Growth and Structure of the First Layers of Ice on Ru(0001) and Pt(111)

Scanning tunneling microscopy was used to probe the structure and growth of the first few layers of water on Ru(0001) and Pt(111) at the molecular level. The surface-bound first layer is composed of a mixture of water molecules forming hexagonal structures, both in registry and out-of-registry with the substrate atoms. The hexagons are connected by pentagonal and heptagonal units. At temperatures below 140 K, this layer structure gives rise to the growth of metastable amorphous structures in the second and higher layers. We found that in the transition from amorphous to crystalline ice the structure of the original bottom layer changes to one in perfect local registry with the hexagonal surfaces of Ru(0001) and Pt(111). We further discovered structural defects in the form of extended one-dimensional lines of five- and eight-membered rings that are domain boundaries and stacking faults in the growing ice layers, which lead to the formation of metastable cubic ice.