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O: Fachverband Oberflächenphysik

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

O 55.2: Vortrag

Mittwoch, 14. März 2018, 10:45–11:00, MA 005

cooperative formation of long-range ordering in water ad-layers on fe3o4(111) — •francesca mirabella¹, eman zaki¹, francisco ivars-barcelo¹, jan seifert¹, xiaoke li², joachim paier², joachim sauer², shamil shaikhutdinov¹, and hans-joachim freund¹ — ¹Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany — ²Humboldt Universität zu Berlin, Berlin, Germany

Adsorption of water on magnetite surfaces has intensively been investigated on both single crystals and well-ordered epitaxial films. The initial stage of water adsorption on Fe3O4(111) surfaces remains poorly understood. In this work, we re-examined the water adsorption models on well-characterized Fe3O4(111) films, employing TPD, IRAS, and single crystal microcalorimetry. TPD data revealed sharp desorption peaks in the region 200-300 K. Each desorption peak, showing a first order kinetics, is associated with individual desorption of molecularly adsorbed water molecules having discrete adsorption energies. Both TPD and microcalorimetry results show that the desorption energy considerably decreases at increasing water coverage, from ~100 to ~50 kJ/mol. Also, combined IRAS and TPD measurements suggest that, before the formation of ASW sets in, water readily dissociates on the surface to form two hydroxyl species, involving oxygen atoms from the water itself and from the oxide surface, respectively. These species act as anchors for molecular water which self assemble into a (2x2) ordered structure. The results are rationalized by DFT in the framework of cooperative formation of the hydrogen bonding network.