Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 55: Focus Session: Structure and Chemistry of Metal-Oxide Surfaces II

O 55.3: Vortrag

Mittwoch, 14. März 2018, 11:00–11:15, MA 005

Water adsorption on magnetite — Francesca Mirabella¹, Eman Zaki¹, Francisco Ivars-Barcelo¹, Xiaoke Li², •Joachim Paier², Shamil Shaikhutdinov¹, Joachim Sauer², and Hans-Joachim Freund¹ — ¹Fritz-Haber-Institut-der-Max-Planck-Gesellschaft, Berlin, Deutschland — ²Humboldt-Universität zu Berlin, Deutschland

Fe3O4(001), well known as one of the natural growth facets of the magnetite iron oxide phase, has been recently resolved by Diebold and Parkinson. With respect to the molecular structure of water on that surface, much transferable knowledge has been generated by the pioneering work of Diebold on TiO2 as well as ZnO.

Regarding the Fe3O4(111) surface, its termination was resolved by Freund and coworkers using LEED-I/V resulting in a model with a very small R factor of 0.14. It involves a single Fe cation in its outermost atomic layer. The termination has been confirmed by a combined IRAS and DFT study using CO as a probe molecule. Recently a unique (2x2) long-range ordered structure in water adlayers on Fe3O4(111) has been studied by LEED and TPD. Upon determining relevant water ad-structures starting from 1/4 ML up to one ML coverage using DFT, the TPD can be understood. In the initial stages of H2O adsorption, individual molecules dissociate creating terminal water-related Ow-H and surface Os-H groups, serving as anchors for additional water molecules ordering via H-bonding and thus forming a (2x2) 2D structure. Adsorption energies of the modelled structures cluster in three characteristic regimes corresponding well to observed peak temperatures.