Hütner, J. I., Kugler, D., Sabath, F., Schmid, M., Kühnle, A., Diebold, U., & Balajka, J. (2024, March 21). Silver Iodide: Polar Surfaces as Ice Nuclei? [Presentation]. DPG 2024 - German Physical Society annual meeting, Berlin, Germany.
Silver iodide (AgI) is one of the most effective ice nucleating agents due to its structural similarity with hexagonal ice. Many countries worldwide utilize AgI for cloud seeding in weather modification programs, such as drought management or hail and storm suppression. From a surface point of view, however, a puzzling conundrum remains: The basal (0001) cleavage plane, lattice-matched to ice, is thermodynamically unstable. An AgI crystal lacks inversion symmetry and terminates with only silver atoms on one side and only iodine on the other side, causing a nonzero electrical dipole perpendicular to the surface. To compensate polarity, the surface is expected to rearrange at the atomic level. How can AgI promote heterogeneous ice nucleation if its surface is altered? Noncontact atomic force microscopy provides a direct visualization of the polarity compensation mechanism. Atomically resolved images reveal two distinct surface reconstructions of the differently (Ag+ and I−) terminated surfaces and show that only one of them assumes a surface structure that allows an epitaxial relationship with hexagonal ice.
