Water adsorption on alkali halide surfaces in air observed with force microscopy

We have investigated the behavior of water adsorption on alkali halide surfaces in air and at room temperature observed with the non-contact monitoring mode of a scanning force microscope (SFM). We have found a formation of water droplet pattern on LiF(001) surface and thereafter the formation of a uniform film, in the similar way as observed on the BaF2(111) surface[1]. However, there appears to be no water droplet pattern on the NaCl(001) surface. The SFM image from the NaF(001) surface has revealed complicated features with water droplet pattern resulting in films formed with different thickness. These results indicate that in those cases where a water-water interaction is stronger than a water-substrate interaction, water droplets would grow easily on the surfaces, but in the opposite case, the uniform film with a monolayer or submonolayer would be formed.