Water clusters on Cu(110): chain versus cyclic structures.

Water clusters are assembled and imaged on Cu(110) by using a scanning tunneling microscope. Water molecules are arranged along the Cu row to form "ferroelectric" zigzag chains of trimer to hexamer. The trimer prefers the chain form to a cyclic one in spite of the reduced number of hydrogen bonds, highlighting the crucial role of the water-substrate interaction in the clustering of adsorbed water molecules. On the other hand, the cyclic form with maximal hydrogen bonds becomes more favorable for the tetramer, indicating the crossover from chain to cyclic configurations as the constituent number increases.