Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 32: Oxides and Insulators: Clean Surfaces
O 32.5: Vortrag
Dienstag, 26. Februar 2008, 14:00–14:15, MA 042
Lattice Dynamics of Cu2O: Bulk and (110) Surface — •Klaus-Peter Bohnen1, Rolf Heid1, Aloysius Soon2, and Catherine Stampfl2 — 1Forschungszentrum Karlsruhe, Institut für Festkörperphysik — 2School of Physics, The University of Sydney
A number of theoretical studies have been carried out in the past to investigate the stability of various surface oxides for the O/Cu system however despite the fact that catalytic processes usually proceed at elevated temperatures stability at finite temperatures has never been studied for these systems. Modern ab-initio methods however allow for the determination of the lattice dynamics and the phononic contribution to the free energy. Using density functional perturbation theory we have studied the lattice dynamics of Cu2O-bulk as well as Cu2O(110). In calculating the free energy as function of lattice constant we obtained for the bulk a negative thermal expansion up to roughly 300 K in excellent agreement with experiments. This is due to anomalous mode Grüneisen parameters for vibrational modes in the low energy regime. Due to the anomalous behavior of the mode Grüneisen parameter the bulk system is highly unstable against variations of the lattice constant by more than 2%. To investigate the stability of the O/Cu surfaces we have investigated the lattice dynamics of Cu2O(110) as a prototype. Despite a large number of low lying modes no instability has been found. These calculations allow also for the O/Cu system for the first time for a realistic estimation of the surface free energy which is important for the determination of surface thermodynamic properties.