文摘
The complete bilayer is commonly considered as the termination of the (0001) surface of hexagonal ice. Experiments on thin crystalline ice structures grown on Cu(111) demonstrated a termination by admolecule structures on top of the bilayer. Modeling of complex admolecule terminations including admolecule clusters and decorated hexagon adrows within density functional theory and high-resolution STM imaging are combined for the structural analysis and to reveal possible causes for the apparent distinction. A dominant admolecule structure that appears during a short anneal at 130 K is identified as an arrangement of water dimer and trimers. By the combined approach, detailed models for decorated hexagon adrows are derived. Such structures possess low energy; however, the proton-ordered bilayer is more favorable at a small margin. Yet, energetically unfavorable bonding of water, for example, in thin ice films may drive the formation of admolecule terminations, for which kinetic effects still are an important factor. The results also shine light on the edge termination of bilayer islands.