Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)

O 15.47: Poster

Friday, March 4, 2005, 17:00–20:00, Poster TU D

Growth and electronic structure of epitaxial Ba_0.7Sr_0.3O layers on the Si(001) surface — •Anddreas Gerdes, Jan Zachariae, and Herbert Pfnür — Institut für Festkörperphysik, Universität Hannover, Appelstr. 2, 30167 Hannover

We investigated the growth conditions, crystalline quality and stoichiometry of the medium k (є_r≈30) Ba_0.7Sr_0.3O films using high resolution LEED, UPS, XPS and EELS. Lattice matched Ba_0.7Sr_0.3O layers were grown on a intermediate layer on the Si(001) substrate in UHV by evaporation of the metals in an ambient oxygen pressure. The quality of oxide layers depends on two conditions: the kind of the intermediate layer and the accurate oxygen dose, which was determined by mass accumulation on a quartz crystal micro balance. A correct fraction of Ba and Sr in the mixed oxide layers leads to well ordered and lattice matched oxide films from a few monolayers up to 20 nm and more. To obtain monocrystalline Ba_0.7Sr_0.3O layers, although of different quality, it is necessary to start the growth on one of the three following types of intermediate layers: strontium silicide layers Θ≤ 1 ML grown at T≥ 750 ^∘C , strontium metal layers Θ> 1 ML grown at T≤ 650 ^∘C and the silicate layers (1 ML of Sr₂SiO₄). The electronic structure, surface roughness and interface oxidation for the growth on different intermediate layers will be discussed.First results of the growth of Ba_0.7Sr_0.3O on vicinal Si(001) surfaces to generate a stepped insulator surface and the formation mechanism of surface F-centers will also be presented.