Tapping mode atomic force microscopy in liquid

We show that standard silicon nitride cantilevers can be used for tapping mode atomic force microscopy (AFM) in air, provided that the energy of the oscillating cantilever is sufficiently high to overcome the adhesion of the water layer. The same cantilevers are successfully used for tapping mode AFM in liquid. Acoustic modes in the liquid excite the cantilever. On soft samples, e.g., biological material, this tapping mode AFM is much more gentle than the regular contact mode AFM. Not only is the destructive influence of the lateral forces minimized, but more important, the intrinsic viscoelastic properties of the sample itself are effectively used to ‘‘harden’’ the soft sample.