Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 48: Oxide and Insulator Surfaces: Structure, Epitaxy and Growth
O 48.2: Poster
Dienstag, 21. März 2017, 18:30–20:30, P1A
NiO growth on Ag(001): A layer-by-layer vibrational study — •Florian O. Schumann1, Krasimir L. Kostov2, Sebastian Polzin1, and Wolf Widdra1,3 — 1Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany — 2Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria — 3Max Planck Institute for Microstructure Physics, 06120 Halle, Germany
The vibrational properties of NiO(001) films on Ag(001) with thicknesses up to 50 monolayers (ML) are characterized with high-resolution electron energy loss spectroscopy (HREELS). The film-thickness-dependent Fuchs-Kliewer (FK) phonon frequency shifts and intensity changes are identified from the NiO monolayer to bulklike thick films. Characteristic changes of the vibrational properties are analyzed to resolve restructuring processes during annealing and thermal decomposition of NiO films. A quantitative comparison of the experimental data with the calculated loss function based on dielectric theory reveals an excellent agreement between the bulk and the NiO phonon properties for film thicknesses above 15 ML. In contrast, a strong FK phonon softening is observed for thin films below 5 ML that cannot be explained by dielectric theory nor phonon standing waves. This softening is attributed to the presence of surface stress, which results from the -2 % lattice mismatch between NiO and Ag. Furthermore the dispersion of six different phonon branches in the X direction for a fully relaxed 25 ML and a pseudomorphically 4 ML film will be compared.