G. Thornton

University College London, Londinium, England, United Kingdom

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Publications (347)1083.82 Total impact

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    ABSTRACT: Local defects present in CeO2−x films result in a mixture of Ce3+ and Ce4+ oxidation states. Previous studies of the Ce 3d region with XPS have shown that depositing metal nanoparticles on ceria films causes further reduction, with an increase in Ce3+ concentration. Here, we compare the use of XPS and resonant photoemission spectroscopy (RESPES) to estimate the concentration of Ce3+ and Ce4+ in CeO2−x films grown on Pt (111), and the variation of this concentration as a function of Pd deposition. Due to the nature of the electronic structure of CeO2−x, resonant peaks are observed for the 4d–4f transitions when the photon energy matches the resonant energy; (hν=121.0eV) for Ce3+ and (hν=124.5eV) for Ce4+. This results in two discrete resonant photoemission peaks in valence band spectra. The ratio of the difference of these peaks with off-resonance scans gives an indication of the relative contribution of Ce3+. Results from RESPES indicate reduction of CeO2−x on deposition of Pd, confirming earlier findings from XPS studies.
    Surface Science 06/2011; 605(11):1062-1066. DOI:10.1016/j.susc.2011.03.005 · 1.93 Impact Factor
  • Chi Lun Pang · Geoff Thornton
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    ABSTRACT: There has been an explosion of interest in metal oxide surfaces in the past decade. This reflects the technological importance of these surfaces in, for instance, catalysis and electronics, as well as the availability of techniques to make their study tractable. There still remains a problem in connection with the large and important class of oxides that are insulating. This prevents their study by a number of techniques, including STM. In principle, NC-AFM offers an alternative imaging tool for insulators. As a step towards this goal we have explored the use of NC-AFM in imaging surface reconstructions and metal growth on a number of oxide surfaces at atomic or close-to-atomic resolution. Most of these surfaces were chosen to have a sufficiently high conductivity to allow their characterisation using conventional methods.
    02/2011: pages 147-165;
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    ABSTRACT: We have used scanning tunneling microscopy (STM), noncontact atomic force microscopy (NC-AFM), low energy electron diffraction (LEED), and ab initio calculations to study adsorbates resulting from exposure of rutile TiO2(110)1 × 1 to methyl phosphonic acid (CH3P═O(OH)2). At low exposures, adsorbates appear on the 5-fold coordinated Ti (Ti5c) rows. As the coverage of adsorbates approaches 0.5 ML, STM images show an ordered 2 × 1 overlayer consistent with LEED. We propose that the phosphonic acid is deprotonated with the resulting phosphonate bridging across two adjacent Ti5c atoms in the [001] direction. This bridging conformation would lead to the observed 2 × 1 overlayer and is analogous to that found for a range of carboxylates adsorbed on TiO2(110).
    The Journal of Physical Chemistry C 10/2010; 114(40). DOI:10.1021/jp1018923 · 4.77 Impact Factor
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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 10/2010; 82(16). DOI:10.1103/PhysRevB.82.161415 · 3.66 Impact Factor
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    David C. Grinter · Roslinda Ithnin · Chi L. Pang · Geoff Thornton
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    ABSTRACT: Atomically resolved scanning tunnelling microscopy (STM) images have been obtained on ultrathin films of CeO2(111) supported on Pt(111). The ultrathin films were grown in two ways, by reactive deposition in an oxygen atmosphere and by postoxidation of Ce/Pt surface alloys. STM results are compared with previously reported high-temperature STM and noncontact atomic force microscopy (NC-AFM) images of the native CeO2(111) surface. The similarity between these images is striking and allows a number of defects and adsorbates in our ultrathin film to be assigned. Moreover, the similarity in structure between the native oxide and the ceria ultrathin film indicates that it is an excellent topographic mimic of the native oxide.
    The Journal of Physical Chemistry C 06/2010; 114(40). DOI:10.1021/jp102895k · 4.77 Impact Factor
  • C M Yim · C L Pang · G Thornton
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    ABSTRACT: A Reply to the Comment by S. Wendt et al.
    Physical Review Letters 06/2010; 104(25):259704. DOI:10.1103/PhysRevLett.104.259704 · 7.51 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 04/2010; 81(15). DOI:10.1103/PhysRevB.81.153404 · 3.74 Impact Factor
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    ABSTRACT: Oxygen vacancies on metal oxide surfaces have long been thought to play a key role in the surface chemistry. Such processes have been directly visualized in the case of the model photocatalyst surface TiO(2)(110) in reactions with water and molecular oxygen. These vacancies have been assumed to be neutral in calculations of the surface properties. However, by comparing experimental and simulated scanning tunneling microscopy images and spectra, we show that oxygen vacancies act as trapping centers and are negatively charged. We demonstrate that charging the defect significantly affects the reactivity by following the reaction of molecular oxygen with surface hydroxyl formed by water dissociation at the vacancies. Calculations with electronically charged hydroxyl favor a condensation reaction forming water and surface oxygen adatoms, in line with experimental observations. This contrasts with simulations using neutral hydroxyl where hydrogen peroxide is found to be the most stable product.
    Proceedings of the National Academy of Sciences 02/2010; 107(6):2391-6. DOI:10.1073/pnas.0911349107 · 9.67 Impact Factor
  • C M Yim · C L Pang · G Thornton
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    ABSTRACT: Scanning tunneling microscopy and photoemission spectroscopy have been used to determine the origin of the band-gap state in rutile TiO2(110). This state has long been attributed to oxygen vacancies (O{b} vac). However, recently an alternative origin has been suggested, namely, subsurface interstitial Ti species. Here, we use electron bombardment to vary the O{b} vac density while monitoring the band-gap state with photoemission spectroscopy. Our results show that O{b} vac make the dominant contribution to the photoemission peak and that its magnitude is directly proportional to the O{b} vac density.
    Physical Review Letters 01/2010; 104(3):036806. DOI:10.1103/PhysRevLett.104.036806 · 7.51 Impact Factor
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    ABSTRACT: We report a new method for introducing metal atoms into silicon wafers, using negligible thermal budget. Molecular thin films are irradiated with ultra-violet light releasing metal species into the semiconductor substrate. Secondary ion mass spectrometry and x-ray absorption spectroscopy show that Mn is incorporated into Si as an interstitial dopant. We propose that our method can form the basis of a generic low-cost, low-temperature technology that could lead to the creation of ordered dopant arrays.
    Nanotechnology 01/2010; 21(2):025304. DOI:10.1088/0957-4484/21/2/025304 · 3.82 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 11/2009; 603(22):3255-3261. DOI:10.1016/j.susc.2009.09.027 · 1.93 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(13):2015-2020. DOI:10.1016/j.susc.2009.03.021 · 1.93 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. DOI:10.1021/nl802703e · 13.59 Impact Factor
  • Chi Lun Pang · Robert Lindsay · Geoff Thornton
    ChemInform 12/2008; 39(51). DOI:10.1002/chin.200851226
  • 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. DOI:10.1039/b719085a · 33.38 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. DOI:10.1103/PhysRevLett.101.185501 · 7.51 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.
    The Journal of Physical Chemistry C 09/2008; 112(36):14154-14157. DOI:10.1021/jp804016d · 4.77 Impact Factor
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    ABSTRACT: Photoelectron spectroscopy and scanning tunneling microscopy have been used to investigate how the oxidation state of Ce in CeO2-x(111) ultrathin films is influenced by the presence of Pd nanoparticles. Pd induces an increase in the concentration of Ce3+ cations, which is interpreted as charge transfer from Pd to CeO2-x(111) on the basis of DFT+U calculations. Charge transfer from Pd to Ce4+ is found to be energetically favorable even for individual Pd adatoms. These results have implications for our understanding of the redox behavior of ceria-based model catalyst systems.
    The Journal of Physical Chemistry C 07/2008; 112(29):10918-10922. DOI:10.1021/jp8004103 · 4.77 Impact Factor
  • R. S. Cutting · C.A. Muryn · D. J. Vaughan · G. Thornton
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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 03/2008; 602(6-602):1155-1165. DOI:10.1016/j.susc.2008.01.012 · 1.93 Impact Factor
  • Anthoula C Papageorgiou · Chi L Pang · Qiao Chen · Geoff Thornton
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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. DOI:10.1021/nn700158s · 12.88 Impact Factor

Publication Stats

7k Citations
1,083.82 Total Impact Points


  • 2004–2014
    • University College London
      • • London Centre for Nanotechnology
      • • Department of Chemistry
      Londinium, England, United Kingdom
  • 1979–2013
    • University of California, Berkeley
      • • Department of Materials Science and Engineering
      • • Department of Chemistry
      Berkeley, California, United States
    • CSU Mentor
      • Department of Chemistry
      Long Beach, California, United States
  • 2010–2012
    • London Centre for Nanotechnology
      Londinium, England, United Kingdom
    • University of Vic
      Vic, Catalonia, Spain
  • 1983–2011
    • The University of Manchester
      • School of Chemistry
      Manchester, England, United Kingdom
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
  • 2009
    • Fritz Haber Institute of the Max Planck Society
      Berlín, Berlin, Germany
  • 2007
    • Graz University of Technology
      • Institute for Technical Informatics
      Gratz, Styria, Austria
  • 1992–1999
    • University of Liverpool
      • Surface Science Research Centre
      Liverpool, England, United Kingdom
  • 1998
    • The University of York
      • Department of Physics
      York, ENG, United Kingdom
  • 1993
    • University of Adelaide
      Tarndarnya, South Australia, Australia
  • 1988–1992
    • University of Michigan
      • Department of Physics
      Ann Arbor, MI, United States
  • 1987–1991
    • Boston University
      • Department of Physics
      Boston, Massachusetts, United States
  • 1989
    • Imperial College London
      Londinium, England, United Kingdom
    • University of Utah
      • Department of Physics and Astronomy
      Salt Lake City, Utah, United States
  • 1986
    • Trinity College Dublin
      Dublin, Leinster, Ireland