G. Thornton

University College London, Londinium, England, United Kingdom

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Publications (353)1103.18 Total impact

  • David C. Grinter · Geoff Thornton
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    ABSTRACT: IntroductionStructure Determination TechniquesSpectroscopic TechniquesSummary
    No preview · Article · Jan 2012
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    ABSTRACT: Scanning tunneling microscopy (STM) has been used to investigate the adsorption of benzoic acid on the rutile TiO2(110)(1 � 1) and the reconstructed TiO2(110)(1 � 2) surfaces. Benzoic acid binds to both surfaces dissociatively via a bridging geometry to two Ti5c sites. At a slightly elevated sample temperature during deposition onto the (110) (1 � 1) surface, a well-ordered (2�1) overlayer was formed at saturated benzoate coverage.On the reconstructed (110) (1 � 2) surface, benzoate was observed to adsorb between the (1 � 2) strands leading to a (2�2) superstructure at higher coverage. Elongation along the [110] direction in the STM images indicates a rotation of the benzene ring of 90� relative to the carboxylate group, which is reasonably explained by hydrogen bond interactions between terminating O-atoms on the surface and H-atoms of the ring.
    Full-text · Article · Dec 2011 · The Journal of Physical Chemistry C
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    ABSTRACT: We present a new generic method to synthesize nanostructured metal(II) oxide films on a substrate such as silicon. Vacuum ultraviolet (VUV) excimer lamps rupture metal–organic precursors, creating volatile organic fragments, while the metal species at the surface form oxides. X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) confirm that 172 nm VUV irradiation of manganese and copper phthalocyanines yields manganese(II) and copper(II) oxides, respectively. The morphology of the precursor film provides a template from which metal oxide nanoparticles are formed, which we demonstrate for particles with dimensions 40 × 40 × 10 nm3. Our procedure is both simple and flexible, with low thermal budget and potential for patterning.
    Full-text · Article · Jun 2011 · The Journal of Physical Chemistry C
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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.
    Full-text · Article · Jun 2011 · Surface Science
  • 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.
    No preview · Chapter · Feb 2011
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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).
    Full-text · Article · Oct 2010 · The Journal of Physical Chemistry C
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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.
    No preview · Article · Oct 2010 · Physical review. B, Condensed matter
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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.
    Full-text · Article · Jun 2010 · The Journal of Physical Chemistry C
  • C M Yim · C L Pang · G Thornton
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    ABSTRACT: A Reply to the Comment by S. Wendt et al.
    No preview · Article · Jun 2010 · Physical Review Letters
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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.
    Full-text · Article · Apr 2010 · Physical Review B
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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.
    Full-text · Article · Feb 2010 · Proceedings of the National Academy of Sciences
  • C.L. Pang · G. Thornton

    No preview · Article · Feb 2010
  • 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.
    No preview · Article · Jan 2010 · Physical Review Letters
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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.
    Full-text · Article · Jan 2010 · Nanotechnology
  • 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.
    No preview · Article · Nov 2009 · Surface Science
  • 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.
    No preview · Article · Jul 2009 · Surface Science
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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.
    Full-text · Article · Jan 2009 · Nano Letters
  • Chi Lun Pang · Robert Lindsay · Geoff Thornton

    No preview · Article · Dec 2008 · ChemInform
  • 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).
    No preview · Article · Nov 2008 · Chemical Society Reviews
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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.
    Full-text · Article · Nov 2008 · Physical Review Letters

Publication Stats

8k Citations
1,103.18 Total Impact Points


  • 2004-2015
    • 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
  • 1998
    • The University of York
      • Department of Physics
      York, ENG, United Kingdom
  • 1992-1997
    • University of Liverpool
      • Surface Science Research Centre
      Liverpool, England, United Kingdom
  • 1990-1993
    • University of Adelaide
      Tarndarnya, South Australia, Australia
  • 1987-1992
    • 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