Growth of nanometer thin ice films from water vapor studied using scanningpolarization force microscopy

Atomic force microscopy (AFM) was used to study the growth and morphology o f ice films on the cleavage surface of mica. Measurements performed in cont act, as well as in noncontact operation modes of the microscope, allowed us to distinguish the solid and liquid parts of the film. At temperatures bel ow -30 degrees C, supercooled water droplets formed on top of a thin (nanom eter range) ice layer in contact with the substrate. After annealing, a con tiguous flat film was formed. Between -20 and -10 degrees C and at a relati ve humidity of similar to 83%, the film consisted of a solid ice layer simi lar to 7 Angstrom thick, covered by a liquid-like layer 50 +/- 5 Angstrom t hick. When the temperature was raised above 0 degrees C, droplets formed, w hich subsequently evaporated. Comparison of results obtained in the various AFM operation modes allowed us to conclude the existence of a liquid-like layer on the ice surface. (C) 1999 American Institute of Physics. [S0021-96 06(99)70539-8].