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SUMMARY:Crystalline growth of ice – Restructuring of the first wetting l
 ayer during multilayer formation - Barbara Lechner\, Department of Chemist
 ry\, Technical University of Munich\, Germany
DTSTART:20161103T160000Z
DTEND:20161103T170000Z
UID:TALK67291@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:The first water layer on hexagonal single crystal surfaces has
  a surprisingly complex structure\, releasing the strain caused by a misma
 tch of the ice crystal structure and the substrate lattice by forming rota
 ted hexagons\, pentagons and heptagons of molecules in addition to strongl
 y bound hexagonal rings commensurate with the substrate. In a vacuum envir
 onment\, the water monolayer does not expose any dangling hydrogen bonds a
 nd all water molecules adsorb either flat-lying or with a hydrogen atom po
 inting towards the surface. The growth of the entropically favourable prot
 on-disordered ice\, however\, requires flipping some of the molecules in t
 he first layer to expose dangling hydrogen bonds. Using scanning tunnellin
 g microscopy (STM) we studied this transition from the first layer to wate
 r multilayers on Pt(111) and Ru(0001). We observed that a second water lay
 er initially forms an amorphous structure when grown on the crystalline mo
 nolayer containing pentagons\, hexagons and heptagons of water molecules. 
 To facilitate the growth of ice in a bulk-like hexagonal arrangement\, the
  first wetting layer needs to rearrange into a hexagonal structure commens
 urate with the surface. Complementary STM measurements confirmed the facil
 e re-orientation of certain molecules in the water monolayer on Pt(111) up
 on adsorption of ammonia (NH3) molecules. We found that NH3 binds preferen
 tially to H2O molecules that are slightly elevated from the surface and we
 akly bound to the metal. Ammonia molecules thus detect locations in the we
 tting layer where a water molecule can change its orientation relatively e
 asily to flip up a hydrogen atom.
LOCATION:Small Lecture Theatre\, Cavendish Laboratory
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