Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 38: Struktur und Dynamik reiner Oberfl
ächen

O 38.2: Vortrag

Freitag, 28. März 2003, 11:30–11:45, FOE/ANOR

Stability of ordered CoAl (100) surface structures — •O. Wieckhorst, S. Müller, and K. Heinz — Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg Staudtstr. 7, 91058 Erlangen

For ideal bulk stoichiometry, the (100)-surface of B2-ordered Co-Al shows a termination by the Al-sublattice. However, a tiny surplus of Co-atoms in the bulk leads to the segregation of these so called anti-site atoms to the (100)-surface [1]. We applied density functional theory to study the structural behaviour of these Co anti-sites in the topmost layer of a CoAl(100) surface by calculating the surface formation energy for a number of ordered structures. The determination of the relative stability of surface structures with arbitrary anti-site concentrations demands the consideration of the chemical potentials. We found that a c( √2 × 3 √2 ) R45^∘ superstructure of the Co anti-sites in the top layer has the lowest energy for all possible subsurface compositions. The results are compared with the (100) surface of B2-ordered Ni-Al, which shows a similar behaviour (supported by DFG).

[1] V. Blum et al., Phys. Rev. Lett. 89 (2002) 266102