Measuring the thickness of the liquid-like layer on ice surfaces with atomic force microscopy

Atomic force microscopy was used to study the surface melting of ice in a temperature range above -35 degrees C. The thickness of the liquid-like layer (d) on ice was determined from the jump-in distance of force-versus-distance curves. The layer thickness of ice formed from distilled water was roughly 32 nm at -1 degrees C and 11 nm at -10 degrees C. The temperature dependence of d could best be described by d proportional to -log Delta T, where Delta T is the difference between the melting temperature and the actual temperature. The addition of salt increased the thickness of the liquid-like layer, and the temperature dependency agreed with predictions by Wettlaufer (Phys. Rev. Lett. 1999, 82, 2516).