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O: Fachverband Oberflächenphysik
O 17: Oxides and insulators III
O 17.5: Vortrag
Dienstag, 24. März 2009, 11:30–11:45, SCH A01
Theoretical evidence for mixed adsorption of water on Fe3O4(001) — •Narasimham Mulakaluri1,2, Rossitza Pentcheva1, Maria Wieland1, Wolfgang Moritz1, and Matthias Scheffler2 — 1Section Crystallography, Dept. for Earth and Environmental Sciences, University of Munich — 2Fritz-Haber-Institut der MPG, Berlin
The interaction of water with a mineral surface is a fundamental process towards understanding surface reactivity. Based on density functional theory (DFT) calculations we investigate the adsorption of water and its influence on the electronic properties and surface reconstruction of Fe3O4(001). Starting from a single water molecule per (√2× √2)R45∘ unit cell, we vary the concentration and configuration of water and hydroxyl groups. The surface phase diagram compiled within the framework of ab-initio thermodynamics indicates that a clean wave-like distorted bulk termination (modified B-layer) [1] is favorable over a substantial range of O2 and H2O partial pressures, but competes with a B-layer with oxygen vacancies in the oxygen poor limit. Such vacancies can promote dissociation of isolated water molecules. With increasing pressure in the gas phase there is a crossover to a mixed molecular and dissociative adsorption mode. A quantitative low energy electron diffraction (LEED) analysis confirms two distinct Fe-O-distances. DFT and LEED results indicate a suppression of the (√2× √2)R45∘-reconstruction.
[1] R. Pentcheva et al., Phys. Rev. Lett. 94,126101 (2005).