The distinct vibrational signature of grain-boundary water in nano-crystalline ice films

We have characterized the vibrational response of grain-boundary water in crystalline ice films consisting of nanometer-sized crystalline domains. The crystalline ice is grown isothermally on Ru(0 0 0 1), and the crystalline domain size is controlled by varying the crystallization temperature. A distinct vibrational feature in the OD stretching region is observed, which we attribute to grain-boundary water. The relative contribution of the grain-boundary vibrational response to the overall spectrum increases with decreasing crystal domain size. Its central frequency is located around 2500 cm^-1, between that of amorphous solid water and crystalline ice.