Atomic Resolution FM-AFM Imaging on Solid Surfaces Covered with Thin Water Layers
Abstract: Atom-resolved images of KBr(001), NaCl(001), and mica(001) surfaces were successfully observed in air by using a frequency modulation atomic force microscope (FM-AFM). The key of the imaging was in forming of a water layer with a thickness of a few nm on their surfaces by increasing the humidity of the environment in a controlled manner. This indicated that no bare surfaces in air were imaged, but their solid-water interfaces were imaged. Noteworthy, the water-soluble ionic crystal surfaces were reproducibly imaged under an ultra-thin water layer, in which the quasi-equilibrium conditions in regard to the dissolution and precipitation of the ions at their interfaces with water were soon achieved, although it was with difficulty when they were in bulk water. In addition, since the cantilever of an AFM force sensor was in air, while the tip end of the sensor was being immersed in the ultra-thin water layer, the Q value of the sensor was enough high of the order of a few hundreds, which was beneficial in FM-AFM imaging at a high resolution.
Key words: FM-AFM, thin water layer, water-solid interface