Atomic-Resolution Imaging on Alkali Halide Surfaces in Viscous Ionic Liquid Using Frequency Modulation Atomic Force Microscopy

Structural analysis of interfaces between ionic liquid (IL) and alkali-halide (100) surface was demonstrated by frequency modulation atomic force microscopy (FM-AFM). A quartz tuning fork sensor with a sharpened tungsten tip, the so-called qPlus sensor, was used as a force sensor. Atomic-resolution topographic imaging on a KCl(100) surface was successfully achieved in a viscous IL. The square lattice structure with a period of ∼0.4 nm was clearly imaged, which indicated that only K + or Cl – ions were imaged. An abrupt shift of the tip position occurred during the topographic imaging, suggestting that the dissolution of KCl atomic layers was detected by the FM-AFM. In addition, two-dimensional force mapping was carried out, and the presence of the KCl-based layered structure on the interface was recognized.