G. Thornton

University College London, Londinium, England, United Kingdom

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Publications (309)799.08 Total impact

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    ABSTRACT: Water on TiO2(110) is the most widely studied water-oxide interface, yet questions about water dissociation and hydrogen bonding are controversial. Here we report density-functional theory simulations which show that water does not dissociate at the coverages examined. The aqueous film is layered, with slow moving molecules in the contact layer and fast moving molecules in a second layer, revealing strongly inhomogeneous dynamics of the interfacial water. Hydrogen bonding between the first and second layers is observed as is the exchange of water molecules. These results help to resolve a number of controversies pertaining to the molecular scale behavior of water on TiO2 and provide insight in to the structure and dynamics of water-solid interfaces by, e.g., demonstrating that water dynamics can vary on the Angström length scale and that the presence of second layer water molecules can cause those in the first layer to reorient.
    Physical review. B, Condensed matter 01/2010; 82(16). · 3.66 Impact Factor
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    ABSTRACT: Low-energy electron-diffraction and surface x-ray diffraction data acquired from TiO2(110)(1×1) are reanalyzed to confirm the integrity of the previously reported optimized geometries. This work is performed in response to ab initio density-functional theory calculations that suggest that the atomic displacements determined from low-energy electron-diffraction measurements may be compromised by the limited number of optimized atom positions. Performing structural optimizations as a function of depth into the selvedge, this present study validates the previous experimental structure determinations.
    Physical Review B 01/2010; 81(15). · 3.66 Impact Factor
  • B. G. Daniels, O. Bikondoa, G. Thornton
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    ABSTRACT: Surface X-ray diffraction has been used to investigate the structure of TiO2(1 1 0)(3 × 1)–S. In concert with existing STM and photoemission data it is shown that on formation of a (3 × 1)–S overlayer, sulphur adsorbs in a position bridging 6-fold titanium atoms, and all bridging oxygens are lost. Sulphur adsorption gives rise to significant restructuring of the substrate, detected as deep as the fourth layer of the selvedge. The replacement of a bridging oxygen atom with sulphur gives rise to a significant motion of 6-fold co-ordinated titanium atoms away from the adsorbate, along with a concomitant rumpling of the second substrate layer.
    Surface Science 07/2009; 603:2015-2020. · 1.87 Impact Factor
  • C. L. Pang, G. Thornton
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    ABSTRACT: Metal oxides have considerable potential as insulating supports for nanoscale electronic devices. One of the key attributes of metal oxide surfaces is their capacity to be modified by electron beams and scanning probe tips. Such modifications can involve the creation of O vacancies or an area of a different reconstruction, which in principle can act as anchoring points or templates for molecules or metal interconnects. In this Prospective we describe previous attempts at well-defined modification in order to illustrate this potential.
    Surface Science 01/2009; 603(22):3255-3261. · 1.87 Impact Factor
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    ABSTRACT: Palladium nanoparticles supported on rutile TiO(2)(110)-1 x 1 have been studied using the complementary techniques of scanning tunneling microscopy and X-ray photoemission electron microscopy. Two distinct types of palladium nanoparticles are observed, namely long nanowires up to 1000 nm long, and smaller dotlike features with diameters ranging from 80-160 nm. X-ray photoemission electron microscopy reveals that the nanoparticles are composed of metallic palladium, separated by the bare TiO(2)(110) surface.
    Nano Letters 01/2009; 9(1):155-9. · 13.03 Impact Factor
  • Chi Lun Pang, Robert Lindsay, Geoff Thornton
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    ABSTRACT: Understanding the surface chemistry of TiO2 is key to the development and optimisation of many technologies, such as solar power, catalysis, gas sensing, medical implantation, and corrosion protection. In order to address this, considerable research effort has been directed at model single crystal surfaces of TiO2. Particular attention has been given to the rutile TiO2(110) surface because it is the most stable face of TiO2. In this critical review, we discuss the chemical reactivity of TiO2(110), focusing in detail on four molecules/classes of molecules. The selected molecules are water, oxygen, carboxylic acids, and alcohols-all of which have importance not only to industry but also in nature (173 references).
    Chemical Society Reviews 11/2008; 37(10):2328-53. · 24.89 Impact Factor
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    ABSTRACT: Surface x-ray diffraction has been employed to elucidate the surface structure of the (011)-(2 x 1) termination of rutile TiO2. The data are inconsistent with previously proposed structures. Instead, an entirely unanticipated geometry emerges from the structure determination, which is terminated by zigzag rows of twofold coordinated oxygen atoms asymmetrically bonded to fivefold titanium atoms. The energetic stability of this structure is demonstrated by ab initio total energy calculations.
    Physical Review Letters 11/2008; 101(18):185501. · 7.73 Impact Factor
  • Chi Lun Pang, Robert Lindsay, Geoff Thornton
    ChemInform 01/2008; 39(51).
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    Journal of Physical Chemistry C - J PHYS CHEM C. 01/2008; 112(29):10918-10922.
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    ABSTRACT: Reduced phases of ultrathin rutile TiO(2)(110) grown on Ni(110) have been characterized with scanning tunneling microscopy and low-energy electron diffraction. Areas of 1 x 2 reconstruction are observed as well as {132} and {121} families of crystallographic shear planes. These phases are assigned by comparison with analogous phases on native rutile TiO(2)(110).
    ACS Nano 01/2008; 1(5):409-14. · 12.03 Impact Factor
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    ABSTRACT: The reaction of Fe3O4(1 1 1) with water vapour has been studied with scanning tunnelling microscopy (STM) and with X-ray and UV-photoemission as a function of water partial pressure and temperature. The photoemission results point to dissociation to form surface hydroxyls at a partial pressure of 10−6 mbar H2O and a substrate temperature of about 200 K. At 298 K it is known that dissociation occurs at around 10−3 mbar [Kendelewicz et al., Surf. Sci. 453 (2000) 32]. This difference suggests that an intermolecular mechanism of dissociation is involved. It also suggests that the pressure dependence arises from a coverage term rather than differences in the Gibbs Free Energies of the oxide and hydroxide, as previously proposed. The STM results indicate that dissociation takes place on a termination of Fe3O4(1 1 1) thought to contain a 1/4 monolayer (ML) of Fe3+ ions on top of a close-packed oxygen monolayer.
    Surface Science 01/2008; · 1.87 Impact Factor
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    ABSTRACT: The structure of an ordered (2x1) overlayer of formate ([HCOO]-) on rutile TiO2(110)(1x1) has been elucidated using quantitative low energy electron diffraction. In agreement with previous work, it is concluded that the formate moiety binds to the surface through both of its oxygens to two adjacent five-fold surface titanium atoms, so that its molecular plane is aligned with the [001] azimuth, i.e. it lies parallel to the rows of bridging oxygens. Most notably, the determined structure is essentially identical to that derived in a recent photoelectron diffraction study of the same system.
    Journal of Physical Chemistry C - J PHYS CHEM C. 01/2008; 112(36):14154-14157.
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    The Journal of Physical Chemistry C 01/2008; 112(29):10918-10922. · 4.84 Impact Factor
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    ABSTRACT: Metal supported oxide nanostructures are discussed within the framework of the “inverse model catalyst” concept. We show that oxide nanostructures on metal surfaces may be regarded as artificial oxide materials, which display novel properties as compared to bulk oxide compounds and are stabilised by interfacial interactions and two-dimensional confinement effects. This is illustrated for prototypical examples of vanadium oxide overlayers on Rh(111) and Pd(111) surfaces. Structure and morphological changes of the oxide phase on V-oxide/Rh and V-oxide/Pd inverse catalyst surfaces are discussed, and the mass transport problem in catalyst systems during oxidation-reduction cycles is addressed. We demonstrate that the diffusion of oxide cluster over the metal surface provides a effective means of mass transport. The role of metal-oxide interface in determining the oxide nanolayer structure on particular substrate surfaces is investigated, and interfacial chemistry and interfacial strain effects are identified as important parameters.
    Topics in Catalysis 08/2007; 46(1):137-149. · 2.61 Impact Factor
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    ABSTRACT: X-ray photoelectron spectroscopy (XPS) has been used to investigate the stoichiometry of CeO2-x(111) ultrathin films grown on Rh(111), as well as the modification of the average Ce oxidation state by Pd and CO at room temperature. The stoichiometry of three-layer CeO2-x(111) has been varied between CeO1.91 and CeO1.61 by altering the oxygen pressure during Ce deposition. Pd deposition induces a change in the Ce oxidation state that is highly dependent on the initial stoichiometry of the CeO2-x films. The difference in behavior of CeO2-x thin films with different oxidation states is ascribed to the presence of a Ce2O3(0001) termination of the more reduced thin films. CO adsorbs only in the presence of Pd, independent of the stoichiometry of the original film, without changing the oxidation state of the CeO2-x thin film.
    Journal of Physical Chemistry C - J PHYS CHEM C. 08/2007; 111(38).
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    ABSTRACT: The electronic structure of cobalt nanocrystals suspended in liquid as a function of size has been investigated using in situ X-ray absorption and emission spectroscopy. A sharp absorption peak associated with the ligand molecules is found that increases in intensity upon reducing the nanocrystal size. X-ray Raman features due to d-d and to charge-transfer excitations of ligand molecules are identified. The study reveals the local symmetry of the surface of epsilon-Co phase nanocrystals, which originates from a dynamic interaction between Co nanocrystals and surfactant + solvent molecules.
    NANO LETTERS. 07/2007; 7(7):1919-1922.
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    ABSTRACT: Surface x-ray diffraction has been employed to elucidate the surface structure of TiO2(110)(1×1). The atomic coordinates emerging from this study are in excellent agreement with those derived in other recent quantitative structure determinations of this surface. Most importantly, debate over the relaxation of the surface bridging oxygen has been resolved. In a previous surface x-ray diffraction study, it was concluded that this atom relaxes toward the bulk by 0.27±0.08 Å, whereas in this present work we determined this displacement to be 0.10±0.04 Å away from the bulk, which is in accord with the results of other experimental techniques.
    Physical Review B 06/2007; 75(24). · 3.66 Impact Factor
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    ABSTRACT: Soft X-ray photoelectron spectroscopy (SXPS) and X-ray absorption near-edge structure (XANES) have been combined with low-energy electron diffraction (LEED) to examine the growth of titanium dioxide thin films on Ni(110). Depending on the initial titanium coverage, the formation of two different films is observed, a quasi-hexagonal phase and a film with rutile (110) rods. Spectroscopy (SXPS and XANES) results indicate that all films consist of fully oxidized titanium. Furthermore, the reactivity of the higher coverage phase, consisting partly of rutile TiO2(110), was investigated after exposure to molecular water at 190 K. The formation of molecular water and hydroxyls was observed for low-pressure exposure (less than 10-7 mbar). High-pressure exposure (on the order of 10-6 mbar) resulted in hydroxylation of the thin film, which was found to be reversible upon annealing.
    Journal of Physical Chemistry C - J PHYS CHEM C. 05/2007; 111(21).
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    ABSTRACT: Using density functional and STM theory we model the images of TiO2(1 1 0), its defects, molecularly adsorbed water, its recently suggested pseudo-dissociated precursor and final dissociation product. The simulated STM images and the corresponding line scans agree with the available experimental data: oxygen vacancies are imaged as smaller protrusions than unpaired or paired hydroxyl groups. Finally, we obtain simulated images of undissociated and pseudo-dissociated water molecules. These simulations are discussed in view of their appearance in the experiments.
    Chemical Physics Letters 03/2007; 437(s 1–3):73–78. · 2.15 Impact Factor
  • A J Limb, O Bikondoa, C A Muryn, Geoff Thornton
    Angewandte Chemie International Edition 02/2007; 46(4):549-52. · 11.34 Impact Factor

Publication Stats

2k Citations
799.08 Total Impact Points

Institutions

  • 2004–2014
    • University College London
      • • London Centre for Nanotechnology
      • • Department of Chemistry
      Londinium, England, United Kingdom
  • 2008–2012
    • London Centre for Nanotechnology
      Londinium, England, United Kingdom
    • Materials Science Institute of Barcelona
      Barcino, Catalonia, Spain
  • 1983–2012
    • The University of Manchester
      • School of Chemistry
      Manchester, England, United Kingdom
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
  • 1979–2001
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, CA, United States
    • CSU Mentor
      Long Beach, California, United States
  • 2000
    • Heinrich-Heine-Universität Düsseldorf
      • Institute of Experimental Physics of condensed materials
      Düsseldorf, North Rhine-Westphalia, Germany
  • 1998
    • Trinity College Dublin
      • School of Physics
      Dublin, Leinster, Ireland
  • 1992–1998
    • University of Liverpool
      • Surface Science Research Centre
      Liverpool, ENG, United Kingdom
  • 1991
    • University of Bath
      • Department of Physics
      Bath, ENG, United Kingdom
  • 1988
    • Trinity College
      Hartford, Connecticut, United States