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Séminaire de l’équipe « Oxydes en basses dimensions » - INSP

Surface structures of ultrathin TiOx and BaO films on Au (111) - Chen Wu - Vendredi 6 septembre 2013 à 10 h 30

Chen Wu, Department of Materials, University of Oxford
Vendredi 6 septembre 2013 à 10 h 30 - Barre 22-32 - Salle 407 - 4e étage

Following the discovery of enhanced catalytic properties of oxide supported nanoparticles of noble metals, especially Au, interactions between the two have become a focus in research [1-3]. The growth of oxides on Au(111) surfaces serves as an inverse model and provides insights into their interactions. Well-ordered TiOx and BaO layers were grown on -reconstructed Au(111) surfaces by Ti and Ba deposition and oxidation. Surface structures of these ultrathin oxide films were studied by scanning tunneling microscopy (STM) and auger electron spectroscopy (AES). In the growth of TiOx thin films on Au(111), three different structures were observed with increased amounts of Ti deposited [4]. The first structure occurs for Ti surface coverages of <0.5 monolayer (ML), and exhibits a -reconstructed structure resembling a honeycomb pattern. The second structure arises after depositing 0.5 ML - 1.8MLs of Ti and exhibits a pinwheel shape. The pinwheel structure forms a Moiré pattern. The third structure occurs for >0.5 ML Ti depositions and forms triangular shaped islands. Film growth continues via the coalescence of triangular islands with further increased Ti coverage. Auger electron spectroscopy (AES) indicates that the structures have different chemical compositions. For BaO ultrathin film growth on Au(111), coexistence of a honeycomb and a hexagonal periodicity were observed. Both structures lift the Au herringbone reconstruction [5]. Using the sub-monolayer TiOx structures on Au(111) as templates, new reconstructions were created following Ba deposition which were not observed when BaO was grown on Au directly. Atomic models are proposed for the observed structures and we demonstrate the possibility of creating novel epitaxial oxide structures on both metal substrates and other oxide templates.

References :
[1] Chen, M.S. and Goodman, D.W. Science, 2004, 306, 252-255.
[2] Overbury, S.H. ; Ortiz-Soto, L. ; Zhu, H.G. ; Lee, B. ; Amiridis, M.D. ; Dai, S. Catal. Lett., 2004, 95, 99-106.
[3] Zheng, N. and Stucky, G.D. J. Am. Chem. Soc., 2006, 128, 14278-14280.
[4] Wu, C. ; Marshall, M.S.J. and Castell, M.R. J. Phys. Chem. C, 2011, 115, 8643-8652. [5] Wu, C. and Castell, M.R. Surf. Sci. 2012, 606, 181-185.