Surface-induced ferroelectric ice

Summary form only given. Can ice be ferroelectric! This question has long attracted much attention. In crystalline ice, water molecules are held together by tetrahedralhydrogen bonding. The molecular orientations at the lattice points should obey the ice rules, which require that each molecule donate two protons to two of the attached water molecules and accept two protons from the other two. We used infrared-visible sum-frequency generation (SFG) spectroscopy as a probe in our experiment. As a second-order nonlinear optical process, SFG is forbidden in a medium with inversion symmetry. In its application to an ice film, the spectrum could be weak if the water molecules in the film are non-polar oriented.