P Krüger

Publications (6)16.18 Total impact

• Article: Intrinsic nature of the excess electron distribution at the TiO2(110) surface.

  P Krüger, J Jupille, S Bourgeois, B Domenichini, A Verdini, L Floreano, A Morgante
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  ABSTRACT: The gap state that appears upon reduction of TiO2 plays a key role in many of titania's interesting properties but its origin and spatial localization have remained unclear. In the present work, the TiO2(110) surface is reduced in a chemically controlled way by sodium adsorption. By means of resonant photoelectron diffraction, excess electrons are shown to be distributed mainly on subsurface Ti sites strikingly similar to the defective TiO2(110) surface, while any significant contribution from interstitial Ti ions is discarded. In agreement with first principles calculations, these findings demonstrate that the distribution of the band gap charge is an intrinsic property of TiO2(110), independent of the way excess electrons are produced.
  Physical Review Letters 03/2012; 108(12):126803. · 7.37 Impact Factor
• Article: Defect states at the TiO2(110) surface probed by resonant photoelectron diffraction.

  P Krüger, S Bourgeois, B Domenichini, H Magnan, D Chandesris, P Le Fèvre, A M Flank, J Jupille, L Floreano, A Cossaro, A Verdini, A Morgante
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  ABSTRACT: The charge distribution of the defect states at the reduced TiO(2)(110) surface is studied via a new method, the resonant photoelectron diffraction. The diffraction pattern from the defect state, excited at the Ti-2p-3d resonance, is analyzed in the forward scattering approach and on the basis of multiple scattering calculations. The defect charge is found to be shared by several surface and subsurface Ti sites with the dominant contribution on a specific subsurface site in agreement with density functional theory calculations.
  Physical Review Letters 03/2008; 100(5):055501. · 7.37 Impact Factor
• Article: Dynamics of molybdenum nano structure formation on the TiO2(110) surface: A kinetic Monte Carlo approach

  G. Le Saux, P. Krüger, B. Domenichini, L. Imhoff, S. Bourgeois
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  ABSTRACT: The rutile TiO2(1 1 0) surface is a highly anisotropic surface exhibiting “channels” delimited by oxygen rows. In previous experimental and theoretical DFT works we could identify the molybdenum adsorption sites. They are located inside the channels. Moreover, experimental studies have shown that during subsequent annealing after deposition, special molybdenum nano structures can be formed, especially two monolayer high pyramidal chains of atoms.In order to better understand the dynamics of nano structure formation, we present a kinetic Monte Carlo study on diffusion and adsorption of molybdenum atoms on a TiO2(1 1 0) surface. A quasi one-dimensional lattice gas model has been used which describes the possible adsorption sites of a Mo atom in a single channel of the surface. The atomic positions of a 1.5 monolayer thick Mo film formed of pyramidal chains define the lattice sites of the model. Thereby the formation of three-dimensional clusters could be studied. Here we have studied the cluster formation as a function of parameters that can be controlled in a growth experiment by physical vapor deposition: deposition and annealing temperature, flux and total amount of deposited Mo. Good qualitative agreement with recent experiments is obtained.
  Applied Surface Science.
• Article: Molybdenum thin film growth on a TiO2 (110) substrate

  P. Krüger, M. Petukhov, B. Domenichini, S. Bourgeois
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  ABSTRACT: We report a first principles study on the structure and energetics of thin films of molybdenum on a (1 1 0) surface of rutile TiO2. Mo films with 1 × 1 epitaxy in the coverage range between 0.5 and 2 monolayer are investigated. The most stable structures are those which maximize the number of Mo–Mo bonds. This leads to two-dimensional structures with zigzag Mo–Mo coordination for 1 monolayer coverage and three-dimensional structures with approximately body-centered cubic coordination for higher coverage. For a coverage up to 1.5 monolayers, the interface Mo atoms preferentially occupy the so-called upper hollow adsorption site with three Mo–O bonds.
  Journal of Molecular Structure THEOCHEM 903:67-72. · 1.44 Impact Factor
• Article: Field-induced tip–sample oxygen transfer in scanning tunneling microscopy on TiO2(110) (1×1)

  M. Petukhov, P. Krüger, B. Domenichini, S. Bourgeois
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  ABSTRACT: A study on the field-induced tip–surface oxygen transfer at room temperature and its influence on the tunneling conditions for stable STM imaging of the TiO2(1 1 0) (1 × 1) surface is reported. A simple model of field-induced transfer is applied to tungsten and platinum–iridium tips. The oxygen transition rates from the sample to the tip or from the tip to the sample depend on the oxygen desorption barriers formed at tunneling distance. For stable imaging the applied bias voltage has to balance the oxygen transfer probabilities in both directions. In the case of Pt/Ir tips, the tunneling conditions for images with clear evidence of bridging oxygen point defects have been established.
  Surface Science. 602(14):2558-2562.
• Article: Resonant photoelectron and photoelectron diffraction across the Fe L3 edge of Fe3O4

  H. Magnan, P. Le Fèvre, D. Chandesris, P. Krüger, S. Bourgeois, B. Domenichini, A. Verdini, L. Floreano, A. Morgante
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  ABSTRACT: We combined measurements of valence-band photoemission and valence-band photoelectron diffraction on Fe3O4 at the Fe 2p-3d resonance. The different structures in the valence band of magnetite due to the different sites of iron were identified experimentally. Specifically the structure near the Fermi level is unambiguously attributed only to octahedral Fe2+ sites (B-Fe2+). We showed that tuning the photon energy to the resonance of B-Fe2+, the whole valence band is dominated by signal coming from B sites of iron. Moreover this work shows how resonant photoelectron diffraction is a powerful tool for the study of mixed valence oxides.
  Phys. Rev. B. 81(8).