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O: Oberflächenphysik

O 11: Epitaxy and growth I

O 11.4: Vortrag

Montag, 27. März 2006, 15:45–16:00, WIL A317

Al-Enriched Surface Phases on NiAl(100) — •Roland Schurr, Andreas Klein, Lutz Hammer, and Klaus Heinz — Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, D-91058 Erlangen

The thermal evolution of Al-films evaporated on the cold NiAl(100) surface was studied by means of LEED, STM and AES. Deposition of several monolayers of Al at 100 K on clean NiAl(100) leads to rather flat but poorly ordered epitaxial films with (111) orientation. With annealing at about 500 K reordering occurs within the films leading to both pseudomorphic (100) grains and epitaxially aligned (111) oriented grains of pure Al as identified by comparison with single crystal LEED intensity spectra. With increasing temperature Al dissolves into the bulk leading to a sequence of different Al-rich surface phases of NiAl(100). At first a (√5×√5)R26.6^∘ phase at about 600 K appears, followed by a 1D-incommensurate superstructure at about 750 K. This can be tentatively ascribed to a transition state towards the then following structure, an Al-rich c(√2× 3√2)R45^∘ phase (="(3×3)diag"), which develops at 800 K. Further annealing eventually produces a (1×1) structure which corresponds to the (100) surface of stoichiometric NiAl. At even higher temperatures (>1150 K) Al starts to desorb from the surface leading to another "(3×3)diag" phase of the Ni-enriched surface known since earlier [1]. LEED intensity spectra taken from both "(3×3)diag" phases differ completely proving the existence of two distinct phases with the same periodicity. [1] D.R. Mullins and S.H. Overbury, Surf. Sci. 199 (1988) 141