Berlin 2005 – wissenschaftliches Programm

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O: Oberflächenphysik

O 27: Phasenüberg
änge

O 27.2: Vortrag

Samstag, 5. März 2005, 15:15–15:30, TU EB107

Reversible surface phase transitions between quasicrystalline modifications — •K. J. Franke^1,2, W. Theis¹, P. Kury³, M. Horn-von Hoegen³, P. Gille⁴, and K. H. Rieder¹ — ¹Inst. f. Experimentalphysik, FU Berlin — ²IPN, EPFL, Lausanne, Switzerland — ³Inst. f. Experimentalphysik, Uni Essen — ⁴Dept. f. Geo- und Umweltwiss., LMU, München

Due to the complexity of quasicrystalline structures and their derivation from periodic lattices in higher dimensional space, mechanisms such as phason flips, which are nonexistent in periodic crystals, play a key role in transitions between quasicrystalline phases. Decagonal Al_72.3Ni_9.5Co_18.2 exists in three different modifications between 30 ^∘C and 850 ^∘C. It therefore provides the opportunity to study the effects of phase transitions on the surface. By using low-energy electron microscopy (LEEM), rough and smooth morphologies have been observed on the nanometer scale for all three low-index surfaces at temperatures below and above 650 ^∘C, respectively. The transition between the medium and high temperature modification at 730 ^∘C leads to a structural change at the surfaces. Both surface phase transitions and their relation to the respective bulk transitions will be discussed.