Growth of thin crystalline ice films on Pt(1 1 1)

Adsorption of water on Pt(1 1 1) 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 (39×39)R16.1° 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 (39×39)R16.1° structure until the film reaches a thickness of ≈ 5 bilayers at 137 K, after which further adsorption reorients the overlayer to form an incommensurate hexagonal film aligned at 30° to the Pt(1 1 1) 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 R30° structure stabilising the multilayer film at the cost of reducing the binding of the first layer of water to the Pt(1 1 1) surface. The (39×39)R16.1° overlayer becomes increasingly unstable to electron exposure as its thickness increases towards five bilayers, the ice rapidly restructuring to form islands with the R30° structure and exposing bare Pt.