March 16, 2011 Wednesday 15:30
Mehmet Erbudak, Bogazici University and ETH Zurich
Formation of nanometer-size alumina islands

Abstract: Quasicrystals, a new form of matter, lack periodicity, yet exhibit a high degree of long-range orientational and quasiperiodic translational order contrary to ordinary crystals that possess a periodic arrangement of atoms. Owing to this fundamental difference, the epitaxial growth of matter on a quasicrystalline substrate is influenced by the structural mismatch at the interface and often leads to well-ordered and self-size-selected clusters with a lateral size of typically 3 – 5 nm [1]. The bulk of the icosahedral quasicrystalline alloy shows twofold, threefold, and fivefold symmetries. Upon oxygen exposure of an otherwise atomically clean fivefold-symmetry surface at 750 K, a 0.5-nm-thick aluminium oxide layer grows on the surface. Electron diffraction patterns show that the film consists of five distinct domains. Each domain is a few-nanometer large, has the sixfold symmetry of an hexagonal structure like for the alpha-alumina(111), and rotated azimuthally by 72 degrees with respect to others [2]. The same experiment with a threefold-symmetry surface shows that the clean surface is stable, yet oxygen exposure at high temperatures makes the surface completely facet. Triangular pyramids are formed exposing oxide-covered pentagonal surfaces [3]. As a result of faceting, the effective surface area is significantly enlarged, relevant for catalysis. Thermodynamic aspects and kinectic considerations of faceting will be reviewed.
[1] T. Fluckiger et al., Nano Letters 3, 1717 (2003).
[2] S. Burkardt, M. Erbudak, Phys.Rev. B 81, 085417 (2010).
[3] S. Burkardt, M. Erbudak, Surf. Sci. 603, 2248 (2009).


Biography:
64 Abitur at the German High School
68 BS, Electrical Engineering, Robert College
72 MPhil, MSc, and PhD, Applied Science, Yale University, New Haven
72-73 Research Associate at Cambridge Electron Accelerator, Harvard University and MIT
75 Principal assistant at the Laboratory for Solid State Physics, ETH
79 Doçent at the Physics Dept., Middle East Technical University
84 Faculty member at the Physics Department of ETHZ
05 Adjunct professor at the Boğaziçi University