Growth of thin crystalline ice films on Pt(111)

Adsorption of water on Pt(111) at 135 K or above proceeds by a Stranski-Krastanov mechanism to form crystalline ice films. The structure of thin films reflects a conflict between maximising the binding to the surface and minimising the stress in the multilayer film. The first bilayer of water forms an ordered hexagonal overlayer which shows a (root39 x root39)R16.1degrees LEED pattern. Water condensation on this overlayer is initially slow, accelerating as second layer nucleation sites form and allow multilayer growth. Adsorption continues to grow the (root39 x root39)R16.1degrees structure until the film reaches a thickness of approximate to 5 bilayers at 137 K, after which further adsorption reorients the overlayer to form an incommensurate hexagonal film aligned at 30degrees to the Pt(111) close packed direction. Thermal desorption measurements reveal a change in the water desorption rate as the multilayer re-crystallises during heating, formation of the hexagonal R30degrees structure stabilising the multilayer film at the cost of reducing the binding of the first layer of water to the Pt(111) surface. The (root39 x root39)R16.1degrees overlayer becomes increasingly unstable to electron exposure as its thickness increases towards five bilayers, the ice rapidly restructuring to form islands with the R30degrees structure and exposing bare Pt. (C) 2002 Published by Elsevier Science B.V.