Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 24: Postersitzung (Epitaxie und Wachstum, Oxide und Isolatoren, Elektronische Struktur, Oberfl
ächenreaktionen, Adsorption an Oberfl
ächen, Organische Dünnschichten)

O 24.35: Poster

Mittwoch, 26. März 2003, 14:30–17:30, P1

Ab-initio study of the geometric and electronic structure of relaxed FeSi(CsCl) surfaces — •Michael Straß, Michel Bockstedte, and Oleg Pankratov — Lehrstuhl für theor. Festkörperphysik, UniversitätErlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen

The experimental investigation of the chemical termination of thin films of iron silicides with CsCl-type structure epitaxially grown on Si(111) led to controversial results. It was not clear if these films are either iron or silicon terminated. In this context we investigated the unreconstructed (100), (110) and (111) surface with help of an ab-initio method based on Density Functional Theory. The calculations revealed by means of the surface tension that for both, iron and silicon-rich conditions, the (100) and (111) surfaces are clearly silicon terminated. This is for (111) in agreement with LEED measurements [1]. With respect to the facetting of vinicial surfaces we conclude that silicon terminated (111) and mixed terminated (110) facets should dominate depending on the excess of silicon and iron. Moreover, the silicon terminated (100) and (111) surfaces show an unusual multi-layer relaxation with an expansion of the topmost layer spacing. This behaviour is explained in terms of covalent bonding. The iron terminated (100) and (111) surfaces exhibit a magnetic moment localised at the surface due to the exchange splitting between spin-minority and spin-majority states. In addition, we discuss the anisotropy of the work function and the existence of surface states.

[1] S. Walter et al. Phys. Rev. B, accepted