Multilayer growth and wetting of Ru(0001)

We describe the growth of intact D2O multilayers on Ru(0001) using LEED, RAIRS, and gas adsorption to probe ice crystallization and the structures formed. At low temperatures, where water mobility is limited, continuous amorphous solid water films are formed. These films are unstable, roughening on annealing to form multilayer ice crystallites and expose regions of water monolayer. Nucleation of multilayer ice clusters occurs above a critical coverage and temperature, and is followed by a rapid increase in thickness to expose more monolayer water. The ice clusters are stabilized by hydrogen bonding within the 3D structure and minimize their contact to the water monolayer. This behavior is attributed to the strong interaction between first layer water and Ru(0001), which pins the monolayer into a structure that is unfavorable for bonding to a multilayer ice film. No ordered multilayer ice structures were seen by LEED, even at high coverage (similar to 100 layers), indicating that the wetting layer will not reconstruct to accommodate an incommensurate ice Ih-(0001) film to the metal surface. This behavior is discussed in the light of recent calculations for the structure of water on Ru(0001) and contrasted with the behavior of the labile wetting layer found on Pt(111).