Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 12: Postersitzung (Struktur und Dynamik reiner Oberfl
ächen, Grenzfl
äche fest-flüssig, Nanostrukturen, Teilchen und Cluster, Halbleiteroberfl
ächen und Grenzfl
ächen, Zeitaufgelöste Spektroskopie, Rastersondentechniken, Methodisches)
O 12.44: Poster
Montag, 24. März 2003, 18:00–21:00, P1
Formation mechanisms of decagonal and orthorhombic layers on icosahedral quasicrystals — •Mariya Yurechko, Philipp Ebert, Benjamin Grushko, and Knut Urban — Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich, Germany
The appearance of crystalline or decagonal quasiperiodic layers on five-fold surfaces of the single icosahedral Al-Pd-Mn quasicrystals after annealing was observed by different groups using STM and LEED. By a precision determination of the relevant parts of the ternary phase diagram we show that the formation of orthorhombic and decagonal surface layers is governed by two different driving forces distinguished by the annealing temperature: (a) For low annealing temperatures below the evaporation onset, the system moves to its phase equilibrium, which is outside of the single phase area for the compositions obtained during growth of icosahedral Al-Pd-Mn quasicrystals. This leads to phase separation and formation of the D and H (also called T) phases on the surface. (b) For high annealing temperatures the surface of icosahedral Al-Pd-Mn quasicrystal moves toward a Pd-enriched and Mn-depleted composition due to preferential evaporation. Eventually the surface evolves into the δ phase.