Ion hydration is of relevance for a wide range of systems,including electrochemistry,biological environments and atmospheric aerosols.In spite of massive experimental and theoretical efforts,the effect of ions on the structure and dynamics of water has been under persistent debate.Based on the ability to probe interfacial water at atomic scale [1-3],we further explore the interaction between water molecules and ionic species on a salt surface.Combining scanning tunneling microscopy(STM)with noncontact atomic force microscopy(NC-AFM),we directly identified the microscopic structure of various hydration clusters on the NaCl(001)surface,which were artificially built up using atom manipulation techniques.We found that the diffusion dynamics of planar and non-planar hydration clusters shows completely different behavior,mainly due to the subtle balance between Coulomb forces and hydrogen bonding.In addition,the interaction strength between the water and the ions was assessed at single bond limit using inelastic electron tunneling spectroscopy(IETS)[4].The quantum component of the water-ion interaction was unambiguously revealed.