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  • 1. Amft, M.
    et al.
    Walle, L. E.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Borg, A.
    Uvdal, P.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO22013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17078-17083Article in journal (Refereed)
    Abstract [en]

    We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations.

  • 2.
    Beyerlein, Kenneth
    et al.
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Hamburg, Germany.
    Jönsson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Alonso-Mori, Roberto
    SLAC National Accelerator Laboratory, USA.
    Aquila, Andrew
    SLAC National Accelerator Laboratory, USA.
    Bajt, Sasa
    Photon Science, DESY, Hamburg, Germany.
    Barty, Anton
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Hamburg, Germany.
    Bean, Richard
    Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Hamburg, Germany.
    Koglin, Jason E.
    SLAC National Accelerator Laboratory, USA.
    Messerschmidt, Marc
    SLAC National Accelerator Laboratory, USA.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Soklaras, Dimosthenis
    SLAC National Accelerator Laboratory, USA.
    Williams, Garth J.
    SLAC National Accelerator Laboratory, USA.
    Hau-Riege, Stefan
    Lawrence Livermore National Laboratory, USA.
    Boutet, Sebastien
    SLAC National Accelerator Laboratory, USA.
    Chapman, Henry N.
    Center for Free-Electron Laser Science,Deutsches Elektronen-Synchrotron, Hamburg, Germany; Department of Physics, University of Hamburg, Hamburg, Germany; Centre for Ultrafast Imaging, University of Hamburg, Hamburg, Germany .
    Timneanu, Nicusor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Center for Free-Electron Laser Science,Deutsches Elektronen-Synchrotron, Hamburg, Germany.
    Ultrafast non-thermal heating of water initiated by an X-ray laser2018In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 115, no 22, p. 5652-5657Article in journal (Refereed)
    Abstract [en]

    X-ray Free-Electron Lasers have opened the door to a new era in structural biology, enabling imaging of biomolecules and dynamics that were impossible to access with conventional methods. A vast majority of imaging experiments, including Serial Femtosecond Crystallography, use a liquid jet to deliver the sample into the interaction region. We have observed structural changes in the carrying water during X-ray exposure, showing how it transforms from the liquid phase to a plasma. This ultrafast phase transition observed in water provides evidence that any biological structure exposed to these X-ray pulses is destroyed during the X-ray exposure.The bright ultrafast pulses of X-ray Free-Electron Lasers allow investigation into the structure of matter under extreme conditions. We have used single pulses to ionize and probe water as it undergoes a phase transition from liquid to plasma. We report changes in the structure of liquid water on a femtosecond time scale when irradiated by single 6.86 keV X-ray pulses of more than 106 J/cm2. These observations are supported by simulations based on molecular dynamics and plasma dynamics of a water system that is rapidly ionized and driven out of equilibrium. This exotic ionic and disordered state with the density of a liquid is suggested to be structurally different from a neutral thermally disordered state.

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  • 3.
    Farstad, M. H.
    et al.
    Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway..
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Groenbeck, H.
    Chalmers, Competence Ctr Catalysis, SE-41296 Gothenburg, Sweden.;Chalmers, Dept Appl Phys, SE-41296 Gothenburg, Sweden..
    Strömsheim, M. D.
    Norwegian Univ Sci & Technol, Dept Chem Engn, NO-7491 Trondheim, Norway..
    Stavrakas, Camille
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Gustafson, J.
    Lund Univ, Div Synchrotron Radiat Res, Box 118, SE-22100 Lund, Sweden..
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Borg, A.
    Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway..
    TiOx thin films grown on Pd(100) and Pd(111) by chemical vapor deposition2016In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 649, p. 80-89Article in journal (Refereed)
    Abstract [en]

    The growth of ultrathin TiOx (0 <= x <= 2) films on Pd(100) and Pd(111) surfaces by chemical vapor deposition (CVD), using Titanium(IV)isopropoxide (TTIP) as precursor, has been investigated by high resolution photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. Three different TiOx phases and one Pd-Ti alloy phase have been identified for both surfaces. The Pd-Ti alloy phase is observed at the initial stages of film growth. Density functional theory (DFT) calculations for Pd(100) and Pd(111) suggest that Ti is alloyed into the second layer of the substrate. Increasing the TTIP dose yields a wetting layer comprising Ti2+ species (TiOx, x similar to 0.75). On Pd(100), this phase exhibits a mixture of structures with (3 x 5) and (4 x 5) periodicity with respect to the Pd(100) substrate, while an incommensurate structure is formed on Pd(111). Most importantly, on both surfaces this phase consists of a zigzag pattern similar to observations on other reactive metal surfaces. Further increase in coverage results in growth of a fully oxidized (TiO2) phase on top of the partially oxidized layer. Preliminary investigations indicate that the fully oxidized phase on both Pd(100) and Pd(111) may be the TiO2(B) phase.

  • 4.
    Farstad, M. H.
    et al.
    Norwegian Univ Sci & Technol, Dept Chem Engn, Trondheim.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Strømsheim, M. D.
    Norwegian Univ Sci & Technol, Dept Chem Engn, Trondheim.
    Gustafson, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Borg, A.
    Norwegian Univ Sci & Technol, Dept Phys, Trondheim.
    Oxidation and Reduction of TiOx Thin Films on Pd(111) and Pd(100)2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 2, p. 688-694Article in journal (Refereed)
    Abstract [en]

    Thin films of TiOx on Pd(100) and Pd(111) have been investigated with respect to their properties after oxidation and reduction cycles. High-resolution photoemission spectroscopy (HRPES) and low energy electron diffraction (LEED) have been applied to characterize the thin film oxidation states and structure before and after oxidation and reduction under ultrahigh vacuum conditions. Fully oxidized TiO2 films were formed on both surfaces. These structures display Moiré patterns in LEED, in one dimension for Pd(100) and in two dimensions for Pd(111), and they have previously not been reported for TiO2/Pd. The oxidation process causes strong reduction in the interaction between the oxide thin film and the Pd substrate, most significantly for Pd(111). Reversible oxidation/reduction cycling of TiOx thin films on Pd(111) and Pd(100) was possible.

  • 5. Farstad, M. H.
    et al.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Walle, L. E.
    Schaefer, A.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Borg, A.
    Water Adsorption on TiOx Thin Films Grown on Au(111)2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 12, p. 6660-6669Article in journal (Refereed)
    Abstract [en]

    High resolution photoelectron spectroscopy has been used to investigate water adsorption on four different TiOx ultrathin film structures, grown on Au(111) by chemical vapor deposition. Two of the structures are reduced TiOx single layer phases, forming a honeycomb (HC) and a pinwheel (PW) structure, respectively. The other two phases have TiO2 stoichiometry, one in the form of islands and one in the form of a TiO2(B)(001) extended layer. Partial water dissociation is observed for all phases but the HC phase, and the dissociation propensity and adsorbate thermal stability structure result from interplay between the atomic structure of the particular TiOx phase and defects formed in the preparation. The dissociation on the TiO2(B) film is mainly related to different types of defect sites. The TiO2 islands, interpreted as surface reconstructed rutile TiO2(100), generate the highest amount of hydroxyls with a behavior consistent with reconstruction into a mixed (100) and (110) termination. Water dissociation on the PW layer can be assigned to particular sites of the structure and it stands out by leading to oxidation of Ti species.

  • 6.
    Grånäs, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Timneanu, Nicusor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Eliah Dawod, Ibrahim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Trygg, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Souvatzis, Petros
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Femtosecond bond breaking and charge dynamics in ultracharged amino acids2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 14, article id 144307Article in journal (Refereed)
    Abstract [en]

    Historically, structure determination of nanocrystals, proteins, and macromolecules required the growth of high-quality crystals sufficiently large to diffract X-rays efficiently while withstanding radiation damage. The development of the X-ray free-electron laser has opened the path toward high resolution single particle imaging, and the extreme intensity of the X-rays ensures that enough diffraction statistics are collected before the sample is destroyed by radiation damage. Still, recovery of the structure is a challenge, in part due to the partial fragmentation of the sample during the diffraction event. In this study, we use first-principles based methods to study the impact of radiation induced ionization of six amino acids on the reconstruction process. In particular, we study the fragmentation and charge rearrangement to elucidate the time scales involved and the characteristic fragments occurring.

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  • 7.
    Kamal, C.
    et al.
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden.;Raja Ramanna Ctr Adv Technol, Theory & Simulat Lab, HRDS, Indore 452013, India.;Homi Bhabha Natl Inst, Training Sch Complex, Mumbai 400094, Maharashtra, India..
    Stenberg, Nader
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Walle, Lars Erik
    SINTEF Ind, Petr Dept, Format Phys, NO-7465 Trondheim, Norway..
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Borg, Anne
    NTNU Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway..
    Uvdal, Per
    Lund Univ, Dept Chem, Chem Phys, POB 124, SE-22100 Lund, Sweden..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Multiscale Mat Modelling, SE-10044 Stockholm, Sweden..
    Odelius, Michael
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Core-Level Binding Energy Reveals Hydrogen Bonding Configurations of Water Adsorbed on TiO2 (110) Surface2021In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 126, no 1, article id 016102Article in journal (Refereed)
    Abstract [en]

    Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D2O) and dissociated (OD) water in the hydrated stoichiometric TiO2 (110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D2O:OD ratio and the core-level binding energy of D2O (Delta BE) decrease with temperature. The observed variations in Delta BE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

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  • 8.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Chemical vapor deposition of ordered TiOx nanostructures on Au(111)2013In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 617, p. 211-217Article in journal (Refereed)
    Abstract [en]

    The deposition of TiOx (x ≤ 2) structures on Au(111) by chemical vapor deposition (CVD) in ultrahigh vacuum (UHV) has been investigated with high-resolution core level photoelectron spectroscopy (PES), low-energy electron diffraction (LEED) and scanning tunnelingmicroscopy (STM). Using titanium tetra-isopropoxide as single source precursor it is possible to form different TiOx phases on the surface after deposition: at low coverages, we observe large two-dimensional (2D) honeycomb-lattice Ti2O3 islands with a (2 × 2) registry with the substrate. Higher coverages are dominated by the formation of three-dimensional (3D) TiO2 structures. The TiO2 structures are atomically well ordered provided that the deposition temperature is high enough (500 °C). The ordered structure exhibits a LEED pattern characteristic for a rectangular surface unit cell. By performing the deposition at different temperatures it is possible to tune the balance between the 2D and 3D phases: Growth at 500 °C significantly favors the formation of 3D TiO2 islands as compared to growth at 200 °C and 300 °C.

  • 9.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Titania Nanoscale Films and Surfaces: Surface Science Investigation of Structure and Properties2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents surface science studies, investigating several aspects of titanium dioxide at the atomic scale. The greater part of this work is devoted to the preparation by chemical vapor deposition (CVD) of titanium(IV) tetraisopropoxide (TTIP) of ultrathin TiO2 or TiOx films on Au(111). Four ordered structures were growth and characterized. It was also demonstrated how the morphology of the film (wetting film vs island) can be tailored. The acquired knowledge about the CVD process was exploited to load nano porous gold with titania, enhancing its catalytic activity. The reactivity towards water adsorption of the titania structures on Au(111) was also investigated. Finally, part of this work concerned the studying of the behavior of water on the stoichiometric rutile TiO2(110) surface, combining the experiments with density-functional theory (DFT) calculations and (kinetic) Monte Carlo simulations. The main experimental techniques used in this work are low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and photoelectron spectroscopy (PES).

    List of papers
    1. Chemical vapor deposition of ordered TiOx nanostructures on Au(111)
    Open this publication in new window or tab >>Chemical vapor deposition of ordered TiOx nanostructures on Au(111)
    2013 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 617, p. 211-217Article in journal (Refereed) Published
    Abstract [en]

    The deposition of TiOx (x ≤ 2) structures on Au(111) by chemical vapor deposition (CVD) in ultrahigh vacuum (UHV) has been investigated with high-resolution core level photoelectron spectroscopy (PES), low-energy electron diffraction (LEED) and scanning tunnelingmicroscopy (STM). Using titanium tetra-isopropoxide as single source precursor it is possible to form different TiOx phases on the surface after deposition: at low coverages, we observe large two-dimensional (2D) honeycomb-lattice Ti2O3 islands with a (2 × 2) registry with the substrate. Higher coverages are dominated by the formation of three-dimensional (3D) TiO2 structures. The TiO2 structures are atomically well ordered provided that the deposition temperature is high enough (500 °C). The ordered structure exhibits a LEED pattern characteristic for a rectangular surface unit cell. By performing the deposition at different temperatures it is possible to tune the balance between the 2D and 3D phases: Growth at 500 °C significantly favors the formation of 3D TiO2 islands as compared to growth at 200 °C and 300 °C.

    National Category
    Atom and Molecular Physics and Optics Materials Chemistry Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-212702 (URN)
    Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2022-01-28
    2. Growth of TiO2(B)(001) on Au(111) by Chemical Vapor Deposition
    Open this publication in new window or tab >>Growth of TiO2(B)(001) on Au(111) by Chemical Vapor Deposition
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    2015 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 633, p. 102-108Article in journal (Refereed) Published
    Abstract [en]

    This study presents how a TiO2(B) film exposing the (001) face can be grown on Au(111) by chemical vapor deposition. Identification and characterization of the TiO2(B)(001) layer are carried out with low-energy electron diffraction (LEED), synchrotron radiation photoelectron spectroscopy (PES), scanning tunneling microscopy (STM) and X-ray absorption spectroscopy (XAS). Formation of the TiO2(B) film requires a two-step preparation procedure: deposition at 280 °C followed by annealing to 500 °C. This suggests that the interaction between a substrate and an overlayer stabilizes the TiO2(B) film, preventing the formation of thermodynamically more stable rutile islands. The study thus gives insight into how the morphology and the atomic structure of the titania overlayer can be controlled.

    Keywords
    TiO2, Au(111), CVD, titania, gold
    National Category
    Condensed Matter Physics Atom and Molecular Physics and Optics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-224091 (URN)10.1016/j.susc.2014.10.011 (DOI)000348336000015 ()
    Available from: 2014-05-04 Created: 2014-05-02 Last updated: 2017-12-05Bibliographically approved
    3. Structure of a pinwheel-like TiOx single layer phase on Au(111)
    Open this publication in new window or tab >>Structure of a pinwheel-like TiOx single layer phase on Au(111)
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:uu:diva-224104 (URN)
    Available from: 2014-05-04 Created: 2014-05-04 Last updated: 2014-06-30
    4. Controlled modification of nanoporous gold: Chemical vapor deposition of TiO2 in ultrahigh vacuum
    Open this publication in new window or tab >>Controlled modification of nanoporous gold: Chemical vapor deposition of TiO2 in ultrahigh vacuum
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    2013 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 282, p. 439-443Article in journal (Refereed) Published
    Abstract [en]

    TiO2 has been deposited in the first 400 nm of a nanoporous gold (NPG) structure using metal organic chemical vapor deposition with titanium-tetraisopropoxide as single source precursor in ultra high vacuum. The NPG has been pretreated by ozone to clean and stabilize the structure for deposition. The deposited oxide stabilizes the porous structure, otherwise prone to coarsening at elevated temperatures, up to 300 degrees C. The study combines the controlled sample preparation with a functional test of the prepared catalyst under real conditions in a continuous gas flow reactor. The catalytic activity of the loaded NPG at 60 degrees C for CO oxidation is found to be superior to unloaded as-prepared NPG.

    Keywords
    Nanoporous gold, Titania, Chemical vapor deposition, Heterogeneous catalysis, Ultrahigh vacuum
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-206545 (URN)10.1016/j.apsusc.2013.05.148 (DOI)000322314800064 ()
    Available from: 2013-09-02 Created: 2013-09-02 Last updated: 2017-12-06Bibliographically approved
    5. Water adsorption on TiOx thin films grown on Au(111)
    Open this publication in new window or tab >>Water adsorption on TiOx thin films grown on Au(111)
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Atom and Molecular Physics and Optics Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-224106 (URN)
    Available from: 2014-05-04 Created: 2014-05-04 Last updated: 2014-06-30
    6. A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO2
    Open this publication in new window or tab >>A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO2
    Show others...
    2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17078-17083Article in journal (Refereed) Published
    Abstract [en]

    We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-208369 (URN)10.1021/jp405208x (DOI)000323593100037 ()
    Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2017-12-06Bibliographically approved
    7. Kinetics of water adsorption on TiO2(110)
    Open this publication in new window or tab >>Kinetics of water adsorption on TiO2(110)
    Show others...
    (English)Manuscript (preprint) (Other (popular science, discussion, etc.))
    National Category
    Atom and Molecular Physics and Optics Condensed Matter Physics Theoretical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-224107 (URN)
    Available from: 2014-05-04 Created: 2014-05-04 Last updated: 2014-06-30
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  • 10.
    Ragazzon, Davide
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Farstad, Mari Helene
    Norwegian University of Science and Technology (NTNU).
    Schaefer, Andreas
    University of Bremen.
    Walle, Lare Erik
    Norwegian University of Science and Technology (NTNU).
    Uvdal, Per
    Lund University.
    Borg, Anne
    Norwegian University of Science and Technology (NTNU).
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Growth of TiO2(B)(001) on Au(111) by Chemical Vapor Deposition2015In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 633, p. 102-108Article in journal (Refereed)
    Abstract [en]

    This study presents how a TiO2(B) film exposing the (001) face can be grown on Au(111) by chemical vapor deposition. Identification and characterization of the TiO2(B)(001) layer are carried out with low-energy electron diffraction (LEED), synchrotron radiation photoelectron spectroscopy (PES), scanning tunneling microscopy (STM) and X-ray absorption spectroscopy (XAS). Formation of the TiO2(B) film requires a two-step preparation procedure: deposition at 280 °C followed by annealing to 500 °C. This suggests that the interaction between a substrate and an overlayer stabilizes the TiO2(B) film, preventing the formation of thermodynamically more stable rutile islands. The study thus gives insight into how the morphology and the atomic structure of the titania overlayer can be controlled.

  • 11.
    Ragazzon, Davide
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Schaefer, A.
    Farstad, M. H.
    Walle, L. E.
    Palmgren, P.
    Borg, A.
    Uvdal, P.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Chemical vapor deposition of ordered TiOx nanostructures on Au(111)2013In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 617, p. 211-217Article in journal (Refereed)
    Abstract [en]

    The deposition of TiOx (x <= 2) structures on Au(111) by chemical vapor deposition (CVD) in ultrahigh vacuum (UHV) has been investigated with high-resolution core level photoelectron spectroscopy (PES), low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Using titanium tetra-isopropoxide as single source precursor it is possible to form different TiOx phases on the surface after deposition: at low coverages, we observe large two-dimensional (2D) honeycomb-lattice Ti2O3 islands with a (2 x 2) registry with the substrate. Higher coverages are dominated by the formation of three-dimensional (3D) TiO2 structures. The TiO2 structures are atomically well ordered provided that the deposition temperature is high enough (500 degrees C). The ordered structure exhibits a LEED pattern characteristic for a rectangular surface unit cell. By performing the deposition at different temperatures it is possible to tune the balance between the 2D and 3D phases: Growth at 500 degrees C significantly favors the formation of 3D TiO2 islands as compared to growth at 200 degrees C and 300 degrees C.

  • 12.
    Sandell, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Schaefer, A.
    Lund Univ, Div Synchrotron Radiat Res, Box 118, SE-22100 Lund, Sweden..
    Farstad, M. H.
    Norwegian Univ Sci & Technol NTNU, Dept Phys, NO-7491 Trondheim, Norway..
    Borg, A.
    Norwegian Univ Sci & Technol NTNU, Dept Phys, NO-7491 Trondheim, Norway..
    Photochemistry of Carboxylate on TiO2(110) Studied with Synchrotron Radiation Photoelectron Spectroscopy2016In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 44, p. 11456-11464Article in journal (Refereed)
    Abstract [en]

    We present a dedicated synchrotron radiation photoelectron spectroscopy (SR-PES) study of a photochemical reaction on the surface of rutile TiO2(110). The photoreaction kinetics of carboxylate species (trimethyl acetate, TMA) upon irradiation by UV and soft X-rays were monitored, and we show that it is possible to control the reaction rates from UV light and soft X-rays independently. We directly observe Ti4+ -> Ti3+ conversion upon irradiation, attributed to electron trapping at Ti sites close to surface OH groups formed by deprotonation of the parent molecule, trimethylacetic acid (TMAA). TMA photolysis on two surface preparations with different oxygen vacancy densities shows that the vacancy-related charge quenches the amount of charge that can be trapped at hydroxyls upon irradiation. During the initial stages of reaction the correlation between the amount of photodepleted TMA and the amount of charge trapped in the Ti 3d band gap state is nearly 1:1. A first-order kinetics analysis reveals that the reaction rate decreases with decreasing TMA coverage. There is also a coverage-dependent difference in the electronic structure of TMA moieties, primarily involving the carboxyl anchor group. These changes are consistent with a decreased hole affinity of the adsorbed TMA and hence a decreased reaction rate. This discovery adds to the previously presented picture of a reactivity that is inversely proportional to the number of surface hydroxyls, suggesting that the balance between the amounts of TMA, OH, and trapped charge needs to be considered.

  • 13.
    Sandell, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Schaefer, A.
    Lund Univ, Dept Synchrotron Radiat Res, POB 118, SE-22100 Lund, Sweden..
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Farstad, M. H.
    NTNU Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway..
    Borg, A.
    NTNU Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway..
    Adsorption and photolysis of trimethyl acetate on TiO2(B)(001) studied with synchrotron radiation core level photoelectron spectroscopy2017In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 666, p. 104-112Article in journal (Refereed)
    Abstract [en]

    We present a synchrotron radiation photoelectron spectroscopy study of the adsorption and photooxidation of trimethyl acetate (TMA) on TiO2(B)(001). The TiO2(B)(001) substrate was realized in the form of 2nm thick film on Au(111). The TMA species adopt the bidentate bonding configuration, as expected for carboxylic acids on TiO2, but cannot coordinate to all surface Ti ions due to steric hindrance. The proposed arrangement of the TMA species thus allows for the formation of an overlayer with a (2 x 1) periodicity. The thermal stability is found to be comparable to that on rutile (110) although the results indicate differences in the threshold for the TMA+H -> TMAA reaction. Photolysis using both ultraviolet (UV) light and soft x-ray synchrotron radiation (SR) was studied and compared to the reaction on the reduced ruffle (110) surface. A kinetic analysis suggests that the photoreaction rate for TMA on the TiO2(B) thin film is initially two times faster than that on the reduced rutile TiO2(110) surface. The higher activity of the TiO2(B) film is assigned to a reduced influence from surplus electrons associated with reduced Ti species, thereby decreasing the probability for hole-annihilation at high TMA coverage.

  • 14. Schaefer, A.
    et al.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Walle, L. E.
    Farstad, M. H.
    Wichmann, A.
    Baeumer, M.
    Borg, A.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Controlled modification of nanoporous gold: Chemical vapor deposition of TiO2 in ultrahigh vacuum2013In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 282, p. 439-443Article in journal (Refereed)
    Abstract [en]

    TiO2 has been deposited in the first 400 nm of a nanoporous gold (NPG) structure using metal organic chemical vapor deposition with titanium-tetraisopropoxide as single source precursor in ultra high vacuum. The NPG has been pretreated by ozone to clean and stabilize the structure for deposition. The deposited oxide stabilizes the porous structure, otherwise prone to coarsening at elevated temperatures, up to 300 degrees C. The study combines the controlled sample preparation with a functional test of the prepared catalyst under real conditions in a continuous gas flow reactor. The catalytic activity of the loaded NPG at 60 degrees C for CO oxidation is found to be superior to unloaded as-prepared NPG.

  • 15.
    Schaefer, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Wittstock, A.
    Walle, L. E.
    Borg, A.
    Baeumer, M.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Toward Controlled Modification of Nanoporous Gold: A Detailed Surface Science Study on Cleaning and Oxidation2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 7, p. 4564-4571Article in journal (Refereed)
    Abstract [en]

    Nanostructured metals and especially unsupported nanoporous gold (np-Au) have attracted considerable attention in a variety of fields because of their special surface chemical properties. For applications in catalysis and sensorics, the oxidation, of the metal and the availability of oxygen at the very surface are crucial and also are capable of altering structural properties. In this article, we will discuss the state of the np-Au surface after annealing in vacuum. We shed light on the nature of Au-oxide obtained after cleaning the surface from carbon impurities with atomic oxygen provided by ozone decomposition, and we consider the effect of this procedure on silver residues. The results provide new insight into possible oxide species at the np-Au surface and represent a vital step toward controlled modification of the np-Au surface in the future.

  • 16. Walle, L. E.
    et al.
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Borg, A.
    Uvdal, P.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Competing water dissociation channels on rutile TiO2(110)2014In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 621, p. 77-81Article in journal (Refereed)
    Abstract [en]

    The interplay between two different water dissociation channels on rutile TiO2(110) was studied with the use of synchrotron radiation photoelectron spectroscopy. It was found that water dissociation at oxygen vacancies competes with water dissociation on defect-free regions such that one vacancy assisted dissociation event cancels one dissociation event on defect-free regions. The quenching affects the thermally most stable dissociated species that form at low coverage on the defect free surface but does not affect the stability of molecular water. As a result, molecular adsorption becomes favored at low coverage on a surface where all vacancies have been hydroxylated. The presence of competitive dissociation channels rationalizes the difficulties in identifying dissociated species on defect-free regions in previous studies.

  • 17.
    Walle, Lars Erik
    et al.
    Norwegian University of Science and Technology (NTNU).
    Ragazzon, Davide
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Borg, Anne
    Norwegian University of Science and Technology (NTNU).
    Uvdal, Per
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Photoemission studies of water dissociation on rutile TiO2(110): Aspects on experimental procedures and the influence of steps2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 303, p. 245-249Article in journal (Refereed)
    Abstract [en]

    The composition of the first water layer on the stoichiometric rutile TiO2 (1 1 0) surface was studied with the use of synchrotron radiation photoelectron spectroscopy. The same H2O–OH balance was reached using different preparation procedures and there was no difference between H2O and D2O. On this basis, we rule out the possibility that the partially dissociated layer is an artifact caused by photon irradiation during measurements. Pre-deposition of Au at room temperature, primarily decorating step edges [e.g. S.A. Tenney et al. J. Phys. Chem. C 115 (2011) 11112] decreases the water uptake but does not change the relative amount that dissociates. This implies that the observed H2O–OH balance is not controlled by dissociation at steps and subsequent out-diffusion of hydrogens on the terraces. That is, the formation of a partially dissociated water layer is an inherent property of stoichiometric terraces.

1 - 17 of 17
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