Imaging the Condensation and Evaporation of Molecularly Thin Films of Water with Nanometer Resolution

TLDR

The polarization force between an electrically charged AFM tip and a mica substrate was used to image the condensation and evaporation of a monolayer of water at room temperature. Condensation of the water film on mica proceeds in two stages: below ~25 % humidity it forms small two‑dimensional clusters, while above ~25 % it grows into large epitaxial islands that saturate at ~45 % humidity, and the reverse evaporation process was also visualized.

Abstract

The polarization force between an electrically charged atomic force microscope tip and a substrate has been used to follow the processes of condensation and evaporation of a monolayer of water on mica at room temperature. Condensation proceeds in two distinct structural phases. Up to about 25 percent humidity, the water film grows by forming two-dimensional clusters of less than a few 1000 angstroms in diameter. Above about 25 percent humidity, a second phase grows, forming large two-dimensional islands with geometrical shapes in epitaxial relation with the underlaying mica lattice. The growth of this second water phase is completed when the humidity reaches about 45 percent. The reverse process of evaporation has also been imaged.