Regensburg 2002 – scientific programme

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DS: Dünne Schichten

DS 4: Prozeßcharakterisierung

DS 4.1: Talk

Monday, March 11, 2002, 15:00–15:15, HS 31

Yttrium on CaF₂ and BaF₂ - model systems for the growth of metals on ionic crystals — •A. Borgschulte, S. Weber, L. Bizdoaca, and J. Schoenes — Institut für Halbleiterphysik und Optik, TU Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig

The epitaxial growth of yttrium on CaF₂ (111) and BaF₂ (111) was investigated by reflecting high-energy electron diffraction and atomic force microscopy. A nearly layer-by-layer growth and Stranski-Krastanov mode is observed for Y deposition on CaF₂ and BaF₂, respectively. The growth modes are highly sensitive to the residual gas pressure. From RHEED analysis, the origin of the Y ridges on CaF₂ (first observed by Nagengast et al. [Appl. Phys. Lett. 75, 1724 (1999)]) is considered to be due to strain relaxation processes. High-resolution Auger electron spectroscopy and angular-resolved photoemission are used to study the electronic structure and bonding at the Y/CaF₂ interface. A large amount of fluorine is detected in thin yttrium films. The fluorine KLL Auger electrons show an interface shift of 2.0 eV. The F interface shift and the change of the width of the yttrium MNN lines indicate a strong interface reaction. The oxidation state of yttrium is found to be >0 at the interface. This observation is corroborated by photoemission measurements. The intensity at the Fermi level increases with increasing thickness. The results are discussed in the framework of a structure model for the interface using the electronegativity concept.