search

Using a combination of STM and molecular beam reactor data we summarise some important features of a model reaction (formic\\u000a acid oxidation on Cu(110)) which is of general significance to surface reactivity and to catalysis. Three such features are\\u000a highlighted here. The first concerns the role of weakly held species (possibly physisorbed) in surface reactions. These species,\\u000a although of very

M. Bowker; R. A. Bennett; S. Poulston; P. Stone

1998-01-01

5

Controlled manipulation of adatoms on the oxidized p(2 x 1) Cu(110) surface using NC-AFM  

NASA Astrophysics Data System (ADS)

Experimentally, large finite regions (islands) of the c(6 x 2) reconstruction bordering (also rather substantial) regions of the p(2 x 1) reconstruction with single super-Cu atoms between some neighboring -Cu-O-Cu- rows can be created on the oxidized Cu(110) surface. We report on our combined theoretical and experimental study of the manipulation of these isolated super-Cu atoms with NC-AFM. Experiments indicate that the manipulation proceeds mostly by vertical manipulation with a small number of lateral manipulation events. Theoretical calculations were performed using the density functional theory (with particular attention paid towards including non-local correlation effects). Two Cu tip models were used terminated either with Cu or O atoms. Placing either of the two tips at various positions around the super-Cu atom on the surface, we calculated maps of the corresponding energy barriers for the transition of the super-Cu atom to the neighboring site and/or for tip adsorption and desorption. Using these comprehensive data and the virtual AFM, mimicking the actual NC AFM apparatus, we modeled the manipulation mechanism and obtained the corresponding tip response during the individual manipulation events.

Bamidele, Joseph; Turansky, Robert; Sugawara, Yasuhiro; Stich, Ivan; Kantorovitch, Lev

2013-03-01

6

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

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

7

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

NASA Astrophysics Data System (ADS)

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

Ren, Jun; Meng, Sheng

2009-03-01

8

Potential Energy Surface of Methanol Decomposition on Cu(110)  

SciTech Connect

Combining the dimer saddle point searching method and periodic density functional theory calculations, the potential energy surface of methanol decomposition on Cu(110) has been mapped out. Each elementary step in the methanol decomposition reaction into CO and hydrogen occurs via one of three possible mechanisms: O?H, C?H or C?O bond scission. Multiple reaction pathways for each bond scission have been identified in the present work. Reaction pathway calculations were started from an initial (reactant) state with methanol adsorbed in the most stable geometry on Cu(110). The saddle point and corresponding final state of each reaction or diffusion mechanism were determined without assuming the reaction mechanism. In this way, the reaction paths are determined without chemical intuition. The harmonic pre-exponential factor of each identified reaction is calculated from a normal mode analysis of the stationary points. Then, using harmonic transition state theory, the reaction rate of each identified reaction pathway in the entire reaction network is obtained. The most favorable decomposition route for methanol on Cu(110) is found as follows: . The rate-limiting step in this route is the dehydrogenation of methoxy to formaldehyde. Our calculation results are in agreement with previous experimental observations and results. This work was supported by a Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL). The computations were performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington.

Mei, Donghai; Xu, Lijun; Henkelman, Graeme A.

2009-03-19

9

Probing enantioselectivity on chirally modified Cu(110), Cu(100), and Cu(111) surfaces.  

PubMed

Temperature programmed desorption methods have been used to probe the enantioselectivity of achiral Cu(100), Cu(110), and Cu(111) single crystal surfaces modified by chiral organic molecules including amino acids, alcohols, alkoxides, and amino-alcohols. The following combinations of chiral probes and chiral modifiers on Cu surfaces were included in this study: propylene oxide (PO) on L-alanine modified Cu(110), PO on L-alaninol modified Cu(111), PO on 2-butanol modified Cu(111), PO on 2-butoxide modified Cu(100), PO on 2-butoxide modified Cu(111), R-3-methylcyclohexanone (R-3-MCHO) on 2-butoxide modified Cu(100), and R-3-MCHO on 2-butoxide modified Cu(111). In contrast with the fact that these and other chiral probe/modifier systems have exhibited enantioselectivity on Pd(111) and Pt(111) surfaces, none of these probe/modifier/Cu systems exhibit enantioselectivity at either low or high modifier coverages. The nature of the underlying substrate plays a significant role in the mechanism of hydrogen-bonding interactions and could be critical to observing enantioselectivity. While hydrogen-bonding interactions between modifier and probe molecule are believed to induce enantioselectivity on Pd surfaces (Gao, F.; Wang, Y.; Burkholder, L.; Tysoe, W. T. J. Am. Chem. Soc. 2007, 129, 15240-15249), such critical interactions may be missing on Cu surfaces where hydrogen-bonding interactions are believed to occur between adjacent modifier molecules, enabling them to form clusters or islands. PMID:20973584

Cheong, Wai Yeng; Huang, Ye; Dangaria, Nikunj; Gellman, Andrew J

2010-11-01

10

The temperature dependence of Cu2O formation on a Cu(110) surface with an energetic O2 molecular beam  

NASA Astrophysics Data System (ADS)

We report a study of the surface temperature (Ts) dependence of Cu2O formation on a Cu(110) surface induced by a hyperthermal O2 molecular beam (HOMB), using x-ray photoemission spectroscopy in conjunction with synchrotron radiation. From the Ts dependence of the O uptake curves, the direct dissociative adsorption process mainly contributes to the formation of the p(2 × 1)-O structure with an O coverage (?) of 0.5 ML for 2.2 eV HOMB incidence. On the other hand, the rate of oxidation at ? > 0.5 ML, particularly in Cu2O formation, strongly depends on the Ts. Thicker Cu2O islands were found inhomogeneously at 400 and 500 K, suggesting the dominant role of the migration of Cu atoms in the Cu2O formations on the Cu(110) surface.

Hashinokuchi, M.; Yoshigoe, A.; Teraoka, Y.; Okada, M.

2012-10-01

11

The temperature dependence of Cu2O formation on a Cu(110) surface with an energetic O2 molecular beam.  

PubMed

We report a study of the surface temperature (T(s)) dependence of Cu(2)O formation on a Cu(110) surface induced by a hyperthermal O(2) molecular beam (HOMB), using x-ray photoemission spectroscopy in conjunction with synchrotron radiation. From the T(s) dependence of the O uptake curves, the direct dissociative adsorption process mainly contributes to the formation of the p(2 × 1)-O structure with an O coverage (?) of 0.5 ML for 2.2 eV HOMB incidence. On the other hand, the rate of oxidation at ? > 0.5 ML, particularly in Cu(2)O formation, strongly depends on the T(s). Thicker Cu(2)O islands were found inhomogeneously at 400 and 500 K, suggesting the dominant role of the migration of Cu atoms in the Cu(2)O formations on the Cu(110) surface. PMID:22941928

Hashinokuchi, M; Yoshigoe, A; Teraoka, Y; Okada, M

2012-09-03

12

Optical reflectance anisotropy of the Si/Cu(110) surface alloy  

NASA Astrophysics Data System (ADS)

Measurements of the optical reflectance anisotropy (RA) of the Si/Cu(110)-c(2 × 2) surface alloy are reported. Significant changes in the RA response of Cu(110) are observed upon the formation of the surface alloy, and with the growth of one-dimensional (1D) anisotropic Si chains on top of the surface alloy. The transitions between the surface states near the Fermi level (EF) at the \\bar {\\mathrm {Y}} symmetry point on the clean Cu(110) surface are no longer observed in RA spectra of 0.3 ML Si coverage. Peaks in RA spectra arising from transitions between surface-modified bands near EF at the L point are found to be sensitive to the formation of the surface alloy. The RA response of the c(2 × 2) surface alloy from 3.0 to 5.5 eV is simulated using a simple three-phase derivative model. The addition of an overlayer phase to this model makes it possible to simulate higher coverage Si/Cu RA profiles where 1D Si chains cover the surface alloy. The success of the models, in which discrete phases contribute to the RA response, supports the view that the Si chains grow on top of the intact c(2 × 2) alloy. Depositing between 1.2 and 1.8 ML Si results in no change to the RA spectroscopy signal, indicating that the signal remains sensitive to the covered alloy interface.

Martin, D. S.

2009-10-01

13

Surface structure of alanine on cu(110) studied by fast atom diffraction.  

PubMed

We demonstrate that quantum scattering of fast atoms and molecules under grazing angles of incidence can be exploited to study the structure of organic molecules on metal surfaces. Making use of keV H and He atoms as well as H_{2} molecules, the surface structures of the chiral amino acid alanine adsorbed on a Cu(110) surface is studied. We present a detailed investigation on the (3×2) phase of a monolayer of enantiopure and racemic alanine on Cu(110), revealing the formation of an elongated surface unit cell of c(n×2) symmetry with n=3.16±0.04 for the sticking out methyl groups of the alanine molecules. PMID:24116817

Seifert, J; Busch, M; Meyer, E; Winter, H

2013-09-25

14

Surface Structure of Alanine on Cu(110) Studied by Fast Atom Diffraction  

NASA Astrophysics Data System (ADS)

We demonstrate that quantum scattering of fast atoms and molecules under grazing angles of incidence can be exploited to study the structure of organic molecules on metal surfaces. Making use of keV H and He atoms as well as H2 molecules, the surface structures of the chiral amino acid alanine adsorbed on a Cu(110) surface is studied. We present a detailed investigation on the (3×2) phase of a monolayer of enantiopure and racemic alanine on Cu(110), revealing the formation of an elongated surface unit cell of c(n×2) symmetry with n=3.16±0.04 for the sticking out methyl groups of the alanine molecules.

Seifert, J.; Busch, M.; Meyer, E.; Winter, H.

2013-09-01

15

Direct determination of atomic positions on the Cu(110)-(1×2)-H surface  

NASA Astrophysics Data System (ADS)

Results of a low-energy ion scattering study of the H-induced 1×2 reconstruction of the Cu(110) surface are presented. The surface was bombarded with 6-keV Ar+ ions under a grazing angle of 5°, 6°, or 8° azimuthal scans of the yields of the scattered Ar and recoiled Cu and H atoms emitted at a scattering angle of 45° were measured. The scans were compared with the results of computer simulations. We confirm that the surface is of the 1×2 ``missing-row'' type. Nine possible positions of H atoms at the Cu(110)-(1×2) surface for different coverages were analyzed. The H atoms were found to be situated in one of the two possible trigonal hollow sites on the missing-row reconstructed surface. To obtain good fits to the experimental data, large thermal vibration amplitudes of the H atoms had to be assumed. These large amplitudes can be due to a nonharmonic potential.

Mijiritskii, A. V.; Wahl, U.; Langelaar, M. H.; Boerma, D. O.

1998-04-01

16

Observations of coverage- and temperature-dependent surface structures formed upon Li deposition on Cu(110)  

NASA Astrophysics Data System (ADS)

A systematic study of surface structures of Li-covered Cu(110) was performed by means of low-energy electron-diffraction (LEED) and Auger electron spectroscopy techniques. The experiments were carried out with increasing deposition of Li both at low temperature (90 K) and room temperature (300 K). At 90 K a series of LEED patterns, (3×1), (2×1), (3×1), and successive complicated structures were observed with increasing Li coverage. The sequence of the LEED patterns was interpreted as simple overlayer structures of Li in terms of a continuous increase of the packing density of deposited Li atoms sitting in the trough along the [11¯0] direction of the Cu(110) surface. Marked differences in the sequence of the LEED structures were observed for observations at 300 K; the sequence of the structures was (1×2), (1×1), (4×1), (5×1), and (n×1) where n<8 with an increase of Li coverage. The first (1×2) structure was assigned to a missing-row-type restructuring of the substrate Cu atoms. The structure models for the (4×1), (5×1), and so on were discussed in terms of the formation of Li-Cu surface alloys proposed previously by Tochihara and Mizuno for the Li/Cu(100) system.

Nakanishi, Shigemitsu; Yumura, Takahiro; Umezawa, Kenji; Tochihara, Hiroshi; Mizuno, Seigi

1994-02-01

17

Molecular orientation with visible light: Reflectance-anisotropy spectroscopy of 3-thiophene carboxylate on Cu(110) surfaces  

Microsoft Academic Search

We present reflectance-anisotropy spectroscopy data for the adsorption of 3-thiophene carboxylic acid on the clean and O(2×1)\\/Cu(110) surfaces, which demonstrates the sensitivity to orientation parallel and perpendicular to the surface. Electronic structure calculations were performed to clarify the bonding and assign RAS transitions.

B. G. Frederick; R. J. Cole; J. R. Power; C. C. Perry; Q. Chen; N. V. Richardson; P. Weightman; C. Verdozzi; D. R. Jennison; P. A. Schultz; M. P. Sears

1998-01-01

18

Direct determination of the lattice site of H atoms on the (1x2) reconstructed Cu (110) surface  

NASA Astrophysics Data System (ADS)

In this work we present preliminary results of a low-energy ion scattering (LEIS) study of a H-induced (1x2) reconstruction of the Cu (110) surface. The surface was bombarded with 6keV Ar+ ions. Time-of-flight (TOF) azimuthal and polar scans of scattered Ar and recoiled Cu and H were measured at a scattering angle of 45 deg. To interpret the results obtained, the azimuthal scans were simulated using a new computer program ``MATCH'' and fitted to the experimental data. The surface was found to be of the (1x2) ``missing row'' reconstruction type. A number of positions for H atoms at the reconstructed surface mentioned were analyzed. The H atoms were observed to be situated in one of two possible trigonal hollow sites as was found before. The desorption and adsorption of H were studied. Desorption from the Cu (110)-(1x2) surface was observed in the temperature range 250-300K. Above 300K complete desorption results in de-reconstruction. In the adsorption measurements, the H-saturation took place after an exposure equivalent to 1.4L at the sample temperature 230K.

Mijiritskii, A. V.; Wahl, U.; Langelaar, M. H.; Boerma, D. O.

1998-03-01

19

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

Microsoft Academic Search

We propose a method to deduce the free energies gamma and stresses tau of plane surfaces and solid-liquid interfaces in elemental systems from atomistic simulations involving nonhydrostatically stressed solid phases. The method is applied to compute the temperature dependencies of gamma and tau for the (110) Cu surface using Monte Carlo simulations with an embedded-atom potential. Both quantities decrease with

T. Frolov; Y. Mishin

2009-01-01

20

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

21

Influence of Glycine Adsorption on Segregation of Ni-Cu (110) Surface  

NASA Astrophysics Data System (ADS)

An atomic group model of the disordered binary alloy NixCu1-x (x=0.4) was constructed to investigate surface segregation. According to the model, the electronic structure of the NixCu1-x alloy surface was calculated by the Recursion method when glycine atoms are adsorbed on the NixCu1-x (110) surface under the condition of 0.33 coverage. The calculation results indicate that Cu is segregated on the surface of the NixCu1-x alloy, and the chemisorption of glycine restrains the segregation. In addition, the chemical adsorption of glycine greatly changes the density of states of the alloy surface near the Fermi level, and there is electric charge transfer between the alloy surface and the glycine.

Zhang, Hui; Zhang, Guo-ying; Wang, Rui-dan

2007-10-01

22

Completion of the Determination of Complex Surface Structures Formed on Low-Index Planes of Copper Single Crystal by li Deposition:. Cu(110)-(4×1)-3Li  

NASA Astrophysics Data System (ADS)

With increasing Li coverage on Cu(110), (n×1) (4?n?8) structures follow the (1×2) missing-row structure at room temperature. We determine the (4×1) structure by a dynamical low-energy electron diffraction (LEED) analysis with symmetrized automated tensor LEED. This completes the solution of the complex surface structures formed on low-index planes of copper single crystal by Li deposition. Every fourth Cu row in the [001] direction is substituted by Li atoms and the remaining Cu rows are covered by Li adatoms. Features of this structure, denoted as Cu(110)-(4×1)-3Li, are very similar to those of the previously determined Cu(001)-(3×3)-5Li, Cu(001)-(4×4)-10Li and Cu(111)-(2×2)-3Li structures.

Mizuno, Seigi; Jiang, Hong; Tochihara, Hiroshi

23

Interactions between alkali metals and oxygen on a reconstructed surface: An STM study of oxygen adsorption on the alkali-metal-covered Cu(110) surface  

NASA Astrophysics Data System (ADS)

Room-temperature adsorption of oxygen on potassium- and cesium-precovered Cu(110) surfaces was studied by scanning tunneling microscopy. Depending on the alkali-metal precoverage, two different scenarios exist for the structural evolution of the surfaces. For alkali-metal coverages ?alk<=0.13 ML [?alk=0.13 corresponds to the (1×3) missing-row reconstructed Cu(110) surface], oxygen adsorption leads first to a transient contraction of the missing rows into islands of a (1×2) structure. After longer exposures it causes the local removal of the alkali-metal-induced reconstruction, and the (2×1) Cu-O ``added-row'' structure with ?O=0.5 is formed. In this structure the alkali-metal atoms are incorporated in the Cu-O chains. For higher alkali-metal precoverages, in the range of the (1×2) reconstruction (?alk~=0.2), more than one-half a monolayer of oxygen can be incorporated into the (1×2) phase with only a minor structural effect before, at higher oxygen coverages, complex oxygen-alkali-metal-Cu structures with oxygen coverages well above 0.5 ML are formed. The saturation oxygen coverage is drastically enhanced beyond ?O=0.5, the quasisaturation value of the clean surface. Based on mass-transport arguments the substrate is reconstructed for all ratios of oxygen and alkali metal investigated here. Hence, adsorbate-substrate interactions are essential for these structures; they are not dominated by interactions between alkali metals and oxygen, i.e., by adsorbate-adsorbate interactions.

Schuster, R.; Barth, J. V.; Wintterlin, J.; Behm, R. J.; Ertl, G.

1994-12-01

24

Density-functional study of the methoxy intermediates at Cu(111), Cu(110) and Cu(001) surfaces  

NASA Astrophysics Data System (ADS)

Although the geometry of the methoxy intermediates on copper surfaces has been investigated in a number of experimental and also in several theoretical papers, the situation remains controversial for the (110) and (001) surface orientations. In the present study, we perform density-functional calculations for the Cu(111), (110) and (001) surfaces. The stress is laid upon the models and ideas proposed in the literature. At the (111) face, the fcc three-fold adsorption site is found to be slightly more favourable than the hcp one. At the (110) surface, we predict the methoxy to adsorb close to the short-bridge site in a tilted geometry. Metastable long-bridge positions are less stable by more than 0.3 eV. Since for coverages up to ? = 0.5 the interaction between the methoxy groups is weak, we see no reason for the presence of two different adsorbed methoxy forms unless the copper surface is reconstructed. For the (001) surface we obtain almost the same adsorption energy for the upright adsorbed methoxy in the hollow site, and a tilted methoxy form in a position between the bridge and the hollow site. The calculations agree semiquantitatively with the available experimental data, and admit the presence of two distinct methoxy surface forms.

Pick, Št?pán

2010-10-01

25

An STM, TPD and XPS investigation of formic acid adsorption on the oxygen-precovered c(6×2) surface of Cu(110)  

Microsoft Academic Search

X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD) and scanning tunnelling microscopy (STM) have been employed to investigate the adsorption of formic acid on O-c(6×2)\\/Cu(110) at 300K. Formic acid adsorption results in the production of adsorbed formate. TPD profiles indicate that the formate decomposes predominantly via dehydrogenation, with two peak maxima being observed at 415 and 460K. Following complete decomposition of

Peter Stone; Stephen Poulston; Roger A Bennett; Nicola J Price; Michael Bowker

1998-01-01

26

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

PubMed

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

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

2009-04-02

27

Autocatalytic Water Dissociation on Cu(110) at Near Ambient Conditions  

SciTech Connect

Autocatalytic dissociation of water on the Cu(110) metal surface is demonstrated on the basis of 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.

Andersson, K.; Ketteler, G.; Bluhm, H.; Yamamoto, S.; Ogasawara, H.; Pettersson, L.G.M.; Salmeron, M.; Nilsson, A.; /SLAC, SSRL /Stockholm U. /LBL, Berkeley /UC, Berkeley

2009-04-30

28

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

29

Unexpected deformations induced by surface interaction and chiral self-assembly of Co(II)-tetraphenylporphyrin (Co-TPP) adsorbed on Cu(110): a combined STM and periodic DFT study.  

PubMed

In a combined scanning tunnelling microscopy (STM) and periodic density functional theory (DFT) study, we present the first comprehensive picture of the energy costs and gains that drive the adsorption and chiral self-assembly of highly distorted Co(II)-tetraphenylporphyrin (Co-TPP) conformers on the Cu(110) surface. Periodic, semi-local DFT calculations reveal a strong energetic preference for Co-TPP molecules to adsorb at the short-bridge site when organised within a domain. At this adsorption site, a substantial chemical interaction between the molecular core and the surface causes the porphyrin macrocycle to accommodate close to the surface and in a flat geometry, which induces considerable tilting distortions in the phenyl groups. Experimental STM images can be explained in terms of these conformational changes and adsorption-induced electronic effects. For the ordered structure we unambiguously show that the substantial energy gain from the molecule–surface interaction recuperates the high cost of the induced molecular and surface deformations as compared with gas phase molecules. Conversely, singly adsorbed molecules prefer a long-bridge adsorption site and adopt a non-planar, saddle-shape conformation. By using a van der Waals density functional correction scheme, we found that the intermolecular ?–? interactions make the distorted conformer more stable than the saddle conformer within the organic assembly. These interactions drive supramolecular assembly and also generate chiral expression in the system, pinning individual molecules in a propeller-like conformation and directing their assembly along non-symmetric directions that lead to the coexistence of mirror-image chiral domains. Our observations reveal that a strong macrocycle–surface interaction can trigger and stabilise highly unexpected deformations of the molecular structure and thus substantially extend the range of chemistries possible within these systems. PMID:20853297

Donovan, Philip; Robin, Abel; Dyer, Matthew S; Persson, Mats; Raval, Rasmita

2010-09-17

30

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

SciTech Connect

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

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

2008-07-15

31

Temperature dependent effects during Ag deposition on Cu(110)  

SciTech Connect

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

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

1989-01-01

32

Growth and stability of Ag layers on Cu(110)  

SciTech Connect

Combined surface science and high energy ion beam techniques have been used to characterize the composition, structure and thermal stability of Ag layers < 900A thick on Cu(110). A uniform Ag/Cu surface composite is formed for one monolayer coverage. Analysis of its growth with LEED shows that the Ag is initially confined to the (110) troughs and that further deposition results in a Ag(111) layer exhibiting c(2 x 4) symmetry. This surface science determination of Ag coverage is consistent with absolute coverages measured with Rutherford backscattering. Beyond one monolayer coverage, the deposition of Ag at 300K produces clustering (Stranski-Krastanov mechanism) in contrast to a poorly ordered but more uniform layering mode when deposited at 130K. Following nucleation for a deposition between one and two monolayers at 300K, Ag clusters approx.20 A thick grow laterally across the surface up to 5 or 6 monolayers deposition. Continuous films grown cold at thicknesses less than or equal to 115A are found to agglomerate above 500K exposing a tenacious Ag-Cu interface like that formed by one monolayer Ag deposition.

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

1986-01-01

33

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

PubMed

Adsorption of phenol and thiophenol (benzenethiol) on Cu(110) is investigated by a scanning tunneling microscope and electron energy loss spectroscopy. Phenol adsorbs intact and forms a cyclic trimer at 78 K. It is dehydrogenated to yield a phenoxy (C6H5O) group at 300 K. On the other hand, thiophenol is dehydrogenated to a thiophenoxy (C6H5S) group even at 78 K. Both products are bonded via chalcogen atom to the short-bridge site with the phenyl ring oriented nearly parallel to the surface. The C6H5O and C6H5S groups are preferentially assembled into the chains along the [001] and [112] directions, respectively. Dipole-dipole interaction is responsible for the chain growth, while the chain direction is ruled by the steric repulsion between chalcogen atoms and adjacent phenyl ring. This work demonstrates a crucial role of chalcogen atom of phenol species in their overlayer growth on the surface. PMID:23902004

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

2013-07-28

34

Nanostripe pattern of NaCl layers on Cu(110).  

PubMed

A sodium chloride monolayer on a Cu(110) surface gives rise to a highly corrugated periodic nanostripe pattern of the (100) lattice as observed by scanning tunneling microscopy and low-energy electron diffraction. As revealed by density-functional calculations, this pattern is a consequence of the frustration of the overlayer-substrate chemical bonding produced by epitaxial mismatch. The coexistence of regions of strong Cu-Cl covalent and weak nonbonding interactions leads to a chemically induced topographic modulation here realized in a two-dimensional dielectric. The carpetlike growth of the NaCl layer across Cu step edges induces a distinct contrast inversion in the stripe pattern as a result of the change in epitaxial relationship due to the stacking sequence of the (110) Cu layers. It is demonstrated that the competition between local substrate-overlayer and intraoverlayer interactions can support a well-defined heteroepitaxial relationship of a ionic dielectric film and a metal surface, with important consequences for the nanoscale morphology and related properties. PMID:23745897

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

2013-05-22

35

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

36

Mechanisms for chemical transformations of (R,R)-tartaric acid on Cu(110): A first principles study  

NASA Astrophysics Data System (ADS)

Periodic density functional theory calculations are used to systematically investigate, for the first time, the mechanisms for chemical transformations of (R,R)-tartaric acid on a model Cu(110) surface. The overall potential energy surface for the chemical transformations is revealed. The calculations show that the adsorption of the intact biacid molecules of (R,R)-tartaric acid on Cu(110) surface is not strong, but upon adsorption on Cu(110), the biacid molecules will chemically transform immediately, rather than desorb from the surface. It is found that the chemical transformations of (R,R)-tartaric acid on Cu(110) is a thermodynamically favorable process, to produce the monotartrate species, bitartrate species, and H atoms. Kinetically, the initial reaction step is only one O-H bond scission in either one of the COOH group of a biacid molecule of (R,R)-tartaric acid leading to the formation of a monotartrate species and a H atom, which is an almost spontaneous process. The rate-controlling step is the O-H bond scission in the COOH group of a monotartrate species producing a bitartrate species and a H atom. The concerted reaction for simultaneously breaking the two O-H bonds in both COOH groups of a biacid molecule cannot proceed.

Zhang, Ji; Lu, Tao; Jiang, Chen; Zou, Jianwei; Cao, Fengqi; Chen, Yadong

2009-10-01

37

Water clusters on Cu(110): Chain versus cyclic structures  

NASA Astrophysics Data System (ADS)

Water clusters are assembled and imaged on Cu(110) by using a scanning tunneling microscope. Water molecules are arranged along the Cu row to form ``ferroelectric'' zigzag chains of trimer to hexamer. The trimer prefers the chain form to a cyclic one in spite of the reduced number of hydrogen bonds, highlighting the crucial role of the water-substrate interaction in the clustering of adsorbed water molecules. On the other hand, the cyclic form with maximal hydrogen bonds becomes more favorable for the tetramer, indicating the crossover from chain to cyclic configurations as the constituent number increases.

Kumagai, T.; Okuyama, H.; Hatta, S.; Aruga, T.; Hamada, I.

2011-01-01

38

p(n×1) superstructures of Pb on Cu(110)  

NASA Astrophysics Data System (ADS)

The structures of the p(n×1) superstructures (n=4, 5, and 9) of Pb on Cu(110) in the coverage range between FTHETA=0.75 and 0.8 are revealed by atomically resolved scanning tunneling microscopy. All three superstructures are formed by substitution of every nth row of Cu atoms (n=4, 5, and 9) in the [001] direction by Pb atoms. The Pb atoms in between are lined up in the [1¯10] direction. The p(4×1) structure appears in two different modifications: one with substitutional rows of Pb atoms and one with a simple overlayer structure without substituted rows of Cu atoms. Alternating succession of these two modifications results in p(12×1) domains. It is further shown that the p(9×1) structure is not a succession of p(4×1) and p(5×1) but a superstructure on its own. The p(5×1) structure proposed here agrees with previous x-ray-diffraction data at least as well as the quasihexagonal model proposed earlier. We have, in addition, identified the nature of the phase that has been described incommensurate obtained by desorption of Pb upon annealing above 600 K.

Nagl, C.; Pinczolits, M.; Schmid, M.; Varga, P.; Robinson, I. K.

1995-12-01

39

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

SciTech Connect

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

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

1989-01-01

40

c(2×2) Water-Hydroxyl Layer on Cu(110): A Wetting Layer Stabilized by Bjerrum Defects  

NASA Astrophysics Data System (ADS)

Understanding the composition and stability of mixed water-hydroxyl layers is a key step in describing wetting and how surfaces respond to redox processes. Here we show that, instead of forming a complete hydrogen bonding network, structures containing an excess of water over hydroxyl are stabilized on Cu(110) by forming a distorted hexagonal network of water-hydroxyl trimers containing Bjerrum defects. This arrangement maximizes the number of strong bonds formed by water donation to OH and provides uncoordinated OH groups able to hydrogen bond multilayer water and nucleate growth.

Forster, Matthew; Raval, Rasmita; Hodgson, Andrew; Carrasco, Javier; Michaelides, Angelos

2011-01-01

41

Chemical Transformations, Molecular Transport, and Kinetic Barriers in Creating the Chiral Phase of ( R, R)Tartaric Acid on Cu(110)  

Microsoft Academic Search

Metal surfaces modified by chiral molecules have been shown to be effective heterogeneous catalysts for enantioselective reactions; however, their performance is found to be critically affected by modification conditions. Recently, model chirally modified surfaces created by the adsorption of the well-known chiral modifier, (R, R)-tartaric acid on a Cu(110) single crystal surface, have been shown to exhibit a variety of

M. Ortega Lorenzo; V. Humblot; P. Murray; C. J. Baddeley; S. Haq; R. Raval

2002-01-01

42

Near-UV photodissociation of oriented CH{sub 3}I adsorbed on Cu(110)-I  

SciTech Connect

Methyl iodide adsorbed on a Cu(110)-I surface has been found to be highly orientationally ordered. We have exploited this orientation to select different CH{sub 3}I excited states for photodissociation by using polarized near-UV light at wavelengths of 308, 248, and 222 nm. Using p-polarized light at all three wavelengths, we find that dissociation proceeds largely via the {sup 3}Q{sub 0} state, consistent with the picture from gas-phase photolysis. In contrast, using s-polarized light we find contributions from the {sup 3}Q{sub 1} state at {lambda}=308 nm, the {sup 1}Q{sub 1} state at {lambda}=248 nm, and the (E,1) state at {lambda}=222 nm--the latter being a state that has not been implicated in gas-phase studies of CH{sub 3}I A-band photolysis. We also note the contribution to surface photodissociation from low-energy photoelectrons causing dissociative electron attachment to adsorbed CH{sub 3}I and have identified the promotion of direct photodissociation pathways during {lambda}=308 nm photolysis.

Jensen, E.T. [Physics Department, University of Northern British Columbia, 3333 University Way, Prince George, British Columbia V2N 4Z9 (Canada)

2005-11-22

43

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

NASA Astrophysics Data System (ADS)

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

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

2001-01-01

44

Elevated temperature scanning tunneling microscopy study of formic acid adsorption and reaction on oxygen (2×1) covered Cu(110)  

NASA Astrophysics Data System (ADS)

The adsorption and reaction of formic acid on a fully oxygen (2×1) covered Cu(110) surface maintained at 353 K has been studied by scanning tunneling microscopy (STM). Formic acid adsorption is followed in a sequence of images that show the removal of oxygen (2×1) rows preferentially in the <001> direction. The added copper atoms which were associated with the oxygen reconstruction are liberated and diffuse to create significant areas of the high oxygen coverage O-c(6×2) structure. The adsorbed formate produces a (4×1) structure. Analysis of the STM images allows limits to be placed upon the surface structure of the final formate (4×1) surface revealing a lower local formate density than produced for room temperature adsorption. These two observations lead to an understanding of the significant drop in formic acid uptake which has been reported for a narrow temperature window between 350-420 K on this surface.

Bennett, Roger A.; Poulston, Stephen; Bowker, Michael

1998-04-01

45

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

PubMed

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

Peljhan, Sebastijan; Kokalj, Anton

2011-10-13

46

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

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

47

UHV adsorption studies of K/H2O on Pt(111) and O/CH3COOH on Cu(110): orientation and intermediates  

NASA Astrophysics Data System (ADS)

Two model adsorption systems simulating an electrode/electrolyte interface are studied in UHV by high resolution electron energy loss spectroscopy (EELS) and X-ray photoemission spectroscopy, the latter also in the zero-order diffraction mode (XPD). Vibrational frequencies of molecular H2O coadsorbed with K on Pt(111) at a K coverage of 0.06 indicate the short range interaction between these species, a lack of H2O clustering and a substantial reorientation of the H2O molecule on the surface. At low H2O coverage, hydrogen bonding to the Pt surface is preferred over oxygen lone-pair bonding. The second investigation by XPD concerns the structure and orientation of adsorbed species, here products of acetic acid adsorption on Cu(110). Angular distributions of O 1s and C 1s core level electrons emitted from the adsorbed layer, show pronounced forward scattering peaks whose positions are indicative of an acetate species in bi-dendate configuration, with the OO axis aligned along the [11¯0] azimuth. The CC axis of acetate is perpendicular to the surface. On the other hand, some unexpected emission features, particularly an O 1s forward scattering peak normal to the surface, suggest the presence of additional intermediates on the Cu(110) surface. The data are supportive of acetic anhydride.

Baumann, P.; Pirug, G.; Reuter, D.; Bonzel, H. P.

1995-07-01

48

Quantitative local structure determination of R,R-tartaric acid on Cu(110): Monotartrate and bitartrate phases  

NASA Astrophysics Data System (ADS)

The local adsorption site of the monotartrate and bitartrate species of R,R-tartaric acid deposited on Cu(110) have been determined by scanned-energy mode photoelectron diffraction (PhD). In the monotartrate phase the molecule is found to adsorb upright through the O atoms of the single deprotonated carboxylic acid (carboxylate) group, which are located in different off-atop sites with associated Cu?O bond lengths of 1.92 ± 0.08 Å and 1.93 ± 0.06 Å; the plane of the carboxylate group is tilted by 17 ± 6° off the surface normal. The bitartrate species adopts a 'lying down' orientation, bonding to the surface through all four O atoms of the two carboxylate groups, also in off-atop sites. Three slightly different models give comparably good fits to the PhD data, but only one of these is similar to that predicted by earlier density functional theory calculations. This model is found to have Cu?O bond lengths of 1.93 ± 0.08 Å and 1.95 ± 0.08 Å, while the planes of the carboxylate groups are tilted by 38 ± 6° from the surface normal.

Duncan, D. A.; Unterberger, W.; Jackson, D. C.; Knight, M. K.; Kröger, E. A.; Hogan, K. A.; Lamont, C. L. A.; Lerotholi, T. J.; Woodruff, D. P.

2012-09-01

49

Hybrid interfaces of biological molecules and metals: The prototypical case of adenine on Cu(110)  

NASA Astrophysics Data System (ADS)

Electronic and structural properties of thin, chemisorbed adenine films on Cu(110) have been investigated by ultraviolet photoelectron spectroscopy and reflection high-energy electron diffraction. Molecular reorientation at the particular coverage of about 0.3 ML from a disordered flat-lying to a long-range ordered standing-up phase is accompanied by pronounced changes of the interfacial dipole provided by the alignment of the intrinsic dipole moment of the polar molecule. Similar hybrid interfacial states are observed for ordered flat-lying and standing-up layers, suggesting comparable atomic site-specific N-Cu interactions.

Bussolotti, F.; Friedlein, R.

2010-05-01

50

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

51

``Magic'' Vicinal Zinc Oxide Surfaces  

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

52

Probing conformers and adsorption footprints at the single-molecule level in a highly organized amino acid assembly of (S)-proline on Cu(110).  

PubMed

Establishing the nanoscale details of organized amino acid assemblies at surfaces is a major challenge in the field of organic-inorganic interfaces. Here, we show that the dense (4 x 2) overlayer of the amino acid, (S)-proline on a Cu(110) surface can be explored at the single-molecule level by scanning tunneling microscopy (STM), reflection absorption infrared spectroscopy (RAIRS), and periodic density functional theory (DFT) calculations. The combination of experiment and theory, allied with the unique structural rigidity of proline, enables the individual conformers and adsorption footprints adopted within the organized assembly to be determined. Periodic DFT calculations find two energetically favorable molecular conformations, projecting mirror-image chiral adsorption footprints at the surface. These two forms can be experimentally distinguished since the positioning of the amino group within the pyrrolidine ring leads each chiral footprint and associated conformer to adopt very different ring orientations, producing distinct contrasts in the STM images. DFT modeling shows that the two conformers can generate eight possible (4 x 2) overlayers with a variety of adsorption footprint arrangements. STM images simulated for each structural model enables a direct comparison to be made with the experiment and narrows the (4 x 2) overlayer to one specific structural model in which the juxtaposition of molecules leads to the formation of one-dimensional hydrogen bonded prolate chains directed along the [110] direction. PMID:19580280

Forster, Matthew; Dyer, Matthew S; Persson, Mats; Raval, Rasmita

2009-07-29

53

High surface area tin oxide  

Microsoft Academic Search

High surface area tin oxides are desirable catalyst carriers for emissions control including CO oxidation, VOC removal\\/methane combustion and NOx abatement. We have optimized literature procedures as well as developed proprietary recipes for the synthesis of porous SnO2 carriers. Precipitation of SnCl4 from homogeneous solution by urea and by hydrazine, the dissolution of Sn metal powder in HNO3, sol–gel routes

Alfred Hagemeyer; Zach Hogan; Marco Schlichter; Birgit Smaka; Guido Streukens; Howard Turner; Anthony Volpe Jr.; Henry Weinberg; Karin Yaccato

2007-01-01

54

Surface Oxidation of Carbon Nanofibres  

Microsoft Academic Search

Carbon nanofibres of the fishbone and parallel types were surface-oxidised by several methods. The untreated and oxidised fibres were studied with infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). Oxidation in a mixture of concentrated nitric and sulfuric acids proved to be the most effective method for creating oxygen-containing surface groups. This treatment results not only in the formation

D. C. Koningsberger; T. G. Ros; A. J. van Dillen; John W. Geus

2002-01-01

55

Surface oxidation of carbon nanofibres.  

PubMed

Carbon nanofibres of the fishbone and parallel types were surface-oxidised by several methods. The untreated and oxidised fibres were studied with infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). Oxidation in a mixture of concentrated nitric and sulfuric acids proved to be the most effective method for creating oxygen-containing surface groups. This treatment results not only in the formation of carboxy and carboxyic anhydride groups, but also in the generation of ether-type oxygen groups between graphitic layers that are puckered at their edges. The IR spectroscopic data clearly show that the formation of oxygen-containing surface groups occurs at defect sites on the carbon nanofibres and that oxidation proceeds via carbonyl groups and other oxides to carboxy and carboxyic anhydride groups. Owing to the presence of defects, the two types of fibre have similar surface reactivities. With parallel nanofibres, in contrast to fishbone fibres, the macroscopic structure was severely affected by treatment with HNO(3)/H(2)SO(4). The HNO(3)/H(2)SO(4)-treated fibres are highly wettable by water. PMID:11891903

Ros, Tijmen G; van Dillen, Adrianus J; Geus, John W; Koningsberger, Diederik C

2002-03-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

57

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

PubMed

The system of CH3I adsorbed on submonolayer, monolayer, and multilayer thin films of D2O on Cu(110) has been studied by measuring the time of flight (TOF) distributions of the desorbing CH3 fragments after photodissociation using linearly polarized ? = 248 nm light. For multilayer D2O films (2-120 ML), the photodissociation is dominated by neutral photodissociation via the "A-band" absorption of CH3I. The polarization and angle dependent variation in the observed TOF spectra of the CH3 photofragments find that dissociation is largely via the (3)Q0 excited state, but that also a contribution via the (1)Q1 excitation can be identified. The photodissociation results also indicate that the CH3I adsorbed on D2O forms close-packed islands at submonolayer coverages, with a mixture of C-I bond axis orientations. For monolayer and submonolayer quantities of D2O we have observed a contribution to CH3I photodissociation via dissociative electron attachment (DEA) by photoelectrons. The observed DEA is consistent with delocalized photoelectrons from the substrate causing the observed dissociation- we do not find evidence for an enhanced DEA mechanism via the temporary solvation of photoelectrons in localized states of the D2O ice. PMID:23464167

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

2013-02-28

58

Electrochemical Oxidation of Cu(111) Surfaces  

Microsoft Academic Search

We have investigated aqueous oxide formation on Cu(111) single crystal surface using in situ surface x-ray diffraction technique. The sample surface was prepared by electropolishing and the electrolyte used was dilute perchloric acid at pH 4.5. The oxidation of the Cu(111) electrode led to the formation of the epitaxial oxide of cubic Cu_2O structure or cuprite. Two twin epitaxial structures

Ian Robinson; Yong Chu

1998-01-01

59

Surface properties of electrochemically oxidized carbon fibers  

Microsoft Academic Search

High-strength PAN-based carbon fibers were continuously electrochemically oxidized by applying current through the fibers which served as an anode in 1% wt. KNO3 solutions. NaOH titration showed that the quantity of acidic surface functions increased with the extent of electrochemical oxidation up to oxidation levels of 6360 Cg?1. Fibers with over 1.1 mmolg?1 of total acidic functional groups per gram

C PITTMANJR; W. Jiang; Z. R. Yue; S. Gardner; L. Wang; H. Toghiani; C. A. Leon y Leon

1999-01-01

60

Platinum attachments on iron oxide nanoparticle surfaces  

Microsoft Academic Search

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

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

2010-01-01

61

Platinum Attachments on Iron Oxide Nanoparticle Surfaces  

SciTech Connect

Platinum nanoparticles supported on metal oxide surfaces have shown great potential as heterogeneous catalysts to accelerate electrochemical processes, such as the oxygen reduction reaction in fuel cells. Recently, the use of magnetic supports has become a promising research topic for easy separation and recovery of catalysts using magnets, such as Pt nanoparticles supported on iron oxide nanoparticles. The attachment of Pt on iron oxide nanoparticles is limited by the wetting ability of the Pt (metal) on ceramic surfaces. A study of Pt nanoparticle attachment on iron oxide nanoparticle surfaces in an organic solvent is reported, which addresses the factors that promote or inhibit such attachment. It was discovered that the Pt attachment strongly depends on the capping molecules of the iron oxide seeds and the reaction temperature. For example, the attachment of Pt nanoparticles on oleic acid coated iron oxide nanoparticles was very challenging, because of the strong binding between the carboxylic groups and iron oxide surfaces. In contrast, when nanoparticles are coated with oleic acid/tri-n-octylphosphine oxide or oleic acid/oleylamine, a significant increase in Pt attachment was observed. Electronic structure calculations were then applied to estimate the binding energies between the capping molecules and iron ions, and the modeling results strongly support the experimental observations.

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

2010-04-30

62

Electrochemical Oxidation of Cu(111) Surfaces  

NASA Astrophysics Data System (ADS)

We have investigated aqueous oxide formation on Cu(111) single crystal surface using in situ surface x-ray diffraction technique. The sample surface was prepared by electropolishing and the electrolyte used was dilute perchloric acid at pH 4.5. The oxidation of the Cu(111) electrode led to the formation of the epitaxial oxide of cubic Cu_2O structure or cuprite. Two twin epitaxial structures were found; for the ``aligned'' cuprite, Cu_2O(111) allel Cu(111) and Cu_2O(1bar10) parallel Cu(1bar10), and for the ``reversed'' cuprite, Cu_2O(bar1bar1bar1) allel Cu(111) and Cu_2O(bar110) parallel Cu(1bar10). At the initial stage of the oxidation, both types of oxide were observed to grow at the comparable rates up to a few monolayers. However, the growth of the aligned cuprite was remained ``frozen'' even after further oxidation, whereas the reversed cuprite was oberved to grow into a thick film. The diffraction intensities of the oxides suggest that the oxide growth start out to be highly non-uniform film under large compressive strain and gradually turn into a uniform film with less strain.

Robinson, Ian; Chu, Yong

1998-03-01

63

Electrolysis of water on oxide surfaces  

Microsoft Academic Search

In this paper, density functional theory (DFT) calculations are performed to analyze the electrochemical water-splitting process producing molecular oxygen (O2) and hydrogen (H2). We investigate the trends in the electro-catalytic properties of (110) surfaces of three rutile-type oxides (RuO2, IrO2, and TiO2). The two first of these oxide anodes show lower O2-evolving over-potentials than metal anodes, due to weak O

J. Rossmeisl; Z.-W. Qu; H. Zhu; G.-J. Kroes; J. K. Nørskov

2007-01-01

64

Surface Ionization Gas Detection on Platinum and Metal Oxide Surfaces  

Microsoft Academic Search

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

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

2009-01-01

65

Iron oxide surface catalyzed oxidation of quinoline by hydrogen peroxide  

SciTech Connect

The objective of this research was to examine and compare the surface catalyzed loss of quinoline, a model pollutant, in the presence of three iron oxides: ferrihydrite, goethite, and a semicrystalline iron oxide. These are ubiquitous in the subsurface environment and have been implicated in the possible abiotic loss of contaminants when hydrogen peroxide is injected for augmenting bioremediation. This suggests the possible use of hydrogen peroxide specifically as an oxidant of some compounds in the subsurface. A comparison also reveals the best candidate for use in a supported oxide fixed bed treatment system utilizing hydrogen peroxide as an oxidant. The catalytic activity toward quinoline oxidation was highest for goethite, much less for the semicrystalline material, and negligible in the presence of ferrihydrite. Several water constituents affected reaction rates and stoichiometry by adsorption or through effects on solution chemistry. The stoichiometric efficiency relating quinoline loss to hydrogen peroxide decomposition was not a function of oxide concentration, nor was it affected by the presence of carbonate or phosphate that reduced the rate of hydrogen peroxide decomposition. The effect of humic acid on quinoline loss and hydrogen peroxide decomposition rate depended on its concentration, suggesting that it may act as a radical scavenger, radical chain promoter, and catalytic site inhibitor.

Valentine, R.L.; Wang, H.C.A. [Univ. of Iowa, Iowa City, IA (United States). Dept. of Civil and Environmental Engineering

1998-01-01

66

Characterization of surface oxide films on titanium and bioactivity  

Microsoft Academic Search

Biological properties of titanium implant depend on its surface oxide film. In the present study, the surface oxide films on titanium were characterized and the relationship between the characterization and bioactivity of titanium was studied. The surface oxide films on titanium were obtained by heat-treatment in different oxidation atmospheres, such as air, oxygen and water vapor. The bioactivity of heat-treated

B. Feng; J. Y. Chen; S. K. Qi; L. He; J. Z. Zhao; X. D. Zhang

2002-01-01

67

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

2010-02-24

68

Selective surfaces of anodic copper oxide for solar collectors  

SciTech Connect

The hemispherical spectral reflectance and the hemispherical total emittance were measured for copper oxide films produced by anodic oxidation. The anodic copper oxide films are shown to have desirable selective surface properties for use as solar absorbers.

Milgram, A.A.

1983-06-01

69

Physics and Chemistry at Oxide Surfaces  

NASA Astrophysics Data System (ADS)

This book summarizes the present state of knowledge on the microscopic behavior of oxide surfaces. It includes classical approaches, introduces the concept of ionicity, and describes the mixed iono-covalent character of the oxygen cation bond in bulk materials. It emphasizes the characterisitics of the atomic structure (relaxation, rumpling and reconstruction effects), the electronic structure (band width, gap width, etc) and the excitations of clean surfaces. Intended for graduate students in material science, condensed matter physics and physical chemistry, this book proposes theoretical models to clearly illustrate the experimental results obtained on given systems. A comprehensive list of references is included.

Noguera, Claudine

2005-08-01

70

Initial oxidation of the Rh(110) surface: ordered adsorption and surface oxide structures.  

PubMed

The initial oxidation of the Rh(110) surface was studied by scanning tunneling microscopy, core level spectroscopy, and density functional theory. The experiments were carried out exposing the Rh(110) surface to molecular or atomic oxygen at temperatures in the 500-700 K range. In molecular oxygen ambient, the oxidation terminates at oxygen coverage close to a monolayer with the formation of alternating islands of the (10x2) one-dimensional surface oxide and (2x1)p2mg adsorption phases. The use of atomic oxygen facilitates further oxidation until a structure with a c(2x4) periodicity develops. The experimental and theoretical results reveal that the c(2x4) structure is a "surface oxide" very similar to the hexagonal O-Rh-O trilayer structures formed on the Rh(111) and Rh(100) substrates. Some of the experimentally found adsorption phases appear unstable in the phase diagram predicted by thermodynamics, which might reflect kinetic hindrance. The structural details, core level spectra, and stability of the surface oxides formed on the three basal planes are compared with those of the bulk RhO2 and Rh2O3. PMID:16965099

Dri, C; Africh, C; Esch, F; Comelli, G; Dubay, O; Köhler, L; Mittendorfer, F; Kresse, G; Dudin, P; Kiskinova, M

2006-09-01

71

Wetting of Ceramic Opaque Suspensions on Oxidized Alloy Surfaces.  

National Technical Information Service (NTIS)

Liquid mediums used with opaque porcelain powders are crucial in the application of opaque slurries to oxidized metal surfaces. To augment the effective application of opaque porcelain, liquid mediums should wet oxidized metal surfaces well (indicated by ...

G. D. Woolsey L. Lorton W. J. O'Brien

1984-01-01

72

Electrolysis of water on (oxidized) metal surfaces  

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

73

Structural Imaging of Surface Oxidation and Oxidation Catalysis on Ru(0001)  

SciTech Connect

Using simultaneous imaging and structural fingerprinting under reaction conditions, we probe the initial oxidation pathway and CO oxidation catalysis on Ru(0001). Oxidation beyond an initial (1 x 1)-O adlayer phase produces a heterogeneous surface, comprising a disordered trilayerlike surface oxide and an ordered RuO{sub 2}(110) thin-film oxide, which form independently and exhibit similar stability. The surface oxide and RuO{sub 2} phases both show high intrinsic catalytic activity. The oxygen adlayer is inactive in isolation but becomes active due to cooperative effects in close proximity to the surface oxide.

Flege, J.; Hrbek, J; Sutter, P

2008-01-01

74

Surface electron accumulation layers in oxide semiconductors  

NASA Astrophysics Data System (ADS)

In contrast to the electron depletion at the surface of almost all n-type semiconductors, electron accumulation has long been known to be observable at ZnO surfaces. It has recently been found to be a characteric of several other oxide semiconductors, including CdO [1,2], In2O3 [3] and SnO2. They all have a significant size and electronegativity mismatch between their cation and anion. As a result, they have a particularly low ?-point conduction band minimum which is ultimately responsible for the propensity for electron accumulation. In addition to the mere existence of an electron-rich surface layer, it has been found, using angle-resolved photoemission spectroscopy (ARPES), to be quantized into two dimensional subbands [1]. Moreover, the conventional one-electron picture of surface space-charge in semiconductors is shown to be inconsistent with the electronic structure that we observe directly from ARPES, indicating that many-body interactions play a large role in the surface electronic properties of these semiconductors. Such interactions lead to a depth-dependent shrinkage of the semiconductor band gap, resulting in a surface band gap which differs from the bulk value [1]. The most recent studies have focussed on the influence of depositing alkali metals onto the surface of these semiconductors. Many collaborators are acknowledged for samples and ARPES expertise.[4pt] [1] P. D. C. King, T. D. Veal et al., Phys. Rev. Lett. 104, 256803 (2010)[0pt] [2] P. D. C. King, T. D. Veal et al., Phys. Rev. B 79, 035203 (2009)[0pt] [3] P. D. C. King, T. D. Veal et al., Phys. Rev. Lett. 101, 116808 (2008)

Veal, Tim

2013-03-01

75

Oxide modified air electrode surface for high temperature electrochemical cells  

DOEpatents

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

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

1992-01-01

76

Native Oxidation Growth on Ge(111) and (100) Surfaces  

NASA Astrophysics Data System (ADS)

We studied the native oxide growth on Ge(100) and (111) surfaces treated by HCl and HF cleaning in clean room air by high-resolution X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The native oxidation of both HCl- and HF-last Ge(100) surfaces exhibited likely layer-by-layer fashion. The native oxide growth of the n-Ge(100) was significantly faster than the p-Ge(100) at the early stage of native oxidation. This can be explained by the formation of an O2- ion through free electron transfer from the Ge to the adsorbed O2 molecules, which induces the surface electric field that can initiate the oxidation. In the case of different crystallographic orientations, the oxide rate of the Ge(100) surface was faster than that of the Ge(111) surface. This might be attributed to larger open space of the Ge(100) surface than that of the Ge(111) surface.

Sahari, Siti Kudnie; Murakami, Hideki; Fujioka, Tomohiro; Bando, Tatsuya; Ohta, Akio; Makihara, Katsunori; Higashi, Seiichiro; Miyazaki, Seiichi

2011-04-01

77

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

78

Energetics of nanoparticle oxides: interplay between surface energy and polymorphism+  

PubMed Central

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

Navrotsky, Alexandra

2003-01-01

79

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

NASA Astrophysics Data System (ADS)

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

Mittendorfer, Florian

2010-10-01

80

Electrochemical oxidation of carbon fibres in aqueous solutions and analysis of the surface oxides  

Microsoft Academic Search

Carbon fibres with notably different surface oxides can be prepared by varying the electrochemical oxidation conditions. Through correlation of voltammetric analysis and mass spectroscopy, interpretation of the reduction peaks of the surface oxides on the basis of their potential and width is possible. Narrow voltammetric reduction peaks at strongly negative potential are indicative of the predominance of -COOH type groups,

A. D. Jannakoudakis; P. D. Jannakoudakis; E. Theodoridou; J. O. Besenhard

1990-01-01

81

Step-Edge-Induced Oxide Growth During the Oxidation of Cu Surfaces  

NASA Astrophysics Data System (ADS)

Using in situ atomic-resolution electron microscopy observations, we report observations of the oxide growth during the oxidation of stepped Cu surfaces. Oxidation occurs via direct growth of Cu2O on flat terraces with Cu adatoms detaching from steps and diffusing across the terraces. This process involves neither reconstructive oxygen adsorption nor oxygen subsurface incorporation and is rather different from the mechanism of solid-solid transformation of bulk oxidation that is most commonly postulated. These results demonstrate that the presence of surface steps can promote the development of a flat metal-oxide interface by kinetically suppressing subsurface oxide formation at the metal-oxide interface.

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

2012-12-01

82

Effects of surface poisons on the oxidation of binary alloys  

SciTech Connect

A system of reaction-diffusion equations describing the oxidation of binary alloys in environments containing small amounts of surface poisons is analyzed. These poisons reduce the oxygen flux into the alloy, which causes the alloy to oxidize in two stages.During the initial stage, the oxidation reaction occurs in a stationary boundary layer at the alloy surface. Consequently, a thin zone containing a very high concentration of the metal oxide is created at the alloy surface. During the second stage, the oxidation reaction occurs in a moving boundary layer. This leads to a Stefan problem, which is analyzed by using asymptotic and numerical techniques. By comparing the solutions to those of alloys in unpoisoned environments, it is concluded that surface poisons can lead to the formation of protective external oxide scales in alloys which would not normally form such scales. 11 references.

Hagan, P.S.; Polizzotti, R.S.; Luckman, G.

1985-10-01

83

Native Oxidation Growth on Ge(111) and (100) Surfaces  

Microsoft Academic Search

We studied the native oxide growth on Ge(100) and (111) surfaces treated by HCl and HF cleaning in clean room air by high-resolution X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The native oxidation of both HCl- and HF-last Ge(100) surfaces exhibited likely layer-by-layer fashion. The native oxide growth of the n-Ge(100) was significantly faster than the p-Ge(100) at the

Siti Kudnie Sahari; Hideki Murakami; Tomohiro Fujioka; Tatsuya Bando; Akio Ohta; Katsunori Makihara; Seiichiro Higashi; Seiichi Miyazaki

2011-01-01

84

Stability of oxides grown on tantalum silicide surfaces  

Microsoft Academic Search

The oxidation of TaSi2 and Ta2Si surfaces prepared under ultrahigh vacuum conditions has been studied by x-ray photoemission spectroscopy. For both silicides, Si and Ta oxides comprise the native oxide formed at room temperature. Annealing at 550 °C induces a solid state reaction within the native oxide. Ta2O5 is partially decomposed, and the liberated oxygen bonds to Si. This reaction

A. Cros; K. N. Tu

1986-01-01

85

Structure and Metal Overlayer Growth on Oxide Surfaces  

Microsoft Academic Search

This thesis discusses experimental structural studies of oxide surfaces and metal\\/oxide systems. We discuss the surface and interface properties of these materials by examining several simple model systems, and try to understand these systems using some general rules. The main experimental technique is medium-energy ion-scattering, a quantitative in-situ probe of surfaces and interfaces. Chapter 1 discusses some fundamental issues in

Jin Bao Zhou

1993-01-01

86

Surface characterization of electrochemically oxidized carbon fibers  

Microsoft Academic Search

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

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

1999-01-01

87

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

2012-12-17

88

High-Temperature Oxide Regrowth on Mechanically-Damaged Surfaces  

SciTech Connect

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

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

2008-01-01

89

Surface Barrier Silicon Radiation Detectors Improved by Using a Tungsten Oxide for the Surface Stability  

Microsoft Academic Search

The improvements of surface barrier silicon radiation detectors have been accomplished by evaporating a tungsten oxide material on the surface of n-type silicon substrate as the surface stabilized film before gold electrode deposition, the structure of which is metal-metal oxide-semiconductor type. The stability and electrical characteristics of improved silicon detectors are better than those of the conventional surface barrier silicon

Y. Ishizuka; C. Kim; Y. Kim; S. Ohkawa; K. Husimi; S. Osada; M. Ishii

1986-01-01

90

The Electronic Structure of Nonpolar Surfaces in Insulating Metal Oxides  

NASA Astrophysics Data System (ADS)

Understanding the electronic and geometric structures of metal oxide surfaces has a key interest in many technological areas. A randomly chosen crystal surface has a high probability of being polar, unstable and containing in-gap states due to surface dangling bonds. As a result, the surface should be stabilized by passivation or reconstruction. However, do the nonpolar surfaces of ionic crystals of insulating metal oxides need the passivation or reconstruction similar to covalent crystals? We address this question by analyzing the nonpolar surfaces and their electronic structure for the common crystal structures of metal oxides. The study using periodic DFT calculations is performed for following representatives: Cu2O, ZnO, Al2O3, TiO2, V2O5, WO3, CaTiO3, Mg2SiO4. It has been shown that the nonpolar surface can be constructed out of dipole-free, charge-neutral and stoichiometric unit cells for each crystal. We demonstrate that all constructed and relaxed nonpolar surfaces of the metal oxides show a clear band gap. It should be emphasized that the constructed surfaces are neither reconstructed nor passivated. Additionally, we show a correlation between the electronic structure of the relaxed surfaces and Ewald energies calculated for the surface ions.

Zherebetskyy, Danylo; Wang, Lin-Wang

2013-03-01

91

Monte Carlo simulation of a surface oxide model of CO oxidation  

NASA Astrophysics Data System (ADS)

A kinetic Monte Carlo surface reaction lattice gas model is investigated for CO oxidation under sub-atmospheric conditions. The present Letter incorporates recent experimental observations suggesting the formation of surface oxide phase with higher catalytic activity than chemisorbed oxygen. Rate oscillations occur due to collective oxidation of the adsorbed oxygen sites as soon as their coverage reaches a critical threshold. While the chemisorbed oxygen follows the Langmuir-Hinshelwood (LH) mechanism, with the reaction taking place between adsorbed neighboring CO and O, the surface oxide can also directly react with the gas phase CO molecule.

Sinha, I.; Mukherjee, A. K.

2012-11-01

92

Optical glass surfaces polishing by cerium oxide particles  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

93

Reporting central tendencies of chamber measured surface emission and oxidation.  

PubMed

Methane emissions, concentrations, and oxidation were measured on eleven MSW landfills in eleven states spanning from California to Pennsylvania during the three year study. The flux measurements were performed using a static chamber technique. Initial concentration samples were collected immediately after placement of the flux chamber. Oxidation of the emitted methane was evaluated using stable isotope techniques. When reporting overall surface emissions and percent oxidation for a landfill cover, central tendencies are typically used to report "averages" of the collected data. The objective of this study was to determine the best way to determine and report central tendencies. Results showed that 89% of the data sets of collected surface flux have lognormal distributions, 83% of the surface concentration data sets are also lognormal. Sixty seven percent (67%) of the isotope measured percent oxidation data sets are normally distributed. The distribution of data for all eleven landfills provides insight of the central tendencies of emissions, concentrations, and percent oxidation. When reporting the "average" measurement for both flux and concentration data collected at the surface of a landfill, statistical analyses provided insight supporting the use of the geometric mean. But the arithmetic mean can accurately represent the percent oxidation, as measured with the stable isotope technique. We examined correlations between surface CH(4) emissions and surface air CH(4) concentrations. Correlation of the concentration and flux values using the geometric mean proved to be a good fit (R(2)=0.86), indicating that surface scans are a good way of identifying locations of high emissions. PMID:20933379

Abichou, Tarek; Clark, Jeremy; Chanton, Jeffery

2010-10-08

94

Search for Surface Modes of Lattice Vibrations in Magnesium Oxide.  

National Technical Information Service (NTIS)

The report describes inelastic neutron scattering experiments which were performed on crystalline samples of magnesium oxide with various grain sizes in order to get information about the change of the frequency spectrum due to surface effects.

K. H. Rieder E. M. Horl

1967-01-01

95

Oxidation of silicon surface with atomic oxygen radical anions  

Microsoft Academic Search

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

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

2008-01-01

96

Surface chemistry dependence of native oxidation formation on silicon nanocrystals  

Microsoft Academic Search

The growth of silicon oxide on bare and SF6-etched silicon nanocrystals (Si-NCs), which were synthesized by an all gas phase approach, was investigated by examining the surface chemistry and optical properties of the NCs over time. Consistent with previous work in the low temperature oxidation of silicon, the oxidation follows the Cabrera–Mott mechanism, and the measured data are well fitted

R. W. Liptak; U. Kortshagen; S. A. Campbell

2009-01-01

97

Surface chemistry dependence of native oxidation formation on silicon nanocrystals  

Microsoft Academic Search

The growth of silicon oxide on bare and SF6-etched silicon nanocrystals (Si-NCs), which were synthesized by an all gas phase approach, was investigated by examining the surface chemistry and optical properties of the NCs over time. Consistent with previous work in the low temperature oxidation of silicon, the oxidation follows the Cabrera-Mott mechanism, and the measured data are well fitted

R. W. Liptak; U. Kortshagen; S. A. Campbell

2009-01-01

98

Two-Step Oxidation of Pb(111) Surfaces  

Microsoft Academic Search

We report on a two-step method for oxidation of Pb(111) surfaces, which consists of low temperature (90K) adsorption of O2 and subsequent annealing to room temperature. In situ scanning tunnelling microscopy observation reveals that oxidation of Pb(111) can occur effectively by this method, while direct room temperature adsorption results in no oxidation. Temperature-dependent adsorption behaviour suggests the existence of a

Peng Jiang; Li-Li Wang; Yan-Xiao Ning; Yun Qi; Xu-Cun Ma; Jin-Feng Jia; Qi-Kun Xue

2009-01-01

99

Mechanism of glucose electrochemical oxidation on gold surface  

Microsoft Academic Search

The complex oxidation of glucose at the surface of gold electrodes was studied in detail in different conditions of pH, buffer and halide concentration. As observed in previous studies, an oxidative current peak occurs during the cathodic sweep showing a highly linear dependence on glucose concentration, when other electrolyte conditions are unchanged. The effect of the different conditions on the

Mauro Pasta; Fabio La Mantia; Yi Cui

2010-01-01

100

Role of Surface Oxide on Gun Barrel Wear.  

National Technical Information Service (NTIS)

Earlier analysis of gun tubes and steel nozzles exposed to propellant combustion gases showed that a tenacious oxide layer is left on the surface after firing. The thickness of the oxide layer was inversely proportional to the flame temperature of the pro...

J. R. Ward R. P. Kaste I. C. Stobie B. D. Bensinger

1982-01-01

101

Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies  

Microsoft Academic Search

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely\\u000a used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation,\\u000a structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application\\u000a briefly. In order to implement the practical application,

Wei Wu; Quanguo He; Changzhong Jiang

2008-01-01

102

Dependence of oxide surface structure on surface topology and local chemical bonding  

Microsoft Academic Search

The atomic geometries of the charge neutral surfaces of several oxides exhibiting different crystal structures and varying participation of O(2{ital p}) electrons in the chemical bonding have been calculated using tight-binding total energy models. Surface structures have been computed for exemplary cubic (MgO), wurtzite (ZnO), β-tridymite, and ideal β-cristobalite (SiOâ) oxides. The cubic oxide exhibits a minimum energy structure involving

John P. LaFemina; C. B. Duke

1991-01-01

103

First-principles study of water on copper and noble metal (110) surfaces  

NASA Astrophysics Data System (ADS)

Water structure and dissociation kinetics on a model open metal surface: Cu(110), has been investigated in detail based on first-principles electronic structure calculations. We revealed that in both monomer and overlayer forms, water adsorbs molecularly, with a high tendency for diffusion and/or desorption rather than dissociation on clean surfaces at low temperature. Studying water on other noble metal (110) surfaces confirms that Cu(110) is the borderline between intact and dissociative water adsorption, differing in energy by only 0.08eV . This may lead to promising applications in hydrogen generation and fuel cells.

Ren, Jun; Meng, Sheng

2008-02-01

104

First-principles study of water on copper and noble metal (110) surfaces  

SciTech Connect

Water structure and dissociation kinetics on a model open metal surface: Cu(110), has been investigated in detail based on first-principles electronic structure calculations. We revealed that in both monomer and overlayer forms, water adsorbs molecularly, with a high tendency for diffusion and/or desorption rather than dissociation on clean surfaces at low temperature. Studying water on other noble metal (110) surfaces confirms that Cu(110) is the borderline between intact and dissociative water adsorption, differing in energy by only 0.08 eV. This may lead to promising applications in hydrogen generation and fuel cells.

Ren, Jun; Meng, Sheng [Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

2008-02-01

105

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

106

Surface Morphology of Si(111) during Electrochemical Oxidation  

NASA Astrophysics Data System (ADS)

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

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

1997-03-01

107

Angle resolved autoionization spectra of adsorbates on metal oxide surfaces  

Microsoft Academic Search

The autoionization of excited core hole states of simple adsorbates has attracted considerable attention. It provides information on the local electronic density of the valence levels. However, mainly simple adsorbates on different metal surfaces have been investigated. Here it was of considerable interest to study autoionization on oxide surfaces because effects due to the substrate are expected to be different

J. Klinkmann; D. Cappus; H.-J. Freund

1995-01-01

108

Wet chemical surface functionalization of oxide-free silicon  

NASA Astrophysics Data System (ADS)

Silicon is by far the most important semiconductor material in the microelectronic industry mostly due to the high quality of the Si/SiO2 interface. Consequently, applications requiring chemical functionalization of Si substrates have focused on molecular grafting of SiO2 surfaces. Unfortunately, there are practical problems affecting homogeneity and stability of many organic layers grafted on SiO2, such as silanes and phosphonates, related to polymerization and hydrolysis of Si-O-Si and Si-O-P bonds. These issues have stimulated efforts in grafting functional molecules on oxide-free Si surfaces, mostly with wet chemical processes. This review focuses therefore directly on wet chemical surface functionalization of oxide-free Si surfaces, starting from H-terminated Si surfaces. The main preparation methods of oxide-free H-terminated Si and their stability are first summarized. Functionalization is then classified into indirect substitution of H-termination by functional organic molecules, such as hydrosilylation, and direct substitution by other atoms (e.g. halogens) or small functional groups (e.g. OH, NH2) that can be used for further reaction. An emphasis is placed on a recently discovered method to produce a nanopattern of functional groups on otherwise oxide-free, H-terminated and atomically flat Si(1 1 1) surfaces. Such model surfaces are particularly interesting because they make it possible to derive fundamental knowledge of surface chemical reactions.

Thissen, Peter; Seitz, Oliver; Chabal, Yves J.

2012-09-01

109

Fractional surface termination of diamond by electrochemical oxidation.  

PubMed

The crystalline form of sp(3)-hybridized carbon, diamond, offers various electrolyte-stable surface terminations. The H-termination-selective attachment of nitrophenyl diazonium, imaged by AFM, shows that electrochemical oxidation can control the fractional hydrogen/oxygen surface termination of diamond on the nanometer scale. This is of particular interest for all applications relying on interfacial electrochemistry, especially for biointerfaces. PMID:22172282

Hoffmann, René; Obloh, Harald; Tokuda, Norio; Yang, Nianjun; Nebel, Christoph E

2011-12-19

110

Dependence of oxide surface structure on surface topology and local chemical bonding  

SciTech Connect

The atomic geometries of the charge neutral surfaces of several oxides exhibiting different crystal structures and varying participation of O(2{ital p}) electrons in the chemical bonding have been calculated using tight-binding total energy models. Surface structures have been computed for exemplary cubic (MgO), wurtzite (ZnO), {beta}-tridymite, and ideal {beta}-cristobalite (SiO{sub 2}) oxides. The cubic oxide exhibits a minimum energy structure involving small outward relaxations of the oxygens and inward relaxations of the cations. For the cleavage faces of wurtzite ZnO, large bond-length-conserving relaxations occur because the surface atoms can relax without appreciable distortion of the local bond lengths. The charge neutral faces of {beta}-tridymite and ideal {beta}-cristobalite SiO{sub 2} also undergo bond-length-conserving relaxations. Thus the mechanism for the surface relaxation of tetrahedrally coordinated oxides is significantly different from that of the cubic oxides as is the role of the oxygen {ital p} electrons in the surface chemical bonding. Most importantly, the surface structural chemistry of charge neutral oxide surfaces reflects the interplay of both surface topology (via the ability to undergo bond-length-conserving relaxations) and local coordination chemistry (via the participation of {ital p} electrons in bonding versus nonbonding surface state bands).

LaFemina, J.P. (Molecular Science Research Center, Pacific Northwest Laboratory, P.O. Box 999, Richland, Washington 99352 (USA)); Duke, C.B. (Xerox Webster Research Center, 800 Phillips Road 0114-38D, Webster, New York 14580 (USA))

1991-05-01

111

Surface carbonyl groups on oxidized diamond electrodes  

Microsoft Academic Search

Oxygen-containing functional groups can be introduced onto the surface of polycrystalline boron-doped diamond electrodes by either anodic polarization or oxygen plasma treatment. Of these, the carbonyl groups are of particular interest and can be studied specifically by means of specific chemical modification with dinitrophenylhydrazine (DNPH). The modification of the surface carbonyl groups with DNPH retards the Fe2+\\/3+ redox reaction, which

Hideo Notsu; Ichizo Yagi; Tetsu Tatsuma; Donald A Tryk; Akira Fujishima

2000-01-01

112

Heterogeneous nucleation of calcium oxalate on native oxide surfaces  

SciTech Connect

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

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

1994-04-01

113

Detection of DNA hybridization on indium tin oxide surfaces  

Microsoft Academic Search

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

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

2007-01-01

114

Topographic control on silicone surface using chemical oxidization method  

Microsoft Academic Search

The paper describes a wet process for modifying the surface of polydimethylsiloxane (PDMS) using H2SO4\\/HNO3 solutions. The oxidation on the surface of PDMS was confirmed by the examinations of Fourier transform infrared spectrometry (FTIR), contact angle of water drop and X-ray photoelectron spectroscopy (XPS). The hydrophobic surface of pristine PDMS was not only changed to hydrophilic, but also formed wrinkles

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

2007-01-01

115

The intermediate oxidation of the Pd(100) surface  

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

116

Surface oxidation of selenium treated GaAs(100)  

SciTech Connect

The surface oxidation of Se treated GaAs(100) has been investigated in order to understand in greater detail the degradation of the Se passivated GaAs surface upon exposure to atmosphere. An increase in band bending is initially observed at relatively low exposure times, which corresponds to an increase in the O 2p intensity in the valence band. At this stage, oxygen is thought to weakly physisorb at the Ga vacancy sites. At intermediate exposure levels, the other unadsorbed oxygen atom of O{sub 2} attacks the nearest Ga atom. The bond between the nearest Ga atom and Se is then severed, resulting in the formation of Se, which closely resembles amorphous Se. Ultimately, both Se states are converted to the amorphouslike state and at longer exposure times are oxidized. At longer exposure times, the oxidation of Se is also accompanied by As oxidation. In contrast to S treated GaAs, Se/GaAs is relatively resistant to oxidation where only about 10% of the As is oxidized (As{sub 2}O{sub 3}) after 180 min of exposure versus oxidation of 34% of the As atoms for S/GaAs after only 20 min of atmosphere exposure. This relative oxidation resistance is attributed to greater penetration of Se into GaAs relative to S into GaAs. 11 refs., 7 figs., 1 tab.

Scimeca, T.; Watanabe, Y.; Maeda, F.; Berrigan, R.; Oshima, M. [NTT Interdisciplinary Research Laboratories, Tokyo (Japan)

1994-11-01

117

Chemisorption and the electronic structure of transition metal oxides and transition metals bonded to oxide surfaces  

Microsoft Academic Search

Some simple transition metal oxides such as NiO have incomplete atomic subshells and yet are highly insulating. This implies a high degree of electronic localization and also indicates that the chemical bonds are saturated. In this respect these oxides are similar to alkaline earth oxides such as MgO. The analogy extends to their surface properties. MgO and NiO, for example,

A. Barry Kunz

1985-01-01

118

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

119

Nanoscale oxidation of zirconium surfaces: Kinetics and mechanisms  

Microsoft Academic Search

We show that atomic force microscope-induced oxide features can be formed reproducibly on both Zr and ZrN surfaces, and that the growth rate decreases rapidly with increasing time. There is an increase in oxide-feature height with humidity for both systems, and an approximately linear dependence of the height of the structures on the applied voltage for all films for short

N. Farkas; G. Zhang; E. A. Evans; R. D. Ramsier; J. A. Dagata

2003-01-01

120

Reducing Wear Using the Ceramic Surface on Oxidized Zirconium Heads  

Microsoft Academic Search

\\u000a Wear-related complications remain a major cause of revisions following total hip arthroplasty. Oxide ceramic modular heads\\u000a were introduced as an alternative to metallic cobalt-chromium (CoCr) heads because their surfaces are more abrasion-resistant\\u000a and produce less friction, thereby reducing abrasive and adhesive wear of the opposing polyethylene[1]. The use of oxide ceramic heads can reduce wear by 25 to 50% [2–5].

V. Good; K. Widding; D. Heuer; G. Hunter

121

Oxidative destruction of polymeric material on the surface of Europa  

NASA Astrophysics Data System (ADS)

Data are presented from two experiments that address the oxidative degradation of polymeric materials in an icy solar system environment such as that of Europa. The abundance of water ice on the surface of Europa, combined with the high flux of charges particles from the Jovian magnetosphere, should result in radiolysis of water ice to produce a highly oxidizing chemical environment. A decrease in absorptance in the UV is predicted for initially dark organic materials in such an environment.

McDonald, G. D.; Ockert-Bell, M. E.

1997-03-01

122

The oxidation state of the surface of Venus  

NASA Astrophysics Data System (ADS)

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

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

1994-07-01

123

Surface chemistry dependence of native oxidation formation on silicon nanocrystals  

SciTech Connect

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

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

2009-09-15

124

Surface chemistry dependence of native oxidation formation on silicon nanocrystals  

NASA Astrophysics Data System (ADS)

The growth of silicon oxide on bare and SF6-etched silicon nanocrystals (Si-NCs), which were synthesized by an all gas phase approach, was investigated by examining the surface chemistry and optical properties of the NCs over time. Consistent with previous work in the low temperature oxidation of silicon, the oxidation follows the Cabrera-Mott mechanism, and the measured data are well fitted to the Elovich equation. The use of the SF6 plasma is found to reduce the surface Si-H bond density and dramatically increase the monolayer growth rate. This is believed to be due to the much larger volatility of Si-F bonds compared to Si-H bonds on the surface of the NC.

Liptak, R. W.; Kortshagen, U.; Campbell, S. A.

2009-09-01

125

Microwave surface impedance measurements on reduced graphene oxide.  

PubMed

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

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

2012-06-25

126

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

127

Topographic control on silicone surface using chemical oxidization method  

NASA Astrophysics Data System (ADS)

The paper describes a wet process for modifying the surface of polydimethylsiloxane (PDMS) using H2SO4/HNO3 solutions. The oxidation on the surface of PDMS was confirmed by the examinations of Fourier transform infrared spectrometry (FTIR), contact angle of water drop and X-ray photoelectron spectroscopy (XPS). The hydrophobic surface of pristine PDMS was not only changed to hydrophilic, but also formed wrinkles on it after chemical modification. Bilayer systems, stiff oxidized PDMS layers were capped on soft PDMS foundations, would generate easily compressive stresses due to the large difference in volumetric contraction rates and led to form wrinkles on the surface. Experimental results demonstrated the periodicity of wrinkles was controllable by controlling the duration of oxidation. Therefore, wrinkles could be arranged orderly by the guidance of external forces before oxidization. The potential technology for generating and ordering wrinkles on the PDMS surface is valuable in the applications of pressure sensors, biology, micro-optics and nano-/micro-fabrication in the future.

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

2007-10-01

128

Octadecanethiol Island Formation on Single Crystal Zinc Oxide Surfaces  

NASA Astrophysics Data System (ADS)

Organic photovoltaic devices, comprised of zinc oxide (ZnO) nanorod electron acceptor arrays intercalated with organic polymers, could lead to low-cost renewable energy generation. Surface modifications of ZnO with octadecanethiol (ODT) monolayers can help to improve charge transfer in such devices. In the present work, single crystals of ZnO provided well-defined oxygen-terminated and zinc-terminated surfaces on which to learn fundamentally about the attachment and growth of ODT. Both bare zinc oxide and ODT-functionalized surfaces were characterized with atomic force microscopy, Fourier transform infrared spectroscopy, x-ray photoemission spectroscopy, and contact angle analysis. ODT seemed to form islands of multilayers on zinc-terminated surfaces, while it formed islands of monolayers on oxygen-terminated surfaces. While ODT was expected to preferentially bond along defects and terraces on oxygen-terminated surfaces, this was not observed. ODT was also expected to more effectively bond to the zinc-terminated surface, which was observed. Finally, surface preparation treatments designed to leave atomically-flat oxygen terminated surfaces were developed. This work was made possible by the National Science Foundation Division of Materials Research and the Renewable Energy Materials Research Science and Engineering Center at the Colorado School of Mines.

Yocom, Andrea

2009-10-01

129

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

NASA Astrophysics Data System (ADS)

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

Jiang, Wenbo

1999-10-01

130

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

131

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

Microsoft Academic Search

The surface tension of aqueous solutions of seven poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) Pluronic copolymers, covering a wide range of molecular weights (3400-14600) and PPO\\/PEO ratios (0.19-1.79), was determined over the 10[sup [minus]5]-10% w\\/v concentration range, at two temperatures (25 and 35[degree]C). Two breaks (changes in slope) were observed in the surface tension vs log concentration curve for most of

Paschalis Alexandridis; Vassiliki Athanassiou; Shinya Fukuda; T. Alan Hatton

1994-01-01

132

Long-Term Oxidation Behaviour of Lead Sulfide Surfaces  

NASA Astrophysics Data System (ADS)

We have applied nanospectroscopy to examine the surface oxidation of the prototypic mineral lead sulfide in two states: `oxidised' (oxidised in air for one year); and `clean' (cleaved in air and inserted into the vacuum system within about 10 minutes). The elements detected on the surfaces were Pb, S, O, Cl (a natural impurity) and C (adventitious or natural, carbonate). Images showed strong topographic contrast and weak chemical contrast for the oxygen 1s maps. Near defects such as st eps, there is a higher concentration of oxygen, indicating a higher oxidation rate in this zone. From the O 1s and Pb 4f binding energies, it is concluded that the oxidation products present are Pb3O4, PbCO3 and Pb(OH)2, while PbO, PbSO4 and PbO2 were excluded. Sulfur is present on the oxidised sample in two chemical states: one with the same binding energy as for the clean sample, due to the native PbS below the oxide film; and another of hi gher binding energy. The binding energy is assigned to S present as polysulfide and/or sulfur located at the oxide/sulfide interface. Spectra taken at different points on the surface show energy shifts up to about 0.5 eV, due to band bending and pinning of the Fermi level by defects or impurities.

Prince, K. C.; Heun, S.; Gregoratti, L.; Barinov, A.; Kiskinova, M.

133

Surface modification of nickel based alloys for improved oxidation resistance  

SciTech Connect

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

Jablonski, Paul D.; Alman, David E.

2005-02-01

134

Indium tin oxide surface smoothing by gas cluster ion beam  

NASA Astrophysics Data System (ADS)

CO2 cluster ions are irradiated at the acceleration voltage of 25 kV to remove hillocks on indium tin oxide (ITO) surfaces and thus to attain highly smooth surfaces. CO2 monomer ions are also bombarded on the ITO surfaces at the same acceleration voltage to compare sputtering phenomena. From the atomic force microscope results, the irradiation of monomer ions makes the hillocks sharper and the surfaces rougher from 1.31 to 1.6 nm in roughness. On the other hand, the irradiation of CO2 cluster ions reduces the height of hillocks and planarize the ITO surfaces as smooth as 0.92 nm in roughness. This discrepancy could be explained by large lateral sputtering yield of the cluster ions and re-deposition of sputtered particles by the impact of the cluster ions on surfaces.

Song, Jae-Hoon; Choi, Duck-Kyun; Choi, Won-Kook

2002-11-01

135

Adhesion between Oxide Nanoparticles: Influence of Surface Complexation  

Microsoft Academic Search

Colloidal cerium oxide particles of nanometer size are irreversibly adsorbed on molecularly smooth mica sheets from bulk dispersions. The approach to equilibrium, the homogeneity and stability of the adsorbed films, and the effects of pH and solution conditions, are determined by means of the surface force apparatus and atomic force microscopy techniques. Driven by electrostatic interactions between oppositely charged substrate

Olivier Spalla; Patrick Kékicheff

1997-01-01

136

Aqueous synthesis of high surface area metal oxides  

Microsoft Academic Search

By applying high throughput synthesis and characterization technologies, we have been optimizing common dry or aqueous synthetic routes for the preparation of high surface area metals and oxides, such as precipitation and modified Pechini methods. For wet combustion synthesis, we have been screening a variety of organic acids as dispersants and developed proprietary recipes for individual metals. By resorting to

Christian Bluthardt; Carola Fink; Klemens Flick; Alfred Hagemeyer; Marco Schlichter; Anthony Volpe

2008-01-01

137

Surface phase separation between polythylene oxide of different molecular weight  

NASA Astrophysics Data System (ADS)

In-plane phase separation of polyelethylene oxide of different molecular weight has been observed. A systematic investigation on a broad range of Mw show that the process is originated from the conformatinal entropy for a polymer confined on a surface (thin film).

Chen, Rui; Yang, Jingfa; Zhao, Jiang

2013-03-01

138

[Oxidation of membrane proteins and modification of erythrocyte surface characteristics].  

PubMed

It is shown that the oxidation of membrane protein SH-groups of human erythrocytes by diamide leads to the intensification of vesiculation and the formation on the cell surface of "senescent antigens". These processes were studied during prolonged incubation of erythrocytes at 37 degrees C in the absence of glucose. It was found that the formation of vesicules in ATP-depleted cells correlated with the appearance of "senescent antigens" (r = 0.9, p < 0.01). The oxidation of protein SH-groups takes place at the early stages of vesiculation and strengthening of autologous immunoglobulin binding, indicating that the oxidation of the other groups of membrane proteins plays the leading role in the modification of surface properties. PMID:9702341

Kozlova, N M; Slobozhanina, E I; Chernitski?, E A

139

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

140

Surface science investigations of oxidative chemistry on gold.  

PubMed

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

Gong, Jinlong; Mullins, C Buddie

2009-08-18

141

Oxidation-reduction induced roughening of platinum (111) surface  

SciTech Connect

Platinum (111) single crystal surface was roughened by repeated cycles of oxidation and reduction to study dynamic evolution of surface roughening. The interface roughens progressively upon repeated cycles. The measured width of the interface was fit to an assumed pow law, W {approximately}t{sup {beta}}, with {beta} = 0.38(1). The results are compared with a simulation based on a random growth model. The fraction of the singly stepped surface apparently saturates to 0. 25 monolayer, which explains the apparent saturation to a steady roughness observed in previous studies.

You, H.; Nagy, Z.

1993-06-01

142

Electrostatic Cooperativity of Hydroxyl Groups at Metal Oxide Surfaces  

SciTech Connect

The O-H bond distribution of hydroxyl groups at the {110} goethite (R-FeOOH) surface was investigated by molecular dynamics. This distribution was strongly affected by electrostatic interactions with neighboring oxo and hydroxo groups. The effects of proton surface loading, simulated by emplacing two protons at different distances of separation, were diverse and generated several sets of O-H bond distributions. DFT calculations of a representative molecular cluster were also carried out to demonstrate the impact of these effects on the orientation of oxygen lone pairs in neighboring oxo groups. These effects should have strong repercussions on O-H stretching vibrations of metal oxide surfaces.h

Boily, Jean F.; Lins, Roberto D.

2009-09-24

143

Temperature Dependence of Oxide Decomposition on Titanium Surfaces in UHV  

SciTech Connect

It is well known that the titanium surface forms stable oxides of Ti{sub 2}O, TiO, Ti{sub 2}O{sub 3}, Ti{sub 3}O{sub 5}, Ti{sub n}O{sub 2n-1} (4 < n < 38) and TiO{sub 2} and, as a result, exhibits a high degree of immunity against attack by acids and chlorides. However, titanium is also a very active getter. In the gettering characterizing the process, we have investigated the temperature dependence of stable titanium oxides on titanium in ultra-high vacuum (UHV) using Auger electron spectroscopy (AES), quadrupole mass spectrometry (QMS) and x-ray photoelectron spectroscopy (XPS) in the temperature range RT- 600 C. Surfaces of titanium specimens were prepared by electropolishing (EP) and a thin titanium oxide layer was formed on the surface, principally TiO{sub 2}. On increasing the temperature to above 300 C, the O{sub KLL} Auger intensity began to decrease in a drastic way while, in contrast, the Ti{sub LMM} Auger intensity was increased. Above 450 C, no oxygen was detected on the titanium surface in UHV. However, the outgassing rates of H{sub 2}O, O{sub 2}, CO, and CO{sub 2} from the surface did not show any changes in QMS measurements below 450 C. This behavior is explained as gettering, which is an enhancement of diffusion of oxygen from the surface into the bulk. To investigate the temperature dependence of the chemical states of titanium oxides on an EP surface, XPS analysis was also performed in the range 200-450 C in the same way. The results showed drastic changes of the titanium oxide core levels such that the TiO{sub 2} decomposed to suboxides at 180 C, and even the remaining TiO{sub 2} was still decreasing on heating up to 420 C. The titanium surface has a very sensitive oxide composition, depending on temperature.

Mizuno, Yoshiyuki

2001-11-09

144

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

PubMed Central

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

Lapin, Norman A.; Chabal, Yves J.

2009-01-01

145

Bacterial adhesion to glass and metal-oxide surfaces.  

PubMed

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

Li, Baikun; Logan, Bruce E

2004-07-15

146

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

147

Reactions of metal ions at surfaces of hydrous iron oxide  

USGS Publications Warehouse

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

Hem, J. D.

1977-01-01

148

Mechanically reliable surface oxides for high-temperature corrosion resistance  

SciTech Connect

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

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

1995-05-01

149

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

PubMed

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

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

2005-11-10

150

Iron oxide films in tribological surfaces of alloy steel  

NASA Astrophysics Data System (ADS)

The formation of iron oxide films and their roles in determining the dry wear properties of low alloy steel couples are described. Essentially, alpha-Fe2O3, haematites (Fe3O4), wustite (FeO) and oxide mixtures were the predominant compositions found in four regions of mild oxidational wear. The oxides were initially formed during subsequent rubbing and removal of material from the surfaces where oxidation, nucleation and agglomeration processes took place, followed by plastic deformation and work-hardening of underlying layers which supported the films. These films were found to be protective against wear; stable film of Fe3O4 reduced wear rate down to as low as 10-13 m3m-1, while loose particles of FeO maintained wear rate greater than 10-12 m3m-1. The wear protective nature of (alpha) -Fe2O3 and mixed films were found to lie between these extreme limits. Hence, the role of oxide films, in particular Fe3O4, is very significant in minimizing the wear and friction of alloy steel.

Sakrani, S. B.; Sullivan, J. L.

1998-02-01

151

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

152

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

153

Effect of surface oxidation on the surface condition and deuterium permeability of a palladium membrane  

NASA Astrophysics Data System (ADS)

Oxidation and deoxidation of a Pd membrane was conducted in a quartz tube oven in a temperature range of 23-500 °C. The micromorphology and chemical composition of the Pd membrane surface was characterized using scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Micropores and PdO began to form on the Pd membrane surface after oxidation at 240 °C for 1 h and their quantity increased gradually with increasing temperature. A rough Pd membrane surface was obtained when the temperature rose to 500 °C. The PdO on the Pd membrane surface was completely deoxidized once more using H 2 at room temperature, but the rough surface morphology caused by oxidation remained. The deuterium permeability of the Pd membrane was tested using special equipment in the China National Key Laboratory and the results indicated that the rough Pd membrane surface had higher deuterium permeability than the original membrane. The improved deuterium permeability could be attributed to the higher Pd membrane surface area, which provided deuterium atoms with more adsorption sites and dissociation sites.

Feng, Wei; Liu, Ying; Lian, Lixian; Peng, Lixia; Li, Jun

2011-09-01

154

Facets of protein assembly on nanostructured titanium oxide surfaces.  

PubMed

One key for the successful integration of implants into the human body is the control of protein adsorption by adjusting the surface properties at different length scales. This is particularly important for titanium oxide, one of the most common biomedical interfaces. As for titania (TiO(2)) the interface is largely defined by its crystal surface structure, it is crucial to understand how the surface crystallinity affects the structure, properties and function of protein layers mediating subsequent biological reactions. For rutile TiO(2) we demonstrate that the conformation and relative amount of human plasma fibrinogen (HPF) and the structure of adsorbed HPF layers depend on the crystal surface nanostructure by employing thermally etched multi-faceted TiO(2) surfaces. Thermal etching of polycrystalline TiO(2) facilitates a nanoscale crystal faceting and, thus, the creation of different surface nanostructures on a single specimen surface. Atomic force microscopy shows that HPF arranges into networks and thin globular layers on flat and irregular crystal grain surfaces, respectively. On a third, faceted category we observed an alternating conformation of HPF on neighboring facets. The bulk grain orientation obtained from electron backscatter diffraction and thermodynamic mechanisms of surface reconstruction during thermal etching suggest that the grain and facet surface-specific arrangement and relative amount of adsorbed proteins depend on the associated free crystal surface energy. The implications for potentially favorable TiO(2) crystal facets regarding the inflammatory response and hemostasis are discussed with a view to the advanced surface design of future implants. PMID:23142481

Keller, Thomas F; Reichert, Jörg; Thanh, Tam Pham; Adjiski, Ranko; Spiess, Lothar; Berzina-Cimdina, Liga; Jandt, Klaus D; Bossert, Jörg

2012-11-07

155

In Situ Investigations of Ion Transport at Oxide Surfaces  

NASA Astrophysics Data System (ADS)

Ion transport through materials driven by electric potential is essential to many processes, including electrical energy storage. Here we study in situ the behavior of oxide surfaces in the presence of applied electric fields with low-energy electron microscopy (LEEM), angle-resolved photoemission spectroscopy (ARPES), and related structural and spectroscopic measurement techniques. We measure with high spatial resolution the electric potential on the surface of yttria-stabilized zirconia (YSZ), a prototypical oxygen ion conductor, as a function of distance from a metallic electrode. The dependence of the potential distribution on temperature and oxygen gas pressure is determined. Finally we explore which types of surface sites facilitate the gas-surface reactions that create and annihilate the oxygen ions.

Siegel, David; McCarty, Kevin; El Gabaly, Farid

2013-03-01

156

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

157

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

158

Surface Diffusion on Solid Oxide Fuel Cell Catalysts  

SciTech Connect

This paper demonstrates how detailed surface science data bases can lead to improved results in practical applications. The case investigated concerns how surface diffusivities affect concentration polarization on metal electrocatalyst particles. The application is to solid oxide fuel cells (SOFCs). A common assumption for SOFCs is that the hydrogen-oxygen reaction that produces the electrical current is strictly localized at the triple phase boundary (TPB) between the metal catalyst particle, the zirconia support, and the gas atmosphere. Detailed treatment of oxygen spillover indicates that the reactive area simply spreads over the catalyst surface as needed to support the current, leading to TPB widths of several hundred Angstroms. Lower adspecies surface diffusivities (due to catalyst crystallography), lower reactant partial pressures (due to electrode design), higher temperatures, and higher current demands, generally shift the peak turnover number (TON) for H2O generation away from the TPB in practical SOFCs with cermet anodes. The diffusivity-coverage relationship (repulsive, neutral, or attractive adspecies interactions) affects the location of the TON peak on the catalyst surface in a non-monotonic manner, indicating that detailed surface science data are needed for decisive determination of the source of anodic concentration polarization in SOFCs. The most detailed surface diffusion model investigated in this work indicates that the catalytic process is limited by oxygen surface diffusion on the metal particle.

Williford, Rick E.

2005-10-01

159

Diffusion of adatoms and small clusters on magnesium oxide surfaces  

NASA Astrophysics Data System (ADS)

The diffusion of isolated adatoms and small clusters is reviewed for transition and noble metals adsorbed on the (001) surface of magnesium oxide. While isolated adatoms diffuse by hopping among adsorption sites, small clusters such as dimers, trimers and tetramers already display a variety of diffusion mechanisms, from cluster hopping to rotation, sliding, leapfrog, walking, concertina, flipping, twisting, rolling and rocking. Since most of the available results are computational, the review is mostly related to theoretical work. Connection to experiments is discussed where possible, mostly by dealing with the consequences that adatom and small cluster mobility may have on the growth of larger aggregates on the MgO(001) surface.

Ferrando, Riccardo; Fortunelli, Alessandro

2009-07-01

160

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

161

The Spectral Reflection Characteristics of a Smoked Magnesium Oxide Surface  

Microsoft Academic Search

This paper describes an absolute determination of the spectral luminance factors of a flat smoked magnesium oxide surface, in the wavelength range 0.4-0.72 micron, for normal incidence and 45° view The results give an almost constant luminance factor of 1.005 over the middle of this range, with an increase to about 1.01 at the ends of the spectrumThe selectivity of

G W Gordon-Smith

1952-01-01

162

Deformation of oxide scale on steel surface during hot rolling  

Microsoft Academic Search

Although oxide scale has significant influence on surface quality of hot-worked products, deformation of the scale during hot working has not been understood sufficiently. The authors propose an experimental technique to observe the scale as hot-worked using glass coating, in this study. Immediately after hot rolling at 1273K, glass powder was sprinkled over a mild steel sheet. The glass coating

Hiroshi Utsunomiya; Shoichi Doi; Ken-ichiro Hara; Tetsuo Sakai; Shusuke Yanagi

2009-01-01

163

Surface oxide debonding in field assisted powder sintering  

Microsoft Academic Search

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

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

1999-01-01

164

Molecular cluster models of aluminum oxide and aluminum hydroxide surfaces  

Microsoft Academic Search

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

J. D. KUBICKI; S. E. APITZ

1998-01-01

165

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

SciTech Connect

Work during the first budget period has thus far concentrated on the surface chemistry of the CC{sub 1} oxygenates (methanol, formaldehyde, formic acid), and its dependence on surface defects and tin cation coordination numbers on the SnO{sub 2}(110) surface. During the remaining six months of the first budget period, these initial C{sub 1} studies will be completed and work will be initiated on understanding the scrambling of lattice oxygen into the oxidation products from the C{sub 1} molecules. This upcoming work will utilize the preferential labeling of bridging lattice oxygen positions on the SnO{sub 2}(110) surface with {sup 18}O (1) so that the specific crystallographic origin of the oxidizing atoms can be determined. 6 refs.

Cox, D.F.

1991-07-01

166

Graphitic features on SiC surface following oxidation and etching using surface enhanced Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Graphitic features are detected on 4H-SiC surface following oxidation and etching using surface enhanced Raman spectroscopy (SERS). The electronic state of the carbon is sp2 on both the Si- and C-faces of 4H-SiC. The structures of the ``carbon clusters'' consist of two-dimensional graphitic flakes less than 2 nm and one-dimensional polyenes. The degree of graphitization on the C-face SiC is higher than those on the Si-face SiC. This study provides experimental evidence for ``carbon clusters'' existing on SiC surfaces following oxidation at atmospheric pressure and demonstrates that SERS is an effective technique to probe low concentration species on the SiC surface.

Lu, Weijie; Feldman, L. C.; Song, Y.; Dhar, S.; Collins, W. E.; Mitchel, W. C.; Williams, J. R.

2004-10-01

167

Surface Hydroxyl Site Densities on Metal Oxides as a Measure for the Ion-Exchange Capacity  

Microsoft Academic Search

Hydroxyl groups on metal oxide in water are the sites for ion exchange, and the surface hydroxyl site density on oxides is a measure of the ion-exchange capacity. Here, the Grignard reagent method was applied to determine the surface hydroxyl site density of oxide samples. The results were similar to those reported for different oxides with other methods (dehydration by

Hiroki Tamura; Akio Tanaka; Ken-ya Mita; Ryusaburo Furuichi

1999-01-01

168

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

169

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

Microsoft Academic Search

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

Jagdeep Singh

2010-01-01

170

Interaction forces between polyethylene oxide-polypropylene oxide ABA copolymers adsorbed to hydrophobic surfaces.  

PubMed

Block and graft copolymers are frequently used as stabilizing agents in colloidal dispersions. One common material is the range of polymers known as "Pluronics," which is a BASF trade name for ABA block copolymers composed of a propylene oxide anchoring block (B block) and two ethylene oxide buoy or stabilizing blocks (A block); the equivalent ICI (Uneqima) trade name is Synperonic. In the work presented here the interactions between adsorbed layers of these materials immersed in 10(-2) M sodium sulfate solutions are presented. The block copolymers investigated had an approximately fixed molecular weight of around 3250 Da for the anchoring B block, whilst the molecular weight of the stabilizing polyethylene oxide chains varies around 800-6500 Da. Hydrophobic glass surfaces were used as the test substrate. It was found that in the absence of polymer a long ranged attractive interaction is observed, typical for the interaction between hydrophobic surfaces in aqueous media, but that in the presence of the polymers a repulsion was observed. The repulsion became longer ranged as the molecular weight of the ethylene oxide chain increased. On separation of the surfaces, the interaction was slightly longer ranged, suggesting that the two polymer layers intertwine and stretch each other on separation. This effect was more noticeable for the higher molecular weight polymers. The compression data were well described using a scaling analysis for the interaction between polymer brushes. PMID:15276039

Musoke, Michael; Luckham, Paul F

2004-09-01

171

Attachment of pathogenic prion protein to model oxide surfaces.  

PubMed

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

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

2013-05-30

172

First principles study on InP (001)-(2 × 4) surface oxidation  

NASA Astrophysics Data System (ADS)

A theoretical study of the oxidation of InP(001)-(2 × 4) surface is performed using density functional theory methods. Our results on surface oxidation show that the oxygen adsorption does not produce any gap states in the bulk InP band gap, due to the saturation of surface In dangling bonds, whereas substitutional oxygen atoms produce gap states. This study also shows that the surface stability increases with the oxygen content, indicating a strong tendency for surface oxidation. Our results help to clarify the origin of surface gap states upon surface oxidation and provide an insight at the atomic level the mechanism of surface oxidation, which will assist in the understanding of the degradation of III-V devices upon oxygen exposure or interfacial oxidation with high dielectric constant oxides.

Santosh, K. C.; Wang, Weichao; Dong, Hong; Xiong, Ka; Longo, Roberto C.; Wallace, Robert M.; Cho, Kyeongjae

2013-03-01

173

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

NASA Astrophysics Data System (ADS)

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

Zhang, Waigen

174

Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis.  

PubMed

Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis for probe liquids were prepared by chemical vapor deposition (CVD) of bis((tridecafluoro-1,1,2,2,-tetrahydrooctyl)-dimethylsiloxy)methylsilane (CF(3)(CF(2))(5)CH(2)CH(2)Si(CH(3))(2)O)(2)SiCH(3)H, (R(F)Si(Me)(2)O)(2)SiMeH). Oxidized aluminum surfaces were prepared by photooxidation/cleaning of sputter-coated aluminum on silicon wafers (Si/Al(Al(2)(O(3)))) using oxygen plasma. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) confirmed that this facile CVD method produces a monolayer with a thickness of 1.1 nm on the Si/Al(Al(2)(O(3))) surface without a discernible change in surface morphology. After monolayer deposition, the hydrophilic Si/Al(Al(2)(O(3))) surface became both hydrophobic and oleophobic and exhibited essentially no contact angle hysteresis for water and n-hexadecane (advancing/receding contact angles (theta(A)/theta(R)) = 110 degrees/109 degrees and 52 degrees/50 degrees, respectively). Droplets move very easily on this surface and roll off of slightly tilted surfaces, independently of the contact angle (which is a practical definition of ultralyophobic). A conventional fluoroalkylsilane monolayer was also prepared from 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (CF(3)(CF(2))(7)CH(2)CH(2)Si(OCH(3))(3), R(F)Si(OMe)(3)) for comparison. The theta(A)/theta(R) values for water and n-hexadecane are 121 degrees/106 degrees and 76 degrees/71 degrees, respectively. The larger hysteresis values indicate the "pinning" of probe liquids, even though advancing contact angles are larger than those of the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers. The (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers have excellent hydrolytic stability in water. We propose that the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers are flexible and liquidlike and that drops in contact with these surfaces experience very low energy barriers between metastable states, leading to the formation of nonhysteretic ultralyophobic surfaces. PMID:20030348

Hozumi, Atsushi; McCarthy, Thomas J

2010-02-16

175

2-Dimensional oxide electronic gases: Interfaces and surfaces  

NASA Astrophysics Data System (ADS)

Numerous solid-state properties depend on the crystal structure. Recently, the idea of searching for novel properties or novel functionalities at artificial interfaces - where a breaking of inversion symmetry and a change in the atomic environment occur - has been developing rapidly and has led to a large new field of research. In this short paper, we will summarize the properties of the 2-d electron gas found at the interface between the two band insulators LaAlO3 and SrTiO3, discuss briefly the recent observations of electron gases at oxide surfaces and examine the possible similarities and differences between these exciting systems.

Gabay, M.; Gariglio, S.; Triscone, J.-M.; Santander-Syro, A. F.

2013-07-01

176

STM-induced surface aggregates on metals and oxidized silicon  

NASA Astrophysics Data System (ADS)

We have observed an aggregation of carbon or carbon derivatives on platinum and natively oxidized silicon surfaces during STM measurements in ultra-high vacuum on solvent-cleaned samples previously structured by e-beam lithography. We imaged the aggregated layer with scanning tunneling microscopy (STM) as well as scanning electron microscopy (SEM). The amount of the aggregated material increases with the number of STM scans and with the tunneling voltage. Film thicknesses of up to 10 nm with five successive STM measurements of the same area have been obtained.

Stöffler, Dominik; Löhneysen, Hilbert V.; Hoffmann, Regina

2011-08-01

177

Oxidation of a polycrystalline titanium surface by oxygen and water  

Microsoft Academic Search

Reactions of a well-characterized polycrystalline titanium surface with oxygen and water molecules at 150–850K were studied in UHV by X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS) and Fourier transform reflectance–absorption infrared spectroscopy (FT-RAIRS). At 150K, O2 oxidizes Ti0 to TiIV, TiIII and TiII, but Ti exposure to H2O at this temperature produces only TiII species. At temperatures above 300K,

Gang Lu; Steven L. Bernasek; Jeffrey Schwartz

2000-01-01

178

Iron oxide nanoparticle powders with high surface area  

NASA Astrophysics Data System (ADS)

Iron oxide nanomaterials with desired properties synthesized in the form of nanoparticle powders can find attractive applicability, e.g. in catalysis. Hence it is necessary to thoroughly characterize the materials by several measuring techniques. Two selected samples of amorphous Fe2O3 nanoparticles with high specific surface area values were prepared by the thermal treatment of different iron-bearing precursors. In addition to Mössbauer and microscopy methods, the nitrogen sorption based surface analysis is discussed from the viewpoint of textural morphology characterization of mentioned nanomaterials. The nitrogen adsorption-desorption isotherms have been measured and indicate the presence of micro and mesoporosity. One can conclude that the porosity arises from intra-aggregate voids and spaces formed by inter-particle contacts. The state of agglomeration can be estimated and appropriate application chosen.

K?ížek, M.; Pechoušek, J.; Tu?ek, J.; Šafá?ová, K.; Med?ík, I.; Machala, L.

2012-10-01

179

Electron capture and loss processes on oxides and oxidised surfaces  

NASA Astrophysics Data System (ADS)

Electron capture and loss processes on MgO (100) and oxygen covered Mg and Al surfaces are studied on the example of formation and destruction of H-, O- and F- in atom/anion scattering. Electron capture is demonstrated to occur very efficiently on MgO (100) and can be understood in terms of a localised non-resonant capture mechanism between the incident atom and a lattice O anion. Electron loss from incident negative ions is observed and is attributed to loss to the conduction band. Changes in capture rates on oxygen covered surfaces are studied from the limit corresponding to chemisorption to oxide film formation. In the chemisorption range capture is attenuated because of changes in the local density of states (LDOS) and in the positions and widths of the anion level near the adsorbate.

Ustaze, S.; Guillemot, L.; Verucchi, R.; Lacombe, S.; Esaulov, V. A.

1998-02-01

180

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

181

Dynamic elasticity of triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) on a water surface  

Microsoft Academic Search

Dilatational viscoelasticity of adsorbed and spread films of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene\\u000a oxide) triblock copolymer at the air-water interface is studied by the capillary waves and oscillating barrier techniques.\\u000a At the surface pressure below 10 mN\\/m, dynamic surface properties of these films coincide with those of poly(ethylene oxide).\\u000a At higher surface pressures, the results obtained indicate the desorption of poly(propylene

B. A. Noskov

2006-01-01

182

Characteristics of the surface oxides on turned and electrochemically oxidized pure titanium implants up to dielectric breakdown  

Microsoft Academic Search

Titanium implants have been used widely and successfully for various types of bone-anchored reconstructions. It is believed that properties of oxide films covering titanium implant surfaces are of crucial importance for a successful osseointegration, in particular at compromized bone sites. The aim of the present study is to investigate the surface properties of anodic oxides formed on commercially pure (c.p.)

Young-Taeg Sul; Carina B. Johansson; Sarunas Petronis; Anatol Krozer; Yongsoo Jeong; Ann Wennerberg; Tomas Albrektsson

2002-01-01

183

Lithium peroxide surfaces are metallic, while lithium oxide surfaces are not.  

PubMed

The thermodynamic stability and electronic structure of 40 surfaces of lithium peroxide (Li(2)O(2)) and lithium oxide (Li(2)O) were characterized using first-principles calculations. As these compounds constitute potential discharge products in Li-oxygen batteries, their surface properties are expected to play a key role in understanding electrochemical behavior in these systems. Stable surfaces were identified by comparing 23 distinct Li(2)O(2) surfaces and 17 unique Li(2)O surfaces; crystallite areal fractions were determined through application of the Wulff construction. Accounting for the oxygen overbinding error in density functional theory results in the identification of several new Li(2)O(2) oxygen-rich {0001} and {1 ?100} terminations that are more stable than those previously reported. Although oxygen-rich facets predominate in Li(2)O(2), in Li(2)O stoichiometric surfaces are preferred, consistent with prior studies. Surprisingly, surface-state analyses reveal that the stable surfaces of Li(2)O(2) are half-metallic, despite the fact that Li(2)O(2) is a bulk insulator. Surface oxygens in these facets are ferromagnetic with magnetic moments ranging from 0.2 to 0.5 ?(B). In contrast, the stable surfaces of Li(2)O are insulating and nonmagnetic. The distinct surface properties of these compounds may explain observations of electrochemical reversibility for systems in which Li(2)O(2) is the discharge product and the irreversibility of systems that discharge to Li(2)O. Moreover, the presence of conductive surface pathways in Li(2)O(2) could offset capacity limitations expected to arise from limited electron transport through the bulk. PMID:22148314

Radin, Maxwell D; Rodriguez, Jill F; Tian, Feng; Siegel, Donald J

2011-12-28

184

Altering iron oxide nanoparticle surface properties induce cortical neuron cytotoxicity.  

PubMed

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

2011-12-06

185

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

186

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

SciTech Connect

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

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

2009-06-15

187

Rapid surface oxidation as a source of surface degradation factor for Bi?Se?.  

PubMed

Bismuth selenide (Bi(2)Se(3)) is a topological insulator with metallic surface states (SS) residing in a large bulk bandgap. In experiments, synthesized Bi(2)Se(3) is often heavily n-type doped due to selenium vacancies. Furthermore, it is discovered from experiments on bulk single crystals that Bi(2)Se(3) gets additional n-type doping after exposure to the atmosphere, thereby reducing the relative contribution of SS in total conductivity. In this article, transport measurements on Bi(2)Se(3) nanoribbons provide additional evidence of such environmental doping process. Systematic surface composition analyses by X-ray photoelectron spectroscopy reveal fast formation and continuous growth of native oxide on Bi(2)Se(3) under ambient conditions. In addition to n-type doping at the surface, such surface oxidation is likely the material origin of the degradation of topological SS. Appropriate surface passivation or encapsulation may be required to probe topological SS of Bi(2)Se(3) by transport measurements. PMID:21568290

Kong, Desheng; Cha, Judy J; Lai, Keji; Peng, Hailin; Analytis, James G; Meister, Stefan; Chen, Yulin; Zhang, Hai-Jun; Fisher, Ian R; Shen, Zhi-Xun; Cui, Yi

2011-05-23

188

Surface engineering of iron oxide nanoparticles for targeted cancer therapy  

PubMed Central

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

Kievit, Forrest M.; Zhang, Miqin

2011-01-01

189

HREM of the [111] surfaces of iron oxide nanoparticles.  

PubMed

Mixed phase Fe3O4-gamma-Fe2O3 (magnetite-maghemite) iron oxide nanoparticles have been fabricated by colloidal routes. HRTEM/HRSTEM images of the nanoparticles show the presence of [111] facets that terminate with enhanced contrast, which is shown to be caused by the presence of additional cations at the edges of the nanoparticles. HRTEM images were taken on a FEI CM200 FEGTEM, a JEOL 3100 with a LaB6 source, and a double aberration corrected JEOL-JEM 2200FS FEGTEM. The enhanced contrast effect was observed on the [111] surface atomic layers resolved using each machine. HRSTEM images, taken on an aberration corrected STEM, resolved enhanced contrast at specific surface sites. Exit wave reconstruction was also carried out on focal series taken on a double aberration corrected JEOL-JEM 2200FS and showed similar highly resolved enhanced contrast at specific surface cation sites. It is apparent that additional cations are occupying the [111] terminating layers of these nanoparticle surfaces. The use of different microscopes and techniques in this paper provides strong evidence that the enhanced contrast is a real effect and not an effect caused by microscope aberrations. PMID:16563776

Lovely, G R; Brown, A P; Brydson, R; Kirkland, A I; Meyer, R R; Chang, L Y; Jefferson, D A; Falke, M; Bleloch, A

2006-02-21

190

A kinetic study of ozone decomposition on illuminated oxide surfaces.  

PubMed

The heterogeneous chemistry and photochemistry of ozone on oxide components of mineral dust aerosol, including ?-Fe(2)O(3), TiO(2), and ?-Al(2)O(3), at different relative humidities have been investigated using an environmental aerosol chamber. The rate and extent of ozone decomposition on these oxide surfaces are found to be a function of the nature of the surface as well as the presence of light and relative humidity. Under dark and dry conditions, only ?-Fe(2)O(3) exhibits catalytic decomposition toward ozone, whereas the reactivity of TiO(2) and ?-Al(2)O(3) is rapidly quenched upon ozone exposure. However, upon irradiation, TiO(2) is active toward O(3) decomposition and ?-Al(2)O(3) remains inactive. In the presence of relative humidity, ozone decay on ?-Fe(2)O(3) subject to irradiation or under dark conditions is found to decrease. In contrast, ozone decomposition is enhanced for irradiated TiO(2) as relative humidity initially increases but then begins to decrease at higher relative humidity levels. A kinetic model was used to obtain heterogeneous reaction rates for different homogeneous and heterogeneous reaction pathways taking place in the environmental aerosol chamber. The atmospheric implications of these results are discussed. PMID:21910407

Chen, Haihan; Stanier, Charles O; Young, Mark A; Grassian, Vicki H

2011-10-11

191

Surface oxides produced during discharge in water ambient iron surface: A conversion electron Mössbauer spectroscopic study  

Microsoft Academic Search

Oxide layers are produced on iron surface, under discharge in water ambient, applying both anodic and cathodic potentials to iron foil. Non-stoichiometric Fe1-xO containing different ratios of Fe3+ and Fe2+ has been detected by using CEMS. Corrosion of these samples in 0.5 M H2SO4 shows that, cathodically discharge treated iron foil has higher corrosion resistance as compared to the anodically

N. R. Bulakh; S. V. Ghaisas; S. A. Kulkarni; S. M. Kanetkar; S. B. Ogale; S. K. Date

1988-01-01

192

Surface oxides produced during discharge in water ambient iron surface: A conversion electron Mössbauer spectroscopic study  

Microsoft Academic Search

Oxide layers are produced on iron surface, under discharge in water ambient, applying both anodic and cathodic potentials\\u000a to iron foil. Non-stoichiometric Fe1?xO containing different ratios of Fe3+ and Fe2+ has been detected by using CEMS. Corrosion of these samples in 0.5 M H2SO4 shows that, cathodically discharge treated iron foil has higher corrosion resistance as compared to the anodically

N. R. Bulakh; S. V. Ghaisas; S. A. Kulkarni; S. M. Kanetkar; S. B. Ogale; S. K. Date

1988-01-01

193

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

194

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

PubMed

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

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

2000-11-01

195

Probing and mapping electrode surfaces in solid oxide fuel cells.  

PubMed

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

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

2012-09-20

196

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

197

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

SciTech Connect

High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited on surfaces can represent the largest remaining background. To control these backgrounds, a copper cleaning chemistry has been developed. Designed to replace an effective, but overly aggressive concentrated nitric acid etch, this peroxide-based solution allows for a more controlled cleaning of surfaces. The acidified hydrogen peroxide solution will generally target the Cu+/Cu2+ species which are the predominant surface participants, leaving the bulk of copper metal intact. This preserves the critical tolerances of parts and eliminates significant waste disposal issues. Accompanying passivation chemistry has also been developed that protects copper surfaces from oxidation. Using a high-activity polonium surface spike, the most difficult-to-remove daughter isotope of radon, the performance of these methods are quantified. © 2001 Elsevier Science. All rights reserved

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

2007-08-21

198

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

NASA Astrophysics Data System (ADS)

High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited on surfaces can represent the largest remaining background. To control these backgrounds, a copper cleaning chemistry has been developed. Designed to replace an effective, but overly aggressive concentrated nitric acid etch, this peroxide-based solution allows for a more controlled cleaning of surfaces. The acidified hydrogen peroxide solution will generally target the Cu+/Cu2+ species which are the predominant surface participants, leaving the bulk of copper metal intact. This preserves the critical tolerances of parts and eliminates significant waste disposal issues. Accompanying passivation chemistry has also been developed that protects copper surfaces from oxidation. Using a high-activity polonium surface spike, the most difficult-to-remove daughter isotope of radon, the performance of these methods are quantified.

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

2007-08-01

199

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

2013-10-11

200

Water oxidation at hematite photoelectrodes: the role of surface states.  

PubMed

Hematite (?-Fe(2)O(3)) constitutes one of the most promising semiconductor materials for the conversion of sunlight into chemical fuels by water splitting. Its inherent drawbacks related to the long penetration depth of light and poor charge carrier conductivity are being progressively overcome by employing nanostructuring strategies and improved catalysts. However, the physical-chemical mechanisms responsible for the photoelectrochemical performance of this material (J(V) response) are still poorly understood. In the present study we prepared thin film hematite electrodes by atomic layer deposition to study the photoelectrochemical properties of this material under water-splitting conditions. We employed impedance spectroscopy to determine the main steps involved in photocurrent production at different conditions of voltage, light intensity, and electrolyte pH. A general physical model is proposed, which includes the existence of a surface state at the semiconductor/liquid interface where holes accumulate. The strong correlation between the charging of this state with the charge transfer resistance and the photocurrent onset provides new evidence of the accumulation of holes in surface states at the semiconductor/electrolyte interface, which are responsible for water oxidation. The charging of this surface state under illumination is also related to the shift of the measured flat-band potential. These findings demonstrate the utility of impedance spectroscopy in investigations of hematite electrodes to provide key parameters of photoelectrodes with a relatively simple measurement. PMID:22303953

Klahr, Benjamin; Gimenez, Sixto; Fabregat-Santiago, Francisco; Hamann, Thomas; Bisquert, Juan

2012-02-23

201

Approach to Nanoglasses through Anodic Oxidation of Sputtered Aluminum on Glass Surface.  

National Technical Information Service (NTIS)

The new processes for the preparation of nanoglasses have been developed through anodic oxidation. The aluminum thin film sputtered on the ITO thin film on the glass surface was decomposed into alumina by anodic oxidation technique. The alumina layer poss...

K. Wada S. Chu S. Inoue

2003-01-01

202

Model for the growth and reactivity of metal films on oxide surfaces: Cu on ZnO(000[bar 1])--O  

SciTech Connect

This occurs even when the metal's adsorption energy on itself significantly exceeds its adsorption energy on the oxide (i.e., when 3D clustering is thermodynamically favored), provided the difference in these energies does not exceed the energy of 2D evaporation from island edges onto terraces. As soon as islands nucleate in the second layer, 2D spreading ceases and energetic pathways open that allow metal atoms to migrate up from the oxide terrace into this new layer. This can lead to thick, flat-topped islands. Atom-thin (2D) Cu islands on ZnO(000[bar 1])--O react with CO, O[sub 2], H[sub 2]O, HCOOH, and CH[sub 3]OH very much like Cu(110), although there are some differences: The transiently adsorbed H and CO[sub 2] products of HCOOH dissociation migrate off or under the Cu islands and interact strongly with ZnO sites, and O[sub [ital a

Campbell, C.T.; Ludviksson, A. (Chemistry Department, University of Washington, Seattle, Washington 98195 (United States))

1994-07-01

203

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

NASA Astrophysics Data System (ADS)

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.

Lee, Myungjin; Kim, Kijeong; Lee, Hangil

2013-09-01

204

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

PubMed Central

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

2013-01-01

205

In situ thermal treatment of UV-oxidized diamond hydrogenated surface  

Microsoft Academic Search

Surface properties of polycrystalline hydrogenated diamond produced by chemical vapour deposition upon oxidation under UV irradiation are studied. The diamond surfaces were cleaned in vacuum by thermal treatment. They were characterized estimating the electron affinity of the virgin surface by UV photoelectron spectroscopy and controlling the surface composition by X-ray photoelectron spectroscopy. The cleaned surfaces were then exposed to pure

G. Speranza; S. Torrengo; M. Filippi; L. Minati; E. Vittone; A. Pasquarelli; M. Dipalo; E. Kohn

2010-01-01

206

Kinetics of oxidation on hydrogen-terminated Si(100) and (111) surfaces stored in air  

Microsoft Academic Search

We have investigated the oxidation of hydrogen-terminated Si(111) and (100) surfaces stored in air, using synchrotron radiation photoemission spectroscopy and infrared absorption spectroscopy in the multiple internal reflection geometry. We demonstrate that water present in air is predominantly involved in the oxidation of surface Si–H bonds, and that native oxide starts to grow when the surface hydrogen coverage is decreased.

Taka-Aki Miura; Michio Niwano; Daisei Shoji; Nobuo Miyamoto

1996-01-01

207

Oxidation of Cell Surface Thiol Groups by Contact Sensitizers Triggers the Maturation of Dendritic Cells  

Microsoft Academic Search

p38 mitogen-activated protein kinase (MAPK) has a crucial role in the maturation of dendritic cells (DCs) by sensitizers. Recently, it has been reported that the oxidation of cell surface thiols by an exogenous impermeant thiol oxidizer can phosphorylate p38 MAPK. In this study, we examined whether sensitizers oxidize cell surface thiols of monocyte-derived DCs (MoDCs). When cell surface thiols were

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

2010-01-01

208

Native Oxide Growth on Silicon Surface in Ultrapure Water and Hydrogen Peroxide  

Microsoft Academic Search

The effects of n-type dopant (P, As) concentration in silicon (100), temperature, and oxidizing species on native oxide growth in liquid water are described. The oxide growth on phosphorus (P)- and arsenic (As)-doped n+-Si surfaces (1020 cm-3) in ultrapure water exhibits saturation of oxide thickness, suggesting a field-assisted mechanism. Oxide thickness saturation was also found on n-Si in hydrogen peroxide

Mizuho Morita; Tadahiro Ohmi; Eiji Hasegawa; Akinobu Teramoto

1990-01-01

209

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

210

The electrochemical surface forces apparatus: the effect of surface roughness, electrostatic surface potentials, and anodic oxide growth on interaction forces, and friction between dissimilar surfaces in aqueous solutions.  

PubMed

We present a newly designed electrochemical surface forces apparatus (EC-SFA) that allows control and measurement of surface potentials and interfacial electrochemical reactions with simultaneous measurement of normal interaction forces (with nN resolution), friction forces (with ?N resolution), and distances (with Å resolution) between apposing surfaces. We describe three applications of the developed EC-SFA and discuss the wide-range of potential other applications. In particular, we describe measurements of (1) force-distance profiles between smooth and rough gold surfaces and apposing self-assembled monolayer-covered smooth mica surfaces; (2) the effective changing thickness of anodically growing oxide layers with Å-accuracy on rough and smooth surfaces; and (3) friction forces evolving at a metal-ceramic contact, all as a function of the applied electrochemical potential. Interaction forces between atomically smooth surfaces are well-described using DLVO theory and the Hogg-Healy-Fuerstenau approximation for electric double layer interactions between dissimilar surfaces, which unintuitively predicts the possibility of attractive double layer forces between dissimilar surfaces whose surface potentials have similar sign, and repulsive forces between surfaces whose surface potentials have opposite sign. Surface roughness of the gold electrodes leads to an additional exponentially repulsive force in the force-distance profiles that is qualitatively well described by an extended DLVO model that includes repulsive hydration and steric forces. Comparing the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer allowed the identification of its chemical structure as a hydrated Au(OH)(3) phase formed at the gold surface at high positive potentials. The EC-SFA allows, for the first time, one to look at complex long-term transient effects of dynamic processes (e.g., relaxation times), which are also reflected in friction forces while tuning electrochemical surface potentials. PMID:22877582

Valtiner, Markus; Banquy, Xavier; Kristiansen, Kai; Greene, George W; Israelachvili, Jacob N

2012-08-29

211

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

212

Electroless coating of tungsten oxide on the surface of copper powder  

SciTech Connect

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

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

2008-08-04

213

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

SciTech Connect

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

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

2010-01-01

214

Spectroscopic investigations of hydrogen termination, oxide coverage, roughness, and surface state density of silicon during native oxidation in air  

Microsoft Academic Search

By simultaneous surface photovoltage (SPV) as well as ultraviolet-visible (UV-Vis) and Fourier-transform infrared (FTIR) spectroscopic ellipsometry (SE) measurements on H-terminated Si(111) and Si(100) wafers as well as ?c-Si:H surfaces directly after preparation and after storage in clean-room air, correlations were established between the preparation-induced surface morphology and the stability of the surface passivation against native oxidation. It was shown that

W. Henrion; M Rebien; H Angermann; A Röseler

2002-01-01

215

Nitrous Oxide Emissions from Bare Peat Surfaces on Permafrost Peatlands  

NASA Astrophysics Data System (ADS)

Pronounced warming predicted for the arctic areas may enhance the release of soil carbon and nitrogen as greenhouse gases to the atmosphere. While carbon dioxide and methane fluxes in high-latitude ecosystems have been widely investigated, fewer studies have been published on nitrous oxide (N2O) dynamics in the North. Although most pristine ecosystems in the Arctic do not emit N2O due to strict nitrogen limitation, recent findings show that there are specific surfaces capable of high N2O production and release (Repo et al., 2009). In this study we used a static chamber technique to study N2O emissions from bare peat surfaces on two subarctic permafrost peatland types, peat plateau and palsa mire. The peat plateau site is located in the discontinuous permafrost zone in Komi Republic, Russia (67°03' N, 62°57' E). Field data from this Russian site from snow-free season 2007 showed high emissions from peat circles (bare peat surfaces affected by cryoturbation; 1.9 to 31 mg N2O m-2 d-1) and negligible N2O release from all the vegetated surfaces (Repo et al. 2009). Peat circles were emitting N2O at rates comparable to those measured typically from agricultural and tropical soils. These observations were confirmed by field campaign in 2008. Partly vegetated palsas on the top of the peat plateau, included in the study in 2008, showed also significant N2O emissions, intermediate to those from peat circles and fully vegetated sites. No particularly high peak emissions were observed during cold season from either of the studied surfaces, in contrast to what has been reported from many boreal soils. To get evidence on the spatial coverage of high N2O emissions from subarctic peatlands, N2O emissions were measured from three palsa mires in Finnish Lapland (69°34'-69°50' N, 26°10'-27°10' E) during a short campaign in peak season 2009. The region has less permafrost extent and milder climatic conditions than the Russian site. Bare peat surfaces on palsas, created by wind abrasion, were significant N2O sources, with emissions similar to those from bare peat plateau surfaces at the Russian site. Based on geomorphology, physico-chemical properties of peat and climatic conditions at the study sites, the key factors leading to high N2O emissions from subarctic peatlands are presence of surfaces lifted up by frost (palsas, peat plateaus), absence of vegetation, low C:N ratio of peat and sufficient, but not too high moisture. We discuss the consequences of climate warming on the N2O emissions from peat circles and palsas, the overall area of these N2O hot-spots and their importance for the total atmospheric impact of subarctic peatlands. Repo M.E., Susiluoto S., Lind S.E., Jokinen S., Elsakov V., Biasi C., Virtanen T.&. Martikainen P.J. 2009. Large N2O emissions from cryoturbated peat soil in tundra. Nature Geoscience, doi:10.1038/ngeo434.

Repo, M. E.; Pitkämäki, A.; Biasi, C.; Seppälä, M.; Martikainen, P. J.

2009-12-01

216

In situ surface oxidation of Ti44Al11Nb alloy at room temperature  

Microsoft Academic Search

The in situ surface oxidation of polycrystalline Ti-44Al-11Nb (compositions are in atomic %) alloy was studied at room temperature in an ultrahigh vacuum (66.6 to 80.0 nPa). The native oxide of Ti-44Al-11Nb was removed by sputtering the surface using 2.8 kV argon ions and then high-purity oxygen was carefully dosed onto the aluminide surface. After each oxygen dosing the surface

P. W. Wang; J. Woo; M. Avila; J. Garcia; A. Bronson; S. K. Varma

2003-01-01

217

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

SciTech Connect

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

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

2007-10-29

218

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

NASA Astrophysics Data System (ADS)

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

Okada, Michio; Teraoka, Yuden

219

Surface oxidation behavior of MgNd alloys  

NASA Astrophysics Data System (ADS)

The oxidation kinetics of MgNd alloys oxidized in pure O2 at high temperatures has been investigated. The results revealed two stages of the reaction: A fast initial oxidation was followed by a slow oxide growth with a parabolic kinetics. For MgNd alloys (Nd = 25 wt.%), the oxidation rate increased with the enhancement of the oxidation temperature. A sudden ignition was found for this alloys oxidized at 873 K up to about 80 min. Moreover, the increase of the Nd content would harm the oxidation resistance of the MgNd alloys. By Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, it was found that a triplex structure of oxide film formed. The outer layer was composed of MgO, Nd2O3 and Nd(OH)3, the middle layer mainly consisted of MgO and Nd2O3, and the inner layer was the transitional layer made of MgO, Nd2O3 and the content of the substrate. The protective oxidation was associated with the formation of the dense Nd2O3/MgO layer during isothermal oxidation process. The oxidation mechanisms for the formation of oxide film are discussed.

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

2007-09-01

220

Apatite deposition on thermally and anodically oxidized titanium surfaces in a simulated body fluid  

Microsoft Academic Search

By application of a special specimen set-up, thermally oxidized titanium specimen pairs were found able to deposit apatite on the contact surfaces after soaking for 7 days in the simulated body fluid (SBF) of Kokubo's recipe. The specimens oxidized at 400°C and 500°C showed the highest ability of apatite deposition. Both increase and decrease in oxidation temperature from this range

Xiao-Xiang Wang; Wei Yan; Satoshi Hayakawa; Kanji Tsuru; Akiyoshi Osaka

2003-01-01

221

Carbon oxide in the surface air (Obninsk monitoring station)  

NASA Astrophysics Data System (ADS)

The results of measurements of the concentration of carbon oxide (CO) in the atmospheric surface layer over the town of Obninsk (in European Russia, 105 km to the southwest of Moscow) are presented. Air samples were analyzed with the aid of a measuring system consisting of a Fourier-spectrometer and an optic multipass cell. The CO concentration was measured simultaneously with the measurements of air temperature up to a height of 300 m. The measurement data obtained from February 1998 to January 2009 suggest the presence of variations within the range 100-450 ppb (˜80% of all the data) and nonperiodic relatively short-term and anomalously high CO concentrations that reach several ppm. The highest concentrations are due to CO accumulated in the surface air in the presence of temperature inversion and during forest fires. The measurements of the concentration of CO throughout a day revealed its morning and evening maxima, which coincide in time with the increased traffic current. The maxima and minima of seasonal variations in the monthly mean concentrations of CO, which are due to variations in the sources and sinks of CO that happen within a year, are observed in January and June, respectively. The amplitudes of seasonal variations amounted to (53 ± 10)% of the annual mean. The annual mean concentration of CO decreased by ˜12% over the measurement period. A comparison was made with observational data obtained at five monitoring stations located in the latitudes that are close to the latitude of Obninsk. Over the European continent, the concentration of CO tends to decrease with a longitude decrease as it goes from east to west.

Kashin, F. V.; Akimenko, R. M.; Aref'ev, V. N.; Baranov, Yu. I.; Bugrim, G. I.; Sizov, N. I.; Upenek, L. B.

2010-02-01

222

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

223

In situ observation of surface oxide layers on medical grade Ni-Ti alloy during straining.  

PubMed

Medical grade Ni-Ti alloys with shape memory or pseudo-elastic behavior exhibit good biocompatibility because of an electrochemically passive oxide layer on the surface. In this work, the mechanical stability of surface oxide layers is investigated during reversible pseudo-elastic deformation of commonly applied medical grade Ni-Ti wires. Surface oxide layers with varying thickness were generated by varying annealing times under air atmosphere. The thicknesses of the surface oxide layers were determined by means of Rutherford backscattering spectrometry. In situ scanning electron microscopy investigations reveal a damage mechanism, which is assumed to have a significant influence on the biocompatibility of the material. The conditions that lead to the appearance of cracks in the surface oxide layer or to the flaking of surface oxide layer particles are identified. The influence of the thickness of the surface oxide layer on the damage mode is characterized. The possible impact of the damaged surface oxide layer on the material's biocompatibility and the potentials to reduce or avoid the damage are discussed. PMID:18384174

Undisz, A; Schrempel, F; Wesch, W; Rettenmayr, M

2009-03-15

224

Corrosion resistance of the surface layers formed on titanium by plasma electrolytic oxidation and hydrothermal treatment  

Microsoft Academic Search

This study is concerned with the modification of titanium surface by plasma electrolytic oxidation (PEO) and hydrothermal treatment. The samples were oxidized in an electrolytic solution that contained calcium ?-glycerophosphate and calcium acetate. Then, the specimens were hydrothermally heated at a temperature of 220°C for 4h using an autoclave. The chemical composition of the surface layers was examined by XPS.

J. Baszkiewicz; D. Krupa; J. Mizera; J. W. Sobczak; A. Bili?ski

2005-01-01

225

Abiotic formation of elemental selenium and role of iron oxide surfaces  

Microsoft Academic Search

The possible abiotic reduction of selenite to form elemental Se was studied under controlled conditions in the presence of ferrous iron. The reduction of selenite and formation of Se (0) was found to be a surface- mediated reaction by iron oxides. Without the presence of the reactive surface of freshly precipitated iron oxides, the reduction reaction could not be detected,

Yu-Wei Chen; Hoang-Yen Thi Truong; Nelson Belzile

2008-01-01

226

Evaluation of Surface Oxidation Behavior on Silver Film for Active Oxygen Detector  

Microsoft Academic Search

In this study, the mechanism of oxidation on silver-coated quartz crystal was investigated from the standpoint of future application to active oxygen monitoring under ultraviolet lamp processing. The effect of excited atomic oxygen (O (1D)) on the silver surface was monitored in real time utilizing the quartz crystal microbalance (QCM) method. To clarify the surface oxidation behavior on silver thin

Hiroyuki Matsumoto; Yoshihisa Shibata; Fumio Suzuki; Kiyoshi Yoshino; Mikihiko Matsuoka; Tatsuyuki Iwasaki; Shinobu Kinoshita; Kazutoshi Noda; Satoru Iwamori

2010-01-01

227

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

Microsoft Academic Search

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

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

1995-01-01

228

HREELS investigation of the surfaces of nanocrystalline diamond films oxidized by different processes.  

PubMed

This article reports on the use of high-resolution electron energy loss spectroscopy (HREELS) for the investigation of as-grown (hydrogen-terminated) and oxidized nanocrystalline diamond films (NCD) using chemical, physical, and electrochemical approaches. The results indicate that the nature and number of oxygen-related chemical groups generated on the NCD surface depend strongly on the oxidation process. A high concentration of C-O functions has been obtained on the NCD surface oxidized by rf (radio frequency) oxygen plasma, whereas the highest C?O/C-O ratio has been achieved by electrochemical oxidation. The NCD surface oxidized by rf plasma was totally free of C?O groups. Traces of surface hydroxyl groups (C-OH) have been detected upon annealing in air or through UV/ozone oxidation. PMID:21117632

Ghodbane, Slimane; Haensel, Thomas; Coffinier, Yannick; Szunerits, Sabine; Steinmüller-Nethl, Doris; Boukherroub, Rabah; Ahmed, Syed Imad-Uddin; Schaefer, Juergen A

2010-11-30

229

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

PubMed Central

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

2010-01-01

230

Long Jumps in the Surface Diffusion of Large Molecules  

Microsoft Academic Search

We have studied the diffusion of the two organic molecules DC and HtBDC on the Cu(110) surface by scanning tunneling microscopy. Surprisingly, we find that long jumps, spanning multiple lattice spacings, play a dominating role in the diffusion of these molecules-the root-mean-square jump lengths are as large as 3.9 and 6.8 lattice spacings, respectively. The presence of long jumps is

M. Schunack; T. R. Linderoth; F. Rosei; E. Lægsgaard; I. Stensgaard; F. Besenbacher

2002-01-01

231

Resonantly excited photoluminescence from porous silicon: Effects of surface oxidation on resonant luminescence spectra  

Microsoft Academic Search

We have studied the photoluminescence mechanism of freshly prepared and naturally oxidized porous silicon by fluorescence-line-narrowing spectroscopy. The surfaces of fresh and oxidized porous silicon are terminated by silicon hydrides and silicon dioxide, respectively. The TO-phonon-related structure in resonantly excited luminescence is clearly observed in H-terminated porous silicon. After surface oxidation, the luminescence intensity increases and a structure in the

Yoshihiko Kanemitsu; Shinji Okamoto

1997-01-01

232

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

233

Effects of topography and composition of titanium surface oxides on osteoblast responses  

Microsoft Academic Search

To investigate the roles of composition and characteristics of titanium surface oxides in cellular behaviour of osteoblasts, the surface oxides of titanium were modified in composition and topography by anodic oxidation in two kinds of electrolytes, (a) 0.2m H3PO4, and (b) 0.03m calcium glycerophosphate (Ca-GP) and 0.15m calcium acetate (CA), respectively. Phosphorus (P: ca.10at%) or both calcium (Ca: 1–6at%) and

Xiaolong Zhu; Jun Chen; Lutz Scheideler; Rudolf Reichl; Juergen Geis-Gerstorfer

2004-01-01

234

Oxidation of aqueous Cr(III) at birnessite surfaces: constraints on reaction mechanism  

Microsoft Academic Search

X-ray Photoelectron Spectroscopy (XPS) was used to investigate oxidation of aqueous Cr(III) at the surface of 7 Å-birnessite [MnO1.75(OH)0.25]. Special emphasis was placed on detection of intermediate oxidation states of chromium due to their critical environmental significance. No previous studies have been able to identify these intermediate oxidation states of chromium (namely, Cr[IV] and Cr[V]) on mineral surfaces or in

D. Banerjee; H. W. Nesbitt

1999-01-01

235

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

SciTech Connect

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

Cox, D.F.

1997-12-31

236

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

SciTech Connect

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

Doyle, F.M.

1996-01-26

237

Origin of complex impact craters on native oxide coated silicon surfaces  

NASA Astrophysics Data System (ADS)

Crater structures induced by impact of keV-energy Arn+ cluster ions on silicon surfaces are measured with atomic force microscopy. Complex crater structures consisting of a central hillock and outer rim are observed more often on targets covered with a native silicon oxide layer than on targets without the oxide layer. To explain the formation of these complex crater structures, classical molecular dynamics simulations of Ar cluster impacts on oxide coated silicon surfaces, as well as on bulk amorphous silica, amorphous Si, and crystalline Si substrates, are carried out. The diameter of the simulated hillock structures in the silicon oxide layer is in agreement with the experimental results, but the simulations cannot directly explain the height of hillocks and the outer rim structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5keV /atom Ar12 cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.

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

2008-02-01

238

On the stability and oxidation of single crystal (100) InAs surfaces  

SciTech Connect

We report on a method to prepare clean and smooth surfaces of InAs (100) along with in-situ high-resolution studies of the nanoscale oxidation of the pristine surface. A hydrogen molecular cleaning (HMC) technique has been developed that results in complete removal of native oxide. This has been verified in-depth by in-situ nuclear reaction analysis (NRA) using the 16O(d,p)17O reaction and X-ray photoelectron spectroscopy. Further, ion channeling studies have been performed to verify atomically smooth surfaces after post cleaning. We derive kinetic boundaries for oxide formation on cleaned InAs surfaces using NRA measurements.

Chang, Chia-Lin; Shutthanandan, V.; Singhal, Subhash C.; Ramanathan, Shriram

2007-12-31

239

Controlled growth of aluminum oxide thin films on hydrogen terminated Si(0 0 1) surface  

NASA Astrophysics Data System (ADS)

Auger electron spectroscopy, energy electron loss spectroscopy, atomic force microscopy and transmission electron microscopy were used to characterize ultra-thin aluminum oxide films grown on hydrogen-terminated Si(0 0 1) H substrates via a specific atomic layer deposition and oxidation technique. Oxide thin films grown in such a way are highly stable with temperature at least up to 700 °C. Band gap was estimated to be 6.6±0.2 eV, independent of thickness. Formation of the oxide layer slightly increases the initial roughness of silicon surface. Furthermore, no silicon oxide was found at the aluminum oxide silicon interface.

Vizzini, S.; Oughaddou, H.; Léandri, C.; Lazarov, V. K.; Kohn, A.; Nguyen, K.; Coudreau, C.; Bibérian, J.-P.; Ealet, B.; Lazzari, J.-L.; Arnaud D'Avitaya, F.; Aufray, B.

2007-07-01

240

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

PubMed

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

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

2010-07-26

241

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

242

GaAs surface passivation using in-situ oxide deposition  

Microsoft Academic Search

In-site deposition of Ga2O3, SiO2, and MgO films on clean, atomically ordered (100) GaAs surfaces grown by molecular beam epitaxy using a multiple-chamber ultra high vacuum system has been investigated. Using this technique, direct bonding of oxide molecules to GaAs surface atoms revealing intrinsic oxide-GaAs interface properties has been achieved. The GaAs surface reconstruction prior to deposition as observed by

M. Passlack; M. Hong; R. L. Opila; J. P. Mannaerts; J. R. Kwo

1996-01-01

243

Surface characterization of radio frequency water plasma treated and annealed polycrystalline tin oxide thin films  

Microsoft Academic Search

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and electron energy loss spectroscopy (EELS) have been used to examine the consequences of the interaction of radio frequency water plasmas with polycrystalline tin oxide surfaces. Results from AR-XPS and EELS indicate that an extensive surface hydroxylation or gel layer (> 10 â«) does not form on the tin oxide surface from exposure to atmosphere

M. J. Tarlov; J. F. Evans

2009-01-01

244

Structure of the SiC(0001)- 3 × 3 -R30° surface after initial oxidation  

Microsoft Academic Search

The structure of the 3×3-R30° reconstruction on the (0001) surface of silicon carbide before and after initial oxidation at room temperature was determined with reflection high-energy electron diffraction (RHEED) rocking curves in the one-beam condition and density-functional theory calculations. The structural parameters of the clean surface are in good agreement with previous reports. For the oxidized surface, good agreement between

Wolfgang Voegeli; Tomohiro Aoyama; Koichi Akimoto; Ayahiko Ichimiya; Yoshiyuki Hisada; Yoshihito Mitsuoka; Shinichi Mukainakano

2010-01-01

245

Surface oxidation study of single wall carbon nanotubes.  

PubMed

Functionalization of single wall carbon nanotubes (SWCNTs) is desirable to enhance their ability to be incorporated into polymers and enhance their bonding with the matrix. One approach to carbon nanotube functionalization is by oxidation via a strong oxidizing agent or refluxing in strong acids. However, this approach can damage the nanotubes, leading to the introduction of defects and/or shorter nanotubes. Such damage can adversely affect the mechanical, thermal, and electrical properties. A more benign approach to nanotube functionalization has been developed involving photo-oxidation. Chemical analysis by XPS revealed that the oxygen content of the photo-oxidized SWCNTs was 11.3 at.% compared to 6.7 at.% for SWCNTs oxidized by acid treatment. The photo-oxidized SWCNTs produced by this method can be used directly in various polymer matrices or can be further modified by additional chemical reactions. PMID:22020272

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

2011-10-21

246

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

SciTech Connect

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

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

2011-04-14

247

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

248

Surface characterization of thin layers of aluminium oxide  

Microsoft Academic Search

Thin oxide layers of commercial pure aluminium (1100-Al) and AlZnMgCu alloy (7075-Al) were characterized after oxidation in a 2.45 GHz microwave discharge in oxygen plasma at low temperature (400 ± 50 °C). The composition and structure of the oxide layers were studied by Auger electron spectroscopy (AES) and Fourier transform IR (FTIR) spectroscopy. In addition, atomic force microscopy (AFM) and

A. Raveh; Z. K. Tsameret; E. Grossman

1997-01-01

249

Chemical stability and surface stoichiometry of vanadium oxide phases studied by reactive molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

Compositional stability of various vanadium oxides and oxide growth on vanadium surfaces have been studied using reactive molecular dynamics simulation methods. Vanadium dioxide (VO2), sesquioxide (V2O3), pentoxide (V2O5), and hexavanadium tridecaoxide (V6O13) are studied in bulk crystalline and thin film structures, investigating charge distribution and pair distribution functions of particle interactions. The stability is estimated to be pentoxide, hexavanadium tridecaoxide, sesquioxide, and dioxide respectively in decreasing order in thin film structures. We then analyze oxide growth kinetics on vanadium (100) and (110) surfaces. The oxidation rate, stoichiometry, charge distribution, and the effect of surface orientation on kinetic phenomena are noted. In the early stages of surface oxidation of our simulation configurations, sesquioxide is found to be the dominant component. The modeling and simulation results are compared with experiments where available.

Jeon, Byoungseon; Ko, Changhyun; van Duin, Adri C. T.; Ramanathan, Shriram

2012-02-01

250

Laser removal of oxides and particles from copper surfaces for microelectronic fabrication.  

PubMed

Laser removal of surface oxides and small particles from copper surfaces was carried out using a Q-switched Nd:YAG laser. Oxide layers and small particles on copper surfaces should be removed for the improvement of solder quality on printed circuit boards (PCBs) and for the prevention of circuit failure or loss of production yield during the fabrication of microelectronic devices. A selective removal of surface oxides from a copper surface was achieved by the laser treatment, which was confirmed by on-line acoustic monitoring of the process. An angular laser cleaning technique in which the laser irradiates the surface at a glancing angle was used for effective removal of the particles from the surface. The unique characteristics of this technique and the cleaning mechanism are discussed. PMID:19404371

Lee, J M; Watkins, K

2000-07-17

251

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

252

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

253

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

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

254

Reporting central tendencies of chamber measured surface emission and oxidation  

Microsoft Academic Search

Methane emissions, concentrations, and oxidation were measured on eleven MSW landfills in eleven states spanning from California to Pennsylvania during the three year study. The flux measurements were performed using a static chamber technique. Initial concentration samples were collected immediately after placement of the flux chamber. Oxidation of the emitted methane was evaluated using stable isotope techniques. When reporting overall

Tarek Abichou; Jeremy Clark; Jeffery Chanton

2011-01-01

255

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

PubMed

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

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

2012-09-01

256

Decontaimination of U-Metal Surface by an Oxidation Etching System.  

National Technical Information Service (NTIS)

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 at...

E. J. Kansa H. C. Weed R. B. Stout R. J. Shaffer

2000-01-01

257

An Unprecedented Surface Oxidation of Polystyrene Substrates by Wet Chemistry under Basic Conditions  

Microsoft Academic Search

The surface of polystyrene substrates has been modified by wet chemistry consisting of a treatment with sodium hydroxide in a water-methanol solution at 50°C for 15 h, under air atmosphere. The resulting samples were analyzed by XPS and AFM. The surface functional groups (hydroxyl and carboxyl functions) were assayed by radiolabeling. All the results are consistent with a surface oxidation

Arayik Hambardzumyan; Stéphane Biltresse; Yves Dufrêne; Jacqueline Marchand-Brynaert

2002-01-01

258

Synthesis and Properties of Surface Chemically Pure Alkylamidoamine- N -oxides at the Air\\/Water Interface  

Microsoft Academic Search

A homologous series of surface active 2-(alkanoylamino)ethyldimethylamine-N-oxides, EDA-p(O), and 3-(alkanoylamino)propyldimethylamine-N-oxides, PDA-p(O), were synthesized. Their aqueous stock solutions were processed by the automatically operating apparatus to remove surface-active\\u000a contamination and provide chemical purity at the air\\/water interface. In case of 3-(tetradecanoylamino)propyldimethylamine-N-oxide, PDA-14(O), the difference between equilibrium surface tension values of the purified surfactant solutions and the corresponding values\\u000a of the solutions

Andrzej Piasecki; Dorota Pi?akowska-Pietras; Anna Baran; Anna Krasowska

2008-01-01

259

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

Microsoft Academic Search

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

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

2010-01-01

260

Optical Measurements of Surface Oxide Layer Formation on Metal Films.  

National Technical Information Service (NTIS)

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 ...

M. L. Scott

1987-01-01

261

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

262

Extending ellipsometry capabilities for ultrathin gate oxide metrology using rapid optical surface treatment technology  

NASA Astrophysics Data System (ADS)

Today's advanced IC manufacturers are already beginning production on 0.18 micrometer process technology. This requires gate oxidation processes that are capable of thicknesses in the 30 angstrom to 40 angstrom range. The gate oxide thickness specification will be pushed even lower as the industry moves toward sub-0.18 micrometer technology in the next few years. In order to maintain device performance and yields, it is necessary that the gate oxide thickness be very tightly controlled. Current ellipsometry techniques do not provide the precision-to-tolerance ratios required for good statistical process control of these ultra-thin gate oxides. This work demonstrates that a significant portion of the error in ellipsometry measurements is the result of organic surface contamination. Furthermore, the Rapid Optical Surface Treatment is shown as a good method for removing organic surface contaminants and extending the capabilities of ellipsometry techniques for ultra-thin gate oxides.

Tardif, Francois; Danel, Adrien; Kamieniecki, Emil; Harrington, James

1999-09-01

263

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

SciTech Connect

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

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

1999-06-15

264

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

265

Change of black shale organic material surface area during oxidative weathering: Implications for rock-water surface evolution  

NASA Astrophysics Data System (ADS)

Black shale oxidative weathering plays a significant role in a variety of processes including acid mine drainage and atmospheric CO 2 control. The modeling of weathering is highly dependent on reactive surface area. In this study it is shown that black shale oxidative weathering is regulated mainly by the external, geometrical surface area of rock polyhedrons and the organic matter's (OM) internal surface area. The internal rock surface area decreases dramatically during OM dissolution from ˜15 m 2/g to ˜5 m 2/g. A linear relationship was found between the decrease of internal rock surface area and quantity of OM dissolved. Optical roughness analyses of black and bleached shale surface area reveal the formation of macropores due to the dissolution of mesoporous and probably microporous OM. However, due to deconsolidation, the geometrical external rock polyhedron surface area increases during weathering. Black shale polyhedrons show a doubling of their external surface area as OM decreases. This provokes an increase of the shale volume which is easily accessible by fluids. The increase of the external rock surface area seems to be self-accelerating during weathering. The upscaling of external and internal rock surface area evolution during weathering presented in this study demonstrates the possible application of these results to the improved understanding of a chemical transport in a variety of natural systems.

Fischer, Cornelius; Gaupp, Reinhard

2005-03-01

266

Surface modification of oxidic nanoparticles using 3-methacryloxypropyltrimethoxysilane  

Microsoft Academic Search

Tin oxide, antimony-doped tin oxide (ATO), and silica nanosized particles in aqueous dispersion were reacted with various amounts of 3-methacryloxypropyltrimethoxysilane (MPS). The kinetics were followed by 29Si NMR and the products were analyzed by FTIR and 29Si NMR. The kinetic experiments on ATO and silica revealed that the hydrolysis is the rate-determining step in these reactions. The reaction of MPS with

W. Posthumus; P. C. M. M. Magusin; J. C. M. Brokken-Zijp; A. H. A. Tinnemans; R. van der Linde

2004-01-01

267

Effect of Light Irradiation on Native Oxidation of Silicon Surface  

Microsoft Academic Search

We found that shielding wafers from visible light is effective to prevent native oxidation of silicon. Hydrogen terminated p-Si(100) (8-12 Omega{\\\\cdot}cm) wafers were stored in wafer boxes under various brightness levels. The oxidation rate in a dark box (˜0 lx) is less than 0.01 nm\\/12 h, while that in a light box (˜1000 lx) is approximately 0.1 nm\\/12 h.

Takenobu Yoshino; Shin Yokoyama; Toshiaki Fujii

2001-01-01

268

Surface Resonance X-Ray Scattering Observation of Core-Electron Binding-Energy Shifts of Pt(111)-Surface Atoms during Electrochemical Oxidation  

NASA Astrophysics Data System (ADS)

Surface resonance x-ray scattering, sensitive to the monolayer-level change of an oxidation state of a buried interface, is used for the investigation of electrochemical oxidation of Pt(111) single crystal surface. The strongly Q-dependent energy scans through the LIII resonance energy of Pt atoms were accounted for by a large increase of the electron binding energy of the surface atoms as a result of surface anodic oxidation.

Chu, Y. S.; You, H.; Tanzer, J. A.; Lister, T. E.; Nagy, Z.

1999-07-01

269

Interaction of hydrogen ions with oxidized GaAs(100) and AlAs(100) surfaces  

SciTech Connect

We have performed photoemission experiments, using a tunable soft x-ray synchrotron radiation source to study the chemical changes of oxidized GaAs and AlAs surfaces subject to exposure from hydrogen ions. Results indicate that the net effects for hydrogen ion irradiation are (i) the reduction of arsenic and (ii) the growth of the cation oxide components. The reduction of arsenic can result from the formation/desorption of arsine. The oxide overlayer after hydrogen ion treatments is dominated by cation oxides which are the more stable chemical species as described in the phase diagram. This oxide layer should then remain stable in atmosphere. These results can provide insight into the chemical reaction between hydrogen ions and oxidized AlGaAs surfaces. {copyright} {ital 1996 American Vacuum Society}

Chang, Y. [Center for Quantized Electronic Structures (QUEST), University of California, Santa Barbara, California 93106 (United States); Cao, R.; Spicer, W.E.; Pianetta, P. [Stanford Synchrotron Radiation Lab (SSRL), Stanford University, Stanford, California 94305 (United States); Shi, S.; Hu, E. [Center for Quantized Electronic Structures (QUEST), University of California, Santa Barbara, California 93106 (United States); Merz, J. [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

1996-07-01

270

Direct Observation of the Precession of Individual Paramagnetic Spins on Oxidized Silicon Surfaces.  

National Technical Information Service (NTIS)

The precession of individual spins on partially oxidized Si(111) (Silicon) surfaces has been detected using a scanning tunneling microscope. The spin precession in a constant magnetic field induces a modulation in the tunneling current at the Larmor frequ...

Y. Manassen R. J. Hamers J. E. Demuth A. J. Castellano

1990-01-01

271

Characterization Study of Polycrystalline Tin Oxide Surfaces Before and after Reduction in CO.  

National Technical Information Service (NTIS)

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 ...

J. E. Drawdy G. B. Hoflund M. R. Davidson D. R. Schryer

1990-01-01

272

Role of Ferric Oxide Surface Area in Propellant Burn Rate Enhancement (First Step Toward Modeling).  

National Technical Information Service (NTIS)

Results of efforts to correlate composite propellant burn rate, ammonium perchlorate particle size distribution, and ferric oxide specific surface and level are presented. Results from laboratory-scale motor firings with HTPB- and CTPB-based propellants c...

C. H. Burnside

1975-01-01

273

Evolution of relief of asperited polycrystalline silicon surface in the process of thermal oxidation  

Microsoft Academic Search

A simple phenomenological model of changing asperity surface, in the process of thermal oxidation of polycrystalline silicon, is examined. This allows to prognosticate and consequently deliberately change electrical characteristics of the dielectric layer

G. V. Perov; E. G. Salman; A. N. Ignatov

2000-01-01

274

Chemical and Catalytic Activation of Methane by Metal Oxide Surfaces. Annual Report, September 1989-August 1990.  

National Technical Information Service (NTIS)

The objectives of the research are to investigate the nature of surface oxygen centers capable of selective conversion of methane into hydrocarbon fuels through catalytic selective oxidation and to determine the role of homogeneous reactions in the cataly...

J. G. McCarty E. D. Wachsman

1992-01-01

275

Biomembrane Phospholipid–Oxide Surface Interactions: Crystal Chemical and Thermodynamic Basis  

Microsoft Academic Search

Quartz has the least favored surface among many oxides for bacterial attachment and for lipid bilayer or micelle interactions. Tetrahedrally coordinated crystalline silica polymorphs are membranolytic toward liposomes, lysosomes, erythrocytes, and macrophages. Amorphous silica, the octahedral silica polymorph, (stishovite), and oxides such as Al2O3, Fe2O3, and TiO2 are less cytotoxic. Existing theories for membrane rupture that invoke interactions between oxide

Nita Sahai

2002-01-01

276

Microstructure and morphology of surface oxide films on Ti6Al4V  

Microsoft Academic Search

The microstructure of anodic oxide films grown on Ti6Al4V in HâSOâ was investigated by SEM, TEM, STEM, EDX, and AES, as a complement to a recent surface spectroscopic investigation of the same oxides by XPS, AES, and SIMS. The anodic oxide films are heterogenous and the texture reflects the duplex microstructure (α and β phases) of the underlying metal. Porous

M. Ask; U. Rolander; J. Lausmaa; B. Kasemo

1990-01-01

277

Development of the Arc-Induced Erosion Surface in SilverCadmium Oxide  

Microsoft Academic Search

Evaluation of silver-cadmium oxide contacts at intermittent stages during their static gap electrical testing allows their inherent anodic and cathodic erosion behaviors to be studied. The cathodes tend to develop a few low mounds of oxide-depleted metal on their surfaces. These oxide-depleted mounds are believed to be the features with the greatest potential for welding when in operation. The limited

PHILIP C. WINGERT; HAN J. KIM

1985-01-01

278

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

SciTech Connect

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

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

2010-09-01

279

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

NASA Astrophysics Data System (ADS)

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

Smith, Billy

280

Raman and surface-enhanced Raman spectroscopy of adsorbed phthalic acid on oxidized aluminum foil  

NASA Astrophysics Data System (ADS)

Adsorption of phthalic acid on anodically oxidized aluminum has been investigated at different pHs and ionic strengths by means of FT-Raman and surface-enhanced FT-Raman spectroscopy (SERS). The surface-enhancement was achieved by deposition of silver sol after adsorption. The spectra of the surface species obtained by the two techniques were significantly different. Raman spectra of the adsorbed phthalic compounds were pH and ionic strength dependent, but the surface-enhanced spectra appeared to be identical at each conditions. Supported by further spectroscopic evidences of the phthalic acid and the silver sol interaction (without aluminum oxide), it is plausible that the deposition of the silver sol results in a new surface complex. The evolution of the SER effect is therefore suggested to be a result of two steps: at first an adsorption occurs on aluminum oxide, and when depositing the aqueous silver sol onto the surface the phthalate ligands form complexes rather with the silver than with the aluminum oxide. However, the aluminum oxide surface may contribute to the non-linear spectroscopic effect due to its surface structure and charge.

Klug, O.; Parlagh, Gy.; Forsling, W.

1998-06-01

281

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

PubMed

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

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

2010-01-01

282

A study of the oxidation of phenol at platinum and preoxidized platinum surfaces  

Microsoft Academic Search

The effects of electrode surface oxide on the oxidation reactions of phenol and on Pt electrode passivation by reaction products were investigated using cyclic voltammetry and chronoamperometry. X-ray photoelectron spectrometry was used to detect changes in the nature of the passive film. Phenol reacted at both the inner and outer Helmholtz layers at platinum metal electrodes. Phenol in the inner

M. Gattrell; D. W. Kirk

1993-01-01

283

Oxidation of TiAl surface with hyperthermal oxygen molecular beams  

NASA Astrophysics Data System (ADS)

We report the initial oxidation process of TiAl with a hyperthermal O2 molecular beam.The precursor-mediated adsorption is the dominant initial step of oxidation.Blue colored TiO2 and Al2O3 containing layers was fabricated on TiAl surface.

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

2013-07-01

284

Investigations of thick metal oxide films on steel surface using proton non-Rutherford backscattering technique  

NASA Astrophysics Data System (ADS)

Protective oxide films on steel surface were investigated using proton elastic backscattering (EBS) technique. Proton elastic scattering cross sections for oxygen and iron needed for spectra simulation were measured in the energy range from 3.2 to 4.1 MeV. Oxide films structure and films penetrability by heavy metal under different conditions were studied.

Gurbich, A. F.

2005-12-01

285

Vertical Gradient of Net Oxidant near the Ground Surface at Barrow Alaska  

Microsoft Academic Search

surface were investigated. This investigation was corollary to a general long-term ozone program [Kelley, 1967] at a field site near Barrow, Alaska. The measurements, performed by microcoulombmetric analysis, may have been biased by oxides of nitrogen and reductants such as SO2, which are generally found in urban and industrial atmospheres, and by oxidation products produced within the plant canopy. Contamination

J. J. Kelley Jr.; J. D. McTaggart-Cowan

1968-01-01

286

Metal-aluminum oxide interactions: Effects of surface hydroxylation and high electric fields  

Microsoft Academic Search

Metal and oxide interactions are of broad scientific and technological interest in areas such as heterogeneous catalysis, microelectronics, composite materials, and corrosion. In the real world, such interactions are often complicated by the presence of interfacial impurities and\\/or high electric fields that may change the thermodynamic and kinetic behaviors of the metal\\/oxide interfaces. This research includes: (1) the surface hydroxylation

Chengyu Niu

2002-01-01

287

Studies on surface properties of asbestos. IV. Catalytic role of asbestos in fluorene oxidation  

SciTech Connect

To determine whether asbestos is a basic catalyst, catalytic oxidation of fluorene to fluorenone in a heterogeneous system was tested. It was shown that oxidation was quantitatively possible on the surface of all basic minerals, such as asbestos (chrysotile and crocidolite) and magnesia, but was not possible with acidic mineral materials such as silica. The effects of different factors are discussed.

Zalma, R.; Guignard, J.; Copin, E.; Pezerat, H.

1986-10-01

288

Modification of surface layer of magnesium oxide via partial dissolution and re-growth of crystallites  

Microsoft Academic Search

A procedure to modify surface layer of metal oxide is presented. By way of partial dissolution and re-growth of crystallites, a new MgO surface layer on the “core” of the original MgO particles was formed. XRD analyses indicate that the new surface layer is different from the original MgO particles in crystallinity. Thus a higher reducibility of surface non-lattice oxygen

Zhiming Gao; Lingyan Wei; Tingting Yan; Ming Zhou

2011-01-01

289

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

290

Comparison of different oxidation techniques on single-crystal and nanocrystalline diamond surfaces  

Microsoft Academic Search

Various oxidation techniques (plasma-beam, sulfo-chromic acid, UV-ozone, heating in air) were applied to single-crystalline (111) and (100) diamond surfaces as well as nanocrystalline diamond (NCD) films and analyzed by X-ray photoelectron spectroscopy (XPS) with respect to oxygen content and type of carbon–oxygen groups formed upon oxidation. Due to their increased surface, NCD films show a significantly higher oxygen uptake as

Frederik Klauser; Slimane Ghodbane; Rabah Boukherroub; Sabine Szunerits; Doris Steinmüller-Nethl; Erminald Bertel; Norbert Memmel

2010-01-01

291

Influences of Surface Iron Oxide Layer on Magnetic Properties of Iron Pigment  

Microsoft Academic Search

Mössbauer spectroscopy and other methods were used to study the oxide layer on the surface of fine Fe particles. On the basis of X-ray and electron diffraction, the surface oxide phase was characterized as consisting of extremely fine spinel crystals of Fe3O4 and ¿-Fe2O3, and mixtures of these. Comparisons of the Mössbauer spectra under strong magnetic fields (25 and 50

K. Haneda; K. Goto

1985-01-01

292

Correlations between structure and chemical composition on oxidized (Pt, Ni) 3Al(1 1 1) surfaces  

Microsoft Academic Search

We have investigated the fully-oxidized surface that forms on (Pt,Ni)3Al(111) at temperatures ranging from 300 to 1000K and at oxygen pressures of ca. 10?6 to 10?7Torr, using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Based on X-ray photoelectron spectroscopy data that were published previously, oxidation temperatures below 700K at these pressures produces a mixture of surface Al2O3 and

F. Qin; B. Hunt; B. Unal; D. Jing; M. Shen; C. J. Jenks; B. Gleeson; D. J. Sordelet; P. A. Thiel

2008-01-01

293

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

Microsoft Academic Search

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

E. McCafferty; J. P. Wightman

1997-01-01

294

Thermal Desorption from Si(111) Surfaces with Native Oxides Formed During Chemical Treatments  

Microsoft Academic Search

The thermal desorption process during thermal cleaning of Si(111) surfaces with native oxides formed by various chemical treatments is studied using TDS (thermal desorption spectroscopy) under UHV. The reaction product of the process is identified to be SiO. The surface cleanliness after the cleaning is virtually independent of the oxide formation method. However, the desorption temperature of SiO strongly depends

Yoshihiro Kobayashi; Yukinobu Shinoda; Kiyomasa Sugii

1990-01-01

295

Gold clusters alloyed to nanoporous palladium surfaces as highly active bimetallic oxidation catalysts.  

PubMed

Gold rush: Nanoporous palladium particles are decorated with gold clusters by galvanic replacement. The bimetallic pPd@Au nanocatalysts feature a well-defined nanoporous morphology coupled to a highly accessible surface area with segregated Au clusters, and are highly active in both benzyl alcohol oxidation and formic acid electro-oxidation. The amount of Au in the catalyst system determines the extent of alloying as well as the accessibility to catalytically more active Pd surface atoms. PMID:24039061

Li, Yongjia; Zhu, Enbo; Chen, Yu; Chiu, Chinyi; Yu, Hang; Huang, Xiaoqing; Hicks, Robert; Huang, Yu

2013-09-12

296

Accelerated and Enhanced Bone Formation on Novel Simvastatin-Loaded Porous Titanium Oxide Surfaces.  

PubMed

BACKGROUND: With increasing application of dental implants in poor-quality bones, the need for implant surfaces ensuring accelerated osseointegration and enhanced peri-implant bone regeneration is increased. PURPOSE: A study was performed to evaluate the osseointegration and bone formation on novel simvastatin-loaded porous titanium oxide surface. MATERIALS AND METHODS: Titanium screws were treated by micro-arc oxidation to form porous oxide surface and 25 or 50??g of simvastatin was loaded. The nontreated control, micro-arc oxidized, and simvastatin-loaded titanium screws were surgically implanted into the proximal tibia of 16-week-old male Wistar rats (n?=?36). Peri-implant bone volume, bone-implant contact, and mineral apposition rates were measured at 2 and 4 weeks. Data were analyzed by one-way analysis of variance followed by Tukey's post hoc test. RESULTS: New bone was formed directly on the implant surface in the bone marrow cavity in simvastatin-loaded groups since 2 weeks. Bone-implant contact values were significantly higher in simvastatin-loaded groups than control and micro-arc oxidized groups at both time points (p?oxidized groups at 2 weeks (p?oxide surface provides faster osseointegration and peri-implant bone formation and it would be potentially applicable in poor-quality bones. PMID:23399109

Nyan, Myat; Hao, Jia; Miyahara, Takayuki; Noritake, Kanako; Rodriguez, Reena; Kasugai, Shohei

2013-02-01

297

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

SciTech Connect

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

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

1997-10-15

298

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

299

Microstructure and morphology of surface oxide films on Ti6Al4V  

SciTech Connect

The microstructure of anodic oxide films grown on Ti6Al4V in H{sub 2}SO{sub 4} was investigated by SEM, TEM, STEM, EDX, and AES, as a complement to a recent surface spectroscopic investigation of the same oxides by XPS, AES, and SIMS. The anodic oxide films are heterogenous and the texture reflects the duplex microstructure ({alpha} and {beta} phases) of the underlying metal. Porous oxide regions are observed with different appearances on {alpha}-phase and mixed-phase regions. The oxide films are essentially amorphous in the investigated thickness range 60--300 nm (in contrast to as grown anodic films on pure Ti), but crystallize to the anatase structure upon annealing. Considerable lateral variation of the V content in the oxide is observed, reflecting the corresponding variation in the underlying metal. The results are compared with a previous, similar investigation of anodic oxides on pure Ti.

Ask, M.; Rolander, U.; Lausmaa, J.; Kasemo, B. (Department of Physics, Chalmers University of Technology, S-412 96 Goeteborg (Sweden))

1990-08-01

300

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

NASA Astrophysics Data System (ADS)

The adsorption of water monomers, small water clusters, water chains and water thin films on the Cu(110) surface is studied by density-functional theory (DFT) as well as using a semi-empirical scheme to include dispersion forces (DFT-D). Among the cluster structures, tetramers are most favorable. The calculated surface phase diagrams show that out of the multitude of Cu(110)-adsorbed water structures studied here (and proposed in earlier experimental and theoretical works) only monolayers resembling water ice, water-hydroxyl group layers stabilized by Bjerrum defects, and - in a narrow range of the water chemical potential - chains assembled from water pentagons are thermodynamically stable. The inclusion of van der Waals interaction increases the calculated adsorption energies, but has only minor consequences for the energetic ordering of adsorption geometries. It increases the calculated desorption temperatures from 60 K in low pressures until 150 K in near ambient pressures.

Baghbanpourasl, Amirreza; Hingerl, Kurt; Wippermann, Stefan; Schmidt, Wolf Gero

2013-06-01

301

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

302

Manganese-Cobalt Mixed Spinel Oxides as Surface Modifiers for Stainless Steel Interconnects of Solid Oxide Fuel Cells  

Microsoft Academic Search

Ferritic stainless steels are promising candidates for interconnect applications in low- and mid-temperature solid oxide fuel cells (SOFCs). A couple of issues however remain for the particular application, including the chromium poisoning due to chromia evaporation, and long-term surface and electrical stability of the scale grown on these steels. Application of a manganese colbaltite spinel protection layer on the steels

Gordon Xia; Z Gary Yang; Jeffry W. Stevenson

2006-01-01

303

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

PubMed

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

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

2008-06-01

304

Methane oxidation at a surface-sealed boreal landfill.  

PubMed

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

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

2009-03-04

305

Chemical speciation of adsorbed glycine on metal surfaces  

NASA Astrophysics Data System (ADS)

Experimental studies have reported that glycine is adsorbed on the Cu(110) and Cu(100) surfaces in its deprotonated form at room temperature, but in its zwitterionic form on Pd(111) and Pt(111). In contrast, recent density functional theory (DFT) calculations indicated that the deprotonated molecules are thermodynamically favored on Cu(110), Cu(100), and Pd(111). To explore the source of this disagreement, we have tested three possible hypotheses. Using DFT calculations, we first show that the kinetic barrier for the deprotonation reaction of glycine on Pd(111) is larger than on Cu(110) or Cu(100). We then report that the presence of excess hydrogen would have little influence on the experimentally observed results, especially for Pd(111). Lastly, we perform Monte Carlo simulations to demonstrate that the aggregates of zwitterionic species on Pt(111) are energetically preferred to those of neutral species. Our results strongly suggest that the formation of aggregates with relatively large numbers of adsorbed molecules is favored under experimentally relevant conditions and that the adsorbate-adsorbate interactions in these aggregates stabilize the zwitterionic species.

Han, Jeong Woo; James, Joanna N.; Sholl, David S.

2011-07-01

306

Outer cell surface components essential for Fe(III) oxide reduction by Geobacter metallireducens.  

PubMed

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

Smith, Jessica A; Lovley, Derek R; Tremblay, Pier-Luc

2012-11-26

307

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

SciTech Connect

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

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

2009-10-13

308

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

SciTech Connect

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

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

2009-01-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

310

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

PubMed

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

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

2009-11-17

311

dc triode sputtered zinc oxide surface elastic wave transducers  

Microsoft Academic Search

A piezoelectric film layer in proximity to an interdigital metal electrode provides a simple means for the excitation and detection of surface elastic waves on nonpiezoelectric substrates. These film transducer structures can be effectively used for the study of the surface elastic wave properties of solids and the development of monolithic acoustic and electronic circuit assemblies. Theory predicts that high

F. S. Hickernell

1973-01-01

312

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

PubMed

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

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

2011-09-24

313

Rates of oxidative weathering on the surface of Mars  

NASA Astrophysics Data System (ADS)

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

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

1993-02-01

314

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

315

The h-BN surface effect on CO oxidation reaction catalyzed by supported gold atom  

NASA Astrophysics Data System (ADS)

The mechanism of CO oxidation by O2 on Au atoms supported on the pristine and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. Two possible routes for catalytic oxidation are considered. The first route consists in a preliminary dissociation of the adsorbed O2 followed by consequential oxidation of a reactant molecule by atomic oxygen. Although the presence of h-BN surface can change the O2 dissociation barrier, it remains relatively high. The second route is a direct oxidation reaction between the activated molecular oxygen and the reactant. We have found two different pathways for CO oxidation: a two-step pathway where two CO2 molecules are formed independently, and a self-promotion pathway where oxidation of the first CO molecule is promoted by the second CO molecule. Interaction of Au with the defect-free and defected h-BN surface considerably affects the CO oxidation reaction pathways and barriers. Therefore, Au supported on the h-BN surface (pristine or defected) cannot be considered as pseudo-free atom and support effects have to be taken into account, even when the interaction of Au with the support is weak.

Gao, Min; Lyalin, Andrey; Taketsugu, Tetsuya

2013-06-01

316

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

NASA Astrophysics Data System (ADS)

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

Tien, Li-Chia; Chen, Yu-Jyun

2013-06-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

318

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

NASA Astrophysics Data System (ADS)

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

Entringer, Anthony G.

319

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

SciTech Connect

The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical coal cleaning processes. The results will provide fundamental insight into oxidation, in terms of the bulk and surface chemistry, the microstructure, and the semiconductor properties of the pyrite. During the sixth quarter, oxidized samples of Upper Freeport coal from the Troutville {number sign} Mine, Clearfield County, Pennsylvania were studied by ion-exchange methods. Film flotation tests were done to characterize the floatability of as-received coal, and samples subjected to different oxidation procedures. In addition, electrochemical studies were started on electrodes prepared from coal pyrite samples.

Doyle, F.M.

1992-01-01

320

Comparison of semiclassical calculations to experiment for spin valve films grown on oxide surfaces  

SciTech Connect

The physical properties of spin valve films grown on the surface of nano-oxide layers were studied as a function of Cu spacer layer thickness. In comparison to identical structures without the oxide surface, the films exhibited an increase in {Delta}R/R of 30% accompanied by a reduction of only 5% in resistance. Semiclassical calculations were preformed on these films with a close match to experiment. Assuming the oxide layer did not cause drastic changes in the properties of the other film layers, the specular reflection was changed to obtain a match with experiment. The increase in giant magnetoresistance response was achieved by increasing the specular reflection at the metal/oxide interfaces from 15% to 85%, indicating high efficiency for specular reflection at the nano-oxide interface. {copyright} 2001 American Institute of Physics.

Gibbons, Matthew R.; Mao, Ming; Chien, Chester

2001-06-01

321

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

322

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

323

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

2009-10-29

324

Ni/sub 3/Nb alloy species in oxide surfaces of INCONEL 718  

SciTech Connect

INCONEL 718 has been studied by Auger and X-ray photoelectron spectroscopy to determine the effect on the surface stoichiometry caused by heat treating in argon to 1000 C. Two surface regions are produced, the one closest to the argon-metal oxide interface being rich in O, Ti, Al, and Cr, and the one closest to the alloy being rich in O, Al, and Nb. Profiles show a gradual increase in the Ni and Nb signals as the profiling time increases. It is noted that during the profile, Al remains an oxide, and that the Ni and Nb signals have metal-like character even in the aluminum oxide phase, suggesting that N/sub 3/Nb exists with oxide at the surface. 6 references.

Moddeman, W.E.; Craven, S.M.; Kramer, D.P.

1986-02-01

325

Nature of native oxide on GaN surface and its reaction with Al  

SciTech Connect

In this letter, we describe the surface properties of GaN thin films grown on sapphire substrate by molecular beam epitaxy, as revealed by ultraviolet and x-ray photoelectron spectroscopic and Auger electron spectroscopic studies. The samples are seen to contain overlayer of native oxides, which are predominantly in the Ga{sub 2}O{sub 3} form. Ammonia is shown to be a good etchant for these native oxides. Furthermore, we investigated the early stages of the reaction of monolayer Al with a GaN surface covered with native oxide. Aluminum reacts preferentially with the surface oxygen and leads to the formation of a mixture of oxides at the interface. {copyright} {ital 1996 American Institute of Physics.}

Prabhakaran, K.; Andersson, T.G.; Nozawa, K. [NTT Basic Research Laboratories, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa-ken 243-01 (Japan)

1996-11-01

326

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

327

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

1998-02-01

328

Octadecanethiol Island Formation on Single Crystal Zinc Oxide Surfaces  

NASA Astrophysics Data System (ADS)

Organic photovoltaic devices, containing ZnO nanorod electron acceptor arrays intercalated with organic polymers, could lead to low-cost solar cells. Surface modifications of ZnO with octadecanethiol (ODT) monolayers have been shown to improve charge transfer in such devices. The present work is an effort to understand these monolayers through studies of ODT on single crystals of ZnO with well-defined oxygen-terminated or zinc-terminated surfaces. Both bare and ODT- functionalized surfaces were characterized with atomic force microscopy, Fourier transform infrared spectroscopy, x-ray photoemission spectroscopy, and water contact angle measurements. ODT seemed to form islands of multilayers on zinc-terminated surfaces and islands of monolayers on oxygen- terminated surfaces. While ODT was expected to preferentially bond along defects and terraces on oxygen-terminated surfaces, this was not observed. ODT was also expected to more effectively bond to the zinc-terminated surface, which was observed. This work was supported by the National Science Foundation Division of Materials Research DMR-0606054, DMR-0907409, and the Renewable Energy Materials Research Science and Engineering Center at the Colorado School of Mines.

Yocom, Andrea; Collins, Reuben; Furtak, Thomas; Baker, Darick; Ohno, Timothy

2010-03-01

329

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

330

Reactivity of Surface Peroxo Species: Oxidation of HCN on Pt(111),  

National Technical Information Service (NTIS)

Surface peroxo species were produced by adsorption of O2 on a Pt(111) surface at 87 K. The reactivity of the peroxo species has been studied through the oxidation reaction of HCN using temperature programmed desorption (TPD) in the temperature range from ...

X. Guo A. Winkler P. J. Hagans J. T. Yates

1988-01-01

331

Oxidative Damage to DNA of Ovarian Surface Epithelial Cells Affected by Ovulation: Carcinogenic Implication and Chemoprevention  

Microsoft Academic Search

The majority of cancers of the ovary are thought to originate from a surface epithelial cell perturbed by ovulation. Outgrowth of a follicle destined to ovulate brings it into apposition with the ovarian epithelium. Ovarian surface cells are consequently exposed, within a limited diffusion radius, to inflammatory agents and reactive oxidants generated during periovulatory processes. Cells that overlie the formative

WILLIAM J. MURDOCH; JAMES F. MARTINCHICKy

332

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

Microsoft Academic Search

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

Chengchu Liu; Jingyun Duan; Yi-Cheng Su

2006-01-01

333

On the Nature of the Oxygen Species Absorbed on Oxide Surfaces.  

National Technical Information Service (NTIS)

Electron spin resonance studies of adsorbed oxygen on oxide surfaces (principally ZnO) have been out using 17O enriched oxygen. An ESR triplet attributed to an O2(-) species at the surface was recently reported by this laboratory. Under identical experime...

M. Codell J. Weisberg H. Gisser R. D. Iyengar

1969-01-01

334

Initial stage of native oxide growth on hydrogen terminated silicon (111) surfaces  

Microsoft Academic Search

We investigated the initial stage of native oxide growth on an atomically flat hydrogen terminated silicon (Si) (111) surface by immersion in pure water using Fourier transformed infrared attenuated total reflection spectroscopy and reflection absorption spectroscopy. There is a sharp absorption peak at 2083 cm?1 arising from silicon monohydrides at surface terraces, this peak decreases and broadens with immersion time

Hiroki Ogawa; Kenji Ishikawa; Carlos Inomata; Shuzo Fujimura

1996-01-01

335

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

336

Preparation and Characterization of Porous Yttrium Oxide Powders with High Specific Surface Area  

Microsoft Academic Search

The porous cubic yttrium oxides with high specific surface area were prepared by the explosive decomposition of yttrium nitrate and its complex formed with methyl salicylate. The specific surface area and properties of powders synthesized at various temperatures were characterized using BET, X-ray diffraction (XRD), infrared spectra (IR), and scanning electron microscopy (SEM). The results indicate that the highest specific

Yongxiu Li; Xiaoyun Lin; Yizheng Wang; Junming Luo; Weili Sun

2006-01-01

337

Correlation between surface area reduction and ultrasonic velocity in sintered zinc oxide powders  

Microsoft Academic Search

Specific surface area and longitudinal wave ultrasonic velocity were measured in zinc oxide (ZnO) powder compacts partially sintered to different pore fractions (P). A linear correlation was observed between the reduction in surface area and the increase in ultrasonic velocity at all P up to the onset of pore closure. During the initial stage of sintering, the ultrasonic velocity increased

L. P. Martin; M. Rosen

1997-01-01

338

Titania formation by TiCl 4 gas phase oxidation, surface growth and coagulation  

Microsoft Academic Search

Titania particle formation by TiCl4 gas phase oxidation, surface growth and coagulation is investigated by a moving sectional population balance model. The dynamic evolution of the detailed particle size distribution is studied accounting for and neglecting the effect of surface growth. The effects of process temperature, T, and precursor volume fraction, ?, on the average diameter, dp, and geometric standard

Patrick T. Spicer; Olivier Chaoul; Stavros Tsantilis; Sotiris E. Pratsinis

2002-01-01

339

The role of the surface structure in the oxidation mechanism of methanol  

Microsoft Academic Search

Pulsed voltammetry has been used to study methanol oxidation in acid media on platinum stepped surfaces to determine the kinetics of the reaction and the role of the surface structure in the reactivity. From the current transients at different potentials, the intrinsic activity of the electrode through the active intermediate reaction path (jdir,ini), as well as the rate constant for

Vitali Grozovski; Víctor Climent; Enrique Herrero; Juan M. Feliu

2011-01-01

340

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

PubMed

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

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

2013-05-13

341

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

Microsoft Academic Search

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

Maria Advincula; Xiaowu Fan; Jack Lemons; Rigoberto Advincula

2005-01-01

342

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 InOIn 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

343

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

344

Characterization by CEMS, XRD and XPS of oxidized layers formed on the surface of carbonitrided low-carbon steel  

Microsoft Academic Search

The surface structure and oxidation characteristics of carbonitrided low-carbon steel, prepared by oxidizing the surfaces in salt-baths after the carbonitriding process, have been studied using conversion electron Mössbauer spectrometry, X-ray diffractometry, and X-ray photoelectron spectrometry. The formation of an iron oxide layer in the carbonitrided surface improved the corrosion resistance significantly. The steel surface after carbonitriding for 3600 s consisted

Kazuyoshi Kurosawa; Hong-Ling Li; Yusuke Ujihira; Kiyoshi Nomura; Eiichi Mochizuki; Hiroki Hayashi

1995-01-01

345

Surface analysis of polysiloxane\\/metal oxide interfaces  

Microsoft Academic Search

The interfaces between various types of silane-based primers and abraded mild-steel surfaces have been investigated using two surface-specific techniques in an attempt to ascertain the bonding mechanism between primer and metal. The XPS technique gave semi-quantitative information about the relative concentrations of primer and exposed steel while the SSIMS technique enabled the chemical state of the first few monolayers of

M. Gettings; A. J. Kinloch

1977-01-01

346

Oxidation of hydrogen terminated Ge(1 0 0) surface in the presence of iodine in methanol  

NASA Astrophysics Data System (ADS)

Surface reaction on Ge(1 0 0) in liquid methanol (MeOH) was systematically studied. In particular, the characteristics of the Ge surface in the presence of iodine (I 2) in MeOH were investigated. MeOH treatment of the Ge surface in the presence of 0.05 or 0.005 mM of I 2 exhibited a similar result to that without I 2, which produces a GeO x-dominant oxide structure. However, when the concentration of I 2 in MeOH increased to 0.5 mM, Ge surface revealed a GeO 2-dominant oxide structure. Therefore, it is believed that the addition of enough I 2 in MeOH modifies the Ge oxidation mechanism. Hydroxide produced by the reaction between MeOH and the iodine radical may oxidize the Ge surface to form a Ge-O layer. Because MeOH is greatly consumed by chain and series reactions when I 2 concentration is high, a GeO 2 structure is not etched and a GeO 2-dominant oxide structure is obtained with the addition of 0.5 mM I 2 in MeOH. The modified oxide layer prepared in MeOH with 0.5 mM I 2 exhibited an atomically smoother surface compared to a pure MeOH- or H 2O 2-treated Ge surface and a much thinner oxide layer than H 2O 2 treatment.

Lee, Younghwan; Park, Kibyung; Lim, Sangwoo

2008-12-01

347

Characterization of treated indium-tin-oxide surfaces used in electroluminescent devices  

NASA Astrophysics Data System (ADS)

The influence of oxidative and reductive treatments of indium-tin-oxide (ITO) on the performance of electroluminescent devices is presented. The improvement in device performance is correlated with the surface chemical composition and work function. The work function is shown to be largely determined by the surface oxygen concentration. Oxygen-glow discharge or ultraviolet-ozone treatments increase the surface oxygen concentration and work function in a strongly correlated manner. High temperature, vacuum annealing reduces both the surface oxygen and work function. With oxidation the occupied, density of states (DOS) at the Fermi level is also greatly reduced. This process is reversible by vacuum annealing and it appears that the oxygen concentration, work function, and DOS can be cycled by repeated oxygen treatments and annealing. These observations are interpreted in terms of the well-known, bulk properties of ITO.

Mason, M. G.; Hung, L. S.; Tang, C. W.; Lee, S. T.; Wong, K. W.; Wang, M.

1999-08-01

348

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.

Zhang, Guandong; Liao, Yifeng; Baker, Ian

2011-01-01

349

Oxidation of organic materials with perchlorates: relevance to the chemistry on the Martian surface  

NASA Astrophysics Data System (ADS)

No organic materials have been found on the Martian surface, based on the results from the Viking and Phoenix missions. The Phoenix mission detected the inorganic perchlorates in the Martian soil. Perchlorates are potent oxidizing substances. The high-temperature oxidative properties of perchlorates may promote combustion of organics in pyrolytic experiments. This may compromise the ability of Phoenix's TEGA (Thermal and Evolved Gas Analyzer) experiments to detect organics. The high temperature conditions of TEGA instrument are not representative of the environment on Mars. In this paper we pose a question if organic materials can survive oxidation with perchlorates at less drastic temperatures. We have surveyed the literature on oxidations of various groups of organic materials by perchlorates. Several amino acids, notably glycine and alanine, are quite resistant to this oxidation. The same is true for some heterocycles, purines and purimidines. These organic materials may have survived perchlorate oxidation in the natural environment on Mars.

Kolb, Vera M.

2009-08-01

350

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

351

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

NASA Astrophysics Data System (ADS)

In order to understand the behaviour of ruthenium oxides in the reactor coolant system during an air ingress accident, new tests were performed in the frame of the RUSET (RUthenium Separate Effect Test) experimental program. These aimed to ascertain the effects of different surfaces (quartz, stainless steel (SS), zirconium alloy, alumina, oxidised metal, and surfaces with Mo or Cs deposits) on the transport and decomposition of ruthenium oxides in air stream along the temperature gradient zone (1100-100 °C). The results demonstrated that the heterogeneous phase decomposition of RuO3 and RuO4 to RuO2 is catalysed more efficiently by the quartz surface than by the SS or alumina surfaces. The presence of MoO3 layers decreased the RuOx precipitation extent on all investigated surfaces. The trapping effect of Cs deposit on Ru in the temperature gradient zone was proved in the case of the SS surface. On the contrary, presence of Cs precipitate on alumina and especially on quartz surfaces was found to decrease their catalytic effect on the decomposition of ruthenium oxides, and thus increased the RuO4 concentration in the outlet air. Similarly to the effect observed for Cs deposition, the presence of other fission products in the evaporation area (at 1100 °C) decreased the partial pressure of RuO4 in the outlet air at the SS surface and increased it at quartz and alumina surfaces. When zirconium (E110) cladding material was placed in the temperature gradient zone, no Ru transmittance occurred until the high temperature end of the zirconium tube was completely oxidised. After the intense oxidation of E110, Ru release occurred only in the presence of other fission product species. Pre-oxidation of SS surfaces in steam had no significant effect on the Ru passage.

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

2012-01-01

352

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

2012-02-22

353

Reactive molecular dynamics simulation of early stage of dry oxidation of Si (100) surface  

NASA Astrophysics Data System (ADS)

Initial stage of oxidation of Si (100) surface by O2 molecules was investigated in atomic scale by molecular dynamics (MD) simulation at 300 K and 1200 K without external constraint on the oxygen molecules. A reactive force field was used for the simulation to handle charge variation as well as breaking and forming of the chemical bonds associated with the oxidation reaction. Results of the present simulation are in good agreement with previous first principle calculations and experimental observations: the oxygen molecules spontaneously dissociated on the Si (100) surface and reacted with Si first layer without energy barrier. The simulation also exhibited that the reacted oxygen preferentially located in the back bonds of the surface dimer. Consecutive oxidation simulation with 300 O2 molecules showed that the diffusion of oxygen atom into the subsurface of clean Si surface can occur during very short time of the present oxidation simulation. The present MD simulation also revealed that the oxidation at 300 K results in more stoichiometric oxide layer than that at 1200 K.

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

2011-09-01

354

Enhancement of octacalcium phosphate deposition on a titanium surface activated by electron cyclotron resonance plasma oxidation.  

PubMed

The present study was designed to investigate whether the formation of octacalcium phosphate (OCP) is accelerated on titanium (Ti) surface by an electron cyclotron resonance (ECR) plasma oxidation at various pressures and temperatures. X-ray diffraction (XRD) of Ti-oxidized substrates showed that the rutile TiO(2) phase on its surfaces appeared at 300 degrees C and was crystallized when the oxidation temperature increased up to 600 degrees C. The thickness of TiO(2) film on the substrates increased progressively as the temperature increased. The oxidized Ti surfaces were soaked in calcium and phosphate solutions supersaturated with respect to both hydroxyapatite (HA) and OCP but slightly supersaturated with dicalcium phosphate dihydrate (DCPD). OCP crystals with a blade-like morphology were deposited as the primary crystalline phase on Ti substrates, while DCPD was included as a minor constituent. The amount of OCP deposition was maximized under 0.015 Pa in 300 degrees C. On the other hand, the oxidation temperature did not show a significant effect on the deposit in the range examined. The phase conversion from OCP to HA, determined by XRD, was demonstrated to occur even at 1 day and to advance until 7 days by immersing the Ti substrate with the deposit in simulated body fluid at 37 degrees C. The present results suggest that ECR plasma oxidation could be used to improve a Ti surface regarding its bioactivity due to the enhancement of osteoconductive OCP deposition. PMID:20166123

Orii, Yusuke; Masumoto, Hiroshi; Honda, Yoshitomo; Anada, Takahisa; Goto, Takashi; Sasaki, Keiichi; Suzuki, Osamu

2010-05-01

355

Parallel-local anodic oxidation of silicon surfaces by soft stamps  

NASA Astrophysics Data System (ADS)

We investigate the fabrication of nanometric patterns on silicon surfaces by using the parallel-local anodic oxidation technique with soft stamps. This method yields silicon oxide nanostructures 15 nm high, namely at least five times higher than the nanostructures made with local anodic oxidation using atomic force microscopy, and thanks to the size of the stamp enables one to pattern the surface across a centimetre length scale. To implement this technique, we built a machine to bring the metallized polydimethylsiloxane stamp in contact with the silicon surface, subsequently inserted in a sealed chamber with controlled relative humidity. The oxide nanostructures are fabricated when a bias voltage of 36 V is applied between the stamp and the silicon for 2 min, with a relative humidity of 90%. The flexibility of the stamp enables a homogeneous conformal contact with the silicon surface, resulting in an excellent reproducibility of the process. Moreover, by means of two subsequent oxidations with the same stamp and just rotating the sample, we are able to fabricate complex nanostructures. Finally, a detailed study of the oxidation mechanism, also using a finite element analysis, has been performed to understand the underlying mechanism.

Albonetti, Cristiano; Martinez, Javier; Losilla, Nuria S.; Greco, Pierpaolo; Cavallini, Massimiliano; Borgatti, Francesco; Montecchi, Monica; Pasquali, Luca; Garcia, Ricardo; Biscarini, Fabio

2008-10-01

356

Electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) surfaces.  

PubMed

The electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) has been studied using voltammetry, chronoamperometry, and in situ infrared spectroscopy. The oxidative adsorption of ammonia results in the formation of NH(x) (x = 0-2) adsorbates. On Pt(111), ammonia oxidation occurs in the double-layer region and results in the formation of NH and, possibly, N adsorbates. The experimental current transients show a hyperbolic decay (t(-1)), which indicates strong lateral (repulsive) interactions between the (reacting) species. On Pt(100), the NH(2) adsorbed species is the stable intermediate of ammonia oxidation. Stabilization of the NH and NH(2) fragments on Pt(111) and Pt(100), respectively, is in an interesting agreement with recent theoretical predictions. The Pt(111) surface shows extremely low activity in ammonia oxidation to dinitrogen, thus indicating that neither NH nor N (strongly) adsorbed species are active in dinitrogen production. Neither nitrous oxide nor nitric oxide is the product of ammonia oxidation on Pt(111) at potentials up to 0.9 V, as deduced from the in situ infrared spectroscopy measurements. The Pt(100) surface is highly active in dinitrogen production. This process is characterized by a Tafel slope of 30 mV decade(-1), which is explained by a rate-determining dimerization of NH(2) fragments followed by a fast decay of the resulting surface-bound hydrazine to dinitrogen. Therefore, the high activity of the Pt(100) surface for ammonia oxidation to dinitrogen is likely to be related to its ability to stabilize the NH(2) adsorbate. PMID:16721436

Rosca, Victor; Koper, Marc T M

2006-04-24

357

Surface Termination Effects on Zinc Oxide Quantum Dots.  

NASA Astrophysics Data System (ADS)

We investigate the effects of surface terminations on the optical properties of 2-6 nm ZnO quantum dots. Nanocrystals were grown by wet chemical synthesis in a short-chain alcohol solvent from zinc acetate and sodium hydroxide. Quenching of particle growth with various capping agents is necessary to maintain and enhance the unique characteristics of the nanocrystals. We reproduce results of previous work and expand on characterization of naked and surface terminated ZnO quantum dots. The nanoparticle properties were investigated by UV absorption spectrophotometry, photoluminescence, infrared spectroscopy, scanning electron microscopy , and atomic force microscopy techniques.

Whitesell, Steve; Spalenka, Joe; Jack, Christopher; Allen, Cary; Collins, Reuben; Furtak, Thomas

2007-03-01

358

Arsenic growth on the gallium arsenide surface during oxidation  

SciTech Connect

Crystalline arsenic was observed to grow on the surface of GaAs during exposure to continuous-wave laser radiation. A study of the time development of the arsenic growth as revealed by Raman backscattering indicated that a surface diffusion process was responsible for limiting the growth process. Temperature measurements were performed from which the diffusion-barrier energies were obtained for various GaAs samples. From these results the diffusion process was shown to depend on the Fermi level of sample.

Martin, R.; Braunstein, R.

1987-01-01

359

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

PubMed Central

Solar-to-fuel energy conversion relies on the invention of efficient catalysts enabling water oxidation through low-energy pathways. Our aerobic life is based on this strategy, mastered by the natural Photosystem II enzyme, using a tetranuclear Mn–oxo complex as oxygen evolving center. Within artificial devices, water can be oxidized efficiently on tailored metal-oxide surfaces such as RuO2. The quest for catalyst optimization in vitro is plagued by the elusive description of the active sites on bulk oxides. Although molecular mimics of the natural catalyst have been proposed, they generally suffer from oxidative degradation under multiturnover regime. Here we investigate a nano-sized Ru4–polyoxometalate standing as an efficient artificial catalyst featuring a totally inorganic molecular structure with enhanced stability. Experimental and computational evidence reported herein indicates that this is a unique molecular species mimicking oxygenic RuO2 surfaces. Ru4–polyoxometalate bridges the gap between homogeneous and heterogeneous water oxidation catalysis, leading to a breakthrough system. Density functional theory calculations show that the catalytic efficiency stems from the optimal distribution of the free energy cost to form reaction intermediates, in analogy with metal-oxide catalysts, thus providing a unifying picture for the two realms of water oxidation catalysis. These correlations among the mechanism of reaction, thermodynamic efficiency, and local structure of the active sites provide the key guidelines for the rational design of superior molecular catalysts and composite materials designed with a bottom–up approach and atomic control.

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

2013-01-01

360

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

PubMed

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

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

2011-11-17

361

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

362

Chiral close-packing of achiral star-shaped molecules on solid surfaces.  

PubMed

From the interplay of scanning tunneling microscopy and theoretical calculations, we study the chiral self-assembly of achiral HtB-HBC molecules upon adsorption on the Cu(110) surface. We find that chirality is expressed at two different levels: a +/-5 degrees rotation of the molecular axis with respect to the close-packed direction of the Cu(110) substrate and a chiral close-packed arrangement expected for star-shaped molecules in 2D. Out of the four possible chiral expressions, only two are found to exist due the effect of van der Waals (vdW) interactions forcing the molecules to simultaneously adjust to the atomic template of the substrate geometry and self-assemble in a close-packed geometry. PMID:16805577

Schöck, Maya; Otero, Roberto; Stojkovic, Sladjana; Hümmelink, Frauke; Gourdon, André; Laegsgaard, Erik; Stensgaard, Ivan; Joachim, Christian; Besenbacher, Flemming

2006-07-01

363

Coupled Ferric Oxides and Sulfates on the Martian Surface  

Microsoft Academic Search

The Mars Exploration Rover (MER), Opportunity, showed that layered sulfate deposits in Meridiani Planum formed during a period of rising acidic ground water. Crystalline hematite spherules formed in the deposits as a consequence of aqueous alteration and were concentrated on the surface as a lag deposit as wind eroded the softer sulfate rocks. On the basis of Mars Express Observatoire

J.-P. Bibring; R. E. Arvidson; A. Gendrin; B. Gondet; Y. Langevin; S. Le Mouelic; N. Mangold; R. V. Morris; J. F. Mustard; F. Poulet; C. Quantin; C. Sotin

2007-01-01

364

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

NASA Astrophysics Data System (ADS)

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

Wu, Huiquan

365

Initial oxidation behaviors of nitride surfaces of uranium by XPS analysis  

NASA Astrophysics Data System (ADS)

The nitride surfaces of uranium were prepared by the surface glow plasma nitriding (SGPN) and plasma immersion ion implantation (PIII) methods. The initial oxidation behaviors of modified surfaces were studied by X-ray photoelectron spectroscopy (XPS). The SGPN on the uranium surface led to a single layer of uranium sesquinitride (U2N3), while the PIII on the surface resulted in a compound layer composed of U2N3 and uranium dioxide (UO2). The oxygen covered on these modified layers led to the formation of UO2 from U2N3 and U2N3 from UN. The oxidized nitrogen species were also observed on the two types of nitriding layers, with the discussion of the N–O coaction behaviors.

Liu, Kezhao; Luo, Lizu; Luo, Lili; Long, Zhong; Hong, Zhanglian; Yang, Hui; Wu, Sheng

2013-09-01

366

Influence of surface oxidation on the valence electron energy-loss spectrum of wurtzite aluminum nitride  

NASA Astrophysics Data System (ADS)

The influence of surface oxidation on the low-loss spectrum of aluminum nitride (AlN) is investigated in electron energy-loss spectroscopy with scanning transmission electron microscopy. Contrary to intrinsic bulk AlN, oxidized AlN exhibits considerable spectral broadening both in the full width at half maximum of bulk plasmon and the subsidiary features. The modification in the low-loss lineshapes due to oxidation significantly complicates the determination of the dielectric function intrinsic to AlN. Simulations based on dielectric theory qualitatively consist with the experimental results while incorporating thick overlayers, further suggesting that the surface oxide of AlN can be rough and porous in nature.

Huang, Michael R. S.; Erni, Rolf; Liu, Chuan-Pu

2013-02-01

367

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

368

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

SciTech Connect

The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical cleaning processes. The results will provide fundamental insight into oxidation, in terms of the bulk and surface chemistry, the microstructure, and the semiconductor properties of the pyrite. During the eighth quarter, wet chemical and dry oxidation tests were done on Upper Freeport coal from the Troutville [number sign]2 Mine, Clearfield County, Pennsylvania. In addition electrochemical experiments were done on electrodes prepared from Upper Freeport coal pyrite and Pittsburgh coal pyrite samples provided by the US Bureau of Mines, Pittsburgh Research Center, Pennsylvania.

Doyle, F.M.

1992-01-01

369

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

SciTech Connect

The objective of this research is to develop a mechanistic understanding of the oxidation of coal and coal pyrite, and to correlate the intrinsic physical and chemical properties of these minerals, along with changes resulting from oxidation, with those surface properties that influence the behavior in physical coal cleaning processes. The results will provide fundamental insight into oxidation, in terms of the bulk and surface chemistry, the microstructure, and the semiconductor properties of the pyrite. During the fourth quarter, characterization and oxidation tests were done on Upper Freeport coal from the Troutville {number sign}2 Mine, Clearfield County, Pennsylvania. In addition, standard test methods for characterizing pyrite-bearing materials were studied. 3 figs., 2 tabs.

Doyle, F.M.

1991-09-24

370

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

SciTech Connect

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

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

1993-10-01

371

A theoretical investigation on photocatalytic oxidation on the TiO2 surface  

NASA Astrophysics Data System (ADS)

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

Suzuki, Satoshi; Tsuneda, Takao; Hirao, Kimihiko

2012-01-01

372

In vivo biostability of polyether polyurethanes with fluoropolymer and polyethylene oxide surface modifying endgroups; resistance to metal ion oxidation.  

PubMed

Polyether polyurethanes are subject to oxidation catalyzed by, and through direct (redox) reaction with transition metal ions (metal ion oxidation, MIO). The source of the ions is corrosion of metallic parts within an implanted device. A Shore 80A polyether polyurethane was modified with fluoropolymer (E80AF) or polyethylene oxide (E80AP) surface modifying end groups (SME). The SME migrates to the surface to form a covalently bonded monolayer, while maintaining the bulk properties of the polyurethane. In vitro tests in H(2)O(2) solution indicated that both SME's accelerated MIO. Tubing samples containing cobalt mandrels were implanted in the subcutis of rabbits for up to 2 years. In vivo, E80AF significantly slowed the rate of visible degradation, but did not prevent MIO. E80AP had virtually identical visual performance to the unmodified control in vivo. Infrared spectroscopy and molecular weight correlated well with visual appearance. When cracks were seen, polyether soft segment oxidation was occurring. Both E80AP and the control developed severe loss of molecular weight in vivo. The changes were much less severe for E80AF. Thus, contrary to in vitro test results, the PEO SME had no effect at all on MIO resistance, while the fluoropolymer SME produced a significant improvement in biostability. PMID:16958046

Ward, Robert; Anderson, James; McVenes, Rick; Stokes, Ken

2007-01-01

373

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

NASA Astrophysics Data System (ADS)

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

Lu, Weier

1995-01-01

374

Oxidation behavior of surface-modified titanium for titanium-ceramic restorations  

Microsoft Academic Search

Statement of problem. Titanium-ceramic bonding is an unsolved problem for the current use of titanium-ceramic restorations.Purpose. The purpose of the study was to characterize oxide formation on titanium surfaces at porcelain sintering temperatures and to determine the effect of chromium coating methods on titanium oxide formation.Material and methods. Sputter coating and electroplating methods of chromium application were compared and combined.Results.

Russell R. Wang; Kon K. Fung

1997-01-01

375

Cavity-induced antiguiding in a selectively oxidized vertical-cavity surface-emitting laser  

Microsoft Academic Search

Cavity-induced antiguiding of a lasing mode is demonstrated in a vertical-cavity surface-emitting laser (VCSEL). Selective oxidation of a distributed Bragg reflector (DBR) layer is used to generate a spectrally red-shifted cavity region cladding the lasing mode, with a second selectively oxidized aperture used to form the current confinement to the antiguided mode. Near-field, far-field, and spectral measurements are used to

T.-H. Oh; M. R. McDaniel; D. L. Huffaker; D. G. Deppe

1998-01-01

376

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

PubMed Central

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

2010-01-01

377

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

NASA Astrophysics Data System (ADS)

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.

Cai, Jiaying; Gervasio, D. F.

2010-03-01

378

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

Microsoft Academic Search

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

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

1998-01-01

379

Anodic surface oxidation mechanisms of PAN-based and pitch-based carbon fibres  

Microsoft Academic Search

In order to clarify the differences in the anodic surface oxidation mechanisms of PAN-based and pitch-based carbon fibres, the fibres were oxidized in an electrolyte and characterized using the coulostatic method, X-ray photoelectron spectroscopy, laser Raman spectroscopy, and X-ray diffraction. The interfacial bonding strength to an epoxy resin was evaluated based on the interlaminar shear strength (ILSS). The results showed

A. Fukunaga; S. Ueda; M. Nagumo

1999-01-01

380

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

2013-01-10

381

Surface Termination Effects on Zinc Oxide Quantum Dots  

Microsoft Academic Search

We investigate the effects of surface terminations on the optical properties of 2-6 nm ZnO quantum dots. Nanocrystals were grown by wet chemical synthesis in a short-chain alcohol solvent from zinc acetate and sodium hydroxide. Quenching of particle growth with various capping agents is necessary to maintain and enhance the unique characteristics of the nanocrystals. We reproduce results of previous

Steve Whitesell; Joe Spalenka; Christopher Jack; Cary Allen; Reuben Collins; Thomas Furtak

2007-01-01

382

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

Microsoft Academic Search

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

Chin-Chen Chiu

1994-01-01

383

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

384

The interaction of water with environmentally relevant surfaces  

SciTech Connect

Probing the coverage and chemical speciation of molecules at surfaces are of fundamental interest in molecular environmental science. The concentration of water and its dissociation fragments at surfaces affect many highly important interfacial chemical processes and there exist no previous quantitative determinations of the coverage of water on clean metal surfaces at near ambient conditions. We have utilized Ambient Pressure Photoelectron Spectroscopy (AP-PES) to study the water/Cu(111) and Cu(110) systems at pressures up to 1 Torr in the temperature range 270-470 K.

Andersson, K.; Yamamoto, S.; Ketteler, G.; Starr, D.E.; Nilsson, A.; Salmeron, M.; Bluhm, H.

2006-04-05

385

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

PubMed Central

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

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

2009-01-01

386

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

NASA Astrophysics Data System (ADS)

The oxidation behavior of grade 304L stainless steel (SS) subjected to different surface finishing (machining and grinding) operations was followed in situ by contact electric resistance (CER) and electrochemical impedance spectroscopy (EIS) measurements using controlled distance electrochemistry (CDE) technique in high purity water (conductivity < 0.1 ?S cm-1) at 300 °C and 10 MPa in an autoclave connected to a recirculation loop system. The results highlight the distinct differences in the oxidation behavior of surface worked material as compared to solution annealed material in terms of specific resistivity and low frequency Warburg impedance. The resultant oxide layer was characterized for (a) elemental analyses by glow discharge optical emission spectroscopy (GDOES) and (b) morphology by scanning electron microscopy (SEM). Oxide layers with higher specific resistivity and chromium content were formed in case of machined and ground conditions. Presence of an additional ionic transport process has also been identified for the ground condition at the metal/oxide interface. These differences in electrochemical properties and distinct morphological features of the oxide layer as a result of surface working were attributed to the prevalence of heavily fragmented grain structure and presence of martensite.

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

2013-01-01

387

Surface oxidation of ZnHgTe and its interface reaction with metals  

NASA Astrophysics Data System (ADS)

Migration processes of the constituent atoms and the interface properties in p-type and n-type ZnHgTe crystals subjected to thermal oxidation or to metal deposition have been studied using XPS and AES in combination with an ion-depth profile technique. Both the Hg evaporation and Zn migration during oxidation are found to play an important role in the oxidation process. The ZnTeO3 resulting from ZnO and TeO2 formation is suggested to be a major constituent of the oxide surfaces, as in the case of CdHgTe oxidation. Both out-diffusion of Te and in-diffusion of Au at room temperature have been noted in Au/ZnHgTe and Au/ZnTe.

Taguchi, Tsunemasa; Sasaki, Tokuhito; Terada, Toshiyuki; Ekawa, Mitsuru; Hiraki, Akio

1988-01-01

388

Speciation of adsorbed yttrium and rare earth elements on oxide surfaces  

NASA Astrophysics Data System (ADS)

The distribution of yttrium and the rare earth elements (YREE) between natural waters and oxide mineral surfaces depends on adsorption reactions, which in turn depend on the specific way in which YREE are coordinated to mineral surfaces. Recent X-ray studies have established that Y 3+ is adsorbed to the rutile (1 1 0) surface as a distinctive tetranuclear species. However, the hydrolysis state of the adsorbed cation is not known from experiment. Previous surface complexation models of YREE adsorption have suggested two to four cation hydrolysis states coexisting on oxide surfaces. In the present study, we investigate the applicability of the X-ray results to rare earth elements and to several oxides in addition to rutile using the extended triple-layer surface complexation model. The reaction producing a hydrolyzed tetranuclear surface species 4>SOH+M+2HO=(>SOH)2_M(OH)2++4H was found to account for a significant fraction of the adsorbed Y 3+, La 3+, Nd 3+, Gd 3+, and Yb 3+ on rutile, hematite, alumina and silica over wide ranges of pH and ionic strength. Where adsorption data were available as a function of surface coverage for hematite and silica, an additional reaction involving a mononuclear species could be used to account for the higher surface coverages. However, it is also possible that some of the higher surface coverage data refer to surface precipitation rather than adsorption. The results of the present study provide an internally consistent basis for describing YREE adsorption which could be used to investigate more complex systems in which YREE compete both in aqueous solution and on mineral surfaces with alkaline earths and ligands such as carbonate, sulfate, chloride and organic species, in order to build a predictive adsorption model applicable to natural waters.

Piasecki, Wojciech; Sverjensky, Dimitri A.

2008-08-01

389

Dependence of cryogenic strength of hydroxide catalysis bonded silicon on type of surface oxide  

NASA Astrophysics Data System (ADS)

Hydroxide catalysis bonding is a joining technique used in the construction of highly stable opto-mechanical systems including quasi-monolithic silica suspensions for first and second generation gravitational wave detectors. Future generations of detector are likely to operate at cryogenic temperatures necessitating a change in testmass/suspension material. A promising candidate material is silicon, which requires an oxide surface layer for hydroxide catalysis bonding to be reliable. Here, we present first results showing the influence of the type of oxide layer applied on bond strength, measured at room temperature and 77 K, and identify preferred oxide deposition methods.

Beveridge, N. L.; van Veggel, A. A.; Cunningham, L.; Hough, J.; Martin, I. W.; Nawrodt, R.; Reid, S.; Rowan, S.

2013-01-01

390

Functionalization of graphite, glassy carbon, and polymer surfaces with highly oxidized sulfur species by plasma treatments  

NASA Astrophysics Data System (ADS)

SO2 and SO2+H2O plasma treatments have been performed on highly oriented pyrolytic graphite, glassy carbon and several polymers in order to functionalize their surface with sulfur in different oxidation states. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy measurements prove that highly oxidized sulfur species (SO3, SO3H, SO4, and SO4)H as well as covalently bound sulfur and low oxidized sulphur species (SO and SO2) are formed and chemisorbed at the surface by plasma treatment. The oxidation state of the adsorbed sulfur species depends on the bias potential applied to the sample. The greater the bias, the lower the oxidation state. The same behavior as a function of the plasma parameters is found for all substrates. The maximal coverage of the surface with sulfur functionalities has been estimated to be about one monolayer. The modifications of the surface topography have also been measured with atomic force microscopy.

Collaud Coen, M.; Keller, B.; Groening, P.; Schlapbach, L.

2002-11-01

391

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

392

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

SciTech Connect

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

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

1991-01-01

393

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

394

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)ONi(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

395

Synthesis-Dependent Atomic Surface Structures of Oxide Nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

396

Coupled ferric oxides and sulfates on the Martian surface.  

PubMed

The Mars Exploration Rover (MER), Opportunity, showed that layered sulfate deposits in Meridiani Planum formed during a period of rising acidic ground water. Crystalline hematite spherules formed in the deposits as a consequence of aqueous alteration and were concentrated on the surface as a lag deposit as wind eroded the softer sulfate rocks. On the basis of Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) orbital data, we demonstrate that crystalline hematite deposits are associated with layered sulfates in other areas on Mars, implying that Meridiani-like ground water systems were indeed widespread and representative of an extensive acid sulfate aqueous system. PMID:17673623

Bibring, J-P; Arvidson, R E; Gendrin, A; Gondet, B; Langevin, Y; Le Mouelic, S; Mangold, N; Morris, R V; Mustard, J F; Poulet, F; Quantin, C; Sotin, C

2007-08-02

397

Synthesis-dependent atomic surface structures of oxide nanoparticles.  

PubMed

Using SrTiO_{3} nanocuboids as a model system, we show with aberration-corrected high resolution electron microscopy at sub-Å resolution that surface relaxations or reconstructions are present on the nanocuboids, depending on the synthetic process. Oleic acid synthesis, acetic acid synthesis, and microwave-assisted acetic acid synthesis result in a SrO termination, TiO_{2}-rich reconstruction, and mixed termination, respectively. The experimental atomic positions are in better agreement with density functional theory calculations using an exact-exchange corrected PBEsol functional than the Perdew-Burke-Ernzerhof (PBE) functional. PMID:24160614

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

2013-10-08

398

Coupled Ferric Oxides and Sulfates on the Martian Surface  

NASA Astrophysics Data System (ADS)

The Mars Exploration Rover (MER), Opportunity, showed that layered sulfate deposits in Meridiani Planum formed during a period of rising acidic ground water. Crystalline hematite spherules formed in the deposits as a consequence of aqueous alteration and were concentrated on the surface as a lag deposit as wind eroded the softer sulfate rocks. On the basis of Mars Express Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) orbital data, we demonstrate that crystalline hematite deposits are associated with layered sulfates in other areas on Mars, implying that Meridiani-like ground water systems were indeed widespread and representative of an extensive acid sulfate aqueous system.

Bibring, J.-P.; Arvidson, R. E.; Gendrin, A.; Gondet, B.; Langevin, Y.; Le Mouelic, S.; Mangold, N.; Morris, R. V.; Mustard, J. F.; Poulet, F.; Quantin, C.; Sotin, C.

2007-08-01

399

Electron stimulated desorption of hydronium ions from chromium oxide surfaces  

NASA Astrophysics Data System (ADS)

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

Cole, Charles Randal

400

MicroRNA functionalized microporous titanium oxide surface by lyophilization with enhanced osteogenic activity.  

PubMed

Developing biomedical titanium (Ti) implants with high osteogenic ability and consequent rigid osseointegration is a constant requirement from the clinic. In this study, we fabricate novel miRNA functionalized microporous Ti implants by lyophilizing miRNA lipoplexes onto a microporous titanium oxide surface formed by microarc oxidation (MAO). The microporous titanium oxide surface provides a larger surface area for miRNA loading and enables spatial retention of the miRNAs within the pores until cellular delivery. The loading of lipoplexes into the micropores on the MAO Ti surface is facilitated by the superhydrophilicity and Ti-OH groups gathering of the MAO surface after UV irradiation followed by lyophilization. A high miRNA transfection efficiency was observed in mesenchymal stem cells (MSCs) seeded onto the miRNA functionalized surface with no apparent cytotoxicity. When functionalizing the Ti surface with miR-29b that enhances osteogenic activity and antimiR-138 that inhibits miR-138 inhibition of endogenous osteogenesis, clear stimulation of MSC osteogenic differentiation was observed, in terms of up-regulating osteogenic expression and enhancing alkaline phosphatase production, collagen secretion and ECM mineralization. The novel miRNA functionalized Ti implants with enhanced osteogenic activity promisingly lead to more rapid and robust osseointegration of a clinical bone implant interface. Our study implies that lyophilization may constitute a versatile method for miRNA loading to other biomaterials with the aim of controlling cellular function. PMID:23459382

Wu, Kaimin; Song, Wen; Zhao, Lingzhou; Liu, Mengyuan; Yan, Jun; Andersen, Morten Østergaard; Kjems, Jørgen; Gao, Shan; Zhang, Yumei

2013-03-21

401

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

SciTech Connect

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

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

2011-09-01

402

Radicals and Oxidants Instrument (ROXI) for Mars surface analyses  

NASA Astrophysics Data System (ADS)

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

Yen, Albert S.; Kim, Soon S.

2004-12-01

403

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

NASA Astrophysics Data System (ADS)

The surface of commercially pure titanium (grade 4) was modified by micro-arc oxidation treatment. A porous TiO2 coating layer was formed on the Ti surface and its crystal structure was analyzed as rutile phase. Both the thickness of the TiO2 layer and the pore size on the surface were strongly dependent on the applied current density as well as the micro-arc oxidizing time during the oxidation treatment. When a current density of 50 mA/cm2 had been applied for 10 minutes, the thickness and the pore size of the oxide layer were 1.2 µm and 230 nm, respectively. The thickness and the pore size of the layer continued to increase with increasing the applied current density. The TiO2 passive layer of the titanium surface can attribute to the excellent biocompatibility and the formation of nano-sized pores may maximize the interlocking between mineralized bone and the surface of the Ti implant.

Kim, Yeon-Wook; Nam, Tae-Hyun

404

Facile electrochemical oxidation of polyaromatic hydrocarbons to surface-confined redox-active quinone species on a multiwalled carbon nanotube surface.  

PubMed

Polyaromatic hydrocarbon (PAH) oxidation: PAHs, which are considered major environmental pollutants, are carcinogenic, and cannot be electrochemically oxidized on conventional electrodes (gold, platinum, and glassy carbon), can be electrochemically oxidized on multiwalled carbon nanotube surfaces at a potential of 1?V versus Ag/AgCl at pH?7. This results in the formation of stable surface-confined quinone systems (see scheme; AN = anthracene; AQ = anthraquinone). PMID:23296450

Barathi, Palani; Kumar, Annamalai Senthil

2013-01-07

405

Efficient modification of metal oxide surfaces with phosphonic acids by spray coating.  

PubMed

We report a rapid method of depositing phosphonic acid molecular groups onto conductive metal oxide surfaces. Solutions of pentafluorobenzyl phosphonic acid (PFBPA) were deposited on indium tin oxide, indium zinc oxide, nickel oxide, and zinc oxide by spray coating substrates heated to temperatures between 25 and 150 °C using a 60 s exposure time. Comparisons of coverage and changes in work function were made to the more conventional dip-coating method utilizing a 1 h exposure time. The data show that the work function shifts and surface coverage by the phosphonic acid were similar to or greater than those obtained by the dip-coating method. When the deposition temperature was increased, the magnitude of the surface coverage and work function shift was also found to increase. The rapid exposure of the spray coating was found to result in less etching of zinc-containing oxides than the dip-coating method. Bulk heterojunction solar cells made of polyhexylthiophene (P3HT) and bis-indene-C60 (ICBA) were tested with PFBPA dip and spray-modified ITO substrates as well as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS)-modified ITO. The spray-modified ITO solar cells showed a similar open circuit voltage (VOC) and fill factor (FF) and a less than 5% lower short circuit current density (JSC) and power conversion efficiency (PCE) than the dip- and PEDOT:PSS-modified ITO. These results demonstrate a potential path to a scalable method to deposit phosphonic acid surface modifiers on metal oxides while overcoming the limitations of other techniques that require long exposure and post-processing times. PMID:23421597

Bulusu, Anuradha; Paniagua, Sergio A; MacLeod, Bradley A; Sigdel, Ajaya K; Berry, Joseph J; Olson, Dana C; Marder, Seth R; Graham, Samuel

2013-03-13

406

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

USGS Publications Warehouse

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

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

1996-01-01

407

Effect of annealing temperature on PL spectrum and surface morphology of zinc oxide thin films  

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) thin films were produced by thermal oxidation of Zn layers (200 nm thickness) which were coated on Si (1 0 0) substrate by DC magnetron sputtering. In order to study the effect of annealing temperature on photoluminescence (PL) properties and the surface morphology of the ZnO samples, the annealing temperature range of 500-700 °C was employed. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) for investigation of surface morphology of the ZnO samples were carried out. The surface statistical characteristics of these ZnO thin films are then evaluated against data which outcome from AFM. SEM and AFM results indicated that the annealing temperature produces larger grains and rough surfaces at higher temperatures. The results of PL spectra represent an increase in interstitial zinc with increasing annealing temperature.

Zendehnam, A.; Mirzaee, M.; Miri, S.

2013-04-01

408

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

409

Interaction between surface migrating pentacene molecules and chemically modified surfaces of silicon oxides studied by pulsed molecular beam scattering  

NASA Astrophysics Data System (ADS)

The interaction between pentacene molecules and organic self-assembling monolayers formed on silicon oxides (SiO2) was studied by measuring the surface scattering time profile of the pulsed molecular beam of pentacene. It was found that the surface residence time (SRT) of pentacene was significantly reduced on a surface treated with hexamethyl silazarane (HMDS) compared with that on a bare SiO2 surface. The activation energies derived from the temperature dependence of the SRT were 24 kJ/mol and 100 kJ/mol for HMDS SiO2 and the bare SiO2, respectively. A surface treated with octadecyltrichlorosilane (OTS) showed SRT values almost the same as those on the bare SiO2 surface, which was due to exposed SiO2 regions on the thermally-degraded OTS SiO2. The growth mechanism with improved quality is due to the shallower adsorption potential and enhanced migration of pentacene by the surface alkylation.

Ichikawa, H.; Koma, A.; Saiki, K.; Shimada, T.

2006-09-01

410

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

SciTech Connect

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

Narkiewicz, U.; Arabczyk, W.

1999-08-31

411

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

SciTech Connect

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

Doyle, F.M.

1993-09-30

412

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

413

The variation of multipole polarizability at the surface of alkaline earth oxides and sulfides  

NASA Astrophysics Data System (ADS)

Multipole polarizabilities of O2- and S2- ions at the {100}, {110} and {111} surfaces of oxides and sulfides of rocksalt structure were calculated variationally using the Kirkwood-Pople-Schofield (KPS) approach, and the method of Parry of calculating the electrostatic potential in the surface region of an ionic crystal. These results including various effects such as relaxation and rumpling were compared with bulk values for these systems. The initial wavefunctions of Harker have been used in the calculations.

Al-Mulla, S. Y. Yousif

2005-06-01

414

Adsorption of polyethylene oxide on surface modified silica – stability of bare and covered particles in suspension  

Microsoft Academic Search

The adsorption of poly-ethylene oxide (PEO) on modified colloidal silica and the stability of the aqueous suspension was\\u000a investigated. With octanol some silanol groups at the silica surface were replaced by octylgroups. The size of the modified\\u000a silica particles and the charge and chemical groups on the surface were charaterized by ultracentrifugation, photon correlation\\u000a spectrometry, polyelectrolyte titration and IR spectrometry.

B. Wind; E. Killmann

1998-01-01

415

Metal-oxide-semiconductor-compatible ultra-long-range surface plasmon modes  

Microsoft Academic Search

Long-range surface plasmons traveling on thin metal films have demonstrated promising potential in subwavelength waveguide applications. In work toward device applications that can leverage existing silicon microelectronics technology, it is of interest to explore the propagation of surface plasmons in a metal-oxide-semiconductor geometry. In such a structure, there is a high refractive index contrast between the semiconductor (n~3.5 for silicon)

C. G. Durfee; T. E. Furtak; R. T. Collins; R. E. Hollingsworth

2008-01-01

416

Metal-oxide-semiconductor-compatible ultra-long-range surface plasmon modes  

Microsoft Academic Search

Long-range surface plasmons traveling on thin metal films have demonstrated promising potential in subwavelength waveguide applications. In work toward device applications that can leverage existing silicon microelectronics technology, it is of interest to explore the propagation of surface plasmons in a metal-oxide-semiconductor geometry. In such a structure, there is a high refractive index contrast between the semiconductor (n≈3.5 for silicon)

C. G. Durfee; T. E. Furtak; R. T. Collins; R. E. Hollingsworth

2008-01-01

417

On the surface basic properties of sulfated magnesia–silica sol–gel mixed oxides  

Microsoft Academic Search

The morphology and surface base properties of a family of sulfated MgO–SiO2 mixed oxides prepared by the sol–gel method were studied. Morphological features of the sulfated system are found to vary with preparative conditions. Electron dispersive spectroscopy (EDS) analysis of the samples show a very high homogeneous distribution of sulfur and magnesium on the surface. It was found by CO2-Thermal

T López; R Gómez; M. E Llanos; E Garc??a-Figueroa; J Navarrete; E López-Salinas

1999-01-01