| 1. |
- Nilsson, Anders, et al.
(författare)
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X-ray absorption spectroscopy and X-ray Raman scattering of water and ice; an experimental view
- 2010
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 177:03-feb, s. 99-129
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a review of X-ray absorption spectroscopy and X-ray Raman scattering with the perspective to understand the spectra of water including changes with temperature, mass of the water molecule and presence of monovalent ions. The different detection schemes are discussed and it is concluded that transmission X-ray absorption measurements, using a small area where the thickness is uniform, and X-ray Raman scattering give the most reliable spectra. Different model systems are discussed such as the surface and bulk of ice and various adsorbed monolayer structures on metal surfaces.
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| 2. |
- Schiros, Theanne, et al.
(författare)
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Chemical bonding of water to metal surfaces studied with core-level spectroscopies
- 2010
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 177, s. 85-98
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Tidskriftsartikel (refereegranskat)abstract
- The nature of the contact layer of water on surfaces is of relevance for many practical fields, including corrosion, electrochemistry, environmental science and heterogeneous catalysis. Here we focus on the geometric and electronic structure of the water contact layer on transition metal surfaces and the interaction between the water monolayer and the surface. By combining synchrotron radiation-based X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) techniques with density functional theory (DFT) computational methods we obtain element-specific information on the partial local density of states, local atomic structure, geometrical parameters and molecular orientation, allowing general principles for water–metal interaction to be derived.
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| 3. |
- Schiros, Theanne, et al.
(författare)
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Connecting Dopant Bond Type with Electronic Structure in N-Doped Graphene
- 2012
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 12:8, s. 4025-4031
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Tidskriftsartikel (refereegranskat)abstract
- Robust methods to tune the unique electronic properties of graphene by chemical modification are in great demand due to the potential of the two dimensional material to impact a range of device applications. Here we show that carbon and nitrogen core-level resonant X-ray spectroscopy is a sensitive probe of chemical bonding and electronic structure of chemical dopants introduced in single-sheet graphene films. In conjunction with density functional theory based calculations, we are able to obtain a detailed picture of bond types and electronic structure in graphene doped with nitrogen at the sub-percent level. We show that different N-bond types, including graphitic, pyridinic, and nitrilic, can exist in a single, dilutely N-doped graphene sheet. We show that these various bond types have profoundly different effects on the carrier concentration, indicating that control over the dopant bond type is a crucial requirement in advancing graphene electronics.
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| 4. |
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| 5. |
- Schiros, Theanne, et al.
(författare)
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Cooperativity in Surface Bonding and Hydrogen Bonding of Water and Hydroxyl at Metal Surfaces
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:22, s. 10240-10248
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- We examine the balance of surface bonding and hydrogen bonding in the mixed OH + H2O overlayer on Pt(111), Cu(111), and Cu(110) via density functional theory calculations. We find that there is a cooperativity effect between surface bonding and hydrogen bonding that underlies the stability of the mixed phase at metal surfaces. The surface bonding can be considered to be similar to accepting a hydrogen bond, and we can thereby apply general cooperativity rules developed for hydrogen-bonded systems. This provides a simple understanding of why water molecules become more strongly bonded to the surface upon hydrogen bonding to OH and why the OH surface bonding is instead weakened through hydrogen bonding to water. We extend the application of this simple model to other observed cooperativity effects for pure water adsorption systems and H3O+ on metal surfaces.
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| 6. |
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| 7. |
- Schiros, Theanne, et al.
(författare)
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Structure of water adsorbed on the open Cu(110) surface: H-up, H-down, or both?
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:4-6, s. 415-419
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the structure of the water monolayer on an open surface, Cu(1 1 0), at low temperature. We found that water adsorbs molecularly, adopting a 2:1 ratio of H-down and H-up configurations. This behavior of water on an open surface is quite different to the behavior on close-packed surfaces, such as Pt(1 1 1) and Ru(0 0 0 1), where water adsorbs primarily H-down, but can be understood on the basis of a range of different water adsorption sites across the observed (7 × 8) unit cell.
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| 8. |
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| 9. |
- Schiros, Theanne, et al.
(författare)
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The Role of Substrate Electrons in the Wetting of a Metal Surface
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 132:9, s. 094701-
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Tidskriftsartikel (refereegranskat)abstract
- We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution of charge that enables surface wetting. On open d-shell Pt(111), the ligand field of water alters the distribution of metal d-electrons to reduce the repulsion. The closed-shell Cu d10 configuration of isostructural Cu(111), however, does not afford this mechanism, resulting in a hydrophobic surface and three-dimensional ice cluster formation. On the geometrically corrugated Cu(110) surface, however, charge depletion involving the mobile sp-electrons at atomic rows reduces the exchange repulsion sufficiently such that formation of a two-dimensional wetting layer is still favored in spite of the d10 electronic configuration
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| 10. |
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| 11. |
- Schiros, Theanne, et al.
(författare)
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Unique water-water coordination tailored by a metal surface
- 2013
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 138:23, s. 234708-
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Tidskriftsartikel (refereegranskat)abstract
- At low coverage of water on Cu(110), substrate-mediated electrostatics lead to zigzagging chains along [001] as observed with STM [T. Yamada, S. Tamamori, H. Okuyama, and T. Aruga, Anisotropic water chain growth on Cu(110) observed with scanning tunneling microscopy Phys. Rev. Lett. 96, 036105 (2006)]. Using x-ray absorption spectroscopy we find an anomalous low-energy resonance at similar to 533.1 eV which, based on density functional theory spectrum simulations, we assign to an unexpected configuration of water units whose uncoordinated O-H bonds directly face those of their neighbors; this interaction repeats over trough sites with enhanced electron density and is analogous to the case of a hydrated electron.
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| 12. |
- Schiros, Theanne, 1975-
(författare)
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Water-Metal Surfaces : Insights from core-level spectroscopy and density functional theory
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computational methods are combined with synchrotron-based techniques to analyze the structure and bonding of water and water plus hydroxyl at metal surfaces under UHV and at near-ambient conditions. Water-metal interaction plays a crucial role in a multitude of cosmic, atmospheric and biological phenomena as well as heterogeneous catalysis, electrochemistry and corrosion. A spotlight of renewed interest has recently been cast on water-metal systems due to their relevance for surface chemical reactions related to the production and utilization of hydrogen as a clean energy carrier. In particular, H2O and OH are essential reaction intermediates in the renewable production of hydrogen from sunlight and water and in fuel cell electrocatalysis.Fuel cells are considered one of the most promising power generation technologies for a sustainable energy future. A mechanistic understanding of the oxygen reduction reaction (ORR) pathway, including the role of electronic and geometric structure of the catalyst, is essential to the design of more efficient fuel cell catalysts. This is intimately connected to fundamental factors that affect the ability to form water-metal bonds as well as the site occupation and orientation of the adsorbed H2O and OH at active metal surfaces.Key relationships related to critical issues in the fuel cell reaction are illuminated by the synergy of theory and experiment in this thesis. We emerge with a detailed understanding of the structure of the water-metal interface and the factors that rule the wettability of a metal surface, including geometric and electronic structure effects and the influence of coadsorbed species. We show that the preferred microscopic orientation of the water monolayer has consequences for macroscopic properties, and reveal the origin of the hydrophobic water layer. Finally, we identify a cooperativity effect that drives the stability of the mixed water/hydroxyl layer at metal surfaces, an important ORR intermediate.
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| 13. |
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| 14. |
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