Radosław Włodarczyk

Humboldt-Universität zu Berlin, Berlín, Berlin, Germany

Are you Radosław Włodarczyk?

Claim your profile

Publications (16)64.49 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Ultrathin Fe-doped silicate films were prepared on a Ru(0001) surface and, as a function of the Fe/Si ratio, structurally characterized by low-energy electron diffraction, X-ray photoelectron spectroscopy, infrared reflection-absorption spectroscopy, and scanning tunneling microscopy. Density functional theory (DFT) was used to identify the atomic structure. The results show that uniform substitution of Si by Fe in the silicate bilayer frame is thermodynamically unfavorable: the film segregates into a pure silicate and an Fe-silicate phase. The DFT calculations reveal that the Fe-silicate film with an Fe/Si = 1:1 ratio consists of a monolayer of [SiO4] tetrahedra on top of an iron oxide monolayer. As such, it closely resembles the structure of the clay mineral nontronite, a representative of the Fe-rich smectites. Furthermore, the DFT calculations predict formation of bridging Fe-O-Ru bonds between the Fe-silicate film and the Ru substrate accompanied by charge transfer from the metal substrate to the film, so that iron is in the oxidation state +III as in nontronite.
    Journal of the American Chemical Society 12/2013; · 10.68 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: The atomic structure of thin silica films grown over a Ru(0001) substrate was studied by X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, low energy electron diffraction, helium ion scattering spectroscopy, CO temperature programmed desorption, and scanning tunneling microscopy in combination with density functional theory calculations. The films were prepared by Si vapor deposition and subsequent oxidation at high temperatures. The silica film first grows as a monolayer of corner-sharing [SiO(4)] tetrahedra strongly bonded to the Ru(0001) surface through the Si-O-Ru linkages. At increasing amounts of Si, the film forms a bilayer of corner-sharing [SiO(4)] tetrahedra which is weakly bonded to Ru(0001). The bilayer film can be grown in either the crystalline or vitreous state, or both coexisting. Further increasing the film thickness leads to the formation of vitreous silica exhibiting a three-dimensional network of [SiO(4)]. The principal structure of the films can be monitored by infrared spectroscopy, as each structure shows a characteristic vibrational band, i.e., ∼1135 cm(-1) for a monolayer film, ∼1300 cm(-1) for the bilayer structures, and ∼1250 cm(-1) for the bulk-like vitreous silica.
    Physical Chemistry Chemical Physics 07/2012; 14(32):11344-51. · 3.83 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Flat pore models: Thin, well-defined aluminosilicate films with tetrahedral [SiO(4/2) ] and [AlO(4/2) (-) ] building blocks that are weakly bound to an underlying metal support contain highly acidic bridging OH species, which exhibit H-D exchange (see picture; Si yellow, O red, Al gray, C black, H white). These films are a model system for surface-science studies of the inner walls of zeolite pores.
    Angewandte Chemie International Edition 04/2012; 51(24):6005-8. · 13.73 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Fast neutral atoms and molecules with energies from 0.4 up to 3keV are scattered under a grazing angle of incidence from a clean and flat MgO(001) surface. For “axial surface channeling” conditions, we observe defined diffraction patterns in the angular intensity distributions for scattered 3He and 4He atoms as well as H2 molecules. The diffraction patterns are analyzed in terms of semiclassical trajectory calculations making use of projectile surface interaction potentials derived from density functional theory and from pair potentials calculated from Hartree–Fock wave functions. From comparison of measured and calculated diffraction patterns we deduced the rumpling of the topmost surface layer of MgO(001), i.e. an inward shift of Mg2+ ions with respect to O2− ions, of (0.03±0.03)Å.
    Surface Science 02/2012; · 1.84 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: A combination of density functional theory calculations and photoelectron spectroscopy provides new insights into the atomistic picture of ultrathin silica films grown on Ru(0001). The silica film features a double-layer silicate sheet formed by corner-sharing [SiO4] tetrahedra and is weakly bound to the Ru(0001) substrate. This allows oxygen atoms to reversibly adsorb directly on the metal surface underneath the silica film. We demonstrate that the amount of adsorbed oxygen can be reversibly varied by vacuum annealing and oxidation, which in turn result in gradual changes of the silica/Ru electronic states. This finding opens the possibility for tuning the electronic properties of oxide/metal systems without altering the thickness or the structure of an oxide overlayer.
    Physical review. B, Condensed matter 02/2012;
  • Angew. Chem. 01/2012; 124(24):6107-6111.
  • [show abstract] [hide abstract]
    ABSTRACT: The hydrodesulfurization (HDS) of the refractory compound 4,6-dimethyldibenzothiophene (DMDBT) normally proceeds through a hydrogenation pathway that removes the planarity of the ring system and makes the hindered sulfur atom more accessible to the desulfurization centers. In this study, a highly active dispersed bimetallic NiFeP catalyst is found to have high selectivity for a direct desulfurization pathway, which does not require prior hydrogenation. The compound has equal numbers of Ni and Fe atoms which extended X-ray absorption fine structure analysis indicates are distributed randomly in the hexagonal Fe2P structure, with just a slight enrichment of Fe on the surface. This is supported by density functional theory calculations. The remarkable properties of the catalyst are ascribed to a ligand effect of Fe on the active Ni atoms.
    Journal of Catalysis - J CATAL. 01/2012;
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: Clear as glass: The atomic structure of a metal-supported vitreous thin silica film was resolved using low-temperature scanning tunneling microscopy (STM). Based on the STM image, a model was constructed and the atomic arrangement of the thin silica glass determined (see picture). The total pair correlation function of the structural model shows good agreement with diffraction experiments performed on vitreous silica.
    Angewandte Chemie International Edition 11/2011; 51(2):404-7. · 13.73 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: This work demonstrates that the most stable structures of even small gas-phase aggregates of cerium oxide with 2-5 cerium atoms show structural motifs reminiscent of the bulk ceria. This is different from main group and transition metal oxide clusters, which often display structural features that are distinctly different from the bulk structure. The structures of Ce(2)O(2)(+), Ce(3)O(4)(+), and (CeO(2))(m)CeO(+) clusters (m = 0-4) are unambiguously determined by a combination of global structure optimizations at the density functional theory level and infrared vibrational predissociation spectroscopy of the cluster-rare gas atom complexes. The structures of Ce(2)O(2)(+) and Ce(2)O(3)(+) exhibit a Ce-O-Ce-O four-membered ring with characteristic absorptions between 430 and 680 cm(-1). Larger clusters have common structural features containing fused Ce-O-Ce-O four-membered rings which lead to intense absorption bands at around 500 and 650 cm(-1). Clusters containing a terminal Ce=O bond show a characteristic absorption band between 800 and 840 cm(-1). For some cluster sizes multiple isomers are observed. Their individual infrared signatures are identified by tuning their relative population through the choice of He, Ne or Ar messenger atoms. The present results allow us to benchmark different density functionals which yield different degrees of localization of unpaired electrons in Ce 4f states.
    Physical Chemistry Chemical Physics 11/2011; 13(43):19393-400. · 3.83 Impact Factor
  • M. Busch, K. Gärtner, R. Włodarczyk, M. Sierka, J. Sauer
    [show abstract] [hide abstract]
    ABSTRACT: Fast He, Ne, Ar, and N atoms with projectile energies from 1 up to 60 keV are scattered under grazing polar angles of incidence from a flat and clean KCl(001) surface. For the scattering along low-index directions (axial surface channeling) we observe pronounced peaks in the angular distributions of scattered projectiles which can be attributed to rainbow scattering. From classical trajectory calculations based on universal and individual pair as well as density functional theory (DFT) potentials, we obtained corresponding rainbow angles for comparison with the experimental data. Fair agreement was found for DFT and individual pair potentials calculated from Hartree-Fock wave functions.
    Physical review. B, Condensed matter 09/2011; 84(12).
  • [show abstract] [hide abstract]
    ABSTRACT: The local structure of the hydroxyl species on the rutile TiO2(110) surface has been determined both experimentally and computationally. The experimental study exploited chemical state–specific O 1s scanned-energy mode photoelectron diffraction from a surface exposed to atomic hydrogen, while density functional theory calculations were used to provide complementary information. As expected on the basis of previous studies, the bridging O atoms of the clean surface are hydroxylated, but this causes surprisingly small changes in the surrounding surface relaxation. Experiment and theory are in good agreement regarding the magnitude of these atomic movements. Specifically, the Ti-OOH surface bond is significantly longer (by 0.10–0.15 Å) than that of Ti-Obridging bonds on the clean surface.
    Physical Review B 09/2011; 84(11). · 3.77 Impact Factor
  • Radosław Włodarczyk, Marek Sierka, Karolina Kwapień, Joachim Sauer
    [show abstract] [hide abstract]
    ABSTRACT: Global ab initio structure optimizations combined with statistical thermodynamics and experimental studies reveal atomic structures of the ordered water monolayer on the MgO(001) surface. Calculations based on density functional theory predict the existence of two stable surface structures: a c(4×2) structure containing ten water molecules per unit cell stable at low temperature and a p(3×2) structure containing six water molecules per unit cell stable at high temperature. Both structures feature four surface hydroxyl groups resulting from the dissociation of two water molecules per surface cell. The calculated properties of the two structures are in agreement with a multitude of experimental data, including infrared reflection absorption, sum frequency generation and X-ray photoelectron spectroscopy. Comparison of calculated and experimental vibrational spectra allows for assignment of the observed vibrational modes.
    03/2011;
  • [show abstract] [hide abstract]
    ABSTRACT: Thin SiO₂ films were grown on a Ru(0001) single crystal and studied by photoelectron spectroscopy, infrared spectroscopy and scanning probe microscopy. The experimental results in combination with density functional theory calculations provide compelling evidence for the formation of crystalline, double-layer sheet silica weakly bound to a metal substrate.
    Physical Review Letters 10/2010; 105(14):146104. · 7.94 Impact Factor
  • Grzegorz Mazur, Marcin Makowski, Radosław Włodarczyk, Yuriko Aoki
    [show abstract] [hide abstract]
    ABSTRACT: Dressed TDDFT method is applied to the calculations of low-lying electronic excited states of selected linear polyenes and α,ω-diphenylopolyenes. It is shown that proper accounting for doubly excited configurations is necessary to correctly describe excitation energies and geometrical structure of the 21Ag state in these systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
    International Journal of Quantum Chemistry 09/2010; 111(4):819 - 825. · 1.31 Impact Factor
  • J. Seifert, R. Włodarczyk, J. Sauer, M. Sierka
    [show abstract] [hide abstract]
    ABSTRACT: He atoms and H2 molecules with energies of 2 keV are scattered under grazing angles of incidence ranging from 0.2° to 1.8° from the surface of a monolayer silica film grown on a Mo(112). We observe for scattering along low indexed atomic strings in the topmost surface layer pronounced diffraction pattern owing to diffraction effects for the elastically scattered projectiles. The diffraction patterns are analyzed in terms of semiclassical trajectory calculations making use of interaction potentials derived from density-functional theory. We find good agreement with the experiments, for a two-dimensional [Si-O-Si] network structural model for the ultrathin silica film.
    Physical review. B, Condensed matter 07/2010; 82(3).
  • Grzegorz Mazur, Radosław Włodarczyk
    [show abstract] [hide abstract]
    ABSTRACT: Dressed Time-Dependent Density Functional Theory (Maitra et al., J Chem Phys 2004, 120, 5932) is applied to selected linear polyenes. Limits of validity of the approximation are briefly discussed. The implementation strategy is described. Results for the 2(1)B(u) and 2(1)A(g) states of selected linear polyenes are presented and compared with accessible experimental and theoretical results.
    Journal of Computational Chemistry 09/2008; 30(5):811-7. · 3.84 Impact Factor

Publication Stats

30 Citations
738 Views
64.49 Total Impact Points

Institutions

  • 2010–2013
    • Humboldt-Universität zu Berlin
      • Department of Chemistry
      Berlín, Berlin, Germany
  • 2012
    • Fritz Haber Institute of the Max Planck Society
      • Department of Physical Chemistry
      Berlin, Land Berlin, Germany
  • 2011–2012
    • Max Planck Society
      München, Bavaria, Germany
  • 2008
    • Jagiellonian University
      • Department of Computational Methods in Chemistry
      Kraków, Lesser Poland Voivodeship, Poland