Proton segregation on a growing ice interface

摘要

Hydronium segregates to the surface of H_2O (D_2O) ice films grown on Pt(111) above 151 K (158 K). This is observed via the voltage that develops across the films, utilizing work function measurements. The dependence of this voltage on the film's thickness is explained by a simple equilibrium model: as the film grows, most of the surface ions migrate so as to remain at the ice-vacuum interface, while a fixed percentage (～0.05%) take the thermodynamically-unfavored route, to become incorporated into the growing bulk ice. This model implies a △G of about +0.1 eV for the movement of ions from the ice surface into the bulk ice.