Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 95: Metal Substrates: Adsorption of Atoms and Inorganic Molecules
O 95.11: Vortrag
Donnerstag, 23. März 2017, 17:45–18:00, WIL A317
Solvation in molecularly thin water films and their growth — •Barbara A J Lechner1,2, Sabine Maier3, Youngsoon Kim4, Heon Kang4, and Miquel Salmeron1 — 1Materials Sciences Division, Lawrence Berkeley Lab, Berkeley, CA — 2Department of Chemistry, Technical University of Munich — 3Department of Physics, Friedrich-Alexander University of Erlangen-Nürnberg — 4Department of Chemistry, Seoul National University, Seoul, Korea
The first water layer on hexagonal single crystal surfaces typically forms rotated hexagons, pentagons and heptagons of molecules in addition to strongly bound hexagonal rings commensurate with the substrate. Furthermore, the water monolayer does not expose any dangling hydrogen bonds in a vacuum environment. The growth of the entropically favorable proton-disordered ice, however, requires flipping some of the molecules in the first layer to expose dangling bonds. Using scanning tunneling microscopy (STM) we studied this transition from the first layer to water multilayers on Pt(111) and Ru(0001). We observed that a second layer initially forms an amorphous structure when grown on the crystalline monolayer. To facilitate the growth of ice in a bulk-like hexagonal arrangement, the first wetting layer needs to rearrange into a purely hexagonal structure commensurate with the surface. Ammonia (NH3) molecules can adsorb to certain water molecules in the monolayer on Pt(111), specifically those that are slightly elevated from the surface and weakly bound to the metal. Ammonia molecules thus detect locations in the wetting layer where a water molecule can change its orientation relatively easily to flip up a hydrogen atom.